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Sample records for oxidation kinetic studies

  1. Kinetic Studies of Catalytic Oxidation of Cyclohexene Using ...

    African Journals Online (AJOL)

    acer

    Kinetic Studies of Catalytic Oxidation of Cyclohexene Using Chromium VI Oxide in. Acetic Acid ... respect to the oxidant using pseudo-order approximation method. .... making the concentration of the cyclohexene in ..... on Titanium Silicate.

  2. Study of internal oxidation kinetics of molybdenum base alloys

    International Nuclear Information System (INIS)

    Krushinskij, Yu.Yu.; Belyakov, B.G.; Belomyttsev, M.Yu.

    1989-01-01

    Metallographic and microdurometric method as well as new technique were used to study kinetics of internal oxidation (IO). It is shown that study of IO kinetics on the base of metallographic measurements of layers depth is not correct because it is related with insufficient sensitivity of the method. IO kinetics under conditions of formation of molybdenum oxide layer on saturated material surface as well as IO of alloy with high carbon content were investigated. Oxide film formation does not affect the IO kinetics; decarburization observed along with oxidation increases the apparent activation energy and K exponent on time dependence of diffusion layer depth

  3. Kinetic study of the alkaline metals oxidation by dry oxygen

    International Nuclear Information System (INIS)

    Touzain, Ph.

    1967-06-01

    The oxidation of lithium, sodium, potassium, rubidium, cesium and sodium-potassium alloys by dry oxygen is studied at several temperatures and in the oxygen pressure range 40 to 400 mmHg. One distinguishes three different oxidation behaviours (inflammation, ignition and slow combustion) whose zones are precised in function of the temperature. The slow oxidation kinetic laws, the composition of oxides and the motive of oxides colorations are determined. At least, the experimental data are construed theoretically. (author) [fr

  4. Kinetic Studies of Catalytic Oxidation of Cyclohexene Using ...

    African Journals Online (AJOL)

    Cyclohexene was oxidized using chromium (VI) oxide (CrO3) in pure acetic acid medium. The products of oxidation were analysed using simple qualitative analysis, IR spectroscopy and Gas chromatography-Mass spectrometry (GC/MS). Kinetics studies were carried out to determine the order of reaction, rate constant and ...

  5. Study of the oxidation kinetics of the MA 956 superalloy

    International Nuclear Information System (INIS)

    Garcia-Alonso, M.C.; Gonzalez-Carrasco, J.L.; Escudero, M.L.

    1998-01-01

    This work deals with the oxidation kinetics of the MA 956 superalloy in the temperature range of 800-1,200 degree centigree for up to 200 h exposure. During oxidation the alloy develops a fine, compact and very well adhered α-alumina layer, the thickness of which increases with increasing time and temperature. The oxidation kinetics obeys a sub parabolic type behaviour. The scale growth seems to occur by two different oxidation mechanisms; above 1,050 degree centigree, the oxidation process would be controlled by α-alumina, and below 900 degree centigree by γ-alumina. (Author) 17 refs

  6. Kinetics of ethylcyclohexane pyrolysis and oxidation: An experimental and detailed kinetic modeling study

    KAUST Repository

    Wang, Zhandong

    2015-07-01

    Ethylcyclohexane (ECH) is a model compound for cycloalkanes with long alkyl side-chains. A preliminary investigation on ECH (Wang et al., Proc. Combust. Inst., 35, 2015, 367-375) revealed that an accurate ECH kinetic model with detailed fuel consumption mechanism and aromatic growth pathways, as well as additional ECH pyrolysis and oxidation data with detailed species concentration covering a wide pressure and temperature range are required to understand the ECH combustion kinetics. In this work, the flow reactor pyrolysis of ECH at various pressures (30, 150 and 760Torr) was studied using synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (PIMS) and gas chromatography (GC). The mole fraction profiles of numerous major and minor species were evaluated, and good agreement was observed between the PIMS and GC data sets. Furthermore, a fuel-rich burner-stabilized laminar premixed ECH/O2/Ar flame at 30Torr was studied using synchrotron VUV PIMS. A detailed kinetic model for ECH high temperature pyrolysis and oxidation was developed and validated against the pyrolysis and flame data performed in this work. Further validation of the kinetic model is presented against literature data including species concentrations in jet-stirred reactor oxidation, ignition delay times in a shock tube, and laminar flame speeds at various pressures and equivalence ratios. The model well predicts the consumption of ECH, the growth of aromatics, and the global combustion properties. Reaction flux and sensitivity analysis were utilized to elucidate chemical kinetic features of ECH combustion under various reaction conditions. © 2015 The Combustion Institute.

  7. Study of water vapour adsorption kinetics on aluminium oxide materials

    Science.gov (United States)

    Livanova, Alesya; Meshcheryakov, Evgeniy; Reshetnikov, Sergey; Kurzina, Irina

    2017-11-01

    Adsorbents on the basis of active aluminum oxide are still of demand on the adsorbent-driers market. Despite comprehensive research of alumina adsorbents, and currently is an urgent task to improve their various characteristics, and especially the task of increasing the sorption capacity. In the present work kinetics of the processes of water vapours' adsorption at room temperature on the surface of desiccant samples has been studied. It was obtained on the basis of bayerite and pseudoboehmite experimentally. The samples of pseudoboehmite modified with sodium and potassium ions were taken as study objects. The influence of an adsorbent's grain size on the kinetics of water vapours' adsorption was studied. The 0.125-0.25 mm and 0.5-1.0 mm fractions of this sample were used. It has been revealed that the saturation water vapor fine powder (0.125-0.25 mm) is almost twofold faster in comparison with the sample of fraction 0.5-1.0 mm due to the decrease in diffusion resistance in the pores of the samples when moving from the sample of larger fraction to the fine-dispersed sample. It has been established that the adsorption capacity of the pseudoboehmite samples, modified by alkaline ions, is higher by ˜40 %, than for the original samples on the basis of bayerite and pseudoboehmite.

  8. In-Situ Optical Studies of Oxidation/Reduction Kinetics on SOFC Cermet Anodes

    Science.gov (United States)

    2010-12-28

    DATES COVERED (From - To) 1/29/10-9/30/10 4. TITLE AND SUBTITLE In situ optical studies of oxidation/reduction kinetics on SOFC cermet anodes 5a...0572 In-situ Optical Studies of Oxidation/Reduction Kinetics on SOFC Cermet Anodes Department of Chemistry and Biochemistry Montana State University...of Research In-situ Optical Studies of Oxidation/Reduction Kinetics on SOFC Cermet Anodes Principal Investigator Robert Walker Organization

  9. Ab initio and kinetic modeling studies of formic acid oxidation

    DEFF Research Database (Denmark)

    Marshall, Paul; Glarborg, Peter

    2015-01-01

    A detailed chemical kinetic model for oxidation of formic acid (HOCHO) in flames has been developed, based on theoretical work and data from literature. Ab initio calculations were used to obtain rate coefficients for reactions of HOCHO with H, O, and HO2. Modeling predictions with the mechanism...

  10. The kinetic study of oxidation of iodine by hydrogen peroxide

    International Nuclear Information System (INIS)

    Cantrel, L.; Chopin, J.

    1996-01-01

    Iodine chemistry is one of the most important subjects of research in the field of reactor safety because this element can form volatile species which represent a biological hazard for environment. As the iodine and the peroxide are both present in the sump of the containment in the event of a severe accident on a light water nuclear reactor, it can be important to improve the knowledge on the reaction of oxidation of iodine by hydrogen peroxide. The kinetics of iodine by hydrogen peroxide has been studied in acid solution using two different analytical methods. The first is a UV/Vis spectrophotometer which records the transmitted intensity at 460 nm as a function of time to follow the decrease of iodine concentration, the second is an amperometric method which permits to record the increase of iodine+1 with time thanks to the current of reduction of iodine+1 to molecular iodine. The iodine was generated by Dushman reaction and the series of investigations were made at 40 o C in a continuous stirring tank reactor. The influence of the initial concentrations of iodine, iodate, hydrogen peroxide, H + ions has been determined. The kinetics curves comprise two distinct chemical phases both for molecular iodine and for iodine+1. The relative importance of the two processes is connected to the initial concentrations of [I 2 ], [IO 3 - ], [H 2 O 2 ] and [H + ]. A rate law has been determined for the two steps for molecular iodine. (author) figs., tabs., 22 refs

  11. Experimental kinetic study and modeling of calcium oxide carbonation

    International Nuclear Information System (INIS)

    Rouchon, L.

    2012-01-01

    Anthropogenic carbon dioxide (CO 2 ) emissions, major contributors to the greenhouse effect, are considered as the main cause of global warming. So, decrease of CO 2 emitted by large industrial combustion sources or power plants, is an important scientific goal. One of the approaches is based on CO 2 separation and capture from flue gas, followed by sequestration in a wide range of geological formations. In this aim, CO 2 is captured by sorbents like calcium oxide (CaO) in multi-cycle process of carbonation/de-carbonation. However, it was shown that the most important limitations of such process are related to the reversibility of reaction. CaO rapidly loses activity towards CO 2 , so the maximum extent of carbonation decreases as long as the number of cycles increases. In order to well understand the processes and parameters influencing the capture capacity of CaO-based sorbents, it appears important to get details on the kinetic law governing the reaction, which have not been really studied up to now. To investigate this reaction, CaO carbonation kinetics was followed by means of thermogravimetric analysis (TGA) on divided materials. Special care was given to the validation of the usual kinetic assumptions such as steady state and rate-determining step assumptions. The aim was to obtain a model describing the reaction in order to explain the influence of intensive variables such as carbonation temperature and CO 2 partial pressure. TGA curves obtained under isothermal and isobaric conditions showed an induction period linked to the nucleation process and a strong slowing down of the reaction rate once a given fractional conversion was reached. Both phenomena were observed to depend on carbonation temperature and CO 2 partial pressure. To explain these results, the evolution of texture and microstructure of the solid during the reaction was regarded as essential. Reaction at the grain scale induces a volume increase from CaO to CaCO 3 which causes a change in the

  12. The kinetic study of oxidation of iodine by hydrogen peroxide

    Energy Technology Data Exchange (ETDEWEB)

    Cantrel, L [Institut de Protection et de Surete Nucleaire, IPNS, CEN Cadarache, Saint Paul lez Durance (France); Chopin, J [Laboratoire d` Electrochimie Inorganique, ENSSPICAM, Marseille (France)

    1996-12-01

    Iodine chemistry is one of the most important subjects of research in the field of reactor safety because this element can form volatile species which represent a biological hazard for environment. As the iodine and the peroxide are both present in the sump of the containment in the event of a severe accident on a light water nuclear reactor, it can be important to improve the knowledge on the reaction of oxidation of iodine by hydrogen peroxide. The kinetics of iodine by hydrogen peroxide has been studied in acid solution using two different analytical methods. The first is a UV/Vis spectrophotometer which records the transmitted intensity at 460 nm as a function of time to follow the decrease of iodine concentration, the second is an amperometric method which permits to record the increase of iodine+1 with time thanks to the current of reduction of iodine+1 to molecular iodine. The iodine was generated by Dushman reaction and the series of investigations were made at 40{sup o}C in a continuous stirring tank reactor. The influence of the initial concentrations of iodine, iodate, hydrogen peroxide, H{sup +} ions has been determined. The kinetics curves comprise two distinct chemical phases both for molecular iodine and for iodine+1. The relative importance of the two processes is connected to the initial concentrations of [I{sub 2}], [IO{sub 3}{sup -}], [H{sub 2}O{sub 2}] and [H{sup +}]. A rate law has been determined for the two steps for molecular iodine. (author) figs., tabs., 22 refs.

  13. Kinetic study on anaerobic oxidation of methane coupled to denitrification.

    Science.gov (United States)

    Yu, Hou; Kashima, Hiroyuki; Regan, John M; Hussain, Abid; Elbeshbishy, Elsayed; Lee, Hyung-Sool

    2017-09-01

    Monod kinetic parameters provide information required for kinetic analysis of anaerobic oxidation of methane coupled to denitrification (AOM-D). This information is critical for engineering AOM-D processes in wastewater treatment facilities. We first experimentally determined Monod kinetic parameters for an AOM-D enriched culture and obtained the following values: maximum specific growth rate (μ max ) 0.121/d, maximum substrate-utilization rate (q max ) 28.8mmol CH 4 /g cells-d, half maximum-rate substrate concentration (K s ) 83μΜ CH 4 , growth yield (Y) 4.76gcells/mol CH 4 , decay coefficient (b) 0.031/d, and threshold substrate concentration (S min ) 28.8μM CH 4 . Clone library analysis of 16S rRNA and mcrA gene fragments suggested that AOM-D reactions might have occurred via the syntrophic interaction between denitrifying bacteria (e.g., Ignavibacterium, Acidovorax, and Pseudomonas spp.) and hydrogenotrophic methanogens (Methanobacterium spp.), supporting reverse methanogenesis-dependent AOM-D in our culture. High μ max and q max , and low K s for the AOM-D enrichment imply that AOM-D could play a significant role in mitigating atmospheric methane efflux. In addition, these high kinetic features suggest that engineered AOM-D systems may provide a sustainable alternative to nitrogen removal in wastewater treatment. Copyright © 2017 Elsevier Inc. All rights reserved.

  14. Oxidation of L-cystine by chromium(VI) - a kinetic study | Kumar ...

    African Journals Online (AJOL)

    The kinetics of the title reaction was studied spectrophotometrically in HClO4 medium at 380 nm. The data suggested that the order with respect to cystine is fractional, whereas chromium(VI) follows first order kinetics. The reaction was second order in [H+]. Cysteic acid was found to be the main product of oxidation.

  15. Kinetic studies on the degradation of crystal violet by the Fenton oxidation process.

    Science.gov (United States)

    Wu, H; Fan, M M; Li, C F; Peng, M; Sheng, L J; Pan, Q; Song, G W

    2010-01-01

    The degradation of dye crystal violet (CV) by Fenton oxidation process was investigated. The UV-Vis spectrogram has shown that CV can be degraded effectively by Fenton oxidation process. Different system variables namely initial H(2)O(2) concentration, initial Fe(2 + ) concentration and reaction temperature, which have effect on the degradation of CV by Fenton oxidation process, have been studied systematically. The degradation kinetics of CV was also elucidated based on the experimental data. The degradation of CV obeys the first-order reaction kinetics. The kinetic model can be described as k=1.5 exp(-(7.5)/(RT))[H(2)O(2)](0)(0.8718)[Fe(2+)](0)(0.5062). According to the IR spectrogram, it is concluded that the benzene ring of crystal violet has been destroyed by Fenton oxidation. The result will be useful in treating dyeing wastewater containing CV by Fenton oxidation process.

  16. Kinetics of ethylcyclohexane pyrolysis and oxidation: An experimental and detailed kinetic modeling study

    KAUST Repository

    Wang, Zhandong; Zhao, Long; Wang, Yu; Bian, Huiting; Zhang, Lidong; Zhang, Feng; Li, Yuyang; Sarathy, Mani; Qi, Fei

    2015-01-01

    species were evaluated, and good agreement was observed between the PIMS and GC data sets. Furthermore, a fuel-rich burner-stabilized laminar premixed ECH/O2/Ar flame at 30Torr was studied using synchrotron VUV PIMS. A detailed kinetic model for ECH high

  17. Kinetic studies of sulfide mineral oxidation and xanthate adsorption

    Science.gov (United States)

    Mendiratta, Neeraj K.

    2000-10-01

    Sulfide minerals are a major source of metals; however, certain sulfide minerals, such as pyrite and pyrrhotite, are less desirable. Froth flotation is a commonly used separation technique, which requires the use of several reagents to float and depress different sulfide minerals. Xanthate, a thiol collector, has gained immense usage in sulfide minerals flotation. However, some sulfides are naturally hydrophobic and may float without a collector. Iron sulfides, such as pyrite and pyrrhotite, are few of the most abundant minerals, yet economically insignificant. Their existence with other sulfide minerals leads to an inefficient separation process as well as environmental problems, such as acid mine drainage during mining and processing and SO 2 emissions during smelting process. A part of the present study is focused on understanding their behavior, which leads to undesired flotation and difficulties in separation. The major reasons for the undesired flotation are attributed to the collectorless hydrophobicity and the activation with heavy metal ions. To better understand the collectorless hydrophobicity of pyrite, Electrochemical Impedance Spectroscopy (EIS) of freshly fractured pyrite electrodes was used to study the oxidation and reduction of the mineral. The EIS results showed that the rate of reaction increases with oxidation and reduction. At moderate oxidizing potentials, the rate of reaction is too slow to replenish hydrophilic iron species leaving hydrophobic sulfur species on the surface. However, at higher potentials, iron species are replaced fast enough to depress its flotation. Effects of pH and polishing were also explored using EIS. Besides collectorless hydrophobicity, the activation of pyrrhotite with nickel ions and interaction with xanthate ions makes the separation more difficult. DETA and SO2 are commonly used as pyrrhotite depressants; however, the mechanism is not very well understood. Contact angle measurements, cyclic voltammetry and Tafel

  18. Detailed kinetic modeling study of n-pentanol oxidation

    KAUST Repository

    Heufer, Karl Alexander; Sarathy, Mani; Curran, Henry J.; Davis, Alexander C.; Westbrook, Charles K.; Pitz, William J.

    2012-01-01

    To help overcome the world's dependence upon fossil fuels, suitable biofuels are promising alternatives that can be used in the transportation sector. Recent research on internal combustion engines shows that short alcoholic fuels (e.g., ethanol or n-butanol) have reduced pollutant emissions and increased knock resistance compared to fossil fuels. Although higher molecular weight alcohols (e.g., n-pentanol and n-hexanol) exhibit higher reactivity that lowers their knock resistance, they are suitable for diesel engines or advanced engine concepts, such as homogeneous charge compression ignition (HCCI), where higher reactivity at lower temperatures is necessary for engine operation. The present study presents a detailed kinetic model for n-pentanol based on modeling rules previously presented for n-butanol. This approach was initially validated using quantum chemistry calculations to verify the most stable n-pentanol conformation and to obtain C-H and C-C bond dissociation energies. The proposed model has been validated against ignition delay time data, speciation data from a jet-stirred reactor, and laminar flame velocity measurements. Overall, the model shows good agreement with the experiments and permits a detailed discussion of the differences between alcohols and alkanes. © 2012 American Chemical Society.

  19. Detailed kinetic modeling study of n-pentanol oxidation

    KAUST Repository

    Heufer, Karl Alexander

    2012-10-18

    To help overcome the world\\'s dependence upon fossil fuels, suitable biofuels are promising alternatives that can be used in the transportation sector. Recent research on internal combustion engines shows that short alcoholic fuels (e.g., ethanol or n-butanol) have reduced pollutant emissions and increased knock resistance compared to fossil fuels. Although higher molecular weight alcohols (e.g., n-pentanol and n-hexanol) exhibit higher reactivity that lowers their knock resistance, they are suitable for diesel engines or advanced engine concepts, such as homogeneous charge compression ignition (HCCI), where higher reactivity at lower temperatures is necessary for engine operation. The present study presents a detailed kinetic model for n-pentanol based on modeling rules previously presented for n-butanol. This approach was initially validated using quantum chemistry calculations to verify the most stable n-pentanol conformation and to obtain C-H and C-C bond dissociation energies. The proposed model has been validated against ignition delay time data, speciation data from a jet-stirred reactor, and laminar flame velocity measurements. Overall, the model shows good agreement with the experiments and permits a detailed discussion of the differences between alcohols and alkanes. © 2012 American Chemical Society.

  20. Kinetic study on electrochemical oxidation of catechols in the ...

    Indian Academy of Sciences (India)

    glassy carbon electrode in different experimental conditions. The electrogenerated ... cancer activities.5 Catechols can be easily oxidized electrochemically to ... from unity and approaches to zero in basic solution. This behavior is related to the ...

  1. Study of the oxidation kinetics of the nickel-molybdenum alloy

    International Nuclear Information System (INIS)

    Gouillon, Marie-Josephe

    1974-01-01

    This research thesis reports the study of the oxidation of a nickel-molybdenum alloy in the high-nickel-content part of this alloy. After a bibliographical study on the both metals, the author proposes a physical model based on observed phenomena and based on experimental results. Based on a thermodynamic study, the author compares the stability of the different oxides which may be formed, and reports a prediction of oxides obtained on the alloy during oxidation. Qualitative and quantitative studies have been performed by scanning electron microscopy coupled with electronic microprobe analysis to investigate morphological characteristics on oxidation films. A kinetic study by thermogravimetry shows a decrease of the alloy oxidation rate with respect to that of pure nickel at temperatures lower than 800 degrees C. This result is interpreted by the intervention of two opposed diffusion phenomena which act against each other [fr

  2. Kinetics studies of oxidation of niacinamide by alkaline potassium permanganate

    Directory of Open Access Journals (Sweden)

    Sandipsingh Gour

    2012-04-01

    Full Text Available The oxidation of niacinamide in alkaline media is carried out using potassium permanganate as a oxiding agent. The reaction was monitored using UV-Visible spectrophotometer at 525 nm. It was found to be zero order with respect to oxidant,, fractional order with respect to hydrogen ion concentration and first order with respect to substrate. The thermodynamic parameters(were determinied . The average (?G# was found to be 87.60 KJ/mol. The values ?S# was found to be -0.2132 KJ/mole and energy of activation was found to be 23.95 KJ/mole. A suitable mechanism is proposed based on the experimental conditions.

  3. Oxidation kinetics of corium pool

    Energy Technology Data Exchange (ETDEWEB)

    Sulatsky, A.A., E-mail: andrei314@mail.ru [Alexandrov Research Institute of Technologies (NITI), Sosnovy Bor (Russian Federation); Smirnov, S.A. [D.V. Efremov Scientific Research Institute of Electrophysical Apparatus (NIIEFA), St. Petersburg (Russian Federation); Granovsky, V.S.; Khabensky, V.B.; Krushinov, E.V.; Vitol, S.A.; Kotova, S.Yu. [Alexandrov Research Institute of Technologies (NITI), Sosnovy Bor (Russian Federation); Fischer, M.; Hellmann, S. [AREVA NP GmbH, Erlangen (Germany); Tromm, W.; Miassoedov, A. [Forschungzentrum Karlsruhe (FZK), Karlsruhe (Germany); Bottomley, D. [EUROPÄISCHE KOMMISSION, Joint Research Centre Institut für Transurane (ITU), Karlsruhe (Germany); Piluso, P. [CEA Cadarache-DEN/DTN/STRI, St.Paul-lez-Durance (France); Barrachin, M. [Institut de Radioprotection et Sûreté Nucléaire, St.Paul-lez-Durance (France)

    2013-09-15

    Highlights: • The analysis of experimental data on molten corium oxidation was been carried out. • The analysis has revealed the main factors influencing the oxidation kinetics. • The analysis was used for developing a qualitative analytical model. • The numerical modeling has confirmed the results of experimental data analysis. -- Abstract: Experimental, theoretical and numerical studies of oxidation kinetics of an open surface corium pool have been reported. The experiments have been carried out within OECD MASCA program and ISTC METCOR, METCOR-P and EVAN projects. It has been shown that the melt oxidation is controlled by an oxidant supply to the melt free surface from the atmosphere, not by the reducer supply from the melt. The project experiments have not detected any input of the zirconium oxidation kinetics into the process chemistry. The completed analysis puts forward a simple analytical model, which gives an explanation of the main features of melt oxidation process. The numerical modeling results are in good agreement with experimental data and theoretical considerations.

  4. Oxidation kinetics of corium pool

    International Nuclear Information System (INIS)

    Sulatsky, A.A.; Smirnov, S.A.; Granovsky, V.S.; Khabensky, V.B.; Krushinov, E.V.; Vitol, S.A.; Kotova, S.Yu.; Fischer, M.; Hellmann, S.; Tromm, W.; Miassoedov, A.; Bottomley, D.; Piluso, P.; Barrachin, M.

    2013-01-01

    Highlights: • The analysis of experimental data on molten corium oxidation was been carried out. • The analysis has revealed the main factors influencing the oxidation kinetics. • The analysis was used for developing a qualitative analytical model. • The numerical modeling has confirmed the results of experimental data analysis. -- Abstract: Experimental, theoretical and numerical studies of oxidation kinetics of an open surface corium pool have been reported. The experiments have been carried out within OECD MASCA program and ISTC METCOR, METCOR-P and EVAN projects. It has been shown that the melt oxidation is controlled by an oxidant supply to the melt free surface from the atmosphere, not by the reducer supply from the melt. The project experiments have not detected any input of the zirconium oxidation kinetics into the process chemistry. The completed analysis puts forward a simple analytical model, which gives an explanation of the main features of melt oxidation process. The numerical modeling results are in good agreement with experimental data and theoretical considerations

  5. Kinetic Study of Hydroxyl and Sulfate Radical-Mediated Oxidation of Pharmaceuticals in Wastewater Effluents.

    Science.gov (United States)

    Lian, Lushi; Yao, Bo; Hou, Shaodong; Fang, Jingyun; Yan, Shuwen; Song, Weihua

    2017-03-07

    Advanced oxidation processes (AOPs), such as hydroxyl radical (HO • )- and sulfate radical (SO 4 •- )-mediated oxidation, are alternatives for the attenuation of pharmaceuticals and personal care products (PPCPs) in wastewater effluents. However, the kinetics of these reactions needs to be investigated. In this study, kinetic models for 15 PPCPs were built to predict the degradation of PPCPs in both HO • - and SO 4 •- -mediated oxidation. In the UV/H 2 O 2 process, a simplified kinetic model involving only steady state concentrations of HO • and its biomolecular reaction rate constants is suitable for predicting the removal of PPCPs, indicating the dominant role of HO • in the removal of PPCPs. In the UV/K 2 S 2 O 8 process, the calculated steady state concentrations of CO 3 •- and bromine radicals (Br • , Br 2 •- and BrCl •- ) were 600-fold and 1-2 orders of magnitude higher than the concentrations of SO 4 •- , respectively. The kinetic model, involving both SO 4 •- and CO 3 •- as reactive species, was more accurate for predicting the removal of the 9 PPCPs, except for salbutamol and nitroimidazoles. The steric and ionic effects of organic matter toward SO 4 •- could lead to overestimations of the removal efficiencies of the SO 4 •- -mediated oxidation of nitroimidazoles in wastewater effluents.

  6. Oxidative desulfurization: kinetic modelling.

    Science.gov (United States)

    Dhir, S; Uppaluri, R; Purkait, M K

    2009-01-30

    Increasing environmental legislations coupled with enhanced production of petroleum products demand, the deployment of novel technologies to remove organic sulfur efficiently. This work represents the kinetic modeling of ODS using H(2)O(2) over tungsten-containing layered double hydroxide (LDH) using the experimental data provided by Hulea et al. [V. Hulea, A.L. Maciuca, F. Fajula, E. Dumitriu, Catalytic oxidation of thiophenes and thioethers with hydrogen peroxide in the presence of W-containing layered double hydroxides, Appl. Catal. A: Gen. 313 (2) (2006) 200-207]. The kinetic modeling approach in this work initially targets the scope of the generation of a superstructure of micro-kinetic reaction schemes and models assuming Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms. Subsequently, the screening and selection of above models is initially based on profile-based elimination of incompetent schemes followed by non-linear regression search performed using the Levenberg-Marquardt algorithm (LMA) for the chosen models. The above analysis inferred that Eley-Rideal mechanism describes the kinetic behavior of ODS process using tungsten-containing LDH, with adsorption of reactant and intermediate product only taking place on the catalyst surface. Finally, an economic index is presented that scopes the economic aspects of the novel catalytic technology with the parameters obtained during regression analysis to conclude that the cost factor for the catalyst is 0.0062-0.04759 US $ per barrel.

  7. Oxidative desulfurization: Kinetic modelling

    International Nuclear Information System (INIS)

    Dhir, S.; Uppaluri, R.; Purkait, M.K.

    2009-01-01

    Increasing environmental legislations coupled with enhanced production of petroleum products demand, the deployment of novel technologies to remove organic sulfur efficiently. This work represents the kinetic modeling of ODS using H 2 O 2 over tungsten-containing layered double hydroxide (LDH) using the experimental data provided by Hulea et al. [V. Hulea, A.L. Maciuca, F. Fajula, E. Dumitriu, Catalytic oxidation of thiophenes and thioethers with hydrogen peroxide in the presence of W-containing layered double hydroxides, Appl. Catal. A: Gen. 313 (2) (2006) 200-207]. The kinetic modeling approach in this work initially targets the scope of the generation of a superstructure of micro-kinetic reaction schemes and models assuming Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms. Subsequently, the screening and selection of above models is initially based on profile-based elimination of incompetent schemes followed by non-linear regression search performed using the Levenberg-Marquardt algorithm (LMA) for the chosen models. The above analysis inferred that Eley-Rideal mechanism describes the kinetic behavior of ODS process using tungsten-containing LDH, with adsorption of reactant and intermediate product only taking place on the catalyst surface. Finally, an economic index is presented that scopes the economic aspects of the novel catalytic technology with the parameters obtained during regression analysis to conclude that the cost factor for the catalyst is 0.0062-0.04759 US $ per barrel

  8. A kinetic study of the enhancement of solution chemiluminescence of glyoxylic acid oxidation by manganese species.

    Science.gov (United States)

    Otamonga, Jean-Paul; Abdel-Mageed, Amal; Agater, Irena B; Jewsbury, Roger A

    2015-08-01

    In order to study the mechanism of the enhancement of solution chemiluminescence, the kinetics of the decay of the oxidant and the chemiluminescence emission were followed for oxidations by permanganate, manganese dioxide sol and Mn(3+) (aq) of glyoxylic acid, using stopped-flow spectrophotometry. Results are reported for the glyoxylic acid oxidized under pseudo first-order conditions and in an acidic medium at 25 °C. For permanganate under these conditions, the decay is sigmoidal, consistent with autocatalysis, and for manganese dioxide sol and Mn(3+) it is pseudo first order. The effects of the presence of aqueous formaldehyde and Mn(2+) were observed and a fit to a simple mechanism is discussed. It is concluded that chemiluminescent enhancement in these systems is best explained by reaction kinetics. Copyright © 2014 John Wiley & Sons, Ltd.

  9. Study the oxidation kinetics of uranium using XRD and Rietveld method

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Yanzhi; Guan Weijun; Wang Qinguo; Wang Xiaolin; Lai Xinchun; Shuai Maobing, E-mail: yanzhizh@163.com [China Academy of Engineering Physics, PO Box 919-71, Mianyang, Sichuan, 621900 (China)

    2010-03-15

    The surface oxidation of uranium metal has been studied by X-ray diffraction (XRD) and Rietveld method in the range of 50{approx}300deg. C in air. The oxidation processes are analyzed by XRD to determine the extent of surface oxidation and the oxide structure. The dynamics expression for the formation of UO{sub 2} was derived. At the beginning, the dynamic expression was nonlinear, but switched to linear subsequently for uranium in air and humid oxygen. That is, the growth kinetics of UO{sub 2} can be divided into two stages: nonlinear portion and linear portion. Using the kinetic data of linear portion, the activation energy of reaction between uranium and air was calculated about 46.0 kJ/mol. However the content of oxide as a function of time was linear in humid helium ambience. Contrast the dynamics results, it prove that the absence of oxygen would accelerate the corrosion rate of uranium in the humid gas. We can find that the XRD and Rietveld method are a useful convenient method to estimate the kinetics and thermodynamics of solid-gas reaction.

  10. Study the oxidation kinetics of uranium using XRD and Rietveld method

    Science.gov (United States)

    Zhang, Yanzhi; Guan, Weijun; Wang, Qinguo; Wang, Xiaolin; Lai, Xinchun; Shuai, Maobing

    2010-03-01

    The surface oxidation of uranium metal has been studied by X-ray diffraction (XRD) and Rietveld method in the range of 50~300°C in air. The oxidation processes are analyzed by XRD to determine the extent of surface oxidation and the oxide structure. The dynamics expression for the formation of UO2 was derived. At the beginning, the dynamic expression was nonlinear, but switched to linear subsequently for uranium in air and humid oxygen. That is, the growth kinetics of UO2 can be divided into two stages: nonlinear portion and linear portion. Using the kinetic data of linear portion, the activation energy of reaction between uranium and air was calculated about 46.0 kJ/mol. However the content of oxide as a function of time was linear in humid helium ambience. Contrast the dynamics results, it prove that the absence of oxygen would accelerate the corrosion rate of uranium in the humid gas. We can find that the XRD and Rietveld method are a useful convenient method to estimate the kinetics and thermodynamics of solid-gas reaction.

  11. Electrochemical oxidation of COD from real textile wastewaters: Kinetic study and energy consumption.

    Science.gov (United States)

    Zou, Jiaxiu; Peng, Xiaolan; Li, Miao; Xiong, Ying; Wang, Bing; Dong, Faqin; Wang, Bin

    2017-03-01

    In the present study, the electrochemical oxidation of real wastewaters discharged by textile industry was carried out using a boron-doped diamond (BDD) anode. The effect of operational variables, such as applied current density (20-100 mA·cm -2 ), NaCl concentration added to the real wastewaters (0-3 g·L -1 ), and pH value (2.0-10.0), on the kinetics of COD oxidation and on the energy consumption was carefully investigated. The obtained experimental results could be well matched with a proposed kinetic model, in which the indirect oxidation mediated by electrogenerated strong oxidants would be described through a pseudo-first-order kinetic constant k. Values of k exhibited a linear increase with increasing applied current density and decreasing pH value, and an exponential increase with NaCl concentration. Furthermore, high oxidation kinetics resulted in low specific energy consumption, but this conclusion was not suitable to the results obtained under different applied current density. Under the optimum operational conditions, it only took 3 h to complete remove the COD in the real textile wastewaters and the specific energy consumption could be as low as 11.12 kWh·kg -1  COD. The obtained results, low energy consumption and short electrolysis time, allowed to conclude that the electrochemical oxidation based on BDD anodes would have practical industrial application for the treatment of real textile wastewater. Copyright © 2016 Elsevier Ltd. All rights reserved.

  12. Radical-induced oxidation of RAFT agents : a kinetic study

    NARCIS (Netherlands)

    Li, Changxi; He, Junpo; Zhou, Yanwu; Gu, Yuankai; Yang, Yuliang

    2011-01-01

    Radical-induced oxidn. of reversible addn.-fragmentation chain transfer (RAFT) agents is studied with respect to the effect of mol. structure on oxidn. rate. The radicals are generated by homolysis of either azobisisobutyronitrile or alkoxyamine and transformed in situ immediately into peroxy

  13. Experimental and Chemical Kinetic Modeling Study of Dimethylcyclohexane Oxidation and Pyrolysis

    KAUST Repository

    Eldeeb, Mazen A.

    2016-08-30

    A combined experimental and chemical kinetic modeling study of the high-temperature ignition and pyrolysis of 1,3-dimethylcyclohexane (13DMCH) is presented. Ignition delay times are measured behind reflected shock waves over a temperature range of 1049–1544 K and pressures of 3.0–12 atm. Pyrolysis is investigated at average pressures of 4.0 atm at temperatures of 1238, 1302, and 1406 K. By means of mid-infrared direct laser absorption at 3.39 μm, fuel concentration time histories are measured under ignition and pyrolytic conditions. A detailed chemical kinetic model for 13DMCH combustion is developed. Ignition measurements show that the ignition delay times of 13DMCH are longer than those of its isomer, ethylcyclohexane. The proposed chemical kinetic model predicts reasonably well the effects of equivalence ratio and pressure, with overall good agreement between predicted and measured ignition delay times, except at low dilution levels and high pressures. Simulated fuel concentration profiles agree reasonably well with the measured profiles, and both highlight the influence of pyrolysis on the overall ignition kinetics at high temperatures. Sensitivity and reaction pathway analyses provide further insight into the kinetic processes controlling ignition and pyrolysis. The work contributes toward improved understanding and modeling of the oxidation and pyrolysis kinetics of cycloalkanes.

  14. Experimental and Kinetic Modeling Study of Methanol Ignition and Oxidation at High Pressure

    DEFF Research Database (Denmark)

    Aranda, V.; Christensen, J. M.; Alzueta, Maria

    2013-01-01

    A detailed chemical kinetic model for oxidation of CH3OH at high pressure and intermediate temperatures has been developed and validated experimentally. Ab initio calculations and Rice–Ramsperger–Kassel–Marcus/transition state theory (RRKM/TST) analysis were used to obtain rate coefficients for CH...... the conditions studied, the onset temperature for methanol oxidation was not dependent on the stoichiometry, whereas increasing pressure shifted the ignition temperature toward lower values. Model predictions of the present experimental results, as well as rapid compression machine data from the literature, were...

  15. Palladium nanoparticles anchored on graphene nanosheets: Methanol, ethanol oxidation reactions and their kinetic studies

    International Nuclear Information System (INIS)

    Nagaraju, D.H.; Devaraj, S.; Balaya, P.

    2014-01-01

    Highlights: • Palladium nanoparticles decorated graphene is synthesized in a single step. • Electro-catalytic activity of Gra/Pd toward alcohol oxidation is evaluated. • 1:1 Gra/Pd exhibits good electro-catalytic activity and efficient electron transfer. - Abstract: Palladium nanoparticles decorated graphene (Gra/Pd nanocomposite) was synthesized by simultaneous chemical reduction of graphene oxide and palladium salt in a single step. The negatively charged graphene oxide (GO) facilitates uniform distribution of Pd 2+ ions onto its surface. The subsequent reduction by hydrazine hydrate provides well dispersed Pd nanoparticles decorated graphene. Different amount of Pd nanoparticles on graphene was synthesized by changing the volume to weight ratio of GO to PdCl 2 . X-ray diffraction studies showed FCC lattice of Pd with predominant (1 1 1) plane. SEM and TEM studies revealed that thin graphene nanosheets are decorated by Pd nanoparticles. Raman spectroscopic studies revealed the presence of graphene nanosheets. The electro-catalytic activity of Gra/Pd nanocomposites toward methanol and ethanol oxidation in alkaline medium was evaluated by cyclic voltammetric studies. 1:1 Gra/Pd nanocomposite exhibited good electro-catalytic activity and efficient electron transfer. The kinetics of electron transfer was studied using chronoamperometry. Improved electro-catalytic activity of 1:1 Gra/Pd nanocomposite toward alcohol oxidation makes it as a potential anode for the alcohol fuel cells

  16. Palladium nanoparticles anchored on graphene nanosheets: Methanol, ethanol oxidation reactions and their kinetic studies

    Energy Technology Data Exchange (ETDEWEB)

    Nagaraju, D.H., E-mail: dhnagu@gmail.com [Department of Mechanical Engineering, 117 576 (Singapore); Materials Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900 (Saudi Arabia); Devaraj, S. [Department of Mechanical Engineering, 117 576 (Singapore); School of Chemical and Biotechnology, SASTRA University, Thanjavur, 613 401 (India); Balaya, P., E-mail: mpepb@nus.edu.sg [Department of Mechanical Engineering, 117 576 (Singapore); Engineering Science Program, National University of Singapore, 117 576 (Singapore)

    2014-12-15

    Highlights: • Palladium nanoparticles decorated graphene is synthesized in a single step. • Electro-catalytic activity of Gra/Pd toward alcohol oxidation is evaluated. • 1:1 Gra/Pd exhibits good electro-catalytic activity and efficient electron transfer. - Abstract: Palladium nanoparticles decorated graphene (Gra/Pd nanocomposite) was synthesized by simultaneous chemical reduction of graphene oxide and palladium salt in a single step. The negatively charged graphene oxide (GO) facilitates uniform distribution of Pd{sup 2+} ions onto its surface. The subsequent reduction by hydrazine hydrate provides well dispersed Pd nanoparticles decorated graphene. Different amount of Pd nanoparticles on graphene was synthesized by changing the volume to weight ratio of GO to PdCl{sub 2}. X-ray diffraction studies showed FCC lattice of Pd with predominant (1 1 1) plane. SEM and TEM studies revealed that thin graphene nanosheets are decorated by Pd nanoparticles. Raman spectroscopic studies revealed the presence of graphene nanosheets. The electro-catalytic activity of Gra/Pd nanocomposites toward methanol and ethanol oxidation in alkaline medium was evaluated by cyclic voltammetric studies. 1:1 Gra/Pd nanocomposite exhibited good electro-catalytic activity and efficient electron transfer. The kinetics of electron transfer was studied using chronoamperometry. Improved electro-catalytic activity of 1:1 Gra/Pd nanocomposite toward alcohol oxidation makes it as a potential anode for the alcohol fuel cells.

  17. Kinetic studies of oxidation of {gamma}-AlON-TiN composites

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Zuotai; Wang Xidong; Li Wenchao

    2005-01-25

    The present article deals with the investigation of the oxidation kinetics of {gamma}-aluminum oxynitride-Titanium Nitride composites (AlON-TiN) in the temperature range of 1100-1300 deg. C by thermogravimetry. Oxidation experiments with AlON-TiN composite plates have been carried out in air both in isothermal and nonisothermal modes. The results showed that the rate of oxidation was negligible below 1000 deg. C, and showed an increase with increasing temperature at higher temperature. Both isothermal studies as well as experiments with ramped temperature clearly indicated that the mechanism of the reaction changes around 1400 deg. C. In the nonisothermal mode, the oxidation curve showed an increased reaction rate in this temperature range. Oxidation of AlON-TiN composite results in {alpha}-Al{sub 2}O{sub 3} and TiO{sub 2} at a low temperature and Al{sub 2}TiO{sub 5} at higher temperature. The buildup of the product layer leads to diffusion controlled kinetics. In the nonisothermal experiments, the phase transformation from Al{sub 2}O{sub 3} and TiO{sub 2}, to a Al{sub 2}TiO{sub 5} product layer at higher temperature would lead to crack formation, thereby leading to direct chemical reaction. From the experiments for the isothermal oxidation of AlON-TiN composite plates, the overall reactions are separated into three stages: chemistry reaction-controlling stage; chemical reaction- and diffusion-mixed-controlled stage; diffusion-controlled stage. The apparent activation energy for the experiments were calculated to be 10.109, 2.19 and 5.614 kJ mol{sup -1}, respectively, in the above three stages.

  18. Corrosion mechanisms of zirconium alloys - study of the initial oxidation kinetics and of the mechanical behaviour of the metal/oxide system

    International Nuclear Information System (INIS)

    Parise, M.

    1996-12-01

    Nuclear fuel claddings are made of zirconium alloys. The conditions of use lead the cladding oxidize outside. The so-formed layers behaves like a thermal barrier and prevents from using oxidized claddings with an oxide thickness larger than 100 μm. The oxidation kinetic is approximately cubic for oxide thicknesses smaller than about 2μm, linear beyond. A kinetic model has been proposed which estimates the post-transition growth rate from the kinetic parameters of the pre-transition state and morphological features of post-transition layers. This work aims at providing the necessary elements to validate this model and studying the layers around the kinetic transition, in order to determine whether the oxidation mechanisms before and after the transition are similar. Thicknesses of the 50 - 500 nm range of the oxide layers are measured by an optical method; pre-transition kinetics are thus precisely determined. The effect of the composition, the thermal treatment and the presence of oxygen in solid solution is studied. The morphological and crystallographic study of the layers show that they exhibit a lot of similarities before and after the kinetic transition. The results concerning the kinetic aspects and the morphology of the post-transition layers point out that the proposed model leads to realistic post-transition growth rates. Furthermore, the kinetic transition corresponds to the appearance of cracks in the oxide layer. The mechanical behaviour of the metal/oxide system has been modelled at different scales. When the specific behaviours of the metal and the oxide are taken into account together with the interface geometry, radial stresses appear, which are high enough to locally open cracks. The appearance and localization of cracks depend on both the interface geometry and the stress distribution in the metal/oxide system. (author)

  19. Kinetic study of the hydration of propylene oxide in the presence of heterogeneous catalyst

    Directory of Open Access Journals (Sweden)

    Akyalcin Sema

    2017-01-01

    Full Text Available The kinetics of the hydration of propylene oxide was studied using a pressurized batch reactor for both uncatalyzed and heterogeneously catalyzed reactions. Lewatit MonoPlus M500/HCO3 - was used as heterogeneous catalyst, which showed better performance than Dowex Marathon A/HCO3 -. The effects of the parameters, namely internal and external diffusion resistances, temperature, catalyst loading and mole ratios of reactants, on the reaction rate were studied. The uncatalyzed and heterogeneously catalyzed reactions were proven to follow a series-parallel irreversible homogeneous mechanism. The temperature dependencies of the rate constants appearing in the rate expressions were determined.

  20. Oxidation of Methionine by Tripropylammonium Fluorochromate-A Kinetic and Mechanistic Study

    Directory of Open Access Journals (Sweden)

    S. Sheik Mansoor

    2011-01-01

    Full Text Available The kinetics of oxidation of methionine (Met by tripropylammonium fluorochromate (TriPAFC has been studied in the presence of chloroacetic acid in aqueous acetic acid medium. The reaction is first order with respect to methionine, TriPAFC and acid. The reaction rate has been determined at different temperatures and activation parameters calculated. With an increase in the amount of acetic acid in its aqueous mixture, the rate increases. The reaction does not induce polymerization of acrylonitrile. A suitable mechanism has been proposed.

  1. Palladium nanoparticles anchored on graphene nanosheets: Methanol, ethanol oxidation reactions and their kinetic studies

    KAUST Repository

    Nagaraju, Doddahalli H.

    2014-12-01

    Palladium nanoparticles decorated graphene (Gra/Pd nanocomposite) was synthesized by simultaneous chemical reduction of graphene oxide and palladium salt in a single step. The negatively charged graphene oxide (GO) facilitates uniform distribution of Pd2+ ions onto its surface. The subsequent reduction by hydrazine hydrate provides well dispersed Pd nanoparticles decorated graphene. Different amount of Pd nanoparticles on graphene was synthesized by changing the volume to weight ratio of GO to PdCl2. X-ray diffraction studies showed FCC lattice of Pd with predominant (1 1 1) plane. SEM and TEM studies revealed that thin graphene nanosheets are decorated by Pd nanoparticles. Raman spectroscopic studies revealed the presence of graphene nanosheets. The electro-catalytic activity of Gra/Pd nanocomposites toward methanol and ethanol oxidation in alkaline medium was evaluated by cyclic voltammetric studies. 1:1 Gra/Pd nanocomposite exhibited good electro-catalytic activity and efficient electron transfer. The kinetics of electron transfer was studied using chronoamperometry. Improved electro-catalytic activity of 1:1 Gra/Pd nanocomposite toward alcohol oxidation makes it as a potential anode for the alcohol fuel cells. © 2014 Elsevier Ltd.

  2. Mechanism of pyrogallol red oxidation induced by free radicals and reactive oxidant species. A kinetic and spectroelectrochemistry study.

    Science.gov (United States)

    Atala, E; Velásquez, G; Vergara, C; Mardones, C; Reyes, J; Tapia, R A; Quina, F; Mendes, M A; Speisky, H; Lissi, E; Ureta-Zañartu, M S; Aspée, A; López-Alarcón, C

    2013-05-02

    Pyrogallol red (PGR) presents high reactivity toward reactive (radical and nonradical) species (RS). This property of PGR, together with its characteristic spectroscopic absorption in the visible region, has allowed developing methodologies aimed at evaluating the antioxidant capacity of foods, beverages, and human fluids. These methods are based on the evaluation of the consumption of PGR induced by RS and its inhibition by antioxidants. However, at present, there are no reports regarding the degradation mechanism of PGR, limiting the extrapolation to how antioxidants behave in different systems comprising different RS. In the present study, we evaluate the kinetics of PGR consumption promoted by different RS (peroxyl radicals, peroxynitrite, nitrogen dioxide, and hypochlorite) using spectroscopic techniques and detection of product by HPLC mass spectrometry. The same pattern of oxidation and spectroscopic properties of the products is observed, independently of the RS employed. Mass analysis indicates the formation of only one product identified as a quinone derivative, excluding the formation of peroxides or hydroperoxides and/or chlorinated compounds, in agreement with FOX's assays and oxygen consumption experiments. Cyclic voltammetry, carried out at different pH's, shows an irreversible oxidation of PGR, indicating the initial formation of a phenoxy radical and a second charge transfer reaction generating an ortho-quinone derivative. Spectroelectrochemical oxidation of PGR shows oxidation products with identical UV-visible absorption properties to those observed in RS-induced oxidation.

  3. Fenton-Like Oxidation of Malachite Green Solutions: Kinetic and Thermodynamic Study

    Directory of Open Access Journals (Sweden)

    Saeedeh Hashemian

    2013-01-01

    Full Text Available Oxidation by Fenton-like (Fe3+/H2O2 reactions is proven to be an economically feasible process for destruction of a variety of hazardous pollutants in wastewater. In this study, the degradation and mineralization of malachite green dye are reported using Fenton-like reaction. The effects of different parameters like pH of the solution, the initial concentrations of Fe3+, H2O2, and dye, temperature, and added electrolytes (Cl− and on the oxidation of the dye were investigated. Optimized condition was determined. The efficiency of 95.5% degradation of MAG after 15 minutes of reaction at pH 3 was obtained. TOC removal indicates partial and insignificant mineralization of malachite green dye. The results of experiments showed that degradation of malachite green dye in Fenton-like oxidation process can be described with a pseudo-second-order kinetic model. The thermodynamic constants of the Fenton oxidation process were evaluated. The results implied that the oxidation process was feasible, spontaneous, and endothermic. The results will be useful for designing the treatment systems of various dye-containing wastewaters.

  4. Levofloxacin oxidation by ozone and hydroxyl radicals: kinetic study, transformation products and toxicity.

    Science.gov (United States)

    Hamdi El Najjar, Nasma; Touffet, Arnaud; Deborde, Marie; Journel, Romain; Leitner, Nathalie Karpel Vel

    2013-10-01

    This work was carried out to investigate the fate of the antibiotic levofloxacin upon oxidation with ozone and hydroxyl radicals. A kinetic study was conducted at 20 °C for each oxidant. Ozonation experiments were performed using a competitive kinetic method with carbamazepin as competitor. Significant levofloxacin removal was observed during ozonation and a rate constant value of 6.0×10(4) M(-1) s(-1) was obtained at pH 7.2. An H2O2/UV system was used for the formation of hydroxyl radicals HO. The rate constant of HO was determined in the presence of a high H2O2 concentration. The kinetic expressions yielded a [Formula: see text] value of 4.5×10(9) M(-1) s(-1) at pH 6.0 and 5.2×10(9) M(-1) s(-1) at pH 7.2. These results were used to develop a model to predict the efficacy of the ozonation process and pharmaceutical removal was estimated under different ozonation conditions (i.e. oxidant concentrations and contact times). The results showed that levofloxacin was completely degraded by molecular ozone during ozonation of water and that hydroxyl radicals had no effect in real waters conditions. Moreover, LC/MS/MS and toxicity assays using Lumistox test were performed to identify ozonation transformation products. Under these conditions, four transformation products were observed and their chemical structures were proposed. The results showed an increase in toxicity during ozonation, even after degradation of all of the observed transformation products. The formation of other transformation products not identified under our experimental conditions could be responsible for the observed toxicity. These products might be ozone-resistant and more toxic to Vibrio fisheri than levofloxacin. Copyright © 2013 Elsevier Ltd. All rights reserved.

  5. Kinetic Studies on the Selective Oxidation of Benzyl Alcohols in Organic Medium under Phase Transfer Catalysis

    Directory of Open Access Journals (Sweden)

    K. Bijudas

    2014-07-01

    Full Text Available Kinetic studies on the oxidation of benzyl alcohol and substituted benzyl alcohols in benzene as the reaction medium have been studied by using potassium dichromate under phase transfer catalysis (PTC. The phase transfer catalysts (PT catalysts used were tetrabutylammonium bromide (TBAB and tetrabutylphosphonium bromide (TBPB.  Benzyl alcohols were selectively oxidised to corresponding benzaldehydes in good yield (above 90%.  The order of reactivity among the studied benzyl alcohols is p - OCH3 > p - CH3 > - H > p - Cl.  Plots of log k2 versus Hammett's substituent constant (s has been found to be curve shaped and this suggests that there should be a continuous change in transition state with changes in substituent present in the substrate from electron donating to electron withdrawing. A suitable mechanism has been suggested in which the rate determining step involves both C - H bond cleavage and C - O bond formations in concerted manner. © 2014 BCREC UNDIP. All rights reserved.Received: 16th March 2014; Revised: 18th May 2014; Accepted: 18th May 2014[How to Cite: Bijudas, K., Bashpa, P., Nair, T.D.R. (2014. Kinetic Studies on the Selective Oxidation of Benzyl Alcohol and Substituted Benzyl Alcohols in Organic Medium under Phase Transfer Catalysis. Bulletin of Chemical Reaction Engineering & Catalysis, 9 (2: 142-147. (doi:10.9767/bcrec.9.2.6476.142-147][Permalink/DOI: http://dx.doi.org/10.9767/bcrec.9.2.6476.142-147] 

  6. Phenol oxidation by mushroom waste extracts: a kinetic and thermodynamic study.

    Science.gov (United States)

    Pigatto, Gisele; Lodi, Alessandra; Aliakbarian, Bahar; Converti, Attilio; da Silva, Regildo Marcio Gonçalves; Palma, Mauri Sérgio Alves

    2013-09-01

    Tyrosinase activity of mushroom extracts was checked for their ability to degrade phenol. Phenol oxidation kinetics was investigated varying temperature from 10 to 60 °C and the initial values of pH, enzyme activity and phenol concentration in the ranges 4.5-8.5, 1.43-9.54 U/mL and 50-600 mg/L, respectively. Thermodynamic parameters of phenol oxidation and tyrosinase reversible inactivation were estimated. Tyrosinase thermostability was also investigated through residual activity tests after extracts exposition at 20-50 °C, whose results allowed exploring the thermodynamics of enzyme irreversible thermoinactivation. This study is the first attempt to separate the effects of reversible unfolding and irreversible denaturation of tyrosinase on its activity. Extracts were finally tested on a real oil mill wastewater. Copyright © 2013 Elsevier Ltd. All rights reserved.

  7. Experimental Study and Mathematical Modeling of Self-Sustained Kinetic Oscillations in Catalytic Oxidation of Methane over Nickel.

    Science.gov (United States)

    Lashina, Elena A; Kaichev, Vasily V; Saraev, Andrey A; Vinokurov, Zakhar S; Chumakova, Nataliya A; Chumakov, Gennadii A; Bukhtiyarov, Valerii I

    2017-09-21

    The self-sustained kinetic oscillations in the oxidation of CH 4 over Ni foil have been studied at atmospheric pressure using an X-ray diffraction technique and mass spectrometry. It has been shown that the regular oscillations appear under oxygen-deficient conditions; CO, CO 2 , H 2 , and H 2 O are detected as the products. According to in situ X-ray diffraction measurements, nickel periodically oxidizes to NiO initiating the reaction-rate oscillations. To describe the oscillations, we have proposed a five-stage mechanism of the partial oxidation of methane over Ni and a corresponding three-variable kinetic model. The mechanism considers catalytic methane decomposition, dissociative adsorption of oxygen, transformation of chemisorbed oxygen to surface nickel oxide, and reaction of adsorbed carbon and oxygen species to form CO. Analysis of the kinetic model indicates that the competition of two processes, i.e., the oxidation and the carbonization of the catalyst surface, is the driving force of the self-sustained oscillations in the oxidation of methane. We have compared this mechanism with the detailed 18-stage mechanism described previously by Lashina et al. (Kinetics and Catalysis 2012, 53, 374-383). It has been shown that both kinetic mechanisms coupled with a continuous stirred-tank reactor model describe well the oscillatory behavior in the oxidation of methane under non-isothermal conditions.

  8. Kinetic studies of isooctane partial oxidation over a nickel-based catalyst

    International Nuclear Information System (INIS)

    Ibrahim, Hussameldin; Idem, Raphael; Aboudheir, Ahmed

    2006-01-01

    The production of hydrogen (H 2 ) for fuel cell applications in mobile vehicles by reforming technologies such as partial oxidation of various fossil fuels has gained much attention recently. In this study, the production of H 2 by the catalytic partial oxidation of isooctane ((C 8 H 18 ) used here as a surrogate for gasoline) was investigated over alumina (AI 2 O 3 )supported nickel (Ni) catalyst. The work investigated the kinetics of the partial oxidation of isooctane over a stable Ni/□-AI 2 O 3 catalyst in the range of 863 to 913 K, at atmospheric pressure, W/F i c8 in the range of 1.97 to 8.58 g h mol - 1, and molar feed ratio in the range of 2.0 to 8.0 experiments to obtain kinetic data were performed in a 12.7 mm diameter Inconel micro-reactor housed in an electrically controlled furnace. The chemical reaction was then modeled using rate models developed from the Langmuir-Hinshelwood-hougen-Watson (LHHW) and Eley-Rideal (ER) formulations. The model parameters were estimated using an adaptive Gauss-Newton and Marquardi-Levenberg minimization algorithm. Rival models were screened for their thermodynamic consistency and physicochemical significance of estimated parameters. Langmuir-Hinshelwood-hougen-Watson mechanism requiring the dissociative adsorption of isooctane and oxygen on two different sites appeared to be the most likely pathway for the partial oxidation reaction of isooctane. Reaction order with respect to isooctane indicates the strong coverage of nickel by isooctane. The activation energy of 73±3.1 kJ mol - 1 estimated from the LHHW model is consistent with the trend observed with lower hydrocarbons.(Author)

  9. Kinetic Modeling of Methionine Oxidation in Monoclonal Antibodies from Hydrogen Peroxide Spiking Studies.

    Science.gov (United States)

    Hui, Ada; Lam, Xanthe M; Kuehl, Christopher; Grauschopf, Ulla; Wang, Y John

    2015-01-01

    When isolator technology is applied to biotechnology drug product fill-finish process, hydrogen peroxide (H2O2) spiking studies for the determination of the sensitivity of protein to residual peroxide in the isolator can be useful for assessing a maximum vapor phase hydrogen peroxide (VPHP) level. When monoclonal antibody (mAb) drug products were spiked with H2O2, an increase in methionine (Met 252 and Met 428) oxidation in the Fc region of the mAbs with a decrease in H2O2 concentration was observed for various levels of spiked-in peroxide. The reaction between Fc-Met and H2O2 was stoichiometric (i.e., 1:1 molar ratio), and the reaction rate was dependent on the concentrations of mAb and H2O2. The consumption of H2O2 by Fc-Met oxidation in the mAb followed pseudo first-order kinetics, and the rate was proportional to mAb concentration. The extent of Met 428 oxidation was half of that of Met 252, supporting that Met 252 is twice as reactive as Met 428. Similar results were observed for free L-methionine when spiked with H2O2. However, mAb formulation excipients may affect the rate of H2O2 consumption. mAb formulations containing trehalose or sucrose had faster H2O2 consumption rates than formulations without the sugars, which could be the result of impurities (e.g., metal ions) present in the excipients that may act as catalysts. Based on the H2O2 spiking study results, we can predict the amount Fc-Met oxidation for a given protein concentration and H2O2 level. Our kinetic modeling of the reaction between Fc-Met oxidation and H2O2 provides an outline to design a H2O2 spiking study to support the use of VPHP isolator for antibody drug product manufacture. Isolator technology is increasing used in drug product manufacturing of biotherapeutics. In order to understand the impact of residual vapor phase hydrogen peroxide (VPHP) levels on protein product quality, hydrogen peroxide (H2O2) spiking studies may be performed to determine the sensitivity of monoclonal antibody

  10. Heterocatalytic Fenton oxidation process for the treatment of tannery effluent: kinetic and thermodynamic studies.

    Science.gov (United States)

    Karthikeyan, S; Ezhil Priya, M; Boopathy, R; Velan, M; Mandal, A B; Sekaran, G

    2012-06-01

    BACKGROUND, AIM, SCOPE: Treatment of wastewater has become significant with the declining water resources. The presence of recalcitrant organics is the major issue in meeting the pollution control board norms in India. The theme of the present investigation was on partial or complete removal of pollutants or their transformation into less toxic and more biodegradable products by heterogeneous Fenton oxidation process using mesoporous activated carbon (MAC) as the catalyst. Ferrous sulfate (FeSO(4)·7H(2)O), sulfuric acid (36 N, specific gravity 1.81, 98% purity), hydrogen peroxide (50% v/v) and all other chemicals used in this study were of analytical grade (Merck). Two reactors, each of height 50 cm and diameter 6 cm, were fabricated with PVC while one reactor was packed with MAC of mass 150 g and other without MAC served as control. The oxidation process was presented with kinetic and thermodynamic constants for the removal of COD, BOD, and TOC from the wastewater. The activation energy (Ea) for homogeneous and heterogeneous Fenton oxidation processes were 44.79 and 25.89 kJ/mol, respectively. The thermodynamic parameters ΔG, ΔH, and ΔS were calculated for the oxidation processes using Van't Hoff equation. Furthermore, the degradation of organics was confirmed through FTIR and UV-visible spectroscopy, and cyclic voltammetry. The heterocatalytic Fenton oxidation process efficiently increased the biodegradability index (BOD/COD) of the tannery effluent. The optimized conditions for the heterocatalytic Fenton oxidation of organics in tannery effluent were pH 3.5, reaction time-4 h, and H(2)O(2)/FeSO(4)·7H(2)O in the molar ratio of 2:1.

  11. Kinetic studies of potassium permanganate adsorption by activated carbon and its ability as ethylene oxidation material

    Science.gov (United States)

    Aprilliani, F.; Warsiki, E.; Iskandar, A.

    2018-03-01

    Generally, ethylene production in many horticultural products has been seen to be detrimental to the quality during storage and distribution process. For this reason, removing ethylene from storage or distribution atmosphere is needed to maintain the quality. One of the technologies that can be applied is the use of potassium permanganate (KMnO4). KMnO4 is an active compound that can be used as an oxidizing agent on ethylene removal process. KMnO4 is not recommended for direct used application. As the result, additional material is required to impregnate the potassium permanganate. The inert materials used are commercial activated carbon. Activated carbon is chosen because it has high surface area. The purpose of this research is to determine kinetics adsorption and oxidation model of ethylene removal material. The kinetics adsorption was determined using the pseudo-first and second-order kinetic models. The data on adsorption process show that the second-order equation is more suitable to express the adsorption process on this research. The analyzing of the ethylene oxidation capacity increased with time until it reaches an optimal value. The ethylene oxidation rate is able to be estimated by the formula r = 0.1967 [C2H4]0.99 [KMnO4]0.01; MSE = 0.44 %. The actual and estimation data of ethylene oxidation show that the model is fitted to describe the actual ethylene oxidation under same experimental conditions.

  12. Efficient removal of cobalt from aqueous solution by zinc oxide nanoparticles. Kinetic and thermodynamic studies

    Energy Technology Data Exchange (ETDEWEB)

    Khezami, L.; Modwi, A. [Al Imam Mohammad Ibn Saud Islamic Univ. (IMSIU), Riyadh (Saudi Arabia). Dept. of Chemistry; Taha, Kamal K. [Al Imam Mohammad Ibn Saud Islamic Univ. (IMSIU), Riyadh (Saudi Arabia). Dept. of Chemistry; Univ. of Bahri, Khartoum (Sudan). College of Applied and Industrial Sciences

    2017-08-01

    This article deals with the removal of cobalt ions using zinc oxide nanopowder. The nanomaterial was prepared via the sol-gel method under supercritical drying. The nanomaterial was characterised via XRD, SEM, EDX, FTIR, and BET surface area techniques. The kinetics, equilibrium, and thermodynamic studies of the metal ions adsorption on the nanomaterial were conducted in batch mode experiments by varying some parameters such as pH, contact time, initial ion concentrations, nanoparticles dose, and temperature. The data revealed significant dependence of the adsorption process on concentration, and the temperature was found to enhance the adsorption rate indicating an endothermic nature of the adsorption. The adsorption complied well with the pseudo-second-order kinetics model. The adsorption process was found to match the Langmuir adsorption isotherm. The ZnO nanoparticles could successfully remove up to 125 mg.g{sup -1} of Co(II) ions at elevated temperature. The metal ions adsorption could be described as an endothermic, spontaneous physisorption process. A mechanism for the metal ions adsorption was proposed.

  13. Efficient removal of cobalt from aqueous solution by zinc oxide nanoparticles. Kinetic and thermodynamic studies

    International Nuclear Information System (INIS)

    Khezami, L.; Modwi, A.; Taha, Kamal K.; Univ. of Bahri, Khartoum

    2017-01-01

    This article deals with the removal of cobalt ions using zinc oxide nanopowder. The nanomaterial was prepared via the sol-gel method under supercritical drying. The nanomaterial was characterised via XRD, SEM, EDX, FTIR, and BET surface area techniques. The kinetics, equilibrium, and thermodynamic studies of the metal ions adsorption on the nanomaterial were conducted in batch mode experiments by varying some parameters such as pH, contact time, initial ion concentrations, nanoparticles dose, and temperature. The data revealed significant dependence of the adsorption process on concentration, and the temperature was found to enhance the adsorption rate indicating an endothermic nature of the adsorption. The adsorption complied well with the pseudo-second-order kinetics model. The adsorption process was found to match the Langmuir adsorption isotherm. The ZnO nanoparticles could successfully remove up to 125 mg.g -1 of Co(II) ions at elevated temperature. The metal ions adsorption could be described as an endothermic, spontaneous physisorption process. A mechanism for the metal ions adsorption was proposed.

  14. Oxidation of phenyl alanine by pyridinium chlorochromate in acidic DMF–water medium: A kinetic study

    Directory of Open Access Journals (Sweden)

    B.L. Hiran

    2016-11-01

    Full Text Available The kinetics of oxidation of phenyl alanine by pyridinium chlorochromate in DMF–water (70:30% mixture in presence of perchloric acid leads to the formation of corresponding aldehyde. The reaction is of first order each in [PCC], [HClO4] and [AA]. Michaelis–Menten type kinetics was observed with phenyl alanine. The reaction rates were determined at different temperatures [25, 30, 35, 40, 45, 50 °C] and the activation parameters were calculated. The reaction does not induce polymerization of acrylonitrile. With an increase in the amount of DMF in its aqueous mixture, the rate increases. A suitable mechanism for the reaction was postulated.

  15. Chlorine dioxide oxidation of Escherichia coli in water - A study of the disinfection kinetics and mechanism.

    Science.gov (United States)

    Ofori, Isaac; Maddila, Suresh; Lin, Johnson; Jonnalagadda, Sreekantha B

    2017-06-07

    This study investigated the kinetics and mechanism of chlorine dioxide (ClO 2 ) inactivation of a Gram-negative bacteria Escherichia coli (ATCC 35218) in oxidant demand free (ODF) water in detail as a function of disinfectant concentration (0.5-5.0 mg/L), water pH (6.5-8.5), temperature variations (4-37°C) and bacterial density (10 5 -10 7 cfu/mL). The effects of ClO 2 on bacterial cell morphology, outer membrane permeability, cytoplasmic membrane disruption and intracellular enzymatic activity were also studied to elucidate the mechanism of action on the cells. Increasing temperature and disinfectant concentration were proportional to the rate of cell killing, but efficacy was found to be significantly subdued at 0.5 mg/L and less dependent on the bacterial density. The bactericidal efficiency was higher at alkaline pH of 8 or above as compared to neutral and slightly acidic pH of 7 and 6.5 respectively. The disinfection kinetic curves followed a biphasic pattern of rapid inactivation within the initial 2 min which were followed by a tailing even in the presence of residual biocide. The curves were adequately described by the C avg Hom model. Transmission Electron Microscopy images of the bacteria cells exposed to lethal concentrations of ClO 2 indicated very little observable morphological damage to the outer membranes of the cells. ClO 2 however was found to increase the permeability of the outer and cytoplasmic membranes leading to the leakage of membrane components such as 260 nm absorbing materials and inhibiting the activity of the intracellular enzyme β-D-galactosidase. It is suggested that the disruption of the cytoplasmic membrane and subsequent efflux of intracellular components result in the inactivation of the Gram-negative bacteria.

  16. Kinetics and Mechanistic Study of Permanganate Oxidation of Fluorenone Hydrazone in Alkaline Medium

    Directory of Open Access Journals (Sweden)

    Ahmed Fawzy

    2016-01-01

    Full Text Available The oxidation kinetics of fluorenone hydrazone (FH using potassium permanganate in alkaline medium were measured at a constant ionic strength of 0.1 mol dm−3 and at 25°C using UV/VIS spectrophotometer. A first-order kinetics has been monitored in the reaction of FH with respect to [permanganate]. Less-than-unit order dependence of the reaction on [FH] and [OH−] was revealed. No pronounced effect on the reaction rate by increasing ionic strength was recorded. Intervention of free radicals was observed in the reaction. The reaction mechanism describing the kinetic results was illustrated which involves formation of 1 : 1 intermediate complex between fluorenone hydrazones and the active species of permanganate. 9H-Fluorenone as the corresponding ketone was found to be the final oxidation product of fluorenone hydrazone as confirmed by GC/MS analysis and FT-IR spectroscopy. The expression rate law for the oxidation reaction was deduced. The reaction constants and mechanism have been evaluated. The activation parameters associated with the rate-limiting step of the reaction, along with the thermodynamic quantities of the equilibrium constants, have been calculated and discussed.

  17. Kinetic Studies on the Oxidation of Some para and meta-Substituted Cinnamic Acids by Pyridinium Bromochromate in the Presence of Oxalic Acid (A Co-oxidation Study

    Directory of Open Access Journals (Sweden)

    G. Vanangamudi

    2009-01-01

    Full Text Available The kinetics of oxidation of cinnamic acids by pyridinium bromochromate (PBC in the presence of oxalic acid has been studied in acetic acid-water (60:40% medium. The reaction shows unit order dependence each with respect to oxidant as well as oxalic acid [OX], the order with respect to [H+] and [CA] are fractional. The reaction is acid catalyzed and a low dielectric constant favours the reaction. Increase the ionic strength has no effect on the reaction rate. In the case of substituted cinnamic acids the order with respect to substrate vary depending upon the nature of the substituent present in the ring. In general, the electron withdrawing substituents retard the rate while the electron releasing substituents enhance the rate of reaction. From the kinetic data obtained the activation parameters have been computed and a suitable mechanism has been proposed.

  18. Experimental and Chemical Kinetic Modeling Study of Dimethylcyclohexane Oxidation and Pyrolysis

    KAUST Repository

    Eldeeb, Mazen A.; Jouzdani, Shirin; Wang, Zhandong; Sarathy, Mani; Akih-Kumgeh, Benjamin

    2016-01-01

    A combined experimental and chemical kinetic modeling study of the high-temperature ignition and pyrolysis of 1,3-dimethylcyclohexane (13DMCH) is presented. Ignition delay times are measured behind reflected shock waves over a temperature range

  19. Decomposition of clofibric acid in aqueous media by advance oxidation techniques: kinetics study and degradation pathway

    International Nuclear Information System (INIS)

    Syed, M.; Khan, A.M.; Khan, R.A.

    2016-01-01

    This study investigates the decomposition of clofibric acid (CLF) by different advanced oxidation processes (AOPs), such as UV (254 nm), VUV (185 nm), UV / TiO/sub 2/ and VUV / TiO/sub 2/. The removal efficiencies of applied AOPs were compared in the presence and absence of dissolved oxygen. The removal efficiency of the studied AOPs towards degradation of CLF were found in the order of VUV / TiO/sub 2/ + O/sub 2/ > VUV/TiO/sub 2/ + N/sub 2/ > VUV alone > UV / TiO/sub 2/ + O/sub 2/ > UV / TiO/sub 2/ +N/sub 2/ > UV alone. The decomposition kinetics of CLF was found to follow pseudo-first order rate law. VUV / TiO2 process was found to be most cheap and effective one for decomposition of CLF as compared to other applied AOPs in terms of electrical energy per order. Degradation products resulting from the degradation processes were also investigated using UPLC-MS /MS, accordingly degradation pathway was proposed. (author)

  20. Adsorption Properties of Doxorubicin Hydrochloride onto Graphene Oxide: Equilibrium, Kinetic and Thermodynamic Studies

    Directory of Open Access Journals (Sweden)

    Zonghua Wang

    2013-05-01

    Full Text Available Doxorubicin hydrochloride (DOX is an effective anticancer agent for leukemia chemotherapy, although its clinical use has been limited because of its side effects such as cardiotoxicity, alopecia, vomiting, and leucopenia. Attention has been focussed on developing new drug carriers with high adsorption capacity and rapid adsorption rate in order to minimize the side effects of DOX. Graphene oxide (GO, a new type of nanomaterial in the carbon family, was prepared by Hummers method and used as adsorbent for DOX from aqueous solution. The physico-chemical properties of GO were characterized by transmission electron microscope (TEM, Fourier transform infrared spectroscopy (FTIR, zeta potential, and element analysis. The adsorption properties of DOX on GO were studied as a function of contact time, adsorbent dosage, temperature and pH value. The results showed that GO had a maximum adsorption capacity of 1428.57 mg/g and the adsorption isotherm data fitted the Langmuir model. The kinetics of adsorption fits a pseudo-second-order model. The thermodynamic studies indicate that the adsorption of DOX on GO is spontaneous and endothermic in nature.

  1. Studies of equilibrium and kinetics of adsorption of cesium ions by graphene oxide

    International Nuclear Information System (INIS)

    Oliveira, Fernando M.; Bueno, Vanessa N.; Oshiro, Maurício T.; Potiens Junior, Ademar J.; Hiromoto, Goro; Sakata, Solange K.; Rodrigues, Debora F.

    2017-01-01

    Cesium is one of the fission products of major radiological concern, it is often found in nuclear radioactive waste generated at nuclear power plants. Graphene Oxide (GO) has attracted great attention due to its functionalized surface, which includes hydroxyl, epoxy, carbonyl and carboxyl groups, with great capacity of complexation with metal ions and can be used as adsorbent to remove cations from aqueous solutions. In this work, a treatment of radioactive waste containing 137 Cs was studied. For the batch experiments of Cs + removal, 133 Cs concentrations remained after the adsorption were determined by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) and the results obtained were analyzed according to the Langmuir and Freundlich isotherms models. The kinetics of adsorption and Gibbs free energy were also determined. The Langmuir model was the best fit and defined a favorable adsorption. The cesium adsorption process is the pseudo-second model and the Gibbs free energy calculation indicated that the adsorption process is spontaneous. (author)

  2. Studies of equilibrium and kinetics of adsorption of cesium ions by graphene oxide

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, Fernando M.; Bueno, Vanessa N.; Oshiro, Maurício T.; Potiens Junior, Ademar J.; Hiromoto, Goro; Sakata, Solange K., E-mail: fmoliveira@ipen.br [Instituto de Pesquisas Energéticas e Nucleares (IPEN/CNEN-SP), São Paulo, SP (Brazil); Rodrigues, Debora F., E-mail: dfrigiro@central.uh.edu [Department of Civil and Environmental Engineering, University of Houston, TX (United States)

    2017-07-01

    Cesium is one of the fission products of major radiological concern, it is often found in nuclear radioactive waste generated at nuclear power plants. Graphene Oxide (GO) has attracted great attention due to its functionalized surface, which includes hydroxyl, epoxy, carbonyl and carboxyl groups, with great capacity of complexation with metal ions and can be used as adsorbent to remove cations from aqueous solutions. In this work, a treatment of radioactive waste containing {sup 137}Cs was studied. For the batch experiments of Cs{sup +} removal, {sup 133}Cs concentrations remained after the adsorption were determined by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) and the results obtained were analyzed according to the Langmuir and Freundlich isotherms models. The kinetics of adsorption and Gibbs free energy were also determined. The Langmuir model was the best fit and defined a favorable adsorption. The cesium adsorption process is the pseudo-second model and the Gibbs free energy calculation indicated that the adsorption process is spontaneous. (author)

  3. A study of sodium oxide crystallization mechanisms and kinetics in cold traps

    International Nuclear Information System (INIS)

    Latge, C.

    1984-04-01

    After showing up the present lack of data on crystallization mechanisms and kinetics, a number of tests were conducted on a sodium test loop equipped with two experimental cold traps. The effects of several geometric and thermohydraulic parameters on purification efficiency were also studied. The test results were used to develop a simulation model. An optimization code based on the model can be used to determine the nucleation and growth kinetics

  4. Ru (III) Catalyzed Oxidation of Aliphatic Ketones by N-Bromosuccinimide in Aqueous Acetic Acid: A Kinetic Study

    Science.gov (United States)

    Giridhar Reddy, P.; Ramesh, K.; Shylaja, S.; Rajanna, K. C.; Kandlikar, S.

    2012-01-01

    Kinetics of Ru (III) catalyzed oxidation of aliphatic ketones such as acetone, ethyl methyl ketone, diethyl ketone, iso-butylmethyl ketone by N-bromosuccinimide in the presence of Hg(II) acetate have been studied in aqueous acid medium. The order of [N-bromosuccinimide] was found to be zero both in catalyzed as well as uncatalyzed reactions. However, the order of [ketone] changed from unity to a fractional one in the presence of Ru (III). On the basis of kinetic features, the probable mechanisms are discussed and individual rate parameters evaluated. PMID:22654610

  5. Experimental and Kinetic Modeling Study of Ethyl Levulinate Oxidation in a Jet-Stirred Reactor

    KAUST Repository

    Wang, Jui-Yang

    2017-06-01

    A jet-stirred reactor was designed and constructed in the Clean Combustion Research Center (CCRC) at King Abdullah University of Science and Technology (KAUST); was validated with n-heptane, iso-octane oxidation and cyclohexene pyrolysis. Different configurations of the setup have been tested to achieve good agreement with results from the literature. Test results of the reactor indicated that installation of a pumping system at the downstream side in the experimental apparatus was necessary to avoid the reoccurrence of reactions in the sampling probe. Experiments in ethyl levulinate oxidation were conducted in the reactor under several equivalence ratios, from 600 to 1000 K, 1 bar and 2 s residence time. Oxygenated species detected included methyl vinyl ketone, levulinic acid and ethyl acrylate. Ethylene, methane, carbon monoxide, hydrogen, oxygen and carbon dioxide were further quantified with a gas chromatography, coupled with a flame ionization detector and a thermal conductivity detector. The ethyl levulinate chemical kinetic model was first developed by Dr. Stephen Dooley, Trinity College Dublin, and simulated under the same conditions, using the Perfect-Stirred Reactor code in Chemkin software. In comparing the simulation results with experimental data, some discrepancies were noted; predictions of ethylene production were not well matched. The kinetic model was improved by updating several classes of reactions: unimolecular decomposition, H-abstraction, C-C and C-O beta-scissions of fuel radicals. The updated model was then compared again with experimental results and good agreement was achieved, proving that the concerted eliminated reaction is crucial for the kinetic mechanism formulation of ethyl levulinate. In addition, primary reaction pathways and sensitivity analysis were performed to describe the role of molecular structure in combustion (800 and 1000 K for ethyl levulinate oxidation in the jet-stirred reactor).

  6. Proton non-Rutherford backscattering study of oxidation kinetics in Cu and Fe sulphides

    International Nuclear Information System (INIS)

    Chiari, M.; Giuntini, L.; Pratesi, G.; Santo, A.P.

    1998-01-01

    Non-Rutherford backscattering spectrometry (NBS) with 2.4 MeV protons was performed for depth profiling of oxygen in three species of copper and iron sulphides - pyrite, chalcopyrite and bornite - on both altered and fresh surfaces. The tarnished surfaces were obtained by bathing samples in H 2 O 2 (35% vol.) for 100 and 1000 s. The spectra collected were compared to simulations to extract quantitative data on oxygen depth distributions for the different bathing times. The measurements have shown that the kinetics of oxidation has completely different patterns in the three investigated minerals. (orig.)

  7. A first principles study of the oxidation energetics and kinetics of realgar

    Science.gov (United States)

    Renock, Devon; Becker, Udo

    2010-08-01

    Quantum-mechanical calculations allow resolving and quantifying in detail important aspects of reaction mechanisms such as spin transitions and oxygen dissociation that can be the major rate-limiting steps in redox processes on sulfide and oxide surfaces. In addition, this knowledge can help experimentalists in setting up the framework of rate equations that can be used to describe the kinetics of, e.g., oxidation processes. The unique molecular crystal structure of realgar, As 4S 4 clusters held together by van der Waals bonds, allows for a convenient quantum-mechanical (q.m.) cluster approach to investigate the thermodynamics and kinetic pathways of oxidation. The interaction of As 4S 4 clusters with oxygen and co-adsorbed ions provides a model system for understanding the molecular-scale processes that underpin empirically-derived rate expressions, and provides clues to the oxidation mechanisms of other sulfides and oxides. Two activated processes are shown to dominate the kinetics of oxidation by molecular oxygen: (i) a paramagnetic 3O to diamagnetic 1O spin transition and (ii) oxygen dissociation on the surface, in that order. The activation energies for the spin transition and O 2 dissociation step were determined to be 1.1 eV (106 kJ/mol) and 0.9 eV (87 kJ/mol), respectively, if molecular oxygen is the only reactant on the surface. In the case of As 4S 4, q.m. calculations reveal that 3O transfers its spin to the cluster and forms a low-spin, peroxo intermediate on the surface before dissociating. The adsorption of a hydroxide ion on the surface proximate to the 3O adsorption site changes the adsorption mechanism by lowering the activation energy barriers for both the spin transition (0.30 eV/29 kJ/mol) and the O 2 dissociation step (0.72 eV/69 kJ/mol). Thus, while spin transition is rate limiting for oxidation with O 2 alone, dissociation becomes the rate-limiting step for oxidation with co-adsorption of OH -. First-principles, periodic calculations of the

  8. Study of photo-oxidative reactivity of sunscreening agents based on photo-oxidation of uric acid by kinetic Monte Carlo simulation

    International Nuclear Information System (INIS)

    Moradmand Jalali, Hamed; Bashiri, Hadis; Rasa, Hossein

    2015-01-01

    In the present study, the mechanism of free radical production by light-reflective agents in sunscreens (TiO 2 , ZnO and ZrO 2 ) was obtained by applying kinetic Monte Carlo simulation. The values of the rate constants for each step of the suggested mechanism have been obtained by simulation. The effect of the initial concentration of mineral oxides and uric acid on the rate of uric acid photo-oxidation by irradiation of some sun care agents has been studied. The kinetic Monte Carlo simulation results agree qualitatively with the existing experimental data for the production of free radicals by sun care agents. - Highlights: • The mechanism and kinetics of uric acid photo-oxidation by irradiation of sun care agents has been obtained by simulation. • The mechanism has been used for free radical production of TiO 2 (rutile and anatase), ZnO and ZrO 2 . • The ratios of photo-activity of ZnO to anastase, rutile and ZrO have been obtained. • By doubling the initial concentrations of mineral oxide, the rate of reaction was doubled. • The optimum ratio of initial concentration of mineral oxides to uric acid has been obtained

  9. Study of photo-oxidative reactivity of sunscreening agents based on photo-oxidation of uric acid by kinetic Monte Carlo simulation

    Energy Technology Data Exchange (ETDEWEB)

    Moradmand Jalali, Hamed; Bashiri, Hadis, E-mail: hbashiri@kashanu.ac.ir; Rasa, Hossein

    2015-05-01

    In the present study, the mechanism of free radical production by light-reflective agents in sunscreens (TiO{sub 2}, ZnO and ZrO{sub 2}) was obtained by applying kinetic Monte Carlo simulation. The values of the rate constants for each step of the suggested mechanism have been obtained by simulation. The effect of the initial concentration of mineral oxides and uric acid on the rate of uric acid photo-oxidation by irradiation of some sun care agents has been studied. The kinetic Monte Carlo simulation results agree qualitatively with the existing experimental data for the production of free radicals by sun care agents. - Highlights: • The mechanism and kinetics of uric acid photo-oxidation by irradiation of sun care agents has been obtained by simulation. • The mechanism has been used for free radical production of TiO{sub 2} (rutile and anatase), ZnO and ZrO{sub 2}. • The ratios of photo-activity of ZnO to anastase, rutile and ZrO have been obtained. • By doubling the initial concentrations of mineral oxide, the rate of reaction was doubled. • The optimum ratio of initial concentration of mineral oxides to uric acid has been obtained.

  10. Kinetic Study of Zn2+ and Cd2+ Ions Sorption by Ceric Oxide Powder

    International Nuclear Information System (INIS)

    Hassan, H.S.; Abd El-Rahman, K.M.; El Sayed, A.A.

    2008-01-01

    Ceric Oxide powder was chemically synthesized and characterized using infrared spectra and x-ray diffraction. The sorptive removal of Zinc and Cadmium ions from aqueous waste solution using synthetic ceric oxide powder was investigated using batch technique. Experiments were carried out as a function of ph, particle size, solute concentration and temperature. The uptake of zinc was found to be greater than that of cadmium. A comparison of kinetic models applied to the sorption process of each ion was evaluated for the pseudo first order, the pseudo second order, and homogeneous particle diffusion kinetic models, respectively. The results showed that both the pseudo second order and the homogeneous particle diffusion model (HPDM) were found to best correlate the experimental rate data. The numerical values of the rate constants and particle diffusion coefficients were determined from the graphical representation of the proposed models. Activation energy (Ε a ) and entropy (δ S * ) of activation for each sorption process were also calculated from the linearized form of Arrhenius equation

  11. Shock tube and chemical kinetic modeling study of the oxidation of 2,5-dimethylfuran.

    Science.gov (United States)

    Sirjean, Baptiste; Fournet, René; Glaude, Pierre-Alexandre; Battin-Leclerc, Frédérique; Wang, Weijing; Oehlschlaeger, Matthew A

    2013-02-21

    A detailed kinetic model describing the oxidation of 2,5-dimethylfuran (DMF), a potential second-generation biofuel, is proposed. The kinetic model is based upon quantum chemical calculations for the initial DMF consumption reactions and important reactions of intermediates. The model is validated by comparison to new DMF shock tube ignition delay time measurements (over the temperature range 1300-1831 K and at nominal pressures of 1 and 4 bar) and the DMF pyrolysis speciation measurements of Lifshitz et al. [ J. Phys. Chem. A 1998 , 102 ( 52 ), 10655 - 10670 ]. Globally, modeling predictions are in good agreement with the considered experimental targets. In particular, ignition delay times are predicted well by the new model, with model-experiment deviations of at most a factor of 2, and DMF pyrolysis conversion is predicted well, to within experimental scatter of the Lifshitz et al. data. Additionally, comparisons of measured and model predicted pyrolysis speciation provides validation of theoretically calculated channels for the oxidation of DMF. Sensitivity and reaction flux analyses highlight important reactions as well as the primary reaction pathways responsible for the decomposition of DMF and formation and destruction of key intermediate and product species.

  12. Kinetic study of Cs+ and Eu3+ ions sorption by zirconium oxide powder

    International Nuclear Information System (INIS)

    Hanafi, H.A.; Hassan, H.S.; Hamed, M.M.

    2009-01-01

    Full text: Zirconium oxide powder was chemically synthesized by sol-gel method and characterized using infrared spectra and x-ray diffraction. The sorptive removal of cesium and europium ions from aqueous waste solution using synthetic zirconium oxide powder was investigated using batch technique. Experiments were carried out as a function of pH, time and temperature. The uptake of europium was found to be greater than that of cesium. A comparison of kinetic models applied to the sorption process of each ion was evaluated for the pseudo first order, the pseudo second order, and homogeneous particle diffusion kinetic models, respectively. The results showed that both the pseudo second order and the homogeneous particle diffusion models (HPDM) were found to best correlate the experimental rate data. The numerical values of the rate constants and particle diffusion coefficients were determined from the graphical representation of the proposed models. Activation energy (Ea) and entropy (Δ S*) of activation for each sorption process were also calculated from the linearized form of Arrhenius equation. (author)

  13. KINETICS OF THE OXIDATION OF VITAMIN C

    Directory of Open Access Journals (Sweden)

    Sitti Rahmawati

    2012-12-01

    Full Text Available Vitamin C or ascorbic acid is needed by the human body but it is already damaged by the rise in temperature due to be oxidized to L-dehydroascorbic acid. This research aims to determine the kinetics of oxidation of ascorbic acid due to an increase if temperature (40-80 °C and to design an ascorbic acid oxidation reaction laboratory module to be applied in the senior high school reaction kinetics curriculum. The determination of the kinetics of the oxidation of ascorbic acid applies the integral and half-change time methods, while the concentration of the remained ascorbic acid in sixty minute intervals is determined by iodimetric titration method. Decomposition of ascorbic acid was measured at 40, 50, 60, 70 and 80 °C. The results of this research indicate that at 40, 50, 60, 70 and 80 °C the kinetics of the oxidation of ascorbic acid is a first-order reaction with rate constants of 4.55 x 10-4, 5.85 x 10-4, 8.4 x 10-4, 1.1 x 10-3 and 1.015 x 10-3 min-1, respectively. Pre-exponential factor or the frequency of collisions is a factor which is a measure of the collision rate. The activation energy and the pre-exponential factor for the oxidation of ascorbic acid were found to be 20.73 kJ.mol-1 and 1.372 min-1. The procedure used in this study was modified into a laboratory module will be applied in the teaching of reaction kinetics at the senior high school level.

  14. High temperature oxidation kinetics of dysprosium particles

    Energy Technology Data Exchange (ETDEWEB)

    Jaques, Brian J.; Butt, Darryl P., E-mail: DarrylButt@BoiseState.edu

    2015-09-25

    Highlights: • The oxidation behavior of dysprosium particles was studied from 500 to 1000 °C. • Activation energy in initial region found as 8–25 kJ/mol, depending on atmosphere. • Activation energy in intermediate region found as 80–95 kJ/mol. • The oxide grows at the metal–oxide interface. • Generally, the formed oxide behaved as a p-type semiconductor. - Abstract: Rare earth elements have been recognized as critical materials for the advancement of many strategic and green technologies. Recently, the United States Department of Energy has invested many millions of dollars to enhance, protect, and forecast their production and management. The work presented here attempts to clarify the limited and contradictory literature on the oxidation behavior of the rare earth metal, dysprosium. Dysprosium particles were isothermally oxidized from 500 to 1000 °C in N{sub 2}–(2%, 20%, and 50%) O{sub 2} and Ar–20% O{sub 2} using simultaneous thermal analysis techniques. Two distinct oxidation regions were identified at each isothermal temperature in each oxidizing atmosphere. Initially, the oxidation kinetics are very fast until the reaction enters a slower, intermediate region of oxidation. The two regions are defined and the kinetics of each are assessed to show an apparent activation energy of 8–25 kJ/mol in the initial region and 80–95 kJ/mol in the intermediate oxidation reaction region. The effects of varying the oxygen partial pressure on the reaction rate constant are used to show that dysprosium oxide (Dy{sub 2}O{sub 3}) generally acts as a p-type semiconductor in both regions of oxidation (with an exception above 750 °C in the intermediate region)

  15. A study of the kinetics and mechanisms of electrocrystallization of indium oxide on an in situ prepared metallic indium electrode

    International Nuclear Information System (INIS)

    Omanovic, S.; Metikos-Hukovic, M.

    2004-01-01

    The mechanisms and kinetics of nucleation and growth of indium oxide film on an in situ prepared metallic indium electrode was studied in a borate buffer solution of pH 10.0 using cyclic voltammetry and chroanoamperometry techniques. It was shown that the initial stage of nucleation of the oxide film includes a three-dimensional progressive nucleation process, combined with a diffusion-controlled growth of the stable indium oxide crystals. The thermodynamic data obtained indicated a strong tendency of indium to form an indium oxide film on its surface in an aqueous solution. It was found that the rate-determining step in the nucleation and growth process is the surface diffusion of electroactive species. The nucleation rate constant, and the number of nucleation active sites were calculated independently. It was shown that between 2 and 15% of sites on the indium surface act as active nucleation centers, and that each active site represents a critical nucleus

  16. Experimental and kinetic modeling study of C2H4 oxidation at high pressure

    DEFF Research Database (Denmark)

    Lopez, Jorge Gimenez; Rasmussen, Christian Lund; Alzueta, Maria

    2009-01-01

    of conditions (0.003-100 bar, 200-3000 K). The results indicate that at 60 bar and medium temperatures vinyl peroxide, rather than CH2O and HCO, is the dominant product. The experiments, involving C2H4/O-2 mixtures diluted in N-2, were carried out in a high pressure flow reactor at 600-900 K and 60 bar, varying......A detailed chemical kinetic model for oxidation of C2H4 in the intermediate temperature range and high pressure has been developed and validated experimentally. New ab initio calculations and RRKM analysis of the important C2H3 + O-2 reaction was used to obtain rate coefficients over a wide range...

  17. Kinetic study of methanol oxidation on Pt2Ru3/C catalyst in the alkaline media

    Directory of Open Access Journals (Sweden)

    A. V. TRIPKOVIC

    2007-11-01

    Full Text Available The interaction of acridine orange (AO with double-stranded (ds The electrochemical oxidation of methanol in NaOH solution was examined on a thin film Pt2Ru3/C electrode. The XRD pattern revealed that the Pt2Ru3 alloy consisted of a solid solution of Ru in Pt and a small amount of Ru or a solid solution of Pt in Ru. It was shown that in alkaline solution, the difference in activity between Pt/C and Pt2Ru3/C is significantly smaller than in acid solution. It is proposed that the reaction follows a quasi bifunctional mechanism. The kinetic parameters indicated that the chemical reaction between adsorbed COad and OHad species could be the rate limiting step.

  18. Kinetics Study of Silver Electrocrystallization on (3-mercaptopropyl)trimethoxysilane-grafted Indium Tin Oxide Plastic Substrate

    International Nuclear Information System (INIS)

    Hau, Nga Yu; Chang, Ya-Huei; Feng, Shien-Ping

    2015-01-01

    Highlights: • The larger charge transfer coefficient supports that MPS promotes electrodeposition. • ACV shows that electron-transfer rate enhanced by 2.5 times after MPS treatment. • The fitting of CA defined the Ag nucleation mode on blank and MPS-grafted ITO-PEN. • MPS treatment changed the nucleation mode from 2-step to a single step one. - Abstract: 3-mercaptopropyl-trimethoxysilane (MPS) self-assembled monolayer (SAM) has been demonstrated as effective promoters to enable direct electroplated metallization on indium tin oxide (ITO) plastic substrate. In this paper, the detail kinetics in Ag electrocrystallization on MPS-grafted ITO-PEN is reported. Contact angle measurement provides evidence of bridging-link effect between the sulfur head groups of MPS and the Ag + ions in the electrolyte. Electrochemical techniques including cyclic voltammetry and Tafel plot were used to investigate the redox kinetics. Quantitative evaluation was conducted by alternating current voltammetry to determine the rate constant of electron transfer. The chronoamperograms and their fitting results suggest a combined model with two-dimensional/three-dimensional nucleation transition and Shariker-Hills model for electroplated Ag on blank ITO-PEN and MPS-grafted ITO-PEN respectively

  19. Palladium nanoparticles anchored on graphene nanosheets: Methanol, ethanol oxidation reactions and their kinetic studies

    KAUST Repository

    Nagaraju, Doddahalli H.; Devaraj, Sappani; Balaya, Palani

    2014-01-01

    nanosheets. The electro-catalytic activity of Gra/Pd nanocomposites toward methanol and ethanol oxidation in alkaline medium was evaluated by cyclic voltammetric studies. 1:1 Gra/Pd nanocomposite exhibited good electro-catalytic activity and efficient

  20. Kinetic studies of electrochemical generation of Ag(II) ion and catalytic oxidation of selected organics

    International Nuclear Information System (INIS)

    Zawodzinski, C.; Smith, W.H.; Martinez, K.R.

    1993-01-01

    The goal of this research is to develop a method to treat mixed hazardous wastes containing selected organic compounds and heavy metals, including actinide elements. One approach is to destroy the organic via electrochemical oxidation to carbon dioxide, then recover the metal contaminants through normally accepted procedures such as ion exchange, precipitation, etc. The authors have chosen to study the electrochemical oxidation of a simple alcohol, iso-propanol. Much of the recent work reported involved the use of an electron transfer mediator, usually the silver(I)/(II) redox couple. This involved direct electrochemical generation of the mediator at the anode of a divided cell followed by homogeneous reaction of the mediator with the organic compound. In this study the authors have sought to compare the mediated reaction with direct electrochemical oxidation of the organic. In addition to silver(I)/(II) they also looked at the cobalt(II)/(III) redox coupled. In the higher oxidation state both of these metal ions readily hydrolyze in aqueous solution to ultimately form insoluble oxide. The study concluded that in a 6M nitric acid solution at room temperature iso-propanol can be oxidized to carbon dioxide and acetic acid. Acetic acid is a stable intermediate and resists further oxidation. The presence of Co(III) enhances the rate or efficiency of the reaction

  1. Study of photo-oxidative reactivity of sunscreening agents based on photo-oxidation of uric acid by kinetic Monte Carlo simulation.

    Science.gov (United States)

    Moradmand Jalali, Hamed; Bashiri, Hadis; Rasa, Hossein

    2015-05-01

    In the present study, the mechanism of free radical production by light-reflective agents in sunscreens (TiO2, ZnO and ZrO2) was obtained by applying kinetic Monte Carlo simulation. The values of the rate constants for each step of the suggested mechanism have been obtained by simulation. The effect of the initial concentration of mineral oxides and uric acid on the rate of uric acid photo-oxidation by irradiation of some sun care agents has been studied. The kinetic Monte Carlo simulation results agree qualitatively with the existing experimental data for the production of free radicals by sun care agents. Copyright © 2015 Elsevier B.V. All rights reserved.

  2. Tantalum high-temperature oxidation kinetics

    International Nuclear Information System (INIS)

    Grigor'ev, Yu.M.; Sarkisyan, A.A.; Merzhanov, A.G.

    1981-01-01

    Kinetics of heat release and scale growth during tantalum oxidation within 650-1300 deg C temperature range in oxygen-containing media is investigated. Kinetic equations and temperature and pressure dependences of constants are ound Applicability of the kinetic Lorie mechanism for the description of the tantalum oxidation kinetics applicably to rapid-passing processes is shown. It is stated that the process rate (reaction ability) is determined by adsorption desorption factors on the external surface of the ''protective'' oxide for the ''linear'' oxidation stage [ru

  3. Kinetic Studies of Oxidative Coupling of Methane Reaction on Model Catalysts

    KAUST Repository

    Khan, Abdulaziz M.

    2016-04-26

    With the increasing production of natural gas as a result of the advancement in the technology, methane conversion to more valuable products has become a must. One of the most attractive processes which allow the utilization of the world’s most abundant hydrocarbon is the oxidative coupling. The main advantage of this process is the ability of converting methane into higher paraffins and olefins (primarily C2) in a direct way using a single reactor. Nevertheless, low C2+ yields have prevented the process to be commercialized despite the fact that great number of attempts to prepare catalysts were conducted so that it can be economically viable. Due to these limitations, understanding the mechanism and kinetics of the reaction can be utilized in improving the catalysts’ performance. The reaction involves the formation of methyl radicals that undergo gas-phase radical reactions. CH4 activation is believed to be done the surface oxygen species. However, recent studies showed that, in addition to the surface oxygen mediated pathway, an OH radical mediated pathway have a large contribution on the CH4 activation. The experiments of Li/MgO, Sr/La2O3 and NaWO4/SiO2 catalysts revealed variation of behavior in activity and selectivity. In addition, water effect analysis showed that Li/MgO deactivate at the presence of water due to sintering phenomena and the loss of active sites. On the other hand, negative effect on the C2 yield and CH4 conversion rate was observed with Sr/La2O3 with increasing the water partial pressure. Na2WO4/SiO2 showed a positive behavior with water in terms of CH4 conversion and C2 yield. In addition, the increment in CH4 conversion rate was found to be proportional with PO2 ¼ PH2O ½ which is consistent with the formation of OH radicals and the OH-mediated pathway. Experiments of using ring-dye laser, which is used to detect OH in combustion experiments, were tried in order to detect OH radicals in the gas-phase of the catalyst. Nevertheless

  4. Studies of U(4) oxidation kinetics in nitric acid and TBP phases

    International Nuclear Information System (INIS)

    Taylor, R.J.; Denniss, I.S.; Koltunov, V.S.; Marchenko, V.I.; Dvoeglazov, K.N.; Savilova, O.A.; Broan, C.J.

    2000-01-01

    U(IV) is an important reagent in current reprocessing plants since it is used to reduce Pu(IV) to Pu(III), therefore, allowing the efficient separation of U and Pu in multi-stage counter-current solvent extraction contactors. The benefits of U(IV) are that it is a kinetically fast reductant and it is a salt free reagent, since U(IV) is oxidised to U(VI) and so does not add to the aqueous waste volumes. Many kinetic reactions of U(IV) have been studied in the past and these are used by BNFL to model the behaviour of U(IV) in process flowsheets. However, some reactions have either not been studied or have been studied many times without conclusive resolution. Therefore, to expand our understanding of U(IV) in the process and to generate data that underpins process models, we are studying a series of U(IV) reactions, and this paper will summarize the results of our kinetic and mechanistic studies. (authors)

  5. Kinetic Study of Methyl Acetate Oxidation in a Pt/Al2O3 Fixed-Bed Reactor

    Science.gov (United States)

    Hoy, Michael; Li, K. Y.; Li, Jeffrey S.; Chen, S. M.; Yaws, C. L.; Chu, H. W.; Simon, W. E.

    1994-01-01

    To support technology development for future long-term missions, a metabolic simulator will be used in a closed chamber to test the functions of a Controlled Ecological Life Support System (CELSS). Methyl acetate (MA) was selected as the fuel because its metabolic respiratory quotient is near that of humans. A kinetic study of the catalytic oxidation of MA over Pt/Al203 was then conducted to support the design and operation of the simulator. Kinetic data were obtained as a conversion percentage of MA versus retention time. The reaction was studied at one atmosphere and temperatures from 220 to 340 deg. C. The inlet MA concentration was varied from 100 to 2000 ppm with retention times from 0.01 to 10 sec. A first-order rate law and a Langmuir-Hinshelwood rate equation were tested by nonlinear regression of the kinetic data to estimate rate constants in the rate law. Regression results of the L-H equation explain the kinetic data better than the results of the first-order rate law. A Taguchi experimental design was used to study the effects of temperature, retention time, and concentrations of MA, CO2, and O2 on the conversion of MA. Results indicate that temperature has greatest effect, followed by retention time, and finally MA concentration. It was further determined that the effects of CO2 and O2 concentrations, and the cross effects, are negligible.

  6. KINETIC STUDY OF SELECTIVE GAS-PHASE OXIDATION OF ISOPROPANOL TO ACETONE USING MONOCLINIC ZRO2 AS A CATALYST

    Directory of Open Access Journals (Sweden)

    Mohammad Sadiq

    2015-08-01

    Full Text Available Zirconia was prepared by a precipitation method and calcined at 723 K, 1023 K, and 1253 K in order to obtain monoclinic zirconia. The prepared zirconia was characterized by XRD, SEM, EDX, surface area and pore size analyzer, and particle size analyzer. Monoclinic ZrO2 as a catalyst was used for the gas-phase oxidation of isopropanol to acetone in a Pyrex-glass-flow-type reactor with a temperature range of 443 K - 473 K. It was found that monoclinic ZrO2 shows remarkable catalytic activity (68% and selectivity (100% for the oxidation of isopropanol to acetone. This kinetic study reveals that the oxidation of isopropanol to acetone follows the L-H mechanism.

  7. Crystallographic and oxidation kinetic study of uranium dioxide by high temperature X-ray diffractometry

    International Nuclear Information System (INIS)

    Teixeira, S.R.

    1981-01-01

    The structural behavior of UO 2 sintered plates was studied as a function of temperature by X-ray diffractometry. All the experiments were carried out under an inert atmosphere with low oxygen content (approximated 140 ppm). The thermal expansion coefficient of UO 2 05 was found to be 10,5 x 10 - 6 0 C - 1 for temperatures above 165 0 C. Structural transformations during oxidation were observed at 170,235 and 275 0 C. The isothermal oxidation of UO 2 to U 3 O 7 follows a parabolic form and the diffusion of oxygen through the product layer U 4 O 9 is the mechanism controlling the oxidation rate. The phases observed were UO 2 (cubic) - U 4 O 9 (cubic) - U 3 O 7 (tetragonal). Activation energies of oxidation were found for different crystallographic planes (hkl). From this one can conclude that there is a preferential occupation of interstitial oxygen within the UO 2 structure. (Author) [pt

  8. Mechanistic and kinetic studies on the OH-initiated atmospheric oxidation of fluoranthene

    International Nuclear Information System (INIS)

    Dang, Juan; Shi, Xiangli; Zhang, Qingzhu; Hu, Jingtian; Chen, Jianmin; Wang, Wenxing

    2014-01-01

    The atmospheric oxidation of polycyclic aromatic hydrocarbons (PAHs) can generate toxic derivatives which contribute to the carcinogenic potential of particulate organic matter. In this work, the mechanism of the OH-initiated atmospheric oxidation of fluoranthene (Flu) was investigated by using high-accuracy molecular orbital calculations. All of the possible oxidation pathways were discussed, and the theoretical results were compared with the available experimental observation. The rate constants of the crucial elementary reactions were evaluated by the Rice–Ramsperger–Kassel–Marcus (RRKM) theory. The main oxidation products are a range of ring-retaining and ring-opening chemicals containing fluoranthols, fluoranthones, fluoranthenequinones, nitro-fluoranthenes, dialdehydes and epoxides. The overall rate constant of the OH addition reaction is 1.72 × 10 −11 cm 3 molecule −1 s −1 at 298 K and 1 atm. The atmospheric lifetime of Flu determined by OH radicals is about 0.69 days. This work provides a comprehensive investigation of the OH-initiated oxidation of Flu and should help to clarify its atmospheric conversion. - Highlights: • We studied a comprehensive mechanism of OH-initiated oxidation of fluoranthene. • We reported the formation pathways of fluoranthone, fluoranthenequinone and epoxide. • The rate constants of the crucial elementary steps were evaluated

  9. Mechanistic and kinetic studies on the OH-initiated atmospheric oxidation of fluoranthene

    Energy Technology Data Exchange (ETDEWEB)

    Dang, Juan; Shi, Xiangli; Zhang, Qingzhu, E-mail: zqz@sdu.edu.cn; Hu, Jingtian; Chen, Jianmin; Wang, Wenxing

    2014-08-15

    The atmospheric oxidation of polycyclic aromatic hydrocarbons (PAHs) can generate toxic derivatives which contribute to the carcinogenic potential of particulate organic matter. In this work, the mechanism of the OH-initiated atmospheric oxidation of fluoranthene (Flu) was investigated by using high-accuracy molecular orbital calculations. All of the possible oxidation pathways were discussed, and the theoretical results were compared with the available experimental observation. The rate constants of the crucial elementary reactions were evaluated by the Rice–Ramsperger–Kassel–Marcus (RRKM) theory. The main oxidation products are a range of ring-retaining and ring-opening chemicals containing fluoranthols, fluoranthones, fluoranthenequinones, nitro-fluoranthenes, dialdehydes and epoxides. The overall rate constant of the OH addition reaction is 1.72 × 10{sup −11} cm{sup 3} molecule{sup −1} s{sup −1} at 298 K and 1 atm. The atmospheric lifetime of Flu determined by OH radicals is about 0.69 days. This work provides a comprehensive investigation of the OH-initiated oxidation of Flu and should help to clarify its atmospheric conversion. - Highlights: • We studied a comprehensive mechanism of OH-initiated oxidation of fluoranthene. • We reported the formation pathways of fluoranthone, fluoranthenequinone and epoxide. • The rate constants of the crucial elementary steps were evaluated.

  10. Electrochemical oxidation of chlorpheniramine at polytyramine film doped with ruthenium (II) complex: Measurement, kinetic and thermodynamic studies

    International Nuclear Information System (INIS)

    Khudaish, Emad A.; Al-Hinaai, Mohammed; Al-Harthy, Salim; Laxman, Karthik

    2014-01-01

    Highlights: • XPS data confirm doping of ruthenium onto the polytyramine moiety. • Doping of Ru decreases the Pty resistivity and increases the electron transfer kinetics. • The resulting sensor is stable for a large range of CPM concentration. • Estimated values of thermodynamic and kinetic parameters were comparable. • Application to commercial dosage forms was excellent and satisfactory. - Abstract: A solid-state sensor based on polytyramine film deposited at glassy carbon electrode doped with tris(2,2′-bipyridyl)Ru(II) complex (Ru/Pty/GCE) was constructed electrochemically. A redox property represented by [Ru(bpy) 3 ] 3+/2+ couple immobilized at the Pty moiety was characterized using typical voltammetric techniques. The XPS data and AFM images confirm the grafting of Ru species on the top of Pty while the electrochemical impedance spectroscopy (EIS) data supports the immobilization of both surface modifiers onto the GCE. The constructed sensor exhibits a substantial reactivity, stability and high sensitivity to chlorpheniramine maleate (CPM) oxidation. The detection limit (S/N = 3) was brought down to 338 nM using differential pulse voltammetry method. Thermodynamic and kinetic parameters were evaluated using hydrodynamic method. The apparent diffusion coefficient and the heterogeneous electron transfer rate constant for the CPM oxidation were 2.67 × 10 −5 cm 2 s −1 and 3.21 × 10 −3 cm s −1 , respectively. Interference studies and real sample analysis were conducted with excellent performance and satisfactory results

  11. Comparative study of electrochemical oxidation of herbicide 2,4,5-T: Kinetics, parametric optimization and mineralization pathway

    Directory of Open Access Journals (Sweden)

    Hicham Zazou

    2017-01-01

    Full Text Available Oxidative degradation of herbicide 2,4,5-T was studied by electrochemical advanced oxidation processes anodic oxidation and electro-Fenton (EF using Pt/carbon felt and BDD/carbon felt cells. The effect of main operating parameters on oxidation of 2,4,5-T and mineralization of its aqueous solution were investigated. The rate constant for oxidation of 2,4,5-T by ·≡OH was determined as (3.7 ± 0.2 × 109 M−1 s−1 using competition kinetics method. The EF process with BDD anode was shown to be very efficient reaching 94% mineralization in 3 h treatment. Based on identified aromatic intermediates, short-chain carboxylic acids, released inorganic ions and total organic carbon removal measurements, a plausible oxidation pathway for mineralization of 2,4,5-T by hydroxyl radical was proposed. In addition, the evolution of solution toxicity during treatment was monitored by Microtox method showing the formation of toxic aromatic/cyclic intermediates. The results showed also that EF process was able to remove efficiently toxic intermediates and consequently solution toxicity.

  12. A DMS kinetic study of the boron oxides vapor in the combustion front of SHS system Mo + B

    International Nuclear Information System (INIS)

    Kashireninov, O.E.; Yuranov, I.A.

    1994-01-01

    The distribution of the boron oxides vapor in the combustion wave of the SHS system Mo + B has been studied by the dynamic mass spectrometry technique (DMS) to test the thermodynamically based hypothesis for the key role of gas-phase transport in solid-state combustion. The molecular beam sampling of the gases over the burning tablet was performed by a stationary probe cone from the moving combustion wave. Ion currents of boron oxides were recorded at 10--20 ms intervals that afforded spatial resolution of 0.1--0.2 mm. It has been found that the distribution of the boron oxides vapor pressure along the combustion wave corresponds to the known zones of preheating, reaction, and postcombustion. The rapid increase of B 2 O 2 pressure takes place in the preheating zone as a result of the reaction B(s) + B 2 O 3 (g) = B 2 O 2 (g). Boron oxides are not observed over the reaction zone because of their complete decay in the reaction with Mo(s) to form molybdenum boride(s). The appearance The appearance of boron oxide vapors over the postcombustion zone is due to the evaporation of B 2 O 3 (l). The effective kinetic parameters are estimated from the data obtained. The results show that solid-state combustion of the Mo + B system proceeds predominantly through formation of gas-phase boron oxides

  13. Kinetics of oxidic phase dissolution in acids

    International Nuclear Information System (INIS)

    Gorichev, I.G.; Kipriyanov, N.A.

    1981-01-01

    The critical analysis of the experimental data on dissolution kinetics of metal oxides (BeO, V 2 O 5 , UO 2 , Nb 2 O 5 , Ta 2 O 5 etc.) in acid media is carried out. Kinetic peculiarities of oxide dissolution are explained on the basis of the notions of electron- proton theory. It is established that the surface nonstoichiometric ccomposition of oxide phase and potential jump, appearing on the interface of the oxide-electrolyte phase are the important factors, determining the dissolution rate of a solid phase. The dissolution rate of metal oxides is limited by the transition of protons into the solid oxide phase. Morphological models of heterogeneous kinetics are used when explaining kinetic regularities of oxide dissolution process [ru

  14. Experimental and Kinetic Modeling Study of C2H2Oxidation at High Pressure

    DEFF Research Database (Denmark)

    Lopez, Jorge Gimenez; Rasmussen, Christian Tihic; Hashemi, Hamid

    2016-01-01

    diagram for C2H3 + O2 by Goldsmith et al. and on new ab initio calculations, respectively. The C2H2 + HO2 reaction involves nine pressure- and temperature-dependent product channels, with formation of triplet CHCHO being dominant under most conditions. The barrier to reaction for C2H2 + O2 was found......A detailed chemical kinetic model for oxidation of acetylene at intermediate temperatures and high pressure has been developed and evaluated experimentally. The rate coefficients for the reactions of C2H2 with HO2 and O2 were investigated, based on the recent analysis of the potential energy...... to be more than 50 kcal mol−1 and predictions of the initiation temperature were not sensitive to this reaction. Experiments were conducted with C2H2/O2 mixtures highly diluted in N2 in a high-pressure flow reactor at 600–900 K and 60 bar, varying the reaction stoichiometry from very lean to fuel...

  15. chemical kinetic study of nitrogen oxides formation in methane flameless combustion

    International Nuclear Information System (INIS)

    Alvarado T, Pedro N; Cadavid S, Francisco; Mondragon, P Fanor; Ruiz, Wilson

    2009-01-01

    The present paper deals with the nitrogen oxides formation in a flameless combustion process characterized for using air highly diluted and preheated at high temperatures. The combustion model used in this study was the one dimensional counterflow methane air diffusion flame. The NOx production rate analysis showed that the thermal and prompt mechanisms are the most important for the formation and consumption of NO under dilution conditions for the oxidant in N 2 and combustion products. These mechanisms are related since the starting reaction for NO formation (N2 molecular dissociation) belongs to the prompt mechanism while the NO formation is reported mainly for the thermal mechanism reactions. On the other hand, the NO - NO 2 equilibrium showed that the reaction rates are comparable to that obtained by the thermal and prompt mechanisms, but its global contribution to NO formation are almost insignificant due to the oxidation reaction with radicals HO 2 .

  16. Absorption of calcium ions on oxidized graphene sheets and study its dynamic behavior by kinetic and isothermal models

    Directory of Open Access Journals (Sweden)

    Mahmoud Fathy

    2016-07-01

    Full Text Available Abstract Sorption of calcium ion from the hard underground water using novel oxidized graphene (GO sheets was studied in this paper. Physicochemical properties and microstructure of graphene sheets were investigated using Raman spectrometer, thermogravimetry analyzer, transmission electron microscope, scanning electron microscope. The kinetics adsorption of calcium on graphene oxide sheets was examined using Lagergren first and second orders. The results show that the Lagergren second-order was the best-fit model that suggests the conception process of calcium ion adsorption on the Go sheets. For isothermal studies, the Langmuir and Freundlich isotherm models were used at temperatures ranging between 283 and 313 K. Thermodynamic parameters resolved at 283, 298 and 313 K indicating that the GO adsorption was exothermic spontaneous process. Finally, the graphene sheets show high partiality toward calcium particles and it will be useful in softening and treatment of hard water.

  17. Nonlinear oxidation kinetics of nickel cermets

    International Nuclear Information System (INIS)

    Galinski, Henning; Bieberle-Huetter, Anja; Rupp, Jennifer L.M.; Gauckler, Ludwig J.

    2011-01-01

    The oxidation of a cermet of screen-printed nickel (Ni) and gadolinia-doped ceria (CGO) with an approximate median porosity of 50 vol.% has been studied via in situ X-ray diffraction and focused ion beam nanotomography in the temperature range 773-848 K. The oxidation kinetics of Ni to NiO is found to be highly nonlinear with an apparent activation energy of 2.8(2) eV in this temperature range. The nonlinear oxidation kinetics found is in good agreement with theoretical works on oxide growth driven by nonlinear inbuilt fields. Stress-induced Kirkendall void formation has been identified as the physical process that enhances the oxidation of Ni/CGO cermets. Compressive stresses within the Ni matrix result from the thermal expansion mismatch of Ni and CGO and cause plastic deformation as they exceed the yield stress of the Ni matrix. The pore size distribution of Kirkendall voids formed has been measured by FIB nanotomography and shows a significant temperature dependence. It is shown that even one cycle of reoxidation changes irreversibly the microstructure of the cermet which can be interpreted as the onset and main contribution to the mechanical degradation of the cermet.

  18. Astaxanthin degradation and lipid oxidation of Pacific white shrimp oil: kinetics study and stability as affected by storage conditions

    Directory of Open Access Journals (Sweden)

    Sirima Takeungwongtrakul

    2016-02-01

    Full Text Available Abstract The kinetics of astaxanthin degradation and lipid oxidation in shrimp oil from hepatopancreas of Pacific white shrimp (Litopenaeus vannamei as affected by storage temperature were studied. When shrimp oil was incubated at different temperatures (4, 30, 45 and 60 °C for 16 h, the rate constants (k of astaxanthin degradation and lipid oxidation in shrimp oil increased with increasing temperatures (p < 0.05. Thus, astaxanthin degradation and lipid oxidation in shrimp oil were augmented at high temperature. When shrimp oils with different storage conditions (illumination, oxygen availability and temperature were stored for up to 40 days, astaxanthin contents in all samples decreased throughout storage (p < 0.05. All factors were able to enhance astaxanthin degradation during 40 days of storage. With increasing storage time, the progressive formation of primary and secondary oxidation products were found in all samples as evidenced by the increases in both peroxide values (PV and thiobarbituric acid reactive substances (TBARS (p < 0.05. Light, air and temperatures therefore had the marked effect on astaxanthin degradation and lipid oxidation in shrimp oils during the extended storage.

  19. Kinetics and Photodegradation Study of Aqueous Methyl tert-Butyl Ether Using Zinc Oxide: The Effect of Particle Size

    Directory of Open Access Journals (Sweden)

    Zaki S. Seddigi

    2013-01-01

    Full Text Available Zinc oxide of different average particle sizes 25 nm, 59 nm, and 421 nm as applied in the photodegradation of MTBE. This study was carried out in a batch photoreactor having a high pressure mercury lamp. Zinc oxide of particle size of 421 nm was found to be the most effective in degrading MTBE in an aqueous solution. On using this type of ZnO in a solution of 100 ppm MTBE, the concentration of MTBE has decreased to 5.1 ppm after a period of five hours. The kinetics of the photocatalytic degradation of MTBE was found to be a first order reaction.

  20. A kinetic study of the oxidation of some amino acids by peroxydisulphate

    International Nuclear Information System (INIS)

    Hamed, H. A.

    2005-07-01

    The present work deals with the study of redox reactions of some amino-acids (Leucine, Aspartic and Arganine) with peroxydisulphate. The kinetic study of the above reactions showed that these reactions followed first order with respect to peroxydisulphate and silver ion as catalyst and zero order with respect to the amino-acids. For these reactions, the activation energies and other thermodynamic parameters, namely entropy (ΔS ≠ ) and free energy of activation (ΔG ≠ ) were evaluated. The analysis of the reaction products by the (IR) revealed the presence of 2-butanone in the case of leucine, propanone in the case of aspartic and 2-3 butanone in the case of arganine. Plausible mechanisms were proposed for there are reactions in accordance with the experimentally observed rate law and the products formed. (Author)

  1. Origin of two time-scale regimes in potentiometric titration of metal oxides. A replica kinetic Monte Carlo study

    International Nuclear Information System (INIS)

    Zarzycki, Piotr P.; Rosso, Kevin M.

    2009-01-01

    Replica Kinetic Monte Carlo simulations were used to study the characteristic time scales of potentiometric titration of the metal oxides and (oxy)hydroxides. The effect of surface heterogeneity and surface transformation on the titration kinetics were also examined. Two characteristic relaxation times are often observed experimentally, with the trailing slower part attributed to surface non-uniformity, porosity, polymerization, amorphization, and other dynamic surface processes induced by unbalanced surface charge. However, our simulations show that these two characteristic relaxation times are intrinsic to the proton binding reaction for energetically homogeneous surfaces, and therefore surface heterogeneity or transformation do not necessarily need to be invoked. However, all such second-order surface processes are found to intensify the separation and distinction of the two kinetic regimes. The effect of surface energetic-topographic non-uniformity, as well dynamic surface transformation, interface roughening/smoothing were described in a statistical fashion. Furthermore, our simulations show that a shift in the point-of-zero charge is expected from increased titration speed and the pH-dependence of the titration measurement error is in excellent agreement with experimental studies.

  2. Origin of two time-scale regimes in potentiometric titration of metal oxides. A replica kinetic Monte Carlo study.

    Science.gov (United States)

    Zarzycki, Piotr; Rosso, Kevin M

    2009-06-16

    Replica kinetic Monte Carlo simulations were used to study the characteristic time scales of potentiometric titration of the metal oxides and (oxy)hydroxides. The effect of surface heterogeneity and surface transformation on the titration kinetics were also examined. Two characteristic relaxation times are often observed experimentally, with the trailing slower part attributed to surface nonuniformity, porosity, polymerization, amorphization, and other dynamic surface processes induced by unbalanced surface charge. However, our simulations show that these two characteristic relaxation times are intrinsic to the proton-binding reaction for energetically homogeneous surfaces, and therefore surface heterogeneity or transformation does not necessarily need to be invoked. However, all such second-order surface processes are found to intensify the separation and distinction of the two kinetic regimes. The effect of surface energetic-topographic nonuniformity, as well dynamic surface transformation, interface roughening/smoothing were described in a statistical fashion. Furthermore, our simulations show that a shift in the point-of-zero charge is expected from increased titration speed, and the pH-dependence of the titration measurement error is in excellent agreement with experimental studies.

  3. Kinetic and Mechanistic Studies of Oxidation of an Antiallergic Drug with Bromamine-T in Acid and Alkaline Media

    International Nuclear Information System (INIS)

    Puttaswamy; Anu Sukhdev

    2012-01-01

    Cetrizine dihydrochloride (CTZH) is widely used as an anti-allergic drug. Sodium N-bromo-p-toluenesulfonamide or bromamine-T (BAT) is the bromine analogue of chloramine-T (CAT) and is found to be a better oxidizing agent than CAT. In the present research, the kinetics of oxidation of CTZH with BAT in acid and alkaline media was studied at 313 K. The experimental rate laws obtained are: -d[BAT]/dt = k[BAT] [CTZH] 0.80 [H + ] -0.48 in acid medium and -d[BAT]/dt = k[BAT][CTZH] 0.48 [OH - ] 0.52 [PTS] -0.40 in alkaline medium where PTS is p-toluenesulfonamide. Activation parameters and reaction constants were evaluated. The solvent isotope effect was studied using D 2 O. The dielectric effect is positive. The stoichiometry of the reaction was found to be 1:1 and the oxidation products were identified as 4-chlorobenzophenone and (2-piperazin-1-yl-ethoxy)-acetic acid in both media. The rate of oxidation of CTZH is faster in acid medium. Suitable mechanisms and related rate laws have been worked out

  4. Kinetic and Mechanistic Studies of Oxidation of an Antiallergic Drug with Bromamine-T in Acid and Alkaline Media

    Energy Technology Data Exchange (ETDEWEB)

    Puttaswamy; Anu Sukhdev [Bangalore Univ., Bangalore (India)

    2012-11-15

    Cetrizine dihydrochloride (CTZH) is widely used as an anti-allergic drug. Sodium N-bromo-p-toluenesulfonamide or bromamine-T (BAT) is the bromine analogue of chloramine-T (CAT) and is found to be a better oxidizing agent than CAT. In the present research, the kinetics of oxidation of CTZH with BAT in acid and alkaline media was studied at 313 K. The experimental rate laws obtained are: -d[BAT]/dt = k[BAT] [CTZH]{sup 0.80}[H{sup +}]{sup -0.48} in acid medium and -d[BAT]/dt = k[BAT][CTZH]{sup 0.48}[OH{sup -}]{sup 0.52}[PTS]{sup -0.40} in alkaline medium where PTS is p-toluenesulfonamide. Activation parameters and reaction constants were evaluated. The solvent isotope effect was studied using D{sub 2}O. The dielectric effect is positive. The stoichiometry of the reaction was found to be 1:1 and the oxidation products were identified as 4-chlorobenzophenone and (2-piperazin-1-yl-ethoxy)-acetic acid in both media. The rate of oxidation of CTZH is faster in acid medium. Suitable mechanisms and related rate laws have been worked out.

  5. Experimental and Kinetic Modeling Study of Ethyl Levulinate Oxidation in a Jet-Stirred Reactor

    KAUST Repository

    Wang, Jui-Yang

    2017-01-01

    levulinate chemical kinetic model was first developed by Dr. Stephen Dooley, Trinity College Dublin, and simulated under the same conditions, using the Perfect-Stirred Reactor code in Chemkin software. In comparing the simulation results with experimental

  6. Kinetic Studies of Oxidative Coupling of Methane Reaction on Model Catalysts

    KAUST Repository

    Khan, Abdulaziz M.

    2016-01-01

    the process to be commercialized despite the fact that great number of attempts to prepare catalysts were conducted so that it can be economically viable. Due to these limitations, understanding the mechanism and kinetics of the reaction can be utilized

  7. Treatment of selected pharmaceuticals by ferrate(VI): performance, kinetic studies and identification of oxidation products.

    Science.gov (United States)

    Zhou, Zhengwei; Jiang, Jia-Qian

    2015-03-15

    The performance of ferrate(VI) in treating sulfamethoxazole (SMX), diclofenac (DCF), carbamazepine (CBZ) and bezafibrate (BZF) in test solutions containing the four compounds was investigated. A series of jar-test experiments was performed on a bench-scale at pH 6-9 and at a ferrate(VI) dose of 1-5 mg Fe/L. The results suggested that ferrate(VI) can effectively remove SMX, DCF and CBZ from the test solutions, with greater than 80% removal under optimum conditions. However, the removal efficiency of BZF was very low, less than 25% under the studied conditions. Increasing the dose of ferrate(VI) improved the treatment performance, while the influence of solution pH on ferrate(VI) performance varied among the different target compounds. Ferrate(VI) demonstrated the highest reactivity with SMX at pH 8 and pH 9 (20 °C), with apparent second-order rate constants of 360±17 M(-1) s(-1) and 1.26±0.02 M(-1) s(-1), respectively. However, BZF showed the lowest removal by ferrate(VI) with the smallest rate constants (less than 0.5 M(-1) s(-1)) at pH 8 and pH 9. Furthermore, a number of oxidation products (OPs) of SMX, DCF and CBZ during ferrate(VI) oxidation were detected by liquid chromatography and mass spectrometry (LC-MS), and their degradation pathways were tentatively proposed. No OPs of BZF were detected during ferrate(VI) oxidation. Copyright © 2014 Elsevier B.V. All rights reserved.

  8. Experimental and chemical kinetic modeling study of small methyl esters oxidation: Methyl (E)-2-butenoate and methyl butanoate

    Energy Technology Data Exchange (ETDEWEB)

    Gail, S.; Sarathy, S.M.; Thomson, M.J. [Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, ON M5S 3G8 (Canada); Dievart, P.; Dagaut, P. [CNRS, 1C, Ave de la Recherche Scientifique, 45071 Orleans Cedex 2 (France)

    2008-12-15

    This study examines the effect of unsaturation on the combustion of fatty acid methyl esters (FAME). New experimental results were obtained for the oxidation of methyl (E)-2-butenoate (MC, unsaturated C{sub 4} FAME) and methyl butanoate (MB, saturated C{sub 4} FAME) in a jet-stirred reactor (JSR) at atmospheric pressure under dilute conditions over the temperature range 850-1400 K, and two equivalence ratios ({phi}=0.375,0.75) with a residence time of 0.07 s. The results consist of concentration profiles of the reactants, stable intermediates, and final products, measured by probe sampling followed by on-line and off-line gas chromatography analyses. The oxidation of MC and MB in the JSR and under counterflow diffusion flame conditions was modeled using a new detailed chemical kinetic reaction mechanism (301 species and 1516 reactions) derived from previous schemes proposed in the literature. The laminar counterflow flame and JSR (for {phi}=1.13) experimental results used were from a previous study on the comparison of the combustion of both compounds. Sensitivity analyses and reaction path analyses, based on rates of reaction, were used to interpret the results. The data and the model show that MC has reaction pathways analogous to that of MB under the present conditions. The model of MC oxidation provides a better understanding of the effect of the ester function on combustion, and the effect of unsaturation on the combustion of fatty acid methyl ester compounds typically found in biodiesel. (author)

  9. Kinetic studies on the oxidation of oxyhemoglobin by biologically active iron thiosemicarbazone complexes: relevance to iron-chelator-induced methemoglobinemia.

    Science.gov (United States)

    Basha, Maram T; Rodríguez, Carlos; Richardson, Des R; Martínez, Manuel; Bernhardt, Paul V

    2014-03-01

    The oxidation of oxyhemoglobin to methemoglobin has been found to be facilitated by low molecular weight iron(III) thiosemicarbazone complexes. This deleterious reaction, which produces hemoglobin protein units unable to bind dioxygen and occurs during the administration of iron chelators such as the well-known 3-aminopyridine-2-pyridinecarbaldehyde thiosemicarbazone (3-AP; Triapine), has been observed in the reaction with Fe(III) complexes of some members of the 3-AP structurally-related thiosemicarbazone ligands derived from di-2-pyridyl ketone (HDpxxT series). We have studied the kinetics of this oxidation reaction in vitro using human hemoglobin and found that the reaction proceeds with two distinct time-resolved steps. These have been associated with sequential oxidation of the two different oxyheme cofactors in the α and β protein chains. Unexpected steric and hydrogen-bonding effects on the Fe(III) complexes appear to be the responsible for the observed differences in the reaction rate across the series of HDpxxT ligand complexes used in this study.

  10. The oxidation kinetics of zircaloy - 4 under isothermal conditions

    International Nuclear Information System (INIS)

    Santos, A.M.M. dos; Cardoso, P.E.

    1982-01-01

    The oxidation kinetics of zircaloy-4 tubes was studied by means of isothermal tests in the temperature interval 500 0 C to 900 0 C. Dry oxygen and water steam, were used as oxidant agents. The results show that the oxidation kinetics law exhibits a behaviour from cubic to parabolic in the range of the time and temperatures of the experiment. Dry oxygen shows a stronger oxidation effect than water steam. A special mechanical test to study the embrittlement effect in the small samples of zircaloy tubes was used. (Author) [pt

  11. Kinetics of Oxidation of Fe–6Si

    Czech Academy of Sciences Publication Activity Database

    Lashin, Abdel Rahman; Schneeweiss, Oldřich; Svoboda, Milan

    2008-01-01

    Roč. 69, č. 5-6 (2008), s. 359-374 ISSN 0030-770X R&D Projects: GA AV ČR IAA1041404 Institutional research plan: CEZ:AV0Z20410507 Keywords : iron silicon * Mössbauer spectroscopy * XRD * iron oxides * oxidation kinetics Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.359, year: 2008

  12. Mechanistic and Kinetic Study of Singlet O2 Oxidation of Methionine by On-Line Electrospray Ionization Mass Spectrometry.

    Science.gov (United States)

    Liu, Fangwei; Lu, Wenchao; Yin, Xunlong; Liu, Jianbo

    2016-01-01

    We report a reaction apparatus developed to monitor singlet oxygen ((1)O2) reactions in solution using on-line ESI mass spectrometry and spectroscopy measurements. (1)O2 was generated in the gas phase by the reaction of H2O2 with Cl2, detected by its emission at 1270 nm, and bubbled into aqueous solution continuously. (1)O2 concentrations in solution were linearly related to the emission intensities of airborne (1)O2, and their absolute scales were established based on a calibration using 9,10-anthracene dipropionate dianion as an (1)O2 trapping agent. Products from (1)O2 oxidation were monitored by UV-Vis absorption and positive/negative ESI mass spectra, and product structures were elucidated using collision-induced dissociation-tandem mass spectrometry. To suppress electrical discharge in negative ESI of aqueous solution, methanol was added to electrospray via in-spray solution mixing using theta-glass ESI emitters. Capitalizing on this apparatus, the reaction of (1)O2 with methionine was investigated. We have identified methionine oxidation intermediates and products at different pH, and measured reaction rate constants. (1)O2 oxidation of methionine is mediated by persulfoxide in both acidic and basic solutions. Persulfoxide continues to react with another methionine, yielding methionine sulfoxide as end-product albeit with a much lower reaction rate in basic solution. Density functional theory was used to explore reaction potential energy surfaces and establish kinetic models, with solvation effects simulated using the polarized continuum model. Combined with our previous study of gas-phase methionine ions with (1)O2, evolution of methionine oxidation pathways at different ionization states and in different media is described.

  13. A comprehensive experimental and detailed chemical kinetic modelling study of 2,5-dimethylfuran pyrolysis and oxidation

    Science.gov (United States)

    Somers, Kieran P.; Simmie, John M.; Gillespie, Fiona; Conroy, Christine; Black, Gráinne; Metcalfe, Wayne K.; Battin-Leclerc, Frédérique; Dirrenberger, Patricia; Herbinet, Olivier; Glaude, Pierre-Alexandre; Dagaut, Philippe; Togbé, Casimir; Yasunaga, Kenji; Fernandes, Ravi X.; Lee, Changyoul; Tripathi, Rupali; Curran, Henry J.

    2013-01-01

    The pyrolytic and oxidative behaviour of the biofuel 2,5-dimethylfuran (25DMF) has been studied in a range of experimental facilities in order to investigate the relatively unexplored combustion chemistry of the title species and to provide combustor relevant experimental data. The pyrolysis of 25DMF has been re-investigated in a shock tube using the single-pulse method for mixtures of 3% 25DMF in argon, at temperatures from 1200–1350 K, pressures from 2–2.5 atm and residence times of approximately 2 ms. Ignition delay times for mixtures of 0.75% 25DMF in argon have been measured at atmospheric pressure, temperatures of 1350–1800 K at equivalence ratios (ϕ) of 0.5, 1.0 and 2.0 along with auto-ignition measurements for stoichiometric fuel in air mixtures of 25DMF at 20 and 80 bar, from 820–1210 K. This is supplemented with an oxidative speciation study of 25DMF in a jet-stirred reactor (JSR) from 770–1220 K, at 10.0 atm, residence times of 0.7 s and at ϕ = 0.5, 1.0 and 2.0. Laminar burning velocities for 25DMF-air mixtures have been measured using the heat-flux method at unburnt gas temperatures of 298 and 358 K, at atmospheric pressure from ϕ = 0.6–1.6. These laminar burning velocity measurements highlight inconsistencies in the current literature data and provide a validation target for kinetic mechanisms. A detailed chemical kinetic mechanism containing 2768 reactions and 545 species has been simultaneously developed to describe the combustion of 25DMF under the experimental conditions described above. Numerical modelling results based on the mechanism can accurately reproduce the majority of experimental data. At high temperatures, a hydrogen atom transfer reaction is found to be the dominant unimolecular decomposition pathway of 25DMF. The reactions of hydrogen atom with the fuel are also found to be important in predicting pyrolysis and ignition delay time experiments. Numerous proposals are made on the mechanism and kinetics of the previously

  14. Mechanistic and kinetic studies on the OH-initiated atmospheric oxidation of fluoranthene.

    Science.gov (United States)

    Dang, Juan; Shi, Xiangli; Zhang, Qingzhu; Hu, Jingtian; Chen, Jianmin; Wang, Wenxing

    2014-08-15

    The atmospheric oxidation of polycyclic aromatic hydrocarbons (PAHs) can generate toxic derivatives which contribute to the carcinogenic potential of particulate organic matter. In this work, the mechanism of the OH-initiated atmospheric oxidation of fluoranthene (Flu) was investigated by using high-accuracy molecular orbital calculations. All of the possible oxidation pathways were discussed, and the theoretical results were compared with the available experimental observation. The rate constants of the crucial elementary reactions were evaluated by the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The main oxidation products are a range of ring-retaining and ring-opening chemicals containing fluoranthols, fluoranthones, fluoranthenequinones, nitro-fluoranthenes, dialdehydes and epoxides. The overall rate constant of the OH addition reaction is 1.72×10(-11) cm(3) molecule(-1) s(-1) at 298 K and 1 atm. The atmospheric lifetime of Flu determined by OH radicals is about 0.69 days. This work provides a comprehensive investigation of the OH-initiated oxidation of Flu and should help to clarify its atmospheric conversion. Copyright © 2014 Elsevier B.V. All rights reserved.

  15. Indoor air purificaton using heterogeneous photocatalytic oxidation, Part 2: Kinetic study

    NARCIS (Netherlands)

    Yu, Q.; Ballari, M.; Brouwers, H.J.H.

    2010-01-01

    In part I to this article [1], the application of the heterogeneous photocatalytic oxidation (PCO) theory for the indoor air quality improvement was presented. With a modified TiO2 that can be activated by visible light as the photocatalyst coated on a special wall paper, and one typical indoor air

  16. Heterogeneous reactions of carbonyl sulfide on mineral oxides: mechanism and kinetics study

    Directory of Open Access Journals (Sweden)

    Y. Liu

    2010-11-01

    Full Text Available The heterogeneous reactions of carbonyl sulfide (OCS on the typical mineral oxides in the mineral dust particles were investigated using a Knudsen cell flow reactor and a diffuse reflectance UV-vis spectroscopy. The reaction pathway for OCS on mineral dust was identified based on the gaseous products and surface species. The hydrolysis of OCS and succeeding oxidation of intermediate products readily took place on α-Al2O3, MgO, and CaO. Reversible and irreversible adsorption of OCS were observed on α-Fe2O3 and ZnO, respectively, whereas no apparent uptake of OCS by SiO2 and TiO2 was observed. The reactivity of OCS on these oxides depends on both the basicity of oxides and the decomposition reactivity of oxides for H2S. Based on the individual uptake coefficients and chemical composition of authentic mineral dust, the uptake coefficient (γBET of mineral dust was estimated to be in the range of 3.84×10−7–2.86×10−8. The global flux of OCS due to heterogeneous reactions and adsorption on mineral dust was estimated at 0.13–0.29 Tg yr−1, which is comparable to the annual flux of OCS for its reaction with ·OH.

  17. Kinetic, mechanistic, and spectroscopic studies of permanganate oxidation of azinylformamidines in acidic medium, with autocatalytic behavior of manganese(II

    Directory of Open Access Journals (Sweden)

    Basim H. Asghar

    2016-09-01

    Full Text Available The kinetics of permanganate oxidation of two substituted azinylformamidines (Azn-Fs, namely N,N-dimethyl-N′-(pyridin-2-ylformamidine (Py and N,N-dimethyl-N′-(pyrimidin-2-ylformamidine (Pym, in sulfuric acid were investigated using conventional spectrophotometry. Kinetic evidence for the formation of 1:1 intermediate complexes between the oxidant and substrates was obtained. The reactions of both substrates with permanganate showed similar kinetics, i.e. first order in [MnO4−]0 and fractional-first-order with respect to both [Azn-F]0 and [H+]. The initial product, Mn2+, was found to autocatalyze the oxidation process. Changes in the ionic strength and dielectric constant of the medium had no significant effect on the rate. The final oxidation products of Py and Pym were identified as 2-aminopyridine and 2-aminopyrimidine, respectively, in addition to dimethylamine and carbon dioxide. A plausible reaction mechanism is suggested and the reaction constants involved in the mechanism were evaluated.

  18. Chemical Kinetic Study of Nitrogen Oxides Formation Trends in Biodiesel Combustion

    Directory of Open Access Journals (Sweden)

    Junfeng Yang

    2012-01-01

    Full Text Available The use of biodiesel in conventional diesel engines results in increased NOx emissions; this presents a barrier to the widespread use of biodiesel. The origins of this phenomenon were investigated using the chemical kinetics simulation tool: CHEMKIN-2 and the CFD KIVA3V code, which was modified to account for the physical properties of biodiesel and to incorporate semidetailed mechanisms for its combustion and the formation of emissions. Parametric ϕ-T maps and 3D engine simulations were used to assess the impact of using oxygen-containing fuels on the rate of NO formation. It was found that using oxygen-containing fuels allows more O2 molecules to present in the engine cylinder during the combustion of biodiesel, and this may be the cause of the observed increase in NO emissions.

  19. Solid oxide electrode kinetics in light of in situ surface studies

    DEFF Research Database (Denmark)

    Mogensen, Mogens Bjerg

    2014-01-01

    The combination of in situ and in particular in operando characterization methods such as electrochemical impedance spectroscopy (EIS) on both technical and model electrode are well known ways to gain some practical insight in electrode reaction kinetics. Yet, is has become clear that in spite...... of the strengths it is not sufficient to reveal much details of the electrode mechanisms mainly because it provide average values only. Therefore it has to be combined with surface science methods in order to reveal the interface structure and composition. Ex situ methods have been very useful over the latest....... Furthermore, it seems that detailed mathematical modeling using new tools like COMSOL is necessary for the synthesis of the large amount of data for a well-characterized electrode into one physical meaningful picture. A brief review of literature an own data will be presented with a practical example of SOFC...

  20. Oxidative degradation of triazine- and sulfonylurea-based herbicides using Fe(VI): The case study of atrazine and iodosulfuron with kinetics and degradation products

    Science.gov (United States)

    The occurrence of common herbicides (Atrazine, ATZ and Iodosufuron, IDS), in waters presents potential risk to human and ecological health. The oxidative degradation of ATZ and IDS by ferrate(VI) (FeVIO42-, Fe(VI)) is studied at different pH levels where kinetically observed se...

  1. Kinetic Studies on State of the Art Solid Oxide Cells – A Comparison between Hydrogen/Steam and Reformate Fuels

    DEFF Research Database (Denmark)

    Njodzefon, Jean-Claude; Graves, Christopher R.; Mogensen, Mogens Bjerg

    2015-01-01

    Electrochemical reaction kinetics at the electrodes of Solid Oxide Cells (SOCs) were investigated at 700 °C for two cells with different fuel electrode microstructures as well as on a third cell with a reduced active electrode area. Three fuel mixtures were investigated – hydrogen/steam and refor......Electrochemical reaction kinetics at the electrodes of Solid Oxide Cells (SOCs) were investigated at 700 °C for two cells with different fuel electrode microstructures as well as on a third cell with a reduced active electrode area. Three fuel mixtures were investigated – hydrogen....../steam fuel split into two processes with opposing temperature behavior in the reformate fuels. An 87.5% reduction in active electrode area diminishes the gas conversion impedance in the hydrogen/steam fuel at high fuel flow rates. In both reformates, the second and third lowest frequency processes merged...

  2. Cure kinetics and chemorheology of EPDM/graphene oxide nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Allahbakhsh, Ahmad [Department of Polymer Engineering, Islamic Azad University, South Tehran Branch, 17776-13651 Tehran (Iran, Islamic Republic of); Mazinani, Saeedeh, E-mail: s.mazinani@aut.ac.ir [Amirkabir Nanotechnology Research Institute (ANTRI), Amirkabir University of Technology, Tehran (Iran, Islamic Republic of); Kalaee, Mohammad Reza [Department of Polymer Engineering, Islamic Azad University, South Tehran Branch, 17776-13651 Tehran (Iran, Islamic Republic of); Sharif, Farhad [Department of Polymer Engineering and Color Technology, Amirkabir University of Technology, Tehran (Iran, Islamic Republic of)

    2013-07-10

    Graphical abstract: - Highlights: • Graphene oxide content and dispersion as effective parameters on cure kinetics. • Graphene oxide as an effective controlling factor of crosslink density. • Interaction of graphene oxide with curing system (ZnO) during curing process. - Abstract: In this study, the effect of graphene oxide on cure behavior of ethylene–propylene–diene rubber (EPDM) nanocomposite is studied. In this regard, the cure kinetics of nanocomposite is studied employing different empirical methods. The required activation energy of nth-order cure process shows about 160 kJ/mol increments upon 5 phr graphene oxide loading compared to 1 phr graphene oxide loading. However, the required activation energy is significantly reduced followed by incorporation of graphene oxide in nanocomposites compared to neat EPDM sample. Furthermore, the effect of graphene oxide on structural properties of nanocomposites during the cure process is studied using X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectrometry techniques. As the results show, graphene oxide interestingly affects the structure of zinc oxide during the vulcanization process. This behavior could be probably related to high tendency of zinc oxide to react with oxidized surface of graphene oxide.

  3. Studying the effect of particle size and coating type on the blood kinetics of superparamagnetic iron oxide nanoparticles

    Directory of Open Access Journals (Sweden)

    Roohi F

    2012-08-01

    Full Text Available Farnoosh Roohi, Jessica Lohrke, Andreas Ide, Gunnar Schütz, Katrin DasslerMR and CT Contrast Media Research, Bayer Pharma AG, Berlin, GermanyPurpose: Magnetic resonance imaging (MRI, one of the most powerful imaging techniques available, usually requires the use of an on-demand designed contrast agent to fully exploit its potential. The blood kinetics of the contrast agent represent an important factor that needs to be considered depending on the objective of the medical examination. For particulate contrast agents, such as superparamagnetic iron oxide nanoparticles (SPIOs, the key parameters are particle size and characteristics of the coating material. In this study we analyzed the effect of these two properties independently and systematically on the magnetic behavior and blood half-life of SPIOs.Methods: Eleven different SPIOs were synthesized for this study. In the first set (a, seven carboxydextran (CDX-coated SPIOs of different sizes (19–86 nm were obtained by fractionating a broadly size-distributed CDX–SPIO. The second set (b contained three SPIOs of identical size (50 nm that were stabilized with different coating materials, polyacrylic acid (PAA, polyethylene glycol, and starch. Furthermore, small PAA–SPIOs (20 nm were synthesized to gain a global insight into the effects of particle size vs coating characteristics. Saturation magnetization and proton relaxivity were determined to represent the magnetic and imaging properties. The blood half-life was analyzed in rats using MRI, time-domain nuclear magnetic resonance, and inductively coupled plasma optical emission spectrometry.Results: By changing the particle size without modifying any other parameters, the relaxivity r2 increased with increasing mean particle diameter. However, the blood half-life was shorter for larger particles. The effect of the coating material on magnetic properties was less pronounced, but it had a strong influence on blood kinetics depending on the

  4. Studying the effect of particle size and coating type on the blood kinetics of superparamagnetic iron oxide nanoparticles.

    Science.gov (United States)

    Roohi, Farnoosh; Lohrke, Jessica; Ide, Andreas; Schütz, Gunnar; Dassler, Katrin

    2012-01-01

    Magnetic resonance imaging (MRI), one of the most powerful imaging techniques available, usually requires the use of an on-demand designed contrast agent to fully exploit its potential. The blood kinetics of the contrast agent represent an important factor that needs to be considered depending on the objective of the medical examination. For particulate contrast agents, such as superparamagnetic iron oxide nanoparticles (SPIOs), the key parameters are particle size and characteristics of the coating material. In this study we analyzed the effect of these two properties independently and systematically on the magnetic behavior and blood half-life of SPIOs. Eleven different SPIOs were synthesized for this study. In the first set (a), seven carboxydextran (CDX)-coated SPIOs of different sizes (19-86 nm) were obtained by fractionating a broadly size-distributed CDX-SPIO. The second set (b) contained three SPIOs of identical size (50 nm) that were stabilized with different coating materials, polyacrylic acid (PAA), poly-ethylene glycol, and starch. Furthermore, small PAA-SPIOs (20 nm) were synthesized to gain a global insight into the effects of particle size vs coating characteristics. Saturation magnetization and proton relaxivity were determined to represent the magnetic and imaging properties. The blood half-life was analyzed in rats using MRI, time-domain nuclear magnetic resonance, and inductively coupled plasma optical emission spectrometry. By changing the particle size without modifying any other parameters, the relaxivity r(2) increased with increasing mean particle diameter. However, the blood half-life was shorter for larger particles. The effect of the coating material on magnetic properties was less pronounced, but it had a strong influence on blood kinetics depending on the ionic character of the coating material. In this report we systematically demonstrated that both particle size and coating material influence blood kinetics and magnetic properties of

  5. Kinetic study of methanol oxidation on carbon-supported PtRu electrocatalyst

    International Nuclear Information System (INIS)

    Gojkovic, S.Lj.; Vidakovic, T.R.; Durovic, D.R.

    2003-01-01

    Methanol electrooxidation was investigated on the carbon-supported PtRu electrocatalyst (1:1 atomic ratio) in acid media. X-ray diffraction measurement indicated alloying of Pt and Ru. Cyclic voltammetry of the sample reflects the amount of Ru in the catalyst and its ability to adsorb OH radicals. Tafel plots for the oxidation of 0.02-3 M methanol in the solutions containing 0.05-1 M HClO 4 and in the temperature range 27-40 deg. C showed reasonably well-defined linear region with the slope of about 115 mV dec -1 at the low currents, irrespective of the experimental conditions employed. Reaction order with respect to methanol was found to be 0.5. A correlation between methanol oxidation rate and pseudocapacitive current of OH adsorption on Ru sites was established. It was proposed that bifunctional mechanism is operative with the reaction between methanol residues adsorbed on Pt sites and OH radicals adsorbed on Ru sites as the rate-determining step

  6. Oxidation kinetics of (B6O) boron oxide

    International Nuclear Information System (INIS)

    Makarov, V.S.; Solov'ev, N.E.; Ugaj, Ya.A.

    1987-01-01

    Reactivity of B 6 O to oxygen is investigated. It is shown that the process of B 6 O oxidation in the air in the temperature range 760-1150 K results in the maximum transformation degree equal to 0.35. At the initial stages oxidation proceeds in kinetic regime, at final stages - in diffusion one, and high viscosity of B 2 O 3 probably affects the oxidation process

  7. Pulmonary toxicity and kinetic study of Cy5.5-conjugated superparamagnetic iron oxide nanoparticles by optical imaging

    International Nuclear Information System (INIS)

    Cho, Wan-Seob; Cho, Minjung; Kim, Seoung Ryul; Choi, Mina; Lee, Jeong Yeon; Han, Beom Seok; Park, Sue Nie; Yu, Mi Kyung; Jon, Sangyong; Jeong, Jayoung

    2009-01-01

    Recent advances in the development of nanotechnology and devices now make it possible to accurately deliver drugs or genes to the lung. Magnetic nanoparticles can be used as contrast agents, thermal therapy for cancer, and be made to concentrate to target sites through an external magnetic field. However, these advantages may also become problematic when taking into account safety and toxicological factors. This study demonstrated the pulmonary toxicity and kinetic profile of anti-biofouling polymer coated, Cy5.5-conjugated thermally cross-linked superparamagnetic iron oxide nanoparticles (TCL-SPION) by optical imaging. Negatively charged, 36 nm-sized, Cy5.5-conjugated TCL-SPION was prepared for optical imaging probe. Cy5.5-conjugated TCL-SPION was intratracheally instilled into the lung by a non-surgical method. Cy5.5-conjugated TCL-SPION slightly induced pulmonary inflammation. The instilled nanoparticles were distributed mainly in the lung and excreted in the urine via glomerular filtration. Urinary excretion was peaked at 3 h after instillation. No toxicity was found under the concentration of 1.8 mg/kg and the half-lives of nanoparticles in the lung and urine were estimated to be about 14.4 ± 0.54 h and 24.7 ± 1.02 h, respectively. Although further studies are required, our results showed that Cy5.5-conjugated TCL-SPION can be a good candidate for use in pulmonary delivery vehicles and diagnostic probes.

  8. Zirconium oxide-coated sand based batch and column adsorptive removal of arsenic from water: Isotherm, kinetic and thermodynamic studies

    Directory of Open Access Journals (Sweden)

    Saif Ali Chaudhry

    2017-06-01

    Full Text Available This paper reports zirconium oxide-coated sand preparation, characterization by SEM, EDX, XRD, FT-IR and thermoanalytical techniques, and use as an adsorbent for the removal of most toxic form of arsenic, As(III, from aqueous solution in both batch and column methods. Batch experimental parameters such as contact time, concentration, dose of adsorbent, pH of As(III solution and temperature were optimized. The adsorption data was fitted to Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms at 303, 308 and 313 K. The maximum Langmuir monolayer adsorption capacity was found to be 136.98 μg/g at 313 K. Values of ΔH°, ΔG° and ΔS° were found to be −12.90, −8.74 to –8.28 and 0.014 kJ/mol, suggesting exothermic and spontaneous adsorption process with slight increase in entropy. The adsorption process followed pseudo-second order kinetics and was controlled by film diffusion step. The column studies showed that when flow rate was increased from 3.0 to 5.0 mL/min, the arsenic adsorption capacity of ZrOCS increased from 33.104 to 42.231 μg/g and breakthrough, and exhaustion times got reduced reduced. The results indicated that zirconium oxide-coated sand (ZrOCS is an excellent adsorbent for the removal of As(III from water.

  9. Carbonate effects and pH-dependence of uranium sorption onto bacteriogenic iron oxides: Kinetic and equilibrium studies

    International Nuclear Information System (INIS)

    Katsoyiannis, Ioannis A.

    2007-01-01

    The removal of U(VI) from groundwaters by adsorption onto bacteriogenic iron oxides (BIOS) has been investigated under batch mode. The adsorbent dosage, the uranium concentration, the concentration of carbonate and the use of a real groundwater spiked with uranium comprised the examined parameters. In addition, the effect of pH was examined in two different water matrixes, i.e., in distilled water and in real groundwater. Equilibrium studies were carried out to determine the maximum adsorption capacity of BIOS and the data correlated well with the Langmuir and Freundlich models. The presence of carbonate affected adversely the adsorption of U(VI) onto BIOS. The maximum adsorption capacity of BIOS was 9.25 mg g -1 at 0.1 mM carbonate concentration and decreased to 6.93 mg g -1 at 0.5 mM carbonate concentration, whereas at carbonate concentration of 2 mM practically no adsorption occurred. The data were further analyzed using the pseudo-second order kinetic equation, which fitted best the experimental results. The initial adsorption rate (h) was found to increase with decreasing the concentration of carbonate in all cases. When experiments were accomplished in the absence of carbonate, the pH values did not have an effect on the adsorption of U(VI). However, the extent of U(VI) adsorption was strongly pH-dependent when the experiments were carried out in the real groundwater. The maximum adsorption capacity increased sharply as the pH decreased and optimum removal was obtained in the pH range 3.2-4.0, thus bacteriogenic iron oxides can found application in the removal of U(VI) by adsorption from low pH or low carbonate waters

  10. Oxidation kinetics of polycyclic aromatic hydrocarbons by permanganate.

    Science.gov (United States)

    Forsey, Steven P; Thomson, Neil R; Barker, James F

    2010-04-01

    The reactivity of permanganate towards polycyclic aromatics hydrocarbons (PAHs) is well known but little kinetic information is available. This study investigated the oxidation kinetics of a selected group of coal tar creosote compounds and alkylbenzenes in water using permanganate, and the correlation between compound reactivity and physical/chemical properties. The oxidation of naphthalene, phenanthrene, chrysene, 1-methylnaphthalene, 2-methylnaphthalene, acenaphthene, fluorene, carbazole isopropylbenzene, ethylbenzene and methylbenzene closely followed pseudo first-order reaction kinetics. The oxidation of pyrene was initially very rapid and did not follow pseudo first-order kinetics at early times. Fluoranthene was only partially oxidized and the oxidation of anthracene was too fast to be captured. Biphenyl, dibenzofuran, benzene and tert-butylbenzene were non-reactive under the study conditions. The oxidation rate was shown to increase with increasing number of polycyclic rings because less energy is required to overcome the aromatic character of a polycyclic ring than is required for benzene. Thus the rate of oxidation increased in the series naphthalenepermanganate. 2010 Elsevier Ltd. All rights reserved.

  11. Thorium oxide dissolution kinetics for hydroxide and carbonate complexation

    International Nuclear Information System (INIS)

    Jardin, R.; Curran, V.; Czerwinski, K.R.

    2002-01-01

    The purpose of this project was to determine the kinetics and thermodynamics of thorium oxide dissolution in the environment. Solubility is important because it establishes an upper concentration limit on the concentration of a dissolved radionuclide in solution L1. While understanding the behavior of thorium fuels in the proposed repository at Yucca Mountain is most applicable, a more rigorous study of thorium solubility over a wide pH range was performed so that the data could also be used to model the behavior of thorium fuels in any environmental system. To achieve this, the kinetics and thermodynamics of thorium oxide dissolution under both pure argon and argon with P CO2 of 0. 1 were studied under the full pH range available in each atmosphere. In addition, thorium oxide powder remnants were studied after each experiment to examine structural changes that may affect kinetics

  12. Oxidation kinetics and soot formation

    Science.gov (United States)

    Glassman, I.; Brezinsky, K.

    1983-01-01

    The research objective is to clarify the role of aromaticity in the soot nucleation process by determining the relative importance of phenyl radical/molecular oxygen and benzene/atomic oxygen reactions in the complex combustion of aromatic compounds. Three sets of chemical flow reactor experiments have been designed to determine the relative importance of the phenyl radical/molecular oxygen and benzene/atomic oxygen reactions. The essential elements of these experiments are 1) the use of cresols and anisole formed during the high temperature oxidation of toluene as chemical reaction indicators; 2) the in situ photolysis of molecular oxygen to provide an oxygen atom perturbation in the reacting aromatic system; and 3) the high temperature pyrolysis of phenol, the cresols and possibly anisole.

  13. Kinetics and oxidation mechanisms of polycrystaline niobium

    International Nuclear Information System (INIS)

    Paschoal, J.O.A.

    1979-01-01

    The oxidation kinetics of annealed niobium was determined by thermogravimetric analysis between 450 and 800 0 C and for oxygen pressures varying from 20 to 700 mmHg. The oxidation kinetics of cold worked and/or irradiated niobium for temperatures between 500 and 700 0 C, with oxygen pressures varying from 100 to 300 mmHg. Was also determined. Using X-ray diffraction it was found that the oxide formed in the range of temperature and oxygen pressure considered in this research is γ-Nb 2 O 5 . Optical and scanning eletronic microscopy showed that for annealed niobium oxidized under 600 0 C there was formation of non-uniform oxide layers, containing cracks and pores, presenting very irregular metal/pentoxide interface. The presence of sub-oxide NbOsub(z) platelets was observed in this interface. This sub-oxide platelets where not observed in annealed oxidized niobium samples over 600 0 C; the oxide layers formed were compact. At 800 0 C and the beginning at 700 0 C the interfaces were quite regular. Through microhardness measurements for the metal near the metal/pentoxide interface, the formation of oxygen solid solution was found and the oxygen diffusion coefficient was calculated. The results showed that at 600 0 C the oxygen diffusion coefficient in cold worked niobium is three times larger than the value obtained for annealed niobium. The results suggest that the reaction between annealed niobium and oxygen undaer 600 0 C is controlled by reaction in interface where the oxide layers are not compacted, parcially due to Nb sub(z) platelets formation.(Author) [pt

  14. Studies on the kinetics of UO2 dissolution in carbonate-bicarbonate medium using sodium hypochlorite as oxidant

    International Nuclear Information System (INIS)

    Sharma, J.N.; Bhattacharya, K.; Swami, R.G.; Tangri, S.K.; Mukherjee, T.K.

    1996-01-01

    The dissolution of UO 2 in carbonate-bicarbonate solutions containing sodium hypochlorite as an oxidant has been investigated. The effect of temperature, sodium hypochlorite concentration and stirring speed was examined. In the temperature range of 303 to 318 K, the leaching reaction displayed linear kinetics. Apparent activation energy obtained from the differential approach was found to be 57 kJ mol -1 . This relatively high activation energy value indicates a chemically controlled behavior of UO 2 dissolution. The order of reaction with respect to sodium hypochlorite concentration was found to be unity. (author). 18 refs., 6 figs

  15. Kinetics of Photoelectrochemical Oxidation of Methanol on Hematite Photoanodes

    Science.gov (United States)

    2017-01-01

    The kinetics of photoelectrochemical (PEC) oxidation of methanol, as a model organic substrate, on α-Fe2O3 photoanodes are studied using photoinduced absorption spectroscopy and transient photocurrent measurements. Methanol is oxidized on α-Fe2O3 to formaldehyde with near unity Faradaic efficiency. A rate law analysis under quasi-steady-state conditions of PEC methanol oxidation indicates that rate of reaction is second order in the density of surface holes on hematite and independent of the applied potential. Analogous data on anatase TiO2 photoanodes indicate similar second-order kinetics for methanol oxidation with a second-order rate constant 2 orders of magnitude higher than that on α-Fe2O3. Kinetic isotope effect studies determine that the rate constant for methanol oxidation on α-Fe2O3 is retarded ∼20-fold by H/D substitution. Employing these data, we propose a mechanism for methanol oxidation under 1 sun irradiation on these metal oxide surfaces and discuss the implications for the efficient PEC methanol oxidation to formaldehyde and concomitant hydrogen evolution. PMID:28735533

  16. Oxidation kinetics of polycyclic aromatic hydrocarbons by permanganate

    Energy Technology Data Exchange (ETDEWEB)

    Forsey, S.P.; Thomson, N.R.; Barker, J.F. [University of Waterloo, Waterloo, ON (Canada). Dept. of Civil & Environmental Engineering

    2010-04-15

    The reactivity of permanganate towards polycyclic aromatics hydrocarbons (PAHs) is well known but little kinetic information is available. This study investigated the oxidation kinetics of a selected group of coal tar creosote compounds and alkylbenzenes in water using permanganate, and the correlation between compound reactivity and physical/chemical properties. The oxidation of naphthalene, phenanthrene, chrysene, 1-methylnaphthalene, 2-methylnaphthalene, acenaphthene, fluorene, carbazole isopropylbenzene, ethylbenzene and methylbenzene closely followed pseudo first-order reaction kinetics. The oxidation of pyrene was initially very rapid and did not follow pseudo first-order kinetics at early times. Fluoranthene was only partially oxidized and the oxidation of anthracene was too fast to be captured. Biphenyl, dibenzofuran, benzene and tert-butylbenzene were non-reactive under the study conditions. The oxidation rate was shown to increase with increasing number of polycyclic rings because less energy is required to overcome the aromatic character of a polycyclic ring than is required for benzene. Thus the rate of oxidation increased in the series naphthalene < phenanthrene < pyrene. The rate of side chain reactivity is controlled by the C-H bond strength. For the alkyl substituted benzenes an excellent correlation was observed between the reaction rate coefficients and bond dissociation energies, but for the substituted PAHs the relationship was poor. A trend was found between the reaction rate coefficients and the calculated heats of complexation indicating that significant ring oxidation occurred in addition to side chain oxidation. Clar's aromatic sextet theory was used to predict the relative stability of arenes towards ring oxidation by permanganate.

  17. Colorimetric study of oxidation kinetics of thiolactic acid (2 - mercaptopropionic acid) by hexacyanoferrate (III) in acid and alkaline media

    International Nuclear Information System (INIS)

    Kachhwaha, O.P.; Potter, P.C.; Kapoor, R.C.

    1985-01-01

    The oxidation kinetics of thiolactic acid by hexacyanoferrate (III) in acid and alkaline media employing the calorimetric method have been described. The two compounds react in equimolar ratio in both media, but the kinetic results are different in both media. In acid medium the total order is three, two with respect to thiol and one in oxidant. The rate of the reaction shows an inverse proportionality to (H + ) and also varies inversely with decreasing dielectric constant of the medium. In alkaline medium, the total order of the reaction is two, being unity in each reactant. The rate increases with increased pH value. Additions of ferrocyanide and dithio dilactic acid have no effect on the rate in both media. Additions of a neutral electrolyte does not affect the rate in the acid medium, while a positive salt effect was observed in an alkaline medium. Activation parameters have been evaluated in both media and in a medium of low dialectric. Different reaction schemes have been proposed for acid and alkaline media and have satisfactory explained the experimental data, except for the pH rate. (author)

  18. Study on the effects of titanium oxide based nanomaterials as catalysts on the hydrogen sorption kinetics of magnesium hydride

    Energy Technology Data Exchange (ETDEWEB)

    Pereira, Anderson de Farias; Jardim, Paula Mendes; Santos, Dilson Silva dos, E-mail: anderso.n@poli.ufrj.br [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil); Conceicao, Monique Osorio Talarico da [Centro Universitario de Volta Redonda (UniFOA), RJ (Brazil)

    2016-07-01

    Full text: Magnesium hydride is highly attractive for hydrogen storage in solid state in reason of its high gravimetric capacity (7,6 wt% of H{sub 2}) and low density (1,7 g/cm³), making it a promissory candidate for mobile applications [1]. However, its low sorption kinetics and desorption temperature are the main obstacles for its application. In the present study the catalytic role of TiO{sub 2} based nanomaterials with different morphologies on the sorption kinetics of MgH{sub 2} was evaluated. The additions consisted on titanate nanotubes (TTNT-Low), TiO{sub 2} nanorods (TTNT-550) and nanoparticles (KA-100, TTNT-ACID). Transmission and Scanning Transmission Electron Microscopy (S/TEM) associated with X-ray Energy Dispersive Spectroscopy (XEDS) mapping was used to characterize the catalysts' morphology and crystalline structure and their dispersion within magnesium hydride, altogether with other characterization techniques such as X-ray diffraction (XRD) and BET technique for structure and surface area analysis. The sorption kinetics were evaluated by means of a volumetric gas absorption/desorption (Sievert-type) apparatus. The results indicated that all additives improved the sorption kinetics of MgH{sub 2}, but the samples with TTNT-550 (TiO{sub 2} nanorods) and TTNT-ACID (TiO{sub 2} nanoparticles) presented the best and the second best performances, respectively, suggesting that the 1D morphology may promote a slightly superior kinetics than particulate catalysts. (author)

  19. Kinetics of oxidation of nickel(II) aza macrocycles by ...

    Indian Academy of Sciences (India)

    The kinetics of the oxidation of nickel (II) hexaaza and nickel (II) pentaaza macrocycles by the peroxydisulphate anion, S2O8 2-, were studied in aqueous media. Effect of H on reaction rate was also studied. The rate increases with increase of S2OO8 2- concentration. Rates are almost independent of acid between H 4 ...

  20. Kinetic Studies on Enzyme-Catalyzed Reactions: Oxidation of Glucose, Decomposition of Hydrogen Peroxide and Their Combination

    Science.gov (United States)

    Tao, Zhimin; Raffel, Ryan A.; Souid, Abdul-Kader; Goodisman, Jerry

    2009-01-01

    The kinetics of the glucose oxidase-catalyzed reaction of glucose with O2, which produces gluconic acid and hydrogen peroxide, and the catalase-assisted breakdown of hydrogen peroxide to generate oxygen, have been measured via the rate of O2 depletion or production. The O2 concentrations in air-saturated phosphate-buffered salt solutions were monitored by measuring the decay of phosphorescence from a Pd phosphor in solution; the decay rate was obtained by fitting the tail of the phosphorescence intensity profile to an exponential. For glucose oxidation in the presence of glucose oxidase, the rate constant determined for the rate-limiting step was k = (3.0 ± 0.7) ×104 M−1s−1 at 37°C. For catalase-catalyzed H2O2 breakdown, the reaction order in [H2O2] was somewhat greater than unity at 37°C and well above unity at 25°C, suggesting different temperature dependences of the rate constants for various steps in the reaction. The two reactions were combined in a single experiment: addition of glucose oxidase to glucose-rich cell-free media caused a rapid drop in [O2], and subsequent addition of catalase caused [O2] to rise and then decrease to zero. The best fit of [O2] to a kinetic model is obtained with the rate constants for glucose oxidation and peroxide decomposition equal to 0.116 s−1 and 0.090 s−1 respectively. Cellular respiration in the presence of glucose was found to be three times as rapid as that in glucose-deprived cells. Added NaCN inhibited O2 consumption completely, confirming that oxidation occurred in the cellular mitochondrial respiratory chain. PMID:19348778

  1. Two oxidation sites for low redox potential substrates: a directed mutagenesis, kinetic, and crystallographic study on Pleurotus eryngii versatile peroxidase.

    Science.gov (United States)

    Morales, María; Mate, María J; Romero, Antonio; Martínez, María Jesús; Martínez, Ángel T; Ruiz-Dueñas, Francisco J

    2012-11-30

    Versatile peroxidase shares with manganese peroxidase and lignin peroxidase the ability to oxidize Mn(2+) and high redox potential aromatic compounds, respectively. Moreover, it is also able to oxidize phenols (and low redox potential dyes) at two catalytic sites, as shown by biphasic kinetics. A high efficiency site (with 2,6-dimethoxyphenol and p-hydroquinone catalytic efficiencies of ∼70 and ∼700 s(-1) mM(-1), respectively) was localized at the same exposed Trp-164 responsible for high redox potential substrate oxidation (as shown by activity loss in the W164S variant). The second site, characterized by low catalytic efficiency (∼3 and ∼50 s(-1) mM(-1) for 2,6-dimethoxyphenol and p-hydroquinone, respectively) was localized at the main heme access channel. Steady-state and transient-state kinetics for oxidation of phenols and dyes at the latter site were improved when side chains of residues forming the heme channel edge were removed in single and multiple variants. Among them, the E140G/K176G, E140G/P141G/K176G, and E140G/W164S/K176G variants attained catalytic efficiencies for oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) at the heme channel similar to those of the exposed tryptophan site. The heme channel enlargement shown by x-ray diffraction of the E140G, P141G, K176G, and E140G/K176G variants would allow a better substrate accommodation near the heme, as revealed by the up to 26-fold lower K(m) values (compared with native VP). The resulting interactions were shown by the x-ray structure of the E140G-guaiacol complex, which includes two H-bonds of the substrate with Arg-43 and Pro-139 in the distal heme pocket (at the end of the heme channel) and several hydrophobic interactions with other residues and the heme cofactor.

  2. Oxyhalogen-Sulfur Chemistry: Kinetics and Mechanism of Oxidation ...

    African Journals Online (AJOL)

    NICOLAAS

    The oxidation of N-acetylthiourea (ACTU) by acidic bromate has been studied by observing formation of bromine in excess .... kinetics experiments were performed at 25.0 ± 0.1 °C and at an ..... thiourea compounds with potent anti-HIV activity.

  3. Kinetics and mechanism of the oxidation of some diols by ...

    Indian Academy of Sciences (India)

    Abstract. The kinetics of oxidation of five vicinal and four non-vicinal diols, and two of their monoethers by benzyltrimethylammonium tribromide (BTMAB) have been studied in 3:7 (v/v) acetic acid–water mixture. The vicinal diols yield the carbonyl compounds arising out of the glycol bond fission while the other diols give.

  4. Thermal oxidative degradation kinetics of agricultural residues using distributed activation energy model and global kinetic model.

    Science.gov (United States)

    Ren, Xiu'e; Chen, Jianbiao; Li, Gang; Wang, Yanhong; Lang, Xuemei; Fan, Shuanshi

    2018-08-01

    The study concerned the thermal oxidative degradation kinetics of agricultural residues, peanut shell (PS) and sunflower shell (SS). The thermal behaviors were evaluated via thermogravimetric analysis and the kinetic parameters were determined by using distributed activation energy model (DAEM) and global kinetic model (GKM). Results showed that thermal oxidative decomposition of two samples processed in three zones; the ignition, burnout, and comprehensive combustibility between two agricultural residues were of great difference; and the combustion performance could be improved by boosting heating rate. The activation energy ranges calculated by the DAEM for the thermal oxidative degradation of PS and SS were 88.94-145.30 kJ mol -1 and 94.86-169.18 kJ mol -1 , respectively. The activation energy obtained by the GKM for the oxidative decomposition of hemicellulose and cellulose was obviously lower than that for the lignin oxidation at identical heating rate. To some degree, the determined kinetic parameters could acceptably simulate experimental data. Copyright © 2018 Elsevier Ltd. All rights reserved.

  5. Oxidation of methionine by tetraethylammonium chlorochromate in non-aqueous media – A kinetic and mechanistic study

    Directory of Open Access Journals (Sweden)

    S. Sheik Mansoor

    2015-07-01

    Full Text Available The kinetics of oxidation of methionine (Met by tetraethylammonium chlorochromate (TEACC in dimethyl sulfoxide (DMSO leads to the formation of the corresponding sulfoxide. The reaction is first order each in Met and TEACC. The reaction is catalyzed by hydrogen ions. The hydrogen ion dependence has the form : kobs = a + b [H+]. The reaction rate has been determined at different temperatures and activation parameters are calculated. The solvent effect has been analyzed using Kamlet’s multi parametric equation. A correlation of data with Kamlet–Taft solvatochromic parameters (α, β, π∗ suggests that the specific solute–solvent interactions play a major role in governing the reactivity. The reaction does not induce polymerization of acrylonitrile. A suitable mechanism has been proposed.

  6. Simple and Efficient Synthesis of Iron Oxide-Coated Silica Gel Adsorbents for Arsenic Removal: Adsorption Isotherms and Kinetic Study

    Energy Technology Data Exchange (ETDEWEB)

    Arifin, Eric; Lee, Jiukyu [Interdisciplinary Program in Nanoscience and Technology, Virginia (United States); Cha, Jinmyung [Seoul National Univ., Seoul (Korea, Republic of)

    2013-08-15

    Iron oxide (ferrihydrite, hematite, and magnetite) coated silica gels were prepared using a low-cost, easily-scalable and straightforward method as the adsorbent material for arsenic removal application. Adsorption of the anionic form of arsenic oxyacids, arsenite (AsO{sup 2-}) and arsenate (AsO{sub 4}{sup -3}), onto hematite coated silica gel was fitted against non-linear 3-parameter-model Sips isotherm and 2-parameter-model Langmuir and Freundlich isotherm. Adsorption kinetics of arsenic could be well described by pseudo-second-order kinetic model and value of adsorption energy derived from non-linear Dubinin-Radushkevich isotherm suggests chemical adsorption. Although arsenic adsorption process was not affected by the presence of sulfate, chloride, and nitrate anions, as expected, bicarbonate and silicate gave moderate negative effects while the presence of phosphate anions significantly inhibited adsorption process of both arsenite and arsenate. When the actual efficiency to remove arsenic was tested against 1 L of artificial arsenic-contaminated groundwater (0.6 mg/L) in the presence competing anions, the reasonable amount (20 g) of hematite coated silica gel could reduce arsenic concentration to below the WHO permissible safety limit of drinking water of 10 μg/L without adjusting pH and temperature, which would be highly advantageous for practical field application.

  7. Oxidation of alginate and pectate biopolymers by cerium(IV) in perchloric and sulfuric acid solutions: A comparative kinetic and mechanistic study.

    Science.gov (United States)

    Fawzy, Ahmed

    2016-03-15

    The kinetics of oxidation of alginate (Alg) and pectate (Pec) carbohydrate biopolymers was studied by spectrophotometry in aqueous perchloric and sulfuric acid solutions at fixed ionic strengths and temperature. In both acids, the reactions showed a first order dependence on [Ce(IV)], whereas the orders with respect to biopolymer concentrations are less than unity. In perchloric acid, the reactions exhibited less than unit orders with respect to [H(+)] whereas those proceeded in sulfuric acid showed negative fractional-first order dependences on [H(+)]. The effect of ionic strength and dielectric constant was studied. Probable mechanistic schemes for oxidation reactions were proposed. In both acids, the final oxidation products were characterized as mono-keto derivatives of both biopolymers. The activation parameters with respect to the slow step of the mechanisms were computed and discussed. The rate laws were derived and the reaction constants involved in the different steps of the mechanisms were calculated. Copyright © 2015 Elsevier Ltd. All rights reserved.

  8. Predicting the Kinetic Properties Associated with Redox Imbalance after Oxidative Crisis in G6PD-Deficient Erythrocytes: A Simulation Study

    Directory of Open Access Journals (Sweden)

    Hanae Shimo

    2011-01-01

    Full Text Available It is well known that G6PD-deficient individuals are highly susceptible to oxidative stress. However, the differences in the degree of metabolic alterations among patients during an oxidative crisis have not been extensively studied. In this study, we applied mathematical modeling to assess the metabolic changes in erythrocytes of various G6PD-deficient patients during hydrogen peroxide- (H2O2- induced perturbation and predict the kinetic properties that elicit redox imbalance after exposure to an oxidative agent. Simulation results showed a discrepancy in the ability to restore regular metabolite levels and redox homeostasis among patients. Two trends were observed in the response of redox status (GSH/GSSG to oxidative stress, a mild decrease associated with slow recovery and a drastic decline associated with rapid recovery. The former was concluded to apply to patients with severe clinical symptoms. Low max and high mG6P of G6PD were shown to be kinetic properties that enhance consequent redox imbalance.

  9. Dehydrogenation Kinetics and Modeling Studies of MgH2 Enhanced by Transition Metal Oxide Catalysts Using Constant Pressure Thermodynamic Driving Forces

    Directory of Open Access Journals (Sweden)

    Saidi Temitope Sabitu

    2012-06-01

    Full Text Available The influence of transition metal oxide catalysts (ZrO2, CeO2, Fe3O4 and Nb2O5 on the hydrogen desorption kinetics of MgH2 was investigated using constant pressure thermodynamic driving forces in which the ratio of the equilibrium plateau pressure (pm to the opposing plateau (pop was the same in all the reactions studied. The results showed Nb2O5 to be vastly superior to other catalysts for improving the thermodynamics and kinetics of MgH2. The modeling studies showed reaction at the phase boundary to be likely process controlling the reaction rates of all the systems studied.

  10. Revisiting the Kinetics and Thermodynamics of the Low-Temperature Oxidation Pathways of Alkanes: A Case Study of the Three Pentane Isomers

    KAUST Repository

    Bugler, John

    2015-07-16

    © 2015 American Chemical Society. This paper describes our developing understanding of low-temperature oxidation kinetics. We have investigated the ignition of the three pentane isomers in a rapid compression machine over a wide range of temperatures and pressures, including conditions of negative temperature coefficient behavior. The pentane isomers are small alkanes, yet have structures that are complex enough to allow for the application of their kinetic and thermochemical rules to larger molecules. Updates to the thermochemistry of the species important in the low-temperature oxidation of hydrocarbons have been made based on a thorough literature review. An evaluation of recent quantum-chemically derived rate coefficients from the literature pertinent to important low-temperature oxidation reaction classes has been performed, and new rate rules are recommended for these classes. Several reaction classes have also been included to determine their importance with regard to simulation results, and we have found that they should be included when developing future chemical kinetic mechanisms. A comparison of the model simulations with pressure-time histories from experiments in a rapid compression machine shows very good agreement for both ignition delay time and pressure rise for both the first- and second-stage ignition events. We show that revisions to both the thermochemistry and the kinetics are required in order to replicate experiments well. A broader validation of the models with ignition delay times from shock tubes and a rapid compression machine is presented in an accompanying paper. The results of this study enhance our understanding of the combustion of straight- and branched-chained alkanes.

  11. Kinetics of molybdenite oxidizing leaching in alkali medium by ozone

    International Nuclear Information System (INIS)

    Medvedev, A.S.; Sokratova, N.B.; Litman, I.V.; Zelikman, A.N.

    1985-01-01

    On the basis of investigation of the process kinetics proposed is a model of oxidizing leaching of molybdenite in alkali medium while ozonization of the solution by ozoneair mixture. A kinetic equation is derived, that describes experimental data satisfactorily

  12. The effect of natural iron oxide and oxalic acid on the photocatalytic degradation of isoproturon: a kinetics and analytical study.

    Science.gov (United States)

    Boucheloukh, H; Remache, W; Parrino, F; Sehili, T; Mechakra, H

    2017-05-17

    The photocatalytic degradation of isoproturon, a persistent toxic herbicide, was investigated in the presence of natural iron oxide and oxalic acid and under UV irradiation. The influence of the relevant parameters such as the pH and the iron oxide and oxalic acid concentrations has been studied. The presence of natural iron oxide and oxalic acid in the system effectively allow the degradation of isoproturon, whereas the presence of t-butyl alcohol adversely affects the phototransformation of the target pollutant, thus indicating that an OH radical initiated the degradation mechanism. The degradation mechanism of isoproturon was investigated by means of GC-MS analysis. Oxidation of both the terminal N-(CH 3 ) 2 and isopropyl groups is the initial process leading to N-monodemethylated (NHCH 3 ), N-formyl (N(CH 3 )CHO), and CHCH 3 OH as the main intermediates. The substitution of the isopropyl group by an OH group is also observed as a side process.

  13. COMPARATIVE KINETICS STUDY OF THE THERMAL AND THERMO-OXIDATIVE DEGRADATION OF A POLYSTYRENE-CLAY NANOCOMPOZITE BY TGA AND DSC

    Directory of Open Access Journals (Sweden)

    Ion Dranca

    2010-12-01

    Full Text Available The methods of thermogravimetry (TGA and differential scanning calorimetry (DSC have been used to study the thermal and thermo-oxidative degradation of polystyrene (PS and a PS-clay nanocomposite. An advanced isoconversional method has been applied for kinertic analysis. Introduction of the clay phase increasers the activation energy and affects the total heat of degradation, which suggests a change in the reaction mechanism. The obtained kinetic data permit a comparative assessment of the fire resistance of the studied materials

  14. Kinetics of the H 2O 2-dependent ligninase-catalyzed oxidation of veratryl alcohol in the presence of cationic surfactant studied by spectrophotometric technique

    Science.gov (United States)

    Liu, Airong; Huang, Xirong; Song, Shaofang; Wang, Dan; Lu, Xuemei; Qu, Yinbo; Gao, Peiji

    2003-09-01

    The kinetics of ligninase-catalyzed oxidation of veratryl alcohol (VA) by H 2O 2 in the aqueous medium containing cationic surfactant cetyltrimethylammonium bromide (CTAB) has been investigated using spectrophotometric technique. Steady-state kinetic studies at different concentrations of CTAB indicate that the reaction follows a ping pong mechanism and the mechanism always holds but the kinetic parameters vary with CTAB concentrations. CTAB is a weak inhibitor for ligninase; it lowers the maximum initial velocity. CTAB also causes the Michaelis constant of H 2O 2 to decrease dramatically and that of VA to increase markedly. Based on the changes in kinetic parameters of the enzyme-catalyzed reaction at different CTAB concentrations (lower than, near to and larger than its critical micelle concentration) and the effects of the CTAB monomer and the micelles on the spectra of VA and its corresponding aldehyde, a conclusion could be made that modification of the enzymatic protein by the surfactant monomer should be responsible for the above-mentioned results.

  15. The mechanism of the catalytic oxidation of hydrogen sulfide: II. Kinetics and mechanism of hydrogen sulfide oxidation catalyzed by sulfur

    NARCIS (Netherlands)

    Steijns, M.; Derks, F.; Verloop, A.; Mars, P.

    1976-01-01

    The kinetics of the catalytic oxidation of hydrogen sulfide by molecular oxygen have been studied in the temperature range 20–250 °C. The primary reaction product is sulfur which may undergo further oxidation to SO2 at temperatures above 200 °C. From the kinetics of this autocatalytic reaction we

  16. Chemical kinetic study of a novel lignocellulosic biofuel: Di-n-butyl ether oxidation in a laminar flow reactor and flames

    KAUST Repository

    Cai, Liming; Sudholt, Alena; Lee, Dongjoon; Egolfopoulos, Fokion N.; Pitsch, Heinz G.; Westbrook, Charles K.; Sarathy, Mani

    2014-01-01

    The combustion characteristics of promising alternative fuels have been studied extensively in the recent years. Nevertheless, the pyrolysis and oxidation kinetics for many oxygenated fuels are not well characterized compared to those of hydrocarbons. In the present investigation, the first chemical kinetic study of a long-chain linear symmetric ether, di-n-butyl ether (DBE), is presented and a detailed reaction model is developed. DBE has been identified recently as a candidate biofuel produced from lignocellulosic biomass. The model includes both high temperature and low temperature reaction pathways with reaction rates generated using appropriate rate rules. In addition, experimental studies on fundamental combustion characteristics, such as ignition delay times and laminar flame speeds have been performed. A laminar flow reactor was used to determine the ignition delay times of lean and stoichiometric DBE/air mixtures. The laminar flame speeds of DBE/air mixtures were measured in the stagnation flame configuration for a wide rage of equivalence ratios at atmospheric pressure and an unburned reactant temperature of 373. K. All experimental data were modeled using the present kinetic model. The agreement between measured and computed results is satisfactory, and the model was used to elucidate the oxidation pathways of DBE. The dissociation of keto-hydroperoxides, leading to radical chain branching was found to dominate the ignition of DBE in the low temperature regime. The results of the present numerical and experimental study of the oxidation of di-n-butyl ether provide a good basis for further investigation of long chain linear and branched ethers. © 2013 The Combustion Institute.

  17. Chemical kinetic study of a novel lignocellulosic biofuel: Di-n-butyl ether oxidation in a laminar flow reactor and flames

    KAUST Repository

    Cai, Liming

    2014-03-01

    The combustion characteristics of promising alternative fuels have been studied extensively in the recent years. Nevertheless, the pyrolysis and oxidation kinetics for many oxygenated fuels are not well characterized compared to those of hydrocarbons. In the present investigation, the first chemical kinetic study of a long-chain linear symmetric ether, di-n-butyl ether (DBE), is presented and a detailed reaction model is developed. DBE has been identified recently as a candidate biofuel produced from lignocellulosic biomass. The model includes both high temperature and low temperature reaction pathways with reaction rates generated using appropriate rate rules. In addition, experimental studies on fundamental combustion characteristics, such as ignition delay times and laminar flame speeds have been performed. A laminar flow reactor was used to determine the ignition delay times of lean and stoichiometric DBE/air mixtures. The laminar flame speeds of DBE/air mixtures were measured in the stagnation flame configuration for a wide rage of equivalence ratios at atmospheric pressure and an unburned reactant temperature of 373. K. All experimental data were modeled using the present kinetic model. The agreement between measured and computed results is satisfactory, and the model was used to elucidate the oxidation pathways of DBE. The dissociation of keto-hydroperoxides, leading to radical chain branching was found to dominate the ignition of DBE in the low temperature regime. The results of the present numerical and experimental study of the oxidation of di-n-butyl ether provide a good basis for further investigation of long chain linear and branched ethers. © 2013 The Combustion Institute.

  18. Kinetics and Mechanistic Study of the Ruthenium(III Catalysed Oxidative Decarboxylation of L-Proline by Alkaline Heptavalent Manganese (Stopped flow technique

    Directory of Open Access Journals (Sweden)

    R. S. Shettar

    2005-01-01

    Full Text Available The kinetics of ruthenium(III catalysed oxidation of L-Proline by permanganate in alkaline medium at a constant ionic strength has been studied spectrophotometrically using a rapid kinetic accessory. The reaction between permanganate and L-Proline in alkaline medium exhibits 2:1 stoichiometry (KMnO4: L-Proline. The reaction shows first order dependence on [permanganate] and [ruthenium(III] and apparent less than unit order dependence each in L-Proline and alkali concentrations. Reaction rate increases with increase in ionic strength and decrease in solvent polarity of the medium. Initial addition of reaction products did not affect the rate significantly. A mechanism involving the formation of a complex between catalyst and substrate has been proposed. The activation parameters were computed with respect to the slow step of the mechanism and discussed

  19. A physiologically based kinetic model for bacterial sulfide oxidation.

    Science.gov (United States)

    Klok, Johannes B M; de Graaff, Marco; van den Bosch, Pim L F; Boelee, Nadine C; Keesman, Karel J; Janssen, Albert J H

    2013-02-01

    In the biotechnological process for hydrogen sulfide removal from gas streams, a variety of oxidation products can be formed. Under natron-alkaline conditions, sulfide is oxidized by haloalkaliphilic sulfide oxidizing bacteria via flavocytochrome c oxidoreductase. From previous studies, it was concluded that the oxidation-reduction state of cytochrome c is a direct measure for the bacterial end-product formation. Given this physiological feature, incorporation of the oxidation state of cytochrome c in a mathematical model for the bacterial oxidation kinetics will yield a physiologically based model structure. This paper presents a physiologically based model, describing the dynamic formation of the various end-products in the biodesulfurization process. It consists of three elements: 1) Michaelis-Menten kinetics combined with 2) a cytochrome c driven mechanism describing 3) the rate determining enzymes of the respiratory system of haloalkaliphilic sulfide oxidizing bacteria. The proposed model is successfully validated against independent data obtained from biological respiration tests and bench scale gas-lift reactor experiments. The results demonstrate that the model is a powerful tool to describe product formation for haloalkaliphilic biomass under dynamic conditions. The model predicts a maximum S⁰ formation of about 98 mol%. A future challenge is the optimization of this bioprocess by improving the dissolved oxygen control strategy and reactor design. Copyright © 2012 Elsevier Ltd. All rights reserved.

  20. Reaction kinetics of oxygen on single-phase alloys, oxidation of nickel and niobium alloys

    International Nuclear Information System (INIS)

    Lalauze, Rene

    1973-01-01

    This research thesis first addresses the reaction kinetics of oxygen on alloys. It presents some generalities on heterogeneous reactions (conventional theory, theory of jumps), discusses the core reaction (with the influence of pressure), discusses the influence of metal self-diffusion on metal oxidation kinetics (equilibrium conditions at the interface, hybrid diffusion regime), reports the application of the hybrid diffusion model to the study of selective oxidation of alloys (Wagner model, hybrid diffusion model) and the study of the oxidation kinetics of an alloy forming a solid solution of two oxides. The second part reports the investigation of the oxidation of single phase nickel and niobium alloys (phase α, β and γ)

  1. Kinetics of oxidation of H2 and reduction of H2O in Ni-YSZ based solid oxide cells

    DEFF Research Database (Denmark)

    Ebbesen, Sune Dalgaard; Mogensen, Mogens Bjerg

    2012-01-01

    Reduction of H2O and oxidation of H2 was studied in a Ni-YSZ electrode supported Solid Oxide Cells produced at DTU Energy conversion (former Risø DTU). Polarisation (i-V) and electrochemical impedance spectroscopic characterisation show that the kinetics for reduction of H 2O is slower compared...... to oxidation of H2. The kinetic differences cannot be explained by the reaction mechanisms which are similar in the two cases but are rather an effect of the thermodynamics. The preliminary analysis performed in this study show that the slow kinetic for reduction is partly related to the endothermic nature...... of the reaction, cooling the active electrode, thereby leading to slower kinetics at low current densities. Likewise, the increased kinetic for oxidation was found to be related to the exothermic nature of the reaction, heating the active electrode, and thereby leading to faster kinetics. At higher current...

  2. Kinetics and mechanism of oxidation of carbidized electrolytic chromium coatings

    International Nuclear Information System (INIS)

    Arkharov, V.I.; Yar-Mukhamedov, Sh.Kh.

    1978-01-01

    Thermal stability carbidized electrolytic chromium coatings has been studied depending on the conditions of their formation; the specific features of the mechanism of oxidation at 1200 deg in an air atmosphere have been elucidated. It has been established that kinetics of high temperature oxidation of the coatings depends essentially on the conditions of their formation and on the composition of steel to which the coating is applied. It has been shown that two oxidation mechanisms are possible: by diffusion of the residual chromium through a carbide layer along the carbide grain boundaries outwards or, when there is no residual chromium, by chemical reaction of carbon combustion and oxidation of the liberated chromium. The comparison of oxidation kinetic curves of the samples of 38KhMYuA, 35KhGSA, and DI-22 steels with and without coating has shown that the coatings under study have a better protective effect on 38KhMYuA steel than on 35KhGSA, although without coating oxidability of the first steel is higher than that of the second

  3. Oxidation kinetics of Si and SiGe by dry rapid thermal oxidation, in-situ steam generation oxidation and dry furnace oxidation

    Science.gov (United States)

    Rozé, Fabien; Gourhant, Olivier; Blanquet, Elisabeth; Bertin, François; Juhel, Marc; Abbate, Francesco; Pribat, Clément; Duru, Romain

    2017-06-01

    The fabrication of ultrathin compressively strained SiGe-On-Insulator layers by the condensation technique is likely a key milestone towards low-power and high performances FD-SOI logic devices. However, the SiGe condensation technique still requires challenges to be solved for an optimized use in an industrial environment. SiGe oxidation kinetics, upon which the condensation technique is founded, has still not reached a consensus in spite of various studies which gave insights into the matter. This paper aims to bridge the gaps between these studies by covering various oxidation processes relevant to today's technological needs with a new and quantitative analysis methodology. We thus address oxidation kinetics of SiGe with three Ge concentrations (0%, 10%, and 30%) by means of dry rapid thermal oxidation, in-situ steam generation oxidation, and dry furnace oxidation. Oxide thicknesses in the 50 Å to 150 Å range grown with oxidation temperatures between 850 and 1100 °C were targeted. The present work shows first that for all investigated processes, oxidation follows a parabolic regime even for thin oxides, which indicates a diffusion-limited oxidation regime. We also observe that, for all investigated processes, the SiGe oxidation rate is systematically higher than that of Si. The amplitude of the variation of oxidation kinetics of SiGe with respect to Si is found to be strongly dependent on the process type. Second, a new quantitative analysis methodology of oxidation kinetics is introduced. This methodology allows us to highlight the dependence of oxidation kinetics on the Ge concentration at the oxidation interface, which is modulated by the pile-up mechanism. Our results show that the oxidation rate increases with the Ge concentration at the oxidation interface.

  4. Kinetic study of the alkaline metals oxidation by dry oxygen; Etude cinetique de l'oxydation des metaux alcalins par l'oxygene sec

    Energy Technology Data Exchange (ETDEWEB)

    Touzain, Ph. [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires

    1967-06-15

    The oxidation of lithium, sodium, potassium, rubidium, cesium and sodium-potassium alloys by dry oxygen is studied at several temperatures and in the oxygen pressure range 40 to 400 mmHg. One distinguishes three different oxidation behaviours (inflammation, ignition and slow combustion) whose zones are precised in function of the temperature. The slow oxidation kinetic laws, the composition of oxides and the motive of oxides colorations are determined. At least, the experimental data are construed theoretically. (author) [French] L'oxydation du lithium, du sodium, du potassium, du rubidium, du cesium et des alliages sodium-potassium par l'oxygene sec est etudiee a diverses temperatures et a des pressions comprises entre 40 et 400 mmHg d'oxygene. On distingue trois processus d'oxydation differents (l'inflammation, l'ignition et la combustion lente) dont les domaines en fonction de la temperature sont precises. Les lois cinetiques d'oxydation lente, la nature des oxydes formes ainsi que les causes des colorations de ces oxydes sont determinees. Enfin les resultats obtenus sont interpretes theoriquement. (auteur)

  5. Kinetic study of the alkaline metals oxidation by dry oxygen; Etude cinetique de l'oxydation des metaux alcalins par l'oxygene sec

    Energy Technology Data Exchange (ETDEWEB)

    Touzain, Ph [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires

    1967-06-15

    The oxidation of lithium, sodium, potassium, rubidium, cesium and sodium-potassium alloys by dry oxygen is studied at several temperatures and in the oxygen pressure range 40 to 400 mmHg. One distinguishes three different oxidation behaviours (inflammation, ignition and slow combustion) whose zones are precised in function of the temperature. The slow oxidation kinetic laws, the composition of oxides and the motive of oxides colorations are determined. At least, the experimental data are construed theoretically. (author) [French] L'oxydation du lithium, du sodium, du potassium, du rubidium, du cesium et des alliages sodium-potassium par l'oxygene sec est etudiee a diverses temperatures et a des pressions comprises entre 40 et 400 mmHg d'oxygene. On distingue trois processus d'oxydation differents (l'inflammation, l'ignition et la combustion lente) dont les domaines en fonction de la temperature sont precises. Les lois cinetiques d'oxydation lente, la nature des oxydes formes ainsi que les causes des colorations de ces oxydes sont determinees. Enfin les resultats obtenus sont interpretes theoriquement. (auteur)

  6. Kinetics of FeII-polyaminocarboxylate oxidation by molecular oxygen

    Science.gov (United States)

    Wilson, Jessica M.; Farley, Kevin J.; Carbonaro, Richard F.

    2018-03-01

    Complexation of iron by naturally-occurring and synthetic organic ligands has a large effect on iron oxidation and reduction rates which in turn affect the aqueous geochemistry of many other chemical constituents. In this study, the kinetics of FeII oxidation in the presence of the polyaminocarboxylate synthetic chelating agents ethylene glycol tetraacetic acid (EGTA) and trimethylenediamine-N,N,N‧,N‧-tetraacetic acid (TMDTA) was investigated over the pH range 5.50-8.53. Batch oxidation experiments in the presence of molecular oxygen were conducted using a 2:1 M concentration ratio of polyaminocarboxylate (ligand, L) to FeII. The experimental data resembled first order kinetics for the oxidation of FeII-L to FeIII-L and observed rate constants at pH 6.0 were comparable to rate constants for the oxidation of inorganic FeII. Similar to other structurally-similar FeII-polyaminocarboxylate complexes, oxidation rates of FeII-EGTA and FeII-TMDTA decrease with increasing pH, which is the opposite trend for the oxidation of FeII complexed with inorganic ligands. However, the oxidation rates of FeII complexed with EGTA and TMDTA were considerably lower (4-5 orders of magnitude) than FeII complexed to ethylenediaminetetraacetic acid (EDTA). The distinguishing feature of the slower-reacting complexes is that they have a longer backbone between diamine functional groups. An analytical equilibrium model was developed to determine the contributions of the species FeIIL2- and FeII(H)L- to the overall oxidation rate of FeII-L. Application of this model indicated that the protonated FeII(H)L species are more than three orders of magnitude more reactive than FeIIL2-. These rate constants were used in a coupled kinetic equilibrium numerical model where the ligand to iron ratio (TOTL:TOTFe) and pH were varied to evaluate the effect on the FeII oxidation rate. Overall, increasing TOTL:TOTFe for EGTA and TMDTA enhances FeII oxidation rates at lower pH and inhibits FeII oxidation

  7. Kinetic and mechanistic studies of reactive intermediates in photochemical and transition metal-assisted oxidation, decarboxylation and alkyl transfer reactions

    Science.gov (United States)

    Carraher, Jack McCaslin

    Reactive species like high-valent metal-oxo complexes and carbon and oxygen centered radicals are important intermediates in enzymatic systems, atmospheric chemistry, and industrial processes. Understanding the pathways by which these intermediates form, their relative reactivity, and their fate after reactions is of the utmost importance. Herein are described the mechanistic detail for the generation of several reactive intermediates, synthesis of precursors, characterization of precursors, and methods to direct the chemistry to more desirable outcomes yielding 'greener' sources of commodity chemicals and fuels. High-valent Chromium from Hydroperoxido-Chromium(III). The decomposition of pentaaquahydroperoxido chromium(III) ion (hereafter Cr aqOOH2+) in acidic aqueous solutions is kinetically complex and generates mixtures of products (Craq3+, HCrO 4-, H2O2, and O2). The yield of high-valent chromium products (known carcinogens) increased from a few percent at pH 1 to 70 % at pH 5.5 (near biological pH). Yields of H 2O2 increased with acid concentration. The reproducibility of the kinetic data was poor, but became simplified in the presence of H2O2 or 2,2‧-azinobis(3-ethylbenzothiazoline-6-sulfonate) dianion (ABTS2-). Both are capable of scavenging strongly oxidizing intermediates). The observed rate constants (pH 1, [O2] ≤ 0.03 mM) in the presence of these scavengers are independent of [scavenger] and within the error are the same (k,ABTS2- = (4.9 +/- 0.2) x 10-4 s-1 and kH2O2 = (5.3 +/- 0.7) x 10-4 s-1); indicating involvement of the scavengers in post-rate determining steps. In the presence of either scavenger, decomposition of CrOOH2+ obeyed a two-term rate law, k obs / s-1 = (6.7 +/- 0.7) x 10-4 + (7.6 +/- 1.1) x 10-4 [H+]. Effect of [H+] on the kinetics and the product distribution, cleaner kinetics in the presence of scavengers, and independence of kobs on [scavenger] suggest a dual-pathway mechanism for the decay of Craq OOH2+. The H+-catalyzed path

  8. Kinetic studies of the radical oxidation in gaseous phase of organic iodides and of the formation of iodine oxide particles under the simulated conditions of a nuclear reactor containment submitted to a severe accident

    International Nuclear Information System (INIS)

    Zhang, S.

    2012-01-01

    Within the framework of the research in the nuclear reactor safety field, the iodine oxides formation by organic iodides destruction in the containment has been studied with the means of the atmospheric chemistry field. The destruction kinetics and their activation energy of organic iodides by . OH and . O radical has been quantified by a Flash Photolysis system able to monitor the oxidant radicals by resonance fluorescence. Those results have been published and some of them for the first time in the literature. The mechanisms leading to the organic iodides destruction are either by a hydrogen atom abstraction, either by the formation of a complex, depending on the organic iodide involved. Then, certain kinetics reactions have been updated in the IODAIR code. Other reactions have been added based on the recent literature available. A comparison of the kinetics destruction of CH 3 I by . OH and . O with IODAIR and the global kinetics of destruction in ASTEC/IODE showed a difference of about 2 which shows the importance of these two radicals (and mainly . O) in those destruction processes. The other main path of destruction would be by electron radiation. Other radicals like . H and . N would not contribute significantly to organic iodides destruction. A sensitivity analysis highlighted that organic iodides would mostly be destroyed into iodine oxides with a almost complete conversion within a few hours. Finally, an atmospheric chamber has been used to quantify iodine oxides growth, density and composition. Under the conditions studied, their formation is fast. Particles sizes of about 200-400 nm are formed within a few hours. The main parameters influencing their growth are the relative humidity and the presence of ozone (whose function is to create . O and . OH radicals). (author)

  9. Oxidation kinetics of hazelnut oil treated with ozone

    Directory of Open Access Journals (Sweden)

    H. Uzun

    2018-01-01

    Full Text Available The present study investigates the oxidation kinetics of hazelnut oil ozonated in different treatment periods (1, 5, 60 and 180 min. The kinetic rate constant (k was taken as the inverse of oxidation onset time (To observing a linear relationship from the plot of lnTo to isothermal temperatures (373, 383, 393, and 403 K carried out at differential scanning calorimetry. Kinetic parameters, activation energy (Ea, activation enthalpy (ΔH‡ and entropy (ΔS‡ were calculated based on the Arrhenius equation and activated complex theory. k values showed an exponential rise with the increase of ozone treatment time. The increase in k correlated well with the increase in the peroxide and free fatty acid values of all samples. Ea and ∆H‡ of the ozone treated oils showed a reducing trend and reflected an increased oxidation sensitivity after ozone treatment. Consistently, an increase in ∆S‡ indicated a faster oxidation reaction with an increase in ozone exposure time. However, no significant difference was observed in k, Ea, ΔH‡, ΔS‡ (p < 0.05 as a function of storage period, after the hazelnut oil was treated with ozone for 1 min.

  10. Developments in kinetic modelling of chalcocite particle oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Jaervi, J; Ahokainen, T; Jokilaakso, A [Helsinki Univ. of Technology, Otaniemi (Finland). Lab. of Materials Processing and Powder Metallurgy

    1998-12-31

    A mathematical model for simulating chalcocite particle oxidation is presented. Combustion of pure chalcocite with oxygen is coded as a kinetic module which can be connected as a separate part of commercial CFD-package, PHOENICS. Heat transfer, fluid flow and combustion phenomena can be simulated using CFD-calculation together with the kinetic model. Interaction between gas phase and particles are taken into account by source terms. The aim of the kinetic model is to calculate the particle temperature, contents of species inside the particle, oxygen consumption and formation of sulphur dioxide. Four oxidation reactions are considered and the shrinking core model is used to describe the rate of the oxidation reactions. The model is verified by simulating the particle oxidation reactions in a laboratory scale laminar-flow furnace under different conditions and the model predicts the effects of charges correctly. In the future, the model validation will be done after experimental studies in the laminar flow-furnace. (author) 18 refs.

  11. Developments in kinetic modelling of chalcocite particle oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Jaervi, J.; Ahokainen, T.; Jokilaakso, A. [Helsinki Univ. of Technology, Otaniemi (Finland). Lab. of Materials Processing and Powder Metallurgy

    1997-12-31

    A mathematical model for simulating chalcocite particle oxidation is presented. Combustion of pure chalcocite with oxygen is coded as a kinetic module which can be connected as a separate part of commercial CFD-package, PHOENICS. Heat transfer, fluid flow and combustion phenomena can be simulated using CFD-calculation together with the kinetic model. Interaction between gas phase and particles are taken into account by source terms. The aim of the kinetic model is to calculate the particle temperature, contents of species inside the particle, oxygen consumption and formation of sulphur dioxide. Four oxidation reactions are considered and the shrinking core model is used to describe the rate of the oxidation reactions. The model is verified by simulating the particle oxidation reactions in a laboratory scale laminar-flow furnace under different conditions and the model predicts the effects of charges correctly. In the future, the model validation will be done after experimental studies in the laminar flow-furnace. (author) 18 refs.

  12. Oxidation kinetics of hazelnut oil treated with ozone

    International Nuclear Information System (INIS)

    Uzun, H.; Ibanoglu, E.

    2017-01-01

    The present study investigates the oxidation kinetics of hazelnut oil ozonated in different treatment periods (1, 5, 60 and 180 min). The kinetic rate constant (k) was taken as the inverse of oxidation onset time (To) observing a linear relationship from the plot of ln To to isothermal temperatures (373, 383, 393, and 403 K) carried out at differential scanning calorimetry. Kinetic parameters, activation energy (Ea), activation enthalpy (ΔH‡) and entropy (ΔS‡) were calculated based on the Arrhenius equation and activated complex theory. k values showed an exponential rise with the increase of ozone treatment time. The increase in k correlated well with the increase in the peroxide and free fatty acid values of all samples. Ea and ΔH‡ of the ozone treated oils showed a reducing trend and reflected an increased oxidation sensitivity after ozone treatment. Consistently, an increase in ΔS‡ indicated a faster oxidation reaction with an increase in ozone exposure time. However, no significant difference was observed in k, Ea, ΔH‡, ΔS‡ (p < 0.05) as a function of storage period, after the hazelnut oil was treated with ozone for 1 min. [es

  13. Adsorption of Zinc(II) on diatomite and manganese-oxide-modified diatomite: a kinetic and equilibrium study.

    Science.gov (United States)

    Caliskan, Necla; Kul, Ali Riza; Alkan, Salih; Sogut, Eda Gokirmak; Alacabey, Ihsan

    2011-10-15

    The removal of Zn(II) ions from aqueous solution was studied using natural and MnO(2) modified diatomite samples at different temperatures. The linear Langmuir, Freundlich and Dubinin-Radushkevich (D-R) adsorption equations were applied to describe the equilibrium isotherms. From the D-R model, the mean adsorption energy was calculated as >8 kJ mol(-1), indicating that the adsorption of Zn(II) onto diatomite and Mn-diatomite was physically carried out. In addition, the pseudo-first-order, pseudo-second-order and intraparticle diffusion models were used to determine the kinetic data. The experimental data were well fitted by the pseudo-second-order kinetic model. Thermodynamic parameters such as the enthalpy (ΔH(0)), Gibbs' free energy (ΔG(0)) and entropy (ΔS(0)) were calculated for natural and MnO(2) modified diatomite. These values showed that the adsorption of Zn(II) ions onto diatomite samples was controlled by a physical mechanism and occurred spontaneously. Copyright © 2011 Elsevier B.V. All rights reserved.

  14. Kinetics of Oxidation of Aliphatic Alcohols by Potassium Dichromate ...

    African Journals Online (AJOL)

    The kinetics of oxidation of four aliphatic alcohols in acidic aqueous and micellar media were investigated. The reaction was found to be first-order with respect to both alcohol and oxidant. Pseudo-first-order kinetics were found to be perfectly applicable with ethanol, 1-propanol and 2-propanol while deviation was observed ...

  15. Finite element modelling of the oxidation kinetics of Zircaloy-4 with a controlled metal-oxide interface and the influence of growth stress

    International Nuclear Information System (INIS)

    Zumpicchiat, Guillaume; Pascal, Serge; Tupin, Marc; Berdin-Méric, Clotilde

    2015-01-01

    Highlights: We developed two finite element models of zirconium-based alloy oxidation using the CEA Cast3M code to simulate the oxidation kinetics of Zircaloy-4: the diffuse interface model and the sharp interface model. We also studied the effect of stresses on the oxidation kinetics. The main results are: • Both models lead to parabolic oxidation kinetics in agreement with the Wagner’s theory. • The modellings enable to calculate the stress distribution in the oxide as well as in the metal. • A strong effect of the hydrostatic stress on the oxidation kinetics has been evidenced. • The stress gradient effect changes the parabolic kinetics into a sub-parabolic law closer to the experimental kinetics because of the stress gradient itself, but also because of the growth stress increase with the oxide thickness. - Abstract: Experimentally, zirconium-based alloys oxidation kinetics is sub-parabolic, by contrast with the Wagner theory which predicts a parabolic kinetics. Two finite element models have been developed to simulate this phenomenon: the diffuse interface model and the sharp interface model. Both simulate parabolic oxidation kinetics. The growth stress effects on oxygen diffusion are studied to try to explain the gap between theory and experience. Taking into account the influence of the hydrostatic stress and its gradient into the oxygen flux expression, sub-parabolic oxidation kinetics have been simulated. The sub-parabolic behaviour of the oxidation kinetics can be explained by a non-uniform compressive stress level into the oxide layer.

  16. Adsorption of Zinc(II) on diatomite and manganese-oxide-modified diatomite: A kinetic and equilibrium study

    Energy Technology Data Exchange (ETDEWEB)

    Caliskan, Necla, E-mail: ncaliskan7@hotmail.com [Department of Physical Chemistry, Faculty of Science, Yuezuencue Yil University, Van 65080 (Turkey); Kul, Ali Riza; Alkan, Salih; Sogut, Eda Gokirmak; Alacabey, Ihsan [Department of Physical Chemistry, Faculty of Science, Yuezuencue Yil University, Van 65080 (Turkey)

    2011-10-15

    Highlights: {center_dot}The removal of Zn(II) ions from aqueous solution was studied using natural and MnO{sub 2} modified diatomite samples at different temperatures. {center_dot} The sorption of Zn(II) on the natural and modified diatomite was an endothermic processes, controlled by physical mechanisms and spontaneously. {center_dot} Adsorption of zinc metal ion on diatomite samples is more or less a two step process. {center_dot} Adsorption of Zn(II) on natural and modified diatomite could be explained by the mechanism of pseudo-second-order. - Abstract: The removal of Zn(II) ions from aqueous solution was studied using natural and MnO{sub 2} modified diatomite samples at different temperatures. The linear Langmuir, Freundlich and Dubinin-Radushkevich (D-R) adsorption equations were applied to describe the equilibrium isotherms. From the D-R model, the mean adsorption energy was calculated as >8 kJ mol{sup -1}, indicating that the adsorption of Zn(II) onto diatomite and Mn-diatomite was physically carried out. In addition, the pseudo-first-order, pseudo-second-order and intraparticle diffusion models were used to determine the kinetic data. The experimental data were well fitted by the pseudo-second-order kinetic model. Thermodynamic parameters such as the enthalpy ({Delta}H{sup 0}), Gibbs' free energy ({Delta}G{sup 0}) and entropy ({Delta}S{sup 0}) were calculated for natural and MnO{sub 2} modified diatomite. These values showed that the adsorption of Zn(II) ions onto diatomite samples was controlled by a physical mechanism and occurred spontaneously.

  17. The oxidation kinetics and the structure of the oxide film on Zircaloy before and after the kinetic transition

    International Nuclear Information System (INIS)

    Arima, T.; Masuzumi, T.; Furuya, H.; Idemitsu, K.; Inagaki, Y.

    2001-01-01

    Oxidation kinetics of Zircaloy-4 have been measured using a micro-balance technique in CO-CO 2 gas mixtures between 450 deg. C and 600 deg. C. Oxidation kinetics of Zircaloy-4 obeyed a cubic rate law with time at 450-600 deg. C up to 24 h. At 600 deg. C, the kinetic transition occurred after about 36 h. After the transition, oxidation kinetics obeyed a linear rate law. X-ray diffraction patterns for the samples oxidized at 600 deg. C showed that the volume fraction of tetragonal phase of zirconia decreased with time until the kinetic transition occurred and was almost constant after that. In addition, stresses in the oxide films were found to be larger for the pre-transition samples than for the post-transition ones. (authors)

  18. Application of X-ray computed micro-tomography to the study of damage and oxidation kinetics of thermostructural composites

    Energy Technology Data Exchange (ETDEWEB)

    Caty, Olivier, E-mail: caty@lcts.u-bordeaux1.fr [Laboratory of Thermostructural Composites (LCTS), Université de Bordeaux, CNRS, SAFRAN, CEA, 3 Allée La Boétie, 33600 Pessac (France); Ibarroule, Philippe; Herbreteau, Mathieu; Rebillat, Francis [Laboratory of Thermostructural Composites (LCTS), Université de Bordeaux, CNRS, SAFRAN, CEA, 3 Allée La Boétie, 33600 Pessac (France); Maire, Eric [MATEIS Laboratory, INSA Lyon, 7 Avenue Jean Capelle, 69621 Villeurbanne Cedex (France); Vignoles, Gérard L. [Laboratory of Thermostructural Composites (LCTS), Université de Bordeaux, CNRS, SAFRAN, CEA, 3 Allée La Boétie, 33600 Pessac (France)

    2014-04-01

    Thermostructural composites are three-dimensionally (3D) structured materials. Weakening phenomena (mechanical and chemical) take place inside the material following its 3D structure and are thus hard to describe accurately. X-ray computed micro-tomography (μCT) is a recent solution that allows their experimental investigation. The technique is applied here to the study of failure under tensile loading and to the self healing processes during oxidation. Results are useful data to verify or invalidate hypotheses or estimations made in current models.

  19. Probing the oxidation kinetics of small permalloy particles

    International Nuclear Information System (INIS)

    Dong, Xiaolei; Song, Xiao; Yin, Shiliu; Shirolkar, Mandar M.; Li, Ming; Wang, Haiqian

    2017-01-01

    The oxidation of permalloys is important to apply in a wide range. The oxidation and diffusion mechanisms of small permalloy particles with different Fe content are studied by using thermal gravimetric analysis (TGA) and microstructure characterizations. Fe 2 O 3 /(Ni, Fe) 3 O 4 plays a key role in the morphology evolution and diffusion mechanisms of small NiFe particles upon oxidation. The activation energies of grain boundary diffusion for the NiFe alloys increase from 141 kJ/mol to 208 kJ/mol as the Fe content increases from 0 to ~50 wt%. We have developed a diffusion process resolved temperature programed oxidation (PR-TPO) analysis method. Three diffusion mechanisms have been recognized by using this method: In addition to the grain boundary diffusion and lattice diffusion, our TGA analysis suggests that the phase conversion from Fe 2 O 3 to (Ni, Fe) 3 O 4 induces diffusion change and affects the diffusion process at the intermediate temperature. Relevant oxidation kinetics and diffusion mechanisms are discussed. - Graphical abstract: The oxidation mechanisms of small Permalloy particles with different Fe content is studied by using thermal gravimetric analysis (TGA) and microstructure characterizations. The activation energies of grain boundary diffusion for the NiFe alloys increases from 140 kJ/mol to 208 kJ/mol as the Fe content increases from 0 to 50 wt% as determined by TGA. We have developed a diffusion process resolved temperature programed oxidation (DPR-TPO) analysis method, and three diffusion mechanisms have been recognized by using this method: In addition to the well-known grain boundary diffusion and lattice diffusion, we found that the phase conversion from Fe 2 O 3 to (Ni, Fe) 3 O 4 will induce diffusion changes and affect the diffusion process at the intermediate temperature. The diffusion processes can be characterized by the corresponding characteristic peak temperatures in temperature programmed oxidation (TPO) analysis. This work not only

  20. A stability indicating HPLC method for determination of mebeverine in the presence of its degradation products and kinetic study of its degradation in oxidative condition.

    Science.gov (United States)

    Souri, E; Aghdami, A Negahban; Adib, N

    2014-01-01

    An HPLC method for determination of mebeverine hydrochloride (MH) in the presence of its degradation products was developed. The degradation of MH was studied under hydrolysis, oxidative and photolysis stress conditions. Under alkaline, acidic and oxidative conditions, degradation of MH was observed. The separation was performed using a Symmetry C18 column and a mixture of 50 mM KH2PO4, acetonitrile and tetrahydrfuran (THF) (63:35:2; v/v/v) as the mobile phase. No interference peaks from degradation products in acidic, alkaline and oxidative conditions were observed. The linearity, accuracy and precision of the method were studied. The method was linear over the range of 1-100 μg/ml MH (r(2)>0.999) and the CV values for intra-day and inter-day variations were in the range of 1.0-1.8%. The limit of quantification (LOQ) and the limit of detection (LOD) of the method were 1.0 and 0.2 μg/ml, respectively. Determination of MH in pharmaceutical dosage forms was performed using the developed method. Furthermore the kinetics of the degradation of MH in the presence of hydrogen peroxide was investigated. The proposed method could be a suitable method for routine quality control studies of mebeverine dosage forms.

  1. Green Synthesis of Zinc Oxide Nanoparticles for Enhanced Adsorption of Lead Ions from Aqueous Solutions: Equilibrium, Kinetic and Thermodynamic Studies

    Directory of Open Access Journals (Sweden)

    Susan Azizi

    2017-06-01

    Full Text Available In the present study, ZnO nanoparticles (NPs were synthesized in zerumbone solution by a green approach and appraised for their ability to absorb Pb(II ions from aqueous solution. The formation of as-synthesized NPs was established by X-ray diffraction (XRD, Transmission Electron Microscopy (TEM, and UV–visible studies. The XRD and TEM analyses revealed high purity and wurtzite hexagonal structure of ZnO NPs with a mean size of 10.01 ± 2.6 nm. Batch experiments were performed to investigate the impact of process parameters viz. Pb(II concentration, pH of solution, adsorbent mass, solution temperature, and contact time variations on the removal efficiency of Pb(II. The adsorption isotherm data provided that the adsorption process was mainly monolayer on ZnO NPs. The adsorption process follows pseudo-second-order reaction kinetic. The maximum removal efficiencies were 93% at pH 5. Thermodynamic parameters such as enthalpy change (ΔH0, free energy change (ΔG0, and entropy change (ΔS0 were calculated; the adsorption process was spontaneous and endothermic. The good efficiency of the as-synthesized NPs makes them attractive for applications in water treatment, for removal of heavy metals from aqueous system.

  2. The kinetics of nonequilibrium chain plasma-chemical oxidation in heterogeneous media

    International Nuclear Information System (INIS)

    Deminskii, M.A.; Potapkin, B.V.; Rusanov, V.D.

    1994-01-01

    The kinetics of oxidation of low-impurity components in air mixtures under heterogeneous conditions was studied. The principal kinetic features of the process were determined on the basis of theoretical analysis of plasma-chemical oxidation in heterogeneous media. The analysis also showed that low concentrations of impurities in liquid aerosol particles can be efficiently oxidized via a chain process induced by reactive species formed in the gas

  3. The kinetics for ammonium and nitrite oxidation under the effect of hydroxylamine.

    Science.gov (United States)

    Wan, Xinyu; Xiao, Pengying; Zhang, Daijun; Lu, Peili; Yao, Zongbao; He, Qiang

    2016-01-01

    The kinetics for ammonium (NH4(+)) oxidation and nitrite (NO2(-)) oxidation under the effect of hydroxylamine (NH2OH) were studied by respirometry using the nitrifying sludge from a laboratory-scale sequencing batch reactor. Modified models were used to estimate kinetics parameters of ammonia and nitrite oxidation under the effect of hydroxylamine. An inhibition effect of hydroxylamine on the ammonia oxidation was observed under different hydroxylamine concentration levels. The self-inhibition coefficient of hydroxylamine oxidation and noncompetitive inhibition coefficient of hydroxylamine for nitrite oxidation was estimated by simulating exogenous oxygen-uptake rate profiles, respectively. The inhibitive effect of NH2OH on nitrite-oxidizing bacteria was stronger than on ammonia-oxidizing bacteria. This work could provide fundamental data for the kinetic investigation of the nitrification process.

  4. Zircaloy oxidation studies

    International Nuclear Information System (INIS)

    Prater, J.T.; Beauchamp, R.H.; Saenz, N.T.

    1985-06-01

    The oxidation kinetics of Zircaloy-4 in steam have been determined at 1300-2400 0 C. Growth of the ZrO 2 and α-Zr layers display parabolic behavior over the entire temperature range studied. A discontinuity in the oxidation kinetics at 1510 0 C causes rates to increase above those previously established by the Baker-Just relationship. This increase coincides with the tetragonal-to-cubic phase transformation in ZrO/sub 2-x/. No discontinuity in the oxide growth rate is observed upon melting of Zr(0). The effects of temperature gradients have been taken into account and corrected values representative of near-isothermal conditions have been computed

  5. Kinetic and equilibrium studies of acrylonitrile binding to cytochrome c peroxidase and oxidation of acrylonitrile by cytochrome c peroxidase compound I.

    Science.gov (United States)

    Chinchilla, Diana; Kilheeney, Heather; Vitello, Lidia B; Erman, James E

    2014-01-03

    Ferric heme proteins bind weakly basic ligands and the binding affinity is often pH dependent due to protonation of the ligand as well as the protein. In an effort to find a small, neutral ligand without significant acid/base properties to probe ligand binding reactions in ferric heme proteins we were led to consider the organonitriles. Although organonitriles are known to bind to transition metals, we have been unable to find any prior studies of nitrile binding to heme proteins. In this communication we report on the equilibrium and kinetic properties of acrylonitrile binding to cytochrome c peroxidase (CcP) as well as the oxidation of acrylonitrile by CcP compound I. Acrylonitrile binding to CcP is independent of pH between pH 4 and 8. The association and dissociation rate constants are 0.32±0.16 M(-1) s(-1) and 0.34±0.15 s(-1), respectively, and the independently measured equilibrium dissociation constant for the complex is 1.1±0.2 M. We have demonstrated for the first time that acrylonitrile can bind to a ferric heme protein. The binding mechanism appears to be a simple, one-step association of the ligand with the heme iron. We have also demonstrated that CcP can catalyze the oxidation of acrylonitrile, most likely to 2-cyanoethylene oxide in a "peroxygenase"-type reaction, with rates that are similar to rat liver microsomal cytochrome P450-catalyzed oxidation of acrylonitrile in the monooxygenase reaction. CcP compound I oxidizes acrylonitrile with a maximum turnover number of 0.61 min(-1) at pH 6.0. Copyright © 2013 Elsevier Inc. All rights reserved.

  6. Role of Ru(IlI) as an inhibitor in oxidation of lactose by (Cu(bipy)2)2+ in alkaline medium: spectrophotometric and kinetic studies

    International Nuclear Information System (INIS)

    Singh, Ashok Kumar; Singh, Manjula; Srivastava, Jaya; Rahmani, Shahla

    2013-01-01

    Kinetics of oxidation of lactose by (Cu(bipy) 2 ) 2+ in alkaline medium using Ru(III) as an inhibitor has been studied spectrophotometrically at 40 °C. The studies show that the rate of the reaction is zero order with respect to (Cu(bipy) 2 ) 2+ and first order with respect to (lactose). The order of reaction is found to be two at low concentrations of OH - (from 1.48×10 5 to 3.47×10 5 M) and less than two at its high concentrations (from 4.27×10 5 to 6.31×10 5 M). There is a substantial decrease in the pseudo-zero order rate constant with increase in the concentration of Ru(III) chloride, indicating the role of Ru(III) chloride as an inhibitor. Decrease in the rate with increase in dielectric constant of the medium is observed, while ionic strength of the medium and bipyridyl concentration has no influence on the rate. Based on kinetic data and spectrophotometric evidences, a suitable mechanism is proposed for the studied reaction. (author)

  7. Oxidation of 3,4,5-trimethoxybenzaldehyde by pyridinium fluorochromate in N,N-dimethyl formamide medium: A kinetic and mechanistic study

    Directory of Open Access Journals (Sweden)

    Basanti Lal Hiran

    2016-09-01

    Full Text Available Kinetics of oxidation of 3,4,5-trimethoxybenzaldehyde (TMBA by pyridinium fluorochromate (PFC in N,N-dimethyl formamide (DMF medium in the presence of toluene para-sulfonic acid (TsOH has been studied. The reaction is first order each in [PFC], [TMBA] and [TsOH]. The rate of oxidation remains unaltered by the variation of NaClO4 but addition of MnSO4 decreases the rate. The effects of the dielectric constant of the medium and the ionic strength indicate the reaction to be of ion–dipole type. The stoichiometry of the reaction is 1:1 and the product of oxidation is the corresponding 3,4,5-trimethoxybenzoic acid and Cr(III. The reaction rates have been determined at different temperatures and the activation parameters were calculated. The reaction failed to induce the polymerization of acrylonitrile, i.e., absence of free radicals. A suitable mechanism involving the slow formation of an unstable chromate ester and a rate law has been proposed.

  8. Oxidation kinetics of CVD silicon carbide and silicon nitride

    Science.gov (United States)

    Fox, Dennis S.

    1992-01-01

    The long-term oxidation behavior of pure, monolithic CVD SiC and Si3N4 is studied, and the isothermal oxidation kinetics of these two materials are obtained for the case of 100 hrs at 1200-1500 C in flowing oxygen. Estimates are made of lifetimes at the various temperatures investigated. Parabolic rate constants for SiC are within an order of magnitude of shorter exposure time values reported in the literature. The resulting silica scales are in the form of cristobalite, with cracks visible after exposure. The oxidation protection afforded by silica for these materials is adequate for long service times under isothermal conditions in 1-atm dry oxygen.

  9. Influence of oxalic acid on the dissolution kinetics of manganese oxide

    Science.gov (United States)

    Godunov, E. B.; Artamonova, I. V.; Gorichev, I. G.; Lainer, Yu. A.

    2012-11-01

    The kinetics and electrochemical processes of the dissolution of manganese oxides with various oxidation states in sulfuric acid solutions containing oxalate ion additives is studied under variable conditions (concentration, pH, temperature). The parameters favoring a higher degree of the dissolution of manganese oxides in acidic media are determined. The optimal conditions are found for the dissolution of manganese oxides in acidic media in the presence of oxalate ions. The mechanism proposed for the dissolution of manganese oxides in sulfuric acid solutions containing oxalic acid is based on the results of kinetic and electrochemical studies. The steps of the dissolution mechanism are discussed.

  10. The Oxidation of 2-(2-Methoxyethoxyethanol and 2-(2-Ethoxyethoxyethanol by Ditelluratocuprate(III: A Kinetic and Mechanistic Study

    Directory of Open Access Journals (Sweden)

    Jin-huan Shan

    2013-01-01

    Full Text Available The oxidation of 2-(2-methoxyethoxyethanol (MEE and 2-(2-ethoxyethoxyethanol (EEE by ditelluratocuprate(III (DTC had been studied spectrophotometrically in alkaline medium. The reaction between and showed first-order dependence in DTC and fractional order in MEE and EEE. The rate constant of the pseudo-first-order reaction decreased with an increase of [TeO4  2−], whereas adding [OH−] enhanced the constant. In addition, the reaction had a negative salt effect. The rate of EEE was higher than that of MEE. A suitable assumption involving preequilibriums before the rate-controlling step and a free radical mechanism was proposed, based on the kinetic data. Activation parameters and the rate constant of the rate-determining step were calculated.

  11. Kinetics of the addition reaction of methyl radicals with nitric oxide studied by pulse radiolysis combined with infrared diode laser spectroscopy

    DEFF Research Database (Denmark)

    Jodkowski, J.T.; Ratajczak, E.; Sillesen, A.

    1993-01-01

    The reaction CH3 + NO (+ M) --> CH3NO ( + M) was initiated by pulse radiolysis of acetone/nitric oxide mixtures and the kinetics of methyl radicals was studied by time-resolved infrared absorption spectroscopy. The rate constant was found to be strongly pressure dependent in the range of p (M) = 6.......5-150 mbar at 298 K with M = acetone as the third body. The experimental results are represented in terms of a fall-off curve centered at 37 mbar with limiting high- and low-pressure rate constants of k(rec,infinity) = (6.6 +/- 0.9) x 10(9) x (T/300)0.6 M-1 s-1 and k(rec,0)/[M] = (4.4 +/- 0.4) x 10(12) x (T...

  12. Improved Understanding of In Situ Chemical Oxidation. Technical Objective I: Contaminant Oxidation Kinetics Contaminant Oxidation Kinetics

    Science.gov (United States)

    2009-05-01

    methyl tert butyl ether NAPL non-aqueous phase liquid NOD natural oxidant demand •OH hydroxide radical Ox oxidant O3 ozone PCE...and persulfate; and Technical Objective 2, assess how soil properties (e.g., soil mineralogy , natural carbon content) affect oxidant mobility and...to develop a general description of kobs vs. T because there are many reactions that can contribute to the concentration of the reactive intermediate

  13. Influence of radiational oxidation on the kinetics of electrization of polypropylene by electron irradiation

    International Nuclear Information System (INIS)

    Rozno, A.G.; Romanov, A.V.; Sukhov, N.L.; Gromov, V.V.; Ershov, B.G.

    1992-01-01

    Kinetics of volumetric electric charge and accumulation of paramagnetic centres (PMC) in polypropylene (PP) of two crystal modifications, subjected to radiational oxidation were studied. A correlation between volumetric charge and PMC in radiationally oxidation PP was detected. Considerable influence of crystal phase on the processes of charging and radiational oxidation was revealed

  14. A kinetics and mechanistic study of the OH and NO2 initiated oxidation of cyclohexa-1,3-diene in the gas phase

    DEFF Research Database (Denmark)

    Jenkin, M. E.; Andersen, Mads Peter Sulbæk; Hurley, M. D.

    2005-01-01

    The kinetics and products of the OH and NO2-initiated oxidation of cyclohexa-1,3-diene have been investigated at 296 K and 700 Torr using long path FTIR spectroscopy. Relative rate methods were employed using the photolysis of cyclohexa-1,3-diene/CH3ONO/NO/air mixtures to measure k(OH + cyclohexa...

  15. Kinetics and Mechanism of the Oxidation of Coomassie Brilliant Blue ...

    African Journals Online (AJOL)

    , in aqueous solution by hypochlorite as a function of pH was investigated. While the degradation of dye obeyed pseudo-first-order kinetics, the oxidation of the dye occurred through two competitive reactions facilitated by [OCl–] and [HOCl].

  16. Studies of the kinetics and mechanism of the oxidation of uranium by dry and moist air. A model for determining the oxidation rate over a wide range of temperatures and water vapour pressures

    Energy Technology Data Exchange (ETDEWEB)

    McGillivray, G.W. (Atomic Weapons Establishment, Aldermaston, Reading (United Kingdom)); Geeson, D.A. (Atomic Weapons Establishment, Aldermaston, Reading (United Kingdom)); Greenwood, R.C. (Atomic Weapons Establishment, Aldermaston, Reading (United Kingdom))

    1994-01-01

    The rate of oxidation of uranium metal by moist air has been measured at temperatures from 115 to 350 C and water vapour pressures from 0 to 47 kPa (350 Torr). From this and from previously reported data, a model has been developed which allows the rate of uranium oxidation to be calculated at any particular combination of temperature and water vapour pressure of interest, in the range 0-350 C and 0-101.3 kPa (760 Torr). The model is based on the assumption that the surface concentration of water determines the rate of reaction and that the adsorption of water onto the oxide follows a Langmuir type isotherm. Theoretical plots of rate as a function of water vapour pressure and Arrhenius plots derived from the model have been shown to be in good agreement with experimental data. The model assumes separate contributions to the overall observed rate from oxygen and water vapour. Surface studies have been carried out using SIMS (secondary ion mass spectrometry). Depth profiling of the oxide produced by isotopically labelled reagents ([sup 18]O[sub 2] and H[sup 18][sub 2]O), has shown that oxygen from both reactants is incorporated into the oxide layer in the ratio predicted by the kinetic model. This supports a mechanism in which oxygen and water vapour produce separate diffusing species (possibly O[sup 2-] and OH[sup -]). (orig.)

  17. Studies of the kinetics and mechanism of the oxidation of uranium by dry and moist air A model for determining the oxidation rate over a wide range of temperatures and water vapour pressures

    Science.gov (United States)

    McGillivray, G. W.; Geeson, D. A.; Greenwood, R. C.

    1994-01-01

    The rate of oxidation of uranium metal by moist air has been measured at temperatures from 115 to 350°C and water vapour pressures from 0 to 47 kPa (350 Torr). From this and from previously reported data, a model has been developed which allows the rate of uranium oxidation to be calculated at any particular combination of temperature and water vapour pressure of interest, in the range 0-350°C and 0-101.3 kPa (760 Torr). The model is based on the assumption that the surface concentration of water determines the rate of reaction and that the adsorption of water onto the oxide follows a Langmuir type isotherm. Theoretical plots of rate as a function of water vapour pressure and Arrhenius plots derived from the model have been shown to be in good agreement with experimental data. The model assumes separate contributions to the overall observed rate from oxygen and water vapour. Surface studies have been carried out using SIMS (secondary ion mass spectrometry). Depth profiling of the oxide produced by isotopically labelled reagents ( 18O 2 and H 218O), has shown that oxygen from both reactants is incorporated into the oxide layer in the ratio predicted by the kinetic model. This supports a mechanism in which oxygen and water vapour produce separate diffusing species (possibly O 2- and OH -).

  18. Kinetic study of diesel soot oxidation: application to simulation of diesel particulate filter regeneration; Etude cinetique de la combustion des suies diesel: application a la modelisation de la regeneration du filtre a particule

    Energy Technology Data Exchange (ETDEWEB)

    Huguet, Ch.

    2005-11-15

    Because of their toxicity, soot are considered as the most important pollutant from Diesel engines. The Diesel Particulate Filter (DPF) is widely deployed in Europe to address the significant reductions in particulate emissions required by increasingly stringent emission standards, both for heavy duty vehicles and passenger cars. Such a DPF filtrates above 99% of soot emissions and must be regularly regenerated. The use of additive allows to decrease the soot oxidation temperature to values which can be reached by appropriate engine tuning. The soot addition is a dominant parameter for the development of regeneration strategies. Its influence must be correctly represented by models. This Ph-D was performed at IFP in collaboration with ADEME and was supported by the LCSR at Orleans. The aim of the present research is to develop a kinetic mechanism characteristic of Diesel soot oxidation, which can be integrated into a DPF regeneration model and used for engine control. The oxidation study was based on soot characterisation and reaction kinetics investigations. The samples of Diesel soot were collected, without and with Cerium/Iron additive, by using two engines points representative of two normalized European cycles (ECE and EUDC). Thermal and composition analyses with techniques such as XPS, XRD or TEM were used to determine their physical and chemical properties. Their oxidation kinetics was experimentally studied on a synthetic gas bench (SGB) with a fixed bed reactor. Different tests were performed: temperature-programmed oxidation (TPO), Isothermal oxidation (IO), and sequential oxidation. The results allowed to correlate Diesel soot physical and chemical properties with their oxidation rate. A kinetic model was developed, which is based on global carbon consummation law and distinguishes the oxidation of different soot components. The simulation results agree very well with the experimental results of Diesel soot oxidation. (author)

  19. Kinetics and mechanism of oxidation of chloramphenicol by 1

    Indian Academy of Sciences (India)

    Chloramphenicol (CAP) is an antibiotic drug having a wide spectrum of activity. The kinetics of oxidation of chloramphenicol by 1-chlorobenzotriazole (CBT) in HClO4 medium over the temperature range 293-323 K has been investigated. The reaction exhibits first-order kinetics with respect to [CBT]o and zero-order with ...

  20. A kinetic study of ozone and nitric oxides in dielectric barrier discharges for O2/NOx mixtures

    International Nuclear Information System (INIS)

    Sun Jizhong; Stirner, T.; Wang Dezhen

    2002-01-01

    A simple model is described to simulate kinetic processes in dielectric barrier discharges for O 2 /NO x mixtures. A threshold of ozone production found experimentally is confirmed by the calculations of this modeling, and the underlying chemical reaction mechanisms are discussed. It is also found that the effects of diffusion processes in the period of the lifetime of O atoms are not important to micro-discharge channels with a large radius, i.e. larger than 150 μm

  1. A kinetic and mechanistic study on the oxidation of l-methionine and N-acetyl l-methionine by cerium(IV) in sulfuric acid medium

    OpenAIRE

    T. Sumathi; P. Shanmugasundaram; G. Chandramohan

    2016-01-01

    The kinetics of oxidation of l-methionine and N-acetyl l-methionine by Ce(IV) in sulfuric acid–sulfate media in the range of 288.1–298.1 K has been investigated. The major oxidation products of methionine and N-acetyl l-methionine have been identified as methionine sulfoxide and N-acetyl methionine sulfoxide. The major oxidation products have been confirmed by qualitative analysis and boiling point. The reaction was first order with respect to l-methionine, N-acetyl l-methionine and Ce(IV). I...

  2. Kinetics and mechanism of synthetic CoS oxidation process

    Directory of Open Access Journals (Sweden)

    Štrbac N.

    2006-01-01

    Full Text Available The results of investigation of kinetics and mechanism for synthetic a-CoS oxidation process are presented in this paper. Based on experimental data obtained using DTA and XRD analysis and constructed PSD diagrams for Co-S-O system, mechanism of synthetic a-CoS oxidation process is suggested. Characteristic kinetic parameters were obtained for experimental isothermal investigations of desulfurization degree using Sharp method.

  3. Internal steam reforming in solid oxide fuel cells: Status and opportunities of kinetic studies and their impact on modelling

    DEFF Research Database (Denmark)

    Mogensen, David; Grunwaldt, J.-D.; Hendriksen, Peter Vang

    2011-01-01

    Solid oxide fuel cells (SOFC) systems with internal steam reforming have the potential to become an economically competitive technology for cogeneration power plants, exploiting its significantly higher electrical efficiency compared to existing technologies. Optimal design and operation of such ......Solid oxide fuel cells (SOFC) systems with internal steam reforming have the potential to become an economically competitive technology for cogeneration power plants, exploiting its significantly higher electrical efficiency compared to existing technologies. Optimal design and operation...

  4. Nitrogen metabolism and kinetics of ammonia-oxidizing archaea.

    Science.gov (United States)

    Martens-Habbena, Willm; Stahl, David A

    2011-01-01

    The discovery of ammonia-oxidizing mesophilic and thermophilic Group I archaea changed the century-old paradigm that aerobic ammonia oxidation is solely mediated by two small clades of Beta- and Gammaproteobacteria. Group I archaea are extremely diverse and ubiquitous in marine and terrestrial environments, accounting for 20-30% of the microbial plankton in the global oceans. Recent studies indicated that many of these organisms carry putative ammonia monooxygenase genes and are more abundant than ammonia-oxidizing bacteria in most natural environments suggesting a potentially significant role in the nitrogen cycle. The isolation of Nitrosopumilus maritimus strain SCM1 provided the first direct evidence that Group I archaea indeed gain energy from ammonia oxidation. To characterize the physiology of this archaeal nitrifier, we developed a respirometry setup particularly suited for activity measurements in dilute microbial cultures with extremely low oxygen uptake rates. Here, we describe the setup and review the kinetic experiments conducted with N. maritimus and other nitrifying microorganisms. These experiments demonstrated that N. maritimus is adapted to grow on ammonia concentrations found in oligotrophic open ocean environments, far below the survival threshold of ammonia-oxidizing bacteria. The described setup and experimental procedures should facilitate physiological studies on other nitrifying archaea and oligotrophic microorganisms in general. Copyright © 2011 Elsevier Inc. All rights reserved.

  5. Sulfur Tolerant Solid Oxide Fuel Cell for Coal Syngas Application: Experimental Study on Diverse Impurity Effects and Fundamental Modeling of Electrode Kinetics

    Science.gov (United States)

    Gong, Mingyang

    With demand over green energy economy, fuel cells have been developed as a promising energy conversion technology with higher efficiency and less emission. Solid oxide fuel cells (SOFC) can utilize various fuels in addition to hydrogen including coal derived sygas, and thus are favored for future power generation due to dependence on coal in electrical industry. However impurities such as sulfur and phosphorous present in coal syngas in parts per million (p.p.m.) levels can severely poison SOFC anode typically made of Ni/yttria-stabilized-zirconia (Ni-YSZ) and limit SOFC applicability in economically derivable fuels. The focus of the research is to develop strategy for application of high performance SOFC in coal syngas with tolerance against trace impurities such as H2S and PH3. To realize the research goal, the experimental study on sulfur tolerant anode materials and examination of various fuel impurity effects on SOFC anode are combined with electrochemical modeling of SOFC cathode kinetics in order to benefit design of direct-coal-syngas SOFC. Tolerant strategy for SOFC anode against sulfur is studied by using alternative materials which can both mitigate sulfur poisoning and function as active anode components. The Ni-YSZ anode was modified by incorporation of lanthanum doped ceria (LDC) nano-coatings via impregnation. Cell test in coal syngas containing 20 ppm H2S indicated the impregnated LDC coatings inhibited on-set of sulfur poisoning by over 10hrs. Cell analysis via X-ray photon spectroscopy (XPS), X-ray diffraction (XRD) and electrochemistry revealed LDC coatings reacted with H2S via chemisorptions, resulting in less sulfur blocking triple--phase-boundary and minimized performance loss. Meanwhile the effects of PH3 impurity on SOFC anode is examined by using Ni-YSZ anode supported SOFC. Degradation of cell is found to be irreversible due to adsorption of PH3 on TPB and further reaction with Ni to form secondary phases with low melting point. The

  6. Kinetic studies of oxidation of MgAlON and a comparison of the oxidation behaviour of AlON, MgAlON, O'SiAlON-ZrO{sub 2}, and BN-ZCM ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Wang Xidong; Seetharaman, S. [Div. of Metallurgy, Royal Inst. of Tech., Stockholm (Sweden); Li Wenchao [Dept. of Physical Chemistry, Univ. of Science and Technology Beijing (USTB), Beijing, BJ (China)

    2002-06-01

    The kinetics and morphology of the oxidation process of magnesium-aluminium oxynitride (MgAlON), aluminium oxynitride (AlON), O'SiAlON-ZrO{sub 2}, and BN-ZCM have been studied in the temperature range 1373-1773 K (ZCM=30 wt% ZrO{sub 2}, 52 wt% Al{sub 2}O{sub 3} and 18 wt% 3 Al{sub 2}O{sub 3}.2 SiO{sub 2}). Oxidation experiments with powder and plate samples of the above materials have been carried out in air. MgAlON shows the best resistance to oxidation at lower temperatures (< 1473 K), whereas at higher temperatures ({proportional_to} 773 K), AlON shows the best resistance. O'SiAlON-ZrO{sub 2} shows very good oxidation resistance up to 1673 K. But its oxidation rate increases strongly above 1673 K, presumably due to the formation of liquid phase. BN-ZCM has the poorest oxidation resistance due to the evaporation of B{sub 2}O{sub 3}. The activation energies for the chemical oxidation reaction of AlON, MgAlON, and O'SiAlON-ZrO{sub 2} are 214, 330 and 260 kJ/mol, respectively. The overall diffusion activation energies for AlON, MgAlON, O'SiAlON-ZrO{sub 2} and BN-ZCM are 227, 573, 367 and 289 kJ/mol, respectively. (orig.)

  7. Kinetic and equilibrium studies of acrylonitrile binding to cytochrome c peroxidase and oxidation of acrylonitrile by cytochrome c peroxidase compound I

    Energy Technology Data Exchange (ETDEWEB)

    Chinchilla, Diana, E-mail: Diana_Chinchilla@yahoo.com; Kilheeney, Heather, E-mail: raindropszoo@yahoo.com; Vitello, Lidia B., E-mail: lvitello@niu.edu; Erman, James E., E-mail: jerman@niu.edu

    2014-01-03

    Highlights: •Cytochrome c peroxidase (CcP) binds acrylonitrile in a pH-independent fashion. •The spectrum of the CcP/acrylonitrile complex is that of a 6c–ls ferric heme. •The acrylonitrile/CcP complex has a K{sub D} value of 1.1 ± 0.2 M. •CcP compound I oxidizes acrylonitrile with a maximum turnover rate of 0.61 min{sup −1}. -- Abstract: Ferric heme proteins bind weakly basic ligands and the binding affinity is often pH dependent due to protonation of the ligand as well as the protein. In an effort to find a small, neutral ligand without significant acid/base properties to probe ligand binding reactions in ferric heme proteins we were led to consider the organonitriles. Although organonitriles are known to bind to transition metals, we have been unable to find any prior studies of nitrile binding to heme proteins. In this communication we report on the equilibrium and kinetic properties of acrylonitrile binding to cytochrome c peroxidase (CcP) as well as the oxidation of acrylonitrile by CcP compound I. Acrylonitrile binding to CcP is independent of pH between pH 4 and 8. The association and dissociation rate constants are 0.32 ± 0.16 M{sup −1} s{sup −1} and 0.34 ± 0.15 s{sup −1}, respectively, and the independently measured equilibrium dissociation constant for the complex is 1.1 ± 0.2 M. We have demonstrated for the first time that acrylonitrile can bind to a ferric heme protein. The binding mechanism appears to be a simple, one-step association of the ligand with the heme iron. We have also demonstrated that CcP can catalyze the oxidation of acrylonitrile, most likely to 2-cyanoethylene oxide in a “peroxygenase”-type reaction, with rates that are similar to rat liver microsomal cytochrome P450-catalyzed oxidation of acrylonitrile in the monooxygenase reaction. CcP compound I oxidizes acrylonitrile with a maximum turnover number of 0.61 min{sup −1} at pH 6.0.

  8. Radio-Oxidation in Polyolefins: Non-Stationary Kinetic Conditions

    International Nuclear Information System (INIS)

    Dely, N.

    2006-01-01

    In the last fifty years, many authors have been interested in the radio-oxidation processes occurring in polymers. The polymer degradation under ionising radiations in presence of dioxygen is well described by a radical chemistry. The radio-oxidation process occurs in three steps: the first one is the production of radicals P degree by interaction between the polymer and the ionising radiations; then radicals P degree react spontaneously with O 2 solved in the polymer giving a peroxy radical POO degree which attacks the polymer forming a hydroperoxide POOH and a new radical P degree (propagation). The third step corresponds to the termination step, that is bimolecular reactions between radicals. It is generally assumed that the stationary state is rapidly reached and consequently that the oxidation induced during the built-up period of the radical concentration can be neglected. However, to our best knowledge, the temporal evolution of radical concentrations before reaching the steady state regime has never been studied in details. We recently performed a complete study of oxygen consumption under electron irradiation for an EPDM elastomer. An analysis, as function of dose rate and oxygen pressure, and assuming steady state conditions, allowed extracting all the kinetic constants. Starting for these experimental data, we calculated the build-up of the radical concentration by solving numerically the differential equations with help of the Minichem code. We conclude that, in fact, the oxidation induced during the built-up period is negligible. In this paper we show that [P degree] could present a quasi-stationary plateau before reaching its stationary level. Consequently, the full radical time evolution is essentially determined by two characteristic times for reaching the quasi and stationary levels and three concentrations: [P degree] and [POO degree] at the stationary level and [P degree] at the quasi-stationary plateau. We show that realistic approximations can

  9. Kinetics of high-temperature oxidation of (Ti,Ta)(C,N)-based cermets

    International Nuclear Information System (INIS)

    Chicardi, E.; Córdoba, J.M.; Gotor, F.J.

    2016-01-01

    Highlights: • The kinetic of high-temperature oxidation of (Ti,Ta)(C,N)-Co cermets was studied. • A parabolic oxidation kinetic was determined in cermets between 700 °C and 1200 °C. • This parabolic kinetic behaviour is due to the existence of a protective layer. • The protective layer formed was a complex Ti_xTa_1_−_xO_2 oxide with rutile structure. • The oxidation rate is controlled by the Ti and O_2 diffusion through the Ti_xTa_1_−_xO_2. - Abstract: The kinetics of the high-temperature oxidation of titanium–tantalum carbonitride-based cermets with different Ti/Ta ratios was studied. Isothermal oxidation tests were conducted under static air for 48 h at temperatures between 700 °C and 1200 °C. The oxidation satisfied the parabolic kinetics, characteristic of the existence of a protective oxide layer. The apparent activation energy suggests the rate-controlling process during oxidation is the simultaneous inward and outward diffusion of oxygen and titanium, respectively, through the formed protective layer, consisting mainly of a rutile phase. A higher Ta(V) content in the rutile decreased the oxygen diffusivity due to the reduction of oxygen vacancy concentration.

  10. Kinetics of lactate turnover and oxidation in man

    International Nuclear Information System (INIS)

    Searle, G.L.; Shames, D.; Cavalieri, R.R.; DeGrazia, J.; Zarcone, V.; Porte, D. Jr.; Bagdade, J.D.

    1975-01-01

    The turnover and oxidation of lactic acid have been studied in man by means of 14 C-lactic acid, 14 C-glucose, and 14 C-alanine. The use of these labels in separate studies has enabled us to describe a complete scheme for the kinetics of lactic acid in man. We have determined that lactate arises from a minimum of two sources in overnight fasted man. 66% of lactate at this time arises from the metabolism of glucose while approximately 15% is derived from alanine. These sources and others unidentified supply lactate to the body pool at a rate of approximately 95 mg per kg per h. The disposal of this quantity of lactate is achieved through a minimum of three routes. Approximately 57% of the lactate turnover is oxidized to carbon dioxide, 15% is reduced to glucose, and approximately 25% is converted to alanine. The quantitative changes in the kinetics of this system that are brought on by fasting add an interesting dimension to the system. In agreement with the concepts of fuel economy in fasting the contribution of glucose carbon to lactic acid falls and, in turn, the contribution of lactate carbon to body glucose rises. The study of additional permutations of this system suggest that lactate, with pyruvate, is in the main stream of the intermediary metabolism of the body. The authors suggest that the study of this system offers promise of a fuller understanding of the derangements of metabolic disease. (author)

  11. Zirconium metal-water oxidation kinetics. I. Thermometry

    International Nuclear Information System (INIS)

    Cathcart, J.V.; McElroy, D.L.; Pawel, R.E.; Perkins, R.A.; Williams, R.K.; Yurek, G.J.

    1976-02-01

    A description is given of the thermometry techniques used in the Zirconium Metal--Water Oxidation Kinetics Program. Temperature measurements in the range 900 to 1500 0 C are made in three experimental systems: two oxidation apparatuses and the annealing furnace used in a corollary study of the diffusion of oxygen in β-Zircaloy. Carefully calibrated Pt vs Pt--10 percent Rh thermocouples are employed in all three apparatuses, while a Pt--6 percent Rh vs Pt-- 30 percent Rh thermocouple and an optical pyrometer are used in addition in the annealing furnace. Features of the experimental systems pertaining to thermocouple installation, temperature control, emf measurements, etc. are described, and potential temperature-measurement error sources are discussed in detail. The accuracy of the temperature measurements is analyzed

  12. Kinetics and mechanism of oxidation of chloramphenicol by 1 ...

    Indian Academy of Sciences (India)

    Unknown

    the kinetics and mechanism of oxidation of CAP by. CBT in HClO4 medium at 323 K for elucidating the mechanism of oxidation of this drug. 2. Experimental. Chloramphenicol (Sigma, USA) was purified before use. CBT was prepared and purified as reported ear- lier.10 AnalaR grade chemicals and double distilled.

  13. Kinetic determinations of accurate relative oxidation potentials of amines with reactive radical cations.

    Science.gov (United States)

    Gould, Ian R; Wosinska, Zofia M; Farid, Samir

    2006-01-01

    Accurate oxidation potentials for organic compounds are critical for the evaluation of thermodynamic and kinetic properties of their radical cations. Except when using a specialized apparatus, electrochemical oxidation of molecules with reactive radical cations is usually an irreversible process, providing peak potentials, E(p), rather than thermodynamically meaningful oxidation potentials, E(ox). In a previous study on amines with radical cations that underwent rapid decarboxylation, we estimated E(ox) by correcting the E(p) from cyclic voltammetry with rate constants for decarboxylation obtained using laser flash photolysis. Here we use redox equilibration experiments to determine accurate relative oxidation potentials for the same amines. We also describe an extension of these experiments to show how relative oxidation potentials can be obtained in the absence of equilibrium, from a complete kinetic analysis of the reversible redox kinetics. The results provide support for the previous cyclic voltammetry/laser flash photolysis method for determining oxidation potentials.

  14. Atmospheric Oxidation Mechanism and Kinetic Studies for OH and NO3 Radical-Initiated Reaction of Methyl Methacrylate

    Directory of Open Access Journals (Sweden)

    Rui Gao

    2014-03-01

    Full Text Available The mechanism for OH and NO3 radical-initiated oxidation reactions of methyl methacrylate (MMA was investigated by using density functional theory (DFT molecular orbital theory. Geometrical parameters of the reactants, intermediates, transition states, and products were fully optimized at the B3LYP/6-31G(d,p level. Detailed oxidation pathways were presented and discussed. The rate constants were deduced by the canonical variational transition-state (CVT theory with the small-curvature tunneling (SCT correction and the multichannel Rice-Ramspergere-Kassele-Marcus (RRKM theory, based on the potential energy surface profiles over the general atmospheric temperature range of 180–370 K. The calculated results were in reasonable agreement with experimental measurement.

  15. Mechanistic understanding and kinetic studies of highly selective oxidative dehydrogenation of ethane over novel supported molten chloride catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Gaertner, C.; Veen, A.C. van; Lercher, J.A. [Technische Univ. Muenchen, Garching (Germany). Dept. of Chemistry

    2012-07-01

    Ethene is one of the most important feedstocks for chemical industry, nowadays mainly produced via steam cracking. However, oxidative dehydrogenation becomes a more important process route, allowing to produce ethene selectively and at lower temperatures. Supported alkali chloride catalysts are promising materials. However, the ODH mechanism of this class of catalysts is not well investigated so far. The investigation of the reaction mechanism is thus the aim of this contribution. (orig.)

  16. Kinetics and mechanism of oxidation of tellurium (IV) by periodate in alkaline medium

    International Nuclear Information System (INIS)

    Srinivas, K.; Vani, P.; Dikshitulu, L.S.A.

    1995-01-01

    Detailed kinetic study of the oxidation of tellurium (IV) by periodate in alkaline medium has been carried out to compare the mechanisms of oxidation in the acid and alkaline media. It is interesting to note that the rate step involves a two-electron transfer from tellurium (IV) to periodate in alkaline medium although the kinetic pattern is somewhat different from that in the acid medium. 7 refs., 1 tab

  17. Gas-Phase Photocatalytic Oxidation of Dimethylamine: The Reaction Pathway and Kinetics

    Directory of Open Access Journals (Sweden)

    Anna Kachina

    2007-01-01

    Full Text Available Gas-phase photocatalytic oxidation (PCO and thermal catalytic oxidation (TCO of dimethylamine (DMA on titanium dioxide was studied in a continuous flow simple tubular reactor. Volatile PCO products of DMA included ammonia, formamide, carbon dioxide, and water. Ammonia was further oxidized in minor amounts to nitrous oxide and nitrogen dioxide. Effective at 573 K, TCO resulted in the formation of ammonia, hydrogen cyanide, carbon monoxide, carbon dioxide, and water. The PCO kinetic data fit well to the monomolecular Langmuir-Hinshelwood model, whereas TCO kinetic behaviour matched the first-order process. No deactivation of the photocatalyst during the multiple long-run experiments was observed.

  18. Kinetics of the gas-phase tritium oxidation reaction

    International Nuclear Information System (INIS)

    Failor, R.A.

    1989-01-01

    Homogeneous gas-phase kinetics of tritium oxidation (2T 2 + O 2 →2T 2 O) have been studied with a model that accounts explicitly for radiolysis of the major species and the kinetics of the subsequent reactions of ionic, excited-state, and neutral species. Results from model calculations are given for 10 -4 -1.0 mol% T 2 in O 2 (298 K, 1 atm). As the reaction evolves three different mechanisms control T 2 O production, each with a different overall rate expression and a different order with respect to the T 2 concentration. The effects of self-radiolysis of pure T 2 on the tritium oxidation reaction were calculated. Tritium atoms, the primary product of T 2 self-radiolysis, altered the oxidation mechanism only during the first few seconds following the initiation of the T 2 -O 2 reaction. Ozone, an important intermediate in T 2 oxidation, was monitored in-situ by U.V. absorption spectroscopy for 0.01-1.0 mol% T 2 an 1 atm O 2 . The shape of the experimental ozone time profile agreed with the model predictions. As predicted, the measured initial rate of ozone production varied linearly with initial T 2 concentration ([T 2 ] 0.6 o ), but at an initial rate one-third the predicted value. The steady-state ozone concentration ([O 3 ]ss) was predicted to be dependent on [T 2 ] 0.3 o , but the measured value was [T 2 ] 0.6 o , resulting in four times higher [O 3 ]ss than predicted for a 1.0% T 2 -O 2 mixture. Adding H 2 to the T 2 -O 2 mixture, to provide insight into the differences between the radiolytic and chemical behavior of the tritium, produced a greater decrease in [O 3 ]ss than predicted. Adjusting the reaction cell surface-to-volume ratio showed implications of minor surface removal of ozone

  19. Kinetic study of formic acid oxidation on Ti/IrO{sub 2} electrodes prepared using the spin coating deposition technique

    Energy Technology Data Exchange (ETDEWEB)

    Fierro, Stephane, E-mail: stephane.fierro@epfl.c [Institute of Chemical Sciences and Engineering, Swiss Federal Institute of Technology, ISIC-EPFL, CH-1015 Lausanne (Switzerland); Comninellis, Christos [Institute of Chemical Sciences and Engineering, Swiss Federal Institute of Technology, ISIC-EPFL, CH-1015 Lausanne (Switzerland)

    2010-09-30

    In the first part of this paper, IrO{sub 2} electrodes produced by thermal decomposition of H{sub 2}IrCl{sub 6} precursor were manufactured using the spin coating deposition technique, where centrifugal forces spread the precursor solution with simultaneous evaporation of the solvent on the rotating Ti substrate. It was found using this technique, that it is possible to obtain thin and uniform IrO{sub 2} coatings with controlled loadings. The influence of the concentration of iridium salt in the precursor solution (c{sub 0}) as well as the influence of the rotation speed at which the substrate spins ({omega}) on the IrO{sub 2} loading have been studied using voltammetric charge measurements. From these results, a simple relation has been proposed for the estimation of the IrO{sub 2} loading for a given c{sub 0} and {omega}. In the second part of this paper and from measurements performed using different IrO{sub 2} loadings and formic acid concentrations, the kinetic parameters of the oxidation of formic acid have been quantitatively determined using a model that involves the redox couple IrO{sub 3}/IrO{sub 2} as mediator of this reaction. Furthermore, using the kinetic parameters obtained together with the Nernst equation and the I-V curves of the supporting electrolyte (1 M HClO{sub 4}), theoretical I-V curves could be constructed for different concentrations of formic acid and different IrO{sub 2} loadings.

  20. Ammonia removal in electrochemical oxidation: Mechanism and pseudo-kinetics

    International Nuclear Information System (INIS)

    Li Liang; Liu Yan

    2009-01-01

    This paper investigated the mechanism and pseudo-kinetics for removal of ammonia by electrochemical oxidation with RuO 2 /Ti anode using batch tests. The results show that the ammonia oxidation rates resulted from direct oxidation at electrode-liquid interfaces of the anode by stepwise dehydrogenation, and from indirect oxidation by hydroxyl radicals were so slow that their contribution to ammonia removal was negligible under the condition with Cl - . The oxidation rates of ammonia ranged from 1.0 to 12.3 mg N L -1 h -1 and efficiency reached nearly 100%, primarily due to the indirect oxidation of HOCl, and followed pseudo zero-order kinetics in electrochemical oxidation with Cl - . About 88% ammonia was removed from the solution. The removed one was subsequently found in the form of N 2 in the produced gas. The rate at which Cl - lost electrons at the anode was a major factor in the overall ammonia oxidation. Current density and Cl - concentration affected the constant of the pseudo zero-order kinetics, expressed by k = 0.0024[Cl - ] x j. The ammonia was reduced to less than 0.5 mg N L -1 after 2 h of electrochemical oxidation for the effluent from aerobic or anaerobic reactors which treated municipal wastewater. This result was in line with the strict discharge requirements

  1. Kinetics of tetravalent plutonium oxidation by cerium (4)

    Energy Technology Data Exchange (ETDEWEB)

    Nikitina, G P; Shumakov, V G; Egorova, V P

    1975-01-01

    Stoichiometry and kinetics of the Pu(4) + Ce(4) reaction is studied by spectrophotometric method at 5-30 deg C in nitric acid solutions (..mu..=(HNO/sub 3/)+(NaNO/sub 3/) = 1.0 - 5.7; (Ce(4)) = 5.10/sup -5/ - 1.2.10/sup -3/ g-ion/1, (Pu(4)) =1.10/sup -5/ - 8.5.10/sup -4/ g-ion/1. Oxidation of one Pu(4) ion to a hexavalent state requires two Ce(4) ions. The plutonium oxidation is not complicated by by-processes. Reverse Ce(3) + PuO/sub 2//sup +/ reaction does not contribute essentially to the process at (Ce(3)) 2.6.10/sup -2/ g-ion/1. The reaction rate obeys the kinetic equation - d(Pu(4))/dt = ksub(eff)(Pu(4))(Ce(4))/a sub(+-HNO/sub 3/). The thermodynamical activation parameters are found for solutions at the varied nitric acid concentrations:..delta..Gsup(not equal) = 17.0+-0.2 and ..delta..Hsup(not equal) = 21.8+-2 kcal/mole(..mu..=1.0); ..delta..Gsup(not equal) = 19.1+-0.1 and ..delta..Hsup(not equal) = 23.1+-1 kcal/mole(..mu..=4.9). The reaction mechanism is discussed in terms of the theory of absolute reaction rates and the model of long-range charge transfer.

  2. Multicomponent kinetic analysis and theoretical studies on the phenolic intermediates in the oxidation of eugenol and isoeugenol catalyzed by laccase.

    Science.gov (United States)

    Qi, Yan-Bing; Wang, Xiao-Lei; Shi, Ting; Liu, Shuchang; Xu, Zhen-Hao; Li, Xiqing; Shi, Xuling; Xu, Ping; Zhao, Yi-Lei

    2015-11-28

    Laccase catalyzes the oxidation of natural phenols and thereby is believed to initialize reactions in lignification and delignification. Numerous phenolic mediators have also been applied in laccase-mediator systems. However, reaction details after the primary O-H rupture of phenols remain obscure. In this work two types of isomeric phenols, EUG (eugenol) and ISO (trans-/cis-isoeugenol), were used as chemical probes to explore the enzymatic reaction pathways, with the combined methods of time-resolved UV-Vis absorption spectra, MCR-ALS, HPLC-MS, and quantum mechanical (QM) calculations. It has been found that the EUG-consuming rate is linear to its concentration, while the ISO not. Besides, an o-methoxy quinone methide intermediate, (E/Z)-4-allylidene-2-methoxycyclohexa-2,5-dienone, was evidenced in the case of EUG with the UV-Vis measurement, mass spectra and TD-DFT calculations; in contrast, an ISO-generating phenoxyl radical, a (E/Z)-2-methoxy-4-(prop-1-en-1-yl) phenoxyl radical, was identified in the case of ISO. Furthermore, QM calculations indicated that the EUG-generating phenoxyl radical (an O-centered radical) can easily transform into an allylic radical (a C-centered radical) by hydrogen atom transfer (HAT) with a calculated activation enthalpy of 5.3 kcal mol(-1) and then be fast oxidized to the observed eugenol quinone methide, rather than an O-radical alkene addition with barriers above 12.8 kcal mol(-1). In contrast, the ISO-generating phenoxyl radical directly undergoes a radical coupling (RC) process, with a barrier of 4.8 kcal mol(-1), while the HAT isomerization between O- and C-centered radicals has a higher reaction barrier of 8.0 kcal mol(-1). The electronic conjugation of the benzyl-type radical and the aromatic allylic radical leads to differentiation of the two pathways. These results imply that competitive reaction pathways exist for the nascent reactive intermediates generated in the laccase-catalyzed oxidation of natural phenols, which is

  3. High-temperature steam oxidation kinetics of the E110G cladding alloy

    International Nuclear Information System (INIS)

    Király, Márton; Kulacsy, Katalin; Hózer, Zoltán; Perez-Feró, Erzsébet; Novotny, Tamás

    2016-01-01

    In the course of recent years, several experiments were performed at MTA EK (Centre for Energy Research, Hungarian Academy of Sciences) on the isothermal high-temperature oxidation of the improved Russian cladding alloy E110G in steam/argon atmosphere. Using these data and designing additional supporting experiments, the oxidation kinetics of the E110G alloy was investigated in a wide temperature range, between 600 °C and 1200 °C. For short durations (below 500 s) or high temperatures (above 1065 °C) the oxidation kinetics was found to follow a square-root-of-time dependence, while for longer durations and in the intermediate temperature range (800–1000 °C) it was found to approach a cube-root-of-time dependence rather than a square-root one. Based on the results a new best-estimate and a conservative oxidation kinetics model were created. - Highlights: • Steam oxidation kinetics of E110G was studied at MTA EK based on old and new data. • New best-estimate and conservative steam oxidation kinetics were proposed for E110G. • The exponent of oxidation time changed depending on oxidation temperature. • A simple exponential curve was used instead of Arrhenius-type curve for the factor.

  4. Pure rotational CARS thermometry studies of low-temperature oxidation kinetics in air and ethene-air nanosecond pulse discharge plasmas

    International Nuclear Information System (INIS)

    Zuzeek, Yvette; Choi, Inchul; Uddi, Mruthunjaya; Adamovich, Igor V; Lempert, Walter R

    2010-01-01

    Pure rotational CARS thermometry is used to study low-temperature plasma assisted fuel oxidation kinetics in a repetitive nanosecond pulse discharge in ethene-air at stoichiometric and fuel lean conditions at 40 Torr pressure. Air and fuel-air mixtures are excited by a burst of high-voltage nanosecond pulses (peak voltage, 20 kV; pulse duration, ∼ 25 ns) at a 40 kHz pulse repetition rate and a burst repetition rate of 10 Hz. The number of pulses in the burst is varied from a few pulses to a few hundred pulses. The results are compared with the previously developed hydrocarbon-air plasma chemistry model, modified to incorporate non-empirical scaling of the nanosecond discharge pulse energy coupled to the plasma with number density, as well as one-dimensional conduction heat transfer. Experimental time-resolved temperature, determined as a function of the number of pulses in the burst, is found to agree well with the model predictions. The results demonstrate that the heating rate in fuel-air plasmas is much faster compared with air plasmas, primarily due to energy release in exothermic reactions of fuel with O atoms generated by the plasma. It is found that the initial heating rate in fuel-air plasmas is controlled by the rate of radical (primarily O atoms) generation and is nearly independent of the equivalence ratio. At long burst durations, the heating rate in lean fuel air-mixtures is significantly reduced when all fuel is oxidized.

  5. Oxidation behaviour of Zr-Ce alloys. Kinetic and microstructure aspects

    International Nuclear Information System (INIS)

    Rouillon, Ludovic

    1996-01-01

    As Zircaloy alloys are used for fuel rods in pressurized water nuclear reactors, this research thesis aims at studying and improving corrosion resistance of zirconium alloys while maintaining their mechanical properties. It more precisely deals with the kinetic and microstructure aspects of the external corrosion of the cladding by the coolant. In the case of Zircaloys, this corrosion is characterized by a kinetic transition from an initially parabolic to a linear regime. This research aims at intervening on this transition by elaborating zirconium alloys containing an element which stabilizes zirconia, in this case cerium. After having reported a bibliographical study on sheath oxidation, on parameters which influence sheath oxidation kinetics, on zirconia stabilization by doping elements, on the interest of lanthanide oxides, the author reports a feasibility study on the use of cerium (choice and preparation, sintered ceramic characterization, annealing of stabilized zirconia), reports a metallurgical study of Zr-Ce alloys, reports the study of the oxidation behaviour of these alloys (in autoclave, in presence of oxygen, under oxygen and then water) and the characterization of the microstructures of the oxide layers. He finally discusses the relationship between microstructure and oxidation kinetics, the role of cerium in the oxidation process, and the role of water in the oxidation process [fr

  6. Novel differential refractometry study of the enzymatic degradation kinetics of poly(ethylene oxide)-b-poly(epsilon-caprolactone) particles dispersed in water.

    Science.gov (United States)

    Lam, HiuFung; Gong, Xiangjun; Wu, Chi

    2007-02-22

    A poly(ethylene oxide)-b-poly(epsilon-caprolactone) (PEO-b-PCL) diblock copolymer was micronized into small micelle-like particles (approximately 80 nm) via dialysis-induced microphase inversion. The enzymatic biodegradation of the PCL portion of these particles in water was in situ investigated inside a recently developed novel differential refractometer. Using this refractometry method, we were able to monitor the real-time biodegradation via the refractive index change (Deltan) of the dispersion because Deltan is directly proportional to the particle mass concentration. We found that the degradation rate is proportional to either the polymer or enzyme concentration. Our results directly support previous speculation on the basis of the light-scattering data that the biodegradation follows the first-order kinetics for a given enzyme concentration. This study not only leads to a better understanding of the enzymatic biodegradation of PCL, but also demonstrates a novel, rapid, noninvasive, and convenient way to test the degradability of polymers.

  7. Kinetic studies on the reaction of cob(II)alamin with hypochlorous acid: Evidence for one electron oxidation of the metal center and corrin ring destruction.

    Science.gov (United States)

    Dassanayake, Rohan S; Farhath, Mohamed M; Shelley, Jacob T; Basu, Soumitra; Brasch, Nicola E

    2016-10-01

    Kinetic and mechanistic studies on the reaction of a major intracellular vitamin B 12 form, cob(II)alamin (Cbl(II)), with hypochlorous acid/hypochlorite (HOCl/OCl - ) have been carried out. Cbl(II) (Co(II)) is rapidly oxidized by HOCl to predominately aquacobalamin/hydroxycobalamin (Cbl(III), Co(III)) with a second-order rate constant of 2.4×10 7 M -1 s -1 (25.0°C). The stoichiometry of the reaction is 1:1. UHPLC/HRMS analysis of the product mixture of the reaction of Cbl(II) with 0.9mol equiv. HOCl provides support for HOCl being initially reduced to Cl and subsequent H atom abstraction from the corrin macrocycle occurring, resulting in small amounts of corrinoid species with two or four H atoms fewer than the parent cobalamin. Upon the addition of excess (H)OCl further slower reactions are observed. Finally, SDS-PAGE experiments show that HOCl-induced damage to bovine serum albumin does not occur in the presence of Cbl(II), providing support for Cbl(II) being an efficient HOCl trapping agent. Copyright © 2016 Elsevier Inc. All rights reserved.

  8. Preliminary Study on the Kinetics and Mechanism of the Oxidation of Naphthol Green B by Dichromate Ion in Aqueous Hydrochloric Acid Medium

    Directory of Open Access Journals (Sweden)

    Bako Myek

    2014-04-01

    Full Text Available The kinetics of the oxidation of naphthol green B (NGB3- by Cr2O7 2- has been studied in aqueous hydrochloric acid medium at an ionic strength, I = 0.50 mol dm-3 (NaCl, H+ =1.0  10-4 mol dm-3 (HCl and T = 25  1C. The redox reaction displayed a stoichiometry of 1:1 and obeys the rate law: -dNGB3-/dt = k2NGB3-]Cr2O7 2- . The second order rate constant increases with increase in acid concentration and in the ionic strength of reaction medium. The rates of reaction displayed a positive salt effect. Addition of acrylonitrile to a partially reacted mixture in the presence of excess methanol did not lead to gel formation. Added cations and anions inhibited the naphthol green B - Cr2O7 2- reaction. Results of the Michaelis – Menten plot gave no evidence of intermediate complex formation during the course of the reaction. Based on the results obtained, the reaction is believed to proceed through the outersphere mechanistic pathway.

  9. Real-time Kinetics of High-mobility Group Box 1 (HMGB1) Oxidation in Extracellular Fluids Studied by in Situ Protein NMR Spectroscopy*

    Science.gov (United States)

    Zandarashvili, Levani; Sahu, Debashish; Lee, Kwanbok; Lee, Yong Sun; Singh, Pomila; Rajarathnam, Krishna; Iwahara, Junji

    2013-01-01

    Some extracellular proteins are initially secreted in reduced forms via a non-canonical pathway bypassing the endoplasmic reticulum and become oxidized in the extracellular space. One such protein is HMGB1 (high-mobility group box 1). Extracellular HMGB1 has different redox states that play distinct roles in inflammation. Using a unique NMR-based approach, we have investigated the kinetics of HMGB1 oxidation and the half-lives of all-thiol and disulfide HMGB1 species in serum, saliva, and cell culture medium. In this approach, salt-free lyophilized 15N-labeled all-thiol HMGB1 was dissolved in actual extracellular fluids, and the oxidation and clearance kinetics were monitored in situ by recording a series of heteronuclear 1H-15N correlation spectra. We found that the half-life depends significantly on the extracellular environment. For example, the half-life of all-thiol HMGB1 ranged from ∼17 min (in human serum and saliva) to 3 h (in prostate cancer cell culture medium). Furthermore, the binding of ligands (glycyrrhizin and heparin) to HMGB1 significantly modulated the oxidation kinetics. Thus, the balance between the roles of all-thiol and disulfide HMGB1 proteins depends significantly on the extracellular environment and can also be artificially modulated by ligands. This is important because extracellular HMGB1 has been suggested as a therapeutic target for inflammatory diseases and cancer. Our work demonstrates that the in situ protein NMR approach is powerful for investigating the behavior of proteins in actual extracellular fluids containing an enormous number of different molecules. PMID:23447529

  10. Oxidation Kinetics and Strength Degradation of Carbon Fibers in a Cracked Ceramic Matrix Composite

    Science.gov (United States)

    Halbig, Michael C.

    2003-01-01

    Experimental results and oxidation modeling will be presented to discuss carbon fiber susceptibility to oxidation, the oxidation kinetics regimes and composite strength degradation and failure due to oxidation. Thermogravimetric Analysis (TGA) was used to study the oxidation rates of carbon fiber and of a pyro-carbon interphase. The analysis was used to separately obtain activation energies for the carbon constituents within a C/SiC composite. TGA was also conducted on C/SiC composite material to study carbon oxidation and crack closure as a function of temperature. In order to more closely match applications conditions C/SiC tensile coupons were also tested under stressed oxidation conditions. The stressed oxidation tests show that C/SiC is much more susceptible to oxidation when the material is under an applied load where the cracks are open and allow for oxygen ingress. The results help correlate carbon oxidation with composite strength reduction and failure.

  11. Kinetics of reactions of chromium, molybdenum and tungsten hexacarbonyls with hydroxylamine and trimethylamine oxide

    International Nuclear Information System (INIS)

    Maksakov, V.A.; Ershova, V.A.

    1994-01-01

    Mechanism of M(CO) 6 (M = Cr, Mo, W) reaction with hydroxylamine was studied. On the basis of kinetic data it was ascertained that as a result of the reaction CO oxidation to CO 2 and intramolecular transfer of amine formed to the central atom of metal occur. Mechanisms of M(CO) 6 reactions with hydroxylamine and trimethylamine oxide are compared

  12. Kinetics and mechanism of the oxidation of organic sulphides by 2,2 ...

    Indian Academy of Sciences (India)

    Unknown

    In the present article, we report the kinetics of oxidation of thirty-four organic sulphides by BPCC in ..... t-Butyl alcohol. 24⋅0. Acetone. 40⋅7 .... different sensitivity to the electronic demand for the phenomenon being studied. It has the ... 144. Table 5. Temperature dependence for the reaction constants for the oxidation of.

  13. Improved Understanding of In Situ Chemical Oxidation Contaminant Oxidation Kinetics

    Science.gov (United States)

    2007-12-01

    natural oxidant demand •OH hydroxide radical Ox oxidant O3 ozone PCE perchloroethylene HSO5− peroxymonosulfate PNDA p...properties (e.g., soil mineralogy , natural carbon content) affect oxidant mobility and stability in the subsurface, and develop a standardized natural...chlorinated ethenes For contaminant oxidation by activated S2O82−, it is more difficult to develop a general description of kobs vs. T because there are

  14. Thermodynamic controls on the kinetics of microbial low-pH Fe(II) oxidation.

    Science.gov (United States)

    Larson, Lance N; Sánchez-España, Javier; Kaley, Bradley; Sheng, Yizhi; Bibby, Kyle; Burgos, William D

    2014-08-19

    Acid mine drainage (AMD) is a major worldwide environmental threat to surface and groundwater quality. Microbial low-pH Fe(II) oxidation could be exploited for cost-effective AMD treatment; however, its use is limited because of uncertainties associated with its rate and ability to remove Fe from solution. We developed a thermodynamic-based framework to evaluate the kinetics of low-pH Fe(II) oxidation. We measured the kinetics of low-pH Fe(II) oxidation at five sites in the Appalachian Coal Basin in the US and three sites in the Iberian Pyrite Belt in Spain and found that the fastest rates of Fe(II) oxidation occurred at the sites with the lowest pH values. Thermodynamic calculations showed that the Gibbs free energy of Fe(II) oxidation (ΔG(oxidation)) was also most negative at the sites with the lowest pH values. We then conducted two series of microbial Fe(II) oxidation experiments in laboratory-scale chemostatic bioreactors operated through a series of pH values (2.1-4.2) and found the same relationships between Fe(II) oxidation kinetics, ΔG(oxidation), and pH. Conditions that favored the fastest rates of Fe(II) oxidation coincided with higher Fe(III) solubility. The solubility of Fe(III) minerals, thus plays an important role on Fe(II) oxidation kinetics. Methods to incorporate microbial low-pH Fe(II) oxidation into active and passive AMD treatment systems are discussed in the context of these findings. This study presents a simplified model that describes the relationship between free energy and microbial kinetics and should be broadly applicable to many biogeochemical systems.

  15. Simulation and comparative study on the oxidation kinetics of atrazine by UV/H₂O₂, UV/HSO₅⁻ and UV/S₂O₈²⁻.

    Science.gov (United States)

    Luo, Congwei; Ma, Jun; Jiang, Jin; Liu, Yongze; Song, Yang; Yang, Yi; Guan, Yinghong; Wu, Daoji

    2015-09-01

    This study comparatively investigated atrazine (ATZ) degradation by irradiation at the wavelength of 254 nm in the presence of peroxides including hydrogen peroxide (H2O2), peroxymonosulfate (HSO5(-)), and persulfate (S2O8(2-)) at various initial ATZ concentrations and oxidant dosages. The effects of water matrix, such as carbonate/bicarbonate (HCO3(-)/CO3(2-)), chloride ions (Cl(-)), and natural organic matter (NOM), were evaluated on these three advanced oxidation processes. A simple steady-state kinetic model was developed based on the initial rates of ATZ destruction, which could well describe the apparent pseudo-first-order rate constants (k(app), s(-1)) of ATZ degradation in these three processes. The specific roles of reactive species (i.e., HO·, SO4(-·), CO3(-·), and Cl2(-·)) under various experimental conditions were quantitatively evaluated based on their steady-state concentrations obtained from this model. Modeling results showed that the steady-state concentrations of HO· and SO4(-·) decreased with the increase of CO3(2-)/HCO3(-) concentration, and the relative contribution of HO· to ATZ degradation significantly decreased in UV/H2O2 and UV/HSO5(-) systems. On the other hand, the scavenging effect of HCO3(-)/CO3(2-) on the relative contribution of SO4(-·) to ATZ degradation was lower than that on HO·. The presence of Cl(-) (0.5-10 mM) significantly scavenged SO4(-·) but had slightly scavenging effect on HO· at the present experimental pH, resulting in greater decrease of k(app) in the UV/S2O8(2-) than UV/H2O2 and UV/HSO5(-) systems. Higher levels of Cl2(-·) were generated in the UV/S2O8(2-) than those in the UV/H2O2 and UV/HSO5(-) systems at the same Cl(-) concentrations. NOM significantly decreased k(app) due to its effects of competitive UV absorption and radical scavenging with the latter one being dominant. These results improve the understanding of the effects of water constituents for ATZ degradation in the UV-based oxidation

  16. Study on platelet kinetics

    International Nuclear Information System (INIS)

    Yui, Tokuo

    1981-01-01

    Fundamental study: Factors influencing the labeling on human platelets were evaluated and optimal labeling conditions were chosen. Then, platelet survival times were measured and organ distribution of labeled platelets was observed in rat by four different methods. These results were compared with each other. Based on the findings of those studies, the protocol of human platelet labeling with 111 In-oxine for clinical use was established. Clinical study: In normal cases, a platelet survival time and a platelet turnover rate were quite similar to the results from 51 Cr method. In gamma camera imaging, a radioactivity on the heart decreased with the lapse of time, while that on the spleen and liver gradually increased. In patients with idiopathic thrombocytopenic purpura, platelet survival time was markedly shortened and both a platelet turnover rate and an effective production increased. In patient with congestive splenomegaly, a platelet survival time was normal, whereas a platelet pooling on the spleen markedly increased. In patients who were implanted dacron-graft for abdominal aortic aneurysm, a radioactivity accumulated to the graft and a platelet survival time shortened. In a patient with myocardial infarction, the camera imaging clearly showed the thrombus in the left ventricular aneurysm. In three patients with mitral stenosis, thrombi in left atrium were observed at the camera images. Imaging of a platelet distribution and measurement of platelet survival time using 111 In-oxine labeled platelets are considered to be an excellent method for the diagnosis and decision of treatment on various disorders with thrombocytopenia and thrombosis. (J.P.N.)

  17. Determination of oxygen diffusion kinetics during thin film ruthenium oxidation

    NARCIS (Netherlands)

    Coloma Ribera, R.; van de Kruijs, Robbert Wilhelmus Elisabeth; Yakshin, Andrey; Bijkerk, Frederik

    2015-01-01

    In situ X-ray reflectivity was used to reveal oxygen diffusion kinetics for thermal oxidation of polycrystalline ruthenium thin films and accurate determination of activation energies for this process. Diffusion rates in nanometer thin RuO2 films were found to show Arrhenius behaviour. However, a

  18. Kinetics and mechanism of oxidation of aliphatic primary alcohols by ...

    Indian Academy of Sciences (India)

    Unknown

    Kinetics and mechanism of oxidation of aliphatic primary alcohols by quinolinium bromochromate. SONU SARASWAT, VINITA SHARMA and K K BANERJI*. Department of Chemistry, JNV University, Jodhpur 342 005, India e-mail: banerjikk@rediffmail.com. MS received 4 December 2001; revised 2 November 2002.

  19. Oxidation Kinetics of Copper: An Experiment in Solid State Chemistry.

    Science.gov (United States)

    Ebisuzaki, Y.; Sanborn, W. B.

    1985-01-01

    Oxidation kinetics in metals and the role defects play in diffusion-controlled reactions are discussed as background for a junior/senior-level experiment in the physical or inorganic chemistry laboratory. Procedures used and typical data obtained are provided for the experiment. (JN)

  20. Kinetics and Mechanism of the Oxidation of Coomassie Brilliant Blue ...

    African Journals Online (AJOL)

    NICOLAAS

    Kinetics and Mechanism of the Oxidation of Coomassie Brilliant Blue-R dye by Hypochlorite and Role of Acid there in. Srinivasu Nadupalli, Venkata D.B.C. Dasireddy, Neil A. Koorbanally and Sreekantha B. Jonnalagadda*. School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Private.

  1. Simplified kinetic models of methanol oxidation on silver

    DEFF Research Database (Denmark)

    Andreasen, A.; Lynggaard, H.; Stegelmann, C.

    2005-01-01

    Recently the authors developed a microkinetic model of methanol oxidation on silver [A. Andreasen, H. Lynggaard, C. Stegelmann, P. Stoltze, Surf. Sci. 544 (2003) 5-23]. The model successfully explains both surface science experiments and kinetic experiments at industrial conditions applying...

  2. Some current problems in oxidation kinetics

    Science.gov (United States)

    Benson, S. W.

    1972-01-01

    Experimental data in low temperature and high temperature oxidations are examined from the point of view of reported quantitative inconsistencies. Activation energies for tBuO2 metathesis reactions with alkanes appear to be 7 kcal/mole higher than for comparable reactions of HO2. Related isomerization reactions are examined in the light of these differences without reaching any simple conclusions. The Russell mechanism for a 6-membered, cyclic, transition state for termination of primary and secondary alkyl peroxy radicals is shown to be either inconsistent with thermochemical data, or else unique to solution reactions. Addition reactions of O3 with olefins and acetylenes are shown thermochemically to have the possibility of following concerted and biradical pathways, respectively. Recent data showing strong inhibition by PbO coated surfaces of both oxidation and pyrolysis of i-C4H10 are examined in terms of mechanism.

  3. Port wine oxidation management: a multiparametric kinetic approach.

    Science.gov (United States)

    Martins, Rui Costa; Monforte, Ana Rita; Silva Ferreira, António

    2013-06-05

    Port wine is a flagship fortified wine of Portugal, which undergoes a particularly long aging period, developing a dynamic sensory profile over time, responsible for several wine categories, which is dependent upon the type of aging (bottle or barrel). Therefore, the quality of the product is dependent upon the chemical mechanisms occurring during the aging process, such as oxidation or Maillard reactions. To attain the desired quality management, it is necessary to understand how technological parameters, such as temperature or oxygen exposure, affect the kinetics of the formation of key odorants, such as sotolon. There is a lack of information about the impact of the storage conditions (oxygen and temperature) on Port wine quality. In this study, the effect of these two parameters were investigated to increase the knowledge database concerning aging management of Port wines. It was found that sotolon formation is highly dependent upon oxygen and temperature. There is however a synergistic effect between these two parameters that could significantly increase the concentration. The kinetic parameters of oxygen, sotolon, and other compounds related to Port aging (cis- and trans-5-hydroxy-2-methyl-1,3-dioxan, 2-furfural, 5-hydroxy-methyl-furfural, and 5-methyl-furfural) are also reported. Kinetic models with Monte Carlo simulations, where the oxygen permeability dispersion and temperature are the parameters under evaluation, were applied. On the basis of the modeling predictions, it would seem that the temperature of a cellar would have a more significant impact on the Port wines stored in containers where the oxygen intake is higher (barrels) when compared to containers with low oxygen permeability (bottles using cork stoppers).

  4. Kinetic modeling of antimony(III) oxidation and sorption in soils.

    Science.gov (United States)

    Cai, Yongbing; Mi, Yuting; Zhang, Hua

    2016-10-05

    Kinetic batch and saturated column experiments were performed to study the oxidation, adsorption and transport of Sb(III) in two soils with contrasting properties. Kinetic and column experiment results clearly demonstrated the extensive oxidation of Sb(III) in soils, and this can in return influence the adsorption and transport of Sb. Both sorption capacity and kinetic oxidation rate were much higher in calcareous Huanjiang soil than in acid red Yingtan soil. The results indicate that soil serve as a catalyst in promoting oxidation of Sb(III) even under anaerobic conditions. A PHREEQC model with kinetic formulations was developed to simulate the oxidation, sorption and transport of Sb(III) in soils. The model successfully described Sb(III) oxidation and sorption data in kinetic batch experiment. It was less successful in simulating the reactive transport of Sb(III) in soil columns. Additional processes such as colloid facilitated transport need to be quantified and considered in the model. Copyright © 2016 Elsevier B.V. All rights reserved.

  5. Nitrous oxide production kinetics during nitrate reduction in river sediments.

    Science.gov (United States)

    Laverman, Anniet M; Garnier, Josette A; Mounier, Emmanuelle M; Roose-Amsaleg, Céline L

    2010-03-01

    A significant amount of nitrogen entering river basins is denitrified in riparian zones. The aim of this study was to evaluate the influence of nitrate and carbon concentrations on the kinetic parameters of nitrate reduction as well as nitrous oxide emissions in river sediments in a tributary of the Marne (the Seine basin, France). In order to determine these rates, we used flow-through reactors (FTRs) and slurry incubations; flow-through reactors allow determination of rates on intact sediment slices under controlled conditions compared to sediment homogenization in the often used slurry technique. Maximum nitrate reduction rates (R(m)) ranged between 3.0 and 7.1microg Ng(-1)h(-1), and affinity constant (K(m)) ranged from 7.4 to 30.7mg N-NO(3)(-)L(-1). These values were higher in slurry incubations with an R(m) of 37.9microg Ng(-1)h(-1) and a K(m) of 104mg N-NO(3)(-)L(-1). Nitrous oxide production rates did not follow Michaelis-Menten kinetics, and we deduced a rate constant with an average of 0.7 and 5.4ng Ng(-1)h(-1) for FTR and slurry experiments respectively. The addition of carbon (as acetate) showed that carbon was not limiting nitrate reduction rates in these sediments. Similar rates were obtained for FTR and slurries with carbon addition, confirming the hypothesis that homogenization increases rates due to release of and increasing access to carbon in slurries. Nitrous oxide production rates in FTR with carbon additions were low and represented less than 0.01% of the nitrate reduction rates and were even negligible in slurries. Maximum nitrate reduction rates revealed seasonality with high potential rates in fall and winter and low rates in late spring and summer. Under optimal conditions (anoxia, non-limiting nitrate and carbon), nitrous oxide emission rates were low, but significant (0.01% of the nitrate reduction rates). Copyright 2009 Elsevier Ltd. All rights reserved.

  6. Determination of oxygen diffusion kinetics during thin film ruthenium oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Coloma Ribera, R., E-mail: r.colomaribera@utwente.nl; Kruijs, R. W. E. van de; Yakshin, A. E.; Bijkerk, F. [MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede (Netherlands)

    2015-08-07

    In situ X-ray reflectivity was used to reveal oxygen diffusion kinetics for thermal oxidation of polycrystalline ruthenium thin films and accurate determination of activation energies for this process. Diffusion rates in nanometer thin RuO{sub 2} films were found to show Arrhenius behaviour. However, a gradual decrease in diffusion rates was observed with oxide growth, with the activation energy increasing from about 2.1 to 2.4 eV. Further exploration of the Arrhenius pre-exponential factor for diffusion process revealed that oxidation of polycrystalline ruthenium joins the class of materials that obey the Meyer-Neldel rule.

  7. Kinetic Study of Oxygen Adsorption over Nanosized Au/γ-Al2O3 Supported Catalysts under Selective CO Oxidation Conditions

    Directory of Open Access Journals (Sweden)

    George Karaiskakis

    2012-04-01

    Full Text Available O2 adsorption is a key process for further understanding the mechanism of selective CO oxidation (SCO on gold catalysts. Rate constants related to the elementary steps of O2 adsorption, desorption and surface bonding, as well as the respective activation energies, over a nanosized Au/γ-Al2O3 catalyst, were determined by Reversed-Flow Inverse Gas Chromatography (RF-IGC. The present study, carried-out in a wide temperature range (50–300 °C, both in excess as well as in the absence of H2, resulted in mechanistic insights and kinetic as well as energetic comparisons, on the sorption processes of SCO reactants. In the absence of H2, the rate of O2 binding, over Au/γ-Al2O3, drastically changes with rising temperature, indicating possible O2 dissociation at elevated temperatures. H2 facilitates stronger O2 bonding at higher temperatures, while low temperature binding remains practically unaffected. The lower energy barriers observed, under H2 rich conditions, can be correlated to O2 dissociation after hydrogenation. Although, H2 enhances both selective CO reactant’s desorption, O2 desorption is more favored than that of CO, in agreement with the well-known mild bonding of SCO reactant’s at lower temperatures. The experimentally observed drastic change in the strength of CO and O2 binding is consistent both with well-known high activity of SCO at ambient temperatures, as well as with the loss of selectivity at higher temperatures.

  8. Kinetic Study of Oxygen Adsorption over Nanosized Au/γ-Al2O3 Supported Catalysts under Selective CO Oxidation Conditions

    Directory of Open Access Journals (Sweden)

    George Karaiskakis

    2012-04-01

    Full Text Available O2 adsorption is a key process for further understanding the mechanism of selective CO oxidation (SCO on gold catalysts. Rate constants related to the elementary steps of O2 adsorption, desorption and surface bonding, as well as the respective activation energies, over a nanosized Au/γ-Al2O3 catalyst, were determined by Reversed-Flow Inverse Gas Chromatography (RF-IGC. The present study, carried-out in a wide temperature range (50–300 °C, both in excess as well as in the absence of H2, resulted in mechanistic insights and kinetic as well as energetic comparisons, on the sorption processes of SCO reactants. In the absence of H2, the rate of O2 binding, over Au/γ-Al2O3, drastically changes with rising temperature, indicating possible O2 dissociation at elevated temperatures. H2 facilitates stronger O2 bonding at higher temperatures, while low temperature binding remains practically unaffected. The lower energy barriers observed, under H2 rich conditions, can be correlated to O2 dissociation after hydrogenation. Although, H2 enhances both selective CO reactant’s desorption, O2 desorption is more favored than that of CO, in agreement with the well-known mild bonding of SCO reactant’s at lower temperatures. The experimentally observed drastic change in the strength of CO and O2 binding is consistent both with well-known high activity of SCO at ambient temperatures, as well as with the loss of selectivity at higher temperatures.

  9. Adsorption mechanism and kinetics of azo dye chemicals on oxide nanotubes: a case study using porous CeO_2 nanotubes

    International Nuclear Information System (INIS)

    Wu, Junshu; Wang, Jinshu; Du, Yucheng; Li, Hongyi; Jia, Xinjian

    2016-01-01

    Metal oxide nanotubes are believed to be promising materials with adsorption functionality for water purification due to their synergistic effect of the overall microscale morphology for easy separation and nanoscale surface characters providing enough surface active absorption sites. This work shows the synthesis of uniform hierarchical porous CeO_2 nanotubes via nanowire-directed templating method and describes the adsorption behavior of CeO_2 nanotubes for a typical azo dye Congo red which has resistance to oxidation and decoloration in natural conditions. Fourier transform infrared spectroscopy spectra provided the evidence that Congo red was successfully coated on the surface of CeO_2 nanotubes by both bidentate-type bridge link of Ce"4"+ cations from sulfonate SO_3"− groups and the electrostatic attraction between the protonated surface generated by oxygen vacancies and dissociated sulfonate groups. The adsorption kinetic data fitted well to the pseudo-second-order kinetic equation, whereas the Langmuir isotherm equation exhibited better correlation with the experimental data. The calculated maximum adsorption capacity from the isothermal model was 362.32 mg/g. In addition, the prepared CeO_2 nanotubes exhibited good recyclability and reusability as highly efficient adsorbents for Congo red removal after regeneration. These favorable performances enable the obtained CeO_2 nanotubes to be promising materials for dye removal from aqueous solution.Graphical AbstractCeO_2 nanotubes composed of crystallized nanoparticles exhibit well adsorption ability for a typical azo dye Congo red.

  10. A kinetic and mechanistic study on the oxidation of l-methionine and N-acetyl l-methionine by cerium(IV in sulfuric acid medium

    Directory of Open Access Journals (Sweden)

    T. Sumathi

    2016-09-01

    Full Text Available The kinetics of oxidation of l-methionine and N-acetyl l-methionine by Ce(IV in sulfuric acid–sulfate media in the range of 288.1–298.1 K has been investigated. The major oxidation products of methionine and N-acetyl l-methionine have been identified as methionine sulfoxide and N-acetyl methionine sulfoxide. The major oxidation products have been confirmed by qualitative analysis and boiling point. The reaction was first order with respect to l-methionine, N-acetyl l-methionine and Ce(IV. Increase in [H+], ionic strength and HSO4- did not affect the reaction rate. Under the experimental conditions, Ce4+ was the effective oxidizing species of cerium. Increase in dielectric constant of the medium decreased the reaction rate. Under nitrogen atmosphere, the reaction system can initiate polymerization of acrylonitrile, indicating the generation of free radicals. Activation parameters associated with the overall reaction have been calculated.

  11. Studies of combustion kinetics and mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Gutman, D. [Catholic Univ. of America, Washington, DC (United States)

    1993-12-01

    The objective of the current research is to gain new quantitative knowledge of the kinetics and mechanisms of polyatomic free radicals which are important in hydrocarbon combustion processes. The special facility designed and built for these (which includes a heatable tubular reactor coupled to a photoionization mass spectrometer) is continually being improved. Where possible, these experimental studies are coupled with theoretical ones, sometimes conducted in collaboration with others, to obtain an improved understanding of the factors determining reactivity. The decomposition of acetyl radicals, isopropyl radicals, and n-propyl radicals have been studied as well as the oxidation of methylpropargyl radicals.

  12. Kinetic Studies of Iron Deposition Catalyzed by Recombinant Human Liver Heavy, and Light Ferritins and Azotobacter Vinelandii Bacterioferritin Using O2 and H2O2 as Oxidants

    Science.gov (United States)

    Bunker, Jared; Lowry, Thomas; Davis, Garrett; Zhang, Bo; Brosnahan, David; Lindsay, Stuart; Costen, Robert; Choi, Sang; Arosio, Paolo; Watt, Gerald D.

    2005-01-01

    The discrepancy between predicted and measured H2O2 formation during iron deposition with recombinant heavy human liver ferritin (rHF) was attributed to reaction with the iron protein complex [Biochemistry 40 (2001) 10832-10838]. This proposal was examined by stopped-flow kinetic studies and analysis for H2O2 production using (1) rHF, and Azotobacter vinelandii bacterial ferritin (AvBF), each containing 24 identical subunits with ferroxidase centers; (2) site-altered rHF mutants with functional and dysfunctional ferroxidase centers; and (3) rccombinant human liver light ferritin (rLF), containing 110 ferroxidase center. For rHF, nearly identical pseudo-first-order rate constants of 0.18 per second at pH 7.5 were measured for Fe(2+) oxidation by both O2 and H2O2, but for rLF, the rate with O2 was 200-fold slower than that for H2O2 (k-0.22 per second). A Fe(2+)/O2 stoichiometry near 2.4 was measured for rHF and its site altered forms, suggesting formation of H2O2. Direct measurements revealed no H2O2 free in solution 0.5-10 min after all Fe(2+) was oxidized at pH 6.5 or 7.5. These results are consistent with initial H2O2 formation, which rapidly reacts in a secondary reaction with unidentified solution components. Using measured rate constants for rHF, simulations showed that steady-state H2O2 concentrations peaked at 14 pM at approx. 600 ms and decreased to zero at 10-30 s. rLF did not produce measurable H2O2 but apparently conducted the secondary reaction with H2O2. Fe(2+)/O2 values of 4.0 were measured for AvBF. Stopped-flow measurements with AvBF showed that both H2O2 and O2 react at the same rate (k=0.34 per second), that is faster than the reactions with rHF. Simulations suggest that AvBF reduces O2 directly to H2O without intermediate H2O2 formation.

  13. Kinetic and reaction pathways of methanol oxidation on platinum

    International Nuclear Information System (INIS)

    McCabe, R.W.; McCready, D.F.

    1986-01-01

    Methanol oxidation kinetics were measured on Pt wires in a flow reactor at pressures between 30 and 130 Pa. The kinetics were measured as a function of oxygen-to-methanol equivalence ratio phi and wire temperature. In methanol-lean feeds (phi 2 CO, CO 2 , and H 2 O were the only products; in methanol-rich feeds (phi > 1), CO, H 2 , H 2 CO, CO 2 , and H 2 O were observed. Experiments with 18 O 2 showed that the principal methanol oxidation pathway does not involve C-O bond dissociation. However, the 18 O 2 experiments, together with other features of the methanol oxidation data, also provided evidence for a minor oxidation pathway (accounting for less than 1% of the product CO 2 ) which proceeds through a carbon intermediate. A mathematical model is presented which describes the principal CH 3 OH oxidation pathway as a series reaction involving adsorbed H 2 CO and CO intermediates. Consistent with experimental results, the model predicts that inhibition by adsorbed CO should be weaker for CH 3 OH and H 2 CO oxidation than for CO oxidation. 34 references, 10 figures, 2 tables

  14. Fenton and Fenton-like oxidation of pesticide acetamiprid in water samples: kinetic study of the degradation and optimization using response surface methodology.

    Science.gov (United States)

    Mitsika, Elena E; Christophoridis, Christophoros; Fytianos, Konstantinos

    2013-11-01

    The aims of this study were (a) to evaluate the degradation of acetamiprid with the use of Fenton reaction, (b) to investigate the effect of different concentrations of H2O2 and Fe(2+), initial pH and various iron salts, on the degradation of acetamiprid and (c) to apply response surface methodology for the evaluation of degradation kinetics. The kinetic study revealed a two-stage process, described by pseudo- first and second order kinetics. Different H2O2:Fe(2+) molar ratios were examined for their effect on acetamiprid degradation kinetics. The ratio of 3 mg L(-1) Fe(2+): 40 mg L(-1) H2O2 was found to completely remove acetamiprid at less than 10 min. Degradation rate was faster at lower pH, with the optimal value at pH 2.9, while Mohr salt appeared to degrade acetamiprid faster. A central composite design was selected in order to observe the effects of Fe(2+) and H2O2 initial concentration on acetamiprid degradation kinetics. A quadratic model fitted the experimental data, with satisfactory regression and fit. The most significant effect on the degradation of acetamiprid, was induced by ferrous iron concentration followed by H2O2. Optimization, aiming to minimize the applied ferrous concentration and the process time, proposed a ratio of 7.76 mg L(-1) Fe(II): 19.78 mg L(-1) H2O2. DOC is reduced much more slowly and requires more than 6h of processing for 50% degradation. The use to zero valent iron, demonstrated fast kinetic rates with acetamiprid degradation occurring in 10 min and effective DOC removal. Copyright © 2013 Elsevier Ltd. All rights reserved.

  15. Isothermal Kinetics of Catalyzed Air Oxidation of Diesel Soot

    Directory of Open Access Journals (Sweden)

    R. Prasad

    2011-01-01

    Full Text Available To comply with the stringent emission regulations on soot, diesel vehicles manufacturers more and more commonly use diesel particulate filters (DPF. These systems need to be regenerated periodically by burning soot that has been accumulated during the loading of the DPF. Design of the DPF requires rate of soot oxidation. This paper describes the kinetics of catalytic oxidation of diesel soot with air under isothermal conditions. Kinetics data were collected in a specially designed mini-semi-batch reactor. Under the high air flow rate assuming pseudo first order reaction the activation energy of soot oxidation was found to be, Ea = 160 kJ/ mol. ©2010 BCREC UNDIP. All rights reserved(Received: 14th June 2010, Revised: 18th July 2010, Accepted: 9th August 2010[How to Cite: R. Prasad, V.R. Bella. (2010. Isothermal Kinetics of Catalyzed Air Oxidation of Diesel Soot. Bulletin of Chemical Reaction Engineering and Catalysis, 5(2: 95-101. doi:10.9767/bcrec.5.2.796.95-101][DOI:http://dx.doi.org/10.9767/bcrec.5.2.796.95-101 || or local:  http://ejournal.undip.ac.id/index.php/bcrec/article/view/796]Cited by in: ACS 1 |

  16. Kinetic investigations of quinoline oxidation by ferrate(VI).

    Science.gov (United States)

    Luo, Zhiyong; Li, Xueming; Zhai, Jun

    2016-01-01

    Quinoline is considered as one of the most toxic and carcinogenic compounds and is commonly found in industrial wastewaters, which require treatment before being discharged. Removal of quinoline by the use of an environmentally friendly oxidant, potassium ferrate(VI) (K2FeO4), was assessed by studying the kinetics of the oxidation of quinoline by ferrate(VI) (Fe(VI)) as a function of pH (8.53-10.53) and temperature (21-36°C) in this work. The reaction of quinoline with Fe(VI) was found to be first order in Fe(VI), half order in quinoline, and 1.5 order overall. The observed rate constant at 28°C decreased non-linearly from 0.5334 to 0.2365 M(-0.5) min(-1) with an increase in pH from 8.53 to 10.03. Considering the equilibria of Fe(VI) and quinoline, the reaction between quinoline and Fe(VI) contained two parallel reactions under the given pH conditions. The individual rate constants of these two reactions were determined. The results indicate that the protonated species of Fe(VI) reacts more quickly with quinoline than the deprotonated form of Fe(VI). The reaction activation energy Ea was obtained to be 51.44 kJ·mol(-1), and it was slightly lower than that of conventional chemical reaction. It reveals that the oxidation of quinoline by Fe(VI) is feasible in the routine water treatment.

  17. Reverse Stability Kinetics of Meat Pigment Oxidation in Aqueous Extract from Fresh Beef.

    Science.gov (United States)

    Frelka, John C; Phinney, David M; Wick, Macdonald P; Heldman, Dennis R

    2017-12-01

    The use of kinetic models is an evolving approach to describing quality changes in foods during processes, including storage. Previous studies indicate that the oxidation rate of myoglobin is accelerated under frozen storage conditions, a phenomenon termed reverse stability. The goal of this study was to develop a model for meat pigment oxidation to incorporate the phenomenon of reverse stability. In this investigation, the model system was an aqueous extract from beef which was stored under a range of temperatures, both unfrozen and frozen. The kinetic analysis showed that in unfrozen solutions, the temperature dependence of oxidation rate followed Arrhenius kinetics. However, under in frozen solutions the rate of oxidation increased with decreasing temperature until reaching a local maximum around -20 °C. The addition of NaCl to the model system increased oxidation rates at all temperatures, even above the initial freezing temperature. This observation suggests that this reaction is dependent on the ionic strength of the solution as well as temperature. The mechanism of this deviant kinetic behavior is not fully understood, but this study shows that the interplay of temperature and composition on the rate of oxidation of meat pigments is complicated and may involve multiple mechanisms. A better understanding of the kinetics of quality loss in a meat system allows for a re-examination of the current recommendations for frozen storage. The deviant kinetic behavior observed in this study indicates that the relationship between quality loss and temperature in a frozen food is not as simple as once thought. Product-specific recommendations could be implemented in the future that would allow for a decrease in energy consumption without a significant loss of quality. © 2017 Institute of Food Technologists®.

  18. A feasible kinetic model for the hydrogen oxidation on ruthenium electrodes

    International Nuclear Information System (INIS)

    Rau, M.S.; Gennero de Chialvo, M.R.; Chialvo, A.C.

    2010-01-01

    The hydrogen oxidation reaction (hor) was studied on a polycrystalline ruthenium electrode in H 2 SO 4 solution at different rotation rates (ω). The experimental polarization curves recorded on steady state show the existence of a maximum current with a non-linear dependence of the current density on ω 1/2 . On the basis of the Tafel-Heyrovsky-Volmer kinetic mechanism, coupled with a process of inhibition of active sites by the reversible electroadsorption of hydroxyl species, it was possible to appropriately describe the origin of the maximum current. The corresponding set of kinetic parameters was also calculated from the correlation of the experimental results with the proposed kinetic model.

  19. Adsorption mechanism and kinetics of azo dye chemicals on oxide nanotubes: a case study using porous CeO{sub 2} nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Junshu; Wang, Jinshu, E-mail: wangjsh@bjut.edu.cn; Du, Yucheng; Li, Hongyi; Jia, Xinjian [Beijing University of Technology, School of Materials Science and Engineering (China)

    2016-07-15

    Metal oxide nanotubes are believed to be promising materials with adsorption functionality for water purification due to their synergistic effect of the overall microscale morphology for easy separation and nanoscale surface characters providing enough surface active absorption sites. This work shows the synthesis of uniform hierarchical porous CeO{sub 2} nanotubes via nanowire-directed templating method and describes the adsorption behavior of CeO{sub 2} nanotubes for a typical azo dye Congo red which has resistance to oxidation and decoloration in natural conditions. Fourier transform infrared spectroscopy spectra provided the evidence that Congo red was successfully coated on the surface of CeO{sub 2} nanotubes by both bidentate-type bridge link of Ce{sup 4+} cations from sulfonate SO{sub 3}{sup −} groups and the electrostatic attraction between the protonated surface generated by oxygen vacancies and dissociated sulfonate groups. The adsorption kinetic data fitted well to the pseudo-second-order kinetic equation, whereas the Langmuir isotherm equation exhibited better correlation with the experimental data. The calculated maximum adsorption capacity from the isothermal model was 362.32 mg/g. In addition, the prepared CeO{sub 2} nanotubes exhibited good recyclability and reusability as highly efficient adsorbents for Congo red removal after regeneration. These favorable performances enable the obtained CeO{sub 2} nanotubes to be promising materials for dye removal from aqueous solution.Graphical AbstractCeO{sub 2} nanotubes composed of crystallized nanoparticles exhibit well adsorption ability for a typical azo dye Congo red.

  20. Acid-catalyzed kinetics of indium tin oxide etching

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Jae-Hyeok; Kim, Seong-Oh; Hilton, Diana L. [School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 (Singapore); Centre for Biomimetic Sensor Science, Nanyang Technological University, 50 Nanyang Drive, 637553 (Singapore); Cho, Nam-Joon, E-mail: njcho@ntu.edu.sg [School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 (Singapore); Centre for Biomimetic Sensor Science, Nanyang Technological University, 50 Nanyang Drive, 637553 (Singapore); School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, 637459 (Singapore)

    2014-08-28

    We report the kinetic characterization of indium tin oxide (ITO) film etching by chemical treatment in acidic and basic electrolytes. It was observed that film etching increased under more acidic conditions, whereas basic conditions led to minimal etching on the time scale of the experiments. Quartz crystal microbalance was employed in order to track the reaction kinetics as a function of the concentration of hydrochloric acid and accordingly solution pH. Contact angle measurements and atomic force microscopy experiments determined that acid treatment increases surface hydrophilicity and porosity. X-ray photoelectron spectroscopy experiments identified that film etching is primarily caused by dissolution of indium species. A kinetic model was developed to explain the acid-catalyzed dissolution of ITO surfaces, and showed a logarithmic relationship between the rate of dissolution and the concentration of undisassociated hydrochloric acid molecules. Taken together, the findings presented in this work verify the acid-catalyzed kinetics of ITO film dissolution by chemical treatment, and support that the corresponding chemical reactions should be accounted for in ITO film processing applications. - Highlights: • Acidic conditions promoted indium tin oxide (ITO) film etching via dissolution. • Logarithm of the dissolution rate depended linearly on the solution pH. • Acid treatment increased ITO surface hydrophilicity and porosity. • ITO film etching led to preferential dissolution of indium species over tin species.

  1. Steam oxidation of ferritic steels: kinetics and microestructure

    Directory of Open Access Journals (Sweden)

    Aríztegui, A.

    2000-06-01

    Full Text Available The ferritic 2.25Cr–1Mo steel has been subjected to isothermal and non-isothermal oxidation treatments in water steam at several temperatures ranging from 550 to 700 °C for up to 56 days. Under isothermal conditions this steel follows a parabolic oxidation kinetics, with an activation energy of 324 kJ mol–1. This value corresponds to an apparent activation energy for the global process, which includes both outward diffusion of Fe cations and inward diffusion of oxygen. The oxidation products present in the oxide scales, which were characterised by X-ray diffraction and SEM, are in total agreement with the Fe-O phase diagram. Thus, magnetite is the most stable oxide at low temperatures and wustite starts to form above 570 °C. Further studies of the effect of cooling rate have shown that wustite formed at 700 °C transforms into magnetite during a slow cooling, whereas a rapid cooling inhibits this transformation to a certain extent. For non-isothermal oxidation treatments consisting of a holding period at 550 °C followed by a single or double 4 hours exposure at 700 °C, the oxidation process seems to occur in sequence, thus presenting an additive effect of the oxidation treatments carried out at each temperature. This effect was observed both, for the type of oxide grown, and for the kinetics of the process. Microscopic observations of the oxide scales formed after the various oxidation treatments revealed that the oxide scales are constituted by sublayers of distinct microstructure and chemical composition changing from their surface to the substrate interface.

    Se han realizado tratamientos de oxidación isotermos y no isotermos a un acero ferrítico 2,25Cr–1Mo en vapor de agua, a temperaturas comprendidas entre 550 y 700 °C y tiempos de hasta 56 días. En condiciones isotermas, este acero tiene una cinética de oxidación parabólica, con una energía de activación de 324 kJ mol–1. Este valor corresponde a una energía de

  2. The Kinetics and Mechanism for the Oxidation of Nicotinic Acid by Peroxomonosulfate in Acidic Aqueous Medium

    Energy Technology Data Exchange (ETDEWEB)

    Agrawal, Anju; Sailani, Riya; Gupta, Beena; Khandelwal, C. L.; Sharma, P. D. [Univ. of Rajasthan, Jaipur (India)

    2012-04-15

    The kinetics of oxidation of nicotinic acid by peroxomonosulfate (PMS) has been studied in acetate buffers. Stoichiometry of the reaction corresponds to the reaction of one mole of the oxidant with a mole of nicotinic acid. N→O product has been confirmed both by UV visible and IR spectroscopy. The reaction is second order viz. first order with respect to each reactant. Activation parameters have also been evaluated. A plausible reaction mechanism is mentioned and the derived kinetic rate law accounts for experimental observations.

  3. The Kinetics and Mechanism for the Oxidation of Nicotinic Acid by Peroxomonosulfate in Acidic Aqueous Medium

    International Nuclear Information System (INIS)

    Agrawal, Anju; Sailani, Riya; Gupta, Beena; Khandelwal, C. L.; Sharma, P. D.

    2012-01-01

    The kinetics of oxidation of nicotinic acid by peroxomonosulfate (PMS) has been studied in acetate buffers. Stoichiometry of the reaction corresponds to the reaction of one mole of the oxidant with a mole of nicotinic acid. N→O product has been confirmed both by UV visible and IR spectroscopy. The reaction is second order viz. first order with respect to each reactant. Activation parameters have also been evaluated. A plausible reaction mechanism is mentioned and the derived kinetic rate law accounts for experimental observations

  4. Kinetics and Mechanism of Oxidation of Benzyl Alcohol by Benzimidazolium Fluorochromate

    Directory of Open Access Journals (Sweden)

    J. Dharmaraja

    2008-01-01

    Full Text Available The kinetics of oxidation of benzyl alcohol (BzOH by benzimidazolium fluorochromate (BIFC has been studied in 50% aqueous acetic acid medium at 308 K. The reaction is first order with respect to [oxidant] and [benzyl alcohol]. The reaction is catalysed by hydrogen ions. The decrease in dielectric constant of the medium increases the rate of the reaction. Addition of sodium perchlorate increases the rate of the reaction appreciably. No polymerization with acrylonitrile. The reaction has been conducted at four different temperature and the activation parameters were calculated. From the observed kinetic results a suitable mechanism was proposed.

  5. Oxidation kinetics of zircaloy-4 in the temperature range correspondent to alpha phase

    International Nuclear Information System (INIS)

    Medeiros, L.F.

    1975-12-01

    Oxidation kinetics of Zry-4 in the alpha phase is isothermally studied in the temperature range from 600 0 C to 800 0 C, by continuous and discontinuous gravimetric methods. The total mass gain during the oxidation takes place by two distinct ways: oxide formation and solid solution formation. The first one has been studied by microscopy: the latter by microhardness. The oxygen diffusion coefficients in the zirconium are experimentally determined by microhardness measurements and are compared with those obtained by the oxide layer thickness and by oxygen mass in the oxide. The oxygen diffusion coefficients in the oxide are obtained too by oxide layer thickness and by oxygen diffusivities in the alpha phase and compared with literature. (author)

  6. Enzyme catalyzed oxidative gelation of sugar beet pectin: Kinetics and rheology

    DEFF Research Database (Denmark)

    Abang Zaidel, Dayang Norulfairuz; Chronakis, Ioannis S.; Meyer, Anne S.

    2012-01-01

    Sugar beet pectin (SBP) is a marginally utilized co-processing product from sugar production from sugar beets. In this study, the kinetics of oxidative gelation of SBP, taking place via enzyme catalyzed cross-linking of ferulic acid moieties (FA), was studied using small angle oscillatory...

  7. Oxidation kinetics of a Pb-64 at.% In single-phase alloy

    International Nuclear Information System (INIS)

    Zhang, M.X.; Chang, Y.A.; Marcotte, V.C.

    1991-01-01

    The solid-state oxidation kinetics of a Pb-64 at.% IN(50 wt.%) single-phase alloy were studied from room temperature to 150C using AES (Auger Electron Spectroscopy) depth profiling technique. The general oxidation behavior of this alloy is different from that of a Pb-3 at.% In alloy but similar to that of a Pb-30 at.% In alloy. The oxide formed on this alloy is almost pure In oxide (In 2 O 3 ) with the possible existence of some In suboxide near the oxide/alloy interface. At room temperature, oxidation of the alloy follows a direct logarithmic law, and the results can be described by the model proposed previously by Zhang, Chang, and Marcotte. At temperatures higher than 75C, rapid oxidation occurred initially followed by a slower parabolic oxidation at longer time. These data were described quantitatively by the model which assumes the existence of short-circuit diffusion in addition to lattice diffusion in the oxide as proposed by Smeltzer, Haering, and Kirkaldy. The effects of alloy composition in the oxidation kinetics of (pb, In) alloy are also examined by comparing the data for Pb-3, 30, and 64 at.% In alloys

  8. A kinetic model of municipal sludge degradation during non-catalytic wet oxidation.

    Science.gov (United States)

    Prince-Pike, Arrian; Wilson, David I; Baroutian, Saeid; Andrews, John; Gapes, Daniel J

    2015-12-15

    Wet oxidation is a successful process for the treatment of municipal sludge. In addition, the resulting effluent from wet oxidation is a useful carbon source for subsequent biological nutrient removal processes in wastewater treatment. Owing to limitations with current kinetic models, this study produced a kinetic model which predicts the concentrations of key intermediate components during wet oxidation. The model was regressed from lab-scale experiments and then subsequently validated using data from a wet oxidation pilot plant. The model was shown to be accurate in predicting the concentrations of each component, and produced good results when applied to a plant 500 times larger in size. A statistical study was undertaken to investigate the validity of the regressed model parameters. Finally the usefulness of the model was demonstrated by suggesting optimum operating conditions such that volatile fatty acids were maximised. Copyright © 2015 Elsevier Ltd. All rights reserved.

  9. Experimental investigation on oxidation kinetics of germanium by ozone

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Xiaolei, E-mail: wangxiaolei@ime.ac.cn [Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029 (China); Zhao, Zhiqian; Xiang, Jinjuan [Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029 (China); Wang, Wenwu, E-mail: wangwenwu@ime.ac.cn [Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029 (China); Zhang, Jing, E-mail: zhangj@ncut.edu.cn [Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029 (China); Microelectronics Department, North China University of Technology, Beijing 100041 (China); Zhao, Chao; Ye, Tianchun [Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029 (China)

    2016-12-30

    Highlights: • Kinetics mechanism of Ge surface oxidation by ozone at low temperature is experimentally investigated. • The growth process contains initially linear growth region and following parabolic growth region. • The GeO{sub x} thickness vs. oxidation time plot obeys the well-known Deal-Grove or linear parabolic model. • The linear growth region includes the oxidation of two topmost Ge layers, and the oxidation of third layer and following layers of Ge is diffusion limited. • The activation energies for linear and parabolic regions are 0.04 and 0.55 eV, respectively. - Abstract: Oxidation kinetics of germanium surface by ozone at low temperature (≤400 °C) is experimentally investigated. The growth process contains two regions: initial linear growth region and following parabolic growth region. The GeO{sub x} thickness vs. oxidation time plot obeys the well-known Deal-Grove or linear parabolic model. The linear growth region contains reaction of oxygen atoms with surface bond and back bonds of outmost Ge layer. And the activation energy is experimentally estimated to be 0.06 eV. Such small activation energy indicates that the linear growth region is nearly barrier-less. The parabolic growth region starts when the oxygen atoms diffuse into back bonds of second outmost Ge layers. And the activation energy for this process is found to be 0.54 eV. Furthermore, in the ozone oxidation it is not O{sub 3} molecules but O radicals that go through the GeO{sub x} film.

  10. The kinetic of photoreactions in zinc oxide microrods

    Science.gov (United States)

    Fiedot, M.; Rac, O.; Suchorska-Woźniak, P.; Nawrot, W.; Teterycz, H.

    2016-01-01

    Zinc oxide is the oldest sensing material used in the chemical resistive gas sensors which allow to detect many gases, such as carbon oxide, nitrogen oxides and other. This material is also widely used in medicine and daily life as antibacterial agent. For this reason this semiconductor is often synthesized on the polymer substrates such as foils and textiles. In presented results zinc oxide was deposited on the surface of poly(ethylene terephthalate) foil to obtain antibacterial material. As synthesis method chemical bath deposition was chosen. The growth of zinc oxide structures was carried out in water solution of zinc nitrate (V) and hexamethylenetetramine in 90°C during 9 h. Because antibacterial properties of ZnO are strongly depended on photocatalytic and electric properties of this semiconductor impedance spectroscopy measurements were carried out. During the measurements material was tested with and without UV light to determinate the kinetic of photoreactions in zinc oxide. Moreover the composite was analyzed by XRD diffraction and scanning electron microscope. The X-ray analysis indicated that obtained material has the structure of wurtzite which is typical of zinc oxide. SEM images showed that on the PET foil microrods of ZnO were formed. The impedance spectroscopy measurements of ZnO layer showed that in UV light significant changes in the conductivity of the material are observed.

  11. The kinetic of photoreactions in zinc oxide microrods

    International Nuclear Information System (INIS)

    Fiedot, M; Rac, O; Suchorska-Woźniak, P; Nawrot, W; Teterycz, H

    2016-01-01

    Zinc oxide is the oldest sensing material used in the chemical resistive gas sensors which allow to detect many gases, such as carbon oxide, nitrogen oxides and other. This material is also widely used in medicine and daily life as antibacterial agent. For this reason this semiconductor is often synthesized on the polymer substrates such as foils and textiles. In presented results zinc oxide was deposited on the surface of poly(ethylene terephthalate) foil to obtain antibacterial material. As synthesis method chemical bath deposition was chosen. The growth of zinc oxide structures was carried out in water solution of zinc nitrate (V) and hexamethylenetetramine in 90°C during 9 h. Because antibacterial properties of ZnO are strongly depended on photocatalytic and electric properties of this semiconductor impedance spectroscopy measurements were carried out. During the measurements material was tested with and without UV light to determinate the kinetic of photoreactions in zinc oxide. Moreover the composite was analyzed by XRD diffraction and scanning electron microscope. The X-ray analysis indicated that obtained material has the structure of wurtzite which is typical of zinc oxide. SEM images showed that on the PET foil microrods of ZnO were formed. The impedance spectroscopy measurements of ZnO layer showed that in UV light significant changes in the conductivity of the material are observed

  12. Kinetics and mechanism of methane oxidation in supercritical water

    International Nuclear Information System (INIS)

    Rofer, C.K.; Streit, G.E.

    1988-10-01

    This project, is a Hazardous Waste Remedial Actions Program (HAZWRAP) Research and Development task being carried out by the Los Alamos National Laboratory. Its objective is to achieve an understanding of the technology for use in scaling up and applying oxidation in supercritical water as a viable process for treating a variety of Department of Energy Defense Programs (DOE-DP) waste streams. This report presents experimental results for the kinetics of the oxidation of methane and methanol in supercritical water and computer modeling results for the oxidation of carbonmonoxide and methane in supercritical water. The experimental and modeling results obtained to date on these one-carbon model compounds indicate that the mechanism of oxidation in supercritical water can be represented by free-radical reactions with appropriate modifications for high pressure and the high water concentration. If these current trends are sustained, a large body of existing literature data on the kinetics of elementary reactions can be utilized to predict the behavior of other compounds and their mixtures. 7 refs., 4 figs., 3 tabs

  13. Kinetics and mechanism of oxidation of glycine by iron(III)

    Indian Academy of Sciences (India)

    Kinetics and mechanism of oxidation of glycine by iron(III)-1,10-phenanthroline complex has been studied in perchloric acid medium. The reaction is first order with respect to iron(III) and glycine. An increase in (phenanthroline) increases the rate, while increase in [H+] decreases the rate. Hence it can be inferred that the ...

  14. Kinetics and mechanism of the oxidation of some vicinal and non ...

    Indian Academy of Sciences (India)

    Kinetics of oxidation of five vicinal and four non-vicinal diols, and two of their monoethers, by tetrabutylammonium tribromide (TBATB) has been studied. The vicinal diols yield products arising out of glycol-bond fission, while the non-vicinal diols produce the hydroxycarbonyl compounds. The reaction is first-order with ...

  15. Kinetics of the partial oxidation of methanol over a Fe-Mo catalyst

    NARCIS (Netherlands)

    Deshmukh, S.A.R.K.; Sint Annaland, van M.; Kuipers, J.A.M.

    2005-01-01

    The intrinsic steady-state kinetics of the partial oxidation of methanol to formaldehyde over a commercial Fe-Mo catalyst has been studied experimentally in a differentially operated reactor at temperatures of 230–260 °C, over a wide range of methanol and oxygen concentrations. The principal

  16. Kinetics of the partial oxidation of methanol over a Fe-Mo catalyst

    NARCIS (Netherlands)

    Deshmukh, S.A.R.K.; van Sint Annaland, M.; Kuipers, J.A.M.

    2005-01-01

    The intrinsic steady-state kinetics of the partial oxidation of methanol to formaldehyde over a commercial Fe-Mo catalyst has been studied experimentally in a differentially operated reactor at temperatures of 230¿260 °C, over a wide range of methanol and oxygen concentrations. The principal

  17. Sensitivity analysis in oxidation ditch modelling: the effect of variations in stoichiometric, kinetic and operating parameters on the performance indices

    NARCIS (Netherlands)

    Abusam, A.A.A.; Keesman, K.J.; Straten, van G.; Spanjers, H.; Meinema, K.

    2001-01-01

    This paper demonstrates the application of the factorial sensitivity analysis methodology in studying the influence of variations in stoichiometric, kinetic and operating parameters on the performance indices of an oxidation ditch simulation model (benchmark). Factorial sensitivity analysis

  18. Ammonia oxidation kinetics and temperature sensitivity of a natural marine community dominated by Archaea

    Science.gov (United States)

    Horak, Rachel E A; Qin, Wei; Schauer, Andy J; Armbrust, E Virginia; Ingalls, Anitra E; Moffett, James W; Stahl, David A; Devol, Allan H

    2013-01-01

    Archaeal ammonia oxidizers (AOAs) are increasingly recognized as prominent members of natural microbial assemblages. Evidence that links the presence of AOA with in situ ammonia oxidation activity is limited, and the abiotic factors that regulate the distribution of AOA natural assemblages are not well defined. We used quantitative PCR to enumerate amoA (encodes α-subunit of ammonia monooxygenase) abundances; AOA amoA gene copies greatly outnumbered ammonia-oxidizing bacteria and amoA transcripts were derived primarily from AOA throughout the water column of Hood Canal, Puget Sound, WA, USA. We generated a Michaelis–Menten kinetics curve for ammonia oxidation by the natural community and found that the measured Km of 98±14 nmol l−1 was close to that for cultivated AOA representative Nitrosopumilus maritimus SCM1. Temperature did not have a significant effect on ammonia oxidation rates for incubation temperatures ranging from 8 to 20 °C, which is within the temperature range for depths of measurable ammonia oxidation at the site. This study provides substantial evidence, through both amoA gene copies and transcript abundances and the kinetics response, that AOA are the dominant active ammonia oxidizers in this marine environment. We propose that future ammonia oxidation experiments use a Km for the natural community to better constrain ammonia oxidation rates determined with the commonly used 15NH4+ dilution technique. PMID:23657360

  19. Oxidation Kinetics of Cast TiAl3

    Science.gov (United States)

    Smialek, J. L.; Humphrey, D. L.

    1992-01-01

    The isothermal oxidation kinetics of the TiAl3 compound over a wide temperature range is documented, and these rates are related to exclusive alpha-Al2O3 scale growth. The specific weight change vs time curves are shown. Two abnormalities are immediately apparent. One is that a rapid initial uptake of oxygen occurs at times less than 5 h, followed by a lower oxidation rate at longer times, for tests at 900 C and below. The other is that the final weight changes for the 700, 800, and 900 C tests are not in the sequence expected with respect to temperature. Isothermal oxidation of drop cast TiAl above 1000 C was found to exhibit parabolic oxidation controlled by protective alpha-Al2O3 scale formation. TiAl is the only phase in the binary Ti-Al system that forms exclusive scales of alpha-Al2O3 in isothermal oxidation. High anomalous rates at short times and at temperatures below 1000 C resulted from the internal oxidation of a second phase of aluminum.

  20. Effect of a 1-hour single bout of moderate-intensity exercise on fat oxidation kinetics.

    Science.gov (United States)

    Chenevière, Xavier; Borrani, Fabio; Ebenegger, Vincent; Gojanovic, Boris; Malatesta, Davide

    2009-12-01

    The present study aimed to examine the effects of a prior 1-hour continuous exercise bout (CONT) at an intensity (Fat(max)) that elicits the maximal fat oxidation (MFO) on the fat oxidation kinetics during a subsequent submaximal incremental test (IncrC). Twenty moderately trained subjects (9 men and 11 women) performed a graded test on a treadmill (Incr), with 3-minute stages and 1-km.h(-1) increments. Fat oxidation was measured using indirect calorimetry and plotted as a function of exercise intensity. A mathematical model (SIN) including 3 independent variables (dilatation, symmetry, and translation) was used to characterize the shape of fat oxidation kinetics and to determine Fat(max) and MFO. On a second visit, the subjects performed CONT at Fat(max) followed by IncrC. After CONT performed at 57% +/- 3% (means +/- SE) maximal oxygen uptake (Vo(2max)), the respiratory exchange ratio during IncrC was lower at every stage compared with Incr (P rates from 35% to 70% Vo(2max) (P .05), whereas symmetry tended to be greater in IncrC (P = .096). This study showed that the prior 1-hour continuous moderate-intensity exercise bout increased Fat(max), MFO, and fat oxidation rates over a wide range of intensities during the postexercise incremental test. Moreover, the shape of the postexercise fat oxidation kinetics tended to have a rightward asymmetry.

  1. Evolution of zirconium-based precipitates during oxidation and irradiation of Zr alloys (impact on the oxidation kinetics of Zr alloys)

    International Nuclear Information System (INIS)

    Pecheur, Dominique

    1993-01-01

    As the oxidation of the zircaloy sheath is one of the factors which limit the lifetime of nuclear fuel rods, this research thesis aims at a better knowledge of the involved oxidation mechanisms and to improve the oxidation resistance in order to increase rod lifetime. Oxidation test performed in autoclave to study zirconium alloy oxidation without irradiation showed that oxidation kinetics is significantly higher under irradiation. This difference is attributed to a different evolution of the sheath material under irradiation. Thus, this research focused on the role of precipitates in the oxidation process of zirconium alloys, and on the impact of their amorphization on this oxidation. After a detailed description of the context and of the various implemented experimental means, the author presents the results obtained on a reference material on the one hand, and on a material irradiated by ions or neutrons on the other hand. More particularly, the author studied in these both cases the introduction of precipitates in the oxide layer by transmission electronic microscopy, and oxidation kinetics obtained in autoclave on these two types of material. He reports the analysis of the introduction of precipitates in the oxide layer formed on the reference material. He proposes interpretations for the evolutions of structure and of chemical compositions of precipitates in the oxide layer. These observations are then correlated with oxidation kinetics in these alloys. Finally, the author discusses results of oxidation tests obtained on materials irradiated by ions and by neutrons [fr

  2. Generalized kinetic model of reduction of molecular oxidant by metal containing redox

    International Nuclear Information System (INIS)

    Kravchenko, T.A.

    1986-01-01

    Present work is devoted to kinetics of reduction of molecular oxidant by metal containing redox. Constructed generalized kinetic model of redox process in the system solid redox - reagent solution allows to perform the general theoretical approach to research and to obtain new results on kinetics and mechanism of interaction of redox with oxidants.

  3. Development of Kinetics for Soot Oxidation at High Pressures Under Fuel-Lean Conditions

    Energy Technology Data Exchange (ETDEWEB)

    Lighty, JoAnn [Univ. of Utah, Salt Lake City, UT (United States); Vander Wal, Randy [Pennsylvania State Univ., University Park, PA (United States)

    2014-04-21

    The focus of the proposed research was to develop kinetic models for soot oxidation with the hope of developing a validated, predictive, multi-­scale, combustion model to optimize the design and operation of evolving fuels in advanced engines for transportation applications. The work focused on the relatively unstudied area of the fundamental mechanism for soot oxidation. The objectives include understanding of the kinetics of soot oxidation by O2 under high pressure which require: 1) development of intrinsic kinetics for the surface oxidation, which takes into account the dependence of reactivity upon nanostructure and 2) evolution of nanostructure and its impact upon oxidation rate and 3) inclusion of internal surface area development and possible fragmentation resulting from pore development and /or surface oxidation. These objectives were explored for a variety of pure fuel components and surrogate fuels. This project was a joint effort between the University of Utah (UU) and Pennsylvania State University (Penn State). The work at the UU focuses on experimental studies using a two-­stage burner and a high- pressure thermogravimetric analyzer (TGA). Penn State provided HRTEM images and guidance in the fringe analysis algorithms and parameter quantification for the images. This report focuses on completion done under supplemental funding.

  4. Electro-oxidation of the dye azure B: kinetics, mechanism, and by-products.

    Science.gov (United States)

    Olvera-Vargas, Hugo; Oturan, Nihal; Aravindakumar, C T; Paul, M M Sunil; Sharma, Virender K; Oturan, Mehmet A

    2014-01-01

    In this work, the electrochemical degradation of the dye azure B in aqueous solutions was studied by electrochemical advanced oxidation processes (EAOPs), electro-Fenton, and anodic oxidation processes, using Pt/carbon-felt and boron-doped diamond (BDD)/carbon-felt cells with H₂O₂ electrogeneration. The higher oxidation power of the electro-Fenton (EF) process using BDD anode was demonstrated. The oxidative degradation of azure B by the electrochemically generated hydroxyl radicals ((•)OH) follows a pseudo-first-order kinetics. The apparent rate constants of the oxidation of azure B by (•)OH were measured according to pseudo-first-order kinetic model. The absolute rate constant of azure B hydroxylation reaction was determined by competition kinetics method and found to be 1.19 × 10(9) M(-1) s(-1). It was found that the electrochemical degradation of the dye leads to the formation of aromatic by-products which are then oxidized to aliphatic carboxylic acids before their almost mineralization to CO₂ and inorganic ions (sulfate, nitrate, and ammonium). The evolution of the TOC removal and time course of short-chain carboxylic acids during treatment were also investigated.

  5. Cholesterol photo-oxidation: A chemical reaction network for kinetic modeling.

    Science.gov (United States)

    Barnaba, Carlo; Rodríguez-Estrada, Maria Teresa; Lercker, Giovanni; García, Hugo Sergio; Medina-Meza, Ilce Gabriela

    2016-12-01

    In this work we studied the effect of polyunsaturated fatty acids (PUFAs) methyl esters on cholesterol photo-induced oxidation. The oxidative routes were modeled with a chemical reaction network (CRN), which represents the first application of CRN to the oxidative degradation of a food-related lipid matrix. Docosahexaenoic acid (DHA, T-I), eicosapentaenoic acid (EPA, T-II) and a mixture of both (T-III) were added to cholesterol using hematoporphyrin as sensitizer, and were exposed to a fluorescent lamp for 48h. High amounts of Type I cholesterol oxidation products (COPs) were recovered (epimers 7α- and 7β-OH, 7-keto and 25-OH), as well as 5β,6β-epoxy. Fitting the experimental data with the CRN allowed characterizing the associated kinetics. DHA and EPA exerted different effects on the oxidative process. DHA showed a protective effect to 7-hydroxy derivatives, whereas EPA enhanced side-chain oxidation and 7β-OH kinetic rates. The mixture of PUFAs increased the kinetic rates several fold, particularly for 25-OH. With respect to the control, the formation of β-epoxy was reduced, suggesting potential inhibition in the presence of PUFAs. Copyright © 2016 Elsevier Inc. All rights reserved.

  6. Comparison of NBG-18, NBG-17, IG-110 and IG-11 oxidation kinetics in air

    Science.gov (United States)

    Lee, Jo Jo; Ghosh, Tushar K.; Loyalka, Sudarshan K.

    2018-03-01

    The oxidation rates of several nuclear-grade graphites, NBG-18, NBG-17, IG-110 and IG-11, were measured in air using thermogravimetry. Kinetic parameters and oxidation behavior for each grade were compared by coke type, filler grain size and microstructure. The thickness of the oxidized layer for each grade was determined by layer peeling and direct density measurements. The results for NBG-17 and IG-11 were compared with those available in the literature and our recently reported results for NBG-18 and IG-110 oxidation in air. The finer-grained graphites IG-110 and IG-11 were more oxidized than medium-grained NBG-18 and NBG-17 because of deeper oxidant penetration, higher porosity and higher probability of available active sites. Variation in experimental conditions also had a marked effect on the reported kinetic parameters by several studies. Kinetic parameters such as activation energy and transition temperature were sensitive to air flow rates as well as sample size and geometry.

  7. Oxidation kinetics of crystal violet by potassium permanganate in acidic medium

    Science.gov (United States)

    Khan, Sameera Razi; Ashfaq, Maria; Mubashir; Masood, Summyia

    2016-05-01

    The oxidation kinetics of crystal violet (a triphenylmethane dye) by potassium permanganate was focused in an acidic medium by the spectrophotometric method at 584 nm. The oxidation reaction of crystal violet by potassium permanganate is carried out in an acidic medium at different temperatures ranging within 298-318 K. The kinetic study was carried out to investigate the effect of the concentration, ionic strength and temperature. The reaction followed first order kinetics with respect to potassium permanganate and crystal violet and the overall rate of the reaction was found to be second order. Thermodynamic activation parameters like the activation energy ( E a), enthalpy change (Δ H*), free energy change (Δ G*), and entropy change (Δ S*) have also been evaluated.

  8. Comparison of the Isothermal Oxidation Behavior of As-Cast Cu-17%Cr and Cu-17%Cr-5%Al. Part 1; Oxidation Kinetics

    Science.gov (United States)

    Raj. Sai V.

    2008-01-01

    The isothermal oxidation kinetics of as-cast Cu-17%Cr and Cu-17%Cr-5%Al in air were studied between 773 and 1173 K under atmospheric pressure. These observations reveal that Cu- 17%Cr-5%Al oxidizes at significantly slower rates than Cu-17%Cr. The rate constants for the alloys were determined from generalized analyses of the data without an a priori assumption of the nature of the oxidation kinetics. Detailed analyses of the isothermal thermogravimetric weight change data revealed that Cu-17%Cr exhibited parabolic oxidation kinetics with an activation energy of 165.9 9.5 kJ mol-1. In contrast, the oxidation kinetics for the Cu-17%Cr- 5%Al alloy exhibited a parabolic oxidation kinetics during the initial stages followed by a quartic relationship in the later stages of oxidation. Alternatively, the oxidation behavior of Cu-17%CR- 5%Al could be better represented by a logarithmic relationship. The parabolic rate constants and activation energy data for the two alloys are compared with literature data to gain insights on the nature of the oxidation mechanisms dominant in these alloys.

  9. Comparison of the Isothermal Oxidation Behavior of As-Cast Cu-17 Percent Cr and Cu-17 Percent Cr-5 Percent Al. Part 1; Oxidation Kinetics

    Science.gov (United States)

    Raj, S. V.

    2008-01-01

    The isothermal oxidation kinetics of as-cast Cu-17%Cr and Cu-17%Cr-5%Al in air were studied between 773 and 1173 K under atmospheric pressure. These observations reveal that Cu-17%Cr-5%Al oxidizes at significantly slower rates than Cu-17%Cr. The rate constants for the alloys were determined from generalized analyses of the data without an a priori assumption of the nature of the oxidation kinetics. Detailed analyses of the isothermal thermogravimetric weight change data revealed that Cu-17%Cr exhibited parabolic oxidation kinetics with an activation energy of 165.9+/-9.5 kJ/mol. In contrast, the oxidation kinetics for the Cu-17%Cr-5%Al alloy exhibited a parabolic oxidation kinetics during the initial stages followed by a quartic relationship in the later stages of oxidation. Alternatively, the oxidation behavior of Cu-17%CR-5%Al could be better represented by a logarithmic relationship. The parabolic rate constants and activation energy data for the two alloys are compared with literature data to gain insights on the nature of the oxidation mechanisms dominant in these alloys.

  10. Highly efficient ultrasonic-assisted removal of Hg(II) ions on graphene oxide modified with 2-pyridinecarboxaldehyde thiosemicarbazone: Adsorption isotherms and kinetics studies.

    Science.gov (United States)

    Tadjarodi, Azadeh; Moazen Ferdowsi, Somayeh; Zare-Dorabei, Rouholah; Barzin, Ahmad

    2016-11-01

    A novel adsorbent, based on modifying graphene oxide (GO) chemically with 2-pyridinecarboxaldehyde thiosemicarbazone (2-PTSC) as ligand, was designed by facile process for removal of Hg(II) from aqueous solution. Characterization of the adsorbent was performed using various techniques, such as FT-IR, XRD, XPS, SEM and AFM analysis. The adsorption capacity was affected by variables such as adsorbent dosage, pH solution, Hg(2+) initial concentration and sonicating time. These variables were optimized by rotatable central composite design (CCD) under response surface methodology (RSM). The predictive model for Hg(II) adsorption was constructed and applied to find the best conditions at which the responses were maximized. In this conditions, the adsorption capacity of this adsorbent for Hg(2+) ions was calculated to be 309mgg(-1) that was higher than that of GO. Appling the ultrasound power combined with adsorption method was very efficient in shortening the removal time of Hg(2+) ions by enhancing the dispersion of adsorbent and metal ions in solution and effective interactions among them. The adsorption process was well described by second-order kinetic and Langmuir isotherm model in which the maximum adsorption capacity (Qm) was found to be 555mgg(-1) for adsorption of Hg(2+) ions over the obtained adsorbent. The performance of adsorbent was examined on the real wastewaters and confirmed the applicability of adsorbent for practical applications. Copyright © 2016 Elsevier B.V. All rights reserved.

  11. Kinetics of transuranium element oxidation-reduction reactions in solution

    International Nuclear Information System (INIS)

    Gourisse, D.

    1966-09-01

    A review of the kinetics of U, Np, Pu, Am oxidation-reduction reactions is proposed. The relations between the different activation thermodynamic functions (compensatory effect, formal entropy of the activated complex, magnitude of reactions velocities) are considered. The effects of acidity, ionic strength deuterium and mixed solvents polarity on reactions rates are described. The effect of different anions on reactions rates are explained by variations of the reaction standard free energy and variations of the activation free energy (coulombic interactions) resulting from the complexation of dissolved species by these anions. (author) [fr

  12. Oxidation kinetics of zirconium nitride. I. Planar symmetry

    International Nuclear Information System (INIS)

    Desmaison, Jean; Billy, Michel

    1976-01-01

    The oxidation behavior of ZrNsub(0.93) plates was investigated at temperatures in the range 625-800 deg C in oxygen over the pressure range 10-730 torr. The reaction product consists of monoclinic zirconia accompanied with trace amounts of cubic or tetragonal zirconia. Although the kinetic results are well interpreted by a Prout and Tompkins type model. The morphological observations suggest a transformation governed by a phase boundary reaction, this being confirmed by the oxygen pressure dependence on the rate law [fr

  13. [Flavonoid oxidation kinetics in aqueous and aqueous organic media in the presence of peroxidase, tyrosynase, and hemoglobin].

    Science.gov (United States)

    Barsukova, M E; Tokareva, A I; Buslova, T S; Malinina, L I; Veselova, I A; Shekhovtsova, T N

    2017-01-01

    The kinetics of oxidation reactions of flavonoids, quercetin, dihydroquercetin, and epicatechin has been studied in the presence of biocatalysts of different natures: horseradish peroxidase, mushroom tyrosinase, and hemoglobin from bull blood. Comparison of the kinetic parameters of the oxidation reaction showed that peroxidase appeared to be the most effective biocatalyst in these processes. The specificity of the enzyme for quercetin increased with increasing the polarity of the solvent in a series of ethanol–acetonitrile–dimethyl sulfoxide.

  14. Oxidation kinetics of amorphous AlxZr1−x alloys

    International Nuclear Information System (INIS)

    Weller, K.; Wang, Z.M.; Jeurgens, L.P.H.; Mittemeijer, E.J.

    2016-01-01

    The oxidation kinetics of amorphous Al x Zr 1−x alloys (solid solution) has been studied as function of the alloy composition (0.26 ≤ x ≤ 0.68) and the oxidation temperature (350 °C ≤ T ≤ 400 °C; at constant pO 2  = 1 × 10 5  Pa) by a combinatorial approach using spectroscopic ellipsometry (SE), Auger electron spectroscopy (AES) depth profiling, transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. Thermal oxidation of the am-Al x Zr 1−x alloys results in the formation of an amorphous oxide overgrowth with a thermodynamically preferred singular composition, corresponding to a constant Al ox /Zr ox ratio of 0.5. Both the solubility and the diffusivity of oxygen in the am-Al x Zr 1−x alloy substrate increase considerably with increasing Zr content, in particular for Zr contents above 49 at.% Zr. Strikingly, the oxidation kinetics exhibit a transition from parabolic oxide growth kinetics for Al-rich am-Al x Zr 1−x alloys (x ≥ 0.51) to linear oxide growth kinetics for Zr-rich am-Al x Zr 1−x alloys (x < 0.35). The underlying oxidation mechanism is discussed. It is concluded that the oxidation kinetics of the amorphous Al x Zr 1−x alloys for 0.26 ≤ x ≤ 0.68 and 350 °C ≤ T ≤ 400 °C are governed by: (i) the atomic mobilities of O and Al in the alloy substrate at the reacting oxide/alloy interface, (ii) the solubility of O in the substrate and (iii) the compositional constraint due to the thermodynamically preferred formation of an amorphous oxide phase of singular composition.

  15. Investigation of effect of air flow rate on Zircaloy-4 oxidation kinetics and breakaway phenomenon in air at 850 .deg. C

    International Nuclear Information System (INIS)

    Maeng, Yunhwan; Lee, Jaeyoung; Park, Sanggil

    2016-01-01

    This paper analyzed an effect of flow rate on oxidation kinetics of Zircaloy-4 in air at 850 .deg. C. In case of the oxidation of Zircaloy-4 in air at 850 .deg. C, acceleration of oxidation kinetics from parabolic to linear (breakaway phenomenon) occurs. Oxidation and breakaway kinetics of the Zircaloy-4 in air was experimentally studied by changing a flow rate of argon/air mixture. Tests were conducted at 850 .deg. C under constant ratio of argon and air. The effects of flow rate on the oxidation and breakaway kinetics was observed. This paper is based on a revised and considerably extended presentation given at the 21 st International Quench Workshop. The effects of flow conditions on the oxidation kinetics of Zircaloy-4 samples were explained with residence time and percent flow efficiency. In addition, several issues were observed from this study, interdiffusion at breakaway and deformation of oxide structure by breakaway phenomenon

  16. FT-IR kinetic and product study of the Br-radical initiated oxidation of α, β-unsaturated organic carbonyl compounds

    Science.gov (United States)

    Sauer, C. G.; Barnes, I.; Becker, K. H.

    Using the relative kinetic technique the kinetics of the gas-phase reactions of Br radicals with acrolein, methacrolein and methylvinyl ketone have been investigated at (301±3) K in 1013 mbar of (N 2+O 2) bath gas at varying proportions. In 1013 mbar of synthetic air the following rate coefficients have been obtained (in units of cm 3 molecule -1 s -1): acrolein (3.21±0.11)×10 -12; methacrolein (2.33±0.08)×10 -11; methyl vinyl ketone (1.87±0.06)×10 -11. This study represents the first determination of the rate coefficients for these compounds. As for other unsaturated hydrocarbons the rate coefficient with Br was found to increase with increasing partial pressure of O 2. From the product studies of the reactions it has been established that addition of Br radicals to the terminal C-atom is the major pathway in all three cases. However, for acrolein H atom abstraction from the -CO-H group is also significant. Mechanisms are proposed to explain the observed products, mainly β-brominated carbonyl compounds.

  17. Oxidation kinetics and auger microprobe analysis of some oxidized zirconium alloys

    International Nuclear Information System (INIS)

    Ploc, R.A.

    1989-01-01

    Oxidation kinetics at 300 o C in dry oxygen of 0.5 wt% binary alloys of iron, nickel, and chromium in zirconium were determined for several surface preparations. Further, chemical profiles of the oxides as they existed on the matrix and on the precipitates were obtained by sputtering and Auger electron analysis. The appearance of 'breakaway' oxidation was controlled by the surface finish of the alloy, a variable that could be used to eliminate the phenomenon for all alloys except the Zr/Ni binary, which required β-quenching to accomplish the same purpose. (author)

  18. In situ photoemission spectroscopy using synchrotron radiation for O2 translational kinetic energy induced oxidation processes of partially-oxidized Si(001) surfaces

    International Nuclear Information System (INIS)

    Teraoka, Yuden; Yoshigoe, Akitaka

    2001-01-01

    The influence of translational kinetic energy of incident O 2 molecules for the passive oxidation process of partially-oxidized Si(001) surfaces has been studied by photoemission spectroscopy. The translational kinetic energy of O 2 molecules was controlled up to 3 eV by a supersonic seed beam technique using a high temperature nozzle. Two translational kinetic energy thresholds (1.0 eV and 2.6 eV) were found out in accordance with the first-principles calculation for the oxidation of clean surfaces. Si-2p photoemission spectra measured in representative translational kinetic energies revealed that the translational kinetic energy dependent oxidation of dimers and the second layer (subsurface) backbonds were caused by the direct dissociative chemisorption of O 2 molecules. Moreover, the difference in chemical bonds for oxygen atoms was found out to be as low and high binding energy components in O-1s photoemission spectra. Especially, the low binding energy component increased with increasing the translational kinetic energy that indicates the translational kinetic energy induced oxidation in backbonds. (author)

  19. Kinetic studies on the hafnium nad deuterium

    International Nuclear Information System (INIS)

    Bing Wenzeng; Long Xinggui; Zhu Zuliang

    2009-04-01

    Through the method of reaction rate analysis in a constant volume reactor, the time dependence of the pressure drop of the hafnium deuteride formation are studied over a temperature range 573-873 K on a metal hydride thermodynamic and kinetic parameters measuring apparatus. The rate constants of the hafnium deuteride formation, which are 0.0530 s -1 , 0.0452 s -1 , 0.0319 s -1 , 0.0261 s -1 , are calculated at a serial temperatures of 573 K, 673 K, 773 K, 873 K and the initial pressure of 13 kPa. The activation energy of the reaction is (-10.1±1.5) kJ·mol -1 . Comparing the above results with those of titanium deuteride formation on the same measuring apparatus, the kinetic mechanism of the deuteride formation of hafnium and titanium is considered different. It is concluded that the reaction rate of hafnium absorbing deuterium may be controlled by phase transformation and surface oxidation. (authors)

  20. Characteristics of SME biodiesel-fueled diesel particle emissions and the kinetics of oxidation.

    Science.gov (United States)

    Jung, Heejung; Kittelson, David B; Zachariah, Michael R

    2006-08-15

    Biodiesel is one of the most promising alternative diesel fuels. As diesel emission regulations have become more stringent, the diesel particulate filter (DPF) has become an essential part of the aftertreatment system. Knowledge of kinetics of exhaust particle oxidation for alternative diesel fuels is useful in estimating the change in regeneration behavior of a DPF with such fuels. This study examines the characteristics of diesel particulate emissions as well as kinetics of particle oxidation using a 1996 John Deere T04045TF250 off-highway engine and 100% soy methyl ester (SME) biodiesel (B100) as fuel. Compared to standard D2 fuel, this B100 reduced particle size, number, and volume in the accumulation mode where most of the particle mass is found. At 75% load, number decreased by 38%, DGN decreased from 80 to 62 nm, and volume decreased by 82%. Part of this decrease is likely associated with the fact that the particles were more easily oxidized. Arrhenius parameters for the biodiesel fuel showed a 2-3times greater frequency factor and approximately 6 times higher oxidation rate compared to regular diesel fuel in the range of 700-825 degrees C. The faster oxidation kinetics should facilitate regeneration when used with a DPF.

  1. Zirconium metal-water oxidation kinetics. III. Oxygen diffusion in oxide and alpha Zircaloy phases

    International Nuclear Information System (INIS)

    Pawel, R.E.

    1976-10-01

    The reaction of Zircaloy in steam at elevated temperature involves the growth of discrete layers of oxide and oxygen-rich alpha Zircaloy from the parent beta phase. The multiphase, moving boundary diffusion problem involved is encountered in a number of important reaction schemes in addition to that of Zircaloy-oxygen and can be completely (albeitly ideally) characterized through an appropriate model in terms of oxygen diffusion coefficients and equilibrium concentrations for the various phases. Conversely, kinetic data for phase growth and total oxygen consumption rates can be used to compute diffusion coefficients. Equations are developed that express the oxygen diffusion coefficients in the oxide and alpha phases in terms of the reaction rate constants and equilibrium solubility values. These equations were applied to recent experimental kinetic data on the steam oxidation of Zircaloy-4 to determine the effective oxygen diffusion coefficients in these phases over the temperature range 1000--1500 0 C

  2. Exploring the chemical kinetics of partially oxidized intermediates by combining experiments, theory, and kinetic modeling.

    Science.gov (United States)

    Hoyermann, Karlheinz; Mauß, Fabian; Olzmann, Matthias; Welz, Oliver; Zeuch, Thomas

    2017-07-19

    Partially oxidized intermediates play a central role in combustion and atmospheric chemistry. In this perspective, we focus on the chemical kinetics of alkoxy radicals, peroxy radicals, and Criegee intermediates, which are key species in both combustion and atmospheric environments. These reactive intermediates feature a broad spectrum of chemical diversity. Their reactivity is central to our understanding of how volatile organic compounds are degraded in the atmosphere and converted into secondary organic aerosol. Moreover, they sensitively determine ignition timing in internal combustion engines. The intention of this perspective article is to provide the reader with information about the general mechanisms of reactions initiated by addition of atomic and molecular oxygen to alkyl radicals and ozone to alkenes. We will focus on critical branching points in the subsequent reaction mechanisms and discuss them from a consistent point of view. As a first example of our integrated approach, we will show how experiment, theory, and kinetic modeling have been successfully combined in the first infrared detection of Criegee intermediates during the gas phase ozonolysis. As a second example, we will examine the ignition timing of n-heptane/air mixtures at low and intermediate temperatures. Here, we present a reduced, fuel size independent kinetic model of the complex chemistry initiated by peroxy radicals that has been successfully applied to simulate standard n-heptane combustion experiments.

  3. Thermoactivated persulfate oxidation of pesticide chlorpyrifos in aquatic system: kinetic and mechanistic investigations.

    Science.gov (United States)

    Zhou, Lei; Zhang, Ya; Ying, Rongrong; Wang, Guoqing; Long, Tao; Li, Jianhua; Lin, Yusuo

    2017-04-01

    The widespread occurrence of organophosphorus pesticides (OPPs) in the environment poses risks to both ecologic system as well as human health. This study investigated the oxidation kinetics of chlorpyrifos (CP), one of the typical OPPs, by thermoactivated persulfate (PS) oxidation process, and evaluated the influence of key kinetic factors, such as PS concentrations, pH, temperature, bicarbonate, and chloride ions. The reaction pathways and mechanisms were also proposed based on products identification by LC-MS techniques. Our results revealed that increasing initial PS concentration and temperature favored the decomposition of CP, whereas the oxidation efficiency was not affected by pH change ranging from 3 to 11. Bicarbonate was found to play a detrimental role on CP removal rates, while chloride showed no effect. The oxidation pathways including initial oxidation of P=S bond to P=O, dechlorination, dealkylation, and the dechlorination-hydroxylation were proposed, and the detailed underlying mechanisms were also discussed. Molecular orbital (MO) calculations indicated that P=S bond was the most favored oxidation site of the molecule. The toxicity of reaction solution was believed to increase due to the formation of products with P=O structures. This work demonstrates that OPPs can readily react with SO 4 ·- and provides important information for further research on the oxidation of these contaminants.

  4. Kinetics and Mechanism of Oxidation of Isoleucine by N-Bromophthalimide in Aqueous Perchloric Acid Medium

    Directory of Open Access Journals (Sweden)

    N. M. I. Alhaji

    2011-01-01

    Full Text Available The kinetics of oxidation of isoleucine with N-bromophthalimide has been studied in perchloric acid medium potentiometrically. The reaction is of first order each in [NBP] and [amino acid] and negative fractional order in [H+]. The rate is decreased by the addition of phthalimide. A decrease in the dielectric constant of the medium increases the rate. Addition of halide ions or acrylonitrile has no effect on the kinetics. Similarly, variation of ionic strength of the medium does not affect the reaction rate. The reaction rate has been determined at different temperatures and activation parameters have been calculated. A suitable mechanism involving hypobromous acid as reactive species has been proposed.

  5. Model-fitting approach to kinetic analysis of non-isothermal oxidation of molybdenite

    International Nuclear Information System (INIS)

    Ebrahimi Kahrizsangi, R.; Abbasi, M. H.; Saidi, A.

    2007-01-01

    The kinetics of molybdenite oxidation was studied by non-isothermal TGA-DTA with heating rate 5 d eg C .min -1 . The model-fitting kinetic approach applied to TGA data. The Coats-Redfern method used of model fitting. The popular model-fitting gives excellent fit non-isothermal data in chemically controlled regime. The apparent activation energy was determined to be about 34.2 kcalmol -1 With pre-exponential factor about 10 8 sec -1 for extent of reaction less than 0.5

  6. The effects of iron(II) on the kinetics of arsenic oxidation and sorption on manganese oxides.

    Science.gov (United States)

    Wu, Yun; Li, Wei; Sparks, Donald L

    2015-11-01

    In this study, As(III) oxidation kinetics by a poorly-crystalline phyllomanganate (δ-MnO2) in the presence and absence of dissolved Fe(II) was investigated using stirred-flow and batch experiments. Chemically synthetic δ-MnO2 was reacted with four influent solutions, containing the same As(III) concentration but different Fe(II) concentrations, at pH 6. The results show an initial rapid As(III) oxidation by δ-MnO2, which is followed by an appreciably slow reaction after 8h. In the presence of Fe(II), As(III) oxidation is inhibited due to the competitive oxidation of Fe(II) as well as the formation of Fe(III)-(hydr)oxides on the δ-MnO2 surface. However, the sorption of As(III), As(V) and Mn(II) are increased, for the newly formed Fe(III)-(hydr)oxides provide additional sorption sites. This study suggests that the competitive oxidation of Fe(II) and consequently the precipitation of Fe(III) compounds on the δ-MnO2 surface play an important role in As(III) oxidation and As sequestration. Understanding these processes would be helpful in developing in situ strategies for remediation of As-contaminated waters and soils. Copyright © 2015 Elsevier Inc. All rights reserved.

  7. Less Stress : Oxidative stress and glutathione kinetics in preterm infants

    NARCIS (Netherlands)

    D. Rook (Denise)

    2013-01-01

    textabstractDue to immature antioxidant defenses, preterm infants are at susceptible to oxidative stress, which is associated with bronchopulmonary dysplasia, retinopathy of prematurity and periventricular leukomalacia. The general aim of this thesis was to study oxidative stress in preterm infants

  8. Kinetics and mechanisms of the oxide film growth on the surface of α-Fe in transitional domains

    International Nuclear Information System (INIS)

    Mukhambetov, D.G.; Berber, N.N.; Kargin, D.B.; Chalaya, O.V.

    2003-01-01

    The object of this work was to study the kinetics of the α-Fe surface oxidation with prevailing cubic texture at temperatures of 450-500 deg. C. The basic conformity to natural laws and mechanisms of the two-phase thin oxide films grows are determined. (author)

  9. Synthesis, electropolymerization and oxidation kinetics of an anthraquinone-functionalized poly(3,4-ethylenedioxythiophene)

    International Nuclear Information System (INIS)

    Arias-Pardilla, J.; Otero, T.F.; Blanco, R.; Segura, J.L.

    2010-01-01

    The chemical synthesis of an EDOT derivative endowed with an electron acceptor anthraquinone moiety (AQ-EDOT) is described. The electrochemical polymerization of the monomer has been studied by cyclic voltammetry, chronoamperometry and chronopotentiometry. The monomer oxidation-polymerization takes places on platinum at potentials more positive than 1.3 V vs. Ag/AgCl. The polymer film presents a stable redox process with E 0 = 0.22 V, that can be assigned to the characteristic exchange process of the parent unsubstituted PEDOT polymer. An unstable redox process at E 0 = -1.00 V, present decreasing charges on the consecutive cycles despite that the lost reduction charge is recovered by two irreversible oxidation processes taking place at high anodic potentials 0.00 and 0.16 V. A structural charge trapping effects occurring by reduction at -1.1 V and re-oxidation at 0.16 V of the anthraquinone moiety is suggested. The stable redox process is not affected by cycling allowing the obtention of the oxidation empirical kinetics, kinetic coefficients and reaction orders. Different initial states attained by reduction at different cathodic potentials for a constant time were explored for the kinetic study.

  10. Synthesis, electropolymerization and oxidation kinetics of an anthraquinone-functionalized poly(3,4-ethylenedioxythiophene)

    Energy Technology Data Exchange (ETDEWEB)

    Arias-Pardilla, J. [Centre for Electrochemistry and Intelligent Materials (CEMI), Universidad Politecnica de Cartagena, ETSII, E-30203 Cartagena (Spain); Otero, T.F., E-mail: toribio.fotero@uptc.e [Centre for Electrochemistry and Intelligent Materials (CEMI), Universidad Politecnica de Cartagena, ETSII, E-30203 Cartagena (Spain); Blanco, R.; Segura, J.L. [Departamento de Quimica Organica, Facultad de Quimica, Universidad Complutense, E-28040 Madrid (Spain)

    2010-02-01

    The chemical synthesis of an EDOT derivative endowed with an electron acceptor anthraquinone moiety (AQ-EDOT) is described. The electrochemical polymerization of the monomer has been studied by cyclic voltammetry, chronoamperometry and chronopotentiometry. The monomer oxidation-polymerization takes places on platinum at potentials more positive than 1.3 V vs. Ag/AgCl. The polymer film presents a stable redox process with E{sup 0} = 0.22 V, that can be assigned to the characteristic exchange process of the parent unsubstituted PEDOT polymer. An unstable redox process at E{sup 0} = -1.00 V, present decreasing charges on the consecutive cycles despite that the lost reduction charge is recovered by two irreversible oxidation processes taking place at high anodic potentials 0.00 and 0.16 V. A structural charge trapping effects occurring by reduction at -1.1 V and re-oxidation at 0.16 V of the anthraquinone moiety is suggested. The stable redox process is not affected by cycling allowing the obtention of the oxidation empirical kinetics, kinetic coefficients and reaction orders. Different initial states attained by reduction at different cathodic potentials for a constant time were explored for the kinetic study.

  11. Iron-Mediated Oxidation of Methoxyhydroquinone under Dark Conditions: Kinetic and Mechanistic Insights.

    Science.gov (United States)

    Yuan, Xiu; Davis, James A; Nico, Peter S

    2016-02-16

    Despite the biogeochemical significance of the interactions between natural organic matter (NOM) and iron species, considerable uncertainty still remains as to the exact processes contributing to the rates and extents of complexation and redox reactions between these important and complex environmental components. Investigations on the reactivity of low-molecular-weight quinones, which are believed to be key redox active compounds within NOM, toward iron species, could provide considerable insight into the kinetics and mechanisms of reactions involving NOM and iron. In this study, the oxidation of 2-methoxyhydroquinone (MH2Q) by ferric iron (Fe(III)) under dark conditions in the absence and presence of oxygen was investigated within a pH range of 4-6. Although Fe(III) was capable of stoichiometrically oxidizing MH2Q under anaerobic conditions, catalytic oxidation of MH2Q was observed in the presence of O2 due to further cycling between oxygen, semiquinone radicals, and iron species. A detailed kinetic model was developed to describe the predominant mechanisms, which indicated that both the undissociated and monodissociated anions of MH2Q were kinetically active species toward Fe(III) reduction, with the monodissociated anion being the key species accounting for the pH dependence of the oxidation. The generated radical intermediates, namely semiquinone and superoxide, are of great importance in reaction-chain propagation. The kinetic model may provide critical insight into the underlying mechanisms of the thermodynamic and kinetic characteristics of metal-organic interactions and assist in understanding and predicting the factors controlling iron and organic matter transformation and bioavailability in aquatic systems.

  12. Kinetic studies on leucite precursors

    Czech Academy of Sciences Publication Activity Database

    Mrázová, M.; Kloužková, A.; Kohoutková, Martina

    2009-01-01

    Roč. 7, č. 2 (2009), s. 205-210 ISSN 1895-1066 R&D Projects: GA MPO 2A-1TP1/063 Institutional research plan: CEZ:AV0Z40320502 Keywords : leucite * crystallization kinetics * hydrothermal Subject RIV: JH - Ceramics, Fire-Resistant Materials and Glass Impact factor: 1.065, year: 2009

  13. Uranium oxidation kinetics monitored by in-situ X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Zalkind, S., E-mail: shimonzl@nrcn.org.il; Rafailov, G.; Halevy, I.; Livneh, T.; Rubin, A.; Maimon, H.; Schweke, D.

    2017-03-15

    The oxidation kinetics of U-0.1 wt%Cr at oxygen pressures of 150 Torr and the temperature range of 90–150 °C was studied by means of in-situ X-ray diffraction (XRD). A “breakaway” in the oxidation kinetics is found at ∼0.25 μm, turning from a parabolic to a linear rate law. At the initial stage of oxidation the growth plane of UO{sub 2}(111) is the prominent one. As the oxide thickens, the growth rate of UO{sub 2}(220) plane increases and both planes grow concurrently. The activation energies obtained for the oxide growth are Q{sub parabolic} = 17.5 kcal/mol and Q{sub linear} = 19 kcal/mol. Enhanced oxidation around uranium carbide (UC) inclusions is clearly observed by scanning electron microscopy (SEM).

  14. Kinetic modeling of low density lipoprotein oxidation in arterial wall and its application in atherosclerotic lesions prediction.

    Science.gov (United States)

    Karimi, Safoora; Dadvar, Mitra; Modarress, Hamid; Dabir, Bahram

    2013-01-01

    Oxidation of low-density lipoprotein (LDL) is one of the major factors in atherogenic process. Trapped oxidized LDL (Ox-LDL) in the subendothelial matrix is taken up by macrophage and leads to foam cell generation creating the first step in atherosclerosis development. Many researchers have studied LDL oxidation using in vitro cell-induced LDL oxidation model. The present study provides a kinetic model for LDL oxidation in intima layer that can be used in modeling of atherosclerotic lesions development. This is accomplished by considering lipid peroxidation kinetic in LDL through a system of elementary reactions. In comparison, characteristics of our proposed kinetic model are consistent with the results of previous experimental models from other researches. Furthermore, our proposed LDL oxidation model is added to the mass transfer equation in order to predict the LDL concentration distribution in intima layer which is usually difficult to measure experimentally. According to the results, LDL oxidation kinetic constant is an important parameter that affects LDL concentration in intima layer so that existence of antioxidants that is responsible for the reduction of initiating rates and prevention of radical formations, have increased the concentration of LDL in intima by reducing the LDL oxidation rate. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

  15. Zirconium metal-water oxidation kinetics. V. Oxidation of Zircaloy in high pressure steam

    International Nuclear Information System (INIS)

    Pawel, R.E.; Cathcart, J.V.; Campbell, J.J.; Jury, S.H.

    1977-12-01

    A series of scoping tests to determine the influence of steam pressure on the isothermal oxidation kinetics of Zircaloy-4 PWR tubing was undertaken. The oxidation experiments were conducted in flowing steam at 3.45, 6.90, and 10.34 MPa (500, 1000, and 1500 psi) at 905 0 C (1661 0 F), and at 3.45 and 6.90 MPa at 1101 0 C (2014 0 F). A comparison of the results of these experiments with those obtained for oxidation in steam at atmospheric pressure under similar conditions indicated that measurable enhancement of the oxidation rate occurred with increasing pressure at 905 0 C, but not at 1100 0 C

  16. Oxidation kinetics of model compounds of metabolic waste in supercritical water

    Science.gov (United States)

    Webley, Paul A.; Holgate, Henry R.; Stevenson, David M.; Tester, Jefferson W.

    1990-01-01

    In this NASA-funded study, the oxidation kinetics of methanol and ammonia in supercritical water have been experimentally determined in an isothermal plug flow reactor. Theoretical studies have also been carried out to characterize key reaction pathways. Methanol oxidation rates were found to be proportional to the first power of methanol concentration and independent of oxygen concentration and were highly activated with an activation energy of approximately 98 kcal/mole over the temperature range 480 to 540 C at 246 bar. The oxidation of ammonia was found to be catalytic with an activation energy of 38 kcal/mole over temperatures ranging from 640 to 700 C. An elementary reaction model for methanol oxidation was applied after correction for the effect of high pressure on the rate constants. The conversion of methanol predicted by the model was in good agreement with experimental data.

  17. Insights into the Mechanism and Kinetics of Thermo-Oxidative Degradation of HFPE High Performance Polymer.

    Science.gov (United States)

    Kunnikuruvan, Sooraj; Parandekar, Priya V; Prakash, Om; Tsotsis, Thomas K; Nair, Nisanth N

    2016-06-02

    The growing requisite for materials having high thermo-oxidative stability makes the design and development of high performance materials an active area of research. Fluorination of the polymer backbone is a widely applied strategy to improve various properties of the polymer, most importantly the thermo-oxidative stability. Many of these fluorinated polymers are known to have thermo-oxidative stability up to 700 K. However, for space and aerospace applications, it is important to improve its thermo-oxidative stability beyond 700 K. Molecular-level details of the thermo-oxidative degradation of such polymers can provide vital information to improve the polymer. In this spirit, we have applied quantum mechanical and microkinetic analysis to scrutinize the mechanism and kinetics of the thermo-oxidative degradation of a fluorinated polymer with phenylethenyl end-cap, HFPE. This study gives an insight into the thermo-oxidative degradation of HFPE and explains most of the experimental observations on the thermo-oxidative degradation of this polymer. Thermolysis of C-CF3 bond in the dianhydride component (6FDA) of HFPE is found to be the rate-determining step of the degradation. Reaction pathways that are responsible for the experimentally observed weight loss of the polymer is also scrutinized. On the basis of these results, we propose a modification of HFPE polymer to improve its thermo-oxidative stability.

  18. Precise control of Si(001) initial oxidation by translational kinetic energy of O2 molecules

    International Nuclear Information System (INIS)

    Teraoka, Yuden; Yoshigoe, Akitaka

    2002-01-01

    The influence of translation kinetic energy of incident O 2 molecules on the passive oxidation of the clean Si(001) surface and the partially oxidized-Si(001) surface has been studied by high-resolution photoemission spectroscopy using synchrotron radiation. The incident energy of O 2 molecules was controlled up to 3 eV by a supersonic seeded molecular beam technique. Although two incident energy thresholds (1.0 eV and 2.6 eV) have been determined for the partially oxidized-surface oxidation in accordance with the first-principle calculation, the monotonic increase of oxygen saturation coverage was observed for the clean surface oxidation. The difference is caused by the initial dangling bond termination (Si-H and Si-OH) on the partially oxidized surface. Si-2p and O-1s photoemission spectra measured at representative incident energies showed the incident-energy-induced oxidation at the back bonds of Si dimers and the second-layer (subsurface) Si atoms. Moreover, the low-and high-binding-energy components in the O-1s photoemission spectra were assigned to bridge site oxygen and dangling bond site oxygen for the partially oxidized-surface oxidation. (author)

  19. On an aspect of kinetics both defects accumulation and gas absorption in an irradiated metals oxides

    International Nuclear Information System (INIS)

    Tuseev, T.; Polyakov, A.I.; Bitenbaev, M.I.

    2001-01-01

    In the work an analysis of experimental data during study both gases adsorption processes and radiation defects accumulation in irradiated (ultraviolet, gamma-, neutron-, alpha-particle- and proton radiation) in the oxides (SiO 2 , Al 2 O 3 , BeO, Se 2 O 3 , Dy 2 O 3 , La 2 O 3 , Er 2 O 3 ) is carried out. It is determined, that these processes are correlating with each other and equivalent kinetic equations for its description are proposed

  20. Determination of equilibration kinetics of oxide electrode materials using a manometric method

    International Nuclear Information System (INIS)

    Badwal, S.P.S.; Jiang, S.P.; Love, J.; Nowotny, J.; Rekas, M.

    1998-01-01

    The gas/solid equilibration kinetics for electrode oxide materials, such as (La 0.8 Sr 0.2 )MnO 3 , using a manometric method, was determined. The reaction kinetics between oxygen and the oxide material was monitored using the measurements of the P(O 2 ) changes during isothermic experiments of oxidation and reduction. The procedure of the determination will be described and relevant kinetic equations was derived. The equilibration kinetic data obtained can be used to determine the chemical diffusion coefficient. Copyright (1998) Australasian Ceramic Society

  1. Modelling of elementary kinetics of H2 and CO oxidation on ceria pattern cells

    International Nuclear Information System (INIS)

    Patel, HC; Tabish, AN; Aravind, PV

    2015-01-01

    Elementary kinetic mechanisms of fuel oxidation on ceria have not been dealt with in detail in literature. An elementary kinetic model is developed considering charge transfer and adsorption steps for electrochemical H 2 and CO oxidation on ceria. The reaction chemistry is solved by fitting previously obtained impedance spectra for H 2 and CO oxidation on ceria. The rate determining step is found to be the charge transfer rather than the adsorption for both H 2 and CO. A method is presented to extend the kinetics obtained from pattern anodes to macroscopic simulations in which the activation overvoltage can be calculated on the basis of elementary kinetics.

  2. Oxidation Kinetics of Ferritic Alloys in High-Temperature Steam Environments

    Science.gov (United States)

    Parker, Stephen S.; White, Josh; Hosemann, Peter; Nelson, Andrew

    2018-02-01

    High-temperature isothermal steam oxidation kinetic parameters of several ferritic alloys were determined by thermogravimetric analysis. The oxidation kinetic constant ( k) was measured as a function of temperature from 900°C to 1200°C. The results show a marked increase in oxidation resistance compared to reference Zircaloy-2, with kinetic constants 3-5 orders of magnitude lower across the experimental temperature range. The results of this investigation supplement previous findings on the properties of ferritic alloys for use as candidate cladding materials and extend kinetic parameter measurements to high-temperature steam environments suitable for assessing accident tolerance for light water reactor applications.

  3. Statistical model for grain boundary and grain volume oxidation kinetics in UO2 spent fuel

    International Nuclear Information System (INIS)

    Stout, R.B.; Shaw, H.F.; Einziger, R.E.

    1989-09-01

    This paper addresses statistical characteristics for the simplest case of grain boundary/grain volume oxidation kinetics of UO 2 to U 3 O 7 for a fragment of a spent fuel pellet. It also presents a limited discussion of future extensions to this simple case to represent the more complex cases of oxidation kinetics in spent fuels. 17 refs., 1 fig

  4. Kinetics, Mechanism, and Secondary Organic Aerosol Yield of Aqueous Phase Photo-oxidation of α-Pinene Oxidation Products.

    Science.gov (United States)

    Aljawhary, Dana; Zhao, Ran; Lee, Alex K Y; Wang, Chen; Abbatt, Jonathan P D

    2016-03-10

    Formation of secondary organic aerosol (SOA) involves atmospheric oxidation of volatile organic compounds (VOCs), the majority of which are emitted from biogenic sources. Oxidation can occur not only in the gas-phase but also in atmospheric aqueous phases such as cloudwater and aerosol liquid water. This study explores for the first time the aqueous-phase OH oxidation chemistry of oxidation products of α-pinene, a major biogenic VOC species emitted to the atmosphere. The kinetics, reaction mechanisms, and formation of SOA compounds in the aqueous phase of two model compounds, cis-pinonic acid (PIN) and tricarballylic acid (TCA), were investigated in the laboratory; TCA was used as a surrogate for 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA), a known α-pinene oxidation product. Aerosol time-of-flight chemical ionization mass spectrometry (Aerosol-ToF-CIMS) was used to follow the kinetics and reaction mechanisms at the molecular level. Room-temperature second-order rate constants of PIN and TCA were determined to be 3.3 (± 0.5) × 10(9) and 3.1 (± 0.2) × 10(8) M(-1) s(-1), respectively, from which were estimated their condensed-phase atmospheric lifetimes. Aerosol-ToF-CIMS detected a large number of products leading to detailed reaction mechanisms for PIN and MBTCA. By monitoring the particle size distribution after drying, the amount of SOA material remaining in the particle phase was determined. An aqueous SOA yield of 40 to 60% was determined for PIN OH oxidation. Although recent laboratory studies have focused primarily on aqueous-phase processing of isoprene-related compounds, we demonstrate that aqueous formation of SOA materials also occurs from monoterpene oxidation products, thus representing an additional source of biogenically driven aerosol formation.

  5. Kinetics and mechanism of oxidation of acetanilide by quinquevalent vanadium in acid medium

    International Nuclear Information System (INIS)

    Gupta, R.

    1990-01-01

    The kinetics of the oxidation of acetanilide with vanadium(V) in sulphuric acid medium at constant ionic strength has been studied. The reaction is first order with oxidant. The order of reaction in acetanilide varies from one to zero. The reaction follows an acid catalyzed independent path, exhibiting square dependence in H + . A Bunnett plot indicates that the water acts as a nucleophile. The thermodynamic parameters have been computed. A probable reaction mechanism and rate law consistent with these data are given. (Author)

  6. Oxidation kinetics of reaction products formed in uranium metal corrosion

    International Nuclear Information System (INIS)

    Totemeier, T. C.

    1998-01-01

    The oxidation behavior of uranium metal ZPPR fuel corrosion products in environments of Ar-4%O 2 and Ar-20%O 2 were studied using thermo-gravimetric analysis (TGA). These tests were performed to extend earlier work in this area specifically, to assess plate-to-plate variations in corrosion product properties and the effect of oxygen concentration on oxidation behavior. The corrosion products from two relatively severely corroded plates were similar, while the products from a relatively intact plate were not reactive. Oxygen concentration strongly affected the burning rate of reactive products, but had little effect on low-temperature oxidation rates

  7. Oxidation kinetics of reaction products formed in uranium metal corrosion.

    Energy Technology Data Exchange (ETDEWEB)

    Totemeier, T. C.

    1998-04-22

    The oxidation behavior of uranium metal ZPPR fuel corrosion products in environments of Ar-4%O{sub 2} and Ar-20%O{sub 2} were studied using thermo-gravimetric analysis (TGA). These tests were performed to extend earlier work in this area specifically, to assess plate-to-plate variations in corrosion product properties and the effect of oxygen concentration on oxidation behavior. The corrosion products from two relatively severely corroded plates were similar, while the products from a relatively intact plate were not reactive. Oxygen concentration strongly affected the burning rate of reactive products, but had little effect on low-temperature oxidation rates.

  8. Concentration-dependent photodegradation kinetics and hydroxyl-radical oxidation of phenicol antibiotics.

    Science.gov (United States)

    Li, Kai; Zhang, Peng; Ge, Linke; Ren, Honglei; Yu, Chunyan; Chen, Xiaoyang; Zhao, Yuanfeng

    2014-09-01

    Thiamphenicol and florfenicol are two phenicol antibiotics widely used in aquaculture and are ubiquitous as micropollutants in surface waters. The present study investigated their photodegradation kinetics, hydroxyl-radical (OH) oxidation reactivities and products. Firstly, the photolytic kinetics of the phenicols in pure water was studied as a function of initial concentrations (C0) under UV-vis irradiation (λ>200nm). It was found that the kinetics was influenced by C0. A linear plot of the pseudo-first-order rate constant vs C0 was observed with a negative slope. Secondly, the reaction between the phenicol antibiotics and OH was examined with a competition kinetic method under simulated solar irradiation (λ>290nm), which quantified their bimolecular reaction rate constants of (2.13±0.02)×10(9)M(-1)s(-1) and (1.82±0.10)×10(9)M(-1)s(-1) for thiamphenicol and florfenicol, respectively. Then the corresponding OH oxidated half-lives in sunlit surface waters were calculated to be 90.5-106.1h. Some main intermediates were formed from the reaction, which suggested that the two phenicols underwent hydroxylation, oxygenation and dehydrogenation when OH existed. These results are of importance to assess the phenicol persistence in wastewater treatment and sunlit surface waters. Copyright © 2014 Elsevier Ltd. All rights reserved.

  9. Oxidation kinetics of common Kilka (Clupeonella cultiventris caspia) oil in presence of bene oils' unsaponifiable matter.

    Science.gov (United States)

    Pazhouhanmehr, Samaneh; Farhoosh, Reza; Sharif, Ali; Esmaeilzadeh Kenari, Reza

    2016-01-01

    The oxidation mechanisms and kinetics of the purified common Kilka (Clupeonella cultiventris caspia) triacylglycerols (PKO) as affected by 1-1.5% (w/w) of unsaponifiable matters of bene kernel (UKO) and hull (UHO) oils were studied and compared with that of 100 mg/kg of butylated hydroxytoluene (BHT) and α-tocopherol in the Rancimat test at 50-70 °C. There were good correlations between the oxidative stability index (OSI) and time required to reach a 50%-increase in PV (t50). The frequency factor (A) and activation energy (Ea) were correlated well with the values of entropy and enthalpy, respectively. The values of free energy of activation (ΔG(++)) could describe the values of t50 or OSI well. Kinetic data indicated that the UKO with higher contents of tocopherols and tocotrienols, and terpenoid compounds was more effective than the UHO on the PKO stability. Copyright © 2015 Elsevier Ltd. All rights reserved.

  10. Anaerobic digestion of amine-oxide-based surfactants: biodegradation kinetics and inhibitory effects.

    Science.gov (United States)

    Ríos, Francisco; Lechuga, Manuela; Fernández-Arteaga, Alejandro; Jurado, Encarnación; Fernández-Serrano, Mercedes

    2017-08-01

    Recently, anaerobic degradation has become a prevalent alternative for the treatment of wastewater and activated sludge. Consequently, the anaerobic biodegradability of recalcitrant compounds such as some surfactants require a thorough study to avoid their presence in the environment. In this work, the anaerobic biodegradation of amine-oxide-based surfactants, which are toxic to several organisms, was studied by measuring of the biogas production in digested sludge. Three amine-oxide-based surfactants with structural differences in their hydrophobic alkyl chain were tested: Lauramine oxide (AO-R 12 ), Myristamine oxide (AO-R 14 ) and Cocamidopropylamine oxide (AO-cocoamido). Results show that AO-R 12 and AO-R 14 inhibit biogas production, inhibition percentages were around 90%. AO-cocoamido did not cause inhibition and it was biodegraded until reaching a percentage of 60.8%. Otherwise, we fitted the production of biogas to two kinetic models, to a pseudo first-order model and to a logistic model. Production of biogas during the anaerobic biodegradation of AO-cocoamido was pretty good adjusted to the logistics model. Kinetic parameters were also determined. This modelling is useful to predict their behaviour in wastewater treatment plants and under anaerobic conditions in the environment.

  11. The influence of the texture and microstructure of a Zr-2.5Nb substrate upon the oxidation kinetics

    International Nuclear Information System (INIS)

    Lin, J.; Cao Xiaohui; Szpunar, J.A.

    2002-01-01

    The thin oxide layer growing on the zirconium alloy is dense and adherent and therefore is protective against further oxidation and hydrogen ingress, which is deleterious to zirconium pressure tube used in nuclear power stations because it facilitates formation of zirconium hydrides. Heat treatment and other surface modification methods were applied to zirconium alloys and the texture was investigated. Thermogravimetric analytic (TGA) was used for oxidation kinetics studies. The oxidation kinetics data show the variation of the oxidation rate due to the difference of texture and microstructure and the oxidation resistance is improved after the substrate is cold worked and heat treated. After cold work and heat treatment, the texture of substrate changes from (11-20)[1-100] to (11-23)[1-100]. (orig.)

  12. Evaluation of the kinetic oxidation of aqueous volatile organic compounds by permanganate.

    Science.gov (United States)

    Mahmoodlu, Mojtaba G; Hassanizadeh, S Majid; Hartog, Niels

    2014-07-01

    The use of permanganate solutions for in-situ chemical oxidation (ISCO) is a well-established groundwater remediation technology, particularly for targeting chlorinated ethenes. The kinetics of oxidation reactions is an important ISCO remediation design aspect that affects the efficiency and oxidant persistence. The overall rate of the ISCO reaction between oxidant and contaminant is typically described using a second-order kinetic model while the second-order rate constant is determined experimentally by means of a pseudo first order approach. However, earlier studies of chlorinated hydrocarbons have yielded a wide range of values for the second-order rate constants. Also, there is limited insight in the kinetics of permanganate reactions with fuel-derived groundwater contaminants such as toluene and ethanol. In this study, batch experiments were carried out to investigate and compare the oxidation kinetics of aqueous trichloroethylene (TCE), ethanol, and toluene in an aqueous potassium permanganate solution. The overall second-order rate constants were determined directly by fitting a second-order model to the data, instead of typically using the pseudo-first-order approach. The second-order reaction rate constants (M(-1) s(-1)) for TCE, toluene, and ethanol were 8.0×10(-1), 2.5×10(-4), and 6.5×10(-4), respectively. Results showed that the inappropriate use of the pseudo-first-order approach in several previous studies produced biased estimates of the second-order rate constants. In our study, this error was expressed as a function of the extent (P/N) in which the reactant concentrations deviated from the stoichiometric ratio of each oxidation reaction. The error associated with the inappropriate use of the pseudo-first-order approach is negatively correlated with the P/N ratio and reached up to 25% of the estimated second-order rate constant in some previous studies of TCE oxidation. Based on our results, a similar relation is valid for the other volatile

  13. Kinetics of Oxidation of Metochlopramide withChloramine-T in HClO4 Medium

    Directory of Open Access Journals (Sweden)

    K. M. Meenakshi

    2009-01-01

    Full Text Available The kinetics of oxidation of metochlopramide hydrochloride (MCP with sodium N-chloro p-toluenesulfonamide (CAT in perchloric acid solution has been studied at 313K. The reaction rate shows a first order dependence on [CAT], fractional order on [MCP] and inverse fractional order on [H+]. There is a negative effect of dielectric constant of the solvent. The addition of the reduction product of CAT has no significant effect on the rate. The rate remained unchanged with the variation in the ionic strength of the medium. The reaction fails to induce the polymerization of acrylonitrile. Thermodynamic parameters have been computed by Arrhenius plot. The stoichiometry of the reaction was found to be 1:2 and oxidation products were identified. The Michaelis-Menten type of kinetics has been proposed. CH3C6H4SO2NHCl have been assumed to be the reactive oxidizing species. Thermodynamic parameters were computed by studying reactions at different temperatures. A mechanism consistent with observed kinetics is proposed.

  14. Kinetics of 25-hydroperoxycholesterol formation during photo-oxidation of crystalline cholesterol.

    Science.gov (United States)

    Medina-Meza, Ilce Gabriela; Rodriguez-Estrada, Maria Teresa; Lercker, Giovanni; Barnaba, Carlo; García, Hugo Sergio

    2014-06-01

    25-Hydroxycholesterol (25-OH), a side-chain product of cholesterol oxidation, has emerged as one of the important issues in food chemistry and biochemistry, because of its involvement in several human pathologies. This oxysterol is derived from both enzymatic and non-enzymatic pathways. However, the latter mechanism has been scarcely studied in either food or model systems. In this work, a kinetic model was developed to evaluate the formation of 25-OH and its precursor 25-hydroperoxycholesterol (25-OOH) during photo-oxidation of cholesterol for 28 days under fluorescent light. 25-OOH was estimated by an indirect method, using thin-layer chromatography coupled with gas chromatography-mass spectrometry. Peroxide value (POV) and cholesterol oxidation products (COPs) were determined. POV showed a hyperbolic behavior, typical of a crystalline system in which the availability of cholesterol is the limiting factor. Further reactions of hydroperoxides were followed; in particular, after photo-oxidation, 25-OOH (0.55 mg g(-1) ) and 25-OH (0.08 mg g(-1) ) were found in cholesterol, as well as seven other oxysterols, including 7-hydroxy and 5,6-epoxy derivatives. The application of kinetic models to the data showed good correlation with theoretical values, allowing derivation of the kinetic parameters for each oxidation route. The results of this work confirm that cholesterol in the crystalline state involves different oxidation patterns as compared to cholesterol in solution. Moreover, the numerical fit proved that hydroperoxidation is the rate-limiting step in 25-OH formation. © 2013 Society of Chemical Industry.

  15. Kinetics of heterogeneous catalysis oxidation of carbon monoxide

    International Nuclear Information System (INIS)

    Khawaja, Y.; Sadiq, A.

    1987-10-01

    An irreversible kinetic surface-reaction model, based upon the reaction of carbon monoxide nd oxygen on a catalyst surface is investigated by means of Monte Carlo simulation. The adsorbed molecules/atoms on the surface undergo both first and second order kinetic phase transitions. The first order transition is found to occur at x/sub/co=x/sub/2=0.5255 with an error bar of 0.0003, where x/sub/co is the concentration of carbon monoxide in the gas phase. The time evolution of this catalytic reaction is studied both analytically and by computer simulation. Slightly above x/sub/2, the oxygen coverage relaxation time for the oxygen is found to diverage as the inverse of 3.54 times the absolute of the difference of x/sub/2 and x/sub/co. (orig./A.B.)

  16. Kinetics of catalyzed tritium oxidation in air at ambient temperature

    International Nuclear Information System (INIS)

    Sherwood, A.E.

    1980-01-01

    Tritium/air oxidation kinetic data are derived from measurements carried out with three catalysts. All experiments were carried out at room temperature - a regime that provides a severe test for catalyst effectiveness. Each catalyst consists of a high-surface-area substrate in pelletized form, onto which precious metal has been dispersed. The metal/substrate combinations investigated are: platinum/alumina, palladium/kaolin, and paladium/zeolite. Each of the dispersed-metal catalysts is extremely effective in promoting tritium oxidation in comparison with self-catalyzed atmospheric conversion; equivalent first-order rate constants are higher by roughly nine orders of magnitude. Electron-microprobe scans reveal that the dispersed metal is deposited near the outer surface of the catalyst, with metal concentration decreasing exponentially from the pellet surface. The platinum-based catalyst is more effective than the palladium catalysts on a surface-area basis by about a factor of three. Rate coefficients are determined from concentration decay following a spike injection of tritium into an air-filled enclosure processed by recirculation through an oxidation/adsorption system. The catalytic reaction is first-order in tritium concentration in the range 10 to 10 5 μCi/m 3 (4 ppt-40 ppB). Addition of hydrogen carrier gas is unnecessary. Catalytic activity for all three catalysts declines with time of exposure to air after activation, following a power-law decay with an exponent of -1/2. Reactivation with hot hydrogen gas effectively restores initial catalytic activity

  17. Kinetic models of controllable pore growth of anodic aluminum oxide membrane

    Science.gov (United States)

    Huang, Yan; Zeng, Hong-yan; Zhao, Ce; Qu, Ye-qing; Zhang, Pin

    2012-06-01

    An anodized Al2O3 (AAO) membrane with apertures about 72 nm in diameter was prepared by two-step anodic oxidation. The appearance and pore arrangement of the AAO membrane were characterized by energy dispersive x-ray spectroscopy and scanning electron microscopy. It was confirmed that the pores with high pore aspect ratio were parallel, well-ordered, and uniform. The kinetics of pores growth in the AAO membrane was derived, and the kinetic models showed that pores stopped developing when the pressure ( σ) trended to equal the surface tension at the end of anodic oxidation. During pore expansion, the effects of the oxalic acid concentration and expansion time on the pore size were investigated, and the kinetic behaviors were explained with two kinetic models derived in this study. They showed that the pore size increased with extended time ( r= G· t+ G'), but decreased with increased concentration ( r = - K·ln c- K') through the derived mathematic formula. Also, the values of G, G', K, and K' were derived from our experimental data.

  18. Generalized first-order kinetic model for biosolids decomposition and oxidation during hydrothermal treatment.

    Science.gov (United States)

    Shanableh, A

    2005-01-01

    The main objective of this study was to develop generalized first-order kinetic models to represent hydrothermal decomposition and oxidation of biosolids within a wide range of temperatures (200-450 degrees C). A lumping approach was used in which oxidation of the various organic ingredients was characterized by the chemical oxygen demand (COD), and decomposition was characterized by the particulate (i.e., nonfilterable) chemical oxygen demand (PCOD). Using the Arrhenius equation (k = k(o)e(-Ea/RT)), activation energy (Ea) levels were derived from 42 continuous-flow hydrothermal treatment experiments conducted at temperatures in the range of 200-450 degrees C. Using predetermined values for k(o) in the Arrhenius equation, the activation energies of the various organic ingredients were separated into 42 values for oxidation and a similar number for decomposition. The activation energy values were then classified into levels representing the relative ease at which the organic ingredients of the biosolids were oxidized or decomposed. The resulting simple first-order kinetic models adequately represented, within the experimental data range, hydrothermal decomposition of the organic particles as measured by PCOD and oxidation of the organic content as measured by COD. The modeling approach presented in the paper provide a simple and general framework suitable for assessing the relative reaction rates of the various organic ingredients of biosolids.

  19. Liquefaction chemistry and kinetics: Hydrogen utilization studies

    Energy Technology Data Exchange (ETDEWEB)

    Rothenberger, K.S.; Warzinski, R.P.; Cugini, A.V. [Pittsburgh Energy Technology Center, PA (United States)] [and others

    1995-12-31

    The objectives of this project are to investigate the chemistry and kinetics that occur in the initial stages of coal liquefaction and to determine the effects of hydrogen pressure, catalyst activity, and solvent type on the quantity and quality of the products produced. The project comprises three tasks: (1) preconversion chemistry and kinetics, (2) hydrogen utilization studies, and (3) assessment of kinetic models for liquefaction. The hydrogen utilization studies work will be the main topic of this report. However, the other tasks are briefly described.

  20. Synthesis and characterization of sulfur functionalized graphene oxide nanosheets as efficient sorbent for removal of Pb2+, Cd2+, Ni2+ and Zn2+ ions from aqueous solution: A combined thermodynamic and kinetic studies

    Science.gov (United States)

    Pirveysian, Mahtab; Ghiaci, Mehran

    2018-01-01

    A very simple, one pot method was used for preparation of sulfur functionalized graphene oxide (GO-SOxR) with sodium sulfide and water in reflux condition. The elemental analysis data showed high sulfur content up to 15%. EDS and XPS analysis also proved introduction of sulfur element. To make the sorbent more efficient operationally, the GO-SOxR was coated with a mesoporous shell of TiO2 or SiO2. The prepared sorbents were characterized by SEM, TEM, TGA, XPS, XRD, IR and EDS. GO-SOxR@TiO2 and GO-SOxR@SiO2 composites were tested for removal of Pb(II), Cd(II), Ni(II) and Zn(II) as heavy metal ions from aqueous solution in batch method. Adsorption of the heavy metal ions was studied kinetically, and the adsorption capacities of GO-SOxR, GO-SOxR@TiO2, and GO-SOxR@SiO2 were evaluated using equilibrium adsorption isotherms, and compared to other adsorbents used for removal of these heavy metals. Kinetic studies showed that the experimental data was fitted with pseudo second order model. The adsorption capacity of GO was significantly improved by sulfur functionalization and TiO2 coating.

  1. Electric-Loading Enhanced Kinetics in Oxide Ceramics: Pore Migration, Sintering and Grain Growth: Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Chen, I-Wei [Univ. of Pennsylvania, Philadelphia, PA (United States). Dept. of Materials Science & Engineering

    2018-02-02

    Solid oxide fuel cells and solid oxide electrolysis cells rely on solid electrolytes in which a large ionic current dominates. This project was initiated to investigate microstructural changes in such devices under electrochemical forces, because nominally insignificant processes may couple to the large ionic current to yield non-equilibrium phenomena that alter the microstructure. Our studies had focused on yttria-stabilized cubic zirconia (YSZ) widely used in these devices. The experiments have revealed enhanced grain growth at higher temperatures, pore and gas bubble migration at all temperatures, and the latter also lead to enhanced sintering of highly porous ceramics into fully dense ceramics at unprecedentedly low temperatures. These results have shed light on kinetic processes that fall completely outside the realm of classical ceramic processing. Other fast-oxygen oxide ceramics closely related to, and often used in conjunction with zirconia ceramics, have also be investigated, as are closely related scientific problems in zirconia ceramics. These include crystal structures, defects, diffusion kinetics, oxygen potentials, low temperature sintering, flash sintering, and coarsening theory, and all have resulted in greater clarity in scientific understanding. The knowledge is leveraged to provide new insight to electrode kinetics and near-electrode mixed conductivity and to new materials. In the following areas, our research has resulted in completely new knowledge that defines the state-of-the-art of the field. (a) Electrical current driven non-equilibrium phenomena, (b) Enhanced grain growth under electrochemically reducing conditions, (c) Development of oxygen potential polarization in electrically loaded electrolyte, (d) Low temperature sintering and grain growth, and (e) Structure, defects and cation kinetics of fluorite-structured oxides. Our research has also contributed to synthesis of new energy-relevant electrochemical materials and new understanding

  2. Fat oxidation, hormonal and plasma metabolite kinetics during a submaximal incremental test in lean and obese adults.

    Science.gov (United States)

    Lanzi, Stefano; Codecasa, Franco; Cornacchia, Mauro; Maestrini, Sabrina; Salvadori, Alberto; Brunani, Amelia; Malatesta, Davide

    2014-01-01

    This study aimed to compare fat oxidation, hormonal and plasma metabolite kinetics during exercise in lean (L) and obese (O) men. Sixteen L and 16 O men [Body Mass Index (BMI): 22.9 ± 0.3 and 39.0 ± 1.4 kg · m(-2)] performed a submaximal incremental test (Incr) on a cycle-ergometer. Fat oxidation rates (FORs) were determined using indirect calorimetry. A sinusoidal model, including 3 independent variables (dilatation, symmetry, translation), was used to describe fat oxidation kinetics and determine the intensity (Fat(max)) eliciting maximal fat oxidation. Blood samples were drawn for the hormonal and plasma metabolite determination at each step of Incr. FORs (mg · FFM(-1) · min(-1)) were significantly higher from 20 to 30% of peak oxygen uptake (VO2peak) in O than in L and from 65 to 85% VO2peak in L than in O (p ≤ 0.05). FORs were similar in O and in L from 35 to 60% VO2peak. Fat max was 17% significantly lower in O than in L (poxidation kinetics were characterized by similar translation, significantly lower dilatation and left-shift symmetry in O compared with L (poxidation at high exercise intensities suggest that the difference in the fat oxidation kinetics is likely linked to impaired muscular capacity to oxidize NEFA in O. These results may have important implications for the appropriate exercise intensity prescription in training programs designed to optimize fat oxidation in O.

  3. Study of the oxidation-reduction kinetics involved in the Np(V) + Fe(II) in equilibrium Np(IV) + Fe(III) system in nitric acid solutions

    International Nuclear Information System (INIS)

    Jao, Y.

    1975-08-01

    Ferrous nitrate-hydrazine is one of the more attractive alternate reactants to the currently used reagent, ferrous sulfamate, for partitioning plutonium from neptunium and uranium. An understanding of the kinetics of the reduction of Np(VI) to Np(IV) by ferrous nitrate-hydrazine is needed before a satisfactory evaluation of the feasibility of this reductant in actinide element separations can be made. The purpose of this work was to study the kinetics and mechanisms of the reduction of Np(V) by Fe(II) and the oxidation of Np(IV) by Fe(III) in 1-2 M nitric acid solutions. The acid concentration range was chosen to include that typically used in the separation of plutonium from neptunium and uranium by solvent extraction with tributylphosphate. The forward and reverse rate constants, hydrogen ion dependence, temperature dependence, ionic strength effects and nitrate ion influence were determined. The proposed reaction mechanisms involve protonation of the NpO 2 + ions and hydroxyoxygenation of Np 4 + ions. (LK)

  4. Is automated kinetic measurement superior to end-point for advanced oxidation protein product?

    Science.gov (United States)

    Oguz, Osman; Inal, Berrin Bercik; Emre, Turker; Ozcan, Oguzhan; Altunoglu, Esma; Oguz, Gokce; Topkaya, Cigdem; Guvenen, Guvenc

    2014-01-01

    Advanced oxidation protein product (AOPP) was first described as an oxidative protein marker in chronic uremic patients and measured with a semi-automatic end-point method. Subsequently, the kinetic method was introduced for AOPP assay. We aimed to compare these two methods by adapting them to a chemistry analyzer and to investigate the correlation between AOPP and fibrinogen, the key molecule responsible for human plasma AOPP reactivity, microalbumin, and HbA1c in patients with type II diabetes mellitus (DM II). The effects of EDTA and citrate-anticogulated tubes on these two methods were incorporated into the study. This study included 93 DM II patients (36 women, 57 men) with HbA1c levels > or = 7%, who were admitted to the diabetes and nephrology clinics. The samples were collected in EDTA and in citrate-anticoagulated tubes. Both methods were adapted to a chemistry analyzer and the samples were studied in parallel. In both types of samples, we found a moderate correlation between the kinetic and the endpoint methods (r = 0.611 for citrate-anticoagulated, r = 0.636 for EDTA-anticoagulated, p = 0.0001 for both). We found a moderate correlation between fibrinogen-AOPP and microalbumin-AOPP levels only in the kinetic method (r = 0.644 and 0.520 for citrate-anticoagulated; r = 0.581 and 0.490 for EDTA-anticoagulated, p = 0.0001). We conclude that adaptation of the end-point method to automation is more difficult and it has higher between-run CV% while application of the kinetic method is easier and it may be used in oxidative stress studies.

  5. Kinetic Modeling of a Heterogeneous Fenton Oxidative Treatment of Petroleum Refining Wastewater

    Science.gov (United States)

    Basheer Hasan, Diya'uddeen; Abdul Raman, Abdul Aziz; Wan Daud, Wan Mohd Ashri

    2014-01-01

    The mineralisation kinetics of petroleum refinery effluent (PRE) by Fenton oxidation were evaluated. Within the ambit of the experimental data generated, first-order kinetic model (FKM), generalised lumped kinetic model (GLKM), and generalized kinetic model (GKM) were tested. The obtained apparent kinetic rate constants for the initial oxidation step (k 2′), their final oxidation step (k 1′), and the direct conversion to endproducts step (k 3′) were 10.12, 3.78, and 0.24 min−1 for GKM; 0.98, 0.98, and nil min−1 for GLKM; and nil, nil, and >0.005 min−1 for FKM. The findings showed that GKM is superior in estimating the mineralization kinetics. PMID:24592152

  6. Kinetics and mechanism of oxidation of super-reduced cobalamin and cobinamide species by thiosulfate, sulfite and dithionite.

    Science.gov (United States)

    Dereven'kov, Ilia A; Salnikov, Denis S; Makarov, Sergei V; Boss, Gerry R; Koifman, Oskar I

    2013-11-21

    We studied the kinetics of reactions of cob(I)alamin and cob(I)inamide with thiosulfate, sulfite, and dithionite by UV-Visible (UV-Vis) and stopped-flow spectroscopy. We found that the two Co(I) species were oxidized by these sulfur-containing compounds to Co(II) forms: oxidation by excess thiosulfate leads to penta-coordinate complexes and oxidation by excess sulfite or dithionite leads to hexa-coordinate Co(II)-SO2(-) complexes. The net scheme involves transfer of three electrons in the case of oxidation by thiosulfate and one electron for oxidation by sulfite and dithionite. On the basis of kinetic data, the nature of the reactive oxidants was suggested, i.e., HS2O3(-) (for oxidation by thiosulfate), S2O5(2-), HSO3(-), and aquated SO2 (for oxidation by sulfite), and S2O4(2-) and SO2(-) (for oxidation by dithionite). No difference was observed in kinetics with cob(i)alamin or cob(i)inamide as reductants.

  7. Comparison of Oxidation Kinetics of Nitrite-Oxidizing Bacteria: Nitrite Availability as a Key Factor in Niche Differentiation

    Science.gov (United States)

    Nowka, Boris; Daims, Holger

    2014-01-01

    Nitrification has an immense impact on nitrogen cycling in natural ecosystems and in wastewater treatment plants. Mathematical models function as tools to capture the complexity of these biological systems, but kinetic parameters especially of nitrite-oxidizing bacteria (NOB) are lacking because of a limited number of pure cultures until recently. In this study, we compared the nitrite oxidation kinetics of six pure cultures and one enrichment culture representing three genera of NOB (Nitrobacter, Nitrospira, Nitrotoga). With half-saturation constants (Km) between 9 and 27 μM nitrite, Nitrospira bacteria are adapted to live under significant substrate limitation. Nitrobacter showed a wide range of lower substrate affinities, with Km values between 49 and 544 μM nitrite. However, the advantage of Nitrobacter emerged under excess nitrite supply, sustaining high maximum specific activities (Vmax) of 64 to 164 μmol nitrite/mg protein/h, contrary to the lower activities of Nitrospira of 18 to 48 μmol nitrite/mg protein/h. The Vmax (26 μmol nitrite/mg protein/h) and Km (58 μM nitrite) of “Candidatus Nitrotoga arctica” measured at a low temperature of 17°C suggest that Nitrotoga can advantageously compete with other NOB, especially in cold habitats. The kinetic parameters determined represent improved basis values for nitrifying models and will support predictions of community structure and nitrification rates in natural and engineered ecosystems. PMID:25398863

  8. Determination of kinetics and stoichiometry of chemical sulfide oxidation in wastewater of sewer networks

    DEFF Research Database (Denmark)

    Nielsen, Asbjørn Haaning; Vollertsen, Jes; Hvitved-Jacobsen, Thorkild

    2003-01-01

    A method for determination of kinetics and stoichiometry of chemical sulfide oxidation by dissolved oxygen (DO) in wastewater is presented. The method was particularly developed to investigate chemical sulfide oxidation in wastewater of sewer networks at low DO concentrations. The method is based...... be considered constant during the course of the experiments although intermediates accumulated. This was explained by an apparent slow oxidation rate of the intermediates. The method was capable of determining kinetics and stoichiometry of chemical sulfide oxidation at DO concentrations lower than 1 g of O2 m...... on continuous measurement of the reactants allowing the kinetics to be determined at varying reactant concentrations during the course of the experiment. The kinetics determined was simulated by a rate equation. The precision of the method was assessed in terms of the standard deviation of the kinetic...

  9. High-temperature oxidation kinetics of sponge-based E110 cladding alloy

    Science.gov (United States)

    Yan, Yong; Garrison, Benton E.; Howell, Mike; Bell, Gary L.

    2018-02-01

    Two-sided oxidation experiments were recently conducted at 900°C-1200 °C in flowing steam with samples of sponge-based Zr-1Nb alloy E110. Although the old electrolytic E110 tubing exhibited a high degree of susceptibility to nodular corrosion and experienced breakaway oxidation rates in a relatively short time, the new sponge-based E110 demonstrated steam oxidation behavior comparable to Zircaloy-4. Sample weight gain and oxide layer thickness measurements were performed on oxidized E110 specimens and compared to oxygen pickup and oxide layer thickness calculations using the Cathcart-Pawel correlation. Our study shows that the sponge-based E110 follows the parabolic law at temperatures above 1015 °C. At or below 1015 °C, the oxidation rate was very low when compared to Zircaloy-4 and can be represented by a cubic expression. No breakaway oxidation was observed at 1000 °C for oxidation times up to 10,000 s. Arrhenius expressions are given to describe the parabolic rate constants at temperatures above 1015 °C and cubic rate constants are provided for temperatures below 1015 °C. The weight gains calculated by our equations are in excellent agreement with the measured sample weight gains at all test temperatures. In addition to the as-fabricated E110 cladding sample, prehydrided E110 cladding with hydrogen concentrations in the 100-150 wppm range was also investigated. The effect of hydrogen content on sponge-based E110 oxidation kinetics was minimal. No significant difference was found between as-fabricated and hydrided samples with regard to oxygen pickup and oxide layer thickness for hydrogen contents below 150 wppm.

  10. Estimation of Oxidation Kinetics and Oxide Scale Void Position of Ferritic-Martensitic Steels in Supercritical Water

    Directory of Open Access Journals (Sweden)

    Li Sun

    2017-01-01

    Full Text Available Exfoliation of oxide scales from high-temperature heating surfaces of power boilers threatened the safety of supercritical power generating units. According to available space model, the oxidation kinetics of two ferritic-martensitic steels are developed to predict in supercritical water at 400°C, 500°C, and 600°C. The iron diffusion coefficients in magnetite and Fe-Cr spinel are extrapolated from studies of Backhaus and Töpfer. According to Fe-Cr-O ternary phase diagram, oxygen partial pressure at the steel/Fe-Cr spinel oxide interface is determined. The oxygen partial pressure at the magnetite/supercritical water interface meets the equivalent oxygen partial pressure when system equilibrium has been attained. The relative error between calculated values and experimental values is analyzed and the reasons of error are suggested. The research results show that the results of simulation at 600°C are approximately close to experimental results. The iron diffusion coefficient is discontinuous in the duplex scale of two ferritic-martensitic steels. The simulation results of thicknesses of the oxide scale on tubes (T91 of final superheater of a 600 MW supercritical boiler are compared with field measurement data and calculation results by Adrian’s method. The calculated void positions of oxide scales are in good agreement with a cross-sectional SEM image of the oxide layers.

  11. Revisiting the Kinetics and Thermodynamics of the Low-Temperature Oxidation Pathways of Alkanes: A Case Study of the Three Pentane Isomers

    KAUST Repository

    Bugler, John; Somers, Kieran P.; Silke, Emma J.; Curran, Henry J.

    2015-01-01

    pertinent to important low-temperature oxidation reaction classes has been performed, and new rate rules are recommended for these classes. Several reaction classes have also been included to determine their importance with regard to simulation results

  12. Moessbauer spectroscopy characterization and electrochemical study of the kinetics of oxidation of iron in chlorinated aqueous media: structure and equilibrium diagram of green rust one

    International Nuclear Information System (INIS)

    Genin, J.M.R.; Rezel, D.; Bauer, Ph.; Olowe, A.; Beral, A.

    1986-01-01

    Moessbauer spectroscopy allows to precise the structure of akaganeite, lepidocrocite, green rust I and initial hydroxide of a simulated corrosion process of iron in chlorinated aqueous media. The characterization of the compounds during the process is coupled with E - pH recordings, yielding the kinetics of the various reactions (order and activation energy) as well as the Pourbaix diagram of Green Rust I by scanning the [Cl - ]/[OH - ] ratio. (author) 16 refs., 15 figs

  13. Kinetics of solid-gas reactions characterized by scanning AC nano-calorimetry with application to Zr oxidation

    International Nuclear Information System (INIS)

    Xiao, Kechao; Lee, Dongwoo; Vlassak, Joost J.

    2014-01-01

    Scanning AC nano-calorimetry is a recently developed experimental technique capable of measuring the heat capacity of thin-film samples of a material over a wide range of temperatures and heating rates. Here, we describe how this technique can be used to study solid-gas phase reactions by measuring the change in heat capacity of a sample during reaction. We apply this approach to evaluate the oxidation kinetics of thin-film samples of zirconium in air. The results confirm parabolic oxidation kinetics with an activation energy of 0.59 ± 0.03 eV. The nano-calorimetry measurements were performed using a device that contains an array of micromachined nano-calorimeter sensors in an architecture designed for combinatorial studies. We demonstrate that the oxidation kinetics can be quantified using a single sample, thus enabling high-throughput mapping of the composition-dependence of the reaction rate.

  14. Kinetics of the reduction of uranium oxide catalysts

    International Nuclear Information System (INIS)

    Heynen, H.W.G.; Camp-van Berkel, M.M.; Bann, H.S. van der

    1977-01-01

    The reduction of uranium oxide and uranium oxide on alumina catalysts by ethylbenzene and by hydrogen has been studied in a thermobalance. Ethylbenzene mole fractions between 0.0026 and 0.052 and hydrogen mole fractions between 0.1 and 0.6 were applied at temperatures of 425--530 0 C. During the reduction the uranium oxides are converted into UO 2 . The rate of reduction of pure uranium oxide appears to be constant in the composition region UO/sub 2.6/-UO/sub 2.25/. The extent of this region is independent of the concentration of the reducing agents and of the reaction temperature. The constant rate is explained in terms of a constant oxygen pressure which is in equilibrium with the two solid phases, U 3 O/sub 8-x/ and U 4 O 9 . The reduction rate is first order in hydrogen and zero order in ethylbenzene with activation energies of 120 and 190 kJ mol -1 , respectively. Oxygen diffusion through the lattice is probably not rate limiting. The reduction behavior of uranium oxide on alumina is different from that of pure uranium oxide; the rate of reduction continuously decreases with increasing degree of reduction. An explanation for this behavior has been given by visualizing this catalyst as a set of isolated uranium oxide crystallites with a relative wide variation of diameters, in an alumina matrix. At the beginning of the reduction, carbon dioxide and water are the only reaction products. Thereafter, benzene is found as well and, finally, at U/O ratios below 2.25, styrene also appears in the reactor outlet

  15. Thermoluminescence of magnesium oxide and its trapping kinetics

    International Nuclear Information System (INIS)

    Nagpal, J.S.; Kathuria, S.P.

    1984-01-01

    MgO (Norton), on u.v. and γ irradiation, exhibits TL glow peaks around 88, 150, 172, 195 and 250degC (heating rate 55degC min -1 ). TL emission is observed around 340, 390, 445 and 705 nm and can be attributed to the impurities Fe 3+ and Cr 3+ , which act as luminescence centers. ESR studies rule out any participation of Mn 2+ ions. The glow peak around 88degC has E = 1.055 eV, s = 4.3 x 10 13 s -1 and has order of kinetics b = 1.7. (author)

  16. Oxidizer Scoping Studies

    Energy Technology Data Exchange (ETDEWEB)

    Chancellor, Christopher John [Los Alamos National Laboratory

    2016-11-07

    The purpose of this report is to present the results of the acceptable knowledge (AK) review of oxidizers present in active waste streams, provide a technical analysis of the oxidizers, and report the results of the scoping study testing. This report will determine the fastest burning oxidizer to be used in the development of a Test Plan for Preparation and Testing of Sorbents Mixed with Oxidizer found in Transuranic Waste (DWT-TP-001). The companion report, DWT-RPT-002, Sorbent Scoping Studies, contains similar information for sorbents identified during the AK review of TRU waste streams. The results of the oxidizer and sorbent scoping studies will be used to inform the QL1 test plan. The QL1 test results will support the development of a basis of knowledge document that will evaluate oxidizing chemicals and sorbents in TRU waste and provide guidance for treatment.

  17. Quantitative production of compound I from a cytochrome P450 enzyme at low temperatures. Kinetics, activation parameters, and kinetic isotope effects for oxidation of benzyl alcohol.

    Science.gov (United States)

    Wang, Qin; Sheng, Xin; Horner, John H; Newcomb, Martin

    2009-08-05

    Cytochrome P450 enzymes are commonly thought to oxidize substrates via an iron(IV)-oxo porphyrin radical cation transient termed Compound I, but kinetic studies of P450 Compounds I are essentially nonexistent. We report production of Compound I from cytochrome P450 119 (CYP119) in high conversion from the corresponding Compound II species at low temperatures in buffer mixtures containing 50% glycerol by photolysis with 365 nm light from a pulsed lamp. Compound I was studied as a reagent in oxidations of benzyl alcohol and its benzylic mono- and dideuterio isotopomers. Pseudo-first-order rate constants obtained at -50 degrees C with concentrations of substrates between 1.0 and 6.0 mM displayed saturation kinetics that gave binding constants for the substrate in the Compound I species (K(bind)) and first-order rate constants for the oxidation reactions (k(ox)). Representative results are K(bind) = 214 M(-1) and k(ox) = 0.48 s(-1) for oxidation of benzyl alcohol. For the dideuterated substrate C(6)H(5)CD(2)OH, kinetics were studied between -50 and -25 degrees C, and a van't Hoff plot for complexation and an Arrhenius plot for the oxidation reaction were constructed. The H/D kinetic isotope effects (KIEs) at -50 degrees C were resolved into a large primary KIE (P = 11.9) and a small, inverse secondary KIE (S = 0.96). Comparison of values extrapolated to 22 degrees C of both the rate constant for oxidation of C(6)H(5)CD(2)OH and the KIE for the nondeuterated and dideuterated substrates to values obtained previously in laser flash photolysis experiments suggested that tunneling could be a significant component of the total rate constant at -50 degrees C.

  18. Kinetic Study of Curcumin on Modal Fabric

    Directory of Open Access Journals (Sweden)

    Abu Naser Md. Ahsanul Haque

    2018-03-01

    Full Text Available A kinetic study of curcumin on modal fabric was carried out using an initial dye concentration of 1 g/L at three different temperatures, 70 °C, 85 °C and 100 °C, at pH 7 and an material to liquor ratio of 1:20. Pseudo first-order and pseudo second-order kinetics were applied, and it was found that the adsorption kinetics of curcumin on modal fabric matched the pseudo second-order kinetic model. The activation energy was found to be equal to 71.14 kJ/mol, while the enthalpy and entropy of activation were 68.16 kJ/mol and –66.02 J/molK respectively.

  19. Oxyhalogen-Sulfur Chemistry: Kinetics and Mechanism of Oxidation ...

    African Journals Online (AJOL)

    The oxidation of N-acetylthiourea (ACTU) by acidic bromate has been studied by observing formation of bromine in excess bromate conditions. The reaction displays an induction period before formation of bromine. The stoichiometry of the reaction was determined to be 4:3: 4BrO3 ...

  20. Kinetics and mechanism of the oxidation of substituted ...

    Indian Academy of Sciences (India)

    Unknown

    Oxidation of meta- and para-substituted benzylamines by cetyltrimethyl- ... method.12 As per this method, the aldimine is hydrolysed to the aldehyde and then ... reactions were studied at constant temperature (± 0⋅1 K) and were followed by .... electronic interaction between the substituent and the reaction centre, (σ+–σ0) is ...

  1. The kinetics of iodide oxidation by the manganese oxide mineral birnessite

    Science.gov (United States)

    Fox, P.M.; Davis, J.A.; Luther, G. W.

    2009-01-01

    The kinetics of iodide (I-) and molecular iodine (I2) oxidation by the manganese oxide mineral birnessite (??-MnO2) was investigated over the pH range 4.5-6.25. I- oxidation to iodate (IO3-) proceeded as a two-step reaction through an I2 intermediate. The rate of the reaction varied with both pH and birnessite concentration, with faster oxidation occurring at lower pH and higher birnessite concentration. The disappearance of I- from solution was first order with respect to I- concentration, pH, and birnessite concentration, such that -d[I-]/dt = k[I-][H+][MnO2], where k, the third order rate constant, is equal to 1.08 ?? 0.06 ?? 107 M-2 h-1. The data are consistent with the formation of an inner sphere I- surface complex as the first step of the reaction, and the adsorption of I- exhibited significant pH dependence. Both I2, and to a lesser extent, IO3- sorbed to birnessite. The results indicate that iodine transport in mildly acidic groundwater systems may not be conservative. Because of the higher adsorption of the oxidized I species I2 and IO3-, as well as the biophilic nature of I2, redox transformations of iodine must be taken into account when predicting I transport in aquifers and watersheds.

  2. Evaluation of the kinetic oxidation of aqueous volatile organic compounds by permanganate

    NARCIS (Netherlands)

    Mahmoodlu, M.G.; Hassanizadeh, S.M.; Hartog, Niels

    2014-01-01

    The use of permanganate solutions for in-situ chemical oxidation (ISCO) is a well-established groundwater remediation technology, particularly for targeting chlorinated ethenes. The kinetics of oxidation reactions is an important ISCO remediation design aspect that affects the efficiency and oxidant

  3. Kinetic study and thermal decomposition behavior of viscoelastic memory foam

    International Nuclear Information System (INIS)

    Garrido, María A.; Font, Rafael; Conesa, Juan A.

    2016-01-01

    Highlights: • The thermal degradation has been studied under three different atmospheres. • Pyrolysis and combustion kinetic models have been proposed. • Evolved products under different atmospheres have been analyzed by TG-FTIR and TG-MS. - Abstract: A systematic investigation of the thermal decomposition of viscoelastic memory foam (VMF) was performed using thermogravimetric analysis (TGA) to obtain the kinetic parameters, and thermogravimetric analysis coupled to Fourier Transformed Infrared Spectrometry (TGA-FTIR) and thermogravimetric analysis coupled to Mass Spectrometry (TGA-MS) to obtain detailed information of evolved products on pyrolysis and oxidative degradations. Two consecutive nth-order reactions were employed to correlate the experimental data from dynamic and isothermal runs performed at three different heating rates (5, 10 and 20 K/min) under an inert atmosphere. On the other hand, for the kinetic study of the oxidative decomposition, the data from combustion (synthetic air) and poor oxygen combustion (N_2:O_2 = 9:1) runs, at three heating rates and under dynamic and isothermal conditions, were correlated simultaneously. A kinetic model consisting of three consecutive reactions presented a really good correlation in all runs. TGA-FTIR analysis showed that the main gases released during the pyrolysis of VMF were determined as ether and aliphatic hydrocarbons, whereas in combustion apart from the previous gases, aldehydes, amines and CO_2 have also been detected as the main gases. These results were confirmed by the TGA-MS.

  4. Oxidation kinetic changes of UO2 by additive addition and irradiation

    International Nuclear Information System (INIS)

    You, Gil-Sung; Kim, Keon-Sik; Min, Duck-Kee; Ro, Seung-Gy

    2000-01-01

    The kinetic changes of air-oxidation of UO 2 by additive addition and irradiation were investigated. Several kinds of specimens, such as unirradiated-UO 2 , simulated-UO 2 for spent PWR fuel (SIMFUEL), unirradiated-Gd-doped UO 2 , irradiated-UO 2 and -Gd-doped UO 2 , were used for these experiments. The oxidation results represented that the kinetic patterns among those samples are remarkably different. It was also revealed that the oxidation kinetics of irradiated-UO 2 seems to be more similar to that of unirradiated-Gd-doped UO 2 than that of SIMFUEL

  5. Smouldering Combustion of Soil Organic Matter: Inverse Modelling of the Thermal and Oxidative Degradation Kinetics

    Science.gov (United States)

    Huang, Xinyan; Rein, Guillermo

    2013-04-01

    Smouldering combustion of soil organic matter (SOM) such as peatlands leads to the largest fires on Earth and posses a possible positive feedback mechanism to climate change. In this work, a kinetic model, including 3-step chemical reactions and 1-step water evaporation is proposed to describe drying, pyrolysis and oxidation behaviour of peat. Peat is chosen as the most important type of SOM susceptible to smoudering, and a Chinese boreal peat sample is selected from the literature. A lumped model of mass loss based on four Arrhenius-type reactions is developed to predict its thermal and oxidative degradation under a range of heating rates. A genetic algorithm is used to solve the inverse problem, and find a group of kinetic and stoichiometric parameters for this peat that provides the best match to the thermogravimetric (TG) data from literature. A multi-objective fitness function is defined using the measurements of both mass loss and mass-loss rate in inert and normal atmospheres under a range of heating rates. Piece-wise optimization is conducted to separate the low temperature drying (450 K). Modelling results shows the proposed 3-step chemistry is the unique simplest scheme to satisfy all given TG data of this particular peat type. Afterward, this kinetic model and its kinetic parameters are incorporated into a simple one-dimensional species model to study the relative position of each reaction inside a smoulder front. Computational results show that the species model agrees with experimental observations. This is the first time that the smouldering kinetics of SOM is explained and predicted, thus helping to understanding this important natural and widespread phenomenon.

  6. Kinetics of Oxidation of 3-Benzoylpropionic Acid by N-Bromoacetamide in Aqueous Acetic Acid Medium

    Directory of Open Access Journals (Sweden)

    N. A. Mohamed Farook

    2011-01-01

    Full Text Available The kinetics of oxidation of 3-benzoylpropionic acid (KA with N-bromoacetamide (NBA have been studied potentiometrically in 50:50 (v/v aqueous acetic acid medium at 298 K The reaction was first order each with respect to [KA], [NBA] and [H+]. The main product of the oxidation is the corresponding carboxylic acid. The rate decreases with the addition of acetamide, one of the products of the reaction. Variation in ionic strength of the reaction medium has no significant effect on the rate of oxidation. But the rate of the reaction is enhanced by lowering the dielectric constant of the reaction medium. A mechanism consistent with observed results have been proposed and the related rate law was deduced.

  7. Global Kinetic Constants for Thermal Oxidative Degradation of a Cellulosic Paper

    Science.gov (United States)

    Kashiwagi, Takashi; Nambu, Hidesaburo

    1992-01-01

    Values of global kinetic constants for pyrolysis, thermal oxidative degradation, and char oxidation of a cellulosic paper were determined by a derivative thermal gravimetric study. The study was conducted at heating rates of 0.5, 1, 1.5, 3, and 5 C/min in ambient atmospheres of nitrogen, 0.28, 1.08, 5.2 percent oxygen concentrations, and air. Sample weight loss rate, concentrations of CO, CO2, and H2O in the degradation products, and oxygen consumption were continuously measured during the experiment. Values of activation energy, preexponential factor, orders of reaction, and yields of CO, CO2, H2O, total hydrocarbons, and char for each degradation reaction were derived from the results. Heat of reaction for each reaction was determined by differential scanning calorimetry. A comparison of the calculated CO, CO2, H2O, total hydrocarbons, sample weight loss rate, and oxygen consumption was made with the measured results using the derived kinetic constants, and the accuracy of the values of kinetic constants was discussed.

  8. Status of Chronic Oxidation Studies of Graphite

    Energy Technology Data Exchange (ETDEWEB)

    Contescu, Cristian I. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Mee, Robert W. [Univ. of Tennessee, Knoxville, TN (United States)

    2016-05-01

    Graphite will undergo extremely slow, but continuous oxidation by traces of moisture that will be present, albeit at very low levels, in the helium coolant of HTGR. This chronic oxidation may cause degradation of mechanical strength and thermal properties of graphite components if a porous oxidation layer penetrates deep enough in the bulk of graphite components during the lifetime of the reactor. The current research on graphite chronic oxidation is motivated by the acute need to understand the behavior of each graphite grade during prolonged exposure to high temperature chemical attack by moisture. The goal is to provide the elements needed to develop predictive models for long-time oxidation behavior of graphite components in the cooling helium of HTGR. The tasks derived from this goal are: (1) Oxidation rate measurements in order to determine and validate a comprehensive kinetic model suitable for prediction of intrinsic oxidation rates as a function of temperature and oxidant gas composition; (2) Characterization of effective diffusivity of water vapor in the graphite pore system in order to account for the in-pore transport of moisture; and (3) Development and validation of a predictive model for the penetration depth of the oxidized layer, in order to assess the risk of oxidation caused damage of particular graphite grades after prolonged exposure to the environment of helium coolant in HTGR. The most important and most time consuming of these tasks is the measurement of oxidation rates in accelerated oxidation tests (but still under kinetic control) and the development of a reliable kinetic model. This report summarizes the status of chronic oxidation studies on graphite, and then focuses on model development activities, progress of kinetic measurements, validation of results, and improvement of the kinetic models. Analysis of current and past results obtained with three grades of showed that the classical Langmuir-Hinshelwood model cannot reproduce all

  9. Kinetics of sodium borohydride direct oxidation and oxygen reduction in sodium hydroxide electrolyte

    International Nuclear Information System (INIS)

    Chatenet, Marian; Micoud, Fabrice; Roche, Ivan; Chainet, Eric

    2006-01-01

    The direct oxidation of sodium borohydride in concentrated sodium hydroxide medium has been studied by cyclic and linear voltammetry, chronoamperometry and chronopotentiometry for silver and gold electrocatalysts, either bulk and polycrystalline or nanodispersed over high area carbon blacks. Gold and silver yield rather complete utilisation of the reducer: around 7.5 electrons are delivered on these materials, versus 4 at the most for platinum as a result of the BH 4 - non-negligible hydrolysis taking place on this latter material. The kinetic parameters for the direct borohydride oxidation are better for gold than for silver. A strong influence of the ratio of sodium hydroxide versus sodium borohydride is found: whereas the theoretical stoichiometry does forecast that eight hydroxide ions are needed for each borohydride ion, our experimental results prove that a larger excess hydroxide ion is necessary in quasi-steady state conditions. When the above-mentioned ratio is unity (1 M NaOH and 1 M NaBH 4 ), the tetrahydroborate ions direct oxidation is limited by the hydroxide concentration, and their hydrolysis is no longer negligible. The hydrolysis products are probably BH 3 OH - ions, for which gold displays a rather good oxidation activity. Additionally, silver, which is a weak BH 4 - oxidation electrocatalyst, exhibits the best activity of all the studied materials towards the BH 3 OH - direct oxidation. Finally, carbon-supported gold nanoparticles seem promising as anode material to be used in direct borohydride fuel cells

  10. The Effect of Temperature and Ionic Strength on the Oxidation of Iodide by Iron(III): A Clock Reaction Kinetic Study

    Science.gov (United States)

    Bauer, Jurica; Tomisic, Vladislav; Vrkljan, Petar B. A.

    2012-01-01

    A laboratory exercise has recently been reported in which the students use the initial rates method based on the clock reaction approach to deduce the rate law and propose a reaction mechanism for the oxidation of iodide by iron(III) ions. The same approach is used in the exercise proposed herein; the students determine the dependence of the…

  11. The reaction mechanism of the partial oxidation of methane to synthesis gas: a transient kinetic study over rhodium and a comparison with platinum

    NARCIS (Netherlands)

    Mallens, E.P.J.; Hoebink, J.H.B.J.; Marin, G.B.M.M.

    1997-01-01

    The partial oxidation of methane to synthesis gas over rhodium sponge has been investigated by admitting pulses of pure methane and pure oxygen as well as mixtures of methane and oxygen to rhodium sponge at temperatures from 873 to 1023 K. Moreover, pulses of oxygen followed by methane and vice

  12. To the problem on formation kinetics of absorption and polylayer films in anodic oxidation of cadmium in alkali hydroxides. Kinetics of irreversible absorption of oxide

    International Nuclear Information System (INIS)

    Grachev, D.K.

    1978-01-01

    An attempt is made to substantiate the formation of adsorption and polylayer films on cadmium electrode during its oxidation in KOH diluted solutions based on the interpretation of data from methods of the potential control. Using relaxation methods (voltammetry and chronoammetry) the conditions were determined at which irreversible abd sorption kinetics of the passivating oxide turns out to dominate the anodic dissolution process in the KOH 1-0.1 N solutions. Parts of monolayer and polylayer surface filling are shown. Kinetics of monolayer oxide growth is interpreted based on the Temkin-Zeldovich type equation for irreversible adsorption process. Ways of the kinetic equation precision are discussed for its full correspondence with the experiment obtained

  13. Kinetic analysis of dechlorination and oxidation of PrOCl by using a non-isothermal TG method

    International Nuclear Information System (INIS)

    Yang, H.C.; Eun, H.C.; Cho, Y.Z.; Lee, H.S.; Kim, I.T.

    2009-01-01

    Thermal dechlorination and oxidation process of praseodymium oxychloride, PrOCl, was studied from the view point of reaction kinetics. On the basis of data of thermogravimetry under different oxygen partial pressures at various heating rates, a kinetic analysis was performed using an isoconversional method and a master plot method. The results of the isoconversional method of TG data suggested that the dechlorination and oxidation of PrOCl followed a single step with activation energy of 112.6 ± 3.4 kJ mol -1 , and from master plot methods, the reaction was described by a linear-contracting phase boundary reaction

  14. Pyrite oxidation in the presence of hematite and alumina: I. Batch leaching experiments and kinetic modeling calculations.

    Science.gov (United States)

    Tabelin, Carlito Baltazar; Veerawattananun, Suchol; Ito, Mayumi; Hiroyoshi, Naoki; Igarashi, Toshifumi

    2017-02-15

    Pyrite is one of the most common and geochemically important sulfide minerals in nature because of its role in the redox recycling of iron (Fe). It is also the primary cause of acid mine drainage (AMD) that is considered as a serious and widespread problem facing the mining and mineral processing industries. In the environment, pyrite oxidation occurs in the presence of ubiquitous metal oxides, but the roles that they play in this process remain largely unknown. This study evaluates the effects of hematite (α-Fe 2 O 3 ) and alumina (α-Al 2 O 3 ) on pyrite oxidation by batch-reactor type experiments, surface-sensitive characterization of the oxidation layer and thermodynamic/kinetic modeling calculations. In the presence of hematite, dissolved sulfur (S) concentration dramatically decreased independent of the pH, and the formation of intermediate sulfoxy anionic species on the surface of pyrite was retarded. These results indicate that hematite minimized the overall extent of pyrite oxidation, but the kinetic model could not explain how this suppression occurred. In contrast, pyrite oxidation was enhanced in the alumina suspension as suggested by the higher dissolved S concentration and stronger infrared (IR) absorption bands of surface-bound oxidation products. Based on the kinetic model, alumina enhanced the oxidative dissolution of pyrite because of its strong acid buffering capacity, which increased the suspension pH. The higher pH values increased the oxidation of Fe 2+ to Fe 3+ by dissolved O 2 (DO) that enhanced the overall oxidative dissolution kinetics of pyrite. Copyright © 2016 Elsevier B.V. All rights reserved.

  15. Kinetics and mechanism of auto- and copper-catalyzed oxidation of 1,4-naphthohydroquinone.

    Science.gov (United States)

    Yuan, Xiu; Miller, Christopher J; Pham, A Ninh; Waite, T David

    2014-06-01

    Although quinones represent a class of organic compounds that may exert toxic effects both in vitro and in vivo, the molecular mechanisms involved in quinone species toxicity are still largely unknown, especially in the presence of transition metals, which may both induce the transformation of the various quinone species and result in generation of harmful reactive oxygen species. In this study, the oxidation of 1,4-naphthohydroquinone (NH2Q) in the absence and presence of nanomolar concentrations of Cu(II) in 10 mM NaCl solution over a pH range of 6.5-7.5 has been investigated, with detailed kinetic models developed to describe the predominant mechanisms operative in these systems. In the absence of copper, the apparent oxidation rate of NH2Q increased with increasing pH and initial NH2Q concentration, with concomitant oxygen consumption and peroxide generation. The doubly dissociated species, NQ(2-), has been shown to be the reactive species with regard to the one-electron oxidation by O2 and comproportionation with the quinone species, both generating the semiquinone radical (NSQ(·-)). The oxidation of NSQ(·-) by O2 is shown to be the most important pathway for superoxide (O2(·-)) generation with a high intrinsic rate constant of 1.0×10(8)M(-1)s(-1). Both NSQ(·-) and O2(·-) served as chain-propagating species in the autoxidation of NH2Q. Cu(II) is capable of catalyzing the oxidation of NH2Q in the presence of O2 with the oxidation also accelerated by increasing the pH. Both the uncharged (NH2Q(0)) and the mono-anionic (NHQ(-)) species were found to be the kinetically active forms, reducing Cu(II) with an intrinsic rate constant of 4.0×10(4) and 1.2×10(7)M(-1)s(-1), respectively. The presence of O2 facilitated the catalytic role of Cu(II) by rapidly regenerating Cu(II) via continuous oxidation of Cu(I) and also by efficient removal of NSQ(·-) resulting in the generation of O2(·-). The half-cell reduction potentials of various redox couples at neutral p

  16. Growth kinetics of tin oxide nanocrystals in colloidal suspensions under hydrothermal conditions

    International Nuclear Information System (INIS)

    Lee, Eduardo J.H.; Ribeiro, Caue; Longo, Elson; Leite, Edson R.

    2006-01-01

    Colloidal suspensions of tin oxide nanocrystals were synthesized at room temperature by the hydrolysis reaction of tin chloride (II), in an ethanolic solution. The coarsening kinetics of such nanocrystals was studied by submitting the as-prepared suspensions to hydrothermal treatments at temperatures of 100, 150 and 200 deg. C for periods between 60 and 12,000 min. Transmission electron microscopy (TEM) was used to characterize the samples (i.e. distribution of nanocrystal size, average particle radius and morphology). The results show that the usual Ostwald ripening coarsening mechanism does not fit well the experimental data, which is an indicative that this process is not significant for SnO 2 nanocrystals, in the studied experimental conditions. The morphology evolution of the nanocrystals upon hydrothermal treatment indicates that growth by oriented attachment (OA) should be significant. A kinetic model that describes OA growth is successfully applied to fit the data

  17. Combustion Kinetic Studies of Gasolines and Surrogates

    KAUST Repository

    Javed, Tamour

    2016-11-01

    Future thrusts for gasoline engine development can be broadly summarized into two categories: (i) efficiency improvements in conventional spark ignition engines, and (ii) development of advance compression ignition (ACI) concepts. Efficiency improvements in conventional spark ignition engines requires downsizing (and turbocharging) which may be achieved by using high octane gasolines, whereas, low octane gasolines fuels are anticipated for ACI concepts. The current work provides the essential combustion kinetic data, targeting both thrusts, that is needed to develop high fidelity gasoline surrogate mechanisms and surrogate complexity guidelines. Ignition delay times of a wide range of certified gasolines and surrogates are reported here. These measurements were performed in shock tubes and rapid compression machines over a wide range of experimental conditions (650 – 1250 K, 10 – 40 bar) relevant to internal combustion engines. Using the measured the data and chemical kinetic analyses, the surrogate complexity requirements for these gasolines in homogeneous environments are specified. For the discussions presented here, gasolines are classified into three categories: (i)\\tLow octane gasolines including Saudi Aramco’s light naphtha fuel (anti-knock index, AKI = (RON + MON)/2 = 64; Sensitivity (S) = RON – MON = 1), certified FACE (Fuels for Advanced Combustion Engines) gasoline I and J (AKI ~ 70, S = 0.7 and 3 respectively), and their Primary Reference Fuels (PRF, mixtures of n-heptane and iso-octane) and multi-component surrogates. (ii)\\t Mid octane gasolines including FACE A and C (AKI ~ 84, S ~ 0 and 1 respectively) and their PRF surrogates. Laser absorption measurements of intermediate and product species formed during gasoline/surrogate oxidation are also reported. (iii)\\t A wide range of n-heptane/iso-octane/toluene (TPRF) blends to adequately represent the octane and sensitivity requirements of high octane gasolines including FACE gasoline F and G

  18. Oxidation Kinetics of Chemically Vapor-Deposited Silicon Carbide in Wet Oxygen

    Science.gov (United States)

    Opila, Elizabeth J.

    1994-01-01

    The oxidation kinetics of chemically vapor-deposited SiC in dry oxygen and wet oxygen (P(sub H2O) = 0.1 atm) at temperatures between 1200 C and 1400 C were monitored using thermogravimetric analysis. It was found that in a clean environment, 10% water vapor enhanced the oxidation kinetics of SiC only very slightly compared to rates found in dry oxygen. Oxidation kinetics were examined in terms of the Deal and Grove model for oxidation of silicon. It was found that in an environment containing even small amounts of impurities, such as high-purity Al2O3 reaction tubes containing 200 ppm Na, water vapor enhanced the transport of these impurities to the oxidation sample. Oxidation rates increased under these conditions presumably because of the formation of less protective sodium alumino-silicate scales.

  19. Kinetic and catalytic analysis of mesoporous metal oxides on the oxidation of Rhodamine B

    Science.gov (United States)

    Xaba, Morena S.; Noh, Ji-Hyang; Mokgadi, Keabetswe; Meijboom, Reinout

    2018-05-01

    In this study, we demonstrate the synthesis and catalytic activity of different mesoporous transition metal oxides, silica (SiO2), copper oxide (CuO), chromium oxide (Cr2O3), iron oxide (Fe2O3) cobalt oxide (Co3O4), cerium oxide (CeO2) and nickel oxide (NiO), on the oxidation of a pollutant dye, Rhodamine B (RhB). These metal oxides were synthesized by inverse micelle formation method and characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), adsorption-desorption isotherms (BET) and H2-temperature programmed reduction (TPR). UV-vis spectrophotometry was used to monitor the time-resolved absorbance of RhB at λmax = 554 nm. Mesoporous copper oxide was calcined at different final heating temperatures of 250, 350, 450 and 550 °C, and each mesoporous copper oxide catalyst showed unique physical properties and catalytic behavior. Mesoporous CuO-550 with the smallest characteristic path length δ, proved to be the catalyst of choice for the oxidation of RhB in aqueous media. We observed that the oxidation of RhB in aqueous media is dependent on the crystallite size and characteristic path length of the mesoporous metal oxide. The Langmuir-Hinshelwood model was used to fit the experimental data and to prove that the reaction occurs on the surface of the mesoporous CuO. The thermodynamic parameters, EA, ΔH#, ΔS# and ΔG# were calculated and catalyst recycling and reusability were demonstrated.

  20. Kinetics and mechanisms of thiol-disulfide exchange covering direct substitution and thiol oxidation-mediated pathways.

    Science.gov (United States)

    Nagy, Péter

    2013-05-01

    Disulfides are important building blocks in the secondary and tertiary structures of proteins, serving as inter- and intra-subunit cross links. Disulfides are also the major products of thiol oxidation, a process that has primary roles in defense mechanisms against oxidative stress and in redox regulation of cell signaling. Although disulfides are relatively stable, their reduction, isomerisation, and interconversion as well as their production reactions are catalyzed by delicate enzyme machineries, providing a dynamic system in biology. Redox homeostasis, a thermodynamic parameter that determines which reactions can occur in cellular compartments, is also balanced by the thiol-disulfide pool. However, it is the kinetic properties of the reactions that best represent cell dynamics, because the partitioning of the possible reactions depends on kinetic parameters. This review is focused on the kinetics and mechanisms of thiol-disulfide substitution and redox reactions. It summarizes the challenges and advances that are associated with kinetic investigations in small molecular and enzymatic systems from a rigorous chemical perspective using biological examples. The most important parameters that influence reaction rates are discussed in detail. Kinetic studies of proteins are more challenging than small molecules, and quite often investigators are forced to sacrifice the rigor of the experimental approach to obtain the important kinetic and mechanistic information. However, recent technological advances allow a more comprehensive analysis of enzymatic systems via using the systematic kinetics apparatus that was developed for small molecule reactions, which is expected to provide further insight into the cell's machinery.

  1. Kinetics of abiotic nitrous oxide production via oxidation of hydroxylamine by particulate metals in seawater

    Science.gov (United States)

    Cavazos, A. R.; Taillefert, M.; Glass, J. B.

    2016-12-01

    The oceans are a significant of nitrous oxide (N2O) to the atmosphere. Current models of global oceanic N2­O flux focus on microbial N2O cycling and often ignore abiotic reactions, such as the thermodynamically favorable oxidation of the nitrification intermediate hydroxylamine (NH2OH) by Mn(IV) or Fe(III). At circumneutral pH, NH2OH oxidation is more thermodynamically favorable via Mn(IV) than Fe(III) reduction. We characterized the kinetics of NH2OH oxidation in synthetic ocean water at pH 5.1-8.8 using microsensor electrodes to measure real-time N2O production. N2O production rates and yield were greater when NH2OH was oxidized by Mn(IV) than Fe(III). Accordingly, the reduction of Mn(IV) was first order with respect to NH2OH whereas the reduction of Fe(III) was zero order with respect to NH2OH. Interestingly, the order of the reaction with respect to Mn(IV) appears to be negative whereas the reaction is second order with respect to Fe(III). The inverse order with respect to Mn(IV) may be due to the aggregation of particles in seawater, which decreases their surface area and changes their reactivity. Finally, the reaction is first order with respect to protons with Fe(III) as the oxidant but zero order with Mn(IV). The stronger effect of the pH on the reaction with Fe(III) as the oxidant compared to Mn(IV) reflects the stoichiometry of these two reactions, as each mole of N2O produced by Fe(III) reduction consumes eight protons while each mole of N2O produced with Mn(IV) as the oxidant requires only four protons. Our data show that abiotic NH2OH oxidation by Mn(IV) or Fe(III) particles may represent a significant source of N2O in seawater. These findings suggest that abiotic N2O production in marine waters may be significant in areas of the oceans where particulate metals originating from aerosols, dust, or rivers may react with NH2OH released from ammonia-oxidizing microorganisms.

  2. Kinetic studies of elementary chemical reactions

    Energy Technology Data Exchange (ETDEWEB)

    Durant, J.L. Jr. [Sandia National Laboratories, Livermore, CA (United States)

    1993-12-01

    This program concerning kinetic studies of elementary chemical reactions is presently focussed on understanding reactions of NH{sub x} species. To reach this goal, the author is pursuing experimental studies of reaction rate coefficients and product branching fractions as well as using electronic structure calculations to calculate transition state properties and reaction rate calculations to relate these properties to predicted kinetic behavior. The synergy existing between the experimental and theoretical studies allow one to gain a deeper insight into more complex elementary reactions.

  3. First-order hydrothermal oxidation kinetics of digested sludge compared with raw sludge.

    Science.gov (United States)

    Shanableh, A; Imteaz, M

    2008-09-01

    This article presents an assessment of the first-order hydrothermal oxidation kinetics of a selected digested sludge at subcritical ( 374 degrees C) temperatures in the range of 250-460 degrees C. Furthermore, the results were compared with reported oxidation kinetics of raw sludge treated under identical experimental conditions. In the assessment, oxidation was considered to proceed in two steps: (1) decomposition of the particulate, or non-filterable, chemical oxygen demand (PCOD); followed by (2) ultimate oxidation and removal of the total, particulate and soluble, COD. The accumulation and removal of soluble COD (SCOD) was determined from the difference between the rates of sludge decomposition and ultimate oxidation. Using results from batch and continuous-flow hydrothermal treatment experiments, the reacting organic ingredients were separated into groups according to the ease or difficulty at which they were decomposed or removed, with Arrhenius-type activation energy levels assigned to the different groups. The analysis confirmed that within the treatment range of 75% to more than 97% COD removal, the oxidation kinetics of the digested and raw sludges were nearly identical despite differences in the proportions of their original organic ingredients. The original organic ingredients were mostly removed above 75% COD removal, and the oxidation kinetics appeared to be dominated by the removal of acetic acid, an intermediate by-product which constituted 50% to more than 80% of the remaining COD. Furthermore, the oxidation kinetics of both sludge types were consistent with reported first-order oxidation kinetics of pure acetic acid solutions. The resulting kinetic models adequately represented hydrothermal oxidation of digested sludge, in terms of COD and PCOD removals, as well as accumulation and removal of the soluble SCOD.

  4. Cu(II)-catalyzed oxidation of dopamine in aqueous solutions: mechanism and kinetics.

    Science.gov (United States)

    Pham, A Ninh; Waite, T David

    2014-08-01

    Spontaneous oxidation of dopamine (DA) and the resultant formation of free radical species within dopamine neurons of the substantia nigra (SN) is thought to bestow a considerable oxidative load upon these neurons and may contribute to their vulnerability to degeneration in Parkinson's disease (PD). An understanding of DA oxidation under physiological conditions is thus critical to understanding the relatively selective vulnerability of these dopaminergic neurons in PD and may support the development of novel neuro-protective approaches for this disorder. In this study, the oxidation of dopamine (0.2-10μM) was investigated both in the absence and the presence of copper (0.01-0.4μM), a redox active metal that is present at considerable concentrations in the SN, over a range of background chloride concentrations (0.01-0.7M), different oxygen concentrations and at physiological pH7.4. DA was observed to oxidize extremely slowly in the absence of copper and at moderate rates only in the presence of copper but without chloride. The oxidation of DA however was significantly enhanced in the presence of both copper and chloride with the rate of DA oxidation greatest at intermediate chloride concentrations (0.05-0.2M). The variability of the catalytic effect of Cu(II) on DA oxidation at different chloride concentrations can be explained and successfully modeled by appropriate consideration of the reaction of Cu(II) species with DA and the conversion of Cu(I) to Cu(II) through oxygenation. This model suggests that the speciation of Cu(II) and Cu(I) is critically important to the kinetics of DA oxidation and thus the vulnerability to degradation of dopaminergic neuron in the brain milieu. Copyright © 2014 Elsevier Inc. All rights reserved.

  5. The role of surface oxides on hydrogen sorption kinetics in titanium thin films

    Science.gov (United States)

    Hadjixenophontos, Efi; Michalek, Lukas; Roussel, Manuel; Hirscher, Michael; Schmitz, Guido

    2018-05-01

    Titanium is presently discussed as a catalyst to accelerate the hydrogenation kinetics of hydrogen storage materials. It is however known that H absorption in Ti decisively depends on the surface conditions (presence or absence of the natural surface oxide). In this work, we use Ti thin films of controlled thickness (50-800 nm) as a convenient tool for quantifying the atomic transport. XRD and TEM investigations allow us to follow the hydrogenation progress inside the film. Hydrogenation of TiO2/Ti bi-layers is studied at 300 °C, for different durations (10 s to 600 min) and at varying pressures of pure H2 atmosphere. Under these conditions, the hydrogenation is found to be linear in time. By comparing films with and without TiO2, as well as by studying the pressure dependence of hydrogenation, it is demonstrated that hydrogen transport across the oxide represents the decisive kinetic barrier rather than the splitting of H2 molecules at the surface. Hydrogenation appears by a layer-like reaction initiated by heterogeneous nucleation at the backside interface to the substrate. The linear growth constant and the H diffusion coefficient inside the oxide are quantified, as well as a reliable lower bound to the hydrogen diffusion coefficient in Ti is derived. The pressure dependence of hydrogen absorption is quantitatively modelled.

  6. Learning the Fundamentals of Kinetics and Reaction Engineering with the Catalytic Oxidation of Methane

    Science.gov (United States)

    Cybulskis, Viktor J.; Smeltz, Andrew D.; Zvinevich, Yury; Gounder, Rajamani; Delgass, W. Nicholas; Ribeiro, Fabio H.

    2016-01-01

    Understanding catalytic chemistry, collecting and interpreting kinetic data, and operating chemical reactors are critical skills for chemical engineers. This laboratory experiment provides students with a hands-on supplement to a course in chemical kinetics and reaction engineering. The oxidation of methane with a palladium catalyst supported on…

  7. Effect of Dunaliella tertiolecta organic exudates on the Fe(II) oxidation kinetics in seawater.

    Science.gov (United States)

    González, A G; Santana-Casiano, J M; González-Dávila, M; Pérez-Almeida, N; Suárez de Tangil, M

    2014-07-15

    The role played by the natural organic ligands excreted by the green algae Dunaliella tertiolecta on the Fe(II) oxidation rate constants was studied at different stages of growth. The concentration of dissolved organic carbon increased from 2.1 to 7.1 mg L(-1) over time of culture. The oxidation kinetics of Fe(II) was studied at nanomolar levels and under different physicochemical conditions of pH (7.2-8.2), temperature (5-35 °C), salinity (10-37), and dissolved organic carbon produced by cells (2.1-7.1 mg L(-1)). The experimental rate always decreased in the presence of organic exudates with respect to that in the control seawater. The Fe(II) oxidation rate constant was also studied in the context of Marcus theory, where ΔG° was 39.31-51.48 kJ mol(-1). A kinetic modeling approach was applied for computing the equilibrium and rate constants for Fe(II) and exudates present in solution, the Fe(II) speciation, and the contribution of each Fe(II) species to the overall oxidation rate constant. The best fit model took into account two acidity equilibrium constants for the Fe(II) complexing ligands with pKa,1=9.45 and pKa,2=4.9. The Fe(II) complexing constants were KFe(II)-LH=3×10(10) and KFe(II)-L=10(7), and the corresponding computed oxidation rates were 68±2 and 36±8 M(-1) min(-1), respectively.

  8. Solving the master equation without kinetic Monte Carlo: Tensor train approximations for a CO oxidation model

    International Nuclear Information System (INIS)

    Gelß, Patrick; Matera, Sebastian; Schütte, Christof

    2016-01-01

    In multiscale modeling of heterogeneous catalytic processes, one crucial point is the solution of a Markovian master equation describing the stochastic reaction kinetics. Usually, this is too high-dimensional to be solved with standard numerical techniques and one has to rely on sampling approaches based on the kinetic Monte Carlo method. In this study we break the curse of dimensionality for the direct solution of the Markovian master equation by exploiting the Tensor Train Format for this purpose. The performance of the approach is demonstrated on a first principles based, reduced model for the CO oxidation on the RuO 2 (110) surface. We investigate the complexity for increasing system size and for various reaction conditions. The advantage over the stochastic simulation approach is illustrated by a problem with increased stiffness.

  9. Solving the master equation without kinetic Monte Carlo: Tensor train approximations for a CO oxidation model

    Science.gov (United States)

    Gelß, Patrick; Matera, Sebastian; Schütte, Christof

    2016-06-01

    In multiscale modeling of heterogeneous catalytic processes, one crucial point is the solution of a Markovian master equation describing the stochastic reaction kinetics. Usually, this is too high-dimensional to be solved with standard numerical techniques and one has to rely on sampling approaches based on the kinetic Monte Carlo method. In this study we break the curse of dimensionality for the direct solution of the Markovian master equation by exploiting the Tensor Train Format for this purpose. The performance of the approach is demonstrated on a first principles based, reduced model for the CO oxidation on the RuO2(110) surface. We investigate the complexity for increasing system size and for various reaction conditions. The advantage over the stochastic simulation approach is illustrated by a problem with increased stiffness.

  10. Solving the master equation without kinetic Monte Carlo: Tensor train approximations for a CO oxidation model

    Energy Technology Data Exchange (ETDEWEB)

    Gelß, Patrick, E-mail: p.gelss@fu-berlin.de; Matera, Sebastian, E-mail: matera@math.fu-berlin.de; Schütte, Christof, E-mail: schuette@mi.fu-berlin.de

    2016-06-01

    In multiscale modeling of heterogeneous catalytic processes, one crucial point is the solution of a Markovian master equation describing the stochastic reaction kinetics. Usually, this is too high-dimensional to be solved with standard numerical techniques and one has to rely on sampling approaches based on the kinetic Monte Carlo method. In this study we break the curse of dimensionality for the direct solution of the Markovian master equation by exploiting the Tensor Train Format for this purpose. The performance of the approach is demonstrated on a first principles based, reduced model for the CO oxidation on the RuO{sub 2}(110) surface. We investigate the complexity for increasing system size and for various reaction conditions. The advantage over the stochastic simulation approach is illustrated by a problem with increased stiffness.

  11. Kinetics of the oxidation of Ba2YCu3O/sub x/ ceramics

    International Nuclear Information System (INIS)

    O'Bryan, H.M.; Gallagher, P.K.

    1988-01-01

    The kinetics of the oxidation of dense and porous samples of Ba 2 YCu 3 O/sub x/ ceramic have been determined by gravimetric analysis at 400--700 0 C. At 600 0 C and above, the rate decreases as the thickness of the oxidized layer increases. At 500 0 C and below, the kinetics show a linear relation that indicates that the oxidized layer does not protect the ceramic. Dilatometric, microscopic, and high-temperature x-ray data suggest that fractures in the oxide layer at the lower temperatures are caused by the large volume decrease that accompanies the change in oxygen stoichiometry

  12. Behaviour of defective CANDU fuel: fuel oxidation kinetic and thermodynamic modelling

    International Nuclear Information System (INIS)

    Higgs, J.

    2005-01-01

    The thermal performance of operating CANDU fuel under defect conditions is affected by the ingress of heavy water into the fuel element. A mechanistic model has been developed to predict the extent of fuel oxidation in defective fuel and its affect on fuel thermal performance. A thermodynamic treatment of such oxidized fuel has been performed as a basis for the boundary conditions in the kinetic model. Both the kinetic and thermodynamic models have been benchmarked against recent experimental work. (author)

  13. Kinetics and mechanism of the deep electrochemical oxidation of sodium diclofenac on a boron-doped diamond electrode

    Science.gov (United States)

    Vedenyapina, M. D.; Borisova, D. A.; Rosenwinkel, K.-H.; Weichgrebe, D.; Stopp, P.; Vedenyapin, A. A.

    2013-08-01

    The kinetics and mechanism of the deep oxidation of sodium diclofenac on a boron-doped diamond electrode are studied to develop a technique for purifying wastewater from pharmaceutical products. The products of sodium diclofenac electrolysis are analyzed using cyclic voltammetry and nuclear magnetic resonance techniques. It is shown that the toxicity of the drug and products of its electrolysis decreases upon its deep oxidation.

  14. Oxidation kinetics and mechanisms of carbon/carbon composites and their components in water vapour at high temperatures

    International Nuclear Information System (INIS)

    Qin, Fei; Peng, Li-na; He, Guo-qiang; Li, Jiang; Yan, Yong

    2015-01-01

    Highlights: • 4D-C/C composite was fabricated using carbon fibre and coal tar pitch. • The rate of mass loss and oxidation kinetics parameters of fibres-H 2 O and matrix-H 2 O are obtained. • The rate of mass loss and oxidation kinetics parameters of C/C–H 2 O are obtained. • Oxidation rate of the fibre bundle is greater than the oxidation rate of the matrix. - Abstract: Thermogravimetric analysis and scanning electron microscopy were used to study the oxidation kinetics of four-direction carbon/carbon composites and their components (fibres and matrices) in a H 2 O–Ar atmosphere at high temperatures. The oxidation processes were restricted to reaction-limited oxidation. The rate of mass loss was estimated for the four-direction carbon/carbon composites and their components at high temperature. The pressure exponent for the reaction of the carbon/carbon composites with H 2 O was 0.59, and the pre-exponential factor and activation energy for the reactions of H 2 O with the carbon/carbon composites, carbon fibres and matrices were determined

  15. Thermoluminescence of magnesium oxide and its trapping kinetics

    Energy Technology Data Exchange (ETDEWEB)

    Nagpal, J.S. (Bhabha Atomic Research Centre, Bombay (India). Div. of Radiological Protection); Kathuria, S.P. (Bhabha Atomic Research Centre, Bombay (India). Health Physics Div.)

    1984-06-01

    MgO (Norton), on u.v. and ..gamma.. irradiation, exhibits TL glow peaks around 88, 150, 172, 195 and 250degC (heating rate 55degC min/sup -1/). TL emission is observed around 340, 390, 445 and 705 nm and can be attributed to the impurities Fe/sup 3 +/ and Cr/sup 3 +/, which act as luminescence centers. ESR studies rule out any participation of Mn/sup 2 +/ ions. The glow peak around 88degC has E = 1.055 eV, s = 4.3 x 10/sup 13/s/sup -1/ and has order of kinetics b = 1.7.

  16. Kinetics of YBa2Cu3O6+γ oxidation

    International Nuclear Information System (INIS)

    Mozhaev, A.P.; Chernyaev, S.V.; Udal'tsova, T.I.; Kotov, N.M.

    1992-01-01

    Kinetics of the processes taking place during thermal treatment of YBa 2 Cu 3 O 6+γ samples and change in oxygen nonstoichiometry, related to the processes, were studied. The coefficient of oxygen diffusion was determined (D=D 0 x exp x (-E α /RT) a = 118 kJ/mol, D 0 = 4x10 -6 m 2 /s), which gave a satisfactory description of behaviour of powders and ceramics with the density below 5200 kg/m 3 . It is shown that in the course of annealing of denser samples considerable deviations of the calculated curves γ(T) from the experimental ones are observed. The deviations mentioned can be explained by the appearance of closed porosity and additional diffusion impediments

  17. Lithium hydride hydrolysis: experimental and kinetic study

    International Nuclear Information System (INIS)

    Charton, S.; Maupoix, C.; Brevet, A.; Delaunay, F.; Heintz, O.; Saviot, L.

    2006-01-01

    In this work has been studied the contribution of various analyses techniques in the framework, on the one hand of revealing the mechanisms implied in lithium hydride hydrolysis, and on the other hand of studying the kinetics of hydrogen production. Among the methods recently investigated, Raman spectroscopy, XPS and SIMS seem to be particularly attractive. (O.M.)

  18. Kinetic and mechanistic evaluation of tetrahydroborate ion electro-oxidation at polycrystalline gold

    International Nuclear Information System (INIS)

    Iotov, Philip I.; Kalcheva, Sasha V.; Bond, Alan M.

    2009-01-01

    The anodic oxidation of tetrahydroborate ion is studied in NaOH at stationary and rotating polycrystalline Au disk electrodes. Linear sweep and cyclic voltammetry are applied varying the scan and rotation rate from 0.005 to 51.200 V s -1 and from 52.3 to 314.1 rad s -1 , correspondingly. The effects of variation of BH 4 - and NaOH concentrations as well as of the potential limits of the ranges studied have been initially followed. Most of the experiments have been carried out with 10.9 mM NaBH 4 in 1.04 M NaOH at 293 K in the potential range from -1.300 to 0.900 V (vs. Ag/AgCl). It is found that 6 electrons are exchanged in the overall oxidation transformation. The kinetic analysis of the processes determining the two anodic peaks recorded under static conditions at scan rates lower than 0.500 V s -1 shows that 1.4 electrons are exchanged in the potential range of the first one (at ca -0.5 V), while the rate of the second one (at ca +0.3 V) is determined by a quasi-reversible 1-electron transfer reaction. A kinetic evidence for the participation of surface bound intermediates in the electro-oxidation process is provided. Two additional well outlined anodic peaks are recorded in the aforementioned potential range under specific experimental conditions. A quasi-8 electron mechanism involving four oxidation and hydrolysis steps is advanced to explain the experimental results. It accounts for the involvement of borohydride oxidation species and the Au + /Au 3+ mediator couple.

  19. Kinetics that govern the release of tritium from neutron-irradiated lithium oxide

    International Nuclear Information System (INIS)

    Bertone, P.C.

    1986-01-01

    The Lithium Blanket Module (LBM) program being conducted at the Princeton Plasma Physics Laboratory requires that tritium concentrations as low as 0.1 nCi/g, bred in both LBM lithium oxide pellets and gram-size lithium samples, be measured with an uncertainty not exceeding +/-6%. This thesis reports two satisfactory methods of assaying LBM pellets and one satisfactory method of assaying lithium samples. Results of a fundamental kinetic investigation are also reported. The thermally driven release of tritium from neutron-irradiated lithium oxide pellets is studied between the temperatures of 300 and 400 0 C. The observed release clearly obeys first-order kinetics, and the governing activation energy appears to be 28.4 kcal/mole. Finally, a model is presented that may explain the thermally driven release of tritium from a lithium oxide crystal and assemblies thereof. It predicts that under most circumstances the release is controlled by either the diffusion of a tritiated species through the crystal, or by the desorption of tritiated water from it

  20. Oxidation of β-lactam antibiotics by peracetic acid: Reaction kinetics, product and pathway evaluation.

    Science.gov (United States)

    Zhang, Kejia; Zhou, Xinyan; Du, Penghui; Zhang, Tuqiao; Cai, Meiquan; Sun, Peizhe; Huang, Ching-Hua

    2017-10-15

    Peracetic acid (PAA) is a disinfection oxidant used in many industries including wastewater treatment. β-Lactams, a group of widely prescribed antibiotics, are frequently detected in wastewater effluents and surface waters. The reaction kinetics and transformation of seven β-lactams (cefalexin (CFX), cefadroxil (CFR), cefapirin (CFP), cephalothin (CFT), ampicillin (AMP), amoxicillin (AMX) and penicillin G (PG)) toward PAA were investigated to elucidate the behavior of β-lactams during PAA oxidation processes. The reaction follows second-order kinetics and is much faster at pH 5 and 7 than at pH 9 due to speciation of PAA. Reactivity to PAA follows the order of CFR ∼ CFX > AMP ∼ AMX > CFT ∼ CFP ∼ PG and is related to β-lactam's nucleophilicity. The thioether sulfur of β-lactams is attacked by PAA to generate sulfoxide products. Presence of the phenylglycinyl amino group on β-lactams can significantly influence electron distribution and the highest occupied molecular orbital (HOMO) location and energy in ways that enhance the reactivity to PAA. Reaction rate constants obtained in clean water matrix can be used to accurately model the decay of β-lactams by PAA in surface water matrix and only slightly overestimate the decay in wastewater matrix. Results of this study indicate that the oxidative transformation of β-lactams by PAA can be expected under appropriate wastewater treatment conditions. Copyright © 2017. Published by Elsevier Ltd.

  1. Simplified modeling of simultaneous reaction kinetics of carbon oxidation and nitrification in biofilm processes

    Energy Technology Data Exchange (ETDEWEB)

    Tsuneda, S.; Auresenia, J.; Hibiya, K.; Hirata, A. [Waseda University, Department of Chemical Engineering, 3-4-1 Ohkubo, Shinjuku-ku, Tokyo 169-8555 (Japan)

    2004-06-01

    Batch experiments with varying initial substrate concentrations and biomass volumes were performed in a three-phase fluidized bed biofilm reactor treating simulated domestic wastewater to study the simultaneous carbon oxidation and nitrification in the biofilm process. A simplified mass balance equation for the biofilm was proposed and five different kinetic rate equations were used to match the actual data. The kinetic parameters were obtained by nonlinear regression analysis on a set of two differential equations representing the simultaneous carbon oxidation and nitrification. The competitive inhibition model incorporating the effects of total organic carbon (TOC) concentrations on nitrification rates was the best-suited model based on the average r{sup 2}. In this model, oxygen concentration and its affinity constants were not included. Instead, it was assumed that the rate of carbon oxidation is independent of the NH{sub 4}{sup +}-N, while nitrification is affected by TOC. The number of parameters was successfully minimized without reducing its ability to accurately predict the bulk concentration time course, which would reduce computational complexity and possibly enhance the availability for an actual wastewater treatment process. (Abstract Copyright [2004], Wiley Periodicals, Inc.)

  2. Kinetics of irreversible thermal decomposition of dissociating nitrogen dioxide with nitrogen oxide or oxygen additions

    International Nuclear Information System (INIS)

    Gvozdev, A.A.

    1987-01-01

    The effect of NO or O 2 admixtures on kinetics of the irreversible thermal decomposition of nitrogen dioxide at temperatures 460-520 deg C and pressures 4-7 MPa has been studied. It follows from experimental data that the rate of N 2 O 4 formation reduces with the increase of partial pressure of oxygen or decrease of partial pressure of nitrogen oxide. The same regularity is seen for the rate of nitrogen formation. The rate constants of N 2 O formation in dissociating nitrogen tetroxide with oxygen or nitrogen oxide additions agree satisfactorily with previously published results, obtained in stoichiometric mixtures. The appreciable discrepancy at 520 deg C is bind with considerable degree of nitrogen oxide transformation which constitutes approximately 14%. It is determined that the kinetics of formation of the products of irreversible N 2 O and N 2 decomposition in stoichiometric and non-stoichiometric 2NO 2 ↔ 2NO+O 2 mixtures is described by identical 3NO → N 2 O+NO 2 and N 2 O+NO → N 2 +NO 2 reactions

  3. Effects of preconditioning the rhizosphere of different plant species on biotic methane oxidation kinetics.

    Science.gov (United States)

    Ndanga, Éliane M; Lopera, Carolina B; Bradley, Robert L; Cabral, Alexandre R

    2016-09-01

    The rhizosphere is known as the most active biogeochemical layer of the soil. Therefore, it could be a beneficial environment for biotic methane oxidation. The aim of this study was to document - by means of batch incubation tests - the kinetics of CH4 oxidation in rhizosphere soils that were previously exposed to methane. Soils from three pre-exposure to CH4 zones were sampled: the never-before pre-exposed (NEX), the moderately pre-exposed (MEX) and the very pre-exposed (VEX). For each pre-exposure zone, the rhizosphere of several plant species was collected, pre-incubated, placed in glass vials and submitted to CH4 concentrations varying from 0.5% to 10%. The time to the beginning of CH4 consumption and the CH4 oxidation rate were recorded. The results showed that the fastest CH4 consumption occurred for the very pre-exposed rhizosphere. Specifically, a statistically significant difference in CH4 oxidation half-life was found between the rhizosphere of the VEX vegetated with a mixture of different plants and the NEX vegetated with ryegrass. This difference was attributed to the combined effect of the preconditioning level and plant species as well as to the organic matter content. Regardless of the preconditioning level, the oxidation rate values obtained in this study were comparable to those reported in the reviewed literature for mature compost. Copyright © 2016 Elsevier Ltd. All rights reserved.

  4. Theoretical Kinetic Study of the Unimolecular and H-Assisted Keto-Enol Tautomerism Propen-2-ol ↔Acetone. Pressure Effects and Implications in the Pyrolysis and Oxidation of tert- And 2-Butanol

    KAUST Repository

    Grajales Gonzalez, Edwing Javier

    2018-05-01

    The need for renewable and cleaner sources of energy has made biofuels an interesting alternative to fossil fuels, especially in the case of butanol isomers, with their favorable blend properties and low hygroscopicity. Although C4 alcohols are prospective fuels, some key reactions governing their pyrolysis and combustion have not been adequately studied, leading to incomplete kinetic models. Butanol reactions kinetics is poorly understood. Specifically, the unimolecular and H-assisted tautomerism of propen-2-ol to acetone, which are included in butanol combustion kinetic models, are assigned rate parameters based on the analogous unimolecular tautomerism vinyl alcohol ↔ acetaldehyde and H addition to the double bound of iso-butene, respectively. In an attempt to update current kinetic models for tert- and 2-butanol, a theoretical kinetic study of the unimolecular and H-assisted tautomerism, i-C3H5OH⟺CH3COCH3 and i-C3H5OH+Ḣ⟺CH3COCH3+Ḣ, was carried out by means of CCSD(T,FULL)/aug-cc-pVTZ//CCSD(T)/6-31+G(d,p) and CCSD(T)/aug-cc-pVTZ//M062X/cc-pVTZ ab initio calculations, respectively. For H-assisted tautomerism, the reaction takes place in two consecutive steps: i-C3H5OH+Ḣ⟺CH3ĊOHCH3 and CH3ĊOHCH3⟺CH3COCH3+Ḣ. Multistructural torsional anharmonicity and variational transition state theory were considered in a wide temperature and pressure range (200 K – 3000 K, 0.1 kPa – 108 kPa). It was observed that decreasing pressure leads to a decrease in rate constants, describing the expected falloff behavior for both isomerizations. Results for unimolecular tautomerism differ from vinyl alcohol ↔ acetaldehyde analogue reactions, which shows lower rate constant values. Tunneling turned out to be important, especially at low temperatures. Accordingly, pyrolysis simulations in a batch reactor for tert- and 2-butanol with computed unimolecular rate constants showed important differences in comparison with previous results, such as larger acetone yield and

  5. Oxidation kinetics of hydride-bearing uranium metal corrosion products

    Science.gov (United States)

    Totemeier, Terry C.; Pahl, Robert G.; Frank, Steven M.

    The oxidation behavior of hydride-bearing uranium metal corrosion products from Zero Power Physics Reactor (ZPPR) fuel plates was studied using thermo-gravimetric analysis (TGA) in environments of Ar-4%O 2, Ar-9%O 2, and Ar-20%O 2. Ignition of corrosion product samples from two moderately corroded plates was observed between 125°C and 150°C in all environments. The rate of oxidation above the ignition temperature was found to be dependent only on the net flow rate of oxygen in the reacting gas. Due to the higher net oxygen flow rate, burning rates increased with increasing oxygen concentration. Oxidation rates below the ignition temperature were much slower and decreased with increasing test time. The hydride contents of the TGA samples from the two moderately corroded plates, determined from the total weight gain achieved during burning, were 47-61 wt% and 29-39 wt%. Samples from a lightly corroded plate were not reactive; X-ray diffraction (XRD) confirmed that they contained little hydride.

  6. Oxidation kinetics of hydride-bearing uranium metal corrosion products

    International Nuclear Information System (INIS)

    Totemeier, T.C.; Pahl, R.G.; Frank, S.M.

    1998-01-01

    The oxidation behavior of hydride-bearing uranium metal corrosion products from zero power physics reactor (ZPPR) fuel plates was studied using thermo-gravimetric analysis (TGA) in environments of Ar-4%O 2 , Ar-9%O 2 , and Ar-20%O 2 . Ignition of corrosion product samples from two moderately corroded plates was observed between 125 C and 150 C in all environments. The rate of oxidation above the ignition temperature was found to be dependent only on the net flow rate of oxygen in the reacting gas. Due to the higher net oxygen flow rate, burning rates increased with increasing oxygen concentration. Oxidation rates below the ignition temperature were much slower and decreased with increasing test time. The hydride contents of the TGA samples from the two moderately corroded plates, determined from the total weight gain achieved during burning, were 47-61 wt% and 29-39 wt%. Samples from a lightly corroded plate were not reactive; X-ray diffraction (XRD) confirmed that they contained little hydride. (orig.)

  7. Oxidative kinetics of amino acids by peroxydisulfate: Effect of dielectric constant

    International Nuclear Information System (INIS)

    Khalid, Mohammad A. A.

    2008-01-01

    The kinetics and mechanism of oxidation of alanine, asparagines, cysteine, glutamic acid, lysine, phenylalanine and serine by peroxydisulfate ion have been studied in aqueous acidic (sulfuric acid) medium at the temperature range 60-80C. The rate shows first order dependence on peroxydisulfate concentration and zero order dependence on amino acid concentration. The rate law observed is: -d [S2O82-] /dt = Kobs [S2O82-] [amino acid]0. An autocatalytic effect has been observed in amino acids oxidation due to formation of Schiff's base between the formed aldehyde and parent amino acid. A decrease in the dielectric constant of the medium-adding acetic acid (5-15% v/v) results in a decrease in the rate in all cases studied. Reactions were carried out at different temperature (60-80C) and the thermodynamics parameters have been calculated. The logarithm of the rate constant is linearly interrelated to the square root of the ionic strength. (author)

  8. The effect of substrate orientation on the kinetics and thermodynamics of initial oxide-film growth on metals

    Energy Technology Data Exchange (ETDEWEB)

    Reichel, Friederike

    2007-11-19

    This thesis addresses the effect of the parent metal-substrate orientation on the thermodynamics and kinetics of ultra-thin oxide-film growth on bare metals upon their exposure to oxygen gas at low temperatures (up to 650 K). A model description has been developed to predict the thermodynamically stable microstructure of a thin oxide film grown on its bare metal substrate as function of the oxidation conditions and the substrate orientation. For Mg and Ni, the critical oxide-film thickness is less than 1 oxide monolayer and therefore the initial development of an amorphous oxide phase on these metal substrates is unlikely. Finally, for Cu and densely packed Cr and Fe metal surfaces, oxide overgrowth is predicted to proceed by the direct formation and growth of a crystalline oxide phase. Further, polished Al single-crystals with {l_brace}111{r_brace}, {l_brace}100{r_brace} and {l_brace}110{r_brace} surface orientations were introduced in an ultra-high vacuum system for specimen processing and analysis. After surface cleaning and annealing, the bare Al substrates have been oxidized by exposure to pure oxygen gas. During the oxidation, the oxide-film growth kinetics has been established by real-time in-situ spectroscopic ellipsometry. After the oxidation, the oxide-film microstructures were investigated by angle-resolved X-ray photoelectron spectroscopy and low energy electron diffraction. Finally, high-resolution transmission electron microscopic analysis was applied to study the microstructure and morphology of the grown oxide films on an atomic scale. (orig.)

  9. Microstructural evolution and growth kinetics of thermally grown oxides in plasma sprayed thermal barrier coatings

    Directory of Open Access Journals (Sweden)

    Xiaoju Liu

    2016-02-01

    Full Text Available The formation of thermally grown oxide (TGO during high temperature is a key factor to the degradation of thermal barrier coatings (TBCs applied on hot section components. In the present study both the CoNiCrAlY bond coat and ZrO2-8 wt.% Y2O3 (8YSZ ceramic coat of TBCs were prepared by air plasma spraying (APS. The composition and microstructure of TGO in TBCs were investigated using scanning electron microscopy (SEM, energy dispersive spectroscopy (EDS and X-ray diffraction (XRD analysis. The growth rate of TGO for TBC and pure BC were gained after isothermal oxidation at 1100 °C for various times. The results showed that as-sprayed bond coat consisted of β and γ/γ′phases, β phase reducesd as the oxidation time increased. The TGO comprised α-Al2O3 formed in the first 2 h. CoO, NiO, Cr2O3 and spinel oxides appeared after 20 h of oxidation. Contents of CoO and NiO reduced while that of Cr2O3 and spinel oxides increased in the later oxidation stage. The TGO eventually consisted of a sub-Al2O3 layer with columnar microstructure and the upper porous CS clusters. The TGO growth kinetics for two kinds of samples followed parabolic laws, with oxidation rate constant of 0.344 μm/h0.5 for TBCs and 0.354 μm/h0.5 for pure BCs.

  10. Composition dependence of the kinetics and mechanisms of thermal oxidation of titanium-tantalum alloys

    International Nuclear Information System (INIS)

    Park, Y.S.; Butt, D.P.

    1999-01-01

    The oxidation behavior of titanium-tantalum alloys was investigated with respective concentrations of each element ranging from 0 to 100 wt.%. Alloys were exposed to argon-20% oxygen at 800 to 1400 C. The slowest oxidation rates were observed in alloys with 5--20% Ta. The oxidation kinetics of alloys containing less than approximately 40% Ta were approximately parabolic. Pure Ta exhibited nearly linear kinetics. Alloys containing 50% or more Ta exhibited paralinear kinetics. The activation energies for oxidation ranged between 232 kJ/mole for pure Ti and 119 kJ/mole for pure Ta, with the activation energies of the alloys falling between these values and generally decreasing with increasing Ta content. The activation energies for oxidation of the end members, Ti and Ta, agree well with published values for the activation energies for diffusion of oxygen in α-Ti and Ta. Scale formation in the alloys was found to be complex exhibiting various layers of Ti-, Ta-, and TiTa-oxides. The outermost layer of the oxidized alloys was predominantly rutile (TiO 2 ). Beneath the TiO 2 grew a variety of other oxides with the Ta content generally increasing with proximity to the metal-oxide interface. It was found that the most oxidation-resistant alloys had compositions falling between Ti-5Ta and Ti-15Ta. Although Ta stabilizes the β-phase of Ti, the kinetics of oxidation appeared to be rate limited by oxygen transport through the oxygen-stabilized α-phase. However, the kinetics are complicated by the formation of a complex oxide, which cracks periodically. Tantalum appears to increase the compositional range of oxygen-stabilized α-phase and reduces both the solubility of oxygen and diffusivity of Ti in the α- and β-phases

  11. Analysis of the laser oxidation kinetics process of In-In(2)O(3) MTMO photomasks by laser direct writing.

    Science.gov (United States)

    Xia, Feng; Zhang, Xinzheng; Wang, Meng; Liu, Qian; Xu, Jingjun

    2015-11-02

    One kind of novel grayscale photomask based on Metal-transparent-metallic-oxides (MTMOs) system fabricated by laser direct writing was demonstrated recently. Here, a multilayer oxidation model of In-In(2)O(3) film with a glass substrate was proposed to study the pulsed laser-induced oxidation mechanism. The distribution of the electromagnetic field in the film is calculated by the transfer matrix method. Temperature fields of the model are simulated based on the heat transfer equations with the Finite-Difference Time-Domain method. The oxidation kinetics process is studied based on the laser-induced Cabrera-Mott theory. The simulated oxidation processes are consistent with the experimental results, which mean that our laser-induced oxidation model can successfully interpret the fabrication mechanism of MTMO grayscale photomasks.

  12. Growth kinetics and morphology of plasma electrolytic oxidation coating on aluminum

    Energy Technology Data Exchange (ETDEWEB)

    Erfanifar, Eliyas; Aliofkhazraei, Mahmood, E-mail: maliofkh@gmail.com; Fakhr Nabavi, Houman; Sharifi, Hossein; Rouhaghdam, Alireza Sabour

    2017-01-01

    Plasma electrolytic oxidation (PEO) was carried out on AA1190 aluminum alloy in mixed silicate-phosphate-based electrolyte in order to fabricate ceramic coating under constant current density. The variations of PEO coating duration with kinetics, surface roughness, amount and size of discharge channels were studied with respect to PEO processing time. The growth mechanism of the ceramic coating was described considering a variation of volume and diameters of discharge channels and pancakes during the PEO. Scanning electron microscope (SEM), atomic force microscope (AFM), and roughness tester were used to study the plasma discharge channels of the PEO coatings. In addition, the effect of alumina nanoparticles in the electrolyte as the suspension was studied on the geometric parameters of discharge channels. It seems that the nanoparticles are adsorbed to the locations of erupted molten oxide, where the dielectric breakdown occurs. Nanoparticles were embedded in the dense oxide layer and were adsorbed at the walls of voids and coatings surface. As a result, they caused significant changes in roughness parameters of the samples containing nanoparticles compared to those without nanoparticles. The obtained results showed that growth kinetics followed a linear trend with respect to PEO coating duration. It was also observed that in the absence of alumina nanoparticles, the average volume of the pancakes is 150% greater than the ones fabricated in the suspension of nanoparticles. Besides, increasing the PEO coating duration leads to adsorbing more nanoparticles on the coating surface, filling the voids, and flattening the surface, and alterations in R{sub v}, R{sub sk}, and R{sub lo} parameters. Correlation between the diameter of discharge channel (d{sub c}) and thickness of the pancake (h) also showed a linear relation. - Highlights: • Precise calculation of thickness of pancake with AFM. • Study of different roughness parameters for PEO coating. • Calculation

  13. Growth kinetics and morphology of plasma electrolytic oxidation coating on aluminum

    International Nuclear Information System (INIS)

    Erfanifar, Eliyas; Aliofkhazraei, Mahmood; Fakhr Nabavi, Houman; Sharifi, Hossein; Rouhaghdam, Alireza Sabour

    2017-01-01

    Plasma electrolytic oxidation (PEO) was carried out on AA1190 aluminum alloy in mixed silicate-phosphate-based electrolyte in order to fabricate ceramic coating under constant current density. The variations of PEO coating duration with kinetics, surface roughness, amount and size of discharge channels were studied with respect to PEO processing time. The growth mechanism of the ceramic coating was described considering a variation of volume and diameters of discharge channels and pancakes during the PEO. Scanning electron microscope (SEM), atomic force microscope (AFM), and roughness tester were used to study the plasma discharge channels of the PEO coatings. In addition, the effect of alumina nanoparticles in the electrolyte as the suspension was studied on the geometric parameters of discharge channels. It seems that the nanoparticles are adsorbed to the locations of erupted molten oxide, where the dielectric breakdown occurs. Nanoparticles were embedded in the dense oxide layer and were adsorbed at the walls of voids and coatings surface. As a result, they caused significant changes in roughness parameters of the samples containing nanoparticles compared to those without nanoparticles. The obtained results showed that growth kinetics followed a linear trend with respect to PEO coating duration. It was also observed that in the absence of alumina nanoparticles, the average volume of the pancakes is 150% greater than the ones fabricated in the suspension of nanoparticles. Besides, increasing the PEO coating duration leads to adsorbing more nanoparticles on the coating surface, filling the voids, and flattening the surface, and alterations in R v , R sk , and R lo parameters. Correlation between the diameter of discharge channel (d c ) and thickness of the pancake (h) also showed a linear relation. - Highlights: • Precise calculation of thickness of pancake with AFM. • Study of different roughness parameters for PEO coating. • Calculation the amount of

  14. Kinetic and mechanistic investigations of the degradation of sulfamethazine in heat-activated persulfate oxidation process.

    Science.gov (United States)

    Fan, Yan; Ji, Yuefei; Kong, Deyang; Lu, Junhe; Zhou, Quansuo

    2015-12-30

    Sulfamethazine (SMZ) is widely used in livestock feeding and aquaculture as an antibiotic agent and growth promoter. Widespread occurrence of SMZ in surface water, groundwater, soil and sediment has been reported. In this study, degradation of SMZ by heat-activated persulfate (PS) oxidation was investigated in aqueous solution. Experimental results demonstrated that SMZ degradation followed pseudo-first-order reaction kinetics. The pseudo-first-order rate constant (kobs) was increased markedly with increasing concentration of PS and temperature. Radical scavenging tests revealed that the predominant oxidizing species was SO4·(-) with HO playing a less important role. Aniline moiety in SMZ molecule was confirmed to be the reactive site for SO4·(-) attack by comparison with substructural analogs. Nontarget natural water constituents affected SMZ removal significantly, e.g., Cl(-) and HCO3(-) improved the degradation while fulvic acid reduced it. Reaction products were enriched by solid phase extraction (SPE) and analyzed by liquid chromatography-electrospray ionization-triple quadrupole mass spectrometry (LC-ESI-MS/MS). 6 products derived from sulfonamide S--N bond cleavage, aniline moiety oxidation and Smiles-type rearrangement were identified, and transformation pathways of SMZ oxidation were proposed. Results reveal that heat-activated PS oxidation could be an efficient approach for remediation of water contaminated by SMZ and related sulfonamides. Copyright © 2015 Elsevier B.V. All rights reserved.

  15. Kinetic Effects Of Increased Proton Transfer Distance On Proton-Coupled Oxidations Of Phenol-Amines

    Science.gov (United States)

    Rhile, Ian J.

    2011-01-01

    To test the effect of varying the proton donor-acceptor distance in proton-coupled electron transfer (PCET) reactions, the oxidation of a bicyclic amino-indanol (2) is compared with that of a closely related phenol with an ortho CPh2NH2 substituent (1). Spectroscopic, structural, thermochemical and computational studies show that the two amino-phenols are very similar, except that the O⋯N distance (dON) is >0.1 Å longer in 2 than in 1. The difference in dON is 0.13 ± 0.03 Å from X-ray crystallography and 0.165 Å from DFT calculations. Oxidations of these phenols by outer-sphere oxidants yield distonic radical cations •OAr–NH3+ by concerted proton-electron transfer (CPET). Simple tunneling and classical kinetic models both predict that the longer donor-acceptor distance in 2 should lead to slower reactions, by ca. two orders of magnitude, as well as larger H/D kinetic isotope effects (KIEs). However, kinetic studies show that the compound with the longer proton-transfer distance, 2, exhibits smaller KIEs and has rate constants that are quite close to those of 1. For example, the oxidation of 2 by the triarylamminium radical cation N(C6H4OMe)3•+ (3a+) occurs at (1.4 ± 0.1) × 104 M-1 s-1, only a factor of two slower than the closely related reaction of 1 with N(C6H4OMe)2(C6H4Br)•+ (3b+). This difference in rate constants is well accounted for by the slightly different free energies of reaction: ΔG°(2 + 3a+) = +0.078 V vs. ΔG°(1 + 3b+) = +0.04 V. The two phenol-amines do display some subtle kinetic differences: for instance, compound 2 has a shallower dependence of CPET rate constants on driving force (Brønsted α, Δln(k)/Δln(Keq)). These results show that the simple tunneling model is not a good predictor of the effect of proton donor-acceptor distance on concerted-electron transfer reactions involving strongly hydrogen-bonded systems. Computational analysis of the observed similarity of the two phenols emphasizes the importance of the highly

  16. Morphological impact on the reaction kinetics of size-selected cobalt oxide nanoparticles

    International Nuclear Information System (INIS)

    Bartling, Stephan; Meiwes-Broer, Karl-Heinz; Barke, Ingo; Pohl, Marga-Martina

    2015-01-01

    Apart from large surface areas, low activation energies are essential for efficient reactions, particularly in heterogeneous catalysis. Here, we show that not only the size of nanoparticles but also their detailed morphology can crucially affect reaction kinetics, as demonstrated for mass-selected, soft-landed, and oxidized cobalt clusters in a 6 nm to 18 nm size range. The method of reflection high-energy electron diffraction is extended to the quantitative determination of particle activation energies which is applied for repeated oxidation and reduction cycles at the same particles. We find unexpectedly small activation barriers for the reduction reaction of the largest particles studied, despite generally increasing barriers for growing sizes. We attribute these observations to the interplay of reaction-specific material transport with a size-dependent inner particle morphology

  17. [Kinetics of catalytic wet air oxidation of phenol in trickle bed reactor].

    Science.gov (United States)

    Li, Guang-ming; Zhao, Jian-fu; Wang, Hua; Zhao, Xiu-hua; Zhou, Yang-yuan

    2004-05-01

    By using a trickle bed reactor which was designed by the authors, the catalytic wet air oxidation reaction of phenol on CuO/gamma-Al2O3 catalyst was studied. The results showed that in mild operation conditions (at temperature of 180 degrees C, pressure of 3 MPa, liquid feed rate of 1.668 L x h(-1) and oxygen feed rate of 160 L x h(-1)), the removal of phenol can be over 90%. The curve of phenol conversion is similar to "S" like autocatalytic reaction, and is accordance with chain reaction of free radical. The kinetic model of pseudo homogenous reactor fits the catalytic wet air oxidation reaction of phenol. The effects of initial concentration of phenol, liquid feed rate and temperature for reaction also were investigated.

  18. Kinetics and Mechanism of Oxidation of Aromatic Aldehydes by Imidazolium Dichromate in Aqueous Acetic Acid Medium

    Directory of Open Access Journals (Sweden)

    S. Sheik Mansoor

    2009-01-01

    Full Text Available The kinetics of oxidation of benzaldehyde (BA and para-substituted benzaldehydes by imidazolium dichromate (IDC has been studied in aqueous acetic acid medium in the presence of perchloric acid. The reaction is first order each in [IDC], [Substrate] and [H+]. The reaction rates have been determined at different temperatures and the activation parameters calculated. Electron withdrawing substituents are found to increase the reaction and electron releasing substituents are found to retard the rate of the reaction and the rate data obey the Hammett relationship. The products of the oxidation are the corresponding acids. The rate decreases with the increase in the water content of the medium. A suitable mechanism is proposed.

  19. Performance of the periodic pulse technique--4. Periodic pulse reaction kinetics of oxidative dehydrogenation of isobutyraldehyde

    Energy Technology Data Exchange (ETDEWEB)

    Hattori, T.; Ii, M.; Murakami, Y.

    1980-07-01

    The periodic pulse method was used to study the reaction mechanism and kinetics of the oxidative dehydrogenation of isobutyraldehyde (IBA) by following the formation rates of methacrolein (MA), carbon monoxide and dioxide (CO/sub x/), and other products (P) as a function of pulse widths and reactant partial pressures at 350/sup 0/C over a 2:3 antimony oxide/molybdenum trioxide catalyst. The results were consistent with a mechanism according to which IBA reacts with oxygen retained by the catalyst to form MA, causing reduction of the catalyst. The IBA also adsorbed on the surface as an oxygenated species which either reacted with gas-phase oxygen to form CO/sub x/ or desorbed as an oxygenated P. The reduced catalyst surface was reoxidized by oxygen adsorption. Implications of catalyst tailoring for increased MA yields by improving the redox mechanism and inhibiting the surface reactions, are discussed.

  20. Kinetic studies of anomalous transport

    International Nuclear Information System (INIS)

    Tang, W.M.

    1990-11-01

    Progress in achieving a physics-based understanding of anomalous transport in toroidal systems has come in large part from investigations based on the proposition that low frequency electrostatic microinstabilities are dominant in the bulk (''confinement'') region of these plasmas. Although the presence here of drift-type modes dependent on trapped particle and ion temperature gradient driven effects appears to be consistent with a number of important observed confinement trends, conventional estimates for these instabilities cannot account for the strong current (I p ) and /or q-scaling frequently found in empirically deduced global energy confinement times for auxiliary-heated discharges. The present paper deals with both linear and nonlinear physics features, ignored in simpler estimates, which could introduce an appreciable local dependence on current. It is also pointed out that while the thermal flux characteristics of drift modes have justifiably been the focus of experimental studies assessing their relevance, other transport properties associated with these microinstabilities should additionally be examined. Accordingly, the present paper provides estimates and discusses the significance of anomalous energy exchange between ions and electrons when fluctuations are present. 19 refs., 3 figs

  1. Oxidative conversion of propane over lithium-promoted magnesia catalyst. I. Kinetics and mechanism

    NARCIS (Netherlands)

    Leveles, L.; Seshan, Kulathuiyer; Lercher, J.A.; Lefferts, Leonardus

    2003-01-01

    Oxidative conversion of lower alkanes over lithium-promoted magnesia catalysts offers a viable alternative for propene and ethene production. The catalytic performance of propane oxidative dehydrogenation and cracking shows yields up to 50% of olefin (propene and ethene). The reaction kinetics were

  2. The initial oxidation of epsilon-Fesub2Nsub1-x: growth kinetics

    DEFF Research Database (Denmark)

    Graat, Peter C.J.; Somers, Marcel A. J.; Mittemeijer, Eric J.

    1999-01-01

    The oxidation kinetics of epsilon-Fe2N1-x, subjected either to a sputter cleaning pretreatment or a sputter cleaning and an additional annealing pretreatment, at P-O2 = 1 x 10(-4) Pa and at temperatures ranging from 300 to 500 K, was investigated with ellipsometry. The initial oxidation rate of s...

  3. Kinetics and mechanism of the oxidation of formic and oxalic acids ...

    Indian Academy of Sciences (India)

    The oxidation of formic and oxalic acids by benzyltrimethylammonium dichloroiodate (BTMACI), in the presence of zinc chloride, leads to the formation of carbon dioxide. The reaction is first order with respect to BTMACI, zinc chloride and organic acid. Oxidation of deuteriated formic acid indicates the presence of a kinetic ...

  4. Degradation kinetics of chlorinated aliphatic hydrocarbons by methane oxidizers naturally-associated with wetland plant roots

    Science.gov (United States)

    Powell, C. L.; Goltz, M. N.; Agrawal, A.

    2014-12-01

    Chlorinated aliphatic hydrocarbons (CAHs) are common groundwater contaminants that can be removed from the environment by natural attenuation processes. CAH biodegradation can occur in wetland environments by reductive dechlorination as well as oxidation pathways. In particular, CAH oxidation may occur in vegetated wetlands, by microorganisms that are naturally associated with the roots of wetland plants. The main objective of this study was to evaluate the cometabolic degradation kinetics of the CAHs, cis-1,2-dichloroethene (cisDCE), trichloroethene (TCE), and 1,1,1-trichloroethane (1,1,1TCA), by methane-oxidizing bacteria associated with the roots of a typical wetland plant in soil-free system. Laboratory microcosms with washed live roots investigated aerobic, cometabolic degradation of CAHs by the root-associated methane-oxidizing bacteria at initial aqueous [CH4] ~ 1.9 mg L- 1, and initial aqueous [CAH] ~ 150 μg L- 1; cisDCE and TCE (in the presence of 1,1,1TCA) degraded significantly, with a removal efficiency of approximately 90% and 46%, respectively. 1,1,1TCA degradation was not observed in the presence of active methane oxidizers. The pseudo first-order degradation rate-constants of TCE and cisDCE were 0.12 ± 0.01 and 0.59 ± 0.07 d- 1, respectively, which are comparable to published values. However, their biomass-normalized degradation rate constants obtained in this study were significantly smaller than pure-culture studies, yet they were comparable to values reported for biofilm systems. The study suggests that CAH removal in wetland plant roots may be comparable to processes within biofilms. This has led us to speculate that the active biomass may be on the root surface as a biofilm. The cisDCE and TCE mass losses due to methane oxidizers in this study offer insight into the role of shallow, vegetated wetlands as an environmental sink for such xenobiotic compounds.

  5. Iron oxidation kinetics and phosphate immobilization along the flow-path from groundwater into surface water

    Science.gov (United States)

    van der Grift, B.; Rozemeijer, J. C.; Griffioen, J.; van der Velde, Y.

    2014-11-01

    The retention of phosphorus in surface waters through co-precipitation of phosphate with Fe-oxyhydroxides during exfiltration of anaerobic Fe(II) rich groundwater is not well understood. We developed an experimental field set-up to study Fe(II) oxidation and P immobilization along the flow-path from groundwater into surface water in an agricultural experimental catchment of a small lowland river. We physically separated tube drain effluent from groundwater discharge before it entered a ditch in an agricultural field. Through continuous discharge measurements and weekly water quality sampling of groundwater, tube drain water, exfiltrated groundwater, and surface water, we investigated Fe(II) oxidation kinetics and P immobilization processes. The oxidation rate inferred from our field measurements closely agreed with the general rate law for abiotic oxidation of Fe(II) by O2. Seasonal changes in climatic conditions affected the Fe(II) oxidation process. Lower pH and lower temperatures in winter (compared to summer) resulted in low Fe oxidation rates. After exfiltration to the surface water, it took a couple of days to more than a week before complete oxidation of Fe(II) is reached. In summer time, Fe oxidation rates were much higher. The Fe concentrations in the exfiltrated groundwater were low, indicating that dissolved Fe(II) is completely oxidized prior to inflow into a ditch. While the Fe oxidation rates reduce drastically from summer to winter, P concentrations remained high in the groundwater and an order of magnitude lower in the surface water throughout the year. This study shows very fast immobilization of dissolved P during the initial stage of the Fe(II) oxidation process which results in P-depleted water before Fe(II) is completely depleted. This cannot be explained by surface complexation of phosphate to freshly formed Fe-oxyhydroxides but indicates the formation of Fe(III)-phosphate precipitates. The formation of Fe(III)-phosphates at redox gradients

  6. Phase-field modeling of corrosion kinetics under dual-oxidants

    Science.gov (United States)

    Wen, You-Hai; Chen, Long-Qing; Hawk, Jeffrey A.

    2012-04-01

    A phase-field model is proposed to simulate corrosion kinetics under a dual-oxidant atmosphere. It will be demonstrated that the model can be applied to simulate corrosion kinetics under oxidation, sulfidation and simultaneous oxidation/sulfidation processes. Phase-dependent diffusivities are incorporated in a natural manner and allow more realistic modeling as the diffusivities usually differ by many orders of magnitude in different phases. Simple free energy models are then used for testing the model while calibrated free energy models can be implemented for quantitative modeling.

  7. Contribution to the identification of the processes kinetically limiting of the zirconium alloys oxidation; characterization of the oxide films formed at high temperature by solids electrochemistry

    International Nuclear Information System (INIS)

    Vermoyal, J.J.

    2000-06-01

    The corrosion behavior of zirconium alloys used for cladding tubes has been extensively studied under several oxidation conditions (temperature, steam, dry air, oxygen...) in order to clarify the mechanism(s) of oxide growth and breakdown. Oxidation rate is generally assumed to be controlled by oxygen diffusion inwards the oxide layer. Nevertheless, several experimental facts, such as acceleration or inhibition of corrosion rate in coupling conditions, suggest that electrochemical processes are involved as a rate determining step. This work is an attempt to shed light about the rate-limiting-mechanism of two zirconium alloys oxidation: Zircaloy-4 (Zy-4) and Zr-Nb(1%)O(0,13%). Impedance spectroscopy characterizations of oxide films formed in high temperature water and studied in gaseous atmosphere clearly show the difference of electrical properties between the two alloys. The in situ electrochemical and thermogravimetric investigations in gaseous medium, and the polarization effects on oxidation and hydridation of Zr alloys in PWRs conditions indicate that oxygen diffusion can be considered as the limiting kinetic step for Zy-4 oxidation. On the contrary, the acceleration of oxide growth on Zr-Nb(1%)O(0,13%) under anodic polarization in PWRs conditions (360 deg C) suggests that either the electronic conductivity in the oxide or an interfacial process at least partially control the oxidation rate. Catalytic effects observed in gaseous medium when noble metals increase the oxygen reduction rate would tend to corroborate the oxidation control of this alloy by an interfacial mechanism. An electrochemical description and a heterogeneous kinetics approach based on a diffusion-interfacial process as rate determining step are then proposed. (author)

  8. Kinetics and Mechanism of Oxidation of Diethyl Ether by Chloramine-T in Acidic Medium

    Directory of Open Access Journals (Sweden)

    Y. I. Hassan

    2012-01-01

    Full Text Available The kinetics of oxidation of diethyl ether (DE with sodium N-chloro-p-toluenesulphonamide (CAT in hydrochloric acid solution has been studied at (313°K.The reaction rate show a first order dependence on [CAT] and fractional order dependence on each [DE] and [H+] .The variation of ionic strength of the medium has no significant effect on the reaction rate , addition of p-toluenesulphonamide (p-TSA affects the reaction rate marginally the rate increased with decreasing dielectric constant of the medium , the stochiometry of the reaction was found to be 1:2 and oxidation products were identified , A Michaelis – Menten type mechanism has been suggested to explain the results.The equilibrium and the decomposition constants of CAT – diethyl ether complex have been evaluated. Thermodynamic parameters were computed by studying reaction at temperatures range ( 308 – 323°K for the rate limiting step and for the observed first order constants by the linear Arrhenius plot. The mechanism proposed and the derived rate law are consistent with observed kinetics.

  9. Kinetics of oxidation of bilirubin and its protein complex by hydrogen peroxide in aqueous solutions

    Science.gov (United States)

    Solomonov, A. V.; Rumyantsev, E. V.; Antina, E. V.

    2010-12-01

    A comparative study of oxidation reactions of bilirubin and its complex with albumin was carried out in aqueous solutions under the action of hydrogen peroxide and molecular oxygen at different pH values. Free radical oxidation of the pigment in both free and bound forms at pH 7.4 was shown not to lead to the formation of biliverdin, but to be associated with the decomposition of the tetrapyrrole chromophore into monopyrrolic products. The effective and true rate constants of the reactions under study were determined. It was assumed that one possible mechanism of the oxidation reaction is associated with the interaction of peroxyl radicals and protons of the NH groups of bilirubin molecules at the limiting stage with the formation of a highly reactive radical intermediate. The binding of bilirubin with albumin was found to result in a considerable reduction in the rate of the oxidation reaction associated with the kinetic manifestation of the protein protection effect. It was found that the autoxidation of bilirubin by molecular oxygen with the formation of biliverdin at the intermediate stage can be observed with an increase in the pH of solutions.

  10. Oxidation kinetics of the combustible fraction of construction and demolition wastes.

    Science.gov (United States)

    Chang, N B; Lin, K S; Sun, Y P; Wang, H P

    2001-01-01

    Proper disposal of construction and demolition wastes (CDW) has received wide attention recently due to significantly large quantities of waste streams collected from razed or retrofitted buildings in many metropolitan regions. Burning the combustible fractions of CDW (CCDW) and possibly recovering part of the heat content for economic uses could be valuable for energy conservation. This paper explores the oxidation kinetics of CCDW associated with its ash characterization. Kinetic parameters for the oxidation of CCDW were numerically calculated using thermal gravimetric analysis (TGA) and the resultant rate equations were therefore developed for illustrating the oxidation processes of CCDW simultaneously. Based on three designated heating rates, each of the oxidation processes can be featured distinctively with five different stages according to the rate of weight change at the temperature between 300 K and 923 K. In addition, Fourier transform infrared (FTIR) spectroscopy was employed, associated with a lab-scale fixed-bed incinerator for monitoring the composition of flue gas. Carbon dioxide (CO2) was found as a major component in the flue gas. The fuel analysis also included an ash composition analysis via the use of X-ray powder diffraction (XRD), atomic absorption (AA) spectroscopy, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDX). The ash streams were identified as nonhazardous materials based on the toxicity characteristic leaching procedure (TCLP). Overall, the scientific findings gained in this study will be helpful for supporting a sound engineering design of real-world CCDW incineration systems.

  11. Oxidation of indometacin by ferrate (VI): kinetics, degradation pathways, and toxicity assessment.

    Science.gov (United States)

    Huang, Junlei; Wang, Yahui; Liu, Guoguang; Chen, Ping; Wang, Fengliang; Ma, Jingshuai; Li, Fuhua; Liu, Haijin; Lv, Wenying

    2017-04-01

    The oxidation of indometacin (IDM) by ferrate(VI) (Fe(VI)) was investigated to determine the reaction kinetics, transformation products, and changes in toxicity. The reaction between IDM and Fe(VI) followed first-order kinetics with respect to each reactant. The apparent second-order rate constants (k app ) decreased from 9.35 to 6.52 M -1  s -1 , as the pH of the solution increased from 7.0 to 10.0. The pH dependence of k app might be well explained by considering the species-specific rate constants of the reactions of IDM with Fe(VI). Detailed product studies using liquid chromatography-tandem mass spectrometry (LC-MS/MS) indicated that the oxidation products were primarily derived from the hydrolysis of amide linkages, the addition of hydroxyl groups, and electrophilic oxidation. The toxicity of the oxidation products was evaluated using the Microtox test, which indicated that transformation products exhibited less toxicity to the Vibrio fischeri bacteria. Quantitative structure-activity relationship (QSAR) analysis calculated by the ecological structure activity relationship (ECOSAR) revealed that all of the identified products exhibited lower acute and chronic toxicity than the parent pharmaceutical for fish, daphnid, and green algae. Furthermore, Fe(VI) was effective in the degradation IDM in water containing carbonate ions or fulvic acid (FA), and in lake water samples; however, higher Fe(VI) dosages would be required to completely remove IDM in lake water in contrast to deionized water.

  12. Kinetics of oxidation of the alloy-MR-47VP with nitrogen dioxide

    International Nuclear Information System (INIS)

    Vasil'eva, A.G.; Rakova, N.N.; Vladimirskaya, I.N.; Kabanova, O.V.; Miklyaev, A.D.

    1978-01-01

    The kinetic dependences of oxidation of MR-47VP grade molybdenum-rhenium alloy with nitrogen dioxide have been examined within the temperature range of 350 to 550 deg C. It has been shown that the processes take place in the transition region. The specific oxidation rate of the alloy with the nitrogen dioxide is but small, and it is comparable as to its value with the specific rate of its oxidation in oxygen under identical conditions

  13. On kinetics and mechanism of' furfural oxidation by ions of heterovalent metals

    International Nuclear Information System (INIS)

    Krupenskij, V.I.

    1983-01-01

    Real constants of rate of furfural oxidation by Cu 2+ , Fe 3+ , Ce 4+ , Ag + , Hg 2+ 2 ions are determined, other kinetic and activation parameters of reactions are calculated, constants of stability and other thermodynamic characteristics of furfural complex with cations-oxidizers are found. Schemes of furfural transformations at one- and two-electron oxidation by ions of variable-valency metals are suggested

  14. Kinetics and mechanism of furfural oxidation by ions of heterovalent metals

    Energy Technology Data Exchange (ETDEWEB)

    Krupenskij, V.I. (Ukhtinskij Industrial' nyj Inst. (USSR))

    1983-01-01

    Real constants of rate of furfural oxidation by Cu/sup 2 +/, Fe/sup 3 +/, Ce/sup 4 +/, Ag/sup +/, Hg/sup 2 +//sub 2/ ions are determined, other kinetic and activation parameters of reactions are calculated, constants of stability and other thermodynamic characteristics of furfural complex with cations-oxidizers are found. Schemes of furfural transformations at one- and two-electron oxidation by ions of variable-valency metals are suggested.

  15. Evaluation of dilatometric techniques for studies of sintering kinetics

    International Nuclear Information System (INIS)

    El-Sayed Ali, M.; Toft Soerensen, O.

    1985-04-01

    The kinetics of the initial sintering stage of CeO 2 is evaluated by three different techniques: constant heating rate dilatometry, constant shrinkage rate dilatometry and a new technique recently introduced by the authors called Stepwise Isothermal Dilatometry (SID). Comparative measurements with these techniques showed that too high activation energies were obtained with the two first techniques, both of which can be termed as nonisothermal, whereas activation energies comparable to those reported for cation diffusion in other fluorite oxides were obtained with the latter technique. Of the three techniques SID is thus considered to be the most accurate for studies of the sintering kinetics. In contrast to the two nonisothermal techniques SID has the further advantage that both the controlling mechanism and its activation energy can be determined in a single experiment. From the SID-measurement it was concluded that the initial sintering stage of CeO 2 is controlled by grain-boundary diffusion. (author)

  16. Oxygen Reduction Kinetics Enhancement on a Heterostructured Oxide Surface for Solid Oxide Fuel Cells

    KAUST Repository

    Crumlin, Ethan J.

    2010-11-04

    Heterostructured interfaces of oxides, which can exhibit transport and reactivity characteristics remarkably different from those of bulk oxides, are interesting systems to explore in search of highly active cathodes for the oxygen reduction reaction (ORR). Here, we show that the ORR of ∼85 nm thick La0.8Sr0.2CoO3-δ (LSC113) films prepared by pulsed laser deposition on (001)-oriented yttria-stabilized zirconia (YSZ) substrates is dramatically enhanced (∼3-4 orders of magnitude above bulk LSC113) by surface decorations of (La 0.5Sr0.5)2CoO4±δ (LSC214) with coverage in the range from ∼0.1 to ∼15 nm. Their surface and atomic structures were characterized by atomic force, scanning electron, and scanning transmission electron microscopy, and the ORR kinetics were determined by electrochemical impedance spectroscopy. Although the mechanism for ORR enhancement is not yet fully understood, our results to date show that the observed ORR enhancement can be attributed to highly active interfacial LSC113/LSC214 regions, which were shown to be atomically sharp. © 2010 American Chemical Society.

  17. Oxygen Reduction Kinetics Enhancement on a Heterostructured Oxide Surface for Solid Oxide Fuel Cells

    KAUST Repository

    Crumlin, Ethan J.; Mutoro, Eva; Ahn, Sung-Jin; la O’ , Gerardo Jose; Leonard, Donovan N.; Borisevich, Albina; Biegalski, Michael D.; Christen, Hans M.; Shao-Horn, Yang

    2010-01-01

    Heterostructured interfaces of oxides, which can exhibit transport and reactivity characteristics remarkably different from those of bulk oxides, are interesting systems to explore in search of highly active cathodes for the oxygen reduction reaction (ORR). Here, we show that the ORR of ∼85 nm thick La0.8Sr0.2CoO3-δ (LSC113) films prepared by pulsed laser deposition on (001)-oriented yttria-stabilized zirconia (YSZ) substrates is dramatically enhanced (∼3-4 orders of magnitude above bulk LSC113) by surface decorations of (La 0.5Sr0.5)2CoO4±δ (LSC214) with coverage in the range from ∼0.1 to ∼15 nm. Their surface and atomic structures were characterized by atomic force, scanning electron, and scanning transmission electron microscopy, and the ORR kinetics were determined by electrochemical impedance spectroscopy. Although the mechanism for ORR enhancement is not yet fully understood, our results to date show that the observed ORR enhancement can be attributed to highly active interfacial LSC113/LSC214 regions, which were shown to be atomically sharp. © 2010 American Chemical Society.

  18. The oxidation kinetics for sublimates formed during niobium electron-beam remelting

    International Nuclear Information System (INIS)

    Chumarev, V.M.; Gulyaeva, R.I.; Mar'evich, V.P.; Upolovnikova, A.G.; Udoeva, L.Yu.

    2003-01-01

    The oxidation of sublimates of Nb-Al electron beam remelting is investigated under conditions of isothermal and continuous heating in the air. It is stated that basic oxidation products are niobium and aluminium oxides, as well as aluminium niobates of variable composition of Al 2 O 3 · mNb 2 O 5 . The more aluminium enriched sublimates possess an increased resistance to oxidation. Formed in sublimates NbAl 3 intermetallic compound features the highest heat resistance. Oxidation parameters are determined by the method of nonisothermic kinetics. It is noted that the running processes exhibit a multistage nature and are limited by internal diffusion [ru

  19. Destruction kinetic of PCDDs/Fs in MSWI fly ash using microwave peroxide oxidation.

    Science.gov (United States)

    Chang, Yu-Min; Fang, Wen-Bin; Tsai, Kuo-Sheng; Kao, Jimmy C M; Lin, Kae-Long; Chen, Ching-Ho

    2015-01-01

    Microwave peroxide oxidation is a less greenhouse gas emission and energy-efficient technology to destroy toxic organic compounds in hazardous waste. The research novelty is to adopt the innovative microwave peroxide oxidation in H2SO4/HNO3 solution to efficiently destroy the polychlorinated dibenzo-p-dioxins (PCDDs)/Fs in municipal solid waste incineration fly ash. The major objective of this paper is to study dynamic destruction of PCDDs/Fs using the microwave peroxide oxidation. Almost all PCDDs/Fs in the raw fly ash can be destructed in 120 min at a temperature of 423 K using the microwave peroxide oxidation treatment. It was found that the microwave peroxide oxidation provides the potential to destruct the PCDDs/Fs content in municipal solid waste incinerator (MSWI) fly ash to a low level as a function of treatment time. A useful kinetic correlation between destruction efficiency and treatment conditions is proposed on the basis of the experimental data obtained in this study. The significance of this work in terms of practical engineering applications is that the necessary minimum treatment time can be solved using a proposed graphic illustration method, by which the minimum treatment time is obtained if the desired destruction efficiency and treatment temperature are known. Because of inorganic salt dissolution, the temperature would be a critical factor facilitating the parts of fly ash dissolution. Material loss problem caused by the microwave peroxide oxidation and the effects of treatment time and temperature are also discussed in this paper.

  20. Kinetics and mechanism of the oxidation of ZrC

    International Nuclear Information System (INIS)

    Rama Rao, G.A.; Venugopal, V.; Sood, D.D.

    1993-01-01

    The oxidation behaviour of sintered ZrC powder was studied under iso and non-isothermal heating conditions under varied oxygen pressures from 0.05 to 0.5 atm and the weight changes during the reaction were followed by thermogravimetry. The sample ignited under oxygen pressure of 1 atm when heated non-isothermally at 5 K/min. The end product was identified by X-ray diffraction method as cubic ZrO 2 at temperatures below 1073 K and monoclinic above that. The rate of the reaction was found to be diffusion controlled. The mechanism of the reaction was discussed in terms of the diffusion of oxygen through the product layer. (author). 8 refs., 1 fig., 1 tab

  1. The kinetics and properties of thermal oxidation of silicon in TCA-O/sub 2/

    International Nuclear Information System (INIS)

    Ahmed, W.; Ahmed, E.

    1993-01-01

    The oxidation of silicon using dry O/sub 2/ is now well established as a key process for the fabrication of electronic devices in the semiconductor industry. However, this process is complicated by its sensitivity to impurities which reduce device yields. HCl can be added to O/sub 2/ to remove these impurities but due to its highly corrosive nature a safer and cleaner alternative such as trichloroethane (TCA) is desirable. In this paper, the thermal oxidation of silicon using a mixture of TCA-O/sub 2/ has been investigated in a large scale industrial system. The growth kinetics and the properties of these films have been studies and compared to oxides produced from dry 2. The addition of TCA generates HCl in situ, enhances the oxidation rate by approximately 54% nd improves the electrical properties. It was found that a 1 mol.% mixture gives the optimum process. An analysis of the data suggests that a liner parabolic growth model is applicable and provides a valuable insight into the physical phenomena governing this important process. (author)

  2. Methane oxidation in a landfill cover soil reactor: Changing of kinetic parameters and microorganism community structure.

    Science.gov (United States)

    Xing, Zhi L; Zhao, Tian T; Gao, Yan H; Yang, Xu; Liu, Shuai; Peng, Xu Y

    2017-02-23

    Changing of CH 4 oxidation potential and biological characteristics with CH 4 concentration was studied in a landfill cover soil reactor (LCSR). The maximum rate of CH 4 oxidation reached 32.40 mol d -1 m -2 by providing sufficient O 2 in the LCSR. The kinetic parameters of methane oxidation in landfill cover soil were obtained by fitting substrate diffusion and consumption model based on the concentration profile of CH 4 and O 2 . The values of [Formula: see text] (0.93-2.29%) and [Formula: see text] (140-524 nmol kg soil-DW -1 ·s -1 ) increased with CH 4 concentration (9.25-20.30%), while the values of [Formula: see text] (312.9-2.6%) and [Formula: see text] (1.3 × 10 -5 to 9.0 × 10 -3 nmol mL -1 h -1 ) were just the opposite. MiSeq pyrosequencing data revealed that Methylobacter (the relative abundance was decreased with height of LCSR) and Methylococcales_unclassified (the relative abundance was increased expect in H 80) became the key players after incubation with increasing CH 4 concentration. These findings provide information for assessing CH 4 oxidation potential and changing of biological characteristics in landfill cover soil.

  3. Kinetic study on Iranian furfural extract hydrocracking

    Energy Technology Data Exchange (ETDEWEB)

    Zarkesh, J.; Akbarnejad, M. M. [NIOC Research Institute of Petroleum Industry, Tehran (Iran, Islamic Republic of); Khorasheh, F. [Sharif Univ. of Technology, Tehran (Iran, Islamic Republic of); Badakhshan, A. [Calgary Univ., AB (Canada)

    1998-05-01

    Upgrading heavy crude oil to light crude oil is one of the most important refining processes. Familiarity with the kinetics and related kinetic models is one of the important aspects of developing expertise in this field. This joint study between the NIOC Institute of Research of the Petroleum Industry and Sharif University was undertaken to determine the most appropriate upgrading process for Iranian heavy feed stock and to predict the conversion and product distribution in commercial hydrocracking units. The study involved the evaluation of stoichiometry of the hydrocracking process, focusing on the catalytic hydrocracking of furfural extract (a by-product of the lubricating oil plant) of the Tehran refinery. A pilot plant reactor was used. Good correspondence between model predictions and theoretical values was obtained.

  4. [Oxidation behavior and kinetics of representative VOCs emitted from petrochemical industry over CuCeOx composite oxides].

    Science.gov (United States)

    Chen, Chang-Wei; Yu, Yan-Ke; Chen, Jin-Sheng; He, Chi

    2013-12-01

    CuCeOx composite catalysts were synthesized via coprecipitation (COP-CuCeO,) and incipient impregnation (IMP-CuCeOx) methods, respectively. The physicochemical properties of the samples were characterized by XRD, low-temperature N2 sorption, H2-TPR and O2-TPD. The influences of reactant composition and concentration, reaction space velocity, O2 content, H2O concentration, and catalyst type on the oxidation behaviors of benzene, toluene, and n-hexane emitted from petrochemical industry were systematically investigated. In addition, the related kinetic parameters were model fitted. Compared with IMP-CuCeOx, COP-CuCeOx had well-dispersed active phase, better low-temperature reducibility, and more active surface oxygen species. The increase of reactant concentration was unfavorable for toluene oxidation, while the opposite phenomenon could be observed in n-hexane oxidation. The inlet concentration of benzene was irrelevant to its conversion under high oxidation rate. The introduction of benzene obviously inhibited the oxidation of toluene and n-hexane, while the presence of toluene had a positive effect on beuzene conversion. The presence of n-hexane could promote the oxidation of toluene, while toluene had a negative influence on e-hexane oxidation. Both low space velocity and high oxygen concentration were beneficial for the oxidation process, and the variation of oxygen content had negligible effect on n-hexane and henzene oxidation. The presence of H2O noticeably inhibited the oxidation of toluene, while significantly accelerated the oxidation procedure of henzene and n-hexane. COP-CuCeOx had superior catalytic performance for toluene and benzene oxidation, while IMP-CuCeOx showed higher n-hexane oxidation activity under dry condition. The oxidation behaviors under different conditions could be well fitted and predicted by the pseudo first-order kinetic model.

  5. Influence of organic substrates on the kinetics of bacterial As(III) oxidation

    Science.gov (United States)

    Lescure, T.; Joulian, C.; Bauda, P.; Hénault, C.; Battaglia-Brunet, F.

    2012-04-01

    on the bacterial speciation of arsenic in contaminated soils. Moreover, the biogeochemical consequences of this phenomenon on the mobility and ecotoxicity of this metalloid will be studied. The first task of this program is the precise and systematic investigation of the influence of different types and concentrations of organic matters on the activity of As(III)-oxidizing pure strains. Influence of aspartate, succinate (simple substrates) and yeast extract (complex substrate) on As(III)-oxidation kinetics has been studied. For each experiment, the bacterial growth and the expression of genes involved in the speciation of arsenic, i.e. aio and ars genes, has been monitored. A direct perspective of this work will be to perform experiments with humic and fulvic acids (complex organic matter commonly found in soils), and with water-extracted organic matter from polluted soils. Then the As(III)-oxidation activity of bacterial communities extracted from contaminated soils will be followed. These assays should allow the screening of conditions which will be applied in subsequent experiments with several real contaminated soils, including a former mining site, impacted industrial sites, and a forest soil heavily contaminated after arsenical ammunitions storage. This work is co-funded by BRGM and ADEME (convention TEZ 11-16).

  6. Kinetic catalytic studies of scorpion's hemocyanin

    International Nuclear Information System (INIS)

    Queinnec, E.; Vuillaume, M.; Gardes-Albert, M.; Ferradini, C.; Ducancel, F.

    1991-01-01

    Hemocyanins are copper proteins which function as oxygen carriers in the haemolymph of Molluscs and Arthropods. They possess enzymatic properties: peroxidatic and catalatic activities, although they have neither iron nor porphyrin ring at the active site. The kinetics of the catalytic reaction is described. The reaction of superoxide anion with hemocyanin has been studied using pulse radiolysis at pH 9. The catalytic rate constant is 3.5 X 10 7 mol -1 .l.s -1 [fr

  7. The effect of preparation conditions and the ionizing radiation on the kinetics of cupric oxide reduction by hydrogen

    International Nuclear Information System (INIS)

    Pospisil, M.; Taras, P.

    1977-01-01

    Cupric oxide reduction in the temperature interval 170 to 350 degC was studied by thermogravimetry. The reduction kinetics can be quantitatively described by the modified Prout-Tompkinson equation, with the apparent activation energy varying within the limits (4.94 to 5.82)x10 4 J/mol. Irregularities observed during the reduction of the oxide of the oxalate origin are due to the high content of the metallic phase. The p-semiconducting nature of these oxides was proved for all samples. The effect of the pre-irradiation of samples with γ-rays (with an absorbed dose of (1.4 to 4.75)x10 6 J/kg) on the reduction kinetics depends on the origin of the cupric oxide. In contrast to NiO no correlation between the content of super-stoichiometric oxygen and the reduction kinetics was found. After irradiation with γ-rays or with fast neutrons at a dose of 79.8 J/kg the reduction rate increases and the activation energy decreases regardless of the oxide origin. At the same time the concentration of the ionic form of super-stoichiometric oxygen increases. (author)

  8. Kinetics and mechanism of oxidation of aliphatic alcohols by ...

    Indian Academy of Sciences (India)

    TBATB) in aqueous acetic acid leads to the formation of the corresponding aldehydes. The reaction is first order with respect to TBATB. Michaelis-Menten type kinetics is observed with respect to alcohols. The reaction failed to induce the ...

  9. Force-dominated non-equilibrium oxidation kinetics of tantalum

    International Nuclear Information System (INIS)

    Kar, Prasenjit; Wang, Ke; Liang, Hong

    2008-01-01

    Using a combined electrochemical and mechanical manipulation technique, we compared the equilibrium and non-equilibrium oxidation processes and states of tantalum. Experimentally, a setup was developed with an electrochemical system attached to a sliding mechanical configuration capable of friction force measurement. The surface chemistry of a sliding surface, i.e., tantalum, was modified through the electrolyte. The mechanically applied force was fixed and the dynamics of the surface was monitored in situ through a force sensor. The formation of non-equilibrium oxidation states of tantalum was found in oxidation limiting environment of acetic acid. An oxidative environment of deionized water saturated with KCl was used as comparison. We proposed a modified Arrhenius-Eyring equation in which the mechanical factor was considered. We found that the mechanical energy induced the non-stable-state reactions leading to metastable oxidation states of tantalum. This equation can be used to predict mechanochemical reactions that are important in many industrial applications

  10. Perturbation of parabolic kinetics resulting from the accumulation of stress in protective oxide layers

    International Nuclear Information System (INIS)

    Evans, H.E.; Norfolk, D.J.; Swan, T.

    1978-01-01

    A frequent observation in metal oxidation is the development of subparabolic kinetics, variously described as cubic or quartic. Although a number of detailed mechanisms have been proposed to account for this effect, none seem generally applicable. A model is presented of the oxidation process which is divorced from such restrictions. It is argued that deviations from parabolic behavior occur as a result of the concurrent development of stresses within the oxide. It is shown that the presence of stress fields can influence significantly the rate of transport of vacancy defects within the oxide such that tensile stresses produce positive deviations and compressive stresses, negative deviations from parabolic behavior. The model is applied in detail to Zircaloy-2 oxidation at 773 0 K. It is predicted that the kinetics should be insensitive to the oxygen potential of the environment and this has been confirmed by previous experimental work. 31 refs

  11. Transient Kinetic Analysis of Hydrogen Sulfide Oxidation Catalyzed by Human Sulfide Quinone Oxidoreductase*

    Science.gov (United States)

    Mishanina, Tatiana V.; Yadav, Pramod K.; Ballou, David P.; Banerjee, Ruma

    2015-01-01

    The first step in the mitochondrial sulfide oxidation pathway is catalyzed by sulfide quinone oxidoreductase (SQR), which belongs to the family of flavoprotein disulfide oxidoreductases. During the catalytic cycle, the flavin cofactor is intermittently reduced by sulfide and oxidized by ubiquinone, linking H2S oxidation to the electron transfer chain and to energy metabolism. Human SQR can use multiple thiophilic acceptors, including sulfide, sulfite, and glutathione, to form as products, hydrodisulfide, thiosulfate, and glutathione persulfide, respectively. In this study, we have used transient kinetics to examine the mechanism of the flavin reductive half-reaction and have determined the redox potential of the bound flavin to be −123 ± 7 mV. We observe formation of an unusually intense charge-transfer (CT) complex when the enzyme is exposed to sulfide and unexpectedly, when it is exposed to sulfite. In the canonical reaction, sulfide serves as the sulfur donor and sulfite serves as the acceptor, forming thiosulfate. We show that thiosulfate is also formed when sulfide is added to the sulfite-induced CT intermediate, representing a new mechanism for thiosulfate formation. The CT complex is formed at a kinetically competent rate by reaction with sulfide but not with sulfite. Our study indicates that sulfide addition to the active site disulfide is preferred under normal turnover conditions. However, under pathological conditions when sulfite concentrations are high, sulfite could compete with sulfide for addition to the active site disulfide, leading to attenuation of SQR activity and to an alternate route for thiosulfate formation. PMID:26318450

  12. Transient Kinetic Analysis of Hydrogen Sulfide Oxidation Catalyzed by Human Sulfide Quinone Oxidoreductase.

    Science.gov (United States)

    Mishanina, Tatiana V; Yadav, Pramod K; Ballou, David P; Banerjee, Ruma

    2015-10-09

    The first step in the mitochondrial sulfide oxidation pathway is catalyzed by sulfide quinone oxidoreductase (SQR), which belongs to the family of flavoprotein disulfide oxidoreductases. During the catalytic cycle, the flavin cofactor is intermittently reduced by sulfide and oxidized by ubiquinone, linking H2S oxidation to the electron transfer chain and to energy metabolism. Human SQR can use multiple thiophilic acceptors, including sulfide, sulfite, and glutathione, to form as products, hydrodisulfide, thiosulfate, and glutathione persulfide, respectively. In this study, we have used transient kinetics to examine the mechanism of the flavin reductive half-reaction and have determined the redox potential of the bound flavin to be -123 ± 7 mV. We observe formation of an unusually intense charge-transfer (CT) complex when the enzyme is exposed to sulfide and unexpectedly, when it is exposed to sulfite. In the canonical reaction, sulfide serves as the sulfur donor and sulfite serves as the acceptor, forming thiosulfate. We show that thiosulfate is also formed when sulfide is added to the sulfite-induced CT intermediate, representing a new mechanism for thiosulfate formation. The CT complex is formed at a kinetically competent rate by reaction with sulfide but not with sulfite. Our study indicates that sulfide addition to the active site disulfide is preferred under normal turnover conditions. However, under pathological conditions when sulfite concentrations are high, sulfite could compete with sulfide for addition to the active site disulfide, leading to attenuation of SQR activity and to an alternate route for thiosulfate formation. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

  13. Investigation of the kinetics of the reactions of oxidation, nitration, and hydrogenation of uranium

    International Nuclear Information System (INIS)

    Adda, Y.

    1955-06-01

    Various physico-chemical methods have been used to investigate the kinetics of the oxidation hydridation and nitridation of uranium. The experimental results show that the kinetics of these reactions are influenced by many factors also the Pilling and Bedworth rule is valid only under very limited conditions. The disagreement between this rule and the experimental results could be explained by the existence of numerous mechanical faults in the compounds obtained by the dry corrosion of the metal. (author) [fr

  14. Kinetic Investigations on Pd(II) Catalyzed Oxidation of Some Amino ...

    African Journals Online (AJOL)

    Kinetic investigations on Pd(II) catalyzed oxidation of dl-serine and dl-threonine by acidic solution of potassium bromate in the presence of mercuric acetate, as a scavenger have been made in the temperature range of 30–45°C. The rate shows zero order kinetics in bromate [BrO3‾] and order of reaction is one with respect ...

  15. Effect of ionization on the oxidation kinetics of aluminum nanoparticles

    Science.gov (United States)

    Zheng, Yao-Ting; He, Min; Cheng, Guang-xu; Zhang, Zaoxiao; Xuan, Fu-Zhen; Wang, Zhengdong

    2018-03-01

    Molecular dynamics simulation (MD) of the observed stepwise oxidation of core-shell structured Al/Al2O3 nanoparticles is presented. Different from the metal ion hopping process in the Cabrera-Mott model, which is assumed to occur only at a certain distance from the oxide layer, the MD simulation shows that Al atoms jump over various interfacial gaps directly under the thermal driving force. The energy barrier for Al ionization is found to be increased along with the enlargement of interfacial gap. A mechanism of competition between thermal driving force and ionization potential barrier is proposed in the interpretation of stepwise oxidation behavior.

  16. The investigation of the kinetics of hydrochemical oxidation of metal sulphides with the aim of determination of the optimal conditions for the selective extraction of molybdenum from ores

    Directory of Open Access Journals (Sweden)

    Lutsik V.

    2005-01-01

    Full Text Available The kinetics of the oxidation of molybdenyte, pyrite and sphalerite in solutions of nitric acid, hydrogen peroxide, and sodium hypochlorite was studied by the rotating disk method. The influence of the molar concentration of reagent, pH of solution, temperature, disk rotation frequency, and duration of measurements on the specific rate of hydrochemical oxidation of sulpfides was determined. The kinetic models allowing to calculate the dissolution rate of sulphides when these parameters change simultaneously were obtained. The conditions of kinetically and diffusion-controlled processes were detected. The details of mechanism of the studied processes were revealed. The nature of intermediate solid products, the reasons and the conditions of their formation as well as the character of their influence on the kinetics of dissolution processes were determined. The probable schemes of interactions corresponding to the observable kinetic dependences were offered. The conditions of the effective and selective molybdenum leaching directly from ore without its concentration were found.

  17. Kinetic isotope effects in reaction of ferment oxidation of tritium-labelled D-galactosamine

    International Nuclear Information System (INIS)

    Akulov, G.P.; Korsakova, N.A.

    1992-01-01

    Primary, secondary and intramolecular kinetic isotopic effects in reaction of ferment oxidation of D-galactosamine labelled by tritium in position 6, were measured. When comparing values of the effects with previously obtained results for similar reaction D-[6- 3 H]galactose, it was ascertained that the presence of aminogroup in galactopyranosyl mainly affects kinetics of substrate-ferment complex formation stage. The possibility to use kinetic isotope effects for increase in molar activity of D-galactosamine, labelled by tritium in position 6, is shown

  18. The catalytic oxidation of 1-butene over bismuth molybdate catalysts : V. The kinetics of the oxidation: A. Pulse reaction kinetics; exploratory experiments for a kinetic investigation

    NARCIS (Netherlands)

    Keizer, K.; Batist, P.A.; Schuit, G.C.A.

    1969-01-01

    The kinetics of oxidn. of 1-butene with O on three types of bismuth molybdate catalysts were investigated in pulse expts. For all the catalysts mentioned the kinetics can be expressed by a first-order dependency on the butene pressure and a zero-order dependency on the O pressure. A slight deviation

  19. Kinetics of Oxidation of Aliphatic Alcohols by Potassium Dichromate ...

    African Journals Online (AJOL)

    NICO

    2011-10-10

    Oct 10, 2011 ... 1Department of Chemistry, Faculty of Science, Ibb University, Ibb 7027, Yemen. 2Department of Chemistry ... The presence of TX-100 enhanced the rate of the ... oxidation of alcohols, namely, methanol, ethanol, 1-propanol.

  20. Non-Parametric Kinetic (NPK Analysis of Thermal Oxidation of Carbon Aerogels

    Directory of Open Access Journals (Sweden)

    Azadeh Seifi

    2017-05-01

    Full Text Available In recent years, much attention has been paid to aerogel materials (especially carbon aerogels due to their potential uses in energy-related applications, such as thermal energy storage and thermal protection systems. These open cell carbon-based porous materials (carbon aerogels can strongly react with oxygen at relatively low temperatures (~ 400°C. Therefore, it is necessary to evaluate the thermal performance of carbon aerogels in view of their energy-related applications at high temperatures and under thermal oxidation conditions. The objective of this paper is to study theoretically and experimentally the oxidation reaction kinetics of carbon aerogel using the non-parametric kinetic (NPK as a powerful method. For this purpose, a non-isothermal thermogravimetric analysis, at three different heating rates, was performed on three samples each with its specific pore structure, density and specific surface area. The most significant feature of this method, in comparison with the model-free isoconversional methods, is its ability to separate the functionality of the reaction rate with the degree of conversion and temperature by the direct use of thermogravimetric data. Using this method, it was observed that the Nomen-Sempere model could provide the best fit to the data, while the temperature dependence of the rate constant was best explained by a Vogel-Fulcher relationship, where the reference temperature was the onset temperature of oxidation. Moreover, it was found from the results of this work that the assumption of the Arrhenius relation for the temperature dependence of the rate constant led to over-estimation of the apparent activation energy (up to 160 kJ/mol that was considerably different from the values (up to 3.5 kJ/mol predicted by the Vogel-Fulcher relationship in isoconversional methods

  1. Structural and silver/vanadium ratio effects on silver vanadium phosphorous oxide solution formation kinetics: impact on battery electrochemistry.

    Science.gov (United States)

    Bock, David C; Takeuchi, Kenneth J; Marschilok, Amy C; Takeuchi, Esther S

    2015-01-21

    The detailed understanding of non-faradaic parasitic reactions which diminish battery calendar life is essential to the development of effective batteries for use in long life applications. The dissolution of cathode materials including manganese, cobalt and vanadium oxides in battery systems has been identified as a battery failure mechanism, yet detailed dissolution studies including kinetic analysis are absent from the literature. The results presented here provide a framework for the quantitative and kinetic analyses of the dissolution of cathode materials which will aid the broader community in more fully understanding this battery failure mechanism. In this study, the dissolution of silver vanadium oxide, representing the primary battery powering implantable cardioverter defibrillators (ICD), is compared with the dissolution of silver vanadium phosphorous oxide (Ag(w)VxPyOz) materials which were targeted as alternatives to minimize solubility. This study contains the first kinetic analyses of silver and vanadium solution formation from Ag0.48VOPO4·1.9H2O and Ag2VP2O8, in a non-aqueous battery electrolyte. The kinetic results are compared with those of Ag2VO2PO4 and Ag2V4O11 to probe the relationships among crystal structure, stoichiometry, and solubility. For vanadium, significant dissolution was observed for Ag2V4O11 as well as for the phosphate oxide Ag0.49VOPO4·1.9H2O, which may involve structural water or the existence of multiple vanadium oxidation states. Notably, the materials from the SVPO family with the lowest vanadium solubility are Ag2VO2PO4 and Ag2VP2O8. The low concentrations and solution rates coupled with their electrochemical performance make these materials interesting alternatives to Ag2V4O11 for the ICD application.

  2. Mechanistic Investigation of Oxidation of Phenylpropanolamine with N-Bromobenzenesulfonamide in Alkaline Medium: A Kinetic Approach

    Directory of Open Access Journals (Sweden)

    Ningegowda Prasad

    2008-01-01

    Full Text Available The kinetics of oxidation of phenylpropanolamine (PPA with sodium N-bromobenzenesulfonamide or bromamine-B (BAB has been investigated in alkaline medium at 308 K. The oxidation reaction obeys the rate law, – d[BAB]/dt = k [BAB] [PPA]x [OH-], where x is less than unity. The variation of ionic strength of the medium, addition of the reduction product, benzenesulfonamide, and chloride ion had no pronounced effect on the reaction rate. Decrease of dielectric permittivity of the medium by increasing the CH3CN content increased the rate. The reaction was studied at different temperatures and the activation parameters have been evaluated from the Arrhenius plot. The stiochiometry of the reaction was found to be 1:1, and the oxidation product of phenylpropanolamine was identified as benzaldehyde and ethylideneamine. The rate decreased in D2O medium and the normal isotope effect k' (H2O / k' (D2O is 2.18. Proton inventory studies have been made in H2O - D2O mixtures. Formation and decomposition constant of BAB-PPA complexes in the reaction scheme have been determined. The conjugate acid, C6H5SO2NHBr is assumed to be the reactive species. The proposed mechanism and the derived rate law are consistent with the observed experimental results.

  3. Oxidation of Tetracaine Hydrochloride by Chloramine-B in Acid Medium: Kinetic Modeling

    Directory of Open Access Journals (Sweden)

    Jayachamarajapura Pranesh Shubha

    2014-01-01

    Full Text Available Tetracaine hydrochloride (TCH is one of the potent local anaesthetics. A kinetic study of oxidation of tetracaine hydrochloride by sodium N-chlorobenzenesulfonamide (chloramine-B or CAB has been carried in HClO4 medium at 303 K. The rate shows first-order dependence on [CAB]o, shows fractional–order dependence on [substrate]o, and is self-governing on acid concentration. Decrease of dielectric constant of the medium, by adding methanol, increased the rate. Variation of ionic strength and addition of benzenesulfonamide or NaCl have no significant effect on the rate. The reaction was studied at different temperatures and the activation parameters have been evaluated. The stoichiometry of the reaction was found to be 1 : 5 and the oxidation products were identified by spectral analysis. The conjugate free acid C6H5SO2NHCl of CAB is postulated as the reactive oxidizing species. The observed results have been explained by plausible mechanism and the related rate law has been deduced.

  4. Kinetics of aerobic oxidation of volatile sulfur compounds in wastewater and biofilm from sewers

    DEFF Research Database (Denmark)

    Rudelle, Elise Alice; Vollertsen, Jes; Hvitved-Jacobsen, Thorkild

    2013-01-01

    Laboratory experiments were conducted to investigate the kinetics of aerobic chemical and biological oxidation of selected odorous volatile sulfur compounds (VSCs) by wastewater and biofilm from sewers. The VSCs included methyl mercaptan (MeSH), ethyl mercaptan (EtSH), dimethyl sulfide (DMS......-spot downstream of a force main and the other was a gravity sewer transporting young aerobic wastewater. The kinetics of VSC oxidation for both wastewater and suspended biofilm samples followed a first-order rate equation. The average values of the reaction rate constants demonstrated the following order...... in the aerobic wastewater....

  5. Oxidation kinetics of a continuous carbon phase in a nonreactive matrix

    Science.gov (United States)

    Eckel, Andrew J.; Cawley, James D.; Parthasarathy, Triplicane A.

    1995-01-01

    Analytical solutions of and experimental results on the oxidation kinetics of carbon in a pore are presented. Reaction rate, reaction sequence, oxidant partial pressure, total system pressure, pore/crack dimensions, and temperature are analyzed with respect to the influence of each on an overall linear-parabolic rate relationship. Direct measurement of carbon recession is performed using two microcomposite model systems oxidized in the temperature range of 700 to 1200 C, and for times to 35 h. Experimental results are evaluated using the derived analytical solutions. Implications on the oxidation resistance of continuous-fiber-reinforced ceramic-matrix composites containing a carbon constituent are discussed.

  6. Molybdenum Disilicide Oxidation Kinetics in High Temperature Steam

    Energy Technology Data Exchange (ETDEWEB)

    Wood, Elizabeth Sooby [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Parker, Stephen Scott [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Nelson, Andrew Thomas [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-09-07

    The Fuel Cycle Research and Development program’s Advanced Fuels Campaign is currently supporting a range of experimental efforts aimed at the development and qualification of ‘accident tolerant’ nuclear fuel forms. One route to enhance the accident tolerance of nuclear fuel is to replace the zirconium alloy cladding, which is prone to rapid oxidation in steam at elevated temperatures, with a more oxidation-resistant cladding. Several cladding replacement solutions have been envisaged. The cladding can be completely replaced with a more oxidation resistant alloy, a layered approach can be used to optimize the strength, creep resistance, and oxidation tolerance of various materials, or the existing zirconium alloy cladding can be coated with a more oxidation-resistant material. Molybdenum is one candidate cladding material favored due to its high temperature creep resistance. However, it performs poorly under autoclave testing and suffers degradation under high temperature steam oxidation exposure. Development of composite cladding architectures consisting of a molybdenum core shielded by a molybdenum disilicide (MoSi2) coating is hypothesized to improve the performance of a Mo-based cladding system. MoSi2 was identified based on its high temperature oxidation resistance in O2 atmospheres (e.g. air and “wet air”). However, its behavior in H2O is less known. This report presents thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and x-ray diffraction (XRD) results for MoSi2 exposed to 670-1498 K water vapor. Synthetic air (80-20%, Ar-O2) exposures were also performed, and those results are presented here for a comparative analysis. It was determined that MoSi2 displays drastically different oxidation behavior in water vapor than in dry air. In the 670-1498 K temperature range, four distinct behaviors are observed. Parabolic oxidation is exhibited in only 670

  7. Heterogeneous Oxidation of Atmospheric Organic Aerosol: Kinetics of Changes to the Amount and Oxidation State of Particle-Phase Organic Carbon.

    Science.gov (United States)

    Kroll, Jesse H; Lim, Christopher Y; Kessler, Sean H; Wilson, Kevin R

    2015-11-05

    Atmospheric oxidation reactions are known to affect the chemical composition of organic aerosol (OA) particles over timescales of several days, but the details of such oxidative aging reactions are poorly understood. In this study we examine the rates and products of a key class of aging reaction, the heterogeneous oxidation of particle-phase organic species by the gas-phase hydroxyl radical (OH). We compile and reanalyze a number of previous studies from our laboratories involving the oxidation of single-component organic particles. All kinetic and product data are described on a common basis, enabling a straightforward comparison among different chemical systems and experimental conditions. Oxidation chemistry is described in terms of changes to key ensemble properties of the OA, rather than to its detailed molecular composition, focusing on two quantities in particular, the amount and the oxidation state of the particle-phase carbon. Heterogeneous oxidation increases the oxidation state of particulate carbon, with the rate of increase determined by the detailed chemical mechanism. At the same time, the amount of particle-phase carbon decreases with oxidation, due to fragmentation (C-C scission) reactions that form small, volatile products that escape to the gas phase. In contrast to the oxidation state increase, the rate of carbon loss is nearly uniform among most systems studied. Extrapolation of these results to atmospheric conditions indicates that heterogeneous oxidation can have a substantial effect on the amount and composition of atmospheric OA over timescales of several days, a prediction that is broadly in line with available measurements of OA evolution over such long timescales. In particular, 3-13% of particle-phase carbon is lost to the gas phase after one week of heterogeneous oxidation. Our results indicate that oxidative aging represents an important sink for particulate organic carbon, and more generally that fragmentation reactions play a major

  8. Kinetics and Mechanisms of Thiol–Disulfide Exchange Covering Direct Substitution and Thiol Oxidation-Mediated Pathways

    Science.gov (United States)

    2013-01-01

    Abstract Significance: Disulfides are important building blocks in the secondary and tertiary structures of proteins, serving as inter- and intra-subunit cross links. Disulfides are also the major products of thiol oxidation, a process that has primary roles in defense mechanisms against oxidative stress and in redox regulation of cell signaling. Although disulfides are relatively stable, their reduction, isomerisation, and interconversion as well as their production reactions are catalyzed by delicate enzyme machineries, providing a dynamic system in biology. Redox homeostasis, a thermodynamic parameter that determines which reactions can occur in cellular compartments, is also balanced by the thiol–disulfide pool. However, it is the kinetic properties of the reactions that best represent cell dynamics, because the partitioning of the possible reactions depends on kinetic parameters. Critical Issues: This review is focused on the kinetics and mechanisms of thiol–disulfide substitution and redox reactions. It summarizes the challenges and advances that are associated with kinetic investigations in small molecular and enzymatic systems from a rigorous chemical perspective using biological examples. The most important parameters that influence reaction rates are discussed in detail. Recent Advances and Future Directions: Kinetic studies of proteins are more challenging than small molecules, and quite often investigators are forced to sacrifice the rigor of the experimental approach to obtain the important kinetic and mechanistic information. However, recent technological advances allow a more comprehensive analysis of enzymatic systems via using the systematic kinetics apparatus that was developed for small molecule reactions, which is expected to provide further insight into the cell's machinery. Antioxid. Redox Signal. 18, 1623–1641. PMID:23075118

  9. Iron oxidation kinetics and phosphorus immobilization at the groundwater-surface water interface

    Science.gov (United States)

    van der Grift, Bas; Rozemeijer, Joachim; Griffioen, Jasper; van der Velde, Ype

    2014-05-01

    Eutrophication of freshwater environments following diffuse nutrient loads is a widely recognized water quality problem in catchments. Fluxes of non-point P sources to surface waters originate from surface runoff and flow from soil water and groundwater into surface water. The availability of P in surface waters is controlled strongly by biogeochemical nutrient cycling processes at the soil-water interface. The mechanisms and rates of the iron oxidation process with associated binding of phosphate during exfiltration of anaerobic Fe(II) bearing groundwater are among the key unknowns in P retention processes in surface waters in delta areas where the shallow groundwater is typically pH-neutral to slightly acid, anoxic, iron-rich. We developed an experimental field set-up to study the dynamics in Fe(II) oxidation and mechanisms of P immobilization at the groundwater-surface water interface in an agricultural experimental catchment of a small lowland river. We physically separated tube drain effluent from groundwater discharge before it entered a ditch in an agricultural field. The exfiltrating groundwater was captured in in-stream reservoirs constructed in the ditch. Through continuous discharge measurements and weekly water quality sampling of groundwater, tube drain water, exfiltrated groundwater, and ditch water, we quantified Fe(II) oxidation kinetics and P immobilization processes across the seasons. This study showed that seasonal changes in climatic conditions affect the Fe(II) oxidation process. In winter time the dissolved iron concentrations in the in-stream reservoirs reached the levels of the anaerobic groundwater. In summer time, the dissolved iron concentrations of the water in the reservoirs are low, indicating that dissolved Fe(II) is completely oxidized prior to inflow into the reservoirs. Higher discharges, lower temperatures and lower pH of the exfiltrated groundwater in winter compared to summer shifts the location of the redox transition zone

  10. Analysis of the kinetics of methanol oxidation in a porous Pt-Ru anode

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Yan-Ping; Xing, Lei [Chemical Engineering Department, Taiyuan University of Technology, Shanxi 030024 (China); Scott, Keith [School of Chemical Engineering and Advanced Materials, Merz Court, University of Newcastle, Newcastle upon Tyne NE1 7RU (United Kingdom)

    2010-01-01

    A kinetic model of a porous Pt-Ru anode for methanol oxidation is presented. It was based on the dual-site mechanism for methanol oxidation and used to predict anode performance and the influence of species adsorption on the overall oxidation (macro-) kinetics. The performance of the porous Pt-Ru anode depended on the parameters of the intrinsic chemical kinetics of methanol oxidation and physical parameters such as electrode thickness, surface area, effective diffusion and charge transfer coefficients and concentration of methanol and temperature. The model was solved by using the finite difference method with a subroutine for solving a set of nonlinear algebraic equations in each step. Surface coverage ratio distributions of adsorbed species, effectiveness of the porous electrode and macro-polarisation curves were obtained. The simulated polarisation curves were compared to experimental polarisation data for methanol oxidation on Pt-Ru porous anodes at different temperatures and methanol concentrations. The intrinsic kinetic parameters were regressed from the corresponding experimental data. The predicted polarisation curves calculated by the model, were consistent with experimental polarisation data at lower current densities. The departure of experimental data from the predicted polarisation curves at high concentration and high apparent current densities was believed to be due to two-phase flow in the electrode. (author)

  11. Oxidation of nonylphenol and octylphenol by manganese dioxide: Kinetics and pathways

    International Nuclear Information System (INIS)

    Lu, Zhijiang; Gan, Jay

    2013-01-01

    Due to their potent estrogenicity and ubiquitous occurrence, non-ionic surfactant metabolites nonylphenol (NP) and octylphenol (OP) are of significant concern. Abiotic chemical oxidation by naturally abundant metal oxides may be an important route of their environmental attenuation, but is poorly understood. We investigated the reaction kinetics and pathways of NP and OP with MnO 2 . At pH 5.5 and 100 mg/L δ-MnO 2 , 92, 84 and 76% of 4-n-NP, 4-tert-OP and technical nonylphenol (tNP) was transformed in 90 min, respectively. A further experiment using a Mn-containing soil and Mn-removed soil confirmed that soil MnO 2 caused NP removal. Multiple reaction products, including hydroquinone, hydroxylated products, dimers and trimers were identified through fragmentation analysis by GC–MS/MS and UPLC–MS/MS, allowing the construction of tentative pathways. This study suggested that abiotic oxidation by MnO 2 may contribute to the dissipation of tNP, 4-n-NP, 4-tert-OP and their analogues in the natural environment. Highlights: •The oxidation of nonylphenol and octylphenol by manganese dioxide was efficient and pH dependent. •The importance of soil MnO 2 was further confirmed by experiment using Mn-containing soil. •The reaction in environment is substantially slower than with synthetic MnO 2 . •The oxidation was inhibited by metal ions and enhanced by humic acids. •Reaction pathway is proposed based on reaction intermediates identified. -- Naturally occurring MnO 2 may contribute significantly to the attenuation of nonylphenol and octylphenol in soil, water and sediment

  12. Kinetics of plasma oxidation of germanium-tin (GeSn)

    Science.gov (United States)

    Wang, Wei; Lei, Dian; Dong, Yuan; Zhang, Zheng; Pan, Jisheng; Gong, Xiao; Tok, Eng-Soon; Yeo, Yee-Chia

    2017-12-01

    The kinetics of plasma oxidation of GeSn at low temperature is investigated. The oxidation process is described by a power-law model where the oxidation rate decreases rapidly from the initial oxidation rate with increasing time. The oxidation rate of GeSn is higher than that of pure Ge, which can be explained by the higher chemical reaction rate at the GeSn-oxide/GeSn interface. In addition, the Sn atoms at the interface region exchange positions with the underlying Ge atoms during oxidation, leading to a SnO2-rich oxide near the interface. The bandgap of GeSn oxide is extracted to be 5.1 ± 0.2 eV by XPS, and the valence band offset at the GeSn-oxide/GeSn heterojunction is found to be 3.7 ± 0.2 eV. Controlled annealing experiments demonstrate that the GeSn oxide is stable with respect to annealing temperatures up to 400 °C. However, after annealing at 450 °C, the GeO2 is converted to GeO, and desorbs from the GeSn-oxide/GeSn, leaving behind Sn oxide.

  13. Electrode Kinetics and Gas Conversion in Solid Oxide Cells

    DEFF Research Database (Denmark)

    Njodzefon, Jean-Claude

    The solid oxide fuel cell (SOFC) converts hydrogen, carbon monoxide and hydrocarbon fuels (directly) into electricity with very high efficiencies and has demonstrated almost comparable performance when operated in reverse mode as a solid oxide electrolysis cell (SOEC). In this case electrical (and...... thermal) energy is stored as chemical energy of reaction products. To this end, the cells are fed with steam (H2O electrolysis), carbon dioxide (CO2 electrolysis) or a mixture of both (H2O/CO2 co-electrolysis) and of course electrical (ΔG) and thermal (TΔS) energies for the splitting of reactant compounds...... of the solid oxide cell (SOC) and independent of polarization mode (fuel cell mode or electrolysis mode), the current flowing through the cell is limited by processes such as adsorption and desorption of reactants or products, diffusion through the porous electrodes, activation or charge transfer...

  14. Pyrolysis and thermal oxidation kinetics of sugar mill press mud

    International Nuclear Information System (INIS)

    Gangavati, P.B.; Safi, M.J.; Singh, A.; Prasad, B.; Mishra, I.M.

    2005-01-01

    Press mud, a solid waste obtained from the sugar mills, has the potential of energy generation through pyrolysis and gasification. The paper reports its proximate and ultimate analyses, deformation and fusion ash temperatures, lower and higher heating values, physico-chemical and thermal degradation in nitrogen and air atmospheres. The thermal degradation was conducted in a thermogravimetric analyzer from room temperature to 900 deg C at heating rates of 20 and 40 K min -1 . The thermogravimetric, derivative thermogravimetric and differential thermal analyses were carried out to determine the rate of volatiles evolution, the effect of heating rates on the thermal degradation characteristics and to determine the global mass loss kinetics of thermal degradation. The thermal degradation was found to occur in several distinct phases: each phase giving volatile evolution in an independent parallel lump. Each decomposition phase was modeled by a single irreversible reaction with respect to the solid mass. Global mass loss kinetics was also determined for the entire decomposition process, as if occurring in one single step. The integral and differential techniques were used for the determination of kinetic parameters. Using the method of Agrawal and Sivasubramanian [R.K. Agrawal, M.S. Sivasubramanian, AIChE J. 33 (1987) 7] for the total degradation zone, the orders of reaction were found in the range of 1.00-2.50 in both the atmospheres (i.e. nitrogen and air) and the activation energy in the range of 27.84-33.44 and 57.41-88.92 kJ mol -1 in nitrogen and air, respectively. The pre-exponential factor was found in the range of 32.1-95.1 and 5.10 x 10 4 to 5.46 x 10 9 min -1 in nitrogen and air atmospheres, respectively

  15. Determination of Model Kinetics for Forced Unsteady State Operation of Catalytic CH4 Oxidation

    Directory of Open Access Journals (Sweden)

    Effendy Mohammad

    2016-01-01

    Full Text Available The catalytic oxidation of methane for abating the emission vented from coal mine or natural gas transportation has been known as most reliable method. A reverse flow reactor operation has been widely used to oxidize this methane emission due to its capability for autothermal operation and heat production. The design of the reverse flow reactor requires a proper kinetic rate expression, which should be developed based on the operating condition. The kinetic rate obtained in the steady state condition cannot be applied for designing the reactor operated under unsteady state condition. Therefore, new approach to develop the dynamic kinetic rate expression becomes indispensable, particularly for periodic operation such as reverse flow reactor. This paper presents a novel method to develop the kinetic rate expression applied for unsteady state operation. The model reaction of the catalytic methane oxidation over Pt/-Al2O3 catalyst was used with kinetic parameter determined from laboratory experiments. The reactor used was a fixed bed, once-through operation, with a composition modulation in the feed gas. The switching time was set at 3 min by varying the feed concentration, feed flow rate, and reaction temperature. The concentrations of methane in the feed and product were measured and analysed using gas chromatography. The steady state condition for obtaining the kinetic rate expression was taken as a base case and as a way to judge its appropriateness to be applied for dynamic system. A Langmuir-Hinshelwood reaction rate model was developed. The time period during one cycle was divided into some segments, depending on the ratio of CH4/O2. The experimental result shows that there were kinetic regimes occur during one cycle: kinetic regime controlled by intrinsic surface reaction and kinetic regime controlled by external diffusion. The kinetic rate obtained in the steady state operation was not appropriate when applied for unsteady state operation

  16. ENZYMATIC KINETIC STUDY HYDROLASE FROM CITRUS

    Directory of Open Access Journals (Sweden)

    Israel Hernández

    2015-09-01

    Full Text Available In this paper the degrading activity of enzymes derived from orange peels (Citrus x sinensis, grapefruit (Citrus paradise and pineapple (Ananas comosus on the organic matter in wastewater is evaluated. This activity is measured indirectly by quantifying the biochemical oxygen demand (COD before and after degradation process based on a period of time using the HACH DR / 2010, and then the kinetic study was performed by the differential method and integral with the experimental data, obtaining a reaction order of 1 to pectinase (orange, and order 2 for bromelain (pineapple.

  17. Degradation of oxcarbazepine by UV-activated persulfate oxidation: kinetics, mechanisms, and pathways.

    Science.gov (United States)

    Bu, Lingjun; Zhou, Shiqing; Shi, Zhou; Deng, Lin; Li, Guangchao; Yi, Qihang; Gao, Naiyun

    2016-02-01

    The degradation kinetics and mechanism of the antiepileptic drug oxcarbazepine (OXC) by UV-activated persulfate oxidation were investigated in this study. Results showed that UV/persulfate (UV/PS) process appeared to be more effective in degrading OXC than UV or PS alone. The OXC degradation exhibited a pseudo-first order kinetics pattern and the degradation rate constants (k obs) were affected by initial OXC concentration, PS dosage, initial pH, and humic acid concentration to different degrees. It was found that low initial OXC concentration, high persulfate dosage, and initial pH enhanced the OXC degradation. Additionally, the presence of humic acid in the solution could greatly inhibit the degradation of OXC. Moreover, hydroxyl radical (OH•) and sulfate radical (SO4 (-)••) were identified to be responsible for OXC degradation and SO4 (-)• made the predominant contribution in this study. Finally, major intermediate products were identified and a preliminary degradation pathway was proposed. Results demonstrated that UV/PS system is a potential technology to control the water pollution caused by emerging contaminants such as OXC.

  18. Oxidation and reduction kinetics of eutectic SnPb, InSn, and AuSn: a knowledge base for fluxless solder bonding applications

    DEFF Research Database (Denmark)

    Kuhmann, Jochen Friedrich; Preuss, A.; Adolphi, B.

    1998-01-01

    : (1) SnPb; (2) InSn; (3) AuSn. The studies of the oxidation kinetics show that the growth of the native oxide, which covers the solder surfaces from the start of all soldering operations is self-limiting. The rate of oxidation on the molten, metallic solder surfaces is significantly reduced...... and reduction kinetics, are applied to flip-chip (FC) bonding experiments in vacuum with and without the injection of H2. Wetting in vacuum is excellent but the self-alignment during flip-chip soldering is restricted. The desired, perfectly self-aligned FC-bonds have been only achieved, using evaporated...

  19. Kinetic and geometric aspects of solid oxide fuel cell electrodes

    DEFF Research Database (Denmark)

    Mogensen, Mogens Bjerg; Skaarup, Steen

    1996-01-01

    The paper gives an overview of the main factors controlling the performance of the solid oxide fuel cell (SOFC) electrodes, emphasizing the most widely chosen anodes and cathodes, Ni-YSZ and LSM-YSZ. They are often applied as composites (mixtures) of the electron conducting electrode material...

  20. Kinetics and correlation analysis of reactivity in the oxidation of ...

    Indian Academy of Sciences (India)

    The oxidation of a number of monosubstituted aryl methyl, alkyl phenyl, dialkyl, and diphenyl sulfides by butyltriphenylphosphonium dichromate (BTPPD), to the corresponding sulfoxides, is first order with respect to BTPPD and is second order with respect to sulfide. The reaction is catalysed by hydrogen ions and the ...

  1. Kinetic investigation of vanadium (V)/(IV) redox couple on electrochemically oxidized graphite electrodes

    International Nuclear Information System (INIS)

    Wang, Wenjun; Wei, Zengfu; Su, Wei; Fan, Xinzhuang; Liu, Jianguo; Yan, Chuanwei; Zeng, Chaoliu

    2016-01-01

    Highlights: • The VO_2"+/VO"2"+ redox reaction of the electrode could be facilitated to some extent with the increasing anodic corrosion. • A real reaction kinetic equation for the oxidation of VO"2"+ on the electrochemically oxidized electrode has been firstly obtained. • The establishment of the kinetic equation is conducive to predict polarization behaviors of the electrodes in engineering application. - Abstract: The morphology, surface composition, wettability and the kinetic parameters of the electrochemically oxidized graphite electrodes obtained under different anodic polarization conditions have been examined by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), contact angle measurements, steady-state polarization and cyclic voltammetry (CV) tests, with an attempt to investigate the inherent correlation between the physicochemical properties and the kinetic characteristics for carbon electrodes used in an all-vanadium redox flow battery (VRFB). When the anodic polarization potential raises up to 1.8 V vs. SCE, the anodic corrosion of the graphite might happen and a large number of oxygen-containing functional groups generate. The VO_2"+/VO"2"+ redox reaction can be facilitated and the reaction reversibility tends to become better with the increasing anodic potential, possibly owing to the increased surface oxides and the resulting improved wettability of the electrode. Based on this, a real reaction kinetic equation for the oxidation of VO"2"+ has been obtained on the electrode polarized at 1.8 V vs. SCE and it can be also well used to predict the polarization behavior of the oxidized electrode in vanadium (IV) acidic solutions.

  2. Effects of pH, Chloride, and Bicarbonate on Cu(I) Oxidation Kinetics at Circumneutral pH

    Science.gov (United States)

    Yuan, X.; Pham, A.; Waite, T.; Xing, G.; Rose, A.

    2012-12-01

    The redox chemistry of copper species in the upper water column plays a significant role in its speciation, transport and bioavailability. Most previous studies have focused primarily on Cu(II), principally because Cu(I) is easily oxidized to Cu(II) by oxygen or other oxidants. However, a growing body of evidence indicates that a number of potentially important reactions may lead to Cu(I) formation and result in a significant steady-state concentration of Cu(I) in natural waters. Redox reactions of Cu(I) could result in the production of reactive oxygen species (ROS), such as superoxide and hydroxyl radical, that may subsequently induce a cascade of radical-promoted reactions with other constituents in natural waters. As such, a better understanding of copper-catalysed processes that produce and consume O2- is important in furthering our insight into factors contributing to global biogeochemical cycles. In this study, the oxidation kinetics of nanomolar concentrations of Cu(I) in NaCl solutions have been investigated over the pH range 6.5-8.0.The overall apparent oxidation rate constant was strongly affected by chloride, moderately by bicarbonate and, and to a lesser extent, by pH. In the absence of bicarbonate, an equilibrium-based speciation model indicated that Cu+ and CuClOH- were the most kinetically reactive species, while the contribution of other Cu(I) species to the overall oxidation rate was minor. A kinetic model based on recognized key redox reactions for these two species further indicated that oxidation of Cu(I) by oxygen and superoxide were important reactions at all pH values and [Cl-] considered, but back reduction of Cu(II) by superoxide only became important at relatively low chloride concentrations. Bicarbonate concentrations from 2-5 mM substantially accelerated Cu(I) oxidation. Kinetic analysis over a range of bicarbonate concentrations revealed that this was due to the formation of CuCO3-, which reacts relatively rapidly with oxygen, and not

  3. Deuterium oxide dilution kinetics to predict body composition in dairy goats

    International Nuclear Information System (INIS)

    Brown, D.L.; Taylor, S.J.

    1986-01-01

    Body composition and D2O dilution kinetics were studied in 15 female goats ranging from 38.0 to 70.1 kg live weight. Infrared spectrophotometric analyses of blood samples drawn during the 4 d following D2O injections were used to estimate D2O space. All does were slaughtered without shrinking and analyzed for dry matter, fat, nitrogen, and ash content. Estimates of D2O space from the late slope of the dilution curve, together with live weight, were used to predict body composition. Conclusions were 1) deuterium oxide space with live body weight accounts for about 90% of the variation in dairy goat empty body fat, empty body nitrogen, and empty body dry matter; 2) less than half the variation in empty body ash is related to live weight and D2O space; and 3) D2O space estimates would be biased by accelerations in water turnover

  4. Single-Site Palladium(II) Catalyst for Oxidative Heck Reaction: Catalytic Performance and Kinetic Investigations

    Energy Technology Data Exchange (ETDEWEB)

    Duan, Hui; Li, Mengyang; Zhang, Guanghui; Gallagher, James R.; Huang, Zhiliang; Sun, Yu; Luo, Zhong; Chen, Hongzhong; Miller, Jeffrey T.; Zou, Ruqiang; Lei, Aiwen; Zhao, Yanli

    2015-01-01

    ABSTRACT: The development of organometallic single-site catalysts (SSCs) has inspired the designs of new heterogeneous catalysts with high efficiency. Nevertheless, the application of SSCs in certain modern organic reactions, such as C-C bond formation reactions, has still been less investigated. In this study, a single-site Pd(II) catalyst was developed, where 2,2'-bipyridine-grafted periodic mesoporous organosilica (PMO) was employed as the support of a Pd(II) complex. The overall performance of the single-site Pd(II) catalyst in the oxidative Heck reaction was then investigated. The investigation results show that the catalyst displays over 99% selectivity for the product formation with high reaction yield. Kinetic profiles further confirm its high catalytic efficiency, showing that the rate constant is nearly 40 times higher than that for the free Pd(II) salt. X-ray absorption spectroscopy reveals that the catalyst has remarkable lifetime and recyclability.

  5. Kinetics of the process of formation and high-temperature oxidation of electrospark coatings on steel

    International Nuclear Information System (INIS)

    Verkhoturov, A.D.; Chiplik, V.N.; Egorov, F.F.; Lavrenko, V.A.; Podchernyaeva, I.A.; Shemet, V.Z.

    1986-01-01

    This work is a study of the kinetics of formation and of the heat resistance of electrospark coatings based on the composite TiB 2 -Mo with varying molybdenum content. In the process of electrospark alloying they measured the specific erosion of the anode and the increase in weight of the cathode with an accuracy not worse than 5%. Electrospark coatings of TiB 2 -Mo on steel 45 are marked by improved scaling resistance at temperatures above 900 C. Their scaling resistance and also the effectiveness of the process of electrospark alloying increase with increasing content of the phase B-MoB in the coating because molybdenum borate forms during its high-temperature oxidation. Illustrations and table are included

  6. Kinetics of uranium (4) oxidation with nitrous acid in the presence of oxalate-ions in nitric and perchloric acid solutions

    International Nuclear Information System (INIS)

    Nikitenko, S.I.; Astafurova, L.N.

    1991-01-01

    Kinetics of uranium (4) oxidation with nitrous acid in the presence of oxalate-ions are studied spectrometrically. It is shown that even at small oxalate concentrations a notable effect of tetravalent uranium stabilization is observed relatively to the oxidation with nitrous acid. In case of a significant excess of oxalate-ions the oxidation rate will be considerably slower as a result of the formation of U(4) bisoxalate complex

  7. Effect of the kinetics of ammonium and nitrite oxidation on nitritation success or failure for different biofilm reactor geometries

    DEFF Research Database (Denmark)

    Lackner, Susanne; Smets, Barth F.

    2012-01-01

    was on the influence of key biokinetic parameters (maximum specific growth rates, oxygen and nitrogen affinity constants of AOB (ammonium oxidizing bacteria) and NOB (nitrite oxidizing bacteria)) and their ratios on nitritation efficiency in these geometries. This exhaustive simulation study revealed that nitritation...... strongly depends on the chosen kinetic parameters of AOB and NOB. The maximum specific growth rates (μmax,AOB and μmax,NOB) had the strongest impact on nitritation efficiency (NE). In comparison, the counter-diffusion geometry yielded more parameter combinations (27.5%) that resulted in high NE than the co...

  8. Oxidative kinetic resolution of racemic alcohols catalyzed by chiral ferrocenyloxazolinylphosphine-ruthenium complexes.

    Science.gov (United States)

    Nishibayashi, Yoshiaki; Yamauchi, Akiyoshi; Onodera, Gen; Uemura, Sakae

    2003-07-25

    Oxidative kinetic resolution of racemic secondary alcohols by using acetone as a hydrogen acceptor in the presence of a catalytic amount of [RuCl(2)(PPh(3))(ferrocenyloxazolinylphosphine)] (2) proceeds effectively to recover the corresponding alcohols in high yields with an excellent enantioselectivity. When 1-indanol is employed as a racemic alcohol, the oxidation proceeds quite smoothly even in the presence of 0.0025 mol % of the catalyst 2 to give an optically active 1-indanol in good yield with high enantioselectivity (up to 94% ee), where turnover frequency (TOF) exceeds 80,000 h(-1). From a practical viewpoint, the kinetic resolution is investigated in a large scale, optically pure (S)-1-indanol (75 g, 56% yield, >99% ee) being obtained from racemic 1-indanol (134 g) by employing this kinetic resolution method twice.

  9. The hydrogen evolution and oxidation kinetics during overdischarging of sealed nickel-metal hydride batteries

    NARCIS (Netherlands)

    Ayeb, A.; Otten, W.M.; Mank, A.J.G.; Notten, P.H.L.

    2006-01-01

    The hydrogen evolution and oxidation kinetics in NiMH batteries have been investigated under temperature-controlled, steady-state, overdischarging conditions within a temperature range of 10 and 50°C and at discharging currents of 1–330 mA (0.0009 to 0.3 C rate). In situ Raman spectroscopic analyses

  10. Effect of ambient air pressure on the oxidation kinetics of Fe–6 at.% Si alloy

    Czech Academy of Sciences Publication Activity Database

    Lashin, Abdel Rahman; Schneeweiss, Oldřich; Houbaert, Y.

    2008-01-01

    Roč. 50, č. 9 (2008), s. 2580-2587 ISSN 0010-938X R&D Projects: GA AV ČR IAA1041404 Institutional research plan: CEZ:AV0Z20410507 Keywords : Iron-silicon * Mössbauer spectroscopy * XRD * Oxidation kinetics Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.293, year: 2008

  11. Investigation on CO catalytic oxidation reaction kinetics of faceted perovskite nanostructures loaded with Pt

    KAUST Repository

    Yin, S. M.

    2017-01-18

    Perovskite lead titanate nanostructures with specific {111}, {100} and {001} facets exposed, have been employed as supports to investigate the crystal facet effect on the growth and CO catalytic activity of Pt nanoparticles. The size, distribution and surface chemical states of Pt on the perovskite supports have been significantly modified, leading to a tailored conversion temperature and catalytic kinetics towards CO catalytic oxidation.

  12. Kinetic investigation of the oxidation of N-alkyl anilines by ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Chemical Sciences; Volume 112; Issue 6. Kinetic investigation of the oxidation of N-alkyl anilines by peroxomonophosphoric acid in anionic surfactant sodium lauryl sulphate. G P Panigrahi Jagannath Panda. Physical and Theoretical Volume 112 Issue 6 December 2000 pp 615-622 ...

  13. Development of the kinetic model of platinum catalyzed ammonia oxidation in a microreactor

    NARCIS (Netherlands)

    Rebrov, E.V.; Croon, de M.H.J.M.; Schouten, J.C.

    2002-01-01

    The ammonia oxidation reaction on supported polycrystalline platinum catalyst was investigated in an aluminum-based microreactor. An extensive set of reactions was included in the chemical reactor modeling to facilitate the construction of a kinetic model capable of satisfactory predictions for a

  14. Mechanism and kinetics of the oxidation of synthetic alpha-NiS

    Directory of Open Access Journals (Sweden)

    BOYAN BOYANOV

    2008-02-01

    Full Text Available The results of an investigation of the mechanism and kinetics of the oxidation process of synthetic a-NiS are presented in this paper. The mechanism of a-NiS oxidation was investigated based on the comparative analysis of DTA–TG–DTG and XRD results, as well as the constructed phase stability diagrams (PSD for the Ni–S–O system. The kinetic investigations of the oxidation process were performed under isothermal conditions (temperature range 823–1073 K. The obtained degrees of desulfurization were used in the calculation process according to the Sharp model and the kinetic parameters, including the activation energies and the rate constants of the characteristic reactions, for the oxidation of a-NiS were determined. These results enabled the formulation of a kinetic equation for the desulfurization process: ‑ln(1−a = k1t = 27.89 exp(–9860/Tt, with an activation energy of 82±4 kJ mol-1, for the first stage of the process and –ln (1 − a = k2t = 1.177 exp(–4810/Tt, with an activation energy of 40±2 kJ mol-1, for the second stage.

  15. Kinetics and mechanism of the oxidation of some α-hydroxy acids by ...

    Indian Academy of Sciences (India)

    Unknown

    2004-11-08

    Nov 8, 2004 ... presence of a substantial kinetic isotope effect (kH/kD = 5⋅91 at 298 K). The rates of oxidation ... have been made to correlate rate and structure in this reaction. Mechanistic ... The solvent was glacial acetic acid and temperature was ≈ 298 K. .... glacial acetic acid was evaporated to dryness under reduced ...

  16. Investigation on CO catalytic oxidation reaction kinetics of faceted perovskite nanostructures loaded with Pt

    KAUST Repository

    Yin, S. M.; Duanmu, J. J.; Zhu, Yihan; Yuan, Y. F.; Guo, S. Y.; Yang, J. L.; Ren, Z. H.; Han, G. R.

    2017-01-01

    Perovskite lead titanate nanostructures with specific {111}, {100} and {001} facets exposed, have been employed as supports to investigate the crystal facet effect on the growth and CO catalytic activity of Pt nanoparticles. The size, distribution and surface chemical states of Pt on the perovskite supports have been significantly modified, leading to a tailored conversion temperature and catalytic kinetics towards CO catalytic oxidation.

  17. High-Temperature Oxidation Behavior and Kinetics of Forged 12Cr-MoVW Steel

    Directory of Open Access Journals (Sweden)

    Kim Yong Hwan

    2017-06-01

    Full Text Available The oxidation kinetics of forged 12Cr-MoVW steel was investigated in an air (N2+O2 atmosphere at 873-1073 K (Δ50 K using thermogravimetric analysis. The oxidized samples were characterized using X-ray diffraction, and the surface and cross-sectional morphologies were examined using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. The forged 12Cr-MoVW steel samples exhibited parabolic behavior and a low oxidation rate compared with their as-cast counterparts. A protective oxide layer was uniformly formed at relatively low temperature (≤973 K for the forged samples, which thus exhibited better oxidation resistance than the as-cast ones. These oxides are considered solid-solution compounds such as (Fe, Cr2O3.

  18. Kinetics and mechanisms of the oxidation of cobalt at 600-8000C

    International Nuclear Information System (INIS)

    Hsu, H.S.; Yurek, G.J.

    1982-01-01

    Two-phase layered scales comprising CoO and Co 3 O 4 formed on cobalt during oxidation at 600 0 , 700 0 , and 800 0 C and at oxygen partial pressures in the range 0.001-1 atm. The kinetics, which were obtained by thermogravimetric analysis, obeyed a parabolic rate law after an initial, nonparabolic stage of oxidation. The monoxide consisted of relatively large grains (10μ) and the spinel comprised small grains (3μ) for all conditions of oxidation. Grain boundary diffusion of cations played a significant role in the growth of the spinal layer. Thermogravimetric data and the steady-state ratio of the oxide layer thicknesses were employed to calculate the rates of thickening of the individual oxide layers and the rate of oxidation of CoO to Co 3 O 4

  19. Stochastic optimization-based study of dimerization kinetics

    Indian Academy of Sciences (India)

    To this end, we study dimerization kinetics of protein as a model system. We follow the dimerization kinetics using a stochastic simulation algorithm and ... optimization; dimerization kinetics; sensitivity analysis; stochastic simulation ... tion in large molecules and clusters, or the design ..... An unbiased strategy of allocating.

  20. On direct internal methane steam reforming kinetics in operating solid oxide fuel cells with nickel-ceria anodes

    Science.gov (United States)

    Thallam Thattai, A.; van Biert, L.; Aravind, P. V.

    2017-12-01

    Major operating challenges remain to safely operate methane fuelled solid oxide fuel cells due to undesirable temperature gradients across the porous anode and carbon deposition. This article presents an experimental study on methane steam reforming (MSR) global kinetics for single operating SOFCs with Ni-GDC (gadolinium doped ceria) anodes for low steam to carbon (S/C) ratios and moderate current densities. The study points out the hitherto insufficient research on MSR global and intrinsic kinetics for operating SOFCs with complete Ni-ceria anodes. Further, it emphasizes the need to develop readily applicable global kinetic models as a subsequent step from previously reported state-of-art and complex intrinsic models. Two rate expressions of the Power law (PL) and Langmuir-Hinshelwood (LH) type have been compared and based on the analysis, limitations of using previously proposed rate expressions for Ni catalytic beds to study MSR kinetics for complete cermet anodes have been identified. Firstly, it has been shown that methane reforming on metallic (Ni) current collectors may not be always negligible, contrary to literature reports. Both PL and LH kinetic models predict significantly different local MSR reaction rate and species partial pressure distributions along the normalized reactor length, indicating a strong need for further experimental verifications.