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1.
Experimental profiles of stable species concentrations and temperature are reported for the flow reactor oxidation of ethanol at atmospheric pressure, initial temperatures near 1100 K and equivalence ratios of 0.61–1.24. Acetaldehyde, ethene, and methane appear in roughly equal concentrations as major intermediate species under these conditions. A detailed chemical mechanism is validated by comparison with the experimental species profiles. The importance of including all three isomeric forms of the C2H5O radical in such a mechanism is demonstrated. The primary source of ethene in ethanol oxidation is verified to be the decomposition of the C2H4OH radical. The agreement between the model and experiment at 1100 K is optimized when the branching ratio of the reactions of C2H5OH with OH and H is defined by (30% C2H4OH + 50% CH3CHOH + 20% CH3CH2O) + XH. As in methanol oxidation, HO2 chemistry is very important, while the H + O2 chain branching reaction plays only a minor role until late in fuel decay, even at temperatures above 1100 K. 相似文献
2.
New experimental results were obtained for the mutual sensitization of the oxidation of NO and methane in a fused silica jet‐stirred reactor operating at 105 Pa, over the temperature range 800–1150 K. The effect of the addition of sulfur dioxide was studied. Probe sampling followed by online FTIR analyses and off‐line GC‐TCD/FID analyses allowed the measurement of concentration profiles for the reactants, stable intermediates, and final products. A detailed chemical kinetic modeling of the present experiments was performed. An overall reasonable agreement between the present data and modeling was obtained. According to the present modeling, the mutual sensitization of the oxidation of methane and NO proceeds via the NO to NO2 conversion by HO2 and CH3O2. The conversion of NO to NO2 by CH3O2 is more important at low temperatures (800 K) than at higher temperatures (850–900 K) where the production of NO2 is mostly due to the reaction of NO with HO2. The NO to NO2 conversion is favored by the production of the HO2 and CH3O2 radicals yielded from the oxidation of the fuel. The production of OH resulting from the oxidation of NO accelerates the oxidation of the fuel: NO + HO2 → OH+ NO2 followed by OH + CH4→ CH3. In the lower temperature range of this study, the reaction further proceeds via CH3 + O2→ CH3O2; CH3O2+ NO → CH3O + NO2. At higher temperatures, the production of CH3O involves NO2: CH3+ NO2→ CH3O. This sequence of reactions is followed by CH3O → CH2O + H; CH2O +OH → HCO; HCO + O2 → HO2 and H + O2 → HO2 → CH2O + H; CH2O +OH → HCO; HCO + O2 → HO2 and H + O2 → HO2. The data and the modeling show that unexpectedly, SO2 has no measurable effect on the kinetics of the mutual sensitization of the oxidation of NO and methane in the present conditions, whereas it frequently acts as an inhibitor in combustion. This result was rationalized via a detailed kinetic analysis indicating that the inhibiting effect of SO2 via the sequence of reactions SO2+H → HOSO, HOSO+O2 → SO2+HO2, equivalent to H+O2?HO2, is balanced by the reaction promoting step NO+HO2 → NO2+OH. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 406–413, 2005 相似文献
3.
A comprehensive detailed chemical kinetic mechanism for methanol oxidation has been developed and validated against multiple experimental data sets. The data are from static-reactor, flow-reactor, shock-tube, and laminar-flame experiments, and cover conditions of temperature from 633–2050 K, pressure from 0.26–20 atm, and equivalence ratio from 0.05–2.6. Methanol oxidation is found to be highly sensitive to the kinetics of the hydroperoxyl radical through a chain-branching reaction sequence involving hydrogen peroxide at low temperatures, and a chain-terminating path at high temperatures. The sensitivity persists at unusually high temperatures due to the fast reaction of CH2OH+O2=CH2O+HO2 compared to CH2OH+M=CH2O+H+M. The branching ratio of CH3OH+OH=CH2OH/CH3O+H2O was found to be a more important parameter under the higher temperature conditions, due to the rate-controlling nature of the branching reaction of the H-atom formed through CH3O thermal decomposition. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 805–830, 1998 相似文献
4.
In the present work, the detailed reaction mechanism and possible products of the OH-initiated oxidation of CH2=C(CH3)CH2CH2OH (MBO331) have been revealed theoretically for the first time. The potential energy surfaces of various reaction channels
both in the absence and presence of O2 and NO are evaluated at the CCSD(T)/6−31++G(d,p)//MP2(full)/6−311G(d,p)+ZPE*0.95 level. The major products of HCHO + CH3C(O)CH2CH2OH predicted for the title reaction in the presence of O2 and NO are in agreement with those of similar reactions of unsaturated alcohols with OH radical. 相似文献
5.
Tomohiro Ohta 《国际化学动力学杂志》1984,16(12):1495-1503
The yield of benzene in the reaction of 1,4- and 1,3-cyclohexadiene with OH radicals in the presence of oxygen was determined using H2O2 and CH3ONO as OH radical sources. Both in the H2O2 and the CH3ONO systems, the yield of benzene from 1,4-cyclohexadiene was 15.3% and the yield from 1,3-cyclohexadiene was 8.9%. On the basis of the obtained yields, the rate constant for allylic hydrogen abstraction per C? H in cyclohexadiene was determined to be 3.8 × 10?12 cm3 molecule?1 s?1. The branching ratio of the hydrogen abstraction to overall reaction for 1-butene and 1-pentene was estimated to be (25–14)% by applying the obtained rate constants. The result was in good agreement with the branching ratio determined directly by use of the discharge flow photoionization mass spectrometer by Biermann, Harris, and Pitts [4]. 相似文献
6.
Venkatesh Vasudevan Robert D. Cook Ronald K. Hanson Craig T. Bowman David M. Golden 《国际化学动力学杂志》2008,40(8):488-495
The reaction between methyl and hydroxyl radicals has been studied in reflected shock wave experiments using narrow‐linewidth OH laser absorption. OH radicals were generated by the rapid thermal decomposition of tert‐butyl hydroperoxide. Two different species were used as CH3 radical precursors, azomethane and methyl iodide. The overall rate coefficient of the CH3 + OH reaction was determined in the temperature range 1081–1426 K under conditions of chemical isolation. The experimental data are in good agreement with a recent theoretical study of the reaction. The decomposition of methanol to methyl and OH radicals was also investigated behind reflected shock waves. The current measurements are in good agreement with a recent experimental study and a master equation simulation. © 2008 Wiley Periodicals, Inc. 40: 488–495, 2008 相似文献
7.
Flow reactor experiments were performed over wide ranges of pressure (0.5–14.0 atm) and temperature (750–1100 K) to study H2/O2 and CO/H2O/O2 kinetics in the presence of trace quantities of NO and NO2. The promoting and inhibiting effects of NO reported previously at near atmospheric pressures extend throughout the range of pressures explored in the present study. At conditions where the recombination reaction H + O2 (+M) = HO2 (+M) is favored over the competing branching reaction, low concentrations of NO promote H2 and CO oxidation by converting HO2 to OH. In high concentrations, NO can also inhibit oxidative processes by catalyzing the recombination of radicals. The experimental data show that the overall effects of NO addition on fuel consumption and conversion of NO to NO2 depend strongly on pressure and stoichiometry. The addition of NO2 was also found to promote H2 and CO oxidation but only at conditions where the reacting mixture first promoted the conversion of NO2 to NO. Experimentally measured profiles of H2, CO, CO2, NO, NO2, O2, H2O, and temperature were used to constrain the development of a detailed kinetic mechanism consistent with the previously studied H2/O2, CO/H2O/O2, H2/NO2, and CO/H2O/N2O systems. Model predictions generated using the reaction mechanism presented here are in good agreement with the experimental data over the entire range of conditions explored. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 705–724, 1999 相似文献
8.
Reactions which proceed through energized adducts, including radical recombinations, insertions, and addition to unsaturates, frequently exhibit unusual kinetic behavior. The branching ratios among various product channels are often complex functions of both temperature and pressure. Four such reactions involving methyl radicals are analyzed by combining chemical activation distribution functions with QRRK methods to predict rate constants for each channel. These include three oxidation paths, CH3 + O, CH3 + O2, CH3 + OH, and the addition reaction CH3 + C2H2. These predictions are compared to experiments wherever possible; generally, the agreement is quite satisfactory. Analysis of the energetics of the various reaction channels, using parameters which are readily available, provides a convenient framework for prediction. Suggested rate constants for the various channels for the four reactions are given at three pressures, 20, 760, and 7600 Torr, for the temperature range 300–2500 K. The approach used here can easily be applied to other reactions. 相似文献
9.
The rate constant of the reaction of OH with DMS has been measured relative to OH + ethene in a 420 l reaction chamber at 760 torr total pressure and 298 ± 3 K in N2 + O2 buffer gas using the 254 nm photolysis of H2O2 as the OH source. In agreement with a recent absolute rate determination of the reaction the measured effective rate constant was found to increase with increasing partial pressure of O2 in the system, for 760 torr air a rate constant of (8.0 ± 0.5) × 10?12 cm3 s?1 was obtained. Product studies have been performed on the reaction in air using FTIR absorption spectrometry for detection of reactants and products. On a molar basis, SO2 was formed with a yield of 70% and dimethyl sulfone (CH3SO2CH3) with a yield of approximately 20%. These results are considerably different to those obtained in other product studies which were carried out in the presence of NOx. These differences are compared and their relevance for the atmospheric oxidation mechanisms of DMS is discussed. 相似文献
10.
The mechanism for the C2H3 + CH3OH reaction has been investigated by the Gaussian‐4 (G4) method based on the geometric parameters of the stationary points optimized at the B3LYP/6–31G(2df, p) level of theory. Four transition states have been identified for the production of C2H4 + CH3O (TSR/P1), C2H4 + CH2OH (TSR/P2), C2H3OH + CH3 (TSR/P3), and C2H3OCH3 + H (TSR/P4) with the corresponding barriers 8.48, 9.25, 37.62, and 34.95 kcal/mol at the G4 level of theory, respectively. The rate constants and branching ratios for the two lower energy H‐abstraction reactions were calculated using canonical variational transition state theory with the Eckart tunneling correction at the temperature range 300–2500 K. The predicted rate constants have been compared with existing literature data, and the uncertainty has been discussed. The branching ratio calculation suggests that the channel producing CH3O is dominant up to about 1070 K, above which the channel producing CH2OH becomes very competitive. 相似文献
11.
R. I. Moshkina S. S. Polyak N. A. Sokolova I. F. Masterovoi A. B. Nalbandyan 《国际化学动力学杂志》1980,12(5):315-338
The kinetics of ethane oxidation was studied at 320, 340, 353 and 380°C, mixture composition 2 C2H6 + 1 O2, and total pressure 609 torr. It was found that at 320°C CH2O and CH3CHO were branching agents. A series of experiments was conducted on 2C2H6 + O2 oxidation in the presence of 0.7% 14C-labeled ethylene. The ethylene oxide was found to form only from C2H4, formaldehyde formed from C2H4 and C2H6; and CH3CHO, C2H5OH, and CH3OH formed only from ethane. The formation rates of C2H4, C2H4O, and CH2O were calculated by the kinetic tracer method. At 320°C the fraction of oxygen-containing products formed from C2H4 was 16–18%, and at 353 and 380°C it was 30–40%. 相似文献
12.
M. Teresa Raventós‐Duran Max McGillen Carl J. Percival Paul D. Hamer Dudley E. Shallcross 《国际化学动力学杂志》2007,39(10):571-579
A temperature and pressure kinetic study for the CH3O2 + HO2 reaction has been performed using the turbulent flow technique with a chemical ionization mass spectrometry detection system. An Arrhenius expression was obtained for the overall rate coefficient of CH3O2 + HO2 reaction: k(T) = (3.82+2.79?1.61) × 10?13 exp[(?781 ± 127)/T] cm?3 molecule?1 s?1. A direct quantification of the branching ratios for the O3 and OH product channels, at pressures between 75 and 200 Torr and temperatures between 298 and 205 K, was also investigated. The atmospheric implications of considering the upper limit rate coefficients for the O3 and OH branching channels are observed with a significant reduction of the concentration of CH3OOH, which leads to a lower amount of methyl peroxy radical. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 571–579, 2007 相似文献
13.
Xiang-Huan Liu Feng-Yang Bai Ting-Ting Meng Dr. Shuang Ni Prof. Dr. Zhen Zhao 《Chemphyschem》2023,24(10):e202300021
The degradation and transformation of iodinated alkanes are crucial in the iodine chemical cycle in the marine boundary layer. In this study, MP2 and CCSD(T) methods were adopted to study the atmospheric transformation mechanism and degradation kinetic properties of CH3I and CH3CH2I mediated by ⋅OH radical. The results show that there are three reaction mechanisms including H-abstraction, I-substitution and I-abstraction. The H-abstraction channel producing ⋅CH2I and CH3C ⋅ HI radicals are the main degradation pathways of CH3I and CH3CH2I, respectively. By means of the variational transition state theory and small curvature tunnel correction method, the rate constants and branching ratios of each reaction are calculated in the temperature range of 200–600 K. The results show that the tunneling effect contributes more to the reaction at low temperatures. Theoretical reaction rate constants of CH3I and CH3CH2I with ⋅OH are calculated to be 1.42×10−13 and 4.44×10−13 cm3 molecule−1 s−1 at T=298 K, respectively, which are in good agreement with the experimental values. The atmospheric lifetimes of CH3I and CH3CH2I are evaluated to be 81.51 and 26.07 day, respectively. The subsequent evolution mechanism of ⋅CH2I and CH3C ⋅ HI in the presence of O2, NO and HO2 indicates that HCHO, CH3CHO, and I-atom are the main transformation end-products. This study provides a theoretical basis for insight into the diurnal conversion and environmental implications of iodinated alkanes. 相似文献
14.
Juan M. Ramírez-Anguita Àngels González-Lafont José M. Lluch 《Theoretical chemistry accounts》2009,123(1-2):93-103
Methane sulfenic acid (CH3SOH, MSEA) has been suggested in the literature as a possible stable product within the addition channel of the OH-initiated oxidation of dimethyl sulfide. In particular, it has been proposed as one of the thermodynamically feasible products of the reaction of CH3S(OH)CH3 adduct with O2. However, MSEA has never been experimentally observed and a detailed theoretical analysis of all the reaction pathways leading to MSEA formation has never been reported. In this study, the first density functional and ab initio electronic structure calculations are carried out to characterize those reaction channels yielding MSEA. The adduct formed by the reaction of DMS-OH with O2 (CH3S(O2)(OH)CH3) has been taken as the starting point. On the other hand, a new reaction pathway, which competes with the MSEA formation yielding DMSO instead, is also presented. The kinetic relevance of those different reaction pathways is discussed to assert their contribution to the experimental measurements of the end-products of DMS-OH-initiated oxidation. 相似文献
15.
Chao Gao Hua‐Qing Yang Jian Xu Song Qin Chang‐Wei Hu 《Journal of computational chemistry》2010,31(5):938-953
The gas‐phase reaction mechanism between methane and rhodium monoxide for the formation of methanol, syngas, formaldehyde, water, and methyl radical have been studied in detail on the doublet and quartet state potential energy surfaces at the CCSD(T)/6‐311+G(2d, 2p), SDD//B3LYP/6‐311+G(2d, 2p), SDD level. Over the 300–1100 K temperature range, the branching ratio for the Rh(4F) + CH3OH channel is 97.5–100%, whereas the branching ratio for the D‐CH2ORh + H2 channel is 0.0–2.5%, and the branching ratio for the D‐CH2ORh + H2 channel is so small to be ruled out. The minimum energy reaction pathway for the main product methanol formation involving two spin inversions prefers to both start and terminate on the ground quartet state, where the ground doublet intermediate CH3RhOH is energetically preferred, and its formation rate constant over the 300–1100 K temperature range is fitted by kCH3RhOH = 7.03 × 106 exp(?69.484/RT) dm3 mol?1 s?1. On the other hand, the main products shall be Rh + CH3OH in the reactions of RhO + CH4, CH2ORh + H2, Rh + CO +2H2, and RhCH2 + H2O, whereas the main products shall be CH2ORh + H2 in the reaction of Rh + CH3OH. Meanwhile, the doublet intermediates H2RhOCH2 and CH3RhOH are predicted to be energetically favored in the reactions of Rh + CH3OH and CH2ORh + H2 and in the reaction of RhCH2 + H2O, respectively. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010 相似文献
16.
Mixtures of hydrocarbons (methane, allene, propyne, propene, and propane)–H2–O2 highly diluted with argon were heated to a temperature ranging from 1200 to 1900 K behind reflected shock waves, and the additive effects of methane, allene, propyne, propene, and propane on OH radical production in H2 oxidation were studied by observing time‐resolved UV‐absorption (306.7 nm). It was found that, in H2 oxidation below 1500 K, the addition of these hydrocarbons prolonged the delay time of the onset of the rapid OH radical production. An analysis using reported kinetic modeling of C1–C4 oxidation gave valuable information for reactions between hydrocarbons and H, O atoms and OH radicals. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 50–55, 2005 相似文献
17.
Juan M. Ramírez‐Anguita Àngels González‐Lafont José M. Lluch 《Journal of computational chemistry》2009,30(9):1477-1489
The production of dimethyl sulfoxide (DMSO) and dimethyl sulfone (DMSO2) in the dimethyl sulfide (DMS) degradation scheme initiated by the hydroxyl (OH) radical has been shown to be very sensitive to nitrogen oxides (NOx) levels. In the present work we have explored the potential energy surfaces corresponding to several reaction pathways which yield DMSO2 from the CH3S(O)(OH)CH3 adduct [including the formation of CH3S(O)(OH)CH3 from the reaction of DMSO with OH] and the reaction channels that yield DMSO or/and DMSO2 from the CH3S(O2)(OH)CH3 adduct are also studied. The formation of the CH3S(O2)(OH)CH3 adduct from CH3S(OH)CH3 (DMS‐OH) and O2 was analyzed in our previous work. All these pathways due to the presence of NOx (NO and NO2) and also due to the reactions with O2, OH and HO2 are compared with the objective of inferring their kinetic relevance in the laboratory experiments that measure DMSO2 (and DMSO) formation yields. In particular, our theoretical results clearly show the existence of NOx‐dependent pathways leading to the formation of DMSO2, which could explain some of these experimental results in comparison with experimental measurements carried out in NOx‐free conditions. Our results indicate that the relative importance of the addition channel in the DMS oxidation process can be dependent on the NOx content of chamber experiments and of atmospheric conditions. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009 相似文献
18.
Shaoliang Zhang Rafal S. Strekowski Loïc Bosland Anne Monod Cornelius Zetzsch 《国际化学动力学杂志》2011,43(10):547-556
A flash photolysis resonance fluorescence technique has been employed to investigate the kinetics and mechanism of the reaction of OH(X2Π) radicals with CH3I over the temperature and pressure ranges 295–390 K and 82–303 Torr of He, respectively. The experiments involved time‐resolved RF detection of the OH (A2Σ+ → X2Π transition at λ = 308 nm) following FP of H2O/CH3I/He mixtures. The OH(X2Π) radicals were produced by FP of H2O in the vacuum‐UV at wavelengths λ > 115 nm using a commercial Perkin‐Elmer Xe flash lamp. Decays of OH in the presence of CH3I are observed to be exponential, and the decay rates are found to be linearly dependent on the CH3I concentration. The measured rate coefficients for the reaction of OH with CH3I are described by the Arrhenius expression kOH+CH3I = (4.1 ± 2.2) × 10?12 exp [(?1240 ± 200)K/T] cm3 molecule?1s?1. The implications of the reported kinetic results for understanding the CH3I chemistry of both atmospheric and nuclear industry interests are discussed. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 547–556, 2011 相似文献
19.
The mechanism of the OH-initiated oxidation of β-pinene in the presence of NO has been investigated using a discharge-flow system at 5 Torr and 300 K. OH radical concentrations were measured as a function of reaction time by laser-induced fluorescence (LIF). The rate constant for the OH +β-pinene reaction was measured to be (7.68 ± 0.72) ×10−11 cm3 molecule−1 s−1. OH radical propagation was observed after the addition of O2 and NO, and the measured OH concentration profiles were compared to simulations based on both the Master Chemical Mechanism and the Regional Atmospheric Chemistry Mechanism for β-pinene oxidation in order to determine the ability of these mechanisms to describe the observed efficiency of radical propagation. Both models are able to reproduce the observed OH concentrations profiles to within 15%. Expanding the MCM to include isomerization of the β-hydroxy alkoxy radicals improves the agreement with the experimental observations. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 522–531, 2005 相似文献
20.
Experimental measurements and kinetic modeling of CH4/O2 and CH4/C2H6/O2 conversion at high pressure
A detailed chemical kinetic model for homogeneous combustion of the light hydrocarbon fuels CH4 and C2H6 in the intermediate temperature range roughly 500–1100 K, and pressures up to 100 bar has been developed and validated experimentally. Rate constants have been obtained from critical evaluation of data for individual elementary reactions reported in the literature with particular emphasis on the conditions relevant to the present work. The experiments, involving CH4/O2 and CH4/C2H6/O2 mixtures diluted in N2, have been carried out in a high‐pressure flow reactor at 600–900 K, 50–100 bar, and reaction stoichiometries ranging from very lean to fuel‐rich conditions. Model predictions are generally satisfactory. The governing reaction mechanisms are outlined based on calculations with the kinetic model. Finally, the mechanism was extended with a number of reactions important at high temperature and tested against data from shock tubes, laminar flames, and flow reactors. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 778–807, 2008 相似文献