The Thermal Decomposition of Methane. I. Kinetics of the Primary Decompositionto C2H6 + H2; Rate Constant for the Homogeneous Unimolecular Dissociation of Methane and its Pressure Dependence

1975 ◽  
Vol 53 (23) ◽  
pp. 3580-3590 ◽  
Author(s):  
C.-J. Chen ◽  
M. H. Back ◽  
R. A. Back
Keyword(s):  
Rate Constant ◽  
Flow System ◽  
Quantitative Agreement ◽  
Radical Mechanism ◽  
Unimolecular Dissociation ◽  
Static System ◽  
System Data ◽  
Decomposition Of Methane ◽  
Kinetics Of ◽  
Good Agreement

The pyrolysis of methane has been studied in a static system at temperatures of 995, 1038, 1068, and 1103 K and pressures from 25 to 700 Torr. It was concluded that the initial stages of the reaction can be described by a simple homogeneous, nonchain radical mechanism:[Formula: see text]Initial rates of reaction were measured, based on analysis of hydrogen, ethane, and ethylene, and k1 was found to be pressure dependent and homogeneous. Quantitative agreement was obtained with values of k1 calculated by R.R.K.M. theory. Values of A∞ = 2.8 × 1016 s−1 and E∞ = 107.6 kcal/mol were obtained, the latter appreciably greater than the value of E0 = 103 kcal/mol used in the calculations. Comparison of previous shock-tube and flow-system data at temperatures up to 2200 K showed good agreement with values of k1 obtained by extrapolation of the present R.R.K.M. calculations. It was concluded that in all previous studies, the initial dissociation was in its pressure-dependent region. Estimates were also made of the rate constant for the reverse of [1] and showed fair agreement with recent experimental measurements.

Kinetics of Reactions Relevant to the Chemical Vapor Deposition of Indium Compounds

1997 ◽  
Vol 495 ◽  
Author(s):  
M. D. Allendorf ◽  
A. H. McDaniel
Keyword(s):  
Molecular Beam ◽  
Flow Reactor ◽  
Chemical Vapor ◽  
Sampling System ◽  
Measured Activation Energy ◽  
Measured Activation ◽  
System Data ◽  
Indium Compounds ◽  
Kinetics Of ◽  
Good Agreement

ABSTRACTThe kinetics of trimethylindium pyrolysis are investigated in a flow reactor equipped with a molecular-beam mass-spectrometric sampling system. Data are analyzed using a new computational approach that accounts for heat and mass transport in the reactor. The measured activation energy, 46.2 kcal mol−1, is in good agreement with previously reported values.

Rates of elementary processes in the chain reaction between hydrogen and oxygen I. Reactions of oxygen atoms

1963 ◽  
Vol 275 (1363) ◽  
pp. 544-558 ◽  
Keyword(s):  
Rate Constant ◽  
Atomic Oxygen ◽  
Elevated Temperatures ◽  
Collision Frequency ◽  
Flow System ◽  
Chain Reaction ◽  
Elementary Processes ◽  
A Value ◽  
Good Agreement ◽  
Oxygen Atoms

The rates of reaction of 3 P oxygen atoms with hydroxyl and hydrogen have been measured in a flow system at pressures around 2 mmHg. The former reaction, O + OH -> H + O 2 , ( — 4) occurred in the products of the rapid reaction between H and NO 2 , and was followed by measurements of atomic oxygen concentrations. k -4 was found to be 5±2 x 10 -11 cm 3 molecule -1 s -1 at 265 and 293 °K. This result, when combined with data on the reverse reaction at elevated temperatures, gives a value of k -4 which is virtually independent of temperature and equal to about 1/20 of the bimolecular collision frequency. The reaction O + H 2 -> OH + H (3) was studied in the absence of molecular oxygen and found to have a rate constant of 6 x 10 -13 exp (-8900/ RT ) cm 3 molecule -1 s -1 in the range 409 to 733 °K. This is in good agreement with values obtained at higher temperatures. The rate constant for O + D 2 was significantly less than that for O + H 2 at temperatures between 491 and 671 °K.

Kinetics and Mechanism of the Thermal Gas-Phase Reaction between NO2 and Perfluoropropene

2004 ◽  
Vol 218 (5) ◽  
pp. 575-598 ◽  
Author(s):  
R. M. Romano ◽  
Joanna Czarnowski
Keyword(s):  
Gas Phase ◽  
Rate Constant ◽  
Total Pressure ◽  
Consumption Rate ◽  
Initial Pressure ◽  
Experimental Results ◽  
Unimolecular Dissociation ◽  
Static System ◽  
Phase Reaction ◽  
Gas Phase Reaction

AbstractThe reaction of NO2 with perfluoropropene (C3F6) has been studied at 413.1, 421.0 and 432.8K, using a conventional static system. The initial pressure of NO2 was varied between 43.6 and 204.0Torr and that of C3F6 between 10.2 and 108.5Torr. Several experiments were made adding CF4, varying its pressure from 338.8 to 433.6Torr. Four products were observed: NO and perfluoropropene oxide (PFPO), formed in equivalent amounts, CF3CF(NO2)CF2NO2 and CF3C(O)CF2NO2. The relation R=[PFPO]/([CF3CF(NO2)CF2NO2] + [CF3C(O)CF2NO2]) increases with temperature and decreases as the concentration of NO2 and the total pressure M increase. The yields of PFPO, based on the amount of C3F6 consumed, varied between 63 and 89% and those of CF3CF(NO2)CF2NO2 between 0.33 and 0.08%. Increasing the temperature, the yields of CF3C(O)CF2NO2 decreased from 0.04 to 0.01%. The reaction is homogenous and the consumption rate of perfluoropropene, −d[C3F6]/dt= k1[C3F6][NO2], is independent of the total pressure. The following mechanism is postulated to explain the experimental results: 1) C3F6 + NO2 → CF3C•FCF2NO2, 2) CF3C•FCF2NO2 → PFPO+NO, 3) CF3C•FCF2NO2 + NO2+M → CF3CF(NO2)CF2NO2+M, 4) CF3C•FCF2NO2 + NO2 → CF3C(O)CF2NO2+FNO. k1=(4.57±1.4)×106exp(−(15.44±1.2) kcal mol−1/RT) dm3mol−1s−1. The value of k2, the rate constant for the unimolecular dissociation of the radical CF3C•FCF2NO2, was found to be of order of 1014s−1.

scholarly journals Effects of the Size, the Number, and the Spatial Arrangement of Reactive Patches on a Sphere on Diffusion-Limited Reaction Kinetics: A Comprehensive Study

2020 ◽  
Vol 21 (3) ◽  
pp. 997 ◽  
Author(s):  
Changsun Eun
Keyword(s):  
Reaction Kinetics ◽  
Rate Constant ◽  
Brownian Dynamics ◽  
Kinetic Studies ◽  
Spatial Arrangement ◽  
The Finite Element Method ◽  
Diffusion Limited ◽  
Diffusion Controlled ◽  
Kinetics Of ◽  
Good Agreement

We investigate how the size, the number, and the spatial arrangement of identical nonoverlapping reactive patches on a sphere influence the overall reaction kinetics of bimolecular diffusion-limited (or diffusion-controlled) reactions that occur between the patches and the reactants diffusing around the sphere. First, in the arrangement of two patches, it is known that the overall rate constant increases as the two patches become more separated from each other but decreases when they become closer to each other. In this work, we further study the dependence of the patch arrangement on the kinetics with three and four patches using the finite element method (FEM). In addition to the patch arrangement, the kinetics is also dependent on the number and size of the patches. Therefore, we study such dependences by calculating the overall rate constants using the FEM for various cases, especially for large-sized patches, and this study is complementary to the kinetic studies that were performed by Brownian dynamics (BD) simulation methods for small-sized patches. The numerical FEM and BD simulation results are compared with the results from various kinetic theories to evaluate the accuracies of the theories. Remarkably, this comparison indicates that our theory, which was recently developed based on the curvature-dependent kinetic theory, shows good agreement with the FEM and BD numerical results. From this validation, we use our theory to further study the variation of the overall rate constant when the patches are arbitrarily arranged on a sphere. Our theory also confirms that to maximize the overall rate constant, we need to break large-sized patches into smaller-sized patches and arrange them to be maximally separated to reduce their competition.

The thermal decomposition of methane. III. Methyl radical exchange in CH4–CD4 mixtures

1977 ◽  
Vol 55 (10) ◽  
pp. 1624-1628 ◽  
Author(s):  
C.-J. Chen ◽  
M. H. Back ◽  
R. A. Back
Keyword(s):  
Thermal Decomposition ◽  
Shock Tube ◽  
Exchange Reaction ◽  
Rate Constant ◽  
Average Rate ◽  
Static System ◽  
Chain Mechanism ◽  
Methyl Radical ◽  
Radical Chain ◽  
Decomposition Of Methane

The thermal methyl-radical exchange reaction, CH4 + CD4 → CH3D + CD3H, has been studied in a static system at temperatures from 880 to 1103 K, with equimolar mixtures at a pressure of 440 Torr. The exchange occurs by a methyl-radical chain mechanism, propagated by the reactions CH3 + CD4 → CH3D + CD3, and CH3 + CD4 → CH3H + CD3. Values of an average rate constant for these reactions have been estimated; kx = 1.42 × 106 ℓ mol−1 s−1 at 995 K. Comparison with shock tube data and photochemical measurements, at higher and lower temperatures respectively, indicates pronounced non-Arrhenius behaviour.

Diffusion model for deposition of epitaxial GaAs layers prepared by the MOCVD method

1991 ◽  
Vol 56 (10) ◽  
pp. 2020-2029
Author(s):  
Jindřich Leitner ◽  
Petr Voňka ◽  
Josef Stejskal ◽  
Přemysl Klíma ◽  
Rudolf Hladina
Keyword(s):  
Experimental Data ◽  
Growth Rate ◽  
Kinetic Model ◽  
Gas Phase ◽  
Substrate Surface ◽  
Deposition Process ◽  
Hydrogen Atmosphere ◽  
Epitaxial Gaas ◽  
Kinetics Of ◽  
Good Agreement

The authors proposed and treated quantitatively a kinetic model for deposition of epitaxial GaAs layers prepared by reaction of trimethylgallium with arsine in hydrogen atmosphere. The transport of gallium to the surface of the substrate is considered as the controlling process. The influence of the rate of chemical reactions in the gas phase and on the substrate surface on the kinetics of the deposition process is neglected. The calculated dependence of the growth rate of the layers on the conditions of the deposition is in a good agreement with experimental data in the temperature range from 600 to 800°C.

Kinetics of Substitution of 4-Methoxyphenylazo Groups of 2,6-Dioxo-5(3)-(4-methoxyphenylazo)-3(5)-(4-methoxyphenylhydrazono)-1,2,3,6-tetrahydropyridine-4-carboxylic Acid by Reaction with 4-Nitrobenzenediazonium Cation

1994 ◽  
Vol 59 (7) ◽  
pp. 1665-1672 ◽  
Author(s):  
Jaroslava Horáčková ◽  
Vojeslav Štěrba
Keyword(s):  
Carboxylic Acid ◽  
Rate Constant ◽  
Kinetics Of

Kinetics have been studied of gradual replacement of 4-methoxyphenylazo groups in 2,6-dioxo-5(3)-(4-methoxyphenylazo)-3(5)-(4-methoxyphenylhydrazono)-1,2,3,6-tetrahydropyridine-4-carboxylic acid (IIIa) by 4-nitrophenylazo groups using the reaction with 4-nitrobenzenediazonium cation (IIc) in acetate and phosphate buffers. The rate constant of replacement of the second methoxyphenylazo group is lower by a factor of ca 60. From the experimentally found pKa values of the corresponding azohydrazone compounds with methoxy, chloro, or nitro substituent at 4-position (IIIa - IIIf) it has been concluded that the 5(3)-(4-methoxyphenylazo)-3(5)-(4-nitrophenylhydrazono) derivative is formed in the first step.

scholarly journals Simultaneous Kinetics of Selenite Oxidation and Sorption on δ-MnO2 in Stirred-Flow Reactors

2021 ◽  
Vol 18 (6) ◽  
pp. 2902
Author(s):  
Zheyong Li ◽  
Yajun Yuan ◽  
Lin Ma ◽  
Yihui Zhang ◽  
Hongwei Jiang ◽  
...  
Keyword(s):  
Rate Constant ◽  
Photoelectron Spectroscopy ◽  
Oxide Surfaces ◽  
Kinetic Rate Constant ◽  
Flow Reactors ◽  
Mn Oxide ◽  
Remediation Strategies ◽  
Process Of Se ◽  
Kinetics Of

Selenium (Se) is an essential and crucial micronutrient for humans and animals, but excessive Se brings negativity and toxicity. The adsorption and oxidation of Se(IV) on Mn-oxide surfaces are important processes for understanding the geochemical fate of Se and developing engineered remediation strategies. In this study, the characterization of simultaneous adsorption, oxidation, and desorption of Se(IV) on δ-MnO2 mineral was carried out using stirred-flow reactors. About 9.5% to 25.3% of Se(IV) was oxidized to Se(VI) in the stirred-flow system in a continuous and slow process, with the kinetic rate constant k of 0.032 h−1, which was significantly higher than the apparent rate constant of 0.0014 h−1 obtained by the quasi-level kinetic fit of the batch method. The oxidation reaction was driven by proton concentration, and its rate also depended on the Se(IV) influent concentration, flow rate, and δ-MnO2 dosage. During the reaction of Se(IV) and δ-MnO2, Mn(II) was produced and adsorbed strongly on Mn oxide surfaces, which was evidenced by the total reflectance Fourier transform infrared (ATR-FTIR) results. The X-ray photoelectron spectroscopy (XPS) data indicated that the reaction of Se(VI) on δ-MnO2 produced Mn(III) as the main product. These results contribute to a deeper understanding of the interface chemical process of Se(IV) with δ-MnO2 in the environment.

scholarly journals Physical properties and water absorption kinetics of three varieties of Mucuna beans

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ajibola B. Oyedeji ◽  
Olajide P. Sobukola ◽  
Ezekiel Green ◽  
Oluwafemi A. Adebo
Keyword(s):  
Physical Properties ◽  
Water Absorption ◽  
Rate Constant ◽  
Geometric Mean ◽  
Seed Mass ◽  
Activation Energies ◽  
Mucuna Pruriens ◽  
Absorption Kinetics ◽  
Kinetics Of ◽  
Soaking Temperature

AbstractThe physical properties and water absorption kinetics of three varieties of Mucuna beans (Mucuna pruriens, Mucuna rajada and Mucuna veracruz) were determined in this study. Physical properties including length, width, thickness, geometric mean diameter, sphericity, porosity, bulk density, area, volume and one thousand seed mass were calculated while hydration kinetics was studied by soaking Mucuna beans in water at 30 °C, 40 °C and 50 °C and measuring water uptake at 9 h interval. Peleg’s equation was used to model the hydration characteristics and Arrhenius equation was used to describe the effect of temperature on Peleg’s rate constant k1 and to obtain the activation energies for soaking. Significant variations were observed in almost all the physical properties of the different varieties, however, there were no significant differences (p < 0.05) in their thicknesses and bulk densities. The effectiveness of fit of Peleg’s model (R2) increased with increase in soaking temperature. Peleg’s rate constant k1 decreased with increase in soaking temperature while k2 increased with temperature increase. Activation energies of Mucuna pruriens, Mucuna rajada and Mucuna veracruz were 1613.24 kJ/mol, 747.95 kJ/mol and 2743.64 kJ/mol, respectively. This study provides useful information about the properties of three varieties of Mucuna beans that could be of importance to processors and engineers for process design and optimization.

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