The carbon dioxide reforming of methane to synthesis gas was investigated in a dielectric barrier discharge reactor at room
temperature. The influence of dilution of reactants by helium was studied. We showed that, at a fixed contact time, the conversions
of CH4 and CO2 increase when the amount of helium in the gas mixture increases. This result is attributed to the “penning ionization” phenomenon,
which corresponds to an energy transfer from excited He to molecules in ground state (CH4, CO2). The selectivity to products is affected by the dilution factor. As soon as helium is present in a large amount the formation
of products resulting from recombination of methyl radicals (such as C2, C3 and C4) is less favourable due to the lowest probability of collisions to proceed. A kinetic model is proposed based on the assumption
that the reactant molecules CH4 or CO2 are attacked by active species produced by the plasma discharges, and the production of this active species are function
of the plasma power. This model which takes into account the dilution by helium fits particularly well the experimental data
we obtained. 相似文献
Conversion of CH4 with a N2 microwave plasma (2.45 GHz) is studied. The experiments cover the absorbed microwave power range 300–700 W with 17–62% of methane in the gas mixture, with pressures of 10–40 mbar and flow rates of 140–650 ml· min–1. The yields of C2 hydrocarbons and dihydrogen are analyzed by gas chromatography. The distance of methane addition downstream of the plasma plays an important role on the composition and the concentration of the products obtained. This distance mainly determines the energy concentrated in the active species of the plasma when they react with methane. Different behaviors for acetylene formation, on the one hand, and for ethane and ethene formation, on the other hand, have been observed, and this finding allows us to propose a kinetic mechanism for the decay of methane and for the formation of C2 hydrocarbons. 相似文献
Results of chemical kinetics modeling in methane subjected to the microwave plasma at atmospheric pressure are presented in this paper. The reaction mechanism is based on the methane oxidation model without reactions involving nitrogen and oxygen. For the numerical calculations 0D and 1D models were created. 0D model uses Calorimetric Bomb Reactor whereas 1D model is constructed either as Plug Flow Reactor or as a chain of Plug Flow Reactor and Calorimetric Bomb Reactor. Both models explain experimental results and show the most important reactions responsible for the methane conversion and production of H2, C2H2, C2H4 and C2H6 detected in the experiment. Main conclusion is that the chemical reactions in our experiment proceed by a thermal process and the products can be defined by considering thermodynamic equilibrium. Temperature characterizing the methane pyrolysis is 1,500–2,000 K, but plasma temperature is in the range of 4,000–5,700 K, which means that methane pyrolysis process is occurring outside the plasma region in the swirl gas flowing around the plasma. 相似文献
A radio-frequency (RF) plasma system was used to convert methane gas. The reactants and final products were analyzed by using an FTIR (Fourier transform infrared spectrometer). The effects of plasma operational parameters, including feeding concentration (C) of CH4, operational pressure (P) in the RF plasma reactor, total gas flow rate (Q) and input power wattage (W) for CH4decomposition were evaluated. The results showed that the CH4decomposition fraction increases with increasing power input, decreasing operational pressure in the RF plasma reactor, decreasing CH4feeding concentration, and decreasing total gas flow rate. In addition, mathematical models based on the obtained experimental data were developed and tested by means of sensitivity analysis.相似文献
The thermal decomposition of ethylbenzene has been investigated behind reflected shock waves over the temperature and pressure ranges of 1350–2080 K and 0.25–0.5 atm using a 1.6% C8H10 ? Ne mixture. Major products of the pyrolysis are C7H8, C7H7, C6H6, C4H2, C2H4, C2H2, and CH4; C8H8 appears throughout the temperature range as a minor product. Comparison of the product profiles obtained by time-of-flight mass spectrometry and the results of model calculations strongly supports the initiation step of β C? C bond homolysis for C8H10 dissociation. A 51 kinetic step reaction mechanism with 24 species was formulated to model the temperature and time dependence of the major products observed in our experiments. 相似文献
The thermal decomposition of acetonitrile was studied behind reflected shocks in a single pulse shock tube over the temperature range 1350–1950 K at overall densities of approximately 3 × 10?5 mol/cc. Methane and hydrogen cyanide are the major reaction products. They are formed by an attack of H and CH3 radicals on acetonitrile. The initiation step of the pyrolysis is the self dissociation of acetonitrile: for which the following rate constant was obtained: k1 = 6.17 × 1015exp(?96.6 × 103/RT)sec?1. Where R is given in units of cal/K mol. Additional reaction products which appear in the pyrolysis are: C2H2, C2H4, CH2?CHCN, CH?CHCN, C2H5CN, C2N2, and C4H2. Acetylene is formed from methane pyrolysis and becomes a major reaction product at high temperatures. Acrilonitrile and cyanoacetylene are secondary products originating from the CH2CN radical. Rate parameters for the formation of the reaction products are given. 相似文献
The physical plasma parameters, temperature and electron number density, are studied in the RF-IC (RF inductively coupled) discharge at a reduced pressure of 3 Torr in mixtures of MoF6 with Ar, H2 and CH4. The emission spectra of mixtures are investigated. It is shown that in the presence of argon, the concentration of free electrons in plasma and dissociation rate of MoF6 increase. A main role of molecular hydrogen is the generation of atomic hydrogen that binds atomic fluorine and leads to the formation of gaseous and solid products. Exhaust gas mixtures exiting the reactor are analyzed by mass spectrometry. It is shown that for all cases, the conversion of MoF6 into reaction products is close to 100%. A thermodynamic analysis of the equilibrium composition of MoF6 systems with Ar, H2 and CH4 was carried out and the obtained results are in good agreement with experimentally observed composition of the solid and gas phases. Analysis of solid deposits from mixture MoF6/H2/Ar revealed the presence of molybdenum powder and large amount of amorphous MoFx. The deposit obtained from mixtures with methane, MoF6/H2/Ar/CH4, contained crystalline molybdenum carbide, Mo3C2.
The formation of gaseous products has been examined for cellulose over the temperature range of 360–595°C. The evolution of CO, CO2, H2, CH4, C2H4, and C2H6 was determined as a function of time. The overall kinetic rate constants for decomposition were determined from the formation rates for each gas, as well as the rate constants for the formation of each specific gas. It has been verified that CO and CO2 are both primary products of decomposition, and further emanate from the same kinetic pathway. By increasing the residence time of the reactor, the production of all gaseous products, including both CO and CO2, further increased, indicating production by a secondary reaction mechanism. None of the gaseous products, save CO and CO2, were detected in measurable quantities except at temperatures above which transport limitations had affected the measurement of the kinetic rates. 相似文献
Using a mass spectrometric sampling method, we have observed the decomposition of CH4 in an rf plasma usedfor diamond deposition. The gas samples were extracted through an orifice located downstream of the plasma zone and analyzed online. For the experiments a dilute mixture of H2 and CH4 containing 0.1–3% CH4 has been used. CH4 is converted to C2H2 and C2H4 quantitatively. Small amounts of heavier hydrocarbons are formed. A comparison of the experimental results with a recent kinetic model treating a purely thermal environment is made and the differences between our experiment and the model are explained. The role of acetylene as a species formed in an atmosphere rich in atomic hydrogen is proposed. The electron impact dissociation process is suggested as the rare-determining step in the plasma-chemical decomposition of methane. 相似文献
Ethane oxidation in jet-stirred reactor has recently been investigated at high temperature (800–1200 K) in the pressure range 1–10 atm and molecular species (H2, CO, CO2, CH4, C2H2, C2H4, C2H6) concentration profiles were obtained by probe sampling and GC analysis. Ethane oxidation was modeled using a comprehensive kinetic reaction mechanism including the most recent findings concerning the kinetics of the reactions involved in the oxidation of C1? C4 hydrocarbons. The proposed mechanism is able to reproduce experimental data obtained in our high-pressure jet stirred reactor and ignition delay times measured in shock tube in the pressure range 1–13 atm, for temperatures extending from 800 to 2000 K and equivalence ratios of 0.1 to 2. It is also able to reproduce atoms concentrations (H,O) measured in shock tube at ≈2 atm. The same detailed kinetic mechanism can also be used to model the oxidation of methane, ethylene, propyne, and allene in similar conditions. 相似文献
The possibility of using a solid-electrolyte reactor in kinetic studies of the catalytic oxidations of hydrocarbon with molecular
oxygen was investigated. A theoretical analysis of processes in a catalytically asymmetric gas-diffusion cell in N2 + O2 + CH4 and N2 + O2 + C3H8 gas mixtures was performed. Analytical expressions are presented for calculating the oxygen, methane, and propane concentrations
and the methane and propane oxidation rates in the inner space of the cell from the emf of the latter. The potentiometric
response was studied experimentally after the addition of methane and propane in the gas mixture in a reactor with silver
electrodes and samples with applied catalytic materials. The concentrations of the components in the inner space of the reactor
and the oxidation rates of hydrocarbons were calculated from the experimental data. 相似文献
The deposition of diamondlike carbon (DLC) film and the measurements of ionic species by means of mass spectrometry were carried out in a CH4/N2 RF (13.56 MHz) plasma at 0.1 Torr. The film deposition rate greatly depended on both CH4/N2 composition ratio and RF power input. It was decreased monotonically as CH4 content decreased in the plasma and then rapidly diminished to negligible amounts at a critical CH4 content, which became large for higher RF power. The rate increased with increasing RF power, reaching a maximum value in 40% CH4 plasma. The predominant ionic products in CH4/N2 plasma were NH+4 and CH4N+ ions, which were produced by reactions of hydrocarbon ions, such as CH+3, CH+2, CH+5, and C2H+5 with NH3 molecules in the plasma. It was speculated that the production of NH+4 ion induced the decrease of C2H+5 ion density in the plasma, which caused a reduction in higher hydrocarbon ions densities and, accordingly, in film deposition rate. The N+2 ion sputtering also plays a major role in a reduction of film deposition rate for relatively large RF powers. The incorporation of nitrogen atoms into the bonding network of the DLC film deposited was greatly suppressed at present gas pressure conditions. 相似文献
High-temperature (>1000°K) pyrolysis of acetaldehyde (~1% in an atmosphere of pure nitrogen) was examined in a turbulent flow reactor which permits accurate determination of the spatial distribution of the stable species. Results show that the products in order of decreasing importance are CO, CH4, H2, C2H6, and C2H4. Rates of formation were consistent with the Rice–Herzfeld mechanism by including reactions to explain C2H4 formation and the possible presence of ketene. A steady-state treatment of the complete mechanism indicates that the overall reaction order decreases from \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{3}{2} $\end{document} to 1, which is supported by the new experimental data. Using earlier low-temperature results, the rate constant for the reaction CH3CHO → CH3 + CHO (1) was found as k1=1015.85±0.21 exp (?81,775±1000/RT) sec?1. Also, data for the ratio of rate constants for reactions CH3CHO + CH3 → CH4 + CH3CO (4) and 2CH3 → C2H6(6) were fitted to the empirical expression k4/k61/2=10?13.89±0.03T6.1 exp(?1720±70/RT) (cm3/mole·sec)1/2 and causes for the curvature are discussed. The noncatalytic effect of oxygen on acetaldehyde pyrolysis at high temperature is explained. 相似文献
According to the mechanism of alkane hydroxylation, whose main postulate is the formation of an intermediate complex containing pentacoordinated carbon, the hydroxylation of methane and ethane by methane monooxygenase was kinetically simulated by the numerical method. The published data on the kinetic isotope effects of oxidation of deuterium-substituted methane molecules (CHD3, CH2D2, and CH3D) and the distribution of products of chiral ethane (R- and S-MeCHDT) oxidation by methane monooxygenase were examined. The kinetic models proposed for the oxidation of isotopically substituted methane and ethane are in good agreement with experimental data. 相似文献
Decomposition of carbon tetrachloride was studied in an inductively coupled thermal plasma reactor and in a low temperature, non-equilibrium plasma reactor, in neutral and oxidative conditions, respectively. In neutral conditions formation of solid soot, aliphatic- and cyclodienes was observed in equilibrium, and products, such as Cl2 and C2Cl6 were detected in non-equilibrium plasma. Feeding of oxygen into the thermal plasma reactor depressed both soot and dienes formation and induced the formation of oxygen containing intermediates and products. GC-MS analyses of the gaseous products and the extract of the soot referred to as complex decomposition and recombination mechanism at given conditions. Presence of oxygen in the low temperature plasma reactor results in the formation of carbonyl compounds as intermediers. CO2 and Cl2 revealed as final products of CCl4 decomposition in cold plasma. 相似文献
Published data on the kinetic isotope effects of the hydroxylation of deuterium-substituted methane molecules (CHD3, CH2D2, and CH3D) by methane monooxygenase are examined in the framework of the two-step nonradical mechanism through the intermediate formation of a complex containing pentacoordinate carbon. The kinetic schemes with the first step involving one, two, and three hydrogen atoms of the oxidized substrate are considered. Contrary to the widely accepted oxygen rebound mechanism, the experimental results obtained for the oxidation of various substrates by methane monooxygenase and cytochrome P450 can be explained from the viewpoint of the dynamics of a general nonradical mechanism. 相似文献
A detailed reaction mechanism is developed and used to model experimental data on the pyrolysis of CHF3 and the non-oxidative gas-phase reaction of CHF3 with CH4 in an alumina tube reactor at temperatures between 873 and 1173 K and at atmospheric pressure. It was found that CHF3 can be converted into C2F4 during pyrolysis and CH2CF2 via reaction with CH4. Other products generated include C3F6, CH2F2, C2H3F, C2HF3, C2H6, C2H2 and CHF2CHF2. The rate of CHF3 decomposition can be expressed as 5.2×1013 [s−1] e−295[kJ mol−1]/RT. During the pyrolysis of CHF3 and in the reaction of CHF3 with CH4, the initial steps in the reaction involve the decomposition of CHF3 and subsequent formation of CF2 difluorocarbene radical and HF. It is proposed that CH4 is activated by a series of chain reactions, initiated by H radicals. The NIST HFC and GRI-Mech mechanisms, with minor modifications, are able to obtain satisfactory agreement between modelling results and experimental data. With these modelling analyses, the reactions leading to the formation of major and minor products are fully elucidated. 相似文献