The present investigation concentrated on the oxidative conversion of methane in an atmospheric pressure, nonthermal plasma formed by negative dc corona discharge. The corona creates negatively charged oxygen species, which react with methane and form methyl radicals. The products contain C2 hydrocarbones (acetylene, ethylene and ethane) and other. carbonaceous species including carbon deposits, CO2, H2O and syngas (H2+ CO). The conversion and selectivity of desired C2 products depend on the residence time (total feed flowrate) and the methane to oxygen ratio in the feed. All the experiments are conducted at room temperature and only with dc negative corona discharge (i.e, no oven or other heat source is used), and the temperature increases slightly (100-200 o C) due to the exothermic reactions and the discharge itself. According to the results: Methane conversion increases significantly with decreasing flowrate or increasing residence time, but C2 hydrocarbon selectivity decreases slightly and therefore, the yield of C2 hydrocarbons increases significantly. Moreover, increasing the methane to oxygen ratio at a constant flowrate leads to an increase in C2 selectivity. Also, the methane conversion and C2 yield go through a maximum at a methane to oxygen ratio of 5. The largest C2 yield is 23.1% with 35% methane conversion.and66% C2 selectivity at a flowrate of .5cm3/min (CH4O2=5, without any diluent), when the dc negative Corona with 4mA input power was used. The results suggest that dc gas discharge technique is a promising method for direct conversion of methane into more valuable hydrocarbons.

The oxidative coupling of methane (OCM) to higher hydrocarbons has been investigated in the absence of catalyst. The reaction was carried out in quartz tubalar reaction with volume of 16.3 ml, at atmospheric pressure and at 750 to 950°C. The total flow rate was 90 to 130 µ/min and the dilution ratio was 0.2 to 0.75. In the same experiments steam was used as a carrier gas in place of helium to study its effect on the reaction. At 850°C, the total flow rate 100 µ/min, methane to oxygen ratio equal 2 and dilution ratio 0.5, when helium and the steam were used as a carrier gas, the Cz yield was 8.4 and 9.5 respectively. The power law kinetic models (relations) as a function of methane and oxygen partial pressures was found for the rate of disappearance of methane and the rates of formations of ethane, ethylene and carbon oxides.

Because of proven enormous natural gas resources in the world, there is a strong incentive to study and develop processes that would convert methane into more valuable chemicals. Among various routes a subject receiving a great deal of interest is oxidative coupling of methane over appropriate catalysts. In this work, direct partial oxidation of methane was studied in fixed bed quartz reactor at atmospheric pressure condition. Catalysts were made with different percentage of La2O3 (0.2, 1, 5, 10, 20) on the TiO2 as support using impregnation method. Reaction feed included methane; oxygen and helium gases and reaction products contained CO2, CO, ethane, ethylene and unconsumed O2 and methane gases. The reaction is thought to proceed via production of methyl radical by a heterogeneous catalysis. Ethane is formed homogeneously and produces ethylene. Various parameters such as temperature, percentage of inert gas, methane to oxygen ratio in the feed, feed flow rate and appropriate catalyst were checked and the optimum conditions were determined. The experimental results reveal that maximum C2 selectivity and maximum methane conversion are 57% and 31%, respectively.      

One method for conversion of methane to more valuable products is by non-catalytic gas-phase oxidative coupling of methane (OCM), through which methane is converted into ethylene. The product of this process is ethylene, accompanied by acetylene, ethane, a small quantity of three carbon compounds as coupling products, and carbon oxides due to complete oxidation of hydrocarbons. The kinetic model proposed for the OCM process consists of 75 elementary reactions and 23 chemical species. In previous studies the reactor-kinetic modeling of this process, was implemented in a laboratory micro-reactor at constant temperature and pressure. Considering that this process proceeds with severe variation in the enthalpy in the present study, in addition to isothermal, the operation of the system has also been modeled for the adiabatic state. The modeling has been carried out in a tubular reactor system. Comparison of the qualitative and quantitative results of the model with experimental data at constant temperature shows that the proposed kinetic model predicts the experimental results properly. Furthermore, in the present study, the effect of various parameters on the operation of the system has also been examined. These studies have been performed in the following ranges of pressure, temperature and CH4/O2 ratio respectively: 1 P£10£ (bar), 950£T£1100 (K), 4 £CH4/O2 £10. It has been shown that, by increasing the temperature, the reaction rate increases. Raising the total pressure of the system causes an increase in methane conversion and selectivities of desired products as well as the reaction rate. On the other hand, increasing the residence time in the reactor will result in conversion of desired products to undesirable ones. Finally, it is shown that by decreasing the ratio of methane to inlet oxygen, conversion of methane increases, selectivities of the desired products decrease and the heat released during the reaction rises.

Oxidative coupling of methane was investigated on the Mn/Na2WO4/SiO2 catalyst in both fixed and fluidized bed reactors. A wide range of operation condition was selected in order to observe the effect of reaction temperature, methane to air ratio, and resident time of reactants in the reactors. The best C2+ yield (the product of methane conversion and C2+ Selectivity) obtained was about %21.9. The ratio of ethylene to ethane selectivity for the whole range of operating conditions was greater than 1 which indicated a high dehydrogenation activity of the catalyst as compared to the other come on catalyst of OCM such as Li/MgO.