Synergetic Effects of Plasma, Temperature and Diluant on Nonoxidative Conversion of Methane to C2+ Hydrocarbons in a Dielectric Barrier Discharge Reactor

Noncatalytic and nonoxidative conversion of methane in a dielectric barrier discharge (DBD) reactor is examined at different temperatures, gas residence times and input powers. In addition, the ratio of methane to helium as a diluant, is changed in the range of 0.6 to 1.8. Results show significant synergetic effects of plasma, temperature and helium on the methane conversion and C2+ selectivities. C2 hydrocarbons are the main products (more than 70%) of the process, however, minor amounts of heavier hydrocarbons up to C8 are formed. At an input power of 230W and gas residence time of 6 sec, when the temperature increases from 100 to 200oC, the methane conversion enhances by 33%. In the temperature of 100-350oC, the methane conversion passes through a maximum at CH4 /He ratio of 1.0, at which the highest effect of the temperature is observed. In addition, at 350oC, when the input power increases from 140 to 230W, the CH4 conversion enhances from 20.3 to 27.0%. As the temperature increases from 100 to 350oC, the selectivity of ethane decreases from 81.5 to 73.0%, while the selectivities of ethylene and acetylene enhances by about 40% and 270%, respectively. The frequency of effective collisions among the reactants, excited helium (He*), and free electrons (e-) seems to increase with temperature, that in turn leads to higher methane conversions and changes in products selectivities.