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 200 o C, the methane conversion enhances by 33%. In the temperature of 100-350 o C, 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 350 o C, 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 350 o C, 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.