Methane and ethane decomposition in an atmospheric-pressure plasma jet

This paper reports on studies obtained from RF-driven atmospheric-pressure plasma-jet excitation of methane and ethane. Differentiation with other works is achieved in that others have considered hydrocarbon decomposition at either low pressure or high temperature. In our experiments, we can clarify the effect of pure-plasma treatment of hydrocarbons, as opposed to the thermal effect of gas heating that results in pyrolysis. Gas-chromatography analysis was used to detect and quantify the main decomposition products. Kinetic modeling of the pertinent chemistry was performed by dividing the reactive system in two main parts: a plasma region where the electron impact processes leading to decomposition are considered and a postplasma region where recombination of nonstable species occurs. A reasonable qualitative agreement between the experimentally measured by-product concentrations and the calculations was achieved. It is observed that our proposed recombination mechanism correctly predicts ethane and ethylene formation from a CH4 discharge and methane, ethylene, propane, and acetylene formation from the C2H6 discharge. By means of calculations, the main role of radicals in the pertinent hydrocarbon chemistry under nonthermal plasma conditions is confirmed.