Methane conversion with carbon dioxide in plasma-catalytic system

The hybrid plasma-catalytic system (HPCS) was used for the oxidative coupling of methane (OCM) with CO2. A dielectric barrier discharge (DBD) reactor was powered at the frequency of about 6 kHz. Molar ratio [CO2]:[CH4] in the inlet gas mixtures (CH4 + CO2 + Ar) was 1. Three kinds of packing were tested: Fe/Al2O3, NaY and Na-ZSM-5. The effects of both temperature (130-340 °C) and gas flow rate on the conversion of methane and CO2 were studied. Hydrogen, carbon oxide, hydrocarbons C2-C4, and alcohols (methanol and ethanol) were identified in the outlet gas. Using the plasma +Fe/Al2O3 catalyst system led to obtaining hydrogen, carbon oxide, hydrocarbons and alcohols. The highest amount of methanol and ethanol was obtained in the system without packing and with a carrier (Al2O3). For the homogeneous system and the system with a carrier the increase of the residence time of gas in the reaction zone decreases the conversion of methane to methanol and ethanol. The conversion of methane to methanol at 240 °C with Na-ZSM-5 was not observed. In the plasma - Na-ZSM-5 system, in the first hour of experiment, the aromatic hydrocarbons and a larger amount of iso-butane were observed in the outlet gas. After approximately 1 h, liquid aromatic hydrocarbons in the gas mixture were not observed and the Na-ZSM-5 catalyst showed no change in selectivity in subsequent experiments. In HPCS with Na-ZSM-5 catalyst the amount of hydrocarbons, containing more than 4 carbon atoms was the highest. The overall methane conversion was 47.5% and 65% and the methane conversion to C2-C4 hydrocarbons reached 19.5% and 14.5% for gas flow rate 2 and 1 Nl/h respectively.