Methane utilization by oxidative coupling: I. A study of reactions in the gas phase during the cofeeding of methane and oxygen

Abstract

The oxidative coupling of methane has been investigated in the absence of catalysts by cofeeding methane and oxygen. A survey on the effects of varying several operating conditions shows that under certain conditions significant gas-phase oxidative coupling can occur in the absence of catalysts. The reaction products were C 2H 6, C 2H 4, C 3H 8, C 3H 6, CO (the main oxidation product), CO 2, H 2, H 2O, and traces of HCHO and C 4 and C 5 hydrocarbons when conversions were high. The general trend dictated by the gas-phase kinetics is that the hydrocarbon product selectivity falls as the conversion increases. Specifically, at methane conversions of 2%, the hydrocarbon product selectivity was around 65%, but when methane conversions were increased to 32%, the hydrocarbon selectivity decreased to 29%. The apparent activation energy for methane conversion in the gas phase was found to be around 55 kcal/mole which is similar to that reported for the gas-phase reaction of methane and molecular oxygen forming methyl and hydroperoxy radicals. Several gas-phase results have been presented for comparative purposes with catalytic oxidative coupling studies. A reaction pathway for the gas-phase oxidative coupling network has been considered and compared to proposed catalytic reaction pathways. The implications that the observed results might have on catalytic oxidative coupling of methane have also been considered.