Oxidative pyrolysis of natural gas in a spouted-bed reactor: reaction stoichiometry and experimental reactor design

Abstract A simple reaction network is developed to understand methane oxidative pyrolysis in a spouted-bed reactor. Oxidative pyrolysis for converting natural gas is attractive because it gives high methane conversions (80–90% per pass) at high selectivities to C 2+ (40%) and carbon monoxide (40%). Based on results reported in a British Petroleum patent, our analysis shows that oxidative pyrolysis is a combination of methane partial oxidation to carbon monoxide which produces heat and of methane pyrolysis to C 2+ (mostly ethylene and acetylene) which consumes heat. The methane pyrolysis reaction is thermodynamically limited and requires temperatures above 1000°C for significant conversion. A pilot-plant oxidative pyrolysis reactor was designed from cold flow studies to verify the BP results obtained at atmospheric pressure and to establish process feasibility at higher pressures. Scoping economic studies show that higher pressure operation is needed to avoid costly product compression in downstream upgrading processes. The pilot-plant spouted-bed reactor evolved from a fragile quartz tube to a more robust one of stainless steel. The stainless steel performs similarly to the quartz reactor when the walls are coated with an aluminum oxide layer to passivate inherent catalytic activity. Although a number of experimental challenges remain, initial runs have been successful in demonstrating that our method of preheating the feed successfully ignites the reaction and that our analytical technique gives excellent closure in detailed material balances. Based on results presented in this paper ways are needed to improve on BP C 2+ yields, such as by process variable optimization and rapid thermal quench to minimize undesirable secondary pyrolysis reactions.