From fundamentals to chemical engineering on oxidative coupling of methane for ethylene production: A review

Abstract A comprehensive overview is presented to summarize the research works since 1982 on oxidative coupling of methane (OCM), a complex reaction network combining heterogeneous and homogeneous reaction steps. Fundamentals on reaction mechanisms and thermodynamics have revealed that the OCM process is highly exothermic and its C2+ selectivity and yield is critical in evaluating its commercial viability. Catalytic strategies have been put to enhance C2+ selectivity, improve C2+ yield and lower reaction temperature. The catalyst Mn-Na2WO4/SiO2 enables methane activation at a temperature of 800 °C and simultaneously a high C2+ selectivity of 70–80%, while the nanowire and La2O3-based catalysts enable to lower the reaction temperature to 200–300 °C and 500 °C, respectively. Reaction engineering aspects have also been dealt in many investigations in order to make the process technically feasible. Particularly, research works on reaction kinetics, reactor selection and reactor operating mode choice have been addressed. Intermediate cooling and distributed oxygen feed have been integrated into a multi-stage adiabatic fixed-bed reactor system to suppress the side oxidation reactions and improve the performance of the catalysts towards CH4 conversion and C2+ yield. This review paper proposes employing a circulating reactor system coupled with catalyst fine particles but having little internal diffusion resistance to maximize one-pass C2+ selectivity and yield of the OCM reaction and evaluate its industrial application potential.