CO2 utilization for enhanced C2 hydrocarbon production in Chemical Looping Oxidative Coupling of Methane

Abstract

Chemical Looping Oxidative Coupling of Methane (CLOCM) offers a sustainable route to C2 production, yet its efficiency is limited by intrinsic lattice oxygen capacity and mobility of oxygen carriers. In this study, CO2 was introduced as a tunable process variable to regulate the availability of surface oxygen species., and the effect of concentration (30–50%) on Mg6MnO8-based CLOCM was investigated at 800 °C and atmospheric pressure. The results revealed that CO2 exerted a concentration-dependent influence on surface oxygen distribution. At moderate CO2 concentrations (30–40%), CO2 promoted C2 formation by regenerating surface oxygen vacancies that facilitate methane activation while forming carbonate species that suppress deep oxidation to CO2. However, when CO2 exceeded 40%, excessive carbonate accumulation competed with methane adsorption sites, redirecting oxidation toward CO and inhibiting C2 generation. This concentration-dependent mechanism enabled optimal performance at 40% CO2, achieving a C2 selectivity of 53.8% and a C2 yield of 11.1%-3.2- and 3.7-fold increase over CO2-free operation. The CO2-mediated process maintained stable performance over 10 redox cycles. Beyond reactor-level performance, an integrated biogas valorization framework was further proposed to enabling co-production of fuels and chemical precursors, increasing carbon utilization efficiency from 2.6% to 23.1% and reducing emissions by 527.1 kg CO2 per 1000 Nm3 of raw biogas. This work provides a scalable strategy that using CO2 as a tunable process variable couples CO2 utilization with high-value chemical synthesis, offering a promising alternative to conventional biogas upgrading and oxygen management improvement in chemical-looping conversion pathways.