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 the intrinsic lattice oxygen capacity and the 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 CO₂ 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 species distribution. At moderate CO₂ concentrations (30–40%), CO₂ promoted C₂ formation by recovering surface oxygen vacancies that facilitate methane activation while forming carbonate species that suppress deep oxidation to CO. However, when CO₂ exceeded 40%, excess 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%, a 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 of the CLOCM framework was further proposed to enable co-production of C₂ and CO, increasing the carbon utilization efficiency from 2.6% to 23.1% and reducing emissions by 527.1 kg CO₂ per 1000 Nm³ of biogas. This work provides a scalable strategy that uses CO₂ as a tunable process variable to couple CO₂ utilization with high-value chemical synthesis, offering a promising alternative to conventional biogas upgrading and oxygen management improvement in chemical-looping conversion pathways.