Impact of OH Radical Generator Involvement in the Gas-Phase Radical Reaction Network on the Oxidative Coupling of Methane—A Simulation Study

Abstract

The impact of OH• generation during the oxidative coupling of methane (OCM) is simulated using state-of-the-art gas-phase chemistry and a comprehensive chemical kinetic model. The inclusion of the quasi-equilibrated formation of OH• from a H2O–O2 mixture into the combustion chemistry network enhances the CH4 conversion rate and C2 selectivity, consistent with the previously proposed mechanism involving catalytically generated OH•. The OH-pathway increases the (Formula presented.) concentration resulting in an enhanced transformation rate from (Formula presented.) to C2H6 (second order in (Formula presented.)) more than CO (first order in (Formula presented.)). Relative to other H-abstracting radical species, the OH• weakens the sensitivity of the H abstraction rate constant to C—H bond energy, or lowers (Formula presented.), which comparatively slows the C2H6 conversion rate relative to CH4, thus enhancing C2 selectivity. Concurrent dehydrogenation of C2H6 to C2H4 maximizes the C2H4 selectivity even after O2 depletion. With the involvement of the OH•-mediated pathway, this study addresses the effects of temperature and CH4/O2 ratio on the achievable C2 selectivity and C2H4 yield. The maximum C2H4 yield reaches 32% at a CH4/O2 ratio of 3, temperature of 1100–1200 °C, and total pressure of 1 atm.