D. Li, W.S. Baslyman, S. M. Sarathy, K. Takanabe
Energy Technology, (2019)
OH radicals, Oxidative coupling of methane, Radicals, Reaction mechanism, Simulations
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 CH•3 concentration resulting in an enhanced transformation rate from CH•3 to C2H6 (second order in CH•3 ) more than CO (first order in CH•3 ). 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 𝑘C2H6/𝑘CH4 , 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.