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 CH3• concentration resulting in an enhanced transformation rate from CH3• to C2H6 (second order in CH3•) more than CO (first order in CH3•). Relative to other H‐ing radical species, the OH• weakens the sensitivity of the H ion 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.
The different extent of OH radicals generated from a O2–H2O mixture is integrated to the state‐of‐the‐art radical chemistry to simulate the performance of oxidative coupling of methane (OCM). Such simulation demonstrates the beneficial role of the OH radical for OCM rates and selectivity, predicting the maximum C2H4 yield to be 32%.