Detailed Kinetic Modeling of NO<i>_x</i>‑Mediated Oxidative Dehydrogenation of Propane

Shale gas is revitalizing America’s chemical industry and shifting ethylene production from oil-based naphtha to shale-derived ethane, causing a short supply of propylene. Oxidative dehydrogenation of propane mediated by NOx (NO and NO2) provides a potential route to convert propane into propylene without solid catalysts. In this work, detailed kinetic modeling was performed to simulate gas-phase homogeneous NOx-mediated oxidative dehydrogenation of propane. Consistent with the experimental findings, our model suggests that propane conversion increases with the amount of NO in the feed, with the selectivity to propylene and ethylene decreased with increasing propane conversion. Our modeling results also revealed that OH radicals are the major species to consume propane. The addition of NOx in the system increases the production of OH radicals due to additional pathways in the NO–NO2 cycle, including (1) oxidation of NO by HO2 radicals, (2) reduction of NO2 by H radicals, and (3) formation and dissociation of HONO and its isomers, facilitating propylene formation. The addition of H2O further accelerates propane conversion by shifting the equilibrium of OH quenching reactions. A reaction network consisting of propane pyrolysis, propane oxidative dehydrogenation, and NOx mediation was sketched to explain the important trends observed in the experiments.