A global kinetic model for the oxidative dehydrogenation of ethane over mixed metal oxide catalysts at supra-ambient pressures

Abstract

Oxidative dehydrogenation of ethane (ODHE), unlike traditional steam cracking processes, can potentially be used to produce ethene at supra-ambient pressures, thereby reducing reactor footprint and alleviating (de)compression energy requirements. Global kinetic models that capture kinetic features of both desired and undesired reactions over an extended range of reactant and product pressures are lacking despite the clear reliance of comparative reactor design assessments on such models. We report herein a global kinetic model that accounts for the rates (between 603 and 703 K) of all 6 of the prevalent reaction network steps, extends up to 6 bar total pressure, and explains a broad set of differential and integral kinetic features measured over MoVTeNbOx catalysts. H2O2-mediated dissolution procedures enable low-temperature measurements which under the extended pressure ranges used in this study evidence significant coverages of reduced sites the contributions of which can be interpreted as being determined by ethane to oxygen molar ratios. Explaining measured kinetic features require invoking an oxygen pool present in quasi-equilibrium with gas phase oxygen that is distinct in identity from lattice oxygens, only the latter of which are wholly responsible for hydrogen abstraction steps in turnovers producing ethene, not COx. We demonstrate how a simplified global kinetic model that employs power law rate expressions for undesired reactions and excludes product inhibitory effects for the entirety of the reaction network is sufficient to explain both co-feed data as well as differential and integral features evaluated in the absence of product co-feeds. The proposed kinetic model can be employed in comparative assessments of high-pressure ODHE reactor configurations operating non-isothermally, especially those carrying a high sensitivity to contributions from highly exothermic total oxidation reactions.