High Propylene Selectivity via Propane Oxidative Dehydrogenation Using a Novel Fluidizable Catalyst: Kinetic Modeling

This study reports propane oxidative dehydrogenation (PODH) kinetic modeling under oxygen-free conditions employing 7.5 wt % vanadium supported on a ZrO2–γAl2O3 (1:1 wt %) catalyst designated as 7.5 V/ZrO2–γAl2O3 (1:1). This fluidizable catalyst is prepared using a wet saturation impregnation technique to achieve high VOx dispersion. Its performance is analyzed in a mini-fluidizable CREC Riser Simulator using successive propane injections, 500–550 °C, close to atmospheric pressure, and 10–20 s reaction time. Propylene selectivities obtained are up to 94% at 25% propane conversion with the catalyst lattice oxygen contributing to the PODH reaction. Using this data, a "parallel-series" model is established based on a Langmuir–Hinshelwood rate equation. Adsorption constants are defined independently with this leading to a six-independent intrinsic kinetic parameters model. These six kinetic parameters are calculated via numerical regression with reduced spans for the 95% confidence interval and low cross-correlation coefficients. On this basis, the high propylene selectivity obtained can be explained given the much larger 2.82 × 10–5 mol.gcat–1s–1 frequency factor for propylene formation versus the 1.65 × 10–6 mol.gcat–1.s–1 frequency factor for propane combustion. Calculated energies of activation (55.7 kJ/mol for propylene formation and 33.3 kJ/mol for propane combustion) appear to moderate this effect, with the influence of frequency factors prevailing. Furthermore, propylene conversion into COx oxidation appears as a nonfavored reaction step given the 98.5 kJ/mol activation energy and 4.80 × 10–6 mol.gcat–1.s–1 frequency factor. This kinetic model is considered of special value for the further development of a scaled-up twin fluidized bed reactor configuration for PODH.