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

Rostom, S., de Lasa, H.
Industrial & engineering chemistry process design and development 2018 v.57 no.31 pp. 10251-10260
activation energy, adsorption, atmospheric pressure, catalysts, combustion, confidence interval, dehydrogenation, equations, kinetics, models, oxygen, process design, propane, propylene, vanadium
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.