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

Author:
Rostom, S., de Lasa, H.
Source:
Industrial & engineering chemistry process design and development 2018 v.57 no.31 pp. 10251-10260
ISSN:
1520-5045
Subject:
activation energy, adsorption, atmospheric pressure, catalysts, combustion, confidence interval, dehydrogenation, equations, kinetics, models, oxygen, process design, propane, propylene, vanadium
Abstract:
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.
Agid:
6087029