Chemical looping oxidative propane dehydrogenation controlled by oxygen bulk diffusion over FeVO4 oxygen carrier pellets

Abstract

The oxygen distribution and evolution within the oxygen carrier exert significant influence on chemical looping processes. This paper describes the influence of oxygen bulk diffusion within FeVO4 oxygen carrier pellets on the chemical looping oxidative propane dehydrogenation (CL-ODH). During CL-ODH, the oxygen concentration at the pellet surface initially decreased and then maintained stable before the final decrease. At the stage with the stable surface oxygen concentration, the reaction showed a stable C3H6 formation rate and high C3H6 selectivity. Therefore, based on Fick’s second law, the oxygen distribution and evolution in the oxygen carrier at this stage were further analyzed. It was found that main reactions of selective oxidation and over-oxidation were controlled by the oxygen bulk diffusion. C3H8 conversion rate kept decreasing during this stage due to the decrease of the oxygen flux caused by the decline of oxygen gradient within the oxygen carrier, while C3H6 selectivity increased due to the decrease of over-oxidation. In addition, reaction rates could increase with the propane partial pressure due to the increase of the oxygen gradient within the oxygen carrier until the bulk transfer reached its limit at higher propane partial pressure. This study provides fundamental insights for the diffusion-controlled chemical looping reactions.