Simulation of oxygen permeation through La0.6Sr0.4Co0.2Fe0.8O3−δ tubular membrane reactor with POM reactions

Abstract

The parameters of the semi-empirical equations of oxygen permeation model have been regressed using different transport mechanisms (n-type and p-type permeation flux equations) and oxidation reaction kinetics. The regression constants were found to be k = 2.31 × 10−6 mol/cm2/s/Pa1/n and n = −4.08 in the semi-empirical equations. From the k and n value, it can be concluded that the oxygen permeation behavior is dominated by n-type transport mechanism for La0.6Sr0.4Co0.2Fe0.8O3−δ membranes reactor under POM reaction conditions. A mathematical model of the oxygen permeation flux for POM reactions in the tubular LSCF6428 membrane has been developed to determine the rate-limiting step of oxygen permeation process, and a series of numerical simulations of oxygen permeation fluxes over a wide range of temperatures and oxygen partial pressures were used under POM reaction for mechanism analysis. Moreover, surface exchange kinetics at each side of the membrane was studied and compared with the bulk diffusion resistance. It is concluded that oxygen permeation (<940 °C) is limited by the surface exchange kinetics, but the controlling step shifts from surface exchange at reaction side to bulk diffusion at 940 °C under POM reaction. The results also suggest that increasing the oxidation reaction rate by increasing the temperature can enhance the oxygen permeation flux. For a membrane with fixed oxygen permeation mechanism, increasing CH4 flow rate lowers the oxygen partial pressure at the reaction side, resulting in an increase in the oxygen permeation flux.