Oxygen permeation of Ba xSr 1 − xCo 0.8Fe 0.2O 3 − δ perovskite-type membrane: Experimental and modeling

Abstract

Ba x Sr 1 − x Co 0 .8 Fe 0 .2 O 0.3 − δ ( x = 0.2, 0.5, 0.8) dense membranes were prepared by a combined EDTA and citrate complexing method. In our previous works, effects of sintering temperature, sintering dwell time and pressing pressure on microstructure and theoretical densities of the membranes were examined and finally the best corresponding values were reported as 1100 °C, 8–9 h and 200–250 MPa, respectively. In the present work, effects of temperature (650–950 °C), feed flow rate (100–200 cm³/min), sweep gas flow rate (40–80 cm³/min) and membrane thickness (4–5 mm) on oxygen permeation behavior of the Ba x Sr 1 − x Co 0 .8 Fe 0 .2 O 0.3 − δ membranes were investigated. Also, a mathematical model based on Nernst–Planck equation was developed to predict oxygen permeation through the perovskite-type membranes. Both bulk diffusion and surface reactions were incorporated into the model. It was observed that surface reactions are not elementary and a correction term should be introduced into the model to compensate this effect. Also, using a dimensionless Reynolds number, effect of feed flow rate on oxygen flux was taken into account. With aids of these modifications, it was realized that, there is a reasonable agreement between predicted results and experimental data with correlation coefficient (R) of higher than 0.960 and mean squared relative error (MSRE) of lower than 0.022 for all the membranes. Oxygen vacancy bulk diffusion coefficient (D v), surface exchange rate constants (k f and k r), contribution of each resistance to oxygen permeation and characteristic thickness (L c) of the BSCF membranes were also estimated.