Ca-containing CO2-tolerant perovskite materials for oxygen separation

Perovskites (La1-xCax)FeO3-delta and (La1-xCax)(Co0.8Fe0.2)O3-delta with varying La and Ca contents (x = 0.4-0.6) were designed by sol-gel route as model membrane materials to be an alternative to Ba- and Sr-based systems for operation in the presence of CO2. It was found that only the first members of the systems with x = 0.4 consisted of almost pure perovskite phases. The materials containing more Ca (x= 0.5-0.6) exhibited a considerable amount of bi-phase material, such as brownmillerite and/or spinel, after calcination at 1223K. The orthorhombicly distorted (La0.6Ca0.4)FeO3-delta and rhombohedrally distorted (La0.6Ca0.4)(Co0.8Fe0.2)O3-delta perovskites showed relatively high oxygen permeation fluxes at 1223 K of 0.26 cm(3) min(-1) cm(-2) and 0.43 cm(3) min(-1) cm(-2), respectively. The oxygen-ionic conductivity of the materials was improved by about 50% via an asymmetric configuration using a porous support and an approximately 10-i.t,m thick dense layer with the same chemical composition. In situ XRD in an atmosphere containing 50 vol.% CO2 and long-term oxygen permeation experiments using pure CO2 as the sweep gas revealed a high tolerance of Ca-based materials toward CO2. Thus, we suggest that Cacontaining perovskite can be considered promising membrane materials if operation in the presence of CO2 is required. (C) 2011 Elsevier B.V. All rights reserved.