Stability of La-Sr-Co-Fe Oxide-Carbonate Dual-Phase Membranes for Carbon Dioxide Separation at High Temperatures

Dual-phase membranes consisting of a mixed ionic-electronic conducting ceramic phase and an ionically conductive molten carbonate phase have the ability to selectively separate CO2 at high temperature with or without the presence of O-2. This study examines the stability of a dual-phase ceramic-carbonate membrane consisting of La0.6Sr0.4Co0.8Fe0.2O3-delta (LSCF) and an eutectic molten carbonate phase composed of Li2CO3, Na2CO3, and K2CO3. LSCF-carbonate membranes exposed to a CO2/N-2 gradient at temperatures between 800 and 900 degrees C result in a drastic decrease in CO2 permeation before reaching steady-state after more than 60 h of exposure to the permeating gases due to a surface reaction between CO2 and the LSCF ceramic phase of the membrane, resulting in decomposition of the membrane surface. The introduction of O-2 in the feed gas, however, helps maintain the LSCF ceramic phase structure and results in stable CO2 permeation flux at a much higher value due to a change in transport mechanism in the membrane. The results suggest that it is critical to find oxygen ionic or mixed-conducting ceramic materials that are stable in CO2 environments in order to ensure stability of the membrane for CO2 permeation.