Properties and manufacturing of asymmetric La0.98-xSrxCo0.2Fe0.8O3-d perovskite-type oxygen separation membranes

One technology to meet the challenge of reducing anthropogenic CO2 emissions is capturing CO2 in fossil fuelled power plants and other combustion processes using the Oxyfuel concept. Oxygen transport membranes (OTM) exhibit high potential to supply the pure oxygen required by most of these technologies. The oxygen transport in such membranes is driven by an oxygen partial pressure gradient across the membrane at temperatures and the practical operation temperature lies in the range 800-900°C. (La,Sr)(Co,Fe)O3-δ (LSCF) already discovered decades ago by Teraoka attracted again increasing interest due to its good compromise between performance and stability against flue gas components and reducing atmosphere. In this work sintering behavior, chemical and thermal expansion, and specific permeability as well as stability towards CO2 of La1-xSrxCo0.2Fe0.8O3- with different La/Sr ratio was investigated to identify suitable compositions for application.To maximize oxygen flux, the membrane should be as thin as possible, which makes a porous support necessary. In this work, thin (30 µm) supported membrane layers were manufactured by sequential tape casting. Support porosity was varied using different amounts of pore forming agent in the tape cast slurry. Influence of support microstructure on oxygen flux was investigated. Limitations by surface exchange were overcome by applying a catalytic, porous layer on top of the membrane surface by screen printing. The effect of CO2 and O2 partial pressure on the O2 flux was thoroughly analyzed as a function of temperature. Permeation rates above 1 ml cm-2 min-1 at 800 – 850°C in an air/Ar and air/CO2 gradient were achieved using La0.6Sr0.4Co0.2Fe0.8O3-δ, which is close to the desired value for oxyfuel power plants.