The most significant anthropogenic greenhouse gas is CO2, which arises mainly from the use of fossil fuels. A new technology called Advanced Zero Emission Power Plant (AZEP) targeting CO2 capture and storage (CCS) is being developed. In the AZEP concept, CO2-diluted O2 is used to combust the fossil fuels, thereby producing a concentrated CO2 gas stream and thus enabling efficient CO2 capture. The O2/CO2 mixture, necessary for combustion, could be supplied by using CO2 as a sweep gas to transport the oxygen separated from the air by an oxygen permeable membrane. After combustion, the concentrated CO2 is partly recycled to the membrane as sweep gas, and the remainder is captured for storage.
Mixed Ionic and Electronic Conductor (MIEC) membranes are one of the most promising oxygen permeable membranes for the AZEP concept. However, most of the MIEC materials, which usually have an oxygen deficient Perovskite structure, are not stable in CO2 containing atmospheres because of the reaction between CO2 and the MIEC materials. In our work, we have found that the CO2 tolerance of some MIEC materials can be greatly enhanced by increasing the oxygen partial pressure in the CO2 and that the presence of oxygen can effectively protect the MIEC membranes. Inspired by this phenomenon, we have developed a new AZEP concept by adding a certain amount of oxygen to the inlet of the separation unit to protect the membranes. Oxygen permeation measurements have shown that the protective effect of oxygen for the membranes is quite remarkable.