High Temperature Oxygen Separation Using Dense Ceramic Membranes

Mixed ionic–electronic conducting (MIEC) ceramic membrane has rapidly become an attractive alternative technology to conventional cryogenic distillation for oxygen separation from air. Given the heat integration opportunity in most energy generation processes, this technology offers lower cost and energy penalty due to its capability to produce pure oxygen at high temperature (>800 °C). Using pure oxygen for combustion in turn facilitates the production of concentrated carbon dioxide gas downstream which can be easily captured and handled to mitigate the greenhouse gas effect. This chapter overviews and discusses all essential aspects to understand oxygen selective MIEC ceramic technology. The basics behind the formation of defects responsible for high-temperature ionic transport are explained together with the transport theory. Two major family structures, e.g., fluorite and perovskite, which become the building blocks of most MIEC materials are discussed. Specific structure and properties as well as the advantages and the drawbacks of each family are explained. Some important structural considerations, e.g., crystal structure packing and Goldschmidt tolerance factor, are elaborated due to its strong relationship with the properties. Two additional concepts, e.g., dual-phase membrane and external short circuit, are given to address the drawbacks associated with fluorite and perovskite MIEC materials. Various geometries and types of MIEC membranes can be prepared, e.g., disk, tube, hollow fiber, or flat plate, each of which fits particular application. A short paragraph is presented at the end of the chapter on another possible application of this technology to facilitate a particular reaction to synthesize value-added products.