Aspects related to the thermal and mechanical stability of oxygen permeable membranes
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Fossil fuels causes CO2 emission to the atmosphere after combustion, and to minimize CO2 emission carbon capture and sequestration (CCS) technologies are under development. CCS involves CO2 capture, compression, transport and storage, and CO2 capture is the most expensive process with ~75 % of the operation cost. Oxygen separation from air is vital for CCS. Available oxygen production technologies includes cryogenic distillation and pressure swing adsorption, while oxygen separation membranes are an attractive alternative. The use of oxygen separation membranes in oxygen production is a promising technology for CCS applications. Oxygen separation occurs at high temperature of about 800 – 1000 °C and gradients in pressure and oxygen partial pressure. These operation conditions makes the materials prone to damage due to cracking or degradation, hence limiting the membrane lifetime. It is therefore important to identify ways to increase the lifetime of such membranes and to make them less vulnerable to failures. One potential method is self-healing, where a material that triggers self-repair of the membrane in case of damages, is incorporated into the membrane system. This would increase the membrane lifetime thereby lowering the overall oxygen production costs. Proof of concepts of self-healing of membranes was the goal in this project, and the fundamental understanding of self-healing phenomenon was investigated for on particular model system. Experimental verification by cation diffusion and solid state reactions in different atmospheres agrees with the proposed self-healing mechanism. Stability of membrane material at high temperature was also studied since lifetime goes hand-in-hand with stability. Finally, surface diffusion of two relevant membrane materials was also investigated as a possible mass transport mechanism contributing to self-healing. Both membrane materials were found to exhibit significant surface diffusion. The results obtained in the work contributes to the progress in the development of oxygen separation membranes.