High-Temperature Sorption Process for Oxygen Removal and Air Separation

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This project is aimed at studying fundamental issues related to the development of a new, efficient high-temperature oxygen sorption process based on perovskite-type ceramic sorbents for oxygen removal and air separation. The new sorption process takes advantage of the unique properties of certain perovskite-type ceramics which can adsorb a large quantity of oxygen, but not other gases, at high temperatures (300-800oC). Three perovskite-type ceramic materials with different compositions are selected as the sorbents for this study. The sorbent pellets and particles of various sizes are prepared by citrate and press-sintering methods. The thermodynamic defect equilibrium for oxygen sites in these ceramics is being studied experimentally by the gravimetric method and theoretically using point-defect and cluster-defect models. This defect equilibrium study provides oxygen-sorption isotherm data for these sorbents. Heat of sorption and order-disorder phase transformation of these ceramic sorbents is studied also by TGA/DSC. Oxygen sorption kinetics on these ceramic sorbents are investigated experimentally by the transient gravimetric method and modeled using a simple linear-driving-force model and a more complex model based on the ambipolar diffusion theory. The chemical and mechanical stability of the ceramic sorbent particles is being studied systematically by dilatometry and attrition tests. Finally, fixed-bed experiments for oxygen removal or air separation are conducted to obtain data for design of a practical separation process based on this new concept. This project represents the first effort in developing sorption processes based on this new group of non-traditional sorbents. On the fundamental side, this project may lead to development of a large number of new sorption processes with unique separation characteristics that are not offered by the traditional sorption processes. If a hydrocarbon is used to regenerate the sorbent, this process can be extended to provide new chemical reactors for partial oxidation of hydrocarbons with improved selectivity. On the practical side, the proposed sorption process is based on perovskite-type ceramics with preferential equilibrium sorption for oxygen. Successful development of this sorption process will have a significant impact on industrial processes for air separation and oxygen removal.