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High Temperature Air Separation by Perovksite-Type Oxide Sorbents-Heat Effect Minimization

Jerry Y. S. Lin, Department of Chemical Engineering, Arizona State University, Tempe, AZ 85287 and Qinghua Yin, Department of Chemical and Materials Engineering, Arizona State University, Tempe, AZ 85287.

High temperature air separation for oxygen production can find a number of applications. One application is for oxycombustion where the fuel is burned in oxygen rather than air. This results in pure carbon dioxide exhaust that requires little separation, facilitating carbon dioxide capture. Key barrier for oxycombustion is the high costs of oxygen production with current best cryogenic technology. Significant reduction in the cost of oxygen production is essential to making the oxycombustion power plant a future option when cabon dioxide capture becomes a requirement. An effective high temperature air separation process may offer a significant cost reduction for oxygen production for this application. Oxygen sorption on perovskite-type oxides can be advantageously used for air separation at high temperature. The large heat of oxygen sorption on these oxide sorbents presents a major challenge for the heat management of the high sorption separation process in practical applications. This paper reports a method to minimize the heat effects by taking advantage of an endothermic process of oxygen vacancy order-disorder phase transition accompanying the oxygen sorption process on perovskite-type oxide sorbents. The oxygen sorption isotherms, phase diagram, exothermic heat of oxygen sorption and endothermic heat of order-disorder phase transition for La0.1Sr0.9Co0.9Fe0.1O3- were measured by simultaneous TGA/DSC and XRD. The conditions for zero apparent heat of sorption are determined. If the oxygen partial pressure change and adsorption temperature are controlled in such that it gives an oxygen adsorption amount equal to the ratio of heat of phase transition to heat of oxygen sorption, the net heat released from the oxygen sorption step can be minimized or controlled to be negligible. This strategy for heat effect minimization is demonstrated with the results of TGA/DSC measurements at different operating conditions, and air separation by a fixed-bed packed with the perovskite-type oxide sorbent.