High temperature air separation by perovskite-type oxide sorbents-Heat effect minimization

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 the order-disorder phase transition for La_0.1 Sr_0.9 Co_0.9 Fe_0.1 O_{3 - δ} 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 such that they give an oxygen adsorption amount, which is numerically 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.