Effects of Oxygen Vacancy Order-Disorder Phase Transition on Air Separation by Perovskite Sorbents

Perovskite oxide sorbents offer promise for adsorption-based separation of air to produce an oxygen enriched stream. The oxygen desorption rate however should be further improved. This work studies the oxygen sorption properties of three La_1-xSr_xCo_1-yFe_yO_3-δ (LSCF) perovskite oxides with and without oxygen vacancy disorder-order phase transition. The LSCF with lower iron content [La_0.1Sr_0.9Co_0.9Fe_0.1O_3-δ (LSCF1991)] shows the highest sorption capacity in 500-800 °C. The material with disorder-order phase transition during desorption also exhibits enhanced oxygen desorption rate during the TGA measurement. However, in the fixed-bed desorption process, no obvious rate enhancement resulting from the disorder-order phase transition in oxygen desorption is observed for the LSCF1991 sorbent. The LSCF1991 sample in the fixed-bed quenched at 600 °C after 2 h of desorption shows occurrence of disorder-order phase transition for the perovskite sorbent in the fixed-bed environment. The difference in oxygen desorption rate observed between the fixed-bed process and the TGA experiment is due to much higher oxygen partial pressure in the gas surrounding the sorbent during the fixed-bed oxygen desorption process under which the disorder-order phase transition does not occur until the late stage of oxygen desorption.