Oxygen absorption/desorption behaviors of Sr_0.72Ca_0.28Fe_1-xAl_xO_3- perovskite oxygen sorbents for air separation

Perovskite-type oxides are extensively studied as oxygen sorbents in pressure swing adsorption (PSA) for air separation at elevated temperatures. However, quantitative analysis of desorption kinetics and the basis of material optimization are rarely reached on a fixed bed. In this study, the effects of Al doping on the oxygen absorption/desorption behaviors of Sr0.72Ca0.28Fe1-xAlxO3-delta (SCFA, x = 0, 0.03, 0.05, 0.07, 0.1) were investigated by temperature programmed desorption (TPD) and fixed bed absorption/desorption experiments. The desorption kinetics were analyzed by a Geometrical contraction model. O-2-TPD results show that Al doping reduces the total absorption amount of Sr0.72Ca0.28FeO3-delta (SCF). Through the peak-differentiation-imitating analysis, it was found that the SCFA series materials have three different oxygen desorption sites, and the desorption peak area and temperature corresponding to each site are different. CO2-TPD results reveal that Al doping improves the CO2 resistance of the perovskite oxides. Compared with SCF, Al doped materials show enhanced equilibrium oxygen absorption capacity at temperature higher than 550 degrees C. The oxygen desorption rates of SCFA series were calculated by fitting the desorption curves with Geometrical contraction model (R2). Both initial oxygen desorption concentration and oxygen desorption rate constants increase with temperature but decrease with the Al doping amount. The similar apparent activation energies of the desorption rate constant of the SCFA series reveal that the desorption mechanism not changes with Al doping. Ideal oxygen production rate, equaling to the multiplication of equilibrium oxygen absorption capacity and the desorption rate constant, is suggested to evaluate the performance of an oxygen sorbent. The x = 0.03 sample shows the highest ideal oxygen production rate among the SCFA series.