Oxygen Separation Performance of Ca₂AlMnO_5+δ as an Oxygen Storage Material for High-Temperature Pressure Swing Adsorption

抄録

High-temperature pressure swing adsorption (HT-PSA) is a promising energy-saving approach for oxygen production from air. Ca₂AlMnO_5+δ, a Brownmillerite-type perovskite, is a promising sorbent for HT-PSA because of its remarkably high oxygen storage capacity (up to 3.3 wt%). In this study, we investigated the redox thermodynamics of Ca₂AlMnO_5+δ by pressure–composition–temperature (PCT) measurements and investigated the HT-PSA performance of Ca₂AlMnO_5+δ pellets in a 100 g-scale packed-bed-type reactor. PCT measurements revealed that Ca₂AlMnO_5+δ can reversibly separate 2.2 wt% of oxygen per cycle under equilibrium conditions between ambient oxygen partial pressure and 5×10⁻⁴ MPa at 525°C. However, in a 5 min switching HT-PSA test, Ca₂AlMnO_5+δ pellets were able to reversibly separate less than 1 wt% oxygen per cycle, which is significantly lower than that estimated from the thermodynamic properties of Ca₂AlMnO_5+δ. On the other hand, the exothermic oxygen storage and endothermic oxygen release reactions cause significant temperature variation of the packed bed. This study clarifies that, in order to increase the energy efficiency of oxygen separation by HT-PSA, there is a need to compensate for the heat of reaction, which changes the reactor temperature in a direction that interferes with the reaction.