Sr-Doped Ca2AlMnO5 + δ for Energy-Saving Oxygen Separation Process

Pressure swing adsorption (PSA) is expected to replace the currently used energy-intensive cryogenic distillation process for oxygen separation. For realizing an energy-saving PSA, an oxygen storage material (OSM) with a high oxygen storage capacity and narrow pressure swing gap during reversible oxygen storage and release is necessary. While Ca2AlMnO5 is a promising candidate for PSA, it exhibits a large pressure hysteresis loop during oxygen storage and release. In this study, we investigated the effect of Sr doping of the Ca sites of Ca2AlMnO5 (Ca2-xSrxAlMnO5) on the phase compositions and oxygen storage/release performance with the aim of realizing an optimum OSM for the PSA process. From the results of structural refinement, while the oxygen release phase has a Brownmillerite (BM) structure (n = 1) at 0 <= x <= 1.0, BM (n = 3) and oxygen-defective perovskite were found to be the main structures in the oxygen storage phase at 0 <= x < 0.50 and 0.50 <= x <= 1.0, respectively. The oxygen storage/release temperature obtained from the thermogravimetry curves decreased in the 0 <= x < 0.50 range and increased in the 0.50 <= x <= 1.0 range with increasing x. This difference may be attributed to the structural differences in the storage phase. The pressure-composition-temperature (PCT) analysis by Sieberts' method was applied to the OSM. Although PCT curves exhibited a remarkable decrease in hysteresis in the PSA process as x increased, the difference between onset and offset temperatures for each oxygen storage/release reaction broadened. A new evaluation method to optimize x of Ca2-xSrxAlMnO5 and operating condition in the PSA process using the OSM was also examined. Plots of the pressure change required to release oxygen versus the amount of oxygen extracted allow for the efficient determination of optimal composition and working temperature. Ca1.2Sr0.8AlMnO5 (x = 0.80), which exhibited excellent repetition durability, was found to be optimal in this evaluation. The ideal PSA oxygen separation process using Ca1.2Sr0.8AlMnO5 has the potential for producing pure oxygen with an energy input of 109.6 kWh/kNm(3-)O(2), which is a significant energy saving compared to conventional processes.

Automated summary

The study investigated the effect of Sr doping on the oxygen storage/release performance of Ca2-xSrxAlMnO5 material, aiming to find the optimal material for the PSA process.