Improved Sorbent for High-Temperature Production of Oxygen-Enriched Carbon Dioxide Stream

Abstract

Perovskite-type La−Sr−Co−Fe metal oxides have been demonstrated as sorbents in a high-temperature sorption separation process for production of an oxygen-enriched gas stream for oxycombustion application. This paper reports on characteristics and fixed-bed performance of improved perovskite-type sorbents, Sr−Ca−Co−Fe oxides, in comparison with a reference La−Sr−Co−Fe oxide sorbent for high-temperature production of an oxygen-enriched carbon dioxide stream. The optimum composition of Sr0.5Ca0.5Co0.5Fe0.5O2.47 (SCCF) is identified through study of carbonation (oxygen desorption) kinetics of Sr−Ca−Co−Fe oxides with different Ca and Fe concentrations. Carbonation kinetics of SCCF were studied at different temperatures from 700 to 900 °C. Below 750 °C, interaction of SCCF with carbon dioxide results in formation of Sr and Ca carbonates. At higher temperature, SCCF turns to form oxides of the respective metals under a stream of carbon dioxide. The improved sorbent has a faster oxygen desorption kinetic rate and higher oxygen storage capacity than the reference material. Effects of the operation temperature on the fixed-bed desorption/adsorption process for production of an oxygen-enriched carbon dioxide stream were investigated. Optimal temperatures for adsorption and desorption processes are determined to be 700 and 850 °C, respectively. The fixed-bed process can produce an oxygen-enriched stream at an oxygen concentration of 50%. The improved sorbent exhibits a gradually decreased carbonation (oxygen desorption) kinetics in the first few cycles of oxygen sorption and desorption and then stable kinetics in cycles afterward.