Development of a novel Ca/Al carbonates for medium-high temperature CO2 capture

Abstract

This study describes the synthesis and characterization of a layered material Ca–Al–CO3 as CO2 sorbent at medium-high temperature conditions. The Ca–Al mixed oxides were prepared by co-precipitation of binary metal nitrates, i.e., Ca(NO3)2 and Al(NO3)3 under alkaline pH condition, and the concentration of calcium oxide was increased by varying the molar ratio of Ca/Al at 1, 3, 5, 7, 13 and 20. Sodium carbonate was utilized as a structural template for conducting the layered structure of Ca–Al carbonate. It was a simple way to synthesize Ca–Al–CO3 composites with at least 45-50 wt% CaO microcrystalline by 100∼200°C hydrothermal treatment. The characteristics of Ca–Al–CO3, such as surface area, morphology/particle size, crystalline and CaO contents, were determined by BET, SEM, PXRD and ICP, respectively. CO2 multiple-cycle sorption activities on the sorbent were performed by a TGA. The major results showed that a synthesized Ca–Al–CO3 was predominately mesoporous and its surface area was intensely dependent on precursors. In addition, a crucial result indicated that the microstructure of Ca–Al–CO3 was improved by using calcium acetate, Ca(Ac)2, instead of calcium nitrate, and thus further enhanced CO2 sorption performance. By using this sorbent, a significant breakthrough is achieved for capturing CO2 from hot gas streams at temperature higher than 600°C, which includes the features of 90% initial carbonation conversion and 90% CO2 capturing performance after 100th cycling tests. The sintering effect of Ca–Al–CO3 due to alternative gas adsorption/desorption reactions was obviously retarded by incorporating Al2O3 and carbonate ions into microscopic structure of synthesized calcium-alumina oxide.