CaO-based sorbents for post combustion CO2 capture via carbonate looping

Abstract

A promising concept for CO2 separation from combustion flue gases is Carbonate Looping (CaL), an ex-situ, post-combustion CO2 capture technology in which CO2 from flue gases is captured by a CaO-based sorbent. In this work, we report the development, preliminary evaluation and bench-scale testing of synthetic and natural sorbents. The synthetic CaO-based materials doped with Zr, Al, Mg, La were prepared via sol-gel auto-combustion synthesis. The natural CO2 sorbents were developed from industrial hydrated lime and were doped with natural kaolin, magnesia and bauxite in an effort to reduce degradation under consecutive sorption/desorption cycles. All sorbents were characterized as to their crystal structure, surface area and morphology (XRD, BET, SEM). After preliminary screening, the most promising materials were further studied at bench-scale in a fixed bed reactor under realistic flue gas feed composition. Zr and Al-doped CaO based sorbents exhibited very high sorption capacity and stability, due to their porous structure that is retained after over 20 consecutive carbonation/calcination cycles. The natural sorbents presented inferior results, however their regeneration via hydration seems possible, although most likely not economically viable. The presence of steam in the flue gases seems to enhance sorption capacity and stability. Ca-Al synthetic sorbent exhibited the most promising performance and shows great potential for process scale up.