Dry Potassium-Based Sorbents for CO2 Capture

Abstract

Dry potassium-based sorbents were prepared by impregnation with potassium carbonate on supports such as activated carbon (AC), TiO2, Al2O3, MgO, CaO, SiO2 and various zeolites. The CO2 capture capacity and regeneration property of various sorbents were measured in the presence of H2O in a fixed bed reactor, during multiple cycles at various temperature conditions (CO2 absorption at 50–100 °C and regeneration at 130–400 °C). The KAlI30, KCaI30, and KMgI30 sorbents formed new structures such as KAl(CO3)2(OH)2, K2Ca(CO3)2, K2Mg(CO3)2, and K2Mg(CO3)2·4(H2O), which did not completely convert to the original K2CO3 phase at temperatures below 200 °C, during the CO2 absorption process in the presence of 9 vol.% H2O. In the case of KACI30, KTiI30, and KZrI30, only a KHCO3 crystal structure was formed during CO2 absorption. The formation of active species, K2CO3·1.5H2O, by the pretreatment with water vapor and the formation of the KHCO3 crystal structure after CO2 absorption are important factors for absorption and regeneration, respectively, even at low temperatures (130–150 °C). In particular, the KTiI30 sorbent showed excellent characteristics with respect to CO2 absorption and regeneration in that it satisfies the requirements of a large amount of CO2 absorption (87 mg CO2/g sorbent) without the pretreatment with water vapor, unlike KACI30, and a fast and complete regeneration at a low temperature condition (1 atm, 150 °C). In addition, the higher total CO2 capture capacity of KMgI30 (178.6 mg CO2/g sorbent) than that of the theoretical value (95 mg CO2/g sorbent) was explained through the contribution of the absorption ability of MgO support. In this review, we introduce the CO2 capture capacities and regeneration properties of several potassium-based sorbents, the changes in the physical properties of the sorbents before/after CO2 absorption, and the role of water vapor and its effects on CO2 absorption.