Alkali metal (Na, Cs and K) promoted hydrotalcites for high temperature CO2 capture from flue gas in cyclic adsorption processes

A hydrotalcite (HT) with a Mg2+/Al3+ molar ratio of 2 was prepared and promoted with different loadings of Na and Cs. After calcination (denoted as CHT), the samples were tested for CO2 sorption at 573 K and 0.15eg bar of CO2 (typical of flue gas). Their performance was compared to that achieved with a commercial HT, MG63, and with a K-doped material for which a significant increase of CO2 sorption capacity has been frequently reported in the literature. However, the presence of K slows down the sorption kinetics, which might compromise the cyclic separation process productivity. In this work, it is aimed to find out a CO2 HT-based sorbent with promising behaviour during continuous sorption/desorption cycles, in terms of sorption capacity, sorption kinetics and cyclic stability. The best compromise was observed for a CHT doped with 9.4 wt% of Cs. A study of the cyclic stability of this material was performed and a kinetic model that can predict the loss of sorption capacity with cycles has been successfully developed. The performance of this sorbent was further investigated in a scenario where other species found in flue gas streams (i.e. O-2, H2O and/or CO) are also present.