Calcium looping for CO2 capture: sorbent enhancement through doping

Calcium oxide has been proposed as a regenerable sorbent for separating CO2 from flue gas at high temperatures. It is well known that natural sorbents (i.e., CaO derived from natural limestone) lose their capture capacity as the number of the carbonation/calcination cycles increases. If the behaviour of the sorbent can be improved (i.e., the decay in reactivity of sorbent reduced or residual reactivity of sorbent increased), the viability of a CaO-based CO2 capture scheme could be improved. One potential method to achieve this is doping the sorbent with different salts. In this work, a simple wet impregnation method has been used to dope two different limestones using solutions of KCl and K2CO3 with different concentrations. Doped samples were then subjected to repeated carbonation/calcination cycles in both a Fluidized Bed Reactor (FBR) and a Thermogravimetric Analyser (TGA) in order to compare their reactivity in both cases. The results obtained show that samples doped with 0.5 M solution of KCl have a decreased reactivity over the initial cycles, but an increased long-term reactivity in both the FBR and the TGA, with improved results observed in the FBR. Sorbent doping could prove to be a relatively inexpensive method of improving the reactivity of sorbent for the calcium looping cycle for CO2 capture.