Effect of preparation temperature on cyclic CO2 capture and multiple carbonation-calcination cycles for a new Ca-based CO2 sorbent

The cyclic CO2 capture, transient phases change, and microstructure appearance of a new kind of Ca-based regenerable CO2 sorbent, CaO/Ca12Al14O33, obtained by the integration of CaO as solid reactant with a composite metal oxide of Ca12Al14O33 as a binder, were investigated by thermogravimetric analysis, XRD, and SEM at different preparation calcination temperatures. When the calcination temperature in the preparation stage is higher than 1000 degrees C, the cyclic CO2 capture of this new sorbent declines. The lowered CO2 capture may mainly be attributed to the formation of Ca3Al2O6, which decreases the ratio of CaO to binder in sorbent, and the severe sintering of sorbent occurs when calcined at such high temperatures in the preparation processes. These results suggest that the calcination temperature for this new sorbent should not be higher than 1000 degrees C in order to obtain its high reactivity. The performance of the new sorbent over 50 cycles was evaluated under mild and severe regeneration conditions, respectively. CaO/Ca12Al14O33 attained 41 wt % CO2 capture after 50 carbonation-calcination cycles under mild calcination conditions (850 degrees C, 100% N-2), and the results obtained here indicate that the new sorbent, CaO/Ca12Al14O33, has significantly improved CO2 capture and cyclic reaction stability over multiple carbonation-calcination cycles compared with limestone and dolomite under mild calcination conditions. When more severe calcination conditions (980 degrees C, 100% CO2) were used, the capture of CaO/Ca12Al14O33 decreased from 52 wt % in the first cycle to about 22 wt % in the 56th cycle; however, the capture of CaO/Ca12Al14O33 sorbent over 56 cycles is still higher than that of dolomite and limestone under the same severe calcination conditions.