Effect of Support Material on Carbonation and Sulfation of Synthetic CaO-Based Sorbents in Calcium Looping Cycle

Calcium looping cycle for post-combustion CO2 capture has gained increasing attention worldwide. However, CaO-based sorbents derived from natural sources for calcium looping cycle experience rapid loss of capacity during high-temperature cyclic carbonation/calcination reactions. Synthesizing sintering-resistant CaO-based sorbents by adding a support material has been extensively studied as an effective method of combating the problem. The support material in the synthetic sorbents plays an important role in retaining the capacity, and various support materials have been tested in the literature. In practical reactors, sulfur is present and it has been reported that sulfation of sorbents will also reduce the CO2 capture capacity. However, thus far, it is not clear whether/how support material would affect sulfation of sorbents and, thus, CO2 capture. In this paper, four different support materials, such as Ca2MnO4, La2O3, Ca12Al14O33, and MgO, were studied. The cyclic CO2 capture performance of the synthetic sorbents made from CaO and the support materials were investigated in detail, in the presence of SO2 and steam. The results showed that a mass ratio of 20-25% support material would be optimum for synthesizing sorbents with high cyclic CO2 capture capacity, and Ca12Al14O33 and MgO seem to be more effective than Ca2MnO4 and La2O3. The 80:20 wt % CaO/MgO synthetic sorbent achieved the highest CO2 capture capacity under ideal conditions over 100 cycles. However, the CaO/MgO sorbent had a strong affinity to SO2 capture during cyclic reactions, especially in the presence of steam. Under realistic conditions (i.e., both SO2 and steam are present during carbonation), the CaO/MgO sorbent showed the highest cumulative SO2 capture capacity, whereas the CaO/Ca12Al14O33 sorbent obtained the highest CO2 capture capacity after 10 cycles. The smaller average crystallite size of MgO in the sorbent was responsible for the strong SO2 affinity of the CaO/MgO sorbent as well as its stable cyclic CO2 capture abilities under ideal conditions.