Calcium Oxide Based Sorbents for Capture of Carbon Dioxide at High Temperatures

Calcium oxide is a promising sorbent for the capture of carbon dioxide. In this work, CaO sorbents were prepared using different precursors, including Ca(NO3)2·4H2O, CaO, Ca(OH)2, CaCO3, and Ca(CH3COO)2·H2O. Of these, the sorbent prepared from calcium acetate (CaAc2-CaO) resulted in the best uptake characteristics for CO2. This sorbent had a higher BET surface area and larger pore volume than the other sorbents. According to SEM images, this sorbent exhibits a "fluffy" structure, which probably contributes to its high surface area and large pore volume. This sorbent also showed almost 100% carbonation, at temperatures between 550 and 800 °C. Moreover, the carbonation progressed dominantly during an initial short period. Under numerous carbonation/decarbonation cycles, the CaAc2-CaO sorbent demonstrated the best reversibility, even in the presence of 10 vol % water vapor. During a 27-cycle operation, the sorbent maintained fairly high conversion of 62 mol % at 700 °C. Pore size distribution measurements indicate that the pore volume decreased as the experimental cycles continued. Silica was doped on the CaAc2-CaO sorbent in various weight percentages, but the resultant sorbents did not exhibit better performance under cyclic operation than those without Si dopant.