PNNL

Abstract

Calcium oxide-based materials are attractive regenerable absorbents for separating CO2 from hot gas streams because of their high reactivity, high CO2 capacity, and low material cost. Their high carbonation temperature makes it possible to recover and use high quality heat released during CO2 capture, which increases overall process efficiency. However, the performance of all reported CaO-based absorbents deteriorates as the number of carbonation-decarbonation cycles increases. This is caused by absorbent sintering during the highly exothermic carbonation process. We have found that sintering can be effectively mitigated by properly mixing with a modest amount of MgO. A class of CaO-based absorbents with improved durability and CO2 reactivity were prepared by physical mixing of Ca(CH3COO)2 with small MgO particles followed by high temperature calcination. With 26 wt% MgO content, a CaO-MgO mixture prepared by this method gives as high as 53 wt% CO2 capacity after 50 carbonation-decarbonation cycles at 758oC. Without MgO addition, the CO2 capacity of pure CaO obtained from same source decreases from 66 wt% for the 1st cycle to 26 wt% for the 50th cycle under the same test conditions.