CaO Powders from Oyster Shells for Efficient CO_2 Capture in Multiple Carbonation Cycles

摘要

The carbonation/calcination loop of CaO/CaCO_3 is an efficient process for CO_2 capture. This study investigated the CO_2 capture capability of CaO powders derived from oyster shells and reagent-grade CaCO_3. The oyster shell-derived CaO powder had an oxide impurity content as high as 9 wt%, and a larger CaO crystal grain size and smaller specific surface area than the CaO derived from the reagent-grade CaCO_3. In cyclic CO_2 capture tests, the cyclability and CO_2 capacity of the oyster shell-derived CaO was significantly improved by inserting an intermediate cooling step between carbonation and calcination. At a carbonation temperature of 740℃, the overall performance of the oyster shell-derived CaO in cyclic carbonation was superior to that of the CaO from the reagent-grade CaCO_3. On the basis of X-ray diffraction analysis, it was suggested that the impurities contained in the oyster shell-derived CaO may have constituted transition zone on the CaO crystal grain-boundary to suppress crystal growth in calcination as well as to ease up lattice expansion in CO_2 fixation. The intermediate cooling enlarged the transition zone to mitigate lattice dislocations resulting from CO_2 fixation and thus, the decay in CO_2 capacity.