The carbonation/calcination loop of CaO/CaCO3
is an efficient process for CO2 capture. This
study investigated the CO2 capture capability of
CaO powders derived from oyster shells and reagent-grade CaCO3.
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 CaCO3.
In cyclic CO2 capture tests, the cyclability
and CO2 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°C, the overall performance of the oyster shell-derived CaO in cyclic
carbonation was superior to that of the CaO from the reagent-grade CaCO3.
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 CO2 fixation. The intermediate
cooling enlarged the transition zone to mitigate lattice dislocations
resulting from CO2 fixation and thus, the decay
in CO2 capacity.