Thermal activation of CaO-based sorbent and self-reactivation during CO₂ capture looping cycles

In this study, the thermal activation of different types of CaO-based sorbents was examined. Pretreatments were performed at different temperatures (800-1300°C) and different durations (6-48 h) using four Canadian limestones. Sieved fractions of the limestones, powders obtained by grinding, and hydroxides produced following multiple carbonation/calcination cycles achieved in a tube furnace were examined. Pretreated samples were evaluated using two types of thermogravimetric reactors/analyzers. The most important result was that thermal pretreatment could improve sorbent performance. In comparison to the original, pretreated sorbents showed better conversions over a longer series of CO₂ cycles. Moreover, in some cases, sorbent activity actually increased with cycle number, and this effect was especially pronounced for powdered samples preheated at 1000°C. In these experiments, the increase of conversion with cycle number (designated as self-reactivation) after 30 cycles produced samples that were ∼50% carbonated for the four sorbents examined here, and there appeared to be the potential for additional increase. These results were explained with the newly proposed pore-skeleton model. This model suggests, in addition to changes in the porous structure of the sorbent, that changes in the pore-skeleton produced during pretreatment strongly influence subsequent carbonation/calcination cycles.