Study of Al2O3 Addition to Synthetic Ca-based Sorbents for CO2 Sorption Capacity and Stability in Cyclic Operations

Synthetic CaO sorbents were prepared using alumina as a sintering inhibitor via a simple precipitation method. The effects of three mixing procedures on the physical properties and CO2 capture performance of the sorbents were examined. The cyclic CO2 capture performance of the sorbent derived from the precipitation of calcium salts over colloidal alumina (highly dispersed alumina gel) showed the best performance of the three mixing methods. It was found that variation of alumina-to-CaO ratios did not significantly change the sintering influence on the sorbent capacity in cyclic operations. CaO particles homogeneously mingled with alumina at higher ratios. Sintering prevention, however, was not observed. This important observation indicates that alumina appeared to merely act as a binder for the fabrication of mechanically enhanced strength particles that are suitable for large-scale operations. It was determined that CO2 uptake was not dependent on either the mixing technique or the type of synthetic materials incorporated into a sorbent in cyclic operation. The sorbent derived from the precipitation of calcium salts over colloidal alumina with an alumina-to-CaO ratio of 20:80 achieved the highest CO2 uptake of 13.1moles/kg sorbent for half an hour of carbonation in the first cycle and retained a sorption capacity of 6.5moles/kg sorbent after 17 successive cycles (50% activity loss), which is in agreement with the reported results. It was demonstrated that the quantity of CO2 uptake increased moderately with decreasing sorbent particle sizes. The effect of pressure on sorbent CO2 uptake was insignificant.