The effect of water on the activation and the CO2 capture capacities of alkali metal-based sorbents

Alkali metal-based sorbents were prepared by the impregnation either of potassium carbonate (K2CO3) or of sodium carbonate (Na2CO3) on the supports (activated carbon (AC) and Al2O3). The CO2 absorption and regeneration properties were measured in a fixed bed reactor at the low temperature conditions (CO2 absorption at 60 ‡C and regeneration at 150 °C). The potassium carbonate which was supported on the activated carbon (K2CO3/AC) was clarified as a leading sorbent, of which the total CO2 capture capacity was higher than those of other sorbents. This sorbent was completely regenerated and transformed to its original phase by heating the used sorbent. The activation process before CO2 absorption needed moisture nitrogen containing 1.3–52 vol% H2O for 2 hours either at 60 ‡C or at 90 °C. The activation process played an important role in CO2 absorption, in order to form new active species defined as K2CO3· 1.5 H2O, by X-ray diffraction. It was suggested that the new active species (K2CO3·1.5H2O) could be formed by drying the K4H2(CO3)3·1.5H2O phase formed after pre-treatment with excess water.