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.