Characterization of potassium carbonate supported on porous materials and the application to the recovery of carbon dioxide from flue gases under moist conditions

Cyclic fixed-bed operations under moist conditions for the recovery of carbon dioxide from flue gases have been carried out employing K2CO3 supported on porous materials. Moisture, usually contained 8-17% in flue gases, badly decreases the adsorption capacity in the conventional fixed-bed adsorption technology. However, since potassium carbonate absorbs carbon dioxide in the presence of water to form potassium hydrogencarbonate (K2CO3+CO2+H2O reversible arrow 2KHCO(3)), the moist conditions are rather necessary. Deliquecent potassium carbonate should be supported on an appropriate porous material in order to use in fixed-bed operations. A drastic decrease in surface area was observed when K2CO3 was supported on the hydrophilic silica gel, reflecting the blockade with K2CO3 in micropores, while K2CO3 was supported on hydrophobic activated carbon without appreciable change in surface area. In the case of pelleted alpha-Al2O3, potassium carbonate filled up the interstices of nonporous alumina powders. The XRD observations suggest hydrothermal reaction of potassium carbonate with silica gel, resulting in the decrease in CO2 adsorption capacity of K2CO3-on-SiO2. On the other hand, reproducible CO2-uptake was observed for K2CO3-on-Carbon. Entrapped CO2 was recovered reversibly by the decomposition of potassium hydrogencarbonate on flashing with steam at 150-200 degrees C.