CYCLIC FIXED-BED OPERATIONS OVER K2CO3-ON-CARBON FOR THE RECOVERY OF CARBON-DIOXIDE UNDER MOIST CONDITIONS

A modified chemical-absorption method capable of cyclic fixed-bed operations under moist conditions for the recovery of carbon dioxide from flue gases has been proposed employing K2CO3-on-carbon. Deliquescent potassium carbonate was favorably supported on activated carbon as well as on bound carbon dioxide in the presence of water vapor by the following reaction: K2CO3 + CO2 + H2O reversible arrow 2KHCO(3). After breakthrough, the entrapped carbon dioxide was released by the decomposition of hydrogencarbonate at a higher temperature above 150 degrees C to shift the reaction in reverse by steam, which could be condensed by cooling to afford high-purity carbon dioxide. An effective use of the pore space as microtanks for aqueous potassium carbonate was verified with XRD evidence under a very humid condition of 7.3% H2O, as anticipated. The amount of CO2 uptake was very small under a dry condition, but increased abruptly in the presence of moisture. Potassium carbonate on carbon was crystalline 2K(2)CO(3) 3H(2)O, even when in contact with moisture of 1.7% H2O; this revealed that it is not necessary for K2CO3 to be in the aqueous phase. Illustrative cyclic fixed-bed operations for the recovery of carbon dioxide under a condition close to the actual flue gas of 13.8% CO2 with 10% H2O at 100 degrees C under atmospheric pressure were demonstrated up to 10 cycles.