Bench-Scale CO₂ Recovery from Moist Flue Gases by Various Alkali Carbonates Supported on Activated Carbon

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As described in the previous papers, K₂CO₃ supported on activated carbon sorbed CO₂ from moist feed gas at 353 K to form KHCO₃ and the entrapped CO₂ was then efficiently released by steam flushing at 423 K, followed by condensation of the excess steam through a heat exchanger to afford CO₂ in high purity. In the present study, various alkali carbonates supported on activated carbon were employed to recover CO₂ from moist gases at different temperatures. Carbon dioxide can be sorbed at higher temperatures in the order of the impregnated salt, Na₂CO₃ < K₂CO₃ < Rb₂CO₃ ~ Cs₂CO₃, indicating the applicability of CO₂ sorbents from moist flue gases at temperatures of 313–393 K by selecting the type of alkali carbonate for impregnation. By employing a bench-scale apparatus packed with the sorbent, materials (CO₂, water) balance and heat balance during CO₂ sorption/release steps were measured in order to elucidate the CO₂ recovery performance. The CO₂ uptake increased in the order of the impregnated salt, Cs₂CO₃ ~ K₂CO₃ < Na₂CO₃, while heat for the CO₂ release per unit mass of recovered CO₂ decreased in the order of Na₂CO₃ > K₂CO₃ > Cs₂CO₃, providing a more energy-conservative CO₂ recovery process for moist flue gases at 313–393 K than conventional amine absorption methods.