CO2 capture with the absorbent of a mixed ionic liquid and amine solution considering the effects of SO2 and O-2

摘要

Room-temperature ionic liquids (ILs) have recently been proposed as a potential candidate for CO2 capture. In this study, experiments were conducted in an absorption-desorption loop system to investigate the effects of SO2 and O-2 on CO2 capture using an aqueous amine solution mixed with IL. The gas mixture containing CO2, O-2, SO2 and N-2 in the composition range of flue gas from a coal-fired power plant after flue gas desulfurization was selected as the feed gas. It was found that the addition of hydrophilic IL of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) to a monoethanolamine (MEA) aqueous solution reduced the losses of MEA and water by lowering the saturated vapour pressure of the mixed absorbent. For hydrophobic IL of 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf2N]), the MEA loss for 30 wt% MEA + 70 wt% [hmim][Tf2N] increased dramatically with the system running because carbonate, which was formed by MEA reacting with CO2, was insoluble in [hmim][Tf2N] at the absorber operation temperature of 323 K. The effects of O-2 and SO2 were relatively insignificant for the MEA and water losses. The aqueous amine solution mixed with [bmim][BEt] showed good performances with a CO2 removal efficiency of above 90% and the SO2 concentration at the absorber outlet below 20 ppb. No obvious IL loss was detected. For the absorbent of 30 wt% MEA + 50 wt% [bmim] [BF4] + 20 wt% H2O, the thermal energy consumption for absorbent regeneration is 33.8% lower than that of the aqueous MEA solution. (C) 2017 Elsevier Ltd. All rights reserved.