Integration of physical solution and ionic liquid toward efficient phase splitting for energy-saving CO2 capture

Abstract

Carbon dioxide (CO2) capture from flue gas is crucial for achieving industrial carbon neutrality. Using a biphasic solvent can significantly reduce the volume of regenerated solvent for energy-saving carbon capture. In this study, a novel strategy for biphasic solvent preparation was proposed by combining amine blends (3,3′-Diaminodipropylamine, DADPA; N-Methyldiethanolamine, MDEA) and composite agents (1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, BN; sulfolane, TMS). The screened proportion of DADPA:MDEA:TMS:BN:H2O was 2:6:2:1:2 (labelled DMTB). Experimental evaluation revealed that the DMTB solvent exhibits a high CO2 capacity of 4.59 mol/L (in the 50 vol% rich phase), an efficient phase splitting rate (within 3 min) and a fast CO2 desorption rate. The dynamic phase-splitting capacity was evaluated by a quasi-two-dimensional separator, under various operational condition. The 13C NMR results indicated the formation of DADPACOO- in the CO2-saturated phase in the presence of water rather than bicarbonate while observing dissociative behaviour in MDEA and TMS. Therefore, the phase separation analysis revealed that the products of protonated amines and carbamic acid species were highly polar and preferred to dissolve in the water phase. This study provides an optional biphasic solvent with phase splitting ability for CO2 capture from flue gas.