An ionic liquid phase change absorbent capable of low-temperature regeneration: Investigation of phase change and regeneration mechanism

In order to address the drawbacks of existing Alkanolamine including high regeneration temperatures and excessive energy consumption, a novel dual fuctionalized ionic liquid (DFILS) biphasic solvent was proposed for CO 2 capture, for which separated into liquid-liquid two phase after CO 2 absorption. The DFILs composed of N,N-diethylpropan-1,3-diamine (DEAPA) as cationic and 1,2,4-triazole (Tz), featured higher CO 2 loading and low temperature desorption capability; while poly(ethylene glycol) dimethyl ether (NHD) and water were used as phase splitter and dissolvant respectively. The saturated loading of [DEAPAH][Tz]-NHD-H 2 O (C ILs  = 0.5 mol L −1 , V NHD :V H2O  = 9:1) was 0.92 mol CO 2 mol −1 ILs at 40 °C, and about 97% of CO 2 (0.89 mol mol −1 ) enriched into the lower phase while occupied only 5% of the total volume. This novel solvent kept 86.83% and 80.78% of its initial loading after 1st and 5th regeneration cycle at 98 °C. Experimental and theoretical analyses reveal that the fresh solution maintains homogeneity through balanced polarities and strong IL-solvent interactions. CO 2 absorption generates carbamate and bicarbonate, for which an increased polarity, enhanced Van der Waals interactions, and repulsive forces between the products and NHD, leading to liquid-liquid phase separation. The [DEAPAH][Tz] structure (tertiary amine sterics and heterocyclic anion proton transfer) destabilizes products, while lean-phase NHD addition weakens product-water hydrogen bonds and facilitates proton transfer, enabling efficient low-temperature regeneration. It was estimated that the regeneration heaty duty of [DEAPAH][Tz]-NHD-H 2 O was 1.51 GJ ton −1 CO 2 , which was 60% lower than that of 30 wt% MEA (3.77 GJ ton −1 CO 2 ), further confirming great energy-saving potential for CO 2 capture.