CO2 absorption enhancement of fluorinated ionic liquids on nonaqueous biphasic absorbents: Experimental and theoretical study

Nonaqueous biphasic absorbent decreasing the regeneration heat consumption by phase separation (lean-phase and rich-phase) and water evaporation elimination is a promising CO 2 capture absorbent, but the low CO 2 loading capacities are of great challenges. In this study, ionic liquids (IL) were proposed as catalysts for enhancing the CO 2 loading in monoethanolamine (MEA)-1-Butanol nonaqueous biphasic absorbents. Three types of fluorinated IL including 1‑butyl‑3-methylimidazolium tetrafluoroborate ([B mim ][BF 4 ]), 1‑butyl‑3-methylimidazolium hexafluorophosphate ([B mim ][PF 6 ]), and 1‑butyl‑3-methylimidazolium bis[( trifluoromethyl ) sulfonyl ]imide ([B mim ][TF 2 N]) under different concentrations (0–10wt%) were detailly analyzed to explore the catalyzation of IL on phase separation behavior and absorption performance. Phase separation study showed that the MEA-1-Butanol-IL system exhibited the wonderful phase separation behavior with a volume ratio (rich-phase) between 30 and 40 %. Three phases were observed in MEA-1-Butanol-[B mim ][BF 4 ] and MEA-1-Butanol-[B mim ][PF 6 ] systems after CO 2 absorption and the components of each phase were identified by 13 C nuclear magnetic resonance (NMR) spectroscopy. In absorption study, the absorption enhancement of IL was in this order: [Bmim][TF 2 N] > [Bmim][BF 4 ] > [Bmim][PF 6 ]. MEA-1-Butanol-10wt% [Bmim][TF 2 N] system could improve 35.9 % CO 2 loading and 24.2 % absorption rate compared to basic MEA-1-Butanol. A molecular scale understanding of the three-steps reaction mechanism of MEA-1-Butanol-IL absorbing CO 2 was revealed, and the different catalyzation of three types of IL can be attributed to the different affinity for CO 2 . This study provides new insights into designing nonaqueous biphasic solvents and a promising MEA-1-Butanol-IL system with high CO 2 capture performance.