High CO2 absorption capacity by chemisorption at cations and anions in choline-based ionic liquids

摘要

The effect of CO2 absorption on the aromaticity and hydrogen bonding in ionic liquids is investigated. Five different ionic liquids with choline based cations and aprotic N-heterocyclic anions were synthesized. Purity and structures of the synthesized ionic liquids were characterized by H-1 and C-13 NMR spectroscopy. CO2 capture performance was studied at 20 degrees C and 40 degrees C under three different pressures (1, 3, 6 bar). The IL [N-1,N-1,N-6,N-2OH][4-Triz] showed the highest CO2 capture capacity (28.6 wt%, 1.57 mol of CO2 per mol of the IL, 6.48 mol of CO2 per kg of the ionic liquid) at 20 degrees C and 1 bar. The high CO2 capture capacity of the [N-1,N-1,N-6,N-2OH][4-Triz] IL is due to the formation of carbonic acid (-OCO2H) together with carbamate by participation of the -OH group of the [N-1,N-1,N-6,N-2OH](+) cation in the CO2 capture process. The structure of the adduct formed by CO2 reaction with the IL [N-1,N-1,N-6,N-2OH][4-Triz] was probed by using IR, C-13 NMR and H-1-C-13 HMBC NMR experiments utilizing C-13 labeled CO2 gas. H-1 and C-13 PFG NMR studies were performed before and after CO2 absorption to explore the effect of cationanion structures on the microscopic ion dynamics in ILs. The ionic mobility was significantly increased after CO2 reaction due to lowering of aromaticity in the case of ILs with aromatic N-heterocyclic anions.