Chemically tunable DILs: Physical properties and highly efficient capture of low-concentration SO2

As a successive work towards exploring suitable IL-based absorbents for SO 2 absorption from flue gas, we developed a species of new dicationic ionic liquids (DILs) with the combination of ether-functionalized dication and N-heterocyclic anions. These dual-functionalized DILs possessed high thermal stability, low vapour pressure, and high SO 2 capacity. The solubilities of SO 2 in the DILs increased with declining of the temperature and elevating of the SO 2 concentration. Notably, the available loading capacity of SO 2 in DIL 4 was up to 0.267 g SO 2 ·(g DIL) -1 at 313.2 K when the concentration of SO 2 in the feed gas was 2000 ppm, which was exceedingly significant for trapping SO 2 from the flue gas with low content of SO 2 . The regeneration experiments demonstrated that the absorption capacities of SO 2 in DIL 4 kept unchanged after six successive cycles of absorption/desorption. The absorption mechanisms based on the results of 1 H NMR, FTIR analysis and quantum chemical calculations indicated that both physical and chemical interactions between the SO 2 molecules and DIL 4 could be found in spite of different concentrations of SO 2 .