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

Abstract

As a successive work towards exploring suitable IL-based absorbents for SO2 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 SO2 capacity. The solubilities of SO2 in the DILs increased with declining of the temperature and elevating of the SO2 concentration. Notably, the available loading capacity of SO2 in DIL4 was up to 0.267 g SO2·(g DIL)-1 at 313.2 K when the concentration of SO2 in the feed gas was 2000 ppm, which was exceedingly significant for trapping SO2 from the flue gas with low content of SO2. The regeneration experiments demonstrated that the absorption capacities of SO2 in DIL4 kept unchanged after six successive cycles of absorption/desorption. The absorption mechanisms based on the results of 1H NMR, FTIR analysis and quantum chemical calculations indicated that both physical and chemical interactions between the SO2 molecules and DIL4 could be found in spite of different concentrations of SO2.