Limited Number of Active Sites Strategy for Improving SO₂ Capture by Ionic Liquids with Fluorinated Acetylacetonate Anion

Abstract

SO2 capture is highly important because this acid gas can react with moisture in the atmosphere to produce acid rain, a kind of atmospheric pollution. In this contribution, we show how SO2 can be efficiently absorbed by a new class of fluorinated acetylacetonate ionic liquids (FILs) with limited number of active sites in the anions. The absorption of SO2 by these functionalized FILs is investigated under different partial pressures and temperatures, and a high SO2 capacity up to 4.27 and 1.82 mol SO2 per mol IL can be achieved under 1 and 0.1 bar, respectively, compared with 1.43 and 0.24 mol SO2 per mol [TFSI]-based FIL ([TFSI] = bis(trifluoromethylsulfonyl)imide anion). From a combined study of quantum chemical calculations, FT-IR and NMR analysis, it is found that the high SO2 absorption capacities by fluorinated acetylacetonate task-specific FILs can be ascribed to the multiple-site interactions between SO2 and limited number of active sites in the anions. Furthermore, the FILs can be easily regenerated and the SO2 absorption process could be recycled.