Unexpectedly efficient absorption of low-concentration SO2 with phase-transition mechanism using deep eutectic solvent consisting of tetraethylammonium chloride and imidazole

Abstract

Deep eutectic solvents (DESs) are environmentally friendly solvents with excellent affinity to acidic gases and have broad application prospect in the field of SO2 capture. In this work, four inexpensive DESs comprising of tetraethylammonium chloride (TEACl) and azoles (imidazole, pyrazole and tetrazole) were designed and prepared for highly efficient and reversible absorption of SO2. Physical properties and chemical structures of the prepared DESs were characterized. High SO2 capacity ranging from 0.756 to 1.251 g/g (3.610–7.231 mol/mol) were obtained at 20 °C and 1.0 bar. Surprisingly, owing to the accompanying phase transition, available SO2 capacity of TEACl-Im (1:3) reaches 0.438 g/g (2.532 mol/mol) at 2000 ppm and 20 °C, which is the highest value reported so far. The absorption mechanism and phase transition were further investigated using FTIR, NMR and XRD, revealing the generation and precipitation of SO2-imdazole adduct. In addition, no significant drop in SO2 absorption capacity was observed after five successive absorption–desorption cycles. Overall, TEACl-Im (1:3) exhibits good absorption performance especially for low-concentration SO2, providing potential alternatives for flue gas desulfurization.