Highly Efficient, Reversible, and Selective Absorption of SO₂ in 1-Ethyl-3-methylimidazolium Chloride Plus Imidazole Deep Eutectic Solvents

The capture of SO2 from industrial tail gas is of great significance to control air pollution and reserve sulfur resource. In this work, we proposed the use of deep eutectic solvents (DESs) formed by 1-ethyl-3-methylimidazolium chloride ([emim]Cl) and imidazole for SO2 capture, considering the strong electron-donating ability of Cl- in [emim]CI and the weak basicity of tertiary N in imidazole. Both components should exhibit strong interaction with SO2, which is electron-deficient and Lewis acidic. The SO2 capture performance of [emim]Cl+imidazole DESs was thus investigated systematically by both pure gas and mixed gas absorption experiments. It is found that highly efficient absorption of SO2 can be achieved in DESs. The SO2 absorption capacities reach as high as 19.15 mol/kg at 101.3 kPa and 5.73 mol/kg at 2.0 kPa, exceeding most other solvents reported in the literature. The DESs also display good reversibility and excellent selectivity for SO2 absorption, which is rather important for practical SO2 capture applications. Moreover, the mechanism of SO2 absorption was analyzed by quantum chemistry calculations and spectroscopic characterizations.