Highly Efficient and Reversible Capture of Low Partial Pressure SO2 by Functional Deep Eutectic Solvents

Deep eutectic solvents (DESs) have been seen as promising absorbents for SO2 capture in recent years. In this work, a series of DESs based on imidazole derivatives were synthesized to investigate the low pressure SO2 absorption. The physical properties were determined, and the DESs exhibited low viscosities and high stability. Effects of composition, operating temperature and pressure, and water content on SO2 absorption capacity were investigated. It was demonstrated that the 1-butyl-3-methylimidazolium chloride (BmimCl):4-methylimidazole (4CH3-Im) (1:2) could absorb 1.42 and 0.189 gSO2/gDES at 101.3 and 1 kPa SO2 partial pressure, respectively, which were higher than most reports to date under this condition. The absorbed SO2 could be released easily under mild condition, and there was no change in absorption performance after 5 cycles. Furthermore, the absorption mechanism studied by FTIR and NMR indicated that the high SO2 absorption capacity originated from the synergistic interaction of BmimCl and 4CH3-Im on SO2. This work opens opportunity for low partial pressure SO2 capture and insight into the formation mechanism of DESs for further investigation.