Surpassingly efficient, selective, and reversible absorption of SO₂ through pyridine based deep eutectic solvents

In this study, deep eutectic solvents (DESs) consisting of 1-ethyl-3-methylimidazolium chloride (EmimCl) and pyridine derivatives were prepared through a facile procedure. The studied DESs exhibit superb absorption behavior for SO2 at 298.15 K and 1.0 bar, of which per g EmimCl: 2-NH2Py (7: 1) could capture 1.247 g SO2, exceeding the vast majority of the previously reported DESs and ionic liquids (ILs). The factors that could affect the absorption capacity were explored orderly, like the category and molar ratio of pyridine derivatives, the absorption temperature, and SO2 partial pressure. Based on the above investigation, EmimCl: 2-NH2Py (7: 1) exhibits rapid equilibration time (<45 s), outstanding SO2/CO2 selectivity (312/1), and ultra-high recycling performance (40 times), which is far superior to the other reported DESs and ILs. In addition, the possible absorption process was studied from both experimental and theoretical aspects. The obtained data indicate that Lewis acid-base interaction and (SO2Cl)-Cl-...- covalent interaction both exist between SO2 and DES, leading to an ideal absorption capacity and selectivity for SO2. This study might provide a novel insight to remove SO2 and other gaseous pollutants.