New deep eutectic solvents formed by 1-ethyl-3-methylimidazolium chloride and dicyandiamide: Physiochemical properties and SO2 absorption performance

The recycling of SO2 is very meaningful not only to the environmental protection but also to the sulfur resource utilization. To realize the recycling of SO2, developing green solvents that enable effective, selective and reversible absorption of SO2 is demanded. In this work, we innovatively found that 1-ethyl-3-methylimidazolium chloride ([emim]Cl) and dicyandiamide (DCDA) can form a new kind of deep eutectic solvents (DESs). The physiochemical properties of [emim]Cl+DCDA DESs were characterized to provide the fundamental data of DESs first. Subsequently, the SO2 absorption performance of [emim]Cl+DCDA DESs were systematically investigated. It is found that the absorption of SO2 in [emim]Cl+DCDA DESs is fast, and the capacities of SO2 absorption are very high (16.58 mol/kg at 298.2 K and 104.7 kPa, and 2.45 mol/kg at 298.2 K and 1.7 kPa). In addition, the absorption of SO2 in [emim]Cl+DCDA DESs is highly selective towards CO2 and N2, and also highly reversible in consecutive absorption-desorption cycles. Finally, the underlying mechanism for SO2 absorption in [emim]Cl+DCDA DESs was examined by quantum chemistry calculations and spectroscopic characterizations.