Functionalized imidazole-alkanolamine deep eutectic solvents with remarkable performance for low-concentration SO₂ absorption

SO2 generated by manufacturing facilities, power plants, and ships must be removed because it adversely affects human health even at low concentrations. Flue gas desulfurization (FGD), which is a conventional method for removing SO2, causes additional environmental issues, including non-recyclable reactants and wastewater. In this study, deep eutectic solvents (DESs) functionalized to absorb SO2 at low concentrations are developed as alternatives for FGD. The physical properties, including thermal stability, of the prepared DESs were analyzed, and an enhancement in thermal stability, attributed to DES formation, was verified. Additionally, absorption capacities and reusability under 500 ppm SO2 were analyzed through experiments involving the absorption, desorption, and reabsorption cycles. The thermal stabilities of the as-prepared DESs significantly improved compared to those of the precursors. In addition, the prepared absorbents exhibited remarkable SO2 absorption performance owing to multi-site absorption, with values of 0.992, 0.684, and 0.628 g SO2/g absorbent, which are more than twice higher than those reported in previous studies. Finally, the absorption mechanism was confirmed using H-1 nuclear magnetic resonance and Fourier Transform Infrared spectroscopy. Owing to the exceptional performance of the proposed absorbents, this study is expected to make a significant contribution to the alternative technology research on SO2 separation.