Physicochemical Properties and Investigation of Azole-Based Deep Eutectic Solvents as Efficient and Reversible SO2 Absorbents

Four azole-based DESs from acetyl choline chloride (ACC) and azoles (imidazole, Im, and 1,2,4-triazole, Tri) were prepared and utilized for SO2 capture. Their physicochemical properties, including density, viscosity, TGA, freezing point, and pH, were determined. The influences of temperature and pressure on the SO2 absorption performance of the DESs were systematically conducted. The results showed that all the DESs exhibited efficient and reversible absorption for SO2, and ACC-Im possessed higher absorption capacity than ACC-Tri, with the maximum value of 0.381 g of SO2 per g of ACC-Im (1:2) DES at 303.15 K and 0.1 bar. The possible absorption mechanism was investigated using 1H NMR and FTIR spectroscopy. Furthermore, the ACC-Tri (1:2) was used to capture SO2 at low partial pressure, showing high available capacity of 0.116 g of SO2 per g of DES for 3300 ppm of SO2. Present DESs emerge as promising absorbents for SO2 due to easy preparation, high absorption capacity, and good reversibility.