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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.

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In this work, the solubility data of CO2 in three kinds of guaiacol-based deep eutectic solvents (DESs) at 293.15, 303.15, 313.15, and 323.15 K and pressures below 600.0 kPa were determined. The DESs were prepared from guaiacol and quaternary ammonium salts (QASs, including choline chloride, acetylcholine chloride, and diethylamine hydrochloride) with a molar ratio of guaiacol to QAS of 3:1, 4:1, and 5:1. Henry’s law was used to correlate the solubility data, and the thermodynamic properties, such as standard Gibbs free energy, standard enthalpy, and standard entropy of these systems were derived. The solubility of CO2 increased with increasing molar ratio of guaiacol to QAS in each kind of DES. The dissolution enthalpies were negative at all conditions. The dissolution capacities of present DESs for CO2 were further compared with those of other DESs and several common ionic liquids.

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