Efficient absorption of low-concentration SO2 in simulated flue gas by functional deep eutectic solvents based on imidazole and its derivatives

Four thermostable functional deep eutectic solvents (DESs) based on imidazole (Im), 2-methylimidazole, 2-ethylimidazole, and 2-propylimidazole as hydrogen bond acceptor (HBA) and glycerol (Gly) as hydrogen bond donor (HBD) were prepared. All prepared DESs can efficiently capture low-concentration SO 2 . The SO 2 solubility increased with decreasing temperature and increasing SO 2 concentration and the available absorption of 2000   ppm SO 2 in Im-Gly DES was high, up to 0.634   mol of SO 2 /mol of Im (0.161   g of SO 2 /g of DES) with n Im : n Gly   =   1:2 at 40   °C. The regeneration experiments showed that the SO 2 absorption capacities in Im-Gly DES did not change after 5 absorption/desorption cycles. Furthermore, the absorption mechanism based on 1 H NMR and FTIR analyses indicated that there was an acid–base interaction between SO 2 and Im.