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

- The prepared four deep eutectic solvents (DESs) can efficiently capture low-concentration SO2.
- Imidazole-based (Im)-glycerol (Gly) DESs are thermostable, cheap and easily prepared.
- The absorption of 2000 ppm SO2 in Im-Gly DESs is high up to 0.643 mol SO2/mol Im (0.163 g SO2/g DES).
- Im-Gly DES is a promising absorbent for capture and recovery of SO2 from flue gas.

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 SO2. The SO2 solubility increased with decreasing temperature and increasing SO2 concentration and the available absorption of 2000 ppm SO2 in Im-Gly DES was high, up to 0.634 mol of SO2/mol of Im (0.161 g of SO2/g of DES) with nIm:nGly = 1:2 at 40 °C. The regeneration experiments showed that the SO2 absorption capacities in Im-Gly DES did not change after 5 absorption/desorption cycles. Furthermore, the absorption mechanism based on 1H NMR and FTIR analyses indicated that there was an acid-base interaction between SO2 and Im.

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