Efficient absorption of SO2 with low-partial pressures by environmentally benign functional deep eutectic solvents.

Sulfur dioxide (SO2) emitted from the burning of fossil fuels is one of the main air contaminants. In this work, we found that environmentally benign solvents, deep eutectic solvents (DESs) could be designed with a function to absorb low-partial pressure SO2 from simulated flue gas. Two kinds of biodegradable functional DESs based on betaine (Bet) and l-carnitine (L-car) as hydrogen bond accepters (HBA) and ethylene glycol (EG) as a hydrogen bond donor (HBD) were prepared with mole ratios of HBA to HBD from 1:3 to 1:5, and they were investigated to absorb SO2 with different partial pressures at various temperatures. The results showed that the two DESs could absorb low-partial pressure SO2 efficiently. SO2 absorption capacities of the DESs with HBA/HBD mole ratio of 1:3 were 0.332mol SO2/mol HBA for Bet+EG DES and 0.820mol SO2/mol HBA for L-car+EG DES at 40°C with a SO2 partial pressure of 0.02atm. In addition, the regeneration experiments demonstrated that the absorption capacities of DESs did not change after five absorption and desorption cycles. Furthermore, the absorption mechanism of SO2 by DESs was studied by FT-IR, 1H NMR and 13C NMR spectra. It was found that there are strong acid-base interactions between SO2 and -COO- on HBA.