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

Sulfur dioxide (SO) 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 SO 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 SO with different partial pressures at various temperatures. The results showed that the two DESs could absorb low-partial pressure SO efficiently. SO absorption capacities of the DESs with HBA/HBD mole ratio of 1:3 were 0.332mol SO/mol HBA for Bet+EG DES and 0.820mol SO/mol HBA for L-car+EG DES at 40°C with a SO 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 SO by DESs was studied by FT-IR, H NMR and C NMR spectra. It was found that there are strong acid-base interactions between SO and -COO on HBA.