Four kinds of deep eutectic solvents (DESs) based on choline chloride (ChCl) with ethylene glycol (EG), malonic acid (MA), urea, and thiourea as hydrogen bond donors were prepared and characterized. All these DESs show good thermal stability and can be stable at 363 K, which is beneficial for the application in flue gas desulfurization. Then, SO 2 absorption capacities of these DESs were determined at different temperatures and SO 2 partial pressures. The absorption results demonstrate that ChCl−EG (1:2) and ChCl−thiourea (1:1) DESs exhibit excellent absorption performances, and the absorption capacities are 2.88 and 2.96 mol SO 2 per mol DES at 293 K and 1 atm, respectively. In addition, the SO 2 absorption and regeneration experiments were conducted. All solvents can be regenerated at 343 K with N 2 bubbling, and the absorption capacities of DESs remain without a significant loss after six absorption and desorption cycles. What's more, the absorption mechanism of SO 2 in these DESs were investigated by IR and 1 H NMR.

Solubilities of SO 2 in ethylene glycol derivatives were determined by dynamic isothermal gas-liquid equilibrium (GLE) experiments, and the thermodynamic parameters of the absorption processes were calculated. The GLE results indicated that the solubilities of SO 2 in ethylene glycol derivatives increase in the order: diols < monomethyl ethers < dimethyl ethers, with the enthalpy values ranging from À23.2 to À43.3 kJ mol À1 . The regeneration experiment found that the absorption of SO 2 in tetraethylene glycol dimethyl ether is reversible, and the solvents can be reused without a significant loss of absorption capacity. The interactions between SO 2 and ethylene glycol derivatives were investigated by UV, IR and NMR. In addition, a 1 H-NMR spectroscopy technique with external references was used to investigate the physical absorption process of SO 2 for the first time, in order to avoid the influence of deuterated solvents. Spectroscopic investigations showed that the interactions between SO 2 and ethylene glycol derivatives are based on both the charge-transfer interaction and hydrogen bond. Ethylene glycol derivatives with desirable absorption capacities and excellent regeneration abilities are promising alternatives to conventional sorbents in SO 2 separation.

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In this work, the isothermal gas–liquid equilibrium (GLE) data were measured for the system of polyethylene glycol 400 (PEG 400) + N,N-dimethylformamide (DMF) + SO2 + N2 at 308.15 K and 123 kPa with SO2 partial pressures in the range of (16.8 to 115) Pa. The Henry’s law constant (H′) and standard Gibbs free energy change (ΔG) were calculated from these GLE data. Furthermore, the densities and viscosities of binary mixtures of DMF + PEG 400 were also measured over the whole concentration range at T = (298.15 to 313.15) K. From the experimental data, including density and viscosity values, the excess molar volumes (V m E), and viscosity deviations (Δη), the calculated results are fitted to a Redlich–Kister equation to obtain the coefficients and estimate the standard deviations between the experimental and the calculated quantities.

A series of glyme-lithium salt ionic liquids were prepared and applied in SO 2 absorption. The formed quasi-aza-crown ether fashioned between Li + and glymes can effectively reduce the solvent volatilization, and have an excellent SO 2 absorption capacity. In addition, the mechanism of the interaction between SO 2 and ionic liquids was investigated by IR and NMR.

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Solubilities of SO 2 in binary mixtures of urea and ethylene glycol were determined by gas−liquid equilibrium experiments at the temperatures from (298.15 to 318.15 K) and 122.7 kPa, with SO 2 partial pressure in gas phase in the range of (0 to 130) Pa. Henry's law constants were calculated based on the solubility data. It indicated that the mixture with urea molality of 6.65 mol•kg −1 has the most desirable capacity. More than 90 % SO 2 can be regenerated by bubbling N 2 at 338.15 K. Density and viscosity data for the binary mixtures were also measured. In addition, UV, IR, and NMR experiments were conducted to investigate the interaction between ethylene glycol, urea, and SO 2 . The result demonstrated that SO 2 can interact with the mixture by both the charge-transfer interaction between S (SO 2 )•••N (urea) and the hydrogen bond between O (SO 2 )•••H (ethylene glycol).