SO2 absorption in acid salt ionic liquids/sulfolane binary mixtures: Experimental study and thermodynamic analysis

• Non-aqueous ASIL/sulfolane binary mixtures were designed for the absorption of SO2.
• Detailed absorption performance of SO2 in the ASIL/sulfolane binary mixtures was investigated systematically.
• A reaction equilibrium thermodynamic model (RETM) was derived to analyze the behaviour of SO2 absorption in the ASIL/sulfolane binary mixtures.

Two new simple acid salt ionic liquids (ASILs), tetraethylammonium diglutarate ([N2222][diglutarate]) and dimethylethanolammonium diglutarate ([DMEA][diglutarate]) were synthesized and the ASILs/sulfolane binary mixtures containing 40 wt% ASILs were prepared for SO2 absorption in this work. The SO2 absorption rate is found to be quite fast with an equilibrium time within 2 min, due to the low viscosity of the mixtures. The solubilities of SO2 in the two binary mixtures were measured under the pressure range of 0–1 bar and the temperature range of 303.15–333.15 K and results demonstrate the binary mixtures could trap as much as 6.836–7.624 mol SO2/kg absorbents at 1 bar and 303.15 K. The solubilities are 0.826–0.954 mol SO2/kg absorbents at a pressure as low as 0.004 bar, which is important for capturing SO2 from the flue gas with low content of SO2. Thermodynamic analysis based on a Reaction Equilibrium Thermodynamic Model (RETM) was used to calculate the Henry’s law constants, reaction equilibrium constants, chemical absorption capacity, physical absorption capacity and thermodynamic functions of SO2 absorption in the mixtures. The calculated absorption enthalpy are −53.73 and −47.15 kJ/mol for the two binary mixtures, respectively. The ASILs/sulfolane binary mixtures are shown to be an attractive alternative to pure ILs to be applied in SO2 absorption due to the large absorption capacity and low absorption enthalpy, as well as the fast absorption rate.