Comparative Study of the Solubilities of SO₂ in Five Low Volatile Organic Solvents (Sulfolane, Ethylene Glycol, Propylene Carbonate, N-Methylimidazole, and N-Methylpyrrolidone)

Solubilities of SO 2 in five selected inexpensive organic solvents with low volatility were measured at temperatures from 303.2 K to 333.2 K and pressures up to 120 kPa. The solvents include sulfolane (SUF), ethylene glycol (EG), propylene carbonate (PC), N -methylimidazole (NMI) and N -methylpyrrolidone (NMP). The obtained results indicated that the solubilities of SO 2 in the five organic solvents followed the sequence NMI > NMP > SUF > PC > EG. The absorption isotherms of SO 2 in SUF, EG, and PC showed ideal profiles, while those in NMI and NMP showed nonideal types. The Henry’s law constants of SO 2 in SUF, EG, and PC in terms of molality were calculated by drawing linear fit between SO 2 solubilities and SO 2 partial pressures. The interactions of SO 2 with NMI and NMP were examined through density functional theory (DFT) calculations, and the solvent–solute complex formations were illustrated. The experimental solubilities of SO 2 in NMI and NMP were successfully correlated by a reaction equilibrium thermodynamic model (RETM) proposed based on the DFT calculations. Subsequently, Henry’s law constants, reaction equilibrium constants, and heat of complex formation were also calculated to evaluate the potential of applying these organic solvents in SO 2 absorption. The performance of SO 2 absorption in these organic solvents were further compared with that in ILs and results illustrated that NMI and NMP were good alternatives to IL for applying in SO 2 absorption.