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 SO2 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 SO2 in the five organic solvents followed the sequence NMI > NMP > SUF > PC > EG. The absorption isotherms of SO2 in SUF, EG, and PC showed ideal profiles, while those in NMI and NMP showed nonideal types. The Henry's law constants of SO2 in SUF, EG, and PC in terms of molality were calculated by drawing linear fit between SO2 solubilities and SO2 partial pressures. The interactions of SO2 with NMI and NMP were examined through density functional theory (DFT) calculations, and the solvent saute complex formations were illustrated. The experimental solubilities of SO2 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 SO2 absorption. The performance of SO2 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 SO2 absorption.