Highly efficient and reversible low-concentration SO2 absorption in flue gas using novel phosphonium-based deep eutectic solvents with different substituents

Four hydrogen bond acceptors (HBAs) with different carbon chain length substituents, including methyltriphenyl phosphonium bromide (MTPB), ethyl-triphenyl phosphonium bromide (ETPB), propyltriphenyl phosphonium bromide (PTPB), and butyl-triphenyl phosphonium bromide (BTPB), combined with ethylene glycol (EG) were developed to synthesize four low-viscosity deep eutectic solvents (DESs). In this study, the effect of different substituents in DESs on low-concentration SO 2 absorption was systematically studied at 30-70 degrees C. Experimental results show that the EG-MTPB DES has a higher SO2 absorption capacity and a lower viscosity than other DESs. The reason for the higher SO2 absorption capacity of EG-MTPB DES was described by viscosity experiments and quantum chemical calculations. It was shown that the strong polarization ability of the CH3- group promotes the absorption of SO2 by DESs. H-1 NMR and FTIR results indicated that chemical interactions primarily exist between the S of SO2 and Br, and the O of SO2 and the H atom of EG form hydrogen bonds. The density functional theory (DFT) results also confirm that the charge of the Br atom migrated to the S atom. Also, thermostability and regeneration experiments showed that the EG-MTPB DES exhibits good stability and can thus be used for industrial flue gas desulfurization. (C) 2021 Elsevier B.V. All rights reserved.