Efficient and Reversible SO2 Absorption by Environmentally Friendly Task-Specific Deep Eutectic Solvents of PPZBr plus Gly

Efficient and reversible absorption of SO2 based on environmentally friendly task-specific deep eutectic solvents (DESs) is highly desired. In this contribution, a series of task-specific DESs of 1-hydroxyethyl-1,4-dimethyl-piperazinium bromide (PPZBr) plus glycerol (Gly) at different molar ratios were designed and prepared. Physical properties such as the density and viscosity of these task-specific DESs were measured, and the performance of SO2 absorption by these DESs was investigated at different concentrations of SO2 and absorption temperatures. It was found that absorption capacity of up to 4.28 mol SO2 per mol DES could be reached by PPZBr+Gly with n(PPZBr):n(Gly) = 1:6 at 20 degrees C and 1 bar. These DESs containing tertiary amine group exhibited chemical interaction with SO2 under low partial pressure or high temperature. About 1.39 mol mol(-1) SO2 could be absorbed at 80 degrees C and desorbed by heating or bubbling N-2, and the DES might be recycled several times without loss of efficiency. An absorption mechanism based on the analysis of FT-IR and NMR spectra showed that the efficient absorption of SO2 was ascribed to the chemical interaction between the tertiary amine group and SO2. Furthermore, the thermodynamic properties of SO2 chemisorption by PPZBr+Gly (1:6), such as molar reaction enthalpy change, molar reaction entropy change, and molar reaction Gibbs free energy change, were calculated, and the molar reaction enthalpy change was the main driving force for SO2 capture.