Synthesis And Application Of PEG-based Functionalized Ionic Liquids For Sulfur Dioxide Absorption

A series of PEG-based imidazolium toluenesulfonates (PEG-based functionalized ionic liquids) with long ether chain were synthesized and characterized by 1H NMR and FT-IR. Physical properties (densities and surface tensions) in range of 293.15～333.15K of the ILs had been measured, and their thermodynamic properties related to densities and surface tensions were calculated and analysed. Their ability to reversibly absorb gaseous sulfur dioxide was investigated via the following aspects:influencing factors such as temperature, SO2 partial pressure and pH of the ILs on absorption capacity; selectivity of the ILs on SO2 absorption; and change of physical properties of the ILs during absorption process. The physical properties of binary mixtures of M-PEG-functionalized ILs and molecular solvents (water/methoxypolyethylene glycols) were determined, the solubility of the binary mixtures were also measured at different temperatures. Experimental result indicates that, all the ILs perform good absorption and regeneration capacity. The absorption capacity of ILs increases with increasing length of ether chain on the cation. The absorption capacity can achieve more than 5.51 mole SO2 per mole IL at 20 ℃, and the absorbed SO2 gas can be readily and completely desorbed from the ILs at 80 ℃. The ILs can be reused at least 10 cycles almost without loss of their mass and initial efficiency. The solubility values of SO2 in these M-PEG-functionalized ILs decrease sharply with the increase of temperature; Increase of SO2 partial pressure in the gas mixture can improve its solubility in the ILs, while, the absorption capacity of M-PEG-functionalized ILs will decrease under a low pH value. The new ILs absorb SO2 by physical interactions at the experimental conditions under 1H NMR, FT-IR and Raman spectrum investigation. The solubility of CO2 in these ILs is lower than the solubility of SO2, therefore, the M-PEG-functionalized ILs is selectively towards SO2. Densities of the ILs increase when the ILs absorb SO2 and turn to be saturated, at same time, surface tensions decrease and viscosities lower sharply. The solidifying point dropt and viscosities decrease when molecular solvents are added into corresponding M-PEG-functionalized ILs, and the binary mixtures also can keep a certain absorption amount of SO2.