Characterization of Functionalized Imidazolium Ionic Liquids and Their Application in SO2 Absorption

Two functionalized imidazolium ionic liquids (ILs) 1-(2-diethylaminoethyl)-3-methylimidazolium thiocyanate (Et(2)NEMImSCN) and 1-(2-hydroxyethyl)-3-methylimidazolium thiocyanate (HOEMImSCN) were synthesized, their thermal decomposition temperature, density, viscosity, and conductivity were determined, and their efficiency to absorb SO2 was studied. Results showed that both Et(2)NEMImSCN and HOEMImSCN had high thermal decomposition temperature as most of imidazolium-based ILs, the density and conductivity data of HOEMImSCN were higher than those of Et(2)NEMImSCN, while the viscosity data of HOEMImSCN were lower than those of Et(2)NEMImSCN. In the tested temperature range (from 303.15 to 343.15 K), the relationship of temperature and density is consistent with a linear equation, and temperature-dependent viscosity and conductivity was described by a Vogel-Tammann-Fulcher equation. Absorption processes proceeded smoothly in both ILs, and the solubility of SO2 in Et(2)NEMImSCN was 1.207 gSO(2)/gIL at 298.15K and atmosphere pressure, which is the highest capacity reported to date under the similar conditions. Et(2)NEMImSCN IL could be easily regenerated and reused at least five times with comparable efficiency. A group contribution method based on the literature data was proposed, with an AAD%=2.07, to assist researchers in predicting the solubility of SO2 in newly designed ILs.