Characterization of amide–thiocyanates eutectic ionic liquids and their application in SO2 absorption

Abstract

Five inorganic salts based eutectic ionic liquids (EILs), acetamide–KSCN (3 : 1), caprolactam (CPL)–KSCN (3 : 1), acetamide–NH4SCN (3 : 1), CPL–NH4SCN (3 : 1) and urea–NH4SCN (3 : 2) were prepared and characterized. These EILs showed similar properties to traditional ionic liquids, such as low melting point, low viscosity, high density, high conductivity and wide liquid range. The density increases linearly with the increase of temperature, the temperature dependence of conductivity and viscosity are described by VTF equations. The solubility of SO2 in these EILs is quite high, for example, the solubility of SO2 in acetamide–KSCN (3 : 1) is 0.588 g g−1 of mass fraction, corresponding to 0.838 mol/mol of mole fraction (according to amide molar loading) at 20 °C and 1 atm. The relationship between solubility and temperature is well fitted with a second-order polynomial equation. The absorbed SO2 was easily removed at 70 °C under vacuum and the recovered EIL could be directly reused for at least 5 times with comparable absorption efficiency. The absorption may probably follow a physical process from 1H NMR characterization results.