Characterization of caprolactam based eutectic ionic liquids and their application in SO2 absorption

► Five caprolactam (CPL) based eutectic ionic liquids (EILs) were prepared and characterized. ► The conductivity and the viscosity of CPL-imidazole (1:1) at 30 °C are 32.3 μs/cm and 48.6 mPa·s respectively. ► SO2 absorption capacity at 30 to 70 °C and 1 atmospheric pressure of pure gas was investigated. ► The solubility of SO2 in CPL-acetamide (1:1) is 0.497 g/g of mass fraction at 30 °C and the absorption is reversible. ► The absorption in CPL-acetamide may probably follow a physical process by 1H NMR analysis.