Dual Lewis Base Functionalization of Ionic Liquids for Highly Efficient and Selective Capture of H₂ S

Three dual Lewis base functionalized ionic liquids (DLB-ILs) tethered with both carboxyl and tertiary amine groups on their anions were designed for highly efficient and selective absorption of H₂ S. It was found that the DLB-ILs could reversibly absorb 0.39-0.84 mol of H₂ S per mole of IL at 1 bar and 60 °C, which is significantly higher than that of other ILs. On the contrary, the CO₂ absorption in this class of DLB-ILs was shown to be quite limited relative to H₂ S owing to the coupling effect of the two Lewis base groups. It is the dual Lewis base functionalization that enables the significantly high values calculated for the ideal absorption selectivity for H₂ S/CO₂ , that is, 13-26 at 1 bar and 29-70 at 0.1 bar (60 °C). The selectivity even goes up to >100 at low pressures and high temperatures. It was further illustrated from DFT calculations and spectroscopy studies that the cooperation interaction of carboxyl⋅⋅⋅H₂ S⋅⋅⋅amine and the reduced binding with CO₂ were the major contributions to the high H₂ S absorption capacity and H₂ S/CO₂ selectivity.