Efficient Hydrogen Sulfide Separation from Carbon Dioxide Achieved by Carbonyl‐Functionalized Ionic Liquids for Natural Gas Upgrading

Natural gas upgrading requires efficient separation of H₂S from CO₂, another acidic impurity, to enhance gas utilization efficiency and enable resource recovery from waste streams. While significant advancements have been achieved in separating H₂S from CH₄, the selective removal of H₂S from CO₂ remains a formidable challenge due to their similar physicochemical properties. Herein, we report a breakthrough strategy utilizing reversible nucleophilic addition reaction between carbonyl group and H₂S, departing from conventional acid-base interaction-based liquid-phase capture processes. Through comprehensive characterization using nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopy, we confirmed the formation of nucleophilic addition products between the designed carbonyl-functionalized ionic liquids (ILs) and H₂S. Dispersion-corrected DFT calculations revealed that the nucleophilic addition products facilitate secondary H₂S capture through two distinct approaches: 1) conformational matching and 2) dissociation of H₂S into [HS]⁻ species. The unique cascade H₂S sorption mechanism demonstrates exceptional affinity for H₂S, endowing the [6ca]-derived ILs with unprecedented high H₂S capacities and record-breaking H₂S/CO₂ selectivities (67-89 at 1.0 bar and 229-319 at 0.1 bar), surpassing previously reported values. Combined with energy-efficient regeneration cycles, these findings establish a new paradigm for H₂S/CO₂ separation with significant potential for natural gas valorization.