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

Abstract Natural gas upgrading requires efficient separation of H 2 S from CO 2 , another acidic impurity, to enhance gas utilization efficiency and enable resource recovery from waste streams. While significant advancements have been achieved in separating H 2 S from CH 4 , the selective removal of H 2 S from CO 2 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 H 2 S, 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 H 2 S. Dispersion‐corrected DFT calculations revealed that the nucleophilic addition products facilitate secondary H 2 S capture through two distinct approaches: 1) conformational matching and 2) dissociation of H 2 S into [HS]⁻ species. The unique cascade H 2 S sorption mechanism demonstrates exceptional affinity for H 2 S, endowing the [6ca]‐derived ILs with unprecedented high H 2 S capacities and record‐breaking H 2 S/CO 2 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 H 2 S/CO 2 separation with significant potential for natural gas valorization.