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.