Simultaneous and exceptionally efficient removal of H2S and CO2 from CH4 by novel protic thiolate ionic liquids

Desulfurization and decarbonization are indispensable processes in natural gas upgrading. Although functionalized ionic liquids (ILs) have demonstrated potential in gas purification, their practical application is hindered by insufficient absorption capacities for H 2 S and CO 2 under low partial pressure condition. To address this limitation, a series of novel protic thiolate ILs (TILs) through acid-base neutralization reactions between organic superbases and thiols have been developed in this work. The capture performance of H 2 S, CO 2 , and CH 4 by these TILs was systematically investigated at temperatures ranging from 303.2 to 343.2 K. Notably, the representative TIL formed by 1,5-diazabicyclo [4.3.0] non-5-ene and 3-mercapto-1-propanol ([DBNH][MP]) demonstrated remarkable absorption capacities, achieving 1.42 mol/mol (6.58 mol/kg) for H 2 S and 0.95 mol/mol (4.37 mol/kg) for CO 2 at 303.2 K and 1.0 bar. Even under reduced pressure condition (0.05 bar), [DBNH][MP] maintained exceptional absorption performance, with capacities of 1.00 mol/mol for H 2 S and 0.81 mol/mol for CO 2 . Moreover, the H 2 S/CH 4 and CO 2 /CH 4 selectivities in [DBNH][MP] also reached 838 and 680 (0.05 bar H 2 S/CO 2 vs. 1.0 bar CH 4 ), respectively, surpassing those of all previously reported absorbents. To elucidate the underlying mechanisms, we conducted comprehensive characterization studies using nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopy. Density functional theory (DFT) calculations coupled with independent gradient model based on Hirshfeld partition (IGMH) analysis revealed that the exceptional gases capture performance originates from strong chemical interactions between thiolate anions (RS⁻) and the target gas molecules. These findings demonstrate that the developed TILs are promising candidates for the simultaneous removal of H 2 S and CO 2 during natural gas upgrading processes.