Task-specific deep eutectic solvents for the highly efficient and selective separation of H2S

Abstract Developing environmental benign and efficient solvents for the natural gas sweetening is of great significance to the development of green chemistry. However, there is no task-specific deep eutectic solvents (DESs) for H2S absorption so far. Herein, we have for the first time developed a series of task-specific DESs for the selective separation of H2S, in which quaternary ammonium salts with free tertiary amine groups are designed as hydrogen bond acceptors (HBAs) and azoles as hydrogen bond donors (HBDs). Density, viscosity, and thermal decomposition temperature, as well as the solubility of H2S (0–1.0 bar), CO2 (0–1.0 bar), and CH4 (0–5.0 bar) were systematically determined. NMR paired with theoretical calculations are applied to characterize the interaction mechanism of H2S and DESs. A reaction equilibrium thermodynamic model (RETM) with a 1:2 stoichiometric reaction mechanism was screened to correlate H2S solubility data. It is found that [C4-TMHDA][Cl]-Im could achieve up to 0.996 mol H2S per mol DES at 303.2 K and 1.0 bar. Moreover, the captured H2S can be easily stripped out at elevated temperature and reduced pressure, with negligible loss in H2S capacities during four absorption–desorption cycles. The results obtained in this work indicate that these DESs are promising candidates for efficient and selective separation of H2S and CO2 from natural gas. This work provides novel insights into the future design of high-performance task-specific DESs for the capture of H2S.