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

Abstract

• A series of novel tertiary amine functionalized DESs were firstly developed. • [C 4 -TMHDA][Cl]-Im can achieve 0.996 mol H 2 S per mol DES at 303.2 K and 1.0 bar. • The ideal selectivities of H 2 S/CO 2 and H 2 S/CH 4 were 12.1 and 215, respectively. • These DESs can be reused for five times with negligible performance loss. 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 H 2 S absorption so far. Herein, we have for the first time developed a series of task-specific DESs for the selective separation of H 2 S, 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 H 2 S (0–1.0 bar), CO 2 (0–1.0 bar), and CH 4 (0–5.0 bar) were systematically determined. NMR paired with theoretical calculations are applied to characterize the interaction mechanism of H 2 S and DESs. A reaction equilibrium thermodynamic model (RETM) with a 1:2 stoichiometric reaction mechanism was screened to correlate H 2 S solubility data. It is found that [C 4 -TMHDA][Cl]-Im could achieve up to 0.996 mol H 2 S per mol DES at 303.2 K and 1.0 bar. Moreover, the captured H 2 S can be easily stripped out at elevated temperature and reduced pressure, with negligible loss in H 2 S 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 H 2 S and CO 2 from natural gas. This work provides novel insights into the future design of high-performance task-specific DESs for the capture of H 2 S.