Highly efficient and selective H2S capture by task-specific deep eutectic solvents through chemical dual-site absorption

Highly efficient and selective H2S capture is of great scientific significance for natural gas sweetening. However, there was seldom research concerned about the chemical absorption of H2S in deep eutectic solvents (DESs) and the absorption capacity is hard to be satisfactory. In this work, we propose a new strategy of designing task-specific DESs endowed with chemical dual sites for H2S capture. Therefore, four task-specific DESs bearing with tertiary amine and acetate anion, including [C1-TMHDA]Ac-MDEA (1:2), [C1-TMHDA]Ac-Pyrol (1:2), [C1-TMHDA]Ac-AA (1:2), and [C1-TMHDA]Ac-Im (1:2), were designed and prepared. Among them, [C1-TMHDA]Ac-MDEA (1:2) showed the unprecedented H2S absorption capacity of 1.44 mol/mol at 313.2 K and 1.0 bar, surpassing all the reported absorbents. The interaction mechanism was elucidated by both spectroscopic analysis and quantum chemical calculations. In addition, five consecutive absorption–desorption cycles were performed and evaluated the recyclability of [C1-TMHDA]Ac-MDEA (1:2) by heating and evacuating. Compared with other absorbents, these task-specific DESs represent prominent superiority on both H2S absorption capacity and H2S/CO2 selectivity, which are expected to be excellent alternatives in the field of acid gas separation.