Hydrophobic protic ionic liquids tethered with tertiary amine group for highly efficient and selective absorption of H₂S from CO₂

Abstract

Developing absorbents with both high absorption capacity of H 2 S and large selectivity of H 2 S/CO 2 is very important for natural gas sweetening process. To this end, a class of novel hydrophobic protic ionic liquids (ILs) containing free tertiary amine group as functional site for the absorption of H 2 S were designed in this work. They were facilely synthesized through a simple neutralization‐metathesis methodology by utilizing diamine compounds and bis(trifluoromethylsulfonyl)imide as the building blocks for cation and anion, respectively. Impressively, the solubility of H 2 S can reach 0.546 mol mol −1 (1 bar) and 0.225 mol mol −1 (0.1 bar), and the selectivity of H 2 S/CO 2 can reach 37.2 (H 2 S solubility at 1 bar vs. CO 2 solubility at 1 bar) and 15.4 (H 2 S solubility at 0.1 bar vs. CO 2 solubility at 1 bar) in the hydrophobic protic ILs at 298.2 K. Comparing the hydrophobic protic ILs with other absorbents justifies their superior performance in the selective absorption of H 2 S from CO 2 . © 2016 American Institute of Chemical Engineers AIChE J , 62: 4480–4490, 2016