Protic ionic liquids for the selective absorption of H 2 S from CO 2 : Thermodynamic analysis

The solubilities of H 2 S and CO 2 in four protic ionic liquids (PILs)—methyldiethanolammonium acetate, methyldiethanolammonium formate, dimethylethanolammonium acetate, and dimethylethanolammonium formate were determined at 303.2–333.2 K and 0–1.2 bar. It is shown PILs have higher absorption capacity for H 2 S than normal ionic liquids (ILs) and the Henry's law constants of H 2 S in PILs (3.5–11.5 bar at 303.2 K) are much lower than those in normal ILs. In contrast, the solubility of CO 2 in PILs is found to be a magnitude lower than that of H 2 S, implying these PILs have both higher absorption capacity for H 2 S and higher ideal selectivity of H 2 S/CO 2 (8.9–19.5 at 303.2 K) in comparison with normal ILs. The behavior of H 2 S and CO 2 absorption in PILs is further demonstrated based on thermodynamic analysis. The results illustrate that PILs are a kind of promising absorbents for the selective separation of H 2 S/CO 2 and believed to have potential use in gas sweetening. © 2014 American Institute of Chemical Engineers AIChE J 60: 4232–4240, 2014