Protic ionic liquids for the selective absorption of H2S from CO2: Thermodynamic analysis

The solubilities of H2S and CO2 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 H2S than normal ionic liquids (ILs) and the Henry's law constants of H2S in PILs (3.5–11.5 bar at 303.2 K) are much lower than those in normal ILs. In contrast, the solubility of CO2 in PILs is found to be a magnitude lower than that of H2S, implying these PILs have both higher absorption capacity for H2S and higher ideal selectivity of H2S/CO2 (8.9–19.5 at 303.2 K) in comparison with normal ILs. The behavior of H2S and CO2 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 H2S/CO2 and believed to have potential use in gas sweetening. © 2014 American Institute of Chemical Engineers AIChE J 60: 4232–4240, 2014