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. (c) 2014 American Institute of Chemical Engineers AIChE J 60: 4232-4240, 2014