Selective Separation of Hydrogen Sulfide with Pyridinium-Based Ionic Liquids

In this work, pyridinium-based ionic liquids (ILs) were prepared and showed excellent performance in selective separation of H₂S owing to existing active proton in H₂S molecule. A series of pyridinium-based ILs were synthesized and characterized, and their physical properties including density, viscosity, and thermal decomposition temperatures as well as H₂S separation performances were systematically studied. The results indicated that the solubilities of H₂S and CO₂ in ILs increased significantly with increasing pressure and decreased with increasing temperature, while slightly increased with the growing length of the alkyl chains on the cations. On the basis of the analysis of experimental results, the molar solubility of H₂S in these ILs declined following the order: [C₈Py]­[SCN] > [C₆Py]­[SCN] > [C₄Py]­[SCN] > [C₄Py]­[NTf₂] > [C₄Py]­[NO₃] > [C₄Py]­[BF₄]. Further, the results revealed that the Henry’s law constants of H₂S in the corresponding ILs were much lower than those of CO₂, indicating that the ILs could effectively and selectively separate H₂S. Among the studied ILs with the same cation, [C₄Py]­[SCN] had the highest H₂S/CO₂ selectivity up to 8.99 at 303.15 K, which was about 1.5–4 times larger than that of the conventional imidazolium-based ILs. Moreover, the [C₄Py]­[SCN] could also keep the stable absorption performance after five consecutive absorption and desorption cycles, implying that ILs could serve as good absorbents for H₂S separation application