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 CO, 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: [CE6Py][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.