Improving SO2 capture by tuning functional groups on the cation of pyridinium-based ionic liquids

Abstract

In this work, three kinds of novel functionalized ionic liquids (ILs) [NEt₂C₂Py][SCN], [C₄OPy][SCN] and [C₄CNPy][SCN] were developed by introducing a tertiary amino group, ether group and nitrile group on the pyridinium cation to improve SO₂ absorption performances. Among the investigated ILs, [NEt₂C₂Py][SCN] showed the highest absorption capacity of 1.06 gSO₂ gIL⁻¹ under ambient conditions due to a combination of chemical and physical absorption. By contrast, the enhancement in SO₂ capacity by [C₄CNPy][SCN] and [C₄OPy][SCN] is mainly ascribed to the stronger physical interaction between ILs and SO₂ than the conventional IL [C₄Py][SCN]. Meanwhile, higher SO₂/CO₂ selectivity was also obtained using these functionalized ILs, which was increased up to 41% comparing with that of [C₄Py][SCN]. Moreover, the effect of water on SO₂ capacity and the absorption mechanism were studied. The results indicated that the presence of water caused a slight decrease in SO₂ capacity of [C₄CNPy][SCN] and [C₄OPy][SCN] because of physical absorption, whereas a slight increase in SO₂ capacity by [NEt₂C₂Py][SCN] due to the formation of hydrogen sulfite salts through chemical absorption. In addition, three kinds of cation-functionalized ILs could remain the stable absorption performance after five cycles of absorption and desorption, implying these ILs show great potentials for SO₂ capture.