Efficient purification of halide-based ionic liquids by means of improved apparatus for continuous liquid-liquid extraction

Abstract

The purity level of Ionic liquids (ILs) is a question of immense importance both from fundamental and applied standpoint. In order to improve the purification process of halide-based ILs, the latter being starting materials for the synthesis of a vast number of other ILs, we constructed an apparatus for continuous liquid-liquid extraction to be used as a tool for purification after the quaternisation step. The apparatus employs the heat of the evaporating solvent to heat up the extraction chamber, thus allowing the liquid-liquid extraction to be conducted at elevated temperature. The latter improves the process efficiency due to facilitated mass transfer. The purification carried out with this tool proved successful in the removal of impurities such as residual starting compounds (N-methylimidazole and haloalkanes) under mild conditions and was shown to give ILs of high purity for considerably reduced consumption of organic solvent and technological time.