Solubility of Halogenated Hydrocarbons in Hydrophobic Ionic Liquids: Experimental Study and COSMO-RS Prediction

Halogenated hydrocarbons are members of priority water contaminants because of their negative health and environmental impacts. In this study, the solubility of three halogenated hydrocarbons, namely, carbon tetrachloride, chloroform, and bromoform was measured in 12 hydrophobic ionic liquids (ILs) for temperature ranging between 25 and 45 °C. We investigated the chemical structure and alkyl chain length effect of three different cations (piperidinium, pyrrolidinium, and ammonium-based) paired with bis(trifluoromethylsulfonyl)imide anion. It was found that carbon tetrachloride and bromoform are partially miscible in all tested ILs while chloroform exhibits full miscibility. For ammonium based ionic liquids, the solubility increases with the increase of the cation molecular weight and alkyl chain length. The results indicate that the solubility of the studied halogenated hydrocarbons in methyltrioctylammonium bis(trifluoromethylsulfonyl)imide, octyltriethylammonium bis(trifluoromethylsulfonyl)imide, and 1-octyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)-imide is substantial. These results confirm the potential use of ionic liquids as powerful alternative solvents for wastewater treatment. Finally, the predictive capability of COSMO-RS model provided excellent qualitative agreement with experimental data both for temperature dependence and for cations structure effect.