Room-Temperature ionic liquids in liquid-liquid extraction: Effects of solubility in aqueous solutions on surface properties

The potential of room-temperature ionic liquids for use in chemical separations was assessed, particularly for liquid-liquid extraction. The solubility, surface tension, and electrical conductivity of a range of imidazolium-based ionic liquids in aqueous solution were measured at room temperature and atmospheric pressure as functions of ionic-liquid, sodium chloride, and potassium-chloride concentrations. Hydrophobic ionic liquids were studied, including 1-C_n -3-methylimidazolium cations, C_nmim⁺, with alkyl substitutions of varying chain length, where C_n=C₂ (ethyl), C₄ (butyl), C₆ (hexyl), and C₈ (octyl), in combination with bis(trifluoromethanesulfonyl)imide, NTf₂^-, and bis(perfluoroethanesulfonyl)imide, BETI^-, anions. Hydrophilic compounds were also studied, with bromide anions and C_nmim⁺ and 1-C_n-2, 3-methylimidazolium, C_nbmim⁺, cations, where C_n=C₁₂, C₁₄ and C₁₆ are solids at room temperature, and C_n=C₈, C₉, and C₁₀ are liquids.