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(n)mim(+) , with alkyl substitutions of varying chain length, where C-n = C-2 (ethyl), C-4 (butyl), C-6 (hexyl), and C-8 (octyl), in combination with bis(trifluoromethanesulfonyl)imide, NTf2- , and bis(perfluoroethanesulfonyl)imide, BETI- , anions. Hydrophilic compounds were also studied, with bromide anions and C-n mim(+) and 1-C-n-2, 3-methylimidazolium, C-n bmim(+) , cations, where C-n = C-12 , C-14 and C-16 are solids at room temperature, and C-n = C-8 , C-9 , and C-10 are liquids.