Study on the salting effect of choline chloride on aqueous solutions of imidazolium-based ionic liquids via the isopiestic measurements

Abstract

In this work, the vapor-liquid equilibrium behavior of aqueous ternary systems composed of choline chloride (ChCl) and imidazolium-based ionic liquids has been investigated using the isopiestic method at 25 °C. The ionic liquids used are 1-butyl-3-methylimidazolium bromide ([C4mim][Br]) and 1-butyl-3-methylimidazolium trifluoromethane sulfonate ([C4mim][CF3SO3]). The effect of ionic liquid anion on water activity, vapor pressure, and isopiestic equilibrium concentrations has been evaluated. The deviation of water iso-activity curves from the linear isopiestic relation has been used as a benchmark to unveil the salting-out or salting-in effect of ChCl on the aqueous solution of ionic liquids. The results show that ChCl plays the role of co-solvent in the studied systems and increases the solubility of the ionic liquids in water, indicating the occurrence of the salting-in phenomenon.

Keywords

• choline chloride
• imidazolium-based ionic liquids
• isopiestic
• salting-in effect