Salting-out effects in aqueous ionic liquid solutions: cloud-point temperature shifts

Area of Science:

• Physical Chemistry
• Solution Chemistry

Background:

• Ionic liquids (ILs) are versatile solvents with tunable properties.
• Understanding phase behavior of ILs in aqueous solutions is crucial for separation processes.
• 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF(4)]) is a model IL used in various applications.

Purpose of the Study:

• To investigate the impact of inorganic salts on the liquid-liquid phase diagram of [bmim][BF(4)] aqueous solutions.
• To quantify the salting-out effects induced by NaCl, Na(2)SO(4), and Na(3)PO(4).
• To correlate the observed phase behavior with salt properties like ionic strength and hydration free energy.

Main Methods:

• Preparation of aqueous solutions of [bmim][BF(4)] with varying concentrations of inorganic salts.
• Determination of liquid-liquid (L-L) phase diagrams by measuring demixing temperatures.
• Analysis of salt effects based on ionic strength and Gibbs free energy of hydration.

Main Results:

• All three investigated inorganic salts (NaCl, Na(2)SO(4), Na(3)PO(4)) induced significant salting-out effects.
• The addition of these salts caused upward shifts in the L-L demixing temperatures.
• The magnitude of the temperature shift was dependent on salt concentration and its water-structuring ability.

Conclusions:

• Inorganic salts effectively modify the phase behavior of [bmim][BF(4)] aqueous solutions.
• Salting-out effects are governed by the ionic strength and hydration properties of the salts.
• The findings provide insights for designing separation processes involving ionic liquids and inorganic salts.