Temperature-dependent phase behavior of ionic liquid solutions containing N-butylpyridinium nitrate, water, and either sodium or ammonium citrate

• We study phase behavior of [BPy]NO3 + Salt + H2O systems at various temperature.
• Good agreements have been obtained with several empirical expressions.
• Salting-out ability is Na3C6H5O7 > (NH4)3C6H5O7.
• The cation effect of organic salt has been further studied.

The aim of this work was to investigate the biphasic systems equilibrium behavior of solutions of N-butylpyridinium nitrate and either sodium citrate or ammonium citrate to understand their liquid–liquid equilibrium and the salting-out ability of these citrate salts. For this purpose, phase diagrams and liquid–liquid equilibrium data of the investigated biphasic systems were determined experimentally from 298.15 K to 328.15 K. The binodal curves were then fit to an empirical nonlinear expression developed by Merchuk and to other models. The tie lines were also described by four equations. The results demonstrated that temperature has little influence on the phase behavior and the liquid–liquid equilibrium within the investigated temperature range. The factors that affect the binodal curves, such as the salts, were also investigated. The salting-out ability, described by the effective excluded volume, of sodium citrate was greater than that of ammonium citrate, which may be related to the Gibbs free energy of hydration for the involved ions.