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

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. (C) 2015 Elsevier B.V. All rights reserved.