Predicting the ionicity of ionic liquids in binary mixtures based on solubility data: II

Abstract

Ionic liquids (ILs) have been deeply investigated as possible substitutes for hazardous organic solvents, but their recently acknowledged ionicity, together with their generally high viscosity, has been hampering their further application. The ionicity (or degree of dissociation) of electrolytes affects properties such as viscosity, solubility and density, so it is of the utmost importance for the proper thermodynamic description of systems containing electrolytes. However, the experimental quantifications of this property are difficult to perform, which creates the need for more predictive approaches. In this work, the ionicity of 12 ionic liquids in binary mixtures composed of water, ethanol, 1-propanol or 1-butanol was predicted based on solubility data available in liter-ature by the Pitzer-Debye-Huckel (PDH) equation combined with the UNIversal QUAsi-Chemical (UNIQUAC) model, which is often referred as PDH+UNIQUAC. The ionicity of the ionic liquids was modelled as function of mole composition for a total of 17 binary systems, comprising ILs of three chemical families: hexa-fluorophosphates, tetrafluoroborates, and bis(trifluoromethylsulfonyl)imides, continuing a previous work. This novel methodology provided a useful tool to estimate the ionicity of ionic liquids containing imidazolium cations without undergoing long experimental determinations, which could be applied in the design of separation processes.