Predicting the degree of dissociation of ionic liquids in binary mixtures with PDH+UNIQUAC

Abstract

The interest in ionic liquids (ILs) as replacements for more hazardous solvents has been growing over the last years, especially in industrial synthesis and liquid-liquid separations. Consequently, it is important to study their degree of dissociation (α), which quantifies the ratio of IL molecules dissociated into their ions and significantly influences viscosity, density, and surface tension. In this work, the dissociation degree of ILs in binary mixtures was predicted based on liquid-liquid equilibria (LLE) data. To do so, the UNIversal QUAsi-Chemical (UNIQUAC) model, which describes short-range interactions, was combined with the Pitzer-Debye-Hückel (PDH) equation, which accounts for long-range interactions. In total, 31 systems comprising 15 different ionic liquids and 4 solvents (water, ethanol, 1-propanol and 1-butanol) were studied. The degree of dissociation as function of the systems' composition was determined by thermodynamic modelling and the results presented a low deviation from the experimental data available in literature, validating this novel approach.