Predictive Modeling of Fluid Phase Equilibria for Systems Containing Ionic Liquids

Ionic liquids (ILs) have become popular in recent years as possible green replacements for conventional organic, volatile solvents. Potential applications that have been purported in the literature include using ILs as reaction media, electrolytes for electrochemical processes, heat transfer fluids, absorption refrigeration media, entrainers for extractive distillation, and extraction solvents among others. In order to determine an IL’s aptitude as an extraction solvent, ability as an entrainer or potential toxicity, phase equilibria of IL-containing systems must be observed or predicted. In this dissertation, the fluid phase equilibria of systems containing ILs are examined in order to gain insight into the predictive capability of conventional and electrolyte excess Gibbs energy (gE) models. Particularly, we assess the prediction quality of these models in terms of their accuracy in calculating ternary liquid-liquid equilibrium (LLE) and binary vapor-liquid equilibrium (VLE), which are compared to experimental data collected both from our research group and the literature. The models are fit to pure component and binary data, also from our group and the literature. Additionally, novel thermodynamic frameworks are derived, presented and demonstrated that allow for symmetric electrolyte reference states with complete ionic dissociation, partial dissociation and different degrees of ionic dissociation in different equilibrium phases. It’s further shown that these novel approaches allow for improved ternary LLE predictions over conventional methods for systems containing ILs and water. Furthermore, n-octanol/water partion coefficients are calculated as an assessment of toxicity for several ILs. Heuristic oriented discussion directs the modeler to an effective model and thermodynamic framework for accurate ternary LLE prediction subject to the system’s components and experimental data available.