Title: Phase Equilibria and Transport Properties of Gas-Saturated Ionic Liquids

Abstract: Hydrofluorocarbons (HFCs), widely used in the refrigeration and cooling industry, are potent greenhouse gases that are now subject to phase-down legislation due to their high global warming potential (GWP). However, HFC blends, which often form azeotropes, cannot be separated using conventional distillation methods. Extractive distillation with ionic liquids (ILs) as entrainers has demonstrated significant promise in effectively separating these azeotropic mixtures. This work focuses on assessing key thermodynamic and transport properties critical for these separation processes. The properties investigated include phase behavior, single- and multicomponent absorption, density, viscosity, thermal conductivity, interfacial tension, electrical conductivity, and self-diffusivity. We evaluate the applicability of various predictive and empirical models, noting significant deviations from those commonly integrated into process simulation software like Aspen Plus. Such deviations can have major implications for unit design. We propose enhancements to these models, including extended versions of the Eyring-NRTL model for viscosity, aimed at improving process simulations and optimizing unit design. High-pressure spectroscopy and scattering techniques reveal the critical role of molecular interactions and charge ordering in influencing macroscopic properties. These insights provide a more detailed understanding of the molecular phenomena driving the anomalous behaviors of IL-based mixtures, ultimately supporting the development of more targeted design strategies for IL-based separation technologies.