(21e) PC-SAFT Parametrization for Ionic Liquids from Density and Viscosity Data Using Entropy Scaling

Ionic liquids are seen as promising candidates for a variety of engineering applications. However, irrespective of the specific use case, successful design of ionic liquid-based processes hinges on a precise description of their transport properties. Many different empirical and semi-empirical models have been applied in the correlation of ionic liquid’s viscosity.

Entropy scaling is a promising semi-empirical approach for the development of engineering models for transport properties. It has been used to correlate transport properties throughout the whole fluid region (gas, liquid, and supercritical conditions) for a wide range of common substances.

Our group has recently reported two different entropy scaling models for the viscosity of a class of ionic liquids and their mixtures: an ion-based approach using the ePC-SAFT equation of state, and a molecular-based approach using the PC-SAFT equation of state (Melfi and Scurto, Journal of Molecular Liquids 401 (2024) 124500).

Interestingly, when developing entropy scaling models for the viscosity of ionic liquids using the PC-SAFT equation of state, we have identified systematic deviations at high pressures (above approximately 500 bar). Such high-pressure deviations are much less pronounced when the ePC-SAFT equation of state is used.

Traditionally, entropy scaling models are developed based upon an equation of state that has been previously regressed to describe thermodynamic properties of the pure fluid. Ionic liquids present extremely small vapor pressures, and, therefore, density data is typically used by itself in their parametrization of SAFT models.

In this work, we include high pressure viscosity data in the ionic liquid PC-SAFT parameter regression in an attempt to remedy the systematic high-pressure deviations in the entropy scaling model for viscosity. The performance of the new parametrization approach is contrasted to some previously published PC-SAFT parameters in the description of liquid density, potential for entropy scaling models for viscosity, and predictive capacity for other thermodynamic properties and binary phase equilibrium.