High-Pressure Solid–Liquid Equilibrium and Volumetric Behavior of Choline Chloride-Based Eutectic Solvents

Over the past two decades, eutectic solvents (ESs) have attracted attention due to their potential in various fields, from chemical processing to materials science. Despite this growing interest, their use is still restricted to fixed stoichiometric mole ratios. This limitation arises from the difficulty in accurately identifying eutectic compositions, a consequence of the scarcity of reliable thermophysical property data. In particular, properties such as density and solid–liquid equilibrium (SLE) remain poorly documented in the literature, especially under elevated pressure. In this context, this work reports SLE and volumetric data for mixtures of choline chloride with four hydrogen-bond donors: ethylene glycol, glycerol, 1,3-propanediol, and glycolic acid. SLE measurements were performed in the pressure range between 6 MPa and 25 MPa and compared with available data at atmospheric pressure. Density measurements were carried out for the ESs at their eutectic compositions over ranges of pressure (5 MPa to 50 MPa) and temperature (293.15 K to 353.15 K). The experimental density data were correlated using the modified Tammann–Tait equation, yielding average relative deviations below 0.45 %. Based on the fitted parameters, the isothermal compressibility ( κT κ T ) and the isobaric thermal expansivity ( αT α T ) were calculated. Both properties exhibited dependence on pressure and temperature, in agreement with the behavior of incompressible liquid systems. This study enlarges the thermodynamic database of ChCl-based ESs by providing the first high-pressure SLE data along with new volumetric measurements. These results improve the understanding of ES phase behavior and offer valuable inputs for thermodynamic modeling, process design, and the development of ES-based applications.