Accurate description of thermophysical properties of Tetraalkylammonium Chloride Deep Eutectic Solvents with the soft-SAFT equation of state

The potential to reduce the environmental impact in industrial processes has led to investigations on greener solvents for a variety of applications that conventionally use organic compounds. In recent years, Deep Eutectic Solvents (DESs) have emerged as a promising new class of solvents and have opened a new field of research. DESs are systems formed from an eutectic mixture of Lewis or Brønsted acids and bases, which can contain a variety of anionic and/or cationic species. Due to a strong hydrogen-bonding effect, their melting point is significantly lower than the melting point of the individual components. DESs are non-volatile, biodegradable and do not react with water, becoming potential candidates for a wide variety of applications. Their inexpensive synthesis is an additional advantage versus other compounds. Unfortunately, the mechanisms behind their physicochemical properties are still not well understood. Consequently, there are almost no available theoretical models able to accurately capture the main physicochemical properties of these compounds. In this work, a novel methodology based on the soft-SAFT statistical mechanics-based equation of state is used to propose different molecular models of variable complexity to describe the density, surface tension, viscosity, and CO₂ solubility of several Tetraalkylammonium Chloride based DESs. Two approaches are explored: treating the DESs as a pseudo-pure compound or describing them as a mixture of two independent constituents. The transferability of the molecular parameters between DESs to describe their thermodynamic behavior is checked in order to predict the properties of new possible DESs and their mixtures if experimental data are not available. A very good description of the density, surface tension, viscosity and gas solubility is found in all cases. This methodology provides a new platform to qualitatively screen multiple physicochemical properties of new DESs in a rapid, efficient and reliable manner.