Activity modelling of the solid-liquid equilibrium of deep eutectic solvents

Area of Science:

• Green Chemistry
• Materials Science
• Thermodynamics

Background:

• Deep eutectic solvents (DESs) are emerging as sustainable alternatives in the chemical industry.
• DESs are binary mixtures exhibiting significant melting point depression due to strong intermolecular interactions.
• Understanding their phase behavior is crucial for their application and design.

Purpose of the Study:

• To experimentally determine phase diagrams for novel DESs with varying non-ideality.
• To evaluate the accuracy of thermodynamic models in describing DES solid-liquid equilibria.
• To correlate model parameters with the non-ideal behavior of DES mixtures.

Main Methods:

• Experimental measurement of solid-liquid phase diagrams for multiple DESs.
• Application and assessment of thermodynamic models, including the orthogonal polynomial (OP) expansion.
• Analysis of activity coefficients to understand asymmetric behavior.

Main Results:

• Presented experimental phase diagrams for various DESs, showcasing a range of non-ideality.
• Demonstrated that the orthogonal Redlich-Kister-like polynomial (OP) expansion accurately describes the solid-liquid equilibria.
• Established a link between model parameters and the observed non-ideal and asymmetric behaviors.

Conclusions:

• The modified OP expansion provides an accurate thermodynamic description of DES phase behavior.
• This model, an extension of regular solution theory, allows for physical interpretation of parameters.
• Findings facilitate the design and application of DESs by predicting their liquid range and behavior.