Modeling the thermodynamic and physical properties of Deep Eutectic Solvents

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The objective of the proposed research program is to develop models for the thermodynamic (mainly phase diagram) and physical (mainly density and viscosity) properties of ternary systems of Deep Eutectic Solvents. The latter have been receiving increasing attention since, compared with "ionic liquids" (which are usually composed of a large organic cation and an inorganic anion, and melt at relatively low temperatures), they are cheaper to produce, less toxic and often biodegradable. For instance, they may be used as solvents for biocatalysis, organic synthesis, and dissolution and extraction processes. A typical binary Deep Eutectic Solvent consists of a mixture of a Hydrogen Bond Acceptor (HBA) - usually a quaternary ammonium salt such as choline chloride - and a Hydrogen Bond Donor (HBD) such as an amide, a carboxylic acid or an alcohol. For the thermodynamic model, the CALPHAD (CALculation of PHAse Diagrams) method will be used. It consists in developing Gibbs energy functions, calibrated on experimental data, for every phase in a chemical system, as a function of temperature, pressure and composition. Then, the combination and composition of phases corresponding to a global energy minimum is found. Models for the density and viscosity of multicomponent inorganic molten salts and "ionic liquid" mixtures of industrial interest, both linked to the thermodynamic model that gives an estimation of the structure of the melt, were previously developed. These models can then be used to estimate the properties of multicomponent salts from the assessed binary (and sometimes ternary) parameters, using standard interpolation techniques. The same methodology will be applied to various ternary Deep Eutectic Solvents, such as choline chloride-ZnCl2-HBA, choline chloride-HBA-HBD, choline chloride-ZnCl2-HBD, and choline chloride-HBD1-HBD2 (where HBA is a quaternary ammonium salt). The thermodynamic and physical property models will be calibrated on both data from the published scientific literature and newly obtained measurements (structural data, phase diagram, density, and viscosity). Using the developed models and databases, one will be able to search for and calculate automatically ternary Deep Eutectic Solvent compositions corresponding to a range of values of the liquidus temperature, density and viscosity, thus permitting to target specific industrial applications while avoiding an extremely tedious and costly trial and error experimental approach. Although Deep Eutectic Solvents emerged only about 15 years ago, they have numerous potential industrial applications, including the dissolution of lignin and the decontamination of recovered paper. A current objective of the scientific community through their use is to achieve a 40% reduction of energy use and an 80% reduction of CO2 emissions in pulp and papermaking, which is of prime importance in Canada.