Density and Viscosity Modeling of Three Deep Eutectic Solvents Using a Volume-Shifted Cubic Equation of State Coupled with the Friction Theory

In this work, a three-parameter viscosity model based on the friction theory (FT) and coupled with a cubic equation of state was developed to correlate and predict the dynamic viscosity of deep eutectic solvents (DESs). The present viscosity model was derived from an existing six-parameter FT-based viscosity model, which was previously applied to pure ionic liquids. By focusing on the most dominant dragging forces affecting the viscosity of DESs, we were able to safely reduce the number of model parameters without a significant loss of model accuracy. The use of a volume-shifted cubic EoS (Soave–Redlich–Kwong or Peng–Robinson) served also to obtain improved density estimations of the DESs under study. The resulting modeling approach was successfully validated during the correlation of experimental dynamic viscosities and mass densities of three archetypal DESs (choline chloride-based DESs): reline, ethaline, and glyceline within a temperature range varying from 283.15 to 373.15 K and at pressures from 1 to 1000 bar. The average absolute relative deviations yielded by the present thermodynamic model varied from 0.27 to 0.93% for the density modeling and from 2.25 to 4.29% for the viscosity modeling of the three DESs.