Viscosity of imidazolium ionic liquids and mixtures of ILs from entropy scaling using the PC-SAFT and ePC-SAFT equations of state

[Display omitted] •Entropy Scaling Theory with SAFT Equations of State to correlate and predict the Viscosity of Ionic Liquids through Two Approaches.•Molecular-Based Approach uses PC-SAFT to calculate reduce entropy considering the ionic liquid (cation & anion) as a single species.•Ion-Based Approach uses ePC-SAFT considering the ionic liquid is a binary mixture of its cation & anion.•Scaling Coefficients correlate with molecular weight within cations allowing interpolation and extrapolation beyond ILs in training set.•Viscosity of mixtures of different Ionic Liquids well-predicted. Entropy scaling is a promising method for the development of engineering models for transport properties of ionic liquids (ILs). Here we present two entropy scaling models for the viscosity of ionic liquids and their mixtures at various temperatures and pressures: 1) a molecular-based approach treating each IL as one pure species and using the PC-SAFT equation of state (EoS); and 2) treating each ion as a separate species and using the ePC-SAFT EoS. Both approaches were correlated to viscosity data of 12 ionic liquids from the imidazolium cation class and three different anions comprising 4233 data points with overall average absolute deviations (%AARDs) of less than 8 % over a wide range of temperature and pressures. The ion-based approach was better able to correlate IL viscosity at low temperatures and/or high pressure (to 4011 bar) than the molecular approach. The functional entropy-scaling coefficients for both models were regressed as linear functions of molecular weight, which allowed good prediction of another nine ionic liquids not in the training set. Interestingly, both approaches well predict the viscosity of binary mixtures of imidazolium ionic liquids. In addition, the effect of various reference viscosities and comparison with the Peng-Robinson EoS was performed.