Diffusion Coefficients of a Highly Nonideal Ternary Liquid Mixture: Cyclohexane-Toluene-Methanol

To better understand diffusion phenomena in highly nonideal ternary liquid mixtures, cyclohexane-toluene-methanol is studied by equilibrium molecular dynamics (EMD) simulation. Intradiffusion and Maxwell-Stefan (MS) diffusion coefficients, being strictly kinetic properties, are predicted by EMD over the entire composition range at ambient conditions. The thermodynamic contribution to the Fick diffusion coefficients is studied with an excess Gibbs energy model. Predictive results from the combination of these two approaches are in convincing agreement with experimental Fick diffusion coefficient data. Different aspects determining the composition dependence of diffusion coefficients, such as their behavior at the binary limits, hydrogen bonding, and stability criteria, are discussed. While the intradiffusion coefficients exhibit only a weak composition dependence, the MS diffusion coefficients are strongly affected by the nonideality of the present mixture. Fick diffusion coefficients reveal pronounced diffusive coupling effects and are mainly governed by the thermodynamic contribution, especially in the vicinity of the miscibility gap.