Theoretical and experimental comparison of the Soret effect for binary mixtures of toluene and n-hexane, and benzene and n-heptane

Thermodiffusion along with molecular diffusion occurs in many engineering systems and in nature. Thermodiffusion has a great effect on concentration distribution in binary mixtures. A new approach to predicting the Soret coefficient in binary mixtures of linear chain and aromatic hydrocarbons using the thermodynamics of irreversible processes is presented. In particular, this approach is based on free volume theory, which explains the diffusivity in diffusion-limited systems. Free volume states that the transfer kinetics of molecules depends greatly on molecular size and shape. The proposed model, combined with Shukla and Firoozabadi's model, was applied to predict the Soret coefficient. The perturbed chain statistical associating fluid theory equation of state (PCSAFT-EoS) was used to calculate the related thermodynamic properties. Comparisons of the theoretical results with experimental data show good agreement.