Prediction of Diffusion Coefficients in Liquid Systems

On the basis of Eyringʹs absolute reaction rate theory, a new model for the Maxwell-Stefan diffusivity has been developed. This model, an extension of the Vignes equation, describes the concentration dependence of the diffusion coefficient in terms of the diffusivities at infinite dilution and an additional excess Gibbs energy contribution. This energy part allows the explicit consideration of thermodynamic nonidealities within the modeling of this transport property. If the same set of interaction parameters, which has been derived from vapor-liquid equilibrium (VLE) data, is applied for this part and for the thermodynamic correction, a theoretically sound modeling of VLE and diffusion can be achieved. The influence of viscosity and thermodynamics on the model accuracy is thoroughly investigated. For this purpose, diffusivities of 85 binary mixtures consisting of alkanes, cycloalkanes, halogenated alkanes, aromatics, ketones, and alcohols are computed. The average relative deviation between experimental data and computed values is approximately 8% depending on the choice of the gE model. These results indicate that this model is superior to some widely used methods.