A kinetic approach for predicting diffusivities in dense fluid mixtures

In this work, the Enskog solution of the Boltzmann equation coupled with the Weeks–Chandler–Andersen perturbation theory of liquids is shown to be an excellent approach for correlating and predicting self-diffusivities of dense fluids. Afterwards, this theory is used to estimate mutual-diffusion coefficients of solutes at infinite dilution in sub- and supercritical solvents. The approach presented here is based on the smooth hard-sphere theory, in which the coupling factor of the rough hard-sphere theory relating translational and rotational motions is made unity, and using the Speedy correlation which has been proposed as a model of self-diffusion coefficient of hard-sphere fluids. The methodology presented here only makes use of pure component information and density of mixtures affording predictions without any binary adjustable parameters. Since the behavior of mutual-diffusion coefficients in the proximity of a binary critical point is of great interest, calculations were also accomplished in the liquid phase along the gas–liquid boundary when experimental data of both binary vapor–liquid equilibrium and densities of mixture were available.