Practical friction‐based approach to modeling multicomponent diffusion

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Abstract
Although most industrial drying and separation technologies are based on transport of multiple components, a convenient and practical means of describing multicomponent diffusion over wide temperature and concentration ranges has not been developed for polymer solutions or even for simple liquid mixtures. We have been able to demonstrate that all of the diffusion coefficients required to describe molecular transport in multicomponent systems can be easily predicted from self‐diffusion coefficients and thermodynamic information when the mass flux with respect to the mass‐average velocity is expressed in terms of the frictional force experienced by a molecule as it undergoes Brownian motion. This approach enables the flux equations for any combination of materials to be written in terms of experimentally measurable quantities. The model was tested by: (1) predicting literature data for principal diffusion coefficients in a ternary system; (2) applying the diffusion model to predict the drying behavior of three ternary systems; (3) predicting experimental values of the principal and cross coefficients for a ternary organic solvent mixture from self‐diffusion data measured by PFG‐NMR and available thermodynamic data; and (4) examining whether the limiting cases in this model are physically realistic. The applicability of the model to gas transport and polymer interdiffusion is also briefly examined.