ABSTRACT
This paper gives a model of membrane transport based on the thermodynamics of irreversible processes (TIP). The membrane is considered as a single phase in which the fluxes of permeants are driven by their gradients of chemical (or electrochemical) potentials. The membrane material itself is considered as the "solvent" in the membrane phase. In the steady state, the gradients of chemical (or electrochemical) potentials
of the permeant species are assumed to be constant through the membrane phase. This allows to define mean phenomenological coefficients in the membrane. These last coefficients account for the various interactions between all the components present in the membrane. They depend on the mean concentrations of permeants in the membrane and consequently, through a local equilibrium hypothesis at both membrane surfaces, they are related to the composition of the neighboring phases. Ultrafiltration and pervaporation data are analyzed in terms of this TIP approach. A major insight is then obtained in the understanding of the membrane resistance in terms of interactions between membrane-permeants and permeants-permeants.
