Solute and Solvent Transport Through Semipermeable Membranes
There have been a number of different approaches used to describe solute and solvent transport through ultrafiltration (UF) and microfiltration (MF) membranes. The Kedem-Katchalsky analysis and the Stefan-Maxwell multicomponent diffusion equations were both developed directly from the principles of irreversible thermodynamics, with the solute and solvent fluxes related to the pressure and concentration driving forces via a set of phenomenological coefficients. Solute-solute interactions can be even more significant in multicomponent systems in which the components form thermodynamically nonideal solutions. The chapter discusses the rate of solute transport across a semipermeable membrane can also be affected by nonhydrodynamic interactions. The strong dependence of the permeability on the pore radius has important implications for understanding the solvent transport characteristics of real MF/UF membranes. The electrical interactions between the solute and the pore wall can also have a dramatic effect on the rate of solute transport since they can significantly alter the solute partition coefficient.