A Numerical Study of the Apparent Selectivity in the Fractionation of Two Macromolecules by Ultrafiltration

Abstract

The fractionation of two macromolecules by ultrafiltration in a parallel plate cell was studied by computational fluid dynamics (CFD). The in-house code developed takes on account of the pressure drop, the variation of the permeate velocity along the cell, the concentration polarization over the membrane, and the variation of the transport properties and of the osmotic pressure with the concentration of the solutes. A convective-diffusive model, to simulate the solute transmission, was also adopted. The real and apparent selectivity, local and mean, were determined, in order to study the effect of transmembrane pressure, Reynolds number, inlet solute concentrations, specific area of the membrane pores, and membrane resistance. The code was applied to study the separation of Bovine Serum Albumin (BSA) and Dextran-T10 macromolecules. The mean apparent selectivity increases with increasing transmembrane pressures until it reaches a maximum after which it decreases. The mean apparent selectivity increases with increasing Reynolds number consequence of a polarization decrease. Moreover, the selectivity increases with a decrease of the pore size and, also, with an increase of the membrane resistance. For low inlet concentrations of the solutes, the variation of the physical properties with the concentration does not produce any appreciable effect on the apparent selectivity.