Simulation of continuous stirred ultrafiltration process: an approach based on surface renewal theory

Abstract

ABSTRACTUltrafiltration (UF) is an important operation in many processes, including foods and pharmaceuticals, and shear enhanced dead‐end systems are particularly suitable for small‐scale operations. Most industrial applications require a high permeate flux and maximum solute rejection, combined with long membrane life. A rigorous surface renewal model has been developed which describes the mass transfer processes occurring in a single stirred UF cell. The model takes into consideration two distribution functions of random surface elements, one with respect to their point of origin and the other related to the corresponding residence time on the membrane surface. The back transport flux and the permeate flux are evaluated at the membrane surface in order to develop a component balance equation. The component balance equation and a rejection–flux relationship arising from irreversible thermodynamics are solved simultaneously to allow a dynamic simulation. The dynamic simulation enables a more complete understanding of the permeate flux, membrane surface concentration and permeate concentration under various operating conditions. For validation of the proposed model, experiments were conducted on UF of polyethylene glycol 6000 (PEG 6000) solution in a continuous stirred UF cell comprising a cellulose acetate membrane of 5000 Da molecular weight cut‐off. Model predicted values are in excellent agreement with the experimental results. The effects of different stirring mechanisms on mass transfer with flat disk, propeller and turbine impellers were also characterized using the developed model. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.