THEORETICAL DESCRIPTIONS OF MEMBRANE FILTRATION OF COLLOIDS AND FINE PARTICLES - AN ASSESSMENT AND REVIEW

Membrane separation technology is a novel and highly innovative process engineering operation. Membrane processes exist for most of the fluid separations encountered in industry. The most widely used are membrane ultrafiltration and microfiltration, pressure driven processes which are capable of separating particles in the approximate size ranges of 1 to 100 nm and 0.1 to 10 mu m, respectively. The design of membrane separation processes, like all other processes, requires quantitative expressions relating material properties to separation performance. The factors controlling the performance of ultra- and microfiltration are extensively reviewed. There have been a number of seminal approaches in this field. Most have been based on the rate limiting effects of the concentration polarisation of the separated colloids at the membrane surface. Various rigorous, empirical and intuitive models exist, which have been critically assessed in terms of their predictive capability and applicability. The decision as to which of the membrane filtration models is the most correct in predicting permeation rates is a matter of difficulty and appears to depend on the nature of the dispersion to separated. Recommendations are made as to which of the existing models can be most appropriately applied to different types of dispersions.