CONCENTRATION POLARIZATION BUILDUP IN HOLLOW FIBERS - A METHOD OF MEASUREMENT AND ITS MODELING IN ULTRAFILTRATION

A simple technique allows both polarisation and fouling to be studied independently at constant permeation flux during ultrafiltration of protein solutions with hollow fibers. The build-up of the concentration polarisation layer was recorded and measurements of the amount of proteins involved in the boundary layer were carried out before fouling had had time to alter polarisation. Using a film model with a linear or an exponential boundary layer concentration profile average values of the wall concentration and of the mass transfer coefficients are calculated, the latter being in good agreement with the predictions of the Leve triple-over-dot que formula. An integral model of the growth of the polarisation layer is compared to direct measurements in the boundary layer, with a generally good agreement being found. The advantage of the integral model is the detailed picture given of what is occuring along the membrane surface. The rate of material deposition on the membrane was also measured. The mechanism of fouling appears to be strongly dependent on the concentration polarisation.