Modelling of flux decline in crossflow ultrafiltration of macromolecules: comparison between predicted and experimental results

Abstract

The purpose of this work was to compare the experimental results on flux decline with time in the ultrafiltration of macromolecules with the results predicted by a model based in the resistance in series model. The model considers the osmotic pressure, gel-layer formation and adsorption as responsible for flux decline. In this paper, the change in permeate flux with time was predicted theoretically, without the use of any empirical data. A ceramic ZrO 2-TiO 2 monotubular Carbosep M2 membrane (Orelis, S.A., France) with a molecular weight cut-off of 15 kDa was selected to perform the experiments. Aqueous solutions of PEG 35000 were used as feed. The experimental results obtained at different flow rates and transmembrane pressures (TMPs) were compared with the theoretical predictions. The best predictions were obtained for low crossflow velocities (1 m/s), especially for long time scales. However, for long time scales permeate flux was under predicted for high crossflow velocities (2 and 3 m/s). The reason for these results may be found in the increased possibilities of gel layer formation at low crossflow velocities.