DIAFILTRATION BY NANOFILTRATION - PREDICTION AND OPTIMIZATION

A predictive model for the performance of a nanofiltration membrane in separating the components of a dye/salt solution was developed It is based on the extended Nernst-Planck equation with incorporation of con centration polarization for mixtures of charged ions. Excellent agreem ent between predicted and experimental rejections of anions and cation s was obtained for batch nanofiltration at different ratios of dye/sal t assuming that the membrane charge density (X-d) depends on the total concentration of negative charges in the solutions. Prediction for di afiltration experiments was also excellent by allowing for variation i n X-d as the salt concentration in the solution changed as a function of time. The model was used to investigate optimization of the process ing conditions. The overall diafiltration process operated best in a t wo-phase mode, in which the dye solution was preconcentrated to the fi nal required dye concentration before diafiltration.