(240a) Separation of Macromolecules by Dynamic Ultrafiltration

Ultrafiltration is mainly used to concentrate macromolecules and removing salts and smaller molecules through the membrane. Sharp separation is rarely seen which is partly due to the coupling of solute and water transport and the concentration polarization at the membrane surface. In case of real fractionation of macromolecules a decoupling of the solute transport from the water transfer together with a minimization of the concentration polarization of the larger molecules have to take place. Using hollow fiber membranes under high-frequency backflushing the concentration polarization can be minimized due to the non-steady state operation. The build-up of the polarized highly concentrated layer at the membrane surface takes typically 10-30 seconds why it is possible to obtain a dynamic layer with a substantially reduced surface concentration thereby increasing the selectivity of the membrane. The paper describes the modeling of the dynamics of the concentration polarization and how it influences the membrane selectivity and productivity. The modeling is further supported by experiments fractionating dextrans and proteins on a hollow fiber system using backflushing intervals from 1 to 30 seconds and backflushing times from 0,1 to 5 seconds.