Critical flux in ultrafiltration of myoglobin and baker's yeast

Critical fluxes were determined by constant flux ultrafiltration (UF) exper iments under laminar flow conditions. The experiments were performed by usi ng hydrophilic C30G and hydrophobic GR51 ultrafiltration membranes and dilu te myoglobin solutions and baker's yeast suspensions as model colloids. Sol ution concentration, pH and cross-flow were investigated. The critical flux increased with increasing flow velocity and decreasing solute concentratio n. The regenerated cellulose C30G membrane exhibited hi-her critical fluxes than the polysulphone GR51 membrane. The highest critical flux was obtaine d at pH 8 in the presence of repulsive electrostatic forces between the mol ecules and the surface of the membrane and the lowest at the isoelectric po ints of the colloids. In the case of baker's yeast below the critical flux, the flux was about the same as the pure buffer solution flux showing a str ong form of the critical flux. This also occurred with the C30G membrane at low concentrations of myoglobin except at pH 6 when a weak form of the cri tical flux was measured. With the GR51 membrane, the permeate flux deviated from the pure buffer solution flux even at the lowest fluxes. (C) 2002 Els evier Science B.V. All rights reserved.