CONSTANT FLOW-RATE BLOCKING LAWS AND AN EXAMPLE OF THEIR APPLICATION TO DEAD-END MICROFILTRATION OF PROTEIN SOLUTIONS

We developed equations for the blocking laws (complete, standard and i ntermediate) at a constant flowrate and we derive a general expression related to the instantaneous hydraulic permeability of the deposit dt /(Delta P). Microfiltration of BSA solutions is carried out at a const ant flowrate and shows that both the type of membrane and the physico- chemical conditions influence the pressure drop. The curves of pressur e as a function of time are fitted by the intermediate law that enable s one to determine the clogging coefficient of the solution a and quan tify the fouling through the ratio (delta/epsilon) of the clogging coe fficient delta and the porosity epsilon. The intermediate law predicts that the increase in pressure drop is inversely proportional to the m embrane porosity. The experimental results are in reasonably good agre ement with the theory as track-etched Nuclepore membranes (epsilon=8%) foul 5 to 10 times more rapidly than microporous Millipore membranes (epsilon=80%). Fouling is more apparent at pH 3.6 than at pH 4.6 and p H 5.6. This is explained by electrical protein-membrane attraction at pH 3.6. Scanning electron micrographs show that the fouling is mostly a surface deposit made up of protein aggregates. The deposit turns to be thicker at pH 5.6 (3-5 mu m) than at pH 4.6 (0.5-1 mu m). At pH 3.6 , the deposit slightly penetrates the membrane and is entangled with m embrane fibers on the upstream side.