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 intermediate) 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 constant flowrate and shows that both the type of membrane and the physico-chemical conditions influence the pressure drop. The curves of pressure as a function of time are fitted by the intermediate law that enables one to determine the clogging coefficient of the solution a and quantify the fouling through the ratio (delta/epsilon) of the clogging coefficient delta and the porosity epsilon. The intermediate law predicts that the increase in pressure drop is inversely proportional to the membrane porosity. The experimental results are in reasonably good agreement 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 pH 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 membrane fibers on the upstream side.