PERMEATE FLUX DECAY DURING CROSS-FLOW MICROFILTRATION OF A CATIONIC SURFACTANT DISPERSION

The transient permeate flux and rejection behaviour of a cationic surf actant dispersion during crossflow microfiltration is studied using me mbranes with different degrees of hydrophobicity which is characterise d by the solubility parameter. It is found that the transient permeate flux behaviour is strongly affected by the membrane hydrophobicity if the feed concentration is low. The mechanism of crossflow membrane fi ltration is evaluated by studying, in addition to transient permeate f lux and rejection, the deposition of the surfactant on the membrane an d within its pores. It is shown that the surfactant deposition results in the formation of a secondary membrane supported by the primary mem brane. To a large extent, the secondary membrane controls the permeate flux and rejection of the surfactant. The secondary membrane is forme d on the surface of the membrane, and penetrates into the pores formin g a region of high surfactant concentration which is an order of magni tude higher than the so-called gel concentration.