PROPERTIES OF FILTER CAKE IN DEAD-END ULTRAFILTRATION OF BINARY PROTEIN MIXTURES WITH RETENTIVE MEMBRANES

The properties of the filter cake formed on the retentive ultrafiltrat ion membranes in downward dead-end ultrafiltration of binary protein m ixtures have been studied in a batchwise filter which has a sudden red uction in its filtration area. Both the average porosity epsilon(av) a nd the average specific filtration resistance alpha(av) of the filter cake were determined accurately on the basis of measurements of the va riation of the filtrate volume with time. It was highlighted through t his study that the electrical nature of macromolecules plays a signifi cant role in determining the filtration flux rate in ultrafiltration o f binary protein mixtures. In the pH range where both protein molecule s are electropositive, the filter cake becomes loose and wet due to th e electrostatic repulsive force acting between both proteins, leading to a higher filtration rate. In contrast, in the pH range where two pr otein molecules have opposite electrical charges, the filter cake beco mes compact and dry because of the attractive force associated with op positely charged solutes. It was, therefore, found that the average po rosity reached a distinct minimum at a specified mixing ratio of two p roteins in the case of oppositely charged proteins.