Effect of Solution Environment on Unstirred Dead-End Ultrafiltration Characteristics of Proteinaceous Solutions

The effects of pH and the addition of such salts as NaCl on the structure of the gel-cake in dead-end ultrafiltration of BSA solutions are examined by using a batchwise filter which has an abrupt reduction in its filtration area. Both the average porosity εav and the average specific filtration resistance αav of the gel-cake may be determined accurately on the basis of measurements of the variation of filtrate volume with time. The most compact gel-cake, which provides a large flow resistance, forms on the membrane around the isoelectric pH. By the addition of NaCl at pH extremes the gel-cake structure becomes compact, thereby decreasing the filtration rate. Such internal structures as the solute concentration and the compressive pressure acting on the solutes within the gel-cake, which may serve as a basis for evaluating the sweeping performance of the gel-cake in crossflow ultrafiltration, are evaluated on the basis of the overall filtration characteristics obtained under various filtration pressure conditions.