Effects of pH and solvent density on dead-end upward ultrafiltration

Upward ultrafiltration experiments, in which the filtrate flow is in the opposite direction of gravity, were conducted under a constant pressure of 98 kPa, using a dead-end filter. The filtration characteristics were studied using a protein (bovine serum albumin) solution of 0.6 wt.% to determine the effects of the solvent environment such as pH and the density of the solvent. A dynamically balanced rate of filtration can be obtained by this newly developed technique. This filtration rate ranges from 3.0 × 10 −4 cm/sec to 1.04 × 10 −3 cm/sec depending on the pH of the solution, with a distinct minimum near the isoelectric point (ca. 5.1). The results obtained from downward ultrafiltration experiments conducted by a batchwise filter having a sudden reduction in its filtration area show that a very compact gel-cake with an average porosity of 0.902, which is not exfoliated easily, forms on the membrane surface at the isoelectric pH. The dynamically balanced filtration rate in upward ultrafiltration is shown to be largely determined by the density of the solvent. A method was developed for determining the buoyant density of protein solutes on the basis of the results of upward ultrafiltration experiments performed at different values of the density of the solvent; a value of about 1.27 g/cm 3 was obtained for bovine serum albumin.