Determination of Limiting Flux and Threshold Pressure in Stirred Ultrafiltration of Colloidal Suspensions
The stationary permeate flux during ultrafiltration of colloidal suspensions reaches a limiting value, J l , at high pressure differences. According to the gel polarization model employed here, the existence of this limiting flux is a consequence of gelation of the solution at the membrane-solution interface. The limiting permeate flux, J l , can easily be determined from experimental data by plotting ∆ p/J s against ∆ p . Furthermore, the membrane resistance at zero pressure difference, R m 0 , and the pressure difference necessary to reach 95 per cent of the limiting flux, i.e. the threshold pressure, ∆ p t , may be calculated, too. The agreement between the model and experimental data is satisfactory. The laboratory-made silica sol consisting of uniform spherical particles with a surface average diameter of 18 nm was selected as a working fluid throughout this study.