In-situ Structural Characterization by SAXS and Flow Properties of Colloidal Suspensions During Cross-flow Ultrafiltration

摘要

The flow properties and induced structures during concentration of colloids near the membrane in ultrafiltration processes where studied on the base of new techniques developed at the “Laboratoire de Rhéologie”. The use of a specific cross-flow ultrafiltration cell combined with in-situ time resolved small angle x-ray scattering (SAXS) allowed to access the pertinent length scales of the filtered colloids. Anisotropic aqueous dispersions composed of sepiolite fibers (1 micrometer long and 0.01 micrometers in diameter) were treated under several cross-flow conditions. The local concentration increase has been obtained from the absolute scattering intensities measured as a function of time at different distances from the membrane (>280 micrometer) with 40 micrometer resolution. During ultrafiltration, the level of concentration in the accumulated layers reaches up to 50 times the initial concentration. The highly anisotropic structure formed has been identified as one of the main mechanisms controlling the filtration flux decrease.