CROSS-FLOW MICROFILTRATION OF SHEAR-THINNING AQUEOUS TITANIUM-DIOXIDEDISPERSIONS

Crossflow microfiltration experiments were performed on aqueous disper sions of rutile (titanium dioxide) through a 0.1 mu m pore size cerami c membrane at various operating parameters. The initial transient flux decline follows deadend filtration theory, with the membrane resistan ce determined from the initial flux and the cake resistance determined from the rate of flux decline due to cake build-up. For a long time, the observed fluxes reached steady or nearly steady-state values, pres umably as a result of the cake growth being arrested by the shear exer ted at its surface. The steady-state fluxes increase with increasing i nlet crossflow velocity and decreasing feed concentration. The steady- state permeate flux values were determined from the steady-state model based on the Kozeny-Carman equation for cake resistance and Darcy's l aw applied over the filter area to relate filtration rate to average p ressure difference between the feed and permeate sides of the filter. The model includes a cake resistance of the cake layer, which was dete rmined for the titanium dioxide dispersions by fitting the experimenta l flux data to the model, The apparent viscosity of the dispersion, wh ich is an input parameter in the flux model, is also adjusted to accou nt for a model of the Herschel-Bulkley type. The resulting fluxes obta ined from the model using simple values for the membrane resistance, c ake resistance, and rheological parameters for each data set are in go od agreement with the measured fluxes. (C) 1998 Elsevier Science S.A.