Crossflow microfiltration of shear-thinning aqueous titanium dioxide dispersions

Abstract

Crossflow microfiltration experiments were performed on aqueous dispersions of rutile (titanium dioxide) through a 0.1 μm pore size ceramic membrane at various operating parameters. The initial transient flux decline follows deadend filtration theory, with the membrane resistance 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, presumably as a result of the cake growth being arrested by the shear exerted at its surface. The steady-state fluxes increase with increasing inlet 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 law applied over the filter area to relate filtration rate to average pressure difference between the feed and permeate sides of the filter. The model includes a cake resistance of the cake layer, which was determined for the titanium dioxide dispersions by fitting the experimental flux data to the model. The apparent viscosity of the dispersion, which is an input parameter in the flux model, is also adjusted to account for a model of the Herschel-Bulkley type. The resulting fluxes obtained from the model using simple values for the membrane resistance, cake resistance, and rheological parameters for each data set are in good agreement with the measured fluxes.