A model for micro-filtration of micro-sized particle suspensions using ceramic membranes

Based on the analysis of the force acting on the particle in the micro-filtration process with ceramic membranes, an equation of calculating the critical size of particles (xcrit) that may deposit on the membrane surface was obtained. According to this equation, the predicted values of xcrit consist with the experimental data, and they both show that the particle size distribution of the deposited layer increases with increasing the particle size at first and then decreases. Based on the discussion of the relationship between the values of the particle size (dp), the membrane pore size (dm) and the xcrit, the process of micro-filtration through the ceramic membrane can be divided into three modes according to the ratio of dp/dm, as following. When dp/dm&le1, the particles plug the membrane pores rapidly, when 1p/dm&le10, the particles form continuous cake on the membrane surface, and when dp/dmp/dm&le120, while the models in literatures can only be used for 1p/dm&le10. When assuming the porosity of the cake layer does not change with the transmembrane pressure, the predicted results consist with experimental data well for different transmembrane pressures. It indicates that the cakes formed from the suspensions used in the study are incompressible. The calculations of the effect of the cross-flow velocity on the permeate flux show that assuming the porosity of the cake layer is the exponential function of the cross-flow velocity is more reasonable than that of assuming it doesn't change with the change of the cross-flow velocity. It indicates that the cross-flow velocity has influence on the particle size distribution and the structure of the cake layer.