Cross-flow microfiltration of soft porous submicron particles

The formation and the properties of the filter cake in the cross-flow microfiltration of soft porous submicron particles are analyzed in this study. Dextran-MnO2 particles are prepared and used in experiments. The effects of operating conditions on the filtration performance are discussed. The results show that the pseudo-steady filtration rates increase with increasing the cross-flow velocity and the filtration pressure. The trajectories and the particle flux arriving at the membrane surface in cross-flow microfiltration are simulated using the Brownian dynamic simulation method. The probabilities of particle deposition under various conditions are estimated using the force balance model. The calculation results show that a higher cross-flow velocity or a higher filtration pressure leads to a higher cake growth rate and a larger cake mass. Based on the retardation cake compression model and the empirical equations for cake properties, a dynamic analysis method is developed for simulating the distributions of local properties in a filter cake, such as the solid compressive pressure, the porosity and the specific filtration resistance. For a soft porous particle, both the variations of internal and external porosities in the cake are taken into consideration. It can be found that a skin layer controlled the filtration rate may form next to the membrane surface. Although the thickness of the skin layer is only about 10% of the whole cake, this layer has about 90% of the overall pressure drop through it, and it plays the major role on the filtration resistance.