Dynamic Microfiltration of Dilute O/W Emulsion in Rotating Cylindrical Membrane Filter

The microfiltration of an oil-in-water emulsion, where only the water permeates through a ceramic membrane at constant pressure, is done using a rotating cylinder type of dynamic filter. Its suitability for the efficient filtration of the dilute emulsion consisting of drops smaller than 7 μm is examined, and a flux-controlling factor for the evaluation of the filtration performance is proposed. The rotational microfiltration of the O/W emulsion shows a gradual reduction in flux initially, and then a roughly uniform value of final flux, in a manner similar to that of a conventional solid-liquid slurry. The time dependent change in unsteady flux at an earlier stage is formulated in the form of a filtration rate equation with a dynamic coefficient (defined as the ratio of static to dynamic cake resistance); this coefficient being estimated as a power-function of filtrate volume. The final steady state flux at the later stage is related to a number of operational variables in terms of a controlling factor composed of the shear stress on the fouling surface and the coefficient of constant pressure filtration, considering the intensive dependence of the flux on the high compressibility of the extremely low permeable fouling-layer. It is confirmed that, due to a powerful sweeping force acting on the residual fouling-layer, the rotating cylinder-type membrane filter can be applied effectively to high-flux microfiltration of poorly filterable oil-water systems.