THE PREDICTION OF FLUX DECLINE AND BLINDING IN CELLULAR CERAMIC MICROFILTRATION MEMBRANES

Cellular ceramic membranes have a structure which resembles that of fo ams. This is not surprising, since a polymer foam is frequently used a s a precursor in the manufacturing process. Like all membranes, the pr ocessing characteristics are determined to a large extent by the inter action of particles in the suspension or mixture to be treated with th e pores of the membrane. If the particle dimensions are near to the di mensions of the pores, then some particles will be trapped, thereby in creasing the hydraulic resistance of the media. This will result, in c onstant pressure filtration, in a decrease in permeate flux. It is the refore important to be able to predict the passage and retention of pa rticles through the media. The retention on the surface to form a cake and within the media is important and should be differentiated, parti cularly if cleaning by backflushing is to be considered. In order to i nvestigate particle retention, a definition of the pore structure of t he membrane is necessary. In the majority of studies in this field, be cause of the complexity of the material, a simplified model is used to describe the internal pores of membranes. The pores are assumed to be cylindrical, parallel (and therefore nonconnecting) capillaries. This is quite inappropriate for the membranes considered in this paper. Th e pores are formed from a highly connected network of shapes with vary ing size and cross section. In this work, a model to simulate the foam structure is briefly presented and then used to investigate condition s for microfiltration of near-pore-sized particles.