Filtration of porous particles

Filtration is a widely used unit operation, particularly in catalyst manufacturing. The process is still largely empirical and requires extensive testing of the material in question and the equipment before predictions can be made about efficiency and performance. Even with extensive testing, subtle, often overlooked variations in input will result in an unexpected outcome, such as a failed filtration run. Our approach is to develop an experimental laboratory scale model that can relate key parameters to filtration behaviour. Experiments were performed on a benchtop Nutsche filter with constant applied pressure. Analysis of the filter cake and comparison with filtration performance provided insight in order to connect packing characteristics with material characteristics. Several porous catalyst materials were investigated. Darcy’s law for constant pressure, which relates the filtrate volume with time, was applied to analyze the results and calculate the cake resistance. Pure materials with various particle size distributions and median particle sizes were tested at several applied pressures. A mixture a 11% fine and 89% coarse porous material was also tested to examine the effect of fine particle addition on filtration behaviour. Even a small percentage of fines (11% of total solids) resulted in cake permeability and filtration time comparable to that of the pure fine particles. The same particle size distributions were also tested in a continuous filtration set up and these results were compared to batch filtration runs with the Nutsche filter. It was observed that the effect of limited settling is favourable and could be a filter aid that does not chemically modify the cake.M.S.Includes bibliographical reference