(652a) Compressible Nutsche Cake Filtration – Retarding Effect of Residual Base-Cake

Production scale filtration of fine needle morphology crystalline solids is often challenging, since needles tend to give rise to compressible, slower filtering cakes. In this study, a slurry comprised of needles that has a difficult Nutsche filtration at production scale was studied in a laboratory setting to better explore the factors that affect this filtration. Laboratory filtration was accomplished on a 1L “pocket” Nutsche filter. The filtration was characterized by measuring the inherent cake resistance and media resistance under different conditions. Increasing the driving pressure showed limited improvement in filtration rate, indicating a moderately high level of compressibility. Filtration at colder temperatures showed a retardation from both increased viscosity and a higher inherent cake resistance. However, while these filtration experiments were insightful, scale-up calculations were under-predicting the filtration times at production scale. Further investigation focused on base-cakes, which are thin 1 – 2 cm heels left behind on many production filters, including the agitated Nutsche used in this process. A thin residual base-cake increased filtration times 2X and then nearly 3X in successive filtrations as the base-cake resistance increased. Incorporating these base-cake resistances into the scale-up calculations resulted in predictions that nearly match the production scale results. Removal of the base-cake in this application holds significant potential to increase productivity of the filtration unit operation.