In an earlier blog, I discussed the use of pressure filters to ensure proper filtration of APIs as an essential element in API development and drug delivery. Since advances in filtration technology are providing more and more ways to complete the task, this blog post addresses a specific filtration method: Basket Centrifuge filtration.
Each chemical component or raw material used in API production has its own unique characteristics. Filters are used to assure that the ingredients are free of harmful particulates and must be chosen based on those characteristics.
At PCI Synthesis, we use a specialized filter called a Centrifuge, to isolate and wash the APIs we manufacture. In a high-speed centrifugal solids/liquids separation device, Solid/liquid mixtures are pumped to the machine through an inlet nozzle that feeds into a cone-shaped sprayer.
The sprayer feeds the mixture to a perforated spinning bowl. While the basket is spinning, centrifugal action caused liquid to separate and solids to remain on the spinning bowl – similar in many ways to a washing machine.
The stainless steel perforated bowl is equipped with a filter cloth designed to retain solids, as liquid is filtered through the cake mass. The solids (or cake) are deposited onto the inner surface of the filter cloth as the basket is spinning at the feed setting. The centrifuge is designed to isolate a thin layer of cake (up to one-inch thickness).
A separate wash is charged through the sprayer on top of the product on the spinning basket. The speed of the basket is increased to de-liquefy the solids. The speed is then decreased so that the cake mass can be peeled off by the plow, and collected through the open bottom centrifuge into carts. The filtrate from the isolation is collected in a liquid tank. The product discharged from the centrifuge can be packaged directly into drums.
The centrifuge is used in many solid/liquid separations in which the prevention of cross-contamination is critical to the quality of the final product. It is a closed, sealed device that is constantly inerted with clean, filtered nitrogen. In addition to ensuring safe operation of the centrifuge, this nitrogen infusion is what eliminates cross-contamination and makes it easier to isolate APIs.
Another way that cross-contamination is prevented is during discharge when the isolated product in the basket is discharged directly to carts. The carts can be sealed and moved out of the immediate area and transferred to the drying area.
The speed and method of de-liquoring via centrifugal force creates another reason to isolate APIs. Certain products may be more difficult to filter and de-liquor as cake thickness increases. The centrifuge is advantageous because it is designed to isolate the product in small, multiple loads, preventing increased cake thickness.
The basket centrifuge assists in de-liquefying solids very quickly and efficiently. As a result, the product from the centrifuge is consistently drier than any other isolation method, and provides more suitable option for isolating APIs that are difficult to filter.
There are many methods for isolating APIs and CMOs should employ the most current practices to best meet the needs of the ones being produced. Effective filtration can ensure that final products are not affected by cross-contamination and other issues that can jeopardize the delivery of safe and effective drugs to consumers.