Weighing Alternative API Filtration Technologies

API filtration technologies
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Being a process engineer is all about making choices. When it comes API filtration technologies, many different types of equipment can be used for removing catalyst residues. While conventional filtration equipment is operated manually, I recently worked with PharmTech on an article outlining how both candle filters and pressure plate filters are operated as automated systems. This article reviews what we discussed.

Pharmaceutical manufacturers are increasingly looking for automated equipment with in-line process control. Well, automated candle and pressure-plate filtration equipment for removing catalyst residues from API slurries are operated in a closed system. This automated filtration also meets the demand for improved safety and reliability by removing the manual operation.

First, though, you need to understand the difference between candle filters and pressure-plate filters and how they differ from tradition filters. 

Conventional or traditional filters can be defined as bag filters, cartridge filters, manual plate filters, and plate and frame filter presses. These are all manually operated filters. They are not really sealed—especially not when solids get discharged.

Candle filters and pressure plate filters are improvements over these types in terms of reproducible quality, multiple process steps, cleanable and reusable filter media, and full containment for solids recovery. 

A major difference is that the operation of plate filters and candle filters is 100% automated. Solids discharge is provided in a sealed and safe way.

When to Use Candle or Pressure Plate Filters

Deciding between candle and pressure plate filters depends largely upon the cake structure developed by the process solids. 

Cake structures that can maintain their integrity in a vertical form are suited for candle filters. If the cakes themselves are too dense or too light or tend to crack, a horizontal plate filter is the better choice of technology. Thickness of the cake structure is another decision parameter. Candle filters typically have maximum cake thickness of 20 mm, while plate filters can handle up to 75 mm.

Generally, the candle filters and pressure plate filters can be used interchangeably based upon the cake structure itself. Some cakes can be handled in either vertical or horizontal form. In that case, the process dictates the choice.

When it comes to deciding the best filtration type for continuous or semi-continuous processing, consider the upstream and downstream equipment. Both candle filters and pressure plate filters are batch operations. For continuous or semi-continuous operations, either multiple units are required or buffer/holding tanks can be installed.

Pharma Disposal or Recycling

We also discussed best practices for disposal or recycling. For non-hazardous disposal, the cakes can be first washed to remove all of the toxic or hazardous compounds and then dried to a standard of no free liquids. The cakes can be fully discharged in a contained and dust-free manner to totes or drums. 

For recycling, the process solids can be reslurried within the candle filter or pressure plate filter to be pumped back as a slurry to the process. The process liquids or filtrates can also be pumped back to the upstream reactors for reuse.

Questions about alternative API filtration technologies? Other decision parameters I didn’t think about? Let me know, I’m always ready to chat. 

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