In filtration, traditional thinking holds that more filter equals better filtration. This simply isn’t true anymore. While PTFE and PVDF membranes have been the material of choice for chemical applications, there are a variety of alternative filtration materials today, such as ultra high molecular weight polyethylene (PE) and polysulfone (PS), which make different filter sizes and shapes possible.
Unlike PTFE membranes, which are stretched, these alternative materials can be cast to create specific pore structures. Asymmetric cast membranes, for example, reduce flow resistance, allowing more capacity to be packed in a much smaller area than with traditional materials. In addition to reducing costs, this results in a smaller surface area, which inherently reduces the potential for defects and extractables.
A 10-inch length asymmetric membrane filter cartridge can produce the same flow rate as a PTFE (or PE) membrane filter cartridge that has as much as 8 sq ft more filter area. This area is equivalent to the surface area of the inside diameter of 50 linear feet of three-quarter inch tubing.
When you count the added surface area of the downstream support material, you’re up to the equivalent of 100 linear feet of tubing, and if you have multiple filters in your process, you could easily have the equivalent of over a mile of three-quarter inch tubing surface area that is in intimate contact with your process fluids.
Is this a problem? Hopefully not, but as processes become more stringent, it is the unobvious contamination sources that may be problematic. So, remember, bigger isn’t always better.
From: “Point of View: Choosing Wet Clean Filters: It’s A Brave New World”
