What is a membrane filter? Let's find out its function and uses.

Membrane filter is also known as a surface filter, where the media has numerous micro-sized pores, which particles larger than a defined rating are retained when a liquid or gas is passed through.

Membrane filter comes in different sizes and shapes, from cartridges, capsules, disks, etc. Fujifilm offers broad lineup of pleated membrane cartridges and capsules.

Filtration using a membrane is also known as surface filtration. In this type of filtration, contaminants are collected on the surface of the media. Depth filters on the other hand are separated by deposition. Microfibers are randomly tangled, and when the liquid is filtered through the media, particles are retained through adhesion on fiber. Retention is done not only at the surface but also deeper within the membrane, so the filter medium is thicker than membrane filters. 

Depth filters allow blockage to be dispersed, however, process conditions such as operating pressure or concentration of contaminant have a significant effect on the retention of the filter. Therefore, depth filters are mainly used as pre filtration, also known as nominal filtration, whereas membrane filters are used as for absolute filtration, where particles larger than the defined rating have to be retained. 

Microfiltration (MF) is defined as a process of membrane separation which removes particles with sizes varying from 0.01 to 10μm. Micro filter is another term used to describe the filters used for microfiltration.

Other than microfiltration, there are different types of membrane filters used in separation processes. They are classified depending on its capability of filtering target. Ultrafiltration (UF) has the pore size of 0.01μm, targeted to remove viruses along with microorganisms. Nanofiltration (NF) removes not only the viruses but also divalent ions, with membrane pore size of 0.001μm. Reverse Osmosis filters (RO) is mainly used as desalination and purification of water with its pore size range up to 0.0001μm.

Filtration is one of the methods of sterilization when heat sterilization cannot be performed. As sizes of bacteria ranges from 0.3μm to 0.5μm, 0.2μm porous filters are suitable for removing contaminating microorganisms. Membrane materials such as Polysulfone (PS/PSF), Polyethersulfone (PES), Polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE) and Nylon are commonly used. Membrane properties vary depending on its material features along with its pore distribution. Therefore, it is important to select the type the membrane that is suitable for its usage conditions.

Polysulfone (PSF) and Polyethersulfone (PES) membranes share similar features, where they have resistance to acidic and alkaline solutions with low extractables. They are also known to have thermal stability and low protein binding. They are commonly used in various industrial fields from F&B, semiconductors to pharmaceutical.

Polytetrafluoroethylene (PTFE) membranes have compatibility to a broad range of chemicals with high thermal resistance. With its resistance to chemical solutions, hydrophilic PTFE membranes are applied to filter fluids such as organic solvents and aggressive solvents, whereas hydrophobic PTFE membranes are mainly used for filtering gases. 

Nylon membranes have resistance to broad range of organic solvents along with its hydrophilicity, flexibility and low elution rate characteristics. 

Polyvinylidene fluoride (PVDF) membranes offer durability and resistance in broad chemical solutions with low extractables. With its low protein binding feature and hydrophilic features, PVDF filters are commonly used as final filters for bioburden reduction in pharmaceutical applications. 

Polypropylene (PP) membranes are known for its compatibility with alkaline solutions and its thermal resistance. PP filters are commonly used for general clarification or prefiltration, in order to capture particles to reduce the burden of final filtration that follows. 

Fujifilm has a long experience in the manufacturing of Polysulfone membranes, offering broad lineup of cartridge filters suitable for each application.

Fujifilm filters come in various sizes and different end caps that fit with the corresponding housing. Fujifilm has its own end cap code, explained in the chart below. 

• *1 O ring size：SAE AS568（US standard） 
• *2 DOE：Double Open End ・・・Filter with flat gasket seals on both open ends.
• *3 SOE：Single Open End

For more information on its feature and its specifications, refer to the product catalog.

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