8 Parameters for You to Better Understand Filter Membrane

Today, HAWACH also discusses the parameters for you to have a better understanding of the filter membrane.

Filtration is a process in a chemical experiment, separating solids from liquids or gases through a filter medium. Only the fluid or the gas is allowed to pass, not the solid. And the keywords of filtration terms can help you understand how the filter works.

Prewet is a useful step before aqueous filtrations. Hydrophobic membranes need to be especially wetted with chromatography-grade methanol, acetone, or compatible fluid with low viscosity and rinsed with water.

Parameters of the filter membrane

1. Aperture
There are different apertures available for HAWACH filter membranes, 0.1um, 0.22um, 0.45um, 0.8um, 1.0um, 3.0um, 5.0um, and 10.0um. But it should be noted that not all membranes or roll membranes have so many pores.

2. Size
The round membrane is represented by diameter. Different diameters are available, 293mm, 142mm, 90mm, 47mm, 25mm, and 13mm. It should also be noted that not all filter membranes of all materials have each diameter above, and the specifics can be confirmed by consulting HAWACH team. The rolling membrane is a rectangular roll together, expressed by the width. The widths are 254, 260; 270; 280; 310mm and the inner core is 22mm.

Pore size: The size of the openings or pores in a filter medium, which determines the size of particles that can pass through.

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3. Bubble point
For the use of a specific liquid wet filter membrane at a specific temperature, it is the minimum pressure of the liquid that must be squeezed out of the filter membrane pores, in the microporous membrane industry. According to the standard, the 0.22μm is ≥0.31mpa; 0.45μm ≥0.17mpa.

Bubble Point refers to the amount of air pressure. The pressure can force liquid from the largest wetted pore of the membrane.

4. Flow rate and flux
The pore size is proportional to the flow rate, the larger the pore size, the faster the flow rate. Flow rate and flux are two important parameters of filter material and design performance, which depend on these aspects:

Viscosity: Viscosity determines the ease of liquid flow. The viscosity of the liquid is inversely proportional to the flow rate.

Pressure difference: it means the filter inlet and outlet pressure difference. It increases when the filter is fully loaded.

Porosity: It is the ratio of all the pores volume in the membrane to the membrane volume. It’s commonly used 50%-90% pore area membranes, which is directly related to the flow rate.

5. Filter material life
It refers to the maximum lifetime of a filter under specific operating conditions. It depends on many factors, such as the nature of the filtrate, the operating temperature, the choice of filter material, etc.

6. Filter efficiency: The filtering efficiency is defined by the amount of filtration and the blocking particle size at their specific pressure. The lower pressure, the greater filter’s effectiveness.

7. Hydrophilic and hydrophobic

Hydrophilic, called “water-loving”, refers to a filter’s ability to absorb water. Hydrophilicity is defined as hydrophilic. Hydrophilic membrane filter usually has a special chemical layer to make the membranes infiltrated by water, such as Hydrophilic PTFE Membrane Filters; Hydrophobicity is a reference to the repulsion of water. Hydrophobic, call as “water-hating”, refers to a filter’s ability to repel water. Hydrophobic membranes rarely absorb water at all. It can be observed that small water droplets stay on the surface of the filter membrane and will not be absorbed by the surface and diffused into the water surface, such as Nylon Membrane Filters.

For instance, the nylon membrane is suitable for the filtration of water and organic solvents, such as sample preparation for high-performance liquid phase and gas chromatography. It is characterized by large flux, low dissolution, and mechanical strength. Nylon’s good physical properties can meet the demanding analysis requirements of various test conditions.

The size of the hydrophobicity depends on the pore size of the filter and the characteristics of the filter membrane material. The hydrophobic membrane, does not absorb moisture, is easy to at a constant weight, can be repeatedly autoclaved, and has the same performance, thin texture, fast flow rate, chemical resistance, and oxidation resistance, and becomes a hydrophilic membrane after alcohol treatment. It can be applied to the purification of suspended particles in the air and sterilization of air in the fermentation industry; purification of insoluble oils and weight analysis of solid particles; separation and purification of non-specific proteins; concentration of aqueous solutions, separation, and recovery of chemical substances.

8. Pack
For different membranes, the number in each box is different. For example, 47mm is 100 pcs/pack, and 142mm is 50 pcs/pack.

9. Other Parameters to Better Understand Filter Membrane

Filter: A device or material that selectively allows certain substances to pass through while retaining others.

Filtrate: The liquid or gas that passes through the filter during the filtration process.

Retention: The ability of a filter to retain or capture particles or substances during filtration.

Micron: A unit of measurement used to indicate the size of particles or the pore size of a filter.

Membrane: A thin, semi-permeable material used as a filter medium to separate particles or substances based on size or properties.

Porosity: The extent to which a filter medium contains open spaces or pores that allow the passage of fluids or gases.

Molecular Weight Cut Off (MWCO): the lowest molecular weight solute, which is 90% retained by the membrane. if the sample loss is acceptable, we can choose a membrane with MWCO the same as the molecular weight of the solute for rapid filtration. But if you want to cut the loss of material of interest, the membrane MWCO must be less than the molecular weight of the compound.

Clarification: The process of removing solid particles or impurities from a liquid to make it clear or transparent.

Sieving: A method of filtration that uses a sieve or mesh to separate particles of different sizes.

Depth Filter: A type of filter medium that operates by trapping particles within the depth of the filter matrix rather than solely on the surface.

Sterile Filtration: Filtration is performed to remove microorganisms or achieve a sterile environment by using filters with specific pore sizes capable of retaining bacteria, fungi, and viruses.

Pre-filter: A filter used before the main filtration process to remove larger particles or debris, protecting the subsequent filters and improving their efficiency.

Pressure Drop: The decrease in pressure that occurs as a fluid passes through a filter due to the resistance offered by the filter medium.

Filter Cake: The accumulated solid material that remains on the surface of the filter medium after filtration.

Adsorption: The process of attracting and retaining molecules or particles onto the surface of a solid material, typically used in activated carbon filters for adsorbing impurities.

Backwashing: The process of reversing the flow of a liquid or gas through a filter to remove accumulated particles or clean the filter medium.

Filter Efficiency: The ability of a filter to remove or retain particles of a certain size or within a specific range.

Filter Validation: The process of verifying the performance and efficiency of a filter through testing and validation procedures.

Filter Sterilization: The process of rendering a filter or filter system free from viable microorganisms through methods such as autoclaving, steam sterilization, or chemical sterilization.