About Principle, Process, and Precautions of Microfiltration Membrane

Principle of microfiltration membrane

Microfiltration is based on the principle of size exclusion, where particles larger than the pore size of the membrane are retained while smaller particles and the liquid phase pass through. The microfiltration membrane typically has pore sizes in the range of 0.1 to 10 micrometers, making it suitable for separating particles such as bacteria, cells, and large proteins.

The filtration mechanism of the microfiltration membrane is mainly the retention effect. The interception effect can be divided into the following types: mechanical interception, adsorption interception, bridging interception, and an interception in the network inside the membrane.

1. Mechanical interception: the screening effect. It means that the membrane has the function of trapping impurities such as particles larger than or equivalent to its pore size.
2. Physical effect or adsorption retention effect: in addition to considering the screening effect, the influence of other factors should be considered, including the influence of adsorption and electrical properties.
3. Bridging: at the entrance of the hole, particles can also be trapped due to bridging.
4. The network retention effect of the network membrane. This trapping traps the particles inside the membrane, not on the surface of the membrane.
Membrane Filter Principle

It can be seen from the above that the sieving function is very important, and the interaction between particles and other impurities and the pore wall is sometimes more important than the pore size.

Microfiltration membrane is mainly used to separate macromolecules, colloidal particles, proteins, and other particles. Their separation mechanism is based on the physical and chemical properties of the molecules or particles, the physical and chemical properties of the membrane used, and the interaction between them (such as size, shape, and electrical properties) to achieve separation.

pvdf membrane filter hydrophobic ptfe membrane filter hydrophobic membrane and hydrophilic membrane

Process of microfiltration membrane

The microfiltration membrane process generally has three stages:
1. Initial stage: particles larger than the membrane pore size are trapped on the surface of the membrane, particles smaller than the membrane enter the die pores, some of them are adsorbed in the membrane pores due to various forces, reducing the effective diameter of the membrane pores;
2. The middle stage of filtration: the particles begin to form a filter cake layer on the membrane surface, and the adsorption inside the membrane pores gradually tends to be saturated;
3. Later stage: as more particles are trapped on the surface of the membrane, the adsorption inside the membrane pores also tends to be saturated, the particles begin to block the membrane pores, and finally the membrane flux stabilizes and then continuously decreases.
Through the above three processes, it can be understood that the adsorption capacity of the filter membrane reaches saturation during the dissolution process, and it becomes more and more difficult to filter as the filtration increases.

Precautions of microfiltration membrane

Microporous filter membranes mainly include CA, MCE, nylon, PTFE, PES, PP, PVDF filter, etc. When using it, we need to know each membrane’s features and usages. Please click here to know Hawach To Talk About The Applications And Differences Filter Membrane, PVDF vs PTFE.

  1. Selecting Membrane Pore Size: Choose a membrane with an appropriate pore size based on the size of particles you want to retain. Too small a pore size may lead to clogging, while too large a pore size may allow unwanted particles to pass through.
  2. Preventing Membrane Fouling: Membrane fouling can occur due to the accumulation of particles on the membrane surface. Consider pre-filtration or backwashing to minimize fouling and prolong membrane life.
  3. Optimizing Pressure or Vacuum: Maintain the appropriate pressure or vacuum conditions to achieve efficient filtration without damaging the membrane. Follow the manufacturer’s recommendations for operating conditions.
  4. Avoiding Air Bubbles: Air bubbles can interfere with filtration efficiency. Ensure proper wetting of the membrane to avoid the entrapment of air, which can create inefficiencies in the process.
  5. Compatibility with Samples: Consider the compatibility of the microfiltration membrane with the chemical and physical properties of the sample. Some membranes may be more suitable for certain solvents or pH conditions.
  6. Regular Quality Checks: Perform regular checks on the quality and integrity of the microfiltration membrane. Inspect for any damage or defects that could compromise the filtration process.
  7. Proper Storage: Store microfiltration membranes according to the manufacturer’s recommendations to maintain their properties and prevent degradation.
  8. The smooth side is best to face up, and the coarse side to face down will have a better filtering effect.
  9. In the drug analysis and dissolution experiment, membrane adsorption is the most disadvantage of using microporous membranes. There are many factors that affect membrane adsorption, including membrane diameter, pore size, material, filter media type, ionic strength, pH value, the nature of the drug itself, etc. The hydrogen bond, van der Waals force, charge adsorption and other interaction forces between filter membranes of different materials and different compounds to be filtered are different, and the degree of adsorption is also different. There are also reports in the literature that different pH buffer salts and different diluents (such as methanol) can reduce or eliminate adsorption.
  10. In the drug analysis-related substance experiment, it is necessary to pay attention to whether new impurities are generated after filtration by the filter membrane.

Microporous membranes play an important role in the current experiments. The types and materials of microporous membranes are also different. Choose a suitable microporous membrane according to your own samples, and inspect it during use, which proves that the membrane has no effect on the results. Do You Know How To Choose A Membrane Filter? Please click here.