The relationship between filtration membrane flux and pressure

The relationship between microporous filtration membrane flux and pressure is described by the concept of transmembrane pressure (TMP). The so-called TMP refers to the pressure difference across the filtration membrane, that is, the feed (input) side of the membrane and the permeate ( The pressure difference between the output) sides. For microporous filtration membranes used in processes such as microfiltration and ultrafiltration, the TMP is the driving force that pushes fluid through the membrane. The size of particles that can pass through these membranes is determined by the membrane pore size. For microfiltration, the pore size is usually around In the range of 0.1 to 10 microns, a typical TMP range is estimated to be about 0.5-3bar. For ultrafiltration, the pore size range is usually in the range of about 0.001 to 0.1 microns, and the TMP range is estimated to be about 1-5bar. ,It can be seen from the data that the smaller the ,membrane pores, the greater the pressure required.

There is a direct relationship between filtration membrane flux and transmembrane pressure. As TMP increases, the filtration rate or flux also tends to increase, so applying higher pressure during filtration will help overcome the resistance to flow through the membrane, thus Allowing more liquid to pass through in a given time, but this relationship is not linear because there are many factors that affect membrane filtration:

1 Membrane characteristics, the permeability and pore structure of a filtration membrane play an important role in determining its flux-pressure relationship, larger pores or higher permeability compared to membranes with smaller pores or lower permeability The membrane can show higher flux at lower pressure. As mentioned at the beginning of the article, the pressure consumed by large pores is relatively smaller than that of membranes with small pores.

2. Fouling is inevitable during filtration. Fouling refers to the accumulation of particles or substances on the membrane surface or in the pores, which will reduce the permeability of the membrane and affect the flux. Since fouling occurs during the filtration process, it will increase the flow resistance. and require higher pressures to maintain the required flux levels.

3. Integrity of the filtration membrane. Membrane integrity is critical to maintaining consistent performance. If the membrane structure is defective or damaged, it may cause uneven flow distribution across the surface and affect flux and pressure requirements, as discussed here. What is more important is the lack of the membrane's own function in the early stage. In practical applications, although increasing the transmembrane pressure can increase the filtration rate to a certain extent, excessive pressure can also cause irreversible damage or compaction of the membrane, thereby affecting performance. Decreases over time.

4. The viscosity of the filtration liquid. Under the same conditions, different liquids will also affect the difference in filtration pressure and filtration performance due to the viscosity. The greater the viscosity, the greater the resistance. Fluids with higher viscosity require higher viscosity. pressure to achieve the desired flux rate.

Therefore, optimizing operating conditions such as transmembrane pressure needs to be based on specific application requirements. The filtration flux determines efficiency, filtration performance is a fixed indicator, and the pressure range provided by the process equipment is also an actual value. Combined with the above analysis With the influencing factors mentioned in , it will be clearer what kind of membrane to choose.