In-depth analysis of the five major factors restricting filters

The filter is often thought of as a simple net or sieve, and the filtration or separation is carried out on a long surface. This is the way in the past, and now most filters have a certain thickness of the filter wall, that is to say, the filter equipment has a depth, and the form of a curved channel plays an auxiliary role in removing contaminants.

　　The filter is a device to remove a small amount of solid particles in the liquid. When the fluid enters the filter cartridge with a certain filter screen, its impurities are blocked, and the clean filtrate is discharged from the filter outlet. When cleaning is required, Rotate the screw plug at the bottom of the tube to drain the fluid, remove the flange cover, take out the filter cartridge, and reinstall it after processing.

　　 As we all know, the core element of the filter is the filter membrane, which is a membrane filled with smaller pores prepared on a microporous supporting layer (support). There are many materials for making filter membranes, including organic membranes (such as polysulfone hollow fiber membranes) and inorganic membranes (such as ceramic membranes). Membrane filters have higher filtration accuracy, relatively less chaotic particle size control, and easy recovery of the function by backwashing. Therefore, it is extremely convenient to use and maintain.

　　 filtration mechanism and influencing factors

　　 filtration mechanism

　　 There are two main filtration mechanisms for fluids. One is separation based on the size of the particles, such as interception, sieving, and surface capture; the other is adsorption, that is, the particles adhere to the filter under chemical/charge action. This requires each pharmaceutical factory to choose different filter membranes according to their actual needs.

The characteristics of 　　 fluid

　　 is related to the characteristics of the fluid. For example, the viscosity and chemical/ionic composition of the fluid. The greater the viscosity of the fluid, the slower the flow rate under the same pressure. There will be more contact between the fluid and the membrane, and the filtration effect will be better; another example is the mixing of fluid and membrane. The contact time also has a greater impact on the filtering effect. The longer the mixing/contact time, the better the filtering effect. In addition, it should be noted that the characteristics of the fluid only affect the adsorption and retention effect of the membrane on the fluid and not the elimination of particle size.

　　 Manipulate the premise

　　 is related to actual operating conditions, such as particle flow rate and filtration pressure. To achieve a good filtration effect, generally choose a lower flow rate, the lower the flow rate, the better the retention effect. Practice has proved that the movement of the membrane structure is unfavorable for filtration. Once the membrane structure changes during the filtration process, particles and fibers can be precipitated from the depth filter, which will affect the filtration effect. However, the velocity/pressure difference only has an important effect on the adsorption retention, and has a relatively small effect on the size exclusion.

　　Particle type

　　The type of particles is also closely related to the filtering effect. There are two types of particles: deformable particles and non-deformable particles. Under a certain pressure, deformable particles will enter the filter membrane and cause more filter meshes to be blocked, thereby affecting the filtration effect, such as the filtration of gels. However, when immutable particles are filtered, a cake-like object is formed on the filter membrane.

　　 filter membrane type

　　 is related to the type of filter membrane. Different filter membranes have different pore sizes and structures. Some membrane structures are rigid, and some membrane structures are movable. The rated pore size of the pre-filtration membrane does not have the same national standard. Different manufacturers have their own definitions and methods. Therefore, you need to pay attention to the selection and replacement of vendors. The same is the 0.22μm pre-filtration membrane, and the filter of different manufacturers should be used. The effect will be very different. The public pore size of sterilization filtration is defined by law, and each business implements a unified standard, and it is relatively simple when selecting and replacing.

　　 filter material

　　 is related to the filter material. According to the relationship with water, the filter material is divided into two types: hydrophilic (water can be wetted) and hydrophobic (water can not be wetted). Hydrophilic filters are mainly used in water or water/organic solution mixing filtration and sterilization filtration, such as cellulose materials (regenerated cellulose, mixed cellulose ester), PVPP polycarbonate, PVDF modified polyvinylidene fluoride ; Hydrophobic filter is through the water is intercepted or guided into the filter membrane, mainly used in solvent, acid, alkali and chemical filtration, tank/equipment respirator, process gas, fermentation intake/exhaust filtration, such as PTFE poly Tetrafluoroethylene, PVDF polyvinylidene fluoride, polypropylene, polysulfone, polycarbonate, etc.

　　 filter characteristics and structure

　　 Filters are generally divided into four types: laminated filter, laminated disc filter, and bag-type air filter dust filter.