What variables affect the performance of microfiltration membranes in an application?
Issuing time:2023-08-31 14:20
The performance of microfiltration membranes is affected by many variables, here is a brief summary:
1. Membrane pore size. The size of the membrane pore size is a key variable that determines the filtration efficiency. The pore size of the microfiltration membrane involves a relatively large range of pore sizes, ranging from 0.1 to 10 microns. The selection of the appropriate pore size depends on the particles or microorganisms to be filtered. Size, at the same time, should take into account potential changes in particle size or shape in actual filtration. For example, in some applications, the particle size distribution may change or the particles may have irregular shapes. Of course, smaller pore sizes can provide better However, it will also lead to higher pressure difference on the membrane and lower flux rate. Therefore, at the beginning of model selection, it is necessary to comprehensively consider the relationship between membrane pore size, filtration efficiency and required flux rate. trade off.
2. Membrane material, the material composition of the membrane affects its chemical and physical properties, including the permeability, selectivity and pollution resistance of the membrane, and is used in microfiltration to ensure the compatibility of chemical and physical properties between the membrane material and the filter material Common membrane materials include polymeric materials such as polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, and polysulfone. Ceramic and metal membranes are also used in some applications, and each material has different characteristics. From the base material of the membrane to the support material, including other modified materials, these characteristics will affect the filtration performance.
3. Membrane morphology, the membrane morphology refers to the membrane structure, including the shape, distribution and surface characteristics of the pores, which will affect the permeability, pollution resistance and mechanical strength of the membrane, because according to the selection of the membrane, the morphology of the membrane is also Different, such as asymmetric, symmetric or gradient structures, etched columnar pores, etc. From the perspective of the pore distribution characteristics of the surface layer, asymmetric membranes with dense surface layers and porous support layers are more commonly used in microfiltration.
4. Working pressure, exerting pressure on the microporous filtration membrane will play an important role in the microfiltration performance. In the case of higher operating pressure, the filtration rate can be increased, but the possibility of membrane fouling may also be increased. Similarly, If it is too low, the expected effect may not be achieved. Therefore, it is necessary to optimize the pressure and set the best pressure range to achieve the required filtration efficiency. At the same time, it can also minimize fouling and energy consumption.
5. Feed characteristics, no matter from the perspective of membrane selection or subsequent practical applications, the characteristics of the feed solution to be filtered must be clearly grasped, such as the particle size distribution, concentration and viscosity of the solution, which will affect the performance of the membrane. Because a high concentration of suspended solids or colloidal particles will lead to increased fouling and reduced flux rate, so to achieve the desired effect, pretreatment methods such as precipitation, coagulation or flocculation of the feed solution in the early stage are the best way to ensure that the filter membrane The most scientific approach to performance.
6. pH value and temperature. The pH value and temperature of the feed solution will affect the performance of the membrane. Extreme pH conditions or high temperatures will cause changes in the characteristics of the membrane material, resulting in a decrease in permeability. In severe cases, it will cause degradation of the membrane. In addition to these important factors that need to be taken into consideration, the membrane must be operated within the recommended pH and temperature ranges specified by the manufacturer for later application.
7. Scaling during filtration, scaling refers to the accumulation of particles, microorganisms or other substances on the membrane surface or in the pores, resulting in reduced filtration performance. This is an inevitable problem for any microfiltration membrane, which causes membrane scaling. The reason depends on many factors, such as the nature of the feed solution, particle size, concentration, and the presence of organic or biological matter. Membrane performance is critical.
8. Cross-flow velocity. In microfiltration, in order to prolong the service life of the membrane, some cross-flow methods are used to allow the feed solution to flow parallel to the membrane surface. The purpose is to reduce fouling by promoting the sweeping action of the fluid. In this method, it should be noted that the cross-flow velocity or shear rate of the fluid on the membrane will affect the removal of trapped particles, thereby affecting the performance of the filtration. Therefore, it is necessary to comprehensively consider various factors to select the optimal cross-flow velocity to achieve effective filtration. At the same time, avoid damage to the membrane itself due to excessive shearing of the fluid.
Among the above-stated variable effects on filtration performance, they are interactive, and the optimization method depends on the specific application and the required filtration goals. It is very important to consider these factors during the design and operation of the microfiltration process. It is also what we said, from the membrane selection, testing, application, maintenance and other stages are not a simple process.