In order to meet the requirements of industrial production and drinking water, various membrane technologies came into being. It is different from traditional filtration in that the membrane can be separated in the molecular range, and this process is a physical process without phase change and adding additives. Membrane is a material with selective separation function. The process of using membrane selective separation to realize the separation, purification, and concentration of different components of feed liquid is called membrane separation. The pore size of the membrane is generally micron. According to the different pore size (or the retained molecular weight), the membrane can be divided into microfiltration membrane, ultrafiltration membrane, nanofiltration membrane and reverse osmosis membrane. According to the different materials, it can be divided into inorganic membrane and organic membrane. The inorganic membrane is mainly ceramic membrane and metal membrane, with low filtration precision and small selectivity. Organic membranes are made of high molecular materials, such as cellulose acetate, aromatic polyamide, polyethersulfone, polyfluoropolymer and so on.
Microfiltration (MF), also known as microporous filtration, belongs to precision filtration. Its basic principle is the process of sieve separation. The materials of microfiltration membrane are divided into organic and inorganic. The organic polymers include cellulose acetate, polypropylene, polycarbonate, polysulfone, polyamide, etc. Inorganic membrane materials include ceramics and metals. In view of the separation characteristics of microporous membrane, the application scope of microporous membrane is mainly to intercept particles, bacteria and other pollutants from the gas phase and liquid phase, so as to achieve the purpose of purification, separation and concentration.
For microfiltration, the interception characteristic of membrane is characterized by the pore size of the membrane, which usually ranges from 0.1 to 1 micron. Therefore, microfiltration membrane can separate large-diameter bacteria and suspended solids. It can be used for clarification of general feed liquid, security filtration and air sterilization.
Ultrafiltration (UF) is a membrane process between microfiltration and nanofiltration. The pore size of the membrane ranges from 0.05um to 1000um molecular weight. Ultrafiltration is a membrane separation technology that can purify, separate and concentrate the solution. The ultrafiltration process can generally be understood as a screening process related to the pore size of the membrane. With the pressure difference on both sides of the membrane as the driving force and the ultrafiltration membrane as the filter medium, when the water flows through the membrane surface under a certain pressure, only water and small molecular substances smaller than the pore diameter of the membrane are allowed to pass through, so as to achieve the purpose of purification, separation and concentration of the solution.
For ultrafiltration, the retention characteristic of the membrane is characterized by the retention molecular weight of the standard organic matter, which usually ranges from 1000 to 300000. Therefore, the ultrafiltration membrane can separate macromolecular organic matter (such as protein, bacteria), colloids, suspended solids, etc., and is widely used in the clarification of material liquid, the separation and purification of macromolecular organic matter, and the removal of heat source.
Application: the membrane used for clarification, purification, and separation is mainly ultrafiltration / microfiltration membrane. Due to its wide distribution of intercepted material diameter, it is widely used in solid-liquid separation, separation of large and small molecular substances, depigmentation, product purification, oil-water separation and other processes.
Ultrafiltration / microfiltration membrane separation can replace the traditional processes such as natural sedimentation, plate and frame filtration, vacuum drum, centrifuge separation, solvent extraction, resin purification, activated carbon decolorization, etc.
The membrane separation components that can be used for clarification and purification technology mainly include: ceramic membrane, flat membrane, stainless steel membrane, hollow fiber membrane, roll membrane and tubular membrane.