What Is an Ultrafiltration Membrane?
The industrial application of ultrafiltration membranes is very extensive and has become one of the new chemical unit operations. It is used for the separation, concentration and purification of biological products, pharmaceutical products and in the food industry; it is also used as a terminal treatment device in blood treatment, wastewater treatment and ultrapure water preparation. In China, ultrafiltration membranes have been successfully used for the concentration and purification of Chinese herbal medicines. With technological progress, the screening function of ultrafiltration membranes will surely be improved and strengthened, and its contribution to human society will grow.
The structure of ultrafiltration membranes is divided into symmetric and asymmetric. The former is isotropic, without a skin layer, with the same pores in all directions, and belongs to depth filtration; the latter has a denser top layer and a bottom layer mainly of finger-like structure, the top layer being 0.1 micron or less thick with orderly arranged micropores, and the bottom layer 200-250 microns thick, belonging to surface filtration. Industrial ultrafiltration membranes are generally asymmetric. The membrane materials mainly include cellulose and its derivatives, polycarbonate, polyvinyl chloride, polyvinylidene fluoride, polysulfone, polyacrylonitrile, polyamide, polysulfonamide, sulfonated polysulfone, cross-linked polyvinyl alcohol, modified acrylic polymers, etc.
The ultrafiltration membrane screening process uses the pressure difference across the membrane as the driving force and the ultrafiltration membrane as the filtration medium. Under a certain pressure, when the raw liquid flows over the membrane surface, the many tiny micropores densely distributed on the ultrafiltration membrane surface allow only water and small-molecule substances to pass through and become permeate, while substances in the raw liquid larger than the membrane surface pore size are retained on the feed side and become concentrate, thus achieving purification, separation and concentration of the raw liquid. Each metre of ultrafiltration membrane fibre tube wall has about 6 billion 0.01-micron micropores, whose pore size allows only water molecules, beneficial minerals and trace elements in water to pass, while the smallest bacteria are larger than 0.02 microns, so bacteria as well as colloids, rust, suspended solids, sediment and macromolecular organic matter much larger than bacteria can all be retained by the ultrafiltration membrane, realizing the purification process.
In addition, many other factors must be taken into account in actual engineering applications.
Polyacrylonitrile. Abbreviation PAN. Obtained by free-radical polymerization of the monomer acrylonitrile. The acrylonitrile units in the polymer chain are linked head-to-tail. It appears as a white powder, with a density of 1.14-1.15 g/cm3, and softens and decomposes when heated to 220-300 degrees C.
Polyacrylonitrile is mainly used to make synthetic fibres (such as acrylic). It is a synthetic fibre imitating a polymer copolymerized from more than 85% acrylonitrile and other second and third monomers. It is the Chinese trade name for polyacrylonitrile fibre, commonly called 'artificial wool.' DuPont developed pure polyacrylonitrile fibre (trade name Orlon) in the 1940s, but it was never put into industrial production because of difficult dyeing and easy fibrillation. Later, on the basis of improving the spinnability of the polymer and the dyeability of the fibre, acrylic was industrialized. Different countries have different trade names, such as Orlon, Acrilan, Creslan and Zefran in the United States, Courtelle in the United Kingdom, and Exlan, Cashmilon, Cashmerene and Beslon in Japan. Acrylic density is generally 1.16-1.18 g/cm3, and the standard moisture regain is 1.0%-2.5%. The fibre is characterized by good bulkiness and warmth retention, soft feel, and good weather resistance and mildew- and moth-proof properties. It is mainly used as an artificial fibre, commonly called artificial wool; for making yarn, knitted fabrics (pure or blended with wool) and woven fabrics, especially suitable for interior decorative fabrics such as curtains. In materials science, polyacrylonitrile is often used as a matrix to synthesize porous materials, e.g. PAN-based activated carbon.
Many materials can be used to make ultrafiltration membranes, including polyvinylidene fluoride (PVDF), polyethersulfone (PES), polypropylene (PP), polyethylene (PE), polysulfone (PS), polyacrylonitrile (PAN), polyvinyl chloride (PVC), etc. In the early 1990s, polyethersulfone materials found commercial application; in the late 1990s, the better-performing PVDF ultrafiltration began to be widely used in the water treatment industry. Therefore PVDF and PES have become the most widely used ultrafiltration membrane materials.
Furthermore, this technology also sees broad application and practice in related fields.
1) The shell is made of impact-resistant ABS material, with a pressure-bearing capacity above 16 kg and a wall thickness increased by 1 mm, fully able to withstand various pressure shocks that may occur in the feed water, ensuring no rupture under shock water pressure and avoiding long-term pressure on the ultrafiltration membrane during use that could cause creep of the material and leakage.
2) Each HUF90 membrane is loaded with 1400 membrane fibres, with the length extended by 100 mm, increasing the membrane area by 15%; the effective membrane area is higher than that of any domestic product of the same specification, increasing the water yield.
3) The end cap has a hemispherical convex structure; compared with the traditional flat end-face structure, it makes the distribution of feed water on the end-face fibres more uniform, and the wall thickness is increased by 1 mm to ensure no rupture under shock water pressure.
It is worth noting that the technologies and standards in this field continue to evolve and improve.
Among inorganic membranes, ceramic ultrafiltration membranes are used more in household water purifiers. Ceramic membranes have a long life and are corrosion-resistant, but the effluent has an earthy taste that affects the mouthfeel. At the same time, ceramic membranes clog easily and are not easy to clean. Hollow-fibre ultrafiltration membranes, with the advantages of high packing density, large effective membrane area, high pure-water flux, simple operation and easy cleaning, are widely used in the household water purification industry.
In addition, many other factors must be taken into account in actual engineering applications.
An ultrafiltration membrane consists of hundreds to thousands of tiny hollow fibres; generally, an ultrafiltration membrane with a hollow-fibre inner diameter between 0.6-6 mm is called a capillary ultrafiltration membrane; because of its larger inner diameter, the capillary type is not easily clogged by large particles.
Taking the Ingle (Yingge) water purifier on the market as an example, the ultrafiltration membrane undergoes special hydrophilic treatment, giving the fibres long-term hydrophilicity; the water contact angle drops from 79-90 degrees before modification to 30-35 degrees. This yields high flux at lower transmembrane pressure while improving the pollution resistance of the fibres.
Ingle hollow-fibre ultrafiltration membranes have uniform micropores smaller than 0.1 micron, which can remove microorganisms, colloids, diatoms and other turbidity-causing substances.
The mechanical strength of an ultrafiltration membrane reflects the fibre's ability to resist fibre breakage; broken fibres cause the membrane to lose its separation performance and are an important indicator for evaluating ultrafiltration membrane performance.
Ingle uses high-quality PVDF as raw material, giving its hollow-fibre ultrafiltration membrane good chemical corrosion resistance, oxidation resistance and light-aging resistance. Therefore, various methods can be used to clean it repeatedly to remove contaminants and restore flux.
Start with the supply of raw materials, the preparation process and product testing. Ensure stable raw material quality, consistent and precise control throughout the preparation process and 100% inspection of products, to guarantee stable product performance.
Ultrafiltration membrane filtration is a membrane filtration method using the pressure difference as the driving force with an ultrafiltration membrane. Ultrafiltration membranes are mostly made of cellulose acetate or similar high-molecular materials. They are most suitable for the separation and concentration of solutes in solutions, and are also often used for the separation of colloidal suspensions that are difficult to accomplish with other separation techniques; their application field is constantly expanding.
Pressure-difference-driven membrane filtration is divided into three types: ultrafiltration, microfiltration and reverse osmosis. They are distinguished by the minimum particle size or molecular weight the membrane layer can retain. Using the rated pore-size range as the criterion, the microfiltration membrane (MF) has a rated pore size of 0.02-10 mum; the ultrafiltration membrane (UF) 0.001-0.02 mum; and the reverse osmosis membrane (RO) 0.0001-0.001 mum. It can be seen that ultrafiltration membranes are most suitable for the separation and concentration of solutes in solutions, or the separation of colloidal suspensions that are difficult with other separation techniques. The membrane-making technology of ultrafiltration-the technology to obtain the desired size and narrow-distribution micropores-is extremely important. There are many factors controlling the pores; for example, different pore sizes and pore-size distributions can be obtained depending on the type and concentration of the solution during membrane formation, and the evaporation and coagulation conditions. Ultrafiltration membranes are generally polymer separation membranes; the polymer materials used include cellulose derivatives, polysulfone, polyacrylonitrile, polyamide and polycarbonate.
The application of ultrafiltration membranes is very wide-in the food industry, pharmaceutical industry, etc., they can be used for the concentration and purification of drugs, fruit juice and dairy products, and the purification of pure and mineral water; ultrafiltration equipment features good filtration effect, large water output and strong stability.
1. The ultrafiltration membrane elements use products from world-renowned membrane companies, ensuring that customers get the highest-quality organic membrane elements currently available, thus ensuring retention performance and membrane flux.
3. The treatment process has no phase change and has no adverse effect on the components of the material; and the separation, purification and concentration processes are always at room temperature, which is especially suitable for the treatment of heat-sensitive substances, completely avoiding the drawback of high temperature destroying biologically active substances, and effectively retaining the biologically active substances and nutrients in the original material system.
4. The system has low energy consumption and a short production cycle; compared with traditional process equipment, the equipment operating cost is low, which can effectively reduce production costs and improve enterprise economic benefits.
Furthermore, this technology also sees broad application and practice in related fields.
7. The control system can be customized according to the user's specific requirements; combined with Shijia's advanced control software, it centrally monitors important process operating parameters online on site, avoids manual misoperation, and ensures the long-term stable operation of the system in multiple ways.
The membrane must be cleaned regularly to maintain a certain permeate flux and extend its life. The cleaning method is generally determined by the nature of the membrane and the material being treated. Usually similar to reverse osmosis, i.e. first hydraulic cleaning, then depending on the situation use different chemical detergents-for example, an ionic solubilizer can be selected for electrodeposition materials, and a 'bridge-bond' type solvent for water-soluble organic coatings. Protein deposits in the food industry can be removed with a protease solvent or an alkaline detergent based on phosphate or silicate. Precipitates formed by inorganic salts on the membrane surface can be dissolved with chelating agents such as EDTA or with acid/alkali. Different cleaning methods can be selected for different membrane modules-for example, tubular modules can be mechanically cleaned with sponge balls, and hollow-fibre modules can be backwashed. Membranes for the food industry also require disinfection (with NaOH, H2O2, etc.).
Physical methods use mechanical force to remove pollutants from the membrane surface, with no chemical reaction, so they are simpler, more convenient and healthier. Here are a few practical ones.
In addition, many other factors must be taken into account in actual engineering applications.
Before use, ultrafiltration membranes are generally immersed in a protective solution and sealed for storage to prevent the wet membrane from shrinking after dehydration, which would reduce the pore size, destroy the membrane structure and lower the water flux.
Short-term storage: if the ultrafiltration membrane is suspended from use (for less than 10 days), it should be sterilized and backwashed once; after adding 15 ppm (ml/L) of HY-240 bactericide to the backwash water, close the inlet valve, drain valve and regulating valve of the ultrafiltration membrane to maintain its sealing and sterilization effect.
Long-term storage: if the ultrafiltration membrane is stopped for a long time (more than 10 days), first sterilize and backwash it once, then inject HY-310 protective solution into the membrane and store it sealed (preferably RO water).
Ultrafiltration equipment uses the ultrafiltration membrane as its core product, exploiting the interception ability of porous materials to remove impurity particles of a certain size from water by physical retention. Driven by pressure, small-sized substances in the solution-water, organic low-molecular-weight substances, inorganic ions, etc.-pass through the micropores in the fibre wall to the other side of the membrane, while large-sized substances such as bacteria, colloids, particulate matter and organic macromolecules are retained, thus achieving the purpose of screening different components in the solution.
Ultrafiltration equipment uses pressure as the driving force and is a physical screening process that uses ultrafiltration membranes of different pore sizes to separate liquids. Its molecular weight cut-off (MWCO) is generally 6,000 to 500,000, with a pore size of 100 nm. The membrane used is an asymmetric membrane whose active separation layer has an average pore size of about 10-200 angstrom and can retain macromolecules and colloidal particles with a molecular weight above 500; the operating pressure difference is 0.1-0.5 MPa.
The application range of ultrafiltration membranes is extremely wide; basically any industry involving filtration can use filtration equipment. The basic filtration industries are as follows: as reverse osmosis pretreatment and ultrapure water terminal treatment in pure and ultrapure water preparation; for separating bacteria, pyrogens, colloids, suspended impurities and macromolecular organics in industrial water; purification of drinking water and mineral water; concentration, purification and clarification in the fermentation, enzyme preparation and pharmaceutical industries; concentration and separation of fruit juice; separation, concentration and clarification of soybean, dairy, sugar, liquor, tea juice, vinegar, etc.; purification and recovery of industrial and domestic sewage; and recovery of electrodeposition paint.
Ultrafiltration membrane separation can replace natural sedimentation, plate-and-frame filtration, vacuum drum, centrifugal separation, solvent extraction, resin purification and activated carbon decolorization in traditional processes. The process operates at room temperature, with no phase change and no secondary pollution.
Abroad, ultrafiltration is mainly applied to drinking water treatment, while in China it is mainly used for wastewater reuse in the industrial field, as reverse osmosis pretreatment. In the domestic water industry market, ultrafiltration technology has been widely applied in the power, steel and chemical industrial wastewater treatment fields.
With economic and social development, there will be more and more large-scale wastewater treatment projects, opening up a broad market space for ultrafiltration membrane technology. Abroad, many waterworks already use ultrafiltration to produce tap water; in China, due to funding and other issues, it has not yet been widely applied. But with the revision of national and local drinking water standards and the introduction of new norms, ultrafiltration technology will surely be adopted by more and more waterworks. According to the analysis in the Ministry of Water Resources' 'China's Water Supply and Demand in the 21st Century,' after 2010 China will begin to enter a severe water-shortage period, and water pollution is gradually becoming the biggest obstacle to safe urban water supply. Municipal domestic sewage treatment and reclaimed water reuse will become one of the effective ways to solve the future urban water resources crisis. Therefore, ultrafiltration membranes will have a broad market space in the future municipal sewage treatment market.
Building on this, industry experts have also carried out extensive research and improvements.
>0.2 um particle removal rate: 100% (under a molecular weight cut-off of 80,000 Daltons)
At the same time, the supporting processes and equipment are being continuously optimized and upgraded.
With the increasingly advanced development of China's water treatment technology, the filtration function of ultrafiltration membranes has also been greatly improved. To date, basically any industry involving filtration equipment and processes can use ultrafiltration membranes.
Almost all industries in China are involved in water treatment, e.g. separation of bacteria, pyrogens, colloids, suspended impurities and macromolecular organics in industrial water; terminal treatment for pure and ultrapure water preparation in drinking water; separation, drinking water and mineral water purification in drinking water; and also concentration, purification and clarification in the fermentation, enzyme preparation and pharmaceutical industries; fruit juice concentration and separation; separation, concentration and clarification of soybean, dairy, sugar, liquor, tea juice, vinegar, etc.; purification and recovery of industrial and domestic sewage; and recovery of electrodeposition paint, etc. It can be seen that the role of ultrafiltration membranes is very wide.
Ultrafiltration is the process of filtering a solution containing macromolecules or fine particles using an ultrafiltration membrane with a pore size of 1 to 20 nm, so that the macromolecules or fine particles are separated from the solution. It uses the pressure difference across the membrane as the driving force and the ultrafiltration membrane as the filtration medium; under a certain pressure, small-molecule solutes and solvent pass through the ultrafiltration membrane of a certain pore size, while macromolecular solutes cannot pass and remain on one side of the membrane, thus achieving the purification, separation and concentration of the solution. It is mainly used to retain macromolecular solutes. For example, it is used to treat feed liquids without solid content, where solutes of lower relative molecular mass and water pass through the membrane while solutes of higher relative molecular mass are retained.
With the development of membrane-making technology and large-scale production, GE ultrafiltration RO membranes have more stable performance and much lower membrane cost; at present, ultrafiltration membranes have been widely used in drinking water purification, industrial water treatment, beverages, biology, food, medicine, environmental protection and many other aspects, and have won unanimous praise from the industry. [1]
In addition, many other factors must be taken into account in actual engineering applications.
Swimming pools use UF ultrafiltration membranes, which effectively solve the pool water purification problem and provide technical support for creating a better entertainment environment for people.
