Applications of membrane separation technology

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Product Overview: The large-scale commercial application of membrane separation technology began with seawater desalination projects in the 1960s. Currently, in addition to being widely used for desalinating seawater and brackish water as well as for producing pure water and ultrapure water, it is also applied in fields such as the food industry, pharmaceutical industry, bioengineering, petroleum, chemical industry, and environmental protection engineering. The membrane industry will be one of the top ten new high-tech industries of the 21st century; just like technologies such as optical fibers and superconductivity, it will also be one of the six key technologies that will shape future industry. Inorganic membranes and their characteristics: Inorganic membranes are a type of solid membrane, made from inorganic materials such as metals, metal oxides, ceramics, porous glass, zeolites, and inorganic polymers. Inorganic membranes possess several advantages that polymer separation membranes do not have: 1. They exhibit excellent chemical stability, resisting acids, bases, and organic solvents; they can be cleaned using a wider range of methods than organic membranes. 2. They have high mechanical strength – the membranes supported on them can withstand external pressures of several dozen atmospheres, and they can also be flushed in reverse direction. 3. They have strong antimicrobial properties and do not interact with microorganisms, making them suitable for use in bioengineering and medical science fields. 4. They are resistant to high temperatures; they can generally operate at 400 degrees Celsius, with some even capable of operating at over 800 degrees Celsius. 5. They have a narrow pore size distribution, resulting in high separation efficiency.

Features of membrane separation technology: Compared to traditional separation techniques such as distillation, adsorption, absorption, extraction, and cryogenic separation, membrane separation has the following advantages: ■ Membrane separation is typically an efficient separation process. ■ The energy consumption during membrane separation processes is usually low. ■ Most membrane separation processes take place at room temperature, which makes them particularly suitable for processing heat-sensitive substances. ■ Membrane separation equipment does not contain moving parts, and since it operates at room temperature, it requires little maintenance, ensuring high reliability. Its operation is very simple, and the time from starting it up to obtaining the product is short, allowing for frequent starts and stops. ■The scale and treatment capacity of membrane separation processes can vary over a wide range, while their efficiency, unit cost of equipment, and operating costs remain relatively constant. ■Due to its high separation efficiency, membrane separation typically results in equipment of relatively small size and less space requirement. The research on our company’s products has spanned 11 years. Laboratory tests, small-scale scale-up trials, and practical applications have proven that these products effectively address the issues of high costs associated with inorganic membranes, difficulties in industrial application, and poor performance. They hold great potential for development and there is a strong market demand for them. The filter element has a disc-shaped structure with radial filtrate channels in the center; compared to traditional inorganic membranes, it increases the filtering area by 1–2 times under the same diameter specifications. Over 85% of the main components of this disc-shaped filter element are SiO2, giving it stable chemical properties and high precision. If installed on filtration equipment, it will **reduce the size of the filter and improve its filtration efficiency. It also solves the problems associated with inorganic and organic membranes, such as high costs, low temperature resistance, poor acid and alkali resistance, low mechanical strength, and uneven pore sizes. Performance characteristics of microfiltration and ultrafiltration membrane element dynamic filters: The series of static filter products using microfiltration and ultrafiltration membrane elements manufactured by our company were granted a health permit for products related to drinking water hygiene and safety by the Ministry of Health in May 2004. The microfiltration and ultrafiltration membrane element dynamic filter uses the diatomite membrane elements produced by our company as filtering media, while the material of the filter body can be selected as high-quality carbon steel or stainless steel according to the customer’s requirements. The features of the DLP4-* type dynamic filter are as follows: (1) Continuous filtering enables a large and stable flow rate, resulting in high production efficiency ； (2) It has strong adaptability, is not sensitive to changes in the turbidity of the feed slurry, and no pre-treatment of the feed filtrate is required ； (3) High filtration and clarification efficiency ； (4) It has good filtration efficiency; the solid content in the filter cake ranges from 25% to 70%, the discharge concentration can be adjusted, and it has a wide range of applications ； (5) There is no need to remove the filter plates; cleaning can be carried out without shutting down or disassembling the equipment, thus maintaining the high filtration capacity of the filtering medium and allowing the device to maintain an almost constant flow rate during continuous operation ； (6) It is convenient for washing; washing and filtering can be carried out simultaneously. By injecting washing liquid into the filter chamber during the filtration process, the mother liquor can be displaced, enabling continuous co-current washing to complete the displacement and washing of the mother liquor ； (7) Fully enclosed structure that prevents secondary pollution, facilitates aseptic operation, and stops odors as well as harmful slurries from leaking out ； (8) Low filtration cost; no need to add any filter aids or coagulants, resulting in savings on filter media expenses ； (9) Low-pressure constant-speed filtration, with low power consumption; operating pressure ≤ 0.6 Mpa ； (10) Useful products recoverable from the filtrate ； (11) It is a new type of environmentally friendly product that **reduces the economic losses and pollution emissions associated with the use of filter aids in traditional static filters** ； (12) It is easy to operate, reducing the workload of the operators and improving the hygiene conditions in the filtration environment. Key performance parameters of the equipment: Filtration area: optional; Water flow rate: 1 ton per square meter per hour; Turbidity: ≤5 (NTU); Operating pressure: ≤0.6 Mpa; Filtration precision: 0.1–1.0 μm; Material: high-quality carbon steel; Temperature resistance: 140°C. Application of inorganic membranes: Microfiltration membranes have a wide range of applications. Since the fluids to be treated, the scale of operation, and the operating environment vary, there is no single pore size design that can meet the requirements of all users; therefore, the pore size should be adjusted according to the specific application area and requirements. The application areas of microfiltration membranes are shown in the table below: Porosity / μm, Applications: 12 – Separation of suspended particles in bacterial solutions in microbiological research; 3–8 – Refining sugar, clarifying liquids, determining the weight of industrial dust, detecting particulate impurities in internal combustion engines and oil pumps, separating water droplets from organic liquids (hydrophobic membranes), cytological research, diagnosis of cerebrospinal fluid, filtering before filling pharmaceutical solutions, determining the amount of malt sediment in beer production, concentrating parasites and eggs. 1–2 – Tissue transplantation, cytological research, diagnosis of cerebrospinal fluid, microscopic monitoring of yeast and molds, analyzing dust weight. 0.6–0.8 – Sterilizing gas filtration, clarifying large-dose injections, quantitative analysis of radioactive aerosols, cytological research, cold sterilization of beverages, clarifying oils, quality control of precious metal solutions, clarifying photoresists and painting solvents, analyzing impurities in oils and fuel oils, detecting E. coli in milk, determining residues in liquids. 0.45 – Sterility testing of antibiotics and other injections, detecting E. coli in water, beverages, and food, determining phosphate levels in drinking water, sterilizing culture media, quality control of aviation fuels and other oils, purifying dielectric solutions used for blood cell counting, checking the color of white sugar, ultra-purification of deionized water, radioimmunoassay of insulin, liquid scintillation analysis, partially removing microorganisms from liquids, determining the iron hydroxide content in boiler water, controlling the quality of water used in reverse osmosis, identifying microorganisms. 0.2 – Sterilizing filtration of pharmaceutical solutions, biological agents, and heat-sensitive liquids, counting bacteria in liquids, sterilizing water used for urinalysis, quantifying viruses in air, used for ultra-purification in the electronics industry. 0.1 – Production of ultra-pure reagents and other liquids, analyzing suspensions, separating precipitates, creating physiological membrane models. Examples of applications of filtration technology by industry: Industry, Application Examples: Experimental analysis – Absolute filtration to collect precipitates, clarifying solutions, measuring enzyme activity, conducting receptor binding studies, etc. Pharmaceutical industry – Sterilizing and removing impurities from drug substances and their formulations, comprehensive treatment of wastewater generated during pharmaceutical production, filtering and clarifying fine flocs in traditional Chinese medicine extracts. Petroleum industry – Liquid-solid separation in catalyst production, treating water used in low-permeability oil fields, etc. Medical industry – Sterilizing and removing particles from eye drops and intravenous injections. Microbiology – Concentrating bacteria, yeast, molds, eggs, etc. Electronics industry – Controlling and detecting particles and bacteria in clean production environments for electronic products, removing impurities from ultra-pure reagents. Metallurgy – Treating wastewater from the metallurgical industry. Water treatment – Removing particles and bacteria in the production of ultra-pure water and drinking water. Wastewater treatment – Used as a wastewater treatment unit to save land space and reduce subsequent treatment costs, decolorizing dyeing wastewater, etc. Applications of inorganic membrane filtration in the food industry: The food industry is the largest market for microporous filtration, with applications ranging from filtering and sterilizing alcoholic beverages such as beer, liquor, rice wine, wine, and fruit wine to achieving clarity in these beverages ； Clarification and filtration of fruit juice beverages, gelatin, glucose, etc ； Filtering and sterilization of milk ； Many fields such as the recycling of beer residues. Since the application of membrane technology in the food industry requires operations such as cleaning and disinfection, and high shear speeds are needed when dealing with highly viscous materials, inorganic membranes represent a suitable choice. These membranes not only feature a long service life, stable operation, and high separation efficiency, but they also allow for in-situ steam disinfection, which is crucial for ensuring food quality. The advancement of membrane separation processes in the food industry: Compared to traditional methods used in this industry, membrane technology offers significant advantages. 1. Energy efficiency: The membrane separation process does not involve phase changes, which gives it the advantage of cold sterilization; it requires less energy compared to separation methods that rely on phase changes or other separation techniques, and it makes use of clean energy – electricity. Therefore, membrane separation technology is also known as energy-saving technology. 2. Preserving color, flavor, aroma, and nutritional components: The membrane separation process is carried out at room temperature, making it particularly suitable for the separation, fractionation, concentration, and enrichment of heat-sensitive substances such as juices, amino acids, vitamins, etc ； At the same time, in membrane separation processes, the materials circulate within a closed loop, which reduces the impact of oxygen in the air; both heat and oxygen have a significant effect on food processing ； The material does not undergo any change in properties as it passes through the membrane ； Membrane separation processes can also be used for cold sterilization, as an alternative to the conventional heat-based pasteurization method ； Therefore, in membrane separation processes, it is possible to keep the color, aroma, taste, and nutritional components of the product unchanged as much as possible, thus preserving its original qualities. 3. Wide range of applications: Any substance larger than 0.1μm can be filtered out using the inorganic membranes produced by our company; bacteria, yeast, and molds can all be trapped, while most of the active ingredients in food can pass through the membranes. 4. Simplified processes and operations: The membrane separation process is relatively simple to operate, allows for easy automation, requires less space, is easy to maintain, has a long service life, and results in reduced operational costs. Microporous filtration for the sterilization and clarification of alcoholic beverages is used for the precise filtration of such drinks, and it can **improve their clarity. The use of polymer membranes or inorganic membranes, along with diatomaceous earth as a filter aid, for filtering beer in order to remove impurities such as yeast, has a history of many years ； Used to filter low-alcohol and high-alcohol baijiu in order to effectively remove suspended particles from the liquor and improve its transparency ； It is used to filter wines and other fruit-based beverages in order to remove yeast and other impurities, and it is also employed in the filtration of traditional Chinese medicine liquors as a substitute for methods such as asbestos filtration that were previously used. Clarification and separation in the beer brewing process: Filtration is the final and crucial step in beer production for improving product quality, especially when the beer is intended for long-term sale or storage; in such cases, it is necessary that the beer maintain biological safety as well as stability in terms of colloidal properties and flavor. Inorganic membranes are used in beer production primarily for removing microorganisms to clarify the beer and for recovering beer from deposits at the bottom of the tanks. (1) Removal of bacterial or microbial cells: The presence of bacteria or microorganisms can affect the flavor of beer and shorten its shelf life. Traditional filtration methods involve the use of diatomaceous earth, etc., which can remove yeast and some bacteria; however, they are not very effective at removing bacteria. Therefore, pasteurization is required before bottling to kill these bacteria or microorganisms. Due to the high-temperature treatment involved, some aromatic compounds get oxidized, affecting the flavor of the beer. Meanwhile, bacterial cells remain in the beer after pasteurization. Porous inorganic membranes represent a promising new technology for replacing pasteurization and enabling the direct clarification filtration of beer. By using this technology, it is possible to avoid heat treatment of beer, thereby achieving both sterilization and clarification while preserving its flavor and taste. The comparison of traditional and modern processes for beer clarification is as follows: Traditional process: Fermentation – pre-clarification by centrifugal sedimentation of unfiltered beer – diatomaceous earth filtration – plate and frame filtration – dead-end filter – sterilizing filter. Microfiltration technology: Fermentation – pre-clarification by centrifugal sedimentation of unfiltered beer – microfiltration to produce a sterile filtrate. In the clarification and filtration of beer, it is very important to select an appropriate membrane pore size; this ensures that suspended particles and microorganisms are retained during filtration, while at the same time preventing changes in the beer’s color, taste, and other quality parameters such as protein content. The 0.2μm membrane has a high retention rate for proteins and pigments in beer, at 12% and 30% respectively; the properties of the beer product change significantly after clarification, which is unacceptable. In contrast, under the same conditions, the 0.5μm membrane can reduce microorganisms to levels below 1 per milliliter, with a removal rate of 99.990%–99.998% for Acetobacter, while its retention rate for pigments is only 3%, and the content of nitrogen and total solids in the retained substances is low. (2) Recovery of yeast and beer from bottom sediment in tanks. Beer production involves four main steps: extracting malted barley and other materials with water; heating the extract to boiling; cooling the extract and adding yeast for fermentation; and clarifying the mixture. Yeast is recovered after fermentation, and the conventional method for this purpose is centrifugation, although inorganic membrane filtration technology holds more potential. The recovery of beer from bottom sediment in tanks represents a potential application area for inorganic membranes in the beer industry. This sediment consists of flocculated liquid extracts that contain suspended solids, collagen particles, yeast, etc., and contains 90% to 99% beer. There are two types of bottom sediment in beer production: sediment from fermentation tanks and sediment from aging tanks, with solid contents of 10–15 grams per liter and 40–50 grams per liter respectively. Traditional treatment methods include vacuum filtration, pressure filtration, and centrifugal separation. Microfiltration technology has become a highly competitive alternative due to its ability to reduce operational costs; it allows for the production of clear beer without the need for filter aids, and membrane filtration can be carried out in a sealed environment, preventing the raw material solution from being exposed to air and thus maintaining a low oxygen content in the beer. The recovery of beer from the sediment at the bottom of membrane filtration tanks is usually carried out after the yeast fermentation process. The clarified beer obtained in this way can account for up to 5% of the total beer production; the residue contains concentrated yeast oils. By using membrane filtration technology, a large amount of diatomaceous earth can be saved, which reduces waste discharge as well as the costs associated with purchasing diatomaceous earth. Compared to traditional diatomaceous earth beer filtration systems, the advantages of membrane filtration are: ■ It enables the production of clear, unsterilized beer from unpurified beer, as a substitute for diatomaceous earth filtration ； ■ To produce clear, sterilized beer as a substitute for diatomaceous earth filtration and pasteurization ； ■ Clear, sterilized beer was produced from unfiltered beer and can bottoms to replace diatomite filtration, pasteurization, and can bottom filtration. The economic efficiency of membrane filtration depends on the cost of the membrane filtration unit, the membrane area and flux (i.e., production capacity), as well as factors such as water, electricity, and gas consumption as well as maintenance costs. Therefore, in equipment design and production practices, the pore size of the microfiltration membrane should be selected based on the solid content and properties of the particles in beer. Membranes with a pore size of 1.3 μm and above are suitable for recovering beer from sediment at the bottom of tanks ； Membranes with a pore size of 0.5–1 μm can replace diatomaceous earth as the primary filtering medium in beer to remove suspended particles from it ； Membranes with smaller pore sizes, such as 0.2–0.5 μm, can replace pasteurization to remove bacteria from beer and produce \"sterile\" beer, thereby reducing costs and expenses. In actual industrial applications, it is often a combination of various types of microfiltration membranes with different pore sizes. Filtering and clarifying baijiu: In recent years, as people’s awareness of health has increased and **whiskey industry policies have changed, there is a greater preference for consuming low-alcohol baijiu, rice wine, wine, and other types of fruit wines. During the reprocessing of low-alcohol baijiu, the decrease in alcohol content easily leads to the formation of white turbidity, causing the sensory quality parameters of the baijiu to fail to meet the standards. The main components of these white turbid substances are ethyl palmitate, ethyl linoleate, ethyl oleate, etc. The particles in these turbid substances are small and evenly distributed, resulting in a very slow natural sedimentation rate. Therefore, filtration is necessary to remove these turbidities during the production of low-alcohol baijiu, while it is also important to minimize any loss of flavor compounds in the baijiu during the filtration process. Replacing traditional separation processes and equipment, such as freezing methods, precipitation adsorption, diatomite adsorption, and ion exchange or molecular sieve adsorption, with microfiltration membranes can **reduce production costs and improve economic efficiency. Using inorganic membranes to remove turbidity from baijiu can significantly improve its clarity, preserve its color, aroma, and taste, and extend its shelf life. Baijiu filtered through microfiltration can effectively remove microorganisms. Application in vinegar production: During the fermentation process of producing vinegar from dilute alcohols, the presence of Pseudomonas aeruginosa causes turbidity in the liquid product. Inorganic membrane filtration can remove this bacterium from the concentrate, thereby clarifying the liquid product, significantly improving its transparency, and eliminating bacteria as well. After treatment with an inorganic membrane, good clarification was achieved, with the turbidity of the permeate remaining within the range of 0.2–0.8 NTU. Applications in soy sauce production: Since the production process of soy sauce takes place in open environments, during the fermentation and decomposition of raw materials, various microorganisms such as bacteria, actinomycetes, and yeasts grow and multiply. The presence of these fungi not only affects the normal decomposition process carried out by enzymes, but also causes unusual odors and phenomena, leading to changes in the flavor of soy sauce or even its spoilage. Therefore, it is crucial to kill or remove these contaminants promptly after soy sauce is produced, in order to maintain its quality. Moreover, as people’s living standards improve, there are higher demands regarding the color, aroma, taste, and hygiene standards of seasonings such as soy sauce and vinegar, which increases the social and economic value of degreasing and clarifying soy sauce. The types and sizes of bacteria in soy sauce are shown in the table below. As can be seen from the table, membranes with a size of no more than 0.5 μm can completely remove the unwanted bacteria in soy sauce. Bacterial categories: Bacteria, Actinomycetes, Yeasts, Molds. Size in μm: 0.5–5, 1, 5–3, 3–10. Filtration and sterilization of yellow rice wine: Since yellow rice wine is a non-distilled beverage, the raw wine contains large amounts of turbidity-causing substances, colloids, bacteria, and other microorganisms. To improve the quality of yellow rice wine and extend its shelf life, it must be filtered and sterilized before it can be released onto the market. The traditional treatment method involves filtering first with cotton cakes, followed by heating for sterilization. The disadvantages of this processing method include high labor intensity, significant loss of yellow rice wine, and severe environmental pollution. Replacing cotton cake filtration and steam sterilization with microfiltration allows E. coli and other contaminants as well as suspended impurities to be removed at lower temperatures, which plays an important role in reducing raw material consumption and production costs while improving the quality of yellow rice wine. The clarification and filtration of fruit juices: The application of inorganic membrane technology is very useful for improving the quality of fruit juices and reducing operational costs. Firstly, it enables the combination of filtration and pressing in a single unit, reducing production costs ； Secondly, inorganic membrane treatment helps to preserve the original flavor of the juice ； Thirdly, injuice filtration using inorganic membranes offers advantages such as high permeation flux, low protein adsorption, good mechanical strength, resistance to high-pressure backwashing and deformation during the process, as well as good thermal stability that allows for high-temperature in-situ disinfection. One of the most successful applications of microfiltration membranes is in the clarification and purification of fruit juices. Inorganic ceramic membranes are more suitable for this purpose than polymer membranes, as they possess strong antimicrobial properties; the equipment using these membranes can be disinfected with steam, and they can be regenerated through backwashing with high-pressure fluids. In the early 1980s, inorganic membranes were widely used in France’s juice industry; the juices filtered using these membranes had excellent quality, and they possessed a more pleasant aroma compared to juices produced by the traditional diatomite filtration and pasteurization method. Inorganic membranes are used for the clarification of fruit juice primarily to remove bacteria, pectin, and crude proteins that can easily cause the juice to spoil. Traditional juice production methods involve centrifugal separation, diatomaceous earth filtration, and pasteurization; in particular, pasteurization results in the loss of most of the aromatic flavors in the juice. Processing process: Clean fruits – crushing – juicing – coarse filtration – enzymatic clarification – microfiltration – sterilization and packaging. Using these methods, the resulting juice is uniform in texture, clear and transparent, with no suspended particles or stratification. Fresh milk is filtered and sterilized. As people’s living standards continue to improve, their expectations regarding their diet become higher and higher. Fresh milk has become a common nutritional product consumed by people. The main types of fresh milk available on the market today are pasteurized milk, ultra-high temperature sterilized (UHT) milk, and microfiltered milk. Among them, UHT milk has gradually been accepted by people due to its long shelf life, safety and hygiene, good taste, and moderate price, and it has partially replaced pasteurized milk. The application of membrane separation technology in the dairy industry began in the 1970s, initially in cheese production, and later expanded to areas such as the concentration of whey protein, the manufacture of milk powder and curd, the separation of proteins and peptides, the sterilization of skim milk, and the concentration of milk. Microfiltered milk is another type of liquid dairy product that has become popular abroad in recent years. Since microfiltration technology uses microfiltration membranes to remove impurities and bacteria from milk under specific temperature and pressure conditions, it not only requires less energy but also avoids high-temperature heating, allowing the fresh milk to retain its original flavor – which is why it is very popular among consumers.