Review of membrane separation technology applications

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Overview of the application of membrane separation technology 1. Membrane separation technology Membrane separation is a new separation technology that appeared in the early 20th century and emerged rapidly after the 1960s. Membrane separation technology has the functions of separation, concentration, purification and refining, as well as high efficiency, energy saving, environmental protection, molecular-level filtration and simple filtration process, easy control. Therefore, it has been widely used in food, medicine, biology, environmental protection, chemical industry, metallurgy, energy, petroleum, water treatment, electronics, bionics and other fields. It has produced huge economic and social benefits and has become one of the most important means in today's separation science. Membranes can be in solid phase, liquid phase, or even gas phase. There are many kinds of membranes made from various natural or artificial materials, showing various properties in terms of physical, chemical and biological properties. Most people would think that membranes are very far away from our lives. In fact, this is not the case. Membrane separation technology is very close to our daily lives. Membrane separation technology will be used in everything we may come into contact with at any time, such as water, juice, milk, health products, traditional Chinese medicine, tea foods, beverages, condiments, etc. With the rapid development of the national economy, the application fields of membrane separation technology will not only become more and more extensive, but also will be recognized and accepted by more and more people. According to preliminary statistics, the sales of membranes and membrane modules in the world in 2001 were close to US$8 billion, and the market for complete equipment and membrane projects has reached tens of billions of US dollars, and is still increasing by 10% to 20% every year, showing the broad prospects of this emerging industry. 2. Development History, Current Situation and Prospects of Membrane Separation Technology (1) Development History Membranes are widely found in nature, especially in living organisms, but the historical process from our human understanding, utilization, simulation to artificial synthesis is long and tortuous. The development of membrane science and technology in my country began with the study of ion exchange membranes in 1958. Entered the pioneering stage in the 1960s. The exploration of reverse osmosis began in 1965, and the national seawater desalination campaign began in 1967. * * Promoted the development of membrane technology in my country. Entered the development stage in the 1970s. During this period, various membranes and components such as microfiltration, electrodialysis, reverse osmosis and ultrafiltration were successively researched and developed. In the 1980s, they entered the stage of promotion and application. The 1980s was another stage of development of gas separation and other new membranes. (2) Current situation With the development of membrane science and technology in my country, corresponding academic and technical groups have also been established one after another. Their establishment plays a decisive role in standardizing the standards of the membrane industry and promoting the development of the membrane industry. Over the past half century, membrane separation has completed the transformation from laboratory to large-scale industrial application, becoming a new separation technology with high efficiency and energy saving. Since 1925, a new membrane process has been applied in industry almost every decade. Due to the superior performance of membrane separation technology itself, the membrane process has now received widespread attention from countries around the world. Today, with energy shortages, resource shortages, and ecological environment deterioration, the industrial and scientific circles regard the membrane process as an extremely important new technology in the transformation of industrial technology in the 21st century. Some experts have pointed out: Whoever masters membrane technology will master the future of the chemical industry. Since the 1980s, my country's membrane technology has entered the application stage, which is also the development stage of new membrane processes. During this period, membrane technology has been developed and applied on a large scale in the fields of food processing, seawater desalination, pure water, ultrapure water preparation, medicine, biology, environmental protection and other fields. And, during this period, * * Key science and technology projects and natural science funds also have membrane topics. At present, this emerging industry with huge potential is challenging the market with vigorous passion, and has brought significant economic, social and environmental benefits to many companies. (3) Looking forward to the present, membrane separation technology has made great progress, but after all, it is still in the rising stage of development, and there is still a lot of work for us to do. Membrane science and technology in the 21st century will further improve and perfect existing membrane processes, continuously explore and develop new processes and materials, and continue to expand original application fields, so that membrane technology can play a greater role. Outlook one: We must be committed to organically combining emerging membrane separation technologies with traditional process technologies, and constantly pushing membrane technology research results from the laboratory to industrial applications. Outlook 2: We must devote ourselves to researching new membrane materials and developing new polymeric membrane materials. Outlook 3: We must devote ourselves to the research and development of new film-forming processes and further prepare ultra-thin, highly uniform, and defect-free asymmetric film skin technologies and processes. Outlook 4: We must be committed to pushing the development of inorganic membranes forward. Inorganic membranes have some advantages that other polymer membranes cannot have, such as: Inorganic membranes are resistant to acids, alkalis, and organic solvents, have good chemical stability, high mechanical strength, strong resistance to microbial contamination, high temperature resistance, narrow pore size distribution, and high separation efficiency, and have attracted more and more attention from academia and industrial applications. In the future development process, it is an inevitable trend to study new materials and new processes for inorganic membranes. Outlook 5: Whether in academic or industrial applications, research on microfiltration, ultrafiltration, nanofiltration, reverse osmosis, electrodialysis, gas separation, pervaporation and other topics will be a top priority. 3. Characteristics of Membrane Separation Technology The membrane separation process is an efficient and environmentally friendly separation process. It is a multidisciplinary process. * It is a high-tech technology that can exhibit various properties in terms of physical, chemical and biological properties and has many advantages. Compared with traditional separation technologies such as distillation, adsorption, absorption, extraction, cryogenic separation, etc., membrane separation technology has the following characteristics. ※ Efficient separation process ※ Low energy consumption ※ Working temperature close to room temperature ※ Good quality stability ※ Continuous operation ※ Strong flexibility ※ Pure physical process ※ Environmentally friendly ※ …… 4. Basic characteristics of membrane separation process Membrane separation technology is widely welcomed by users for its significant energy saving effect, simple equipment, convenient operation and easy control. Selecting an appropriate membrane separation process can replace various traditional separation and filtration methods such as drum vacuum filtration, plate and frame filter press, ion exchange, centrifugal separation, solvent extraction, electrostatic precipitator, bag filtration, adsorption/regeneration, flocculation/copolymerization, decantation/precipitation, evaporation, crystallization, etc. 5. Commonly used membrane separation processes (1) Microfiltration In view of the separation characteristics of microporous filter membranes, the application scope of microporous filter membranes is mainly to intercept particles, bacteria and other pollutants from the gas phase and liquid phase to achieve the purpose of purification, separation and concentration. The specific areas involved mainly include: Pharmaceutical industry, food industry (gelatin, wine, liquor, juice, milk, etc.), high-purity water, urban sewage, industrial wastewater, drinking water, biotechnology, biological fermentation, etc. (2) Ultrafiltration Early industrial ultrafiltration was used in wastewater and sewage treatment. Over the past thirty years, with the development of ultrafiltration technology, ultrafiltration technology has now been involved in many fields such as food processing, beverage industry, pharmaceutical industry, biological preparations, traditional Chinese medicine preparations, clinical medicine, printing and dyeing wastewater, food industry wastewater treatment, resource recovery, environmental engineering, etc. (3) The main application fields of nanofiltration and nanofiltration involve: Food industry, deep processing of plants, beverage industry, deep processing of agricultural products, biomedicine, biological fermentation, fine chemicals, environmentally friendly water purification and sewage treatment and resource industry... (4) Reverse osmosis has been widely used in various sectors of the national economy due to the advanced, efficient and energy-saving characteristics of reverse osmosis separation technology. It is mainly used in water treatment and concentration of heat-sensitive substances. The main application areas include the following: Food industry, milk industry, beverage industry, deep processing of plants (agricultural products), biomedicine, biological fermentation, preparation of drinking water, pure water, ultrapure water, sea water, brackish water desalination, electricity, electronics, semiconductor industrial water, pharmaceutical industry process water, preparation water, water for injection, non-toxic Bacteria-free pyrogen pure water, process water, boiler water, washing water and cooling water in the food and beverage industry, chemical industry and other industries (5) Other commonly used membrane separation processes In addition to the above four commonly used membrane separation processes, there are also dialysis, controlled release, membrane sensors, membrane gas separation, etc. 6. Column on Inorganic Membranes (1) Overview and Characteristics of Inorganic Membranes The development of inorganic membranes began in the 1940s and has gone through three stages so far. Due to the excellent performance of inorganic membranes and the development of inorganic material science, the application fields of inorganic membranes are increasingly expanding. The membrane catalytic reaction process composed of combining inorganic membranes with catalytic reaction processes is considered to be one of the three major development directions of the catalysis discipline in the future. Therefore, the application of inorganic membranes has become a research and development hotspot in the current field of membrane technology. Research on inorganic membranes in my country began in the late 1980s. * * With the support of the Natural Science Foundation and various ministries, my country has been able to prepare inorganic microfiltration membranes, ultrafiltration membranes and metal palladium membranes in the laboratory. Entering the nineties, * * The Ministry of Science and Technology organized scientific and technological research on the industrialization technology of inorganic ceramic microfiltration membranes and promoted the industrialization process of ceramic microfiltration membranes. The Seventh International Inorganic Membrane Conference was held in China in 2002, marking that the research and industrial application of inorganic membranes in my country have reached the international leading level. Inorganic membranes are processed from inorganic materials and are a solid membrane. Inorganic membranes based on inorganic material science have advantages that polymer separation membranes cannot match.: ※ Narrow pore size distribution, high separation efficiency, and stable filtration effect. ※ Good chemical stability, resistant to acid, alkali and organic solvents. ※ It is resistant to high temperatures and can be used for steam recoil regeneration and high-temperature sterilization. ※ It has strong anti-microbial contamination ability and is suitable for application in the field of biomedicine. ※ It has high mechanical strength, can be backwashed under high pressure, and has strong regeneration ability. ※ There is no dissolution, no secondary pollution, and no negative impact on the separated materials. ※ The separation process is simple, the energy consumption is low, and the operation is simple. ※ The membrane has a long service life. (2) Classification of inorganic membranes 1. Inorganic separation membranes can be divided into: There are two categories: dense membrane and porous membrane. In response to the needs of industrial production, porous ceramic membranes are currently relatively mature and widely used. 2. Inorganic membranes can be divided into: Ceramic membrane, metal membrane, alloy membrane, polymer metal complex membrane, molecular sieve composite membrane, zeolite membrane, glass membrane, etc. 3. Inorganic membranes can be divided into: Non-supported membranes (mostly used in laboratories and scientific research work) and supported membranes (mostly used in industrial production). (3) Inorganic membrane structure The inorganic porous separation membrane element, which has been extremely successful in industrial application and promotion, is mainly composed of a three-layer structure.: Porous support, transition layer and active separation layer. (4) Inorganic membrane elements and membrane modules 1. Inorganic membrane elements From a microscopic perspective, inorganic membrane elements have two structures: symmetrical and asymmetrical. Since asymmetric membrane elements have the advantages of stable treatment effect, high mechanical strength, and high permeability flux, they are currently the main form of industrial application. From a geometric perspective, commercial inorganic membranes come in many forms: Multi-channel, tubular, flat plate, honeycomb, etc. In view of the fact that industrial production requires a large filtration area, and the multi-channel membrane element uses a cross-flow filtration method, which is different from other membrane filtration forms, and has the advantages of easy installation, high mechanical strength, and is suitable for industrial large-scale production applications, multi-channel inorganic membranes have become the main product for industrial production applications. 2. Inorganic membrane components In order to ensure the normal use of inorganic membrane components, we require that the membrane components and membrane shells be used together, so the membrane components came into being. Usually, the form of the membrane module is named according to the number of membrane elements loaded, which is very simple and clear. Specific applications of inorganic membranes occur in the form of membrane modules in separation and reaction processes. Inorganic membrane modules are composed of 1, 3, 7, 19, 37 or more membrane elements, which depends on the actual production or experimental requirements of the specific user. An inorganic membrane equipment usually includes many membrane modules. (5) Filtration method of inorganic membrane separation system The inorganic membrane separation system includes membrane components, raw material transportation system, pressure flow measurement and control system, etc. The main method used is cross-flow filtration. Different from terminal filtration, cross-flow filtration has two liquids: permeate and circulating fluid. (6) Inorganic membrane application field Membrane separation technology is generally welcomed by users for its significant energy-saving effect, easy operation and maintenance, and simple control. Selecting an appropriate membrane separation process can replace many traditional separation and filtration methods such as vacuum filtration, plate and frame filter press, and ion exchange. The application of inorganic membranes mainly involves three aspects: liquid phase separation and purification, gas separation and purification, and membrane reactors. The industrial application of inorganic membranes is mainly concentrated in the field of liquid phase separation. The main applications of inorganic membranes in liquid separation are microfiltration and ultrafiltration. Among them, ceramic membranes are the most used, accounting for 80% of the market. Food and beverage plant (drug) deep processing fruit juice, vegetable juice dairy industry agricultural products deep processing sugar food additives, natural pigments, condiments alcoholic beverages and other biochemical medicine biological fermentation liquid protein, enzyme traditional Chinese medicine, health care products oral liquid animal plasma, serum medicine and intermediates chemical industry synthesis printing dyes and intermediates fine chemical chemical raw materials and intermediate synthesis and microbial pesticide catalyst particle recycling recycling of organic chemical raw materials refining chemical acid, Alkaline environmental engineering Beverage industry, food industry and other types of process water preparation Food, biological fermentation, dyes and other processes Wastewater treatment Pulp and paper, textile industry, degreasing wastewater treatment Oily wastewater treatment Air filtration The application in the field of gas separation mainly includes the purification of gas (air) and the separation of gas components. However, currently only the separation of uranium isotopes has been successfully applied, and other gas purification and separation processes are in the process of research and development.