Membrane separation technology is a new separation technique that utilizes the difference in permeation properties of membranes for each component of the mixture to achieve separation, purification or concentration. The ability of the components to penetrate through the membrane depends on the discovery of dialysis, and people began to pay attention to the study of the membrane. For half a century, membrane separation has completed the size and shape of the molecule itself from laboratory to large-scale industrial applications, the physical and chemical properties of the molecule, the physicochemical properties of the separation membrane, and the interaction between the osmotic component and the separation membrane. .
In 1748, Abbe Nollet discovered that water spontaneously penetrated into the bladder of pigs containing alcohol solution, which became the hallmark of people's understanding and research on membrane separation process. However, Graham was transformed into a new energy-efficient separation technology until the mid-19th century. Since 1925, a new membrane process has been applied industrially almost every decade: microporous filtration (MF) in the 1930s; dialysis developed in the 1940s; electrodialysis (ED) in the 1950s; Permeation (RO); ultrafiltration (UF) in the 1970s; gas separation (GS) in the 1980s; pervaporation (PV) in the 1990s. The membrane process has been widely recognized by countries all over the world. In today's energy shortage, resource shortage and ecological environment deterioration, the industry and the scientific and technological circles regard the membrane process as an extremely important high-tech in the 21st century industrial technology transformation.
Microfiltration is to use the pore size of the microporous membrane, with the pressure difference as the driving force, and to cut off the suspended matter of the particles larger than the pore size of the filtrate, bacteria, etc., to achieve the membrane separation technology for removing the particles and the solution clarification in the filtrate. Generally, the pore diameter of the microporous membrane is in the range of 0.05 to 10 μm, and the operating pressure difference is about 0.01 to 0.2 MPa. Microfiltration technology began in the mid-19th century, and it was not until 1907 that Bechhold published the first systematic study of the properties of microfiltration membranes. In 1918, Zsigmondy et al. proposed a method for the mass production of nitrocellulose microfiltration membranes, which was patented in 1921. This opens the curtain for the industrial application of microfiltration technology. The development and production of microporous membranes in China was relatively late, and it was not until the mid-1970s that the development and development work in this area began. After the national “Seventh Five-Year Plan†and “Eighth Five-Year Plan†major scientific and technological projects , the variety and performance of microporous membrane and membrane filter have leapt to a new height. Compared with foreign countries, the performance of China's phase inversion MF membrane is basically the same as that of similar foreign products.
Ultrafiltration is also a membrane process driven by a pressure difference. The macromolecular solute in the solution is retained by the screening mechanism of the membrane to separate the macromolecular solute from the small molecule solvent. In the ultrafiltration process, the size and shape of the membrane pores play a major role in the separation, and the physicochemical properties of the membrane have little effect on the separation performance. Ultrafiltration membranes are mostly made by high molecular polymer materials by phase inversion, and are also made of inorganic ceramic materials. The earliest used ultrafiltration membrane was the sequestration of soluble gum arabic by Sehmidt's bovine heart cell membrane in 1861. In 1963, Michaels developed asymmetric cellulose acetate (CA) ultrafiltration membranes with different pore sizes. 1965-1975 was a major development stage of ultrafiltration technology. China's ultrafiltration technology started in the mid-1970s, and the 1980s was a rapid development stage, which was widely used in the 1990s.
Reverse osmosis is the interception of solute in solution by means of semi-permeable membrane. Under the pressure difference higher than the osmotic pressure of solution, the solvent permeates through the semi-permeable membrane to achieve the purpose of desalting the solution. In 1953, Professor Reid of the University of Florida began research on the permeability of cellulose acetate and proposed the concept of reverse osmosis. At that time, it was targeted at the desalination of seawater and brackish water, and was listed as a national research plan by the United States. After repeated research and experiments, Loeb and Sourirajan of the University of California synthesized the first practical asymmetric cellulose acetate reverse osmosis membrane by wet phase transformation in 1960. China began research on reverse osmosis technology in 1965 and achieved initial industrialization in the 1980s. In 1982, the National Oceanic Administration Hangzhou Water Treatment Technology Development Center successfully developed a reverse osmosis membrane module with a diameter of 100 mm . In 1985, it successfully developed a reverse osmosis membrane module with a diameter of 200 mm and successfully developed an industrialized SPC-801 component and a large-scale. Reverse osmosis membrane module SPC-8014, the module is 4.3 meters long and contains 4 rolls of reverse osmosis components with a diameter of 200mm. At 3.0MPa, the tap water is used as the influent, the initial water production is 3t/h, and the salt rejection rate is 93%. On some reverse osmosis process, China has close to international standards, but the technology and performance of reverse osmosis membrane and components is still a big gap compared with foreign countries.
Nanofiltration (NF) is a pressure-driven membrane separation technique between RO and UF . It has two characteristics: (1) separation performance for small organic molecular components with a molecular weight of several hundred in water; and (2) Donnan effect for anions of different valence states. The chargeability, ion valence and concentration of the material have a great influence on the separation effect of the membrane.
The research of nanofiltration membrane began in the mid-1970s and commercialized in the mid-1980s, mainly aramid composite nanofiltration membrane , cellulose acetate asymmetric nanofiltration membrane , polypiperazine amide composite nanofiltration membrane and sulfonation polymerization. Ether sulfone composite nanofiltration membrane . In the 1980s, the research on composite nanofiltration membranes began , and the development of NF technology was carried out, and some good results were obtained.
The gas membrane separation technology uses the pressure difference between the two sides of the membrane as the driving force, and utilizes the difference in the permeation rate of different gases in the membrane to make the separation of different gases on both sides of the membrane to achieve separation. It was developed in this century a mature class of membrane separation technology, since it has a high separation efficiency, low energy consumption, simple equipment, convenient operation, small footprint, no secondary pollution, the gas separation membrane It is a strong competitor for traditional gas separation methods such as cryogenic separation, absorption and pressure swing adsorption. As early as 1831, Mitchell used a membrane to carry out hydrogen and carbon dioxide gas mixture permeation experiments, and found that the rate of different kinds of gas molecules passing through the membrane is different. First, the possibility of gas separation by membrane is revealed. In 1866, Graham studied the gas permeability of rubber membranes. The membrane can enrich the oxygen in the air from 21% to 41%, and proposes a dissolution-diffusion mechanism, which further engulfs the gas in the membrane. Awareness.
The application of gas membrane separation began in the early 1950s. In the 1960s, Leob and Sourirajan developed the first asymmetric membrane of cellulose acetate, which laid the foundation for the preparation of high permeability flux separation membranes. In the 1970s, Henis developed a resistive composite film on the basis of asymmetric membranes. The silicone rubber was coated on the asymmetric polymer base film to compensate for the surface defects of the membrane, and a gas separation membrane with good permeation flux and selectivity was obtained. A leap in gas membrane separation has been achieved . In 1979, Monsanto Company of the United States developed the "Prism" membrane separation device, which was successfully applied to recover hydrogen from the ammonia-releasing gas. This is a major breakthrough in the development of gas membrane separation technology, marking the gas membrane technology to the industrial application stage. Since 1980, hundreds of units have been in operation for the recovery of hydrogen from ammonia-depleted gas and the recovery of hydrogen from petroleum refinery gases.
In addition to hydrogen and nitrogen separation membranes, oxygen-rich and nitrogen-rich membranes have also made great progress in industrial applications in recent years. Gas membrane separation technology has been widely used in many aspects. With the deepening of the development of gas membrane separation technology and the continuous expansion of the market, gas membrane separation technology has also separated the permanent gases (such as O2, N2 and H2, etc.) from the separation of trace components and condensable gases. Process development.
Pervaporation is a process in which separation is achieved by the difference in dissolution and diffusion rates of the components through the vapor pressure difference of the components in the liquid mixture. It is a new membrane separation process developed in the past 30 years . As early as 1906, Kahlenberg reported the selective permeation of a mixture of alcohol and hydrocarbon through a rubber membrane. In 1917, Kober published a paper on the selective permeation of water in a protein-toluene solution through a fire-cotton glue, thus proposing the concept of pervaporation (PV). In 1935, Farber concentrated the protein solution by pervaporation, which made people realize the application value of pervaporation in separation and concentration. After the 1950s, research on pervaporation was more extensive. Binning et al. recognized the potential development value of the process, made extensive and in-depth research on this, and tried to develop into the industrial application stage, but did not make a big breakthrough. Since then, this field has been silent for more than ten years. With the development of new polymer materials and the development of membrane technology , coupled with the impact of the energy crisis, pervaporation was once again taken seriously in the mid-1970s. Until 1982, Germany GFT company made an important breakthrough, the first to introduce a commercialized polyvinyl alcohol composite membrane, and established the first small ethanol/water separation demonstration plant in Brazil with a production capacity of 430kg/h, marking the beginning of the industrialization stage of pervaporation. . To date, more than 100 PV industrial units have been established in the world, 90% of which are membranes and technologies supplied by GFT, most of which are used for dehydration of organic solvents, of which 24 are used for dehydration of ethanol and 16 are used for dehydration of isopropanol. For the dehydration of esters, ethers and other organic solvents, the output of the plant is mostly from 1,500 tons / year to 10,000 tons / year, and there are several sets of devices with an annual output of 40,000 tons.
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