Abstract: It widely exists in nature, and cannot be used in food industry because of its low content, low early chemical synthesis rate and high cost, and the use of dangerous solvents in production. Membrane separation has the following characteristics: mild operating conditions, low energy consumption, no phase change and good separation selectivity. Application example 1: Japan Asahi Medical Company used hollow fiber polyacrylonitrile membrane for hemodialysis and hemodialysis filtration for the first time.
Keywords: membrane, food, engineering, medicine
Application of 1. in food industry
Protein is one of the most important basic components of organisms, and amino acids are the foundation of protein. γ -aminobutyric acid, or aminobutyric acid, is a naturally occurring non-protein amino acid. It widely exists in nature, and cannot be used in food industry because of its low content, low early chemical synthesis rate and high cost, and the use of dangerous solvents in production. Biosynthesis has the advantages of low cost and safe use, and is widely used in food industry. The separation and purification of ammonia complex acid fermentation broth is the key link to realize the industrial production of ammonia complex acid. Membrane separation has the following characteristics: mild operating conditions, low energy consumption, no phase change and good separation selectivity. Therefore, it has a very broad prospect to obtain high-yield aminocaproic acid products through biosynthesis. By screening and optimizing lactic acid bacteria, the Key Laboratory of Food Science and Safety Education Department of Jiangnan University made the amino acid content in the fermentation broth reach 540mg/ 100ml, which is a high level. Nevertheless, the concentration of aminocaproic acid in fermentation broth is still very low, and the purity of aminocaproic acid still needs to be improved by separation and purification. The results show that the combination of ultrafiltration, dilution filtration and nanofiltration can improve the purity of amino acid complexes in fermentation broth to 3.75 times, and the total recovery rate is close to 75%. If chitosan flocculation and activated carbon adsorption are used for pretreatment, and then ion exchange resin is used for separation, the purity of amino acid complex in fermentation broth can be increased to more than 4 times, and the total recovery rate can reach 64.2%.
2. Engineering application
Acrylonitrile is the main raw material for producing ABS/SAN, acrylic fiber and adiponitrile. Acrylic fiber accounts for more than 50% of the total acrylonitrile consumption products in China, followed by ABS/SAN, accounting for about 25%. The process of producing acrylonitrile by ammoxidation of propylene was invented in 1959. In the process of producing acrylonitrile by ammoxidation of propylene, there are mainly the following kinds of environmental pollution: first, waste gas pollution, second, waste residue pollution and third, waste water pollution. Because the ammoxidation of propylene is carried out in a fluidized bed, the loss of catalysts is inevitable during the reaction, and these catalysts are all composed of some heavy metals. In addition, a large amount of cyanide-containing wastewater will be produced in the process of acrylonitrile production, and a large amount of cyanide-containing wastewater will also be produced in the process of reactor quenching. Among them, the cyanide-containing wastewater produced in the reactor quenching process has higher cyanide content than the wastewater treated in this paper, and the COD content exceeds 40,000 mg/L, up to 80,000 mg/L, which is also quite difficult to treat, and now it can only be incinerated.
The pharmaceutical industry took the lead in using membrane separation technology to treat cyanide-containing wastewater. Generally, the wastewater produced in pharmaceutical industry is relatively clean, with less mechanical impurities and lower cyanide content than that in chemical industry, so it is relatively easy to treat. Therefore, since 1970s, foreign countries have used membrane separation technology to treat cyanide-containing wastewater from pharmaceutical industry, and the cyanide content in the treated wastewater is less than 1ppm, which completely meets the discharge standard. The earliest industrial production in this field was a German pharmaceutical company, which established a membrane separation device in 1980s. During the process, it was found that the cyanide content in raw water was about 120 ~ 180 ppm, and after reverse osmosis treatment, the cyanide content in discharged water was only about 0.2ppm (the concentration of CN- in wastewater discharged by European standards must be less than 0.2ppm). The basic technological process is two-stage ultrafiltration and then four-stage reverse osmosis. The longest running period of the unit is ultrafiltration 18 months and reverse osmosis for 36 months.
3. Application in medicine
Polymer separation membranes are widely used in medical and health fields, from the preparation of medical pure water and the separation, purification and concentration of protein, enzymes and vaccines to artificial organs such as artificial liver, artificial lung and artificial kidney. In the separation process, polymer membranes are the core components.
The development of artificial kidney is the most widely used polymer separation membrane in artificial organs, and it is one of the most successful examples of clinical application of artificial organs. Because its main function is to exclude substances harmful to human body in blood, it must be emphasized that the membrane has good blood compatibility, permeability and mechanical strength suitable for clinical application.
Cellulose membrane has good water permeability, can effectively remove creatinine, urea and other small molecular substances harmful to human body, and has certain mechanical strength. Because cellulose is a natural polymer material, it is basically safe for human body. Therefore, cellulose is the earliest and most widely used important hemodialysis membrane. In fact, the commercialization of cellulose membrane has greatly promoted hemodialysis to become a routine clinical treatment.
Polyacrylonitrile is one of the few synthetic polymer membranes that have been used in clinic. Compared with regenerated cellulose membrane, polyacrylonitrile membrane has strong ability to remove medium molecular weight substances, and the ultrafiltration rate is several times that of the former. At the same time, it has excellent antibacterial and organic solvent resistance. Application example of the complete works of the paper 1: Japan's Asahi Medical Company first hollowed out polyacrylonitrile membrane and used it for hemodialysis and hemodialysis filtration. The membrane is asymmetric, with an inner diameter of 200μm and a wall thickness of 50 μ m; Application example 2: China Textile University spun polyacrylonitrile into hollow fiber and assembled it into hemodialysis machine, which was used in clinic.
With the development of membrane science and medicine, people have higher and higher requirements for membrane materials for blood purification. It is estimated that by the beginning of the next century, it is possible to develop an embedded high-function artificial kidney. This is bound to pose a new challenge to the performance of the existing blood purification membrane. There are two ways to improve and expand the function of polymer membrane in the field of blood purification: developing new membrane system and modifying existing membrane system to approach or reach the performance of biofilm.
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