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Study on Application of Polyacrylamide in drinking water treatment
Polyacrylamide (PAM) is a general designation of acrylamide polymer or polymer with other monomers. The has good thermal stability. Because of the structural elements that contain polar groups, it is easy to form hydrogen bonds, so that it has good water solubility and high chemical activity. So as to have a series of derivatives and a variety of valuable properties, in the water treatment is of great significance, is the most widely used in the organic polymer net water treatment flocculant.
Polyacrylamide is early in 1893 by moureu with acryloyl chloride and ammonia in low temperature was prepared. From 1954 first commercial production in the United States. At first, the acrylamide (AM) monomer was prepared by the catalytic hydration of acrylonitrile (AN), and was prepared by acrylamide polymerization. Then the anionic polyacrylamide (PAM) was developed. 70 time with the second generation of acrylamide production "catalytic water" and the third generation of "microbial engineering" process technology have come out, polyacrylamide series products are constantly being developed. In the 70's, the American Merck company and Halliburton company first developed a cationic polyacrylamide - two methyl two (PDMDAAC) and two methyl two ammonium chloride and acrylamide copolymer [P (DMDAAC/AM)].
Our country of poly (alkenylamide research and production began in the 1960s, production process mainly uses the traditional aqueous solution polymerization, colloidal mining 8 -- 10%AM aqueous solution and in initiating agent under the action of direct polymerization, dry powder with 20 - polymerization concentration 30%AM aqueous solution, colloid aggregation after granulation, kneading, drying, crushing of polyacrylamide, ratio process is safe, simple, cost low. Inverse emulsion polymerization method -- am aqueous solution with surfactant of AM monomer decomposition in the oil phase formation of emulsion system, in initiating agent of emulsion polymerization to form stable high molecular weight instant Polyacrylamide Latex products, after azeotropic distillation dehydration can be powdered polypropylene products. The process for in the preparation of high molecular weight and narrow distribution of molecular weight of Polyacrylamide Latex or dry powder type products. And inverse suspension polymerization, polymerization of am in aqueous solution with small droplets suspended in the organic solution of system of molecular weight high, instant polyacrylamide beads. Radiation caused method -- calcined amide monomer in the R or ultraviolet ray triggered direct polymerization and a solid product, the process is simple, but the investment is larger, the obtained product molecular weight distribution is very wide. The majority of the application of polyacrylamide requires some kind of ion function. The characteristics of the ion can change the solubility, viscosity and solution properties of polyacrylamide. The manufacture of commodity derivatives is made using the copolymerization method or the use of the subsequent reaction of polyacrylamide. So far, it has been produced by non ionic polyacrylamide, cationic polyacrylamide, polyacrylamide, and its derivatives. Its molecular weight from the hundreds of thousands to ten million or more, according to the molecular weight can be divided into low molecular weight (1000000), the molecular weight (1000000 --1000 million), high molecular weight (10000000 ----1500 million), the amount of the super molecular weight (more than 15000000). In the form of goods, there are mainly powder, colloid, emulsion; powder quality is higher, the use of good, easy to dissolve, the use of high cost.
50 years the United States pioneered the development of polyacrylamide as a net water treatment flocculant, its production and application development is rapid, since the 60's, the United States and the European countries have been widely used as a net water treatment of polyacrylamide flocculant. The 1960s, in the Yangtze River, the Yellow River drinking water plant widely used polyacrylamide in high turbidity water purification treatment, and urban sewage and industrial wastewater treatment; 1990s some water from polluted drinking water plant, began using polyacrylamide as net water treatment coagulant. Polyacrylamide is the most widely used synthetic flocculant. The molecular chain is very long and its amide (---CONH2) can be with many substances, adsorption affinity to form hydrogen bonds, which makes it can bridge between the particles and the adsorption, several or even dozens of particles connected together, floc formation, particle acceleration sun sink, make it become the ideal flocculant. There was a test in the partial hydrolysis of polyacrylamide solution in the alumina hydrate into the polymer, the anion adsorption on the alumina, the viscosity of the rapid increase or glue. This is similar to the general flocculation mechanism that a molecule can adsorb a few particles simultaneously, so that they can be pulled together, and the rate of settlement is determined by the concentration of flocculant and the concentration of suspended solids. After net water experts years of water treatment research and application, generally considered to polyacrylamide flocculation is: (1) due to its polarity gene - amide, easy to borrow the hydrogen bond effects in adsorbed on the surface of sediment particles; (2) because of the long molecular chain, long chain of large magnitude in the water has great adsorption surface area, so the flocculation effect is good, with long chain between the particles bridging, large particles of the floc formation and accelerated subsidence. (3) double ionization compression may occur in the coagulation process of water treatment. It can be found that the particles aggregate stability is reduced, and the simple anions can be replaced by the polymer. (4) the chemical interaction between polymer and natural water can be complex; (5) because of the molecular chain is fixed on the surface of different particles. Polyacrylamide is a kind of chemical properties of the polymer compound. Because of the activity of the amino groups in the molecular side chain, many valuable properties of the polymer have been obtained. Non ionic PAM flocculant has the following characteristics: the flocculation performance is less affected by water pH value and salt fluctuation than the anionic functional groups. In the medium or alkaline conditions, the flocculation effect is inferior to that of anionic type, but it is better than that in the acidic condition. The molecular weight of anionic PAM type flocculant is usually lower than that of anionic or nonionic polymers, and its function is obtained by charge neutralization. The main function of this kind of flocculant is to take charge of negative charge, and has the function of removing turbidity and color, which is suitable for the treatment of organic colloid with high content of water.