polyacrylamide in raw water treatment is part of the conventional treatment process is difficult to remove the organic pollutants has better removal effect, but as a result of polyacrylamide products, did not exist in the polymerization of acrylamide monomer acrylamide is a kind of water-soluble carcinogens with neural toxicity and genetic toxicity, greatly limits its application in the raw water treatment at present, the domestic study of polyacrylamide are mostly just stay on how to improve the polymer relative molecular mass, the study of how to reduce the residual monomer content in polymers less, therefore, in order to meet domestic market demand for high purity high molecular weight flocculants research to reduce residual acrylamide content in cationic polyacrylamide again at the same time to ensure that the synthesis of high molecular weight polymer synthesis is suitable for drinking water supply in water treatment of organic polymer flocculant has the vital significance.
1.1 the definition of high molecular weight polyacrylamide PAM (Polyacrylamide, PAM) acrylamide and its derivatives of
homopolymer and copolymer. Molecular weight of polyacrylamide with low, medium, high and ultra-high, in general, for low molecular weight below 1 million, 1 million - 10 million as the low molecular weight, high molecular weight more than 10 million. So the high molecular weight polyacrylamide is over 10 million organic polymer molecular weight.
1.2 the molecular structure of the high molecular weight polyacrylamide The molecular structure of the high molecular weight polyacrylamide is: CH2 CH n CONH2 Structural formula of acrylamide molecular weight is 71.08, the value of n for the 2 x 104 ~ 9 x 105, so the polyacrylamide molecular weight average of 1.5 x 106 ~ 6 x 107. 1.3 the classification of high molecular weight polyacrylamide According to PAM dissociation properties of functional group in aqueous solution, macromolecular chain can be divided into ionic colorful (CPAM), cationic (APAM), nonionic (NPAM) and amphoteric ionic several varieties. Cationic generally contain traces of toxicity, not suitable for use in water supply and drainage engineering, so we come into contact with the water treatment agent belong to the anionic and nonionic polyacrylamide. According to the purity of high molecular weight polyacrylamide products, has two kinds of powder and colloid, powder product is white or light yellow granular or powder, solid content is in commonly 90%, colloidal gel product is a colorless, yellowish, solid content is 8% ~ 9%. 1.4 the characteristics of high molecular weight polyacrylamide High molecular weight polyacrylamide because of its structural unit containing amide, easy to form hydrogen bonding, make it has good water solubility and high chemical activity, can be obtained by grafting and crosslinking reactions such as a variety of derivatives. High molecular weight polyacrylamide is composed of acrylamide monomer polymerization of organic polymer, colorless, tasteless, odourless, soluble in water, no corrosion.
High molecular weight polyacrylamide is stable at room temperature, high temperature, easy degradation, when frozen so its storage and preparation for overtime, temperature should be controlled within 2 ℃ ~ 55 ℃.
2.1 the synthesis of high molecular weight PAM
At present, the synthesis methods of PAM according to whether aggregation
will
join
other
monomer,
can
divide
again
homopolymerization and copolymerization, PAM product form a aqueous solution, emulsion, and powder, etc. AM polymerization methods commonly used at home and abroad with aqueous solution polymerization,
inverse
emulsion
polymerization,
suspension
polymerization and so on, its basic principle is based on AM in under the action of the initiator, carries on the free radical polymerization, generate polyacrylamide, equation is as follows:
By type known AM chain polymerization process, the chain initiation and termination reaction accords with the general law of free radical polymerization, the polymerization reaction of free radical polymerization reaction of reason AM. 2.2 aqueous solution polymerization
Aqueous solution polymerization monomer AM and initiator of polymerization, dissolved in the water is widely used and mature technology. The PAM gel and powder products, the colloid by mass fraction is 8% - 10% or 10% - 30% aqueous solution of AM direct polymerization under the action of a initiator and, after drying can be
powder product. Product molecular weight is 70000-7 million. The advantages of safety, simple process equipment, environmental pollution is small, the disadvantage is that the product solid content is low, only 8% - 8%, and prone to imide reaction, generate gel. In the PAM aqueous solution polymerization, the initiator to a great extent, determines the relative molecular mass of the product resulting from the polymerization reaction, yield, and the development of the new initiator system is the key to AM aqueous solution polymerization research.
2.3 inverse emulsion polymerization
Acrylamide monomer mixture concentration is 30% ~ 60% aqueous solution as the dispersed phase, which add a small amount of diethylamine tetraacetic acid and Na2SO4 and oxidation - reduction initiator and right amount water soluble surfactant, the HLB value should be lower. With aromatic hydrocarbons or saturated
hydrocarbons as continuous phase, which is oil soluble surfactant, the HLB value should be higher, such as dehydration, sorbitan oleate. Na2SO4 have prevent the latex particle bonding effects. The proportion of the dispersed phase and continuous phase is usually 3:7. Aggregate income dispersed phase latex particles was 0.1 ~ 10 microns in diameter, related to the dosage of surface active agent. Reaction temperature is commonly 40 ℃ 6 h conversion rate could reach 98%.
This method has the advantage of heat of reaction is derived, and the material system of low viscosity, easy to operation, products directly without drying applications. Drawback is the use of organic solvent, flammable, effective capacity is lower than the solution polymerization. 2.4 reversed phase suspension polymerization
Reversed phase suspension polymerization is nearly years developed a new method. Reversed phase suspension polymerization to produce soil simple art, low into wood, easy ten industry achieve soil, relative molecular mass of products, tens of millions of dollars to dissolve performance is better than aqueous solution polymerization products, can directly get the powder or granular products, packaging and transportation is convenient. 2.5 new polymerization method
A way of free radicals in the PAM synthesis in recent years research has a new progress, more energy conservation and environmental protection of initiator system, polymerization such as light, heat polymerization, radiation polymerization, plasma polymerization and precipitation polymerization, micellar polymerization, etc.