Polyacrylamide water treatment has a wide range of applications. Learn more about the principle of polyacrylamide, how to make it, its ingredients, and its impact on the environment. This is more conducive to our water treatment and environmental protection.
English alias: Polyacrylamide absorbent Gel; Polyacrylamide solution; Acrylamide resin (low M.Wt.; Acrylamide resin (high M.Wt.); Acrylamide gel
solution; Polyacrylamide,hydrolyzed; Polyacrylamide; PAM
CAS:9003-05-8Molecular formula:(C3H5NO)n Molecular weight:71.07
Polyacrylamide (PAM) is a general term for acrylamide homopolymers or polymers obtained by copolymerization with other monomers, and it is one of the most widely used water-soluble polymers.
Because the polyacrylamide structural unit contains an amide group, it is easy to form hydrogen bonds, making it have good water solubility and high chemical activity, and it is easy to obtain a variety of modified products with branched or network structures through grafting or cross-linking. It is widely used in petroleum exploration, water treatment, textile, papermaking, mineral processing, medicine, agriculture and other industries, and is called "assistant of all walks of life".
The main application fields abroad are water treatment, papermaking, mining, metallurgy, etc. At present, China's consumption is in the field of oil production, and the fast-growing consumption is in the field of water treatment and papermaking. Today, let's take a look at the physical and chemical properties of polyacrylamide for better understanding and application.
Polyacrylamide (PAM) is a water-soluble linear polymer prepared by radical polymerization of acrylamide (AM), which has good flocculation performance and can reduce frictional resistance between liquids.
According to the ionic properties, Pam polyacrylamide can be divided into four types: non-ionic, anionic, cationic and amphoteric. PAM is insoluble in most organic solvents, such as methanol, ethanol, acetone, ether, aliphatic hydrocarbons, and aromatic hydrocarbons, except for a few organic solvents, such as acetic acid, acrylic acid, chloroacetic acid, ethylene glycol, glycerol, molten urea, and formamide. However, these organic solvents have limited solubility and often require heating, otherwise they have little application value.
(Add soda ash to the 21.0-25.0% acrylamide aqueous solution, and adjust the temperature to 5-12 degrees Celsius; (2) pass nitrogen gas, and add chemicals and initiators, after a period of polymerization, the temperature rises to 70 When the temperature is about -90 degrees Celsius, the steam is introduced for hydrolysis, and the gel is formed after hydrolysis for 1-4 hours; (3) the gel block is formed into gel particles by a granulator, and then dried; the dried particles and the added heat stabilizer and After the tackifier is ground and sieved, the final product is formed. The beneficial effect is: by synthesizing polyacrylamide with a molecular weight of more than 25 million, and then through scientific and reasonable compounding, the problem of ordinary polyacrylamide in the treatment of black It can solve the obvious problem of degradation in the liquid, so as to meet the processing requirements of papermaking black liquor.
1. Polyacrylamide is made of acrylamide (acrylamide) as a monomer and is polymerized by benzoyl peroxide (BPO). The operation process is as follows (or you can look up books on polymer chemistry): In a three-necked flask, dissolve acrylamide in distilled water (10% concentration), start to pass nitrogen into the system, and after 30 minutes, add a certain amount of BPO (the dosage of BPO depends on the molecular weight of polyacrylamide you want to get, the more BPO is added, the smaller the molecular weight of polyacrylamide), install a reflux condenser and a stirring device, start stirring, and at the same time water bath After heating to about 50°C, the reaction starts, and nitrogen gas should be continuously passed through the reaction. As the reaction progresses, the viscosity of the system increases. After 1 hour, the reaction stopped.
2. Pour the reactant into the beaker, slowly add absolute ethanol or acetone to the beaker, and keep stirring, this is the beginning of the precipitation of polyacrylamide, when no more white solid is precipitated, put the obtained white solid in the infrared Drying under lamp, grinding to powder to obtain polyacrylamide. The molecular weight of the obtained polyacrylamide can be obtained by measuring the viscosity (generally, the molecular weight is about 5 million). Before using BPO, it should be recrystallized and purified with acetone, and then stored in a desiccator in a cool place, otherwise the polymerization reaction will be difficult to start.
Polyacrylamide aqueous solution polymerization is the main method used in industrial production. The monomer solution in the formula must be extracted by ion exchange. pure. The reaction medium water should be deionized water, and the initiator mostly adopts a redox initiator system composed of persulfate and sulfite to reduce the reaction initiation temperature. In addition, a chain transfer agent is required, and isopropanol is commonly used. In order to eliminate the influence of possible metal ions, the chelating agent ethylenediaminetetraacetic acid (EDTA) is added if necessary. For easy control of the reaction temperature, the monomer concentration is usually less than 25%.
Since the heat of polymerization of polyacrylamide is as high as 82.8kJ/mol, the heat of polymerization must be exported in time. If the monomer concentration is 25% to 30%, even if the polymerization is initiated at 10c(=, if the heat of polymerization is not exported, the temperature of the solution will automatically rise. To 100'E, a large amount of insoluble matter will be generated. Therefore, the thermal conductivity problem has become one of the key problems in production.
When producing low-molecular-weight products, it can be operated intermittently in a tank reactor or continuously produced in series with multiple tanks. The jacket is cooled to keep the reaction temperature at 20 to 25°C, and the conversion rate reaches 95% to 99%. When producing high-molecular-weight products, since the product is in the form of a jelly, it cannot be stirred. In order to export the heat of reaction in time, it is industrially adopted to mix the materials in the formula in the reactor evenly, and then immediately send it into a polyethylene bag. The cooling reaction was carried out in the water tank of the polyethylene unit containing the reaction mass. It should be noted that the preparation and feeding must be carried out in N due to the obvious inhibitory effect of oxygen in the air. When using a persulfate-monosulfite initiator system, the initiation temperature is usually 40%. If it is required to produce ultra-high molecular weight products, the initiation temperature should be lower than 20%: .
Since the monomer is not volatile and cannot be removed after the reaction, the unreacted monomer will remain in the polyacrylamide, prolong the reaction time and increase the reaction temperature although the residual monomer amount can be reduced, but the productivity decreases and the insoluble content increases. In order to reduce the amount of residual monomer, some factories use a composite initiation system, which is composed of a redox initiator and a water-soluble azo initiator. Under low temperature conditions, the redox initiator plays a role. When the temperature of the reaction material rises in the later stage, the azo initiator is decomposed to further play a role. The residual monomer content of polyacrylamide produced by this method can be as low as 0.02% ( determined by gas chromatography). The water-soluble azo initiators are 4,4'-azobis-4-cyanovaleric acid, 2,2'-azobis-4-methylbutyronitrile sodium sulfate and 2,2'-azobis- 2-amidinopentane dihydrochloride, etc.
The types of polyacrylamide are generally divided into four categories: anionic, cationic, nonionic, and zwitterionic. Anionic polyacrylamide is mainly used for suspended particles, which are relatively coarse, high concentration, positively charged, and the water pH value is neutral or alkaline sewage, which can accelerate the sedimentation of particles in the suspension and significantly accelerate the clarification of the solution. , to promote filtering and other effects.
Cationic polyacrylamide exhibits positive charge in acidic or alkaline media, and its molecular weight is usually lower than that of anionic or non-ionic polyacrylamide. Its performance in cleaning sewage is mainly obtained through charge neutralization. The function of this type of flocculant is mainly to flocculate negative charges, and it has the functions of removing turbidity and decolorization.
The advantages of non-ionic polyacrylamide are mainly used as flocculants. Because its molecular chain contains a certain amount of polar genes, it can adsorb the solid particles suspended in the water, so that the particles are bridged to form large flocs. Non-ionic polyacrylamide can accelerate the sedimentation of particles in the suspension, and has a very obvious effect of accelerating the clarification of the solution and promoting filtration. It is widely used in the treatment of chemical industrial wastewater and waste liquid, and municipal sewage treatment. Especially when the sewage is acidic, this product is most suitable. It can be used in combination with inorganic flocculants such as polyiron, polyaluminum and other inorganic salts.
Zwitterionic polyacrylamide contains cationic groups and anionic groups in the molecule, and it has the characteristics of general cationic flocculants and shows more excellent performance. This type of flocculant can be used in a wide range of PH value, with higher water filtration capacity and lower filter cake moisture content, and can also be used for strong acid leaching of ore or recovery of valuable metals from metal-containing acid catalysts. Zwitterionic is by no means a mixture of anionic and cationic. If cationic polyacrylamide is used in combination with anionic polyacrylamide, the reaction will cause precipitation. Therefore, zwitterionic products are ideal.
1. Principle of flocculation water treatment: When PAM is used for flocculation, it is related to the surface properties of the flocculated material, especially the potentiodynamic potential, viscosity, turbidity and PH value of the suspension. The potentiodynamic potential of the particle surface is the reason for the inhibition of particle aggregation. Adding PAM with opposite surface charge can reduce the potentiodynamic potential and cause aggregation.
2. Adsorption bridging water treatment: PAM molecular chains are fixed on the surface of different particles, and polymer bridges are formed between the particles, so that the particles form aggregates and settle.
3. Surface adsorption water treatment: various adsorption of polar group particles on PAM molecules.
4. Enhancement effect of water treatment: PAM molecular chain and disperse phase connect the disperse phase together through various mechanical, physical, chemical and other effects to form a network, thereby enhancing the effect.
It mainly relies on adsorption and bridging, and through the adsorption of charged groups on the polymer chain, the fine particles are pulled together to accelerate the sedimentation and achieve the purpose of accelerating the solid-liquid separation.
1. Because polyacrylamide has a polar gene-amide group, it is adsorbed on the surface of sediment particles by the effect of its hydrogen bond.
2. Because polyacrylamide has a long molecular chain and a large-scale long chain has an infinite adsorption surface area in water, the flocculation effect is good, and the long chain can be used to bridge between particles to form a large particle floc, Accelerate subsidence.
3. With the help of flocculation and coagulation of polyacrylamide, double ionization and compaction may occur in the process of sludge coagulation in clean water treatment, which reduces the stability of particle aggregation. The particles are combined under the effect of molecular gravity, and the simple anions of the dispersed phase can be polymerized. replaced by anionic groups.
4. The chemical interaction between the substances in the polyacrylamide polymer and the natural water composition and the suspended matter in the water, or the ions of the hydrolyzed coagulant added before, may be a complex reaction.
5. Because the molecular chain of polyacrylamide is fixed on the surface of different particles, a polymerization bridge is formed between each solid phase particle.
To reduce the amount of flocculant, under the premise of achieving the same water quality, polyacrylamide as a coagulant and other flocculants can be used in conjunction with other flocculants, which can greatly reduce the amount of flocculants used.
Improve water quality. In drinking water treatment and industrial wastewater treatment, the use of polyacrylamide and inorganic flocculants can significantly change the water quality.
By increasing the floc degree and the settling speed, the flocs formed by polyacrylamide have high strength and good settling performance, thereby increasing the solid-liquid separation speed, which is beneficial to sludge dewatering.
For the anti-corrosion and anti-scaling of circulating cooling system, the use of polyacrylamide can greatly reduce the amount of inorganic flocculants, thereby avoiding the deposition of inorganic substances on the surface of equipment and slowing down the corrosion and scaling of equipment.
1. The main purpose of treating steel mill wastewater is to remove impurities in sewage, sludge dewatering, etc. It is recommended to use anionic polyacrylamide with a molecular weight of 12 million, and an increase of 1‰-2‰ to use 5-7 grams per ton of sewage.
2. Bentonite is thickened, mainly for thickening. High-viscosity powder polyacrylamide is mostly used, the molecular weight is more than 20 million, and the mixing ratio with bentonite is 1‰-3‰
3. Concrete additives mainly play the role of thickening, water retention and non-dispersion. More than 15 million anionic polyacrylamide is used, and the addition amount is 0.1‰-1‰
4. Mining, iron mining, gold mining, feldspar ore, fluorite ore, etc., mainly deal with tailings slurry, mostly use anionic polyacrylamide 15 million-18 million. The dissolution ratio is 1‰-2‰, and the amount of wastewater added is about 5-8 grams per ton.
5. Coal washing, sand washing. Mainly used for slime sedimentation or mud-water separation, 15 million-18 million anionic polyacrylamide is mostly used. Dissolution ratio 1‰-2‰
6. Bridge drilling and slurry mixing, rotary drilling and piling, etc., are mostly called chemical mud. The main function is to increase the arm guard effect and reduce the filtration loss. Instead of bentonite, use anionic polyacrylamide 25 million molecular weight products in 1‰.
7. Coating mortar, which has a thickening effect, mostly uses anionic polyacrylamide with a molecular weight of 15 million.
8. Drilling wall, lubricating drill bit, mostly use anionic polyacrylamide 15 million to 18 million molecular weight products or polyacrylamide emulsion.
9. For oil field flooding, temperature-resistant and salt-resistant polyacrylamide or ultra-high molecular weight polyacrylamide are often used.
10. Shale gas fracturing, drag reducing agent used in slick water fracturing additives, mostly use 18 million molecular weight anionic polyacrylamide emulsion or fine powder products.
1. Coal washing: Part of the coal washing water needs to use non-ionic polyacrylamide 10-12 million products for sedimentation to achieve the expected effect.
2. Sand washing and fluorite ore feldspar ore: Due to the different geology in different regions, some soil particles are fine and sticky. It is necessary to use non-ionic polyacrylamide products with a molecular weight of 10-12 million to fully flocculate and achieve the effect of use.
3. Sewage treatment of titanium dioxide plant: The effluent temperature of titanium dioxide plant is controlled at 50 °C, and the pH generally needs to be neutralized to 7-9 by adding alkali, and then treated with 12 million molecular weight non-ionic polyacrylamide to achieve the effect.
4. Electroplating sewage: Hydroxide treatment, more use of 8 million molecular weight non-ionic polyacrylamide products.
5. For drilling and plugging, non-ionic 12 million molecular weight products are often used together with cross-linking agents.
1. Urban sewage is used for sludge dewatering. Generally, cationic polyacrylamide products with a molecular weight of 8 million to 12 million and an ionic degree of 30 to 60 are used. Addition 1‰-3‰
2. Papermaking sewage is used for sludge dewatering. Generally, cationic polyacrylamide products with a molecular weight of 10 million to 12 million and an ionic degree of 20 to 40 are used.
3. Pharmaceutical sewage, which acts on sludge dewatering, generally uses cationic polyacrylamide products with a molecular weight of 12-15 million and an ionic degree of 50-60.
4. For air flotation, use 10-20 ionic polyacrylamide products.
5. Food factory wastewater, polyacrylamide treatment of organic wastewater, requires high ionicity.
6. Treatment of slaughtering wastewater. After the wastewater is fermented, the polyacrylamide product with 40 ionic degree and 12 million molecular weight is used for desliming.
7. In other fields, such as chemical factory wastewater, some fluorite pulp, acid coal washing wastewater, tanning wastewater, coal chemical enterprise wastewater, etc., cationic polyacrylamide must be used.
The above are some of the more common industrial polyacrylamide usage descriptions summarized by micro-point environmental protection. In the actual selection, we also need to select polyacrylamide according to the site conditions.
Polyacrylamide itself and its hydrolyzate are not toxic, and the toxicity of polyacrylamide comes from its residual monomer acrylamide (AM). Acrylamide is a neuropolyacrylamide poisoning agent, which can damage the nervous system. After poisoning, symptoms such as physical weakness and ataxia appear.
The damage to the environment after polyacrylamide water treatment is minimal.
Therefore, the health departments of various countries have stipulated that the residual acrylamide content in polyacrylamide industrial products is generally 0.5%---0.05%. When polyacrylamide is used in the purification treatment of industrial and urban sewage, the content of acrylamide is generally allowed to be less than 0.2%. When it is used for direct drinking water treatment, the content of acrylamide needs to be less than 0.05%.
Regarding the toxicity of polyacrylamide, the situation of some cationic polyacrylamide is much more complicated, because groups such as amino groups introduced by cationic polyacrylamide are often tens to hundreds of times more toxic than anions. type and non-ionic, their chronic toxicity is under further study.
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