Polyacrylamide (PAM) has a high molecular weight (103-103), good water solubility, adjustable molecular weight and the ability to introduce various ionic groups to achieve specific properties. Low molecular weight is an effective thickener or stabilizer for dispersion materials, and is an important flocculant at high molecular weight. It produces a hydrophilic, water-insoluble gel. It has good adhesion to many solid surfaces and dissolved materials. Due to these properties, PAM can be widely used in the fields of flocculation, thickening, drag reduction, gelation, bonding, scale inhibition and the like. Industrial applications of nonionic, anionic, cationic and amphoteric acrylamide polymers have steadily grown since the 1960s because of their unique chemical and physical properties. It is widely used in sewage and drinking water treatment, paper making, oil exploitation, mining and metallurgy, building materials, textiles, etc., as well as for enhanced oil recovery and as a water-absorbent resin.
1. Water treatment
China is a region with a relatively scarce water resources. The average annual water resources is 2.8 trillion m3, ranking sixth in the world, but the per capita possession is only 2710 m3, which is equivalent to 1/4 of the world's per capita possession. Bit. In June 1992, the “Agenda 21 Agenda” adopted by the United Nations Conference on Environment and Development put forward sustainable development, a common development strategy of mankind. In this strategy, environmental protection is the material basis for ensuring sustainable development, while protecting water sources, controlling and controlling water pollution is an important part of environmental protection. Therefore, the application of PAM in water treatment is of particular importance.
The amide group (—CONH2) of polyacrylamide (PAM) can affinity with many substances and adsorb to form hydrogen bonds. High molecular weight PAM forms a "bridge" between the adsorbed particles, connecting several or even dozens of particles together to form a floc, which accelerates the sinking of the particles. This makes it the most desirable flocculant. PAM flocculants are mainly used to treat water and various wastewaters. Compared with the traditional inorganic flocculant, the advantages are: the variety is large, can adapt to a variety of conditions, the dosage is small, the efficiency is high, the generated sludge is less, and the post-treatment is easy.
Polyacrylamide is currently the most widely used and highly effective polymer organic flocculant in the world, and it is also the most widely used flocculant in China. Polyacrylamides are mainly sold in two forms, one being powdery and one being colloidal. Colloids are not easy to transport and are not convenient to use. Powdered products are commonly used. Polyacrylamide has several types of cationic, anionic and nonionic, which are suitable for different applications and different flocculation targets.
Prior to the application of polyacrylamide, it was first formulated into an aqueous solution. Generally, the powdered polyacrylamide is poured into the stirred cold water slowly and in small batches, and the stirring speed is not too fast, so as to avoid excessive shearing and causing the polymer molecules to break. Stirring is only to ensure that the polyacrylamide solids are immediately dispersed without sticking into agglomerates. The rate of polymer addition should also decrease as the viscosity of the solution increases. A slight increase in temperature can slightly increase the rate of dissolution, but the temperature should not exceed 60 °C. The highest concentration of high molecular weight polyacrylamide solution is 0.5%, while the lower molecular weight polyacrylamide can be formulated to a concentration of 1% or slightly higher. In the flocculation treatment, the solution is further diluted to less than 0.02%. After being formulated into a polyacrylamide solution, it should not be stored for a long time to avoid deterioration.
The PAM for treating drinking water has strict quality standards, the residual monomer content is below 0.05%, and the dosage is below 2×10-6; for treating food industry water such as washing vegetables and washing fruits, or for food packaging paper In other aspects, there must also be strict quality standards, which are approved and guaranteed by specialized agencies.
Non-dissociative PAM flocculants have the following characteristics compared with anionic PAM flocculants because they do not contain ionic functional groups: flocculation performance is less affected by wastewater pH and salt fluctuations; neutral or alkaline Under the condition, the flocculation effect (settling velocity) is not as good as that of anionic, but it is worse than anionic in acidic conditions; the floc strength is stronger than that of anionic polymer flocculant.
The cationic PAM generally has a lower molecular weight than an anionic or nonionic polymer, and its clarifying properties are mainly obtained by charge neutralization. The function of this type of flocculant is mainly flocculation with negatively charged colloid, which has functions such as turbidity removal and decolorization. It is suitable for wastewater with high organic colloid content, such as industrial wastewater such as dyeing, paper making, pulp, food, aquatic product processing and fermentation. And sludge dewatering in urban sewage treatment processes. Urban and industrial sewage are usually treated by activated sludge. The biochemical sludge is often a highly hydrophilic colloid. The water content is extremely difficult to remove. If the PAM flocculant is used, it can receive good dehydration effect. .
The anionic PAM flocculant is suitable for the positively charged slurry on the surface of the particles, compared with the cationic PAM flocculant; the anionic PAM flocculant has a higher molecular weight and, because of the mutual exclusion of the same intramolecular ionic group The molecular stretch in water is relatively large, and thus has good particle flocculation performance. They are effective for the sedimentation separation of mineral suspensions. It is suitable when the treated water is a mineral-rich suspension having a neutral to alkaline pH. For example, it can be used as a sedimentation accelerator in production processes such as magnesium oxide smelting, zinc smelting, and phosphoric acid. In the water treatment, in addition to the waste water treatment of ironmaking blast furnace, aluminum processing, paper making, river gravel washing, etc., it is also applied in the primary treatment of urban sewage.
Sodium polyacrylate is not suitable for negatively charged suspended particles, but exhibits good flocculation properties for positively charged suspended particles such as metal hydroxides. For example, red mud separation and liquid caustic soda production in alumina production have been applied. On the other hand, sodium polyacrylate has also received attention as a food additive. It can also be used in the treatment of wastewater containing protein and casein, such as food and aquatic products processing.
PAM flocculant can adapt to a variety of flocculation objects, and has special value for some cases. The application effect is related to the selection, dosage and flocculation process. For example, flocculation and clarification of dust collection wastewater of a steel plant, originally using PAM with anionic degree of 20%-30%, the unit consumption is up to 2.58/m3 sewage, and the overflow turbidity is above 300×10-6. Switch to the PAM with high anionicity produced by our factory, the unit consumption is only 0.28/m3, and the overflow turbidity is below 50×10-6. Generally, the higher the molecular weight of the PAM, the lower the unit consumption. For example, if a certain acid leached uranium pulp is used, the molecular weight of 11 million PAM is 30g/t ore, and the sedimentation speed is 1.5mm/s. If the molecular weight of 3 million is the same type of PAM, the same sedimentation speed should be achieved, and the single consumption can reach 80g/ t mine.
Polyacrylamide can be used to treat water in power plants. In the treatment of water in power plants, the raw water (such as river water) should first be clarified. A common chemical method is to use polyacrylamide together with an inorganic coagulant such as lime, aluminum sulfate, and polyaluminum. Because, if the inorganic coagulant is used alone, it is effective to require a high concentration. After the polyacrylamide is used, the amount of the inorganic coagulant can be greatly reduced. This can prevent the inorganic coagulant from being easily deposited on the heat exchange surface of the cooling tower or the like due to the large amount, thereby accelerating the corrosion and scaling of the equipment. For example, when lime, ferric chloride and polyacrylamide are used together, the water clarification ability is greatly enhanced.
In industrial water treatment, low molecular weight polyacrylamide can also be used as a scale inhibitor for cooling water. The low molecular weight (104) anionic PAM can prevent the precipitation and growth of salt crystals, suspend the solid particles without depositing, and can inhibit the scale of boilers, cooling towers and heat exchangers. For example, 37.5 parts of a scale inhibitor formulation of polyacrylamide having a molecular weight of less than 1 million and 50 parts of sodium tripolyphosphate can cause the surface of the heavily fouled heat exchanger to become substantially non-fouling.
Industrial water often has more requirements than flocculation suspensions. Therefore, PAM polymer flocculants should be used together with inorganic flocculants and some other additives such as scale inhibitors and bactericidal algaecides.
With the development of environmental protection, the disposal of sewage and sludge generated by the water treatment process has attracted more and more attention.
Due to the serious water pollution in China, nearly half of the seven major river systems in the country are polluted to varying degrees. The eutrophication of lakes and reservoirs is serious, and Taihu Lake, Chaohu Lake and Dianchi Lake are the most serious. More than three types of rivers flowing through the city are not suitable for domestic water use, and more than 50% of urban groundwater is also polluted to varying degrees. After the completion of the first phase of China's Cross-Century Green Project Planning, the newly-built urban centralized sewage treatment capacity of the seven major river basins was 17.99 million t/d, and the annual chemical oxygen demand (COD) was reduced by 3.37 million tons. The centralized sewage treatment capacity is 1.04 million t/d, and the COD is reduced by 290,000 tons per year; the total nitrogen is 29,300 tons, and the total phosphorus is 3,200 tons. The newly-added centralized sewage treatment capacity of key coastal cities is 1.04 million t/d, and the annual COD reduction is about 300,000 tons.
In terms of sewage treatment, in the early 1990s, China formulated a water pollution control master plan target of 20%-30% for urban sewage treatment, 84% for industrial wastewater treatment, and 70% for urban sewage disposal facilities by the year 2000. . According to statistics in 1996, there are 149 major sewage treatment plants in the country, of which the primary sewage treatment plant accounts for about 30%, and the secondary sewage treatment plant accounts for about 70%. It is estimated that by 2000, the annual discharge of urban sewage in China will reach 38.3 billion. M3 or more. China will strive to increase the drainage network penetration rate and sewage purification treatment capacity.
The sewage from municipal sewage treatment plants and industrial wastewater treatment plants must be flocculated and clarified by flocculants such as PAM. Generally, a secondary sewage treatment plant produces about 0.5% to 1.0% by volume of sludge. The resulting sludge needs to be dewatered to produce clean filtered water and high solids filter cake, and to reduce the weight and volume of the waste sludge to increase the effectiveness of incineration and fertilizer production. Many sewage treatment plants use filter presses to increase the rate of dewatering. These sludges are very hydrophilic, negatively charged, and difficult to dehydrate. An effective pretreatment of acrylamide polymer must be used before mechanical dewatering to improve sludge performance and to increase the productivity of mechanical equipment. PAMs used in sludge dewatering are increasingly using cationic products, especially copolymers of acrylamide and propylene hydroxyethane trimethylamine chloride. Anionic polyacrylamides are also widely used, either alone or in combination with cationic polymers.
PAM is mainly used in the paper industry in two aspects. One is to increase the retention rate of fillers, pigments, etc. to reduce the loss of raw materials and environmental pollution; the second is to improve the strength of paper (including dry strength and wet strength). In addition, the use of PAM can also improve the tear resistance and porosity of paper to improve visual and printing performance. With the development of the paper industry in China, the amount of PAM will also increase.
The addition of PAM to the paper stock can increase the retention rate of fine fibers and filler particles on the net and accelerate the dewatering of the paper stock. The mechanism of action of PAM is that the particles in the slurry are flocculated by electrical neutralization or bridging, and are retained on the filter cloth. The formation of the flocs can also make the water in the slurry easier to filter out, reduce the loss of fibers in the white water, reduce environmental pollution, and help to improve the efficiency of filtration and sedimentation equipment. Generally, the PAM used for retention and drainage is mostly cationic, such as a copolymer of acrylamide and dialkylaminoalkyl ester, and other cationic monomers are dimethylaminoethyl acrylate (DMCL), etc. . Nonionic and zwitterionic PAMs have also recently been considered useful.
The use of PAM also promotes sizing and improves the surface properties of the paper (such as porosity, optical properties, printability, etc.). PAM is used as a suspension dispersant for long-fiber papers to promote the dispersion of long fibers during papermaking, to increase the stability of the pulp and the adhesion of fillers and pigments. In the pulp and paper industry, the use of AM copolymers improves the printing performance of paper. This is due to the fact that more filler, mainly kaolin, is retained in the pulp to improve the surface structure of the paper. At pH=6-9, the use of HPAM increases the retention of kaolin by 30%-35%. In addition to HPAM, AM-ethylene and AM-vinyl chloride copolymers and AM-pyrrolidone copolymers can also be used to improve the properties of the paper surface.
PAM can be added into the pulp to improve the wet strength and dry strength (tensile strength, bursting resistance, folding resistance, etc.) of the paper. AM-vinylamine copolymer can not only improve the surface properties of the paper, but also enhance the tensile properties of the paper. . The strength is increased by the action of the amine group in the AM copolymer, especially for paper in a wet state (increased by 1000% and higher). The strength of the paper is enhanced by the AM copolymer because the added polymer forms a complex with the Cr3+ and Cu2+ ions contained in the pulp.
In the paper industry, PAM has a variety of uses, with an average molecular weight of 1000-100% as a dispersant, which can improve the uniformity of the paper.
3 oil production
Polymer PAM is not only a high-efficiency flocculant, but also an extremely excellent thickener because of its high viscosity. PAM can be used as a multi-purpose additive in oilfield oil exploitation due to thickening, flocculation and convection regulation, such as drilling fluid, fracturing fluid, and polymer flooding to enhance oil recovery ( EOR). In oil exploitation, the key to the application lies in the combination of the conditions and requirements, and the rational design and selection of its constituent structures, such as molecular morphology, molecular weight, ionicity, etc., and the correct construction process.
3.1 PAM is used as a drilling fluid additive
Drilling fluid is used as a drilling mud performance regulator in petroleum exploration. The role of PAM is to regulate the rheology of the drilling fluid, carry the cuttings, and lubricate the drill bit for the benefit of drilling. In addition, it can greatly reduce stuck accidents, reduce equipment wear, and prevent the occurrence of lost circulation and collapse, so that the diameter of the well rules. Often used in this regard are partially hydrolyzed polyacrylamides which are obtained by hydrolysis of PAM or polyacrylonitrile.
3.2 PAM is used as polymer flooding
Among the methods for improving oil recovery, polymer flooding technology plays an important role. The role of the polymer is to adjust the rheology of the injected water, increase the viscosity of the driving liquid, improve the water flooding efficiency, reduce the water phase permeability in the formation, and allow the water and oil to flow forward at a constant speed.
Polymer flooding is to increase the viscosity of the injected water by adding a certain amount of high molecular weight polyacrylamide to the injected water to improve the oil-water mobility ratio. Due to the adsorption and trapping effect of the oil layer on the polyacrylamide molecules, the permeability of the high and medium permeable layers or the high and middle water-flooded layers is reduced, and the seepage resistance of the injected water is increased, so that the low-permeability layer is low or not. The water absorption of the flooded layer increases, which expands the range of the injected water on the plane of the oil layer and the thickness of the flooded layer in the longitudinal direction of the oil layer, thereby expanding the flooding volume, and unloading the unutilized crude oil during water flooding to improve the recovery of crude oil. The purpose of the rate.
The concept and technical methods for polymer flooding to enhance oil recovery have been around for 15 years (1949-1964). In 1964, the United States began field trials of polymer flooding and industrial scale use tests. The National Petroleum and Energy Research Center (NIPER) believes that the ultimate recovery factor ET is determined by the oil displacement efficiency Ed, the sweep efficiency Es, and the economic factor Ee, ET = Ed × Es × Ee. The main contribution of the polymer is to increase the viscosity of the displacement working fluid, reduce the oil-water flow ratio and adjust the permeability profile, and improve the ultimate mining efficiency by improving the sweep efficiency.
Yield. Phillips Petroleum Company further explained the role of the polymer: 1 polymer makes the viscosity of the water phase increase, some polymers can reduce the relative permeability of the water phase after flowing through the porous medium; 2 reduce the water-oil ratio, water and oil flow The decrease of the ratio can reduce the fingering phenomenon; 3 the increase of the viscosity of the aqueous phase and the decrease of the relative permeability of the water phase can cause the fluid injected later to be transferred to the unspreaded band, thereby increasing the sweep coefficient.
During the "7th Five-Year Plan" period, the two field trials of Daqing and Dagang Oilfields have achieved encouraging and good results. The development test of Daqing Oilfield shows that this process can greatly improve oil recovery and increase crude oil production. On average, per liter of polymer can increase the production of crude oil by more than 150 tons and increase oil recovery by 10%. Research work shows that this technology has a good application prospect in China. It is expected that in the future, polymer flooding and the use of chemical agents such as polymers will have greater development in China.
3.3 PAM is used as a water blocking agent
In the oilfield production process, due to the heterogeneity of the formation, flooding problems often occur and water shut-off is required. The essence is to change the penetration state of water in the formation to achieve the purpose of reducing oil production, maintaining formation energy and improving ultimate recovery. The PAM chemical water blocking agent has a selective effect on the oil and water permeability, and has less permeability to oil and a lower permeability to water. It can be used without cross-linking. It can also be cross-linked with aluminum salt, chromium salt, zirconium salt, etc. to form a gel. It can also add some resins to form an interpenetrating polymer network (IPN) to make it more temperature resistant. . If the W/O type PAM latex and the modified amino resin are chemically crosslinked, an interpenetrating polymer network water blocking agent can be formed, which has been applied in the oil field blocking water, and has achieved obvious effects. PAM can also be used to adjust the water absorption profile in the formation and block the large pores. Good results have been observed in practice.
3.4 PAM as a fracturing fluid additive
The fracturing process is an important stimulation measure for the development of dense layers in oil fields. Its function is to open the passage of rocks and allow oil to flow through. The fracturing fluid obtained by crosslinking methylene polyacrylamide is widely used due to its high viscosity, low friction, good suspendedness, and ease of preparation and low cost.
4, mining and metallurgy
A large amount of water is usually used in the mining process. Finally, it is often necessary to separate useful solid minerals from water or an aqueous solution, and to purify and recycle the wastewater. The use of PAM flocculant promotes the rapid sinking of useful solid materials, promotes liquid clarification and dewatering of mud cakes, thereby increasing production efficiency, reducing tailings loss and water consumption, reducing equipment investment and processing costs, and reducing Environmental pollution.
Uranium extraction is one of the earliest important applications of PAM. Uranium ore is extracted by leaching its ore with an acid or sulfonate solution. When filtered in an acid immersion liquid, treatment with PAM increases the thickening and filtration rate. In the process of enrichment and filtration of extracted uranium, it is very effective to add PAM for treatment. PAM can also be effectively applied to the treatment of potash in the potash ore to separate the clarified brine. In the aluminum ore refined by the Bayer process, insoluble iron oxide (red mud) can be separated from the aqueous solution of hot caustic soda by PAM.
PAM can be used in the coal washing process of the coal industry. It can be used to treat coal slime water, which can not only recover a large amount of coal slime, but also prevent black water pollution, and can make the coal mine realize water circulation and save water. When flotation of clean coal, PAM is added before filtration to increase the filtration speed and the weight of the filter cake, thereby increasing productivity.
In the metallurgical industry, PAM can be used in such processes as converter dedusting wastewater treatment, steel rolling sewage treatment, blast furnace gas washing water treatment, mine clay quarrying wastewater treatment, and aluminum processing wastewater treatment. PAM plays a unique role in improving the repeated application of water and water.
In the last 15-20 years, AM copolymers have been widely used as high-efficiency adsorbents in gel permeation chromatography. Crosslinked AM copolymer gels have proven superior to the most popular glucan gels. It has high biological stability, is not prone to long bacteria, and does not shrink severely under ionic force. The Biorad Laboratories of the United States have commercialized PAM gels of various porosities.
One of the characteristics of PAM hydrogel is that its swelling in water undergoes a sudden change with a small change in temperature at a critical temperature, and the volume change can be tens to hundreds of times. This property can be applied to the concentration of certain aqueous solutions without the use of high temperatures. This is valuable for the extraction of some organic or biological substances. In addition to substances that can be used to separate biological activities, PAM hydrogels can also be used for controlled release of drugs and entrapment of enzymes, protein electrophoresis, artificial organ materials, contact lenses, gel explosives, gel electrolytes for batteries, Gel hydrazine, column packing, etc. used in rocket fuel.
6, other applications
(l) Food processing PAM can be used as a chemical auxiliaries for the sugar industry. It can also be used for the purification of various meat, fruit and vegetable washing waters as well as the clarification of fruit wines and beer.
In the sugar industry, syrup clarification must use a good flocculant, the type of flocculant and the method of preparation are important. Polymer polyacrylamide (25%-30% hydrolysis) is more suitable for sugar factory applications. The advanced cane juice clarification process, high-efficiency polyacrylamide flocculant, in order to remove as much non-sugar as possible, thereby improving the quality of the clear juice. It can also be used to reduce the build-up of scale in sugar refining equipment.
(2) Building materials industry In the building materials industry, it can be used to improve the production capacity of the settling tank and the filterability of cement in the process of manufacturing wet cement, and improve the uniformity of the kiln. The retention of fibers and additives in inorganic materials and wood fiber based insulation panels can be improved. It can be added to the composite formula of clear water wall bonding cement to improve construction quality.
(3) Construction industry Used as an adhesive for wallboard (paper), asbestos products, etc. in the construction industry. PAM gels can be used for caulking, repair and plugging of buildings. The cauterized cement with PAM exhibits excellent bonding and adhesion over a wide range of temperatures and relative humidity.
(4) Soil improvement is used for grouting of mines, pools, dams and foundations (usually copolymerized with AM and a cross-linking comonomer at the application site) to consolidate the soil to improve its load-bearing properties and to add to the cultivated soil. A small amount (10-3%-10-1% of the surface soil weight) of acrylamide polymer can greatly improve the wind erosion resistance and water immersion performance of the soil, improve its dispersibility and gas permeability, and increase crop yield.
(5) Electroplating industry In the electroplating bath, the addition of PAM can homogenize the metal precipitate and make the coating more bright. PAM can be used as a protective colloid to improve emulsion stability.
(6) Textile, printing and dyeing industry In the textile and printing and dyeing industry, PAM is used as a sizing agent and fabric finishing agent, and can also form a protective layer against mold on the surface of the fabric. It can be used as a warp sizing agent for polyester, cotton and other fibers and as an anti-wrinkle agent for cotton. Formulating the slurry to replace the sizing slurry produced by the grain can save a lot of food. By virtue of its strong hygroscopic property, the wire breakage rate during spinning of the spun yarn can be reduced, and the hydrophilicity of the synthetic fiber can be improved. When used as a paint printing auxiliary, it has high fastness and high vividness, and can also be used as a leveling agent.
(7) Fluid transport One of the most promising applications of acrylamide polymers is to reduce the hydraulic resistance of turbulence. This kind of action has a wide range of applications, such as increasing the coverage of water spray guns; reducing the resistance of the pipeline during fluid transport; and applying it to the surface of a ship or submarine to reduce navigational resistance and increase shipping speed; The coal slurry conveying condition can be improved in the liquid transportation of coal, and can also be used for high-speed suction of suspended water and emulsion.
(8) Use as water-absorbent resin Superabsorbent polymer is a new type of functional polymer material developed in the mid-1970s and has been widely used in industry and daily life. Most of such polymers are crosslinked acrylic acid copolymers of metal acrylates and acrylamides or other monomers such as 2-acrylamide 2-methylpropane sulfonic acid. These gels have a high strength and can absorb more than 2,000 times. Using light oil as the continuous phase, SPAN-60 as the suspension stabilizer, bis-acrylamide as the crosslinking agent and persulfate as the main initiator, the acrylate-acrylamide copolymerization cross-linked high water absorption was synthesized by reversed-phase suspension polymerization. Polymer. The product is microsphere-shaped and has an average particle size of less than 40 um. The average particle size and water absorption of the product are affected by factors such as the stirring speed, the amount of the suspension stabilizer, and the amount of the crosslinking agent. The water absorption of the product is about 300 times.
In addition, PAM can be used as a sand binder in metal casting, a temporary adhesive in the ceramic industry, a metal rust protection film, a fertilizer agglomeration agent, and a stabilizer in inks, paints, drugs, and latex paints. PAM can be used as a protective layer for inorganic granular fertilizers, allowing germicides and herbicides to adhere to the surface of the particles. It can also be used as a microcapsule packaging material for sustained release drugs.