The difference between PAM
1. Structural differences
Cationic polyacrylamide (CPAM): It is a linear polymer compound. Because it has a variety of active groups, it can form hydrogen bonds with affinity and adsorption of many substances. Mainly flocculate ngatively charged colloids.
Anionic polyacrylamide (APAM): is a water-soluble polymer, mainly used for flocculation and sedimentation of various industrial wastewater, precipitation clarification treatment, such as steel plant wastewater, electroplating plant wastewater, metallurgical wastewater, coal washing wastewater and other wastewater treatment, sludge dewatering, etc. It can also be used for drinking water clarification and purification treatment. Due to the fact that its molecular chain contains a certain number of polar groups, it can adsorb solid particles suspended in water, bridge the particles or agglomerate the particles through charge neutralization to form a large flocculant, so it can accelerate the sedimentation of particles in the suspension, which has a very obvious effect of accelerating solution clarification and promoting filtration.
Non-ionic polyacrylamide (NPAM): It is a high molecular polymer or polyelectrolyte. Its molecular chain contains a certain amount of polar genes that can adsorb solid particles suspended in water, so that the particles can bridge to form large flocculates. It accelerates the sedimentation of the particles in the suspension, has a very obvious effect of speeding up the clarification of the solution and promoting filtration. Since the molecular chain contains amide groups or ionic genes, it is characterized by high hydrophilicity and can be dissolved in water in various proportions. Polyacrylamide aqueous solutions have good tolerance to electrolytes, such as amine chloride, sodium sulfate, etc., and are also compatible with surfactants.
2. Differences in use
Use of nonionic polyacrylamide
Sewage treatment agent: When the suspended sewage is acidic, it is more suitable to use non-ionic polyacrylamide as a flocculant. This is PAM to play the role of adsorption and bridging, so that the suspended particles produce flocculation and precipitation to achieve the purpose of purifying sewage. It can also be used for tap water purification, especially when used in combination with inorganic flocculants, with the best effect in water treatment.
Textile industry additives: Adding some chemicals can be used to prepare chemical materials for textile sizing.
Sand prevention and fixation: Dissolve non-ionic polyacrylamide into a 0.3% concentration and add a cross-linking agent, and spray it on the desert to play a role in sand prevention and fixation.
Soil moisturizer: used as a basic raw material for soil moisturizer and various modified polyacrylamides.
Use of cationic polyacrylamide
Sludge dewatering: According to the nature of the sewage, the corresponding grade of this product can be selected, which can effectively carry out gravity sludge dewatering before the sludge enters the pressure filter. During dewatering, large flocs are produced, and the filter cloth is not sticky. It does not disperse during pressure filtration, uses less, and has high dewatering efficiency. The moisture content of the mud cake is below 80%.
Treatment of wastewater and organic wastewater: This product is anodized in acidic or alkaline media, so that it can flocculate and precipitate wastewater with negative charge of suspended particles in wastewater, and it is extremely effective to clarify, such as alcohol factory wastewater, brewery wastewater, monosodium glutamate factory wastewater, sugar factory wastewater, meat factory wastewater, beverage factory wastewater, textile printing and dyeing factory wastewater, etc. The effect of using cationic polyacrylamide is several times or dozens of times higher than that of anionic polyacrylamide, non-ionic polyacrylamide or inorganic salt, because such wastewater generally has a negative charge.
Waterworks water treatment flocculant: This product has the characteristics of low dosage, good effect, and low cost. It is better to use it in combination with inorganic flocculants.
Oilfield chemicals: such as clay anti-swelling agents, thickening agents for oilfield acidification, etc.
Papermaking Auxiliary: Cationic PAM paper reinforcer is a water-soluble cationic polymer containing aminoformyl group, which has the functions of strengthening, retention, filtration, etc., which can effectively improve the strength of paper. At the same time, the product is also an efficient dispersant.
Use of anionic polyacrylamide
Industrial wastewater treatment: For suspended particles, wastewater with high concentration, positive charge, and neutral or alkaline pH, wastewater from steel plants, wastewater from electroplating plants, wastewater from metallurgy, wastewater from coal washing, and other wastewater treatment results are the best.
Drinking water treatment: many water plants in our country come from rivers, with high sediment and mineral content, which is relatively turbid. Although it has been precipitated and filtered, it still cannot meet the requirements. It is necessary to add flocculants. The dosage is 1/50 of inorganic flocculants, but the effect is several times that of inorganic flocculants. For river water with serious organic pollution, inorganic flocculants and cationic polyacrylamide can be used in combination. The effect is better.
Recycling of starch lees from dialysis mills and alcohol plants: Nowadays, the wastewater from many dialysis mills contains a lot of starch. Anionic polyacrylamide is now added to make starch particles flocculate and precipitate, and then the sediment is filtered by a filter press into a cake, which can be used as feed. Alcohol from alcohol plants can also be dehydrated by anionic polyacrylamide and recycled by pressing filters.
Technical indicators of PAM
The technical indicators of polyacrylamide generally include molecular weight, degree of hydrolysis, ionization, viscosity, residual monomer content, etc. Therefore, the quality of PAM can also be judged from these indicators!
1. Molecular weight
The molecular weight of PAM is very high, and it has been greatly improved in recent years. The molecular weight of PAM applied in the 1970s is generally in the millions; after the 1980s, the molecular weight of most high-efficiency PAM is more than 15 million, and some reach 20 million. Each such PAM molecule is polymerized from more than 100,000 acrylamide or sodium acrylate molecules (the molecular weight of acrylamide is 71, and the molecular weight of PAM containing 100,000 monomers is 7.10 million). Generally, the flocculation performance of PAM with high molecular weight is better. The molecular weight of acrylamide is 71, and the molecular weight of PAM containing 100,000 monomers is 7.10 million. The molecular weight of polyacrylamide and its derivatives ranges from hundreds of thousands to more than 10 million, and can be divided into low molecular weight (below 1 million), medium molecular weight (1 million~ 10 million), high molecular weight (10 million~ 15 million), and super molecular weight (above 15 million).
The molecular weight of polymer organics is not completely uniform even in the same product, and the nominal molecular weight is its average.
2. Degree of hydrolysis and ionization
The ionization degree of PAM has a great influence on its use effect, but its appropriate value depends on the type and nature of the material being processed, and there will be different optimal values in different situations. If the ionic strength of the material being processed is high (containing more inorganic substances), the ionization degree of the PAM used should be higher, and vice versa. Usually, the anionic degree is called the degree of hydrolysis. Ionization generally refers to cations.
Ionization = n/(m + n) * 100%
The early-produced PAM was polymerized from a monomer of polyacrylamide, which originally did not contain the -COONa group. Before use, add NaOH to heat to hydrolyze part of the -CONH2 group to -COONa. The reaction formula is as follows:
-CONH2 + NaOH - → -COONa + NH3 ↑
Ammonia gas is released during hydrolysis. The ratio of amide group hydrolysis in PAM is called the degree of hydrolysis of PAM, which is the degree of anionic. This kind of PAM is inconvenient to use and has poor performance (heating hydrolysis will cause a significant decrease in the molecular weight and performance of PAM). It has been rarely used since the 1980s.
Modern production of PAM has a variety of products with different anionic degrees. Users can choose the appropriate variety according to their needs and through actual tests. There is no need for hydrolysis, and it can be used after dissolution. However, due to customary reasons, some people still refer to the dissolution process of flocculants as hydrolysis. It should be noted that hydrolysis means adding water to decompose, which is a chemical reaction. The hydrolysis of PAM has ammonia gas release; while the dissolution is only a physical effect, no chemical reaction. The two are essentially different and should not be confused.
3. Residual monomer content
The residual monomer content of PAM refers to the acrylamide monomer content that does not react completely and eventually remains in the polyacrylamide product during the polymerization of acrylamide to polyacrylamide. It is an important parameter to measure whether it is suitable for the food industry. Polyacrylamide is non-toxic, but acrylamide has certain toxicity. In industrial polyacrylamide, it is inevitable that a small amount of unpolymerized acrylamide monomer will remain. Therefore, the residual monomer content in PAM products must be strictly controlled. International regulations stipulate that the residual monomer content in PAM used in drinking water and food industry does not exceed 0.05%. This value of famous foreign products is less than 0.03%.
4. Viscosity
PAM solutions are very viscous. The higher the molecular weight of PAM, the greater the viscosity of the solution. This is because PAM macromolecules are long and thin chains that have great resistance to movement in the solution. The essence of viscosity is to reflect the size of the friction force in the solution, also known as the internal friction coefficient. The viscosity of various polymer organic compounds is higher and increases with the increase of molecular weight. One way to determine the molecular weight of polymer organic compounds is to determine the viscosity of a solution at a certain concentration under certain conditions, and then calculate its molecular weight according to a certain formula, which is called "viscosity average molecular weight".
Selection of PAM
Polyacrylamide can be divided into non-ionic, anionic, and cationic polyacrylamide types according to ionic characteristics. According to molecular weight, there are many models with different specifications, ionization, etc. In the face of the chaotic specification system of the market, it is indeed very difficult to select the best polyacrylamide model for your sewage system. How to solve the common problems of sewage or sludge polyacrylamide selection.
1. Understand the source of sludge
Sludge is an inevitable product in wastewater treatment. First, we should understand the source, nature, composition and solid content of sludge. According to the main components contained in sludge, sludge can be divided into organic sludge and inorganic sludge.
In general, cationic polyacrylamide is used to treat organic sludge, and anionic polyacrylamide is used to treat inorganic sludge. It is not easy to use cationic polyacrylamide when it is very alkaline, and anionic polyacrylamide is not suitable when it is very acidic. When the solid content of sludge is high, the amount of polyacrylamide is usually large.
2. Molecular weight selection of polyacrylamide
Polyacrylamide molecular weight refers to the length of the molecular chain in the molecule, the molecular weight of polyacrylamide is between 500 and 18 million, generally speaking, the higher the molecular weight of polyacrylamide products, the greater the viscosity, however, in use, not The higher the molecular weight of the product, the better the use effect, specifically in use, according to the actual application industry, water quality, treatment equipment and other conditions, to determine the appropriate polyacrylamide molecular weight.
Polyacrylamide is a polymer coagulant aid, and the products can be divided into three categories according to their average molecular weight: low molecular weight (< 1 million), medium molecular weight (200-4 million) and high molecular weight (> 7 million).
Polyacrylamide is used in wastewater treatment, and the molecular weight is from millions to tens of millions of polymer water-soluble organic polymers. Domestic polymer polyacrylamides include: non-ionic polyacrylamide (abbreviated NPAM, molecular weight 800-15 million), anionic polyacrylamide (abbreviated APAM, molecular weight 800-20 million), cationic polyacrylamide (abbreviated CPAM, molecular weight 800-12 million, ionic degree 10% -80%).
If you simply use coagulant aids, the higher the molecular weight, the tighter the flocculent, and the more economical the medication, but the molecular weight of anionic polyacrylamide is recommended not to exceed 20 million.
If you use a belt filter press for sludge dewatering, the molecular weight should not be too high. If the molecular weight is high, it may cause the filter cloth to clog and affect the dewatering effect. For example, if you use a centrifugal filter press, the molecular weight requirement should be higher, because the centrifugal filter press requires the flocs to be as resistant to shearing as possible, so you should choose products with relatively high molecular weight.
3. Ionization selection of polyacrylamide
For the sludge to be dewatered, flocculants of different ionic degrees can be screened through small experiments to select the best suitable polyacrylamide, so that the best flocculant effect can be achieved, and the amount of dosing can be minimized, saving costs. The key to choosing ionic degrees is:
(1) The size of the flocculent
The size of the flocculent: If the flocculent is too small, it will affect the speed of drainage. If the flocculent is too large, it will bind more water and reduce the degree of mud biscuit. The size of the flocculent can be adjusted by selecting the molecular weight of polyacrylamide.
(2) Flocculent strength (moisture content)
Strength of the flocs: The flocs should remain stable without breaking under shear action. Increasing the molecular weight of polyacrylamide or choosing an appropriate molecular structure can help to improve the stability of the flocs.
(3) Mixing of polyacrylamide and sludge
The polyacrylamide must fully react with the sludge at a certain position in the dewatering equipment to cause flocculation. For this reason, the viscosity of the polyacrylamide solution must be appropriate, and it can be fully mixed with the sludge under the existing equipment conditions. Whether the two are mixed evenly is a key factor for success. The viscosity of the polyacrylamide solution is related to its molecular weight and formulation concentration.
(4) Dissolution of polyacrylamide
Good dissolution can give full play to the flocculation effect. As mentioned earlier, the dissolution process of polyacrylamide is actually the ripening process of polyacrylamide, and sometimes it is necessary to speed up the dissolution speed. At this time, you can consider increasing the concentration of polyacrylamide solution.
Therefore, the best product selection is determined by laboratory beaker experiments.
From the above, it can be seen that the choice of molecular weight and ionization is not absolute. Before selecting polyacrylamide, it is best to do a selection test, and it is best to run the test on the machine. This way, the data obtained is the most accurate, and the preferred polyacrylamide is more cost-effective.