How To Choose The Cationic, Anionic And Non-ionic of Polyacrylamide (PAM) Correctly?

Polyacrylamide (abbreviated as PAM or pAAM) is a polymer with the formula (-CH2CHCONH2-). It has a linear-chain structure. PAM is highly water-absorbent, forming a soft gel when hydrated. and it is the most commonly used agent in our sewage treatment for different industries. In our practical applications, PAM is divided into three types: cationic, anionic and non-ionic. How to choose these three types of PAM, should start with the differences:

The difference between PAM

1. Structural differences

Polyacrylamide is a versatile polymer that finds applications in various industries, ranging from wastewater treatment to oil recovery. It is available in different forms, including cationic, anionic, and non-ionic variants. Each variant possesses distinct structural differences, which contribute to their specific properties and applications. In this article, we will explore the structural differences between cationic, anionic, and non-ionic polyacrylamide, shedding light on their unique characteristics.

Cationic polyacrylamide (CPAM): It is a linear polymer compound. Because it has a variety of active groups, it can form hydrogen bonds with many substances through affinity and adsorption. Mainly flocculates negatively charged colloids.

Anionic polyacrylamide (APAM): It is a water-soluble high molecular polymer. It is mainly used for flocculation, sedimentation, sedimentation and clarification treatment of various industrial wastewaters, such as steel plant wastewater, electroplating plant wastewater, metallurgical wastewater, coal washing wastewater and other sewage treatment, Sludge dehydration, etc. It can also be used for drinking water clarification and purification treatment. Because its molecular chain contains a certain number of polar groups, it can accelerate particles in suspension by adsorbing solid particles suspended in water, forming bridges between particles, or agglomerating particles to form large flocs through charge neutralization. The sedimentation has a very obvious effect of accelerating solution clarification and promoting filtration.

Nonionic 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, forming bridges between particles to form large flocs. It accelerates the sedimentation of particles in suspension, has a very obvious effect of accelerating the clarification of the solution and promoting filtration. Since the molecular chain contains amide groups or ionic genes, its distinctive feature is that it is highly hydrophilic and can be dissolved in water at various proportions. The polyacrylamide aqueous solution has good tolerance to electrolytes, such as amine chloride, sodium sulfate, etc. Not sensitive and compatible with surfactants.

2. Differences in uses

Nonionic polyacrylamide uses

Sewage treatment agent: When the suspended sewage is acidic, it is more appropriate to use non-ionic polyacrylamide as the flocculant. This is because PAM plays an adsorption and bridging role, causing suspended particles to flocculate and settle, achieving the purpose of purifying sewage. It can also be used to purify tap water, especially when used in conjunction with inorganic flocculants, which has the best effect in water treatment.

Textile industry auxiliaries: Adding some chemicals can formulate chemical materials for sizing textiles.

Sand prevention and sand fixation: Dissolve non-ionic polyacrylamide to a concentration of 0.3% and add cross-linking agent, and spray it on the desert to prevent sand and fix sand.

Soil moisturizer: used as the basic raw material for soil moisturizer and various modified polyacrylamide.

Cationic polyacrylamide uses

Sludge dehydration: The corresponding brand of this product can be selected according to the nature of the sewage, which can effectively carry out gravity sludge dehydration before the sludge enters the filter press. During dehydration, large flocs are produced, which do not stick to the filter cloth and do not flow when filtered. The dosage is small, the dehydration efficiency is high, and the moisture content of the mud cake is below 80%.

Treatment of sewage and organic wastewater: This product is electropositive in acidic or alkaline media, so it is extremely effective to flocculate, settle and clarify sewage with negatively charged suspended particles in the sewage, such as alcohol plant wastewater and brewery wastewater. , MSG factory wastewater, sugar factory wastewater, meat factory wastewater, beverage factory wastewater, textile printing and dyeing factory wastewater, etc., using cationic polyacrylamide is more effective than using anionic polyacrylamide, nonionic polyacrylamide or inorganic salts Several times or dozens of times, because this type of wastewater generally has a negative charge.

Flocculant for water treatment in water plants: This product has the characteristics of low dosage, good effect and low cost. It has better effect when combined with inorganic flocculant.

Oilfield chemicals: such as clay anti-swelling agents, thickeners for oilfield acidification, etc.

Papermaking aids: Cationic PAM paper enhancer is a water-soluble cationic polymer containing carbamoyl groups. It has the functions of reinforcing, retaining, and filtering aids, and can effectively improve the strength of paper. At the same time, this product is also an efficient dispersant.

Anionic polyacrylamide uses

Industrial wastewater treatment: For sewage with suspended particles, high concentration, positively charged particles, and neutral or alkaline PH value, steel plant wastewater, electroplating plant wastewater, metallurgical wastewater, coal washing wastewater and other sewage treatment, the effect is most.

Drinking water treatment: The water source of many water plants in our country comes from rivers. It has high sediment and mineral content and is relatively turbid. Even after sedimentation and filtration, it still cannot meet the requirements. It is necessary to add flocculant, and the dosage is 1/1 of the inorganic flocculant. 50, 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 together to achieve better results.

Recovery of lost starch grains from starch plants and alcohol plants: Nowadays, the wastewater of many starch plants contains a lot of starch. Anionic polyacrylamide is now added to flocculate and precipitate the starch particles, and then the sediment is filtered through a filter press and turned into cake. It can be used as feed. The alcohol in the alcohol factory can also be dehydrated using anionic polyacrylamide and recovered by filtering.

Technical indicators of PAM

The technical indicators of polyacrylamide generally include molecular weight, degree of hydrolysis, ionicity, viscosity, residual

monomer content, etc., so the quality of PAM can also be judged based on these indicators.

1. Molecular weight

The molecular weight of PAM is very high and has increased significantly in recent years. The molecular weight of PAM used in the 1970s was generally in the millions; after the 1980s, the molecular weight of most high-efficiency PAM was more than 15 million, and some reached 20 million. Each 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 7.1 million). Generally, PAM with high molecular weight has better flocculation performance. The molecular weight of acrylamide is 71, and the molecular weight of PAM containing 100,000 monomers is 7.1 million. The molecular weight of polyacrylamide and its derivatives ranges from hundreds of thousands to more than 10 million. According to the molecular weight, it can be divided into low molecular weight (less than 1 million), medium molecular weight (1 million to 10 million), and high molecular weight (10 million to 1500 10,000), super molecular weight (more than 15 million).

The molecular weight of polymer organic compounds is not completely uniform even in the same product, and the nominal molecular weight is its average value.

2. Degree of hydrolysis and ionicity

The ionicity of PAM has a great influence on its use effect, but its appropriate value depends on the type and nature of the materials being processed, and the optimal value will be different under different circumstances. If the ionic strength of the material being processed is higher (containing more inorganic substances), the ionicity of the PAM used should be higher, otherwise it should be lower. Usually, the degree of anionicity is called the degree of hydrolysis. Ionicity generally refers to cations.

Ionic degree=n/(m+n)*100%

The PAM produced in the early stage was polymerized from polyacrylamide, a monomer, and originally did not contain -COONa groups. Before use, NaOH must be added and heated to hydrolyze part of the -CONH2 group into -COONa. The reaction formula is as follows:

-CONH2 + NaOH -→ -COONa + NH3↑

Ammonia gas is released during the hydrolysis process. The proportion of hydrolysis of the amide group in PAM is called the degree of hydrolysis of PAM, which is the anionic degree. This kind of PAM is inconvenient to use and has poor performance (heating and hydrolysis will significantly reduce the molecular weight and performance of PAM). It has been rarely used since the 1980s.

Modernly produced PAM has a variety of products with different anionic degrees. Users can select appropriate varieties according to needs and through actual tests. No further hydrolysis is required, and they can be used after dissolution. However, due to habitual reasons, some people still refer to the dissolution process of flocculants as hydrolysis. It should be noted that hydrolysis means decomposition with water, which is a chemical reaction. The hydrolysis of PAM will release ammonia gas; while dissolution is only a physical effect and no chemical reaction. The two are fundamentally different and should not be confused.

3. Residual monomer content

The residual monomer content of PAM refers to the acrylamide monomer content that is not completely reacted and ultimately remains in the polyacrylamide product during the polymerization of acrylamide into 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, trace amounts of unpolymerized acrylamide monomer inevitably remain. Therefore, the residual monomer content in PAM products must be strictly controlled. International regulations require that the residual monomer content in PAM used in drinking water and food industries should not exceed 0.05%. This value for famous foreign products is lower than 0.03%.

4. Viscosity

PAM solution is very viscous. The higher the molecular weight of PAM, the greater the solution viscosity. This is because PAM macromolecules are long and thin chains, which have great resistance to movement in the solution. The essence of viscosity is to reflect the friction force within the solution, also known as the internal friction coefficient. The viscosity of solutions of various polymer organic compounds is relatively high and increases with increasing molecular weight. One method of measuring the molecular weight of polymeric organic matter is to measure the viscosity of a solution of a certain concentration under certain conditions, and then calculate its molecular weight according to a certain formula, which is called "viscosity average molecular weight".

PAM selection

sample test of polyacrylamide

Polyacrylamide can be divided into nonionic, anionic, and cationic polyacrylamide types according to their ionic properties. There are many models derived from different specifications according to molecular weight, ionicity, etc. Faced with the complicated specification system in the market, it is really difficult to select the best polyacrylamide model for your own sewage system. How to deal with sewage or sewage in a few tricks? Frequently Asked Questions about Mud Polyacrylic Selection.

1. Understand the source of sludge

Sludge is an inevitable product in sewage treatment. First of all, we should understand the source, nature, composition and solid content of sludge. According to the main components of sludge, sludge can be divided into organic sludge and inorganic sludge.

Generally speaking, 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 it is not suitable to use anionic polyacrylamide when it is very acidic. When the solid content of mud is high, the amount of polyacrylamide is usually larger.

2. Molecular weight selection of polyacrylamide

The molecular weight of polyacrylamide refers to the length of the molecular chain in the molecule. The molecular weight of polyacrylamide is between 5 million and 18 million. Generally speaking, the higher the molecular weight of the polyacrylamide product, the greater the viscosity. However, when used It does not mean that the higher the molecular weight of the product, the better the use effect. In specific use, the appropriate molecular weight of polyacrylamide must be determined based on the actual application industry, water quality, treatment equipment and other conditions.

Polyacrylamide is a polymer coagulant. The products can be divided into three categories according to their average molecular weight: low molecular weight (<1 million), medium molecular weight (2-4 million) and high molecular weight (>7 million).

Polyacrylamide is used in sewage treatment. It is a high molecular water-soluble organic polymer with a molecular weight ranging from millions to tens of millions. Domestic polymer polyacrylamides include: nonionic polyacrylamide (abbreviated NPAM, molecular weight 8-15 million), anionic polyacrylamide (abbreviated APAM, molecular weight 8-20 million), cationic polyacrylamide (abbreviated CPAM, molecular weight 800 -12 million, ionicity 10%-80%).

If it is used simply as a coagulant, generally the higher the molecular weight, the tighter the flocculation and the less medication, but the molecular weight of anionic polyacrylamide is recommended not to exceed 20 million.

If in terms of sludge dewatering. When using a belt filter press, generally the molecular weight cannot be too high. If the molecular weight is very high, it may cause clogging of the filter cloth and affect the dehydration effect. For example, if you use a centrifugal filter press, the molecular weight requirement must be higher, because the centrifugal filter press The filter requires that the flocs be able to withstand shearing as much as possible, so products with relatively high molecular weights should be selected.

3. Ionic degree selection of polyacrylamide

For the sludge to be dewatered, flocculants with different ionic degrees can be screened through small experiments to select the most suitable polyacrylamide. This can not only achieve the best flocculant effect, but also minimize the amount of dosing and save costs . The key to choosing a degree is:

(1) Size of flocculation

Size of flocculation: Too small flocculation will affect the speed of drainage. Too large flocculation will bind more water and reduce the degree of mud biscuit. The size of the flocs can be adjusted by selecting the molecular weight of the polyacrylamide.

(2) Floc strength (moisture content)

Strength of floc: The floc should remain stable without breaking under shear. Increasing the molecular weight of polyacrylamide or selecting an appropriate molecular structure can help improve flocculation stability.

(3) Mixing of polyacrylamide and sludge

Polyacrylamide must fully react with sludge at a certain location in the dehydration equipment to cause flocculation. To this end, the viscosity of the polyacrylamide solution must be appropriate, and it must be fully mixed with the sludge under the existing equipment conditions. Whether the two are mixed uniformly is a key factor for success. The viscosity of polyacrylamide solution is related to its molecular weight and preparation concentration.

(4) Dissolution of polyacrylamide

Only with good dissolution can the flocculation effect be fully exerted. As mentioned before, the dissolution process of polyacrylamide is actually the maturation process of polyacrylamide. Sometimes it is necessary to speed up the dissolution rate. In this case, you can consider increasing the concentration of the polyacrylamide solution.

Therefore, the best product selection must be determined by laboratory beaker experiments.

It can be seen from the above that the selection of molecular weight and ionicity is not absolute. It is best to do a selection test before choosing polyacrylamide, and it is best to run a machine operation test. Only in this way can the data obtained be the most accurate, and the optimal polyacrylamide will be cost-effective.