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A comprehensive introduction to Polyacrylamide(PAM)

By WHGCM December 8th, 2023 115 views

I, What is Polyacrylamide(PAM)

Polyacrylamide (PAM) is a linear polymer with the chemical formula (C3H5NO)n.
PAM chemical formula
It is a hard, glassy solid at room temperature. Its products include glue, latex and white powder, translucent beads, and flakes. It has good thermal stability. It can be dissolved in water in any proportion, solution is uniform and transparent.

II, Properties

 Density  Molecular weight  CAS No.   EINECS No.
 1.302 g/cm³(23℃)  1×104~2×107  9003-05-8  231-545-4

III, Features

3.1 Flocculation: 

PAM can make the suspended material flocculate through electric neutralization and bridging adsorption.

3.2 Adhesion: 

PAM can play the role of adhesion through mechanical, physical, and chemical effects.

3.3 Reducing resistance: 

PAM can effectively reduce the friction resistance of the fluid, adding a trace of PAM in water can reduce resistance by 50-80%.

3.4 Thickening: 

PAM in neutral and acid conditions has a thickening effect. It is easily hydrolyzed when the PH value is more than 10. The thickening will be more obvious when its structure becomes semi-network.

IV, Types

photo of PAM powder
The structure of polyacrylamide contains two key parameters: molecular weight and ionicity. So, PAM could be sorted as per the above two parameters as well as its physical form.

4.1 According to molecular weight

PAM can be categorized into low molecular weight, medium molecular weight, high molecular weight, and ultra-high molecular weight. 

4.2 According to the ionicity, 

It can be classified into non-ionic, anionic, cationic, and amphoteric. 

4.3 As per physical form, 

Polyacrylamide can be divided into solid, colloid, aqueous solution, emulsion, and others.

V, Applications:

The most valuable properties of PAM are very high molecular weight, strong water solubility, the ability to be made into hydrophilic but water-insoluble gels, the ability to introduce a variety of ionic groups and adjust the molecular weight to get specific properties, and good adhesion to many solid surfaces and dissolved substances. Because of these properties, PAM is widely used in thickening, flocculation, stabilizing colloids, drag reduction, bonding, film-forming, scale inhibition, gels and biomedical materials, and many other aspects. The biggest use of PAM is in the fields of water treatment, papermaking, oil extraction, metallurgy, and mining.
According to statistics, 37% of the total global production of polyacrylamide is used in wastewater treatment, 27% is used in the petroleum industry and 18% is used in the paper industry. 

5.1 Water treatment field.

photo of Water treatment plant
Polyacrylamide is one of the common chemicals in wastewater treatment and sludge dewatering processes and its effectiveness has been widely recognized. 
PAM is mainly used as a flocculant, especially for the flocculation of proteins and starch in the water. It can improve water quality, the strength of flocs, settling speed, and slow down the corrosion and scaling to the circulating cooling system. 

5.1.1 Raw water treatment

PAM is often used with activated carbon, and effectively coagulates and clarifies the suspended particles in the water, thus improving the water purification capacity by more than 20%. 

5.1.2 Sewage treatment

Adding PAM can improve the rate of sewage reuse.

5.1.3 Industrial water

It is an important formulation agent in industrial water treatment.
Polyacrylamide has a broad application prospect and a huge potential market in the water treatment industry.  The application of polyacrylamide in urban wastewater treatment will be more and more important along with the continuously growing demand for environmental protection. 

5.2 Oil extraction

photo of Oil extraction
Polyacrylamide is widely used in applications including drilling, water plugging & profiling, oil repulsion, fracturing, and other aspects, with remarkable effect. 

5.3 Paper industry

The main application of PAM in the paper industry is used as a binder for pulp fiber and additives. PAM is also used for wastewater treatment in the paper process. 

5.4 Textile industry

Polyacrylamide can be used as textile auxiliaries to improve the textile dyeing and finishing effects.

5.5 Agriculture

It increases the efficiency of irrigation water use and soil property. It is also used in the recovery of feed protein, with stable quality and good performance. The protein powder recovered can improve the survival rate of chicken's weight gain, and egg laying, without adverse effects.
photo of Agriculture

5.6 Food industry

PAM is used for cane juice clarification and syrup phosphorus flotation extraction in cane and beet sugar production. 

5.7 Medical and personal care industry

MAP has an indispensable role in personal care products, as a stabilizer, and emulsifier.
Polyacrylamide gels are used as non-prothrombin granulators, surgical, contact lens materials, and microcapsule coating materials, and are used to manufacture high-quality hemostatic tethers, sanitary pads, and diapers.
photo of diapers

5.8 Construction industry

PAM also plays a key role in helping to improve the properties of concrete and mortar.
Enzyme fermentation liquid flocculation clarification, synthetic resin coatings, civil grouting materials plugging, building materials industry,  construction adhesives, caulking repair agent, and water plugging agent.

5.9 Other industries

Includes the electroplating industry, printing, and so on.

VI, How to choose the type and dosage of MAP in water treatment?

It is difficult to give a precise value because of the effect of the following factors water suspended solids content, turbidity, organic content, and heavy metal ion concentration.
Besides, different water treatment objectives also require the use of different types and amounts of polyacrylamide. 
Lastly,  the dosage is also different as per the choice of water treatment process conditions, such as mixing rate, settling time, and settling tank design.
So, we can select the suitable models of polyacrylamide through the method of scale selection, and test its dosage under the best effect, to deduce the dosage required for one ton of water, which will provide a reference for actual use. 
In the polyacrylamide industry, there are almost 100 kinds of polyacrylamide models to select.

VII, Production process

The polyacrylamide production process includes batching, polymerization, granulation, drying & cooling, crushing, and packing. 

7.1 Batching

To input the raw materials to the dosing kettle through the pipeline, add the appropriate additives and mix well, cooling to 0-5 ℃. 

7.2 Polymerization

Transport the raw materials to the polymerization kettle, 
Input nitrogen to deoxygenation, reduce the oxygen content in addition to 1% or so. 
Add the initiator for polymerization.

7.3  Granulation

Chopped up the reacted rubber into pieces, and transported via conveyor to the pelletizing machine for granulation.

7.4 Drying & cooling

Send the particles to the drying bed for drying and cooling.

7.5 Crushing and packing

Crush, grind, and pack the finished products.

VIII, Chemical reactions during the process

photo of Chemical reactions

8.1 acrylamide monomer reaction

It uses acrylonitrile as raw material, which is hydrated under the action of a catalyst to produce a crude product of acrylamide monomer. 
The crude product could be made into a fine product after flash evaporation, and refining.
Acrylonitrile + (aqueous catalyst/water)  → acrylamide

8.2 Polymerization reaction

The polymerization reaction is carried out under the action of the initiator.
Acrylamide + water (initiator/polymerization) → polyacrylamide

8.2.1 Aqueous solution polymerization  method

The monomer solution in the formula shall be purified by ion exchange. 
Reaction medium water should be deionized water, and the initiator is mostly composed of a persulfate oxidation-reducing initiator system to reduce the temperature of the reactor. 
In addition, it needs to add a chain transfer agent, commonly used for isopropyl alcohol to eliminate the effect of possible metal ions.  Add chelating agent ethylenediaminetetraacetic acid (EDTA) to easily control the reaction temperature, the monomer concentration is usually less than 25%.
At present, most industry has given up this method.

8.2.2  Reversed-phase emulsion polymerization  method

This method polymerizes the dispersed phase and continuous phase with a ratio of  3:7 to get dispersed-phase latex particles. The diameter of latex particles is 0.1 ∽ 10μm, which depends on the amount of surfactant. 
The reaction temperature is generally 40 ℃, with 6 hours conversion rate of up to 98%. 
The dispersed phase is a 30% ∽ 60% acrylamide monomer aqueous solution, which is added with a small amount of ethylenediaminetetraacetic acid, sodium persulfate, oxidation-reducing agent, and an appropriate amount of water-soluble surfactants. Its HLB value is low.
While the continuous phase is aromatic or saturated aliphatic hydrocarbons. The oil-soluble is the surfactant and is added into a continuous phase. Its HLB value should be higher. 
Sodium persulfate can prevent emulsion particles from sticking. 
The reaction heat is easy to export, material viscosity is low and easy to operate.
Organic solvents are flammable, their effective production capacity is lower than the aqueous solution polymerization method.

8.2.3 Suspension polymerization method 

This method makes a monomer aqueous solution in the form of small beads, which are suspended in the organic solvent before the reaction. 
So, it is called suspension polymerization, also known as bead polymerization. 
The suspension mixer consists of a monomer, initiator, organic solvent, and suspending agent. 
The initiator dissolved in an aqueous monomer solution. 
The dispersant is also known as the suspending agent, to make the monomer aqueous solution dispersed into small beads under the action of stirring. 
The particle size of the product is generally 100-2000μm.

8.2.4  Dispersion Polymerization Method 

Because of the different solubility properties of acrylamide monomer and polyacrylamide.  The polymer can precipitate out of the polymerization system in the polymerization reaction process. However, due to the similar density of the reaction liquid and the polymers, the precipitated polymer can not be settled. So, the polymers stably disperse in the system. 
This is the reason why it is called dispersion polymerization. The dispersion product is commonly known as water-in-water emulsion.

IX, Polyacrylamide production equipment

photo of equipments

9.1 Working principle

The working principle of polyacrylamide production equipment is to convert acrylamide monomer into polyacrylamide polymer through a series of physical and chemical reactions and treatment of raw materials. The acrylamide monomer is mixed with the polymerization catalyst and heated to a certain temperature so that the catalyst plays the role of initiating the polymerization reaction. Then, through a series of reaction processes, covalent bonds are formed between the monomer molecules, gradually forming polyacrylamide polymer.
During the whole reaction process, the equipment also needs to provide stable temperature and pressure conditions to ensure that the reaction proceeds. At the same time, the reaction process needs to be monitored and controlled to ensure the effectiveness of the polymerization reaction and product quality.

9.2 Structure of the equipment

Polyacrylamide production equipment generally consists of a reaction vessel, agitators, heating and cooling system, control system, and so on.
The reaction vessel is the core part of the whole equipment, which is used to carry out the polymerization reaction.
The agitator is used to stir the reaction system to make the reaction proceed evenly.
The heating and cooling system is used to provide constant temperature conditions to keep the reaction going. The control system is used to monitor and control the operation status of the whole equipment.
The structure and components of the equipment are selected taking into account the characteristics and requirements of the reaction system, as well as factors such as the scale of production and control requirements.
At the same time, factors such as the safety, maintainability, and cost of use of the equipment also need to be considered.
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