The physicochemical properties and preparation method of sodium polyacrylate (PANa)

[Physical and chemical properties] Sodium polyacrylate is an important fine chemical product.
Because its structure is a polyanionic electrolyte and is non-toxic, it has a wide range of uses in food, medicine, textile, chemical, metallurgy, water treatment and other industrial sectors.
Sodium polyacrylate used in thickeners, flocculants, etc.
requires high molecular weight and fast dissolution
.

At present, there are two main types of sodium polyacrylate produced and used in China: 40% colloid and 95% dry powder.

[Preparation method] The preparation methods of polyacrylic acid (sodium) mainly include aqueous solution polymerization and inverse emulsion polymerization
.

(1) Aqueous polymerization

Sodium polyacrylate can be obtained by directly polymerizing the corresponding monomer in an aqueous medium
.

Generally, water, acrylic monomers, initiators and active agents are included in the polymerization formula

Since acrylic acid is neutralized by alkali to generate a salt, a lot of heat is generated, which easily causes the polymerization of the monomer during neutralization, and the difference in the degree of neutralization will affect the degree of polymerization
.

Therefore, the use of monomer salts to prepare polymers will produce disadvantages that monomer acids do not have

The sodium polyacrylate solution prepared by aqueous solution polymerization can be used directly; it can also be dried to become a white, flake solid for use
.

The dried polymer should preferably have 5% moisture so that it is easier to dissolve during use

(2) Inverse emulsion polymerization

In industry, sodium polyacrylate is usually prepared by the solution method.
The disadvantage of the solution method is that the concentration of polymerized monomers is low.
To obtain a solid product in the preparation of sodium polyacrylate by the aqueous solution method, the process of drying and pulverizing for a long time is required, and the process is complicated
.

In addition, some people use the reversed-phase suspension method to prepare sodium polyacrylate.

The preparation process of inverse emulsion polymerization is as follows: the monomer solution is made by neutralizing acrylic acid with sodium hydroxide solution, and then adding a small amount of acrylamide
.

In a 250mL reaction flask, add the monomer solution and sodium lauryl sulfonate, stir to make it evenly mixed, and at the same time ventilate nitrogen for 20 minutes, add reducing agent, emulsifier, solvent and oxidant

① Reaction temperature For radical polymerization, a low polymerization temperature is beneficial to increase the relative molecular weight of the polymer
.

In order to prepare polyacrylate sodium (PANa) with high relative molecular mass, the initiator of the redox system is used, and the reaction is carried out at the temperature of 30℃, 35℃, 40℃, 45℃, 50℃, 55℃ and 60℃ respectively.

②The initiator is at the polymerization temperature of 45℃, and the initiator concentration is in the range of (1～6)mmol/L.
When the initiator concentration is 4.
0mmol/L, the relative molecular mass of PANa is the highest, which is 2.
005×10 ⁷ ; When the agent concentration is less than 4.
0mmol/L, the relative molecular mass of PANa increases with the increase of the oxidant concentration; when the initiator concentration is greater than 4.
0mmol/L, the relative molecular mass of PANa decreases with the increase of the oxidant concentration
.

When the polymerization temperature is 45℃ and the amount of reducing agent is greater than the amount of oxidant, the change in the ratio has little effect on the relative molecular weight, but when the amount of oxidant is greater than the amount of reducing agent, the change in the ratio has a greater impact on the relative molecular weight.
Influence
.

Studies have found that when the oxidant/reductant molar ratio is 2/1, the relative molecular mass of the resulting product can reach 2.

③The emulsifier is emulsified under the test conditions that the polymerization temperature is 45℃, the concentration of oxidant (occupies the water phase) is 3.
7mmol/L, the molar ratio of oxidant/reductant is 1/1, and the neutralization degree of monomer is 80%.
The mass fraction of the agent is in the range of 3% to 7%, and the relative molecular mass of PANa changes with the amount of emulsifier
.
When the mass fraction of emulsifier is 5%, the relative molecular mass of PANa obtained is the highest, which can reach 2.
651×10 ⁷ ; when the mass fraction of emulsifier is less than 5%, as the content of emulsifier in the oil increases, the relative molecular mass of PANa obtained increases ; But when the mass fraction of emulsifier is greater than 5%, as the content of emulsifier in the oil increases, the relative molecular mass of PANa decreases
.
At the same time, the study found that when the mass fraction of emulsifier is 2%, the system is unstable and the product is severely sticky.
This is because the amount of emulsifier in the inverse emulsion is too low, which is not enough to stabilize the water phase particles in the oil phase.
In order to ensure the emulsification system For stability, the amount of emulsifier should not be too low
.

④Monomer neutralization The monomer acrylic acid is neutralized by adding sodium hydroxide solution before polymerization, and then polymerized after being converted into sodium acrylate to form PANa
.
It was found that the neutralization degree of acrylic acid monomer also affects the relative molecular weight of PANa
.
Under the experimental conditions that the polymerization temperature is 45℃, the concentration of the oxidant (occupies the water phase) is 3.
7mmol/L, the oxidant/reductant molar ratio is 1/1, and the mass fraction of the emulsifier (occupies the oil phase) is 4%, when When the monomer neutralization degree is 70%, the relative molecular weight of PANa is the highest, reaching 3.
07×10 ⁷ ; when the monomer neutralization degree is higher than 80%, the relative molecular weight of the polymer is low and has little change
.
This is because sodium acrylate is easy to ionize, so that both the monomer and polymer are negatively charged and repel each other, which affects the progress of the polymerization reaction
.
Therefore, as the degree of monomer neutralization further increases, the relative molecular weight of PANa decreases
.
The study also found that when the monomer neutralization degree is higher than 50%, the system is stable, and when the monomer neutralization degree is lower than 50%, the system is unstable and prone to sticking phenomenon, which affects the discharge; the monomer neutralization degree is 50% and 100%.
%, the reaction system is clear and transparent, the emulsification effect is poor, and the relative molecular weight of the obtained PANa is not high
.
Therefore, the neutralization degree of the monomer should be about 70%
.

[Application] (1) Pretreatment of MSG wastewater Because the MSG wastewater contains a lot of protein, residual sugar, etc.
, it is highly viscous and difficult to compress and settle; at the same time, it is strongly acidic, and the suspended particles have a strong positive charge
.
Therefore, MSG wastewater is one of the difficult industrial wastewaters
.
Based on the above-mentioned characteristics, it is difficult to achieve the expected results in the flocculation test using ordinary low-molecular-weight, neutral-charged inorganic flocculants and organic flocculants
.
Therefore, a strong negative charge and high molecular weight flocculant must be selected
.
First, the suspended particles are produced under the electric neutralization of the strong negatively charged flocculant, and then the high-molecular flocculant is coagulated and bridged to make it highly flocculated
.
Huang Minsheng and Zhu Li selected three flocculating agents: 1% sodium carboxymethyl cellulose, 1% lignin, and 0.
5% sodium polyacrylate, as well as sodium polyacrylate as the main flocculating agent, with sodium carboxymethyl cellulose and lignin as aids Flocculants are used to pretreat MSG wastewater
.
A 150mL sample of MSG wastewater was selected for the experiment.
The wastewater contained COD 43000mg/L, SS 9564mg/L and SO42- 57870mg/L.
In addition, the pH of the wastewater was 1.
3
.
The effects of pH value of wastewater (1.
0～7.
0), stirring time (20～180s) and dosage of chemicals (3～15mL) on the flocculation effect were systematically tested
.
During the test, it was found that the use of sodium polyacrylate as the main flocculant, lignin as the coagulant aid, and natural zeolite as the adsorbent to pretreat MSG concentrated wastewater has achieved very good results
.
Pretreatment process of COD, the SS, SO _.
4 ^2- removal rate were 69%, 91% and 43%, the agent pretreated costs about 6.
24 yuan / tons of waste water, the economic benefit of proteins separated about 27 yuan / ton Wastewater
.

(2) The converter dedusting wastewater treatment of the steel-making plant.
Bian Lihuai separately used polyferric sulfate, basic aluminum chloride and sodium polyacrylate to treat the converter dedusting wastewater of the second steel-making plant of Tiangang Group Co.
, Ltd.
, and it was found that polyacrylic acid was used as the flocculant.
Sodium has the advantages of low dosage and fast settling speed, and its flocculation performance is better than that of polyferric sulfate and basic aluminum chloride.
Its reasonable dosage is 0.
5mg/L, which can solve the problem of high suspended solids in the effluent of the sedimentation tank
.

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