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Abstract: A water-soluble copolymer scale inhibitor was synthesized from acrylic acid (AA) and 2-acryloyl-2-methyl propane sulfonic acid (AMPS). The scale inhibition and dispersion properties of the copolymer were determined. The effects of monomer ratio, reaction temperature and molecular weight modifier on the scale inhibition performance of the copolymer were investigated.

Keywords: sulfonic acid, copolymer, scale inhibitor.

1. Introduction:

Today, there is a shortage of water in the world and environmental pollution is getting worse. The development of water treatment agents has received increasing attention from countries around the world.

As a scale inhibitor and dispersant for circulating cooling water treatment, water-soluble copolymers have been greatly developed at home and abroad in recent years.

The outstanding advantage of sulfonate-containing copolymers is that they are not affected by the presence of metal ions in the water in terms of scale inhibition.

It has a good inhibitory effect on salt scales such as P, S, Ca, Ba, Mg(OH)2 and CaCO3, especially calcium phosphate. And it can effectively disperse particles and stabilize metal ions and organic phosphoric acid. The long-lasting drug, not easy to gel.

In the 1980s, there was an international upsurge in the development of copolymers containing sulfonic acid groups. The introduction of sulfonic acid groups by using 2 acrylamide methyl propyl sulfonic acid (AMPS) has attracted great attention at home and abroad. At that time, the country suffered from this lack of monomer and failed to carry out this work. With the localization of AMPS, the research on this copolymer has been active again.

In this paper, acrylic acid (AA) and AMPS were used as raw materials to study the synthesis method of the acrylic acid 2-acrylamide-2-methylpropane sulfonic acid copolymer. The effects of monomer ratio, molecular weight regulator, reaction temperature, initiator amount and reaction time on the scale inhibition performance of the copolymer were investigated. Find the best ratio and the best process conditions.

2. Experiment

2.1 Raw materials

AA (chemically pure), AMPS (industrial product), benzoic acid (chemically pure), molecular weight regulator (chemically pure).

2.2 Synthesis of the Copolymer

A 500 mL four-necked flask was equipped with a stirrer, a reflux condenser, a thermometer, and a dropping funnel, and a certain proportion of molecular weight regulator, AMPS and water were placed in the bottle.

Place the AA monomer and initiator in the dropping funnel. The temperature was raised to 50 to 100°C, and the monomer and the initiator were added dropwise while stirring, and the mixture was kept for 1-6 hours after the addition. The temperature is lowered to below 40°C to discharge, and a colorless or light yellow transparent viscous carcass is obtained, which is an aqueous solution of the copolymer.

2.3 Determination of Scale Inhibition Performance

2.3.1 Determination of the Scale Inhibition Rate of Calcium Phosphate

First, prepare an aqueous solution. The concentration of Ca2+ is 250 mg/L (calculated as CaC03). The concentration of PO43- is 5 mg/L. Adjust the pH to 9.0. Add a certain concentration of scale inhibitor.

Put the solution into a 100mL volumetric flask. Place the volumetric flask in a water bath that has been warmed to 50°C. Warm-up to 70°C. After 17h, remove and cool. After filtering through three layers of qualitative filter paper, filter the ascorbic acid method to measure PO43- concentration.

Calculate the scale inhibition rate according to the following formula:

In the formula:

r – calcium phosphate scale inhibition rate;

(PO43-)0 — the concentration of PO43- measured before the test;

(PO43-)1 — the concentration of PO43-– measured after the addition of the scale inhibitor test;

(PO43-)2 — the concentration of PO43- measured after no scale inhibitor test;

2.3.2 Determination of Scale inhibition rate of calcium carbonate

The test aqueous solution was first prepared. The Ca2+ concentration was 250mg/L (calculated as CaCO3). Adjust the pH to 8.5. Add a certain concentration of scale inhibitor.

This solution was placed in an l00mL volumetric flask. The volumetric flask was placed in a 60°C water system for 16h. After taking out, it was cooled to room temperature. It was filtered through a two-layer qualitative filter paper, and the filtrate was titrated with EDTA.

The calculation formula of the scale inhibition rate is as follows:

In the formula:

r – scale inhibition rate of calcium carbonate;

V0 – the number of milliliters of EDTA consumed prior to the test;

V1 – the number of milliliters of EDTA consumed after the addition of the scale inhibitor;

V2 – the number of EDTA milliliters consumed after the test without scale inhibition;

2.4 Determination of Solid Content

Accurately weigh 1.000g of the sample in a weighing bottle. Place the sample in an oven. Bake at 120°C to constant weight (about 2.5h). After cooling, the weight is weighed, and the residual amount is calculated as the solid content.

2.5 Viscosity Determination

It was measured with an NDJ-79 type rotational viscometer. Turn on the rotary viscometer power supply. Install the rotor. Place the test sample in the assay tube. Set the constant temperature in a constant temperature bath to the desired temperature. Turn on. The regulator number of the head is the rotational viscosity at this temperature.

3. Results and Discussion

3.1 Effect of Monomer Ratio on Scale Inhibition Performance

The reaction temperature was 80°C, the molecular weight modifier was 20mL, the initiator accounted for 2% by weight of the monomer, and the reaction time was 4h. The scale inhibition rate was measured as described above, and the results are shown in Table-1.

Table-1 Effect of monomer ratio on scale inhibition performance of copolymer.

Sample No.1234567
Monomer Weight Ratio (AA:AMPS)30:7040:6050:5065:3575:2580:2090:10
CaCO3 Scale Inhibition Rate, %43.250.872.478.295.296.799.3
Ca3(PO4)2 Scale Inhibition Rate, %89.496.294.892.791.471.737.6

Note: The amount of scale inhibitor added is 10mg/L, the same below.

The table shows that the copolymer has a scale inhibition rate of more than 90% for calcium carbonate when AA accounts for 75% to 90% of the monomer weight. Below 75%, as the AA content decreases, the scale inhibition rate of the copolymer against calcium carbonate is significantly reduced.

The increase in the AMPS content is beneficial to improve the performance of calcium block. When the AMPS content reaches 20%, the performance of the copolymer calcium phosphate is abrupt.

This indicates that the carboxyl group in the polymer is the main functional group of the calcium carbonate scale, and the sulfonic acid group is beneficial to the calcium phosphate.

3.2 Effect of the Amount of Molecular Weight Regulator on Scale Inhibition Performance

Monomer ratio (AA:AMPS) = 75:25. The remaining conditions are the same as above. Change the amount of molecular weight regulator. The measured results are shown in Table-2.

Table-2 Effect of the amount of molecular weight regulator on the scale inhibition performance of the copolymer.

Sample No.123456
Regulator Dosage, mL01020304050
Viscosity, mPa·s283.470.837.633.829.627.4
CaCO3 Scale Inhibition Rate, %67.183.795.296.693.794.6
Ca3(PO4)2 Scale Inhibition Rate (%)58.379.691.490.889.088.4

According to the literature, the polymer can be used as a scale inhibitor in a certain molecular weight range. And within this molecular weight range, its scale inhibition performance will also vary with the change in molecular weight.

Viscosity is related to molecular weight. As the molecular weight increases. The viscosity also increases. Table-2 shows that as the viscosity increases, the scale inhibition rate decreases rapidly.

An increase in the amount of the molecular weight regulator contributes to a decrease in viscosity. However, after a certain amount of use, the effect is not obvious. From an economic point of view and comprehensive performance, choose between 20-30mL.

3.3 Effect of Reaction Temperature on Scale Inhibition Performance

The other conditions were the same as described above, and the reaction temperature was changed. The results are shown in Table-3.

Table-3 Effect of reaction temperature on scale inhibition performance.

Sample No.1234
Reaction Temperature, °C50607080
CaCO3 Scale Inhibition Rate, %83.489.293.895.2
Ca3(PO4)2 Scale Inhibition Rate (%)77.483.990.291.4

It can be seen from the data in Table-3. The higher the reaction temperature, the better the scale inhibition effect. This is because the reaction temperature is high, and the resulting polymer has a low molecular weight, which is advantageous for scale inhibition and dispersion.

In addition, the reaction temperature is high, the initiator is completely decomposed, and the reaction conversion rate is high, which is also advantageous for the increase of the scale inhibition rate.

3.4 Effect of Other Factors on Scale Inhibition Performance

The amount of initiator has a great influence on the polymerization rate and the molecular weight of the product. Thereby affecting the scale inhibition performance. In the experiment, when the amount of the initiator is 2% by weight of the monomer, better scale inhibition performance is obtained.

The effect of reaction time on scale inhibition performance is not obvious. Generally, it is suitable for 4-6h, which is too short to cause incomplete polymerization.

4. Conclusion

(1) Among the factors investigated, the monomer ratio has the greatest influence on the scale inhibition performance of the acid copolymer.

Followed by the average molecular weight of the copolymer. The average molecular weight is related to the synthesis conditions such as the amount of the regulator, the manner of addition, the reaction temperature, and the monomer concentration.

Therefore, the molecular weight of the copolymer can be controlled by controlling the experimental conditions. However, the addition of molecular weight regulators is the easiest and most convenient method.

(2) The following process conditions were selected by examining various influencing factors.

Monomer ratio (AA:AMPS): 75:25 (weight ratio)

Reaction temperature: 80°C

Molecular weight regulator: 20mL

Initiator dosage (% by weight): 2%

Reaction time: 4h

Copolymerization was carried out according to the ratio and the process conditions, and the obtained copolymer was a pale yellow liquid. The viscosity was 35.6 mPa·s, the solid content was 31.2%, and the scale inhibition rates for CaCO3 and Ca3(P04)2 were 94.8% and 92.1%, respectively.

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