Abstract: Maleic anhydride is used as raw material, sodium tungstate is used as catalyst, hydrogen peroxide is used as a cyclizing agent and Ca(OH)2 is used as an initiator. Polyepoxysuccinic acid (PESA) water treatment chemical was prepared by aqueous solution polymerization. PESA is a green, highly effective scale inhibitor.
The optimal synthesis conditions were determined using orthogonal experiments. The monomer usage is 6%. The molar ratio of the monomer to the calcium hydroxide is 1:0.0. The pH is 11. The reaction temperature was 95 °C. The scale inhibition performance was evaluated by the static ion content change method.
Keywords: polyepoxysuccinic acid, aqueous solution polymerization, orthogonal experiment, scale inhibition rate.
With the increasing awareness of environmental protection, “green chemicals” have received attention. Traditional water treatment chemicals face enormous challenges.
Polyepoxysuccinic acid plays an important role in the petrochemical production process as a green scale inhibitor. The PESA water treatment chemical has high scale inhibition efficiency and good biodegradability. It has a good complexing ability for metal ions such as calcium, magnesium, and barium. Polyepoxysuccinic acid can effectively prevent the formation of scale. It is also possible to destroy the lattice of the scale and disperse it in water, effectively preventing the deposition of scale.
The preparation of polyepoxysuccinic acid mainly includes the “one-step method” and “two-step method”.
The “one-step” method is simple and the raw materials are cheap. It is currently the most widely used synthesis method. However, this method requires a large amount of Ca(OH)2 to initiate polymerization. This will affect the scale inhibition effect of the product.
The “two-step method” process is complicated. The intermediate product ESA is precipitated with acetone. The production cost is high, but the scale inhibition effect of the product is good.
In this paper, maleic anhydride was used as the raw material, sodium tungstate was used as the catalyst, hydrogen peroxide was used as the cyclizing agent, and Ca(OH)2 was used as the initiator. By the aqueous solution polymerization, the “one-step method” and the “two-step method” can be effectively combined. The polyepoxysuccinic acid with high scale inhibition efficiency was synthesized and its scale inhibition performance was evaluated.
1. Experimental Part
1. 1 Reagents and instruments
1. 1. 1 Main Raw Materials
Maleic anhydride (analytical grade), sodium tungstate(analytical grade), Ca( OH)2(analytical grade), NaOH(analytical grade), H2O2(analytical grade), chrome black T indicator (analytical grade), EDTA (analytical grade), CaCl2(analytical grade), NaHCO3(analytical grade), HCl(analytical grade), ethanol (analytical grade).
1. 1. 2 Instruments
DHG-9070A type electric heating constant temperature air drying oven; digital control constant temperature water bath; wind instrumentation company; acid burette, 50mL, one; conical flask, 250mL, several; volumetric flask 250mL, several; funnel, filter paper, constant Speed stirring device.
1. 2 Polyepoxysuccinic Scale Inhibitor Preparation
A quantity of maleic anhydride was added to a four-necked flask equipped with a thermometer, a condenser, a pH acidity meter, and a constant speed stirring device.
Add water to dissolve, slowly add sodium hydroxide solution under stirring. Adjust the pH of the system to 5 to 6.
After a little warming, add an appropriate amount of sodium tungstate. Add a certain amount of 30% hydrogen peroxide. Adjust the pH to about 7 with sodium hydroxide solution. Warm-up to the cyclization reaction temperature.
After 2 hours, adjust the pH of the system between 11 and 13. A certain amount of calcium hydroxide is added in batches. The temperature is raised to the polymerization temperature. The reaction was stopped until a pale yellow transparent viscous liquid was obtained.
x1 – calcium ion concentration after test solution test, mg/mL;
x – is the calcium ion concentration in the blank test solution after heating, mg/mL;
x0 – is the calcium ion in the unheated blank test solution Concentration, mg/mL.
Under the same conditions, the higher the scale inhibition rate, the better the effect of the scale inhibitor on the calcium carbonate scale.
Adjust the pH of the system with hydrochloric acid to about 2, add an appropriate amount of absolute ethanol to precipitate, and filter to obtain pure polyepoxysuccinic acid.
2. Results and Discussion
2. 1 Determination of Synthesis Conditions
In order to obtain a low-price, scale inhibitory effect of the scale inhibitor. The orthogonal experiment table L9( 34 )of 4 factors and 3 levels was designed based on the monomer dosage, monomer and calcium hydroxide molar ratio, pH value and reaction temperature. The arrangement of various factors and their corresponding levels are shown in Table-1. The experimental scheme and results are shown in Table-2.
Table-1 Factor and level of orthogonal experiment
|Level||Factor A||Factor B||Factor C||Factor D|
|Monomer dosage, %||nMA: nCa(OH)2||pH value||Reaction temperature, °C|
Table-2 Scheme and result of the orthogonal experiment
|Experiment No.||Monomer Dosage||nMA: nCa(OH)2||pH value||temperature, °C||Scale inhibition rate, %|
From the above results, the optimum synthesis condition of the scale inhibitor is A2B2C2D3, that is, the monomer amount is 6%, the monomer to calcium hydroxide molar ratio is 1:0.06, the pH value is 11, and the reaction temperature is 95 °C.
It is known from the range R that the molar ratio of the monomer to the calcium hydroxide has the greatest influence on the scale inhibition effect. The scale inhibitor was prepared according to the optimal reaction conditions of the orthogonal experimental design. Under the same conditions, the scale inhibition rate was 93.1%. Greater than the results in the orthogonal experimental protocol. It was confirmed that the experimental conditions were the optimum synthesis conditions.
2. 2 Scale Inhibition Performance Evaluation
Based on the orthogonal experiment, the performance of the scale inhibitor was evaluated. The effects of the molar ratio of monomer and calcium hydroxide and the dosage of scale inhibitor on the scale inhibition were discussed.
2. 2. 1 Effect of the molar ratio of monomer and calcium hydroxide on scale inhibition effect
It can be seen from the orthogonal experimental results that the molar ratio of monomer to calcium hydroxide has the greatest influence on the scale inhibition effect. In this paper, the influence of the molar ratio of monomer and calcium hydroxide on the scale inhibition effect was studied by a single factor experiment. The result is shown in Figure-1.
It can be seen from Fig. 1 that as the amount of Ca(OH)2 increases, the scale inhibition performance of the product increases. When the amount of calcium hydroxide reaches a certain value, the amount of calcium hydroxide is continuously increased, and the scale inhibition property of the product decreases as the amount thereof increases.
This is because the amount of calcium hydroxide directly affects the molecular weight of the product, and the molecular weight of the product has a great relationship with its scale inhibition rate. The product has the best scale inhibition rate only when the molecular weight is in the proper range. It can be seen from the experimental results that when the molar ratio of monomer to calcium hydroxide is 1:0.06, the product has the best scale inhibition effect.
Fig. 1 The effect of the molar ratio of monomer/calcium hydroxide on the scale inhibition effect.
2. 2. 2 Effect of dosage on scale inhibition
The dosage of the scale inhibitor also has an effect on the scale inhibition effect. Under the specified experimental conditions, the effect of dosage on the scale inhibition effect was investigated. The experimental results are shown in Figure-2.
Fig. 2 The effect of the dosage on the scale inhibition effect.
As can be seen from Figure-2, the scale inhibition rate increases as the number of products increases. When the dosage is 11mg/L, the scale inhibition effect is the best. Continue to increase the amount of product, the scale inhibition rate decreased slightly.
This phenomenon is related to the scale inhibition mechanism of the product. When the amount of product added is small, as the amount increases, the product can effectively prevent the deposition of scale by complexation, lattice distortion, aggregation, and dispersion. However, when the amount of the product is too large, the polymer adsorbs on the surface of the scale, so that the scale inhibition rate is lowered.
(1) Maleic anhydride is used as a monomer, sodium tungstate is used as a catalyst, hydrogen peroxide is used as a cyclizing agent, and Ca(OH)2 is used as an initiator. A polyepoxysuccinic scale inhibitor was prepared by aqueous solution polymerization.
(2) The optimal synthesis conditions were determined by orthogonal experiments. That is, the monomer amount is 6%, the monomer to calcium hydroxide molar ratio is 1:0.06, the pH is 11, and the reaction temperature is 95 °C.
(3) It is known from the extreme difference that the molar ratio of monomer to calcium hydroxide has the greatest influence on the scale inhibition performance of the product. The results of the single-factor experiments showed. When the molar ratio of monomer to calcium hydroxide is 1:0.06, the scale inhibition effect is the best.
(4) Polyepoxysuccinic acid water treatment chemical is a polymer scale inhibitor. Due to its scale inhibition mechanism, care should be taken to control the amount of product added.