CN110028168A - For restraining the antisludging agent and preparation method that calcium carbonate scale and calcium sulfate scale are formed - Google Patents

Abstract

The invention discloses a scale inhibitor for inhibiting the formation of calcium sulfate scale and calcium carbonate scale and a preparation method thereof. The scale inhibitor is obtained by using ethylenediaminetetraacetic acid and diethanolamine as raw materials to be dispersed in N,N-dimethylformamide and phosphoric acid as a catalyst through condensation polymerization reaction to obtain ethylenediaminetetraacetic acid-diethanolamine polymerization. thing. The preparation method is as follows: mixing ethylenediaminetetraacetic acid and diethanolamine as monomers, then adding a dispersant to obtain a reaction solution; adding a catalyst to the reaction solution, stirring and mixing evenly, heating for condensation polymerization reaction; after the reaction, adjusting After cooling to room temperature, the reaction solution is dialyzed with a dialysis membrane, and the solution after the dialysis treatment is evaporated to remove the solvent to obtain a crude product, which can be dried. The invention can be used for inhibiting the formation of calcium sulfate scale and calcium carbonate scale in the industrial water system containing calcium ion, sulfate ion and carbonate ion, and the scale inhibition rate can reach more than 95%.

Description

Scale inhibitor and preparation method for inhibiting the formation of calcium carbonate scale and calcium sulfate scale

technical field

The invention relates to a scale inhibitor for inhibiting the formation of calcium carbonate scale and calcium sulfate scale and a preparation method thereof, belonging to the technical field of industrial water treatment.

Background technique

With the increase of industrial water consumption, calcium ions and magnesium ions in water will combine with sulfate ions and carbonate ions to form scale deposits on the surface of industrial equipment or pipes, which not only reduces economic benefits, but also causes corrosion problems , which will reduce the working efficiency of the equipment and even endanger the production safety.

The use of scale inhibitors can effectively reduce scaling. Scale inhibitors can not only effectively inhibit the precipitation of scale-forming ions in water, but also disperse the formed scale in water to prevent the formation of hard scale on the equipment surface. Scale inhibitors can be divided into two categories: organic small molecule scale inhibitors and polymer scale inhibitors. Common polymer scale inhibitors include polyacrylic acid (PAA), polyaspartic acid (PASP), polyepoxysuccinic acid (PESA), polymaleic acid (HPMA), etc. These polymers have good scale inhibition effect and certain environmental friendliness, but are relatively expensive. Therefore, it is necessary to develop new scale inhibitors with low cost and high cost performance.

Ethylenediaminetetraacetic acid and its disodium salt (EDTA) are commonly used chelating agents, which have a strong chelating effect on metal ions in water, and are widely used in the determination of water hardness in water quality analysis. In addition, it can be used as an additive in some foods and is a non-toxic and harmless organic substance. However, ethylenediaminetetraacetic acid has poor scale inhibition performance on calcium scale in water, and new scale inhibitors can be developed through polymerization modification.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a polymer scale inhibitor for inhibiting the formation of calcium carbonate scale and calcium sulfate scale and a preparation method thereof.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is:

A scale inhibitor for inhibiting the formation of calcium sulfate scale and calcium carbonate scale, characterized in that the scale inhibitor is dispersed in N,N-dimethyl ethylenediaminetetraacetic acid and diethanolamine as raw materials The ethylenediaminetetraacetic acid diethanolamine polymer is obtained by condensation polymerization in formamide with phosphoric acid as a catalyst.

Preferably, the number average molecular weight of the amine tetraacetic acid diethanolamine polymer is 5,000-100,000.

The present invention also provides a kind of above-mentioned preparation method of the scale inhibitor that is used to suppress the formation of calcium sulfate scale and calcium carbonate scale, is characterized in that, comprises the following steps:

Step 1): the mixture of ethylenediaminetetraacetic acid and diethanolamine as monomers, and then adding a dispersant to obtain a reaction solution;

Step 2): adding a catalyst to the reaction solution, stirring and mixing evenly, heating to carry out a condensation polymerization reaction;

Step 3): after the reaction is completed, adjust the pH value, dialyze the reaction solution with a dialysis membrane after cooling to room temperature, evaporate the solution after the dialysis treatment to remove the solvent to obtain a crude product, and dry to obtain the scale inhibitor .

Preferably, in the step 1), the molar ratio of EDTA to diethanolamine is 1:2 to 2:1, preferably 1:1.

Preferably, the dispersant in the step 1) is N,N-dimethylformamide; the volume of N,N-dimethylformamide corresponding to each 1 mL of diethanolamine is 2.5-10 mL, preferably 5 mL.

Preferably, the catalyst in the step 2) adopts phosphoric acid; the volume of phosphoric acid corresponding to every 1 mL of diethanolamine is 1.25-5 mL, preferably 2.5 mL.

Preferably, the heating temperature in the step 2) is 180-220°C, preferably 200°C; the reaction time of the condensation polymerization reaction is 0.5-3h, preferably 2h.

Preferably, the pH regulator in the step 3) adopts sodium hydroxide solution, and the pH adjustment range is 6～8.

Preferably, the molecular weight cut-off of the dialysis membrane in the step 3) is more than 1000.

The carboxyl group itself in the EDTA molecule cannot self-polymerize, and the second monomer (diethanolamine) is added to provide a hydroxyl group or an amine group, thereby realizing the condensation reaction of the carboxyl group and the hydroxyl group or the amine group to generate an ester bond or an amide bond. Each EDTA molecule has four carboxyl groups, and each diethanolamine molecule has two hydroxyl groups and one amine group, so condensation polymerization can form high molecular weight polymers, as shown in the following formula:

nHOOCCH ₂ N(CH ₂ COOH)CH ₂ CH ₂ N(CH ₂ COOH)CH ₂ COOH

+nHOCH ₂ CH ₂ NHCH ₂ CH ₂ OH

→

-[-OCCH ₂ N(CH ₂ COOH)CH ₂ CH ₂ N(CH ₂ COOH)CH ₂ CO-OCH ₂ CH ₂ NHCH ₂ CH ₂ O-] _n -

+2nH ₂ O

or →

-[-OCCH ₂ N(CH ₂ COOH)CH ₂ CH ₂ N(CH ₂ COOH)CH ₂ CO-OCH ₂ CH ₂ N(CH ₂ CH ₂ OH)-] _n

-

+2nH ₂ O

It can be seen that there are still unpolymerized carboxyl, hydroxyl and amine groups in the polymer, and these groups have an inhibitory effect on the formation of calcium scale crystals.

Compared with the prior art, the beneficial effects of the present invention are:

The present invention uses ethylenediaminetetraacetic acid and diethanolamine as raw materials to obtain a polymer through condensation polymerization, that is, ethylenediaminetetraacetic acid and diethanolamine are used as monomers, phosphoric acid is used as catalyst, and N,N-dimethyl Formamide is used as a dispersant, and dehydration condensation reaction is carried out under heating to prepare ethylenediaminetetraacetic acid diethanolamine polymer, which can be used in industrial water systems containing calcium ions, sulfate ions, and carbonate ions Inhibit the formation of calcium sulfate scale and calcium carbonate scale, and the scale inhibition rate can reach more than 95%.

The invention adopts ethylenediaminetetraacetic acid and diethanolamine as raw materials, the raw materials are cheap and easy to obtain, non-toxic and harmless, and the polymer is degradable, green and environmentally friendly, and can be popularized and applied.

Description of drawings

Fig. 1 is the variation curve of the scale inhibition rate of the scale inhibitor made in Example 2 to calcium sulfate scale with the change in the amount of scale inhibitor;

Fig. 2 is the variation curve of the scale inhibition rate of the scale inhibitor obtained in Example 2 to calcium carbonate scale with the change in the amount of scale inhibitor.

Detailed ways

In order to make the present invention more obvious and comprehensible, preferred embodiments are described in detail below with reference to the accompanying drawings.

The scale inhibition performance test method of the scale inhibitors prepared in Examples 1-7 is as follows:

(1) Prepare 500 mL of test water sample containing Ca ²⁺ and SO ₄ ^2- ; add a certain amount of the prepared scale inhibitor to become the scale inhibitor test solution. For example, the antiscalant test solutions containing 0 mg/L, 1 mg/L, 3 mg/L, 5 mg/L, 10 mg/L, 15 mg/L, 20 mg/L, and 25 mg/L, respectively.

(2) Put the scale inhibitor test solution into a constant temperature water bath at 80°C, let stand for 10 hours, cool to room temperature, filter, accurately measure 10.00 mL of the filtrate, add chrome black T indicator and ammonia-ammonium chloride buffer (The buffer solution is prepared by mixing and dissolving 87.5 mL of ammonia water and 13.5 g of ammonium chloride in a 250 mL volumetric flask).

(3) Titrate with disodium ethylenediaminetetraacetate (EDTA) standard solution. The scale inhibition rate is calculated as follows:

In formula (1): V ₂ is the volume of EDTA solution consumed by solution titration after heating the test water sample with scale inhibitor added, V ₀ is the EDTA solution consumed by solution titration after heating the test water sample without scale inhibitor The volume of V ₁ is the volume of EDTA solution consumed by the titration of the original test water sample (without adding scale inhibitor, without heating).

The scale inhibition performance test method of the scale inhibitor obtained by the present invention for inhibiting the formation of calcium carbonate scale is as follows:

(1) Prepare 500 mL of test water sample containing Ca ²⁺ and CO ₃ ^2- ; add a certain amount of the prepared polymer scale inhibitor to become the scale inhibitor test solution. For example, the antiscalant test solutions containing 0 mg/L, 1 mg/L, 3 mg/L, 5 mg/L, 10 mg/L, 15 mg/L, 20 mg/L and 25 mg/L, respectively.

(2) Put the prepared scale inhibitor test solution into a constant temperature water bath at 80°C, let stand for 10 hours, cool to room temperature, filter, accurately measure 10.00mL of the filtrate, add chrome black T indicator and ammonia-ammonium chloride Buffer solution (the buffer solution is prepared by mixing and dissolving 87.5mL ammonia water and 13.5g ammonium chloride in a 250mL volumetric flask).

(3) Titrate with disodium ethylenediaminetetraacetate (EDTA) standard solution. The scale inhibition rate is calculated according to formula (1).

Example 1

A scale inhibitor for inhibiting the formation of calcium sulfate scale and calcium carbonate scale. The ethylenediaminetetraacetic acid diethanolamine polymer obtained by the condensation polymerization reaction can be used as a scale inhibitor for inhibiting the formation of calcium sulfate scale and calcium carbonate scale.

The preparation method of the above scale inhibitor comprises the following steps:

(1) 2.92g of EDTA and 1mL of diethanolamine were added to the three-necked round-bottomed flask, and 10mL of solvent was added, and the solvent was N,N-dimethylformamide;

(2) 5mL of catalyst was added to the reagent obtained in step (1), and a condensation polymerization reaction was carried out at a temperature of 180°C for 1h; the catalyst was phosphoric acid;

(3) after the reaction is finished, the pH value of the obtained reaction solution is adjusted to 6-8 with sodium hydroxide solution, and after cooling to room temperature, the reaction solution is dialyzed with a dialysis membrane, and the solution after the dialysis treatment is placed in a constant temperature drying oven. The desired scale inhibitor is obtained by drying in medium for about 24 hours; wherein, the dialysis membrane adopts a regenerated fiber dialysis membrane (M _n >1000);

(4) adopt size exclusion chromatography (SEC) method (take polyethylene glycol as standard sample, and water is mobile phase) to measure the molecular weight and molecular weight distribution of product, and the number-average molecular weight of product is 8000;

(5) After testing, when the dosage of the prepared scale inhibitor is 20mg/L, the scale inhibition rate to calcium sulfate scale is 80%; when the dosage of the prepared scale inhibitor is 20mg/L, the scale inhibition rate to calcium carbonate scale is 80%. The scale rate is 65%.

Example 2

A scale inhibitor for inhibiting the formation of calcium sulfate scale and calcium carbonate scale, namely, ethylenediaminetetraacetic acid diethanolamine polymer obtained by condensation polymerization reaction with ethylenediaminetetraacetic acid and diethanolamine as raw materials, namely scale inhibitor agent.

The preparation method of the above scale inhibitor comprises the following steps:

(1) 2.92g of EDTA and 1mL of diethanolamine were added to the three-necked round-bottomed flask, and 10mL of solvent was added, and the solvent was N,N-dimethylformamide;

(2) 5mL of catalyst was added to the reagent obtained in step (1), and a condensation polymerization reaction was carried out at a temperature of 200°C for 2h; the catalyst was phosphoric acid;

(3) After the reaction in step (2), the pH of the obtained reaction solution is adjusted to be near neutral with sodium hydroxide solution, and the pH value of the solution is between 6-8. After cooling to room temperature, the reaction solution is dialyzed with a dialysis membrane, and the solution after dialysis treatment is dried in a constant temperature drying oven for about 24 hours to obtain a scale inhibitor; wherein, the dialysis membrane adopts a regenerated fiber dialysis membrane (M _n >1000);

(4) The molecular weight and molecular weight distribution of the product were determined by size exclusion chromatography (SEC) method (with polyethylene glycol as the standard sample and water as the mobile phase). The product has a number average molecular weight of 12,000;

(5) After testing, when the prepared polymer dosage is 3mg/L, the scale inhibition rate to calcium sulfate scale is 92%; when the prepared polymer dosage is 20mg/L, the scale inhibition rate to calcium carbonate scale was 92%.

Example 3

A scale inhibitor for inhibiting the formation of calcium sulfate scale and calcium carbonate scale, namely, ethylenediaminetetraacetic acid diethanolamine polymer obtained by condensation polymerization reaction with ethylenediaminetetraacetic acid and diethanolamine as raw materials, namely scale inhibitor agent.

The preparation method of the above scale inhibitor comprises the following steps:

(1) 2.92g of EDTA and 1mL of diethanolamine were added to the three-necked round-bottomed flask, and 10mL of solvent was added, and the solvent was N,N-dimethylformamide;

(2) 5mL of catalyst was added to the reagent obtained in step (1), and a condensation polymerization reaction was carried out at a temperature of 220°C for 1h; the catalyst was phosphoric acid;

(3) After the reaction is completed, the pH of the obtained reaction solution is adjusted to be near neutral with sodium hydroxide solution, and the pH value of the solution is between 6-8. After being cooled to room temperature, the reaction solution is dialyzed with a dialysis membrane, and the solution after the dialysis treatment is dried in a constant temperature drying oven for about 24 hours to obtain the required scale inhibitor; wherein, the dialysis membrane adopts a regenerated fiber dialysis membrane ( M _n >1000);

(4) The molecular weight and molecular weight distribution of the product were determined by size exclusion chromatography (SEC) method (with polyethylene glycol as the standard sample and water as the mobile phase). The number-average molecular weight of the product is 39,580;

(5) After testing, when the prepared scale inhibitor dosage is 5mg/L, the scale inhibition rate to calcium sulfate scale is 91%; when the prepared scale inhibitor dosage is 25mg/L, the scale inhibition rate to calcium carbonate scale is 91%. The scale rate is 65%.

Example 4

A scale inhibitor for inhibiting the formation of calcium sulfate scale and calcium carbonate scale, namely, ethylenediaminetetraacetic acid diethanolamine polymer obtained by condensation polymerization reaction with ethylenediaminetetraacetic acid and diethanolamine as raw materials, namely scale inhibitor agent.

The preparation method of the above scale inhibitor comprises the following steps:

(1) 5.84g of EDTA and 1mL of diethanolamine were added to the three-necked round-bottomed flask, and 10mL of solvent was added, and the solvent was N,N-dimethylformamide;

(2) 5mL of catalyst was added to the reagent obtained in step (1), and a condensation polymerization reaction was carried out at a temperature of 200°C for 2h; the catalyst was phosphoric acid;

(3) After the reaction in step (2), the pH of the obtained reaction solution is adjusted to be near neutral with sodium hydroxide solution, and the pH value of the solution is between 6-8. After cooling to room temperature, the reaction solution is dialyzed with a dialysis membrane, and the solution after the dialysis treatment is dried in a constant temperature drying box for about 24 hours to obtain the required scale inhibitor; wherein, the dialysis membrane adopts a regenerated fiber dialysis membrane ( M _n >1000);

(4) The molecular weight and molecular weight distribution of the product were determined by size exclusion chromatography (SEC) method (with polyethylene glycol as the standard sample and water as the mobile phase). The product has a number average molecular weight of 12,000;

(5) After testing, when the dosage of the prepared scale inhibitor is 20mg/L, the scale inhibition rate to calcium sulfate scale is 74%; when the dosage of the prepared scale inhibitor is 25mg/L, the scale inhibition rate to calcium carbonate scale is 74%. The scale rate is 50%.

Example 5

A scale inhibitor for inhibiting the formation of calcium sulfate scale and calcium carbonate scale, namely, ethylenediaminetetraacetic acid diethanolamine polymer obtained by condensation polymerization reaction with ethylenediaminetetraacetic acid and diethanolamine as raw materials, namely scale inhibitor agent.

The preparation method of the above scale inhibitor comprises the following steps:

(1) 2.92g of ethylenediaminetetraacetic acid and 2mL of diethanolamine were added to the three-necked round-bottomed flask, and 10mL of solvent was added, and the solvent was N,N-dimethylformamide;

(2) 5mL of catalyst was added to the reagent obtained in step (1), and a condensation polymerization reaction was carried out at a temperature of 200°C for 1h; the catalyst was phosphoric acid;

(3) after the reaction finishes, the pH value of the obtained reaction solution is adjusted to near neutrality with sodium hydroxide solution, and the pH value of the solution is between 6-8. After being cooled to room temperature, the reaction solution was dialyzed with a dialysis membrane, and the solution after the dialysis treatment was dried in a constant temperature drying oven for about 24 hours to obtain the required scale inhibitor.

(4) The molecular weight and molecular weight distribution of the product were determined by size exclusion chromatography (SEC) method (with polyethylene glycol as the standard sample and water as the mobile phase). The product had a number average molecular weight of 20,000.

(5) After testing, when the dosage of the prepared scale inhibitor is 5mg/L, the scale inhibition rate to calcium sulfate scale is 92%; when the dosage of the prepared scale inhibitor is 25mg/L, the scale inhibition rate to calcium carbonate scale is 92% The scale rate is 52%.

Example 6

A scale inhibitor for inhibiting the formation of calcium sulfate scale and calcium carbonate scale, namely, ethylenediaminetetraacetic acid diethanolamine polymer obtained by condensation polymerization reaction with ethylenediaminetetraacetic acid and diethanolamine as raw materials, namely scale inhibitor agent.

The preparation method of the above scale inhibitor comprises the following steps:

(1) 2.92g of EDTA and 1mL of diethanolamine were added to the three-necked round-bottomed flask, and 10mL of solvent was added, and the solvent was N,N-dimethylformamide;

(2) 5mL of catalyst was added to the reagent obtained in step (1), and a condensation polymerization reaction was carried out at a temperature of 200°C for 0.5h; the catalyst was orthophosphoric acid;

(3) After the reaction is completed, the pH of the obtained reaction solution is adjusted to be near neutral with sodium hydroxide solution, and the pH value of the solution is between 6-8. After being cooled to room temperature, the reaction solution is dialyzed with a dialysis membrane, and the solution after the dialysis treatment is dried in a constant temperature drying oven for about 24 hours to obtain the required scale inhibitor; wherein, the dialysis membrane adopts a regenerated fiber dialysis membrane ( M _n >1000);

(4) The molecular weight and molecular weight distribution of the product were determined by size exclusion chromatography (SEC) method (with polyethylene glycol as the standard sample and water as the mobile phase). The product has a number average molecular weight of 12,000;

(5) After testing, when the dosage of the prepared scale inhibitor is 25mg/L, the scale inhibition rate to calcium sulfate scale is 85%; when the dosage of the prepared scale inhibitor is 25mg/L, the scale inhibition rate to calcium carbonate scale is 85%. The fouling rate is 49%.

Example 7

A scale inhibitor for inhibiting the formation of calcium sulfate scale and calcium carbonate scale, namely, ethylenediaminetetraacetic acid diethanolamine polymer obtained by condensation polymerization reaction with ethylenediaminetetraacetic acid and diethanolamine as raw materials, namely scale inhibitor agent.

The preparation method of the above scale inhibitor comprises the following steps:

(1) 2.92g of EDTA and 1mL of diethanolamine were added to the three-necked round-bottomed flask, and 10mL of solvent was added, and the solvent was N,N-dimethylformamide;

(2) 5mL of catalyst was added to the reagent obtained in step (1), and a condensation polymerization reaction was carried out at a temperature of 200°C for 3h; the catalyst was phosphoric acid;

(3) After the reaction in step (2), the pH of the obtained reaction solution is adjusted to be near neutral with sodium hydroxide solution, and the pH value of the solution is between 6-8. After cooling to room temperature, the reaction solution is dialyzed with a dialysis membrane, and the solution after the dialysis treatment is dried in a constant temperature drying box for about 24 hours to obtain the required scale inhibitor; wherein, the dialysis membrane adopts a regenerated fiber dialysis membrane ( M _n >1000);

(4) The molecular weight and molecular weight distribution of the product were determined by size exclusion chromatography (SEC) method (with polyethylene glycol as the standard sample and water as the mobile phase). The product had a number average molecular weight of 15,000.

(5) After testing, when the dosage of the prepared scale inhibitor is 25mg/L, the scale inhibition rate to calcium sulfate scale is 86%; when the dosage of the prepared scale inhibitor is 25mg/L, the scale inhibition rate to calcium carbonate scale is 86%. The scale rate is 56%.

Fig. 1 is the change curve of the scale inhibition rate of the scale inhibitor prepared in Example 2 on calcium sulfate scale with the amount of the scale inhibitor, and the test conditions are: the total content of Ca ²⁺ and SO ₄ ^2- in the test solution 2040mg/L, add scale inhibitor, after standing in 80 ℃ water bath for 10 hours, measure the scale inhibition rate.

Fig. 2 is the change curve of the scale inhibition rate of the scale inhibitor prepared in Example 2 to calcium carbonate scale with the amount of scale inhibitor, and the test conditions are: the content of Ca ²⁺ in the test solution is 250mg/L, CO The content of ₃ ^2- was 500 mg/L, the scale inhibitor was added, and the scale inhibition rate was measured after standing in a water bath at 80°C for 10 hours.

Claims (9)

1. a scale inhibitor that is used to suppress the formation of calcium sulfate scale and calcium carbonate scale, is characterized in that, described scale inhibitor, is that raw material is dispersed in N,N-diamine tetraacetic acid and diethanolamine The ethylenediaminetetraacetic acid diethanolamine polymer is obtained by condensation polymerization in methylformamide using phosphoric acid as a catalyst. 2 . The scale inhibitor for inhibiting the formation of calcium sulfate scale and calcium carbonate scale according to claim 1 , wherein the number-average molecular weight of the amine tetraacetic acid diethanolamine polymer is 5,000 to 100,000. 3 . 3. the preparation method of the scale inhibitor for suppressing the formation of calcium sulfate scale and calcium carbonate scale according to claim 1 or 2, is characterized in that, comprises the following steps: Step 1): with EDTA and diethanolamine mixture as monomer, then add dispersant to obtain reaction solution; Step 2): adding a catalyst to the reaction solution, stirring and mixing evenly, heating to carry out a condensation polymerization reaction; Step 3): after the reaction is completed, adjust the pH value, dialyze the reaction solution with a dialysis membrane after cooling to room temperature, evaporate the solution after the dialysis treatment to remove the solvent to obtain a crude product, and dry to obtain the scale inhibitor . 4. the preparation method of the scale inhibitor for inhibiting the formation of calcium sulfate scale and calcium carbonate scale as claimed in claim 3, is characterized in that, in described step 1), the mol ratio of ethylenediaminetetraacetic acid and diethanolamine 1:2～2:1. 5. the preparation method of the scale inhibitor for inhibiting the formation of calcium sulfate scale and calcium carbonate scale as claimed in claim 3, is characterized in that, the dispersant in described step 1) adopts N,N-dimethylformaldehyde Amide; the volume of N,N-dimethylformamide corresponding to 1 mL of diethanolamine is 2.5 to 10 mL. 6. the preparation method of the scale inhibitor for inhibiting the formation of calcium sulfate scale and calcium carbonate scale as claimed in claim 3, is characterized in that, the catalyst in described step 2) adopts phosphoric acid; The phosphoric acid corresponding to every 1mL diethanolamine The volume of 1.25 ~ 5mL. 7. The preparation method of the scale inhibitor for inhibiting the formation of calcium sulfate scale and calcium carbonate scale according to claim 3, wherein the heating temperature in the step 2) is 180-220°C; the condensation polymerization reaction The reaction time is 0.5 ~ 3h. 8. the preparation method of the scale inhibitor for inhibiting the formation of calcium sulfate scale and calcium carbonate scale as claimed in claim 3, is characterized in that, the regulator of pH value in described step 3) adopts sodium hydroxide solution, pH The adjustment range of the value is 6~8. 9 . The method for preparing a scale inhibitor for inhibiting the formation of calcium sulfate scale and calcium carbonate scale according to claim 3 , wherein the molecular weight cut-off of the dialysis membrane in the step 3) is more than 1000. 10 .