A low-cost phosphorus-free scale and corrosion inhibitor and its preparation method

Abstract

This invention provides a low-cost, phosphorus-free scale and corrosion inhibitor and its preparation method, belonging to the field of scale and corrosion inhibition technology. The invention mainly uses sugarcane molasses, N-hydroxyethyl ethylenediamine triacetic acid, citric acid, aminoethyl ethanolamine, sodium hydroxide aqueous solution, and deionized water as raw materials to carry out a polymerization reaction. The resulting polymer has a high content of hydroxyl and sodium carboxylate groups, and is grafted with an appropriate amount of amino groups. This not only effectively complexes calcium ions and other scale-forming ions, but also forms an effective corrosion-inhibiting film on the metal surface, achieving a corrosion inhibition effect. When this polymer is formulated with deionized water and used in circulating water, it exhibits excellent scale and corrosion inhibition performance. This product comprehensively utilizes sugarcane molasses, a byproduct of the sugar industry, resulting in low raw material costs and significant environmental and economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of scale and corrosion inhibition technology, specifically relating to a low-cost phosphorus-free scale and corrosion inhibitor and its preparation method. Background Technology

[0002] In industry, hot or cooling water is widely used in various industrial production processes. Whether it's cooling water or hot water for heaters, the high hardness of the water during circulation leads to scaling and corrosion of equipment and pipelines. For example, during boiler heating, the concentration of certain salts increases with water evaporation. When the concentration reaches supersaturation, these substances crystallize and adhere to the equipment surface, forming scale, such as calcium carbonate (CaCO3) and calcium sulfate (CaSO4). If this scale adheres to the equipment surface during hot or cooling water circulation, it can reduce the equipment's internal diameter, restrict fluid flow, and decrease efficiency. Furthermore, prolonged scale buildup can cause corrosion. Corrosion is primarily a chemical and electrochemical reaction between the medium and the metal material. Prolonged exposure to a corrosive environment can cause perforation on the equipment surface, making it unsafe. In severe cases, it can lead to explosions and leaks in boilers and circulating equipment due to uneven heating or excessive pressure, causing significant harm to society and the economy. Meanwhile, since scale buildup occurs inside equipment, it not only wastes energy and causes significant damage to the equipment, but it is also difficult to remove. Currently, the most economical and commonly used method is to add scale and corrosion inhibitors to prevent or reduce the occurrence of scale and corrosion.

[0003] Currently, most scale and corrosion inhibitors are phosphorus-containing compounds, such as aminotrimethylene phosphate. Due to their high phosphorus content, these compounds pose significant challenges for wastewater treatment and cause environmental pollution. Phosphorus-free scale and corrosion inhibitors, on the other hand, primarily consist of polymeric components such as polyaspartic acid and polyepoxysuccinic acid. These not only have high raw material costs but also require stringent polymerization temperatures and reaction conditions. Improper polymerization control can lead to unsatisfactory product performance and ultimately higher costs. Given the widespread application of scale and corrosion inhibitors in almost all industrial production processes, developing lower-cost, phosphorus-free scale and corrosion inhibitors remains a key research and development direction for the industry. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a low-cost, phosphorus-free scale and corrosion inhibitor and its preparation method. The polymer is obtained by polymerization using sugarcane molasses, N-hydroxyethyl ethylenediamine triacetic acid, citric acid, aminoethyl ethanolamine, sodium hydroxide aqueous solution, and deionized water as raw materials. The resulting polymer contains a high amount of hydroxyl and sodium carboxylate groups, and is grafted with an appropriate amount of amino groups. This not only effectively complexes calcium ions and other scale-forming ions, but also forms an effective corrosion-inhibiting film on the metal surface, achieving a corrosion inhibition effect.

[0005] One of the objectives of this invention is to provide a low-cost, phosphorus-free scale and corrosion inhibitor.

[0006] The second objective of this invention is to provide a method for preparing this low-cost, phosphorus-free scale and corrosion inhibitor.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0008] In a first aspect, the present invention provides a low-cost, phosphorus-free scale and corrosion inhibitor, which is prepared from raw materials comprising the following parts by weight:

[0009]

[0010] Sugarcane molasses is a byproduct of sugarcane sugar production. It is a brown, viscous liquid and its properties meet the requirements of the industry standard QB / T2684-2024 "Sugarcane Molasses".

[0011] Preferably, the solid content of the sugarcane molasses is 80-85%, and it can be purchased from Guangxi Zhongfuxin Sugar Industry Co., Ltd.

[0012] Typical but non-restrictive parts by weight of sugarcane molasses are, for example, 32, 33, 34, 35, 36, or 37 parts.

[0013] Typical, but not limiting, parts by weight of N-hydroxyethyl ethylenediamine triacetic acid (HEDTA) are, for example, 12, 13, 14, 15, or 16 parts.

[0014] Typical, but not limiting, parts by mass of citric acid are, for example, 10, 11, 12, or 13 parts.

[0015] Typical, but not limiting, parts by mass of aminoethylethanolamine are, for example, 4, 5, or 6 parts.

[0016] In some embodiments, the raw materials further include catalysts, including catalyst A and catalyst B. Catalyst A is concentrated sulfuric acid, used in an amount of 0.05-0.08% of the mass of citric acid; catalyst B is p-toluenesulfonic acid, used in an amount of 0.2-0.5% of the mass of sugarcane molasses.

[0017] The amount of catalyst A used is, for example, 0.05%, 0.06%, 0.07%, and 0.08% of the mass of citric acid, and the amount of catalyst B used is, for example, 0.2%, 0.3%, 0.4%, and 0.5% of the mass of sugarcane molasses.

[0018] In some embodiments, the raw materials also include appropriate amounts of sodium hydroxide and deionized water;

[0019] Preferably, the sodium hydroxide is a 30-35 wt% aqueous solution of sodium hydroxide.

[0020] Secondly, the present invention provides a method for preparing the above-mentioned low-cost phosphorus-free scale and corrosion inhibitor, comprising the following steps:

[0021] A. Add the prescribed amounts of aminoethylethanolamine, citric acid, and catalyst A to the reaction vessel, start stirring and heating, and simultaneously start the vacuum system to carry out the amidation reaction;

[0022] B. When the conversion rate of aminoethylethanolamine is greater than 98%, the vacuum system is released and the temperature is lowered to obtain the citric acid amidation intermediate for later use.

[0023] C. Add the prescribed amount of sugarcane molasses to another reaction vessel, heat it up, and at the same time start the vacuum system to remove the residual moisture in the sugarcane molasses during the heating process.

[0024] D. When the moisture content in the system is less than 2%, release the vacuum system, add the formulated amount of catalyst B and N-hydroxyethyl ethylenediamine triacetic acid, stir thoroughly, continue to heat up, start the vacuum system, and carry out the first chain extension polymerization reaction. Remove the small molecule water generated during the polymerization and chain extension process under high vacuum to promote the reaction.

[0025] E. When the acid value of the reactants reaches 150-170 mg KOH / g, add the citric acid amidation intermediate obtained in step B to carry out a secondary grafting chain extension polymerization reaction, increase the reaction temperature and maintain the vacuum degree.

[0026] F. When the acid value of the polymer decreases to 210-235 mg KOH / g, the vacuum system is released, the temperature is lowered, and then sodium hydroxide aqueous solution is added dropwise for neutralization reaction. When the pH value of the polymer solution reaches 7.1-7.6, the reaction is stopped, and the scale and corrosion inhibitor components are obtained. Then, deionized water is added and stirred to dissolve, resulting in a scale and corrosion inhibitor with a solid content of 70-75%.

[0027] In some implementations, in step A, the temperature is raised to 140-145°C; the vacuum degree is -0.08 MPa to -0.085 MPa.

[0028] In some embodiments, in step C, the temperature is raised to 105-110°C; the vacuum degree is -0.097 MPa to -0.099 MPa.

[0029] In some implementations, in step D, the temperature is further increased to 120-125°C; the vacuum degree is -0.096 MPa to -0.098 MPa.

[0030] In some embodiments, in step E, the reaction temperature is increased to 130-135°C; and the vacuum is maintained at -0.096 MPa to -0.098 MPa.

[0031] In some embodiments, in step F, the sodium hydroxide aqueous solution has a mass fraction of 30-35% and is cooled to 90-95°C.

[0032] In one specific embodiment, the preparation method of a low-cost phosphorus-free scale and corrosion inhibitor includes the following steps:

[0033] A. Add the prescribed amounts of aminoethylethanolamine, citric acid, and catalyst A to the reaction vessel, start stirring and heat to 140-145℃ for amidation reaction, and simultaneously start the vacuum system, controlling the vacuum degree at -0.08Mpa to -0.085Mpa;

[0034] B. Take samples and use gas chromatography to detect free aminoethyl ethanolamine. When the conversion rate of aminoethyl ethanolamine is greater than 98%, it indicates that the amidation reaction is basically completed. Remove the vacuum system, cool down to obtain the citric acid amidation intermediate, and set it aside for later use.

[0035] C. Add the formula amount of sugarcane molasses to another reaction vessel, gradually raise the temperature to 105-110℃, and at the same time start the vacuum system, control the vacuum degree at -0.097Mpa to -0.099Mpa, and remove the residual moisture in the sugarcane molasses during the heating process.

[0036] D. Sampling and testing: When the moisture content in the system is below 2%, it indicates that the moisture has been basically removed. At this point, the vacuum system is released, and the formulated amount of catalyst B and N-hydroxyethyl ethylenediamine triacetic acid are added and stirred thoroughly. The temperature is then raised to 120-125℃, and the vacuum system is started to carry out the first chain extension polymerization reaction. The vacuum degree is maintained at -0.096Mpa to -0.098Mpa. Small molecule water generated during the polymerization and chain extension process is removed under high vacuum to promote the reaction.

[0037] E. Take samples to test the acid value of the polymer. When the acid value of the reactants reaches 150-170 mgKOH / g, it indicates that the first chain extension polymerization reaction has met the requirements. At this time, add the citric acid amidation intermediate obtained in step B to carry out the second grafting chain extension polymerization reaction. The reaction temperature is raised to 130-135℃, and the vacuum degree is still maintained at -0.096Mpa to -0.098Mpa.

[0038] F. Take samples to test the acid value of the polymer. When the acid value of the polymer decreases to 210-235 mgKOH / g, it indicates that the secondary grafting chain extension polymerization reaction has been completed. At this time, release the vacuum system, cool down to 90-95℃, and then add an appropriate amount of 30-35 wt% sodium hydroxide aqueous solution for neutralization reaction. At the same time, test the pH of the polymer solution. When the pH value of the polymer solution reaches 7.1-7.6, stop the reaction to obtain the scale and corrosion inhibitor components. Then add an appropriate amount of deionized water and stir to dissolve to obtain a scale and corrosion inhibitor with a solid content of 70-75%.

[0039] The low-cost, phosphorus-free scale and corrosion inhibitor obtained by this invention is a pale yellow transparent solution with a solid content of 70-75% and a pH of 7.1-7.6.

[0040] Beneficial effects:

[0041] (1) This invention mainly uses sugarcane molasses, N-hydroxyethyl ethylenediamine triacetic acid, citric acid, aminoethyl ethanolamine, sodium hydroxide aqueous solution, deionized water and other raw materials to carry out polymerization reaction. The final polymer has more hydroxyl and sodium carboxylate and is grafted with an appropriate amount of amino groups. It can not only effectively complex calcium ions and other scale-forming ions, but also form an effective corrosion-inhibiting film on the metal surface to achieve the corrosion inhibition effect. After the polymer is formulated with deionized water, it is used in circulating water and has excellent scale inhibition and corrosion inhibition performance.

[0042] (2) The product of this invention makes comprehensive use of sugarcane molasses, a by-product of the sugarcane sugar industry. It not only has low raw material costs, but also increases the added value of sugarcane molasses, and has important environmental and economic benefits.

[0043] The present invention has been described in detail above; however, the above embodiments are merely illustrative in nature and are not intended to limit the invention. Furthermore, this document is not limited to the foregoing prior art or the invention itself, or to any theory described in the following embodiments. Detailed Implementation

[0044] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0045] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0046] The sugarcane molasses comes from Guangxi Zhongfuxin Sugar Industry Co., Ltd., and has a solid content of 80-85%.

[0047] Acid value determination: conducted in accordance with GB / T 12008.5-2010 "Plastics Polyether Polyols Part 5: Determination of Acid Value".

[0048] Example 1

[0049] A low-cost, phosphorus-free scale and corrosion inhibitor comprises the following raw materials in parts by weight:

[0050]

[0051] Catalyst A (concentrated sulfuric acid) is used at a concentration of 0.07% of the mass of citric acid.

[0052] Catalyst B (p-toluenesulfonic acid) is used at a rate of 0.5% of the mass of sugarcane molasses.

[0053] The method for preparing the above-mentioned low-cost phosphorus-free scale and corrosion inhibitor includes the following steps:

[0054] A. Add the prescribed amounts of aminoethylethanolamine, citric acid, and catalyst A to the reaction vessel, start stirring and heat to 143°C to carry out the amidation reaction, and simultaneously start the vacuum system, controlling the vacuum degree at -0.083 MPa.

[0055] B. Take samples and use gas chromatography to detect free aminoethyl ethanolamine. When the conversion rate of aminoethyl ethanolamine is greater than 98%, it indicates that the amidation reaction is basically completed. Remove the vacuum system, cool down to obtain the citric acid amidation intermediate, and set it aside for later use.

[0056] C. Add the formula amount of sugarcane molasses to another reaction vessel, gradually heat it to 108°C, and at the same time start the vacuum system, control the vacuum degree at -0.098Mpa, and remove the residual moisture in the sugarcane molasses during the heating process.

[0057] D. Sampling and testing: When the moisture content in the system is below 2%, it indicates that the moisture has been basically removed. At this point, the vacuum system is released, and the formulated amount of catalyst B and N-hydroxyethyl ethylenediamine triacetic acid are added and stirred thoroughly. The temperature is then raised to 122°C, and the vacuum system is started to carry out the first chain extension polymerization reaction. The vacuum degree is maintained at -0.098 MPa. Small molecule water generated during the polymerization and chain extension process is removed under high vacuum to promote the reaction.

[0058] E. Take samples to test the acid value of the polymer. When the acid value of the reactants reaches 150-170 mgKOH / g, it indicates that the first chain extension polymerization reaction has met the requirements. At this time, add the citric acid amidation intermediate obtained in step B to carry out the second grafting chain extension polymerization reaction. The temperature is raised to 132℃, and the vacuum degree is still maintained at -0.098Mpa.

[0059] F. Take samples to test the acid value of the polymer. When the acid value of the polymer decreases to 210-235 mgKOH / g, it indicates that the secondary grafting chain extension polymerization reaction has been completed. At this time, release the vacuum system, cool down to 92℃, and then add an appropriate amount of 30wt% sodium hydroxide aqueous solution for neutralization reaction. At the same time, test the pH of the polymer solution. When the pH value of the polymer solution reaches 7.2, stop the reaction to obtain the scale and corrosion inhibitor components. Then add an appropriate amount of deionized water and stir to dissolve to obtain a scale and corrosion inhibitor with a solid content of 70%.

[0060] The prepared low-cost phosphorus-free scale and corrosion inhibitor is a pale yellow transparent solution with a solid content of 70% and a pH of 7.2.

[0061] Example 2

[0062] A low-cost, phosphorus-free scale and corrosion inhibitor comprises the following raw materials in parts by weight:

[0063]

[0064] Catalyst A (concentrated sulfuric acid) is used at a concentration of 0.06% of the mass of citric acid.

[0065] Catalyst B (p-toluenesulfonic acid) is used at a rate of 0.4% of the mass of sugarcane molasses.

[0066] The preparation method is the same as in Example 1.

[0067] The prepared low-cost phosphorus-free scale and corrosion inhibitor is a pale yellow transparent solution with a solid content of 72% and a pH of 7.3.

[0068] Example 3

[0069] A low-cost, phosphorus-free scale and corrosion inhibitor comprises the following raw materials in parts by weight:

[0070]

[0071] Catalyst A (concentrated sulfuric acid) is used at a concentration of 0.05% of the mass of citric acid.

[0072] Catalyst B (p-toluenesulfonic acid) is used at an amount of 0.3% of the mass of sugarcane molasses.

[0073] The preparation method is the same as in Example 1.

[0074] The prepared low-cost phosphorus-free scale and corrosion inhibitor is a pale yellow transparent solution with a solid content of 75% and a pH of 7.1.

[0075] Example 4

[0076] A low-cost, phosphorus-free scale and corrosion inhibitor comprises the following raw materials in parts by weight:

[0077]

[0078] Catalyst A (concentrated sulfuric acid) is used at a concentration of 0.08% of the mass of citric acid.

[0079] Catalyst B (p-toluenesulfonic acid) is used at a rate of 0.2% of the mass of sugarcane molasses.

[0080] The preparation method is the same as in Example 1.

[0081] The prepared low-cost phosphorus-free scale and corrosion inhibitor is a pale yellow transparent solution with a solid content of 73% and a pH of 7.5.

[0082] Comparative Example 1

[0083] Commercially available scale and corrosion inhibitor product, model LD-ZG001, from Shandong Ludong Environmental Protection Technology Co., Ltd.

[0084] Performance testing

[0085] The scale inhibitor and corrosion inhibitor were added to the test solution at a concentration of 20 mg / L. After stirring evenly, the scale inhibition performance of the agent on calcium carbonate and calcium phosphate was tested according to GB / T16632-2019 "Determination of Scale Inhibition Performance of Water Treatment Agents - Calcium Carbonate Deposition Method" and GB / T22626-2008 "Determination of Scale Inhibition Performance of Water Treatment Agents - Calcium Phosphate Deposition Method".

[0086] The corrosion inhibition performance was determined according to GB / T 18175-2014 "Determination of Corrosion Inhibition Performance of Water Treatment Agents - Rotary Plating Method", with a test temperature of 45±1℃, a specimen linear velocity of 0.3m / s, and a test cycle of 72h.

[0087] The application performance test results are shown in Table 1 below.

[0088] Table 1 Application Performance Test Results

[0089]

[0090] As can be seen from the comparison between Examples 1-4 and Comparative Example 1 in the table above, the scale and corrosion inhibitor products prepared by the present invention not only have excellent storage stability, but also do not exhibit stratification or sedimentation during long-term storage. Furthermore, they have superior scale inhibition performance for calcium carbonate and calcium phosphate, with a scale inhibition rate of over 93% for calcium carbonate and over 85% for calcium phosphate. At the same time, their corrosion inhibition performance is also good, with corrosion inhibition rates of over 95% for both.

[0091] Comparative Example 1 used a commercially available scale and corrosion inhibitor product, which showed slight sedimentation after long-term storage (12 months), and its scale inhibition and corrosion inhibition performance for calcium carbonate and calcium phosphate was also slightly lower than that of the product of this invention.

[0092] The product of this invention not only has excellent scale inhibition and corrosion inhibition properties, but also makes extensive use of sugarcane molasses, a byproduct of the sugar industry. This not only reduces the cost of scale and corrosion inhibitors, but also provides a method for the comprehensive utilization of sugarcane molasses with high added value.

[0093] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and substance defined by the claims of the present invention; and such modifications or substitutions are still within the scope defined by the claims of the present invention.

Claims

1. A low-cost, phosphorus-free scale and corrosion inhibitor, characterized in that, The low-cost, phosphorus-free scale and corrosion inhibitor is prepared from raw materials comprising the following parts by weight: 32-37 parts sugarcane molasses; 12-16 parts of N-hydroxyethyl ethylenediamine triacetic acid; Citric acid 10-13 parts; 4-6 parts of aminoethylethanolamine; The preparation method of the low-cost phosphorus-free scale and corrosion inhibitor includes the following steps: A. Add the prescribed amounts of aminoethylethanolamine, citric acid, and catalyst A to the reaction vessel, start stirring and heating, and simultaneously start the vacuum system to carry out the amidation reaction; B. When the conversion rate of aminoethylethanolamine is greater than 98%, the vacuum system is released and the temperature is lowered to obtain the citric acid amidation intermediate for later use. C. Add the prescribed amount of sugarcane molasses to another reaction vessel, heat it up, and at the same time start the vacuum system to remove the residual moisture in the sugarcane molasses during the heating process. D. When the moisture content in the system is less than 2%, release the vacuum system, add the formulated amount of catalyst B and N-hydroxyethyl ethylenediamine triacetic acid, stir thoroughly, continue to heat up, start the vacuum system, and carry out the first chain extension polymerization reaction. Remove the small molecule water generated during the polymerization and chain extension process under high vacuum to promote the reaction. E. When the acid value of the reactants reaches 150-170 mg KOH / g, add the citric acid amidation intermediate obtained in step B to carry out a secondary grafting chain extension polymerization reaction, increase the reaction temperature and maintain the vacuum degree. F. When the acid value of the polymer reaches 210-235 mg KOH / g, release the vacuum system, cool down, and then add sodium hydroxide aqueous solution dropwise for neutralization reaction. When the pH value of the polymer solution reaches 7.1-7.6, stop the reaction to obtain the scale and corrosion inhibitor component. Then add deionized water and stir to dissolve to obtain the scale and corrosion inhibitor.

2. The low-cost phosphorus-free scale and corrosion inhibitor according to claim 1, characterized in that, The solid content of sugarcane molasses is 80-85%.

3. The low-cost phosphorus-free scale and corrosion inhibitor according to claim 1, characterized in that, The raw materials also include catalysts, which include catalyst A and catalyst B. Catalyst A is concentrated sulfuric acid, and the amount used is 0.05-0.08% of the mass of citric acid; catalyst B is p-toluenesulfonic acid, and the amount used is 0.2-0.5% of the mass of sugarcane molasses.

4. A method for preparing a low-cost, phosphorus-free scale and corrosion inhibitor as described in any one of claims 1-3, characterized in that, Includes the following steps: A. Add the prescribed amounts of aminoethylethanolamine, citric acid, and catalyst A to the reaction vessel, start stirring and heating, and simultaneously start the vacuum system to carry out the amidation reaction; B. When the conversion rate of aminoethylethanolamine is greater than 98%, the vacuum system is released and the temperature is lowered to obtain the citric acid amidation intermediate for later use. C. Add the prescribed amount of sugarcane molasses to another reaction vessel, heat it up, and at the same time start the vacuum system to remove the residual moisture in the sugarcane molasses during the heating process. D. When the moisture content in the system is less than 2%, release the vacuum system, add the formulated amount of catalyst B and N-hydroxyethyl ethylenediamine triacetic acid, stir thoroughly, continue to heat up, start the vacuum system, and carry out the first chain extension polymerization reaction. Remove the small molecule water generated during the polymerization and chain extension process under high vacuum to promote the reaction. E. When the acid value of the reactants reaches 150-170 mg KOH / g, add the citric acid amidation intermediate obtained in step B to carry out a secondary grafting chain extension polymerization reaction, increase the reaction temperature and maintain the vacuum degree. F. When the acid value of the polymer reaches 210-235 mg KOH / g, release the vacuum system, cool down, and then add sodium hydroxide aqueous solution dropwise for neutralization reaction. When the pH value of the polymer solution reaches 7.1-7.6, stop the reaction to obtain the scale and corrosion inhibitor component. Then add deionized water and stir to dissolve to obtain the scale and corrosion inhibitor.

5. The preparation method according to claim 4, characterized in that, In step A, the temperature is raised to 140-145℃; the vacuum degree is -0.08Mpa to -0.085Mpa.

6. The preparation method according to claim 4, characterized in that, In step C, the temperature is raised to 105-110℃; the vacuum degree is -0.097Mpa to -0.099Mpa.

7. The preparation method according to claim 4, characterized in that, In step D, the temperature is further increased to 120-125℃; the vacuum degree is -0.096Mpa to -0.098Mpa.

8. The preparation method according to claim 4, characterized in that, In step E, the reaction temperature is increased to 130-135℃; the vacuum degree is maintained at -0.096Mpa to -0.098Mpa.

9. The preparation method according to claim 4, characterized in that, In step F, the temperature is lowered to 90-95℃.

10. The preparation method according to claim 4, characterized in that, In step F, the solid content of the scale and corrosion inhibitor is 70-75%.

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