Composite non-phosphorus corrosion and scale inhibitor, its preparation method and application

Abstract

The application discloses a kind of composite phosphorus-free corrosion and scale inhibitor and its preparation method and application, it is related to scale inhibitor material technical field.The application is first with formaldehyde, bis (methoxysilylpropyl) amine and 7-hydroxy coumarin-3-carboxylic acid ethyl ester in ethanol medium is prepared by mannich reaction coumarin mannich base, again grafting reaction is carried out with allyl glycidyl ether in methanol, and grafting coumarin mannich base is prepared;Finally, the intermediate is copolymerized with acrylic acid, 2-acrylamide-2-methylpropane sulfonic acid in deionized water, with ammonium persulfate-ferriferrous sulfate as redox initiation system, and a composite phosphorus-free corrosion and scale inhibitor is prepared, which has high efficient corrosion and scale inhibition performance, can realize comprehensive protection for carbon steel, brass and stainless steel, is suitable for high hardness and high alkalinity industrial circulating water conditions, is phosphorus-free and environmentally friendly, effectively solves the defects of traditional phosphorus-free reagent, such as single function, poor synergy, unstable structure and weak scale inhibition effect, and has excellent industrial applicability.

Description

Technical Field

[0001] This invention relates to the field of scale inhibitor materials technology, specifically to a composite phosphorus-free corrosion and scale inhibitor, its preparation method, and its application. Background Technology

[0002] Circulating cooling water systems are widely used in various industrial production fields such as power, chemical, and metallurgy. They are key supporting systems for ensuring the efficient operation of industrial equipment and reducing production energy consumption. Corrosion and scale inhibitors are core water treatment agents that inhibit equipment corrosion, control water scaling, and maintain system stability. With the continuous tightening of ecological and environmental protection policies, the use of traditional phosphorus-containing corrosion and scale inhibitors is being gradually restricted because they easily cause eutrophication of water bodies and lead to water environment problems. Green and efficient phosphorus-free corrosion and scale inhibitors have become the focus of industry research and development. However, most existing phosphorus-free agents are difficult to adapt to the complex operating conditions of industrial circulating water with high hardness, high alkalinity, and medium to high temperature.

[0003] Existing phosphorus-free corrosion and scale inhibitors have significant technical defects. They generally have single functions and poor synergy, failing to achieve efficient corrosion inhibition and scale inhibition simultaneously. In practical applications, they need to be used in combination, which is not only costly but also prone to compatibility failure. These agents rely on single groups such as carboxyl and sulfonic acid groups, resulting in weak metal chelation and substrate protection capabilities. Their corrosion inhibition effect on industrial metals such as carbon steel, brass, and stainless steel is limited, and they lack effective means to inhibit difficult-to-treat scale types such as silica scale. At the same time, some agents have insufficient molecular structure stability and are prone to degradation and failure under medium and high temperature conditions, making it difficult to meet the long-term stable use requirements of industrial circulating water. Summary of the Invention

[0004] The purpose of this invention is to provide a composite phosphorus-free corrosion and scale inhibitor, its preparation method, and its application, so as to solve the problems existing in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A composite phosphorus-free corrosion and scale inhibitor is provided, wherein the composite phosphorus-free corrosion and scale inhibitor is prepared by grafting bis(methoxysilylpropyl)amine onto ethyl 7-hydroxycoumarin-3-carboxylate via a Mannich base reaction to prepare coumarin Mannich base, then grafting the coumarin Mannich base onto allyl glycidyl ether to prepare grafted coumarin Mannich base, and finally copolymerizing the grafted coumarin Mannich base with acrylic acid and 2-acrylamide-2-methylpropanesulfonic acid to prepare the composite phosphorus-free corrosion and scale inhibitor.

[0006] As an optimization, the mass ratio of the grafted coumarin Mannich base, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid is 1:40~50:60~70.

[0007] A method for preparing a composite phosphorus-free corrosion and scale inhibitor, applicable to any of the composite phosphorus-free corrosion and scale inhibitors described above, comprising the following preparation steps: Grafted coumarin Mannich base, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid are weighed according to a mass ratio of 1:40~50:60~70. Then, the grafted coumarin Mannich base, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid are added to deionized water at a mass ratio of 50~60 times that of the grafted coumarin Mannich base. After the addition is complete, the temperature is raised to 75~85℃. After the temperature rise is complete, ammonium persulfate solution at a mass ratio of 28~32 times that of the grafted coumarin Mannich base and ferrous sulfate solution at a mass ratio of 95~100 times that of the grafted coumarin Mannich base are added dropwise. After the dropwise addition is complete, the reaction is maintained at this temperature for 2~2.5 hours. After the reaction is complete, the temperature is cooled to 25~35℃ to obtain the composite phosphorus-free corrosion and scale inhibitor.

[0008] As an optimization, the grafted coumarin Mannich base includes the following preparation steps: coumarin Mannich base, allyl glycidyl ether, and methanol are weighed according to a mass ratio of 1:1.2~1.4:14~16. Then, coumarin Mannich base and allyl glycidyl ether are added to methanol and preheated to 75~85℃. Then, 0.65~0.75 times the mass of coumarin Mannich base of N,N-diisopropylethylamine is added, and the mixture is stirred and refluxed for 7~9 hours. After the reaction is completed, the mixture is cooled to 25~35℃, and methanol is removed by rotary evaporation. The product is then washed with ethyl acetate 3~5 times. After washing, the product is filtered and dried to obtain the grafted coumarin Mannich base.

[0009] As an optimization, the coumarin Mannich base includes the following preparation steps: Formaldehyde and bis(methoxysilylpropyl)amine are added to ethanol at a mass ratio of 1:6-7, in a volume of 2-3 times the mass of bis(methoxysilylpropyl)amine. The pH is adjusted to 4-5 with hydrochloric acid solution, and the mixture is refluxed at 75-80°C for 2.5-3 hours. Then, ethyl 7-hydroxycoumarin-3-carboxylate is added dropwise at a mass ratio of 1-1.2 times the mass of bis(methoxysilylpropyl)amine, and the mixture is refluxed at 75-80°C for 1.5-2 hours. After the reaction is complete, the mixture is extracted with diethyl ether and impurities are removed using a rotary evaporator to obtain the coumarin Mannich base.

[0010] As an optimization, the ammonium persulfate solution has a mass fraction of 10%.

[0011] As an optimization, the ferrous sulfate solution has a mass fraction of 10%.

[0012] As an optimization, the hydrochloric acid solution has a mass fraction of 5%.

[0013] A scale inhibitor comprising the composite phosphorus-free corrosion and scale inhibitor as described above.

[0014] Compared with the prior art, the beneficial effects achieved by the present invention are: This technical solution achieves highly efficient scale inhibition throughout the entire process through multiple synergistic mechanisms, adaptable to various common scale types in circulating water and high-silica conditions. Its core principle is as follows: the carboxyl and sulfonic acid groups on the main chains of acrylic acid and 2-acrylamide-2-methylpropanesulfonic acid can strongly chelate scale-forming ions such as calcium and magnesium in the water, blocking the formation of scale nuclei such as carbonates and sulfates at the source; the synergistic effect of coumarin units and silane groups causes lattice distortion of initially formed scale microcrystals, disrupting the regular crystalline structure of the scale and preventing it from growing into dense, hard scale; simultaneously, the long polymer chains possess excellent steric hindrance and electrostatic repulsion capabilities, effectively dispersing suspended scale particles, silica scale, and iron scale impurities in the water, preventing particle aggregation and deposition on the heat exchange surface of the equipment. It comprehensively inhibits scale formation from the three key stages of nucleation, growth, and deposition, ensuring a stable and long-lasting scale inhibition effect. Furthermore, this application relies on the synergistic effect of coumarin units and silane groups: the coumarin parent ring has natural antibacterial activity, can be embedded in the double helix structure of microbial DNA, inhibit nucleic acid replication and transcription, destroy the microbial metabolic enzyme system, and block its growth and reproduction; the hydroxyl and amino groups on coumarin and Mannich base can chelate metal ions essential for microbial growth, thereby depriving microorganisms of their nutrient source and achieving restricted antibacterial activity; the silane group can destroy the integrity of the microbial cell membrane, reduce cell membrane permeability, and cause intracellular leakage, further enhancing the bactericidal effect, while inhibiting bacterial aggregate aggregation and reducing the risk of under-deposit corrosion caused by slime deposition; The introduction of silane groups into bis(methoxysilylpropyl)amine significantly improves the overall performance and adaptability of the agent, addressing several industry pain points of traditional scale inhibitors. The core technological effects are: firstly, it specifically solves the problem of difficult silica scale treatment in industrial circulating water, achieving efficient dispersion and inhibition of silica scale; secondly, it synergistically forms a double-layer corrosion-inhibiting protective film with Mannich base, enhancing the agent's corrosion inhibition durability and resistance to water erosion; and fourthly, it improves the adhesion between the agent and the metal substrate, reducing agent loss and extending the effective action time. Its working principle is based on the hydrolytic properties and coordination ability of silane groups: silane groups can slowly hydrolyze in aqueous solution to generate silanol groups. The silanol groups can form hydrogen bonds with silica particles in water, dispersing silica scale particles and preventing silica polymerization to form dense silica scale. They can also react with hydroxyl groups on the metal surface to form strong siloxane metal covalent bonds, forming an adsorption-covalent bilayer corrosion inhibition system with the physical adsorption film of Mannich base. At the same time, the strong hydrophilicity and steric hindrance effect of silane groups can help disperse scale particles and corrosion products, improve the water solubility and hydrolysis resistance of the agent, and ensure that the agent can play a stable role under high concentration and high salt conditions. Detailed Implementation

[0015] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0016] Example 1 S1. Formaldehyde and bis(methoxysilylpropyl)amine were added to ethanol at a mass ratio of 1:6, and the pH was adjusted to 4 with 5% hydrochloric acid solution. The mixture was refluxed at 75°C for 2.5 h. Then, 7-hydroxycoumarin-3-carboxylic acid ethyl ester at a mass ratio of 1:6 was added dropwise, and the mixture was refluxed at 75°C for 1.5 h. After the reaction was completed, the mixture was extracted with diethyl ether and impurities were removed by rotary evaporation to obtain coumarin Mannich base. S2. Weigh coumarin Mannich base, allyl glycidyl ether, and methanol according to a mass ratio of 1:1.2:14. Then add coumarin Mannich base and allyl glycidyl ether to methanol and preheat to 75°C. Then add N,N-diisopropylethylamine at 0.65 times the mass of coumarin Mannich base and stir under reflux for 7 hours. After the reaction is completed, cool to 25°C and remove methanol by rotary evaporation. Then wash the product three times with ethyl acetate. After washing, filter and dry the filtered product to obtain grafted coumarin Mannich base. S3. Weigh the grafted coumarin Mannich base, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid according to a mass ratio of 1:40:60. Then, add the grafted coumarin Mannich base, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid to 50 times the mass of the grafted coumarin Mannich base in deionized water. After the addition is complete, heat the water to 75°C. After the heating is complete, add dropwise a 10% ammonium persulfate solution (28 times the mass of the grafted coumarin Mannich base) and a 10% ferrous sulfate solution (95 times the mass of the grafted coumarin Mannich base). After the addition is complete, keep the water at the temperature for 2 hours. After the reaction is complete, cool the water to 25°C to obtain a composite phosphorus-free corrosion and scale inhibitor.

[0017] Example 2 S1. Formaldehyde and bis(methoxysilylpropyl)amine were added to ethanol at a mass ratio of 1:6.5 to 2.5 times the mass of bis(methoxysilylpropyl)amine. The pH was adjusted to 4.5 with 5% hydrochloric acid solution. The mixture was refluxed at 77.5℃ for 2.75 h. Then, 7-hydroxycoumarin-3-carboxylic acid ethyl ester at a mass ratio of 1.1 times the mass of bis(methoxysilylpropyl)amine was added dropwise. The mixture was refluxed at 77.5℃ for 1.75 h. After the reaction was completed, the mixture was extracted with diethyl ether and impurities were removed by rotary evaporation to obtain coumarin Mannich base. S2. Weigh coumarin Mannich base, allyl glycidyl ether, and methanol according to a mass ratio of 1:1.3:15. Then add coumarin Mannich base and allyl glycidyl ether to methanol and preheat to 80°C. Then add N,N-diisopropylethylamine at a mass ratio of 0.7 times that of coumarin Mannich base. Stir and reflux for 8 hours. After the reaction is completed, cool to 30°C and remove methanol by rotary evaporation. Then wash the product four times with ethyl acetate. After washing, filter and dry the filtered product to obtain grafted coumarin Mannich base. S3. Weigh the grafted coumarin Mannich base, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid according to a mass ratio of 1:45:65. Then, add the grafted coumarin Mannich base, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid to deionized water at a mass ratio of 55 times that of the grafted coumarin Mannich base. After the addition is complete, heat the water to 80°C. After the heating is complete, add dropwise a 10% ammonium persulfate solution at a mass ratio of 30 times that of the grafted coumarin Mannich base and a 10% ferrous sulfate solution at a mass ratio of 97.5 times that of the grafted coumarin Mannich base. After the addition is complete, keep the water at the temperature for 2.25 hours. After the reaction is complete, cool the water to 30°C to obtain a composite phosphorus-free corrosion and scale inhibitor.

[0018] Example 3 S1. Formaldehyde and bis(methoxysilylpropyl)amine were added to ethanol at a mass ratio of 1:7, and the pH was adjusted to 5 with 5% hydrochloric acid solution. The mixture was refluxed at 80°C for 3 hours. Then, 7-hydroxycoumarin-3-carboxylic acid ethyl ester at a mass ratio of 1.2 times that of bis(methoxysilylpropyl)amine was added dropwise. The mixture was refluxed at 80°C for 2 hours. After the reaction was completed, the mixture was extracted with diethyl ether and impurities were removed by rotary evaporation to obtain coumarin Mannich base. S2. Weigh coumarin Mannich base, allyl glycidyl ether, and methanol according to a mass ratio of 1:1.4:16. Then add coumarin Mannich base and allyl glycidyl ether to methanol and preheat to 85°C. Then add N,N-diisopropylethylamine at 0.75 times the mass of coumarin Mannich base. Stir and reflux for 9 hours. After the reaction is completed, cool to 35°C and remove methanol by rotary evaporation. Then wash the product 5 times with ethyl acetate. After washing, filter and dry the filtered product to obtain grafted coumarin Mannich base. S3. Weigh the grafted coumarin Mannich base, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid according to a mass ratio of 1:50:70. Then, add the grafted coumarin Mannich base, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid to deionized water at a mass ratio of 60 times that of the grafted coumarin Mannich base. After the addition is complete, heat the water to 85°C. After the heating is complete, add dropwise a 10% ammonium persulfate solution at a mass ratio of 32 times that of the grafted coumarin Mannich base and a 10% ferrous sulfate solution at a mass ratio of 100 times that of the grafted coumarin Mannich base. After the addition is complete, keep the water at the temperature for 2.5 hours. After the reaction is complete, cool the water to 35°C to obtain a composite phosphorus-free corrosion and scale inhibitor.

[0019] Example 4 The difference from Example 2 lies only in step S3: Allyl glycidyl ether, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid were weighed according to a mass ratio of 1:45:65. Then, the grafted coumarin Mannich base, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid were added to deionized water at a mass ratio of 55 times that of the grafted coumarin Mannich base. After the addition was completed, the temperature was raised to 80°C. After the temperature was raised, a 10% ammonium persulfate solution at a mass ratio of 30 times that of the grafted coumarin Mannich base and a 10% ferrous sulfate solution at a mass ratio of 97.5 times that of the grafted coumarin Mannich base were added dropwise. After the addition was completed, the reaction was kept at the temperature for 2.25 hours. After the reaction was completed, the temperature was cooled to 30°C to obtain a composite phosphorus-free corrosion and scale inhibitor. Example 5 The difference from Example 2 lies in step S3: acrylic acid and 2-acrylamide-2-methylpropanesulfonic acid were weighed at a mass ratio of 45:65. Then, the grafted coumarin Mannich base, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid were added to deionized water at a mass ratio of 55 times that of the grafted coumarin Mannich base. After the addition was completed, the temperature was raised to 80°C. After the temperature was raised, a 10% ammonium persulfate solution at a mass ratio of 30 times that of the grafted coumarin Mannich base and a 10% ferrous sulfate solution at a mass ratio of 97.5 times that of the grafted coumarin Mannich base were added dropwise. After the dropwise addition was completed, the reaction was kept at the temperature for 2.25 hours. After the reaction was completed, the temperature was cooled to 30°C to obtain a composite phosphorus-free corrosion and scale inhibitor. Scale inhibition and corrosion inhibition performance tests: According to GB / T18175-2014 "Determination of Corrosion Inhibition Performance of Water Treatment Agents - Rotary Coating Method" and GB / T16632-2008 "Determination of Scale Inhibition Performance of Water Treatment Agents", corrosion inhibition and scale inhibition performance were tested. The corrosion-inhibiting coupons were made of Q235 carbon steel, H62 brass, and 304 stainless steel, commonly used in industrial circulating water, with a specification of 50mm×25mm×2mm. Before use, they were polished, degreased, derusted, dried, and accurately weighed. The test water was simulated industrial circulating water with a calcium hardness of 250ppm, an alkalinity of 200ppm (both calculated as calcium carbonate), and a pH adjusted to 7.8~8.2. The corrosion inhibition test parameters were set as follows: coupon rotation speed 100r / min, test time 168h, temperature 80℃, and agent dosage 30mg / L at three gradients. The scale inhibition test was carried out simultaneously with the same parameters as the corrosion inhibition test, and the test time was 10h, which is consistent with the temperature resistance advantage of the agent and the actual application conditions. The test results are shown in Table 1 below. Table 1 Performance Test Results Examples 1-3 all exhibited excellent corrosion inhibition and scale inhibition performance. Among them, Example 2 had the best overall performance, with corrosion rates of 0.0024 mm / a, 0.0015 mm / a, and 0.0011 mm / a for Q235 carbon steel, H62 brass, and 304 stainless steel, respectively. The scale inhibition rate was as high as 98.2%, which was the highest among all groups. It led in corrosion inhibition balance and scale inhibition efficiency, demonstrating excellent metal corrosion inhibition activity, efficient scale-forming ion chelation and dispersion ability, and structural stability.

[0020] The corrosion and scale inhibition performance of Example 4 was significantly worse than that of Example 2. The corrosion rate of Q235 carbon steel increased by 0.0021 mm / a compared to Example 2, while the corrosion rates of H62 brass and 304 stainless steel increased to 0.0031 mm / a and 0.0028 mm / a, respectively. The scale inhibition rate decreased by 15.9 percentage points compared to Example 2. The core reason is that Example 4 did not use coumarin Mannich base grafting in the polymerization, but only used allyl glycidyl ether to prepare the polymer. The lack of metal chelating and corrosion-inhibiting active sites of coumarin groups completely eliminated the covalent corrosion inhibition and silica scale dispersion functions brought by the disilyl groups, making it impossible to construct an efficient corrosion-scale inhibition synergistic network. At the same time, the lack of synergistic effect between coumarin and silyl groups to enhance the scale-forming ion chelation effect significantly weakened the protective and scale inhibition capabilities of the agent on the metal substrate, ultimately leading to an increase in corrosion rate and a deterioration in scale inhibition efficiency.

[0021] The corrosion and scale inhibition performance of Example 5 was further deteriorated, with all indicators lower than that of Example 2. The corrosion rate of Q235 carbon steel was 0.0033 mm / a, an increase of 0.0009 mm / a compared to Example 2. The corrosion rates of H62 brass and 304 stainless steel reached 0.0022 mm / a and 0.0021 mm / a, respectively, and the scale inhibition rate was only 88.7%, a decrease of 9.5 percentage points compared to Example 2. The overall performance was far lower than that of Example 2. This is because Example 5 did not add the grafted coumarin Mannich base functional monomer, but only formed a basic polymer by copolymerizing acrylic acid and 2-acrylamide-2-methylpropanesulfonic acid. Lacking the core functional support of coumarin Mannich base and silane groups, the polymer only retains the simple scale inhibition effect of basic carboxyl and sulfonic acid groups, without specific metal corrosion inhibition sites and efficient chelating and dispersing ability. The protective effect on various metal substrates is insufficient, and the ability to inhibit scale-forming ions is limited, ultimately leading to a decrease in corrosion inhibition performance, a significant reduction in scale inhibition efficiency, and a comprehensive deterioration in the overall corrosion and scale inhibition performance.

[0022] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A composite phosphorus-free corrosion and scale inhibitor, characterized in that, The composite phosphorus-free corrosion and scale inhibitor is prepared by grafting bis(methoxysilylpropyl)amine onto ethyl 7-hydroxycoumarin-3-carboxylate via the Mannich base reaction to prepare coumarin Mannich base. Then, the coumarin Mannich base is grafted onto allyl glycidyl ether to prepare grafted coumarin Mannich base. Finally, the grafted coumarin Mannich base is copolymerized with acrylic acid and 2-acrylamide-2-methylpropanesulfonic acid to prepare the composite phosphorus-free corrosion and scale inhibitor.

2. The composite phosphorus-free corrosion and scale inhibitor according to claim 1, characterized in that, The mass ratio of the grafted coumarin Mannich base, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid is 1:40~50:60~70.

3. A method for preparing a composite phosphorus-free corrosion and scale inhibitor, applied to the composite phosphorus-free corrosion and scale inhibitor described in any one of claims 1-2, characterized in that, The composite phosphorus-free corrosion and scale inhibitor comprises the following preparation steps: Grafted coumarin Mannich base, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid are weighed according to a mass ratio of 1:40~50:60~70. Then, the grafted coumarin Mannich base, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid are added to deionized water at a mass ratio of 50~60 times that of the grafted coumarin Mannich base. After the addition is complete, the temperature is raised to 75~85℃. After the temperature rise is complete, ammonium persulfate solution at a mass ratio of 28~32 times that of the grafted coumarin Mannich base and ferrous sulfate solution at a mass ratio of 95~100 times that of the grafted coumarin Mannich base are added dropwise. After the dropwise addition is complete, the reaction is maintained at this temperature for 2~2.5 hours. After the reaction is complete, the temperature is cooled to 25~35℃ to obtain the composite phosphorus-free corrosion and scale inhibitor.

4. The preparation method of the composite phosphorus-free corrosion and scale inhibitor according to claim 3, characterized in that, The preparation steps of the grafted coumarin Mannich base are as follows: Coumarin Mannich base, allyl glycidyl ether and methanol are weighed according to a mass ratio of 1:1.2~1.4:14~16. Then, coumarin Mannich base and allyl glycidyl ether are added to methanol and preheated to 75~85℃. Then, 0.65~0.75 times the mass of coumarin Mannich base N,N-diisopropylethylamine is added and the mixture is stirred and refluxed for 7~9 hours. After the reaction is completed, the mixture is cooled to 25~35℃ and methanol is removed by rotary evaporation. The product is then washed with ethyl acetate 3~5 times. After washing, the product is filtered and dried to obtain the grafted coumarin Mannich base.

5. The preparation method of the composite phosphorus-free corrosion and scale inhibitor according to claim 4, characterized in that, The preparation steps of the coumarin Mannich base are as follows: formaldehyde and bis(methoxysilylpropyl)amine are added to ethanol at a mass ratio of 1:6~7, and the pH is adjusted to 4~5 with hydrochloric acid solution. The mixture is refluxed at 75~80℃ for 2.5~3h. Then, 7-hydroxycoumarin-3-carboxylic acid ethyl ester at a mass ratio of 1~1.2 times that of bis(methoxysilylpropyl)amine is added dropwise. The mixture is refluxed at 75~80℃ for 1.5~2h. After the reaction is completed, the mixture is extracted with diethyl ether and impurities are removed by rotary evaporation to obtain the coumarin Mannich base.

6. The preparation method of the composite phosphorus-free corrosion and scale inhibitor according to claim 3, characterized in that, The ammonium persulfate solution has a mass fraction of 10%.

7. The preparation method of the composite phosphorus-free corrosion and scale inhibitor according to claim 3, characterized in that, The ferrous sulfate solution has a mass fraction of 10%.

8. The preparation method of the composite phosphorus-free corrosion and scale inhibitor according to claim 5, characterized in that, The hydrochloric acid solution has a mass fraction of 5%.

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