A non-phosphorus pre-film agent, its preparation and a method for pre-film treatment in a circulating cooling water system

Abstract

The application discloses a kind of phosphorus-free pre-film agent, which is composed of the following components with mass percentage: N-lauroyl sarcosine 12-18%, zinc salt 15-20%, ferrous salt 7-10%, acrylic acid-itaconic acid copolymer 5-9% and soft water 50-60%. The application also discloses a preparation method of the above-mentioned phosphorus-free pre-film agent and a method for pre-film treatment in circulating cooling water system. The pre-film agent can effectively avoid the problem that traditional phosphorus-containing pre-film agent easily causes water eutrophication. The circulating water after pre-film does not contain phosphorus and can be recycled. Therefore, the pre-film agent does not need to be discharged after pre-film is completed and can be directly transferred to normal operation, thereby saving water resources and cleaning pre-film cost. The pre-film agent has good synergistic effect among components, and forms an organic-inorganic composite film interwoven on the metal surface. The composite film has the characteristics of rapid film formation, compactness, smoothness, uniformity, stable adhesion and strong corrosion resistance.

Description

Technical Field

[0001] This invention relates to a phosphorus-free pre-filming agent, a method for preparing the phosphorus-free pre-filming agent, and finally a method for pre-filming the phosphorus-free pre-filming agent in a circulating cooling water system. Background Technology

[0002] Before commissioning a circulating cooling water system, during shutdown maintenance, or after chemical cleaning, adding a pre-filming agent to the system can pre-generate a complete corrosion-resistant protective film on the metal (such as carbon steel / stainless steel) surfaces of the system's pipes, valves, and equipment (such as heat exchanger components). This film helps to slow down the corrosion of system components by highly alkaline / hard concentrated water during long-term operation and extends the service life of the circulating cooling water system.

[0003] Currently, most pre-filming agents on the market use the conventional method of polyphosphate + zinc salt. For example, patent CN1715445A discloses a pre-filming agent for metal surfaces, and patent CN102398944A discloses a pre-filming agent for cooling water. In practical applications, although the above methods have good pre-filming effects and relatively high film stability, the resulting effluent has a high phosphorus content and can decompose into orthophosphate, which can easily cause eutrophication of surrounding water bodies, resulting in significant environmental pollution. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a phosphorus-free pre-filming agent that will not cause eutrophication of natural water bodies; another purpose of this invention is to provide a method for preparing the above-mentioned phosphorus-free pre-filming agent and a method for pre-filming treatment in a circulating cooling water system.

[0005] Technical solution: The phosphorus-free pre-filming agent of the present invention is composed of the following components in mass percentage: 12-18% N-lauroyl sarcosine, 15-20% zinc salt, 7-10% ferrous salt, 5-9% acrylic acid-itaconic acid copolymer and 50-60% softened water.

[0006] The N-lauroyl sarcosine is prepared by the following method, specifically including the following steps:

[0007] (1) Add lauric acid to a three-necked flask, and add thionyl chloride dropwise while heating and stirring in a water bath. After the reaction, purify the reaction mixture, collect the high-temperature fraction and obtain lauroyl chloride. Since the byproducts generated by the reaction are all gases, the main product is easy to purify.

[0008] C 11 H 23 COOH + SOCl2 → C 11 H 23 COCl + SO2↑ + HCl↑

[0009] (2) Weigh out monochloroacetic acid, dissolve it in softened water, add sodium hydroxide in an equal molar amount to monochloroacetic acid, and adjust the pH to alkaline with sodium hydroxide solution to obtain sodium monochloroacetate solution, and put it into a dropping funnel for later use; add methylamine aqueous solution to a three-necked flask, place it in a water bath, and add the sodium monochloroacetate solution prepared above dropwise while stirring. After the reaction is complete, acidify the reaction mixture with hydrochloric acid, and then remove the solvent by vacuum distillation. Recrystallize the obtained product with anhydrous ethanol to obtain purified sarcosine.

[0010] ClCH2COOH+NaOH→ClCH2COONa+H2O

[0011] CH3NH2+ClCH2COONa→CH3NHCH2COONa+HCl

[0012] (3) Dissolve the sarcosine obtained in step (2) in sodium hydroxide solution and add it to a three-necked flask. Add acetone and heat in a water bath. Add lauroyl chloride from step (1) dropwise while stirring. Keep the solution alkaline during the reaction. After the reaction is complete, adjust the pH to strong acidity with hydrochloric acid and extract with ethyl acetate. Remove the solvent under reduced pressure to obtain N-lauroyl sarcosine. Finally, recrystallize with n-hexane to obtain the pure product.

[0013] C 11 H 23 COCl + CH3NHCH2COONa → C 11 H 23 CON(CH3)CH2COONa→C 11 H 23 CON(CH3)CH2COOH

[0014] The zinc salt is a zinc-containing inorganic compound, including zinc chloride, zinc sulfate heptahydrate, zinc nitrate, or zinc gluconate. Zinc chloride is preferred because of its high solubility.

[0015] The ferrous salt is an inorganic compound containing ferrous ions, including ferrous chloride, ferrous sulfate heptahydrate, or ferrous nitrate. Ferrous chloride is preferred because of its high relative iron content and stability.

[0016] The acrylic acid-itaconic acid copolymer has a relative molecular mass between 3000 and 5000. Within this range, itaconic acid and acrylic acid monomers are alternately linked in the polymer, and the copolymer is a narrow molecular weight distribution composition with an approximately homogeneous chemical composition; preferably 4500.

[0017] The film-forming mechanism of N-lauroyl sarcosine prepared by this invention is mixed adsorption film formation. Compared with traditional passivation film formation and precipitation film formation, mixed adsorption film formation occurs in various regions of the metal surface (passivation film formation only occurs in the anodic region of the metal surface, and precipitation film formation only occurs in the cathodic region of the metal surface, and the pre-filming process has limitations), and the film is dense and uniform with strong adhesion to the substrate metal. N-lauroyl sarcosine adsorbs onto the metal surface to form a monomolecular film through its strongly polar -NH2 group; especially when N-lauroyl sarcosine is dissolved in water under an acidic atmosphere, the Onium ions formed by its -NH2 group further enhance the adsorption effect on the metal surface (Onium ions are the lone pair electrons of N on the -NH2 group and H in water). + It forms positively charged coordinate ions, which strongly adsorb onto the free negatively charged metal surface, making the film more stable and with stronger adhesion. Simultaneously, N-lauroyl sarcosine, through its strongly hydrophobic lauryl group (-C) on its molecule... 11 H 23 It hinders water and hydrated ions in the electrolyte solution from reaching the metal surface, increases the reaction barrier for metal corrosion, and thus prevents or slows down the corresponding electrochemical reactions of the metal.

[0018] This invention's pre-filming agent employs two methods: firstly, zinc salt and ferrous salt as film-forming substances to form a Fe-Zn hydroxide precipitate-type inorganic film on the cathode region of a metal surface; secondly, N-lauroyl sarcosine as a film-forming substance to form an adsorbed organic film on the metal surface. The precipitated film forms rapidly, is porous and thick, but has poor adhesion; the adsorbed film forms densely and uniformly, is thinner, and has strong adhesion stability. The two methods synergistically interweave on the metal surface to form an organic + inorganic composite film, thereby improving the film-forming effect and quality. The composite film on the metal surface forms rapidly, is dense and compact, smooth and uniform, and has strong adhesion and corrosion resistance. Simultaneously, the numerous -COO groups on the N-lauroyl sarcosine molecule and the long molecular chain of the acrylic acid-itaconic acid copolymer further enhance the film-forming effect. - The synergistic effect of functional groups, and Zn in water. 2+ Fe 2+ and Ca 2+ The coordination and chelation effect of cations ensures that the film-forming material in the cathode region of the metal surface will not precipitate out as an alkaline metal salt (from the solution), but rather the metal ions will dissolve and disperse in the solution, forming a precipitated inorganic film in the cathode region of the metal surface through co-precipitation, thereby promoting the stability of the pre-film layer on the metal surface.

[0019] The preparation method of the above-mentioned phosphorus-free pre-filming agent includes the following steps:

[0020] (1) Add softened water to beaker A, and slowly add the N-lauroyl sarcosine solid powder of the formula while stirring, until it is completely dissolved and the solution becomes clear and transparent;

[0021] (2) Transfer beaker A to a water bath at a temperature of 80-90°C. Add the formulated amount of acrylic acid-itaconic acid copolymer to the beaker while stirring. React in the water bath for 30-50 minutes. This step can enable the -COOH functional groups in N-lauroyl sarcosine and acrylic acid-itaconic acid copolymer molecules to form a synergistic effect, thereby enhancing the dispersion effect during the pre-filming process.

[0022] (3) Add softened water to beaker B. Under ultrasonic conditions, add the prescribed amount of zinc salt and ferrous salt while stirring. Through the ultrasonic resonance effect, the dissolution of zinc salt and ferrous salt can be accelerated, so that they can quickly form a uniform and clear solution.

[0023] (4) While stirring, the solution in beaker B is added dropwise and slowly to beaker A through a dropper, and stirred for 12-18 hours to obtain a phosphorus-free pre-filming agent.

[0024] The method for pre-filming the above-mentioned phosphorus-free pre-filming agent in a circulating cooling water system is as follows: When pre-filming in a circulating cooling water system, the above-mentioned pre-filming agent is added to the raw water for pre-filming in the circulating cooling water system (tap water is generally used as the raw water for pre-filming). The concentration of the pre-filming agent is 100-400 ppm, the pH of the raw water is controlled at 6.5±0.3 (adjusted to the required pH by using an acid-base adjuster), the calcium hardness of the water (calculated as CaCO3) is controlled at >100 ppm (using soluble calcium salts to control the hardness of the water), the temperature of the pre-filming process is 5-40℃ (i.e., the ambient temperature), the circulating water streamline velocity should be at least >0.5 m / s, and the pre-filming time is 24-48 h.

[0025] Before pre-filming in the circulating cooling water system, the pipelines must be cleaned to remove oil, scale, and rust to obtain a clean and bright metal surface, thus preparing the necessary conditions for pre-filming. After the circulating cleaning is completed, sewage discharge and water replenishment must be carried out until the water quality meets the pre-filming requirements, namely turbidity <20 NTU and total iron <5 ppm, before pre-filming can be carried out.

[0026] After pre-filming, the carbon steel metal fins inside the circulating cooling water system are uniformly and densely covered with a layer of blue-purple colored halo coating. According to the CuSO4 solution titration method of HG / T3778-2005 standard, the red dot color development time of the coated fins is much greater than 10s.

[0027] The film-forming mechanism of the pre-filming agent on the metal surface of this invention:

[0028]

[0029] A is the molecular structure of N-lauroyl sarcosine, B is the molecular structure of acrylic acid-itaconic acid copolymer, and ① is the lauryl strong hydrophobic group (-C). 11 H 23 ), ② is the Onium ion structure, ③ is -COO - Coordination chelation effect between functional groups and metal cations (M n+ Represents Zn 2+ / Fe 2+ / Ca 2+ Plasma), ④ represents the synergistic effect of the -COOH functional groups in molecules A and B.

[0030] Beneficial effects: Compared with the prior art, the present invention has the following significant effects: (1) The pre-filming agent of the present invention can effectively avoid the problem of eutrophication of water bodies caused by traditional phosphorus-containing pre-filming agents. The circulating water after pre-filming is phosphorus-free and can be recycled. Therefore, the pre-filming agent of the present invention can be directly transferred to normal operation without sewage discharge after pre-filming, thereby saving water resources and saving cleaning and pre-filming costs; (2) The components of the pre-filming agent of the present invention have a good synergistic effect, forming an interwoven organic + inorganic composite film on the metal surface. The composite film has the characteristics of rapid film formation, tight and dense, smooth and uniform, stable adhesion and strong corrosion resistance; (3) In the actual application process, the pre-filming agent of the present invention has an outstanding pre-filming effect, which is far greater than the red dot color development time of 10s specified in HG / T3778-2005 standard; The pre-filming agent of the present invention is suitable for various large / medium / small industrial circulating cooling water systems and has a wide range of applications. Attached Figure Description

[0031] Figure 1 The image shows the appearance of specimens obtained with pre-filming water at a pH of 4.5–8.5. Detailed Implementation

[0032] Example 1

[0033] This invention relates to a phosphorus-free pre-filming agent, composed of the following components by weight percentage: 15% N-lauroyl sarcosine, 15% zinc chloride, 7% ferrous chloride, 7% acrylic acid-itaconic acid copolymer, and 56% softened water. The acrylic acid-itaconic acid copolymer has a relative molecular mass of approximately 4500. In this polymer, itaconic acid monomers and acrylic acid monomers are alternately linked, resulting in a copolymer with a narrow molecular weight distribution and approximately homogeneous chemical composition, thereby achieving its effect on the removal of calcium from water. 2+ / Fe 2+ / Zn 2+ To achieve the best dispersion effect for metal ions.

[0034] N-Lauroylsarcosine is prepared by the following method, which specifically includes the following steps:

[0035] (1) Add 20g (0.1mol) lauric acid to a 250mL three-necked flask, heat to 75℃ in a water bath, and add 14.6mL (0.2mol) thionyl chloride dropwise while stirring. After reacting for 20-30min, purify the reaction mixture and collect the fraction at 140-150℃ (2132.8-2216.1Pa) to obtain lauroyl chloride. The obtained lauroyl chloride is used for the condensation of N-lauroylsarcosine in step (3).

[0036] C 11 H 23 COOH + SOCl2 → C 11 H 23 COCl + SO2↑ + HCl↑

[0037] (2) Weigh 9.45 g (0.1 mol) of monochloroacetic acid, dissolve it in 40 mL of softened water, add 4 g (0.1 mol) of sodium hydroxide, and adjust the pH of the mixture to alkaline (pH>10) with 1 mol / L sodium hydroxide aqueous solution. Put the mixture (sodium monochloroacetate solution) into a dropping funnel for later use. Add 24.3 mL (0.2 mol) of monomethylamine aqueous solution to a three-necked flask, place it in a water bath, and add the above sodium monochloroacetate solution dropwise while stirring. After the addition is complete, react for 2 hours. Then acidify the reaction mixture with 1 mol / L hydrochloric acid to pH 1-2, remove the solvent under reduced pressure, and recrystallize the obtained product with anhydrous ethanol to obtain 11 g of purified sarcosine.

[0038] ClCH2COOH+NaOH→ClCH2COONa+H2O

[0039] CH3NH2+ClCH2COONa→CH3NHCH2COONa+HCl

[0040] (3) Weigh 1.31g of sarcosine, dissolve it in 25mL of 1mol / L sodium hydroxide solution and add it to a 250mL three-necked flask. Add 50mL of acetone and heat the flask to 45℃ in a water bath. Add 2.38mL of lauroyl chloride obtained in step (1) dropwise while stirring. After the addition is complete, react for 1h. Keep the solution alkaline during the reaction. After the reaction is complete, adjust the pH to 1 with hydrochloric acid and extract with ethyl acetate. After evaporating the solvent, N-lauroyl sarcosine is generated. The product is recrystallized with n-hexane to obtain 1.65g of pure product.

[0041] The method for preparing N-lauroyl sarcosine in this invention can significantly improve the yield of N-lauroyl sarcosine, making the yield reach more than 75% (this yield = mass of N-lauroyl sarcosine actually obtained in the experiment / mass of N-lauroyl sarcosine calculated theoretically based on the synthetic chemical equation * 100%).

[0042] The preparation method of the phosphorus-free pre-filming agent of the present invention includes the following steps:

[0043] (1) Add 2.8g of softened water to beaker A, and slowly add 1.5g of N-lauroyl sarcosine solid powder prepared by the above method while stirring at 250rpm until it is completely dissolved and the solution becomes clear and transparent;

[0044] (2) Transfer beaker A to a water bath, keep the water bath temperature at 85°C, and add 0.7g of acrylic acid-itaconic acid copolymer while stirring at 300rpm. React in the water bath for 40min.

[0045] (3) Add 2.8g of softened water to beaker B. Under ultrasonic conditions, stir at 300rpm while adding 1.5g of zinc chloride and 0.7g of ferrous chloride until a uniform and clear solution is formed.

[0046] (4) At a stirring speed of 200 rpm, the solution in beaker B is added dropwise and slowly to beaker A through a dropper, and stirred for 15 h to obtain the phosphorus-free pre-filming agent of the present invention.

[0047] Example 2

[0048] The method for pre-filming the phosphorus-free pre-filming agent prepared in Example 1 in a circulating cooling water system is as follows:

[0049] A large-scale circulating cooling water system in an electronics factory uses membrane recycling water from the front-end process as raw water for pre-membrane preparation. The water quality is shown in Table 1.

[0050] Table 1

[0051]

[0052]

[0053] Before pre-filming, the circulating cooling water system uses a functional cleaning agent to clean its pipelines, heat exchangers, and circulating pumps. During the cleaning process, the system is replenished and replaced with water according to the concentration of the water. After 4 to 5 hours of circulating cleaning, the turbidity of the water is measured to be 18 NTU and the total iron in the water is 2.54 ppm. The system is then drained to prepare for the pre-filming process.

[0054] The pre-filming agent of Example 1 was slowly added to the raw water for pre-filming. The concentration of the pre-filming agent was 300 ppm. The pH of the pre-filming water was controlled at 6.4-6.6, the calcium hardness (calculated as CaCO3) of the water was controlled at 150 ppm, the pre-filming temperature was 27℃ (the actual ambient temperature measured on the day of pre-filming), the circulation pump circulation speed was 2.1 m / s, and the pre-filming time was 36 h.

[0055] After the pre-filming was completed, by observing the Type II standard carbon steel plates inside the circulation pipeline, it could be found that a dense and uniform blue-purple halo film had been formed on the originally bright metal surface. The pre-filming plates were tested according to the CuSO4 solution titration method of HG / T3778-2005 standard, and the red dot color development time was 33s, which met the pre-filming standard requirements.

[0056] Comparative Example 1

[0057] The test water sample (raw water for pre-filming) was taken from the tap water makeup water of the circulating cooling water system of an electronics factory. 20# carbon steel pre-filming plates were used as the test objects. Formula A consisted of zinc salt and ferrous salt; Formula B consisted of zinc salt, ferrous salt, and acrylic acid-itaconic acid copolymer; and Formula C consisted of the pre-filming agent from Example 1 of this invention. The film-forming effect, red spot color change time, and water condition after pre-filming of the three formulas were compared under the same dosage concentration. Four parallel experiments (1, 2, 3, and 4) were conducted for each formula under identical experimental conditions. This experiment was conducted according to the standard HG / T3778-2005 "Technical Rules for Chemical Cleaning and Pre-filming Treatment of Cooling Water Systems," with a pre-filming cycle of 48 hours.

[0058] The water quality of the tap water replenishment for the above system is shown in Table 2:

[0059] Table 2

[0060]

[0061] The effects of the above formulations on pre-filming of the film and related data are summarized in Table 3:

[0062] Table 3

[0063]

[0064]

[0065] As can be seen from Table 3, because formulation A did not introduce dispersing groups, the Zn in the water... 2+ / Fe 2+ / Ca 2+When cations cannot effectively form films in the cathodic region of a metal surface, they instead form alkaline metal salt precipitates under the influence of water alkalinity, causing water turbidity. Formula B adds acrylic acid-itaconic acid copolymer as a highly efficient dispersant, which improves the film formation probability on the metal surface through its own coordination chelation mechanism. However, since the zinc / iron salts in the formula are both cathodic precipitation film-forming substances, uneven film formation and porous and loose phenomena appear on the surface of the tablet. The formulation of this invention introduces N-lauroyl sarcosine, which, through its unique onium ion adsorption film formation mechanism and the synergistic effect between its precipitation film formation with zinc / iron salts and acrylic acid-itaconic acid copolymer, forms a dense and uniform blue-purple halo mixed film on the surface of the tablet.

[0066] Table 3 also clearly shows that, under the same dosage concentration, the titration red dot color change time of the pre-film on the surface of the hanging tablet is: Formula of this invention > Formula B > Formula A. This indicates that the metal surface pre-film formed by using the formula of this invention has the best effect and the most stable film formation (the longer the titration red dot color change time of CuSO4 solution, the stronger the adhesion between the protective film of the hanging tablet and the metal substrate and the stronger the protective film's ability to resist electrochemical corrosion of the solution, and the more stable the film formation).

[0067] Comparative Example 2

[0068] The method for pre-filming the phosphorus-free pre-filming agent prepared in Example 1 in a circulating cooling water system is as follows:

[0069] A large-scale circulating cooling water system in an electronics factory uses membrane recycling water from the front-end process as raw water for pre-membrane preparation. The water quality is as follows:

[0070]

[0071] Before pre-filming, the circulating cooling water system uses a functional cleaning agent to clean its pipelines, heat exchangers, and circulating pumps. During the cleaning process, the system is replenished and replaced with water according to the concentration of the water. After 4 to 5 hours of circulating cleaning, the turbidity of the water is measured to be 19 NTU and the total iron in the water is 3.65 ppm. The system is then drained to prepare for the pre-filming process.

[0072] The pre-filming agent from Example 1 was slowly added to the raw water for pre-filming at a concentration of 300 ppm. The pH of the pre-filming water was controlled between 6.4 and 6.6, and the calcium hardness (calculated as CaCO3) was 30, 150, and 400 ppm, respectively. The pre-filming temperature was 27°C, the circulation pump flow rate was 2.1 m / s, and the pre-filming time was 36 h. Four parallel experiments (1, 2, 3, and 4) were conducted under identical conditions for each different calcium hardness condition. The pre-filming effects and related data for each group of experiments are summarized in Table 4.

[0073] Table 4

[0074]

[0075] Table 4 shows that when the calcium hardness concentration is too low (<50ppm), although a film can still form on the metal substrate, the film formation is uneven and cannot fully cover the metal surface. When the calcium hardness concentration is too high (>300ppm), the film on the metal surface appears dark yellow (possibly due to excessive Ca3(PO4)2 precipitate deposited on the metal surface), and the effluent after pre-filming is light milky white and turbid, with the highest turbidity. This indicates that some metal salts precipitate during pre-filming. The red dot color change time comparison for pre-filming is as follows: ① 150ppm calcium hardness condition > ② 400ppm calcium hardness condition > ③ 30ppm calcium hardness condition. In conclusion, the pre-filming effect is best, the color change time is longest, and the impact on the pre-filming effluent is minimal when the calcium hardness (CaCO3) of the pre-filmed water is 150ppm.

[0076] Comparative Example 3

[0077] A large-scale circulating cooling water system in an electronics factory uses membrane recycling water from the front-end process as raw water for pre-membrane preparation. The water quality is as follows:

[0078]

[0079] Before pre-filming, the circulating cooling water system uses a functional cleaning agent to clean its pipelines, heat exchangers, and circulating pumps. During the cleaning process, the system is replenished and replaced with water according to the concentration of the water. After 4 to 5 hours of circulating cleaning, the turbidity of the water is measured to be 17.4 NTU and the total iron in the water is 2.36 ppm. The system is then drained to prepare for the pre-filming process.

[0080] The phosphorus-free pre-filming agents (Formula 1 and Formula 2) were adjusted according to the reagent compatibility ratios shown in Table 5 and compared with the pre-filming agent of Example 1 of this invention. They were added to the circulating water system, with each formula having a concentration of 300 ppm, pH controlled at 6.4–6.6, water calcium hardness (calculated as CaCO3) controlled at 150 ppm, pre-filming temperature at 27°C, circulation pump flow rate at 2.1 m / s, and pre-filming time at 36 h. Four parallel experiments (1, 2, 3, and 4) were conducted under identical conditions for each formula.

[0081] The effects of the above formulations on pre-filming of the film and related data are summarized in Table 5:

[0082] Table 5

[0083]

[0084]

[0085] As can be seen from Table 5, Formula 1 and Formula 2 are not conducive to film formation on the surface of metal pads, resulting in thinner films, uneven pre-film formation on the metal surface, and shortened red spot discoloration time, thereby significantly reducing the ability of the protective film to resist electrochemical corrosion of the solution and the stability of film formation.

[0086] Comparative Example 4

[0087] Comparative Example 4 and Example 2 were conducted under identical experimental conditions, with the only difference being the adjustment of the pH value of the pre-filming water to 4.5, 5.5, 6.5, 7.5, and 8.5, respectively, resulting in different pre-filming effects on the metal workpiece. Figure 1 As shown. Figure 1 The six specimens, from left to right, are: Specimen 1 (original specimen) without pre-filming, Specimen 2 with pH 4.5, Specimen 3 with pH 5.5, Specimen 4 with pH 6.5, Specimen 5 with pH 7.5, and Specimen 6 with pH 8.5. Figure 1 It can be seen that at pH 4.5 and pH 5.5, the overly acidic environment causes corrosion on the metal surface, resulting in blackening. At pH 7.5 and pH 8.5, the environment is too alkaline, causing the zinc and iron active ingredients in the pre-filming agent to precipitate in the solution, preventing the formation of a film on the metal surface, thus leaving the metal surface shiny. Therefore, a pH of 6.5 provides the best pre-filming effect, allowing for the formation of a complete iridescent coating on the metal surface.

Claims

1. A method for pre-filming a phosphorus-free pre-filming agent in a circulating cooling water system, characterized in that, The phosphorus-free pre-filming agent is composed of the following components by weight percentage: 15% N-lauroyl sarcosine, 15% zinc chloride, 7% ferrous chloride, 7% acrylic acid-itaconic acid copolymer, and 56% softened water; The above-mentioned phosphorus-free pre-filming agent was slowly added to the raw water for pre-filming. The concentration of the pre-filming agent was 300 ppm. The pH of the pre-filming water was controlled at 6.4~6.

6. The calcium hardness of the water body was controlled at 150 ppm (calculated as CaCO3). The pre-filming temperature was 27℃. The circulation pump flow rate was 2.1 m / s. The pre-filming time was 36 h.

2. The method for pre-filming the phosphorus-free pre-filming agent in a circulating cooling water system according to claim 1, characterized in that, The N-lauroyl sarcosine was prepared by the following method, specifically including the following steps: (1) Thionyl chloride was added dropwise to lauric acid under water bath heating and stirring. After the reaction, the reaction mixture was purified and the fraction in the high-temperature section was collected to obtain lauroyl chloride. (2) Weigh out monochloroacetic acid, dissolve it in softened water, add sodium hydroxide in an equal molar amount to monochloroacetic acid, and adjust the pH to alkaline with sodium hydroxide solution to obtain sodium monochloroacetate solution; add sodium monochloroacetate solution dropwise to methylamine aqueous solution under water bath heating and stirring. After the reaction is completed, acidify the reaction mixture with hydrochloric acid, then remove the solvent by vacuum distillation, and recrystallize the obtained product with anhydrous ethanol to obtain purified sarcosine. (3) Dissolve the sarcosine obtained in step (2) in sodium hydroxide solution, then add acetone and heat in a water bath; while stirring, add lauroyl chloride from step (1) dropwise, keep the solution alkaline during the reaction, adjust the pH to strong acidity with hydrochloric acid after the reaction is completed, extract with ethyl acetate, remove the solvent by vacuum distillation, and recrystallize to obtain N-lauroylsarcosine.

3. The method for pre-filming the phosphorus-free pre-filming agent in a circulating cooling water system according to claim 1, characterized in that: The relative molecular mass of the acrylic acid-itaconic acid copolymer is between 3000 and 5000.

4. The method for pre-filming the phosphorus-free pre-filming agent in a circulating cooling water system according to claim 1, characterized in that, The phosphorus-free pre-filming agent was prepared by the following method, with the specific steps as follows: (1) While stirring, slowly add the prescribed amount of N-lauroyl sarcosine solid powder to softened water until it is completely dissolved; (2) Heating in a water bath and stirring, adding the prescribed amount of acrylic acid-itaconic acid copolymer to the solution in step (1) to obtain mixture A; (3) Under ultrasound, zinc chloride and ferrous chloride of the formula amount were added to softened water to obtain mixture B; (4) While stirring, add mixture B dropwise to mixture A through a dropper, and after stirring, obtain a phosphorus-free pre-filming agent.

5. The method for pre-filming the phosphorus-free pre-filming agent in a circulating cooling water system according to claim 4, characterized in that: In step (2), the water bath temperature is 80~90℃ and the water bath reaction time is 30~50min.

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