Phosphorus-free pre-filming agent and preparation method therefor, and pre-filming method for water-cooled heat exchanger

Abstract

Provided in the present invention are a phosphorus-free pre-filming agent and a preparation method therefor, and a pre-filming method for a water-cooled heat exchanger. The phosphorus-free pre-filming agent comprises the following raw materials in percentage by weight: 1-10% of an amino acid containing two carboxyl groups in the molecule thereof, and / or a salt thereof; 1-10% of hydroxycarboxylic acid and / or a hydroxycarboxylate; 1-10% of a zinc salt; 1-5% of a molybdate; 1-10% of a polymer; and the balance being water. A film obtained when the addition amount of the phosphorus-free pre-filming agent of the present invention reaches 100 ppm has good performance, and the longest duration of a red dot test of same can reach 30 s.

Description

A phosphorus-free pre-filming agent and its preparation method and a water-cooled heat exchanger pre-filming method

[0001] Cross-reference information

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on November 16, 2023, with application number 202311532815.X and invention name “A phosphorus-free pre-filming agent, its preparation method and water-cooled heat exchanger pre-filming method”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The invention relates to a phosphorus-free pre-filming agent and a preparation method thereof, as well as a water-cooled heat exchanger pre-filming method, and belongs to the field of metal corrosion and protection. Background Art

[0004] Pre-coating is a crucial corrosion protection measure for metal materials. Its purpose is to form a protective film on the surface of metal equipment or pipelines. This protective film is typically formed by adding a pre-coating agent, which adheres to the cleaned metal surface through physical and chemical reactions. Pre-coating is widely used in various industries requiring corrosion protection for metals, and is particularly common in industrial circulating cooling water systems.

[0005] Currently, the most widely used pre-filming agents are phosphorus-based, such as a mixture of sodium hexametaphosphate and zinc sulfate. However, with increasingly stringent environmental regulations, the use of phosphorus is increasingly restricted due to pollution concerns and the negative impact of its application on microbial growth. Therefore, the development of phosphorus-free pre-filming agents has become an inevitable trend.

[0006] Industrial circulating water systems, particularly open-type systems, are widely used for cooling equipment. They require the addition of chemical treatment agents to ensure stable operation, and pre-filming agents are an essential component. Typically, chemical treatment agents used in circulating water systems meet certain basic requirements, such as product stability, effective film formation, minimal impact on water quality, and no significant toxicity. Furthermore, since cooling water splashing is inevitable during operation, the treatment agents must also be free of noticeable odors or other environmentally unfriendly effects.

[0007] CN113981427A discloses a phosphorus-free pre-filming agent for industrial circulating water systems, its preparation method and application, but it only refers to the absence of "inorganic phosphorus" and still uses 2-phosphobutane-1,2,4-tricarboxylic acid, which is an organic phosphorus, so it cannot be called a true phosphorus-free pre-filming agent. CN114057304A discloses a phosphorus-free pre-filming composition, which is a mixture of main components such as o-hydroxybenzaldehyde oxime, polycarboxylic acid and zinc salt. It is suitable for low hardness water quality, but it has high requirements for the pH value of the water body, which needs to be within the range of 6-6.5, and it will cause the water body to turn yellow during use. CN105112900B discloses a phosphorus-free pre-filming agent for cooling water systems, which uses concentrated sulfuric acid in the formula. Concentrated sulfuric acid is a hazardous chemical with strong oxidizing and corrosive properties, which is not convenient for transportation, production and operation. CN106477740B discloses a circulating water treatment composition composed of a heterocyclic compound, a hydrophilic colloid and a phosphorus-free polymer. When the heterocyclic compound is used in an open circulating water system, it will face the problem of unfriendly odor diffusion.

[0008] Therefore, the existing phosphorus-free pre-filming agents have at least the following problems: although the phosphorus content in the raw material formula is reduced, other unsafe and environmentally friendly substances such as heterocyclic organic matter, long-chain water-insoluble organic matter, concentrated acid, etc. are introduced. In addition, there are also problems such as poor adaptability to working conditions and large dosage.

[0009] Summary of the Invention

[0010] In order to solve the above technical problems, the purpose of the present invention is to provide a phosphorus-free pre-filming agent, which is very suitable for industrial circulating cooling water systems. The raw materials are safe, environmentally friendly, non-toxic and harmless, and have strong adaptability to water quality. It is an environmentally friendly phosphorus-free pre-filming agent.

[0011] The present invention also provides a water-cooled heat exchanger pre-filming method based on the pre-filming agent.

[0012] To achieve the above object, the present invention provides a phosphorus-free pre-filming agent, wherein the raw material composition of the phosphorus-free pre-filming agent comprises, by weight percentage:

[0013] Amino acids containing two carboxyl groups in the molecule and / or their salts: 1-10%, preferably 3-7%;

[0014] Hydroxycarboxylic acid and / or hydroxycarboxylate: 1-10%, preferably 3-7%;

[0015] Zinc salt: 1-10%, preferably 4-8%;

[0016] Molybdate: 1-5%, preferably 2-3%;

[0017] Polymer: 1-10%, preferably 3-7%;

[0018] Residual water;

[0019] The amino acid and / or its salt containing two carboxyl groups in the molecule refers to an organic compound containing one basic amino group and at least two acidic carboxyl groups in the molecule;

[0020] The hydroxycarboxylic acid and / or hydroxycarboxylate refers to a compound containing both hydroxyl and carboxyl groups in its molecular structure;

[0021] The polymer is prepared by reacting polysuccinimide with an amino acid containing two carboxyl groups and / or a salt thereof (e.g., aspartic acid and its monovalent salts, cystine and its monovalent salts, glutamic acid and its monovalent salts, a compound represented by formula II, or a compound represented by formula III);

[0022] The mass ratio of the polysuccinimide to the amino acid containing two carboxyl groups and / or its salt is 2:1 to 8:1, preferably 4:1 to 6:1.

[0023] In the above-mentioned phosphorus-free pre-filming agent, preferably, the amino acid containing two carboxyl groups in the molecule and / or its salt (i.e., the amino acid containing two carboxyl groups in the molecule and / or the amino acid salt containing two carboxyl groups in the molecule) is selected from one or a combination of two or more of aspartic acid and its monovalent salts, cystine and its monovalent salts, glutamic acid and its monovalent salts, the compound represented by formula II, and the compound represented by formula III;

[0024] wherein R is selected from an alkyl group of 1 to 10 carbon atoms, an alkyl chain of 1 to 10 carbon atoms with NH2, or an alkyl chain of 1 to 10 carbon atoms with a heteroatom (e.g., sulfur);

[0025] Wherein, R1 and R2 are independently selected from an alkyl group of 1-10 carbon atoms, an alkyl chain of 1-10 carbon atoms with NH2, or an alkyl chain of 1-10 carbon atoms with a heteroatom (such as sulfur).

[0026] In the above-mentioned phosphorus-free pre-filming agent, preferably, the molecular weight of the polysuccinimide is 400-4000.

[0027] In the above-mentioned phosphorus-free pre-filming agent, the hydroxycarboxylic acid (salt) can clean the metal surface and remove corrosion products and deposited scale on the surface; preferably, the hydroxycarboxylic acid and / or hydroxycarboxylic acid salt is selected from one or a combination of two or more of gluconic acid, tartaric acid, citric acid, salicylic acid, lactic acid, gentisic acid, etc. and their salts.

[0028] In the above-mentioned phosphorus-free pre-filming agent, zinc ions react with amino acids containing two carboxyl groups and hydroxycarboxylic acids to form a dense protective film on the metal surface. In particular, the amino acids containing two carboxyl groups not only strongly complex the zinc ions, but the amino groups in their molecular structure also have a certain adsorption effect on the metal surface, allowing the complex to adhere tightly to the metal surface. Moreover, the combination with amino acids (salts) containing two carboxyl groups and hydroxycarboxylic acids (salts) helps to improve the density and integrity of the film. Preferably, the zinc salt includes zinc sulfate and / or zinc chloride.

[0029] In the aforementioned phosphorus-free pre-filming agent, molybdates and organic acids exhibit excellent synergistic effects, providing corrosion protection. In the phosphorus-free pre-filming agent of the present invention, the combination of molybdates and zinc salts enhances the pre-filming agent's adaptability to varying water conditions, providing excellent corrosion protection for low-hardness, low-alkalinity water. Preferably, the molybdates include sodium molybdate and / or ammonium molybdate.

[0030] In the above-mentioned phosphorus-free pre-filming agent, the polymer plays a crucial role. In addition to its conventional scale inhibition effect, it also has the function of dispersing and complexing zinc ions. When used in combination with an amino acid (or salt) and a hydroxycarboxylic acid (or salt) containing two carboxyl groups, it can further enhance the density of the film, so that the pre-filming agent of the present invention can achieve an extremely excellent film-forming effect at a lower addition dosage.

[0031] In the above-mentioned phosphorus-free pre-filming agent, preferably, the molecular weight of the polymer is 500-5000, more preferably 1000-4000, and further preferably 2000-3000.

[0032] In the above-mentioned phosphorus-free pre-filming agent, preferably, the polymer is a compound represented by Formula I:

[0033] According to a specific embodiment of the present invention, the reaction of polysuccinimide and an amino acid containing two carboxyl groups and / or a salt thereof is carried out in an alkaline aqueous solution under mild reaction conditions (about 40° C.). After the reaction is completed, the product is precipitated with a large amount of ethanol, washed, and then dried in a vacuum drying oven to obtain the polymer.

[0034] The present invention also provides a method for preparing the above-mentioned phosphorus-free pre-filming agent, which comprises the following steps:

[0035] Dispersing zinc salt and molybdate in an appropriate amount of water, and adding an amino acid and / or a salt thereof, a hydroxycarboxylic acid and / or a hydroxycarboxylate containing two carboxyl groups in the molecule to obtain a first dispersion;

[0036] dispersing the polymer in an appropriate amount of water to obtain a second dispersion;

[0037] While maintaining stirring, gradually add the second dispersion into the first dispersion, continue to maintain stirring, and mix evenly to obtain the phosphorus-free pre-filming agent.

[0038] According to a specific embodiment of the present invention, preferably, in the above preparation method, the solid content of the second dispersion is 10 wt%-50 wt%.

[0039] According to a specific embodiment of the present invention, preferably, the preparation method includes the following specific steps:

[0040] 1. Weigh a certain amount of water, add zinc salt and molybdate into the water, and stir until fully dissolved;

[0041] 2. Gradually add the amino acid (salt) or hydroxycarboxylic acid (salt) containing two carboxyl groups in the molecule to the solution obtained in step 1, stir thoroughly, and mix evenly;

[0042] 3. Weigh a certain amount of polymer into water to obtain a polymer aqueous solution, wherein the solid content of the polymer aqueous solution is generally 10 wt% to 50 wt%;

[0043] 4. While maintaining stirring, gradually add the polymer aqueous solution to the solution obtained in step 2, continue to stir, mix evenly, and prepare a homogeneous and stable phosphorus-free pre-filming agent.

[0044] All the above stirring is carried out at room temperature, and the order of material addition should not be changed. If the addition is not carried out according to the above steps, it may not be possible to obtain a homogeneous product.

[0045] The present invention also provides a water-cooled heat exchanger pre-filming method, which comprises the following steps:

[0046] The phosphorus-free pre-filming agent is added to the circulating cooling water within the circulating cooling water system, and the concentration of the various raw material components of the phosphorus-free pre-filming agent in the circulating cooling water reaches the concentration requirement of the pre-filming agent. The circulating cooling water in the circulating cooling water system is then continuously operated for an appropriate period of time to form an anti-corrosion protective film on the carbon steel surface within the circulating cooling water system. After the pre-filming is completed, normal operation and management can be resumed. The circulating cooling water system includes a water-cooled heat exchanger, a circulating water main line, a heat exchanger tube bundle, etc.

[0047] In the above pre-filming method, preferably, the amount of the phosphorus-free pre-filming agent added is 100-500 mg / L based on the mass of the circulating cooling water.

[0048] In the above pre-filming method, preferably, the calcium hardness of the circulating cooling water is 100-300 mg / L.

[0049] In the above pre-filming method, preferably, the mixing time of the pre-filming agent and the circulating cooling water is 24-72 hours, and the mixing temperature is 25-45°C.

[0050] In the above pre-filming method, preferably, the operating temperature is 15°C-35°C, more preferably 20°C-30°C.

[0051] In the above pre-filming method, preferably, during the operation, the flow rate of the circulating cooling water is 0.2-3 m / s, more preferably 1 m / s.

[0052] In the above pre-filming method, preferably, the running time is at least 24 hours.

[0053] Effects of the invention:

[0054] 1. The dosage of the agent of the present invention is low. The dosage of ordinary agents needs to reach about 300-600ppm to play a certain role. The addition amount of the phosphorus-free pre-filming agent of the present invention can reach 100ppm, and the performance of the obtained film is good, and the red dot test time can reach up to 30s.

[0055] 2. The phosphorus-free pre-filming agent of the present invention has a wide adaptability temperature range and can form a film at a relatively low temperature. The pre-filming temperature is reduced from the general 40°C to about 25°C. Therefore, the factory does not need to increase the heat load, saving costs and improving operating efficiency.

[0056] 3. The phosphorus-free pre-filming agent of this invention is adaptable to a wide range of water qualities, especially low-hardness water. Pre-filming can be performed with water as low as 100 mg / L calcium hardness. Therefore, for new systems, pre-filming can generally be performed directly based on the quality of the fresh make-up water, without the need for a pre-concentration run.

[0057] 4. The phosphorus-free pre-filming agent of the present invention has a fast film-forming time. Generally, the pre-filming operation takes more than 48 hours, while the phosphorus-free pre-filming agent of the present invention only takes 24 hours.

[0058] 5. The phosphorus-free pre-filming agent of the present invention does not contain phosphorus elements, and does not require special treatment after pre-filming. No large amount of wastewater is generated, and the agent can be directly transferred to normal operation.

[0059] 6. The raw material components of the phosphorus-free pre-filming agent of the present invention are relatively environmentally friendly and have no unpleasant odor. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] FIG1 is an appearance diagram of the pre-filmed test piece in the red dot test in Test Example 1.

[0061] FIG2 is a diagram showing the pre-filming effect under different calcium hardness conditions in Test Example 3 (25° C.).

[0062] FIG3a is an electrochemical impedance spectroscopy diagram at different pre-coating times in Test Example 4. FIG.

[0063] FIG3 b is an electrochemical impedance spectroscopy (EIS) Bode diagram of the test sample 4 at different pre-coating times. DETAILED DESCRIPTION

[0064] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present application, the technical solution of the present application is now described in detail below, but it should not be understood as limiting the scope of implementation of the present application.

[0065] Example 1

[0066] This embodiment provides a polymer, which is prepared by the following steps:

[0067] 1. Weigh 100g of polysuccinimide (molecular weight of about 2000) into a flask, add 100g of deionized water, stir at 40°C and mix well;

[0068] 2. Weigh 70 g of glutamic acid and dissolve it in 100 g of a 15 wt% sodium hydroxide aqueous solution;

[0069] 3. Gradually add the solution obtained in step 2 dropwise to the flask in step 1, maintain the temperature and stir, react for 3 hours, and cool naturally to room temperature;

[0070] 4. The polymer solution obtained in step 3 was precipitated with ethanol, washed and dried to obtain polymer A having a molecular weight of about 2500.

[0071] Example 2

[0072] This embodiment provides a phosphorus-free pre-filming agent, which is prepared by the following steps:

[0073] 1. Weigh 70g of water, add 8g of zinc sulfate heptahydrate and 2g of sodium molybdate into the water, and stir until fully dissolved;

[0074] 2. Weigh 5g of sodium L-glutamate and 5g of sodium gluconate, gradually add them to the solution obtained in step 1, stir thoroughly and mix well;

[0075] 3. Weigh 5 g of polymer A obtained in Example 1 and disperse it in water to obtain a polymer aqueous solution having a solid content of 50 wt %;

[0076] 4. While maintaining stirring, gradually add the polymer aqueous solution to the solution obtained in step 2, continue to stir, mix evenly, and prepare a homogeneous and stable phosphorus-free pre-filming agent.

[0077] The pre-coating effect was investigated at different pre-coating agent addition amounts and pre-coating temperatures. The pre-coating quality evaluation method was based on the "GB / T25149-2010 Test method for quality of carbon steel passivation film in chemical cleaning of industrial equipment - Red dot method".

[0078] Test Example 1

[0079] The water quality conditions of the circulating water used for testing are: calcium hardness 100ppm, alkalinity 100ppm, chloride ion 100ppm.

[0080] Temperature: 25℃, 35℃;

[0081] Pre-filming time: 48h;

[0082] Rotation speed of the test piece: 75 rpm.

[0083] The appearance results of the red dot test on the pre-filmed test piece are shown in Figure 1. The test results are shown in Table 1.

[0084] Table 1

[0085] From the test results of pre-film quality in Table 1, we can see that:

[0086] 1. The pre-filming agent of the present invention achieves excellent pre-filming effect at an extremely low injection concentration of 100ppm, while the injection concentration of similar products is generally above 300ppm;

[0087] 2. The pre-filming agent of the present invention can achieve a better pre-filming effect at a relatively low temperature, i.e., 25°C;

[0088] 3. The water quality of the circulating water does not change significantly after the pre-filming agent of the present invention, especially the turbidity does not change significantly, which is conducive to directly entering the stable operation stage after the pre-filming operation without the need for water replacement;

[0089] 4. When the pre-filming agent of the present invention is added at a higher concentration, the film test time far exceeds the standard requirement of 10s.

[0090] Test Example 2

[0091] The test standards in the following test cases are consistent with those in Test Case 1.

[0092] The water quality conditions of the circulating water used for testing are: calcium hardness 150mg / L, alkalinity 150mg / L.

[0093] Temperature: 25℃, 35℃;

[0094] Pre-filming time: 48h;

[0095] Rotation speed of the test piece: 75 rpm.

[0096] The evaluation results of membrane rupture time are shown in Table 2.

[0097] Table 2

[0098] Test Example 3

[0099] In order to simulate the water quality of fresh water in a purification plant in a certain area, the laboratory prepared simulated fresh water with different calcium hardness and alkalinity to investigate the effect of water quality on film formation. The results are shown in Table 3.

[0100] Test conditions:

[0101] Pre-filming agent dosage: 400mg / L;

[0102] Temperature: 25℃;

[0103] Pre-filming time: 48h;

[0104] Rotation speed of the test piece: 75 rpm.

[0105] The pre-coating effects under different calcium hardness conditions are shown in Figure 2 (25°C).

[0106] It can be seen from the test results in Table 3 that except for the poor pre-filming effect under water quality with a calcium hardness of 50 mg / L, the film-forming effects under other water qualities are good.

[0107] Table 3 Evaluation results of membrane rupture time

[0108] Test Example 4

[0109] Considering the time required for on-site pre-coating, the laboratory simulated the film formation effects at different pre-coating times. The results are shown in Table 4. The electrochemical impedance spectroscopy test results for different pre-coating times are shown in Figures 3a and 3b. The changes in the impedance arc and phase angle can be seen in Figures 3a and 3b, as well as the increase in the radius in the Nernquist plot, both indicate the gradual formation of a film on the metal surface.

[0110] Table 4

[0111] It can be seen from the test results in Table 4 that the phosphorus-free pre-filming agent of Example 2 has a faster film-forming time and can effectively form a film after 24 hours.

Claims

1. A phosphorus-free pre-filming agent, wherein: In terms of weight percentage, the raw material composition of the phosphorus-free pre-filming agent includes: Amino acids containing two carboxyl groups in the molecule and / or their salts: 1-10%; Hydroxycarboxylic acid and / or hydroxycarboxylate: 1-10%; Zinc salt: 1-10%; Molybdate: 1-5%; Polymer: 1-10%; Residual water; The amino acid and / or its salt containing two carboxyl groups in the molecule refers to an organic compound containing one basic amino group and at least two acidic carboxyl groups in the molecule; The hydroxycarboxylic acid and / or hydroxycarboxylate refers to a compound containing both a hydroxyl group and a carboxyl group in the molecular structure; The polymer is prepared by reacting polysuccinimide with an amino acid containing two carboxyl groups and / or a salt thereof; The mass ratio of the polysuccinimide to the amino acid containing two carboxyl groups and / or its salt is 2:1 to 8:

1.

2. The phosphorus-free pre-filming agent according to claim 1, wherein The mass ratio of the polysuccinimide to the amino acid containing two carboxyl groups and / or its salt is 4:1 to 6:

1.

3. The phosphorus-free pre-filming agent according to claim 1, wherein The amino acid and / or salt thereof containing two carboxyl groups in the molecule is selected from one or a combination of two or more of aspartic acid and its monovalent salts, cystine and its monovalent salts, glutamic acid and its monovalent salts, the compound represented by formula II, and the compound represented by formula III; Wherein, R is selected from an alkyl group of 1-10 carbons, an alkyl chain of 1-10 carbons with NH2, or an alkyl chain of 1-10 carbons with heteroatoms; Wherein, R1 and R2 are independently selected from an alkyl group of 1-10 carbon atoms, an alkyl chain of 1-10 carbon atoms with NH2, or an alkyl chain of 1-10 carbon atoms with heteroatoms.

4. The phosphorus-free pre-filming agent according to claim 1, wherein The molecular weight of the polysuccinimide is 400-4000.

5. The phosphorus-free pre-filming agent according to claim 1, wherein The hydroxycarboxylic acid and / or hydroxycarboxylate salt is selected from one or a combination of two or more of gluconic acid, tartaric acid, citric acid, salicylic acid, lactic acid, gentisic acid and salts thereof.

6. The phosphorus-free pre-filming agent according to claim 1, wherein The zinc salt includes zinc sulfate and / or zinc chloride.

7. The phosphorus-free pre-filming agent according to claim 1, wherein The molybdate includes sodium molybdate and / or ammonium molybdate.

8. The phosphorus-free pre-filming agent according to claim 1, wherein The molecular weight of the polymer is 500-5000.

9. The phosphorus-free pre-filming agent according to claim 8, wherein The molecular weight of the polymer is 1000-4000.

10. The phosphorus-free pre-filming agent according to claim 9, wherein: The molecular weight of the polymer is 2000-3000.

11. The phosphorus-free pre-filming agent according to claim 1 or 8, wherein: The polymer is a compound represented by formula I:

12. The method for preparing the phosphorus-free pre-filming agent according to any one of claims 1 to 11, comprising the following steps: Dispersing zinc salt and molybdate in an appropriate amount of water, adding an amino acid and / or a salt thereof, a hydroxycarboxylic acid and / or a hydroxycarboxylate containing two carboxyl groups in the molecule, to obtain a first dispersion; dispersing the polymer in an appropriate amount of water to obtain a second dispersion; While maintaining stirring, gradually add the second dispersion into the first dispersion, continue to maintain stirring, mix evenly, and obtain the phosphorus-free pre-filming agent.

13. The preparation method according to claim 12, wherein: The solid content of the second dispersion is 10 wt%-50 wt%.

14. A method for pre-filming a water-cooled heat exchanger, comprising the following steps: The phosphorus-free pre-filming agent described in any one of claims 1 to 11 is added to the circulating cooling water inside the circulating cooling water system, and then the circulating cooling water in the circulating cooling water system is continuously operated for an appropriate period of time to form an anti-corrosion protective film on the carbon steel surface inside the circulating cooling water system, wherein the circulating cooling water system includes a water-cooled heat exchanger.

15. The pre-filming method according to claim 14, wherein: Based on the mass of the circulating cooling water, the amount of the phosphorus-free pre-filming agent added is 100-500 mg / L.

16. The pre-filming method according to claim 14, wherein: The calcium hardness of the circulating cooling water is 100-300 mg / L.

17. The pre-filming method according to claim 14, wherein: The phosphorus-free pre-filming agent and the circulating cooling water are mixed for 24-72 hours at a mixing temperature of 25-45°C.

18. The pre-filming method according to claim 14, wherein: The operating temperature is 15°C-35°C, the flow rate of circulating cooling water during the operation is 0.2-3m / s, and the operation time is at least 24 hours.

19. The pre-filming method according to claim 18, wherein: The operating temperature is 20°C-30°C.

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