Corrosion inhibitor suitable for closed circulating water system as well as preparation method and application of corrosion inhibitor

Abstract

The invention relates to a corrosion inhibitor suitable for a closed circulating water system as well as a preparation method and application of the corrosion inhibitor. The corrosion inhibitor suitable for softened water as supplemented water for circulating water of the closed system consists of the following components in percentage by weight: 25 to 35 percent of tannic acid, 15 to 40 percent of lauramide betaine surfactant, 1.0 to 2.0 percent of azole compound, 1 to 3 percent of pH regulator and 33 to 64 percent of deionized water. The corrosion inhibitor has a good corrosion inhibition effect on carbon steel and copper equipment. The corrosion inhibitor is resistant to corrosion of high-concentration iron ions in closed circulating water and resistant to high temperature. The agent is free of phosphorus and nitrite, and is green and environment-friendly. And the performance is excellent, and the anti-corrosion performance is excellent in a closed circulation system with softened water as closed water supplement.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and in particular relates to a corrosion inhibitor suitable for a closed circulating water system and a preparation method and application thereof. Background Art

[0002] Circulating cooling water systems can be divided into two types: closed and open. During the production process, the cooling water in the closed system does not come into contact with the air during the circulation process, so the loss rate is very small, and the make-up water is softened water or demineralized water. Therefore, the focus of process control is on system corrosion prevention and prevention of microbial growth; the closed circulating water system will increase the water temperature after heat exchange with the material, but after heat exchange with cold air or low-temperature medium through the heat exchanger, the temperature will decrease to achieve recycling. Because the closed circulating water does not come into contact with other media or air during the heat exchange process, there is no obvious change in water quality indicators and no obvious loss of water volume. Therefore, direct discharge is not required.

[0003] Closed circulating water systems generally require the addition of corrosion inhibitors to control system corrosion and adjust the pH value to operate under alkaline conditions.

[0004] At present, the corrosion inhibitor formulas used by many domestic enterprises mainly include: chromate formula, nitrite formula, silicate formula, molybdate formula and phosphorus formula. Although the older chromate formula has good corrosion inhibition effect and low price, it is highly toxic and pollutes the environment, and has been banned at home and abroad; the classic nitrite formula is restricted in use due to its carcinogenic effect; the silicate formula has high requirements for water quality, and it is easy to produce silicate scale if it is not well controlled, which is difficult to remove. Molybdate is a closed system corrosion inhibitor, but it is expensive.

[0005] Composite nitrite corrosion inhibitor is the most common closed system corrosion inhibitor in China, with the characteristics of low price and easy use. As long as the reproduction of microorganisms is controlled, it can be stable for a long time in a closed system. However, nitrite corrosion inhibitor is an anodic hazardous corrosion inhibitor. If the concentration is insufficient, it may promote the corrosion of carbon steel equipment. The conventional composite nitrite agent in China has a high concentration. The composite agent of the nitrite system in water below 45°C generally controls the concentration of nitrite to be greater than 100mg / l, and the dosage of the agent usually reaches about 500mg / l. In high-temperature water with a temperature greater than 60°C, the concentration of nitrite needs to reach 200-300mg / l. If a closed water system leaks, nitrite itself is a carcinogen and will pollute the environment.

[0006] Chinese patent CN1052763C discloses a silicon-based corrosion inhibitor for a soft water closed circulation cooling system, and a molybdate formula can also be used; the molybdate formula is non-toxic and does not pollute the environment, but it is expensive and inconvenient to promote and use. On the one hand, the phosphorus-based formula will cause eutrophication of local waters due to the discharge of phosphorus. On the other hand, the phosphorus-based formula is often used in combination with zinc, and the pH value of the soft water system is generally around 8-10, zinc is easy to precipitate, thereby losing the corrosion inhibition effect, so this formula should not be used in a soft water closed system. Chinese patent CN102560501B discloses a corrosion inhibitor, which includes borates, alkali metal salts and / or alkalis, salts of rare earth elements, and polybasic organic carboxylates; the polybasic organic carboxylates are organic carboxylates with 6 or 7 carbon atoms. The corrosion inhibitor has a good corrosion inhibition effect on commonly used metal materials, and can be used for metal corrosion inhibition in closed circulation cooling water systems; and it is friendly to the environment and the human body. However, the application contains salts of rare earth elements, which are relatively expensive. Summary of the invention

[0007] In order to overcome the defects of existing closed system corrosion inhibitors such as large dosage, environmental pollution and high cost, the present invention provides a corrosion inhibitor suitable for a closed circulating water system and a preparation method and application thereof.

[0008] The corrosion inhibitor applicable to a closed circulating water system provided by the present invention is a green corrosion inhibitor.

[0009] The purpose of the present invention can be achieved by the following technical solutions:

[0010] The present invention first provides a corrosion inhibitor suitable for a closed circulating water system, the corrosion inhibitor comprising the following components in percentage by weight:

[0011]

[0012] And the sum of each component is 100%.

[0013] In one embodiment of the present invention, the corrosion inhibitor is composed of the following components in weight percentage:

[0014]

[0015]

[0016] In one embodiment of the present invention, the tannic acid is hydrolyzable tannic acid, which is the most commonly used tannin, has a molecular weight of 500-3000, and has an ester bond and a carboxylic acid group in its molecule.

[0017] In one embodiment of the present invention, the azole compound is selected from one or more of tolyltriazole, benzotriazole or mercaptobenzothiazole.

[0018] In one embodiment of the present invention, the pH adjuster is selected from sodium hydroxide, sulfuric acid or nitric acid.

[0019] In one embodiment of the present invention, the pH value of the corrosion inhibitor in a 1% by weight aqueous solution is 10.0-12.0.

[0020] Tannin can cause suspended matter in cooling water to condense and reduce turbidity, and form a tannic acid iron protective film on the surface of steel. Tannin can react well with dissolved oxygen to deoxidize, thereby achieving corrosion inhibition. Since tannic acid can convert rust into a dense tannic acid iron protective film, tannic acid has been widely studied and applied in the protection and restoration of iron cultural relics in recent years. Tannic acid molecules contain a certain amount of bisphenol or triphenol groups, which play a very important role in protecting metal surfaces. However, when tannic acid is used alone as a corrosion inhibitor, the dosage is large and the effect is not obvious.

[0021] In the present invention, lauramide betaine is one of the products of the alkylamide betaine series, is a light yellow transparent liquid, has excellent surface activity, bactericidal property and corrosion inhibition performance.

[0022] The present invention further provides a method for preparing the corrosion inhibitor suitable for the closed circulating water system, wherein tannic acid, lauramide betaine, a pH regulator, an azole compound and deionized water are mixed to obtain the corrosion inhibitor suitable for the closed circulating water system.

[0023] The present invention further provides the use of the corrosion inhibitor suitable for a closed circulating water system, and the corrosion inhibitor suitable for a closed circulating water system is added into the closed circulating water system.

[0024] In one embodiment of the present invention, the corrosion inhibitor is used in a concentration of 60 to 400 mg / L in the closed-circulation cooling water.

[0025] In one embodiment of the present invention, the closed circulating water system is a closed circulating system using softened water as replenishment water.

[0026] In one embodiment of the present invention, the applicable temperature of the closed circulating water system is room temperature-80°C.

[0027] The corrosion inhibitor of the present invention uses tannic acid as a main component, however, the effect of tannic acid when used alone is not good. In a closed circulation system with softened water as water replenishment, the single dosage needs to reach 80 mg / l at a temperature of 45°C to reduce the carbon steel corrosion rate of the closed water to below 0.1 mm / a.

[0028] In the scheme of the present invention, tannic acid is combined with lauramide betaine, and the synergistic effect of the two is very obvious. The dosage of tannic acid can be reduced to 10 mg / l, and the corrosion rate of carbon steel material is much less than 0.01 mm / a. Since lauramide betaine is an amphoteric surfactant with extremely strong permeability, the corrosion inhibitor can be quickly infiltrated into the carbon steel metal surface, reducing the surface tension of tannic acid in aqueous solution, significantly increasing the diffusion rate of tannic acid, and ensuring that tannic acid can be easily diffused from aqueous solution to the metal surface, thereby playing a corrosion inhibition role. Tannic acid has a strong antioxidant, which can chelate the iron ions on the surface of carbon steel equipment to form a dense three-dimensional mesh hydrophobic complex, which plays a role in protecting carbon steel equipment.

[0029] On the other hand, tannic acid is easily adsorbed by some divalent and trivalent cations in water. Commonly used natural water contains a large amount of calcium and magnesium cations. These cations undergo adsorption and polymerization reactions with tannic acid, reducing the amount of tannic acid that diffuses to the metal surface. In order for tannic acid in natural water to play a good corrosion inhibition role, the dosage of the agent is relatively large. However, in softened water, the conductivity is low, generally less than 20us / cm, which means that the ion content in the water is particularly low, basically zero. In this way, tannic acid used in softened water is not easily lost by ion adsorption in water. Most of the tannic acid diffuses to the metal surface. In addition, the penetration of lauramide betaine accelerates the reaction between tannic acid and iron ions in carbon steel, and quickly generates a dense tannic acid iron protective layer.

[0030] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0031] 1) The components of the corrosion inhibitor of the present invention have good synergistic effects, forming a corrosion inhibition synergistic mode of adsorption-deposition coverage-cathode control, so that the corrosion inhibitor has excellent corrosion inhibition performance.

[0032] 2) In the corrosion inhibitor of the present invention, tannic acid can cause suspended matter in cooling water to produce coagulation effect to reduce turbidity, and form a layer of tannic acid iron protective film on the surface of steel, and tannic acid can react well with dissolved oxygen to deoxygenate, thereby achieving corrosion inhibition.

[0033] 3) In the corrosion inhibitor of the present invention, the component lauramide betaine has excellent surface active properties, can quickly penetrate into the metal surface, and play an adsorption, deposition and covering role on the metal surface. It can also well cover the pitting source, inhibit the electron transfer in the galvanic cell reaction process, and thus block the corrosion process. The occurrence of pitting corrosion is greatly inhibited. At the same time, it also has a certain bactericidal function.

[0034] 4) Since the water quality of the closed water system is stable and there are no various oxidizing and reducing substances in the system, the corrosion inhibitor of the present application can determine the effective concentration of the agent by regularly testing the tannin content in the agent. The specific principle is: phosphotungstomolybdic acid is reduced in an alkaline solution to generate a dark blue compound, the depth of which is proportional to the tannin content, and then compared with the standard for quantitative analysis.

[0035] 5) The corrosion inhibitor has a good corrosion inhibition effect on carbon steel and copper equipment. The corrosion inhibitor is resistant to corrosion by high concentrations of iron ions in closed circulating water and is resistant to high temperatures. The agent is phosphorus-free and nitrite-free, and is green and environmentally friendly. It has excellent performance and has excellent anti-corrosion properties in a closed circulation system where softened water is used as closed water replenishment.

[0036] 6) The components of the corrosion inhibitor of the present invention have good synergistic effects. When the temperature is below 45°C, the tannin agent is used alone, and the dosage needs to be 80 mg / l to control the corrosion rate of carbon steel to be less than 0.10 mm / a. When lauramide betaine is added alone, the dosage needs to be 200 mg / l to control the corrosion rate of carbon steel to be less than 0.10 mm / a. However, according to the dosage of the agent of the present invention, the addition of 40 ppm of this agent can control the corrosion rate of carbon steel material to be less than 0.1 mm / a. In softened water with trivalent iron ions less than 2.0 mg / l, the addition of 60 ppm of this agent can control the corrosion rate of carbon steel material to be less than 0.1 mm / a. Even if the iron ions in the softened water are as high as 30 mg / l, the addition of 200 mg / l of this product can also control the corrosion of carbon steel material. In high-temperature closed water with a temperature of 80°C, the addition of 200 mg / l of this product can control the corrosion of carbon steel material. DETAILED DESCRIPTION

[0037] The present invention is described in detail below with reference to specific embodiments.

[0038] Embodiment 1:

[0039] The corrosion inhibitor of this embodiment is composed of the following components in weight percentage:

[0040] Tannic acid: 30%;

[0041] Lauramide Betaine 22%

[0042] pH adjuster (sodium hydroxide) 1.0%

[0043] Azoles (methylbenzotriazole) 2.0%

[0044] Deionized water 45%.

[0045] According to the national standard GB / T18175-2014, a rotating coupon test was carried out to soften the water at a temperature of 45°C and a rotation speed of 72 rpm. After adding the reagent, the pH of the water was adjusted to 8.0-8.5 with 1% sodium hydroxide solution.

[0046] Tannic acid and lauryl amide betaine were added separately for comparison.

[0047] Specific test results:

[0048] Table 1 Corrosion rate of carbon steel material with tannic acid

[0049]

[0050] Table 2 Corrosion rate of carbon steel material after adding lauramide betaine

[0051]

[0052] Table 3 Corrosion rate of carbon steel and brass materials after adding corrosion inhibitor in Example 1

[0053]

[0054] Table 4 Corrosion rate of carbon steel material with corrosion inhibitor added under the condition of 2.0 mg / l iron ion in water

[0055]

[0056] Table 5 Corrosion rate of carbon steel material with corrosion inhibitor at different iron ion concentrations

[0057]

[0058] Table 6 Corrosion rate of carbon steel and brass materials with corrosion inhibitor added at 80℃

[0059]

[0060] From the above results, it can be seen that there is a good synergistic effect between the components of the corrosion inhibitor.

[0061] Example 2

[0062] A polysilicon energy enterprise in Xinjiang has newly built a closed circulation system. The closed water uses desalted water after RO membrane treatment. The closed water has a low temperature of 6-7°C and a high temperature of 20-30°C. The system capacity is 2,000 tons. After the system is cleaned and pre-membrane, the total iron ion concentration in the closed water is 4-6 mg / l, far exceeding the design standard of iron ion concentration less than 1.0 mg / l. Add 200 ppm of the corrosion inhibitor of Example 1, slowly replace the closed water, maintain the corrosion inhibitor concentration of Example 1 in the closed water greater than 200 mg / l, and after more than 3 months of replacement of the closed water, the total iron ion concentration in the water reaches the design standard. During the 3-month replacement period, carbon steel and brass coupons were installed in the closed water system. The corrosion rates of the carbon steel coupons were 0.012, 0.003, and 0.001 mm / a, respectively, and the corrosion rates of the brass coupons were less than 0.005 mm / a.

[0063] Example 3

[0064] A diesel engine manufacturer in Weifang, Shandong, needs to use confined water to test and inspect the engine. The inspection time of each engine is about 3-6 hours. Softened water treated with RO membrane is used. The maximum temperature of the confined water does not exceed 60°C. The material inside the engine is cast iron. After the engine is inspected, the tested confined water is collected in the water tank. The inspection procedure was to replace the water once a week. 400-600 mg / l of the corrosion inhibitor of Example 1 is added, and a cast iron carbon steel monitoring test piece is installed. The surface of the monitoring test piece is rust-free, and the corrosion rate is less than 0.01 mm / a. The replacement cycle of the confined water is also changed to once a month.

[0065] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A corrosion inhibitor suitable for a closed circulating water system, characterized in that: The corrosion inhibitor is composed of the following components in weight percentage: And the sum of each component is 100%.

2. A corrosion inhibitor suitable for a closed circulating water system according to claim 1, characterized in that: The corrosion inhibitor is composed of the following components in weight percentage:

3. A corrosion inhibitor suitable for a closed circulating water system according to claim 1 or 2, characterized in that: The molecular weight of the tannic acid is 500-3000, and the molecule has an ester bond and a carboxylic acid group.

4. A corrosion inhibitor suitable for a closed circulating water system according to claim 1 or 2, characterized in that: The azole compound is selected from one or more of tolyltriazole, benzotriazole or mercaptobenzothiazole.

5. A corrosion inhibitor suitable for a closed circulating water system according to claim 1 or 2, characterized in that: The pH adjuster is selected from sodium hydroxide, sulfuric acid or nitric acid.

6. A corrosion inhibitor suitable for a closed circulating water system according to claim 1 or 2, characterized in that: The pH value of the corrosion inhibitor in a 1% by weight aqueous solution is 10.0-12.

0.

7. The method for preparing a corrosion inhibitor suitable for a closed circulating water system according to claim 1 or 2, characterized in that: Tannic acid, lauramide betaine, a pH regulator, an azole compound and deionized water are mixed to obtain the corrosion inhibitor suitable for a closed circulating water system.

8. The use of the corrosion inhibitor suitable for a closed circulating water system according to claim 1 or 2, characterized in that: The corrosion inhibitor suitable for a closed circulating water system is added into the closed circulating water system.

9. The use according to claim 8, characterized in that: The corrosion inhibitor is used in a concentration of 60-400 mg / L in closed-circulation cooling water.

10. The use according to claim 8, characterized in that: The closed circulating water system is a closed circulating system using softened water as replenishment water; The applicable temperature of the closed circulating water system is room temperature - 80°C.

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