Cleaning method for copper pipes

Abstract

To provide a water treatment composition that provides excellent corrosion prevention effects for iron and copper materials without using water conditioners in an open-type cooling water system where the pH of the circulating water is low due to low hardness water quality and / or absorption of acidic gases, etc. [Solution] By providing a water treatment composition containing an alkaline agent, zinc, and an azole compound with a pH of 13.5 or higher, it is possible to provide a water treatment composition that is highly stable and has an excellent corrosion prevention effect on iron-based materials and copper materials.

Description

Technical Field

[0001] The present invention relates to a water treatment composition used for preventing corrosion and scale in a cooling water system such as a factory or a plant.

Background Art

[0002] In factories, plants, etc., water is used for cooling processes, etc., but problems such as precipitation of dissolved components called scale and corrosion of metals in contact with the water system often occur. Therefore, these are prevented by a water treatment composition containing various scale inhibitors and corrosion inhibitors. As examples of water treatment compositions, inorganic phosphoric acid, various organic phosphoric acids, anionic polymers, zinc, etc. are used, and these components are used in combination depending on the concentration of hardness components in the circulating water.

[0003] [[ID=I5]] For example, in low-hardness water quality, agents containing zinc are often used for cathodic corrosion prevention. Water treatment compositions containing zinc use zinc sulfate or zinc chloride as zinc, but for the stability of the water treatment composition, the pH is made acidic or neutral (Patent Documents 1 to 3).

[0004] Also, Patent Document 4 describes a water treatment agent for corrosion prevention containing an alkali metal hydroxide having a pH of 9 or more when diluted with water so that the volume becomes 10 times, but it lacks stability.

[0005] In a cooling water system such as a combine, industrial water is often used as makeup water, but in a cooling water system in the electronic industry field, etc., water with low hardness treated with an RO membrane or the like may be used as makeup water. Normally, in an open cooling water system, concentration of the circulating water occurs during operation, and the pH, calcium concentration required for cathodic corrosion prevention, and M alkalinity increase. However, since the treated water by an RO membrane or the like has a low calcium concentration and M alkalinity, in a cooling water system using these as makeup water, even if the concentration is increased, the pH hardly rises, and an increase in calcium and M alkalinity required for cathodic corrosion prevention does not occur.

[0006] In addition, depending on the cooling water system, the pH of the circulating water may decrease if the cooling tower absorbs acidic gases from the surrounding environment. Generally, heat exchangers are mainly made of copper, but piping is often made of iron, so corrosion prevention is necessary for both copper and iron materials.

[0007] As mentioned above, inorganic phosphoric acid, various organic phosphoric acid, and anionic polymers are used as corrosion inhibitors for iron-based materials, and these act to prevent anode corrosion. On the other hand, in the case of circulating water with low calcium concentration and M alkalinity, as described above, the cathode corrosion prevention effect is not obtained, leading to deep pitting corrosion. Therefore, when the calcium concentration and M alkalinity of the circulating water are low, zinc-based agents are often used, but because zinc-based agents are acidic, they tend to lower the pH of the circulating water when applied, requiring the use of an alkaline agent or other means to adjust the water quality. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 05-009761 [Patent Document 2] Japanese Patent Publication No. 2014-036912 [Patent Document 3] Japanese Patent Publication No. 2016-511790 [Patent Document 4] Japanese Patent Publication No. 2017-088993 [Overview of the project] [Problems that the invention aims to solve]

[0009] The object of the present invention is to provide a water treatment agent that can prevent corrosion of iron and copper materials in the above-mentioned open-type cooling water system without using water quality adjusters. [Means for solving the problem]

[0010] As a result of diligent research, the inventors have discovered a water treatment composition that contains zinc and other water treatment agent components and has a pH-raising effect by incorporating an alkaline agent and raising the pH to 13.5 or higher, thereby completing the present invention.

[0011] [1] A water treatment composition comprising an alkaline agent, a zinc compound, and an azole compound, characterized in that the pH of the composition is 13.5 or higher. [2][1] The water treatment composition described above, further comprising one or more selected from the group consisting of organic phosphonic acid, phosphinopolycarboxylic acid, phosphonocarboxylic acid, inorganic phosphoric acid compound, and carboxylic acid polymer. A water treatment composition according to [3] [1] to [2], further characterized by comprising a copolymer of acrylic acid and a sulfonic acid-based monoethylenically unsaturated monomer. A water treatment composition according to [4][1] to [2], further comprising an inorganic halogen-based disinfectant and an inorganic halogen stabilizer. A water treatment method characterized by adding the water treatment composition described in [5] [1] to [2] to a target water system. [Effects of the Invention]

[0012] By using the present invention, in an open-type cooling water system where the pH of the circulating water is low due to low hardness water quality and / or absorption of acidic gases, an excellent corrosion prevention effect on iron and copper materials can be obtained without using water conditioners. [Modes for carrying out the invention]

[0013] The present invention will be described in detail below, but is not limited to these descriptions. The water systems to which this invention applies are cooling water systems, particularly open-type cooling water systems and closed-type cooling water spraying systems, and are water systems having piping made of iron material such as carbon steel and / or copper and copper-containing alloys.

[0014] In this cooling water system, there is no restriction on the quality of makeup water. Usually, in addition to municipal water, groundwater, industrial water, etc., treated water obtained by treating drainage with a RO membrane or the like can be used.

[0015] The present invention is a water treatment composition containing an alkali agent, a zinc compound, and an azole-based compound, and is characterized in that the pH of the composition is 13.5 or more.

[0016] There is no particular limitation on the alkali agent contained in the water treatment composition of the present invention. Usually, lithium hydroxide, sodium hydroxide, potassium hydroxide, etc., which are hydroxides of alkali metals, can be used, and sodium hydroxide is preferably used. By setting the pH of the water treatment composition to 13.5 or more with these alkali agents, a stable water treatment composition in which zinc is dissolved can be obtained. From the viewpoint of stability, it is more preferably pH 13.7 or more, and particularly preferably pH 13.9 or more.

[0017] There is no particular limitation on the form of the zinc compound contained in the water treatment composition of the present invention. Usually, zinc oxide, zinc chloride, zinc phosphate, etc. can be used, and it is preferable to use zinc oxide from the viewpoint of cost.

[0018] The zinc compound contained in the water treatment composition of the present invention is considered to be dissolved as zincate ion ([Zn(OH)4] 2- ). However, when the pH is less than 13.5, it becomes zinc hydroxide (Zn(OH)2) and its solubility in water deteriorates, so it is considered that a stable water treatment composition cannot be obtained.

[0019] The zinc compound contained in the water treatment composition of the present invention can be dissolved in acids such as hydrochloric acid, sulfuric acid, and nitric acid, and alkalis such as sodium hydroxide and potassium hydroxide, and it is preferably dissolved in sulfuric acid among them.

[0020] The content of the zinc compound contained in the water treatment composition of the present invention is 0.01 to 10%, more preferably 0.1 to 5%. When the content of the zinc compound is less than 0.01%, in the water system to which the water treatment composition is applied, a good cathodic corrosion prevention effect on carbon steel cannot be obtained, and the corrosion prevention effect deteriorates. On the other hand, when the content of the zinc compound exceeds 10%, the stability of the water treatment composition decreases, which is not preferable.

[0021] There is no particular limitation on the azole compound contained in the water treatment composition of the present invention. For example, triazoles such as 1,2,3-benzotriazole and tolyltriazole, thiazoles such as 2-mercaptobenzothiazole and 2-(3'-aminopropyl)-benzothiazole, imidazoles such as 2-(5'-aminopentyl)-benzimidazole and 2-ethylimidazole, etc., or salts thereof can be used. By using these azole compounds, the corrosion of copper-based materials can be prevented.

[0022] The content of the azole compound contained in the water treatment composition of the present invention is 0.1 to 10%, more preferably 0.5 to 5%, and particularly preferably 1 to 3%. When the content of the azole compound is less than 0.1%, in the water system to which the water treatment composition is applied, a good corrosion prevention effect on copper-based materials cannot be obtained. When the content of the azole compound exceeds 10%, it leads to a decrease in the stability of the water treatment composition and an increase in cost, which is not preferable.

[0023] In the water treatment composition of the present invention, it is preferable to further contain one or more selected from the group consisting of organic phosphonic acids, phosphinopolycarboxylic acids, phosphonocarboxylic acids, inorganic phosphate compounds, and carboxylic acid polymers.

[0024] The above-mentioned organic phosphonic acids are organic compounds having one or more phosphono groups in their molecules. Specifically, examples include 1-hydroxyethylidene-1,1-diphosphonic acid, aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, and hexamethylenediaminetetramethylenephosphonic acid. From the viewpoint of corrosion prevention effect, 1-hydroxyethylidene-1,1-diphosphonic acid is particularly preferred.

[0025] The above-mentioned phosphinopolycarboxylic acids are compounds having one or more phosphino groups and two or more carboxyl groups in their molecule. Specifically, examples include bis-poly(2-carboxyethyl)phosphinic acid obtained by reacting acrylic acid with hypophosphorous acid, bis-poly(1,2-dicarboxyethyl)phosphinic acid obtained by reacting maleic acid with hypophosphorous acid, poly(2-carboxyethyl)(1,2-dicarboxyethyl)phosphinic acid obtained by reacting maleic acid with acrylic acid and hypophosphorous acid, bis-poly[2-carboxy-(2-carboxymethyl)ethyl]phosphinic acid obtained by reacting itaconic acid with hypophosphorous acid, and reaction products of acrylic acid with 2-acrylamido-2-methylpropanesulfonic acid and hypophosphorous acid. Particularly preferred are reaction products of maleic acid with acrylic acid and hypophosphorous acid, and reaction products of itaconic acid with maleic acid and hypophosphorous acid. Phosphinopolycarboxylic acids are commercially available from Italmatch under trade names such as BELCLENE500, BELSPERSE164, and BELCLENE400.

[0026] The phosphonocarboxylic acids mentioned above are organic compounds having one or more phosphono groups and one or more carboxyl groups in their molecules. Specifically, examples include 2-phosphonobutane-1,2,4-tricarboxylic acid, hydroxyphosphonoacetic acid, phosphonopolymaleic acid, and phosphonosuccinic acid, with 2-phosphonobutane-1,2,4-tricarboxylic acid and phosphonopolymaleic acid being preferred. Phosphonocarboxylic acids are commercially available from Rhodey under the trade name BRICORR288 and from Italmatch under the trade name BELCOR585.

[0027] The inorganic phosphate compounds mentioned above are inorganic compounds having a phosphate group or a phosphate skeleton in their molecule. Specifically, examples include phosphoric acid, alkali metal phosphates such as monosodium phosphate, disodium phosphate, monopotassium phosphate, and dipotassium phosphate, and condensed phosphates such as sodium pyrophosphate, sodium tripolyphosphate, and sodium hexametaphosphate.

[0028] Examples of the carboxylic acid polymers mentioned above include homopolymers of monoethylene unsaturated carboxylic acids and their water-soluble salts, copolymers of two or more different monoethylene unsaturated carboxylic acids and their water-soluble salts.

[0029] Examples of homopolymers of monoethylene unsaturated carboxylic acids include acrylic acid polymers, methacrylic acid polymers, maleic acid polymers, hydrolysates of maleic anhydride polymers, itaconic acid polymers, and fumaric acid polymers. Examples of copolymers of two or more different monoethylene unsaturated carboxylic acids include copolymers of acrylic acid and maleic acid, copolymers of acrylic acid and itaconic acid, copolymers of maleic acid and itaconic acid, copolymers of maleic acid and fumaric acid, terpolymers of acrylic acid, itaconic acid, and maleic acid, and terpolymers of acrylic acid, itaconic acid, and fumaric acid. Preferably, the copolymers are homomaleic acid polymers and copolymers of maleic acid with a copolymerizable monoethylene unsaturated monomer, and homoitaconic acid polymers and copolymers of itaconic acid with a copolymerizable monoethylene unsaturated monomer.

[0030] Examples of monoethylene unsaturated monomers copolymerizable with maleic acid or itaconic acid include fumaric acid; alkyl (meth)acrylates, hydroxyl alkyl (meth)acrylates; (meth)acrylamide, N-alkyl-substituted (meth)acrylamide; olefins having 2 to 8 carbon atoms such as ethylene, propylene, isopropylene, butylene, isobutylene, hexene, 2-ethylhexene, pentene, isopentene, octene, isooctene, etc.; vinyl alkyl ethers such as vinyl methyl ether and vinyl ethyl ether; and alkyl maleate esters, and one or more of these can be used. The molecular weight of the maleic acid-based polymer and the itaconic acid-based polymer is preferably 300 to 20,000, and more preferably 400 to 1,000, as a weight-average molecular weight.

[0031] The above-mentioned organic phosphonic acids, phosphinopolycarboxylic acids, phosphonocarboxylic acids, and carboxylic acid polymers are preferable to include in the water treatment composition of the present invention because they not only have a corrosion-preventive effect on carbon steel but also have a dispersion effect on crystalline scales such as calcium carbonate.

[0032] In the water treatment composition of the present invention, it is preferable to further include a copolymer of acrylic acid and a sulfonic acid-based monoethylene unsaturated monomer. The copolymer of acrylic acid and a sulfonic acid-based monoethylene unsaturated monomer has the effect of dispersing amorphous scale generated in aqueous systems.

[0033] In the copolymer of acrylic acid and a sulfonic acid-based monoethylene unsaturated monomer described above, there are no limitations on the sulfonic acid-based monoethylene unsaturated monomer, and examples include 2-(meth)acrylamide-methylpropanesulfonic acid, (meth)alyloxy-hydroxypropanesulfonic acid, conjugated dienesulfonates, styrenesulfonic acid, sulfoalkyl (meth)acrylate esters, sulfoalkyl (meth)allyl ethers, sulfopheno(meth)allyl ethers, (meth)allylsulfonic acid, etc. A particularly preferred copolymer is a copolymer of acrylic acid and 2-acrylamide-methylpropanesulfonic acid.

[0034] The content of organic phosphonic acid, phosphinopolycarboxylic acid, phosphonocarboxylic acid, inorganic phosphoric acid compound, and carboxylic acid polymer contained in the water treatment composition of the present invention is 0.1 to 15%, more preferably 0.5 to 10%, and particularly preferably 1 to 8%. If the content of the compounds is less than 0.1%, a sufficient scale dispersion effect cannot be obtained in the aqueous system to which the water treatment composition is applied, and if the content exceeds 15%, it leads to a decrease in the stability of the water treatment composition and an increase in cost, which is undesirable.

[0035] The water treatment composition in this invention may contain a disinfectant. The inclusion of a disinfectant enables corrosion prevention, scale prevention, and slime control with a single solution. The disinfectant components usable in this invention are reaction products of an inorganic halogen-based disinfectant and a halogen stabilizer. Suitable inorganic halogen-based disinfectants include hypochlorous acid and its salts, and hypobromous acid and its salts.

[0036] To stabilize the inorganic halogen-based disinfectants mentioned above, it is desirable to use halogen stabilizers. Inorganic halogen-based disinfectants alone have poor stability and cannot maintain an effective halogen concentration.

[0037] Compounds having amino, amide, imide, or imino groups can be used as halogen stabilizers, such as sulfamic acid, p-toluenesulfonamide, o-toluenesulfonamide, benzenesulfonamide, and saccharin, with sulfamic acid being particularly preferred. These halogen stabilizers react with inorganic halogen-based disinfectants to produce N-halides, thereby stabilizing the inorganic halogen-based disinfectants.

[0038] The mixing ratio of the inorganic halogen to the halogen stabilizer is 1:0.1 to 1:10 in molar ratio, but more preferably 1:0.2 to 1:5. If the amount of halogen stabilizer is too little relative to the inorganic halogen, a sufficient halogen stabilization effect cannot be obtained, and if it is too much, the stability of the water treatment composition will decrease.

[0039] The effective halogen concentration in the water treatment composition and the effective halogen concentration in the cooling water system in the present invention can be measured by known methods such as the diethyl-p-phenylenediammonium (DPD)-ammonium iron(II) sulfate titration method, the DPD colorimetric method, and the iodine titration method (see JIS K 0101-1991).

[0040] The amount of the water treatment composition of the present invention added is not particularly limited, but from the viewpoint of preventing corrosion and controlling the pH of the target water system, it is preferably 1 to 500 mg / L, more preferably 10 to 200 mg / L, and particularly preferably 30 to 150 mg / L relative to the volume of water in the target water system. If the amount added is less than 1 mg / L, corrosion cannot be sufficiently prevented and the pH in the target water system cannot be brought to an alkaline state, which is undesirable. Also, if it exceeds 500 mg / L, it will lead to increased costs, which is undesirable.

[0041] After adding the water treatment composition of the present invention, the pH of the target water system is preferably alkaline, more preferably 8 or higher, more preferably 8.2 or higher, and most preferably 8.5 or higher, from the viewpoint of preventing corrosion.

[0042] By adding the water treatment composition of the present invention, which has a pH of 13.5 or higher, to the target water system, the pH of the target water system can be made alkaline as described above without the need for a separate alkaline agent, thus offering high convenience. [Examples]

[0043] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0044] The water treatment compositions described in the Examples, Comparative Examples, and Reference Examples were formulated by adding the components (by weight) shown in Tables 1-3 and adjusting the pH of the water treatment composition with sodium hydroxide to match the values ​​shown in Tables 1-3. The formulation was carried out by adding each component while stirring with a stirrer in a plastic container, and the formulation was carried out while cooling the liquid temperature of the water treatment composition to below room temperature.

[0045] <Ingredients used in the test> • Zinc oxide (reagent: manufactured by Fujifilm Wako Pure Chemical Industries) • Phosphate (Reagent: Manufactured by Fujifilm Wako Pure Chemical Industries) • 72% sulfuric acid (reagent: manufactured by Fujifilm Wako Pure Chemical Industries) • HEDP (1-hydroxyethylidene-1,1-diphosphonic acid, trade name: BELCLENE 660LA, manufactured by Italmatch) • PBTC (2-phosphonobutane-1,2,4-tricarboxylic acid, trade name: BELCLENE 650, manufactured by Italmatch) • P-MA (50% polymaleic acid aqueous solution, product name: BELCLENE 200LA, manufactured by Italmatch) • AA-MA-P (35% aqueous solution of a copolymer of acrylic acid, maleic acid, and hypophosphorous acid (weight-average molecular weight 2,000)) • AA-AMPS (40% aqueous solution of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid (copolymerization ratio (mass) 60:40, weight-average molecular weight 10,000)) • BTA (1,2,3-benzotriazole, reagent manufactured by Fujifilm Wako Pure Chemical Industries) • 12% NaOCl (Sodium hypochlorite aqueous solution, reagent, manufactured by Fujifilm Wako Pure Chemical Industries) • Sulfamic acid (reagent, manufactured by Fujifilm Wako Pure Chemical Industries) • NaOH (sodium hydroxide, reagent, manufactured by Fujifilm Wako Pure Chemical Industries)

[0046] <Stability Evaluation> The water treatment compositions prepared as described above were left to stand in constant temperature baths at 40°C, 25°C, 5°C, and -5°C, and the presence or absence of precipitation was visually determined. At any temperature, if precipitation or precipitate was observed after one month, it was marked with "×", and if no precipitation or precipitate was observed, it was marked with "〇". Furthermore, if no precipitation was observed after two months, it was marked with "◎".

[0047] <Corrosion Test> The corrosion test was conducted using the following method. Test specimens were made of copper (C1220) and low-carbon steel (JIS G 3141SPCC-SB) with dimensions of 50mm × 30mm × 1mm and a surface area of ​​0.316 dm². These specimens were polished with #400 grit, degreased with acetone, dried, and their mass was measured. The water treatment compositions listed in Tables 1-3 were added to tap water at a concentration of 50 ppm, and the pH of the tap water was measured after the addition of the water treatment compositions. Then, in accordance with JIS K0100-1990 Industrial Water Corrosion Test Method (Rotation Method), 500 mL of the test solution was placed in a flask with a stirrer connected to a reflux condenser, and the flask was kept warm in a 40°C constant temperature bath. After mounting copper and carbon steel test pieces opposite each other in a test piece holder, the test pieces were immersed in the test solution, and the test piece holder was connected to the motor rotation shaft of the corrosion test apparatus. The test pieces were rotated at a linear speed of 0.3 m / sec for 3 days. After removing the test specimens three days later, corrosive products and scale deposits adhering to the surface were removed with a brush under running water. The specimens were then dried and their mass was measured. The corrosion rate [mdd] was then calculated using the following formula. A lower corrosion rate indicates a better corrosion prevention effect. Corrosion rate [mdd] = (Decrease in specimen [mg]) / {(Surface area of ​​specimen [dm2]) × (Number of test days [days])}

[0048] In Example 7 and Comparative Example 4, the effective halogen concentration of the water treatment composition was measured by the diethyl-p-phenylenediammonium (DPD)-ammonium iron(II) sulfate titration method. Specifically, a solution of the water treatment composition diluted 10,000 times with pure water was used as a sample, DPD, phosphate buffer, and potassium iodide were added, and the solution was titrated with ammonium iron(II) sulfate solution. The endpoint was defined as the point where the red color disappeared, and the effective halogen concentration (in Cl2 equivalent) was calculated.

[0049] The results of the stability test, the pH of the target water system after adding the water treatment composition, and the corrosion test results are shown in Tables 1-3. Note that Comparative Example 1 did not undergo a corrosion test because precipitation and sedimentation were observed. As shown in Examples 1-10, water treatment compositions with a pH of 13.5 or higher exhibited excellent stability and high corrosion prevention effects on copper materials and steel. Furthermore, as shown in Examples 9 and 10, when the pH of the water treatment composition was 13.7 or higher, the corrosion prevention effect was high and the stability was even better.

[0050] On the other hand, as in Comparative Example 1, stability was lacking when the pH was below 13.5, and as in Comparative Examples 2-4, when zinc or azole compounds were not included, the corrosion rate of low-carbon steel and copper was high, and a sufficient corrosion prevention effect could not be obtained. Furthermore, as shown in Example 7, the present invention can include an inorganic halogen-based disinfectant and an inorganic halogen stabilizer as a disinfectant, and an excellent corrosion prevention effect was obtained compared to Comparative Example 4, which does not contain zinc.

[0051] Reference Example 1 is an acidic water treatment composition containing zinc and azole compounds as formulated using conventional technology. When this water treatment composition was added to tap water with a pH of 7.2 at a concentration of 50 mg / L, the pH of the water system became 6.5, a decrease from the original pH. On the other hand, as shown in Examples 1 to 10, when the water treatment composition of the present invention was added, the pH rose to 8 or higher. It was found that by using the water treatment agent of the present invention, a sufficient corrosion prevention effect can be obtained even in water systems in a pH range where it is necessary to raise the pH of the water system, without using a separate alkaline agent.

[0052] [Table 1]

[0053] [Table 2]

[0054] [Table 3]

Claims

1. A water treatment composition comprising an alkaline agent, a zinc compound, and an azole compound, characterized in that the pH of the composition is 13.5 or higher.

2. A water treatment composition according to claim 1, further comprising one or more selected from the group consisting of organic phosphonic acid, phosphinopolycarboxylic acid, phosphonocarboxylic acid, inorganic phosphoric acid compound, and carboxylic acid polymer.

3. A water treatment composition according to claim 1 to 2, further characterized by comprising a copolymer of acrylic acid and a sulfonic acid-based monoethylene unsaturated monomer.

4. A water treatment composition according to claims 1 to 2, further comprising an inorganic halogen-based disinfectant and an inorganic halogen stabilizer.

5. A water treatment method characterized by adding the water treatment compositions of claims 1 to 2 to a target water system.

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