Method for cleaning copper-based piping

Abstract

To provide a method for cleaning less in influence to a copper-based piping and high in removal effect of slime dirt and soft dirt, in aqueous piping cleaning including a copper-based piping.SOLUTION: A method for cleaning piping in water systems, including copper-based piping, using a cleaning agent containing azole compounds and hydrogen peroxide, wherein the hydrogen peroxide concentration in the water system is set to 0.3% or higher. This allows for high cleaning performance while minimizing the corrosive impact on copper-based materials such as pipes and heat exchangers. Furthermore, by applying a film treatment to the inner surfaces of the piping with azole compounds before cleaning, the corrosion protection effect can be further enhanced.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for cleaning slime and soft stains in various water systems such as cooling water systems, various water systems in paper pulp manufacturing processes, various water systems in steel manufacturing processes, dust collection water systems, drainage systems, metal processing water systems such as cutting oil, and particularly in water systems in which copper-based materials are used. [Background technology]

[0002] In water systems such as cooling water systems, various process water systems used in pulp and paper manufacturing processes and steel manufacturing processes, and cutting oil systems, slime fouling consisting of bacteria, fungi, algae, etc. occurs within the system, causing microbial problems such as reduced heat transfer efficiency, clogged pipes, and corrosion of metal materials. In addition, organic matter and muddy fouling brought into the system can adhere to pipes, heat exchangers, etc., resulting in the formation of soft fouling that differs from hard scale. Unlike hard scale, this soft fouling adheres thickly and contains a lot of water, which causes a high rate of heat transfer failure, especially on the heat transfer surfaces of heat exchangers, and is a major problem.

[0003] As a means to solve these problems, cleaning methods have been proposed that involve reacting hypochlorous acid or hypobromous acid with nitrogen compounds such as ammonia or sulfamic acid to produce stable N-chloro compounds (bound chlorine) or N-bromo compounds (bound bromine), as described in Patent Documents 1 and 2, or that combine hydrogen peroxide with a hydrogen peroxide-decomposing enzyme.

[0004] However, cleaning with combined chlorine or combined bromine does not produce foam, so it is less effective at removing slime and soft dirt. Also, while hydrogen peroxide has an excellent cleaning effect, it is highly likely to induce pitting corrosion when copper-based materials are used as piping materials. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2013-22541 [Patent Document 2] Patent Publication No. 2013-244443 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a cleaning method for cleaning pipes in an aqueous system including copper-based pipes, which causes little corrosion and pitting of the copper-based pipes and is highly effective in removing slime stains and soft stains. [Means for solving the problem]

[0007] As a result of extensive research, the present inventors have found that by using a high concentration of hydrogen peroxide in combination with an azole compound, it is possible to obtain an excellent dirt removal effect without worrying about corrosion or pitting, even in aqueous systems containing copper-based piping.

[0008] [1] A method for cleaning pipes in an aqueous system including copper-based pipes using a cleaning agent containing an azole compound and hydrogen peroxide, characterized in that the concentration of hydrogen peroxide in the aqueous system is 0.3% or more. [2] A cleaning method characterized by adding a treatment agent containing an azole compound to a water system, coating the inner surface of a pipe, and then performing the cleaning described in [1]. [Effects of the Invention]

[0009] By using the present invention, it is possible to provide a high dirt removal effect with little effect on copper-based materials when cleaning slime and soft dirt in various water systems such as cooling water systems, various water systems in paper pulp manufacturing processes, various water systems in steel manufacturing processes, dust collection water systems, drainage systems, and water systems for metal processing such as cutting oil, particularly in water systems in which copper-based materials are used. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments for carrying out the present invention will be described, but the present invention is not limited to these. There are no particular restrictions on the water systems installed in various factories to which the dirt cleaning method of the present invention can be applied, and the method can be applied to any water system, including medium- to large-scale drainage systems, circulating cooling water systems, and other general water systems installed in oil refineries, petrochemical plants, power plants, etc., as well as relatively small-scale water supply and drainage systems and cooling water systems installed in buildings and small to medium-sized factories, etc. However, it is particularly preferable to apply the method to water systems that have piping or heat exchangers made of copper-based materials.

[0011] The fouling targeted by the present invention is not hard scale that forms and adheres to the heat transfer surface of a heat exchanger, but organic matter and muddy fouling brought into the system, fouling generally called slime fouling, which is a film-like adhesion of polysaccharides, which are metabolites of microorganisms, and fouling formed by the aggregation of fine particles contained in makeup water, etc. Among these, slime fouling is preferred because the present invention is more likely to be effective against it.

[0012] The material of the copper-based pipe to which the cleaning method of the present invention is applied is not particularly limited, but examples include pipes made of oxygen-free copper, tough pitch copper, phosphorus-deoxidized copper, red brass, brass, cupronickel, bronze, red copper, nickel silver, etc. Among these, the use of phosphorus-deoxidized copper is preferred because it makes it easier to achieve the effects of the present invention.

[0013] The cleaning agent used in the cleaning method of the present invention contains hydrogen peroxide. Hydrogen peroxide is commercially available in various concentrations from various manufacturers, and diluted versions of these can be used. Dilution is usually performed with water. There are no limitations on the type of water used for dilution, and for example, pure water, soft water, tap water, industrial water, groundwater, etc. can be used. There are no particular restrictions on the pH of the water used for dilution, but it is preferably 6.0 to 10.0. If the pH is less than 6, it will be corrosive to the piping material during cleaning, and if the pH exceeds 10, the hydrogen peroxide will decompose and the cleaning effect will not be achieved, which is undesirable.

[0014] The cleaning method of the present invention is characterized in that the concentration of hydrogen peroxide in the aqueous system is 0.3% or more. By adjusting the concentration to this level, when the cleaning agent is added to the aqueous system, the cleaning agent comes into contact with the surface of the copper-based material in the pipe and quickly and uniformly forms an oxide film, thereby preventing corrosion and pitting of the copper-based material. On the other hand, if the hydrogen peroxide concentration is less than 0.3%, the uniformity of the oxide film cannot be maintained and pitting corrosion is induced, which is undesirable.

[0015] The concentration of hydrogen peroxide in the aqueous system in the cleaning method of the present invention is not particularly limited as long as it is 0.3% or more, but is preferably 0.5% or more, and most preferably 1% or more. There is no particular upper limit, but it is preferably 5% or less, more preferably 3% or less. A hydrogen peroxide concentration exceeding 5% is not preferred because it increases costs and has a significant adverse effect on the human body.

[0016] There are no specific analytical methods for measuring the residual concentration of hydrogen peroxide in aqueous systems, and methods such as iodometric titration, potassium permanganate titration, and hydrogen peroxide electrode method can be selected depending on the conditions of the target aqueous system. However, for convenience, semi-quantitative test paper such as "Quantofix Peroxide 1000" (trade name) manufactured by MACHEREY-NAGEL can be used.

[0017] The cleaning agent used in the cleaning method of the present invention is characterized by containing an azole compound in addition to the hydrogen peroxide. The azole compound is not particularly limited, but may be benzotriazole, 5-aminotetrazole, 1-hydroxybenzotriazole, 5-phenylthiolbenzotriazole, 5-chlorobenzotriazole, 4-chlorobenzotriazole, 5-bromobenzotriazole, 4-bromobenzotriazole, 5-fluorobenzotriazole, 4-fluorobenzotriazole, naphthotriazole, tolyltriazole, 5-phenylbenzotriazole, 5-nitrobenzotriazole, 4-nitrobenzotriazole, mercaptobenzothiazole, 3-amino-5-mercapto-1,2,4-triazole, 2-(5-amino-pentyl)benzotriazole, 1-aminobenzotriazole, 5-methylbenzotriazole, benzotriazole-5-carboxylic acid, 4-methylbenzotriazole, 4-ethylbenzotriazole, 5-ethylbenzotriazole, 4-propylbenzotriazole, 5 ... benzotriazole, 4-isopropylbenzotriazole, 5-isopropylbenzotriazole, 4-n-butylbenzotriazole, 5-n-butylbenzotriazole, 4-isobutylbenzotriazole, 5-isobutylbenzotriazole, 4-pentylbenzotriazole, 5-pentylbenzotriazole, 4-hexylbenzotriazole, 5-hexylbenzotriazole, 5-methoxybenzotriazole, 5-hydroxybenzotriazole, dihydroxypropylbenzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]benzotriazole, 5-t-butylbenzotriazole, 5-(1,1-dimethylpropyl)-benzotriazole, 5-(1,1,3-trimethylbutyl)benzotriazole, 5-n-octylbenzotriazole, and 5-(1,1,3,3-tetramethylbutyl)benzotriazole can be used alone or in combination of two or more. From the viewpoint of corrosion prevention performance and cost, benzotriazole and tolyltriazole are preferred, and benzotriazole is most preferred.

[0018] In the cleaning method of the present invention, by using the azole compound in addition to hydrogen peroxide, the thickness of the oxide film formed on the surface of the copper-based material by hydrogen peroxide can be reduced. There is no limitation on the concentration of the azole compound in the aqueous system, but it is preferably 0.1 to 100 ppm, and particularly preferably 2 to 50 ppm. If the concentration of the corrosion inhibitor is less than 0.1 ppm, the effect is insufficient, and if it exceeds 100 ppm, there is a problem that the cost becomes high.

[0019] The cleaning agent used in the cleaning method of the present invention is preferably added to an aqueous system and then circulated or stirred using a pump, agitator, or the like. Circulation and stirring facilitates contact of the hydrogen peroxide in the cleaning agent with the dirt, improving the cleaning effect. There are no particular restrictions on the liquid temperature during cleaning, but it is preferable to adjust it to 10 to 50°C. If the liquid temperature is below 10°C, the decomposition of hydrogen peroxide is slowed, resulting in a longer cleaning time. However, if the liquid temperature exceeds 50°C, the decomposition of hydrogen peroxide is accelerated, resulting in a reduced cleaning effect.

[0020] In the cleaning method of the present invention, the cleaning time varies depending on the level of contamination in the system, but is typically 1 to 48 hours. Completion of cleaning is determined after the above-mentioned time has elapsed by measuring the transparency of the target water system. As cleaning is performed, contamination accumulated in the system is detached and dispersed into the water, resulting in a decrease in the transparency of the target water system and an increase in turbidity and suspended solids. The progress of the decrease in transparency and the increase in turbidity or suspended solids in the water system during cleaning can be tracked, and cleaning can be determined to be complete when the decrease in transparency or the increase in turbidity or suspended solids has almost stopped. Measurement of the turbidity of the target water system is in accordance with JIS K0101-1998, and measurements of the transparency and suspended solids are in accordance with JIS K0102-2008.

[0021] After the completion of the cleaning, it is preferable to add a hydrogen peroxide decomposition catalyst or the like to the cleaning water to decompose the remaining hydrogen peroxide, and then discard the water.

[0022] Furthermore, before the above cleaning, a treatment agent containing the above azole compound can be added to the aqueous system in advance, and the azole compound can be brought into contact with the copper material on the inner surface of the pipe to form a corrosion-resistant film. This treatment improves the effectiveness of preventing copper corrosion and pitting corrosion. This treatment will be referred to as the initial treatment hereinafter.

[0023] The azole compound used in the initial treatment is usually the above-mentioned azole compound dissolved in water, etc. In this case, an acid or alkali may be added to improve the solubility of the azole compound.

[0024] The concentration of the azole compound in the aqueous system during the initial treatment is preferably 1 ppm or more, and particularly preferably 2 to 50 ppm or more. If the amount added is less than 1 ppm, a sufficient anticorrosion film cannot be formed, and if it exceeds 100 ppm, the cost becomes high, which is not preferable.

[0025] During initial treatment, after adding the treatment agent containing the azole compound to the aqueous system, it is desirable to circulate or stir the solution using a pump or agitator to efficiently form a corrosion-resistant film. The time required for initial treatment is approximately 30 minutes to 10 hours. After the required treatment time has elapsed, some or all of the solution containing the azole compound is removed, and hydrogen peroxide solution containing the azole compound is added to the aqueous system to achieve the specified concentration, and the dirt is washed away.

[0026] In the cleaning method of the present invention, corrosion inhibitors, other slime control agents, slime removers, scale inhibitors, dirt dispersants, chelating agents, pH adjusters, surfactants, antifoaming agents, etc. may be used simultaneously within a range that does not reduce the effects of the present invention during cleaning. [Example]

[0027] Examples and effects of the present invention will be described below, but the present invention is not limited to these.

[0028] The test piece used was a stainless steel mesh (100 mesh) cut to 5 cm x 5 cm, with slime soil collected from the actual machine evenly adhered to it. The test piece was hung in a 500 mL beaker, and 500 mL of cleaning agent was added to achieve the concentration listed in Table 1, and stirring was started with a stirrer. After 24 hours, the condition of the dirt on the test piece was visually confirmed and the cleaning effect was judged. A dirt removal rate of over 90% was evaluated as ◎, over 80% to 90% as ○, 40% to 80% as △, and less than 40% as ×. When performing the initial treatment, the test piece was placed in a 500 mL beaker, and 500 mL of the treatment agent was added to achieve the concentration shown in Table 1. The mixture was stirred with a stirrer for 5 hours to coat the test piece, and then the above test was carried out to determine the cleaning effect.

[0029] During the test, in order to evaluate the effect on copper corrosion, in addition to the test specimens, a 3 cm × 5 cm × 1 mm copper (C1220 (phosphorus deoxidized copper)) test piece was also hung in the beaker, and the surface of the test piece after cleaning was observed and the corrosion weight loss was measured to evaluate the effect of the cleaning agent of the present invention on copper. In the surface observation of the test piece, if no pitting corrosion was visible by visual observation, it was evaluated as ○, and if pitting corrosion was visible, it was evaluated as ×. In addition, the corrosion weight loss was calculated by equation (1). The smaller the corrosion weight loss, the higher the effect. Corrosion weight loss [mg] = test piece weight before cleaning [mg] - test piece weight after cleaning [mg] (1)

[0030] The results of the examples and comparative examples are shown in Table 1. For the combined chlorine in Comparative Example 4, sodium hypochlorite and sulfamic acid were mixed in a molar ratio of 1:1, diluted to a predetermined concentration, and used in the test. The effective halogen concentration was measured by the diethyl-p-phenylenediamine (DPD)-ferrous sulfate titration method described in JIS K0101 "Testing Methods for Industrial Water" and other standards.

[0031] Table 1 shows that in the examples in which the present invention was applied, not only was there a high cleaning effect on slime stains, but also no pitting corrosion of copper was observed and corrosion weight loss was low. Furthermore, when the hydrogen peroxide concentration was 3%, the cleaning effect on slime stains was the best and the corrosion weight loss was the lowest. On the other hand, in Comparative Examples 1 and 2, which had a high cleaning effect on slime stains, the corrosion weight loss was large because no azole compound was contained during the initial treatment or cleaning. Furthermore, in Comparative Example 3, in which the hydrogen peroxide concentration was less than 0.3%, despite the inclusion of an azole compound during cleaning, the cleaning effect on slime stains was low, pitting corrosion occurred, and corrosion weight loss was high. Comparative Examples 4 and 5, which were cleaning methods without foaming, had a low cleaning effect on slime stains, and pitting corrosion also occurred when cleaning using combined chlorine in Comparative Example 4. From the above, it can be seen that the inclusion of an azole compound and hydrogen peroxide at a concentration of 0.3% or more provides a high cleaning effect and reduces the effect on copper corrosion.

[0032] [Table 1] BTA (1,2,3-benzotriazole, reagent, Fujifilm Wako Pure Chemical Industries, Ltd.) Hydrogen peroxide (reagent, Fujifilm Wako Pure Chemical Industries, Ltd.) Combined chlorine (a 1:1 molar reaction of sodium hypochlorite (reagent, Fujifilm Wako Pure Chemical Industries, Ltd.) and sulfamic acid (reagent, Fujifilm Wako Pure Chemical Industries, Ltd.) was used) Hydrazine (hydrazine monohydrate, reagent, Fujifilm Wako Pure Chemical Industries, Ltd.)

Claims

1. A method for cleaning pipes in an aqueous system including copper-based pipes using a cleaning agent containing an azole compound and hydrogen peroxide, wherein the concentration of hydrogen peroxide in the aqueous system is 0.3% or more.

2. 2. A cleaning method comprising adding a treating agent containing an azole compound to an aqueous system to form a coating on the inner surface of a pipe, and then carrying out the cleaning according to claim 1.

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