Cleaning liquid for scale removal

Abstract

The present invention provides a cleaning liquid for scale removal, excellent in scale cleaning and corrosion inhibition. The present invention relates to a cleaning liquid for scale removal, comprising water, a fluorine compound, an inorganic acid, a surfactant, and a polyvalent carboxylic acid, and having a pH of less than 6.

Description

Descaling cleaning solution

[0001] The present invention relates to a descaling cleaning solution.

[0002] Scale forms on the surfaces of metal materials that make up pipes and other structures due to the deposition of inorganic salts such as calcium, magnesium, and silica that dissolve in the water that flows through the pipes. The scale that forms in high-temperature environments such as geothermal power plants and heat exchangers where metal materials come into contact with water is made of chemically stable, insoluble substances such as silica. Scale removal cleaning solutions containing fluorine compounds are used to remove scale from metal surfaces, especially silica scale.

[0003] Patent Document 1 describes a scale remover for removing silica scale, which contains ammonium fluoride or acidic ammonium fluoride. Patent Document 2 describes a scale remover containing silicon dioxide (SiO ２ The document describes a chemical cleaning solution for dissolving and removing scale, the chemical cleaning solution containing fluoride as a main component, and containing at least one acid fluoride.

[0004] Fluorine compounds are also used to remove scale made of metal oxides. Patent Documents 3 and 4 describe descaling agents containing fluorine compounds as removers for scale made of metal oxides that is formed under high-temperature conditions, such as welding of metal materials.

[0005] Meanwhile, although descaling cleaning solutions containing fluorine compounds generally have excellent scale cleaning properties, they may react not only with scale but also with the metal materials constituting the piping, causing corrosion of the metal materials. Furthermore, when attempts are made to suppress the corrosiveness to metal materials and improve the corrosion prevention properties of the cleaning agent, the scale cleaning properties tend to decrease. Therefore, there is a demand for descaling cleaning solutions that combine high scale cleaning properties and high corrosion prevention properties.

[0006] Japanese Patent Application Laid-Open No. 62-247089 Japanese Patent Application Laid-Open No. 63-176486 Japanese Patent Application Laid-Open No. 2021-147660 Japanese Patent Application Laid-Open No. 2022-100934

[0007] An object of the present invention is to provide a cleaning solution for removing scale that has excellent scale cleaning properties and excellent anticorrosion properties.

[0008] The present inventors have discovered that by combining a fluorine compound, an inorganic acid, a surfactant, and a polycarboxylic acid and adjusting the pH to less than 6, or by combining a fluorine compound, an inorganic acid, a surfactant, and a nitrogen-containing heterocyclic compound and adjusting the pH to less than 6, it is possible to achieve both high scale cleaning properties and high corrosion prevention properties, and have completed the present invention.

[0009] That is, the present invention includes the following aspects: <1> A scale removal cleaning liquid containing water, a fluorine compound, an inorganic acid, a surfactant, and a polycarboxylic acid, and having a pH of less than 6.

[0010] <2> The scale removal cleaning liquid according to item 1, further comprising a nitrogen-containing heterocyclic compound.

[0011] <3> The scale removal cleaning liquid according to item 1 or 2, wherein the content of the polycarboxylic acid is 10 to 10,000 parts by mass relative to 100 parts by mass of the fluorine compound.

[0012] <4> The scale removal cleaning liquid according to any one of Items 1 to 3, wherein the polycarboxylic acid is a polycarboxylic acid having a hydroxy group.

[0013] <5> A scale removal cleaning solution containing water, a fluorine compound, an inorganic acid, a surfactant, and a nitrogen-containing heterocyclic compound, and having a pH of less than 6.

[0014] <6> The scale removal cleaning liquid according to item 2 or 5, wherein the content of the nitrogen-containing heterocyclic compound is 1 part by mass or more relative to 100 parts by mass of the surfactant.

[0015] <7> The scale removal cleaning liquid according to any one of Items 2, 5, and 6, wherein the nitrogen-containing heterocyclic compound is one or more selected from the group consisting of imidazoles, triazoles, and benzothiazoles.

[0016] <8> The scale removal cleaning liquid according to any one of items 1 to 7, wherein the content of the surfactant is 0.01 parts by mass or more relative to 100 parts by mass of the fluorine compound.

[0017] <9> The scale removal cleaning liquid according to any one of items 1 to 8, which is for removing scale adhering to the surface of an iron-based metal made of Fe or an Fe alloy, or a copper-based metal made of Cu or a Cu alloy.

[0018] <10> The scale removal cleaning liquid according to any one of items 1 to 9, further comprising a rust inhibitor.

[0019] <11> A method for removing scales, comprising contacting the scale removing cleaning solution according to any one of items 1 to 10 with a metal material having scales attached thereto.

[0020] <12> The scale removal method according to item 11, wherein the metal material is an iron-based metal made of Fe or an Fe alloy, or a copper-based metal made of Cu or a Cu alloy.

[0021] <13> The scale removal method according to item 11 or 12, wherein the scale is silica scale.

[0022] According to the present invention, it is possible to provide a cleaning solution for removing scale that has excellent scale cleaning properties and excellent anticorrosion properties.

[0023] <<First scale removal cleaning liquid of the present invention>> The first scale removal cleaning liquid of the present invention contains water, a fluorine compound, an inorganic acid, a surfactant, and a polycarboxylic acid, and has a pH of less than 6. Note that, hereinafter, the first scale removal cleaning liquid of the present invention and the second scale removal cleaning liquid of the present invention described below may be collectively referred to as the scale removal cleaning liquid of the present invention or simply as the scale removal cleaning liquid.

[0024] <Water> The scale removal cleaning solution of the present invention is prepared by dissolving and mixing each component in water. The water is not particularly limited, and examples include various types of water such as pure water, ion-exchanged water, tap water, and industrial water. The water content in the scale removal cleaning solution used in actual scale removal is preferably 60 to 90 mass %, and more preferably 75 to 87 mass %.

[0025] <Fluorine Compound> The fluorine compound is not particularly limited as long as it liberates fluorine ions, and known compounds can be used. Examples of fluorine compounds that serve as a source of fluorine ions include hydrogen fluoride, acidic sodium fluoride (sodium hydrogen fluoride), acidic ammonium fluoride (ammonium hydrogen fluoride), fluorotitanic acid, fluorozirconic acid, fluorosilicic acid, ammonium fluoride, sodium fluoride, potassium fluoride, and potassium hydrogen difluoride. These compounds can be used alone or in combination of two or more. From the viewpoint of scale solubility, the fluorine compound is preferably hydrogen fluoride, acidic ammonium fluoride, or ammonium fluoride, and more preferably ammonium acid fluoride.

[0026] From the viewpoint of scale cleaning ability and corrosion prevention, the content of the fluorine compound in the scale removal cleaning solution is preferably 0.1 to 10 mass%, more preferably 1 to 5 mass%. When the fluorine compound is acid ammonium fluoride or ammonium fluoride, the content of acid ammonium fluoride or ammonium fluoride in the scale removal cleaning solution is preferably 0.1 to 10 mass%, more preferably 1 to 5 mass%. The content of acid ammonium fluoride or ammonium fluoride in the scale removal cleaning solution may be 4 mass% or less. When the fluorine compound is hydrogen fluoride, the content of hydrogen fluoride in the scale removal cleaning solution is preferably 0.1 to 0.5 mass%.

[0027] <Inorganic Acid> The inorganic acid is not particularly limited, and examples thereof include hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, and boric acid. These may be used alone or in combination of two or more. When the scale removal cleaning solution contains an inorganic acid, the scale cleaning ability can be improved. From the viewpoints of scale cleaning ability and corrosion prevention, the inorganic acid is preferably hydrochloric acid.

[0028] The content of inorganic acid in the scale removal cleaning solution is preferably 15% by mass or less, more preferably 10% by mass or less. From the viewpoint of scale cleaning performance, the lower limit of the content of inorganic acid is, for example, preferably 1% by mass or more, more preferably 2.5% by mass or more. Note that the content of inorganic acid means the mass % concentration of inorganic acid as a solute in the scale removal cleaning solution.

[0029] <Surfactant> The surfactant is not particularly limited, and for example, at least one surfactant selected from the group consisting of cationic surfactants, anionic surfactants, nonionic surfactants, and amphoteric surfactants may be used. From the viewpoint of corrosion prevention, the scale removal cleaning liquid of the present invention preferably contains at least one surfactant selected from the group consisting of cationic surfactants, nonionic surfactants, and amphoteric surfactants, and more preferably contains at least one surfactant selected from the group consisting of cationic surfactants and nonionic surfactants.

[0030] <Cationic Surfactant> The cationic surfactant is not particularly limited, but for example, cationic surfactants such as quaternary ammonium salt type, pyridinium salt type, and alkylamine salt type can be used. These can be used alone or in combination of two or more. When the scale removal cleaning liquid contains a cationic surfactant, corrosion prevention can be improved.

[0031] The quaternary ammonium salt type cationic surfactant is not particularly limited, but examples thereof include alkyltrimethylammonium salts (oleyltrimethylammonium chloride, etc.), dialkyldimethylammonium salts, alkylbenzalkonium salts, N,N-dialkyloyloxyethyl-N-methyl, N-hydroxyethylammonium salts, and alkylbenzyldimethylammonium salts.

[0032] The pyridinium salt-type cationic surfactant is not particularly limited, and examples thereof include alkylpyridinium salts. Examples of alkylpyridinium salts include laurylpyridinium chloride and cetylpyridinium. From the viewpoint of solubility, the alkylpyridinium salt is preferably one in which the alkyl group has 12 or less carbon atoms, and laurylpyridinium chloride is more preferred. From the viewpoint of solubility, the alkylpyridinium salt may also be one in which the alkyl group has 10 or less carbon atoms. Commercially available products may be used as the pyridinium salt-type cationic surfactant. Examples of commercially available products include Takesurf B-251 (laurylpyridinium chloride, manufactured by Takemoto Yushi Co., Ltd.).

[0033] The alkylamine salt type cationic surfactant is not particularly limited, but examples thereof include monoalkylamine salts, dialkylamine salts, trialkylamine salts, etc. The alkyl group contained in the alkylamine salt preferably has 8 to 18 carbon atoms, and the alkylamine salt may be a mixture of alkylamine salts each having an alkyl group with 8 to 18 carbon atoms. Commercially available alkylamine salt type cationic surfactants include Rheomix C (alkyl (C8 to C18) amine acetate, manufactured by Lion Specialty Chemicals Co., Ltd.).

[0034] From the viewpoint of corrosion prevention, the cationic surfactant is preferably a pyridinium salt type cationic surfactant or an alkylamine salt type cationic surfactant, more preferably a pyridinium salt type cationic surfactant, further preferably an alkylpyridinium salt, and particularly preferably laurylpyridinium chloride.

[0035] From the viewpoint of corrosion prevention, the content of the cationic surfactant in the scale removal cleaning solution is preferably 0.0001% by mass or more, more preferably 0.001% by mass or more, and even more preferably 0.1% by mass or more. The upper limit of the content of the cationic surfactant is not particularly limited, but is, for example, preferably 5% by mass or less, more preferably 3% by mass or less.

[0036] <Nonionic surfactant> The nonionic surfactant is not particularly limited, and known nonionic surfactants can be used. Examples of nonionic surfactants include amine oxides, glycerin fatty acid esters, sorbitan fatty acid esters, alkyl polyglucosides, sucrose fatty acid esters, alkyl sugar amides, polyglycerin fatty acid esters, polyoxyalkylene alkyl ethers, fatty acid alkanolamides, polyoxyalkylene hydrogenated castor oil, and alkyl monoglyceryl ethers. When the scale removal cleaning solution contains a nonionic surfactant, corrosion prevention can be improved.

[0037] From the viewpoint of corrosion prevention, the nonionic surfactant is preferably an amine oxide surfactant. Examples of amine oxide surfactants include alkylamine oxides such as N,N-dimethyldecylamine oxide, dodecyldimethylamine oxide, coconut alkyl dimethylamine oxide, and tetradecyldimethylamine oxide. Commercially available nonionic surfactants include Cadenax DM10D-W (N,N-dimethyldecylamine oxide, manufactured by Lion Specialty Chemicals Co., Ltd.), Cadenax DM12D-W(C) (dodecyldimethylamine oxide, manufactured by Lion Specialty Chemicals Co., Ltd.), Cadenax DMC-W (coconut alkyl dimethylamine oxide, manufactured by Lion Specialty Chemicals Co., Ltd.), and Cadenax DM14D-N (tetradecyldimethylamine oxide, manufactured by Lion Specialty Chemicals Co., Ltd.).

[0038] From the viewpoint of corrosion prevention, the content of the nonionic surfactant in the scale removal cleaning solution is preferably 0.1 mass% or more, more preferably 0.5 mass% or more. The upper limit of the content of the nonionic surfactant is not particularly limited, but is, for example, preferably 5 mass% or less, more preferably 3 mass% or less.

[0039] From the viewpoint of corrosion prevention, the scale removal cleaning liquid of the present invention preferably contains at least one surfactant selected from the group consisting of cationic surfactants and amine oxide surfactants, and more preferably contains at least one surfactant selected from the group consisting of pyridinium salt type cationic surfactants, alkylamine salt type cationic surfactants, and amine oxide surfactants.

[0040] <Polycarboxylic Acid> The polycarboxylic acid is not particularly limited as long as it has two or more carboxyl groups, and examples thereof include dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, malic acid, phthalic acid, isophthalic acid, terephthalic acid, and tartaric acid; tricarboxylic acids such as tricarballylic acid, citric acid, and trimellitic acid; tetracarboxylic acids such as ethylene tetracarboxylic acid and butane tetracarboxylic acid; and polycarboxylic acids containing nitrogen atoms such as EDTA (ethylenediaminetetraacetic acid). These may be used alone or in combination of two or more. By including a polycarboxylic acid in the scale removal cleaning solution, the scale cleaning ability can be improved.

[0041] From the viewpoint of scale cleaning properties, the polycarboxylic acid is preferably a polycarboxylic acid that does not contain a nitrogen atom.

[0042] From the viewpoint of scale solubility, the polycarboxylic acid is preferably a polycarboxylic acid having a hydroxy group. Examples of polycarboxylic acids having a hydroxy group include succinic acid, malic acid, and citric acid. From the viewpoint of ease of procurement, the polycarboxylic acid is preferably citric acid.

[0043] From the viewpoint of scale cleaning performance, the content of the polycarboxylic acid in the scale removal cleaning solution is preferably 1% by mass or more, more preferably 2.5% by mass or more. The upper limit of the polycarboxylic acid content is not particularly limited, but is, for example, preferably 30% by mass or less, more preferably 20% by mass or less.

[0044] <Nitrogen-Containing Heterocyclic Compound> The first scale removing cleaning liquid of the present invention preferably further contains a nitrogen-containing heterocyclic compound.

[0045] The nitrogen-containing heterocyclic compound is not particularly limited, but may be one or more selected from the group consisting of imidazoles, triazoles, and benzothiazoles. When the scale removal cleaning liquid contains a nitrogen-containing heterocyclic compound, corrosion prevention can be improved.

[0046] The imidazoles are not particularly limited, but examples thereof include imidazole, 2-methylimidazole, 2-ethylimidazole, 2-propylimidazole, 2-isopropylimidazole, 2-butylimidazole, 2-t-butylimidazole, 2-pentylimidazole, 2-hexylimidazole, 2-heptylimidazole, 2-(1-ethylpentyl)imidazole, 2-octylimidazole, 2-nonylimidazole, 2-decylimidazole, 2-undecylimidazole, 2-dodecylimidazole, 2-tridecylimidazole, 2-tetradecylimidazole, 2-pentadecylimidazole, 2-hexadecylimidazole, 2-heptadecylimidazole, 2-(1-methylpentyl)imidazole, 2-(1-ethylpentyl)imidazole, 2-(1-heptyldecyl)imidazole 2-(5-hexenyl)imidazole, 2-(9-octenyl)imidazole, 2-(8-heptadecenyl)imidazole, 2-(4-chlorobutyl)imidazole, 2-(9-hydroxynonyl)imidazole, 2-ethyl-4-methylimidazole, 2-undecyl-4-methylimidazole, 2-heptadecyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole imidazole, 2-(1-naphthyl)imidazole, 2-(1-naphthyl)-4-methylimidazole, 2-(2-naphthyl)imidazole, 2-(2-naphthyl)-4-methylimidazole, 2-methyl-4-phenylimidazole, 4-phenylimidazole, 4-methylimidazole, 4-isopropylimidazole, 4-octylimidazole, 2,4,5-trimethylimidazole, and the like.

[0047] The triazoles are not particularly limited, but examples thereof include 1,2,3-triazole, 1,2,4-triazole, 1-methyl-1,2,4-triazole, 1-ethyl-1,2,4-triazole, 1-propyl-1,2,4-triazole, 1-isopropyl-1,2,4-triazole, 1-butyl-1,2,4-triazole, 1-methyl-1,2,3-triazole, 1-ethyl-1,2,3-triazole, 1-propyl-1,2,3-triazole, 1-isopropyl-1,2,3-triazole, 1-butyl-1,2,3-triazole, benzotriazole, and 1-methylbenzotriazole. The benzothiazoles are not particularly limited, but examples thereof include benzothiazole, 4-chlorobenzothiazole, 5-chlorobenzothiazole, 6-chlorobenzothiazole, 7-chlorobenzothiazole, 4-methylbenzothiazole, 5-methylbenzothiazole, 6-methylbenzothiazole, 5-bromobenzothiazole, 4-phenylbenzothiazole, 5-phenylbenzothiazole, 4-methoxybenzothiazole, 5-methoxybenzothiazole, 6-methoxybenzothiazole, 5-iodobenzothiazole, 6-iodobenzothiazole, 4-ethoxybenzothiazole, 5-ethoxybenzothiazole, 5,6-dimethoxybenzothiazole, 5-hydroxybenzothiazole, 6-hydroxybenzothiazole, 6-dimethylaminobenzothiazole, and 5-ethoxycarbonylbenzothiazole.

[0048] From the viewpoint of corrosion prevention against iron-based metals, the nitrogen-containing heterocyclic compound is preferably an imidazole, more preferably an imidazole, and from the viewpoint of corrosion prevention against copper-based metals, the nitrogen-containing heterocyclic compound is preferably a triazole, more preferably a benzotriazole.

[0049] From the viewpoint of corrosion prevention, the content of the nitrogen-containing heterocyclic compound in the scale removal cleaning solution is preferably 0.005% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.1% by mass or more. The upper limit of the content of the nitrogen-containing heterocyclic compound is not particularly limited, but is, for example, preferably 0.5% by mass or less, and more preferably 0.25% by mass or less.

[0050] <<Second scale removal cleaning solution of the present invention>> The second scale removal cleaning solution of the present invention contains water, a fluorine compound, an inorganic acid, a surfactant, and a nitrogen-containing heterocyclic compound, and has a pH of less than 6. The second scale removal cleaning solution of the present invention may further contain a polycarboxylic acid.

[0051] Specific aspects of the second scale removal cleaning liquid of the present invention, such as the type or content of water, fluorine compound, inorganic acid, surfactant, and nitrogen-containing heterocyclic compound, are as described above for the first scale removal cleaning liquid of the present invention.

[0052] The second scale removal cleaning liquid of the present invention has excellent scale cleaning properties because it contains a fluorine compound and an inorganic acid, and also has excellent corrosion prevention properties because it contains a surfactant and a nitrogen-containing heterocyclic compound.

[0053] <<Scale Removal Cleaning Fluid of the Present Invention>> Hereinafter, the first scale removal cleaning fluid of the present invention and the second scale removal cleaning fluid of the present invention will be collectively described as the scale removal cleaning fluid of the present invention.

[0054] The pH of the scale removal cleaning solution of the present invention is less than 6. When the pH is less than 6, the scale cleaning ability can be improved. From the viewpoint of scale cleaning ability, the pH of the scale removal cleaning solution of the present invention is preferably less than 3, and more preferably less than 1. The pH of the scale removal cleaning solution can be adjusted, if necessary, by using a pH adjuster described below.

[0055] The preferred ratio of the content of each component in the scale removing cleaning solution of the present invention will be described below.

[0056] From the viewpoint of scale cleaning properties, the content of the inorganic acid is preferably 10 to 15,000 parts by mass, and more preferably 25 to 500 parts by mass, per 100 parts by mass of the fluorine compound.

[0057] From the viewpoint of scale cleaning properties, the content of the polycarboxylic acid is preferably 10 to 30,000 parts by mass, and more preferably 25 to 1,000 parts by mass, per 100 parts by mass of the fluorine compound.

[0058] From the viewpoint of scale cleaning properties and corrosion prevention, the content of the nitrogen-containing heterocyclic compound is preferably 0.1 to 500 parts by mass, and more preferably 0.25 to 10 parts by mass, per 100 parts by mass of the fluorine compound.

[0059] From the viewpoint of corrosion prevention, the content of the surfactant is preferably 0.01 part by mass or more, and more preferably 0.02 to 200 parts by mass, per 100 parts by mass of the fluorine compound.

[0060] From the viewpoint of corrosion prevention, the content of the cationic surfactant is preferably 0.01 part by mass or more, and more preferably 0.02 to 200 parts by mass, per 100 parts by mass of the fluorine compound.

[0061] From the viewpoint of corrosion prevention, the content of the nonionic surfactant is preferably 1 part by mass or more, and more preferably 2.5 to 200 parts by mass, per 100 parts by mass of the fluorine compound.

[0062] From the viewpoint of corrosion prevention, the content of the nitrogen-containing heterocyclic compound is preferably 1 part by mass or more, and more preferably 2 to 5,000 parts by mass, per 100 parts by mass of the surfactant.

[0063] From the viewpoint of corrosion prevention, the content of the nitrogen-containing heterocyclic compound is preferably 2 parts by mass or more, and more preferably 100 to 5000 parts by mass, per 100 parts by mass of the cationic surfactant.

[0064] From the viewpoint of corrosion prevention, the content of the nitrogen-containing heterocyclic compound is preferably 1 part by mass or more, and more preferably 2 to 100 parts by mass, per 100 parts by mass of the nonionic surfactant.

[0065] <Method for producing scale removal cleaning liquid> The method for producing the scale removal cleaning liquid is not particularly limited. In the case of the first scale removal cleaning liquid, water, a fluorine compound, an inorganic acid, a surfactant, a polycarboxylic acid, and the optional components described below may be mixed in any order or all at once. In the case of the second scale removal cleaning liquid, water, a fluorine compound, an inorganic acid, a surfactant, a nitrogen-containing heterocyclic compound, and the optional components described below may be mixed in any order or all at once.

[0066] <Rust Inhibitor> The scale removal cleaning solution of the present invention preferably contains a rust inhibitor. The rust inhibitor is not particularly limited, and known rust inhibitors can be used. Examples of rust inhibitors include so-called P-based, S-based, and acetylene-based rust inhibitors. Examples of P-based rust inhibitors include phosphates. Examples of S-based rust inhibitors include santhiol and thiourea. Examples of acetylene-based rust inhibitors include 3-methyl-1-butyn-3-ol, 3-methyl-1-pentyn-3-ol, 2,5-dimethyl-3-hexyne-2,5-diol, and 3,6-dimethyl-4-octyne-3,6-diol. The content of the rust inhibitor per 100 parts by mass of the fluorine compound is preferably 0.05 parts by mass or more, and more preferably 0.1 to 200 parts by mass.

[0067] <Other Components> The scale removal cleaning solution of the present invention may contain other components within a range that does not impair the effect. Examples of other components include a pH adjuster, a storage stabilizer, an antifoaming agent, and an antifreeze agent.

[0068] Examples of the defoaming agent include polyether compounds such as polyoxyalkylene alkyl ether and polyoxyalkylene diglyceryl ether. Commercially available defoaming agents may be used. Examples of commercially available defoaming agents include Takesurf K-25 (polyoxyalkylene alkyl ether, manufactured by Takemoto Oil & Fat Co., Ltd.), Takesurf K-17 (polyoxyalkylene diglyceryl ether, manufactured by Takemoto Oil & Fat Co., Ltd.), SN Deformer PC (manufactured by San Nopco Ltd.), and FS Antifoam 025 (manufactured by Dow Chemical Japan Co., Ltd.). The content of the defoaming agent in the scale removal cleaning solution is not particularly limited, but is preferably 0.001 to 1% by mass, and more preferably 0.005 to 0.1% by mass.

[0069] Examples of pH adjusters include organic acids such as acetic acid and lactic acid, and alkaline agents such as sodium hydroxide and potassium hydroxide.

[0070] The scale removal cleaning solution of the present invention may contain a small amount of a water-miscible organic solvent together with water, if necessary. Examples of the water-miscible organic solvent include alcohols such as methanol, ethanol, 2-propanol, and 1-propanol, glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, and tripropylene glycol, glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and diethylene glycol monobutyl ether, nitrogen-containing heterocyclic compounds such as N-methyl-2-pyrrolidone and 1,3-dimethylimidazolidinone, and sulfur-containing compounds such as dimethyl sulfoxide and sulfolane.

[0071] The cleaning liquid for scale removal of the present invention may be a cleaning liquid used for scale removal without dilution, or may be a cleaning liquid used for scale removal after being diluted with water, for example, 2 to 6 times.

[0072] <Metallic Material> The scale removing cleaning solution of the present invention is preferably used to remove scale adhering to the surface of an iron-based metal made of Fe or an Fe alloy, or a copper-based metal made of Cu or a Cu alloy.

[0073] The iron-based metal is not particularly limited as long as it contains Fe, and an example thereof is SUS304 (nickel-chromium alloy steel).

[0074] The copper-based metal is not particularly limited as long as it contains Cu, and an example thereof is C3604 (brass).

[0075] Furthermore, the descaling cleaning solution of the present invention has excellent cleaning properties for scales made of inorganic salts such as silica, calcium, and magnesium, and also has excellent corrosion prevention properties. Therefore, it is preferably used to remove scale formed by depositing inorganic salts attached to the surface of metal materials, and more preferably to remove silica scale. For example, silica scale is likely to form in places where metal materials come into contact with water in high-temperature environments such as geothermal power plants and heat exchangers. Therefore, the descaling cleaning solution of the present invention may be used as a cleaning solution for the piping and interior of geothermal power generation equipment, or for the piping and interior of heat exchangers. Silica scale refers to scale mainly composed of a polymer of Si and O.

[0076] <<Scale Removal Method of the Present Invention>> The scale removal method of the present invention is characterized by bringing the scale removal cleaning solution of the present invention into contact with a metal material having scales attached thereto. Specific aspects of the scale removal cleaning solution in the scale removal method of the present invention may be as described above for the scale removal cleaning solution of the present invention.

[0077] Specific embodiments of the metal material in the scale removal method of the present invention may be as described above in <Metal Material>. The metal material is preferably an iron-based metal made of Fe or an Fe alloy, or a copper-based metal made of Cu or a Cu alloy. The metal material may be piping for a geothermal power generation system, or may be a metal material inside the geothermal power generation system. The metal material may be piping for a heat exchanger, or may be a metal material inside the heat exchanger system.

[0078] The scale used in the scale removal method of the present invention may be scale made of inorganic salts such as silica, calcium, magnesium, etc., or may be silica scale.

[0079] The scale removal method of the present invention is excellent in scale cleaning properties and corrosion prevention properties.

[0080] The present invention will be described below with reference to examples, but the present invention is not limited to the following examples. Hereinafter, "parts" and "%" mean "parts by mass" and "% by mass", respectively, unless otherwise specified.

[0081] The various chemicals used in the examples and comparative examples will be summarized below. (1) Fluorine compounds: Hydrogen fluoride, ammonium acid fluoride, ammonium fluoride (2) Inorganic acids: Hydrochloric acid, nitric acid, phosphoric acid (3) Polycarboxylic acids: Citric acid, malic acid, EDTA (4) Cationic surfactants: Takesurf B-251 (lauryl pyridinium chloride, effective concentration 40% (the content in Table 1 indicates the amount of Takesurf B-251 added), manufactured by Takemoto Oil & Fat Co., Ltd.); Rheomix C (alkyl (C8 to C18) amine acetate, effective concentration 100%, manufactured by Lion Specialty Chemicals Co., Ltd.); (5) Nonionic surfactants: Cadenax DM10D-W (N,N-dimethyldecylamine oxide, effective concentration 40% (the content in Table 1 indicates the amount of Cadenax DM10D-W added), manufactured by Lion Specialty Chemicals Co., Ltd.); (6) Nitrogen-containing heterocyclic compounds・Imidazole ・Benzotriazole

[0082] Examples 1 to 11 and Comparative Examples 1 to 6 The components were mixed in the mass ratios shown in Table 1 to obtain the scale removal cleaning solutions of Examples 1 to 11 and Comparative Examples 1 to 6.

[0083] The resulting scale removal cleaning solution was used to evaluate its silica scale solubility, corrosion protection against iron-based metals, and corrosion protection against copper-based metals by the following methods. The evaluation results are shown in Table 1.

[0084] <Preparation of test piece with silica scale> A sodium silicate aqueous solution (silicic acid concentration 500 ppm) adjusted to a pH of about 9 was heated to 150°C and poured into a 4 cm２ A silica-scaled test piece was prepared by dropping 0.5 mg of the solution onto an iron substrate (SUS304, nickel-chromium alloy steel) to form 0.5 mg of silica-containing scale on the substrate. A silica-scaled test piece was also prepared in the same manner using a copper substrate (C3604, brass).

[0085] <Evaluation of Silica Scale Solubility> The prepared test pieces were immersed in each of the scale removal cleaning solutions of Examples 1 to 11 and Comparative Examples 1 to 6 at 25°C, left to stand for 1 hour, and then removed and the condition of the test pieces was evaluated based on the change in mass before and after immersion. The results of evaluating the silica scale solubility according to the following criteria are shown in Table 1.

[0086] <Evaluation criteria> ++: No silica scale residue was found on the substrate or in the liquid, and the remaining amount of silica scale was 0% by mass. -: Silica scale residue was found on the substrate and in the liquid.

[0087] Silica scale remaining amount (mass%)=100×[0.5 g−{(mass of test piece before immersion in scale removal cleaning liquid)−(mass of test piece after immersion in scale removal cleaning liquid)}] / 0.5 g

[0088] <Evaluation of corrosion resistance to iron-based metals> Test pieces of iron alloy (SUS304) were immersed in each of the scale removal cleaning solutions of Examples 1 to 11 and Comparative Examples 1 to 6 at 25°C, and the corrosion weight loss (mg) after 240 hours was measured. ２ Corrosion weight loss per day (mg / dm ２ / day, also referred to as mdd) was calculated as the amount of corrosion of iron-based metals. The corrosion resistance of iron-based metals was evaluated according to the following criteria, and the results are shown in Table 1. <Evaluation criteria> +++: Amount of corrosion less than 50 mdd ++: Amount of corrosion 50 mdd or more but less than 100 mdd +: Amount of corrosion 100 mdd or more but less than 200 mdd -: Amount of corrosion 200 mdd or more

[0089] <Evaluation of corrosion resistance to copper-based metals> The corrosion resistance to copper-based metals was evaluated in the same manner as in the evaluation of corrosion resistance to iron-based metals, except that copper alloy (C3604) test pieces were used. The corrosion resistance to copper-based metals was evaluated according to the following criteria, and the results are shown in Table 1. <Evaluation criteria> +++: Amount of corrosion less than 50 mdd ++: Amount of corrosion 50 mdd or more but less than 100 mdd +: Amount of corrosion 100 mdd or more but less than 200 mdd -: Amount of corrosion 200 mdd or more

[0090]

[0091] The scale removal cleaning solutions of Comparative Examples 1 to 3 did not contain a polycarboxylic acid, a surfactant, or a nitrogen-containing heterocyclic compound, and therefore were insufficient in scale cleaning properties and corrosion prevention. The scale removal cleaning solutions of Comparative Examples 4 to 6 did not contain a surfactant or a nitrogen-containing heterocyclic compound, and therefore were insufficient in corrosion prevention. The scale removal cleaning solutions of Examples 1 to 11 were excellent in scale cleaning properties and in corrosion prevention properties for metals.

Claims

1. A scale removal cleaning solution containing water, a fluorine compound, an inorganic acid, a surfactant, and a polycarboxylic acid, and having a pH of less than 6.

2. The scale removing cleaning solution according to claim 1, further comprising a nitrogen-containing heterocyclic compound.

3. A scale removal cleaning solution according to claim 1 or 2, wherein the content of the polycarboxylic acid is 10 to 10,000 parts by mass per 100 parts by mass of the fluorine compound.

4. A scale removal cleaning solution according to any one of claims 1 to 3, wherein the polycarboxylic acid is a polycarboxylic acid having a hydroxy group.

5. A scale removal cleaning solution containing water, a fluorine compound, an inorganic acid, a surfactant, and a nitrogen-containing heterocyclic compound, and having a pH of less than 6.

6. A scale removal cleaning solution as described in claim 2 or 5, wherein the content of the nitrogen-containing heterocyclic compound is 1 part by mass or more per 100 parts by mass of the surfactant.

7. A scale removal cleaning solution according to any one of claims 2, 5 and 6, wherein the nitrogen-containing heterocyclic compound is one or more selected from the group consisting of imidazoles, triazoles and benzothiazoles.

8. A scale removal cleaning solution according to any one of claims 1 to 7, wherein the content of the surfactant is 0.01 parts by mass or more per 100 parts by mass of the fluorine compound.

9. A scale removal cleaning solution according to any one of claims 1 to 8, which is used to remove scale adhering to the surface of an iron-based metal made of Fe or an Fe alloy, or a copper-based metal made of Cu or a Cu alloy.

10. The scale removing cleaning solution according to any one of claims 1 to 9, further comprising a rust inhibitor.

11. A method for removing scales, comprising contacting the scale removing cleaning solution according to any one of claims 1 to 10 with a metal material having scales attached thereto.

12. A scale removal method according to claim 11, wherein the metal material is an iron-based metal made of Fe or an Fe alloy, or a copper-based metal made of Cu or a Cu alloy.

13. A method for removing scales according to claim 11 or 12, wherein the scale is silica scale.

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