Anticorrosion liquids

Abstract

The invention relates to an anticorrosion liquid comprising (a) one or more indoles, preferably 2-methylindole, ethylindol-2-carboxylate, 2-phenylindole, tryptophan, 3-indolemethanol, indole-3-acetamide, 5-methoxyindole, 5-nitroindole, indole-5-carbonitrile, methylindole-6-carboxylate, or a combination thereof; (b) one or more aromatic imides, preferably phthalimide, saccharin, or a combination thereof; and (c) one or more liquid aliphatic polyhydroxy compounds, preferably triethanolamine. The anticorrosion liquid is particularly useful for transferring heat; preferably geothermal heat. It is advantageously used in water circuits, water treatment units, cooling systems, or geothermal heating systems. Its corrosion inhibiting effect is particularly pronounced with respect to items made of copper, brass, iron, steel, aluminum or combinations thereof.

Description

Anticorrosion liquids

[0001] Priority is claimed of European patent application no. 24 184 262 that was filed on June 25, 2024.

[0002] The invention relates to an anticorrosion liquid comprising (a) one or more indoles, preferably 2-methylindole, ethylindol-2-carboxylate, 2-phenylindole, tryptophan, 3 -indolemethanol, indole-3-ac- etamide, 5 -methoxyindole, 5 -nitroindole, indole-5-carbonitrile, methylindole-6 -carboxylate, or a combination thereof; (b) one or more aromatic imides, preferably phthalimide, saccharin, or a combination thereof; and (c) one or more liquid aliphatic polyhydroxy compounds, preferably triethanolamine. The anticorrosion liquid is particularly useful for transferring heat; preferably geothermal heat. It is advantageously used in water circuits, water treatment units, cooling systems, or geothermal heating systems. Its corrosion inhibiting effect is particularly pronounced with respect to items made of copper, brass, iron, steel, aluminum or combinations thereof.

[0003] Geothermal energy provides a renewable source of energy and baseload power that other renewables, including wind and solar power, cannot provide. Conventional geothermal power is produced in areas with naturally occurring hydrothermal reservoirs or in stimulated dried-out geothermal reservoirs. Corrosion can quickly render newly installed geothermal well casings useless, causing damage in the multimillion-dollar range. Corrosion inhibitors are often added to heat transfer fluids for geothermal energy to inhibit the corrosion of system components. Conventional geothermal systems are being explored in deeper and hotter environments where handling corrosive fluids is challenging. Finding reasonably priced materials to minimize corrosion in fluid production and power systems is a significant constraint faced by project developers as exploration extends to these more challenging environments. At the same time, producing conditions in maturing developed geothermal fields are changing as superheating becomes the dominant reservoir condition, resulting in corrosion problems that affect project economics (Electric Power Research Institute, EPRI, A. Coleman, Corrosion of Materials Used in Geothermal Power Production, Review of Materials and Treatment Technologies, 3002007966, April 2016).

[0004] T. Kaya et al., Proceedings World Geothermal Congress 2005, Antalya, Turkey, 24-29 April 2005, relates to corrosion and material selection for geothermal systems.

[0005] M. Mobin et al., Portugaliae Electrochimica Acta 2011, 29(6), 391-403, relates to inhibition of mild steel corrosion using L-tryptophan and synergistic surfactant additives.

[0006] A. Fateh et al., Arabian Journal of Chemistry (2020) 13, 481-544, is a review of corrosive environments for copper and its corrosion inhibitors.

[0007] S. Hadisaputra et al., ACS Omega 2022, 7, 33054-33066, relates to corrosion inhibition properties of phenyl phthalimide derivatives against carbon steel in the acidic medium.

[0008] Products listed by the German Federal / State Working Group on Water (Landerarbeitsgemein- schaft Wasser, LAWA) are mainly used for this purpose. Due to the ban on triazoles as corrosion inhibitors in fluids for transferring geothermal heat, only a few corrosion inhibited products can still be found on the positive list. In most cases, the products are based on a glycol and may contain up to 3% additives of water hazard class 1 (i.e. weakly hazardous, low water hazard).

[0009] The LAWA positive list states whether a product contains additives, but it does not provide any information about the protective effect of the corrosion inhibitor and its corrosion properties. To this end, products are subjected to corrosion tests on six different metals in accordance with ASTM D1384. The measured corrosion rates / removal values are a quantitative measure for the anticorrosive performance. ASTM D3306 specifies the maximum permissible corrosion rates for the various metals so that it is desirable to achieve values below the limit values.

[0010] Anticorrosive effects may depend upon various factors such as the nature of metal or alloy that is subject to corrosion, the pH value of the environment, the temperature of the environment, and the like. As a result, a chemical that has a corrosion inhibiting effect e.g. on steel in an acidic medium at 30°C does not necessarily also have a corrosion inhibiting effect on brass in a slightly alkaline medium at 60°C.

[0011] CN 109 666 458 A provides siliceous organic engine cooling liquids comprising the component of following parts by weight: 25-55 parts of ethylene glycol, 2-10 parts of carboxylate, 0.1-5 parts of silicate, 0.1-5 parts of silicate stabilizers, 0.5-10 parts of corrosion inhibiter, 0.2-2 parts of preservative, 0.5-2 parts of defoaming agent, 30-70 parts of deionized water. The siliceous organic engine cooling liquid have protective action, can prevent corrosion and scale, and have stability and long service life over pH value range.

[0012] US 4 450 088 relates to antifreeze or anticorrosive additive compositions and a process for inhibiting the corrosion of aluminum in contact with aqueous liquids. The antifreeze compositions comprise a combination of an amino acid, an alkali metal phosphate, a heterocyclic nitrogen compound, as defined, and a conventional corrosion inhibitor in effective corrosion inhibiting amounts. The aqueous liquid can be an alcohol such as ethylene glycol.

[0013] EP 0 553 962 Al relates to a corrosion inhibiting composition comprising A) 40-90% by weight of a specified carboxylic acid corrosion inhibitor, or a water-soluble salt thereof, B) 10-60% by weight of one or more specified aminobenzoic acids, C) 0-10% by weight of a specified alkanolamine, and D) 0-10% by weight of an alkali metal borate.

[0014] EP 1 707 609 Al relates to antifreezing fluids including propylene glycol, first material, and second material. The first material is normal aliphatic dicarboxylic acid in which number of carbon atom is from 10 to 12, salt of the normal aliphatic dicarboxylic acid, or mixture thereof. The second material is benzimidazole compound which has a benzimidazole skeleton, salt of benzimidazole compound,triazine compound which has a triazine skeleton and a mercapto group, salt of triazine compound, or mixture thereof.

[0015] EP 1 501 140 Al relates to a coolant composition used for cooling a fuel cell, in particular to a coolant composition used for cooling a fuel cell having low conductivity, anti-freeze properties, and excellent anti-corrosion properties for a metal, especially an aluminum based material, for use in the cooling system of fuel cell and, further, exhibiting no significant increase in conductivity even after long term use. The coolant composition is characterized by comprising a base agent and an additive for sustaining low conductivity of the coolant composition, the anti-corrosive additive being such a substance as suppressing oxidation of the basic agent or blocking ions eluting into a cooling system to prevent conductivity of the coolant composition from increasing.

[0016] It is an object of the invention to provide compositions which inhibit corrosion, meet the environmental requirements of LAWA, and effectively protect components e.g. of geothermal plants, against corrosion. A focus of the invention is primarily on inhibiting corrosion of copper and brass.

[0017] This object has been achieved by the subject-matter of the patent claims.

[0018] A first aspect of the invention relates to anticorrosion liquid comprising(a) one or more indoles of general formula (I) [component (a)]whereinR1 means -H or -Ci-6-alkyl; preferably -H; andR2, R3, R4, R5, R6 and R7 independently of one another mean -H, -F, -Cl, -Br, -Ci-6-alkyl, -Ci.6-alkyl-C(=O)H, -Ci.6-alkyl-C(=O)OH, -Ci.6-alkyl(NH2)C(=O)OH, -Ci.6-alkylC(=O)- C(=O)OH, -Ci.6-alkyl-C(=O)OCi.6-alkyl, -Ci.6-alkyl-C(=O)NH2, -Ci.6-alkyl-C(=O)NHCi.6-al- kyl, -Ci-6-alkyl-C(=O)N(Ci-6-alkyl)2, -Ci-6-alkyl-NH2, -Ci-e-alkyl-NHCi-e-alkyl, -Ci-e-alkyl- N(Ci-6-alkyl)2, -Ci-6-alkyl-NHC(=O)Ci-6-alkyl, -Ci-e-alkyl-OH, -Ci-e-alkyl-OCi-e-alkyl, -CN, -C(=O)H, -C(=O)OH, -C(=O)OCi.6-alkyl, -C(=O)NH2, -C(=O)NHCi.6-alkyl, -C(=O)N(Ci.6-al- kyl)2, -NH2, -NH-Ci-e-alkyl, -N(Ci.6-alkyl)2, -NHC(=O)Ci.6-alkyl, -NO2, -OH, -O-Ci.6-alkyl, or -phenyl; preferably wherein at least 4 of R2, R3, R4, R5, R6 and R7 mean -H;(b) one or more aromatic imides of general formula (II) [component (b)]whereinAl and A2 independently of one another mean C(=O), S(=O), or S(=O)2;R8 means -H, NHZ, N(Ci-6-alkyl)4+, or (Mn+)i / n, wherein M is a metal; andR9, RIO, Rll and R12 independently of one another mean -H, -F, -Cl, -Br, -Ci-6-alkyl, -OH, -O-Ci e-alkyl, -Ci e-alkyl-OH, -C(=O)OH, -Ci.6-alkyl-C(=O)OH, -NH2, -Ci.6-alkyl-NH2, -NH- Ci-6-alkyl, -Ci-e-alkyl-NH-Ci-e-alkyl, -N(Ci-6-alkyl)2, or -Ci-6-alkyl-N(Ci-6-alkyl)2; preferably wherein at least 3 of R9, RIO, Rll and R12 mean -H;(c) one or more liquid aliphatic polyhydroxy compounds [component (c)]; and(d) optionally, water [component (d)] .

[0019] It has been surprisingly found that combinations of certain corrosion inhibitors exert synergistic anticorrosive effects (supraadditive anticorrosive effects), i.e. the anticorrosive effect of the combination exceeds the sum of the individual anticorrosive effects that are observed when the corrosion inhibitors are tested in isolation under the same test conditions. The combination effectively reduces the corrosion of the metals in the test. Indoles such as tryptophan, imides such as phthalimide and saccharin, and phosphonic acids such as octyl phosphonic acid show a strong corrosion inhibition effect.

[0020] Excellent results can be achieved with tryptophan, e.g. at concentrations of about 4.5 wt.-%.

[0021] Excellent results can be achieved with phthalimide, e.g. at concentrations of about 1 wt.-%. Despite the low concentration of phthalimide, the corrosion rate of copper is as low as only 0.28 g m-2, whereas in the absence of phthalimide, the corrosion rate of copper under the same conditions amounts to 15.52 g m-2.

[0022] The anticorrosion liquid according to the invention comprises(a) at least one indole of general formula (I), preferably 2-methylindole, ethylindol-2 -carboxylate, 2- phenylindole, tryptophan, 3 -indolemethanol, indole-3 -acetamide, 5 -methoxyindole, 5 -nitroindole, indole-5-carbonitrile, methylindole-6-carboxylate, or a combination thereof;(b) at least one aromatic imide of general formula (II), preferably phthalimide, saccharin, or a combination thereof;(c) at least one liquid aliphatic polyhydroxy compound, preferably triethanolamine; and(d) optionally water.

[0023] In preferred embodiments, the anticorrosion liquid according to the invention additionally comprises one or more or all of the following components (e) through (j):(e) one or more phosphonic acids [component (e)], preferably octyl phosphonic acid;(f) one or more aliphatic dicarboxylic acids [component (f)], preferably dodecanedioic acid;(g) one or more aliphatic monocarboxylic acids [component (g)], preferably pelargonic acid, isonona- noic acid or a combination thereof;(h) one or more aromatic carboxylic acids [component (h)] excluding indoles of general formula (I) and excluding aromatic imides of general formula (II), preferably benzoic acid, histidine, or a combination thereof;(i) one or more inorganic salts [component (i)], preferably sodium molybdate; and(j) one or more sulfonic acids [component (j)], preferably HEPES.

[0024] Components (a) through (j) are to be understood in a non-overlapping manner, i.e. as separate components. When indoles of general formula (I) or aromatic imides of general formula (II) carry a carboxylic acid group, they are not to be regarded as aromatic carboxylic acids (h).

[0025] The anticorrosion liquid according to the invention typically does not contain any ingredients of water hazard class 2 (i.e. significantly hazardous, significant water hazard), or water hazard class 3 (i.e. strongly hazardous, high water hazard). For the purpose of the specification, the water hazard classes are according to the German Ordinance on Installations for Handling Substances Hazardous to Water (AwSV).

[0026] For the purpose of the specification, the term "amino acid" refers to an organic compound having at least one acid functional group, preferably carboxylic acid functional group, and at least one amine functional group , preferably primary amine functional group, or a salt thereof.

[0027] For the purpose of the specification, the term "imide" refers to an organic compound having an imide functional group or a salt thereof. Imide functional groups encompass imides of carboxylic acids, imides of sulfmic acids, imides of sulfonic acids, and mixed species, e.g. -C(=O)-NR8-C(=O)-, -S=(O)- NR8-C(=O)-, -S(=O)2-NR8-C(=O)-, -S(=O)-NR8-S(=O)-, -S(=O)-NR8-S(=O)2-, and -S(=O)2-NR8- S(=O)2-.

[0028] For the purpose of the specification, the term "liquid aliphatic polyhydroxy compound" refers to a compound that in its neat state is a liquid at 25°C and that has an aliphatic residue carrying at least two hydroxyl functional groups. Optionally, the aliphatic residue may carry an amine functional group. Preferably, the liquid aliphatic polyhydroxy compound is composed of C2-building blocks (oxyethylene) and / or C3-buidling blocks (oxypropylene).

[0029] For the purpose of the specification, the term "aliphatic monocarboxylic acid" refers to an organic compound having an aliphatic residue that carries a single free carboxylic acid functional group or a salt thereof. The "aliphatic monocarboxylic acids" according to the invention may additionally have other functional groups such as amine, amide, hydroxy, thiol, and the like. The term "aliphaticmonocarboxylic acid" therefore encompasses aliphatic amino acids having a single free carboxylic acid functional group such as alanine, arginine, asparagine, cysteine, glutamine, glycine, isoleucine, leucine, lysine, methionine, proline, serine, threonine, or valine (independently of one another in their L-form, D-form, or as racemate).

[0030] For the purpose of the specification, the term "aliphatic dicarboxylic acid" refers to an organic compound having an aliphatic residue that carries two free carboxylic acid functional groups or a salt thereof. The "aliphatic dicarboxylic acids" according to the invention may additionally have other functional groups such as amine, amide, hydroxy, thiol, and the like. The term "aliphatic dicarboxylic acid" therefore encompasses aliphatic amino acids having a single free carboxylic acid functional group such as aspartic acid or glutamic acid (independently of one another in their L-form, D-form, or as racemate).

[0031] For the purpose of the specification, the term "aromatic carboxylic acid" refers to an organic compound having an aromatic residue that carries a carboxylic acid functional group or a salt thereof. Preferably, the carboxylic acid functional group is directly linked to the aromatic residue. The "aromatic carboxylic acids" according to the invention may additionally have other functional groups such as amine, amide, hydroxy, thiol, and the like. The term "aromatic carboxylic acid" therefore encompasses aromatic amino acids such as histidine, phenylalanine or tyrosine (independently of one another in their L-form, D-form, or as racemate).

[0032] For the purpose of the specification, the term "phosphonic acid" refers to an organic compound having a phosphonic acid functional group or a salt thereof.

[0033] For the purpose of the specification, e.g., component (e) "and / or" component (f) means (1) only component (e) but not component (f), (2) only component (f) but not component (e), or (3) both component (e) as well as component (f).

[0034] For the purpose of the specification, "aliphatic" refers to a non-aromatic, non-cyclic hydrocarbon that may be linear or branched, saturated or unsaturated. Thus, "aliphatic" encompasses e.g. linear or branched alkyl, linear or branched alkenyl, and linear or branched alkynyl.

[0035] For the purpose of the specification, "corrosion" is defined as in the IUPAC Gold Book (https: / / goldbook.iupac.org / terms / view / C01351). Preferably, "corrosion" is an irreversible interfacial reaction of a metal with its environment which results in consumption of the metal or in dissolution into the metal of a component of the environment. Often, but not necessarily, corrosion results in effects detrimental to the usage of the metal considered. Exclusively physical or mechanical processes such as melting or evaporation, abrasion or mechanical fracture are not included in the term "corrosion" .

[0036] For the purpose of the specification, an "anticorrosion liquid" has an anticorrosive effect, i.e. may serve as corrosion inhibitor, and is thus useful to prevent and / or control corrosion of a metal, wherein the metal is preferably selected from copper, brass, iron, steel, aluminum, mixtures and alloys thereof.

[0037] For the purpose of the specification, "one or more" of a component means at least one species that can be subsumed under the general term of the component, or more than one species, e.g. two, three, four, five or more of such species that each can be subsumed under the general term of the component.

[0038] For the purpose of the specification, "total content" refers to the sum of all individual contents of all species that can be subsumed under the general term of the same component. For the purpose of the specification, "overall content" refers to the sum of all total contents of all components referred to. For example, when an anticorrosion liquid contains three indoles of general formula (I) and two imides of general formula (II), the total content of the indoles of general formula (I) refers to the sum of individual contents of the three indoles of general formula (I), whereas the total content of imides of general formula (II) refers to the sum of individual contents of both imides of general formula (II). The overall content of the indoles of general formula (I) and the imides of general formula (II) refers to the sum of the total content of the indoles of general formula (I) and the total content of imides of general formula (II).

[0039] Unless expressly stated otherwise, all amounts, quantities, percentages, concentrations, ppm and the like are expressed on the basis of weight, related to the total weight of the anticorrosion liquid.

[0040] When the anticorrosion liquid contains more than a single species that can be subsumed under the general term of a component, and when said species can principally exist in a non-salt form or the salt form, e.g. "one or more aliphatic monocarboxylic acids", the species may independently of one another be in the non-salt form or salt form. When said species are in the salt form, different species may be present in form of the same salt (e.g. all as sodium salt) or different salts (e.g. one as sodium salt, another one as potassium salt), and one and the same species may be present in form of different salts (e.g. one fraction as sodium salt, another fraction as potassium salt). The skilled person recognizes that metathesis reactions might occur in admixture between species of the same components and also between species of different components, and such metathesis is thus contemplated according to the invention.

[0041] Unless expressly stated otherwise, all amounts, quantities, percentages, concentrations, ppm and the like are expressed on the basis of non-salt forms of the components (a), (b), (c), (d), (e), (f), (g) and (h). Thus, the weight contribution of e.g. counter cations other than H+is not taken into consideration.

[0042] Unless expressly stated otherwise, all standards and legal provisions are relevant in their version that is valid on June 1, 2024.

[0043] In preferred embodiments, the anticorrosion liquid according to the invention is selected from solutions, emulsions and suspensions; preferably solutions.

[0044] In preferred embodiments, the anticorrosion liquid according to the invention comprises one or more indoles of general formula (I). Preferably, the anticorrosion liquid according to the inventioncomprises not more than two indoles of general formula (I), more preferably not more than a single indole of general formula (I).

[0045] Preferably, R1 means -H.

[0046] Preferably, R2 means -H, -Ci-6-alkyl, -C(=O)OCi-6-alkyl, or -phenyl; more preferably -H, -CH3, -C(=O)OCH2CH3, or -phenyl.

[0047] Preferably, R3 means -H, -Ci-6-alkyl(NH2)C(=O)OH, -Ci-e-alkyl-OH, -C(=O)H, -Ci-e-alkyl- C(=O)NH2, or -Ci.6-alkyl-C(=O)OH; more preferably -H, -CH2CH(NH2)C(=O)OH, -CH2OH, -C(=O)H, -CH2C(=O)NH2, or -CH2CH2C(=O)OH.

[0048] Preferably, R4 means -H.

[0049] Preferably, R5 means -H, -O-Ci-6-alkyl, -NO2, or -CN; more preferably -H, -OCH3, -NO2, or-CN.

[0050] Preferably, R6 means -H or -C(=O)OCi-6-alkyl; more preferably -H or -C(=O)OCH3.

[0051] Preferably, R7 means -H.

[0052] Preferably, the one or more indoles of general formula (I) are independently of one another selected from-me y n o e ethylindol-2-carboxylate(CAS 95-20-5) 2-phenylindoleindole-3 -acetamide3 -indolemethanol tryptophan (CAS 879-37-8)(CAS 700-06-1)methylindole-6-carboxylate(CAS 50820-65-0) and combinations thereof.

[0053] While the stereochemistry of tryptophan is not particularly relevant for anticorrosive performance, L-tryptophan is preferred. However, D-tryptophan and DL-tryptophan are also contemplated.

[0054] Another suitable indole of general formula (I) is indole.

[0055] In preferred embodiments, the anticorrosion liquid according to the invention comprises one or more aromatic imides of general formula (II). Preferably, the anticorrosion liquid according to the invention comprises not more than two aromatic imides of general formula (II), more preferably not more than a single aromatic imide of general formula (II).

[0056] Preferably, Al and A2 independently of one another mean C(=O) or S(=O)2; more preferably at least one of Al and A2 means C(=O).

[0057] In preferred embodiments, Al and A2 both mean C(=O).

[0058] In other preferred embodiments, Al means C(=O) and A2 means S(=O)2.

[0059] In preferred embodiments, R8 means -H.

[0060] In other preferred embodiments, R8 means NHZ, N(Ci-6-alkyl)4+, or (Mn+)i / n, wherein M is a metal, preferably Na+or K+.

[0061] Preferably, R9 means -H.

[0062] Preferably, RIO means -H.

[0063] Preferably, Rll means -H.

[0064] Preferably, R12 means -H.

[0065] Preferably, the one or more aromatic imides of general formula (II) are independently of one another selected from- phthalimide or a salt thereof (i.e., Al, A2 mean C(=O); R9, RIO, Rll, R12 mean -H);- saccharin or a salt thereof (i.e., Al means C(=O); A2 means S(=O)2; R9, RIO, Rll, R12 mean -H); and combinations thereof.

[0066] The anticorrosion liquid according to the invention comprises one or more liquid aliphatic polyhydroxy compounds (c). Preferably, the anticorrosion liquid according to the invention comprises not more than three liquid aliphatic polyhydroxy compounds (c), more preferably not more than two liquid aliphatic polyhydroxy compounds (c).

[0067] Preferably, the one or more liquid aliphatic polyhydroxy compounds (c) are independently of one another selected from ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, ethanolamine, diethanolamine, triethanolamine, and combinations thereof; preferably ethylene glycol, propylene glycol, triethanolamine and combinations thereof; more preferably triethanolamine.

[0068] Triethanolamine alone, triethanolamine in combination with ethylene glycol, and triethanolamine in combination with propylene glycol are particularly preferred.

[0069] When triethanolamine is present in combination with ethylene glycol, the weight content of ethylene glycol is preferably greater than the weight content of triethanolamine.

[0070] When triethanolamine is present in combination with propylene glycol, the weight content of propylene glycol is preferably greater than the weight content of triethanolamine.

[0071] In preferred embodiments, the anticorrosion liquid according to the invention comprises water and wherein the pH value of the anticorrosion liquid is at least 5.0, preferably at least 5.5, more preferably at least 6.0, still more preferably at least 6.5, yet more preferably at least 7.0, even more preferably at least 7.5, most preferably at least 8.0, and in particular at least 8.5.

[0072] In preferred embodiments, the anticorrosion liquid according to the invention comprises water and wherein the pH value of the anticorrosion liquid is within the range of 9.0±0.9, preferably 9.0±0.8, more preferably 9.0±0.7, still more preferably 9.0±0.6, yet more preferably 9.0±0.5, even more preferably 9.0±0.4, most preferably 9.0±0.3, and in particular 9.0±0.2.

[0073] In preferred embodiments, the anticorrosion liquid according to the invention comprises water and wherein the pH value of the anticorrosion liquid is within the range of 8.5±0.9, preferably 8.5±0.8, more preferably 8.5±0.7, still more preferably 8.5±0.6, yet more preferably 8.5±0.5, even more preferably 8.5±0.4, most preferably 8.5±0.3, and in particular 8.5±0.2.

[0074] In preferred embodiments, the anticorrosion liquid according to the invention comprises water and wherein the pH value of the anticorrosion liquid is within the range of 8.0±0.9, preferably 8.0±0.8, more preferably 8.0±0.7, still more preferably 8.0±0.6, yet more preferably 8.0±0.5, even more preferably 8.0±0.4, most preferably 8.0±0.3, and in particular 8.0±0.2.

[0075] In preferred embodiments, the anticorrosion liquid according to the invention comprises water and wherein the pH value of the anticorrosion liquid is within the range of 7.5±0.9, preferably 7.5±0.8, more preferably 7.5±0.7, still more preferably 7.5±0.6, yet more preferably 7.5±0.5, even more preferably 7.5±0.4, most preferably 7.5±0.3, and in particular 7.5±0.2.

[0076] The pH value may be adjusted by adding e.g. mineral acid (e.g. HC1, H2SO4) and inorganic base (e.g. NaOH, KOH, Na2COs), respectively.

[0077] In particularly preferred embodiments, the anticorrosion liquid according to the invention comprises one or more indoles of general formula (I) and one or more aromatic imides of general formula (II), preferably wherein the one or more indoles of general formula (I) and one or more aromatic imides of general formula (II) provide a synergistic anticorrosive effect.

[0078] Thus, the content of the one or more indoles of general formula (I) and the content of the one or more aromatic imides of general formula (II) is preferably adjusted such that a synergistic anticorrosiveeffect is achieved, i.e. an anticorrosive effect of the combination that is quantitatively higher than the sum of (i) the anticorrosive effect of the one or more indoles of general formula (I) in the absence of the one or more aromatic imides of general formula (II), and (ii) the anticorrosive effect of the one or more aromatic imides of general formula (II) in the absence of the one or more indoles of general formula (I).

[0079] In preferred embodiments, the anticorrosion liquid according to the invention comprises (a) tryptophan and (b) phthalimide; and (c) preferably, triethanolamine.

[0080] In other preferred embodiments, the anticorrosion liquid according to the invention comprises (a) tryptophan and (b) saccharin; and (c) preferably, triethanolamine.

[0081] In further preferred embodiments, the anticorrosion liquid according to the invention comprises (a) tryptophan and (b) a combination of phthalimide and saccharin; and (c) preferably, triethanolamine.

[0082] Preferably, the total weight content of the one or more indoles of general formula (I) is greater than the total weight content of the one or more aromatic imides of general formula (II).

[0083] Preferably, the ratio of the total weight content of the one or more indoles of general formula (I) to the total weight content of one or more aromatic imides of general formula (II) is within the range of from 12: 1 to 1:5; preferably 11 : 1 to 1:4; more preferably 10: 1 to 1:3; still more preferably 9: 1 to 1:2; yet more preferably 8: 1 to 1: 1; even more preferably 7: 1 to 2: 1; most preferably 6: 1 to 3: 1; and in particular 5: 1 to 4: 1.

[0084] Preferably, the ratio of the total molar content of the one or more indoles of general formula (I) to the total molar content of one or more aromatic imides of general formula (II) is within the range of from 12: 1 to 1:5; preferably 11 : 1 to 1:4; more preferably 10: 1 to 1:3; still more preferably 9: 1 to 1:2; yet more preferably 8 : 1 to 1: 1; even more preferably 7 : 1 to 2 : 1 ; most preferably 6 : 1 to 3 : 1 ; and in particular 5: 1 to 4: 1.

[0085] In preferred embodiments, the anticorrosion liquid according to the invention additionally comprises one or more or all of the following (e) through (j):(e) one or more phosphonic acids, preferably octyl phosphonic acid;(f) one or more aliphatic dicarboxylic acids, preferably dodecanedioic acid;(g) one or more aliphatic monocarboxylic acids, preferably pelargonic acid, isononanoic acid or a combination thereof;(h) one or more aromatic carboxylic acids excluding indoles of general formula (I) and excluding aromatic imides of general formula (II), preferably benzoic acid, histidine, or a combination thereof;(i) one or more inorganic salts, preferably sodium molybdate; and(j) one or more sulfonic acids, preferably HEPES.

[0086] In preferred embodiments, the anticorrosion liquid according to the invention comprises one or more phosphonic acids (e); preferably selected from aliphatic phosphonic acids; more preferably Ce- Ci8-alkyl phosphonic acids; still more preferably octyl phosphonic acid.

[0087] Preferably, the anticorrosion liquid according to the invention comprises not more than two phosphonic acids (e), more preferably not more than a single phosphonic acid (e).

[0088] Preferably, the total weight content of the one or more indoles of general formula (I) is greater than the total weight content of the one or more phosphonic acids (e).

[0089] Preferably, the ratio of the total weight content of the one or more indoles of general formula (I) to the total weight content of one or more phosphonic acids (e) is within the range of from 9: 1 to 1:9; preferably 8: 1 to 1:8; more preferably 7: 1 to 1:7; still more preferably 6: 1 to 1:6; yet more preferably 5: 1 to 1:5; even more preferably 4: 1 to 1:4; most preferably 3: 1 to 1:3; and in particular 2: 1 to 1:2.

[0090] Preferably, the total weight content of the one or more phosphonic acids (e) is greater than the total weight content of the one or more aromatic imides of general formula (II).

[0091] Preferably, the ratio of the total weight content of the one or more aromatic imides of general formula (II) to the total weight content of one or more phosphonic acids (e) is within the range of from 6: 1 to 1: 11; preferably 5: 1 to 1: 10; more preferably 4: 1 to 1:9; still more preferably 3: 1 to 1:8; yet more preferably 2: 1 to 1:7; even more preferably 1 : 1 to 1:6; most preferably 1 :2 to 1:5; and in particular 1:3 to 1:4.

[0092] In preferred embodiments, the anticorrosion liquid according to the invention comprises one or more aliphatic dicarboxy lie acids (f); preferably selected from saturated aliphatic dicarboxy lie acids; more preferably Ce-Cis-alkyl aliphatic dicarboxylic acids; still more preferably dodecanedioic acid.

[0093] Preferably, the anticorrosion liquid according to the invention comprises not more than two aliphatic dicarboxylic acids (f), more preferably not more than a single aliphatic dicarboxylic acid (f).

[0094] Preferably, the total weight content of the one or more indoles of general formula (I) is greater than the total weight content of the one or more aliphatic dicarboxylic acids (f).

[0095] Preferably, the ratio of the total weight content of the one or more indoles of general formula (I) to the total weight content of one or more aliphatic dicarboxylic acids (f) is within the range of from 12: 1 to 1:5; preferably 11: 1 to 1:4; more preferably 10: 1 to 1:3; still more preferably 9: 1 to 1:2; yet more preferably 8 : 1 to 1: 1; even more preferably 7 : 1 to 2 : 1 ; most preferably 6 : 1 to 3 : 1 ; and in particular 5 : 1 to 4: 1.

[0096] Preferably, the ratio of the total weight content of the one or more aromatic imides of general formula (II) to the total weight content of one or more aliphatic dicarboxylic acids (f) is within the range offrom 9: l to 1:9; preferably 8: 1 to 1:8; more preferably 7: 1 to 1:7; still more preferably 6: 1 to 1:6; yet more preferably 5 : 1 to 1:5; even more preferably 4: 1 to 1:4; most preferably 3: 1 to 1:3; and in particular 2: I to 1:2.

[0097] In preferred embodiments, the anticorrosion liquid according to the invention comprises one or more aliphatic monocarboxy lie acids (g); preferably selected from saturated aliphatic monocarboxylicacids; more preferably Ce-Cis-alkyl aliphatic monocarboxylic acids; still more preferably having an uneven number of carbon atoms; yet more preferably pelargonic acid, isononanoic acid or a combination thereof.

[0098] Preferably, the anticorrosion liquid according to the invention comprises not more than two aliphatic monocarboxylic acids (g), more preferably not more than a single aliphatic monocarboxylic acid (g).

[0099] Preferably, the total weight content of the one or more indoles of general formula (I) is greater than the total weight content of the one or more aliphatic monocarboxy lie acids (g).

[0100] Preferably, the ratio of the total weight content of the one or more indoles of general formula (I) to the total weight content of one or more aliphatic monocarboxylic acids (g) is within the range of from 9: 1 to 1:9; preferably 8: 1 to 1:8; more preferably 7: 1 to 1:7; still more preferably 6: 1 to 1:6; yet more preferably 5 : 1 to 1:5; even more preferably 4: 1 to 1:4; most preferably 3: 1 to 1:3; and in particular 2: 1 to 1:2.

[0101] Preferably, the total weight content of the one or more aliphatic monocarboxylic acids (g) is greater than the total weight content of the one or more aromatic imides of general formula (II).

[0102] Preferably, the ratio of the total weight content of the one or more aromatic imides of general formula (II) to the total weight content of one or more aliphatic monocarboxylic acids (g) is within the range of from 6: 1 to 1: 12; preferably 5: 1 to 1: 11; more preferably 4: 1 to 1: 10; still more preferably 3: 1 to 1:9; yet more preferably 2: 1 to 1:8; even more preferably l: l to 1:7; most preferably 1:2 to 1:6; and in particular 1:3 to 1:5.

[0103] In preferred embodiments, the anticorrosion liquid according to the invention comprises one or more aromatic carboxylic acids (h); preferably selected from aromatic monocarboxylic acids; more preferably benzoic acid.

[0104] Preferably, the anticorrosion liquid according to the invention comprises not more than two aromatic carboxylic acids (h), more preferably not more than a single aromatic carboxylic acid (h).

[0105] Preferably, the total weight content of the one or more indoles of general formula (I) is greater than the total weight content of the one or more aromatic carboxylic acids (h).

[0106] Preferably, the ratio of the total weight content of the one or more indoles of general formula (I) to the total weight content of one or more aromatic carboxylic acids (h) is within the range of from 9: 1 to 1:9; preferably 8: 1 to 1:8; more preferably 7: 1 to 1:7; still more preferably 6: 1 to 1:6; yet more preferably 5: 1 to 1:5; even more preferably 4: 1 to 1:4; most preferably 3: 1 to 1:3; and in particular 2: 1 to 1:2.

[0107] Preferably, the total weight content of the one or more aromatic carboxylic acids (h) is greater than the total weight content of the one or more aromatic imides of general formula (II).

[0108] Preferably, the ratio of the total weight content of the one or more aromatic imides of general formula (II) to the total weight content of one or more aromatic carboxylic acids (h) is within the range of from 6: l to 1: 12; preferably 5 : 1 to 1: 11; more preferably 4: 1 to 1: 10; still more preferably 3 : 1 to 1:9; yet more preferably 2: 1 to 1:8; even more preferably 1: 1 to 1:7; most preferably 1:2 to 1:6; and in particular 1:3 to 1:5.

[0109] In preferred embodiments, the anticorrosion liquid according to the invention comprises one or more inorganic salts (i); preferably selected from molybdates; more preferably sodium molybdate.

[0110] Preferably, the anticorrosion liquid according to the invention comprises not more than two inorganic salts (i), more preferably not more than a single inorganic salt (i).

[0111] Preferably, the total weight content of the one or more indoles of general formula (I) is greater than the total weight content of the one or more inorganic salts (i).

[0112] Preferably, the ratio of the total weight content of the one or more indoles of general formula (I) to the total weight content of one or more inorganic salts (i) is within the range of from 9: 1 to 1:8; preferably 8: 1 to 1:7; more preferably 7: 1 to 1:6; still more preferably 6: 1 to 1:5; yet more preferably 5: l to 1:4; even more preferably 4: 1 to 1:3; most preferably 3: 1 to 1:2; and in particular 2: 1 to 1: 1.

[0113] Preferably, the total weight content of the one or more inorganic salts (i) is greater than the total weight content of the one or more aromatic imides of general formula (II).

[0114] Preferably, the ratio of the total weight content of the one or more aromatic imides of general formula (II) to the total weight content of one or more inorganic salts (i) is within the range of from 7: 1 to 1: 11; preferably 6: 1 to 1: 10; more preferably 5: 1 to 1:9; still more preferably 4: 1 to 1:8; yet more preferably 3: 1 to 1:7; even more preferably 2: 1 to 1:6; most preferably 1: 1 to 1:5; and in particular 1:2 to 1:4.

[0115] In preferred embodiments, the anticorrosion liquid according to the invention comprises one or more sulfonic acids (j); preferably 4-(2 -hydroxyethyl) 1 -piperazine-ethansulfonic acid (HEPES).

[0116] Preferably, the anticorrosion liquid according to the invention comprises not more than two sulfonic acids (j), more preferably not more than a single sulfonic acid (j).

[0117] Preferably, the total weight content of the one or more indoles of general formula (I) is greater than the total weight content of the one or more sulfonic acids (j).

[0118] Preferably, the total weight content of the one or more aromatic imides of general formula (II) is greater than the total weight content of the one or more sulfonic acids (j).

[0119] Another aspect of the invention relates to anticorrosion liquid according to the invention as describe above, which is a concentrate (i.e. a concentrated anticorrosion liquid). The concentrate is preferably not intended to be used as such but is preferably to be diluted (i.e. for dilution) prior to use.

[0120] Preferably, the concentrated anticorrosion liquid according to the invention comprises or essentially consists of- the one or more indoles of general formula (I), preferably 2-methylindole, ethylindol-2 -carboxylate, 2-phenylindole, tryptophan, 3 -indolemethanol, indole-3 -acetamide, 5 -methoxyindole, 5 -nitroindole, indole-5-carbonitrile, methylindole-6-carboxylate, or a combination thereof;- the one or more aromatic imides of general formula (II), preferably phthalimide, saccharin, or a combination thereof;- the one or more liquid aliphatic polyhydroxy compounds (c), preferably triethanolamine;- optionally, the water (d);- optionally, the one or more phosphonic acids (e), preferably octyl phosphonic acid;- optionally, the one or more aliphatic dicarboxylic acids (f), preferably dodecanedioic acid;- optionally, the one or more aliphatic monocarboxylic acids (g), preferably pelargonic acid, isonona- noic acid or a combination thereof;- optionally, the one or more aromatic carboxylic acids (h), preferably benzoic acid, histidine, or a combination thereof;- optionally, the one or more inorganic salts (i), preferably sodium molybdate; and- optionally, the one or more sulfonic acids (j), preferably HEPES.

[0121] In preferred embodiments, the concentrated anticorrosion liquid according to the invention comprises, relative to the total weight of the liquid:

[0122] Preferably, the concentrated anticorrosion liquid according to the invention comprises one or more indoles of general formula (I), wherein the total weight content of the one or more indoles of general formula (I) is at least 0.5 wt.-%, preferably at least 1.0 wt.-%, more preferably at least 1.5 wt.- %, still more preferably at least 2.0 wt.-%, yet more preferably at least 2.5 wt.-%, even more preferably at least 3.0 wt.-%, most preferably at least 3.5 wt.-%, and in particular at least 4.0 wt.-%, relative to the total weight of the concentrated anticorrosion liquid.

[0123] Preferably, the concentrated anticorrosion liquid according to the invention comprises one or more indoles of general formula (I), wherein the total weight content of the one or more indoles of general formula (I) is at most 8.5 wt.-%, preferably at most 8.0 wt.-%, more preferably at most 7.5 wt.- %, still more preferably at most 7.0 wt.-%, yet more preferably at most 6.5 wt.-%, even more preferably at most 6.0 wt.-%, most preferably at most 5.5 wt.-%, and in particular at most 5.0 wt.-%, relative to the total weight of the concentrated anticorrosion liquid.

[0124] Preferably, the concentrated anticorrosion liquid according to the invention comprises one or more indoles of general formula (I), wherein the total weight content of the one or more indoles of general formula (I) is within the range of from 4.5±4.0 wt.-%, preferably 4.5±3.5 wt.-%, more preferably 4.5±3.0 wt.-%, still more preferably 4.5±2.5 wt.-%, yet more preferably 4.5±2.0 wt.-%, even more preferably 4.5±1.5 wt.-%, most preferably 4.5±1.0 wt.-%, and in particular 4.5±0.5 wt.-%, relative to the total weight of the concentrated anticorrosion liquid.

[0125] Preferably, the concentrated anticorrosion liquid according to the invention comprises one or more aromatic imides of general formula (II), wherein the total weight content of the one or more aromatic imides of general formula (II) is at least 0.2 wt.-%, preferably at least 0.3 wt.-%, more preferably at least 0.4 wt.-%, still more preferably at least 0.5 wt.-%, yet more preferably at least 0.6 wt.-%, even more preferably at least 0.7 wt.-%, most preferably at least 0.8 wt.-%, and in particular at least 0.9 wt.- %, relative to the total weight of the concentrated anticorrosion liquid.

[0126] Preferably, the concentrated anticorrosion liquid according to the invention comprises one or more aromatic imides of general formula (II), wherein the total weight content of the one or more aromatic imides of general formula (II) is at most 5.0 wt.-%, preferably at most 4.5 wt.-%, more preferably at most 4.0 wt.-%, still more preferably at most 3.5 wt.-%, yet more preferably at most 3.0 wt.-%, even more preferably at most 2.5 wt.-%, most preferably at most 2.0 wt.-%, and in particular at most 1.5 wt.- %, relative to the total weight of the concentrated anticorrosion liquid.

[0127] Preferably, the concentrated anticorrosion liquid according to the invention comprises one or more aromatic imides of general formula (II), wherein the total weight content of the one or more aromatic imides of general formula (II) is within the range of from 1.0±0.9 wt.-%, preferably 1.0±0.8 wt.- %, more preferably 1.0±0.7 wt.-%, still more preferably 1.0±0.6 wt.-%, yet more preferably 1.0±0.5 wt.- %, even more preferably 1.0±0.4 wt.-%, most preferably 1.0±0.3 wt.-%, and in particular 1.0±0.2 wt.- %, relative to the total weight of the concentrated anticorrosion liquid.

[0128] In preferred embodiments of the concentrated anticorrosion liquid according to the invention, the total weight content of the one or more liquid aliphatic polyhydroxy compounds (c) is at least 35 wt.-%, more preferably at least 40 wt.-%, still more preferably at least 45 wt.-%, yet more preferably at least 50 wt.-%, even more preferably at least 55 wt.-%, most preferably at least 60 wt.-%, and in particular at least 65 wt.-%, relative to the total weight of the concentrated anticorrosion liquid.

[0129] In preferred embodiments of the concentrated anticorrosion liquid according to the invention, the total weight content of the one or more liquid aliphatic polyhydroxy compounds (c) is at most 87.5 wt.-%, preferably at most 85 wt.-%, more preferably at most 82.5 wt.-%, still more preferably at most 80 wt.-%, yet more preferably at most 77.5 wt.-%, even more preferably at most 75 wt.-%, most preferably at most 72.5 wt.-%, and in particular at most 70 wt.-%, relative to the total weight of the concentrated anticorrosion liquid.

[0130] In preferred embodiments of the concentrated anticorrosion liquid according to the invention, the total weight content of the one or more liquid aliphatic polyhydroxy compounds (c) is within the range of from 65±20 wt.-%, preferably 65±17.5 wt.-%, more preferably 65±15 wt.-%, still more preferably 65±12.5 wt.-%, yet more preferably 65±10 wt.-%, even more preferably 65±7.5 wt.-%, most preferably 65±5.0 wt.-%, and in particular 65±2.5 wt.-%, relative to the total weight of the concentrated anticorrosion liquid.

[0131] Preferably, the concentrated anticorrosion liquid according to the invention comprises water (d), wherein the weight content of the water (d) is at least 2.5 wt.-%, more preferably at least 4.0 wt.-%, still more preferably at least 5.5 wt.-%, yet more preferably at least 7.0 wt.-%, even more preferably at least 8.5 wt.-%, most preferably at least 10 wt.-%, and in particular at least 11.5 wt.-%, relative to the total weight of the concentrated anticorrosion liquid.

[0132] Preferably, the concentrated anticorrosion liquid according to the invention comprises water (d), wherein the weight content of the water (d) is at most 30 wt.-%, preferably at most 27.5 wt.-%, more preferably at most 25 wt.-%, still more preferably at most 22.5 wt.-%, yet more preferably at most 20 wt.-%, even more preferably at most 17.5 wt.-%, most preferably at most 15 wt.-%, and in particular at most 12.5 wt.-%, relative to the total weight of the concentrated anticorrosion liquid.

[0133] Preferably, the concentrated anticorrosion liquid according to the invention comprises water (d), wherein the weight content of the water (d) is within the range of from 12±11.5 wt.-%, preferably 12±10 wt.-%, more preferably 12±8.5 wt.-%, still more preferably 12±7 wt.-%, yet more preferably 12±5.5 wt.-%, even more preferably 12±4 wt.-%, most preferably 12±2.5 wt.-%, and in particular 12±1 wt.-%, relative to the total weight of the concentrated anticorrosion liquid.

[0134] Preferably, the concentrated anticorrosion liquid according to the invention comprises one or more phosphonic acids (e), wherein the total weight content of the one or more phosphonic acids (e) is within the range of from 3.5±3.2 wt.-%, preferably 3.5±2.8 wt.-%, more preferably 3.5±2.4 wt.-%, still more preferably 3.5±2.0 wt.-%, yet more preferably 3.5±1.6 wt.-%, even more preferably 3.5±1.2 wt.- %, most preferably 3.5±0.8 wt.-%, and in particular 3.5±0.4 wt.-%, relative to the total weight of the concentrated anticorrosion liquid.

[0135] Preferably, the concentrated anticorrosion liquid according to the invention comprises one or more aliphatic dicarboxylic acids (f), wherein the total weight content of the one or more aliphatic dicarboxylic acids (f) is within the range of from 1 ,0±0.9 wt.-%, preferably 1 ,0±0.8 wt.-%, more preferably1.0±0.7 wt.-%, still more preferably 1.0±0.6 wt.-%, yet more preferably 1.0±0.5 wt.-%, even more preferably 1.0±0.4 wt.-%, most preferably 1.0±0.3 wt.-%, and in particular 1.0±0.2 wt.-%, relative to the total weight of the concentrated anticorrosion liquid.

[0136] Preferably, the concentrated anticorrosion liquid according to the invention comprises one or more aliphatic monocarboxylic acids (g), wherein the total weight content of the one or more aliphatic monocarboxylic acids (g) is within the range of from 4.0±3.5 wt.-%, preferably 4.0±3.0 wt.-%, more preferably 4.0±2.5 wt.-%, still more preferably 4.0±2.0 wt.-%, yet more preferably 4.0±1.5 wt.-%, even more preferably 4.0±2.0 wt.-%, most preferably 4.0±1.5 wt.-%, and in particular 4.0±1.0 wt.-%, relative to the total weight of the concentrated anticorrosion liquid.

[0137] Preferably, the concentrated anticorrosion liquid according to the invention comprises one or more aromatic carboxylic acids (h), wherein the total weight content of the one or more aromatic carboxylic acids (h) is within the range of from 4.0±3.5 wt.-%, preferably 4.0±3.0 wt.-%, more preferably 4.0±2.5 wt.-%, still more preferably 4.0±2.0 wt.-%, yet more preferably 4.0±l .5 wt.-%, even more preferably 4.0±2.0 wt.-%, most preferably 4.0±1.5 wt.-%, and in particular 4.0±1.0 wt.-%, relative to the total weight of the concentrated anticorrosion liquid.

[0138] Preferably, the concentrated anticorrosion liquid according to the invention comprises one or more inorganic salts (i), wherein the total weight content of the one or more inorganic salts (i) is within the range of from 3.0±2.6 wt.-%, preferably 3.0±2.3 wt.-%, more preferably 3.0±2.0 wt.-%, still more preferably 3.0±1.7 wt.-%, yet more preferably 3.0±1.4 wt.-%, even more preferably 3.0±l.l wt.-%, most preferably 3.0±0.8 wt.-%, and in particular 3.0±0.5 wt.-%, relative to the total weight of the concentrated anticorrosion liquid.

[0139] Another aspect of the invention relates to an anticorrosion liquid according to the invention as described above, which is ready-for-use.

[0140] Preferably, the ready-to-use anticorrosion liquid according to the invention is prepared from the concentrate according to the invention as described above by dilution. Dilution is preferably achieved by adding ethylene glycol or propylene glycol to the concentrate, preferably in an excessive amount. In preferred embodiments, the ethylene glycol or propylene glycol aids the use of the anticorrosion liquid as heat transfer fluid.

[0141] Preferably, the ready-to-use anticorrosion liquid according to the invention comprises or essentially consists of- the one or more indoles of general formula (I), preferably 2-methylindole, ethylindol-2 -carboxylate, 2-phenylindole, tryptophan, 3 -indolemethanol, indole-3 -acetamide, 5 -methoxyindole, 5 -nitroindole, indole-5-carbonitrile, methylindole-6-carboxylate, or a combination thereof;- the one or more aromatic imides of general formula (II), preferably phthalimide, saccharin, or a combination thereof;- the one or more liquid aliphatic polyhydroxy compounds (c); preferably ethylene glycol, triethanolamine, or a combination thereof;- optionally, the water (d);- optionally, the one or more phosphonic acids (e), preferably octyl phosphonic acid;- optionally, the one or more aliphatic dicarboxylic acids (f), preferably dodecanedioic acid;- optionally, the one or more aliphatic monocarboxylic acids (g), preferably pelargonic acid, isonona- noic acid or a combination thereof;- optionally, the one or more aromatic carboxylic acids (h), preferably benzoic acid, histidine, or a combination thereof;- optionally, the one or more inorganic salts (i), preferably sodium molybdate; and- optionally, the one or more sulfonic acids (j), preferably HEPES.

[0142] Preferably, the ready-to-use anticorrosion liquid according to the invention comprises one or more indoles of general formula (I), wherein the total weight content of the one or more indoles of general formula (I) is at least 0.05 wt.-%, preferably at least 0.1 wt.-%, relative to the total weight of the ready-to-use anticorrosion liquid.

[0143] Preferably, the ready-to-use anticorrosion liquid according to the invention comprises one or more indoles of general formula (I), wherein the total weight content of the one or more indoles of general formula (I) is at most 1.0 wt.-%, preferably at most 0.9 wt.-%, more preferably at most 0.8 wt.- %, still more preferably at most 0.7 wt.-%, yet more preferably at most 0.6 wt.-%, even more preferably at most 0.5 wt.-%, most preferably at most 0.4 wt.-%, and in particular at most 0.3 wt.-%, relative to the total weight of the ready-to-use anticorrosion liquid.

[0144] Preferably, the ready-to-use anticorrosion liquid according to the invention comprises one or more aromatic imides of general formula (II), wherein the total weight content of the one or more aromatic imides of general formula (II) is at least 0.01 wt.-%, preferably at least 0.02 wt.-%, relative to the total weight of the ready-to-use anticorrosion liquid.

[0145] Preferably, the ready-to-use anticorrosion liquid according to the invention comprises one or more aromatic imides of general formula (II), wherein the total weight content of the one or more aromatic imides of general formula (II) is at most 0.10 wt.-%, preferably at most 0.09 wt.-%, more preferably at most 0.08 wt.-%, still more preferably at most 0.07 wt.-%, yet more preferably at most 0.06 wt.- %, even more preferably at most 0.05 wt.-%, most preferably at most 0.04 wt.-%, and in particular at most 0.03 wt.-%, relative to the total weight of the ready-to-use anticorrosion liquid.

[0146] In preferred embodiments of the ready-to-use anticorrosion liquid according to the invention, the total weight content of the one or more liquid aliphatic polyhydroxy compounds (c) is at least 80 wt.-%, more preferably at least 85 wt.-%, still more preferably at least 90 wt.-%, yet more preferably at least 92 wt.-%, even more preferably at least 94 wt.-%, most preferably at least 96 wt.-%, and in particular at least 98 wt.-%, relative to the total weight of the ready-to-use anticorrosion liquid.

[0147] In preferred embodiments of the ready-to-use anticorrosion liquid according to the invention, the total weight content of the one or more liquid aliphatic polyhydroxy compounds (c) is at most 99.5 wt.-%, preferably at most 99.0 wt.-%, more preferably at most 98.5 wt.-%, relative to the total weight of the ready-to-use anticorrosion liquid.

[0148] Preferably, the ready-to-use anticorrosion liquid according to the invention comprises water (d), wherein the weight content of the water (d) is at least 0.1 wt.-%, more preferably at least 0.2 wt.-%, still more preferably at least 0.3 wt.-%, relative to the total weight of the ready-to-use anticorrosion liquid.

[0149] Preferably, the ready-to-use anticorrosion liquid according to the invention comprises water (d), wherein the weight content of the water (d) is at most 1.0 wt.-%, preferably at most 0.9 wt.-%, more preferably at most 0.8 wt.-%, still more preferably at most 0.7 wt.-%, yet more preferably at most 0.6 wt.-%, even more preferably at most 0.5 wt.-%, most preferably at most 0.4 wt.-%, and in particular at most 0.3 wt.-%, relative to the total weight of the ready-to-use anticorrosion liquid.

[0150] Preferably, the ready-to-use anticorrosion liquid according to the invention comprises one or more phosphonic acids (e), wherein the total weight content of the one or more phosphonic acids (e) is within the range of from 0.01 to 0.50 wt.-%, preferably 0.05 to 0.25 wt.-%, relative to the total weight of the ready-to-use anticorrosion liquid.

[0151] Preferably, the ready-to-use anticorrosion liquid according to the invention comprises one or more aliphatic dicarboxylic acids (f), wherein the total weight content of the one or more aliphatic dicarboxylic acids (f) is within the range of from 0.005 to 0.50 wt.-%, preferably 0.01 to 0.10 wt.-%, relative to the total weight of the ready-to-use anticorrosion liquid.

[0152] Preferably, the ready-to-use anticorrosion liquid according to the invention comprises one or more aliphatic monocarboxylic acids (g), wherein the total weight content of the one or more aliphatic monocarboxylic acids (g) is within the range of from 0.01 to 0.50 wt.-%, preferably 0.05 to 0.25 wt.-%, relative to the total weight of the ready-to-use anticorrosion liquid.

[0153] Preferably, the ready-to-use anticorrosion liquid according to the invention comprises one or more aromatic carboxylic acids (h), wherein the total weight content of the one or more aromatic carboxylic acids (h) is within the range of from 0.01 to 0.50 wt.-%, preferably 0.05 to 0.25 wt.-%, relative to the total weight of the ready-to-use anticorrosion liquid.

[0154] Preferably, the ready-to-use anticorrosion liquid according to the invention comprises one or more inorganic salts (i), wherein the total weight content of the one or more inorganic salts (i) is within the range of from 0.01 to 0.50 wt.-%, preferably 0.05 to 0.25 wt.-%, relative to the total weight of the ready-to-use anticorrosion liquid.

[0155] Another aspect of the invention relates to an anticorrosion liquid according to the invention as described above, which is a geothermal anticorrosion liquid, preferably a geothermal heat transfer fluid.

[0156] Preferably, the geothermal anticorrosion liquid according to the invention is prepared by dilution from the concentrate according to the invention as described above, or from the ready-to-use anticorrosion liquid according to the invention as described above. Dilution is preferably achieved by adding ethylene glycol, propylene glycol, water or any combination thereof to the concentrate, preferably in an excessive amount. In preferred embodiments, the water aids the use of the anticorrosion liquid as geothermal anticorrosion liquid.

[0157] Preferably, the geothermal anticorrosion liquid according to the invention comprises or essentially consists of- the one or more indoles of general formula (I), preferably 2-methylindole, ethylindol-2 -carboxylate, 2-phenylindole, tryptophan, 3 -indolemethanol, indole-3 -acetamide, 5 -methoxyindole, 5 -nitroindole, indole-5-carbonitrile, methylindole-6-carboxylate, or a combination thereof;- the one or more aromatic imides of general formula (II), preferably phthalimide, saccharin, or a combination thereof;- the one or more liquid aliphatic polyhydroxy compounds (c); preferably ethylene glycol, propylene glycol, triethanolamine, or combinations thereof; more preferably ethylene glycol in combination with triethanolamine, or propylene glycol in combination with triethanolamine;- the water (d);- optionally, the one or more phosphonic acids (e), preferably octyl phosphonic acid;- optionally, the one or more aliphatic dicarboxylic acids (f), preferably dodecanedioic acid;- optionally, the one or more aliphatic monocarboxylic acids (g), preferably pelargonic acid, isonona- noic acid or a combination thereof;- optionally, the one or more aromatic carboxylic acids (h), preferably benzoic acid, histidine, or a combination thereof;- optionally, the one or more inorganic salts (i), preferably sodium molybdate; and- optionally, the one or more sulfonic acids (j), preferably HEPES.

[0158] Preferably, the geothermal anticorrosion liquid according to the invention comprises one or more indoles of general formula (I), wherein the total weight content of the one or more indoles of general formula (I) is with the range of from 20 to 2000 ppmw, preferably 200 to 1000 ppmw, more preferably 350 to 800 ppmw, relative to the total weight of the geothermal anticorrosion liquid.

[0159] Preferably, the geothermal anticorrosion liquid according to the invention comprises one or more aromatic imides of general formula (II), wherein the total weight content of the one or more aromatic imides of general formula (II) is within the range of 20 to 2000 ppmw, preferably 30 to 300 ppmw, more preferably 50 to 200 ppmw, relative to the total weight of the geothermal anticorrosion liquid.

[0160] In preferred embodiments of the geothermal anticorrosion liquid according to the invention, the total weight content of the one or more liquid aliphatic polyhydroxy compounds (c) is at least 10 wt.-%, more preferably at least 12.5 wt.-%, still more preferably at least 15 wt.-%, yet more preferably at least17.5 wt.-%, even more preferably at least 20 wt.-%, most preferably at least 22.5 wt.-%, and in particular at least 25 wt.-%, relative to the total weight of the geothermal anticorrosion liquid.

[0161] In preferred embodiments of the geothermal anticorrosion liquid according to the invention, the total weight content of the one or more liquid aliphatic polyhydroxy compounds (c) is at most 90 wt.- %, preferably at most 85 wt.-%, more preferably at most 80 wt.-%, still more preferably at most 75 wt.- %, yet more preferably at most 70 wt.-%, even more preferably at most 65 wt.-%, most preferably at most 60 wt.-%, and in particular at most 55 wt.-%, relative to the total weight of the geothermal anticorrosion liquid.

[0162] Preferably, the geothermal anticorrosion liquid according to the invention comprises water (d), wherein the weight content of the water (d) is at least 10 wt.-%, more preferably at least 15 wt.-%, still more preferably at least 20 wt.-%, yet more preferably at least 25 wt.-%, even more preferably at least 30 wt.-%, most preferably at least 35 wt.-%, and in particular at least 40 wt.-% relative to the total weight of the geothermal anticorrosion liquid.

[0163] Preferably, the geothermal anticorrosion liquid according to the invention comprises water (d), wherein the weight content of the water (d) is at most 92.5 wt.-%, preferably at most 90 wt.-%, more preferably at most 87.5 wt.-%, still more preferably at most 85 wt.-%, yet more preferably at most 82.5 wt.-%, even more preferably at most 80 wt.-%, most preferably at most 77.5 wt.-%, and in particular at most 75 wt.-%, relative to the total weight of the geothermal anticorrosion liquid.

[0164] Preferably, the geothermal anticorrosion liquid according to the invention comprises one or more phosphonic acids (e), wherein the total weight content of the one or more phosphonic acids (e) is within the range of from 100 to 800 ppmw, preferably 250 to 600 ppmw, relative to the total weight of the geothermal anticorrosion liquid.

[0165] Preferably, the geothermal anticorrosion liquid according to the invention comprises one or more aliphatic dicarboxylic acids (f), wherein the total weight content of the one or more aliphatic dicarboxylic acids (f) is within the range of from 10 to 300 ppmw, preferably 50 to 200 ppmw, relative to the total weight of the geothermal anticorrosion liquid.

[0166] Preferably, the geothermal anticorrosion liquid according to the invention comprises one or more aliphatic monocarboxylic acids (g), wherein the total weight content of the one or more aliphatic monocarboxylic acids (g) is within the range of from 100 to 900 ppmw, preferably 300 to 700 ppmw, relative to the total weight of the geothermal anticorrosion liquid.

[0167] Preferably, the geothermal anticorrosion liquid according to the invention comprises one or more aromatic carboxylic acids (h), wherein the total weight content of the one or more aromatic carboxylic acids (h) is within the range of from 100 to 900 ppmw, preferably 300 to 700 ppmw, relative to the total weight of the geothermal anticorrosion liquid.

[0168] Preferably, the geothermal anticorrosion liquid according to the invention comprises one or more inorganic salts (i), wherein the total weight content of the one or more inorganic salts (i) is within the range of from 100 to 700 ppmw, preferably 200 to 550 ppmw, relative to the total weight of the geothermal anticorrosion liquid.

[0169] Another aspect of the invention relates to the use of an anticorrosion liquid according to the invention as described above for transferring heat; preferably geothermal heat.

[0170] Another aspect of the invention relates to the use of an anticorrosion liquid according to the invention as described above as cooling lubricant.

[0171] In preferred embodiments, the anticorrosion liquid according to the invention is used in water circuits, water treatment units, cooling systems, or geothermal heating systems, preferably for inhibiting or controlling corrosion of items, components, devices and the like that come into direct contact with the anticorrosion liquid.

[0172] In preferred embodiments of the use according to the invention, the total weight content of the one or more indoles of general formula (I) is within the range of from 5 to 1500 ppmw, relative to the total weight of the anticorrosion liquid.

[0173] In preferred embodiments of the use according to the invention, the total weight content of the one or more aromatic imides of general formula (II) is within the range of from 2 to 1000 ppmw, relative to the total weight of the anticorrosion liquid.

[0174] Another aspect of the invention relates to use of an anticorrosion liquid according to the invention as described above as corrosion inhibitor; preferably for items made of copper, brass, iron, steel, aluminum, or combinations thereof.

[0175] Another aspect of the invention relates to the use of a concentrated anticorrosion liquid according to the invention as described above for preparing a ready-to-use anticorrosion liquid according to the invention as described above, or for preparing a geothermal anticorrosion liquid according to the invention as described above.

[0176] Preferably, the concentrated anticorrosion liquid according to the invention is diluted by adding one or more liquid aliphatic polyhydroxy compounds (c) and / or water (d).

[0177] Preferably, the dilution ratio of the volume of the concentrated anticorrosion liquid to the added overall volume of the one or more liquid aliphatic polyhydroxy compounds (c) and / or water (d) is at least 1: 10, preferably at least 1:25, more preferably at least 1:50, still more preferably at least 1:75, yet more preferably at least 1: 100, even more preferably at least 1:200, most preferably at least 1:500, and in particular at least 1 : 1000.

[0178] Another aspect of the invention relates to a method of operating a water circuit, water treatment unit, cooling system, or geothermal heating system comprising circulation of an anticorrosion liquidaccording to the invention, preferably for inhibiting or controlling corrosion and / or for transferring heat and / or as cooling lubricant.

[0179] The anticorrosion liquid according to the invention can be used as a concentrate or ready-to-use anticorrosion liquid as corrosion protection in heat transfer fluids, cooling lubricants and water systems in various industries, applications and processes in which the metals copper, brass, soft solder, steel, cast iron, aluminum are used alone or in combination.

[0180] Exemplified industries include but are not limited to:- motor vehicle industry (e.g. vehicle production, coolants in engines and other vehicle components, vehicles in salty environments (e.g. winter months, road salt);- construction industry (e.g. steel reinforcement in concrete, concrete buildings and foundations);- marine industry (e.g. ships, boats, underwater and saltwater environments);- aerospace industry (e.g. components in extreme climatic conditions);- energy industry, chemical industry (e.g. oil industry, gas industry, pipelines, drilling rigs, power plants, cooling circuits, cooling towers, heat exchangers, production facilities, plants, offshore plants);- mining industry;- paper industry, pulp industry;- textile industry, leather industry;- paint industry, varnish industry;- food industry, beverage industry;- electrical industry.

[0181] Exemplified applications in metalworking include but are not limited to- machining applications (e.g. milling, turning, grinding);- forging, casting;- metal rolling, metal drawing (e.g. lubricants, coolants);- welding processes;- galvanizing, zinc coating;- metal cleaning, metal degreasing;- machine tools, production systems;- hydraulic fluids.

[0182] Exemplified aqueous applications include but are not limited to:- cooling circuits and cooling systems in industry (e.g. cooling systems, machine cooling systems, industrial boilers, generators, heat exchangers, industrial heat transfer systems, power plants, industrial plants);- cooling circuits and cooling systems for vehicles, ships and other means of transportation;- water treatment, water distribution (e.g. drinking water treatment, industrial water treatment, waste water treatment);- heating circuits, heating systems, air conditioning systems (e.g. in residential buildings, large buildings, industrial buildings and plants);- air cooling systems;- aquariums, pond systems;- irrigation systems;- drinking water systems;- waste water systems, sewage treatment plants;- fire extinguishing systems.

[0183] Exemplified applications in the energy sector include but are not limited to:- power plants, cooling circuits (e.g. cooling towers, heat exchangers);- hydroelectric power plants (e.g. in power plants, hydraulic systems);- thermal power plants;- nuclear power plants;- solar thermal energy;- geothermal energy;- heat storage;- wind power plants;- biomass power plants;- fuel cells;- natural gas liquefaction plants.

[0184] The following examples further illustrate the invention but are not to be construed as limiting its scope.Example 1:

[0185] The following anticorrosion liquid (concentrate) according to the invention was prepared by mixing:179 wt.-% masterbatch TEA LFG 85

[0186] The anticorrosive performance was tested in accordance with ASTM D1384 and the results are compiled in the table here below:

[0187] As can be seen, the corrosion rates are very low, especially for copper and brass. This formulation guarantees corrosion protection in copper-based systems.

[0188] The concentrate may be converted into e.g. a heat transfer fluid that is a ready-to-use anticorrosion liquid by adding ethylene glycol (or alternatively e.g. propylene glycol). For use as fluid for transporting geothermal heat, the ready-to-use anticorrosion liquid may be further diluted by adding water:179 wt.-% masterbatch TEA LFG 85 - low freeze grade blend of triethanolamine and 15% waterExample 2:

[0189] The following experiments were performed in accordance with ASTM D 1384 at a temperature of 80°C (instead of 88°C). Results are classified “good” if all measured removal values for copper, soft solder, brass, steel and gray cast iron are below the limit values of ASTM D3306. Results are classified “poor” if at least one measured removal value for copper, soft solder, brass, steel and gray cast iron is above the limit values of ASTM D 3306.

[0190] Solutions with the following composition were used:- 62.6 wt.-% corrosive water (according to ASTM D1384)- 36.28 wt.-% ethylene glycol- 1.12 % wt.-% inhibitor concentrate (anticorrosion liquid).

[0191] Experimental results are shown in Figure 1. Data points with symbols ▲ are good, whereas data points with symbols • are poor.

[0192] The data demonstrate that- indoles alone, i.e. without aromatic imides, provide poor results;- aromatic imides alone, i.e. without indoles, provide poor results;- combinations or aromatic imides with indoles provide synergistic effects, especially when the concentration of the indole exceeds the concentration of the aromatic imide.Example 3:

[0193] In analogy to Examples 1 and 2, it was shown that replacing tryptophan with another amino acid, namely histidine or proline, provides poor results in each case in combination with phthalimide:Example 4:

[0194] In analogy to Examples 1, 2 and 3, it was shown that replacing tryptophan with another indole of general formula (I), namely 5-methoxyindol, also provides good results in each case in combination with phthalimide, whereas isatine (i.e., 2,3-dioxoindolin), which is not in accordance with general formula (I) provides poor results:Example 5:

[0195] In analogy to Examples 1, 2, 3 and 4, it was shown that phthalimide may at least partially be replaced with a corresponding amount of saccharin:Example 6:

[0196] In analogy to Examples 1, 2, 3, 4 and 5, it was shown that replacing phthalimide with imides carrying a substituent at the N-atom such as N-methyl phthalimide or with aliphatic imides such as succinimide provides poor results in each case in combination with tryptophan:

Claims

Patent claims:

1. An anticorrosion liquid comprising(a) one or more indoles of general formula (I)whereinR1 means -H or -Ci-6-alkyl; preferably -H; andR2, R3, R4, R5, R6 and R7 independently of one another mean -H, -F, -Cl, -Br, -Ci-6- alkyl, -Ci-6-alkyl-C(=O)H, -Ci.6-alkyl-C(=O)OH, -Ci.6-alkyl(NH2)C(=O)OH, -Ci.6-al- kylC(=O)-C(=O)OH, -Ci-6-alkyl-C(=O)OCi-6-alkyl, -Ci.6-alkyl-C(=O)NH2, -Ci.6-alkyl- C(=O)NHCi-6-alkyl, -Ci-6-alkyl-C(=O)N(Ci-6-alkyl)2, -Ci-6-alkyl-NH2, -Ci-e-alkyl-NHCi. e-alkyl, -Ci-6-alkyl-N(Ci-6-alkyl)2, -Ci-6-alkyl-NHC(=O)Ci-6-alkyl, -Ci-e-alkyl-OH, -Ci-6- alkyl-OCi.6-alkyl, -CN,-C(=O)H, -C(=O)OH, -C(=O)OCi.6-alkyl, -C(=O)NH2, -C(=O)NHCi-6-alkyl, -C(=O)N(Ci.6-alkyl)2, -NH2, -NH-Ci -e-alkyl, -N(Ci.6-alkyl)2, -NHC(=O)Ci-e-alkyl, -NO2, -OH, -O-Ci-e-alkyl, or -phenyl;(b) one or more aromatic imides of general formula (II)whereinAl and A2 independently of one another mean C(=O), S(=O), or S(=O)2;R8 means -H, NHZ, N(C’i -e-alkyl ) . or (Mn+)i / n, wherein M is a metal; andR9, RIO, Rll and R12 independently of one another mean -H, -F, -Cl, -Br, -Ci-e-alkyl, -OH, -O-Ci-e-alkyl, -Ci-e-alkyl-OH, -C(=O)OH, -Ci-e-alkyl-C(=O)OH, -NH2, -Ci-e-alkyl- NH2, -NH-CI -e-alkyl, -Ci-e-alkyl-NH-Ci. e-alkyl, -N(Ci-e-alkyl)2, or -Ci.e-alkyl-N(Ci.e-al- kyl ;(c) one or more liquid aliphatic polyhydroxy compounds; and(d) optionally, water.. The anticorrosion liquid according to claim 1, which comprises(a) 2-methylindole, ethylindol-2-carboxylate, 2-phenylindole, tryptophan, 3 -indolemethanol, indole-3 -acetamide, 5 -methoxyindole, 5 -nitroindole, indole-5 -carbonitrile, methylindole-6 -carboxylate, or a combination thereof;(b) phthalimide, saccharin, or a combination thereof; and(c) preferably, triethanolamine.

3. The anticorrosion liquid according to claim 1 or 2, which is selected from solutions, emulsions and suspensions; preferably solutions.

4. The anticorrosion liquid according to any of the preceding claims, wherein in general formula (I) at least 4 of R2, R3, R4, R5, R6 and R7 mean -H.

5. The anticorrosion liquid according to any of the preceding claims, wherein in general formula (I) R1 means -H.

6. The anticorrosion liquid according to any of the preceding claims, wherein in general formula (I) R2 means -H, -Ci-6-alkyl, -C(=O)OCi-6-alkyl, or -phenyl; preferably -H, -CH,. -C(=O)OCH2CH3, or -phenyl.

7. The anticorrosion liquid according to any of the preceding claims, wherein in general formula (I) R3 means -H, -Ci 6-alkyl(NH2)C(=O)OH, -Ci e-alkyl-OH, -C(=O)H, -Ci 6-alkyl-C(=O)NH2, or -Ci.6-alkyl-C(=O)OH; preferably -H, -CH2CH(NH2)C(=O)OH, -CH2OH, -C(=O)H, -CH2C(=O)NH2, or -CH2CH2C(=O)OH.

8. The anticorrosion liquid according to any of the preceding claims, wherein in general formula (I) R4 means -H.

9. The anticorrosion liquid according to any of the preceding claims, wherein in general formula (I) R5 means -H, -O-Ci-6-alkyl, -NO2, or -CN; more preferably -H, -OCH3, -NO2, or -CN.

10. The anticorrosion liquid according to any of the preceding claims, wherein in general formula (I) R6 means -H or -C(=O)OCi-6-alkyl; more preferably -H or -C(=O)OCH3.

11. The anticorrosion liquid according to any of the preceding claims, wherein in general formula (I) R7 means -H.

12. The anticorrosion liquid according to any of the preceding claims, wherein the one or more indoles of general formula (I) are independently of one another selected from 2-methylindole, ethyl- indol-2 -carboxylate, 2-phenylindole, tryptophan, 3 -indolemethanol, indole-3-acetamide, 5-meth- oxyindole, 5 -nitroindole, indole-5-carbonitrile, methylindole-6-carboxylate and combinations thereof.

13. The anticorrosion liquid according to any of the preceding claims, wherein in general formula (II) at least 3 of R9, RIO, Rll and R12 mean -H.

14. The anticorrosion liquid according to any of the preceding claims, wherein in general formula (II) Al and A2 both mean C(=O).

15. The anticorrosion liquid according to any of claims 1 to 13, wherein in general formula (II) Al means C(=O) and A2 means S(=O)2.

16. The anticorrosion liquid according to any of the preceding claims, wherein in general formula (II) R8 means -H.

17. The anticorrosion liquid according to any of claims 1 to 15, wherein in general formula (II) R8 means NHZ, N(Ci-6-alkyl)4+, or (Mn+)i / n, wherein M is a metal, preferably Na+or K+.

18. The anticorrosion liquid according to any of the preceding claims, wherein in general formula (II) R9 means -H.

19. The anticorrosion liquid according to any of the preceding claims, wherein in general formula (II) RIO means -H.

20. The anticorrosion liquid according to any of the preceding claims, wherein in general formula (II) Rll means -H.

21. The anticorrosion liquid according to any of the preceding claims, wherein in general formula (II) R12 means -H.

22. The anticorrosion liquid according to any of the preceding claims, wherein the one or more aromatic imides of general formula (II) are independently of one another selected from phthalimide, saccharin, and combinations thereof.

23. The anticorrosion liquid according to any of the preceding claims, wherein the one or more liquid aliphatic polyhydroxy compounds (c) are independently of one another selected from ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, ethanolamine, diethanolamine, triethanolamine, and combinations thereof; preferably ethylene glycol, propylene glycol, triethanolamine and combinations thereof; more preferably triethanolamine.

24. The anticorrosion liquid according to any of the preceding claims, which comprises water and wherein the pH value of the anticorrosion liquid is at least 5.0, preferably at least 5.5, more preferably at least 6.0, still more preferably at least 6.5, yet more preferably at least 7.0, even more preferably at least 7.5, most preferably at least 8.0, and in particular at least 8.5.

25. The anticorrosion liquid according to any of the preceding claims, which comprises water and wherein the pH value of the anticorrosion liquid is within the range of 9.0±0.9, preferably 9.0±0.8, more preferably 9.0±0.7, still more preferably 9.0±0.6, yet more preferably 9.0±0.5, even more preferably 9.0±0.4, most preferably 9.0±0.3, and in particular 9.0±0.2.

26. The anticorrosion liquid according to any of the preceding claims, which comprises water and wherein the pH value of the anticorrosion liquid is within the range of 8.5±0.9, preferably 8.5±0.8, more preferably 8.5±0.7, still more preferably 8.5±0.6, yet more preferably 8.5±0.5, even more preferably 8.5±0.4, most preferably 8.5±0.3, and in particular 8.5±0.2.

27. The anticorrosion liquid according to any of the preceding claims, which comprises water and wherein the pH value of the anticorrosion liquid is within the range of 8.0±0.9, preferably 8.0±0.8, more preferably 8.0±0.7, still more preferably 8.0±0.6, yet more preferably 8.0±0.5, even more preferably 8.0±0.4, most preferably 8.0±0.3, and in particular 8.0±0.2.

28. The anticorrosion liquid according to any of the preceding claims, which comprises water and wherein the pH value of the anticorrosion liquid is within the range of 7.5±0.9, preferably 7.5±0.8, more preferably 7.5±0.7, still more preferably 7.5±0.6, yet more preferably 7.5±0.5, even more preferably 7.5±0.4, most preferably 7.5±0.3, and in particular 7.5±0.2.

29. The anticorrosion liquid according to any of the preceding claims, wherein the one or more indoles of general formula (I) and the one or more aromatic imides of general formula (II) provide a synergistic anticorrosive effect.

30. The anticorrosion liquid according to any of the preceding claims, wherein the total weight content of the one or more indoles of general formula (I) is greater than the total weight content of the one or more aromatic imides of general formula (II).

31. The anticorrosion liquid according to any of the preceding claims, wherein the ratio of the total weight content of the one or more indoles of general formula (I) to the total weight content of one or more aromatic imides of general formula (II) is within the range of from 12: 1 to 1:5; preferably 11: 1 to 1:4; more preferably 10: 1 to 1:3; still more preferably 9: 1 to 1:2; yet more preferably 8: 1 to 1: 1; even more preferably 7: 1 to 2: 1 ; most preferably 6: 1 to 3 : 1 ; and in particular 5 : 1 to 4: 1.

32. The anticorrosion liquid according to any of the preceding claims, which additionally comprises one or more or all of the following (e) through (j):(e) one or more phosphonic acids;(f) one or more aliphatic dicarboxylic acids;(g) one or more aliphatic monocarboxylic acids;(h) one or more aromatic carboxylic acids;(i) one or more inorganic salts; and(j) one or more sulfonic acids.

33. The anticorrosion liquid according to any of the preceding claims, wherein the liquid comprises one or more phosphonic acids (e); preferably selected from aliphatic phosphonic acids; more preferably Ce-Cis-alkyl phosphonic acids; still more preferably octyl phosphonic acid.

34. The anticorrosion liquid according to claim 33, wherein the total weight content of the one or more indoles of general formula (I) is greater than the total weight content of the one or more phosphonic acids (e).

35. The anticorrosion liquid according to claim 33 or 34, wherein the ratio of the total weight content of the one or more indoles of general formula (I) to the total weight content of one or more phosphonic acids (e) is within the range of from 9: 1 to 1:9; preferably 8: 1 to 1:8; more preferably 7: 1 to 1:7; still more preferably 6: 1 to 1 :6; yet more preferably 5: 1 to 1 :5; even more preferably 4: 1 to 1:4; most preferably 3: 1 to 1:3; and in particular 2: 1 to 1:2.

36. The anticorrosion liquid according to any of claims 33 to 35, wherein the total weight content of the one or more phosphonic acids (e) is greater than the total weight content of the one or more aromatic imides of general formula (II).

37. The anticorrosion liquid according to any of claims 33 to 36, wherein the ratio of the total weight content of the one or more aromatic imides of general formula (II) to the total weight content of one or more phosphonic acids (e) is within the range of from 6: 1 to 1: 11; preferably 5: 1 to 1: 10; more preferably 4: 1 to 1:9; still more preferably 3: 1 to 1:8; yet more preferably 2: 1 to 1:7; even more preferably 1: 1 to 1:6; most preferably 1:2 to 1:5; and in particular 1:3 to 1:4.

38. The anticorrosion liquid according to any of the preceding claims, wherein the anticorrosion liquid comprises one or more aliphatic dicarboxylic acids (f); preferably selected from saturated aliphatic dicarboxylic acids; more preferably Ce-Cis-alkyl aliphatic dicarboxylic acids; still more preferably dodecanedioic acid.

39. The anticorrosion liquid according to claim 38, wherein the total weight content of the one or more indoles of general formula (I) is greater than the total weight content of the one or more aliphatic dicarboxylic acids (f).

40. The anticorrosion liquid according to claim 38 or 39, wherein the ratio of the total weight content of the one or more indoles of general formula (I) to the total weight content of one or more aliphatic dicarboxylic acids (f) is within the range of from 12: 1 to 1:5; preferably 11 : 1 to 1:4; more preferably 10: 1 to 1:3; still more preferably 9: 1 to 1:2; yet more preferably 8: 1 to 1: 1; even more preferably 7: 1 to 2: 1 ; most preferably 6: 1 to 3 : 1 ; and in particular 5 : 1 to 4: 1.

41. The anticorrosion liquid according to any of claims 38 to 40, wherein the ratio of the total weight content of the one or more aromatic imides of general formula (II) to the total weight content of one or more aliphatic dicarboxylic acids (f) is within the range of from 9: 1 to 1:9; preferably 8: 1 to 1:8; more preferably 7: 1 to 1:7; still more preferably 6: 1 to 1:6; yet more preferably 5: 1 to 1:5; even more preferably 4: 1 to 1:4; most preferably 3: 1 to 1:3; and in particular 2: 1 to 1:2.

42. The anticorrosion liquid according to any of the preceding claims, wherein the anticorrosion liquid comprises one or more aliphatic monocarboxylic acids (g); preferably selected from saturated aliphatic monocarboxylic acids; more preferably Ce-Cis-alkyl aliphatic monocarboxylic acids; still more preferably having an uneven number of carbon atoms; yet more preferably pelargonic acid, isononanoic acid or a combination thereof.

43. The anticorrosion liquid according to claim 42, wherein the total weight content of the one or more indoles of general formula (I) is greater than the total weight content of the one or more aliphatic monocarboxylic acids (g).

44. The anticorrosion liquid according to claim 42 or 43, wherein the ratio of the total weight content of the one or more indoles of general formula (I) to the total weight content of one or more aliphatic monocarboxylic acids (g) is within the range of from 9: 1 to 1:9; preferably 8: 1 to 1:8; more preferably 7: 1 to 1:7; still more preferably 6: 1 to 1:6; yet more preferably 5: 1 to 1:5; even more preferably 4: 1 to 1:4; most preferably 3 : 1 to 1:3; and in particular 2: 1 to 1:2.

45. The anticorrosion liquid according to any of claims 42 to 44, wherein the total weight content of the one or more aliphatic monocarboxylic acids (g) is greater than the total weight content of the one or more aromatic imides of general formula (II).

46. The anticorrosion liquid according to any of claims 42 to 45, wherein the ratio of the total weight content of the one or more aromatic imides of general formula (II) to the total weight content of one or more aliphatic monocarboxylic acids (g) is within the range of from 6: 1 to 1: 12; preferably 5: 1 to 1: 11; more preferably 4: 1 to 1: 10; still more preferably 3: 1 to 1:9; yet more preferably 2: 1 to 1:8; even more preferably 1: 1 to 1:7; most preferably 1:2 to 1:6; and in particular 1:3 to 1:5.

47. The anticorrosion liquid according to any of the preceding claims, wherein the anticorrosion liquid comprises one or more aromatic carboxylic acids (h); preferably selected from aromatic monocarboxy lie acids; more preferably benzoic acid, histidine, or a combination thereof.

48. The anticorrosion liquid according to claim 47, wherein the total weight content of the one or more indoles of general formula (I) is greater than the total weight content of the one or more aromatic carboxylic acids (h).

49. The anticorrosion liquid according to claim 47 or 48, wherein the ratio of the total weight content of the one or more indoles of general formula (I) to the total weight content of one or more aromatic carboxylic acids (h) is within the range of from 9: 1 to 1:9; preferably 8: 1 to 1:8; more preferably 7: 1 to 1:7; still more preferably 6: 1 to 1:6; yet more preferably 5: 1 to 1:5; even more preferably 4: 1 to 1:4; most preferably 3: 1 to 1:3; and in particular 2: 1 to 1:2.

50. The anticorrosion liquid according to any of claims 47 to 49, wherein the total weight content of the one or more aromatic carboxylic acids (h) is greater than the total weight content of the one or more aromatic imides of general formula (II).

51. The anticorrosion liquid according to any of claims 47 to 50, wherein the ratio of the total weight content of the one or more aromatic imides of general formula (II) to the total weight content of one or more aromatic carboxylic acids (h) is within the range of from 6: 1 to 1: 12; preferably 5 : 1 to 1: 11; more preferably 4: 1 to 1: 10; still more preferably 3: 1 to 1:9; yet more preferably 2: 1 to 1:8; even more preferably 1: 1 to 1:7; most preferably 1:2 to 1:6; and in particular 1:3 to 1:5.

52. The anticorrosion liquid according to any of the preceding claims, wherein the anticorrosion liquid comprises one or more inorganic salts (i); preferably selected from molybdates; more preferably sodium molybdate.

53. The anticorrosion liquid according to claim 52, wherein the total weight content of the one or more indoles of general formula (I) is greater than the total weight content of the one or more inorganic salts (i).

54. The anticorrosion liquid according to claim 52 or 53, wherein the ratio of the total weight content of the one or more indoles of general formula (I) to the total weight content of one or more inorganic salts (i) is within the range of from 9: 1 to 1:8; preferably 8: 1 to 1:7; more preferably 7: 1 to 1:6; still more preferably 6: 1 to 1:5; yet more preferably 5: 1 to 1:4; even more preferably 4: 1 to 1:3; most preferably 3: 1 to 1:2; and in particular 2: 1 to 1: 1.

55. The anticorrosion liquid according to any of claims 52 to 54, wherein the total weight content of the one or more inorganic salts (i) is greater than the total weight content of the one or more aromatic imides of general formula (II).

56. The anticorrosion liquid according to any of claims 52 to 55, wherein the ratio of the total weight content of the one or more aromatic imides of general formula (II) to the total weight content of one or more inorganic salts (i) is within the range of from 7: 1 to 1: 11; preferably 6: 1 to 1: 10; more preferably 5: 1 to 1:9; still more preferably 4: 1 to 1:8; yet more preferably 3: 1 to 1:7; even more preferably 2: 1 to 1:6; most preferably 1 : 1 to 1:5; and in particular 1 :2 to 1 :4.

57. The anticorrosion liquid according to any of the preceding claims, wherein the anticorrosion liquid comprises one or more sulfonic acids (i); preferably HEPES.

58. The anticorrosion liquid according to any of the preceding claims, which is a concentrate; preferably for dilution prior to use.

59. The anticorrosion liquid according to claim 58, which comprises or essentially consists of- the one or more indoles of general formula (I), preferably 2-methylindole, ethylindol-2 -carboxylate, 2-phenylindole, tryptophan, 3 -indolemethanol, indole-3-acetamide, 5-methoxyin- dole, 5 -nitroindole, indole-5 -carbonitrile, methylindole-6-carboxylate, or a combination thereof;- the one or more aromatic imides of general formula (II), preferably phthalimide, saccharin, or a combination thereof;- the one or more liquid aliphatic polyhydroxy compounds (c), preferably triethanolamine;- optionally, the water (d);- optionally, the one or more phosphonic acids (e), preferably octyl phosphonic acid;- optionally, the one or more aliphatic dicarboxylic acids (f), preferably dodecanedioic acid;- optionally, the one or more aliphatic monocarboxylic acids (g), preferably pelargonic acid, isononanoic acid or a combination thereof;- optionally, the one or more aromatic carboxylic acids (h), preferably benzoic acid, histidine, or a combination thereof;- optionally, the one or more inorganic salts (i), preferably sodium molybdate; and- optionally, the one or more sulfonic acids (j), preferably HEPES.

60. The anticorrosion liquid according to claim 58 or 59, wherein the total weight content of the one or more indoles of general formula (I) is at least 0.5 wt.-%, preferably at least 1.0 wt.-%, more preferably at least 1.5 wt.-%, still more preferably at least 2.0 wt.-%, yet more preferably at least 2.5 wt.-%, even more preferably at least 3.0 wt.-%, most preferably at least 3.5 wt.-%, and in particular at least 4.0 wt.-%, relative to the total weight of the anticorrosion liquid.

61. The anticorrosion liquid according to any of claims 58 to 60, wherein the total weight content of the one or more indoles of general formula (I) is at most 8.5 wt.-%, preferably at most 8.0 wt.-%, more preferably at most 7.5 wt.-%, still more preferably at most 7.0 wt.-%, yet more preferably at most 6.5 wt.-%, even more preferably at most 6.0 wt.-%, most preferably at most 5.5 wt.-%, and in particular at most 5.0 wt.-%, relative to the total weight of the anticorrosion liquid.

62. The anticorrosion liquid according to any of claims 58 to 61, wherein the total weight content of the one or more indoles of general formula (I) is within the range of from 4.5±4.0 wt.-%, preferably 4.5±3.5 wt.-%, more preferably 4.5±3.0 wt.-%, still more preferably 4.5±2.5 wt.-%, yet morepreferably 4.5±2.0 wt.-%, even more preferably 4.5±1.5 wt.-%, most preferably 4.5±1.0 wt.-%, and in particular 4.5±0.5 wt.-%, relative to the total weight of the anticorrosion liquid.

63. The anticorrosion liquid according to any of claims 58 to 62, wherein the total weight content of the one or more aromatic imides of general formula (II) is at least 0.2 wt.-%, preferably at least 0.3 wt.-%, more preferably at least 0.4 wt.-%, still more preferably at least 0.5 wt.-%, yet more preferably at least 0.6 wt.-%, even more preferably at least 0.7 wt.-%, most preferably at least 0.8 wt.-%, and in particular at least 0.9 wt.-%, relative to the total weight of the anticorrosion liquid.

64. The anticorrosion liquid according to any of claims 58 to 63, wherein the total weight content of the one or more aromatic imides of general formula (II) is at most 5.0 wt.-%, preferably at most 4.5 wt.-%, more preferably at most 4.0 wt.-%, still more preferably at most 3.5 wt.-%, yet more preferably at most 3.0 wt.-%, even more preferably at most 2.5 wt.-%, most preferably at most 2.0 wt.-%, and in particular at most 1.5 wt.-%, relative to the total weight of the anticorrosion liquid.

65. The anticorrosion liquid according to any of claims 58 to 64, wherein the total weight content of the one or more aromatic imides of general formula (II) is within the range of from 1.0±0.9 wt.- %, preferably 1.0±0.8 wt.-%, more preferably 1.0±0.7 wt.-%, still more preferably 1.0±0.6 wt.- %, yet more preferably 1.0±0.5 wt.-%, even more preferably 1.0±0.4 wt.-%, most preferably 1.0±0.3 wt.-%, and in particular 1.0±0.2 wt.-%, relative to the total weight of the anticorrosion liquid.

66. The anticorrosion liquid according to any of claims 58 to 65, wherein the total weight content of the one or more liquid aliphatic polyhydroxy compounds (c) is at least 35 wt.-%, more preferably at least 40 wt.-%, still more preferably at least 45 wt.-%, yet more preferably at least 50 wt.-%, even more preferably at least 55 wt.-%, most preferably at least 60 wt.-%, and in particular at least 65 wt.-%, relative to the total weight of the anticorrosion liquid.

67. The anticorrosion liquid according to any of claims 58 to 66, wherein the total weight content of the one or more liquid aliphatic polyhydroxy compounds (c) is at most 87.5 wt.-%, preferably at most 85 wt.-%, more preferably at most 82.5 wt.-%, still more preferably at most 80 wt.-%, yet more preferably at most 77.5 wt.-%, even more preferably at most 75 wt.-%, most preferably at most 72.5 wt.-%, and in particular at most 70 wt.-%, relative to the total weight of the anticorrosion liquid.

68. The anticorrosion liquid according to any of claims 58 to 67, wherein the total weight content of the one or more liquid aliphatic polyhydroxy compounds (c) is within the range of from 65±20 wt.-%, preferably 65±17.5 wt.-%, more preferably 65±15 wt.-%, still more preferably 65±12.5 wt.-%, yet more preferably 65±10 wt.-%, even more preferably 65±7.5 wt.-%, most preferably65±5.0 wt.-%, and in particular 65±2.5 wt.-%, relative to the total weight of the anticorrosion liquid.

69. The anticorrosion liquid according to any of claims 58 to 68, which comprises water (d), wherein the weight content of the water (d) is at least 2.5 wt.-%, more preferably at least 4.0 wt.-%, still more preferably at least 5.5 wt.-%, yet more preferably at least 7.0 wt.-%, even more preferably at least 8.5 wt.-%, most preferably at least 10 wt.-%, and in particular at least 11.5 wt.-%, relative to the total weight of the anticorrosion liquid.

70. The anticorrosion liquid according to any of claims 58 to 69, which comprises water (d), wherein the weight content of the water (d) is at most 30 wt.-%, preferably at most 27.5 wt.-%, more preferably at most 25 wt.-%, still more preferably at most 22.5 wt.-%, yet more preferably at most 20 wt.-%, even more preferably at most 17.5 wt.-%, most preferably at most 15 wt.-%, and in particular at most 12.5 wt.-%, relative to the total weight of the anticorrosion liquid.

71. The anticorrosion liquid according to any of claims 58 to 70, which comprises water (d), wherein the weight content of the water (d) is within the range of from 12±11.5 wt.-%, preferably 12±10 wt.-%, more preferably 12±8.5 wt.-%, still more preferably 12±7 wt.-%, yet more preferably 12±5.5 wt.-%, even more preferably 12±4 wt.-%, most preferably 12±2.5 wt.-%, and in particular 12±1 wt.-%, relative to the total weight of the anticorrosion liquid.

72. The anticorrosion liquid according to any of claims 58 to 71, which comprises one or more phos- phonic acids (e), wherein the total weight content of the one or more phosphonic acids (e) is within the range of from 3.5±3.2 wt.-%, preferably 3.5±2.8 wt.-%, more preferably 3.5±2.4 wt.- %, still more preferably 3.5±2.0 wt.-%, yet more preferably 3.5±1.6 wt.-%, even more preferably 3.5±1.2 wt.-%, most preferably 3.5±0.8 wt.-%, and in particular 3.5±0.4 wt.-%, relative to the total weight of the anticorrosion liquid.

73. The anticorrosion liquid according to any of claims 58 to 72, which comprises one or more aliphatic dicarboxylic acids (f), wherein the total weight content of the one or more aliphatic dicarboxylic acids (f) is within the range of from 1.0±0.9 wt.-%, preferably 1.0±0.8 wt.-%, more preferably 1.0±0.7 wt.-%, still more preferably 1.0±0.6 wt.-%, yet more preferably 1.0±0.5 wt.-%, even more preferably 1.0±0.4 wt.-%, most preferably 1.0±0.3 wt.-%, and in particular 1.0±0.2 wt.-%, relative to the total weight of the anticorrosion liquid.

74. The anticorrosion liquid according to any of claims 58 to 73, which comprises one or more aliphatic monocarboxylic acids (g), wherein the total weight content of the one or more aliphatic monocarboxylic acids (g) is within the range of from 4.0±3.5 wt.-%, preferably 4.0±3.0 wt.-%, more preferably 4.0±2.5 wt.-%, still more preferably 4.0±2.0 wt.-%, yet more preferably 4.0±1.5wt.-%, even more preferably 4.0±2.0 wt.-%, most preferably 4.0±1.5 wt.-%, and in particular 4.0±1.0 wt.-%, relative to the total weight of the anticorrosion liquid.

75. The anticorrosion liquid according to any of claims 58 to 74, which comprises one or more aromatic carboxylic acids (h), wherein the total weight content of the one or more aromatic carboxylic acids (h) is within the range of from 4.0±3.5 wt.-%, preferably 4.0±3.0 wt.-%, more preferably 4.0±2.5 wt.-%, still more preferably 4.0±2.0 wt.-%, yet more preferably 4.0±1.5 wt.-%, even more preferably 4.0±2.0 wt.-%, most preferably 4.0±1.5 wt.-%, and in particular 4.0±1.0 wt.-%, relative to the total weight of the anticorrosion liquid.

76. The anticorrosion liquid according to any of claims 58 to 75, which comprises one or more inorganic salts (i), wherein the total weight content of the one or more inorganic salts (i) is within the range of from 3.0±2.6 wt.-%, preferably 3.0±2.3 wt.-%, more preferably 3.0±2.0 wt.-%, still more preferably 3.0±1.7 wt.-%, yet more preferably 3.0±1.4 wt.-%, even more preferably 3.0±l.l wt.- %, most preferably 3.0±0.8 wt.-%, and in particular 3.0±0.5 wt.-%, relative to the total weight of the anticorrosion liquid.

77. The anticorrosion liquid according to any of claims 1 to 57, which is ready-for-use.

78. The anticorrosion liquid according to claim 77, which comprises or essentially consists of- the one or more indoles of general formula (I), preferably 2-methylindole, ethylindol-2 -carboxylate, 2-phenylindole, tryptophan, 3 -indolemethanol, indole-3-acetamide, 5-methoxyin- dole, 5 -nitroindole, indole-5 -carbonitrile, methylindole-6-carboxylate, or a combination thereof;- the one or more aromatic imides of general formula (II), preferably phthalimide, saccharin, or a combination thereof;- the one or more liquid aliphatic polyhydroxy compounds (c); preferably ethylene glycol, triethanolamine, or a combination thereof;- optionally, the water (d);- optionally, the one or more phosphonic acids (e), preferably octyl phosphonic acid;- optionally, the one or more aliphatic dicarboxylic acids (f), preferably dodecanedioic acid;- optionally, the one or more aliphatic monocarboxylic acids (g), preferably pelargonic acid, isononanoic acid or a combination thereof;- optionally, the one or more aromatic carboxylic acids (h), preferably benzoic acid, histidine, or a combination thereof;- optionally, the one or more inorganic salts (i) , preferably sodium molybdate; and- optionally, the one or more sulfonic acids (j), preferably HEPES.

79. The anticorrosion liquid according to claim 77 or 78, wherein the total weight content of the one or more indoles of general formula (I) is at least 0.05 wt.-%, preferably at least 0.1 wt.-%, relative to the total weight of the anticorrosion liquid.

80. The anticorrosion liquid according to any of claims 77 to 79, wherein the total weight content of the one or more indoles of general formula (I) is at most 1.0 wt.-%, preferably at most 0.9 wt.-%, more preferably at most 0.8 wt.-%, still more preferably at most 0.7 wt.-%, yet more preferably at most 0.6 wt.-%, even more preferably at most 0.5 wt.-%, most preferably at most 0.4 wt.-%, and in particular at most 0.3 wt.-%, relative to the total weight of the anticorrosion liquid.

81. The anticorrosion liquid according to any of claims 77 to 80, wherein the total weight content of the one or more aromatic imides of general formula (II) is at least 0.01 wt.-%, preferably at least 0.02 wt.-%, relative to the total weight of the anticorrosion liquid.

82. The anticorrosion liquid according to any of claims 77 to 81, wherein the total weight content of the one or more aromatic imides of general formula (II) is at most 0.10 wt.-%, preferably at most 0.09 wt.-%, more preferably at most 0.08 wt.-%, still more preferably at most 0.07 wt.-%, yet more preferably at most 0.06 wt.-%, even more preferably at most 0.05 wt.-%, most preferably at most 0.04 wt.-%, and in particular at most 0.03 wt.-%, relative to the total weight of the anticorrosion liquid.

83. The anticorrosion liquid according to any of claims 77 to 82, wherein the total weight content of the one or more liquid aliphatic polyhydroxy compounds (c) is at least 80 wt.-%, more preferably at least 85 wt.-%, still more preferably at least 90 wt.-%, yet more preferably at least 92 wt.-%, even more preferably at least 94 wt.-%, most preferably at least 96 wt.-%, and in particular at least 98 wt.-%, relative to the total weight of the anticorrosion liquid.

84. The anticorrosion liquid according to any of claims 77 to 83, wherein the total weight content of the one or more liquid aliphatic polyhydroxy compounds (c) is at most 99.5 wt.-%, preferably at most 99.0 wt.-%, more preferably at most 98.5 wt.-%, relative to the total weight of the anticorrosion liquid.

85. The anticorrosion liquid according to any of claims 77 to 84, which comprises water (d), wherein the weight content of the water (d) is at least 0. 1 wt.-%, more preferably at least 0.2 wt.-%, still more preferably at least 0.3 wt.-%, relative to the total weight of the anticorrosion liquid.

86. The anticorrosion liquid according to any of claims 77 to 85, which comprises water (d), wherein the weight content of the water (d) is at most 1.0 wt.-%, preferably at most 0.9 wt.-%, more preferably at most 0.8 wt.-%, still more preferably at most 0.7 wt.-%, yet more preferably at most 0.6 wt.-%, even more preferably at most 0.5 wt.-%, most preferably at most 0.4 wt.-%, and in particular at most 0.3 wt.-%, relative to the total weight of the anticorrosion liquid.

87. The anticorrosion liquid according to any of claims 77 to 86, which comprises one or more phos- phonic acids (e), wherein the total weight content of the one or more phosphonic acids (e) is within the range of from 0.01 to 0.50 wt.-%, preferably 0.05 to 0.25 wt.-%, relative to the total weight of the anticorrosion liquid.

88. The anticorrosion liquid according to any of claims 77 to 87, which comprises one or more aliphatic dicarboxylic acids (f), wherein the total weight content of the one or more aliphatic dicarboxylic acids (f) is within the range of from 0.005 to 0.50 wt.-%, preferably 0.01 to 0.10 wt.-%, relative to the total weight of the anticorrosion liquid.

89. The anticorrosion liquid according to any of claims 77 to 88, which comprises one or more aliphatic monocarboxylic acids (g), wherein the total weight content of the one or more aliphatic monocarboxylic acids (g) is within the range of from 0.01 to 0.50 wt.-%, preferably 0.05 to 0.25 wt.-%, relative to the total weight of the anticorrosion liquid.

90. The anticorrosion liquid according to any of claims 77 to 89, which comprises one or more aromatic carboxylic acids (h), wherein the total weight content of the one or more aromatic carboxylic acids (h) is within the range of from 0.01 to 0.50 wt.-%, preferably 0.05 to 0.25 wt.-%, relative to the total weight of the anticorrosion liquid.

91. The anticorrosion liquid according to any of claims 77 to 90, which comprises one or more inorganic salts (i), wherein the total weight content of the one or more inorganic salts (i) is within the range of from 0.01 to 0.50 wt.-%, preferably 0.05 to 0.25 wt.-%, relative to the total weight of the anticorrosion liquid.

92. The anticorrosion liquid according to any of claims 1 to 57, which is a geothermal anticorrosion liquid, preferably a geothermal heat transfer fluid.

93. The anticorrosion liquid according to claim 92, which comprises or essentially consists of- the one or more indoles of general formula (I), preferably 2-methylindole, ethylindol-2 -carboxylate, 2-phenylindole, tryptophan, 3 -indolemethanol, indole-3-acetamide, 5-methoxyin- dole, 5 -nitroindole, indole-5 -carbonitrile, methylindole-6-carboxylate, or a combination thereof;- the one or more aromatic imides of general formula (II), preferably phthalimide, saccharin, or a combination thereof;- the one or more liquid aliphatic polyhydroxy compounds (c); preferably ethylene glycol, propylene glycol, triethanolamine, or combinations thereof; more preferably ethylene glycol in combination with triethanolamine, or propylene glycol in combination with triethanolamine;- the water (d);- optionally, the one or more phosphonic acids (e), preferably octyl phosphonic acid;- optionally, the one or more aliphatic dicarboxylic acids (f), preferably dodecanedioic acid;- optionally, the one or more aliphatic monocarboxylic acids (g), preferably pelargonic acid, isononanoic acid or a combination thereof;- optionally, the one or more aromatic carboxylic acids (h) , preferably benzoic acid, histidine, or a combination thereof;- optionally, the one or more inorganic salts (i) , preferably sodium molybdate; and- optionally, the one or more sulfonic acids (j), preferably HEPES;94. The anticorrosion liquid according to claim 92 or 93, wherein the total weight content of the one or more indoles of general formula (I) is with the range of from 20 to 2000 ppmw, preferably 200 to 1000 ppmw, more preferably 350 to 800 ppmw, relative to the total weight of the anticorrosion liquid.

95. The anticorrosion liquid according to any of claims 92 to 94, wherein the total weight content of the one or more aromatic imides of general formula (II) is within the range of 20 to 2000 ppmw, preferably 30 to 300 ppmw, more preferably 50 to 200 ppmw, relative to the total weight of the anticorrosion liquid.

96. The anticorrosion liquid according to any of claims 92 to 95, wherein the total weight content of the one or more liquid aliphatic polyhydroxy compounds (c) is at least 10 wt.-%, more preferably at least 12.5 wt.-%, still more preferably at least 15 wt.-%, yet more preferably at least 17.5 wt.- %, even more preferably at least 20 wt.-%, most preferably at least 22.5 wt.-%, and in particular at least 25 wt.-%, relative to the total weight of the anticorrosion liquid.

97. The anticorrosion liquid according to any of claims 92 to 96, wherein the total weight content of the one or more liquid aliphatic polyhydroxy compounds (c) is at most 90 wt.-%, preferably at most 85 wt.-%, more preferably at most 80 wt.-%, still more preferably at most 75 wt.-%, yet more preferably at most 70 wt.-%, even more preferably at most 65 wt.-%, most preferably at most 60 wt.-%, and in particular at most 55 wt.-%, relative to the total weight of the anticorrosion liquid.

98. The anticorrosion liquid according to any of claims 92 to 97, which comprises water (d), wherein the weight content of the water (d) is at least 10 wt.-%, more preferably at least 15 wt.-%, still more preferably at least 20 wt.-%, yet more preferably at least 25 wt.-%, even more preferably at least 30 wt.-%, most preferably at least 35 wt.-%, and in particular at least 40 wt.-% relative to the total weight of the anticorrosion liquid.

99. The anticorrosion liquid according to any of claims 92 to 98, which comprises water (d), wherein the weight content of the water (d) is at most 92.5 wt.-%, preferably at most 90 wt.-%, more preferably at most 87.5 wt.-%, still more preferably at most 85 wt.-%, yet more preferably at most82.5 wt.-%, even more preferably at most 80 wt.-%, most preferably at most 77.5 wt.-%, and in particular at most 75 wt.-%, relative to the total weight of the anticorrosion liquid.

100. The anticorrosion liquid according to any of claims 92 to 99, which comprises one or more phos- phonic acids (e), wherein the total weight content of the one or more phosphonic acids (e) is within the range of from 100 to 800 ppmw, preferably 250 to 600 ppmw, relative to the total weight of the anticorrosion liquid.

101. The anticorrosion liquid according to any of claims 92 to 100, which comprises one or more aliphatic dicarboxy lie acids (f), wherein the total weight content of the one or more aliphatic dicarboxylic acids (f) is within the range of from 10 to 300 ppmw, preferably 50 to 200 ppmw, relative to the total weight of the anticorrosion liquid.

102. The anticorrosion liquid according to any of claims 92 to 101, which comprises one or more aliphatic monocarboxylic acids (g), wherein the total weight content of the one or more aliphatic monocarboxylic acids (g) is within the range of from 100 to 900 ppmw, preferably 300 to 700 ppmw, relative to the total weight of the anticorrosion liquid.

103. The anticorrosion liquid according to any of claims 92 to 102, which comprises one or more aromatic carboxylic acids (h), wherein the total weight content of the one or more aromatic carboxylic acids (h) is within the range of from 100 to 900 ppmw, preferably 300 to 700 ppmw, relative to the total weight of the anticorrosion liquid.

104. The anticorrosion liquid according to any of claims 92 to 103, which comprises one or more inorganic salts (i), wherein the total weight content of the one or more inorganic salts (i) is within the range of from 100 to 700 ppmw, preferably 200 to 550 ppmw, relative to the total weight of the anticorrosion liquid.

105. Use of an anticorrosion liquid according to any of the preceding claims for transferring heat; preferably geothermal heat.

106. Use of an anticorrosion liquid according to any of the preceding claims as cooling lubricant.

107. Use of an anticorrosion liquid according to any of claims 1 to 105 in water circuits, water treatment units, cooling systems, or geothermal heating systems.

108. The use according to claim 107, wherein the total weight content of the one or more indoles of general formula (I) is within the range of from 5 to 1500 ppmw, relative to the total weight of the anticorrosion liquid.

109. The use according to claim 107 or 108, wherein the total weight content of the one or more aromatic imides of general formula (II) is within the range of from 2 to 1000 ppmw, relative to the total weight of the anticorrosion liquid.

110. Use of an anticorrosion liquid according to any of claims 1 to 104 as corrosion inhibitor; preferably for items made of copper, brass, iron, steel, aluminum, or combinations thereof.

111. Use of an anticorrosion liquid according to any of claims 58 to 76 for preparing an anticorrosion liquid according to any of claims 77 to 104.

112. The use according to claim 111, wherein the anticorrosion liquid according to any of claims 58 to 76 is diluted by adding one or more liquid aliphatic polyhydroxy compounds (c) and / or water (d).

113. The use according to claim 112, wherein the dilution ratio of the volume of the anticorrosion liquid according to any of claims 58 to 76 to the added overall volume of the one or more liquid aliphatic polyhydroxy compounds (c) and / or water (d) is at least 1: 10, preferably at least 1:25, more preferably at least 1:50, still more preferably at least 1:75, yet more preferably at least 1: 100, even more preferably at least 1:200, most preferably at least 1:500, and in particular at least 1: 1000.

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