How to Provide Corrosion Protection for Pressurized Water and Steam Systems

Abstract

The present invention relates to a method for providing corrosion protection in pressurized water and steam systems using very small amounts of N-acylsarcosine or its salts, and to a method for measuring the concentration of N-acylsarcosine in aqueous solutions or emulsions.

Description

[Technical Field]

[0001] The present invention relates to a method for providing corrosion protection to pressurized water and steam systems using very small amounts of N-acylsarcosine or salts thereof. Furthermore, the present invention relates to a method for determining the concentration of an N-acylsarcosine in an aqueous solution or emulsion. [Background technology]

[0002] Water and steam systems, particularly water and steam circuits, and steam generators in general, for example steam generators in power plants, require water treatment to prevent corrosion damage to surfaces in contact with water.

[0003] Organic water additives based on film-forming amines (FFA) provide excellent corrosion protection for water-steam systems. This is especially true for plants operating in a cyclical mode, where preservation is required during shutdown and component protection must be maintained both in contact with water and in the dry state. Film-forming amines are characterized by having at least one long-chain alkyl or alkenyl group and one or more amino groups. Film-forming amines form a protective layer between the metal or metal oxide surface and the corrosive medium. The polar amino group chemisorbs to the metal (oxide) surface, while the lipophilic long-chain alkyl or alkenyl group renders the surface water-resistant, thereby repelling corrosive agents.

[0004] However, from the perspective of a power plant manufacturer or operator, any organic matter included in the steam-water cycle poses a risk of harmful side effects. Possible side effects include corrosive decomposition products, interference with cation conductivity monitoring, effects on boiling and condensation, or fouling. For example, organic amines, which lower pH and promote corrosion, produce volatile acidic decomposition products (although the amino groups of intact amines may offset some of the acidity). Therefore, it is desirable to limit the general use of organic additives to the minimum possible extent.

[0005] However, the concentration of FFA cannot be restricted beyond a certain limit without unacceptable loss of activity.

[0006] Another concern regarding FFAs is their toxicity. Oleylamine, for example, is classified as a health and environmental hazard. It can damage organs with prolonged or repeated exposure and can be fatal if swallowed or inhaled. Furthermore, it is highly toxic to aquatic organisms, with long-term effects. While this risk may be manageable in closed steam-water circuits, for example, in power plants, it is clearly desirable to avoid such hazards in steam cycles used directly or indirectly in connection with food, cosmetic, or pharmaceutical processing. However, even in systems that do not directly or indirectly come into contact with toxicologically unacceptable materials, it is desirable to avoid the use of hazardous substances, since all water ultimately is released into the environment. After geothermal power generation / heating, water is released into the environment, often deep underground, where it can migrate further and have uncontrollable effects, for example, in or above groundwater. This also applies to geothermal systems, such as geothermal power plants and geothermal heating units.

[0007] N-acylsarcosines are carboxamides of carboxylic acids and sarcosine (N-methylglycine). They have been proposed as components of corrosion inhibitor compositions.

[0008] German Publication No. 1916628 describes a mixture containing A) 57-89.5 wt. % of a reaction product of a sulfochloride with ammonia or a primary lower amine, followed by reaction with a halogenated carboxylic acid, or a reaction product of a sulfochloride with an aminocarboxylic acid having 2-9 carbon atoms in the presence of a base, or a salt of these reaction products; B) 5-30 wt. % of an acyl sarcosinate salt of a fatty acid having an alkali metal or ammonium counteranion; C) 5-10 wt. % of cyclohexylamine; and D) 0.5-3 wt. % of a mixture of benzotriazole and / or 2-mercaptobenzothiazole as a corrosion inhibitor. This mixture is added in an amount of 0.05-5 wt. %, which corresponds to at least 25 ppm of sarcosinate salt. In the examples, the sarcosinate salt is used in an amount of 250-750 ppm when used in the claimed composition. In a comparative example where it is used alone, the dosage is 5000 ppm. In the examples, no pressurized system is used.

[0009] Japanese Patent Publication No. 57-185988 relates to a corrosion inhibitor composition containing polymaleic acid or its salts and a sarcosine compound RC(O)-N(CH3)-CH2-COOH, where R is C8-C 22 -hydrocarbyl group. In the examples, the sarcosine compound, when used in the claimed composition, is used in an amount of 4 to 30 ppm. In the comparative examples where it is used alone, the dosage is 40 ppm. In the examples, mild steel test specimens are rotated in test water at 50°C or 90°C for 5 days. No pressurized system is described or employed. The corrosion protection effect is tested only on steel test specimens in boiler water and on the wall of a beaker in which the test water is boiling. The corrosion protection behavior of steam or condensate or parts in contact with them is not tested. European Patent Publication No. 1092788 relates to corrosion-inhibiting formulations containing acylamino acids and triazole derivatives. The definition of acylamino acids includes N-acylsarcosines. In the examples, the formulations are used in a total amount of 0.2% by weight. Considering the mixing ratio of N-acylsarcosines to triazole derivatives shown in Table 1 of this reference, N-acylsarcosines are used in an amount of about 0.09-0.13% by weight (corresponding to 900-1300 ppm). Summary of the Invention

[0010] The objective of this invention was to provide a corrosion inhibitor that provides corrosion protection in pressurized water and steam systems with significantly smaller amounts of activator. Corrosion protection should be provided even when the agent is added only to the feedwater, particularly in parts of the system that come into contact with steam and condensate. Furthermore, the agent should be non-toxic or at least significantly less toxic than FFA. Effective corrosion protection should also be obtained when the agent is used alone or, at best, in combination with an alkaline amine. That is, mixing partners for the compositions of German Publication No. 1916628, Japanese Patent Publication No. 185988 / 1982, and European Publication No. 1092788 should not be required to achieve these effects.

[0011] This objective is achieved by using specific N-acylsarcosinates as corrosion inhibitors in amounts up to 10 ppm (total).

[0012] Accordingly, the present invention relates to a method for providing corrosion protection to a pressurized water-steam system comprising the addition of an N-acylsarcosine compound of formula (I) or a mixture of different N-acylsarcosine compounds of formula (I). RC(=O)-N(CH3)-CH2-COOH (I) wherein R is a linear or branched acyclic hydrocarbon group having 10 to 24 carbon atoms, or a salt thereof. When a mixture of different N-acylsarcosine compounds of formula (I) is used, R is a linear or branched acyclic hydrocarbon group having 4 to 9 carbon atoms in up to 30 wt. % of the N-acylsarcosine compounds (I), based on the total weight of the mixture. wherein an N-acylsarcosine compound of formula (I), a mixture of different N-acylsarcosine compounds of formula (I), or a salt thereof, is added to water used to operate the water-steam system in an amount such that the average total concentration of the one or more compounds of formula (I) in the water contained in the water-steam system is in the range of 0.01 to 10 mg / kg.

[0013] The present invention further relates to the use of an N-acylsarcosine compound or a mixture of N-acylsarcosine compounds of formula (I) or a salt thereof to provide the above and below corrosion protection to pressurized water and steam systems. The use comprises adding to water used to operate a water-steam system an N-acylsarcosine compound of formula (I) or a mixture of different N-acylsarcosine compounds or salts thereof in an amount such that the average total concentration of the compound of formula (I) in the water contained in the water-steam system is in the range of 0.01 to 10 mg / kg, preferably in the range of 0.01 to 8 mg / kg, more preferably in the range of 0.02 to 6 mg / kg, particularly in the range of 0.02 to 5 mg / kg, more particularly in the range of 0.05 to 5 mg / kg, even more particularly in the range of 0.1 to 5 mg / kg, such as 0.5 to 5 mg / kg, particularly in the range of 0.1 to 3.5 mg / kg, more particularly in the range of 0.5 to 3.5 mg / kg, even more particularly in the range of 0.5 to 3 mg / kg, and very particularly in the range of 0.8 to 2.5 mg / kg.

[0014] Another objective was to provide a method for measuring the concentration of corrosion inhibitors present in pressurized water-steam systems. FFA's long-standing experience has shown that depletion of corrosion inhibitor concentrations can occur over time. Therefore, concentration monitoring is an important tool for safe and efficient corrosion control. Control of treatment effectiveness is generally performed by measuring the corrosion inhibitor remaining in the aqueous phase of the steam-cycle system. This is considered indirect evidence that the surface is fully protected.

[0015] Possible methods for this purpose include titration, voltammetry, spectrophotometry, sensor-based methods, flow injection, or chromatography. Chromatography is highly sensitive and accurate, but too complex and expensive for most purposes. Spectrophotometry is a good compromise. Used to measure the concentration of substances that do not absorb within the spectrophotometer's emission spectrum, spectrophotometry generally uses complexation of the test substance with a compound that exhibits high absorption in the desired range. For example, B. Wyrwas et al. describe the measurement of anionic surfactants, such as dodecylbenzenesulfonic acid, in river water in J. Surfact Deterg. 2014, 17, 191–198. For this purpose, dodecylbenzenesulfonic acid-containing water is mixed with methylene blue, and the complex formed is extracted into a chloroform phase, which is then examined spectrophotometrically. However, chloroform is classified as a hazardous substance—more precisely, as being toxic by inhalation and suspected of causing cancer and genetic defects. It was therefore an object of the present invention to provide a method that allows the determination of N-acylsarcosine compounds of formula (I) without requiring the use of hazardous solvents.

[0016] Therefore, a further aspect of the present invention relates to a method for determining the concentration of a compound of formula (I), in the form of its acid or a salt thereof, in an aqueous solution or emulsion of the compound of formula (I) (or a salt thereof), which comprises the following steps: i) Addition of a cationic phenothiazine dye to a defined amount of an aqueous solution or emulsion containing a compound of formula (I) or a salt thereof. ii) of the mixture of step i), C8-C 10 Extraction with a liquid extractant containing an alkanol, in particular 1-nonanol, in at least 95% by weight of the total amount of the extractant. iii) Separation of the liquid extractant from the aqueous phase. iv) Photometric determination of the concentration of phenothiazine dyes in the extractant. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 shows Nyquist plots of electrochemical impedance measurements of a mild steel electrode in deionized water containing 50 ppm oleyl sarcosine (C-1) or cocoyl sarcosine (C-2); or 44.7 ppm oleylamine (Cmp-1) at pH 9.0 (measured by the Bengal rose method) at the fifth measurement point at t=100 min performed according to Example 2. [Figure 2] FIG. 2 shows a calibration curve for determining the concentration of cocoyl sarcosine (compound C-2) in the absence of chloride ions, established by measuring the absorbance of the complex formed between methylene blue and five concentrations of C-2 in Example 9. The absorbances obtained at five concentrations of C-2 are plotted against the C-2 concentration [mg / L] and are connected by regression line A. FIG. 2 also shows a calibration curve for determining five or six defined C-2 concentrations in the presence of various defined amounts of chloride according to Example 10. The absorbances obtained at five concentrations of C-2 are plotted against the respective C-2 concentrations [mg / L] and are connected by regression lines B to F. Here, B is the regression line for Cl-concentration = 31 mg / L, C is the regression line for Cl-concentration = 62 mg / L, D is the regression line for Cl-concentration = 156 mg / L, and E is the regression line for Cl-concentration = 218 mg / L. F is the regression line of Cl- concentration = 311 mg / l. [Figure 3] FIG. 3 is a graph in which the absorbance at a C-2 concentration of 0 mg / l for lines A to F in FIG. 2 is plotted against the absorbance on the y-axis (vertical axis), and a regression line has been drawn. Detailed Description of the Invention

[0018] definition Unless otherwise stated, the following definitions pertain to both the methods and uses of the present invention.

[0019] The method for providing corrosion protection is generally referred to hereinafter simply as the "method (of the invention)" and the method for determining the concentration of the compound of formula (I) is generally referred to as the "determining method (of the invention)."

[0020] When a mixture of different N-acylsarcosine compounds of formula (I) or salts thereof is used, it will be understood that the concentration range of 0.01 to 10 mg / kg (as well as the preferred ranges given above, below and in the claims) relates to the total amount of compound (I) and not to a single compound (I) contained in the mixture.

[0021] In the concentration range, the weight of the compounds (I) relates to their acid form.

[0022] "Average total concentration" is understood as the time average of the concentration, as detailed below.

[0023] In the present invention, the linear or branched acyclic hydrocarbon group having 10 to 24 carbon atoms is a linear or branched aliphatic group having 10 to 24 carbon atoms. The aliphatic group may be a saturated alkyl group or an unsaturated alkenyl or alkynyl group. Generally, the unsaturated aliphatic group is an alkenyl group. Therefore, the linear or branched acyclic hydrocarbon group having 10 to 24 carbon atoms is generally a C 10 -C 24 -Alkyl or C 10 -C 24 -alkenyl.

[0024] C1-C6-Alkyl is a saturated linear or branched aliphatic hydrocarbon radical having 1 to 6 carbon atoms. Examples of C1-C6-alkyl are methyl, ethyl, propyl, isopropyl, n-butyl, 1-methylpropyl (sec-butyl), 2-methylpropyl (isobutyl), 1,1-dimethylethyl (tert-butyl), pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl, 1-ethylpropyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, hexyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 3,3-dimethylbutyl, 1-ethylbutyl, 2-ethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-tri-methylpropyl, 1-ethyl-1-methylpropyl or 1-ethyl-2-methylpropyl.

[0025] C 10 -C 11 -Alkyl is a saturated, linear or branched aliphatic hydrocarbon radical having 10 or 11 carbon atoms. 10 -C 11 Examples of -alkyl are positional isomers such as n-decyl, n-undecyl, and 2-propylheptyl. 12 -C 18 -Alkyl is a saturated linear or branched aliphatic hydrocarbon radical having 12 to 18 carbon atoms. 12 -C 18 Examples of -alkyl are n-dodecyl, n-tridecyl, n-tetradecyl, n-hexadecyl, n-heptadecyl, n-octadecyl and positional isomers thereof. 12 -C 20 -Alkyl is a saturated linear or branched aliphatic hydrocarbon radical having 12 to 20 carbon atoms. 12 -C 20Examples of -alkyl are n-dodecyl, n-tridecyl, n-tetradecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecyl, n-eicosyl and positional isomers thereof. 10 -C 24 -Alkyl is a saturated linear or branched aliphatic hydrocarbon radical having 10 to 24 carbon atoms. 10 -C 24 Examples of -alkyl are n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecyl, n-eicosyl, n-henicosyl, n-docosyl and positional isomers thereof.

[0026] Strictly speaking, the term "alkenyl" refers to a monounsaturated (i.e., containing one C-C double bond) straight-chain or branched aliphatic hydrocarbon radical, which may be in any position. However, as used herein, the term also encompasses "alkapolyenyl" groups, i.e., straight-chain or branched aliphatic hydrocarbon radicals having two or more conjugated or isolated but non-cumulative C-C double bonds.

[0027] C 10 -C 11 -Alkenyl is a linear or branched aliphatic hydrocarbon radical having 10 or 11 carbon atoms and one or more, preferably one, two or three, conjugated or separated but not cumulative C-C double bonds. 10 -C 11 Examples of -alkenyl (only one CC double bond) are 1-decenyl, 2-decenyl, 3-decenyl, 4-decenyl, 5-decenyl, 1-undecenyl, 2-undecenyl, 3-undecenyl, 4-undecenyl, 5-undecenyl and positional isomers thereof. 10 -C 11Examples of -alkalipolyenyl groups (i.e., "alkenyl" having two or more, preferably two or three, C-C double bonds) are n-deca-1,3-dienyl, n-deca-1,4-dienyl, n-deca-1,5-dienyl, n-deca-1,6-dienyl, n-deca-1,7-dienyl, n-deca-1,8-dienyl, n-deca-1,9-dienyl, n-deca-2,4-dienyl, n-deca-2,5-dienyl, n-deca-2,6-dienyl, n-deca-2,7-dienyl, n-deca-2,8-dienyl, n-deca-2,9-dienyl, n-deca-3,5-dienyl, Dienyl, n-deca-3,6-dienyl, n-deca-3,7-dienyl, n-deca-3,8-dienyl, n-deca-3,9-dienyl, n-deca-4,6-dienyl, n-deca-4,7-dienyl, n-deca-4,8-dienyl, n-deca-4,9-dienyl, n-deca-5,7-dienyl, n-deca-5,8-dienyl, n-deca-5,9-dienyl, n-deca-6,8-dienyl, n-deca-6,9-dienyl, n-deca-7,9-dienyl, n-undeca-1,3-dienyl, n-undeca-1,4-dienyl, n-undeca-1,5-dienyl , n-undeca-1,6-dienyl, n-undeca-1,7-dienyl, n-undeca-1,8-dienyl, n-undeca-1,9-dienyl, n-undeca-1,10-dienyl, n-undeca-2,4-dienyl, n-undeca-2,5-dienyl, n-undeca-2,6-dienyl, n-undeca-2,7-dienyl, n-undeca-2,8-dienyl, n-undeca-2,9-dienyl, n-undeca-2,10-dienyl, n-undeca-3,5-dienyl, n-undeca-3,6-dienyl, n-undeca-3,7-dienyl, n-undeca n-undeca-3,8-dienyl, n-undeca-3,9-dienyl, n-undeca-3,10-dienyl, n-undeca-4,6-dienyl, n-undeca-4,7-dienyl, n-undeca-4,8-dienyl, n-undeca-4,9-dienyl, n-undeca-4,10-dienyl, n-undeca-5,7-dienyl, n-undeca-5,8-dienyl, n-undeca-5,9-dienyl, n-undeca-5,10-dienyl, n-undeca-6,8-dienyl, n-undeca-6,9-dienyl, n-undeca-6,10-dienyl, n-undeca-7,9-dienyl, n-undeca-7,10-dienyl, n-undeca-8,10-dienyl, n-deca-1,3,5-trienyl, n-deca-1,3,6-trienyl, n-deca-1,3,7-trienyl, n-deca-1,3,8-trienyl, n-deca-1,3,9-trienyl, n-deca-1,4,6-trienyl, n-deca-1,4,7-trienyl, n-deca-1,4,8-trienyl, n-deca-1,4,9-trienyl, n-deca-1,5,7-trienyl, n-deca-1,5,8-trienyl, n-deca-1,5,9-trienyl, n-deca Deca-1,6,8-trienyl, n-deca-1,6,9-trienyl, n-deca-1,7,9-trienyl, n-deca-2,4,6-trienyl, n-deca-2,4,7-trienyl, n-deca-2,4,8-trienyl, n-deca-2,4,9-trienyl, n-deca-2,5,7-trienyl, n-deca-2,5,8-trienyl, n-deca-2,5,9-trienyl, n-deca-2,6,8-trienyl, n-deca-2,6,9-trienyl, n-deca-2,7,9-trienyl, n-deca-3,5,7-trienyl, n-deca-3,5,8-trienyl enyl, n-deca-3,5,9-trienyl, n-deca-3,6,8-trienyl, n-deca-3,6,9-trienyl, n-deca-3,7,9-trienyl, n-deca-4,6,8-trienyl, n-deca-4,6,9-trienyl, n-deca-4,7,9-trienyl, n-deca-5,7,9-trienyl, n-undeca-1,3,5-trienyl, n-undeca-1,3,6-trienyl, n-undeca-1,3,7-trienyl, n-undeca-1,3,8-trienyl, n-undeca-1,3,9-trienyl, n-undeca-1,3,10 -trienyl, n-undeca-1,4,6-trienyl, n-undeca-1,4,7-trienyl, n-undeca-14,8-trienyl, n-undeca-1,4,9-trienyl, n-undeca-1,4,10-trienyl, n-undeca-1,5,7-trienyl, n-undeca-1,5,8-trienyl, n-undeca-1,5,9-trienyl, n-undeca-1,5,10-trienyl, n-undeca-1,6,8-trienyl, n-undeca-1,6,9-trienyl, n-undeca-1,6,10-trienyl, n-undeca-1,7,9-trienyl, n-undeca-1,7,10-trienyl, n-undeca-1,8,10-trienyl, n-undeca-2,4,6-trienyl, n-undeca-2,4,7-trienyl, n-undeca-2,4,8-trienyl, n-undeca-2,4,9-trienyl, n-undeca-2,4,10-trienyl, n-undeca-2,5,7-trienyl, n-undeca-2,5,8-trienyl n-undeca-2,5,9-trienyl, n-undeca-2,5,10-trienyl, n-undeca-2,6,8-trienyl, n-undeca-2,6,9-trienyl, n-undeca-2,6,10-trienyl, n-undeca-2,7,9-trienyl, n-undeca-2,7,10-trienyl, n-undeca-2,8,10-trienyl, n-undeca-3,5,7 ... n-undeca-3,5,8-trienyl, n-undeca-3,5,9-trienyl, n-undeca-3,5,10-trienyl, n-undeca-3,6,8-trienyl, n-undeca-3,6,9-trienyl, n-undeca-3,6,10-trienyl, n-undeca-3,7,9-trienyl, n-undeca-3,7,10-trienyl, n-undeca-3,8,10-trienyl, n-undeca-4, 6,8-trienyl, n-undeca-4,6,9-trienyl, n-undeca-4,6,10-trienyl, n-undeca-4,7,9-trienyl, n-undeca-4,7,10-trienyl, n-undeca-4,8,10-trienyl, n-undeca-5,7,9-trienyl, n-undeca-5,7,10-trienyl, n-undeca-5,8,10-trienyl, and their positional isomers.

[0028] C 12 -C 18 -Alkenyl is a straight-chain or branched aliphatic hydrocarbon radical having 12 to 18 carbon atoms and one or more, preferably one, two, or three, conjugated or separated, but not cumulative, C-C double bonds. 12 -C 18Examples of -alkenyl (only one CC double bond) are 1-dodecenyl, 2-dodecenyl, 3-dodecenyl, 4-dodecenyl, 5-dodecenyl, 6-dodecenyl, 1-tridecenyl, 2-tridecenyl, 3-tridecenyl, 4-tridecenyl, 5-tridecenyl, 6-tridecenyl, 1-tetradecenyl, 2-tetradecenyl, 3-tetradecenyl, 4-tetradecenyl, 5-tetradecenyl, 6-tetradecenyl, 7-tetradecenyl, 1-pentadecenyl, 2-pentadecenyl, 3-pentadecenyl, 4-pentadecenyl, 5-pentadecenyl, 6-pentadecenyl, 7-pentadecenyl, decenyl, 1-hexadecenyl, 2-hexadecenyl, 3-hexadecenyl, 4-hexadecenyl, 5-hexadecenyl, 6-hexadecenyl, 7-hexadecenyl, 8-hexadecenyl, 1-heptadecenyl, 2-heptadecenyl, 3-heptadecenyl, 4-heptadecenyl, 5-heptadecenyl, 6-heptadecenyl, 7-heptadecenyl, 8-heptadecenyl, 1-octadecenyl, 2-octadecenyl, 3-octadecenyl, 4-octadecenyl, 5-octadecenyl, 6-octadecenyl, 7-octadecenyl, 8-octadecenyl and their positional isomers. 12 -C 20 Some selected examples of -alkapolyenyl groups (i.e., "alkenyl" having two or more, preferably two or three, C-C double bonds) are n-octa-9,12-dienyl, n-octa-9,12,15-trienyl, and the like.

[0029] C 12 -C 20 -Alkenyl is a straight-chain or branched aliphatic hydrocarbon radical having 12 to 20 carbon atoms and one or more, preferably one, two or three, conjugated or isolated but non-cumulative C-C double bonds. 12 -C 20 An example of an -alkenyl (only one CC double bond) is C 12 -C 18Examples of -alkenyl include 9-octadecenyl, 1-nonadecenyl, 2-nonadecenyl, 3-nonadecenyl, 4-nonadecenyl, 5-nonadecenyl, 6-nonadecenyl, 7-nonadecenyl, 8-nonadecenyl, 9-nonadecenyl, 1-eicosadecenyl, 2-eicosadecenyl, 3-eicosadecenyl, 4-eicosadecenyl, 5-eicosadecenyl, 6-eicosadecenyl, 7-eicosadecenyl, 8-eicosadecenyl, 9-eicosadecenyl and positional isomers thereof. 12 -C 20 Some selected examples of -alkapolyenyl groups (i.e., "alkenyl" having two or more, preferably two or three, C-C double bonds) are n-octa-9,12-dienyl, n-octa-9,12,15-trienyl, and the like.

[0030] C 10 -C 24 -Alkenyl is a straight-chain or branched aliphatic hydrocarbon radical having 10 to 24 carbon atoms and one or more, preferably one, two, or three, conjugated or separated, but not cumulative, C-C double bonds. 10 -C 24 An example of an -alkenyl is C 10 -C 11 -alkenyl and C 12 -C 20 -alkenyl are those listed above and also include tricosyl, tetracosyl and positional isomers thereof.

[0031] The C—C double bond of an alkenyl group can be cis- or trans-substituted. When the alkenyl radical is derived from a naturally occurring fatty acid, the C—C double bond is generally cis.

[0032] C1-C6-Hydroxyalkyl is a C1-C6-alkyl group as defined above in which one hydrogen atom is replaced by a hydroxyl group. Examples of C1-C6-hydroxyalkyl are hydroxymethyl, 1-hydroxyethyl, 2-hydroxyethyl, 1-hydroxyprop-1-yl, 1-hydroxyprop-2-yl, 2-hydroxyprop-1-yl, 2-hydroxyprop-2-yl, 3-hydroxyprop-1-yl, 1-hydroxybut-1-yl, 1-hydroxybut-2-yl, 1-hydroxybut-3-yl, 2-hydroxybut-1-yl, 2-hydroxybut-2-yl, 2-hydroxybut-3-yl, 3-hydroxybut-1-yl, 4-hydroxybut-1-yl, 1-hydroxy-2-methyl-propyl-1-yl, 2-hydroxy-2-methyl-propyl-1-yl or 2-(hydroxymethyl)-2-methyl-eth-1-yl.

[0033] C1-C6-alkoxy is a C1-C6-alkyl group, as defined above, bonded via an oxygen atom. Examples of C1-C6-alkoxy are methoxy, ethoxy, n-propoxy, 1-methylethoxy (isopropoxy), butoxy, 1-methylpropoxy (sec-butoxy), 2-methylpropoxy (isobutoxy), 1,1-dimethylethoxy (tert-butoxy), pentoxy, 1-methylbutoxy, 2-methylbutoxy, 3-methylbutoxy, 1,1-dimethylpropoxy, 1,2-dimethylpropoxy, 2,2-dimethylpropoxy, 1-ethylpropoxy, hexoxy. , 1-methylpentoxy, 2-methylpentoxy, 3-methylpentoxy, 4-methylpentoxy, 1,1-dimethylbutoxy, 1,2-dimethylbutoxy, 1,3-dimethylbutoxy, 2,2-dimethylbutoxy, 2,3-dimethylbutoxy, 3,3-dimethylbutoxy, 1-ethylbutoxy, 2-ethylbutoxy, 1,1,2-trimethylpropoxy, 1,2,2-trimethylpropoxy, 1-ethyl-1-methylpropoxy or 1-ethyl-2-methylpropoxy.

[0034] C8-C 10-Alkanol is a linear or branched C8-C as defined above substituted at any position with a hydroxyl group. 10 -alkyl groups. Specific examples are n-octanol, n-nonanol, n-decanol, 2-ethylhexanol, neononanol, 2-propylheptanol, neodecanol and other positional isomers thereof.

[0035] When mixtures of different compounds I are used, the compounds generally have different definitions of R.

[0036] Unless otherwise stated, when the amount or concentration of a component is given as "ppm," this corresponds to 1 g of the component per 1,000,000 g of reference material (or 1 mg / kg). When the unit "ppm" is used to define the concentration of a component in water, assuming the density of water is close to 1 g / L, 1 ppm is 1 m 3 This can also be understood as the component of 1 g (or 1 mg / l) of water.

[0037] Embodiments of the invention Unless otherwise stated, the following description of general and preferred embodiments of the invention relates to both the methods and uses of the invention.

[0038] In certain embodiments, in the methods and uses of the present invention, polymaleic acid or a salt thereof (e.g., as contained in the formulations of JP 57-185988) is not added to the water used or present in the pressurized water-steam system. In certain embodiments, in the methods and uses of the present invention, the reaction products of sulfochlorides of aromatic, alkylaromatic, aliphatic or cycloaliphatic hydrocarbons having 12 to 24 carbon atoms with ammonia or primary aliphatic amines, followed by reaction of the resulting sulfamides with halogenated carboxylic acids having 2 to 9 carbon atoms, reaction products of aminocarboxylic acids having 2 to 9 carbon atoms with sulfochlorides in the presence of a base, and salts of these reaction products (component A) of the German publication) are not added to the water used or present in the pressurized water-steam system.

[0039] In a particular embodiment, in the methods and uses of the present invention, polymaleic acid or a salt thereof, products of the reaction of sulfochlorides of aromatic, alkylaromatic, aliphatic or cycloaliphatic hydrocarbons having 12 to 24 carbon atoms with ammonia or a primary aliphatic amine and the subsequent reaction of the resulting sulfamide with a halogen carboxylic acid having 2 to 9 carbon atoms, products of the reaction of an aminocarboxylic acid having 2 to 9 carbon atoms with a sulfochloride in the presence of a base, salts of these reaction products (component A) of German Publication No. 1916628) are not added to the water used or present in the pressurized water-steam system. In another particular embodiment, in the methods and uses of the present invention, no N,N'-disubstituted aminomethyltriazole derivatives of the following formula are added to the water used or present in the pressurized water-steam system. T-CH2-NR2 where T is an optionally substituted 1,2,3-benzothiazole group or an optionally substituted 1,2,4-triazole group and R is a hydroxyalkyl group (component b) of EP 1 092 788 A2). In very particular embodiments, the polymaleic acid or salt thereof, the reaction product of the sulfochloride of the aromatic, alkylaromatic, aliphatic or cycloaliphatic hydrocarbon having 12 to 24 carbon atoms with ammonia or a primary aliphatic amine, followed by reaction of the resulting sulfamide with a halogenated carboxylic acid having 2 to 9 carbon atoms, the reaction product of an aminocarboxylic acid having 2 to 9 carbon atoms with a sulfochloride in the presence of a base, or a salt of these reaction products, and the triazole derivative are not added to water used or present in a pressurized water-steam system.

[0040] N-Acylsarcosine Compounds (I) When a mixture of different compounds I is used, the definition of R in the compound varies. Such mixtures can be obtained by mixing different N-acylsarcosines (I), by amidating a mixture of different carboxylic acids RC(=O)OH with sarcosine, or by subjecting a mixture of different carboxylic acids RC(=O)OH to an amidation reaction with methylamine and then reacting the resulting amide with formaldehyde. Mixtures of different carboxylic acids can be obtained by mixing different carboxylic acids, but are more conveniently obtained from the hydrolysis of natural fats and oils. Natural fats and oils are generally mixtures of different triglycerides, and a single triglyceride molecule may originate from different fatty acids. Hydrolysis of such natural triglycerides and subsequent amidation of the resulting fatty acid mixture with sarcosine, of course, results in a mixture of compounds I with different radicals R.

[0041] Examples of natural oils (vegetable oils) from which mixtures of different compounds (I) may be derived are sunflower oil, rapeseed oil, soybean oil, coconut oil, palm oil, palm kernel oil, corn oil (maize oil), olive oil, peanut oil, cottonseed oil, linseed oil, sesame oil, safflower oil, etc. An example of a natural fat from which mixtures of different compounds (I) may be derived is tallow.

[0042] R in formula (I) is preferably C 12 -C 20 - alkyl and C with 1, 2 or 3 C=C double bonds 12 -C 20 When a mixture of different N-acylsarcosine compounds of formula (I) is used, in up to 25 wt. % of the N-acylsarcosine compounds (I), R is also C5-C9 alkyl, based on the total weight of the mixture; 10 -C 11 Alkyl and C with one C=C double bond 10 -C 11 -alkenyl.

[0043] Preferably, R in formula (I) has an average of 12 to 18 carbon atoms.

[0044] In certain embodiments, a single compound I (i.e., not a mixture of compounds I) is used, and in this compound, R is preferably C 12 -C 18 -Alkyl or C with one C=C double bond 12 -C 18 -alkenyl, where R is more preferably C═C double bond. 14 -C 18 -alkenyl, in particular C═C having one double bond 16 -C 18 -alkenyl. In certain embodiments, R is derived from oleic acid ((9Z)-octadecenoic acid), i.e., R is (8Z)-heptadecenyl.

[0045] In another particular embodiment, mixtures of different compounds I with different meanings of R are used. In this mixture, R is preferably a C═C group with 1, 2 or 3 C═C double bonds. 12 -C 20 -Alkyl and C 12 -C 20 -alkenyl, wherein in up to 25 wt. % of the N-acylsarcosine compound (I), based on the total weight of the mixture, R may also be C5-C9 alkyl, and in up to 55 wt. % of the N-acylsarcosine compound (I), based on the total weight of the mixture, R may also be C 10 -C 11 -Alkyl and C with one C=C double bond 10 -C 11 In other words, in such a mixture, in at least 20% by weight of the compounds I present in the mixture, based on the total weight of the mixture, R is preferably selected from the group consisting of C 12 -C 20 -Alkyl and C with 1, 2 or 3 C=C double bonds 12 -C20 -alkenyl groups.

[0046] Preferably, when a mixture of different compounds (I) is used, the group RC(=O) in acyl sarcosine (I) is derived from natural fats and oils, particularly vegetable oils. Examples of suitable vegetable oils are sunflower oil, rapeseed oil, soybean oil, coconut oil, palm oil, palm kernel oil, corn oil, olive oil, peanut oil, cottonseed oil, linseed oil, sesame oil and safflower oil. Among these, preference is given to sunflower oil, rapeseed oil, soybean oil, coconut oil, palm oil, palm kernel oil, corn oil and olive oil. A specific example is coconut oil. Thus, a specific example of a mixture of different compounds I is the mixture (formally) obtained by hydrolysis of coconut oil and subsequent amidation of the fatty acid obtained from hydrolysis with sarcosine.

[0047] Among the use of a single compound (I) and a mixture of different compounds (I), preference is given to the use of a mixture of different compounds (I).Among the mixtures of different compounds (I), preference is given to mixtures derived from vegetable oils such as sunflower oil, rapeseed oil, soybean oil, coconut oil, palm oil, palm kernel oil, corn oil (corn oil), olive oil, peanut oil, cottonseed oil, linseed oil, sesame oil or safflower oil, preferably sunflower oil, rapeseed oil, soybean oil, coconut oil, palm oil, palm kernel oil, corn oil (corn oil) or olive oil, in particular coconut oil. More precisely, preference is given to mixtures obtained by hydrolysis of vegetable oils such as sunflower oil, rapeseed oil, soybean oil, coconut oil, palm oil, palm kernel oil, corn oil (maize oil), olive oil, peanut oil, cottonseed oil, linseed oil, sesame oil or safflower oil, preferably sunflower oil, rapeseed oil, soybean oil, coconut oil, palm oil, palm kernel oil, corn oil (maize oil) or olive oil, especially coconut oil, and subsequent amidation with sarcosine of the fatty acids obtained in the hydrolysis.

[0048] N-acyl sarcosine compounds (I) are known and commercially available. They can be obtained by well-known methods, such as the amidation of carboxylic acids RC(=O)OH or their more reactive derivatives, such as halides, especially chlorides or anhydrides, or their esters, with sarcosine or its salts. Another approach is the reaction of the amide RC(=O)-NHCH3 with formaldehyde to give RC(=O)-N(CH3)-CH2OH, followed by carbonylation with CO using a suitable carbonylation catalyst.

[0049] The N-acyl sarcosine compound of formula (I), a mixture of different N-acyl sarcosine compounds of formula (I), or a salt thereof is added to the water used to operate the water-steam system so that the average total concentration of the compounds of formula (I) in the water contained in the water-steam system is in the range of 0.01 to 10 mg / kg, i.e., 0.01 to 10 mg of all compounds (I) (calculated as the acid form) per kg of water contained in the water-steam system. In a preferred embodiment, the N-acyl sarcosine compound of formula (I), a mixture of different N-acyl sarcosine compounds of formula (I), or a salt thereof is added to the water used to operate the water-steam system. The compound of formula (I) is added in an amount such that the average total concentration of the compound of formula (I) in the water contained in the water-steam system is in the range of 0.01 to 8 mg / kg, more preferably in the range of 0.02 to 6 mg / kg, in particular in the range of 0.02 to 5 mg / kg, more particularly in the range of 0.05 to 5 mg / kg, even more particularly in the range of 0.1 to 5 mg / kg, for example in the range of 0.5 to 5 mg, particularly in the range of 0.1 to 3.5 mg / kg, more particularly in the range of 0.5 to 3.5 mg / kg, even more particularly in the range of 0.5 to 3 mg / kg, and very particularly in the range of 0.8 to 2.5 mg.

[0050] In this context, the term "average total concentration" refers to the time average of the concentration, which means the overall concentration of the N-acyl sarcosine compound of formula (I) or its salt during the operation of the water-steam system. The salts of the N-acyl sarcosine compound of formula (I) or its salt in the water used to operate the water-steam system are, on average, within the above-mentioned range. In fact, the concentration of the N-acyl sarcosine compound of formula (I) or its salt does not necessarily have to be within the above-mentioned range at all times the water-steam system is in operation. Rather, the concentration may be outside the above-mentioned range for a certain period of time. However, the period during which the concentration of the N-acyl sarcosine compound of formula (I) or its salt is outside the above-mentioned range will typically not exceed 4 hours, particularly 2 hours. Furthermore, during these periods, the concentration typically does not exceed twice the above-mentioned upper limit, and it drops to zero within a short period of time, preferably within 4 hours.

[0051] The above concentration ranges refer to the concentrations of the N-acyl sarcosine compounds of formula (I) or their salts in those portions of the water-steam system where the water used to operate the system is in a liquid state. Skilled artisans will also understand that the concentrations of the N-acyl sarcosine compounds of formula (I) or their salts in the water used to operate the system may vary to some extent within the system and will not be the same at every point in the system. However, the deviations are not significant, and generally, the above average concentration ranges are maintained in any portion of the water-steam system where the water is in a liquid state.

[0052] To monitor the concentration of the N-acyl sarcosine compound of formula (I) or its salt and maintain it within the above range, the concentration of the N-acyl sarcosine compound of formula (I) or its salt is typically measured periodically or continuously at at least one point in the water-steam system, particularly at at least two points in the water-steam system. For example, if the water-steam system is a water-steam circuit, reference is made to point 8.2 of IAPWS Technical Guidance Document 816 (2016) and the references cited therein. Suitable points for determining the concentration of the N-acyl sarcosine compound of formula (I) or its salt are, in particular, points where water is in a liquid state. Preferred points for controlling the concentration of the N-acyl sarcosine compound of formula (I) or its salt include, for example: - Feedwater, i.e., water supplied to the water-steam circuit from the feedwater tank; -Condensate and -Water in the steam drum, i.e., the water contained in the steam-generating section of the boiler.

[0053] To monitor the actual concentration of the N-acyl sarcosine compound of formula (I) or its salt, a sample is usually taken, and the concentration of the N-acyl sarcosine compound of formula (I) or its salt in the sample is measured by a standard method for measuring the concentration of anionic surfactants, such as that disclosed in S. Chitikelaetal et al., Analyst, July 1995, 120, 2001-2004, or B. Wyrwas et al., J. Surfact. Deterg. 2014, 17, 191-198, or the references cited therein. However, preferably, the concentration of the N-acyl sarcosine compound of formula (I) or its salt is measured by the novel measuring method of the present invention, which will be described in more detail below. Of course, it is also possible to determine the concentration of the N-acylsarcosine compounds of formula (I) or their salts in an in-line measurement, for example, by passing a portion of the water used to operate the water-steam system through a bypass equipped with a flow-through sensor or flow-through measuring cell, as described by B. Wyrwas et al., J. Surfact. Deterg. 2014, 17, 191-198 or by a similar method described by M. Lendie et al., Power Plant Chemistry 2015, 17(1), pp. 8-13. In this regard, further reference is made to point 8.4 of IAPWS Technical Guidance Document 816 (2016) and the references cited therein. Alternatively, the concentration of the N-acyl sarcosine compound of formula (I) or a salt thereof can be calculated from the added amount and the total water content of the system. This is a very practical method for systems in which the N-acyl sarcosine compound of formula (I) or a salt thereof is added only once, as well as for systems in which the N-acyl sarcosine compound of formula (I) or a salt thereof is added periodically or continuously to compensate for losses inherent in the system, where the amount of loss can be determined, calculated, or estimated.

[0054] To maintain the concentration of the N-acyl sarcosine compound of formula (I) or its salt within the above-mentioned range, any consumed N-acyl sarcosine compound (I) or its salt is replenished in an amount such that compound (I) is present in the above-mentioned concentration range. To this end, the N-acyl sarcosine compound of formula (I) or its salt is administered to the water used to operate the water-steam system in an amount such that at least the above-mentioned concentration is achieved during operation of the water-steam system.

[0055] To maintain an appropriate concentration of the N-acyl sarcosine compound of Formula (I) or its salt in the water used to operate the water-steam circuit, the compound can be added in portions or continuously. The amount or rate of addition will, of course, depend on the concentration of the N-acyl sarcosine compound of Formula (I) or its salt measured in a control measurement. If the water-steam system was previously operated without the N-acyl sarcosine compound of Formula (I) or its salt, the amount of the N-acyl sarcosine compound of Formula (I) or its salt should initially be added to achieve a low concentration near the lower limit noted above, with further additions made to achieve the desired concentration range. In particular, initial overdosing should be avoided.

[0056] For this purpose, the N-acylsarcosine compounds of formula (I) or their salts can be added at any point in the water-steam system, particularly at points where water is present in liquid form. Suitable points for adding the N-acylsarcosine compounds are primarily the same as those for film-forming amines or other corrosion inhibitors, and are known to those skilled in the art, primarily from A. Bursike et al., Power Plant Chemistry 2015, 17(6), pp. 342-353 and IAPWS Technical Guidance Document 816 (2016), point 8.5, and the references cited therein. Suitable points include any point between the boiler feedwater tank and the boiler, such as the boiler feedwater pump inlet, the deaerator heater (degasser), especially the deaerator outlet, the feed pump inlet of an economizer, especially a low-pressure or high-pressure economizer circuit, the condenser, and the pipeline to the air-cooled condenser, condensate extraction pump, and / or drum. Although it may be useful to add at least a portion of the N-acylsarcosine compounds of formula (I) or salts thereof to the condensate, in particular to the condensate discharge pump, it is also possible to add them only via the feedwater, for example to the boiler feedwater tank or feedwater pump inlet.

[0057] The inventors have observed that the steam / water partition ratio of compound (I) is high enough to allow volatility to transport into the vapor phase and subsequently into the condensate, but sufficient amounts remain to protect it. In a preferred embodiment, the methods and uses of the present invention also provide corrosion protection to those portions of a pressurized water-steam system that are in contact with steam and / or condensate. Due to the favorable steam / water partition ratio, this protective effect is achieved even when compound (I) is introduced into the system via the feedwater only.

[0058] In one embodiment, a compound of formula (I) or mixtures thereof is added in its acid form to the water used to operate the water-steam system.

[0059] In another embodiment, the compound of formula (I) or mixtures thereof is added in the form of a salt to the water used to operate the water-steam system. Suitable salts include salts containing alkali metal cations, such as Li, Na, or K salts, and ammonium (NH4 + ) or substituted ammonium salts. Preference is given to ammonium salts and substituted ammonium salts. Suitable substituted ammonium cations are of the formula [NHR 1 R 2 R 3 ] + where R 1 , R 2 and R 3 are independently selected from the group consisting of hydrogen, C-C-alkyl, C-C-hydroxyalkyl and C-C-alkoxy, provided that R 1 , R 2 , and R 3 At least one of R is not hydrogen. 1 and R 2 together with N form a monocyclic or bicyclic 5- to 10-membered ring which may contain an additional heteroatom selected from O and N as a ring member, and R 3 is selected from the group consisting of hydrogen, C1-C6-alkyl, C1-C6-hydroxyalkyl and C1-C6-alkoxy. +Examples of amines that can be derivatized (by addition of ) are dimethylamine, trimethylamine, ethylamine, diethylamine, monoethanolamine (=2-aminoethanol), diethylhydroxylamine, N,N-dimethyl-2-aminoethanol, N,N-diethyl-2-aminoethanol (=diethylethanolamine; DEAE), 2-amino-2-methylpropanol, methoxypropylamine, isopropoxypropylamine, 3-methoxypropyleneamine, 5-aminopentanol, methylaminoethylpropanol, 1,2-diaminoethane, and morpholine. Specific amines are monoethanolamine (=2-aminoethanol), N,N-dimethyl-2-aminoethanol, N,N-diethyl-2-aminoethanol (=diethylethanolamine), methoxypropylamine, and 2-amino-2-methylpropanol. A specific amine is N,N-diethyl-2-aminoethanol.

[0060] In a specific embodiment, the compound of formula (I) or mixtures thereof is added in its acid form to the water used to operate the water-steam system.

[0061] In another specific embodiment, the compounds of formula (I) or mixtures thereof are added to the water used to operate the water-steam system in the form of their salts, particularly their ammonium or substituted ammonium salts.

[0062] In a specific embodiment, the compound of Formula (I), whether used in acid or salt form, is added to the water used to operate the water-steam system in the form of an aqueous solution or emulsion of the acid or salt of the compound of Formula (I), where the salt is preferably an ammonium salt or a substituted ammonium salt. Preferably, the concentration of the compound of Formula (I) in the aqueous solution or emulsion, calculated as the acid form of the compound of Formula (I), based on the total weight of the aqueous solution or emulsion, is in the range of 0.5 to 10% by weight. Preferably, the aqueous solution or emulsion ultimately consists of 99.9% of a mixture consisting of the compound of Formula (I), water, and optionally ammonia and / or at least one organic amine. When the compound of Formula (I) is added at least partially in the form of an ammonium or substituted ammonium salt, ammonia and / or at least one organic amine are present.

[0063] Pressurized Water and Steam Systems A "pressurized" water and steam system means that the system operates at a pressure higher than ambient pressure, typically at least 2 bar (0.2 MPa). Preferably, the pressure in the water and steam system during operation is at least 10 bar (1 MPa), particularly at least 20 bar (2 MPa), and specifically at least 30 bar (3 MPa). Generally, the pressure is 2-300 bar (0.2-30 MPa), preferably 10-200 bar (1-20 MPa), more preferably 20-150 bar (2-15 MPa), and specifically 30-100 bar (3-10 MPa), e.g., 30-70 bar (3-7 MPa) or 30-50 bar (3-5 MPa). However, the pressure may be lower in parts of the water and steam system, such as the feedwater tank or pretreatment system, if present.

[0064] A water / steam system, within the meaning of this invention, is any system in which steam is generated and whose internal surfaces are primarily susceptible to corrosion. "Internal surfaces" refer to the surfaces of the water / steam system that come into contact with the water or steam passing through or circulating through the system and are therefore primarily exposed to conditions that can cause corrosion. Examples of susceptible components of such systems include boilers (= steam generators), steam lines, more generally pipes connecting various components, condensers, coolers, turbines, turbine blades, feedwater tanks, deaerators, economizers, flash tanks, pretreatment systems, etc., which are primarily made of or contain non-ferrous materials such as iron and steel, aluminum, and their alloys, which are also susceptible to corrosion. The system may also include circuits in which steam is condensed, circulated, and re-evaporated, such as steam-water circuits (WSCs). Alternatively, it may be a non-circulating system in which steam is not recycled. Water / steam systems may be part of an industrial plant, such as power plants, including fossil power plants such as coal-fired and gas turbine power plants, biogas power plants, nuclear power plants, geothermal power plants, and power plants containing heat recovery steam generators (HRSGs) or dilution steam generators. Water and steam systems may be utility-sized. Water and steam systems generally include at least a steam generator / boiler, e.g., a drum boiler or once-through steam generator. An exception may be a geothermal plant, which uses steam formed by the release of high-pressure water from a geothermal source.

[0065] In a preferred embodiment, the water and steam system is a water and steam circuit. As mentioned above, the water and steam system can be part of a power plant, including fossil power plants such as coal-fired and gas turbine power plants, biogas power plants, nuclear power plants, and power plants including heat recovery steam generators (HRSGs) or dilution steam generators. The method of the present invention is not only suitable for plants operated in continuous mode, but also for meeting the high demands of water and steam circuits that are part of power plants operated in cycling mode. In contrast to continuous mode, cycling mode is understood as discontinuous operation with frequent short standby periods (off periods). Cycling mode of a power plant is also understood to refer to the operation of power generating units at various load levels (power demand), including on / off and low load fluctuations, in response to changing system load (demand) requirements. The method of the present invention enables efficient and economical corrosion protection under these difficult conditions.

[0066] Advantageously, the N-acylsarcosines (I) and their salts used in the present invention are substantially non-toxic. Therefore, they are suitable for use in water-steam systems directly or indirectly related to the manufacturing, purification, sterilization (including pasteurization), packaging, or storage of sensitive products, such as food (including food additives, beverages, and animal feed), cosmetics, or pharmaceuticals. Thus, in certain embodiments, the methods and uses of the present invention are useful for providing corrosion protection to pressurized water-steam systems used to generate steam for the direct or indirect processing of food (including food additives, beverages, and animal feed), cosmetics, or pharmaceuticals.

[0067] "Processing" means any stage of a product from the point of manufacture to the user / consumer, including manufacturing, refining, sterilizing, pasteurizing, cleaning, polishing, packaging, storage, and distribution.

[0068] "Direct processing" means that the steam directly contacts the product or its components at some stage from the point of production to the user / consumer. "Indirect processing" means that the steam does not directly contact the product or its components. For example, steam directly contacts a sensitive product or its components during its manufacturing, refining, polishing, packaging, or storage in the processes of extraction, distillation, drying, sterilization, or pasteurization. Indirect contact means that the steam does not directly contact the sensitive product or its components, but rather contacts other products, materials, or surfaces, which then contact those products or their components. Examples include steam contact with packaging materials, or surfaces, areas, spaces, equipment, or materials where sensitive products or components are processed, such as during manufacturing, refining, sterilization, pasteurization, cleaning, polishing, packaging, or storage. Direct or indirect vapor contact with sensitive products or their components occurs, for example, in extraction or distillation processes in the manufacture of food, food additives, beverages, feed, cosmetics or pharmaceuticals, in high-pressure food storage, in the packaging of food, food additives, beverages, feed, cosmetics or pharmaceuticals, and in the cleaning or sterilization of areas, spaces, surfaces, equipment or work materials in bakeries, dairies, factories where sugar is produced or processed, canneries, breweries, butcher shops, packaging sites for pharmaceuticals, cosmetics, etc.

[0069] Direct contact with food is described as the steam coming into direct contact with food during bleaching, thawing or cooking, for example, sealing cans, cooking mussels, processing meat and poultry, e.g. plucking feathers (of chicken, duck, goose, turkey, etc.) or removing hair from pigs.

[0070] An example of indirect contact is a water-steam circuit used in a paper machine used to produce paper, such as packaging paper, suitable for contact with food, feed, cosmetics, or pharmaceuticals. Thus, in a preferred embodiment, the water-steam system is a water-steam circuit used in a paper machine, particularly a paper machine used to produce paper, such as packaging paper, suitable for contact with food, feed, cosmetics, or pharmaceuticals. Another example of indirect contact is steam used in the purification and / or sterilization of packaging materials, such as bottles and cans, in breweries (e.g., tunnel pasteurizers) or other beverage industries (e.g., for juices, soft drinks, mineral water, syrups, etc.) or canneries.

[0071] In an alternative embodiment, the N-acylsarcosine compound of formula (I) or a mixture of different N-acylsarcosine compounds or salts thereof is added to production wells, injection wells, heat exchangers, steam separators, above-ground and underground pipelines, geothermal power plants such as dry steam power plants, flash steam power plants, or binary cycle power plants, or geothermal heating units such as geothermal district heating units. Clearly, it is undesirable to release water containing sensitive components into the environment after the power generation / heating cycle.

[0072] The N-acylsarcosine compound of formula (I) or a mixture of different N-acylsarcosine compounds or their salts can be used in combination with substances commonly used in such facilities, such as phosphonic acids, polymer additives, or chelating agents. Examples of suitable phosphonic acids include EDTMP (ethylenediaminetetra(methylenephosphonic acid), ATMP (aminotris(methylenephosphonic acid), PBTC (phosphonobutanetricarboxylic acid), TDTMP (tetramethylenediaminetetra(methylenephosphonic acid), HDTMP (hexamethylenediaminetetra(methylenephosphonic acid), etidronic acid, HEDP (1-hydroxyethylidene-1,1-diphosphonic acid), DMMP (dimethylmethylphosphonate), vinylphosphonic acid, AMP (aminotris(methylenephosphonic acid), HPAA (2-hydroxyphosphonocarboxylic acid), or CEPA (2-carboxyethylphosphonic acid). Examples of suitable polymer additives are acrylic acid homopolymers, copolymers and terpolymers, phosphinopolycarboxylic acids, acrylate / acrylamide copolymers, homopolymers, copolymers and terpolymers of acrylamide and their salts, polyethylene glycol, copolymers and terpolymers based on acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), copolymers and terpolymers based on (meth)acrylic acid and allyl ethers, etc.

[0073] Pressure in such geothermal systems can vary between 2 and 60 bar (0.2 and 6 MPa). Temperatures can vary between 55 and 300 °C, depending on the system. pH values ​​typically range from 4 to 10.

[0074] In another embodiment, the N-acylsarcosine compound of formula (I) or a mixture of different N-acylsarcosine compounds or their salts is added to a dilution steam generator (DSG). A dilution steam generator is a low-pressure boiler that supplies dilution steam for the cracking process typically used in ethylene plants. In most cases, the water system is a closed loop, circulating from the cracking furnace to the oil quench unity, then to the water quench unity, oil / water separator, stripper to the DSG, and back to the furnace. A challenge in DSG processing is often the high concentration of C1-C4 carboxylic acids (primarily formic acid and acetic acid). Therefore, a major issue is corrosion prevention in the boiler and dilution steam lines.

[0075] Indeed, N-acylsarcosine compounds, their mixtures, and salts are, of course, suitable for use in any pressurized water and steam system. The above-mentioned systems (direct or indirect water and steam systems involving the processing of sensitive products, geothermal power plants / heating equipment, DSG) in particular highlight the advantages of N-acylsarcosine compounds, their mixtures, and salts.

[0076] Operating conditions As explained above, the system operates at a pressure higher than ambient pressure, typically at least 2 bar (0.2 MPa). Preferably, the pressure in the water / steam system during operation is at least 10 bar (1 MPa), particularly at least 20 bar (2 MPa), and specifically at least 30 bar (3 MPa). Generally, the pressure is 2-300 bar (0.2-30 MPa), preferably 10-200 bar (1-20 MPa), more preferably 20-150 bar (2-15 MPa), specifically 30-100 bar (3-10 MPa), e.g., 30-70 bar (3-7 MPa) or 30-50 bar (3-5 MPa). However, the pressure in some parts of the water / steam system may be lower, if present, for example, in a feedwater tank or pretreatment system.

[0077] Preferably, the temperature of the water / steam system during operation is at least 100° C., preferably 150-570° C., especially 200-400° C., especially 200-350° C. However, parts of the water / steam system, such as the condenser, feedwater tank, or pre-treatment system, if present, may have lower temperatures.

[0078] During operation of a water / steam system, the pH is preferably at least neutral (i.e., at least pH 7, e.g., 7 to 14, 7 to 12, or 7 to 10). The optimal pH level varies depending on the particular water / steam system, the materials contained in contact with the water or steam, and the mode of operation. As a general rule, systems operating continuously are less susceptible to corrosion due to lower or higher pH levels than systems operating discontinuously (e.g., in cycling mode) or during shutdown. Systems containing aluminum or aluminum alloy components in contact with water or steam generally operate at a lower pH than steel, at least in discontinuous operation modes. However, while a geothermal power plant or heating unit can also be operated at a pH below 7, the pH is preferably at least 4, more preferably at least 5, particularly at least 6, and more preferably at least 7, e.g., 4 to 10, 5 to 10, 6 to 9.5, or 7 to 9. Thus, in summary, the pH of a water-steam system will typically be in the range of 4 to 14, preferably 5 to 12, more preferably 6 to 12, for example 7 to 12 or 7 to 11 or 7.5 to 11, or 8.0 to 10 or 8.5 to 10. pH values ​​are measured at 20°C.

[0079] If the water-steam system is a water-steam circuit, the pH of the water, measured at 20°C, is preferably maintained in the range of 7.5 to 12, more preferably 8.0 to 11, and especially 8.5 to 10, more preferably 8.7 to 10, particularly 9.0 to 10, and very especially 9.2 to 10. This is usually achieved by adding a suitable base. Suitable bases are, for example, alkali metal hydroxides, sodium hydroxide, potassium hydroxide, or lithium hydroxide, phosphates, such as sodium phosphate, ammonia, and alkalizing amines. Alkylated amines are volatile amines, especially amine NR. 1 R 2 R 3 where R 1 , R 2 , and R 3 are independently selected from the group consisting of hydrogen, C-C-alkyl, C-C-hydroxyalkyl and C-C-alkoxy, provided that R 1 , R 2 , and R 3 At least one of R is not hydrogen. 1 and R 2 together with N form a monocyclic or bicyclic 5- to 10-membered ring which may contain an additional heteroatom selected from O and N as a ring member, and R 3 is selected from the group consisting of hydrogen, C1-C6-alkyl, C1-C6-hydroxyalkyl and C1-C6-alkoxy. Suitable amines NR 1 R 2 R 3Examples of amines are dimethylamine, trimethylamine, ethylamine, diethylamine, monoethanolamine (=2-aminoethanol), diethylhydroxylamine, N,N-dimethyl-2-aminoethanol, N,N-diethyl-2-aminoethanol (=diethylethanolamine; DEAE), 2-amino-2-methylpropanol, methoxypropylamine, isopropoxypropylamine, 3-methoxypropyleneamine, 5-aminopentanol, methylaminoethylpropanol, 1,2-diaminoethane, and morpholine, and mixtures thereof. Specific amines are monoethanolamine (=2-aminoethanol), N,N-dimethyl-2-aminoethanol, N,N-diethyl-2-aminoethanol (=diethylethanolamine), methoxypropylamine, and 2-amino-2-methylpropanol. A specific amine is N,N-diethyl-2-aminoethanol.

[0080] During the operation of the water-steam circuit, the pH value of the water used to operate the water-steam circuit will, on average, be within the above range. In fact, the pH value of the water will not necessarily be within the above range at all times that the water-steam circuit is in operation. Rather, the pH value may fall outside the above range for short periods of time. However, the period during which the pH level is outside the above range will usually not exceed one hour, and especially 30 minutes, to avoid increased corrosion. Furthermore, during these periods, the pH level will usually not deviate by more than 0.2 pH units, and especially not by more than 0.1 pH units of the above limit.

[0081] The skilled artisan will also appreciate that the pH level of the water used to operate the water-steam circuit may vary to some extent within the water-steam circuit and may not be the same at all points in the water-steam circuit, although the deviations will not be significant and generally the above average pH level will be maintained in any part of the water-steam circuit where the water is in a liquid state.

[0082] To monitor the pH level of the water used to operate the water-steam circuit and maintain it within the above range, the pH level is usually measured periodically or continuously at at least one point in the water-steam circuit, preferably at least two points in the water-steam circuit. Suitable points for measuring the pH level are particularly those points where the water is in a liquid state. Preferred points for controlling the pH level include, for example: - Feedwater, i.e., water supplied to the water-steam circuit from the feedwater tank - condensation water, and - Water in the steam drum, i.e., the water contained in the steam-generating section of the boiler; There is.

[0083] To monitor the actual pH level of the water used to operate the water-steam circuit, a sample is taken and the pH of the sample is measured according to the standard procedures mentioned above, for example as described in DIN EN ISO 10253:2012-04 or other methods known in the art. Of course, it is also possible to measure the pH value in-line, for example by passing a portion of the water used to operate the water-steam circuit through a bypass equipped with a flow-through measuring cell with a pH meter.

[0084] The base used to adjust or maintain the desired pH can be added at any point in the water-steam circuit, particularly at points where water is present in liquid form. Suitable points for adding the base are those mentioned above for adding N-acylsarcosine or its salt, such as the feedwater tank, any point between the feedwater tank and the boiler, such as the boiler feedwater pump inlet, deaerator heaters (degassers), especially economizers, especially deaerator outlets in low-pressure or high-pressure economizer circuits, condensers, and pipelines to air-cooled condensers, condenser extraction pumps, and / or drums.

[0085] To maintain the proper pH level of the water used to run the water-steam circuit, additional base may be added in portions or continuously, the amount or rate of addition depending, of course, on the results of the pH measurement.

[0086] When the water-steam system is a water-steam circuit, it has been found to be even more beneficial to maintain the conductivity of the water used to operate the water-steam circuit at a maximum of 30 μS / cm, especially at a maximum of 20 μS / cm or even at a maximum of 10 μS / cm. The conductivity values ​​shown here refer to the conductivity measured at 22°C on a sample of water used to operate the water-steam circuit. Conductivity can be measured by standard procedures, such as those described in DIN EN 27888:1993-11. It is clear to the skilled worker that there are cases where it is not possible to measure conductivity at 22°C. However, skilled workers are familiar with the temperature dependence of conductivity and therefore do not need to measure conductivity at 22°C. Therefore, conductivity can be measured at temperatures different from 22°C and appropriate corrections can be made. Modern conductivity meters usually have temperature compensation means. Conductivity is often measured on samples at temperatures between 20 and 27°C to minimize temperature effects.

[0087] During the operation of the water-steam circuit, the conductivity of the water used to operate the water-steam circuit is, on average, below the above limits. In fact, the conductivity of the water is not necessarily below the above limits at all times that the water-steam circuit is in operation. Rather, the conductivity may be slightly higher than the above limits for short periods. However, periods during which the conductivity is higher than the above limits will usually not exceed 4 hours, and especially 2 hours. Furthermore, during these periods, the conductivity will usually not exceed 50 μS / cm, especially 30 μS / cm or 20 μS / cm.

[0088] The skilled person will also appreciate that the conductivity of the water used to operate the water-steam circuit may vary to some extent within the water-steam circuit and may not be the same at all points in the water-steam circuit, but the deviations will not be so great that the above conductivity limits will generally be maintained in any part of the water-steam circuit where the water is in a liquid state.

[0089] To monitor the conductivity of the water used to operate the water-steam circuit and maintain it within the above range, the conductivity is usually measured periodically or continuously, in particular at least one point in the water-steam circuit, in particular at least two points. Suitable points for measuring the conductivity of the water used to operate the water-steam circuit are those where the water is in a liquid state. Preferred points for controlling the pH level include, for example: - Feedwater, i.e., water supplied to the water-steam circuit from the feedwater tank; - condensation water, and -Water in the steam drum, i.e., the water contained in the steam-generating section of the boiler is.

[0090] To monitor the actual conductivity of the water used in the operation of the water-steam circuit, samples are taken and their conductivity measured according to standard procedures, in particular those described in DIN EN 27888:1993-11. Of course, it is also possible to determine the conductivity value by in-line measurement, e.g. by passing a portion of the water used in the operation of the water-steam circuit through a bypass equipped with a flow-through measuring cell with a conductivity meter.

[0091] To keep the conductivity below the above limits, it may be necessary to remove conductivity-causing ions from the water. For this purpose, the water circulating in the water-steam circuit is passed through ion exchange resin beds, especially mixed beds of cation and anion exchange resins, to remove ionic impurities. These units are also called polishing units. Preferably, the condensate is passed through the polishing unit.

[0092] The N-acylsarcosine compounds (I) are useful for providing corrosion protection to a variety of metals, particularly ferrous materials and their alloys (such as various steel grades), but also non-ferrous metals and alloys such as copper, copper alloys, aluminum, or aluminum alloys.

[0093] Steam generators and turbines are often made of iron or steel, typically steel, but other components such as condensers, coolers, piping, and other water / steam systems may be made of or contain non-ferrous materials such as copper, copper alloys, aluminum, or aluminum alloys.

[0094] The type of steel or non-ferrous metal / alloy varies depending on the type of component and its structural requirements. Steel types frequently used in the construction of water and steam circuit components can be high-alloy or low-alloy steels, but are not limited to martensitic steels, especially those with a chromium content of 9-14%, e.g., martensitic steels T / P92 and VM12 / VM12-SHC, austenitic and ferritic steels, e.g., low-alloy ferritic steels such as T / P24, as well as nickel-based alloys.

[0095] Typical aluminum materials include, among others, pure aluminum having an aluminum content of more than 99% and aluminum alloys such as aluminum-magnesium alloys, aluminum-magnesium-silicon alloys, and aluminum-zinc alloys.

[0096] Typical copper materials include pure copper and brass.

[0097] In particular, the N-acylsarcosine compounds (I) are useful for providing corrosion protection to steel, copper and their alloys, particularly steel and copper, especially steel.

[0098] In addition to Compound (I) or a salt thereof, and any bases and pH adjusters described above in connection with salts of Compound (I), further additives can be added to the water of the steam water system. These include polymeric additives as dispersants or scale inhibitors, or oxygen scavengers.

[0099] Examples of polymer additives are homopolymers, copolymers and terpolymers of (meth)acrylic acid such as polyacrylic acid, polymethacrylic acid, or copolymers and terpolymers or higher polymers of (meth)acrylic acid and (meth)acrylates, copolymers and terpolymers or higher polymers of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and copolymers and terpolymers or higher polymers of (meth)acrylic acid and allyl ethers; homo-, co- and terpolymers or higher polymers of (meth)acrylates different from those mentioned above, for example co- and terpolymers or higher polymers of acrylates and acrylamides, homo-, co- and terpolymers or higher polymers of acrylamides different from those mentioned above, phosphinopolycarboxylic acids and polyethylene glycols.

[0100] Examples of oxygen scavengers are hydrazine, carbohydrazide, diethylhydroxylamine, ascorbic acid and its salts, sulfites and bisulfites.

[0101] The present invention further relates to a method for determining the concentration of a compound of formula (I) in an aqueous solution or emulsion of the compound of formula (I), comprising the steps of: i) Addition of a cationic phenothiazine dye to a defined amount of an aqueous solution or emulsion containing a compound of formula (I) or a salt thereof. ii) Reconstituting the mixture of step i) with C8-C 10 Extraction is carried out with a liquid extractant which comprises at least 95% by weight of the total amount of the extractant of an alkanol, in particular 1-nonanol. iii) separating the liquid extractant from the aqueous phase; iv) The concentration of the phenothiazine dye in the extractant is determined photometrically.

[0102] The measurement method is based on the fact that compounds of formula (I), when present as salts, form ionic associations (complexes) with (cationic) phenothiazine dyes. These complexes are more sensitive to C8-C6 than to water. 10Because it is highly soluble in alkanols, it can be extracted into the organic phase formed by these solvents. The absorbance of this complex, or more precisely, the absorbance of its phenothiazine dye moiety, is then measured photometrically. The absorbance is a measure of the dye concentration. By continuously measuring the absorbance of the complex formed by a compound of formula (I) and a defined concentration of phenothiazine dye, a calibration curve can be constructed, which gives the relationship between the absorbance and the concentration of the phenothiazine dye, and ultimately the concentration of compound (I).

[0103] Because compound (I) is a weak acid with a pKa in the range of approximately 3-5, it can potentially form a buffer system with the corresponding anion in water. It exists primarily as a salt well above the pH range where it forms a buffer system. This is generally the case above pH 9. However, given the complexation with the phenothiazine dye and its extraction into the organic phase, even low pH values ​​clearly shift the acid / salt equilibrium toward the salt. Thus, we have observed that a pH of 6 or lower is sufficient to shift the acid / salt equilibrium in steps i) and ii) toward the salt to an extent that allows essentially complete extraction of compound (I) in the form of the phenothiazine dye into the organic phase. Therefore, before, during, or immediately after step i), and in either case before step ii), the aqueous solution or emulsion containing the compound of formula (I) is preferably adjusted to at least pH 6 if the pH of the solution or emulsion is below this value. More preferably, the aqueous solution or emulsion containing the compound of formula (I) is adjusted to a pH of at least 6.5 if the solution or emulsion has a pH below this limit. Preferably, the pH adjustment is carried out before the phenothiazine dye is added. Preferably, the aqueous solution or emulsion is adjusted to a pH of 6.5 to 7.5, particularly 6.9 to 7.1, and particularly 7.0, measured at 20°C.

[0104] If the pH of an aqueous solution or emulsion containing a compound of formula (I) or a salt thereof is already in the basic range, it is usually not necessary to adjust the pH. For safety or other reasons, it may still be desirable to perform the measurement at a near-neutral pH. Therefore, in this case too, the aqueous solution or emulsion can be adjusted to a pH of preferably 6.5 to 7.5, particularly 6.9 to 7.1, and particularly 7.0, measured at 20°C.

[0105] The pH adjustment can be carried out primarily using any water-miscible base (if the pH of the starting aqueous solution or emulsion is in the acidic range) or water-miscible acid (if the pH of the starting aqueous solution or emulsion is in the acidic range), but it is preferable to use a buffer. Suitable buffers are all buffers with good buffering capacity near neutral pH, such as phosphate buffers, bicarbonate buffers, or phosphate / citrate buffers. In particular, phosphate buffers are used, such as buffers containing dihydrogen phosphate and hydrogen phosphate, for example, potassium dihydrogen phosphate and dipotassium hydrogen phosphate, or sodium dihydrogen phosphate and disodium hydrogen phosphate, or potassium dihydrogen phosphate and disodium hydrogen phosphate.

[0106] The base, acid or buffer is usually added in the form of an aqueous solution.

[0107] Preferably, a buffer is added to the sample being tested, regardless of whether the pH is within the required range.

[0108] Suitable phenothiazine dyes are methylene blue (N,N,N',N'-tetramethylthionichloride), new methylene blue (3,7-bis(ethylamino)-2,8-dimethylphenothiazine-5-ium chloride) and toluidine blue (N',N',2-trimethylphenothiazine-3,7-diaminochloride). Preferably, methylene blue is used.

[0109] Preferably, the phenothiazine dye is used in step i) in a molar amount equal to or exceeding the maximum molar amount of compound (I) expected in the water sample (i.e., in the aqueous solution or emulsion containing the compound of formula (I) or its salt). Preferably, the phenothiazine dye is added in step i) in an amount exceeding the maximum molar amount of compound (I) expected in the water sample. More preferably, the phenothiazine dye is used in a molar excess of at least 1.05, more preferably at least 1.1, and especially at least 1.5, relative to 1 mole of compound (I) expected in the water sample. The amount of phenothiazine dye can far exceed the amount of compound (I) without interfering with the measurement method. However, for practical reasons, the molar excess is generally no more than 300 or 200 times the molar amount of compound (I) expected in the water sample. In particular, the phenothiazine dye is added in step i) by a molar factor of 1.05 to 200, more preferably by a molar factor of 1.1 to 150 higher than the maximum expected amount of compound (I) in the water sample, and particularly by a molar factor of 3 to 100 higher than the maximum expected amount of compound (I) in the water sample. The maximum expected amount of compound (I) in the water sample can be easily calculated or estimated from the amount added to the system and the amount of water present in the system. If the amount to be added is unknown, an approximate amount can be determined by preliminary testing.

[0110] The phenothiazine dye is generally added as an aqueous solution.

[0111] If a predetermined phenothiazine dye solution and buffer solution are used, the final volume of the resulting aqueous solution (containing Compound (I), the phenothiazine dye, and the base or preferably the buffer, if present) is measured or calculated before step ii) is performed.

[0112] In step i), the temperature should generally not exceed 70° C. Preferably, the temperature is between 15 and 35° C., in particular between 20 and 25° C.

[0113] The extractant in step ii) is at least 95% by weight of C8-C8, based on the total weight of the extractant. 10 Contains alkanols.

[0114] C8-C suitable as a liquid extractant 10 Among the alkanols, preference is given to 1-nonanol.

[0115] The extraction may be carried out one or several times, for example 1, 2 or 3 times, although one extraction is usually sufficient. Thus, in certain embodiments, the aqueous phase is extracted with alkanol only once.

[0116] C8-C 10 The alkanol is preferably used in an amount such that the volume ratio of water sample to alkanol is 3:1 to 1:3, more preferably 2:1 to 1:2, in particular 1.5:1 to 1:1.5, and particularly 1.5:1 to 1.1:1. This amount relates to a single extraction step. In the case of multiple extractions, the total amount of alkanol used for the extractions will generally be higher. In this case, it is advisable to concentrate the organic phase obtained after phase separation by removing part of the alkanol, for example by distillation under reduced pressure, if necessary.

[0117] In each case, the amount of alkanol used is a defined amount.

[0118] Extraction is generally carried out by intimate contact of the alkanol with the aqueous phase, e.g., by vigorous shaking or mixing for a minimum time, e.g., at least 5 seconds, or preferably at least 10 seconds, e.g., from 5 seconds to 1 minute, preferably from 10 to 40 seconds.

[0119] Phase separation of the organic and aqueous phases (step iii) can be carried out in the usual manner, for example in a separatory funnel or by removing a portion of the (upper) organic phase with a pipette or syringe.

[0120] Next, in step iii), a defined amount of the organic phase is subjected to photometric measurement of the concentration of phenothiazine in the complex formed by the phenothiazine dye and compound (I), from which the concentration of compound (I) can then be determined.

[0121] The concentration of phenothiazine can be determined by measuring absorbance in a photometer. Suitable photometers are well known. A specific example is the Spektralphotometer DR3900 from Hach Lange GmbH, Germany.

[0122] In a typical photometer, a constant standard light source emits light that passes through a cuvette containing a liquid sample. Depending on the concentration of light-absorbing substances in the sample, some of the light is absorbed, and the light that passes is measured by a photocell. The light that passes can be correlated to the concentration of the absorbing substance by comparing it to a pre-constructed correlation curve or table with a series of defined concentrations of the substance determined under defined conditions that closely correspond to those applied to testing a sample of unknown concentration.

[0123] The measurement of the concentration of the phenothiazine dye in the organic phase is based on the Beer-Lambert law: absorption (which may alternatively be expressed as extinction) is defined as: Aλ=ελ·c·d where: Aλ is the absorption at a specific wavelength λ; ελ is the spectral extinction coefficient at the same wavelength λ; c is the concentration of the absorbing substance (here, the phenothiazine dye), e.g., mol / m 3 is; and d is the optical path length of the cuvette containing the solution of the absorbing substance, for example m.

[0124] Therefore, the concentration can be calculated by solving the equation for c. c=Aλ / (ελ d)

[0125] The extinction coefficient is substance-specific and also depends on the solvent, pH, and emitted wavelength. Therefore, it must be determined for specific conditions by measuring the extinction at a defined concentration of the substance being tested in a specific solvent at a specific pH and a defined path length.

[0126] Absorption is determined as the logarithm (base 10) of the ratio of the intensity of the irradiated (emitted) light to the intensity of the transmitted light. A=log 10 (I0 / I t ) where: I0 is, for example, W / m 2 The intensity of the irradiated light is expressed as I t is, for example, W / m 2 is the intensity of the transmitted light expressed in .

[0127] Of course, the wavelength λ of the emitted light must be within the absorption range of the phenothiazine dye used. Typically, λ is in the range of 550 to 700 nm, preferably 600 to 680 nm, and particularly 610 to 660 nm, such as 610 nm, 650 nm, or 660 nm. In a specific embodiment, light having a λ of 660 nm is used.

[0128] The absorption or extinction should generally not exceed 1.6. If an absorption above 1 is observed, it is recommended to dilute the water sample with a defined amount of water before, during, or after performing step i), and in any case before performing step ii).

[0129] The sample photometrically measured in step iii) has a temperature in the range of from 10 to 35°C, preferably from 15 to 30°C, in particular from 20 to 25°C.

[0130] In practice, the concentration of compound (I) is determined by comparing the absorption with an absorption calibration curve established by measuring solutions of compound (I) at determined concentrations. Because absorption depends not only on the concentration of the test compound but also on further factors such as the specific compound used, the dye with which the compound forms a complex, the extractant, the pH of the initial solution, the wavelength of the emitted light, the path length of the light through the sample (hence the dimensions of the cuvette), and the photometer used, a calibration curve must be established under the same conditions as the test to reliably determine the unknown concentration of compound (I). A calibration curve for a specific compound (I) or a specific mixture of compounds (I) must be established by measuring the absorption of the specific compound (I)-dye complex at defined concentrations of compound (I) or the specific mixture. If the calibration curve [absorption vs. concentration of compound (I)] shows a linear dependence of absorption and concentration, the concentration can be more easily determined by mathematical calculation. If there is a linear dependence between absorption and concentration, the absorption value (y-axis) can be plotted against the corresponding concentration of compound (I) used in the calibration curve (x-axis), resulting in a (regression) line with a slope "a" and an ordinate (x=0) "b." b can be determined experimentally (absorption without compound (I) but including all other components) or by extrapolating the regression line to x=0. The absorption can be expressed as the product of the slope and concentration plus the ordinate. Absorption = a × concentration (compound I) + b (1)

[0131] Solving the concentration equation leads to the following equation: This equation can be used to calculate the concentration of the tested compound (I) by determining the absorbance (under the same conditions as for generating the calibration curve). Concentration (Compound I) = (Absorption - b): a (2)

[0132] For compound (I), the dependence of absorption on concentration was found to be linear at least between 0.1 and 2 mg / L. This is the appropriate range for determining the concentration of compound (I). For higher concentrations where the dependence is no longer linear or where it is unclear whether it is linear, the sample can be diluted by a defined factor, if necessary, to reach a concentration where linearity is given. Otherwise, the obtained absorption can be correlated with the concentration simply by comparing it with a calibration curve.

[0133] It has been found that high chloride ion concentrations can lead to erroneous determinations of the concentration of compound (I). Therefore, if a sample contains chloride at a concentration above 30 mg / L, the chloride concentration must be measured and the absorption results adjusted. Chloride concentrations can be measured by conventional methods, such as titration (e.g., various argentometric titrations) or commercially available test kits, such as test strips from Hach Lange GmbH in Germany, which can measure chloride concentrations in the range of 30-300 mg / L. To adjust the absorption results, a calibration curve for various defined chloride concentrations can be established by measuring the absorption of the chloride-dye complex over a range of defined chloride concentrations. If the calibration curve (absorption vs. chloride concentration) shows a linear dependence of absorption and concentration, the absorption values ​​(y-axis) can be plotted against the corresponding chloride concentrations (x-axis) used to construct the calibration curve. The result is a regression line with a slope "d" and abscissa "b" at x = 0. b can be determined experimentally (absorption excluding compound (I) but including all other components) or by extrapolating the regression line to x=0. In theory, b in this case should be the same as b in equation (1) or 2. Absorption can be expressed as the product of the slope and concentration plus the ordinate. Absorption = d × concentration (chloride) + b (3)

[0134] Solving the concentration equation, we get the following equation (4). Concentration (chloride) = (absorption - b): d (4)

[0135] Combining equations (2) and (4) gives equation (5), which allows the concentration of compound (I) to be determined taking into account the interference from chloride ions. Concentration (Compound I) = (Absorption - d × Concentration (Chloride) - b): a (5)

[0136] Outside of linearity, a calibration curve of various concentrations of Compound (I) in the presence of various concentrations of chloride ions must be used. Furthermore, it has been found that high concentrations of bicarbonate ions can lead to erroneous determinations of the concentration of compound (I). Therefore, if a sample contains bicarbonate at a concentration greater than 1.4 mmol / L, the bicarbonate concentration must be measured and the absorption results adjusted. The bicarbonate concentration is measured by conventional means, e.g., titration or using commercially available test kits, such as test strips from Hach Lange GmbH, Germany, or Macherey Nagel GmbH H&Co.KG, Germany. Given that most test strips are calibrated for calcium carbonate measurement, for practical reasons, the bicarbonate concentration is measured as calcium carbonate, which can be calculated based on the bicarbonate content depending on the sample's pH. The test strips can measure carbonate concentrations in the range of 0 to 240 mg / L. To adjust the absorption results, for example, a calibration curve for various defined carbonate concentrations is established by performing measurements of the absorption of the carbonate-dye complex over a range of defined carbonate concentrations. If the calibration curve (absorption vs. carbonate concentration) shows a linear dependence of absorption and concentration, the absorption values ​​(y-axis) can be plotted on a graph against the corresponding carbonate concentration (x-axis) used for calibration. This results in a (regression) line with a slope "d" and abscissa "b" of the ordinate (x=0). b can be determined experimentally (absorption without compound (I) but including all other components) or by extrapolating the regression line to x=0. However, in most applications, bicarbonate anions are rarely present in the absence of chloride ions, so both interfering species must be considered in determining the concentration of compound (I). Therefore, the absorption in this case is expressed as a linear combination of three lines: Outside of linearity, a calibration curve of various concentrations of Compound (I) in the presence of various concentrations of bicarbonate and chloride ions must be used.

[0137] The current determination method can also be adapted for in-line measurements by passing part of the water used to operate the water-steam system through a bypass equipped with a flow-through sensor or flow-through measuring cell, for example by analogy with the methods of B. Wyrwase et al., J. Surfact Deterg. 2014, 17, 191-198 or M. Lendi et al., Power Plant Chemistry 2015, 17(1), pp. 8-13.

[0138] This determination method is suitable for samples (aqueous solutions or emulsions of compounds of formula (I)) containing a total concentration of the acid form of the compound of formula (I) of at least 0.01 mg / kg, preferably at least 0.05 mg / kg, and more preferably at least 0.1 mg / kg, calculated based on the total weight of the aqueous solution or emulsion. The method works well up to total concentrations of 2 mg / kg or somewhat higher. For higher concentrations, e.g., when the absorbance exceeds 1.6, it is recommended to dilute the sample in a defined manner.

[0139] The method of the present invention uses relatively harmless C8-C 10 The use of an alkanol avoids the significantly more hazardous chloroform used in prior art methods for determining the concentration of anionic surfactants such as dodecylbenzenesulfonic acid.

[0140] The invention is illustrated in more detail in the following examples and figures. [Example]

[0141] Products and equipment used The following products were used in the test procedure: C-1: Crodasinic TMO: oleyl sarcosine; from Croda C-2: Crodasinic TM C: Cocoyl sarcosine; sarcosinamide of coconut oil fatty acids; from Croda Cmp-1:Armeen TM OD: Oleylamine; from Nouryon Cmp-2:Duomeen TM O: oleyl propylene diamine; from Nouryon P-1: A composition comprising 2.0 wt% of C-1, 27.0 wt% of diethylethanolamine, and 71 wt% of deionized water. P-2: A composition containing 2.0% by weight of C-2, 27.0% by weight of diethylethanolamine, and 71% by weight of deionized water. Cmp-P-1: A composition containing 2.0% by weight of Cmp-1, 27.0% by weight of diethylethanolamine, 0.6% by weight of caprylic acid, and 70.4% by weight of deionized water. Note: Cmp-P-1 contains caprylic acid for stabilization, which is not necessary for P-1 and P-2.

[0142] The following pilot boiler systems were used: A natural circulation 1.5 liter pilot boiler configured to allow samples to be taken from the steam and water phases throughout the test. It should be noted that industrial-scale pressurized water-steam systems require significantly lower concentrations than those used in the pilot boiler experiments below. One reason is that retention times, i.e., the time it takes for steam to completely pass through a defined section of the system, are generally longer in industrial systems than in current pilot boilers. As an example, the retention time of a triple pressure CCGT (combined cycle gas turbine) power plant is compared to the retention time of a currently used pilot boiler. [Table 1a] As can be seen, the pilot boiler has a significantly shorter retention time. A shorter retention time means that the N-acylsarcosine has less time to exert its corrosion inhibitory effect. Therefore, a higher concentration is required to achieve the same effect as a system with a longer retention time. Furthermore, in many industrial-scale plants, corrosion inhibitors are dosed continuously or periodically, which also reduces the concentration needed to obtain the desired degree of corrosion protection compared to pilot boilers, where the inhibitor is dosed all at once at the start of the experiment.

[0143] Example 1: Determination of the partition ratio The partition ratio (DR) indicates how a substance distributes between the water and vapor phases. Values ​​greater than 1 indicate a higher concentration accumulates in the vapor phase than in the water phase, while values ​​less than 1 indicate a higher concentration of the substance in the water than in the vapor.

[0144] The distribution rate is calculated as follows: DR (distribution ratio) = c (substance in steam):c (substance in water)

[0145] The distribution ratios were measured in a pilot boiler system at 20–60 bar (2–6 MPa) and 213–277°C. The concentrations of each substance were measured as COD values ​​(mg O2 / L) using a cuvette test from Hach Lange GmbH, Germany (LCK314).

[0146] 1.5 liters of ultrapure water (18.2 mΩ) was charged into the boiler. All valves were closed, the stirring speed was set to 150 rpm, and the internal temperature was set to 60°C. The entire system was purged with nitrogen at approximately 5 bar (0.5 MPa). After holding at 60°C for 15 minutes, 300 mg of the test substance was added (concentration in the boiler: 200 mg / L). The internal temperature was then set to 213°C. Samples were taken after the set temperature and pressure had remained constant for at least 6 hours. The internal temperature was then set to 252°C. Samples were taken after the set temperature and pressure had remained constant for at least 6 hours. The concentrations of each substance were measured as COD values ​​(mg O2 / L) using a cuvette test from Hach Lange GmbH, Germany (LCK314). The results are summarized in Tables 1b, 2, and 3.

[0147] [Table 1b]

[0148] [Table 2]

[0149] [Table 3]

[0150] As can be seen, C-1 and C-2 have partition ratios comparable to that of Cmp-1, which is suitable for the purpose. In these experiments, N-acylsarcosines (as well as oleylamine) were used at higher concentrations than those provided in the method of the present invention. Higher concentrations allow for more accurate analysis of partition ratios than lower concentrations, which are more susceptible to measurement error. The purpose of these experiments is precisely to demonstrate that the present N-acylsarcosines have a similar water / vapor distribution to the established oleylamine. The same (relative) behavior is expected when lower concentrations are used.

[0151] Example 2: Corrosion inhibition using unformulated products C-1, C-2, and Cmp-1 measured by electrochemical impedance spectroscopy (EIS) EIS measurements were used as a method to demonstrate the corrosion protection behavior of the test compounds.

[0152] The following equipment was used for the electrochemical impedance measurements. -Hach EDI 101 rotating disc with speed control unit CTV101 (500 rpm); -Potentiometer Autolab PG Stat 12 controlled by Nova 1.11 software (Methrom); -Working electrode: diameter 5mm, tip surface 0.196cm 2 Origalys mild steel electrode tips; - Counterpole: Radiometer platinum; -Origalys Ag / AgCl reference electrode; -600mL beaker; -heating plate; - pH meter Knick Portamess with temperature compensation unit and SE102N electrode; - Pt100 thermometer for temperature control at the beginning and end of the experiment.

[0153] The working electrode was prepared by grinding a mild steel electrode tip at 150 rpm using a grinder with grits of P1200, P2500, and P4000 and silicon carbide grinding paper until a flat surface was produced.

[0154] 0.2 g of NaCl was dissolved in 1 L of ultrapure water (18.2 mΩ) in a beaker, and the substances to be tested (C-1, C-2, and Cmp-1) were added to a concentration of 50 mg / L. The pH was set to 9.0 (+ / - 0.05) with ammonia (1% dilution). EIS measurements were performed as described below.

[0155] EIS measurement A 600 mL beaker was filled with 400 mL of test water. A rotating disk working electrode with a mild steel electrode tip, a Pt reference electrode, and an Ag / AgCl reference electrode were positioned in the solution as follows: from the center electrode tip, the counter electrode was placed 0.03 cm to the left and the reference electrode was placed 4.5 cm to the right. The electrode tips were positioned approximately 90% deep in the solution, and the other electrodes were positioned at approximately the same height in the solution.

[0156] To prevent surface oxidation and ensure test reproducibility, the test was started within 2 minutes after polishing the electrode tip. The speed control unit of the rotating disk was started at a rotation speed of 500 rpm.

[0157] The measurements were started at the open circuit potential (OCP). For this, the voltage of the working electrode was measured relative to the reference electrode to set the starting potential for the actual measurements. The actual potentiostatic measurements were performed by frequency scanning using a frequency response analyzer (FRA). All the main parameters of the OCP and FRA are listed below:

[0158] Test-parameters: -Current range: 1mA, -OCP measurement up to 120 seconds, -Detection limit: 10 -6 , -Amplitude: 0.01, -logarithm, - Frequency: 65000Hz~0.005Hz (total 72 frequencies), -Integration time: 0.125 seconds, -Automatic current range: 100nA~100mA; -Wave Type: Single Sign

[0159] Five measurements were taken every 20 minutes (from 0 to 100 minutes).

[0160] The observed parameters (frequency ω, excitation signal E t , response signal I t , and phase shift φ), the impedance Z(φ) was calculated, which is Z'' vs. Z' (Ω cm 2) is a complex number with real part Z' and imaginary part Z'' displayed as a Nyquist or Bode plot of Z''. Reference is further made to C. Foret et al., Power Plant Chemistry 2014,16(5),pp.284-292, in particular equations (1) to (4) on page 364. Data evaluation is either graphical or calculated via Nova software or Excel. Measurement results are expressed as Z'' vs. Z' (Ω cm). 2 ) for actual results, 0.196cm 2 From the Nyquist diagram, the polarization resistance R p is obtained from the intercept of the Nyquist plot between the X axis at low frequency Z'(ω→0) and the intercept at high frequency Z'(ω→∞) by the following formula R p = Z'(ω→0) - Z'(ω→∞). Polarization resistance R p A possible fit to determine the polarization resistance R is created by the nova software. p The higher the value, the better the corrosion resistance. For practical reasons, the polarization resistance R is calculated using the following formula: p It is sufficient to calculate R p =Z'(ω=0.32Hz)-Z'(ω=63kHz)

[0161] The Nyquist plot for the measurement at t = 100 min is shown in Figure 1. These results are representative of those obtained at four other measurement points, which all showed similar behavior. To interpret the plot, the ΔZ (ohm cm) from left to right on the Nyquist plot is 2 It should be noted that the larger the value of (-x-axis), the better the corrosion protection of mild steel.

[0162] As the plot shows, compounds C-1 and C-2 exhibit better corrosion inhibition compared to Cmp-1.

[0163] Example 3: Corrosion testing of unformulated products C-1, C-2, and Cmp-1 on carbon steel surfaces at 252°C (40 bar: 4 MPa) 16.6cm 2Two mild steel C1010 test specimens (steel St37) were suspended in the vapor phase of a pilot boiler. The test substances were added to 1.7 L of ultrapure water (18.2 mΩ) at concentrations of 10 mg / L, 5 mg / L, 2.5 mg / L, or 1 mg / L (the latter concentration was only used for C-2). Cmp-1 was tested only at 10 mg / L. For comparison tests, no substance was added. The pH was set to 9.2 (+ / - 0.05) in all cases using ammonia (24.5%). 200 ml of test water was removed for separate analysis, and the remaining 1.5 L was filled into the boiler. With all valves closed and the agitator set to 150 rpm, the test water in the boiler was heated to 252°C and maintained at this temperature and pressure of 40 (4 MPa) bar for 24 hours. Samples were taken from the vapor phase when the desired temperature was reached and after 2, 20, 22, and 24 hours. The final sample from the boiler vessel was taken after shutdown (i.e., after pressure relief and cooling).

[0164] The total iron content in the samples was determined by FAAS (flame atomic absorption spectroscopy). For this purpose, the samples were shaken and 10 ml was transferred to a 15 ml vial. 0.5 ml of HCl (32%) was added and the vial was heated at 170 °C for 30 min. After cooling, the iron concentration was determined by FAAS. The detection limit of this method is 0.1 mg Fe / L. The results are summarized in Table 4.

[0165] [Table 4]

[0166] As can be seen, the Fe concentration in the steam generated from water treated with N-acylsarcosines C-1 and C-2 is clearly lower than that of untreated water as well as oleylamine-treated water.

[0167] The corrosion rate of steel specimens was determined as follows: After shutdown, the specimens were removed from the boiler, and corrosion products and deposits were roughly removed with water and a soft brush. The specimens were then placed in a pickling solution (230 ml HCl (37%), 5 ml Koranthin TM The specimens were washed with PP (consisting of PP containing propargyl alcohol, manufactured by BASF SE) and 765 ml of deionized water for 3 minutes, carefully rinsed first with deionized water and then with ethanol, dried at 105°C, and weighed. It should be noted that the average loss of the steel specimens due to pickling was 0.45 mg per minute of pickling time. The corrosion rate CR (mm / a) was calculated by the weight loss (d weight [mg]). [Formula 1]

[0168] TIFF0007750245000006.tif41140

[0169] The results are summarized in Table 5.

[0170] [Table 5]

[0171] Specimen Number: 11, 12, and 13 indicate treatments with C-1 at 10 ppm (11), 5 ppm (12), and 2.5 ppm (13). 21, 22, 23, and 24 indicate treatments with C-2 at 10 ppm (21), 5 ppm (22), 2.5 ppm (23), and 1 ppm (24). Cmp-11 indicates treatment with Cmp-1 at 10 ppm. DI indicates no treatment (but alkalized to pH > 9.2, like treated water).

[0172] In detail: 11a / b, 12a / b, and 13a / b represent specimens placed in steam of water treated with 10 ppm (11), 5 ppm (12), and 2.5 ppm (13) of C-1, respectively. 21a / b, 22a / b, 23a / b, and 24a / b represent specimens placed in steam containing water treated with 10 ppm (21), 5 ppm (22), 2.5 ppm (23), and 1 ppm (24) of C-2, respectively. Cmp-11a / b indicates specimens placed in water vapor treated with 10 ppm Cmp-1. DI-1a / b indicates specimens placed in water vapor without water treatment.

[0173] As can be seen, the corrosion rates of the specimens placed in the steam generated from water treated with N-acylsarcosines C-1 and C-2 are clearly lower than those from untreated water and oleylamine-treated water.

[0174] Example 4: Corrosion test of carbon steel surfaces at 252°C (40 bar: 4 MPa) using compositions P-1 and P-2 16.6 cm in the boiler vessel (aqueous phase) 2 Two mild steel C1010 test specimens (steel St37) were mounted on a 1000-mΩ pipe, and two more specimens were suspended in the vapor phase. The test composition was added to 1.7 L of ultrapure water (18.2 mΩ) to a concentration of 500 mg / L (=10 mg / L of active compound C-1 or C-2). 200 mL of test water was removed for separate analysis, and the remaining 1.5 L was charged to the boiler. With all valves closed and the agitation speed set to 150 rpm, the test water in the boiler was heated to 252°C and maintained at this temperature and resulting pressure of 40 bar (4 MPa) for 96 hours. Samples were taken from the aqueous and vapor phases after 2, 48, 72, and 96 hours. The final sample from the boiler vessel was taken after shutdown (i.e., after pressure release and cooling).

[0175] The total iron content in the samples was determined by FAAS (flame atomic absorption spectroscopy). For this purpose, the samples were shaken and 10 ml was transferred to a 15 ml vial. 0.5 ml of HCl (32%) was added and the vial was heated at 170 °C for 30 min. After cooling, the iron concentration was determined by FAAS. The detection limit of this method is 0.1 mg Fe / L. The results are summarized in Table 6.

[0176] [Table 6]

[0177] The corrosion rate of steel specimens was determined as follows: After shutdown, the specimens were removed from the boiler, and corrosion products and deposits were roughly removed with water and a soft brush. The specimens were then placed in a pickling solution (230 ml HCl (37%), 5 ml Koranthin TM The specimens were washed with PP (consisting of PP containing propargyl alcohol, manufactured by BASF SE) and 765 ml of deionized water for 3 minutes, carefully rinsed first with deionized water and then with ethanol, dried at 105°C, and weighed. It should be noted that the average loss of the steel specimens due to pickling was 0.45 mg per minute of pickling time. The corrosion rate CR (mm / a) was calculated by the weight loss (d weight [mg]). [Formula 2]

[0178] TIFF0007750245000009.tif41140

[0179] The results are summarized in Table 7.

[0180] [Table 7]

[0181] Specimen Number: S indicates specimens placed in steam and W indicates specimens placed in water. 11 indicates treatment with P-1. 21 indicates treatment with P-2.

[0182] For more information: SP-11a and SP-11b show two specimens (a and b) placed in water vapor treated with 500 ppm of P-1. WP-11a and WP-11b show two specimens (a and b) placed in water treated with 500 ppm of P-1. SP-21a and SP-21b show two specimens (a and b) placed in water vapor treated with 500 ppm P-2. WP-21a and WP-21b show two specimens (a and b) placed in water treated with 500 ppm P-2.

[0183] Example 5: Corrosion test of carbon steel surfaces using composition P-2 at 277°C (60 bar: 6 MPa) 16.6cm 2 Two mild steel C1010 test specimens (steel St37) were suspended in the vapor phase of a pilot boiler. Composition P-2 was added to 1.7 L of ultrapure water (18.2 mΩ) to a concentration of 500 mg / L (=10 mg / L of active compound C-2). For comparative testing, deionized water alkalized with 135 ppm diethylethanolamine was used. 200 mL of test water was removed for separate analysis, and the remaining 1.5 L was charged to the boiler. With all valves closed and the agitation speed set to 150 rpm, the test water in the boiler was heated to 277°C and maintained at this temperature and pressure of 60 bar (6 MPa) for 72 hours. Samples were taken from the aqueous and vapor phases after 2, 24, 48, and 72 hours. The final sample from the boiler vessel was taken after shutdown (i.e., after pressure release and cooling).

[0184] The total iron content in the samples was determined by FAAS (flame atomic absorption spectroscopy). For this purpose, the samples were shaken and 10 ml was transferred to a 15 ml vial. 0.5 ml of HCl (32%) was added and the vial was heated at 170 °C for 30 min. After cooling, the iron concentration was determined by FAAS. The detection limit of this method is 0.1 mg Fe / L. The results are summarized in Table 8.

[0185] [Table 8]

[0186] The corrosion rate of steel specimens was determined as follows: After shutdown, the specimens were removed from the boiler, and corrosion products and deposits were roughly removed with water and a soft brush. The specimens were then placed in a pickling solution (230 ml HCl (37%), 5 ml Koranthin TM They were washed with PP (composed of propoxylated propargyl alcohol, manufactured by BASF SE) and 765 ml of deionized water) for 3 min, carefully rinsed first with deionized water and then with ethanol, dried at 105 °C and weighed. It should be noted that the average loss of steel specimens due to pickling was 0.45 mg per minute of pickling time.

[0187] The corrosion rate CR (mm / a) was calculated by the weight loss (d weight [mg]). [Formula 3]

[0188] TIFF0007750245000012.tif41140

[0189] The results are summarized in Table 9.

[0190] [Table 9]

[0191] Specimen Number: 21 indicates treatment with P-2. DI indicates no treatment (but alkalized with 135 ppm diethylethanolamine).

[0192] For more information: P-21c and P-21d show two specimens (c and d) placed in water vapor treated with 500 ppm of P-2. DI-1c and DI-1d show two specimens (c and d) placed in water vapor without treatment.

[0193] Example 6: Corrosion Tests on Copper Surfaces at 252°C (40 bar: 4 MPa) Using Compositions P-1, P-2, and Cmp-P-1 Two copper test specimens (copper SF-Cu; CDA > 110; 99.9 wt.% Cu, 0.04 wt.% O) were suspended in the vapor phase of a pilot boiler. The test compositions were added to 1.7 L of ultrapure water (18.2 mΩ) to a concentration of 500 mg / L (= 10 mg / L Cmp-1) or 125 mg / L (= 2.5 mg / L active compounds C-1 or C-2). For comparative testing, deionized water alkalized with 135 ppm diethylethanolamine was used. 200 ml of test water was removed for separate analysis, and the remaining 1.5 L was charged to the boiler. With all valves closed and the agitator set to 150 rpm, the test water in the boiler was heated to 252 °C and maintained at this temperature and pressure of 40 bar (4 MPa) for 72 hours. Samples were taken from the vapor phase after 2, 24, 48, and 72 hours. The final sample from the boiler vessel was taken after shutdown (i.e., after pressure relief and cooling).

[0194] The total copper content in the samples was determined by FAAS (flame atomic absorption spectroscopy). For this purpose, the samples were shaken and 10 ml was transferred to a 15 ml vial. 0.5 ml of HCl (32%) was added and the vial was heated at 170 °C for 30 min. After cooling, the Cu concentration was determined by FAAS. The detection limit of this method is 0.1 mg Cu / l. The results are summarized in Table 10.

[0195] [Table 10]

[0196] The corrosion rate of copper specimens was determined as follows: After shutdown, the specimens were removed from the boiler, and corrosion products and deposits were roughly removed with water and a soft brush. They were then rinsed with a pickling solution (Kurita's Ferroline). t The specimens were washed in 8621 (containing amidosulfonic acid) (100 g) and 900 g deionized water) for 3 minutes, carefully rinsed first with deionized water and then with ethanol, dried at 105 °C, and weighed. It should be noted that the average loss of copper specimens during pickling was 0.12 mg per minute of pickling time.

[0197] The corrosion rate CR (mm / a) was calculated by the weight loss (d weight [mg]). [Formula 4]

[0198] TIFF0007750245000015.tif36140

[0199] The results are summarized in Table 11.

[0200] [Table 11]

[0201] Specimen Number: 11 indicates treatment with 125 ppm P-1. 22 indicates treatment with 125 ppm P-2. Cmp-P-11 indicates treatment with 500 ppm Cmp-P-1. DI indicates no treatment (but alkalized with 135 ppm diethylethanolamine).

[0202] For more information: P-11e and P-11f show two specimens (e and f) subjected to steam treatment of water with 125 ppm of P-1. P-22e and P-22f show two specimens (e and f) subjected to steam treatment of water with 125 ppm of P-2. Cmp-P-11e and Cmp-P-11f show two specimens (e and f) placed in steam. Water treatment with 500 ppm Cmp-P-1. DI-1e and DI-1f show two specimens (e and f) placed in steam without water treatment.

[0203] Example 7: Corrosion testing of carbon steel surfaces at 311°C (100 bar; 10 MPa) using unformulated products C-2 and CmP-2 16.6cm 2Two mild steel C1010 test specimens (steel St37) were suspended in the steam phase of a pilot boiler. The test substance was added to 1.7 liters of ultrapure water (18.2 mΩ) to a concentration of 2.5 mg / L. In both cases, the pH was set to 9.2 (+ / - 0.05) using ammonia (24.5%). 200 ml of test water was removed for separate analysis, and the remaining 1.5 liters was charged to the boiler. With all valves closed and the agitation speed set to 150 rpm, the test water in the boiler was heated to 311°C and maintained at this temperature and pressure of 100 bar (10 MPa) for 24 hours. Samples were taken from the steam and boiler water phases when the desired temperature was reached and after 2, 4, and 24 hours. The final sample from the boiler vessel was taken after shutdown (i.e., after pressure relief and cooling).

[0204] The total iron content in the samples was determined by FAAS (flame atomic absorption spectroscopy). For this purpose, the samples were shaken and 10 ml was transferred to a 15 ml vial. 0.5 ml of HCl (32%) was added and the vial was heated at 170 °C for 30 min. After cooling, the iron concentration was determined by FAAS. The detection limit of this method is 0.1 mg Fe / L. The results are summarized in Table 12.

[0205] [Table 12]

[0206] As can be seen, the Fe concentration in the steam produced from water treated with N-acylsarcosine C-2 is clearly lower than that produced from untreated water, and lower than that produced from water treated with oleylpropylenediamine.

[0207] The corrosion rate of steel specimens was determined as follows: After shutdown, the specimens were removed from the boiler, and corrosion products and deposits were roughly removed with water and a soft brush. The specimens were then placed in a pickling solution (230 ml HCl (37%), 5 ml Koranthin TMThe specimens were washed with PP (consisting of PP containing propargyl alcohol, manufactured by BASF SE) and 765 ml of deionized water for 3 minutes, carefully rinsed first with deionized water and then with ethanol, dried at 105°C, and weighed. It should be noted that the average loss of the steel specimens due to pickling was 0.45 mg per minute of pickling time. The corrosion rate CR (mm / a) was calculated by the weight loss (d weight [mg]). [Formula 5]

[0208] TIFF0007750245000018.tif32140The f of steel St37 is 0.028.

[0209] The results are summarized in Table 13.

[0210] [Table 13]

[0211] Specimen Number: S indicates specimens placed in steam and W indicates specimens placed in water. 25 indicates treatment with 2.5 ppm C-2. CmP-25 indicates treatment with 2.5 ppm CmP-2. DI indicates no treatment (but alkalized to pH > 9.2, as in treated water).

[0212] For more information: S-25a and S-25b show two specimens (a and b) placed in water vapor treated with 2.5 ppm of C-2, respectively. W-25a and W-25b represent two specimens (a and b), respectively, placed in water treated with 2.5 ppm of C-2. Cmp-S-25a and Cmp-S-25b represent two specimens (a and b) placed in water vapor treated with 2.5 ppm of Cmp-2, respectively. Cmp-W-25a and Cmp-W-25b represent two specimens (a and b), respectively, placed in water treated with 2.5 ppm of Cmp-2. S-DI-a and S-DI-b show two specimens (a and b) placed in water steam without water treatment. W-DI-a and W-DI-b indicate two specimens (a and b) placed in water without water treatment.

[0213] As can be seen, the corrosion rates of the specimens placed in the steam and water generated from the water treated with N-acylsarcosine C-2 are clearly lower than the corrosion rates from the untreated water and the oleylpropylenediamine-treated water.

[0214] Example 8: Power Plant Corrosion Testing Using C-2 and CmP-2 Tests were conducted on a shell boiler with a design pressure of 15 bar (1.5 MPa) and typically operated at 10 bar (1 MPa) under low-load conditions. At the start of the tests, the boiler had been in normal, established operating conditions for several years, using water continuously dosed with oleyl propylene diamine (CmP-2), a standard corrosion inhibitor that provides excellent corrosion protection. Fe concentrations in the steam condensate, as a measure of corrosion, were measured weekly from January 10, 2020, to July 28, 2020. During this time, the pump was operated at 60% of its stroke (dosing rate of 1.5 l / h).

[0215] On July 28, 2020, CmP-2 addition was discontinued, and treatment with C-2 was initiated by continuously adding C-2 to the feedwater at the same volume as the CmP-2 pre-addition. By September 16, 2020, CmP-2 had been completely replaced by C-2. The period from July 28, 2020 to September 16, 2020, is hereafter referred to as the "transition period." During this transition period, Fe concentrations in the steam condensate were further monitored weekly. During this period, the pump was operated at 30% pump stroke (dosing rate of 0.8 l / h).

[0216] September 16, 2020, is considered the starting point for C-2 treatment. Current results are available up to April 14, 2021. The amount of C-2 in the feedwater (= return condensate and freshwater to compensate for water losses) and steam condensate was measured on April 14, 2021, using the method described in Example 10 below. The concentration of C-2 in the feedwater was 0.16 mg / L (0.16 ppm) (average of two measurements showing 0.15 and 0.17 mg / L), and the concentration of C-2 in the steam condensate was 0.1 mg / L (0.1 ppm; below the detection limit) (two measurements).

[0217] Fe concentrations in the steam condensate were measured weekly as a measure of corrosion. During the majority of the observed C-2 treatment (until February 13, 2021), the pump was operated at 30% pump stroke, which was then increased to 60%.

[0218] Weekly samples were taken by the operator to determine the Fe concentration. For this purpose, the sample valve was opened and the initial liquid was flushed for 1 minute to create a representative sample. The sample vial was rinsed twice with sample water to saturate the vial surface with the corrosion inhibitor and minimize its absorption on the vial surface of the sample being examined. The Fe concentration was measured using a FerroVer solution from Hach Lange GmbH, Germany. TM Iron was measured using a reagent powder pillow.

[0219] The following table summarizes the weekly average Fe concentrations in steam condensate during treatment at CmP-2, during the transition period, and during treatment at C-2.

[0220] [Table 14]

[0221] The higher Fe concentrations during the transition period are probably due to chemical desorption and adsorption processes at the plant surface where Cmp-2 was gradually replaced by C-2.

[0222] Surprisingly, C-2 demonstrated superior corrosion protection to Cmp-2, even though the pump was operated at only 30% pump stroke for the majority of the observed C-2 treatments—half the 60% pump stroke applied during the observed Cmp-2 treatments. A reduced pump stroke means the inhibitor moves less quickly through the system, thus reducing its chances of exerting its protective effect. Therefore, at 60% pump stroke, C-2's corrosion protection is expected to be even better.

[0223] Furthermore, as can be seen, the standard deviation of Fe concentration is obviously lower for the C-2 treatment compared to the Cmp-2 treatment, indicating that C-2 provides more reliable corrosion protection than Cmp-2.

[0224] Example 9: Determination of C-2 concentration in water samples without chloride interference 9.1 Preparation of calibration curve Five test samples, each containing 10.0 ml of C-2 (2 wt. % C-2, 20 wt. % DEAE, and 78 wt. % water), were prepared in deionized water. Each test sample and blank was treated as follows: (1) 0.1 mg / L, (2) 0.2 mg / L, (3) 0.5 mg / L, (4) 1 mg / L, and (5) 2 mg / L of C-2 (used as a composition containing 2 wt. % C-2, 20 wt. % DEAE, and 78 wt. % water). A blank sample containing only deionized water was provided.

[0225] The sample was filled into a 25 ml 1-inch cuvette. 2 ml of buffer solution, pH 7.00 ± 0.02 (20 °C) (composed of potassium dihydrogen phosphate, disodium hydrogen phosphate, and water, manufactured by VWR Chemicals), was then added, followed by 0.2 ml of methylene blue solution (0.05% in water), and the solution was carefully mixed. 1-nonanol was filled into the cuvette up to the 20 ml mark (equivalent to 7.8 ml of 1-nonanol), and the cuvette was vigorously shaken for 10 seconds. After 7–9 minutes, the organic phase separated from the aqueous phase. Approximately 5 ml of the organic phase was carefully removed with a Pasteur pipette and transferred to a 1-inch cuvette. First, a cuvette containing the organic extract from a blank sample was measured photometrically at 660 nm in a DR3900 photometer (Hach Lange GmbH, Germany) for calibration. The resulting value was set to '0' and subtracted from the results of the test samples. The cuvette containing the organic extract from the test sample was then subjected to a blank-calibrated photometric measurement at 660 nm.

[0226] The absorbances obtained at the five concentrations were plotted on a graph with concentration (mg / L) on the x-axis (horizontal axis) and absorbance on the y-axis (vertical axis), and a regression line was drawn, which is shown as line A in Figure 2.

[0227] The slope of the line was determined to be 0.40540 and the extrapolated absorption at 0 mg / L was determined to be 0.0615, which leads to equation (6). Absorption = 0.40540 x concentration C-2 +0.0615 (6)

[0228] From this, the unknown concentration of C-2 can be determined by solving equation (6) for the concentration. concentration C-2 =(Absorption-0.0615) / 0.40540 (7)

[0229] 9.2 Measuring the concentration of C-2 in an unknown A 10.0 ml sample of water containing C-2 was filled into a 25 ml 1-inch cuvette. A separate 25 ml 1-inch cuvette was filled with 10.0 ml of deionized water for the blank value test. The following steps were performed for both the test sample and the blank: 2 ml of buffer solution pH 7.00 ± 0.02 (20°C) (composed of potassium dihydrogen phosphate, disodium hydrogen phosphate, and water, VWR Chemicals) was added, followed by 0.2 ml of methylene blue solution (0.05% in water), and the solution was carefully mixed. 1-nonanol was filled into the cuvette up to the 20 ml mark (equivalent to 7.8 ml of 1-nonanol), and the cuvette was vigorously shaken for 10 seconds. After 7–9 minutes, the organic phase separated from the aqueous phase. Approximately 5 ml of the organic phase was carefully removed with a Pasteur pipette and transferred to a 1-inch cuvette. First, a cuvette containing the organic extract from the blank was subjected to a photometric measurement at 660 nm on a DR3900 photometer from Hach Lange GmbH, Germany, and used as a calibration. Therefore, the obtained value was set to '0' and subtracted from the results of the test samples. Next, a cuvette containing the organic extract from the test sample containing C-2 was subjected to a blank-calibrated photometric measurement at 660 nm.

[0230] The concentration of C-2 was determined by inserting the observed absorption values ​​into Eq. (7). concentration C-2 =(Absorption-0.0615) / 0.40540 (7)

[0231] Example 10: Determination of C-2 concentration in chloride-interfered water samples 10.1 Preparation of calibration curve Twenty-four test samples, each 10.0 ml in volume, containing chloride ions (added as HCl) and C-2 (used as a composition containing 2 wt. % C-2, 20 wt. % DEAE, and 78 wt. % C-2) in deionized water in the amounts listed in the table below were prepared and loaded into 25 ml, 1-inch cuvettes. Another 25 ml, 1-inch cuvette, was loaded with 10.0 ml of deionized water for use in the blank value test.

[0232] [Table 15]

[0233] Each test sample and blank sample was treated as follows. The sample was filled into a 25 ml 1-inch cuvette. 2 ml of buffer solution, pH 7.00 ± 0.02 (20 °C) (composed of potassium dihydrogen phosphate, disodium hydrogen phosphate, and water, VWR Chemicals) was added, followed by 0.2 ml of methylene blue solution (0.05% in water), and the solution was carefully mixed. 1-nonanol was filled into the cuvette up to the 20 ml mark (equivalent to 7.8 ml of 1-nonanol), and the cuvette was vigorously shaken for 10 seconds. After 7–9 minutes, the organic phase separated from the aqueous phase. Approximately 5 ml of the organic phase was carefully removed with a Pasteur pipette and transferred to a 1-inch cuvette. First, the cuvette containing the organic extract from the blank sample was measured photometrically at 660 nm in a DR3900 photometer (Hach Lange GmbH, Germany) for calibration. The resulting value was set to '0' and subtracted from the test sample results. The cuvette containing the organic extract from the test sample was then subjected to a blank-calibrated photometric measurement at 660 nm.

[0234] 5 or 6 Cl - The absorbance obtained with the concentrations was plotted on a graph with the concentration of C-2>[mg / l] on the x-axis (horizontal axis) and the absorbance on the y-axis (vertical axis), and a regression line was drawn. conc. Cl- The regression line for =31 mg / l is shown as line B in Figure 2. conc. Cl- The regression line for =62 mg / l is shown as line C in Figure 2. conc. Cl- The regression line for =156 mg / l is shown as line D in Figure 2. conc. Cl- The regression line for =218 mg / l is shown as line E in Figure 2. conc. Cl-The regression line for =311 mg / l is shown as line F in Figure 2.

[0235] Figure 2 conc. C-2 The absorption values ​​of lines A to F at 0 mg / l are plotted on the x-axis (horizontal axis) and Cl - The concentration [mg / l] versus absorption was plotted on the y-axis (vertical axis) and a regression line was drawn as shown in Figure 3 .

[0236] The slope of this line was determined to be 0.00107, and the extrapolated absorption at 0 mg / L was determined to be 0.0727, which leads to equation (8). Absorption = 0.00107 x concentration Cl- +0.0727 (8)

[0237] Combining equations (7) and (8) results in equation (9) (Note: As the extrapolated absorption at ordinate intercept = 0 mg / l, the value from equation (8) was used (0.0727). This is considered more accurate because it was determined with more data and therefore points higher than the value used in equation (7)): Absorption = 0.40540 x concentration C-2 +0.00107×concentration Cl- +0.072 (9)

[0238] Solving equation (9) for the concentration of C-2, we obtain the following equation (10). [Formula 6]

[0239] TIFF0007750245000022.tif28140

[0240] 10.2 Determination of the concentration of unknown C-2 in chloride-containing water The chloride ion concentration in the tested water was measured using commercially available test strips from Hach Lange GmbH, Germany. A 10.0 ml water test sample containing C-2 and chloride ions was filled into a 25 ml 1-inch cuvette. A separate 25 ml 1-inch cuvette was filled with 10.0 ml of deionized water for the blank value test. The following steps were performed on both the test sample and the blank: 2 ml of buffer solution pH 7.00 ± 0.02 (20 °C) (composed of potassium dihydrogen phosphate, disodium hydrogen phosphate, and water, manufactured by VWR Chemicals) was added, followed by 0.2 ml of methylene blue solution (0.05% in water) and careful mixing of the solution. 1-nonanol was filled into the cuvette up to the 20 ml mark (equivalent to 7.8 ml of 1-nonanol), and the cuvette was vigorously shaken for 10 seconds. After 7–9 minutes, the organic phase separated from the aqueous phase. Approximately 5 ml of the organic phase was carefully removed with a Pasteur pipette and transferred to a 1-inch cuvette. First, the cuvette containing the organic extract from the blank was subjected to photometric measurement at 660 nm in a DR3900 photometer from Hach Lange GmbH, Germany, and used as a calibration. Therefore, the obtained value was set to '0' and subtracted from the results of the test samples. Next, the cuvette containing the organic extract from the test sample containing C-2 was subjected to blank-calibrated photometric measurement at 660 nm.

[0241] The concentration of C-2 was determined by inserting the observed absorption values ​​into the following equation (11): [Formula 7]

[0242] TIFF0007750245000023.tif24140

[0243] conc.=concentration

[0244] Example 11: Determining the concentration of C-2 in water samples with chloride and bicarbonate interferences A calibration curve was prepared in the same manner as in Example 10.1. By linear combination, the following equation (12) was obtained: [Formula 8]

[0245] TIFF0007750245000024.tif26140c=Concentration

Claims

1. A method for providing corrosion protection to a pressurized water / steam system, the method comprising adding an N-acylsarcosine compound of formula (I) or a mixture of different N-acylsarcosine compounds of formula (I) below, wherein the pressure within the water / steam system during operation is at least 0.2 MPa (2 bar). R-C(=O)-N(CH ３ )-CH ２ -COOH (I) wherein R is a linear or branched acyclic hydrocarbon group having 10 to 24 carbon atoms, or a salt thereof. When a mixture of different N-acylsarcosine compounds of formula (I) is used, R is also a linear or branched acyclic hydrocarbon group having 4 to 9 carbon atoms in up to 30 wt. % of the N-acylsarcosine compounds of formula (I), based on the total weight of the mixture. wherein the N-acyl sarcosine compound of formula (I), a mixture of different N-acyl sarcosine compounds of formula (I), or a salt thereof, is added to the water used to operate the water-steam system in an amount such that the average total concentration of the N-acyl sarcosine compound of formula (I) in the water contained in the water-steam system is in the range of 0.01 to 10 mg / kg.

2. 2. The method of claim 1, wherein the N-acyl sarcosine compound of formula (I), a mixture of different N-acyl sarcosine compounds of formula (I), or a salt thereof, is added to the water used to operate the water-steam system in an amount such that the average total concentration of the N-acyl sarcosine compound of formula (I) in the water contained in the water-steam system is in the range of 0.01 to 8 mg / kg.

3. 3. The method of claim 2, wherein the N-acyl sarcosine compound of formula (I), a mixture of different N-acyl sarcosine compounds of formula (I), or a salt thereof, is added to the water used to operate the water-steam system in an amount such that the average total concentration of the N-acyl sarcosine compound of formula (I) in the water contained in the water-steam system is in the range of 0.05 to 5 mg / kg.

4. 4. The method of claim 3, wherein the N-acyl sarcosine compound of formula (I), a mixture of different N-acyl sarcosine compounds of formula (I), or a salt thereof, is added to the water used to operate the water-steam system in an amount such that the average total concentration of the N-acyl sarcosine compound of formula (I) in the water contained in the water-steam system is in the range of 0.5 to 3 mg / kg.

5. 5. A method according to any one of claims 1 to 4 for providing corrosion protection to parts of a pressurised water and steam system in contact with steam and / or condensate.

6. 6. The method according to any one of claims 1 to 5, wherein the pressurized water or steam system comprises an inner surface made of or comprising a ferrous material, in particular steel, copper, a copper alloy, aluminium, an aluminium alloy, or two or more of these materials.

7. In formula (I), R is C １２ -C ２０ - alkyl and C with 1, 2 or 3 C=C double bonds １２ -C ２０ 7. The method of claim 1, wherein in the case of a mixture of different N-acylsarcosine compounds of formula (I), R is also selected from the group consisting of C, C, C-alkenyl ... ５ -C ９ and in up to 55% by weight, based on the total weight of the mixture, of the N-acylsarcosine compounds of formula (I), R is also C １０ -C １１ - alkyl and C with one C=C double bond １０ -C １１ -alkenyl.

8. 8. The method of claim 1, wherein R in formula (I) has an average of 12 to 18 carbon atoms.

9. 9. The method of any one of claims 1 to 8, comprising adding an N-acylsarcosine compound of formula (I) or a salt thereof, wherein R is derived from oleic acid, or adding a mixture of different N-acylsarcosines of formula (I) or salts thereof, derived from coconut oil.

10. 10. The method according to any one of claims 1 to 9, wherein the compound of formula (I) is added in its acid form to the water used to operate the water-steam system.

11. 10. The method according to any one of claims 1 to 9, wherein the compound of formula (I) is added in the form of a salt to the water used to operate the water-steam system.

12. 10. The method of any one of claims 1 to 9, wherein the compound of formula (I) is added to the water used to operate the water-steam system in the form of an acid or an aqueous solution or emulsion of the ammonium or substituted ammonium salt of the compound of formula (I).

13. 13. The method according to claim 12, wherein the concentration of the compound of formula (I) in the aqueous solution or emulsion is in the range of 0.5 to 10% by weight, calculated as the acid form of the compound of formula (I), based on the total weight of the aqueous solution or emulsion.

14. 14. The method according to claim 12 or 13, wherein the aqueous solution or emulsion consists of at least 99.9% of a mixture consisting of the compound of formula (I), water, and optionally ammonia and / or at least one organic amine.

15. 15. The method according to any one of claims 1 to 14, wherein the pressure in the water-steam system during operation is at least 1 MPa (10 bar).

16. 16. The method of any one of claims 1 to 15, wherein the water and steam system is a water and steam circuit.

17. 17. The method of any one of claims 1 to 16, wherein the water and steam system comprises a boiler.

18. 18. The method according to claim 17, wherein the water / steam system is a water / steam circuit, and the pH value of the water measured at 20°C is maintained in the range of 7.5 to 12 during operation of the water / steam circuit.

19. 19. The method of claim 17 or 18, wherein the water and steam system is a water and steam circuit, and during operation of the water and steam circuit, the water contained in the water and steam cycle has a conductivity of at most 30 μS / cm measured at 22°C.

20. 20. The method of any one of claims 1 to 19 for providing corrosion protection to a pressurized water and steam system used to generate steam for the direct or indirect processing of food, cosmetics or pharmaceuticals.

21. 16. The method according to any one of claims 1 to 15, wherein the N-acylsarcosine compound or a mixture of different N-acylsarcosine compounds of formula (I) or salts thereof is added to a production well of a geothermal power plant.

22. 1. A method for providing corrosion protection to a pressurized water / steam system, the method comprising the steps of: providing an N-acylsarcosine compound of formula (I) or a mixture of N-acylsarcosine compounds or a salt thereof to a pressurized water / steam system, the pressure in the water / steam system being at least 0.2 MPa (2 bar) during operation; RC(=O)-N(CH 3 )-CH 2 -COOH (I) wherein R is a linear or branched acyclic hydrocarbon group having 10 to 24 carbon atoms, or a salt thereof. When a mixture of different N-acylsarcosine compounds of formula (I) is used, R is also a linear or branched acyclic hydrocarbon group having 4 to 9 carbon atoms in up to 30 wt. % of the N-acylsarcosine compounds of formula (1), based on the total weight of the mixture. The use herein includes adding an N-acylsarcosine compound or a mixture of different N-acylsarcosine compounds of formula (I) or salts thereof to water used to operate a water-steam system in an amount such that the average total concentration of N-acylsarcosine compounds of formula (I) in the water contained in the water-steam system is in the range of 0.01 to 10 mg / kg.

23. The method of claim 12, for determining the concentration of the N-acylsarcosine compound of formula (I) in an aqueous solution or emulsion, comprising the steps of: i) Adding a cationic phenothiazine dye to a defined amount of an aqueous solution or emulsion containing an N-acylsarcosine compound of formula (I) or a salt thereof. ii) adding the mixture of step i) to C ８ -C １０ Extraction is carried out with a liquid extractant containing at least 95% by weight of the total amount of alkanol extractant. iii) separating the liquid extractant from the aqueous phase; iv) Measuring the concentration of the cationic phenothiazine dye in the extractant photometrically.

24. 24. The method according to claim 23, wherein the pH of the aqueous solution or emulsion of the N-acyl sarcosine compound of formula (I) is adjusted to a pH in the range of 6.5 to 7.5, measured at 20°C, before extraction.

25. 25. The method of claim 24, wherein an inorganic buffer is used to adjust the pH of the aqueous solution or emulsion of the N-acylsarcosine compound of formula (I).

26. 26. The method of any one of claims 23 to 25, wherein the cationic phenothiazine dye is methylene blue.

27. 27. The method of any one of claims 23 to 26, wherein the aqueous solution or emulsion of the N-acyl sarcosine compound of formula (I) being analyzed has a concentration of the N-acyl sarcosine compound of formula (I) of at least 0.01 mg / kg, calculated as the acid form of the N-acyl sarcosine compound of formula (I), based on the total weight of the aqueous solution or emulsion.

Images