EP0026878B1 - Corrosion inhibitors stable in hard water - Google Patents

Description

In the entire field of metal processing and metal surface treatment as well as in cooling circuits, it is customary to use more or less strongly alkaline aqueous solutions which contain corrosion-inhibiting additives for ferrous and non-ferrous metals in order to avoid undesirable corrosion phenomena. This applies, for example, to processes as widespread as metal-cutting and non-cutting metal forming, the cleaning treatment of metal surfaces or the internal protection of flowing aqueous systems.

Known and widespread corrosion-inhibiting additives are, for example, inorganic salts such as sodium nitrite or chromates, but against their further use in these fields, there are increasingly toxicological and ecological reasons.

Recently, organic inhibitor systems have therefore been switched to which no longer have the disadvantages mentioned. For example, according to DE-B-1 298 672 alkylarylsulfonamidocarboxylic acids or their salts are proposed for this purpose. The use of alkyl-substituted benzoic acids is also known. The types mentioned also have serious disadvantages. Salts of alkyl-substituted benzoic acids, for example, have a strong sensitivity to water hardness, which greatly reduces their usability in the mineral oil-free cutting fluid sector, for example. Similar negative properties, but less pronounced, are also shown by alkanolamine salts of the alkylarylsulfonamidocarboxylic acids mentioned. With increasing service life of the functional liquids due to evaporation losses in pure water and the associated hardening of the working solution, there is an elimination of poorly soluble calcium or magnesium salts, which leads to the formation of crystalline residues on the machines and to the depletion of the solution of active substance.

The use of acylated aminocarboxylic acid salts as corrosion inhibitors is also known, the acyl radical being derived from long-chain fatty acids. In practice, however, these products have proven to be very disadvantageous because they foam very much.

wobei

• R, verzweigtes C₆-C₁₃-Alkyl oder C₅- oder C₆-Cycloalkyl und Polycycloalkyl mit 6 bis 13 C-Atomen, die durch 1 oder 2 C,-C₄-Alkylgruppen substituiert sein können,
• R₂ Wasserstoff oder C,-C₆-Alkyl und
• R₃ C₁-C₁₁-Alkylen in gerader oder verzweigter Kette bedeuten.

The present invention relates to water-miscible, hard water-stable corrosion protection agents with improved properties, which essentially consist of an alkali metal, alkaline earth metal or amine salt of a compound of the formula

in which

• R, branched C ₆ -C ₁₃ alkyl or C ₅ - or C ₆ cycloalkyl and polycycloalkyl with 6 to 13 C atoms, which can be substituted by 1 or 2 C, -C ₄ alkyl groups,
• R _{2 is} hydrogen or C, -C ₆ alkyl and
• R _{3 is} C ₁ -C ₁₁ alkylene in a straight or branched chain.

Suitable bases which are suitable for neutralizing the carboxylic acid described above are alkali metal hydroxides and alkali metal carbonates and the corresponding alkaline earth metal compounds, such as, for example, sodium hydroxide, sodium carbonate, potassium hydroxide and barium hydroxide. Organic amines, such as, for example, triethanolamine, diethanolamine, triisopropanolamine, mono-, di- and triethylamine, monoisopropylamine, mono-2'-ethylcyclohexylamine, mono-i-nonylamine, 2-methyl-2 'are also suitable as bases. -aminoprop-anol, cyclohexylamine-N, N'-dimethylcyclohexylamine, N-hexylamine, N-octylamine, triisobutylamine, di-N-hexylamine, ethylenediamine, diethylenetriamine, piperidine, piperazine or morpholine. For the salt formation, the acids and the base can be used in stoichiometric amounts or one component each in excess.

The claimed anticorrosive agents can be used alone or in a mixture with known metalworking fluids or aqueous oil emulsions. The anti-corrosion agents can be used as aqueous solutions, dispersions or emulsions. The application concentration in which the claimed anti-corrosion agents are used depends on the intended use of the liquid with which the ferrous and non-ferrous metals come into contact. It is generally between 0.5 and 10% by weight, preferably 2 to 5% by weight. For the effect of the claimed anticorrosive agents, it is essential that the alkyl group R of the formula given above is branched. These acids are obtained in a known manner by reacting aminocarboxylic acids with carboxylic acid chlorides by known processes in the presence of alkali in the sense of a Schotten-Baumann reaction. The aminocarboxylic acids are obtained, for example, by hydrolysis of lactams such as e-caprolactam or y-butyrolactam or by the addition of primary amines to acrylic acid, methacrylic acid or crotonic acid esters or nitriles and subsequent saponification. Examples of aminocarboxylic acids are Q-aminoundecanoic acid, e-aminocaproic acid, y-aminobutyric acid, β-alanine glycine-Nn-butyl-β-aminopropionic acid, Ni-propyl-β-aminopropionic acid, N-cyclohexyl-β-aminopropionic acid, N-cyclohexyl-a -methyl-ß-aminopropionic acid and N-cyclohexyl-ß-methyl-ßaminopropionsäure called. Examples of acid chlorides are pivalic acid chloride, 2-ethylhexanoic acid chloride, isononanoic acid chloride, bicycloheptenic acid chloride, tricyclodecanoic acid chloride, naphthenic acid chloride and neodecanoic acid chloride. Isononanoic acid chloride, 2-ethylhexanoic acid chloride and neodecanoic acid chloride are preferred.

The salts of the carboxylic acids described above have excellent corrosion protective effect against iron and, which is extremely important for practical use, has only a slight tendency to foam. In addition, they are very largely insensitive to the hardness constituents of the water and leave residues even under extreme electrolyte loads when drying, which can be described as low-viscosity and oily, and which do not stick. These residues can be easily dissolved with the working solution as well as with fresh water.

example 1 2-ethylhexanoyl-e-aminocaproic acid

113 g (1.0 mol) of _E- caprolactam are dissolved in 280 ml of water and with 120 g (1.0 mol) of 33 percent. Sodium hydroxide solution heated under piece flow for 4 hours. The mixture is cooled to 20 ° C. and 158.4 g (0.975 mol) of 2-ethylhexanoic acid chloride are added dropwise over the course of 1 hour, and at the same time about 120 g of 33 percent are maintained to maintain a pH of 12. Sodium hydroxide solution at 20-25 ° C. The solution is stirred until no more sodium hydroxide solution is used and then at 50 ° C. with halkonz. Acidified to pH 1 hydrochloric acid. It is separated off in the heat and washed with 350 ml of water. The acid is dewatered on a rotary evaporator at 75 ° C / 100 ml Hg and falls off as an almost colorless viscous oil, which solidifies in crystalline form after some time. Yield 233 g (93%). Acid number 225, water content 0.4%.

Example 2 Mixture of 2-ethyl-hexanoyl- _E- aminocaproic acid and isononanoyl- _E- aminocaproic acid

113 g (1 mol) of _E- caprolactam are hydrolyzed as described in Example 1 and then with a mixture of 79.6 g (0.49 mol) of 2-ethylhexanoic acid chloride and 86.5 g (0.49 mol) of isononanoic acid chloride, which can be prepared separately or from an equimolar mixture of 3-ethyl-hexanoic acid and isononic acid by known processes, in accordance with Example 1. 238.6 g (90.4%) of an almost colorless oil, acid number 216, are obtained.

Example 3 Tricyclodecanoyl- _E- aminocaproic acid

113 g (1 mol) of _E- caprolactam are hydrolyzed according to Example 1 and reacted with 181.7 g (0.91 mol) of tricyclodecanoic acid chloride. The title compound is obtained as a yellow, highly viscous oil in a yield of 236.1 g (88.5%) with an acid number of 194.

Example 4 Isononanoyl- _E- aminocaproic acid

113 g (1 mol) of _E- caprolactam are hydrolyzed as in Example 1 and reacted with 172 g (0.975 mol) of isononanoic acid chloride. The workup provides 257.5 g (95%) of an almost colorless viscous oil which solidifies in crystalline form after some time, acid number 210.

To produce an aqueous corrosion inhibitor, 35 g of acid from Examples 1-4 were mixed with 50 g of triethanolamine and 15 g of water to give a clear, homogeneous solution.

The residue formation of the products obtained according to the exemplary embodiments was checked by means of a long-term pumping test. The principle of this test method is that around 10 1 of an aqueous solution of the anti-corrosion agent is pumped in large-volume open glass vessels over a longer period of time at room temperature in a way that is suitable for causing deposits on the glass wall by spraying and evaporation processes. For this purpose, an electrically operated, commercially available laboratory pump with a delivery rate of 10 l / min. introduced, which sucks the solution through a hose line of 0.8 cm diameter, conveys it above level and presses it back onto the surface of the bath contents in a sharp jet. The exit opening of the jet is approx. 15 cm above the liquid level, the entry angle of the jet can be chosen as desired.

The desired formation of deposits on the parts of the vessel wall which have not been rinsed out now occurs in two ways. First, the normal spraying process ensures wetting. On the other hand, when immersed, the jet continuously entrains a large number of smaller air bubbles into deeper layers, which, again bursting at the surface of the liquid, spray the wall of the vessel continuously with a film of liquid. This procedure also guarantees high evaporation rates even at room temperature. With filling quantities of 10 I it is in the order of 1 I / day. The losses are replaced by drinking water of 20 dH (approx. 350 ppm), whereby the system is continuously hardened. The increase in hardness constituents is determined arithmetically using the replenishment quantities added.

• Vergleich A:
  • Homogene Mischung aus
  • 35% Para-tertiär-butyl-benzoesäure
  • 50% Triethanolamin
  • 15% H₂0
• Vergleich B:
  • Homogene Mischung aus
  • 35% _E-(Benzolsulfonyl-methyl-amino)-n-capronsäure gemäss DE-C-1 298 672
  • 50% Triethanolamin
  • 15% H₂

Aqueous preparations with an active ingredient content of 3% were used for the tests. The following products were used as comparative samples:

• Comparison A:
  • Homogeneous mix of
  • 35% para-tertiary-butyl-benzoic acid
  • 50% triethanolamine
  • 15% H ₂ 0
• Comparison B:
  • Homogeneous mix of
  • 35% _E - (benzenesulfonyl-methyl-amino) -n-caproic acid according to DE-C-1 298 672
  • 50% triethanolamine
  • 15% H ₂

The test results are summarized in the table below.

Claims (2)

1. Anticorrosive stable to hard water, which comprises an alkali metal salt, alkaline earth metal salt, or amine salt of a compound of the formula

in which

R₁ is branched C₆-C₁₃-alkyl or C₅- or C₆-cycloalkyl, or polycycloalkyl having from 6 to 13 carbon atoms optionally substituted by 1 or 2 C₁-C₄-alkyl groups,

R₂ is hydrogen or C₁-C₆-alkyl, and

R₃ is C₁-C₁₁-alkylene in linear or branched chain.

2. Anticorrosive stable to hard water consisting of a 0.5 to 10 weight % aqueous solution, dispersion or emulsion of the compound as claimed in claim 1.