EP0797692B1 - Nitrogen-free corrosion inhibitors with good buffering action - Google Patents

Abstract

PCT No. PCT/EP95/04844 Sec. 371 Date Jun. 16, 1997 Sec. 102(e) Date Jun. 16, 1997 PCT Filed Dec. 8, 1995 PCT Pub. No. WO96/18757 PCT Pub. Date Jun. 20, 1996Nitrogen-free aqueous anticorrosion composition containing a) a carboxylic acid having 6 to 44 carbon atoms; and b) aromatic hydroxy compounds having a pKa value in the range of 7.0 to 11 for the hydroxy group, in a weight ratio of 1:2 to 20:1, in the form of a concentrate to be diluted with water by a factor of between 20 and 200 and in the form of a ready-to-use aqueous preparation that preferably contains 0.2 to 2 wt % component a) and 0.1 to 0.6 wt % component b) and has a pH value in the range of 7 to 11.

Description

The invention relates to anti-corrosion agents for temporary corrosion protection metallic, especially ferrous, surfaces that as aqueous emulsion or preferably as an aqueous solution. they are free of nitrogen for wastewater reasons and stand out by a good buffering effect, so that its alkaline pH despite a possible acid input and / or microbiological acid development can be maintained for a longer period of time.

Protection of metals at risk of corrosion such as iron, aluminum, Zinc, copper or their alloys against corrosion is a wide range technical task. It arises particularly when the Metal parts due to their processing status or due to their area of application not or not yet with a permanent anti-corrosive Cover such as a varnish are covered. Examples of this are metal parts during technical processing stages such as cutting or non-cutting shaping or cleaning as well as finished metal components such as heat exchangers or piping, which during their function come into contact with corrosive aqueous media. Around corrosion during or between the individual processing steps or to prevent or contain during intended use, you bring the metal surfaces into contact with corrosion inhibitors, which provide temporary protection against corrosion. It is common required for technical reasons, for example in aqueous cooling or heating circuits, or desirable for environmental reasons, for example during or after an aqueous cleaning of the metal surfaces, that the corrosion inhibitors in the aqueous phase with the metal surfaces can be brought into contact. Therefore, it is a desirable one Property of corrosion inhibitors, water soluble or to be at least dispersible in water.

As water-soluble or water-dispersible corrosion inhibitors a variety of inorganic and organic compounds known. Inorganic Corrosion inhibitors can, for example, on chromates, nitrites or be constructed from phosphates, which, however, from toxicological and ecological reasons are more or less disadvantageous. Organic corrosion inhibitors are often based on carboxylates, amines, or amides on nitrogen-containing heterocyclic compounds. Against use of secondary amines or of compounds which can split them off, there are serious toxicological problems due to the possibility of nitrosamine formation Concerns. But there are also other nitrogenous compounds not toxicologically harmless or at least because of possible water pollution disadvantageous. Carboxylic acids do not have these disadvantages in practice, however, do not prove to be sufficiently long-term effective, if by an acid entry in the inhibitor baths or by microbiological processes the pH is lowered so far that the carboxylic acids rather than in the less effective acid form in the salt form.

EP-B-341 536 describes a water-soluble corrosion inhibitor system, containing alkenyl succinic acid, arylsulfonylanthranilic acid and alkanolamines. This system does not meet the nitrogen-free requirement. GB-B-1 238 205 is a water-soluble corrosion protection combination known, which consists of gluconate and benzoate or salicylate salts. This combination is due to the strong hydrophilicity of the salts used only effective to a limited extent. EP-A-294 649 teaches the use of partially or completely neutralized hydroxyaryl fatty acids as corrosion inhibitors. These have a good anti-corrosion effect but are difficult to access.

The use of carboxylic acids as anti-corrosion agents in, for example Cooling lubricants, cleaners and corrosion protection emulsions is common in the prior art. For example, the DE-A-42 29 848 a cooling lubricant emulsion, its corrosion protection system on a combination of long chain fatty acids, short chain fatty acids, Dimer fatty acids and aromatic carboxylic acids such as benzoic acid or salicylic acid. Here, the carboxylic acids with potassium hydroxide neutralized. This system does not contain a buffer component in the The meaning of the present invention.

i) wenigstens einer Carbonsäure der allgemeinen Formel (III): R-COOY wobei R einen geradkettigen oder verzweigten, gesättigten oder ungesättigten Alkyl- oder Alkenylrest mit 5 bis 21 C-Atomen oder einen Rest der allgemeinen Formel (IV)

mit R¹ = gesättigter, geradkettiger oder verzweigter Alkylrest mit 6 bis 18 C-Atomen darstellt und Y für Wasserstoff, ein Alkalimetallionenäquivalent oder ein Ammoniumion steht,

ii) substituierten Benzoesäuren,

ii) Benzolsulfonamidocarbonsäuren,

iii) aliphatischen Dicarbonsäuren mit 2 bis 36 C-Atomen, und

iiii) den Salzen der unter i) bis iii) genannten Säuren sowie deren Gemische.

German patent application DE-A-43 23 909 teaches two-component agents for cleaning and / or passivating metal surfaces, one component containing the anticorrosive agents. The corrosion inhibitor active ingredients are selected from

i) at least one carboxylic acid of the general formula (III): R-COOY where R is a straight-chain or branched, saturated or unsaturated alkyl or alkenyl radical having 5 to 21 carbon atoms or a radical of the general formula (IV)

where R ¹ = saturated, straight-chain or branched alkyl radical having 6 to 18 carbon atoms and Y represents hydrogen, an alkali metal ion equivalent or an ammonium ion,

ii) substituted benzoic acids,

ii) benzenesulfonamidocarboxylic acids,

iii) aliphatic dicarboxylic acids with 2 to 36 carbon atoms, and

iiii) the salts of the acids mentioned under i) to iii) and their mixtures.

This system also does not contain any buffer components for stabilization of the alkaline pH value when acid is introduced or when acid is formed.

Finally, EP-A-556 087 reveals the knowledge that monocarboxylic acids with an odd number of carbon atoms, in particular the heptanoic acid, nonanoic acid and undecanoic acid, particularly effective corrosion inhibitors represent.

US-A-5 085 793 relates to an antifreezing agent for engine cooling circuits, which contains a corrosion inhibitor. Such formulations consist of a larger amount of a liquid alcohol and a smaller amount of a hydroxyl-substituted aromatic carboxylic acid in which the OH group is adjacent to the carboxyl group. Corrosion inhibitors are, for example, 2-hydroxybenzoic acid, mandelic acid and homophthalic acid. Alkali metal borates, silicates, benzoates, nitrates, nitrites, molybdates and aliphatic C _8-12 dicarboxylic acids can serve as additional corrosion inhibitors.

Database WPI (Derwent), Section Ch, Week 7640, Class E14, AN 76-74595X - presentation JP-A-51 093 741 - discloses corrosion inhibitors for metals, preferably for use in open cooling water systems. As a corrosion inhibitor Mixture of dihydroxybenzene and mono- or polycarboxylic acids in concentrations from 2 to 10 ppm.

Patent Abstract of Japan, Vol. 005, No. 200 (C-084) - Unit of JP-A-56 120 791 - describes a stabilizer composition with antioxidative properties Prevention of discoloration and corrosion of copper. This composition contains 4,4-thiobis (3-methyl-6-tert-butyl-phenol) and a polyvalent aliphatic Carboxylic acid, for example oxalic acid, tartaric acid or citric acid.

The invention is based, nitrogen-free water-soluble or water-dispersible To provide anti-corrosion agents, their anti-corrosion agents consists of carboxylic acids and therefore a longer service life and use safety that they are against pH shifts are stabilized.

a) Carbonsäure-Anionen mit 6 bis 44 C-Atomen und

b) aromatische Hydroxyverbindungen mit einem pK_s-Wert für die Hydroxygruppe im Bereich von 7,0 bis 11

im Gewichtsverhältnis 1 : 2 bis 20 : 1, dadurch gekennzeichnet, daß es in anwendungsfertigen wäßrigen Zubereitungen Konzentrationen der Komponenten a) im Bereich von 0,2 bis 2 Gew.-% und der Komponenten b) im Bereich von 0,1 bis 0,6 Gew.-% sowie eine Pufferkapazität im Bereich von 1 bis 8 aufweist, wobei die Pufferkapazität definiert ist als der Verbrauch von 0,1 normaler Salzsäure, gemessen in ml, um den pH-Wert von 50 g des Korrosionsschutzmittels um 1,3 Einheiten abzusenken. This object is achieved by containing a nitrogen-free aqueous corrosion protection agent

a) carboxylic acid anions with 6 to 44 carbon atoms and

b) aromatic hydroxy compounds with a pK _s value for the hydroxy group is in the range 7.0 to 11

in a weight ratio of 1: 2 to 20: 1, characterized in that, in ready-to-use aqueous preparations, there are concentrations of components a) in the range from 0.2 to 2% by weight and components b) in the range from 0.1 to 0, 6% by weight and a buffer capacity in the range from 1 to 8, the buffer capacity being defined as the consumption of 0.1 normal hydrochloric acid, measured in ml, around the pH of 50 g of the corrosion protection agent by 1.3 units lower.

The aromatic hydroxy compound serves as a buffer component, which makes an additional contribution to the corrosion protection effect. The buffered corrosion protection system according to the invention is used in the form of an aqueous emulsion or preferably as an aqueous solution, the particularly effective pH range being from 8.5 to 10. The invention is based on the recognition that the aromatic hydroxy compounds with a pK _s value for the hydroxy group in the range of 7.0 to 11 in the mentioned pH range of the ready preparation to develop a particularly good buffering action. For use in the preferred pH range from 8.5 to 10 aromatic hydroxy compounds with a pK _s value for the hydroxy group in the range of 8.5 to 10 are particularly favorable. Salicylic acid which has a _pK a value with respect to the hydroxyl group of 13.4 comprising (N.Konopik, O.Leberl "dissociation constants of very weak acids," Monatshefte 80 (1949), pp 660-662), does not satisfy this condition.

The pK _S value is known to be the negative decimal logarithm of the acid constant K _S , which is generally known as the thermodynamic variable and is a measure of the completeness of the proton transfer reaction from the acid to water and thus of the acid strength. Details on this can be found in general chemistry textbooks. HRChristen is mentioned as an example: "Fundamentals of General and Inorganic Chemistry", Verlag Sauerländer, Aarau and Disterweg.Salle, Frankfurt, 4th edition 1973, pp. 353-372. The _pK a value for the hydroxy group of the aromatic hydroxy compounds according to the invention refers to the acid-base reaction of the hydroxy group of the aromatic hydroxy compound with water. The invention aromatic hydroxy compounds to be used can be carboxylic acid or sulfonic acid groups whose _pK a values are much deeper and have for the inventively exploited buffer effect no meaning, but can improve the corrosion protection effect of the overall system.

The anti-corrosion agent according to the invention comes in an aqueous preparation, i.e. as an aqueous emulsion or preferably as an aqueous solution for use. This preparation contains 0.2 to 2% by weight of the component a), 0.1 to 0.6 wt .-% of component b) and the rest water and Agents for adjusting an alkaline pH, preferably alkali metal hydroxides, potassium hydroxide for reasons of solubility in the concentrate is preferred. Depending on the application, this aqueous preparation contain other auxiliary substances. The pH of the aqueous preparation is in the range from 7 to 11, preferably in the range from 8.5 to 10, for example at 9.3.

Component a) is preferably selected from mono- or polybasic, preferably monobasic, saturated or mono- or polyunsaturated linear or branched carboxylic acids with 6 to 22 carbon atoms and / or unsaturated polybasic, preferably dibasic carboxylic acids with 36 to 44 carbon atoms . Examples of carboxylic acids having 6 to 22 carbon atoms are the unbranched saturated carboxylic acids hexanoic acid, octanoic acid and decanoic acid and in particular the monocarboxylic acids with an odd number of carbon atoms to be preferably used according to the teaching of EP-A-556 087, in particular heptanoic acid, nonanoic acid and undecanoic acid . Branched saturated carboxylic acids, in particular 2-ethylhexanoic acid, 3,5,5, -trimethylhexanoic acid and 2,2-dimethyloctanoic acid, also offer particular technical advantages. A preferred example of an unsaturated short-chain carboxylic acid is 1,4-hexadienoic acid (sorbic acid). In addition, generally saturated or unsaturated fatty acids with 12 to 22 carbon atoms in the molecule or technical mixtures thereof can be used, such as are obtained, for example, when natural fats and oils are cleaved or are also synthetically accessible. Examples include oleic acid and the technical mixture of different fatty acids called tall oil fatty acid, which can be obtained from tall oil and which mainly consists of linoleic and conjugated C ₁₈ fatty acids, oleic acid and 5,9,12-octadecatrienoic acid. Furthermore, alkylphenyl-substituted unsaturated carboxylic acids of the type R'- C ₆ H ₄ - C (O) - CH = CH - COOH or R'- C ₆ H ₄ - CH = CH - COOH are used in which R 'is a linear or branched alkyl radical having 8 to 14 carbon atoms.

Unsaturated polybasic carboxylic acids with 36 to 44 carbon atoms, of which the dibasic representatives are preferably used, are also referred to as "dimer fatty acids". They are technically accessible through - usually acid catalyzed - dimerization of suitable unsaturated fatty acids with 18 to 22 carbon atoms. The reaction products are generally mixtures of acids of different degrees of oligomerization together with unreacted or isomerized starting materials. Such products are commercially available, for example from Unichema under the product group name Pripol ^R or from Henkel KGaA under the product group name Empol ^R .

In addition to the carboxylic acid components a), the corrosion-inhibiting effect of which is already known in the prior art, the aromatic hydroxy compound b), which acts as a buffer, is of particular importance in order to stabilize the anti-corrosion agent against acid entry or acid formation and thus without further maintenance measures for an extended system compared to unbuffered systems Keep period usable. The selected aromatic hydroxy compounds have the advantage over other conceivable buffer systems for the pH range 7 to 11 that they support the anti-corrosion effect of the carboxylic acid components. Component b) is preferably selected from mono-, di- or trinuclear aromatic hydroxy compounds of the general formula (I) HO - Arom - X where X is selected from substituents COOH, SO ₃ H or SO ₂ -C ₆ H ₄ -OH and "aroma" represents a mono-, dinuclear or trinuclear carbocyclic aromatic six-ring system of the benzene, naphthalene, anthracene or phenanthrene type, and the other Can carry substituents X, OH and / or alkyl, hydroxyalkyl and / or hydroxyalkyl ether radicals having 1 to about 4 carbon atoms. Hydroxyalkyl ether residues such as ethylene glycol ether or propylene glycol ether residues can be obtained, for example, by ethoxylation or propoxylation of phenols.

wobei X ausgewählt ist aus Substituenten COOH, SO₃H oder SO₂-C₆H₄-OH und R¹, R², R³ und R⁴ unabhängig voneinander eine Gruppe X, H, OH oder einen Alkyl-, Hydroxyalkyl- oder Hydroxyalkyletherrest mit 1 bis 4 C-Atomen bedeuten.Mononuclear aromatic hydroxy compounds which can be described by the general formula (II) are preferably used as component b):

where X is selected from substituents COOH, SO ₃ H or SO ₂ -C ₆ H ₄ -OH and R ¹ , R ² , R ³ and R ⁴ independently of one another a group X, H, OH or an alkyl, hydroxyalkyl or Hydroxyalkyl ether radical with 1 to 4 carbon atoms.

Preferred compounds of the general formula (II) are those which contain only a single substituent X, which is preferably para to the hydroxyl group and in which the substituents R ¹ , R ² , R ³ and R ^{4 are} preferably hydrogen . The substituent X is preferably one of the groups COOH, SO ₃ H or SO ₂ -C ₆ H ₄ -OH. Particularly suitable examples of such compounds are 4-hydroxybenzoic acid, 4-phenolsulfonic acid and 4,4'-dihydroxydiphenyl sulfone (bisphenol S).

Compounds with a carbon or sulfonic acid function will largely exist in the form of their carboxylate or sulfonate anions under the pH conditions of the application solution in the range from 7 to 11. Present invention, since such hydroxyl compounds are used whose _pK a is for the hydroxy group in the range of 7.0 to 11, is to be expected that the hydroxyl groups in the selected pH range are partially deprotonated. The possibility of determining the _pK a values of the only weakly acidic hydroxy groups, reference is made to the previously mentioned reference of Konopik. Further pK _S determinations are contained in: B.Jones, JCSpeakman: "Thermodynamic Dissociation Constants of Hydroxy- and Alkoxy-benzoic Acids", J.Chem.Soc. 1944, pp. 19-20. M- and accordingly have to p-hydroxybenzoic acid _pK a values of 9.94 or 9.39. The _pK a value of 4-phenolsulfonic acid for the phenolic hydroxy group was about 8.9, the one intended to 9.5 of bisphenol S. In contrast, the dissociation constant of salicylic acid with respect to the OH group is so low that it could not be determined by the method of potentiometric titration selected here using a glass electrode.

For the long-term stability of the ready-to-use that is aimed at according to the task aqueous corrosion protection solution or corrosion protection dispersion it is important that this have a buffering capacity in the range of 1 to 8 has. The buffer capacity is defined as the consumption of 0.1 normal hydrochloric acid, measured in ml, around the pH of 50 g of the anti-corrosion agent to lower 1.3 units, for example by 50 g of Corrosion protection agent from a pH of 9.3 to a pH of 8 to titrate. Such buffer capacities can be achieved when using the components a) achieve that according to the invention with components b) combined.

Buffer capacities of a similar size could also be achieved if components a) with other buffers such as suitable amines, Combined borates or phosphates. On the use of amines however, be waived for the reasons mentioned at the beginning. Also on that other ecologically disadvantageous buffer systems such as borates or phosphates can be dispensed with by the present inventive teaching.

The above-mentioned concentration information for the invention Use of suitable anti-corrosion agents refer to the ready-to-use aqueous preparations. In principle, these can Place by dissolving or dispersing the individual components in water in the specified concentration ranges. On the affected technical field, however, it is common to use such combinations of active ingredients to market in the form of concentrates, all components already included in the required proportions and from ready-to-use treatment baths by diluting with water getting produced. Accordingly, the invention also relates to aqueous Active substance concentrates which contain the components a) and b) in the in claim 1 specified proportions included. The drug concentrations in these concentrates are preferably adjusted so that they can be diluted of the concentrate with water by a factor between about 20 and about 200 an aqueous anticorrosive with those described above Contains properties.

Embodiments

According to the table, active ingredient concentrates were made from the inhibitor component a) and the buffer component b) prepared by the individual components in the concentrations given in the table in fully desalinated Water dissolved or dispersed and added so much KOH that one with demineralized water a factor of 50 diluted solution 9.3 had.

The buffer capacity was determined using 50 g of the ratio 1:50 diluted concentrate solution with 0.1 normal hydrochloric acid of pH 9.3 titrated to pH 8. The required consumption of hydrochloric acid in ml is called buffer capacity.

A plate climate test was carried out to check the corrosion protection effect. For this purpose, steel sheets of the quality ST 1405 with the dimensions 5 cm x 10 cm were brushed with an aqueous surfactant solution, rinsed with water and alcohol and dried. The sheets were then immersed in the concentrate solutions diluted with deionized water by a factor of 50 according to the table, drained and stored in a climatic chamber at 22 ° C. and a relative air humidity of 76%. All examples provided the required corrosion protection (less than 30% corrosion after 40 days of testing). The formulation according to Example 10 was also tested in a larger dilution. The required corrosion protection effect was also achieved by diluting the concentrate by a factor of 75. Active substance concentrates: Figures in% by weight in water / KOH No. Inhibitor a) Conc. Buffer b) Conc (%) Buffer capacity (ml) Compare 1 Heptanoic acid 20th - 0.06 Compare 2 Sorbic acid 20th - 0.03 Compare 3 Heptanoic acid 20th Salicylic acid 5 <0.1 Ex. 1 Tall oil fatty acid 20th 4-hydroxybenzoic acid 5 1.6 Ex. 2 Oleic acid 20th 4-hydroxybenzoic acid 5 2.6 Ex. 3 Dimer fatty acid (Empol ^R 1022, Henkel KGaA) 20th 4-hydroxybenzoic acid 5 1.6 Ex. 3 Heptanoic acid 20th 4-hydroxybenzoic acid 5 2.0 Ex.4 Sorbic acid 20th 4-hydroxybenzoic acid 5 1.8 Ex. 5 Sorbic acid 20th 4-hydroxybenzoic acid 10th 5.0 Ex. 6 Sorbic acid 20th 4-hydroxybenzoic acid 20th 6.0 Ex. 7 Sorbic acid 20th Bisphenol S 5 1.6 Ex. 8 Heptanoic acid 20th 4-phenolsulfonic acid 5 1.6 Ex. 9 Heptanoic acid 10th 4-hydroxybenzenesulfonic acid 5 2.0 + Sorbic acid 10th Ex. 10 3,5,5-trimethylhexanoic acid 10th 4-hydroxybenzenesulfonic acid 10th 5.2 + Sorbic acid 10th

Claims (9)

1. A nitrogen-free water-based corrosion control formulation containing

   a) carboxylic acid anions containing 6 to 44 carbon atoms and

   b) aromatic hydroxy compounds with a pK_s value for the hydroxy group of 7.0 to 11

   in a ratio by weight of 1:2 to 20:1,
   characterized in that , in ready-to-use aqueous preparations, it has concentrations of 0.2 to 2% by weight of components a) and 0.1 to 0.6% by weight of components b) and a buffering capacity of 1 to 8, the buffering capacity being defined as the consumption of 0.1 normal hydrochloric acid, as measured in ml, required to lower the pH value of 50 g of the corrosion control formulation by 1.3 units.
2. A corrosion control formulation as claimed in claim 1, characterized in that, in ready-to-use aqueous preparations, it contains for the rest water, chemicals for establishing an alkaline pH value, preferably alkali metal hydroxides, more particularly potassium hydroxide, and optionally other auxiliaries and is present as an emulsion or preferably in the form of an aqueous solution.
3. A corrosion control formulation as claimed in claim 2, characterized in that it has a pH value of 7 to 11.
4. A corrosion control formulation as claimed in claim 3, characterized in that it has a pH value of 8.5 to 10.
5. A corrosion control formulation as claimed in one or more of claims 1 to 4, characterized in that component a) is selected from monobasic or polybasic, saturated or mono- or polyunsaturated linear or branched carboxylic acids containing 6 to 22 carbon atoms and/or unsaturated polybasic carboxylic acids containing 36 to 44 carbon atoms.
6. A corrosion control formulation as claimed in one or more of claims 1 to 5, characterized in that component b) is selected from mononuclear, dinuclear or trinuclear aromatic hydroxy compounds corresponding to general formula (I): HO - Arom - X where X is selected from the substituents COOH, SO₃H or SO₂-C₆H₄-OH and "Atom" represents a mono-, di- or trinuclear carbocyclic aromatic 6-ring system of the benzene, naphthalene, anthracene or phenanthrene type which may contain further substituents X, OH and/or alkyl, hydroxyalkyl and/or hydroxyalkyl ether groups containing 1 to 4 carbon atoms.
7. A corrosion control formulation as claimed in claim 6, characterized in that component b) is selected from aromatic hydroxy compounds corresponding to general formula (II):

   

   in which X is selected from the substituents COOH, SO₃H or SO₂-C₆H₄-OH and R', R², R³ and R⁴ independently of one another represent a group X, H, OH or an alkyl, hydroxyalkyl or hydroxyalkyl ether group containing 1 to 4 carbon atoms.
8. A corrosion control formulation as claimed in claim 7, characterized in that component b) is selected from compounds corresponding to general formula (II) which contain only one substituent X and in which the substituents R¹, R², R³ and R⁴ are hydrogen.
9. A corrosion control formulation as claimed in one or more of claims 1 to 8, characterized in that it is obtained by dilution of corresponding active-substance concentrates with water by a factor of 20 to 200.