Description:
This invention relates to the inhibition of the corrosion of steel by acids.
Our copending United Kingdom Patent Application No. 45814/70 describes and claims a method of inhibiting the corrosion of steel by acidic compounds which comprises adding to the acidic compound an effective amount of an organic nitrogen compound containing at least one unsaturated carbon-nitrogen bond, or by pre-treatment of the steel with the organic nitrogen compound, or by a combination of both methods, provided that the organic nitrogen compound is other than a cyclic vicinal dinitrile.
It has now been found that mixtures of certain compounds selected from those having the above-defined structural feature, and also mixtures of these compounds with other compounds which themselves have some or no inhibitory value including known commercial inhibitors, have better corrosion inhibition properties than a compound containing an unsaturated carbon-nitrogen bond when used alone. According to the present invention there is provided a method of inhibiting the corrosion of steel by acidic compounds which comprises adding to the acidic compound an effective amount of a mixture of a nitrile and an oxime or a mixture of a compound selected from nitriles and oximes with at least one compound selected from aliphatic and aromatic aldehydes and ketones and organic amines, or by pre-treatment of the steel with the inhibitor mixture or by a combination of both methods, provided that the nitrile is other than a cyclic vicinal dinitrile.
As examples of nitriles and oximes which may be used there may be mentioned acrylonitrile and substituted acrylonitriles, for example, crotononitrile, cinnamonitrile, o-, m- and p-methoxycinnamonitriles, 1-cyano-4-phenylbuta-1,3-diene and, 1-cyano-6-phenyl hexa-1,3,5-triene; benzonitrile and naphthonitriles and substituted benzonitriles and naphthonitriles carrying non-ionised electron-donating groups, for example, hydroxy, alkoxy, alkyl, halogen, trihalogenomethyl, thiol and thioether groups, specific examples of which include p-chloro-benzonitrile, p-methoxybenzonitrile, p-dodecylbenzonitrile, p-trichloromethylbenzonitrile, m-tolunitrile and 1-cyano-4-methoxynaphthalene; other substituted benzonitriles, including p-nitrobenzonitrile, p-dimethylaminobenzonitrile, and p-aminobenzonitrile; N,N,N', N'-tetrakis-(cyanomethyl)hexamethylenediamine, N,N'-bis(α-cyanobenzyl)ethylenediamine, diphenylmethane nitriles, for example, 3,3'-dicyanodiphenylmethane, diphenylnitriles, for example 4,4'-dicyanodiphenyl, o- and p-cyanobenzaldehyde, 2-pentenenitrile, 2,4,6-heptatrienonitrile, cyanoacetic acid, cyanovaleric acid, cyanocaproic acid, 2-3- and 4-cyanopyridines, alkyl nitriles, for example, capronitrile, caprinitrile, cenanthonitrile, caprylonitrile, pelargononitrile, tridecanonitrile, octadecanonitrile, succinonitrile, adiponitrile, azelaonitrile, sebaconitrile, decane-1,10-dicarbonitrile, dodecane dinitrile, 1,4-dicyanobutene-2, 1,4-bis(cyanoethoxy)-butyne-2, fumaronitrile, maleonitrile, phenylmaleonitrile, acetonitrile and substituted acetonitriles, for example, benzyl cyanide, diphenylacetonitrile and triphenylacetonitrile; 2-cyanocyclopentylideneimine, dimethyl glyoxime, cyclohexanoneoxime, 1,2- and 1,4-cyclohexane diketoxime, acetoxime, benzalacetoxime; dibenzalacetoxime, benzamideoxime, o- and p-benzoquinone monoximes and dioximes, acetophenoneoxime, benzophenoneoxime, benzaldoxime and cinnamaldoxime.
Compounds in which the nitrile or oxime group forms part of a conjugated unsaturated system are partiularly useful.
Examples of aliphatic and aromatic aldehydes, ketones and organic amines are acetaldehyde, aldol, propionaldehyde, butyraldehyde, crontonaldehyde, cinnamaldehyde, furfuraldehyde, benzaldehyde, acetone, methyl vinyl ketone, methyl isobutylketone, benzylidene acetone, dibenzylidene acetone, cyclohexanone, cyclopentanone, pyridine, piperidine, morpholine, pyrrolidine, benzylamine, aniline, p-aminodiphenylamine, hexylamine, hexamethylene diamine, hexamethyleneimine, hexamethylenetetramine, cyclohexylamine and dicyclohexylamine.
Nitriles, oximes, aldehydes and amines which are substituted by hydroxyl, halogen, alkyl, aryl, alkoxy, polyoxyethylene or polyoxypropylene groups may also be used.
The addition of trace amounts of halogens or halide salts, for example, bromine and iodine, to the inhibitor mixture is often advantageous.
As examples of organic acids against the corrosive attack of which the mixtures of compounds are effective there may be mentioned monocarboxylic acids such as formic acid, acetic acid, propionic acid, n-butyric acid, isobutyric acid, stearic acid, monochloro-, dichloro- and trichloroacetic acids and the corresponding bromoacetic acids, lactic acid, dicarboxylic acids such as oxalic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, terephthalic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic and dodecanedioic acid, tartaric acid and tricarboxylic acids such as citric acid and trimesic acid.
The method of the present invention is also effective against attack by organic sulphonic acids.
As examples of inorganic acids, the corrosive effects on steel of which are minimised according to the invention, there may be mentioned aqueous sulphurous acid, sulphuric acid, aqueous solutions of hydrogen halides, e.g. hydrochloric acid, sulphamic acid and nitric acid.
The method is also effective against the corrosion of steels by derivatives of acids which may undergo chemical reaction with consequent liberation of the free acids, for example, anhydrides, esters and amides in the case of carboxylic acids and is applicable both to the anhydrous acids and aqueous solutions thereof.
The corrosion-inhibiting mixtures used according to the present invention are effective at temperatures from ambient temperature or below up to 240°C or even higher.
By `an effective amount` we mean an amount of the inhibitor mixture which is effective in inhibiting corrosion under the prevailing conditions.
In the case where the inhibitor mixture is added to the organic or inorganic acid an amount of from 0.001 up to 10% by weight of each component of the mixture may be used. However, it is preferred to use from 0.005 to 5.0% and more particularly 0.01 to 0.5% by weight of each component.
Pre-treatment of steel with the inhibitor mixture may be carried out using the mixture neat, as vapour or as a solution in a suitable solvent, for example water, alcohols, acids, bases such as pyridine and quinoline, and nitriles and at temperatures up to 300°C.
The inhibitor mixtures may also be incorporated in paints, primers, and wax or polish compositions intended for application to steel and in impregnated interlining and packing materials such as paper intended for wrapping and protecting steel. The inhibitor mixtures may also be used as corrosion inhibitors in acid pickling baths which are employed in removing oxide scale from ferrous metals, and these uses form further features of the invention.
A wide variety of steels may be protected against corrosion using the methods described above, for example, stainless steels of American Iron and Steel Institute Types 304, 316 and 321 (the compositions of which are defined in, for example, British Standard No. 1449, part 4, page 20) and mild steels. The corrosion-inhibiting mixtures of compounds hereinbefore described are also effective in protecting steels from attack by high performance (jet) lubricants. The invention is illustrated but not limited by the following Examples.
EXAMPLE
For control purposes, the inhibiting effect of 1-cyano-4-phenylbutadiene-1,3, cinnamonitrile, cinnamaldoxime and cinnamaldehyde used alone was evaluated by measuring the loss in weight of a mild steel sample having dimensions 4 × 11/4 × 1/32 inch immersed in 14% hydrochloric acid at 85°C for 24 hours.
The following results were obtained:-
Inhibitor Concentration % Weight loss in (%) 24 hours ______________________________________ None -- 100% (less than 10 hours) A. 1-cyano-4- 0.025 78.0 phenylbutadiene-1,3 0.05 5.38 0.10 1.94 0.15 2.0 B. Cinnamonitrile 0.025 75.11 0.05 67.0 0.10 1.01 C. Cinnamaldoxime 0.05 87.8 0.1 1.17 0.5 1.75 D. Cinnamaldehyde 0.025 65.3 0.05 76.0 0.10 80.5 0.50 66.68 ______________________________________
The following mixtures were evaluated by the same method:
Inhibitor Concentration Total % Weight loss (%) Concentration (%) in 24 hours ______________________________________ A 0.016 0.05 1.66 D 0.036 A 0.016 0.05 1.03 C 0.036 A 0.05 0.55 3.1 Morpholine 0.50 B 0.025 0.05 0.84 D 0.025 B 0.05 0.55 2.0 Morpholine 0.50 ______________________________________
The greatly superior effect achieved by the use of mixture inhibitors is evident.