Inhibition of corrosion
United States Patent Costain et a1.  
 [ 1 Apr. 8, 1975 221 Filed:  
 [ 1 INHIBITION OF CORROSION [73] Assignee: Imperial Chemicals Industries Limited, London. England .Ian. 24, 1974 211 Appl. No.: 436.351  
  Related U.S. Application Data [631 Continuation of Ser. No. 180.231. Sept. 13. 1971.  
 abandoned.  
 [30] Foreign Application Priority Data Sept. 24. 1970 United Kingdom 45814/70 Mar. 25. 1971 United Kingdom 7807/71 [521 U.S. Cl. 2l/2.5 R; 2l/2.7 R. 252/148; 252/390; 252/392; 252/394 [51] Int. Cl. ..C23fIl/04;C23fll/14 [58] Field of Search 21/2.5 R. 2.7 R; 252/148. 252/390. 392. 394  
 [56] References Cited UNITED STATES PATENTS 2.043.260 6/1936 Missbach 21/2.5 R UX 2.239.752 4/1941 Lewis 252/392 X 2.387.323 10/1945 Gaynor et a1. 252/392 X 2.700.652 [/1955 Mcnaul 21/25 R X 2.863.837 12/1958 Kowald et a1 252/394 3.031.411 4/1962 Petering et 252/392 X 3.081.304 3/1963 Rogier 1/ 7 R X 3.096.147 7/1963 R 3.096.341 7/1963 X 3.098.700 7/1963 R 3.255.121 6/1966 X 3.553.101 1/1971 X 3.658.720 4/1972 X 3.669.612 6/1972 R FOREIGN PATENTS OR APPLICATIONS 38/26754 12/1963 Japan 252/394 OTHER PUBLICATIONS Betz; Handbook of Industrial Water Conditioning; 6th Edition. 1962. Phila.. Pa.. pp. 276-278.  
 Chemical Abstracts; Vol. 46. No. 11. 4983b. June. 1952 Action of Inhibitors in Pickling&#34;; lndelli et al.  
 Primary Examiner-Barry S. Richman Attorney. Agent. or FirmCushman. Darby &amp; Cushman [57] ABSTRACT A method of inhibiting the corrosion of steel by acidic compounds. which comprises adding to the acidic compound an organic nitrogen compound containing at least one unsaturated carbon-nitrogen bond (other than a cyclic vicinal dinitrile) or by pre-treatment of the steel with the organic nitrogen compound or by a combination of both methods.  
 5 Claims, No Drawings INHIBITION OF CORROSION This is a continuation, of application Ser. No. l80,23l filed Sept. 13, 1971, now abandoned.  
  This invention relates to the inhibition of the corrosion of steel by acids, and more particularly to the use of certain organic nitrogen compounds as corrosion inhibitors.  
  Steel is widely used as material of construction, particularly for chemical plant, and is consequently subjected to attack by a wide variety of corrosive substances, including organic and inorganic acids. Such corrosion presents serious problems, for not only is the structure itself attacked by contact with corrosive substances, thereby making necessary more frequent maintenance and replacement of expensive equipment than would otherwise be the case, but the products made in, for example the chemical plant are contaminated by material resulting from such corrosive attack.  
  We have found that the corrosion of steel by organic and inorganic acids is inhibited by the addition to the acid of an effective amount of an organic nitrogen compound containing at least one unsaturated carbonnitrogen bond, or by pre-treatment of the steel with the said organic nitrogen compound, or by a combination of both methods. provided that the organic nitrogen compound is other than a cyclic vicinal dinitrile.  
  As examples of organic compounds containing at least one unsaturated carbon-nitrogen bond which may be used as corrosion inhibitors according to the present invention there may be mentioned those classes of compounds containing one or more nitrile, isonitrile, oxime, hydrazone, amidine, amidoxime, semicarbazone, hydrazone or imine group, the latter class including groups which form part of a heterocyclic ring system as in, for example, oxazoles, oxadiazoles, furazans, furoxans, iminazoles, pyrazoles, pyrazolones, pyrazolines and triazoles.  
  Suitable compounds include acrylonitrile and substituted acrylonitriles, for example, crotononitrile, cinnamonitrile, p-methoxycinnamonitrile and l-cyano-4- phenylbuta-l ,3-diene; 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, pmethoxybenzonitrile, p-dodecylbenzonitrile, ptrichloromethylbenzonitrile, m-tolunitrile and l-cyano- 4-methoxy-naphthalene; other substituted benzonitriles, including p-nitro-benzonitrile, pdimethylaminobenzonitrile, and p-aminobenzontrile; N ,N ,N ,N &#39;-tetrakis-(cyanomethyl )hexam ethylenediamine, N,N&#39;-bis(a-cyano-benzyl)ethylenediamine, diphenylmethane nitriles, for example, 3,3- dicyanodiphenylmethane, diphenylnitriles, for examv ple, 4,4&#39;-dicyanodiphenyl, naphthylnitriles, for examime, acetoximc, benzalacetoxime; dibenzalacetoxime, benzamideoxime, oand p-benzoquinone monoximes and dioximes, acetophenoneoxime, benzophenoneoxime, benzaldoxime, cinnamaldoxime, guanidine salts, for example, guanidine carbonate, pyridine, 2,2- bipyridyl, 4,4-bipyridyl, quinoline, isoquinoline, lcyanoisoquinoline, benzofurazan, cyclohexylfurazan, benzofuroxan, cyclohexylfuroxan, pyridine-N-oxide and substituted pyridine-N-oxides, benzoxazone, benziminazole and metal-free phthalocyanines.  
  Polymers and iron-complexing agents such as bipyridyl, ethlyene diamine diacetic acid, phenanthrolines, quinolines and isoquinolines containing unsaturated carbon-nitrogen groupings as defined above are also satisfactory. Mixtures of inhibitors according to the present invention may also be used for wider effects, as synergists or as compositions having a wide vapour pressure range. The compounds are also effective when used together with copper cyanide.  
  A preferred class of compounds, particularly effective in protecting mild steels as well as stainless steels against acid attack, consists of conjugated unsaturated nitriles. As examples of such compounds there may be mentioned lcyano-4-pyrimidin-2-ylbutal .3-diene, l-cyanobut-l-ene-3-yne, l-cyanohexa-l,5-diene-3-yne and 6-cyanohexa-l,3,5-triene-l-yl dimethyl phenyl ammonium salts, for example, the chloride, bromide, iodide, methosulphate or ethosulphate, but preferred compounds in this class are cinnamonitrile, p-methoxycinnamonitrile, crotononitrile and l-cyano-4- phenylbuta-l ,3-diene.  
  A second preferred class of compounds, also particularly effective in inhibiting acid attack on mild steel, consists of conjugated unsaturated oximes, of which preferred compounds are cinnamaldoxime, benzalacetoxime and dibenzalacetoxime.  
  As examples of organic acids against the corrosive attack of which the above 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-, dichloroand trichloroacetic acids and the corresponding bromoacetic acids, lactic acid, dicarboxylic acids such as oxalic acid, succinic acid, gluratic acid, adipic acid, pimelic acid, ter&#39;ephthalic 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 exaples 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 carboxlic acids and is applicable both to the anhydrous acids and aqueous solutions thereof.  
  The corrosion-inhibiting compounds used according to the present invention are effective at temperatures from ambient temperature or below up to 240C or even higher.  
  By an effective amount we mean an amount of the organic nitrogen compound which is effective in inhibiting corrosion under the prevailing conditions.  
  In the case where the inhibitor is added to the organic or inorganic acid an amount of inhibitor from a trace up to percent by weight, more usually up to 5 percent by weight, based on the weight of acid, is generally effective.  
  Pre-treatment of steel with the inhibitor compound may be carried out using the compound 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 300C.  
  The inhibitor compounds 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 compounds 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 maybe protected against corrosion using the methods described above, for example, stainless steels of American Iron and Steel Institute EXAMPLE l-27 A weighed rectangular prism of steel, -35 g. in weight, stamped and drilled with an 0.375 inch hole, was placed in a 8 X 1 inch glass tube (fitted with air and 15 water reflux condensers) together with adipic acid g), inhibitor lg. ofa solid or 1 ml. ofa liquid) and distilled water (l ml.). The mixture was heated in a Wood&#39;s Metal bath at 240 i 10C for hours and the sample was removed, washed, dried, weighed and its 20 appearance noted. Some samples were given a preliminary treatment by heating for 1 hour with a 2 percent w/v solution of inhibitor in an appropriate solvent at the boil and then allowed to cool during 24 hours before testing.  
 Results are given in the following table.  
 Exam- Type of Steel lNHlBlTOR Weight REMARKS ple loss ppm Stainless Type 321 None (Control) 10.165 Severe general corrosion 1. do. Adiponitrile 38 Undrilled sample. Bright metal surface unchanged on exposure. Slight pitting on edges 2. do. succinonitrile surface slightly dulled on exposure 3 do. 2-cyano cyclopentyl- 32 bright surface unchanged idcneimine 4. do. cyclohexane 1.2-dione 64 Bright surface unchanged dioxime 5v do. cyclohexanone oxime 1 l Bright surface unchanged 6. do. 0 benzoquinone dioxime 15 do. 7. do. p benzoquinone dioxime 24 do. 8. do. benzaldoxime 234 Surface dulled and slight corrosion 9, do. Bcnzofuroxan 15 Bright surface unchanged 10. do. 22&#39; Bipyridyl 0 Sample pretreated prior to testing 1 l. dov Dimethyl glyoxime 1,050 Corrosion round hole and stamping some pitting on sides 12 do Guanidinc carbonate 43 Bright surface retained. Slight evidence of pitting. 13 do. Fumaronitrile 440 Some dulling on edges. Slight pitting 14 do. Aeetonitrile 1,975 General corrosion less than control 15 do. Cyano acetic acid 2.267 do. 16 do. phthalonitrile 4,135 Severe general corrosion 17 do. metal free phthalo- 49 Sample pretreated in inhibitor in cyanine quinoline solvent in addition to that added in normal test. Slight tarnishno pitting 18 do. C uprous cyanide 2,604 General corrosion 19 do. C uprous cyanide 26.5 Sample pretreated with inhibitors adiponitrile Inhibitors present during test slight bloom on sample 20. do Cyclohexane-LZ-dione 646 Sample pretreated with inhibitor in dioxime ethyl alcohol. No inhibitor in test.  
  Surfade of sample after test generally bright some areas of corrosion 21. Mild steel 57,500 Severe general corrosion 22. do. Cyclohexane 1,2-dione 25,400 General corrosion. Sample surface dioxime smoother than control. Corrosion less severe than control 23. Stainless Type 321 Pyridine N-oxide 10 Bright surface unchanged 24. do. 2-cyano pyridine 26 I do. 25. do. Acetoxime 19 do. 26 do. Acetophenoneoxime 0 27. do. Benzamideoxime 7.5  
  EXAMPLES 28-44 before and after exposure to the acid.  
 EXAMPLES 48-55 A rectangular mild steel strip. 3.5 g. in weight, approximately 2 X X 1/32 inch is placed in an 8 X 1 inch test-tube fitted with air and water-cooled condensers in series, together with l6 w/w hydrochloric acid (50 ml) to which the inhibitor is added and is then heated at 80 1 1C for the times indicated in the following table. The metal samples were weighed before and after exposure to the acid.  
 EXAMPLES 56-82 A bright metal steel rectangular ticket, 2 X X 1/32 inch. was immersed in 25 ml 16 w/w percent hydro- 1 chloric acid containing approximately 2 percent w/v of inhibitor in a 6 X 1 inch boiling tube and boiled for 10-20 seconds. Gas evolution was initiated in the boiling acid by contact of the mild steel ticket with an aluminum rod and the tube and contents were then allowed to cool during minutes. The hydrogen evolution rate and the final appearance of the metal sample were noted.  
 Example Acid INHIBITOR Time Temp. Weight Loss (hours) (C) 28 98 71 acetic acid None (Control) I00 I 2600 p.p.m. 29 do. Nioximc I00 I20 3 3 do. 30 do. Bcnzimidazole I00 I20 65 do. 31 do. C yclohcxanonc oximc I00 I20 0 do. 32 do. Benzofuroxan I00 I20 23 do. 33 do. None (Control) I00 I20 1400 do 34 90 Formic acid None (Control) I00 I00 460 do 35 do. C yclohexanone oximc I00 I00 63 do 36 do. None (Control) I00 I00 6500 do 37 20 Sulphuric acid None (Control) 72 80 10.792 38 do. Cyclohexanonc oximc 72 80 2. VI 39 do. Z-cyanopyridinc 72 80 I .27: 40 do. Acctoximc 72 80 L371 41 do. None (Control) 72 80 8.39? 42 I4 /r \v/v Hydro- None (Control) 24 86 9.8%  
  chloric acid 43 do. 2-cyanopyridine 24 80 5. W 44 do. None (Control) 24 80 29.67: 45 do. l-cyano-4-phcnyl hutadiene 24 80 0.0139: 46 do. cinnamaldoximc 24 80 0.04% 47 do. cinnamonitrile 24 80 0.01371 Example INHIBITOR EXPOSURE AT 80C Compound Conc. in 4 hours 24 hours acid (71 w/v) weight loss 7r weight loss I:  
 48 Benzonitrile 0.2 24.5 Dissolved 49 Dodccane dinitrile 0.2 3.2 9.2 50 Fumaronitrile 0.2 6.0 43.0 5 I p-methoxyhenzonitrile 0.2 0.67 L) 52 l-cyano-4methoxy naphthalene 0.2 0.34 0.72 53 p-dodecylbenzonitrile 0.2 2.6 5.9 54 cinnamonitrile 0.l 0.15 0.47 5 5 Control NIL Dissolved Dissolved Example INHIBITOR Hydrogen Evolution Appearance of metal Rate after exposure.  
 56 henzyl cyanide practically nil no apparent change 5 7 N.N .N &#39;.N .-tetrakis-( cyanomethyl )hcxado. do.  
  mcthylenediamine 58 octadecyl cyanide do. do. 59 l-cyanoisoquinoline do. do. 60 l-cyanonaphthalene do. do. 6 I 4.4 -dicyanodiphenyl do. do. 62 3 .3 &#39;-dicyanodiphenylmcthanc do. do. 63 p-chlorobenzonitrile do. do. 64 acrylonitrile do. do. 65 2-pentenenitrile do. do. 66 phenylmaleonitrile do. do. 67 p-trichloromethyl benzonitrile do. do. 68 m-toluonitrile do.  
  do. 69 p-nitrobenzonitrile fast &amp; continuous dull &amp; corroded 7O p-dimethylaminobenzonitrile 0. do.  
 71 p-aminohenzonitrilc Fairly slow but dulled continuous 72 p-cyanobcnzaldehyde slow but continuous dulled 73 o-cyanobenzaldehyde fairly slow but dulled continuous 74 N.N&#39;-bis(acyanobenzyl)cthylencdiamine very slow bright 75 cinnamonitrile practically nil no apparent change 76 pmethoxy cinnamonitrile do. do.  
 77 lphcnyl-4cyano butadienc do. do.  
 78 crotononitrile do. do.  
 79 cinnamaldoxime do. do.  
 80 bcnzalacetoximc do. do.  
 8l bibenzal acetoxime do. do.  
 82 none (Control) very fast and dull and severely continuous corroded We claim:  
  l. A method of inhibiting the corrosion of steel by acidic compounds which comprises adding to the acidic compound an effective amount of a compound selected from the group consisting of nitriles, aldoximcs and ketoximes. wherein the nitrile is further selected from the group consisting of nitriles in which the nitrile group is attached to an unsaturated aliphatic carbon chain to form a conjugated system including the nitrile group and at least two double bonds in the chain, and nitriles in which the nitrile group is attached to an unsaturated aliphatic carbon chain which is itself attached to a benzene nucleus to form a conjugated system including the nitrile group. the benzene nucleus and at least one double bond in the unsaturated aliphatic carbon chain; and wherein the aldoximes and ketoximes are further selected from the group consisting of orthobenzene quinone dioxime, parabenzoquinone dioxime, aldoximes and ketoximes in which the oxime group is directly attached to a benzene nucleus and aldoximes and ketoximes in which the oxime group is attached to a benzene nucleus through an unsaturated aliphatic carbon chain to form a conjugated system including the benzene nucleus, the oxime group and at least one double bond in the unsaturated aliphatic carbon chain.  
  2. A method as claimed in claim 1 wherein the acidic compound is a carboxylic acid.  
  3. A method as claimed in claim 1 wherein the acidic compound is an organic sulphonic acid or an inorganic acid.  
  4. A method as claimed in claim 1 wherein the corrosion inhibiting compound is a conjugated unsaturated nitrile selected from the group consisting of cinnamonitrile, p-methoxy-cinnamonitrile, phenylmaleonitrile and l-cyano-4-phenylbuta-l,3-diene.  
  5. A method as claimed in claim 1 wherein the corrosion inhibiting compound is a conjugated unsaturated oxime selected from the group consistingof cinnamaldoxime, benzalacetoxime, acetophenoneoxime and dibenzalacetoxime.