GB2045738A - Corrosion and/or rust inhibitors - Google Patents

Abstract

In a process for inhibiting the corrosion and/or rusting of a metal e.g. iron, steel or a ferrous alloy which is in contact with an aqueous system, there is added to the system, in an amount sufficient to inhibit corrosion and/or rust, a compound of formula:- <IMAGE> wherein R is a straight- or branched chain alkyl or alkenyl residue containing on average 7 to 17 carbon atoms or a cycloalkyl residue having from 5 to 12 carbon atoms and X and Y are the same or different and each is hydrogen, or a water-soluble cation, preferably an alkali metal or an alkaline earth metal, or an optionally substituted ammonium radical, preferably ammonium or an alkylamine salt optionally substituted by one or more hydroxyl groups.

Description

SPECIFICATION Corrosion and/or rust inhibitors The present invention relates to a process for inhibiting the corrosion of a metal in contact with an aqueous composition.

In recent years, a great deal of technical effort has been directed towards coping with the problems associated with inhibiting the corrosion and/or rusting of metals in contact with water circulating systems. Various synergistic corrosion-inhibiting compositions have been proposed, e.g. those described in British Patent Specification No. 1374270, using mixtures of organic materials with zinc salts; and in U.S. Patent Specification No. 3133028, using mixtures of organic materials with chromates. Such known compositions are associated, however, with certain disadvantages. For instance, the use of heavy metals such as chromium and zinc creates effluent problems because of their toxicity, and environmental restrictions have brought about a search for alternatives.Other synergistic corrosion-inhibiting mixtures containing no heavy metals are known e.g. those disclosed in British Patent Specification No. 1392044, using mixtures of organic materials and nitrites. These compositions have the disadvantage that, under operating conditions, the nitrite component can be oxidised to nitrate, thus reducing the efficiency of the inhibitor, and promoting algalgrowth or can interact with amines to form toxic N-nitroso compounds.

Furthermore, various N-acyl aspartic acids and N-alkyl-N-acyl aspartic acids have been described in German Patent Application No. 201 5075 and Jap. Pat. Publication No. 3449/74 for use as surface-active agents in cleaning compositions.

Surprisingly, we have now found that certain specific N-alkyl-N-acyl aspartic acids show significant improvements over their non-alkylated analogues, as corrosion inhibitors in aqueous systems.

Accordingly, the present invention provides a process for inhibiting the corrosion and/or rusting of a metal e.g. iron steel or a ferrous alloy, which is in contact with an aqueous system, comprising adding to the system, an amount sufficient to inhibit corrosion and/or rust of a compound of formula:

wherein R is a straight- or branched chain alkyl or alkenyl residue containing on average 7 to 1 7 carbon atoms or a cycloalkyl residue having from 5 to 1 2 carbon atoms and X and Y are the same or different and each is hydrogen, or a water-soluble cation, preferably an alkali metal an alkaline earth metal, or an optionally substituted ammonium radical, preferably ammonium or an alkylamine salt optionally substituted by one or more hydroxyl groups.

The group R, when it denotes an alkyl or alkenyl residue, may be derived from a simple fatty acid or from a complex mixture of fatty acids containing a range of residues of differing carbon content.

Examples of alkyl residues R are n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, ntridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl and n-heptadecyl, as well as various branched chain analogues of these substitutents; preferably, however, R is n-undecyl. Alkenyl groups R include n-heptenyl, n-octenyl, n-nonenyl, n-decerlyl, n-undecenyl, n-dodecenyl, n-tridecenyl, ntetradecenyl, n-pentadecenyl, n-hexadecenyl and n-heptadecenyl groups. Cycloalkyl residues R may be e.g. cyclopentyl, cyclohexyl, cyclooctyl and cyclododecyl.

When X and/or Y is an alkali metal atom, it is preferably a sodium or potassium atom.

When X and/or Y is an alkaline earth metal, each may be a magnesium, calcium or strontium atom. Alkylamine radicals X and/or Y may be e.g. mono-, di- or tri-alkylamine radicals wherein each alkyl group contains from 1 to 6, preferably from 1 to 4 carbon atoms. Examples are e.g.

methylamine, ethylamine, n-propylamine, trimethylamine, triethylamine, n-butylamine, n-hexylamine, ethanolamine, diethanolamine or triethanolamine residues.

Specific examples of compounds of formula I Disodium-N-lauroyl-N-methyl-DL-asparate Dipotassium-N-lauroyl-N-methyl-DL-aspartate Monosodium-N-lauroyl-N-methyl-DL-aspartate Disodium-N-myristoyl-N-methyl-DL-aspartate Disodium-N-octanoyl-N-methyl-DL-aspartate Dipotassium-N-octanoyl-N-methyl-DL-aspartate Disodium-N-palmitoyl-N-methyl-DL-aspartate Dipotassium-N-palmitoyl-N-methyl-DE-aspartate Disodium-N-decanoyl-N-methyl-DL-aspartate Disodium-N-stearoyl-N-methyl-DL-aspartate Monosodium-N-decanoyl-N-methyl-D L-aspartate Monosodium-N-myristoly-N-methyl-DL-aspartate Monosodium-N-palmitoyl-N-methyl-D L-aspartate Monosodiu m-N-myristoyl-N-methyl-D L-aspartate N-lauroyl-N-methyl-DL-aspartic acid N-octanoyl-N-methyl-DL-aspartic acid N-decanoyl-N-methyl-DL-aspartic acid N-myristoyl-N-methyl-DL-aspartic acid N-palmitoyl-N-methyl-DL-aspartic acid N-stearoyl-N-methyl-DL-aspartic acid N-lauroyl-N-methyl-DL-aspartic acid di-methylamine salt N-lauroyl-N-methyl-DL-aspartic acid di-triethanolamine salt N-lauroyl-N-methyl-D L-aspartic acid di-triethylamine salt N-lauroyl-N-methyl-DL-aspartic acid di-cyclohexylamine salt N-myristoyl-N-methyl-DL-aspartic acid di(dibutylamine) salt N-octanoyl-N-methyl-DL-aspartic acid di-ethylamine salt N-palmitoyl-N-methyl-DL-aspartic acid di-N-methylethanolamine salt N-stearoyl-N-methyl-DL-aspartic acid di(monobutylamine) salt N-decanoyl-N-methyl-DL-aspartic acid di(monethanolamine) salt and mixtures thereof.

Compounds of formula I are conveniently produced by first (a) reacting methylamine with a maleic acid derivative of formula:

wherein X' and Y' are each hydrogen or an alkali- or alkaline earth metal, and each is preferably hydrogen, sodium or potassium to produce, as intermediate, an N-methyl-DL-aspartic acid derivative of formula:

wherein X' and Y' have their previous significance; and then (b) reacting this compound, in aqueous alkaline solution, with an acid chloride of formula: RCOZ wherein R has its previous significance and Z is halogen e.g. chlorine, bromine or fluorine; and then (c) optionally reacting the product of step (b) with ammonia or the appropriate amine to give a compound of formula I wherein X and/or Y is an ammonium or an alkylamine radical.

A consistently alkaline pH value is preferably maintained throughout the reaction by the addition of a suitable salt of X and/or Y.

The compounds of formula I are very effective corrosion and/or rust inhibitors for metals such as iron, steel and ferrous alloys in contact with aqueous systems such as cooling waters and cutting fluids. In particular, the compounds find utility in the inhibition of corrosion of pipes and/or other equipment which is in contact with circulating water e.g. water which is being moved through condensers, engine jackets, cooling towers or distributive systems. However, the compounds can also be employed to inhibit corrosion of metal surfaces in other aqueous corrosive media.

Accordingly, the present invention further provides aqueous compositions comprising a compound of formula I in an amount sufficient to inhibit corrosion and/or rusting of a metal, e.g. iron, steel or a ferrous alloy, in contact with the composition.

In aqueous compositions of the present invention, compounds of formula I may be used singly or in admixture with other known corrosion inhibitors such as phosphonates, phosphonocarboxylic acids as well as N-acyl sarcosines, imidazolidines, triethanolamines and fatty amines and polycarboxylic acids; O.1 -5% by weight of water-soluble azoles e.g. triazoles such as benzotriazole, bis-benzotriazole and other copper-passivating benzotriazole derivatives, pyrazoie, imidazole, isoxazole and thiazoles such as isothiazole. The compounds of formula I may be used in conjuction with those known corrosion inhibitors e.g. soluble zinc salts, nitrites, chromates, nitrates, phosphates and polyphosphates, discussed hereinbefore.Preferably, however, compounds of formula I are used in the absence of said inhibitors because of the aforementioned disadvantages associated with such co-additives. Further co-additives are dispersing and/or threshold agents, such as for example polymerised acrylic acid and its salts, hydrolysed polyacrylonitrile, polymerised methacrylic acid and its salt, polyacrylamide and copolymers thereof from acrylic and methacrylic acids, lignin sulphonic acid and its salts, tannin, naphthalene sulphonic acid/formaldehyde condensation products, starch and its derivatives, and cellulose. Specific threshold agents such as, for example, alkyl phosphonic acids, 1-aminoalkyl 1 , 1 -diphosphonic acids and their salts, polycarboxylic acids e.g. polymaleic acids and alkali metal phosphates, may also be used together with the compound of formula I.

Precipitating agents such as alkali metal orthophosphates, carbonates, oxygen scavengers such as alkali metal sulphites and hydrazines, sequestering agents such as nitrilotriacetic acid and their salts, ethylene diamine tetraacetic acid and its salts, antifoaming agents such as distearylsebacamide, distearyl adipamide and related products derived from ethylene oxide and/or propylene oxide condensations, in addition to fatty alcohols, such as capryl alcohols and their ethylene oxide condensates, may also be used together with the compounds of formula I.

The amount of the compound of formula I which may be used in the aqueous compositions according to the invention is preferably within the range of from 0.1 to 500 parts per million especially 2 to 200 parts per million, based on the water to be treated.

The new corrosion inhibitors of formula I are biodegradable and have satisfactory toxicity properties and, in the case of amine salts, are totally organic in nature.

The following Examples further illustrate the present invention. Parts and percentages shown therein are by weight.

Example A A solution of 1 9.6 parts maleic anhydride in 100 parts water is refluxed for 30 minutes and cooled to 20"C., whereupon 20 parts of 40% sodium hydroxide solution are added, followed by 26.5, parts of a 25-30% aqueous solution of methylamine, added over 30 minutes, maintaining the temperature at 25-30"C by cooling. After the addition is complete, the reaction mixture is refluxed for 4 hours, cooled, and 20 parts of 40% sodium hydroxide solution are added with stirring. Nitrogen is passed through the mixture and the mixture is boiled for 1 hour to remove excess methylamine.

Analysis of the reaction mixture indicates an approximately 85% yield of di-sodium-N-methyl DL-aspartate.

To the solution are added 55 parts acetone and, simultaneously, 36.5 parts lauroyl chloride and 21.0 parts 8M sodium hydroxide are dripped in over 1-1+ hours, maintaining the temperature between 25"-30"C and the pH at 10.5 to 11.5. When the addition of acid chloride is complete, the mixture is stirred a further 30 minutes and the acetone evaporated under reduced pressure.

The alkaline solution is acidified with hydrochloric acid to precipitate N-methyl-N-lauroyl-DLaspartic acid. This can be purified by recrystallisation from toluene-petroleum spirit giving 46 parts of the required product, m.pt. 1 08'-1 11 'C [Calculated for C17 H31NOs:C,62.01%; H,9.42%; N,4.26%: Found: C,62.34%; H,9.40%; N,4.38%].

Example B Following an exactly similar method to that outlined in Example A, but using 27.1 parts octanoyl chloride, 37 parts of N-methyl-N-octanoyl-DL-aspartic acid here obtained, m.pt.

100"-103"C [Calcd. for C13H23NOs: C,57.12%; H,8.48%; N,5.13%. Found: C,56.37%; H,8.62%; N,5.50%] Example C Following the same procedure outlined in Example A, but using 40.7 parts myristoyl chloride, 42 parts of N-methyl-N-myristoyl-DL-aspartic acid were obtained, m.pt. 103"-8"C[Calculated for C19H3sNOs:C,63.83%; H, 9.87%; N 3.92%. Found: C, 63.96%; H, 10.18%; N, 3.88%].

Examples 1 to 3 Demonstration of Corrosion Inhibitor Activity of Product of Examples A, B and C Corrosion inhibitor activity of the product of Example 1 was demonstrated in the following way by the Aerated Solution Bottle Test and using a standard corrosive water made up as follows: 20 g. CaSO4 2H2O 15g. MgSO4 7H2O 4.6 g. NaHC03 7.7 g. CaC12 6H2O 45 gallons Distilled water Mild steel coupons, 5 cms x 1.5 cms are scrubbed with pumice, immersed for one minute in hydrochloric acid and then rinsed, dried and weighed.

The desired proportion of additive combination was dissolved in 100 ml. of standard corrosive water. A steel coupon is suspended in the solution, and the whole is stored in a bottle in a thermostat at 40"C. During the storage period, air is passed into the solution at 500 mlXminute, the passage of the air being screened from the steel coupon; any water losses by evaporation are replaced as they occur with distilled water from a constant head apparatus.

After 48 hours, the steel coupon is removed, scrubbed with pumice, immersed for one minute in hydrochloric acid inhibited with 1 % by weight of hexamine and then rinsed, dried and reweighed. A certain loss in weight was observed to have occurred. A blank test i.e. immersion of a mild steel specimen in the test water in the absence of any potential corrosion inhibitor, is carried out with each series of tests.The corrosion rates are calculated in milligrams of weight loss/sq. decimeter/day(m.d.d.} but for convenience the results are shown as percentage protection, which is defined as follows: % Protection = Corrosion rate for blank (in mddl corrosion rate for sample (in mdd) x 100 Corrosion rate for blank (in mdd) The results obtained using 100 parts per million of the product of Examples A, B and C are given in Table I.

TABLE I Example Compound/Additive % Protection by 100ppm additive - C,1H23CONHCH COOH I CH2COOH 66 1 Product of Example A 98 - C7H1SCONH CH COOH CH2COOH 30 2 Product of Example B 72 - C13H27CONHCH COOH CH2 COOH 56 3 Product of Example C 68 The results in Table I demonstrate that the N-methyl substituted compounds of formula I have superior corrosion-inhibiting properties relative to the known NH analogues.

Claims (20)

1. A process for inhibiting the corrosion and/or rusting of a metal, which is in contact with an aqueous system, comprising adding to the system, an amount sufficient to inhibit corrosion and/or rust of a compound of formula:

wherein R is a straight- or branched chain alkyl or alkenyl residue containing on average 7 to 1 7 carbon atoms or a cycloalkyl residue having from 5 to 1 2 carbon atoms and X and Y are the same or different and each is hydrogen, or a water-soluble cation, or an optionally substituted ammonium radical.

2. A process as claimed in claim 1 wherein X and Y are each are alkali metal or an alkaline earth metal.

3. A process as claimed in claim 1 wherein X and Y are ammonium or an alkylamine salt optionally substituted by one or more hydroxyl groups.

4. A process as claimed in any of the preceding claims wherein the metal substrate is iron, steel or a ferrous alloy.

5. A process as claimed in any of the preceding claims wherein R is an alkyl or alkenyl residue having from 7 to 1 7 carbon atoms.

6. A process as claimed in claim 5 wherein R is n-heptyl, n-octyl, n-nonyl, n-decyl, nundecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl or n-heptadecyl or a branched-chain analogue thereof; or n-heptenyl, n-octenyl n-nonenyl, n-decenyl, n-undecenyl, ndodecenyl, n-tridecenyl, n-tetradecenyl, n-pentadecenyl, n-hexadecenyl or n-heptadecenyl.

7. A process as claimed in claim 5 wherein R is n-undecyl.

8. A process as claimed in claim 2 wherein X and/or Y is sodium or potassium.

9. A process as claimed in claim 3 wherein X and/or Y is magnesium calcium or strontium.

10. A process as claimed in claim 3 wherein X and/or Y is a mono-, di- or trialkylamine radical wherein each alkyl group contains from 1 to 4 carbon atoms.

11. A process for inhibiting the corrosion and/or rusting of a metal substantially as described with reference to any of the Examples.

12. Metal inhibited against corrosion and/or rusting when produced by a process claimed in any of the preceding claims.

1 3. An aqueous composition comprising a compound of formula I, as defined in claim 1, in an amount sufficient to inhibit corrosion and/or rusting of a metal in contact with the composition.

14. A composition as claimed in claim 1 3 wherein the metal substrate is iron, steel or a ferrous alloy.

1 5. A composition as claimed in claim 1 3 or 14 wherein a further phosphonate, phosphonocarboxylic acid, N-acyl sarcosine, imidazolidine, triethanolamine, fatty amine, polycarboxylic acid or water-soluble azole corrosion inhibitor is also present.

1 6. A composition as claimed in any of claims 1 3 to 1 5 wherein further corrosion inhibitors comprising soluble zinc salts, nitrites, chromates, nitrates, phosphates and polyphosphates, are absent.

1 7. A composition as claimed in any of claims 1 3 to 1 5 wherein one or more of a dispersing- and/or threshold agent, a precipitating agent, an oxygen scavenger, a sequestering agent or an antifoaming agent is used together with the compound of formula I.

1 8. A composition as claimed in any of claims 1 3 to 1 7 wherein the amount of the compound of formula I is within the range of from 0.1 to 500 parts per million, based on the water to be treated.

1 9. A composition as claimed in claim 1 8 wherein the amount of the compound of formula I is within the range of from 2 to 200 parts per million, based on the water to be treated.

20. A composition as claimed in claim 1 3 substantially as described with reference to any of the Examples.