WO1990010732A1

WO1990010732A1 - Benzotriazole based corrosion inhibiting compositions

Info

Publication number: WO1990010732A1
Application number: PCT/AU1990/000099
Authority: WO
Inventors: Fred Bolza; Michael Hudson
Original assignee: Ici Australia Operations Proprietary Limited
Priority date: 1989-03-09
Filing date: 1990-03-09
Publication date: 1990-09-20

Abstract

A corrosion-inhibiting composition comprising the reaction product of a benzotriazole of formula (I), a compound of formula (II) and at least one alkylene oxide, the composition optionally including halide ions. Formulae (I) and (II), wherein R1 is the same or different and is selected from the group consisting of hydrogen, halogen, C1 to C6 alkyl, C1 to C6 haloalkyl, C2 to C6 alkenyl, C2 to C6 alkynyl, C1 to C6 alkoxy, C1 to C6 alkylthio, aryloxy, arylthio, substituted C1 to C6 alkyl wherein the alkyl group is substituted with a substituted or unsubstituted phenyl, C1 to C6 alkoxycarbonyl, amino, C1 to C6 alkylamino, di(C1 to C6) alkylamino or -NHQ, wherein Q is selected from substituted or unsubstituted phenyl, nitro, cyano and thiocyanato; and n has a value of from 1 to 3; R2 is selected from straight or branched-chain alkyl, alkenyl or alkynyl having an average of from 8 to 24 carbon atoms per chain optionally substituted with substituted or unsubstituted phenyl; R3 is the same or different and is selected from the group consisting of hydrogen and C1 to C6 alkyl; x and y are integers being the same or different, the sum of x + y being from 0 to 30.

Description

BENZOTRIAZOLE BASED CORROSION INHIBITING COMPOSITIONS

This invention relates to corrosioninhibiting compositions and more particularly, compositions for inhibiting the corrosion of ferrous metals in. acid pickling baths.

Ferrous metals, such as steel, which are subjected to working at elevated temperatures during the course of manufacture, become coated with a layer of oxide impurity, often referred to as mill scale. For most subsequent processing operations, such as coating or plating, it is necessary to remove the layer of oxide scale. Typically, the metal is treated in a bath of aqueous acid, an operation referred to as acid pickling. Acids commonly used for this purpose include acid such as sulphuric acid, hydrochloric acid, phosphoric acid, sulphamic acid and others. Once the layer of oxide scale is removed, however, the acid may then be free to attack the exposed surface of the metal itself. In order to minimise acid action on exposed metal it is advantageous to add a corrosion inhibitor to the acid pickling bath.

Many compounds may be used to inhibit corrosion of metals. For example, halide ions, which have often been thought of as corrosion accelerators, may act as inhibitors under some circumstances such as in strong acid solutions.

Many nitrogen-containing compounds are also

effective as corrosion inhibitors in acid. These compounds include alkyl and aryl amines, saturated and unsaturated nitrogen ring compounds, compounds such as Mannich bases which may be synthesised from amines and amines condensed with ethylene oxide and the like.

A novel corrosion-inhibiting composition has been developed which shows a surprisingly good corrosion inhibitor efficiency. "Corrosion

inhibitor efficiency" is a measure, in percentage terms, of the ability of an inhibitor to restrain corrosion of a metal in an acid pickling solution. For example, a corrosion and inhibiting composition efficiency of 99% means that only 1% of the metal is affected by corrosion.

According to the present invention there is provided a corrosion-inhibiting composition which comprises a reaction product of a benzotriazole of formula I

a compound of formula II

and at least one alkylene oxide,

the composition optionally including

halide ions.

In the compound of formula I, R. may be the same or different and may be selected from the group

consisting of hydrogen, halogen, C₁ to C₆ alkyl, C₁ to C₆ haloalkyl, C₂ to C₆ alkenyl, C₂ to C₆

haloalkenyl, C₂ to C₆ alkynyl, C₁ to C₆ alkoxy, C₁ to C₆ alkylthio, aryl, aryloxy, arylthio,

substituted C₁ to C₆ alkyl wherein the alkyl group is substituted with a substituted or unsubstituted phenyl, C₁ to C₆ alkoxycarbonyl, amino, C₁ to C₆ alkylamino, di(C₁ to C₆) alkylamino, the group-NHO wherein O is selected from substituted or

unsubstituted phenyl, nitro, cyano and thiocyanato; and n has a value of from 1 to 3.

Preferably R₁ may be selected from the group consisting of hydrogen, halogen, C₁ to C₄ alkyl, C₁ to C₄ alkoxy, C₁ to C₄ alkylthio, aryl, aryloxy, arylthio, substituted C₁ to C₄ alkyl wherein the alkyl group is substituted with a member selected from the group consisting of phenyl, amino, C₁ to C₄ alkylamino, di(C₁ to C₄) alkylamino, -NHO wherein O is selected from phenyl, nitro, cyano and

thio-cyanato; and n is 1 or 2.

Particularly preferred compounds of formula I are those wherein R₁ is selected from hydrogen and methyl; and n is 1. For the purposes of the

present invention it has been found that a compound of formula 1 wherein R₁ is methyl and n is 1, (i.e., tolyltriazole) is particularly suitable.

The composition according to the invention comprises the reaction product of a benzotriazόle of formula I, a compound of formula II and at least one alkylene oxide. The benzotriazole is dissolved in the compound of formula II and is subsequently alkoxylated on addition of alkylene oxide. A benzotrlazole alone has an Inhibitor efficiency of about 60%, however, alkoxylation appears to increase inhibitor efficiency to about 95%. Without

intending to be bound by theory, it seems that, although the major function of the compound of formula II is to dissolve the benzotriazole, it is believed that 1t also plays a part in alkoxylation of the benzotriazole, although the reaction

mechanism is not fully understood.

In the compound of formula II, R₂ may be selected from the group consisting of a straight- or branched-chain alkyl, alkenyl or alkynyl group having an average of from 8 to 24 carbon atoms per chain, optionally substituted with a substituted or unsubstituted phenyl. The term "average" is used since reagents utilised in the art seldom comprise a single compound, but rather a range of compounds having different chain lengths, a distribution curve of which indicates a mean or "average" chain length. Preferably, R₂ may be selected from a straight - chain alkyl, alkenyl or alkynyl group having an average of from 12 to 16 carbon atoms per chain. More preferably R₂ is a straight-chain alkenyl having an average of 16 carbon atoms per chain.

In the compound of formula II, the groups R₃ are the same or different and may be selected from the group consisting of hydrogen and a C₁ to C₆ alkyl. Preferably R₃ is the same or different and may be selected from hydrogen or methyl.

In the compound of formula II, x and y are integers, being the same or different and the sum of x + y is an integer in the range of from 0 to 30. Preferably, (x + y) is 0, that is, the compound of formula II is an amine. When (x + y) is greater than 0, then the compound of formula II is an amine alkoxylate. Amine alkoxylates may be prepared by the condensation of amines with alkylene oxide. Suitable amines for preparation of amine alkoxylates can be derived from natural sources such as tallow and coconuts. Such compounds are well known in the art.

Preferably the alkylene oxide is a C₂ to C₄ alkylene oxide, since alkylene oxides having more than four carbon atoms are less soluble in water and therefore may not be suitable for use in the

invention. More preferably, the alkylene oxide is selected from ethylene oxide and propylene oxide, either singly or in combination. It is particularly preferred, however, that a combination of ethylene oxide and propylene oxide be used.

The composition according to the present invention may additionally include halide ions.

Addition of halide ions produces a composition having an inhibitor efficiency of about, and

sometimes in excess of, 99%. Without intending to be bound by theory, it is believed that the mechanism by which the halide ions function is that they improve the corrosion inhibitor efficiency by physically interacting with other components of the corrosion inhibiting composition and the metal in the add pickling solution.

The halide ions are provided by a compound having a general formula R₄ ⁺X- wherein R₄ ⁺ is a cation and X- is a halide ion. It is usual to use a single type of halide ion; however, a mixture of halide ions may also be used. Preferably X- is selected from I-, Br- or Cl-; more preferably X- is I-. The nature of R₄ ⁺ is not narrowly critical, however, R₄ ⁺ is usually an inorganic cation.

Suitable Inorganic cations include the alkali and alkaline earth metal ions and heavy metal ions

Including the transition metal ions. R₄ ⁺ may also be an organic cation or acyl group, provided that on addition of the compound R₄ ⁺X- to the reaction

mixture, the compound readily dissociates to provide X ions, and R₄ does not excessively alter the

nature of the corrosion inhibiting composition. For the purposes of the invention a particularly

suitable compound of formula R.⁺X - is potassium iodide, KI.

The present invention further provides a

process for the production of a corrosion inhibiting composition as hereinbefore described, which process comprises

(a) dissolving benzotriazole of formula I in

a compound of formula II; (b) alkoxylating the benzotriazole by addition

of at least one alkylene oxide to the

solution of benzotriazole and compound of formula II; and optionally

(c) adding of halide ion in the form of a

compound of formula R₄ ⁺X- to the alkoxylated benzotriazole reaction mixture.

In the process for production of the

composition of the present invention, the ratio of moles of benzotriazole to moles of compound of

formula II is selected to be in the range 2:1 to

1:2, preferably 1:1. The ratio of moles of alkylene oxide to the sum of moles of benzotriazole and

compound of formula II is selected to be in the

range 12:1 to 1:1, preferably in the range 10:1 to 9:1. The amount of R₄ ⁺X- is selected such that the ratio of the mass of R₄ ⁺X- to the sum of the mass of the amine/amine alkoxylate, the benzotriazole and the alkylene oxide is in the range 1:30 to 1:10, preferably 1:10 to 1:20, and most preferably about 1:17. To prevent corrosion of metals in an acid pickling bath, the composition of the present invention is added to the bath. Therefore, as a further embodiment of the present invention there is provided an acid pickling bath comprising a

composition according to the present invention. The invention still further provides a process for the prevention of corrosion of metal in acid pickling baths, said process comprising the addition to the bath of a composition according to the present invention.

The composition of the present invention may be used in any pickling add known in the art. The pickling acids commonly used with ferrous metals are hydrochloric, nitric, sulphuric, and acetic acids. Mixtures of adds may be used and frequently these show a higher rate of scale dissolution than

individual constituent adds by themselves. The concentration ranges of the acids used are well known in the art, and would be easily determined by the skilled artisan. For example, the concentration of hydrochloric acid in an acid pickling bath lies commonly between 1 and 30% by weight.

The amount of the composition according to the present invention which is added to the acid pickling bath in order to inhibit corrosion is not narrowly critical to the invention, and may be of from 0.01 to 10% w/w; preferably, however, between 0.05 and 2% w/w of the pickling acid used. In order to make up the acid pickling bath, the corrosion- inhibiting composition can be stirred into the pickling acid or the composition may be added to the concentrated acid prior to dilution to normal working concentration. Pickling may be carried out at temperatures of from 10°C to 100°C in the case of a sulphuric acid bath, a preferred temperature range being from 90°C to 100°C. The compositions of the present invention are also effective in inhibiting the corrosion of

ferrous metals "in situ". An example is in the acidification of oil and water wells where

hydrochloric acid is used to open or enlarge the limestone fissures and where protection of the ferrous metal well casing is essential.

There now follow examples of the present invention. It is to be understood that the breadth and scope of the present invention is not intended to be limited to the examples. Example 1

"Cobratec TT 100" (registered trade mark), a tolyltriazole, (1.33 kg; 10 mol) was dissolved in a C₁₆ unsaturated amine "Farmin 0" (registered trade mark) (2.99 kg; 10.20 mol) at 65°C. This mixture of a benzotriazole and a compound of formula II is hereinafter referred to as the "initial charge". The mixture was evacuated, nitrogen purged three times and then dehydrated to less than 0.1% water. Ethylene oxide (0.88 kg; 20 mol) was added followed by a 1:1 w/w mixture of ethylene oxide and propylene oxide (3.26 kg; 37.0 mol ethylene oxide; 28.1 mol propylene oxide). The reaction process was then catalysed by addition of 50% KOH (26 g; 0.6% w/w of initial charge). The mixture was evacuated, nitrogen purged three times and then dehydrated to less than 0.1% water. A 1:1 w/w mixture of ethylene oxide and propylene oxide (4.58 kg; 51.9 mol ethylene oxide; 39.5 mol propylene oxide) was added followed by a 55% solution of KI (0.739 kg KI in 0.605 kg water). The batch was neutralised with acetic acid. Yield: 12 kg.

The properties of the composition were determined:

Total Basicity Value = 52 mg KOH/gm

Total Amine Value = 45 mg KOH/gm

1% w/w aqueous pH = 8.8

Specific Gravity = 1.04 g/ml

Soluble in : Ethanol, acetone, water, monoethylene glycol/water mixtures

Dispersable in : Toluene, monoethylene

glycol

Insoluble in : Hexane

Viscosity @ 52 Deg C = 55 cs

Viscosity @ 25 Deg C = 182 cs

The corrosion inhibition efficiency of the composition was determined by addition of the composition to an acid pickling bath consisting of

Concentrated H₂SO₄ 214 g

Ferrous sulphate pentahydrate 273.8 g

Water 761 g

The composition was added to the bath at a known concentration. Strips of hot rolled mild steel from which the oxide layer had been removed were suspended from glass hooks and immersed in the pickling bath for up to 30 minutes. These metal strips were of known mass and surface area. The temperature of the bath was maintained at 98°C. After a preselected time period, the metal strips were washed, cleaned, dried and the mass was determined. A pickling bath to which no corrosion

inhibitor had been added was used as a control.

The corrosion efficiency was determined as fol lows: corrosion rate corrosion rate

in control bath - in inhibited bath X 100

corrosion rate in control bath where corrosion rate is expressed as mg of metal lost/cm²/day.

The results are presented in the following table:

Example 2

"Cobratec TT100" (887 g; 6.670 mol) was dissolved in "Farmin 0" (2.02 kg; 6.895 mol) at 65°C, The mixture was nitrogen purged. To catalyse the reaction 50% KOH was added (35 g; 0.61 w/w of initial charge). The reaction mixture

was evacuated, purged three times

and then dehydrated to maximum 0.1% water.

Ethylene oxide (590 g; 13.41 mol) was added,

followed by a 1:1 w/w mixture of ethylene oxide and propylene oxide (5310 g; 60.3 mol ethylene oxide; 45.8 mol propylene oxide). Additional ethylene oxide/propylene oxide mixture was added (530 g; 6.0 mol ethylene oxide; 4.58 mol propylene oxide). The moles of ethylene oxide/propylene oxide were calculated as in Example 1. KI was then added (506g in 414g water) and the batch was neutralised with acetic acid. Yield: 8 Kg.

The properties of the composition were as follows:

Total Basicity Value = 48.5 mg KOH/g

Total Amine Value = 44 mg KOH/g

1% w/w aqueous pH 9.4

Specific Gravity 1.07

Soluble in : Ethanol, acetone, water Dispersable in : Toluene, monoethylene

glycol, monoethylene/ glycol/water mixtures

Insoluble in : Hexane

Viscosity @ 50 Deg C = 53 cs

Viscosity @ 25 Deg C = 253 cs The corrosion inhibition efficiency was determined according to the method described in Example 1. The results were as follows:

Example 3

The same procedure was followed as in Example 2, using the following quantities: "Farmin 0" 3.58 kg (12.22 mol)

"Cobratec TT100" 1.59 kg (11.95 mol)

50% KOH 31.59 (0.56 mol; 0.6% w/w of initial charge)

Ethylene oxide 1.04 kg (23.64 mol)

1:1 w/w mixture of 8.50 kg (96.6 mol ethylene ethylene oxide and oxide; 73.2 mol propylene propylene oxide oxide)

+ a further 1.91 kg (21.7 mol ethylene oxide; 16.5 mol propylene oxide)

50% KI 0.9294 kg KI in 0.7604 kg water

Yield 15.84 kg

The properties of the composition were as follows

Total Basicity Value = 48 mg KOH/gm

Total Amine Value = 43 mg KOH/gm

1% w/w aqueous pH 9.6

Specific Gravity 1.04

Soluble in : Ethanol, acetone, water Dispersable in : Toluene, monoethylene

glycol, monoethylene glycol /water

mixtures

Insoluble in : Hexane

Viscosity @ 50 Deg C = 52 cs

Viscosity @ 25 Deg C = 235 cs

The corrosion inhibition efficiency was determined using the method described in Example 1:

Examp l e 4

A corrosion bath was made up using a mixture of the compositions resulting from Example 1, 2 and 3. The compositions were used in equal volumes. The corrosion inhibitor efficiency was determined:

Claims

The claims defining the invention are as follows: 1. A corrosion-inhibiting composition which comprises a reaction product of a benzotriazole of formula I

a compound of formula II

and at least one alkylene oxide wherein R₁ is the same or different and is selected from the group consisting of hydrogen, halogen, C₁ to C₆ alkyl, C₁ to C₆ haloaolkyl, C₂ to C₆ alkenyl, C₂ to C₆

haloalkenyl, C₂ to C₆ alkynyl, C₁ to C₆ alkoxy, C₁ to C₆ alkylthio, aryl, aryloxy, aryl

substituted ^{C1 to C6 alkyl wherein the alkyl group} is substitute^{d with a substituted or unsubstituted} phenyl, C₁ to C₆ alkoxycarbonyl, amino, C₁ to C₆ alkylamino, di(C₁ to C₆) alkylamino or -NHO wherein O is selected from substituted or unsubstituted phenyl, nitro, cyano and thiocyanato; a^{nd n has a} value of from 1 to 3; R2 is selected from straight or branched-chain alkyl, alkenyl or alkynyl having an average of from8 to 24 carbon atoms per chain optionally substiiutrd with substituted or

unsubstituted phenyl; R₃ is the same or different and is selected from the group consisting of hydrogen and C₁ to C₆ alkyl; x and y are integers being the same or different, the sum of x + y being from 0 to 30.

2. A composition according to claim 1 wherein R₁ is selected from the group consisting of hydrogen, halogen, C₁ to C₄ alkyl, C₁ to C₄ alkoxy, C₁ to C₄ alkylthio, aryl, aryloxy, arylthio, substituted C₁ to C₄ alkyl wherein the alkyl group is substituted with a member selected from the group consisting of phenyl, amino, C₁ to C₄ alkylamino, di(C₁ to

C₄)alkylamino, -NHO wherein O is selected from phenyl, nitro, cyano and thiocyanate; and n is 1 or 2; R₂ is selected from a straight-chain alkyl, alkenyl or alkynyl having an average of from 12 to 16 carbon atoms per chain; R₃ and (x + y) being as hereinbefore described.

3. A composition according to claim 1 or claim 2 wherein R ₁ is selected from hydrogen and methyl; and n is 1; R₂ is a straight-chain alkenyl having an average of 16 carbon atoms per chain; R₃ is the same or different and is selected from hydrogen or methyl; (x + y) being as hereinbefore defined.

4. A composition according to claim 3 wherein the sum of (x + y) is 0.

5. A composition according to any one of the preceding claims wherein the alkylene oxide is selected from a member of the group of C₂ to C₄ alkylene oxide.

6. A composition according to any one of the preceding claims wherein the alkylene oxide is selected from ethylene oxide or propylene oxide or a mixture thereof.

7. A composition according to any one of the preceding claims wherein the composition includes halide ions.

8. A composition according to claim 7 wherein the halide ions are provided by the addition to the composition αf a compound having general formula R₄ ⁺X- wherein R₄ ⁺ is a cation and X- is a halide ion.

9. A composition according to claim 8 wherein

R₄ ⁺ is an inorganic cation selected from the alkali metal cations and X- is selected from the group consisting of I-, Br- and Cl-.

10. A composition according to claim 8 wherein

R₄ ⁺ is either an organic cation or acyl group characterised in that the R₄ ⁺ ion does not

substantially alter the nature of the corrosioninhibiting composition.

11. A process for the production of a corrosion inhibiting composition, which process comprises

(A) dissolving a benzotriazole of formula I

in a compound of formula II;

wherein R₁, R₂, R₃, n, x and y are as hereinbefore described;

(B) alkoxylating the benzotriazole by addition of at least one alkylene oxide to the solution of benzotriazole and compound of formula II; and

(C) optionally adding halide ion in the form of formula R₄ ⁺χ- to the alkoxylated

benzotriazole reaction mixture wherein R₄ ⁺ and X- are as hereinbefore described.

12. A process according to claim 11 wherein the ratio of moles of benzotriazole to moles of compound of formula II is in the range from 2:1 to 1:2 and the ratio of moles of alkylene oxide to the sum of moles of benzotriazole and compound of formula II is in the range from 12:1 to 1:1.

13. A process according to claim 11 or claim 12 wherein the ratio of moles of benzotriazole to moles of compound of formula II is 1:1 and the ratio of moles of alkylene oxide to the sum of moles of benzotriazole and compound of formula II is in the range from 10:1 to 9:1.

14. A process according to any one of claims 11 to 13 wherein the ratio of the mass of R₄ ⁺X- to the sum of the other components as hereinbefore

described is in the range of from 1:30 to 1:10.

15. A process according to claim 14 wherein the said ratio is in the range of from 1:10 to 1:20.

16. A process according to claim 15 wherein the said ratio is 1:17.

17. An acid pickling bath including a composition according to any one of the claims 1 to 10

inclusive.

18. An acid pickling bath according to claim 17 wherein the amount of the composition according to any one of claims 1 to 10 is from 0.01 to 10% w/w of the pickling acid employed therein.

19. An acid pickling bath according to claim 17 or claim 18 wherein the amount of the composition is between 0.05 and 2% w/w of the pickling acid employed therein.

20. A process for the prevention of corrosion of metal in an acid pickling bath comprising the addition to a bath of a composition according to any one of claims 1 to 10 inclusive.

21 A process according to claim 20 wherein the add pickling is carried out at a temperature in the range of from 10°C to 100°C.

22. A process according to either claim 20 or claim 21 wherein acid pickling is carried out at a temperature of from 90°C to 100°C.

23. A process for inhibiting the corrosion of ferrous metals in situ which comprises treating the metals with a solution containing a composition according to any one of claims 1 to 10 inclusive.

24. A composition according to claim 1

substantially as hereinbefore described with reference to any one of the examples.

25. A process according to claim 11 substantially as hereinbefore described with reference to any one of the examples.

26 A process according to claim 20 substantially as hereinbefore described with reference to any one of the examples.