CA1162726A

CA1162726A - Prevention of corrosion in aqueous systems

Info

Publication number: CA1162726A
Application number: CA000387564A
Authority: CA
Inventors: Stuart W. Longworth
Original assignee: Dearborn Chemicals Ltd
Current assignee: Suez WTS USA Inc
Priority date: 1981-03-11
Filing date: 1981-10-08
Publication date: 1984-02-28
Also published as: FR2501709A1; ES510242A0; SE8201509L; ES8302795A1; GB2094776B; DE3208119A1; JPS57161072A; GB2094776A; IT8220056A0; IT1150645B

Abstract

Ref. 5932 PREVENTION OF CORROSION IN AQUEOUS SYSTEMS
Abstract of the Disclosure The invention involves the use of 5-amino-3-carboxylic acid triazoles in inhibiting corrosion in aqueous systems.

Description

ilL6Z~

PREVENTION OF CORROSION IN AQuEous SYSTEMS

This invention relates to the prevention of corrosion in aqueous systems.
The use of certain arylene triazoles to - prevent corrosion in a~ueous systems, in particular systems in contact with ferrous metal, has been known for some time. Likewise, certain phosphonates, low molecular weight polymers and zinc salts show some corrosion inhibiting properties but are not of sufficient effectiveness to be used alone. The present invention resides in the discovery that a particular type of triazole is effective for protecting ferrous metals from corrosion. This triazole is 5-amino-1,2,4~triazole-3-carboxylic acid which has the formula:

H

H2~ ~ ~ COOH
~/

Accordingly the present invention provides a method of p~venting corrosion in an aqueous system ; which comprises adding to the aqueous system 5-amino-1,2,4-triazole-3-carboxylic acid. In general the - 20 concentration of the triazole is 0.5 to 20, especially 1 to 10, mg/litre.

- 2 -~ .

Not only does this particular triazole provide superior corrosion inhibition to, say, benzotriazole but it has also been found that by combining this triazole with (a) a zinc salt, or (b) with a phosphonate, or (c) with a low molecular weight polymer and a phosphonate, or (d) with a zinc salt and a phosphonate, synergistic effects can be obtained. In other words, results can be obtained which are better than one would expect from the summation of the results of the individual ingredients.
Accordingly, the present invention also provides a composition suitable for addition to aqueous media which comprises 5-amino-1,2,4-triazole-3-carboxylic acid with (a) a zinc salt, or (b) with a phosphonate, or (c) with a low molecular weight polymer and a phosphonate, or (d) ]5 with a zinc salt and a phosphonate. Of course, it is possible to incorporate the ingredients individually in the system.
Typical phosphonates which can be used in the present invention include those of the general formula:

H203p _ I P3H2 II

X

where Rl is hydrogen or lower ~i.e. of 1 to 6, especiall~
1 t~ 4 carbon atoms ) alkyl and X i5 hydr~gen, lower ; alkyl or hydroxyl, or of general formula:

,- R2 ~CHP03}I2 R3 / \ III

where each R2 independently i~ hydrogen or lower alkyl, and R3 is: R2 _c~-po3~2, or -(CH)X ~ \ CHP03H2 _., R2 where x is an integer from 1 to 6, or (R2~(C2~ ~CHP03~2 -~ Hh- N ~Jy - ~ \
CHP03~2 C~R2 R

where y is an integer from 1 to 3;
lo or of general formula:

H O P - C - COOH IV

. ~ ( `H2COOH
~ I I
where R4 is hydrogen, alkyl or -CH-CH-COOH where R5 is hydrogen, alkyl or carboxyl and ~ is hydrogen or alkyl.
The preferred phosphonates are hydroxy ethylidene diphosphonic acid (HEDPA), i.e. of formula (II) where Rl is methyl and X is hydroxyl; and nitrilo tris methylene phosphonic acid, i.e. of formula (III) where R2 is hydrogen and R3 is R2 The concentration of phosphonate in the system is .
- suitably 1 to 50, especially 2 to 10, mg/litre.
- The polymers which can be used in the present invention are vinyl addition products with molecular weight from, say, 500 to 100,000, possessing recurring units of general formula:

, l I
--C~ _ V

where R7 is hydrogen or lower alkyl, and Y is -COOH, and ('' I~.OE7~; ''") Z is hydrogen or -COOH, or Y and Z together represent -CO-O-CO-. The preferred polymers are polymethacrylic acid, i.e. where R is methyl, Y is -C~H and Z is hydrogen, in particular of molecular weight about 5000, and polyacrylic acid i.e. where R and Z are . ~
-~ both hydrogen and Y is -COOH, in particular of molecular~ weight about 1000. The polymer concentration is suitably 1 to 50, preferably 2 to 10, mg/litre.
5-Amino-1l2,4-triazole-3-carboxylic acid can be prepared ~ dehydration of oxalylaminoguanidine (HOOC-CONH.NH-CNH2) (see, e.g. Ann 1~98, 303, 52) ~H
or by heating ethyl diazoacetate and potassium hydroxide (see, e.g. Ber 1907, 40, 815, 1194). This latter method also gives some 4-amino-1,2,4-triazole-

3,5-dicarboxylic acid.
_ Typical zinc salts which may be used are the -- chloride, sulphate, nitrate and acetate. ~ypically the zinc salts can be present in an amount from 0~5 to 20, especially 1 to 10, mg of Zn/litre.
-- Although the formulae of the phosphonates and - polymers have been given in the form of the free ._ .
acids, it is to be understood that they can also be _ used in the form of organic or,inorganic salts, in ~ 25 particular, an alkali metal salt, which is preferred, such as sodium or potassium~ ammonium or a lower amine salt or other metal salt. The triazole not only forms ~, 2~

salts as above but can also form amine salts with inorganic acids, it can be used in these fon~s.
It will be appreciated that other low-toxic materials conventionally used in water treatment can be ~.
- 5 included, such as silicate, inorganic phosphate or - polyphosphate, and lignin derivatives.

_.

;~
-. - . I

, 7:~

The following Examples further illustrate the present inven'ion.

Effect on Mild Steel . . .
Mild steel test specimens were immersed in aerated water and stood at 18C for five days. The specimens were cleaned and weighed before and after the test, and the average corrosion rate - in mils per year calculated from the weight loss recorded. The water used in these tests was Widnes mains water, total hardness 140 mg/l, M. alkalinity 100 mg/l, Langelier Index minus 0.5.
,.
_. . .
~ Example No Dosage Rate,I,mg/l Corrosion rate mils/year L r ~ ¦ 18 2 3 50 14.8 4__ 100 12.9 .

-E X A ~ P L E S 5 T ~ 12 Effect in Admixture with Zinc and Phosphonate - Mild steel test specimens were suspended in a stirred reservoir of water maintained at a temperature of 60C, the stirring being of such a rate as to - ensure air entrainment 30 as to keep the water oxygen-saturated. Water lost by evaporation was replaced from an elevated tank through a syphon constant level control to maintain a constant volume in the reservoir. The water used in these tests was Widnes mains water which concentrated three times during the test due to evaporation.
In each test treatment was applied at three - times normal dose for 24 hours in order to passivate ~ 15 the steel; then the water was diluted to the normal dose level for the remainder of the testO Each test was carried out for a minimum of three days.
-, ~p Additives mg/l Corrosion rate Example ~o _ ~ mils/year Zinc ~alt Phosphonate Triazole ~
~as Zn) _ _ _ _ _ 105.4 ~_ . 6 10 _ _80.4 7 _ 10 _62.0 ` _ - 8 _ _ 105902 -~ 9 5 4.25 _ 32.7 _ 222.0 11 _ 10 235.7 12 5 4.25 2 3.0 ,,~ _ g _ In these examples the zinc salt is zinc chloride and the phosphonate is nitrilo tris methylene phosphonic acid. Examples 9 and 12 also contain 5 mg/l of a lignin sulphonate.

Effect in Admixture with Phosphonate_and Polymer A laboratory test apparatus was used in which water was circulated by means of a pump from a reservoir maintained at a temperature of 40C, through a glass tube assembly holding the metal test specimens, and returned to the reservoir entraining air so as to keep the water saturated with oxygen as it would be in an open recirculating cooling system. Water lost by evaporation was replaced from an elevated tank through a float control to maintain a constant volume in the system, the water used being Widnes mains water, which, in this test, concentrated two times due to evaporation.
In each test treatment was applied at three times normal dose for 24 hours in order to passivate the steel, then the water was diluted to the normal dose level for the remainder of the test. Each test was carried out for a minimum of three days.
-- Additive mg/l _ Example No Corrosion rate mlls/year Phosphonate Polymer Triazole I
I t 6 7 _ 5 18 3 18 _ 3 5 14.6 19 _ _ 10 12.9 i 20 7 3 5 2~3 _ In these Examples the phosphonate was a 1:1 mixture of hydroxy ethylidene diphosphonic acid and nitrilo tris methylene phosphonic acid, and the polymer was polymethacrylic acid of 5000 molecular weight, all present as their potassium salts. Examples 16 and 20 also contained 3 mg/l of potassium orthophosphate.

Comparison with Benzotriazole These Examples were carried out under the conditions described for Examples 5 to 12, (Example 21) and for Examples 13 to 20, (Example 22).

---h h h-~

O
~ I ~ 1 11~

" . .
;' ~ ~1 _ E-l '..................... ~_ ._ ;~ N u~ In I I

.~4 1~ ~l ~ O I ~('t)/~7 ~, ~ ~C

'~ ' _ ~ ~ ~ O ~
. _ _ In Examples 12 and 21 the phosphonate is nitrilo tris methylene phosphonic acid, the zinc salt is zinc chloride and the compositions also include 5 mg/l of a lignin sulphonate. In Examples 20 and 22 the phosphonate is a 1:1 mixture of hydroxy ethylidene diphosphonic acid and nitrilo tris methylene phosphonic acid, the polymer is polymethacrylic acid of molecular wei~ht 5000, all present as their potassium salts: and the compositions also include 3 mg/l of potassium orthophosphate.
These Examples .show that while the triazole I itself has corrosion inhibiting properties these are vastly increas~d wh~n it is incorporated into the formulations described above, thus demonstrating synergism; it is clearly superior to benzotriazole in performance.

.; .

Claims

I CLAIM:
l. A method of preventing corrosion of ferrous metals in an aqueous system which comprises adding to the system 5-amino-1,2,4-triazole-3-carboxylic acid or a salt thereof.
2. A method according to Claim l which comprises adding the triazole to the system to provide a concentration of 0.5 to 20 mg/liter.
3. A method according to Claim 2 in which the concentration of the said triazole is l to 10 mg/liter.
4. A method according to Claim l which comprises also adding to the system (a) a zinc salt or (b) a phosphonate.
5. A method according to Claim 1 which comprises also adding a zinc salt and a phosphonate.
6. A method according to Claim 1 which comprises also adding to the system a phosphonate and a polymer.
7. P method according to Claim 4, Claim 5, or Claim 6, in which the phosphonate is hydroxyethylidene diphosphonic acid or nitrilo tris methylene phosphonic acid.
8. A method according to Claim 6 in which the polymer is polyacrylic or polymethacrylic acid.
9. A method according to Claim 5 in which the zinc salt is zinc chloride, sulphate, nitrate or acetate.
10. A composition which comprises 5-amino-1,2,4-triazole-3-carboxylic acid or a salt thereof and (a) a zinc salt, or (b) a phosphonate, or (c) a zinc salt and a phosphonate.
11. A composition according to Claim 10 which comprises a zinc salt and a phosphonate.
12. A composition according to Claim 10 which comprises a phosphonate and also comprises a polymer.
13. A composition according to any one of Claim 10.
Claim 11, or Claim 12 in which the phosphonate is hydroxy-ethylidene diphosphonic acid or nitrilo tris methylene phosphonic acid.
14. A composition according to Claim 12 in which the polymer is polyacrylic or polymethacrylic acid.
15. A composition according to Claim 10 or 11 in which the zinc salt is zinc chloride, sulphate, nitrate or acetate.
16. A composition according, to Claim 10 which also comprises polyacrylic or polymethacrylic acid.