CA1176049A

CA1176049A - Corrosion inhibitor

Info

Publication number: CA1176049A
Application number: CA000415827A
Authority: CA
Inventors: Tadahiko Asano; Kazuo Marugame; Yoshinari Kawasaki; Sadaoki Kanada; Sakae Katayama
Original assignee: Katayama Chemical Inc
Current assignee: Katayama Chemical Inc
Priority date: 1982-11-18
Filing date: 1982-11-18
Publication date: 1984-10-16
Also published as: BE903357Q

Abstract

ABSTRACT OF THE DISCLOSURE

A corrosion inhibitor for ferrous metals com-prizing four different components of (a) an inorganic acid component (such as molybdate or tungstate), (b) an alipha-tic hydroxycarboxylic or aliphatic dicarboxylic acid or its salt (such as citric acid, gluconic acid or succinic acid), (c) an inorganic heavy metal compound (such as zinc chloride or stannous chloride) and (d) a water soluble polymer component having a mlecular weight of 500 - 100,000 (such as acylic homo or copolymer), which is especially advantageous for use in water recycling system.

Description

S P E C I F I C A T I O N

TITLE OF THE INVENTION
CORROSION INHIBITOR

BACK&ROUND OF THE INVENTION
1. Field of the invention The present invention relates to a composition and a method for using the same for the prevention of ferrous metals in machines and equipment for using water in the petroleum industry, chemical industry, paper making industry, iron industry, and other industries.

2~ Description of the Prior Art In view of the worsening supply condi-tion of industrial water, efforts are being made to save water by recycling. For instance, efforts are being made to reduce water to be discharged from the water cooling system and to run the boiler without blowing water. Recycling of water, however, involves problems. The recycled water increases in concentration of salts, which leads to the formation of scale and to cause corrosion of metals in contact with it. Thus, the measure for these problems,or the treatment of recycled water, is a matter of great im-portance.
In order to solve the problems, we have proposed ~L~ 7~

a corrosion inhibitor composed of gluconic acid or a salt thereof, a molybdate, and a specific acrylic acid polymer, for high concentrated recycli.ng water (Japanese Patent Publication No. 43376/1978); a corrosion inhibiting compo-sition of an aliphatic dicarboxylic acid, molybdate and nitrite (Japanese Unexamined Patent Publication No.62181/
1978) and a corrosion inhibitor of an aliphatic dicarboxy-lic acid and nitrite (Japanese Unexamined Patent Publica-tion No. 62182/1978). A further corrosion inhibiting com-position of polymaleic acid, an aliphatic hydroxycarboxylic acid, zinc ion and a triazole was proposed in JapaneseUnexamined Patent Publication No. 149836/1978.

SUMMARY OF THE INVENTION
The present invention provides a corrosion inhibi-tor for ferrous metals such as iron, mild steel, and cast iron in water systems, which can exhibit an excellent effect when added to water, especially high concentrated recycling water in an apparatus such as heat exchanger, - cooler, radiator, boiler and so forth.

More particularly, this invention provides a corrosion inhibitor which contains as the active ingredients:
(a) one or more inorganic acid components of molybdic acid or its alkali salt, tungstic acid or its alkali sal-t, or alkali salt of nitrous acid;
(b) an aliphatic hydroxycarboxylic acid or aliphatic di-carbo~ylic acid having up to seven carbon atoms or salt thereof;
(c) an inorganic heavy metal com~ound which may readily release a heavy metal ion in water; and (d) a water-saluble polymer component having a molecular weight in the range of 500 to 100,000, of a homo- or co-polymer of acryl~c acid, methacrylic acid or maleic acid;
a copolymer of any of said three monomers with other co-polymerizable compound having an ethylenic double bond;
or a mixture of said homopolymer and copolymer.

`:
-` - The inhibitor of this invention is non-phosphorous ~ composition and is highly effective for preventing ferrous -- - metal corrosion in high concentrated water recycling system~

or a ~oiler operating at a high temperature of 100 - 200C, -`~ ; coinciden-tly preventing scale formation in such a system.

PREFERRED E~IBODIMENTS OF THE INVENTION
The alkali salts of molybdic acid, tungstic acid, -` and nitrous acid which are used in this invention include, for example, alkali metal salts such as lithium sal-t, so-dium salt, and potassium salt, and arnmonium salt Econo-: mically preferable among therr; are sodium molybdate, ammo-nium molybdate, sodium tungstate, sodium nitrite, and ammonium nitrite. They may be used in combination.
The aliphatic hydroxycarboxylic acid having the carbon number of 7 or less that is used in this inven-tion includes, for example, glycolic acid, citric acid, malic acid, tartaric acid, lactic acid, gluconic acid, and tartronic acid. The aliphatic dicarboxylic acid having the carbon number of 7 or less includes, for example, glutaric acid, adipic acid succinic acid.
The salts of the above-mentioned carboxylic acids include, for example, alkali metal salts such as lithium, sodium or potassium salt and ammonium salt; and salts with aliphatic amines having 6 or less carbon atoms such as mono, di or tri-alkylamine (e.g., methylamine, ethylamine, propyl-amine, butylamine, pentylamine, hexylamine, or dimethylamine, diethylamine or dipropylamine, or trimethylamine or tri-ethylamine), cyclic alkylamine (e.g., cyclohexylamine or morpholine), or mono, di or tri-hydroxyalkylamine (e.g~, ethanolamine, propanolamine, 3-hydroxy-2-methyl-propylamine, diethanolamine or dipropanolamine).
If the hydroxycarboxylic acids or dicarboxylic acids having a carbon number greater than 7 are used, the resulting corrosion inhibitor decreases in corrosion in-hibiting effect and in solubility in wa-ter. In addition, if they are used in the form of salt, the resulting cor-rosion inhibitor causes foaming due to increased surface activity and combines with the compounds that make water hard to form insoluble salts which pass into sludge and scale.
If a salt of the hydroxycarboxylic acid or di-carboxylic acid with an aliphatic amine having 7 or more ~7~

is used, the resulting corrosion inhibitor will increase in surface activity.
Preferable among the above-mentioned components (b) are gluconic acid, succinic acid, citric acid, malic acid, glutaric acid, and adipic acid, and sodium salts, cyclohexvlamine salts, and morpholine salts thereof.
Citric acid, malic acia, and gluconic acid, and sodium salt, ammoniul~ salt, cyclohexylamine salt, and morpholine salt thereof are preferable in the case where an aliphatic hydroxycarboxylic acid is used. Glutaric acid, succinic acid, and adipic acid, and sodium salt, ammonium salt, cyclohexylamine salt, and morpholine salt thereof are preferable in the case where an aliphatic dicarboxylic acid is used.
In the meantime, if an aliphatic monocarboxylic acid or salt thereof (e.g., acetic acid, propionic acid, and salt thereof), which is a homologue of the aliphatic hydroxylcarboxylic acid and dicarboxylic acid, is used, the outstanding corrosion inhibiting effect of this inven-tion cannot be obtained. This suggests that the action on metals differs even among homologous compounds, depending on the functional group contained -therein.
The compound that readily may release a heavy metal ion in water includes, for example, sulfates, chlo-rides, nitrates, and sulfamates of zinc,manganese, tin, cobalt, nickel, titanium, copper, and lead, and mi.YtureS

~7~

thereof. Preferable among them are salts of manganese, tin, zinc and nickel~ The first two are particularly preferable when the cor.-osion inhibitor is added to boiler water.
The polymer or copolymer of acrylic acid, metha-crylic acid, or maleic acid which is used in this invention is a water-soluble polymer which has a molecular weight of 500 to 100,000, preferably 500 to 20,000. Examples of such polymer or copolymer include homopolymers of acrylic acid, methacrylic acid, or maleic acid or mixtures thereof;
and copolymers or terpolymers thereof; copolymers of one of said three monomers and a copolymerizable compound hav-ing a ethylenic double bond such as methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, acryl-amide, methacrylamide, acrylamide-N-propanesulfonic acid, fumaric acid, itaconic acid, and vinyl alcohol, whose co-polymers are composed of at least 20 mol% of any of said three monomers, preferably 50 mol% or more. Preferable among them are acrylic acid homopolymer, methacrylic acid homopolymer, maleic acid homopolymer, acylic acid-methacylic acid copolymer, acrylic acid-maleic acid copolymer, meth-acrylic acid-maleic acid copolymer, acrylic acid-acrylamide copolymer, acrylic acid~acrylamide-N-propanesulfonic acid copolymer, and acrylic acid-methacrylic acid-methyl acrylate terpolymer.
The above-mentioned homopolymers or copolymers ~7~

should be soluble in water and have a molecular weight of about 500 to 100,000. Those which have a molecular weight greater than about 100,000 is not preferable, because it tends to show a flocculation even though it is soluble in water. From the standpoint of ease of synthe-sis, an acrylic acid polymer or methacrylic acid polymer having a molecular weight of about 1,000 to 20,000 is preferred and a maleic acid homopolymer having a molecular weight of about 500 to 2,000 is preferred. If the polymer is not readily soluble in water even though it has a mole-cular weight in the specified range, it may be made solu-ble by converting the free acid or ester thereof in the polymer molecule into a soluble salt (alkali metal salt, ammonium salt, or amine salt).
The above-mentioned four components are formu-lated into a liquid formulation or mixed directly into a powdery formulation. The aqueous solution should be neutral to alkaline. If it is acidic, molybdic acid or tungstic acid liberates and condenses, or the nitrous acid deco~oses, ort'nealiphatic hydroxycarboxylic acid oxidizes slowly. Thus, it is desirable to add an alkali such as sodium hydroxide and lower amine to adjust the pH.
The preferred weight ratio that permits the four components to exhibit their synergistic effect is 1 : 0.2 - 30 : 0.1 - 5 : 0.1 - 5, preferably 1 : 0.5 -10 : 0.1 - 1.5 : 0.2 - 1.6, for (a) : (b) : (c) : (d) by weight. In the case of liquid formulation, the total concentration of the four components is dependent on the solubility and pH of each component. A concentration of 5 to 60 wt% is suitable from the standpoint of stability -of the formulation. In addition, the liquid formulation may contain a small quantity of stabilizer and other ad-ditives.
The formulation composed of the above-mentioned four components should be added to water in an amount of 1 to 200 ppm, preferably 15 to 100 ppm, in terms of the total quantity of the four components, depending on the water quality and the area that requires corrosion inh;.bition.
Thus, the present invention also provides the method for the co-rrosion inhibition of metals by adding the above-mentioned four compounds (a), (b), (c), and (d).
Each the active ingredients may be added to water indi-vidually in the form of single formulation.
The corrosion inhibitor of this invention is effective 6~

for pr-~venting heat e~ch~ngers, coolers, radiators, boilers,-and the like ~rom water corrosion. It is particularly effec-tive when added to recvcled water which contains salts at high concentrations. It protects ferrous metals from corrosion and pitting corrosion and prevents the forma-tion of scale.
It is nct elucidated yet how the four components of this invention act on t~e metal surface, but it is believed that they form a strong protective coating due to the combined effect of their passivating action, dispersing action, and film forming action, in view of the fact that the effect o the four components is much better than that of any three components of them.
The invention is now described in detail with ref-erence to the following non-limitative examples.

Corrosion inhibition tests were conducted as fol-lows using corrosion inhibitors composed of the above-mentioned four ccimponents in varied quantiti.es.

A mild steel test piece (tradç name: SPCC) ~.easuring 30 x 50 x 1 mm, suspended by a stainless steel sti~ring rod, was immersed in one liter of test liquid containing chemicals at pLedetermined concentrations, contained in a flat bottcim beaker enclosed in a circular ~antle heater in which water temperature is kept constant by a ther~o-~'7~ 3 stat. The stirring rod was turned by a motor at a rate of 100 rpm. The tests were carried out for five days with agitation while keeping the water temperature at 50C. The test water was prepared by concentrating city water (Osaka City) five times. The quality of the tes~ water is shown in Table 1.

Table 1 Item Value _ pH 8.3 Electric conductivity (~s/cm) 910.2 P alkalinity (ppm) 0 M alkalinity (ppm) 71.0 Total hardness (ppm)238.8 Chloride ion (ppm) 94.5 Sulfate ion (ppm) 172.0 Silica (SiO2) (ppm) 28.5 Total iron (ppm) 0.50 Calcium hardness (ppm)190.0 A-fter the prescribed period of test, the test piece was removed and dried. The weight Ml (mg) was measured. The test piece was then treated according to JIS K-0101. After drying, the weight M2 (mg) was ~ ~ 76~

measured. The m.d.d. (mg/day.dm2) was calcurated according to the following formula.

m.d.d. = (A - M2)~(B x C) = D/0.3142 x 5 where:
A : ~eight (mg) of test piece before testing, B : Area (dm2) of test piece, C : Number of days of test, and D : Corrosion weight loss.

After completion of test, 500 ml of the test liquid was filtered using Toyo Filter Paper No. 6 and the weight of the solids was measured after drying at 110C for one day. The weight of the substance formed on the test piece was calculated by subtracting M2 from Ml. The quantity of scale formed from 1 liter of test liquid is defined by the following formula.
Scale (mg/liter) = P x 2 + (Ml - M2) where P : dry weight of precipitates.
The results obtained in Examples and Comparative Examples are shown in Table 2.

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~ ~ 7 ~ * 3 It is to be noted from Table 2 that the corrosion inhibitors composed of the four components according to this invention are superior to the conventional corrosion inhibitors composed of three components of sodium m~lybdate, sodium gluconate, and polyacrylate.
It is also to be noted that the corrosion inhab-itors of this invention decreases the quantity of scale to a great extent.

Several formulations composed of the four com-ponents of this invention were prepared as shown in Table 3. Using these formulations, the same tests as in TEST 1 were carried out. The results are shown in Table 3.

:~ 7~

Table 3 Concentration Quantity I of corrosion of scale No. Formulation (wtg6) ~ inhibitor (ppm) (mg/l) m.d.d.
1 Sodium molybdate 10% ~
Sodium gluconate 15g6 ¦
Zinc chloride 2% 1 Sodium hydroxide 1% ¦ 100 5.7 3.3 Acrylic acid-metha-crylic acid copolymer (1:1) (MW: 4000) 3%
Water 69% 1 . __ 2 Sodium tungstate 3%
Sodium gluconate 20%
Stannous chloride 3%
Sodium hydroxide 0.5% ~ 100 5.8 4.0 Acrylie acid-metha-crylic acid-methyl acrylate terpolymer (2:2:1) (MW: 4500) 3%
Water 70.5%
_ ! _ _ 3 Sodium molybdate lOgo Sodium gluconate 10%
Sodium citrate 5g6 Sodium hydroxide 1%
Zinc chloride 1% 100 5.7 3.5 Polyacrylic acid 4gO ¦
(MW: 8000) Water 69% ;

Table 3 (cont'd)

4 Sodium molybdate 5% ¦
Dimorpholine salt of adipic acid 5%
Morpholine salt of gluconic acid 15~ 100 6.3 3.5 Stannous chloride 3~
Acrylic acid- 3%
maleic acid co-polymer Water 69%

~.~ 7~!~D49 The following tests were conducted for medium- and low-pressure boilers. The SPCC test piece as used in TEST 1 was attached to an apparatus which rotates the test piece at 100 rpm in an autoclave containing 800 ml of test water. The test piece was subjected to corrosion at 200C under a prssure of 16 kg/cm2 for 2 days. For accelerated corrosion, the test water was prepared by concentrating city water (Osaka City) 20 times and adjusting to pH 9. A prescribed quantity of the corrosion inhibitor was added to the test water and the test piece suspended by the stirring rod was immersed in the test water.
The corrosion weight loss of the test pieces was measured, and the number of pittings was counted. The quality of the test water is shown in Table 4 and the results are shown in Table 5.

Table 4 I _ Value pH 9.0 Electric conduc~i.vity (~s/cm) 3750 P alkalinity (ppm) 35 M alkalinity (ppm) 470 Total hardness (ppm) 0 Chloride ion (ppm) 530 Sulfate ion (ppm) 520 Silica (ppm) 144.0 Total iron (ppm) 0.1 3 L~ 9 tn rn Q~
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It is ~:o be noted from the above results that the corrosion inhibitor of this invention is also effective to prevent pitting. Especially the corrosion inhibitor containing tin or manganse ions of this invention is effective for corrosion prevention of boilers.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLU-SIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A corrosion inhibitor comprising: (a) one or more inorganic acid components selected from molybdic acid or its alkali salt, tungstic acid or its alkali salt, and an alkali salt of nitrous acid; (b) an aliphatic hydroxycarboxylic acid or aliphatic dicarbocylic acid having up to seven carbon atoms or salt therof; (c) an inorganic heavy metal compound which readily releases a heavy metal ion in water; and (d) a water-soluble polymer component having a molecular weight in the range of 500 to 100,000 of a homo or copolymer of acrylic acid, methacylic acid of maleic acid; or a copolymer of any of said three monomers with another copolymerizable compound having an ethylenic double bond; or a mixture of said homopolymer and copolymer.

2. A corrosion inhibitor as claimed in claim 1, wherein the alkali salt of molybdic acid, tungstic acid or nitrous acid is the alkali metal salt.

3. A corrosion inhibitor as claimed in claim 2, in which the alkali metal salt is the lithium, sodium or potassium salt or ammomiun salt.

4. A corrosion inhibitor as claimed in claim 1, wherein the salt of the aliphatic hydroxycarboxylic acid or aliphatic dicarboxylic acid is the alkali metal salt.

5. A corrosion inhibitor as claimed in claim 1, wherein the salt of the aliphatic hydroxycarboxylic acid or aliphatic dicarboxylic acid is the lithium, sodium or potas-sium salt, or ammonium salt; or the salt with an aliphatic amine having up to 6 carbon atoms.

6. A corrosion inhibitor as claimed in claim 4 or 5, wherein the aliphatic amine is a mono, di or tri-alkylamine or a cycloalkylamine, or a mono, di or tri-hydroxyalkyl amine.

7. A corrosion inhibitor as claimed in claim 4 or 5, wherein the aliphatic amine is methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, dimethy-lamine, diethylamine, dipropylamine, trimethylamine or triethy-lamine.

8. A corrosion inhibitor as claimed in claim 4 or 5, wherein the aliphatic amine is cyclohexylamine or morpholine.

9. A corrosion inhibitor as claimed in claim 4 or 5, wherein the aliphatic amine is ethanolamine, propanolamine, 3-hydroxy-2-methyl-propylamine, diethanolamine or dipropanol-amine.

10. A corrosion inhibitor as claimed in claim 1, 2 or 3, wherein the aliphatic hydroxycarboxylic acid or its salt is citric acid, malic acid or gluconic acid, or its sod-ium, ammonium, cyclohexylamine or morpholine salt.

11. A corrosion inhibitor as claimed in claim 1, 2 or 3, wherein the aliphatic dicarboxylic acid or its salt is glutaric acid, succinic acid, or adipic acid, or its sodium, ammonium, cyclohexylamine, or morpholine salt.

12. A corrosion inhibitor as claimed in claim 1, 2 or 3, wherein the inorganic heavy metal compound is a sulfate, chloride, nitrate, or sulfamate of zinc, manganese, tin, cobalt, nickel, titanium, copper, or lead, or mixtures thereof.

13. A corrosion inhibitor as claimed in claim 1, 2 or 3, wherein the homopolymer and the copolymer as a water-soluble polymer component have a moleculer weight in the range of 500 to 20,000.

14. A corrosion inhibitor as claimed in claim 1, 2 or 3, wherein the weight ratio of (a) ; (b) ; (c) ; (d) is 1 : 0.2 - 30 : 0.1 - 5 : 0.1 - 5.

15. A corrosion inhibitor as claimed in claim 1, 2 or 3, wherein the weight ratio of (a) : (b) : (c) : (d) is 1: 0.5 - 10 : 0.1 - 1.5 : 0.2 - 1.6.

16. A method for inhibiting the corrosion of ferrous metals in a water system which comprises by adding in water system (a) one or more inorganic acid components sel-ected from molybdic acid or its alkali salt, tungstic acid or its alkali salt, and an alkali salt of nitrous acid; (b) an aliphatic hydroxycarboxylic acid or aliphatic dicarboxylic acid having up to seven carbon atoms or salt thereof; (c) an inorganic heavy metal compound which readily releases a heavy metal ion in water; and (d) a water-soluble polymer component having a molecular weight in the range of 500 to 100,000 of a homo- or copolymer of acrylic acid, methacrylic acid or maleic acid; or a copolymer of any of said three monomers with another copolymerizable compound having an ethylenic double bond; or a mixture of said homopolymer and copolymer, at a total con-centration of said four components of 1 to 200 ppm.