JPS5922790B2 - Corrosion inhibitor for metals - Google Patents

Description

[Detailed description of the invention] The present invention relates to corrosion inhibitors for metals.

More specifically, it relates to a corrosion inhibitor for metals that come into contact with aqueous systems. Conventionally, chromates and various phosphates are well known as corrosion inhibitors used in open and closed cooling water systems. However, since chromate is highly toxic, wastewater regulations are implemented, making it practically difficult to use. Furthermore, although phosphates have low toxicity, they cause eutrophication when discharged into rivers or inland seas, making active use undesirable from an environmental standpoint. Therefore, research is being conducted in various fields on corrosion inhibitors that do not contain harmful heavy metals such as chromium and phosphates. Examples of currently known corrosion inhibitor components include oxycarboxylic acids such as tartaric acid, citric acid, and gluconic acid. When these oxycarboxylic acids are used alone, they are susceptible to the concentration and temperature of dissolved salts, especially corrosive ions such as chloride ions and sulfate ions, and the higher the concentration of corrosive ions, the higher the temperature. Indeed, the corrosion inhibition effect is reduced, and it is biodegradable, making it difficult to apply to a wide range of water systems. As a result of intensive research aimed at making use of the anticorrosion properties of oxycarboxylic acids and improving the corrosion inhibition effect, the present inventors have discovered that the present invention is non-polluting, does not contain harmful heavy metals such as chromium, and phosphates. We have completed a corrosion inhibitor.

That is, the present invention relates to the general formula (where n is an integer of 1 to 6, R1 and R2 represent a hydrogen atom or a methyl group).

) is a metal corrosion inhibitor characterized by containing a copolymer containing a structural unit having an alcoholic hydroxyl group and a structural unit having a carboxyl group as an active ingredient.

General formula (1) showing a structural unit having an alcoholic hydroxyl group
), n is an integer from 1 to 6.

If n is less than 1, the corrosion inhibiting effect will be insufficient, and if n is greater than 6, no significant effect will be exhibited. Examples of specific monomers constituting the structural unit having an alcoholic hydroxyl group include allyl alcohol, methallyl alcohol, 2-buten-1-ol, 3-buten-1-ol, 3-benzen-1-ol, Examples include 6-hepten-1-ol and 6-octen-1-ol, among which allyl alcohol is preferred.

The monomers constituting these structural units having alcoholic hydroxyl groups are not limited to one type, and two or more types of monomers can be used as necessary. Examples of the monomer constituting the structural unit having a carboxyl group include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, cinnamic acid, vinylbenzoic acid, and salts thereof. However, maleic acid and its salts are particularly preferred.

It is preferable that the above-mentioned carboxyl group is in the form of a salt of a monovalent cation from the viewpoint of water solubility.

Examples of salts include alkali metal salts (such as Li.Na.K salts), ammonium salts, and amine salts (salts of methylamine, dimethylamine, ethylamine, mono-, ditriethanolamine, methylethanolamine, etc.). can. In this case, 1 that forms a salt with the carboxyl group
The valent cation may be composed of two or more types. In the copolymer of the present invention, the ratio of the structural unit having a carboxyl group to the structural unit having an alcoholic hydroxyl group may be any ratio, but preferably the structural unit having a carboxyl group/the structural unit having an alcoholic hydroxyl group The molar ratio of structural units is 0.5 or more, more preferably 0.5 to 2
．． 2, particularly preferably 1-2. If the number of structural units having carboxyl groups is too large compared to the number of structural units having alcoholic hydroxyl groups, a sufficient corrosion inhibiting effect cannot be obtained. The corrosion inhibitor of the present invention does not necessarily need to be composed only of the above-mentioned structural units, and can also contain other structural units (hereinafter referred to as arbitrary units).

Examples of monomers constituting such arbitrary units include (meth)acrylate, ethyl(meth)acrylate, dimethylamino(meth)acrylate, diethylaminoethyl(meth)acrylate, etc.
Examples include acrylic acid esters, 9-styrene compounds such as styrene and α-methylstyrene, fatty acid esters of vinyl alcohol such as vinyl acetate and vinyl propionate, (meth)acrylamides, and (meth)acrylonitrile. The content of the arbitrary units can be varied, but from the viewpoint of anticorrosion effect, the content of the arbitrary units is 3.
It is preferably 0 mol% or less. Production method The copolymer related to the present invention is usually synthesized as follows.

That is, a monomer having a carboxyl group, a monomer having an alcoholic hydroxyl group, and any monomer are combined with a polymerization initiator (for example, a peroxide such as benzoyl peroxide, an azo compound such as azobisisobutyronitrile). , persulfates such as sodium persulfate) in water or an organic solvent.
It can be obtained by copolymerization at 150°C, preferably 70 to 130°C.

The obtained copolymer is purified by separating water or an organic solvent and separating residual monomers, if necessary. The structural unit having a carboxyl group is a monomer having a carboxylic anhydride group (e.g. itaconic anhydride, maleic anhydride) or a monomer having a lower alcohol ester group (e.g. methyl acrylate), or a monomer having a lower alcohol ester group (e.g. methyl acrylate). By copolymerizing with the above method and then hydrolyzing, a structural unit having an alcoholic hydroxyl group can be obtained by copolymerizing a monomer having a lower carboxylic acid ester group (for example, allyl acetate) with another monomer by the above method. They can also be introduced as copolymers by copolymerizing and then hydrolyzing them.

Furthermore, when obtaining a carboxylic acid salt type copolymer as a corrosion inhibitor according to the present invention, it is usually preferable to convert it to a neutralized salt after the copolymerization reaction, but the neutralized salt monomer is obtained in advance. Later, it can also be obtained by copolymerizing this product.

The copolymer in the present invention is a colorless or pale yellow liquid or solid water-soluble polymer, and its molecular weight range is usually 500 to 200,000, preferably 1,500 to 1,500.
100,000, particularly preferably 3,000 to 1,000
It is 0.

If the molecular weight of this copolymer is too low, biodegradability will become significant and the corrosion inhibiting effect will be reduced. The corrosion inhibitor of the present invention contains the above-mentioned copolymer as an active ingredient, and is used by being directly added to the target water system in the same manner as conventional corrosion inhibitors.

The usage concentration of the corrosion inhibitor of the present invention is determined depending on the purpose, but generally the active ingredient is 5 to 500%
It is sufficiently effective at ppm.

The pH range of the target aqueous system does not need to be particularly adjusted, but is generally PH6 to PHL3, preferably PH6 to 10. Target water systems to which this corrosion inhibitor is applied include open and closed cooling water systems. The corrosion inhibitor of the present invention is
Even when used alone, it is sufficiently effective against aqueous systems made of steel, but if necessary, such as when other metals are also used, other corrosion inhibitors such as oxycarboxylic acids and thiazoles such as mercaptobenzothiazole may be used. , azoles such as benzotriazole, cyclohexylamine,
Water-soluble amines such as hydrazine alkylamines and polyamines; imines such as ethyleneimine, pyrrolidine, piperidine, piperazine, and ketimine; organic compounds such as hydroxamic acids such as formhydroxamic acid, acetohydroxamic acid, and benzohydroxamic acid; nitrites; Silicates, ortho-, condensed-, various organic phosphates, borates,
It can also be used in combination with inorganic salts such as zinc salts, nickel salts, and molybdenum salts. In addition, if necessary, conventional scale dispersants such as acrylic acid homo and copolymers (sodium polyacrylate, partial hydrolyzate of polyacrylamide, etc.), maleic acid homo and copolymers, itaconic acid homopolymers, etc. It can be used in combination with copolymers, acrylic acid copolymers containing 2-hydroxyethyl methacrylic acid, and the like.

It is preferable to use it in combination with a scale dispersant because corrosion prevention and scale adhesion prevention effects are synergistically exhibited. The corrosion inhibitor of the present invention is not easily affected by the concentration and temperature of dissolved salts, especially corrosive ions such as chloride ions and sulfate ions, and even if the concentration of the above corrosive ions increases or the temperature increases. Corrosion inhibition effect does not decrease.
Moreover, it is a corrosion inhibitor with lower biodegradability than ordinary oxycarboxylic acids.
The present invention will be further explained below with reference to Examples.
The present invention is not limited to this. Example 1 The performance of the corrosion inhibitor of the present invention was tested using a rotating disk corrosion test method.

The test water used was synthesized by adding various ingredients to Yokohama city water, and its water quality is as follows.

After adding 100 ppm of each of the following corrosion inhibitors to this test water and adjusting the pH to 7.0 and the water temperature to 50°C, a rotating disk at a rotation speed of 16011) m was immersed for 20 minutes.
This state was maintained for some time.

The corrosion inhibitors used are shown below.

A: Acrylic acid - allyl alcohol (mole ratio 2:1, molecular weight approximately 15,000) B: Maleic acid - allyl alcohol (mole ratio 2:1, molecular weight approximately 15,000)
5000) C maleic acid-allylic alcohol (molar ratio 1:1 molecular weight approximately 5000) D maleic acid-allylic alcohol (molar ratio 1:2 molecular weight approximately 5000) The following terpolymer-based corrosion inhibitor was also used for reference.

E Maleic acid monoallyl alcohol-styrene (mole ratio 2:1:0.5 molecular weight approximately 5000) F Maleic acid-
Alalcohol-styrene (molar ratio 2:1:0.3
Molecular weight: approx. 5000) G Maleic acid monoalcohol-styrene (molar ratio 2:1:0.1 molecular weight: approx. 5000)
The disc is made of mild steel (diameter 50 mm, thick wall, material SPC)
C) was used.

The results are shown in Table-1. For comparison, sodium polyacrylate (molecular weight approximately 4500), polyvinyl alcohol (
The case where a molecular weight of about 15,000) is used is also shown. From this result, it can be seen that the corrosion inhibitor of the present invention has a far more corrosion inhibiting effect than the chemicals shown for comparison. Furthermore, as shown for reference, it can be seen that even when ternary material is added such as styrene, the corrosion inhibiting effect is exactly the same. Example 2 The following was carried out to demonstrate that the corrosion inhibitor of the present invention has lower biodegradability than existing oxycarboxylic acids and the like.

First, 100 ppm of B as a corrosion inhibitor was added to the same test water used in Example 1, and activated sludge was added to MLSS.
A corrosion test was conducted for 7 days at a water temperature of 30°C.

The test piece was a mild steel round bar (diameter 10n, length 3
011), and the change in corrosion rate over time was measured using a commercially available corrosion meter.

Citric acid was chosen as a conventional oxycarboxylic acid corrosion inhibitor.

The results are shown in Table-2.

The results show that the corrosion inhibitor of the present invention has a stable corrosion inhibiting effect over the entire test period, whereas the effect of citric acid is seen to decrease significantly from the second day onwards.

Claims (1)

[Claims] 1 Alcohol represented by the general formula ▲ Numerical formulas, chemical formulas, tables, etc. ▼ (1) (where n is an integer from 1 to 6, and R_1 and R_2 represent a hydrogen atom or a methyl group) A corrosion inhibitor for metals, characterized in that the active ingredient is a copolymer containing a structural unit having a hydroxyl group and a structural unit having a carboxyl group. 2. The corrosion inhibitor according to claim 1, wherein the structural unit having a carboxyl group is a structural unit derived from maleic acid. 3. The corrosion inhibitor according to claim 1 or 2, wherein the copolymer has a molecular weight of 1,500 to 100,000. 4 The molar ratio of the structural unit having a carboxyl group to the structural unit having an alcoholic hydroxyl group is 0.5 to 2.2
The corrosion inhibitor according to any one of claims 1 to 3.