KR101582794B1 - Method of preventing corrosion in closed cooling water system - Google Patents

Abstract

(PROBLEMS TO BE SOLVED BY THE INVENTION) A corrosion inhibiting method in an enclosed cooling water system capable of reducing the amount of nitrite (salt) used without requiring a bactericide is provided.
A method for suppressing corrosion of an iron member and a copper member by adding nitrous acid to an enclosed cooling water system, wherein the pH of the cooling water system is 9 to 10.5 and the nitrite (salt) concentration is 25 to 150 Mg / l, and the azole compound concentration is 0.2 to 10 mg / l. Further, a hydrophobically substituted nitrogen-unsaturated heterocyclic compound may be added.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of suppressing corrosion in a closed cooling water system,

The present invention relates to a method for suppressing corrosion of steel members and copper members in a closed cooling water system, and particularly relates to a corrosion inhibiting method using a nitrite and / or a salt thereof (hereinafter referred to as "nitrite (salt)") .

As a method for suppressing the corrosion of the closed cooling water system such as the general factory reaction tank system, the steel cooling water system, the engine cooling water system for power generation or marine, the general factory cooling water system, and the power plant bearing cooling water system, ) Have been widely used (Patent Document 1, Patent Document 2).

Japanese Laid-Open Patent Publication No. 2006-305462 Japanese Patent Application Laid-Open No. 2002-177988

Since the nitrite (salt) exhibits a high corrosive effect, the nitrite (salt) method is widely applied to the closed cooling water system. However, when the facility is not in a completely sealed environment, nitrifying bacteria are mixed, Nitrite (salt) is metabolized by nitrifying bacteria and the concentration of nitrite (salt) in the system is lowered, and corrosion occurs. Therefore, in order to prevent corrosion caused by nitrifying bacteria, a fungicide is used in combination or a nitrite (salt) corrosion inhibitor is additionally added. However, when a germicide is used in combination or a nitrite (salt) type anticorrosive agent is further added, it takes time to manage the water quality in the water system, and it takes time to treat the wastewater containing the germicide. In addition, if the disinfectant is insufficiently controlled, deterioration of the nitrite (salt) concentration by the nitrifying bacteria can not be prevented, and the corrosion sometimes progresses in the closed cooling water system.

An object of the present invention is to provide a corrosion inhibiting method in an enclosed cooling water system which does not require a bactericide and can reduce the amount of nitrite (salt) used.

The method for suppressing corrosion in the closed cooling water system of the present invention is a method of suppressing corrosion in a closed cooling water system in which nitrite and / or a salt thereof (hereinafter referred to as " nitrite (salt) ") is added to a closed cooling water system, A method for suppressing corrosion, wherein the pH of the cooling water system is adjusted to 9 to 10.5, the nitrite (salt) concentration is set to 20 to 150 mg / l, and the azole compound concentration is set to 0.2 to 10 mg / It is characterized by.

In the present invention, it is preferable that the nitric acid (salt) concentration of the cooling water system is 25 to 100 mg / L and the azole compound concentration is 1 to 4 mg / L.

The azole compound is preferably at least one selected from the group consisting of tolyltriazole, benzotriazole, mercaptothiazole and derivatives thereof.

The azole compound is preferably benzotriazole.

In the present invention, a hydrophobic substituted nitrogen-containing unsaturated heterocyclic compound and / or a compound represented by the following formula (1) (hereinafter also referred to as "compound (1)") may be added to the cooling water system.

[Chemical Formula 1]

X, Y, and Z each independently represent a hydrogen atom, an alkyl group, a benzyl group, a hydroxyalkyl group, or a carboxyalkyl group, and a hydroxyalkyl group, a carboxyalkyl group May form a salt.)

Nitrite (salt) forms an oxide film on the surface of iron to suppress the corrosion of the iron member. In the present invention, by adjusting the pH of the cooling water system to 9 to 10.5, the effect of the corrosion on the steel member is improved and the activity of the nitrifying bacteria is suppressed. Therefore, it is possible to prevent the concentration of nitrite (salt) from being lowered by metabolism by nitrifying bacteria without adding a bactericide, thereby effectively suppressing the corrosion by the addition of nitrite (salt) while maintaining the concentration of nitrite (salt) .

In addition, since the above-mentioned pH is improved, the effect of the system by nitrite (salt) is improved, and a high system effect can be obtained even if the nitrite (salt) concentration required for the system is low. Lowering the concentration of nitrite (salt) in the system can also reduce the nutrient source of nitrifying bacteria, thereby suppressing the growth of nitrifying bacteria and preventing deterioration of the nitrite (salt) concentration by nitrifying bacteria more reliably do.

With respect to the copper member, the azole compound forms a complex with copper to form a deposit film on the surface of the copper member to suppress corrosion of the copper member.

Further, by using a combination of the hydrophobic substituted nitrogen-containing unsaturated heterocyclic compound and / or the compound (1), the corrosion inhibiting effect of the copper member can be improved.

1 is an explanatory diagram of a test apparatus used in the embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the corrosion inhibiting method in the closed cooling water system of the present invention will be described in detail.

In the present invention, the closed cooling water system includes, but is not limited to, the general plant reaction tank system, the steel cooling water system, the engine cooling water system for power generation or marine, the general plant cooling water system, and the power plant bearing cooling water system. Among the above-mentioned closed cooling water systems, the present invention is not particularly effective for a completely closed cooling water system, but is particularly effective for a closed cooling water system in which nitrifying bacteria are likely to invade.

In the present invention, nitrous acid (salt) is added to such a closed cooling water system to obtain a predetermined nitrite (salt) concentration and the pH is adjusted to 9 to 10.5. By adjusting the pH to 9 to 10.5, the corrosion effect of the iron member is improved, and the activity of the nitrifying bacteria is suppressed, so that the decrease of the nitrite (salt) concentration in the cooling water is suppressed.

As the nitrite to be added to the cooling water system, sodium nitrite, potassium nitrite and the like can be used. The nitrite (salt) may be used singly or in combination of two or more species.

If the concentration of nitrite (salt) in the cooling water system is too low, a sufficient system effect can not be obtained. On the other hand, if the concentration is too high, the effect of improving the system effect is not confirmed. The nitrite (salt) is added so that the concentration of nitrite (salt) in the cooling water system is 20 to 150 mg / l, preferably 25 to 100 mg / l.

In order to adjust the pH of the cooling water system, an alkali such as sodium hydroxide or an acid such as sulfuric acid is optionally added as a pH adjusting agent, if necessary. Here, when the pH of the cooling water system is less than 9, the activity of the nitrifying bacteria can not be suppressed, and the corrosion inhibiting effect becomes inferior due to the reduction of the nitrite (salt) concentration. In addition, the effect of improving the corrosion effect on the iron member is also low. However, if the pH of the cooling water system is excessively high, corrosion of the copper member tends to proceed, and the cost of the pharmaceutical agent for adjusting the pH is also high, so that the pH of the cooling water system is 10.5 or less, preferably 9.5 to 10 .

As the azole compound to be added to the cooling water system for suppressing the corrosion of the copper member, one or two or more of tolyltriazole, benzotriazole, mercaptobenzothiazole and derivatives thereof are preferable, and benzotriazole .

The azole compound is added so that the concentration in the cooling water system is 0.2 to 10 mg / l, preferably 0.4 to 4 mg / l. When the concentration of the azole compound in the cooling water system is less than the lower limit described above, corrosion of the copper member can not be sufficiently suppressed, and even if the upper limit is exceeded, further corrosion inhibiting effect can not be obtained. The amount of the azole compound to be added can be reduced by the combination of the hydrophobic heterocyclic compound substituted with a nitrogen-containing group and / or the compound (1) described below, and the heterocyclic substituted nitrogen-containing unsaturated heterocyclic compound and / It is preferably 0.1 to 5 mg / l.

In the present invention, in order to more reliably inhibit the corrosion of the copper member, a further hydrophobic substituted nitrogen-unsaturated heterocyclic compound and / or compound (1) may be added to the cooling water system.

Specific examples of the hydrophobic substituted nitrogen-unsaturated heterocyclic compound include the following. In the following, the alkyl group having 6 to 18 carbon atoms as the hydrophobic group is referred to as " C ₆ to C ₁₈ alkyl ".

2-heptylimidazole, 2-octylimidazole, 2-nonylimidazole, 2-decylimidazole, 2-undecylimidazole, 2-dodecylimidazole 2-hexadecylimidazole, 2-heptadecylimidazole, 2-octadecylimidazole, 2-octadecylimidazole, 2-hexadecylimidazole, C ₆ -C ₁₈ alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine, 2 -C ₆ -C ₁₈ alkyl-N-hydroxyethyl-N-carboxylate methylimidazolinium salts, 2-C ₆ -C ₁₈ alkyl-N, N-bishydroxyethylimidazolinium salts, 1-methyl-1-hydroxyethyl-uroalkyl-imidazolium salts

Examples of the imidazolinium salt include a chloride salt (Cl salt) and the like.

Considering the addition to the aqueous system, it is preferable that a hydrophilic group is attached to the nitrogen atom at the 1-position, and especially 2-C ₆ -C ₁₈ alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine is used .

The compound (1) is a compound represented by the following formula (1).

(2)

X, Y, and Z each independently represent a hydrogen atom, an alkyl group, a benzyl group, a hydroxyalkyl group, or a carboxyalkyl group, and a hydroxyalkyl group, a carboxyalkyl group May form a salt.)

The alkyl group or alkenyl group of R in the formula (1) preferably has 6 to 18 carbon atoms, particularly preferably 11 carbon atoms.

In addition, X, Y and Z each independently represent a hydrogen atom, a hydroxyethyl group, a carboxymethyl group (a hydroxyethyl group, and a carboxymethyl group may form a salt such as an alkali metal salt such as a sodium salt or a potassium salt) desirable.

As the compound (1), it is particularly preferable that R in the formula (1) is an alkyl group having a carbon number of 11, X is a hydrogen atom, Y is a hydroxyethyl group, and Z is a carboxymethyl group or a salt.

The hydrophobic substituted nitrogen-containing unsaturated heterocyclic compound may be used singly or in combination of two or more species. The compound (1) may be used singly or in combination of two or more kinds. The compound (1) may be used alone or in combination of two or more of the hydrophobic group-substituted nitrogen-unsaturated heterocyclic compounds and one kind of the compound Or two or more of them may be used in combination.

The addition concentration of the hydrophobically substituted nitrogen-containing unsaturated heterocyclic compound and / or the compound (1) to the cooling water system can be adjusted to a concentration at which an optimum effect can be obtained, depending on the water quality of the object to be treated and the surface area of the copper- , Usually 0.2 to 10 mg / l, and particularly preferably 0.1 to 5 mg / l.

(1) is used in combination with the azo compound to form a film having excellent corrosion resistance and durability on the surface of the copper-based member to suppress corrosion such as pitting corrosion However, the action mechanism of this corrosion inhibition is considered as follows.

Generally, the corrosion reaction proceeds by a pair of an elution reaction (an anode reaction) of a metal and a reduction reaction (a cathode reaction) of an oxidant. For example, in a pH-neutral to weakly alkaline environment such as cooling water, dissolved oxygen in water is responsible for the cathode reaction as an oxidizing agent.

The azole compound is excellent in the effect of suppressing the elution reaction (anodic reaction) of the metal in the corrosion reaction, and exhibits a good overall corrosion inhibiting effect. However, if the corrosion-resistant coating made of an azole compound is locally destroyed for some reason, the azole compound can not completely inhibit the elution of copper from the broken portion of the coating, so that the film breakdown portion becomes a local anode, .

Therefore, in order to suppress such a formulation, it is effective to form a corrosion-inhibiting coating film excellent in the effect of suppressing the reaction of the cathode. However, by using the hydrophobic substituted nitrogen-containing unsaturated heterocyclic compound and / or compound (1) Has a property that the cathode reaction suppressing effect is excellent. Therefore, it is possible to maintain the excellent corrosion resistance and durability, and to more effectively suppress the occurrence of the formula.

In the present invention, agents such as a nitrite, a pH adjuster, an azole compound, a hydrophobic substituted nitrogen-unsaturated heterocyclic compound, and a compound (1) may be added to the closed cooling water system as a single solution or may be separately added.

When the sealed cooling water storage tank is not in a completely sealed environment, it is preferable to prevent mixing of outside air by nitrogen purge, thereby suppressing the pH of the cooling water and mixing of nitrifying bacteria.

Example

Hereinafter, a test example showing the effect of the present invention will be described.

[Test Example 1]

The sample tube 1 was set in the test apparatus shown in Fig. 1, and various kinds of pH and nitrite (salt) concentrations shown in Table 1 were passed through as a test water to determine the corrosion rate. Sodium nitrite was used as the nitrite. The pH was adjusted by NaOH.

As the sample tube 1, a carbon steel tube having an outer diameter of 24 mm and an inner diameter of 16 mm was degreased with toluene and polished.

As shown in the figure, an electric heater 2 was provided inside the sample tube 1, and the surface temperature of the sample tube 1 was set at 80 캜. The sample tube 1 is accommodated in the container 3 and the test water with a water temperature of 30 캜 is supplied from the test water tank 4 to the test water tank 4 at a rate of 12.5 l / hr by the circulation pump 5 and the flow rate adjusting valve 6, Circulated. The test water is supplied to the test water tank 4 from the water supply tank 7 by the pump 8 and overflows from the overflow pipe 9 so that the test water tank 4 is always supplied with 100 liters of test water Respectively.

The weight of the sample tube 1 before and after the water flow test was measured, and the corrosion rate was calculated according to the following equation. The results are shown in Table 1.

Corrosion rate (mdd) =

{Weight before test (mg) - Weight after test (mg)} / {Surface area of sample tube (d㎡) x number of test days (days)}

From Table 1, the following are confirmed.

(a) When the pH is raised, the corrosion rate is lowered.

(b) When the nitrite concentration held in the system is increased, the corrosion rate is lowered.

(c) When the pH is raised, the corrosion rate does not increase even if the nitrite concentration held in the system is lowered.

(d) By increasing the pH from 6.5 to 10, even if the nitrite concentration is reduced from 50 mg / l to 25 mg / l, no increase in the corrosion rate is observed.

(e) At a pH of 6.5, the corrosion rate is not less than 1.0 mdd unless the nitrite concentration is 50 mg / l or more. However, when the pH is 9 or more, the corrosion rate is 1.0 mdd or less even at the nitrite concentration of 25 mg / do.

[Test Example 2]

Corrosion test of the copper member was carried out according to the following procedures (1) to (6).

(1) A copper test piece (C1220P) having dimensions of 50 mm × 30 mm × 1 mm and a surface area of 0.31 dm 2 is degreased with toluene, and the weight is measured, and the weight is taken as the weight before the test.

(2) 1000 ml of pure water was placed in a 1 liter beaker, and benzotriazole, 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine (the number of carbon atoms of the alkyl group was 6-18 or less, A ") or the following compound B is added, and NaOH is added as needed to the pH shown in Table 2. [ The amounts of benzotriazole, compound A and compound B added were as shown in Table 2.

Compound B: A mixture containing a substance having a structure in which X, Y, and Z are selected from a hydrogen atom, a hydroxyethyl group, a carboxymethyl group, or a salt thereof in the formula (1) Compound-based mixture

(3)

(A mixture consisting essentially of a compound wherein R is an alkyl group or an alkenyl group having 6 to 18 carbon atoms and R is an alkyl group having a carbon number of 11)

(3) Dip copper test piece into each beaker and semi-seal with a lap while blowing nitrogen gas.

(4) Stir at 250 rpm for 3 days in a thermostat equipped with a stirrer at 50 ° C.

(5) Adjust the pH of the water quality to the target value once per day.

(6) Calculate the corrosion rate from the weight of the copper test piece before and after the test according to the following formula.

Corrosion rate (mdd) =

{Weight before test (mg) - Weight after test (mg)} / {Surface area of copper test piece (d㎡) x number of test days (days)}

The test results are shown in Table 2.

From Table 2, the following are confirmed.

(a) Increasing the pH increases the corrosion rate, and at pH 11 the corrosion rate is significantly higher.

(b) When the benzotriazole concentration is increased, the corrosion rate is lowered.

(c) When the compound A or the compound B is used in combination with the benzotriazole, the corrosion rate can be kept low even if the concentration of the benzotriazole is lowered.

[Test Example 3]

The consumption rate of sodium nitrite by nitrifying bacteria was measured according to the following procedure.

(1) Prepare a nitrifying bacteria solution using the active clay of the drainage system.

(2) Sodium nitrite is added to the nitrifying bacteria solution so as to have a sodium nitrite concentration of 50 mg / l, and NaOH is added as needed to prepare a test liquid having a pH shown in Table 3 and maintained at 25 캜 for one week .

(3) The nitrite concentration after 1 week is measured, and the consumption rate (%) of sodium nitrite is calculated according to the following equation.

(%) = 100- {Na nitrate concentration after the test (mg / l) / Na nitrate concentration before the test (mg / l) x 100}

The results are shown in Table 3.

As shown in Table 3, when the pH is 9 or more, no decrease in sodium nitrite concentration is observed, and nitrite consumption by nitrifying bacteria is suppressed.

1: sample tube
2: Electric heater
4: Test water tank
7: Supply water tank

Claims (5)

A method for suppressing corrosion of a steel member and a copper member in a cooling water system by adding at least one of nitrite and its salt (hereinafter referred to as "nitrite (salt)") to a closed cooling water system,
The pH of the cooling water system is adjusted to 9 to 10.5,
The nitrite (salt) concentration is 20 to 150 mg / l,
As a method for preventing the concentration of nitrite (salt) in the system from being lowered by metabolism by nitrifying bacteria in the cooling water system by setting the azole compound concentration to 0.2 to 10 mg /
Wherein the azole compound is at least one member selected from the group consisting of tolyltriazole, benzotriazole, and mercaptothiazole,
Wherein at least one of a hydrophobic group substituted nitrogen-containing unsaturated heterocyclic compound selected from the following compound group (2) and a compound represented by the following formula (1) is added at a concentration of 0.2 to 10 mg / L in addition to the cooling water system A corrosion inhibiting method in a closed cooling water system;
[Chemical Formula 1]

X, Y, and Z each independently represent a hydrogen atom, an alkyl group, a benzyl group, a hydroxyalkyl group, or a carboxyalkyl group, and a hydroxyalkyl group, a carboxyalkyl group May form a salt)
Compound group (2): Compound (2): 2-hexylimidazole, 2-heptylimidazole, 2-octylimidazole, 2-nonylimidazole, 2-decylimidazole, -Dodecylimidazole, 2-tridecylimidazole, 2-tetradecylimidazole, 2-pentadecylimidazole, 2-hexadecylimidazole, 2-heptadecylimidazole, 2- 2-C ₆ -C ₁₈ alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine, 2-C ₆ -C ₁₈ alkyl-N-hydroxyethyl-N-carboxylate methylimidazolium salt Jolly, 2-C ₆ ~ C ₁₈ alkyl -N, N- bis-hydroxy ethyl imidazole Jolly salt, 1-methyl-1-hydroxyethyl-tallow alkyl-imidazolium salt (where, "C ₆ To C ₁₈ alkyl "refers to an" alkyl group having 6 to 18 carbon atoms "). The method according to claim 1,
Wherein the cooling water system has a nitrite (salt) concentration of 25 to 100 mg / l and an azole compound concentration of 0.4 to 4 mg / l. delete delete delete

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