JPH0426783A - Corrosion inhibitor for high temperature water system - Google Patents

Abstract

PURPOSE:To provide the title inhibitor ensuring safety, hardly increasing electrical conductivity and having superior corrosion inhibiting ability by blending tannic acid and/or tannate with a reducing phenol compd. in a prescribed ratio. CONSTITUTION:Tannic acid and/or water soluble tannate such as sodium tannate is blended with a reducing phenol compd. such as gallic acid preferably in about (8:2)-(4:6) weight ratio to prepare the title inhibitor. This inhibitor ensures high safety because of no hydrazine content, has superior corrosion inhibiting ability and can reduce the amt. of a blow because it does not increase the electrical conductivity of water.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a corrosion inhibitor for high-temperature water systems such as boilers and hydrothermal systems.

<Prior art> Conventionally, as a method of suppressing corrosion in high-temperature water systems such as inside boiler cans or in heating or cooling circulation systems, oxygen scavengers and alkaline agents have been added in combination. Sodium is mainly used. Tannic acid or its salts are also used in some cases.

<Problems to be Solved by the Invention> In recent years, there has been increasing interest in the safety of water treatment chemicals and the energy-saving effect of using them, and high-temperature water-based corrosion inhibitors are no exception. However, hydrazine is toxic and has safety issues, so it cannot be used in hospitals, food factories, etc. where the generated steam and high-temperature water may come into direct contact with the human body or products. Furthermore, although there is no safety issue with sodium sulfite, the amount used is large and increases the electrical conductivity, which increases the amount of blowing, which increases the amount of water and fuel used, which not only increases energy costs, but also increases the amount of water and fuel used. The reaction product (sulfate ion) becomes a corrosion factor and does not exhibit sufficient corrosion inhibition effect. Furthermore, although tannic acid or its salt has no safety problems, when used alone it does not exhibit a sufficient corrosion inhibiting effect, especially in the initial stage.

The present invention solves the problems of these conventional methods, and aims to provide a high-temperature water-based corrosion inhibitor that has no safety problems, exhibits a low increase in electrical conductivity, and exhibits an excellent corrosion inhibiting effect. shall be.

Means for Solving the Problems> The high-temperature water-based corrosion inhibitor according to the present invention, which has been made to achieve the above object, is characterized by containing tannic acid and/or a tannic acid salt and a reducing phenol compound. be.

The tannic acid used in the present invention is a polyphenol compound extracted from plants such as persimmon, tea, and quince, and is classified as a hydrolyzable tannis-type tannin, but any of them may be used.

The tannic acid salt used in the present invention refers to water-soluble salts such as the above-mentioned sodium and potassium salts of tannic acid.

In addition, the reducing phenolic compounds used in the present invention include acids and salts thereof of reducing phenolic compounds such as gallic acid, pyrogallol, talologenic acid, quinic acid, caffeic acid, coumaric acid, cinnamic acid, and tocopherol derived from natural products. Yes, you can use one or more of these.

The high-temperature water-based corrosion inhibitor of the present invention comprises (1) tannic acid and a reducing phenol compound, (2) a tannic acid salt and a reducing phenol compound 4N, and (3) tannic acid, a tannic acid salt and a reducing phenol compound. 1), (2), (
Either one of 3) is essential, and when both tannic acid and tannate salt of (3) are used, the mixing ratio is arbitrary. Furthermore, in common with the above (1), (2), and (3), the weight ratio of tannic acid and/or tannate salt to the reducing phenol compound is 9=1 to 2:8, preferably 8:2 to 4:6. Use within the range. Each may be added separately in the above proportions, or may be mixed in advance in the above proportions before use. Note that if tannic acid or tannate salts are dissolved in a highly alkaline solution (if tannic acid is used, it becomes tannate salts immediately after dissolution) and left to stand, part of the tannate salts will decompose and form reducing phenols. It has the property of producing certain gallic acid or pyrogallol.

Therefore, the high-temperature water-based corrosion inhibitor of the present invention actively utilizes this property to mix tannic acid or a tannic acid salt with a reducing phenol by dissolving the tannic acid or tannic acid salt in a highly alkaline solution and leaving it to stand. It is also possible to manufacture

The amount of tannic acid and/or tannate salt and reducing phenol compound to be used is 30 to 1000 mg/concentration in water of the total of each substance blended in the above weight ratio.
I is appropriate.

The high-temperature water referred to in the invention refers to water at a temperature of 40° C. or higher and 200° C. or lower, and the present agent can be used for corrosion protection of heating circulation systems or boiler water systems having these water temperatures.

The corrosion inhibitors of the present invention may also include pH adjusting agents such as sodium hydroxide and sodium carbonate; phosphates such as sodium phosphate and sodium hexametaphosphate; dispersants such as sodium polyacrylate and sodium polymaleate; There is no problem in using it in combination or in combination with steam-based corrosion inhibitors such as octadecylamine and cyclohexylamine.

Tannic acid and/or tannate salts not only have oxygen scavenging ability, but also have excellent corrosion inhibiting ability on metals by forming an anticorrosion film on the metal surface and passivating the metal surface, but they do not react with oxygen. The speed is not necessarily high, and when added alone, the deoxidizing effect at the initial stage of addition is insufficient, and therefore the corrosion inhibiting effect at the early stage of addition is not sufficient.

On the other hand, reducing phenol compounds have a very fast reaction rate with oxygen, but their anticorrosive film formation and passivation effects are small.

By using the re-compound in the above ratio and amount, the reduction in initial corrosion inhibiting power seen when using only tannic acid and/or tannate salts can be compensated for by the excellent oxygen scavenging ability of the reducing phenolic compound, and The presence of tannic acid and/or tannate salts and a reducing phenol compound creates an excellent corrosion inhibiting effect due to the synergistic effect of forming a stable and dense anti-corrosion film on the metal surface that cannot be formed with tannic acid and/or tannate salts alone. It is thought that this will be effective.

The present invention will be explained in detail below.

Example 1 A mild steel test tube (inner diameter 50 mm,
length 500mm), mild steel test piece (20x50
x 2 mm) was installed and operated continuously for 150 hours under the following conditions while automatically replenishing soft water and chemicals. T island operating conditions Boiler pressure: 10 kg/crri'-G blow %
・10% Boiler water quality (average): pH; 11.3 Chloride ion; 255mgCl/IM alkalinity;
630mgCaC0a/IP strength; 51
0mgCaCOg/l phosphate ion; 37mgP
After the Oa/1 test was completed, the test tube and test piece were taken out, and the surface of the test tube was observed, and the degree of corrosion of the test piece was measured using the following formula.

The test results are shown in Table 1, and t is also shown in Table 1.Table 1 shows that the corrosion inhibitor of the present invention exhibits excellent effects.

Example 2 Sodium sulfite and the high-temperature water-based corrosion inhibitor of the present invention (weight ratio of tannic acid and gallic acid 7:3) were sequentially added to ion-exchanged water (electrical conductivity 0.6 μS/crrr) to improve its electrical conductivity. The change in rate was measured.

The test results are shown in Table 2.

Table 2 From Table 2, the increase in electrical conductivity due to the addition of the corrosion inhibitor of the present invention is very small compared to sodium sulfite. Therefore, in high-temperature water systems, the amount of blowing required to maintain electrical conductivity below a certain value can be reduced, contributing to energy savings.

<Effects> As explained in Section 2, the high temperature water-based corrosion inhibitor of the present invention does not use hydrazine, so it is highly safe, has excellent corrosion inhibiting ability, and does not increase the electrical conductivity of water. Therefore, it leads to a reduction in the amount of blowing and contributes to energy conservation, which brings great benefits to industry.

hand Continued Supplementary Positive book (spontaneous) July 5, 1991 Commissioner of the Patent Office Toshi Ue Matsu 1.Display of the incident 1990 Patent Application No. 129324 2. Name of the invention High temperature water based corrosion inhibitor 3. Person who makes corrections Relationship to the incident: Patent applicant 〔contact address〕 〒113 5-5-16 Hongo, Bunkyo-ku, Tokyo Organo Co., Ltd. Legal and Patent Department Phone number 03-5689-5115 4. Subject of correction Detailed description of the invention in the specification Please correct the following items in the statement.

1, page 5, line 4 "Invention" There is a certain thing "Book I say it by invention.” I am corrected.

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Claims (1)

[Claims] A high-temperature water-based corrosion inhibitor characterized by containing tannic acid and/or a tannic acid salt and a reducing phenol compound