JP2845572B2 - High-temperature water-based corrosion inhibitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a high-temperature water-based corrosion inhibitor such as a boiler or a hot water-based one.

<Prior Art> Conventionally, an oxygen scavenger and an alkali agent have been added as a method for inhibiting high-temperature water-based corrosion in a boiler can or in a heating or cooling circulation system, and hydrazine or sulfurous acid is used as the oxygen scavenger. Sodium is mainly used. Tannic acid or a salt thereof is also partially used.

<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 a problem in terms of safety. Therefore, it cannot be used in hospitals and food factories where the generated steam or high-temperature water may come into direct contact with the human body or products. In addition, sodium sulfite has no problem with safety, but it is used in a large amount to increase the electric conductivity, so that the amount of blow increases, and as a result, the amount of water and fuel used increases. The reaction product (sulfate ion) becomes a corrosion factor and does not exert a sufficient corrosion inhibitory effect. Further, tannic acid or a salt thereof has no problem in safety, but does not exhibit a sufficient corrosion inhibitory effect, especially in the initial stage.

An object of the present invention is to solve the problems of these conventional methods, and to provide a high-temperature water-based corrosion inhibitor which has no problem in safety and exhibits an excellent corrosion inhibitory effect with a low increase in electric conductivity. And

<Means for Solving the Problems> The high-temperature water-based corrosion inhibitor according to the present invention made to achieve the above object contains tannic acid and / or a tannate salt and a reducing phenol compound. It is.

The tannic acid used in the present invention is a polyphenol compound extracted from plants such as persimmons, teas, and quintessence, and is classified into hydrolyzable tannins and condensed tannins, and any of them may be used.

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

Examples of the reducing phenol compound used in the present invention include acids and salts of reducing phenol compounds such as gallic acid, pyrogallol, chlorogenic acid, quinic acid, caffeic acid, coumaric acid, cinnamic acid and tocopherol derived from natural products. Yes, one or more of these can be used.

The high-temperature water-based corrosion inhibitor of the present invention comprises (1) tannic acid and a reducing phenol compound, (2) tannate and a reducing phenol compound, and (3) tannic acid, a tannate and a reducing phenol compound. 1), (2), (3)
When both the tannic acid and the tannic acid salt of (3) are used, the mixing ratio is optional. In addition, tannic acid and / or tannate and the reducing phenol compound are commonly used in the above (1), (2) and (3) in a weight ratio of 9: 1 to 2: 8, preferably 8: 2 to
Use in the range of 4: 6. Each of them may be added separately at the above ratio, or may be used by being previously blended at the above ratio. In addition, tannic acid or tannate is dissolved in a highly alkaline solution (if tannic acid is used, it becomes tannate immediately after dissolution), and when this is left, part of the tannate decomposes to form a reducing phenol. It has the property of producing certain gallic acid or pyrogallol. Accordingly, the high-temperature water-based corrosion inhibitor of the present invention, in which tannic acid and a reducing phenol are mixed by dissolving tannic acid or a tannate in a highly alkaline solution and allowing the tannate or tannate to stand, by positively utilizing this property. Can also be manufactured.

The amount of the tannic acid and / or tannate and the reducing phenol compound to be used is suitably 30 to 1000 mg / l as the total concentration of the respective substances mixed in the above weight ratio in water.

The high-temperature water referred to in the present invention refers to water having a temperature of 40 ° C. or more and 200 ° C. or less, and the agent can be used for anticorrosion of a heating circulation system or a boiler water system having these water temperatures. Further, the corrosion inhibitor of the present invention includes a pH adjuster such as sodium hydroxide and sodium carbonate, a phosphate such as sodium phosphate and sodium hexametaphosphate, a dispersant such as sodium polyacrylate and sodium polymaleate, and It can be used in combination with or combined with a vapor-based corrosion inhibitor such as octadecylamine or cyclohexylamine.

<Action> Tannic acid and / or tannate exhibits not only a deoxidizing ability but also an excellent corrosion inhibiting ability for a metal due to the formation of an anticorrosive film on the metal surface and a passivating action on the metal surface. The reaction rate is not always high, and the deoxygenation effect at the initial stage of addition is insufficient by itself, and therefore the corrosion inhibitory effect at the initial stage of addition is not sufficient.

On the other hand, the reducing phenol compound has a very high reaction rate with oxygen, but has a small anticorrosive film formation and passivation effect.

By using both compounds in the above proportions and amounts, the decrease in the initial corrosion inhibition power seen when only tannic acid and / or tannate is used is supplemented by the excellent deoxygenating ability of the reducing phenol compound, Further, excellent corrosion due to the synergistic effect of forming a stable and dense anticorrosion film which cannot be formed by tannic acid and / or tannate alone on the metal surface due to the presence of tannic acid and / or tannate and a reducing phenol compound. It is thought that it exerts a suppressing effect.

 Hereinafter, embodiments of the present invention will be described.

Example 1 A mild steel test tube (inner diameter 50 mm, length 500 mm) and a mild steel test piece (20x50x2 mm) were installed in an experimental boiler, and continuous operation was performed for 150 hours under the following conditions while automatically supplying soft water and chemicals. .

Operating conditions _: boiler pressure; 10 kg / cm ² -G blow%; 10% boiler water quality (average): pH; 11.3 chloride ion; 255 mg Cl / l M alkalinity; 630 mg CaCO ₃ / l P alkalinity; 510 mg CaCO ₃ / l phosphorus Acid ion; 37 mgPO ₄ / l After the test, the test tube and the test piece were taken out, the surface of the test tube was observed, and the corrosion degree of the test piece was measured by the following formula.

The test results are shown in Table 1.

Table 1 shows that the corrosion inhibitor of the present invention exerts an excellent effect.

Example-2 Sodium sulfite and a high-temperature aqueous corrosion inhibitor (weight ratio of tannic acid to gallic acid: 7: 3) were sequentially added to ion-exchanged water (electrical conductivity: 0.6 μS / cm ² ), and the electric conductivity was increased. The change in rate was measured.

 Table 2 shows the test results.

From Table 2, the increase in electrical conductivity due to the addition of the corrosion inhibitor of the present invention is very small as compared with sodium sulfite. Therefore, the amount of blowing performed to maintain the electric conductivity at a certain value or less in the high-temperature water system is reduced, which contributes to energy saving.

<Effect> As described above, the high-temperature water-based corrosion inhibitor of the present invention does not use hydrazine, so that it has high safety, and has excellent corrosion inhibiting ability, and does not increase the electric conductivity of water. This leads to a reduction in blow volume, contributing to energy savings, and has a great profit for the industry.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C23F 11/00, 11/12 F28F 19/00 C09K 15/00, 15/08

Claims (1)

(57) [Claims] 1. A high-temperature aqueous corrosion inhibitor comprising tannic acid and / or a tannate and a reducing phenol compound.