JPH0250999B2 - - Google Patents

Description

[Detailed description of the invention]

B. Field of Industrial Application The present invention relates to a corrosion inhibitor for iron-based metals under acidic conditions. For more details, see the general formula below [In the formula, X represents hydrogen, halogen, a lower alkyl group, a lower alkoxy group, or an amino group, and n is 1-2. R is hydrogen or chlorine, and m is 1-2. ] This relates to a corrosion inhibitor for iron-based metals under acidic conditions using a compound represented by the following. B. Prior Art Conventionally, acid treatment methods for ferrous metals include pickling during the production of iron and stainless steel, chemical cleaning of chemical plants, large boilers for thermal power generation, various heat exchangers, etc. The purpose is also to remove scale attached to metal. The acids used vary depending on the usage situation; inorganic acids include hydrochloric acid, sulfuric acid, phosphoric acid, hydrofluoric acid, sulfamic acid, etc., and organic acids include acetic acid, citric acid, lactic acid, oxalic acid, Succinic acid, tartaric acid, formic acid,
Examples include hydroxyacetic acid, monochloroacetic acid, dichloroacetic acid, malic acid, thiomalic acid, propionic acid, thioglycolic acid, chloropropionic acid, ethylenediaminetetraacetic acid, and the like. When descaling with these acids, only the scale is dissolved or the scale is peeled off.
Corrosion inhibitors (hereinafter referred to as inhibitors) are usually added to minimize dissolution of the base metal. To give an example of the descaling mechanism of steel, the heat-treated iron surface contains α-Fe ₂ O ₃ (hematite) and Fe ₃ O _{4 .}
Since iron oxides such as (magnetite) or FeO (vistite) are formed, scale is usually dissolved and removed using 10-15% hydrochloric acid at 40-50°C. The reaction mechanism is expressed by the following formula. FeO＋2HCl→FeCl ₂ ＋H ₂ O Fe ₃ O ₄ ＋8HCl→ FeCl ₂ ＋2FeCl ₃ ＋4H ₂ O Fe ₂ O ₃ ＋6HCl→2FeCl ₃ ＋3H ₂ O At this time, in order to prevent the base metal from dissolving, the inhibitor was added at 0.1% to the acid solution. Approximately 3.0% is added. The inhibition mechanism of the inhibitor is that NOPS atoms of organic compounds are adsorbed only to the base metal.
Since it is hardly adsorbed to scale, it is thought to suppress the dissolution of the base metal without affecting the descaling speed. C. Problems to be Solved by the Invention Currently used inhibitors include alkyl amines such as tallow amine, stearyl amine and lauryl amine, thiourea compounds such as diethyl thiourea, dibutyl thiourea, diphenyl thiourea and ethylene thiourea, and benzyl thiourea. Examples include thiazole compounds such as thiazole and 2-mercaptobenzothiazole, and polyethylene glycol type surfactants to which ethylene oxide is added. The overall problem with descaling is speeding up the process, and this pickling also
High-temperature treatment of 80 to 100°C is desired, and higher inhibitor performance is also required. D. Structure of the Invention As a result of intensive research, the present inventors have discovered that by introducing a benzyl group into the mercapto group of a 2-mercaptobenzothiazole compound, an inhibitory effect that could not be expected with conventional inhibitors can be exerted. , led to the present invention. Examples of the compounds of the present invention include 2-benzylthiobenzothiazole, 2-(P-chlorobenzylthio)benzothiazole, 2-(O-chlorobenzylthio)benzothiazole, 2-(3,4-dichlorobenzylthio). )-benzothiazole, 5-
Chlor-2-(3,4-dichlorobenzylthio)-
Benzothiazole, 5-chloro-2benzylthiobenzothiazole, 5-chloro-2-(P-chlorobenzylthio)benzothiazole, 4-methyl2-(P-chlorobenzylthio)benzothiazole, 4-methyl-2- Benzylthio-benzothiazole, 5,6-dichloro-2-(P-chlorobenzylthio)benzothiazole, 5-methoxy-
Examples include 2-(P-chlorobenzylthio)-benzothiazole and 6-amino-(P-chlorobenzylthio)benzothiazole. E Effect The compound of the present invention can stably suppress the dissolution of iron-based metals not only at low temperatures but also at high temperatures by adding 0.01 to 5.0% by weight, preferably 0.05 to 1.0% by weight, to the acid solution. It is something. The inhibitor of the present invention may be used in combination with known inhibitors, or may be used in combination with necessary drugs for solubilization or formulation. F. Examples The effectiveness of the present invention will be explained below with reference to Examples. Iron as test piece (SPCC) 50×10×1
After polishing with #320 water-resistant abrasive paper, degrease with acetone and dry before use. The most widely used test fluid10
% hydrochloric acid, 10% sulfuric acid, and 10% acetic acid at 80° C. with a predetermined concentration of inhibitor addition. In addition, in order to accelerate corrosion, each acid solution contains
Add 50g/Fe ²⁺ . Comparative examples include additive-free, diethylthiourea, dibutylthiourea, 2-mercaptobenzothiazole, and a commercially available inhibitor (Ivit No.
700: An inhibitor for ordinary steel of unknown structure (sold by Sumitomo Chemical Co., Ltd.) was used. The corrosion inhibition rate is calculated using the following formula. Corrosion inhibition rate (%) = (A-B)/A×100 A: Corrosion loss when no inhibitor is added B: Corrosion loss when inhibitor is added 1 10% hydrochloric acid (Fe ²⁺ 50g/)

【table】

[Table] 2 10% sulfuric acid (Fe ²⁺ 10g/)

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[Table] 3 10% acetic acid (Fe ²⁺ 50g/)

[Table] Effects of the Invention From the above Examples and Comparative Examples, it was found that the present invention is useful as a corrosion inhibitor for iron-based metals.

Claims (1)

[Claims] 1. General formula [In the formula, X is hydrogen, halogen, lower alkyl group,
Represents a lower alkoxy group or an amino group, and n is 1 to 2
It is. R is hydrogen or chlorine, m is 1-2
A corrosion inhibitor for iron-based metals under acidic conditions using a compound represented by the following.