JPH0261557B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Industrial Application Field 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 is hydrogen, halogen, lower alkyl group,
Represents a lower alkoxy group or an amino group, and n is 1 to
It is 2. ] This relates to a corrosion inhibitor for iron-based metals under acidic conditions using a compound represented by the following. (b) Conventional technology 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. Both are aimed at removing scale attached to metal.
The acids used vary depending on the usage situation.
Inorganic acids include hydrochloric acid, sulfuric acid, phosphoric acid, hydrofluoric acid, and sulfamic acid, and organic acids include acetic acid, citric acid, lactic acid, oxalic acid, succinic acid, tartaric acid, formic acid, hydroxyacetic acid, monochloroacetic acid, and dichloroacetic acid. , malic acid, thiomalic acid, propionic acid,
Examples include thioglycolic acid, chloropropionic acid, and ethylenediaminetetraacetic acid. 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) and 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 dissolution of the base metal, an inhibitor is added at 0.1% to the acid solution. Approximately 3.0% is added. The inhibition mechanism of the inhibitor is that the N, O, P, S atoms, etc. of organic compounds are adsorbed only to the base metal, and are hardly adsorbed to the scale, so the dissolution of the base metal does not affect the rate of descaling. It is believed that it suppresses (c) Problems to be Solved by the Invention Currently used inhibitors include alkyl amines such as tallow amine, stearyl amine and lauryl amine, thiourea series such as diethyl thiourea, dibutyl thiourea, diphenyl thiourea and ethylene thiourea. Examples include thiazole compounds such as benzothiazole and 2-mercaptobenzothiazole, and polyethylene glycol type surfactants to which ethylene oxide is added. Also, for example, Industrial and Engineering Chemistry (Industrial and Engineering Chemistry).
Engineering Chemistry) VoL.51No7.P825~
828 (1959) states that the corrosion inhibiting effect of propargyl alcohol derivatives is effective even at high temperatures, but this is not satisfactory. 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 propargyl group into the 3-position of a benzothiazolone compound, an inhibitory effect not expected with conventional inhibitors can be exerted. I've reached it. Examples of the compounds of the present invention include 3-propargylbenzothiazolone, 5-bromo-3-propargylbenzothiazolone, 5-chloro-3-propargylbenzothiazolone, 5,6-dichloro-3
-Propargylbenzothiazolone, 4-methyl-
3-propargylbenzothiazolone, 4,5-dimethyl-3-propargylbenzothiazolone, 5
-methyl-3-propargylbenzothiazolone,
6-Methyl-3-propargylbenzothiazolone, 6-amino-3-propargylbenzothiazolone, 5-amino-3-propargylbenzothiazolone, 5-methoxy-3-propargylbenzothiazolone, 4-ethoxy-3- Examples include propargylbenzothiazolone. Among the compounds used in the present invention, 3-propargylbenzothiazolone was synthesized by the following method. 6 g of benzothiazolone is dissolved in 100 ml of 2% aqueous sodium hydroxide solution, and 20 ml of an acetone solution of 4.8 g of propargyl bromide is added dropwise while stirring with heating. After reacting for 2 hours, the acetone was distilled off and the resulting crystals were filtered to obtain 7.1 g of the desired product. m.
p.60-61°C This compound was found as one spot on thin layer chromatography. Other compounds were synthesized in a similar manner. (E) Effect The compound of the present invention, when added in an amount of 0.01 to 5.0% by weight, preferably 0.05 to 1.0% by weight, to an acid solution stably suppresses the dissolution of iron-based metals not only at low temperatures but also at high temperatures. It is something that can be done. The inhibitor of the present invention may be used in combination with known inhibitors, or may be mixed with drugs necessary for solubilization or formulation. (f) Examples The effectiveness of the present invention will be explained below with reference to Examples. Iron (SPCC) 50×10×1 as test piece
After polishing with #320 water-resistant abrasive paper, degrease with acetone and dry before use. 10% is the most widely used test solution.
It is carried out using hydrochloric acid, 10% sulfuric acid, 10% acetic acid at 80°C with an inhibitor loading of 1000 ppm. In addition, in order to accelerate corrosion, each acid solution contains
Add 50g/Fe ²⁺ . As comparative examples, additive-free, diethylthiourea, dibutylthiourea, 2-mercaptobenzothiazole, a commercially available inhibitor (Ivit #700: manufactured by Sumitomo Chemical Industries), and propargyl alcohol were 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 an inhibitor is added

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[Table] (G) Effect of the invention From the above examples and comparative examples, it was found that the compound described in this patent application is effective 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
It is 2. ] Corrosion inhibitor for iron-based metals under acidic conditions using the compound shown by