JPH0192388A - Corrosion inhibitor - Google Patents

Abstract

PURPOSE:To obtain a corrosion inhibitor by which the dissolution of iron-based metals is effectively inhibited by using a compd. prepd. by introducing two or three thiocyanato or alkylenethiocyanato residues into a benzene ring. CONSTITUTION:This corrosion inhibitor is made of a compsn. contg. a compd. represented by the general formula (where m=0-5 and n=2-3). The compd. may be o- or m-phenylene bis(methylenethiocyanate). The corrosion inhibitor is used to inhibit the corrosion of iron-based metals under acidic conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION A) Industrial Application Field The present invention relates to a corrosion inhibitor for iron-based metals. The present invention relates to a corrosion inhibitor for iron-based metals under acidic conditions using a compound represented by the following formula: n is 2 to 3.

Conventional technology Conventionally, acid treatment of ferrous metals includes pickling during the production of iron and stainless steel, chemical cleaning of chemical plants, large boilers for thermal power generation, various heat exchangers, etc. It is also used for the purpose of removing scale attached to metal. The acids used vary depending on the usage situation; for example, 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, Examples include succinic acid, tartaric acid, formic acid, hydroxyacetic acid, monochloroacetic acid, malic acid, thiomalic acid, propionic acid, thioglycolic acid, chloropropionic acid, and ethylenediaminetetraacetic acid.

In descaling using these acids, it is ideal to dissolve only the scale or peel off the scale and minimize the dissolution of the base metal, and for this purpose, corrosion inhibitors (hereinafter referred to as inhibitors) are usually used. has been added. On the surface of heat-treated iron, a Fe2O3<hematite)
Since iron oxides such as , Fe5C)s (magnetite) and Fed (bistite) are formed, it is usually 10 to 15
Dissolution and removal of scale is carried out at 40-50°C under % hydrochloric acid.

At this time, an inhibitor is added in an amount of about 0.1 to 3% to the acid solution in order to prevent dissolution of the base metal. The inhibition mechanism of the inhibitor is that of organic compounds such as nitrogen, oxygen,
Since heteroatoms such as phosphorus and sulfur are adsorbed only to the base metal, and are hardly adsorbed to scale, it is thought that they suppress the dissolution of the base metal without affecting the rate of descaling.

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 even in this pickling process, the temperature is 80 to 100°C.
High-temperature treatment is desired, and higher inhibitor performance is also required.

2) Structure of the Invention As a result of intensive research, the present inventors have discovered that a compound in which 2 to 3 residues of thiocyanate are introduced into the benzene ring, or a compound in which 2 to 3 residues of alkylene thiocyanate are introduced, is different from the conventional one. It was discovered that an inhibitor exhibits an unexpected suppressive effect, leading to the present invention. Examples of the compounds of the present invention include 0-phenylenebis(methylthiocyanate), m-phenylenebis(methylthiocyanate),
p-Phenylenebis(methylthiocyanate), p-phenylenebis(1,2-ethanediylthiocyanate)
, p-phenylenebis(1,4-butanediylthiocyanate), and the like.

e) Effect The compound of the present invention can be added stably not only at low temperatures but also at high temperatures by adding 0.01 to 50 weight percent, preferably 0.05 to 50 weight percent, to the acid solution. It is possible to suppress the dissolution of iron-based metals.

The inhibitor of the present invention may be used in combination with known inhibitors, or may be mixed with necessary drugs for solubilization or formulation.

f) Example Hereinafter, the present invention will be explained in detail with reference to Examples.

Iron (SPCC) 50X10X1mm as test piece
After polishing with waterproof abrasive paper #320, degrease with acetone and dry before use.

Try it! , Wi, is the most widely used 1
The test is carried out using 0% hydrochloric acid, 10% sulfuric acid, and 10% acetic acid at 80° C. with a predetermined concentration of inhibitor added.

In addition, in order to accelerate corrosion, each acid solution contains Fe"50
Add g/l.

As a comparative example, additive-free, diethylthiourea, dibutylthiourea, benzylthiocyanate, and a commercially available inhibitor (IBIT #700, manufactured by Sumitomo Chemical Co., Ltd.) were used.

Calculate the corrosion inhibition rate (%) using the formula below.

Corrosion inhibition rate (%) = (A-B)/AXI00A: Corrosion loss when no inhibitor is added B: Corrosion loss when inhibitor is added 1) 10% salt f! ! (Fe”50g/1
) 2) 10% sulfur a (Fe"50g/I) 3) 10% vinegar 1it (Fe"50g/I) g) Effect of the invention From the above examples and comparative examples, thiocyanate or alkylene thiocyanate was added to the benzene ring. It has been found that compounds into which two or three residues have been introduced are useful as corrosion inhibitors for iron-based metals.

Claims (1)

[Claims] general formula ▲Contains mathematical formulas, chemical formulas, tables, etc.▼ [In the formula, m is 0 to 5 and n is 2 to 3] Corrosion inhibitor for ferrous metals using compounds shown by