JPH07118882A - Metal corrosion inhibitor - Google Patents

Abstract

PURPOSE:To obtain a metal corrosion inhibitor which generates less foaming at the time of using it in an aqueous system and does not contain any heavy metal, phosphorus and nitrogen and has excellent corrosion inhibition effect by using an S- alkylthiocarboxylic acid having a specified range of number of carbon atoms and not using any halide as a component of the inhibitor. CONSTITUTION:This corrosion inhibitor is a metal corrosion inhibitor which contains an S-alkylthiocarboxylic acid having 12 to 18 carbon atoms as the active component and no halide, and can be used in an aqueous system. The S-alkylthiocarboxylic acid has preferably 12 to 16 carbon atoms and preferably in particular 14 carbon atoms. The alkyl group is optionally either branched or straight chained. However, the S- alkylthiocarboxylic acid having a straight chain alkyl group shows superior corrosion inhibition effect as compared with that having a branched chain alkyl group provided that each of the alkyl groups has the same number of carbon atoms. When the alkyl group has <12 carbon atoms, the corrosion inhibition effect of the inhibitor is reduced since the hydrophobic group that forms a coating film on the surface of a metal is short in length. On the other hand, when the alkyl group has >18 carbon atoms, the corrosion inhibition effect becomes insufficient since the solubility of the inhibitor in water is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a treatment agent for preventing corrosion of metals in contact with neutral to alkaline water in cooling water systems, warm water systems, washing water, aqueous metalworking oil agents, dust collecting water systems and the like. .

[0002]

2. Description of the Related Art Conventionally, heavy metals such as chromates and zinc salts, various phosphorus compounds, and nitrogen-containing azole compounds have been used as corrosion inhibitors for metals that come into contact with water. Due to environmental concerns, these compounds are in the direction of regulation. Therefore, a corrosion inhibitor that does not contain heavy metals, phosphorus and nitrogen has been sought, but none has yet been found that exhibits a sufficient effect.

US Pat. No. 5,081,209 describes alkyl mercaptans and vinyl monomers containing acrylic acid in a ratio of 1: 2.
To a polymer obtained by polymerizing at a molar ratio of 1:40 to
The use as a corrosion inhibitor is disclosed. However, this polymer not only does not show a sufficient anticorrosion effect, but also has a problem of high foaming depending on the composition.
When foaming occurs in the water system, problems such as cavitation, erosion, idling of a circulation pump, and release of bubbles into the atmosphere occur, which is not preferable.

CORROSION, 31 volumes, P123 (1975)
And S-Alkylthiopropionic acid obtained by reacting an alkyl halide with sodium 3-mercaptopropionate is used as a corrosion inhibitor in acidic water for P287, Proc. It is disclosed. However, the S-alkylthiopropionic acid synthesized by this method has a problem that not only the yield is low, but also sodium halide in an equimolar amount to the reaction product is produced as an impurity. Sodium halide must be removed in advance because it dissociates in water to form halogen ions and is corrosive to metals. Further, in the same document, S- having a carbon number of 8 or more in acid
Alkylthiopropionic acid is said to have low anticorrosion effect due to its low solubility. On the other hand, MATERIAL P
ERFORMANCE, No. 4, P33 (1976) describes S-decylthiopropionic acid (having 1 carbon atom) in neutral water.
(Alkyl of 0) has been shown to have anticorrosion effect, but not sufficient effect.

[0005]

DISCLOSURE OF THE INVENTION The object of the present invention is to reduce foaming when used in an aqueous system and to prevent heavy metals, phosphorus,
And to provide a corrosion inhibitor which does not contain nitrogen and has an excellent anticorrosion effect.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above-mentioned object, and is S-containing 12 to 18 carbon atoms.
The object is achieved by a metal corrosion inhibitor in an aqueous system which contains an alkylthiocarboxylic acid as an active ingredient and does not substantially contain a halogenated salt.

S-alkylthiocarboxylic acid has 12 carbon atoms.
-18, preferably 12-16, particularly preferably 14. The alkyl group may be linear or branched,
If the number of carbon atoms is the same, the straight-chain type has better anticorrosion effect than the branched type. If the number of carbon atoms is less than 12, the length of the hydrophobic group that forms a film on the metal surface is short, and the anticorrosion effect is reduced. If the carbon number exceeds 18,
Solubility in water decreases and the anticorrosion effect becomes insufficient.

The S-alkylthiocarboxylic acid is suitably obtained by reacting an alkyl mercaptan with an unsaturated carboxylic acid. The alkyl mercaptan used as a reaction raw material corresponds to the S-alkylthiocarboxylic acid to be produced. The unsaturated carboxylic acid is preferably selected from acrylic acid, methacrylic acid and itaconic acid, with acrylic acid being particularly preferred. The molar ratio of unsaturated carboxylic acid to alkyl mercaptan is
1 or more and less than 2 is suitable. When it is less than 1, unreacted alkyl mercaptan remains, which is not preferable in terms of anticorrosion, and gives off an offensive odor of alkyl mercaptan. Further, when the molar ratio is 2 or more, not only the anticorrosion effect is lowered but also the foamability is increased. A preferred molar ratio is 1 or more and 1.8 or less, and particularly preferably 1 or more and 1.5 or less.

When the alkyl mercaptan is reacted with an unsaturated carboxylic acid such as acrylic acid, methacrylic acid or itaconic acid, a peroxide or an azo compound is used in order to complete the reaction at a relatively low temperature in a short time. Radical initiators are required. Known compounds can be used as the radical initiator for the peroxide and the azo compound, but the optimum initiator varies depending on the reaction temperature and the solvent used.
Specific examples of the radical initiator include 2,2′-azobis.
Azo compounds such as (2,4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), benzoyl peroxide,
Examples thereof include organic peroxides such as t-butyl peroxypivalate. The amount of the radical initiator used may be about 0.05 to 5 with respect to the unsaturated carboxylic acid.

At the time of the reaction, the reaction raw materials may be dissolved in a suitable solvent, but the reaction raw materials can be directly reacted without using a solvent, but since the alkyl mercaptan is insoluble in water, it is suitable. You may use an organic solvent. The optimum reaction temperature depends on the type of initiator,
Usually in the range of 40 to 200 ° C. As a procedure for charging the reaction raw materials, all the raw materials may be charged all at once, but it is easier to control the reaction temperature if the unsaturated carboxylic acid and the initiator are sequentially added after charging the alkyl mercaptan. . The product after the reaction can be used as it is or after being diluted to an appropriate concentration without separation and purification. The reaction formula of this synthesis is as follows.

[0011]

[Chemical 1]

The above-mentioned synthesis method has an advantage in that it is not necessary to remove salts such as sodium chloride, potassium chloride such as sodium bromide, and salts such as halogenated salts, which have a corrosive action on metals, as by-products. .

The S-alkylthiocarboxylic acid of the present invention may be applied to the water system as it is, but may be an alkali metal salt such as sodium or potassium, an ammonium salt,
It may be added in the form of a neutralized salt such as an amine salt. In order to increase the solubility and dispersibility in water, anionic and / or
Alternatively, a nonionic surfactant may be used in combination. The combined use of these surfactants improves the corrosive effect by increasing the dispersibility of the S-alkylthiocarboxylic acid in water. The amount of the corrosion inhibitor of the present invention added to the water system is usually 1 to 1000 ppm, preferably 2 to 500 ppm, but is not limited to this range.

In addition to the corrosion inhibitor of the present invention, a corrosion inhibitor,
Compounds known as scale inhibitors, dispersants, slime control agents, and defoamers may be used in combination. Examples of such compounds are described in JP-A 1-299699 and JP-A 1-299700.
And Japanese Patent Laid-Open No. 63-258697.

The corrosion inhibitor of the present invention is particularly effective against iron, copper, aluminum, zinc and alloys thereof.

[0016]

EXAMPLES Preparation of Corrosion Inhibitor Compound of the Invention Compound A: n-dodecyl mercaptan: acrylic acid molar ratio = 1: 1.1 500 ml four bottles equipped with a thermometer, stirring bar, reflux condenser and nitrogen gas inlet tube. Into a necked flask, 101.2 g of n-dodecyl mercaptan was placed, and the temperature was raised to 80 ° C. Acrylic acid 39.6
g and 1.0 g of 2,2'-azobis (2,4-dimethylvaleronitrile) as an initiator dissolved in 5 ml of methyl ethyl ketone were added dropwise by separate dropping funnels over 30 minutes. An exotherm occurred at the same time as the initiator was added dropwise, so the temperature was maintained at 80 to 95 ° C by cooling. Then, the temperature was maintained at 100 ° C. for 3.5 hours to complete the reaction. After cooling, solid white crystals were obtained at room temperature (yield 94% or more).

Hereinafter, Compound B to Compound G are synthetic products A
Was synthesized by a method similar to. Compound B: n-dodecyl mercaptan: acrylic acid molar ratio = 1: 1 Compound C: n-dodecyl mercaptan: acrylic acid molar ratio = 1: 1.5 Compound D: n-tetradecyl mercaptan: acrylic acid molar ratio = 1 : 1 Compound E: n-octadecyl mercaptan: acrylic acid molar ratio = 1: 1 Compound F: n-dodecyl mercaptan: itaconic acid molar ratio = 1: 1 Compound G: n-dodecyl mercaptan: methacrylic acid molar ratio = 1: 1

Compounds used for comparison Hereinafter, the compounds H to M were synthesized in the same manner as the synthetic product A. Compound H: n-dodecyl mercaptan: acrylic acid molar ratio = 1: 2 Compound I: n-dodecyl mercaptan: acrylic acid molar ratio = 1: 2.5 Compound J: n-dodecyl mercaptan: acrylic acid molar ratio = 1: 4 Compound K: n-dodecyl mercaptan: acrylic acid molar ratio = 1: 8 Compound L: n-octyl mercaptan: acrylic acid molar ratio = 1: 1 Compound M: n-decyl mercaptan: acrylic acid molar ratio = 1 : 1

Evaluation of Corrosion Prevention Effect A rolled steel material for general structure (JIS SPCC) having a thickness of 1 mm was cut into a disk shape with an outer diameter of 50 mm, and a fixing mounting hole having a diameter of 8 mm was formed at the center to obtain a test piece. The stains on the surface of the test piece were removed, the entire surface was polished with No. 400 polishing paper, washed and degreased with acetone, and dried and weighed accurately to 0.1 g. Attach the test piece to the rotating shaft, immerse it in 500 ml of test water, and 100 rpm
I rotated it. The water quality of the test water was pH 7.8 to 8.5, calcium hardness 80 ppm, magnesium hardness 30 ppm, and M alkalinity 60 ppm. Inventive and comparative corrosion inhibitors were added respectively and kept at 40 ° C. for 18 hours. After the test was completed, the corrosion product was removed, and after drying, the weight was accurately measured to 0.1 g.

The corrosion weight loss was determined from the weight difference of the test piece before and after the test. The test results are shown in Tables 1 and 2.

[0021]

[Table 1]

From Table 1, it is clear that when the molar ratio of acrylic acid, methacrylic acid and itaconic acid to alkyl mercaptan is 1 or more and less than 2, a good anticorrosion effect is exhibited. Further, it is understood that the S-alkylthiocarboxylic acid using the alkyl mercaptan having 12 to 18 carbon atoms has an excellent anticorrosion effect.

[0023]

[Table 2]

From Table 2, the corrosion inhibitor of the present invention, 2-phosphonobutane-1,2,3-tricarboxylic acid (PBTC),
It has been shown that the anticorrosion effect is improved by the combined use with a compound known as a corrosion inhibitor such as sodium molybdate or zinc salt.

Evaluation of Foamability 1 liter of Yokkaichi-shi water was placed in an acrylic cylindrical container with an inner diameter of 70 mm and a height of 470 mm and having a scale,
It was recirculated at a flow rate of liter / min. The recirculated water was sprinkled from a height of 450 mm from the bottom of the container, and the rising height of the liquid surface due to the generated bubbles was read and recorded 2 minutes after the start of circulation. The test results are shown in Table 3. Circulation stop 3
The foam height after minutes was recorded.

[0026]

[Table 3]

Table 3 shows that when the molar ratio of acrylic acid to alkyl mercaptan exceeds 2, foamability increases.

[0028]

INDUSTRIAL APPLICABILITY The corrosion inhibitor of the present invention does not contain heavy metals, phosphorus, nitrogen, etc., which are harmful to the environment, and has an excellent anticorrosion effect. And stable operation. Further, the corrosion inhibitor of the present invention does not generate a side reaction product that adversely affects the corrosion, and therefore does not require a separation operation of the reaction product and can be obtained in a high yield.

Claims (2)

[Claims] 1. A corrosion inhibitor for metals in an aqueous system, which contains an S-alkylthiocarboxylic acid having 12 to 18 carbon atoms as an active ingredient and is substantially free of halogenated salts. 2. The S-alkylthiocarboxylic acid is one in which one or more unsaturated carboxylic acid selected from acrylic acid, methacrylic acid and itaconic acid is added to alkyl mercaptan having 12 to 18 carbon atoms. The metal corrosion inhibitor according to claim 1, which is obtained by reacting in the presence of a radical initiator at a molar ratio of at least 2 and less than 2.