JPH0128104B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a solution containing seawater, freshwater, and sour gas;
This invention relates to a corrosion inhibitor that is effective for steel materials that come into contact with strong acids. Conventionally, corrosion inhibitors mainly composed of inorganic compounds such as phosphates, chromates, nitrites, and silicates have been used as corrosion inhibitors for steel materials in neutral environments, and organic amines have been used in acidic environments. Organic nitrogen compounds such as are mainly used. However, at present, corrosion inhibitors that are effective in neutral environments do not exhibit corrosion inhibiting effects in acidic environments, and corrosion inhibitors that are effective in acidic environments do not exhibit corrosion inhibiting effects in neutral environments, so corrosion It is necessary to use different corrosion inhibitors depending on the environment. However, in reality, the pH of the corrosive environment changes over time, which can lead to unexpected corrosion accidents. For example, it is said that water that has accumulated under an oil storage tank can cause hydrogen sulfide and carbon dioxide to leach out of the oil, lowering the pH. There is a problem in that even if a corrosion inhibitor is added, even if a corrosion inhibitor for acidic environments is added, corrosion of steel cannot be suppressed well. The present invention was obtained as a result of research as an alternative to the conventional corrosion inhibitor mentioned above, and is suitable for use in steel materials ranging from neutral environments such as seawater and fresh water to acidic environments such as sour and strong acids. The purpose of the present invention is to provide a corrosion inhibitor that can sufficiently suppress the corrosion of. That is, the present invention provides (1) a corrosion inhibitor characterized by containing an imidazoline derivative, a carboxylic acid, and a phosphate compound as a corrosion-inhibiting component, and (2) an imidazoline derivative containing at least one carboxyl group and a phosphorus compound. The present invention relates to a corrosion inhibitor characterized by containing an acid salt compound as a corrosion inhibiting component. In the corrosion inhibitor of the present invention, as the imidazoline derivative, those having the molecular structure shown below can be used. or However, at least one of the substituents R ₁ to _{R 7} is an aliphatic, alicyclic, or aromatic hydrocarbon group. And these hydrocarbon groups contain 5 carbon atoms.
It is desirable to contain at least 9, preferably 9 to 17. Other substituents R that do not fall under this category include hydrogen, aliphatic hydrocarbon groups, alicyclic hydrocarbon groups, aromatic hydrocarbon groups,

【formula】

【formula】

[Formula] −R″−OH, −R″−OH, −R″− SH, −R″−COOH,

【formula】

[Formula] −R″−COONa,

【formula】

【formula】

[Formula] etc. can be used. Here, R′: hydrogen, aliphatic hydrocarbon group, alicyclic hydrocarbon group, or aromatic hydrocarbon group, R″:
aliphatic, alicyclic or aromatic divalent hydrocarbon group,
x: A positive integer of 1 or more. In addition, in the molecular structure of the imidazoline derivative,
X ^- is a monovalent anion (e.g. chloride ion,
(bromine ion, etc.). Carboxylic acids in the present invention include aromatic carboxylic acids such as benzoic acid and phthalic acid, fatty acids such as stearic acid and oleic acid, aliphatic dimer acids such as succinic acid and adipic acid, and their derivatives. Carboxylic acids, ketocarboxylic acids, aminocarboxylic acids, etc. can be used. Furthermore, metal salts of these carboxylic acids can also be used. Further, various phosphate compounds such as calcium dihydrogen phosphate, sodium dihydrogen phosphate, sodium tripolyphosphate, and sodium hexametaphosphate can be used as the phosphate compound in the present invention. The mixing ratio of these is such that the imidazoline derivative has a concentration of 25 to 1000 ppm, preferably 100 to 500 ppm in the usage environment, and the carboxylic acid has a concentration of 10 to 100 ppm, preferably 20 to 500 ppm.
It is desirable that the concentration is about 30 ppm, and the concentration of the phosphate compound is about 25 to 200 ppm, preferably about 50 to 100 ppm. In addition, when using an imidazoline derivative containing a carboxyl group or a carboxyl group in which a hydrogen atom is replaced with a metal atom, as shown in the following example, the imidazoline derivative must already contain both an adsorptive nitrogen atom and a carboxyl group in the molecule. Therefore, there is no need to add any other carboxylic acid. Example 1 Example 2 It is already known that the imidazoline derivative in the corrosion inhibitor of the present invention can very effectively inhibit corrosion of steel materials in weak acid environments including sour environments and strong acid environments. The corrosion inhibiting effect is said to be due to the imidazoline derivative forming a strong adsorption film on the steel material in such a corrosive environment, thereby blocking chemical substances that cause corrosion reactions from the steel material. However, many imidazoline derivatives cannot form a strong adsorption film in a neutral environment, and therefore exhibit little or only a weak corrosion inhibiting effect on steel materials. As a result of studying the relationship between the molecular structure and composition (addition of other types of compounds) of imidazoline derivatives and the corrosion inhibiting function in a neutral environment, the present inventor found that imidazoline derivatives and carboxylic acids or metal salts of carboxylic acids are used as corrosion inhibiting components. Corrosion inhibitors whose corrosion inhibiting ingredients include at least one carboxyl group or an imidazoline derivative containing at least one carboxyl group in which a hydrogen atom is substituted with a metal atom can cause significant corrosion not only in acidic environments but also in fresh water. It was found that it exhibits a suppressive effect. Furthermore, if a phosphate compound that exhibits a remarkable corrosion inhibitory effect on aqueous solutions with high ion concentrations such as seawater is added to the above corrosion inhibitor, it can be used in acid environments and aqueous solutions with low ion concentrations such as fresh water. It has been discovered that not only does it have a good corrosion-inhibiting effect against water, but it can also have a high corrosion-inhibiting function against aqueous solutions with high ion concentrations such as seawater. And further 3-methyl-5-hydroxypyrazole, 1-hydroxybenzotriazole,
It is preferable to add a compound having a chelating effect to iron atoms, such as kojic acid, to the corrosion inhibitor having the above composition, since this can stabilize the corrosion inhibitory effect and reduce the concentration of the corrosion inhibitor added. If necessary, other additives such as surfactants and antifoaming agents can be added to adjust the composition. It is necessary to be careful. The corrosion inhibitor obtained in the present invention can be used in various forms and by various means. For example, the corrosion inhibitor may be dissolved or dispersed in water or a water-oil mixture to prevent corrosion of steel materials in water. or a method of preventing corrosion by dissolving or dispersing the present corrosion inhibitor in water or an organic solvent and applying it to the surface of the steel material. The corrosion inhibitor according to the present invention can sufficiently inhibit corrosion of steel materials in an extremely wide range of environments, from neutral environments such as seawater and fresh water to sour environments and strong acid environments. In addition to the convenience of not having to change the type of agent,
Even in environments where PH fluctuates widely and is difficult to control, once this corrosion inhibitor is added, the corrosion inhibiting function of the steel material will not deteriorate even if the PH changes thereafter, which is a very important feature. be. Hereinafter, the effects of the corrosion inhibitor according to the present invention will be specifically illustrated by examples. Although this example shows the results of an immersion test in water or an aqueous solution, the effects of the present invention are not limited to this example. Example 1 A corrosion inhibitor having the following composition was used. (Corrosion inhibitor) Imidazoline derivative having the following molecular structure
A corrosion inhibitor consisting of 70 parts of succinic acid and 20 parts of calcium dihydrogen phosphate. However, R: Soybean oil fatty acid residue (corrosion inhibitor) Imidazoline derivative having the following molecular structure
80 and 20 parts of calcium dihydrogen phosphate. However, R: Soybean oil fatty acid residue (corrosion inhibitor) Imidazoline derivative having the following molecular structure
Corrosion inhibitor consisting of 75 parts and 25 parts of calcium dihydrogen phosphate. However, R': Coconut oil fatty acid residue The following commercially available corrosion inhibitor was used as a comparative example. (Commercially available corrosion inhibitor A) Corrosion inhibitor for seawater containing phosphoric acid as a main component. (Commercially available corrosion inhibitor B) A corrosion inhibitor for freshwater containing a nitrite compound as a main component. (Commercial Corrosion Inhibitor C) A corrosion inhibitor for pickling containing an organic amine as a main component. The following four types of corrosive liquids were used. (1) Tap water (continuously blown air). (2) Artificial seawater (continuously blown air) with the following composition.

[Table] Finally, adjust the pH to 8.20 with 0.1N NaOH aqueous solution. (3) NACE solution (standard corrosive solution for sour environments) with the following composition:

[Table] (4) 10% sulfuric acid aqueous solution
Thickness x 15mm width x 30mm thickness, #320 polishing) into corrosive liquid
The samples were immersed at 60°C for 3 days, and the weight loss during that time was compared using the corrosion protection rate obtained from the following formula. Corrosion protection rate=w ₀ −w/w ₀ ×100 (%) However, {w: weight reduction when a corrosion inhibitor is added. w ₀ : Weight loss when no corrosion inhibitor is added.

[Table] The results obtained are shown in Table 1, and the following things became clear from the results. (1) The corrosion inhibitor according to the present invention exhibits a good corrosion inhibiting effect in any freshwater, seawater, sour, or strong acid environment. (2) All commercially available corrosion inhibitors showed good corrosion inhibition effects only in some environments. Example 2 A corrosion inhibitor having the following composition was used. (Corrosion inhibitor) Imidazoline derivative having the following molecular structure
A corrosion inhibitor consisting of 80 parts and 20 parts of calcium dihydrogen phosphate. However, R': Coconut oil fatty acid residue (corrosion inhibitor) 40 parts of an imidazoline derivative having the same molecular structure as the corrosion inhibitor and calcium dihydrogen phosphate
Corrosion inhibitor consisting of 40 parts and 20 parts of kojic acid. (Corrosion inhibitor) 40 parts of an imidazoline derivative with the same molecular structure as the corrosion inhibitor and calcium dihydrogen phosphate
Corrosion inhibitor consisting of 40 parts and 20 parts of 3-methyl-5-oxypyrazole. The same four types of corrosive liquids as in Example 1 were used. Similar to Example 1, the corrosion inhibitory function of the above corrosion inhibitor against various corrosive liquids was compared in terms of corrosion protection rate. The experiment was repeated 5 times to confirm the stability of the corrosion inhibiting effect. The results obtained are shown in Table 2.

【table】

[Table] From the above results, it is clear that when a chelating agent is added to the corrosion inhibitor according to the present invention, corrosion of steel materials can be stably inhibited even at a lower concentration.

Claims (1)

[Scope of Claims] 1. A corrosion inhibitor characterized by containing an imidazoline derivative, a carboxylic acid or a metal salt compound of a carboxylic acid, and a phosphate compound. 2. A corrosion inhibitor characterized by containing an imidazoline derivative containing at least one carboxyl group or a carboxyl group in which a hydrogen atom is replaced with a metal atom, and a phosphate compound.