JPH0445590B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a composition for inhibiting metal corrosion in a steam generation system, and more particularly to a steam corrosion inhibitor composition that uses a combination of a film-forming corrosion inhibitor and a neutralizing corrosion inhibitor in a steam condensate system. Prior Art In equipment that generates steam, such as boilers and concentrators, points that come into contact with steam and condensed water are affected by a decrease in pH due to the action of oxygen, carbon dioxide, or other acidic substances contained in the feed water. often corrodes. Measures to prevent this corrosion include ion exchange treatment and deaeration treatment of the feed water, as well as treatment with chemicals, and long-chain aliphatic amines are mainly used as chemicals. By the way, long-chain aliphatic amines are water-insoluble, and it is difficult to directly and uniformly disperse them in water. One way to use them as corrosion inhibitors is to mix them with acetate. There are known methods in which the amine is converted into an aqueous solution by converting it into a soluble salt, or the amine is directly added to the feed water as an alcohol solution. However, when these corrosion inhibitor solutions are diluted with feed water, the solutes tend to coagulate and precipitate due to the influence of electrolytes present in the feed water, accumulating on the vessel walls and pipe walls. There are drawbacks that make it difficult to manage. On the other hand, the method of using a long-chain aliphatic amine as an emulsified dispersion is not affected by electrolytes and the like. However, the point that the emulsified dispersion state must be stably maintained when diluted with feed water is the same as the previous solution corrosion inhibitor, and apart from this, since it is an emulsified dispersion, It is required that the emulsified dispersion state is stable even if the undiluted solution is stored for a long period of time. In addition, in recent years, boilers have become larger and processes have become more labor-saving, so water tanks with larger capacities than before are being used, and the residence time of boiler supply water in the water tank has also increased. Due to the trend toward significantly longer retention times, steam-based corrosion inhibitors have become required to be stable over time in water tanks. Therefore, the ingredients of steam-based corrosion inhibitors are considered safe because the steam-based corrosion inhibitors supplied to the boiler vaporize together with the steam, and the steam is often released into the atmosphere due to various reasons such as pressure adjustment. Taking into account the fact that higher corrosion resistance is better, an emulsion-dispersed corrosion inhibitor was developed using an emulsifier that was highly safe for the human body and had the requirements as a vapor-based corrosion inhibitor (Japanese Patent Application Laid-Open No. 174884-1983). reference). However, these conventional film-based corrosion inhibitors require a long period of time (several months or more) to become effective, during which time the pipes are exposed to corrosive gases (CO ₂ or O ₂ ).
The drawback was that it corroded due to water. In other words, in order for a film-based corrosion inhibitor to exhibit sufficient corrosion-preventing effect, a film-forming substance (alkylamine) must be applied to the entire pipe.
must be adsorbed to form a complete anti-corrosion film. However, in plants where the area of condensate piping is large and the amount of evaporation is small, it takes a long time (3 months or more) to form an anticorrosive film. As a result, corrosion of the piping progressed due to CO ₂ and O ₂ , and corrosion, especially in thin-walled threaded sections, could not be prevented. Purpose In order to solve the drawbacks of these conventional film-forming corrosion inhibitors, the present invention aims to prevent corrosion until a corrosion-resistant film is formed (hereinafter referred to as initial corrosion) by combining it with a neutralizing corrosion inhibitor. The purpose is to prevent Composition As a result of intensive research in order to achieve the above object, the present inventor found that A long chain aliphatic amine having 10 to 24 carbon atoms;
B Fatty acid alkali metal salt having 8 to 24 carbon atoms and C
Formula, RO( _-CH2 ) _-oNH2 (where R is H _{or CH3} ,
n represents 2 or 3), and the composition contains 0.5 to 20% by weight of component A, and component A:component B is 5:
By providing a steam-based corrosion inhibitor composition comprising an aqueous emulsion in which the ratio of component C: component A + component B is 1:99 to 99:1 (weight %). I found out that I can achieve my goal. That is, the present invention is an improved invention of the invention disclosed in JP-A No. 60-174884, and the present invention is an improved invention of the invention disclosed in JP-A-60-174884. The present invention relates to a treatment method in combination with an anticorrosive agent. The vapor-based corrosion inhibitor composition of the present invention comprises an aliphatic amine having 10 to 24 carbon atoms (component A) represented by the formula: CH ₃ (-CH ₂ ) _-o NH ₂ (n=9 to 23); An aqueous solution containing fatty acid alkali metal salts of number 8 to 24 (component B) in a ratio such that the component A is 0.5 to 20% by weight and the weight ratio of the component A to the component B is 5:1 to 1:5. Add alkanolamines represented by the formula RO(-CH ₂ ) _-o NH ₂ (R=H or CH ₃ , n=2 to 3) to the film-forming anticorrosive agent made of emulsion to the sum of component A and component B. against 1:99
~99:1 (wt%) was blended to form a single agent. By combining it into a single agent, it is possible to automatically raise the pH of drain water to 7.0 or higher using the same injection method as conventional film-forming corrosion inhibitors. This makes it possible to prevent initial corrosion caused by gas (CO ₂ or O ₂ ). Here, the film-forming amine does not dissociate, but directly transfers to steam, and when it is condensed, it is adsorbed on the pipe surface to form a film. On the other hand, neutralizing amines dissociate in water (take H from water) and release OH,
Reacts with and neutralizes acidic substances in water. The long-chain aliphatic amine used as component A in the vapor-based corrosion inhibitor composition of the present invention has a carbon number of 10 to
24, preferably 12 to 20 alkyl or alkenyl groups, preferably 1 to 3, preferably 1. An amine having a lower number of carbon atoms than this is inferior in metal corrosion prevention effect, and an amine having a higher number of carbon atoms than this may cause undesirable phenomena such as gelation. Specific examples of long chain aliphatic amines suitable for the present invention include dodecylamine, tridecylamine, tetradecylamine, pentadecylamine,
Saturated aliphatic amines such as hexadecylamine, heptadecylamine, octadecylamine, nonadecylamine, eicosylamine, docosylamine, unsaturated aliphatic amines such as oleylamine, ricinoleylamine, linoleylamine, linolenylamine, coconut oil amine, hydrogenated Mention may be made of mixed amines such as tallow amine and mixtures thereof. By the way, if octadecylamine, which is approved for use as an additive for boiler water according to US FDA standards, is used as component A,
Since there is no safety problem even if the steam generated from the boiler leaks and comes into contact with food, it has the advantage that it can also be used in the food manufacturing industry. Component A is used in an amount of 0.5 to 20% by weight based on the total amount of the composition.
If the amount is less than this, the stability of the composition will be poor, while if it is more than this, it will tend to gel, making dispersion difficult, which is not preferred. Component B used in the present invention is an alkali metal salt of a fatty acid having 8 to 24 carbon atoms, preferably 10 to 22 carbon atoms. Among these, sodium salts and potassium salts of fatty acids produced from edible fats and oils are preferred, especially fatty acids having 14 to 22 carbon atoms.
An alkali metal salt of a fatty acid containing at least 25% by weight of at least one unsaturated fatty acid selected from the group consisting of unsaturated fatty acids, lauric acid or palmitic acid is suitable. Also, B that can be used in the present invention
Examples of ingredients include one or more of alkali metal salts such as capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, oleic acid, erucic acid, linoleic acid, and linolenic acid. be done. In the present invention, component B is based on the total amount of the composition.
It is used in an amount of 0.5 to 30% by weight, and in particular, component A and component B are used in a weight ratio of 5:1 to 1:5. If the proportion of component B is smaller than this, the stability over time will decrease when the composition is diluted, while if it is larger, the long-term storage stability of the composition will decrease, and phase separation or gelation may occur during storage. It becomes easier. The formula used _as the C component of the present invention, RO( _-CH2 ) _-oNH2 (R=H or _CH3 , n=
Specific examples of alkanolamines which are neutralizing amines represented by 2 to 3) include ethanolamine, propanolamine, methoxyethanolamine, and methoxypropanolamine. The amount of component C to be used is 0.5 ppm or more, preferably several tens of ppm or more, and although there is no particular upper limit, it is determined in consideration of economic efficiency and the like. The ratio of component C to other components is usually C:A+B
= 1:99 to 99:1 (wt%), preferably 50:
50-85:15. Since the vapor-based corrosion inhibitor composition of the present invention uses component A as a corrosion inhibiting component and component B as an emulsifier, it itself has excellent long-term storage stability and exhibits good dispersion stability even when diluted with water. Its stability does not deteriorate over time. In addition, since the composition of the present invention is highly safe, it can be used as a corrosion inhibitor in boilers and the like without any problems even in factories where safety restrictions are severe, such as food factories. This effect can be said to be completely unexpected considering that the corrosion-inhibiting component is a long-chain aliphatic amine that tends to form complexes with anionic surfactants. The corrosion inhibitor composition of the present invention comprises three of A, B and C.
Although these ingredients are essential, conventional ingredients for corrosion inhibitors and other auxiliary additive ingredients can be optionally included as needed. Examples of such optional additives include solubilizers such as ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, and briselin, sequestering agents, antifreeze agents, and the like. The corrosion inhibitor composition of the present invention can be added continuously or intermittently to supplied water or steam so that the amine content is 0.1 to 100 ppm, preferably 1 to 10 ppm. Inhibits corrosion. When the corrosion inhibitor composition of the present invention is diluted to near the concentration used, the diluted dispersion exhibits basicity with a pH of about 9 to 11. Can be used together without any problems. Effects The steam-based corrosion inhibitor composition of the present invention, which consists of a three-component system of a long-chain aliphatic amine, a fatty acid alkali metal salt, and a neutralizing alkanolamine, has two components: a long-chain aliphatic amine, a fatty acid alkali metal salt, and a neutralizing alkanolamine. The initial corrosion prevention effect is far superior to that of compositions consisting of component systems. Next, the present invention will be explained in more detail with reference to Examples. Example 1 (storage stability test) 1.4 parts by weight of octadecylamine, 0.9 parts by weight of sodium oleate, 0.4 parts by weight of ethylene glycol,
After thoroughly mixing 40 parts by weight of monoethanolamine and 57.3 parts by weight of pure water, the mixture was allowed to stand at room temperature. I looked at the appearance after 7 days, 1 month and 3 months.
In either case, no phase separation was observed;
It showed a good emulsification state. From now on, C of the present invention
It can be seen that the emulsion stability is not impaired even if the ingredients are added. Example 2 (corrosion test) Soft water containing 30 mg of KOH, 35 mg of Na ₃ PO ₄ and 270 mg of the composition shown in Table 1 below was added to a continuous steam-generating autoclave with an evaporation rate of 12.6/h, and the pressure was increased. It was operated while continuously generating steam at 10 kg/cm ² . At this time, a test piece (mild steel 15 x 15 x 1) was immersed in steam drain water and the corrosion rate was measured. The results obtained are shown in FIG.

[Table] As can be seen from the results shown in Figure 1, the corrosion inhibitor compositions () and () of the present invention have a much better initial corrosion inhibition effect than the conventional corrosion inhibitor composition (). I understand that. Example 3 (Corrosion Test) A corrosion test was carried out in the same manner as in Example 2, except that a predetermined amount of the test sample shown in Table 2 was added. After 48 hours, the test piece was removed and the degree of corrosion was measured. The results are shown in Table-2.

【table】

[Table] As can be seen from the above results, it can be seen that the corrosion inhibiting composition () of the present invention has a superior corrosion inhibiting effect than conventional corrosion inhibitors. Example 4 (Corrosion Test) A corrosion test was carried out in the same manner as in Example 2, except that a predetermined amount of the sample shown in Table 3 was added. After 1, 2, 3, and 4 days, the test piece was removed and the corrosion rate was measured. The results are shown in Figure 2. As can be seen from FIG. 2, the corrosion inhibitor composition of the present invention has better storage stability and excellent initial corrosion prevention effect than conventional compositions.

【table】 [Brief explanation of drawings]

FIGS. 1 and 2 are graphs comparing the corrosion inhibiting effects of the corrosion inhibitor of the present invention and conventional corrosion inhibitors over time.

Claims (1)

[Scope of Claims] 1. A long chain aliphatic amine having 10 to 24 carbon atoms, B fatty acid alkali metal salt having 8 to 24 carbon atoms, and C
The composition contains a neutralizing amine represented by the formula RO(-CH ₂ ) _-o NH ₂ (wherein R represents H or CH ₃ and n represents 2 or 3), and the A component is 0.5 to 0. Steam-based corrosion consisting of an aqueous emulsion in which A component: B component is 5:1 to 1:5 (weight ratio) and C component: A component + B component is 1:99 to 99:1 (weight %). Inhibitor composition.