JP3025933B2 - Boiler water-based corrosion inhibitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a boiler water-based corrosion inhibitor.

[0002]

2. Description of the Related Art In a boiler water system, since it is under high pressure and high heat at which steam is constantly refluxed, even if the amount of oxygen (dissolved oxygen) dissolved in the water system is small,
It causes corrosion and scale on the inner wall of the water supply pipe. Therefore, usually, most of the dissolved oxygen is physically removed, and the rest is removed by adding an oxygen scavenger. In addition, when the pH of the boiler water is on the acidic side, corrosion and the like are promoted, so that the boiler water is usually adjusted to a pH of about 8.0 or more.

Conventionally, hydrazine has been mainly used as an oxygen scavenger. Hydrazine removes dissolved oxygen by its excellent reducing action, and can form and maintain a black iron oxide (magnetite) protective film on the inner wall of the boiler water supply pipe, and does not generate any harmful residue. It is widely used as a corrosion inhibitor in boiler water systems.

More specifically, hydrazine basically reacts with N ₂ H ₄ + O ₂ → N ₂ + 2H ₂ O in the presence of a small amount of oxygen, and further reacts with 2N ₂ H ₄ depending on changes in temperature and pressure. Reacts with → 2NH ₃ + N ₂ + H ₂ and / or 3N ₂ H ₄ → 4NH ₃ + N ₂ , but does not generate harmful acids or other harmful substances in the boiler water system in any case . In addition, hydrazine has an effect of preventing magnetite (Fe ₃ O ₄ ) from being oxidized to produce Fe ₂ O ₃ as a rust component.

Although hydrazine has the above-mentioned excellent effects, it is required that the safety of workers is increased, and at the same time, it has an excellent reducing property comparable to hydrazine and is more safe (especially for humans). For example, carbohydrazide has been proposed (Japanese Patent Publication No. 63-63272). Carbohydrazide is slightly superior to hydrazine in terms of safety, and has the same effect as hydrazine at normal temperature, but is significantly inferior to hydrazine at high temperature. Such properties of carbohydrazide are inferior in boiler water systems in which most of them are at high temperatures, which is problematic.

A hydrazine salt has been proposed as an additive for an open circulation cooling water system which always contains a large amount of dissolved oxygen (Japanese Patent Publication No. 4-46640). In the open circulation cooling water system, water that has received heat from the cooling device and warmed
The cooling tower makes contact with air and evaporates a part of the cooling tower to release heat, cool it, and use it again as cooling water. By the way, the cooling water used in the system is mainly tap water or well water containing inorganic salts and the like, and since it is accompanied by evaporation as described above, the salts in the cooling water are gradually concentrated to a high concentration, and scale and slime are reduced. It caused various obstacles such as occurrence. Conventionally, replenishment of water and discharge of concentrated water have been performed in order to prevent the occurrence of such an obstacle. However, recently, high-concentration operation has been actively performed for the purpose of saving water resources. What is particularly problematic here is that the increase in pH (concentration of the cooling water to be highly alkaline) accompanying the concentration of the cooling water further promotes the occurrence of the obstacle.
The technology disclosed in the above-mentioned publication utilizes the fact that hydrazine salts such as hydrazine carbonate act as an acid (pH adjuster) in an open circulation cooling water system, and the hydrazine salts are added to cooling water which is concentrated and strongly alkalized by circulation use. pH 5.0
It is adjusted to about 7.0 to prevent the generation of scale and slime. That is, the technology disclosed in this publication merely uses hydrazine salts for the purpose not required in boiler water systems in open circulation cooling water systems requiring completely different factors from boiler water systems.

[0007]

The present inventors have conducted intensive studies to solve the above-mentioned problems of the prior art, and as a result, it has been found that carbazic acid and a salt thereof, which are specific hydrazine derivatives, are equivalent to hydrazine even at a high temperature range. It has been found that the present invention has an excellent oxygen removing effect and has a significantly higher safety for the human body than hydrazine, and has completed the present invention.

That is, the present invention relates to a boiler water-based corrosion inhibitor containing at least one selected from carbazic acid and salts thereof as an active ingredient.

In the boiler water-based corrosion inhibitor of the present invention, the carbazic acid used as an active ingredient is of the formula NH ₂
It is a known compound represented by NHCOOH. Known salts of carbazic acid can be used, for example,
Hydrazine salts (CH ₄ N ₂ O ₂ .N ₂ H ₄ ), alkali metal salts such as sodium, alkanolamine salts such as monoethanolamine, isopropanolamine, diethanolamine, diisopropanolamine, triethanolamine, methylamine, ethylamine, Examples thereof include amine salts such as isopropylamine, n-butylamine, cyclohexylamine, morpholine, and 1,8-diazabicycloundecene (DBU), and at least one of these can be used. As a result of the study by the present inventors, it has been found that hydrazine carbonate [(N ₂ H ₄ ) ₂ CO ₂ ], which has been conventionally used, is a hydrazine salt of carbazic acid.

[0010] The boiler water-based corrosion inhibitor of the present invention (hereinafter simply referred to as "corrosion inhibitor") can exhibit its effects irrespective of the pH of the boiler water system, but is usually about pH 7 to 14, preferably pH 8 to 11. It is good to use it for boiler water system.

In order to exert the effect by using the corrosion inhibitor of the present invention, the corrosion inhibitor may be added to a boiler water system. The addition method is not particularly limited, and a known method can be adopted. For example, a method of intermittently charging (specifically, a method of charging every several hours to several tens of hours), a method of continuously charging a fixed amount, and the like. Can be mentioned. When a certain amount is continuously added, the effect can be sufficiently exerted even at a concentration much lower than the usual concentration of the corrosion inhibitor of the present invention described later.

The concentration of the corrosion inhibitor of the present invention in the boiler water system is not particularly limited and can be appropriately selected from a wide range. However, in consideration of economy and the like, it is preferable that the concentration be equal to or higher than the dissolved oxygen concentration to be usually removed.

The corrosion inhibitor of the present invention may contain known additives such as quinones and metal salts in order to further promote the oxidation-reduction reaction between the agent and dissolved oxygen.

Specific examples of quinones include, for example, p-
Benzoquinone, 2-methyl-p-benzoquinone, dimethyl-methyl-p-benzoquinone, 2-phenyl-p-benzoquinone, 2-chloro-p-benzoquinone, hydroquinone, 2-phenyl-phenylhydroquinone, 2-
Examples thereof include methyl-hydroquinone, dimethylbenzohydroquinone, and 2-chloro-hydroquinone. These can be used alone or in combination of two or more. The addition amount of such quinones is not particularly limited, and may be appropriately selected according to the dissolved oxygen concentration and the like.
Usually at least one selected from carbazic acid and salts thereof
The weight ratio between the species and the quinones is usually from 10 to 10,000: 1.
Degree, preferably about 100 to 1000: 1.

As the metal salt, known salts commonly used in this field can be used. For example, cobalt, copper, manganese,
Organic acid salts such as iron, inorganic acid salts, complex salts and the like can be mentioned. More specifically, the following (a) to (d) can be exemplified.

(A) Cobalt salts Cobalt chloride, cobalt nitrate, cobalt sulfate, cobalt acetate, cobalt ammonium chloride, cobalt EDTA complex salt, cobalt acetylacetonate and the like. In this case, cobalt may be divalent or trivalent.

(B) Copper salt Copper chloride, copper nitrate, copper sulfate, copper acetate, copper ammonia complex,
Copper EDTA complex salt, copper acetylacetonate and the like. 1 for copper
It may be either divalent or divalent.

(C) Manganese salts Manganese chloride, manganese nitrate, manganese sulfate, manganese acetate, manganese EDTA complex salt, manganese acetylacetonate and the like. Manganese may be divalent or trivalent.

(D) Iron salt Iron chloride, iron nitrate, iron sulfate, iron acetate, iron EDTA complex salt, iron acetylacetonate and the like. Iron may be divalent or trivalent.

The above metal salts can be used alone or in combination of two or more of the same or different metals.
The addition amount of the metal salt is not particularly limited and may be appropriately selected depending on the concentration of dissolved oxygen and the like. Usually, the weight ratio of at least one selected from carbazic acid and its salt to the metal salt (weight in terms of metal) is determined. It is usually about 10 to 10000: 1, preferably about 100 to 1000: 1.

[0021]

According to the present invention, the corrosion inhibitor containing at least one selected from carbazic acid and salts thereof as an active ingredient is:
The following excellent effects can be achieved.

(1) It has the same excellent oxygen removing effect as hydrazine.

(2) It has significantly higher safety for the human body than hydrazine. Particularly acute toxicity which is a problem in oral, dermal and inhalation toxicity is extremely low.

(3) Since the aqueous solution is alkaline, the boiler feed pipe is not corroded, hydrazine is consumed, ammonia, nitrogen gas, hydrogen gas, etc. are generated, and a trace amount of harmless carbon dioxide gas remains. No harmful residue is generated.

(4) Since it has high stability to heat, it is particularly useful in a boiler water system subjected to a high temperature load.

[0026]

The following examples and comparative examples are given to further clarify the present invention.

Examples 1 to 6 Main pipe height of 250 m equipped with a magnetic stirrer and a dissolved oxygen meter (manufactured by Toshiba Beckman) capable of uniformly stirring.
m, water (dissolved oxygen content: 8.0 ppm) adjusted to pH 10 with sodium hydroxide-monobasic sodium phosphate is added to a glass container having a content of 750 ml, and the mixture is added at 40 ° C or 80 ° C.
The mixture was stirred while being kept at ° C. The deoxidizing agent was added thereto at an initial concentration shown in Table 1 below (ppm, 100 ppm in terms of hydrazine).
And the change with time in the amount of dissolved oxygen was determined.

[0028]

[Table 1]

The results are shown in FIG. 1 and FIG.

Comparative Examples 1 to 6 In the same manner as in the above Examples, except that the type of deoxidizing agent used and the initial concentration (ppm, 100 ppm in terms of hydrazine) were changed as shown in Table 2 below, the amount of dissolved oxygen was Changes over time were determined.

[0031]

[Table 2]

The results are shown in FIGS. 3 and 4.

The following conclusions can be drawn from FIGS.

(A) The corrosion inhibitor of the present invention has a dissolved oxygen removing ability equal to or higher than that of hydrazine regardless of the water temperature and the presence or absence of a catalyst.

(B) The corrosion inhibitor of the present invention, particularly the corrosion inhibitor containing carbazic acid as an active ingredient, is similar to carbohydrazide at 40 ° C., but at 80 ° C. which is close to the actual temperature of the boiler water system, It has significantly better oxygen scavenging capacity than hydrazide.

(C) The corrosion inhibitor of the present invention has a greater synergistic effect exhibited by the addition of a catalyst than carbohydrazide.

[Brief description of the drawings]

FIG. 1 shows the dissolved oxygen concentration (ppm) in Examples 1 to 3.
6 is a drawing showing the relationship between the time and the time (minutes).

FIG. 2 shows the dissolved oxygen concentration (ppm) in Examples 4 to 6.
6 is a drawing showing the relationship between the time and the time (minutes).

FIG. 3 shows the concentration of dissolved oxygen (ppm) in Comparative Examples 1 to 3.
6 is a drawing showing the relationship between the time and the time (minutes).

FIG. 4 shows the dissolved oxygen concentration (ppm) in Comparative Examples 4 to 6.
6 is a drawing showing the relationship between the time and the time (minutes).

──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Hiroyasu Hayashi 463 Kagasuno, Kawauchi-cho, Tokushima City, Tokushima Prefecture Inside Otsuka Chemical Co., Ltd. In the Tokushima Plant (58) Fields surveyed (Int. Cl. ⁷ , DB name) C23F 11/12-11/14

Claims (2)

(57) [Claims] 1. A boiler water-based corrosion inhibitor comprising at least one selected from carbazic acid and salts thereof as an active ingredient. 2. The method according to claim 1, further comprising at least one of a metal salt and a quinone.
The corrosion inhibitor according to claim 1, comprising a seed.