JP6504748B2 - Method of inhibiting metal corrosion - Google Patents

Description

  The present invention relates to a method for inhibiting metal corrosion, and in particular, corrosion of metals in contact with water, particularly metal members in open circulation cooling water systems, without causing environmental pollution problems such as toxicity and eutrophication in closed water areas. It relates to a method of suppressing effectively.

  Since metal members provided in the cooling water system, for example, heat exchangers, reaction pots, and pipes made of carbon steel, copper or copper alloy, are corroded by coming into contact with the cooling water, corrosion protection by chemical addition is generally performed. Processing has been applied.

  For example, in order to suppress corrosion of carbon steel heat exchangers, reaction kettles and pipes, conventionally, phosphorus compounds such as orthophosphates, hexametaphosphates, hydroxyethylidene diphosphonates and phosphonobutane tricarboxylates are used. It is added to the cooling water. In addition, heavy metal salts such as zinc salt and dichromate may be added alone or in combination. However, since large amounts of these phosphorus compounds and heavy metal salts, especially heavy metal salts, may contaminate the water quality and cause serious environmental impact, there is a great deal of caution and expense in handling and waste water treatment. It will be necessary.

As a method of effectively suppressing metal corrosion without causing such environmental problems, Patent Document 1 discloses that the langerian index is 1.5 or more, and [SiO ₂ ] × [CaH] ≧ 2000 (wherein , [SiO ₂ ] is the concentration of SiO _{2 in} water (mg / L), and [CaH] is calcium hardness as CaCO _{3 in} water (mg / L). And / or one or more polymers selected from water-soluble salts thereof, one or more selected from maleic acid, maleic anhydride and water-soluble salts thereof, and one or more nonionic monoethylenically unsaturated monomers A method of inhibiting metal corrosion is disclosed, which comprises the addition of a copolymer of However, good anticorrosion effect can be obtained by this method only when the concentration ratio of cooling water is relatively high, and corrosion prevention under low concentration conditions at the start of operation can not be expected.

  Therefore, even if it is a cooling water system which performs non-phosphorus and non-zinc treatment during normal operation, it is general to adopt a method of adding a phosphorus compound and / or heavy metal salt as initial treatment at low concentration.

In Comparative Example 3 of Patent Document 1, a maleic acid polymer and a maleic acid-isobutylene copolymer are added to an open circulation cooling water system having a langerian index of 1.8 and a [SiO ₂ ] × [CaH] = 1200. It is described that even if 20 mg / L (10 mg / L as a maleic acid polymer) is added, there is much local corrosion. Further, in Comparative Example 4 of this patent document 1, the maleic acid polymer and the maleic acid-isobutylene co-polymer are included in an open circulation cooling water system having a Langerly index of 0.7 and [SiO ₂ ] × [CaH] = 6000. It is described that even when 20 mg / L (10 mg / L for a maleic acid polymer) is added to a 1: 1 mixture with a polymer, the entire surface becomes prone to corrosion.

Patent Document 2 discloses an open circulation having a calcium hardness of 10 to 300 mg-CaCO ₃ / L in circulating water as a method of effectively suppressing metal corrosion under conditions of low concentration multiple without causing environmental problems. An alkaline metal hydroxide is added in an amount of 20 to 300 mg-CaCO ₃ / L to a cooling water system, and the Lithner index at 40 ° C. of circulating water is maintained at 4.0 to 6.0. Methods have been described for adding scale inhibitors such as finopolycarboxylic acids, phosphonocarboxylic acids, maleic acid polymers, acrylic acid polymers and the like. However, the addition of an alkali metal hydroxide to low hardness water quality raises the pH, so that amphoteric metals such as zinc and aluminum have an increased risk of corrosion. In addition, there is a concern of scale adhesion as the pH is increased by the addition of the alkali metal hydroxide.

JP 2007-119835 Japanese Patent Application Laid-Open No. 2005-200721

  The present invention suppresses metal corrosion which can maintain a good anticorrosion effect without raising the pH excessively under low concentration conditions such as the start of operation of an open circulation cooling water system without causing environmental pollution problems. Intended to provide a method.

The present inventors have found that even when the system is a water system having a low langerian index and a [SiO ₂ ] × [CaH] value, the addition of a maleic acid based polymer provides an excellent anticorrosive effect. Completed the invention.
That is, the metal process corrosion inhibition of the present invention is a method of inhibiting corrosion of metal in the cooling water system, lingerie A index 1.5 at less than, and [SiO _2] is 10 mg / L or more (however, [SiO ₂ ] is one or more polymers selected from maleic acid and / or water-soluble salts thereof in water of the cooling water system in which the concentration of SiO ₂ in water (mg / L )) (hereinafter, "maleic acid polymer" 30 to 150 mg / L is added.

  In the present invention, the weight average molecular weight of the maleic acid polymer is preferably 500 to 2,500.

According to the method of inhibiting corrosion of metal of the present invention, even if it is a water system with a langerian index of <1.5 or [SiO ₂ ] × [CaH] <2000, without using a phosphorus compound or a heavy metal salt, therefore The corrosion of metal of the water system can be effectively prevented or suppressed without causing the problem of environmental pollution, which can contribute to the stable operation of the cooling water system and the like.

  The action and effect of the present invention is considered to be exerted by the adsorption of a metal surface with one or more polymers selected from maleic acid and / or a water-soluble salt thereof to form an anticorrosive film. It is known that one or more polymers selected from maleic acid and / or a water-soluble salt thereof are likely to be combined with calcium ions in water to form an insolubilized substance, and forming an insolubilized substance has a sufficient anticorrosive effect Although it is considered that it can not be obtained, it is considered that a high anticorrosion effect can be obtained because insolubilized substances are hardly formed under the condition of low calcium hardness.

Generally, in an open circulation cooling water system, when the concentration of water increases with the passage of operating time, the concentration of calcium ions and bicarbonate ions contained in water increases, and the formation of a CaCO ₃ film suppresses corrosion. It is well known. As a measure to show the tendency of CaCO ₃ precipitation in this water system, the saturation index of langelia has been proposed. This indicates the tendency of CaCO ₃ precipitation of water as one indication from calcium concentration, M alkalinity, total dissolved solid matter and water temperature, pH. Since the tendency of the CaCO ₃ film to adhere is increased when the langeria index is 1.5 or more, the corrosion resistance of water is also increased. In addition, silica contained in the water system plays an extremely important role in corrosion prevention. In Patent Document 1, a maleic acid polymer is added to a water system having a langerian index of 1.5 or more and [SiO ₂ ] × [CaH] ≧ 2000 to obtain an anticorrosive effect. On the other hand, the present invention has a sufficient anticorrosion effect even in low concentrated water quality at the start of operation of an open circulation cooling water system having a langerian index of less than 1.5 or a [SiO ₂ ] × [CaH] of less than 2000. To get

  Hereinafter, an embodiment of the method for inhibiting metal corrosion of the present invention will be described in detail.

[Maleic acid polymer]
The maleic acid polymer is a polymer of maleic acid and / or a water-soluble salt of maleic acid. Examples of water-soluble salts of maleic acid include sodium maleate, potassium maleate, ammonium maleate and the like. The weight average molecular weight of the maleic acid polymer is preferably about 500 to 2,500, and more preferably about 800 to 1,500.

  The addition amount of the maleic acid polymer (retention concentration in the aqueous system) is 30 to 150 mg / L, preferably 30 to 100 mg / L, as the solid content. In addition, when the addition amount of a maleic acid type polymer is more than 150 mg / L, there exists a possibility that it may gelatinize. It is desirable that the maleic acid polymer be added continuously or intermittently.

[Other additives]
In the present invention, only the maleic acid polymer may be added to the aqueous system, or an acrylic acid polymer may be added together with the maleic acid polymer. By using an acrylic acid-based polymer in combination, it is possible to suppress the magnesium silicate scale, to obtain the effect of dispersing iron rust, and the like. As an acrylic acid type polymer, the copolymer of acrylic acid and 2-acryl acid 2-methyl propane sulfonic acid is mentioned. The molecular weight thereof is preferably about 5,000 to 50,000, particularly about 10,000 to 30,000. When using an acrylic acid type polymer together, the addition amount is preferably about 5 to 50 mg / L.

  When using a maleic acid polymer and an acrylic acid type polymer together, you may add separately and you may add what was mixed previously. When separately added, these may be added at the same place or different places.

  In the present invention, other corrosion inhibitors, scale inhibitors, dispersants, slime control agents, release agents, antifoaming agents, etc. may be used in combination, and also in combination with various water treatment equipment such as filters. It is possible. For example, in the case where the aqueous system contains a copper material, the anticorrosive performance on the copper material can be improved by using an azole derivative such as benzotriazole or tolyltriazole in combination.

Treatment target water system
In the present invention, the water system to be treated has a langerian index of less than 1.5, or [SiO ₂ ] × [CaH] of less than 2000, particularly less than 1000. Add 30 mg / L or more of a maleic acid-based polymer even if it is an aqueous system in which the water to be treated has a low langelian index and / or [SiO ₂ ] × [CaH] and a low concentration of CaCO ₃ and / or silica in water. Thus, by incorporating CaCO ₃ and silica, a good anticorrosive film is formed on the metal surface, and an excellent anticorrosive control effect can be obtained.

The silica concentration of the aqueous system is preferably about 1 to 150 mg / L, particularly about 10 to 100 mg / L. If it exceeds 150 mg / L, silica scale may be generated. [CaH] is preferably about 10 to 500 mg / L, particularly about 20 to 200 mg / L. The M alkalinity is preferably 10 to 500 mg / LasCaCO ₃ , and the pH is preferably 7 to 9.

  As such a water system, a cooling water system is mentioned, for example, an open circulation cooling water system etc. are mentioned. More specifically, when the operation of the open circulation cooling water system is started (initial treatment) or when the heat load can not be maintained during steady operation and the cooling water can not be maintained at a high concentration. In the open circulating cooling water system, it is preferable to add a maleic acid polymer to the pits of the cooling tower.

  EXAMPLES The present invention will be more specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

Examples 1 to 5 and Comparative Examples 1 to 4
<Anticorrosive agent (polymer)>
In the following Examples and Comparative Examples, maleic acid polymers, maleic acid / isobutylene copolymers (monomer ratio 50: 50), acrylic acid polymers, acrylic acid / 2-acrylamido-2-methylpropane sulfone as anticorrosive agents. An acid (AMPS) copolymer (monomer ratio 80:20) and acrylic acid / 2-hydroxyethyl methacrylate (HEMA) copolymer (monomer ratio 85:15) were used. The weight average molecular weight of each polymer or copolymer is shown in Table 2.
<Test method>
After adding sodium bicarbonate aqueous solution, sodium silicate aqueous solution, polymer aqueous solution, magnesium sulfate aqueous solution, sodium chloride aqueous solution, calcium chloride aqueous solution to pure water, adjust the pH with a small amount of sodium hydroxide aqueous solution and sulfuric acid aqueous solution, and test water A to D And Table 1 shows the water quality of each test water.

Take 1 L of the above test water in which each anticorrosive agent (polymer) was made to have the concentration shown in Table 2 in a beaker, keep at 30 ° C, stir the test water at 150 rpm using a stirrer, test piece (carbon steel, vertical 50 mm, width 1.5 mm, thickness 1 mm) were immersed. After 72 hours, the test piece was taken out, the corrosion rate was measured, evaluated by the following evaluation criteria, and the results are shown in Table 2.
○: less than 20 mdd ×: 20 mdd or more After 72 hours, the test piece was pulled up, acid-washed with hydrochloric acid containing inhibitor, and after wind drying, the weight was measured. The corrosion rate (mg / dm ² / day) was calculated from the difference in weight before and after the test.

<Discussion>
1) Comparing Examples 1 to 3 in which 100 mg / L of polymer was added and Comparative Examples 1 to 5, no corrosion was observed in visual observation in the case of using a maleic acid polymer (Example 1, In contrast to 2), corrosion was observed when other polymers were used (Comparative Examples 1 to 5)
2) Even when the maleic acid polymer and the polymer having no corrosion inhibiting effect were used in combination, the occurrence of corrosion could be suppressed (Example 3).
3) In the test waters B and C, when the concentration of the maleic acid polymer was less than 30 mg / L, a sufficient anticorrosive effect was not obtained (Comparative Examples 6 to 9).
4) In the test water B and C, when the density | concentration of a maleic acid polymer is 30 mg / L or more, sufficient anti-corrosion effect was acquired (Examples 4-6).
5) In the test waters B and C, if the concentration of one or more polymers selected from maleic acid and / or its water-soluble salt is 30 mg / L or more, even if other polymers are added, the corrosion prevention function There was no inhibition (Example 6).
6) Even in the case of the polymers of Comparative Examples 8 and 9, the corrosion is suppressed in the case of the test water having many hardness components as in the test water D, but the corrosion is not suppressed in the other test waters A to C.

  From the above Examples and Comparative Examples, according to the present invention, under low concentration conditions such as at the start of operation of an open circulation cooling water system, it is recognized that good metal anticorrosion effects can be maintained without excessively raising pH. It was done.

Claims (4)

In a method of suppressing metal corrosion in a cooling water system,
Lingerie A index is less than 1.5, and [SiO _2] is 10 mg / L or more (however, [SiO _2] is SiO ₂ concentration in water (mg / L)) in water of the cooling water system is,
A method of inhibiting metal corrosion comprising adding 30 to 150 mg / L of one or more polymers (hereinafter referred to as "maleic acid polymers") selected from maleic acid and / or water-soluble salts thereof .   The method for inhibiting metal corrosion according to claim 1, wherein the weight average molecular weight of the maleic acid polymer is 500 to 2,500. The method for suppressing metal corrosion according to claim 1 or 2 , further comprising adding an acrylic polymer to the cooling water system. The method for inhibiting metal corrosion according to any one of claims 1 to 3 , wherein the cooling water system is an open circulation cooling water system.