JP7666979B2 - Metal corrosion inhibitor composition for chillers and method for operating chillers - Google Patents

Description

The present invention relates to a metal corrosion inhibitor composition for chillers and a method for operating a chiller using the metal corrosion inhibitor composition for chillers.

A chiller system (cooling water circulation system), sometimes simply called a chiller, is a device that circulates water or a low-temperature heat medium adjusted to a specified temperature to cool, heat, or regulate the temperature of a target object such as a sample or device. Since most chillers are used for cooling purposes, the circulating chiller water is sometimes called circulating water, circulating cooling water, or cooling water.

Cooling water, hot and cold water, and chiller water are used widely in various facilities and factories for cooling and heating equipment. In such water systems, the pipes and heat exchangers are often made of metals such as iron. How to prevent corrosion of such metal pipes and heat exchangers is a major issue facing cooling water systems, hot and cold water systems, and chiller water systems.

In general, hardness components such as calcium are present in the water used for open cooling towers, and when part of the water evaporates in the cooling tower for cooling, the hardness components in the water become concentrated unless part of the cooling water is forcibly replaced. Water that contains a large amount of hardness components generally does not corrode metals easily, so corrosion can be suppressed by concentrating the cooling water appropriately and increasing the concentration of hardness components. In such systems, it is possible to suppress damage to the cooling water system by adding a scale inhibitor such as a water-soluble polymer dispersant to suppress the formation of scale that can clog pipes or interfere with heat transfer in heat exchangers.

Furthermore, when highly corrosive water, such as recovered water from process cleaning water in semiconductor factories, is used as make-up water for a cooling water system, the water generally has a low concentration of hardness components, and even if concentrated, the circulating cooling water has low hardness (for example, a total hardness of 200 _mgCaCO3 /L or less), making it highly corrosive to iron-based metals. When such water is used as cooling water, the methods for inhibiting corrosion of iron-based metals are limited, and a passive corrosion inhibition method in which an oxide film is formed using a chemical such as molybdate is often used.

On the other hand, closed water systems such as closed cooling water, cold water for air conditioning, hot water, chiller water, etc. do not have cooling towers, the water is rarely concentrated, and generally has low hardness (for example, total hardness of 200 mg _CaCO3 /liter or less), so they are highly corrosive to ferrous metals, and water and chemicals are replaced very infrequently. Furthermore, operating conditions are often intermittent, and a specified flow rate cannot be constantly ensured. For these reasons, passive corrosion inhibition methods using chemicals such as molybdates and nitrites are often adopted.

Based on these technical theories, different chemicals are used depending on whether the water system is open or closed, or on the make-up water used, etc.

In addition, in closed water systems, copper-based and aluminum-based materials are often used as constituent materials for pipes, heat exchangers, water tanks, fins, etc. Corrosion inhibitors are often used for copper-based and aluminum-based materials, but because they are prone to corrosion when the pH becomes acidic or alkaline, methods are also used in which a pH adjuster is used to create an environment that is less susceptible to corrosion.

Azole compounds, which are corrosion inhibitors used to inhibit corrosion of copper-based materials, are generally effective at very low concentrations in the water being treated. Therefore, when an azole compound, which is a copper-based corrosion inhibitor, is used in combination with an iron-based corrosion inhibitor, the proportion of the iron-based corrosion inhibitor is overwhelmingly larger in terms of weight ratio (see, for example, Patent Document 1), and they are used in a weight ratio of, for example, 1:16. There are virtually no examples of using an azole compound in greater amounts than an iron-based corrosion inhibitor, except for antifreeze whose main component is an organic solvent, etc.

Japanese Patent Application Publication No. 5-222555

In particular, in the case of chiller water circulated through a chiller, the chiller is generally a closed system with a cooling water inlet and a cooling water outlet connected to the object to be temperature-adjusted, and depending on the object to be temperature-adjusted, the amount of water held may be small, and operation may be intermittent, such as stopping for one day or more per week, or stopping for three hours or more per day. In addition, the composition ratio of iron-based metals is high, and corrosion is often already progressing within the system. As a result of the inventors' investigation, it was found that azole compounds are consumed particularly quickly compared to general circulating water systems when the fluid temperature received by the chiller is 10°C or higher, when the system is in intermittent operation, or when the composition ratio of iron-based metals is high and corrosion is already progressing within the system. If the azole compound is consumed quickly, it must be replenished separately from the iron-based corrosion inhibitor, and misjudging the timing of replenishing the azole compound could lead to corrosion of copper-based materials and problems such as secondary damage such as leakage to other heat transfer media due to water leakage.

Therefore, there is a demand for a metal corrosion inhibitor composition for chillers that can provide a stable corrosion inhibition treatment effect in chiller water systems.

The object of the present invention is to provide a metal corrosion inhibitor composition for chillers that provides a stable corrosion inhibition treatment effect in chiller water systems, and a method for operating a chiller that uses the metal corrosion inhibitor composition for chillers.

The present invention provides a metal corrosion inhibitor composition for a chiller, comprising water, an azole compound, molybdic acid, and a fungus inhibitor, wherein the weight ratio of the azole compound in the metal corrosion inhibitor composition is 2.5 or more relative to the weight ratio of the molybdic acid (as Mo) and is in the range of 0.1 to 0.2 % by weight , the weight ratio of the water in the metal corrosion inhibitor composition is 90% by weight or more, and the azole compound is at least one of benzotriazole, tolyltriazole, and aminotriazole .

In the metal corrosion inhibitor composition for chillers, it is preferable that the TOC in the metal corrosion inhibitor composition is 10,000 mg/L or less.

The metal corrosion inhibitor composition for chillers preferably further contains at least one of a scale dispersant and a pH adjuster.

In the metal corrosion inhibitor composition for chillers, it is preferable that the pH of the metal corrosion inhibitor composition is 5 or more.

The present invention is a method for operating a chiller using the metal corrosion inhibitor composition for chillers, in which the metal corrosion inhibitor composition for chillers is used as chiller water as is.

In the chiller operation method, it is preferable that the temperature of the fluid received by the chiller from the object to be cooled is equal to or higher than 5°C and lower than 50°C.

In the chiller operation method, it is preferable to operate the chiller intermittently.

The present invention provides a metal corrosion inhibitor composition for chillers that provides a stable corrosion inhibition treatment effect in chiller water systems, and a method for operating a chiller that uses the metal corrosion inhibitor composition for chillers.

FIG. 1 is a schematic diagram showing an experimental apparatus in which a new test piece and a corroded test piece are placed facing each other.

The following describes an embodiment of the present invention. This embodiment is an example of implementing the present invention, and the present invention is not limited to this embodiment.

The metal corrosion inhibitor composition for chillers according to the present embodiment contains water, an azole compound, and at least one of molybdic acid and nitrous acid, and the weight ratio of the azole compound in the metal corrosion inhibitor composition is 1 or more relative to the total weight ratio of at least one of molybdic acid (as Mo) and nitrous acid (as _NO2 ), and is a composition that is 0.005% by weight or more.

The inventors have significantly reconsidered the weight ratio of the azole compound relative to the total weight ratio of at least one of molybdenum and nitrous acid, which is a conventional common practice in composition design, for example, a ratio of 1:16 or 1:100 by weight of an azole compound, which is a copper-based corrosion inhibitor, to an iron-based corrosion inhibitor, and have found that a stable corrosion inhibition treatment effect can be obtained in chiller water systems by incorporating an azole compound in an amount greater than or equal to the iron-based corrosion inhibitor and at 0.005% by weight or more.

By using the metal corrosion inhibitor composition for chillers according to this embodiment, a stable corrosion inhibition treatment effect can be obtained even in a closed chiller water system that holds a small amount of water.

The metal corrosion inhibitor composition for chillers according to this embodiment is mainly applied to closed chiller water systems. The chiller is not limited, and can be applied to, for example, various industrial machines, medical machines, scientific instruments, food machinery, etc. The chiller has, for example, a cooling section, and may also have a water tank, a pump, etc. The chiller may be an air-cooled chiller or a water-cooled chiller. The amount of water held by the chiller is, for example, 100 L or less.

Examples of azole compounds that are copper corrosion inhibitors include benzotriazole, tolyltriazole, and aminotriazole. One of these azole compounds may be used alone, or two or more of them may be used in combination.

Examples of the iron-based corrosion inhibitor include molybdic acid and nitrous acid. Molybdic acid is blended, for example, as a molybdate, and specific examples of the molybdate include molybdates such as orthomolybdate, paramolybdate, and metamolybdate. Specific examples of the salt in this case include sodium salt, potassium salt, and ammonium salt. Among these molybdates, sodium orthomolybdate is particularly preferred. When considering the weight of molybdic acid, it is preferable to convert it to Mo in terms of ease of calculation in terms of composition design. Nitrous acid is blended, for example, as a nitrite, and specific examples of the nitrite include sodium salt, potassium salt, and ammonium salt. When considering the weight of nitrous acid, it is preferable to convert it to NO ₂ in terms of composition design in terms of ease of calculation. The iron-based corrosion inhibitor may be used alone or in combination of two or more of these.

The water to be used may be tap water, pure water, ultrapure water, etc., but it is preferable to use pure water or ultrapure water. Here, pure water means water that has been treated so that both chloride ions and sulfate ions are less than 1 ppm. Ultrapure water is water with an electrical resistivity of 15 MΩ cm or more.

The metal corrosion inhibitor composition for chillers according to this embodiment may contain a fungus inhibitor (also called a bactericide) to inhibit the occurrence of slime and microbial corrosion. Examples of fungus inhibitors include organic sulfur-nitrogen compounds and organic bromine compounds, and specific examples thereof include 2-methyl-3-isothiazolone, 5-chloro-2-methyl-3-isothiazolone, 4,5-dichloro-2-n-octyl-3-isothiazolone, and 2-bromo-2-nitro-1,3-propanediol. The fungus inhibitor may be used alone or in combination of two or more types.

The metal corrosion inhibitor composition for chillers according to this embodiment may contain a scale inhibitor to inhibit the formation of scale. As the scale inhibitor, a polycarboxylic acid compound, a chelating agent, or the like is used. Specific examples of polycarboxylic acid compounds include polyacrylic acid, polymaleic acid, a copolymer of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid, and sodium salts thereof. Specific examples of chelating agents include L-ascorbic acid, erythorbic acid and their sodium salts, ethylenediaminetetraacetic acid (EDTA), ethylenediamine-N,N'-disuccinic acid (EDDS), nitrilotriacetic acid (NTA), diethylenetriaminepentaacetic acid (DTPA), L-aspartic acid diacetic acid (ASDA), L-glutamic acid diacetic acid (GLDA), hydroxyethylethylenediaminetriacetic acid (HEDTA), methylglycine diacetic acid (MGDA), glycol ether diaminetetraacetic acid (GEDTA), triethylenetetraminehexaacetic acid (TTHA), hydroxyethyliminodiacetic acid (HIDA), and their sodium salts, potassium salts, hydrates, etc. The scale inhibitors may be used alone or in combination of two or more.

In a sealed water environment such as chiller water, water is hardly exchanged, so when metal corrosion occurs in the system, the pH may rise due to hydroxide ions generated by the progress of the cathodic reaction, which may cause a problem of promoting copper-based metals secondarily. Therefore, it is desirable to add a pH adjuster to the metal corrosion inhibitor composition for chillers. Examples of pH adjusters include sodium carbonate, potassium carbonate, sodium bicarbonate, sodium phosphate, disodium hydrogen phosphate, potassium phosphate, trisodium citrate, sodium gluconate, etc., and carbonates and bicarbonates such as sodium carbonate, potassium carbonate, and sodium bicarbonate are preferred because they are less likely to become scale components or TOC sources. The pH adjuster may be used alone or in combination of two or more of these.

The pH of the metal corrosion inhibitor composition for chillers is preferably 4 or more, and more preferably 5 or more. The upper limit of the pH of the metal corrosion inhibitor composition for chillers is, for example, 11 or less.

In the metal corrosion inhibitor composition for chillers according to the present embodiment, the azole compound is preferably blended in a weight ratio of at least one of the iron-based corrosion inhibitors molybdic acid and nitrous acid (i.e., the weight ratio of the azole compound is 1 or more relative to the total weight ratio of at least one of molybdic acid and nitrous acid), and the weight ratio of the azole compound: at least one of molybdenum and nitrous acid is preferably in the range of 1:1 to 100:1, more preferably in the range of 1:1 to 10:1. In cases where the proportion of copper-based metals in the composition of the treated metal is low, the weight ratio of the azole compound: at least one of molybdic acid and nitrous acid may be preferably in the range of 1:10 to 10:1. Here, the weight of molybdic acid is the weight as Mo, and the weight of nitrous acid is the weight as NO ₂ .

The weight percentage of the azole compound in the metal corrosion inhibitor composition for chillers according to this embodiment is 0.005% by weight or more, preferably in the range of 0.005 to 1.0% by weight, and more preferably in the range of 0.005 to 0.2% by weight.

The metal corrosion inhibitor composition for chillers according to this embodiment is a composition that is not composed of an organic solvent. "Not composed of an organic solvent" is defined as a composition that has a TOC of 10,000 mg/L or less, taking into consideration the increase in TOC caused by blending an appropriate amount of an azole compound, an organic fungus inhibitor, etc. The TOC is preferably 3,000 mg/L or less. It is preferable that the metal corrosion inhibitor composition for chillers according to this embodiment is a composition in which the TOC components are composed only of an azole compound and an organic fungus inhibitor.

The weight percentage of water in the metal corrosion inhibitor composition for chillers according to this embodiment is, for example, 90% by weight or more, preferably 99% by weight or more, and more preferably 99.5% by weight or more. In general, antifreeze concentrate contains 70 to 80% by weight of the main components ethylene glycol or propylene glycol, and the water content is about 20 to 30% by weight, and is used as is or diluted several times with water. Therefore, it should be considered as having completely different properties from the metal corrosion inhibitor composition for chillers according to this embodiment, which is composed of 99% by weight or more of water.

The metal corrosion inhibitor composition for chillers according to this embodiment may be used as chiller water as it is, rather than being used by adding a concentrated agent to the water system as in typical cooling water compositions.

<How to operate the chiller>
The chiller operating method according to the present embodiment is an operating method using the above-mentioned metal corrosion inhibitor composition for chillers. For example, the above-mentioned metal corrosion inhibitor composition for chillers may be used as circulating water (also called circulating cooling water or cooling water) for the chiller to operate the chiller.

When the fluid temperature that the chiller receives from the object to be temperature-adjusted is, for example, in the range of 5°C or more and less than 50°C, and preferably in the range of 10°C or more and less than 30°C, the above-mentioned metal corrosion inhibitor composition for chillers can be suitably applied as the circulating water of the chiller. By using the above-mentioned metal corrosion inhibitor composition for chillers, a stable corrosion inhibition treatment effect can be obtained even if the fluid temperature that the chiller receives from the object to be temperature-adjusted is in the range of 5°C or more and less than 50°C.

When the chiller is operated intermittently, for example, at an operating rate of 90% or less, preferably at an operating rate of 10% or more and 90% or less, the above-mentioned metal corrosion inhibitor composition for chillers can be suitably used as the circulating water for the chiller. By using the above-mentioned metal corrosion inhibitor composition for chillers, a stable corrosion inhibition treatment effect can be obtained even when the chiller is operated intermittently.

Note that "operation rate of 90% or less" means that the chiller is stopped for one day or more per week, or for three hours or more per day, i.e., the operation time over a seven-day period is intermittent operation with an operation rate of 90% or less.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

<Example 7, Reference Examples 1 to 6, 8, and 9, and Comparative Examples 1 to 3>
In the Examples , Reference Examples and Comparative Examples, a rotary corrosion test was carried out by placing a total of four pieces of test pieces, namely, a brand new mild steel test piece, a copper test piece, and a mild steel test piece and a copper test piece that had been separately corroded, in the following test solution that had been prepared in advance.

The corroded mild steel test pieces were prepared by immersing new mild steel test pieces in Sagamihara City water and corroding them at 35°C with a stirrer stirring at 200 rpm for 7 days.The corroded copper test pieces were prepared by immersing new copper test pieces in an ammonia-containing solution prepared by adding 30% ammonia water to pure water to adjust the ammonium ion concentration to 60 ppm, and corroding them at 35°C with a stirrer stirring at 200 rpm for 7 days.

A new mild steel test piece and a corroded mild steel test piece were placed face to face, and a new copper test piece and a corroded copper test piece were placed face to face. A total of four test pieces were immersed in a beaker filled with 1 L of test liquid using a special cross-shaped test piece attachment resin that can simultaneously attach four test pieces, and a rotary corrosion test was performed. Figure 1 shows a schematic diagram of the experimental device in which the new test piece and the corroded test piece were placed face to face. In the experimental device in Figure 1, the new test piece 12 and the corroded test piece 14 are immersed in the test liquid 16 in the beaker 10 so that they face each other, using the test piece attachment resin 18.

In the rotary corrosion test, the stirring blade (resin for mounting the test specimen) on which the test specimen was installed was rotated at 150 rpm for three days, then the stirring was stopped for two days and the test specimen was left stationary with a zero flow rate, after which the stirring blade on which the test specimen was installed was rotated again at 150 rpm for two days. After seven days, the test specimen was removed, and the originally brand new test specimen was derusted and weighed. The corrosion rates of mild steel and copper were measured by the mass subtraction method in accordance with the Industrial Water Corrosion Test Method (JIS-K0100) from the difference in the test specimen weight measured before the start of the test.

[Test conditions]
Test liquid: Pure water was mixed with the corrosion inhibitor components (benzotriazole and sodium molybdate or sodium nitrite) and fungus inhibitor (only Reference Example 4 and Example 7) shown in Tables 1 and 2 at a predetermined concentration, and sodium bicarbonate was added at 500 mg/L as a pH adjuster to adjust the test pH to 7.2±0.2. 1 L of this was tested in a 1 L beaker. The fungus inhibitor used in Reference Example 4 and Example 7 was a mixture of 2-bromo-2-nitro-1,3-propanediol at a concentration of 100 mg/L and Caisson WT (the trade name of an isothiazolinone fungus inhibitor) at a concentration of 200 mg/L.
Water temperature: 30℃
Stirring speed: 150 rpm
Test piece: Mild steel SS-400 (10 x 30 x 50 mm, #400)
Copper C1220P (10 x 30 x 50 mm, #400)
Test period: 7 days (3 days of continuous operation, 2 days of shutdown, 2 days of continuous operation (assuming 2 days of shutdown in a week))

The test results are shown in Tables 1 and 2. In Tables 1 and 2, "Mo" is sodium molybdate (concentration is expressed as Mo), " _NO2 " is sodium nitrite (concentration is expressed as _NO2 ), "AZ" is benzotriazole (tolyltriazole only in Reference Example 2), and "MDD" is a unit of corrosion rate, which represents mg/ ^dm2 ·day.

The TOC of the test water was measured by a combustion catalytic oxidation method using a total organic carbon meter (Shimadzu Corporation, model: TOC-L-CPN) and was approximately 1,400 mg/L for pure water mixed with 800 mg/L sodium molybdate, 2,000 mg/L benzotriazole, 100 mg/L 2-bromo-2-nitro-1,3-propanediol, 200 mg/L Caisson WT, and 500 mg/L sodium bicarbonate (Example 7).

The HACH "DR-3900" was used to measure the molybdenum concentration. The DIONEX "Integrion" ion chromatography was used to measure the nitrite concentration. The HACH "DR-3900" was used to measure the azole compound concentration.

After the test, the number of general bacteria in the water in the beaker was measured. A Sanai Biochecker TTC manufactured by Sanai Oil Co., Ltd. was placed in the water for 5 seconds, removed, and then cultured in a thermostatic chamber set at 30°C for 48 hours. The colony pattern appearing on the surface of the removed Biochecker medium was compared with the sample and calculated as a logarithmic number of 10.

[Pass/Fail criteria]
In this test, the pass/fail criteria were set as follows:
Corrosion rate of mild steel (MDD): 10 or less is considered to be a pass.
Copper corrosion rate (MDD): 0.5 or less is considered a pass.
Residual concentration of iron-based corrosion inhibitor (molybdic acid (as Mo), nitrous acid (as _NO2 )): 70% or more is considered a pass.
Residual concentration of copper-based corrosion inhibitor (azole compound): 90% or more is considered to be a pass.

As in the comparative example, it was found that when the weight ratio of the azole compound is less than 1 relative to the total weight ratio of at least one of molybdic acid (as Mo) and nitrous acid (as _NO2 ), the concentration of the azole compound and at least one of molybdic acid and nitrous acid in the treated water drops drastically. The reason for this is unclear, but it is presumed that the high concentration of the oxide film type chemical (at least one of molybdic acid and nitrous acid), which is an iron-based corrosion inhibitor, increases the potential of the iron surface, and the potential of the copper surface drops relatively, creating an environment in which the copper-based material is easily corroded, and in such an environment, if the azole compound, which is a copper-based corrosion inhibitor, is not supplied at a predetermined concentration or more, the copper-based material corrodes, and the azole compound, molybdic acid, etc. are consumed in the form of being taken into the corrosion product, creating an environment in which the iron-based material also corrodes secondarily. On the other hand, under conditions where the weight ratio of the azole compound is 1 or more relative to the total weight ratio of at least one of molybdic acid (as Mo) and nitrous acid (as _NO2 ) and is 0.005 wt% or more, such a problem hardly occurs, and it is presumed that a stable corrosion inhibition treatment effect can be obtained.

Moreover, from the results of Reference Example 4 and Example 7, it was confirmed that by adding a fungus inhibitor, a good bactericidal effect of less than 10 to the power of 3 can be obtained.

As described above, the metal corrosion inhibitor composition for chillers of the embodiment provided a stable corrosion inhibition treatment effect in the chiller water system.

10 Beaker, 12 New test piece, 14 Corroded test piece, 16 Test liquid, 18 Resin for mounting test piece.

Claims (7)

A metal corrosion inhibitor composition for a chiller, comprising:
Contains water, an azole compound, molybdic acid, and a fungus inhibitor;
the weight ratio of the azole compound in the metal corrosion inhibitor composition is 2.5 or more and in the range of 0.1 to 0.2 % by weight based on the weight ratio of the molybdic acid (as Mo) ;
The weight ratio of the water in the metal corrosion inhibitor composition is 90% by weight or more,
The metal corrosion inhibitor composition for chillers, wherein the azole compound is at least one of benzotriazole, tolyltriazole, and aminotriazole . The metal corrosion inhibitor composition for chillers according to claim 1 ,
A metal corrosion inhibitor composition for chillers, characterized in that the TOC in the metal corrosion inhibitor composition is 10,000 mg/L or less. The metal corrosion inhibitor composition for chillers according to claim 1 or 2 ,
The metal corrosion inhibitor composition for chillers further comprises at least one of a scale dispersant and a pH adjuster. The metal corrosion inhibitor composition for chillers according to any one of claims 1 to 3 ,
The metal corrosion inhibitor composition for chillers, wherein the pH of the metal corrosion inhibitor composition is 5 or more. A method for operating a chiller using the metal corrosion inhibitor composition for chillers according to any one of claims 1 to 4 , comprising:
A method for operating a chiller, comprising using the above-mentioned metal corrosion inhibitor composition for chillers as chiller water as it is. A method for operating a chiller according to claim 5 , comprising:
A method for operating a chiller, wherein the temperature of a fluid received by the chiller from an object to be temperature-adjusted is equal to or higher than 5°C and lower than 50°C. A method for operating a chiller according to claim 5 or 6 , comprising:
A method for operating a chiller, comprising intermittently operating the chiller.