TW202024310A - Dissolution and removal composition and cleaning method - Google Patents

Abstract

The purpose of the present invention is to provide: a dissolution and removal composition capable of dissolving and removing scale while suppressing corrosion of a base material even in a state in which oxygen remains; and a cleaning method. This dissolution and removal composition contains a main agent that dissolves and removes scale containing a metal oxide, a first reducing agent that is an organic acid having oxygen reduction properties, and at least one type of second reducing agent selected from among a thiourea-based compound, a thiourea dioxide-based compound, a thioglycolic acid salt and a dithionous acid salt. In addition, the dissolution and removal composition preferably further contains at least one type of inhibitor selected from among sulfur-containing compounds having any one of a mercaptan group (-HS), a thiocyanic acid group (-SCN) and an alkali metal salt of a mercaptan group (NaS-, KS- or LiS-).

Description

Composition for dissolution and removal and cleaning method

This disclosure relates to a composition for dissolution and removal and a cleaning method for removing scales including metal oxides.

There is known a cleaning method that dissolves and removes deposits containing metal oxides adhered to the metal surface by using a cleaning solution of a composition for dissolution and removal with a dissolution removal agent as a main agent (see Patent Document 1). The composition for dissolution removal of Patent Document 1 contains a reducing agent and a surfactant in addition to the dissolution removal agent. [Prior Technical Literature] [Patent Literature]

[Patent Document 1] JP 2015-105412 A

[The problem to be solved by the invention]

The cleaning using the composition for dissolving and removing of Patent Document 1 improves the solubility of scales by a reducing agent, and the metal ions dissolved in the cleaning liquid are removed by the action of the dissolving and removing agent. For example, in the cleaning object where the fouling (Fe ₃ O ₄ ) 11 covers the surface of the base material (Fe) 10, the reducing agent R can promote the reduction of the fouling (Fe ₃ O ₄ ) and dissolve in the wash as Fe ²⁺ In the clean liquid (refer to the dotted line in Figure 4). The surface active agent (inhibitor 12) is adsorbed on the surface of the base material 10 after the fouling is removed to improve the corrosion resistance of the metal (base material 10) (refer to FIG. 5).

In the cleaning using a composition for dissolving and removing containing a reducing agent, when there is oxygen in the cleaning environment, the reducing agent will disappear due to the oxygen (oxidizing agent), thereby impairing the reducibility of the cleaning liquid, so it is accumulated The scale solubility will be lower (refer to the x mark in Figure 4). Therefore, the cleaning using the composition for dissolution and removal containing a reducing agent is desirably performed in a reducing environment (in a non-oxidizing environment).

Oxygen is contained in the gas phase part coexisting with the cleaning liquid in the cleaning object. In the conventional cleaning, an inert gas such as nitrogen is used to replace the gas phase part of the cleaning object, and the cleaning is performed after creating an oxygen-free (oxidant) environment. However, even if the gas phase is replaced by an inert gas, if the switch is turned on without warning, oxygen may enter the cleaning object from here, so it is more robust than oxygen (oxidizing environment) during cleaning. Sex becomes an issue. The operation of replacing with inert gas is one of the operations that accounts for a higher proportion of the work and construction cost, and from the viewpoint of operator safety, the use of nitrogen, etc. is not ideal.

Therefore, it is hoped that the operation of removing the oxidant (oxygen) in the environment can be changed, and it can correspond to the environment in which oxygen remains (not replaced by inert gas) or the environment in which oxygen invades the system (not in the airtight containing the coexisting gas phase part) The cleaning in the space is the cleaning work under the environment where the cleaning system is open to the atmosphere.

In addition, in the process of dissolving and removing the deposits containing metal oxides attached to the metal surface, especially the cleaning of conductive deposits, there are 10 parts of base material due to the dissolution process of the deposits or the defects of the deposits. When exposed and formed the exposed portion 13 as shown in FIG. 6. On the cleaning target where the exposed portion 13 has been formed, the reduction of oxygen on the conductive deposit 11 and the oxidation (corrosion) of the base material 10 in the exposed portion 13 will not be excessive or insufficient. The ongoing battery mechanism (corrosion macrocell). At this time, the exposed portion 13 of a narrow area will receive concentrated oxygen reduction current that reacts on a wide area of fouling, and a corrosion current above the performance limit of the surfactant (inhibitor 12) will flow out. Thereby, the effect of the added surfactant (inhibitor 12) becomes difficult to be effective, and the exposed portion 13 may undergo galvanic corrosion (galvanic corrosion).

The present disclosure was made in view of this situation, and its purpose is to provide a composition for dissolving and removing and a cleaning method that can inhibit the corrosion of the base material and dissolve and remove the scale even when oxygen remains. [Means to solve the problem]

In order to solve the above-mentioned problems, the composition for dissolution and removal and the cleaning method of the present disclosure adopt the following means.

The present disclosure provides a composition for dissolution and removal, which contains a main agent, a first reducing agent and a second reducing agent; the main agent dissolves and removes deposits containing metal oxides attached to the base material, and the first reduction The agent is an organic acid having oxygen reducing properties, and the second reducing agent is at least one selected from a thiourea compound, a thiourea dioxide compound, a thioglycolate, and a dithionite.

In the composition for dissolution and removal of the present disclosure, since the first reducing agent is reducing oxygen and the second reducing agent is reducing metal oxides to increase the solubility of scales, it is possible to dissolve and remove scales with the main agent. The oxygen-reducing organic acid of the first reducing agent has high oxygen consumption ability even in the coexistence of metal oxides. By using such an organic acid in combination with the second reducing agent, even if there is oxygen in the open atmosphere, the second reducing agent can be suppressed from being consumed by oxygen. In addition, based on the results of the review conducted by the inventors of the present application, it was found that by using the first reducing agent and the second reducing agent together, the corrosion of the base material to be cleaned can also be suppressed.

One aspect of the foregoing disclosure further comprises an inhibitor, which is selected from alkali metal salts having a thiol group (-HS), a thiocyanate group (-SCN) or a thiol group (NaS-, KS-, LiS-) at least one of the sulfur organic compounds.

The above-mentioned sulfur organic compound has a strong ability to adsorb metals and can be adsorbed on the surface of the base material on a narrow part such as an exposed part. This can suppress galvanic corrosion.

The composition for dissolution and removal of one aspect disclosed above further includes an amphoteric surfactant and a nonionic surfactant.

The specific amphoteric surfactant will be adsorbed on the surface of the metal (base material) to be cleaned in the hydrophobic part, but will not be easily adsorbed on the fouling surface. Therefore, the dissolution and removal of residual fouling will not be hindered, thereby protecting the metal surface from which fouling is dissolved and removed. The nonionic surfactant will enter the gap between the metal surface and the amphoteric surfactant to form a high-volume and stronger protective film. In this way, high corrosion resistance can be achieved.

In one aspect of the above disclosure, the aforementioned organic acid is preferably ascorbic acid or erythorbic acid.

Compared with thiourea-based compounds, thiourea dioxide-based compounds, thioglycolate and disulfinate, the above-mentioned organic acids are relatively inexpensive. By using such an organic acid to consume oxygen, the consumption of the second reducing agent (thiourea compound, thiourea dioxide compound, thioglycolate and disulfinate) due to oxygen can be suppressed. Thereby, the cleaning cost can be reduced.

In one aspect of the above disclosure, the aforementioned second reducing agent may be thiourea or thiourea dioxide.

In one aspect of the above disclosure, the main agent is preferably selected from amino carboxylic acids, phosphonic acids, and salts thereof.

The present disclosure provides a cleaning method, which is a method of cleaning a cleaning object containing metal oxide deposits attached to a base material, and it is cleaned with a main agent and a first reducing agent for a predetermined time , And then wash with a second reducing agent; the main agent is to dissolve and remove the deposits containing metal oxides of the cleaning object, the first reducing agent is an organic acid with oxygen reducing properties, and the second reducing agent is At least one selected from the group consisting of thiourea-based compounds, thiourea dioxide-based compounds, thioglycolate and disulfinate.

The second reducing agent is a component with fouling solubility. Before washing with the second reducing agent, by using the first reducing agent with oxygen reducing properties to consume oxygen, even in an open atmosphere, it can still suppress the oxygen consumption that hinders the dissolution of the scale of the second reducing agent Reduction reaction, and can maintain the solubility of fouling. By reducing the oxygen in advance by the first reducing agent, it is possible to suppress the corrosion of the exposed base material surface due to oxidation by removing the fouling with the second reducing agent.

In one aspect of the above disclosure, after washing and dissolving the object to be removed with the second reducing agent, the exposed base material is brought into contact with an inhibitor; the inhibitor is selected from the group having thiol groups (-HS), sulfur At least one kind of sulfur organic compound of any one of cyanate group (-SCN) or thiol group alkali metal salt (NaS-, KS-, LiS-).

The above-mentioned sulfur organic compound has a strong ability to adsorb metals, and can be adsorbed on the surface of the base material on a narrow part such as an exposed part. This can suppress galvanic corrosion. [Effects of Invention]

According to the present disclosure, by using the first reducing agent and the second reducing agent in combination, it becomes a dissolving and removing composition and a cleaning method that can suppress the corrosion of the base material and dissolve and remove scales even in a state where oxygen remains.

Hereinafter, one embodiment of the composition for dissolution and removal of the present disclosure and the cleaning method using the same will be described with reference to the drawings.

The composition for dissolution and removal of this embodiment contains (A) a main agent, (B) a first reducing agent, (C) a second reducing agent, and (D) an inhibitor.

(A) The main agent is a dissolving and removing agent that can remove scales containing metal oxides such as rust. Examples of components of the dissolution removing agent include chelating agents and organic acids capable of chelating and capturing ions (for example, Fe ions) to be dissolved.

As the chelating agent, it is appropriate to select components that exhibit reducibility to iron complexes and iron salts formed by the iron oxide scale dissolution reaction. Chelating agents are amino carboxylic acids and their salts or phosphonic acids and their salts. For example, the amino carboxylic acids are, for example, nitrilotriacetic acid, ethylenediaminetetraacetic acid, ethylenetriaminepentaacetic acid, and ethylenetetraminehexaacetic acid. For example, phosphonic acids are phosphonic acid, amino ginseng (methylene phosphonic acid), 1-hydroxyethane-1,1-diphosphonic acid, ethylene diamine (methylene phosphonic acid), hexamethylene bis Amine 4 (methylene phosphonic acid), ethylenetetramine (methylene phosphonic acid), and 2-phosphinobutane-1,2,4-tricarboxylic acid, etc. These chelating agents may be used individually by 1 type, and may use 2 or more types together.

Organic acids are, for example, dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, decane-1,10-dicarboxylic acid, and , Diglycolic acid (diglycolic acid), thiodiglycolic acid (thiodiglycolic acid), oxalic acid, oxydisuccinic acid (oxydisuccinic acid), carboxymethyloxysuccinic acid (Carboxymethyloxysuccinic acid), carboxymethyl Carboxymethyltartronic acid, and their salts, malic acid, tartaric acid, citric acid, itaconic acid, methyl succinic acid, 3-methylglutaric acid, 2,2-dimethylmalonic acid Acid, maleic acid, fumaric acid, 1,2,3-propanetricarboxylic acid, aconitic acid, 3-butene-1,2,3-tricarboxylic acid, butane-1,2,3,4- Tetracarboxylic acid, ethane tetracarboxylic acid, ethylene tetracarboxylic acid, n-alkenyl aconitic acid, 1,2,3,4-cyclopentane tetracarboxylic acid, phthalic acid, trimesic acid, trimellitic acid ( hemimellitic acid), pyromellitic acid, mellitic acid, tetrahydrofuran-1,2,3,4-tetracarboxylic acid, tetrahydrofuran-2,2,5,5-tetracarboxylic acid, and their salts. As these organic acids, one type may be used alone, or two or more types may be used in combination.

The compounding amount of the main agent is from the viewpoint of removing the scale containing metal oxides and inhibiting the corrosion of the metal base material, relative to the total mass of the composition for dissolving and removing 0.1 mass% to 40 mass%, and 0.5 mass% to 20 Mass% or less is preferable, and 1 mass% or more and 10 mass% or less are more preferable. If it is less than 0.1% by mass, the solubility of fouling becomes insufficient (refer to Comparative Example 7 described below). If it exceeds 40% by mass, the corrosion resistance becomes insufficient (refer to Comparative Example 8 described below).

Furthermore, the (A) main agent may also include various alkali metal hydroxides such as potassium hydroxide. (A) The main agent may also include inorganic acids and inorganic acid salts such as hydrochloric acid, sulfuric acid and their salts.

(B) The first reducing agent is an organic acid having oxygen reducing properties. The first reducing agent is preferably a component having excellent oxygen removal properties and durability. Examples of such organic acids include ascorbic acid and erythorbic acid.

The compounding quantity of the first reducing agent is from the viewpoint of removing the deposits containing metal oxides and inhibiting the corrosion of the metal base material, relative to 100 parts by mass of the main agent, 0.025 parts by mass to 8000 parts by mass, and 0.5 parts by mass to 1000 parts by mass It is preferable that it is 5 parts by mass or more and 300 parts by mass or less. The compounding amount of the first reducing agent is 0.01% by mass to 8% by mass relative to the total mass of the composition for dissolution and removal, preferably 0.1% by mass to 5% by mass, and preferably 0.5% by mass to 3% by mass the following. If it is less than 0.01% by mass, the solubility of fouling becomes insufficient (refer to Comparative Example 12 described below). If it exceeds 8% by mass, the corrosion resistance becomes insufficient (refer to Comparative Example 13 described below).

(C) The second reducing agent has reducibility of fouling components. Examples of such a second reducing agent include thiourea-based compounds, disulfinates, and thioglycolates. The thiourea compound is thiourea dioxide, formamidine thiourea, and the like. The second reducing agent promotes the dissolution of fouling components by its reducing action. In addition, the sulfur atoms contained in the second reducing agent are adsorbed on the metal to strengthen the protective film.

The compounding amount of the second reducing agent is 0.0025 parts by mass or more and 1000 parts by mass or less relative to 100 parts by mass of the main agent, preferably 0.05 parts by mass or more and 20 parts by mass or less, and preferably 0.2 parts by mass or more and 8 parts by mass or less. The compounding amount of the second reducing agent is 0.01% by mass to 1% by mass relative to the total mass of the composition for dissolution and removal, preferably 0.01% by mass to 0.1% by mass, preferably 0.02% by mass to 0.08% by mass the following. If it is less than 0.01% by mass, the solubility of fouling becomes insufficient (refer to Comparative Example 10 described below). If it exceeds 1% by mass, the corrosion resistance becomes insufficient (refer to Comparative Example 11 described below).

(D) The inhibitor includes a sulfur organic compound having a thiol group (-HS), a thiocyanate group (-SCN) or an alkali metal salt (NaS-, KS-, LiS-) of a thiol group. As a countermeasure for galvanic corrosion, it is advisable to select sulfur organic compounds with strong adsorption to iron as inhibitors. Examples of such organic compounds include 2,5-dithioacetic acid-1,3,4-thiadiazole, 2-thioacetic acid-5-mercapto-1,3,4-thiadiazole, 2 ,5-Dimercapto-1,3,4-thiadiazole, mercaptobenzothiazole, mercaptobenzimidazole, 2,4,6-trimercapto-S-triazine, 2-dibutylamino-4, 6-dimercapto-S-triazine, 2-anilino-4,6-dimercapto-S-triazine, 3-mercapto-1-propane sulfonic acid, 1-thioglycerol, 2-aminothiophenol , 4-aminothiophenol, thiobenzoic acid, glycerol-monothioglycolate, β-mercaptopropionic acid, β-thioglycolic acid, β-mercaptomaleic acid, β-mercaptomalic acid, P-hydroxysulfide Phenol, thiosalicylic acid, thioterephthalic acid, 2-mercaptoethanol, mercaptophenol, thioacetic acid, α-mercaptotoluene, sodium thiocyanate, potassium thiocyanate, lithium thiocyanate, ammonium thiocyanate, Sodium dimethyldithiacarbamate, sodium diethyldithiacarbamate, etc. The above-mentioned sulfur organic compound has a high adsorption force to the metal surface.

The compounding amount of the sulfur organic compound is 0.0025 parts by mass or more and 1000 parts by mass or less relative to 100 parts by mass of the main agent, preferably 0.05 parts by mass or more and 20 parts by mass or less, preferably 0.25 parts by mass or more and 5 parts by mass or less. The compounding amount of the sulfur organic compound is 0.001% by mass to 1% by mass relative to the total mass of the composition for dissolution and removal, preferably 0.005% by mass to 0.1% by mass, and preferably 0.01% by mass to 0.05% by mass. . If it is less than 0.001% by mass, the corrosion resistance becomes insufficient (refer to Comparative Example 14 described below).

(D) The inhibitor system preferably further contains an amphoteric surfactant and a nonionic surfactant.

As amphoteric surfactants, for example, 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine, 2-alkyl-N-carboxyethyl-N-hydroxyethylimidazoline Onium betaine, and alkali metal salts of β-alkylamino carboxylic acids (for example, sodium β-alkylaminopropionate). As the amphoteric surfactant, one type may be used alone, or two or more types may be used in combination. Since the amphoteric surfactant has a carboxylic acid group and a nitrogen atom, the amphoteric surfactant becomes adsorbed on the surface of the metal base material by these substituents, but is not easily adsorbed on the surface of rust and scale. Thereby, it becomes possible to further improve the performance of dissolving and removing rust and scale, and at the same time, the corrosion resistance of the metal base material can be further improved.

The blending amount of the amphoteric surfactant is 0.01 part by mass to 1000 parts by mass relative to 100 parts by mass of the main agent, preferably 0.05 part by mass to 750 parts by mass, and preferably 0.1 part by mass to 500 parts by mass. The blending amount of the amphoteric surfactant is 0.001% by mass to 10% by mass relative to the total mass of the composition for dissolution and removal, preferably 0.005% by mass to 5% by mass, and preferably 0.01% by mass to 2% by mass the following.

Examples of nonionic surfactants include polyoxyalkylene glycol fatty acid esters, polyalkylene glycol fatty acid esters, and polyoxyalkylene alkyl ethers. As the nonionic surfactant, one type may be used alone, or two or more types may be used in combination. For example, from the viewpoint of removing scales containing metal oxides and inhibiting the corrosion of metal base materials, nonionic surfactants are based on polyethylene glycol monooleate, polyethylene glycol monolaurate and polyethylene glycol mono Stearate is ideal.

The blending amount of the nonionic surfactant is 0.01 parts by mass to 500 parts by mass relative to 100 parts by mass of the main agent, preferably 0.05 parts by mass to 400 parts by mass, and preferably 0.1 parts by mass to 300 parts by mass. The blending amount of the non-ionic surfactant is 0.001% by mass to 10% by mass relative to the total mass of the composition for dissolution and removal, preferably 0.005% by mass to 5% by mass, preferably 0.01% by mass to 2% by mass %the following.

The pH of the composition for dissolution and removal is preferably 5-8. The pH system can be adjusted with potassium hydroxide (KOH) or the like.

(Method for manufacturing composition for dissolution and removal) Next, the manufacturing method of the composition for dissolution and removal of this embodiment is demonstrated. The manufacturing method of the composition for dissolution and removal of this embodiment is not specifically limited. As a method of producing the composition for dissolution and removal, for example, a main agent, a first reducing agent, a second reducing agent, an amphoteric surfactant, and an amphoteric surfactant can be added in order to water such as pure water or distilled water at room temperature. And each component such as a nonionic surfactant is mixed, KOH etc. are added, pH is adjusted to the range of 5-8, and it is manufactured.

The composition system for dissolution and removal of this embodiment can be used in a nitrogen environment or an atmospheric environment, so it can be manufactured in an atmospheric environment.

The composition system for dissolution and removal of the present embodiment can also be prepared by supplying water to the boiler and simultaneously adding and mixing the components in order to a part of the supply piping.

(Washing method) When water is supplied to the boiler and the components are added sequentially to a part of the supply piping to prepare the composition for dissolution and removal, the first reducing agent is introduced to reduce the oxygen in the system, and then the second reducing agent is introduced to reduce the product. Scale is fine. After the first reducing agent is added, in this embodiment, the dissolved oxygen can be reduced in about 0.5 to 1 hour, for example.

The thiourea-based compound, thiourea dioxide-based compound, disulfinate or thioglycolate salt of the second reducing agent have both iron oxide reducing ability and oxygen reducing ability. Under the single use of the second reducing agent, since the oxygen reduction rate is faster, the second reducing agent will be consumed by the dissolved oxygen before the iron oxide is reduced, and the amount of reducing agent used to dissolve the iron oxide will be reduced. This embodiment uses organic acids such as ascorbic acid, which do not have the ability to dissolve scales, as the first reducing agent, and is added before the second reducing agent, thereby suppressing the effect of the second reducing agent from interacting with oxygen. The solubility of fouling produced by the reaction and being consumed is reduced.

The cleaning system is ideally performed in a neutral environment (pH 5 to 8). The cleaning system can be performed at room temperature (15 to 55°C) or high temperature (60 to 90°C). The composition system for dissolving and removing can be circulated in the washing system, or can be made into static washing (swing blow). In addition, the washing time depends on the characteristics and amount of fouling. For example, in the case of 10 to 20 mg/cm ² of the fouling layer attached with magnetite (Fe ₃ O ₄ ), it is better to wash for 20 to 100 hours.

In the construction of the chemical cleaning work during the cyclic cleaning, it takes time to put the cleaning solution (composition for dissolving and removing) into the cleaning system through each process (circulation and simultaneous input). Therefore, by filling the washing system with water, adding the first reducing agent and then adding the second reducing agent, the addition of the reducing agent can be minimized both on the price side and on the addition side.

The composition for dissolution and removal of the present embodiment and the cleaning method are suitable for removing iron-based deposits (especially rust) attached to piping of power plants and the like. The composition for dissolution and removal of this embodiment and the cleaning method using it can also be widely used to remove iron-based oxides and/or adhering to heat exchangers of power plants or chemical plants and cooling jackets of internal combustion engines. hydroxide.

Next, the basis for the selection of the components in the composition for dissolution and removal will be explained.

<Test 1: Reduction and dissolution ability of iron oxide> In the composition for dissolution and removal of the above-mentioned embodiment, a component having the ability to reduce and dissolve scale is essential. Therefore, choose reagents that can stably dissolve in the main agent, and the redox potential of the cleaning solution when combined will be below -200mV vs SSE, and confirm the reductive solubility of iron oxide for these reagents.

In the degassed water, put hematite (Fe ₂ O ₃ ) or magnetite (Fe ₃ O ₄ ) powder reagent (calculated as Fe (as Fe) about 5500ppm) as the iron oxide main component Fouling, and any one of reagent a to g (equal molar amount relative to iron oxide, 2.9×10 ^-4 mol/L), seal the gas phase with N ₂ gas, and stir slowly at 40°C After 12 hours, measure the Fe concentration in the degassed water.

The results are shown in Table 1.

From the results of test 1, it was confirmed that thiourea dioxide, sodium dithionite, and ammonium thioglycolate were effective in reducing and dissolving iron oxide. Moreover, although not shown in Table 1, it has been confirmed in other tests that neither erythorbic acid nor hydrazine has the reductive dissolution ability of iron oxide.

<Test 2: Dissolved oxygen consumption capacity in liquid> In the composition for dissolution and removal of the above-mentioned embodiment, a component having oxygen reduction ability is essential. Therefore, the oxygen reduction ability of the reagents a to g selected above was confirmed.

Put any one of reagent a to g (2.9×10 ^-4 mol/L) in ion-exchanged water (oxygen concentration 8ppm), and in the presence of oxygen in an open atmosphere, stir slowly at 40℃. Time, measure the oxygen concentration of ion exchange water.

The results are shown in Table 2.

From the results of Test 2, it was confirmed that ascorbic acid, sodium disulfinate, thiourea dioxide, and ammonium thioglycolate are effective for the consumption of dissolved oxygen. Although not shown in Table 2, erythorbic acid is equivalent or more effective to the consumption of dissolved oxygen as ascorbic acid.

According to the above results, sodium disulfinate, thiourea dioxide and ammonium thioglycolate are reducing agents with iron oxide reduction ability and oxygen consumption ability. Ascorbic acid and erythorbic acid are reducing agents with oxygen consumption ability but not iron oxide reduction ability. .

<Test 3: Base material corrosion resistance> Add reducing agent, inhibitor, and iron oxide to a 20% by mass aqueous solution of phosphonic acid, and make the base material (low alloy steel STBA23, surface area 26cm ² ) coexist, and open the atmosphere at 40°C After standing for 20 hours, the iron oxide reduction ability and the base material corrosion resistance were evaluated. STBA23 is a kind of alloy steel pipe, and it is a specification material (iron steel material containing chromium molybdenum steel, JIS stipulates Rockwell hardness (HRB) in the heat exchanger of the boiler or the heat exchanger of the equipment constituting the machine, etc. ) Below 85).

Use the following as reducing agents. Comparative example 1: Sodium disulfinate 0.05% by mass Example 1: Sodium disulfinate 0.05% by mass + ascorbic acid 2.0% by mass Example 2: Thiourea dioxide 1.0% by mass + ascorbic acid 2.0% by mass

A commercially available product A (Ibit No. 30AR, a product of Asahi Chemical Industry Co., Ltd., 0.5% by mass) was used as the inhibitor. As a powder reagent of iron oxide, 1500ppm of hematite is added as Fe, and 13500ppm of magnetite is added as Fe.

The results are shown in Table 3.

As a result of Test 3, although the corrosion of the base material progressed in Comparative Example 1, the corrosion of the base material in Examples 1 and 2 was significantly suppressed. From this, it can be confirmed that by using a reducing agent with iron oxide reducing ability in combination with an organic acid with oxygen reducing ability, even in the presence of oxygen in an open atmosphere, the iron oxide reducing ability can still be maintained, and the precursor can be reduced. Material corrosion.

<Test 4: Inhibitor-Corrosion Inhibition Contribution> It is desirable that the composition system for dissolution and removal of the above-mentioned embodiment can stably prevent corrosion of the base material in an open atmosphere. Therefore, review the inhibitors that can inhibit the corrosion of base materials even in the presence of oxygen in an open atmosphere.

Add 1000 ppm of inhibitor candidates Ia to In to a 20% by mass aqueous solution of phosphonic acid (with no added reducing agent), and after standing for 24 hours in an atmospheric environment, evaluate the atmospheric environment by electrochemical measurement (normal polarization measurement) Corrosion resistance below. The working electrode is made of low alloy steel STBA23 (1cm ² ) as the base material, the opposite electrode is made of Pt, and the control electrode is made of SSE. Usually, the conditions of polarization measurement are set as reduction scan→oxidation scan, scan speed 1mV/sec, cut-off current 3mA/cm ² .

Inhibitor candidates use the following reagents. I-a: Amphoteric Surfactant A I-b: Non-ionic surfactant A (polyoxyalkylene glycol fatty acid esters) I-c: Sulfur compound (formamidine thiourea) I-d: Fatty acid (oleic acid series) I-e: Cationic surfactant A (lauryl trimethyl ammonium chloride series) I-f: Cationic surfactant B (stearyl trimethylammonium chloride) I-g: Nonionic Surfactant B (Ethylene oxide adduct series of alkylphenol) I-h: Non-ionic surfactant C (Ethylene oxide adduct series of alkylphenol) I-i: Amphoteric surfactant B (palm oil fatty acid amidopropyl betaine) I-j: Sulfur organic compounds (mercaptobenzothiazole series) I-k: Amine A (Triethanolamine series) I-1: Amine B (2-amino-methyl-1-propanol series) I-m: Amine C (monoisopropanolamine series) I-n: Inorganic materials (sodium nitrite series)

The results are shown in Table 4.

From the results of Test 4, it can be confirmed that even in an open atmosphere, Ib (nonionic surfactant A) and Id (fatty acid) can still inhibit the oxidation reaction, and Ia (amphoteric surfactant A) can still inhibit the reduction reaction. , Ic (sulfur compound A) and Ij (sulfur organic compound) can still greatly inhibit both oxidation and reduction reactions.

<Test 5: Combination of inhibitors> Reducing agent, inhibitor, and iron oxide were added to a 20% by mass aqueous solution of phosphonic acid, and the base material (low alloy steel STBA23, surface area 26cm ² ) coexisted, and at 40°C under open air After standing for 20 hours, the corrosion resistance of the base material was evaluated.

The reducing agent used thiourea dioxide (1.0% by mass). The inhibitors were made into the combination and the amount shown in Table 5. As a powder reagent of iron oxide, 1500ppm of hematite based on Fe and 13500ppm of magnetite based on Fe were added.

The results are shown in Table 5.

As a result of Test 5, in Examples 3 to 6 containing I-j (sulfur organic compound), corrosion was particularly suppressed. When comparing Examples 3 and 4 with Samples 5 and 6, there is no difference in corrosion rate regardless of the presence or absence of I-c (sulfur compound A).

<Experiment 6: Observation of the cleaned surface> Add reducing agent and inhibitor to a 20% by mass aqueous solution of phosphonic acid, and make the test substance coexist (liquid ratio is 3ml/cm ² ), and the gas phase part is made into a closed environment for coexistence of atmosphere After slowly stirring for 100 hours at 40°C, the cross-section of the test body was observed with a microscope.

The test system uses the actual mechanical tube of the boiler (with an attached scale of 10 to 15 mg/cm ² ).

The results are shown in Figures 1 to 3 and Table 6.

Figure 1 is a cross-sectional photograph of the test body of Comparative Example 7. 2 is a cross-sectional photograph of the test body of Example 7. 3 is a cross-sectional photograph of the test body of Example 8. In Figures 1 to 3, the whiter part on the right side of the paper is the test body (base material 10), and the darker part on the left side of the paper is the resin material. In the sample 3 shown in FIG. 3 that does not contain sulfur organic compounds, a plurality of small black holes 14 that should be caused by the corrosion of the macro cell are observed on the surface of the base material 10 (exposed portion 13). In the samples shown in Figures 1 and 2 containing sulfur organic compounds, no localized corrosion was observed on the surface of the base material.

<Test 7: Sulfur organic compounds>

A reducing agent and an inhibitor were added to the main agent, and the test sample was allowed to coexist. The gas phase part was made into a closed atmosphere coexisting with the atmosphere, and after slowly stirring at 40°C for 30 hours, the scale removal performance and the base material corrosion resistance were evaluated.

Main agent: 1-hydroxyethane-1,1-diphosphonic acid (HEDP) 7 mass% Reducing agent: sodium disulfinate 0.05 mass% + ascorbic acid 2 mass% Inhibitor: amphoteric surfactant A 0.2 mass% + Sulfur organic compound (A, B or C) 0.02% by mass or sulfur-free organic compound Sulfur organic compound A: 2,5-Dimercapto-1,3,4-thiadiazole sodium sulfur organic compound B: 2,4, 6-Trimercapto-S-triazine monosodium sulfur organic compound C: 2-Dibutylamino-4,6-dimercapto-S-triazine monosodium Test body: actual mechanical tube of the boiler (attached to the amount of fouling 10 to 15mg/cm ² )

The results are shown in Table 7.

As a result of Test 7, in the case of adding sulfur organic compounds (Examples 9 to 11), the scale solubility and base material corrosion resistance can be obtained regardless of the type. On the other hand, in the case where the sulfur organic compound was not added (Comparative Example 8), the corrosion resistance of the base material could not be obtained.

<Test 8: Interaction between reducing agent and inhibitor> The main agent (1-hydroxyethane-1,1-diphosphonic acid 7% by mass) of diphosphonic acid was made into a 1% by mass aqueous solution and put into the reducing agent and inhibitor , And make the test body coexist (liquid ratio is 3ml/cm ² ), make the gas phase part into a N ₂ sealed or air coexisting airtight environment, stir slowly at 40 ℃ for 100 hours, evaluate the fouling removal performance and base material Corrosion resistance.

The test system uses the actual mechanical tube of the boiler (attached fouling amount 10-15mg/cm ² ) and the base material STBA23 (surface area 26cm ² ). Regarding the removal of fouling, the residual amount of fouling after the test was visually judged. Regarding the corrosion resistance of the base material, the corrosion rate is calculated and evaluated from the difference between the iron concentration after the test and the ideal iron concentration when the scale is completely dissolved.

The results are shown in Table 8.

From the results of Test 8, it can be confirmed that there is almost no difference between Comparative Example 9 and Examples 12 and 13 in the scale removal performance and the base material corrosion resistance under the N ₂ sealed environment. However, in an atmosphere coexisting environment, compared with Comparative Example 9, Examples 12 and 13 are superior in scale removal performance and base material corrosion resistance.

<Test 9: pH of the composition for dissolution and removal> Add reducing agent and inhibitor to the main agent, make the test body coexist, and adjust the pH with KOH. The gas phase part was made into a closed environment where the atmosphere coexisted, and after slowly stirring at 40°C for 30 hours, the fouling removal performance and the base material corrosion resistance were evaluated.

Main agent: 1-hydroxyethane-1,1-diphosphonic acid (HEDP) 7 mass% Reducing agent: sodium disulfinate 0.05 mass% + ascorbic acid 2 mass% Inhibitor: amphoteric surfactant A 0.2 mass% +2,5-Dimercapto-1,3,4-thiadiazole sodium 0.02% by mass Test body: actual mechanical tube of the boiler (10-15 mg/cm ^{2 of} attached scale)

The results are shown in Table 9.

As a result of Test 9, when the pH is low, the corrosion resistance of the base material cannot be obtained, and when the pH is high, the fouling solubility cannot be obtained. It can be confirmed that the composition for dissolution and removal of the present embodiment has a pH suitable for obtaining scale solubility and base material corrosion resistance.

<Test 10: Difference in the solubility of fouling caused by the presence or absence of the first reducing agent> The main agent (1-hydroxyethane-1,1-diphosphonic acid 7% by mass) of bisphosphonic acid was made into a 1% by mass aqueous solution. Reducing agent and inhibitor are coexisted with the test substance (liquid ratio is 3ml/cm ² ), and the pH is adjusted to 5.5 with KOH. The gas phase part was made into a closed environment with air coexisting, and after slowly stirring at 40°C for 100 hours, the fouling removal performance was evaluated. The reducing agent is the input of the first reducing agent and the second reducing agent, or only the second reducing agent.

Test body: Boiler actual mechanical pipe (10-15 mg/cm ^{2 of} attached scale) First reducing agent: Ascorbic acid 0.1% by mass Second reducing agent: Sodium disulfite 0.3% by mass Inhibitor: Amphoteric surfactant A0 .1% by mass

The residual amount of fouling after the test was confirmed visually, and the fouling on the surface of the test body with the first reducing agent (ascorbic acid) was almost completely removed. On the other hand, on the test body without the first reducing agent, more than half of the surface area remained fouling.

According to the results of the above test 1, ascorbic acid does not have the reducing and dissolving ability of iron oxide. According to this test, although the input amount of the second reducing agent with the reducing and dissolving ability of iron oxide is the same, there will be a difference in the residual amount of fouling with or without the input of the first reducing agent. It is considered that the test body without the first reducing agent is not consumed because the oxygen contained in the gas phase part is not consumed by the first reducing agent, so the second reducing agent will be consumed due to the reaction with oxygen, and fouling The solubility decreases, and as a result, the remaining amount of fouling increases.

10: Base material 11: fouling 12: inhibitor 13: Exposed part 14: hole

[Figure 1] A cross-sectional photograph of the test body of Comparative Example 7. [Figure 2] A cross-sectional photograph of the test body of Example 7. [Figure 3] A cross-sectional photograph of the test body of Example 8. [Figure 4] A conceptual diagram illustrating the use of detergent to remove scales. [Figure 5] A conceptual diagram illustrating the use of detergent to remove scale. [Figure 6] A conceptual diagram illustrating the use of detergent to remove scale.

Claims (8)

A composition for dissolution and removal, which contains a main agent, a first reducing agent and a second reducing agent; The main agent dissolves and removes the deposits containing metal oxides attached to the base material, The first reducing agent is an organic acid with oxygen reducing properties, The second reducing agent is at least one selected from the group consisting of thiourea-based compounds, thiourea dioxide-based compounds, thioglycolate and disulfinate. Such as the composition for dissolution and removal of claim 1, which further contains an inhibitor, and the inhibitor is selected from alkali metal salts having thiol groups (-HS), thiocyanate groups (-SCN) or thiol groups (NaS -, KS-, LiS-) at least one of sulfur organic compounds. For example, the composition for dissolution and removal of claim 1 or 2, which further contains an amphoteric surfactant and a nonionic surfactant. The composition for dissolution and removal of claim 1 or 2, wherein the aforementioned organic acid is ascorbic acid or erythorbic acid. According to the composition for dissolution and removal of claim 1 or 2, wherein the aforementioned second reducing agent is thiourea or thiourea dioxide. According to the composition for dissolution and removal of claim 1 or 2, wherein the aforementioned main agent is selected from the group consisting of amino carboxylic acids, phosphonic acids, and salts thereof. A cleaning method, which is a method of cleaning a cleaning object containing metal oxide deposits attached to a base material, and after cleaning with a main agent and a first reducing agent for a predetermined time, then Wash the second reducing agent; The main agent is to dissolve and remove the deposits containing metal oxides of the aforementioned cleaning object, The first reducing agent is an organic acid with oxygen reducing properties, The second reducing agent is at least one selected from the group consisting of thiourea-based compounds, thiourea dioxide-based compounds, thioglycolate and disulfinate. The cleaning method of claim 7, wherein after the object is washed and dissolved with the second reducing agent, the exposed base material is brought into contact with the inhibitor; The inhibitor is a sulfur organic compound selected from any one of alkali metal salts (NaS-, KS-, LiS-) with thiol group (-HS), thiocyanate group (-SCN) or thiol group At least one.

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