JP2023006495A - Dissolution removal composition and cleaning method using the same - Google Patents

Abstract

To provide a dissolution removal composition capable of removing a scale in a shorter time more than ever, in cleaning of dissolution removal of a scale containing a metal oxide, and a cleaning method.SOLUTION: A dissolution removal composition includes: a main agent for dissolving and removing scales containing metal oxides attached to a base material; a base material reactant-generating component that reacts with the base material to generate a reactant; and a base material reactant dissolving component that dissolves and removes the reaction product. In cleaning using this dissolution removal composition, the scales can be peeled and removed from the base material side while dissolving and removing the scales from a surface side.SELECTED DRAWING: Figure 7

Description

The present disclosure relates to a dissolution removal composition and a cleaning method using the same.

In a heat transfer tube of a steam power plant or the like, scale mainly composed of iron oxide (Fe ₂ O ₃ , Fe ₃ O ₄ , etc.) adheres to the inner surface during operation. When scale grows due to operation for a certain period of time, there is a possibility of damage caused by an increase in the differential pressure of the fluid flowing through the heat transfer tube, a decrease in heat transfer efficiency, and an excessive rise in the metal temperature of the heat transfer tube due to heat transfer inhibition. be.

In order to prevent the occurrence of such troubles, changes in the amount of scale such as iron oxide adhered are investigated during maintenance and inspection, and chemical cleaning is performed periodically to remove scale such as iron oxide.

Patent Literature 1 discloses a method of dissolving and removing scale such as iron oxide adhering to a base material using a cleaning liquid containing metal oxide as a main agent for dissolving scale.

The dissolving-removing composition (cleaning liquid) described in Patent Document 1 can dissolve and remove both hematite (Fe ₂ O ₃ ) and magnetite (Fe ₃ O ₄ ) scales. Magnetite is an autoxidized scale, and hematite is a powder scale generated by oxygen treatment in boiler water supply management.

JP 2020-84304 A

In Patent Document 1, the concept is to gradually dissolve and remove the scale from the surface side, so it takes time to dissolve and remove the scale. For example, washing at 40° C. takes about 100 hours.

The present disclosure has been made in view of such circumstances, and provides a dissolution-removing composition and a cleaning method that can remove scales in a shorter time than before in cleaning for dissolving and removing scales containing metal oxides. intended to

In order to solve the above problems, the dissolution removal composition of the present disclosure and the cleaning method using the same employ the following means.

The present disclosure comprises a main agent for dissolving and removing scales containing metal oxides adhering to a base material, a base material reaction product-generating component for reacting with the base material to generate a reaction product, and a base material for dissolving and removing the reaction product. and a material reactant dissolving component.

The present disclosure is a method for cleaning an object to be cleaned including a base material to which scales containing metal oxides are attached, wherein the object to be cleaned is cleaned with a cleaning solution containing a main agent, a base material reactant-generating component, and a base material reactant-dissolving component. washing to dissolve and remove at least a portion of the scale from the base material with a base material; reacting a base material reactant-producing component with the base material to form a reactant between the base material and the scale; A cleaning method is provided in which the reactant is dissolved away by a material reactant dissolving component.

In the above disclosure, in addition to dissolving and removing at least a portion of the scale from the scale surface with the main agent, the base material reaction product component is reacted with the base material surface exposed by dissolving and removing the scale, thereby separating the base material surface and the scale. By generating a base material reactant between the base material and dissolving the base material reactant with the base material reactant dissolving component, a gap is generated between the scale and the base material, and even if the scale is in the process of dissolution, the cleaning liquid The scale can be peeled off and removed from the base material by the fluid force of

In the above disclosure, by removing scales with two removal mechanisms, cleaning can be completed in a shorter time than the conventional method of dissolving and removing with a main agent.

FIG. 2 is an image diagram of generation of a base material reactant; It is a more specific image diagram of the base material reactant. FIG. 4 is an image diagram of a scale removing (peeling) mechanism; It is a more specific image diagram of scale removal (peeling). FIG. 2 is an evaluation diagram of scale removal properties; It is a corrosion-resistant evaluation figure. FIG. 3 is a diagram showing the effects of the presence or absence of a base material, a base material reactant-producing component, and a base material reactant-dissolving component on scale removal and corrosion resistance. It is a figure which shows the result of having changed the content of a main agent. FIG. 4 is a diagram showing the relationship between the content of the main agent and the scale removal area ratio. FIG. 4 is a diagram showing the results of varying the content of the matrix reactant-generating component; FIG. 4 is a diagram showing the relationship between the content of base material reaction product-producing components and the scale removal area ratio; FIG. 5 is a diagram showing the results of changing the content of base material reactant dissolved components. FIG. 4 is a diagram showing the relationship between the content of components dissolved in base material reactants and the scale removal area ratio; FIG. 4 is a diagram showing the relationship between the content of base metal reactant dissolved components and the amount of corrosion; FIG. 4 is a diagram showing the relationship between the content of components dissolved in base material reactants and the amount of residual sulfur. It is a figure which shows the result of having changed pH of the test liquid. It is a figure which shows the relationship between pH of a test liquid, and a scale removal area ratio. It is a figure which shows the result of having changed the kind of main agent. FIG. 4 shows the results of changing the type of matrix reactant-producing component. FIG. 10 is a diagram showing the results of changing the type of base material reactant dissolved component;

An object to be cleaned in the present embodiment is a structure in which scales containing metal oxides adhere to a base material. The base material is made of metal. The base material contains iron. The matrix may contain molybdenum. Metal oxides include iron oxides (Fe ₂ O ₃ and Fe ₃ O ₄ ).

[Dissolution removal composition]
The dissolution removal composition according to the present embodiment includes (A) a base material, (B) a matrix reactant-producing component, and (C) a matrix reactant dissolving component.

(A) The main agent is a component capable of dissolving scale containing metal oxides. The main agent can be selected from the group consisting of aminocarboxylic acids, phosphonic acids and salts thereof.

More specifically, the main ingredients are 1-hydroxyethane-1,1-diphosphonic acid, aminotris(methylenephosphonic acid), and ethylenediaminetetraacetic acid.

The main ingredient may be contained in an amount of 11% by weight or more and 25% by weight or less, preferably 15% by weight or more and 20% by weight or less, based on the total weight of the dissolution removal composition. If the amount of the main agent is too small or too large, the descalability will be insufficient.

(B) Matrix reactant-producing component is a component that reacts with the matrix to form a reactant. The reactant has anti-corrosion properties.

The matrix reactant-generating component is a thiazole-based compound having a planar skeleton.

The planar framework of the matrix reactant-generating component comprises a 1,3,4-thiadiazole shown in formula (1).

X ₁ can be substituted with a thiol group (mercaptan group) or an amino group.
X2 can be substituted with a hydrogen atom, a methyl group, a methylthio group or a thiol group ₍ mercaptan group).

More specifically, the matrix reactant-producing components include, for example, 2,5-dimercapto-1,3,4-thiadiazole, 2-mercapto-5-methylthio-1,3,4-thiadiazole, 1,3, 4-thiadiazole-2-thiol, 2-amino-5-mercapto-1,3,4-thiadiazole, or 5-methyl-1,3,4-thiadiazole-2-thiol.

The base material reactant-producing component may be included in an amount of 0.003% by weight or more and 0.1% by weight or less based on the total weight of the dissolution removal composition. If the base material reactant-producing component is low, the production rate of the base material reactant produced between the base material and the scale slows down, resulting in insufficient scale removal.

(C) The base metal reactant-dissolving component is a component capable of dissolving the base metal reactant and imparting anti-corrosion properties to the base metal.

The matrix reactant soluble component is a C3 compound containing a thiol group and a carboxylic acid group. In C3 compounds, the longest carbon chain is three. When the number of carbon chains is small, the steric hindrance ability is lowered due to the small molecular structure, and the anticorrosion ability after dissolution is lowered. When the number of carbon atoms is large, the molecular structure becomes large, so the frequency factor to the reactant becomes small, and the ability to dissolve the reactant decreases.

More specifically, the matrix reactant dissolving component can be selected from the group consisting of 3-mercaptopropionic acid, thiolactic acid and salts thereof.

The matrix reactant dissolving component may comprise from 0.7 wt% to 5 wt% based on the total weight of the dissolving removal composition. If the base material reactant-dissolving component is too small, the descalability will be low and the amount of corrosion will increase. Also, if the base material reactant dissolved component is too small or too large, the remaining amount of sulfur in the base material after washing increases. Since residual sulfur causes corrosion during operation of the boiler, it is preferable that the amount of sulfur is small.

The dissolution removal composition may include (D) a corrosion inhibitor, (E) a reducing agent and (F) an antifoaming agent.

(D) Corrosion inhibitor is an anticorrosion component that suppresses the generation of rust in the base material. Corrosion inhibitors include surfactants. Surfactants are amphoteric and nonionic surfactants.

Amphoteric surfactants include 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine, 2-alkyl-N-carboxyethyl-N-hydroxyethylimidazolinium betaine, β-alkylaminocarboxylic acid Alkali metal salts (eg, sodium β-alkylaminopropionate) and alkali metal salts of alkylaminodicarboxylic acids (eg, sodium 3-[lauryl[3-(sodiooxy)-3-oxopropyl]amino]propionate). . 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, these substituents allow the amphoteric surfactant to be adsorbed onto the surface of the metal matrix. As a result, the amount of metal sulfide produced by the exposed surface of the metal base material reacting with sulfur can be reduced.

The amphoteric surfactant content is 0.001% by weight or more and 10% by weight or less, preferably 0.005% by weight or more and 5% by weight or less, more preferably 0.01% by weight, based on the total mass of the dissolution removal composition. % by weight or more and 2% by weight or less.

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 suppressing corrosion of metal base materials, the nonionic surfactant is polyethylene glycol monooleate, polyethylene glycol monolaurate, and polyethylene glycol monostearate. is desirable.

The content of the nonionic surfactant is 0.001% by weight or more and 10% by weight or less, preferably 0.005% by weight or more and 5% by weight or less, more preferably 0.005% by weight or more and 5% by weight or less, with respect to the total mass of the dissolution removal composition. 01% by weight or more and 2% by weight or less.

(E) The reducing agent is a component that promotes dissolution of scale components by its reducing action. The reducing agent may be a strongly reducing sulfur compound. Examples of strongly reducing sulfur compounds include thiourea compounds and dithionites. Thiourea-based compounds include thiourea dioxide, guanylthiourea, and the like. Sulfur atoms contained in sulfur compounds adsorb to the metal and strengthen the protective film.

The content of the strongly reducing sulfur compound is 0.01% by weight or more and 1% by weight or less, preferably 0.01% by weight or more and 0.1% by weight or less, more preferably 0.1% by weight or less, relative to the total mass of the dissolution removal composition. is 0.02% by weight or more and 0.08% by weight or less. If it is less than 0.01% by weight, the descalability will be insufficient. If it exceeds 1% by weight, the corrosion resistance will be insufficient.

The reducing agent may include an organic acid having oxygen reducing properties. For the organic acid having oxygen reducing properties, it is preferable to select a component that is excellent in oxygen removal properties and persistence. Such organic acids include ascorbic acid and Erythorbic acid.

The content of the oxygen reducing organic acid is 0.01% by weight or more and 8% by weight or less, preferably 0.1% by weight or more and 5% by weight or less, more preferably 0.1% by weight or more and 5% by weight or less, based on the total mass of the dissolution removal composition It is 0.5% by weight or more and 3% by weight or less. If it is less than 0.01% by weight, the descalability will be insufficient. If it exceeds 8% by weight, the corrosion resistance will be insufficient.

(F) Antifoaming agent is a component that suppresses foaming of the dissolution-removing composition. The antifoam agent may be, for example, a silicone antifoam agent.

The pH of the dissolution removal composition is 5 or more and 7 or less. The pH can be adjusted with sodium hydroxide (NaOH) and potassium hydroxide (KOH) and the like.

[Washing method]
The dissolution-removing composition is used as a cleaning liquid to clean the object to be cleaned, thereby removing the scale adhering to the base material.

The cleaning time can be appropriately set according to the properties and amount of scale. For example, when 10 to 20 mg/cm ² of scale containing iron oxide is adhered, the washing time is about 20 to 50 hours.

The temperature of the cleaning liquid may be about 15-55°C. The temperature of the cleaning liquid may be higher than 55°C.

For example, when the object to be cleaned is a heat transfer tube in a power plant, the cleaning solution is circulated inside the heat transfer tube (circulation cleaning), or the inside of the heat transfer tube is filled with the circulating fluid and left to stand (immersion cleaning). to wash. When performing circulating cleaning, the cleaning liquid is preferably pulsated (swing blow). By pulsating the cleaning liquid, the strength of the fluid force of the cleaning liquid is generated, and the scale can be effectively peeled off and removed.

The dissolution-removal composition and cleaning method according to the present embodiment are suitable for removing scale (particularly iron rust) adhering to the inside of pipes containing iron as a main component in power plants and the like. The dissolution-removing composition according to the present embodiment and the cleaning method using the same are also used to remove iron-based oxides and/or hydroxides adhering to heat exchangers of power plants and chemical plants, cooling jackets of internal combustion engines, etc. It is widely transferable.

1 to 4 show image diagrams of cleaning using the dissolution removal composition of the present embodiment. FIG. 1 is an image diagram of generation of a base material reactant. FIG. 2 is a more specific image diagram of the base material reactant. FIG. 3 is an image diagram of a scale removing (peeling) mechanism. FIG. 4 is a more specific image diagram of scale removal (peeling).

In cleaning using the dissolution-removing composition according to the present embodiment as a cleaning liquid, scale (iron oxide scale in FIG. 1) is dissolved and removed from the base material by the main agent contained in the cleaning liquid.

The scale adhering to the object to be cleaned has a non-uniform film thickness and may have cracks.

As shown in FIG. 1, the base material is exposed at the gaps between the scales or at the locations where the scales have been dissolved by the main agent. In the exposed portion of the base metal, the base metal reactant-producing components react with the MoFe components (Mo ⁿ⁺ and Fe ²⁺ ) in the base metal to form base metal reactants between the scale and the base metal. Although the base material reactant is an extremely thin film, it can suppress base material corrosion.

The matrix reactant producing component has a planar framework containing heteroatoms in the organic rings. The lone pair of electrons possessed by this heteroatom exhibits high reactivity with the base material metal, and a strong layered reactant (base material reactant) as shown in FIG. 2 is formed between the scale and the base material. generated.

The matrix reactant dissolving component dissolves the matrix reactant. When the base material reactant generated between the scale and the base material is dissolved, a gap is generated between the scale and the base material, as shown in FIG. 3, and the scale tends to separate.

Also, as shown in FIG. 4, the matrix reactant dissolved by the matrix reactant dissolving component is removed from the matrix surface. At this time, the scale on the base material reactant can be peeled off and removed by the fluid force of the cleaning liquid. Components dissolved in the reactants of the base material are adsorbed on the exposed base material, thereby imparting anticorrosion properties to the base material.

By using a dissolution-removal composition in which the base material, the base material reactant-generating component, and the base material reactant-dissolving component coexist, the base material can be protected from corrosion while removing scale.

In addition, the cleaning method according to the present embodiment may include a step of collecting exfoliated scale.

Next, the grounds for selecting the components in the dissolution removal composition will be described.

The base composition of the dissolution removal composition (test solution) is as follows, and the content or type of each component is changed as appropriate to evaluate the scale removal performance, corrosion resistance, and sulfur residue after washing of the dissolution removal composition. We conducted a test to

1. Test liquid 1.1 Base composition (pH 5.5)
Component A: 1-hydroxyethane-1,1-diphosphonic acid 15% by weight
Component B: 2,5-dimercapto-1,3,4-thiadiazole (MTD) 0.0015% by weight
Component C: 1.5% by weight of 3-mercaptopropionic acid
Component D-1: 3-[lauryl[3-(sodiooxy)-3-oxopropyl]amino]propionic acid 0.5% by weight
Component D-2: Polyoxyalkylene oleyl ether 0.1% by weight
Component E: Sodium dithionite 0.1% by weight
Component F: Silicone antifoaming agent 0.015% by weight

1.2 Manufacturing method The test liquid consists of pure water, (A) main agent, (B) base material reactant-generating component, (C) base material reactant-dissolving component, (D-1) amphoteric surfactant, (D -2) A nonionic surfactant, (E) a reducing agent and (F) an antifoaming agent were sequentially added and mixed at room temperature, and potassium hydroxide (KOH) was used to adjust the pH.

2. 2. Scale removal property 2.1 Preparation of test specimen First, a boiler furnace extubation tube having magnetite (Fe ₃ O ₄ ) and hematite (Fe ₂ O ₃ ) adhered to the inner surface was cut into a length of 24 mm, and then divided in half lengthwise. . Next, the outer periphery of the tube and the cut surface were coated with an epoxy resin except for the portion where the scale was adhered.

The surface area of the scale-adhered part in the test piece (two half-split tubes) was 12.1 cm ² . The amount of scale adhered to the specimen was 18 mg/m ² for magnetite and 0.6 mg/cm ² for hematite.

2.2 Cleaning test As shown in Fig. 5, a rotor was placed in an acrylic beaker with a diameter of 30 mm, and a table with a diameter of 26 mm with a hole was placed so as to cover the rotor. Two half-split tubes (specimen) were placed on the table so that the scale-adhered surface was on the inside. 15.7 mL of the test liquid was poured into the acrylic beaker so that the ratio of the scale-adhered portion to the surface area was 1.3 (mL/cm ² ).

The acrylic beaker was sealed with a rubber stopper under atmospheric conditions and placed in a constant temperature water bath with a stirrer. The liquid temperature in the constant temperature water bath was set at 40°C. After reacting for 30 hours while stirring with a stirrer, the specimen was taken out from the acrylic beaker.

After the sample was washed with water for several seconds, it was subjected to antirust treatment in an aqueous hydrazine solution (0.05% by weight) heated to 80° C. for 30 minutes.

After the rust-proofing treatment, the scale remaining area was visually confirmed, and the scale-removed area ratio (%) was calculated by the following formula (2).

Scale removal area ratio (%)
=(initial scale area−scale remaining area)/initial scale area×100 (2)

3. 3. Corrosion Resistance 3.1 Preparation of Test Specimen A scale-free boiler tube (STBA23) was cut in half lengthwise and then cut into 5 cm wide pieces. After polishing with #150 sandpaper, it was degreased with toluene and acetone in order to prepare a test piece. The surface area of the specimen was 26 cm ² .

3.2 Corrosion Test As shown in Fig. 6, a rotor was placed in a glass container, a perforated stand was placed over the rotor, and a test specimen was placed on the stand. 104 mL of the test liquid was put into the glass container so that the ratio to the surface area of the test body was 4 (mL/cm ² ).

The reagent iron oxide powder was added to the test solution so that the total iron content at the time of dissolution was 2.25% by weight, and the glass container was sealed with a lid in an atmospheric environment. The reagent iron oxide powder contains a 9:1 ratio of reagent magnetite powder and reagent hematite powder.

After standing at 40° C. for 20 hours while stirring with a stirrer, the specimen was taken out from the glass container. After the sample was washed with water for several seconds, it was subjected to antirust treatment in an aqueous hydrazine solution (0.05% by weight) heated to 80° C. for 30 minutes.

The amount of corrosion (mg/cm ² ) was calculated from the weight change of the specimen before and after the test.

4. Remaining amount of sulfur Washed in the same manner as in 2.2 above, removed from the acrylic beaker, washed with water for several seconds, and then subjected to the following treatment (rinse treatment).

First, the specimen was immersed in a hydrogen peroxide solution (2% by weight). After stirring for 1 hour in a constant temperature bath at 50°C, the specimen was transferred to a 2% by weight citric acid aqueous solution. The amount of the 2% by weight aqueous citric acid solution was 1.3 times the surface area of the specimen.

After stirring for 1 hour in a constant temperature bath at 50°C, the specimen was transferred to an aqueous hydrazine solution for antirust treatment. The specimens were thoroughly dried and subjected to elemental analysis (EDX) by scanning electron microscopy (SEM). At a voltage of 20 kV and a magnification of 200, measurements were taken at three points while changing the measurement position, and the average was taken to determine the weight percent of sulfur element.

The residual amount of sulfur may be 0.4% by weight or more and less than 0.8% by weight, preferably less than 0.4% by weight.

5. Results 5.1 Effects of components A, B, and C Fig. 7 shows that the presence or absence of component A (base material), component B (base material reactant-generating component), and component C (base material reactant-dissolving component) indicates scale removal. and the effect on corrosion resistance.

In cleaning using the test liquid of the base composition, the scale removal area ratio was 90% and the corrosion amount was 2.6 mg/cm ² .

The scale removal area ratio may be 40% or more, preferably 70% or more. Even if the acceptance criterion for the scale removal area ratio is set at 70%, the test liquid having the base composition satisfies the acceptance criterion.

The corrosion amount may be 5-10 mg/cm ² and is preferably less than 5 mg/cm ² . Even if the acceptance criterion for the amount of corrosion (corrosion resistance) is less than 5 mg/cm ² , the test solution with the base composition satisfies the acceptance criterion.

The test solution containing no component A had a low scale removal area ratio and did not satisfy the acceptance criteria. From this result, it was confirmed that the presence or absence of component A affects the scale removal property.

The test solution containing no component B had a scale removal area ratio of 20%. The test solution containing no component C had a scale removal area ratio of 90%. The test solution containing neither component B nor component C had a scale removal area ratio of 90%. This suggests that when component C is not included, component A alone exhibits high descalability due to corrosion reaction, but when component C is included, the presence or absence of component B affects descalability. was done.

The test solution containing no component A and the test solution containing no component B had a corrosion amount of less than 5 mg/cm ² , satisfying the acceptance criteria. On the other hand, the test solution containing no component C had a corrosion amount of 46.1 mg/cm ² , which did not meet the acceptance criteria. From this, it was confirmed that the presence or absence of component C affects the anticorrosion properties.

According to the above results, the test solution in which component A, component B and component C coexist was the highest in scale removal and excellent in corrosion resistance. If the amount of adhering scale is the same, the cleaning time can be shortened by using the dissolution removal composition according to the above embodiment.

5.2 Content of main agent Fig. 8 shows the results of changing the content of the main agent (component A) in the test solution from 0 to 28% by weight. FIG. 9 is a diagram showing the relationship between the content of the main agent and the scale removal area ratio. In the figure, the horizontal axis is the content (% by weight) of the main agent in the test solution, and the vertical axis is the scale removal area ratio (%).

According to FIGS. 8 and 9, the scale removal area ratio was low when the content of the main agent was too small or too large. This is attributed to the fact that while the content of the base compound is low, the scale dissolution rate is low, while the viscosity and water content of the test solution are lowered due to the high content of the base compound, resulting in a low scale dissolution rate. guessed.

In the test liquids (Nos. 4 to 6) having a base agent content of 11% by weight or more and 25% by weight or less, the scale removal area ratio was 70% or more. When the content of the main agent was 15% by weight or more and 20% by weight, the scale removal area ratio was about 90%.

According to FIG. 9, the scale removal area ratio changes significantly between the test liquid (No. 3) with a main agent content of 10% by weight and the test liquid (No. 4) with a main agent content of 11% by weight. I understand. Even after the test solution (No. 6) containing 25% by weight of the main agent, the scale removal area rate seemed to change significantly.

Regarding the amount of corrosion, the test solution No. All of 1 to 7 were below 5 mg/cm ² and satisfied the acceptance criteria (see FIG. 8).

5.3 Content of Matrix Reaction Product-Generating Component FIG. 10 shows the results of varying the content of the matrix reaction product-generating component (component B) in the test solution from 0 to 0.004% by weight. FIG. 11 is a diagram showing the relationship between the content of base material reaction product-producing components and the scale removal area ratio. In the figure, the horizontal axis is the content (% by weight) of the base material reaction product-forming component in the test solution, and the vertical axis is the scale removal area ratio (%).

According to FIGS. 10 and 11, the scale removal area ratio increased as the content of the base material reaction product-generating component increased. According to FIG. 11, it can be seen that the scale removal area ratio is 70% or more for the test liquid containing the base material reaction product-forming component in an amount of 0.003% by weight or more.

Regarding the amount of corrosion, the test solution No. All of 8 to 11 were below 5 mg/cm ² (see FIG. 10).

5.4 Content of Base Material Reactant Dissolving Component FIG. 12 shows the results of changing the content of the base material reactant dissolving component (component C) in the test solution from 0 to 5.5% by weight. FIG. 13 is a diagram showing the relationship between the content of base material reactant dissolved components and the scale removal area ratio. In the figure, the horizontal axis represents the content (% by weight) of the component dissolved in the base material reactant in the test solution, and the vertical axis represents the scale removal area ratio (%). FIG. 14 is a diagram showing the relationship between the content of base material reactant dissolved components and the amount of corrosion. In the figure, the horizontal axis represents the content (% by weight) of the component dissolved in the base material reactant in the test liquid, and the vertical axis represents the corrosion amount (mg/cm ² ). FIG. 15 is a diagram showing the relationship between the content of base material reactant dissolved components and the amount of residual sulfur. In the figure, the horizontal axis represents the content (% by weight) of the component dissolved in the base metal reactant in the test solution, and the vertical axis represents the remaining amount of sulfur (% by weight).

12 and 13, the test solution (No. 12) containing no components dissolved in the base material reactant had a scale removal area ratio of 90%. When the base material reactant-dissolving component was added, the scale removal area ratio once decreased to 45%, but then turned to increase, and the test liquid containing the base material reactant-dissolving component content of 0.7% by weight or more. In (Nos. 15 to 17), the scale removal area ratio was 85% or more.

According to FIGS. 12 and 14, the corrosion amount greatly exceeded 10 mg/cm ² in the test solution (No. 12) that did not contain the base metal reactant dissolved component, but the base metal reactant dissolved component decreased as the amount increased. In the test liquids (Nos. 15 to 17) containing 0.7% by weight or more of the component dissolved in the base metal reactant, the corrosion amount was lower than 5 mg/cm ² .

According to FIGS. 12 and 15, the remaining amount of sulfur after rinsing decreased once as the content of the base metal reactant dissolved component increased, but increased when the content of the base metal reactant dissolved component increased too much. turned into With test solutions (Nos. 15 and 16) containing 0.7% by weight or more and 5% by weight or less of components dissolved in base material reactants, the amount of sulfur remaining after rinsing was suppressed to less than 0.4% by weight. .

5.5 pH
FIG. 16 shows the results of changing the pH of the test solution in the range of 5.5 to 9.0. FIG. 17 is a diagram showing the relationship between the pH of the test liquid and the scale removal area ratio. In the figure, the horizontal axis is the pH of the test solution, and the vertical axis is the scale removal area ratio (%).

The higher the pH of the test solution, the lower the scale removal area ratio. According to FIG. 17, if the pH is 7 or less, the scale removal area ratio is 70% or more.

It was thought that the corrosion amount increased as the pH increased, and that the corrosion amount fell below 5 mg/cm ² at pH 7 or less.

5.6 Kinds of main agent Fig. 18 shows the results of changing the kind of the main agent (component A).
In the test liquid using 1-hydroxyethane-1,1-diphosphonic acid, aminotris (methylene phosphonic acid), and ethylenediaminetetraacetic acid as component A, the scale removal area ratio was 80% or more, and the corrosion amount was 5 mg/cm ² . less than 0.4% by weight.

On the other hand, in the test liquid using citric acid as component A, the scale removal area ratio was low and the corrosion amount was higher than 5 mg/cm ² .

5.7 Types of Matrix Reactant-Generating Components FIG. 19 shows the results of changing the type of matrix reactant-generating component (component B).
As component B, 2,5-dimercapto-1,3,4-thiadiazole, 2-mercapto-5-methylthio-1,3,4-diadiazole, 1,3,4-thiadiazole-2-thiol, 2-amino- In the test solution using 5-mercapto-1,3,4-thiadiazole or 5-methyl-1,3,4-thiadiazole-2-thiol, the scale removal area ratio was 80% or more, and the corrosion amount was 5 mg/cm. less than ² , and the remaining amount of sulfur was less than 0.4% by weight.

On the other hand, in the test liquid using benzotriazole as component B, the corrosion amount was less than 5 mg/cm ² and the residual sulfur content was less than 0.4% by weight, while the scale removal area ratio was as low as 20%.

5.8 Types of Matrix Reactant Dissolving Component FIG. 20 shows the results of changing the type of matrix reactant dissolving component (component C).
In the test solution using 3-mercaptopropionic acid and thiolactic acid as component C, the scale removal area ratio was 85% or more, the corrosion amount was less than 5 mg/cm ² , and the residual sulfur was less than 0.4% by weight. .

On the other hand, in the test liquid using thiomalic acid as the component C, the scale removal area ratio was 85% or more, the corrosion amount was less than 5 mg/cm ² , but the residual amount of sulfur exceeded 0.8% by weight.

Thiomalic acid is a C4 compound and has a large molecular structure, so it has high steric hindrance and high corrosion resistance after dissolution. However, it is presumed that the larger the molecular structure, the smaller the frequency factor of the thiol group to the base material reactant, and the lower the ability to dissolve the base material reactant.

In the test liquid using thioglycolic acid as the component C, the scale removal area ratio was 85% or more, the residual amount of sulfur was less than 0.4% by weight, but the corrosion amount was higher than 10 mg/cm ² .

Thioglycolic acid has a strong ability to dissolve the matrix reactant. However, since thioglycolic acid is a C2 compound and has a small molecular structure, it is presumed that the steric hindrance ability was low and the anticorrosion ability after dissolution was poor.

In the test liquid using thioacetic acid as the component C, the scale removal area ratio was 20% or more, and the corrosion amount exceeded 10 mg/cm ² .

Since thioacetic acid has a small molecular structure, it is presumed that, like thioglycolic acid, it was inferior in anticorrosion ability after dissolution. It is speculated that thioacetic acid has lower descaling properties because it does not have carboxylic acid groups that are believed to exhibit matrix reactant solubility.

<Appendix>
The dissolution removal composition and cleaning method described in the embodiments described above are grasped, for example, as follows.

The present disclosure comprises a main agent for dissolving and removing scales containing metal oxides adhering to a base material, a base material reaction product-generating component for reacting with the base material to generate a reaction product, and a base material for dissolving and removing the reaction product. and a material reactant dissolving component.

The present disclosure is a method for cleaning an object to be cleaned including a base material to which scales containing metal oxides are attached, wherein the cleaning object is cleaned with a cleaning solution containing a main agent, a base material reactant-producing component, and a base material reactant-dissolving component. washing to dissolve and remove at least a portion of the scale from the base material with a base material; reacting a base material reactant-producing component with the base material to form a reactant between the base material and the scale; A cleaning method is provided in which the reactant is dissolved away by a material reactant dissolving component.

Scales containing metal oxides are dissolved and removed from the surface side by the main agent.

At the locations where the scale has dissolved or where the base material is exposed at the interstices of the scale, the base material components react with the base material reactant-producing components to form base material reactants. The matrix reactant imparts corrosion protection to the matrix.

The matrix reactant dissolving component dissolves the matrix reactant. As a result, the scale is peeled off and removed.

In the above disclosure, by removing scales with two removal mechanisms, cleaning time can be shortened compared to the conventional method of dissolving and removing with a main agent.

Under conditions in which the component dissolved in the base metal reactant is not contained, the scale exfoliation progresses, but the amount of corrosion increases. In the above disclosure, by including the base material reactant-dissolving component, it is possible to suppress the amount of corrosion of the base material, promote the peeling of scale, and shorten the cleaning time.

In one aspect of the above disclosure, the matrix reactant-dissolving component may be a C3 compound having a thiol group and a carboxylic acid group or a salt thereof.

A C3 compound having a thiol group and a carboxylic acid group or a salt thereof has a reactant-dissolving ability and moderate corrosion-preventing ability after dissolution.

In one aspect of the above disclosure, the base material reactant-dissolving component may be included at 0.7 wt % or more and 5 wt % or less based on the total weight.

If the base material reactant-dissolving component is too small, the descalability and anti-corrosion properties will deteriorate, and the amount of residual sulfur after rinsing treatment will also increase. If there are too many components dissolved in the base metal reactants, the amount of residual sulfur after rinsing increases.

In one aspect of the above disclosure, the main agent may be selected from the group consisting of aminocarboxylic acids, phosphonic acids and salts thereof.

In one aspect of the above disclosure, the main agent may be contained at 11% by weight or more and 25% by weight or less with respect to the total weight.

If the amount of the main agent is too much or too little, the descalability will be lowered. If the content of the main agent is within the above range, the descalability will be enhanced.

In one aspect of the above disclosure, the pH of the dissolution composition can be from 5 to 7.

In one aspect of the above disclosure, the matrix reactant-generating component can be a thiadiazole-based compound having a planar skeleton.

By having a planar skeleton, a layered and strong matrix reactant can be generated. A layered and strong matrix reactant can have good release properties.

In one aspect of the above disclosure, the planar scaffold may be 1,3,4-thiadiazole.

In one aspect of the above disclosure, the matrix reactant-producing component may comprise 0.003 weight percent or more, based on the total weight.

Claims (10)

a main agent for dissolving and removing scales containing metal oxides adhering to the base material;
a matrix reactant-producing component that reacts with the matrix to form a reactant;
a base material reactant dissolving component for dissolving and removing the reactant;
A dissolution removal composition comprising: 2. The dissolving removal composition according to claim 1, wherein the base material reactant dissolving component is a C3 compound having a thiol group and a carboxylic acid group or a salt thereof. 3. The dissolution removal composition according to claim 1, wherein the base material reactant dissolution component is contained in an amount of 0.7 wt % or more and 5 wt % or less based on the total weight. The dissolution removal composition according to any one of claims 1 to 3, wherein the main agent is selected from the group consisting of aminocarboxylic acids, phosphonic acids and salts thereof. The dissolution removal composition according to any one of claims 1 to 4, wherein the main agent is contained in an amount of 11% by weight or more and 25% by weight or less with respect to the total weight. The dissolution removal composition according to any one of claims 1 to 5, which has a pH of 5 to 7. 7. The dissolution removal composition according to any one of claims 1 to 6, wherein the base material reaction product-generating component is a thiadiazole compound having a planar skeleton. 8. The dissolution removal composition according to claim 7, wherein the planar skeleton is 1,3,4-thiadiazole. The dissolution removal composition according to any one of claims 1 to 8, wherein the base material reactant-producing component is contained in an amount of 0.003% by weight or more based on the total weight. A method for cleaning a target to be cleaned including a base material to which scales including metal oxide are attached, comprising:
cleaning the object to be cleaned with a cleaning liquid containing a main agent, a base material reactant-generating component, and a base material reactant-dissolving component;
dissolving and removing at least part of the scale from the base material with a main agent;
reacting a matrix reactant-producing component with the matrix to form a reactant between the matrix and the scale;
A cleaning method comprising dissolving and removing the reactant with a matrix reactant dissolving component.

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