JP2009155701A - Descaling agent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a descaling agent which contains a thiocarboxylic acid as an organic acid of a main component, shows superior descaling properties when used, and merely produces a remarkably reduced amount of an odor peculiar to sulfur. <P>SOLUTION: The descaling agent includes at least one compound selected from a thiocarboxylic acid and a salt thereof and at least one reducing agent. A thiodicarboxylic acid and a salt thereof are particularly preferably employed as the thiocarboxylic acid and the salt thereof, and among them, a thiomalic acid and a salt thereof are preferably employed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a scale remover for dissolving and removing a scale containing a metal oxide generated on a metal surface.

  Conventionally, the scale remover used to dissolve and remove scales containing metal oxides from the metal surface is roughly divided into inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, phosphoric acid and sulfamic acid. And those containing organic acids such as citric acid, hydroxyacetic acid, formic acid, malic acid, oxalic acid, and gluconic acid as the main component.

  Since both the inorganic acid and the organic acid as described above are strongly acidic, there is a possibility that the metal substrate is corroded during the scale removal. Therefore, various auxiliary agents such as a corrosion inhibitor and a metal oxide dissolution accelerator are added to these scale removers.

  In general, inorganic acids are characterized by low cost and high ability to dissolve metal oxides. However, on the other hand, depending on the material type of the metal to be cleaned, problems such as peracid cleaning, hydrogen embrittlement, and metal discoloration may occur. Furthermore, neutralization after washing is difficult, and since it is strongly acidic, there is a danger in handling, and there are problems such as contamination of surrounding facilities and environment due to generation of gas and mist.

  In order to avoid the above problem in the scale remover mainly composed of an inorganic acid, cleaning with an organic acid is performed. That is, the scale remover mainly composed of an organic acid is expensive and has a disadvantage that it needs to be heated to 70 ° C. or higher at the time of cleaning because of its low scale dissolving ability at room temperature. On the other hand, it has a mild corrosive action and is easy to neutralize after washing.

  Among scale removers mainly composed of organic acids, those mainly composed of phosphonic acid and salts thereof are attracting attention because they can dissolve iron oxide in a neutral pH range. For example, the following “Patent Document 1” discloses a method for removing a scale containing a metal oxide by using a detergent mainly composed of phosphonic acid or a salt thereof in a neutral pH range of pH 5-9. ing.

JP-A-6-346261 In addition, in Patent Document 2 below, if a reducing agent, a corrosion inhibitor, and a surfactant are added to phosphonic acid, an effective rust-removing agent is obtained. It is disclosed that can be obtained. Furthermore, Patent Document 3 below discloses a scale solution adjusted to pH 5.0 to 8.5 with an aqueous solution of a tertiary alkanolamine salt of 1-hydroxyethylidene-1,1-diphosphonic acid.

U.S. Pat. No. 4,810,405 However, in recent years, phosphorus is considered to be an environmental pollutant (eutrophication substance) in rivers and seas together with nitrogen, and reduction of phosphorus sources has been called out. From such a standpoint, it is preferable to avoid the use of a scale remover mainly composed of phosphonic acid and its salts.

  The inventor of the present application paid attention to thiocarboxylic acid as an organic acid used for the scale remover. The thiocarboxylic acid as the acid component of the scale remover is very excellent in terms of environmental load. However, the method of use is limited due to inferior rust removal performance and the occurrence of sulfur-specific odors during use.

  For example, Patent Document 4 below proposes a red rust remover using an ammonium salt of thiocarboxylic acid (specifically, thioglycolic acid). However, this red rust-removing composition takes a long time to dissolve red rust as confirmed as “Comparative Example” in the Examples section described later, and generates a specific odor during use. That is, the above-mentioned problems are not escaped.

JP, 9-241877, A Therefore, this invention is a scale remover which contains thiocarboxylic acid or its salt as an organic acid which is the main ingredients, and is excellent in scale removal performance at the time of use, and generation of odor peculiar to sulfur. It is a problem to be solved to provide a scale remover with significantly reduced

(First invention)
The configuration of the first invention of the present application for solving the above problems is a scale remover containing one or more selected from thiocarboxylic acids and salts thereof and one or more reducing agents.

  In the process of studying the means for solving the above problems, the inventor of the present application contains a reducing agent in combination with a scale removing agent containing thiocarboxylic acid or a salt thereof as a main component, and the scale removing performance is remarkably improved. It has been found that the generation of sulfur-specific odor is significantly reduced.

The general action of the first invention is considered as follows. That is, thiocarboxylic acid and its salt have a reducing action and a chelating action. Therefore, for example, when the metal to be cleaned is various iron materials, these thiocarboxylic acids dissolve iron rust to generate trivalent iron ions (Fe ³⁺ ). These trivalent iron ions are converted into thiocarboxylic acids or reduced substances. Iron rust is removed by reduction to divalent iron ions (Fe ²⁺ ) by the action of the agent, and then the divalent iron ions form a chelate complex with thiocarboxylic acid ions.

  In the first invention, the reason why the scale removal performance of thiocarboxylic acids is remarkably improved and the generation of odor is remarkably reduced is not necessarily clearly understood. However, a scale remover based on thiocarboxylic acid or its salt generally forms a dimer by oxidation over time with air, etc., and has a different odor from thiocarboxylic acid or its salt along with a decrease in rust removal ability. appear. However, in the scale remover of the first invention, it is presumed that the formation of the dimer is suppressed by the presence of the reducing agent. This point is considered to have an important relationship with the effect of the first invention.

(Second invention)
The configuration of the second invention of the present application for solving the above problem is a scale remover in which the thiocarboxylic acid and its salt according to the first invention are thiodicarboxylic acid and its salt.

  In the second invention, the following effects can be expected. That is, among thiocarboxylic acids, thiodicarboxylic acid and its salt originally have relatively little odor generation but have low rust removal ability. Thus, it has been found that when thiodicarboxylic acids are used in combination with a reducing agent, the improvement in rust removal performance is particularly remarkable, and the odor during use is particularly significantly reduced. This effect is thought to be related to the fact that thiodicarboxylic acids have two carboxyl groups.

(Third invention)
The configuration of the third invention of the present application for solving the above problem is a scale remover in which the thiodicarboxylic acid according to the second invention is thiomalic acid, and the salt of the thiodicarboxylic acid is a salt of thiomalic acid.

  The thiodicarboxylic acid and its salt according to the second invention described above are particularly preferably exemplified by the thiomalic acid and its salt defined in the third invention from the viewpoint of rust removal performance and the reduction of odor during use. can do.

(Fourth invention)
The structure of the fourth invention of the present application for solving the above-described problem is that the scale remover according to any one of the first invention to the third invention is adjusted to a pH in the range of 5.0 to 8.5. It is an agent.

  It is preferable that the scale removing agent according to the first to third inventions is adjusted within the range of pH 5.0 to 8.5 by blending an appropriate pH adjusting agent such as NaOH (caustic soda). If the scale remover has a pH of less than 5.0, neutralization of the cleaning surface is required after cleaning, and handling of the cleaning liquid tends to be difficult. On the other hand, when the pH of the scale remover exceeds 8.5, the scale removal performance tends to be lowered.

  ADVANTAGE OF THE INVENTION According to this invention, the scale removal agent which contains thiocarboxylic acid as an organic acid which is a main component, is excellent in the scale removal performance at the time of use, and generation | occurrence | production of the odor peculiar to sulfur is reduced significantly is provided.

  Next, an embodiment of the present invention including the best embodiment will be described.

[Scale remover]
The scale remover of the present invention contains at least one or more selected from thiocarboxylic acids and salts thereof and one or more reducing agents. The scale remover is usually formulated as an aqueous solution. “Thiocarboxylic acid” refers to a compound having at least one carboxyl group and at least one thiol group (—SH). It does not matter whether the reducing agent is an inorganic compound or an organic compound.

  The pH of the scale remover of the present invention is not particularly limited, but in the range of pH 5.0 to 8.5 in consideration of the ease of neutralization after washing, the safety in handling the scale remover, and the like. It is preferable that Such pH adjustment can be performed, for example, by blending an appropriate pH adjuster. Although the kind of pH adjuster is not limited, As a preferable pH adjuster, inorganic alkalis, such as NaOH and KOH, ammonium water, and alkanolamines, such as monoethanolamine and triethanolamine, are illustrated.

[Thiocarboxylic acid and its salt]
The kind of thiocarboxylic acid or salt thereof contained in the scale remover of the present invention is not limited. Preferred examples of the thiocarboxylic acid include thiomalic acid, thioglycolic acid, thiolactic acid, thiosuccinic acid, and thiosalicylic acid. Preferred examples of the thiocarboxylic acid salt include metal salts, ammonium salts and amine salts of various thiocarboxylic acids. Examples of thioglycolic acid include sodium thioglycolate, calcium thioglycolate, potassium thioglycolate, ammonium thioglycolate, monoethanolamine thioglycolate, diethanolamine thioglycolate, triethanolamine thioglycolate, thioglycol Examples include ethylamine acid, thioglycolic acid monoisopropanolamine, and thioglycolic acid triisopropanolamine.

  Of the thiocarboxylic acids and salts thereof, thiodicarboxylic acids having two carboxyl groups and salts thereof are particularly preferred. Of the thiodicarboxylic acids and salts thereof, thiomalic acid and salts thereof are particularly preferred. Examples of the salt of thiomalic acid include sodium thiomalate, ammonium thiomalate, monoethanolamine thiomalate, diethanolamine thiomalate, triethanolamine thiomalate, and the like.

  The content of thiocarboxylic acid and its salt in the scale remover is not particularly limited, but is generally preferably in the range of 0.1 to 50.0% by mass. If the content is less than 0.1% by mass, the effect of the present invention may not be ensured due to a lack of the absolute amount, and even if the content exceeds 50.0% by mass, the effect of the present invention is saturated and costly. Disadvantageous. The content of thiocarboxylic acid or a salt thereof is particularly preferably in the range of 1.0 to 30.0% by mass.

[Reducing agent]
Although the kind of reducing agent contained in the scale removing agent of the present invention is not limited, sodium sulfite, isoascorbic acid, L-ascorbic acid, glucose, hydrazine and the like can be preferably exemplified. The reducing agent is used as a metal oxide remover rather than an oxygen scavenger.

  The content of the reducing agent in the scale remover is not particularly limited, but is generally preferably in the range of 0.1 to 20.0% by mass. If the content is less than 0.1% by mass, the removal rate of rust may be insufficient due to the lack of absolute amount, and if the content exceeds 20.0% by mass, the metal base material to be cleaned may be corroded. . As for content of a reducing agent, it is especially preferable that it exists in the range of 0.1-10.0 mass%.

[Other components in scale remover]
The scale remover of the present invention may contain phosphonic acid or a salt thereof in addition to the above-described thiocarboxylic acid or salt or reducing agent. By containing phosphonic acid or a salt thereof, the dissolution and removal performance of the scale can be further improved, and the liquid life of the scale removal agent can be extended. The upper limit of the content can be up to about 30.0% by mass, or even about 50.0% by mass from the viewpoint of the effect, but for the reason of the environmental load described above, the environmental load is substantially given. It is preferable to consider the content not present. The lower limit of the content can be about 0.1% by mass, more preferably about 1.0% by mass.

  Preferred examples of the phosphonic acid include organic phosphonic acids such as 1-hydroxyethylidene-1,1-diphosphonic acid and triaminomethylphosphonic acid, and metal salts thereof or water-soluble salts such as ammonium salts.

  In order to further enhance the scale removal performance, the scale remover of the present invention may contain a surfactant as necessary. As the type of the surfactant, one or more of nonionic, anionic, cationic, and zwitterionic can be appropriately selected and contained, and the content thereof is 0.5% by mass or less. It is preferable.

  Furthermore, the scale remover of the present invention may contain various known components that may be contained in this type of preparation as long as the effects of the invention are not impaired. For example, depending on the type of metal to be cleaned, benzotriazole, sodium nitrite, or the like as a corrosion inhibitor can be contained within a range of about 0.01 to 5.00% by mass. A chelating agent can also be included for the purpose of extending the life of the scale remover. As the chelating agent, metal salts such as ethylenediaminetetraacetic acid, hydroxyethylenediaminetriacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid, amine salts, ammonium salts, etc. within a range of about 0.1 to 10.0% by mass. It can be included.

  Next, examples of the present invention will be described. The technical scope of the present invention is not limited by the following examples.

[Preparation of scale remover]
A scale remover having a composition according to Examples 1 to 10 shown in Table 1 at the end and Comparative Examples 1 to 7 shown in Table 2 at the end was prepared. The numerical value described after each compounding component name in each table | surface is the compounding quantity (mass%). In each of the examples and comparative examples, the remainder of the composition other than the mass% component shown in the table is water. The scale remover according to each example and comparative example contains NaOH (caustic soda) which is a pH adjuster. And in Examples 1-10, by adjusting content of NaOH, pH was set to 7.0 in all, but about the comparative example, pH of comparative example 1 is 4.0, and comparative example The pH of 3 is 10.0, and the pH of the other comparative examples is 7.0.

[Test method and evaluation]
Using the scale remover according to each of the above Examples and Comparative Examples, the rust removal property and odor were evaluated as follows.

That is, first, a SPCC steel plate having a width of 70 mm, a length of 150 mm, and a thickness of 0.8 mm was degreased with an organic solvent. , 5% salt aqueous solution, spray amount 1.0-2.0 ml / hr / 80 cm ² , 3 hours), and washed with water to remove excess salt, and allowed to stand naturally for 24 hours. A rust test piece was prepared.

  In addition, each 500 ml of the test solution of the scale remover according to each of the above examples and comparative examples was placed in a circular container at 400 r. p. m. The above rust test piece was immersed in this test solution for 10 minutes while rotating at a stirring speed of, and the rust removal property was visually observed. At the same time, the occurrence of odor during rust removal was determined by the tester's sense of smell.

  The evaluation standard for rust removal is “◎” for a removal rate of 90% or more, “◯” for a removal rate of 70% or more and less than 90%, and a removal rate of 50% or more and less than 70%. “Δ” means that the ratio is less than 50% and “x” means that the removal rate is less than 50%. The odor evaluation criteria are “◎” when almost no bad odor is felt, “○” when a little bad odor is felt, but “△” when a little bad odor is felt. The case where the bad odor was strong was designated as “x”. These evaluation results are shown in Table 1.

  According to the present invention, there is provided a scale remover which contains thiocarboxylic acids as an organic acid as a main component, has excellent scale removal performance at the time of use and significantly reduces the generation of sulfur-specific odor.

Claims (4)

A scale remover comprising at least one selected from thiocarboxylic acids and salts thereof and at least one reducing agent. The scale removing agent according to claim 1, wherein the thiocarboxylic acid and a salt thereof are thiodicarboxylic acid and a salt thereof. The scale removing agent according to claim 2, wherein the thiodicarboxylic acid is thiomalic acid, and the salt of the thiodicarboxylic acid is a salt of thiomalic acid. The scale remover according to any one of claims 1 to 3, wherein the scale remover is adjusted within a range of pH 5.0 to 8.5.