JPH0119958B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to scale removers. In various water supply and distribution systems, especially in heat exchange systems such as boilers, heat exchangers, and cooling tower systems, scale that forms inside piping due to concentration of water, corrosion of metal surfaces, and inorganic substances in the water can cause heat transfer and cooling effects. As this is a significant impediment to descaling, the removal of scale has become one of the most important tasks. Among scales, iron-based scale containing a large amount of iron oxide, calcium-based scale, and silicic acid-based (also referred to as silica-based) scale are generally considered to be problematic. Conventionally, acid cleaning with inorganic acids such as hydrochloric acid and sulfuric acid, and organic acids such as formic acid and citric acid has been widely used to remove scale, but it is not effective in removing scale that contains a large amount of silicic acid (SiO ₂ ). is not sufficient. However, since there are no other effective methods, the treatment of such silica-based scales requires time-consuming and cumbersome methods, namely:
A method used was to alternately apply caustic soda and hydrochloric acid many times. Recently, there have been proposals to remove silica scale by using acidic fluorine compounds in combination with organic acids or hydrogen peroxide (Japanese Patent Publication No. 55-33679, Japanese Patent Application Laid-Open No. 55-109498), but there are concerns regarding toxicity and work safety. It has many disadvantages, such as corrosion resistance, corrosiveness to base metals, and waste liquid treatment. In addition, there is currently no other suitable method for removing silica-based scale, and there is a strong desire to develop a new method. The present inventors surprisingly discovered that α-hydroxyacetic acid,
It has been found that silica scale can be effectively removed by using a polycarboxylic acid or a salt thereof in combination with an anionic or nonionic surfactant. The present invention is based on this new finding. α-Hydroxyacetic acid is also called glycolic acid. It is used especially in combination with formic acid or citric acid for the removal of iron-based scale. However, such a formulation cannot remove silica scale. The polycarboxylic acid used in the present invention may be in a free form or a water-soluble salt form, such as polyacrylic acid (for example, Kayacrylic Resin H-32 (trade name) manufactured by Nippon Kayaku Co., Ltd.), polyacrylic acid sodium (For example, Nippon Kayaku
Kayacrylic Resin H-35N (trade name) manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd., Marposol RA-40 (trade name) manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.), ammonium polyacrylate (e.g. Matsumoto Yushi Pharmaceutical Co., Ltd.)
Organic acid polymers such as Marposol RA-40A (trade name); aminopolycarboxylic acids such as ethylenediaminetetraacetate acid (EDTA) and nitrilotriacetate acid (NTA); e.g. Compound represented by (Ciba Geigy, Verklein 500 (trade name)), 2-phosphono-1,2,4-
Tricarboxybutane (Bayer, PBS-AM
Phosphino or phosphono such as (trade name)
It can include polycarboxylic acids and the like. The anionic surfactant used in the present invention is a surfactant having a hydrophilic group such as a sulfonate, a sulfate ester salt, a phosphate ester salt, etc., such as an alkyl sulfate, an alkylaryl sulfonate, a dialkyl sulfosuccinate ester salt, Examples include alkylamide sulfonates, ricinoleic acid ester sulfates, α-sulfo fatty acid alkyl ester salts, α-phosphono fatty acid ester salts, dialkyl phosphate ester salts, among which dialkyl sulfosuccinate ester salts are particularly effective. . On the other hand, as the nonionic surfactant, ordinary ether type, ether ester type, ester type, nitrogen-containing type surfactants, etc. can be used. For example, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenol ether, polyoxyethylene alkyl phenol ether, Oxyethylene/polyoxypropylene block polymer, polyoxyethylene fatty acid ester, polyoxyethylene-9,10-octadecanediol, polyoxyethylene-9,10-
Examples include dihydroxystearonitrile and ethylene oxide adducts of linear secondary alcohols. The scale remover of the present invention can be provided as an aqueous solution by mixing α-hydroxyacetic acid, a polycarboxylic acid or a salt thereof, and an anionic or nonionic surfactant using a conventional method. The basic formulation example is 10 to 50% (by weight) of α-hydroxyacetic acid and 1 to 50% of polycarboxylic acid or its salt based on the total amount (based on 100% purity).
It is an aqueous solution containing 20% and 0.1 to 2% of the above surfactant. At the time of formulation, corrosion inhibitors commonly used in this field and, in some cases, antifoaming agents and other additives preferred for scale removal and which do not significantly impair the effectiveness of the drug of the present invention may be optionally added. Of course you can. It goes without saying that the above formulation examples can be suitably changed to a blending ratio convenient for use, depending on the concentration, ie, dilution, at the time of actual use. When the drug of the present invention is actually used,
After preliminary investigation of the amount of water held by the system to be treated and the type and degree of scale, the chemicals may be added in accordance with the usual method. According to the present invention, not only calcium scale and iron scale, but also silica scale, which has been considered difficult in the past, can be effectively removed. The details of the mechanism of action of the scale remover of the present invention will require further research, but the metals contained in scale (calcium, magnesium,
It is thought that the chemical first acts on the iron (iron) and dissolves a part of it, and then the chemical penetrates deep from the dissolved part, causing cracks in the scale, resulting in peptization and flaking, and due to the combined effects of each component. Dissolution, peptization, and exfoliation progress. In this sense, the addition of dissolution promoters, agents or means that promote peptization or exfoliation may further advantageous embodiments of the present invention. Example 1 A test chemical solution (aqueous solution) containing each component in the proportions shown in the table below was prepared, 100 ml of it was placed in a 200 ml beaker, and a block scale (1 cm x 1
cm) was immersed and left at room temperature for 5 hours, and the peptized state of the scale was observed. Scale composition (%) SiO ₂ Fe ₂ O ₃ CaO MgO Al ₂ O ₃ 36.8 0.89 19.3 31.3 0.06 Note) Appearance of scale: Evaluation criteria for gray-white peptization No change is (-), complete peptization is () The evaluation was performed by dividing the range into (±), (+), and ().

[Table] These results indicate that even if α-hydroxyacetic acid is used in combination with a surfactant, or α-hydroxyacetic acid is used in combination with polycarboxylic acid, no scale peptizing effect is obtained, or even if it is obtained, it is not practical. This shows that a good peptizing effect was obtained in the inventive plot, on the other hand. In addition, the results of the present invention area can be seen as model test results for on-site treatment, and therefore provide suggestions regarding the amount and concentration of each component to be used. Example 2 A comparative test of the peptizing effect of silica scale was conducted using the same method as in Example 1 for various organic acids and inorganic acids shown in the table below. The scale is the same as that used in Example 1. In addition, the acids shown in the table below were added to the test chemical solution (aqueous solution) containing 0.2% and 0.02% of the polymaleic acid and surfactant used in Example 1 to a predetermined concentration. .

[Table] These results show that α-hydroxyacetic acid is specifically effective. A 2% hydrochloric acid solution is commonly used to remove iron scale and calcium scale, but no peptizing effect on silica scale was observed. In addition, sulfamic acid, malic acid, oxalic acid, citric acid, tartaric acid, etc., which are provided as powders for the removal of iron-based scale and have been pointed out to be problematic because the powder often remains in pipes, are also effective against silica-based scale. No peptizing effect was observed. Example 3 Regarding the test chemical solution (aqueous solution) shown in the table below,
The peptizing performance of silica-based scale was investigated. The test scale, polymaleic acid, surfactant, and test method are the same as in Example 1.

[Table] These results indicate that the scale remover formulated according to the present invention has an effect of effectively deflocculating silica scale in a short period of time, which was conventionally considered difficult.
In addition, this result provides suggestions for how to use the scale remover formulated according to the present invention in the field.
This shows that a more effective peptizing effect can be obtained when the treatment concentration of α-hydroxyacetic acid is 2.5 to 3% or more. Example 4 The scale removal effect of various polycarboxylic acids was observed using the same method as in Example 1. The scale and surfactant are the same as in Example 1. Soaking time is 5 hours. Test chemical solution (aqueous solution) composition α-hydroxyacetic acid 5% Polycarboxylic acid (salt) 0.2% Surfactant 0.02%

[Table] Example 5 The scale removal effect of various surfactants was observed using the same method as in Example 1. The scale and polycarboxylic acid are the same as in Example 1. Soaking time is 5 hours. Test chemical solution (aqueous solution) composition α-hydroxyacetic acid 5% Polymaleic acid 0.2% Surfactant 0.02%

[Table] This result shows that anionic and nonionic surfactants are effective. Example 6 100 ml of a test chemical solution (aqueous solution) having the following composition was placed in a 200 ml beaker, and lump scales (1 cm x 1 cm) of various compositions were immersed in this to observe the peptized state of the scale. As a result, both scales are 2~
Complete peptization occurred within 5 hours. Test chemical composition α-hydroxyacetic acid 5% Polyacrylic acid (Kayacryl Resin H-32)
0.5% sodium dioctyl sulfosuccinate (Marpomerse PT) 0.04% dissolved in water.

[Table] (Note) “Others” includes loss due to ignition. same as below.
This result shows that the scale remover of the present invention is effective not only against silica scale but also against calcium scale. Example 7 A scale remover of the present invention was added to a 5HP condenser and a 15RT cooling tower at the following treatment concentrations, and scale cleaning was carried out for about 2 hours during normal operation. The temperature was 27-32°C. α-Hydroxyacetic acid 5.0% Polyacrylic acid (Kayacryl Resin H-32)
0.5% Sodium dioctyl sulfosuccinate (Marpomerce PT) 0.04% Ibitu 30AR (corrosion inhibitor) 0.01% Scale composition (%) Appearance SiO ₂ Fe ₂ O ₃ CaO MgO Gray 42.5 11.7 1.46 1.24 Appearance P ₂ O ₅ Other gray 0.75 1.91 As a result, the high voltage in the condenser is 10
The weight decreased from Kg/cm ² to 8 Kg/cm ² , and when the condenser was opened, the scale had been completely removed. Example 8 α-Hydroxyacetic acid 25 parts (weight, same below) Polyacrylic acid 2 parts Sodium octylsulfosuccinate 0.2 parts These were dissolved in water to make a total amount of 100 parts. In this formulation, small amounts of corrosion inhibitors and antifoaming agents may be added. For example, apply this scale remover to
It is added to water piping systems such as cooling towers, boilers, and heat exchangers to clean scale at a concentration of 10 times diluted. Example 9 α-Hydroxyacetic acid 28 parts Polymaleic acid 2.5 parts Sodium octylsulfosuccinate 0.3 parts These were dissolved in water to make a total amount of 100 parts. Small amounts of corrosion inhibitors and antifoaming agents may be added to this formulation. For example, apply this scale remover to 3 to 10
A cooling tower to obtain a concentration of double dilution,
Add to water piping systems such as boilers and heat exchangers to clean scale.

Claims (1)

[Claims] 1. A scale remover containing α-hydroxyacetic acid, a polycarboxylic acid or a salt thereof, and an anionic or nonionic surfactant.