JPH0454520B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] This invention relates to a water-based scale inhibitor. [Prior Art] Scales such as calcium salts, magnesium salts, silica, etc. are formed on walls of boiler water systems, cooling water systems, etc. that come into contact with water, and sometimes on heat transfer surfaces. Conventionally, as scale inhibitors for preventing or removing such scale formation, sodium polyacrylate (e.g., Japanese Patent Publication No. 30914/1982), Mannitz decomposition products of polyacrylamide (e.g., Japanese Patent Publication No. 30914/1986),
Polymer compounds such as No. 58-223497) have been proposed. [Problems to be solved by the invention] Conventional scale inhibitors containing polymeric compounds as active ingredients have shown excellent scale prevention effects in limited fields of application, but they are not always satisfactory; There was a demand for a scale inhibitor with high scale prevention effect. [Means for Solving the Problems] The present invention is intended to meet the above-mentioned needs, and provides a scale inhibitor with a high scale prevention effect by using a polymer compound with a specific structure. This invention is a scale inhibitor characterized by containing a polymer compound represented by the following general formula []. (In the formula, R ₁ , R ₂ , R ₃ are hydrogen atoms or methyl groups,
M is a hydrogen atom, ammonium group, organic amine group, or alkali metal, l, m, n are mole% of each unit
So, 0<l, 0≦m, 10≦l+m≦99, 1≦n≦
90, l+m+n=100. ) The polymer compound of the general formula [] has the following general formula [] to [], The units represented by are randomly copolymerized, and the molecular weight is 500 to 300,000, preferably 1,000.
~50000 or so, l+m is 75~99 mol%, n is 1~
25 mol% is preferred. The polymer compound of the general formula [] is produced by subjecting an acrylamide polymer or its hydrolyzate to Hoffmann degradation or, if necessary, further hydrolyzing it. Examples of acrylamide-based polymers include polyacrylamide and polymethacrylamide, which can be obtained by dissolving acrylamide or methacrylamide in a solvent such as water or methanol, adding a polymerization initiator, and polymerizing. As the polymerization initiator, hydrogen peroxide, ammonium persulfate, potassium persulfate, benzoyl peroxide, azobisisobutyronitrile, and other commonly used initiators can be used alone or in combination. Furthermore, a redox polymerization initiator may be used in combination with a reducing agent. These acrylamide polymers may be hydrolyzed with an alkali in advance. Hydrolysis rate depends on alkali concentration, reaction temperature,
It can be controlled by time etc. Further, as the acrylamide polymer, a copolymer of acrylamide or methacrylamide or the like and acrylic acid or methacrylic acid may be used. Hoffman decomposition products of acrylamide polymers are
The above acrylamide polymer is made into an aqueous solution, and hypohalites such as sodium subzinc chlorite, sodium hypobromite, and calcium hypochlorite are applied in the presence of alkali such as sodium hydroxide and potassium hydroxide. It can be obtained by Hofmann decomposition. The Hoffman decomposition rate is expressed by the general formula []
The alkali or hypohalite concentration, reaction temperature, time, etc. are controlled so that the unit of is 1 to 90 mol %. The Huffman-decomposed product thus obtained may be used as it is, or may be used in the form of an acid salt. The Hofmann decomposition product obtained by the above production method has a high pH
Since the stability over time is poor, it is desirable to use it as an acid salt after neutralizing it with an acid that does not impair solubility, such as hydrochloric acid or acetic acid. The above Hoffmann decomposition product may be hydrolyzed with an alkali. The scale inhibitor of the present invention contains the polymer compound represented by the above general formula [] as an active ingredient, and may contain other ingredients in addition to this. [Function] The scale inhibitor of the present invention is added as it is or dissolved in water etc. to water systems such as boiler water systems, geothermal water systems, open or closed circulation cooling water systems, and one-time cooling water systems to prevent scale. . The amount added varies depending on the molecular weight, the ratio of (l+m) to n, the metal ion and silica concentration of the target water system, etc., but is generally about 1 to 200 mg/. By adding the scale inhibitor of the present invention to the target water system, it suppresses the formation of metal salt scale such as calcium salts and magnesium salts and silica scale, and also prevents scale by removing scale that has already been formed. Highly effective in preventing scale. In addition, unlike conventional cationic polymer compounds, it is not absorbed by slime and consumed, and maintains its scale prevention effect over a long period of time. The scale inhibitor of the present invention can be used in combination with other scale inhibitors, anticorrosives, slime control agents, etc. [Effects of the Invention] According to the present invention, since a polymer compound having a specific structure is used as an active ingredient, the scale prevention effect,
In particular, it has a high scale prevention effect on silica scale, and can maintain the scale prevention effect for a long period of time without being adsorbed by slime. [Examples] Examples of the present invention will be described below. Table 1 lists the scale inhibitors used in the examples.

【table】

[Table] Example 1 500 mg/(as CaCO ₃ ) of NaHCO ₃ , 210 mg/(as SiO ₂ ) of Na ₂ SiO ₃ ·9H ₂ O, and 200 mg/(as CaCO ₃ ) of MgSO ₄ ·7H ₂ O in distilled water.
A predetermined amount of the scale inhibitor shown in Table 1 was added to the aqueous system, the pH was adjusted to 9.0, the liquid temperature was maintained at 70°C, and the mixture was allowed to stand for 40 hours. After 40 hours, this liquid was filtered, and the silica concentration (mg/) and magnesium hardness (mg/, as CaCO ₃ ) in the filtrate were measured according to the analysis method of JIS K0101. The results are shown in Table 2. From the results in Table 2, it can be seen that the examples have a higher scale prevention effect than similar compounds (comparative examples) and are sufficiently practical.

【table】

[Table] Example 2 Yokohama city water was added to an open circulating cooling water system with a heat exchanger made of SUS304 with a heat transfer area of approximately 0.25 m ² and a holding water volume of 0.45 m ³ , and the circulating water inlet temperature of the heat exchanger was 30°C. It was operated for 30 days with the outlet temperature at 50°C, the circulating water flow rate at 0.5 m/s, and the concentration factor at 5 times. Circulating water quality is conductivity 1050μS/cm, PH9.0, calcium hardness 250mg/, magnesium hardness 125mg/,
The SiO ₂ concentration was 150 mg/, and the M alkalinity was 250 mg/. A predetermined amount of the scale inhibitor shown in Table 1 was added to this aqueous system, and the rate of scale adhesion to the heat exchanger tube was measured. The results are shown in Table 2. From the results in Table 2, it can be seen that the scale deposition rate of the examples was extremely low compared to that of the comparative examples.

【table】

【table】

Claims (1)

[Scope of Claims] 1. A scale inhibitor characterized by containing a polymer compound represented by the following general formula []. (In the formula, R ₁ , R ₂ , R ₃ are hydrogen atoms or methyl groups,
M is a hydrogen atom, ammonium group, organic amine group, or alkali metal, l, m, n are mole% of each unit
So, 0<l, 0≦m, 10≦l+m≦99, 1≦n≦
90, l+m+n=100. ) 2. The scale inhibitor according to claim 1, wherein the polymer compound is a Hofmann decomposition product of an acrylamide polymer. 3. The scale inhibitor according to claim 1, wherein the polymer compound is a Hofmann decomposition product of a hydrolyzate of an acrylamide polymer. 4. The scale inhibitor according to claim 1, wherein the polymer compound is a hydrolyzate of a Hofmann decomposition product of an acrylamide polymer.