JP2002219491A - Scale inhibitor - Google Patents

Abstract

(57) [Problem] To provide a scale inhibitor which is effective for scale prevention in a boiler water system, a cooling water system, and the like, and is particularly effective in preventing silica scale. A scale inhibitor containing a polymer having a structural unit represented by the general formula [1].
Here, in the formula, R is hydrogen or a methyl group. Embedded image

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a scale inhibitor. More specifically, the present invention relates to a scale inhibitor which is effective in preventing scale in boiler water systems, cooling water systems, and the like, and particularly exhibits an effect in preventing silica scale.

[0002]

2. Description of the Related Art A scale failure occurs on a heat transfer surface or a pipe in contact with water, such as a cooling water system and a boiler water system. Particularly, in the open-circulation type cooling water system, from the viewpoint of resource saving and energy saving, when performing high concentration operation with less discharge (blowing) of the cooling water outside the system, dissolved salts are concentrated, The heat transfer surface becomes easily corroded and becomes a hardly soluble salt to be scaled. The generated scale causes serious obstacles to the operation of the boiler and the heat exchanger, such as a decrease in thermal efficiency and a blockage of piping. Examples of scale species to be generated include calcium carbonate, calcium sulfate, calcium sulfite, calcium phosphate, calcium silicate, magnesium silicate, magnesium hydroxide, zinc phosphate, zinc hydroxide, and basic zinc carbonate. For calcium and magnesium scales, a polymer having a carboxyl group obtained by polymerizing maleic acid, acrylic acid, itaconic acid, etc. is effective. If necessary, vinyl sulfonic acid, allyl sulfonic acid, 2-acrylamide- A copolymer obtained by combining a vinyl monomer having a sulfonic acid group such as 2-methylpropanesulfonic acid in accordance with the quality of a target water is generally used as a scale inhibitor. JP-A-61-107998 proposes a scale inhibitor containing an acrylamide-based polymer and an acrylic acid-based polymer as a scale inhibitor having an excellent effect of preventing silica-based scale, and is disclosed in JP-A-2-31894. A scale inhibitor containing polyethylene glycol and a phosphonic acid or carboxylic acid-based polymer has been proposed as a composite water treatment agent having effects such as prevention of scale in a cooling water system, corrosion protection, and slime prevention.
No. 266 discloses a water treatment method capable of preventing slime, scale, corrosion damage and generation of Legionella bacteria irrespective of water quality fluctuations and operating conditions of a cooling water. And a method of adding a phosphonic acid or carboxylic acid polymer. As described above, polymers are properly used depending on the scale type. The water used in the cooling water system is usually industrial water, tap water, or the like, and thus various ionic species are present in the water. Therefore, especially when performing a high concentration operation, a scale inhibitor capable of effectively coping with all scale types is required, but such a scale inhibitor does not yet exist. In particular, at present, there is no polymer effective for preventing the adhesion of silica-based scale. For example, an acrylamide polymer has a scale preventing effect when the silica concentration is low, but has no effect when the silica concentration is high. This is considered to be because the action of the amide group on silica is reduced due to the carboxyl group generated by partial hydrolysis of acrylamide. As described above, Japanese Patent Application Laid-Open No. 7-256266 proposes the use of a cationic polymer. However, since it is cationic, it reacts not only with silica in water but also with dirt (slime) derived from piping and microorganisms. Easy and not stable. The present inventors have disclosed in Japanese Patent Application Laid-Open No. 10-1659.
No. 86 proposes the use of a polymer having an N-vinyl carboxylic acid amide unit or a polymer having an amino group obtained by hydrolyzing the same, but because it is also cationic, it is necessary to use only silica in water. And it easily reacts with dirt (slime) derived from pipes or microorganisms, and the effect of preventing silica scale is not stable.

[0003]

The present invention is effective for preventing scale in boiler water systems, cooling water systems, and the like.
In particular, it has been made to provide a scale inhibitor which is effective in preventing silica-based scale.

[0004]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that a polymer having 3 units of nylon obtained by hydrogen transfer polymerization of (meth) acrylamide has an excellent scale. The inventors have found that the present invention has a preventive effect, and have completed the present invention based on this finding. That is, the present invention provides (1) a scale inhibitor comprising a polymer having a structural unit represented by the general formula [1],

Embedded image (Wherein, R is hydrogen or a methyl group). Furthermore, as a preferred embodiment of the present invention, (2) the scale inhibitor according to item 1, wherein the polymer is a water-soluble polymer having a structural unit represented by the general formula [1] of 10 mol% or more. it can.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The scale inhibitor of the present invention contains a polymer having a structural unit represented by the general formula [1].

Embedded image However, in the general formula [1], R is hydrogen or a methyl group. The polymer having a structural unit represented by the general formula [1] as a basic skeleton can be produced by heating acrylamide or methacrylamide together with a strong base in a solution and performing hydrogen transfer anion polymerization. The polymerization method is described in Am. Chem. Soc., 79, 3960 (195
7). Polym. Sci. Part A-1, Volume 6, 3187
(1968); Polym. Sci. Polym. Phys., 23rd
Vol. 733 (1985), Makromol. Chem., No. 193
Vol., Page 2561 (1992). The polymer having the structural unit represented by the general formula [1] is β-
It can also be produced by polymerization or copolymerization of alanine, 2-methyl-β-alanine or derivatives thereof.

In the present invention, as the polymer having a structural unit represented by the general formula [1], a homopolymer in which R is hydrogen in the general formula [1], that is, nylon 3,
A homopolymer in which R is a methyl group, a copolymer having a structural unit in which R is hydrogen and a structural unit in which R is a methyl group, a structural unit represented by the general formula [1], and -CH ₂ CR (C
Examples include an apparent copolymer having a structural unit represented by ONH ₂ ) — and a copolymer having a structural unit represented by the general formula [1] and a structural unit of another comonomer. Other comonomers include, for example, ε-caprolactam, δ-valerolactone, β-methyl-δ-valerolactone, and the like. The polymer used in the present invention is water-soluble, and preferably has at least 10 mol% of a structural unit represented by the general formula [1].
More preferably, it has at least mol%. If the amount of the structural unit represented by the general formula [1] is less than 10 mol%, the effect of preventing scale may be insufficient.

The proportion of the structural unit represented by the general formula [1] in the polymer can be determined based on an infrared absorption spectrum, a proton nuclear magnetic resonance spectrum and the like. For example, nylon 3 obtained by polymerization of acrylamide
Unit -CH ₂ CH ₂ CONH- and acrylamide unit -C
In the case of a polymer having H ₂ CH (CONH ₂ ) —, the infrared absorption spectrum was measured, and 1 was derived from the nylon 3 structure.
675 cm ⁻¹ , 1540 cm ⁻¹ absorption intensity of secondary amide,
1660 cm ^-1 , 1620 derived from acrylamide structure
The ratio of 3 units of nylon can be calculated from the ratio of the absorption intensity of amide I and amide II in cm ^-1 . The molecular weight of the polymer having the structural unit represented by the general formula [1] used in the present invention is not particularly limited, but is preferably from 1,000 to 100,000, and preferably from 2,000 to 20,000. Is more preferred. When the molecular weight is less than 1,000,
The effect of preventing scale may be insufficient. When the molecular weight exceeds 100,000, the polymer aqueous solution may have a high viscosity and may be difficult to handle. The molecular weight of the polymer having the structural unit represented by the general formula [1] can be determined by determining a molecular weight distribution curve by gel permeation chromatography and converting polyethylene glycol as a standard substance.

The form of the scale inhibitor of the present invention is not particularly limited. For example, a polymer aqueous solution or a polymer aqueous dispersion prepared at an arbitrary concentration can be added to a target aqueous system. There is no particular limitation on the place where the scale inhibitor of the present invention is added, and it can be directly added to the place where the scale adheres, or it can be added to an arbitrary place preceding the place. For example, in a cooling water system, it can be directly added to an arbitrary place such as a heat exchanger main body, a circulating water pit, a piping line of a cooling tower, etc. You can also. When using the scale inhibitor of the present invention, there are no particular restrictions on water quality conditions, boiler, heat exchanger operating conditions, and the like, and operation can be performed under ordinary water quality, boiler, and heat exchanger operating conditions. By the scale inhibitor of the present invention, calcium carbonate, calcium sulfate, calcium phosphate, zinc phosphate, zinc hydroxide, magnesium silicate,
Although it is possible to prevent adhesion of scale such as silica generated in a normal boiler or a cooling water system, it is particularly effective in preventing silica-based scale. Although the detailed mechanism of action of the scale inhibitor of the present invention is unknown, the weak positive charge of the carbonyl group of the polarized amide group to the negative charge of silica causes the silica-based scale pipe wall and heat transfer surface. It is considered that adhesion to a cooling tower filler or the like is effectively prevented. Further, the polymer having the structural unit represented by the general formula [1] is a polymer having a weak positive charge, and has a weaker positive charge than a conventional cationic polymer. Few.

[0009]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. Production Example 1 10 g of acrylamide powder recrystallized from ethyl acetate and dried under reduced pressure was placed in a 100 mL four-necked flask, and 0.5 mol% of calcium hydride relative to acrylamide was added as an initiator under a nitrogen atmosphere. After mixing well with a stirrer, 1
The four-necked flask was immersed in an oil bath preheated to 50 ° C., and polymerized for 30 minutes under a nitrogen atmosphere. The obtained polymer was pulverized to obtain a powder polymer. The whole amount of the powdered polymer was poured into 200 mL of pure water, stirred for 6 hours, and then filtered through a 3G glass filter to remove insolubles. A part of the filtrate was collected, and the evaporation residue was measured. As a result, the yield was 79.5% by weight. As a result of GPC measurement using polyethylene glycol as a standard, the molecular weight was about 8,000. In addition, the infrared absorption spectrum 1
540 cm ^-1 and 1620 cm ^{- 1} intensity ratio, nylon 3 structural units was estimated to be contained about 65 mole%. Production Example 2 The same operation as in Production Example 1 was carried out except that the amount of the initiator was 1.0 mol% based on acrylamide, to obtain a powder polymer.
It was estimated that the yield was 83.3% by weight, the molecular weight was about 4,500, and the nylon 3 structural unit was about 58 mol%. In the examples and comparative examples, the scale adhesion test
It carried out by the following method. That is, the heat transfer area is about 0.
To a 0.45 m ³ open circulation cooling water system having a 25 m ² heat exchanger, tap water plus pure water and salts is added as circulating water and makeup water, and the quality of the circulating water is adjusted to pH 8.
5. The system was operated for 30 days while controlling to have a calcium hardness of 150 mg CaCO ₃ / L, an M alkalinity of 150 mg CaCO ₃ / L, silica of 180 mg SiO ₂ / L, and a magnesium hardness of 160 mg CaCO ₃ / L. The heat exchanger tubes are
The material used was SUS304 having an outer diameter of 19 mm. The circulating water inlet temperature was maintained at 45 ° C., the outlet temperature was maintained at 75 ° C., and the circulating water flow rate was set at 0.5 m / s. After the operation for 30 days, the scale deposition rate was determined from the increase in the weight of the tubes of the heat exchanger. The silica content in the scale was calculated. Table 1 shows the drugs used in Examples and Comparative Examples.

[0010]

[Table 1]

Example 1 About 65 mol% of the nylon 3 structural unit obtained in Production Example 1 was used.
The polymer having a molecular weight of about 8,000 contained in the circulating water
Add it to a concentration of 20 mg / L and run for 30 days.
Rolled. Scale deposition rate is 0.8mg / cm^Two/ 30 days
And the silica content in the scale was 3% by weight. Example 2 About 58 mol% of the nylon 3 structural unit obtained in Production Example 2 was used.
The polymer having a molecular weight of about 4,500 contained in the circulating water
Add it to a concentration of 20 mg / L and run for 30 days.
Rolled. Scale deposition rate is 1.0mg / cm^Two/ 30 days
And the silica content in the scale was 5% by weight. Comparative Example 1 Sodium hexametaphosphate having a concentration in circulating water of 20 mg /
L and the operation was performed for 30 days. S
Kale deposition rate is 28mg / cm^Two/ 30 days,
The silica content in the oil was 55% by weight. Comparative Example 2 Acrylic acid having a molecular weight of 8,500 and 2-acrylamide-
2-methylpropanesulfonic acid (molar ratio 80:20)
The copolymer was adjusted to a concentration of 20 mg / L in circulating water.
And operated for 30 days. Scale deposition speed
The degree is 35mg / cm ^Two/ 30 days, silica in scale
Was 51% by weight. Comparative Example 3 Polyacrylamide having a molecular weight of 3,000 was
Add it to a concentration of 20 mg / L and run for 30 days.
Rolled. Scale deposition rate is 32mg / cm^Two/ 30 days
And the silica content in the scale was 43% by weight.
Table 2 shows the results of Examples 1 and 2 and Comparative Examples 1 to 3.
You.

[0012]

[Table 2]

As can be seen from Table 2, in Examples 1 and 2 in which a polymer having three structural units of nylon was added, the rate of scale adhesion was lower than in Comparative Examples 1 to 3 in which a conventional scale inhibitor was added. Extremely small and low in silica content in the scale.

[0014]

The scale inhibitor of the present invention has a remarkable effect on scale prevention in boiler water systems, cooling water systems and the like, and is particularly effective in preventing silica scale.

Claims (1)

[Claims] 1. A scale inhibitor comprising a polymer having a structural unit represented by the general formula [1]. Embedded image (Wherein, R is hydrogen or a methyl group.)