JP2002059193A - Method of preventing silica-base scale - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of preventing scale which is effective for preventing the adhesion of the silica-base scale generated in a cooling water system and boiler water system. SOLUTION: One or more kind of the water-soluble cyclic compound expressed by general formula (I) is added to the water system. [R1 and R2 are respectively independently hydrogen, methyl groups, ethyl groups, propyl groups, isopropyl groups, hydroxymethyl group; X and Y are respectively independently -O-, -N-R3-, -CR4R5-; Z is C=O, -CH(OR6)-, -CH2-; R3, R4, R5 and R6 are respectively independently hydrogen, methyl groups, ethyl groups, propyl groups, isopropyl groups, vinyl groups; (n) is an integer of 1, 2 or 3].

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for preventing scale adhesion, and more particularly to a method for effectively preventing silica-based scale generated in a cooling water system or a boiler water system.

[0002]

2. Description of the Related Art In a cooling water system, a boiler water system, or the like, a scale failure occurs on a heat transfer surface or a pipe in contact with water.
In particular, in the open circulation cooling water system, from the viewpoint of resource saving and energy saving, there is a case where a high concentration operation is performed by limiting a waste amount (blowing amount) of cooling water, and salts dissolved in water are concentrated. Forms poorly soluble salts and scales. Examples of scale species to be generated include calcium carbonate, calcium sulfate, calcium sulfite, calcium phosphate, magnesium hydroxide, zinc phosphate, zinc hydroxide and the like. For these general scales, water-soluble polymers such as acrylic acid and maleic acid, organic phosphonic acids such as hydroxyethylidene diphosphonic acid and phosphonobutane tricarboxylic acid, and inorganic phosphoric acid are added to aqueous systems. It is possible to solve the problem, and these antiscalants are widely and generally used.

[0003] However, silica-based scales have become a problem with recent high concentration. Silica-based scale means that silica ions contained in water combine with metal ions such as calcium ions and magnesium ions to form sparingly soluble silicates such as calcium silicate, magnesium silicate, and aluminum silicate, and in some cases, these silicates and silica And a complex with a hardly soluble inorganic compound such as calcium carbonate and magnesium carbonate, and refers to a scale-like substance attached to a metal surface or the like. Generally, silica has low solubility, and the silica concentration is 100 to 150 m in a cooling water system.
It has the property of being scaled even at about g / L, and at present, the concentration is set by the silica concentration.

There are several proposals as scale inhibitors for silica-based scale, but none of the scale inhibitors are effective enough. For example, an acrylamide-based scale inhibitor [Japanese Patent No. 1851103] exhibits a certain effect when the silica concentration is low, but is effective for aqueous systems having a relatively high silica concentration such as a silica concentration exceeding 200 mg / L. Is not effective enough. Also, a method using a quaternary ammonium salt [JP-A-57-11039]
No. 8], and a method using a polyethyleneimine compound [Patent No. 2974378] has a problem that the inhibitor itself is deposited and deposited on pipes and walls of heat exchange under the influence of coexisting ions depending on water quality conditions. There is a practical problem.

[0005] Since the scale causes a serious trouble in the operation of the apparatus such as a decrease in heat efficiency or a blockage in a heat exchanger or a pipe, a countermeasure is required. In particular, once a silica-based scale is formed, it is very difficult to remove the scale once it is formed. Therefore, it is important to suppress the formation of the scale.

[0006]

SUMMARY OF THE INVENTION The present invention provides a cooling water system,
An object of the present invention is to provide a scale prevention method effective for preventing silica-based scale from being generated in a boiler water system.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, by adding a compound having a specific structure to a target aqueous system, a silica-based scale was obtained. They have found that they exhibit an excellent effect of preventing adhesion, and have completed the present invention based on this finding.

That is, the invention of claim 1 is a method for preventing silica-based scale, wherein R ¹ and R ² are represented by the general formula (I):
Each independently represents hydrogen, a methyl group, an ethyl group, a propyl group, or an isopropyl group, and X and Y each independently represent -O-,
—NR ³ —, —CR ⁴ R ⁵ —, and Z represents C は O, −
CH (OR ⁶ ) —, —CH ₂ —, and R ³ , R ⁴ , R ⁵ ,
R ⁶ is each independently hydrogen, methyl, ethyl, propyl, isopropyl, vinyl, or hydroxymethyl, and n is an integer of 1, 2, or 3. At least one of the water-soluble cyclic compounds represented by the formula (1) is added to an aqueous system.

[0009]

Embedded image

[0010] The invention of claim 2 is the silica-based scale prevention method of claim 1, wherein the water-soluble cyclic compound represented by the general formula (I) is ethylene carbonate, propylene carbonate, 2-pyrrolidone, γ-butyrolactone. ,
It is characterized by being at least one selected from γ-valerolactone, ε-caprolactam, ε-caprolactone, and 2-methoxy-1,3-dioxolane.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a water-soluble cyclic compound represented by the general formula (I) (hereinafter simply referred to as "water-soluble cyclic compound").
) Is added to an aqueous system for the purpose of preventing silica-based scale.

In the general formula (I), R ¹ and R ² are each independently hydrogen, methyl, ethyl, propyl, isopropyl or hydroxymethyl, preferably hydrogen or methyl. X and Y are each independently -O-
^{, -N-R 3 -, -} CR 4 R 5 - and it is, preferably -O
-, -N-R ³ - it is [R ^3, R ^4, R ⁵ are each independently hydrogen, a methyl group, an ethyl group, a propyl group, an isopropyl group, a vinyl group, preferably hydrogen or a methyl group is there. ]. Z represents C = O, -CH (OR ⁶ )-,-
CH ₂ —, preferably C ＝ O or —CH (O
R ⁶ ) — wherein R ⁶ is hydrogen, methyl, ethyl, propyl, isopropyl or vinyl, preferably hydrogen or methyl. ]. n is 1, 2, 3
And preferably 1.

Specific examples of the water-soluble cyclic compound include ethylene carbonate, propylene carbonate, glycerol carbonate, γ-butyrolactone, 2-methoxy-1,3-dioxolan, γ-valerolactone, δ-
Valerolactone, δ-valerolactam, ε-caprolactone, ε-caprolactam, ethylene urea, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-vinylpyrrolidone, 1,3-dioxolan, 2-oxazolidone, and the like, Preferably, ethylene carbonate, propylene carbonate, 2-pyrrolidone, γ-butyrolactone, γ-valerolactone, ε-caprolactam, ε-caprolactone, 2-methoxy-1,3-dioxolane are exemplified. In particular, ethylene carbonate has a high scale prevention effect aimed at by the present invention, has high handling safety, is inexpensive, and can be suitably used.

A method for applying the water-soluble cyclic compound to an aqueous system is as follows.
Although not particularly limited, usually, the silica-based scale is continuously or intermittently added to a portion where a silica-based scale is generated or an upstream portion of the process by a pump. The amount added
It depends on the degree of scale generation, silica concentration in water, operating conditions of water system (temperature, flow rate, shape of pipes and heat exchangers), etc., and cannot be determined uniformly.
It is 200 mg / L, preferably 50-100 mg / L. The silica-based scale is often hindered when the silica concentration in water is 150 mg / L or more, but even when the silica concentration is lower than 150 mg / L, the metal ion such as magnesium ion coexists. Is coprecipitated with silica when it is combined with hydroxide ions in water to form hydroxide and precipitates, which may greatly promote scaling. Therefore, even if the silica concentration is low,
In the pH range where the metal cations become hydroxides, the silica-based scale may be hindered. For example, when magnesium ions are present, scale hindrance may occur when the pH of the aqueous system is 8 or more. The present invention is directed to the prevention of silica-based scales in open cooling water systems, boiler water systems, steel dust collection water systems, geothermal water systems, and the like. Is often effective.

The water-soluble cyclic compound is usually added to an aqueous system as such or as an aqueous solution.
At this time, other scale inhibitors and anticorrosives, may be mixed with a bactericide or added, or may be mixed in an aqueous system, but may be used in combination with these as long as the effects of the present invention are not impaired It does not hinder anything. In particular, scales such as calcium carbonate, calcium sulfate, calcium sulfite, calcium phosphate, magnesium hydroxide, zinc phosphate, and zinc hydroxide often occur simultaneously with silica scale, and it is important to perform these scale measures simultaneously. .

As a scale inhibitor and an anticorrosive which can be used in combination, water-soluble polymers having a carboxylic acid group such as polyacrylic acid, polymaleic acid, and a copolymer of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid;
And phosphates, polymerized phosphates, phosphates, phosphonates, phosphinates, polyvalent metals such as zinc, aluminum and nickel, azoles such as benzotriazole, tolyltriazole and mercaptobenzothiazole, and hydrazine. No. Examples of disinfectants that can be used in combination include quaternary ammonium salts, chloromethyltrithiazoline, methylisothiazoline, bromochlorodimethylhydantoin, and sodium hypochlorite.

[0017]

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. (Chemicals used: water-soluble cyclic compound) A: Ethylene carbonate (manufactured by Tokyo Chemical Industry Co., Ltd.) B: Propylene carbonate (manufactured by Tokyo Chemical Industry Co., Ltd.) C: γ-butyrolactone (manufactured by Wako Pure Chemical Industries, Ltd.) D: γ- Valerolactone (Tokyo Kasei Co., Ltd.) E: 2-Pyrrolidone (Tokyo Kasei Co., Ltd.) F: 2-Methoxy-1,3-dioxolan (Tokyo Kasei Co., Ltd.) G: δ-Valerolactam (Tokyo) H: ε-caprolactone (Tokyo Kasei Co., Ltd.) I: ε-caprolactam (Tokyo Kasei Co., Ltd.) (Comparative drug) J: Polyethyleneimine (Wako Pure Chemical Co., Ltd., molecular weight) K: Acrylic acid / 2-acrylamide-2-methylpropanesulfonic acid (60:40 weight ratio copolymer, average molecular weight about 10,000) L: Homopolymaleic acid [molecular weight about 2000, F MC, "Belcle 200" (trade name)] (Evaluation of scale inhibitor) 200 MgSO ₄ .7H ₂ O
mg / L (magnesium hardness: 200 mgCaCO ₃ /
L), 210 mg / L of Na ₂ SiO ₃ .9H ₂ O (Si
O ₂ concentration: 210 mg SiO ₂ / L), and NaHCO
₃ at 500 mg / L (M-alkalinity: 500 mg Ca
(CO ₃ / L) in ion-exchanged water to prepare a test solution. The test solution was placed in a glass container, a predetermined amount of a scale inhibitor (50 mg / L and 100 mg / L) was added, the pH was adjusted to 9.0, and the mixture was allowed to stand in a 70 ° C. hot air drier for 48 hours. .

Next, the solution was filtered through a 0.45 μm PTFE membrane filter, and the filtrate was subjected to a flame method using a polarized Zeeman atomic absorption spectrometer (Hitachi Z-6100).
The concentration was measured and converted to SiO ₂ concentration. The scale inhibition rate (%) was calculated from the SiO ₂ concentration by the following equation. Scale suppression rate (%) = {(AB) / (CB)} × 1
00 A: SiO ₂ concentration in the filtrate after the test (mg / L) B: SiO _{2 in} the filtrate after the test when no inhibitor was added
₂ Concentration (mg / L) C: SiO ₂ concentration before test (mg / L) The results are shown in Table 1.

[0019]

[Table 1]

It has been found that the water-soluble cyclic compound mentioned in the present invention has a large ability to suppress the formation of silica as a scale, and that even if the silica concentration is high, the effect is obtained.

[0021]

The method for preventing silica-based scale of the present invention has a high silica-based scale prevention effect, can maintain the scale-preventive effect for a long period of time, reduces the thermal efficiency,
It is possible to prevent problems such as blockage of piping.

Claims (2)

[Claims] 1. A compound of the formula (I) wherein R ¹ and R ² are each independently hydrogen, methyl, ethyl, propyl, isopropyl or hydroxymethyl, and X and Y are each independently ^{-O-, -N-R 3 -,} - CR 4 R 5 - and is, Z
Is, C = O, -CH (OR 6) -, - CH 2 - and is, R
³ , R ⁴ , R ⁵ and R ⁶ are each independently hydrogen, methyl, ethyl, propyl, isopropyl or vinyl;
n is an integer of 1, 2, or 3. ] At least one of the water-soluble cyclic compounds represented by the formula (I) is added to an aqueous system. Embedded image 2. The method according to claim 1, wherein the water-soluble cyclic compound represented by the general formula (I) is ethylene carbonate, propylene carbonate, 2-pyrrolidone, γ-butyrolactone, γ-valerolactone, ε-caprolactam, ε-caprolactone,
The method for preventing silica-based scale according to claim 1, wherein the method is at least one selected from 2-methoxy-1,3-dioxolane.