JP7657045B2 - Water Treatment Chemicals - Google Patents

Description

The present invention relates to a water treatment agent. More specifically, the present invention relates to a water treatment agent used to inhibit scale such as silica scale.

For example, the generation of calcium carbonate, silica, and other scales can be a problem in geothermal power generation, industrial cooling water, boiler water systems, wastewater treatment, and seawater desalination.

For example, the copolymer described in Patent Document 1 improves the dispersibility of hydrophobic particles and also exhibits excellent chelating ability for calcium ions, making it possible to exhibit extremely good scale inhibition ability for the piping and inside of geothermal power generation equipment, and it is disclosed that it can be suitably used as a scale inhibitor for geothermal power generation equipment.

JP 2016-64382 A

As mentioned above, various scale inhibitors have been proposed, but there has been a demand for further improvement in the silica scale inhibition ability.
Therefore, an object of the present invention is to provide a water treatment agent that has superior silica scale inhibition capability compared to conventional agents and can therefore be suitably used, for example, as an inhibitor of silica scale.

The present inventors have conducted various investigations to achieve the above object and have arrived at the present invention.
That is, the water treatment agent of the present disclosure is a water treatment agent that includes a copolymer including a structural unit derived from (meth)acrylic acid (salt), a structural unit derived from a sulfonic acid (salt) group-containing monomer, and a structural unit derived from an ether bond-containing monomer, and a basic pH adjuster.

The water treatment agent disclosed herein exhibits good suppression capabilities for silica components and the like. Therefore, the water treatment agent disclosed herein can be preferably used as a water treatment agent for suppressing scale such as silica scale.

The present invention will be described in detail below.
In addition, a combination of two or more of the individual preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.

[Water treatment chemicals of the present disclosure]
The water treatment agent of the present disclosure includes a copolymer including a structural unit derived from (meth)acrylic acid (salt), a structural unit derived from a monomer containing a sulfonic acid (salt) group, and a structural unit of a monomer containing an ether bond, and a basic pH adjuster. The copolymer may be referred to as the copolymer of the present disclosure.

<Structural Unit Derived from (Meth)acrylic Acid (Salt)>
In this disclosure, (meth)acrylic acid refers to acrylic acid, methacrylic acid, and salts thereof.
The above salt is not particularly limited, but examples thereof include alkali metal salts, alkaline earth metal salts, transition metal salts, and ammonium salts.
In the present disclosure, a structural unit derived from (meth)acrylic acid (salt) refers to a structural unit in which a carbon-carbon double bond of (meth)acrylic acid (salt) is replaced with a carbon-carbon single bond. For example, if acrylic acid is CH ₂ ═CH(COOH), then the structural unit derived from acrylic acid can be represented as —CH ₂ —CH(COOH)—. A structural unit derived from (meth)acrylic acid (salt) can be formed, for example, by radical polymerization of (meth)acrylic acid (salt). Note that the structural unit derived from (meth)acrylic acid (salt) is not limited to a structural unit formed by polymerization of (meth)acrylic acid (salt), as long as it has the same structure as the structure in which a carbon-carbon double bond of (meth)acrylic acid (salt) is replaced with a carbon-carbon single bond, and may be, for example, a structural unit formed by a post-reaction after polymerization.
The content of the structural unit derived from (meth)acrylic acid (salt) in the copolymer of the present disclosure is 15% by mass or more and 94% by mass or less, preferably 30% by mass or more and 89% by mass or less, more preferably 50% by mass or more and 85% by mass or less, based on 100% by mass of the structural units derived from all monomers constituting the copolymer of the present disclosure. The content of the structural unit derived from the (meth)acrylic acid (salt) is calculated in terms of (meth)acrylic acid. The term "in terms of (meth)acrylic acid" means that even if the structural unit derived from (meth)acrylic acid (salt) is a structural unit derived from a (meth)acrylic acid salt, the mass is calculated as (meth)acrylic acid. By being in the above range, the scale inhibition ability of the scale inhibitor of the present disclosure tends to be improved.

<Structural Unit Derived from Sulfonic Acid (Salt) Group-Containing Monomer>
In the present disclosure, a sulfonic acid (salt) group-containing monomer refers to a compound that contains at least one carbon-carbon double bond and a sulfonic acid (salt) group. The at least one carbon-carbon double bond is usually radically polymerizable.
The above salt is not particularly limited, but examples thereof include alkali metal salts, alkaline earth metal salts, transition metal salts, and ammonium salts.
In the present disclosure, the structural unit derived from a sulfonic acid (salt) group-containing monomer refers to a structural unit in which at least one carbon-carbon double bond of a sulfonic acid (salt) group-containing monomer is replaced with a carbon-carbon single bond. Note that the structural unit derived from a sulfonic acid (salt) group-containing monomer may have the same structure as the structure in which at least one carbon-carbon double bond of a sulfonic acid (salt) group-containing monomer is replaced with a carbon-carbon single bond, and is not limited to a structural unit formed by polymerization of a sulfonic acid (salt) group-containing monomer, and may be, for example, a structural unit formed by a post-reaction after polymerization.
The content of the structural unit derived from the sulfonic acid (salt) group-containing monomer in the copolymer of the present disclosure is 5% by mass or more and 55% by mass or less, preferably 8% by mass or more and 45% by mass or less, more preferably 10% by mass or more and 30% by mass or less, based on 100% by mass of the structural units derived from all monomers constituting the copolymer of the present disclosure. The content of the structural unit derived from the sulfonic acid (salt) group-containing monomer is calculated in terms of sodium salt. The calculation in terms of sodium salt means that even if the sulfonic acid (salt) group contained in the structural unit derived from the sulfonic acid (salt) group-containing monomer is, for example, an acid-type sulfonic acid group, the mass is calculated as the sodium salt of the sulfonic acid group. By being in the above range, the scale inhibition ability of the scale inhibitor of the present disclosure tends to be improved.

Specific examples of sulfonic acid (salt) group-containing monomers include vinyl sulfonic acid and its salts, styrene sulfonic acid and its salts, (meth)allyl sulfonic acid and its salts, 3-(meth)allyloxy-2-hydroxypropanesulfonic acid and its salts, 3-(meth)allyloxy-1-hydroxypropanesulfonic acid (hereinafter also referred to as HAPS) and its salts, 2-(meth)allyloxyethylenesulfonic acid and its salts, 2-acrylamido-2-methylpropanesulfonic acid and its salts, etc. Since the scale inhibitor of the present disclosure tends to have improved scale inhibition ability, 3-(meth)allyloxy-2-hydroxypropanesulfonic acid and its salts are preferred, and 3-allyloxy-2-hydroxypropanesulfonic acid and its sodium salt are more preferred.

<Structural Unit Derived from Ether Bond-Containing Monomer>
In the present disclosure, the ether bond-containing monomer refers to a compound containing at least one carbon-carbon double bond and an ether bond. However, a sulfonic acid (salt) group-containing monomer is not included in the ether bond-containing monomer even if it is a compound containing an ether bond. The at least one carbon-carbon double bond is usually radically polymerizable.
In the present disclosure, the structural unit derived from an ether bond-containing monomer refers to a structural unit in which at least one carbon-carbon double bond of an ether bond-containing monomer is replaced with a carbon-carbon single bond. Note that the structural unit derived from an ether bond-containing monomer may have the same structure as the structure in which at least one carbon-carbon double bond of an ether bond-containing monomer is replaced with a carbon-carbon single bond, and is not limited to a structural unit formed by polymerization of an ether bond-containing monomer, and may be, for example, a structural unit formed by a post-reaction after polymerization.
The content of the structural unit derived from the ether bond-containing monomer in the copolymer of the present disclosure is 1% by mass or more and 30% by mass or less, preferably 3% by mass or more and 25% by mass or less, more preferably 3% by mass or more and 20% by mass or less, and most preferably 3% by mass or more and 15% by mass or less, based on 100% by mass of the structural units derived from all the monomers constituting the copolymer of the present disclosure. In addition, when the structural unit derived from the ether bond-containing monomer contains an acid group such as a carboxyl group (salt), the content is calculated in terms of acid. The acid conversion means that even when the structural unit derived from the monomer contains a salt of an acid group, the mass is calculated as the corresponding acid. The mass of the structural unit derived from the other monomers described later is also calculated in the same manner. By being in the above range, the scale inhibition ability of the scale inhibitor of the present disclosure tends to be improved.
Examples of ether bond-containing monomers include vinyl ethers such as ethyl vinyl ether, butyl vinyl ether, and benzyl vinyl ether; (meth)allyl ethers such as ethyl methallyl ether, butyl methallyl ether, and benzyl methallyl ether; and isoprenyl ethers such as ethyl isoprenyl ether, butyl isoprenyl ether, and benzyl isoprenyl ether. However, since there is a tendency in particular to improve the dispersibility of scale, a monomer represented by the following general formula (1) is preferred.

（前記一般式（１）中、Ｒ^０は、水素原子又はメチル基を表す。Ｒ^１は、ＣＨ_２基、ＣＨ_２ＣＨ_２基又は直接結合を表す。Ｘは、水酸基、下記一般式（２）で表される基、又は、下記一般式（３）で表される基を表す。Ｙは、水酸基、下記一般式（２）で表される基、又は、下記一般式（３）で表される基を表す。但し、Ｘ、Ｙのいずれか一方は、水酸基を表し、他方は、下記一般式（２）で表される基、又は、下記一般式（３）で表される基を表す。）

(In the general formula (1), ^R0 represents a hydrogen atom or a methyl group. ^R1 represents a _CH2 group, a _{CH2CH2 group} , or a direct bond. X represents a hydroxyl group, a group represented by the following general formula (2), or a group represented by the following general formula (3). Y represents a hydroxyl group, a group represented by the following general formula (2), or a group represented by the following general formula (3). However, one of X and Y represents a hydroxyl group, and the other represents a group represented by the following general formula (2) or a group represented by the following general formula (3).)

（前記一般式（２）、（３）中、Ｒ^２は、同一又は異なって、炭素数２～４のアルキレン基を表す。ｎは、オキシアルキレン基（－Ｏ－Ｒ^２－）の平均付加モル数であって、０～５の数を表す。Ｒ^３、Ｒ^４、Ｒ^５は、それぞれ独立して炭素数１～２０のアルキル基を表す。）
本開示のスケール抑制剤のスケールの抑制能が向上する傾向にあることから、Ｒ^３、Ｒ^４、Ｒ^５は、炭素数が１～１２であることがより好ましく、１～８であることがさらに好ましく、1～4であることが最も好ましい。なお、上記アルキル基は直鎖状、分岐状であってもよく、環状構造を含んでいてもよく、置換基を有していてもよい。置換基としては、アルコキシ基、アリール基、水酸基、カルボキシ基、アミノ基、複素環基などが例示される。置換基を有する場合は１つまたは２つ以上であってもよく、置換基を含めたアルキル基が上記炭素数であることが好ましい。

(In the general formulas (2) and (3), R ² may be the same or different and represents an alkylene group having 2 to 4 carbon atoms. n is the average number of moles of oxyalkylene groups (-O-R ² -) added and represents a number from 0 to 5. R ³ , R ⁴ , and R ⁵ each independently represent an alkyl group having 1 to 20 carbon atoms.)
Since the scale inhibitor of the present disclosure tends to have improved scale inhibition ability, R ³ , R ⁴ , and R ⁵ preferably have 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms, and most preferably 1 to 4 carbon atoms. The alkyl group may be linear or branched, may contain a cyclic structure, and may have a substituent. Examples of the substituent include an alkoxy group, an aryl group, a hydroxyl group, a carboxy group, an amino group, and a heterocyclic group. When the alkyl group has a substituent, the number of the substituents may be one or more, and it is preferable that the alkyl group including the substituent has the above carbon number.

<Structural units derived from other monomers>
The copolymer of the present disclosure may, if desired, have structural units derived from monomers other than (meth)acrylic acid (salt), structural units derived from sulfonic acid (salt) group-containing monomers, and structural units derived from ether bond-containing monomers (also referred to as structural units derived from other monomers).
In the present disclosure, the structural unit derived from another monomer refers to a structural unit in which at least one carbon-carbon double bond of another monomer is replaced with a carbon-carbon single bond. Note that the structural unit derived from another monomer may have the same structure as the structure in which at least one carbon-carbon double bond of the other monomer is replaced with a carbon-carbon single bond, and is not limited to a structural unit formed by polymerization of the other monomer, and may be, for example, a structural unit formed by a post-reaction after polymerization.
In the copolymer of the present disclosure, the content of structural units derived from other monomers is 0% by mass or more and 15% by mass or less, preferably 0% by mass or more and 10% by mass or less, and more preferably 0% by mass or more and 5% by mass or less, relative to 100% by mass of structural units derived from all monomers constituting the copolymer of the present disclosure.
Examples of the other monomers include carboxyl group-containing monomers such as maleic acid, itaconic acid, and salts thereof; unsaturated alcohols such as (meth)allyl alcohol and isoprenol, and monomers obtained by adding alkylene oxides thereto; polyalkylene glycol chain-containing monomers such as (meth)acrylic acid esters of alkoxyalkylene glycols; vinyl aromatic monomers having heterocyclic aromatic hydrocarbon groups such as vinylpyridine and vinylimidazole; amino group-containing monomers such as dialkylaminoalkyl (meth)acrylates such as dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, and dimethylaminopropyl acrylate; dialkylaminoalkyl (meth)acrylamides such as dimethylaminoethyl acrylamide, dimethylaminoethyl methacrylamide, and dimethylaminopropyl acrylamide; allylamines such as diallyl alkylamines such as diallyl amine and diallyl dimethylamine; and quaternized products thereof; N-vinylpyrrolidone, N amide monomers such as (meth)acrylamide, N,N-dimethylacrylamide, N-isopropylacrylamide, t-butylacrylamide; hydroxyl group-containing monomers such as (meth)allyl alcohol, isoprenol; (meth)acrylic acid alkyl ester monomers such as butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate; (meth)acrylic acid hydroxyalkyl monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxyhexyl (meth)acrylate; vinyl aryl monomers such as styrene, indene, vinyl aniline; isobutylene, vinyl acetate, etc.

<Physical properties of copolymers of the present disclosure>
The copolymer of the present disclosure preferably has a weight average molecular weight (Mw) of 3000 or more and 200000 or less, more preferably 5000 or more and 100000 or less, even more preferably 7000 or more and 60000 or less, particularly preferably 8000 or more and 60000 or less, even more preferably 10000 or more and 60000 or less, and most preferably 10000 or more and 45000 or less. By being in the above range, the scale inhibitory ability of the scale inhibitor of the present disclosure tends to be further improved.
The copolymer of the present disclosure contains one or more structural units derived from (meth)acrylic acid (salt), one or more structural units derived from a monomer containing a sulfonic acid (salt), and one or more structural units derived from an ether bond-containing monomer, and may contain one or more structural units derived from other monomers as necessary. The copolymer of the present disclosure may contain structural units derived from a polymerization initiator or a chain transfer agent, such as a hydroxyl group, a sulfonic acid (salt) group, or a hypophosphorous acid (salt) group, at the main chain end or the like.
The copolymer of the present disclosure contains an acid group such as a carboxylic acid (salt) group or a sulfonic acid (salt) group, but the acid group of the copolymer of the present disclosure may be neutralized. The neutralization rate can be calculated, for example, by conventional acid-base titration.

<Method for producing the copolymer of the present disclosure>
The method for producing the copolymer of the present disclosure is not particularly limited, but it is usually preferable to produce the copolymer by polymerizing structural units derived from (meth)acrylic acid (salt), a sulfonic acid (salt) group-containing monomer, and an ether bond-containing monomer, and, as necessary, other monomers.
In the process of producing the copolymer of the present disclosure, a polymerization initiator is usually used. In the process of producing the copolymer of the present disclosure, it is preferable to use a polymerization solvent and a chain transfer agent. Examples of the chain transfer agent include hydrogen peroxide, hypophosphorous acid (salt) such as sodium hypophosphite, hydrogen sulfite (salt) such as sodium hydrogen sulfite, and mercapto compounds.

[pH adjuster of the present disclosure]
The pH adjuster of the present disclosure is a component constituting a water treatment agent, and has a role of adjusting the pH of the agent to an appropriate value. By adjusting the pH of the agent to an appropriate value, it is effective in suppressing scale such as silica scale, and further, by adjusting the pH of the water under actual use conditions to an appropriate range, it is also effective in preventing corrosion. From the viewpoint of preventing scale and corrosion of piping, etc., the pH adjuster of the present disclosure is preferably basic, and any chemical substance exhibiting basicity can be used. Examples of chemical substances exhibiting basicity include inorganic substances such as hydroxides of alkali metals and alkaline earth metals, and organic compounds such as ammonium salts and amine salts. Among them, inorganic substances are preferred for reasons of ease of availability and price, and for example, sodium hydroxide, potassium hydroxide, calcium hydroxide, etc. are preferred, and for reasons of price, substances exhibiting strong basicity such as sodium hydroxide and potassium hydroxide are particularly preferred, and sodium hydroxide is particularly preferred.

[Water treatment chemicals of the present disclosure]
The water treatment agent of the present disclosure essentially contains the copolymer of the present disclosure and the basic pH adjuster of the present disclosure. The content of the copolymer of the present disclosure in the water treatment agent of the present disclosure is preferably 1% by mass or more and 90% by mass or less, more preferably 1% by mass or more and 70% by mass or less, and most preferably 1% by mass or more and 60% by mass or less. The water treatment agent of the present disclosure may contain a solvent such as water, other scale inhibitors, preservatives, etc.
In order to improve anticorrosive properties and scale inhibition ability, the water treatment agent of the present disclosure preferably has a pH of 8.0 or more when it contains water. By being in the above range, the anticorrosive properties of the piping are improved and the amount of metal ion components eluted in the water is reduced, so that the scale inhibition ability of the water treatment agent of the present disclosure tends to be further improved.

[Water treatment method of the present disclosure]
The water treatment method of the present disclosure is preferably a water treatment method using the copolymer of the present disclosure and the pH adjuster of the present disclosure in combination. The copolymer of the present disclosure and the pH adjuster of the present disclosure may be added simultaneously or separately. The copolymer of the present disclosure is preferably 20% by mass or more, more preferably 25% by mass or more, and particularly preferably 30% by mass or more, based on a total of 100% by mass of the copolymer of the present disclosure and the pH adjuster. On the other hand, 95% by mass or less is preferable, 90% by mass or less is more preferable, and 80% by mass or less is even more preferable. By adding at this ratio, the scale inhibition ability tends to be improved in the water treatment of the present disclosure.

[Use of water treatment chemicals of the present disclosure]
The water treatment chemicals disclosed herein can exhibit high performance in aqueous applications, and can be preferably used as scale inhibitors in geothermal power generation processes, oil well and gas well processes, seawater desalination processes or waste liquid concentration processes using forward osmosis or reverse osmosis membranes, boiler water circulation systems, cooling water circulation systems, and the like.

The water treatment agent of the present disclosure can be preferably used as a scale inhibitor for silica scale or calcium carbonate, for example.
The water treatment chemicals of the present disclosure are preferably adjusted so that the polymer content is 0.01 ppm or more and 20% or less, preferably 0.01 ppm or more and 10% or less, in terms of polymer, relative to the various types of water that are the target of scale prevention treatment applications.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In addition, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".
<Conditions for measuring weight average molecular weight (GPC)>
Equipment: Tosoh Corporation HLC8320
Column: SHODEX Asahipak GF-310-HQ manufactured by Showa Denko Corporation;
GF-710-HQ, GF-1G-7B
Column temperature: 40°C
Flow rate: 0.5ml/min
Calibration curve: Polyacrylic acid standard manufactured by American Polymer Standards Corporation
Eluent: 0.1N sodium acetate

<Synthesis of Monomer (1)>
In a 500 mL glass four-neck flask equipped with a reflux condenser and a stirrer (paddle blade),
370.0 g of n-butyl alcohol and 4.27 g of sodium hydroxide pellets were added, and the temperature was raised to 60° C. while stirring. Next, allyl glycidyl ether (hereinafter, “AG”) was added.
57.0 g of 1,2-dichlorophenyl ether (also referred to as "E") was added over 30 minutes, and the mixture was allowed to react for 5 hours. The solution was transferred to a 1,000 ml eggplant flask, and the solvent was removed using a rotary evaporator.
To this was added 200.0 g of a 20% by weight aqueous solution of sodium chloride, and this aqueous solution was diluted to 500 ml.
The mixture was transferred to a separating funnel, shaken thoroughly, and then left to stand until the layers were separated, and the lower layer was removed. The remaining upper layer was transferred to a 300 ml eggplant flask, and the solvent was removed using a rotary evaporator. The precipitated salt was removed by filtration to obtain monomer (1).

<Synthesis Example 1>
A 2000 mL glass separable flask equipped with a reflux condenser and a stirrer (paddle blade) was charged with 184.1 g of pure water and 0.0252 g of Mohr's salt, and the temperature was raised to 85° C. while stirring to prepare a polymerization reaction system. Next, 400.0 g of an 80% aqueous acrylic acid solution (hereinafter also referred to as "80% AA"), 166.9 g of a 40% aqueous 3-(meth)allyloxy-1-hydroxypropanesulfonic acid solution (hereinafter also referred to as "40% HAPS"), 20.0 g of monomer (1), 102.4 g of a 15% aqueous sodium persulfate solution (hereinafter also referred to as "15% NaPS"), and 22.2 g of a 35% aqueous sodium hydrogensulfite solution (hereinafter also referred to as "35% SBS") were each dropped from separate nozzles into the polymerization reaction system maintained at 85° C. under stirring. The drop time of each solution was 180 minutes for 80% AA, 120 minutes for 40% HAPS, 150 minutes for monomer (1), 200 minutes for 15% NaPS, and 175 minutes for 35% SBS. The drop speed of each solution was constant, and each solution was continuously dropped. After the drop of 80% AA was completed, the reaction solution was kept at 85°C (aged) for another 30 minutes to complete the polymerization. After the polymerization was completed, 298.2 g of 48% aqueous sodium hydroxide solution (manufactured by Kaname Yakuhin Co., Ltd.) was gradually dropped while stirring and cooling the polymerization reaction solution to neutralize the polymerization reaction solution. In this way, a polymer aqueous solution (1) containing the polymer (1) of the present invention and having a solid content concentration of 41.7% was obtained. The weight average molecular weight of the polymer (1) was 31,000.

<Synthesis Example 2>
In a 5,000 mL capacity glass separable flask equipped with a reflux condenser and a stirrer (paddle blade), 600.1 g of pure water and 0.064 g of Mohr's salt were charged, and the temperature was raised to 85° C. while stirring to prepare a polymerization reaction system. Next, 1070.0 g of 80% AA, 446.5 g of 40% HAPS, 53.5 g of monomer (1), 287.4 g of 15% NaPS, and 37.1 g of 35% SBS were dropped from separate nozzles into the polymerization reaction system maintained at 85° C. under stirring. The drop times of each solution were 180 minutes for 80% AA, 120 minutes for 40% HAPS, 120 minutes for monomer (1), 210 minutes for 15% NaPS, and 170 minutes for 35% SBS. The drop speed of each solution was constant, and each solution was continuously dropped. After the dropwise addition of 15% NaPS was completed, the reaction solution was maintained (aged) at 85° C. for an additional 20 minutes to complete the polymerization. After the polymerization was completed, 29.4 g of a 48% aqueous sodium hydroxide solution (manufactured by Kaname Yakuhin Co., Ltd.) was gradually added dropwise to the polymerization reaction solution while stirring and allowing it to cool, to neutralize the polymerization reaction solution.
In this way, polymer (2) of the present invention having a solid content of 46.7% was obtained. The weight average molecular weight of polymer (2) was 36,600.

<Silica scale inhibition rate evaluation test>
Sodium silicate aqueous solution: 129 g of sodium metasilicate nonahydrate (manufactured by Aldrich) is mixed with ion-exchanged water to make a total of 150 g.
Magnesium sulfate aqueous solution: 8.115 g of magnesium sulfate heptahydrate (manufactured by Wako Pharmaceuticals Co., Ltd.) is mixed with ion-exchanged water to make a total of 1000 g.
Water treatment chemical: 48% sodium hydroxide aqueous solution (Kaname Chemical Co., Ltd.) was diluted with ion-exchanged water to prepare a 10% sodium hydroxide aqueous solution. A 10% sodium hydroxide aqueous solution and ion-exchanged water were added to the polymer aqueous solution obtained in the synthesis example as described in the examples to prepare a 10% sodium hydroxide aqueous solution.
2.3 g of the above water treatment agent diluted with ion-exchanged water to a polymer concentration of 1000 ppm, 32.4 g of deionized water, 2.8 g of the above sodium silicate aqueous solution, and 2.5 g of magnesium sulfate aqueous solution were mixed, placed in an oven at 70° C. and left for 48 hours, and then the test liquid was suction-filtered using a filter with 0.45 μm openings, and the Si concentration of the obtained filtrate after the test was measured in terms of _SiO2 using ICP (optical emission spectroscopy).
Silica scale inhibition rate (%) = SiO ₂ after test (ppm) / SiO ₂ concentration before test (ppm) × 100
The silica scale inhibition rate was judged according to the following criteria.
<Inhibition rate evaluation criteria>
46% or more: ○
Less than 46%: ×

Example 1
To 5.25 g of the polymer (1) obtained in Synthesis Example 1, 3.12 g of a 10% aqueous solution of sodium hydroxide (manufactured by Kaname Chemical Co., Ltd.) as a pH adjuster and 44 g of ion-exchanged water were added to obtain a water treatment agent with a pH of 9.0. This water treatment agent was further diluted with ion-exchanged water so that the polymer concentration became 1000 ppm, and a polymer-containing aqueous solution was obtained.
When the silica scale inhibition rate evaluation test was carried out, the pH of the test liquid after being left for 48 hours was 11.2.

Example 2
To 3.8 g of the polymer (2) obtained in Synthesis Example 2, 7.9 g of a 10% aqueous sodium hydroxide solution as a pH adjuster and 27 g of ion-exchanged water were added to obtain a water treatment agent with a pH of 9.2.
A silica scale inhibition rate evaluation test was carried out in the same manner as in Example 1. The solution pH after the test was 11.2.

<Comparative Example 1>
56.9 g of ion-exchanged water was added to 5.2 g of the polymer (1) obtained in Synthesis Example 1 to obtain a water treatment agent having a pH of 5.5. A silica scale inhibition rate evaluation test was carried out in the same manner as in Example 1. The pH of the solution after the test was 11.1.

The results are shown in Table 1.

表１中、「組成」は、アクリル酸（塩）に由来する構造単位／３－アリルオキシ－２－ヒドロキシプロパンスルホン酸ナトリウム（ＨＡＰＳ）に由来する構造単位／単量体（１）に由来する構造単位」を表す。
表１の結果から、本開示の水処理薬剤は、シリカスケール抑制能に優れることがわかった。

In Table 1, "composition" represents "structural units derived from acrylic acid (salt)/structural units derived from sodium 3-allyloxy-2-hydroxypropanesulfonate (HAPS)/structural units derived from monomer (1)."
The results in Table 1 show that the water treatment agent of the present disclosure has excellent silica scale inhibition ability.

Claims (6)

A copolymer including a structural unit derived from (meth)acrylic acid (salt), a structural unit derived from a sulfonic acid (salt) group-containing monomer, and a structural unit derived from an ether bond-containing monomer, and a basic pH adjuster, the pH being 8 or higher;
The water treatment agent, wherein the structural unit derived from the ether bond-containing monomer is a structural unit derived from a monomer represented by the following general formula (1):

(In the general formula (1), ^R0 represents a hydrogen atom or a methyl group. ^R1 represents a _CH2 group, a _{CH2CH2 group} , or a direct bond. X represents a hydroxyl group, a group represented by the following general formula (2), or a group represented by the following general formula (3). Y represents a hydroxyl group, a group represented by the following general formula (2), or a group represented by the following general formula (3). However, one of X and Y represents a hydroxyl group, and the other represents a group represented by the following general formula (2) or a group represented by the following general formula (3).)

(In the general formulas (2) and (3), R ² may be the same or different and represents an alkylene group having 2 to 4 carbon atoms. n is the average number of moles of oxyalkylene groups (-O-R ² -) added and represents 0. R ³ , R ⁴ , and R ⁵ each independently represent an alkyl group having 1 to 20 carbon atoms.) The water treatment agent according to claim 1, wherein the content of structural units derived from ether bond-containing monomers in the copolymer is 1% by mass or more and 30% by mass or less, based on 100% by mass of structural units derived from all monomers constituting the copolymer. The water treatment agent according to claim 1 or 2, wherein the content of structural units derived from sulfonic acid (salt) group-containing monomers in the copolymer is 5% by mass or more and 55% by mass or less, based on 100% by mass of structural units derived from all monomers constituting the copolymer. The water treatment agent according to any one of claims 1 to 3, wherein the weight average molecular weight of the copolymer is 3,000 or more and 200,000 or less. The water treatment agent according to any one of claims 1 to 4, wherein the structural unit derived from the sulfonic acid (salt) group-containing monomer is a structural unit derived from 3-allyloxy-2-hydroxypropanesulfonic acid or a salt thereof. A method for preventing scale buildup, comprising using a water treatment agent according to any one of claims 1 to 5 for water treatment.