JP7507701B2 - Silica scale inhibitor - Google Patents

Description

The present invention relates to a silica scale inhibitor. More specifically, the present invention relates to a silica scale inhibitor used to inhibit silica scale generation during various water treatment processes.

For example, in geothermal power generation, industrial cooling water, and seawater desalination, the generation of scale such as calcium carbonate and silica can be a problem.
For example, it is disclosed that a copolymer having 5 mol% or more and 22 mol% or less of a structural unit derived from a sulfonic acid group-containing monomer, 78 mol% or more and 95 mol% or less of a structural unit derived from (meth)acrylic acid (salt), a sulfonic acid (salt) group at at least one main chain end, and a weight average molecular weight of 13,000 to 50,000 has excellent gel resistance and high calcium ion chelating ability, and therefore can be suitably used as a water treatment agent such as a scale inhibitor. For example, it is disclosed that the copolymer described in Patent Document 2 improves the dispersibility of hydrophobic particles and also exhibits excellent chelating ability to calcium ions, so that it is possible to exhibit extremely good scale prevention ability for the piping and inside of a geothermal power generation device, and therefore can be suitably used as a scale inhibitor for a geothermal power generation device.

JP 2012-188586 A JP 2016-064382 A

As described above, water treatment agents such as scale inhibitors have been proposed, but there is a demand for further improvement in the silica scale inhibition ability, and there has been a demand for a silica scale inhibitor that can be applied to prevent silica scale in various water treatment applications and is made of a polymer produced using a general-purpose monomer that is easily available. The present invention aims to provide a (meth)acrylic acid-based copolymer that has excellent silica scale inhibition ability and can therefore be suitably used, for example, as a silica scale inhibitor.

The present inventors have conducted various investigations to achieve the above object and have arrived at the present invention.
That is, the scale inhibitor of the present disclosure is a copolymer containing structural units derived from (meth)acrylic acid (salt) and structural units derived from a sulfonic acid (salt) group-containing monomer, wherein the structural units derived from the sulfonic acid (salt) group-containing monomer account for 11 mol % or more of the structures derived from all monomers (100 mol %), the copolymer has a sulfonic acid (salt) group at at least one main chain end, and includes a (meth)acrylic acid-based copolymer having a weight average molecular weight of 20,000 or more.

The silica scale inhibitor containing the (meth)acrylic acid-based copolymer of the present disclosure exhibits good silica scale inhibition ability and can therefore be preferably used as a silica scale inhibitor.

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.

[Copolymer of the present disclosure]
The copolymer of the present disclosure is a copolymer containing a structural unit derived from (meth)acrylic acid (salt) and a structural unit derived from a monomer containing a sulfonic acid (salt), the structural unit derived from the monomer containing a sulfonic acid (salt) group is 11 mol% or more relative to 100 mol% of the structures derived from all monomers, the copolymer has a sulfonic acid (salt) group at at least one main chain end, and is a (meth)acrylic acid-based copolymer characterized by having a weight average molecular weight of 20000 or more. The above 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), 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 structural units derived from (meth)acrylic acid (salt) in the copolymer of the present disclosure is preferably 50 mol% or more, more preferably 60 mol% or more, and even more preferably 70 mol% or more, based on 100 mol% of structural units derived from all monomers constituting the copolymer of the present disclosure. Also, it is preferably 89 mol% or less, more preferably 86 mol% or less, and even more preferably 82 mol% or less. The content of structural units derived from (meth)acrylic acid (salt) is calculated in terms of (meth)acrylic acid. "In terms of (meth)acrylic acid" means that even if the structural units derived from (meth)acrylic acid (salt) are structural units derived from a (meth)acrylic acid salt, the mass is calculated as (meth)acrylic acid. By being in the above range, the silica scale inhibition ability of the scale prevention 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.
Examples of the sulfonic acid (salt) group-containing monomer 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 and its salts, 2-(meth)allyloxyethylenesulfonic acid and its salts, and 2-acrylamido-2-methylpropanesulfonic acid and its salts.

（一般式（１）中、Ｒ_１は、水素原子またはメチル基を表し、ＸおよびＹは、それぞれ独立
に水酸基またはスルホン酸（塩）基を表す（但し、Ｘ、Ｙのうち少なくとも一方はスルホ
ン酸（塩）基を表す。スルホン酸（塩）とは、スルホン酸、スルホン酸塩をいう。スルホン酸塩における塩とは、金属塩、アンモニウム塩、有機アミン塩である。具体的には、ナトリウム塩、リチウム塩、カリウム塩等のアルカリ金属塩；マグネシウム塩、カルシウム塩等のアルカリ土類金属塩；鉄の塩等の遷移金属塩；モノエタノールアミン塩、ジエタノールアミン塩、トリエタノールアミン塩等のアルカノールアミン塩；モノエチルアミン塩、ジエチルアミン塩、トリエチルアミン塩等のアルキルアミン塩；エチレンジアミン塩、トリエチレンジアミン塩等のポリアミン等の有機アミンの塩；等が挙げられる。この中でもナトリウム塩、カリウム塩が特に好ましい。アスタリスクは、一般式（１）で表される構造単位が結合している同種もしくは異種の他の構造単位に含まれる原子を表す。）上記アスタリスクが表す原子が含まれる構造単位としては、特に制限はないが、単量体由来の構造単位、開始剤由来の構造単位、連鎖移動剤に由来する構造単位等が例示される。
本開示のスケール抑制剤のスケール抑制能が向上する傾向にあることから、３－（メタ）アリルオキシ－２－ヒドロキシプロパンスルホン酸及びその塩であることが好ましく、より好ましくは、３－アリルオキシ－２－ヒドロキシプロパンスルホン酸及びそのナトリウム塩である For example, a structural unit derived from a sulfonic acid (salt) group-containing monomer is represented by the following general formula (1).

(In the general formula (1), _R1 represents a hydrogen atom or a methyl group, and X and Y each independently represent a hydroxyl group or a sulfonic acid (salt) group (provided that at least one of X and Y represents a sulfonic acid (salt) group. Sulfonic acid (salt) refers to sulfonic acid and sulfonate salts. The salts of sulfonate salts are metal salts, ammonium salts, and organic amine salts. Specific examples of such salts include alkali metal salts such as sodium salts, lithium salts, and potassium salts; alkaline earth metal salts such as magnesium salts and calcium salts; transition metal salts such as iron salts; and alkali salts such as monoethanolamine salts, diethanolamine salts, and triethanolamine salts. Nolamine salts; alkylamine salts such as monoethylamine salts, diethylamine salts, and triethylamine salts; salts of organic amines such as polyamines such as ethylenediamine salts and triethylenediamine salts; and the like. Among these, sodium salts and potassium salts are particularly preferred. The asterisk represents an atom contained in another structural unit of the same type or different type to which the structural unit represented by general formula (1) is bonded.) The structural unit containing the atom represented by the asterisk is not particularly limited, but examples thereof include a structural unit derived from a monomer, a structural unit derived from an initiator, and a structural unit derived from a chain transfer agent.
Since the scale inhibitor of the present disclosure has a tendency 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.

The content of the structural unit derived from the sulfonic acid (salt) group-containing monomer in the copolymer of the present disclosure is 11 mol% or more, preferably 12 mol% or more, more preferably 13 mol% or more, based on 100% by mass of the structural units derived from all monomers constituting the copolymer of the present disclosure. It is also preferably 40 mol% or less, preferably 30 mol% or less, more preferably 25 mol% or less. 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, it is calculated as the sodium salt of the sulfonic acid group.
The above ranges tend to improve the silica scale inhibition ability of the scale inhibitor of the present disclosure. For example, the above ranges tend to improve the silica scale inhibition ability of the scale inhibitor of the present disclosure, and thus improve the dispersibility of the silica particles and suppress the aggregation of the silica particles.

<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)-derived structural units and sulfonic acid (salt) group-containing monomers (also referred to as structural units derived from other monomers).
In the present disclosure, the structural unit derived from the other monomer refers to a structural unit in which at least one carbon-carbon double bond of the other monomer is replaced with a carbon-carbon single bond. Note that the structural unit derived from the other 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, relative to 100 mol% of structural units derived from all monomers constituting the copolymer of the present disclosure, is 0 mol% or more and 15 mol% or less, preferably 0 mol% or more and 10 mol% or less, more preferably 0 mol% or more and 5 mol% or less, even more preferably 0 mol% or more and 3 mol% or less, particularly preferably 0 mol% or more and 2 mol% or less, and most preferably 0 mol%.

The other monomers include carboxyl group-containing monomers such as maleic acid, itaconic acid, and their salts; unsaturated alcohols such as (meth)allyl alcohol and isoprenol, and monomers obtained by adding alkylene oxides to these, 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; dialkyl monomers such as dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, and dimethylaminopropyl acrylate. amino group-containing monomers such as dialkylaminoalkyl(meth)acrylates, dialkylaminoalkyl(meth)acrylamides such as dimethylaminoethylacrylamide, dimethylaminoethylmethacrylamide, dimethylaminopropylacrylamide, and allylamines such as diallylamine and diallyldimethylamine; N-vinyl monomers such as N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, N-vinyl-N-methylformamide, N-vinyl-N-methylacetamide, and N-vinyloxazolidone; Amide monomers such as (meth)acrylamide, N,N-dimethylacrylamide, N-isopropylacrylamide, and t-butylacrylamide; hydroxyl group-containing monomers such as (meth)allyl alcohol and isoprenol; (meth)acrylic acid alkyl ester monomers such as butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and dodecyl (meth)acrylate; 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxypropyl ... Examples of monomers containing an ether bond include hydroxyalkyl (meth)acrylate monomers such as hydroxyhexyl (meth)acrylate; vinyl aryl monomers such as styrene, indene, and vinyl aniline; isobutylene and vinyl acetate; and examples of monomers containing an ether bond 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.

<Other structural units>
The copolymer of the present disclosure is characterized in that it has a sulfonic acid (salt) group at at least one end of the main chain of the polymer. Having a sulfonic acid (salt) group at at least one end of the main chain of the polymer means having a sulfonic acid (salt) group at one or more main chain ends. For example, if the polymer is linear, there are two main chain ends, one or both of which may have a sulfonic acid group, and if the polymer has a branched structure, there are three or more main chain ends, one or more of which may have a sulfonic acid group. By having a sulfonic acid (salt) group at at least one chain end, the silica scale inhibition ability is improved. The mass% of the sulfonic acid group at the main chain end of the copolymer relative to 100 mass% of the copolymer is preferably 0.01% or more and 10% or less, and more preferably 0.01% or more and 5% or less. The conversion of the sulfonic acid group is calculated based on the acid group.

<Physical properties of copolymers of the present disclosure>
The copolymer of the present disclosure preferably has a weight average molecular weight (Mw) of 20,000 or more, more preferably 30,000 or more, and even more preferably 37,000 or more. It is preferably 100,000 or less, more preferably 80,000 or less, and even more preferably 60,000 or less. By being in the above range, the silica scale inhibition ability of the scale inhibitor of the present disclosure tends to be further improved.
The copolymer of the present disclosure contains acid groups such as carboxylic acid (salt) groups and sulfonic acid (salt) groups, but the acid groups of the copolymer of the present disclosure may be neutralized. The total neutralization rate of the acid groups is preferably 1 mol% or more and 90 mol% or less. The neutralization rate can be calculated, for example, by ordinary 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 other monomers as necessary. In the production process of the copolymer of the present disclosure, a polymerization initiator can be used in the polymerization of the monomer. In the production process of the copolymer of the present disclosure, a chain transfer agent can be used as necessary to adjust the molecular weight.

Chain Transfer Agents of the Present Disclosure
The chain transfer agent of the present disclosure can be used to adjust the molecular weight. Examples of the chain transfer agent include thiol-based chain transfer agents such as bisulfite (salts) such as bisulfite, metabisulfite, sodium bisulfite, potassium bisulfite, sodium metabisulfite, potassium metabisulfite, mercaptoethanol, thioglycerol, thioglycolic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, thiomalic acid, octyl thioglycolate, octyl 3-mercaptopropionate, 2-mercaptoethanesulfonic acid, n-dodecyl mercaptan, octyl mercaptan, and butyl thioglycolate; halides such as carbon tetrachloride, methylene chloride, bromoform, and bromotrichloroethane; secondary alcohols such as isopropanol and glycerin; phosphorous acid, hypophosphorous acid, and salts thereof (sodium hypophosphite, potassium hypophosphite, etc.); and the like. Among these, in the production of the copolymer according to the present disclosure, bisulfites (salts) can be used to contain a sulfonic acid group at at least one main chain end. This allows efficient introduction of a sulfonic acid group at at least one main chain end of the copolymer obtained. One type of chain transfer agent may be used, or two or more types may be used. The amount of the chain transfer agent added is not limited as long as the monomers can be polymerized well, but is preferably 0.001 mol or more and 0.02 mol or less per mol of the monomer mixture to be copolymerized.

<Polymerization initiator of the present disclosure>
In the process of producing the copolymer of the present disclosure, a polymerization initiator is usually used. Known polymerization initiators can be used. For example, persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate, hydrogen peroxide, dimethyl 2,2-'azobis(2-methylpropionate), 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(isobutyric acid) dimethyl, 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-methylpropionate), Examples of the azo compounds that can be used include 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] dihydrochloride, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] n-hydrate, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] disulfate dihydrate, and 1,1'-azobis(cyclohexane-1-carbonitrile), as well as organic peroxides such as benzoyl peroxide, lauroyl peroxide, peracetic acid, di-t-butyl peroxide, and cumene hydroperoxide. Among these, persulfates are preferred, and by combining the above chain transfer agent, sulfonic acid groups can be efficiently introduced into the polymer main chain terminals.

[Uses of the copolymer of the present disclosure]
The copolymer of the present disclosure can exhibit high performance in aqueous applications and can be preferably used as a scale inhibitor for use in geothermal power generation processes, oil well and gas well processes, seawater desalination processes or waste liquid concentration processes using forward osmosis membranes or reverse osmosis membranes, boiler water circulation systems, cooling water circulation systems, and the like.
The copolymer of the present disclosure can be preferably used as a scale inhibitor for, for example, silica scale or calcium carbonate, and is most preferably used as a silica scale inhibitor because of its excellent silica scale inhibition ability.

[Silica scale inhibitor of the present disclosure]
The silica scale inhibitor of the present disclosure includes the copolymer of the present disclosure. The silica scale inhibitor of the present disclosure preferably includes, for example, 1% by mass or more and 100% by mass or less of the copolymer of the present disclosure. More preferably, the silica scale inhibitor includes 1% by mass or more and 80% by mass or less, and even more preferably, the silica scale inhibitor includes 1% by mass or more and 50% by mass or less of the copolymer of the present disclosure.
The silica scale inhibitor of the present disclosure may contain a component other than the copolymer of the present disclosure. Examples of the component other than the copolymer of the present disclosure include a solvent such as water, a pH adjuster such as an alkali or acid, an oxygen scavenger, an anticorrosive agent, a chelating agent, a phosphonic acid (salt) such as aminotrimethylenephosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, and salts thereof, a carboxyl group-containing polymer other than the copolymer of the present disclosure, a surfactant, an antifoaming agent, a pitch control agent, a slime control agent, and the like.

[Water treatment agent of the present disclosure]
The water treatment agent of the present disclosure includes the scale inhibitor of the present disclosure. The water treatment agent of the present disclosure preferably contains, for example, 1% by mass or more and 70% by mass or less of the copolymer of the present disclosure. It is more preferable to contain 1% by mass or more and 50% by mass or less, even more preferable to contain 1% by mass or more and 40% by mass or less, particularly preferable to contain 1% by mass or more and 30% by mass or less, and most preferable to contain 1% by mass or more and 20% by mass or less. The water treatment agent of the present disclosure may contain components other than the scale inhibitor of the present disclosure. Examples of components other than the scale inhibitor of the present disclosure include solvents such as water; pH adjusters such as alkalis and acids; oxygen scavengers; anticorrosive agents; chelating agents; phosphonic acids (salts) such as aminotrimethylenephosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, and salts thereof; carboxyl group-containing polymers other than the copolymer of the present disclosure; surfactants; defoamers; pitch control agents; slime control agents, etc.

[Silica scale prevention method of the present disclosure]
The silica scale prevention method of the present disclosure uses the silica scale inhibitor of the present disclosure or the copolymer of the present disclosure. The silica scale prevention method of the present disclosure preferably includes a step of adding the silica scale inhibitor of the present disclosure or the copolymer of the present disclosure to a system to be prevented from silica scale. Also, preferably, the method includes a step of controlling the amount of the copolymer of the present disclosure in the system to be prevented from silica scale so that it is within a predetermined range. The content of the copolymer of the present disclosure in the system to be prevented from silica scale is preferably 0.1 ppm or more and 500 ppm or less, more preferably 0.1 ppm or more and 300 ppm.

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: 0.5 ml/min
Calibration curve: Polyacrylic acid standard manufactured by American Polymer Standards Corporation
Eluent: 0.1N sodium acetate

<Synthesis Example 1>
In a 3 L SUS reaction vessel equipped with a reflux condenser and a stirrer (paddle blade), 251.5 g of pure water and 0.031 g of Mohr's salt were charged and heated to 85° C. with stirring to prepare a polymerization reaction system. Next, 517.5 g of an 80% aqueous acrylic acid solution (hereinafter also referred to as "80% AA"), 533.2 g of a 40% aqueous solution of sodium 3-allyloxy-2-hydroxypropanesulfonate (hereinafter also referred to as "40% HAPS"), 179.3 g of a 15% aqueous sodium persulfate solution (hereinafter also referred to as "15% NaPS"), and 18.6 g of a 32.5% aqueous sodium hydrogensulfite solution (hereinafter also referred to as "32.5% SBS") were dropped from separate nozzles into the polymerization reaction system maintained at 85° C. with stirring. The drop time of each solution was 180 minutes for 80% AA, 140 minutes for 40% HAPS, 200 minutes for 15% NaPS, and 170 minutes for 32.5% SBS. The drop speed of each solution was constant, and each solution was continuously dropped. After the drop of 15% NaPS was completed, the reaction solution was kept at 85°C (ripening) for another 30 minutes to complete the polymerization. In this way, a polymer aqueous solution (1) with a solid content concentration of 44.8% was obtained. The weight average molecular weight of the polymer (1) was 37,000. The composition ratio of the charged polymer and the produced polymer was the same.

<Synthesis Example 2>
250.78g of pure water and 0.031g of Mohr's salt were charged into a 3L SUS reaction vessel equipped with a reflux condenser and a stirrer (paddle blade), and the temperature was raised to 85°C while stirring to prepare a polymerization reaction system. Next, 508.9g of 80% AA, 524.3g of 40% HAPS, 176.3g of 15% NaPS, and 39.7g of 10% SBS were 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, 140 minutes for 40% HAPS, 200 minutes for 15% NaPS, and 170 minutes for 10% SBS. The drop speed of each solution was constant, and each solution was continuously dropped. After the drop of 15% NaPS was completed, the reaction solution was maintained (aged) at 85°C for another 30 minutes to complete the polymerization. In this way, an aqueous polymer solution (2) having a solid content of 44.5% was obtained. The weight average molecular weight of the polymer (2) was 49000. The composition ratio of the charged polymer and the produced polymer was the same.

<Synthesis Example 3>
250.8g of pure water and 0.031g of Mohr's salt were charged into a 3L SUS reaction vessel equipped with a reflux condenser and a stirrer (paddle blade), and the temperature was raised to 85°C while stirring to prepare a polymerization reaction system. Next, 457.2g of 80% AA, 609.7g of 40% HAPS, 165.2g of 15% NaPS, and 17.2g of 32.5% SBS were 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, 140 minutes for 40% HAPS, 200 minutes for 15% NaPS, and 170 minutes for 32.5% 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 30 minutes to complete the polymerization.
In this way, an aqueous polymer solution (3) having a solid content of 43.6% was obtained. The weight average molecular weight of the polymer (3) was 37000. The composition ratio of the charged polymer and the produced polymer was the same.

<Synthesis Example 4>
462.6 g of pure water and 0.031 g of Mohr's salt were charged into a 3 L SUS reactor equipped with a flow condenser and a stirrer (paddle blade), and the temperature was raised to 85° C. while stirring to prepare a polymerization reaction system. Next, 674.3 g of 80% AA, 238.0 g of 40% HAPS, 103.1 g of 15% NaPS, and 21.9 g of 32.5% 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, 155 minutes for 40% HAPS, 200 minutes for 15% NaPS, and 170 minutes for 32.5% SBS. The drop speed of each solution was constant, and each solution was continuously dropped. After the dropwise addition of 80% AA was completed, the reaction solution was kept (aged) at 85° C. for another 30 minutes to complete the polymerization. In this way, a polymer aqueous solution (4) having a solid content concentration of 43.6% was obtained. The weight average molecular weight of the polymer (4) was 44,000. The composition ratio of the charged polymer and the produced polymer was the same.

<Synthesis Example 5>
611.3g of ion-exchanged water was charged into a 5L SUS reaction vessel equipped with a reflux condenser and an agitator, and the temperature was raised to the boiling point reflux state while stirring. Next, 57.6g of 80% AA, 1145.9g of 37% sodium acrylate (hereinafter also referred to as "37% SA"), 502.9g of 40% HAPS, 132.2g of 15% NaPS, 19.0g of 35% hydrogen peroxide solution (hereinafter also referred to as "35% H ₂ O ₂ "), and 367.9g of ion-exchanged water were dropped from separate nozzles into the polymerization reaction system in the boiling point reflux state while stirring. The dropping time of each solution was 120 minutes for 80% AA and 37% SA, 90 minutes for 40% HAPS and ion-exchanged water, 140 minutes for 15% NaPS, and 120 minutes for 35% H ₂ O ₂ . In this way, an aqueous polymer solution (5) having a solid content of 50.2% was obtained. The weight average molecular weight of the polymer (5) was 5000. The composition ratio of the charged polymer and the produced polymer was the same.

<Synthesis Example 6>
1620 g of ion-exchanged water was charged into a 5 L SUS reaction vessel equipped with a reflux condenser and a stirrer, and the temperature was raised to a boiling point reflux state while stirring. Next, 455 g of 80% AA and 133 g of 15% NaPS were dropped from separate nozzles into the polymerization reaction system in a boiling point reflux state while stirring. The drop times of each solution were 180 minutes for 80% AA, 185 minutes for 15% NaPS, and 170 minutes for ion-exchanged water. After the drop of the 15% NaPS solution was completed, the reaction solution was kept in a boiling point reflux state (ripening) for another 30 minutes to complete the polymerization. In this way, a polymer aqueous solution (6) with a solid content of 45.7% was obtained. The weight average molecular weight of the polymer (6) was 10,000. The composition ratio of the charged polymer and the produced polymer was the same.

<Silica scale inhibition rate evaluation test>
Sodium silicate aqueous solution: 2.129 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 Pure Chemical Industries, Ltd.) is mixed with ion-exchanged water to make a total of 1000 g.
Boric acid buffer: 7.42 g of boric acid (Kanto Chemical Co., Ltd.) and 19.07 g of sodium borate decahydrate (Wako Pure Chemical Industries, Ltd.) are mixed to prepare a boric acid buffer.
A container was charged with 73 g of deionized water, and while stirring, 2 g of the boric acid buffer, 10 g of the sodium silicate aqueous solution, 5 g of a polymer aqueous solution diluted to a polymer concentration of 1000 ppm, and 10 g of the magnesium sulfate aqueous solution were added, and the mixture was left in a warm bath at 60°C for 5 hours. After leaving the mixture for 5 hours, the test liquid was suction filtered using a suction filtration device and a filter paper with 0.1 μm openings. The obtained filtrate was measured by XR-F to measure the Si concentration in terms of _SiO2 .
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>
Over 90%: ◎
70-90%: ○
30-70%: △
Less than 30%: ×
Example 1
The above-mentioned silica scale inhibition rate test was carried out on 5 g of a 1000 ppm aqueous solution of the polymer (1) obtained in Synthesis Example 1.
Example 2
The above-mentioned silica scale inhibition rate evaluation test was carried out on 5 g of a 1000 ppm aqueous solution of the polymer (2) obtained in Synthesis Example 2.
Example 3
The above-mentioned silica scale inhibition rate evaluation test was carried out on 5 g of a 1000 ppm aqueous solution of the polymer (3) obtained in Synthesis Example 3.
<Comparative Example 1>
The above-mentioned silica scale inhibition rate evaluation test was carried out on 5 g of a 1000 ppm aqueous solution of the polymer (4) obtained in Synthesis Example 4.
<Comparative Example 2>
The above-mentioned silica scale inhibition rate evaluation test was carried out on 5 g of a 1000 ppm aqueous solution of the polymer (5) obtained in Synthesis Example 5.
<Comparative Example 3>
The above-mentioned silica scale inhibition rate evaluation test was carried out on 5 g of a 1000 ppm aqueous solution of the polymer (6) obtained in Synthesis Example 6.
<Comparative Example 4>
The evaluation test was carried out in the same manner as in the above silica scale inhibition rate evaluation test, except that the aqueous polymer solution was not added.

The experimental results for Examples 1 to 3 and Comparative Examples 1 to 4 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／スルホン酸（塩）基に由来する構造単位を表す。
表１の結果から、本開示の共重合体は、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" indicates the ratio of structural units derived from acrylic acid (salt) to structural units derived from sulfonic acid (salt) groups.
The results in Table 1 show that the copolymer of the present disclosure has excellent silica scale inhibition ability.

Claims (4)

A silica scale inhibitor containing a (meth)acrylic acid-based copolymer, which is a copolymer containing structural units derived from (meth)acrylic acid (salt) and structural units derived from a monomer containing a sulfonic acid (salt) group, characterized in that the structural units derived from the monomer containing a sulfonic acid (salt) group account for 11 mol% or more of the total monomer-derived structures (100 mol%), the copolymer has a sulfonic acid (salt) group at at least one main chain end, and has a weight average molecular weight of 20,000 or more. 2. The silica scale inhibitor according to claim 1, wherein the structural unit derived from the sulfonic acid (salt) group-containing monomer is represented by general formula (1).

In the general formula (1), _R1 represents a hydrogen atom or a methyl group, and X and Y each independently represent a hydroxyl group or a sulfonic acid (salt) group (provided that at least one of X and Y represents a sulfonic acid (salt) group. An asterisk represents an atom contained in another structural unit of the same type or different type to which the structural unit represented by the general formula (1) is bonded). The silica scale inhibitor according to claim 1 or 2, 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. Water treatment agent containing a silica scale inhibitor according to any one of claims 1 to 3