High molecular coagulant and method for producing the same

Abstract

To provide a high molecular coagulant of water-in-oil emulsion capable of simultaneously achieving extremely high polymerization stability and storage stability, and a method for producing the same.SOLUTION: This method for producing a high molecular coagulant comprises, under the presence of a surfactant having a weighted average of a HLB value of 6.0-10.0, which contains at least one type of a surfactant [A] having a HLB value of 3.0-5.0 and at least two types of surfactants [B] having HLB values of 8.0-15.0 in a monomer mixture containing acrylamide and / or a monomer copolymerizable with the acrylamide, performing water-in-oil emulsion polymerization to obtain water-in-oil emulsion containing a polymer; and then adding a hydrophilic surfactant [C] to the water-in-oil emulsion.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a polymer flocculant and a method for producing the same. More specifically, the present invention relates to a polymer flocculant composed of a water-in-oil emulsion having a small amount of coagulum and excellent storage stability, and a method for producing the same.

Background Art

[0002] Polymer flocculants are used for the purpose of aggregating, sedimenting, and separating suspended substances contained in domestic wastewater, industrial wastewater, etc., and also as retention improvers in the paper industry, admixtures, and sludge conditioners in civil engineering and construction. There are nonionic, anionic, cationic, or amphoteric types of polymer flocculants, and which type of polymer flocculant to select depends on the properties of the water to be treated and the water treatment method. Among these, cationic polymer flocculants are often used as sludge dewatering agents for flocculating and dehydrating excess sludge after treating industrial wastewater and domestic wastewater by activated sludge treatment, or as retention improvers in the paper industry. For sludge that is difficult to dehydrate, polymers having a branched structure or a crosslinked structure are used. In addition, amphoteric polymer flocculants are used to coarsely flocculate suspended particles charge-neutralized with a coagulant and can also be applied to sludge that is difficult to dehydrate or aggregate.

[0003] Conventionally, as product forms of polymer flocculants, powder forms, forms of water suspensions of salting-out polymer particles called dispersions, forms of water-in-oil emulsions containing polymers, etc. are known. Among these, water-in-oil emulsions have the advantages of excellent solubility in water to be treated, being able to uniformly dissolve the polymer in a short time, and not generating dust, and are widely used.

[0004] Patent Document 1 discloses a method for producing a polymer flocculant, in which a monomer mixture containing at least a cationic monomer is emulsion-polymerized in the presence of a surfactant whose weighted average HLB value is adjusted to the range of 5.0 to 9.0 by mixing at least two surfactants with HLB values in the range of 1.5 to 7.0 and at least one surfactant with an HLB value in the range of 10 to 17 to obtain a water-in-oil emulsion, and then a hydrophilic surfactant is added to the water-in-oil emulsion. This polymer flocculant is a relatively highly stable polymer flocculant with a coagulum amount of 0.04 to 0.08% by mass and a sedimentation separation amount of 5 to 19% by mass.

[0005] Patent Document 2 discloses a method for producing a polymer flocculant, in which a monomer mixture containing no cationic monomer but containing a nonionic monomer and / or an anionic monomer is emulsion-polymerized in the presence of a surfactant whose weighted average HLB value of each surfactant is adjusted to the range of 4.0 to 8.0 by mixing at least two surfactants with HLB values in the range of 1.5 to 7.0 and at least one surfactant with an HLB value in the range of 10 to 17 to obtain a water-in-oil emulsion containing a polymer obtained by emulsion polymerization, and then a hydrophilic surfactant is added to the water-in-oil emulsion. The nonionic monomer is at least one selected from the group consisting of (meth)acrylamide, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, styrene, acrylonitrile, and vinyl acetate, and the anionic monomer is at least one selected from the group consisting of (meth)acrylic acid, vinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, maleic acid, and salts thereof. This polymer flocculant does not contain cationic monomer units, has a coagulum amount of 0 to 0.07% by mass, and is a relatively highly stable polymer flocculant with a sedimentation separation amount of 5 to 19% by mass. In Example 2 of Patent Document 2, the coagulum amount is 0 and the polymerization stability can be said to be extremely high, but the sedimentation separation amount is 11% by mass, and there is still room for improvement in storage stability.

[0006] Patent Document 3 discloses a method for producing a polymer flocculant in which a monomer mixture containing at least a cationic monomer and a radically polymerizable polyfunctional crosslinkable monomer is subjected to oil-in-water emulsion polymerization in the presence of a surfactant adjusted so that the weighted average of the HLB values is in the range of 5.0 to 9.0 by mixing three or more surfactants including at least two surfactants with an HLB in the range of 3 to 7 and at least one surfactant with an HLB in the range of 10 to 17. Although the amount of coagulum and the amount of sedimentation separation of this polymer flocculant are not disclosed, since the combination of surfactants is similar to that in Patent Document 1, it is estimated that the amount of coagulum and the amount of sedimentation separation are similar to those in Patent Document 1.

[0007] Patent Document 4 discloses a method for producing a water-soluble or hydrophilic polymer reverse emulsion in which a water-soluble or hydrophilic monomer is emulsion polymerized in an oil phase using three types of surfactants (1) to (3) below, and then three types of surfactants (3) to (5) below are added. (1) Sorbitan fatty acid ester with an HLB of 3 to 5 (2) Nonionic oil-soluble surfactant with a molecular weight of 2000 or more (3) Nonionic oil-soluble surfactant with a molecular weight of less than 2000 and an HLB of 8 to 10 (4) Water-soluble polyoxyethylene polyoxypropylene derivative (5) Nonionic water-soluble surfactant with an HLB of 12 to 14 other than the above (4) According to the above production method, the surfactants (4) and (5) are not added during the emulsion polymerization, but are added as so-called phase inversion agents after the completion of the emulsion polymerization.

[0008] The water-in-oil emulsion containing the polymer is obtained by preparing an emulsion in which an aqueous monomer solution is emulsified and dispersed in a hydrocarbon oil using a surfactant, and subjecting the monomer to radical polymerization in the state of the emulsion. Before the start of polymerization, the aqueous monomer solution is the dispersed phase, but after the completion of polymerization, the polymer formed by polymerizing the monomer becomes the dispersed phase. That is, it is characterized in that the properties (degree of polymerization, etc.) of the dispersed phase gradually change after the start of polymerization. In the prior art, in a system where the properties of the dispersed phase continuously change in this way, it cannot be said that both polymerization stability and storage stability are sufficient, and there is room for improvement.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Documents

[0010]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0011] An object of the present invention is to provide a polymer flocculant composed of a water-in-oil emulsion that achieves both polymerization stability and storage stability at an extremely high level, and a method for producing the same.

Means for Solving the Problems

[0012] As a result of intensive studies on the above problems, the present inventors have found that by performing emulsion polymerization using at least three surfactants having different HLB values and using a surfactant having a weighted average HLB value of a predetermined value, it is possible to achieve both polymerization stability and storage stability at an extremely high level, and thus have completed the present invention.

[0013] The present invention for solving the above problems is as described below.

[0014] 〔1〕 A monomer mixture containing acrylamide and / or a monomer copolymerizable with acrylamide is in the presence of a surfactant having a weighted average HLB value of 6.0 to 10.0, which comprises at least one surfactant [A] having an HLB value in the range of 3.0 to 5.0 and at least two surfactants [B] having an HLB value in the range of 8.0 to 15.0, and subjected to water-in-oil emulsion polymerization to obtain a water-in-oil emulsion containing a polymer, and then a hydrophilic surfactant [C] is added to the water-in-oil emulsion. A method for producing a polymer flocculant, characterized by this.

[0015] 〔2〕 The method for producing a polymer flocculant according to [1], wherein the surfactant [B] is at least two selected from diolethanolamide oleate, polyoxyethylene lauryl ether, and polyoxyethylene monooleate.

[0016] 〔3〕 The method for producing a polymer flocculant according to [1] or [2], wherein the monomer mixture contains at least one of acrylamide, a quaternary salt of dimethylaminoethyl (meth)acrylate, acrylic acid or its salt, or 2-acrylamido-2-methylpropanesulfonic acid or its salt.

[0017] 〔4〕 The method for producing a polymer flocculant according to any one of [1] to [3], wherein the monomer mixture contains a crosslinkable monomer.

[0018] The production method of the polymer flocculant according to any one of [1] to [4], wherein the W / O ratio, which is the value obtained by dividing the mass of the aqueous phase in the water-in-oil emulsion by the mass of the oil phase, is 2.0 to 3.5.

[0019] The production method of the polymer flocculant according to any one of [1] to [5], wherein the particle size measured by the laser diffraction method of the water-in-oil emulsion is 0.7 to 10 μm in median diameter.

[0020] (7) A monomer mixture containing acrylamide and / or a monomer copolymerizable with acrylamide is polymerized in a water-in-oil emulsion in the presence of a surfactant having a weighted average HLB value of 6.0 to 10.0, which comprises at least one surfactant [A] having an HLB value in the range of 3.0 to 5.0 and at least two surfactants [B] having an HLB value in the range of 8.0 to 15.0, to obtain a water-in-oil emulsion containing a polymer, and then a hydrophilic surfactant [C] is added to the water-in-oil emulsion. A polymer flocculant characterized by being obtained.

[0021] (8) A polymer containing acrylamide and / or a monomer copolymerizable with acrylamide as a structural unit, a surfactant having a weighted average HLB value of 6.0 to 10.0, which comprises at least one surfactant [A] having an HLB value in the range of 3.0 to 5.0 and at least two surfactants [B] having an HLB value in the range of 8.0 to 15.0, and a water-in-oil emulsion containing the same; a hydrophilic surfactant [C]; A polymer flocculant characterized by containing the same. [Effect of the Invention]

[0022] The polymer flocculant obtained by the production method of the present invention can achieve both extremely high polymerization stability and storage stability. [Embodiments for Carrying Out the Invention]

[0023] The present invention will be described in detail below. In this specification, acrylate and / or methacrylate may be described as (meth)acrylate; acrylamide and / or methacrylamide may be described as (meth)acrylamide; acrylic acid and / or methacrylic acid may be described as (meth)acrylic acid. Also, acrylic acid and / or its salt may be described as acrylic acid (salt); 2-acrylamido-2-methylpropanesulfonic acid and / or its salt may be described as 2-acrylamido-2-methylpropanesulfonic acid (salt). Unless otherwise specified, each physical property value is the physical property value at 25°C and atmospheric pressure.

[0024] The present invention relates to a monomer mixture containing acrylamide and / or a monomer copolymerizable with acrylamide, in the presence of a surfactant having a weighted average HLB value of 6.0 to 10.0, which comprises at least one surfactant [A] having an HLB value in the range of 3.0 to 5.0 and at least two surfactants [B] having an HLB value in the range of 8.0 to 15.0, and performing water-in-oil emulsion polymerization to obtain a water-in-oil emulsion containing a polymer, and then adding a hydrophilic surfactant [C] to the water-in-oil emulsion, which is a method for producing a polymer flocculant. In the method for producing a polymer flocculant of the present invention, an aqueous phase composed of an aqueous solution of the above monomer mixture and an oil phase containing a hydrocarbon substantially immiscible with water and the above surfactant are mixed and emulsified to prepare a water-in-oil monomer emulsion, and then the monomer in the aqueous phase is polymerized in the state of the emulsion to prepare a water-in-oil polymer emulsion. The aqueous phase constitutes the dispersed phase of the emulsion, and the oil phase constitutes the continuous phase of the emulsion.

[0025] (1) Monomer mixture The monomer mixture used in the present invention is acrylamide alone; or a monomer copolymerizable with acrylamide; or a mixture of these acrylamide and a monomer copolymerizable with acrylamide. Acrylamide has the structural formula CH2 =CHCONH 2 It is a monomer represented by Examples of monomers copolymerizable with acrylamide include various cationic, nonionic, and anionic monomers described below. These may be used alone or in combination of two or more.

[0026] The cationic monomer used in the present invention can be used as long as it is a monomer having a radically polymerizable double bond capable of radical polymerization and a cationic group. Specifically, in addition to the compound represented by the following general formula (1), diallyldialkylammonium halides such as diallyldimethylammonium chloride can be mentioned. Among these cationic monomers, the compound represented by the following general formula (1) is preferred because it has excellent radical polymerization reactivity, is easily polymerized into a high molecular weight, and has excellent performance as a polymer flocculant of the resulting polymer. CH 2 =CR 1 -CO-X-Q-N + R 2 R 3 R 4 ·Z - ···Formula (1) However, R 1 is a hydrogen atom or a methyl group, R 2 and R 3 are each independently an alkyl group having 1 to 3 carbon atoms or a benzyl group, R 4 is a hydrogen atom, an alkyl group having 1 to 3 carbon atoms or a benzyl group, which may be the same or different. X is an oxygen atom or NH, Q is an alkylene group having 1 to 4 carbon atoms or a hydroxyalkylene group having 2 to 4 carbon atoms, Z - each represents a counter anion, and examples of Z - include halide ions such as chloride ions and sulfate ions.

[0027] Specific examples of the cationic monomer represented by the general formula (1) include dialkylaminoalkyl (meth) acrylates such as dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, and dimethylamino-2-hydroxypropyl (meth) acrylate, and hydrochlorides and sulfates of dialkylaminoalkyl (meth) acrylamides such as dimethylaminopropyl (meth) acrylamide. Further, quaternary salts such as alkyl halide adducts such as methyl chloride adducts of dialkylaminoalkyl (meth) acrylates and dialkylaminoalkyl (meth) acrylamides, benzyl halide adducts such as benzyl chloride, and dialkyl sulfate adducts such as dimethyl sulfate are exemplified.

[0028] Among these preferred cationic monomers, the quaternary salts of dimethylaminoethyl (meth) acrylate and the methyl chloride quaternary salt of dimethylaminoethyl methacrylate, which are particularly easy to polymerize to a high molecular weight required for a polymer flocculant, are most preferred. These cationic monomers may be used alone or in combination of two or more.

[0029] Examples of the nonionic monomer include (meth) acrylamide, alkyl (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and hydroxyethyl (meth) acrylate, styrene, acrylonitrile, and vinyl acetate. Among these nonionic monomers, (meth) acrylamide is preferred because it is easy to polymerize to a high molecular weight required for a polymer flocculant and has excellent performance as a polymer flocculant. Acrylamide, which is water-soluble and particularly excellent in performance as a polymer flocculant, is most preferred. These nonionic monomers may be used alone or in combination of two or more.

[0030] Examples of anionic monomers include (meth)acrylic acid (salt), vinylsulfonic acid (salt), 2-acrylamido-2-methylpropanesulfonic acid (salt), and maleic acid (salt). Among these anionic monomers, (meth)acrylic acid (salt) and 2-acrylamido-2-methylpropanesulfonic acid (salt) are preferred because it is easy to increase the molecular weight required for a polymer flocculant and the performance as a polymer flocculant is excellent. As salts, alkali metal salts such as ammonium salts, sodium salts, and potassium salts are preferred. These anionic monomers may be used alone or in combination of two or more.

[0031] In the present invention, the monomer mixture preferably contains at least one of acrylamide, quaternary salt of dimethylaminoethyl (meth)acrylate, acrylic acid or its salt, or 2-acrylamido-2-methylpropanesulfonic acid or its salt because the performance as a polymer flocculant is particularly excellent.

[0032] In the present invention, there is no particular limitation on the mixing ratio of each monomer in the monomer mixture. That is, acrylamide and / or a monomer copolymerizable with acrylamide may be used alone, or these monomers may be mixed and used at an arbitrary ratio. When a cationic monomer is used in combination with an anionic monomer or a nonionic monomer, the content of the cationic monomer in the monomer mixture is preferably 1 to 99 mol%, particularly preferably 15 to 95 mol%. When an anionic monomer is used in combination with a cationic monomer or a nonionic monomer, the content of the anionic monomer in the monomer mixture is preferably 1 to 99 mol%, particularly preferably 2 to 17 mol%. When a nonionic monomer is used in combination with a cationic monomer or an anionic monomer, the content of the nonionic monomer in the monomer mixture is preferably 1 to 99 mol%, particularly preferably 5 to 98 mol%.

[0033] In the present invention, a crosslinkable monomer may be included in the monomer mixture. The crosslinkable monomer is used for the purpose of introducing a branched or crosslinked structure into the polymer chain. As the crosslinkable monomer, methylene bisacrylamide or a di(meth)acrylate represented by the following general formula (2) is preferable. CH 2 =CR 5 -CO-Y-CO-CR 6 =CH 2 ···Formula (2) However, R 5 and R 6 are each independently H or CH 3 , Y is O(C 2 H 4 O) n or O(C 3 H 6 O) n and n represents an integer of 1 to 10. In particular, the latter is preferably a di(meth)acrylate modified with highly water-soluble ethylene oxide and / or propylene glycol. Among these, methylene bisacrylamide having a small molecular weight, being water-soluble, and having high reactivity is particularly preferable.

[0034] When using a crosslinkable monomer, the amount thereof is preferably 0.5 to 1000 ppm, more preferably 1 to 500 ppm, based on the total monomer mass of the monomer mixture. If added in excess of 1000 ppm, the degree of crosslinking may be too high, and the flocculation performance as a polymer flocculant may be significantly reduced.

[0035] (2) Surfactant In the present invention, as the surfactant, three or more surfactants having different HLB values are used from the viewpoint of improving the storage stability while maintaining the stability of the emulsion during polymerization. At least one surfactant [A] having an HLB value in the range of 3.0 to 5.0 and at least two surfactants [B] having an HLB value in the range of 8.0 to 15.0 are used together. Further, these surfactants are adjusted and used in a proportion such that the weight-average HLB value is in the range of 6.0 to 10.0.

[0036] The surfactant described here is not the hydrophilic surfactant [C] (phase inversion agent) added at the final stage after emulsion polymerization, but the surfactant added before emulsion polymerization.

[0037] The addition amount of the surfactant added before emulsion polymerization is preferably 0.25 to 15% by mass, more preferably 0.5 to 10% by mass, based on the total amount of the water-in-oil emulsion.

[0038] The HLB value of the surfactant is a value determined by the Griffin method for polyethylene glycol type and polyhydric alcohol type, and by the Oda method described in Non-Patent Document 1 for others. The weighted average HLB value of a mixed surfactant composed of two or more nonionic surfactants is determined by the following formula (1). Weighted average HLB value = Σ(HLB X × W X ) / ΣW X ···Equation (1) (In Equation (1), HLB X represents the HLB value of nonionic surfactant X. Also, W X represents the mass (g) of nonionic surfactant X having the value of HLB X ).)

[0039] The HLB value of surfactant [A] is 3.0 to 5.0, preferably 3.2 to 4.8, and more preferably 3.5 to 4.5. When the HLB value is less than 3.0, the emulsion may not invert during use even when surfactant [C], which is finally used as a phase inversion agent, is added.

[0040] The addition amount of surfactant [A] is preferably 10 to 80% by mass, more preferably 20 to 70% by mass, and particularly preferably 21 to 63% by mass with respect to the total amount of surfactants added until the completion of emulsion polymerization (the surfactant [C] used as a phase inversion agent is not included in this amount. The same applies hereinafter). If it is outside the range of 10 to 80% by mass, the stability of the water-in-oil emulsion may decrease. As a result, the emulsion may be partially destroyed during polymerization, and the amount of core coagulum may increase. Also, even when the surfactant [C] finally used as a phase inversion agent is added, the emulsion may not invert when the polymer flocculant is used.

[0041] At least two types of surfactant [B] are used, and their HLB values are each 8.0 to 15.0. The HLB value of at least one type of surfactant [B] is preferably 11.0 or more, and more preferably 11.0 to 15.0. If the HLB value exceeds 15.0, the stability of the water-in-oil emulsion may decrease. Also, the HLB value of at least one other type of surfactant of surfactant [B] is preferably 10.0 or less, and more preferably 8.0 to 10.0. Further, the HLB values of at least two types of each surfactant in surfactant [B] preferably have a difference of 2.0 or more, and more preferably a difference of 2.5 or more. By using two or more types of surfactants with different HLB values as surfactant [B], the emulsion stability during polymerization can be made higher, and the generation of core coagulum can be more suppressed.

[0042] The addition amount of surfactant [B] is preferably 20 to 90% by mass in total, more preferably 30 to 80% by mass, and particularly preferably 37 to 79% by mass with respect to the total amount of surfactants added until the completion of emulsion polymerization. Also, the addition amount of each of the two types of surfactant [B] is preferably 2 to 88% by mass, more preferably 4 to 76% by mass, and particularly preferably 6 to 64% by mass with respect to the total amount of surfactants added before emulsion polymerization. If either one is less than 2% by mass, the effect of using the two types of surfactant [B] in combination may be poor.

[0043] The weighted average HLB value of surfactant [A] and surfactant [B] is 6.0 to 10.0, preferably 6.3 to 9.5, and more preferably 6.4 to 9.3.

[0044] By combining a surfactant with an HLB value of 3.0 to 5.0 and a surfactant with an HLB value of 8.0 to 15.0 to make the weighted average HLB value 6.0 to 10.0, the emulsion stability under conditions where the properties of the aqueous phase (degree of polymerization, etc.) gradually change as the polymerization progresses can be made higher, the generation of core coagulum can be more suppressed, and the storage stability of the emulsion after the polymerization is completed can be increased. The reason for this is presumed to be that by combining three or more surfactants with widely separated HLB values, the surfactant layer present at the particle interface of the emulsion particles becomes thicker, and the emulsion stability is maintained even when the properties of the aqueous phase change.

[0045] As examples of surfactants [A] and [B] to be used, nonionic surfactants are preferred. Specifically, polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, and polyoxyethylene oleyl ether; sorbitan alkylates such as sorbitan monooleate, sorbitan sesquioleate, and sorbitan monolaurate; polyoxyethylene sorbitan monooleates such as polyoxyethylene sorbitan monooleate and polyoxyethylene sorbitan monolaurate; polyoxyethylene sorbitan trioleate, polyoxyethylene sorbitol tetraoleate, polyethylene glycol monooleate, polyethylene glycol dioleate, diethanolamine oleate, monoethanolamine laurate, monoethanolamine stearate, etc. can be mentioned. As surfactant [B], among these, it is preferably composed of two of diolethanolamine oleate, polyoxyethylene lauryl ether, and polyoxyethylene monooleate.

[0046] (3) Hydrocarbons that are substantially immiscible with water The hydrocarbons used in the present invention are substantially immiscible with water. In the present invention, being substantially immiscible with water means that the solubility in water at 25 °C is less than 1000 mg / L. The hydrocarbons used in the present invention preferably have a boiling point in the range of 65 to 180 °C at normal pressure, and more preferably in the range of 65 to 130 °C. Specifically, in addition to hydrocarbons such as n-hexane, cyclohexane, n-heptane, n-octane, isooctane, paraffins, various mineral oils, and mixtures thereof can be mentioned. The amount of the hydrocarbon used is preferably 15 to 50% by mass of the total amount of the water-in-oil emulsion.

[0047] (4) Emulsion polymerization The method for producing the polymer flocculant of the present invention comprises an emulsification step of mixing and emulsifying an aqueous phase composed of an aqueous solution of the above monomer mixture and an oil phase containing a hydrocarbon that is substantially immiscible with water and the above surfactant to prepare a water-in-oil monomer emulsion; a polymerization step of polymerizing the monomer in the dispersed phase of the water-in-oil monomer emulsion in the presence of a radical polymerization initiator to prepare a water-in-oil polymer emulsion containing a polymer that is a polymer of the monomer in the dispersed phase; and a step of adding a hydrophilic surfactant [C] as a phase inversion agent to the water-in-oil emulsion.

[0048] The emulsification conditions are appropriately set according to the compositions of the aqueous phase and the oil phase and the emulsifier used. The ratio of the aqueous phase to the oil phase in the water-in-oil emulsion is not particularly limited, but the W / O ratio, which is the value obtained by dividing the mass of the aqueous phase by the mass of the oil phase, is preferably 2.0 to 3.5, and more preferably 2.2 to 3.2. By setting the W / O ratio within this range, the polymerization stability and storage stability can be made higher, and it becomes easier to invert the water-in-oil emulsion during use. When the W / O ratio is less than 2.0, since the amount of the oil phase is large, the emulsion particles tend to sediment, and the storage stability may decrease.

[0049] The pure content of the polymer in the water-in-oil emulsion is preferably 10 to 50% by mass, more preferably 25 to 45% by mass. The higher the pure content of the polymer, the less the amount of the polymer flocculant added can be, so the economy is excellent. Note that the pure content of the polymer in the water-in-oil emulsion substantially coincides with the pure content of the charged monomer.

[0050] In the present invention, the median diameter of the emulsion particles composed of the aqueous solution of the monomer mixture is preferably 0.7 to 10 μm. The median diameter of the emulsion particles is more preferably 0.8 to 8 μm, and even more preferably 1 to 5 μm. Note that in the present invention, the median diameter of the emulsion particles means the median diameter (D 50 ) in the volume average particle size distribution measured by the laser diffraction method. Also, in the present invention, the emulsion particles in the water-in-oil monomer emulsion and the emulsion particles in the water-in-oil polymer emulsion obtained by polymerizing the same preferably have substantially the same particle size distribution. That is, the median diameter of the emulsion particles containing the polymer is preferably 0.7 to 10 μm, more preferably 0.8 to 8 μm, and even more preferably 1 to 5 μm. When the median diameter of the emulsion particles exceeds 10 μm, the solubility of the polymer flocculant may decrease. Even if the median diameter is made smaller than 0.7 μm, the performance of the polymer flocculant is not improved, and it may be necessary to increase the amount of the surfactant, or it may be difficult to invert the emulsion when using the polymer flocculant.

[0051] The polymerization conditions are appropriately set according to the monomers, initiators, and physical properties of the polymer used. The polymerization temperature is preferably 0 to 100°C, more preferably 10 to 80°C. The monomer concentration in the aqueous monomer solution is preferably 20 to 50% by mass, more preferably 25 to 45% by mass. The polymerization time is preferably 1 to 10 hours.

[0052] Examples of the polymerization initiator include persulfates such as sodium persulfate and potassium persulfate; organic peroxides such as benzoyl peroxide, t-butyl hydroperoxide, and paramethane hydroperoxide; redox catalysts formed by combinations of these with sodium bisulfite, ferrous ammonium sulfate, sulfur dioxide, etc.; and known azo compounds such as 2,2'-azobis-(amidinopropane) hydrochloride, azobiscyanovaleric acid, 2,2'-azobisisobutyronitrile, and 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide]. These polymerization initiators may be used alone or in combination of two or more.

[0053] As a method for adjusting the molecular weight, known chain transfer agents can be used. Examples of known chain transfer agents include thiol compounds such as mercaptoethanol and mercaptopropionic acid, reducing inorganic salts such as sodium sulfite, sodium bisulfite, and sodium hypophosphite, alcohols such as ethanol and isopropyl alcohol, and allyl compounds such as sodium methallyl sulfonate.

[0054] After polymerization, by adding a hydrophilic surfactant [C] called a phase inversion agent, when the emulsion is added to the water to be treated (such as wastewater), the emulsion can be phase-inverted or demulsified, making the emulsion particles containing the polymer more compatible with water and easier to dissolve in water. Examples of the surfactant [C] include cationic surfactants and nonionic surfactants with an HLB value of 9 to 17. Examples of the hydrophilic surfactant [C] to be used include polyoxyethylene alkyl ethers such as polyethylene glycol monooleate and polyoxyethylene lauryl ether. Among these, polyethylene glycol monooleate is preferred as the hydrophilic surfactant [C]. The addition amount of the surfactant [C] may be appropriately determined according to the types of the surfactants [A] and [B], their weight-average HLB value, and the HLB value of the surfactant [C], but it is preferably 1 to 5% by mass in the total mass of the emulsion.

[0055] In addition, additives such as stabilizers, pH adjusters, and antioxidants may be added as long as they do not inhibit the effects of the present invention.

[0056] The water-in-oil emulsion of the present invention preferably has a standard viscosity of 1 to 9 mPa·s. The standard viscosity refers to the viscosity measured at 60 revolutions per minute and 25°C using a B-type viscometer with a BL adapter for an aqueous 1N sodium chloride solution in which 0.10% by mass of the polymer is dissolved. If the standard viscosity is less than 1 mPa·s, the performance as a flocculant may be insufficient even when the polymer is dissolved. If the standard viscosity exceeds 9 mPa·s, the solubility of the polymer is poor, and as a result, the performance as a flocculant may be insufficient.

[0057] (5) Polymer flocculant The polymer flocculant of the present invention comprises a polymer containing acrylamide and / or a monomer copolymerizable with acrylamide as a constituent unit, at least one surfactant A having an HLB value in the range of 3.0 to 5.0 and at least two surfactants B having an HLB value in the range of 8.0 to 15.0, and a surfactant having a weighted average HLB value of 6.0 to 10.0, a water-in-oil emulsion containing the same; a hydrophilic surfactant; and is composed of these. The polymer flocculant of the present invention is prepared by mixing an aqueous phase composed of an aqueous solution of the above monomer mixture and an oil phase containing a hydrocarbon substantially immiscible with water and the above surfactant, followed by emulsification to form a water-in-oil monomer emulsion, and then polymerizing the monomer in the aqueous phase in the state of the emulsion to form a water-in-oil polymer emulsion. The aqueous phase constitutes the dispersed phase of the emulsion, and the oil phase constitutes the continuous phase of the emulsion. The composition of the monomers in the monomer mixture substantially coincides with the composition of the monomer units in the polymer obtained by polymerizing the monomer mixture. Therefore, the polymer flocculant of the present invention can be produced by the above-described production method of the present invention. Details of the monomers and surfactants are as described in the above-described production method of the present invention.

[0058] The polymer flocculant of the present invention preferably has a standard viscosity of 1 to 9 mPa·s. When the standard viscosity is less than 1 mPa·s, even if the polymer dissolves, the performance as a flocculant may be insufficient. When the standard viscosity exceeds 9 mPa·s, the solubility of the polymer is poor, and as a result, the performance as a flocculant may be insufficient.

[0059] The polymerization stability of the polymer flocculant of the present invention can be evaluated by the amount of coagulum. That is, when the stability of the emulsion is poor during polymerization, aggregates of emulsion particles (polymer particles) are generated. This aggregate is called coagulum. The smaller the amount of coagulum, the better the polymerization stability. In the present invention, when the amount of coagulum is less than 0.03% by mass, it can be evaluated that it has sufficient polymerization stability. The measurement method of the amount of coagulum will be described in detail in the examples.

[0060] The storage stability of the polymer flocculant of the present invention can be evaluated by the sedimentation separation amount. That is, when the stability of the emulsion after the completion of polymerization is poor, the emulsion particles (polymer particles) sediment and separate over time. The smaller the sedimentation separation amount, the better the storage stability. In the present invention, when the sedimentation separation amount is less than 4% by mass, it can be evaluated that it has sufficient storage stability. The measurement method of the sedimentation separation amount will be described in detail in the examples.

[0061] (6) Method of using the polymer flocculant The polymer flocculant of the present invention is used for sludge dewatering. Specific examples of the dewatering method are exemplified as follows. That is, an inorganic flocculant is added to the sludge as necessary, and preferably the pH is adjusted to 4 to 7. Then, the polymer flocculant of the present invention is added to this sludge, and the suspension in the sludge and the polymer flocculant are allowed to act by stirring and / or mixing by a known method to form sludge flocs. The formed sludge flocs are mechanically dehydrated by known means to be separated into treated water and dehydrated cake. When a crosslinked amphoteric polymer is used as the polymer flocculant of the present invention, it is preferable to use the inorganic flocculant in combination. Further, when the purpose is deodorization, dephosphorization, denitrification, etc., it is preferable to make the pH of the sludge less than 5. The inorganic flocculant is not particularly limited, and examples thereof include band sulfate, polyaluminum chloride, ferric chloride, ferrous sulfate, polyferric sulfate, etc. The dehydrator is not particularly limited, and examples thereof include a screw press type dehydrator, a belt press type dehydrator, a filter press type dehydrator, a screw decanter, multiple disks, etc.

[0062] The sludge to be treated is not particularly limited. In addition to the sludge generated in sewage treatment, night soil treatment, and domestic wastewater treatment, etc., the sludge generated in various industrial wastewater treatments such as food factories, meat processing, and chemical factories, the raw night soil generated in livestock-related industries such as pig farms and the sludge generated in its wastewater treatment, various sludges such as the sludge generated in the pulp or paper industry are the objects to be treated. There is no limitation on the type of sludge, and primary sedimentation sludge, excess sludge, and their mixed sludge, concentrated sludge, anaerobically digested sludge, etc. are all objects to be treated.

Examples

[0063] Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited by these examples. The measurement methods for various physical properties are as follows. The temperature condition in the measurement of various physical properties is 25 °C unless otherwise specified.

[0064] (1) Coagulum amount (evaluation of polymerization stability) The accurately weighed approximately 20 g of water-in-oil emulsion was filtered through a #150 mesh stainless steel wire mesh. The emulsion adhering to the wire mesh was washed away using a hydrocarbon oil (paraffin oil) in which 10 mass% of sorbitan sesquioleate was dissolved. The hydrocarbon oil was thoroughly wiped off with a paper towel, the remaining mass on the wire mesh was measured, and the core gum amount was calculated using the following formula. Core gum amount (mass%) = (remaining mass / amount of emulsion subjected to filtration) × 100

[0065] (2) Sedimentation separation amount (evaluation of storage stability) Approximately 65 - 70 g of water-in-oil emulsion was accurately weighed into a glass centrifuge tube and centrifuged at 1310 G for 23 minutes. The obtained supernatant was discarded, the amount of the emulsion residue remaining at the bottom was accurately weighed, and the sedimentation separation amount was calculated using the following formula. Sedimentation separation amount (mass%) = (residue mass / mass of emulsion subjected to centrifugation) × 100 In this measurement method, since a small amount of emulsion inevitably remains in the centrifuge tube, even if no emulsion residue is observed, the sedimentation separation amount is about 2 mass%.

[0066] (3) Particle size distribution (median diameter) Using a laser diffraction / scattering type particle size measuring device Microtrac MT3300EXII manufactured by Nikkiso Co., Ltd., the emulsion was appropriately dispersed in a paraffin oil in which 0.5 mass% of sorbitan sesquioleate, a nonionic surfactant, was dissolved and measured. The median diameter (D 50 ) was read from the obtained volume particle size distribution.

[0067] (4) Standard viscosity The emulsion was dissolved in a 1N aqueous sodium chloride solution to a concentration of 0.10 mass% in terms of polymer. Using a B-type viscometer (using a BL adapter, rotation speed: 60 revolutions per minute), the viscosity of this aqueous solution at 25°C was measured.

[0068] (Example 1) Weighed 26.9 g of surfactant into a five-neck separable flask, added and dissolved 242.0 g of paraffin oil to prepare 268.8 g of an oil phase. As the breakdown of the surfactant, 11.7 g (44 mass%) of sorbitan sesquioleate with an HLB value of 3.7 as surfactant [A], 3.9 g (14 mass%) of diethanolamine oleate with an HLB value of 9.2 as surfactant [B], and 11.3 g (42 mass%) of polyethylene glycol monooleate with an HLB value of 13.5 as surfactant [B]. The weighted average HLB value of the surfactant is 8.6. Mixed 389.4 g of a 79 mass% aqueous solution of methyl chloride quaternary salt of dimethylaminoethyl acrylate (DAC) and 184.8 g of a 50 mass% aqueous solution of acrylamide (AM), added 0.008 g of methylenebisacrylamide (MBA), 2.4 g of isopropyl alcohol, 0.2 g of chelating agent EDTA, 0.01 g of t-butyl hydroperoxide as an initiator, and ion-exchanged water, adjusted the pH to 4.0 with 98% sulfuric acid to prepare 672.3 g of an aqueous phase. The molar ratio of DAC to AM is 55:45. The addition amount of MBA is 20 ppm based on the total mass of the monomers. The addition amount of the surfactant is 2.9 mass% based on the total amount of the aqueous phase and the oil phase. The mass ratio of the aqueous phase to the oil phase (W / O ratio) is 2.5. While stirring the oil phase, the aqueous phase was added, and high-speed stirring was performed with a homogenizer to prepare a water-in-oil emulsion. A five-neck separable flask was equipped with a nitrogen gas blowing tube, a reflux condenser, and a thermometer, and while stirring with a stirring blade, nitrogen gas was supplied to replace the gas phase in the system with nitrogen. After setting the water-in-oil emulsion at 20 °C, while supplying nitrogen gas, nitrogen gas containing 0.02 vol% of sulfur dioxide was blown into the water-in-oil emulsion at a supply rate of 12 ml / min to initiate polymerization. After reaching 50 °C and maintaining this temperature for 2 hours, the supply rate of nitrogen gas containing sulfur dioxide was increased to 190 ml / min and maintained at 50 °C for 1 hour. Then, the supply of nitrogen gas containing sulfur dioxide was stopped, 3.9 g of a 1% aqueous solution of sodium bisulfite was added, and the mixture was maintained for 30 minutes. The supply of nitrogen gas was stopped to terminate the polymerization. Here, 39.4 g of malic acid and 15.4 g of polyethylene glycol monooleate having an HLB value of 13.5 as the hydrophilic surfactant [C] were added to obtain a water-in-oil polymer emulsion having a polymer pure content of 40.0 mass% and a median diameter of emulsion particles of 1.6 μm. The physical properties of the obtained water-in-oil polymer emulsion were evaluated, and the results are shown in Table 1. Note that the blending amount of the hydrophilic surfactant [C] is not described in Table 1.

[0069] (Examples 2 to 6, Comparative Examples 1 to 2) A water-in-oil polymer emulsion was obtained in the same manner as in Example 1 except that the mixing ratio shown in Table 1 was changed.

[0070] (Example 7) 23.9 g of a surfactant was weighed into a five-neck separable flask, 249.7 g of paraffin oil was added and dissolved to prepare 273.6 g of an oil phase. The breakdown of the surfactant was 15.1 g (63 mass%) of sorbitan sesquioleate having an HLB value of 3.7 as the surfactant [A], 5.0 g (21 mass%) of diethanolamine oleate having an HLB value of 9.2 as the surfactant [B], and 3.8 g (16 mass%) of polyethylene glycol monooleate having an HLB value of 13.5 as the surfactant [B]. The weighted average HLB value of the surfactant was 6.4. To 535.0 g of a 50 mass% aqueous acrylamide (AM) solution, 69.4 g of 80 mass% acrylic acid (AcA) was added and neutralized with 48 mass% aqueous sodium hydroxide to adjust the pH to 7.0. To this, 0.06 g of chelating agent EDTA, 1.9 g of isopropyl alcohol, 0.008 g of t-butyl hydroperoxide as an initiator, and ion-exchanged water were added to prepare 684.2 g of an aqueous phase. The molar ratio of AM to AcA is 83:17. The addition amount of the surfactant is 2.5 mass% based on the total amount of the aqueous phase and the oil phase. The mass ratio W / O of the aqueous phase to the oil phase is 2.5. While stirring the oil phase, the aqueous phase was added and rapidly stirred with a homogenizer to prepare a water-in-oil emulsion. A five-neck separable flask was equipped with a nitrogen gas blowing tube, a reflux condenser, and a thermometer, and while stirring with a stirring blade, nitrogen gas was supplied to replace the gas phase in the system with nitrogen. After setting the water-in-oil emulsion to 10 °C, while supplying nitrogen gas, nitrogen gas containing 0.02 vol% of sulfur dioxide was blown into the water-in-oil emulsion at a supply rate of 20 ml / min to initiate polymerization. After reaching 40 °C, this temperature was maintained for 2 hours, then the supply rate of nitrogen gas containing sulfur dioxide was increased to 160 ml / min and maintained at 40 °C for 1 hour. Then, the supply of nitrogen gas containing sulfur dioxide was stopped, 11.3 g of a 30% aqueous solution of sodium bisulfite was added, and it was maintained for 30 minutes. The supply of nitrogen gas was stopped to terminate the polymerization. Here, 30.8 g of polyethylene glycol monooleate with an HLB value of 13.5 was added as the hydrophilic surfactant [C] to obtain a polymer emulsion with a polymer pure content of 34.0 mass% and a median diameter of emulsion particles of 1.2 μm. The physical properties of the obtained water-in-oil polymer emulsion were evaluated, and the results are shown in Table 1. Note that the blending amount of the hydrophilic surfactant [C] is not described in Table 1.

[0071] (Examples 8 to 10, Comparative Examples 3 to 5) A water-in-oil polymer emulsion was obtained in the same manner as in Example 7 except that the mixing ratio shown in Table 1 was changed.

[0072]

Table 1

[0073] The abbreviations of the monomers in Table 1 are as follows. 「DAC」: Methyl chloride quaternary salt of dimethylaminoethyl acrylate, 「DMC」: Methyl chloride quaternary salt of dimethylaminoethyl (meth)acrylate, 「AcA」: Acrylic acid, 「AMPS」: 2-Acrylamido-2-methylpropanesulfonic acid, 「AM」: Acrylamide, 「MBA」: Methylenebisacrylamide

[0074] The abbreviations of the surfactants in Table 1 are as follows. (a): Sorbitan sesquioleate (HLB value 3.7), (b): Diethanolamine oleate (HLB value 5.0), (c): Polyoxyethylene lauryl ether (HLB value 8.1), (d): Diethanolamine oleate (HLB value 9.2), (e): Polyoxyethylene monooleate (HLB value 13.5)

[0075] Examples 1 to 10 included at least one surfactant [A] with an HLB value in the range of 3.0 to 5.0 and at least two surfactants [B] with an HLB value in the range of 8.0 to 15.0, and used a surfactant with a weighted average HLB value of 6.0 to 10.0. Therefore, the polymerization stability and storage stability were excellent. In Comparative Example 1, although the weighted average HLB value of the surfactant was in the range of 6.0 to 10.0, only one type of surfactant [B] with an HLB value in the range of 8.0 to 15.0 was used. Therefore, the polymerization stability and storage stability were low. In Comparative Examples 2 and 3, the weighted average HLB value of the surfactant was outside the range of 6.0 to 10.0, and only one type of surfactant [B] with an HLB value in the range of 8.0 to 15.0 was used. Therefore, the polymerization stability and storage stability were extremely low. Comparative Example 4 used one surfactant [A] with an HLB value in the range of 3.0 to 5.0 and two surfactants [B] with an HLB value in the range of 8.0 to 15.0. However, since the weighted average HLB value of the surfactants was outside the range of 6.0 to 10.0, the polymerization stability and storage stability were low. Comparative Example 5 had a weighted average HLB value of the surfactant outside the range of 6.0 to 10.0, used only one type of surfactant [B] with an HLB value in the range of 8.0 to 15.0, and had a high W / O ratio, so the polymerization stability and storage stability were extremely low.

Claims

1. A monomer mixture containing acrylamide and / or a monomer copolymerizable with acrylamide is in the presence of a surfactant having a weight-average HLB value of 6.0 to 10.0, which comprises at least one surfactant [A] having an HLB value in the range of 3.0 to 5.0 and at least two surfactants [B] having an HLB value in the range of 8.0 to 15.0, subjected to water-in-oil emulsion polymerization to obtain a water-in-oil emulsion containing a polymer, and then a hydrophilic surfactant [C] is added to the water-in-oil emulsion. A method for producing a polymer flocculant, characterized by this.

2. The method for producing a polymer flocculant according to claim 1, wherein the surfactant [B] is at least two selected from diolethanolamide oleate, polyoxyethylene lauryl ether, and polyoxyethylene monooleate.

3. The method for producing a polymer flocculant according to claim 1, wherein the monomer mixture comprises at least one or more of acrylamide, a quaternary salt of dimethylaminoethyl (meth)acrylate, acrylic acid or its salt, or 2-acrylamido-2-methylpropanesulfonic acid or its salt.

4. The method for producing a polymer flocculant according to claim 1, wherein the monomer mixture contains a crosslinkable monomer.

5. The method for producing a polymer flocculant according to claim 1, wherein the W / O ratio, which is the value obtained by dividing the mass of the aqueous phase by the mass of the oil phase in the water-in-oil emulsion, is 2.0 to 3.

5.

6. The method for producing a polymer flocculant according to claim 1, wherein the particle size measured by the laser diffraction method of the water-in-oil emulsion is 0.7 to 10 μm in median diameter.

7. A monomer mixture containing acrylamide and / or a monomer copolymerizable with acrylamide is in the presence of a surfactant having a weight-average HLB value of 6.0 to 10.0, which comprises at least one surfactant [A] having an HLB value in the range of 3.0 to 5.0 and at least two surfactants [B] having an HLB value in the range of 8.0 to 15.0, subjected to water-in-oil emulsion polymerization to obtain a water-in-oil emulsion containing a polymer, and then a hydrophilic surfactant [C] is added to the water-in-oil emulsion. A polymer flocculant, characterized by being obtained in this way.

8. A polymer containing acrylamide and / or a monomer copolymerizable with acrylamide as a structural unit, and At least one surfactant [A] having an HLB value in the range of 3.0 to 5.0 and at least two surfactants [B] having an HLB value in the range of 8.0 to 15.0, a surfactant having a weighted average HLB value of 6.0 to 10.0, An oil-in-water emulsion containing the same; A hydrophilic surfactant [C]; A polymer flocculant characterized by containing the same.

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