Polymer flocculant, method for producing the same, and method for dehydrating sludge

Abstract

To provide a polymer flocculant excellent in flocculation performance, and a method for producing the same.SOLUTION: A polymer flocculant according to the present invention is a water-in-oil emulsion containing a high molecular weight polymer obtained by subjecting a monomer mixture containing the following components (a) to (d) to water-in-oil emulsion polymerization, the components (a) to (d) including: (a) a cationic monomer having a quaternary ammonium salt group; (b) an anionic monomer; (c) a nonionic monomer; and (d) a crosslinkable monomer, where a content of an anionic monomer having a neutralized acid group among the anionic monomers is more than 30 mol% and 70 mol% or less with respect to the anionic monomer; the water-in-oil emulsion contains one or more nonionic surfactants having an HLB value of 3 to 5 and two or more nonionic surfactants having an HLB value of 8 to 15; and viscosity at 25°C of a 1M sodium chloride aqueous solution containing 0.1 mass% of the water-in-oil emulsion in terms of the polymer is 1.3 to 3.5 mPa s.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a polymer flocculant, a method for producing the same, and a method for dewatering sludge. More specifically, the present invention relates to an oil-in-water emulsion polymer flocculant having excellent flocculation performance, a method for producing the same, and a method for dewatering sludge.

Background Art

[0002] Conventionally, cationic polymer flocculants have been widely used for dewatering sludge discharged from general industrial wastewater treatment plants, sewage treatment plants, night soil treatment plants, etc. However, due to the increase in the amount of sludge generated and the deterioration of sludge properties, the dehydration method using conventional cationic polymer flocculants can no longer achieve a sufficiently satisfactory dehydration treatment.

[0003] In order to improve the dehydration efficiency, it has been proposed to use amphoteric polymer flocculants for sludge dewatering. However, depending on the sludge to be applied, it is necessary to add a large amount to the sludge, the floc particle size becomes small, or the filtration rate is insufficient, so the treatment amount per unit time cannot be increased, and furthermore, the cake water content obtained cannot be reduced.

[0004] Under such circumstances, there is a demand for further performance improvement of flocculants that exhibit a dehydration function.

[0005] Patent Document 1 discloses a method for producing an amphoteric polymer by polymerizing an anionic monomer in which 3 to 30 mol% of acid groups are neutralized with an alkaline substance, a cationic monomer, and a nonionic monomer.

[0006] The amphoteric polymer produced by the emulsion polymerization method described in Patent Document 1 exhibits excellent dehydration performance. However, according to the verification by the present inventors, it has not yet been possible to achieve a dehydration treatment performance that is sufficiently satisfactory in response to the deterioration of sludge properties.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Non-Patent Document

[0008]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] An object of the present invention is to provide a polymer flocculant having excellent flocculation performance and a method for producing the same.

Means for Solving the Problems

[0010] As a result of intensive studies on the above problems, the present inventors have found that an amphoteric polymer obtained by polymerizing a predetermined monomer mixture using a predetermined surfactant with the content of a monomer in which a part of the acid groups of an anionic monomer is neutralized with an alkali being more than 30 mol% and not more than 70 mol% exhibits extremely excellent flocculation performance, and thus the present invention has been completed.

[0011] The present invention for solving the above problems is as described below.

[0012] 〔1〕 An oil-in-water emulsion containing a polymer obtained by subjecting a monomer mixture containing the following components (a) to (d) (a) A cationic monomer having a quaternary ammonium base, (b) An anionic monomer, (c) A nonionic monomer, and (d) A crosslinkable monomer to oil-in-water emulsion polymerization, Among the anionic monomers, the content of the anionic monomer with the acid group neutralized is more than 30 mol% and at most 70 mol% with respect to the anionic monomer. The oil-in-water emulsion comprises at least one nonionic surfactant having an HLB value of 3 to 5 and at least two nonionic surfactants having an HLB value of 8 to 15. A polymer flocculant characterized in that the viscosity of a 1 M aqueous sodium chloride solution containing 0.1% by mass of the oil-in-water emulsion in terms of polymer is 1.3 to 3.5 mPa·s at 25°C.

[0013] 〔2〕 The polymer flocculant according to 〔1〕, wherein the content of the cationic monomer is 20 to 55 mol% with respect to the total monomers.

[0014] 〔3〕 The cationic monomer is at least the following formula (1): CH2=CR 1 -CO-X-Q-N + R 2a R 2b R 2c ·Z - ··· Formula (1) (However, in formula (1), R 1 is a hydrogen atom or a methyl group, R 2a and R 2b are each independently an alkyl group having 1 to 3 carbon atoms or a benzyl group, R 2c is 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, and Z - each represents a counter anion.) The polymer flocculant according to 〔1〕, comprising a cationic monomer represented by the formula.

[0015] 〔4〕 The polymer flocculant according to 〔1〕, wherein the content of the anionic monomer is 1 to 35 mol% with respect to the total monomers.

[0016] 〔5〕The polymer flocculant according to 〔1〕, wherein the anionic monomer is (meth)acrylic acid (salt).

[0017] 〔6〕The polymer flocculant according to 〔1〕, wherein the content of the nonionic monomer is 20 to 79 mol% based on the total monomers.

[0018] 〔7〕The polymer flocculant according to 〔1〕, wherein the nonionic monomer is (meth)acrylamide.

[0019] 〔8〕The following components (a) to (d) (a) A cationic monomer having a quaternary ammonium base, (b’) An anionic monomer whose acid group is not neutralized, (c) A nonionic monomer, and (d) A crosslinkable monomer A monomer mixture containing the same is A method for producing a polymer flocculant, which comprises subjecting to water-in-oil emulsion polymerization in the presence of a surfactant containing at least one nonionic surfactant having an HLB value of 3 to 5 and at least two nonionic surfactants having an HLB value of 8 to 15 to obtain a water-in-oil emulsion containing a polymer polymer, The method for producing a polymer flocculant according to 〔1〕, which comprises adding an alkali to a mixture containing the (c) nonionic monomer, the (b’) anionic monomer whose acid group is not neutralized, and water, neutralizing more than 30 mol% and at most 70 mol% of the (b’) anionic monomer whose acid group is not neutralized, and then adding the (a) cationic monomer.

[0020] 〔9〕A method for dewatering sludge, which comprises adding an organic flocculant and / or an inorganic flocculant to the sludge and then adding the polymer flocculant according to 〔1〕 for dewatering.

Advantages of the Invention

[0021] The polymer flocculant of the present invention has high flocculation performance and dewatering performance for sludge.

Embodiments for Carrying Out the Invention

[0022] The present invention will be described in detail below. In the present 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. Further, 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.

[0023] 1. Polymer flocculant The polymer flocculant of the present invention is an oil-in-water emulsion containing a polymer obtained by oil-in-water emulsion polymerization of a monomer mixture containing the following components (a) to (d): (a) A cationic monomer having a quaternary ammonium base, (b) An anionic monomer, (c) A nonionic monomer, and (d) A crosslinkable monomer wherein the content of the anionic monomer in which the acid group is neutralized among the anionic monomers is more than 30 mol% and 70 mol% or less with respect to the anionic monomer, the oil-in-water emulsion comprises one or more nonionic surfactants having an HLB value of 3 to 5 and two or more nonionic surfactants having an HLB value of 8 to 15, and the viscosity of a 1M aqueous sodium chloride solution containing 0.1% by mass of the oil-in-water emulsion in terms of polymer at 25°C is 1.3 to 3.5 mPa·s.

[0024] ​By increasing the neutralization rate of the anionic group, the viscosity of the polymer solution is moderately decreased, and the reactivity with highly viscous sludge particles with poor dewaterability is increased. In addition, by adding a crosslinking monomer, the resulting polymer forms a three-dimensional structure, and the performance is improved in combination with the improved reactivity with sludge. If the degree of neutralization of the anionic group is too high, the anionic group and the cationic group during polymerization form a complex and the polymerization becomes unstable, so that the emulsion aggregates. A neutralization rate of more than 30 mol% to 70 mol% is preferable. Moreover, when the degree of neutralization of the anionic group is within the above range, the polymerization rate becomes fast, the residual acrylamide decreases, which is preferable for the environment. When the HLB value of the emulsifier is within the above range, the thickness of the emulsifier layer at the emulsion particle interface increases, and the particle stability is improved, so that the polymerization stability is improved and the storage stability is also improved.

[0025] In the method for producing the 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 and a surfactant that are substantially immiscible with water are mixed and emulsified to prepare a water-in-oil monomer emulsion. 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.

[0026] In the present invention, the composition of the monomers in the monomer mixture and the composition of the monomer units in the polymer obtained by polymerizing the monomer mixture substantially coincide.

[0027] The standard viscosity of the polymer flocculant of the present invention is 1.3 to 3.5 mPa·s, preferably 1.4 to 3.0 mPa·s. When the standard viscosity is less than 1.3 mPa·s, the solubility of the polymer is low and the performance as a flocculant is insufficient. When the standard viscosity exceeds 3.5 mPa·s, the polymer becomes close to a linear polymer and the performance as a flocculant is insufficient.

[0028] 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. These aggregates are called core coagulums. The smaller the amount of core coagulums, the better the polymerization stability. In the present invention, when the amount of core coagulums is less than 0.03% by mass, it can be evaluated that sufficient polymerization stability is achieved. The measurement method of the amount of core coagulums will be described in detail in the examples.

[0029] The storage stability of the polymer flocculant of the present invention can be evaluated by the amount of sedimentation separation. 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 amount of sedimentation separation, the better the storage stability. In the present invention, when the amount of sedimentation separation is less than 4% by mass, it can be evaluated that sufficient storage stability is achieved. The measurement method of the amount of sedimentation separation will be described in detail in the examples.

[0030] When acrylamide is used as the monomer, the amount of residual acrylamide is preferably less than 1000 ppm (relative to the emulsion), more preferably less than 800 ppm, still more preferably less than 600 ppm, and particularly preferably less than 500 ppm.

[0031] 2. Method for producing polymer flocculant The method for producing the polymer flocculant of the present invention comprises an emulsification step of emulsion polymerization in the presence of a surfactant containing an aqueous phase composed of an aqueous solution of a monomer mixture of the above components (a) to (d), an oil phase containing a hydrocarbon substantially immiscible with water and the above surfactant, at least one nonionic surfactant having an HLB value of 3 to 5, and at least two nonionic surfactants having an HLB value of 8 to 15 to produce a water-in-oil type monomer emulsion; a polymerization step of polymerizing the monomer in the dispersed phase of the water-in-oil type monomer emulsion in the presence of a radical polymerization initiator to produce a water-in-oil type polymer emulsion containing a polymer which is a polymer of the monomer in the dispersed phase; and it consists of these. In the method for producing the polymer flocculant of the present invention, when preparing an aqueous phase composed of an aqueous solution of a monomer mixture, an alkali is added to a mixture containing the (c) nonionic monomer, the (b') anionic monomer whose acid group is not neutralized, and water, and after neutralizing more than 30 mol% and at most 70 mol% of the (b') anionic monomer whose acid group is not neutralized, it preferably has a step of adding a (a) cationic monomer having a quaternary ammonium base.

[0032] (1) Monomer mixture The monomer mixture used in the present invention comprises (a) a cationic monomer having a quaternary ammonium base, (b) an anionic monomer, (c) a nonionic monomer, and (d) a crosslinkable monomer.

[0033] (1-1) (a) Cationic monomer component having a quaternary ammonium base As the cationic monomer component having a quaternary ammonium base, a compound represented by the following general formula (1) is preferred because it is excellent in radical polymerization reactivity, easy to increase in molecular weight, and the resulting polymer has excellent performance as a polymer flocculant. CH2=CR 1 -CO-X-Q-N + R 2a R 2b R 2c ·Z - ···Formula (1) However, in formula (1), R 1 is a hydrogen atom or a methyl group, R 2a and R 2b are each independently an alkyl group having 1 to 3 carbon atoms or a benzyl group, R 2c is 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, and Z - each represents a counter anion. Examples of Z - include halide ions such as chloride ions and sulfate ions.

[0034] Specific examples of the cationic monomer represented by the general formula (1) include quaternary salts such as dialkylaminoalkyl (meth)acrylates such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylamino-2-hydroxypropyl (meth)acrylate, and alkyl halide adducts such as methyl chloride of dialkylaminoalkyl (meth)acrylamides such as dimethylaminopropyl (meth)acrylamide, benzyl halide adducts such as benzyl chloride, and dialkyl sulfate adducts such as dimethyl sulfate.

[0035] Among these preferred cationic monomers, the quaternary methyl chloride salt of dimethylaminoethyl (meth)acrylate, which is particularly easy to achieve high molecular weight required for the polymer flocculant, is most preferred. These cationic monomers may be used alone or in combination of two or more.

[0036] The content of the cationic monomer having a quaternary ammonium base is preferably 20 to 55 mol% based on the total monomers, and more preferably 20 to 50 mol%. If it is less than 20 mol%, the amount of cationic groups in the polymer flocculant may be small and the flocculation performance may not be sufficiently high. If it exceeds 55 mol%, the amount of nonionic monomer will be relatively small, so the copolymerizability with the neutralized anionic monomer will be low and the flocculation performance will decrease.

[0037] (1-2) (b’) Anionic monomer with unneutralized acid groups Examples of anionic monomers with unneutralized acid groups include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, etc., and one or more of these can be used. Among them, acrylic acid and / or methacrylic acid are preferred. In the present invention, during emulsion polymerization, it is necessary that more than 30 mol% and 70 mol% or less of the acid groups of the anionic monomer are neutralized. That is, more than 30 mol% and 70 mol% or less of the acid groups of the anionic monomer are neutralized by an alkali. When the degree of neutralization of the acid groups is 30 mol% or less or more than 70 mol%, the target aggregation performance and dehydration performance cannot be obtained. Note that the degree of neutralization in the present invention means the ratio (mol%) of the monomer in which the acid groups of the anionic monomer are neutralized by an alkali to the total number of moles of the anionic monomer. The alkali used for neutralization is not particularly limited, and examples include metal hydroxides such as sodium hydroxide and potassium hydroxide, and ammonium hydroxide. The degree of neutralization is preferably 35 to 68 mol%, more preferably 40 to 65 mol%.

[0038] In the production process of the present invention, an alkali may be added to the anionic monomer with unneutralized acid groups to neutralize more than 30 mol% and 70 mol% or less of the acid groups, or an anionic monomer with neutralized acid groups, such as acrylate or methacrylate, may be blended at more than 30 mol% and 70 mol% or less.

[0039] The total content of the anionic monomer with unneutralized acid groups and the anionic monomer with neutralized acid groups is preferably 1 to 35 mol%, more preferably 2 to 32 mol%, and particularly preferably 10 to 30 mol% with respect to the total monomer.

[0040] (1-3) (c) Nonionic monomer As nonionic monomers, in addition to (meth)acrylamide, alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and hydroxyethyl (meth)acrylate, styrene, acrylonitrile, vinyl acetate, and the like can be mentioned. Among these nonionic monomers, (meth)acrylamide is preferable because it is easy to increase the 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 preferable. These nonionic monomers may be used alone or in combination of two or more.

[0041] The content of the nonionic monomer is 20 to 79 mol% based on the total monomers, preferably 22 to 72 mol%, and more preferably 25 to 70 mol%.

[0042] It is preferable that the blending ratios of the above components (a) to (c) are satisfied and the molar ratio of component (a) to component (b) is 1 or more, more preferably 1.5 or more. If it is less than 1, the anionic property of the resulting polymer becomes too strong, the sludge flocculation performance may be significantly impaired, or the particles may become unstable and aggregate during polymerization.

[0043] (1-4) (d) Crosslinkable monomer In the present invention, the crosslinkable monomer is used for the purpose of introducing a branched or crosslinked structure into the polymer chain. As the crosslinkable monomer, methylenebisacrylamide or a di(meth)acrylate represented by the following general formula (2) is preferable. CH2=CR 5 -CO-Y-CO-CR 6 =CH2···Formula (2) However, R 5 and R 6 are each independently H or CH3, Y is O(C2H4O) n or O(C3H6O) 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 preferred.

[0044] The amount of the crosslinkable monomer is preferably 0.5 to 1000 ppm, more preferably 1 to 500 ppm, based on the total monomer mass of the monomer mixture. When 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.

[0045] (2) Emulsion polymerization The emulsification conditions during emulsion preparation 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, 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 are likely to settle, and the storage stability may decrease.

[0046] 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 to be added, so it is excellent in economy. Note that the pure content of the polymer in the water-in-oil emulsion substantially coincides with the pure content of the charged monomer.

[0047] In the present invention, the median diameter of the water-in-oil polymer emulsion particles obtained by polymerization is preferably 0.7 to 10 μm, more preferably 0.8 to 8 μm, and even more preferably 0.9 to 5 μm. If 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 will not improve, and it may be necessary to increase the amount of surfactant or it may become difficult to invert the emulsion when using the polymer flocculant.

[0048] 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.

[0049] 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 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.

[0050] 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.

[0051] After the polymerization, by adding a hydrophilic surfactant [C] called an 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.

[0052] In addition, additives such as stabilizers, pH adjusters, and antioxidants may be added within the range that does not inhibit the effects of the present invention.

[0053] (2-1) Surfactant In the present invention, three or more types of surfactants with 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 type of surfactant [A] with an HLB value in the range of 3.0 to 5.0 and at least two types of surfactants [B] with an HLB value in the range of 8.0 to 15.0 are used together. Moreover, these surfactants are preferably adjusted and used at a ratio such that the weight-average HLB value is in the range of 6.0 to 10.0.

[0054] It should be noted that the surfactant described here is not the hydrophilic surfactant [C] (inversion agent) added at the final stage after emulsion polymerization, but the surfactant added before emulsion polymerization.

[0055] 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.

[0056] 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 found in Non-Patent Document 1 for the 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 Formula (1) (In formula (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 .)

[0057] 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, even if surfactant [C] finally used as a phase inversion agent is added, the emulsion may not invert during use.

[0058] 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 (surfactant [C] used as a phase inversion agent is not included in the amount. The same applies hereinafter). When 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 broken during polymerization, and the amount of coagulum may increase. Also, even if surfactant [C] finally used as a phase inversion agent is added, the emulsion may not invert during the use of the polymer flocculant.

[0059] 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, more preferably 11.0 to 15.0. When 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, more preferably 8.0 to 10.0. Furthermore, the HLB values of at least two types of each surfactant in surfactant [B] preferably have a difference of 2.0 or more, 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.

[0060] 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, based on 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, based on 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.

[0061] 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.

[0062] By combining a surfactant having an HLB value of 3.0 to 5.0 and a surfactant having an HLB value of 8.0 to 15.0 to make the weight-average HLB value 6.0 to 10.0, it is possible to further improve the emulsion stability under conditions where the properties of the aqueous phase (degree of polymerization, etc.) gradually change as the polymerization proceeds, further suppress the generation of core coagulum, and improve the storage stability of the emulsion after the polymerization is completed. 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.

[0063] Examples of the surfactants [A] and [B] to be used are preferably nonionic surfactants. 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 the surfactant [B], among these, a combination of two of diolethanolamine oleate, polyoxyethylene lauryl ether, and polyoxyethylene sorbitan monooleate is preferred.

[0064] (2-2) Hydrocarbons that are substantially immiscible with water The hydrocarbon used in the present invention is 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 hydrocarbon used in the present invention preferably has a boiling point in the range of 65 to 300°C at normal pressure. Specifically, hydrocarbons such as n-hexane, cyclohexane, n-heptane, n-octane, isooctane, etc., as well as paraffins, various mineral oils and their mixtures 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.

[0065] 3. 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 organic coagulant and / or an inorganic coagulant 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 dewatered cake. When using the polymer flocculant of the present invention, it is preferable to use the coagulant in combination. Also, when the purpose is deodorization, dephosphorization, denitrification, etc., it is preferable to make the pH of the sludge less than 5. The inorganic coagulant is not particularly limited, and examples include band sulfate, polyaluminum chloride, ferric chloride, ferrous sulfate, polyferric sulfate, etc. The organic coagulant is not particularly limited, and examples include polydiallyldimethylammonium chloride and polyamines. The dewatering device is not particularly limited, and examples include a screw press type dewatering machine, a belt press type dewatering machine, a filter press type dewatering machine, a screw decanter, a multi-disc, etc.

[0066] The sludge to be treated is not particularly limited. In addition to the sludge generated in sewage treatment, night soil treatment, domestic wastewater treatment, etc., various sludges such as those generated in the treatment of various industrial wastewaters such as food factories, meat processing, and chemical factories, raw night soil generated in livestock-related industries such as pig farms and the sludge generated in the treatment of its wastewater, and sludges 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, thickened sludge, anaerobically digested sludge treated with anaerobic microorganisms, etc. are all objects to be treated.

Examples

[0067] Hereinafter, the present invention will be described more specifically with reference to 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.

[0068] 1. Measurement conditions for various physical properties (1) Degree of neutralization It is the value obtained by multiplying the total number of moles of alkali used for neutralizing the anionic monomer by 100 and dividing it by the total number of moles of the anionic monomer, and is expressed in mol%.

[0069] (2) Standard viscosity The polymer flocculant was dissolved in a 1M aqueous sodium chloride solution to a concentration of 0.10 mass% in terms of polymer. The viscosity of this aqueous solution at 25°C was measured using a B-type viscometer (using a BL adapter, rotation speed: 60 revolutions per minute).

[0070] (3) Viscosity of 0.1 mass% solution The polymer flocculant was added to distilled water at a concentration of 0.1 mass% in terms of polymer and dissolved. The viscosity of this aqueous solution at 25°C was measured using a B-type viscometer.

[0071] (4) Measurement of the amount of residual acrylamide 1 g of an emulsion prepared in 10 g of water / acetone = 20 / 80 (vol / vol) containing methacrylamide as an internal standard was taken, and while grinding the polymer with a spatula, residual AM was extracted. After filtering the supernatant with a disposable filter, analysis was performed using a capillary column with helium as the carrier gas and 95% dimethylpolysiloxane as the stationary phase in an Agilent Technologies 7820A gas chromatography device, and the remaining amount relative to the emulsion was calculated.

[0072] (5) Amount of coagulum (evaluation of polymerization stability) Approximately 20 g of the water-in-oil emulsion precisely weighed was filtered through a #150 mesh stainless steel wire mesh. Using a hydrocarbon oil (paraffin oil) in which 10 mass% of sorbitan sesquioleate was dissolved, the emulsion adhering to the wire mesh was washed away. The hydrocarbon oil was thoroughly wiped with a paper towel, the mass of the residue on the wire mesh was measured, and the amount of coagulum was calculated using the following formula. Amount of coagulum (mass%) = (mass of residue / amount of emulsion subjected to filtration) × 100

[0073] (6) Amount of sedimentation separation (evaluation of storage stability) Approximately 65 - 70 g of the water-in-oil emulsion precisely weighed was placed in 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 precisely weighed, and the amount of sedimentation separation was calculated using the following formula. Amount of sedimentation separation (mass%) = (mass of residue / 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 amount of sedimentation separation is about 2 mass%.

[0074] (7) Floc size Measured visually.

[0075] (8) Amount of water filtered A coagulant was added to the sludge and thoroughly stirred and mixed. 200 mL of this mixed sludge was placed in a 300 mL beaker, and the polymer flocculants produced in Production Examples 1 to 4 and Comparative Production Examples 1 to 4 were each added in a predetermined amount based on the mass of the sludge. A jar tester was used to stir at a predetermined rotational speed for a predetermined time to form sludge flocs. The floc size of the formed sludge flocs was visually measured. Next, the entire amount of the aggregated sludge was poured all at once into a stainless steel sieve with a mesh opening of 250 μm and gravity filtered. At this time, the funnel was set so that the filtrate would enter a 200 mL measuring cylinder, and the volume of the filtrate 10 seconds after the start of filtration was measured to evaluate the gravity filtration performance.

[0076] (9) Filtrate state (evaluation of flocculation performance) The state of the filtrate obtained by measuring the above-mentioned filtrate volume was visually evaluated according to the following criteria. ○: No outflow of suspended components (SS) is observed in the filtrate. △: A small amount of outflow of suspended components (SS) is observed in the filtrate. ×: A large amount of outflow of suspended components (SS) is observed in the filtrate.

[0077] (10) Cake moisture content (evaluation of dewatering performance) The water-containing cake of the sludge remaining on the stainless steel sieve after evaluating the filtrate volume was taken out, placed on a filter cloth, and squeezed with a test belt press at a surface pressure of 0.05 MPa to obtain a dewatered cake. A part of the center was sampled from the obtained dewatered cake, weighed into an aluminum pan, dried in a hot air dryer at 105 °C for 16 hours, and then the mass after drying was measured. The moisture content was determined from the reduction amount due to drying and the mass before drying.

[0078] 2. Production of polymer flocculant (Production Example 1) 9.5 g of sorbitan sesquioleate with an HLB value of 3.7, 9.5 g of oleic acid diethanolamide with an HLB value of 9.2, and 7.7 g of polyethylene glycol monooleate with an HLB value of 13.5 were weighed into a five-neck separable flask, and 240.3 g of paraffin oil was added and dissolved to prepare an oil phase. 313.1 g of a 50% by mass aqueous acrylamide solution and 33.1 g of an 80% by mass aqueous acrylic acid solution were added to the container. To neutralize part of the anionic monomer, 12.2 g of a 48% aqueous sodium hydroxide solution was added. Then, 261.0 g of an aqueous solution of 79% by mass quaternary methyl chloride of dimethylaminoethyl acrylate and 9.8 g of 78% by mass quaternary methyl chloride of dimethylaminoethyl methacrylate were mixed. Further, 0.002 g of methylenebisacrylamide, 1.2 g of isopropyl alcohol, 0.2 g of the chelating agent EDTA, and 2.0 g of an aqueous solution containing 0.02 g of t-butyl hydroperoxide as an initiator were added, and then ion-exchanged water was added to prepare 667.5 g of an aqueous phase. While stirring the oil phase, the aqueous phase was added and rapidly stirred with a homogenizer to prepare a water-in-oil emulsion. A nitrogen gas blowing tube, a reflux condenser, and a thermometer were attached to the flask, and while stirring with a stirring blade, degassing was started with nitrogen gas. After sufficient degassing, while supplying nitrogen gas, nitrogen gas containing 0.02 vol% of sulfur dioxide was blown into the emulsion at a supply rate of 90 ml / min to initiate polymerization. After reaching 50 °C, this temperature was maintained for 2 hours. After increasing the supply rate of nitrogen gas containing sulfur dioxide to 150 ml / min and maintaining it for 1 hour, the nitrogen gas containing sulfur dioxide was stopped, 3.5 g of a 1% aqueous solution of sodium sulfite was added and held for 30 minutes. The nitrogen gas was stopped to terminate the polymerization. 39.1 g of malic acid and 22.9 g of polyethylene glycol monooleate with an HLB value of 13.5 as a hydrophilic surfactant were added to produce a polymer flocculant in the form of a water-in-oil emulsion.

[0079] (Production Example 2, 4, Comparative Production Examples 1 to 9) A polymer flocculant in the form of a water-in-oil emulsion was produced in the same manner as in Production Example 1 except that the compounding ratio and neutralization degree shown in Table 1 were changed.

[0080]

Table 1

[0081]

Table 2

[0082] 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, "AM": acrylamide, "MBA": methylenebisacrylamide "IPA": isopropyl alcohol "NaH2PO2": sodium hypophosphite monohydrate

[0083] The abbreviations of the surfactants in Table 1 are as follows. A: sorbitan sesquioleate (HLB value 3.7), B: diethanolamide oleate (HLB value 5.0), C: diethanolamide oleate (HLB value 9.2), D: polyoxyethylene monooleate (HLB value 13.5)

[0084] 3. Sludge evaluation The results of sludge evaluation are shown below. Comparative Production Example 9 was excluded from the evaluation because the sedimentation stability of EM was extremely poor. 3-1. Sludge evaluation 1 Examples 1 to 4, Comparative Examples 1 to 6) Regarding surplus sludge collected from a chemical factory, table tests of flocculation filtration and dewatering treatment were carried out. The properties of the sludge were pH = 7.0, TS (Total Solid) = 18,000 mg / L, VTS (Volatile Total Solids) / TS = 65% by mass, SS (Suspended Solids) = 13,500 mg / L, VSS (Volatile Suspended Solids) / SS = 82% by mass, and fiber content / SS = 1.0% by mass. 1000 ppm of ferric polysulfate, an inorganic coagulant, was added to this sludge and thoroughly stirred and mixed. 200 mL of this mixed sludge was placed in a 300 mL beaker, and the polymer flocculants produced in Production Examples 1 to 4 and Comparative Production Examples 1 to 6 were each added at 160 ppm in terms of polymer based on the sludge mass. Stirring was carried out at 250 rpm for 30 seconds using a jar tester to form sludge flocs. After visually measuring the floc diameter of the formed sludge flocs, the amount of filtrate was measured. Thereafter, the filtrate state was evaluated and the cake moisture content was measured. The results of these evaluations are shown in Table 3.

[0085]

Table 3

[0086] 3-2. Sludge Evaluation 2 (Examples 5 to 8, Comparative Examples 7 to 12) Regarding the surplus sludge collected from a food factory, table tests of coagulation filtration and dewatering treatment were carried out. The properties of the sludge were pH = 6.2, TS = 16,000 mg / L, VTS / TS = 65% by mass, SS = 11,500 mg / L, VSS / SS = 84% by mass, and fiber content / SS = 0.6% by mass. 1200 ppm of ferric polysulfate, an inorganic coagulant, was added to this sludge and thoroughly stirred and mixed. 200 mL of this mixed sludge was placed in a 300 mL beaker, and the polymer flocculants produced in Production Examples 1 to 4 and Comparative Production Examples 1 to 4 were each added at 150 ppm in terms of polymer based on the sludge mass. Stirring was carried out at 250 rpm for 30 seconds using a jar tester to form sludge flocs. After visually measuring the floc diameter of the formed sludge flocs, the amount of filtrate was measured. Thereafter, the filtrate state was evaluated and the cake moisture content was measured. The results of these evaluations are shown in Table 4.

[0087]

Table 4

Claims

1. A water-in-oil emulsion comprising a polymer obtained by subjecting a monomer mixture containing the following components (a) to (d) to water-in-oil emulsion polymerization: (a) A cationic monomer having a quaternary ammonium base, (b) An anionic monomer, (c) A nonionic monomer, and (d) A crosslinkable monomer , wherein the content of the anionic monomer having a neutralized acid group among the anionic monomers is more than 30 mol% and 70 mol% or less with respect to the anionic monomer, the water-in-oil emulsion comprises one or more nonionic surfactants having an HLB value of 3 to 5 and two or more nonionic surfactants having an HLB value of 8 to 15, and the viscosity of a 1 M aqueous sodium chloride solution containing 0.1% by mass of the water-in-oil emulsion in terms of polymer at 25°C is 1.3 to 3.5 mPa·s. A polymer flocculant characterized by the above.

2. The polymer flocculant according to Claim 1, wherein the content of the cationic monomer is 20 to 55 mol% with respect to the total monomers.

3. The polymer flocculant according to Claim 1, wherein the cationic monomer contains at least the cationic monomer represented by the following formula (1): CH ２ =CR １ -CO-X-Q-N ＋ R ２ａ R ２ｂ R ２ｃ ·Z － ・・・ Chemical reaction (1) (However, in formula (1), R １ is a hydrogen atom or a methyl group, R ２ａ and R ２ｂ are each independently an alkyl group having 1 to 3 carbon atoms or a benzyl group, R ２ｃ is 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, and Z － each represents a counter anion.)

4. The polymer flocculant according to Claim 1, wherein the content of the anionic monomer is 1 to 35 mol% with respect to the total monomers.

5. The polymer flocculant according to Claim 1, wherein the anionic monomer is (meth)acrylic acid (salt).

6. The polymer flocculant according to Claim 1, wherein the content of the nonionic monomer is 20 to 79 mol% with respect to the total monomers.

7. The polymer flocculant according to Claim 1, wherein the nonionic monomer is (meth)acrylamide.

8. A method for producing a polymer flocculant, which comprises subjecting a monomer mixture containing the following components (a) to (d) to water-in-oil emulsion polymerization in the presence of a surfactant containing one or more nonionic surfactants having an HLB value of 3 to 5 and two or more nonionic surfactants having an HLB value of 8 to 15 to obtain a water-in-oil emulsion containing a polymer: (a) A cationic monomer having a quaternary ammonium base, (b') An anionic monomer having an unneutralized acid group, (c) A nonionic monomer, and (d) A crosslinkable monomer ​ ​ A step of adding an alkali to a mixture containing the (c) nonionic monomer, the (b') anionic monomer having an unneutralized acid group, and water to neutralize more than 30 mol% and 70 mol% or less of the (b') anionic monomer having an unneutralized acid group, and then adding the (a) cationic monomer. The method for producing a polymer flocculant according to claim 1.

9. A method for dewatering sludge, characterized in that after adding an organic flocculant and / or an inorganic flocculant to the sludge, the polymer flocculant according to claim 1 is added for dewatering.

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