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 less than 3 mol% with respect to the whole anionic monomers; a proportion of the nonionic monomer is 20 mol% or less with respect to the whole monomers; 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, it 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 an amphoteric polymer flocculant for dewatering sludge. 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 throughput per unit time cannot be increased, and furthermore, the cake moisture content obtained cannot be reduced.

[0004] Under such circumstances, further performance improvement is required for the flocculant that exhibits the 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 by 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 able 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

Summary of the Invention

Problems to be Solved by the Invention

[0008] 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

[0009] 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 with the content of a monomer in which a part of the acid groups of an anionic monomer is neutralized with an alkali being 3 mol% or less exhibits extremely excellent flocculation performance, and have completed the present invention.

[0010] The present invention for solving the above problems is as described below.

[0011] 〔1〕 A water-in-oil 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 water-in-oil emulsion polymerization, wherein among the anionic monomers, the content of the anionic monomer in which the acid group is neutralized is less than 3 mol% with respect to all the anionic monomers, the proportion of the nonionic monomer is 20 mol% or less with respect to all the monomers, and the viscosity of the 1M aqueous sodium chloride solution containing 0.1% by mass of the polymer in terms of the polymer in the water-in-oil emulsion at 25°C is 1.3 to 3.5 mPa·s. A polymer flocculant characterized by this.

[0012] 〔2〕The polymer flocculant according to 〔1〕, wherein the content of the cationic monomer is 60 to 90 mol% based on the total monomers.

[0013] 〔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〕, which contains a cationic monomer represented by the above formula.

[0014] 〔4〕The polymer flocculant according to 〔1〕, wherein the content of the anionic monomer is 1 to 39 mol% based on the total monomers.

[0015] 〔5〕The polymer flocculant according to 〔1〕, wherein the anionic monomer is (meth)acrylic acid (salt).

[0016] 〔6〕The polymer flocculant according to 〔1〕, wherein the nonionic monomer is (meth)acrylamide.

[0017] 〔7〕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 A method for producing the polymer flocculant according to [1], which comprises subjecting a monomer mixture containing [0] to water-in-oil emulsion polymerization in the presence of a surfactant to obtain a water-in-oil emulsion containing a high molecular polymer.

[0018] 〔8〕 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.

Effects of the Invention

[0019] The polymer flocculant of the present invention has high flocculation performance and dewatering performance for sludge.

Modes for Carrying Out the Invention

[0020] 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. 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.

[0021] 1. Polymer Flocculant The polymer flocculant of the present invention is a water-in-oil emulsion containing a high molecular 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 water-in-oil emulsion polymerization. Among the anionic monomers, the content of the anionic monomer with a neutralized acid group is less than 3 mol% based on all the anionic monomers, the proportion of the nonionic monomer is 20 mol% or less based on all the monomers, and the viscosity at 25 °C of a 1 M aqueous sodium chloride solution containing 0.1% by mass of the water-in-oil emulsion in terms of the polymer (hereinafter also referred to as "standard viscosity") is 1.3 to 3.5 mPa·s.

[0022] In the amphoteric polymer flocculant, when the molar ratio of the nonionic monomer decreases, if the acid group of the anionic monomer is neutralized, the copolymerizability of the dissociated anionic monomer and the cationic monomer decreases, so that the anionic monomer units do not randomly enter the polymer. Therefore, by not neutralizing the anionic groups or neutralizing them at a very small ratio, the copolymerizability is improved, and the anionic monomer units and the cationic monomer units can be present in the polymer in a well-balanced manner. Furthermore, by adding a crosslinkable monomer and polymerizing, the resulting polymer has a three-dimensional structure, so that each of the anionic groups and the cationic groups can easily react with sludge efficiently, and the flocculation performance is improved.

[0023] 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, and then the monomers in the aqueous phase are 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.

[0024] In the present invention, 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.

[0025] The polymer flocculant of the present invention has a standard viscosity of 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.

[0026] 2. Method for producing polymer flocculant The method for producing the polymer flocculant of the present invention includes an emulsification step of mixing an aqueous phase composed of an aqueous solution of a monomer mixture of the above components (a) to (d) and an oil phase containing a hydrocarbon substantially immiscible with water and the above surfactant to form a water-in-oil monomer emulsion; a polymerization step of polymerizing the monomers in the dispersed phase of the water-in-oil monomer emulsion in the presence of a radical polymerization initiator to form a water-in-oil polymer emulsion containing a polymer which is a polymer of the monomers in the dispersed phase; and consists of.

[0027] (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.

[0028] (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 preferable because it has excellent radical polymerization reactivity, is easily polymerized to a high 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, R2a 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, Z - each represents a counter anion. Z - Examples of Z include halide ions such as chloride ions and sulfate ions.

[0029] 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 quaternary salts such as alkyl halide adducts such as methyl chloride of dialkylaminoalkyl (meth) acrylamide such as dimethylaminopropyl (meth) acrylamide, benzyl halide adducts such as benzyl chloride, and dialkyl sulfate adducts such as dimethyl sulfate.

[0030] Among these preferred cationic monomers, the quaternary salt of dimethylaminoethyl (meth) acrylate chloride, which is particularly easy to polymerize to a high molecular weight required for a polymer flocculant, is most preferred. These cationic monomers may be used alone or in combination of two or more.

[0031] The content of the cationic monomer having a quaternary ammonium base is preferably 60 to 90 mol% based on the total monomer, and more preferably 63 to 90 mol%. If it is less than 60 mol%, the flocculation performance of the polymer flocculant may not be sufficiently high. If it exceeds 90 mol%, the polymer flocculant tends to approach the flocculation performance similar to that of conventional cationic polymers, and it becomes difficult to exhibit good flocculation performance.

[0032] (1-2) (b) Anionic monomer Examples of anionic monomers 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 the acid groups of the anionic monomer are not neutralized at all or the degree of neutralization is 3 mol% or less. That is, 0 to 3 mol% of the acid groups of the anionic monomer are neutralized by an alkali. When the degree of neutralization of the acid group exceeds 3 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 group of the anionic monomer is 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, etc. The degree of neutralization is preferably 0 to 2 mol%, more preferably 0 to 1 mol%, and particularly preferably 0 mol%.

[0033] In the production process of the present invention, 0 to 3 mol% of the acid groups of the anionic monomer may be neutralized with an alkali, or salts in which the acid groups of the anionic monomer are neutralized, such as acrylate and methacrylate, may be blended at 0 to 3 mol%.

[0034] The content of the anionic monomer (when a salt in which the acid group of the anionic monomer is neutralized is blended, including the content of the salt) is preferably 1 to 39 mol%, more preferably 1 to 30 mol%, and particularly preferably 1 to 22 mol% with respect to the total monomers.

[0035] (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.

[0036] The content of the nonionic monomer is 20 mol% or less, preferably 1 to 20 mol%, and more preferably 1 to 15 mol% based on the total monomers.

[0037] 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 2 times or more, more preferably 2.5 times or more. If it is less than 2 times, the anionic property of the resulting polymer becomes too strong, the sludge flocculation performance is significantly impaired, or particles may aggregate during polymerization.

[0038] (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, methylene bisacrylamide 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 ethylene oxide and / or propylene glycol having high water solubility. Among these, methylene bisacrylamide having a small molecular weight, high water solubility, and high reactivity is particularly preferable.

[0039] 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.

[0040] (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.

[0041] 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. The pure content of the polymer in the water-in-oil emulsion substantially coincides with the pure content of the charged monomer.

[0042] 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. In the present invention, the median diameter of the emulsion particles means the median diameter (D50) in the volume average particle size distribution measured by the laser diffraction method.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] After polymerization, by adding a hydrophilic surfactant called a phase inversion agent, when the emulsion is added to the treated water (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 phase inversion agent include cationic surfactants and nonionic surfactants with an HLB value of 9 to 17. Specifically, polyoxyethylene alkyl ethers such as polyethylene glycol monooleate and polyoxyethylene lauryl ether can be mentioned. The addition amount of the phase inversion agent may be appropriately determined according to the type of surfactant used in the emulsion polymerization, its weight-average HLB value, and the HLB value of the phase inversion agent, but it is preferably 1 to 5% by mass in the total mass of the emulsion.

[0047] In addition, additives such as stabilizers, pH adjusters, and antioxidants may be added within a range that does not inhibit the effects of the present invention.

[0048] (2-1) Surfactant As the surfactant, a nonionic surfactant is 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.

[0049] From the viewpoint of improving the storage stability while maintaining the stability of the emulsion during polymerization, it is preferable to use a plurality of surfactants having different HLB values in the present invention. That is, it is preferable because the emulsion stability can be made higher under the condition that the properties (degree of polymerization, etc.) of the aqueous phase gradually change as the polymerization proceeds.

[0050] The addition amount of the surfactant 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.

[0051] (2-2) Hydrocarbons 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, in addition to hydrocarbons such as n-hexane, cyclohexane, n-heptane, n-octane, and isooctane, 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.

[0052] 3. Method of Using 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 flocculant and / or an inorganic flocculant is added to the sludge as necessary, and preferably the pH is adjusted to 4-7. 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 dewatered by a 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 flocculant 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 flocculant is not particularly limited, and examples thereof include band sulfate, polyaluminum chloride, ferric chloride, ferrous sulfate, polyferric sulfate, etc. The organic flocculant is not particularly limited, and examples thereof include polydiallyldimethylammonium chloride and polyamines. The dewatering device is not particularly limited, and examples thereof include a screw press type dewatering machine, a belt press type dewatering machine, a filter press type dewatering machine, a screw decanter, multiple disks, etc.

[0053] 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, the sludge generated in the pulp or paper industry, etc. are all 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 treated digested sludge, etc. are all the objects to be treated.

Example

[0054] Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to 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.

[0055] 1. Measurement conditions for various physical properties (1) Degree of neutralization It is the value obtained by multiplying the value obtained by dividing the total number of moles of alkali used for neutralizing the anionic monomer by the total number of moles of the anionic monomer by 100 and is expressed in mol%.

[0056] (2) Standard viscosity The polymer flocculant was dissolved in a 1M aqueous sodium chloride solution to a concentration of 0.10% by 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.

[0057] (3) Floc size Measured visually.

[0058] (4) Filtration water volume 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 sludge mass. Using a jar tester, the mixture was stirred at a predetermined rotation speed for a predetermined time to form sludge flocs. The floc size of the formed sludge flocs was measured visually. 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 graduated cylinder, and the volume of the filtrate 10 seconds after the start of filtration was measured to evaluate the gravity filterability.

[0059] (5) Filtrate state (evaluation of flocculation performance) The state of the filtrate obtained in the measurement of the above filtration water volume was visually evaluated according to the following criteria. ○: No outflow of suspended components (SS) is observed in the filtrate. △: A small amount of suspended components (SS) is observed to flow out into the filtrate. ×: A large amount of suspended components (SS) is observed to flow out into the filtrate.

[0060] (6) Cake moisture content (evaluation of dewatering performance) After evaluating the filtrate volume, the water-containing cake of the sludge remaining on the stainless-steel sieve was taken out, placed on the 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, then the mass after drying was measured, and the moisture content was determined from the mass reduction due to drying and the mass before drying.

[0061] 2. Production of polymer flocculant (Production Example 1) Weighed 8.3 g of sorbitan sesquioleate, 8.3 g of oleic acid diethanolamide, and 10.8 g of polyethylene glycol monooleate into a five-neck separable flask, added 244.5 g of paraffin oil and dissolved it to prepare an oil phase. In a container, 9.4 g of a 50% by mass aqueous acrylamide solution, 13.9 g of an 80% by mass aqueous acrylic acid solution, 480.5 g of an aqueous solution of a 79% by mass quaternary methyl chloride salt of dimethylaminoethyl acrylate, and 5.9 g of a 78% by mass quaternary methyl chloride salt of dimethylaminoethyl methacrylate were mixed. Further, 0.004 g of methylenebisacrylamide, 1.2 g of isopropyl alcohol, 0.2 g of chelating agent EDTA, and 0.01 g of t-butyl hydroperoxide as an initiator were added, and then ion-exchanged water was added to prepare 679.2 g of an aqueous phase. The neutralization degree of acrylic acid is 0 mol%. While stirring the oil phase, the aqueous phase was added, and the mixture was vigorously 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 60 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 170 ml / min and holding for 1 hour, the nitrogen gas containing sulfur dioxide was stopped, and 4.0 g of a 1% aqueous solution of sodium sulfite was added and held for 30 minutes. Nitrogen gas was stopped to terminate the polymerization. 29.5 g of malic acid and 15.5 g of polyethylene glycol monooleate as a hydrophilic surfactant were added to produce a polymer flocculant in the form of a water-in-oil emulsion. The standard viscosity of the obtained polymer flocculant was 2.5 mPa·s.

[0062] (Production Example 2, 4, Comparative Production Example 2 - 5) 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 blending ratio shown in Table 1 was changed.

[0063] (Production Example 3) The blending ratio shown in Table 1 was changed. Also, when preparing the aqueous phase, 0.5 g of a 48% aqueous sodium hydroxide solution was added to neutralize a part of the acrylic acid after mixing the monomer aqueous solution. The degree of neutralization of acrylic acid was 1 mol%. Otherwise, a polymer flocculant in the form of a water-in-oil emulsion was produced in the same manner as in Production Example 1.

[0064] (Comparative Production Example 1) A polymer flocculant in the form of a water-in-oil emulsion was produced in the same manner as in Production Example 3, except that the blending ratio and the degree of neutralization shown in Table 1 were changed.

[0065]

Table 1

[0066] 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」: Methylene bisacrylamide 「IPA」: Isopropyl alcohol 「NaH2PO2」: Sodium hypophosphite monohydrate

[0067] 3. Sludge evaluation 3-1. Sludge evaluation 1 (Examples 1-4, Comparative Examples 1-4) For surplus sludge collected from a food factory, bench tests of agglomeration filtration and dewatering treatment were carried out. The properties of the sludge were pH = 6.0, TS (Total Solid) = 17,000 mg / L, VTS (Volatile Total Solids) / TS = 62% by mass, SS (Suspended Solids) = 12,000 mg / L, VSS (Volatile Suspended Solids) / SS = 86% by mass, and fiber content / SS = 0.5% by mass. To this sludge, 1200 ppm of ferric polysulfate, an inorganic coagulant, was added 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 1-4 and Comparative Production Examples 1-4 were each added at 160 ppm in terms of polymer conversion based on the sludge mass. The sludge was stirred 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 water was measured. Then, the filtrate state was evaluated and the cake moisture content was measured. The results of these evaluations are shown in Table 2.

[0068] TIFF2025105286000002.tif91131

[0069] 3-2. Sludge evaluation 2 (Examples 5-8, Comparative Examples 5-8) Table tests of coagulation filtration and dewatering treatment were carried out on surplus sludge collected from a chemical plant. The properties of the sludge were pH = 7.1, TS = 18,500 mg / L, VTS / TS = 70% by mass, SS = 14,500 mg / L, VSS / SS = 88% by mass, and fiber content / SS = 1.0% by mass. To this sludge, 1000 ppm of ferric polysulfate, an inorganic coagulant, was added 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. The sludge was stirred 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 filtrate volume was measured. Then, the filtrate state was evaluated and the cake moisture content was measured. These evaluation results are shown in Table 3.

[0070] TIFF2025105286000003.tif92130

Claims

1. 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 An oil-in-water emulsion containing a polymer obtained by subjecting a monomer mixture containing the same to oil-in-water emulsion polymerization, wherein among the anionic monomers, the content of the anionic monomer in which the acid group is neutralized is less than 3 mol% based on all the anionic monomers, the proportion of the nonionic monomer is 20 mol% or less based on all the monomers, and the viscosity at 25°C of a 1M aqueous sodium chloride solution containing 0.1% by mass of the oil-in-water emulsion in terms of the polymer is 1.3 to 3.5 mPa·s. A polymer flocculant characterized by this.

2. The polymer flocculant according to Claim 1, wherein the content of the cationic monomer is 60 to 90 mol% based on all the monomers.

3. The cationic monomer contains at least 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.) The polymer flocculant according to Claim 1, which contains a cationic monomer represented by.

4. The polymer flocculant according to Claim 1, wherein the content of the anionic monomer is 1 to 39 mol% based on all the 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 nonionic monomer is (meth)acrylamide.

7. 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 A method for producing the polymer flocculant according to Claim 1, characterized in that a monomer mixture containing the same is subjected to oil-in-water emulsion polymerization in the presence of a surfactant to obtain an oil-in-water emulsion containing a polymer.

8. 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 dehydration.

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