Flocculation treatment agent comprising anionic water-soluble polymer dispersion

Abstract

To provide a coagulation treatment agent having excellent coagulation treatment effect and comprising an anionic water-soluble polymer dispersion liquid without using ammonium sulfate, the anionic water-soluble polymer dispersion liquid obtainable by dispersion polymerization in a salt solution in coexistence with a polymer dispersant.SOLUTION: In a salt solution comprising magnesium sulfate, a monomer or a monomer mixture comprising a specific monomer as an essential component is dispersed and polymerized in coexistence with a polymer dispersant comprising 2-acrylamido-2-methylpropanesulfonic acid or a salt thereof as a constitutional unit, making it possible to provide a coagulation treatment agent comprising an anionic water-soluble polymer dispersion liquid having excellent coagulation treatment effect without using ammonium sulfate.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a flocculating agent comprising an anionic water-soluble polymer dispersion obtained by dispersion polymerization in a salt solution in the presence of a polymer dispersant, and to a sludge dewatering method and a wastewater treatment method using the same. [Background technology]

[0002] Polyacrylamide (PAM) water-soluble polymers are widely used as flocculating agents for wastewater treatment and sludge dewatering, and come in various forms, including water-in-oil emulsions and aqueous solution polymers. Among these, ionic water-soluble polymer dispersions, which are produced by dispersion polymerization using an ionic polymer dispersant in a salt solution, are often used in many fields because they are superior to other forms in terms of product solubility and mixing with the material being treated. Among ionic water-soluble polymers, anionic water-soluble polymer dispersions are effective in many cases, but high molecular weight water-soluble polymers are often required, and various reports on their production techniques have been published, such as in Patent Documents 1 and 2. However, ammonium sulfate is typically used as an inorganic salt in the production of these anionic water-soluble polymer dispersions. The total nitrogen content derived from the ammonium sulfate salt that constitutes the dispersion is approximately 75,000 ppm (relative to the water-soluble polymer dispersion product). This total nitrogen content has a significant impact on agricultural crops. Plants absorb nitrogen in the form of ammonium nitrogen or nitrate nitrogen and use it for their growth. However, excessive nitrogen is known to have adverse effects, and there is a demand for reducing the nitrogen content. Furthermore, following the amendment of the Water Pollution Control Act in 2014, ammonium compounds were designated as hazardous substances. Therefore, there is a demand for anionic water-soluble polymer dispersions that can reduce the amount of ammonium sulfate, particularly for coagulation treatment agents based on highly versatile high-molecular-weight anionic water-soluble polymers.

[0003] [Patent Document 1] Special Publication No. 2001-508473 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-302521 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide an anionic water-soluble polymer dispersion obtained by dispersion polymerization in an aqueous salt solution in the presence of a polymeric dispersant, which has an excellent flocculation treatment effect without using ammonium sulfate. [Means for solving the problem]

[0005] As a result of intensive investigations to solve the above problems, the present inventors have found that an anionic water-soluble polymer dispersion obtained by dispersion polymerization of a monomer or a monomer mixture essentially containing a specific monomer in an aqueous salt solution containing magnesium sulfate in the presence of a polymeric dispersant containing 2-acrylamido-2-methylpropanesulfonic acid or a salt thereof as a constituent unit during polymerization can exhibit excellent flocculation treatment effects, which led to the present invention. [Effects of the Invention]

[0006] The anionic water-soluble polymer dispersion of the present invention does not use ammonium sulfate, so that it can suppress the release of salt-derived nitrogen into the environment.Furthermore, it can obtain a high-molecular-weight anionic water-soluble polymer, which exhibits excellent flocculation treatment effects in sludge dewatering and wastewater treatment applications. DETAILED DESCRIPTION OF THE INVENTION

[0007] The anionic water-soluble polymer dispersion in the present invention is an anionic water-soluble polymer dispersion obtained by dispersing an aqueous solution of a monomer or a monomer mixture containing, as an essential component, a monomer represented by the following general formula (1) in the presence of a polymer dispersant soluble in the aqueous salt solution under stirring. TIFF0007736266000001.tif2853 General formula (1) R1 represents hydrogen, a methyl group, or a carboxymethyl group; Q represents SO3, C6H4SO3, CONHC(CH3)2CH2SO3, C6H4COO, or COO; R2 represents hydrogen or COOY2; and Y1 or Y2 represents hydrogen or a cation.

[0008] The anionic monomer represented by the general formula (1) used in producing the anionic water-soluble polymer dispersion of the present invention is in the range of 1 to 100 mol %. To obtain a high molecular weight polymer with the effect of the anionic group, the content is preferably 5 to 80 mol %, more preferably 5 to 60 mol %. Examples of anionic monomers include vinyl sulfonic acid, vinylbenzenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, methacrylic acid, acrylic acid, itaconic acid, maleic acid, phthalic acid, p-carboxystyrene acid, and salts thereof. Two or more of these may be used in combination. During production, the anionic monomer can be neutralized to a desired degree of neutralization with an alkaline substance such as an alkali metal hydroxide (e.g., sodium hydroxide) or an amine, and then polymerized.

[0009] An anionic monomer represented by general formula (1) and a nonionic monomer may be used. Examples of nonionic monomers used when copolymerizing an anionic monomer represented by general formula (1) and a nonionic monomer include (meth)acrylamide, N,N-dimethylacrylamide, acrylonitrile, 2-hydroxyethyl (meth)acrylate, diacetone acrylamide, N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, and acryloylmorpholine. Two or more of these may be used in combination.

[0010] When producing the water-soluble polymer dispersion of the present invention, a cationic monomer can be used within a range that does not inhibit the effect of the anionic group.

[0011] Examples of cationic monomers include quaternized products of dimethylaminoethyl (meth)acrylate or dimethylaminopropyl acrylamide with halides of lower alkyl groups, such as methyl chloride or ethyl chloride. Examples include (meth)acryloyloxyethyl trimethylammonium chloride, (meth)acryloyloxyethyl dimethylbenzylammonium chloride, (meth)acryloylaminopropyl trimethylammonium chloride, (meth)acryloylaminopropyl dimethylbenzylammonium chloride, and (meth)acryloyloxy-2-hydroxypropyl trimethylammonium chloride. Two or more of these may be combined. The content of the cationic monomer is preferably less than 10 mol%, more preferably less than 5 mol%. Alternatively, the anionic monomer represented by general formula (1), the cationic monomer, and the nonionic monomer may be copolymerized.

[0012] The dispersion polymerization in saltwater in the present invention can be carried out by a conventional method disclosed in JP-A-62-20511, JP-A-10-212320, JP-A-2004-231822, etc. In the present invention, a monomer or monomer mixture aqueous solution essentially containing a monomer represented by general formula (1) is dispersion polymerized in a saltwater solution in the presence of a polymeric dispersant having 2-acrylamido-2-methylpropanesulfonic acid or a salt thereof as a constituent unit, and using magnesium sulfate as an inorganic salt. During dispersion polymerization, adding a polymerization retarder in an amount of 0.5 to 5% by mass based on the total monomers has the effect of suppressing thickening, and can be added appropriately in production. Examples of polymerization retarders include itaconic acid, maleic acid, and phthalic acid.

[0013] In the present invention, the polymeric dispersant used in dispersion polymerization in saltwater contains 2-acrylamido-2-methylpropanesulfonic acid or its salt as a constituent unit. While poly(2-acrylamido-2-methylpropanesulfonic acid) or its salt may be used, copolymers of 2-acrylamido-2-methylpropanesulfonic acid or its salt with nonionic monomers are also usable. Examples of nonionic monomers include acrylamide, N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone, N,N-dimethylacrylamide, acrylonitrile, diacetone acrylamide, and 2-hydroxyethyl (meth)acrylate, with copolymers with acrylamide being preferred. Other cationic monomers, such as (meth)acryloyloxyethyl trimethylammonium chloride, may also be included in the polymeric dispersant composition.

[0014] The molecular weight of the polymer dispersant is preferably not too high, as this increases the viscosity of the dispersion. Therefore, it is 5,000 to 2,000,000, and preferably 50,000 to 1,000,000. The addition rate of the polymer dispersant is 1 to 20% by mass, preferably 3 to 20% by mass, relative to the monomer. It is preferably less than 5% by mass relative to the dispersion. This is because a content of 5% by mass or more is economically disadvantageous and may inhibit the function of the polymer.

[0015] Ammonium sulfate is generally used as the inorganic salt used during dispersion polymerization in salt water. In the present invention, magnesium sulfate is used as the inorganic salt used during polymerization. The essential use of magnesium sulfate prevents significant thickening and enables the production of a water-soluble polymer dispersion with a high molecular weight and excellent separation stability. An amount of magnesium sulfate added is 5% by mass or more relative to the total amount of the water-soluble polymer dispersion, which reaches a saturated concentration in the salt water solution. Hydrates such as the heptahydrate are preferably used as magnesium sulfate. Other salts such as sodium chloride, potassium chloride, calcium chloride, lithium chloride, sodium sulfate, sodium carbonate, and calcium carbonate may be contained, but magnesium sulfate must account for 50% by mass or more of the total amount of inorganic salts during polymerization, preferably 70% by mass or more. The monomers are dissolved in an aqueous solution of these inorganic salts, and a polymer dispersant is further added. The pH is adjusted to 2 to 5, and then the atmosphere is purged with nitrogen and polymerization is initiated with a polymerization initiator.

[0016] The present invention was based on the discovery that thickening can be suppressed and high-molecular-weight anionic water-soluble polymer dispersions can be stably produced by using a polymer dispersant that contains magnesium sulfate as an inorganic salt during polymerization and 2-acrylamido-2-methylpropanesulfonic acid or a salt thereof as a constituent unit.

[0017] The use of a polymer dispersant containing magnesium sulfate as an inorganic salt during polymerization and 2-acrylamido-2-methylpropanesulfonic acid or its salt as a structural unit has the effect of suppressing thickening. There are many theoretically unknown aspects that cannot be explained, but the following can be estimated from the phenomenon. Specifically, as polymerization progresses in a salt solution, the concentration of the resulting polymer exceeds its solubility, initiating the precipitation of polymer particles. However, prior to this, the viscosity of the polymer itself (polymerization system) increases due to the dissolved polymer, resulting in a coexistence of dissolved polymer and precipitated particles. After this, the proportion of precipitated polymer increases, and the viscosity of the polymer gradually decreases, resulting in a phase transition to a dispersed state. During this coexistence state, the primary role of the dispersant during the phase transition is thought to be to improve the slip between the precipitated particles and the gel-like dissolved polymer, facilitating a smooth transition from the thickened state before the phase transition to a dispersed state. In the early stages of polymerization, the dispersant's structural unit, 2-acrylamido-2-methylpropanesulfonic acid or its salt, contributes to the phase separation of the relatively low molecular weight product polymer, facilitating the smooth phase transition. In the later stages of polymerization, the strong salting-out properties of magnesium sulfate promote the salting-out effect of the relatively high molecular weight product polymer, resulting in the stable production of polymer dispersions. This is thought to be a synergistic effect of the action of 2-acrylamido-2-methylpropanesulfonic acid or its salt to smooth the phase change and the action of magnesium sulfate to promote the salting-out effect.

[0018] Ammonium sulfate is generally used as the inorganic salt for water-soluble polymer dispersions such as those of the present invention. However, general-purpose products contain approximately 75,000 ppm of total nitrogen derived from ammonium sulfate (relative to the water-soluble polymer dispersion product). By eliminating this nitrogen derived from ammonium sulfate, the total nitrogen content can be reduced to approximately 20,000 ppm (relative to the water-soluble polymer dispersion product). Total nitrogen content has a significant impact on agricultural crops. Plants absorb nitrogen in the form of ammonium nitrogen or nitrate nitrogen and use it for their growth, but excessive nitrogen is known to have adverse effects, and therefore reduction of the nitrogen content is required. Furthermore, with the amendment of the Water Pollution Control Act in 2014, ammonium compounds were designated as hazardous substances, raising concerns about their impact on the environment. The water-soluble polymer dispersion of the present invention is therefore extremely useful because it does not use ammonium sulfate.

[0019] The polymerization concentration is 2% by mass to 25% by mass in terms of monomer concentration. This is because a low monomer concentration is less practical, and a higher monomer concentration is economically advantageous in terms of transportation costs, but a monomer concentration exceeding 25% by mass increases viscosity during production, making it difficult to obtain a dispersion. A preferred monomer concentration is 5% by mass to 20% by mass. The monomer may be charged all at once at the start of polymerization, or may be charged in appropriate portions.

[0020] Polymerization conditions are typically determined based on the monomers used and the copolymerization mole percentage, with temperatures ranging from 0 to 100°C. A radical polymerization initiator is used to initiate polymerization. These initiators may be either oil-soluble or water-soluble, and polymerization can be carried out using any of azo, peroxide, and redox initiators. Examples of oil-soluble azo initiators include 2,2'-azobisisobutyronitrile, 1,1'-azobis(cyclohexanecarbonitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2-methylpropionate), and 2,2'-azobis(4-methoxy-2,4-dimethyl)valeronitrile. These are dissolved in a water-miscible solvent and added.

[0021] Examples of water-soluble azo initiators include 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis(2-amidinopropane) dihydrochloride, and 4,4'-azobis(4-cyanovaleric acid). Examples of redox initiators include combinations of ammonium persulfate with sodium sulfite, sodium hydrogen sulfite, trimethylamine, and tetramethylethylenediamine. Examples of peroxides include ammonium or potassium persulfate, hydrogen peroxide, benzoyl peroxide, lauroyl peroxide, octanoyl peroxide, succinic peroxide, and t-butylperoxy-2-ethylhexanoate.

[0022] The azo initiator or peroxide initiator is added at a rate of 50 to 500 ppm, preferably 70 to 200 ppm, per monomer at the start of polymerization. However, since a single addition results in a low polymerization rate, it is preferable to add it in several portions. When copolymerizing with a redox initiator, initiating polymerization at temperatures above 40°C makes it difficult to control the polymerization, and a rapid temperature rise and clumping of the polymerization solution occur, making it impossible to obtain a stable dispersion with a high degree of polymerization. Therefore, a temperature of 15 to 35°C is preferred. The initiator is added at the start of polymerization in an amount of 5 to 100 ppm, preferably 10 to 100 ppm, per monomer. However, since a single addition results in a low polymerization rate, it is preferable to add the initiator several times. The number of additions is 2 to 5 times, preferably 2 to 3 times.

[0023] In order to adjust the degree of polymerization, it is effective to use sodium formate, isopropyl alcohol, or the like in an amount of 0.1 to 5% by mass relative to the monomer.

[0024] After the polymerization reaction is complete, salts can be added to adjust the stabilization of the product. The salt to be added may be magnesium sulfate, but sodium chloride, potassium chloride, calcium chloride, lithium chloride, sodium sulfate, sodium thiosulfate, sodium carbonate, calcium carbonate, or the like can also be used. These salts may also be used in combination. Particularly, one or more salts selected from magnesium sulfate, sodium sulfate, and sodium thiosulfate are preferred. These salts are added in an amount ranging from 1 to 10% by mass based on the total amount of the water-soluble polymer dispersion.

[0025] The flocculating agent of the present invention can be used for sludge dewatering, including excess sludge generated during biological treatment of wastewater from papermaking, chemical industry, and food industry, as well as organic sludge (so-called raw sludge, excess sludge, mixed raw sludge, digested sludge, coagulated and flotation sludge, and mixtures thereof) generated during treatment of municipal sewage, human waste, and industrial wastewater. However, it is particularly effective for inorganic sludge generated from steelmaking, civil engineering, waste disposal, and other processes. The agent is diluted with water to a desired concentration and added to the sludge. A range of 0.01 to 1.0% by mass is preferred. The addition rate to the sludge varies depending on the type of sludge and the dewatering machine, but is generally 1 to 1,000 ppm relative to the sludge liquid volume. The dewatering machine used can be a belt press, centrifugal dewatering machine, screw press, multi-disk dewatering machine, rotary press, filter press, or other dewatering machine.

[0026] When the flocculating agent of the present invention is used for wastewater treatment, it is added to the target wastewater, mixed and flocculated, and then subjected to solid-liquid separation. Depending on the type of suspended solids in the wastewater, either a flocculating sedimentation treatment or a flocculating flotation treatment can be used. The present invention can be applied to various industrial wastewaters, such as those from automobile manufacturing plants, machinery manufacturing plants, semiconductor manufacturing plants, steel mills, pulp and paper manufacturing industries, cleaning and gravel industries, chemical plants, food manufacturing plants, printing plants, maintenance factories, oil refineries, and waste disposal plants. In particular, the use of the flocculating agent of the present invention in combination with an alkaline agent can be particularly effective. For example, in the hydroxide precipitation method used to treat metal-containing waters, such as fluorine-containing wastewaters (e.g., hydrogen fluoride and ammonium fluoride) discharged from semiconductor manufacturing plants and related factories, cyanide-containing wastewaters discharged from coke manufacturing processes in steel mills, metal plating plants, and chemical plants, and smoke washing wastewater and plating cleaning wastewater discharged from garbage incinerators and steel mills, high alkalinity treatment using an alkaline agent is required. The addition of the flocculating agent of the present invention is effective in treating these wastewaters. Examples of alkaline agents include slaked lime (calcium hydroxide), caustic soda, sodium carbonate, potassium carbonate, and potassium hydroxide. These agents can be used alone or in combination. In the treatment of the waste water, particularly fluorine-containing waste water, slaked lime, which is a calcium compound, is added to form calcium fluoride, and the fluorine can also be treated by the coagulation treatment of the anionic water-soluble polymer dispersion of the present invention, which is extremely effective.

[0027] When an alkaline agent is used in combination, the anionic water-soluble polymer dispersion may be added simultaneously or in either order, but it is preferable to add the alkaline agent first and then the anionic water-soluble polymer dispersion. The alkaline agent addition rate varies depending on the type and properties of the wastewater, but is 5 to 5,000 ppm, with 10 to 1,000 ppm being a preferred range based on the amount of wastewater. The treatment effect is enhanced by adjusting the pH of the wastewater to a neutral to weakly alkaline range, with a pH of 6 to 11 being preferred, a pH of 7 to 11 being more preferred, and a pH of 8 to 11 being even more preferred.

[0028] The water-soluble polymer dispersion of the present invention has excellent solubility and can be added as is, or can be dissolved and diluted with water to any desired concentration before being added to wastewater. When dissolved, a dissolution concentration of 0.05 to 0.3 mass% is generally applied. The addition rate to wastewater is usually 1 to 100 ppm, preferably 2 to 50 ppm. It may also be used in combination with inorganic flocculants such as ferric chloride, ferric sulfate, PAC, and aluminum sulfate.

[0029] The viscosity of a 0.4% by mass salt solution, which is an indicator of the molecular weight of the water-soluble polymer dispersion of the present invention, i.e., the viscosity of a 0.4% by mass aqueous solution of the water-soluble polymer constituting the dispersion in a 4% by mass sodium chloride aqueous solution (adjusted to pH 8.5) measured at 25°C, is in the range of 5 to 200 mPa·s. High-molecular-weight anionic water-soluble polymers are often desired, in which case 10 to 60 mol% of the anionic monomer is generally used, and the viscosity of a 0.4% by mass aqueous solution in a 4% by mass sodium chloride aqueous solution is preferably 20 to 200 mPa·s, more preferably 50 to 200 mPa·s, and even more preferably 80 to 200 mPa·s. The viscosity of a 0.4% by mass salt solution is measured using a Brookfield viscometer (such as a Toki Sangyo TVB-10M) with a No. 2 rotor at 60 rpm. The intrinsic viscosity of the water-soluble polymer dispersion at 0.5% by mass measured at 25° C. in a 4% by mass aqueous sodium chloride solution (adjusted to pH 8.5) is preferably in the range of 10 to 30 dl / g. [Example]

[0030] The flocculating treatment agent comprising the anionic water-soluble polymer dispersion of the present invention will be specifically explained below, but the present invention is not limited to the following examples.

[0031] First, an example of the production of the anionic water-soluble polymer dispersion of the present invention will be shown. (Production Example 1) 91.4 g of demineralized water and 71.8 g of magnesium sulfate heptahydrate were added to a 0.5 L separable flask equipped with an anchor blade stirrer, a condenser, and a nitrogen inlet tube, and the mixture was stirred to form a homogeneous solution. Next, 15.9 g of 80% by weight acrylic acid, 2.4 g of 48% by weight sodium hydroxide, 58.6 g of 50% by weight acrylamide, 0.4 g of sodium formate, 0.4 g of itaconic acid, and 15.4 g of 15% by weight sodium poly(2-acrylamido-2-methylpropanesulfonate) were added to form a homogeneous solution, which was then immersed in a 33°C water bath to stabilize the temperature. Next, under a nitrogen atmosphere, 4% by weight aqueous ammonium persulfate and 4% by weight aqueous sodium bisulfite were added as polymerization initiators at 55 ppm per monomer, and the mixture was polymerized at 30°C for 10 hours with stirring. Subsequently, 300 ppm of the above polymerization initiator was added, and the mixture was polymerized for 5 hours. After the reaction was complete, 5.0 g of sodium sulfate, 38.8 g of magnesium sulfate heptahydrate, and 0.9 g of sodium thiosulfate were added to the resulting dispersion and stirred until no residue remained, yielding a water-soluble polymer dispersion. The molar composition of this water-soluble polymer was acrylamide / acrylic acid = 70 / 30 mol%. The viscosity of this dispersion was 390 mPa·s, and when the water-soluble polymer dispersion was dissolved in a 4% by weight aqueous sodium chloride solution to a concentration of 0.4% by weight, the viscosity was 120 mPa·s. The theoretical total nitrogen content of this water-soluble polymer dispersion was 19,650 ppm (relative to the dispersion). Separation stability tests were also conducted by centrifugation. This is shown in Table 1 as Production Example 1.

[0032] (Production Example 2) 65.0 g of demineralized water and 67.7 g of magnesium sulfate heptahydrate were added to a 0.5 L separable flask equipped with an anchor blade stirrer, a condenser, and a nitrogen inlet tube, and the mixture was stirred to form a homogeneous solution. Next, 21.6 g of 80% by weight acrylic acid, 3.2 g of 48% by weight sodium hydroxide, 79.5 g of 50% by weight acrylamide, 0.4 g of sodium formate, 0.6 g of itaconic acid, and 20.9 g of 15% by weight sodium poly(2-acrylamido-2-methylpropanesulfonate) were added to form a homogeneous solution, which was then immersed in a 33°C water bath to stabilize the temperature. Next, under a nitrogen atmosphere, 4% by weight aqueous ammonium persulfate and 4% by weight aqueous sodium bisulfite were added as polymerization initiators at 55 ppm per monomer, and the mixture was polymerized at 30°C for 10 hours with stirring. Subsequently, 300 ppm of the above polymerization initiator was added, and the mixture was polymerized for 5 hours. After the reaction was complete, 4.7 g of sodium sulfate, 36.5 g of magnesium sulfate heptahydrate, and 0.9 g of sodium thiosulfate were added to the resulting dispersion and stirred until no residue remained, yielding a water-soluble polymer dispersion. The molar composition of this water-soluble polymer was acrylamide / acrylic acid = 70 / 30 mol%. The viscosity of this dispersion was 1050 mPa·s, and when the water-soluble polymer dispersion was dissolved in a 4% by weight aqueous sodium chloride solution to a concentration of 0.4% by weight, the viscosity was 131 mPa·s. The theoretical total nitrogen content of this water-soluble polymer dispersion was 26670 ppm (relative to the dispersion). Separation stability tests were also conducted by centrifugation. This result is shown in Table 1 as Production Example 2.

[0033] (Production Example 3) 114.3 g of demineralized water and 75.2 g of magnesium sulfate heptahydrate were added to a 0.5 L separable flask equipped with an anchor blade stirrer, a condenser, and a nitrogen inlet tube, and the mixture was stirred to form a homogeneous solution. Next, 15.1 g of 80% by weight acrylic acid, 2.2 g of 48% by weight sodium hydroxide, 35.8 g of 50% by weight acrylamide, 0.4 g of sodium formate, 0.3 g of itaconic acid, and 10.8 g of 15% by weight sodium poly(2-acrylamido-2-methylpropanesulfonate) were added to form a homogeneous solution, which was then immersed in a 33°C water bath to stabilize the temperature. Next, under a nitrogen atmosphere, 4% by weight aqueous ammonium persulfate and 4% by weight aqueous sodium bisulfite were added as polymerization initiators at 55 ppm per monomer, and the mixture was polymerized at 30°C for 10 hours with stirring. Subsequently, 300 ppm of the above polymerization initiator was added, and the mixture was polymerized for 5 hours. After the reaction was complete, 5.3 g of sodium sulfate, 40.6 g of magnesium sulfate heptahydrate, and 0.9 g of sodium thiosulfate were added to the resulting dispersion and stirred until no residue remained, yielding a water-soluble polymer dispersion. The molar composition of this water-soluble polymer was acrylamide / acrylic acid = 60 / 40 mol%. The viscosity of this dispersion was 183 mPa·s, and when the water-soluble polymer dispersion was dissolved in a 4% by weight aqueous sodium chloride solution to a concentration of 0.4% by weight, the viscosity was 46.6 mPa·s. The theoretical total nitrogen content of this water-soluble polymer dispersion was 12,060 ppm (relative to the dispersion). A separation stability test was also conducted by centrifugation. This result is shown in Table 1 as Example 3.

[0034] (Production Example 4) 116.5 g of demineralized water and 75.2 g of magnesium sulfate heptahydrate were added to a 0.5 L separable flask equipped with an anchor blade stirrer, a condenser, and a nitrogen inlet tube, and the mixture was stirred to form a homogeneous solution. Next, 26.4 g of 80% by weight acrylic acid, 7.8 g of 48% by weight sodium hydroxide, 17.8 g of 50% by weight acrylamide, 0.4 g of sodium formate, 0.3 g of itaconic acid, and 12.0 g of 15% by weight sodium poly(2-acrylamido-2-methylpropanesulfonate) were added to form a homogeneous solution, which was then immersed in a 33°C water bath to stabilize the temperature. Next, under a nitrogen atmosphere, 4% by weight aqueous ammonium persulfate and 4% by weight aqueous sodium bisulfite were added as polymerization initiators at 55 ppm per monomer, and the mixture was polymerized at 30°C for 10 hours with stirring. Subsequently, 300 ppm of the above polymerization initiator was added, and the mixture was polymerized for 5 hours. After the reaction was complete, 5.3 g of sodium sulfate and 0.8 g of sodium thiosulfate were added to the resulting dispersion and stirred until no residue remained, yielding a water-soluble polymer dispersion. The molar composition of this water-soluble polymer was acrylamide / acrylic acid = 30 / 70 mol%. The viscosity of this dispersion was 250 mPa·s, and when the water-soluble polymer dispersion was dissolved in a 4% by weight aqueous sodium chloride solution to a concentration of 0.4% by weight, the viscosity was 25.3 mPa·s. The theoretical total nitrogen content of this water-soluble polymer dispersion was 7120 ppm (relative to the dispersion). A separation stability test was also conducted by centrifugation. This is shown in Table 1 as Production Example 4.

[0035] (Production Example 5) 91.4 g of demineralized water and 71.8 g of magnesium sulfate heptahydrate were added to a 0.5 L separable flask equipped with an anchor blade stirrer, a condenser, and a nitrogen inlet tube, and the mixture was stirred to form a homogeneous solution. Next, 15.9 g of 80% by weight acrylic acid, 2.4 g of 48% by weight sodium hydroxide, 58.6 g of 50% by weight acrylamide, 0.4 g of sodium formate, 0.4 g of itaconic acid, and 15.4 g of 15% by weight acrylamide / sodium 2-acrylamido-2-methylpropanesulfonate (5 / 95 mol%) copolymer were added to form a homogeneous solution, which was then immersed in a 33°C water bath to stabilize the temperature. Next, under a nitrogen atmosphere, 4% by weight aqueous ammonium persulfate and 4% by weight aqueous sodium bisulfite solutions were added as polymerization initiators at 55 ppm per monomer, and the mixture was polymerized at 30°C for 10 hours with stirring. Subsequently, 300 ppm of the above polymerization initiator was added, and the mixture was polymerized for 5 hours. After the reaction was complete, 5.0 g of sodium sulfate, 38.8 g of magnesium sulfate heptahydrate, and 0.9 g of sodium thiosulfate were added to the resulting dispersion and stirred until no residue remained, yielding a water-soluble polymer dispersion. The molar composition of this water-soluble polymer was acrylamide / acrylic acid = 70 / 30 mol%. The viscosity of this dispersion was 180 mPa·s, and when the water-soluble polymer dispersion was dissolved in a 4% by weight aqueous sodium chloride solution to a concentration of 0.4% by weight, the viscosity was 120 mPa·s. The theoretical total nitrogen content of this water-soluble polymer dispersion was 19,650 ppm (relative to the dispersion). Separation stability tests were also conducted by centrifugation. This is shown in Table 1 as Production Example 5.

[0036] (Comparative Production Examples 1 and 2) Similar to Production Example 1, dispersions were produced using the same monomer composition and polymerization conditions, but with different polymer dispersants, polymerization salts, monomer concentrations, or inorganic salt concentrations. These are shown in Table 1 as Comparative Production Examples 1 and 2. In Comparative Production Example 1, the viscosity of the reaction solution increased during the reaction, making stirring difficult and resulting in solidification. The theoretical total nitrogen content of the water-soluble polymer dispersion of Comparative Production Example 2 was 74,870 ppm (relative to the dispersion).

[0037] (Table 1) TIFF0007736266000002.tif4391Monomer composition: AAM: acrylamide, AAC: acrylic acid polymeric dispersants; p-AMPS: Poly(2-acrylamido-2-methylpropanesulfonic acid sodium salt) AAM / AMPS: acrylamide / sodium 2-acrylamido-2-methylpropanesulfonate (5 / 95 mol%) copolymer p-AAC: Polyacrylic acid, polymer dispersant addition rate (mass%): relative to monomer Polymerization salt: a; magnesium sulfate heptahydrate, b; ammonium sulfate Monomer concentration: mass ratio of monomer to aqueous polymer dispersion Inorganic salt concentration: mass ratio of inorganic salt to water-soluble polymer dispersion Dispersion viscosity: Viscosity of water-soluble polymer dispersion measured at 25°C Viscosity of 0.4% by mass salt solution: Viscosity (pH 8.5) measured at 25°C when the polymer is dissolved in 4% by mass sodium chloride water to a polymer concentration of 0.4% by mass. Intrinsic viscosity: Intrinsic viscosity of a 0.5% by mass aqueous polymer dispersion measured at 25°C in a 4% by mass saline solution (pH 8.5)

[0038] In Examples 1 to 5, which are anionic water-soluble polymer dispersions obtained using magnesium sulfate as the inorganic salt during polymerization and a polymer having 2-acrylamido-2-methylpropanesulfonic acid or a salt thereof as a constituent unit as the dispersant, thickening could be suppressed even without using ammonium sulfate during polymerization, and anionic water-soluble polymer dispersions with good product stability were obtained.

[0039] Example 1 The product of Production Example 1 was used in the test as flocculating treatment agent sample A comprising an anionic water-soluble polymer dispersion of the present invention.

[0040] (Comparative Example 1) Comparative Production Example 2 was used in the test as flocculating treatment agent sample B. This had a composition and physical properties within the ranges commonly used for anionic water-soluble polymer dispersions. In addition, various flocculating treatment agent samples 1 to 9 were prepared and prepared. These are shown in Table 2.

[0041] (Table 2) TIFF0007736266000003.tif5191 Monomer composition: AAC: acrylic acid, AAM: acrylamide, DMQ: acryloyloxyethyl dimethylammonium chloride, DMBZ: acryloyloxyethyl dimethylbenzylammonium chloride Form: EM: water-in-oil emulsion, P: powder, DR: dispersion polymer in salt water

[0042] (Test Example 1) A dehydration test was conducted on a chemical inorganic coagulated sludge (pH 8.6, electrical conductivity 6340 mS / m, SS content 13500 mg / L, VSS 18.5 mass% / SS, VTS 10.9 mass% / TS, M-alkalinity 190 mg / L, anion content 2.42 meq / L) generated from a waste treatment plant. 200 mL of sludge was collected in a plastic beaker, and a 0.2 mass% aqueous solution of coagulation treatment agent sample A from Example 1 was added at 40 ppm or 70 ppm (pure polymer content) relative to the sludge liquid volume. After stirring 50 times with a spatula, the sludge was filtered through a 40 mesh filter, and the filtrate volume was measured. The sludge was then pressed using a nylon filter cloth (#202) at a pressure of 4 kg / cm. 2 The cake was dehydrated at 105°C for 60 seconds, and the moisture content of the cake was measured (dried at 105°C for 20 hours). The results are shown in Table 3.

[0043] (Comparative Test Example 1) Similar tests were conducted on the same sludge as in Experimental Test Example 1, using flocculating treatment agent sample B or the flocculating treatment agent samples in Table 2. The results are shown in Table 3.

[0044] (Table 3) TIFF0007736266000004.tif6988

[0045] (Test Example 2) A dehydration test was conducted on a chemical inorganic coagulated sludge (pH 8.5, electrical conductivity 4590 mS / m, SS content 27500 mg / L, VSS 19.1 mass% / SS, VTS 6.4 mass% / TS, M-alkalinity 3200 mg / L, anion content 4.48 meq / L) generated from a waste treatment plant. 100 mL of sludge was collected in a plastic beaker, and a 0.2 mass% aqueous solution of coagulation treatment agent sample A from Example 1 was added at 40 ppm or 70 ppm relative to the sludge liquid volume (pure polymer content). After stirring 50 times with a spatula, the sludge was filtered through a 40 mesh filter, and the filtrate volume was measured. The sludge was then pressed using a nylon filter cloth (#202) at a pressure of 4 kg / cm. 2 The cake was dehydrated at 105°C for 60 seconds, and the moisture content of the cake was measured (dried at 105°C for 20 hours). The results are shown in Table 4.

[0046] (Comparative Test Example 2) Similar tests were conducted on the same sludge as in Experimental Test Example 2, using flocculating treatment agent sample B or the flocculating treatment agent samples in Table 2. The results are shown in Table 4.

[0047] (Table 4) TIFF0007736266000005.tif3771

[0048] Adding the anionic water-soluble polymer dispersion of the present invention to sludge followed by dehydration treatment resulted in superior sludge dehydration performance compared to conventional anionic water-soluble polymer dispersions and other forms of anionic water-soluble polymers. In particular, the effect is superior to that of the conventional anionic water-soluble polymer dispersion sample B, making it extremely useful for suppressing the release of ammonium compounds into the environment.

[0049] (Test Example 3) A cylinder settling test was conducted on acid cleaning wastewater (pH 7.6, SS content 83 mg / L, turbidity 94 NTU) generated by a machinery manufacturing plant. 200 mL of wastewater was collected in a plastic beaker, and alum sulfate (an inorganic flocculant) and caustic soda were added in predetermined amounts (relative to the wastewater volume). The pH was measured, and a 0.2% by mass solution of the flocculating agent sample A from Example 1 was added to the wastewater volume at 1 ppm. The cylinder was then shaken left and right five times, with a strong shake and five times with a weak shake. After allowing the cylinder to stand, the sedimentation interfacial volume and floc settling velocity were measured after 30 minutes, and the turbidity of the supernatant was measured. Similar tests were also conducted using different types of alkaline agent or without any additives. The results are shown in Table 5.

[0050] (Comparative Test Example 3) Similar tests were conducted on the same wastewater as in Experimental Test Example 3 using flocculating treatment agent sample B or the flocculating treatment agent samples in Table 2. The results are shown in Table 5.

[0051] (Table 5) TIFF0007736266000006.tif5091

[0052] (Test Example 4) A settling test was conducted using a jar tester on food wastewater (pH 4.2, SS content 174 mg / L, turbidity 266 NTU) generated from a food manufacturing plant. 200 mL of wastewater was collected in a plastic beaker, and alum sulfate (an inorganic flocculant) and caustic soda were added in predetermined amounts (relative to the wastewater volume). The pH was measured, and a 0.2% by weight solution of flocculating agent Sample A from Example 1 was added to the wastewater at 1 ppm. The mixture was stirred at 150 rpm for 60 seconds, 150 rpm for 30 seconds, and 40 rpm for 30 seconds. The settling velocity of the flocs, and the turbidity and sludge volume (SV) of the supernatant after 5 minutes of standing were measured. Similar tests were also conducted using different types of alkaline agents. The results are shown in Table 6.

[0053] (Comparative Test Example 4) Similar tests were conducted on the same wastewater as in Experimental Test Example 4 using flocculating treatment agent sample B or the flocculating treatment agent samples in Table 2. The results are shown in Table 6.

[0054] (Table 6) TIFF0007736266000007.tif5191

[0055] The anionic water-soluble polymer dispersion of the present invention, when added to wastewater and subjected to coagulation treatment, exhibited superior wastewater treatment performance compared to conventional anionic water-soluble polymer dispersions and other forms of anionic water-soluble polymers. In particular, the effect was superior to that of the conventional anionic water-soluble polymer dispersion sample B, making it extremely useful for suppressing the release of ammonium compounds into the environment.

Claims

1. A flocculation treatment agent comprising an anionic water-soluble polymer dispersion obtained by dispersing and polymerizing, under stirring, an aqueous salt solution containing 70% by mass or more of magnesium sulfate out of the total amount of inorganic salts at the time of polymerization, an aqueous solution of a monomer or monomer mixture essentially containing a monomer represented by the following general formula (1), in the presence of a polymer dispersant having 2-acrylamido-2-methylpropanesulfonic acid or a salt thereof as a constituent unit: General formula (1) R １ is hydrogen, a methyl group or a carboxymethyl group, and Q is SO ３ , C ６ H ４ SO ３ , CONHC (CH ３ ) ２ CH ２ SO ３ , C ６ H ４ COO or COO, R ２ is hydrogen or COOY ２ , Y １ Or Y ２ represents a hydrogen atom or a cation, respectively.

2. 2. The flocculating treatment agent according to claim 1, wherein the viscosity of a 4% by mass aqueous sodium chloride solution of the anionic water-soluble polymer at 0.4% by mass measured at 25°C is in the range of 20 to 200 mPa·s.

3. A method for dewatering sludge, comprising adding the flocculating agent according to claim 1 or 2 to sludge and then dewatering the sludge.

4. 3. A method for treating wastewater, comprising adding the flocculating agent according to claim 1 or 2 to wastewater to carry out flocculation treatment.

5. 5. The method for treating wastewater according to claim 4, wherein an alkaline agent is added to the wastewater.

6. 6. The method for treating wastewater according to claim 5, wherein the alkaline agent is at least one selected from the group consisting of slaked lime, caustic soda, sodium carbonate, potassium carbonate, and potassium hydroxide.

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