JP2008194677A - Method for dehydrating papermaking sludge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method which neither causes breaking of flocks nor lowers dehydration efficiency, but can lower the water content of a cake even when applied to a dehydrator which provides high shear in the dehydration process. <P>SOLUTION: A nonionic water-soluble polymer comprising constituent units composed mainly of an acrylamide is added and mixed. Thereafter, cationic and/or amphoteric polymer coagulating agents are added and mixed. The mixture is then dehydrated with a dehydrator. In this case, an aqueous solution, in which the nonionic water-soluble polymer, the cationic polymer coagulating agent, or the amphoteric polymer coagulating agent has been dissolved, has a viscosity of 100 to 2000 mPa s (as measured at 25°C with a Brookfield viscometer) when papermaking sludge is added thereto. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a paper sludge dewatering method, and more specifically, to a paper sludge, a nonionic water-soluble polymer composed mainly of acrylamide is added to and mixed with the paper sludge, and then the cationic sludge is mixed. And / or when the amphoteric polymer flocculant is added and mixed, and then dehydrated by a dehydrator, the paper sludge of an aqueous solution in which the nonionic water-soluble polymer, cationic polymer flocculant or amphoteric polymer flocculant is dissolved The present invention relates to a method for dewatering a papermaking sludge having a viscosity at the time of addition of 25 ° C. and a viscosity of 100 to 2000 mPa · s when measured with a B-type viscometer.

In the case of dewatering sludge, a cationic flocculant has been conventionally used. However, in the case of a hardly dewaterable sludge, an inorganic flocculant is added and then a cationic organic polymer flocculant is used in combination (Patent Document 1). ) Or similar formulation with amphoteric organic polymer flocculant (Patent Document 2), inorganic flocculant, anionic flocculant and cationic flocculant (Patent Document 3), and nonionic polyvinyl Formulations using alcohol in combination with cationic and / or amphoteric flocculants are disclosed. However, it is possible to handle sludge fluctuations sufficiently, stable treatment is possible, the moisture content of the dewatering cake is sufficiently reduced, and if the process after dewatering can be performed efficiently, it is still a complete recipe The current situation has not been proposed. In addition, after adding and mixing a nonionic water-soluble polymer composed of a polymer dispersion prepared by a dispersion polymerization method in the presence of an ionic polymer dispersant in a salt solution, cationic and / or amphoteric polymer aggregation A method of adding an agent is disclosed (Patent Document 4). However, this method has a low aqueous solution viscosity because the polymer has a special structure because of dispersion polymerization in an aqueous salt solution. Therefore, there is a problem that the floc breaks first instead of generating the floc early because the polymer is well dispersed in the sludge. Especially when a dehydrator such as a screw press is used, the floc is severely broken because the sludge is “bricked”.
JP-A-7-214100 JP-A-4-322800 JP-A-8-52477 JP 2001-286899 A

It is an object of the present invention to efficiently perform a dehydration process on a dewatering machine in which a papermaking sludge such as a screw press is “bricked” and a state in which a strong share of flocs is generated and the water content of the dewatering cake is obtained. It is to provide a paper sludge dewatering method whose rate can be lower than that of conventional formulations.

As a result of detailed studies in order to solve the above problems, the present inventor has reached the invention as described below. That is, the invention of claim 1 of the present invention is to add a nonionic water-soluble polymer composed mainly of acrylamide to papermaking sludge and mix it, and then add a cationic and / or amphoteric polymer flocculant. When added and mixed, and then dehydrated by a dehydrator, the viscosity of the aqueous solution in which the nonionic water-soluble polymer, cationic polymer flocculant or amphoteric polymer flocculant is dissolved is 100 to 2000 mPa · s. It is a method for dewatering papermaking sludge (measured with a B-type viscometer at 25 ° C.).

The invention of claim 2 is the method for dewatering papermaking sludge according to claim 1, wherein the product form of the nonionic water-soluble polymer is a powder or a water-in-oil emulsion.

The invention according to claim 3 is the method for dewatering papermaking sludge according to claim 1, wherein the product form of the nonionic water-soluble polymer is a dispersion in a salt solution.

In the invention of claim 4, when the mole% of the repeating unit having a cationic group, an anionic group and a nonionic group in the cationic and / or amphoteric polymer flocculant is a, b and c, respectively, 10 3. The method of dewatering a papermaking sludge according to claim 1 or 2, wherein a ≦ b ≦ c, 90 ≦ 10 ≦ c ≦ 90, a + b + c = 100.

The invention according to claim 5 is the method for dewatering papermaking sludge according to any one of claims 1 to 3, wherein the dehydrator is a Vescrew press.

The method of dewatering the papermaking sludge of the present invention comprises adding and mixing a nonionic water-soluble polymer composed of a structural unit mainly composed of acrylamide whose product form is a powder or a water-in-oil emulsion to the papermaking sludge. In the case where the cationic and / or amphoteric polymer flocculant is added and mixed and then dehydrated by a dehydrator, the viscosity of the aqueous solution in which the nonionic water-soluble polymer solution is dissolved is 100 to 2000 mPa · s (measured with a B-type viscometer at 25 ° C.). The molecular weight of the nonionic water-soluble polymer is preferably 5 million or more and 20 million or less. When the mole% of the repeating unit having a cationic group, an anionic group and a nonionic group in the cationic and / or amphoteric polymer flocculant is a, b and c, respectively, 10 ≦ a ≦ 60, 0 ≦ b ≦ 30, 10 ≦ c ≦ 90, but preferably a + b + c = 100. And it is most suitable that the dehydrator is Vescrew press.

First, a nonionic water-soluble polymer composed of structural units mainly composed of acrylamide, which is a water-in-oil emulsion, will be described. The synthesis method of the water-in-oil type water-soluble polymer emulsion is performed as follows. (A) To form an oily substance mainly composed of acrylamide, other nonionic water-soluble vinyl monomer, (B) water, (C) at least one hydrocarbon, and (D) water-in-oil emulsion. It is synthesized by mixing an effective amount and at least one surfactant having HLB, and vigorously stirring to form a water-in-oil emulsion, followed by polymerization. Examples of the other nonionic water-soluble vinyl monomer (A) to be copolymerized include the following. That is, N, N-dimethylacrylamide, vinyl acetate, acrylonitrile, methyl acrylate, 2-hydroxyethyl (meth) acrylate, diacetone acrylamide, N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide and the like. In addition, as a ratio of the nonionic water-soluble vinyl monomer to be copolymerized,
30 mol%, preferably 5 to 20 mol%.

Examples of oily substances composed of hydrocarbons of (C) include paraffins, mineral oils such as kerosene, light oil, and middle oil, or hydrocarbon-based synthetic oils having characteristics such as boiling point and viscosity in substantially the same range as these, Alternatively, a mixture thereof can be mentioned.

Examples of at least one surfactant having an HLB and an amount effective to form the water-in-oil emulsion of (D) include HLB 3-6 nonionic oil-soluble surfactants, and specific examples thereof are as follows. Examples thereof include sorbitan monooleate, sorbitan monostearate, sorbitan monopalmitate and the like. Nonionic water-soluble surfactants include polyoxyethylene alkyl ether, polyoxyethylene alcohol ether, and polyoxyethylene alkyl ester. Specifically, polyoxyethylene (20) sorbitan trioleate, polyoxyethylene (4) sorbitan monostearate, polyoxyethylene (5) sorbitan monooleate and the like. The amount of these surfactants to be added is 0.5 to 10% by weight, preferably 1 to 5% by weight, based on the total amount of the water-in-oil emulsion.

(A) to (D) are mixed, and after forming a water-in-oil emulsion with an emulsifier or the like, nitrogen substitution is performed, and after setting the water-in-oil emulsion to a certain polymerization temperature, a radical polymerization initiator To initiate the polymerization. As the initiator, any azo, peroxide, or redox polymer can be polymerized. Examples of oil-soluble azo initiators are 2,2′-azobisisobutyronitrile, 1,1′-azobis (cyclohexanecarbonitrile), 2,2′-azobis (2-methylbutyronitrile), 2,2′-azobis (2-methylpropionate), 4,4′-azobis (4-methoxyl2,4-dimethyl) valeronitrile and the like.

Examples of water-soluble azo initiators include 2,2′-azobis (amidinopropane) dichloride, 2,2′-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] And dihydrochloride, 4,4′-azobis (4-cyanovaleric acid), and the like. Examples of redox systems include a combination of ammonium or potassium peroxodisulfate and sodium sulfite, sodium hydrogen sulfite, trimethylamine, tetramethylethylenediamine, and the like. Examples of peroxides include ammonium peroxodisulfate, hydrogen peroxide, benzoyl peroxide, lauroyl peroxide, octanoyl peroxide, succinic peroxide, and t-butylperoxy 2-ethylhexanoate. Can do.

The polymerization temperature can be 0 to 80 ° C., but preferably 20 to 60 ° C. The polymerization concentration is generally 10 to 60% by weight, but preferably 20 to 50% by weight easily controls the polymerization reaction, and the production efficiency is good.

In addition to nonionic water-soluble monomers, crosslinkable monomers such as polyfunctional monomers such as methylenebisacrylamide and ethylene glycol di (meth) acrylate, or N, N-dimethylacrylamide It is also possible to appropriately copolymerize such a heat-crosslinkable monomer, modify the copolymer, and improve the performance to cope with various wastewaters.

In the water-in-oil emulsion of the present invention, after polymerization, a hydrophilic surfactant called a phase inversion agent is added to make the emulsion particles covered with the oil film easy to become familiar with water, and the water-soluble polymer therein dissolves. To make it easier to use, diluted with water and used for each application. Examples of hydrophilic interfacial chemicals include cationic interfacial chemicals and HLB 9-15 nonionic interfacial chemicals, such as polyoxyethylene alkyl ethers. However, in the water-in-oil emulsion obtained by polymerization after emulsification using a water-soluble surfactant, the above hydrophilic surfactant may not be necessary, and a small amount may be necessary.

The molecular weight of the polymer constituting the water-in-oil emulsion is 5 million to 20 million, and preferably 8 million to 20 million. If it is 5 million or less, the cohesive force is insufficient and the dewatering effect is lowered, and if it is 20 million or more, the floc becomes enormous and the moisture content of the dewatered sludge does not decrease. In addition, the solution viscosity becomes too high, dispersibility is deteriorated, and handling of the aqueous solution is also deteriorated.

Next, a nonionic water-soluble polymer composed of structural units mainly composed of acrylamide as a product will be described. The chemical composition, molecular weight, and the like are the same as in the water-in-oil emulsion. The polymerization method involves polymerizing a high-concentration aqueous solution, pulverizing with a meat chopper, etc., and then drying and re-pulverizing to a powder, or water-in-oil dispersion polymerization, and drying a granular material comprising a polymer, or oil After polymerization of the water-in-water emulsion, the polymerization method and the production method are arbitrary, such as spray-drying with a spray dryer to obtain a powdery product.

Next, the dispersion in a salt solution will be described. The nonionic water-soluble polymer comprising a polymer dispersion produced by the dispersion polymerization method used in the present invention comprises a water-soluble monomer containing a nonionic monomer in the salt solution. A polymer dispersion produced by a dispersion polymerization method in the presence of a dispersant composed of an ionic polymer soluble in an aqueous solution. When producing a nonionic water-soluble polymer comprising the polymer dispersion used in the present invention, any anionic or cationic polymer can be used as the dispersant. As the cationic polymer, a homopolymer or copolymer of a cationic monomer, or a copolymer with a nonionic monomer can be used. Examples of cationic monomers are diallylamine monomers or (meth) acrylic monomers. Examples include dimethyldiallylammonium chloride, (meth) acryloyloxyethyltrimethylammonium chloride, (meth) acryloylaminopropyltrimethylammonium chloride, (meth) acryloyloxy 2-hydroxypropyltrimethylammonium chloride, and the like. It is a (co) polymer containing one or more of the monomers. Examples of nonionic monomers include acrylamide, N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone, N, N-dimethylacrylamide, acrylonitrile, diacetone acrylamide, and 2-hydroxyethyl (meth) acrylate. -G On the other hand, examples of the anionic polymer include homopolymers such as acrylic acid, methacrylic acid, itaconic acid, acrylamide 2-methylpropanesulfonic acid, and styrenesulfonic acid, and copolymers obtained by combining these monomers. A copolymer with the above nonionic monomer can also be used.

These polymer dispersions can be used as a single ionic polymer, but can also be used by combining two or more of a plurality of cationic polymers or anionic polymers. Moreover, the addition amount with respect to the monomer of these polymer dispersing agents is 100: 1-10: 1, Preferably it is 50: 1-20: 1. If it is less than 100: 1, there is no effect as a dispersant, and if it is more than 10: 1, it is disadvantageous in cost, and the properties of the produced polymer dispersion are different, which is not the object of the present invention. .

Salts used at the time of polymerization are salts of alkali metal ions such as sodium and potassium, ammonium ions, halide ions, sulfate ions, nitrate ions, phosphate ions, etc., but salts with polyvalent anions. More preferred. The concentration of the salt solution is 5% by weight or more and the saturation concentration or less.

Next, the cationic and / or amphoteric polymer flocculant used in combination with the nonionic water-soluble polymer will be described. That is, acrylic cationic monomers, for example, salts of inorganic or organic acids such as dimethylaminoethyl (meth) acrylate and dimethylaminopropyl (meth) acrylamide, or quaternary ammonium salts with methyl chloride or benzyl chloride alone A polymer or a copolymer with acrylamide. For example, as a monomer, (meth) acryloyloxyethyltrimethylammonium chloride, (meth) acryloyloxy 2-hydroxypropyltrimethylammonium chloride, (meth) acryloylaminopropyltrimethylammonium chloride, (meth) acryloyloxyethyldimethylbenzyl Ammonium chloride, (meth) acryloyloxy 2-hydroxypropyldimethylbenzylammonium chloride, (meth) acryloylaminopropyldimethylbenzylammonium chloride, and the like. Copolymerization of these monomers with nonionic monomers It is a coalescence. Acrylamide is preferred as the monomer to be copolymerized. Also, amphoteric polymers can be synthesized and used by copolymerizing anionic monomers such as (meth) acrylic acid. In addition to these acrylic polymers, dimethyldiallylammonium chloride (co) polymers, polyvinylamine polymers, and polyamidine polymers can also be used.

The mol% of the ionic group in the cationic and / or amphoteric polymer flocculant is as follows. That is, papermaking sludge has a high fiber content, and aggregation occurs even with nonionic water-soluble polymers. Second-stage cationic and / or amphoteric polymer to aggregate anionic components that could not be treated by the addition of the first-stage nonionic water-soluble polymer or to strengthen the flocs produced in the first stage Addition of a flocculant is necessary. Therefore, it is sufficient if it is not high as a cationic property. Accordingly, when the mole% of the repeating unit having a cationic group, an anionic group and a nonionic group is a, b, c (where a + b + c = 100), 10 ≦ a ≦ 60, preferably 10 ≦ a ≦ 40. Further, b is 0 ≦ b ≦ 30, and preferably 0 ≦ b ≦ 20. Furthermore, c is 10 ≦ c ≦ 90, and preferably 30 ≦ c ≦ 90. When a is 10 or less, the cationic property is low and the dehydration efficiency is lowered. On the other hand, when b is 30 or more, the anionic property is too strong, and the effect of the cationic group is not manifested and cannot be used.

The molecular weight of these cationic or amphoteric polymer flocculants is 5 million to 20 million, preferably 5 million to 15 million. If it is 5 million or less, the cohesive force is insufficient, and if it is 20 million or more, the cohesive force is too high, and the flocs become enormous and the dewaterability is lowered. In addition, the solution viscosity becomes too high, dispersibility is deteriorated, and handling of the aqueous solution is also deteriorated.

These cationic and / or amphoteric polymer flocculants are not particularly limited, such as powder products, products by water-in-oil emulsion polymerization, and aqueous solution products, and are used as appropriate.

The addition amount of the nonionic polymer to the papermaking sludge is 0.05 weight percent to 0.5 weight percent, preferably 0.05 weight percent to 0.00 weight percent with respect to the total ss in the papermaking sludge. 2 percent by weight. The addition amount of the cationic and / or amphoteric polymer flocculant is 0.05 weight percent to 0.5 weight percent, preferably 0.05 weight percent to 0.2 weight. . As the order of addition, the nonionic water-soluble polymer is added first, and then the cationic and / or amphoteric polymer flocculant is added.

The dehydration method for the papermaking sludge using the nonionic water-soluble polymer of the present invention is the addition amount of the anionic polymer flocculant when the anionic polymer flocculant and the cationic polymer flocculant are combined. Compared to, it can be reduced. It is presumed that aggregation occurs due to an action different from the electrical interaction between the anion and the cation. Although the details have not been elucidated yet, it is a sludge mainly made of paper sludge, so it contains a small amount of anionic colloidal substances and a lot of unstable suspended substances such as pulp. The polyacrylamide structural unit in the water-soluble water-soluble polymer develops a hydrogen bonding action and aggregates the pulp fibers in a cross-linking manner. Thereafter, it is presumed that a larger and stronger floc is further grown by a cationic or amphoteric flocculant.

The dehydrator can be dehydrated using a conventional model such as a decanter, a filter press, a belt press or a screw press, but is suitable for a dehydrator in which a floc such as a screw press is "bricked". . Therefore, in the present invention, a formulation having high solution viscosity and slow dispersion in papermaking sludge was studied. For this reason, the generation of flocs occurs slowly, and as a result, the collapse of the generated flocs is delayed. A dehydrator such as a screw press extrudes sludge with a screw, and the sludge is “bricked” in the process, so the flock is severely broken. Therefore, it is considered that the paper sludge dewatering method of the present invention is suitable for a dehydrator such as a screw press. For the reasons described above, the viscosity at the time of addition of the aqueous solution in which the polymer flocculant is dissolved is 100 to 2000 mPa · s, preferably 100 to 1200 mPa · s when measured with a B-type viscometer at 25 ° C.

Examples of sludge include pulp sludge and general wastewater sludge in the paper industry. Therefore, for the reasons described above, the paper sludge dewatering method of the present invention has an increased sludge throughput, a reduced cake moisture content, and a conventional anionic polymer flocculant / cationic polymer flocculant formulation. There are advantages such as a reduction in fuel costs during incineration, a reduction in the amount of waste dumped, and a positive impact on compost.

(Examples) Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

For paper sludge sludge (pH; 6.65, SS; 19,250 mg / L, TS; 22,000 mg / L) generated from a paper mill, a coagulation test and a squeeze test were conducted for a screw press dehydrator. 200 ml of this sludge was taken in a poly-bicker, and the nonionic polymer flocculants N-1 to N-3 shown in Table 1 below were mixed at a mass% concentration shown in Table 1, and the solution viscosity was measured with a B-type viscometer. Measured (25 ° C.), added each 15 ppm to the solution, transferred to beaker and stirred 40 times, and then added amphoteric polymer flocculants C-1 to C-3 at a concentration of 0.1% by mass to 60 ppm / liquid. Then, the beaker was transferred and stirred 20 times, and the size of the generated floc floc was observed, and then the filtration rate was measured with a 40 mesh nylon filter cloth. Further, the filtered agglomerate was dehydrated at a press pressure of 4 kgf / cm 2 and the cake diameter was measured. Then, the dehydrated cake was dried by a dryer at 105 ° C. for 15 hours to obtain the cake moisture content.

(Table 1) Composition of nonionic, cationic or amphoteric polymer flocculants
DMQ: acryloyloxyethyltrimethylammonium chloride,
AAC: acrylic acid, AAM: acrylamide, unit mPa · s
1) Solution viscosity: 0.05 mass% concentration, 2) Solution viscosity: 0.1 mass% concentration,
3) Solution viscosity: 0.2 mass% concentration, 4) Solution viscosity: 0.3 mass% concentration,

As a result, it was confirmed that the formation of very strong flocculation flocs and the filtration rate were improved, and the cake diameter after press dehydration, which is an index of the goodness of water drainage regarding the dehydrated cake, was reduced and a good cake moisture content was obtained. . These results are shown in Table 2.

(Table 2) Results of Example 1

(Comparative Example 1) By a similar test operation as a comparative test, the solution viscosity was measured with a B-type viscometer at a mass% concentration shown in Table 3 below (25 ° C), and each chemical was 0.05 to 0.1 mass. When the anionic polymer flocculants A-1 and A-2 were added at 0.05% by mass, the dehydration test was conducted. These results are shown in Table 4.

(Table 3) Viscosity of comparative test solution
DMQ: acryloyloxyethyltrimethylammonium chloride,
AAC: acrylic acid, AAM: acrylamide, unit mPa · s
1) Solution viscosity: 0.05 mass% concentration
2) Solution viscosity: 0.1% by weight concentration,

(Table 4) Results of Comparative Example 1
Cake supportability ○>△> Indicates that the effect is good in the order of ×

For paper sludge sludge (pH; 6.73, SS; 43,500 mg / L, TS; 46,000 mg / L) generated from a paper mill, a coagulation test and a squeeze test were conducted for a screw press dehydrator. After taking 200 ml of this sludge in a polyvinyl beaker, adding 30 ppm / liquid of nonionic polymer flocculants N-1 and N-2 shown in Table 1 above, carrying out beaker transfer and stirring 20 times, and further Add amphoteric polymer flocculants AM-1 and AM-2 to 60 ppm / liquid, transfer to a beaker, stir 20 times, observe the size of the resulting floc flocs, and measure the filtration rate with a 40 mesh nylon filter cloth. did. Further, the filtered agglomerate was dehydrated at a press pressure of 4 kgf / cm 2 and the cake diameter was measured. Then, the dehydrated cake was dried by a dryer at 105 ° C. for 15 hours to obtain the cake moisture content.

As a result, it was confirmed that the formation of very strong flocculation flocs and the filtration rate were improved, and the cake diameter after press dehydration, which is an index of the goodness of water drainage regarding the dehydrated cake, was reduced, and a good cake moisture content was obtained. . These results are shown in Table 5.

(Table 5) Results of Example 2

(Comparative Example 2) By the same test operation as a comparative test, when the anionic polymer flocculants A-1 and A-2 shown in Table 3 above were used, the viscosity was reduced by diluting to 0.05% by mass. In some cases, a dehydration test was performed. These results are shown in Table 6.

(Table 6) Results of Comparative Example 2
Cake supportability ○>△> Indicates that the effect is good in the order of ×

Claims (5)

After adding and mixing a nonionic water-soluble polymer composed of acrylamide as a main component to paper sludge, adding and mixing a cationic and / or amphoteric polymer flocculant, dewatering with a dehydrator In this case, the viscosity of the aqueous solution in which the nonionic water-soluble polymer, cationic polymer flocculant or amphoteric polymer flocculant is dissolved is 100 to 2000 mPa · s (measured by a B-type viscometer at 25 ° C.) A method for dewatering a papermaking sludge. The method for dewatering paper sludge according to claim 1, wherein the product form of the nonionic water-soluble polymer is a powder or a water-in-oil emulsion. The method for dewatering papermaking sludge according to claim 1, wherein the product form of the nonionic water-soluble polymer is a dispersion in a salt solution. When the molar percentages of the repeating units having a cationic group, an anionic group and a nonionic group in the cationic and / or amphoteric polymer flocculant are a, b and c, respectively, 10 ≦ a ≦ 60, 0 ≦ The method for dewatering papermaking sludge according to claim 1 or 2, wherein b≤30, 10≤c≤90, wherein a + b + c = 100. The method for dewatering papermaking sludge according to any one of claims 1 to 3, wherein the dehydrator is a screw press.