JP2001149703A - Amphoteric polymeric flocculant for pulp or paper manufacturing industry sludge and dehydrating method for pulp or paper manufacturing industry sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an amphoteric polymeric flocculant capable of obtaining floc well-balanced in strength, the rate of filtration and water content in the dehydration of pulp or paper manufacturing industry sludge, and a dehydrating method of the sludge using the same. SOLUTION: The amphoteric polymeric flocculant for the pulp or paper manufacturing industry sludge has 10-40 mol% cationic monomer unit having acryloyl group, 30-20 mol% anionic monomer unit and 40-87 mol% other radical polymerizable monomer unit as structural monomer units in the molecule to have an (anion equivalent Av)/(cation equivalent Cv) ratio of <1.2. The sludge is more efficiently dehydrated by using an inorganic flocculant in combination.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high molecular weight amphoteric polymer flocculant suitable for treating pulp or paper industry sludge, and a method for dewatering pulp or paper industry sludge using the same. According to the dehydration method using an amphoteric polymer flocculant of the present invention, it is possible to obtain a floc having an excellent balance among strength, filtration speed and water content.

[0002]

2. Description of the Related Art In the pulp industry, a screening process, a cooking process, a bleaching process, a paper making process, and the like.
The wastewater produced is enormous because of the large number of processes that require the use of water. The wastewater generated in these steps is subjected to a physical treatment, and then organic substances are removed by a biochemical treatment such as an activated sludge method. Excess sludge generated at this time is dehydrated by adding a polymer flocculant.

However, the excess sludge generated by the biochemical treatment is very difficult to dehydrate because the main components are cells of living organisms. That is, although a dewatered cake is obtained by adding 1% by weight or more of a polymer flocculant per SS, the water content of the cake is 85% by weight or more, and the cake water content is more than that of other industrial wastewater. The water content increases.
In some cases, aggregate flocs may not be formed unless 3% by weight or more of a polymer flocculant per SS is added.

Further, the obtained floc is often very brittle, and when the floc is dewatered by using a screw press dewatering machine, the floc often flows out of the screen and the belt press dewatering machine is used. In the case of dehydration, peeling of the dehydrated cake was sometimes difficult.

[0005] As a dehydration method for solving these problems, a method of adding and mixing iron polysulfate and then adding a polymer flocculant, which is known as a usual method of dewatering sludge, is a method of condensing polyamine. It is conceivable to divert a method of adding a polymer flocculant after addition and mixing, and a method of adding an amphoteric polymer flocculant after adding and mixing an inorganic flocculant.

[0006] However, none of the dewatering methods is satisfactory, and the obtained floc does not have strength enough to withstand mechanical dehydration, has an insufficient particle size, and has an insufficient filtration rate. As a result, the throughput per unit time could not be increased, and the resulting cake water content could not be further reduced.

[0007]

The present inventors have made various studies to solve the above-mentioned problems, and found that when dewatering pulp or papermaking sludge, a cationic monomer and an anionic monomer were used. It is contained in a specific ratio, and the ratio of the anion equivalent Av and the cation equivalent Cv by titration is Av / C
By using an amphoteric polymer flocculant with v <1.2, it was found that a floc excellent in balance among strength, filtration speed and water content could be obtained, and the present invention was completed. Accordingly, an object of the present invention is to provide an amphoteric polymer flocculant which solves the above-mentioned problems, and a method for dewatering sludge using the amphoteric polymer flocculant.

[0008]

The present invention to achieve the above object is as described below.

[1] A cationic monomer unit having an acryloyl group is 10 to 40 mol%, an anionic monomer unit is 3 to 20 mol%, and other radical polymerizable monomer units are 40 to 40 mol%. Pulp or papermaking sludge characterized by having 87 mol% in the molecule as a constituent monomer unit, and wherein the ratio of anion equivalent Av and cation equivalent Cv by titration is Av / Cv <1.2. For amphoteric polymer flocculants.

[2] The cationic monomer unit having an acryloyl group has the formula (1)

[0011]

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(In the formula (1), R ¹ is a hydrogen atom and has 1 carbon atom.
To 8 hydrocarbon groups or hydroxyalkyl groups, R ² and R ³ are each independently an alkyl group having 1 to 8 carbon atoms. X ^- is an anion. The amphoteric polymer flocculant for pulp or paper industry sludge according to the above [1], which is a monomer unit represented by the formula (1).

[3] The anionic monomer unit represented by the formula (2)

[0014]

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In the formula (2), R ⁴ is a hydrogen atom or a methyl group; M is a hydrogen atom, an ammonium ion or an alkali metal ion. Or the amphoteric polymer flocculant for pulp or paper industry sludge according to [2].

[4] The above-mentioned [1] to wherein the other radically polymerizable monomer units are acrylamide monomer units.
The amphoteric polymer flocculant for pulp or paper industry sludge according to any one of [3].

[5] Dehydration of pulp or papermaking sludge characterized by adding the amphoteric polymer flocculant described in any of the above [1] to [4] to pulp or papermaking sludge. Method.

[6] An inorganic coagulant is added to pulp or papermaking sludge, and then the amphoteric polymer coagulant described in any of [1] to [4] above is added and dewatered. Method for dewatering pulp or papermaking sludge.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, the amphoteric polymer flocculant of the present invention comprises 10 to 40 mol% of a cationic monomer unit having an acryloyl group and 3 to 3 anionic monomer units.
20 mol% and 4 units of other radically polymerizable monomer units.
0 to 87 mol% in the molecule as a constituent monomer unit, and the anion equivalent Av and the cation equivalent C are determined by titration.
The ratio with v is Av / Cv <1.2.

The amphoteric polymer flocculant of the present invention is obtained by copolymerizing a cationic monomer having an acryloyl group, an anionic monomer and another radical polymerizable monomer at a predetermined ratio. Can be manufactured.

(Cationic monomer having acryloyl group) Examples of the cationic monomer having an acryloyl group include hydrochloride, sulfate, nitrate of dialkylaminoalkyl acrylate such as dialkylaminoethyl acrylate and dialkylaminopropyl acrylate. Examples include tertiary monomers such as acetate, and quaternary salts obtained by reacting dialkylaminoalkyl acrylate with methyl chloride, methyl bromide, methyl iodide, dimethyl sulfate, benzyl chloride, benzyl bromide, and the like.

Hereinafter, cationic monomers having an acryloyl group which can be used in the present invention will be described more specifically.

Acryloyloxyethyldimethylamine hydrochloride, acryloyloxyethyldiethylamine hydrochloride, acryloyloxy-2-hydroxypropyldimethylamine hydrochloride, or a sulfate thereof.

Acryloyloxyethyltrimethylammonium chloride, acryloyloxyethyldiethylmethylammonium chloride, acryloyloxy-2-hydroxypropyltrimethylammonium chloride, or methyl sulfate in place of these chlorides.

A particularly preferred cationic monomer having an acryloyl group is a dialkylaminoethyl acrylate salt represented by the following formula (3).

[0026]

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In the formula (3), R ¹ is a hydrogen atom and has 1 to 1 carbon atoms.
8 hydrocarbon groups or hydroxyalkyl groups. As the hydrocarbon group, a methyl group, an ethyl group, a propyl group, a phenyl group, a benzyl group and the like are preferable. As the hydroxyalkyl group, a hydroxymethyl group, a hydroxyethyl group and the like are preferable.

In the formula (3), R ² and R ³ independently represent a group having 1 carbon atom such as a methyl group, an ethyl group, a propyl group, a butyl group and the like.
To 8 alkyl groups. X is an anion, a halogen ion such as fluorine, chlorine, bromine and iodine, a sulfite ion,
Examples thereof include sulfate ions, nitrate ions, acetate ions, methyl sulfate ions, and ethyl sulfate ions.

Specifically, quaternary methyl chloride of dimethylaminoethyl acrylate, quaternary benzyl chloride of dimethylaminoethyl acrylate and the like are preferable.

These may be used alone or in combination of two or more.

(Anionic monomer) As the anionic monomer, acrylic acid or methacrylic acid represented by the following formula (4) (hereinafter, both may be referred to as (meth) acrylic acid), or These salts, vinyl sulfonic acid,
2-acrylamido-2-methylpropanesulfonic acid,
Examples thereof include maleic acid and alkali metal salts thereof, and (meth) acrylic acid or salts thereof are preferable.

[0032]

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In the formula (4), R ⁴ is a hydrogen atom or a methyl group. M is a hydrogen atom, an ammonium ion, or an alkali metal ion such as sodium or potassium.

These may be used alone or in combination of two or more.

(Other Radical Polymerizable Monomer) Examples of other radical polymerizable monomers include a cationic radical polymerizable monomer and a nonionic radical polymerizable monomer.

Examples of the cationic radical polymerizable monomer include methacryloyloxyethyldimethylamine hydrochloride, methacryloyloxyethyldiethylamine hydrochloride, methacryloyloxy-2-hydroxypropyldimethylamine hydrochloride, and sulfates thereof, and methacryloyloxyethyl. Trimethylammonium chloride, methacryloyloxyethyl diethylmethylammonium chloride, methacryloyloxy-2-hydroxypropyltrimethylammonium chloride, or methyl sulfate in place of these chlorides.

Examples thereof include vinylpyridine, quaternized derivatives of vinylpyridine, vinylimidazole, allylamine and the like.

These cationic radical polymerizable monomers may be used alone or in combination of two or more.

Examples of the nonionic radical polymerizable monomer include (meth) acrylamide, styrene, acrylonitrile, vinyl acetate, and alkyl (meth) acrylate. These nonionic monomers can be used alone or in combination of two or more.

Of these, acrylamide is particularly preferred.

The amphoteric polymer flocculant of the present invention is prepared by blending the above monomers in a predetermined ratio and copolymerizing them so that the cationic monomer unit having an acryloyl group has a content of 10 to 4 units.
0 mol% and 3 to 20 mol% of anionic monomer units
And 40 to 87 mol% of other radically polymerizable monomer units in the molecule, and an anion equivalent A by titration.
v (hereinafter also simply referred to as Av) and the ratio of the cation equivalent Cv (hereinafter simply referred to as Cv) are Av / Cv <1.2.
It is something to be.

When the proportion of the cationic monomer unit having an acryloyl group is less than 10 mol%, the sludge having a charge cannot be sufficiently neutralized, and the water content of the obtained cake increases. If the amount exceeds mol%, the cohesive force of the floc decreases, and the floc strength decreases.

If the proportion of the anionic monomer unit is less than 3 mol%, the particle size of the floc becomes small or the water content of the obtained cake becomes large. The particle size becomes small and the flock strength decreases.

If the proportion of the other radically polymerizable monomer units is less than 40 mol%, the flocculence of the floc is reduced and the floc strength is reduced. On the other hand, if it exceeds 87 mol%, the floc is formed. It will be difficult to do. Also,
When the value of Av / Cv is 1.2 or more, it is difficult to form flocs.

In the present invention, Av and Cv are values measured by a colloid titration method, and Av is pH = 7.
And Cv is the result measured under the condition of pH = 3. Details of the colloid titration method will be described later.

Since the reaction rate of the monomer is high, the composition of the obtained flocculant generally matches the compounding ratio of the monomer to be charged.

Particularly preferred monomer charging ratios are as follows. Cationic monomer having an acryloyl group: anionic monomer: other radically polymerizable monomer = 15 to 35: 5 to 10:55 to 80 (mol%) Phase suspension polymerization, reversed-phase emulsion polymerization, etc. can be adopted, but aqueous solution polymerization is preferred because of easy handling. In the case of aqueous solution polymerization, the total charged concentration of each monomer is preferably 25 to 60% by weight.

The polymerization initiator is not particularly limited. In the case of aqueous solution polymerization, potassium persulfate, ammonium persulfate, an azo-based initiator, a redox-based initiator and the like can be appropriately used.

The pH of the monomer solution is preferably adjusted to 2 to 3.5.

The polymerization initiation temperature is usually preferably from 0 to 35 ° C.

The polymerization time is usually preferably 0.1 to 3 hours. Further, the polymerization reaction is preferably performed in an inert atmosphere in the absence of oxygen. These polymerization conditions are known.

After the completion of the polymerization reaction, the amphoteric polymer flocculant of the present invention is obtained by appropriately using a known method as necessary.

By polymerizing under the above conditions, a high molecular weight amphoteric polymer flocculant having an average molecular weight of several million can be produced. Hereinafter, a method for dewatering pulp or paper industry sludge using the amphoteric polymer flocculant of the present invention will be described.

The subject of the dewatering method of the present invention is sludge generated when treating wastewater discharged from the pulp or paper industry. Pulp wastewater includes kraft pulp wastewater, sulfite pulp wastewater, bleached wastewater, ground pulp wastewater, and semi-chemical pulp wastewater.

Specific examples of the sludge include a coagulated sludge obtained by a coagulation treatment in which an inorganic coagulant is added to pulp or paper industry wastewater, and if necessary, an organic polymer coagulant is further added. And excess sludge obtained by treating wastewater after coagulation treatment with activated sludge, mixed sludge of coagulation sludge and excess sludge, and the like. The present invention is particularly preferably applicable to mixed sludge.

The sludge may include domestic wastewater generated in a pulp or paper mill, and various sludges generated by wastewater treatment.

The dewatering method is, specifically, for example, adding an inorganic flocculant and / or
Alternatively, an organic cationic compound is added, and if necessary, the pH is adjusted to preferably 4 to 8, more preferably 5 to 7, and then the amphoteric polymer flocculant of the present invention is added, thereby forming a sludge floc. It is to let. The method of forming the flocks conforms to a known method.

Examples of the inorganic coagulant include a sulfate band, polyaluminum chloride, ferric chloride, ferrous sulfate, and polyiron sulfate.

Examples of the organic cationic compound include polymer polyamines, polyamidines, and cationic surfactants.

The addition amount of the amphoteric polymer flocculant, the inorganic flocculant, and the cationic compound, the stirring speed, the stirring time, and the like substantially follow the conventional dehydration conditions.

The floc thus formed is dehydrated using a known means to obtain a dewatered cake.

Examples of the dehydrator include a screw press dehydrator, a belt press dehydrator, a filter press dehydrator, and a screw decanter.

[0063]

The present invention will be described more specifically with reference to the following examples.

Cv and Av were measured by the following methods.

(1) Measurement of Cation Equivalent Value Take 90 ml of deionized water in a conical beaker, add 10 ml of a 500 ppm solution of the sample, and adjust the pH with aqueous hydrochloric acid.
To 3.0 and stir for about 1 minute. After addition of a few drops of toluidine blue indicator, titration with N / 400-polyvinyl potassium sulfate reagent (N / 400-PVSK).

The titration speed is 2 ml / min, and the point at which the sample changes color from blue to magenta and is maintained for at least 10 seconds is the end point.

2. Preparation of a 500 ppm aqueous solution of a sample A 0.2 g sample (not converted to dry product) is precisely weighed and placed in a stoppered Erlenmeyer flask, and dissolved in 100 ml of deionized water. This 25 ml is put into a 100 ml measuring flask, and the volume is made up to 100 ml using ion exchanged water.

3. Calculation method

[0069]

## EQU1 ## Cv (meq / g) = (N / 400-PVSK titer × N / 400-PVS
K titer) / 2 (2) Measurement of anion equivalent value In a conical beaker, take 90 ml of distilled water, add 5.0 ml of N / 200-methylglycol chitosan reagent to the sample with a measuring pipette, stir for 1 minute, and sample 500 p.
pm solution, and pH = 10 with N / 10 NaOH.
After adjusting to 7.0, stir for 5 minutes. Thereafter, 2 to 3 drops of toluidine blue indicator are added, and titrated with N / 400-polyvinyl potassium sulfate reagent (N / 400-PVSK).

The titration speed is 2 ml / min, and the point at which the sample changes color from blue to magenta and this color change lasts for 10 seconds or more is the end point.

In the above operation, the case where no sample is added is defined as a blank test.

2. Preparation of a 500 ppm aqueous solution of a sample 0.1 g of a sample (not converted to dried product) is precisely weighed and placed in a stoppered Erlenmeyer flask, and dissolved in 100 ml of deionized water. This 50 ml is put into a 100 ml measuring flask, and the volume is made up to 100 ml with deionized water.

3. Calculation method

[0074]

## EQU2 ## Av (meq / g) = Cv + av av = (titration of blank−titration of sample) × N / 400−PV
SK titer / 2 (Example 1) An aqueous solution of dimethylaminoethyl acrylate methyl chloride quaternary salt (hereinafter referred to as DAC), acrylic acid, and an aqueous solution of acrylamide (hereinafter referred to as AM) were placed in a stainless steel dewar bottle, and Is 25.
Distilled water was added so that the composition was 0 mol%, 68.0 mol%, and 7.0 mol%, the total weight was 1 kg, and the total monomer concentration was 28 wt%. The pH of this solution was adjusted to 2.9.
The solution temperature was increased to 35 while nitrogen gas was blown into the solution for 60 minutes.
C. to obtain a monomer mixture aqueous solution for polymerization.

Then, based on the total monomer weight, cupric chloride is used as a copper ion in an amount of 0.3 ppm, and azobisamidinopropane hydrochloride (Wako Pure Chemical Industries, Ltd.) is used as a polymerization initiator.
Polymerization was started by adding 60 ppm of trade name (V-50) and 30 ppm of sodium bisulfite (NaHSO ₃ ).

The polymerization was continued for 3 hours while standing. afterwards,
Take out the obtained hydrogel polymer from the Dewar bottle,
Shredded. This was dried at 80 ° C. for 5 hours and then pulverized to obtain a target amphoteric polymer flocculant A.

Example 2, Comparative Example 1 Polymerization was carried out in the same manner as in Example 1, except that the amounts of the polymerization initiator and the monomers were changed as shown in Table 1. An amphoteric polymer flocculant B and an amphoteric polymer flocculant C of Comparative Example 1 were obtained.

Using the amphoteric polymer flocculants obtained in Examples 1 and 2 and Comparative Example 1, the following physical properties were measured. Table 1 shows the results.

Insoluble content: The amphoteric polymer coagulant was dissolved in pure water to prepare 400 ml of a 0.1% by weight (solid content) solution. The whole amount of the solution was filtered with a sieve having a diameter of 20 cm and a mesh of 83 mesh, the insoluble matter remaining on the sieve was collected, and the volume was measured.

0.5% Salt Viscosity: The above amphoteric polymer flocculant was dissolved in a 4% by weight aqueous sodium chloride solution to prepare a 0.5% by weight flocculant solution. Using a B-type viscometer, 25
The coagulant solution viscosity after 5 minutes at 60 ° C. and 60 rpm was measured.

[0081]

[Table 1]

Table 1 Amphoteric polymer flocculant (Examples 3, 4 and Comparative Example 2) Mixed sludge of coagulated sludge of paper mill wastewater and excess sludge generated by activated sludge treatment (p
H = 6.8, TS = 36600 mg / l, SS = 334
00 mg / l, VSS (vs. SS = 61.7%) 200
ml was collected in a 300 ml beaker. After adding 2% by weight of sulfuric acid band (vs. SS), the pH was adjusted to 5.5. After adding any of the amphoteric polymer flocculants produced in Examples 1 and 2 and Comparative Example 1, the sludge was stirred at 150 rpm for 2 minutes using a jar tester to generate sludge flocs.

Subsequently, the sludge was stirred at 560 rpm for 15 seconds using a handy mixer, and the particle size of the generated floc was measured. As shown in Table 2, the floc diameter of each of the present examples was as large as more than 10 mm.

Thereafter, the sludge floc dispersion was subjected to gravity filtration using a 60-mesh net as a filter.
The filtration capacity after 10 seconds was measured and indicated as the filtration rate. Further, using a centrifuge, 1 rpm at 2000 rpm
The sludge after filtration was dehydrated under the condition of 0 minutes, and the water content of the obtained cake was measured. Table 2 shows the measurement results.

[0085]

[Table 2]

[0086]

The amphoteric polymer flocculant of the present invention essentially comprises a cationic monomer unit having an acryloyl group in the molecule, an anionic monomer unit and another radically polymerizable monomer unit. Since the composition has a predetermined ratio and the value of anion equivalent / cation equivalent is less than 1.2,
When this is used for dewatering pulp or papermaking sludge, flocculants exhibit extremely efficient coagulation action and are excellent in balance between strength, filtration speed, and moisture content. In general, the higher the molecular weight of a polymer flocculant, the better the flocculant effect. The amphoteric polymer flocculant of the present invention,
Low content of anionic monomer units such as acrylic acid. For this reason, the content of the anionic monomer in the charged monomer when producing the amphoteric polymer flocculant is also reduced,
As a result, a high molecular weight amphoteric polymer flocculant can be produced.

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Claims (6)

[Claims] 1. An acryloyl group-containing cationic monomer unit of 10 to 40 mol%, an anionic monomer unit of 3 to 20 mol%, and other radically polymerizable monomer units of 40 to 87 mol. Pulp or papermaking sludge, characterized in that the ratio of anionic equivalent Av to cation equivalent Cv as determined by titration is Av / Cv <1.2. Amphoteric polymer flocculant. 2. The cationic monomer unit having an acryloyl group has a formula (1): (In the formula (1), R ¹ is a hydrogen atom, an alkyl group having 1 to 8 carbon atoms hydrocarbon group or a hydroxyalkyl group having 1 to 8 carbon atoms, R ² and R ³ are independently .X ^- Yin The amphoteric polymer flocculant for pulp or paper industry sludge according to claim 1, which is a monomer unit represented by the formula: 3. An anionic monomer unit represented by the formula (2): (In the formula (2), R ⁴ is a hydrogen atom or a methyl group.
Is a hydrogen atom, an ammonium ion, or an alkali metal ion. The amphoteric polymer flocculant for pulp or papermaking industrial sludge according to claim 1 or 2, which is a monomer unit represented by the formula: 4. The amphoteric polymer flocculant for pulp or paper industry sludge according to claim 1, wherein the other radically polymerizable monomer unit is an acrylamide monomer unit. 5. A method for dewatering pulp or paper industry sludge, comprising adding the amphoteric polymer flocculant according to claim 1 to pulp or paper industry sludge and dewatering. 6. Pulp or papermaking characterized by adding an inorganic flocculant to pulp or papermaking industrial sludge and then adding the amphoteric polymer flocculant according to claim 1 to dewater. Dewatering method for industrial sludge.