JP5170563B2 - Humic substance removing agent and method for removing humic substance contained in water - Google Patents

Description

The present invention relates to a humic substance removing agent and a method for removing humic substances contained in water from water, and more particularly, to a humic substance removing agent comprising a cationic polymer containing an amidine structure, and amidine containing water containing humic substances. The present invention relates to a method for removing humic substances, comprising adding a cationic polymer containing a structure to form a complex, and then separating the complex from water.

Since humic substances become a causative substance of trihalomethane and are contained as a COD component in waste water, it is necessary to remove the humic substances. In general, humic substances are adsorbed and removed by activated charcoal, or the decomposition products after chlorination are activated charcoal. However, humic substances reduce the adsorption performance of activated carbon and result in a large amount of activated carbon. There is a problem of needing. Also, removal by a flocculant is being studied. If the inorganic coagulant is used for coagulation precipitation, a large amount of coagulant is required, and a large amount of sludge is generated. When a conventional high molecular weight organic flocculant is used, there are problems that the generated floc is small and separation from the drainage is not easy. Although a method of using an inorganic flocculant and an organic flocculant in combination has been disclosed (Patent Document 1), there is a problem that handling is complicated, for example, it is necessary to mix both in advance.

Although a method of adding a cationic surfactant to humic substance-containing water and removing the humic substance has been disclosed (Patent Document 2), the aggregate formed is small only with the cationic surfactant, and polypropylene is used in the subsequent step. An operation such as adsorption to beads such as resin is required.
JP-A-6-182355 Japanese Patent No. 3639872

The subject of this invention is providing the method of removing the humic substance in water effectively.

As a method for solving the above-mentioned problem, a cationic polymer containing an amidine structure in the molecule is added to water containing humic substance, and a complex is formed between the humic substance and the cationic polymer. It has been found that this can be achieved by removing.

A cationic polymer having an amidine structure in the molecule is composed of an ionic interaction between the cationic group and the anionic group of the humic substance, as well as a ring structure derived from the amidine structure and a humic benzene. It is considered that a complex is formed by a synergistic effect with the interaction of the ring portion and can be effectively removed.

The cationic polymer having an amidine structure can be obtained by a usual method. For example, it can be obtained by hydrolyzing a copolymer of N-vinylformamide and acrylonitrile with hydrochloric acid or the like. Further, it can be obtained by subjecting a copolymer of acrylamide and acrylonitrile to a Hofmann reaction with sodium hypochlorite or the like.

A cationic polymer having an amidine structure obtained by hydrolyzing a copolymer of N-vinylformamide and acrylonitrile with hydrochloric acid or the like can be produced by a production method described in JP-A-5-192513. That is, in general, a copolymer of an ethylenically unsaturated monomer having a primary amino group or a substituted amino group capable of forming a primary amino group by a conversion reaction, and an nitrile of acrylonitrile or methacrylonitrile, It can be obtained by reacting a cyano group and a primary amino group in the copolymer to form an amidine.

Examples of the ethylenically unsaturated monomer include the general formula CH ₂ ═CR ² —NHCOR ³ (wherein R ² represents a hydrogen atom or a methyl group, and R ³ represents an alkyl group having 1 to 4 carbon atoms or a hydrogen atom). .) Are preferred. In the copolymer, a substituted amino group derived from such a compound is easily converted to a primary amino group by hydrolysis or alcoholysis. Furthermore, this primary amino group reacts with an adjacent cyano group to be amidined. Examples of the compound include N-vinylformamide (R ² = H, R ³ = H), N-vinylacetamide (R ² = H, R ³ = Me) and the like.

The polymerization molar ratio of these ethylenically unsaturated monomers and nitriles is usually 20:80 to 80:20, but if desired, a polymerization molar ratio outside this range, such as further ethylenically unsaturated monomers. It is also possible to employ a polymerization molar ratio with a large ratio. Generally, the higher the ratio of amidine units in the cationic polymer flocculant, the better the performance as the flocculant. Moreover, it is thought that the amine unit has also contributed favorably to the performance as a flocculant. Accordingly, the polymerization molar ratio of ethylenically unsaturated monomer and nitrile that gives a copolymer suitable as a flocculant is generally 20:80 to 80:20, particularly 40:60 to 60:40.

When the N-vinylamide compound represented by the above general formula is used as the ethylenically unsaturated monomer, the amidine reaction is performed by converting the substituted amino group of the copolymer into a primary amino group, and then forming the primary amino group. The cationic polymer flocculant according to the present invention can be produced by a two-step reaction in which an amidine structure is formed by reacting with an adjacent cyano group. Preferably, the copolymer is heated in water or an alcohol solution in the presence of a strong acid or a strong base to produce an amidine structure in one step. Even in this case, it is considered that a primary amino group is first generated as an intermediate structure.

Specific conditions for the reaction include, for example, 0.9 to 5.0 times, preferably 1.0 to 3.0 times equivalent of strong acid, preferably 1.0 to 3.0 times the substituted amino group of the copolymer. By adding hydrochloric acid and heating at a temperature of usually 80 to 150 ° C., preferably 90 to 120 ° C. for usually 0.5 to 20 hours, a cationized polymer having amidine units can be obtained. In general, the larger the equivalent ratio of strong acid to substituted amino group and the higher the reaction temperature, the more the amidation proceeds. In addition, in the case of amidine formation, water of usually 10% by weight or more, preferably 20% by weight or more is present in the reaction system with respect to the copolymer used for the reaction.

The flocculant composed of the cationic polymer according to the present invention is most typically prepared by copolymerizing N-vinylformamide and acrylonitrile in accordance with the above-described manner, and the resulting copolymer is usually subjected to water suspension. It is produced by heating in the presence of hydrochloric acid as a suspension to form amidine units from cyano groups adjacent to substituted amino groups. And the cationic polymer of various compositions can be manufactured by selecting the molar ratio of N-vinylformamide and acrylonitrile to be subjected to copolymerization, and the amidation conditions of the copolymer.

The content of the amidine structural unit of the cationic polymer having these amidine structures is 10 to 90 mol%, preferably 30 to 90 mol%. If the content of the amidine structural unit is less than these ranges, the ionic interaction between the cationic group and the anionic group of the humic substance, and the ring structure derived from the amidine structure and the benzene ring part of the humic substance Due to a synergistic effect with the interaction, complex formation is not sufficient and performance is degraded.

On the other hand, a method for producing a copolymer of acrylamide and acrylonitrile by amidating with a Hofmann reaction with sodium hypochlorite or the like is disclosed in Japanese Patent Application Laid-Open No. 2008-156542, and is performed as follows. That is, the copolymerization ratio of (meth) acrylamide and (meth) acrylonitrile is acrylamide 60 to 90 mol%, (meth) acrylonitrile 10 to 40 mol%, preferably 60 to 80 mol%, and (meth) acrylonitrile 20 -40 mol%. In addition, other copolymerizable monomers can be copolymerized as long as the polyamidine reaction is not affected. Furthermore, since the Hoffman reaction is carried out in a strongly alkaline region, the copolymer must be resistant to alkali hydrolysis. Examples of such monomers are ethylene, styrene, (meth) acrylic acid, itaconic acid or maleic acid. Therefore, the range of such a monomer is 0 to 10 mol%.

The copolymerization method before the Hoffman reaction can be synthesized by a known polymerization method such as an aqueous solution polymerization method, a water-in-oil emulsion polymerization method, a water-in-oil dispersion polymerization method, or a salt-water dispersion polymerization method. it can. Therefore, the polymerization concentration can be in the range of 5 to 60% by weight, preferably 20 to 50% by weight. Moreover, as reaction temperature, it can carry out in the range of 10-100 degreeC.

The weight average molecular weight of the polyacrylamide copolymer before the Hoffman reaction can be arbitrarily adjusted depending on the application, and is about 100,000 to 15 million, preferably 100,000 to 10 million. If so, there is no problem in manufacturing.

Next, the conditions for the Hoffman reaction will be described. Examples of hypohalous acid to be used include sodium hypochlorite, potassium hypochlorite, sodium hypobromite, potassium hypobromite, sodium hypoiodite, potassium hypoiodite and the like. Examples of the coexisting alkali include sodium hydroxide and potassium hydroxide. The addition amount of hypohalous acid is 10 mol% to 150 mol% with respect to the amide group, preferably 20 group% to 120 mol%. Further, the amount of alkali to be coexisted is 10 to 250 mol% with respect to the amide group. After the reaction, the solution pH is neutralized to a range of 0.5 to 6.0, preferably 0.5 to 4. This is a pH range in consideration of the amidation reaction in the next step.

The reaction temperature of the Hoffman reaction can be selected from the range of 0 to 50 ° C, but more preferably 0 to 30 ° C. Although the reaction time depends on the reaction temperature and the polymer concentration in the reaction solution, it cannot be generally stated. For example, when the polymer concentration is 10% by weight, the reaction time is within several tens of minutes at 5 ° C and within several minutes at 20 ° C. It is enough. Furthermore, the higher the polymer concentration, the shorter the reaction time. Next, after performing the Hoffman reaction under the above-described conditions, it is desirable to stop the reaction in order to suppress the progress of the side reaction. However, when used immediately after the reaction, it may not be necessary to stop the reaction. As a method for stopping the reaction, methods such as (1) adding a reducing agent, (2) cooling, and (3) lowering the pH of the solution by adding an acid can be used alone or in combination. (1) is a method in which the remaining hypohalite or the like is deactivated by reaction with a reducing agent. Specific examples of the reducing agent used include sodium sulfite, sodium thiosulfate, ethyl malonate, thioglycerol, triethylamine and the like. The amount of the reducing agent to be used is 0.005 to 0.15 times mol, preferably 0.01 to 0.10 times mol, of the hypohalite used in the normal reaction. (2) is a method of suppressing the progress of the reaction by cooling, and examples of the method include cooling with a heat exchanger or diluting with cold water. The temperature at that time is usually 50 ° C. or lower, preferably 45 ° C. or lower, more preferably 40 ° C. or lower. (3) is a method of stopping the Hoffman reaction by lowering the pH of a reaction completion solution, which usually shows pH 12-13, using an acid, and at the same time suppressing the progress of hydrolysis. The pH at that time may be not more than neutral and may be in the range of pH 0.5 to 6, but is preferably pH 0.5 to 4 in consideration of the subsequent amidation reaction. Examples of the acid used for pH adjustment include mineral acids such as hydrochloric acid, sulfuric acid, phosphoric acid and nitric acid, and organic acids such as formic acid, acetic acid and citric acid. The most preferred acid is hydrochloric acid.

The content of the primary amino group in the polymer after the Hoffman reaction is 5 to 60 mol%, preferably 10 to 50 mol%. If it is less than 5 mol%, it is difficult to proceed with the amidation reaction. Further, if it is attempted to introduce a primary amino group higher than 50 mol%, the copolymerization ratio of (meth) acrylamide must be increased, and as a result, the copolymerization ratio of (meth) acrylonitrile is lowered.

After the Hoffmann reaction, the reaction solution is acidified to carry out an amidation reaction. As this condition, the amidine reaction can be carried out by keeping the reaction product at a temperature of 20 to 100 ° C., preferably 30 to 80 ° C., pH 0.5 to 6, preferably pH 0.5 to 4. The acid used is preferably a strong acid such as hydrochloric acid, nitric acid or sulfamic acid, and most preferably hydrochloric acid. As specific conditions, for example, 0.7 to 5.0 times, preferably 1.0 to 2.5 times equivalent of strong acid is added to the substituted amino group in the copolymer, and usually 20 to 100 ° C. The cationized polymer having an amidine unit can be obtained by heating at a temperature of preferably 30 to 90 ° C., usually for 0.5 to 20 hours. This is because the primary amino group, which is a side chain functional group, reacts with a cyano group to become an imino group and amidine. In general, the larger the equivalent ratio of strong acid to substituted amino group, and the higher the reaction temperature, the more the amidine formation proceeds. In addition, in the case of amidine formation, it is preferable that 10% by weight or more, preferably 20% by weight or more of water is usually present in the reaction system with respect to the copolymer used for the reaction.

The content of the amidine structural unit of the cationic polymer having these amidine structures is the same as in the case of N-vinylformamide / acrylonitrile copolymer, but is 20 to 80 mol%, preferably 30 to 80 mol%. If the content of the amidine structural unit is less than these ranges, the ionic interaction between the cationic group and the anionic group of the humic substance, and the ring structure derived from the amidine structure and the benzene ring part of the humic substance Due to a synergistic effect with the interaction, complex formation is not sufficient and performance is degraded.

In the humic substance removing method of the present invention, a method obtained by hydrolyzing a copolymer of N-vinylformamide and acrylonitrile with hydrochloric acid or the like, or a copolymer of acrylamide and acrylonitrile with sodium hypochlorite or the like is used. The molecular weight of the cationic polymer having an amidine structure is preferably 10,000 to 5,000,000 in terms of the weight average molecular weight in both the method for producing amidine after the reaction. If it exceeds 5 million, the time required for membrane separation becomes long, and it is not suitable for actual use. It is presumed that the complex formed by the high molecular weight cationic polymer and the humic substance has a structure that easily causes clogging on the membrane surface (easy to foul). When it is less than 10,000, formation of a complex with humic substances and insolubilization are insufficient.

The addition amount of the cationic polymer having an amidine structure is preferably 0.1 to 10 times by weight with respect to the mass of humin in water. When the amount is smaller or larger than this, complex formation is insufficient and the removal rate is lowered.

The complex formed by the humic substance and the polymer of the present invention can be separated by sedimentation separation, flotation separation, membrane separation or the like. Membrane separation is particularly preferred in that reliable removal is possible. The complex formed by the cationic polymer and the humic substance can be removed with a filter having a pore size of about 1 micrometer. Therefore, a microfiltration membrane, an ultrafiltration membrane, a reverse osmosis membrane, or the like can be used as the membrane.

In order to further promote the complex formation between the humic substance and the polymer of the present invention, other auxiliary agents can be used in combination. Examples of such auxiliary agents include organic polymer flocculants such as general cationic polymers, anionic polymers, and nonionic polymers, or inorganic flocculants such as ferric chloride.

EXAMPLES The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

(Production Example 1) In a 500 ml four-necked flask equipped with a stirrer, a nitrogen inlet tube, and a condenser tube, 60.0 g of a mixture of 50 mol% of acrylonitrile and 50 mol% of N-vinylformamide and 240.0 g of demineralized water Put. The temperature was raised to 30 ° C. with stirring in a nitrogen gas stream, and 0.3 g of a 10% 2,2′-azobis-2-amidinopropane dihydrochloride aqueous solution was added. After stirring and holding at 40 ° C. for 4 hours, the temperature was raised to 50 ° C. and further maintained for 3 hours to obtain a suspension in which the polymer was precipitated in water. 20 g of water was added to the suspension, and then 1.25 equivalents of concentrated hydrochloric acid with respect to the formyl group in the polymer was added and kept at 100 ° C. for 4 hours with stirring to amidinate the polymer. . The obtained polymer solution was added to acetone and precipitated to obtain Sample-1. The obtained sample was analyzed for amidation rate by ¹³ C-NMR spectrum ( ¹³ C-magnetic resonance spectrum). As a result, the amidation rate was 83 mol%, primary amino group 8 mol%, and N-vinylformamide group. They were 5 mol% and cyano group 4 mol%. The molecular weight determined by the light scattering method was about 3 million.

(Production Example 2) 60.0 g of a mixture composed of 40 mol% of acrylonitrile and 60 mol% of acrylamide and 240.0 g of demineralized water were placed in a 500 ml four-necked flask equipped with a stirrer, a nitrogen introduction tube, and a cooling tube. . After raising the temperature to 30 ° C. with stirring in a nitrogen gas stream, 0.3 g of a 1% 2,2′-azobis-2-amidinopropane dihydrochloride aqueous solution was added. After stirring and maintaining at 30 ° C. for 4 hours, the temperature was raised to 50 ° C. and further maintained for 3 hours to obtain a suspension in which a polymer was precipitated in water. Next, the temperature of the reaction product was cooled to 10 ° C., sodium hypochlorite was added at 120 mol% with respect to acrylamide, and sodium hydroxide was added at 100 mol% with respect to acrylamide, and Hoffman reaction was carried out. After the reaction, 0.08 mol% of sodium sulfite is added to sodium hypochlorite to treat the unreacted substance, and further, 120 mol% of hydrochloric acid is added to sodium hydroxide to neutralize the alkali and make it acidic. The polymer was amidined by holding at 85 ° C. for 4 hours. The obtained polymer solution was added to acetone to cause precipitation, and this was vacuum-dried to obtain Sample-2. The amidation rate of Sample-2 was 57 mol%, primary amino group 10 mol%, acid amide group 18 mol%, cyano group 10 mol%, and carboxyl group 5 mol%. The molecular weight determined by the light scattering method was about 1.15 million.

(Comparative Production Example 1) In a four-necked 500 ml separable flask equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen introduction tube, 225.0 g of deionized water and 75.0 g of 80% methacryloyloxyethyltrimethylammonium chloride aqueous solution were added. In addition, a uniform mixed solution was obtained. Thereafter, nitrogen is introduced from the nitrogen introduction tube while stirring to remove dissolved oxygen. During this time, the internal temperature is adjusted to 33 to 35 ° C. using a constant temperature water bath. 30 minutes after the introduction of nitrogen, 0.06 g of 2,2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride was added to initiate polymerization. Polymerization was continued for 7 hours to complete the reaction. This is designated as comparative sample-1. The molecular weight by the light scattering method was about 900,000.

(Comparative Production Example 2) 225.0 g of deionized water and 75.0 g of 80% acryloyloxyethyltrimethylammonium chloride aqueous solution were added to a four-necked 500 ml separable flask equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen inlet tube. In addition, a uniform mixed solution was obtained. Thereafter, nitrogen is introduced from the nitrogen introduction tube while stirring to remove dissolved oxygen. During this time, the internal temperature is adjusted to 33 to 35 ° C. using a constant temperature water bath. 30 minutes after the introduction of nitrogen, 0.06 g of 2,2′-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride was added to initiate polymerization. Polymerization was continued for 7 hours to complete the reaction. This is designated as Comparative Sample-2. The average molecular weight by the light scattering method was about 1 million.

After mixing and dissolving 0.002 g of humic acid (manufactured by Wako Pure Chemical Industries, Ltd.), 0.014 g of 1N sodium hydroxide and 100 ml of demineralized water, the insoluble part was removed with No2 filter paper, and further diluted to 2000 ml with demineralized water, and 1 ppm humic acid An aqueous solution was obtained. An amidinized Hoffman reaction product of acrylamide / acrylonitrile copolymer as a polymer having an amidine structure in the molecule (sample-2, molecular weight 1.15 million) , comparative sample-1 of comparative production example 1 (molecular weight 900,000), Comparative sample 2 of comparative production example 2 (molecular weight 1 million), comparative sample 3 (commercially available cationic flocculant; acrylamide / acryloyloxyethyltrimethylammonium chloride copolymer, weight average molecular weight 5 million) each 0.1 weight % Was dissolved. The polymer aqueous solution dissolved in 0.1% was added to 50 ml of the humic acid aqueous solution so as to have a predetermined concentration with respect to the humic acid aqueous solution, followed by stirring for 5 minutes. Thereafter, the mixture was filtered through GS-25 (manufactured by Toyo Roshi Kaisha, Ltd.), and the absorbance of the filtrate at a wavelength of 254 nm was measured. The removal rate was determined from this value and the absorbance of the filtrate filtered through GS-25 without adding a polymer to the humic acid aqueous solution. The results are shown in Table 1. The polymer having an amidine structure showed a good removal rate.

( Table 1 )

Claims (4)

A cationic polymer containing an amidine structure produced by carrying out a Hoffman reaction on a copolymer of (meth) acrylamide and (meth) acrylonitrile followed by an amidination reaction. The amidine structural unit of the cationic polymer is 57-80. A humic substance-removing agent characterized by being in mol%. The humic substance-removing agent according to claim 1 , wherein the molecular weight of the cationic polymer containing an amidine structure is 10,000 to 5,000,000 as a weight average molecular weight. A cationic polymer containing an amidine structure produced by carrying out a Hoffman reaction of a copolymer of (meth) acrylamide and (meth) acrylonitrile in water containing humic substance, followed by an amidation reaction, and the cationic polymer A method for removing humic substances, comprising adding a cationic polymer having an amidine structural unit of 57 to 80 mol% to form a complex, and then separating the complex from water. The method for removing humic substances according to claim 3 , wherein the step of separating the complex is a separation step using a membrane.