JP2014128752A - Organic matter desalination method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiency desalting an organic matter in an electrodialysis vessel.SOLUTION: An organic matter desalination method is provided in which an organic matter containing inorganic salts is desalinated by desalinating the organic matter in an electrodialysis vessel. An electrodialysis vessel 3 is an electrodialysis vessel which is constructed in such a manner that anion exchange membranes 5 and cation exchange membranes 6 are alternately arranged between electrodes 4, 7. The cation exchange membrane 6 contains polyvinyl alcohol copolymer having anionic polymer segment having anionic group and vinyl alcohol polymer segment. As the cation exchange membrane 6, a cation exchange membrane is used which has a microphase separation structure in which domain size (X) is in a range 0 nm<X≤150 nm.

Description

  The present invention relates to a method for desalting organic substances in an electrodialysis tank.

  In general, in the process of synthesizing organic substances in the fields of food, pharmaceuticals, agricultural chemicals, etc., salts are often produced as a by-product. In addition, organic substances such as sugar solution and pulp extract also contain a considerable amount of salt (ash). As means for separating salts contained in such organic substances, for example, crystallization separation methods and methods using ion exchange resins or ion exchange membranes have been proposed. Among these, the method using an ion exchange membrane is carried out in an electrodialysis tank in which a cation exchange membrane and an anion exchange membrane are alternately arranged between an anion and a positive electrode to constitute a desalination chamber and a concentration chamber. Is done.

  In an electrodialysis tank, a direct-current voltage is applied between both electrodes while a solution of an organic substance containing salts is circulated in a desalting chamber and a liquid containing an electrolyte (such as dilute saline) is circulated in a concentration chamber. As a result, salts (ash) present in the organic solution permeate through the ion exchange membrane as ions and move to the concentration side to be desalted.

  In Patent Document 1, a composite cation exchange membrane having an anion exchange layer on at least one surface and an anion exchange membrane having an anion exchange group bonded with one or more alkyl groups having 4 to 30 carbon atoms are interposed between the electrodes. A method for desalting organic substances is described in which an organic substance containing salts is supplied to the desalting chamber and electrodialyzed using electrodialysis tanks arranged alternately.

Further, Patent Document 2 discloses that, in an electrodialysis tank constituted by alternately arranging anion exchange membranes and cation exchange membranes between electrodes, an organic substance solution containing inorganic salts is mainly desalted by electrodialysis. An anion exchange membrane produced using vinylpyridines and / or haloalkylstyrenes as monomers and bisvinylphenylalkylene as a cross-linking agent, and having a diffusion constant of 1 × 10 4 for a 4N saline solution at 25 ° C. ^A method for desalting organic substances using an anion exchange membrane of ^{−5 to} 5 × 10 ⁻⁵ centimeters / second is described.

JP-A-63-77504 Japanese Unexamined Patent Publication No. Sho 63-116708

  A method for desalting salts contained in organic substances in such an ion exchange membrane electrodialysis tank is effective. However, in the desalting method for organic substances described in Patent Documents 1 and 2, the components of the organic substances may be altered. There are problems such as an increase in the number of membrane cleanings. Further, in any case, the technical disclosure is substantially related to an anion exchange membrane, and since the dirt substance is related to an anionic surfactant, a method for solving the dirt substance that causes a problem in the cation exchange membrane. Is not disclosed.

An object of the present invention is to provide a method for desalinating an organic substance that not only can efficiently desalinate salts from the organic substance but also can suppress leakage of the organic substance.
Another object of the present invention is to provide a method for desalinating organic matter that can prevent an increase in cell voltage due to contamination of the membrane with organic matter in addition to the above-mentioned purpose.

  As a result of intensive studies to solve the above problems, the present inventors conducted demineralization of organic substances using a specific cation exchange membrane in an ion exchange membrane electrodialysis tank. It has been found that by using a microphase separation structure that is much smaller than conventional ones, not only can salts be efficiently desalted from organic substances, but also leakage of organic substances can be suppressed. The inventors have also found out that the rise of the cell voltage can be prevented by contamination of the water and arrived at the present invention.

The first configuration of the present invention is a method of desalting an organic solution containing inorganic salts in an electrodialysis tank, and desalting the organic substance. The electrodialysis tank includes an anion exchange membrane and a cation exchange between electrodes. The cation exchange membrane comprises a polyvinyl alcohol-based copolymer having an anionic polymer segment having an anionic group and a vinyl alcohol polymer segment. , A method for desalting an organic substance, wherein a cation exchange membrane having a microphase separation structure having a domain size (X) in a range of 0 nm <X ≦ 150 nm is used.
In the present invention, microphase separation means that in a copolymer containing two or more types of chain polymers, the same kind of polymer segments aggregate together and a repulsive interaction acts between different polymer segments. A periodic structure obtained by forming a periodic self-organized structure from nanoscale to submicron scale. In the present invention, the domain means a mass formed by aggregating polymer segments of the same kind in one or a plurality of polymer chains.

  Furthermore, the polyvinyl alcohol copolymer may contain a vinyl alcohol polymer that does not contain an anionic group.

  It is preferable that a crosslinked structure is introduced into the vinyl alcohol polymer.

The polyvinyl alcohol copolymer is preferably an anionic block copolymer having a vinyl alcohol polymer block and an anionic polymer block having an anionic group.
The polyvinyl alcohol-based copolymer is preferably an anionic graft copolymer having a vinyl alcohol polymer block and an anionic polymer block having an anionic group.

The ion exchange capacity of the cation exchange membrane is preferably 0.30 meq / g or more, and the membrane resistance of the cation exchange membrane is preferably 10 Ωcm ² or less.

  The polyvinyl alcohol copolymer used for forming a cation exchange membrane contains salts, and the ratio of the weight (C) of the salt to the weight (P) of the polyvinyl alcohol copolymer [(C ) / (P)] may be a polyvinyl alcohol copolymer adjusted so as to be 4.5 / 95.5 or less.

  The cation exchange membrane is formed by heat-treating a film obtained from a polyvinyl alcohol copolymer solution containing salts at a temperature of 100 ° C. or higher, and then in water, alcohol or a mixed solvent thereof. It is preferable to manufacture by carrying out a crosslinking treatment with a dialdehyde compound under a condition and then washing with water.

  The second configuration of the present invention is a method for producing a desalted organic substance by desalting an organic substance solution containing inorganic salts in an electrodialysis tank, wherein the electrodialysis tank includes an anion exchange membrane and an electrode. An electrodialysis tank constituted by alternately arranging cation exchange membranes, wherein the cation exchange membrane comprises an anionic polymer segment having an anionic group and a polyvinyl alcohol copolymer having a vinyl alcohol polymer segment. And a domain size (X) having a microphase-separated structure in a range of 0 nm <X ≦ 150 nm.

  The third configuration of the present invention is a desalted organic substance produced by the production method.

In the desalting method of the present invention, a specific cation exchange membrane in an electrodialysis tank, that is, a cation exchange membrane composed of a polyvinyl alcohol copolymer having an anionic polymer segment and a vinyl alcohol polymer segment. In addition, since a cation exchange membrane having a very small microphase separation structure can be used, an organic matter containing salts is supplied to the electrodialysis tank, and the organic matter can be prevented from leaking while suppressing leakage of the organic matter. Salts can be removed efficiently.
Moreover, in this invention, salt can be efficiently removed from organic substance, preventing the raise of a tank voltage by the contamination of the film | membrane with organic substance.

It is a TEM photograph of the ion exchange membrane used in the desalting method of Example 5 which is an example of the ion exchange membrane used in the desalting method of this invention. It is a TEM photograph of the ion exchange membrane used in the desalting method of Example 7 which is an example of the ion exchange membrane used in the desalting method of this invention. 4 is a TEM photograph of an ion exchange membrane used in the desalting method of Comparative Example 1. 4 is a TEM photograph of an ion exchange membrane used in the desalting method of Comparative Example 2. 4 is a TEM photograph of an on-exchange membrane used in the desalting method of Comparative Example 3. It is the schematic for demonstrating the desalting method of the organic substance which is one Embodiment of this invention. It is explanatory drawing sectional drawing of the apparatus used for the measurement of the membrane resistance of the cation exchange membrane used in the desalting method of this invention.

  The present invention is a method for desalting an organic solution containing inorganic salts in an electrodialysis tank, and desalting the organic substance, wherein the electrodialysis tank has an anion exchange membrane and a cation exchange membrane alternately disposed between electrodes. The cation exchange membrane comprises a polyvinyl alcohol copolymer having an anionic polymer segment having an anionic group and a vinyl alcohol polymer segment, and having a domain size ( X) is characterized by using a cation exchange membrane having a microphase separation structure in a range of 0 nm <X ≦ 150 nm.

(Cation exchange membrane)
The cation exchange membrane used in the present invention is composed of an anionic polymer segment having an anionic group and a polyvinyl alcohol copolymer having a vinyl alcohol polymer segment. Usually, an anionic polymer segment and a vinyl alcohol polymer segment are bonded by a covalent bond to constitute a polyvinyl alcohol copolymer. In the present invention, the polymer segment means a polymer chain containing the same repeating unit in which two or more of the same monomer units are linked, and is a polymer block in a block copolymer, a trunk chain or a branch in a graft polymer. It is used as a term encompassing polymer blocks corresponding to chains. In the anionic polymer segment having an anionic group, the anionic group may be contained at the end of the polymer, so that the unit having the anionic group may not be a repeated unit.

  As described above, the cation exchange membrane used in the present invention is composed of an anionic polymer segment having an anionic group and a polyvinyl alcohol copolymer having a vinyl alcohol polymer segment. In addition to this copolymer, in addition to an anionic polymer segment, a polyvinyl alcohol polymer not having an anionic group, an anionic polymer not bound to a vinyl alcohol polymer, It may be included to the extent that it does not affect the phase separation structure.

  The cation exchange membrane used in the present invention is formed by reducing the content of salts contained in the polyvinyl alcohol copolymer, so that the polyvinyl alcohol copolymer constituting the membrane has a microphase separation structure. The present inventors have found that the domain size can be reduced to 150 nm or less. The cation exchange membrane used in the present invention is usually put to practical use after the vinyl alcohol polymer segment is cross-linked, but the domain size (X) is specified in the range of 0 nm <X ≦ 150 nm. In addition, a cation exchange membrane useful for electrodialysis can be obtained which has no change in ion path structure, a stable membrane structure, and excellent electrical characteristics such as charge density and membrane resistance. The domain size (X) becomes smaller as the salt content is lowered, and can be set to 0 nm <X ≦ 130 nm, and further 0 nm <X ≦ 100 nm.

  Since the cation exchange membrane used in the present invention is composed of the polyvinyl alcohol copolymer having the vinyl alcohol polymer segment as described above, it is a hydrophilic ion exchange membrane. This has the advantage that contamination due to adhesion of organic pollutants in the liquid to be treated can be suppressed. Here, that the constituent polymer is hydrophilic means that the polymer has hydrophilicity in a structure having no functional group (anionic group) necessary for the anionic polymer. As described above, since the constituent polymer is a hydrophilic polymer, a cation exchange membrane having a high degree of hydrophilicity is obtained, and organic contaminants in the liquid to be treated adhere to the cation exchange membrane and the performance of the membrane. The problem of lowering can be reduced. Moreover, it has the advantage that film | membrane intensity | strength becomes high.

(Anionic polymer)
The anionic polymer constituting the anionic polymer segment used in the present invention is a polymer containing an anionic group in the molecular chain. The anionic group may be contained in any of the main chain, side chain, and terminal. Examples of the anionic group include a sulfonate group, a carboxylate group, and a phosphonate group. In addition, functional groups that can be converted into sulfonate groups, carboxylate groups, and phosphonate groups at least partially in water, such as sulfonic acid groups, carboxyl groups, and phosphonic acid groups are also included in the anionic groups. Of these, a sulfonate group is preferred because of its large ion dissociation constant. The anionic polymer may contain only one type of anionic group or may contain a plurality of types of anionic groups. Moreover, the counter cation of an anionic group is not specifically limited, A hydrogen ion, an alkali metal ion, etc. are illustrated. Of these, alkali metal ions are preferred from the viewpoint of less equipment corrosion problems. The anionic polymer may contain only one type of counter cation or may contain a plurality of types of counter cation.

  The anionic polymer used in the present invention may be a polymer composed only of a structural unit containing the anionic group, or may be a polymer further containing a structural unit not containing the anionic group. Good. Moreover, it is preferable that these polymers have a crosslinking property. An anionic polymer may consist of only one type of polymer, or may include a plurality of types of anionic polymers. Moreover, you may be a mixture of these anionic polymers and another polymer. Here, the polymer other than the anionic polymer is preferably not a cationic polymer.

  As an anionic polymer, what has the structural unit of the following general formula (1) and (2) is illustrated.

[Wherein R ⁵ represents a hydrogen atom or a methyl group. G is _{-SO 3 H, -SO 3 -M +} , - PO 3 H, -PO 3 -M +, - represents a CO ₂ H or _-CO 2 -M +. M + represents an ammonium ion or an alkali metal ion. ]

  Examples of the anionic polymer containing the structural unit represented by the general formula (1) include 2-acrylamido-2-methylpropanesulfonic acid homopolymer or copolymer.

[Wherein R ⁵ represents a hydrogen atom or a methyl group, and T represents a phenylene group or a naphthylene group in which the hydrogen atom may be substituted with a methyl group. G is synonymous with the general formula (1). ]

  Examples of the anionic polymer containing the structural unit represented by the general formula (2) include homopolymers or copolymers of p-styrene sulfonate such as sodium p-styrene sulfonate.

  Examples of the anionic polymer include homopolymers or copolymers of sulfonic acids such as vinyl sulfonic acid and (meth) allyl sulfonic acid or salts thereof, fumaric acid, maleic acid, itaconic acid, maleic anhydride, itaconic anhydride. Examples include dicarboxylic acids such as acids, homopolymers or copolymers of derivatives or salts thereof.

  In the general formula (1) or (2), G is preferably a sulfonate group, a sulfonic acid group, a phosphonate group, or a phosphonic acid group that gives a higher charge density. In the general formulas (1) and (2), examples of the alkali metal ion represented by M + include sodium ion, potassium ion, and lithium ion.

(Vinyl alcohol polymer segment)
In the present invention, as the polyvinyl alcohol constituting the vinyl alcohol polymer segment, those obtained by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester monomer and using the vinyl ester unit as a vinyl alcohol unit are used. Examples of the vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valelate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatate, and the like. Of these, vinyl acetate is preferably used.
When the vinyl ester monomer is copolymerized, a monomer that can be copolymerized, if necessary, within a range that does not impair the effects of the invention (preferably 50 mol% or less, more preferably 30 mol% or less). It may be copolymerized.
Examples of the monomer copolymerizable with the vinyl ester monomer include olefins having 3 to 30 carbon atoms such as ethylene, propylene, 1-butene and isobutene; acrylic acid and salts thereof; methyl acrylate and acrylic acid. Acrylic acid such as ethyl, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, octadecyl acrylate Esters; methacrylic acid and salts thereof; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, methacrylic acid 2 -Ethylhexyl, dodecyl methacrylate, Methacrylic acid esters such as octadecyl tacrylate; acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and its salt, acrylamidopropyldimethylamine and its salt, N Acrylamide derivatives such as methylolacrylamide and its derivatives; methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and its salts, methacrylamidepropyldimethylamine and its salts, N-methylolmethacrylamide and Methacrylamide derivatives such as derivatives thereof; N such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone Vinyl amides; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; acrylonitrile, methacrylonitrile, etc. Nitriles; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid and its salts or esters; itaconic acid and its salts or its Examples include esters; vinylsilyl compounds such as vinyltrimethoxysilane; and isopropenyl acetate.

  The structural units other than the anionic group in the polyvinyl alcohol-based copolymer can be independently selected, but the copolymer is preferably composed of monomers having the same structural unit. . Thereby, since the affinity between domains becomes high, the mechanical strength of a cation exchange membrane increases. The polyvinyl alcohol copolymer preferably has 50 mol% or more of the same structural unit, more preferably 70 mol% or more.

  Moreover, since it is desirable that it is hydrophilic, it is particularly preferable that the same structural unit is a vinyl alcohol unit. By having a vinyl alcohol unit, the domains can be chemically crosslinked with a crosslinking agent such as glutaraldehyde, so that the mechanical strength of the cation exchange membrane can be further increased.

  As described above, in the present invention, the polyvinyl alcohol copolymer having an anionic polymer segment and a vinyl alcohol polymer segment has a structure in which the anionic polymer segment and the vinyl alcohol polymer segment are bonded. preferable.

  The cation exchange membrane used in the present invention is composed of a polyvinyl alcohol copolymer having a vinyl alcohol polymer segment in an anionic polymer segment as described above. It may be composed of a mixture containing a vinyl alcohol polymer not containing a functional group.

(Block or graft copolymer)
In the present invention, the polyvinyl alcohol copolymer preferably has a block copolymer or graft copolymer in which the anionic polymer segment and the vinyl alcohol polymer segment. Among these, a block copolymer is more preferably used. By doing this, the vinyl alcohol polymer block responsible for the function of improving the strength of the entire cation exchange membrane, suppressing the degree of swelling of the membrane, and maintaining the shape, and the amount of anionic group responsible for the permeation of the cation The anionic polymer block obtained by polymerizing the polymer can share the role, and both the ion permeation function and the dimensional stability of the cation exchange membrane can be achieved. The structural unit of the polymer block obtained by polymerizing the anionic group monomer is not particularly limited, and examples thereof include those represented by the general formulas (1) to (2). Among these, from the viewpoint of easy availability, as the monomer constituting the anionic polymer, p-styrene sulfonate or 2-acrylamido-2-methylpropane sulfonate is used. Anionic block copolymer containing an anionic polymer block obtained by polymerizing an acid salt and a vinyl alcohol polymer block, or an anionic polymer obtained by polymerizing 2-acrylamido-2-methylpropanesulfonate A block copolymer comprising a block and a vinyl alcohol polymer block is preferably used.
The graft copolymer includes an anionic polymer segment as a backbone and a vinyl alcohol polymer segment as a branched chain, and a vinyl alcohol polymer segment as a backbone and an anionic polymer segment as a branch. Sometimes it is a chain. Although it is not particularly limited in the present invention, a graft copolymer having vinyl alcohol as a main chain and an anionic polymer segment as a branched chain is preferable from the viewpoint of easily obtaining strength properties. A known method is applied as the graft copolymerization method.

(Method for producing block copolymer)
The method for producing a block copolymer containing an anionic polymer block obtained by polymerizing an anionic monomer used in the present invention and a vinyl alcohol polymer block is mainly classified into the following two methods. . (1) a method in which a desired block copolymer is produced and then an anionic group is bonded to a specific block; and (2) at least one anionic group monomer is polymerized to form a desired block copolymer. It is a method for producing a polymer. Among these, for (1), one or more types of monomers are block copolymerized in the presence of polyvinyl alcohol having a mercapto group at the terminal, and then one or more types of polymer in the block copolymer are copolymerized. For the method of introducing an ionic group into the coalescing component, (2), a block copolymer is produced by radical polymerization of at least one anionic group monomer in the presence of polyvinyl alcohol having a mercapto group at the terminal. However, these methods are preferable because of industrial ease. In particular, the type and amount of constituent monomers in each block of an anionic polymer block obtained by polymerizing a vinyl alcohol block and an anionic group monomer in the block copolymer can be easily controlled. A method of producing a block copolymer by radical polymerization of at least one anionic group monomer in the presence of a group-containing polyvinyl alcohol is preferred. The block copolymer containing a polymer block obtained by polymerizing the anionic group monomer thus obtained and a vinyl alcohol polymer block contains unreacted polyvinyl alcohol having a mercapto group at the terminal. It doesn't matter.

  The vinyl alcohol polymer having a mercapto group at the end used for the production of these block copolymers can be obtained, for example, by the method described in JP-A-59-187003. That is, a method of saponifying a vinyl ester polymer obtained by radical polymerization of a vinyl ester monomer such as vinyl acetate in the presence of thiolic acid can be mentioned. A method for obtaining a block copolymer using a polyvinyl alcohol having a mercapto group at the terminal thus obtained and an anionic group monomer is described in, for example, JP-A-59-189113. Method. That is, a block copolymer can be obtained by radical polymerization of an anionic group monomer in the presence of polyvinyl alcohol having a mercapto group at the terminal. This radical polymerization can be carried out by a known method such as bulk polymerization, solution polymerization, pearl polymerization, emulsion polymerization, etc., but mainly contains a solvent capable of dissolving polyvinyl alcohol containing a mercapto group at the terminal, such as water or dimethyl sulfoxide. It is preferable to carry out in the medium. As the polymerization process, any of a batch method, a semi-batch method, and a continuous method can be employed.

  The above radical polymerization may be carried out using a conventional radical polymerization initiator such as 2,2′-azobisisobutyronitrile, benzoyl peroxide, lauroyl peroxide, diisopropyl peroxycarbonate, 4,4′-azobis- (4-cyano Pentanoic sodium), 4,4'-azobis- (4-cyanopentanoic ammonium), 4,4'-azobis- (4-cyanopentanoic potassium), 4,4'-azobis- (4- Cyanopentanoic lithium), 2,2'-azobis {2-methyl-N- [1,1'-bis (hydroxymethyl) -2-hydroxyethyl] propionamide}, potassium persulfate, ammonium persulfate, etc. However, in the case of polymerization in an aqueous system, vinyl alcohol can be used. Start of redox with mercapto group at the end of polymer and oxidant such as potassium bromate, potassium persulfate, ammonium persulfate, hydrogen peroxide, 2'-azobis [2-methyl-N (2-hydroxyethyl) propionamide] Etc. are also possible. In particular, those that do not generate ionic residues after decomposition are particularly preferred.

  Alkaline substances are usually used as catalysts for saponification reactions of vinyl ester polymers. Examples thereof include alkali metal hydroxides such as potassium hydroxide and sodium hydroxide, and alkali metal alkoxides such as sodium methoxide. It is done. The saponification catalyst may be added all at once in the early stage of the saponification reaction, or a part thereof may be added in the early stage of the saponification reaction, and the rest may be added and added during the saponification reaction. Examples of the solvent used for the saponification reaction include methanol, methyl acetate, dimethyl sulfoxide, diethyl sulfoxide, dimethylformamide and the like. Of these solvents, methanol is preferred. The saponification reaction can be carried out by either a batch method or a continuous method. After completion of the saponification reaction, the remaining saponification catalyst may be neutralized as necessary, and usable neutralizing agents include organic acids such as acetic acid and lactic acid, and ester compounds such as methyl acetate. .

(Degree of saponification of vinyl alcohol polymer)
Although the saponification degree of a vinyl alcohol polymer is not specifically limited, It is preferable that it is 40-99.9 mol%. If the degree of saponification is less than 40 mol%, the crystallinity is lowered and the strength of the cation exchange membrane may be insufficient. The saponification degree is more preferably 60 mol% or more, and further preferably 80 mol% or more. Usually, the saponification degree is 99.9 mol% or less. At this time, the saponification degree when the polyvinyl alcohol is a mixture of plural kinds of polyvinyl alcohols refers to the average saponification degree of the whole mixture. The saponification degree of polyvinyl alcohol is a value measured according to JIS K6726.

(Polyvinyl alcohol polymerization degree)
The viscosity average degree of polymerization of the polyvinyl alcohol constituting the vinyl alcohol polymer segment (hereinafter sometimes simply referred to as the degree of polymerization) is not particularly limited, but is preferably 50 to 10,000. When the degree of polymerization is less than 50, there is a possibility that the cation exchange membrane cannot maintain sufficient strength in practical use. More preferably, the degree of polymerization is 100 or more. If the degree of polymerization exceeds 10,000, the viscosity of the aqueous polymer solution is too high, making it difficult to apply, and possibly causing defects in the resulting film. The degree of polymerization is more preferably 8000 or less. At this time, the polymerization degree in the case where the polyvinyl alcohol is a mixture of plural kinds of polyvinyl alcohols means an average polymerization degree as the whole mixture. In addition, the viscosity average polymerization degree of polyvinyl alcohol is a value measured according to JIS K6726. The polymerization degree of polyvinyl alcohol containing no ionic group used in the present invention is also preferably within the above range.

(Content of anionic group monomer unit)
The content of the anionic group monomer unit in the polyvinyl alcohol copolymer constituting the cation exchange membrane is not particularly limited, but the content of the anionic group monomer unit of the copolymer, that is, the above The ratio of the number of anionic group monomer units to the total number of monomer units in the copolymer is preferably 0.1 mol% or more. When the content of the anionic group monomer unit is less than 0.1 mol%, the effective charge density in the cation exchange membrane is lowered, and the electrolyte permselectivity may be lowered. The content of the anionic group monomer unit is more preferably 0.5 mol% or more, and further preferably 1 mol% or more. Moreover, it is preferable that content of an anionic group monomer unit is 50 mol% or less. When the content of the anionic group monomer unit exceeds 50 mol%, the degree of swelling of the cation exchange membrane increases, the effective charge density in the cation exchange membrane decreases, and the electrolyte permselectivity may decrease. There is. The content of the anionic group monomer unit is more preferably 30 mol% or less, and further preferably 20 mol% or less. When the polyvinyl alcohol copolymer is a mixture of a polymer containing an anionic group and a polymer not containing an anionic group, or a mixture of a plurality of polymers containing an anionic group The content of anionic group monomer units refers to the ratio of the number of anionic group monomer units to the total number of monomer units in the mixture.

(Method for producing cation exchange membrane)
The cation exchange membrane used in the present invention is characterized by a vinyl alcohol polymer segment and a polyvinyl alcohol copolymer (preferably a block copolymer) comprising an anionic polymer segment having an anionic group as constituent components. The main component is a polymer), the amount of salts in the copolymer is reduced, and the phase separation domain size is reduced by forming a film. The salts referred to herein have an anionic group that constitutes an anionic polymer segment having an anionic group, such as sulfate and acetate which are impurities contained in the polyvinyl alcohol constituting the vinyl alcohol polymer segment. Examples thereof include metal salts such as bromide salts, chloride salts, nitrates, and phosphates contained as impurities in the monomer. These salts are inevitably mixed as impurities in the polyvinyl alcohol copolymer, and the present inventors have mixed these impurities into the anionic heavy polymer in the polyvinyl alcohol copolymer at the time of film formation. It has been found that the microphase separation of the coalesced segment is increased to adversely affect the membrane characteristics. In the present invention, the phase separation domain size of the membrane can be reduced by reducing the content of salts contained in the polyvinyl alcohol copolymer to form a membrane. At this time, the ratio (weight ratio) (C) / (P) of the weight (C) of the salt to the weight (P) of the polyvinyl alcohol-based copolymer needs to be 4.5 / 95.5 or less. In order to reduce the separation domain size, it is 4.0 / 96.0 or less, more preferably, 3.5 / 96.5 or less, and the weight ratio (C) / (P) is 4.5 / 95.5. If it exceeds 1, the microphase separation domain size of the anionic group polymer segment will increase, and when used as a cation exchange membrane, the ion path structure will change, and a durable cation exchange membrane cannot be obtained. .

The content of the salt contained in the polyvinyl alcohol-based copolymer is not particularly limited in order to reduce it to a predetermined value or less. For example, for impurities contained in the polyvinyl alcohol constituting the vinyl alcohol polymer segment, polymer flakes are used. Can be reduced by washing with water.
In addition, impurities contained in the polymer constituting the anionic polymer segment can be reduced by reprecipitation purification in a poor solvent of a polymer solution obtained by dissolving the polymer in an appropriate solvent, thereby purifying the polymer. Can do.
In the present invention, the salt content only needs to be reduced as described above. Therefore, one or both of polyvinyl alcohol and anionic polymer are purified to reduce the content to the above-described content. Just do it.

(Film formation)
The polyvinyl alcohol copolymer having a salt content adjusted as described above is dissolved in a solvent composed of water, a lower alcohol such as methanol, ethanol, 1-propanol, 2-propanol, or a mixed solvent thereof, A film having a predetermined thickness can be formed by extruding from a die, forming into a film, and removing the solvent by volatilization. The film forming temperature when the film is formed on a plate or a roller is not particularly limited, but a temperature range of about room temperature to about 100 ° C. is usually appropriate. Solvent removal can be performed by heating as appropriate.

(Film thickness)
The cation exchange membrane used in the present invention preferably has a film thickness of about 30 to 1000 μm from the viewpoints of performance, mechanical strength, handling properties, etc. required as an electrolyte membrane for electrodialysis. When the film thickness is less than 30 μm, the mechanical strength of the film tends to be insufficient. On the other hand, when the film thickness exceeds 1000 μm, the membrane resistance increases and sufficient ion exchange properties are not exhibited, so that the electrodialysis efficiency tends to decrease. Preferably it is 40-500 micrometers, More preferably, it is 50-300 micrometers.

(Crosslinking treatment)
In the method for producing a cation exchange membrane used in the present invention, it is preferable to perform a crosslinking treatment after the membrane formation. By performing the crosslinking treatment, the mechanical strength of the resulting cation exchange membrane is increased. The method for the crosslinking treatment is not particularly limited, and may be a method of chemically bonding the molecular chains of the polymer or introducing physical bonds by heat treatment or the like.

  When chemically bonding, a method of immersing in a solution containing a crosslinking agent is usually used. Examples of the crosslinking agent include polyvinyl alcohol acetalizing agents such as glutaraldehyde, formaldehyde, and glyoxal. The concentration of the crosslinking agent is usually 0.001 to 1% by volume of the crosslinking agent relative to the solution. The crosslinking reaction can be performed by treating the polyvinyl alcohol copolymer with the above aldehyde in water, alcohol or a mixed solvent thereof under acidic conditions to chemically introduce a crosslinking bond. . After the crosslinking reaction, it is preferable to remove unreacted aldehyde, acid and the like by washing with water.

  Moreover, as a method for the crosslinking treatment, physical crosslinking may be introduced between the molecular chains by performing a heat treatment. By performing the heat treatment, physical crosslinking occurs, and the mechanical strength of the resulting ion exchange membrane is increased. The method of heat treatment is not particularly limited, and a hot air dryer or the like is generally used. Although the temperature of heat processing is not specifically limited, In the case of polyvinyl alcohol, it is preferable that it is 50-250 degreeC. If the temperature of the heat treatment is less than 50 ° C., the mechanical strength of the obtained ion exchange membrane may be insufficient. The temperature is more preferably 80 ° C. or higher, and further preferably 100 ° C. or higher. When the temperature of the heat treatment exceeds 250 ° C., the crystalline polymer may be melted. The temperature is more preferably 230 ° C. or less, and further preferably 200 ° C. or less.

  In the manufacturing method, both heat treatment and chemical crosslinking treatment may be performed, or only one of them may be performed. When both the heat treatment and the crosslinking treatment are performed, the crosslinking treatment may be performed after the heat treatment, the heat treatment may be performed after the crosslinking treatment, or both may be performed simultaneously. It is preferable from the viewpoint of the mechanical strength of the resulting ion exchange membrane to perform a crosslinking treatment after the heat treatment.

(Ion exchange capacity)
In order to express sufficient ion exchange properties for use as a cation exchange membrane for electrodialysis, the ion exchange capacity of the obtained polyvinyl alcohol copolymer is preferably 0.30 meq / g or more, More preferably, it is 0.50 meq / g or more. The upper limit of the ion exchange capacity of the polyvinyl alcohol-based copolymer is preferably 3.0 meq / g or less because if the ion exchange capacity becomes too large, hydrophilicity increases and it becomes difficult to suppress the degree of swelling.

(Charge density)
Further, in order to develop sufficient electrical characteristics to be used as a cation exchange membrane for electrodialysis, the charge density of the obtained cation exchange membrane is preferably 0.6 mol / dm ³ or more. More preferably, it is 0.0 mol / dm ³ or more. As the charge density of the cation exchange membrane, a higher one is preferred, but in view of the membrane resistance, the one having a relatively low membrane resistance and expressing the charge density is preferred.

  The cation exchange membrane used in the present invention can be reinforced by being laminated with a support such as a nonwoven fabric, a woven fabric, or a porous material, if necessary.

(Desalination method of organic matter)
The organic matter desalting method of the present invention is a method of desalting an organic matter solution containing inorganic salts in an electrodialysis tank to desalt the organic matter.
FIG. 2 shows a schematic diagram for explaining a method for desalting organic matter in one embodiment of the present invention. The electrodialysis apparatus includes electrodes 4 and 7 and anion exchange membranes 5 and cation exchange membranes 6 arranged alternately. During the positive phase operation, an anion exchange membrane 5 and a cation exchange membrane 6 are alternately arranged between the anode 4 and the cathode 7 between the electrodes to alternately form a desalting chamber and a concentration chamber. The organic solution containing inorganic salts supplied from the liquid tank 8 is supplied to the desalting chambers 11 and 11. Although not shown, a liquid containing an electrolyte (for example, a diluted saline solution) is supplied to the concentration chamber. When voltage is passed to the electrodes at both ends, cations and anions move from the desalting chambers 11 and 11 to the cathode side and the anode side, respectively. Then, the desalting solution 10 is discharged from the desalting chamber, and the concentrated solution 9 is discharged from the concentration chamber 12.

  The organic substance to be desalted is not particularly limited, but is generally an organic substance containing inorganic salts such as salt, for example, sugar solutions such as fructose, glucose, sucrose, glucose, fructose, maltose, xylose, sucrose, raffinose, and other oligosaccharides. , Sugar and waste sugar, alcohols such as methanol, ethanol, propanol and glycerin, organic acids such as glycolic acid and gluconic acid or salts thereof, amino acids such as glutamic acid and glycic acid or salts thereof, vitamins, plum extract, etc. Extracts such as pulp, fish and shellfish, other oligopeptides, antibiotics, coenzymes, amines and other food additives, pharmaceuticals, fragrances, biochemicals, low molecular weight compounds known as general chemicals, starch, etc. High molecular polysaccharides, various proteins, nucleic acids, natural polymers such as enzymes, There is polyvinyl alcohol, polyethylene glycol, a solution can be dialyzed like itself electrodialysis possible liquids and organic aqueous solution such as water-soluble synthetic polymers such as polyvinylpyrrolidone.

The concentration of the salt contained in such an organic material may be, for example, about 1 to 50% by weight, and preferably about 5 to 40% by weight.
The current density during electrodialysis may be, for example, about 0.5 to 5 A / dm ² , and preferably about 1 to 4 A / dm ² .

  The present invention includes a method for producing an organic substance desalted by the above-described method for desalting an organic substance, and further includes a desalted organic substance itself.

  Hereinafter, examples will be given to describe the present invention in more detail, but the present invention is not limited to these examples. In the examples, “%” and “parts” are based on weight unless otherwise specified.

  The characteristics of the cation exchange membranes shown in Examples and Comparative Examples were measured by the following methods.

1) Membrane moisture content (H)
The dry weight of the ion exchange membrane was measured in advance, and then the wet weight was measured when it was immersed in deionized water and reached a swelling equilibrium. The membrane water content (H) was calculated by the following equation. _{H = <(W w -D w} ) / 1.0> / <(W w -D w) / 1.0+ (D w /1.3)>
Here, 1.0 and 1.3 indicate the specific gravity of water and polymer, respectively.
-H: membrane water content [-]
_Dw : dry weight of membrane [g]
W _w : wet weight of the film [g]

2) Measurement of cation exchange capacity A cation exchange membrane is immersed in a 1 mol / L aqueous HCl solution for 10 hours or more. Thereafter, the hydrogen ion type was replaced with the nitrate ion type with 1 mol / L NaNO ₃ aqueous solution, and the liberated hydrogen ions were quantified by acid-base titration (Amol).

Next, the same cation exchange membrane is immersed in a 1 mol / L NaCl aqueous solution for 4 hours or more, washed thoroughly with ion exchange water, dried in a hot air drier at 105 ° C. for 8 hours, and the weight when dried W (G) was measured.
The ion exchange capacity was calculated by the following formula.
・ Ion exchange capacity = A × 1000 / W [mmol / g-dry membrane]

3) Measurement of the salt in the polyvinyl alcohol copolymer The amount of the salt in the polyvinyl alcohol copolymer was determined by Soxhlet extraction of the film before crosslinking of the polyvinyl alcohol copolymer with a methanol solution for 48 hours. The product was dried and then measured by ion chromatography (ICS-5000, manufactured by DIONEX).

4) Measurement of membrane resistance The membrane resistance was measured by sandwiching a cation exchange membrane in a two-chamber cell having a platinum black electrode plate as shown in Fig. 2, and filling a 0.5 mol / L-NaCl solution on both sides of the membrane. The resistance between the electrodes at 25 ° C. was measured by (frequency 10 cycles / second), and was determined by the difference between the resistance between the electrodes and the resistance between the electrodes when no cation exchange membrane was installed. The membrane used for the above measurement was previously equilibrated in a 0.5 mol / L-NaCl solution.

5) Measurement of domain size A cation exchange membrane immersed in distilled water was cut into a 1 cm square to prepare a measurement sample. This measurement sample was stained with lead acetate (II) and then observed using a TEM (transmission electron microscope) to obtain an image of a particle group in the measurement sample. The obtained image was subjected to image processing using image processing software “WINROOF” manufactured by Mitani Corporation, and the maximum particle size of each particle was determined. The maximum particle size was determined for about 400 particles, and the particle size at which the cumulative frequency of the maximum particle size was 50% was defined as the domain size of the anionic group polymer segment of the cation exchange membrane.

<Preparation of PVA-1 (Synthesis of polyvinyl alcohol copolymer having a mercapto group at the molecular terminal)>
Polyvinyl alcohol (PVA-1) having a mercapto group at the molecular end shown in Table 1 was synthesized by the method described in JP-A-59-187003. Table 1 shows the polymerization degree and saponification degree of PVA-1.

<NaSS-1 (anionic monomer)>
The polystyrene sulfonate sodium monomer (NaSS: manufactured by Tosoh Corporation) shown in Table 2 was used as it was. The salt content was measured by ion chromatography (ICS-5000, manufactured by DIONEX). The impurities in the monomer other than the total salt amount shown in Table 2 were moisture.

<Preparation of NaSS-2>
1000 g of sodium polystyrene sulfonate monomer (NaSS: manufactured by Tosoh Corp.), 950 g of pure water, 40 g of sodium hydroxide, 1 g of sodium nitrate were dissolved at 60 ° C. for 1 hour, cooled to 20 ° C. and recrystallized. Thereafter, the polystyrenesulfonic acid monomer crystals were separated by centrifugal filtration, and the crystals were dried to obtain NaSS-2 (purified polystyrenesulfonic acid monomer) shown in Table 2. The content of the salt was measured by ion chromatography (ICS-5000, manufactured by DIONEX).

<Synthesis of P-1 (anionic block copolymer)>
In a 1 L four-necked separable flask equipped with a reflux condenser and a stirring blade, 660 g of water, 80 g of PVA-1 shown in Table 1 as a vinyl alcohol polymer having a mercapto group at the end, and NaSS-146.6 g The resulting mixture was heated to 95 ° C. with stirring to dissolve the vinyl alcohol polymer and NaSS-1. The system was purged with nitrogen for 30 minutes while bubbling nitrogen into the aqueous solution. After nitrogen substitution, the solution was cooled to 90 ° C., and 13 ml of a 5.4% solution of 2,2′-azobis [2-methyl-N (2-hydroxyethyl) propionamide] was sequentially added to the above aqueous solution over 1.5 hours. After the addition and the block copolymerization was started and proceeded, the system temperature was maintained at 90 ° C. for 1 hour to further proceed the polymerization, followed by cooling to a solid content concentration of 15% PVA- (b) -p -A sodium styrenesulfonate aqueous solution was obtained. A part of the obtained aqueous solution was dried, dissolved in heavy water, and subjected to ¹ H-NMR measurement at 400 MHz. As a result, the amount of modification of the sodium parastyrenesulfonate unit was 10 mol%. Table 3 shows the properties of the obtained anionic block copolymer.

<Synthesis of P-2>
The type and amount of the anionic group-containing monomer were changed to those shown in Table 3. Except for this, a PVA- (b) -p-sodium styrenesulfonate aqueous solution having a solid concentration of 15% was obtained in the same manner as P-1. Table 3 shows the properties of the obtained anionic block copolymer.

<Synthesis of P-3>
In a 1 L four-necked separable flask equipped with a reflux condenser and a stirring blade, 676 g of water, 80 g of PVA-1 shown in Table 1 as a vinyl alcohol polymer having a mercapto group at the end, and 46. NaSS-1 were obtained. 6 g was charged and heated to 95 ° C. with stirring to dissolve the vinyl alcohol polymer and NaSS-1, and then cooled to room temperature. 1/2 N sulfuric acid was added to the aqueous solution to adjust the pH to 3.0. The system was heated to 90 ° C., and the system was purged with nitrogen for 30 minutes while bubbling nitrogen into the aqueous solution. After nitrogen substitution, 63 mL of a 2.5% aqueous solution of potassium persulfate was sequentially added to the aqueous solution over 1.5 hours to start and proceed with block copolymerization, and then the system temperature was increased to 90 ° C. for 1 hour. The polymerization was further continued to proceed, followed by cooling to obtain a PVA- (b) -p-sodium styrenesulfonate block copolymer aqueous solution having a solid concentration of 15%. A part of the obtained aqueous solution was dried, dissolved in heavy water, and subjected to ¹ H-NMR measurement at 400 MHz. As a result, the amount of modification of the sodium p-styrenesulfonate unit was 10 mol%. Table 3 shows the properties of the obtained anionic block copolymer.

<Synthesis of P-4 to 5>
The type and amount of the anionic group-containing monomer were changed to those shown in Table 3. Except for this, a PVA- (b) -p-sodium styrenesulfonate aqueous solution having a solid concentration of 15% was obtained in the same manner as P-3. Table 3 shows the properties of the obtained anionic block copolymer.

<Synthesis of P-6>
A 6 L separable flask equipped with a stirrer, temperature sensor, dropping funnel and reflux condenser was charged with 2450 g of vinyl acetate, 762 g of methanol, and 27 g of sodium 2-acrylamido-2-methylpropanesulfonate (AMPS) under stirring. After the system was purged with nitrogen, the internal temperature was raised to 60 ° C. To this system, 20 g of methanol containing 0.8 g of 2,2′-azobisisobutyronitrile (AIBN) was added to initiate the polymerization reaction. While adding 568 g of methanol solution containing 25% by mass of sodium 2-acrylamido-2-methylpropanesulfonate (AMPS) to the system from the start of polymerization, the polymerization reaction was stopped for 4 hours, and then the polymerization reaction was stopped. The solid content concentration in the system when the polymerization reaction was stopped, that is, the solid content with respect to the entire polymerization reaction slurry was 30% by mass. Subsequently, methanol vapor was introduced into the system to drive out unreacted vinyl acetate monomer, thereby obtaining a methanol solution containing 30% by mass of a vinyl ester copolymer.

  In a methanol solution containing 30% by mass of this vinyl ester copolymer, the molar ratio of sodium hydroxide to vinyl acetate units in the copolymer is 0.02, and the solid content concentration of the vinyl ester copolymer is 30% by mass. Then, a methanol solution containing 10% by mass of methanol and sodium hydroxide was added in this order with stirring, and the saponification reaction was started at 40 ° C.

Immediately after the saponification reaction has occurred, a gelled product is formed and taken out from the reaction system and pulverized. Then, when 1 hour has passed since the gelated product was formed, methyl acetate was added to the pulverized product. By carrying out neutralization, an aqueous solution of a random block copolymer of polyvinyl alcohol-poly (sodium 2-acrylamido-2-methylpropanesulfonate) in a swollen state was obtained. To this swollen anionic polymer, 6 times the amount of methanol (6 times the bath ratio) of methanol was added and washed under reflux for 1 hour, and the polymer was collected by filtration. The polymer was dried at 65 ° C. for 16 hours. When the obtained polymer was dissolved in heavy water and subjected to ¹ H-NMR measurement at 400 MHz, the content of the anionic monomer in the anionic polymer, that is, the monomer in the polymer The ratio of the number of sodium 2-acrylamido-2-methylpropanesulfonate monomer units to the total number of units was 5 mol%. The properties of the obtained anionic block copolymer are shown in Table 4.

<Production of CEM-1>
The resin of P-3 was diluted to a concentration of 10 wt%, and the resin from which salts were removed by reprecipitation with 1 volume of methanol of the resin solution was taken out. At this time, the salt content (C) was 4.5 wt%. Next, a necessary amount of distilled water was added to prepare an aqueous solution having a concentration of 15 wt%. This aqueous solution was poured into a cast board made of acrylic having a length of 270 mm and a width of 210 mm to remove excess liquid and bubbles, and then dried on a hot plate at 50 ° C. for 24 hours to prepare a film.

  The film thus obtained was heat treated at 160 ° C. for 30 minutes to cause physical crosslinking. Subsequently, the film was immersed in an aqueous electrolyte solution of 2 mol / L sodium sulfate for 24 hours. Concentrated sulfuric acid was added to the aqueous solution so that the pH was 1, and then the film was immersed in a 1.0% by volume glutaraldehyde aqueous solution and stirred with a stirrer at 25 ° C. for 24 hours to carry out a crosslinking treatment. Here, as the glutaraldehyde aqueous solution, a product obtained by diluting “glutaraldehyde” (25% by volume) manufactured by Ishizu Pharmaceutical Co., Ltd. with water was used. After the crosslinking treatment, the film was immersed in deionized water, and the film was immersed until the film reached a swelling equilibrium while exchanging the deionized water several times in the middle to obtain a cation exchange membrane.

(Evaluation of ion exchange membrane)
The cation exchange membrane thus prepared was cut into a desired size to prepare a measurement sample. Using the obtained measurement sample, the membrane water content, charge density, cation exchange capacity, membrane resistance, and phase separation domain size were measured according to the above methods. The results obtained are shown in Table 5.

<Production of CEM-2>
The resin of P-3 was diluted to a concentration of 10 wt%, and the resin from which salts were removed by reprecipitation with twice the volume of methanol as the resin solution was taken out. Next, a necessary amount of distilled water was added to prepare an aqueous solution having a concentration of 15 wt%. This aqueous solution was poured onto an acrylic cast plate having a length of 270 mm and a width of 210 mm to remove excess liquid and bubbles, and then dried on a hot plate at 50 ° C. for 24 hours to prepare a film. At this time, the salt content (C) was 4.0 wt%. Except for this, the membrane characteristics of the cation exchange membrane were measured in the same manner as in Example 1. The obtained measurement results are shown in Table 5.

<Preparation of CEM-3>
An aqueous solution of P-2 was poured onto an acrylic cast plate having a length of 270 mm and a width of 210 mm to remove excess liquid and bubbles, and then dried on a hot plate at 50 ° C. for 24 hours to prepare a film. At this time, the salt content (C) was 2.8 wt%. Except for this, the membrane characteristics of the cation exchange membrane were measured in the same manner as CEM1. The obtained measurement results are shown in Table 5.

<CEM-4 production>
In CEM-3, the membrane characteristics of the cation exchange membrane were measured in the same manner as in Example 3 except that the heat treatment temperature was changed as shown in Table 5. The obtained measurement results are shown in Table 5.

<CEM-5 production>
The resin of P-3 was diluted to a concentration of 10 wt%, and the resin from which salts were removed by reprecipitation with 5 times the volume of methanol of the resin solution was taken out. Next, a necessary amount of distilled water was added to prepare an aqueous solution having a concentration of 15 wt%. This aqueous solution was poured onto an acrylic cast plate having a length of 270 mm and a width of 210 mm to remove excess liquid and bubbles, and then dried on a hot plate at 50 ° C. for 24 hours to prepare a film. At this time, the salt content (C) was 2.0 wt%. Except for this, the membrane characteristics of the cation exchange membrane were measured in the same manner as in Example 1. The obtained measurement results are shown in Table 5.

<CEM-6 production>
The P-3 resin was diluted to a concentration of 10 wt%, and the resin from which salts were removed by reprecipitation with 10 times the volume of methanol of the resin solution was taken out. Next, a necessary amount of distilled water was added to prepare an aqueous solution having a concentration of 15 wt%. This aqueous solution was poured into a cast board made of acrylic having a length of 270 mm and a width of 210 mm to remove excess liquid and bubbles, and then dried on a hot plate at 50 ° C. for 24 hours to prepare a film. At this time, the salt content (C) was 1.5 wt%. Except for this, the membrane characteristics of the cation exchange membrane were measured in the same manner as in Example 1. The obtained measurement results are shown in Table 5.

<Production of CEM-7 to 11>
Membrane characteristics of the cation exchange membrane were measured in the same manner as in Example 1 except that the cation exchange resin was changed to the contents shown in Table 5. The obtained measurement results are shown in Table 5.

<Example 1>
Small electrodialyzer S3 (with a cation exchange membrane CEM-1 and an anion exchange membrane AMX (manufactured by Astom Co., Ltd.) and clamped alternately between the cathode and anode. The desalting test of the organic compound was conducted using Astom Co., Ltd. At this time, an aqueous solution containing 1 mol / L of saccharose, 0.3 mol / L of sodium chloride and 0.1 mol / L of benzalkonium chloride is supplied to the desalting chamber, and one pass at a current density of 1 to ^{2 A} / dm ² at 25 ° C. For 1 hour. Table 6 shows the results of measuring the desalting rate after 1 hour, the leakage rate of sucrose, and the degree of organic contamination (the rate of increase in voltage after 1 hour of operation from the voltage at the start).

<Examples 2 to 7>
An organic matter desalting test was conducted in the same manner as in Example 1 except that the cation exchange membrane used was changed to the contents shown in Table 6. The results obtained are shown in Table 6.

<Comparative Examples 1-3>
An organic matter desalting test was conducted in the same manner as in Example 1 except that the cation exchange membrane used was changed to the contents shown in Table 6. The results obtained are shown in Table 6.

<Comparative example 4>
It measured on the same conditions as Example 1 using the commercial item AMX (made by Astom Co., Ltd.) for a cation exchange membrane. The results are shown in Table 6.

  1 (a), 1 (b), 1 (c), 1 (d) and 1 (e) are TEM photographs of cation exchange membranes using block copolymers having different salt contents. (See Table 5 for salt content). From the TEM photographs of FIGS. 1 (a) to 1 (e), the phase separation structure varies depending on the salt content, and the domain size decreases with decreasing salt-containing weight (C) / block copolymer weight (P). I understand that In particular, in FIG. 1 (b) [Example 7] in which the weight (C) of the salt contained at the modification amount of 10 mol% is the smallest, the compatibility of the film was improved and the domain size was as small as 4 nm. . On the other hand, in FIG. 1 (C) [Comparative Example 1] having the largest salt content (C), phase separation was severe and voids were generated.

From the results in Table 5, the cation exchange membrane using the block copolymer (P) having a salt-containing weight (C) of 4.0% or less in particular has a domain size of 150 nm or less, a high charge density, It turns out that it becomes a film | membrane with low resistance, and is excellent as a cation exchange membrane (CEM1-7). Furthermore, a membrane having a salt-containing weight (C) of 3.5% or less has a domain size of 130 nm or less, and the characteristics of the cation exchange membrane and the charge density of 1.0 mol / dm ³ or more may decrease the membrane resistance. Yes (CEM 2-7). On the other hand, a cation exchange membrane using a block copolymer having a salt content of more than 4.0% has a domain size larger than 150 nm, a low charge density and a high membrane resistance. Characteristics were not expressed (CEM 8-10). In particular, those having a high salt content (C) have severe phase separation of the polymer segment of the membrane, and voids are generated throughout the ion exchange membrane, which does not exhibit satisfactory characteristics as an ion exchange membrane (CEM8). In CEM9, purified NaSS-2 is used, but since KPS is used as a polymerization initiator, the salt content in the obtained cation exchange resin is high.

  From the results in Table 6, the electrodialysis using a cation exchange membrane using a block copolymer (P) having a salt-containing weight (C) of 4.0% or less has a low leak rate and a desalting rate. It can be seen that the rate of electrical rise is low (contamination of the film is small) (Examples 1 to 7). Furthermore, it can be seen that electrodialysis using a cation exchange membrane having a salt-containing weight (C) of 3.5% or less has a higher desalting rate (Examples 2 to 7). On the other hand, in electrodialysis using a cation exchange membrane using a block copolymer having a salt content of more than 4.0%, the leak rate was high and the desalination rate was low (Comparative Examples 1 to 3). . On the other hand, when the cation exchange membrane CEM-11 made of a random block copolymer in which microphase separation, which is considered to be a completely compatible system, was not confirmed (Comparative Example 4), the phase separation domain size was small. Compared with the cation exchange membrane CEM-7 (Example 5) which consists of a block copolymer, a desalination rate is low. When a commercially available cation exchange membrane was used, the voltage increase rate was remarkably high (Comparative Example 5).

  In the desalting method of the present invention, a specific cation exchange membrane in an electrodialysis tank, that is, a cation exchange membrane composed of a polyvinyl alcohol copolymer having an anionic polymer segment and a vinyl alcohol polymer segment. In addition, since a cation exchange membrane having a very small microphase separation structure can be used, an organic matter containing salts is supplied to the electrodialysis tank, and the organic matter can be prevented from leaking while suppressing leakage of the organic matter. Salts can be removed efficiently.

  Although the preferred embodiments of the present invention have been described above by way of example, those skilled in the art can make various modifications, additions and substitutions without departing from the scope and spirit of the present invention disclosed in the claims. It will be understandable.

A Ion exchange membrane B Platinum electrode C NaCl aqueous solution D Water bath E LCR meter 3 Electrodialysis tank 4 Anode 5 Anion exchange membrane 6 Cation exchange membrane 7 Cathode 8 Liquid tank 11 Desalination chamber 12 Concentration chamber

Claims (11)

  A method of desalting an organic solution containing inorganic salts in an electrodialysis tank and desalting the organic substance, wherein the electrodialysis tank has an anion exchange membrane and a cation exchange membrane arranged alternately between electrodes. The cation exchange membrane comprises an anionic polymer segment having an anionic group and a polyvinyl alcohol copolymer having a vinyl alcohol polymer segment, and the domain size (X) is A method for desalinating an organic substance, comprising using a cation exchange membrane having a microphase separation structure in a range of 0 nm <X ≦ 150 nm.   The said polyvinyl alcohol-type copolymer is a desalting method of the organic substance of Claim 1 containing the vinyl alcohol polymer which does not contain an anionic group.   The method for desalinating an organic substance according to claim 1 or 2, wherein a cross-linked structure is introduced into the polyvinyl alcohol copolymer.   The said polyvinyl alcohol-type copolymer is an anionic block copolymer which has an anionic polymer block which has a vinyl alcohol polymer block and an anionic group, The any one of Claims 1-3 characterized by the above-mentioned. 2. A method for desalinating organic substances according to 1.   The said polyvinyl alcohol-type copolymer is an anionic graft copolymer which has a vinyl alcohol polymer block and an anionic polymer block which has an anionic group, The any one of Claims 1-3 characterized by the above-mentioned. 2. A method for desalinating organic substances according to 1.   The method for desalinating an organic substance according to any one of claims 1 to 5, wherein the ion exchange capacity of the cation exchange membrane is 0.30 meq / g or more. The membrane resistance of a cation exchange membrane is 10 ohm-cm < ² > or less, The desalting method of the organic substance of any one of Claims 1-6.   The polyvinyl alcohol copolymer used for forming a cation exchange membrane contains salts, and the ratio of the weight (C) of the salt to the weight (P) of the polyvinyl alcohol copolymer [(C ) / (P)] is a polyvinyl alcohol copolymer adjusted so as to be 4.5 / 95.5 or less. The method for desalinating an organic substance according to any one of claims 1 to 7.   A film obtained by forming a cation exchange membrane from a polyvinyl alcohol copolymer solution containing salts is heat-treated at a temperature of 100 ° C. or higher, and then in water, alcohol or a mixed solvent thereof under acidic conditions. The method for desalinating an organic substance according to any one of claims 1 to 8, wherein the cation exchange membrane is subjected to a crosslinking treatment with a dialdehyde compound and then washed with water.   A method for producing a desalted organic substance by desalting an organic substance solution containing inorganic salts in an electrodialysis tank, wherein the electrodialysis tank has an anion exchange membrane and a cation exchange membrane alternately disposed between electrodes. The cation exchange membrane comprises an anionic polymer segment having an anionic group and a polyvinyl alcohol copolymer having a vinyl alcohol polymer segment, and has a domain size (X ) Has a microphase-separated structure in the range of 0 nm <X ≦ 150 nm.   A desalted organic substance produced by the production method according to claim 10.

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