JP7524617B2 - Strongly acidic cation exchanger and its manufacturing method - Google Patents

Description

The present invention relates to a strongly acidic cation exchanger and a method for producing the same.

Strongly acidic cation exchangers have strong acidic cation exchange groups, and therefore, unlike cation exchangers with weakly acidic cation exchange groups such as carboxyl groups, they can capture cations even in the neutral pH range, and have excellent properties as ion exchangers. Taking advantage of these excellent ion exchange properties, strongly acidic cation exchangers are used as ion exchange resins and ion exchange membranes in a wide range of fields, such as pure water and ultrapure water production equipment, electrodialysis equipment, sugar purification and isomerization, chromatography packing materials, catalysts, and fuel cells. However, conventional strongly acidic cation exchangers are made by introducing strongly acidic cation exchange groups such as sulfonic acid groups into parent polymers such as polystyrene, styrene-divinylbenzene copolymers, and fluoropolymers, and therefore the parent polymers are highly hydrophobic, and hydrophobic substances such as oils and proteins with hydrophobic parts are adsorbed to the ion exchanger due to hydrophobic adsorption, contaminating the ion exchanger and reducing the ion exchange properties.

On the other hand, it has been proposed to produce a strongly acidic cation exchanger by selecting a highly hydrophilic polysaccharide as the base polymer and introducing strongly acidic cation exchange groups such as sulfate groups (see, for example, Patent Documents 1 to 3). Although it is possible to suppress hydrophobic adsorption by using a polysaccharide as the base polymer, these methods have the problem that the molecular chain scission reaction of the base polymer occurs simultaneously during the sulfate group introduction reaction, resulting in a decrease in the molecular weight of the strongly acidic cation exchanger and a significant decrease in mechanical properties.

As a method for introducing functional groups into polysaccharides, Patent Document 4 discloses a method of graft polymerizing a cationic monomer onto an anionic polysaccharide, and Patent Document 5 discloses graft polymerizing vinyl acetate onto a polysaccharide derived from seaweed, but there is no description of graft polymerization of an anionic monomer onto a polysaccharide.

Japanese Unexamined Patent Publication No. 59-133201 JP 2005-344073 A JP 2008-27767 A Special Publication No. 2008-516891 Special table 2016-500721 publication

The object of the present invention is to provide a strong acid cation exchanger with a large strong acid cation exchange capacity and a high molecular weight, which was difficult to achieve with conventional technology.

As a result of intensive research conducted by the inventors to solve the above problems, they discovered that by graft polymerizing a monomer having a sulfonic acid group onto a polysaccharide under specific conditions, a strong acid cation exchanger having a large strong acid cation exchange capacity and a high molecular weight can be obtained, and thus completed the present invention.

That is, each aspect of the present invention relates to [1] to [3] shown below.
[1] A strongly acidic cation exchanger in which a polymer segment having a sulfonic acid group is grafted to a polysaccharide, the strongly acidic cation exchanger having a weight average molecular weight of 30,000 to 3,000,000 and a strongly acidic cation exchange capacity of 2.5 to 4.9 meq/g.
[2] The strongly acidic cation exchanger according to claim 1, which has a structure represented by the following general formula (1):

(In the formula, m and n are each independently an integer of 1 or greater; R ₁ may be the same or different and each represents hydrogen, an alkali metal, an alkaline earth metal or a group represented by -R ₃ -OH; R ₃ represents a divalent hydrocarbon group having 2 to 6 carbon atoms; R ₂ may be the same or different and each represents a polymer segment having a sulfonic acid group or hydrogen, and at least one of R ₂ is a polymer segment having a sulfonic acid group.)
[3] A method for producing a strongly acidic cation exchanger by graft polymerizing a sulfonic acid group-containing vinyl monomer onto a polysaccharide in a polar solvent, characterized in that a polysaccharide insoluble in the polar solvent is used and the reaction is carried out in a slurry system.

According to the present invention, it is possible to provide a strong acid cation exchanger having a large strong acid cation exchange capacity and a high molecular weight, using a highly hydrophilic polysaccharide as the base polymer.

The strong acid cation exchanger of the present invention has a large ion exchange capacity and excellent mechanical properties, and therefore has excellent practical applications in a wide range of fields, such as as an ion exchange resin or ion exchange membrane in pure water/ultrapure water production equipment, electrodialysis equipment, sugar purification and isomerization, chromatography packing, catalysts, and fuel cells.

1 is a GPC elution curve of the part of the graft polymer produced in Example 1 that is insoluble in an aqueous calcium chloride solution, which was measured using a combination of an RI detector and a UV detector. 1 is a GPC elution curve of the calcium chloride aqueous solution soluble portion of the graft polymer produced in Example 1, which was measured using a combination of an RI detector and a UV detector. 1 is a 1H-NMR spectrum of the graft polymer produced in Example 3.

The present invention will be described in detail below with reference to preferred embodiments.

The strongly acidic cation exchanger according to one embodiment of the present invention is a graft polymer in which a polymer segment having a sulfonic acid group is grafted onto a polysaccharide.

Polysaccharides refer to those having a structure in which a large number of monosaccharides are linked together by glycosidic bonds. Examples of polysaccharides include amylose, amylopectin, dextrin, glycogen, cellulose, carboxymethylcellulose, hydroxyalkylcellulose, acetylcellulose, pectin, pullulan, curdlan, chitin, chitosan, agarose, xanthan gum, guar gum, gellan gum, locust bean gum, carrageenan, alginic acid, alginates, alginic acid esters, heparin, hyaluronic acid, chondroitin sulfate, xyloglucan, glucomannan, etc. In the present invention, neutral polysaccharides and acidic polysaccharides are preferably used, and specific examples include amylose, amylopectin, cellulose, carboxymethylcellulose, guar gum, gellan gum, alginic acid, alginates, alginic acid esters, agarose, carrageenan, curdlan, xanthan gum, and chondroitin sulfate. More preferred polysaccharides include alginic acid, alginates, and alginate esters represented by the following general formula (2):

(In the formula, m and n are each independently an integer of 1 or more, R ₁ may be the same or different and each represents hydrogen, an alkali metal, an alkaline earth metal or a group represented by -R ₃ -OH, and R ₃ represents a divalent hydrocarbon group having 2 to 6 carbon atoms.)
Examples of the hydrocarbon group having 2 to 6 carbon atoms for _R3 include an ethylene group, an ethylidene group, a vinylene group, a trimethylene group, a methylethylene group, a 1-methylethylidene group, a propenylene group, a tetramethylene group, a methyltrimethylene group, a dimethylethylene group, a 1-ethylethylidene group, an ethylethylene group, a pentamethylene group, a methyltetramethylene group, a dimethyltrimethylene group, a methylethylethylene group, a hexamethylene group, a cyclohexylene group, and a cyclohexylidene group. Examples of the group represented by _-R3 -OH include a hydroxyethyl group, a hydroxypropyl group, a hydroxybutyl group, a hydroxypentyl group, a hydroxyhexyl group, and a hydroxycyclohexyl group.

Alginic acid refers to the case where all of R ₁ in formula (2) are hydrogen. Alginate refers to the case where at least a part of R ₁ in formula (2) is an alkali metal (e.g., lithium, sodium, potassium) or an alkaline earth metal (e.g., magnesium, calcium). Alginic acid ester refers to the case where at least a part of R ₁ in formula (2) is a group represented by -R ₃ -OH (R ₃ is a hydrocarbon group having 2 to 6 carbon atoms). Such alginic acid ester can be produced by reacting alginic acid with an epoxy compound.

The ratio of mannuronic acid and guluronic acid, which are the components of alginic acid, can be any ratio, and either alginic acid with a high ratio of mannuronic acid, which produces a flexible gel, or alginic acid with a high ratio of guluronic acid, which produces a rigid gel, can be used.

The sulfonic acid group introduced into the strongly acidic cation exchanger is a strongly acidic cation exchange group capable of ion-exchanging not only basic salts but also neutral salts such as NaCl and _CaCl2 . The position of introduction of the graft chain consisting of a polymer segment having a sulfonic acid group is the 2-carbon and/or 3-carbon of the polysaccharide. The sulfonic acid group may be a regenerated type ( _-SO3H ), but may also be an alkali metal sulfonate base ( _-SO3M ', M' represents an alkali metal) in which the hydrogen ion of the sulfonic acid group is ion-exchanged with an alkali metal ion.

The strong acid cation exchange capacity (neutral salt decomposition capacity) derived from the sulfonic acid groups contained in the graft segment is 2.5 to 4.9 meq/g, preferably 2.7 to 4.9 meq/g. An ion exchange capacity of less than 2.5 meq/g is undesirable because the ion exchange properties are insufficient, while an ion exchange capacity of more than 4.9 meq/g is undesirable because the proportion of graft chains in the strong acid cation exchanger becomes too high, causing the excellent properties derived from the polysaccharide to be lost.

There are no particular restrictions on the type of graft segment as long as it contains a sulfonic acid group, and some examples include poly(2-sulfoethyl methacrylate), poly(2-sulfoethyl acrylate), poly(3-sulfopropyl methacrylate), poly(3-sulfopropyl acrylate), poly(4-sulfobutyl methacrylate), poly(4-sulfobutyl acrylate), poly(2-acrylamido-2-methylpropanesulfonic acid), poly(2-methacrylamido-2-methylpropanesulfonic acid), poly(vinyl sulfonic acid), poly(styrenesulfonic acid), and salts thereof, as well as copolymers between vinyl monomers having sulfonic acid groups that constitute the above segments, and copolymers of vinyl monomers having sulfonic acid groups and vinyl monomers not having sulfonic acid groups that constitute the above segments.

The molecular weight of the strong acid cation exchanger is 30,000 to 3,000,000 in weight average molecular weight. If the weight average molecular weight is less than 30,000, the ion exchanger becomes brittle and has poor mechanical properties, which is undesirable. On the other hand, if the weight average molecular weight exceeds 3,000,000, the viscosity of the system becomes too high during graft polymerization, making it difficult to control the polymerization, which is undesirable. There is no restriction on the molecular weight of the main chain polysaccharide, but since the mechanical properties of the strong acid cation exchanger reflect the properties of the main chain polysaccharide, the weight average molecular weight is preferably in the range of 20,000 to 1,500,000. There is also no particular restriction on the molecular weight of the graft segment, but considering the balance between cation exchange capacity and mechanical properties, the weight average molecular weight is preferably in the range of 10,000 to 2,000,000.

In addition, m and n in the general formula (1) may each independently be an integer of 1 or more, but each is preferably 30 to 3000.

The method for producing a strong acid cation exchanger according to one aspect of the present invention is characterized in that a polysaccharide insoluble in a polar solvent is used and reacted in a slurry system in a polar solvent. The use of a polysaccharide soluble in a polar solvent is undesirable because it causes problems such as a significant increase in the viscosity of the polymerization system, which makes the polymerization reaction non-uniform, a decrease in the quality of the strong acid cation exchanger, and difficulty in removing the heat of polymerization, which causes the polymerization reaction to go out of control. Even if a polysaccharide soluble in a polar solvent is used, the above problems can be solved by carrying out the polymerization in a dilute state, but this is undesirable because it significantly reduces productivity.

The polar solvent used in the method for producing a strong acid cation exchanger refers to a protic polar solvent, an aprotic polar solvent, or a mixture of these. A protic polar solvent has acidic hydrogen, hydrogen bonding properties, and a high dielectric constant. Specific examples of protic polar solvents include water; alcohols such as methanol, ethanol, propanol, and butanol; glycols such as ethylene glycol, propylene glycol, tetramethylene glycol, and diethylene glycol; carboxylic acids such as formic acid, acetic acid, propionic acid, and benzoic acid, and mixtures thereof. On the other hand, aprotic polar solvents are solvents that do not have acidic hydrogen but have a high dielectric constant and a high dipole moment. Specific examples of such solvents include ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; esters such as ethyl acetate, isopropyl acetate, and butyl acetate; ethers such as diethyl ether, tetrahydrofuran, and dioxane; acetonitrile; dimethyl sulfoxide; amide-based solvents such as formamide, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, and hexamethylphosphoric acid triamide; urea-based solvents such as 1,3-dimethyl-2-imidazolidinone, tetramethylurea, and N,N'-dimethylpropyleneurea; and carbonate-based solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate.

The polysaccharides used in the method for producing a strongly acidic cation exchanger are preferably polysaccharides that are insoluble in polar solvents. When the polar solvent is water, cellulose, alginic acid, curdlan, etc. can be used. When the polar solvent is alcohol, amylose, amylopectin, cellulose, carboxymethylcellulose, guar gum, gellan gum, alginic acid, alginate, alginate ester, agarose, carrageenan, curdlan, xanthan gum, etc. can be used.

Specific examples of vinyl monomers having a sulfonic acid group that constitute the graft segment include 2-sulfoethyl methacrylate, 2-sulfoethyl acrylate, 3-sulfopropyl methacrylate, 3-sulfopropyl acrylate, 4-sulfobutyl methacrylate, 4-sulfobutyl acrylate, 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, vinyl sulfonic acid, styrenesulfonic acid, and salts thereof. These monomers may be used alone or in combination of two or more.

The above-mentioned vinyl monomers having sulfonic acid groups can also be copolymerized with vinyl monomers not having sulfonic acid to form graft segments. Examples of vinyl monomers not having sulfonic acid include acrylic acid, methyl acrylate, ethyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, acrylonitrile, styrene, vinyl toluene, chloromethylstyrene, divinylbenzene, vinyl chloride, vinylidene chloride, vinylidene fluoride, tetrafluoroethylene, isobutene, butadiene, isoprene, chloroprene, vinyl acetate, maleic anhydride, N-methylmaleimide, N-phenylmaleimide, N-cyclohexylmaleimide, diethyl fumarate, diisopropyl fumarate, itaconic acid, itaconic anhydride, dimethyl itaconate, vinylene carbonate, and the like.

There are no particular limitations on the radical polymerization initiator used in the graft polymerization of the sulfonic acid group-containing vinyl monomer, and examples of the initiator include azo compounds such as azobisisobutyronitrile, azobis(4-methoxy-2,4-dimethylvaleronitrile, azobis(2,4-dimethylvaleronitrile), 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-methylpropionamidine), and 2,2'-azobis(2-(2-imidazolin-2-yl)propane), organic peroxides such as benzoyl peroxide, di-t-butyl peroxide, t-butyl peroxide, and methyl ethyl ketone peroxide, redox initiators such as hydrogen peroxide and iron(II) salts, persulfates and sodium hydrogen sulfite, ammonium cerium(IV) nitrate, and potassium persulfate.

A general graft polymerization method can be used for the graft polymerization. For example, after dissolving or dispersing the monomer in a polar solvent, polysaccharide is added and stirred to prepare a slurry. Next, the system is replaced with nitrogen, and then an initiator solution is dropped into the slurry and heated with stirring to perform graft polymerization. The monomer concentration at the start of graft polymerization can be appropriately set in the range of 0.1 to 5 mol/L. The amount of polysaccharide added is in the range of 5 to 200 parts by weight per 100 parts by weight of monomer, and the initiator concentration varies depending on the type of initiator, but is about 1 to 10 mmol/L. The polymerization temperature can be selected from a wide range depending on the type of monomer and the type of initiator, and can be selected from a range of 10 to 120°C. The polymerization time can also be selected from a wide range, and can be selected from a range of 10 minutes to 50 hours.

There are no particular limitations on the method for isolating the graft polymer from the solution after the polymerization is completed. For example, the solvent is heated and removed to isolate the polymer, or the polymer is precipitated by dropping the solution after the polymerization into a poor solvent and then collected by filtration. Note that the polymer after the graft polymerization contains ungrafted polysaccharides and polymers that are not grafted to polysaccharides, so it is preferable to purify the polymer by fractional precipitation or the like.

In the strong acid cation exchanger obtained by the above-mentioned production method, the sulfonic acid group is often in an alkali metal salt form (-SO ₃ M', M' represents an alkali metal), but when used as an ion exchanger, it is convenient that the sulfonic acid group is in a regenerated form (-SO ₃ H). In that case, the sulfonic acid group, which is an ion exchange group, is ion-exchanged from the alkali metal salt form to the regenerated form. The ion exchange from the alkali metal salt form to the regenerated form can be performed by contacting the strong acid cation exchanger in the alkali metal salt form with hydrochloric acid, sulfuric acid, or the like, as in the case of a normal strong acid ion exchange resin. Specifically, the strong acid cation exchanger in the alkali metal salt form is dissolved in hydrochloric acid, mixed for a certain period of time, and then the excess acid and salt are removed by dialysis. There is no particular restriction on the concentration of the strong acid cation exchanger when performing the ion exchange, but if the concentration is too high, stirring becomes difficult, which is not preferable, and a range of 0.1 to 5% by weight is preferable. There is also no particular restriction on the ion exchange reaction time, which can be appropriately selected within the range of 10 minutes to 5 hours.

Although the strongly acidic cation exchanger of the present invention is often soluble in water, some applications require it to retain its shape in water. In such cases, the polysaccharide, which is the parent polymer, can be crosslinked as appropriate. For example, when the parent polymer is sodium alginate, the sodium can be ion-exchanged with a divalent cation such as calcium, magnesium, or zinc to ionically crosslink the parent polymer, thereby preparing a hydrogel that can retain its shape even in water.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Example 1
5.51 g (29 mmol) of lithium styrene sulfonate (manufactured by Toso Finechem, hereinafter abbreviated as LiSS) was added little by little to 30 ml of ethanol under stirring to form a slurry. Then, 1.0 g (5.7 mmol as monosaccharide unit) of alginic acid (manufactured by Kimika Co., Ltd., Kimika Acid SA) was added little by little under stirring to form a slurry, and stirring was continued for 8 hours under nitrogen to purge oxygen in the system. A solution in which 27 mg of azobis(isobutyronitrile) (hereinafter abbreviated as AIBN) was dissolved in 2.5 ml of methanol was dropped with a syringe under nitrogen, and after the dropwise addition, the system was sealed and heated to perform graft polymerization at 60 ° C. for 15 hours. After the polymerization was completed, the slurry was dropped into tetrahydrofuran (hereinafter abbreviated as THF), and the solid matter was collected with a glass filter, washed with THF, and then dried under reduced pressure at room temperature to isolate the product. The isolated yield was 6.3 g and the yield was 95%. The yield was calculated by subtracting the amount of alginic acid charged from the isolated yield and dividing the result by the amount of monomer charged.

Since there is a possibility that unreacted alginic acid or ungrafted polyLiSS may be mixed in the isolated product, purification was performed by fractional precipitation. When 1 g of the isolated product was dissolved in 15 ml of pure water and dropped into a 10% calcium chloride aqueous solution, an insoluble component was generated. When the insoluble component was washed with ethanol, isolated and dried, the yield was 0.14 g. When this fraction was measured using aqueous GPC with a RI detector and a UV detector in combination, no UV absorption was observed in the main peak (see FIG. 1), and the weight average molecular weight of the main peak of 68,000 almost coincided with the weight average molecular weight of the raw alginic acid of 60,000, and the sulfur content was low at 0.7%, it was identified as a fraction of unreacted alginic acid to which LiSS was not grafted. On the other hand, the calcium chloride aqueous solution soluble portion was dropped and precipitated in ethanol to isolate it. The yield was 0.84 g. When aqueous GPC was used and an RI detector and a UV detector were used in combination, the peak shape was the same regardless of which detector was used (see FIG. 2). FT-IR measurement showed both an ester carbonyl absorption (1650 cm ⁻¹ ) derived from alginic acid and an S═O absorption (1190 cm ⁻¹ ) derived from polyLiSS, and therefore the fraction was identified as a graft polymer fraction. The number average molecular weight was 82,000, the weight average molecular weight was 311,000, and the sulfur content was 10.6% by weight. The strong acid cation exchange capacity (neutral salt decomposition capacity) measured by the method described below was 3.3 meq/g. The results are summarized in Table 1. By using the production method of the present invention, a strong acid cation exchanger with a large strong acid cation exchange capacity and a high molecular weight could be obtained.
(Method for measuring strong acid cation exchange capacity)
A predetermined amount of the reaction product was collected and dissolved in water, and the aqueous solution was dropped into a 1N aqueous hydrochloric acid solution to regenerate the graft polymer. After removing salts by dialysis, the aqueous solution was dropped into THF, and the resulting precipitate was collected by filtration, dried, and isolated. A predetermined amount of the resulting regenerated graft polymer was collected and immersed in a saturated aqueous sodium chloride solution for 2 hours, and the aqueous solution was separated to determine the amount of hydrochloric acid produced (quantified by titration using indicators: phenolphthalein and an aqueous sodium hydroxide solution), and the strong acid cation exchange capacity was determined.

Example 2
A graft polymer was produced and purified in the same manner as in Example 1, except that a mixture of LiSS and 3-sulfopropyl potassium methacrylate (hereinafter abbreviated as SPMAK) was used instead of LiSS as a monomer, ammonium cerium nitrate (IV) (hereinafter abbreviated as CAN) was used instead of AIBN as an initiator, and water was used instead of ethanol as a solvent, and polymerization was performed at 60° C. for 24 hours. The results are shown in Table 1. The isolated yield was 6.9 g, the yield was 93%, and the number average molecular weight of the purified graft polymer was 80,000, the weight average molecular weight was 570,000, the sulfur content was 10.2 wt%, and the strong acid cation exchange capacity (neutral salt decomposition capacity) was 3.2 meq/g.

Example 3
A graft polymer was produced and purified in the same manner as in Example 2, except that the amount of alginic acid charged was 0.75 g, SPMAK was used alone as the monomer, and the polymerization conditions were 55 ° C. and 15 hours. The results are shown in Table 1. The isolated yield was 3.6 g, the yield was 101%, and the number average molecular weight of the purified graft polymer was 60,000, the weight average molecular weight was 270,000, the sulfur content was 9.0 wt%, and the strong acid cation exchange capacity (neutral salt decomposition capacity) was 2.8 meq / g. In addition, 1H-NMR measurement was performed on the purified graft polymer. The NMR spectrum is shown in Figure 3, and a peak derived from the 1st position of alginic acid was observed at 4.5 to 5.0 ppm, and a peak derived from the SPMAK polymer was observed at 0.8 to 3.0 ppm, confirming the generation of the graft polymer.

Example 4
A graft polymer was produced and purified in the same manner as in Example 3, except that 0.2 g of Chimica Acid G was used as the alginic acid. The results are shown in Table 1. The isolated yield was 3.0 g, the yield was 100%, and the number average molecular weight of the purified graft polymer was 90,000, the weight average molecular weight was 430,000, the sulfur content was 9.5 wt%, and the strong acid cation exchange capacity (neutral salt decomposition capacity) was 3.0 meq/g.

Example 5
A graft polymer was produced and purified in the same manner as in Example 43, except that the amount of alginic acid charged was 1.0 g and that lithium 2-acrylamido-2-methylpropanesulfonate (hereinafter abbreviated as AMPSLi) was used as the monomer instead of SPMAK. The results are shown in Table 1. The isolated yield was 4.4 g, the yield was 56%, and the number average molecular weight of the purified graft polymer was 70,000, the weight average molecular weight was 1,300,000, the sulfur content was 9.3 wt%, and the strong acid cation exchange capacity (neutral salt decomposition capacity) was 2.9 meq/g.

Example 6
A graft polymer was produced and purified in the same manner as in Example 4, except that the amount of alginic acid charged was 0.5 g, potassium 2-acrylamido-2-methylpropanesulfonate (hereinafter abbreviated as AMPSK) was used as the monomer instead of SPMAK, and the polymerization time was 24 hours. The results are shown in Table 1. The isolated yield was 6.7 g, the yield was 88%, and the number average molecular weight of the purified graft polymer was 120,000, the weight average molecular weight was 1,900,000, the sulfur content was 10.6 wt%, and the strong acid cation exchange capacity (neutral salt decomposition capacity) was 3.3 meq/g.

Example 7
A graft polymer was produced and purified in the same manner as in Example 6, except that sodium 2-acrylamido-2-methylpropanesulfonate (hereinafter abbreviated as AMPSNa) was used as the monomer instead of AMPSK. The results are shown in Table 1. The isolated yield was 6.9 g, the yield was 90%, and the number average molecular weight of the purified graft polymer was 180,000, the weight average molecular weight was 2,400,000, the sulfur content was 10.6% by weight, and the strong acid cation exchange capacity (neutral salt decomposition capacity) was 3.3 meq/g.

Comparative Example 1
An attempt was made to produce a graft polymer in the same manner as in Example 3, except that sodium alginate (Kimika Algin I-3G, manufactured by Kimika Co., Ltd.) was used as the polysaccharide, but the viscosity of the system was too high to stir, and the graft polymerization was abandoned (see Table 1).

The strong acid cation exchanger of the present invention has a large ion exchange capacity, excellent mechanical properties, high hydrophilicity, and excellent resistance to contamination, and therefore can be used as an ion exchange resin or ion exchange membrane in a wide range of fields, such as in pure water/ultrapure water production equipment, electrodialysis equipment, sugar purification and isomerization, chromatography packing materials, catalysts, and fuel cells.

Claims (2)

The strongly acidic cation exchanger is a polysaccharide to which a polymer segment having a sulfonic acid group is grafted, the strongly acidic cation exchanger having a weight average molecular weight of 30,000 to 3,000,000 and a strongly acidic cation exchange capacity of 2.5 to 4.9 meq/g , and having a structure represented by the following general formula (1) :
(In the formula, m and n are each independently an integer of 1 or more; R ₁ may be the same or different and each represents hydrogen, an alkali metal, an alkaline earth metal or a group represented by -R ₃ -OH; R ₃ represents a divalent hydrocarbon group having 2 to 6 carbon atoms; R ₂ may be the same or different and each represents a polymer segment having a sulfonic acid group or hydrogen, and at least one of R ₂ is a polymer segment having a sulfonic acid group.) A method for producing a strongly acidic cation exchanger by graft polymerizing a sulfonic acid group-containing vinyl monomer onto a polysaccharide in a polar solvent, characterized in that the polysaccharide is an alginic acid, an alginate, or an alginate ester represented by the following general formula (2) which is insoluble in polar solvents, and the reaction is carried out in a slurry system.
(In the formula, m and n are each independently an integer of 1 or more, R ₁ may be the same or different and each represents hydrogen, an alkali metal, an alkaline earth metal or a group represented by -R ₃ -OH, and R ₃ represents a divalent hydrocarbon group having 2 to 6 carbon atoms.)