JP4401334B2 - Manufacturing method of ion exchange net - Google Patents

Description

  The present invention relates to an ion exchange net made of a thermoplastic resin into which an ion exchange group is introduced, and more particularly to an ion exchange net used for desalting an electrolyte solution using an electrodialyzer.

  Electrodialysis desalination of electrolyte solution was first developed in the 1950s for the purpose of desalination of brackish water, followed by concentration of seawater for the production of salt, soy sauce and whey desalination, and various chemicals. It has been used for various purposes such as process rationalization, wastewater treatment, and separation of impurities in wine.

  The electrodialyzer has an anode chamber and a cathode chamber at both ends, and an anion exchange membrane and a cation exchange membrane are alternately disposed between the anode chamber and the cathode chamber, and a desalting chamber and a concentration chamber are alternately formed. In such an electrodialysis apparatus, the ion exchanger, which is an ion conductor, is accommodated in the desalting chamber, so that the electrical conductivity is improved and is mainly caused by a potential difference at the interface (contact point) with the exchanger of different ions. It is known that the “hydrolysis” phenomenon is less likely to occur, and the electrolyte can be desalted in a low concentration range.

  As an ion exchanger used in such an electrodialysis apparatus, a nonwoven fabric made of a fibrous ion exchanger is known. As such a nonwoven fabric, for example, a polyolefin or a fluorinated polyolefin is used, and a nonwoven fabric made of porous fibers is formed by a stretch opening method, and the pores are filled with a styrene / divinylbenzene-based ion exchange polymer. (See Patent Document 1), and a non-woven fabric made of polyolefin or fluorinated polyolefin fiber, which is obtained by introducing an ion exchange group after performing graft polymerization with radiation (see Patent Document 2), etc. have been proposed. However, when these fibrous ion exchangers are used for electrodialysis, the solution not only passes through a narrow fiber gap, but also passes through a long distance in the width or length direction of the nonwoven fabric, so there is a problem that the pressure loss is large. is there.

  Therefore, it has been proposed to dispose an ion exchange net between a cation exchange membrane and an anion exchange membrane in place of the nonwoven fabric made of the fibrous ion exchanger as described above. In the first place, in an electrodialysis apparatus, a net called a spacer is interposed between a cation exchange membrane and an anion exchange membrane. The role of the spacer includes intervening between the membranes to prevent contact between the membranes, and a partition between the desalting chamber and the concentration chamber, mechanical support of the membrane, and stirring and mixing of the desalted solution. By adding an ion exchange group to this spacer to form an ion exchange net, the limit current density can be improved, and as a result, the required membrane area can be reduced and desalting can be performed in a low electrolyte concentration region. Become. Furthermore, it becomes possible to prevent the desalination performance from being lowered by the ion exchange resin and the pressure loss in the fibrous ion exchanger.

  By introducing an ion exchange spacer, when performing desalting in an electrodialysis apparatus, the spacer also captures ions in addition to the ion exchange membrane that serves as a water passageway. Ions can move efficiently with voltage. Therefore, for example, when taking out water from seawater, pure water with high purity can be taken out.

  As a method for producing an ion exchange spacer, a pulverized ion exchange resin is mixed with an aqueous solution of a hydrophilic polymer, the solution is applied to a commercially available net polymer material, and dried to crosslink the hydrophilic polymer (Patent Document). 3), but the practical use has not been achieved because of the low exchange capacity of the obtained ion exchange spacer.

  In addition, as a method for producing an ion exchange net, there is a method of introducing ion exchange groups by radiation graft polymerization. Here, ionizing radiation used for radiation graft polymerization includes α, β, γ rays, electron beams, ultraviolet rays, etc., and ion-exchange nets that have been put to practical use on the market are grafted using γ rays or electron beams. However, this method is very complicated and requires an expensive apparatus (see Patent Documents 4 to 6).

In addition, there is a net-like conductive spacer in which conductive carbon fine particles are applied to a net-like material obtained by forming a synthetic resin such as polyolefin or polyvinyl alcohol into a string shape and winding it so as to intersect at right angles (see Patent Document 7). ), Lack of practicality due to the complexity of the production method.
JP2002-95978 JP 4-293811 US Pat. No. 6,090,258 International Publication No. 2003/55604 Pamphlet Korean Patent 2003-18635 Korean Patent 2003-70398 JP 2004-97897 A

An object of the present invention is to provide a method for producing an ion exchange net by introducing an ion exchange group into a non-ion exchangeable thermoplastic resin by a simple method.
Another object of the present invention is to provide a method for producing an ion exchange net that is suitably used for desalting using an electrodialyzer, and that exhibits excellent desalting performance especially when desalting an electrolyte solution in a low concentration range. It is to provide.

According to the present invention,
Preparing a thermoplastic resin containing at least one functional group selected from the group consisting of a glycidyl group, an epoxy group, an acid anhydride group and a styrene group at a concentration of 0.1 to 80 mmol / g;
The thermoplastic resin is integrally extruded into a net shape to produce an ion exchange precursor net,
Next, the functional group in the ion exchange precursor net is converted into an ion exchange group.
An ion exchange net manufacturing method is provided.

  According to the production method of the present invention, when the anion exchange net is produced as the thermoplastic resin, an ethylene-glycidyl methacrylate copolymer is used, and when the cation exchange net is produced, styrene-ethylene-butylene is produced. It is preferable to use a copolymer.

  According to the production method of the present invention, an ion exchange net in which an ion exchange group is introduced into a thermoplastic resin can be produced easily and inexpensively without using complicated and costly means such as radiation graft polymerization. . Moreover, in this method, the ion exchange group concentration and the like can be easily adjusted by changing the reaction conditions and the like. In addition, the ion exchange net obtained in the present invention is less likely to leave the ion exchange group, and can be used stably for a long time without impairing the function.

(Raw material thermoplastic resin)
In the present invention, as the raw material thermoplastic resin, one containing a glycidyl group, an epoxy group, an acid anhydride group and a styrene group as a functional group is used. That is, a glycidyl group, an epoxy group, and an acid anhydride group are reactive with an anion-exchangeable amino group, and a thermoplastic resin having such a functional group is used for producing an anion exchange net. used. The styrene group is reactive with a sulfonic acid group having a cation exchange ability, and a thermoplastic resin having such a functional group is used when a cation exchange net is produced.

  Moreover, said functional group needs to be contained in a thermoplastic resin in the density | concentration of 0.1-80 mmol / g in a thermoplastic resin. If the functional group concentration is 0.1 mmol / g or less, a sufficient exchange capacity cannot be obtained, and if it is 80 mmol / g or more, it is extremely difficult to form a net.

  Accordingly, the thermoplastic resin is not particularly limited as long as the functional group concentration is within the above range, but generally, considering the ease of molding into a net shape, the melt flow rate (MFR, 230 ° C.) Is preferably in the range of 0.5 to 60 g / 10 min.

In the present invention, examples of the thermoplastic resin used for producing the anion exchange net include olefin resins and acrylic resins modified with the above-described functional groups (glycidyl group, epoxy group, maleic anhydride group). Preferably, ethylene-glycidyl (meth) acrylate copolymer, negligible maleic acid-modified (meth) acrylate, maleic anhydride-modified polyolefin, and most preferable is ethylene-glycidyl methacrylate copolymer. is there. Further, as the thermoplastic resin used for the production of the cation exchange net, a styrene copolymer containing a styrene unit in the amount described above, for example, a styrene-ethylene copolymer, a styrene-ethylene-butylene copolymer, and Examples of the hydrogenated product include styrene-ethylene-butylene copolymer and the hydrogenated product thereof.
The copolymerization ratio and molecular weight of these thermoplastic resins are such that physical properties such as functional group concentration and MFR are within the above ranges.

  The thermoplastic resin can be used in the form of a blend with other thermoplastic resins as long as the functional group concentration is within the above range, and various inorganic fillers or A high melting point polymer such as liquid crystal polyester may be blended.

(Preparation of ion exchange precursor net)
In the present invention, an ion exchange precursor net is produced using the above thermoplastic resin. The ion exchange precursor net is produced by integral extrusion molding of a thermoplastic resin.

  Such integral extrusion can be performed by a known method described in, for example, Japanese Patent Publication No. 34-4185 and Japanese Patent Laid-Open No. 53-49170. As an example, as shown in FIG. 1, for example, as shown in FIG. 1, a die mold provided at the tip of the extruder includes an outer mold 1 that can rotate relatively and a core mold 2 provided inside the outer mold. Use a structure. A plurality of grooves 1a serving as resin flow paths are formed on the inner surface of the outer mold 1 at appropriate intervals. On the other hand, a plurality of grooves 2a serving as resin flow paths are formed on the outer surface of the core mold 2 at appropriate intervals. Has been. Therefore, a cylindrical ion exchange precursor net is obtained by melt-extruding the resin while relatively rotating the outer mold 1 and the core mold 2 (usually rotating in opposite directions to each other). be able to. That is, the portion that is pushed out when the groove 1a and the groove 2a are matched becomes the bridging portion of the net. According to such a method, the size of the opening of the net can be easily adjusted by adjusting the rotational speed of the outer mold and the core mold.

  The ion exchange precursor net extruded into a cylindrical shape as described above is cooled and solidified to stabilize the shape, and then taken up and cut. The cooling and solidification is performed, for example, by introducing it into water immediately after extrusion. At this time, it is preferable to place a cylindrical mandrel (sizing) in the water and perform extrusion so as to wrap the mandrel. That is, the inner diameter of the cylindrical ion exchange precursor net can be adjusted according to the outer diameter of the mandrel by performing cooling and solidification while pressing the molten cylindrical ion exchange precursor on the mandrel. For example, if the inner diameter is adjusted so that the circumference of this cylindrical ion exchange net corresponds to the spacer width when used as a spacer of an electrodialyzer, without post-processing such as shape adjustment, The ion exchange net can be used as a spacer as it is. The take-off / cutting after cooling and solidification is performed by a method known per se, whereby a sheet-like ion exchange precursor net is obtained.

(Introduction of ion exchange groups)
In the present invention, ion exchange groups are introduced into the sheet-like ion exchange precursor net obtained as described above.

  For example, in order to produce an anion exchange net, a thermoplastic resin constituting the net and an amino compound are reacted to fix the amino compound on the net, and then quaternary ammoniumization is performed. Such an amino compound is not particularly limited, but has at least one primary or secondary amino group in consideration of the reactivity of the amino group with the functional group reactive with the amino group of the thermoplastic resin. For example, methylamine, dimethylamine, allylamine, methylenediamine, ethylenediamine, polyallylamine, polyethyleneimine, etc. can be suitably used, and these amino compounds should be used alone. It is also possible to use a mixture of two or more.

  The reaction between the thermoplastic resin and the amino compound is carried out by immersing the ion exchange precursor net in the liquid of the amino compound. The amino compound liquid to be used is a functional group in the amino resin and the thermoplastic resin, if necessary. It can be diluted with an organic solvent that does not react with the group and is incompatible with the thermoplastic resin. However, the concentration of the amino compound in such a diluted solution is preferably 1% by weight or more. This is because if the concentration is too low, the reaction efficiency between the amino group and the functional group decreases, and the reaction takes a long time.

  The reaction between the thermoplastic resin (ion exchange precursor net) and the amino compound varies depending on the type of functional group of the thermoplastic resin, but is generally 10 ° C. or higher and lower than the deformation temperature of the ion exchange precursor net. For example, it is performed by heating in the range of 10 to 130 ° C. When the temperature is lower than 10 ° C., the progress of the reaction becomes rate-determined, it takes a long time to distribute a sufficient amount of amino compound in the net to obtain a sufficient exchange capacity, and the productivity is reduced. This is because if the temperature is higher than 130 ° C., the net may be melted and deformed. This reaction is usually performed for about 1 to 50 hours. By this reaction, the functional group of the thermoplastic resin present on the surface of the net reacts with the amino compound, and the amino compound is fixed on the net. That is, a coating layer of the reacted amino compound is formed on the net surface.

  The quaternary ammonium formation performed after fixing the amino compound in this way uses a quaternary ammonium agent, and converts amino groups present in the surface amino compound coating layer, particularly tertiary amino groups to quaternary ammonium groups. This is done. As such a quaternary ammonium agent, monohalogenated alkyls such as methyl fluoride, methyl chloride, methyl bromide, methyl iodide and the like are preferably used. Methyl is used.

  In the quaternization reaction, a solution in which a quaternary ammonium agent is dissolved in a suitable organic solvent is used, and the ion exchange precursor net on which the amino compound coating layer is formed is immersed in the solution. This is easily done. In this case, in the quaternization reaction with methyl iodide, since the boiling point of methyl iodide is as low as 43 ° C., it is desirable that the quaternization is performed at a temperature equal to or lower than the boiling temperature over about one day.

  After the quaternary ammonium conversion is performed as described above, washing is performed using a sodium sulfite aqueous solution or the like to remove free iodine and the like, thereby obtaining a final anion exchange net.

  Further, in order to produce a cation exchange net, a sulfonic acid group is introduced into the thermoplastic resin constituting the ion exchange precursor net. The introduction of the sulfonic acid group is derived from a glycidyl group, an epoxy group, an acid anhydride group, and a styrene group. The introduction method of a sulfonic acid group is used without any limitation. For example, a sulfonated product can be reacted with an ion exchange precursor net composed of a thermoplastic resin having a styrene group as a functional group, and a sulfonic acid group can be fixed on the surface of the net. Such a sulfonated product is not particularly limited, but generally, concentrated sulfuric acid, chlorosulfonic acid and the like can be mentioned. These sulfonating agents can be used alone or in combination of two or more.

  Sulfonation using the sulfonating agent varies depending on the type of functional group possessed by the thermoplastic resin, but is generally preferably carried out at 10 ° C. or more and less than 130 ° C. If the temperature is higher than 130 ° C., the net may be melted and deformed. This reaction is usually performed for about 0.5 to 5 hours. By this reaction, a sulfonic acid group is introduced on the surface of the ion exchange precursor net, and a cation exchange net is obtained.

  The cation exchange net obtained by the sulfonation is neutralized with an aqueous sodium hydroxide solution and stored in a neutral salt form.

(Ion exchange net)
The ion exchange net produced in this way has, for example, an ion exchange capacity of 0.3 meq / g or more, a particularly high surface ion exchange group concentration, and an ion exchange group is introduced into the resin constituting the net. Therefore, there is an advantage that deformation due to swelling of water or the like hardly occurs. In particular, the spacer is used by being disposed between an anion exchange membrane and a cation exchange membrane in an electrodialysis apparatus. The ion exchange net used as the spacer is not particularly limited in the setting of the opening area ratio and thickness per unit area, but the opening area ratio per unit area is set to about 30 to 70%, The thickness is preferably set to about 0.3 to 2.0 mm.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples. The names of the compounds used in the examples and comparative examples are shown below.

(Thermoplastic resin)
Ethylene-glycidyl methacrylate copolymer (glycidyl group content: 0.93 mmol / g)
Maleic anhydride-methacrylate copolymer (maleic anhydride content 0.23 mmol / g)
Maleic anhydride grafted polypropylene (maleic anhydride content 0.04 mmol / g)
Hydrogenated styrene-ethylene elastomer terminal carboxylic acid type (styrene content 2.50 mmol / g)
Hydrogenated styrene-ethylene elastomer (styrene content 2.50 mmol / g)

(Amino compound and sulfonating agent)
Methylamine (Wako Pure Chemical Industries)
Dimethylamine (Wako Pure Chemical Industries)
Epomin SP-003:
Polyethyleneimine (Nippon Shokubai, average molecular weight 300, concentration 99%)
Epomin SP-006:
Polyethyleneimine (Nippon Shokubai, average molecular weight 600, concentration 99%)
Epomin SP-018:
Polyethyleneimine (Nippon Shokubai, average molecular weight 1800, concentration 99%)
PEI MW800:
Polyethyleneimine (Sigma Aldrich, average molecular weight 800, concentration 99%)
Chlorsulfonic acid (Wako Pure Chemical Industries)
Special grade sulfuric acid (manufactured by Wako Pure Chemical Industries)

(Quaternary ammonium agent, solvent, etc.)
Quaternary ammonium agent: methyl iodide (manufactured by Tokyo Chemical Industry)
Special grade hexane (Wako Pure Chemical Industries)
Sodium sulfite (Wako Pure Chemical Industries)

<Example 1>
A cylindrical die having a structure in which the outer mold and the core mold shown in FIG. 1 are provided at the lower end of the 65 mm extruder and the outer mold and the core mold rotate in directions opposite to each other is mounted. An ethylene-glycidyl methacrylate copolymer (glycidyl group content: 0.93 mmol / g) is charged into this extruder and extruded through the cylindrical die while being heated and melted at 220 ° C., and the ion exchange is continued downward. A precursor net cylinder was extruded. The extruded precursor net cylindrical product was guided to a mandrel (sizing) in a water tank, cooled and solidified, and then cut in the extrusion direction to obtain a continuous sheet of ion exchange precursor net.

The above sheet was immersed in Epomin SP-003 and reacted at 100 ° C. for 10 hours. Then, quaternization reaction was carried out at 30 ° C. for 1 day in methyl iodide / hexane = mass ratio 40/60, and further immersed in a 0.2 N sodium sulfite aqueous solution to remove free iodine. An anion exchange net was obtained. The an open area ratio per unit area (1 m ² ) of this anion exchange net is 50 to 56%, and the thickness is 0.63 to 0.80 mm.

About the obtained anion exchange net | network, the anion exchange capacity | capacitance and the moisture content were measured with the following method.
The obtained anion exchanger was immersed in a 0.5 N hydrochloric acid aqueous solution for 2 hours or more. Then, it was immersed in ion exchange water for 1 hour. Further, it was immersed in an aqueous 0.2 N sodium nitrate solution for 1 hour or more. The immersion liquid was subjected to precipitation titration with a 0.1 N aqueous silver nitrate solution, and the eluted chlorine ions were quantified (Pmeq).
The anion exchanger taken out from the aqueous sodium nitrate solution was immersed in seawater, washed thoroughly with ion-exchanged water, the liquid was thoroughly dropped, and the wet weight (W) of the anion exchanger was measured. Then, it dried at 60 degreeC overnight with the vacuum dryer, and measured the dry weight (D). From the above results, the anion exchange capacity and water content were calculated from the following formula.

Anion exchange capacity (meq / g) = P / D
Moisture content (%) = (W−D) / D

  The anion exchange capacity was 2.53 meq / g, and the water content was 20%.

<Example 2>
Except that a hydrogenated styrene-ethylene elastomer terminal carboxylic acid type (styrene content: 2.50 mmol / g) was used as the thermoplastic resin, the ion exchange precursor net of A sheet was obtained. This sheet was reacted by being immersed in 98% sulfuric acid / 90% chlorosulfonic acid = mass ratio 50/50 at 40 ° C. for 1 hour, and further immersed in a 0.5 N aqueous sodium hydroxide solution overnight. In sum, a cation exchange net of the same size as in Example 1 was obtained.

Moreover, about the obtained cation exchange net | network, the cation exchange capacity | capacitance and the moisture content were measured with the following method.
The obtained cation exchanger was immersed in a 0.5 N aqueous hydrochloric acid solution for 2 hours or more. Then, it was immersed in ion exchange water for 1 hour. Further, it was immersed in a 0.5 N aqueous sodium chloride solution for 1 hour or longer. The immersion liquid was subjected to neutralization titration with a 0.1 N sodium hydroxide aqueous solution, and the eluted hydrogen ions were quantified (Qmeq).
The cation exchange net taken out from the aqueous sodium chloride solution was immersed in seawater, thoroughly washed with ion exchange water, and after the liquid was thoroughly dropped, the wet weight (W) of the cation exchange net was measured. Then, it dried at 60 degreeC overnight with the vacuum dryer, and measured the dry weight (D). From the above results, the cation exchange capacity and water content were calculated from the following formula. The results are shown in Table 1 together with the results of Example 1.

Cation exchange capacity (meq / g) = Q / D
Moisture content (%) = (W−D) / D

  The cation exchange capacity was 1.22 meq / g, and the water content was 10%.

<Examples 3 to 7 and Comparative Examples 1 and 2>
The reaction was carried out in the same manner as in Example 1 or Example 2 except that the thermoplastic resin was changed as shown in Table 1. Further, the anion exchange net and cation exchange obtained in the same manner as in Example 1 or Example 2 were used. The net was evaluated. The results are shown in Table 1.

  From Table 1, it can be seen that the ion exchange net obtained by the production method of the present invention exhibits an excellent ion exchange capacity value.

It is a figure which shows schematic structure of the die | dye used when shape | molding a net | network by extrusion molding.

Explanation of symbols

1: Outer mold 2: Core mold 1a, 2a: Groove to be a resin flow path

Claims (3)

Preparing a thermoplastic resin containing at least one functional group selected from the group consisting of a glycidyl group, an epoxy group, an acid anhydride group and a styrene group at a concentration of 0.1 to 80 mmol / g;
The thermoplastic resin is integrally extruded into a net shape to produce an ion exchange precursor net,
Next, the functional group in the ion exchange precursor net is converted into an ion exchange group.
An ion exchange net manufacturing method characterized by the above.   The method for producing an anion exchange net according to claim 1, wherein the thermoplastic resin is an ethylene-glycidyl methacrylate copolymer.   The method for producing a cation exchange net according to claim 1, wherein the thermoplastic resin is a styrene-ethylene-butylene copolymer.

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