JPH10192717A - Porous ion exchanger and production of demineralized water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the mechanical strength of a porous ion exchanger obtd. by bonding ion exchange resin particles with a crosslinkable polymer by specifying the crosslinkable polymer content and crosslinking the polymer in the form of a mixture with the ion exchange resin particles. SOLUTION: When ion exchange resin particles are bonded with a crosslinkable polymer to obtain a porous ion exchanger for producing demineralized water by electrodialysis, the amt. of a thermoplastic polymer as the crosslinkable polymer is regulated to 0.5-20wt.% of the amt. of the exchanger and the polymer is crosslinked in the form of a mixture with the ion exchange resin particles. The void volume of open voids in the exchanger is regulated to 5-50vol.%. The resultant porous ion exchanger is used as an ion exchanger in the case where demineralized water is produced by supplying electric current while feeding water to be treated into the demineralization chamber of an electrodialytic apparatus with cation and anion exchange membranes between cathode and anode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid-permeable porous ion exchanger, and more particularly to an ion exchanger for producing deionized water by electrodialysis.

[0002]

2. Description of the Related Art As a method for producing deionized water, generally, a method is used in which water to be treated is flowed through a packed bed of an ion exchange resin, and impurity ions are adsorbed and removed by the ion exchange resin to obtain deionized water. . Here, a method of regenerating an ion-exchange resin having reduced adsorption capacity using an acid or an alkali is employed. However, in this method, there is a problem that an acid or alkali waste liquid used for regeneration is discharged, so that a method for producing deionized water that does not require regeneration of an ion exchange resin is desired.

[0003] From such a viewpoint, a self-regeneration type electrodialysis deionized water production method using an ion exchange resin and an ion exchange membrane in recent years has attracted attention. In this method, a mixture of an anion exchanger and a cation exchanger is placed in a desalting chamber of an electrodialysis apparatus in which an anion exchange membrane and a cation exchange membrane are alternately arranged, and water to be treated is placed in the desalting chamber. This is a method for producing deionized water by applying voltage while flowing and performing electrodialysis.

[0004] Regarding this method, a method for limiting the width and thickness of the desalting chamber (Japanese Patent Application Laid-Open No. 61-107906) and a method using a uniform ion exchange resin filled in the desalting chamber (particularly, Japanese Unexamined Patent Publication (Kokai) No. 3-207487), a method of converting an ion exchange resin to be filled in a portion through which water to be treated first passes into an anion exchange resin (Japanese Patent Laid-Open No. 4-71624). A method of preparing a mixture of ion-exchange fibers (JP-A-5-277344) and the like have been studied.

However, since the ion-exchanger cross-linked ion-exchange resin is not immobilized, the ion-exchanger of the same sign agglomerates during use, or particles or fibers of the ion-exchange resin are crushed by a water flow, resulting in an increase in efficiency. Desalination and regeneration are no longer performed, and there is a problem in the stability of the purity of the obtained water.

As a method of compensating for these disadvantages, a method of introducing ion-exchange groups by performing radiation grafting on a non-woven fabric such as polyethylene or polypropylene (Japanese Patent Laid-Open No. 5-6472).
6, Japanese Unexamined Patent Publication No. 5-131120), and a sheet formed by combining an ion-exchange polymer and a reinforcing polymer into a sea-island composite fiber (Japanese Unexamined Patent Publication No. 6-79268).

[0007] In these methods, the ion exchanger is immobilized, but it has disadvantages such as the need to use radiation, the complicated process of producing composite fibers, and the insufficient mechanical strength. Was.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a self-regenerating electrodialysis method for producing deionized water using a combination of an ion exchanger and an ion exchange membrane, which is immobilized regardless of complicated steps such as the use of radiation. An object of the present invention is to produce an ion exchanger having sufficient strength and to stably produce high-purity deionized water.

[0009]

The present invention relates to a porous ion exchanger in which ion exchange resin particles are bonded using a crosslinkable polymer, wherein the crosslinkable polymer is contained in the porous ion exchanger in an amount of 0.5%. The present invention provides a porous ion exchanger which is contained in an amount of about 20% by weight and is crosslinked in a state where a crosslinkable polymer is mixed with ion exchange resin particles.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The material of the ion exchange resin particles is not particularly limited, and various ion exchange resins can be used. Specifically, those obtained by introducing an ion exchange group into a styrene-divinylbenzene copolymer are preferred. As the ion exchange group, from the viewpoint of ion exchangeability and chemical stability, the cation exchange group is preferably a sulfonic acid type which is a strong acid, and the anion exchange group is a quaternary ammonium salt type or a pyridinium salt type which is a strong base. Is preferred.

The ion exchange capacity of the ion exchange resin particles is as follows:
0.5 to 7 meq / g dry resin is preferred. When the ion exchange capacity is smaller than 0.5 meq / g dry resin, the ion exchange performance is insufficient, and when the porous ion exchanger is disposed in the desalting chamber of the electrodialysis chamber, the adsorption and desorption of ions are performed. It is not preferable because the salt is not sufficiently formed and the purity of deionized water may decrease. Ion exchange capacity is 7 meq /
g If the resin is larger than the dry resin, the stability of the ion exchange resin itself may be impaired, which is not preferable. Further, when the ion exchange capacity is 1 to 5 meq / g dry resin, a resin having excellent performance stability and high purity of deionized water is obtained, which is particularly preferable.

The particle size of the ion exchange resin particles is 50 to 10
It is preferably in the range of 00 μm, particularly 300 to 600 μm. When the particle size is smaller than 50 μm, the pores of the porous ion exchanger become small, and water permeability may be reduced, which is not preferable. If the particle size is larger than 1000 μm, the surface area of the ion exchanger becomes insufficient, and the processing efficiency of ion exchange may decrease, such being undesirable. As the ion-exchange resin particles, those synthesized so as to have the above-mentioned particle size range or those crushed so as to have the above-mentioned particle size range can be used.

The shape of the ion-exchange resin particles is not particularly limited, but a spherical shape is preferable because of excellent water permeability.

As for the porosity of the porous ion exchanger, the porosity of the voids open to the outside involved in the passage of the liquid is preferably 5 to 50% by volume. If the porosity is less than 5% by volume, the flow rate of the liquid decreases and the pressure loss increases, which is not preferable. If the porosity is larger than 50% by volume, the mechanical strength of the porous ion exchanger may be reduced, and handling may be difficult. When the porosity is 10 to 40%, the water permeability is good, the desalination performance is excellent, and high-purity deionized water is obtained. In the above porosity, voids that do not actually come into contact with the liquid when the porous ion exchanger is disposed in the flow path of the liquid are not regarded as voids open to the outside.

[0015] In the porous ion exchanger of the present invention,
Although the contact between the ion-exchange resin particles is improved by bonding with the cross-linkable polymer, the contact may be impaired by the presence of the cross-linkable polymer between the ion-exchange resin particles. Therefore, for the purpose of disposing the porous ion exchanger in the desalting chamber of the electrodialysis device, it is preferable that the porous ion exchanger has low electric resistance.

When the porous ion exchanger is placed in an electrodialysis apparatus, the specific resistance is determined by filling the ion exchange resin particles contained in the porous ion exchanger into a desalting chamber of the same apparatus without a crosslinkable polymer. It is preferable that the value is not more than twice the specific resistance measured by the above method. If the specific resistance is more than twice, the voltage at the time of operation increases and the running cost increases, which is not preferable. It is particularly preferable that the specific resistance of the porous ion exchanger measured in this way is lower than that of the resin particles.

The porous ion exchanger may be one containing only cation exchange resin particles, one containing only anion exchange resin particles, or one containing a mixture of cation exchange resin particles and anion exchange resin particles.

In the case of containing cation-exchange resin particles and anion-exchange resin particles, not only those obtained by uniformly mixing them but also a portion containing only cation-exchange resin particles and a portion containing only anion-exchange resin particles In addition, those having a sea-island structure or a layered layer separation structure can also be used.

When the electrodialysis apparatus is used by placing it in a desalting chamber, it is preferable to use a mixture containing a mixture of cation exchange resin particles and anion exchange resin particles. The ratio of the cation exchange resin particles to the anion exchange resin particles used in the entire desalting chamber should be cation exchange resin particles / anion exchange resin particles = 30/70 to 60/40 in total ion exchange capacity ratio. Is preferred. If the total ion exchange capacity ratio is out of this range, the purity of the treated water may be reduced.

The water permeability of the porous ion exchanger is 10 kg · cm ⁻¹ · h ^{−1 at} a pressure of 0.35 kg · cm ⁻² .
It is preferable that it is above. When it is smaller than 10 kg · cm ⁻¹ · h ⁻¹ or more, the flow path resistance when the porous ion exchanger is used in the flow path is increased, and the amount of treated water is reduced or the operation is performed under a high pressure. Is not preferred. It is particularly preferable that the water permeability is 100 kg · cm ⁻¹ · h ⁻¹ or more. The higher the water permeability is, the more preferable. However, if a material having a large void is formed in order to produce a material having a high water permeability, the ion exchange performance and the mechanical strength may be reduced. Therefore, the substantial upper limit is 10,000 kg · cm ^−1.・
h ^-1 .

The water permeability is determined by preparing a sample of a columnar body (for example, a prism or a cylinder) having two bottom surfaces parallel to each other, and preventing water from leaking from the side surface to 0.35 kg from one bottom surface. ^-Water is introduced at a pressure of cm ^-2 and the amount of water flowing out from the other bottom surface is measured and determined. At this time, assuming that the area of the bottom surface is A (cm ² ), the height of the columnar body, that is, the interval between the bottom surfaces is L (cm), and the amount of permeated water per hour is W (kg · h ⁻¹ ), Water permeability is WL / A (k
g · cm ⁻¹ · h ^-1 ). A and L can be arbitrarily determined, but A is about 1 to 1000 cm ² and L is 1 to 100.
It is preferable to measure in about cm.

The amount of the crosslinkable polymer used is 0.5 to 20% by weight of the porous ion exchanger, particularly preferably 1 to 7% by weight. If the amount is less than 0.5% by weight, the mechanical strength of the porous ion exchanger is reduced, and handling becomes difficult, which is not preferable. If the use amount is more than 20% by weight, the surface of the ion-exchange resin particles is coated with a crosslinkable polymer, so that the adsorptivity decreases, and the porosity decreases.

In the present invention, in order to increase the mechanical strength of the porous ion exchanger, a crosslinkable polymer which can be crosslinked at the time of molding or after molding is used.

The crosslinkable polymer is not particularly limited, but preferably has an unsaturated double bond as a crosslinkable site. The unsaturated double bond may be included in the main chain or side chain of the crosslinkable polymer. In addition, the crosslinkable polymer is preferably thermoplastic in order to facilitate molding. on the other hand,
From the viewpoint of the heat resistance of the ion-exchange group, it is preferable that the molding temperature of the ion exchanger is low. Therefore, the crosslinkable polymer is preferably liquid at room temperature.

As preferred crosslinkable polymers, specifically, 1,2-polybutadiene, 1,4-polybutadiene, ethylene-propylene-diene copolymer (EPD)
M), natural rubber, butyl rubber, polyisoprene, polychloroprene, styrene-butadiene rubber, nitrile rubber and the like.

Among them, 1,2-polybutadiene is particularly preferable because it has a low softening temperature and a low molding temperature. In addition, 1,2-polybutadiene is preferable because it has higher crosslinking efficiency and higher mechanical strength than other polymers having a double bond.

As a method for producing the porous ion exchanger of the present invention, the following method is preferred. That is, a method in which the ion-exchange resin particles and the cross-linkable polymer are heated and kneaded, and then formed into a sheet by thermoforming such as a flat plate press, or a flat plate press after applying the cross-linkable polymer solution to the surface of the ion-exchange resin particles and removing the solvent. A method of forming a sheet by thermoforming, a method of mixing a crosslinkable polymer, a pore-forming agent, and an ion-exchange resin particle by heating and extracting the pore-forming agent; A method of extracting the pore-forming agent after coating and curing the surface of the particles, and the like.

Among them, a method in which the ion-exchange resin particles and the crosslinkable polymer are heated and kneaded, and then formed into a sheet by thermoforming such as a flat plate press, etc .; The method of extracting the agent is particularly preferable from the viewpoint of the moldability and the specific resistance of the obtained porous ion exchanger. The thermoforming temperature of the crosslinkable polymer is not particularly limited, but is preferably from 120 to 180 ° C from the viewpoint of the heat resistance of the ion exchange resin particles.

When a pore-forming agent is used, it is preferable to add 5 to 40% by weight of the pore-forming agent based on the weight of the crosslinkable polymer. The type of pore-forming agent is not particularly limited, and any pore-forming agent can be used as long as it can be extracted later with a solvent. Polymer powders such as polyvinyl alcohol and polyester are particularly preferable.

In the present invention, the desired porous ion exchanger can be obtained by crosslinking the crosslinkable polymer in a state of being mixed with the ion exchange resin particles. At this time, it is considered that the crosslinkable polymers are mainly crosslinked with each other, but it is considered that the ion exchange resin particles and the crosslinkable polymer may be partially crosslinked.

The method for crosslinking the crosslinkable polymer is not particularly limited, and conventional methods can be used. When the crosslinking site is an unsaturated double bond, crosslinking by heating or crosslinking by irradiation with light or radiation is possible. It is. Crosslinking is performed simultaneously with or after the thermoforming of the porous ion exchanger.

Further, another crosslinking agent may be added to crosslink the crosslinkable polymer. For example, when the crosslinking site is an unsaturated double bond, an organic peroxide such as benzoyl peroxide or an azo organic compound such as azoisobutyronitrile can be used as a crosslinking agent. Among them, organic peroxides such as t-butyl hydroperoxide and t-hexyl hydroperoxide are particularly preferable because they do not crosslink during heating and kneading, but crosslink during molding.

The porous ion exchanger of the present invention can be used in various apparatuses for performing ion exchange by being disposed in a liquid flow path. In particular, the porous ion exchanger is provided by alternately disposing cation exchange membranes and anion exchange membranes. It can be preferably used for a method for continuously producing deionized water by filling a desalting chamber of an electrodialysis apparatus.

Specifically, the following method is preferred as a method for producing deionized water. That is, a plurality of cation exchange membranes and anion exchange membranes are alternately arranged between an anode chamber having an anode and a cathode chamber having a cathode, and the anode side is partitioned by an anion exchange membrane and the cathode side is positive. 2 to 300 sets of desalting chambers partitioned by an ion exchange membrane and enrichment chambers partitioned by a cation exchange membrane on the anode side and partitioned by an anion exchange membrane on the cathode side are alternately arranged in parallel. Desalination can be performed by flowing current while flowing water to be treated into the desalting chamber and flowing water for discharging concentrated salts into the concentration chamber. At the time of desalting by electrodialysis, it is preferable to apply a voltage of about 4 V at which water dissociation occurs in the desalting chamber to each unit cell.

When the porous ion exchanger of the present invention is disposed in the above-mentioned deionization chamber, deionized water can be produced by a so-called self-regeneration type electrodialysis method. By forming the porous ion exchanger according to the size of the desalting chamber, an apparatus in which the ion exchanger is filled in the desalting chamber can be easily assembled. In the case of a conventional electrodialysis device, the direction of the current flows perpendicular to the membrane surface, that is, in the thickness direction of the plate-like ion exchanger, and the water flow flows perpendicular to it.

The thickness of the porous ion exchanger is 1 to 30 m
m, particularly preferably 3 to 12 mm. Thickness 1
If the thickness is less than 30 mm, the water in the desalting chamber may not flow easily, and the amount of treated water may decrease. If the thickness is more than 30 mm, the electric resistance may increase.

Since the ion exchange resin particles may swell when immersed in water, it is necessary to form a porous ion exchanger in consideration of the swelling ratio when incorporating the particles into an electrodialyzer or the like. Conversely, by using the swelling to bring the porous ion exchanger into close contact with the flow channel, it is possible to prevent the occurrence of unnecessary side flow. Using a material similar to the crosslinkable polymer, the porous ion exchanger can be tightly joined in the channel.

The porous ion exchanger of the present invention can be used in such a manner that current is not supplied when ion exchange is performed while being placed in a flow path, but current is supplied when adsorbed ions are desorbed. At the time of regeneration, a porous ion exchanger is arranged between the anode and the cathode, and a diaphragm is arranged between the porous ion exchanger and the anode, and between the porous ion exchanger and the cathode, and current flows. . The membrane need not be an ion exchange membrane, but for efficient regeneration, it is preferable to arrange an anion exchange membrane on the anode side and a cation exchange membrane on the cathode side of the porous ion exchanger. .

[0039]

【Example】

[Example] A sulfonic acid type cation exchange resin having a particle size of 400 to 550 μm and an ion exchange capacity of 4.2 meq / g (Rohm and Haas Co., Ltd. product name: Amberlite 201CT), and a particle size of 400 After drying a quaternary ammonium salt type anion exchange resin (Rohm and Haas product name: Amberlite IRA400) with a dry resin of ~ 530 μm and an ion exchange capacity of 3.7 meq / g, anion exchange with the cation exchange resin The resin and the resin are mixed at a ratio of 50/50 (volume ratio in a dry state), and the ion exchange capacity ratio is 6
0/40 mixture.

3% by weight of pelletized 1,2-polybutadiene was mixed with the mixture and kneaded at 130 ° C. The obtained kneaded material was thermoformed at 130 ° C. with a flat plate press to obtain a thickness of 8 mm.
mm porous sheet material was obtained.

The porous ion exchanger had a tensile strength of 0.65 kg / cm ² , and the voids opened to the outside had a porosity of 23% by volume. When the value of the specific resistance in water having an electric conductivity of 10 μS / cm was measured in a cell, it was 400 Ω · cm when the current density was 0.005 A / cm ² .
The value was significantly lower than 680 Ω · cm when the same amount of the mixture of the granular cation exchange resin and the anion exchange resin having the same mixing ratio as above was measured in the cell.

The porous sheet ion exchanger was assembled in a desalting chamber of an electrodialyzer and subjected to a deionized water test. The electrodialysis apparatus used had a cation exchange membrane (Asahi Glass Co., Ltd. product name: Selemion CMT) and an anion exchange membrane (Asahi Glass Co., Ltd. product name: Selemion AMP) having an effective area of 500 cm ² × 5 pairs. Dewatering was performed using water having a conductivity of 5 μS / cm as raw water and applying a voltage of 4 V per unit cell. As a result, deionized water having a conductivity of 0.07 μS / cm was obtained stably.

Comparative Example A porous sheet having a thickness of 8 mm was obtained in the same manner as in Example except that 1,2-polybutadiene was changed to low-density polyethylene. The tensile strength of this porous ion exchanger was 0.25 kg / cm ² .

[0044]

The porous ion exchanger of the present invention has high mechanical strength and excellent ion exchange performance, so that deionized water having a stable purity can be obtained. Further, since the ion exchanger can be obtained in a sheet form, it is easy to handle, and since a complicated process is not required for production, a stable performance can be easily obtained.

The method for producing deionized water of the present invention can continuously produce high-purity deionized water stably for a long period of time. In addition, since a porous ion exchanger is used, the electrodialysis apparatus can be easily assembled.

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Claims (5)

[Claims] 1. A porous ion exchanger to which ion exchange resin particles are bonded using a crosslinkable polymer, wherein the crosslinkable polymer is contained in the porous ion exchanger in an amount of 0.5 to 20% by weight. A porous ion exchanger, wherein the crosslinkable polymer is crosslinked in a state of being mixed with ion exchange resin particles. 2. The porous ion exchanger according to claim 1, wherein the voids open to the outside have a porosity of 5 to 50% by volume. 3. The porous ion exchanger according to claim 1, wherein the crosslinkable polymer is a thermoplastic polymer. 4. The porous ion exchanger according to claim 1, wherein the crosslinkable polymer is 1,2-polybutadiene. 5. A deionized water producing apparatus in which an ion exchanger is accommodated in a desalting chamber of an electrodialysis apparatus in which a cation exchange membrane and an anion exchange membrane are alternately arranged between a cathode and an anode. In the method of producing deionized water by energizing while flowing the water to be treated in the salt chamber, as the ion exchanger,
A method for producing deionized water using the porous ion exchanger according to claim 1, 2, 3, or 4.