WO2014132888A1

WO2014132888A1 - Desalination method and desalination apparatus

Info

Publication number: WO2014132888A1
Application number: PCT/JP2014/054157
Authority: WO
Inventors: 澄田　康光; 山中　弘次
Original assignee: オルガノ株式会社
Priority date: 2013-03-01
Filing date: 2014-02-21
Publication date: 2014-09-04

Abstract

A desalination device for desalinating water of interest is equipped with: a pair of electrodes having such a property that the polarity of a direct-current voltage to be applied to the electrodes can be reversed; a bipolar membrane; and an ion exchange zone in which a cation exchanger and an anion exchanger are arranged in a mixed state. Both of the bipolar membrane and the ion exchange zone are arranged in a space to which a voltage can be applied through the pair of electrodes. The cation exchanger is, for example, a weakly acidic cation exchanger, and the anion exchanger is, for example, a weakly basic anion exchanger. A desalination treatment of water of interest is carried out by passing the water through the apparatus while applying a voltage between the pair of electrodes in such a manner that one of the electrodes which faces a cation exchange membrane in the bipolar membrane acts as an anode and the other of the electrodes which faces an anion exchange membrane in the bipolar membrane acts as a cathode. When a regeneration treatment is to be carried out, the polarity of a direct-current voltage to be applied to the pair of electrodes is reversed.

Description

Desalination method and desalting apparatus

The present invention relates to a water treatment for removing salts contained in water, and more particularly, to a desalting method and a desalting apparatus using a bipolar membrane.

Conventionally, a method using an ion exchange resin or a method using a reverse osmosis membrane (RO membrane) is known as a method for removing ion components in water to be treated such as tap water and desalting the water to be treated. Yes. Although desalting by these methods is widely used in the industrial field, it is widely used for removing salt from water used in household appliances that use water, such as washing machines and dishwashers, for example, removing hardness components. Not done. The reason is that in the method using an ion exchange resin, it is necessary to supply salt in order to regenerate the resin periodically. However, this is troublesome for the user, and in the method using a reverse osmosis membrane, desalting is performed. For example, it is difficult to save water because concentrated water in which ions are concentrated together with the treated water is discharged.

In addition, a cation (cation) exchange membrane and an anion (anion) exchange membrane are alternately arranged between a pair of electrodes, and a space between these membranes is filled with an ion exchange resin, and then unidirectional between the electrodes. There is an electric regenerative desalinator (EDI) that removes salts from water to be treated by moving ions in the liquid to be treated by applying a DC voltage to the water. The electric regenerative desalinator is also called a continuous desalter (CDI). In the electric regeneration type desalination apparatus, for example, a demineralization chamber in which water to be treated is passed between a cathode chamber in which a cathode is disposed and an anode chamber in which an anode is disposed; It has a structure in which the concentrating chambers that are concentrated by moving are repeatedly arranged with the ion exchange membrane interposed therebetween. In the electric regeneration type desalination apparatus, it is not necessary to regenerate the ion exchange membrane or ion exchange resin using a chemical, but for example, when desalting water to be treated having a hardness of tap water level, In addition, a scale is generated mainly on the anion exchange membrane side of the concentrating chamber, the operating voltage rises, and stable operation cannot be performed. Therefore, it is difficult to use the electric regeneration type desalination apparatus when the desalination treatment is directly performed on the water to be treated containing a hardness component such as tap water.

Therefore, ion exchangers such as ion exchange resins and ion exchange membranes can be automatically regenerated, and the amount of water required for the regeneration treatment is small, and the water to be treated contains hardness components such as tap water. On the other hand, a method for removing ions by applying a voltage to a bipolar membrane has been proposed as a water treatment method capable of performing desalting treatment.

The bipolar membrane is an ion exchange membrane having a structure in which a cation exchange membrane and an anion exchange membrane are joined. A bipolar membrane is arranged so as to partition the space between the electrodes by providing a pair of electrodes, and the space between the electrodes is filled with water, the anion exchange membrane side electrode is the anode, the cation exchange membrane side electrode When a voltage of 0.83 V or more, which is the theoretical decomposition voltage of water, is applied between the electrodes so that becomes a cathode, water (H ₂ O) is converted into hydrogen ions (H ⁺ ) and hydroxide ions (OH ⁻ ). Can be dissociated. This dissociation occurs at the junction surface between the cation exchange membrane and the anion exchange membrane in the bipolar membrane, the generated hydrogen ions move to the cathode side through the cation exchange membrane, and the hydroxide ions are exchanged with anions. It moves to the anode side through the membrane. Many patents relating to acid and alkali production methods utilizing water dissociation by bipolar membranes have been filed. For example, Japanese Patent Laid-Open No. 2006-43549 (Patent Document 1) shows an example in which hydrogen ions and hydroxide ions generated in a bipolar membrane are used for regeneration of an ion exchange resin of an electric regeneration type desalination apparatus. Has been. Thus, the bipolar membrane is generally used to dissociate water and generate acid and alkali.

When the voltage application direction is reversed from when water is dissociated, that is, when the voltage is applied between the electrodes so that the anion exchange membrane side electrode is a cathode and the cation exchange membrane side electrode is an anode, Cations in water move in the direction of the cation exchange membrane and exchange with hydrogen ions to be taken into the cation exchange membrane, and the anions in water move in the direction of the anion exchange membrane and become hydroxide ions. Ion exchange is performed and it is taken into the anion exchange membrane. Hydrogen ions and hydroxide ions generated by the ion exchange reaction are recombined to form water. Thereby, since the salt in water was removed, the desalination process was performed.

When water is dissociated in the bipolar membrane and hydrogen ions and hydroxide ions are generated, if any cation is contained in the cation exchange membrane, the cation exchanges with the hydrogen ion and is discharged outside the membrane. If any anion is contained in the anion exchange membrane, the anion exchanges with hydroxide ions and is discharged out of the membrane. After all, it can be said that the process of dissociating water in the bipolar film by applying a voltage is a process of regenerating the bipolar film. Therefore, by changing the direction of the voltage applied to the bipolar film, it is possible to switch between the desalting process using the bipolar film and the regeneration process of the bipolar film. Japanese Patent Application Publication No. 2001-509074 (Patent Document 2) and Japanese Patent Application Laid-Open No. 2011-94938 (Patent Document 3) repeatedly perform desalting and regeneration by switching the polarity of an electrode for applying a voltage to a bipolar membrane. Water treatment equipment has been proposed.

Thus, unlike the case of the electric regeneration type desalination apparatus, the desalting method using the bipolar membrane repeats the desalting process and the regeneration process by reversing the polarity of the DC voltage applied between the pair of electrodes. The desalting process is performed in a batch system. Instead, the desalting method using the bipolar membrane does not require a mechanism corresponding to the concentration chamber in the electric regeneration type desalting apparatus, and scales generated at the cathode or the like can be removed by polarity switching, and include a hardness component. The desalted water can be desalted.

JP 2006-43549 A JP 2001-509074 gazette JP 2011-94938 A JP 2011-78936 A

Although the bipolar membrane has the advantage that it can be easily regenerated, the conventional desalting apparatus using the bipolar membrane has sufficient desalination for the exchange capacity of the cation exchange membrane or anion exchange membrane constituting the bipolar membrane. There is a problem that ability is not demonstrated.

For example, when removing calcium ions (Ca ²⁺ ) and magnesium ions (Mg ²⁺ ) for the purpose of removing hardness components, compared to when desalting using a normal ion exchange resin, bipolar Sufficient desalting ability is not exhibited with respect to the exchange capacity of the cation exchange membrane constituting the membrane. As an example, when the same raw water is treated to the same hardness using an ion exchange resin and a bipolar membrane having the same exchange capacity, when the bipolar membrane is used, the treatment is possible when the ion exchange resin is used. It became clear that only about one fifth of the amount of raw water can be treated. That is, in order to perform a desalting treatment equivalent to that of the ion exchange resin without performing regeneration using the bipolar membrane, a large amount of the bipolar membrane must be used as compared with the amount of the ion exchange resin used. Therefore, when desalting is continuously performed on a large amount of water using a bipolar membrane, there arises a problem that the apparatus becomes large. One of the reasons for the low desalting performance in the desalting treatment with the bipolar membrane is to arrange the bipolar membrane so that the membrane surface of the bipolar membrane is parallel to the direction of water flow of the water to be treated. Since ions are moved from the water to be treated in contact with the water in a direction perpendicular to the direction of water flow by an electric field, ions that do not reach the membrane remain in the water to be treated without being adsorbed. In other words, the desalting performance is low because the contact efficiency between the bipolar membrane functioning as an ion exchanger and the water to be treated is poor.

Japanese Patent Application Laid-Open No. 2011-78936 (Patent Document 4) discloses a water treatment apparatus using an ion exchange membrane having a two-layer structure in which a cation exchanger and an anion exchanger are joined, that is, a bipolar membrane. There is provided a water treatment apparatus in which the exchanger can be made granular or fibrous, for example, and the ion exchanger can be regenerated by hydrogen ions and hydroxide ions generated by the dissociation action of water in the bipolar membrane. It is shown. By using a granular or fibrous ion exchanger, the contact efficiency with water to be treated can be expected. However, in the thing shown in patent document 4, since a voltage is not applied at the time of a desalination process, or only the voltage less than the decomposition voltage of water is applied, a strong basic anion exchange resin and a strong acidic cation exchange are used as an ion exchanger. If the resin is not used, sufficient desalting performance cannot be obtained depending on the pH of the water to be treated. The use of strongly basic anion exchange resins and strongly acidic cation exchange resins also brings about the problem that much energy is required for regeneration.

An object of the present invention is a desalting method and desalting apparatus using a bipolar membrane, which has a high desalting performance, can reduce the size of the apparatus, and has a high regeneration efficiency. It is to provide.

In order to solve the above-mentioned problems, the present inventors have conducted intensive studies. As a result, in a desalination apparatus including a bipolar membrane, a cation exchanger is provided in the space between the bipolar membranes or in the space between the bipolar membrane and the electrode. And an anion exchanger are arranged, and a DC voltage is applied between these electrodes so that the electrode facing the cation exchange membrane in the bipolar membrane is an anode and the electrode facing the anion exchange membrane is a cathode. Thus, it was found that desalting can be performed efficiently. It has also been found that both the bipolar membrane and the ion exchange region can be regenerated by reversing the polarity of the DC voltage applied to the electrode.

Therefore, the desalinating apparatus of the present invention comprises a pair of electrodes capable of reversing the polarity of the DC voltage to be applied, and a bipolar membrane disposed in a space to which a voltage is applied by the pair of electrodes, In a desalination apparatus for performing a desalting treatment, the space has an ion exchange region in which a cation exchanger and an anion exchanger are arranged, and the cation exchanger and the anion exchanger are weakly acidic cation exchangers. And a weakly basic anion exchanger, a weakly acidic cation exchanger and a strongly basic anion exchanger, and a strongly acidic cation exchanger and a weakly basic anion exchanger. The voltage between a pair of electrodes is such that the electrode facing the cation exchange membrane in the bipolar membrane becomes the anode and the electrode facing the anion exchange membrane in the bipolar membrane becomes the cathode. The water to be treated is passed through the space while being applied, and desalting is performed. The electrode facing the cation exchange membrane serves as the cathode, and the electrode facing the anion exchange membrane serves as the anode. The bipolar membrane, the cation exchanger and the anion exchanger are regenerated by applying a voltage to them.

The desalinating method of the present invention is a desalting method of water to be treated, in which a space in which an ion exchange region and a bipolar membrane are disposed, which is a region in which a cation exchanger and an anion exchanger are disposed, is treated. While passing water, by applying a voltage between a pair of electrodes so that the electrode facing the cation exchange membrane in the bipolar membrane becomes the anode and the electrode facing the anion exchange membrane in the bipolar membrane becomes the cathode Applying a voltage between a pair of electrodes so that the electrode facing the cation exchange membrane serves as a cathode and the electrode facing the anion exchange membrane serves as an anode. The polarity of the applied voltage is reversed, and a regeneration process for regenerating the bipolar membrane, the cation exchanger, and the anion exchanger is alternately performed, and the cation exchanger and the anion exchanger are weakly acidic cation. A combination of an on-exchanger with a weakly basic anion exchanger, a combination of a weakly acidic cation exchanger and a strongly basic anion exchanger, and a combination of a strongly acidic cation exchanger with a weakly basic anion exchanger It is characterized by being any combination of combinations.

In the present invention, the voltage E applied to the pair of electrodes during the desalting treatment is preferably equal to or higher than the theoretical decomposition voltage of water. In particular, it is preferable that the distance between the electrodes is L, and E / L is 0.1 V / mm or more and 15 V / mm or less.

In the present invention, the ion exchange region in which the cation exchanger and the anion exchanger are arranged is a water-permeable region, for example, a mixture of the cation exchanger and the anion exchanger is arranged. It is an area. In such an ion exchange region, for example, a cation exchanger is disposed so as to be in contact with or close to the cation exchange membrane constituting the bipolar membrane, and an anion is so formed as to be in contact with or close to the anion exchange membrane of the bipolar membrane. It is configured by arranging an exchanger. Alternatively, on the contrary, an anion exchanger may be disposed on the cation exchange membrane side of the bipolar membrane, and the cation exchanger may be disposed on the anion exchange membrane side to constitute the ion exchange region. An ion exchange region is formed by arranging the cation exchanger and anion exchanger in this order along the direction of water flow in the space between the bipolar membranes, or vice versa. May be. Further, for example, the ion exchange region may be configured as a mixed bed in which a granular cation exchange resin and a granular anion exchange resin are uniformly dispersed. When the space between the pair of electrodes is divided into a large number of small spaces by the bipolar membrane, one of the cation exchanger or the anion exchanger is provided for each small space along the direction connecting one electrode. Thus, the ion exchange region may be configured such that the cation exchanger and the anion exchanger are alternately arranged with the bipolar membrane interposed therebetween.

According to the knowledge of the present inventors, a water-permeable cation exchange region having a cation exchanger provided in contact with the cation exchange membrane in the bipolar membrane and an anion exchange membrane in the bipolar membrane are provided. A water-permeable anion exchange region having an anion exchanger and forming an ion exchange region, and the cation exchange region and the anion exchange region are mutually connected in a space where a voltage is applied by a pair of electrodes. By arranging so as to contact or face each other, not only the desalting performance but also the regeneration efficiency is improved. In the case of providing a cation exchange region in contact with a cation exchange membrane in a bipolar membrane, and in providing an anion exchange region in contact with an anion exchange membrane, a cation exchange region is provided even in contact with one of a pair of electrodes, It is preferable to provide an anion exchange region even in contact with the other electrode. In this case, the anion exchange region is disposed in contact with the electrode facing the cation exchange membrane in the bipolar membrane, and the cation exchange region is disposed in contact with the electrode facing the anion exchange membrane in the bipolar membrane. Also, at this time, when the space between the pair of electrodes is divided into a large number of small spaces by the bipolar membrane, one electrode, the anion exchange region, the cation exchange region along the direction connecting the pair of electrodes , Cation exchange region, bipolar membrane, anion exchange region repeatedly appear, such as bipolar membrane, anion exchange region, cation exchange region, bipolar membrane, ..., cation exchange region, the other electrode Become.

According to the configuration described above, by applying a voltage, a weakly acidic cation exchange resin or a weakly basic anion exchange resin, which generally has a large ion exchange capacity but does not exhibit a deionizing ability in a neutral pH region, is used. It becomes possible to use in a wide pH range, and the desalting performance is improved. The amount of water to be treated that can be desalted in one cycle of desalting and regeneration increases, and the desalination apparatus can be miniaturized to the extent that it can be mounted on home appliances. In addition, the weak acid cation exchange resin and the weak base anion exchange resin have higher regeneration efficiency than the strong acid cation exchange resin and the strong base anion exchange resin, respectively. It is possible to save power. In particular, when a cation exchange region is provided in contact with the cation exchange membrane in the bipolar membrane, and an anion exchange region is provided in contact with the anion exchange membrane in the bipolar membrane, hydrogen ions from the bipolar membrane during the regeneration process are provided. In addition, the hydroxide ions move efficiently to the cation exchange region and the anion exchange region, respectively, and the cation exchange region and the anion exchange region can be regenerated with high efficiency.

It is a figure which shows the structure of the desalination apparatus of one Embodiment of this invention. It is a figure which shows the structure of the desalination apparatus of another embodiment of this invention. 5 is a graph showing changes in hardness over time in Example 1 and Comparative Example 1. It is a graph which shows the time change of the hardness in Example 2 and Comparative Example 2. FIG. It is a figure which shows the structure of the desalination apparatus used in Example 3. FIG. 6 is a graph showing a change with time in hardness in Example 3; It is a graph which shows the relationship between the desalination frequency in Examples 4 and 5, and hardness.

FIG. 1 shows a desalination apparatus according to an embodiment of the present invention. This desalination apparatus is provided between the desalting module 10, a DC power source 21 that generates a DC voltage applied to the electrodes 12 and 13, and the polarity of the electrodes 12 and 13 provided between the DC power source 21 and the electrodes 12 and 13. And a changeover switch 22 for switching between. The desalting module 10 includes a bipolar membrane 11, a pair of electrodes 12 and 13, and an ion exchange resin layer 16.

In the desalting module 10, a pair of electrodes 12 and 13 are arranged separately in a container to which the

pipes

23 and 24 are connected, and a voltage can be applied to the space between them by the electrodes 12 and 13. Yes. The bipolar film 11 is disposed away from the electrodes 12 and 13 so as to partition the space between the electrodes 12 and 13 into a plurality of portions when viewed as a cross-sectional configuration. In the illustrated example, the space between the electrodes 12 and 13 is divided into five parts by the bipolar film 11. In each of the partitioned parts, that is, the space between the electrode 12 and the bipolar film 11, the space between the adjacent bipolar films 11, and the space between the bipolar film 11 and the electrode 13, an ion exchange resin layer is provided. 16 is arranged.

The electrodes 12 and 13 are not particularly limited as long as they function as a cathode and an anode, and examples thereof include noble metals such as platinum, palladium and iridium, or net-like or plate-like electrodes in which these noble metals are coated with titanium or the like. be able to. The shape of the electrodes 12 and 13 may be a flat plate, expand, punching, round bar, wire, or the like. In accordance with the shape of the bipolar film 11, a voltage is uniformly applied to the bipolar film 11 and the space between the bipolar films 11. It must be something that can be applied.

The bipolar membrane 11 has a structure in which a cation exchange membrane 14 and an anion exchange membrane 15 are bonded together. In FIG. 1, the cross-sectional configuration is illustrated such that a plurality of bipolar films 11 are arranged between the electrodes 12 and 13, but the electrodes 12 and 13 having parallel plate shapes are parallel to each other and the electrodes 12. , 13 may be arranged in parallel so that a plurality of bipolar films 11 may actually be arranged, or electrodes 12, 13 are arranged concentrically with one electrode as a central electrode and the other electrode as a cylindrical electrode. However, one bipolar film may be wound between these electrodes in a spiral shape. Whatever configuration is adopted for the arrangement of the bipolar membrane 11, the water to be treated supplied from the pipe 23 to the desalting module 10 is not limited to the space between the electrodes 12, 13 and the bipolar membrane 11 or between the bipolar membranes 11. It is necessary to allow the ion exchange resin layer 16 provided in the space between them to pass evenly. At this time, both bipolar membranes 11 are arranged between the electrodes 11 and 12 so that the surface on the cation exchange membrane 14 side faces the electrode 12 and the surface on the anion exchange membrane 15 side faces the other electrode 13. Is arranged.

Next, the ion exchange resin layer 16 in this embodiment will be described. The ion exchange resin layer 16 has water permeability and serves as an ion exchange region in which a cation exchanger and an anion exchanger are mixed and arranged. The cation exchanger is, for example, a cation exchange resin, and the anion exchanger is, for example, an anion exchange resin. The combination of the cation exchanger and the anion exchanger constituting the ion exchange resin layer 16 is a combination of a weakly acidic cation exchanger and a weakly basic anion exchanger, or a weakly acidic cation exchanger and a strongly basic substance. Either a combination with an anion exchanger or a combination of a strongly acidic cation exchanger and a weakly basic anion exchanger.

In the illustrated example, a granular cation exchange resin and a granular anion exchange resin are mixed, and a state in which both are uniformly mixed is used as an ion exchange resin layer 16. The space between the electrodes 12 and 13 and the bipolar film 11 and the space between the bipolar films 11 are filled. However, the ion exchange resin layer 16 that can be used in the present embodiment is not limited to this. The cation exchange resin is in contact with the cation exchange membrane 14 of the bipolar membrane 11 and the anion exchange membrane 15 is in contact with the anion exchange membrane 15. Both ion exchange resins are arranged so as to be in contact with each other, and conversely, both ion exchanges are made so that the cation exchange membrane 14 is in contact with the anion exchange resin and the anion exchange membrane 15 is in contact with the cation exchange resin. A resin may be provided. Further, each space partitioned by the bipolar membrane 11 is filled with either a cation exchange resin or an anion exchange resin so that the cation exchange resin and the anion exchange resin are alternately arranged as a whole. An ion exchange resin layer may be provided.

Next, the desalting process using this desalting apparatus will be described.

The changeover switch 22 is operated so that the electrode 12 becomes an anode and the electrode 13 becomes a cathode, that is, the changeover switch 22 shown in FIG. 1 is set, and a DC voltage is applied between the electrodes 12 and 13 by the DC power source 21. At this time, in the bipolar membrane 11, the cation exchange membrane 14 is on the anode side, and the anion exchange membrane 15 is on the cathode side. When the water to be treated is passed through the desalination module 10 via the pipe 23, the cations contained in the water to be treated move to the cation exchange membrane 14 side of the bipolar membrane 11, where they are ion exchanged with hydrogen ions. And adsorbed in the cation exchange membrane 14. Similarly, anions contained in the water to be treated move to the anion exchange membrane 15 side of the bipolar membrane 11, where they are ion-exchanged with hydroxide ions and adsorbed in the anion exchange membrane 15. Hydrogen ions and hydroxide ions that have moved into the water to be treated by ion exchange are recombined to become water. Of the cations and anions in the water to be treated, those not ion-exchanged in the bipolar membrane 11 are also ion-exchanged and adsorbed by the ion-exchange resin layer 16. As a result, demineralized water, that is, treated water is obtained from the pipe 24.

In the desalting apparatus of the present embodiment, the ion exchange resin layer 16 includes at least one of a weakly acidic cation exchange resin and a weakly basic anion exchange resin. Normally, a weakly acidic cation exchange resin does not exhibit sufficient desalting performance unless the liquidity of the water to be treated is alkaline, and a weakly basic anion exchange resin is not acidic. However, in the desalination apparatus according to the present embodiment, since a microscopic pH deviation occurs in the water to be treated by applying a DC voltage by the electrodes 12 and 13, it is weakly acidic regardless of the liquidity of the water to be treated. Desalination treatment can be performed using a cation exchange resin or a weakly basic anion exchange resin, and the large ion exchange capacity of those ion exchange resins can be utilized.

Next, the playback process will be described.

In the state where water is present in the desalting module 10, the voltage polarity is reversed from that in the desalting process, and a DC voltage is applied between the electrodes 12 and 13 so that the electrode 12 becomes a cathode and the electrode 13 becomes an anode. Then, dissociation of water occurs at the interface between the cation exchange membrane 14 and the anion exchange membrane 15 in the bipolar membrane 11, and hydrogen ions and hydroxide ions are generated. Hydrogen ions move in the cation exchange membrane 14, thereby regenerating the cation exchange membrane 14, and hydroxide ions move in the anion exchange membrane 15, thereby regenerating the anion exchange membrane 15. The bipolar film 11 has been regenerated. When the voltage is further applied, hydrogen ions and hydroxide ions generated in the bipolar membrane 11 move to the cation exchange resin and the anion exchange resin in the ion exchange resin layer 16 respectively, and the regeneration of these ion exchange resins is performed. Will be done. The ion exchange resin layer 16 includes at least one of a weakly acidic cation exchange resin and a weakly basic anion exchange resin. The weakly acidic cation exchange resin and the weakly basic anion exchange resin are strongly acidic cation exchanges. Since the regeneration efficiency is higher than that of a resin or a strongly basic anion exchange resin, the desalination apparatus according to the present embodiment enables regeneration processing with power saving.

Thus, in the desalination apparatus of this embodiment, by switching the polarity of the DC voltage applied to the electrodes 12 and 13, the desalting process by the bipolar membrane 11 and the ion exchange resin layer 16 and these regeneration processes are performed. Can be repeated.

In the desalination apparatus shown in FIG. 1, an ion exchange region is formed by mixing a granular cation exchange resin and a granular anion exchange resin. The ion exchange region in the present invention is shown in FIG. It is not restricted to the thing. A water-permeable cation exchange region having a cation exchanger provided in contact with a cation exchange membrane in a bipolar membrane, and a water-permeable cation exchange region provided in contact with an anion exchange membrane in a bipolar membrane and having an anion exchanger. It is also possible to use an anion exchange region that is composed of an anion exchange region and is arranged so that the cation exchange region and the anion exchange region are in contact with each other or face each other.

FIG. 2 shows an embodiment of the present invention in which a cation exchange region is provided in contact with a cation exchange membrane in a bipolar membrane, and an anion exchange region is provided in contact with an anion exchange membrane. The structure of a salt apparatus is shown. In this desalting apparatus, as in the desalting apparatus shown in FIG. 1, a desalting module 10, a DC power source 21 and a switch 22 are provided. The configuration of the desalting module 10 is shown in FIG. Is different.

pipes

23 and 24 are connected, and a voltage can be applied to the space between them by the electrodes 12 and 13. Yes. The bipolar film 11 is disposed away from the electrodes 12 and 13 so as to partition the space between the electrodes 12 and 13 into a plurality of portions when viewed as a cross-sectional configuration. In the illustrated example, the space between the electrodes 12 and 13 is divided into five parts by the bipolar film 11. Here, both bipolar membranes 11 are arranged between the electrodes 12 and 13 so that the surface on the cation exchange membrane 14 side faces the electrode 12 and the surface on the anion exchange membrane 15 side faces the other electrode 13. Is arranged.

With respect to each part thus partitioned, in the space between the electrode 12 and the bipolar membrane 11, an anion exchange resin layer 18 is provided in contact with the surface of the electrode 12 and in contact with the cation exchange membrane 14 of the bipolar membrane 11. A cation exchange resin layer 17 is provided. In the space between the adjacent bipolar membranes 11, an anion exchange resin layer 18 is provided in contact with the anion exchange membrane 15 of the bipolar membrane 11 located on the electrode 12 side in the drawing, and the bipolar membrane 11 located on the electrode 13 side is provided. A cation exchange resin layer 17 is provided in contact with the cation exchange membrane 14. In the space between the electrode 13 and the bipolar membrane 11, a cation exchange resin layer 17 is provided in contact with the surface of the electrode 13, and an anion exchange resin layer 18 is provided in contact with the anion exchange membrane 15 of the bipolar membrane 11. ing. In each part partitioned by the bipolar membrane 11, the cation exchange resin layer 17 and the anion exchange resin layer 18 in the part are in contact with each other in the vicinity of the center of the part. As will be described later, a water-permeable spacer or the like is disposed between the cation exchange resin layer 17 and the anion exchange resin layer 18 so that the cation exchange resin layer 17 and the anion exchange resin layer 18 face each other. It may be arranged.

As the electrodes 12 and 13, the same electrodes as those used in the embodiment shown in FIG. 1 are used. As the bipolar film 11, the same film as that used in the embodiment shown in FIG. 1 is used. When one electrode is a center electrode and the other electrode is a cylindrical electrode, the electrodes 12 and 13 are arranged concentrically, and a bipolar film is wound between these electrodes so as to be spirally wound. For example, a sheet-like laminate in which the cation exchange resin layer 17 and the anion exchange resin layer 18 are previously provided on both surfaces of the bipolar membrane 11 is prepared, and the laminate may be wound around the center electrode. Whatever configuration is adopted for the arrangement of the bipolar membrane 11, the water to be treated supplied from the pipe 23 to the desalting module 10 is not limited to the space between the electrodes 12, 13 and the bipolar membrane 11 or between the bipolar membranes 11. It is necessary to allow the cation exchange resin layer 17 and the anion exchange resin layer 18 provided in the space between them to pass evenly.

Next, the cation exchange resin layer 17 and the anion exchange resin layer 18 will be described.

The cation exchange resin layer 17 has water permeability and serves as a cation exchange region in which the cation exchanger is arranged. The anion exchange resin layer 18 has water permeability and has an anion exchanger. Is an anion exchange region in which is arranged. The cation exchanger and the anion exchanger are, for example, a cation exchange resin and an anion exchange resin, respectively. The combination of the cation exchanger constituting the cation exchange resin layer 17 and the anion exchanger constituting the anion exchange resin layer 18 is a combination of a weakly acidic cation exchanger and a weakly basic anion exchanger, Either a combination of a weakly acidic cation exchanger and a strongly basic anion exchanger, or a combination of a strongly acidic cation exchanger and a weakly basic anion exchanger.

In the illustrated example, the cation exchange resin layer 17 is composed of a granular cation exchange resin layer, and the anion exchange resin layer 18 is composed of a granular anion exchange resin layer. The cation exchange resin layer 17 and the anion exchange resin layer 18 are disposed in contact with each partitioned part. As will be described later, in order to increase the regeneration efficiency in the regeneration process, it is preferable that the granular cation exchange resin and the granular anion exchange resin are not mixed with each other. For example, a water-permeable spacer may be provided between the anion exchange resin layer 18 and the mixing of both ion exchange resins may be prevented. Further, by providing the spacer, it is possible to improve the efficiency of the filling operation of the cation exchange resin constituting the cation exchange resin layer 17 and the anion exchange resin constituting the anion exchange resin layer 18.

Furthermore, as the cation exchange resin layer 17, a porous cation exchanger, a fibrous cation exchanger, a cation exchange fiber, or the like can be used. Similarly, a porous anion exchanger, a fibrous anion exchanger, an anion exchange fiber, or the like can be used as the anion exchange resin layer 18.

Next, the desalting process using this desalting apparatus will be described.

The changeover switch 22 is operated so that the electrode 12 becomes an anode and the electrode 13 becomes a cathode.
That is, when the direct current voltage is applied between the electrodes 12 and 13 by the direct current power source 21 in the state of the changeover switch 22 shown in FIG. 2, the cation contained in the water to be treated is the same as in the case of the desalination apparatus shown in FIG. And anion is ion-exchanged by the bipolar membrane 11, and a desalination process is performed. At this time, among the cations and anions in the water to be treated, those not ion-exchanged in the bipolar membrane 11 are also ion-exchanged when passing through the cation exchange resin layer 17 or the anion exchange resin layer 18. Adsorbed on the ion exchange resin layer. As a result, demineralized water is obtained from the pipe 24.

In the desalting apparatus shown in FIG. 2, at least one of the weakly acidic cation exchange resin and the weakly basic anion exchange resin is included in the region where the cation exchange resin layer 17 and the anion exchange resin layer 18 are combined. It is. Normally, a weakly acidic cation exchange resin does not exhibit sufficient desalting performance unless the liquidity of the water to be treated is alkaline, and a weakly basic anion exchange resin is not acidic. However, in the desalination apparatus shown in FIG. 2, when a DC voltage is applied by the electrodes 12 and 13, a local pH deviation occurs in the water to be treated, so that it is weakly acidic regardless of the liquidity of the water to be treated. Desalination treatment can be performed using a cation exchange resin or a weakly basic anion exchange resin, and the large ion exchange capacity of those ion exchange resins can be utilized. As a result, the desalting apparatus of this embodiment comes to show high desalting performance.

Next, the playback process will be described.

In the state where water is present in the desalting module 10, the voltage polarity is reversed from that in the desalting process, and a DC voltage is applied between the electrodes 12 and 13 so that the electrode 12 becomes a cathode and the electrode 13 becomes an anode. Then, dissociation of water occurs at the interface between the cation exchange membrane 14 and the anion exchange membrane 15 in the bipolar membrane 11, and hydrogen ions and hydroxide ions are generated. Hydrogen ions move in the cation exchange membrane 14, thereby regenerating the cation exchange membrane 14, and hydroxide ions move in the anion exchange membrane 15, thereby regenerating the anion exchange membrane 15. The bipolar film 11 has been regenerated. When the voltage is further applied, the hydrogen ions generated in the bipolar membrane 11 move into the cation exchange resin layer 17 provided in contact with the cation exchange membrane 14 to form the cation exchange resin layer 17. The ion exchange resin is regenerated. Similarly, hydroxide ions generated in the bipolar membrane 11 move into the anion exchange resin layer 18 provided in contact with the anion exchange membrane 15 to form the anion exchange resin layer 18. The resin is regenerated. Further, during the regeneration process, hydroxide ions are also generated at the interface between the electrode 12 and the anion exchange resin layer 18 in contact with the electrode 12, and the anion exchange resin layer 18 in contact with the electrode 12 is regenerated by the hydroxide ion. Is done. Hydrogen ions are generated at the interface between the electrode 13 and the cation exchange resin layer 17 in contact with the electrode 13, and the cation exchange resin layer 17 in contact with the electrode 13 is regenerated by this hydrogen ion. Eventually, not only the bipolar membrane 11 but also the cation exchange resin layer 17 and the anion exchange resin layer 18 are regenerated during the regeneration process.

Here, let us consider a case where a granular cation exchange resin and a granular anion exchange resin are mixed together in the space between adjacent bipolar membranes 11 as in the desalting apparatus shown in FIG. In this case, the anion exchange resin existing near the cation exchange membrane 14 of the bipolar membrane 11 should be regenerated by the hydroxide ions released from the anion exchange membrane 15 of the bipolar membrane 11. Since there are hydrogen ions released from the cation exchange membrane 14 around the anion exchange resin, the hydroxide ions to be regenerated from the anion exchange resin are hydrogen ions before reaching the anion exchange resin. May be converted to water, and as a result, the anion exchange resin may not be sufficiently regenerated. For the same reason, there is a possibility that the cation exchange resin existing near the anion exchange membrane 15 of the bipolar membrane 11 is not sufficiently regenerated. As a result, when the cation exchange resin and the anion exchange resin are mixed and present, there is a concern that the desalting performance is lowered when the cycle of the desalting treatment and the regeneration treatment is repeated.

On the other hand, a cation exchange resin layer 17 is provided in contact with the cation exchange membrane 14 of the bipolar membrane 11 so that the cation exchange resin and the anion exchange resin do not mix with each other. When the anion exchange resin layer 18 is provided in contact, the regeneration of the cation exchange resin layer 17 by hydrogen ions moving from the cation exchange membrane 14 side and the hydroxide ions moving from the anion exchange membrane 15 side are performed. Thus, the anion exchange resin layer 18 can be efficiently regenerated. In the desalination apparatus of this embodiment, at least one of the weakly acidic cation exchange resin and the weakly basic anion exchange resin is in the region where the cation exchange resin layer 17 and the anion exchange resin layer 18 are combined. Although it is included, the weakly acidic cation exchange resin and weakly basic anion exchange resin have higher regeneration efficiency than the strongly acidic cation exchange resin and strong basic anion exchange resin. However, it enables playback processing with low power consumption.

As described above, in the desalting apparatus shown in FIG. 2, desalting by the bipolar membrane 11, the cation exchange resin layer 17, and the anion exchange resin layer 18 is performed by switching the polarity of the DC voltage applied to the electrodes 12 and 13. The process and these reproduction processes can be repeated many times.

Hereinafter, the present invention will be described in detail based on examples. However, the present invention is not limited to the following examples.

[Example 1]
The desalination apparatus shown in FIG. 1 was assembled. The bipolar membrane 11 used was a laminate of a weakly acidic cation exchange membrane and a strongly basic anion exchange membrane. The ion exchange capacity (cation exchange capacity) of the weakly acidic cation exchange membrane is 2.2 meq / g-bipolar membrane, and the ion exchange capacity (anion exchange capacity) of the strongly basic anion exchange membrane is 0.8 meq / g. g-bipolar membrane). As the cation exchange resin and anion exchange resin constituting the ion exchange resin layer 16, a weakly acidic cation exchange resin (Amberlite (registered trademark) IRC76, manufactured by Dow Chemical Company) and a weakly basic anion exchange resin (Amber) are used. Light (registered trademark) IRA96, manufactured by Dow Chemical Co., Ltd. was used.

Two 40 × 50 × 1 mm platinum iridium-coated titanium electrodes are placed in a container with an internal volume of 40 × 50 × 20 mm, and four bipolar membranes cut into a size of 40 × 50 mm are provided between the electrodes. And the bipolar film are arranged so that the distance between the bipolar films and the distance between the bipolar films are equal. Then, the weakly acidic cation exchange resin and the weakly basic anion exchange resin are mixed at a volume ratio of 1: 3, and the ion exchange resin is mixed with the electrode and the bipolar so that they are uniformly dispersed. Packed between membranes and between bipolar membranes. Water having a hardness adjusted to 250 mg-CaCO ₃ / L was used as the water to be treated, and the desalting treatment was performed by passing the water to be treated at a water flow rate of 40 ml / min. The maximum values of the voltage and current applied to the electrode during the desalting treatment were 200 V and 0.5 A, respectively, and the hardness of the treated water after the desalting treatment was examined over time. The results are shown in FIG.

As shown in FIG. 3, in the apparatus of Example 3, the treated water hardness was 30 mg-CaCO ₃ / L even after the desalting treatment was continued for 150 minutes, and about 90% desalting was possible.

[Comparative Example 1]
The desalting treatment was performed under the same conditions as in Example 1 except that no DC voltage was applied to the electrode during the desalting treatment, and the change over time in the hardness of the treated water was examined. The results are shown in FIG. When no voltage was applied, the treated water hardness exceeded 100 mg-CaCO ₃ / L after 30 minutes, and sufficient desalting could not be performed.

[Example 2]
The desalination apparatus shown in FIG. 1 was assembled. The dimensions of the container, the configuration and dimensions of the electrodes, and the configuration and arrangement of the bipolar membrane were the same as in Example 1. As the cation exchange resin and anion exchange resin constituting the ion exchange resin layer 16, a weakly acidic cation exchange resin (Amberlite (registered trademark) IRC76, manufactured by Dow Chemical Company) and a strongly basic anion exchange resin (Amber) Jet (registered trademark) 4002 (OH), manufactured by Dow Chemical Co., Ltd.), a weakly acidic cation exchange resin and a strongly basic anion exchange resin are mixed at a volume ratio of 1: 3, Such an ion exchange resin was filled between the electrode and the bipolar membrane and between the bipolar membranes so as to be evenly dispersed. Desalination treatment was performed under the same treatment conditions as in Example 1, and the change over time in the hardness of the treated water was examined. The results are shown in FIG.

As shown in FIG. 4, in the apparatus of Example 2, the treated water hardness was 30 mg-CaCO ₃ / L even after the desalting treatment was continued for 150 minutes, and about 90% desalting was possible.

[Comparative Example 2]
A desalting treatment was performed under the same conditions as in Example 2 except that no DC voltage was applied to the electrode during the desalting treatment, and the change over time in the hardness of the treated water was examined. The results are shown in FIG. When no voltage was applied, the treated water hardness exceeded 90 mg-CaCO ₃ / L after 100 minutes, and sufficient desalting could not be performed.

[Example 3]
The desalination apparatus shown in FIG. 5 was assembled. This desalting apparatus is the same as the desalting apparatus in Example 1, but instead of providing an ion exchange resin layer in which a weakly acidic cation exchange resin and a weakly basic anion exchange resin are uniformly mixed. The second embodiment is different from the first embodiment in that a cation exchange resin layer 17 made of weakly acidic cation exchange resin and an anion exchange resin layer 18 made of weakly basic anion exchange resin are separately provided. More specifically, the dimensions of the container, the configuration and dimensions of the electrode, and the configuration and arrangement of the bipolar membrane are the same as those in Example 1, and the cation exchange resin layer 16 is formed in the space between the electrode and the bipolar membrane. In the space between the bipolar membranes, either the anion exchange resin layer 17 or the cation exchange resin layer 16 is provided for each space. As a whole, the cation exchange resin layer 16 and the anion exchange resin layer 17 are alternately arranged with the bipolar membrane 11 interposed therebetween. As weakly acidic cation exchange resin and weakly basic anion exchange resin, weakly acidic cation exchange resin (Amberlite (registered trademark) IRC76, manufactured by Dow Chemical Company) and weakly basic anion exchange resin (Amberlite (registered)) (Trademark) IRA96, manufactured by Dow Chemical Co., Ltd.).

Desalination treatment was performed under the same treatment conditions as in Example 1, and the change over time in the hardness of the treated water was examined. The results are shown in FIG. As shown in FIG. 6, in Example 3, the treated water hardness exceeded 50 mg-CaCO ₃ / L after 20 minutes, and the weakly acidic cation exchange resin and the weakly basic anion exchange resin were uniformly mixed. It was confirmed that the desalting performance was higher.

[Example 4]
Using the desalination apparatus of Example 1, 20 minutes of desalination treatment and 20 minutes of regeneration treatment were combined to form one cycle, and the change in the hardness of the treated water when such a cycle was repeated was examined. . As water to be treated, water having a hardness adjusted to 250 mg-CaCO ₃ / L was used, and water was passed through at a water flow rate of 40 ml / min for desalting treatment. The maximum values of the voltage and current applied to the electrodes during the desalting treatment and the regeneration treatment were 200 V and 0.5 A, respectively. The treated water 15 minutes after the start of desalting was collected every 10 cycles, and the hardness was measured. The results are shown in FIG.

[Example 5]
Desalination treatment was performed under the same conditions as in Example 4 except that a strongly acidic cation exchange resin (Amberlite (registered trademark) 252 manufactured by Dow Chemical Company) was used as the cation exchange resin contained in the ion exchange resin layer 16. The change in the hardness of the treated water was examined when the cycle of the regeneration treatment was repeated. The results are shown in FIG.

From FIG. 7, the treatment water hardness in the repetition of the desalting treatment and the regeneration treatment is more when the weak acid cation exchange resin is used as the cation exchange resin contained in the ion exchange resin layer 16 than the strong acid cation exchange resin. It was confirmed that the desalting was performed stably.

[Example 6]
The desalination apparatus shown in FIG. 2 was assembled. The bipolar membrane 11 used was a laminate of a weakly acidic cation exchange membrane and a strongly basic anion exchange membrane. The ion exchange capacity (cation exchange capacity) in the weakly acidic cation exchange membrane is 2.2 meq / g-bipolar membrane, and the ion exchange capacity in the strongly basic anion exchange membrane (anion exchange capacity is 0.8 meq). / G-bipolar membrane A weakly acidic cation exchange resin (Amberlite (registered trademark) IRC76, manufactured by Dow Chemical Company) was used as the cation exchange resin constituting the cation exchange resin layer 17. As the anion exchange resin constituting the exchange resin layer 18, a weakly basic anion exchange resin (Amberlite (registered trademark) IRA96, manufactured by Dow Chemical Co., Ltd.) was used.

Two 40 × 50 × 1 mm platinum iridium-coated titanium electrodes are placed in a container with an internal volume of 40 × 50 × 20 mm, and four bipolar membranes cut into a size of 40 × 50 mm are provided between the electrodes. The cation exchange resin layer 17 and the anion exchange resin layer 18 are provided within the gaps so that the gap between the bipolar membranes and the gap between the bipolar membranes are equal. Actually, after placing one of the electrodes, the cation exchange resin layer 17 and the anion exchange resin layer 18 are arranged in this order, and the anion exchange membrane side is on top of the cation exchange resin layer 17 and the anion exchange resin layer 18. Two bipolar membranes are placed, and the cation exchange resin layer 17 and the anion exchange resin layer 18 are again arranged in this order on the bipolar membrane, that is, the cation exchange membrane of the bipolar membrane, and further the bipolar membrane is placed. The desalin module was completed by placing the other electrode at the end. The amount of the cation exchange resin constituting the cation exchange resin layer 17 and the amount of the anion exchange resin constituting the anion exchange resin layer 18 were set to 1: 1.

Water whose hardness was adjusted to 250 mg-CaCO ₃ / L was used as water to be treated at the time of desalting treatment and water to be used for regeneration treatment, and water was passed at a flow rate of 40 ml / min. The maximum values of the voltage and current applied to the electrodes during the desalting treatment and the regeneration treatment were 200 V and 0.5 A, respectively. A desalting treatment was performed for 5 minutes under these conditions, followed by a regeneration treatment for 5 minutes as one cycle, and this cycle was repeated 100 cycles. By measuring the hardness of the treated water after the desalting treatment in the first cycle, the 20th cycle and the 100th cycle, and dividing the measured treated water hardness by the treated water hardness from 100% The desalting rate was calculated. The results are shown in Table 1.

[Example 7]
Desalination module similar to that used in Example 6, but without the cation exchange resin layer and anion exchange resin layer, instead, between the electrode and the bipolar membrane, and between the bipolar membranes, A uniform mixture of a granular cation exchange resin and a granular anion exchange resin was filled. As the cation exchange resin and the anion exchange resin, the same ones as used in Example 6 were used, and the mixing ratio thereof was 1: 1.

The cycle of the desalting treatment and the regeneration treatment was repeated 100 cycles under the same conditions as in Example 6, and the hardness of the treated water after the desalting treatment in the first cycle, the 20th cycle and the 100th cycle was measured. The desalting rate was calculated by the same calculation. The results are shown in Table 1.

When comparing Example 6 and Example 7, when the cycle of desalting treatment and regeneration treatment was repeated, the desalting rate of Example 7 was higher. The desalination rate is high even when the cycle progresses. The fact that the desalination treatment of the cycle immediately before the start of the cycle is performed between the bipolar membrane and the cation exchange resin and the anion exchange resin disposed between the bipolar membranes. It shows that the reproduction is performed sufficiently. Therefore, a water-permeable cation exchange resin layer is provided so as to be in contact with the cation exchange membrane of the bipolar membrane, and a water-permeable anion exchange resin layer is provided so as to be in contact with the anion exchange membrane of the bipolar membrane. Example 7 in which the exchange resin layer and the anion exchange resin layer are in contact with each other is an example in which the space between the bipolar membranes is filled with a cation exchange resin and an anion exchange resin in a mixed bed It can be seen that the reproduction efficiency in the reproduction process was higher than that in FIG.

DESCRIPTION OF SYMBOLS 10 Desalination module 11 Bipolar membrane 12, 13 Electrode 14 Cation exchange membrane 15 Anion exchange membrane 16 Ion exchange resin layer 17 Cation exchange resin layer 18 Anion exchange resin layer 21 DC power supply 22

Changeover switch

23, 24 Piping

Claims

A desalting apparatus comprising a pair of electrodes capable of reversing the polarity of a DC voltage to be applied, and a bipolar membrane disposed in a space to which a voltage is applied by the pair of electrodes, and performing a desalting treatment on water to be treated In
An ion exchange region in which the cation exchanger and the anion exchanger are arranged in the space;
The cation exchanger and the anion exchanger are a combination of a weakly acidic cation exchanger and a weakly basic anion exchanger, a combination of a weakly acidic cation exchanger and a strongly basic anion exchanger, and A combination of a strong acid cation exchanger and a weakly basic anion exchanger,
The water to be treated is applied while applying a voltage between the pair of electrodes so that the electrode facing the cation exchange membrane in the bipolar membrane serves as an anode and the electrode facing the anion exchange membrane in the bipolar membrane serves as a cathode. Desalination treatment is performed by passing water through the space,
By applying a voltage between the pair of electrodes so that the electrode facing the cation exchange membrane becomes a cathode and the electrode facing the anion exchange membrane becomes an anode, the bipolar membrane, the cation exchanger, and A desalting apparatus, wherein the anion exchanger is regenerated.
The deionization apparatus according to claim 1, wherein the ion exchange region is a region where the cation exchanger and the anion exchanger are mixed and arranged.
The deionization apparatus according to claim 2, wherein the ion exchange region is a region in which a granular cation exchange resin and a granular anion exchange resin are mixed.
The desalination apparatus according to any one of claims 1 to 3, further comprising: a power source that generates a DC voltage applied between the pair of electrodes; and a changeover switch that reverses the polarity of the pair of electrodes.
The desalting apparatus according to any one of claims 1 to 3, wherein a voltage applied between the pair of electrodes during the desalting treatment is a voltage equal to or higher than a theoretical decomposition voltage of water.
The ion exchange region is provided in contact with the cation exchange membrane in the bipolar membrane and has a water-permeable cation exchange region having a cation exchanger, and is provided in contact with the anion exchange membrane in the bipolar membrane. A water-permeable anion exchange region having an ion exchanger,
The desalination apparatus according to claim 1, wherein the cation exchange region and the anion exchange region are disposed so as to contact or face each other in the space.
In the space, the anion exchange region is disposed in contact with the electrode facing the cation exchange membrane in the bipolar membrane, and the cation exchange region in contact with the electrode facing the anion exchange membrane in the bipolar membrane. The desalination apparatus according to claim 6, which is arranged.
The desalination apparatus according to claim 6 or 7, wherein the cation exchange region is composed of a granular cation exchange resin layer, and the anion exchange region is composed of a granular anion exchange resin layer.
The desalination apparatus according to claim 6 or 7, further comprising: a power source that generates a DC voltage applied between the pair of electrodes; and a changeover switch that reverses the polarity of the pair of electrodes.
The desalting apparatus according to claim 6 or 7, wherein a voltage applied between the pair of electrodes during the desalting treatment is a voltage equal to or higher than a theoretical decomposition voltage of water.
In the desalting method of treated water,
A surface of the cation exchange membrane in the bipolar membrane is passed through the treated water through the space in which the ion exchange region and the bipolar membrane are arranged, where the cation exchanger and the anion exchanger are arranged. A desalting treatment in which a voltage is applied to the space by applying a voltage between the pair of electrodes such that the electrode to be an anode and the electrode facing the anion exchange membrane in the bipolar membrane is a cathode;
By applying a voltage between the pair of electrodes so that the electrode facing the cation exchange membrane becomes a cathode and the electrode facing the anion exchange membrane becomes an anode, the polarity of the voltage applied to the space is changed. Reversing and regenerating the bipolar membrane, the cation exchanger and the anion exchanger;
Alternately
The cation exchanger and the anion exchanger are a combination of a weakly acidic cation exchanger and a weakly basic anion exchanger, a combination of a weakly acidic cation exchanger and a strongly basic anion exchanger, and A desalting method, which is a combination of any combination of a strongly acidic cation exchanger and a weakly basic anion exchanger.
The deionization method according to claim 11, wherein the ion exchange region is a region where the cation exchanger and the anion exchanger are mixed and arranged.
The deionization method according to claim 12, wherein the ion exchange region is a region in which a granular cation exchange resin and a granular anion exchange resin are mixed.
The desalting method according to any one of claims 11 to 13, wherein a voltage applied between the pair of electrodes during the desalting treatment is a voltage equal to or higher than a theoretical decomposition voltage of water.
The ion exchange region is provided in contact with the cation exchange membrane in the bipolar membrane and has a water-permeable cation exchange region having a cation exchanger, and is provided in contact with the anion exchange membrane in the bipolar membrane. A water-permeable anion exchange region having an ion exchanger, wherein the cation exchange region and the anion exchange region are arranged so as to contact or face each other in the space. A desalting method according to 1.
In the space, the anion exchange region is disposed in contact with the electrode facing the cation exchange membrane in the bipolar membrane, and the cation exchange region in contact with the electrode facing the anion exchange membrane in the bipolar membrane. The desalting method according to claim 15, which is arranged.
The desalting method according to claim 15 or 16, wherein a voltage applied between the pair of electrodes during the desalting treatment is a voltage equal to or higher than a theoretical decomposition voltage of water.