JP2014069120A - Desalination method, and desalination apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a desalination method in which a pair of electrodes and a bipolar membrane to be disposed between the pair of electrodes are used, a voltage is applied between the pair of electrodes so that the electrode of the side of a cation exchange membrane becomes an anode and that of the side of an anion exchange membrane becomes a cathode, and an exchange capacity of the bipolar membrane can be utilized satisfactorily and which can allow the size of a desalination apparatus to be smaller.SOLUTION: The water to be treated is made to pass through an ion exchanger having the ion exchange capacity, which is larger than a difference between the ion exchange capacity of the cation exchange membrane and that of the anion exchange membrane in the bipolar membrane and which is an anion or cation exchange capacity corresponding to the insufficient anion or cation exchange capacity thereof. The water, which is to be treated and is made to pass through the ion exchanger, is treated in a bipolar membrane desalination module. The bipolar membrane comprises a weakly-acidic cation exchange membrane and a strongly-basic anion exchange membrane or a strongly-acidic cation exchange membrane and a weakly-acidic anion exchange membrane.

Description

  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 for removing ions using the ion exchange ability of 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, salt removal of water used in home appliances that use water, such as washing machines and dishwashers (for example, removal of hardness components) Not popular. 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.

  Therefore, although included in the method using ion exchange resin, voltage is applied to the bipolar membrane as a water treatment method that can automatically regenerate the resin and requires only a small amount of water for regeneration. Thus, a method for removing ions has been proposed.

A bipolar membrane is an ion exchange membrane having a structure in which a cation exchange membrane and an anion exchange membrane are bonded together. 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, and the cation exchange membrane side electrode is the cathode Thus, when a voltage of 0.83 V or higher, which is the theoretical decomposition voltage of water, is applied between the electrodes, water can be dissociated into hydrogen ions (H ⁺ ) and hydroxide ions (OH ⁻ ). This dissociation occurs at the interface 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 pass through the anion exchange membrane. Move to the anode side. Many patents relating to acid and alkali production methods utilizing water dissociation by bipolar membranes have been filed. For example, 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. 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 the cathode and the cation exchange membrane side electrode is the anode, Cations move in the direction of the cation exchange membrane, exchange ions with hydrogen ions, and are taken into the cation exchange membrane. Anions (anions) in the water move in the direction of the anion exchange membrane and become hydroxide ions Are ion-exchanged and taken into the anion exchange membrane (see FIG. 2). 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 to generate hydrogen ions and hydroxide ions, if any cation is contained in the cation exchange membrane, the cation is ion exchanged with the hydrogen ion and discharged out of 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 (see FIG. 3). 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. Patent Documents 2 and 3 propose water treatment apparatuses that repeatedly perform desalting and regeneration by switching the polarity of an electrode that applies a voltage to a bipolar membrane. In particular, Patent Document 3 discloses a water treatment apparatus suitable for incorporation in a washing machine or a dishwasher.

  The combination of the cation exchange membrane and the anion exchange membrane constituting the bipolar membrane includes a combination of a weakly acidic cation exchange membrane and a strongly basic anion exchange membrane, and a combination of a strongly acidic cation exchange membrane and a weakly basic anion exchange membrane. Combinations are common. Bipolar membranes combining strong acidic cation exchange membranes and strongly basic anion exchange membranes do not have stable characteristics. For example, the voltage for dissociating water into hydrogen ions and hydroxide ions increases and efficiency decreases. Therefore, it is practically difficult to use a bipolar membrane composed of a strongly acidic cation exchange membrane and a strongly basic anion exchange membrane.

JP 2006-43549 A JP-T-2001-509074 JP 2010-29753 A

  Although the bipolar membrane has the advantage that it can be easily regenerated, the conventional desalination apparatus using the bipolar membrane has a sufficient desalting capacity for the exchange capacity of the cation exchange membrane or anion exchange membrane constituting the bipolar membrane. It turned out that there was a problem that it was not demonstrated. In particular, it has been found that the tendency is remarkable in a bipolar membrane using a combination of a weakly acidic cation exchange membrane and a strongly basic anion exchange membrane.

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 There is a problem that 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.

  An object of the present invention is to provide a desalination method and desalination apparatus using a bipolar membrane, which can fully utilize the exchange capacity of the bipolar membrane and can reduce the apparatus size. There is to do.

  In order to solve the above problems, the present inventors have conducted intensive studies. As a result, in a bipolar membrane that is a combination of a weakly acidic cation exchange membrane and a strongly basic anion exchange membrane, the ion exchange capacity of the weakly acidic cation exchange membrane is strong. When the ion exchange capacity is larger than that of the basic anion exchange membrane, it was found that the ion exchange capacity capable of desalting depends on the strongly basic anion exchange membrane having a lower ion exchange capacity. Similarly, in the bipolar membrane formed by combining a strong acid cation exchange membrane and a weakly basic anion exchange membrane, the present inventors show that the ion exchange capacity of the weakly basic anion exchange membrane is higher than the ion exchange capacity of the strongly acidic cation exchange membrane. When it is large, it was found that the ion exchange capacity capable of desalting depends on the strongly acidic cation exchange membrane having the lower ion exchange capacity. This is because if the ion exchange capacity of the cation exchange membrane and the anion exchange membrane constituting the bipolar membrane are different, the treatment capacity of the membrane with the smaller ion exchange capacity decreases as the desalting continues, and the ion exchange capacity It is thought that this is because only the membrane having the larger diameter is treated, and the pH of the liquid to be treated fluctuates. Specifically, when the membrane having a larger ion exchange capacity in the bipolar membrane is a weakly acidic cation exchange membrane, the pH of the liquid to be treated is shifted to the acidic side, and as a result, a sufficient ion exchange capacity is still not obtained. Nevertheless, the carboxyl group, which is an exchange group of the weakly acidic cation exchange membrane, is not dissociated and the ion exchange capacity is lowered, and the treatment efficiency is lowered. Similarly, when the membrane having a larger ion exchange capacity in the bipolar membrane is a weakly basic anion exchange membrane, the pH of the liquid to be treated is shifted to the alkaline side, and as a result, the exchange of the weakly basic anion exchange membrane is performed. The primary amine, secondary amine, and tertiary amine, which are groups, do not dissociate and the ion exchange capacity is reduced, resulting in a reduction in processing efficiency.

  Therefore, a desalting method of the present invention is a desalting method for performing desalting treatment on water to be treated, a treatment for passing water to be treated through an ion exchanger module including an ion exchanger, a pair of electrodes, and a pair of electrodes. A bipolar membrane having a bipolar membrane disposed between the bipolar membrane desalination module composed of a cation exchange membrane and an anion exchange membrane, and the electrode facing the cation exchange membrane in the bipolar membrane is an anode, an anion exchange membrane The bipolar membrane is a weakly acidic cation exchange membrane, with the treatment of passing water to be treated from the ion exchanger module while applying a voltage between the pair of electrodes so that the electrode facing the cathode becomes a cathode And a bipolar membrane composed of a strongly basic anion exchange membrane, or a bipolar membrane composed of a strong acidic cation exchange membrane and a weakly basic anion exchange membrane. When the ion exchange capacity of the cation exchange membrane is larger than the ion exchange capacity of the cation exchange membrane and anion exchange membrane constituting the bipolar membrane, the ion exchanger module includes an anion exchanger, A cation exchanger is provided when the exchange capacity is larger.

  The desalination apparatus of the present invention is a desalination apparatus that performs desalination treatment on water to be treated, and includes a pair of electrodes and a bipolar membrane disposed between the pair of electrodes. The bipolar membrane includes a weakly acidic cation exchange membrane and A bipolar membrane desalting module composed of a strongly basic anion exchange membrane, or a strongly acidic cation exchange membrane and a weakly basic anion exchange membrane, and an ion exchanger module provided in the preceding stage of the bipolar membrane desalting module; The ion exchanger module includes an anion exchanger when the ion exchange capacity of the cation exchange membrane is larger than the ion exchange capacity of the cation exchange membrane and the anion exchange membrane constituting the bipolar membrane, and the anion exchange membrane When the ion exchange capacity of the membrane is larger, a cation exchanger is provided, and the electric current facing the cation exchange membrane in the bipolar membrane is While the voltage is applied between the pair of electrodes so that the electrode facing the anode and the anion exchange membrane becomes the cathode, the water to be treated is passed in the direction from the ion exchanger module to the bipolar membrane desalting module to remove it. It is characterized by performing salt treatment.

  In the present invention, when the ion exchange capacity of the cation exchange membrane in the bipolar membrane is larger than that of the anion exchange membrane, the ion exchange capacity of the anion exchanger provided in the ion exchanger module is, for example, The ion exchange capacity of the cation exchanger provided in the ion exchanger module when the ion exchange capacity of both ion exchange membranes is larger than the difference between the ion exchange capacities of both ion exchange membranes and the ion exchange capacity of the anion exchange membrane in the bipolar membrane is an example. As the difference between the ion exchange capacities of both ion exchange membranes in the bipolar membrane is larger.

  In the present invention, the bipolar membrane is treated by an ion exchanger before the desalting treatment by the bipolar membrane in a form that compensates for the imbalance of the ion exchange capacity between the cation exchange membrane and the anion exchange membrane in the bipolar membrane. It is possible to carry out a desalting treatment that sufficiently exhibits the ion exchange capacity of. As a result, as a whole, the apparatus size can be reduced as compared with the case where the desalting process is performed using only the bipolar membrane. In addition, when the bipolar membrane is regenerated by dissociating water, excess hydrogen ions or hydroxides depending on the ion exchange capacity imbalance between the cation exchange membrane and the anion exchange membrane in the bipolar membrane Ions are generated, but this excess hydrogen ion or hydroxide ion can be used for regeneration of the ion exchanger provided in the front stage of the bipolar membrane, so it is necessary to supply salt for regeneration of the ion exchanger. Absent. Therefore, according to the present invention, in the desalting treatment using the bipolar membrane, the amount of water to be treated that can be desalted without regenerating the bipolar membrane can be increased. The effect that it can be set as the desalination apparatus miniaturized to the extent which can be mounted in a household appliance etc. is acquired.

It is a figure which shows the structure of the desalination apparatus of one Embodiment of this invention, Comprising: (a) is a figure explaining a desalination process, (b) is a figure explaining a regeneration process. It is a figure which shows the principle of the desalination by a bipolar membrane. It is a figure which shows the principle of reproduction | regeneration of a bipolar film. 4 is a graph showing the relationship between desalting time and hardness in Example 1. 4 is a graph showing the relationship between desalting time and hardness in Comparative Example 1.

  FIG. 1 shows a desalination apparatus according to an embodiment of the present invention. This desalination apparatus includes a bipolar membrane desalting module 10 including a bipolar membrane 11 and a pair of electrodes 12, 13, an ion exchanger module 20 provided in the preceding stage of the bipolar membrane desalting module 10, and electrodes 12, 13. And a changeover switch 22 provided between the DC power supply 21 and the electrodes 12 and 13 for switching the polarities of the electrodes 12 and 13. The ion exchanger module 20 and the bipolar membrane desalting module 10 are connected via a pipe 30. A flow path switching valve 31 to which raw water is supplied is provided, and one outlet of the flow path switching valve 31 is provided as raw water as treated water to the ion exchanger module 20 during the desalting process via the pipe 32. Is connected to the ion exchanger module 20 so as to be supplied. A pipe 33 for discharging reclaimed water (concentrated water in which salts are concentrated) is connected to the pipe 32, and a valve 34 is provided in the pipe 33. The other outlet of the flow path switching valve 31 is connected to the bipolar membrane desalting module 10 via a pipe 35 so as to supply raw water to the bipolar membrane desalting module 10 during the regeneration process. The bipolar membrane desalting module 10 is connected with a pipe 36 for supplying desalted water (demineralized water) to the outside, and a valve 37 is provided in the pipe 36.

<Bipolar membrane desalination module>
The bipolar membrane desalting module 10 will be described in more detail.

  In the bipolar membrane desalting module 10, a pair of electrodes 12 and 13 are arranged separately in the container, and the space between them is filled with the water to be treated. And the bipolar film 11 is arrange | positioned away from the electrodes 12 and 13 so that the space between the electrodes 12 and 13 may be partitioned off. The electrodes 12 and 13 are not particularly limited as long as they function as a cathode and an anode. 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. In the example shown in FIG. 1, flat electrodes 12 and 13 are used.

  The bipolar membrane 11 has a structure in which a cation exchange membrane 14 and an anion exchange membrane 15 are bonded together. In the example shown in FIG. 1, a plurality of bipolar films 11 are arranged between the electrodes 12 and 13 so as to be parallel to each other and to the electrodes 12 and 13. At this time, both bipolar membranes 11 are arranged between the electrodes 11 and 12 such 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. ing. In this embodiment, the combination of the cation exchange membrane 14 and the anion exchange membrane 15 in the bipolar membrane 11 is a combination of a weakly acidic cation exchange membrane and a strongly basic anion exchange membrane, or a strongly acidic cation exchange membrane and a weakly basic anion. It is a combination with an exchange membrane.

  The ion exchange membrane can be roughly classified into a homogeneous membrane formed by impregnating a raw material monomer solution into a reinforcing body and then polymerized, and a homogenous membrane formed by pulverization and molding together with a polyolefin resin capable of dissolving and molding the ion exchange resin. There are two types: homogeneous membranes. In the bipolar membrane 11, either a homogeneous membrane or a heterogeneous membrane can be used as the cation exchange membrane 14 and the anion exchange membrane 15 that are both included in the category of ion exchange membranes.

Here, the principle of the desalting process using the bipolar membrane 11 will be described with reference to FIG. Here, it is assumed that both the cation exchange membrane 14 and the anion exchange membrane 15 are regenerative. When a voltage is applied with the electrode 12 facing the cation exchange membrane 14 of the bipolar membrane 11 as an anode and the other electrode 13 as a cathode, cations such as sodium ions (Na ⁺ ) contained in the raw water are bipolar. The membrane 11 moves to the cation exchange membrane 14 side, where it is ion-exchanged with hydrogen ions (H ⁺ ) contained in the cation exchange membrane 14 and captured by the cation exchange membrane 14. Hydrogen ions liberated by ion exchange are released from the cation exchange membrane 14 through the anion exchange membrane 15 by the electric field between the electrodes 12 and 13 into the water. Similarly, anions such as chloride ions (Cl ⁻ ) contained in the raw water move to the anion exchange membrane 15 side of the bipolar membrane 11, where there are hydroxide ions (OH ⁻ ) contained in the anion exchange membrane 15. The ions are exchanged with each other and captured by the anion exchange membrane 15. The hydroxide ions liberated by the ion exchange are released from the anion exchange membrane 15 into the water by the electric field into the water and combined with the hydrogen ions released from the anion exchange membrane 15 to become water.

  Next, the principle of the process for regenerating the bipolar membrane 11 used in the desalting process will be described with reference to FIG. The polarity of the electrodes 12 and 13 is reversed from that at the time of the desalting treatment, so that the electrode 12 on the cation exchange membrane 14 side is a cathode and the electrode 13 on the anion exchange membrane 15 side is an anode. Apply voltage. Then, water in the membrane dissociates into hydrogen ions and hydroxide ions at the junction surface of the cation exchange membrane 14 and the anion exchange membrane 15 in the bipolar membrane 11. Of these, hydrogen ions migrate to the cation exchange membrane 14 and ion exchange with cations (for example, sodium ions) trapped on the cation exchange membrane 14, thereby regenerating the cation exchange membrane 14. Similarly, hydroxide ions migrate to the anion exchange membrane 15 and ion exchange with anions (for example, chloride ions) trapped in the anion exchange membrane 15 to regenerate the anion exchange membrane 15. The cations and anions liberated by ion exchange are released into the liquid, thereby concentrating salts in the liquid.

  Thus, in the bipolar membrane desalting module 10, desalting and regeneration by the bipolar membrane 11 can be repeated by changing the polarities of the electrodes 12 and 13. In the bipolar membrane desalting module 10, the bipolar membrane 11 may be a plurality of flat membranes or may be wound in a roll shape, but the raw water is uniformly distributed on any part of the surface of the bipolar membrane 11. In the case where a plurality of bipolar membranes 11 are provided, the raw water must flow uniformly on the surface of any bipolar membrane 11. The shape of the electrodes 12 and 13 may be a flat plate, expand, punching, round bar, wire, or the like, but it needs to have a shape that can uniformly apply a potential to the bipolar film 11 according to the shape of the bipolar film 11. is there.

<Ion exchanger module>
Next, the ion exchanger module 20 will be described. In the ion exchanger module 20, when the ion exchange capacity of the cation exchange membrane 14 is larger than that of the anion exchange membrane 15 with respect to the cation exchange membrane 14 and the anion exchange membrane 15 constituting the bipolar membrane 11 in the bipolar membrane desalting module 10. The anion exchanger having an ion exchange capacity larger than the difference in ion exchange capacity between the cation exchange membrane 14 and the anion exchange membrane 15 is filled. Examples of the anion exchanger include anion exchange resins and monolithic anion exchangers. Conversely, when the anion exchange membrane 15 has a larger ion exchange capacity than the cation exchange membrane 14 in the bipolar membrane 11, the ion exchange capacity of the anion exchange membrane 15 and the cation exchange membrane 14 is included in the ion exchanger module 20. A cation exchanger having an ion exchange capacity larger than the difference is filled. Examples of the cation exchanger include cation exchange resins and monolithic cation exchangers. Eventually, the ion exchanger module 20 has a shortage in the form of compensating for the imbalance in ion exchange capacity between the cation exchange membrane 14 and the anion exchange membrane 15 in the bipolar membrane 11 in the bipolar membrane desalting module 10. An ion exchange resin (cation exchange resin or anion exchange resin) having ion exchange capacity for ions corresponding to the ion exchange capacity is provided.

  The ion exchange capacity of the ion exchanger filled in the ion exchanger module 20 may be larger than the difference in ion exchange capacity between the cation exchange membrane 14 and the anion exchange membrane 15 in the bipolar membrane 11. If the ion exchange capacity of 20 is too large, the ion exchanger module 20 becomes too large, and it becomes impossible to achieve downsizing of the desalination apparatus as a whole. Therefore, in order to achieve miniaturization of the desalination apparatus as a whole, the ion exchange capacity in the ion exchanger module 20 is the difference in ion exchange capacity between the cation exchange membrane 14 and the anion exchange membrane 15 in the bipolar membrane 11. It is preferable to set it to 2 times or less.

  The ion exchanger used in the ion exchanger module is desirably a weakly acidic cation exchanger or a weakly basic anion exchanger that can be regenerated with a dilute acid or alkali.

<how to drive>
Next, the process by the desalination apparatus of this embodiment is demonstrated.

  First, desalting treatment from raw water will be described with reference to FIG. When performing the desalting process, the flow path switching valve 31 is switched to the ion exchanger module 20 side, the valve 34 is closed, and the valve 37 is opened. Further, the selector switch 22 is operated to apply a voltage from the DC power source 21 to the electrodes 12 and 13 so that the electrode 12 becomes an anode and the electrode 13 becomes a cathode. The raw water containing salts (here, sodium chloride (NaCl)) passes through the ion exchanger module 20 from the flow path switching valve 31 through the pipe 32, and the ion exchange module 20 is filled with ion exchange. Depending on the resin (cation exchange resin or anion exchange resin), one ion (sodium ion or chloride ion) is removed in the ion exchanger module 20. The liquid that has passed through the ion exchanger module 20 is sent to the bipolar membrane desalting module 10 through the pipe 30 and is subjected to desalting treatment based on the principle described with reference to FIG. 2 to remove the remaining ions. . As a result, salt-free water (demineralized water) is generated, and the demineralized water is supplied to the outside through the pipe 36.

  The ion exchange capacity of the ion exchanger module 20 exceeds the difference in ion exchange capacity between the cation exchange membrane 14 and the anion exchange membrane 15 in the bipolar membrane 11 and cannot be said to be so large. The ion exchange resin in the module 20 may break with respect to the one ion, but even if the ion exchanger module 20 breaks, the problem arises because the one ion can be removed by the bipolar membrane desalting module 10. Absent. Further, in the configuration of the present embodiment, the bipolar membrane desalting module 10 so as to compensate for an imbalance in ion exchange capacity between the cation exchange membrane 14 and the anion exchange membrane 15 in the bipolar membrane 11 in the bipolar membrane desalting module 10. The ion exchange module 20 is provided in the preceding stage, and as a whole, the ion exchange capacity for cations and anions is uniform. Therefore, no pH shift occurs in the water to be treated in the bipolar membrane desalting module 10 due to a decrease in the ion exchange capacity of one ion exchange membrane, and desalting is performed until the total ion exchange capacity of the bipolar membrane 11 is almost used up. Processing can be performed. According to this embodiment, the exchange capacity of the bipolar membrane can be fully utilized, the amount of water to be treated that can be desalted without regenerating the bipolar membrane can be increased, and the apparatus size can be reduced. It becomes possible to.

  Next, the regeneration process after the desalting process as described above will be described with reference to FIG. When performing the regeneration process, the flow path switching valve 31 is switched to the bipolar membrane desalting module 10 side, the valve 34 is opened, and the valve 37 is closed. Further, the selector switch 22 is operated to apply a voltage from the DC power source 21 to the electrodes 12 and 13 so that the electrode 12 becomes a cathode and the electrode 13 becomes an anode. The raw water is first introduced into the bipolar membrane desalting module 10 via the pipe 35 by the flow path switching valve 1. At this time, if the water introduced into the bipolar membrane desalting module 10 contains salts, it takes time for the regeneration process due to ion exchange in the bipolar membrane 11, so that pure water is converted into the bipolar membrane. It is preferable to introduce into the desalting module 10, and for that purpose, pure water may be introduced into the bipolar membrane desalting module 10 from another route. In the bipolar membrane desalting module 10, regeneration processing is performed based on the principle described with reference to FIG. 3, and the cation exchange membrane 14 and the anion exchange membrane 15 of the bipolar membrane 11 are regenerated. When voltage is further applied to the electrodes 12 and 13, regeneration is completed on the side of the exchange membrane having a smaller ion exchange capacity, and if the ion exchange capacity of the cation exchange membrane 14 is smaller, hydrogen ions and ions of the anion exchange membrane 15 are more ionized. If the exchange capacity is small, hydroxide ions are directly introduced into the ion exchanger module 20 via the pipe 30. Since the ion exchanger module 20 is provided with an ion exchange resin having ion exchange capacity for ions having a smaller ion exchange capacity in the bipolar membrane 11, ions introduced into the ion exchanger module 20 (hydrogen ions or The ion exchange resin in the ion exchanger module 20 is also regenerated by the hydroxide ions.

  Thus, in the desalination apparatus of this embodiment, salts, acids, and alkalis are not required for the regeneration of the ion exchange resin in the ion exchanger module 20.

  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]
In the configuration shown in FIG. 1, a part composed of the ion exchanger module 20, the pipe 30, the bipolar membrane desalting module 10 and the DC power source 21 was assembled and subjected to desalting. As the bipolar membrane 11, a weakly acidic cation exchange membrane (ion exchange capacity (cation exchange capacity) 2.2 meq / g-bipolar membrane) and a strongly basic anion exchange membrane (ion exchange capacity (anion exchange capacity) each having a thickness of 0.25 cm. ) 0.8 meq / g-bipolar membrane) was used. The bipolar membrane 11 was wound in a roll shape by overlapping 10 sheets (mass 20 g / sheet) cut to a size of 15 × 40 cm. As the electrodes 12 and 13, wire-like platinum-coated titanium electrodes were used, and the electrodes 12 and 13 were disposed on the center and the outside of the bipolar film 11 wound in a roll shape, respectively. The ion exchange capacity (cation exchange capacity) of the weak acid cation exchange membrane as a whole of the bipolar membrane 11 is 440 meq (2.2 meq / g × 20 g / sheet × 10), and the ion exchange of the entire strongly basic anion exchange membrane is performed. The capacity (anion exchange capacity) was 150 meq (0.75 meq / g × 20 g / sheet × 10 sheets). Here, as the entire bipolar membrane 11, the ion exchange capacity (cation exchange capacity) of the cation exchange membrane is larger, and the ion exchange capacity (cation exchange capacity) of the weakly acidic cation exchange membrane and the ions of the strongly basic anion exchange membrane. The difference in exchange capacity (anion exchange capacity) is 440 meq-150 meq = 290 meq.

  The ion exchange resin of the ion exchanger module 20 was filled with 300 ml of weakly basic anion exchange resin (exchange capacity 1 meq / ml) (that is, 1 meq / ml × 300 ml = 300 meq of weakly basic anion exchange resin). .

As raw water, water containing a hardness of 250 mg-CaCO ₃ / L was used, and the raw water was passed through the ion exchanger module 20 side at 1 L / min. The voltage applied to the electrodes 12 and 13 in the desalting treatment was 300V. The target water quality of the desalted water obtained from the outlet of the bipolar membrane desalting module 10 was set to a hardness of 50 mg-CaCO ₃ / L or less. The result of measuring the hardness of the desalted water is shown in FIG. As shown in FIG. 4, the target water quality was achieved over 20 minutes.

[Comparative Example 1]
A desalting treatment was performed under the same conditions as in the example without installing an ion exchanger module in the previous stage of the bipolar membrane desalting module 10. The hardness of the desalted water from the outlet of the bipolar membrane desalting module 10 at this time was measured. The results are shown in FIG. As shown in FIG. 5, the hardness exceeding the target water quality leaked in about 10 minutes as shown in the figure, and sufficient hardness could not be removed.

DESCRIPTION OF SYMBOLS 10 Bipolar membrane desalination module 11 Bipolar membrane 12,13 Electrode 14 Cation exchange membrane 15 Anion exchange membrane 20 Ion exchanger module 21 DC power supply 22 Changeover switch 30,32,33,35,36 Piping 31 Flow path switching valve 34,37 valve

Claims (8)

In a desalination apparatus that performs desalination treatment on water to be treated,
A bipolar membrane disposed between the pair of electrodes and the pair of electrodes, the bipolar membrane comprising a weakly acidic cation exchange membrane and a strongly basic anion exchange membrane, or a strongly acidic cation exchange membrane and a weakly basic anion exchange membrane A bipolar membrane desalination module composed of a membrane;
An ion exchanger module provided in a preceding stage of the bipolar membrane desalting module;
Have
The ion exchanger module includes an anion exchanger when the ion exchange capacity of the cation exchange membrane is larger than the ion exchange capacity of the cation exchange membrane and the anion exchange membrane constituting the bipolar membrane, and the anion exchange membrane If the ion exchange capacity of is larger, a cation exchanger is provided,
While applying voltage between the pair of 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, the water to be treated is treated with the ion exchanger. A desalination apparatus characterized in that water is passed in a direction from the module toward the bipolar membrane desalting module to perform desalting.   When the ion exchange capacity of the cation exchange membrane is larger than the ion exchange capacity of the cation exchange membrane and anion exchange membrane constituting the bipolar membrane, the ion exchanger module and the anion exchange membrane The anion exchanger having an ion exchange capacity larger than the difference in ion exchange capacity of the anion exchange membrane, the ion exchange capacity of the anion exchange membrane and the cation exchange membrane when the ion exchange capacity of the anion exchange membrane is larger The desalting apparatus according to claim 1, comprising the cation exchanger having an ion exchange capacity larger than the difference. It further comprises a changeover switch that reverses the polarity of the pair of electrodes,
By operating the changeover switch and applying a voltage between the pair of electrodes so that the electrode facing the cation exchange membrane in the bipolar membrane is a cathode and the electrode facing the anion exchange membrane is an anode. The water is passed in a direction from the bipolar membrane desalting module toward the ion exchanger module so that the bipolar membrane and the ion exchanger in the ion exchanger module can be regenerated. The desalination apparatus according to 1 or 2.   The desalination apparatus according to any one of claims 1 to 3, wherein the ion exchanger module includes a weakly acidic cation exchanger or a weakly basic anion exchanger. In a desalting method for performing desalting treatment on water to be treated,
A treatment for passing water to be treated through an ion exchanger module including the ion exchanger;
A bipolar membrane having a pair of electrodes and a bipolar membrane disposed between the pair of electrodes, wherein the bipolar membrane is constituted by a cation exchange membrane and an anion exchange membrane; Treatment for passing water to be treated from the ion exchanger module while applying a voltage between the pair of electrodes so that the electrode facing the membrane is an anode and the electrode facing the anion exchange membrane is a cathode When,
Have
The bipolar membrane is a bipolar membrane composed of a weakly acidic cation exchange membrane and a strongly basic anion exchange membrane, or a bipolar membrane composed of a strongly acidic cation exchange membrane and a weakly basic anion exchange membrane,
The ion exchanger module includes an anion exchanger when the ion exchange capacity of the cation exchange membrane is larger than the ion exchange capacity of the cation exchange membrane and the anion exchange membrane constituting the bipolar membrane, and the anion exchange membrane A demineralization method comprising a cation exchanger when the ion exchange capacity is larger.   When the ion exchange capacity of the cation exchange membrane is greater than the ion exchange capacity of the cation exchange membrane and the anion exchange membrane constituting the bipolar membrane, the ion exchanger module and the anion exchange module When the anion exchanger having an ion exchange capacity larger than the difference in ion exchange capacity of the membrane is provided, and the ion exchange capacity of the anion exchange membrane is larger, the ion exchange capacity of the anion exchange membrane and the cation exchange membrane The desalting method according to claim 5, comprising the cation exchanger having an ion exchange capacity larger than the difference between the two.   In the bipolar membrane desalting module, a voltage is applied between the pair of electrodes so that the electrode facing the cation exchange membrane in the bipolar membrane is a cathode and the electrode facing the anion exchange membrane is an anode. Flowing the water, and flowing the water from the bipolar membrane desalting module to the ion exchanger module, thereby performing a regeneration treatment of the bipolar membrane and the ion exchanger in the ion exchanger module. Item 7. A desalting method according to Item 5 or 6.   The desalination method according to claim 5, wherein the ion exchanger module includes a weakly acidic cation exchanger or a weakly basic anion exchanger.

Images