Patent Application
20240002265
The present invention relates to an electrodeionization device for producing deionized water from water to be treated which contains weak acid components such as boron, and a method for producing deionized water.
There is a demand for removing weak acid components in water to be treated. For example, in recent years, there has been a demand for a further reduction in the content of boron in ultrapure water and the like used in the fabrication of semiconductor devices. Boron in water is a weakly acidic component that is difficult to remove by ion exchange treatment using an ordinary ion exchange resin. As means for removing boron, a reverse osmosis membrane device, a boron-selective ion exchange resin, an electrodeionization (EDI (ElectroDelonization)) device, and the like are known. Of these, the EDI device is a device that combines electrophoresis and electrodialysis, and at least the deionization chamber thereof is filled with an ion exchange resin to generate deionized water from the water to be treated. The EDI device has the advantage that at least the deionization chamber is filled with an ion exchange resin, ion components other than boron can be removed, and there is no need to regenerate the ion exchange resin with chemicals. However, in an EDI device, simply filling the deionization chamber with an ordinary ion exchange resin may not provide sufficient removal performance for weak acid components such as boron. In a such case, two DEI devices may be used by connecting them in series.
Ordinary ion exchange resins have a bead-like or granular shape, and their standard grain size exceeds 0.4 mm and is about 1 mm or less. In order to improve the performance of removing weak acid components such as boron in the EDI device, it has been proposed to fill the deionization chamber with an ion exchange resin having a smaller grain size. For example, Patent Literature 1 discloses that an ion exchange resin having an average grain size of 150 to 250 μm is packed in a single bed in the deionization chamber of an EDI device. Patent Literature 2 discloses packing ion exchange resins with an average diameter of 0.2 to 0.3 mm in a single bed in the deionization chamber. In Patent Literatures 3 and 4, it is disclosed is that. in a deionization chamber in which water to be treated flows vertically, an ion exchange resin having an average grain size of 0.1 to 0.4 mm is filled in the middle region in the vertical direction and the upper and lower regions are filled with an ion exchange resin having an average grain size of more than 0.4 mm.
In order to reduce the electric resistance of the deionization chamber and improve the efficiency of deionization during operation of the EDI device, it is important to control the packing ratio of the ion exchange resin in the deionization chamber. Patent Literature 5 discloses that, in order to reduce electric resistance of the deionization chamber, a plurality of ion exchange resin grain groups of different grain sizes are mixed and filled in the deionization chamber, each ion exchange resin grain group having a uniform grain size.
When an ion exchange resin with a small grain size is packed in the deionization chamber of an EDI device in order to improve the removal performance of weak acid components such as boron, the gaps between the grains of the ion exchange resin are reduced, resulting in an increase in the differential pressure of water flow. Therefore, the water to be treated must be passed through the deionization chamber at a high pressure, and it is necessary to improve the airtightness of the EDI device. Also, passing the water to be treated under high pressure reduces the durability of the EDI device.
An object of the present invention is to provide an electrodeionization device (EDI device) capable of suppressing an increase in the differential pressure of water flow across a deionization chamber while enhancing the performance of removing weak acid components such as boron, and a method for producing such deionized water.
According to an aspect of the present invention, an electrodeionization device comprising a deionization chamber partitioned by a pair of ion exchange membranes between an anode and a cathode, the deionization chamber being filled with an ion exchange resin, is characterized in that: a grain size of 0.1 mm or more and 0.4 mm or less being defined as small grain size, and a grain size of more than 0.4 mm being defined as large grain size, in the deionization chamber, a large grain size layer made of an ion exchange resin of large grain size and a mixed grain size layer in which an ion exchange resin of large grain size and an ion exchange resin of small grain size are mixed are arranged along a flow of water to be treated.
According to another aspect of the present invention, an electrodeionization device comprising a deionization chamber partitioned by a pair of ion exchange membranes between an anode and a cathode, the deionization chamber being filled with an ion exchange resin, is characterized in that: a grain size of 0.1 mm or more and 0.4 mm or less being defined as small grain size, and a grain size of more than 0.4 mm being defined as large grain size, a mixed grain size layer in which an ion exchange resin of large grain size and an ion exchange resin of the small grain size are mixed with a mixing ratio in which L:S is within a range from 1:1 to 20:1 is arranged in the deionization chamber, L being defined as an apparent volume of the ion exchange resin of large grain size, and S being defined as an apparent volume of the ion exchange resin of the small grain size, and water to be treated containing boron is supplied to the deionization chamber to remove boron from the water to be treated.
According to another aspect of the present invention, a method for producing deionized water to obtain deionized water by passing water to be treated through a deionization chamber which is partitioned by a pair of ion exchange membranes and arranged between an anode and a cathode while applying a DC voltage between the anode and the cathode, is characterized in that: a grain size of 0.1 mm or more and 0.4 mm or less being defined as small grain size, and a grain size of more than 0.4 mm being defined as large grain size, in the deionization chamber, the water to be treated is passed through both a large grain size layer made of an ion exchange resin of the large grain size and a mixed grain size layer in which an ion exchange resin of large grain size and an ion exchange resin of small grain size are mixed.
According to a further aspect of the present invention, a method for producing deionized water to obtain deionized water by passing water to be treated containing boron through a deionization chamber which is partitioned by a pair of ion exchange membranes and arranged between an anode and a cathode while applying a DC voltage between the anode and the cathode, is characterized in that: a grain size of 0.1 mm or more and 0.4 mm or less being defined as small grain size, and a grain size of more than 0.4 mm being defined as large grain size, in the deionization chamber, the water to be treated is passed through a mixed grain size layer in which an ion exchange resin of large grain size and an ion exchange resin of the small grain size are mixed with a mixing ratio in which L:S is within a range from 1:1 to 20:1, to remove boron in the water to be treated, L being defined as an apparent volume of the ion exchange resin of large grain size, and S being defined as an apparent volume of the ion exchange resin of the small grain size.
According to the present invention, obtained are an electrodeionization device (EDI device) that suppresses an increase in the differential pressure of water flow across the deionization chamber and enhances the performance of removing weak acid components such as boron, and a method for producing such deionized water.
Next, embodiments of the present invention will be described with reference to the drawings. Generally, in an electrodeionization device (EDI device), a deionization chamber partitioned by a pair of ion exchange membranes is provided between an anode and a cathode, and the deionization chamber is filled with an ion exchange resin. In the EDI device, water to be treated is subjected to desalting (deionization) treatment when the water to be treated is supplied to the deionization chamber in a state in which a DC voltage is applied between the anode and the cathode, and water from which the ion components have been removed is then discharged from the deionization chamber as treated water. Defining a grain size of 0.1 mm or more and 0.4 mm or less as small grain size and defining a grain size of more than 0.4 mm as large grain size, the EDI device according to the present invention is an EDI device in which a mixed grain size layer in which an ion exchange resin of large grain size and an ion exchange resin of small grain size are mixed is arranged in the deionization chamber. By arranging the mixed grain size layer in the deionization chamber of an EDI device, the removal performance of weak acid components including boron is improved. In addition to the mixed grain size layer, a large grain size layer made of an ion exchange resin of large grain size may be arranged in the deionization chamber. When the large grain size layer is arranged, the large grain size layer and the mixed grain size layer are arranged along the flow of the water to be treated in the deionization chamber. Since the grain size of the bead-like or granular ion exchange resin is usually 1 mm or less, the ion exchange resin having a grain size of more than 0.4 mm and 1 mm or less may be used as the ion exchange resin of large grain size. Although the grain size of the ion exchange resin can be measured using a sieve, the catalog value by the manufacturer of the ion exchange resin may be used as the grain size in the present invention. In the present invention, an anion exchange resin of large grain size and an anion exchange resin of small grain size may be mixed to form a mixed grain size layer of the anion exchange resin, or a cation exchange resin of large grain size and a cation exchange resin of small grain size may be mixed to form a mixed grain size layer of the cation exchange resin.
In the present invention, when the weak acid component is mainly boron, the concentration of boron contained in the water to be treated is, for example, 1 ppb or more and 100 ppb or less. Of course, even when the concentration of the weak acid component in the water to be treated is less than 1 ppb or exceeds 100 ppb, the weak acid component in the water to be treated can be removed based on the present invention.
Water to be treated is supplied to deionization chambers 23, and treated water obtained as a result of deionization of the water to be treated, that is, deionized water, flows out from deionization chamber 23. The interior of deionization chamber 23 is filled with an ion exchange resin, and in the example shown here, deionization chamber 23 is filled with an anion exchange resin (AER). The interior of deionization chamber 23 is divided into two regions along the flow of the water to be treated in deionization chamber 23. The region on the inlet side of the water to be treated is filled with an anion exchange resin of large grain size to form a large grain size layer. In the area on the outlet side of the treated water, an ion exchange resin of large grain size and an ion exchange resin of small grain size are mixed and filled to form a mixed grain size layer. In the figure, the large grain size layer made of an anion exchange resin is indicated as “L-AER,” and the mixed grain size layer made of an anion exchange resin is indicated as “LS mixed AER.” In the illustrated example, the boundary between the large grain size layer and the mixed grain size layer is near the center of deionization chamber 23 along the flow direction of the water to be treated.
In EDI device 10, a cation exchange resin (CER) is packed in anode chamber 21, and an anion exchange resin is packed in concentration chambers 22, 24, and cathode chamber 25. Although anode chamber 21, concentration chambers 22, 24, and cathode chamber 25 do not necessarily need to be filled with an ion exchange resin (i.e., an anion exchange resin or a cation exchange resin), it is preferable to fill anode chamber 21, concentration chambers 22, 24 and cathode chamber 25 with ion exchange resins as well, in order to reduce the DC voltage to be applied between anode 11 and cathode 12. Concentration chambers 22, 24 are supplied with supply water for concentration chamber and discharge concentrated water. Supply water for electrode chamber is supplied to cathode chamber 25, and the supply water for electrode chamber supplied to cathode chamber 25 is supplied to anode chamber 21 after passing through cathode chamber 25, and then discharged from anode chamber 21 as electrode water. It should be noted that it can use a configuration which functions as both the concentration chamber and the electrode chamber.
Assuming that the concentration chamber is denoted by “C,” the ion exchange membrane by “M,” and the deionization chamber by “D,” generally in the EDI device, a plurality of basic configurations each consisting of [C|M|D|M|C] can be juxtaposed between an anode and a cathode. At this time, two concentration chambers adjacent to each other with an ion exchange membrane interposed therebetween can be made into a single concentration chamber by removing the sandwiched ion exchange membrane. In EDI device 10 shown in
Next, production of the deionized water (i.e., treated water) by EDI device 10 shown in
In EDI device 10 of the present embodiment, the order of arrangement of the large grain size layer and the mixed grain size layer along the direction of flow of the water to be treated is arbitrary. One large grain size layer and one mixed grain size layer may be provided, or two or more layers of at least one of the large grain size layer and the mixed grain size layer may be provided. However, since the configuration it is preferable to initially remove components that are relatively easy to remove in the water to be treated and then remove components that are relatively difficult to remove, it is preferable that the mixed grain size is arranged near the outlet of the treated water in deionization chamber 23. In this case, the mixed grain size layer may be arranged so as to be in contact with the outlet of the treated water, or at least a portion of the mixed grain size layer may be included in a region within 25% of the length of deionization chamber 23 along the flow of the water to be treated from the outlet of the treated water. Both the mixed grain size layer and the large grain size layer are arranged in deionization chamber 23, and it is preferable that the ratio of the mixed grain size layer among them is such that, for example, a total filling height of the ion exchange resin along the flow of the water to be treated in the mixed grain size layer is 20% or more and 80% or less of a length of deionization chamber 23 along the flow of the water to be treated. If the ratio of the mixed grain size layer is too small, the removal performance of the weak acid components including boron is lowered. If the ratio of the mixed grain size layer is too large, the differential pressure of water flow in deionization chamber 23 becomes large. As will be described later, when the purpose is to remove particularly boron among the weak acid components, deionization chamber 23 may be configured without the large grain size layer. In this Description, the filling height of the ion exchange resin along the flow of the water to be treated in the large grain size layer or the mixed grain size layer is sometimes referred to as the filling height of that layer. The length of deionization chamber 23 means the length of deionization chamber 23 along the flow of the water to be treated which is the length of the portion of deionization chamber 23 where the ion exchange resin is provided.
Weak acid components in the water to be treated are adsorbed by the anion exchange resin forming the mixed grain size layer by ion exchange, and then pass through anion exchange membrane 32 as anions and move to concentration chamber 22 on the side of anode 11. Since the lower the anion concentration in concentration chamber 22, the easier the weak acid component moves to concentration chamber 22, a low anion concentration is preferred in water flowing through a position of concentration chamber 23 which is opposed to the mixed grain size layer of deionization chamber 23 via anion exchange membrane therebetween. Further, as described above, it is preferable that the mixed grain size layer is provided at a position close to the outlet in deionization chamber 23. For these reasons, it is preferable that the flow of the outlet water in deionization chamber 23 and the flow of supply water supplied to concentration chamber 22 are countercurrent.
The mixing ratio of the ion exchange resin of large grain size and the ion exchange resin of small grain size in the mixed grain size layer will be described. Since the ion exchange resin is in the form of beads or granules regardless of whether the grain size is large or small, the apparent volume including voids between grains can be measured. The mixing ratio L:S is preferably between 1:1 and 20:1, and more preferably between 5:1 and 10:1, where L is the apparent volume of the ion exchange resin of large grain size before mixing, and S is the apparent volume of the ion exchange resin of small grain size. If the ratio of the ion exchange resin of large grain size is too high, sufficient performance for removing weak acid components such as boron cannot be obtained, and if the ratio of the ion exchange resin of small grain size is too high, the differential pressure of water flow increases. Even after the mixed grain size layer is formed by mixing the ion exchange resin of large grain size and the ion exchange resin of small grain size, the mixing ratio of the ion exchange resin of large grain size and the ion exchange resin of small grain size can be determined. For example, the mixed grain size layer is taken out from deionization chamber 23 and classified using a sieve and separated into ion exchange resins having a grain size of 0.1 mm or more and 0.4 mm or less and ion exchange resins having a grain size of more than 0.4 mm. By separating and measuring the apparent volume of each, the mixing ratio L:S can be determined.
In EDI device 10 shown in
In addition to the anion exchange resin, deionization chamber 23 may be filled with a cation exchange resin (CER) to remove ionic impurities that are cations. In the example shown in
Deionization chamber 23 shown in
The EDI device according to the present invention may be configured such that the deionization chamber itself is divided into two small deionization chambers by an ion exchange membrane, the water to be treated is supplied to one of the small deionization chambers, and the water flowing out from the one small deionization chamber is then supplied to the other small deionization chamber. Deionized water is obtained as the treated water from the other small deionization chamber. EDI device 10 of the second embodiment of the present invention shown in
In EDI device 10 shown in
Also in the second embodiment in which the deionization chamber is divided into two small deionization chambers by an intermediate ion exchange membrane, the preferred mixing ratio of the ion exchange resin of large grain size and the ion exchange resin of small grain size in the mixed grain size layer and the preferred ratio of the total filling height of the mixed grain size layer to the length of the deionization chamber are the same as those described in the first embodiment. Also in the second embodiment, it is preferable to provide the mixed grain size layer at a position close to the outlet of the treated water in the entire deionization chamber. At least a portion of the mixed grain size layer may be included within a range of 25% of the length of the deionization chamber from the outlet of the treated water.
Next, production of deionized water by EDI device 10 shown in
The EDI devices according to the present invention has been described above. The EDI device can be used, for example, when pure water or ultrapure water is produced from raw water.
By applying a DC voltage between the anode (not shown in
As described above, according to the EDI device according to the present invention, by arranging, in deionization chamber, the mixed grain size layer in which an ion exchange resin of large grain size and an ion exchange resin of small grain size are mixed, it is possible to improve the removal rate of weak acid components such as boron, and to obtain pure water and ultrapure water of higher water quality. An improvement in the removal rate of weak acid components in an EDI device leads achievement of the miniaturization of a device such as a reverse osmosis membrane device installed in the preceding stage of the EDI device, and the miniaturization of a device, such as ion exchange device, which may be installed in the subsequent stage of the EDI device.
The present invention will be described in more detail below using Examples and Comparative Examples. In the following description, the mixing ratio when forming a mixed grain size layer by mixing an ion exchange resin of large grain size and an ion exchange resin of small grain size is expressed as L:S. L is the apparent volume of the ion exchange resin of large grain size before mixing, and S is the apparent volume of the ion exchange resin of small grain size before mixing.
As the EDI device of Example 1, EDI device 10 shown in
Permeate water which was obtained by permeating raw water through two stages of reverse osmosis membrane devices and was added with boric acid so that the boron concentration was 50 ppb was used as the water to be treated supplied to deionization chamber 23. The electrical conductivity of the water to be treated was 0.3 to 0.4 μS/cm. The water to be treated was passed through deionization chamber 23 at a flow rate of 30 L/h. The permeated water obtained by permeating the raw water through two stages of reverse osmosis membrane devices was used as the supply water, and was supplied to each of concentration chambers 22, 24 at a flow rate of 10 L/h, and supplied to cathode chamber 25 at 5 L/h. A DC voltage was applied between anode 11 and cathode 12 so that the current was 0.5 A, and operated the EDI device. Then, the concentration of boron in the outlet water of deionization chamber 23, that is, the treated water was measured, and the boron removal rate by the EDI device was found to be 96.2%.
As the EDI device of Comparative Example 1, EDI device 10 shown in
From the results of Example 1 and Comparative Example 1, it was found that the removal rate of boron was improved by making the anion exchange resin filled in deionization chamber 23 into the mixed grain size layer.
EDI device 10 shown in
Permeate water which was obtained by permeating raw water through two stages of reverse osmosis membrane devices and added with boric acid so that the boron concentration was 50 ppb was used as the water to be treated supplied to first small deionization chamber 26. The electrical conductivity of the water to be treated was 0.3 to 0.4 μS/cm. The water to be treated was passed through deionization chamber 23 at a flow rate of 30 L/h. Permeated water obtained by permeating raw water through two stages of reverse osmosis membrane devices was supplied as supply water to each of concentration chambers 22, 24 at a flow rate of 10 L/h and to cathode chamber 25 at 5 L/h. A DC voltage was applied between anode 11 and cathode 12 so that the current was 0.5 A, and operated the EDI device. Then, the boron concentration in the outlet water of second small deionization chamber 27, that is, the treated water, was measured. In addition, the pressure of the water to be treated at the inlet of first small deionization chamber 26 and the pressure of the treated water at the outlet of second small deionization chamber 27 were measured, and the difference between them was calculated to obtain the differential pressure of water flow. The results are shown in Table 1.
As the EDI device of Example 2-2, EDI device 10 shown in
As the EDI device of Example 2-3, EDI device 10 shown in
As the EDI device of Examples 2-4, EDI device 10 shown in
As the EDI device of Comparative Example 2, EDI device 10 shown in
From Table 1 as well, it was found that the boron removal performance was improved by providing an EDI device with a mixed grain size layer in which an anion exchange resin of large grain size was mixed with an anion exchange resin of small grain size. By using an anion exchange resin having a uniform grain size as the anion exchange resin of small grain size contained in the mixed grain size layer, the removal rate of boron was further improved. Further, by arranging the mixed grain size layer on the outlet side of the flow of the water to be treated in the deionization chamber, in the example shown here, by arranging the mixed grain size layer in the second small deionization chamber, boron removal performance is improved furthermore. There is concern about an increase in the differential pressure of water flow when an ion exchange resin of large grain size is mixed with an ion exchange resin of small grain size. However, it was found that, when the mixing ratio L:S is 5:1 or the ratio of the anion exchange resin of large grain size was higher than that, the differential pressure of water flow was almost the same as the case in which only the anion exchange resin of large grain size was used, and that the increase in the differential pressure of water flow could be suppressed. From Table 1, it can be seen that by forming the mixed grain size layer of the anion exchange resin in the area of 25% of the length of the deionization chamber from the outlet side of the deionization chamber, it is possible to achieve improvement of boron removal performance while suppressing the increase in the differential pressure of water flow.
An increase in the differential pressure of water flow by providing a mixed grain size layer in which an ion exchange resin of large grain size and an ion exchange resin of small grain size are mixed was investigated. A cylindrical column with a diameter of 5 cm and a length of 5 cm was prepared, and permeated water obtained by permeating raw water through two stages of reverse osmosis membrane devices was run into the column at each flow rate of 100, 140, 210 and 250 mL/h. At that time, the pressure at the inlet and the pressure at the outlet of the column were obtained, and the difference between them was taken as the differential pressure of water flow when the column was in a blank state. Next, the same column was filled with an anion exchange resin and the permeated water was passed at the same flow rate as in the blank state, and similarly the pressure at the inlet and the pressure at the outlet were obtained to obtain the pressure difference of water flow. At this time, an anion exchange resin of large grain size and an anion exchange resin of small grain size were prepared as anion exchange resins, and these were packed in the column singly or in combination. As the anion exchange resin of large grain size, AMBERJET® 4002 manufactured by DuPont was used. The grain size of this anion exchange resin of large grain size was 0.5 to 0.65 mm, and the uniformity coefficient was 1.20 or less. As the anion exchange resin of small grain size, DOWEX® 1×4 50-100 mesh anion exchange resin manufactured by DuPont was used. The grain size of this anion exchange resin of small grain size was 0.15 to 0.3 mm, and the uniformity coefficient was 1.3 or less. The mixing ratio L:S of grains of large grain size and grains of small grain size in the anion exchange resin packed in the column was 0:1, 1:1, 5:1, 10:1, 20:1 and 1:0. L:S=0:1 indicates that it is composed only of an anion exchange resin of small grain size, and L:S=1:0 indicates that it is composed only of an anion exchange resin of large grain size.
For each water flow rate in the column and for each mixing ratio in the anion exchange resin packed in the column, the differential pressure of water flow due to only the anion exchange resin was calculated by subtracting the pressure difference of water flow in the blank state from the pressure difference of water flow in the column packed with the anion exchange resin. Then, the differential pressures of water flow due to only the anion exchange resin were compared. Furthermore, in order to simulate the fact that the deionization chamber of the EDI device is composed of a cell with a thickness of 9 mm, a width of 160 mm, and a height of 280 mm, the differential pressures of water flow due to only the anion exchange resin obtained by the column were converted by calculation to the differential pressures of water flow due to only the anion exchange resin in the cell. The results are shown in
From
In the same manner as in Example 3, an increase in the differential pressure of water flow by providing a mixed grain size layer in which an anion exchange resin of large grain size and an anion exchange resin of small grain size are mixed was examined. However, in Example 4, as the ion exchange resin of small grain size, those having a uniform grain size were used. Using the same cylindrical column as used in Example 3, the differential pressure of water flow in the blank state and the differential pressure of water flow in the case of filling with the anion exchange resin were determined in the same manner as in Example 3. As the anion exchange resin of large grain size, the same one as used in Example 2 was used. Also, DOWEX® 1×4 50-100 mesh anion exchange resin manufactured by DuPont having a grain size of 0.15 to 0.3 mm and a uniformity factor of 1.3 or less was used, and, by separating this anion exchange resin with a sieve, only grains having a grain size of about 0.3 mm were taken out. Then, the grains thus obtained were used as an anion exchange resin having a small grain size and a uniform grain size, which constitutes the mixed grain size layer. At this time, the uniformity coefficient of the anion exchange resin of small grain size constituting the mixed grain diameter layer was 1.15. The mixing ratio L:S of the grains of large grain size and the grains of small grain size in the anion exchange resin packed in the column was 0:1, 1:1, 5:1, 10:1, 20:1 and 1:0.
For each water flow rate in the column and for each mixing ratio in the anion exchange resin packed in the column, the differential pressure of water flow due to only the anion exchange resin was calculated by subtracting the pressure difference of water flow in the blank state from the pressure difference of water flow in the column packed with the anion exchange resin. Then, the differential pressures of water flow due to only the anion exchange resin were compared. Furthermore, in order to simulate the fact that the deionization chamber of the EDI device is composed of a cell with a thickness of 9 mm, a width of 160 mm, and a height of 280 mm, the differential pressures of water flow due to only the anion exchange resin obtained by the column were converted by calculation to the differential pressure of water flow due to only the anion exchange resin in the cell. The results are shown in
From
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-201779 | Dec 2020 | JP | national |
| 2020-201780 | Dec 2020 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/039731 | 10/28/2021 | WO |
