JP3966104B2 - Operation method of electrodeionization equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an operation method of an electrodeionization apparatus, and more particularly to an operation method of an electrodeionization apparatus in which the removal rate of silica and boron in the electrodeionization apparatus is increased.
[0002]
[Prior art]
Conventionally, in the manufacture of deionized water used in various industries such as semiconductor manufacturing factory, liquid crystal manufacturing factory, pharmaceutical industry, food industry, electric power industry, etc. or consumer use or research facilities, as shown in FIG. A plurality of anion exchange membranes (A membranes) 13 and cation exchange membranes (C membranes) 14 are alternately arranged between the anode 11 and the cathode 12) to alternately form the concentration chambers 15 and the desalting chambers 16. An electrodeionization apparatus in which the salt chamber 16 is mixed with an anion exchanger and an cation exchanger made of an ion exchange resin, an ion exchange fiber, a graft exchanger, or the like or filled in multiple layers is used (Japanese Patent No. 17842943, Patent No. 1). 2751090, Japanese Patent No. 2699256). In FIG. 2, 17 is an anode chamber and 18 is a cathode chamber.
[0003]
The ions that flow into the desalting chamber 16 react with the ion exchanger based on their affinity, concentration and mobility, move in the ion exchanger in the direction of the potential gradient, and further move across the membrane. Charge neutralization is maintained in the chamber. The ions are reduced in the desalting chamber 16 and concentrated in the adjacent concentrating chamber 15 due to the semi-osmotic properties of the membrane and the directionality of the potential gradient. That is, cations permeate the cation exchange membrane 14 and anions permeate the anion exchange membrane 13 and are concentrated in the concentration chamber 15 respectively. For this reason, deionized water (pure water) is recovered from the desalting chamber 16 as production water.
[0004]
Electrode water is also passed through the anode chamber 17 and the cathode chamber 18, and in general, as the electrode water, effluent water (concentrated water) from the concentrating chamber 15 having a high ion concentration in order to ensure electrical conductivity. Is being passed.
[0005]
That is, raw water is introduced into the desalting chamber 16 and the concentration chamber 15, and deionized water (pure water) is taken out from the desalting chamber 16. On the other hand, the concentrated water in which the ions flowing out of the concentration chamber 15 are concentrated is partly circulated to the inlet side of the concentration chamber 15 by a pump (not shown) to improve the water recovery rate, and a part of the concentrated water is an anode. It is fed to the inlet side of the chamber 17 and the remainder is discharged out of the system as waste water to prevent the concentration of ions in the system. The outflow water from the anode chamber 17 is fed to the inlet side of the cathode chamber 18, and the outflow water from the cathode chamber 18 is discharged out of the system as waste water.
[0006]
The electrodeionization device generates H ⁺ ions and OH ⁻ ions by water dissociation and continuously regenerates the ion exchanger filled in the desalting chamber, enabling efficient desalting treatment. Thus, it does not require a regeneration treatment using chemicals such as the ion exchange resin apparatus that has been widely used so far, and complete continuous water sampling is possible, and an excellent effect that high-purity water is obtained is exhibited.
[0007]
In such an electrodeionization apparatus, the anion exchanger and the cation exchanger filled therein are initially in a salt form. For example, the anion exchanger is a Cl-type anion exchanger, and the cation exchanger is a Na-type cation exchanger. The salt-type anion exchanger and cation exchanger become a regenerative ion exchanger, that is, an OH-type anion exchanger or an H-type cation exchanger by the generated OH ⁻ and H ⁺ at the start of operation. In the desalting chamber, anions and cations in the raw water are captured by this regenerative ion exchanger and ion exchange reaction, and move mainly on the surface of the ion exchanger according to the potential.
[0008]
[Problems to be solved by the invention]
In such an electrodeionization apparatus, Cl ⁻ is dissociated from the Cl-type anion exchanger at the beginning of operation to increase the Cl ⁻ concentration, and a part of this Cl ⁻ is Cl ₂ by the action of the applied voltage. Alternatively, an oxidizing compound such as chlorate ion or perchlorate ion (hereinafter sometimes referred to as Cl ₂ or the like) is generated, which may cause oxidative degradation of an ion exchanger such as an ion exchange resin or an ion exchange membrane. is there.
[0009]
The present invention aims at providing a method of operating an electrodeionization apparatus which can suppress the deterioration of such Cl ₂ ion exchangers or ion exchange membrane by like.
[0010]
[Means for Solving the Problems]
The operation method of the electrodeionization apparatus of the present invention comprises one or more demineralization chambers formed by arranging one or more pairs of anion exchange membranes and cation exchange membranes between an anode and a cathode. In a method of operating an electrodeionization apparatus in which a salt chamber is filled with an ion exchanger, the rate of voltage increase applied between the anode and the cathode at the start of operation of the electrodeionization apparatus is 0.02 V / cell / Min or less.
[0011]
By reducing the voltage increase rate at the start of operation in this way, the Cl ⁻ desorption rate from the anion exchanger is reduced, the generation of Cl _{2 and the} like is suppressed, and the ion exchanger and the ion exchange membrane are deteriorated due to oxidation. Is suppressed.
[0012]
In the present invention, when the electrical conductivity of the effluent water from the concentrating chamber adjacent to the desalting chamber is 500 μS / cm or more, the oxidative deterioration of the ion exchanger or ion exchange membrane is more reliably prevented by stopping the voltage increase. Can be prevented.
[0013]
The method of the present invention is formed by alternately arranging an anode chamber having an anode, a cathode chamber having a cathode, and a plurality of anion exchange membranes and cation exchange membranes between the anode chamber and the cathode chamber. A concentration chamber and a desalting chamber, an ion exchanger filled in the desalting chamber, an ion exchanger, activated carbon or an electric conductor filled in the concentration chamber, and electrode water in the anode chamber and the cathode chamber, respectively. Means for passing water, concentrated water passing means for passing concentrated water through the concentration chamber, and means for passing deionized water through the raw water through the desalting chamber. Water means introduces water having a lower silica or boron concentration than the raw water into the concentration chamber from the side close to the deionized water outlet of the demineralization chamber, and is close to the raw water inlet of the demineralization chamber of the concentration chamber At least a portion of the concentrated water flowing out of the concentration chamber It is very suitable for application to the electrodeionization apparatus to discharge into.
[0014]
In this electrodeionization apparatus, water having a lower silica or boron concentration than the raw water is used as the concentrated water, and water having a good water quality is thus supplied from the deionized water (product water) extraction side of the demineralization chamber to the raw water. Since water is passed through the concentrating chamber in the direction toward the inflow side, high-quality product water with the silica and boron concentrations reduced to an extremely low concentration can be obtained. In this way, when producing high quality water (deionized water), the deterioration of the ion exchanger and ion exchange membrane has a great effect on the water quality, so that the deterioration of the water can be prevented by applying the method of the present invention. Is very suitable.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0016]
In the present invention, the rate of voltage increase at the start of operation of the electrodeionization apparatus is set to 0.02 V / cell / min or less. For example, the rate of increase may be a value measured intermittently, for example, 0.1 V / cell every 5 minutes or 0.2 V / cell every 10 minutes. However, since reliability is lowered when a long time is used as a reference, it is preferable to use 10 minutes or less as a reference. This unit V / cell / min is a value obtained by dividing the applied voltage increase rate V / min per minute between the anode and the cathode by the number of desalting chambers (number of cells).
[0017]
By setting the voltage increase rate to 0.02 V / cell / min or less, generation of Cl _{2 and the} like is suppressed, and deterioration of the ion exchanger and the ion exchange resin is suppressed. If the voltage increase rate is excessively slow, it takes a long time to reach the steady operation state, so the voltage increase rate is preferably set to 0.002 V / cell / min or more. A preferred voltage increase rate is 0.004 to 0.018 V / cell / min, particularly 0.008 to 0.015 V / cell / min.
[0018]
When the electrical conductivity of the concentrated water is 500 μS / cm or more, it is preferable to stop the voltage increase because the Cl ⁻ concentration is high and Cl ₂ or the like is easily generated.
[0019]
In the present invention, when the electrical conductivity of the concentrated water effluent is lower than 500 μS / cm, the applied voltage may be controlled so that the rate of increase in electrical conductivity decreases as the electrical conductivity increases.
[0020]
The start of the operation of the electrodeionization apparatus is not only when a new ion exchanger is filled and the operation of the electrodeionization apparatus is started, but also when the ion exchanger is returned to a salt form (for example, a concentrated NaCl solution is added). This includes the case where the operation of the electrodeionization apparatus is resumed after the flow process).
[0021]
The present invention can be applied regardless of the type of electrodeionization apparatus, but is suitable for application to the electrodeionization apparatus for producing high-quality deionized water shown in FIGS.
[0022]
FIG. 1 is a schematic cross-sectional view of an electrodeionization apparatus suitable for applying the method of the present invention. This electrodeionization apparatus, like the conventional electrodeionization apparatus shown in FIG. 2, has a plurality of anion exchange membranes (A membranes) 13 and cation exchange membranes (C membranes) 14 between electrodes (anode 11 and cathode 12). Are alternately arranged to form the concentration chamber 15 and the desalting chamber 16, and the desalting chamber 16 includes an anion exchanger and a cation made of an ion exchange resin, an ion exchange fiber, a graft exchanger, or the like. The exchanger is mixed or packed in multiple layers.
[0023]
The concentration chamber 15, the anode chamber 17, and the cathode chamber 18 are also filled with an electric conductor such as an ion exchanger, activated carbon, or metal.
[0024]
The raw water is introduced into the desalting chamber 16, and the production water is taken out from the desalting chamber 16. A part of this product water is passed through the concentrating chamber 15 in a counter-current and transient manner in the direction opposite to the water passing direction of the desalting chamber 16, and the outflow water of the concentrating chamber 15 is discharged out of the system. That is, in this electric deionization apparatus, the concentrating chambers 15 and the desalting chambers 16 are alternately arranged in parallel, and the inlet of the concentrating chamber 15 is provided on the product water take-out side of the desalting chamber 16. An outlet of the concentrating chamber 15 is provided on the 16 raw water inflow side. Further, a part of the production water is fed to the inlet side of the anode chamber 17, and the effluent water of the anode chamber 17 is fed to the inlet side of the cathode chamber 18, and the effluent water of the cathode chamber 18 is used as drainage. It is discharged outside.
[0025]
In this way, by passing the production water through the concentration chamber 15 in a counter-current and transient manner with the desalination chamber 16, the concentration of the concentrated water in the concentration chamber 15 becomes lower toward the production water take-out side, which is caused by concentration diffusion. The influence on the desalting chamber 16 is reduced, and the ion removal rate, particularly the removal rate of silica and boron, can be dramatically increased.
[0026]
Conventionally, as shown in FIG. 2, the concentrated water of the electrodeionization device (the effluent of the concentration chamber) is circulated to the inlet side of the concentration chamber after discharging only a part of it to improve the water recovery rate. For example, the LV of the concentrating chamber was 80 m / hr or more.
[0027]
By filling the concentration chamber with an ion exchanger, deionization performance can be ensured even if the LV of the concentration chamber is 20 m / hr or less. This is because when the concentrating chamber is a spacer, it was necessary to diffuse the silica and boron membrane surfaces on the concentrating chamber membrane surface by a water flow, but by filling the concentrating chamber with an ion exchanger, etc. This is probably because ions diffuse through the exchanger so that a high water flow rate (LV) is not required.
[0028]
Since the water flow rate may be low in this way, even if the concentrated water is passed through in a transient manner, the water recovery rate can be improved as compared with the conventional one, and it is not necessary to use a circulation pump. It is more economical.
[0029]
The concentrating chamber filling may be activated carbon or the like in order to secure the necessary current, but it is preferable to fill the ion exchanger from the viewpoint of the ion diffusion action.
[0030]
In the electrodeionization apparatus of FIG. 1, the product water is also supplied to the electrode chambers 17 and 18, but in the electrode chambers 17 and 18 as well as the concentration chamber 15, an ion exchanger or activated carbon is used to secure current. Or, by filling metal or the like that is an electrical conductor, the consumption voltage becomes constant regardless of the water quality, and it is possible to secure the necessary current even when passing high quality water such as ultrapure water. Become.
[0031]
In the electrode chamber, since generation of oxidizing agents such as chlorine and ozone occurs in the anode chamber in particular, it is preferable to use activated carbon as a filling material in the long term rather than using an ion exchange resin or the like. Further, supplying the production water to the electrode chamber as shown in FIG. 1 can prevent generation of chlorine because there is almost no Cl ^{− in} the electrode chamber supply water. desirable.
[0032]
In addition, the electrode chamber may be made porous so that the water passage surface side of the electrode plate can be made porous without using the filler as described above, and in this case, the electrode water can be passed. Since the plate and the electrode chamber can be integrated, there are advantages such as easy assembly.
[0033]
By the way, when circulating the concentrated water, if it is circulated as a whole, the temperature of the silica and boron in the concentration chamber, particularly on the outflow side of the production water, will rise, so the concentration chamber is divided as shown in FIG. If the concentration gradient is taken on the inlet side and the outlet side, the quality of the produced water can be equivalent to that of the counter-flowing water shown in FIG.
[0034]
FIG. 3A is a schematic perspective view showing an electrodeionization apparatus of a type in which the concentration chamber is divided, and FIG. 3B is the same system diagram.
[0035]
As shown in the figure, this electrodeionization apparatus is configured such that a cation exchange membrane and an anion exchange membrane are alternately arranged between an anode 11 and a cathode 12 to alternately form concentration chambers 15 and demineralization chambers 16. However, the concentrating chamber 15 is divided into two or more (two in FIG. 3) concentrated water circulation portions 15A and 15B by the partition wall 15S. The point from which the water flow direction of the concentrated water of water distribution part 15A, 15B is made into the direction which crosses the water flow direction in the demineralization chamber 16 differs from the conventional electrodeionization apparatus.
[0036]
That is, in FIG. 3, in the desalting chamber 16, the upper side in FIG. 3A is the inlet side and the lower side is the outlet side, and water flows in the desalting chamber 16 from the top to the bottom.
[0037]
On the other hand, in the concentrating chamber 15, the direction intersecting with the water flow direction in the desalting chamber 16 (the orthogonal direction in FIG. 3A (note that this orthogonal direction is not necessarily strict, Partition wall 15S extending in a range (including a range of about 100 °), and the inside of the concentrating chamber 15 is divided into two stages in the upper and lower parts in the figure, and each of the concentrated water circulation parts 15A and 15B has a front side in the figure. Water is carried from one side to the other side.
[0038]
As shown in FIG. 3 (b), a part of the product water taken out from the desalination chamber is introduced into the circulation system of the concentrated water circulation part 15B circulated by a pump, and the concentrated water circulation part 15B on the production water take-out side is introduced. Circulate. A part of the circulated concentrated water in this circulatory system is introduced into the circulatory system of the concentrated water circulation part 15A circulated by the pump, circulates through the concentrated water circulation part 15A on the raw water inflow side, and a part thereof is discharged out of the system. The
[0039]
Even in this electrodeionization apparatus, the production water circulates through the concentrated water circulation section 15B on the production water take-out side, then flows into the concentrated water circulation section 15A on the raw water inflow side, circulates, and is then discharged out of the system. As a result, the concentrated water is passed from the product water take-out side to the raw water inflow side, and then a part of the concentrate is discharged out of the system. The same effect as in the case of flow-through water flow is achieved.
[0040]
In addition, the concentration water circulation part formed by partitioning the concentration chamber with a partition wall may be three or more. However, considering the increase in the number of members by increasing the number of partition walls, the complexity of the apparatus configuration, and the like, it is preferable to partition the concentration chamber into two or three concentrated water circulation portions.
[0041]
In such an electrodeionization apparatus, when it is attempted to remove not only silica but also boron in particular, it has been found as a result of intensive studies that the thickness of the demineralization chamber is better. The thickness of the desalting chamber is preferably 5 mm or less, and the smaller the better, but in view of water permeability, handling at the time of production, etc., it is preferably 2 mm or more in practice.
[0042]
Further, it is an object of the present invention to improve the removal rate of silica and boron by securing the current and eliminating the influence of concentration diffusion. In order to secure the current, the concentration chamber and further the electrode chamber are used. Although the devices described above are required, the current required for high removal of silica and boron is a current value equivalent to 10% or less as a current efficiency, and further silica and boron removal rate of 99.9% or more. In order to obtain this, a current value corresponding to a current efficiency of 5% or less is required. The current efficiency is expressed by the following formula.
Current efficiency (%) = 1.31 × flow rate per cell (L / min) × (raw water equivalent conductivity (μS / cm) −treated water equivalent conductivity (μS / cm)) / current (A)
[0043]
In such an electrodeionization apparatus of the present invention, the raw water of the electrodeionization apparatus has a high specific resistance, and even when it is desired to further reduce only the silica and boron of this water, the necessary current can be secured, If the current does not flow through either the concentration chamber or the electrode chamber, the conventional problem that the current of the entire electrodeionization apparatus does not flow is solved.
[0044]
For this reason, even when trying to remove silica and boron from raw water having a high specific resistance, an electrodeionization device can be used, and therefore the applicable water quality range of the electrodeionization device can be greatly expanded. The industrial utility is extremely large.
[0045]
For example, when it is used mainly as a primary pure water production device in a semiconductor factory, the required current can be secured even when the production water is returned to the raw water and circulated. It can be activated stably even when it is raised.
[0046]
In addition, the necessary current can be ensured also in the latter-stage electrodeionization apparatus in which the electrodeionization apparatus is installed in a plurality of stages in series and multistage water flow is performed.
[0047]
In addition, in the secondary pure water system (subsystem) of the ultrapure water production process, the necessary current can be secured even if water with a specific resistance of 10 MΩ · cm or more is used as the raw water, so the deminer (non-regenerative mixed bed ion exchange device) Can be used as an alternative.
[0048]
【The invention's effect】
As described above in detail, according to the present invention, generation of Cl _{2 and the} like at the start of operation of the electrodeionization apparatus can be suppressed, and deterioration of the ion exchanger, ion exchange membrane, and the like can be suppressed.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of an electrodeionization apparatus suitable for applying the method of the present invention.
FIG. 2 is a schematic cross-sectional view showing a conventional electrodeionization apparatus.
FIG. 3 (a) is a schematic perspective view showing another example of an electrodeionization apparatus suitable for applying the method of the present invention, and FIG. 3 (b) is the same system diagram.
[Explanation of symbols]
11 Anode 12 Cathode 13 Anion exchange membrane (A membrane)
14 Cation exchange membrane (C membrane)
15 Concentration chambers 15A, 15B Concentrated water circulation section 15S Partition wall 16 Desalination chamber 17 Anode chamber 18 Cathode chamber

Claims (4)

Comprising one or more demineralization chambers formed by arranging one or more pairs of anion exchange membrane and cation exchange membrane between an anode and a cathode;
In a method for operating an electrodeionization apparatus in which the demineralization chamber is filled with an ion exchanger,
A method for operating an electrodeionization apparatus, characterized in that an increase rate of a voltage applied between the anode and the cathode at the start of operation of the electrodeionization apparatus is 0.02 V / cell / min or less. 2. The operation method of an electrodeionization apparatus according to claim 1, wherein the rate of voltage increase is 0.02 V / cell / min. 3. The method of operating an electrodeionization apparatus according to claim 1 or 2, wherein the voltage rise is stopped when the electric conductivity of the effluent from the concentration chamber adjacent to the demineralization chamber is 500 μS / cm or more. The electrodeionization apparatus according to any one of claims 1 to 3, wherein the electrodeionization device includes an anode chamber having an anode;
A cathode chamber having a cathode;
A concentration chamber and a desalting chamber alternately formed by alternately arranging a plurality of anion exchange membranes and cation exchange membranes between the anode chamber and the cathode chamber;
An ion exchanger filled in the desalting chamber;
An ion exchanger, activated carbon or electrical conductor filled in the concentrating chamber;
Means for passing electrode water through the anode chamber and the cathode chamber,
Concentrated water flow means for passing concentrated water through the concentration chamber;
Means for passing raw water through the desalting chamber and taking out deionized water;
The concentrated water flow means introduces water having a silica or boron concentration lower than that of the raw water into the concentration chamber from the side close to the deionized water outlet of the demineralization chamber. An operation method of an electrodeionization apparatus, characterized in that the electrodeionization apparatus is an electrodeionization apparatus that discharges at least a part of the concentrated water that has flowed out from the side close to the raw water inlet and out of the concentration chamber.

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