TWI801595B - Electric deionization device, ultrapure water production system, and ultrapure water production method - Google Patents

Abstract

Provided are an electric deionization device capable of improving boron removal performance and removal efficiency of ionic components, an ultrapure water production system and an ultrapure water production method using the same. An electrical deionization device comprising: an electrical deionization stack (stack), which has an anode chamber with an anode, a cathode chamber with a cathode, and a plurality of alternately arranged between the anode chamber and the cathode chamber. Anion-exchange membranes and cation-exchange membranes, and concentrating chambers and desalination chambers formed alternately between the aforementioned plurality of anion-exchange membranes and aforementioned cation-exchange membranes, and ion exchangers filled in the aforementioned desalination chambers; The anode and cathode for applying voltage to the deionization stack; and the power supply device, which applies a DC voltage between the anode and the cathode; and the electrical deionization device, the DC voltage supplied by the power supply device, when the maximum voltage for a specified period is set as When Vmax and the minimum voltage are set as Vmin, the relational expression: (Vmax-Vmin)/(Vmax+Vmin)≦0.3 is satisfied.

Description

Electric deionization device, ultrapure water production system, and ultrapure water production method

The present invention relates to an electric deionization device, an ultrapure water manufacturing system and an ultrapure water manufacturing method.

There is known an ion exchange device in which water to be treated is deionized by an ion exchange reaction by passing through an ion exchanger such as an ion exchange resin. A typical ion exchange device is an ion exchange resin device using an ion exchange resin as an ion exchanger. In this ion exchange resin device, when the ion exchange group of the ion exchange resin is saturated, it is necessary to inject a chemical such as acid or alkali to regenerate the ion exchange resin. Therefore, in the ion-exchange resin device, there are problems to be solved that the continuous operation cannot be carried out, and there is troublesome replenishment of the chemical agent. In view of this, in recent years, electrical deionization (EDI (Electro Deionization)) devices that do not require regeneration of ion exchangers have been gradually put into practical use.

In the electrical deionization device, ion exchangers (anion exchangers and/or cation exchangers) are filled between a cation exchange membrane that allows only cations to pass through and an anion exchange membrane that allows only anions to pass through. The desalination chamber is constituted, and the concentrating chamber is arranged outside the cation exchange membrane and the anion exchange membrane. Also, the anode is arranged on the side of the anion exchange membrane and the cathode is arranged on the side of the cation exchange membrane as viewed from the desalination chamber. When the water to be treated passes through the desalination chamber under the state of applying a DC voltage between the anode and the cathode, the ion components in the water to be treated will be captured by the ion exchanger in the desalination chamber, and generated by the dissociation reaction of water Hydrogen ions (H ⁺ ) and hydroxide ions (OH ^- ) are used to regenerate the ion exchanger.

In the ultrapure water production system using the electric deionization device, the system configuration is adjusted according to the desired purpose. For example, in order to accelerate the improvement of water quality when restarting the operation from a stop state, an electric deionization device has been proposed. A device that arranges a diode between the EDI stack (stack) and the DC power supply (for example, refer to Patent Document 1). In addition, for the purpose of reducing the boron concentration, an ultrapure water production system using a two-stage EDI device in which an electric deionization device is connected in series in two stages, or a combination of an electric deionization device and a boron-selective resin has been proposed. Ultrapure water production system, etc. (for example, refer to Patent Documents 2 and 3).

However, the boron concentration reduction has not yet been sufficiently achieved in the above known systems. In addition, in the above-mentioned two-stage EDI device, or the combined use of the electric deionization device and boron selective resin, there is a problem that the configuration of the ultrapure water production system becomes complicated. In particular, in the two-stage EDI device, the electric deionization device As the number of devices used increases, there is a problem of increased power consumption. In addition, in the ultrapure water production system using an electric deionization device, if the boron concentration is to be significantly reduced, depending on the power supply of the electric deionization device, the supply voltage is likely to become significantly unstable, and the power supply device A new problem to be solved is the increase in switching frequency. [Prior Art Literature] [Patent Document]

[Patent Document 1] Japanese Patent Laid-Open No. 2015-83287 [Patent Document 2] Japanese Unexamined Patent Publication No. 2014-575 [Patent Document 3] Japanese Patent Application Laid-Open No. 9-192661

[Problem to be solved by the invention]

The present invention was developed to solve the above-mentioned unsolved problems, and an object of the present invention is to provide an electric deionization device capable of improving the boron removal performance and the removal efficiency of ion components, and stably maintaining the supply voltage of the power supply device for a long period of time, and using the same Ultrapure water production system and ultrapure water production method. [Technical means to solve the problem]

。The electrical deionization device of the present invention has: an electrical deionization stack (stack), which has an anode, a cathode, and an anode chamber arranged between the anode and the cathode and connected to the anode, and The cathode chamber connected to the cathode, the anion exchange membrane and the cation exchange membrane arranged alternately between the anode chamber and the cathode chamber, and the concentration chamber and the desalination chamber alternately formed between the anion exchange membrane and the cation exchange membrane chamber, and the ion exchanger filled in the aforementioned desalination chamber; and the power supply device, which applies a DC voltage between the aforementioned anode and the aforementioned cathode; the electrical deionization device, the aforementioned DC voltage, when the maximum voltage for a specified period is set as Vmax , when the minimum voltage is set as Vmin, the following relationship (1) is satisfied:

.

In the electrical deionization device of the present invention, the electrical deionization stack preferably has an ion exchanger or an electrical conductor filled in the concentration chamber, the anode chamber, and the cathode chamber. In addition, in the electric deionization device of the present invention, the power supply device is preferably an inverter that converts the AC voltage supplied to the power supply device into the DC voltage and outputs the above.

In the electric deionization device of the present invention, the predetermined period is preferably 1/2 or more of the AC cycle of the AC voltage.

In the electrical deionization device of the present invention, the aforementioned converter is preferably a full-wave rectifying converter that converts the AC voltage into the aforementioned DC voltage by means of full-wave rectification, or converts the AC voltage into the aforementioned DC voltage by means of switching. The switching converter.

The ultrapure water production system of the present invention is an ultrapure water production system having a reverse osmosis membrane device and an ion exchange device in sequence, and the aforementioned ion exchange device is preferably constituted by the above-mentioned electric deionization device of the present invention .

In the ultrapure water production system of the present invention, the reverse osmosis membrane device is preferably a two-stage reverse osmosis membrane device formed by connecting two reverse osmosis membrane devices in series.

The ultrapure water manufacturing system of the present invention is an ultrapure water manufacturing system having an ion exchange resin device, a degassing device, and an ion exchange device in sequence. Constructed without an ion device.

In the ultrapure water production system of the present invention, the boron concentration in the permeated water of the electrical deionization device is preferably 1 μg/L (as B) or less.

。The ultrapure water production method of the present invention is an ultrapure water production method including the process of treating the water to be treated with an electrical deionization device, characterized in that the electrical deionization device has: an anode; and a cathode; An electrical deionization stack (stack), which has an anode chamber arranged between the anode and the cathode and connected to the anode, a cathode chamber connected to the cathode, and an anode chamber connected to the cathode chamber Anion-exchange membranes and cation-exchange membranes arranged alternately between them, concentrating chambers and desalting chambers formed alternately between the aforementioned anion-exchange membranes and the aforementioned cation-exchange membranes, and ion exchangers filled in the aforementioned desalting chambers; and a power supply unit, for A DC voltage is applied between the aforementioned anode and the aforementioned cathode; when the aforementioned DC voltage is set as the maximum voltage for a specified period as Vmax and the minimum voltage as Vmin, the condition of the following relationship (1) is satisfied to treat the aforementioned treated water:

.

In the ultrapure water production method of the present invention, the electrical deionization stack preferably has ion exchangers or electrical conductors filled in the concentration chamber, the anode chamber, and the cathode chamber.

In the ultrapure water production method of the present invention, it is preferable to further have the process of treating the raw water through a reverse osmosis membrane device to obtain the aforementioned treated water, and then the process of passing the aforementioned treated water through the aforementioned electrical deionization device deal with. In addition, the aforementioned reverse osmosis membrane device is preferably a two-stage reverse osmosis membrane device formed by connecting two reverse osmosis membrane devices in series.

In the ultrapure water production method of the present invention, it is preferable to further have the process of treating the raw water with an ion exchange resin device and a degassing device to obtain the aforementioned treated water, and then use the process to convert the aforementioned treated water through the aforementioned electrical Type deionization device treatment.

In the ultrapure water production method of the present invention, the boron concentration in the permeated water of the electrical deionization device is preferably 1 μg/L (as B) or less. [Efficacy of Invention]

According to the electric deionization device of the present invention, the boron removal performance and the removal efficiency of ion components in the electric deionization device can be improved. In addition, the supply voltage of the power supply device can be maintained stably under long-term use, and the load on the power supply device can be reduced. In addition, according to the ultrapure water production system and ultrapure water production method of the present invention, the boron removal performance and the removal efficiency of ion components in the electrical deionization device can be improved, so it is possible to efficiently obtain ultrapure water with a significantly reduced boron concentration. pure water.

Embodiments will be described in detail below with reference to the drawings. In addition, this invention is not limited to these embodiment, These embodiment can be changed or deform|transformed in the range which does not deviate from this invention.

[Electrical deionization device] Fig. 1 is a schematic diagram of a model of an electrical deionization device 11 in this embodiment. The electrical deionization device 11 has an electrical deionization stack 110, and an anode 111 and a cathode 112 configured to hold the electrical deionization stack 110 in order to apply a voltage to the electrical deionization stack 110, and an anode 111 and a cathode 112 is applied to the power supply device 113 of DC voltage.

The electrical deionization stack 110 has an anode chamber 115a connected to the anode 111, a cathode chamber 115b connected to the cathode 112, and alternating arrangements between the anode chamber 115a and the cathode chamber 115b starting from the anode chamber 115a. A plurality of cation exchange membranes 11c and a plurality of anion exchange membranes 11a. Between the anion exchange membrane 11a and the cation exchange membrane 11c, desalination chambers 114 and concentrating chambers 116 are alternately provided. In the desalination chamber 114, an ion exchanger is filled. The deflection chamber 116, the anode chamber 115a, and the cathode chamber 115b are filled with, for example, an ion exchanger or an electrical conductor made of activated carbon or metal.

In the electrical deionization stack 110, the ion exchange membrane connected to the desalination chamber 114 and arranged on the anode 111 side is an anion exchange membrane 11a, and the ion exchange membrane connected to the desalination chamber 114 and arranged on the cathode 112 side is a cation exchange membrane. 11c. The electrical deionization stack 110 constitutes a cell with a desalination chamber 114 and a pair of concentrating chambers 116 disposed on both sides of the desalination chamber 114 with an anion exchange membrane 11a or a cation exchange membrane 11c interposed therebetween. At least one of the pair of concentrating chambers 116 may be filled with ion exchangers such as ion exchange resins. In addition, the electrical deionization stack 110 can also be configured such that a plurality of units are arranged side by side between the anode 111 and the cathode 112 .

As the cation exchange membrane 11c and the anion exchange membrane 11a, there are heterogeneous membranes, semi-homogeneous membranes, and homogeneous membranes in terms of membrane structure, but in terms of the removal efficiency of ionic components and the suppression of resistance increase in the electrical deionization device In terms of this point, a homogeneous membrane is better.

As the ion exchanger filled in the demineralization chamber 114, an ion exchanger obtained by mixing a cation exchange resin and an anion exchange resin can be used. The mixing ratio of the cation exchange resin and the anion exchange resin is expressed in terms of volume ratio in terms of the removal efficiency of ionic components and the suppression of the increase in resistance in the electrical deionization device. The ratio of the anion exchange resin is 20 to 80% is better. As the ion exchanger, an ion exchanger obtained by laminating a cation exchange resin and an anion exchange resin in the direction of the flow path can also be used.

In the electrical deionization stack 110 , the water to be treated is supplied from one end of the desalination chamber 114 and flows out from the other end of the desalination chamber 114 . During this process, the ionic components in the treated water are adsorbed to the ion exchanger in the desalination chamber. In addition, at this time, a rectified DC voltage is applied between the anode 111 and the cathode 112 , and the DC current flows in a direction perpendicular to the flow of the water to be treated in the desalination chamber 114 . By this current, water is dissociated into hydrogen ions and hydroxide ions, and the dissociated hydrogen ions and hydroxide ions are exchanged with ion components adsorbed to the ion exchanger, respectively. The exchanged ion components move to the concentrating chamber 116, the anode chamber 115a, and the cathode chamber 115b, and flow out from the electrical deionization stack through them.

As the electrical deionization stack 110, a commercially available electrical deionization stack can be used. As a commercial product of the electrical deionization stack 110, for example, VNX50, VNX55, VNX-55EX (manufactured by Evoqua Co.), E -CELL MK3, MK2 (manufactured by the above GE company), etc.

另，式(1)中的Vmax表示規定期間中的最大電壓，Vmin表示規定期間中的最小電壓。In the electric deionization device 11 , as the power supply device 113 , one capable of applying a DC voltage satisfying the following relational expression (1) between the anode 111 and the cathode 112 can be used.

In addition, Vmax in Formula (1) represents the maximum voltage in a predetermined period, and Vmin represents the minimum voltage in a predetermined period.

The power supply device 113 is, for example, an AC-DC converter that converts an alternating voltage supplied from an alternating current (AC) power supply into a direct current (DC) voltage satisfying the above-mentioned expression (1).

In conventional electrical deionization devices, especially in the case of producing ultrapure water with a large flow rate, in order to reduce the cost of power supply, a simple AC-DC converter is used. This is because it is expected that the amount of ultra-pure water is large, and the quality of the DC voltage converted from AC-DC, that is, the presence or absence of voltage ripple (ripple) has little effect on the water quality. Therefore, when seeking to improve the quality of ultrapure water, especially in order to highly remove weak electrolytes such as boron (B) or silica (Si), the method of increasing the effective value of the voltage is adopted.

In contrast, in the present invention, the quality of treated water is improved by focusing on the quality of DC voltage applied to the electrical deionization stack of the electrical deionization device. Specifically, the DC voltage applied to the electrical deionization stack 110 through the anode 111 and the cathode 112 by the power supply device 113 satisfies the requirements of formula (1), thereby reducing the electrical deionization device 11 early and significantly. permeates boron in water.

In addition, the DC voltage satisfies the formula (1). As explained below, it means that the voltage ripple of the DC voltage is reduced. By reducing the voltage ripple like this, when a plurality of electrical deionization devices 11 are connected in series to operate There is also an advantage that the supply voltage from the power supply device can be stably maintained for a long period of time. In particular, in order to highly remove weak electrolytes such as boron and silica, the effective value of the voltage is increased to increase the load on the power supply device, and it is easy to maintain the supply voltage from the power supply device for a long period of time. Excellent effect.

Here, in Japan, an AC voltage with a power supply frequency of 50 Hz or 60 Hz is supplied from a power supply company, so if it is converted into a DC voltage, a voltage ripple may be generated at a cycle corresponding to the above power frequency. For example, in the single-phase full-wave rectification method, which is a simple rectification method, voltage ripples are generated approximately periodically at a period of 1/2 of the power supply frequency.

The power supply device 113 used in the present invention, for example, sets the cycle of such voltage ripple generation as a predetermined period, and uses the difference between the maximum value Vmax and the minimum value Vmin of the voltage during this period and the difference between the voltage during the predetermined period. The ratio of the average value (approximately (Vmax+Vmin)/2) is the smaller one. That is to say, Equation (1) ((Vmax-Vmin)/(Vmax+Vmin)≦0.3) is an expression for regulating the voltage ripple as an index in order to exert the effect of the present invention. By satisfying Equation (1), The effect of reducing the voltage ripple and reducing the boron in the permeated water of the electrical deionization device 11 early and obviously is realized. Although this principle is only conjecture, it can be assumed as follows as an example.

As mentioned above, in the electric deionization stack 110, when the water to be treated is circulated in the desalination chamber 114, the ion components in the water to be treated are adsorbed to the ion exchanger, and the ion components adsorbed to the ion exchanger are depleted at the same time. It performs ion exchange with hydrogen ions and hydroxide ions generated by dissociation of water due to electric current, thereby detaching from the ion exchanger and moving to the concentration chamber 116 .

At this time, when the ripple of the DC voltage applied between the anode and the cathode is large, the fluctuation of the current value flowing from the anode to the cathode becomes large due to the voltage ripple, and a relatively large current occurs during a predetermined period. The period and the small period. Also, during this period of low current, the detachment of ion components adsorbed by the ion exchanger becomes difficult to occur, so as a result, during the period when the current flowing from the anode to the cathode is small, the ion exchange group of the ion exchanger can absorb The amount of ionic components decreases, and the incompletely removed ionic components tend to remain in the permeated water. In particular, weak electrolytes such as boron and silica tend to remain in the permeated water.

In contrast, when a DC voltage with a small voltage ripple is applied, a constant current flows, so the detachment of ionic components from the ion exchanger and the adsorption of ionic components to the ion exchange base are continuously and constantly performed, As a result, the ion components in the water to be treated can be further reduced. In particular, the concentration of weak electrolytes such as boron and silica can be drastically reduced. In addition, the stagnation of ion components in the electrical deionization stack is less likely to occur, so the ion components can be quickly discharged into the concentrated water, so the removal efficiency of ion components can be improved.

In the electrical deionization device 11 of the present invention, when the power supply device 113 is an AC-DC converter, the method of supplying power to the power supply device 113 from the outside can be, for example, a three-phase three-wire type or a single-phase three-phase line style. In either case, the effect of improving the removal efficiency of ionic components and improving boron removal performance can be obtained. The supply voltage is usually in the range of 100-240V, and the frequency is either 50Hz or 60Hz, which can be selected in conjunction with the power supply device used.

In addition, as the period for regulating the maximum value Vmax and the minimum value Vmin of the voltage in formula (1), that is, a predetermined period, for example, when the power supply device 113 is supplied with power from a single-phase AC power supply, it is preferable to supply The frequency of the AC voltage is more than 1/2 of the AC cycle. Alternatively, for example, when the power supply device 113 is supplied with power from a three-phase AC power supply, the predetermined period is preferably 1/6 or more of the AC cycle of the frequency of the supplied AC voltage.

In addition, in the electrical deionization device 11 of the present invention, from the viewpoint of higher removal of weak electrolytes such as boron or silica, the water recovery rate is preferably 90-96%, and the current density in the electrical deionization stack 111 , preferably 500-3000mA/dm ² , more preferably 1500-2500mA/dm ² .

As the power supply device 113 , an AC-DC converter by a switching method can be used as the voltage ripple in the output DC voltage is small. The basic structure of the AC-DC converter caused by this switching method has a primary side circuit and a secondary side circuit. The primary side circuit includes a diode bridge formed by combining diodes, an electrolytic capacitor, a switching element, and a high frequency transformer, and the secondary side circuit includes a high frequency transformer, diodes, and an electrolytic capacitor. The above-mentioned diode bridge typically combines four diodes to invert the negative side of the AC voltage, thereby rectifying the full wave.

In the AC-DC converter due to the switching method, first, the AC voltage supplied to the primary side circuit by the AC power supply is rectified by the diode bridge and then smoothed by the electrolytic capacitor to be converted into DC Voltage. The DC voltage is converted into a high-frequency DC voltage by the switching element, and then transferred to the secondary-side circuit by the high-frequency transformer of the primary-side circuit and the secondary-side circuit. Then, the transferred DC voltage is rectified and smoothed by the diode and electrolytic capacitor of the secondary side circuit, and output. A control circuit is also provided to perform feedback control on the switching element in such a manner that the output voltage is kept constant. According to the AC-DC converter obtained by this switching method, the value represented by (Vmax-Vmin)/(Vmax+Vmin) in the above formula (1) can be preferably set to 0.1 or less, more preferably set to 0.01 or less.

The AC-DC converter caused by the switching method used in the present invention can be a forward method in which the energy transfer from the primary side circuit to the secondary side circuit is performed when the switching is ON, or it can be in the switching mode. Flyback mode when OFF. In addition, the number of switching elements, diodes, and electrolytic capacitors on the primary side and the secondary side is not limited to one, and can be more than two depending on the conversion method.

As a commercial item of the AC-DC converter by a switching method, the PAT-T series by Kikusui Kogyo Co., Ltd. etc. are mentioned, for example.

As the power supply unit 113, for example, an AC-DC converter by a full-wave rectification method can be used other than the switching method. The basic configuration of the AC-DC converter by the full-wave rectification method includes a diode bridge composed of diodes and an electrolytic capacitor. This diode bridge typically combines four diodes to invert the negative side of the AC voltage, thereby rectifying the full wave. In the AC-DC converter due to the full-wave rectification method, the AC voltage supplied by the AC power supply is rectified by the diode bridge, smoothed by the electrolytic capacitor, and output as a DC voltage. In the AC-DC converter caused by the full-wave rectification method, the voltage ripple of the output DC voltage is adjusted by the capacitance and load of the electrolytic capacitor. According to the AC-DC converter due to this full-wave rectification method, the value represented by (Vmax-Vmin)/(Vmax+Vmin) in the above formula (1) can be preferably set to 0.27 or less, more preferably It is set to be 0.15 or less.

As a commercial item of the AC-DC converter by a full-wave rectification method, IP-POWER600-G2 etc. by Evoqua company are mentioned, for example.

The effective value of the DC voltage supplied by the power supply device 113 varies depending on the electrical deionization device used, but as an example, in order to flow a sufficient current through the electrical deionization stack 110, it is preferable to use a DC voltage of about 100 to 150V. Applied between the anode 111 and the cathode 112.

When evaluating the characteristics of the power supply device used in the electrical deionization device of the embodiment, especially the ripple degree of the output DC voltage, it can be evaluated by making it output a constant voltage of 50-200V, for example, it is better to make it output 70 ~ 90V DC voltage to evaluate.

According to the electric deionization device of the embodiment described above, the boron removal performance and the removal efficiency of ion components in the electric deionization device can be improved. In addition, the supply voltage of the power supply device can be maintained stably under long-term use, and the load on the power supply device can be reduced.

[Ultrapure water production method and ultrapure water production system] The ultrapure water production method of the embodiment includes the process of treating the water to be treated under the condition that the DC voltage applied between the anode and the cathode satisfies the above formula (1) using an electric deionization device having the following structure. In the ultrapure water production method of the embodiment, as the condition for treating the water to be treated, the DC voltage applied between the anode and the cathode is represented by (Vmax-Vmin)/(Vmax+Vmin) in the above formula (1) The value is preferably at most 0.27, more preferably at most 0.15, still more preferably at most 0.1, still more preferably at most 0.01.

The electric deionization device used in the ultrapure water production method of the embodiment has: an electric deionization stack having an anode, a cathode, and an anode chamber arranged between the anode and the cathode and connected to the anode, and A cathode chamber connected to the cathode, an anion exchange membrane and a cation exchange membrane alternately arranged between the anode chamber and the cathode chamber, and a concentration chamber and a desalination chamber formed alternately between the anion exchange membrane and the cation exchange membrane, and filling The ion exchanger in the desalination chamber; and the power supply device, which applies a DC voltage between the anode and the cathode. As this electric deionization device, for example, the electric deionization device of this embodiment can be used.

The water to be treated by the electric deionization device is, for example, obtained by treating raw water through a pretreatment unit. That is to say, the ultrapure water production method of the embodiment includes, for example, the process of obtaining the treated water by treating the raw water through the pretreatment unit, and supplying the obtained treated water to the above-mentioned electric deionization device for the above-mentioned Conditional processing works are also available. As the raw water, tap water, well water, ground water, industrial water, and pre-treated water (recycled water) used in semiconductor manufacturing plants are used. Raw water may be obtained by treating tap water, well water, ground water, industrial water, recycled water, etc., with sand filters, precision filters, etc., to remove suspended substances. In addition, the temperature of the raw water can also be adjusted by a heat exchanger or the like.

The pretreatment unit may be a reverse osmosis membrane device, may have an ion exchange resin device and a degassing device in this order, or may be composed of them. The reverse osmosis membrane device is preferably a two-stage reverse osmosis membrane device formed by connecting two reverse osmosis membrane devices in series. In addition, depending on the quality of the raw water, part or all of the pre-treatment section can also be omitted.

The method for producing ultrapure water according to the embodiment is preferably carried out using an ultrapure water production system according to an embodiment including a pretreatment unit described below and an electric deionization device according to the embodiment. Referring to Fig. 2, an ultrapure water production system according to an embodiment and an ultrapure water production method using the system will be described below.

Fig. 2 is a schematic block diagram of an ultrapure water production system 1 using an electric deionization device 11 according to this embodiment. The ultrapure water production system 1 has a 2-stage reverse osmosis membrane device 12 formed by connecting two reverse osmosis membrane devices (the first-stage reverse osmosis membrane device RO1 and the second-stage reverse osmosis membrane device RO2) in series, and Electrical deionization device (EDI)11. In the ultrapure water production system 1 shown in FIG. 2 , the two-stage reverse osmosis membrane device 12 corresponds to a pretreatment section.

When performing the ultrapure water production method of the embodiment using the ultrapure water production system 1 , raw water is supplied to the two-stage reverse osmosis membrane device 12 . The reverse osmosis membrane devices RO1 and RO2 in the first and second stages of the two-stage reverse osmosis membrane device remove salts, ionic organic substances, and colloidal organic substances in raw water, respectively. As the reverse osmosis membranes used in the reverse osmosis membrane devices RO1 and RO2 of the first stage and the second stage, for example, triacetate cellulose-based asymmetric membranes, polyamide-based, polyvinyl alcohol-based, or polyamide-based Department of composite film and so on. Membrane shapes include, but are not limited to, sheet-like flat membranes, spiral membranes, tubular membranes, hollow fiber membranes, and the like. Among them, polyamide-based composite membranes are preferable in terms of a high removal rate of salts, and cross-linked wholly aromatic polyamide-based composite membranes are more preferable. The shape of the membrane is preferably a spiral membrane.

The desalination ratios (removal ratios of sodium ions) of the reverse osmosis membrane devices RO1 and RO2 constituting the first and second stages of the two-stage reverse osmosis membrane device 12 are preferably 96 to 99.8%, respectively. The removal rate of sodium ions is measured by the removal rate of sodium ions when feed water at 25°C, pH = 7, and NaCl concentration 0.2% by mass passes through the reverse osmosis membrane at a water recovery rate of 15% and a feed water pressure of 1.5 MPa.

In the reverse osmosis membrane device 12 of the second stage, the water recovery rate is preferably 60-98%, more preferably 80-95%, in the reverse osmosis membrane device RO1 of the first stage, in order to efficiently remove ion components. In the reverse osmosis membrane device RO2 of the second stage, it is preferably 80-95%, more preferably 85-95%. In addition, scale inhibitors, bacteriostats, pH regulators, etc. may also be added to the feed water of RO1 of the first-stage reverse osmosis membrane device if necessary.

The reverse osmosis membrane devices RO1 and RO2 of the first stage and the second stage can also be any of ultra-low pressure type, low pressure type, and high pressure type reverse osmosis membrane devices. From the point of view of the production efficiency of ultrapure water, It is preferably an ultra-low pressure type or a low pressure type reverse osmosis membrane device. In addition, it is preferable to provide a feed water pump that pressurizes the raw water to a predetermined pressure and supplies it to the two-stage reverse osmosis membrane device 12 at the front stage of the two-stage reverse osmosis membrane device 12 .

Here, the operating pressure of the ultra-low pressure reverse osmosis membrane device is 0.4MPa-0.8MPa, preferably 0.6MPa-0.7MPa. The operating pressure of the low-pressure reverse osmosis membrane device is more than 0.8 MPa and less than 2.5 MPa, preferably 1 MPa to 1.6 MPa. The operating pressure of the high-pressure reverse osmosis membrane device is more than 2MPa and less than 8MPa, preferably more than 5MPa and less than 6MPa. In addition, the operating pressures of the above-mentioned ultra-low pressure type, low pressure type, and high pressure type reverse osmosis membrane devices can be distinguished by the design pressure (standard pressure) during the manufacture of each reverse osmosis membrane device, but in fact sometimes also in the above-mentioned Operate at pressures outside the range.

As commercially available products of the reverse osmosis membrane devices RO1 and RO2 constituting the first stage and the second stage of the two-stage reverse osmosis membrane device 12, TM820K-400, TM720-400, TM720D-400, TM720D-400, and SUL-G20, BW30-400, BW30-400FR manufactured by DOW Corporation, CPA5, CPA5-LD manufactured by Nitto Denko Co., Ltd., etc.

As the electrical deionization device 11, the electrical deionization device of the above-mentioned embodiment is used. The permeated water from the two-stage reverse osmosis membrane device 12 is supplied to the electric deionization device 11 as water to be treated, where it undergoes ion exchange treatment to generate permeated water. This permeated water is supplied to a place of use (POU; Place of Use) 13 for ultrapure water as ultrapure water.

The water quality of the permeated water that has passed through the electrical deionization device 11 has a boron concentration, for example, below 1 μg/L (as B), preferably below 0.2 μg/L (as B), more preferably 0.1 μg/L (as B). B) or less, specific resistance (resistivity) of 17.5MΩ･cm or more can be obtained. The boron concentration can be measured by, for example, the SIEVERS online boron analyzer sold by Central Kagaku Co., Ltd., or by sampling ultrapure water and using ICP-MS (Inductively Coupled Plasma Mass Spectrometer). The electrical deionization device 11 may be used as a single stage, or may be used as a plurality of stages by connecting two or more in series. In particular, if more than 10 or even more than 50 electrical deionization devices 11 are installed, the problem of the power supply device caused by voltage ripple is likely to occur, so it is easy to obtain the great effect of the present invention.

In addition, the ultrapure water production system 1 may include a degassing device between the two-stage reverse osmosis membrane device 12 and the electrical deionization device 11 . Since the carbon dioxide gas in water is highly removed by this, the generation of scale in the electric deionization device 11 can be suppressed, and the removal efficiency of ion components can be improved. As the degassing device, for example, a degassing membrane device can be used. The degassing membrane device is to pass the liquid on the primary side of the gas-permeable membrane, in this case, the permeated side of the two-stage reverse osmosis membrane device is passed through, and the secondary side of the membrane is decompressed as necessary. This device removes only the dissolved gas in the liquid to the secondary side.

In addition, the ultrapure water production system 1 may include an ion exchange resin device for removing hardness components instead of the second-stage reverse osmosis membrane device RO2 of the two-stage reverse osmosis membrane device 12 . Thereby, the generation of scale in the electric deionization device 11 can be suppressed, and the ion component removal efficiency can be improved. As the ion exchange resin apparatus for removing the hardness component, an ion exchange resin apparatus using a salt-type strongly acidic cation exchange resin, etc. can be used.

In addition, the ultrapure water production system 1 may have an ion exchange resin device and a degassing device in this order instead of the two-stage reverse osmosis membrane device 12 . The same thing as above can be used for the ion exchange resin device and the degassing device. In addition, a secondary pure water device combining an ultraviolet irradiation device, a non-regenerative ion exchange resin device, a degassing device, an ultrafiltration device, and the like may be installed in the latter stage of the ultrapure water production system 1 .

According to the ultrapure water production system and the ultrapure water production method of the embodiments described above, the boron removal performance and the removal efficiency of ion components in the electric deionization device will be improved, thereby achieving a significant reduction in boron concentration efficiently. of ultrapure water. [Example]

Next, examples will be described. The present invention is not limited to the following examples.

(Example 1) An ultrapure water production system A having a 2-stage reverse osmosis membrane device, a degassing membrane device, and an electrical deionization device in order of the specifications shown below was manufactured.

2-stage reverse osmosis membrane device: The reverse osmosis membrane device of the first stage (TM820K-400 manufactured by Toray Co., Ltd., the water supply pressure is 2.5MPa (the range of standard operating pressure), and the water recovery rate is 80%), The reverse osmosis membrane device of the second stage (SUL-G20 manufactured by Toray Co., Ltd., the water supply pressure is 0.5MPa (the range of standard operating pressure), and the water recovery rate is 90%) Degassing membrane device (manufactured by Polypore, X40) Electrical deionization device (VNX50 manufactured by Evoqua as an electrical deionized stack with anode and cathode, PAT-650-12.3 manufactured by Kikusui Kogyo Co., Ltd., AC-DC converter due to switching mode (measured by the method described later (Vmax- Vmin)/(Vmax+Vmin) is 0) As a power supply unit, use them in combination.)

Using ultrapure water production system A, raw water (tap water) was treated as follows to produce ultrapure water. That is, after the raw water is treated by the 2-stage reverse osmosis membrane device, it is stored in the tank, the 2-stage reverse osmosis membrane treated water in the tank is supplied to the degassing membrane device, and the treated water of the degassed membrane device is supplied to the electrical degassing The sub-device is used as the treated water, and the permeated water of the electrical deionization device is obtained as ultra-pure water. The boron concentration of the obtained ultrapure water was 0.03-0.04 μg/L (as B), and the resistivity was 18.1-18.2 MΩ･cm. For the boron degree, the sample water was measured by an inductively coupled plasma mass spectrometry (ICP-MS) device, and the resistivity was measured by HE-960RW manufactured by HORIBA. Also, the ultrapure water production system A was operated for 17 days, and the performance was evaluated.

In addition, the quality of treated water supplied to the electric deionization device throughout the measurement period had a conductivity of 0.5-2.9 μS/cm and a boron concentration of 9.4-11 ppb (approximately 9.4-11 μg/L) (as B). The water recovery rate in the electric deionization device is 95 to 97%, and a DC voltage is applied so that the current becomes 10A. In this example, the current density in the electrical deionization device was 2000 mA/dm ² .

The boron concentration in the permeated water of the electric deionization device, the resistivity of the permeated water, and the time-dependent changes in the electrical conductivity of the concentrated water were measured. The boron transmittance in the electric deionization device was calculated using the boron concentration in the feed water of the electric deionization device and the boron concentration in the permeated water. FIG. 3 shows the time-dependent change of the boron permeability, FIG. 4 shows the time-dependent change of the resistivity of the permeated water, and FIG. 5 shows the time-dependent change of the electrical conductivity of the concentrated water.

(Example 2) Except that the power supply device of the electric deionization device in Example 1 was changed to IP-POWER600-G2 (AC-DC converter due to full-wave rectification method (measured by the method described later) (Vmax-Vmin) manufactured by Evoqua Corporation /(Vmax+Vmin) was 0.27)) In the same manner, ultrapure water production system B was fabricated. Using the ultrapure water production system B, it carried out similarly to Example 1, and obtained the permeated water of the electric deionization apparatus as ultrapure water. The boron concentration of the obtained ultrapure water was 0.08-0.09 μg/L (as B), and the resistivity was 18.1-18.2 MΩ·cm. Also, the ultrapure water production system B was operated for 17 days, and the performance was evaluated.

The boron concentration, resistivity, and conductivity of concentrated water in the feed water and permeate water of the electric deionization device were measured, and the boron permeability in the electric deionization device was calculated. The time-dependent change of boron permeability is shown in Figure 3, the time-dependent change of permeated water resistivity is shown in Figure 4, and the time-dependent change of concentrated water conductivity is shown in Figure 5.

(comparative example 1) Except that the power supply device of the electric deionization device in Example 1 was changed to IP-DCR600V15A-R2/M manufactured by Evoqua (AC-DC converter of half-wave rectification method (measured by the method described later (Vmax-Vmin) /(Vmax+Vmin) was 0.96)) In the same manner, an ultrapure water production system C was fabricated. Using the ultrapure water production system C, it carried out similarly to Example 1, and obtained the permeated water of the electric deionization apparatus as ultrapure water. The boron concentration of the obtained ultrapure water was 0.3-0.4 μg/L (as B), and the resistivity was 18.1-18.2 MΩ･cm. Also, the ultrapure water production system C was operated for 17 days, and the performance was evaluated.

The boron concentration, resistivity, and conductivity of concentrated water in the feed water and permeate water of the electric deionization device were measured, and the boron permeability in the electric deionization device was calculated. The time-dependent change of the boron concentration is shown in Fig. 3, the time-dependent change of the resistivity of the permeated water is shown in Fig. 4, and the time-dependent change of the electrical conductivity of the concentrated water is disclosed together with Example 1.

In addition, the waveforms of the output voltages of the power supply devices used in Examples 1 and 2 and Comparative Example 1 are shown in FIGS. 6 to 8 . The waveform of the output voltage of the power supply device was measured with an analog oscilloscope (type: AD-5132A, manufactured by A&D Corporation). The value of (Vmax-Vmin)/(Vmax+Vmin) of each power supply device calculated from Figs. 6 to 8 is as follows.

Example 1: (Vmax-Vmin)/(Vmax+Vmin)=0 Embodiment 2: (Vmax-Vmin)/(Vmax+Vmin)=0.27 Comparative example 1: (Vmax-Vmin)/(Vmax+Vmin)=0.96

As shown in FIG. 4 , there is no significant difference between the Examples and the Comparative Examples in the resistivity of permeated water. This indicates that there is no significant difference between the examples and the comparative examples regarding the removal of strong electrolytes such as sodium (Na) ions that greatly affect the resistivity of permeated water. However, as shown in FIG. 3 , in the examples, it can be seen that the transmittance of boron is less than 1% (that is, the removal rate is more than 99%), and a better boron removal rate is achieved than in the comparative examples. In addition, it can also be seen from FIG. 5 that the conductivity of the concentrated water increases faster in the embodiment than in the comparative example, that is, the removal rate of ion components in the electric deionization device is faster. This indicates that ion components can be efficiently removed with the same effective current value.

(Example 4) An ultrapure water production system having the same basic configuration as in Example 1 was operated continuously for 2 years at an ultrapure water production flow rate of 1000 m ³ /h. The electric deionization device installed in the ultrapure water production system is a stack of 100 electric deionization devices with anode and cathode (manufactured by Evoqua, VNX50), and a power supply unit (manufactured by Kikusui Kogyo Co., Ltd., PAT-650-12) ) 100 units are arranged in parallel to form. Two-stage reverse osmosis membrane devices and degassing membrane devices are arranged in increasing numbers according to the amount of treated water supplied to the electric deionization device. In this example, the power supply unit successfully produced ultrapure water for two years without any problems.

(Example 5) Continuous operation was performed under the same conditions as in Example 4 except that the power supply device in Example 4 was changed to IP-POWER600-G2 manufactured by Evoqua Corporation. In this example, during the production of ultrapure water, the supply voltage from the power supply unit became unstable, and the power supply unit had to be replaced several times. The number of exchange units (superposition) is 5 units.

(comparative example 2) Continuous operation was performed in the same manner as in Example 4, except that the power supply unit of Example 4 was changed to IP-DCR600V15A-R2/M manufactured by Evoqua Corporation. In this example, during the production of ultrapure water, the supply voltage from the power supply unit became unstable, and the power supply unit had to be replaced several times. The number of exchange units (superposition) is 22 units. These results are collectively disclosed in Table 1.

As can be seen from the results in Table 1, as shown in Examples 4 and 5, by using a power supply device with a small voltage ripple, the voltage supply from the power supply device will remain stable for a long time, and ultrapure water can be produced safely for a long time.

In addition, although the cause of the failure of the power supply unit is not necessarily clear, it is speculated that the interference between the power supply units caused by the use of multiple power supply units, or the periodic increase and decrease of the supply voltage or supply current due to voltage ripples, resulting in electromagnetic waves. impact. In addition, in order to obtain a high removal rate of weak electrolytes such as boron and silica, it is necessary to flow a high current compared to the case of desalination of other ions. For this reason, it is operated at a high voltage, so it is expected that the burden on the power supply device will also increase. .

From the above facts, according to the electric deionization device of the embodiment and the ultrapure water production system using the same, boron removal performance and removal efficiency of ion components can be improved.

1: Ultrapure water manufacturing system 11: Electric deionization device 11a: Anion exchange membrane 11c: Cation exchange membrane 12: 2-stage reverse osmosis membrane device 110:Electrical deionization stack 11: Electric deionization device 111: anode 112: Cathode 113: Power supply unit 114: Desalination chamber 115a: anode chamber 115b: cathode chamber 116: Concentration chamber

[ Fig. 1 ] A schematic block diagram of a model of an electric deionization device according to an embodiment. [ Fig. 2 ] A schematic block diagram of an ultrapure water production system according to an embodiment. [ Fig. 3 ] A schematic graph showing changes over time of boron transmittance in electrical deionization devices of Examples and Comparative Examples. [ Fig. 4 ] A schematic graph showing changes over time in resistivity of permeated water in electrical deionization devices of Examples and Comparative Examples. [ Fig. 5 ] A schematic graph showing changes over time in electrical conductivity of concentrated water in electric deionization devices of Examples and Comparative Examples. [Fig. 6] A schematic diagram of the output voltage waveform of the AC-DC converter due to the switching method used in the embodiment. [Fig. 7] A schematic diagram of the output voltage waveform of the AC-DC converter due to the full-wave rectification method used in another embodiment. [Fig. 8] Schematic diagram of the output voltage waveform of the AC-DC converter due to the half-wave rectification method used in the comparative example.

11: Electric deionization device

11a: Anion exchange membrane

11c: Cation exchange membrane

110:Electrical deionization stack

111: anode

112: Cathode

113: Power supply unit

114: Desalination chamber

115a: anode chamber

115b: cathode chamber

116: Concentration chamber

Claims (15)

An electrical deionization device comprising: an anode; and a cathode; and an electrical deionization stack (stack), which has an anode chamber disposed between the anode and the cathode and connected to the anode, and the cathode a connected cathode chamber, an anion exchange membrane and a cation exchange membrane alternately arranged between the aforementioned anode chamber and the aforementioned cathode chamber, and a concentrating chamber and a desalination chamber alternately formed between the aforementioned anion exchange membrane and the aforementioned cation exchange membrane, and an ion exchanger filled in the aforementioned desalination chamber; and a power supply device for applying a DC voltage between the aforementioned anode and the aforementioned cathode; When it is Vmax and the minimum voltage is Vmin, the following relationship (1) is satisfied: (Vmax-Vmin)/(Vmax+Vmin)≦0.3...(1). The electrical deionization device described in Claim 1, wherein the electrical deionization stack has ion exchangers or electrical conductors filled in the concentration chamber, the anode chamber and the cathode chamber. The electrical deionization device described in item 1 or 2 of the scope of the patent application, Wherein, the aforementioned power supply device is an inverter that converts the AC voltage supplied to the aforementioned power supply device into the aforementioned DC voltage and outputs it. The electric deionization device as described in claim 3 of the patent claims, wherein the aforementioned predetermined period is more than 1/2 of the AC cycle of the aforementioned AC voltage. The electrical deionization device described in Claim 3 of the patent application, wherein the aforementioned converter is a full-wave rectifying converter that converts the AC voltage into the aforementioned DC voltage by means of full-wave rectification, or converts the AC voltage by means of switching A switching converter for converting to the aforementioned DC voltage. An ultrapure water manufacturing system, which sequentially comprises: a reverse osmosis membrane device; and an electrical deionization device as described in any one of items 1 to 5 of the scope of the patent application. The ultrapure water production system described in item 6 of the scope of the patent application, wherein the aforementioned reverse osmosis membrane device is a two-stage reverse osmosis membrane device formed by connecting two reverse osmosis membrane devices in series. An ultra-pure water production system, which sequentially has: an ion exchange resin device; and a degassing device; The ultrapure water production system according to any one of claims 6 to 8, wherein the boron concentration in the permeated water of the electrical deionization device is 1 μg/L or less (as B). A method of producing ultrapure water, which is an ultrapure water production method including the process of treating the water to be treated with an electrical deionization device, characterized in that the aforementioned electrical deionization device has: an electrical deionization stack, which has An anode, a cathode, and an anode chamber arranged between the anode and the cathode and connected to the anode, a cathode chamber connected to the cathode, and anions arranged alternately between the anode chamber and the cathode chamber The exchange membrane and the cation exchange membrane, the concentration chamber and the desalination chamber formed alternately between the aforementioned anion exchange membrane and the aforementioned cation exchange membrane, and the ion exchanger filled in the aforementioned desalination chamber; and a power supply device for the aforementioned anode and the aforementioned cathode Apply a DC voltage between them, the aforementioned DC voltage, when the maximum voltage of the specified period is set as Vmax, and the minimum voltage is set as Vmin, the condition of the following relationship (1) is satisfied to treat the aforementioned treated water: (Vmax-Vmin) /(Vmax+Vmin)≦0.3...(1). The ultrapure water production method described in claim 10, wherein the electrical deionization stack has ion exchangers or electrical conductors filled in the concentration chamber, the anode chamber, and the cathode chamber. The method for producing ultrapure water as described in claim 10 or 11 of the patent application, further includes the process of treating the raw water with a reverse osmosis membrane device to obtain the aforementioned treated water. The ultrapure water production method described in claim 12 of the patent application, wherein the aforementioned reverse osmosis membrane device is a two-stage reverse osmosis membrane device formed by connecting two reverse osmosis membrane devices in series. The method for producing ultrapure water as described in claim 10 or 11 of the scope of the patent application further includes the process of treating the raw water with an ion exchange resin device and a degassing device to obtain the aforementioned treated water. The method for producing ultrapure water according to claim 10 or 11, wherein the boron concentration of the treated water treated by the electric deionization device is 1 μg/L or less (as B).

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