JP2002066259A - Pure water production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently increase the electric current value necessary for desalination and stably obtain treated water with a high water quality at a high water recovery ratio with a low electric power consumption by reliably keeping the conductivity in an electric deionization apparatus, in a pure water production apparatus comprising an RO membrane apparatus and the electric deionization apparatus. SOLUTION: In a pure water production method comprising the step of passing filtrate passed through an RO membrane apparatus 2 through an electric deionization apparatus 3, object water to be treated having pH 3.0-5.5 is introduced into the RO membrane apparatus 2 to recover water at 90% or higher water recovery ratio and 5% or higher salt leakage ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing pure water for producing deionized water used in various industries in the fields of semiconductors, liquid crystals, pharmaceuticals, foods, electric power, etc., for consumer use or in research facilities. In particular, reverse osmosis (RO) membrane devices (hereinafter “RO membrane devices”)
Called. ) And an electric deionization device, a pure water production device capable of producing high-purity deionized water stably with a high water recovery rate while reducing power consumption of the electrodeionization device. It relates to a manufacturing method.

[0002]

2. Description of the Related Art Conventionally, in the production of deionized water used in various industries such as a semiconductor manufacturing plant, a liquid crystal plant, a food industry, an electric power industry, and a consumer or research facility, as shown in FIG. , A plurality of anion exchange membranes 13 and a plurality of cation exchange membranes 14 are alternately arranged between the cathodes 12) to form a concentration chamber 15 and a desalination chamber 16 alternately. Electrodeionizers in which an anion exchanger composed of fibers or graft exchangers and a cation exchanger are mixed or filled in a multi-layered form are frequently used. In FIG. 2, reference numeral 17 denotes an anode chamber, and 18 denotes a cathode chamber.

[0003] The electrodeionization apparatus uses water to dissociate H ⁺
Ions and OH ^- to produce the ions, by continuously reproducing ion exchanger filled in the desalting compartment, but may be efficient desalination process, widely used in desalination conventionally It does not require a regeneration treatment using chemicals like the ion exchange resin equipment that has been used, so it is possible to perform perfect continuous water sampling and has the excellent effect of obtaining high-purity water. Widely used.

FIG. 3 is a system diagram showing a general pure water production apparatus incorporating such an electrodeionization apparatus. Raw water such as city water is treated by an activated carbon apparatus 1 and an RO membrane apparatus 2. After that, it is processed in the electrodeionization device 3. Where R
The O film device 2 is provided to reduce the load of organic substances, hardness components, and salts of the electrodeionization device. As the RO film, an RO film made of polyamide is usually used.

[0005]

As shown in FIG. 4, in the electrodeionization apparatus, the conductivity of the concentrated water is 10%.
When the water quality reaches 0 μS / cm or less, the electric resistance (electric resistance (Ω) = cell voltage (V / cell) / current density (A)
/ M ² )) increases and the conductivity of the concentrated water is 10 to ²⁰ μS / c.
At m, no current flows at all. And as a result, the quality of the to-be-processed water passed into the desalination room does not improve at all.

For this reason, as shown in FIG. 3, in a pure water production apparatus in which an RO membrane apparatus is arranged in front of the electrodeionization apparatus in order to reduce the load on the electrodeionization apparatus, the electric deionization apparatus is used. In some cases, the electrical conductivity of the water supplied to the ion device was too low, so that the quality of the resulting treated water was reduced.

To solve this problem, electrodeionization
Increase the water recovery rate of the device to increase the conductivity of concentrated water and electrode water.
Method and increase the water recovery rate of the RO membrane device, and
A method to increase the conductivity of the water supply to the ion device is also conceivable
But CaCO by high concentration ₃Of precipitation of silica, silica, etc.
There is also a limit on the degree of increase in the water recovery rate.
No solution.

On the other hand, as is well known, improvement of the water recovery rate in a pure water production system is always desired from the viewpoint of global environmental protection and resource saving in recent years.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional circumstances, and when producing pure water using a pure water producing apparatus having an RO membrane device and an electrodeionizing device, the present invention relates to an electric deionizing device. It is an object of the present invention to provide a method for producing pure water capable of sufficiently increasing the current value required for desalination by securing electrical conductivity, and stably obtaining high-quality treated water with a low power consumption and a high water recovery rate. Aim.

[0010]

The method for producing pure water according to the present invention has an RO membrane device and an electrodeionization device, and supplies permeated water from the reverse osmosis membrane desalination device to the electrodeionization device. In the method for producing pure water, the pH value of the RO
It is characterized in that 3.0 to 5.5 water to be treated is introduced, and the RO membrane apparatus is treated at a water recovery rate of 90% or more and a salt leak rate of 5% or more.

[0011] The water recovery rate of the RO membrane device is a ratio of water taken out as permeated water to water flowing into the RO membrane device. Here, the water flowing into the RO membrane device is the sum of the water to be treated in the RO membrane device and the circulating water of the concentrated water of the RO membrane device. Therefore, when operating at a water recovery of 90%, 90 parts of the water to be treated and 10 parts of the concentrated circulating water flow into the RO membrane device, and 90 parts of the permeated water are taken out.

The salt leak rate of the RO membrane device is the ratio of the salt (monovalent salt) concentration of the permeated water to the salt (monovalent salt) concentration of the water to be treated.

In the present invention, the pH of the water to be treated in the RO membrane device is
Is set to 3.0 to 5.5, and the RO membrane device is set to a water recovery rate of 90.
% By operating at a high recovery rate of not less than 0.1% to leak ions such as NaCl into the permeated water of the RO membrane apparatus.
The ions necessary for the electrodeionization device into which the permeated water of the O membrane device is introduced are secured.

As is apparent from FIG. 4, in order to ensure current efficiency in the electrodeionization apparatus, the conductivity of the concentrated water and electrode water of the electrodeionization apparatus is at least 50 μS /.
cm, preferably 100 μS / cm or more. For example, when the electrodeionization apparatus is operated at a water recovery rate of 90%, the water supply of the electrodeionization apparatus, that is, the conductivity of the permeated water of the RO membrane apparatus is 5 μS / cm or more, preferably 10 μS / cm or more.
It is necessary to be at least μS / cm.

On the other hand, as shown in FIG.
By operating at a water recovery rate of 90% or more, 5% or more of the ions of the water to be introduced are leaked (salt leak rate of 5% or more). However, the RO membrane of the RO membrane apparatus used here has a high desalination rate of 99% or more, which is employed in an ordinary pure water production apparatus. Therefore, when treating water of a city water level (conductivity of about 150 to 200 μS / cm), which is usually used as raw water for a pure water production apparatus, the RO membrane apparatus is treated at a water recovery rate of 90% or more. Permeated water having a conductivity of 10 μS / cm or more can be obtained.

When the water quality of silica or TOC is not required, an NF film (nanofiltration, loose RO) may be used instead of the RO film. For example, “LES90” and “NTR-729HF” manufactured by Nitto Denko Corporation can be used.

By the way, in city water, usually 20 mg / L
(In terms of SiO ₂ ), silica is contained, and when such water is treated at a water recovery rate of 90% or more in the RO membrane device, the silica concentration of the concentrated water in the RO membrane device is 200 mg / L at 10-fold concentration. About. On the other hand, since the saturation solubility of silica is as shown in FIG. 6, 200 mg / L
In this case, silica is precipitated in the concentrated water, and there is a concern that the RO membrane may be blocked by silica scale.

However, according to the study of the present inventors, the concentration at which silica scale precipitates in the RO film is as shown by the broken line in FIG. 6, and if the pH is 3.0 to 5.5, the concentration exceeds the saturation solubility. Even if silica is precipitated, it does not adhere to the RO film. For example, at pH 3.0, silica concentration of 500 mg / L
However, it was found that there was no scale deposition and there was no problem of a decrease in the amount of permeated water due to membrane blockage. Also, like this
By using H acid, the problem of scale generated in an alkaline region such as calcium carbonate is also avoided.

Therefore, according to the present invention, even if the water recovery rate in the RO membrane device is increased, the conductivity in the electrodeionization device can be ensured and high-quality treated water can be obtained without causing scale disturbance or the like. it can.

In the present invention, it is preferable that the conductivity of the concentrated water and / or the electrode water of the electrodeionization device be 50 μS / cm or more by leaking ions into the permeated water of the RO membrane device.

As described above, since silica scale can be prevented in the present invention, the present invention has a silica concentration of 20 m.
It is effective for treating water to be treated having a high silica concentration such as g / L (equivalent to SiO ₂ ) or more.

In the present invention, it is preferable that water introduced into the RO membrane device or permeated water of the RO membrane device is treated by a degassing device, whereby carbon dioxide gas which is difficult to remove by an electrodeionization device is removed in advance. By reducing the carbon dioxide (CO ₂ ) concentration of water introduced into the electrodeionization apparatus to 1 mg / L or less, the removal rate of weak electrolytes such as silica and boron other than CO ₂ in the electrodeionization apparatus is also improved. In addition, it is possible to obtain treated water having higher quality.

[0023]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of the method for producing pure water of the present invention.

In the method shown in the figure, raw water such as city water is treated in an activated carbon apparatus 1, and then an acid such as HCl is added to adjust the pH to 3.0.
It is adjusted to 5.5, and this is treated by the degassing device 4, and then sequentially treated by the RO membrane device 2 and the electrodeionization device 3 to obtain treated water.

In the treatment with such a pure water production apparatus, in the present invention, the pH of the water to be treated in the RO membrane apparatus 2 is adjusted.
3.0-5.5, water recovery rate 90% or more, salt leak rate 5%
The processing is performed as described above.

If the pH of the water to be treated in the RO membrane device 2 exceeds 5.5, the amount of water permeated through the RO membrane device decreases over time on a silica scale. When the pH is less than 3.0, p
It is not preferable because there are problems such as an increase in the cost of chemicals for adjusting H and corrosion of the apparatus.

The acid used for pH adjustment is not particularly limited, but a monovalent acid, for example, HCl is preferable in order to secure a salt leak rate of 5% or more.

When the water recovery rate of the RO membrane device is less than 90%, it is difficult to achieve a salt leak rate of 5% or more, and it is not possible to secure conductivity in the electrodeionization device.

If the water recovery rate is excessively high, the conductivity of the permeated water of the RO membrane device becomes too high, and the effect of the pretreatment by the RO membrane device is impaired.
The water recovery rate of the O membrane device is particularly preferably 90 to 95%, and it is desirable to obtain permeated water having a salt leak rate of about 5 to 25% and a conductivity of about 5 to 40 μS / cm.

In the present invention, the water recovery rate of the RO membrane device is 90% or more and the salt leakage rate is 5% or more.
Preferably the conductivity is 5 μS / cm or more, more preferably 1
In order to obtain permeated water of 0 μS / cm or more, it is preferable to employ the following conditions.

Raw water quality: conductivity 150 to 200 μS / c
About m of city water and industrial water. In addition, from the viewpoint of the above-mentioned silica scale prevention effect, the present invention particularly provides a silica concentration of 20 mg /
It is effective for raw water of L or more, especially 25 mg / L or more. RO membrane of RO membrane apparatus: RO membrane having a desalination rate of 99% or more.

Further, such a permeated water is treated and the electric conductivity of the concentrated water and / or the electrode water in the electrodeionization apparatus is 50 μS / cm or more, preferably 100 to 500 μS / cm.
cm, the electrical resistance of the electrode chamber is preferably 2Ω (V / (A / m ² )) or less. In the electrodeionization apparatus, it is preferable to perform the treatment at a water recovery of about 75 to 90%.

By performing the process under such operating conditions, the process can be performed with high current efficiency without injecting the electrolyte into the electrode water supply water of the electrodeionization apparatus or filling the electrode chamber with the ion exchanger. It becomes possible.

The pure water producing apparatus shown in FIG. 1 is an example of the embodiment of the present invention, and the constitution of the pure water producing apparatus used in the present invention is not limited to the one shown in the drawings unless it exceeds the gist. It is not limited to.

For example, two or more RO membrane devices may be used and arranged in series. In this case, the effects of reducing the calcium scale load of the electrodeionization apparatus, stabilizing the processing operation by preventing the generation of slime, and improving the water quality (silica, specific resistance) are exhibited. Although the degassing device is not necessarily required, by previously removing the hard CO ₂ which is removed by the electrodeionization apparatus provided with a degassing device, can increase the quality of treated water, it is advantageous. As shown in FIG. 1, the degassing device may be provided before the RO membrane device or may be provided after the RO membrane device. However, the pH of the water introduced into the degassing device is in an acidic range. is important. The treatment by the degassing device is preferably performed so that the CO ₂ concentration of the feed water of the electrodeionization device becomes 1 mg / L or less.

[0037]

The present invention will be described more specifically with reference to experimental examples and examples.

EXPERIMENTAL EXAMPLE 1 An RO membrane device having the following specifications was used, and treatment was performed at a water recovery rate shown in Table 1 using water having the following water quality as raw water. [Specification of RO membrane device] "Membrane Ace KN200" manufactured by Kurita Kogyo Co., Ltd. "NTR759" manufactured by Nitto Denko Corporation (desalting rate: 99%) was loaded as an RO membrane. [Raw water quality] Silica concentration: 30 mg / L Conductivity: 150 μS / cm pH: 5.0

The inflow water of the RO membrane device at each water recovery rate,
The conductivity of the concentrated water and the permeated water and the salt leak rate are as shown in Table 1. By performing the treatment at a water recovery rate of 90% or more, the conductivity of the permeated water is 5 to 10 μm at a salt leak rate of 5% or more.
It can be seen that S / cm or more can be secured.

[0040]

[Table 1]

Experimental Example 2 In Experimental Example 1, the pH of the raw water was changed as shown in Table 2,
The same treatment was performed at a water recovery of 95%. The rate of increase in operating pressure when the treatment was continued for 10 days (the rate of increase in pressure after 10 days of operation relative to the pressure in the initial operation) was determined. The results are shown in Table 2. In addition, RO of RO membrane device after 10 days of operation
The film was taken out, and the presence or absence of silica scale was examined. The results are shown in Table 2.

[0042]

[Table 2]

From Table 2, it can be seen that if the pH is 5.5 or less, there is no problem of a decrease in the amount of permeated water due to the silica scale even if the water recovery is 90% or more.

Example 1 Using a pure water production apparatus in which the following activated carbon apparatus, degassing apparatus, RO membrane apparatus and electrodeionization apparatus were installed in series as shown in FIG. 100 as raw water
L / hr.

[0045]

[Table 3]

Activated carbon device: “Crycol KW10-30” manufactured by Kurita Kogyo Co., Ltd. Degassing device: “Oxyace” manufactured by Kurita Kogyo Co., Ltd. RO membrane device: same as that used in Experimental Example 1 Electrodeionizer : "Pure Ace PA-200" manufactured by Kurita Kogyo Co., Ltd. Processing volume: 100 L / hr

The following are used as the ion exchange membrane of the above electrodeionization apparatus, and the following anion exchange resin and cation exchange resin are used as the ion exchange resin to be filled in the desalting chamber: anion exchange resin: cation exchange resin = 6: 4
An electrodeionization device as shown in FIG. 2 was assembled by using the mixture (volume ratio). The anion exchange resin and the cation exchange resin used were sufficiently washed with ultrapure water. Anion exchange membrane: “Neoceptor AHA” manufactured by Tokuyama Corporation Cation exchange membrane: “Neosepta CMB” manufactured by Tokuyama Corporation Anion exchange resin: “SA10A” manufactured by Mitsubishi Chemical Corporation Cation exchange resin: “Made by Mitsubishi Chemical Corporation” SK1B "

HCl was added to the effluent of the activated carbon unit to adjust the pH to 3.5. The water recovery of the RO membrane device was 95%, the water recovery of the electrodeionization device was 90%, the applied voltage was 30 V, and the current was 0.5 A.

At this time, the water supply (RO)
Table 3 shows the quality of the permeated water of the membrane device), concentrated water and deionized water.
As shown in the figure, high quality treated water can be obtained.
Was. At this time, the electricity in the electrode chamber of the electrodeionization device
The resistance is 0.5Ω (V / (A / m ²))Met.

[0050]

As described above in detail, according to the method for producing pure water of the present invention, in a pure water producing apparatus composed of an RO membrane device and an electrodeionization device, the electric water can be removed without causing scale disturbance. The electric current required for desalination can be sufficiently increased by securing the conductivity in the ion device, and the treated water with low power and high quality can be stably obtained at a high water recovery rate.

[Brief description of the drawings]

FIG. 1 is a system diagram illustrating an embodiment of a method for producing pure water of the present invention.

FIG. 2 is a schematic sectional view showing a configuration of a general electrodeionization apparatus.

FIG. 3 is a system diagram of a general pure water production apparatus.

FIG. 4 is a graph showing the relationship between the electrical conductivity of the concentrated water and the electrical resistance in the electrodeionization apparatus.

FIG. 5 is a graph showing a relationship between a water recovery rate and a salt leak rate of the RO membrane device.

FIG. 6 is a graph showing the saturation solubility of silica.

[Description of Signs] 1 Activated carbon device 2 RO membrane device 3 Electrodeionization device 4 Degassing device

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 1/20 C02F 1/20 A 1/44 1/44 H 1/469 9/00 502F 9/00 502 502H 502M 502Z 503B 503 503C 504D 504 504E 1/46 103 (72) Inventor Kiminobu Osawa 3-7, Nishishinjuku, Shinjuku-ku, Tokyo F-term in Kurita Kogyo Co., Ltd. 4D006 GA03 KA02 KA72 KB01 KB12 KD03 KE03Q KE12Q KE13Q KE15Q KE19P MC54 PA02 PB06 PB23 PC03 4D037 AA03 AB11 BA23 BB01 BB02 CA01 CA03 CA04 CA14 4D061 DA03 DB18 EA09 EB13 EB17 EB19 EB37 EB39 FA06 FA09 FA11 GA21 GC05 GC18 GC18

Claims (4)

[Claims] 1. A method for producing pure water, comprising: a reverse osmosis membrane device and an electrodeionization device, wherein permeated water of the reverse osmosis membrane desalination device is supplied to the electrodeionization device. Pure water characterized by introducing water to be treated having a pH of 3.0 to 5.5 into an osmosis membrane device and treating the reverse osmosis membrane device at a water recovery rate of 90% or more and a salt leak rate of 5% or more. Production method. 2. The water introduced into the electrodeionization apparatus according to claim 1, wherein water introduced into the reverse osmosis membrane apparatus or water permeated through the reverse osmosis membrane apparatus is treated by a degassing apparatus. A method for producing pure water, wherein the carbon dioxide concentration of the water is 1 mg / L or less. 3. The electric deionization apparatus according to claim 1, wherein the electric conductivity of the concentrated water and / or the electrode water of the electrodeionization device is 50 μS /.
cm or more. 4. The method according to claim 1, wherein the silica concentration of the water to be treated is 20 mg / L (SiO ₂
A method for producing pure water.