JP2000301145A - Pure water production equipment - Google Patents

Abstract

(57) [Summary] [PROBLEMS] Suitable for the production of pure water requiring high-purity water quality used in power plants, pharmaceutical manufacturing plants, semiconductor manufacturing plants, etc., particularly to silica and boron at extremely low concentrations. Provided is a pure water production apparatus capable of removing the pure water to obtain pure water of high quality. (A) A pH adjusting mechanism for adjusting the pH of the water to be treated to 9.2 or higher, (B) a reverse osmosis membrane device through which the water to be treated whose pH has been adjusted is passed, and (C) a membrane permeation. An apparatus for producing pure water, comprising: a strongly basic anion exchange resin tower through which water is passed; and a cation exchange resin tower through which effluent of the strongly basic anion exchange resin tower is passed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a pure water producing apparatus. More specifically, the present invention is suitable for the production of pure water requiring high-purity water quality, which is used in power plants, pharmaceutical plants, semiconductor manufacturing plants, etc., and in particular, removes silica and boron to extremely low concentrations. The present invention relates to a pure water production apparatus capable of performing the above.

[0002]

2. Description of the Related Art Reverse osmosis membrane devices are widely used for producing pure water.
Have been. Also, to obtain pure water with higher purity
In addition, reverse osmosis membrane devices are arranged in multiple stages in series,
The permeated water of the membrane device is supplied to the reverse osmosis
Enhancement devices are often used. Recently, this
Add acid or alkali to the feed water of the reverse osmosis membrane device to adjust the pH.
Water, especially with reduced silica and boron concentrations.
A way to get it is being developed. However, the supply of reverse osmosis
Adding an acid or alkali to water can reduce excess ions.
These drugs enter the reverse osmosis membrane device and reverse osmosis
If it is not sufficiently removed by the membrane device and leaks into the permeated water
There is a case. Therefore, such ions are surely removed.
And a cation exchange resin after the reverse osmosis membrane
A mixed-bed ion-exchange resin tower mixed with a nonion-exchange resin is installed.
Is generally performed. Mix with ion exchange resin
In the case of a mixed-bed type pure water production system that passes water as a floor, for example,
If the pH of the water at the inlet of the ion exchange resin column is alkaline
Is also ion-exchanged by the ion-exchange resin in the tower, and is almost neutral
The water flows out. In particular, if the water is alkaline
Cation exchange when the drug is sodium hydroxide
Na by exchange resin ⁺Is H⁺Will be replaced. Therefore,
Before the interface where this ion exchange takes place, the pH will be around 7
Become. By the way, boron and silica are difficult to dissociate
But on the alkaline side, that is, OH^-Is supplied
Dissociated and found to exist in ionic form in water.
Have been. Strongly basic anion exchange resin has no surface
It has a number of --OH groups as functional groups and even neutral salts
Can be exchanged for ion exchange. For this, Ho
In the vicinity of functional groups on the resin surface, even for silicon and silica
Is OH^-Behaves as if
Can be adsorbed on. However, silica and boron
It is originally a substance that is difficult to dissociate.
When the number of -OH groups on the surface of the anionic resin decreases, insufficient dissociation occurs.
And cannot diffuse into the anion exchange resin,
The adsorption capacity becomes saturated. Because of this, silica and boron
Which substances have higher ion adsorption than substances like NaCl
The amount is extremely low, and the pure water production equipment using the reverse osmosis membrane
Removes silica and boron to extremely low concentrations to improve water quality.
It was difficult to obtain pure water.

[0003]

SUMMARY OF THE INVENTION The present invention relates to a method for producing pure water, particularly silica and boron, which is used in power plants, pharmaceutical manufacturing plants, semiconductor manufacturing plants and the like and requires high purity water quality. It is an object of the present invention to provide a pure water production apparatus capable of obtaining pure water of high quality by removing it to an extremely low concentration.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, passed raw water having a pH adjusted to 9.2 or more through a reverse osmosis membrane device. By passing the permeated water through a strongly basic anion exchange resin tower and then a cation exchange resin tower, silica and boron in the water can be removed to an extremely low concentration, and pure water of high quality can be obtained. And completed the present invention based on this finding. That is, the present invention provides (1)
(A) a pH adjusting mechanism for adjusting the pH of the water to be treated to 9.2 or more; (B) a reverse osmosis membrane device through which the water to be treated whose pH has been adjusted; A pure water production apparatus, comprising: a strongly basic anion exchange resin tower; and (D) a cation exchange resin tower through which effluent of the strong basic anion exchange resin tower is passed. ) The water to be treated is
It is intended to provide a pure water production apparatus according to the above (1), which is water containing silica or boron.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The pure water producing apparatus of the present invention comprises (A) a pH adjusting mechanism for adjusting the pH of the water to be treated to 9.2 or more, and (B) a pH adjusting mechanism.
Reverse osmosis membrane device through which the water to be treated is adjusted, (C)
Strongly basic anion exchange resin tower through which permeated water is passed; and
(D) A cation exchange resin tower through which the effluent of the strongly basic anion exchange resin tower is passed. The device of the present invention can be particularly suitably used when the water to be treated is water containing silica or boron. The apparatus of the present invention can be used by attaching a known water treatment apparatus at the preceding stage as necessary. FIG. 1 is a process flow diagram of one embodiment of a pure water production process using the apparatus of the present invention. The water to be treated is
Water is passed through the activated carbon packed tower 1 to adsorb and remove organic substances and residual chlorine in the water. The effluent from the activated carbon packed tower is guided by a vacuum pump 2 to a membrane deaerator 3 in which the gas phase side is kept at a reduced pressure, and carbon dioxide and oxygen dissolved in the water are removed. Instead of the membrane deaerator, a deaeration tower or the like can be provided. The effluent from the membrane deaerator is passed through the reverse osmosis membrane device 4 at the preceding stage, and after preliminary impurities are removed, it is supplied to the pure water production device of the present invention. In the embodiment shown in FIG. 1, the device of the present invention has a pH adjustment mechanism including an alkaline storage tank 5 and a pump 6, and further includes a reverse osmosis membrane device 7,
A strong basic anion exchange resin tower 8 and a cation exchange resin tower 9 are provided.

[0006] There is no particular limitation on the pH adjusting mechanism (A) for adjusting the pH of the water to be treated to 9.2 or more in the apparatus of the present invention. For example, an apparatus for adding an alkaline aqueous solution such as sodium hydroxide or a basic resin ion may be used. Exchange towers, or both, can be installed. As an apparatus for adding an aqueous alkali solution, for example, a pH adjusting tank with a stirrer may be provided, or an alkali aqueous solution injection port may be provided in a water flow line, and a static mixer may be provided downstream of the inlet. When the pH is adjusted by adding an alkali, the pH adjusting mechanism adds an alkali to the water to be treated, and adjusts the pH of boric acid to p.
It can be adjusted to Ka 9.2 (25 ° C.) or more, more preferably pH 9.5 or more. In the embodiment shown in FIG.
The alkaline aqueous solution stored in the alkaline storage tank 5 is added to the permeated water of the preceding reverse osmosis membrane device by the pump 6,
Is adjusted to 9.2 or more. (B) pH in the device of the present invention
The reverse osmosis membrane device through which the water to be treated is passed is preferably provided with an alkali-resistant reverse osmosis membrane which is not deteriorated even when the pH becomes 10 or more, more preferably 11 or more in the long term. preferable. In this case, since the concentrated water has a higher pH than the supplied alkaline to-be-treated water, it is preferable to select an alkali-resistant reverse osmosis membrane in consideration of the pH of the concentrated water. As such an alkali-resistant reverse osmosis membrane, for example, FILMT manufactured by Film Tec, which is commercially available as having long-term durability up to pH 11
EC Type FT30 and the like.
As long-term durability up to pH 10, Nitto Denko Corporation's ES20, ES10, NTR759, Toray
And a polyamide-based film such as SU700 (trade name).

In the apparatus of the present invention, there is no particular limitation on the strongly basic anion exchange resin packed in the strongly basic anion exchange resin tower through which the (C) membrane permeated water flows. For example, a strongly basic anion exchange resin having a trimethylammonium group may be used. Either type I or strongly basic type II having a dimethylhydroxyethylammonium group can be used, and both gel type and macroporous type can be used. Among these,
A gel type strong basic anion exchange resin having a degree of crosslinking of about 4% can be suitably used. Examples of such a strong basic anion exchange resin include, for example, EX-
AG, SAF12A of Mitsubishi Chemical Corporation, OC of Bayer AG
1241 and the like. In the apparatus of the present invention, the strongly basic anion exchange resin is preferably used in a sufficiently regenerated state. If the regeneration of the strongly basic anion exchange resin is insufficient, if the pH of the permeated water is high, impurities remaining in the strongly basic anion exchange resin without being regenerated may be eluted, thereby deteriorating the water quality. There is. Therefore, it is preferable to adopt a countercurrent regeneration system in which the regeneration level of the strongly basic anion exchange resin is sufficiently high, and the flow direction is opposite to the injection direction. When regenerating a strong basic anion exchange resin adsorbing silica or boron,
The countercurrent regeneration method is particularly effective. However, by setting the temperature of the regenerating agent to 35 ° C. or higher, efficient regeneration can be performed, and the amount of the regenerating agent used can be reduced.
When performing regeneration at 35 ° C. or higher, pure water at 35 ° C. or higher can be passed through a strong basic anion exchange resin tower and heated in advance. There is no particular limitation on the regenerant of the strongly basic anion exchange resin. For example, an aqueous sodium hydroxide solution having a concentration of 2% by weight or more and a temperature of about 50 ° C. can be suitably used.

[0008] Silica maintains an equilibrium represented by the following formula in water. SiO ₂ + H ₂ O⇔HSiO ₃ ⁻ + H ⁺ ... [1] Equation [1] can also be expressed as the following equation. ^{_{SiO 2 + OH - ⇔ HSiO 3}} - ... [2] In this state, when in contact with a strongly basic anion exchange resin,
Silica is adsorbed on the resin according to the following equation. However,
In the formula, R represents a base of a strongly basic anion exchange resin. ^{_{R-OH + HSiO 3 - →}} R-HSiO 3 + OH - ... [3] As can be seen from equation [1] and [2], silica, the pH is weakly dissociated at low water, when the pH is high In the meantime, the equilibrium of the formula [2] shifts rightward, and the dissociation of silica proceeds in a high pH region. In the device of the present invention, the pH is 9.2.
Since the permeated water of the reverse osmosis membrane device through which the water to be treated adjusted as described above is passed through the strongly basic anion exchange resin tower, the high pH permeated water is exchanged with the strongly basic anion exchange resin. It can contact and efficiently adsorb and remove silica. The equilibrium of boron in water can be expressed by the following equation. ^{_{H 3 BO 3 + OH - ⇔}} B (OH) 4 - ... [4] In this state, when in contact with a strongly basic anion exchange resin,
Adsorbed on resin according to the following formula. R-OH + B (OH) 4 - → R-B (OH) 4 + OH - ... [5] Boron also when the pH is high, the equilibrium equation [4] moves to the right, high pH region In, the anionization of boron proceeds. In the apparatus of the present invention, since the permeated water of the reverse osmosis membrane apparatus through which the water to be treated whose pH has been adjusted to 9.2 or more is passed through the strong basic anion exchange resin tower, the pH is high. The permeated water comes into contact with the strongly basic anion exchange resin, and boron can also be efficiently adsorbed and removed.

When water having a high pH is supplied to the strongly basic anion exchange resin tower, silica and boron are efficiently adsorbed, and pure water having a very low concentration of silica and boron can be obtained. There is also the problem of lowering.
For this reason, before the adsorption capacity is saturated in the strong basic anion exchange resin tower, the amount of ion It is preferable to design so as to meet the starting point of cross-flow. In the apparatus of the present invention, the permeated water of the reverse osmosis membrane apparatus can be passed through the strongly basic anion exchange resin tower as it is. However, if the pH is too high, the amount of water taken is reduced. To adjust the pH to 8.5
By adjusting to 9.5, the amount of water sampled can be increased. In a conventional pure water production system in which reverse osmosis membrane permeated water is passed through a mixed-bed ion exchange resin tower, water at the inlet of the tower is used.
Even if the pH is alkaline, it is ion-exchanged by the ion-exchange resin in the column and becomes almost neutral water. For example, when the pH is adjusted by adding sodium hydroxide, sodium ions are exchanged by the cation exchange resin, and the pH becomes about 7 before the interface where the ion exchange is performed. Silica and boron cannot be efficiently adsorbed and removed.

The cation exchange resin to be filled in the cation exchange resin column through which the effluent of the strongly basic anion exchange resin column (D) in the apparatus of the present invention is passed is not particularly limited.
Either a strongly acidic cation exchange resin having a sulfonic acid group or a weakly acidic cation exchange resin having a carboxylic acid group can be used, and any of a gel type and a macroporous type can be used. Among these, a strongly acidic cation exchange resin can be suitably used. Examples of such strongly acidic cation exchange resin include Kurita Kogyo
EX-CG of Mitsubishi Chemical Corporation, SKF110 of Mitsubishi Chemical Corporation, and OC1213 of Bayer Corporation. The regenerant for the cation exchange resin is not particularly limited, and examples thereof include hydrochloric acid and sulfuric acid. For example, hydrochloric acid having a concentration of 2% by weight or more and a temperature of about 40 ° C. can be suitably used. By passing the effluent of the strongly basic anion exchange resin tower through the cation exchange resin tower, cation components in the water can be adsorbed and removed, and pure water having high specific resistance can be obtained. Generally, when compared with a mixed-bed type pure water apparatus, a multi-bed tower type pure water apparatus has poor water quality start-up properties, but this is due to the regenerated chemical remaining slightly in the ion-exchange resin layer. Since it is often, the solution can be solved by providing a still standing step after the extruding and washing steps after chemical injection, and diffusing and removing the agent in the resin layer. After that, washing is performed again and water is collected, whereby a water quality rising property equal to that of the mixed-bed type pure water apparatus can be obtained. In addition, the conventional multi-bed tower type pure water apparatus usually has a structure in which water is first passed through a cation exchange resin tower and then water is passed through an anion exchange resin tower. There were problems such as an increase in the carbon (TOC) component. However, in the apparatus of the present invention, the effluent of the anion exchange resin is adsorbed and removed by the cation exchange resin tower in order to pass the effluent of the strongly basic anion exchange resin tower through the cation exchange resin tower. The eluate adsorbed on the can be desorbed by using a high temperature regenerant. By using the apparatus of the present invention, silica and boron contained in the water to be treated can be removed to an extremely low concentration, and pure water having high water quality can be obtained.

[0011]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. Example 1 Pure water was produced by the process shown in FIG. 1 using Nogimachi water as raw water. Raw water is supplied to the activated carbon packed tower 1 at a rate of 62 L / h to remove residual chlorine, and then decarbonated by passing water through a membrane deaerator 3 in which the gas phase is kept at a reduced pressure by a vacuum pump 2. Was. The decarbonated water is guided to a reverse osmosis membrane [SU700, Toray Co., Ltd.] device 4, and an aqueous sodium hydroxide solution is added to the permeated water by a pump 6 from an alkaline storage tank 5, and further a reverse osmosis membrane in a subsequent stage [Film
Tec, FILMTEC Type FT30] Apparatus 7
Led to. The addition amount of the aqueous sodium hydroxide solution was controlled so that the pH of the permeated water in the subsequent reverse osmosis membrane device became 9.8. The reverse osmosis membrane device permeate in the latter stage has a flow rate of 50 liters /
h, electric conductivity 36 μS / cm, pH 9.8, silica concentration 4
The concentration was 3 μg / liter and the boron concentration was 2.5 μg / liter. The permeated water of the latter reverse osmosis membrane device is passed through a strongly basic anion exchange resin tower 8 and then a cation exchange resin tower 9,
2.5 m ³ of pure water was sampled. The strong basic anion exchange resin tower has an inner diameter of 40 mm and a height of 1,000 mm, and is filled with 1 liter of anion exchange resin [Bayer, OC1241] and 200 ml of inert resin [Bayer, EN-42]. The cation exchange resin tower has an inner diameter of 40 mm and a height of 500 mm, and a cation exchange resin [Bayer, O.
C1213] 500 ml and inert resin [Bayer, E
N-42]. The water flow was performed as upward flow. After sampling 2.5 m ³ of pure water, the production of pure water was interrupted, and the strongly basic anion exchange resin tower and cation exchange resin tower were regenerated. Regeneration of the strong basic anion exchange resin tower is performed by using 50 g of sodium hydroxide per liter of resin.
By passing the solution as a 4% by weight aqueous solution at 50 ° C. as a downward flow at a flow rate of SV 5 h ⁻¹ ,
Pure water of 8 MΩ · cm was extruded by passing water at 5 times the capacity of the resin at SV 5 h ⁻¹ , and pure water having a specific resistance of 18 MΩ · cm was passed at a volume of 10 times the resin and SV of 20 h ⁻¹ for washing. Regeneration of the cation exchange resin tower requires 4 hydrogen chloride per liter of resin.
0 g, 5% by weight hydrochloric acid was passed through at 40 ° C. as a downward flow at a flow rate of SV 5 h ⁻¹ , and then pure water having a specific resistance of 18 MΩ · cm was applied to the resin in a volume 5 times the SV 5.
The resin was extruded by passing water at h ^-1 , and further washed with pure water having a specific resistance of 18 MΩ · cm at SV 20 h ^-1 of 10 times the volume of the resin. After the regeneration, extrusion and washing were completed, the production of pure water was restarted, and 2.5 m ³ of pure water was sampled. Thereafter, the regeneration of the resin and the production of pure water were repeated in the same manner. Pure water total 12.5m ³
The water quality of pure water immediately before the end of the fifth pure water production from which water was sampled was 0.1 μg / liter or less for silica and 1 ng /
g, organic carbon 5 μg / liter, specific resistance 17.0 MΩ ·
cm.

Comparative Example 1 In the same manner as in Example 1 except that a mixed-bed type ion exchange resin tower was provided in the subsequent stage of the reverse osmosis membrane apparatus in place of the strong basic anion exchange resin tower and the cation exchange resin tower. To produce pure water. Mixed bed type ion exchange resin tower, inner diameter 40mm
× height 1,500 mm, filled with 500 ml of cation exchange resin [Bayer, OC1213] and 1 liter of strong basic anion exchange resin [Bayer, OC1241]. The permeated water of the latter reverse osmosis membrane is passed through a mixed-bed type ion exchange resin tower in an upward flow to collect 2.5 m ³ of pure water, and then the production of pure water is interrupted to regenerate the ion exchange resin. went. The cation exchange resin and the strongly basic anion exchange resin are separated by backwashing with water, and the cation exchange resin is converted into 5% by weight hydrochloric acid so as to be 80 g of hydrogen chloride per liter of the resin.
It is carried out by passing the solution at 40 ° C. at a flow rate of SV5h ⁻¹ , and then adding pure water having a specific resistance of 18 MΩ · cm to the resin by 5 times the volume of SV5.
The resin was extruded by passing water at h ^-1 , and further washed with pure water having a specific resistance of 18 MΩ · cm at SV 20 h ^-1 of 10 times the volume of the resin. Strongly basic anion exchange is carried out by converting 50 g of sodium hydroxide per liter of resin into a 4% by weight aqueous solution.
C. by passing the solution at a flow rate of SV5h ^-1 at a flow rate of SV5h ^-1.
And then extruded, and further washed with pure water having a specific resistance of 18 MΩ · cm at a SV of 10 h times the resin volume of 20 h ⁻¹ .
After the washing was completed and the water level was adjusted, air was sent from below to mix the cation exchange resin and the strongly basic anion exchange resin. After restarting the production of pure water and sampling 2.5 m ^{3 of} water, the operation of regenerating the ion exchange resin was repeated in the same manner as in Example 1. The quality of pure water immediately before the end of the fifth pure water production in which a total of 12.5 m ³ of pure water was sampled was 1.0 μm of silica.
g / liter, boron 10ng / g, organic carbon 3μg
/ Liter and specific resistance of 18.0 MΩ · cm. Comparative Example 2 The order of the strongly basic anion exchange resin tower and the cation exchange resin tower was changed, and a cation exchange resin tower was provided immediately after the reverse osmosis membrane device in the subsequent stage, and then a strong basic anion exchange resin tower was provided in the subsequent stage. Except for the above, pure water was produced in the same manner as in Example 1. The operation of regenerating the cation exchange resin tower and the strongly basic anion exchange resin after sampling 2.5 m ³ of pure water was repeated in the same manner as in Example 1. Pure water total 1
The quality of pure water immediately before the end of the fifth pure water production, in which 2.5 m ³ was sampled, was as follows: silica 0.5 μg / liter and boron 8 ng.
/ G, organic carbon 10 μg / liter, specific resistance 17.5
MΩ · cm. Table 1 shows the results of Example 1 and Comparative Examples 1 and 2.

[0013]

[Table 1]

As can be seen from Table 1, the pH of the raw water is adjusted to 9.8 by the process having the apparatus of the present invention, and then the water is passed through a reverse osmosis membrane apparatus, and the permeated water is subjected to strong basic anion exchange resin. In Example 1 in which water was passed through the column and then through the cation exchange resin column, the silica concentration of pure water obtained was 0.1 μg / L or less, and the boron concentration was 1 ng / L, and silica and boron were removed to extremely low concentrations. Have been. On the other hand, in Comparative Example 1 using a mixed-bed type ion exchange resin tower, the same type and the same amount of ion exchange resin as in Example 1 were used, and despite the fact that the regeneration was carried out at the same frequency, the results were obtained. The concentration of silica and boron in the purified water is 10 times or more the concentration of silica and boron in the pure water obtained in Example 1. Further, in Comparative Example 2 in which the permeated water was first passed through the cation exchange resin tower, and then the effluent was passed through the strongly basic anion exchange resin tower, the same type and the same amount of ion exchange resin as in Example 1 were also used. Despite the use and regeneration at the same frequency, the concentration of silica and boron in the obtained pure water is 5 to 8 times the concentration of silica and boron in the pure water obtained in Example 1. . From these results, (A) a pH adjusting mechanism for adjusting the pH of the water to be treated to 9.2 or more, (B) a reverse osmosis membrane device through which the water to be treated whose pH has been adjusted, and (C) a membrane permeation. Use of the pure water production apparatus of the present invention including a strong basic anion exchange resin tower through which water is passed and a cation exchange resin tower through which the effluent of the strong basic anion exchange resin tower is passed Thus, it can be seen that pure water having a very low concentration of silica and boron and excellent water quality can be obtained.

[0015]

By using the pure water producing apparatus of the present invention, silica and boron contained in raw water can be removed until the concentration becomes extremely low, and pure water of high quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a process system diagram of one embodiment of a pure water production process using the apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Activated carbon packed tower 2 Vacuum pump 3 Membrane deaerator 4 Reverse osmosis membrane device 5 Alkaline storage tank 6 Pump 7 Reverse osmosis membrane device 8 Strongly basic anion exchange resin tower 9 Cation exchange resin tower

Claims (2)

[Claims] (A) a pH adjusting mechanism for adjusting the pH of the water to be treated to 9.2 or more; (B) a reverse osmosis membrane device through which the water to be treated whose pH has been adjusted is passed; A pure water production apparatus comprising a strong basic anion exchange resin tower through which permeated water is passed and a cation exchange resin tower through which (D) effluent of the strong basic anion exchange resin tower is passed. . 2. The pure water production apparatus according to claim 1, wherein the water to be treated is water containing silica or boron.