JPH0326390A - Pure water production equipment - Google Patents

Abstract

PURPOSE:To improve the removal rate of SiO2 and to stably obtain high-purity water by weakly acidifying raw water to be supplied to an electrodialyzer packed with a mixture of anion-exchange resin and cation-exchange resin in its dilution chamber. CONSTITUTION:The pure water producing device is formed by a reverse-osmosis membrane separator 1 (RO) and an electrodialyzer 2 (CDI), and a pipeline 10 for supplying acid to RO-treated water is connected to a pipeline 12. A concentration chamber 35a is formed between an anion-exchange membrane 31 and a cation-exchange membrane 32, a dilution chamber 36 is formed below the cation-exchange membrane 32 and an anion-exchange membrane 33, and a concentration chamber 35b is formed between the anion-exchange membrane 33 and a cation-exchange membrane 34. A mixed bed of the cation-exchange resin 37 and anion exchange resin 38 is packed in the dilution chamber 36. The weakly acidified raw water is supplied to the CDI to elute the SiO2 saturated and adsorbed in the ion-exchange membrane of the CDI, and the SiO2 adsorptivity of the ion-exchange resin of the CDI is restored.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a pure water production device that continuously produces pure water or so-called ultrapure water, which is widely used in semiconductor manufacturing factories, nuclear power plants, etc. .

[Prior Art] In the manufacture of LSIs and VLSIs, large amounts of pure water and ultrapure water are used.

Conventionally, an electrodialyzer (hereinafter sometimes abbreviated as rCDIJ) loaded with an ion-exchange membrane and an ion-exchange resin has been known as a pure water production device (Japanese Patent Laid-Open No. 61-10
No. 7906). CDI is capable of effectively deionizing a wide range of raw water, from mass removal of salts to purification of manufactured water by reverse osmosis.

The deionization effect of water by CDI will be explained with reference to FIG.

In FIG. 3, the applied DC potentials are represented by (+) and (=). In this example, the concentration chamber 35a is located between the anion exchange membrane 31 and the cation exchange membrane 32, the dilution chamber 36 is located between the cation exchange membrane 32 and the anion exchange membrane 33, and the dilution chamber 36 is located between the anion exchange membrane 33 and the cation exchange membrane 34. Concentration chamber 3 between
5b is formed. The dilution chamber 36 is filled with a cation exchange resin 37, an anion exchange resin 38, and a kelp resin. Ions in raw water are Na+ and C
It is represented by j2-. Ions entering the dilution chamber 36 are transferred to the ion exchange resin 37 based on their affinity, concentration and mobility.
, 38. The ions move through the resin in the direction of the potential gradient and then across the membrane 32 or 33, maintaining charge neutralization in all chambers. And, due to the semi-osmotic properties of the membrane as well as the directionality of the potential gradient,
Ions in the solution are reduced in the dilution chamber 36 and concentrated in the adjacent concentration chambers 35a and 35b. For this reason,
Deionized water is recovered from the dilution chamber 36.

Unlike ion-exchange resins, CDI does not require regeneration, allows completely continuous water sampling, and has the excellent effect of producing extremely high-purity water.

[Problems to be Solved by the Invention] However, in the production of pure water using CDI, there was a drawback that SiO2 in the raw water could not be sufficiently removed. In other words, the Si02 removal rate with CDI is relatively high at the beginning of water flow, but after water flow is 141! Subsequently, when the ion exchange resin becomes saturated, the removal rate of Sto2 decreases, for example, at a voltage of 100 V and a current of 0.2 A, the removal rate of Sto2 becomes 30% or less after 10 to 30 days of water flow.

The present invention solves the above conventional problems and
It is an object of the present invention to provide a pure water production apparatus that can stably obtain treated water of extremely high purity by improving the iO2 removal rate.

[Means for Solving the Problems] The pure water production apparatus of the present invention includes a plurality of anion exchange membranes and cation exchange membranes arranged alternately to form concentration chambers and dilution chambers alternately. Regarding a pure water production apparatus equipped with an electrodialyzer (CDI) in which the dilution chamber is filled with a mixture of anion exchange resin and cation exchange resin, this CDI
It is equipped with a means to make the raw water supplied to the plant slightly acidic.

[Effects] As mentioned above, in the production of pure water using conventional CDI, it is not possible to stably obtain a sufficiently high SiO2 removal rate, but this is because SiO2 is not dissociated and its movement speed by electricity is slow. It's for a reason.

As a result of various studies on methods for improving the Si02 removal rate by CDI, the present inventors discovered that by supplying weakly acidified raw water to CDI, the Si02 removal rate in CDI's ion exchange resin could be improved.
By eluting 02, the SiO2 removal rate is greatly improved, and according to this elution of Si02,
It was found that only i02 was removed without adversely affecting other water quality. The present invention has been completed based on such knowledge.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a system diagram showing one embodiment of the pure water production apparatus of the present invention, and FIG. 2 is a system diagram showing one embodiment of the CDI.

The pure water production equipment shown in Figure 1 is a reverse osmosis membrane separator (RO)
1 and an electrodialyzer (Cl:l) 2, and in order to make the RO treated water weakly acidic, a piping 10 for supplying acid to it converts the water discharged from the Rot into a carbon dialysis machine.
Piping 12 for feeding to DI2 (this piping 12
The water supply pipe 12a branches into a water supply pipe 12a to the concentration chamber of the CDI and a water supply pipe 12b to the dilution chamber, which will be described later. )It is connected to the. Pipes 13 and 14 are piping for taking out treated water of CDI2 and piping for taking out concentrated water of CDI2, respectively, and piping 15 is a piping for taking out R O fl4 condensed water.

In the present invention, as a weak acidification means, as shown in FIG. Children can be treated by employing methods such as contacting with a strongly acidic cation exchange resin.

In the present invention, raw water that has been made weakly acidic by such a weakly acidifying means is supplied to the CDI to elute the SiO2 saturated and adsorbed in the ion exchange resin of the CDI, thereby reducing the adsorption of SiO2 on the ion exchange resin of the CDI. restore ability.

In the present invention, SiO2 in the ion exchange resin of CDI
If the pH of the slightly acidified water that flows into the CDI to elute is too high, the effect of the present invention cannot be obtained sufficiently, but if it is too low, other ions in the ion exchange resin of the CDI will also be desorbed. If separated, the quality of treated water will deteriorate. Therefore, C
The pH of the slightly acidified water flowing into the DI is 4 to 6.5,
In particular, it is preferable to set it to 5 to 6. Further, it is preferable that the weakly acidified water is passed through the CDI once every 10 to 30 days, and the duration of each water pass is preferably about 0.5 to 3 days. Note that it is preferable that a weakly acidifying means such as an acid adding means be provided immediately before the CDI as shown in FIG. 1, but it is not particularly limited thereto.

In the pure water production apparatus having the configuration shown in Fig. 1, industrial water,
Raw water, such as city water or well water, is treated in the ROI, and then an appropriate amount of acid is added at a predetermined period for a predetermined period through the pipe 10 to make it weakly acidic, and then supplied to the CDI 2.

Next, the process of inputting C to the CDI 2 will be explained with reference to FIG. As shown in the figure, in the CDI 2, a plurality of anion exchange membranes 111A and cation exchange membranes C are alternately arranged in parallel in a container 20, and concentration chambers 21 and dilution chambers 22 are alternately separated from each other. The dilution chamber 22 contains a mixture 2 of anion exchange resin and cation exchange resin.
3 is filled. 24 is one pole, and 25 is ten poles.

The pretreated raw water is transferred from the pipe 12 to the water supply pipe 12a to the concentration chamber 21 of the CDI 2 and the water supply pipe 1 to the dilution chamber 22.
2b, and are supplied to a concentration chamber 21 and a dilution chamber 22, respectively.

In the water supplied to the CDI 2, according to the principle explained in FIG. They pass through and are concentrated in the concentration chamber 21, respectively. H CO 3 produced by the conversion of C 0 2 also passes through the anion exchange membrane A and is concentrated in the concentration chamber 21 . The treated water from which anions and cations have been removed in this way is transported to the dilution chamber 2.
2 through piping 13, and after being post-treated as necessary, is sent to the point of use. The concentrated water in the concentration chamber 21 is discharged from the pipe 14.

In the embodiment shown in FIG. 1, a reverse osmosis membrane separator (RO
) 1 is provided. Although this RO is not essential and can be omitted, by installing an RO, electrolytic trade in raw water can be improved.
TOC components can be efficiently removed, the load on CDI can be reduced, and highly purified treated water can be obtained. When the RO is provided in this manner, the concentrated water of the CDI may be circulated upstream of the RO. In this case, it is possible to reduce the amount of wastewater and save the amount of raw water.

Note that as the reverse osmosis membrane to be attached to the RO, ordinary commercially available membranes such as polyamide membranes, cellulose acetate membranes, and arakudo membranes can be used.

By the way, when producing pure water using CDI, CO2 dissolved in raw water has an adverse effect on the treatment in CDI.

That is, in electrical regeneration using CDI, the balance of all adsorbed cations and all anions is preferably 1:1. If this ratio deviates significantly, it is presumed that more ions will remain unregenerated and leak into the treated water. When using industrial water as raw water, considering the balance between the cations and anions contained, C.
The presence of 02 has a big influence. Therefore, it is important to reduce CO2 contained in raw water as much as possible.
Required for stabilization treatment in

For this reason, in the present invention, by decarboxylating the raw water supplied to the CDI, dissolved CO
It is preferable to remove 2.

Alternatively, it is preferable to reduce the amount of dissolved CO2 by adding an alkali to the raw water supplied to the CDI to convert dissolved CO2 into HCO3-. In this case, by adding alkali to the raw water to make the pH about 7 or more, dissolved CO2 (H2 COs) is converted to HCO3-, and HCO2- can be easily removed by treatment with CDI.

In the present invention, it is particularly preferable to remove dissolved CO2 by decarboxylating the raw water.

Examples of the above decarboxylation means include the following means (1) to (2).

■ Vacuum degassing tower.

■ Decarboxylation tower. That is, aeration is performed using N2 gas. In this case, an acid is added and the p'H is lowered (pH: 5.0-55
It is advantageous to aerate the area (to a certain degree).

■ Membrane degassing tower.

An experimental example will be explained below.

Experimental Example 1 (Example of the Present Invention) Water in Atsugi City, Kanagawa Prefecture was treated using the pure water production apparatus of the present invention shown in FIG. As RO1, a reverse osmosis separator incorporating a spiral type 8-inch module having a crosslinked aramid composite membrane was arranged. From the pipe 10, sulfuric acid was intermittently injected into the RO treated water as an acid to make it weakly acidic to a predetermined pH.

In addition, as CDI2, polypropylene resin anion exchange membranes and cation exchange membranes (approximately 0.5 mF per membrane)
) are arranged alternately as shown in Figure 2.
In the diagram shown, only three dilution chambers are formed, but in this example, 30 anion exchange membranes and 30 cation exchange membranes were used to form 30 dilution chambers.)
, H-type strongly acidic anion exchange resin and OH-type strongly basic anion exchange resin mixed at a volume ratio of 40:60, approximately 3
Each dilution chamber was filled with 0°C.

The conditions for water flow through the CDI were as follows.

Water supply amount: 1.2rn'/hr Treated water flow rate 1. Orn'/hr Concentrated water flow rate: 0.2 m'/hr Voltage: 100 V Water temperature: 13 to 15°C After running water for 25 days using such a device (i.e., removing the acid from pipe 10) After passing water without injection (water passing process), acid was injected from piping 10 for three days to elute Si02 (S i 02 elution process), and then acid injection was stopped. water for 5 days.
(Water passage step II).

Table 1 shows the treated water quality, St○2 removal rate, etc. on the final day of the water flow process, SiO2 elution process, and water flow process II.

11 12 Table 1 As is clear from Table 1, the CD on the 25th day of water flow process I
The 'I treated water has a high Sto2 concentration and a low SiO2 removal rate, but the CDI treated water in the water passing step II has a low Sto2 concentration and Si02 is removed to a high degree. That is, by providing a SiO2 elution step in which weakly acidified raw water is supplied to the CDI and Si02 adsorbed in the ion exchange resin of the CDI is eluted, the St○2 removal rate of the CDI is recovered and the CDI treated water is It is clear that water quality will be significantly improved.

Note that the 1A water in the SiO2 elution step can also be passed through an anion exchange resin tower to remove SiO2.

[Effect of the invention] As detailed above, according to the pure water production apparatus of the present invention, C.
In the treatment using DI, it is possible to increase the removal rate of Si02 and to stably and efficiently produce extremely high-purity pure water with high specific resistance.

[Brief explanation of drawings]

Fig. 1 is a system diagram showing an example of the journey of the pure water production apparatus of the present invention, Fig. 2 is a system diagram showing an example of CDI, and Fig.
It is a block diagram explaining the principle of DI.

Claims (1)

[Claims] (1) A plurality of anion exchange membranes and cation exchange membranes are arranged alternately to form concentration chambers and dilution chambers alternately, and the dilution chamber is filled with a mixture of an anion exchange resin and a cation exchange resin. 1. A pure water producing apparatus equipped with an electrodialyzer according to the present invention, characterized by comprising means for making raw water supplied to the electrodialyzer weakly acidic.