JPH08168784A - Production of pure water - Google Patents

Abstract

PURPOSE: To prevent an undesirable influence to a deionizing stage due to a residual oxidizing agent and to improve a production efficiency by subjecting a raw water to a deionizing treatment after heat treating a raw water under the presence of the oxidizing agent to decompose a TOC content in the raw water and removing a residual oxide in a heated water. CONSTITUTION: The pure water is produced by deionizing the raw water after decomposing the TOC content in the raw water by heat treating the raw water under the presence of the oxidizing agent and removing the residual oxide incorporated in a heat treated water. That is, a recovered water from a semiconductor washing stage and a water in which a replenishing water such as industrial water is mixed with the recovered water is used generally as the raw water. Flocculation and filtration, etc., are executed in response to the quality of the raw water at a pre-treating stage 1. Moreover, a heating temp. at a thermally decomposing stage 2 is kept >=70 deg.C, for example, and a packed column of activated carbon, etc., is used at an oxidizing agent removing stage 3. Then, an ion exchange column and a reverse osmosis membrane separating device, etc., are used in combination at a deionizing stage 4, and a sterilization, etc., by UV oxidation is applied at a post-treating stage 5.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is pure water (including ultrapure water).
In particular, the present invention relates to a method for producing pure water capable of significantly reducing TOC (total organic carbon) in pure water produced.

[0002]

2. Description of the Prior Art In ultrapure water mainly used for cleaning semiconductor substrates, removal of TOC is as important as removal of other impurities (fine particles, ions, etc.). For this reason, in order to obtain treated water with TOC reduced to the target level, currently two-stage reverse osmosis membrane separation treatment and low-pressure ultraviolet oxidation treatment combined with an ion exchange tower are being performed. In addition, the cost required for operation is high, which is a factor of increasing the cost of the entire ultrapure water production system. Moreover, it has been found that these means cannot be used to further reduce the TOC.

Under these circumstances, the applicant of the present invention has previously proposed a method of thermally decomposing TOC in raw water by adding an oxidizing agent such as persulfate (PCT / JP94 / 001).
52. Hereinafter referred to as "first application". ). According to this method, by adding an appropriate amount or more of an oxidizing agent according to the TOC concentration of the raw water, the TOC can be obtained by a reaction at a predetermined temperature for a predetermined time.
Can be reduced to 5 ppb or less in one step, and since a heating step is included, biofouling can also be reduced.

[0004]

However, the above-mentioned thermal decomposition method of the prior application has a problem that the added oxidizing agent may remain in the water for thermal decomposition treatment. If this residual oxidant is passed as it is to the subsequent treatment step, the ion exchange resin and the reverse osmosis membrane in the deionization part will be oxidatively deteriorated, and problems such as an increase in TOC due to the elution of the deteriorated resin will occur. In order to completely eliminate this oxidant residue, it is necessary to enlarge the reaction vessel in order to make the residence time (reaction time) in the reactor sufficiently long, or to set the reaction temperature sufficiently high. However, an increase in the number of reaction vessels and an increase in reaction temperature are not industrially preferable.

The present invention solves the above-mentioned problems of the prior application, and in a method for producing pure water in which an oxidizing agent is added to raw water to thermally decompose and remove TOC components in the raw water and then deionized, residual oxidizing agent remains. It is an object of the present invention to provide a method for producing pure water capable of preventing the adverse effect on the deionization part in the subsequent step and relaxing the thermal decomposition reaction conditions.

[0006]

In the method for producing pure water of the present invention, raw water is heat treated in the presence of an oxidant to obtain TOC in the raw water.
After the components are decomposed, the residual oxidant contained in the heat-treated water is removed, and then deionized.

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

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

In the method of this embodiment, raw water is sequentially treated in a pretreatment step 1, a heat decomposition treatment step 2, an oxidant removal step 3, a deionization treatment step 4 and a posttreatment step 5. An oxidant addition means is provided on the inflow side of the heat decomposition treatment step 2.

As the raw water, generally, water recovered from the semiconductor cleaning process and a mixture of this with supplemental water such as industrial water, city water, and well water are used. After the pretreatment step, it is preferably introduced into the heat decomposition treatment step.

As the pretreatment step 1, any means can be provided depending on the quality of raw water, for example, flocculation, filtration,
Means such as levitation, adsorption and ion exchange can be adopted. The following are examples of specific pretreatment steps. In particular, with respect to the water recovered from the semiconductor washing step, H ₂ O ₂ contained in the activated carbon adsorption tower is removed by the following pretreatment, and then fluorine is removed in the strong anion exchange tower to the thermal decomposition treatment step. It is preferably introduced.

Coagulation / Pressure Flotation / Filtration Device Ion Exchange Tower Activated Carbon Adsorption Tower → Anion Exchange Tower In the present invention, sodium peroxydisulfate (Na ₂
S ₂ O ₈ ), potassium peroxydisulfate (K ₂ S ₂ O
Examples thereof include persulfates such as ₈ ) and hydrogen peroxide (H ₂ O ₂ ), and persulfates such as Na ₂ S ₂ O ₈ and K ₂ S ₂ O ₈ are preferable.

The amount of the oxidizing agent added is arbitrarily determined according to the raw water quality and the required treated water quality. In the present invention, however, the oxidizing agent removing step 3 is provided after the thermal decomposition treatment step 2. It is also possible to increase the amount of the oxidizing agent added, and by increasing the amount of the oxidizing agent added, it is possible to alleviate the thermal decomposition treatment conditions, that is, to lower the thermal decomposition treatment temperature. In the usual case, it is preferable to add about 50 to 300 parts by weight of S ₂ O ₈ ²⁻ per 1 part by weight of TOC in the raw water.

The heating temperature in the heat decomposition treatment step 2 is
The temperature is 70 ° C or higher, preferably 90 to 170 ° C, more preferably 110 to 150 ° C or 95 to 100 ° C. When the heating temperature is 110 to 150 ° C., the TOC decomposition and removal efficiency is high, and when the heating temperature is 95 to 100 ° C., there is an advantage that the treatment can be performed at normal pressure.

The reaction time of this thermal decomposition treatment varies depending on the heating temperature and the addition amount of the oxidizing agent, but usually 1 to
It is preferably 15 minutes, particularly 1 to 6 minutes when the heating temperature is 110 to 150 ° C., and 2 to 15 minutes when the heating temperature is 95 to 100 ° C.

In this heat decomposition treatment, a platinum-based oxidation catalyst such as a platinum-supported catalyst or a platinum plating catalyst may be brought into contact as a catalyst.

In the present invention, as the oxidizing agent removing step 3, a packed column packed with activated carbon and / or a suitable catalyst can be adopted.

The activated carbon may be granular, powdery or fibrous, but granular or fibrous is particularly advantageous in terms of water flow efficiency. There is no particular limitation on the type of activated carbon (coconut shell type, coal type, etc.). On the other hand, as the catalyst, various catalysts such as commonly used platinum catalyst and palladium catalyst can be used.

The purpose of the above-mentioned activated carbon and catalyst can be achieved by using either one of them, but depending on the case,
You may use both together. In addition, ultraviolet irradiation can also be adopted as the oxidizing agent removing means.

The water passing conditions in the oxidizing agent removing step 3 are sufficient so that the oxidizing agent remaining in the treated water in the heat decomposition treatment step does not cause oxidative deterioration of the ion exchange resin or the reverse osmosis membrane in the subsequent deionization treatment step 4. Any condition that can remove to a low concentration may be used, depending on the residual oxidant concentration in the treated water of the thermal decomposition treatment step and the specifications of the oxidant removal step, that is, the shape, particle size, filling amount of activated carbon and catalyst, etc. It is decided as appropriate. For example, when the treated water in the thermal decomposition treatment step containing 10 ppm of residual Na ₂ S ₂ O ₅ is treated in the 20/40 mesh granular activated carbon packed tower, it is preferable that SV = 40 hr ⁻¹ or less.

Since the heat-decomposed water is usually acidic with a pH of 4 or less, in order to protect such a residual oxidant removing device from corrosion, the pH between the heat-decomposing step and the oxidant removing step is adjusted. It is preferable to provide an alkali injecting means for adjustment, neutralize the acidic water, and then introduce the oxidant removal step.

In the present invention, it is preferable to remove the residual oxidant in such an oxidant removal step to reduce the residual oxidant concentration to a low concentration of 1 ppm or less.

In the deionization treatment step 4, an ion exchange column, a reverse osmosis membrane separation device, etc. can be used in combination as required. That is, for example, an ion exchange column → reverse osmosis membrane separation device, a reverse osmosis membrane separation device → ion exchange tower, or a reverse osmosis membrane separation device → reverse osmosis membrane separation device can be used.

As the post-treatment step 5, any means can be adopted depending on the required quality of treated water, such as sterilization by ultraviolet oxidation, TOC decomposition, or ion exchange, reverse osmosis membrane separation, Microfiltration membrane separation, ultrafiltration membrane separation equipment, etc., which generally correspond to the secondary pure water production process (subsystem) in ultrapure water production, that is, low-pressure ultraviolet irradiation device (organic matter decomposition) → mixed bed ion Exchange tower (non-regenerative ion exchanger: removal of decomposed organic matter) → ultrafiltration membrane separator (separation of fine particles of ion exchange resin flowing out from the ion exchange tower) is adopted.

Specific examples of the deionization treatment step and the post-treatment step are as follows.

Decarbonation tower → anion exchange tower → reverse osmosis membrane separation device → second pure water production process reverse osmosis membrane separation device → low pressure reverse osmosis membrane separation device → second pure water production process anion exchange tower → decarbonation tower → Cation exchange tower → Anion exchange tower → Reverse osmosis membrane separation device → Secondary pure water production process Weak anion exchange tower → Strong cation exchange tower → Strong anion exchange tower → Secondary pure water production process Reverse osmosis membrane separation device → Ion exchange tower (Mixed bed ion exchange tower or (strong cation exchange tower → strong anion exchange tower)) →
Secondary pure water production step Then, since the TOC component is removed in advance by the heat treatment in the deionization treatment step and the post-treatment step, the load is reduced and a small capacity small size apparatus can be adopted.

[0027]

By performing heat treatment in the presence of an oxidizing agent, TOC in raw water can be efficiently decomposed and removed.

According to the present invention, since the deoxidizing treatment is carried out after removing the residual oxidizing agent in the water subjected to the thermal decomposition treatment, the ion exchange resin, the reverse osmosis membrane and the like in the deionizing treatment step are deteriorated by the oxidizing agent due to the residual oxidizing agent. Effectively protected from. Therefore, the deionization efficiency can be maintained high, and high-purity pure water can be stably obtained without the problem of an increase in TOC due to oxidative deterioration.

By the way, as described above, in the method of the prior application,
In order to avoid the problem of residual oxidant, it was not possible to lower the heat decomposition treatment temperature, and it was necessary to perform heat decomposition treatment at a high temperature, but in the present invention, by providing an oxidant removal means. The thermal decomposition treatment under low temperature conditions of less than 110 ° C., which was considered to be unsuitable for practical use in the prior application, is possible, and the lower limit of the thermal decomposition treatment temperature can be lowered to about 70 ° C.

In the heat decomposition treatment, the oxidizing agent such as persulfate added to the raw water is used when the heat decomposition treatment is carried out at a sufficiently high temperature such as 130 ° C. or higher for 5 minutes or longer for a sufficiently long time. Almost all of them decompose in the heat decomposition treatment step regardless of their concentration, and even in this case, the oxidizing agent removing means according to the present invention effectively functions as a means for surely preventing the leakage of the oxidizing agent.

[0031]

EXAMPLES The present invention will be described more specifically with reference to Examples, Comparative Examples and Experimental Examples below.

Example 1 TOC derived from isopropyl alcohol was 1000 ppb.
The contained water was used as raw water and treated according to the present invention.

First, Na ₂ S ₂ O ₈ was added to raw water as an oxidizing agent.
Was added in an amount of 70 ppm and subjected to thermal decomposition treatment at a reaction temperature of 130 ° C. and a reaction time of 2 minutes. The water quality of this heat-decomposition-treated water was as follows.

Water quality of heat-decomposition-treated water TOC: about 5 ppb Na ₂ S ₂ O ₈ : about 10 ppm pH: 3.3 This heat-decomposition-treated water is applied to an activated carbon column having the following specifications by SV =
After water was passed for 10 hr ^-1 , water was passed through an ion exchange resin column having the following specifications at SV = 30 hr ^-1 .

Activated carbon column specification Glass column filled with 300 ml of coconut shell activated carbon (“Kuraray Coal GW 10/32” manufactured by Kuraray Chemical Co., Ltd.) Ion exchange resin column specification Strong acidic cation exchange resin and strong basic anion exchange resin are mixed Done (Diaion SMN manufactured by Mitsubishi Chemical Corporation)
After passing water through a glass column filled with 100 ml of -UP) for 10 days, the outflow water from the ion exchange resin column was collected and analyzed for TOC. The results are shown in Table 1.

Comparative Example 1 Water was continuously passed for 10 days in the same manner as in Example 1, except that the heat-decomposed water was directly passed through the ion exchange resin column without passing through the activated carbon column. The TOC was analyzed by collecting the effluent water from the ion exchange resin column. The results are shown in Table 1.

[0037]

[Table 1]

The following is clear from Table 1. That is,
In Comparative Example 1 in which water was not passed through the activated carbon column before being passed through the ion exchange resin column, the ion exchange resin was oxidized by the residual Na ₂ S ₂ O _{8 in the} heat-decomposition-treated water, and the organic matter was eluted, so that the outflow occurred. The water TOC was higher than the inflow water TOC, whereas in Example 1 in which water was passed through the activated carbon column and then through the ion exchange resin column, residual Na ₂ S ₂
Since the O ₈ was removed by the activated carbon column, the TOC was significantly reduced because the ion exchange resin did not undergo oxidation.

Experimental Example 1 Water in which Na ₂ S ₂ O ₈ was dissolved in ultrapure water to a concentration of 670 ppm in a column packed with activated carbon of coal type (“Kuraray Coal GW 10/32” manufactured by Kuraray Chemical Co., Ltd.) After passing water, the Na ₂ S ₂ O ₈ concentration of the activated carbon column outflow water was measured to determine its adsorption capacity. Table 2 shows the results.

[0040]

[Table 2]

From Table 2, 1300 to 1500 Bed Volum
Adsorbs water up to about e, Na ₂ S ₂ O ₈ <1p
It was confirmed that pm could be processed.

Experimental Example 2 TOC was 500 ppb (derived from isopropyl alcohol)
A thermal decomposition experiment with Na ₂ S ₂ O ₈ was performed using the water containing the raw water. Fix the reaction time at 6 minutes (however, No.
In No. 12, the reaction time was 12 minutes. ), Reaction temperature,
The amount of Na ₂ S ₂ O ₈ added was appropriately changed as shown in Table 3, and the results are shown in Table 3.

[0043]

[Table 3]

From Table 3, it is apparent that treated water having a TOC of 10 ppb or less (decomposition rate of 98% or more) can be obtained by increasing the amount of Na ₂ S ₂ O ₈ added even at a reaction temperature of less than 110 ° C.

Example 2 No. 9 treated water of Experimental Example 1 (97 ° C., Na ₂ S ₂ O ₈ 5
2 ppm addition of heat-decomposition treated water was passed through a column filled with activated carbon of the coal type (“Kuraray Coal KW 20/40” manufactured by Kuraray Chemical Co., Ltd.) at SV = 10 hr ⁻¹ , and then Example 1 Water was passed through an ion exchange resin column similar to that used in step SV = 30 hr ⁻¹ . The TOC and Na ₂ S ₂ O ₈ concentration of the sample water collected at important points were analyzed, and the results are shown in Table 4.

[0046]

[Table 4]

From Table 4, the combination of the thermal decomposition at a temperature of less than 100 ° C. and the activated carbon and the ion exchange resin in the subsequent stage, without causing the oxidative deterioration of the ion exchange resin,
It is clear that high-purity pure water having a TOC of 10 ppb or less can be obtained.

[0048]

As described in detail above, according to the method for producing pure water of the present invention, TOC in raw water is obtained by adding an oxidizing agent to raw water.
In the method for producing pure water in which the components are decomposed and removed by heating and then deionized, the high-purity pure water whose TOC is significantly reduced is stably and stably maintained for a long period of time by preventing the deoxidation process from being adversely affected by the residual oxidizing agent. It can be manufactured efficiently. Since it is not necessary to completely thermally decompose the oxidizing agent in the thermal decomposition step, the thermal decomposition reaction temperature can be set low. And the like, and is industrially extremely advantageous.

[Brief description of drawings]

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

[Explanation of symbols]

 1 Pretreatment Step 2 Heat Decomposition Treatment Step 3 Oxidizing Agent Removal Step 4 Deionization Treatment Step 5 Post Treatment Step

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication C02F 1/58 CDV A CDX Q

Claims (1)

[Claims] 1. A method of treating raw water by heat treatment in the presence of an oxidant to decompose TOC components in the raw water, removing residual oxidant contained in the heat-treated water, and then performing deionization treatment. Pure water manufacturing method.