JP3528287B2 - Pure water production method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to pure water (including ultrapure water).
More particularly, the present invention relates to a method for producing pure water capable of significantly reducing the TOC (total organic carbon) in pure water to be produced, compared with the current situation.

[0002]

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

[0003] Under such circumstances, the present applicant 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, it is referred to as “first application”. ). According to this method, by adding an oxidizing agent in an appropriate amount or more according to the TOC concentration of the raw water, the TOC is reacted for a predetermined time at a predetermined temperature.
Can be reduced to 5 ppb or less in one step, and since the heating step is included, biofouling can also be reduced.

[0004]

However, in the above-mentioned pyrolysis method of the prior application, there is a problem that the added oxidizing agent may remain in the pyrolysis-treated water. If this residual oxidizing agent is passed through the subsequent processing step as it is, the ion exchange resin and the reverse osmosis membrane in the deionized portion will be oxidatively degraded, causing a problem such as an increase in TOC due to elution of the degraded resin. In order to completely eliminate the residual oxidizing agent, it is necessary to increase the size of the reaction vessel or to set the reaction temperature sufficiently high in order to obtain a sufficiently long residence time (reaction time) in the reactor. However, an increase in the number of reaction vessels and an increase in the reaction temperature are not industrially preferable.

The present invention solves the above-mentioned problems of the prior application and provides a method for producing pure water in which a persulfate is added as an oxidizing agent to raw water to thermally decompose and remove the TOC component in the raw water and then deionize. It is an object of the present invention to provide a method for producing pure water that prevents persulfate from remaining, prevents adverse effects on a deionized part in a subsequent step, and enables relaxation of heat decomposition reaction conditions.

[0006]

According to the method for producing pure water of the present invention , persulfate is added to raw water in a ratio of S ₂ per part by weight of TOC in raw water.
O ₈ ^2-a were added 50 to 300 parts by weight, 85 to 100
After heat treatment to to decompose TOC components in raw water at ° C., the residual peroxide residual persulfate contained in heated water to remove
The sulfate concentration is set to 1 ppm or less , followed by deionization.

Hereinafter, the present invention will be described in detail with reference to the drawings.

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

In the method of this embodiment, raw water is sequentially treated in a pretreatment step 1, a thermal decomposition treatment step 2, an oxidizing agent removing step 3, a deionization treatment step 4, and a post-treatment step 5. Note that an oxidizing agent adding means is provided on the inflow side of the thermal decomposition process step 2.

As the raw water, generally used is water recovered from the semiconductor cleaning process and a mixture thereof with replenishment water such as industrial water, city water, well water and the like. After passing through the pretreatment step, it is preferable to introduce it into the heat decomposition treatment step.

In the pretreatment step 1, any means can be provided according to the quality of the raw water.
Means such as levitation, adsorption, and ion exchange can be employed. Specific pretreatment steps include the following (1) to (3) . In particular, with respect to the recovered water from the semiconductor cleaning step, after the H ₂ O ₂ contained in the activated carbon adsorption tower is removed by the pretreatment of the following (3) , fluorine is removed in the strong anion exchange tower to perform thermal decomposition. Preferably, it is introduced into the processing step. (1) Coagulation / pressure flotation / filtration equipment (2) Ion exchange tower (3) Activated carbon adsorption tower → anion exchange tower

In the present invention, the oxidizing agent to be added to the raw water in the thermal decomposition treatment includes sodium peroxydisulfate (Na ₂ S ₂ O ₈ ), potassium peroxydisulfate (K ₂ S ₂ O ₈ ) and the like. Ru using sulfuric acid salt.

The amount of the persulfate to be added is arbitrarily determined according to the quality of the raw water and the required quality of the treated water. In the present invention, the oxidizing agent removing step 3
To increase the amount of persulfate added,
By increasing the amount of persulfate added, the conditions for the thermal decomposition treatment can be relaxed, that is, the temperature of the thermal decomposition treatment can be lowered. Normally, persulfate, TOC1 parts by weight per the raw _water, 50 to 300 parts by weight of added pressure to the ^2-S 2 _{O 8}
You.

The heating temperature in the thermal decomposition treatment step 2 is as follows :
And 8 5~100 ℃. When pressurized heat temperature of 8 5 to 100 ° C. has the advantage that it can be processed at normal pressure.

[0015] The reaction time of the thermal decomposition treatment varies depending on the heating temperature and the amount of persulfate added.
It is preferably from 15 to 15 minutes, especially from 2 to 15 minutes.

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

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

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, coal, etc.). On the other hand, as the catalyst, various catalysts such as generally used platinum-based catalyst and palladium-based catalyst can be used.

Although the above-mentioned activated carbon and catalyst can achieve their purpose only by using either one of them, in some cases,
You may use both together. In addition, as the oxidizing agent removing means, ultraviolet irradiation can be adopted.

The water passing conditions in the oxidizing agent removing step 3 are such that the persulfate remaining in the treated water in the thermal decomposition step does not oxidatively degrade the ion exchange resin or the reverse osmosis membrane in the subsequent deionizing step 4. may be a condition that can be removed to a low concentration of less 1 ppm, and residual persulfate concentration in the treated water heating decomposition process, specification of oxidizing agent removing step, i.e.,
It is appropriately determined according to the shape, particle size, filling amount and the like of the activated carbon and the catalyst. For example, when treated water in a thermal decomposition treatment step containing 10 ppm of residual Na ₂ S ₂ O ₅ is treated in a 20/40 mesh granular activated carbon packed tower, it is preferable that the SV be about 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, a pH between the heat-decomposition treatment step and the oxidant removal step is reduced. It is preferable to provide an alkali injection means for adjustment, neutralize the acidic water, and then introduce it to the oxidizing agent removing step.

In the present invention, the removal of residual persulfate in such oxidizing agent removing step, you remove residual persulfate <br/> concentration to a low concentration of less 1 ppm.

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

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

The following (1) to (5) are specific examples of the deionization step and the post-treatment step. (1) Decarbonation tower → anion exchange tower → reverse osmosis membrane separation device →
Secondary pure water production process (2) Reverse osmosis membrane separator → Low pressure reverse osmosis membrane separator → Secondary pure water production process (3) Anion exchange tower → Decarbonation tower → Cation exchange tower → Anion exchange tower → Reverse osmosis membrane Separation equipment → secondary pure water production process (4) Weak anion exchange tower → strong cation exchange tower → strong anion exchange tower → secondary pure water production process (5) Reverse osmosis membrane separation equipment → ion exchange tower (mixed bed type ion Exchange tower or (strong cation exchange tower → strong anion exchange tower))
→ Secondary pure water production process

Since the TOC component is previously removed by heat treatment in the deionization treatment process and the post-treatment treatment device, the load is reduced and a small-capacity compact device can be adopted.

[0027]

[Action] By heat treatment in the presence of persulfate ,
TOC in raw water can be efficiently decomposed and removed.

According to the present invention, after removing the residual persulfate in the pyrolysis water, the deionization is performed.
Ion exchange resin and reverse osmosis membrane in the deionization process remain
It is effectively protected from oxidative degradation by persulfate . Therefore, high deionization efficiency can be maintained, and high-purity pure water can be stably obtained without a 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 the residual oxidant, the thermal decomposition treatment temperature could not be lowered, and it was necessary to perform the thermal decomposition treatment at a high temperature, but in the present invention, by providing the oxidant removal means, , thermal decomposition treatment at 1 0 0 ° C. or less of the low-temperature conditions has been considered practical unsuitable in the prior application also becomes possible, the lower limit of the thermal decomposition treatment temperature can be lowered to about 85 ° C..

[0030] Note that hits the thermal decomposition treatment, persulfate added to raw water, in the case of a sufficiently long time thermal decomposition treatment at a temperature sufficiently high such 5 minutes or more, for example 130 ° C. or higher, the concentration Irrespective of this, almost all of them are decomposed in the heat decomposition process, but also in this case, the oxidizing agent removing means according to the present invention effectively functions as a means for reliably preventing persulfate leakage.

[0031]

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

Reference Example 1 TOP derived from isopropyl alcohol was 1000 ppb
Water containing as raw water, was subjected to treatment.

First, Na ₂ S ₂ O ₈ was added to raw water as an oxidizing agent.
Was added, and a thermal decomposition treatment was performed at a reaction temperature of 130 ° C. for a reaction time of 2 minutes. The water quality of this pyrolysis treatment water was as follows. Thermal decomposition water quality TOC: about 5 ppb Na ₂ S ₂ O ₈ : about 10 ppm pH: 3.3

[0034] After passed through at SV = 10 hr ^-1 the thermal decomposition treated water activated charcoal column of the following specifications was passed through at SV = 30 hr ^-1 to an ion exchange resin column following specifications. Activated carbon column specification A glass column filled with 300 ml of coconut shell activated carbon (“Kuraray Coal GW 10/32” manufactured by Kuraray Chemical Co., Ltd.) Column specification A mixture of a strongly acidic cation exchange resin and a strongly basic anion exchange resin Diaion SMN manufactured by Mitsubishi Chemical Corporation
-UP) glass column packed with 100 ml

After continuous water passage for 10 days, the effluent from the ion exchange resin column was collected and analyzed for TOC. Table 1 shows the results.

Comparative Example 1 In Reference Example 1, water was continuously supplied for 10 days in the same manner as in Reference Example 1 except that the pyrolysis water was directly passed through the ion exchange resin column without passing through the activated carbon column. The effluent from the ion exchange resin column was collected and analyzed for TOC. Table 1 shows the results.

[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 water was passed through the ion-exchange resin column, the ion-exchange resin was oxidized by residual Na ₂ S ₂ O _{8 in the} heat-decomposed water and eluted organic substances, so that the outflow occurred. While the water TOC was higher than the influent TOC, in Reference 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
TOC was significantly reduced because the ion exchange resin was not oxidized because O ₈ was removed on the activated carbon column.

Experimental Example 1 Na ₂ S ₂ O ₈ was charged into a column packed with coal-based activated carbon (“Kuraray Coal GW 10/32” manufactured by Kuraray Chemical Co., Ltd.).
Was dissolved in ultrapure water, and water adjusted to a concentration of 670 ppm was passed therethrough. The concentration of Na ₂ S ₂ O _{8 in the} effluent of the activated carbon column was measured to determine the adsorption capacity. Table 2 shows the results.

[0040]

[Table 2]

From Table 2, 1300 to 1500 Bed Volum
e can be adsorbed up to about e, and Na ₂ S ₂ O ₈ <1p
pm.

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 contained water as raw water. The reaction time was fixed at 6 minutes (however, no.
In No. 12, the reaction time was 12 minutes. ), Reaction temperature,
The results were shown in Table 3 by appropriately changing the amount of added Na ₂ S ₂ O ₈ as shown in Table 3.

[0043]

[Table 3]

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

Example 1 No. 1 of Experimental Example 1 9 the treated water _{(97 ℃, Na 2 S 2} O 8 5
Coal-based activated carbon ("Kuraray Coal KW 20/40" manufactured by Kuraray Chemical Co., Ltd.)
After passing through a column packed with, at SV = 10 hr ^-1 , water was further passed through the same ion exchange resin column as used in Reference Example 1 at SV = 30 hr ^-1 . The TOC, NaNa ₂ S ₂ O ₈ concentration and the like of the sample water collected at important points were analyzed, and the results are shown in Table 4.

[0046]

[Table 4]

From Table 4, it can be seen that the thermal decomposition at a temperature lower than 100 ° C. and the combination of the activated carbon and the ion exchange resin at the subsequent stage do not cause the oxidative deterioration of the ion exchange resin.
It is clear that highly pure water having a TOC of 10 ppb or less can be obtained.

[0048]

As described above in detail, according to the method for producing pure water of the present invention, persulfate is added to raw water to reduce the TO
In the method for producing pure water in which the C component is decomposed by heating and then deionized, (1) high-purity pure water having significantly reduced TOC by preventing the adverse effect of the residual persulfate on the deionization step. It can be manufactured stably and efficiently for a long time. (2) Since the persulfate does not need to be completely thermally decomposed in the heat decomposition step, the heat decomposition reaction temperature can be set low. This is extremely advantageous industrially.

[Brief description of the drawings]

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

[Explanation of symbols]

1 Pretreatment process 2 Heat decomposition process 3 Oxidant removal process 4 Deionization process 5 Post-processing steps

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI C02F 1/58 CDV C02F 1/58 CDVA CDX CDXQ (56) References JP-A-57-1497 (JP, A) JP-A-63 -270596 (JP, A) JP-A-58-223482 (JP, A) WO 94/018127 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 1/72-1 / 78,1 / 58

Claims (1)

(57) [Claims] 1. Persulfate in raw water 1 weight of TOC in raw water
50 to 300 parts by weight as S ₂ O ₈ ^2- per part,
After decomposing the TOC component in the raw water by heat treatment at 5 to 100 ° C., remove the residual persulfate contained in the heat-treated water to reduce the residual persulfate concentration to 1 ppm or less, and then perform deionization treatment. A method for producing pure water.