JP2733573B2 - Ultrapure water production method and apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus for producing ultrapure water.

(Prior Art) Conventionally, pure water with high purity has been demanded in various fields. In particular, recently, extremely high-purity ultrapure water quality standards required in semiconductor manufacturing, pharmaceutical fields, etc.
In addition to satisfying the standards of electrical conductivity and silica, the demand for TOC (total organic carbon), removal of viable bacteria, and the like is becoming higher.

For this purpose, a system for producing ultrapure water, which combines various units such as a membrane treatment device using an ion exchange resin and a reverse osmosis membrane, an ultraviolet sterilizer, and an ultraviolet organic substance decomposer, is used.

An example outline of this system is described as follows. That is, raw water that has been subjected to appropriate pretreatment with a sedimentation / sedimentation treatment device, a filtration device, and if necessary, an activated carbon filtration device, etc.
Treated with, for example, a two-bed three-bed pure water production system (2B3T) or a mixed-bed pure water production system (MB) using an ion exchange resin, and obtaining pure water (hereinafter referred to as “primary pure water” for convenience) ) Is passed through a reverse osmosis membrane device to remove organic substances and the like, and to remove remaining impurities, an ultraviolet irradiation device for decomposing and sterilizing organic materials, a polisher, an ultrafiltration membrane device, or a reverse osmosis membrane device. Ultrapure water is produced by passing through a terminal treatment device that combines the above.

In the above system, since the reverse osmosis membrane device is installed at the subsequent stage of the pure water production device using the ion-exchange resin, compared with the system installed at the previous stage of the pure water production device, the middle stage RO type ultrapure water device and It may be called. As is well known, a reverse osmosis membrane device supplies raw water to a reverse osmosis membrane under a pressure higher than the osmotic pressure,
Organic matter, salts and fine particles are blocked by a reverse osmosis membrane to obtain treated water on the permeate side, and the above-mentioned organic matter and the like are discharged to the specific permeate side. With the recent improvement of reverse osmosis membranes, the middle-stage RO system has been recognized for its features such as high organic matter removal capacity and a large amount of permeated water at a large concentration ratio.

(Problems to be Solved by the Invention) Incidentally, in the above-mentioned middle-stage RO type ultrapure water production apparatus, it is necessary to sterilize and clean the element of the apparatus with chlorine or hydrogen peroxide for sterilization. Since the amount of permeated water of the reverse osmosis membrane device gradually decreases with the operation, it is usually necessary to stop and clean the device every certain operation period, and there is a problem that the operation efficiency decreases accordingly. . It is considered that this decrease in the amount of permeated water over time is due to the clogging of the reverse osmosis membrane with some substance, which is caused by the elution of unreacted substances and the like used in the production thereof from the ion exchange resin, the semiconductor cleaning step. When the recovered water is reused, mixing of a surfactant or the like contained in the washing water, elution of a trace substance from a tube constituting the process, or the inner surface of the tank may be considered.

In addition, according to the inventors' repeated studies on ultrapure water production equipment, for example, the TOC standard of ultrapure water used as cleaning water in a semiconductor production process was required in the case of producing a 256 KB memory IC. The 50 to 200 ppb level is about 30 to 50 ppb in a 1 Mbyte memory IC, and the water quality standard required for ultrapure water becomes even higher as the degree of integration of LSIs increases, but the ultrapure water of the above middle RO method When the water production system is implemented as it is, the reverse osmosis membrane with weak anion polarity has a permeate side TOC exceeding 50 ppb, so that permeate water (ultra pure water) satisfying the above high water quality standard cannot be obtained. I understood that. A reverse osmosis membrane having a strong anion polarity satisfies high water quality standards, but has a problem that it is difficult to obtain a large amount of permeated water.

Therefore, the present inventors have conducted intensive studies on these problems, and found that the problem of the decrease in the amount of permeated water is derived from the fact that organic substances are adsorbed in the reverse osmosis membrane, which causes clogging. Was. According to the analysis, the organic substance mainly has an amine as a functional group, and it is considered that the organic substance ion-exchanges with the carboxylic acid group of the functional group of the reverse osmosis membrane to cause clogging.

Therefore, the present inventors prepared the water to be treated at a pH at which the ion-exchange action of the carboxylic acid group, which is a weakly acidic functional group, cannot be exerted so that the amine-based organic substance is not adsorbed to the reverse osmosis membrane. It is thought that the problem can be improved and the present invention has been made.

Also, when performing this pH adjustment, surprisingly,
The reverse osmosis membrane with weak anion polarity, which was considered to be insufficient to satisfy the high water quality standards as described above, exhibited a remarkable TOC removal ability improved to the same extent as a strong anion polarity reverse osmosis membrane, and It has been found that a large permeated water state is maintained.

Japanese Patent Application Laid-Open No. 58-6297 describes that the pH of treated water is adjusted to pH 5 to 7 for the purpose of preventing membrane degradation due to hydrolysis of a cellulosic reverse osmosis membrane, which was common at that time. There is no suggestion of the invention, and no other proposals for adjusting the pH of pure water at the time of producing ultrapure water have been made.

The present invention has been made based on the above findings,
Its purpose is to provide a method and an apparatus suitable for the production of high-purity ultrapure water from which TOC contained in pure water has been efficiently removed. An object of the present invention is to provide a method and an apparatus for producing ultrapure water which is excellent for producing cleaning water in a process.

Another object of the present invention is to provide a method and an apparatus for producing ultrapure water that can operate the apparatus without clogging the reverse osmosis membrane during TOC removal and without reducing the amount of permeated water. .

Still another object of the present invention is to use a reverse osmosis membrane having a relatively weak anion polarity and further use an amphoteric membrane, and to significantly improve the TOC removal rate while maintaining a large amount of permeated water. It is an object to provide a manufacturing method and an apparatus.

(Means for Solving the Problems) The feature of the method for producing ultrapure water of the present invention made for the realization of the object is a process of passing pure water treated with an ion exchange resin through a reverse osmosis membrane. In the method for producing ultrapure water provided with, an amphoteric membrane having a carboxylic acid group or an anionic polar membrane having a carboxylic acid group is used for the reverse osmosis membrane, and pure water passed through the reverse osmosis membrane is subjected to ion exchange of the carboxylic acid group. The pH is adjusted so that the function cannot be substantially exhibited.

The amphoteric membrane having a carboxylic acid group and the anionic polar membrane having a carboxylic acid group used in the present invention refer to a synthetic membrane, not a natural membrane such as cellulose acetate.

In general, to improve the water permeability of the synthetic membrane,
Although it has an anionic group such as a carboxylic acid group or a cationic group such as an amine group, the amphoteric film having a carboxylic acid group in the present invention is substantially compatible with the carboxylic acid group and the cationic group. The term “anionic polar membrane having a carboxylic acid group” refers to a reverse osmosis membrane having a carboxylic acid group stronger than the cationic group. Further, anionic polar films having a carboxylic acid group are generally classified into a film having a weak anionic polarity and a film having a strong anionic polarity according to the relative strength of the carboxylic acid group.

Although there are various types of the synthetic film used in the present invention, a film having excellent oxidation resistance for sterilization and washing is preferable, and in general, a polyvinyl alcohol-based synthetic film is preferably used.

In the above, the pH of the water to be treated passed through the reverse osmosis membrane device is preferably adjusted by adding sulfuric acid. PH to be prepared
Is prepared under conditions that maintain the state in which the ion exchange function of the carboxylic acid group cannot be exhibited, although this is not necessarily the same depending on the type of the reverse osmosis membrane. In particular, when an anionic polar membrane is used as a reverse osmosis membrane, the pH is usually 5 or less, preferably 4.5.
It is often appropriate to adjust it to about 5 or less. Also
As described in JP-A-58-6297, for example, the pH is adjusted by passing a part of the treated water from the decarbonation tower of a two-bed, three-bed pure water production system through an anion exchange resin tower. Alternatively, it may be carried out by bypassing and mixing with the outlet water of the anion exchange resin tower.

The present invention is applied without limitation as long as it is a field using ultrapure water, but is particularly suitable as an effective method for satisfying the TOC water quality standard required for ultrapure water used for cleaning water in a semiconductor manufacturing process. Applied to In this case, the cleaning water recovered in the semiconductor manufacturing process can be reused as raw water. This recovered washing water is used by being mixed with ordinary raw water.

A feature of the present invention also resides in an ultrapure water production apparatus having the following configuration for realizing the above method.

That is, a pure water production apparatus using an ion exchange resin,
A pH adjusting means for adjusting the pH of the pure water obtained by the pure water producing apparatus, and a reverse osmosis membrane device for passing the pH adjusted pure water,
The reverse osmosis membrane of the reverse osmosis membrane device is constituted by an amphoteric membrane having a carboxylic acid group or an anionic polar membrane, and the pH adjusting means adjusts the pure water to a pH at which the ion exchange function of the carboxylic acid group cannot be exhibited. It is a device having a configuration.

The above-mentioned pure water production apparatus is a two-bed three-bed pure water production apparatus (2B3T) using an ion exchange resin, and a mixed-bed pure water production apparatus (M
B) or a combined pure water production apparatus thereof is exemplified.

Specifically, an acid addition device such as sulfuric acid is preferably used as the pH adjusting means.

(Function) The present invention is to maintain the amount of permeated water and improve the TOC of permeated water without exerting the ion exchange function of the reverse osmosis membrane used mainly for removing organic substances in the subsequent stage by adjusting the pH as described above. Can be.

(Examples) Hereinafter, the present invention will be described based on examples shown in the drawings.
This example is formed as a system for supplying ultrapure water as cleaning water to a cleaning process in semiconductor manufacturing.

FIG. 1 is a flow chart showing an example of a schematic configuration example of an ultrapure water production apparatus configured according to the present invention.

In this figure, reference numeral 2 denotes a pure water production apparatus, and raw water treated through a sedimentation apparatus (not shown) is passed through a filter F, a cation exchange tower K, a decarboxylation tower D, and an anion exchange tower A in this order. Treated and obtained primary pure water in primary pure water storage tank ST ₁
Accumulate in

Next, this is passed through a reverse osmosis membrane device RO by a pump P via a microfilter MF.

The reverse osmosis membrane device RO of this example has, for example, an anion polar membrane having a carboxylic acid group as an ion exchange group, and sulfuric acid is added to the inlet water of the reverse osmosis membrane device RO from the sulfuric acid addition device 1. By doing so, the pH is adjusted to 4.5-5.

Permeate through the reverse osmosis unit is introduced into the subsystem 3 is the terminal apparatus of ultrapure water, vacuum Datsuki搭VD, the secondary pure water tank ST ₂ after passing through a mixed bed polisher MBP Can be stored. This is further sent to a semiconductor cleaning process, which is a use point, through an ultraviolet irradiation device UV, a cartridge polisher CP, and an ultrafiltration membrane device UF.

Example 1 In the system shown in FIG. 1, a reverse osmosis membrane device RO was made of a membrane having a weak anion polarity (NTR-729 manufactured by Nitto Denko Corporation), and the pH of the inlet water of the reverse osmosis membrane device RO was adjusted by adding an acid. 4.5 ~
The treatment was carried out while maintaining at 5. The test conditions and results are shown in Table 1 below.

Comparative Example 1 A test was conducted in the same manner as in Example 1 except that the pH of the inlet water of the reverse osmosis membrane device RO was changed to 7.2 to 8.0, and the results are shown in Table 1 above.

As is clear from these Example 1 and Comparative Example 1, by setting the inlet water to pH 4.5 to 5, the TOC of the treated water quality on the permeation side becomes 34 to 37 ppb, and the comparative example without pH adjustment was used. It can be seen that the organic matter removing ability was greatly improved as compared with the case of No. 1 of 60 to 80 ppb.

Example 2 Example 1 except that the membrane used for the reverse osmosis membrane device RO was changed to a membrane having a strong anion polarity (NTR-739: manufactured by Nitto Denko Corporation).
A test was conducted in the same manner as in Example 1. As shown in Table 2 below, substantially the same results as in Example 1 were obtained for the TOC of the treated water quality on the permeation side.

Comparative Example 2 A test was conducted in the same manner as in Example 2 except that the pH of the inlet water of the reverse osmosis membrane device RO was changed to 6.9 to 8.0, and the results are shown in Table 2 below.

Example 3 In order to measure the change in the amount of permeated water with time of the reverse osmosis membrane device RO, a membrane having a weak anion polarity (NTR-729: reverse osmosis in the device of Example 1 using Nitto Denko Corporation) was used. The TOC of the inlet water of the membrane device RO was adjusted to 50 ppb by adding an amine-based epoxy resin curing agent (Chemikrete E: manufactured by ABC trading company) to the water to be treated, and this was adjusted to pH 4.5 to 5 (Example 3). )When
It was adjusted to pH 6.9 to 8.0 (Comparative Example 3) and passed through a reverse osmosis membrane device to measure the change in the amount of permeated water.

The results are as shown in FIG. 2. In the comparative example, the permeated water amount was reduced by about 20% in one month.
In the examples, the amount of permeated water hardly decreased.

(Effect of the Invention) According to the present invention, TO contained in pure water which is water to be treated
C can be removed to produce high-purity ultrapure water,
In particular, in the production of cleaning water in the semiconductor production process, which requires increasingly strict standards for the quality of ultrapure water or the like, the results are extremely large.

In addition, there is also an effect that the amount of permeated water does not decrease because the RO is not clogged when removing the TOC, and the apparatus can be operated at a high concentration ratio.

Further, according to the present invention, even if RO having a relatively low anion polarity, which is generally regarded as having a low TOC removal rate, is used, by adjusting the pH of the water to be treated to 5 or less and passing it through it, the amount of permeated water can be reduced. It is possible to significantly improve the TOC removal rate and maintain the same effect as a RO membrane with high anion polarity while maintaining the same, thus making it possible to effectively use the feature that the amount of water permeated by a RO membrane with weak polarity is large. This is an extremely excellent effect.

[Brief description of the drawings]

FIG. 1 is a flow chart showing an example of the configuration of an ultrapure water production apparatus according to the present invention, and FIG. 2 is a comparison of the results obtained by measuring the change in the amount of permeated water for the embodiment of the present invention and the conventional example. FIG. 1: Acid addition equipment 2: Pure water production equipment, 3: Subsystem F: Filter, K: Cation exchange tower D: Decarbonation tower, A: Anion exchange tower ST ₁ : Primary pure water storage tank, MF: Precision Filter RO: Reverse osmosis membrane device, VD: Vacuum deaeration tower MBP: Mixed-bed polisher ST ₂ : Secondary pure water storage tank, UV: Ultraviolet irradiation device CP: Cartridge polisher UF: Ultrafiltration membrane device

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-62-61691 (JP, A) JP-A-64-75092 (JP, A) JP-A-62-204893 (JP, A) JP-A-63-1986 39685 (JP, A) JP-A-63-59387 (JP, A) JP-A-61-287492 (JP, A)

Claims (11)

(57) [Claims] 1. A method for producing ultrapure water comprising passing pure water treated with an ion exchange resin through a reverse osmosis membrane, wherein the reverse osmosis membrane has an amphoteric membrane having a carboxylic acid group or an anion polarity having a carboxylic acid group. A method for producing ultrapure water, comprising using a membrane, preparing the pure water at a pH at which the ion exchange function of the carboxylic acid group cannot be exerted, and passing the purified water through the reverse osmosis membrane. 2. The method according to claim 1, wherein the pH is 5 or less. 3. The method for producing ultrapure water according to claim 1, wherein the pH is adjusted by adding an acid. 4. The method according to claim 3, wherein the acid is sulfuric acid.
3. The method for producing ultrapure water according to 1. 5. The method for producing ultrapure water according to claim 1, wherein the pure water contains a polymer having an amino group as a functional group. 6. The method according to claim 1, wherein said pure water is a mixture of recovered water obtained from a semiconductor manufacturing process.
6. The method for producing ultrapure water according to any one of claims 1 to 5. 7. The method for producing ultrapure water according to claim 1, wherein said reverse osmosis membrane is a polyvinyl alcohol-based membrane. 8. The method for producing ultrapure water according to claim 1, wherein pure water adjusted to pH 4.5 to 5 is passed through a reverse osmosis membrane of anionic polarity. 9. An apparatus for producing pure water using an ion exchange resin,
A pH adjusting means for adjusting the pH of the pure water obtained by the pure water producing apparatus, and a reverse osmosis membrane device for passing the pH adjusted pure water,
The reverse osmosis membrane of the reverse osmosis membrane device is constituted by an amphoteric membrane having a carboxylic acid group or an anionic polar membrane having a carboxylic acid group, and the pH adjusting means is adjusted to a pH at which the ion exchange function of the carboxylic acid group is not exhibited. The apparatus for producing ultrapure water used in the method according to claim 1, wherein pure water is prepared. 10. The apparatus for producing ultrapure water according to claim 9, wherein the reverse osmosis membrane is a polyvinyl alcohol-based membrane. 11. The ultrapure water production apparatus according to claim 9, wherein the apparatus is used for producing semiconductor cleaning water.