JP2921763B2 - Ultrapure water production method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a method for producing ultrapure water having a very high degree of purification in a pure water production system for the semiconductor industry, which particularly requires ultrapure water.
It relates to a method of manufacturing in stages.

(Prior Art) In general, in the semiconductor industry, as the degree of integration is improved, pure water for producing the same is required to be more and more pure, and the process is becoming a process having a complicated combination.

In particular, recently, a semipermeable ultra-permeable membrane has come to be used as the final filter, and in particular, the ability to cut fine particles, colloidal substances, and TOC removal has become important.

In general, an ion exchange resin called a polisher is used before the ultra-membranous membrane as a final filter, and before that, a mixed bed type ion exchange resin, a reverse osmosis membrane, or the like is used.

The polisher is composed of a mixture of a cation exchange resin and an anion exchange resin, and is replaced and filled with a new resin by a trader after an appropriate period of use. The purpose of this polisher is to thoroughly cut ionic substances in water.In the semiconductor industry, the electric resistivity of this treated water is usually increased to 17 mΩcm or more, and generally to 18 mΩcm or more. I have to do it.

In the combination of the above ion exchange resin and the subsequent semipermeable membrane, the following points are important issues. That is, it is a measure against the elution component (TOC) from the ion exchange resin, and this causes clogging of the ultra-perm membrane, and eventually causes insufficient removal of the TOC and the like. This eluted component includes an eluted component (low-molecular-weight organic substance) generated inside the polisher, but includes, for example, an eluted component (residue) in the preceding process, for example, during regeneration washing in a mixed-bed ion exchange tower. Have been.

There is also a method of reducing the fine particles of the resin for the purpose of reducing the eluted components, but there is a limit due to the increase in pressure.

Further, a method of irradiating ultraviolet rays before the polisher has been studied, but it is still insufficient in removing TOC.

Recently, high-purity water has been obtained by installing a reverse osmosis membrane in two stages in the previous stage and installing multi-stage polishers in the subsequent operation, but the process becomes complicated and expensive. This is extremely disadvantageous in terms of efficiency.

As described above, since it is manufactured in a complicated process, the management of water quality is inevitably complicated. In addition, the reverse osmosis membrane is used for the purpose of ion removal, but in the case of high-purity water, it is difficult to extremely increase the level, and since high exclusion is required, the water permeability is small, It becomes impossible economically.

(Problems to be Solved by the Invention) An object of the present invention is to provide the above-mentioned high-purity water, specifically 18
Extremely simple and easy to handle, ultra-pure water with an electrical resistivity value of mΩcm or more and TOC is greatly reduced, and water quality is greatly reduced in a single step. It is to provide an excellent method for producing ultrapure water.

(Means for Solving the Problems) The present inventors have found that the above-mentioned problems are achieved by the following means, and have completed the present invention.

That is, the present invention provides: (1) In a pure water production step of removing ions and low molecular organic components in water, after irradiating raw water with ultraviolet light, polyethylene glycol having an average pore size of 5 μm or less and an average molecular weight of 6000 is used. The present invention relates to a method for producing ultrapure water, wherein a filtration treatment is performed using both a microporous membrane having an anion or cation exchange function or a microporous membrane having an anion exchange function, which has a removal rate of 90% or less.

 Preferred embodiments of the present invention are as follows.

(A) In the method of the above (1), the anion or cation exchange functional microporous membrane contains 0.1 to 5 milliequivalents of an anion or cation exchange functional group per 1 g of the microporous membrane, and has a porosity. It is a microporous film having a thickness of 10 μm to 5 mm with a thickness of 20% to 80%.

(B) In the method of the above (1), the quality of the raw water irradiated with the ultraviolet ray has an electric resistivity at 25 ° C. of 17.5 mΩ · cm.
Hereinafter, the TOC component is 10 ppb or more.

In the present invention, the ultraviolet irradiation used as the treatment before the overtreatment by the anion or cation exchange functional microporous membrane is for oxidizing the organic components in the raw water. For this purpose, a low-pressure mercury lamp generating 1849 nm is preferable if possible, and is effective even in the case of a small amount of dissolved oxygen. Of course, in a special case, a wavelength of 250 μm may be used and the power of an oxidizing agent such as ozone may be used. Thereby, most of the organic components are oxidized to carbonate ions and the like.

As the microporous membrane having an anion or cation exchange function used in the present invention, preferably, the material of the porous membrane as a base material is polyolefin, a copolymer of olefin and halogenated olefin, polyvinylidene fluoride or polysulfone. It is preferable to use a microporous membrane in which a functional group having a cation or anion exchange function is chemically bonded to at least a part of the inner and outer surface portions of the membrane and the surface portion of the pores inside the membrane. Bonding to the membrane may be direct or a case where a polymer containing a functional group is bonded as a side chain.

Further, a functional group may be added indirectly to the membrane surface or the pore surface by means such as coating or surface polymerization treatment.

More preferably, the material of the porous membrane is a polyolefin, and the membrane structure forms a three-dimensional network structure, and cations or cations are formed on at least a part or the front surface of both the inner and outer surfaces of the membrane and the surface of the pores inside the membrane. The treatment and purification are preferably performed using a microporous membrane to which a functional group having an anion exchange function or a polymer having such a functional group is chemically bonded.

Examples of the functional group having a cation exchange function in the present invention include a sulfone group, a carboxylic acid group, and an H ⁺ type of a phosphoric acid group (including polyvalent and chelated). The functional groups having an anion exchange function include -N ⁺ , R ₃ X ^- ,-
NR ₂ , -NHR and the like (where N is a nitrogen atom, RH
A hydrocarbon group, X is a halogen or a hydroxyl group).

Each of these functional groups must contain from 0.1 to 5 meq / g of membrane. If it is less than this range, the ion removal capability of the membrane will be reduced.

The average pore size of the microporous membrane is less than 5 microns and 6,
The removal rate of polyethylene glycol having an average molecular weight of 000 is 90% or less.

Preferably, it is selected from the range of 0.01 μm to 1 μm. When the pore size is smaller than this range, the water permeability is not sufficient for practical performance, and when the pore size is larger than this range, an increase in the electrical resistivity becomes a problem.

There are many methods for measuring the average pore size.In the present invention, ASTM F-316 is used as long as the pore size can be measured.
-70. It is based on a method called air flow method, which is measured from the air permeation flux of a dry film and a wet film when the air pressure is changed.

In the case of a small pore diameter, polyethylene glycol having an average molecular weight of 6,000 is set to a concentration of 0.1%, and a linear velocity of 1 m / sec is set to 1 kg / cm ^2.
It is calculated from the concentration of the polyethylene glycol solution when passed at 25 ° C. under the differential pressure of

The porosity of the microporous membrane is 20% to 80%, preferably 50% to 80%.
% Are used. Here, the porosity is
The film is immersed in a liquid such as water in advance, then dried, and measured based on a change in weight before and after the drying. When the porosity is out of the above range, it is not preferable in terms of the transmission speed and the mechanical properties. The film thickness is 10μ to 5m
It is preferably in the range of m.

As the shape of the microporous membrane, a flat membrane shape (including a pleated shape and a spiral shape), a tube shape, a hollow fiber shape and the like are used.
Particularly, a hollow fiber shape is preferable.

The pore structure of the porous membrane serving as a substrate can be variously formed by a molding method. For example, when the base polymer is polysulfone, a mixed solution is formed using a solvent or the like, and then discharged from a nozzle in the form of a hollow fiber, and a three-dimensional network structure film is formed by employing a so-called wet method of molding with a coagulant or the like. can do. In the case of polyolefin, it is possible to form a porous film by a stretching method or a so-called etching method made by a chemical treatment after electron beam irradiation, but the pore structure is directly obtained by a stretching method or an etching method. Rather than a through-hole type pore structure, for example, it is formed by a microphase separation method or a mixed extraction method disclosed in JP-B-59-37292, JP-B-40-957 and JP-B-47-17460. Those having a three-dimensional network structure are preferable in terms of practical performance.

In particular, it is preferable to use a film having the structure shown in JP-A-55-131028.

As a method for introducing a functional group having a cation exchange function into a side chain of the polymer constituting the porous membrane, a known method is employed. For example, as a method for introducing a sulfone group into the side chain of polyethylene, a method of reacting with sulfuric anhydride in a non-reactive solvent or sulfuric acid, or a method of reacting sulfuric anhydride in a gaseous state, is mentioned. The method of irradiating with a wire or the like, grafting, and then performing the above-mentioned sulfonation is preferable in terms of physical properties.

In the case of introducing a carboxylic acid group, for example, a method of irradiating a film with an electron beam or the like in advance and then grafting acrylic acid in a gas phase is employed.

On the other hand, an anion exchange functional microporous membrane is obtained by irradiating a porous membrane composed of a polyolefin or a copolymer of olefin and a halogenated olefin with ionizing radiation, and then grafting styrene into a gas phase to perform chloromethylation. After doing
It is obtained by adding an organic amine.

In order to introduce the functional group into the side chain of the polymer constituting the porous membrane, it may be introduced before molding into the membrane, but at least the outer surface of the membrane and the surface portion of the pores after molding into the membrane. A method of chemically adding a bond to a part is preferable.
It is desirable that the functional groups are bonded as uniformly as possible to the surfaces of the membrane and the pores.

The amount of the functional group having a cation or anion exchange function in the present invention refers to a milliequivalent per 1 g of a microporous membrane, where 1 g of the membrane is a value based on a fairly macro weight of the membrane. Yes, for example, does not mean the weight of a portion of the membrane surface or only a portion of the pore surface.
In order to bind a functional group having a cation or anion exchange function while maintaining the excellent functional properties of the membrane, it is preferable to make the functional groups exist as uniformly and preferentially as possible on the surface of the pores of the membrane. So, of course, partial heterogeneity is acceptable. Therefore, the meaning of the film 1g here indicates a value measured by taking the entire surface of the film into consideration uniformly, and does not mean the weight from an extremely microscopic viewpoint.

The role of the microporous membrane having cation or anion exchange function in the present invention is very important. That is, when the anion or cation exchange functional microporous membrane is used, excellent ion removal characteristics are obtained as compared with the case where an ion exchange resin is used, and above all, the amount of the regenerating solution can be significantly reduced, And it is completely reproduced. This is a great advantage in reducing the elution component (TOC).

Further, the anion or cation exchange functional microporous membrane has a pore size so small as to be incomparable compared to ion exchange resins (resin is several tens μm to 100 μm,
Since the film has a thickness of 5 μm or less, leakage of the eluted components can be remarkably reduced.

In the present invention, it is generally preferable to use an anion exchange functional microporous membrane in the former stage, but in some cases, a microporous membrane having a cation exchange function may be used in the former stage. The anion exchange functional microporous membrane alone can be used depending on the process before the ultraviolet irradiation.

Further, depending on the process, a semi-permeable membrane such as an ultra-permeable membrane is further used.

In the present invention, in both the anion or cation exchange functional membrane, the electrical resistivity at 25 ° C. is 7 mΩcm or less,
After irradiating raw water of C10ppb or more with ultraviolet light, the electrical resistivity of water obtained by overtreatment is 18mΩcm or more, TOC component is 3p
pb, often less than 2 ppb.

Further, when using both an anion exchange functional microporous membrane and a cation exchange functional microporous membrane, refer to Japanese Patent Application No. 63-126000.
It is possible to perform the processing in one stage by using a module disclosed in Japanese Patent Application Laid-Open Publication No. HEI 10-26139. The electrical resistivity is measured using a commercially available measuring instrument of each company. TOC is wet oxidation TOC
A meter is used.

(Example) After pre-mixing a composition of 22.0 parts by weight of finely divided silica (Nipsil VN3LP), 55.1 parts by weight of dibutyl phthalate (DBP), and 23.0 parts by weight of polyethylene resin powder [SH-800-grade, manufactured by Asahi Kasei Corporation] 0.7m inner diameter with 30mm twin screw extruder
After extruding into a hollow fiber shape having a thickness of 0.25 mm and a thickness of 0.25 mm, it was immersed in 1,1,1-trichloroethane [chlorocene VC (trade name)] for 60 minutes to extract DBP. Furthermore, after extracting fine silica powder immersed in a 40% aqueous solution of caustic soda at a temperature of 60 ° C for about 20 minutes, washing with water,
Dried.

The obtained porous film is irradiated with an electron beam at 100 kgy under a nitrogen atmosphere using an electron accelerator (pressurizing voltage 1.5 MeV, electron beam current 1 mA), and then styrene (containing 10% divinylbenzene).
Was grafted to the membrane almost completely in a gas phase at 60% by weight, washed and dried, and then sulfonated with SO ₃ in EDC to give an average pore diameter of 0.15 μm, a porosity of 62%, and a sulfone group of 1.6 meq /
1 g of a film (Example film (A)) was obtained.

Here, the quantification of the sulfone group of the example membrane (A) was as follows.

(Quantification of sulfone group)

1 g of the sulfonated porous membrane was immersed in 1N HClaq. To make it H-shaped, washed with water, and then immersed in 1N CaCl ₂ aq.
l was titrated with 0.1 N NaOHaq. using phenolphthalein as an indicator.

Next, an untreated film to which the functional group was not added was used during the production of the film (A) of the example, and the obtained porous film was subjected to an electron accelerator (pressing voltage 1.5 MeV, electron beam current). 1m
After irradiating an electron beam with 20 Mrad in a nitrogen atmosphere using the method A), styrene was grafted in the gas phase so as to be approximately 100% by weight to the film in an amount of 80% by weight.

The obtained graft porous membrane was sufficiently neutralized, washed, chlormethylated with methyl chloromethyl ether, and then reacted with trimethylamine. The total ion capacity of the obtained anion exchange group was 1.50 meq / g polymer, the average pore diameter was 0.17 μm, and the porosity was 56% (Example membrane (B)). The measurement method of the anion exchange capacity was in accordance with the measurement method by Hiroshi Shimizu, Kyoritsu Shuppan Co., Ltd., “Ion-exchange resin”, page 89.

By using the thus-obtained example film (A) and the example film (B), a multifunctional module disclosed in Japanese Patent Application No. 63-126000 was obtained. The effective film area was 4.0 m ^{2 for the} example film (A) and 4.9 m ² for the example film (B) (based on the inner diameter).

Using the multifunctional module obtained in this way, 25
Raw water having an electrification resistance of 17 mΩ · cm at 15 ° C., a TOC of 15 ppb, and a dissolved oxygen concentration of 70 μg / was passed at an overspeed of 5 / min. Irradiate raw water with ultraviolet rays (low pressure 0.05mmHg)
did. In addition, treatments were performed in the order of passing through the anion exchange functional microporous membrane first.

The electrical resistivity of the obtained pure water is 18.15 mΩcm, TOC is
It was 1.5ppb.

The electrical resistivity was measured with KX-4 manufactured by Kurita Kogyo Co., Ltd., and the TOC was measured with a 1800 ppB apparatus manufactured by Torayastro.

(Comparative Example) Using the same raw water as in the example, instead of the multifunctional module, using an ion exchange function (polisher: Mitsubishi Kasei Diaion SKIB (CA) and SA10A (AN), capacity 1.5 / 1.5)
The same processing as in the example was performed except that the processing was performed at a space velocity (SV) of 35. The electrical resistivity of the obtained water is 18.0 mΩcm, TOC
Was 9.5 ppb.

(Effect of the Invention) According to the present invention, the electric resistivity is extremely high and the TO
Since water quality with an extremely low C component can be obtained by one-stage overtreatment, it is useful as a method for producing ultrapure water for semiconductor industry.

Claims (1)

(57) [Claims] In a pure water producing process for removing ions and low molecular weight organic components in water, the raw water is irradiated with ultraviolet rays, and the removal rate of polyethylene glycol having an average pore size of 5 μm or less and an average molecular weight of 6000 is reduced. A method for producing ultrapure water, wherein the filtration is performed using both the microporous membrane having an anion or cation exchange function of 90% or less or the anion exchange functional microporous membrane alone.