JP2022126354A - Fine particle removal apparatus and fine particle removal method - Google Patents

Abstract

To provide a fine particle removal apparatus capable of removing fine particles in a liquid stably and efficiently, regardless of pH fluctuations of the liquid.SOLUTION: A fine particle removal apparatus for removing fine particles in a liquid has a plurality of fine particle capturing means installed in parallel and having different characteristics or properties, and has switching means for switching the fine particle capturing means through which the liquid is made to pass according to the water quality of the liquid. Preferably, the plurality of fine particle capturing means includes positively-charged fine particle capturing means and negatively-charged fine particle capturing means, and the switching means switches the water flow to the positively-charged fine particle capturing means or the negatively-charged fine particle capturing means depending on the pH of the liquid.SELECTED DRAWING: Figure 1

Description

The present invention relates to a microparticle removal apparatus and a microparticle removal method for removing microparticles in a liquid in a pure water or ultrapure water manufacturing process, or in an electronic component manufacturing process, a semiconductor cleaning process, or the like, and a pure water or ultrapure It relates to water production equipment. In particular, the present invention is highly effective in removing fine particles with a particle diameter of 50 nm or less in liquids in systems such as subsystems and water supply lines before the point of use in ultrapure water production and supply systems, and electronic component manufacturing processes and semiconductor cleaning processes. It is useful as a technique for removing

Filtration filters for manufacturing semiconductors and electronic parts, and filtration filters used in the manufacturing process of semiconductors and electronic parts. , tertiary amino groups, and quaternary ammonium salts.

On the other hand, as the negatively charged membrane, 1 selected from the group consisting of a polyketone membrane, a sulfonic acid group, a sulfonic acid ester group, a carboxylic acid group, a carboxylic acid ester group, a phosphoric acid group, a phosphoric acid ester group, and a hydroxyl group There is a method using a membrane having one or more anionic functional groups (Patent Document 2).

Liquids to be treated that pass through these charged films include ultrapure water with a neutral pH, carbonated water with a low pH, and ammonia water with a high pH.

JP 2014-173013 A JP 2014-171979 A

A positively charged membrane (cationic membrane) has poor removal performance for positively charged microparticles, and a negatively charged membrane (anionic membrane) has poor removal performance for negatively charged microparticles.
However, since the charged state of fine particles in a liquid changes according to the pH of the liquid, a single type of charged film can be charged with various charges depending on the water quality in both the low pH region and the high pH region. Efficient removal of fine particles is difficult.

The present invention overcomes the drawbacks of the conventional method and provides a particle removal apparatus and a particle removal method capable of stably and efficiently removing particles in a liquid in response to pH fluctuations of the liquid to be treated, and the particle removal method. It is an object of the present invention to provide a pure water or ultrapure water production device equipped with a removal device.

As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention installed a plurality of fine particle trapping means having different characteristics or physical properties in parallel, and according to water quality such as pH of the liquid to be treated, fine particles that pass through the water. It was found that by switching the trapping means, fine particles in the liquid to be treated can be stably and efficiently removed even if the water quality such as pH of the liquid to be treated fluctuates.
That is, the gist of the present invention is as follows.

[1] A particle removing device for removing particles in a liquid, which has a plurality of particle capturing means with different characteristics or physical properties installed in parallel, and allows the liquid to pass through according to the quality of the liquid. 1. A particle removing apparatus, comprising a switching means for switching the means.

[2] The particle removing device according to [1], wherein the switching means switches the flow of water to the particle trapping means in accordance with the pH of the liquid.

[3] The particle removing device according to [1] or [2], wherein the plurality of particle trapping means includes particle trapping means having different charges.

[4] In [3], the plurality of particle trapping means includes positively charged particle trapping means and negatively charged particle trapping means, and the switching means switches the liquid when the pH of the liquid is 6 or more. A fine particle removing apparatus, characterized in that switching is performed between passing water through positively charged fine particle trapping means and passing said liquid through negatively charged fine particle trapping means when said liquid has a pH of less than 6.

[5] The particle removing apparatus according to [4], further comprising a size exclusion filter installed in series after the positively charged particle trapping means and/or the negatively charged particle trapping means.

[6] A particle removing apparatus according to [5], further comprising positively charged particle trapping means or negatively charged particle trapping means installed in series after the size exclusion filter.

[7] A pure water or ultrapure water production apparatus comprising the particle removal device according to any one of [1] to [6].

[8] A method for removing particles in a liquid using the particle removing device according to any one of [1] to [6].

According to the present invention, fine particles in a liquid can be stably and efficiently removed regardless of water quality fluctuations such as the pH of the liquid.
INDUSTRIAL APPLICABILITY According to the present invention, it is possible to efficiently remove fine particles from aqueous systems in general, particularly pure water or ultrapure water manufacturing processes, or various liquids used in electronic component manufacturing and semiconductor cleaning processes to achieve high purity. .

1 is a system diagram showing an embodiment of a particle removing device of the present invention; FIG. FIG. 4 is a schematic diagram for explaining a fine particle trapping mechanism by a membrane having a cationic functional group or an anionic functional group. 4 is a graph showing the relationship between the pH of a liquid to be treated and the zeta potential of fine particles in the liquid; It is a systematic diagram which shows the test apparatus used by the test example.

Embodiments of the present invention will be described in detail below.

[mechanism]
The mechanism of the particle removal technology of the present invention will be described below by exemplifying a charged film as the particle trapping means.

As shown in FIG. 2(a), a positively charged film having cationic functional groups easily adsorbs negatively charged fine particles, but does not easily adsorb positively charged fine particles. Therefore, the efficiency of trapping and removing negatively charged fine particles is high, but the efficiency of trapping and removing positively charged fine particles is low.
Conversely, as shown in FIG. 2(b), a negatively charged film having an anionic functional group easily adsorbs positively charged fine particles, but does not readily adsorb negatively charged fine particles. Therefore, the efficiency of trapping and removing positively charged fine particles is high, but the efficiency of trapping and removing negatively charged fine particles is low.

On the other hand, fine particles in a liquid change their charge state according to the pH of the liquid. That is, as shown in FIG. 3, regardless of the type of microparticles, microparticles in a liquid generally have a positive charge when the liquid has a low pH and are acidic, and have a positive charge when the liquid has a high pH and are alkaline. will have a negative charge.

In this way, since the charged state of the fine particles in the liquid changes according to the pH of the liquid to be treated, in the present invention, a plurality of fine particle trapping means having different characteristics or physical properties are provided in parallel, and the pH of the liquid to be treated is adjusted. By switching the particle trapping means to which the water is passed according to the water quality, etc., stable and efficient particle removal is realized regardless of the fluctuation of the pH of the liquid to be treated.

[Particle removal device]
An embodiment of the particle removing apparatus of the present invention will be described in detail below with reference to FIG. 1, but the particle removing apparatus of the present invention is not limited to that shown in FIG.

For example, FIG. 1 shows a particle removing device using a particle removing film as the particle capturing means, but the particle capturing means used in the present invention is not limited to the particle removing film. An ion exchange resin or the like can also be used in addition to the membrane.
Also, in FIG. 1, two particle removal membrane modules as particle trapping means are installed in parallel, but three or more particle trapping means such as particle removal membrane modules may be provided.

In the microparticle removal apparatus of FIG. 1, after the pH of the liquid to be treated introduced from the pipe 1 is measured by the pH meter 2, the flow path is switched by the switching means 3 based on the measured pH value of the pH meter 2. It is configured to be treated by being passed through the charged membrane module 4A or the negatively charged membrane module 4B.

<Liquid to be treated>
In the present invention, the liquid to be treated from which fine particles are removed is not particularly limited. Examples include an aqueous solution, thinner, carbonated water, hydrogen peroxide solution, and hydrogen fluoride solution.

The present invention is effective in removing ultrafine particles having a particle size of 50 nm or less, for example, about 3 to 30 nm, in these liquids.

Although the fine particles are not particularly limited, fine particles of inorganic oxides such as silica, alumina, iron oxide, and titania, fluorine-based fine particles, organic resin fine particles, and the like can be mentioned.
Also, the fine particle concentration in the liquid to be treated is not particularly limited, but is usually 100 μg/L or less, or 1 to 10 ¹⁰ particles/mL.

In the microparticle removing apparatus of FIG. 1, in the case of an acid liquid having a pH of less than 6, the microparticles in the liquid are positively charged. When the liquid to be treated is alkaline and has a pH of 6 or higher, the fine particles in the liquid are negatively charged. Therefore, the switching means 3 such as a three-way valve is switched so that the positively charged particle removal membrane module (hereinafter sometimes simply referred to as the "positively charged membrane module") 4A is supplied with water.

Examples of the liquid to be treated having a pH of less than 6 include, but are not limited to, carbonated water, hydrochloric acid aqueous solution, hydrogen fluoride solution, and the like, which are typical examples of acidic liquids.
Liquids to be treated having a pH of 6 or higher include ultrapure water, and representative alkaline liquids such as ammonia water and aqueous sodium hydroxide solutions, but are not limited to these.

In particular, in the present invention, as shown in FIG. 3, in the case of an acidic liquid to be treated having a pH of 5 or less, which is a region in which fine particles in the liquid are positively charged, the water is passed through the positively charged membrane module 4A, and the liquid is In the case of an alkaline liquid to be treated having a pH of 9 or higher, which is a region in which fine particles therein are negatively charged, it is preferable to switch the flow path so as to pass the water through the negatively charged membrane module 4B.
In this case, in the case of the liquid to be treated in the pH range between pH 5 and pH 9, either the positively charged membrane module 4A or the negatively charged membrane module 4B is used depending on the properties of the positively charged membrane module 4A and the negatively charged membrane module 4B. It is preferable to allow water to pass through.

<Positively charged fine particle removal film/negatively charged fine particle removal film>
The positively charged particle-removing film and the negatively charged particle-removing film that are preferably used in the present invention are described below.
Hereinafter, the positively charged particle-removing film will be referred to as "positively charged film", the negatively charged particle-removing film will be referred to as "negatively charged film", and they will be collectively referred to as "charged film".

These charged films need only be arranged in parallel, and even if containers containing the respective charged films are provided separately, a positively charged film region and a negatively charged film region are provided in one container. It doesn't matter if When each membrane is packed in separate containers and arranged in parallel, it is desirable that the distance between the containers is as close as possible.
As will be described later, each charged film arranged in parallel may be followed by another charged film or a size exclusion film having no chargeability. Alternatively, each charged membrane may be provided after the size exclusion membranes arranged in parallel.

The form of the charged membrane may be hollow fiber membrane, flat membrane, fiber, or the like. Hollow fiber membranes are generally used as terminal membrane modules for removing fine particles in ultrapure water production processes. On the other hand, a pleated flat membrane can also be used for the filter attached to the process washing machine.

<Porous membrane>
The porous membrane that serves as the base material of the charged membrane may be a polymer membrane, an inorganic membrane, or a metal membrane.

Polymer membranes include polyolefins such as polyethylene and polypropylene, polyethers such as polyethylene oxide and polypropylene oxide, fluororesins such as PTFE, CTFE, PFA, and polyvinylidene fluoride (PVDF), halogenated polyolefins such as polyvinyl chloride, and nylon. -6, nylon-66 and other polyamides, urea resins, phenolic resins, melamine resins, polystyrene, cellulose, cellulose acetate, cellulose nitrate, polyetherketone, polyetherketoneketone, polyetheretherketone, polysulfone, polyethersulfone, poly Materials such as arylsulfone, polyimide, polyetherimide, polyamideimide, polybenzimidazole, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polyacrylonitrile, polyethernitrile, polyvinyl alcohol, and copolymers thereof can be used. However, it is not limited to this. There is no particular limitation to one type of material, and various materials can be selected as required.
Other polymers such as polyolefins and polyethers may be mixed with the chargeable or conductive polymer.

Materials such as alumina, zirconia, and titania can be used as the inorganic film, but the materials are not limited to these.

A material such as stainless steel can be used as the metal film, but the material is not limited to this.

<Chargeable functional group>
The charged functional groups to be introduced into the porous membrane include sulfonic acid groups, phosphoric acid groups, phosphonic acid groups, phosphinic acid groups, carboxylic acid groups, hydroxyl groups, phenol groups, quaternary ammonium groups, and primary to tertiary amines. groups, pyridine groups, amide groups, etc., but are not limited to these. These functional groups may be not only H-type and OH-type but also salt-type such as Na.

<Method for Introducing Chargeable Functional Group>
A method for introducing the chargeable functional group is not particularly limited, and various methods can be adopted. For example, in the case of polystyrene, sulfonic acid groups can be introduced by adding an appropriate amount of paraformaldehyde to a sulfuric acid solution and heat-crosslinking. In the case of polyvinyl alcohol, a functional group can be introduced by reacting a hydroxyl group with a trialkoxysilane group, a trichlorosilane group, an epoxy group, or the like. If it is not possible to directly introduce a functional group depending on the material, first introduce a highly reactive monomer (called a reactive monomer) such as styrene, and then introduce the functional group in two or more steps. The target functional group may be introduced through the process. These reactive monomers include, but are not limited to, glycidyl methacrylate, styrene, chloromethylstyrene, acrolein, vinylpyridine, acrylonitrile, and the like.

<Cationization Method and Functional Group>
The cationization method for introducing the positively charged functional group is not particularly limited, but examples include a coating method and a combination of these methods. A dehydration condensation reaction etc. are mentioned as the method by a chemical reaction. Plasma treatment, corona treatment and the like can also be used. The coating method includes a method of impregnating with an aqueous solution containing a polymer.

(1) Direct introduction of cationic functional groups into porous membrane by chemical modification For example, chemical modification methods for imparting cationic amino groups to polyketone membranes include chemical reaction with primary amines. ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, 1,2-cyclohexanediamine, N-methylethylenediamine, N-methylpropanediamine, N,N-dimethylethylenediamine, N,N-dimethylpropanediamine, N Polyfunctionalized amines such as diamines, triamines, tetraamines, polyethylenimines, including primary amines such as acetylethylenediamine, isophoronediamine, N,N-dimethylamino-1,3-propanediamine, etc., have many activities. It is preferable because points can be given.

(2) Substitution of at least one hydrogen atom constituting the porous membrane with another group from the viewpoint of imparting a positive zeta potential Substitution methods include, for example, irradiation with electron beams, γ-rays, plasma, etc. After generating radicals by graft polymerization, a monomer having a reactive side chain such as glycidyl methacrylate is polymerized, and a reactive monomer having a functional group that expresses the desired function is added. Examples of reactive monomers include derivatives of acrylic acid, methacrylic acid, vinylsulfonic acid including primary amines, secondary amines, tertiary amines, quaternary ammonium salts, allylamine, p-vinylbenzyltrimethylammonium chloride, and the like. be done. More specific examples include 3-(dimethylamino)propyl acrylate, 3-(dimethylamino)propyl methacrylate, N-[3-(dimethylamino)propyl]acrylamide, N-[3-(dimethylamino) propyl]methacrylamide, (3-acrylamidopropyl)trimethylammonium chloride, trimethyl[3-(methacryloylamino)propyl]ammonium chloride and the like.

(3) Polymers having a positive zeta potential Examples of polymers for imparting a positive zeta potential include PSQ (polysilsesquioxane), polyethyleneimine, polydiallyldimethylammonium chloride, amino group-containing cationic poly(meth) Acrylic acid ester, amino group-containing cationic poly(meth)acrylamide, polyamineamide-epichlorohydrin, polyallylamine, polydicyandiamide, chitosan, cationized chitosan, amino group-containing cationized starch, amino group-containing cationized cellulose, amino Group-containing cationized polyvinyl alcohols and acid salts of the above polymers are included. Further, the polymer or the acid salt of the polymer may be a copolymer with another polymer.

<Anionization method and functional group>
The anionization method for introducing the negatively chargeable functional group is not particularly limited, but the following methods may be mentioned.

(1) From the viewpoint of imparting a negative zeta potential, negatively chargeable functional groups include a sulfonic acid group, a sulfonic acid ester group, a carboxylic acid group, a carboxylic acid ester group, a phosphoric acid group, a phosphoric acid ester group, One or more functional groups selected from the group consisting of hydroxyl groups are included.
Examples of forms having these functional groups include chemical bonding and physical bonding states. A chemical bond may be such as a covalent bond. A covalent bond includes a CC bond, a C=N bond, a bond via a pyrrole ring, and the like. A chemically bonding substance may be a polymer or a monomer having a small molecular weight. On the other hand, the physically bonded state includes states such as adsorption and adhesion in which intermolecular forces such as hydrogen bonding, van der Waals force, electrostatic attraction, and hydrophobic interaction are bonded without chemical bonding. be done.

Polymers for imparting negative zeta potential include polystyrenesulfonic acid, sodium polystyrenesulfonate, polyvinylsulfonic acid, sodium polyvinylsulfonate, poly(meth)acrylic acid, sodium poly(meth)acrylate, anionic polyacrylamide , poly(2-acrylamido-2-methyl group propanesulfonic acid), poly(2-acrylamido-2-methyl group sodium propanesulfonate), carboxymethylcellulose, anionized polyvinyl alcohol, polyvinyl phosphonic acid and the like.

(2) From the viewpoint of imparting negative zeta, the porous membrane may be attached or coated with a polymer having a negative zeta potential. As described above, polymers having a negative zeta potential include polystyrenesulfonic acid, polystyrenesulfonic acid, sodium polystyrenesulfonate, polyvinylsulfonic acid, sodium polyvinylsulfonate, poly(meth)acrylic acid, and sodium poly(meth)acrylate. , anionic polyacrylamide, poly(2-acrylamide-2-methyl group propanesulfonic acid), poly(2-acrylamido-2-methyl group sodium propanesulfonate), carboxymethylcellulose, anionized polyvinyl alcohol, polyvinyl phosphonic acid, etc. mentioned. Further, the polymer or the acid salt of the polymer may be a copolymer with another polymer.

(3) From the viewpoint of imparting a negative zeta potential to the porous membrane, when at least one hydrogen atom of the polymer constituting the porous membrane is replaced with another group, examples of the replacement method include electron beams, gamma rays, A method of generating radicals by irradiation with plasma or the like and then adding a reactive monomer having a functional group that exhibits a desired function can be mentioned.
Examples of reactive monomers include sulfonic acid groups, sulfonic acid ester groups, carboxylic acid groups, carboxylic acid ester groups, phosphoric acid groups, phosphoric acid ester groups, acrylic acid containing hydroxyl groups, methacrylic acid, vinyl sulfonic acid derivatives, and the like. is mentioned. More specific examples include acrylic acid, methacrylic acid, vinylsulfonic acid, styrenesulfonic acid and sodium salts thereof, 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid , 2-acrylamido-2-methylpropanecarboxylic acid, 2-methacrylamido-2-methylpropanecarboxylic acid, and the like.

<Size exclusion filter>
In the fine particle removing apparatus of the present invention, a size exclusion filter having a size exclusion membrane may be provided in series after the positively charged membrane module 4A and the negatively charged membrane module 4B.
The size exclusion membrane is a porous membrane that does not intentionally introduce the anionic or cationic functional group described above, or a porous membrane that is not intentionally modified to have chargeability, and has a predetermined particle size. The object is to eliminate the fine particles described above.
If the membrane material itself has an electric charge, it is included in the size exclusion membrane.

As for the porous membrane that constitutes the size exclusion membrane, the same ones as in the aforementioned charged membrane can be employed.

In addition, when a size exclusion filter is provided, a positively charged membrane module or a negatively charged membrane module may be provided in series after this. That is, fine particles are removed in multiple stages in the order of positively charged membrane module→size exclusion filter→positive charged membrane module or negatively charged membrane module, or in the order of negatively charged membrane module→size exclusion filter→negatively charged membrane module or positively charged membrane module. Such a multi-stage particle removal process can perform particle removal to a higher degree.
Alternatively, a size exclusion filter having a size exclusion membrane may be provided in series before the positively charged membrane module 4A and the negatively charged membrane module 4B.

<Preferred application area>
INDUSTRIAL APPLICABILITY The particle removal apparatus of the present invention is suitably used as a subsystem for producing ultrapure water from a primary pure water system in an ultrapure water production/supply system, particularly as a particle removal apparatus at the final stage of the subsystem. It may also be provided in a water supply line that delivers ultrapure water from the subsystem to the point of use. Furthermore, it can also be used as a final particle removal device at the point of use.

The present invention will be described more specifically below with reference to test examples instead of working examples.

In the following, a fine particle removal test was carried out using the test apparatus shown in FIG. The test apparatus shown in FIG. 4 prepares fine particle-containing test water by injecting fine particles from a fine particle tank 12 into a flow path 11 of a liquid to be treated by a pump P, and measures the pH of this test water with a pH meter 13. The microparticle removal membrane module 14 removes microparticles in the test water, and the microparticle monitors 15 and 16 provided at the inlet and outlet of the microparticle removal membrane module 14 measure the microparticle concentration of the inlet water and the outlet water. It is configured to calculate the fine particle removal rate from the results. The water flow condition (water flow rate) of the liquid to be treated was set to 10 m/d.
The following items were used as a pH meter and a fine particle monitor.
pH meter: D52S (manufactured by HORIBA)
Particle monitor: UDI20 (manufactured by PMS)

As the positively charged film and the negatively charged film, the following were used.
Positively charged membrane: "Qyu speed D" manufactured by Asahi Kasei Medical
DEA-diol (diethylamine-diol) is added to the polyethylene porous membrane
Membrane introduced Negatively charged membrane: Pall: "ABDIUPW3EH1"
Membrane in which sulfone groups are introduced into a polyethylene porous membrane

The following microparticles were used.
Silica fine particles: manufactured by Sigma-Aldrich, average particle size 22 nm
Alumina fine particles: manufactured by Sigma-Aldrich, average particle size 22 nm
As is clear from FIG. 3, both silica fine particles and alumina fine particles are positively charged in acidic liquids and negatively charged in alkaline liquids.

[Test Example 1]
Carbonated water with a pH of 4.5 was used as the liquid to be treated, silica fine particles or alumina fine particles were injected, and the water was passed through the negatively charged membrane module to examine the fine particle removal rate.
Table 1 shows the results.

[Test Example 2]
Aqueous ammonia of pH 10.5 was used as the liquid to be treated, silica fine particles or alumina fine particles were injected, and the water was passed through the positively charged membrane module to examine the fine particle removal rate.
Table 1 shows the results.

[Comparative Test Example 1]
Aqueous ammonia of pH 10.5 was used as the liquid to be treated, silica fine particles or alumina fine particles were injected, and the water was passed through the negatively charged membrane module to examine the fine particle removal rate.
Table 1 shows the results.

[Comparative Test Example 2]
Carbonated water with a pH of 4.5 was used as the liquid to be treated, silica fine particles or alumina fine particles were injected, and the water was passed through the positively charged membrane module to examine the fine particle removal rate.
Table 1 shows the results.

Table 1 shows the following.
Since both silica fine particles and alumina fine particles are positively charged in acidic carbonated water, they are efficiently removed by a negatively charged film (Test Example 1). In addition, since it is negatively charged in alkaline ammonia water, it is efficiently removed by a positively charged membrane (Test Example 2).
On the other hand, negatively charged fine particles in alkaline ammonia water cannot be efficiently removed by a negatively charged membrane (Comparative Test Example 1), and positively charged fine particles in acidic carbonated water are positively charged. The membrane is inferior in removal efficiency (Comparative Test Example 2).

From these results, by switching the charged membrane through which water passes according to the pH of the liquid to be treated, that is, when the liquid to be treated has an acidic pH, water passes through the negatively charged membrane, and when the liquid to be treated has an alkaline pH, water passes through the negatively charged membrane. It can be seen that by passing water through the positively charged membrane, stable and efficient particle removal can be achieved regardless of pH fluctuations in the liquid to be treated.

2 pH meter 3 switching means 4A positively charged particle removal membrane module 4B negatively charged particle removal membrane module 12 particle tank 13 pH meter 14 particle removal membrane module 15, 16 particle monitor

Claims (8)

A particle removing device for removing particles in a liquid has a plurality of particle capturing means with different characteristics or physical properties installed in parallel, and switches the particle capturing means through which the liquid passes according to the water quality of the liquid. A particle removing device, comprising a switching means. 2. The particle removing apparatus according to claim 1, wherein said switching means switches the flow of water to said particle trapping means according to the pH of said liquid. 3. The particle removing apparatus according to claim 1, wherein said plurality of particle trapping means include particle trapping means having different charges. 4. A device according to claim 3, wherein said plurality of particle trapping means includes positively charged particle trapping means and negatively charged particle trapping means, and said switching means switches said liquid to positively charged particle trapping means when said liquid has a pH of 6 or higher. 1. A particle removing apparatus, characterized in that switching is performed between passing water through a trapping means and passing the liquid through the negatively charged particle trapping means when the liquid has a pH of less than 6. 5. A particle removing apparatus according to claim 4, further comprising a size exclusion filter installed in series after said positively charged particle trapping means and/or said negatively charged particle trapping means. 6. A particle removing apparatus according to claim 5, further comprising positively charged particle trapping means or negatively charged particle trapping means installed in series after said size exclusion filter. A pure water or ultrapure water producing apparatus comprising the fine particle removing apparatus according to any one of claims 1 to 6. A method for removing particles in a liquid using the particle removing device according to any one of claims 1 to 6.

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