Ultra-pure water production apparatus and its water quality management method

Abstract

To provide an ultrapure water production system and a water quality management method thereof allowing for easy confirmation of degradation in cleanliness of a filtration membrane of an ultrapure water production system.SOLUTION: A water quality management method of an ultrapure water production system equipped with a filtration membrane is provided, the method includes an analysis step of analyzing a metal concentration of filtration membrane inlet water to be supplied to the filtration membrane and a metal concentration of filtration membrane outlet water having passed through the filtration membrane, each of the analysis being performed by a concentration method. The ultrapure water production system equipped with the filtration membrane includes analysis means analyzing the metal concentration of filtration membrane inlet water to be supplied to the filtration membrane and the metal concentration of filtration membrane outlet water having passed through the filtration membrane, each of the analysis being performed by a concentration method.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an ultrapure water production apparatus and a water quality management method thereof.

Background Art

[0002] In the semiconductor manufacturing industry, silicon wafers are washed using ultrapure water with highly removed impurities. Ultrapure water is generally produced by removing some of the suspended substances, organic substances, etc. contained in raw water (river water, groundwater, industrial water) in a pretreatment step, and then sequentially treating the treated water with a primary pure water system and a secondary pure water system (subsystem), and then supplied to a use point for wafer washing. At the end of the subsystem of the ultrapure water production apparatus, a filtration membrane apparatus for removing fine particles, bacteria, colloids, polymer compounds, etc. from ultrapure water is generally installed.

[0003] Note that ultrapure water generally refers to highly purified water (secondary pure water) produced by a pure water production apparatus provided with a secondary pure water system following the primary pure water system as described above, but is not necessarily defined by the treatment procedure, and refers to water (high-purity water) suitable as washing water for electronic components such as semiconductor substrates that require an extremely clean surface.

[0004] In recent years, the requirements for the number of fine particles in ultrapure water have become increasingly strict. For example, conventionally, ultrapure water was managed based on fine particles of 50 nm or more, but management based on small fine particles of the 10 nm level is required (IRDS: International Technology Roadmap for Semiconductors). Therefore, the operation management of the filtration membrane apparatus for removing fine particles has become difficult. On the other hand, extremely low concentrations are also required for metals other than fine particles. Since it has been found that metals can affect the characteristics of electronic components even at trace concentrations, strict monitoring is necessary. The current metal concentration in ultrapure water is extremely low, in the range of ng / L to pg / L.

[0005] Patent Document 1 discloses a method for evaluating the particle removal performance of a filtration membrane. In this method, a sample solution with intentionally added metal particles is prepared, the sample solution is passed through the filtration membrane, and the capture ability of fine particles of the filtration membrane is confirmed from the difference in metal concentration between the inlet water and the outlet water of the filtration membrane.

[0006] Patent Document 2 discloses a direct inspection method (SEM method) as a method for measuring and analyzing fine particles in ultrapure water. In this method, ultrapure water is filtered through a filtration membrane, fine particles are captured on the surface of the filtration membrane, and the number and particle size of the fine particles are observed with an SEM (scanning electron microscope).

[0007] Patent Document 3 discloses that after washing an ultrafiltration membrane before use with ultrapure water, the cleanliness of the ultrafiltration membrane device is confirmed by analyzing the permeated water of the ultrafiltration membrane.

[0008] Patent Document 4 discloses an ion adsorption membrane method as a technique for trace metal analysis.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0010] In the operation management of an ultrapure water production apparatus, conventionally, only the metal concentration in the permeated water of the ultrafiltration membrane, that is, in the ultrapure water, has been analyzed, and the metal concentration of the feed water to the ultrafiltration membrane has not been considered. Therefore, when there is an abnormality in the metal concentration (deterioration of water quality) in the ultrapure water, it has not been easy to determine whether it is due to a decrease in the cleanliness of the ultrafiltration membrane or other causes (for example, elution of metal ions from an ion exchange device located upstream of the ultrafiltration membrane).

[0011] In addition, in the method disclosed in Patent Document 1, although the metal concentration of the inlet water of the filtration membrane is also used, this method only confirms the microparticle capture ability of the filtration membrane using a sample solution to which metal particles have been intentionally added.

[0012] An object of the present invention is to provide an ultrapure water production apparatus and a water quality management method therefor that can easily confirm a decrease in the cleanliness of the filtration membrane of the ultrapure water production apparatus during the operation of the ultrapure water production apparatus.

Means for Solving the Problems

[0013] According to one aspect of the present invention, A water quality management method for an ultrapure water production apparatus, The ultrapure water production apparatus includes a filtration membrane, An analysis step of analyzing, during the operation of the ultrapure water production apparatus, the metal concentration of the filtration membrane inlet water supplied to the filtration membrane and the metal concentration of the filtration membrane outlet water that has passed through the filtration membrane, respectively, using a concentration method is included, When the metal concentration of the filtered membrane outlet water is higher than the metal concentration of the filtered membrane inlet water, it is determined that the cleanliness of the filtered membrane has already decreased. When the metal concentration of the filtered membrane inlet water is higher than the metal concentration of the filtered membrane outlet water, it is determined that metal fine particles are adhering to the filtered membrane. When the metal concentration of the filtered membrane inlet water is equal to the metal concentration of the filtered membrane outlet water, it is determined that the contamination of the filtered membrane by metal has not progressed. A water quality management method for an ultrapure water production apparatus is provided, characterized in that for at least one kind of metal analyzed in the analysis step, the quantitative lower limit value of the metal concentration is 0.01 ng / L or less.

[0014] According to another aspect of the present invention, An ultrapure water production apparatus including a filtration membrane, 、 Before Analysis means for analyzing, during operation of the ultrapure water production apparatus, the metal concentration of the filtered membrane inlet water supplied to the filtration membrane and the metal concentration of the filtered membrane outlet water that has permeated through the filtration membrane, respectively, using a concentration method, When the metal concentration of the filtered membrane outlet water is higher than the metal concentration of the filtered membrane inlet water, it is determined that the cleanliness of the filtered membrane has already decreased. When the metal concentration of the filtered membrane inlet water is higher than the metal concentration of the filtered membrane outlet water, it is determined that metal fine particles are adhering to the filtered membrane. When the metal concentration of the filtered membrane inlet water is equal to the metal concentration of the filtered membrane outlet water, it is determined that the contamination of the filtered membrane by metal has not progressed. There is provided an ultrapure water production apparatus characterized in that, for at least one of the metals analyzed by the analysis means, the lower limit value for quantification of the metal concentration is 0.01 ng / L or less.

Advantages of the Invention

[0015] According to the present invention, there are provided an ultrapure water production apparatus and a water quality management method thereof, which can easily confirm a decrease in the cleanliness of the filtration membrane of the ultrapure water production apparatus during operation of the ultrapure water production apparatus.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0017] The present invention relates to an ultrapure water production apparatus including a filtration membrane and a method for managing the water quality thereof. The ultrapure water production apparatus includes, for example, a subsystem including a filtration membrane, particularly a subsystem including an ultrafiltration membrane at the terminal. This method includes an analysis step of analyzing the metal concentration of the filtration membrane inlet water (the water to be treated by the filtration membrane) supplied to the filtration membrane and the metal concentration of the filtration membrane outlet water that has passed through the filtration membrane, respectively, using a concentration method. For this purpose, analysis means for analyzing the metal concentration of the filtration membrane inlet water and the metal concentration of the filtration membrane outlet water, respectively, using a concentration method can be used. The analysis means can include concentration means for concentrating the metal in the sample water (filtration membrane inlet water, filtration membrane outlet water) to obtain a concentrated solution, and a measuring device for measuring the metal concentration of the concentrated solution. Based on the magnitude relationship between the metal concentration of the filtration membrane inlet water and the metal concentration of the filtration membrane outlet water, the cleanliness of the ultrafiltration membrane can be evaluated, and specifically, the following cases can be discriminated. In this specification, unless otherwise specified, the terms "upstream" and "downstream" respectively mean upstream and downstream with respect to the flow direction of the water to be treated.

[0018] · Case 1 When the metal concentration of the filtration membrane outlet water is higher than the metal concentration of the filtration membrane inlet water In this case, it is considered that the filtration membrane has already been considerably contaminated by metal fine particles (including metal colloids that cannot pass through the filtration membrane), and metal is eluting from the filtration membrane into the water. Therefore, it is determined that the cleanliness of the filtration membrane has already decreased. In order to improve the metal concentration of the water at the end of the subsystem to a lower concentration, consideration should be given to replacing the filtration membrane.

[0019] · Case 2 When the metal concentration of the filtration membrane inlet water is higher than the metal concentration of the filtration membrane outlet water In this case, it is considered that metal fine particles are contained in the filtration membrane inlet water and the metal fine particles are adhering to the filtration membrane. It is considered that the re-elution of the adhered metal may cause a decrease in the water quality at the end of the subsystem. For good water quality management, the metal concentration analysis of the filtration membrane outlet water should be periodically performed to determine the replacement time of the filtration membrane.

[0020] · Case 3 When the metal concentration of the inlet water of the filtration membrane is approximately the same as the metal concentration of the outlet water of the filtration membrane In this case, it is considered that the filtration membrane is not contaminated by the metal. Such a situation can occur when all the metals contained in the inlet water of the filtration membrane are substantially ions. However, even if the metal concentration of the inlet water and the outlet water is approximately the same, if it exceeds the normal value, typically, leakage or elution of metal ions from the ion exchange device in the front stage of the filtration membrane is suspected.

[0021] For example, for at least one of the metals to be analyzed, typically for all the metals to be analyzed, the metal concentration (normal value) of ultrapure water, that is, the outlet water of the filtration membrane, is 1 ng / L or less. Metal analysis using a concentration method is suitable for such trace analysis.

[0022] The metal to be analyzed is not particularly limited, but is, for example, at least one selected from the group consisting of Na, Ca, Al, Fe, Cr, Pb, and Zn. The metal species can be selected based on the control items of ultrapure water, etc. Also, based on experience at each site, it is preferable to measure elements that are likely to be detected.

[0023] It is preferable to sample the inlet water of the filtration membrane and the outlet water of the filtration membrane simultaneously. By sampling simultaneously, the influence of fluctuations (temporal variations) in the metal concentration can be eliminated.

[0024] For at least one type of metal to be analyzed, the lower limit of quantification of the metal concentration in the analysis process is preferably 0.1 ng / L or less, more preferably 0.01 ng / L or less. By performing metal analysis at an even lower trace level compared to the level of the metal concentration (normal value) in ultrapure water, a more accurate determination can be made. Also, the lower limit of quantification may be 1 pg / L or more. This is because if the lower limit of quantification is about 1 pg / L, the metal concentration can be quantitatively analyzed down to a low level of 1 / 1000 of 1 ng / L. When analyzing only one type of metal, the lower limit of quantification referred to here means the lower limit of quantification of that metal. When analyzing multiple types of metals, it is preferable that the lower limit of quantification for at least one of the multiple types of metals to be analyzed is within the above range, and it is more preferable that the lower limit of quantification for all metals is within the above range.

[0025] The filtration membrane to be evaluated is, for example, a filtration membrane provided in a subsystem of an ultrapure water production device, particularly an ultrafiltration membrane provided at the end of the subsystem (the ultrafiltration membrane located on the most downstream side of the subsystem). The filtration membrane may be modularized or may be in the form of an element of a membrane filtration device. The ultrafiltration membrane device installed at the end of the subsystem is installed for the purpose of removing fine particles in ultrapure water. Usually, metal ions are removed by a non-regenerable ion exchange resin in the stage before the ultrafiltration membrane.

[0026] As a concentration method, an ion exchanger concentration method is preferable, in which impurities in the water to be analyzed are captured by a porous ion exchanger, then the captured impurities are eluted using an eluent, and the impurity concentration in the obtained eluent is measured. As the porous ion exchanger, an ion adsorption membrane or a monolithic ion exchanger described later can be used.

[0027] It is preferable to use a monolithic ion exchanger as the porous ion exchanger used in the ion exchanger concentration method. Since the monolithic ion exchanger allows water to flow through at a high flow rate, the sampling time can be shortened.

[0028] 〔Ultrapure Water Production Device〕 Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

[0029] FIG. 1 shows a schematic configuration example of an ultrapure water production apparatus 1. The ultrapure water production apparatus 1 includes a primary pure water tank 2, an ultraviolet oxidation apparatus 3, an ion exchange apparatus 4, and an ultrafiltration membrane apparatus 5. These constitute a secondary pure water system (subsystem) of the ultrapure water production apparatus, and the primary pure water produced in a primary pure water system (not shown) is processed in this order to produce ultrapure water, and the ultrapure water is supplied to a use point. The apparatuses constituting the subsystem are not limited to the ultraviolet oxidation apparatus 3, the ion exchange apparatus 4, and the ultrafiltration membrane apparatus 5, and can be appropriately changed according to the required water quality and the like. For example, another apparatus (for example, a deaeration membrane apparatus) may be arranged between the ion exchange apparatus 4 and the ultrafiltration membrane apparatus 5. Further, the present invention can be applied not only to ultrafiltration membranes but also to microfiltration membranes.

[0030] Primary pure water is appropriately supplied to the primary pure water tank 2 from the primary pure water system via a line L1, and the primary pure water is stored as water to be treated. The water to be treated stored in the primary pure water tank 2 is supplied to the ultraviolet oxidation apparatus 3 via a line L2 connecting the primary pure water tank 2 and the ultraviolet oxidation apparatus 3. Here, the water to be treated is irradiated with ultraviolet rays, and the organic substances in the water to be treated are decomposed. The water to be treated extracted from the ultraviolet oxidation apparatus 3 is supplied to the ion exchange apparatus 4 via a line L3 connecting the ultraviolet oxidation apparatus 3 and the ion exchange apparatus 4. Here, metal ions and the like in the water to be treated are removed by ion exchange treatment. The water to be treated (the water at the outlet of the ion exchange apparatus 4) extracted from the ion exchange apparatus 4 is supplied to the ultrafiltration membrane apparatus 5 via a line L4 connecting the ion exchange apparatus 4 and the ultrafiltration membrane apparatus 5. Here, fine particles in the water to be treated are removed. From the ultrafiltration membrane apparatus 5, the water to be treated (the water at the outlet of the ultrafiltration membrane apparatus) that has passed through the ultrafiltration membrane is extracted as ultrapure water into a line L5. The line L5 is an ultrapure water feed line that feeds ultrapure water toward a use point, and connects the permeate water outlet of the ultrafiltration membrane apparatus 5 and the use point. Although not shown, concentrated water (the water to be treated that has not passed through the ultrafiltration membrane) can be discharged from the ultrafiltration membrane apparatus 5.

[0031] From the ultrapure water supply line L5, at the branch point 8, a return line L6 that returns a part of the ultrapure water to the primary pure water tank branches off. The line L6 is connected to the primary pure water tank 2. A part of the water flowing upstream of the branch point 8 of the ultrapure water supply line L5 is supplied to the use point, and the remaining part flows back to the primary pure water tank 2 via the return line L6.

[0032] For each device constituting the ultrapure water production apparatus including the pretreatment system, the primary pure water system, and the secondary pure water system, devices known in the field of ultrapure water production can be appropriately used. For example, as the ion exchange device 4, a non-regenerative mixed bed type ion exchange resin column (cartridge polisher) can be used. The ultrafiltration membrane device 5 includes, for example, an appropriate hollow fiber membrane module in the housing. For example, for lines L4, L5, and L6, non-metallic materials (resins) such as polyvinyl chloride (PVC) and polyvinylidene fluoride (PVDF) can be used to prevent elution of metals.

[0033] 〔Ultrapure Water〕 The resistivity (25 °C) of the ultrapure water is, for example, more than 15 MΩ·cm, and in some cases, more than 18 MΩ·cm. The resistivity of the primary pure water is lower than that of the ultrapure water and is, for example, 0.1 to 15 MΩ·cm.

[0034] 〔Sampling Line〕 At the branch point 6, the sampling line L11 branches off from the line L4. At the branch point 7, the sampling line L12 branches off from the line L5. The branch point 7 is located upstream of the branch point 8. Samples for metal analysis of the inlet water and the outlet water of the ultrafiltration membrane device 5 are respectively sampled in the sampling lines L11 and L12. Analytical means 14 and 15 for performing metal analysis are respectively connected to the sampling lines L11 and L12 (appropriately provided with on-off valves). In FIG. 1, the analytical means 14 and 15 are separately provided for each of the sampling lines L11 and L12, but this is not necessarily the case. For example, the concentration means can be separately provided for each sampling line to concentrate each sample water, and the concentrated solutions can be analyzed by a shared measuring device.

[0035] 〔Analysis using the concentration method〕 In the analysis process, the metal in the sample water (water to be analyzed) can be concentrated to obtain a concentrated solution, and the metal concentration in the concentrated solution can be measured using a measuring device for metal concentration, such as an inductively coupled plasma mass spectrometer (ICP-MS). At this time, the water to be treated can be continuously passed through the filtration membrane, and the filtration membrane inlet water (line L11) supplied to the filtration membrane and the filtration membrane outlet water (line L12) that has passed through the filtration membrane can be continuously sampled. The concentration ratio of the concentration operation can be determined as appropriate.

[0036] In the subsystem of the ultrapure water production device, for the concentration of extremely trace metal fine particles (including colloids), there may be fluctuations over time and not be constantly constant. For example, metal fine particles may peel off from the liquid contact part of the device at a certain moment, and the concentration of the metal may increase (spike) at a trace level. Even in such a case, if the metal concentration is analyzed using the concentration method, since the sampling time is relatively long, the fluctuations in water quality can be averaged, and a determination can be made based on the average value.

[0037] As a concentration method, as described above, after capturing impurities (metals) in the sample water with a porous ion exchanger, the captured impurities are eluted using an eluent, and the concentration of impurities in the obtained eluent is measured. The ion exchanger concentration method is preferred. As other concentration methods, there is a heating concentration method (heating the sample water for concentration), but the ion exchanger concentration method is preferred for high magnification and clean concentration.

[0038] As an example of the ion exchanger concentration method, there is an ion adsorption membrane method (see Patent Document 4) using an ion adsorption membrane as the ion exchanger for concentration. Alternatively, instead of the ion adsorption membrane, a method using a monolithic organic porous ion exchanger (hereinafter sometimes referred to as the "monolithic exchanger method") may be adopted. In the monolithic exchanger method, since the differential pressure applied to the ion exchanger is smaller than that in the ion adsorption membrane method, water can be passed through the ion exchanger at a high SV (space velocity), and the required time can be shortened.

[0039] 〔Ion Adsorption Membrane Method〕 An ion adsorption membrane (particularly a porous membrane having cation exchange ability) can be produced, for example, by the method described in T. Hori et al., J. Membr. Sci., 132 (1997) 203 - 211. The functional groups introduced into the ion adsorption membrane are preferably contained in an amount of 0.1 meq to 5 meq per 1 g of the membrane. The average pore diameter of the porous membrane is preferably in the range of 0.01 μm to 5 μm. The porosity of the porous membrane is preferably in the range of 20% to 80%. The membrane thickness of the porous membrane is preferably in the range of 10 μm to 5 mm.

[0040] 〔Monolithic Exchanger Method〕 In the monolithic exchanger method, a monolithic organic porous cation exchanger (hereinafter also referred to as "monolithic cation exchanger") is used. For example, as the monolithic cation exchanger, a co-continuous structure composed of a three-dimensionally continuous skeleton with an average thickness of 1 to 60 μm in the dry state made of an aromatic vinyl polymer containing 0.1 to 5.0 mol% of a cross-linked structural unit in all constituent units, and three-dimensionally continuous pores with an average diameter of 10 to 200 μm in the dry state between the skeletons is preferable. The monolithic cation exchanger preferably has a total pore volume in the dry state of 0.5 to 10 mL / g, has cation exchange groups, has a cation exchange capacity per volume in the water-wetted state of 0.3 to 5.0 meq / mL (water-wetted state), the cation exchange groups are uniformly distributed in the organic porous cation exchanger, and is in the H form, because it can increase the liquid passing rate and can shorten the time required for metal capture and elution.

[0041] According to the monolithic exchanger method, the captured impurities are easily eluted by the eluent. Therefore, the acid concentration of the eluent can be lowered, and thus the lower limit of quantification becomes lower. In addition, since the time required for elution is shortened, the analysis time can be shortened. Further, according to the monolithic exchanger method, the liquid passing rate of the water to be analyzed can be increased, so the time required for capturing impurities is shortened, and thus the analysis time can be shortened.

[0042] The average diameter of the openings of the monolithic cation exchanger in the dry state and the average diameter of the openings of the monolithic intermediate described below are determined by the mercury intrusion method and refer to the maximum value of the pore size distribution curve obtained by the mercury intrusion method. In addition, the average thickness of the skeleton of the monolithic cation exchanger in the dry state is determined by SEM (scanning electron microscope) observation of the monolithic cation exchanger in the dry state (SEM observation is performed at least 3 times, the thickness of the skeleton in the obtained images is measured, and their average value is taken as the average thickness). Note that the skeleton is rod-shaped and has a circular cross-sectional shape, but those with an elliptical cross-sectional shape or other non-uniform cross-sectional shapes may be included. In this case, the thickness is the average of the minor axis and the major axis.

[0043] In the case of the monolithic cation exchanger, it is preferable that the introduced cation exchange groups are uniformly distributed not only on the surface of the porous body but also inside the framework of the porous body.

[0044] <Method for producing a monolithic cation exchanger> The monolith (the monolithic material of the monolithic cation exchanger before introduction of the ion exchange group) can be obtained, for example, by performing the following steps. Step I: Prepare a water-in-oil emulsion by stirring a mixture of an oil-soluble monomer not containing an ion exchange group, a surfactant, and water, and then polymerize the water-in-oil emulsion to obtain a monolithic organic porous intermediate (hereinafter also referred to as "monolithic intermediate") having a continuous macroporous structure with a total pore volume exceeding 16 mL / g and not exceeding 30 mL / g. Step II: Prepare a mixture consisting of an aromatic vinyl monomer, an oil-soluble monomer having at least 2 or more vinyl groups in one molecule, a crosslinking agent in an amount of 0.3 to 5 mol%, an organic solvent in which the aromatic vinyl monomer and the crosslinking agent are dissolved but the polymer formed by polymerization of the aromatic vinyl monomer is not dissolved, and a polymerization initiator. Step III: Polymerize the mixture obtained in Step II under static conditions and in the presence of the monolithic intermediate obtained in Step I to obtain a monolith which is an organic porous body having a co-continuous structure. Note that the order of Step I and Step II is not fixed, and Step II may be performed after Step I, or Step I may be performed after Step II.

[0045] Step I may be performed in accordance with the method described in JP-A-2002-306976.

[0046] Among the oil-soluble monomers used in the first step, preferred ones are aromatic vinyl monomers, such as styrene, α-methylstyrene, vinyltoluene, vinylbenzyl chloride, divinylbenzene, etc. These monomers can be used alone or in combination of two or more. However, it is preferable to select at least one component of the crosslinkable monomers such as divinylbenzene and ethylene glycol dimethacrylate as an oil-soluble monomer, and the content thereof is 0.3 to 5 mol%, preferably 0.3 to 3 mol% in all the oil-soluble monomers, which is advantageous for the formation of the co-continuous structure.

[0047] The surfactant used in the first step is not particularly limited as long as it can form a water-in-oil (W / O) emulsion when an oil-soluble monomer containing no cation exchange group and water are mixed. For example, an amphoteric surfactant can be used. The surfactant can be used alone or in combination of two or more. The water-in-oil emulsion refers to an emulsion in which the oil phase is the continuous phase and water droplets are dispersed therein. The addition amount of the above surfactant varies greatly depending on the type of the oil-soluble monomer and the size of the target emulsion particles (macropores), so it cannot be generally stated, but it can be selected in the range of about 2 to 70% by mass based on the total amount of the oil-soluble monomer and the surfactant.

[0048] In addition, in the first step, a polymerization initiator may be used as necessary when forming the water-in-oil emulsion. As the polymerization initiator, a compound that generates radicals by heat or light irradiation is preferably used. The polymerization initiator may be water-soluble or oil-soluble.

[0049] In the first step, there are no particular restrictions on the mixing method for forming an oil-in-water emulsion by mixing an oil-soluble monomer that does not contain an ion-exchange group, a surfactant, water, and a polymerization initiator. Methods such as mixing all components at once in one batch or separately and uniformly dissolving the oil-soluble components, namely the oil-soluble monomer, surfactant, and oil-soluble polymerization initiator, and the water-soluble components, namely water and water-soluble polymerization initiator, and then mixing the respective components can be used. There are also no particular restrictions on the mixing device for forming the emulsion, and ordinary mixers, homogenizers, high-pressure homogenizers, etc. can be used, and an appropriate device can be selected to obtain the target emulsion particle size. Also, there are no particular restrictions on the mixing conditions, and the stirring rotation speed and stirring time that can obtain the target emulsion particle size can be arbitrarily set.

[0050] The monolith intermediate obtained in the first step is an organic polymer material having a crosslinked structure, preferably an aromatic vinyl polymer. The crosslink density of the polymer material is not particularly limited, but it preferably contains 0.1 to 5 mol%, preferably 0.3 to 3 mol% of crosslinked structural units with respect to all the constituent units constituting the polymer material. In particular, when the total pore volume is 16 to 20 mL / g, in order to form a co-continuous structure, the crosslinked structural units are preferably less than 3 mol%.

[0051] The total pore volume per mass of the monolith intermediate obtained in the first step in the dry state exceeds 16 mL / g and is 30 mL / g or less, preferably exceeds 16 mL / g and is 25 mL / g or less. That is, this monolith intermediate basically has a continuous macroporous structure, but the openings (mesopores), which are the overlapping parts of the macropores, are extremely large, so the skeleton constituting the monolith structure has a structure that is infinitely close to a one-dimensional rod-shaped skeleton from a two-dimensional wall surface. When this is coexisted in the polymerization system, a porous body with a co-continuous structure is formed using the structure of the monolith intermediate as a mold. To make the total pore volume of the monolith intermediate within the above range, the ratio of the monomer to water may be generally 1:20 to 1:40.

[0052] In addition, the monolith intermediate obtained in the first step has an average diameter of the openings (mesopores), which are the overlapping parts of the macropores, of 5 to 100 μm in the dry state. The monolith intermediate is preferably a uniform structure with uniform macropore sizes and pore diameters, but is not limited thereto, and may have non-uniform macropores larger than the uniform macropore sizes scattered in the uniform structure.

[0053] As the aromatic vinyl monomer used in the second step, there is no particular limitation as long as it contains a polymerizable vinyl group in the molecule and is a lipophilic aromatic vinyl monomer with high solubility in an organic solvent. However, it is preferable to select a vinyl monomer that produces the same type or a similar polymer material as the monolith intermediate coexisting in the polymerization system.

[0054] The addition amount of the aromatic vinyl monomer used in the second step is 5 to 50 times, preferably 5 to 40 times by mass, based on the monolith intermediate coexisting during polymerization.

[0055] The crosslinking agent used in the second step preferably contains at least two polymerizable vinyl groups in the molecule and has high solubility in an organic solvent. Preferred crosslinking agents are aromatic polyvinyl compounds such as divinylbenzene, divinylnaphthalene, and divinylbiphenyl due to their high mechanical strength and stability against hydrolysis. The amount of the crosslinking agent used is 0.3 to 5 mol%, particularly 0.3 to 3 mol%, based on the total amount of the vinyl monomer and the crosslinking agent (total oil-soluble monomers). It is preferable to use the amount of the crosslinking agent used so that it is approximately equal to the crosslinking density of the monolith intermediate coexisting during the polymerization of the vinyl monomer / crosslinking agent.

[0056] The organic solvent used in the second step is an organic solvent that dissolves the aromatic vinyl monomer and the crosslinking agent but does not dissolve the polymer formed by the polymerization of the aromatic vinyl monomer. The amount of the organic solvent used is preferably such that the concentration of the aromatic vinyl monomer is 30 to 80% by mass.

[0057] In the second step, a compound that generates radicals upon heat or light irradiation is preferably used as the polymerization initiator. The polymerization initiator is preferably oil-soluble. The amount of the polymerization initiator used varies greatly depending on the type of monomer, polymerization temperature, etc., but it can be used in the range of about 0.01 to 5% by mass based on the total amount of the vinyl monomer and the crosslinking agent.

[0058] When a monolith intermediate having a specific continuous macroporous structure is present in the polymerization system in the third step, the particle aggregation structure disappears, and a monolith having the above-mentioned co-continuous structure can be obtained.

[0059] In the method for producing the monolith, the internal volume of the reaction vessel is not particularly limited as long as it is of a size that allows the monolith intermediate to be present in the reaction vessel. When the monolith intermediate is placed in the reaction vessel, it may be such that there is a gap around the monolith in plan view, or it may be such that the monolith intermediate fits into the reaction vessel without a gap. Among these, a case where the thick monolith after polymerization fits into the reaction vessel without a gap without being pressed by the inner wall of the vessel is efficient without waste of reaction raw materials, etc., and without causing distortion in the monolith. Even when the internal volume of the reaction vessel is large and there is a gap around the monolith after polymerization, since the vinyl monomer and the crosslinking agent are adsorbed and distributed on the monolith intermediate, no particle aggregation structure is generated in the gap portion in the reaction vessel.

[0060] In the third step, in the reaction vessel, the monolith intermediate is placed in a state of being impregnated with a mixture (solution). As described above, the mixing ratio of the mixture obtained in the second step and the monolith intermediate is preferably adjusted so that the addition amount of the vinyl monomer is 3 to 50 times, preferably 4 to 40 times, by mass with respect to the monolith intermediate. Thereby, the monolith having a thick skeleton while having an appropriate pore diameter can be obtained. In the reaction vessel, the vinyl monomer and the crosslinking agent in the mixture are adsorbed and distributed on the skeleton of the stationary monolith intermediate, and polymerization proceeds within the skeleton of the monolith intermediate.

[0061] In the third step, in the reaction vessel, the monolith intermediate is placed in a state of being impregnated with a mixture (solution). As described above, the mixing ratio of the mixture obtained in the second step and the monolith intermediate is preferably adjusted so that the addition amount of the aromatic vinyl monomer is 5 to 50 times, preferably 5 to 40 times by mass with respect to the monolith intermediate. Thereby, a monolith having a co-continuous structure in which pores of an appropriate size are three-dimensionally continuous and a thick skeleton is three-dimensionally continuous can be obtained. In the reaction vessel, the aromatic vinyl monomer and the crosslinking agent in the mixture are adsorbed and distributed on the skeleton of the stationary monolith intermediate, and polymerization proceeds within the skeleton of the monolith intermediate.

[0062] The polymerization conditions in the third step are selected according to various conditions depending on the type of monomer and the type of initiator. By heat polymerization, the vinyl monomer and the crosslinking agent adsorbed and distributed on the skeleton of the monolith intermediate polymerize within the skeleton, and the skeleton can be thickened. After the polymerization is completed, the content is taken out, and for the purpose of removing the unreacted vinyl monomer and the organic solvent, extraction is performed with a solvent such as acetone to obtain the monolith.

[0063] The monolith cation exchanger is obtained by performing a fourth step of introducing a cation exchange group into the monolith obtained in the third step.

[0064] Examples of the cation exchange group introduced into the monolith cation exchanger include a carboxylic acid group, an iminodiacetic acid group, a sulfonic acid group, a phosphoric acid group, and a phosphoric acid ester group.

[0065] In addition, as a method for introducing a cation exchange group into the monolith, for example, as a method for introducing a sulfonic acid group, if the monolith is a styrene-divinylbenzene copolymer or the like, sulfonation is performed using chlorosulfuric acid, concentrated sulfuric acid, or fuming sulfuric acid; A method of introducing a radical initiator or a chain transfer group uniformly into the surface and inside of the monolith skeleton and graft-polymerizing sodium styrenesulfonate or acrylamide-2-methylpropanesulfonic acid; Similarly, after graft-polymerizing glycidyl methacrylate, a method of introducing a sulfonic acid group by functional group conversion, etc. can be mentioned. Among these methods, the method of introducing sulfonic acid into a styrene-divinylbenzene copolymer using chlorosulfuric acid is preferable in that a cation exchange group can be introduced uniformly and quantitatively.

[0066] Although the size of the three-dimensionally continuous pores of the monolith and the monolith cation exchanger is remarkably large, they have a thick skeleton and thus have high mechanical strength. In addition, since the monolith cation exchanger has a thick skeleton, the cation exchange capacity per unit volume in the water-wet state can be increased, and furthermore, it is possible to pass the liquid to be treated at a low pressure and a large flow rate for a long period of time.

Example

[0067] 〔Example 1〕 The ion adsorption membrane used for concentration in the analysis step was prepared by the method described in T. Hori et al., J. Membr. Sci., 132(1997)203-211 (ion exchange groups per 1 g of the membrane: 1.6 milliequivalents, ion exchange groups as a module 1.5 milliequivalents, average pore diameter 0.1 μm).

[0068] The above ion adsorption membrane was installed in the sampling lines L11 and L12 of the ultrapure water production apparatus having the subsystem with the configuration shown in FIG. 1, respectively. As the ultrafiltration membrane provided in the ultrafiltration membrane device 5 at the end of the subsystem, the product name OLT-6036 (polysulfone hollow fiber) manufactured by Asahi Kasei Corporation was used, and its water flux was about 10m 3 / h or so.

[0069] This ultrapure water production device was operated to produce ultrapure water. During the operation of the ultrapure water production device, sample water was passed through each ion adsorption membrane through sampling lines L11 and L12. The concentration time was set to about 3 days, and about 2000 L of sample water was passed through the ion adsorption membrane for concentration at a rate of 500 mL / min. After capturing the metals in the sample water by the ion adsorption membrane, the captured metal ions were eluted using 100 mL of 1N nitric acid obtained by diluting high-purity nitric acid TAMAPURE AA-100 (trade name) manufactured by Tama Chemical Co., Ltd., and the amount of metals in the eluate was measured by ICP-MS. Since the concentration ratio is 2000 / 0.1 = 20000 times, the value obtained by dividing the amount of metals (ng) in the eluate by the concentration ratio is the metal concentration in the sample water.

[0070] Figure 2 is a graph showing the results of analyzing the metal concentrations before and after the ultrafiltration membrane by the ion adsorption membrane method as described above. The metal concentration of the water at the outlet of the filtration membrane is higher than that of the inlet water, and the concentrations of calcium and zinc in particular are significantly higher. From this, it can be estimated that the cleanliness of the ultrafiltration membrane has already decreased. By evaluating the water quality upstream and downstream of the ultrafiltration membrane in this way, it becomes possible to evaluate the cleanliness of the filtration membrane.

[0071] 〔Example 2〕 The same test as in Example 1 was conducted on the ultrapure water production device at another site. The results are shown in Figure 3. Note that for Li and Cd, since they were present in trace amounts that could not be shown in the figure, they were omitted in Figure 3. Compared with the metal concentration of the inlet water of the ultrafiltration membrane, the metal concentration of the outlet water is lower, and the concentrations of calcium and iron in particular are significantly lower. Therefore, it can be seen that metals exist in the form of fine particles in the inlet water of the ultrafiltration membrane, and the cleanliness of the ultrafiltration membrane is being reduced. By regularly performing metal analysis at the outlet of the ultrafiltration membrane thereafter, the replacement time of the ultrafiltration membrane can be determined, and as a result, good water quality management can be achieved.

Explanation of symbols

[0072] 1 Ultrapure water production device 2 Primary pure water tank 3 Ultraviolet oxidation device 4 Ion exchange device 5 Ultrafiltration membrane device 6, 7, 8 Branch points 14, 15 Analysis means

Claims

1. A method for water quality management of an ultrapure water production apparatus, wherein the ultrapure water production apparatus is provided with a filtration membrane, and includes an analysis step of analyzing, during operation of the ultrapure water production apparatus, the metal concentration of the filtration membrane inlet water supplied to the filtration membrane and the metal concentration of the filtration membrane outlet water that has passed through the filtration membrane, respectively, using a concentration method, when the metal concentration of the filtration membrane outlet water is higher than the metal concentration of the filtration membrane inlet water, it is determined that the cleanliness of the filtration membrane has already decreased, when the metal concentration of the filtration membrane inlet water is higher than the metal concentration of the filtration membrane outlet water, it is determined that metal fine particles are adhering to the filtration membrane, when the metal concentration of the filtration membrane inlet water is equal to the metal concentration of the filtration membrane outlet water, it is determined that the contamination of the filtration membrane by metal has not progressed, A method for water quality management of an ultrapure water production apparatus, characterized in that, for at least one kind of metal analyzed in the analysis step, the quantitative lower limit value of the metal concentration is 0.01 ng / L or less.

2. The method for water quality management of an ultrapure water production apparatus according to claim 1, wherein, for at least one kind of metal analyzed in the analysis step, the metal concentration of the ultrapure water is 1 ng / L or less.

3. The method for water quality management of an ultrapure water production apparatus according to claim 2, wherein the metal analyzed in the analysis step is at least one selected from the group consisting of Na, Ca, Al, Fe, Cr, Pb, and Zn.

4. The method for water quality management of an ultrapure water production apparatus according to any one of claims 1 to 3, wherein in the analysis step, sampling of the filtration membrane inlet water and the filtration membrane outlet water is performed simultaneously.

5. The method for water quality management of an ultrapure water production apparatus according to any one of claims 1 to 4, wherein the filtration membrane is an ultrafiltration membrane provided in a subsystem of the ultrapure water production apparatus.

6. The method for water quality management of an ultrapure water production apparatus according to any one of claims 1 to 5, wherein the concentration method is an ion exchanger concentration method in which metals in the water to be analyzed are captured by a porous ion exchanger, then the captured metals are eluted using an eluent, and the metal concentration in the obtained eluent is measured.

7. The method for water quality management of an ultrapure water production apparatus according to claim 6, wherein a monolithic ion exchanger is used as the porous ion exchanger.

8. An ultrapure water production apparatus provided with a filtration membrane, and includes analysis means for analyzing, during operation of the ultrapure water production apparatus, the metal concentration of the filtration membrane inlet water supplied to the filtration membrane and the metal concentration of the filtration membrane outlet water that has passed through the filtration membrane, respectively, using a concentration method. When the metal concentration of the filtered membrane outlet water is higher than that of the filtered membrane inlet water, it is determined that the cleanliness of the filtered membrane has already decreased. When the metal concentration of the filtered membrane inlet water is higher than that of the filtered membrane outlet water, it is determined that metal fine particles are adhering to the filtered membrane. When the metal concentration of the filtered membrane inlet water is equal to that of the filtered membrane outlet water, it is determined that the contamination of the filtered membrane by metal has not progressed. An ultrapure water production apparatus, characterized in that, for at least one kind of metal analyzed by the analysis means, the lower limit value of the metal concentration quantification is 0.01 ng / L or less.

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