JP2021084045A - Ultrapure water production system and water quality management method thereof - Google Patents

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

The present invention relates to an ultrapure water production apparatus and a water quality control method thereof.

In the semiconductor manufacturing industry, silicon wafers are washed using ultrapure water from which impurities are highly removed. Ultrapure water generally removes some of the suspended substances and organic substances contained in raw water (river water, groundwater, industrial water) in the pretreatment process, and then removes the treated water in the primary pure water system and secondary water. It is manufactured by sequential processing in a pure water system (subsystem) and then supplied to use points for wafer cleaning. Generally, a filtration membrane device for removing fine particles, bacteria, colloids, polymer compounds, etc. from ultrapure water is installed at the end of the subsystem of the ultrapure water production device.

As described above, ultrapure water generally refers to advanced water (secondary pure water) produced by a pure water production apparatus provided with a secondary pure water system following a primary pure water system. However, it is not necessarily defined by the treatment procedure, and refers to water (high-purity water) suitable for cleaning electronic parts and the like that are required to obtain an extremely clean surface such as a semiconductor substrate.

In recent years, the demand for the number of fine particles in ultrapure water has become stricter year by year. For example, in the past, ultrapure water was controlled based on fine particles of 50 nm or more, but management based on small particles of 10 nm level is required (IRDS: International Technology Roadmap for Semiconductors). Therefore, it is difficult to manage the operation of the filtration membrane device that removes fine particles. On the other hand, extremely low concentrations are required for metals other than fine particles. Strict monitoring is required because metals are known to affect the characteristics of electronic components even at trace concentrations. The current metal concentration in ultrapure water is extremely low, ng / L to pg / L.

Patent Document 1 discloses a method for evaluating the particle removal performance of a filtration membrane. In this method, a sample solution to which metal particles are intentionally added is prepared, the sample solution is circulated through the filtration membrane, and the difference in metal concentration between the inlet water and the outlet water of the filtration membrane is used to capture fine particles of the filtration membrane. To confirm.

Patent Document 2 discloses a direct examination 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 filtration membrane surface, and the number and particle size of the fine particles are observed with an SEM (scanning electron microscope).

Patent Document 3 discloses that the cleanliness of the ultrafiltration membrane device is confirmed by washing the ultrafiltration membrane before use with ultrapure water and then analyzing the permeated water of the ultrafiltration membrane. Will be done.

Patent Document 4 discloses an ion adsorption membrane method as a method for analyzing trace metals.

JP-A-2015-226906 Japanese Unexamined Patent Publication No. 2016-55240 Japanese Unexamined Patent Publication No. 2018-144013 Japanese Unexamined Patent Publication No. 2001-153854

Conventionally, in the operation management of the ultrapure water production equipment, only the metal concentration in the permeated water of the ultrafiltration membrane, that is, the ultrapure water is analyzed, and the metal concentration of the water supplied to the ultrapure membrane is taken into consideration. There wasn't. Therefore, when the ultrapure water has an abnormal metal concentration (deterioration of water quality), it may be due to a decrease in the cleanliness of the ultrafiltration membrane, or from another cause (for example, from the ion exchange device in front of the ultrafiltration membrane). It was not easy to judge whether it was due to the elution of metal ions.

The method disclosed in Patent Document 1 also utilizes the metal concentration of the inlet water of the filtration membrane, but this method uses a sample solution to which metal particles are intentionally added and has a fine particle trapping property of the filtration membrane. I'm just checking.

An object of the present invention is to provide an ultrapure water production apparatus and a water quality management method thereof, which can easily confirm a decrease in cleanliness of a filtration membrane of the ultrapure water production apparatus during operation of the ultrapure water production apparatus. That is.

According to one aspect of the invention
It is a water quality control method for ultrapure water production equipment.
The ultrapure water production apparatus includes a filtration membrane and has a filtration membrane.
Ultrapure water characterized by including an analysis step of analyzing 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 permeated the filtration membrane by using a concentration method, respectively. A water quality control method for a pure water production apparatus is provided.

According to another aspect of the invention
An ultrapure water production device equipped with a filtration membrane.
Ultrapure water characterized by including an analysis means for analyzing 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 permeated the filtration membrane by using a concentration method, respectively. Pure water production equipment is provided.

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

It is a process flow diagram which shows the schematic configuration example of the ultrapure water production apparatus. It is a graph which shows the metal analysis result of Example 1. FIG. It is a graph which shows the metal analysis result of Example 2.

The present invention relates to an ultrapure water production apparatus provided with a filtration membrane and a water quality control method thereof. Ultrapure water production equipment includes, for example, a subsystem having a filtration membrane, particularly a subsystem having an ultrafiltration membrane at the end. In this method, the metal concentration of the filtration membrane inlet water (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 permeated the filtration membrane are concentrated by using a concentration method. Includes analysis steps to analyze. For this purpose, it is possible to use analytical means for analyzing the metal concentration of the filtration membrane inlet water and the metal concentration of the filtration membrane outlet water by using the concentration method. The analytical means can include a concentrating 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. The cleanliness of the ultrafiltration membrane can be evaluated 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. Specifically, the following cases can be discriminated. it can. In the present specification, unless otherwise specified, the terms "upstream" and "downstream" mean upstream and downstream in the flow direction of the water to be treated, respectively.

・ 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, the filtration membrane is already considerably contaminated with metal fine particles (including metal colloids that cannot pass through the filtration membrane), and the filtration membrane It is considered that the metal is eluted from the water. Therefore, it is determined that the cleanliness of the filtration membrane has already decreased. Replacement of filtration membranes should be considered to improve the metal concentration of water at the end of the subsystem to a lower concentration.

・ 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 the metal fine particles are contained in the filtration membrane inlet water and the metal fine particles are adhering to the filtration membrane. The re-eluting of the attached metal may contribute to the deterioration of the water quality at the end of the subsystem. For good water quality control, the metal concentration of the filtration membrane outlet water should be analyzed regularly and filtered. The timing of membrane replacement should be determined.

・ Case 3
When the metal concentration of the filtration membrane inlet water is about the same as the metal concentration of the filtration membrane outlet water In this case, it is considered that the filtration membrane contamination by the metal has not progressed. This situation can occur when the metals contained in the water at the inlet of the filtration membrane are substantially all ions. However, even if the metal concentration of the inlet water and the metal concentration of the outlet water are about the same, if they exceed the normal value, typically, metal ions leak from the ion exchange device in front of the filtration membrane or Elution is suspected.

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 the concentration method is suitable for such microanalysis.

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

It is preferable to sample the filtration membrane inlet water and the filtration membrane outlet water at the same time. By performing sampling at the same time, it is possible to eliminate the influence of fluctuations in metal concentration (fluctuations over time).

For at least one of the metals to be analyzed, the lower limit of quantification of the metal concentration in the analysis step is preferably 0.1 ng / L or less, more preferably 0.01 ng / L or less. A more accurate judgment can be made by performing a metal analysis at a trace level compared to the level of the metal concentration (normal value) of ultrapure water. 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 to a level as low as 1/1000 of 1 ng / L. When analyzing only one kind of metal, the lower limit of quantification referred to here means the lower limit of quantification of the metal. When analyzing a plurality of kinds of metals, it is preferable that the lower limit of quantification is in the above range for at least one of the plurality of kinds of metals to be analyzed, but the lower limit of quantification for all the metals is in the above range. Is more preferable.

The filtration membrane to be evaluated is, for example, a filtration membrane provided in a subsystem of an ultrapure water production apparatus, particularly an ultrafiltration membrane provided at the end of the subsystem (an ultrafiltration membrane located on the most downstream side of the subsystem). The filtration membrane may be modular or may be in the form of an element of a membrane filtration apparatus. 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-renewable ion exchange resin in the pre-stage of the ultrafiltration membrane.

As a concentration method, impurities in the water to be analyzed are captured by a porous ion exchanger, the captured impurities are eluted using an eluent, and the concentration of impurities in the obtained eluent is measured. Ion exchanger concentration. The method is preferred. As the porous ion exchanger, an ion adsorption membrane or a monolithic ion exchanger described later can be used.

It is preferable to use a monolithic ion exchanger as the porous ion exchanger used in the ion exchanger enrichment method. Since the monolithic ion exchanger can pass water at a high flow velocity, the sampling time can be shortened.

[Ultrapure water production equipment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

FIG. 1 shows a schematic configuration example of the ultrapure water production apparatus 1. The ultrapure water production apparatus 1 includes a primary pure water tank 2, an ultraviolet oxidizing apparatus 3, an ion exchange apparatus 4, and an ultrafiltration membrane apparatus 5. These constitute the secondary pure water system (subsystem) of the ultrapure water production equipment, and the primary pure water produced by the primary pure water system (not shown) is processed in this order to produce ultrapure water. , Supply ultrapure water to youth points. The apparatus constituting the subsystem is not limited to the ultraviolet oxidizing 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 device (for example, a degassing membrane device) may be arranged between the ion exchange device 4 and the ultrafiltration membrane device 5. Further, the present invention can be applied not only to ultrafiltration membranes but also to microfiltration membranes.

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

At the branch point 8, the return line L6 for returning a part of the ultrapure water to the primary pure water tank branches from the ultrapure water supply line L5. The line L6 is connected to the primary pure water tank 2. A part of the water flowing upstream from the branch point 8 of the ultrapure water supply line L5 is supplied to the use point, and the remaining part is returned to the primary pure water tank 2 via the return line L6.

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

[Ultrapure water]
The resistivity of ultrapure water (25 ° C.) 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 ultrapure water, for example, 0.1 to 15 MΩ · cm.

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

[Analysis using the concentration method]
In the analysis step, the metal in the sample water (water to be analyzed) is concentrated to obtain a concentrated solution, and the metal concentration in the concentrated solution is obtained using a metal concentration measuring device, for example, an inductively coupled plasma mass spectrometer (ICP-MS). Can be measured. At this time, the water to be treated is 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 are continuously passed. Can be sampled. The concentration ratio of the concentration operation can be appropriately determined.

In the subsystem of the ultrapure water production apparatus, the concentration of extremely small amounts of metal fine particles (including colloids) may not be constantly constant and may have fluctuation spots over time. For example, metal fine particles may peel off from the wetted portion 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 by using the concentration method, the sampling time is relatively long, so that the fluctuation of water quality can be averaged and the judgment can be made based on the average value.

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 with an eluent, and the impurity concentration in the obtained eluent is determined. The ion exchanger concentration method for measurement is preferable. As another concentration method, there is a heat concentration method (concentration by heating sample water), but the ion exchanger concentration method is preferable for clean concentration at a high magnification.

As an example of the ion exchanger enrichment method, there is an ion adsorption membrane method (see Patent Document 4) in which an ion adsorbent membrane is used as the ion exchanger used for concentration. Alternatively, a method of using a monolithic organic porous ion exchanger instead of the ion adsorption membrane "hereinafter, may be referred to as a" monolith exchanger method ") may be adopted. In the monolith exchange 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.

[Ion adsorption membrane method]
Ion adsorption membranes (particularly porous membranes capable of exchanging cations) can be prepared, for example, by the method described in T. Hori et al., J. Membr. Sci., 132 (1997) 203-211. The functional group to be introduced into the ion adsorption membrane is preferably contained in an amount of 0.1 mm to 5 mm equivalent per 1 g of the membrane. The average pore size 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 film thickness of the porous membrane is preferably in the range of 10 μm to 5 mm.

[Monolith exchange method]
In the monolith exchanger method, a monolith-like organic porous cation exchanger (hereinafter, also referred to as “monolith cation exchanger”) is used. For example, the monolith cation exchanger is three-dimensionally having an average thickness of 1 to 60 μm in a dry state, which is composed of an aromatic vinyl polymer containing 0.1 to 5.0 mol% of crosslinked structural units among all the structural units. A co-continuous structure consisting of a continuous skeleton and three-dimensionally continuous pores having an average diameter of 10 to 200 μm between the skeletons is preferable. The monolith cation exchanger has a total pore volume of 0.5 to 10 mL / g in a dry state, has a cation exchange group, and has a cation exchange capacity of 0 per volume in a water-wet state. .3 to 5.0 mg equivalent / mL (water-wet state), uniform distribution of cation exchange groups in the organic porous cation exchanger, and H-form make it possible to control the liquid flow rate. It is preferable in that it can be increased and the time required for metal capture and elution can be shortened.

According to the monolith exchanger method, the trapped impurities are easily eluted by the eluent. Therefore, the acid concentration of the eluent can be lowered, and thus the lower limit of quantification is lowered. Moreover, since the elution time is shortened, the analysis time can be shortened. Further, according to the monolith exchange method, since the liquid passing speed of the water to be analyzed can be increased, the time required for capturing impurities is shortened, so that the analysis time can be shortened.

The average diameter of the openings of the monolith cation exchanger in the dry state and the average diameter of the openings of the monolith intermediate described below refer to the maximum value of the pore distribution curve obtained by the mercury intrusion method. The average thickness of the skeleton of the monolith cation exchanger in the dry state is determined by SEM (scanning electron microscope) observation of the dry monolith cation exchanger (the image obtained by performing SEM observation at least 3 times). Measure the thickness of the skeleton inside and use the average value as the average thickness). The skeleton is rod-shaped and has a circular cross-section, but may include a skeleton having a different diameter such as an elliptical cross-section. The thickness in this case is the average of the minor axis and the major axis.

In the monolith cation exchanger, the introduced cation exchange groups are preferably uniformly distributed not only on the surface of the porous body but also inside the skeleton of the porous body.

<Manufacturing method of monolith cation exchanger>
A monolith (a monolith-like substance of a monolith cation exchanger before the introduction of an ion exchange group) can be obtained, for example, by performing the following steps.
Step I: A water-in-oil emulsion is prepared by stirring a mixture of oil-soluble monomer, surfactant and water that does not contain ion-exchange groups, and then the water-in-oil emulsion is polymerized to obtain a total pore volume. A step of obtaining a monolithic organic porous intermediate having a continuous macropore structure of more than 16 mL / g and 30 mL / g or less (hereinafter, also referred to as “monolith intermediate”).
Step II: In the aromatic vinyl monomer, a total oil-soluble monomer having at least two or more vinyl groups in one molecule, 0.3 to 5 mol% of the cross-linking agent, the aromatic vinyl monomer and the cross-linking agent are dissolved. A step of preparing a mixture consisting of an organic solvent in which the polymer produced by polymerizing an aromatic vinyl monomer is insoluble and a polymerization initiator.
Step III: The mixture obtained in Step II is polymerized in the presence of the monolith intermediate obtained in Step I to obtain a monolith which is an organic porous body which is a co-continuous structure. The process of obtaining.
In addition, there is no order of the first step and the second step, and the second step may be performed after the first step, or the first step may be performed after the second step.

The first step may be performed in accordance with the method described in JP-A-2002-306976.

Among the oil-soluble monomers used in the step I, suitable are aromatic vinyl monomers, and examples thereof include styrene, α-methylstyrene, vinyltoluene, vinylbenzyl chloride, and divinylbenzene. These monomers can be used alone or in combination of two or more. However, a crosslinkable monomer such as divinylbenzene or ethylene glycol dimethacrylate is selected as at least one component of the oil-soluble monomer, and the content thereof is 0.3 to 5 mol%, preferably 0.3 to 0.3 to the total oil-soluble monomer. 3 mol% is preferable because it is advantageous for forming a co-continuous structure.

The surfactant used in the step I 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 may 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 a continuous phase and water droplets are dispersed therein. The amount of the above-mentioned surfactant added varies greatly depending on the type of the oil-soluble monomer and the size of the target emulsion particles (macropores), and therefore cannot be unequivocally determined, but the total amount of the oil-soluble monomer and the surfactant. It can be selected in the range of about 2 to 70% by mass.

Further, in the first step, a polymerization initiator may be used as necessary when forming a 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.

In the first step, the mixing method for mixing an oil-soluble monomer containing no ion-exchange group, a surfactant, water and a polymerization initiator to form a water-in-oil emulsion is not particularly limited, and each component is not particularly limited. The oil-soluble monomer, surfactant, and oil-soluble polymerization initiator, which are oil-soluble components, and the water-soluble component, which is water or a water-soluble polymerization initiator, are uniformly and uniformly dissolved separately. Later, a method of mixing each component can be used. The mixing device for forming the emulsion is also not particularly limited, and a normal mixer, homogenizer, high-pressure homogenizer, or the like can be used, and an appropriate device may be selected to obtain the desired emulsion particle size. Further, the mixing conditions are not particularly limited, and the stirring rotation speed and the stirring time capable of obtaining the desired emulsion particle size can be arbitrarily set.

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

The total pore volume per mass of the monolith intermediate obtained in the step I in a dry state is more than 16 mL / g and less than 30 mL / g, preferably more than 16 mL / g and less than 25 mL / g. That is, although this monolith intermediate basically has a continuous macropore structure, the skeleton constituting the monolith structure is primary from the two-dimensional wall surface because the opening (mesopore), which is the overlapping part of the macropore and the macropore, is remarkably large. It has a structure that is as close as possible to the original rod-shaped skeleton. When this is allowed to coexist in the polymerization system, a porous body having a co-continuous structure is formed using the structure of the monolith intermediate as a mold. In order to make the total pore volume of the monolith intermediate within the above range, the ratio of the monomer to water may be approximately 1:20 to 1:40.

Further, in the monolith intermediate obtained in the first step, the average diameter of the openings (mesopores) which are the overlapping portions of the macropores and the macropores is 5 to 100 μm in a dry state. The monolith intermediate preferably has a uniform structure having the same macropore size and opening diameter, but is not limited to this, and non-uniform macropores larger than the uniform macropore size are scattered in the uniform structure. It may be something to do.

The aromatic vinyl monomer used in the second step is not particularly limited as long as it is an oil-based aromatic vinyl monomer containing a polymerizable vinyl group in the molecule and having high solubility in an organic solvent. It is preferable to select a vinyl monomer that produces a polymer material of the same type or similar to the monolith intermediate coexisting in the polymerization system.

The amount of the aromatic vinyl monomer added in the second step is 5 to 50 times, preferably 5 to 40 times, the mass of the monolith intermediate coexisting at the time of polymerization.

As the cross-linking agent used in the second step, one containing at least two polymerizable vinyl groups in the molecule and having high solubility in an organic solvent is preferably used. Preferred cross-linking agents are aromatic polyvinyl compounds such as divinylbenzene, divinylnaphthalene and divinylbiphenyl because of their high mechanical strength and stability against hydrolysis. The amount of the cross-linking 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 cross-linking agent (total oil-soluble monomer). The amount of the cross-linking agent used is preferably substantially equal to the cross-linking density of the monolith intermediate coexisting during the polymerization of the vinyl monomer / cross-linking agent.

The organic solvent used in the second step is an organic solvent that dissolves the aromatic vinyl monomer and the cross-linking agent but does not dissolve the polymer produced by polymerizing the aromatic vinyl monomer, and the amount of the organic solvent used is the above-mentioned aromatic. It is preferable to use it so that the concentration of the vinyl monomer is 30 to 80% by mass.

As the polymerization initiator used in the second step, a compound that generates radicals by heat or light irradiation is preferably used. The polymerization initiator is preferably oil-soluble. The amount of the polymerization initiator used varies greatly depending on the type of monomer, the polymerization temperature, etc., but can be used in the range of about 0.01 to 5% by mass with respect to the total amount of the vinyl monomer and the cross-linking agent.

When a monolith intermediate having a specific continuous macropore structure is present in the polymerization system of the third step, the particle agglomeration structure disappears and the monolith having the above-mentioned co-continuous structure is obtained.

In the method for producing a monolith, the internal volume of the reaction vessel is not particularly limited as long as it has a size that allows the monolith intermediate to exist in the reaction vessel, and when the monolith intermediate is placed in the reaction vessel, it is flat. It may be either one in which a gap is visually formed around the monolith, or one in which the monolith intermediate enters the reaction vessel without a gap. Of these, the monolith with a thick bone after polymerization does not receive pressure from the inner wall of the container and enters the reaction vessel without a gap, but the monolith is not distorted and the reaction raw material is not wasted and is efficient. Even when the internal volume of the reaction vessel is large and there is a gap around the monolith after polymerization, the vinyl monomer and the cross-linking agent are adsorbed and distributed to the monolith intermediate, so that the gap in the reaction vessel No particle agglomerate structure is formed in the portion.

In step III, the monolith intermediate is placed in the reaction vessel in a state of being impregnated with the mixture (solution). As described above, the blending ratio of the mixture obtained in the second step and the monolith intermediate is such that the amount of the vinyl monomer added is 3 to 50 times, preferably 4 to 40 times, the mass of the monolith intermediate. It is preferable to blend in. This makes it possible to obtain the monolith having a thick skeleton while having an appropriate opening diameter. In the reaction vessel, the vinyl monomer and the cross-linking agent in the mixture are adsorbed and distributed to the skeleton of the stationary monolith intermediate, and the polymerization proceeds in the skeleton of the monolith intermediate.

In step III, the monolith intermediate is placed in the reaction vessel in a state of being impregnated with the mixture (solution). As described above, the blending ratio of the mixture obtained in the second step and the monolith intermediate is such that the amount of the aromatic vinyl monomer added is 5 to 50 times, preferably 5 to 40 times by mass, with respect to the monolith intermediate. It is preferable to mix them in such a manner. As a result, it is possible to obtain a monolith having a co-continuous structure in which pores of an appropriate size are three-dimensionally continuous and the skeleton of the bone is three-dimensionally continuous. In the reaction vessel, the aromatic vinyl monomer and the cross-linking agent in the mixture are adsorbed and distributed to the skeleton of the stationary monolith intermediate, and the polymerization proceeds in the skeleton of the monolith intermediate.

Various conditions are selected for the polymerization conditions in the third step depending on the type of monomer and the type of initiator. By heat polymerization, the vinyl monomer adsorbed and distributed on the skeleton of the monolith intermediate and the cross-linking agent are polymerized in the skeleton, and the skeleton can be thickened. After completion of the polymerization, the contents are taken out and extracted with a solvent such as acetone for the purpose of removing the unreacted vinyl monomer and the organic solvent to obtain the monolith.

The monolith cation exchanger is obtained by performing the IV step of introducing a cation exchange group into the monolith obtained in the III step.

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.

Further, 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, chlorosulfate, concentrated sulfuric acid, or fuming sulfuric acid is used. A method of uniformly introducing a radical initiator group or a chain transfer group into a monolith and graft-polymerizing sodium styrene sulfonate or acrylamide-2-methylpropane sulfonic acid on the surface of the skeleton and inside the skeleton; similarly, glycidyl methacrylate. A method of introducing a sulfonic acid group by functional group conversion after graft polymerization of the above can be mentioned. Of these methods, the method of introducing sulfonic acid into the styrene-divinylbenzene copolymer using chlorosulfate is preferable because the cation exchange group can be introduced uniformly and quantitatively.

Although the monolith and the monolith cation exchanger have a remarkably large size of three-dimensionally continuous pores, they have a skeletal skeleton and therefore have high mechanical strength. Further, since the monolith cation exchanger has a thick skeleton, the cation exchange capacity per volume in a water-wet state can be increased, and the liquid to be treated can be passed through at a low pressure and a large flow rate for a long period of time.

[Example 1]
An 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 group per gram of membrane: 1). 6.6 mm equivalent, 1.5 mm equivalent of the ion exchange group as a module, average pore size 0.1 μm).

The ion adsorption membranes were installed on the sampling lines L11 and L12 of the ultrapure water production apparatus having the subsystem 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 the water flow rate was about 10 m ³ / h. ..

This ultrapure water device was operated to produce ultrapure water, and sample water was passed through the respective ion adsorption films from the operating ultrapure water production device through sampling lines L11 and L12. The concentration time was about 3 days, and about 2000 L of sample water was passed through the ion adsorption membrane for concentration at 500 mL / min. After capturing the metal in the sample water with an ion adsorption membrane, the captured metal ions were eluted with 100 mL of 1N nitric acid diluted with high-purity nitric acid TAMAPURE AA-100 (trade name) manufactured by Tama Chemical Co., Ltd., and contained in the eluent. The amount of metal was measured by ICP-MS. Since the concentration ratio is 2000 / 0.1 = 20000 times, the value obtained by dividing the amount of metal (ng) in the eluent by the concentration ratio is the metal concentration in the sample water.

FIG. 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 filtration membrane outlet water is higher than the metal concentration of the inlet water, and the calcium and zinc concentrations are particularly high. From this, it can be estimated that the cleanliness of the ultrafiltration membrane has already deteriorated. By evaluating the water quality upstream and downstream of the ultrafiltration membrane in this way, it is possible to evaluate the cleanliness of the filtration membrane.

[Example 2]
The same test as in Example 1 was carried out for the ultrapure water production apparatus at another site. The result is shown in FIG. Since the amounts of Li and Cd were so small that they could not be shown, they were omitted in FIG. The metal concentration of the outlet water is lower than the metal concentration of the inlet water of the ultrafiltration membrane, and the concentrations of calcium and iron are particularly low. Therefore, it can be seen that the metal exists in the state of fine particles in the water at the inlet of the ultrafiltration membrane, and the cleanliness of the ultrafiltration membrane is being lowered. After that, by regularly performing metal analysis at the outlet of the ultrafiltration membrane, it is possible to determine the replacement time of the ultrafiltration membrane, and as a result, good water quality management becomes possible.

1 Ultrapure water production equipment 2 Primary pure water tank 3 Ultraviolet oxidation equipment 4 Ion exchange equipment 5 Ultrafiltration membrane equipment 6, 7, 8 Branch points 14, 15 Analytical means

Claims (10)

It is a water quality control method for ultrapure water production equipment.
The ultrapure water production apparatus includes a filtration membrane and has a filtration membrane.
Ultrapure water characterized by including an analysis step of analyzing 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 permeated the filtration membrane by using a concentration method, respectively. Water quality control method for pure water production equipment. The water quality control method for an ultrapure water production apparatus according to claim 1, wherein the metal concentration of the ultrapure water is 1 ng / L or less for at least one of the metals analyzed in the analysis step. The water quality control method for an ultrapure water production apparatus according to claim 2, wherein the metal to be analyzed in the analysis step is at least one selected from the group consisting of Na, Ca, Al, Fe, Cr, Pb and Zn. The water quality control method for an ultrapure water production apparatus according to any one of claims 1 to 3, wherein in the analysis step, the filtration membrane inlet water and the filtration membrane outlet water are sampled at the same time. The water quality control of the ultrapure water production apparatus according to any one of claims 1 to 4, wherein the lower limit of quantification of the metal concentration is 0.1 ng / L or less for at least one of the metals analyzed in the analysis step. Method. The water quality control method for an ultrapure water production apparatus according to any one of claims 1 to 5, wherein the filtration membrane is an ultrafiltration membrane provided in a subsystem of the ultrapure water production apparatus. The concentration method captures impurities in the water to be analyzed with a porous ion exchanger, elutes the captured impurities with an eluent, and measures the impurity concentration in the obtained eluent. Ion exchanger enrichment. The water quality management method for an ultrapure water producing apparatus according to any one of claims 1 to 6, which is a law. The water quality control method for an ultrapure water production apparatus according to claim 7, wherein a monolithic ion exchanger is used as the porous ion exchanger. 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 the metal fine particles are adhering to the filtration membrane.
The invention according to any one of claims 1 to 8, wherein 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 metal contamination of the filtration membrane has not progressed. Water quality management method for ultrapure water production equipment. An ultrapure water production device equipped with a filtration membrane.
Ultrapure water characterized by including an analysis means for analyzing 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 permeated the filtration membrane by using a concentration method, respectively. Pure water production equipment.

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