Method for evaluating the quality of ion exchange resin and method for producing ultrapure water

Abstract

This method for evaluating the quality of an ion exchange resin includes: a step for causing ultrapure water that serves as sample water to pass through a container filled with the ion exchange resin; a step for quantifying metal components contained in the ultrapure water after passage through the container; and a step for assessing, on the basis of the result of quantification, whether or not the quality of the ion exchange resin is satisfactory.

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the quality of an ion exchange resin and a method for producing ultrapure water. [Background technology]

[0002] In the manufacturing processes of semiconductor devices and liquid crystal devices, ultrapure water, from which impurities have been highly removed, is used for various purposes, such as cleaning processes. Metal components contained in ultrapure water, even in trace amounts, can have a significant impact on device characteristics, so their concentration must be strictly controlled. In recent years, with the rapid increase in integration and miniaturization of semiconductor devices, the requirements for metal concentrations in ultrapure water have become increasingly strict, and ultrapure water with metal concentrations at the pg / L level is required.

[0003] Ultrapure water is generally produced by sequentially treating raw water (river water, groundwater, industrial water, etc.) through a pretreatment system, a primary pure water system, and a secondary pure water system (subsystems). Among these systems, the ion exchanger plays a key role in controlling the metal concentration in the ultrapure water. The ion exchanger is filled with ion exchange resin and is typically located third downstream in the subsystem (upstream of the membrane degassing unit, which is immediately upstream of the ultrafiltration membrane unit). While metal components are known to leach from the piping and pumps used in the ultrapure water production process, an ion exchanger can prevent the effects of metal leaching upstream from affecting the quality of the ultrapure water.

[0004] On the other hand, it is known that metal components may leach from the ion exchange device itself. Therefore, when managing the metal concentration in ultrapure water, it is important to minimize the leaching of metal components, especially from ion exchange resins. To achieve this, it is necessary to use ion exchange resins whose quality has been confirmed in advance as being good for the ion exchange device to be filled with. Patent Document 1 describes a method for evaluating the quality of ion exchange resins and determining whether they are good or bad. In this method, an anion exchange resin is immersed in hydrochloric acid and shaken, and the quality of the anion exchange resin is determined based on the quantitative results of the metal components leached into the hydrochloric acid. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-112944 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the method described in Patent Document 1 does not produce ultrapure water with a metal concentration at the pg / L level, even if the anion exchange resin is determined to be of good quality, and it is difficult to select an anion exchange resin that satisfies the recent strict requirements for metal concentrations in ultrapure water.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method for evaluating the quality of ion exchange resins and a method for producing ultrapure water, which are capable of controlling the metal concentrations in ultrapure water to lower concentrations. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the method for evaluating the quality of an ion exchange resin of the present invention comprises: Before filling the ion exchange unit Anion Exchange Resin and Cation exchange resin Each Product QualityThe step of separately evaluating the quality of the ion exchange resin to be evaluated includes the step of separately evaluating the quality of the ion exchange resin to be evaluated. In a separate container from the ion exchange unit Filling 、 The method includes the steps of passing ultrapure water as sample water through a container, quantifying the amount of metal components contained in the ultrapure water after passing through the container, and determining whether the quality of the ion exchange resin being evaluated is good based on the results of the quantification.

[0009] The method for producing ultrapure water of the present invention is a method for producing ultrapure water by treating water to be treated, and includes the steps of filling an ion exchange device with an ion exchange resin selected based on the evaluation results of the above-mentioned quality evaluation method, and passing the water to be treated through the ion exchange device to obtain treated water.

[0010] This method allows the quality of ion exchange resins to be evaluated by simulating the actual operating conditions of an ultrapure water production system, making it possible to appropriately determine the quality of ion exchange resins according to the required quality level of ultrapure water, and to select ion exchange resins of better quality. [Effects of the Invention]

[0011] As described above, according to the present invention, the metal concentration in ultrapure water can be controlled to a lower concentration. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram showing the configuration of an ultrapure water production apparatus according to one embodiment of the present invention. [Figure 2] 1 is a schematic diagram illustrating a configuration of an evaluation device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0014] 1 is a schematic diagram showing the configuration of an ultrapure water production system according to one embodiment of the present invention. Note that the configuration of the ultrapure water production system shown in the figure is merely an example and does not limit the present invention.

[0015] The ultrapure water production system 1 has a primary pure water tank 2, a pump 3, a heat exchanger 4, an ultraviolet oxidation device 5, an ion exchange device 6, a membrane degassing device 7, and an ultrafiltration (UF) membrane device 8. These components constitute a secondary pure water system (subsystem) that sequentially processes primary pure water produced in a primary pure water system (not shown) to produce ultrapure water, and supplies the ultrapure water to a point of use 9.

[0016] The water to be treated (primary pure water) stored in the primary pure water tank 2 is pumped by a pump 3 and supplied to a heat exchanger 4. After passing through the heat exchanger 4 and having its temperature adjusted, the water is supplied to an ultraviolet oxidation device 5 and irradiated with ultraviolet light. In this way, total organic carbon (TOC) in the water to be treated is decomposed. The water to be treated then undergoes ion exchange treatment in an ion exchanger 6 to remove metals and other impurities. The water to be treated then undergoes membrane degassing treatment in a membrane degassing device 7 to remove dissolved gases, and then undergoes UF membrane treatment in a UF membrane device 8 to remove fine particles. A portion of the ultrapure water thus obtained is supplied to a point of use 9, and the remainder is returned to the primary pure water tank 2. Primary pure water is supplied to the primary pure water tank 2 from a primary pure water system (not shown) as needed. The primary pure water tank 2, pump 3, heat exchanger 4, ultraviolet oxidation device 5, ion exchanger 6, membrane degassing device 7, and UF membrane device 8 can be components commonly used in subsystems of ultrapure water production systems. For example, the ion exchange device 6 may be a non-regenerative mixed-bed ion exchange device (cartridge polisher) filled with a mixed bed of cation exchange resin and anion exchange resin.

[0017] When the ultrapure water produced by the ultrapure water production system 1 is used to clean semiconductor devices, liquid crystal devices, and the like, strict control of the metal concentration in the ultrapure water is required, as described above. The metal concentration in this case also depends on the quality of the ion exchange resin filled in the ion exchange unit 6. In other words, if the quality of the ion exchange resin is poor, metal components will leach out from the ion exchange resin itself in excess of the allowable amount, resulting in the ultrapure water not meeting the required quality level. Therefore, as part of operational management to supply ultrapure water of stable quality to the point of use 9, it is necessary to analyze the metal components leaching from the ion exchange resin in advance, evaluate the quality of the ion exchange resin based on the analysis results, and select and use the ion exchange resin that is determined to be good. Hereinafter, a method for evaluating the quality of such an ion exchange resin will be described with reference to FIG. 2. FIG. 2 is a schematic diagram showing the configuration of an evaluation device used to implement the quality evaluation method for ion exchange resins of this embodiment. In this embodiment, the quality of the anion exchange resin and the cation exchange resin are evaluated separately using a similar method, and the anion exchange resin and the cation exchange resin that are determined to be good quality are mixed and filled into the ion exchange unit 6. Therefore, it should be noted that the ion exchange resin in the following description applies to both anion exchange resins and cation exchange resins.

[0018] First, a nonmetallic test column (container) 11 is packed with the ion exchange resin to be evaluated, and a concentrating column (container) 12 packed with a porous ion exchanger as a capture material is installed at the outlet of the column. Ultrapure water is then passed through the test column 11 as sample water, and then the water is passed through the concentrating column 12. This causes metal components to elute from the ion exchange resin in the test column 11 into the sample water, and the eluted metal components are captured and concentrated by the porous ion exchanger in the concentrating column 12. The water flow time (concentration time) depends on the amount of water passed through the test column 11, but is not particularly limited as long as the metal components to be analyzed are concentrated to a level that allows for sufficient accuracy in quantification, and is, for example, several days. Furthermore, while an ion adsorption membrane (particularly a porous membrane with cation exchange capacity) can be used as the porous ion exchanger to be packed into the concentrating column 12, it is preferable to use a monolithic organic porous ion exchanger because it allows water to pass through at a higher space velocity and shortens the time required for concentration. After that, when a predetermined water flow time has elapsed, the water flow through the test column 11 is stopped, and the porous ion exchanger is recovered from the concentration column 12.

[0019] Next, the metal components captured on the recovered porous ion exchanger are eluted into an eluent (e.g., nitric acid diluted to a predetermined concentration). The metal components in the eluent are then quantified, and the metal concentration in the sample water is calculated from the obtained metal amount. For example, an inductively coupled plasma mass spectrometer (ICP-MS) can be used to quantify the metal components, and the metal concentration in the sample water can be calculated by dividing the obtained metal amount by the concentration factor of the eluent. Using a monolithic organic porous ion exchanger as the capture member for the concentration column 12 is also preferable because it reduces the differential pressure caused by water flow and allows water to flow at a predetermined flow rate.

[0020] While there are no particular limitations on the type of metal component to be analyzed, it is preferable to analyze Na (sodium), which is known to be a metal component that is likely to leach from ion exchange resins. This is because an OH-type anion exchange resin is used, and a sodium hydroxide solution is used for regeneration. Therefore, if the post-regeneration cleaning is insufficient, sodium from this is likely to be leached. Note that the metal component referred to here includes both metal ions and metal particles (microparticles). Furthermore, it is preferable that the ultrapure water used as sample water has as few impurities as possible removed. For example, it is preferable that the concentrations of Na (sodium) and Ni (nickel) are each less than 5 pg / L.

[0021] Based on the calculated metal concentration in the sample water, it is determined whether the quality of the ion exchange resin is good. Specifically, if the calculated metal concentration is less than a predetermined value, the quality of the ion exchange resin is determined to be good, and if the calculated metal concentration is equal to or greater than the predetermined value, the quality is determined to be poor. Note that the predetermined value is not particularly limited and is set appropriately depending on the type of metal component to be analyzed, the required water quality of the ultrapure water to be produced, etc., and is determined in advance based on experimental verification as shown in the examples described below.

[0022] As described above, according to this embodiment, by using ultrapure water to evaluate the quality of the ion exchange resin, it is possible to simulate the actual operating conditions of the ultrapure water production system 1. Then, by analyzing the amount of metal components eluted from the ion exchange resin, the quality of the ion exchange resin can be appropriately determined according to the required water quality level of the ultrapure water. As a result, it is possible to select an ion exchange resin of better quality and control the metal concentration in the produced ultrapure water to a lower concentration. Furthermore, the quality evaluation method according to this embodiment may be performed again on a mixture of anion exchange resin and cation exchange resin determined to be of good quality before filling the ion exchange device 6. This allows the concentration of metal components contained in the treated water from the ion exchange device 6 to be estimated in advance. As a result, even if metal components exceeding the allowable amount are eluted from the ion exchange device 6 during actual operation, it is possible to determine whether the cause is, for example, the ion exchange resin itself or contamination occurring when the ion exchange resin is filled into the ion exchange device 6.

[0023] When selecting the ion exchange resin to be filled in the ion exchange device 6, it may be difficult to perform the quality evaluation method of this embodiment for each anion exchange resin and each cation exchange resin individually due to issues such as workload and time. To prepare for such a case, the quantification results (amounts of eluted metal components) obtained by the quality evaluation method of this embodiment in the past may be stored in a storage medium as a database in association with other information related to the quality of the ion exchange resin. Thus, even if the quality evaluation method of this embodiment is difficult to perform due to operational reasons, if the other quality information can be obtained, the amount of eluted metal components can be estimated using a previously prepared database. Then, based on the estimated amount of eluted metal components, it is possible to determine whether the quality of the ion exchange resin is good. A database related to the quantification results is preferably created for each anion exchange resin and each cation exchange resin, but it may also be created for a mixture of these resins. That is, to estimate the amount of eluted metal components from a mixture of anion exchange resin and cation exchange resin, it is preferable to use a database created for each resin, but it is also possible to use a database created for the mixture.

[0024] The other quality information mentioned above includes, but is not limited to, the resistivity of the wash water (ultrapure water) used in the cleaning process performed during the purification of ion exchange resins. This is because, in the purification process of ion exchange resins, ultrapure water is used for finishing the cleaning process, and the resistivity of such wash water is often used as an index for evaluating the purification quality of the ion exchange resins. Storing the resistivity of the wash water in a database is also preferable because it allows for flexible response to various requirements regarding the quality of ultrapure water. In other words, by utilizing such a database, even when it is required to control not only the metal concentration but also the resistivity as the quality of ultrapure water, it becomes possible to quickly and appropriately select an ion exchange resin that satisfies both requirements.

[0025] In addition to the method using ultrapure water as in this embodiment, other methods using hydrochloric acid, as described above, are also known for evaluating the quality of ion exchange resins. Specifically, a method is known in which an ion exchange resin is immersed in hydrochloric acid, shaken, and the amount of metal components eluted in the hydrochloric acid is quantified to determine the quality of the ion exchange resin. While this method cannot simulate the actual operating conditions of the ultrapure water production system 1 as in this embodiment, it is considered preferable in that if the amount of eluted metal components during actual operation can be predicted from the analysis results, there is no need to concentrate the metal components and the analysis time is not required. However, the inventors have found that the amount of eluted metal components by hydrochloric acid has a low correlation with the amount of eluted metal components by ultrapure water, and therefore the amount of eluted metal components during actual operation cannot be predicted from the amount of eluted metal components by hydrochloric acid as in this embodiment. Therefore, the method using hydrochloric acid described above is not suitable for cases where the metal concentration in ultrapure water must be maintained at a lower level. The experimental results that led to this finding are described below.

[0026] The inventors measured the amount (concentration) of metal components eluted when hydrochloric acid was passed through an ion exchange resin, and calculated the correlation coefficient with the results obtained by the quality evaluation method according to this embodiment.

[0027] Specifically, eight different brands of anion exchange resins and nine different brands of cation exchange resins were prepared and washed with ultrapure water, and 20 ml of each was packed into a fluororesin container. 1N hydrochloric acid was then passed through the container, and the concentration of metal components eluted in the hydrochloric acid was measured using ICP-MS. Similarly, eight types of anion exchange resins and nine types of cation exchange resins were washed with ultrapure water, and 500 ml of each was packed into a fluororesin test column. The test column was then left for 50 hours. -1Ultrapure water was passed through the test column at a space velocity of 1000 kJ / s for 18 hours, and the metal components eluted into the ultrapure water were captured by a concentration column (monolithic organic porous cation exchanger) installed at the outlet of the test column. The captured metal components were then eluted into an eluent, and the amount of metal in the eluent was measured. As the eluent, 100 mL of nitric acid, prepared by diluting high-concentration nitric acid (trade name: TAMAPURE AA-100) manufactured by Tama Chemicals Co., Ltd. to 1N or more, was used. The amount of metal was measured using ICP-MS, and the metal concentration was calculated by dividing the measured amount of metal by the concentration factor of the eluent.

[0028] The correlation coefficients between the metal concentrations eluted with hydrochloric acid and those eluted with ultrapure water were calculated for both anion exchange resins and cation exchange resins. As a result, when the metal component was sodium, for example, the correlation coefficients were less than 0.5 for anion exchange resins and greater than 0.99 for cation exchange resins. This indicates that, at least for anion exchange resins, there is no high correlation between the amount of metal components eluted with hydrochloric acid and the amount of metal components eluted with ultrapure water. In other words, even if an anion exchange resin is judged to be of good quality because the amount of metal components eluted with hydrochloric acid is less than the specified value, there is a possibility that metal components exceeding the allowable amount may be eluted when ultrapure water quality is passed through the resin during actual operation.

[0029] The quality evaluation method according to this embodiment may be performed on ion exchange resins packed in a non-regenerative ion exchange device installed in a primary pure water system, as well as on ion exchange resins packed in an ion exchange device installed in a subsystem as described above. The quality evaluation method according to this embodiment may be performed on anion exchange resins or cation exchange resins individually, not only when anion exchange resins and cation exchange resins are packed in a mixed bed in an ion exchange device, but also when anion exchange resins or cation exchange resins are packed in a single bed.

[0030] (Example) Next, the effects of the present invention will be described with reference to specific examples.

[0031] First, in this example, six different brands of anion exchange resins (resins A to F) were prepared, and the amount (concentration) of metal components eluted from each resin was measured using the quality evaluation method according to this embodiment. Specifically, after washing resins A to F with ultrapure water, 500 ml of each was packed into a test column made of fluororesin. Then, the test column was left for 50 hours. -1 Ultrapure water was passed through the test column at a space velocity of 1000 kJ / s for 18 hours, and the metal components eluted into the ultrapure water were captured by a concentration column (monolithic organic porous cation exchanger) installed at the outlet of the test column. The captured metal components were then eluted into an eluent, and the amount of metal in the eluent was measured. As the eluent, 100 mL of nitric acid, prepared by diluting high-concentration nitric acid (trade name: TAMAPURE AA-100) manufactured by Tama Chemicals Co., Ltd. to 1N or more, was used. The amount of metal was measured using ICP-MS, and the metal concentration was calculated by dividing the measured amount of metal by the concentration factor of the eluent.

[0032] Table 1 shows the measurement results of the amount (concentration) of sodium eluted from Resins A to C and the measurement results of the amount (concentration) of Ni (nickel) eluted from Resins D to F.

[0033] [Table 1]

[0034] Comparing Resins A to C, it can be seen that Resins A and B have significantly less sodium elution than Resin C, indicating better quality. Furthermore, Resin B elutes less sodium than Resin A, indicating that Resin B is of better quality than Resin A. On the other hand, comparing Resins D to F, it can be seen that the amount of nickel elution decreases in the order of Resin F, Resin E, and Resin D, indicating that the quality improves in this order.

[0035] Next, in this example, six types of anion exchange resins (resins A to F) were mixed with cation exchange resins to prepare six mixtures (mixtures A to F). The amounts (concentrations) of eluted metal components from each mixture were measured using the same procedure as described above. The anion exchange resin and cation exchange resin were mixed in a 1:2 ratio, and a total of 500 ml of the mixture was packed into the test column. The cation exchange resins used were those whose quality had been confirmed to be good, i.e., whose elution amounts of metal components were confirmed to meet the required ultrapure water quality by measurements similar to those described above. Specifically, for mixtures A to C (mixtures with resins A to C), cation exchange resins of the same brand were used, which had been confirmed to have sodium elution amounts of less than 5 pg / L. For mixtures D to F (mixtures with resins D to F), cation exchange resins of the same brand were used, which had been confirmed to have nickel elution amounts of less than 5 pg / L.

[0036] Table 2 shows the measurement results of the amount (concentration) of eluted sodium in mixtures A to C and the measurement results of the amount (concentration) of eluted nickel in mixtures D to F.

[0037] [Table 2]

[0038] Comparing Mixtures A to C, the amount of sodium eluted from Mixtures A and B was lower than that from Mixture C, indicating that Resins A and B were of better quality than Resin C. On the other hand, the amount of sodium eluted from both Mixtures A and B reached a level (less than 5 pg / L) that met the required quality for ultrapure water. This indicates that there is no significant difference in the quality of Resin A and Resin B as long as they are used in an ion exchange system as a mixture with a cation exchange resin. Therefore, of Resins A to C, Resin A and Resin B are suitable as anion exchange resins for use in ultrapure water production systems (subsystems). Furthermore, it can be seen that the reference value (the above-mentioned predetermined value) for determining the quality of anion exchange resins is preferably 100 pg / L, more preferably 50 pg / L, and even more preferably 30 pg / L, when sodium is the target of analysis.

[0039] Similarly, the amount of nickel eluted from mixtures D and E was smaller than that from mixture F, and both reached a level (less than 5 pg / L) that satisfied the required quality of ultrapure water. This indicates that, of resins D to F, resins D and E are suitable as anion exchange resins to be used in ultrapure water production systems (subsystems), and that the reference value (the above-mentioned predetermined value) for determining the quality of the resins is preferably 80 pg / L, and more preferably 60 pg / L, when nickel is the target of analysis. [Explanation of symbols]

[0040] 1 Ultrapure water production equipment 2 Primary pure water tank 3. Pump 4 Heat exchanger 5. UV oxidation equipment 6. Ion exchange unit 7. Membrane degassing device 8. Ultrafiltration Membrane Device 9 Use Points 11 Test column 12 Concentration column

Claims

1. A method for evaluating the quality of an ion exchange resin, comprising: the step of separately evaluating the quality of each of the anion exchange resin and the cation exchange resin before they are packed into an ion exchange device, separately assessing the quality, a step of filling an ion exchange resin to be evaluated in a container separate from the ion exchange device, and passing ultrapure water as sample water through the container; A step of quantifying metal components contained in the ultrapure water after passing through the container; and determining whether the quality of the ion exchange resin to be evaluated is good based on the results of the quantification.

2. 2. The quality evaluation method for ion exchange resins according to claim 1, wherein the determining step includes calculating the concentration of the metal component from the quantification result, and determining that the quality of the ion exchange resin being evaluated is good if the calculated concentration is less than a predetermined value.

3. The quality of the anion exchange resin is evaluated as the ion exchange resin, 3. The method for evaluating the quality of an ion exchange resin according to claim 2, wherein the metal component is sodium, and the predetermined value is 50 pg / L or less.

4. The quality of the cation exchange resin as the ion exchange resin is further evaluated, 4. The method for evaluating the quality of an ion exchange resin according to claim 3, wherein the metal component is sodium, and the predetermined value is 5 pg / L or less.

5. The method further comprises a step of evaluating the quality of the ion exchange resin comprising a mixture of the anion exchange resin determined to be of good quality and the cation exchange resin determined to be of good quality before the ion exchange resin comprising the mixture is filled into an ion exchange device; The step of evaluating the quality comprises: a step of filling an ion exchange resin comprising the mixture into a container separate from the ion exchange device, and passing ultrapure water as sample water through the container; A step of quantifying metal components contained in the ultrapure water after passing through the container; The method for evaluating the quality of an ion exchange resin according to claim 4, further comprising a step of determining whether or not the quality of the ion exchange resin comprising the mixture is good based on the results of the quantification.

6. 6. The quality evaluation method for ion exchange resins according to claim 1, wherein the quantifying step comprises passing the ultrapure water, which has been passed through the container, through another container filled with a porous ion exchanger, thereby capturing the metal components in the ultrapure water, which has been passed through the container, with the porous ion exchanger, eluting the captured metal components into an eluent, and quantifying the metal components in the eluent.

7. An ultrapure water manufacturing method for manufacturing ultrapure water by treating water to be treated, comprising the steps of: a step of filling an ion exchange device with an ion exchange resin selected based on the evaluation result obtained by the quality evaluation method according to any one of claims 1 to 5; and passing the water to be treated through the ion exchange device to obtain treated water.

8. A step of quantifying the metal components contained in the treated water; 8. The method for producing ultrapure water according to claim 7, further comprising a step of determining whether or not contamination has occurred in the ion exchange device based on the results of the quantification and the results of quantifying the metal components contained in ultrapure water when ultrapure water is passed as sample water through a container filled with the selected ion exchange resin.

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