Ion exchange resin cleaning system and water quality measurement method

Abstract

Properly manage the cleaning of ion exchange resins. [Solution] The ion exchange resin cleaning system 1 comprises a container 2 for cleaning the ion exchange resin 3, a cleaning water supply pipe L2 for supplying cleaning water to the container 2, a discharge pipe L4 for discharging the cleaning wastewater, and a measuring device 5 connected to the discharge pipe L4 for measuring the water quality of the cleaning wastewater. The measuring device 5 comprises an evaporation unit 52 that evaporates the cleaning wastewater to form residual particles, and a measuring unit 53 that measures the number of residual particles.

Description

Technical Field

[0001] The present invention relates to a cleaning system for ion exchange resins and a water quality measurement method.

Background Art

[0002] In a water treatment system including an ion exchange device filled with an ion exchanger, there is a method of determining the performance deterioration of the ion exchanger based on the number of fine particles contained in the treated water of the ion exchange device (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In addition to particles, the treated water of the ion exchange device may contain non-volatile dissolved substances that become particulate residues when dried. Such non-volatile dissolved substances may be harmful depending on the use of pure water. For example, in the cleaning and drying process of semiconductor wafers, non-volatile dissolved substances may precipitate from ultrapure water and become residues on the wafers. Although the ion exchange resin filled in the ion exchange device may be washed in advance, if the ion exchange device is filled with washing drainage containing non-volatile dissolved substances above a specific concentration, non-volatile dissolved substances may flow out from the ion exchange device and the water quality of the treated water may deteriorate.

[0005] An object of the present invention is to provide a cleaning system for ion exchange resins that can appropriately manage the cleaning of ion exchange resins.

Means for Solving the Problems

[0006] The ion exchange resin cleaning system comprises a container for cleaning the ion exchange resin, a cleaning water supply pipe for supplying cleaning water to the container, a discharge pipe for discharging the cleaning wastewater, and a measuring device connected to the discharge pipe for measuring the water quality of the cleaning wastewater. The measuring device comprises an evaporation unit for evaporating the cleaning wastewater to form residual particles, and a measuring unit for measuring the number of residual particles. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an ion exchange resin cleaning system that can appropriately control the cleaning of the ion exchange resin. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram of a cleaning system for ion exchange resin according to one embodiment. [Figure 2] This is a schematic diagram of the measuring device. [Figure 3] This is a schematic diagram showing an example of a water treatment system. [Figure 4] This graph shows the relationship between the TOC concentration of the cationic resin eluate and the number of residual particles. [Figure 5] This graph shows the relationship between the TOC concentration and the number of residual particles in a PSS standard solution. [Figure 6] This graph shows the relationship between the TOC concentration of the anionic resin eluate and the number of residual particles. [Modes for carrying out the invention]

[0009] An embodiment of the ion exchange resin cleaning system of the present invention will be described with reference to the drawings. In the following description, pure water means water with an electrical resistivity of 0.1 MΩ·cm or higher, and ultrapure water is pure water with an electrical resistivity of 15 MΩ·cm or higher (the maximum value is 18.24 MΩ·cm for theoretically pure water). In the following description, when it is not necessary to distinguish between pure water and ultrapure water, the term "pure water" will be used simply. Also, since no distinction is made between fine particles and particles in this specification, fine particles and particles are used interchangeably.

[0010] An embodiment of a washing system for ion exchange resins will be described. Ion exchange resins are shipped after undergoing a purification process and a washing process of the raw material resin. Anion exchange resins and cation exchange resins are supplied separately, so they are purified and washed separately, and then mixed as needed before shipment. Anion exchange resins and cation exchange resins may be purified, washed, and mixed in the same column. The purification process is a process of changing the ionic form of the ion exchange group of the ion exchange resin; in the case of cation exchange resins, the ionic form is changed to the H form, and in the case of anion exchange resins, the ionic form is changed to the OH form. As chemicals for this, in the case of cation exchange resins, for example, an acidic solution such as HCl or HNO3 is used, and in the case of anion exchange resins, an alkaline solution such as NaOH or TMAH (tetramethylammonium hydroxide) is used. The washing process is a process of washing away the chemicals used in purification with ultrapure water.

[0011] Figure 1 shows a schematic configuration of the ion exchange resin washing system 1. The purification, washing, and mixing of the ion exchange resin may be performed in the same container or in separate containers, but in this embodiment, the purification, washing, and mixing are performed in the same container 2. Figure 1 shows the state during washing, and therefore, the container 2 shown in Figure 1 is filled with the purified ion exchange resin. Since there is no significant difference in the purification and washing processes between anion exchange resin and cation exchange resin, in the following description, anion exchange resin and cation exchange resin will not be distinguished and will be referred to as ion exchange resin 3. Ion exchange resin 3 may be a mixture of anion exchange resin and cation exchange resin.

[0012] The cleaning system 1 includes a container 2 for cleaning the ion exchange resin 3, a chemical solution supply pipe L1 for supplying a purification chemical solution to the container 2, a cleaning water supply pipe L2 for supplying cleaning water (ultrapure water) to the container 2, and a discharge pipe L4 for discharging the used chemical solution and cleaning wastewater. The chemical solution supply pipe L1 and the cleaning water supply pipe L2 merge and connect to the container 2. For this reason, switching valves V1 and V2 are provided in the chemical solution supply pipe L1 and the cleaning water supply pipe L2. The chemical solution supply pipe L1 and the cleaning water supply pipe L2 may also be configured to connect to the container 2 separately without a merging section. Similarly, the discharge pipe L4 may be provided separately for discharging the used chemical solution and the cleaning wastewater.

[0013] For water quality management standards of pure water, it is common to use concentrations of particulate matter, total organic carbon (TOC), hydrogen peroxide, metals, anions, and boron. Particulate matter is what originally existed as a solid in pure water and is also called native particle. However, although no control standards have been established, it has recently been pointed out that particulate precursors may be a contributing factor to the formation of residues on semiconductor wafers (see, for example, the International Roadmap for Devices and Systems (IRDS®)). Particulate precursors are non-volatile dissolved substances, and it is believed that the main source of particulate precursors in pure water is high-molecular-weight organic substances leached from resins, etc. Particulate precursors also include high-molecular-weight substances that are not detected as particles due to refractive index, such as live bacteria and microorganisms, substances that normally dissolve in water but easily precipitate and form precipitates, such as silicic acid, and substances that are completely dissolved in water, such as NaCl and KCl. Although particulate precursors dissolve in pure water, they precipitate as the surrounding water evaporates, becoming particulate residues. In the semiconductor wafer cleaning and drying process, semiconductor wafers are cleaned with ultrapure water and then dried, so particulate precursors contained in the cleaning wastewater may become particulate residues due to water evaporation and remain on the wafer surface. Since particulate precursors may not be removable even with the ultrafiltration membrane equipment of ultrapure water production systems, it is becoming increasingly important to appropriately control and suppress the concentration of particulate precursors in the ion exchange resin cleaning process.

[0014] To address this challenge, the cleaning system 1 includes a sampling line L3 branching from a discharge pipe L4, and a measuring device 5 connected to the sampling line L3 for measuring the water quality of the cleaning wastewater. The sampling line L3 is equipped with a valve V3. The measuring device 5 is a water quality measuring device using the spray drying method, and cleaning wastewater flows continuously into the sampling line L3, while the measuring device 5 continuously measures the water quality of the cleaning wastewater. The sampling line L3 can be formed from metal or resin pipes, resin tubes, etc. The measuring device 5 includes a spray unit 51, an evaporation unit 52, a measurement unit 53, and a determination unit 54. In this embodiment, the spray unit 51, evaporation unit 52, and measurement unit 53 are a single unit, and the determination unit 54 is a device independent of the spray unit 51, evaporation unit 52, and measurement unit 53. An example of the unit of the spray unit 51, evaporation unit 52, and measurement unit 53 is the STPC-3 from KANOMAX. The configuration of the measuring device 5 is not limited to this; for example, the spraying unit 51, evaporation unit 52, measurement unit 53, and determination unit 54 may be in a single unit. Since the determination unit 54 includes an arithmetic circuit, it can be configured as a personal computer, or as part of the control device of the cleaning system 1.

[0015] Figure 2 shows the schematic configuration and measurement principle of the measuring device 5. The spray unit 51 has an introduction line 55 for the cleaning wastewater to be measured, an introduction line 56 for nitrogen gas, and a spray nozzle 57. The spray nozzle 57 sprays the cleaning wastewater to be measured using the driving force of the nitrogen gas, and condenses the cleaning wastewater into droplets. Purified air from which impurities such as organic matter and water have been removed can also be used instead of nitrogen gas.

[0016] The evaporation unit 52 evaporates the washing wastewater to form residual particles. That is, the evaporation unit 52 heats the droplets W generated by spraying and evaporates the water. The specific particles P1 are present in the washing wastewater in the same size and shape as, or close to, that they were in when the washing wastewater was removed. The specific particles that were present in the washing wastewater are dried by the evaporation unit 52 as the surrounding water evaporates, forming an aerosol. The fine particle precursors are dissolved in the washing wastewater, but as the surrounding water evaporates, they precipitate as particulate residue P2, also forming an aerosol. Therefore, the residual particles P include both the specific particles P1 formed by the removal of water by the evaporation unit 52 and the particulate residue P2 formed (precipitated) by the removal of water by the evaporation unit 52.

[0017] The measurement unit 53 continuously measures the number (concentration) of residual particles P contained per unit volume of washing wastewater. The measurement unit 53 includes an alcohol supply unit 58 and an agglomerated particle counter 59. The alcohol supply unit 58 supplies, for example, n-butyl alcohol to form supersaturated alcohol vapor around the residual particles P. The supersaturated alcohol vapor cools and condenses, causing alcohol droplets to condense and grow with the residual particles P as nuclei. The agglomerated particle counter 59 counts the number of alcohol droplets A using the light scattering method. This makes it possible to detect residual particles P that are too small to be directly detected by the light scattering method. The agglomerated particle counter 59 allows setting the minimum detectable particle size of alcohol droplets A, measures the number (concentration) of alcohol droplets A corresponding to the set minimum detectable particle size, and transmits the result to the determination unit 54. The measurement unit 53 may also include a display device that displays the number (concentration) of alcohol droplets A. Since alcohol without residual particles does not grow sufficiently as droplets, the agglomerated particle counter 59 mainly counts the number of alcohol droplets A containing residual particles. By multiplying the obtained measurement value by a pre-calibrated coefficient, the number (concentration) of residual particles in the washing wastewater can be obtained.

[0018] Thus, since the measuring device 5 includes processes such as evaporation and drying, it is possible to measure the concentration of the combined total of the intrinsic particles P1 that originally existed in the liquid as a solid and the particulate residue P2 derived from non-volatile dissolved substances. Since the residual particles P form alcohol droplets, this method can, in principle, measure up to residual particles with a particle size of about 2.5 nm, which is the detection limit of the agglomerate particle counter 59, and has the advantage that the measurement result is not affected by the refractive index or shape of the intrinsic particles or residual particles.

[0019] For example, in the case of STPC-3, the agglomerate particle counter 59 can set the minimum detectable particle size of the residual particles P to 3 nm or more, 9 nm or more, and 15 nm or more. That is, the agglomerate particle counter 59 can measure the number of residual particles with a particle size of 3 nm or more, the number of residual particles with a particle size of 9 nm or more, and the number of residual particles with a particle size of 15 nm or more. The agglomerate particle counter 59 cannot distinguish between the intrinsic particles and the particulate residue, but most of the residual particles with a particle size of 3 nm or more are considered to be particulate residues derived from the fine particle precursors, and most of the residual particles with a particle size of 15 nm or more are considered to be intrinsic particles. Therefore, in order to control the concentration of the fine particle precursors, it is preferable to measure the concentration of the residual particles with a particle size of 3 nm or more.

[0020] The determination unit 54 determines whether or not the number of residual particles P measured by the measurement unit 53 is less than the reference value. The determination unit 54 stores the reference value in advance and compares the measured number with the reference value. When the determination unit 54 determines that the number of residual particles P is less than the reference value, it generates at least one of a signal indicating that the number of residual particles P is less than the reference value and a signal indicating that the cleaning has ended.

[0021] Next, the operation method of the cleaning system 1 and the method for measuring the quality of the cleaning wastewater will be described. The container 2 is pre-filled with the ion exchange resin 3. Open valve V1, close valves V2 and V3, and inject the chemical solution from the chemical solution supply pipe L1 into the container 2 to purify the ion exchange resin 3. The used chemical solution is discharged from the discharge pipe L4. Next, as shown in FIG. 1, close valve V1, open valves V2 and V3, and inject the cleaning water from the cleaning water supply pipe L2 into the container 2 to clean the ion exchange resin 3. The cleaning wastewater is discharged from the discharge pipe L4. From the ion exchange resin 3, the polymer organic matter (particle precursor) constituting the matrix elutes. A part of the cleaning wastewater is introduced from the sampling line L3 into the measuring device 5. In this embodiment, a configuration in which a part of the cleaning wastewater is introduced into the measuring device 5 via the sampling line L3 is illustrated. However, for example, a part of the cleaning wastewater may be sampled in a container or the like and introduced into the measuring device 5. The measuring device 5 evaporates the cleaning wastewater introduced into the measuring device 5 to form residual particles P, and continuously measures the number (concentration) of residual particles P contained per unit amount of the cleaning wastewater.

[0022] When the number of the measured residual particles P falls below the reference value, the determination unit 54 generates at least one of a signal indicating that the number has fallen below the reference value and a signal indicating that the cleaning has ended. The measuring device 5 can report these signals to the outside by an arbitrary method such as a message or voice. The operator can determine that the cleaning has ended based on the report and proceed to the next process such as mixing and shipping of the ion exchange resin 3.

[0023] In this embodiment, the process of purifying and washing new ion exchange resin has been described, but the process of purifying and washing used anion exchange resin and cation exchange resin can be carried out in the same manner. In this case, purification is synonymous with regeneration. If used anion exchange resin and cation exchange resin are supplied separately, purification and washing are performed in the same way as with new ion exchange resin. If used anion exchange resin and cation exchange resin are supplied in a mixed state, they are separated into anion exchange resin and cation exchange resin using the difference in specific gravity. After that, the anion exchange resin and cation exchange resin can be purified and washed together in the same container, or they can be purified and washed in separate containers. If the same container is used, the chemical solutions for the anion exchange resin and cation exchange resin are injected from different parts of the container and recovered from near the boundary between the anion exchange resin and cation exchange resin. If separate containers are used, the anion exchange resin and cation exchange resin are separated into separate containers, purified and washed, and then the anion exchange resin and cation exchange resin are mixed. Purification and washing can be carried out in the same way as with new ion exchange resin.

[0024] The present invention relates to a purified or regenerated ion exchange resin, which can be applied to ion exchange resins before they are filled into ion exchange devices in a water treatment system. Figure 3 shows a schematic diagram of an example of a water treatment system. The water treatment system 11 includes a primary pure water system 21 that produces pure water from raw water, and a secondary pure water system (hereinafter referred to as a subsystem) 31 that further removes impurities from the pure water produced in the primary pure water system 21 to produce ultrapure water of the required quality at use point 4. The primary pure water system 21 includes a raw water tank, a heat exchanger, a turbidity removal membrane device, an activated carbon tower, a decarboxylation membrane device, a reverse osmosis membrane device, an ultraviolet irradiation device, a degassing membrane device, etc. (not shown). The subsystem 31 includes a pure water tank 32, an ion exchange device 33, and an ultrafiltration membrane device 34, which are arranged in this order along the main pipe L5 and in series along the flow direction D of the water to be treated. Between the pure water tank 32 and the ion exchange device 33, a pure water supply pump, an ultraviolet oxidation device, a hydrogen peroxide removal device, an ion exchange device, a membrane degasser (these are not shown), etc., can be installed. Ultrapure water not used at use point 4 is returned to the pure water tank 32 by a return line L6 connected to the main pipe L5. The pure water tank 32 stores pure water produced by the primary pure water system 21. The ion exchange device 33 is filled with a mixed bed of cation exchange resin and anion exchange resin to remove ionic components from the water to be treated. The ultrafiltration membrane device 34 removes fine particles and the like. The ion exchange device 33 is an example of the ion exchange device described above.

[0025] (Examples) A new cation exchange resin (product name: AMBERJET® ESG1024(H), manufactured by Organo Corporation) was mixed with 100 mL of pure water and shaken at 40°C for 16 hours to prepare an aqueous solution containing substances eluted from the cation exchange resin (hereinafter referred to as the cation resin eluate). Similarly, a new anion exchange resin (product name: AMBERJET® ESG4002(OH), manufactured by Organo Corporation) was mixed with 100 mL of pure water and shaken at 40°C for 16 hours to prepare an aqueous solution containing substances eluted from the anion exchange resin (hereinafter referred to as the anion resin eluate). Next, the TOC concentrations of the cation resin eluate and the anion resin eluate were measured using a TOC meter (Sievers M9e). The TOC concentration of the cation resin eluate was 78200 μg / L, and the TOC concentration of the anion resin eluate was 25867 μg / L.

[0026] Next, dilutions were prepared by diluting the cationic resin eluate 100-fold, 200-fold, and 300-fold with ultrapure water, and these were analyzed using KANOMAX's STPC-3. To determine the blank values, the ultrapure water used for dilution was also analyzed as a sample using the STPC-3. In addition to the samples, pure water, nitrogen gas (0.35 MPa), and 1-butanol (special grade, manufactured by Kanto Chemical Co., Ltd.) were supplied to the STPC-3. The analysis was performed using the batch mode of the STPC-3.

[0027] Figure 4 shows the relationship between TOC concentration and the number of residual particles measured by STPC-3. Multiple residual particle measurements were obtained for each TOC concentration, and the graph shows the average value of the measured residual particle numbers (Figures 5 and 6 are similar). The minimum detectable particle size for STPC-3 was set to 3 nm. As mentioned above, the cation resin eluate supplied to STPC-3 is diluted at a dilution ratio of 100 to 300 times (let's call it A), but the sample supplied to STPC-3 is further diluted inside STPC-3 at a dilution ratio (let's call it B) equal to the flow rate ratio of pure water to the sample. Therefore, the TOC concentration on the horizontal axis of Figure 4 is not the value actually measured by the TOC meter, but the value obtained by dividing the TOC concentration of the cation resin eluate measured by the TOC meter by the dilution ratio A × B. The flow rate of pure water was 100 mL / min, and the flow rate of the sample was determined from the sample addition time and weight change. Since the flow rate of the sample was approximately 0.2 mL / min, the dilution ratio B inside STPC-3 was approximately 500.

[0028] Figure 4 shows an exponential correlation between the TOC concentration of the sample and the number of residual particles. It is generally believed that polystyrene sulfonic acid (PSS) elutes from cation exchange resins, and this example confirms the possibility that PSS eluted from the cation exchange resin could be detected by STPC-3. PSS is a high-molecular-weight organic substance that is a source of particulate precursors. Therefore, to evaluate how much PSS elutes from the cation exchange resin, the cation resin eluate was analyzed by gel permeation chromatography (GPC). 126 mg / L of PSS with molecular weights of 2400-575, 39 mg / L of PSS with molecular weights of 575-310, and 20 mg / L of PSS with molecular weights of 310-180 were detected. A small amount of substances with molecular weights below 180 were also detected, but these are likely ions. From the above, it was found that virtually only PSS with a molecular weight of less than 2400 elutes from new cation exchange resin, and that it is highly likely that PSS eluted from the cation exchange resin was detected by STPC-3.

[0029] Next, PSS standard samples (polystyrene sulfonate sodium salt, manufactured by SAS Co., Ltd.) with molecular weights of 246, 2010, and 9680 were diluted to a PSS concentration of 1000 μg / L, and the TOC concentration was measured. Additionally, samples were prepared by diluting the PSS standard samples to PSS concentrations of 10, 50, and 100 μg / L, and these were analyzed using STPC-3. As mentioned earlier, the samples were further diluted inside the STPC-3. Figure 5 shows the relationship between TOC concentration and the number of residual particles measured by STPC-3. The TOC concentration on the horizontal axis is not the value actually measured by the TOC meter, but rather the value obtained by proportionally converting the measured TOC concentration of the 1000 μg / L diluted solution according to the PSS concentration of the sample. In all cases, a correlation was observed between TOC concentration and the number of residual particles in the range of TOC concentration between 0.005 μg / L and 0.053 μg / L. Although PSS with a molecular weight of 9680 does not leach from new cation exchange resin, it was found that detection is possible even if PSS with a large molecular weight leaches for some reason. Generally, the detection accuracy of TOC meters is on the order of 0.1 μg / L (for this reason, the TOC concentration of the sample was calculated in this example as well), and it was difficult to control the concentration of PSS in the range of TOC concentration from 0.005 μg / L to 0.053 μg / L, but this example showed that it is possible.

[0030] Next, dilutions were prepared by diluting the anionic resin eluate 100, 200, and 300 times with pure water, and these were supplied to STPC-3 for analysis in the same manner as the cationic resin eluate. Figure 6 shows the relationship between TOC concentration and the number of residual particles measured by STPC-3. It is thought that mainly amines leach from the anionic resin eluate, and a similar trend was observed as with the cationic resin eluate, indicating that amine concentration can be detected using a similar method. Amines are high-molecular-weight organic substances that are the source of microparticle precursors. [Explanation of symbols]

[0031] 1. Ion exchange resin cleaning system 2 containers 3 Ion exchange resin 5. Measuring device 52 Evaporation section 53 Measurement Unit 54 Judgment section L2 Cleaning water supply piping L4 Discharge Piping

Claims

1. A container for washing ion exchange resin, A cleaning water supply pipe for supplying cleaning water to the aforementioned container, A discharge pipe for discharging cleaning wastewater, It includes a measuring device connected to the aforementioned discharge pipe for measuring the water quality of the washing wastewater, The measuring device is an ion exchange resin cleaning system comprising an evaporation unit that evaporates the cleaning wastewater to form residual particles, and a measuring unit that measures the number of residual particles.

2. The cleaning system according to claim 1, wherein the residual particles include particles dissolved in the cleaning wastewater and precipitated when the cleaning wastewater is evaporated in the evaporation section.

3. The cleaning system according to claim 1, wherein the ion exchange resin filled in the container is an ion exchange resin that has been purified by passing a chemical solution through it.

4. The cleaning system according to claim 1, wherein the ion exchange resin filled into the container is the ion exchange resin before it is filled into the ion exchange device provided in the water treatment system.

5. The cleaning system according to claim 1, wherein the measuring device has a determination unit that determines whether the number measured by the measuring unit is below a reference value, and when the determination unit determines that the number is below the reference value, it generates a signal indicating that the number is below the reference value.

6. The cleaning system according to claim 5, wherein when the number falls below the reference value, the determination unit generates a signal indicating that cleaning is complete.

7. The cleaning system according to claim 1, wherein the measuring device continuously measures the number of residual particles.

8. A water quality measurement method for measuring the water quality of wastewater from washing ion exchange resins, The aforementioned washing wastewater is introduced into the measuring device, The washing wastewater introduced into the measuring device is evaporated to form residual particles, A water quality measurement method comprising measuring the number of residual particles using the measuring device.

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