Method and device for cleaning filtration membrane

Abstract

To provide a method for cleaning a filtration membrane that can further reduce the number of particulates that flow out from a filtration membrane.SOLUTION: A method for cleaning a filtration membrane 14 includes a step of providing ultrasonic vibration energy to washing water while immersing the filtration membrane 14 into the washing water and rotating or oscillating the filtration membrane 14 in the washing water.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for cleaning a filtration membrane. [Background technology]

[0002] Ultrapure water production systems typically include a pretreatment device that treats raw water, a primary pure water system that produces pure water from the treated water of the pretreatment device, and a secondary pure water system that produces ultrapure water from the treated water of the primary pure water system. The secondary pure water system often includes devices such as an ultraviolet oxidation device and an ion exchange resin filling device, as well as a filtration membrane device such as an ultrafiltration membrane device or a microfiltration membrane device at the most downstream location. Because these filtration membrane devices are used to finally filter the ultrapure water supplied to the point-of-use facility, strict management is required to minimize the amount of fine particles that flow out of the filtration membrane devices. As part of this management, it is known that the filtration membranes included in these filtration membrane devices are cleaned before use. Patent Document 1 describes a cleaning method for filtration membranes in which the filtration membranes removed from the casing of the filtration membrane device are immersed in ammonia water and ultrasonic waves are applied to the ammonia water. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-52322 Summary of the Invention [Problem to be solved by the invention]

[0004] Although Patent Document 1 describes that the above cleaning method can achieve a certain level of cleaning effect, it still cannot sufficiently reduce the number of fine particles that flow out from the filtration membrane.

[0005] An object of the present invention is to provide a method for cleaning a filtration membrane that can further reduce the number of fine particles that flow out from the filtration membrane. [Means for solving the problem]

[0006] The method for cleaning a filtration membrane of the present invention includes a step of immersing the filtration membrane in cleaning water and applying ultrasonic vibration energy to the cleaning water while rotating or oscillating the filtration membrane in the cleaning water. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a method for cleaning a filtration membrane that can further reduce the number of fine particles that flow out from the filtration membrane. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of a secondary pure water system of an ultrapure water production apparatus. [Figure 2] FIG. 1 is an exemplary schematic diagram of a filtration membrane module. [Figure 3] 1 is a schematic configuration diagram of a cleaning device for a filtration membrane according to an embodiment of the present invention. [Figure 4] FIG. 10 is a conceptual diagram showing a modified example of a method for moving the filtration membrane. [Figure 5] 1 is a schematic diagram showing the configuration of an apparatus in an example and a graph showing the results of particle count measurement. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment and examples of the present invention will be described with reference to the drawings. FIG. 1 shows an overview of a secondary pure water system 1 of an ultrapure water production apparatus according to one embodiment of the present invention. The ultrapure water production apparatus produces ultrapure water used in the manufacturing process of electronic components such as semiconductors. The secondary pure water system 1 is a system, also called a subsystem, for producing ultrapure water to be supplied to a point of use 9 from the pure water produced in the primary pure water system.

[0010] The secondary pure water system 1 of the ultrapure water production equipment has a pure water tank 2, pure water supply pump 3, heat exchanger 4, ultraviolet oxidation device 5, ion exchange device 6, membrane degassing device 7, and ultrafiltration membrane device 8, which are installed in the above order on the main line L1 along the flow direction D of the water to be treated. The main line L1 is connected to a use point 9, and the ultrapure water produced in the secondary pure water system 1 is supplied to the use point 9. The ultrapure water not used at the use point 9 is returned to the pure water tank 2 through a return line L2 connected to the main line L1.

[0011] The pure water tank 2 stores pure water produced in the primary pure water system. The pure water supply pump 3 supplies the pure water stored in the pure water tank 2 to the heat exchanger 4. The ultraviolet oxidation device 5 irradiates the pure water, whose temperature has been adjusted in the heat exchanger 4, with ultraviolet light to decompose the organic matter contained in the pure water. The ion exchange device 6 removes ionic components from the pure water. The ion exchange device 6 is a non-regenerative cartridge polisher filled with a mixed bed of cation exchange resin and anion exchange resin. The membrane degassing device 7 degasses the pure water, that is, removes dissolved oxygen and carbon dioxide from the pure water. The ultrafiltration membrane device 8 finally removes fine particles contained in the pure water.

[0012] FIG. 2(a) shows an exemplary perspective view of a filtration membrane module 11 of an ultrafiltration membrane device 8, and FIG. 2(b) shows an exemplary side view of a filtration membrane 14 of the filtration membrane module 11. The ultrafiltration membrane device 8 has at least one filtration membrane module 11, and each filtration membrane module 11 has an elongated casing 12, a cap member 13, and a filtration membrane 14 packed in the casing 12. The filtration membrane 14 has a filter medium 15 with filtration function, a support member 16 that supports the filter medium 15, and a core 17. In the following description, the filtration membrane 14 refers to a component that combines the filter medium 15 with filtration function and components without filtration function, such as the support member 16 and core 17. Depending on its structure, the filter medium 15 may also include components without filtration function. The filtration membrane 14 is the target of cleaning in this embodiment and has an overall cylindrical shape. The filter medium 15 has a hollow fiber membrane or a sheet-like membrane, and these membranes are made of, for example, polysulfone or polytetrafluoroethylene (PTFE). The filtration membrane 14 may be of a bundle of hollow fiber membranes, a laminated type in which a plurality of sheet-like filter media are wound around, or a pleated type in which a sheet-like filter media is wound in a pleated shape.

[0013] The casing 12 is provided with an inlet 12A for water to be treated and air vent openings 12B and 12C. The support member 16 is provided with multiple openings 16A through which the water to be treated flows. The water to be treated flows into the casing 12 from the inlet 12A, passes through the openings 16A of the support member 16, and enters the inside of the filtration membrane 14, where fine particles contained in the water to be treated are captured by the filter medium 15. The filtered water passes through the inside of the filter medium 15, flows into the inner space of the core 17 (not shown), and flows out through an outlet 12D that communicates with the inner space of the core 17. Air contained in the water to be treated is discharged through the air vent openings 12B and 12C. The cap member 13 is fixed to the casing 12 by means of screws or the like, so the filtration membrane 14 can be removed from the casing 12 by removing the cap member 13.

[0014] Next, we will explain the cleaning device and cleaning method for the filtration membrane 14 of the ultrafiltration membrane device 8 described above. As mentioned above, the ultrafiltration membrane device 8 is used to finally filter the ultrapure water supplied to the point of use 9, so strict control of cleanliness is required. To improve the quality of ultrapure water, it is important to reduce the number of particles that pass through the filtration membrane, i.e., to increase the particle capture efficiency of the filtration membrane. However, it has recently been recognized that improving the quality of ultrapure water is hindered by the detachment and outflow of particulates from the filter media. For this reason, filtration membranes have traditionally been cleaned before installation in ultrapure water production systems, and various cleaning methods have been investigated. The present inventors have previously investigated various cleaning methods, such as passing ammonia water through the membrane, heated ammonia water through the membrane, and warm pure water through the membrane, but no clear effects were observed.

[0015] Based on these circumstances, the inventors of the present application have come up with a new method and device for cleaning filtration membranes. Note that although the subject here is an ultrafiltration membrane device 8, a similar cleaning method can also be applied to microfiltration membrane devices.

[0016] FIG. 3(a) shows a schematic configuration of a cleaning device 21 for the filtration membrane 14. FIG. 3(b) is a cross-sectional view taken along line AA in FIG. 3(a). The cleaning device 21 for the filtration membrane 14 includes a cleaning tank 22 for the filtration membrane 14, a heater 23, a pH adjuster 24, a cleaning water supply device 25, a cleaning water receiving tank 27, an ultrasonic generator 28, and a plurality of spacers 34. Hydrogen-dissolved water, which is ultrapure water in which alkaline water such as an ammonia solution and hydrogen gas are dissolved, is used as the cleaning water for the filtration membrane 14. Nitrogen gas or the like can also be used instead of hydrogen gas.

[0017] The cleaning tank 22 is a tank for cleaning the filtration membrane 14 and stores cleaning water. The cleaning tank 22 has a floor area and depth that allows the filtration membrane 14 to be completely immersed or submerged in the cleaning water. The cleaning water receiving tank 27 accommodates the cleaning tank 22, and a gap 29 is provided between the cleaning tank 22 and the cleaning water receiving tank 27 around the entire periphery of the cleaning tank 22. The cleaning water receiving tank 27 receives cleaning water supplied to and overflowing from the cleaning tank 22. This allows the cleaning tank 22 to be filled with cleaning water during cleaning, ensuring that the filtration membrane 14 is immersed or submerged in the cleaning water. This also creates a water flow of cleaning water within the cleaning tank 22, as described below. A drain line L4 is connected near the bottom of the cleaning water receiving tank 27 to drain cleaning water that overflows from the cleaning tank 22 and flows into the cleaning water receiving tank 27. Because the spacer 34 is a rod-shaped member, the space below the cleaning tank 22 communicates with the gap 29, and the ultrasonic generator 28 is submerged. Ultrasonic generator 28 can perform a process of applying ultrasonic vibration energy to the water stored in cleaning water receiving tank 27, and further applying ultrasonic vibration energy to the cleaning water inside cleaning tank 22 via bottom plate 22A of cleaning tank 22. The frequency of the ultrasonic waves is not particularly limited, but is preferably 0.8 to 3 MHz, and more preferably 0.9 to 1.5 MHz.

[0018] The cleaning water supply device 25 includes, for example, an electrolysis device that generates hydrogen gas and a gas-permeable membrane. The cleaning water supply device 25 can perform a cleaning water production process, which includes dissolving the hydrogen gas generated in the electrolysis device in ultrapure water through the gas-permeable membrane, and a process of supplying the produced cleaning water to the cleaning tank 22. The electrolysis device may be provided separately from the cleaning water supply device 25. Ultrapure water for producing cleaning water is supplied from an ultrapure water production device. The ultrapure water production device may be, but is not limited to, an ultrapure water production device to which a cleaned filtration membrane 14 is attached. In this embodiment, the cleaning water supply device 25 is provided on a line L3 connecting the ultrapure water production device and the cleaning tank 22. The hydrogen concentration of the cleaning water is not particularly limited, but is preferably 1 ppm or more.

[0019] The heater 23 and the pH adjuster 24 are provided on the line L3. The heater 23 heats the temperature of the cleaning water supplied to the cleaning tank 22 to 30 to 100°C. Although not shown, it is preferable to provide a thermometer on the line L3 between the heater 23 and the cleaning tank 22 to measure the temperature of the cleaning water. The pH adjuster 24 includes, for example, an ammonia adding device, and adjusts the pH of the cleaning water supplied to the cleaning tank 22 to 7 or more. Although not shown, it is preferable to provide a pH meter on the line L3 between the pH adjuster 24 and the cleaning tank 22 to measure the pH of the cleaning water. Depending on the object to be cleaned, at least one of the heater 23 and the pH adjuster 24 can be omitted.

[0020] The cleaning device 21 for the filtration membrane 14 includes a holder 30 capable of holding the filtration membrane 14 rotatably in the cleaning tank 22 and immersible in cleaning water. The configuration of the holder 30 is not limited, but in this embodiment, a pair of holders 30 is provided to rotatably hold both ends of the filtration membrane 14. The holder 30 holds the filtration membrane 14 so that its central axis 14A is horizontal. The holder 30 is made of, for example, fluororesin. Because the specific gravity of the filtration membrane 14 is lower than that of water, the holder 30 holds the end of the filtration membrane 14 from above with a forked portion 31 at its tip, preventing the filtration membrane 14 from floating up. In this embodiment, the filtration membrane 14 is held by the tip of the core 17 of the filtration membrane 14. However, the method of supporting the filtration membrane 14 can be changed as appropriate depending on the configuration of the filtration membrane 14. For example, if the filtration membrane 14 has a hollow portion, a shaft may be passed through the hollow portion and rotatably supported in the cleaning tank 22.

[0021] Line L3 is located above the cleaning tank 22 and supplies cleaning liquid to the cleaning tank 22 from above. As shown in FIG. 3(b), branch lines L6 and L7 branch off from line L3 on both sides of the central axis 14A of the filtration membrane 14. The ends of branch lines L6 and L7 (the cleaning water supply points) are located above the cleaning tank 22 and away from the cleaning water, but may be submerged during cleaning. The ends of branch lines L6 and L7 are located away from directly above the central axis 14A of the filtration membrane 14 when viewed in the vertical direction Z. Therefore, cleaning water can be supplied to the cleaning tank 22 from a position away from the central axis 14A when viewed in the vertical direction. Valves V1 and V2 are provided on each branch line L6 and L7, and by opening either valve V1 or V2, cleaning water can be supplied to the cleaning tank 22 only through either branch line L6 or L7.

[0022] The filtration membrane 14 can be rotated by the flow of cleaning water flowing out from the branch lines L6 and L7. In FIG. 3(b), the rotation direction of the filtration membrane 14 is indicated by arrow 33. In this way, lines L3, L6, and L7 constitute a driving means 32 for the filtration membrane 14 that rotates the filtration membrane 14 in the cleaning water supplied to the cleaning tank 22. By switching the opening and closing of valves V1 and V2, the direction of the water flow can be changed, and the filtration membrane 14 can be rotated forward or backward. Either branch line L6 or L7 may be omitted, in which case the filtration membrane 14 will rotate in only one direction.

[0023] Next, a method for cleaning the filtration membrane 14 will be described. First, the filtration membrane 14 is removed from the casing 12 of the filtration membrane module 11 of the ultrafiltration membrane device 8 and placed inside the cleaning tank 22. The filtration membrane 14 is held in place by the holder 30. Ultrapure water is supplied from an ultrapure water production system to the cleaning water supply device 25. The cleaning water supplied from the cleaning water supply device 25 has its pH adjusted by the pH adjuster 24 and is then supplied to the heater 23. The filtration membrane 14 is immersed in the cleaning water and rotated by the flow of the cleaning water. Simultaneously, ultrasonic waves are generated by the ultrasonic generator 28, and vibration energy is applied to the cleaning water in the cleaning tank 22 via the bottom plate 22A of the cleaning tank 22. The hydrogen gas in the cleaning water is broken down by the vibration energy of the ultrasonic waves, and the vibrations generated at this time propagate through the cleaning water and affect the particles adhering to the filtration membrane 14. The impact caused by this process peels off the particles adhering to the surface of the filtration membrane 14. Adjusting the pH to alkaline changes the surface potential of the particles, making them easier to peel off. Alternatively, the filtration membrane 14 may be rotated around a rotating shaft connected to a power source such as a motor. This method requires a more complex structure, but allows for stable movement and easy speed adjustment.

[0024] The filtration membrane 14 is exposed to the atmosphere during storage in the casing 12 and during transfer from the casing 12 to the cleaning tank 22. This air may be adhering to the surface of the filtration membrane 14. This air prevents vibrations caused by the breaking of hydrogen gas bubbles from reaching the surface of the filtration membrane 14. However, in this embodiment, the filtration membrane 14 is rotated in the cleaning water, creating relative motion between the filtration membrane 14 and the cleaning water. This relative motion facilitates the removal of air adhering to the surface of the filtration membrane 14. By rotating the filtration membrane 14 forward and inverting it at least once, the air adhering to the surface of the filtration membrane 14 can be more efficiently removed. The filtration membrane 14 can be rotated forward and inverted, for example, by switching the valves V1 and V2. Alternatively, one of the lines L6 and L7 may be omitted, and the filtration membrane 14 and the holder 30 may be manually moved to a position where water flows in the opposite direction, thereby rotating the filtration membrane 14 forward and inverting it. After a predetermined time has elapsed, the supply of cleaning water is stopped to complete the cleaning, and the filtration membrane 14 is lifted out of the cleaning tank 22 and housed in the casing 12.

[0025] As described above, in this embodiment, cleaning water is supplied to the cleaning tank 22 while the filtration membrane 14 is immersed in the cleaning water supplied to the cleaning tank 22, and the flow of cleaning water generated in the cleaning tank 22 rotates the filtration membrane 14. At the same time, the ultrasonic generator 28 applies ultrasonic vibration energy to the cleaning water in the cleaning tank 22. This makes it possible to efficiently remove fine particles adhering to the surface of the filtration membrane 14. As a result, the number of fine particles flowing out from the filtration membrane 14 during operation of the ultrapure water production system can be reduced.

[0026] The purpose of rotating the filtration membrane 14 is to generate relative motion between the filtration membrane 14 and the cleaning water, thereby removing air bubbles with the water flow generated on the surface of the filtration membrane 14. Therefore, as long as this effect can be achieved, other movements besides rotating the filtration membrane 14 can also achieve the same effect. Figure 4 is a conceptual diagram showing a variation of the method for moving the filtration membrane 14, viewed from the same direction as Figure 3(b). For example, rocking the filtration membrane 14 as shown in Figure 4(a), horizontally moving the filtration membrane 14 as shown in Figure 4(b), vertically moving the filtration membrane 14 as shown in Figure 4(c), or a combination of these are also effective. The center of the rocking motion is located at a position other than the central axis 14A (e.g., the upper end 31 of the holder 30). These movements may be performed simultaneously with the rotational motion or alternately with the rotational motion. The cleaning method for the filtration membrane 14 is not limited as long as the filtration membrane 14 is moved in the cleaning water. The method shown in Figure 4 may be performed manually or using a power source such as a motor.

[0027] In the method shown in FIG. 4, the direction and speed of the wash water impinging on the filtration membrane 14 differ depending on the location of the filtration membrane 14. For example, in part A of FIG. 4(a), the filtration membrane 14 moves relative to the wash water in a direction tangential to the surface of the filtration membrane 14. In part B, the filtration membrane 14 moves relative to the wash water in a direction perpendicular to the surface of the filtration membrane 14. In contrast, in the method of rotating the filtration membrane 14 around the central axis 14A shown in FIG. 3, the filtration membrane 14 moves relative to the wash water in a direction tangential to the surface of the filtration membrane 14 at any location on the filtration membrane 14, thereby enabling uniform removal of air bubbles. Another method of generating relative motion between the filtration membrane 14 and the wash water is to apply a water flow to a stationary filtration membrane 14. However, this method is less efficient at removing air bubbles than a method of moving the filtration membrane 14 because it is difficult to apply a water flow uniformly to the surface of the filtration membrane 14. Furthermore, although the vibrations generated by the ultrasound act on the surface of the filtration membrane 14, the filtration membrane 14 remains stationary.

[0028] In addition to filtration membranes used in ultrapure water production, flat membrane filtration membranes are also available. Flat membrane filtration membranes are generally small in size (for example, about 25 mm in diameter) and are often used for analytical purposes. This embodiment can also be applied to flat membrane filtration membranes for analytical purposes. However, although analytical flat membranes are required to have the function of capturing fine particles, preventing peeling of the membrane itself is not a major issue. For these reasons, this embodiment can be more suitably applied to cylindrical membrane modules.

[0029] Furthermore, while analytical flat membranes have traditionally been cleaned by immersion before use, the filtration membranes used in ultrapure water production are too large for a similar method to be applied. In this embodiment, a large cleaning tank 22 large enough to accommodate the filtration membrane 14 is used, enabling pre-use cleaning. The filtration membrane 14 has a more complex shape than a flat membrane, and even a relatively simple cylindrical filtration membrane inevitably attracts air and is less easy to clean than a flat membrane. Furthermore, the filtration membrane 14 is made up of bundled hollow fibers or pleated, making it prone to air adhesion in some areas and difficult for cleaning solutions to reach, making it less easy to clean than a flat membrane. Therefore, simply immersing the filtration membrane 14 does not improve cleaning effectiveness. However, in this embodiment, the filtration membrane 14 is rotated, allowing cleaning solutions to reach even the finer details, improving performance in removing fine particles.

[0030] (Example) The cleaning effect of the filtration membrane was confirmed using the device shown in FIG. 5(a). As shown in FIG. 5(a), an ultrafiltration membrane device 102 was installed downstream of an ultrafiltration membrane device 101, and the ultrafiltration membrane device 102 was filled with a filtration membrane that had been washed with cleaning water. The number of particles contained in the water outlet from the ultrafiltration membrane device 102 was measured using a liquid particle counter (LPC) 103. A UDI-20 manufactured by PMS was used as the LPC 103. A Micropore 1BC-3SE (pore size: 100 nm) manufactured by Organo Corporation was used as the microfiltration membrane. The cleaning water was prepared by adding ammonia to ultrapure water at a temperature of 50°C to a pH of 10 or higher and dissolving hydrogen gas to a concentration of 1.0 ppm or higher. The cleaning time was 10 minutes in Example 1 and 60 minutes in Example 2. That is, ultrasonic waves were applied to the cleaning water for 10 minutes in Example 1 and for 60 minutes in Example 2. Cleaning was not performed in the comparative example.

[0031] FIG. 5(b) shows the results of measuring the number of particles. In the comparative example, a high number of particles was observed immediately after measurement, then gradually decreased, and remained at approximately 0.2 to 0.4 (particles / mL) from days 3 to 12. In example 1, a high number of particles was observed immediately after measurement, then rapidly decreased, and remained at approximately less than 0.05 (particles / mL) from day 5 onwards. In example 2, a low number of particles was observed immediately after measurement, and remained at a low value thereafter. However, overall, the number of particles was greater than in example 1, and a small number of particles was detected in example 1 even after day 19, when the number of particles stabilized. The daily average number of particles throughout the measurement period was 0.11 (particles / mL) or less in examples 1 and 2, and 0.3 (particles / mL) in the comparative example.

[0032] From the above, the number of fine particles was reduced in Examples 1 and 2 compared to the comparative example, confirming the cleaning effect of the filtration membrane. Furthermore, better results were obtained in Example 1 than in Example 2. This is thought to be because the ultrasonic waves were applied for a longer time in Example 2. That is, the ultrasonic waves break up the bubbles in the hydrogen gas in the cleaning water, and the impact is thought to have damaged the surface of the filtration membrane, generating a small amount of fine particles. In other words, the longer the ultrasonic application time, the better; a higher cleaning effect can be achieved by limiting it to a certain limited time. Therefore, it is preferable to set the ultrasonic irradiation time to between 10 minutes and 1 hour. [Explanation of symbols]

[0033] 14 Filtration membrane 14A Central axis of the filtration membrane 21 Filtration membrane cleaning equipment 22 Cleaning tank 23 Heater 24 pH adjustment device 25 Cleaning water supply device 27 Cleaning water receiving tank 28 Ultrasonic generator 30 Holder 32 Filtration membrane driving means

Claims

1. A method for cleaning a filtration membrane, comprising the step of immersing a filtration membrane in cleaning water and rotating or oscillating the filtration membrane in the cleaning water while applying ultrasonic vibration energy to the cleaning water.

2. the filtration membrane is cylindrical; The method for cleaning a filtration membrane according to claim 1 , wherein rotating the filtration membrane comprises rotating the filtration membrane around a central axis of the cylindrical shape.

3. 3. The method for cleaning a filtration membrane according to claim 2, wherein the filtration membrane is placed in a cleaning tank, the cleaning water is supplied to the cleaning tank from a position away from the central axis when viewed in the vertical direction, and the filtration membrane is rotated by a flow of the cleaning water generated in the cleaning tank.

4. The method for cleaning a filtration membrane according to claim 2 , wherein rotating the filtration membrane includes rotating the filtration membrane forward and inverted at least once each.

5. 2. The method for cleaning a filtration membrane according to claim 1, wherein the temperature of the cleaning water is 30°C or higher and 100°C or lower.

6. The method for cleaning a filtration membrane according to claim 1 , wherein the ultrasonic irradiation time is less than 1 hour.

7. 7. The method for cleaning a filtration membrane according to claim 1, wherein the cleaning water is produced by dissolving hydrogen gas in ultrapure water.

8. 8. The method for cleaning a filtration membrane according to claim 7, wherein the cleaning water comprises ultrapure water in which hydrogen gas is dissolved at a hydrogen concentration of 1 ppm or more.

9. a cleaning water supply device capable of carrying out a cleaning water manufacturing process including dissolving a gas in ultrapure water; a cleaning tank for the filtration membrane to which the cleaning water is supplied from the supply device; a holder that holds the filtration membrane in the cleaning tank so that the filtration membrane can be immersed in the cleaning water; an ultrasonic generator that irradiates the cleaning water with ultrasonic waves, The cleaning device for a filtration membrane, wherein the holder is configured to rotate or swing the filtration membrane in the cleaning water.

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