Ultrapure water production system

Abstract

This invention provides an ultrapure water production system that reduces the power consumption of spent ultrapure water recovery equipment and also reduces the risk of scaling. [Solution] An ultrapure water production system comprising a pre-processing unit, a primary pure water production unit, and a secondary pure water production unit, for supplying the produced ultrapure water to a point of use, comprising: a storage unit provided upstream of the pre-processing unit or between the pre-processing unit and the primary pure water production unit for storing raw water or water to be treated; a recovery processing unit for recovering used ultrapure water from the point of use after impurity removal treatment; and means for returning the recovered water obtained from the recovery processing unit to the storage unit, wherein the recovery processing unit has a permeation flux of 0.6 m³ under the condition of an effective membrane pressure of 0.3 MPa. 3 / (m 2 • (Sun) or higher, permeation flux of 2.0 m under conditions of effective membrane pressure of 1 MPa. 3 / (m 2 A system for producing ultrapure water characterized by having an ultra-low pressure reverse osmosis membrane device of 2000 or higher.

Description

[Technical Field]

[0001] The present invention relates to an ultrapure water production system, and more particularly to an ultrapure water production system suitable for producing ultrapure water for cleaning electronic components and materials in semiconductor manufacturing processes and the like. [Background technology]

[0002] Ultrapure water used for semiconductor cleaning is produced by treating raw water (industrial water, city water, well water, etc.) in an ultrapure water production system consisting of a pretreatment system, a primary pure water system, and a subsystem.

[0003] The pretreatment system includes coagulation, pressurized flotation (sedimentation), and filtration equipment to remove suspended solids and colloidal substances from the raw water. The primary pure water system includes a reverse osmosis (RO) membrane separator, a degasser, and an ion exchange system (mixed bed type, 2-bed 3-column type, or 4-bed 5-column type) to remove ions and organic components from the raw water. In addition to removing salts, the RO membrane separator removes ionic and colloidal total organic oxygen (TOC). In addition to removing salts, the ion exchange system removes TOC components that are adsorbed or ion-exchanged by ion exchange resin. The degasser (nitrogen degassing or vacuum degassing) removes dissolved oxygen.

[0004] The subsystem (secondary pure water system) includes a heat exchanger, a low-pressure ultraviolet (UV) oxidation unit, a mixed-bed ion exchange unit, and an ultrafiltration (UF) membrane separator. In the low-pressure UV oxidation unit, 185nm wavelength ultraviolet light emitted from a low-pressure UV lamp decomposes TOC into organic acids and then CO2. The decomposed organic acids and CO2 are removed by a subsequent ion exchange resin. In the UF membrane separator, fine particles are removed, as well as particles leached from the ion exchange resin.

[0005] The ultrapure water produced in the subsystem is delivered to the point of use, and a portion of it is used to clean electronic components.

[0006] Unused ultrapure water that was not used for cleaning at the point of use is returned to the sub-tank on the upstream side of the subsystem.

[0007] Furthermore, if the ultrapure water used at the user point (used ultrapure water) does not contain large amounts of chemicals or other contaminants, it may be recovered for reuse in ultrapure water production. In this case, the used ultrapure water is purified by removing any impurities, recovered, and returned to the primary pure water system.

[0008] For example, ultrapure water used to clean semiconductor wafers is used with added cleaning chemicals such as SC-2, SPM, and FPM. Therefore, used ultrapure water contains acids such as sulfuric acid, phosphoric acid, and hydrofluoric acid, as well as hydrogen peroxide. For this reason, when recovering ultrapure water used for semiconductor cleaning, the recovery process is carried out using a removal device that removes impurities originating from these cleaning chemicals and introduced during use.

[0009] As an impurity removal device used in such recovery processes, Patent Document 1 describes a combination of an MF membrane (or UF membrane) and a reverse osmosis membrane device. The reverse osmosis membrane device used in Patent Document 1 is a low-pressure RO membrane (TM720D manufactured by Toray Industries, Inc.), and its operating pressure is 0.6 MPa. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2022-68664 [Overview of the project] [Problems that the invention aims to solve]

[0011] Low-pressure RO membranes require a high-pressure pump for water supply, resulting in high power consumption.

[0012] In primary pure water systems, brine recovery reverse osmosis membrane systems have a risk of scaling by calcium phosphate, calcium sulfate, barium sulfate, etc.

[0013] The present invention aims to provide an ultrapure water production system that reduces the power consumption of a spent ultrapure water recovery system and also reduces the risk of scaling. [Means for solving the problem]

[0014] An ultrapure water production system according to one aspect of the present invention is an ultrapure water production system having a pre-processing unit, a primary pure water production unit, and a secondary pure water production unit, which supplies the produced ultrapure water to a point of use, and comprising: a storage unit provided upstream of the pre-processing unit or between the pre-processing unit and the primary pure water production unit for storing raw water or water to be treated; a recovery processing unit for recovering used ultrapure water from the point of use after impurity removal treatment; and means for returning the recovered water obtained from the recovery processing unit to the storage unit, wherein the recovery processing unit has a permeation flux of 0.6 m³ under the condition of an effective membrane pressure of 0.3 MPa. 3 / (m 2 • (Sun) or higher, permeation flux of 2.0 m under conditions of effective membrane pressure of 1 MPa. 3 / (m 2 It is characterized by having an ultra-low pressure reverse osmosis membrane device of 2000 or higher.

[0015] In one embodiment of the present invention, the ultrapure water production system has a salt removal rate of 95% or more and an IPA removal rate of 60% or more in the ultra-low pressure reverse osmosis membrane device.

[0016] In one embodiment of the present invention, the ultrapure water production system has a phosphate ion removal rate of 98% or more in the ultra-low pressure reverse osmosis membrane device. [Effects of the Invention]

[0017] In the ultrapure water production system of the present invention, an ultra-low pressure reverse osmosis membrane device is used in the used ultrapure water recovery and processing section. Therefore, a high-pressure pump is not required as the water supply pump for the reverse osmosis membrane device, resulting in lower electricity costs.

[0018] Also, according to the ultra-low pressure reverse osmosis membrane device used in one aspect of the present invention, phosphate ions can be removed by 98% or more, and similarly sulfate ions can be removed by 99% or more, so the scale risk is significantly reduced.

Brief Description of the Drawings

[0019] [Figure 1] It is a flowchart of the ultrapure water production system according to the embodiment. [Figure 2] It is a flowchart of the recovery device according to the embodiment.

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments will be described with reference to the drawings.

[0021] FIG. 1 is a flowchart of the ultrapure water production system according to the embodiment, and FIG. 2 is a flowchart of its recovery device (recovery processing unit).

[0022] Raw water composed of industrial water, well water, tap water, etc. is sent from the raw water tank 1 to the pretreatment device (pretreatment unit) 2 for treatment. The pretreatment device 2 includes a coagulation, pressure flotation (sedimentation), filtration device, etc., and removes suspended substances and colloidal substances in the raw water.

[0023] The treated water of the pretreatment device 2 is sent to the primary pure water device (primary pure water production unit) 4 through the pretreatment water tank 3 for treatment. As the primary pure water device 4, a multi-bed type ion exchange device + RO (reverse osmosis) membrane device, RO membrane device + high purity type ion exchange device, RO membrane device + decarbonation device + electrodialysis deionization device, etc. can be used, but it is not limited thereto.

[0024] The pure water obtained by treatment in the primary pure water device 4 is sent through the pipe 5 towards the sub-tank 6. Unused returned ultrapure water from the use point 12 is also introduced into the sub-tank 6 through the pipe 13.

[0025] The water in sub-tank 6 is sent through piping 7 to subsystem 10 (secondary pure water production unit). Subsystem 10 is equipped with a cooler (heat exchanger), a low-pressure ultraviolet (UV) oxidation device, an ion exchange device, a degassing membrane device, and an ultrafiltration (UF) membrane device, etc. The ultrapure water produced by processing in subsystem 10 is sent through piping 11 to the use point 12, and the unused ultrapure water is returned to sub-tank 6 through piping 13.

[0026] The used ultrapure water generated at use point 12 is supplied to the recovery device 20 through piping 14, where impurities are removed, and then returned to the pretreatment tank 3 (or raw water tank 1) through piping 15.

[0027] As shown in Figure 2, the recovery device 20 is configured to store used ultrapure water in a storage tank 21, pass the water in the storage tank 21 through a safety filter 23 using a pump 22 to an ultra-low pressure reverse osmosis membrane device 24, and send the permeate from the ultra-low pressure reverse osmosis membrane device 24 to the piping 15 as recovered water.

[0028] As the ultra-low pressure reverse osmosis membrane apparatus 24, one that satisfies (i) below and preferably also satisfies (ii) and / or (iii) below is used. (i) Permeation flux of 0.6 m³ under the condition of effective membrane pressure of 0.3 MPa (water temperature 25°C, pure water (RO permeate)). 3 / (m 2 • Under conditions of effective membrane pressure of 1.0 MPa (water temperature 25°C, pure water (RO permeate)) above, the permeate flux is 2.0 m³. 3 / (m 2 (days) or more (ii) Salt removal rate: 95% or more (effective membrane pressure 0.3 MPa (water temperature 25°C, water supply 500 mg-NaCl / L)) (iii) IPA removal rate: 60% or more (effective pressure on membrane surface 0.3 MPa (water temperature 25°C, water supply 500 mg / L of IPA (isopropanol))

[0029] For use in such an ultra-low pressure RO membrane system, examples of ultra-low pressure RO membranes that can be used include K-RO-A-20P3-FX00 and K-RO-A-20P3-FS00 manufactured by Kurita Water Industries Ltd.

[0030] Pump 22 is used that has a discharge pressure of 1.0 MPa or less, for example, around 0.1 to 1.0 MPa.

[0031] The preferred operating conditions for this ultrapure water production system are as follows:

[0032] The raw water sources used include city water, well water, groundwater, and industrial water.

[0033] In the primary pure water system 4, it is preferable that two-stage treatment is performed by the first and second RO membrane systems. The feedwater quality of the second RO membrane system is preferably Ca: 50-100 mg / L and phosphate ions: <5 mg / L. The recovery rate of the second RO membrane system is preferably 70% or more. It is preferable to return the concentrated water from the second RO membrane system to the pre-treatment tank 3 for recovery.

[0034] If use point 12 is a semiconductor manufacturing plant, ultrapure water is used for cleaning semiconductor wafers after acidic chemicals are added. This cleaning process generates used ultrapure water containing acidic chemicals.

[0035] The phosphate ion concentration in used ultrapure water is preferably around 20-135 mg / L, and the sulfate ion concentration is preferably around 11-125 mg / L.

[0036] This used ultrapure water is supplied to the recovery unit 20, where it becomes recovered water and is used as the treated water for the primary pure water. In this case, in order to suppress scale formation in the second RO membrane unit of the primary pure water unit, it is preferable that the phosphate ion concentration of the recovered water be 7 mg / L or less. Therefore, it is preferable that the phosphate ion removal rate in the ultra-low pressure reverse osmosis membrane unit 24 of the recovery unit 20 be 98% or higher. It is also preferable that the sulfate ion removal rate be 99% or higher.

[0037] In the case of the ultra-low pressure reverse osmosis membrane device 24, a phosphate ion removal rate of 98% or more can be obtained at an operating pressure of 0.3 MPa or less, for example, 0.15 to 0.30 MPa. Further, since a high-pressure pump is not required, the power cost can be reduced.

Example

[0038] [Example 1] Using the ultrapure water production system shown in FIGS. 1 and 2, ultrapure water was produced and used in a semiconductor manufacturing line. The used ultrapure water was treated by the recovery device 20 and sent to the pretreatment water tank 3 for recovery.

[0039] The reverse osmosis membrane of the ultra-low pressure reverse osmosis membrane device 24 used in the recovery device 20 is an ultra-low pressure membrane having the following performance (「K-RO-A-20P3-FX00」manufactured by Kurita Water Industries, Ltd.), and the operating pressure was 0.15 MPa.

[0040] <Performance of ultra-low pressure membrane> Permeate flux under the condition of membrane surface effective pressure of 0.3 MPa: 0.6 m 3 / (m 2 ·day) or more Permeate flux under the condition of membrane surface effective pressure of 1 MPa: 2.0 m 3 / (m 2 ·day) or more Salt removal rate: 95% or more (membrane surface effective pressure 0.3 MPa (water temperature 25 °C, feed water 500 mg / L at NaCl)) IPA removal rate: 60% or more (membrane surface effective pressure 0.3 MPa (water temperature 25 °C, feed water 500 mg / L at IPA))

[0041] The concentration of phosphate ions in the used ultrapure water from the use point 12 was 21 mg / L, and the concentration of sulfate ions was 9 mg / L. The concentration of phosphate ions in the recovered water from the recovery device 20 (permeate water of the ultra-low pressure reverse osmosis membrane device 24) was 0.25 mg / L, and the concentration of sulfate ions was 0.05 mg / L. The phosphate ion removal rate was 98.8%, and the sulfate ion removal rate was 99.4%.

[0042] [Comparative Example 1] In Example 1, the reverse osmosis membrane of the RO membrane apparatus in the recovery device was an ultra-low pressure membrane (Kurita Water Industries Ltd. "K-RO-A-203V-FX00") having the following performance characteristics. The operating pressure was 0.75 MPa.

[0043] <Performance of ultra-low pressure membranes> Permeation flux under conditions of effective membrane pressure of 0.75 MPa: 0.6 m 3 / (m 2 ·day) Permeation flux under the condition of effective membrane pressure of 1 MPa: 0.8 m 3 / (m 2 ·day) Salt removal rate: 98% or higher (effective membrane pressure 0.75 MPa (water temperature 25°C, water supply 500 mg / L at NaCl)) IPA removal rate: 80% (effective pressure on membrane surface 0.75 MPa (water temperature 25°C, water supply 500 mg / L at IPA))

[0044] The spent ultrapure water from Use Point 12 had a phosphate ion concentration of 25 mg / L and a sulfate ion concentration of 8 mg / L. The recovered water had a phosphate ion concentration of 0.27 mg / L and a sulfate ion concentration of 0.14 mg / L, with a phosphate ion removal rate of 98.9% and a sulfate ion removal rate of 98.3%.

[0045] <Consideration> As described above, the recovery device of Example 1 could operate at an operating pressure of 0.3 MPa or less, while maintaining a high phosphate ion removal rate of 98% or more and a sulfate ion removal rate of 99% or more. The operating pressure is approximately proportional to the pump output (operating energy). In other words, comparing Example 1 with Comparative Example 1, the operating pressure in Comparative Example 1 is 0.75 MPa, while in Example 1 it is 0.3 MPa, which shows that the operating energy can be reduced by 60% (kinetic energy reduction rate = {(0.75-0.3) / 0.75} × 100 = 60 (%)). [Explanation of Symbols]

[0046] 1. Raw water tank 2 Pre-treatment device 3. Pre-treatment tank 4 Primary water purification device 6 Sub-tanks 10 subsystems 12 Youth Points 20 Recovery device 22 pumps 24. Ultra-low pressure reverse osmosis membrane apparatus

Claims

1. An ultrapure water production system comprising a pre-processing unit, a primary pure water production unit, and a secondary pure water production unit, which supplies the produced ultrapure water to a point of use, A storage unit is provided in front of the pre-processing unit or between the pre-processing unit and the primary pure water production unit, and stores raw water or water to be treated. A recovery processing unit that recovers spent ultrapure water from the aforementioned use point after removing impurities, The system includes means for returning the recovered water obtained from the recovery processing unit to the storage unit, The recovery processing unit measures a permeation flux of 0.6 m under conditions of an effective membrane pressure of 0.3 MPa. ３ / (m ２ - (Sun) Above, the permeation flux of 2.0 m under the condition of an effective membrane pressure of 1 MPa. ３ / (m ２ A system for producing ultrapure water, characterized by having an ultra-low pressure reverse osmosis membrane device of 2000 or higher.

2. The ultrapure water production system according to claim 1, wherein the salt removal rate of the ultra-low pressure reverse osmosis membrane device is 95% or more, and the IPA removal rate is 60% or more.

3. The ultrapure water production system according to claim 1 or 2, wherein the phosphate ion removal rate of the ultra-low pressure reverse osmosis membrane apparatus is 98% or higher.

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