Method for preparing electronic grade ultra-pure water

Abstract

This invention relates to the field of water treatment technology and discloses a method for preparing electronic-grade ultrapure water. The method involves filtering raw water through a 500-mesh stainless steel screen to remove organic matter, residual chlorine, and odors, followed by softening treatment with ion exchange resin to reduce hardness. The pretreated water is then fed into an MBR reactor, where air bubbles are used to flush the surface of the MBR flat-sheet membrane. The effluent from the MBR biological treatment is then fed into an ultrafiltration permeate tank, where it undergoes a three-stage degassing process, including microbial elimination, removal of residual suspended solids and colloidal particles, and reverse osmosis treatment. After cooling, the water is fed into an intermediate water tank. The effluent from the intermediate water tank is pumped into an EDI water treatment system. After deep purification via EDI, resin debris and microorganisms are removed by filtration. The electronic-grade ultrapure water is then stored in a nitrogen-sealed water tank and returned to the front end of the EDI system via a circulation pipeline. This invention improves desalination rate and impurity removal accuracy, enables automatic replacement of filter materials without shutdown, and ensures continuous production.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to a method for preparing electronic-grade ultrapure water. Background Technology

[0002] Electronic-grade ultrapure water is a key basic material in the field of precision manufacturing. Its purity directly affects the yield and performance of products. The core requirements include extremely low conductivity, turbidity, ion content, and dissolved gas content. Existing preparation processes mostly adopt a combination route of MBR + ultrafiltration-RO + EDI, but there are many technical bottlenecks. For example, the desalination rate of traditional reverse osmosis membranes is generally low, which is difficult to meet the requirements of high-end electronic manufacturing for the removal of trace ions; the removal of dissolved oxygen and carbon dioxide is incomplete, which can easily lead to secondary pollution of water quality; the replacement of filter materials such as activated carbon requires shutdown operation, which affects the continuity of production; the system has high energy consumption and poor adaptability to water quality fluctuations. Summary of the Invention

[0003] The purpose of this invention is to solve the above-mentioned problems by designing a method for preparing electronic-grade ultrapure water.

[0004] This invention provides a method for preparing electronic-grade ultrapure water, the method comprising the following steps: S1. Pretreatment: The raw water is filtered through a 500-mesh stainless steel screen, then passed through a dual-chamber parallel activated carbon adsorption unit to remove organic matter, residual chlorine and odors. Finally, it is softened by ion exchange resin to reduce the hardness of the raw water. S2, MBR biological treatment: The pretreated water is introduced into the MBR reactor and the aeration rate is controlled to use air bubbles to flush the surface of the MBR flat sheet membrane inside the reactor. S3, Ultrafiltration-MOF Composite RO Treatment: The effluent after MBR biological treatment is introduced into the ultrafiltration product water tank. Scale inhibitors and coagulants are added to the ultrafiltration product water tank, followed by the sequential treatment of killing microorganisms, removing residual suspended solids and colloidal particles, and reverse osmosis. S4. Three-stage degassing: First, the effluent after ultrafiltration-MOF composite RO treatment is subjected to three-stage degassing treatment. Then, the degassed water is cooled and passed into an intermediate water tank for further treatment until the dissolved oxygen in the water is less than or equal to 5 μg / L and the carbon dioxide is less than or equal to 10 μg / L. S5, EDI deep purification: The water effluent from the intermediate water tank is sent to the EDI water treatment equipment through a booster pump. After EDI deep purification, the water flow is then filtered through a terminal ultrafiltration membrane with a pore size of less than or equal to 20nm to remove resin debris and microorganisms. S6. Finished Product Storage and Circulation: Store the electronic-grade ultrapure water after deep purification by EDI into a nitrogen-sealed water tank. Maintain a slight positive pressure of 0.01-0.02MPa in the tank through the nitrogen replenishment valve and the nitrogen release valve. Circulate the electronic-grade ultrapure water back to the front end of the EDI equipment through the circulation pipeline at a circulation flow rate of 10-15% / h of the storage capacity.

[0005] Optionally, in the first implementation of the present invention, step S1 specifically includes the following process: Raw water is introduced into a pretreatment tank and filtered using a 500-mesh stainless steel screen to remove suspended solids with a particle size greater than or equal to 20 μm. The activated carbon adsorption unit adopts a dual-chamber parallel structure, which switches the raw water between the two chambers through a diversion component. When one chamber of activated carbon is saturated, the replacement component automatically discharges waste carbon and replenishes new carbon. The adsorption residence time is controlled at 30-40 minutes to remove organic matter, residual chlorine, and odor substances from the water. After softening treatment with ion exchange resin, the hardness of the raw water is reduced to less than or equal to 0.1 mmol / L. The dual-chamber parallel structure has built-in activated carbon packing.

[0006] Optionally, in the second implementation of the present invention, step S2 specifically includes the following process: The pretreated raw water enters the MBR reactor, which is equipped with MBR flat sheet membranes and aeration heads. A rotary blower provides aeration airflow, using air bubbles to wash the surface of the MBR flat sheet membranes inside the reactor. The air velocity is controlled between 0.8 and 1.2 m / s. 3 / (m 2 The hydraulic residence time in the reaction tank is 8-12 hours.

[0007] Optionally, in a third implementation of the present invention, the MBR flat sheet membrane is detachably installed in the MBR reactor via a membrane plate mounting bracket. An aeration head is provided on the inner side of the upper left end of the MBR reactor, with the output end of the aeration head corresponding to the position above the MBR flat sheet membrane. The pore size of the MBR flat sheet membrane is 0.1-0.2 μm.

[0008] Optionally, in the fourth implementation of the present invention, step S3 specifically includes the following process: The effluent from the MBR biological treatment is fed into the ultrafiltration permeate tank. Scale inhibitor and coagulant at a concentration of 5-10 mg / L are added to the tank and evenly dispersed by a dispersing and stirring mechanism. The mixture is then passed through an irradiation system with a wavelength of 254 nm and an intensity greater than or equal to 30 mW / cm². 2 The ultraviolet lamps kill microorganisms in the water, and then the water flows into the ultrafiltration module. The ultrafiltration membrane with a pore size of 50-100nm removes residual suspended solids and colloidal particles. The ultrafiltration water is then passed into the MOF composite reverse osmosis membrane module for reverse osmosis treatment.

[0009] Optionally, in the fifth implementation of the present invention, the dispersion and stirring mechanism includes a dosing pipe, a connecting sleeve, a dispersion cylinder and a stirring motor. The dosing pipe is connected to the dispersion cylinder through the connecting sleeve. Dispersion holes and stirring blades are uniformly opened on the outer wall of the dispersion cylinder. The stirring motor drives the cylinder to rotate and achieve uniform dispersion of the agent.

[0010] Optionally, in the sixth implementation of the present invention, the MOF composite reverse osmosis membrane module is a composite reverse osmosis membrane modified with a metal-organic framework material with a pore size of 0.5-1 nm. During reverse osmosis treatment, the operating pressure of the membrane module is controlled at 1.8-2.2 MPa and the water temperature at 25-30 °C, and the treatment is carried out until the resistivity of the effluent is greater than or equal to 10 MΩ·cm and the desalination rate is greater than or equal to 99.8%.

[0011] Optionally, in the seventh implementation of the present invention, step S4 specifically includes the following process: The effluent from the ultrafiltration-MOF composite RO treatment is first heated to 40-50℃ by the first heat exchange mechanism, and then sequentially introduced into a three-stage degassing mechanism under the control of the flow regulation mechanism. The first stage is a vacuum degassing tower with a vacuum degree of -0.08~-0.09MPa, the second stage is a polytetrafluoroethylene hollow fiber membrane degassing component, and the third stage is a nitrogen purging degassing mechanism that introduces high-purity nitrogen gas with a purity greater than or equal to 99.999%. During the nitrogen purging, gas and liquid are in countercurrent contact. After degassing, the water flows through the second heat exchange mechanism and is cooled to 20-25℃ before being introduced into the intermediate water tank.

[0012] Optionally, in the eighth implementation of the present invention, step S5 specifically includes the following process: Water from the intermediate water tank is pumped into the EDI water treatment equipment via a booster pump. The booster pump outlet pressure is 0.4-0.6 MPa. The EDI water treatment equipment operates at a voltage of 200-300V and a current of 5-10A. The EDI equipment performs deep ion removal and online resin regeneration through a combination of electrodialysis and ion exchange. Water from the intermediate water tank is then pumped into the EDI water treatment equipment for filtration to remove resin debris and microorganisms, ultimately yielding electronic-grade ultrapure water.

[0013] Optionally, in the ninth implementation of the present invention, a level transmitter is installed in the nitrogen-sealed water tank in step S6 to monitor the liquid level in the tank in real time and link with the water replenishment system, so that the final electronic-grade ultrapure water has a conductivity of less than or equal to 0.06 μS / cm and a turbidity of less than or equal to 0.08 NTU.

[0014] The beneficial effects of this invention are: This invention provides a method for preparing electronic-grade ultrapure water. The method combines a MOF composite reverse osmosis membrane with EDI deep purification, resulting in effluent conductivity ≤0.06 μS / cm, turbidity ≤0.08 NTU, desalination rate ≥99.8%, and dissolved oxygen and carbon dioxide content controlled below 5 μg / L and 10 μg / L, respectively, meeting the stringent requirements of high-end electronic manufacturing for ultrapure water. A dual-chamber parallel activated carbon adsorption unit, coupled with an automatic replacement assembly, enables continuous replacement of filter materials, avoiding production interruptions caused by maintenance shutdowns in traditional processes and improving equipment utilization. The synergistic effect of a three-stage degassing and closed-loop control system reduces energy consumption by 15-20% compared to traditional processes. The high water flux of the MOF composite membrane reduces the number of membrane modules, and the EDI equipment eliminates the need for chemical regenerators, reducing environmental treatment costs. The method improves desalination rate and impurity removal accuracy, achieves continuous production through automatic filter material replacement, optimizes energy consumption through closed-loop control, and enhances adaptability to fluctuations in raw water quality. Attached Figure Description

[0015] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention.

[0016] Figure 1 A flowchart illustrating the method for preparing electronic-grade ultrapure water provided in an embodiment of the present invention. Detailed Implementation

[0017] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” or “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, apparatus, product, or device that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0018] For ease of understanding, the specific process of the embodiments of the present invention is described below. Please refer to [link / reference]. Figure 1 A flowchart of the method for preparing electronic-grade ultrapure water provided in this embodiment of the invention is shown. The method specifically includes the following steps: S1. Pretreatment: The raw water is filtered through a 500-mesh stainless steel screen, then passed through a dual-chamber parallel activated carbon adsorption unit to remove organic matter, residual chlorine and odors. Finally, it is softened by ion exchange resin to reduce the hardness of the raw water. S2, MBR biological treatment: The pretreated water is introduced into the MBR reactor and the aeration rate is controlled to use air bubbles to flush the surface of the MBR flat sheet membrane inside the reactor. S3, Ultrafiltration-MOF Composite RO Treatment: The effluent after MBR biological treatment is introduced into the ultrafiltration product water tank. Scale inhibitors and coagulants are added to the ultrafiltration product water tank, followed by the sequential treatment of killing microorganisms, removing residual suspended solids and colloidal particles, and reverse osmosis. S4. Three-stage degassing: First, the effluent after ultrafiltration-MOF composite RO treatment is subjected to three-stage degassing treatment. Then, the degassed water is cooled and passed into an intermediate water tank for further treatment until the dissolved oxygen in the water is less than or equal to 5 μg / L and the carbon dioxide is less than or equal to 10 μg / L. S5, EDI deep purification: The water effluent from the intermediate water tank is sent to the EDI water treatment equipment through a booster pump. After EDI deep purification, the water flow is then filtered through a terminal ultrafiltration membrane with a pore size of less than or equal to 20nm to remove resin debris and microorganisms. S6. Finished Product Storage and Circulation: Store the electronic-grade ultrapure water after deep purification by EDI into a nitrogen-sealed water tank. Maintain a slight positive pressure of 0.01-0.02MPa in the tank through the nitrogen replenishment valve and the nitrogen release valve. Circulate the electronic-grade ultrapure water back to the front end of the EDI equipment through the circulation pipeline at a circulation flow rate of 10-15% / h of the storage capacity.

[0019] Further, step S1 specifically includes the following process: raw water is introduced into the pretreatment tank, and suspended solids with a particle size greater than or equal to 20 μm are removed by filtration using a 500-mesh stainless steel filter screen. The activated carbon adsorption unit adopts a dual-chamber parallel structure. The activated carbon adsorption unit with the dual-chamber parallel structure switches the raw water between the two chambers through a diversion component. When the activated carbon in one chamber is saturated, the replacement component is driven to automatically discharge waste carbon and replenish new carbon. The adsorption residence time is controlled to be 30-40 minutes to remove organic matter, residual chlorine and odor substances from the water. After softening treatment with ion exchange resin, the hardness of the raw water is reduced to less than or equal to 0.1 mmol / L. The dual-chamber parallel structure has built-in activated carbon packing.

[0020] Furthermore, step S2 specifically includes the following process: the pretreated raw water enters the MBR reactor, which is equipped with an MBR flat sheet membrane and aeration heads. An aeration airflow is provided by a rotary blower, and the air bubbles are used to wash the surface of the MBR flat sheet membrane inside the reactor, wherein the air velocity is controlled at 0.8-1.2m. 3 / (m 2 The hydraulic residence time in the reaction tank is 8-12 hours.

[0021] Furthermore, the MBR flat sheet membrane can be detachably installed inside the MBR reactor via a membrane plate mounting bracket. An aeration head is installed on the inner side of the upper left end of the MBR reactor, with the output end of the aeration head corresponding to the position above the MBR flat sheet membrane. The pore size of the MBR flat sheet membrane is 0.1-0.2μm.

[0022] Furthermore, step S3 specifically includes the following process: The effluent from the MBR biological treatment is introduced into the ultrafiltration permeate tank; scale inhibitor and coagulant with a concentration of 5-10 mg / L are added to the ultrafiltration permeate tank; after being uniformly dispersed by a dispersion and stirring mechanism, the mixture is then passed through an irradiation system with a wavelength of 254 nm and an intensity greater than or equal to 30 mW / cm². 2 The ultraviolet lamps kill microorganisms in the water, and then the water flows into the ultrafiltration module. The ultrafiltration membrane with a pore size of 50-100nm removes residual suspended solids and colloidal particles. The ultrafiltration water is then passed into the MOF composite reverse osmosis membrane module for reverse osmosis treatment.

[0023] Furthermore, the dispersion and stirring mechanism includes a dosing pipe, a connecting sleeve, a dispersion cylinder, and a stirring motor. The dosing pipe is connected to the dispersion cylinder through the connecting sleeve. Dispersion holes and stirring blades are evenly opened on the outer wall of the dispersion cylinder. The stirring motor drives the cylinder to rotate, thereby achieving uniform dispersion of the agent.

[0024] Furthermore, the MOF composite reverse osmosis membrane module uses a composite reverse osmosis membrane modified with a metal-organic framework material with a pore size of 0.5-1nm. During reverse osmosis treatment, the operating pressure of the membrane module is controlled at 1.8-2.2MPa and the water temperature at 25-30℃, and the water resistivity is greater than or equal to 10MΩ・cm and the desalination rate is greater than or equal to 99.8%.

[0025] Furthermore, the effluent treated by ultrafiltration-MOF composite RO is first heated to 40-50℃ by the first heat exchange mechanism, and then sequentially introduced into a three-stage degassing mechanism in series under the control of the flow regulation mechanism. The first stage is a vacuum degassing tower with a vacuum degree of -0.08~-0.09MPa, the second stage is a polytetrafluoroethylene hollow fiber membrane degassing component, and the third stage is a nitrogen purging degassing mechanism that introduces high-purity nitrogen gas with a purity greater than or equal to 99.999%. During nitrogen purging, gas and liquid countercurrent contact is formed. After degassing, the water flows through the second heat exchange mechanism and is cooled to 20-25℃ before being introduced into the intermediate water tank.

[0026] Furthermore, the water effluent from the intermediate water tank is pumped into the EDI water treatment equipment via a booster pump. The outlet pressure of the booster pump is 0.4-0.6 MPa. The operating voltage of the EDI water treatment equipment is 200-300V and the operating current is 5-10A. The EDI equipment performs deep ion removal and online resin regeneration through a combination of electrodialysis and ion exchange. The water effluent from the intermediate water tank is pumped into the EDI water treatment equipment for filtration to remove existing resin debris and microorganisms, ultimately yielding electronic-grade ultrapure water.

[0027] Furthermore, in step S6, a level transmitter is installed in the nitrogen-sealed water tank to monitor the liquid level in the tank in real time and link it with the water replenishment system. The final electronic-grade ultrapure water has a conductivity of less than or equal to 0.06 μS / cm and a turbidity of less than or equal to 0.08 NTU.

[0028] Example 1. A method for preparing electronic-grade ultrapure water includes the following steps, in which each unit is connected in series to form a continuous processing flow, supplemented by a closed-loop control system to achieve dynamic parameter control: 1. Pretreatment Unit: Raw water is introduced into the pretreatment tank and undergoes sequential processes including bar filtration, activated carbon adsorption, and softening. The bar filtration uses a 500-mesh stainless steel screen to remove suspended solids with a particle size ≥20μm. The activated carbon adsorption unit employs a dual-chamber parallel structure with built-in modified activated carbon packing. A flow divider allows for switching of raw water between the two chambers. When one chamber becomes saturated with activated carbon, a replacement component automatically discharges waste carbon and replenishes it with new carbon, without interrupting the raw water flow. The adsorption residence time is controlled at 30-40 minutes, removing organic matter, residual chlorine, and some odorous substances from the water. The softening treatment uses ion exchange resin to reduce the hardness of the raw water to ≤0.1mmol / L, preventing scaling of the subsequent membrane modules.

[0029] 2. MBR Biological Treatment Unit: Pretreated raw water enters the MBR reactor. Inside the reactor, MBR flat sheet membranes with 0.1-0.2 μm pore size are detachably installed via membrane plate mounting brackets. Aeration heads are installed on the upper left inner side of the MBR reactor, with their output ends positioned above the MBR flat sheet membrane. A rotary blower provides aeration airflow, with the air velocity controlled at 0.8-1.2 m / s². 3 / (m 2 The bubbles formed (·h) wash the membrane surface, inhibiting membrane fouling. Meanwhile, hooks are installed at the top of the MBR flat-sheet membrane for easy periodic lifting and maintenance. The hydraulic retention time in the reaction tank is 8-12 hours. After MBR treatment, the effluent turbidity is ≤0.2 NTU, and the COD removal rate is ≥95%.

[0030] 3. Ultrafiltration-MOF Composite RO Unit: MBR effluent enters the ultrafiltration product water tank. The tank is equipped with a dosing pipe and a dispersion and stirring mechanism. The dosing pipe is connected to a dispersion cylinder via a connecting sleeve. The outer wall of the dispersion cylinder has evenly distributed dispersion holes and stirring blades. Driven by a stirring motor, the cylinder rotates to evenly disperse the scale inhibitor and coagulant. The dosing concentration is 5-10 mg / L. Simultaneously, multiple sets of ultraviolet lamps are installed via ultraviolet lamp holders, with the wavelength controlled at 254 nm and the irradiation intensity ≥30 mW / cm². 2 The water is then used to kill microorganisms in the water. The water then flows into the ultrafiltration module, where the ultrafiltration membrane has a pore size of 50-100nm to remove residual suspended solids and colloidal particles. The ultrafiltration effluent is fed into a MOF composite reverse osmosis membrane module. This module uses a composite reverse osmosis membrane modified with metal-organic framework (MOF) material. The membrane pore size is controlled at 0.5-1 nm, the operating pressure is controlled at 1.8-2.2 MPa, and the water temperature is maintained at 25-30℃. The precise "molecular sieve" formed by the MOF material can selectively intercept trace ions, achieving a desalination rate of over 99.8%, while maintaining a high water flux and an effluent resistivity of ≥10 MΩ·cm.

[0031] 4. Three-stage degassing unit: The MOF composite RO effluent is heated to 40-50℃ by the first heat exchange mechanism and enters the three-stage degassing unit in series under the control of the flow regulation mechanism: The first stage is a vacuum degassing tower, with the vacuum degree controlled at -0.08~-0.09MPa, to remove most of the dissolved oxygen and carbon dioxide; the second stage is a membrane degassing module, which uses polytetrafluoroethylene hollow fiber membrane to further remove residual dissolved gases; the third stage is nitrogen purging degassing, in which high-purity nitrogen (purity ≥99.999%) is introduced to form gas-liquid countercurrent contact, ultimately reducing the dissolved oxygen in the water to ≤5μg / L and the carbon dioxide to ≤10μg / L; the degassed water flows through the second heat exchange mechanism and is cooled to 20-25℃ before entering the intermediate water tank.

[0032] 5. EDI Deep Purification Unit: Water from the intermediate water tank is pumped into the EDI water treatment equipment via a booster pump. The booster pump outlet pressure is controlled at 0.4-0.6 MPa. The EDI equipment operates at 200-300V and has a current of 5-10A. The EDI equipment combines electrodialysis and ion exchange, achieving deep ion removal and online resin regeneration under an electric field, eliminating the need for chemical regenerants. The treated water then flows through a terminal ultrafiltration membrane (pore size ≤20nm) to remove any resin debris and microorganisms, ultimately yielding electronic-grade ultrapure water.

[0033] 6. Closed-loop control system: Sensor groups, including conductivity sensors, turbidity sensors, dissolved oxygen sensors, carbon dioxide sensors, and temperature sensors, are installed in the inlet and outlet pipelines of each unit. The monitoring data is transmitted to the control unit in real time. Based on the detection results, the control unit adjusts the aeration intensity of the rotary blower, the operating pressure of the MOF composite RO membrane, the vacuum degree and nitrogen flow rate of the three-stage degassing mechanism, and the voltage and current of the EDI equipment to achieve dynamic control when water quality and water temperature fluctuate, ensuring stable effluent indicators and optimizing system energy consumption.

[0034] 7. Finished Product Storage and Circulation Unit: The finished ultrapure water is stored in a nitrogen-sealed water tank, which is sealed with a lid. A slight positive pressure (0.01-0.02MPa) is maintained inside the tank through a nitrogen replenishment valve and a nitrogen release valve to prevent airborne gases and impurities from entering. A level transmitter is installed inside the tank to monitor the level in real time and link it to the water replenishment system. The finished water is periodically returned to the front end of the EDI equipment through a circulation pipeline to maintain water flow and prevent water quality deterioration. The circulation flow rate is 10-15% / h of the storage capacity.

[0035] Example 2. In this embodiment, production wastewater is used as the raw water. The raw water quality indicators are: turbidity 25 NTU, hardness 2.8 mmol / L, COD 85 mg / L, and conductivity 820 μS / cm. Ultrapure water is prepared using the above-mentioned method for preparing electronic-grade ultrapure water. The specific steps are as follows: S1. Pretreatment: The raw water is filtered through a 500-mesh stainless steel screen to remove suspended solids with a particle size ≥20μm. Then, it is passed into a dual-chamber parallel activated carbon adsorption unit. The adsorption residence time is controlled at 35min. The raw water is stably switched between the two chambers through a diversion component to remove organic matter, residual chlorine and odors from the water. The activated carbon in the adsorption saturated chamber is automatically replaced without stopping the machine through a replacement component. Finally, the raw water is softened by ion exchange resin to reduce the hardness to 0.08mmol / L. S2, MBR Biological Treatment: Pretreated water is introduced into an MBR reactor. The MBR flat sheet membrane inside the reactor has a pore size of 0.2 μm. A rotary blower supplies air to the aeration heads inside the reactor, controlling the aeration velocity to 1.0 m / s². 3 / (m 2 •h), using air bubbles to flush the surface of the MBR flat sheet membrane inside the tank, the hydraulic retention time in the reaction tank is controlled to be 10h, and the effluent turbidity is treated to 0.15NTU and COD removal rate is 96%; S3. Ultrafiltration-MOF Composite RO Treatment: The effluent from the MBR biological treatment is fed into the ultrafiltration permeate tank. Scale inhibitors and coagulants at a concentration of 8 mg / L are added to the tank and evenly dispersed by a dispersing and stirring mechanism. The mixture is then passed through a 254 nm wavelength irradiation system with an intensity of 35 mW / cm². 2 Ultraviolet lamps kill microorganisms in the water, and then the water is passed into an ultrafiltration module. The ultrafiltration membrane with a pore size of 80nm removes residual suspended solids and colloidal particles. The ultrafiltration water is then passed into a MOF composite reverse osmosis membrane module for reverse osmosis treatment. The membrane module uses a composite reverse osmosis membrane modified with a metal-organic framework material with a pore size of 0.8nm. The operating pressure is controlled at 2.0MPa and the water temperature at 28℃, and the water is treated to an effluent resistivity of 12MΩ・cm and a desalination rate of 99.85%. S4. Three-stage degassing: The effluent from the ultrafiltration-MOF composite RO treatment is first heated to 45°C by the first heat exchanger. Under the control of the flow regulation mechanism, it is then sequentially introduced into a series of three-stage degassing mechanisms. The first stage is a vacuum degassing tower with a vacuum degree of -0.085MPa, the second stage is a polytetrafluoroethylene hollow fiber membrane degassing module, and the third stage is a nitrogen purging degassing mechanism that introduces high-purity nitrogen gas with a purity of ≥99.999%, forming a gas-liquid countercurrent contact. After completing the three-stage degassing treatment, the degassed water is then cooled to 22°C by the second heat exchanger and introduced into the intermediate water tank, where the dissolved oxygen is reduced to 3.2μg / L and the carbon dioxide to 8.5μg / L. S5, EDI deep purification: The water effluent from the intermediate water tank is sent to the EDI water treatment equipment through a booster pump. The outlet pressure of the booster pump is controlled at 0.5MPa. The working voltage of the EDI water treatment equipment is 250V and the working current is 8A. After EDI deep purification, the water flow is filtered through a terminal ultrafiltration membrane with a pore size of 20nm to remove resin debris and microorganisms. S6. Finished Product Storage and Circulation: The electronic-grade ultrapure water after deep purification by EDI is stored in a nitrogen-sealed water tank. A slight positive pressure of 0.015MPa is maintained in the tank through a nitrogen replenishment valve and a nitrogen release valve. The liquid level transmitter in the nitrogen-sealed water tank monitors the liquid level in real time and links with the water replenishment system to return the electronic-grade ultrapure water to the front end of the EDI equipment through the circulation pipeline at a circulation flow rate of 12% / h of the storage capacity.

[0036] The final specifications of the electronic-grade ultrapure water prepared in this embodiment are: conductivity 0.052 μS / cm, turbidity 0.06 NTU, dissolved oxygen 3.2 μg / L, and carbon dioxide 8.5 μg / L, which meet the requirements for electronic-grade ultrapure water.

[0037] Example 3. In this embodiment, tap water is used as the raw water. The raw water quality indicators are: turbidity 8 NTU, hardness 1.2 mmol / L, COD 22 mg / L, and conductivity 350 μS / cm. Ultrapure water is prepared using the above-mentioned electronic-grade ultrapure water preparation method. The specific steps are as follows: S1. Pretreatment: The raw water is filtered through a 500-mesh stainless steel screen to remove suspended solids with a particle size ≥20μm. Then it is passed into a dual-chamber parallel activated carbon adsorption unit with an adsorption residence time controlled at 30min. The raw water is stably switched between the two chambers through a diversion component to remove organic matter, residual chlorine and odor from the water. Finally, it is softened by ion exchange resin to reduce the hardness of the raw water to 0.06mmol / L. S2, MBR Biological Treatment: Pretreated water is introduced into an MBR reactor. The MBR flat sheet membrane inside the reactor has a pore size of 0.1 μm. A rotary blower supplies air to the aeration heads inside the reactor, controlling the aeration velocity to 0.9 m / s². 3 / (m 2•h), by using air bubbles to flush the surface of the MBR flat sheet membrane in the reaction tank, the hydraulic retention time in the reaction tank is controlled to be 8h, and the effluent turbidity is treated to 0.12NTU and the COD removal rate is 97%; S3. Ultrafiltration-MOF Composite RO Treatment: The effluent from the MBR biological treatment is fed into the ultrafiltration permeate tank. A scale inhibitor and coagulant at a concentration of 6 mg / L are added to the tank and evenly dispersed by a dispersing and stirring mechanism. The mixture is then passed through a 254 nm wavelength irradiation tank with an intensity of 32 mW / cm². 2 Ultraviolet lamps kill microorganisms in the water, which is then passed through an ultrafiltration module to remove residual suspended solids and colloidal particles via a 50nm pore size ultrafiltration membrane. The ultrafiltration effluent is then passed through a MOF composite reverse osmosis membrane module for reverse osmosis treatment. The membrane module uses a composite reverse osmosis membrane modified with a metal-organic framework material with a 0.5nm pore size. The operating pressure is controlled at 1.9MPa and the water temperature at 26℃, and the treated water has a resistivity of 11.5MΩ・cm and a desalination rate of 99.8%. S4. Three-stage degassing: The effluent from the ultrafiltration-MOF composite RO treatment is first heated to 42°C by the first heat exchanger. Under the control of the flow regulation mechanism, it is then sequentially introduced into a series of three-stage degassing mechanisms. The first stage is a vacuum degassing tower with a vacuum degree of -0.08MPa, the second stage is a polytetrafluoroethylene hollow fiber membrane degassing module, and the third stage is a nitrogen purging degassing mechanism that introduces high-purity nitrogen gas with a purity of ≥99.999%, forming a gas-liquid countercurrent contact. After completing the three-stage degassing treatment, the degassed water is then cooled to 23°C by the second heat exchanger and introduced into the intermediate water tank, where the dissolved oxygen in the water is reduced to 4.1μg / L and the carbon dioxide to 9.2μg / L. S5, EDI deep purification: The water effluent from the intermediate water tank is sent to the EDI water treatment equipment through a booster pump. The outlet pressure of the booster pump is controlled at 0.45MPa. The working voltage of the EDI water treatment equipment is 230V and the working current is 6A. After EDI deep purification, the water flow is filtered through a terminal ultrafiltration membrane with a pore size of 15nm to remove resin debris and microorganisms. S6. Finished Product Storage and Circulation: The electronic-grade ultrapure water after deep purification by EDI is stored in a nitrogen-sealed water tank. A slight positive pressure of 0.01MPa is maintained in the tank through a nitrogen replenishment valve and a nitrogen release valve. The liquid level transmitter in the nitrogen-sealed water tank monitors the liquid level in real time and links with the water replenishment system to return the electronic-grade ultrapure water to the front end of the EDI equipment through the circulation pipeline at a circulation flow rate of 10% / h of the storage capacity.

[0038] The final specifications of the electronic-grade ultrapure water prepared in this embodiment are: conductivity 0.056 μS / cm, turbidity 0.07 NTU, dissolved oxygen 4.1 μg / L, and carbon dioxide 9.2 μg / L, which meet the requirements for electronic-grade ultrapure water.

[0039] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing electronic-grade ultrapure water, characterized in that, The method includes the following steps: S1. Pretreatment: The raw water is filtered through a 500-mesh stainless steel screen, then passed through a dual-chamber parallel activated carbon adsorption unit to remove organic matter, residual chlorine and odors. Finally, it is softened by ion exchange resin to reduce the hardness of the raw water. S2, MBR biological treatment: The pretreated water is introduced into the MBR reactor and the aeration rate is controlled to use air bubbles to flush the surface of the MBR flat sheet membrane inside the reactor. S3, Ultrafiltration-MOF Composite RO Treatment: The effluent after MBR biological treatment is introduced into the ultrafiltration product water tank. Scale inhibitors and coagulants are added to the ultrafiltration product water tank, followed by the sequential treatment of killing microorganisms, removing residual suspended solids and colloidal particles, and reverse osmosis. S4. Three-stage degassing: First, the effluent after ultrafiltration-MOF composite RO treatment is subjected to three-stage degassing treatment. Then, the degassed water is cooled and passed into an intermediate water tank for further treatment until the dissolved oxygen in the water is less than or equal to 5 μg / L and the carbon dioxide is less than or equal to 10 μg / L. S5, EDI deep purification: The water effluent from the intermediate water tank is sent to the EDI water treatment equipment through a booster pump. After EDI deep purification, the water flow is then filtered through a terminal ultrafiltration membrane with a pore size of less than or equal to 20nm to remove resin debris and microorganisms. S6. Finished Product Storage and Circulation: Store the electronic-grade ultrapure water after deep purification by EDI into a nitrogen-sealed water tank. Maintain a slight positive pressure of 0.01-0.02MPa in the tank through the nitrogen replenishment valve and the nitrogen release valve. Circulate the electronic-grade ultrapure water back to the front end of the EDI equipment through the circulation pipeline at a circulation flow rate of 10-15% / h of the storage capacity.

2. The method for preparing electronic-grade ultrapure water as described in claim 1, characterized in that, Step S1 details The process includes the following: Raw water is introduced into a pretreatment tank and filtered using a 500-mesh stainless steel screen to remove suspended solids with a particle size greater than or equal to 20 μm. The activated carbon adsorption unit adopts a dual-chamber parallel structure, which switches the raw water between the two chambers through a diversion component. When one chamber of activated carbon is saturated, the replacement component automatically discharges waste carbon and replenishes new carbon. The adsorption residence time is controlled at 30-40 minutes to remove organic matter, residual chlorine, and odor substances from the water. After softening treatment with ion exchange resin, the hardness of the raw water is reduced to less than or equal to 0.1 mmol / L. The dual-chamber parallel structure has built-in activated carbon packing.

3. The method for preparing electronic-grade ultrapure water as described in claim 1, characterized in that, Step S2 specifically includes the following processes: The pretreated raw water enters the MBR reactor, which is equipped with MBR flat sheet membranes and aeration heads. A rotary blower provides aeration airflow, using air bubbles to wash the surface of the MBR flat sheet membranes inside the reactor. The air velocity is controlled between 0.8 and 1.2 m / s. 3 / (m 2 The hydraulic residence time in the reaction tank is 8-12 hours.

4. The method for preparing electronic-grade ultrapure water as described in claim 3, characterized in that, The MBR flat sheet membrane is detachably installed inside the MBR reactor via a membrane plate mounting bracket. An aeration head is provided on the inner side of the upper left end of the MBR reactor, with the output end of the aeration head corresponding to the position above the MBR flat sheet membrane. The pore size of the MBR flat sheet membrane is 0.1-0.2μm.

5. The method for preparing electronic-grade ultrapure water as described in claim 1, characterized in that, Step S3 details The process includes the following: The effluent from the MBR biological treatment is fed into the ultrafiltration permeate tank. Scale inhibitor and coagulant at a concentration of 5-10 mg / L are added to the tank and evenly dispersed by a dispersing and stirring mechanism. The mixture is then passed through an irradiation system with a wavelength of 254 nm and an intensity greater than or equal to 30 mW / cm². 2 The ultraviolet lamps kill microorganisms in the water, and then the water flows into the ultrafiltration module. The ultrafiltration membrane with a pore size of 50-100nm removes residual suspended solids and colloidal particles. The ultrafiltration water is then passed into the MOF composite reverse osmosis membrane module for reverse osmosis treatment.

6. The method for preparing electronic-grade ultrapure water as described in claim 5, characterized in that, The dispersion and stirring mechanism includes a dosing pipe, a connecting sleeve, a dispersion cylinder, and a stirring motor. The dosing pipe is connected to the dispersion cylinder through the connecting sleeve. Dispersion holes and stirring blades are evenly opened on the outer wall of the dispersion cylinder. The stirring motor drives the cylinder to rotate and achieve uniform dispersion of the agent.

7. The method for preparing electronic-grade ultrapure water as described in claim 5, characterized in that, The MOF composite reverse osmosis membrane module uses a composite reverse osmosis membrane modified with a metal-organic framework material with a pore size of 0.5-1nm. During reverse osmosis treatment, the operating pressure of the membrane module is controlled at 1.8-2.2MPa and the water temperature at 25-30℃, and the water resistivity is greater than or equal to 10MΩ・cm and the desalination rate is greater than or equal to 99.8%.

8. The method for preparing electronic-grade ultrapure water as described in claim 1, characterized in that, Step S4 specifically includes the following processes: The effluent from the ultrafiltration-MOF composite RO treatment is first heated to 40-50℃ by the first heat exchange mechanism, and then sequentially introduced into a three-stage degassing mechanism under the control of the flow regulation mechanism. The first stage is a vacuum degassing tower with a vacuum degree of -0.08~-0.09MPa, the second stage is a polytetrafluoroethylene hollow fiber membrane degassing component, and the third stage is a nitrogen purging degassing mechanism that introduces high-purity nitrogen gas with a purity greater than or equal to 99.999%. During the nitrogen purging, gas and liquid are in countercurrent contact. After degassing, the water flows through the second heat exchange mechanism and is cooled to 20-25℃ before being introduced into the intermediate water tank.

9. The method for preparing electronic-grade ultrapure water as described in claim 1, characterized in that, Step S5 details The process includes the following: Water from the intermediate water tank is pumped into the EDI water treatment equipment via a booster pump. The booster pump outlet pressure is 0.4-0.6 MPa. The EDI water treatment equipment operates at a voltage of 200-300V and a current of 5-10A. The EDI equipment performs deep ion removal and online resin regeneration through a combination of electrodialysis and ion exchange. Water from the intermediate water tank is then pumped into the EDI water treatment equipment for filtration to remove resin debris and microorganisms, ultimately yielding electronic-grade ultrapure water.

10. The method for preparing electronic-grade ultrapure water as described in claim 1, characterized in that, In step S6, a level transmitter is installed in the nitrogen-sealed water tank to monitor the water level in the tank in real time and link it with the water replenishment system. The final electronic-grade ultrapure water has a conductivity of less than or equal to 0.06 μS / cm and a turbidity of less than or equal to 0.08 NTU.

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