Method for preparing electronic grade sodium hydroxide based on industrial caustic soda

Abstract

The application provides a method for preparing electronic-grade sodium hydroxide based on industrial caustic soda, comprising the following steps: S1, dissolving and coarse filtering raw materials; S2, chemical precipitation and complex impurity removal; S3, solid-liquid separation and precision filtration; S4, ion exchange deep purification; S5, evaporation concentration and product blending; S6, terminal ultra-clean filtration and packaging. Through multi-stage synergistic purification of chemical precipitation, chelating resin ion exchange and terminal ultra-clean filtration, the application can effectively remove metal impurities and particulate matter to trace level, fully meeting the stringent purity requirements in the field of semiconductor and high-end electronic materials. High-purity corrosion-resistant materials are used in the whole process to completely eliminate secondary pollution of equipment; combined with online monitoring and closed-loop automatic control, the production process achieves high consistency and traceability, ensuring stable quality between batches. Attention is paid to resource recycling, effectively reducing the amount of hazardous waste, and being environmentally friendly; the product form is flexible, which can adapt to the different form requirements of liquid caustic soda and solid caustic soda.

Description

Technical Field

[0001] This invention relates to the field of industrial caustic soda purification, and specifically to a method for preparing electronic-grade sodium hydroxide based on industrial caustic soda. Background Technology

[0002] Existing industrial caustic soda purification technologies (such as recrystallization, membrane separation, and simple precipitation) have the following main technical defects in the preparation of electronic-grade sodium hydroxide: 1. Impurities are not completely removed, making it difficult to meet SEMI electronic grade standards. Traditional methods often use simple recrystallization or chemical precipitation, which are mainly used for common impurities such as NaCl and Na2SO4. However, they have limited ability to remove transition metal ions such as Fe, Cu, Ni, and Cr, as well as silicates. The total metal impurities in the finished product are usually in the ppm level, which cannot meet the ppb or even sub-ppb level standards required by the semiconductor industry.

[0003] 2. Neglecting the deep removal of sodium carbonate; industrial caustic soda readily absorbs CO2 from the air to form Na2CO3 during storage and dissolution. Traditional processes lack effective separation methods for sodium carbonate, and Na2CO3 can affect the consistency of etching rates in electronic applications, which is a strictly controlled indicator for semiconductor customers.

[0004] 3. Secondary pollution introduced by equipment materials: Traditional purification equipment mostly uses ordinary stainless steel (304, 316) or carbon steel. In the high temperature and high concentration alkaline environment, the equipment itself will dissolve metal ions such as Fe, Ni, and Cr, causing the phenomenon of "purification and pollution at the same time", which cannot guarantee the metal impurity level of the final product.

[0005] 4. Lack of particulate matter control: Traditional processes only focus on chemical composition and lack effective filtration and control of fine particulate matter (≥0.2 μm, ≥0.1 μm). In semiconductor wet processes, particulate matter can directly cause wafer surface defects, and traditional processes cannot meet semiconductor-grade cleanliness requirements.

[0006] 5. Poor process stability and lack of online monitoring: Traditional processes are mostly intermittent operations that rely on manual sampling and analysis. They cannot monitor changes in metal ion concentration in real time, resulting in large quality fluctuations between batches. This makes it difficult to achieve continuous and automated production and also fails to meet the quality traceability requirements of high-end customers. Summary of the Invention

[0007] To address the above problems, this invention provides a method for preparing electronic-grade sodium hydroxide based on industrial caustic soda.

[0008] The specific plan is as follows: A method for preparing electronic-grade sodium hydroxide based on industrial caustic soda, characterized by comprising the following steps: S1. Raw material dissolution and coarse filtration: Industrial caustic soda is dissolved in high-purity water to prepare a sodium hydroxide solution with a concentration of 45% to 50%. The solution is stirred and dissolved at 80 to 90°C, and mechanical impurities are removed by coarse filtration. S2. Chemical precipitation and complexation for impurity removal: Oxidizing agent, precipitant and chelating agent are added to the coarsely filtered solution, and chemical precipitation reaction is carried out under pH 12.5-13.5 conditions to remove heavy metal ions, silicates, sulfate and carbonate impurities. S3. Solid-liquid separation and precision filtration: After sedimentation separation, the liquid obtained in step S2 is sequentially passed through a microporous precision filter and a pre-coated filter for solid-liquid separation to remove precipitates. S4. Deep purification by ion exchange: The filtrate obtained in step S3 is subjected to ion exchange adsorption through a chelating resin column to remove residual metal ions and control the content of a single metal ion in the effluent to ≤1 ppb. S5. Evaporation, concentration and product preparation: The purified solution obtained in step S4 is evaporated and concentrated under vacuum conditions, or crystallized, melted and granulated to obtain electronic grade sodium hydroxide liquid alkali or solid alkali. S6. Terminal ultra-clean filtration and packaging: After filtering the product obtained in step S5 through a filter element with a precision of 0.1 μm or less, it is filled and packaged in a clean environment.

[0009] Furthermore, in step S1, the industrial caustic soda is a solid or liquid caustic soda produced by the ion-exchange membrane method, with a purity ≥98.5%; the resistivity of the high-purity water is ≥18 Ω·cm, and the dissolved oxygen is ≤1 ppm; the coarse filtration uses a 200-mesh or 10-20 μm titanium rod or PP melt-blown filter element.

[0010] Further, in step S2, the oxidant is 30% hydrogen peroxide, oxygen, or ozone, and the amount added is 0.1% to 0.5% of the liquid volume; the precipitant is barium salt, and the amount added is 0.5 to 2 g / L; the chelating agent is disodium EDTA, and the amount added is 10 to 50 ppm; carbonate is removed by freezing crystallization, cooling the solution to 15 to 25°C, and keeping it at that temperature for 6 to 12 hours; sulfate is removed by barium salt to generate barium sulfate precipitate; polyacrylamide or sodium polyacrylate flocculant is also added, and the amount added is 1 to 5 ppm.

[0011] Furthermore, in step S3, sedimentation separation is carried out in an insulated jacketed sedimentation tank, with the temperature controlled at 60-80℃ and a settling time of 12-24 hours; the microporous precision filter has a filtration accuracy of 1-5 μm and is made of PTFE or titanium; the pre-coated filter is pre-coated with perlite or activated carbon and has a filtration accuracy of 0.5-1 μm.

[0012] Further, in step S4, the chelating resin is an iminodiacetic acid group chelating resin; the ion exchange temperature is 40-60℃, and the flow rate is 5-10 BV / h; the ion exchange column material is reinforced polypropylene, polyvinylidene fluoride, or fluoroplastic lined; the resin regeneration uses 5%-10% electronic grade hydrochloric acid and 4%-8% electronic grade sodium hydroxide solution.

[0013] Furthermore, in step S5, the evaporation and concentration adopts a falling film evaporator or a multi-effect evaporation system, the heating chamber is made of nickel, the evaporation chamber is made of electropolished 316L stainless steel, the vacuum degree is -0.08 to -0.095 MPa, the evaporation temperature is 80 to 100℃, and the concentration is concentrated to 49% to 50.5% sodium hydroxide; the crystallization adopts vacuum flash crystallization or cooling crystallization, and the crystallization temperature is 30 to 40℃.

[0014] Furthermore, in step S6, the filter element is a PTFE pleated filter element with a filtration accuracy of 0.1 μm or 0.05 μm; the cleanliness of the filling area reaches Class 100 or ISO 5 level; the packaging container is a 316L EP grade stainless steel tanker or HDPE drum with passivated inner wall, or an aluminum-plastic bag lined with PFA or a high-cleanliness PP drum, and is protected by nitrogen.

[0015] Furthermore, during the preparation process, an online ICP-MS is set up to monitor the metal ion content in real time, and an online liquid particle counter is set up to monitor the particle quantity in real time, thereby controlling the process parameters.

[0016] Furthermore, the control of the process parameters includes a host computer, an actuator, and a data platform. Between the host computer and the actuator, the actuator uploads valve position status, pump frequency, and fault codes to the host computer in real time via a fieldbus. The host computer uses this information to determine whether the action is complete; if no feedback is received within a timeout period, an alarm is triggered. Based on logical judgment, the host computer issues switch or adjustment commands to the actuator to drive the equipment. Between the host computer and the data platform, the host computer periodically or event-triggeredly writes all timestamped data into the industrial database. The data platform sends the production formula to the host computer, which the operator can access with a single click.

[0017] Furthermore, the industrial database provides raw data to the data platform. After the data platform completes batch determination, SPC analysis, and report generation, it writes the results back to the database and feeds back the quality status to the host computer through an interface to guide production.

[0018] The beneficial effects of this invention are as follows: 1. Through the synergistic effect of chelating resin ion exchange and multi-stage chemical precipitation, the removal rate of metal ions such as Fe, Cu, Ni, Cr, Zn, Ca, and Mg can reach over 99.9%. The content of individual metal impurities in the final product can be stably controlled at ≤1ppb, and the content of key metals (Fe, Cu, Ni) can reach ≤0.1ppb, fully meeting the SEMI C12 and above electronic grade standards.

[0019] 2. A freeze-crystallization method, combined with full-system nitrogen sealing to prevent secondary CO2 intrusion, reduces the Na2CO3 content in the product to ≤0.01%, ensuring the stability of the etching process. Through 0.1 μm / 0.05 μm PTFE terminal filtration and Class 100 cleanroom filling, the number of particles ≥0.2 μm is controlled to ≤100 particles / mL, meeting the stringent particle size requirements of semiconductor wet processes.

[0020] 3. Key equipment utilizes high-purity alkali-resistant materials such as nickel 200 / 201, electropolished 316L stainless steel, and PTFE / PVDF to effectively inhibit metal leaching from the equipment body. Pipelines and valves are lined with fluoropolymer to avoid dead corners and metal contact points, ensuring product purity from the process equipment level.

[0021] 4. Introducing online ICP-MS and an online particle counter enables real-time monitoring of metal impurity and particulate matter concentrations, achieving closed-loop control. The ion exchange system can employ a dual-column series configuration or a one-in-use-one-standby mode to ensure continuous operation and significantly improve production efficiency and batch consistency.

[0022] 5. Ion exchange regeneration waste liquid (containing NaOH and NaCl) can be reused in the dissolution process of industrial-grade caustic soda, realizing the recovery and utilization of alkali resources. The barium-containing sludge generated in the front-end precipitation is hazardous waste, but the amount generated is reduced by more than 80% compared with the traditional full-volume neutralization method, reducing hazardous waste disposal costs and environmental burden.

[0023] 6. We can flexibly produce 49% to 50.5% electronic grade liquid alkali or high-purity solid alkali (flake / granule) according to customer needs to meet different transportation conditions and application scenarios (such as IC manufacturing, LED epitaxy, high-purity chemical synthesis, etc.). Attached Figure Description

[0024] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0025] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Example 1

[0026] like Figure 1As shown, this invention provides a method for preparing electronic-grade sodium hydroxide based on industrial caustic soda, comprising the following steps: S1. Raw material dissolution and coarse filtration: Industrial caustic soda is dissolved in high-purity water to prepare a 45% sodium hydroxide solution. The solution is stirred and dissolved at 90°C, and mechanical impurities are removed by coarse filtration. Among them, industrial caustic soda is solid or liquid caustic soda produced by ion-exchange membrane method with a purity ≥98.5%; the resistivity of high-purity water is ≥18 Ω·cm and dissolved oxygen is ≤1 ppm; coarse filtration uses 200 mesh or 10 μm titanium rods or PP melt-blown filter elements.

[0027] S2. Chemical precipitation and complexation for impurity removal: Oxidizing agent, precipitant and chelating agent are added to the coarsely filtered solution, and chemical precipitation reaction is carried out under pH 13.5 conditions to remove heavy metal ions, silicates, sulfate and carbonate impurities. The oxidant is 30% hydrogen peroxide, oxygen, or ozone, added at 0.1% of the liquid volume; the precipitant is barium salt, added at 2 g / L; the chelating agent is disodium EDTA, added at 10 ppm; carbonate is removed by freezing crystallization, cooling the solution to 25°C and holding it at that temperature for 6 hours; sulfate is removed by barium salt to form barium sulfate precipitate; polyacrylamide or sodium polyacrylate flocculant is also added at 5 ppm.

[0028] S3. Solid-liquid separation and precision filtration: After sedimentation separation, the liquid obtained in step S2 is sequentially passed through a microporous precision filter and a pre-coated filter for solid-liquid separation to remove precipitates. The sedimentation separation is carried out in an insulated jacketed sedimentation tank, with the temperature controlled at 60℃ and a settling time of 24 hours; the microporous precision filter has a filtration accuracy of 1 μm and is made of PTFE or titanium; the pre-coated filter is pre-coated with perlite or activated carbon and has a filtration accuracy of 1 μm.

[0029] S4. Deep purification by ion exchange: The filtrate obtained in step S3 is subjected to ion exchange adsorption through a chelating resin column to remove residual metal ions and control the content of a single metal ion in the effluent to ≤1 ppb. The chelating resin is an iminodiacetic acid group chelating resin; the ion exchange temperature is 40℃, and the flow rate is 10 BV / h; the ion exchange column material is reinforced polypropylene, polyvinylidene fluoride, or fluoroplastic lined; the resin regeneration uses 5% electronic grade hydrochloric acid and 8% electronic grade sodium hydroxide solution.

[0030] S5. Evaporation, concentration and product preparation: The purified solution obtained in step S4 is evaporated and concentrated under vacuum conditions, or crystallized, melted and granulated to obtain electronic grade sodium hydroxide liquid alkali or solid alkali. The evaporation and concentration process employs a falling film evaporator or a multi-effect evaporation system. The heating chamber is made of nickel, and the evaporation chamber is made of electropolished 316L stainless steel. The vacuum level is -0.08 MPa, the evaporation temperature is 100℃, and the concentration is reduced to 49% sodium hydroxide. The crystallization process employs vacuum flash crystallization or cooling crystallization, with a crystallization temperature of 40℃.

[0031] S6. Terminal ultra-clean filtration and packaging: After filtering the product obtained in step S5 through a filter element with a precision of 0.1 μm or less, it is filled and packaged in a clean environment. The filter element is a PTFE pleated filter element with a filtration accuracy of 0.1 μm or 0.05 μm; the cleanliness of the filling area reaches Class 100 or ISO 5 level; the packaging container is a 316L EP grade stainless steel tanker or HDPE drum with passivated inner wall, or an aluminum-plastic bag lined with PFA or a high-cleanliness PP drum, and is protected by nitrogen.

[0032] In this embodiment, an online ICP-MS is used to monitor the metal ion content in real time during the preparation process, and an online liquid particle counter is used to monitor the particle quantity in real time, thereby controlling the process parameters. The control of these process parameters includes a host computer, an actuator, and a data platform. Between the host computer and the actuator, the actuator uploads valve position status, pump frequency, and fault codes to the host computer in real time via a fieldbus. The host computer uses this information to determine whether the action is completed; if no feedback is received within a timeout period, an alarm is triggered. Based on logical judgment, the host computer issues switch or adjustment commands to the actuator to drive the equipment. Between the host computer and the data platform, the host computer periodically or event-triggeredly writes all timestamped data into the industrial database. The data platform sends the production formula to the host computer, which the operator can access with a single click.

[0033] The industrial database provides raw data to the data platform. After the data platform completes batch determination, SPC analysis, and report generation, it writes the results back to the database and feeds back the quality status to the host computer through an interface to guide production. Example 2

[0034] like Figure 1 As shown, this invention provides a method for preparing electronic-grade sodium hydroxide based on industrial caustic soda, comprising the following steps: S1. Raw material dissolution and coarse filtration: Industrial caustic soda is dissolved in high-purity water to prepare a 50% sodium hydroxide solution. The solution is stirred and dissolved at 80°C, and mechanical impurities are removed by coarse filtration. Among them, industrial caustic soda is solid or liquid caustic soda produced by ion-exchange membrane method with a purity ≥98.5%; the resistivity of high-purity water is ≥18 Ω·cm and dissolved oxygen is ≤1 ppm; coarse filtration uses 200 mesh or 20 μm titanium rods or PP melt-blown filter elements.

[0035] S2. Chemical precipitation and complexation for impurity removal: Oxidizing agent, precipitant and chelating agent are added to the coarsely filtered solution, and chemical precipitation reaction is carried out under pH 12.5 conditions to remove heavy metal ions, silicates, sulfate and carbonate impurities. The oxidant is 30% hydrogen peroxide, oxygen, or ozone, added at 0.5% of the liquid volume; the precipitant is barium salt, added at 0.5 g / L; the chelating agent is disodium EDTA, added at 50 ppm; carbonate is removed by freeze crystallization, cooling the solution to 15°C and holding it at that temperature for 12 hours; sulfate is removed by barium salt to form barium sulfate precipitate; polyacrylamide or sodium polyacrylate flocculant is also added at 1 ppm.

[0036] S3. Solid-liquid separation and precision filtration: After sedimentation separation, the liquid obtained in step S2 is sequentially passed through a microporous precision filter and a pre-coated filter for solid-liquid separation to remove precipitates. The sedimentation separation is carried out in an insulated jacketed sedimentation tank, with the temperature controlled at 80℃ and a settling time of 12 hours; the microporous precision filter has a filtration accuracy of 5 μm and is made of PTFE or titanium; the pre-coated filter is pre-coated with perlite or activated carbon and has a filtration accuracy of 0.5 μm.

[0037] S4. Deep purification by ion exchange: The filtrate obtained in step S3 is subjected to ion exchange adsorption through a chelating resin column to remove residual metal ions and control the content of a single metal ion in the effluent to ≤1 ppb. The chelating resin is an iminodiacetic acid group chelating resin; the ion exchange temperature is 60℃, and the flow rate is 5 BV / h; the ion exchange column material is reinforced polypropylene, polyvinylidene fluoride, or fluoroplastic lined; the resin regeneration uses 10% electronic grade hydrochloric acid and 4% electronic grade sodium hydroxide solution.

[0038] S5. Evaporation, concentration and product preparation: The purified solution obtained in step S4 is evaporated and concentrated under vacuum conditions, or crystallized, melted and granulated to obtain electronic grade sodium hydroxide liquid alkali or solid alkali. The evaporation and concentration process employs a falling film evaporator or a multi-effect evaporation system. The heating chamber is made of nickel, and the evaporation chamber is made of electropolished 316L stainless steel. The vacuum degree is -0.095 MPa, the evaporation temperature is 80℃, and the concentration is reduced to 50.5% sodium hydroxide. The crystallization process employs vacuum flash crystallization or cooling crystallization, with a crystallization temperature of 30℃.

[0039] S6. Terminal ultra-clean filtration and packaging: After filtering the product obtained in step S5 through a filter element with a precision of 0.1 μm or less, it is filled and packaged in a clean environment. The filter element is a PTFE pleated filter element with a filtration accuracy of 0.1 μm or 0.05 μm; the cleanliness of the filling area reaches Class 100 or ISO 5 level; the packaging container is a 316L EP grade stainless steel tanker or HDPE drum with passivated inner wall, or an aluminum-plastic bag lined with PFA or a high-cleanliness PP drum, and is protected by nitrogen.

[0040] In this embodiment, an online ICP-MS is used to monitor the metal ion content in real time during the preparation process, and an online liquid particle counter is used to monitor the particle quantity in real time, thereby controlling the process parameters. The control of these process parameters includes a host computer, an actuator, and a data platform. Between the host computer and the actuator, the actuator uploads valve position status, pump frequency, and fault codes to the host computer in real time via a fieldbus. The host computer uses this information to determine whether the action is completed; if no feedback is received within a timeout period, an alarm is triggered. Based on logical judgment, the host computer issues switch or adjustment commands to the actuator to drive the equipment. Between the host computer and the data platform, the host computer periodically or event-triggeredly writes all timestamped data into the industrial database. The data platform sends the production formula to the host computer, which the operator can access with a single click.

[0041] The industrial database provides raw data to the data platform. After the data platform completes batch determination, SPC analysis, and report generation, it writes the results back to the database and feeds back the quality status to the host computer through an interface to guide production. Example 3

[0042] like Figure 1 As shown, this invention provides a method for preparing electronic-grade sodium hydroxide based on industrial caustic soda, comprising the following steps: S1. Raw material dissolution and coarse filtration: Industrial caustic soda is dissolved in high-purity water to prepare a sodium hydroxide solution with a concentration of 48%. The solution is stirred and dissolved at 85°C, and mechanical impurities are removed by coarse filtration. Among them, industrial caustic soda is solid or liquid caustic soda produced by ion-exchange membrane method with a purity ≥98.5%; the resistivity of high-purity water is ≥18 Ω·cm and dissolved oxygen is ≤1 ppm; coarse filtration uses 200 mesh or 15 μm titanium rods or PP melt-blown filter elements.

[0043] S2. Chemical precipitation and complexation for impurity removal: Oxidizing agent, precipitant and chelating agent are added to the solution after coarse filtration, and chemical precipitation reaction is carried out under pH 13 conditions to remove heavy metal ions, silicates, sulfate and carbonate impurities. The oxidant is 30% hydrogen peroxide, oxygen, or ozone, added at 0.3% of the liquid volume; the precipitant is barium salt, added at 1 g / L; the chelating agent is disodium EDTA, added at 30 ppm; carbonate is removed by freezing crystallization, cooling the solution to 20°C and holding it at that temperature for 8 hours; sulfate is removed by barium salt to form barium sulfate precipitate; polyacrylamide or sodium polyacrylate flocculant is also added at 3 ppm.

[0044] S3. Solid-liquid separation and precision filtration: After sedimentation separation, the liquid obtained in step S2 is sequentially passed through a microporous precision filter and a pre-coated filter for solid-liquid separation to remove precipitates. The sedimentation separation is carried out in an insulated jacketed sedimentation tank, with the temperature controlled at 70℃ and a settling time of 15 hours; the microporous precision filter has a filtration accuracy of 3 μm and is made of PTFE or titanium; the pre-coated filter is pre-coated with perlite or activated carbon and has a filtration accuracy of 0.7 μm.

[0045] S4. Deep purification by ion exchange: The filtrate obtained in step S3 is subjected to ion exchange adsorption through a chelating resin column to remove residual metal ions and control the content of a single metal ion in the effluent to ≤1 ppb. The chelating resin is an iminodiacetic acid group chelating resin; the ion exchange temperature is 45℃, and the flow rate is 7 BV / h; the ion exchange column material is reinforced polypropylene, polyvinylidene fluoride, or fluoroplastic lined; the resin regeneration uses 8% electronic grade hydrochloric acid and 6% electronic grade sodium hydroxide solution.

[0046] S5. Evaporation, concentration and product preparation: The purified solution obtained in step S4 is evaporated and concentrated under vacuum conditions, or crystallized, melted and granulated to obtain electronic grade sodium hydroxide liquid alkali or solid alkali. The evaporation and concentration process employs a falling film evaporator or a multi-effect evaporation system. The heating chamber is made of nickel, and the evaporation chamber is made of electropolished 316L stainless steel. The vacuum level is -0.09 MPa, the evaporation temperature is 90℃, and the concentration is reduced to 50% sodium hydroxide. The crystallization process employs vacuum flash crystallization or cooling crystallization, with a crystallization temperature of 35℃.

[0047] S6. Terminal ultra-clean filtration and packaging: After filtering the product obtained in step S5 through a filter element with a precision of 0.1 μm or less, it is filled and packaged in a clean environment. The filter element is a PTFE pleated filter element with a filtration accuracy of 0.1 μm or 0.05 μm; the cleanliness of the filling area reaches Class 100 or ISO 5 level; the packaging container is a 316L EP grade stainless steel tanker or HDPE drum with passivated inner wall, or an aluminum-plastic bag lined with PFA or a high-cleanliness PP drum, and is protected by nitrogen.

[0048] In this embodiment, an online ICP-MS is used to monitor the metal ion content in real time during the preparation process, and an online liquid particle counter is used to monitor the particle quantity in real time, thereby controlling the process parameters. The control of these process parameters includes a host computer, an actuator, and a data platform. Between the host computer and the actuator, the actuator uploads valve position status, pump frequency, and fault codes to the host computer in real time via a fieldbus. The host computer uses this information to determine whether the action is completed; if no feedback is received within a timeout period, an alarm is triggered. Based on logical judgment, the host computer issues switch or adjustment commands to the actuator to drive the equipment. Between the host computer and the data platform, the host computer periodically or event-triggeredly writes all timestamped data into the industrial database. The data platform sends the production formula to the host computer, which the operator can access with a single click.

[0049] The industrial database provides raw data to the data platform. After the data platform completes batch determination, SPC analysis, and report generation, it writes the results back to the database and feeds back the quality status to the host computer through an interface to guide production.

[0050] The technical means disclosed in this invention are not limited to those disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention.

Claims

1. A method for preparing electronic-grade sodium hydroxide based on industrial caustic soda, characterized in that, Includes the following steps: S1. Dissolve industrial caustic soda in high-purity water to prepare a sodium hydroxide solution with a concentration of 45% to 50%, stir and dissolve at 80 to 90°C, and remove mechanical impurities by coarse filtration; S2. Add oxidant, precipitant and chelating agent to the coarsely filtered solution, and carry out chemical precipitation reaction under pH 12.5-13.5 conditions to remove heavy metal ions, silicates, sulfate and carbonate impurities; S3. After sedimentation separation, the liquid obtained in step S2 is then passed through a microporous precision filter and a pre-coated filter in sequence for solid-liquid separation to remove precipitates. S4. The filtrate obtained in step S3 is passed through a chelating resin column for ion exchange adsorption to remove residual metal ions and control the content of a single metal ion in the effluent to be ≤1 ppb. S5. The purified solution obtained in step S4 is evaporated and concentrated under vacuum conditions, or crystallized, melted and granulated to obtain electronic grade sodium hydroxide liquid alkali or solid alkali. S6. After filtering the product obtained in step S5 through a filter element with a precision of 0.1 μm or less, it is filled and packaged in a clean environment.

2. The method for preparing electronic-grade sodium hydroxide based on industrial caustic soda according to claim 1, characterized in that, In step S1, the industrial caustic soda is a solid or liquid caustic soda produced by the ion-exchange membrane method, with a purity ≥98.5%; the resistivity of the high-purity water is ≥18Ω·cm, and the dissolved oxygen is ≤1 ppm; the coarse filtration uses a 200-mesh or 10-20 μm titanium rod or PP melt-blown filter element.

3. The method for preparing electronic-grade sodium hydroxide based on industrial caustic soda according to claim 1, characterized in that, In step S2, the oxidant is 30% hydrogen peroxide, oxygen, or ozone, and the amount added is 0.1% to 0.5% of the liquid volume; the precipitant is barium salt, and the amount added is 0.5 to 2 g / L; the chelating agent is disodium EDTA, and the amount added is 10 to 50 ppm; carbonate is removed by freezing crystallization, the solution is cooled to 15 to 25°C and kept at that temperature for 6 to 12 hours; sulfate is removed by barium salt to form barium sulfate precipitate; polyacrylamide or sodium polyacrylate flocculant is also added, and the amount added is 1 to 5 ppm.

4. The method for preparing electronic-grade sodium hydroxide based on industrial caustic soda according to claim 1, characterized in that, In step S3, sedimentation separation is carried out in an insulated jacketed sedimentation tank, with the temperature controlled at 60-80℃ and a settling time of 12-24 hours; the microporous precision filter has a filtration accuracy of 1-5 μm and is made of PTFE or titanium; the pre-coated filter is pre-coated with perlite or activated carbon and has a filtration accuracy of 0.5-1 μm.

5. The method for preparing electronic-grade sodium hydroxide based on industrial caustic soda according to claim 1, characterized in that, In step S4, the chelating resin is an iminodiacetic acid group chelating resin; the ion exchange temperature is 40-60℃, and the flow rate is 5-10 BV / h; the ion exchange column material is reinforced polypropylene, polyvinylidene fluoride, or fluoroplastic lined; the resin is regenerated using 5%-10% electronic grade hydrochloric acid and 4%-8% electronic grade sodium hydroxide solution.

6. The method for preparing electronic-grade sodium hydroxide based on industrial caustic soda according to claim 1, characterized in that, In step S5, evaporation and concentration are carried out using a falling film evaporator or a multi-effect evaporation system. The heating chamber is made of nickel, and the evaporation chamber is made of electropolished 316L stainless steel. The vacuum degree is -0.08 to -0.095 MPa, the evaporation temperature is 80 to 100°C, and the concentration of sodium hydroxide is concentrated to 49% to 50.5%. Crystallization is carried out using vacuum flash crystallization or cooling crystallization, and the crystallization temperature is 30 to 40°C.

7. The method for preparing electronic-grade sodium hydroxide based on industrial caustic soda according to claim 1, characterized in that, In step S6, the filter element is a PTFE pleated filter element with a filtration accuracy of 0.1 μm or 0.05 μm; the cleanliness of the filling area reaches Class 100 or ISO 5 level; the packaging container is a 316L EP grade stainless steel tanker or HDPE drum with passivated inner wall, or an aluminum-plastic bag lined with PFA or a high-cleanliness PP drum, and is protected by nitrogen.

8. The method for preparing electronic-grade sodium hydroxide based on industrial caustic soda according to claim 1, characterized in that, During the preparation process, an online ICP-MS system was set up to monitor the metal ion content in real time, and an online liquid particle counter was set up to monitor the particle count in real time, thereby controlling the process parameters.

9. A method for preparing electronic-grade sodium hydroxide based on industrial caustic soda according to claim 8, characterized in that, The control of the process parameters includes a host computer, an actuator, and a data platform. Between the host computer and the actuator, the actuator uploads valve position status, pump frequency, and fault codes to the host computer in real time via fieldbus. The host computer uses this information to determine whether the action is completed. If no feedback is received within a timeout period, an alarm is triggered. Based on logical judgment, the host computer issues switch or adjustment commands to the actuator to drive the equipment to operate. Between the host computer and the data platform, the host computer periodically or event-triggeredly writes all timestamped data into the industrial database. The data platform sends the production formula to the host computer, which the operator can access with a single click.

10. A method for preparing electronic-grade sodium hydroxide based on industrial caustic soda according to claim 8, characterized in that, The industrial database provides raw data to the data platform. After the data platform completes batch determination, SPC analysis, and report generation, it writes the results back to the database and feeds back the quality status to the host computer through an interface to guide production.

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