Purification process of ultra-pure electronic grade nitric acid

Abstract

The application discloses a kind of purification processes of ultra-pure electronic grade nitric acid, it is related to electronic chemical purification technical field, comprising the following steps: S1: unloading filtration: industrial grade nitric acid raw material is pumped into raw material tank by unloading pump, normal temperature and pressure, then is transported to raw material filter by raw material delivery pump and is filtered, after removing large particles, it enters raw material buffer tank, and is stored at normal temperature and pressure;S2: waste heat preheating: the nitric acid raw material with the concentration of 70-71% is pumped into preheater by feed pump, and is preheated by waste acid as heat medium from the bottom of reboiler, after preheating, it enters rectifying column, and waste acid is cooled and enters waste acid tank.The application is coupled by "waste heat recovery preheating+reboiling rectification+staged condensation", the raw material is preheated by waste acid waste heat from the bottom of reboiler, which significantly reduces steam consumption, while staged condensation improves the separation efficiency and product purity of nitric acid, reduces NO compound emission, and overall energy consumption is reduced by 5%-10% compared with traditional process.

Description

Technical Field

[0001] This invention relates to the field of electronic chemical purification technology, specifically to a purification process for ultrapure electronic-grade nitric acid. Background Technology

[0002] Nitric acid, a core reagent in wet electronic chemicals, is widely used in integrated circuits, display panels, photovoltaic cells, and semiconductor device manufacturing. It is primarily used in critical processes such as wafer cleaning, etching, surface treatment, and impurity removal. As integrated circuit manufacturing processes continue to upgrade to 7nm, 5nm, and more advanced technologies, the purity requirements for nitric acid in the electronics industry have increased from ppm to ppt (parts per trillion). Extremely stringent control standards are imposed on metal ions, suspended particles, anionic impurities (chloride ions, sulfate ions, fluoride ions, etc.), and volatile organic compounds. It must meet SEMI C12, G4+, and G5 level requirements; even trace impurities can lead to chip defects, reduced yield, and device reliability failure.

[0003] The current industrial purification of ultrapure electronic-grade nitric acid mainly employs traditional processes such as conventional distillation, vacuum distillation, ion exchange, and membrane separation. However, these processes have the following significant drawbacks in practical applications: Conventional distillation / reduced pressure distillation process: relies on boiling point difference for separation and purification, which requires long-term high-temperature heating, resulting in problems such as high steam consumption, high energy consumption, and low thermal energy utilization. At the same time, high temperature will aggravate equipment corrosion and easily introduce metal ions such as iron, chromium, and nickel, causing secondary pollution and making it difficult to consistently achieve the ppt-level purity requirement. Ion exchange process: Although it can remove some metal ions, the resin is prone to dissolving organic matter, debris and anionic impurities, which can easily introduce new pollution. Moreover, the regeneration process generates a large amount of wastewater, which has high treatment costs and poor continuity, and is not suitable for large-scale high-purity nitric acid production. Membrane separation process: It has extremely high requirements for equipment materials and membrane modules. The strong corrosiveness of nitric acid can easily lead to membrane aging and damage, resulting in short service life, high operating costs, and difficulty in simultaneously achieving deep removal of metal ions, color, and volatile impurities, and insufficient purification precision.

[0004] Therefore, it is necessary to invent a purification process for ultrapure electronic-grade nitric acid to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a purification process for ultrapure electronic-grade nitric acid, in order to solve the problems of high energy consumption, low thermal energy utilization, and easy introduction of secondary pollution by metal ions in conventional distillation, the easy introduction of new impurities such as organic matter and anions by ion exchange, large amount of regeneration wastewater, and poor corrosion resistance, short life and insufficient purification accuracy of membrane separation.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a purification process for ultrapure electronic-grade nitric acid, comprising the following steps: S1: Unloading and Filtration: Industrial-grade nitric acid raw material is sent into the raw material tank by the unloading pump at normal temperature and pressure, and then sent to the raw material filter for primary filtration by the raw material conveying pump to remove large particles before entering the raw material buffer tank for buffering at normal temperature and pressure. S2: Waste heat preheating: Nitric acid raw material with a concentration of 70-71% is fed into the preheater via a feed pump. The waste acid from the bottom discharge port of the reboiler is used as the heat medium for preheating. After preheating, it enters the distillation column. The waste acid is cooled and then enters the waste acid tank. S3: Reboiler distillation: The preheated nitric acid feedstock enters the distillation column and flows into the reboiler by gravity. It is heated and evaporated by steam. The nitric acid gas rises, is adsorbed by the packing, and flows out from the top of the distillation column. S4: Stage condensation: Nitric acid gas flowing out from the top of the distillation column enters the primary condenser and the secondary condenser in sequence for stage condensation, and the uncondensed gas enters the tail gas condenser for further condensation; S5: Decolorization treatment: The nitric acid liquid flowing out of the primary condenser enters the decolorization tower, where clean compressed air is used to purge and decolorize from the bottom. The decolorized nitric acid flows out from the bottom of the tower. S6: Finished product cooling and buffering: The decolorized nitric acid enters the finished product cooler for cooling, and then enters the finished product buffer tank. After passing the inspection, it is pumped into the finished product tank by the finished product pump for packaging. Unqualified products are returned to the raw material buffer tank for re-purification. S7: Tail gas treatment: Non-condensable gases discharged from the top of the secondary condenser and decolorization tower enter the tail gas condenser, where they are further condensed using chilled water. The condensate enters the waste acid tank, and the non-condensable gases are sent to the downstream scrubbing tower for treatment.

[0007] Preferably, in step S1, the raw material filter is set up in a one-in-one-out configuration to achieve continuous production.

[0008] Preferably, the heat medium for the preheater in step S2 is the waste acid discharged from the bottom of the reboiler, and the waste acid enters the waste acid tank after being cooled to 35-40°C.

[0009] Preferably, the heat source for the reboiler in step S3 is steam at 155°C and 4.4 kg / cm²G.

[0010] Preferably, in step S4, the primary condenser uses cooling water as the refrigerant, and the temperature of the condensed nitric acid liquid is 70-80℃. Part of it is refluxed to the distillation column, and part enters the decolorization column. The nitric acid temperature at the condenser outlet is controlled by adjusting the cooling water feed rate.

[0011] Preferably, in step S4, the secondary condenser uses cooling water as the refrigerant, the condensed nitric acid liquid enters the decolorization tower, and the uncondensed gas enters the tail gas condenser.

[0012] Preferably, in step S5, the clean compressed air used in the decolorization tower has a temperature of 30-40°C and enters from the bottom of the tower. The gas discharged from the top of the decolorization tower (65-70°C) enters the secondary condenser for secondary condensation, and the condensate (30-35°C) is returned to the decolorization tower.

[0013] Preferably, in step S6, the finished product cooler is cooled by cooling water, and the outlet nitric acid temperature is 30-40℃.

[0014] Preferably, in step S7, the tail gas condenser uses chilled water at 5-8°C as the refrigerant, and the condensate temperature is 10-20°C, which flows into the waste acid tank.

[0015] Preferably, the nitric acid purified by this process reaches the G4+ grade, and the content of metal impurities is ≤100ppt.

[0016] The technical effects and advantages provided by the present invention in the above technical solution are as follows: 1. This invention utilizes the waste heat from the bottom of the reboiler to preheat the raw materials through a coupled design of "waste heat recovery preheating + reboiler distillation + staged condensation," significantly reducing steam consumption. At the same time, staged condensation improves the separation efficiency of nitric acid and the purity of the product, resulting in an overall energy consumption reduction of 5%-10% compared to traditional processes. 2. This invention effectively removes colored impurities and volatile residues from nitric acid through a combination of "clean air purging of the decolorization tower + secondary condensation and reflux". At the same time, the gas at the top of the decolorization tower is introduced into the secondary condenser to recover the nitric acid components and reflux to the decolorization tower, which improves the product yield (≥92%) and reduces the tail gas treatment load. The staged condensation process and CDA purging can reduce the nitrogen oxide content to 0.000067%. The tail gas is sent to the scrubbing tower for purification to achieve zero pollution emissions that meet the standards. 3. This invention establishes a complete recycling path for non-conforming products and a deep condensation system for tail gas. Non-conforming products can be returned to the raw material buffer tank for re-purification, significantly reducing waste acid volume to 2.5%. Tail gas is further condensed and recovered via 5-8℃ chilled water, significantly reducing material loss and environmental treatment pressure. This achieves continuous, stable, and clean production of ultrapure electronic-grade nitric acid, with products consistently reaching G4 standards. + Grade (metallic impurities ≤100ppt), meeting the requirements for semiconductor and high-end electronic material manufacturing. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the ultrapure electronic-grade nitric acid purification process of the present invention; Detailed Implementation To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0018] This invention provides, for example Figure 1 The purification process for ultrapure electronic-grade nitric acid is shown below, with the following specific steps: Example 1 S1: Unloading and Filtration: Industrial-grade nitric acid raw material is sent from tank truck to raw material tank via unloading pump and stored at room temperature and pressure; it is then sent to raw material filter with one working and one standby for primary filtration to remove large particulate impurities. After filtration, it enters raw material buffer tank for buffering at room temperature and pressure. S2: Waste heat preheating: Take 70.5% nitric acid raw material and send it into the preheater through the feed pump; use the waste acid at the bottom of the reboiler as the heat medium for waste heat preheating; after preheating, send it into the distillation column; after the waste acid is cooled to 38°C, send it into the waste acid tank for storage. S3: Reboiler distillation: The preheated nitric acid feedstock enters the distillation column and flows into the reboiler by gravity; the reboiler is heated and evaporated by steam at 155℃ and 4.4 kg / cm²G; the nitric acid vapor rises and is adsorbed and separated by the packing material inside the column, and flows out from the top of the distillation column; S4: Stage condensation: Nitric acid vapor at 123°C from the top of the distillation column enters the first-stage condenser, where it is condensed to an outlet temperature of 75°C using 33°C cooling water as the refrigerant; a portion of the liquid is returned to the distillation column, and a portion enters the decolorization column; the condensation temperature is precisely controlled by adjusting the cooling water feed rate. Uncondensed gas enters the secondary condenser and is condensed again with 33°C cooling water. The condensate is sent to the decolorization tower, and the remaining non-condensable gas is sent to the tail gas condenser. S5: Decolorization process: The nitric acid liquid flowing out of the primary condenser enters the decolorization tower, and is purged and decolorized by 35°C clean dry air (CDA) from the bottom of the tower; the gas discharged from the top of the decolorization tower at 68°C is sent to the secondary condenser for secondary condensation; the condensate is cooled to 32°C and refluxed back to the decolorization tower; the decolorized nitric acid flows out from the bottom of the tower; S6: Finished product cooling and buffering: After decolorization, nitric acid enters the finished product cooler and is cooled to 35°C with cooling water before entering the finished product buffer tank; after passing online testing, it is pumped into the finished product tank by the finished product pump for packaging; unqualified products are returned to the raw material buffer tank for repurification. S7: Tail gas treatment: Non-condensable gases from the top of the secondary condenser and decolorization tower enter the tail gas condenser, where they are deeply condensed with 6°C chilled water. The condensate temperature is 15°C and flows into the waste acid tank. The non-condensable gases are sent to the downstream scrubbing tower for treatment.

[0019] Waste acid in the waste acid tank is discharged uniformly by the waste acid pump.

[0020] Product specifications for this embodiment: Nitric acid concentration: 70.1%; Total metallic impurities: ≤85ppt; Product yield: 93.2%; Product Grade: G4+ class; Energy consumption is reduced by 10% compared to traditional processes.

[0021] This embodiment is a standard operating condition embodiment, which fully reproduces all steps and technical features of the ultrapure electronic-grade nitric acid purification process of the present invention. It clearly defines the temperature, pressure, medium, flow rate, and control parameters for each process, fully demonstrating that the technical solution of the present invention can be stably implemented and repeatedly achieved; the obtained nitric acid product meets G4 standards. + The product has a purity of ≤85ppt, a yield of ≥92%, and energy consumption is reduced by 10% compared to traditional processes. This directly verifies the technical effectiveness of this invention in terms of product purity, yield, and energy saving.

[0022] Example 2 S1: Unloading and Filtration: Industrial-grade nitric acid is continuously unloaded. The raw material filter adopts a one-in-one-out switching operation to ensure uninterrupted feeding. The entire process is carried out at normal temperature and pressure. S2: Waste heat preheating: Nitric acid concentration 70.8%, waste acid from reboiler is preheated with waste heat, and the waste acid is cooled to 36°C before entering the waste acid tank; S3: Reboiler distillation: Reboiler heat source: 155℃, 4.4kg / cm²G steam; Distillation column top vapor temperature: 124℃; S4: Staged condensation: The first stage condenser outlet temperature is 78℃, and the reflux is stable; the second stage condenser completely captures condensable components. S5: Decolorization treatment: CDA temperature 38℃, top gas temperature 67℃, condensate reflux temperature 33℃, stable decolorization effect; S6: Finished product cooling and buffering: After the finished product is cooled to 36℃ and passes the online ICP-MS test, it is continuously fed into the tank. Unqualified materials are automatically refluxed for repurification. S7: Exhaust gas treatment: The refrigerant in the exhaust gas condenser is at 7°C, and the condensate is at 16°C before being discharged into the waste acid tank, ensuring that the exhaust gas meets emission standards.

[0023] Product specifications for this embodiment: Metallic impurities: ≤92ppt; Product yield: 92.5%; Continuous runtime: 72 hours without fluctuation; Product Grade: G4 + class.

[0024] This embodiment is a continuous pilot-scale production embodiment, which focuses on verifying the technical advantages of the present invention in continuous operation and industrial stability. Through the design of one-in-one standby filter switching, automatic return of non-conforming products, and online ICP-MS detection, 72 hours of continuous and stable operation is achieved with no significant fluctuations in product indicators. This proves that the present invention is suitable for the industrialization needs of small-scale to pilot-scale electronic chemicals, solves the defects of poor stability and difficulty in continuous mass production of traditional processes, and further demonstrates the practicality and industrial value of the present invention.

[0025] Example 3 S1: Same as Example 1; S2: Waste heat preheating: Enhance waste acid waste heat recovery, nitric acid concentration 70.2%, waste acid cooled to 37℃; S3: Reboiler distillation: The steam load of the reboiler is reduced by 10% compared with the conventional method, while still ensuring the distillation separation effect; S4: Staged condensation: The first-stage condenser outlet temperature is 72℃, reducing the cooling water consumption; S5: Decolorization treatment: CDA temperature 32℃, optimized purging gas volume, reduced gas consumption; S6: Finished product cooling and buffering: Cool the finished product to 33℃; S7: Exhaust gas treatment: Same as in Example 1.

[0026] Product Specifications in this Example Metallic impurities: ≤80ppt; Product yield: 92.8%; Overall energy consumption is reduced by 8% compared to traditional processes; Product Grade: G4 + class.

[0027] This embodiment is a low-energy-consumption optimized implementation. By enhancing waste heat recovery, reducing steam load, and optimizing CDA gas volume and cooling water usage, the product purity is maintained at G4. + Under the premise of purity and metal impurities ≤80ppt, the overall energy consumption is reduced by 8% compared with the traditional process, highlighting the outstanding advantages of this invention in energy saving, consumption reduction and low-carbon operation; it proves that under the optimized parameter conditions, this invention can still stably produce ultrapure electronic grade nitric acid, expand the scope of application of the process, and further enhance the creativity and significant progress of this invention compared with the prior art.

[0028] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0029] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A purification process for ultrapure electronic-grade nitric acid, characterized in that, Includes the following steps: S1: Unloading and Filtration: Industrial-grade nitric acid raw material is sent into the raw material tank by the unloading pump at normal temperature and pressure, and then sent to the raw material filter for primary filtration by the raw material conveying pump to remove large particles before entering the raw material buffer tank for buffering at normal temperature and pressure. S2: Waste heat preheating: Nitric acid raw material with a concentration of 70-71% is fed into the preheater via a feed pump. The waste acid from the bottom discharge port of the reboiler is used as the heat medium for preheating. After preheating, it enters the distillation column. The waste acid is cooled and then enters the waste acid tank. S3: Reboiler distillation: The preheated nitric acid feedstock enters the distillation column and flows into the reboiler by gravity. It is heated and evaporated by steam. The nitric acid gas rises, is adsorbed by the packing, and flows out from the top of the distillation column. S4: Stage condensation: Nitric acid gas flowing out from the top of the distillation column enters the primary condenser and the secondary condenser in sequence for stage condensation, and the uncondensed gas enters the tail gas condenser for further condensation; S5: Decolorization treatment: The nitric acid liquid flowing out of the primary condenser enters the decolorization tower, where clean compressed air is used to purge and decolorize from the bottom. The decolorized nitric acid flows out from the bottom of the tower. S6: Finished product cooling and buffering: The decolorized nitric acid enters the finished product cooler for cooling, and then enters the finished product buffer tank. After passing the inspection, it is pumped into the finished product tank by the finished product pump for packaging. Unqualified products are returned to the raw material buffer tank for re-purification. S7: Tail gas treatment: Non-condensable gases discharged from the top of the secondary condenser and decolorization tower enter the tail gas condenser, where they are further condensed using chilled water. The condensate enters the waste acid tank, and the non-condensable gases are sent to the downstream scrubbing tower for treatment.

2. The purification process for ultrapure electronic-grade nitric acid according to claim 1, characterized in that: In step S1, the raw material filter is set up in a one-in-one-out configuration to achieve continuous production.

3. The purification process for ultrapure electronic-grade nitric acid according to claim 1, characterized in that: In step S2, the heat medium for the preheater is the waste acid discharged from the bottom of the reboiler. The waste acid is cooled to 35-40°C and then enters the waste acid tank.

4. The purification process for ultrapure electronic-grade nitric acid according to claim 1, characterized in that: In step S3, the heat source for the reboiler is steam at 155°C and 4.4 kg / cm²G.

5. The purification process for ultrapure electronic-grade nitric acid according to claim 1, characterized in that: In step S4, the primary condenser uses cooling water as the refrigerant. The temperature of the condensed nitric acid liquid is 70-80℃. Part of it is refluxed to the distillation column and part enters the decolorization column. The nitric acid temperature at the condenser outlet is controlled by adjusting the cooling water feed rate.

6. The purification process for ultrapure electronic-grade nitric acid according to claim 1, characterized in that: In step S4, the secondary condenser uses cooling water as the refrigerant. The condensed nitric acid liquid enters the decolorization tower, and the uncondensed gas enters the tail gas condenser.

7. The purification process for ultrapure electronic-grade nitric acid according to claim 1, characterized in that: In step S5, the clean compressed air used in the decolorization tower has a temperature of 30-40℃ and enters from the bottom of the tower. The gas discharged from the top of the decolorization tower (65-70℃) enters the secondary condenser for secondary condensation, and the condensate (30-35℃) is returned to the decolorization tower.

8. The purification process for ultrapure electronic-grade nitric acid according to claim 1, characterized in that: In step S6, the finished product cooler is cooled by cooling water, and the outlet nitric acid temperature is 30-40℃.

9. The purification process for ultrapure electronic-grade nitric acid according to claim 1, characterized in that: In step S7, the tail gas condenser uses chilled water at 5-8℃ as the refrigerant, and the condensate temperature is 10-20℃, which flows into the waste acid tank.

10. The purification process for ultrapure electronic-grade nitric acid according to claim 1, characterized in that: Nitric acid purified by this process reaches G4+ grade, with a metal impurity content of ≤100ppt.

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