Electronic-grade nitric acid preparation device based on series combined discharge

Abstract

The invention belongs to the fields of plasma chemical industry, microelectronic precursor preparation and green nitrogen conversion, and discloses a series combined discharge-based electronic-grade nitric acid preparation device, which comprises a pretreatment module, a dielectric barrier discharge and spark discharge series connection module, a gas-liquid mixed absorption module and a liquid phase refining module. After air is subjected to drying and flow and pressure regulation, O3 is generated in dielectric barrier discharge, and N2O5 is efficiently generated in spark discharge; n2O5 gas rapidly reacts with a circulating absorption liquid through a vortex-Venturi tube to generate primary dilute nitric acid, and then the primary dilute nitric acid is deeply purified through a liquid phase refining module to obtain electronic-grade nitric acid with the mass concentration of HNO3 being greater than or equal to 70% and the content of impurities such as metal ions and TOC being controlled at ppb grade. The system provided by the invention has the advantages of normal temperature and normal pressure, modular operation, low energy consumption and high yield, realizes green, efficient and distributed preparation of high-purity nitric acid, and overcomes the defects of high energy consumption, insufficient purity and the like of the traditional Ostwald process.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of plasma chemical industry, microelectronic precursor preparation and green nitrogen conversion, and more particularly relates to a device for preparing electronic-grade nitric acid based on series combination discharge, which uses series combination air discharge technology to prepare high-purity nitric acid (the mass concentration of nitric acid is 70%, which belongs to electronic-grade nitric acid), generates high-activity nitrogen oxide compounds through multi-stage discharge, and combines high-efficiency absorption and purification process to obtain electronic-grade nitric acid meeting the requirements of the electronic industry. BACKGROUND

[0002] As an important basic chemical raw material and high-purity reagent, nitric acid (HNO3) has a wide range of applications in chemical industry, metallurgy, medicine, environmental protection and microelectronic manufacturing. In particular, in the microelectronic and semiconductor industry, high-purity nitric acid is often used as a key chemical for silicon wafer surface cleaning, organic contaminant removal and collaborative etching. It has very strict control standards for metal impurities, particulate matter, organic carbon content and other trace impurities, and is directly related to the yield and performance stability of devices.

[0003] The current mainstream industrial nitric acid preparation method is mainly based on the Ostwald method. This process uses NH3 as raw material to generate NO under high temperature and high pressure through platinum rhodium catalytic oxidation, and then further oxidizes it to NO2, and generates nitric acid through the absorption process. Although this technology is mature and highly scalable, it has obvious problems such as high energy consumption, dependence on fossil fuels, heavy environmental burden, complex process flow, large equipment investment, etc. When meeting the requirements of electronic-grade applications, it often needs to additionally configure multi-stage distillation, ion exchange, membrane separation and other refining units to further improve the purity of the product, resulting in a significant increase in system complexity and operating cost. In addition, traditional centralized nitric acid plants are difficult to adapt to distributed production and small-scale flexible manufacturing needs, which is not conducive to popularization and use in carbon emission limited areas or energy structure transformation background.

[0004] In recent years, plasma technology has attracted research attention because it can excite N2 and O2 in air to form high-activity nitrogen oxide compounds (such as NO, NO2, N2O5, etc.; in this application, NO x represents NO and NO2, i.e., x is 1, 2) at room temperature and pressure. It is considered to be a promising green nitrogen fixation method. This method can avoid the energy consumption and safety risks brought by high temperature and high pressure, and has good controllability and modularity characteristics, which is suitable for the construction of low-carbon, distributed chemical systems. However, there are still some technical bottlenecks in the current plasma nitrogen fixation technology in practical application: (1) the conversion rate of NO x is relatively low, and the energy consumption of nitric acid is high (more than 30 MJ / mol), which is difficult to meet the industrialization demand; (2) the gas-liquid absorption efficiency is limited, and the yield of nitric acid is limited (less than 15 mmol / h), which is not suitable for high-purity applications. SUMMARY

[0005] In view of the above defects or improvement needs of the prior art, the purpose of the present application is to provide a device for preparing electronic-grade nitric acid based on series combination discharge, wherein by improving each component of the device and their cooperative working relationship, using a series-connected dielectric barrier discharge device and a spark discharge device, by constructing a multi-stage air discharge and gas-liquid absorption system, and combining with a deep purification process, efficient conversion and refining of nitrogen and oxygen in air are realized under normal temperature and pressure conditions, thereby preparing high-purity nitric acid products that meet the requirements of the electronic industry (in the following examples, the mass concentration can be more than 70%, and the metal ion impurities are controlled within the ppb level), which can solve the problems of high energy consumption, dependence on ammonia raw materials, product purity difficult to meet the requirements of electronic grade, and unsuitability for distributed deployment in the traditional nitric acid synthesis process.

[0006] To achieve the above purpose, according to one aspect of the present application, a device for preparing electronic-grade nitric acid based on series combination discharge is provided, characterized in that it comprises a pretreatment module, a series combination discharge module, a gas-liquid mixing absorption module, and a liquid phase refining module, wherein,

[0007] The pretreatment module comprises a gas pump (1), an air drying tube (2), a gas mass flow controller (3), and a pressure gauge (4) connected in sequence; the pretreatment module is connected to the series combination discharge module, and is used to filter and dry air and then deliver it to the series combination discharge module, and adjust the gas flow and pressure of the delivered air;

[0008] The series combination discharge module comprises a dielectric barrier discharge device (5) and a spark discharge device (6) connected in series, wherein,

[0009] The dielectric barrier discharge device (5) comprises an inner stainless steel tube electrode and an outer quartz glass tube arranged coaxially; the outer wall of the stainless steel tube electrode is uniformly provided with a sawtooth-shaped protruding structure along the axial direction, and the top of the sawtooth and the inner wall of the quartz glass tube maintain a constant air gap; the outer wall of the quartz glass tube is tightly covered with a grounded metal strip; the dielectric barrier discharge device (5) is used to implement plasma discharge on the flowing air under the driving of an alternating current power supply, generating ozone (O3);

[0010] The spark discharge device (6) has a needle-needle electrode structure, which is used to perform spark discharge on air plasma, wherein the generated nitric oxide (NO) and nitrogen dioxide (NO2) are oxidized by ozone to generate dinitrogen pentoxide (N2O5);

[0011] The gas-liquid mixed absorption module: comprising an absorption container (10), a water pump (11), and a vortex-venturi tube (12), wherein the absorption container is used to contain absorption liquid, and the water pump (11) is connected with the vortex-venturi tube (12) to form a liquid flow circulation loop; the N2O5 generated by the series combined discharge module as a whole enters the liquid flow circulation through the vortex-venturi tube (12) and is absorbed by the absorption liquid to form primary dilute nitric acid;

[0012] The liquid phase refining module: comprising a distillation or rectification device (16), an ion exchange device (17), and a gas stripping or sub-boiling distillation device (18) connected in sequence, for deep purification of the primary dilute nitric acid to obtain electronic grade nitric acid.

[0013] As a further preferred embodiment of the present application, the control and analysis module is further provided for regulating the gas flow of the gas mass flow controller (3), the power of the dielectric barrier discharge device (5) and the spark discharge device (6), and the circulation flow of the absorption liquid of the liquid flow circulation loop, and for monitoring the concentration of nitric acid contained in the absorption liquid contained in the absorption container (10), the purity of the electronic grade nitric acid generated by the liquid phase refining module, and the concentration of N2O5 generated by the series combined discharge module as a whole;

[0014] Preferably, the control and analysis module comprises an AI algorithm model and data training unit for joint analysis and machine learning of historical operation data and real-time sensor data by AI algorithm, so as to optimize the gas flow of the gas mass flow controller (3), the power of the dielectric barrier discharge device (5) and the spark discharge device (6), the circulation flow of the absorption liquid of the liquid flow circulation loop, and the discharge sequence of the dielectric barrier discharge device (5) and the spark discharge device (6), to maximize the yield of primary dilute nitric acid and minimize the unit energy consumption.

[0015] More preferably, the AI algorithm model and data training unit is a composite machine learning model based on gradient boosting tree (GBDT) and deep neural network (DNN).

[0016] As a further preferred embodiment of the present application, the spark discharge device (6) is multiple, and these spark discharge devices (6) are connected in parallel with each other.

[0017] Preferably, each of the spark discharge devices (6) has a three-stage needle-needle electrode structure with six discharge needles.

[0018] As a further preferred embodiment of the present application, the sawtooth spacing of the sawtooth-shaped protruding structure is 0.5-3 mm, and the sawtooth height is 0.5-3 mm.

[0019] As a further preferred embodiment of the present application, the absorption liquid initially placed in the absorption container is water.

[0020] As a further preferred embodiment of the present application, the discharge voltage of the dielectric barrier discharge device (5) is 6-10 kV, and the frequency is 10-20 kHz.

[0021] The discharge voltage of the spark discharge device (6) is 20-30 kV, and the frequency is 10-15 kHz.

[0022] As a further preferred embodiment of the present application, the vortex-venturi (12) is provided with multiple tangential inlets, and the inner cavity has a spiral flow guide structure.

[0023] As a further preferred embodiment of the present application, the ion exchange device (17) comprises a cation exchange column and an anion exchange column arranged in series, respectively used for removing metal cations and inorganic anions in the solution.

[0024] The control and analysis module comprises an online purity detection device (19) for detecting the nitric acid solution obtained after treatment by the gas stripping or sub-boiling distillation device (18).

[0025] The online purity detection device (19) comprises an ICP-MS, an ion chromatograph, and a total organic carbon (TOC) analyzer, which are used for real-time monitoring of the contents of metal ions, inorganic anions and cations, and organic carbon in the nitric acid.

[0026] As a further preferred embodiment of the present application, the liquid phase refining module is further connected with a nitric acid storage module for storing the generated electronic-grade nitric acid.

[0027] The electronic-grade nitric acid preparation device based on the series combination discharge further comprises a tail gas treatment device (14) connected with the absorption container (10) and used for treating the unabsorbed tail gas; the tail gas treatment device (14) preferably uses calcium hypochlorite or an alkaline solution to absorb residual nitrogen oxides and ozone, so as to achieve standard discharge or closed-loop circulation.

[0028] The dielectric barrier discharge device (5) and the spark discharge device (6) are powered by a power supply device (7); the power supply device (7) is connected with a photovoltaic power generation device (8) and is provided with electric energy by the photovoltaic power generation device (8).

[0029] Preferably, the dielectric barrier discharge device (5) and the spark discharge device (6) are both provided with a replaceable electrode structure and an online electrode cleaning function, so as to prolong the operation cycle of the system and reduce the maintenance cost.

[0030] According to another aspect of the present application, the present application provides an electronic-grade nitric acid preparation method based on the above-mentioned electronic-grade nitric acid preparation device based on a series combination discharge, characterized in that air is used as a raw material, the air is dried, the flow rate and the pressure are adjusted, O3 is generated in the dielectric barrier discharge, and N2O5 is generated in the spark discharge; the N2O5 gas is rapidly reacted with the circulating absorption liquid through the vortex-venturi tube to generate primary dilute nitric acid, and then is deeply purified through a liquid phase refining module, so that electronic-grade nitric acid with a mass concentration of HNO3 of not less than 70% and impurity content controlled at a ppb level is obtained.

[0031] Preferably, the gas flow rate of the air is 9 L / min, the dielectric barrier discharge power is 70 W, the spark discharge power is 25 W, and the circulating flow rate of the absorption liquid is 4 L / min.

[0032] Compared with the prior art, the system of the present application operates at normal temperature and pressure, is modular, has low energy consumption and high yield, realizes green, efficient and distributed preparation of high-purity nitric acid, and overcomes the defects of the traditional Ostwald process, such as high energy consumption and insufficient purity. The device of the present application uses air as the only raw material, and through the multi-stage synergistic effect of the dielectric barrier discharge unit and the spark discharge unit (especially the parallel spark discharge units) with the innovative design of the sawtooth-shaped protrusions, high-water-solubility nitrogen oxide mixed gas mainly containing N2O5 is efficiently generated. Subsequently, the vortex-venturi tube with a high-turbulent swirling structure is used to realize rapid and efficient gas-liquid mass transfer and absorption conversion of N2O5, and high-quality dilute nitric acid is obtained. The obtained dilute nitric acid is subjected to deep refining processes such as multi-stage rectification, ion exchange and sub-boiling distillation, to effectively remove water, metal ions and volatile impurities, and to obtain nitric acid products meeting the high standards of the electronic industry.

[0033] In use, the device of the present application generates O3 in the dielectric barrier discharge and efficiently generates N2O5 in the spark discharge after the air is dried and the flow rate and the pressure are adjusted; the N2O5 gas is rapidly reacted with the circulating absorption liquid through the vortex-venturi tube to generate primary dilute nitric acid, and then is deeply purified through a liquid phase refining module (the liquid phase refining module may, for example, sequentially realize the functions of distillation, ion exchange and sub-boiling distillation, thereby realizing deep purification), so that electronic-grade nitric acid with a mass concentration of HNO3 of not less than 70% and impurity content (such as metal ions and TOC) controlled at a ppb level is obtained.

[0034] The application provides a novel high-purity nitric acid preparation method based on a "series combination air discharge" technology, which realizes synergistic effect of different discharge forms by connecting a dielectric barrier discharge and a spark discharge in the same system. The dielectric barrier discharge device is driven by an alternating current power source, significantly enhances the local electric field by means of a sawtooth electrode, carries out plasma discharge on air flowing through the air, and generates a large amount of ozone. The dielectric barrier discharge has the advantages of uniform discharge, high ozone yield and obvious low-temperature plasma characteristics, while the spark discharge is more conducive to the generation of high-concentration NO x x due to its higher temperature and higher energy density. The ozone generated by the dielectric barrier discharge device is oxidized, and finally N2O5 is generated. The combination of the two can oxidize NO and NO2 into N2O5 by ozone, improve the water solubility and conversion efficiency of N2O5 (the Henry constant of N2O5 is 48.5, and N2O5 is easily soluble in water; the Henry constant of NO2 is 0.28, and the Henry constant of NO is 0.044, and NO is poorly soluble).

[0035] In the absorption and refining process, the application introduces an ion exchange unit and a rectification module to gradually remove metal ions, particulate matter, TOC and other impurities that may exist in nitric acid, so as to realize the product purity reaching the electronic grade requirement. Compared with the traditional process, the method has low energy consumption, compact equipment structure, and renewable energy friendliness, and is particularly suitable for the technical development needs of distributed high-purity chemical product preparation and microelectronic industry chain localization matching.

[0036] Further, the application can introduce an AI machine learning model to intelligently analyze and optimize the discharge conditions of the real-time feedback process parameters, realize the maximization of the primary dilute nitric acid yield and the minimization of the energy consumption.

[0037] Specifically, the application has the following advantages:

[0038] 1. Green raw materials and process: The application uses air as the only nitrogen source, does not depend on ammonia or other harmful raw materials, significantly reduces the raw material cost and storage and transportation risk, and has high safety under normal temperature and pressure conditions.

[0039] 2. Multi-stage discharge synergistically improves the yield of nitric acid: The application connects the dielectric barrier discharge and the spark discharge in series to construct a multi-stage discharge reaction system combining low-temperature excitation and high-temperature ionization. The multi-stage synergistic effect of the dielectric barrier discharge unit and the spark discharge unit (especially the parallel spark discharge unit) with the innovative sawtooth protruding structure efficiently generates high-water-solubility nitrogen oxide mixed gas mainly in the form of N2O5, and then improves the yield of nitric acid.

[0040] ​3. Absorption module design for strengthening gas-liquid conversion capacity: The invention uses a vortex-venturi tube (especially a vortex-venturi tube with a multi-tangential spiral liquid inlet design), combined with CFD flow field optimization, to greatly improve the reaction rate and conversion efficiency of N2O5 absorption into nitric acid. The device can achieve more than 90% N2O5 absorption rate while maintaining low pressure drop, reducing the burden of tail gas treatment.

[0041] The vortex-venturi tube is provided with multiple tangential inlets, combined with a spiral guide structure in the cavity to form a strong vortex field. The flow field structure of the vortex-venturi tube is optimized by computational fluid dynamics (CFD) design, forming a high-speed vortex zone and a low-pressure induction zone, so that N2O5 and other substances are efficiently dissolved in the absorption liquid.

[0042] 4. High product purity: Combined with absorption and multi-step refining process, the impurities such as metal ions, halogens and particulate matter in the obtained nitric acid are controlled at ppb level, meeting the requirements of electronic-grade wet process acid.

[0043] The electronic-grade nitric acid prepared by the invention can be classified and packaged according to different application standards (such as SEMI C64), suitable for high-end manufacturing scenes such as integrated circuits and liquid crystal panels.

[0044] 5. Compact device structure, suitable for distributed deployment: The system is modularly designed, suitable for small-scale and high-cleanliness use, and can be flexibly expanded in capacity according to demand, facilitating deployment in semiconductor plants or distributed chemical nodes.

[0045] The invention is based on an electronic-grade nitric acid preparation device based on series combination discharge, and the system structure is modularly integrated, each unit can be independently deployed or combined for operation according to demand, suitable for distributed or small and medium-scale production.

[0046] 6. Full-process monitoring and control: Each unit is provided with sensors and acquisition interfaces, which can be linked with the control system to automatically adjust the discharge intensity, flow and purification rhythm, improving the yield while ensuring stability.

[0047] The invention can set up a control and analysis module to receive real-time data from the sensors of each module, adjust the discharge power (including voltage, current), air flow rate, and absorption liquid circulation flow rate according to the set parameters, and build a closed-loop control system.

[0048] 7. Environmental treatment covers the whole process: The tail gas that is not absorbed can be further treated by an alkali neutralization tower, and the residual liquid can be discharged or recycled after adjustment, realizing true clean production.

[0049] 8. Introducing AI intelligent optimization control system: through machine learning, the system history and real-time operation data are modeled and analyzed to realize intelligent parameter matching of dielectric barrier discharge and multi-stage spark discharge unit. Compared with the traditional fixed parameter control strategy, this method can dynamically adapt to external condition changes, improve system stability and output efficiency, and further reduce energy consumption and impurity generation rate.

[0050] The electronic-grade nitric acid preparation device based on series combination discharge has the advantages of compact structure, low energy consumption and high degree of modularization, and is particularly suitable for distributed chemical units and high-purity wet process scenarios in the semiconductor industry. Compared with the traditional ammonia oxidation method, the present application does not require the use of ammonia and other dangerous raw materials, avoids harsh conditions such as high temperature and high pressure, and constructs a new path for the production of high-purity nitric acid that is green, safe, efficient and suitable for the electronic industry. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 is the overall process flow schematic diagram of the electronic-grade nitric acid preparation system of the present application;

[0052] Figure 2 is the process flow diagram of the present application;

[0053] Figure 3 is the schematic diagram of the dielectric barrier discharge device provided by the embodiment of the present application;

[0054] Figure 4 is the schematic diagram of the spark discharge device provided by the embodiment of the present application;

[0055] Figure 5 is the schematic diagram of the vortex-venturi device provided by the embodiment of the present application;

[0056] Figure 6 、 Figure 7 is the nitric acid preparation energy consumption and nitric acid preparation yield comparison diagram of the nitric acid preparation device of the embodiment of the present application and other air plasma.

[0057] Figure 1 The meanings of the reference numerals in the drawings are as follows: 1, gas pump; 2, air drying pipe; 3, gas mass flow controller; 4, pressure gauge; 5, dielectric barrier discharge device; 6, spark discharge device; 7, power supply device; 8, photovoltaic power generation device; 9, control device; 10, absorption container; 11, water pump; 12, vortex-venturi; 13, absorption liquid; 14, tail gas treatment device; 15, water pump; 16, distillation or rectification device; 17, ion exchange device; 18, gas stripping or sub-boiling distillation device; 19, online purity detection device; 20, nitric acid storage device. DETAILED DESCRIPTION

[0058] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0059] Example 1

[0060] The present embodiment provides an electronic grade nitric acid preparation system based on series combination discharge, which aims to directly use air as raw material without additional introduction of nitrogen-containing raw materials (such as ammonia, urea, etc.), to generate N2O5 through plasma discharge excitation, and to obtain high-purity nitric acid products meeting electronic grade standards through high-efficiency absorption and multi-stage purification. The system adopts modular design, has compact structure and stable operation, and is suitable for pilot platform, distributed chemical unit or semiconductor wet process precursor supply system.

[0061] I. Overall structure of the system

[0062] As shown in Figure 1 , the electronic grade nitric acid preparation system comprises the following functional modules:

[0063] The pretreatment module comprises an air pump 1, an air drying tube 2, a gas mass flow controller 3 and a pressure gauge 4. It is used for extracting, filtering and drying the ambient air, and stably controlling the flow. The drying material can be selected from silica gel, molecular sieve or membrane separator to reduce humidity and avoid unstable electric arc or byproduct generation.

[0064] The series combination discharge module comprises a dielectric barrier discharge device 5 and a parallel spark discharge device 6 (as shown in Figure 1 , the spark discharge device 6 has two devices in parallel; the dielectric barrier discharge device 5 is connected in series on the dry circuit), which are powered by a power supply system 7. The power supply can be connected to a photovoltaic power generation module 8 to realize green power supply (other power supply modes can also be used). The dielectric barrier discharge is used to generate a large amount of O3, with a voltage range of 6-10 kV and a frequency of 10-20 kHz; the spark discharge is used to strengthen the generation of N2O5 under the condition of transient high temperature (about 6 000-10 000 K), with a voltage of 10-15 kV. The two devices work together to significantly improve the yield of nitric acid. x

[0065] The gas-liquid mixing absorption module: the N2O5-rich gas enters the vortex-venturi tube 12 from top to bottom, and is mixed and absorbed at high speed with the absorption liquid 13 transported by the circulating pump 11, and finally stored in the absorption container 10. The initially added absorption liquid can be deionized water, and after absorbing N2O5, it becomes primary dilute nitric acid. The unabsorbed tail gas will be treated in the tail gas treatment device 14.​

[0066] Liquid refining module: After the water in the absorption liquid reacts with N2O5, primary dilute nitric acid will be formed. The prepared primary dilute nitric acid is transported to the rectification device 16 by the water pump 15 for dehydration and concentration, and then sequentially enters the ion exchange device 17 and the gas stripping / sub-boiling distillation module 18 to remove metal impurities, inorganic ions and volatile components, respectively, to finally obtain electronic-grade nitric acid with high purity, low impurities and low TOC.

[0067] Control and analysis module: The online monitoring device 19 is used to detect the concentration of product nitric acid, metal impurities, TOC and other key indicators in real time. The system control unit 9 receives feedback information and automatically adjusts the gas flow rate, discharge power, water pump rate and other parameters to realize closed-loop control and production stability guarantee. The system control unit 9 also integrates a composite machine learning model based on gradient boosting decision tree (GBDT) and deep neural network (DNN). The model learns and optimizes control in real time according to historical working condition data and online sensor (voltage, current, gas flow rate, water speed, NO x Concentration) data. In this embodiment, the optimized gas flow rate is 9 L / min, the dielectric barrier discharge power is 70 W, the spark discharge power is 25 W, and the water pump water supply flow rate is 4 L / min. Compared with the working condition before adjustment (gas flow rate is 6 L / min, dielectric barrier discharge power is 90 W, spark discharge power is 20 W, and water pump water supply flow rate is 2 L / min), the concentration of primary dilute nitric acid is increased by about 20%, and the energy consumption per unit of acid production is reduced by about 15%, significantly improving the reaction efficiency and energy efficiency ratio.

[0068] Nitric acid storage module: After the high-purity nitric acid is filtered through a 0.22 μm microporous membrane, it is stored in an acid-resistant, light-resistant, high-sealing nitric acid storage device 20, which can be directly used for subsequent experiments or transferred to the application end.

[0069] Wherein:

[0070] As Figure 3As shown, the dielectric barrier discharge device is a coaxial double electrode discharge device. The outer diameter of the inner stainless steel tube electrode (high voltage electrode 4-6kV) is 26mm (excluding the protruding structure part), the outer layer of the stainless steel tube electrode is a quartz glass tube with an inner diameter of 34mm, and the outermost layer is a grounded metal strip (low voltage electrode) tightly attached to the glass tube. The inner stainless steel tube electrode adopts a structure with sawtooth protrusions to enhance the discharge intensity. Further, the dielectric barrier discharge device of the present application adopts a new type of sawtooth metal electrode. This structure can significantly strengthen the local electric field distribution, improve the plasma volume and uniformity, and optimize the ozone generation reaction path. The sawtooth pitch and height can be adjusted within the range of 0.5-3mm according to application requirements. Compared with the same 70W input power, the new type of sawtooth metal electrode (the pitch between two adjacent ring sawteeth is 1.5mm, and the height of the ring sawteeth is 2mm) used in this embodiment can produce 1.6 times the ozone compared with the case without protrusions, and the ozone yield can be increased by 60%.

[0071] As shown in the figure, Figure 4 The spark discharge device includes a cylindrical chamber with tapered transition sections at both ends, which is made of quartz glass. The chamber has a diameter of 20mm and a total height of 110mm (the height of the cylindrical chamber is 80mm, and the height of the tapered transition sections at both ends is 15mm). The wall thickness is uniform at 1mm. The device is provided with a gas inlet at the top and a gas outlet at the bottom. The outer diameter of the inlet and outlet is 6mm, and the height of the protruding part of the chamber is 15mm. Three pairs of through-hole structures are uniformly distributed along the circumferential direction of the side wall of the chamber, corresponding to the installation of tungsten needle electrodes (corresponding to the formation of 3-stage needle-needle electrodes, a total of 6 discharge needles) for realizing spark discharge. The electrode through-hole structure is in the shape of a short tube connected to the chamber as an electrode introduction channel. Each channel has an outer diameter of 6mm and an axial protruding length of 20mm. The tungsten needle electrode is inserted into the chamber through the channel and forms a gap with the chamber. The outside is sealed with sealing glue to prevent gas leakage. The total length of the tungsten needle electrode is 20mm, including a cylindrical section with a diameter of 3.5mm and a length of 10mm, and a tip with a curvature radius of 100μm at the front end. The tip spacing between the electrode pairs is 6mm, and the longitudinal spacing between adjacent electrode pairs is 20mm. Further, the spark discharge module of the present application is a multi-stage series structure. Each stage is connected by insulation, the discharge path is gradually enhanced, and a higher energy density composite discharge zone is formed, which can stably maintain high concentration N2O5 output and suppress the instability of single-stage discharge. Compared with the traditional discharge method, the multi-stage spark discharge device used in the present application can promote the rapid reaction of NO x and other primary products to form stable N2O5 molecules. N2O5 is a highly water-soluble nitrogen oxide that can react with water almost instantaneously to form nitric acid after entering the Venturi mixing section, greatly improving the absorption rate and acid production efficiency.

[0072] As shown in Figure 5 , the diameter of the throat of the vortex-venturi tube is usually within 2-25 mm, the divergence angle and convergence angle vary greatly, as low as 3.5° and as high as 45°. Considering the processing difficulty, the throat diameter is selected as 18 mm, the converging section and the diverging section are both 40 mm long, the inlet and outlet diameters are both 26 mm, the convergence angle and divergence angle are both 5.7°, and the throat length is 0 mm. The gas inlet is a 6 mm hole in the throat; in addition to the main inlet above, there are three tangential inlets below, which are evenly distributed along the ring to generate a swirling flow, thereby strengthening the gas-liquid mixing and dissolution. Among them, the inner diameter of the tangential inlet is 6 mm, and the length is 25 mm. The vortex-venturi tube forms strong turbulent shear and high-speed negative pressure induction through multiple tangential nozzles (as shown in Figure 5 , three tangential nozzles are used in this embodiment), which can complete the mixing and mass transfer of N2O5 and liquid phase in a very short time, and the enhancement factor is increased by more than 1.8 times compared with ordinary venturi tubes. The flow field structure in the swirling region is optimized by CFD simulation, which can suppress the short circuit phenomenon of the gas channel, avoid gas escape, and achieve higher N2O5 capture efficiency.

[0073] II. Work flow description

[0074] may include the following steps:

[0075] Step S01: Clean air is dried and adjusted to 3-9 L / min by a mass flow controller and introduced into the first discharge unit. The unit is a dielectric barrier discharge device, which adopts a cylindrical coaxial electrode design with sawtooth protrusions. The outer wall of the inner electrode is provided with axially uniformly distributed sawtooth structures to enhance the local electric field strength. The AC excitation condition is 6-10 kV, 10-20 kHz. After the air is discharged, mainly ozone (O3) is generated to provide the basis for the oxidation capacity of the subsequent reaction.

[0076] Step S02: Parallel multi-stage spark discharge enhancement: After the air passes through the dielectric barrier discharge, it enters the second discharge unit, which is composed of multiple spark discharge modules connected in parallel. Each module contains three series needle-needle electrodes and uses a stepped voltage excitation. Under the action of spark discharge, NO x is further oxidized to N2O5, which has good water solubility and can significantly improve the gas-liquid absorption efficiency.

[0077] Step S03: The above N2O5-rich gas enters the vortex-venturi tube through the synergistic action of high shear swirling and negative pressure induction, and fully mixes with the absorption liquid. The device forms a stable vortex field through tangential liquid inlet, significantly improves the absorption efficiency of N2O5 in the liquid phase, and finally generates primary dilute nitric acid.

[0078] Step S04: Multi-stage purification and concentration: The obtained dilute nitric acid is subjected to a series of refining processes, including distillation, ion exchange, etc., to remove water, metal ions, anions and cations, etc. impurities, and to improve the concentration and purity of the nitric acid. The specific purification scheme can be selected according to the target purity requirement, and is not limited to a single process. The purity of the purified nitric acid can reach the electronic grade use standard.

[0079] Step S05: Product detection and control: The product is detected for metal impurities, inorganic ions, organic carbon, etc. by ICP-MS, ion chromatography and TOC analyzer to ensure stable product quality. When the detection result exceeds the standard, process parameter adjustment or purification unit maintenance can be triggered to form a closed loop control. The final product is filtered and stored in an inert material container and stored in a low temperature and light shielding environment.

[0080] Step S06: AI intelligent optimization of discharge matching: The system integrates an adaptive optimization model based on machine learning, which dynamically trains and updates the discharge model according to the N2O5 concentration, primary dilute nitric acid concentration and system energy consumption, etc. key performance indicators returned by ICP-MS and gas analysis results, to achieve the optimal combination of voltage, frequency, duty cycle, excitation sequence, etc. parameters between dielectric barrier discharge and spark discharge, thereby maximizing the primary dilute nitric acid yield and minimizing energy consumption and impurity generation.

[0081] In addition, the discharge system supports electrode module replacement and online cleaning operation, which can prolong the stable operation time of the system and reduce the maintenance frequency.

[0082] The operation process of the system is as follows:

[0083] Air is introduced by air pump 1, and then passes through dryer 2, mass flow meter 3 and pressure gauge 4 in sequence to adjust the gas state suitable for discharge;

[0084] The gas first enters the dielectric barrier discharge device 5 to form O3, and then enters the spark discharge device 6 to strengthen NO x to generate N2O5;

[0085] The generated mixed gas enters the vortex-venturi tube 12, where it is strongly mixed with the absorption liquid 13 delivered by the circulating water pump 11, and is converted into dilute nitric acid in the absorption container 10;

[0086] The unreacted nitrogen oxides (such as N2O, NO, NO2, N2O5) and ozone in the tail gas are neutralized by 5% calcium hypochlorite or lye through the tail gas treatment device 14, and are discharged or recycled in a closed loop;

[0087] The primary dilute nitric acid is sent to the distillation or rectification device 16 by the water pump 15 for concentration, and then enters the ion exchange device 17 and the gas stripping or sub-boiling point device 18 for further impurity removal;

[0088] The online detection device 19 continuously monitors the purity index of the final product, and the control device 9 automatically adjusts the system operation state according to the detection feedback information to realize closed-loop control of the reaction process. In the embodiment, the optimized and adjusted gas flow rate is 9 L / min, the dielectric barrier discharge power is 70 W, the spark discharge power is 25 W, and the water pump water supply flow rate is 4 L / min.

[0089] III. Performance verification

[0090] The system of the present application has been tested and verified to be able to stably obtain a standard nitric acid solution with a mass concentration of 70%, and the product has low metal ion content, low TOC level, and stable nitric acid concentration, which is suitable for occasions with strict impurity control requirements. In the embodiment, the optimized and adjusted gas flow rate is 9 L / min, the dielectric barrier discharge power is 70 W, the spark discharge power is 25 W, and the water pump water supply flow rate is 4 L / min. The relevant indicators of performance verification detection are shown in Table 1.

[0091] Table 1

[0092]

[0093]

[0094] Furthermore, the nitric acid preparation energy consumption and the nitric acid preparation yield of the embodiment of the present application and other air plasma nitric acid preparation devices are compared (similar to conventional operation, first find the lowest point of nitric acid energy consumption of each device, then compare the nitric acid energy consumption and the nitric acid yield of each device at the lowest point of energy consumption), wherein,

[0095] a) Bubble pin-plate discharge can be specifically referred to in “Insights on the Mechanism of Surface-Catalyzed Oxidative Nitrogen Fixation Based on Liquid-Phase Bubble Pin-Plate Discharge”;

[0096] b) Water film dielectric barrier discharge can be specifically referred to in “Direct Oxidative Nitrogen Fixation from Air and H2O by a Water Falling Film Dielectric Barrier Discharge Reactor at Ambient Pressure and Temperature”;

[0097] c) For details on gliding arc discharge, please refer to "Influence of Plasma Activated Water Generated in a Gliding Arc Discharge Reactor on Germination of Beetroot and CarrotSeeds";

[0098] d) For details on bubble discharge, please refer to "Plasma in situ gas–liquid nitrogen fixation using concentrated high-intensity electric field";

[0099] e) For details on plasma jets, please refer to "Synthesis of Ammonia through Direct Chemical Reactions between an Atmospheric Nitrogen Plasma Jet and a Liquid".

[0100] The results are as follows Figure 6 , Figure 7 As shown, it is easy to see that the present invention has lower energy consumption than water film dielectric barrier discharge, electrolysis, bubble discharge, plasma jet and droplet dielectric barrier discharge; at the same time, the present invention has a higher nitric acid production rate.

[0101] As can be seen, the electronic-grade nitric acid preparation device based on series combined discharge of the present invention has the following characteristics:

[0102] 1. Synergistic Improvement of Yield Through Discharge Modes: This invention innovatively combines dielectric barrier discharge and multi-stage spark discharge in series to form a multi-field coupling system with complementary temperature and energy density. Specifically, dielectric barrier discharge preferentially excites O3, while spark discharge enhances NO under high temperature and high energy conditions. x The generation and conversion of N2O5, through synergistic effect, significantly improve the concentration and water solubility of nitrogen oxides, solving the bottleneck problem of low nitric acid yield in existing plasma systems.

[0103] 2. Innovative electrode structure enhances discharge efficiency: This invention adopts a novel sawtooth-shaped protruding metal electrode structure, which can increase ozone production by more than 60% under the same power, optimize discharge uniformity and suppress partial discharge instability, and create a plasma environment more suitable for generating highly reactive species.

[0104] 3. Intelligent control achieves energy consumption optimization: The system integrates an AI composite model (GBDT+DNN) to optimize NO. xThe concentration, discharge parameters and energy consumption data are dynamically learned and regulated to realize adaptive optimization of discharge power and gas flow, reduce energy consumption per unit of acid production by about 15% under the premise of ensuring yield, and effectively solve the problems of low energy efficiency and extensive control in traditional technology.

[0105] 4. Modular design facilitates distributed deployment: The device operates at normal pressure, has compact structure, and each module is independently controlled, so it is suitable for distributed deployment and high-cleanliness-required places, especially suitable for microelectronic process end on-site matching use, and is superior to existing centralized nitric acid synthesis systems.

[0106] 5. High selectivity reaction path inhibits impurity generation: By reasonably controlling the discharge window and optimizing the absorption conditions in the later stage, the selectivity conversion ratio of NO and NO2 to N2O5 is significantly improved, reducing the generation of by-products and the risk of impurity entrainment, and providing a key reaction basis for realizing ppb-level electronic-grade purity.

[0107] In summary, the system can realize the whole process of directly preparing electronic-grade nitric acid from air under the conditions of environmental friendliness and high energy efficiency, and has broad industrial application prospects and distributed deployment value.

[0108] Those skilled in the art will readily understand that the above description is only a preferred embodiment of the present application and is not intended to limit the present application, and any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application. For example, those skilled in the art can make various optimization adjustments to the system structure and control logic without departing from the core idea of the present application, which shall be regarded as the reasonable protection scope of the present application.

Claims

1. An electronic grade nitric acid production device based on a series combination discharge, characterized by, It comprises a pretreatment module, a series combination discharge module, a gas-liquid mixed absorption module and a liquid phase refining module, wherein, The pretreatment module comprises a gas pump (1), an air drying tube (2), a gas mass flow controller (3) and a pressure gauge (4) connected in sequence; the pretreatment module is connected with the series combination discharge module, and is used for filtering and drying air and then conveying the filtered and dried air to the series combination discharge module and adjusting the gas flow and pressure of the conveyed air; The series combination discharge module comprises a dielectric barrier discharge device (5) and a spark discharge device (6) connected in series, wherein, The dielectric barrier discharge device (5) comprises a stainless steel tube electrode and an outer quartz glass tube arranged coaxially; the outer wall of the stainless steel tube electrode is uniformly provided with a sawtooth-shaped protruding structure in the axial direction, and a constant air gap is maintained between the sawtooth top and the inner wall of the quartz glass tube; the outer wall of the quartz glass tube is tightly covered with a grounded metal strip; the dielectric barrier discharge device (5) is used for implementing plasma discharge on the flowing air under the driving of an alternating current power supply to generate ozone (O3); The spark discharge device (6) has a needle-needle electrode structure and is used for spark discharge on air plasma, wherein the generated nitrogen monoxide (NO) and nitrogen dioxide (NO2) are oxidized by ozone to generate dinitrogen pentoxide (N2O5); The gas-liquid mixed absorption module comprises an absorption container (10), a water pump (11) and a vortex-venturi tube (12), wherein the absorption container is used for containing absorption liquid and is connected with the vortex-venturi tube (12) through the water pump (11) to form a liquid flow circulation loop; the N2O5 generated by the series combination discharge module as a whole enters the liquid flow circulation through the vortex-venturi tube (12) and is absorbed by the absorption liquid to form primary dilute nitric acid; The liquid phase refining module comprises a distillation or rectification device (16), an ion exchange device (17) and a gas stripping or sub-boiling distillation device (18) connected in sequence, and is used for deep purification of the primary dilute nitric acid to obtain electronic grade nitric acid.

2. The apparatus for preparing electronic grade nitric acid based on series combination discharge according to claim 1, wherein, The control and analysis module is further included, which is used for regulating the gas flow of the gas mass flow controller (3), the power of the dielectric barrier discharge device (5) and the spark discharge device (6), and the circulation flow of the absorption liquid of the liquid flow circulation loop; And is used for monitoring the concentration of nitric acid contained in the absorption liquid contained in the absorption container (10), the purity of the electronic grade nitric acid generated by the liquid phase refining module, and the concentration of N2O5 generated by the series combination discharge module as a whole. Preferably, the control and analysis module comprises an AI algorithm model and data training unit, which is used to jointly analyze historical operation data and real-time sensor data by AI algorithm, and machine learning, so as to optimize the gas flow of the gas mass flow controller (3), the power of the dielectric barrier discharge device (5) and the spark discharge device (6), the absorption liquid circulation flow of the liquid circulation loop, and the discharge sequence of the dielectric barrier discharge device (5) and the spark discharge device (6), so as to maximize the primary dilute nitric acid yield and minimize the unit energy consumption. More preferably, the AI algorithm model and data training unit is a composite machine learning model based on gradient boosting decision tree (GBDT) and deep neural network (DNN).

3. The apparatus for producing electronic grade nitric acid based on series combination discharge according to claim 1, wherein The spark discharge device (6) is multiple, and the spark discharge devices (6) are connected in parallel with each other. Preferably, each of the spark discharge devices (6) has a needle-needle electrode structure in three series, and contains 6 discharge needles.

4. The apparatus for producing electronic grade nitric acid based on series combination discharge according to claim 1, wherein The sawtooth spacing of the sawtooth-shaped protruding structure is 0.5-3 mm, and the sawtooth height is 0.5-3 mm.

5. The apparatus for producing electronic grade nitric acid based on series combination discharge according to claim 1, wherein The absorption liquid initially placed in the absorption container is water.

6. The apparatus for preparing electronic grade nitric acid based on series combination discharge according to claim 1, wherein, The discharge voltage of the dielectric barrier discharge device (5) is 6-10 kV, and the frequency is 10-20 kHz. The discharge voltage of the spark discharge device (6) is 20-30 kV, and the frequency is 10-15 kHz.

7. The apparatus for producing electronic grade nitric acid based on series combination discharge according to claim 1, wherein The vortex-venturi tube (12) is provided with multiple tangential inlets, and the inner cavity has a spiral flow guide structure.

8. The apparatus for preparing electronic grade nitric acid based on series combination discharge according to claim 1, wherein, The ion exchange device (17) comprises a cation exchange column and an anion exchange column arranged in series, and is respectively used to remove metal cations and inorganic anions in the solution. The control and analysis module comprises an online purity detection device (19) for detecting the nitric acid solution obtained after being treated by the gas stripping or sub-boiling distillation device (18). The online purity detection device (19) comprises an ICP-MS, an ion chromatograph, and a total organic carbon (TOC) analyzer, which are used to monitor the contents of metal ions, inorganic anions and organic carbon in the nitric acid in real time.

9. The apparatus for producing electronic grade nitric acid based on series combination discharge according to claim 1, wherein The liquid phase refining module is also connected with a nitric acid storage module for storing the generated electronic grade nitric acid. The electronic grade nitric acid preparation device based on series combination discharge further comprises a tail gas treatment device (14) connected with the absorption container (10) and used for treating unabsorbed tail gas; the tail gas treatment device (14) preferably uses calcium hypochlorite or alkaline solution to absorb residual nitrogen oxides and ozone, so as to achieve standard discharge or closed loop circulation. The dielectric barrier discharge device (5) and the spark discharge device (6) are powered by a power supply device (7); the power supply device (7) is connected with a photovoltaic power generation device (8) and is provided with electric energy by the photovoltaic power generation device (8). Preferably, the dielectric barrier discharge device (5) and the spark discharge device (6) are both provided with replaceable electrode structures and online electrode cleaning functions, so as to prolong the system operation period and reduce the maintenance cost.

10. A method for producing electronic grade nitric acid using the apparatus for producing electronic grade nitric acid based on a series combination discharge according to any one of claims 1 to 9, characterized in that, Air is used as raw material, and after drying, flow rate and pressure regulation, O3 is generated in dielectric barrier discharge, and N2O5 is generated in spark discharge; N2O5 gas is rapidly reacted with circulating absorption liquid through vortex-venturi tube to generate primary dilute nitric acid, and then is deeply purified through liquid phase refining module, so that electronic grade nitric acid with mass concentration of HNO3≥70% and impurity content controlled in ppb level is obtained; Preferably, the gas flow rate of air is 9L / min, the dielectric barrier discharge power is 70W, the spark discharge power is 25W, and the circulating flow rate of absorption liquid is 4L / min.

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