Preparation process of electronic grade nitric acid

Abstract

The present application relates to a kind of preparation processes of electronic grade nitric acid, including raw material delivery, rectification purification, condensation gas-liquid separation, cooling aeration, product storage, closed loop circulation purification, product subpackaging step.After rectification, nitric acid azeotrope is efficiently condensed and deeply impurity-removed by integrated gas-liquid separation vertical condenser, and product tank adopts closed loop circulation purification loop to realize no blind area liquid taking, gradient filtration and two-way liquid return gradient control.The present application solves the problems of poor condensation heat exchange, poor gas-liquid separation, product tank liquid taking blind area, liquid return mixing flow, filter element blockage and tank wall crystallization in the preparation process of electronic grade nitric acid, cooperates to block the vicious cycle of impurity accumulation, stably guarantees the ultra-high cleanliness of electronic grade nitric acid, and adapts to the strict quality requirements of high-end semiconductor process.

Description

TECHNICAL FIELD

[0001] The present invention relates to the technical field of wet electronic chemical preparation, in particular to a process for preparing electronic grade nitric acid. BACKGROUND ART

[0002] Electronic grade nitric acid is an indispensable core wet electronic chemical in the field of high-end electronic manufacturing, which is widely used in critical processes such as wafer cleaning and etching, silicon wafer texturing, and display panel thin film etching. Its purity and cleanliness directly determine the product yield and performance stability of terminal electronic components. With the continuous upgrading of semiconductor processes toward high-end levels, the industry's quality requirements for electronic grade nitric acid have become increasingly stringent: high-end processes not only require the metal impurity content to be controlled within 1ppb, even as low as the 0.1ppb level, with zero detection of particulate matter above 0.2μm, but also put forward near-limit control requirements for dissolved nitrogen oxides (NO x ), anionic impurities and the like.

[0003] The conventional preparation processes of existing electronic grade nitric acid mainly include core links such as raw material storage, transportation, evaporation, rectification, condensation, cooling, aeration, filtration, finished product storage and subpackaging. Among them, the finished product tank, as the final storage unit before the shipment of electronic grade nitric acid, is the last core checkpoint to ensure the quality of the terminal product, and directly determines whether the final finished product can meet the strict requirements of high-end semiconductor processes.

[0004] However, during the storage process of electronic grade nitric acid in the finished product tank, continuous accumulation and a vicious cycle of multi-source impurities inevitably occur. The specific impurity sources include: background impurities such as submicron particulate matter, trace metal ions and dissolved NO remaining from the front-end refining process x ; metal ions and fluoroplastic microparticles leached from the tank body, transportation pipelines and seals that are in long-term contact with nitric acid; nitrate crystalline particulate matter formed by dry crystallization of nitric acid attached to the tank wall above the liquid level when the liquid level in the tank fluctuates; NO generated by the spontaneous decomposition of nitric acid at normal temperature x will further aggravate the corrosion of the tank body and pipelines, forming a vicious cycle of decomposition, corrosion, impurity accumulation, and further intensified decomposition and corrosion.

[0005] In response to the above-mentioned multi-source impurity control requirements during the storage process, the existing purification schemes supporting the electronic grade nitric acid finished product tank cannot form a systematic closed-loop impurity treatment, and mainly have the following core problems: First, single-point liquid extraction at the tank bottom is mostly adopted, which has a liquid extraction blind area and cannot realize effective collection of impurities in the entire tank; Second, the filtered returned liquid mostly adopts a top single-point return mode, in which the clean liquid and the liquid to be treated are directly mixed, and the cleanliness gradient control in the tank cannot be realized; Third, most of them adopt a single-stage filtration structure, and full-size impurities directly impact the high-precision filter element, which can easily cause the filter element to clog quickly and cannot achieve continuous and stable high-precision filtration. Fourth, the design lacks wall wetting protection, which makes the nitric acid on the tank wall prone to drying and crystallizing when the liquid level fluctuates, forming a continuous source of pollution.

[0006] Besides the core pain points in the finished product storage stage, in existing preparation processes, the condensation and liquefaction of nitric acid-water azeotropic vapor at the top of the distillation column is a crucial pre-process connecting distillation purification with subsequent aeration and impurity removal, and finished product storage. Its condensation heat exchange efficiency and gas-liquid separation effect directly determine the background impurities of the material entering the finished product storage stage, further amplifying the impurity control challenges in the aforementioned finished product storage stage. Currently, the industry commonly uses vertical shell-and-tube condensers for the condensation of nitric acid azeotropic vapor, but this approach faces the following core problems in practical industrial applications: Firstly, existing shell-side heat exchangers mostly use bow-shaped baffles to guide steam flow, which can easily cause uneven distribution of the shell-side flow field, resulting in flow dead zones, steam deflection and short-circuiting problems, making it impossible to achieve uniform and sufficient contact between steam and heat exchange tube bundles. At the same time, the liquid nitric acid formed by steam condensation can easily form a continuous thick liquid film on the outer wall of the heat exchange tube bundle, generating a large additional thermal resistance and significantly reducing condensation heat transfer efficiency. Secondly, in the existing technology, the condensed gas-liquid mixture needs to be transported to an independent gas-liquid separation device through an intermediate pipe, which results in the complete loss of the swirling kinetic energy formed by the steam during the condensation process. The gas-liquid separation requires an additional swirling structure, which not only increases the energy consumption and floor space of the equipment, but also easily causes flow field disturbance and pressure fluctuation. Third, all the condensate enters the separation zone along with the gas phase. The excessive liquid load in the separation zone can easily lead to flooding and excessive droplet entrainment, failing to meet the stringent control requirements of electronic-grade nitric acid for metal ions and particulate matter.

[0007] The aforementioned technical defects in the condensation process directly lead to insufficient nitric acid condensation, poor gas-liquid separation, and a higher concentration of dissolved NO in the product. x The background levels of non-condensable gases, particulate matter entrained by droplets, and metal ion impurities are significantly increased, which not only greatly increases the processing load of subsequent aeration and impurity removal processes but also makes it impossible to stably remove dissolved NO. x Furthermore, this will allow nitric acid with high impurity content to enter the finished product storage stage, exacerbating the vicious cycle of corrosion and leaching of tanks and pipelines, nitric acid decomposition, and impurity accumulation, further amplifying the existing technical defects in the finished product storage stage.

[0008] The purpose of this invention is to design a preparation process for electronic-grade nitric acid to address the problems existing in the prior art. Summary of the Invention

[0009] The purpose of this invention is to address the aforementioned deficiencies of existing technologies by providing a process for preparing electronic-grade nitric acid. This process utilizes a dedicated vertical condenser in the condensation stage to solve the core problems of low condensation heat exchange efficiency, poor gas-liquid separation, and high impurity background in existing processes, significantly reducing impurity input from upstream steps. Simultaneously, the closed-loop purification circuit and corresponding purification process in the finished product storage stage thoroughly resolve the core problems of blind spots in finished product tank retrieval, easy mixing of return liquid, easy clogging of filter elements, and easy crystallization on tank walls in existing technologies. These two processes work together to prevent the vicious cycle of impurity accumulation, accelerated corrosion, and nitric acid decomposition, stably ensuring the high cleanliness of the finished electronic-grade nitric acid product and meeting the quality requirements of high-end processes.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: A process for preparing electronic-grade nitric acid includes the following steps: S1. Nitric acid raw material is transported from the raw material tank to the raw material buffer tank; S2. Nitric acid raw material is transported from the raw material buffer tank to the distillation process. After preheating and azeotropic distillation in a reboiler, high-purity nitric acid gaseous azeotrope is obtained. S3. The gaseous azeotrope obtained from distillation is condensed and then enters an aeration tower. Clean, oil-free compressed air is introduced to remove dissolved NO from the product. x The aerated product is then cooled to below 40°C. S4. The cooled electronic-grade nitric acid is then sent to the finished product tank for storage. S6. After high-precision filtration, the product in the finished product tank is packaged into the corresponding packaging materials according to requirements to obtain electronic-grade nitric acid finished product; The finished product tank used in step S4 is equipped with a closed-loop circulation purification circuit. The circulation purification circuit includes a liquid extraction unit, a gradient filtration unit, and a dual-path liquid return unit that are connected in sequence and form a closed loop with the liquid storage chamber of the finished product tank. The preparation process further includes a step performed between step S4 and step S6: S5. Start the circulating purification circuit to continuously circulate and purify the nitric acid material in the storage chamber, specifically including: S51. The impurity-containing liquid at the bottom of the storage chamber is uniformly extracted by the annular liquid extraction pipe located at the bottom of the storage chamber in the liquid extraction unit, in conjunction with the circulation pump. S52. The extracted liquid containing impurities is sent to a gradient filtration unit, and the gradient purification is completed through at least two coaxially nested filtration devices. S53. The purified liquid after gradient purification is sent to the dual-path return unit and divided into two paths to the storage chamber: the first path is through the spiral water distribution branch pipe in the middle of the storage chamber, which creates a low-speed swirling flow towards the bottom of the tank, guiding suspended impurities to gather at the bottom and form a preliminary clean isolation layer; the second path is through the overflow return plate at the top of the storage chamber, which makes the purified liquid form a continuous laminar flow film along the inner wall of the storage chamber, and builds a clean liquid covering layer from top to bottom in the storage chamber, realizing gradient control of cleanliness in the storage chamber.

[0011] As a further improvement, in step S51, the annular liquid extraction pipe includes at least two annular liquid extraction unit pipes and a main drainage pipe. The liquid extraction unit pipes are arranged to fit the bottom edge of the liquid storage cavity and adjacent liquid extraction unit pipes are distributed vertically at intervals along the height direction of the liquid storage cavity. The main drainage pipe connects all the liquid extraction unit pipes in sequence and leads out along the bottom of the finished product tank to the circulation pump. The liquid extraction unit tube has several liquid extraction holes perforated through its inner annular tube wall. These extraction holes are radially distributed along the liquid storage cavity and are inclined toward the center of the bottom of the liquid storage cavity.

[0012] As a further improvement, in step S52, the gradient filtration unit is coaxially nested with two-stage filtration devices, including a pre-filtration stage and a post-high-precision filtration stage, to complete step-by-step gradient purification. Pressure sensors are installed at both the inlet and outlet of the gradient filtration unit. The two pressure sensors constitute a differential pressure monitoring component to determine the filter element blockage of the filtration device based on the differential pressure.

[0013] As a further improvement, in step S53, the spiral water distribution branch pipe is spirally arranged along the inner wall of the liquid storage cavity, and several return holes are opened through the pipe wall around the inner side of the spiral water distribution branch pipe. The several return holes are distributed radially along the liquid storage cavity and are inclined towards the center of the bottom of the liquid storage cavity. The overflow return tray is annular, with a gap between its outer periphery and the side wall of the storage chamber. The discharge port of the finished product tank is fixedly located in the upper area corresponding to the clean liquid covering layer.

[0014] As a further improvement, the overflow return plate includes an outer plate with an annular overflow groove, an inner plate coaxially disposed in the overflow groove and having an annular buffer groove, and a return pipe located at the center of the overflow groove and in the shape of a column. The top of the return pipe protrudes from the highest position of the outer plate, and a return groove extending to the bottom of the outer plate is opened through the return pipe along its axial direction. A plurality of return channels connecting the return groove and the overflow groove are provided between the bottom of the inner plate and the bottom of the outer plate. A plurality of overflow holes connecting the overflow groove are opened around the outer side wall of the outer plate in its circumference.

[0015] As a further improvement, the overflow hole is elongated and extends circumferentially along the outer side wall of the outer disk. The height of the outer side wall of the buffer tank is lower than the height of the outer side wall of the overflow tank but higher than the setting height of the overflow hole. The inner bottom of the return tank is detachably connected to a buffer structure. The top surface of the buffer structure is provided with a continuous arc-shaped guide surface that gradually transitions towards its periphery and bottom.

[0016] As a further improvement, the circulation pump used in step S51 is a fluoropolymer-lined PFA magnetic pump.

[0017] As a further improvement, the filter element of the pre-filter stage has a filter element precision of 5-10μm, and the filter element precision of the post-high-precision filter stage has a filter element precision of 0.1-0.2μm; the liquid inlet is inclined downward at 15°-45° to the horizontal direction; and the liquid return outlet is inclined downward at 10°-30° to the horizontal direction.

[0018] As a further improvement, in step S3, the condensation of the gaseous azeotrope is carried out using a vertical shell-and-tube condenser. The condenser includes a vertical shell, a heat exchange tube bundle, an upper tube box, and a lower tube box. The upper tube box, heat exchange tube bundle, and lower tube box are sequentially connected to form a tube-side flow channel for cooling water. A shell-side flow channel for nitric acid gaseous azeotrope is formed between the outer side of the heat exchange tube bundle and the inner side of the vertical shell. An inlet pipe communicating with the shell-side flow channel is provided at the top of the vertical shell. Continuous baffles are provided inside the shell-side flow channel to divide it into continuous spiral heat exchange channels. A gas-liquid separation module is provided on the outer periphery of the lower tube box. The gas-liquid separation module includes a swirling separation chamber coaxially sleeved on the outer periphery of the lower tube box. The system includes a non-condensable gas buffer chamber connected to the cyclone separation chamber and a condensate collection tank located at the bottom of the cyclone separation chamber. The cyclone separation chamber is equipped with a continuous spiral guide plate, which divides the cyclone separation chamber into a continuous spiral separation channel. The bottom outlet of the heat exchange channel is tangentially connected to the top inlet of the separation channel through a tangential feed port. At least one pre-collection pipe is arranged circumferentially on the inner wall of the vertical shell. The pre-collection pipe penetrates the surface of the baffle plate axially, and liquid collection holes are opened at the intersection of the pre-collection pipe and the surface of the baffle plate. A venturi tube is connected downstream of the condensate outlet pipe at the bottom of the condensate collection tank. The throat section of the venturi tube is connected to the lower side wall of the pre-collection pipe through an ejector pipe.

[0019] As a further improvement, the pitch of the deflector decreases in a linear gradient along the downward direction of its axial direction, the ratio of the pitch of its first section to the inner diameter of the shell-side flow channel is 1.2:1, and the ratio of the pitch of its last section to the inner diameter of the shell-side flow channel is 0.6:1; the outer edge of the baffle plate is provided with a continuous liquid collection groove along the entire spiral path, the pre-collection pipe longitudinally passes through the liquid collection groove, and the liquid collection hole is arranged within the coverage of the liquid collection groove with its bottom flush with the bottom of the liquid collection groove; the top of the shell-side flow channel is provided with an annular flow equalizing cover distributed circumferentially around the inner side thereof, a flow equalizing cavity communicated with the gas inlet pipe is formed on the inner side of the annular flow equalizing cover, and the side wall of the flow equalizing cavity is provided with a plurality of flow equalizing holes communicated with the shell-side flow channel.

[0020] Accordingly, the present invention provides the following effects and / or advantages: In the existing electronic-grade nitric acid preparation process, the liquid extraction scheme supporting the finished product storage link mostly adopts a single-point liquid extraction structure at the tank bottom, which cannot cover the entire tank area where impurities in the tank are naturally stratified. Suspended impurities in the middle and top of the finished product tank and crystalline particles generated by drying and crystallization on the tank wall cannot enter the filtration system, which not only leads to uneven purification effect of the entire tank and low cleanliness compliance rate, but also the impurities that are not effectively collected will continue to accumulate in the tank, further aggravating filter element blockage and tank corrosion, and amplifying the secondary pollution problem caused by returned liquid mixed flow, which is particularly prominent in the long-term storage scenario of high-end electronic-grade nitric acid. In response to this, in the closed-loop circulation purification step of the preparation process, the present invention realizes uniform liquid extraction in the entire circumferential direction through the annular liquid extraction pipe arranged at the bottom of the liquid storage cavity, and at the same time, through the spiral water distribution branch pipes of the two-way liquid return unit, the filtered clean liquid constructs a low-speed swirl flow towards the tank bottom in the middle of the liquid storage cavity, actively guiding the suspended impurities in the tank to gather directionally towards the bottom, eliminating the liquid extraction blind area in the tank, realizing efficient collection and directional conveying of impurities in the entire tank, greatly improving the purification uniformity of the entire tank, while avoiding continuous accumulation of impurities in the tank, alleviating the problems of filter element blockage and tank corrosion from the source, and blocking the vicious cycle of impurity accumulation, aggravated corrosion, and accelerated decomposition.

[0021] In the existing electronic-grade nitric acid preparation process, the filtered return liquid scheme in the finished product storage stage mostly adopts a single-point direct injection return liquid structure at the top of the tank. The filtered clean liquid directly mixes with the untreated dirty liquid in the tank, which not only greatly prolongs the treatment cycle for all materials in the tank to reach the target cleanliness, resulting in problems of high circulating energy consumption and large nitric acid decomposition loss; at the same time, the mixed flow makes it impossible to always realize cleanliness gradient control for the materials in the tank, requiring repeated circulating filtration, which further aggravates the blockage loss of the filter element, and also makes the impurities in the liquid-taking blind area unable to be effectively removed, failing to meet the extreme storage purification control requirements of electronic-grade nitric acid for high-end manufacturing processes. In response to this, in the closed-loop circulating purification step of the preparation process, the present invention adopts a collaborative design of a dual-path liquid return unit. One path uses an annular overflow liquid return tray at the top of the liquid storage chamber to make the filtered clean liquid form a continuous laminar liquid film along the inner wall of the main body of the finished product tank, so as to construct a stable clean liquid covering layer within the finished product storage liquid level from top to bottom, and the delivery liquid taking port is fixedly arranged in the upper area corresponding to the clean liquid covering layer, which completely avoids the direct mixed flow of the clean liquid and the untreated dirty liquid, greatly shortens the treatment cycle for all materials in the tank to reach the standard, and reduces the circulating energy consumption and the decomposition loss of nitric acid at normal temperature; the other path constructs a preliminary clean isolation layer through the spiral water distribution branch pipe in the middle part of the liquid storage chamber, which forms upper and lower coordination with the top clean liquid covering layer, realizes top-down cleanliness gradient control in the tank, can realize stable control of the cleanliness of the entire tank without repeated circulating filtration, effectively alleviates the blockage loss of the filter element, and fully adapts to the storage and purification requirements of electronic-grade nitric acid for high-end manufacturing processes.

[0022] In the existing electronic-grade nitric acid preparation process, the purification filtration scheme supporting the finished product storage stage mostly adopts a single-stage filtration structure. If it is directly adapted to a submicron high-precision filter element, full-size impurities that have not undergone pre-separation will directly impact the high-precision filter element, which is very likely to cause the filter element to be blocked rapidly in a short time, which not only greatly increases the operation cost of the equipment, but also fails to achieve continuous and stable high-precision filtration. In response to this, in the closed-loop circulating purification step of the preparation process, the present invention is provided with a gradient filtration unit composed of two stages of coaxially nested filtration devices outside the main body of the finished product tank. Through the gradient filtration structure with stepwise accuracy matching, the pre-filter stage first removes large-sized particles and crystalline impurities, and then the post high-precision filtration stage removes submicron particles, so as to avoid direct impact of full-size impurities on the high-precision filter element, greatly extend the service life of the filter element, reduce the operation cost of the equipment, and achieve continuous and stable high-precision filtration at the same time, so as to stably guarantee the particle control index of electronic-grade nitric acid; meanwhile, a differential pressure monitoring component is arranged at the inlet and outlet positions of the gradient filtration unit, which can judge the filter element blockage condition of the filtration device in real time according to the change of differential pressure, facilitating timely maintenance and replacement, and ensuring the long-term stable operation of the purification system.

[0023] The existing annular liquid collection structure of the finished product tank used in the electronic-grade nitric acid preparation process mostly adopts a fixed single-layer, single-ring design, which can only achieve liquid collection from a single height at the bottom of the tank. This cannot adapt to the stratified distribution characteristics of impurities settling at the bottom of the tank. The settled impurities in the dead corners at the bottom of the tank cannot be effectively absorbed, and long-term accumulation will lead to impurity caking and local corrosion of the tank body. At the same time, the liquid collection holes are mostly opened vertically and radially, which easily creates local eddies during liquid collection, disturbing the already settled impurities and resuspending and diffusing them, exacerbating the contamination of the material in the tank. To address this, the annular liquid extraction pipe of the finished product tank used in this invention employs two liquid extraction unit pipes spaced vertically along the height of the storage chamber. The liquid extraction unit pipes are positioned close to the bottom edge of the storage chamber, which can adapt to the stratified distribution characteristics of impurities settling at the bottom of the tank. This enables the extraction of impurities at different heights and in the entire circumference of the tank bottom, completely eliminating dead zones in the sedimentation of impurities at the bottom of the tank and preventing long-term accumulation and hardening of impurities and localized corrosion of the tank body. At the same time, the liquid extraction holes of the liquid extraction unit pipes are inclined towards the center of the bottom of the storage chamber, which can form a directional flow towards the center during liquid extraction, preventing disturbing the settled impurities and causing them to re-suspend and diffuse, thus ensuring the stability and efficiency of impurity collection.

[0024] Existing electronic-grade nitric acid preparation processes often employ a swirling water distribution structure in the finished product tank, using a tangential water inlet design at the bottom. This easily disturbs the impurities that have already settled at the bottom, failing to achieve directional guidance of suspended impurities and stable construction of a clean isolation layer. Furthermore, uneven water distribution easily creates localized turbulence, exacerbating the mixing of clean and dirty liquids and amplifying the risk of contamination within the tank. In contrast, the spiral water distribution branch pipes used in this invention are spirally arranged along the inner wall of the storage chamber, with their return holes angled towards the center of the bottom of the storage chamber. This creates a low-speed swirling flow that evenly covers the entire circumference in the middle of the storage chamber. This avoids disturbing the impurities already settled at the bottom while precisely guiding suspended impurities in the middle towards the bottom. Simultaneously, a stable preliminary clean isolation layer is constructed in the middle of the storage chamber, preventing cross-diffusion of impurities from the top and bottom. This, combined with the clean liquid covering layer at the top, creates a synergistic gradient control effect, further improving the overall purification efficiency and long-term stability of cleanliness within the tank.

[0025] The overflow return structure of the finished product tank used in existing electronic-grade nitric acid preparation processes mostly adopts a single-point direct injection design, which cannot form a continuous laminar flow film along the tank wall. The clean liquid directly impacts the material in the tank, creating violent turbulence. At the same time, the fluid impact during return easily generates bubbles and turbulence, which exacerbates the decomposition of nitric acid and NO. xThe lack of a buffer structure will further contaminate the materials in the tank; the design will also lead to large fluctuations in return liquid pressure, making it impossible to form a stable and uniform overflow effect. It is very easy to have problems such as flow interruption and flow deviation, which will cause the laminar liquid film to fail to form a continuous wetting of the liquid level fluctuation area on the tank wall. During the liquid level rise and fall, the nitric acid attached to the tank wall is very easy to crystallize in the drying environment, forming a continuous source of particulate impurity pollution. To address this, the overflow return tank of the finished product tank used in this invention adopts a coaxial nested structure of an inner buffer tank and an outer overflow tank. The filtered clean liquid first enters the return tank of the central return pipe, then uniformly enters the overflow tank through the return channel, and then overflows uniformly through the overflow holes distributed circumferentially on the outer wall of the outer tank, forming a continuous and stable laminar flow film along the inner wall of the finished product tank body, completely avoiding the violent mixing caused by direct spraying of clean liquid. The overflow holes are elongated and distributed circumferentially along the outer wall of the outer tank. Combined with the limiting design where the height of the outer sidewall of the buffer tank is lower than the height of the outer sidewall of the overflow tank but higher than the height of the overflow holes, it can effectively buffer the return pressure fluctuations, ensure the uniformity and continuity of the overflow, avoid the problems of flow interruption and flow deviation, and at the same time avoid the generation of bubbles and turbulence from the return liquid impact, reducing nitric acid decomposition and NO. x The continuous laminar flow liquid film can continuously wet the liquid level fluctuation area on the inner wall of the storage chamber, eliminating the drying environment of the tank wall and preventing the generation of particulate impurities from nitric acid drying crystallization from the source, thus blocking the continuous pollution risk caused by tank wall crystallization. The buffer structure at the bottom of the return tank can further guide and buffer the incoming liquid. Its continuous arc-shaped guide surface can realize the smooth reversal of the fluid, avoiding the direct impact of the fluid to form turbulence, and further improving the construction stability of the laminar flow liquid film.

[0026] Existing circulating pumps used in the finished product tanks of electronic-grade nitric acid preparation processes are mostly ordinary stainless steel centrifugal pumps. Prolonged contact with highly oxidizing nitric acid can easily lead to corrosion, dissolving metal ions and particulate impurities, contaminating the high-purity nitric acid within the tank. Furthermore, the dynamic sealing structure is prone to nitric acid leakage, posing serious safety and quality control risks. To address this, this invention employs a fluoropolymer-lined PFA magnetic pump as the circulating power source for the purification step. The pump's flow-through parts are covered with perfluoropolymer, eliminating direct contact between metal materials and nitric acid, completely preventing secondary contamination from pump corrosion and dissolution. Simultaneously, the magnetically driven, seal-free design completely eliminates the risk of nitric acid leakage, significantly improving the safety of the preparation process and the stability of material quality control.

[0027] In existing electronic-grade nitric acid preparation processes, the condensation stage after distillation often employs conventional vertical shell-and-tube condensers. The bow-shaped baffles in the shell side easily cause uneven flow distribution, dead zones, and vapor deviation. The thick liquid film formed during condensation generates significant additional thermal resistance, resulting in low condensation heat transfer efficiency and insufficient nitric acid yield. Furthermore, the condensed gas-liquid mixture needs to be transported to a separate separation unit, which not only loses the swirl energy of the condensation process and increases equipment energy consumption and floor space, but also easily causes flow field disturbances and pressure fluctuations. Furthermore, allowing all the condensate to enter the separation area can lead to excessive liquid load, easily causing flooding and excessive droplet entrainment, failing to meet the high purity requirements of electronic-grade nitric acid. These defects directly result in a higher concentration of dissolved NO in the product. x The increased background levels of particulate matter and metal ion impurities significantly increase the processing load of subsequent aeration processes, and further exacerbate the vicious cycle of tank corrosion, nitric acid decomposition, and impurity accumulation in the finished product storage stage. To address this, this invention employs a vertical condenser with an integrated gas-liquid separation module in the condensation step of the preparation process. A spiral heat exchange channel is constructed using continuous baffles to guide the nitric acid azeotropic vapor into uniform and sufficient contact with the heat exchange tube bundle, eliminating flow dead zones and flow deviation problems. Combined with a negative pressure suction structure linking the pre-collection tube and the Venturi tube, the condensate formed during the heat exchange process is discharged in real time, fundamentally preventing the formation of a thick liquid film, significantly reducing the additional thermal resistance on the condensation side, and significantly improving condensation heat exchange efficiency and nitric acid product yield. Simultaneously, through the tangential connection design of the heat exchange channel and the swirl separation channel, the swirl kinetic energy generated during the condensation process is directly utilized to achieve efficient gas-liquid separation, eliminating the need for additional swirl power structures and independent separation equipment. This avoids ineffective loss of swirl kinetic energy, reduces equipment energy consumption and floor space, and eliminates flow field disturbances and pressure fluctuations in intermediate conveying stages, ensuring the stability of continuous production line operation. Furthermore, by pre-collecting and discharging the condensate, the liquid load entering the gas-liquid separation area is significantly reduced, avoiding flooding and excessive droplet entrainment at the source. Combined with the deep swirling separation of the gradient pitch guide plate, it can further intercept trace droplets and particulate matter entrained in the gas phase, significantly reducing the impurity background of the nitric acid material entering the subsequent aeration process and finished product storage stage. This greatly reduces the processing load of the aeration and impurity removal process, and can alleviate the vicious cycle of impurity accumulation, increased corrosion, and nitric acid decomposition in the finished product tank from the source. It forms a synergistic effect with the closed-loop purification process in the finished product storage stage, further improving the purity and cleanliness stability of the electronic-grade nitric acid product, and fully meeting the stringent quality requirements of high-end semiconductor manufacturing processes.

[0028] In summary, this invention addresses the core problems in existing electronic-grade nitric acid preparation processes by adding a dedicated condensation and gas-liquid separation step to the electronic-grade nitric acid preparation process, coupled with a closed-loop purification step. It utilizes a dedicated condenser to achieve efficient front-end condensation and deep impurity removal. The closed-loop purification circuit, comprised of a liquid extraction unit, a gradient filtration unit, and a dual-path liquid return unit, solves these problems. Specifically, it addresses issues such as blind spots in liquid extraction, easy mixing of return liquids, easy clogging of filter cartridges, and easy drying and crystallization of tank walls during finished product storage. The synergistic design of the dual-path liquid return system enables gradient control of tank cleanliness, preventing the risk of nitric acid drying and crystallization on tank walls from the source, thus breaking the vicious cycle of impurity accumulation, accelerated corrosion, and nitric acid decomposition. Through a gradient filtration structure and a corrosion-resistant design throughout the process, it achieves continuous, stable, and high-precision purification of electronic-grade nitric acid, ensuring the stringent quality requirements of high-end processes. This invention balances the operational stability, purification efficiency, ease of operation, and long service life of the preparation process while significantly improving the quality control limits and production safety of the finished electronic-grade nitric acid product.

[0029] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained through the structures particularly pointed out in the description and the drawings.

[0030] It should be understood that the above summary and the following detailed description of the invention are exemplary and explanatory, and are intended to provide further explanation of the invention as claimed. Attached Figure Description

[0031] Figure 1 This is a flowchart illustrating the preparation process of electronic-grade nitric acid according to the present invention.

[0032] Figure 2 This is a schematic diagram of the overall structure of the closed-loop purification circuit in this invention.

[0033] Figure 3 This is a three-dimensional structural diagram of the main body of the finished product tank used in this invention. Figure 4 This is a cross-sectional view of the finished product tank used in this invention.

[0034] Figure 5 This is a partial cross-sectional view of the liquid extraction hole in this invention.

[0035] Figure 6 This is a partial cross-sectional view of the structure highlighting the return fluid hole in this invention.

[0036] Figure 7 This is a three-dimensional structural diagram of the overflow return pan in this invention.

[0037] Figure 8This is a cross-sectional view of the overflow return pan in this invention.

[0038] Figure 9 This is a partial cross-sectional view of the distribution of liquid layers within the storage cavity in this invention.

[0039] Figure 10 This is a three-dimensional structural diagram of the vertical condenser used in this invention.

[0040] Figure 11 This is a schematic diagram of the overall structure of the vertical condenser used in this invention.

[0041] Figure 12 This is a schematic cross-sectional view of the vertical condenser used in this invention.

[0042] Figure 13 for Figure 12 A magnified schematic diagram of a portion of region A in the middle.

[0043] Figure 14 for Figure 12 A magnified schematic diagram of a portion of region B.

[0044] Figure 15 This is a schematic cross-sectional view of the pre-collection tube in the vertical condenser used in this invention.

[0045] Figure 16 This is a partial cross-sectional view and three-dimensional structural diagram of the annular flow equalization shroud in the vertical condenser used in this invention.

[0046] Figure 17 This is a partial cross-sectional view of the lower extension section of the vertical condenser used in this invention.

[0047] Label Explanation: 100. Finished product tank body; 110. Liquid storage chamber; 120. Finished product inlet; 130. Discharge outlet; 200. Liquid extraction unit; 210. Circulation pump; 220. Annular liquid extraction pipe; 221. Liquid extraction unit pipe; 222. Main drainage pipe; 223. Liquid extraction hole; 300. Gradient filtration unit; 310. Pre-filtration stage; 320. Post-filtration high-precision stage; 330. Differential pressure monitoring component; 400. Dual-path return unit; 410. Spiral water distribution branch pipe; 411. Return hole; 42 0. Overflow return plate; 421. Outer plate; 422. Overflow trough; 423. Inner plate; 424. Buffer trough; 425. Return pipe; 426. Return trough; 427. Return channel; 428. Overflow hole; 429. Buffer structure; 430. T-junction; 431. First bypass pipe; 432. Second bypass pipe; 433. Flow regulating valve; 500. Vertical housing; 501. Upper tube sheet; 502. Lower tube sheet; 503. Tangential feed inlet; 504. Air inlet pipe; 505. Annular Flow equalization hood; 506, Flow equalization cavity; 507, Flow equalization orifice; 510, Heat exchanger tube bundle; 520, Shell-side flow channel; 530, Tube-side flow channel; 531, Upper head; 532, Upper tube box; 533, Annular cylinder wall; 534, Lower head; 535, Lower tube box; 536, Flange interface; 540, Baffle plate; 541, Heat exchanger flow channel; 542, Liquid collection groove; 543, Guide surface; 550, Gas-liquid separation module; 551, Swirl separation chamber; 552, Non-condensable gas buffer chamber; 553, Non-condensable gas... 554. Exhaust pipe; 555. Condensate collection tank; 556. Condensate outlet pipe; 557. Lower extension section; 558. Guide plate; 559. Separation channel; 560. Guide gap; 561. Air guide hole; 562. Return hole; 570. Liquid collection pipe; 571. Liquid collection hole; 580. Venturi tube; 581. Gradient section; 582. Throat section; 583. Gradient expansion section; 590. Ejector pipe; 591. Main ejector pipe; 592. Annular branch pipe; 593. Ejector unit pipe. Detailed Implementation

[0048] To facilitate understanding by those skilled in the art, the structure of the present invention will now be described in further detail with reference to the accompanying drawings: Example 1 Reference Figure 1 This embodiment provides a process for preparing electronic-grade nitric acid, specifically including the following steps: S1. Raw material conveying: 70% industrial-grade nitric acid raw material is conveyed from the raw material tank to the raw material buffer tank via a fluoropolymer-lined magnetic conveying pump. Feeding continues until the liquid level in the tank reaches 75%, at which point feeding stops. During the feeding process, the liquid level in the tank is monitored in real time by a level transmitter to prevent material overflow.

[0049] S2. Rectification and Purification: Start the raw material delivery pump to deliver the 70% nitric acid raw material in the raw material buffer tank to the distillation process. The material first enters the shell-and-tube preheater, exchanges heat with the high-temperature nitric acid gaseous azeotrope distilled from the top of the rectification tower to raise the temperature to 80°C, and then is sent to the tube side of the reboiler at the bottom of the rectification tower. Saturated steam of 0.6kg / cm² is introduced into the shell side of the reboiler to control the temperature of the material in the tube side of the reboiler to be stably at 115°C. The gas-liquid mass transfer purification is completed by using the azeotropic distillation principle of nitric acid and water to remove metal ions and high-boiling impurities in the raw material, and a high-purity nitric acid gaseous azeotrope is produced at the top of the rectification tower.

[0050] S3. Cooling and Aeration: The gaseous azeotrope produced at the top of the rectification tower is condensed to 80°C~90°C by a condenser, and then sent to the top feed port of the aeration tower. Clean oil-free compressed air (CDA) that has undergone three-stage precision filtration and freeze-drying treatment is introduced into the bottom of the aeration tower, and the volume ratio of gas to liquid is controlled at 15:1. The compressed air comes into countercurrent contact with the nitric acid material in the tower to fully remove the dissolved NO in the material x . The nitric acid material after aeration is discharged from the bottom of the aeration tower, enters the shell-and-tube finished product cooler, and is cooled to below 40°C by 7°C chilled water.

[0051] S4. Finished Product Storage: The cooled electronic-grade nitric acid is delivered through a high-purity PFA pipeline to a finished product tank equipped with a closed-loop circulation purification loop for storage. The liquid level of the material in the tank is controlled to be 80% of the total height of the liquid storage chamber. After feeding is completed, the feed port of the tank body is closed to keep the tank in a sealed state.

[0052] S5. Closed-Loop Circulation Purification: After feeding is completed, start the closed-loop circulation purification loop supporting the finished product tank to perform continuous circulation purification on the nitric acid material in the liquid storage chamber. The specific processes are as follows: S51. No-blind-area liquid extraction for the entire tank: Start the fluorine-lined PFA magnetic circulation pump to uniformly extract the impurity-containing liquid at the bottom of the liquid storage chamber through the annular liquid extraction pipe at the bottom of the liquid storage chamber. The annular liquid extraction pipe comprises two upper and lower coaxial annular liquid extraction unit pipes. The two layers of liquid extraction unit pipes are arranged to fit the arc-shaped edge at the bottom of the liquid storage chamber, with a vertical spacing of 100mm, and the lower layer of the liquid extraction unit pipe is arranged to fit the bottom surface of the liquid storage chamber. A number of liquid extraction holes are evenly opened along the circumferential direction on the annular inner pipe wall of the liquid extraction unit pipe. The liquid extraction holes are distributed along the radial direction of the liquid storage chamber and are arranged at an inclination of 18° downward from the horizontal direction, forming a directional drainage toward the center of the tank bottom during the extraction process, so as to avoid disturbing the settled impurities to resuspend and diffuse again. S52. Gradient Filtration Purification: The extracted liquid containing impurities is sent into the gradient filtration unit along the pipeline. The material first enters the pre-filtration stage, where large particles and crystalline impurities are removed by a 10μm precision filter element. Then it enters the post-high precision filtration stage, where submicron particles are removed by a 0.2μm precision filter element, completing the step-by-step gradient purification. Pressure sensors are installed at both the inlet and outlet of the gradient filtration unit to form a differential pressure monitoring component. The differential pressure data between the inlet and outlet is collected in real time and uploaded to the field control system. When the differential pressure exceeds 0.15MPa, the system automatically triggers a filter element replacement reminder. S53. Dual-path gradient water distribution and return: The purified nitric acid material after gradient purification is divided into two paths through the T-junction at the end of the main pipeline. Each bypass pipeline is equipped with an independent flow regulating valve to control the flow ratio of the first path to the second path at 3:7. The first path of purified material is fed into the spiral water distribution branch pipe in the middle of the storage chamber through the first bypass pipeline. The spiral water distribution branch pipe has a 6-turn spiral structure, fixedly installed along the inner wall of the storage chamber. Several return holes are evenly distributed along the spiral direction on the inner wall of the spiral, radially distributed along the storage chamber and inclined downwards at 16° to the horizontal direction. The purified liquid is directionally sprayed out through the return holes, forming a low-speed swirling flow that evenly covers the entire circumference and faces the bottom of the tank in the middle of the storage chamber, actively guiding the middle of the storage chamber... The suspended impurities at the top converge towards the bottom of the tank, while a stable preliminary clean isolation layer is constructed in the middle of the storage chamber, preventing cross-diffusion of impurities between the top and bottom. The second stream of clean material is delivered to the overflow return plate at the top of the storage chamber through the second bypass pipeline. The clean liquid overflows evenly through the overflow hole of the overflow return plate, forming a continuous and stable laminar flow film along the inner wall of the storage chamber, constructing a stable clean liquid coverage layer from top to bottom within the storage chamber. The outlet of the finished product tank is fixedly located in the upper area corresponding to this clean liquid coverage layer. After the closed-loop purification circuit has been running continuously for 4 hours, the material in the tank is sampled and tested. The test results are as follows: the content of single metal impurities is ≤0.08ppb, and there is zero detection of particulate matter larger than 0.2μm. The dissolved NO content is ≤0.08ppb. x The content is ≤0.5ppm, which fully meets the quality requirements of electronic grade nitric acid.

[0053] S6. Finished Product Packaging: Based on customer needs, the finished product packaging system is activated. Finished product materials are extracted through the outlet in the clean liquid covering area at the top of the finished product tank. After passing through a terminal high-precision filter with a precision of 0.1μm, the finished product is packaged into high-purity fluoroplastic drums or high-purity stainless steel ton containers to obtain electronic-grade nitric acid.

[0054] Example 2 In this embodiment, all components that come into direct contact with electronic-grade nitric acid are made of stainless steel lined with high-purity fluoroplastic or perfluoroplastic (PFA / PTFE), which meets the material control requirements for electronic-grade wet electronic chemicals. All static sealing structures use perfluoroether seals that are resistant to concentrated nitric acid corrosion. The connections between pipelines and equipment are made using standard flange connections in the chemical industry. The basic structures of related connections, seals, and fixed supports are common knowledge in the field and will not be described in detail in this embodiment.

[0055] This embodiment is the finished product tank with a closed-loop purification circuit used in step S4 of Embodiment 1. It is a dedicated device for realizing the closed-loop purification step of the preparation process of this invention. The specific structure is as follows: Reference Figure 2-9 The finished product tank in this embodiment includes a finished product tank body 100 with a sealed liquid storage chamber 110, and a circulating purification circuit that forms a closed loop with the finished product tank body 100. The circulating purification circuit includes a liquid extraction unit 200, a gradient filtration unit 300, and a dual-path liquid return unit 400 connected sequentially along the fluid flow direction. The three units, together with the liquid storage chamber 110 of the finished product tank body 100, constitute a continuous circulating purification channel.

[0056] The main body 100 of the finished product tank is a vertical, sealed cylindrical tank with elliptical arc-shaped heads at the top and bottom. Its storage chamber 110 has a preset rated storage level, which is 70%-85% of the total height of the storage chamber 110; in this embodiment, 80% is preferred. The side wall of the main body 100 of the finished product tank is provided with a finished product inlet 120, which is connected to the outlet pipeline of the upstream refining process. A staggered inlet method can be adopted, meaning the inlet operation and the operation of the circulating purification loop are performed at different times to avoid disturbances from the inlet interfering with the formation of the low-speed vortex and the stability of the cleanliness gradient field within the storage chamber 110; or the influence on the low-speed vortex can be reduced by adjusting the inlet speed. The upper part of the finished product tank body 100 is provided with a liquid outlet 130. The liquid outlet 130 is fixedly located in the upper area corresponding to the rated storage liquid level, specifically below the liquid surface of the rated storage liquid level and in the upper part of the total height of the liquid storage chamber 110, to ensure that the liquid outlet 130 is always within the range of the clean liquid covering layer subsequently constructed, thus ensuring the cleanliness stability of the outgoing material.

[0057] The liquid extraction unit 200 includes a circulation pump 210 and an annular liquid extraction pipe 220. The circulation pump 210 is a fluoropolymer-lined PFA magnetic pump, which is located outside the main body 100 of the finished product tank. Its flow parts are covered with perfluoropolymer material, and no metal material comes into direct contact with nitric acid, which completely avoids secondary pollution caused by the corrosion and leaching of impurities from the pump body. At the same time, the magnetically driven, non-dynamic seal design eliminates the risk of nitric acid leakage.

[0058] An annular liquid extraction pipe 220 is located at the bottom of the storage chamber 110. Its outlet pipe is sealed and led out along the bottom of the finished product tank body 100 and connected to the inlet of the circulation pump 210. It is used to uniformly extract the liquid containing impurities from the bottom of the storage chamber 110. Specifically, the annular liquid extraction pipe 220 includes two annular liquid extraction unit pipes 221 and a main drainage pipe 222. In this embodiment, two coaxial liquid extraction unit pipes 221 are provided. Both layers of liquid extraction unit pipes 221 are set to fit the arc-shaped edge of the bottom of the storage chamber 110 and are distributed vertically at intervals along the height direction of the storage chamber 110. The lower liquid extraction unit pipe 221 is set to fit the bottom surface of the storage chamber 110. The distance between the upper and lower liquid extraction unit pipes 221 is 50-200mm, which is adapted to the stratified distribution characteristics of impurities settling at the bottom of the tank. The main drainage pipe 222 is arranged along the axial direction of the liquid storage chamber 110. Its upper end is connected to all liquid extraction unit pipes 221 in sequence, and its lower end is sealed and led out along the bottom of the finished product tank body 100 and connected to the inlet of the circulation pump 210 through a flange.

[0059] Furthermore, the liquid extraction unit tube 221 has a plurality of liquid extraction holes 223 evenly distributed circumferentially along its inner annular wall. These holes 223 are radially distributed along the storage cavity 110 and are inclined towards the center of the bottom of the storage cavity 110, with an inclination angle α ranging from 15° to 45° downwards from the horizontal direction; in this embodiment, 18° is preferred. This structure enables the extraction of impurities at different heights and in the entire circumference of the tank bottom, completely eliminating dead zones in impurity settling. Simultaneously, during liquid extraction, a directional flow towards the center is formed, preventing disturbance of settled impurities and their re-suspension and diffusion, thus ensuring the stability and efficiency of impurity collection.

[0060] The gradient filtration unit 300 is disposed outside the main body 100 of the finished product tank and includes at least two stages of filtration devices coaxially nested. In this embodiment, two stages of coaxially nested filtration devices are used, namely a pre-filtration stage 310 and a post-high-precision filtration stage 320. The filter element of the pre-filtration stage 310 has a filter element precision of 5-10μm and is used to remove large-sized particles and crystalline impurities. The filter element of the post-high-precision filtration stage 320 has a filter element precision of 0.1-0.2μm and is used to remove submicron-sized particles, achieving gradient filtration with progressively matched precision. The inlet of the pre-filtration stage 310 is connected to the outlet of the circulation pump 210 through a pipeline, and the outlet of the post-high-precision filtration stage 320 is connected to the dual-path return unit 400 through a main pipeline.

[0061] Furthermore, pressure sensors are installed at both the inlet and outlet of the gradient filtration unit 300. The two pressure sensors constitute a differential pressure monitoring component 330. The differential pressure monitoring component 330 is electrically connected to the field control system and can collect the differential pressure data at the inlet and outlet of the filtration device in real time. Based on the changes in differential pressure, the filter element clogging status can be determined, which facilitates timely maintenance and replacement by operation and maintenance personnel and ensures the long-term stable operation of the purification system.

[0062] The dual-path return unit 400 includes a spiral water distribution branch pipe 410 and an overflow return plate 420, which are respectively connected to the outlet of the gradient filtration unit 300. The main outlet pipeline of the gradient filtration unit 300 is divided into two paths through a three-way interface 430. One path is connected to the spiral water distribution branch pipe 410 through a first bypass pipe 431, and the other path is sealed and passed down from the top of the finished product tank body 100 through a second bypass pipe 432 to the liquid storage chamber 110 and connected to the overflow return plate 420. Each of the two bypass pipes is equipped with an independent flow regulating valve 433, which can flexibly adjust the flow ratio of the two return paths according to the working conditions in the liquid storage chamber 110.

[0063] The spiral water distribution branch pipe 410 is located near the middle of the liquid storage chamber 110, specifically at the middle of the rated storage liquid level and below the liquid outlet 130. It is spirally fixed to the inner wall of the liquid storage chamber 110. The spiral water distribution branch pipe 410 has 4-6 spiral turns, preferably 6 turns in this embodiment. Several return holes 411 are evenly opened on the inner wall of the spiral water distribution branch pipe 410 along the spiral direction. The return holes 411 are radially distributed along the liquid storage chamber 110 and are inclined towards the center of the bottom of the liquid storage chamber 110. The inclination angle β is 10°-30° downward with respect to the horizontal direction, preferably 16° in this embodiment.

[0064] This structure allows the filtered clean liquid to form a uniform, low-speed swirling flow in the entire circumference of the storage chamber 110 within the coverage area of ​​the spiral water distribution branch pipe 410. On the one hand, it actively guides suspended impurities in the middle and upper parts of the storage chamber 110 to converge towards the bottom, achieving efficient collection of impurities from the entire tank in conjunction with the annular liquid collection pipe 220 and eliminating blind spots in liquid collection. On the other hand, it constructs a stable preliminary clean isolation layer in the middle of the storage chamber 110, blocking the cross-diffusion of impurities between the top and bottom, and providing a foundation for subsequent cleanliness gradient control.

[0065] The overflow return plate 420 is annular and coaxially fixed at the top of the finished product tank body 100, above the rated storage liquid level. Its outer periphery forms a uniform annular gap with the side wall of the storage chamber 110. Specifically, the overflow return plate 420 includes an outer plate 421 with an annular overflow groove 422, an inner plate 423 coaxially disposed in the overflow groove 422 and with an annular buffer groove 424, and a columnar return pipe 425 located at the center of the overflow groove 422.

[0066] The top of the return pipe 425 protrudes beyond the highest point of the outer disk 421, and a return groove 426 extending to the bottom of the outer disk 421 is formed through the return pipe 425 along its axial direction. The second bypass pipe 432 is sealed and inserted into the top of the storage chamber 110 and extends to the position where it is inserted into the return groove 426. The bottom of the inner disk 423 is integrally formed and fixed with the bottom of the outer disk 421. A plurality of return channels 427 connecting the return groove 426 and the overflow groove 422 are evenly formed circumferentially between the bottom of the inner disk 423 and the bottom of the outer disk 421. A plurality of overflow holes 428 connecting the overflow groove 422 are formed around the outer side wall of the outer disk 421. The overflow holes 428 are elongated and have a waist-shaped cross-section. The overflow holes 428 are horizontally distributed along the outer side wall of the outer disk 421.

[0067] Furthermore, the height h3 of the outer sidewall of the buffer tank 424 is lower than the height h2 of the outer sidewall of the overflow tank 422, but higher than the setting height of the overflow hole 428, forming a two-stage overflow buffer structure 429. This effectively suppresses fluctuations in return liquid pressure and ensures the uniformity and continuity of the overflow. At the same time, the opening height h1 of the return pipe 425 is higher than the height h2 of the outer sidewall of the overflow tank 422. Relying on the liquid level difference and hydraulic connection principle, a stable pressure is continuously applied to the overflow tank 422, allowing the returned clean liquid to flow more smoothly along the overflow hole 428 to the top inner sidewall of the storage chamber 110, forming a uniform and continuous laminar liquid film. When the pressure is excessive, the liquid level in the overflow tank 422 will continue to rise, and the excess clean liquid can flow back to the buffer tank 424 for buffering and temporary storage through the two-stage overflow structure formed by the sidewall of the buffer tank 424, further improving the stability of the return liquid. The bottom of the return liquid tank 426 is detachably connected to a buffer structure 429. The top surface of the buffer structure 429 is provided with a continuous arc-shaped guide surface that smoothly transitions towards its periphery and bottom. This can smoothly guide and redirect the clean liquid entering the return liquid tank 426, avoid direct impact of fluid to generate turbulence and bubbles, and ensure the construction effect of the laminar flow film.

[0068] In this embodiment, in order to facilitate the positioning and installation of the buffer structure 429 and prevent its displacement, a protruding positioning shaft is integrally formed at the center of the inner bottom of the return liquid tank 426, and a corresponding positioning hole is formed at the bottom of the buffer structure 429 to fit and match the positioning shaft. Through the precise fitting of the positioning shaft and the positioning hole, the buffer structure 429 can be quickly positioned and stably installed, avoiding its displacement under the impact of the return liquid.

[0069] This structure allows the filtered clean liquid to first enter the central return tank 426, and after being guided and buffered by the buffer structure 429, it enters the overflow tank 422 evenly through the return channel 427, and then overflows evenly through the overflow holes 428 distributed circumferentially on the outer wall of the outer disk 421, forming a continuous and stable laminar flow liquid film along the inner wall of the finished product tank body 100. Within the rated storage liquid level in the storage chamber 110, a stable clean liquid covering layer is constructed from top to bottom, completely avoiding direct mixing of clean liquid and untreated dirty liquid. At the same time, the continuous laminar flow liquid film can form a continuous circumferential wetting of the liquid level fluctuation area on the inner wall of the storage chamber 110, eliminating the drying environment of the tank wall, avoiding the generation of particulate impurities from nitric acid drying crystallization from the source, and blocking the continuous pollution risk caused by tank wall crystallization.

[0070] The finished product tank for storing electronic-grade nitric acid in this embodiment, combined with... Figure 8 Its working process is as follows: First, the electronic-grade nitric acid product after aeration and cooling is fed into the storage chamber 110 through the product inlet 120. The liquid is fed until the rated storage level is reached and then the liquid feeding stops. Throughout the liquid feeding process, the circulation purification loop is in a stopped state to avoid the liquid feeding disturbance from interfering with the flow field stability and the construction of the gradient clean layer in the subsequent circulation purification process.

[0071] Secondly, after the liquid is fed in, the circulation purification loop is started. The circulation pump 210 draws out the nitric acid material containing impurities from the bottom dirty liquid layer d at the bottom of the storage chamber 110 through the annular liquid collection pipe 220 and delivers it to the gradient filtration unit 300. The material first passes through the pre-filtration stage 310 to remove large particles and crystal impurities, and then passes through the post-high-precision filtration stage 320 to remove submicron particles. The clean nitric acid material after gradient purification is divided into two paths through the three-way interface 430 and sent to the spiral water distribution branch pipe 410 and the overflow return liquid tray 420 respectively, providing a continuous and stable clean liquid source for the construction of the gradient clean layer.

[0072] Subsequently, a stream of clean material overflows evenly through the overflow hole 428 of the overflow return plate 420, flowing from top to bottom along the inner wall of the storage chamber 110, first forming a continuous laminar flow liquid film layer a. This liquid film layer can continuously wet the liquid level fluctuation area of ​​the inner wall of the storage chamber 110 in the entire circumference, eliminating the drying environment of the tank wall and avoiding the generation of particulate impurities from nitric acid drying crystallization from the source. The clean liquid of the continuous laminar flow liquid film layer a continuously flows into the rated storage liquid level area at the top of the storage chamber 110, forming a stable clean liquid covering layer b at the top of the storage chamber 110 from top to bottom, completely avoiding direct mixing of clean liquid and untreated dirty liquid. Another stream of clean material is directionally ejected through the return hole 411 of the spiral water distribution branch pipe 410, forming a low-speed swirling flow that evenly covers the entire circumference and faces the bottom of the tank in the middle of the storage chamber 110. Within this low-speed swirling flow area, a preliminary clean isolation layer c is constructed. This isolation layer prevents cross-diffusion of impurities between the upper clean liquid covering layer b and the lower region. Simultaneously, the low-speed swirling flow actively guides suspended impurities in the middle and upper parts of the storage chamber 110 towards the bottom of the tank, ultimately settling them into the bottom dirty liquid layer d at the very bottom of the storage chamber 110. Through this structure, the continuous laminar flow liquid film layer a, the clean liquid covering layer b, the preliminary clean isolation layer c, and the bottom dirty liquid layer d form a four-layer gradient structure from top to bottom within the storage chamber 110, achieving gradient control of the overall tank cleanliness and preventing cross-diffusion and vicious cycles of impurities.

[0073] Finally, the circulating purification loop continues to operate, maintaining the stability of the four-layer gradient clean structure from top to bottom within the storage chamber 110. Impurities in the bottom dirty liquid layer d are continuously extracted and purified. The purified clean liquid is continuously replenished to the continuous laminar flow film layer a and the preliminary clean isolation layer c, forming a fully closed-loop continuous purification system. The differential pressure monitoring component 330 monitors the inlet and outlet pressure difference of the gradient filtration unit 300 in real time to determine the filter element clogging status, facilitating timely maintenance and replacement, and ensuring long-term stable purification performance. During shipment, the finished product is taken from the discharge port 130, which is fixedly located in the corresponding area of ​​the clean liquid covering layer b, ensuring that the cleanliness of the shipped materials always meets the stringent requirements of high-end semiconductor processes.

[0074] This embodiment solves the core problems of existing electronic-grade nitric acid finished product tanks, such as blind spots in liquid extraction, easy mixing of return liquid, easy clogging of filter elements, and easy drying and crystallization of tank walls, by forming a closed-loop purification circuit consisting of liquid extraction unit 200, gradient filtration unit 300, and dual-path liquid return unit 400. It breaks the vicious cycle of impurity accumulation, accelerated corrosion, and nitric acid decomposition, and achieves continuous, stable, and high-precision purification of electronic-grade nitric acid. It takes into account the safety of equipment operation, purification efficiency, and ease of operation and maintenance, and is fully adapted to the storage and management requirements of high-end process electronic-grade nitric acid.

[0075] Example 3 This embodiment describes the condenser used in step S3 of Embodiment 1 for the preparation and processing of electronic-grade nitric acid. It is a dedicated device for implementing the condensation and gas-liquid separation steps of the preparation process of this invention. In this embodiment, all components in direct contact with the nitric acid medium are made of stainless steel lined with high-purity fluoroplastic or perfluoroplastic (PFA / PTFE), meeting the material control requirements for electronic-grade wet electronic chemicals. The basic structures for related connections, seals, and fixed supports are all common knowledge in the art and will not be described in detail in this embodiment. The specific structure is as follows: refer to Figure 10-16 The condenser for the preparation and processing of electronic-grade nitric acid disclosed in this embodiment includes a vertical shell 500. The vertical shell 500 is a hollow cylindrical shell. An installation cavity extending along its axial direction is formed inside the vertical shell 500. The upper and lower sides of the installation cavity are sealed and fixed by an upper tube sheet 501 and a lower tube sheet 502, respectively. A plurality of heat exchange tube bundles 510 extending along the axial direction of the vertical shell 500 are fixedly connected between the center of the upper tube sheet 501 and the lower tube sheet 502. The outer side of the heat exchange tube bundles 510 and the inner side of the vertical shell 500, as well as the upper tube sheet 501 and the lower tube sheet 502, form a closed shell-side flow channel 520.

[0076] The vertical shell 500 is sealed and fixed at both ends along the axial direction with an upper tube box 532 and a lower tube box 535 respectively: the upper end of the upper tube sheet 501 is directly and sealed to a hemispherical upper end cap 531, and the internal space of the upper end cap 531 and the upper end face of the upper tube sheet 501 enclose the upper tube box 532; the lower end of the lower tube sheet 502 extends downward along its axial direction to form an annular cylindrical wall 533, the outer diameter of the annular cylindrical wall 533 is smaller than the outer diameter of the vertical shell 500, and the radial coverage of the annular cylindrical wall 533 at least includes the vertical projection area of ​​all heat exchange tube bundles 510, and the internal space of the annular cylindrical wall 533 forms the lower tube box 535. The upper tube box 532, the tube channels of the heat exchange tube bundles 510, and the lower tube box 535 are connected in sequence to form a tube-side flow channel 530 for cooling water flow.

[0077] The upper end cap 531 and the lower end cap 534 are respectively provided with corresponding flange interfaces 536 for introducing and drawing out cooling water. In this embodiment, the cooling water is introduced into the tube flow channel 530 from the flange interface 536 of the lower end cap 534, and after heat exchange through the heat exchange tube bundle 510, it is drawn out from the flange interface 536 of the upper end cap 531 to realize counter-current heat exchange and enhance the condensation heat transfer effect.

[0078] The top of the vertical housing 500 is provided with an air inlet pipe 504 that communicates with the shell-side flow channel 520. The top of the shell-side flow channel 520 is provided with an annular flow equalization shroud 505 that is circumferentially distributed around its inner side. The inner side of the annular flow equalization shroud 505 forms a flow equalization cavity 506 that communicates with the air inlet pipe 504. The flow equalization cavity 506 has a plurality of flow equalization holes 507 that communicate with the shell-side flow channel 520 on one side wall near the central axis of the shell-side flow channel 520. The plurality of flow equalization holes 507 are evenly distributed circumferentially along the side wall of the flow equalization cavity 506. The shell-side flow channel 520 is provided with a continuous baffle plate 540 extending along its axial direction. The baffle plate 540 divides the shell-side flow channel 520 into a continuous spiral heat exchange channel 541. The gaseous nitric acid azeotrope enters the flow equalization chamber 506 through the inlet pipe 504 and then enters the heat exchange channel 541, where it completes heat exchange and condensation with the cooling water in the heat exchange tube bundle 510 along the spiral path.

[0079] An integrated gas-liquid separation module 550 is provided on the outer periphery of the lower tube box 535. The gas-liquid separation module 550 includes a cyclone separation chamber 551 coaxially sleeved on the outer periphery of the annular cylindrical wall 533, a non-condensable gas buffer chamber 552 coaxially sleeved on the outer periphery of the cyclone separation chamber 551, and a condensate collection tank 554 located at the bottom of the cyclone separation chamber 551 and the non-condensable gas buffer chamber 552. The axial extension distance of the cyclone separation chamber 551 and the non-condensable gas buffer chamber 552 along the vertical shell 500 is less than the axial extension length of the annular cylindrical wall 533. The condensate collection tank 554 is coaxially sleeved on the lower outer side of the annular cylindrical wall 533 and is located exactly at the common bottom of the cyclone separation chamber 551 and the non-condensable gas buffer chamber 552. The outer diameters of the non-condensable gas buffer chamber 552 and the condensate collection tank 554 are consistent and the same as the outer diameter of the vertical shell 500, so that the condenser as a whole forms a regular cylindrical structure. The lower end of the common condensate collection tank 554 and the annular cylindrical wall 533 is sealed with another hemispherical lower end cap 534. The internal area of ​​the lower end cap 534 is only connected to the interior of the annular cylindrical wall 533 and is not connected to the condensate collection tank 554 or the cyclone separation chamber 551, thus ensuring complete isolation between the tube side flow channel 530 and the shell side and separation module.

[0080] The cyclone separation chamber 551 is provided with a continuous spiral guide plate 557 extending along its axial direction. The guide plate 557 divides the cyclone separation chamber 551 into a continuous spiral separation channel 558. The pitch of the guide plate 557 decreases linearly downward along its axial direction. Specifically, the ratio of its first pitch to the inner diameter of the shell-side channel 520 is 1.2:1, and the ratio of its last pitch to the inner diameter of the shell-side channel 520 is 0.6:1. The plate surface of the guide plate 557 is close to the outer wall of the non-condensable gas buffer chamber 552 along the separation channel 558, extends radially inward toward the cyclone separation chamber 551 and is inclined downward at an angle α. The design range of α is 3-5°. In this embodiment, α is 4°. A guide gap 559 is formed between the inner side of the plate surface of the guide plate 557 and the inner wall of the cyclone separation chamber 551 to guide the gas-liquid mixture to flow stably along the spiral path and enhance the centrifugal separation effect. The bottom of the lower tube sheet 502 is provided with a tangential feed port 503. The top inlet of the separation channel 558 is tangentially connected to the bottom outlet of the heat exchange channel 541 through the tangential feed port 503, so that the gas-liquid mixture that has completed heat exchange in the heat exchange channel 541 enters the separation channel 558 tangentially, and the swirling kinetic energy generated during the heat exchange process is used to complete the swirling gas-liquid separation.

[0081] A plurality of air guide holes 560 are provided on the wall surface of the separation channel 558 near the non-condensable gas buffer chamber 552. The air guide holes 560 are distributed sequentially along the spiral path of the separation channel 558. The air guide holes 560 are located on the upper side of the side wall surface of the separation channel 558 relative to the surface of the guide plate 557, that is, at the upper end of the side wall surface of a single lead area of ​​the separation channel 558. The air guide holes 560 penetrate the outer wall of the swirling separation chamber 551 tangentially along the separation channel 558. The swirling separation chamber 551 is connected to the non-condensable gas buffer chamber 552 through the air guide holes 560. A return hole 561 is provided through the bottom of the outer wall surface where the air guide holes 560 are located. The outer side of the non-condensable gas buffer chamber 552 is connected to a non-condensable gas outlet pipe 553 for discharging the separated non-condensable gas. The bottom of the cyclone separation chamber 551 is provided with several liquid collection pipes 562 that communicate with the condensate collection tank 554. The top of the liquid collection pipes 562 is provided with a funnel-shaped flare (not shown in the figure), and the flare is located below the bottom end face of the cyclone separation chamber 551. The several liquid collection pipes 562 are evenly arranged circumferentially along the bottom of the cyclone separation chamber 551, and the bottom of the liquid collection pipes 562 extends below the lowest designed liquid level of the condensate collection tank 554, forming a liquid seal structure to prevent gas phase from entering the condensate collection tank 554. The bottom of the condensate collection tank 554 is connected to a condensate outlet pipe 555 for discharging the finished condensate to the subsequent aeration process.

[0082] The inner wall of the vertical shell 500 is circumferentially arranged with a pre-collection pipe 570. The pre-collection pipes 570 are evenly distributed around the axial direction of the vertical shell 500 and avoid the locations of the non-condensable gas outlet pipe 553 and the condensate outlet pipe 555. In this embodiment, the inlet pipe 504, the non-condensable gas outlet pipe 553, and the condensate outlet pipe 555 are arranged in the same vertical plane to facilitate the avoidance and arrangement of the pre-collection pipes 570. The pre-collection pipes 570 penetrate all the plates of the baffle plate 540 along the same vertical line, with their upper ends extending to the bottom of the annular flow equalization hood 505 and their lower ends extending above the highest designed liquid level of the condensate collection tank 554.

[0083] The outer edge of the baffle 540 has a continuous liquid collecting groove 542 along the entire spiral path. The pre-collecting pipe 570 is longitudinally arranged through the liquid collecting groove 542. Liquid collecting holes 571 are provided at the intersections of the pre-collecting pipe 570 and the surface of the baffle 540. The liquid collecting holes 571 are located within the coverage area of ​​the liquid collecting groove 542. The liquid collecting holes 571 are evenly distributed along the circumference of the pre-collecting pipe 570, and the bottom of the liquid collecting holes 571 is flush with the bottom of the liquid collecting groove 542. The liquid collecting groove 542 is located along the shell-side flow channel 520. The baffle plate 540 has symmetrically inclined guide surfaces 543 on both radial sides. The two guide surfaces 543 are arranged along the spiral path of the baffle plate 540. The bottom width of the liquid collection groove 542 is adapted to the outer diameter of the pre-collection pipe 570, so that the bottom of the liquid collection hole 571 is connected to the bottom of the guide surface 543 at the corresponding position. The condensate on the surface of the baffle plate 540 can be collected into the liquid collection groove 542 through the guide surface 543 and enter the pre-collection pipe 570 in real time through the liquid collection hole 571, thus completely avoiding the problem of liquid accumulation on the baffle plate 540 and condensate backflow.

[0084] The downstream of the condensate outlet pipe 555 is connected to a Venturi tube 580. The Venturi tube 580 includes a converging section 581, a throat section 582, and a diverging section 583 connected in sequence. The outlet end of the condensate outlet pipe 555 is connected to the inlet of the converging section 581 of the Venturi tube 580, and the outlet of the diverging section 583 of the Venturi tube 580 is connected to the aeration conveying pipeline of the subsequent process. The throat section 582 of the Venturi tube 580 is connected to the lower side wall of the pre-collection pipe 570 through the ejector pipe 590, which is used to provide negative pressure suction power for the pre-collection pipe 570 through the flow of condensate.

[0085] The ejector conduit 590 includes a main ejector pipe 591, an annular branch pipe 592, and ejector unit pipes 593. The annular branch pipe 592 is coaxially arranged around the outer periphery of the condensate collection tank 554. The annular branch pipe 592 is connected to the throat section 582 of the Venturi tube 580 through the main ejector pipe 591. The number of ejector unit pipes 593 is the same as the number of pre-collection pipes 570. The inner annular side of the annular branch pipe 592 is connected to the lower end sidewall of each pre-collection pipe 570 through the ejector unit pipes 593. The main ejector pipe 591 is equipped with a one-way valve (not shown in the figure). The one-way valve is directed from the pre-collection pipe 570 to the throat section 582 of the Venturi tube 580, which can completely avoid the problem of pre-collection pipe 570 suction failure caused by condensate backflow and ensure long-term stable operation of negative pressure suction drainage.

[0086] The working process of this embodiment is as follows: The gaseous nitric acid azeotrope produced at the top of the distillation column enters the shell-side flow channel 520 through the inlet pipe 504. After being evenly distributed by the annular flow equalization hood 505, it enters the heat exchange flow channel 541 and flows along the path guided by the baffle plate 540. It completes countercurrent heat exchange with the cooling water in the heat exchange tube bundle 510, and the steam gradually condenses to form liquid nitric acid. During the condensation process, the condensate on the outer wall of the heat exchange tube bundle 510 is thrown towards the outer inner wall of the vertical shell 500 away from the center under the action of the centrifugal force of the steam swirl and its own gravity. It then converges at the baffle plate through the guide surface 543. The liquid enters the pre-collection tube 570 through the collection hole 571 in the collection groove 542 of plate 540. When the condensate flows through the condensate outlet pipe 555, it is accelerated in the tapering section 581 of the venturi tube 580 and a negative pressure is formed in the throat section 582. The ejector pipe 590 provides a continuous negative pressure suction force to the pre-collection tube 570, which quickly draws the condensate in the pre-collection tube 570 away from the heat exchange area and sends it directly into the condensate collection tank 554. This avoids the formation of a continuous thick liquid film on the outer wall of the heat exchange tube bundle 510, reduces the additional thermal resistance, and improves the heat exchange efficiency.

[0087] The gas-liquid mixture, after heat exchange, enters tangentially into the separation channel 558 of the cyclone separation chamber 551 through the tangential feed inlet 503. Utilizing the swirling kinetic energy generated during the heat exchange process, and guided by the guide plates 557 with gradually decreasing pitch, the cyclone centrifugal separation effect is continuously enhanced. The liquid phase is thrown against the inner wall of the cyclone separation chamber 551 and flows into the condensate collection tank 554 through the liquid collection pipe 562. The separated non-condensable gas enters the non-condensable gas buffer chamber 552 through the gas guide hole 560 and is finally discharged through the non-condensable gas outlet pipe 553. The trace amount of condensate entrained in the non-condensable gas is returned to the condensate collection tank 554 through the return hole 561, avoiding product yield loss. The synergistic design of pre-collection and drainage with cyclone separation significantly reduces the liquid load in the separation zone, fundamentally avoiding flooding and droplet entrainment problems, ensuring the purity and cleanliness of electronic-grade nitric acid, and providing materials with low impurity background for subsequent processes.

[0088] Example 4 refer to Figure 17 The difference between this embodiment and Embodiment 1 lies in the arrangement of the condensate outlet pipe 555 and the venturi tube 580: One end of the condensate outlet pipe 555 is sealed and connected to the bottom of the condensate collection tank 554. The other end of the condensate outlet pipe 555 extends out of the outer side of the gas-liquid separation module 550 and continues to extend downward to form a lower extension section 556. The lower extension section 556 then connects to the inlet of the tapered section 581 of the Venturi tube 580, so that the overall installation position of the Venturi tube 580 is lower than the lowest position of the condensate collection tank 554. A stable static pressure difference is formed between the condensate collection tank 554 and the Venturi tube 580, which further helps the smooth discharge of condensate. At the same time, it can enhance the negative pressure suction effect of the Venturi tube 580 and ensure the stability of the discharge of the pre-collection pipe 570.

[0089] It should be noted that any reference signs placed between parentheses in the claims should not be construed as limiting the claims. The word "comprising" does not exclude the presence of components or steps not listed in the claims. The word "a" or "an" preceding a component does not exclude the presence of a plurality of such components. The invention can be implemented by means of hardware comprising several different components and by means of a suitably programmed computer. In a unit claim enumerating several means, several of these means may be embodied by the same item of hardware. The use of the words first, second, and third, etc., does not indicate any order. These words can be interpreted as names.

[0090] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0091] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0092] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. A process for preparing electronic-grade nitric acid, characterized in that, Includes the following steps: S1. Nitric acid raw material is transported from the raw material tank to the raw material buffer tank; S2. Nitric acid raw material is transported from the raw material buffer tank to the distillation process. After preheating and azeotropic distillation in a reboiler, high-purity nitric acid gaseous azeotrope is obtained. S3. The gaseous azeotrope obtained from distillation is condensed and then enters an aeration tower. Clean, oil-free compressed air is introduced to remove dissolved NO from the product. x The aerated product is then cooled to below 40°C. S4. The cooled electronic-grade nitric acid is then sent to the finished product tank for storage. S6. After high-precision filtration, the product in the finished product tank is packaged into the corresponding packaging materials according to requirements to obtain electronic-grade nitric acid finished product; The finished product tank used in step S4 is equipped with a closed-loop circulation purification circuit. The circulation purification circuit includes a liquid extraction unit, a gradient filtration unit, and a dual-path liquid return unit that are connected in sequence and form a closed loop with the liquid storage chamber of the finished product tank. The preparation process further includes a step performed between step S4 and step S6: S5. Start the circulating purification circuit to continuously circulate and purify the nitric acid material in the storage chamber, specifically including: S51. The impurity-containing liquid at the bottom of the storage chamber is uniformly extracted by the annular liquid extraction pipe located at the bottom of the storage chamber in the liquid extraction unit, in conjunction with the circulation pump. S52. The extracted liquid containing impurities is sent to a gradient filtration unit, and the gradient purification is completed through at least two coaxially nested filtration devices. S53. The purified clean liquid after gradient purification is sent to the dual-path return unit and divided into two paths to the storage chamber: the first path is through the spiral water distribution branch pipe in the middle of the storage chamber, which creates a low-speed swirling flow towards the bottom of the tank, guiding suspended impurities to gather at the bottom and form a preliminary clean isolation layer; the second path is through the overflow return plate at the top of the storage chamber, which makes the clean liquid form a continuous laminar flow film along the inner wall of the storage chamber, and builds a clean liquid covering layer from top to bottom in the storage chamber, realizing gradient control of cleanliness in the storage chamber.

2. The preparation process of electronic-grade nitric acid according to claim 1, characterized in that: In step S51, the annular liquid collection tube includes at least two annular liquid collection unit tubes and a main drainage tube. The liquid collection unit tubes are arranged to fit the bottom edge of the liquid storage cavity and adjacent liquid collection unit tubes are distributed vertically at intervals along the height direction of the liquid storage cavity. The main drainage tube connects all the liquid collection unit tubes in sequence and leads out along the bottom of the finished product tank to the circulation pump. The liquid extraction unit tube has several liquid extraction holes perforated through its inner annular tube wall. These extraction holes are radially distributed along the liquid storage cavity and are inclined toward the center of the bottom of the liquid storage cavity.

3. The preparation process of electronic-grade nitric acid according to claim 1, characterized in that: In step S52, the gradient filtration unit is coaxially nested with two-stage filtration devices, including a pre-filtration stage and a post-high-precision filtration stage, to complete step-by-step gradient purification. Pressure sensors are installed at both the inlet and outlet of the gradient filtration unit. The two pressure sensors constitute a differential pressure monitoring component to determine the filter element blockage of the filtration device based on the differential pressure.

4. The preparation process of electronic-grade nitric acid according to claim 1, characterized in that: In step S53, the spiral water distribution branch pipe is spirally attached to the inner wall of the liquid storage cavity, and several return holes are opened through the pipe wall around the inner side of the spiral water distribution branch pipe. The several return holes are distributed radially along the liquid storage cavity and are inclined towards the center of the bottom of the liquid storage cavity. The overflow return tray is annular, with a gap between its outer periphery and the side wall of the storage chamber. The discharge port of the finished product tank is fixedly located in the upper area corresponding to the clean liquid covering layer.

5. The preparation process of electronic-grade nitric acid according to claim 4, characterized in that: The overflow return plate includes an outer plate with an annular overflow groove, an inner plate coaxially disposed within the overflow groove and having an annular buffer groove, and a return pipe located at the center of the overflow groove and in a columnar shape. The top of the return pipe protrudes from the highest position of the outer plate, and a return groove extending to the bottom of the inner plate is formed through the return pipe along its axial direction. Several return channels connecting the return groove and the overflow groove are provided between the bottom of the inner plate and the bottom of the outer plate. Several overflow holes connecting the overflow groove are formed around the outer side wall of the outer plate in its circumference.

6. The preparation process of electronic-grade nitric acid according to claim 5, characterized in that: The overflow hole is elongated and extends circumferentially along the outer side wall of the outer disk. The height of the outer side wall of the buffer groove is lower than the height of the outer side wall of the overflow groove but higher than the setting height of the overflow hole. The bottom of the return tank is detachably connected to a buffer structure, and the top surface of the buffer structure is provided with a continuous arc-shaped guide surface that gradually transitions towards its periphery and bottom.

7. The preparation process of electronic-grade nitric acid according to claim 1, characterized in that: The circulating pump used in step S51 is a fluoropolymer-lined PFA magnetic pump.

8. The preparation process of electronic-grade nitric acid according to claim 3, characterized in that: The filter element of the pre-filter stage has a filter element precision of 5-10μm, and the filter element of the post-filter high-precision stage has a filter element precision of 0.1-0.2μm; the liquid inlet is inclined downward at 15°-45° to the horizontal direction; the liquid return outlet is inclined downward at 10°-30° to the horizontal direction.

9. The preparation process of electronic-grade nitric acid according to claim 1, characterized in that: In step S3, the condensation of the gaseous azeotrope is performed using a vertical shell-and-tube condenser. The condenser includes a vertical shell, a heat exchange tube bundle, an upper tube box, and a lower tube box. The upper tube box, heat exchange tube bundle, and lower tube box are sequentially connected to form a tube-side flow channel for cooling water. A shell-side flow channel for nitric acid gaseous azeotrope is formed between the outer side of the heat exchange tube bundle and the inner side of the vertical shell. An inlet pipe communicating with the shell-side flow channel is provided at the top of the vertical shell. Continuous baffles are provided within the shell-side flow channel to divide it into continuous spiral heat exchange channels. A gas-liquid separation module is provided on the outer periphery of the lower tube box. The gas-liquid separation module includes a swirling separation chamber coaxially sleeved on the outer periphery of the lower tube box and a swirling... The separation chamber is connected to a non-condensable gas buffer chamber and a condensate collection tank located at the bottom of the cyclone separation chamber. The cyclone separation chamber is equipped with a continuous spiral guide plate, which divides the cyclone separation chamber into a continuous spiral separation channel. The bottom outlet of the heat exchange channel is tangentially connected to the top inlet of the separation channel through a tangential feed port. At least one pre-collection pipe is arranged circumferentially on the inner wall of the vertical shell. The pre-collection pipe penetrates the surface of the baffle plate axially, and liquid collection holes are opened at the intersection of the pre-collection pipe and the surface of the baffle plate. The downstream of the condensate outlet pipe at the bottom of the condensate collection tank is connected to a Venturi tube. The throat section of the Venturi tube is connected to the lower end side wall of the pre-collection pipe through an ejector pipe.

10. The preparation process of electronic-grade nitric acid according to claim 9, characterized in that: The pitch of the guide plate decreases linearly downwards along its axial direction, with the ratio of the pitch of the first section to the inner diameter of the shell-side flow channel being 1.2:1, and the ratio of the pitch of the last section to the inner diameter of the shell-side flow channel being 0.6:

1. The outer edge of the baffle plate has a continuous liquid collection groove along the entire spiral path. The pre-collection pipe passes longitudinally through the liquid collection groove, and the liquid collection hole is located within the coverage area of ​​the liquid collection groove, with its bottom flush with the bottom of the liquid collection groove. The top of the shell-side flow channel is provided with an annular flow equalization shroud that surrounds its inner side in a circumferential manner. The inner side of the annular flow equalization shroud forms a flow equalization cavity that communicates with the air inlet pipe. The sidewall of the flow equalization cavity is provided with several flow equalization holes that communicate with the shell-side flow channel.

Images