Process for preparing electronic grade nitrous oxide by ammonium nitrate method

Abstract

The application discloses an ammonium nitrate method for preparing electronic-grade nitrous oxide, and relates to the technical field of nitrous oxide preparation. The ammonium nitrate method for preparing electronic-grade nitrous oxide comprises ammonium nitrate pyrolysis, cooling, purification, drying, liquefaction and rectification. The purification utilizes a high-intensity sound field to make particles collide and agglomerate, that is, submicron droplets are immediately thrown back to the filler or the shell wall by centrifugal force after directional agglomeration driven by sound radiation force, in-situ self-trapping is realized, efficient absorption is completed in the same equipment and the same cavity, alkali mist escape is avoided, and the problems of high alkali consumption, serious alkali mist entrainment and incomplete NO2 removal in the prior art of preparing nitrous oxide by the ammonium nitrate method are solved.

Description

Technical Field

[0001] This invention relates to the field of nitrous oxide preparation technology, and particularly to the ammonium nitrate method for preparing electronic-grade nitrous oxide. Background Technology

[0002] Currently, nitrous oxide (N2O) is an important oxidant and carrier gas in semiconductor manufacturing, widely used in chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes, requiring purity levels of 5N (99.999%) or even 6N (99.9999%). Industrially, nitrous oxide is mainly produced by the thermal decomposition of ammonium nitrate. The process involves pyrolyzing an ammonium nitrate solution (containing 4-20 wt% water) at 240-260°C to produce a mixed gas containing N2O, water vapor, NH3, HNO3, NO, NO2, N2, O2, and CO2. After cooling, the gas undergoes sequential washing with water, alkali washing (usually using a packed tower), drying, compression, liquefaction, and distillation to obtain electronic-grade products.

[0003] However, the existing alkaline washing process still has the following drawbacks: Traditional packed towers, to ensure absorption efficiency, typically have a liquid-to-gas ratio as high as 8-15 L / m³, generating large amounts of wastewater containing nitrates / nitrites. Furthermore, the NO2 concentration at the outlet after a single-stage alkaline wash is usually 10-50 ppmv, far exceeding the <1 ppmv requirement for electronic grade applications, necessitating subsequent distillation or catalytic conversion, increasing cost and complexity. Simultaneously, the gas velocity in the packed tower is limited, and tiny alkaline droplets (0.5-5 μm) are easily entrained downstream by the gas flow, forming alkaline mist and causing poisoning and inactivation of the molecular sieve desiccant.

[0004] Therefore, how to improve the existing electronic-grade nitrous oxide preparation process to overcome the above-mentioned shortcomings is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a process for preparing electronic-grade nitrous oxide using the ammonium nitrate method, in order to solve the problems of high alkali consumption, severe alkali mist entrainment, and incomplete NO2 removal in the existing ammonium nitrate method for preparing nitrous oxide.

[0006] The technical problem to be solved by this invention can be achieved through the following technical solution: a process for preparing electronic-grade nitrous oxide using the ammonium nitrate method, comprising ammonium nitrate pyrolysis, cooling, purification, drying, liquefaction, and distillation, wherein the purification includes the following steps: S1: Cool the crude nitrous oxide gas obtained from the pyrolysis of ammonium nitrate to 40~60℃; S2: The cooled gas is introduced into a rotating packed bed and acoustic field coupled reactor, which includes a rotatable packed bed rotor and at least one acoustic wave generator. S3: In the reactor, the alkaline solution is sprayed from the center of the rotor and forms a liquid film and droplets under the action of centrifugal force. At the same time, the sound wave generator emits sound waves with a frequency of 8~25 kHz and a sound pressure level of not less than 150 dB, which causes the liquid film to vibrate periodically and break into uniform droplets of 0.3~1.5 μm. S4: Gas and droplets come into countercurrent or crosscurrent contact in the packing layer of the rotating packed bed. Acidic impurities are absorbed, and at the same time, droplets agglomerate and redisperse under the action of the sound field, realizing in-situ separation of alkali mist. S5: The effluent is further separated by a centrifugal demister at the top of the reactor and then enters the subsequent drying step.

[0007] Preferably, the rotational speed of the rotary packed bed rotor is 1200~2500 rpm, and the specific surface area of ​​the packing material in the packed bed is 500~2000 m² / m³.

[0008] Preferably, the alkaline solution is a NaOH or KOH solution with a mass fraction of 8% to 18%, and contains 0.01% to 0.5% surfactant to reduce the surface tension of the liquid film and promote the sound wave-induced breakage of the liquid film.

[0009] Preferably, the operating pressure of the reactor is 0.05~0.3 MPa, and the gas velocity in the empty tower is 0.5~2.5 m / s.

[0010] Preferably, the purity of the obtained nitrous oxide product is ≥99.9995%, the total metal ion content is ≤5 ppbw, and the NO2 content is ≤0.1 ppmv.

[0011] Preferably, the rotating packed bed and acoustic field coupled reactor includes: a shell, on which a gas inlet, a gas outlet, an alkali inlet, and a waste liquid outlet are provided; a rotatable rotor, which is installed inside the shell and filled with porous packing; an alkali distributor, which is located at the center of the rotor and communicates with the alkali inlet; and at least one acoustic generator, which is fixedly installed on the shell and extends into the rotor, and is connected to a power supply and control system.

[0012] Preferably, there are multiple acoustic generators, which are evenly arranged along the circumference of the rotor, with the acoustic output end of each acoustic generator facing the filler layer.

[0013] Preferably, the sound wave emission direction of the sound wave generator is at an angle of 30° to 60° with the gas flow direction to form an obliquely incident standing wave field.

[0014] Preferably, the gas inlet is located on the side of the housing, and the gas outlet is located at the center of the top of the housing; both the upper and lower sides of the gas inlet are provided with sound wave generators, and the sound wave generator on the upper side and the sound wave generator on the lower side are turned on alternately.

[0015] Preferably, a seal is provided between the rotor and the housing to prevent gas short circuit.

[0016] Compared with the prior art, the beneficial effects of this application are as follows: This invention couples the centrifugal force field of the rotating packed bed with a high-intensity sound field in space and time, enabling the four processes of alkaline solution dispersion, absorption, aggregation, and separation to be dynamically cyclically carried out within the same device, rather than being simply sequentially connected. The rotating packed bed utilizes the centrifugal force field to enhance gas-liquid mass transfer, which can reduce the amount of alkaline solution used by 40% to 50%, while also reducing alkaline mist entrainment. Meanwhile, at extremely high speeds, the rotating packed bed tears the liquid into submicron droplets of 0.1~1 μm. These droplets have very low inertia and are difficult to be completely captured by centrifugal force. Some of them still escape with the airflow, causing downstream pollution. To address this, a high-intensity sound field is used to cause the particles to collide and agglomerate. That is, after the submicron droplets undergo directional agglomeration driven by sound radiation force, they are immediately thrown back to the packing or shell wall by centrifugal force, achieving in-situ self-capture. This allows for efficient absorption within the same equipment and chamber, preventing the escape of alkali mist and solving the problems of high alkali consumption, severe alkali mist entrainment, and incomplete NO2 removal in the existing ammonium nitrate method for preparing nitrous oxide. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the rotating packed bed and acoustic field coupling reactor provided by the present invention.

[0018] Explanation of reference numerals in the attached drawings: 1. Shell; 11. Gas inlet; 12. Gas outlet; 13. Alkali inlet; 14. Waste liquid outlet; 2. Rotor; 21. Shaft; 3. Alkali distributor; 4. Acoustic generator. Detailed Implementation

[0019] The present application will be further described below with reference to specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0020] In the description of this application, it should be noted that directional terms such as "center," "lateral," "longitudinal," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. They should not be construed as limiting the specific scope of protection of this application. The terms "first," "second," etc., in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. The terms "comprising" and "having," and any variations thereof, in the specification and claims of this application, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or devices.

[0021] Reference Figure 1 One embodiment of this application provides a process for preparing electronic-grade nitrous oxide using the ammonium nitrate method, including ammonium nitrate pyrolysis, cooling, purification, drying, liquefaction, and distillation. Except for the purification step, all steps adopt existing technologies, which will not be described in detail in this application.

[0022] Purification includes the following steps: S1: Cool the crude nitrous oxide gas obtained from the pyrolysis of ammonium nitrate to 40~60℃; S2: The cooled gas is introduced into a rotating packed bed and acoustic field coupled reactor, which includes a rotatable packed bed rotor 2 and at least one acoustic wave generator 4. S3: In the reactor, the alkaline solution is sprayed from the center of rotor 2 and forms a liquid film and droplets under the action of centrifugal force. At the same time, the sound wave generator 4 emits sound waves with a frequency of 8~25 kHz and a sound pressure level of not less than 150 dB, causing the liquid film to vibrate periodically and break into uniform droplets of 0.3~1.5 μm. S4: Gas and droplets come into countercurrent or crosscurrent contact in the packing layer of the rotating packed bed. Acidic impurities are absorbed, and at the same time, droplets agglomerate and redisperse under the action of the sound field, realizing in-situ separation of alkali mist. S5: The effluent is further separated by a centrifugal demister at the top of the reactor and then enters the subsequent drying step.

[0023] Working Principle: By coupling the centrifugal force field of the rotating packed bed with a high-intensity acoustic field in space and time, the four processes of alkali dispersion, absorption, agglomeration, and separation are dynamically cyclical within the same device, rather than being simply sequentially connected. The rotating packed bed utilizes the centrifugal force field to enhance gas-liquid mass transfer, reducing alkali consumption by 40%–50% and minimizing alkali mist entrainment. Simultaneously, at extremely high speeds, the rotating packed bed tears the liquid into submicron droplets of 0.1–1 μm. These droplets have very low inertia and are difficult to completely capture by centrifugal force; some still escape with the airflow, causing downstream pollution. To address this, a high-intensity acoustic field is used to cause particle collision and agglomeration. Submicron droplets undergo directional agglomeration under the drive of acoustic radiation force and are immediately thrown back to the packing or shell wall by centrifugal force, achieving in-situ self-capture. This allows for efficient absorption within the same device and chamber, preventing alkali mist escape and solving the problems of high alkali consumption, severe alkali mist entrainment, and incomplete NO2 removal in the existing ammonium nitrate method for nitrous oxide preparation.

[0024] It should be noted that adjusting parameters such as rotation speed (1200~2500 rpm), acoustic frequency (8~25 kHz), and alkali concentration (8%~18%) can achieve similar effects, but the optimal range is: rotation speed 1500~2000 rpm, frequency 12~20 kHz, and alkali concentration 10%~15%. The specific surface area of ​​the packing material in the packed bed is preferably 500~2000 m² / m³. The alkali solution is preferably a NaOH or KOH solution with a mass fraction of 8%~18%, containing 0.01%~0.5% surfactant to reduce the surface tension of the liquid film and promote acoustically induced liquid film breakage. The surfactant is a prior art product, such as sodium dodecyl sulfate.

[0025] The purity of the nitrous oxide product obtained through the above process is ≥99.9995%, the total metal ion content is ≤5 ppbw, and the NO2 content is ≤0.1 ppmv.

[0026] like Figure 1 As shown, the rotating packed bed and acoustic field coupled reactor includes: a shell 1, on which a gas inlet 11, a gas outlet 12, an alkali inlet 13, and a waste liquid outlet 14 are provided; a rotatable rotor 2, which is installed inside the shell 1 and filled with porous packing; an alkali distributor 3, which is located at the center of the rotor 2 and communicates with the alkali inlet 13; and at least one acoustic generator 4, which is fixedly installed on the shell 1 and extends into the rotor 2, and is connected to a power supply and control system.

[0027] Waste liquid outlet 14 is located at the bottom of housing 1, and a sealing valve is provided thereon. Rotor 2 is rotatably mounted on housing 1 via shaft 21. A seal is provided between rotor 2 shaft 21 and housing 1 to prevent gas short circuit.

[0028] It should be noted that there are multiple acoustic wave generators 4, evenly arranged around the rotor 2, with the acoustic wave output end of each acoustic wave generator 4 facing the packing layer. The acoustic wave emission direction of the acoustic wave generator 4 forms an angle of 30° to 60° with the gas flow direction to form an obliquely incident standing wave field. Most preferably, the gas inlet 11 is located on the side of the housing 1, and the gas outlet 12 is located at the top center of the housing 1; acoustic wave generators 4 are provided on both the upper and lower sides of the gas inlet 11, and the acoustic wave generator 4 on the upper side and the acoustic wave generator 4 on the lower side are turned on alternately.

[0029] When the direction of sound wave emission is at an angle A of 30° to 60° with the direction of gas flow, the sound wave can generate sound wave components along the axial and radial directions of the rotor 2. When the upper and lower sound wave generators 4 work alternately, the axial sound wave component causes the micro-droplets to oscillate axially in the packing layer, prolonging the effective contact time and preventing the droplets from being quickly blown away by the airflow.

[0030] Example 1 use Figure 1 The coupled reactor is shown. Rotor 2 has an inner diameter of 300 mm, filled with stainless steel wire mesh packing (specific surface area 1200 m² / m³), and rotates at 1800 rpm. The sound generator 4 is a whistle type, with a frequency of 16 kHz and a sound pressure level of 155 dB, mounted on the shell 1. There are eight of them, four on the top and four on the bottom, evenly distributed circumferentially. The alkaline solution is a 12% NaOH solution with 0.1% sodium dodecyl sulfate added. The crude N₂O gas flow rate is 100 Nm³ / h, the temperature is 50℃, and the composition is: N₂O 85 vol%, H₂O 8%, N₂ 3%, O₂ 1%, NO₂ 0.2%, CO₂ 0.5%, with the remainder being trace impurities. The liquid-to-gas ratio is 1.0 L / m³. The operating pressure is 0.15 MPa.

[0031] Results: The NO2 concentration in the outlet gas was 0.03 ppmv, the alkaline mist content was <0.01 mg / m³, and the N2O yield was 98.5%. Subsequent processing involved molecular sieve drying (type 4A, 50 kg packing), compression to 3 MPa, condensation at -25℃, and distillation (30 theoretical plates) to obtain a product with a purity of 99.9996% (GC-MS detection) and a total metal ion content of 3.2 ppbw (ICP-MS detection). After 36 months of continuous operation, the molecular sieve adsorption capacity remained above 95% of its initial value.

[0032] Comparative Example 1 (Traditional Packed Tower) Using the same raw gas conditions, a conventional packed tower (400 mm inner diameter, 3 m packing height, ceramic Raschig rings) was used. The alkali solution was 12% NaOH, and the liquid-to-gas ratio was 10 L / m³. The outlet NO₂ concentration was 35 ppmv, and the alkali mist content was 8 mg / m³. After subsequent distillation, the product purity was 99.995%, and the metal ion content was 28 ppbw. The molecular sieve required regeneration every 4 months.

[0033] Comparative Example 2 (Separate rotating filled bed, no sound field) Using the same raw gas conditions, the rotating packed bed rotated at 1800 rpm, with a liquid-to-gas ratio of 3.5 L / m³, without acoustic treatment. The outlet NO₂ concentration was 8 ppmv, and the alkaline mist content was 1.2 mg / m³. After subsequent distillation, the product purity was 99.998%, and the metal ion content was 15 ppbw. The molecular sieve required regeneration every 8 months.

[0034] Comparative Example 3 (rotating packed bed + post-acoustic agglomerator, in series) After employing a rotating packed bed (same as Comparative Example 2), a sonic agglomerator and a cyclone separator were connected in series (sonic frequency 16 kHz, sound pressure level 155 dB, residence time 2 s). The liquid-to-gas ratio was 3.5 L / m³. The outlet NO₂ concentration was 6 ppmv (due to limited secondary absorption of NO₂ by alkaline mist droplets in the sonic agglomerator), and the alkaline mist content was 0.5 mg / m³. The product purity after subsequent distillation was 99.9985%, and the metal ion content was 12 ppbw. The molecular sieve lifespan was 12 months.

[0035] The comparison shows that Example 1 of the present invention is significantly superior to all comparative examples in terms of alkali dosage, NO2 removal, and product purity. In particular, the alkali dosage is only 28.6% of that of Comparative Example 2, while the product purity is two orders of magnitude higher, demonstrating the synergistic advantages of the coupling technology.

[0036] The basic principles, main features, and advantages of this application have been described above. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely the principles of this application. Various changes and modifications can be made to this application without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed application.

Claims

1. A process for preparing electronic-grade nitrous oxide using the ammonium nitrate method, comprising ammonium nitrate pyrolysis, cooling, purification, drying, liquefaction, and distillation, characterized in that, The purification process includes the following steps: S1: Cool the crude nitrous oxide gas obtained from the pyrolysis of ammonium nitrate to 40~60℃; S2: The cooled gas is introduced into a rotating packed bed and acoustic field coupled reactor, which includes a rotatable packed bed rotor and at least one acoustic wave generator. S3: In the reactor, the alkaline solution is sprayed from the center of the rotor and forms a liquid film and droplets under the action of centrifugal force. At the same time, the sound wave generator emits sound waves with a frequency of 8~25 kHz and a sound pressure level of not less than 150 dB, which causes the liquid film to vibrate periodically and break into uniform droplets of 0.3~1.5 μm. S4: Gas and droplets come into countercurrent or crosscurrent contact in the packing layer of the rotating packed bed. Acidic impurities are absorbed, and at the same time, droplets agglomerate and redisperse under the action of the sound field, realizing in-situ separation of alkali mist. S5: The effluent is further separated by a centrifugal demister at the top of the reactor and then enters the subsequent drying step.

2. The ammonium nitrate method for preparing electronic-grade nitrous oxide according to claim 1, characterized in that, The rotational speed of the rotor of the rotary packed bed is 1200~2500 rpm, and the specific surface area of ​​the packing material in the packed bed is 500~2000 m² / m³.

3. The ammonium nitrate method for preparing electronic-grade nitrous oxide according to claim 1, characterized in that, The alkaline solution is a NaOH or KOH solution with a mass fraction of 8% to 18%, and contains 0.01% to 0.5% surfactant to reduce the surface tension of the liquid film and promote the sound wave-induced breakage of the liquid film.

4. The ammonium nitrate method for preparing electronic-grade nitrous oxide according to claim 1, characterized in that, The reactor operates at a pressure of 0.05~0.3 MPa and a gas velocity of 0.5~2.5 m / s.

5. The ammonium nitrate method for preparing electronic-grade nitrous oxide according to claim 1, characterized in that, The purity of the obtained nitrous oxide product is ≥99.9995%, the total metal ion content is ≤5 ppbw, and the NO2 content is ≤0.1 ppmv.

6. The ammonium nitrate method for preparing electronic-grade nitrous oxide according to any one of claims 1-5, characterized in that, The rotating packed bed and acoustic field coupled reactor includes: The housing is provided with a gas inlet, a gas outlet, an alkaline solution inlet, and a waste liquid outlet. A rotatable rotor, which is mounted inside a housing and filled with porous packing material; An alkali distributor is located at the center of the rotor and is connected to the alkali inlet; At least one acoustic wave generator is fixedly mounted on the housing and extends into the rotor, and the acoustic wave generator is connected to a power supply and control system.

7. The ammonium nitrate method for preparing electronic-grade nitrous oxide according to claim 6, characterized in that, The sound wave generators are multiple and are evenly arranged along the circumference of the rotor, with the sound wave output end of each sound wave generator facing the filler layer.

8. The ammonium nitrate method for preparing electronic-grade nitrous oxide according to claim 7, characterized in that, The sound wave generator emits sound waves at an angle of 30° to 60° to the gas flow direction, so as to form an obliquely incident standing wave field.

9. The ammonium nitrate method for preparing electronic-grade nitrous oxide according to claim 8, characterized in that, The gas inlet is located on the side of the housing, and the gas outlet is located at the top center of the housing; both the upper and lower sides of the gas inlet are equipped with sound wave generators, and the sound wave generator on the upper side and the sound wave generator on the lower side are turned on alternately.

10. The ammonium nitrate method for preparing electronic-grade nitrous oxide according to claim 6, characterized in that, A seal is provided between the rotor and the housing to prevent gas short circuit.

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