A high-pressure continuous rectification purification system and method for silicon tetrafluoride

Abstract

A kind of silicon tetrafluoride high-pressure continuous rectification purification system and method, belong to silicon tetrafluoride purification technical field, system includes: raw material pressurization unit, raw material pretreatment unit, main heat exchanger, first rectification tower, secondary rectification tower and refrigerant closed cycle refrigeration system, the material inlet of main heat exchanger is connected with the outlet of raw material pretreatment unit;First rectification tower feed port is connected with the material outlet of main heat exchanger;Secondary rectification tower feed port is connected with the overhead outlet of first rectification tower, the second reboiler is equipped in the tower kettle of secondary rectification tower, and the second condenser is equipped in the column top.This application adopts raw material pressurization, pretreatment, main heat exchanger cold and hot coupling, double-stage high-pressure rectification and refrigerant closed cycle refrigeration system cooperation overall framework, by first heavy removal, two-stage light removal two-stage coupling rectification mode, solve the industry pain point that silicon tetrafluoride is difficult to liquefy under normal pressure, low separation efficiency.

Description

Technical Field

[0001] This application belongs to the field of silicon tetrafluoride purification technology, and particularly relates to a high-pressure continuous distillation purification system and method for silicon tetrafluoride. Background Technology

[0002] Silicon tetrafluoride (SiF4) is an indispensable special electronic gas in the fields of electronic semiconductors, photovoltaic manufacturing, optical fibers and high-end new materials. It is widely used in core processes such as chip ion implantation, semiconductor epitaxial etching, optical fiber preform doping and solar cell manufacturing. Its product purity and trace impurity content directly determine the yield, optical performance and service life of downstream devices.

[0003] Industrial crude silicon tetrafluoride raw materials have a complex composition, typically containing various light and heavy impurities such as hydrogen fluoride, water, sulfur dioxide, hydrogen sulfide, an oxygen-argon mixture, nitrogen, hydrogen, carbon dioxide, and boron trifluoride. Electronic-grade high-purity silicon tetrafluoride requires stringent impurity control.

[0004] Currently, there are two main technical routes for silicon tetrafluoride purification in the industry, both of which have significant engineering shortcomings. One is the atmospheric distillation process. Silicon tetrafluoride has a sublimation point of -95.7℃ at atmospheric pressure, making it difficult to form a stable gas-liquid two-phase system under these conditions. The distillation mass transfer interface is difficult to establish stably, resulting in extremely low separation efficiency. Furthermore, it requires a cryogenic refrigeration system, often relying on external liquid nitrogen for cooling, leading to significant cooling losses, high operating costs, and temperature fluctuations that can cause system instability, making it unsuitable for large-scale continuous production. The other is the traditional high-pressure distillation process. While increasing the pressure can raise the saturation temperature of silicon tetrafluoride and reduce liquefaction difficulty, it generally uses a single-tower or simple double-tower structure, only achieving a rough separation of light and heavy impurities, and cannot directly meet the requirements of high-end electronic-grade products.

[0005] In summary, the industry urgently needs to develop a high-pressure coupled distillation purification technology that has good purification effect, low energy consumption, and is suitable for large-scale production, in order to solve the core bottlenecks of existing processes such as insufficient separation efficiency, low energy utilization, and limited product purity. Summary of the Invention

[0006] This application aims to at least partially address one of the technical problems in the related art. To this end, this application provides a high-pressure continuous distillation purification system and method for silicon tetrafluoride, which solves the industry pain points of silicon tetrafluoride being difficult to liquefy and having low separation efficiency under normal pressure by using a two-stage coupled distillation mode of primary heavy removal and secondary light removal.

[0007] To achieve the above objectives, in a first aspect, this application provides a silicon tetrafluoride high-pressure continuous distillation purification system, comprising:

[0008] The raw material pressurization unit is used to pressurize the crude silicon tetrafluoride raw material under normal pressure to a high pressure condition;

[0009] The raw material pretreatment unit is used to remove high-boiling-point polar impurities from high-pressure crude silicon tetrafluoride raw materials;

[0010] The main heat exchanger, whose material inlet is connected to the outlet of the raw material pretreatment unit, is used to pre-cool the crude silicon tetrafluoride raw material after removing high-boiling-point polar impurities by countercurrent heat exchange with a low-temperature medium to partially liquefy it, forming a gas-liquid mixed phase.

[0011] A primary distillation column, whose feed inlet is connected to the material outlet of the main heat exchanger, is used to separate heavy component impurities from the gas-liquid mixture. The bottom of the primary distillation column is equipped with a first reboiler, and the top of the column is equipped with a first condenser.

[0012] The secondary distillation column has its feed inlet connected to the top outlet of the primary distillation column. It is used to separate light component impurities from the deweighted material. The reboiler of the secondary distillation column is equipped with a second reboiler, and the top of the column is equipped with a second condenser. The reboiler of the secondary distillation column is also equipped with a high-purity silicon tetrafluoride product outlet.

[0013] A refrigerant closed-loop refrigeration system includes a refrigeration compressor, a first cooler, a first gas supply line connected to the first reboiler and the second reboiler respectively, a throttling expansion valve, and a second liquid supply line connected to the first condenser and the second condenser respectively.

[0014] Preferably, the refrigeration compressor pressurizes the low-pressure gaseous refrigerant to a high-pressure gaseous state. After the compression heat is removed by the first cooler, the high-pressure refrigerant is divided into two paths: one path is introduced into the heat medium inlet of the first reboiler and the second reboiler through the first gas supply pipeline, respectively, to provide a vaporization heat source for the liquid silicon tetrafluoride in the bottom of the tower using the latent heat of phase change of the refrigerant; the other path is pre-cooled by the main heat exchanger and then combined with the refrigerant after reboiling heat exchange, and sent to the throttling expansion valve for pressure reduction and refrigeration.

[0015] Preferably, the throttling expansion valve throttles and depressurizes the high-pressure liquid refrigerant to a low-pressure, low-temperature liquid state, and then introduces it into the cold medium inlets of the first condenser and the second condenser via the second liquid supply pipeline, respectively, to absorb the latent heat of condensation of the gaseous silicon tetrafluoride at the top of the tower; the low-pressure, low-temperature gaseous refrigerant after heat exchange and vaporization flows back to the main heat exchanger, where it undergoes countercurrent heat exchange with the high-temperature feed and returns to the inlet of the refrigeration compressor, completing a closed-loop cycle.

[0016] Preferably, the raw material pressurization unit includes a raw material compressor for pressurizing the crude silicon tetrafluoride raw material at atmospheric pressure from 1 barA to 18 barA to 22 barA. The pressurized raw material is cooled to 35°C to 45°C by a second cooler and then sent to the raw material pretreatment unit.

[0017] Preferably, the raw material pretreatment unit is a temperature-switching adsorption device, including at least two adsorbers connected in parallel. Each adsorber is filled with a special adsorbent and equipped with a regeneration electric heater to remove high-boiling-point polar impurities such as water, carbon dioxide, sulfur dioxide, and hydrogen fluoride from the high-pressure crude silicon tetrafluoride. The two sets of adsorbers alternately perform adsorption and thermal regeneration to achieve continuous production.

[0018] Preferably, the primary distillation column is also used for the pre-separation of low-boiling-point non-condensable light component impurities; the pre-cooled gas-liquid mixed phase feed is fed from the bottom of the de-weighting column, and the low-boiling-point non-condensable light component impurities are enriched at the top of the column, the low-boiling-point non-condensable light component impurities include oxygen-argon mixture, nitrogen and hydrogen.

[0019] Preferably, the reboiler of the first-stage distillation column is equipped with a heavy component residue discharge pipeline, the top of the first-stage distillation column is equipped with a first light component tail gas discharge pipeline, and the top of the second-stage distillation column is equipped with a second light component tail gas discharge pipeline; the heavy component residue discharge pipeline, the first light component tail gas discharge pipeline, and the second light component tail gas discharge pipeline are respectively connected to the tail gas inlet of the main heat exchanger, and after being reheated by the main heat exchanger, they are connected to the tail gas treatment tower; the product outlet of the reboiler of the second-stage distillation column is connected to the product inlet of the main heat exchanger, and the high-purity silicon tetrafluoride product collected is reheated to room temperature by the main heat exchanger and then pressurized and transported by a product booster compressor.

[0020] Preferably, the inlet of the product booster is also connected to a deep chemical adsorption unit, which is filled with aluminum fluoride-based adsorbent. The deep chemical adsorption unit selectively adsorbs trace amounts of boron trifluoride impurities by utilizing the strong coordination between boron trifluoride and the unsaturated coordination sites on the surface of aluminum fluoride, thereby removing the boron trifluoride content in the product to the ppb level.

[0021] Preferably, the operating pressure of the first-stage distillation column is 14 barA to 20 barA, the operating temperature at the top of the column is -35℃ to -28℃, and the operating temperature at the bottom of the column is -30℃ to -25℃; the operating pressure of the second-stage distillation column is 18 barA to 20 barA, the operating temperature at the top of the column is -40℃ to -35℃, and the operating temperature at the bottom of the column is -37℃ to -32℃; after two-stage distillation, the boron trifluoride impurity content in the silicon tetrafluoride product is reduced to below 5 ppm, and the product purity is 5N grade.

[0022] Secondly, this application provides a high-pressure continuous distillation purification method for silicon tetrafluoride, implemented based on any of the purification systems described above, comprising:

[0023] S1. Pressurize the crude silicon tetrafluoride raw material under normal pressure to a high pressure condition, and remove high-boiling-point polar impurities through pretreatment to obtain pretreated raw material;

[0024] S2. The pretreated raw material is introduced into the main heat exchanger and exchanged heat countercurrently with the low-temperature medium in the closed-loop refrigeration system of refrigerant, so that the pretreated raw material is pre-cooled to partial liquefaction and forms a gas-liquid mixed phase.

[0025] S3. The gas-liquid mixture is fed into a primary distillation column for primary distillation. The high-pressure refrigerant provided by the closed-loop refrigerant system provides a heat source for vaporization of the bottom material. The low-pressure, low-temperature refrigerant after throttling expansion refrigeration is used to condense the top gas phase. The bottom liquid of the column is discharged from the heavy component residue enriched with high-boiling-point impurities, and the deweighted material is collected from the top of the column.

[0026] S4. The deweighted material is fed into a secondary distillation column for secondary distillation. The high-pressure refrigerant provided by the closed-loop refrigerant system provides a heat source for vaporization of the material in the bottom of the column. The low-pressure, low-temperature refrigerant after throttling expansion refrigeration is used to condense the gas phase at the top of the column. Light component impurities are discharged from the top of the column, and high-purity silicon tetrafluoride product is collected from the bottom of the column.

[0027] Based on the above technical solution, the silicon tetrafluoride high-pressure continuous distillation purification system and method of this application has at least one of the following beneficial effects compared with the prior art:

[0028] 1. This invention establishes a closed-loop refrigerant system, utilizing the same refrigerant circulation loop to simultaneously provide vaporization heat source for the reboilers of both the primary and secondary distillation columns and cold source for the condensers. It also couples and integrates the cold energy recovery of the main heat exchanger with the refrigerant rewarming process, achieving cascaded utilization and closed-loop circulation of heat and cold, significantly reducing dependence on external heat and cold sources and system energy consumption. Simultaneously, the two-stage continuous distillation under high-pressure conditions, combined with the temperature-switching adsorption of the raw material pretreatment unit, removes high-boiling-point polar impurities, achieving a product purity of 5N grade and reducing boron trifluoride impurity content to below 5 ppm.

[0029] 2. This invention pressurizes the raw material to a high pressure of 18 barA to 22 barA, and combines this with the gradient pressure operating parameters of the first-stage distillation column (14 barA to 20 barA) and the second-stage distillation column (18 barA to 20 barA) to raise the distillation operating temperature to the range of -40℃ to -28℃. Compared with the low temperature conditions of -90℃ to -80℃ required for atmospheric or low-pressure distillation, this invention significantly reduces the cooling capacity requirement of the refrigeration system and the equipment investment cost. At the same time, it avoids the risk of material embrittlement under ultra-low temperature conditions, and improves the reliability and economy of the system.

[0030] 3. This invention includes a heavy component residue discharge pipeline installed in the bottom of the first-stage distillation column. All exhaust gases from each stage (heavy component residue, light components from the top of the first-stage column, and light components from the top of the second-stage column) are uniformly reheated via the main heat exchanger and then sent to the exhaust gas treatment tower. Simultaneously, high-purity silicon tetrafluoride product is reheated to room temperature via the main heat exchanger and then pressurized and transported via a product booster. A deep chemical adsorption unit filled with aluminum fluoride-based adsorbent is connected to the inlet of the product booster. Utilizing the strong coordination between boron trifluoride and the unsaturated coordination sites on the surface of aluminum fluoride, the boron trifluoride content in the product is removed to the ppb level. This achieves a synergistic integration of energy recovery and deep purification, further improving the purity of the product and the environmental friendliness of the system. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram showing the structural connection between the raw material pressurization unit and the raw material pretreatment unit in a high-pressure continuous distillation purification system for silicon tetrafluoride provided in this application;

[0033] Figure 2 This is a schematic diagram of the structural connection between the main heat exchanger and the primary and secondary distillation columns in a high-pressure continuous distillation purification system for silicon tetrafluoride provided in this application.

[0034] Figure 3 This is a schematic diagram of the structural connection of a deep chemical adsorption unit in a silicon tetrafluoride high-pressure continuous distillation purification system provided in this application;

[0035] Figure 4 This is a schematic diagram of a high-pressure continuous distillation purification method for silicon tetrafluoride provided in this application.

[0036] In the diagram: 1. Main heat exchanger; 2. First-stage distillation column; 3. Second-stage distillation column; 4. First reboiler; 5. Second reboiler; 6. First condenser; 7. Second condenser; 8. Raw material compressor; 9. Refrigeration compressor; 10. First gas supply line; 11. Throttling expansion valve; 12. Second liquid supply line; 13. First cooler; 14. Regenerative electric heater; 15. Adsorber; 16. Deep chemical adsorption unit; 17. Second cooler. Detailed Implementation

[0037] To facilitate understanding of this application, a more complete description will be provided below. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0039] In this application, the terms "first aspect," "second aspect," "third aspect," and "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," and "fourth," etc., serve only a non-exhaustive enumeration purpose and should be understood not to constitute a closed limitation on quantity.

[0040] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0041] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0042] The technical terms used in this embodiment are defined as follows: barA refers to the absolute pressure unit "bar (absolute pressure)"; ppm refers to parts per million; ppb refers to parts per billion; 5N refers to a product purity of 99.999%; oxygen-argon mixture refers to a mixture of oxygen and argon, whose boiling points at normal pressure are close and whose distillation separation characteristics are highly similar. In the industry, they are usually classified as the same type of low-boiling-point non-condensable light components for unified control.

[0043] like Figure 1-3 As shown in the embodiments of this application, the present invention provides a silicon tetrafluoride high-pressure continuous distillation purification system. This purification system integrates six core units: raw material compression and precooling, deep adsorption purification, full coupling of cold and heat energy, two-stage high-pressure low-temperature distillation, closed-loop low-temperature refrigeration cycle recovery, and chemical adsorption of BF3. The entire process relies on a closed-loop refrigeration cycle system to achieve low-temperature distillation conditions, which is different from the traditional gas purification route of room temperature adsorption, single distillation, and external low-temperature cold source.

[0044] The purple lines in the diagram represent the liquid refrigerant, and the blue lines represent the gaseous refrigerant; the following descriptions will correspond to this. This purification system includes:

[0045] The raw material pressurization unit is used to pressurize the crude tetrafluoride raw material from atmospheric pressure to a high-pressure condition; the raw material pretreatment unit is used to remove high-boiling-point polar impurities from the high-pressure crude tetrafluoride raw material; the main heat exchanger 1, whose material inlet is connected to the outlet of the raw material pretreatment unit, is used to pre-cool the crude tetrafluoride raw material after the removal of high-boiling-point polar impurities by countercurrent heat exchange with a low-temperature medium to partially liquefy it, forming a gas-liquid mixture; the first-stage distillation column 2, whose feed inlet is connected to the material outlet of the main heat exchanger 1, is used to separate heavy component impurities from the gas-liquid mixture, and the first reboiler 4 is provided in the bottom of the first-stage distillation column 2, and the first condenser is provided at the top of the column. Unit 6; Secondary distillation column 3, the feed inlet of secondary distillation column 3 is connected to the top outlet of primary distillation column 2, used to separate light component impurities from the deweighted material, the bottom of secondary distillation column 3 is equipped with a second reboiler 5, the top of the column is equipped with a second condenser 7, and the bottom of secondary distillation column 3 is equipped with a high-purity silicon tetrafluoride product outlet; Refrigerant closed-loop refrigeration system, including a refrigeration compressor 9, a first cooler 13, a first gas supply line 10 connected to the first reboiler 4 and the second reboiler 5 respectively, a throttling expansion valve 11, and a second liquid supply line 12 connected to the first condenser 6 and the second condenser 7 respectively.

[0046] The aforementioned "raw material pressurization unit" refers to the equipment assembly used to increase the pressure of crude tetrafluoride raw material at atmospheric pressure to a pressure level that meets the requirements of subsequent distillation operations. The pressure of crude tetrafluoride raw material at atmospheric pressure is typically around 1 barA (barA is an absolute pressure unit, referring to pressure measured with absolute vacuum as zero point). However, subsequent distillation operations require high-pressure conditions, thus necessitating the raw material pressurization unit. "High-pressure conditions" refers to pressures relative to atmospheric pressure, meaning a pressure range of 18 barA to 22 barA after pressurization. This pressure level significantly increases the boiling point temperature of tetrafluoride, allowing distillation operations to be performed within a relatively high temperature range (-40℃ to -28℃), reducing energy consumption in the refrigeration system and lowering the requirements for low-temperature equipment selection. Of course, the implementation of the raw material pressurization unit is not limited to using a compressor; other pressurization equipment such as booster pumps or boosters can also be used, as long as the raw material pressure can be increased to the target high-pressure condition.

[0047] The "raw material pretreatment unit" refers to the device used to remove high-boiling-point polar impurities from crude silicon tetrafluoride raw materials. Crude silicon tetrafluoride raw materials typically contain high-boiling-point polar impurities such as water (H2O), carbon dioxide (CO2), sulfur dioxide (SO2), and hydrogen fluoride (HF). If these impurities are not removed before entering the distillation system, they will condense or solidify during the low-temperature distillation process, clogging pipes and equipment and affecting the long-term stable operation of the distillation system. Therefore, it is necessary to set up a raw material pretreatment unit to remove impurities before distillation.

[0048] "Main heat exchanger 1" refers to the equipment used for countercurrent heat exchange between the pretreated crude silicon tetrafluoride raw material and the cryogenic medium. The material inlet of the main heat exchanger 1 is connected to the outlet of the raw material pretreatment unit. The raw material is cooled to a partially liquefied state in the main heat exchanger 1. Partial liquefaction means that the temperature of the raw material is reduced to a temperature range below its boiling point and above its freezing point, causing some components (mainly silicon tetrafluoride) in the raw material to change from a gaseous state to a liquid state, while some components remain in a gaseous state, forming a gas-liquid mixture. This gas-liquid mixture is directly fed into the primary distillation column 2 for distillation separation. Compared with the method of feeding the raw material after complete liquefaction, partial liquefaction feeding can make full use of the sensible heat and latent heat of the raw material itself, reducing the cooling capacity consumption of the main heat exchanger 1.

[0049] "First-stage distillation column 2" refers to a distillation device used for separating heavy component impurities from a gas-liquid mixture. The feed inlet of the first-stage distillation column 2 is connected to the material outlet of the main heat exchanger 1, and the gas-liquid mixture enters the column through the feed inlet. The first-stage distillation column 2 has a first reboiler 4 at the bottom to provide the heat required for vaporization of the liquid material at the bottom; and a first condenser 6 at the top to condense the rising gaseous material into a liquid state. Part of the condensate is returned to the column as reflux, and part is sent to the second-stage distillation column 3 as the top product. In the first-stage distillation column 2, heavy component impurities with boiling points higher than silicon tetrafluoride are enriched in the bottom and discharged through the bottom discharge pipe; light component impurities with boiling points lower than silicon tetrafluoride, and silicon tetrafluoride itself, are enriched at the top and collected from the top and sent to the second-stage distillation column 3.

[0050] "Secondary distillation column 3" refers to a distillation unit used to separate light component impurities from the deweighted material. The feed inlet of secondary distillation column 3 is connected to the top outlet of primary distillation column 2, receiving the deweighted material from the top of primary distillation column 2. Secondary distillation column 3 has a second reboiler 5 in its bottom and a second condenser 7 at its top. In secondary distillation column 3, light component impurities with boiling points lower than silicon tetrafluoride accumulate at the top and are discharged through the top discharge pipe; high-purity silicon tetrafluoride accumulates in the bottom and is collected through the high-purity silicon tetrafluoride product outlet in the bottom. The two-stage distillation column is set up in the order of removing heavy component impurities first (primary distillation column 2), then removing light component impurities (secondary distillation column 3). This "heavy first, light later" separation sequence avoids contaminating the high-purity product in the bottom of the secondary distillation column 3 with heavy component impurities, thus ensuring the purity of the final product.

[0051] A "closed-loop refrigerant system" refers to an integrated refrigeration system that uses refrigerant to circulate in a closed loop, simultaneously providing heat and cold sources for the reboiler and condenser of a distillation system. This system includes a refrigeration compressor 9, a first cooler 13, a first gas supply line 10 connected in a closed loop to the first reboiler 4 and the second reboiler 5 respectively, a throttling expansion valve 11, and a second liquid supply line 12 connected to the first condenser 6 and the second condenser 7 respectively. The refrigeration compressor 9 pressurizes the low-pressure gaseous refrigerant to a high-pressure gaseous state; the first cooler 13 removes the heat of compression generated during the compression process, cooling the high-pressure gaseous refrigerant into a high-pressure liquid state or a high-pressure gas-liquid mixture; the first gas supply line 10 delivers part of the high-pressure refrigerant to the first reboiler 4 and the second reboiler 5, utilizing the latent heat of phase change of the refrigerant to provide the heat required for the vaporization of the liquid silicon tetrafluoride in the bottom of the column; the throttling expansion valve 11 throttles and depressurizes the high-pressure liquid refrigerant to a low-pressure, low-temperature liquid state; the second liquid supply line 12 delivers the throttled and expanded low-pressure, low-temperature liquid refrigerant to the first condenser 6 and the second condenser 7, utilizing the low-temperature refrigerant to absorb the latent heat of condensation of the gaseous silicon tetrafluoride at the top of the column, thereby achieving the condensation of the material at the top of the column. A notable feature of this closed-loop refrigerant refrigeration system is that the same refrigerant simultaneously serves the dual functions of heating the reboiler and cooling the condenser, achieving self-balancing of internal heat and cold without the need for continuous supply of external heat sources (such as steam) and external cold sources (such as liquid nitrogen), thus significantly reducing the system's energy consumption and operating costs.

[0052] It should be noted that the specific type of refrigerant is not limited to a particular refrigerant. Those skilled in the art can select a suitable refrigerant based on the actual operating temperature and pressure range. For example, commonly used medium and low temperature refrigerants such as R134a (1,1,1,2-tetrafluoroethane), R404A (a mixed refrigerant composed of pentafluoroethane, trifluoroethane and tetrafluoroethane), or R507 (an azeotropic mixed refrigerant composed of pentafluoroethane and trifluoroethane) can be used, as long as their phase change temperature range can cover the temperature range required for distillation operation.

[0053] In one possible implementation, the closed-loop refrigerant system uses R404A as the refrigerant. R404A is a mixed refrigerant composed of pentafluoroethane (R125), trifluoroethane (R143a), and tetrafluoroethane (R134a), with the following physical properties: a boiling point of approximately 30°C at a high pressure of 15 barA and a boiling point of approximately -44°C at a low pressure of 1.15 barA. This physical property perfectly meets the dual requirements of this system—the boiling point of approximately 30°C on the high-pressure side (approximately 15 barA) matches the cooling temperature of the first cooler 13 (approximately 40°C), ensuring that the high-pressure gaseous refrigerant can be fully condensed or cooled in the first cooler 13; the boiling point of approximately -44°C on the low-pressure side (approximately 1.15 barA) matches the condensation temperature at the top of the distillation column (-44°C to -35°C), ensuring that the low-pressure, low-temperature liquid refrigerant can effectively absorb the latent heat of condensation of the gaseous silicon tetrafluoride at the top of the column in the condenser. Therefore, using R404A as the preferred refrigerant for this system can simultaneously meet the heat and cold source requirements of the distillation system through a single refrigerant closed-loop cycle without the need for external cold and heat sources, thus achieving energy self-sufficiency.

[0054] It should be noted that the specific type of refrigerant is not limited to R404A. Those skilled in the art can select other refrigerants with similar phase change temperature characteristics according to the actual operating temperature and pressure range. For example, commonly used medium and low temperature mixed refrigerants such as R134a or R507 can also be used as substitutes under certain conditions. However, the operating pressure and temperature parameters need to be adjusted accordingly to adapt to their different phase change characteristics, as long as their high-pressure phase change temperature can match the circulating water cooling temperature and their low-pressure phase change temperature can cover the column top condensation temperature range required for distillation operation.

[0055] The above technical solution significantly increases the boiling point of silicon tetrafluoride by pressurizing the raw material to a high-pressure condition through the raw material pressurization unit, allowing the distillation operation to be carried out at a relatively high temperature, thus reducing the low-temperature requirements of the refrigeration system. The raw material pretreatment unit removes high-boiling-point polar impurities, preventing these impurities from clogging and corroding the equipment during subsequent low-temperature distillation. The main heat exchanger 1 pre-cools the raw material to partial liquefaction before feeding, fully utilizing the raw material's own cooling capacity and reducing the cooling capacity consumption of the main heat exchanger 1. The gradient separation of the two-stage distillation column (first stage for heavy component removal, second stage for light component removal) achieves the separate removal of heavy and light component impurities, ensuring product purity. The integrated design of the closed-loop refrigerant circulation system unifies the supply of heat to the reboiler and cold to the condenser, simplifying the system structure and reducing dependence on external utilities.

[0056] In one possible implementation, such as Figure 2 As shown, the refrigeration compressor 9 pressurizes the 1.1 barA, 25°C low-pressure gaseous refrigerant (blue line) to a 15 barA high-pressure gaseous state. After the heat of compression is removed by the first cooler 13, the refrigerant is cooled to a 15 barA high-pressure gaseous refrigerant (blue line). The high-pressure gaseous refrigerant is divided into two paths: one path is introduced into the heat medium inlet of the first reboiler 4 and the second reboiler 5 via the first gas supply line 10. In the reboiler, the high-pressure gaseous refrigerant condenses and releases heat, utilizing its high-pressure latent heat of phase change to provide a vaporization heat source for the liquid tetrafluoride in the column bottom, causing the liquid tetrafluoride in the column bottom to vaporize and flow upward; after releasing heat, the refrigerant itself condenses into a liquid or gas-liquid mixture (purple line), and is discharged from the reboiler after the temperature decreases.

[0057] Another high-pressure gaseous refrigerant stream is directly fed into the main heat exchanger 1, where it exchanges heat with the low-temperature medium and cools to a liquid state (purple line). This liquid then merges with the refrigerant streams discharged from the two reboilers. The merged high-pressure liquid refrigerant is then sent to the throttling expansion valve 11 for pressure reduction and refrigeration. The throttling expansion valve 11 throttles and reduces the pressure of the high-pressure liquid refrigerant to 1.15 barA, and expands and cools it to a low-pressure, low-temperature liquid refrigerant at -44°C (purple line). The low-pressure, low-temperature liquid refrigerant is then fed through the second liquid supply line 12 into the cold medium inlets of the first condenser 6 and the second condenser 7. In the condensers, the low-pressure, low-temperature liquid refrigerant evaporates and absorbs heat, absorbing the latent heat of condensation of the gaseous silicon tetrafluoride at the top of the column, causing the gaseous phase at the top of the column to condense into a liquid reflux. The refrigerant itself is completely vaporized by heating into a 1.15 barA, -44°C low-pressure, low-temperature gaseous refrigerant (blue line). In this closed-loop system, the refrigerant absorbs the latent heat of condensation and a small amount of sensible heat from the vaporized silicon tetrafluoride at the top of the column in the condenser, completely transforming from a liquid to a gaseous state. The low-pressure, low-temperature gaseous refrigerant, after heat exchange and vaporization, flows back to the main heat exchanger 1, where it exchanges heat counter-currently with the high-temperature feed to reach 25°C, and is then reintroduced into the inlet of the refrigeration compressor 9, completing the closed-loop cycle. The significant advantages of this closed-loop system are: the refrigerant circulates within the system, consuming virtually no refrigerant except for a small amount of unavoidable leakage, resulting in low operating costs; simultaneously, the main heat exchanger 1 performs the dual functions of feed precooling and refrigerant reheating, achieving coupled utilization of heat and cold within the system, leading to high energy efficiency. Furthermore, the closed-loop system does not require continuous emission of waste gas or liquid, making it environmentally friendly.

[0058] In one possible implementation, such as Figure 1 As shown, the raw material pressurization unit includes a raw material compressor 8, which is used to pressurize the crude silicon tetrafluoride raw material at atmospheric pressure from 1 barA to 18 barA to 22 barA. After pressurization, the raw material is cooled to 35°C to 45°C by the second cooler 17 and then sent to the raw material pretreatment unit.

[0059] The pressure of the crude silicon tetrafluoride raw material at atmospheric pressure is approximately 1 barA (i.e., the absolute pressure of one standard atmosphere). The raw material compressor 8 increases the raw material pressure from 1 barA to 18 barA to 22 barA (e.g., ...). Figure 1 As shown, the raw material is pressurized from 1 barA, about 30°C, to about 20 barA, about 40°C after being pressurized by the raw material compressor 8.

[0060] The choice of this pressure range is based on the following considerations: Silicon tetrafluoride has a boiling point of approximately -86°C at atmospheric pressure, which can be raised to around -40°C to -25°C under high pressure conditions of 18 barA to 22 barA. Setting the distillation operating pressure within this range allows the distillation column to operate within a temperature range of -40°C to -28°C. This temperature range can be achieved using a closed-loop refrigeration system with conventional refrigerants (such as R404A and R507) without relying on ultra-low temperature sources such as liquid nitrogen (which has a temperature of approximately -196°C). If the operating pressure is too low (such as atmospheric or low pressure), the distillation operation needs to be carried out at ultra-low temperatures of -90°C to -80°C or even lower, placing extremely high demands on equipment materials, insulation requirements, and the refrigeration system, significantly increasing equipment investment and operating energy consumption. If the operating pressure is too high (exceeding 22 barA), the requirements for the equipment's pressure resistance level increase, raising equipment manufacturing costs and correspondingly increasing safety risks. Therefore, 18 barA to 22 barA is the preferred pressure range after comprehensively considering factors such as distillation operating temperature, refrigeration system feasibility, equipment investment, and operational safety.

[0061] The temperature of the pressurized raw material will rise due to the heat of compression, typically reaching 80℃~120℃. Directly feeding high-temperature raw materials into the raw material pretreatment unit will affect the adsorption efficiency of the adsorbent (the adsorption capacity of most adsorbents decreases at high temperatures), therefore cooling is necessary. Industrial circulating cooling water is used as the cooling medium to reduce the raw material temperature to 35℃~45℃ (e.g., industrial circulating cooling water). Figure 1 As shown, the pressurized crude silicon tetrafluoride raw material is cooled to approximately 40°C by the second cooler 17 before entering the raw material pretreatment unit. This temperature range is close to room temperature, which is beneficial for the efficient adsorption of the adsorbent at room temperature in the subsequent temperature-switching adsorption device.

[0062] In one possible implementation, such as Figure 1 As shown, the raw material pretreatment unit is a temperature-switching adsorption device, including at least two adsorbers 15 connected in parallel. Each adsorber 15 is filled with a special adsorbent and is equipped with a regeneration electric heater 14 to remove high-boiling-point polar impurities such as water, carbon dioxide, sulfur dioxide, and hydrogen fluoride from the high-pressure crude tetrafluoride. The two sets of adsorbers 15 alternately perform adsorption and thermal regeneration to achieve continuous production.

[0063] Wherein, "temperature swing adsorption" (full English name: Temperature Swing Adsorption, abbreviated as TSA) is a technology that realizes gas separation and purification by utilizing the characteristic that the equilibrium adsorption capacity of an adsorbent varies with temperature changes. Its basic principle is: at a relatively low temperature, the adsorbent has a large adsorption capacity for target impurities, and can effectively adsorb and remove impurities from the gas stream; at a relatively high temperature, the adsorption capacity of the adsorbent decreases, and the adsorbed impurities will desorb from the surface of the adsorbent, and are discharged together with the regeneration gas through the venting pipeline, so that the adsorbent recovers its adsorption capacity and the regeneration of the adsorbent is realized.

[0064] The temperature swing adsorption device comprises at least two adsorbers 15 arranged in parallel. This design is intended to realize continuous production: when one adsorber 15 is in an adsorption operation state, another adsorber 15 can perform heating regeneration operation through the regenerative electric heater 14, and the two operations are performed alternately, thereby ensuring that the entire purification system can operate continuously without interruption, and there is no need to shut down to replace or regenerate the adsorbent. Of course, the number of adsorbers 15 is not limited to two. Those skilled in the art can arrange three or more adsorbers 15 according to actual production scale and regeneration time requirements, as long as the alternate continuous operation of adsorption and regeneration can be realized.

[0065] The "special adsorbent" filled in the adsorber 15 is an adsorbent selected or customized according to the adsorption characteristics of high-boiling-point polar impurities such as water, carbon dioxide, sulfur dioxide and hydrogen fluoride in crude silicon tetrafluoride. These high-boiling-point polar impurities have relatively high polarity and strong intermolecular forces, and are prone to adsorb on the active sites on the surface of the adsorbent. The special adsorbent can be molecular sieves (such as 3A, 4A, 5A or 13X molecular sieves), activated alumina, silica gel or a composite combination thereof, and the specific type and proportion need to be optimally selected according to the type and content of impurities in the raw material. The matching regenerative electric heater 14 is used to heat the adsorbent to the regeneration temperature by means of heating after the adsorbent is saturated with adsorption, so that the adsorbed impurities desorb from the surface of the adsorbent, are carried out of the adsorber 15 along with the regeneration gas, and restore the adsorption capacity of the adsorbent. As Figure 1 shown, the regenerative electric heater 14 is connected with the adsorber 15 in a matching manner to provide heat required for regeneration.

[0066] Through the pretreatment by the temperature swing adsorption device, the content of high-boiling-point polar impurities such as water, carbon dioxide, sulfur dioxide and hydrogen fluoride in crude silicon tetrafluoride is reduced to an extremely low level, which prevents these impurities from condensing or solidifying on the inner walls of pipelines and equipment due to their high freezing points in the subsequent low-temperature distillation process, which causes blockage and corrosion, and ensures the long-term stable operation of the distillation system.

[0067] In one possible implementation, the primary distillation column 2 is also used for the pre-separation of low-boiling-point non-condensable light component impurities; the pre-cooled gas-liquid mixed phase feed is fed from the bottom of the de-weighting column, and the low-boiling-point non-condensable light component impurities are enriched at the top of the column. The low-boiling-point non-condensable light component impurities include oxygen-argon mixture, nitrogen and hydrogen.

[0068] "Low-boiling-point non-condensable light component impurities" refer to light component impurities with boiling points much lower than silicon tetrafluoride and difficult to condense into a liquid state under distillation operating conditions. The boiling point of silicon tetrafluoride (under high pressure) is approximately -40℃ to -25℃, while the boiling points of oxygen (O2) are -183℃, argon (Ar) -186℃, nitrogen (N2) -196℃, and hydrogen (H2) -253℃. These impurities have boiling points much lower than silicon tetrafluoride. In a distillation column, components with lower boiling points are more likely to accumulate in gaseous form at the top of the column. Therefore, in the first-stage distillation column 2, these low-boiling-point non-condensable light component impurities are fed from the bottom of the column (bottom of the heavy component removal column) along with the gas-liquid mixed phase feed. During their ascent within the column, they continuously accumulate towards the top and are eventually discharged from the top, thus achieving initial separation from silicon tetrafluoride.

[0069] The first-stage distillation column 2 performs the dual functions of separating heavy component impurities and pre-separating low-boiling-point non-condensable light component impurities. The feed inlet is located near the bottom of the column. This design allows the gaseous-liquid mixed-phase feed to enter from the bottom, with the gas phase flowing directly upwards and the liquid phase accumulating in the bottom and then being heated and vaporized by the reboiler before flowing upwards. This provides a longer residence time for light component impurities within the column and increases the number of theoretical plates available for separation, thus improving the removal efficiency of light component impurities. This "bottom-feed" design also allows the first-stage distillation column 2 to pre-discharge most of the low-boiling-point non-condensable light component impurities from the top while removing heavy component impurities, reducing the separation burden on the second-stage distillation column 3.

[0070] In one possible implementation, such as Figure 2 As shown, the bottom of the first-stage distillation column 2 is equipped with a heavy component residue discharge pipeline, and the top of the first-stage distillation column 2 is equipped with a first light component tail gas discharge pipeline. The top of the second-stage distillation column 3 is equipped with a second light component tail gas discharge pipeline. The heavy component residue discharge pipeline, the first light component tail gas discharge pipeline, and the second light component tail gas discharge pipeline are respectively connected to the tail gas inlet of the main heat exchanger 1. After being reheated by the main heat exchanger 1, they are connected to the tail gas treatment tower. The product outlet of the bottom of the second-stage distillation column 3 is connected to the product inlet of the main heat exchanger 1. The high-purity silicon tetrafluoride product is reheated to room temperature by the main heat exchanger 1 and then pressurized and transported by the product booster.

[0071] The heavy component residue discharged from the bottom of the first-stage distillation column 2 contains enriched high-boiling-point impurities. These residues are in a liquid or gas-liquid mixture state at the bottom temperature, and are at a low temperature (approximately -30℃ to -25℃). The first light component tail gas discharged from the top of the first-stage distillation column 2 contains low-boiling-point non-condensable light component impurities (oxygen-argon mixture, nitrogen, hydrogen, etc.), and is at a low temperature (approximately -35℃ to -28℃). The second light component tail gas discharged from the top of the second-stage distillation column 3 contains remaining light component impurities, and is at an even lower temperature (approximately -40℃ to -35℃). All three tail gas streams have low temperatures, and direct discharge would result in significant cooling loss.

[0072] This scheme connects the three exhaust gases to the exhaust gas inlet of the main heat exchanger 1 via their respective exhaust pipelines. This allows the low-temperature exhaust gases to flow through the main heat exchanger 1 and exchange heat counter-currently with the high-temperature feed (35℃~45℃) from the raw material pretreatment unit. During this heat exchange process, the low-temperature exhaust gases absorb heat from the high-temperature feed and are reheated to near room temperature, while the high-temperature feed is pre-cooled to partial liquefaction. The reheated exhaust gases are then collected and connected to an exhaust gas treatment tower for harmless treatment (such as alkali absorption) before being discharged.

[0073] like Figure 2 As shown, the distillation exhaust gas separated from the top of the first-stage distillation column 2 is depressurized (e.g., from approximately 19 barA to approximately 14.9 barA) before entering the main heat exchanger 1 for reheating. The exhaust gas is then reheated to approximately 40°C before being sent to the exhaust gas treatment tower. This design achieves the recovery and utilization of the cooling capacity in the exhaust gas, reducing the external cooling capacity consumption of the main heat exchanger 1. Simultaneously, the product outlet of the second-stage distillation column 3 is connected to the product inlet of the main heat exchanger 1. The collected high-purity silicon tetrafluoride product is liquid at the column bottom temperature, approximately -37°C to -32°C, and also has low cooling capacity. When the product flows through the main heat exchanger 1, it undergoes countercurrent heat exchange with the high-temperature feed and is reheated to ambient temperature (approximately 20°C to 30°C). The reheated high-purity silicon tetrafluoride product is pressurized by a product booster and transported to the product storage tank or downstream processes.

[0074] In one possible implementation, such as Figure 2 As shown, the product outlet of the reboiler of the secondary distillation column 3 is connected to the product inlet of the main heat exchanger 1. The high-purity silicon tetrafluoride product is liquid at the reboiler temperature, approximately -37°C to -32°C, exhibiting low cooling capacity. As the product flows through the main heat exchanger 1, it exchanges heat counter-currently with the high-temperature feed, and is reheated to ambient temperature (approximately 20°C to 30°C). The reheated high-purity silicon tetrafluoride product is then pressurized and transported to a product storage tank or downstream process via a product booster. This design achieves the recovery and utilization of the product's cooling capacity.

[0075] It should be noted that the high-purity liquid silicon tetrafluoride product produced from the bottom of the third column of the secondary distillation column can be flexibly discharged via one of the following two routes, depending on the content of boron trifluoride impurities in the raw materials and the downstream users' requirements for the boron trifluoride content in the product:

[0076] Pathway 1 (Direct Liquid Product Extraction): When the boron trifluoride impurity content in the raw material is extremely low (e.g., below 1 ppm) or downstream users have relatively lenient requirements for boron trifluoride impurity content (e.g., only requiring 5N purity), the high-purity liquid silicon tetrafluoride product extracted from the bottom of the second-stage distillation column can be directly transported to a cryogenic liquid storage tank for closed temporary storage, achieving direct extraction of the liquid product. This path is suitable for applications that are not sensitive to boron trifluoride impurities, directly meeting customer needs for liquid filling and liquid transportation, while avoiding cross-interference between the distillation section and downstream sections.

[0077] Pathway Two (Deep Boron Removal Pathway for Gaseous Products): When the boron trifluoride impurity content in the raw material is high (e.g., greater than 1 ppm) or downstream users have extremely stringent requirements for boron trifluoride impurity content (e.g., ppb level), the high-purity liquid silicon tetrafluoride product from the bottom of the secondary distillation column 3 is first completely vaporized by the main heat exchanger 1 to obtain high-pressure, high-purity silicon tetrafluoride gas. This gas is then sent to the deep chemical adsorption unit 16 for chemical adsorption treatment, using an aluminum fluoride-based adsorbent to selectively adsorb and remove residual boron trifluoride impurities from the product to the ppb level. Finally, the product is pressurized by a product booster and transported to downstream users or filled into cylinders. This path can meet the stringent requirements for ultra-pure silicon tetrafluoride in high-end applications such as semiconductor and chip manufacturing.

[0078] With the above two optional discharge paths, the present invention realizes flexible production of liquid / gas dual-form products, which can be adapted and adjusted according to the quality of raw materials and customer needs, taking into account the differentiated needs of different application scenarios.

[0079] In one possible implementation, such as Figure 3 As shown, the inlet of the product booster is also connected to a deep chemical adsorption unit 16, which is filled with aluminum fluoride-based adsorbent. It selectively adsorbs trace amounts of boron trifluoride impurities by utilizing the strong coordination between boron trifluoride and the unsaturated coordination sites on the surface of aluminum fluoride, thereby removing the boron trifluoride content in the product to the ppb level.

[0080] "Deep Chemisorption Unit 16" refers to the chemisorption equipment installed after the distillation system and before the product booster, used for the deep removal of trace amounts of boron trifluoride (BF3) impurities remaining in the distilled product. Boron trifluoride is a relatively difficult impurity to separate from crude silicon tetrafluoride. Its boiling point is close to that of silicon tetrafluoride (the boiling point of boron trifluoride at normal pressure is -100.3℃, and the boiling point of silicon tetrafluoride is -94.8℃). Distillation alone is insufficient to completely remove it to the ppb level (ppb is parts per billion, i.e., 10). -9 (Order of magnitude). The boron trifluoride content in the product after distillation can be reduced to below 5 ppm (ppm stands for parts per million, i.e., 10). -6 (On the order of magnitude), but a boron trifluoride content of 5 ppm is still too high for high-end applications such as semiconductors, and further removal is required.

[0081] The "aluminum fluoride-based adsorbent" packed in the deep chemisorption unit 16 refers to an adsorbent with aluminum fluoride (AlF3) as the main active component or carrier component. Boron trifluoride (BF3) is an electron-deficient compound with Lewis acidity (the ability to accept electron pairs), while the aluminum ions on the surface of aluminum fluoride have unsaturated coordination sites (i.e., the coordination number of surface aluminum ions is not saturated, and there are empty orbitals that can accept electron pairs), resulting in a strong coordination interaction between the two. When silicon tetrafluoride gas containing trace amounts of boron trifluoride flows through the deep chemisorption unit 16, the boron atoms in the boron trifluoride molecules coordinate with the unsaturated coordination aluminum sites on the surface of aluminum fluoride and are selectively adsorbed onto the surface of aluminum fluoride, while the silicon tetrafluoride molecules pass smoothly through the adsorption bed due to the weaker coordination interaction with aluminum fluoride. Through this selective chemisorption process, the content of boron trifluoride in the product can be further removed from below 5 ppm to the ppb level (e.g., ...). Figure 3 As shown, silicon tetrafluoride raw material containing BF3 impurities enters the deep chemical adsorption unit 16 at approximately 2 bar A and 10°C. After adsorption treatment, the BF3 content in the product is significantly reduced, meeting the stringent requirements of high-end electronic gases for ultrapure silicon tetrafluoride.

[0082] In one possible implementation, such as Figure 2As shown, in the exemplary operating parameters, the operating pressure of the first-stage distillation column 2 is 14 barA to 20 barA, the top operating temperature is -35℃ to -28℃, and the bottom operating temperature is -30℃ to -25℃; the operating pressure of the second-stage distillation column 3 is 18 barA to 20 barA, the top operating temperature is -40℃ to -35℃, and the bottom operating temperature is -37℃ to -32℃; after two-stage distillation, the boron trifluoride impurity content in the silicon tetrafluoride product is reduced to below 5 ppm, and the product purity is 5N grade (99.999%). This purity level can meet the application requirements of most electronics and semiconductor industries.

[0083] The operating pressure of the first-stage distillation column 2 is 14 barA to 20 barA. This pressure range was chosen considering the following factors: the primary function of the first-stage distillation column 2 is to remove heavy component impurities while pre-separating low-boiling-point non-condensable light component impurities. Setting the operating pressure at 14 barA to 20 barA maintains the column temperature within the range of -35℃ to -25℃. Within this temperature range, heavy component impurities (components with boiling points higher than silicon tetrafluoride) accumulate in liquid form at the bottom of the column, while silicon tetrafluoride and light component impurities accumulate in gaseous form at the top, achieving effective separation of heavy component impurities from silicon tetrafluoride. The operating temperature at the top of the first-stage distillation column 2 is -35℃ to -28℃, and the operating temperature at the bottom is -30℃ to -25℃. The lower top temperature compared to the bottom temperature is a typical characteristic of distillation operation—a lower top temperature favors the light components existing in gaseous form and being discharged from the top, while a higher bottom temperature favors the heavy components existing in liquid form and being discharged from the bottom.

[0084] The operating pressure of the secondary distillation column 3 is slightly higher than that of the primary distillation column 2 because the secondary distillation column 3 needs to process the material from the top of the primary distillation column 2. This material already has a high concentration of silicon tetrafluoride (SiF) in it, and appropriately increasing the operating pressure can further raise the boiling point of SiF, allowing the distillation operation to proceed at a slightly higher temperature, which helps reduce the cooling energy consumption of the refrigeration system. The operating temperature at the top of the secondary distillation column 3 is -40℃ to -35℃, and the operating temperature at the bottom is -37℃ to -32℃. In the secondary distillation column 3, low-boiling-point non-condensable light component impurities (oxygen-argon mixture, nitrogen, hydrogen, etc.) accumulate at the top and are discharged from the top, while high-purity SiF is accumulated in liquid form in the bottom and collected from the bottom. The bottom temperature (-37℃ to -32℃) of the secondary distillation column 3 is slightly higher than the top temperature (-40℃ to -35℃), which is beneficial for the accumulation of SiF in liquid form in the bottom.

[0085] like Figure 4 As shown, in one possible implementation, the present invention also provides a high-pressure continuous distillation purification method for silicon tetrafluoride, implemented based on the purification system described in the above embodiments, the method comprising:

[0086] S1. The crude silicon tetrafluoride raw material under normal pressure is pressurized to a high pressure condition, and high-boiling-point polar impurities are removed by pretreatment to obtain pretreated raw material.

[0087] Specifically, such as Figure 1 As shown, crude silicon tetrafluoride raw material at atmospheric pressure (pressure approximately 1 barA, temperature approximately 30°C) is pressurized to 18 barA to 22 barA by raw material compressor 8 (e.g., Figure 1 (As shown, the pressure is increased to approximately 20 barA). The temperature of the raw material increases due to the heat of compression after pressure increase, and it is cooled to 35°C to 45°C by the second cooler 17 (e.g., Figure 1 After being cooled to approximately 40°C, the raw material is fed into the pretreatment unit. The pretreatment unit is a temperature-switching adsorption device, comprising at least two adsorbers 15 connected in parallel. Each adsorber 15 is filled with a specialized adsorbent and equipped with a regeneration electric heater 14. The raw material undergoes adsorption treatment in the temperature-switching adsorption device to remove high-boiling-point polar impurities such as water, carbon dioxide, sulfur dioxide, and hydrogen fluoride, resulting in pretreated raw material. The two sets of adsorbers 15 alternately perform adsorption and thermal regeneration, achieving continuous production. The content of high-boiling-point polar impurities in the pretreated raw material is reduced to extremely low levels, preventing these impurities from clogging and corroding the equipment during subsequent low-temperature distillation.

[0088] S2. The pretreated raw material is introduced into the main heat exchanger and exchanged heat countercurrently with the low-temperature medium in the closed-loop refrigerant system, so that the pretreated raw material is pre-cooled to partial liquefaction and forms a gas-liquid mixed phase.

[0089] Specifically, the pretreated raw material (temperature 35℃~45℃) enters through the material inlet of the main heat exchanger 1 and undergoes countercurrent heat exchange with the low-pressure, low-temperature gaseous refrigerant from the closed-loop refrigerant system inside the main heat exchanger 1. During the heat exchange process, the pretreated raw material is gradually cooled, its temperature decreasing to a certain temperature range (approximately -30℃~-25℃) below its boiling point and above its freezing point. This causes some of the silicon tetrafluoride in the raw material to change from a gaseous state to a liquid state, but some components (mainly low-boiling-point non-condensable light impurities) remain in a gaseous state, forming a gas-liquid mixture. This gas-liquid mixture is discharged from the material outlet of the main heat exchanger 1 and enters the next process. Simultaneously, the low-pressure, low-temperature gaseous refrigerant is reheated and rewarmed in the main heat exchanger 1 by the pretreated raw material, recovering from a low-temperature state to near ambient temperature (approximately 40℃), and then returns to the inlet of the refrigeration compressor 9, completing one heat exchange cycle in the refrigerant cycle.

[0090] S3. The gas-liquid mixture is fed into a primary distillation column for primary distillation. A high-pressure refrigerant provided by a closed-loop refrigerant system provides a heat source for the vaporization of the bottom material. A low-pressure, low-temperature refrigerant after throttling and expansion refrigeration is used to condense the gas phase at the top of the column. The bottom of the column is discharged with heavy component residues enriched with high-boiling-point impurities, and the top of the column is collected with deweighted material.

[0091] Specifically, the gas-liquid mixture enters the first-stage distillation column 2 through the feed inlet (located near the bottom of the column). The operating pressure of the first-stage distillation column 2 is 14 barA to 20 barA, the operating temperature at the top of the column is -35℃ to -28℃, and the operating temperature at the bottom of the column is -30℃ to -25℃.

[0092] Regarding reboiling heating: High-pressure (approximately 15 barA) gaseous refrigerant from the closed-loop refrigerant system is introduced into the heat medium inlet of the first reboiler 4 via the first gas supply line 10. The high-pressure gaseous refrigerant condenses and releases heat in the first reboiler 4, utilizing its latent heat of phase change to provide a vaporization heat source for the liquid silicon tetrafluoride in the column bottom. This causes the liquid silicon tetrafluoride in the column bottom to vaporize and flow upwards, establishing a gas-liquid mass transfer interface within the column. After releasing heat, the refrigerant condenses into a liquid or gas-liquid mixture and is discharged from the reboiler.

[0093] Regarding the top condensation: The throttling expansion valve 11 reduces the pressure of the high-pressure liquid refrigerant to a low-pressure, low-temperature liquid refrigerant of 1.15 barA and -44°C. The low-pressure, low-temperature liquid refrigerant is then introduced into the cold medium inlet of the first condenser 6 via the second liquid supply line 12. The low-pressure, low-temperature liquid refrigerant evaporates and absorbs heat in the first condenser 6, absorbing the latent heat of condensation of the gaseous silicon tetrafluoride at the top of the tower, causing the gaseous silicon tetrafluoride at the top of the tower to condense into liquid and fall back into the tower or serve as reflux liquid. The refrigerant itself is completely vaporized by heating into a low-pressure, low-temperature gaseous refrigerant of 1.15 barA and -44°C, which is discharged from the first condenser 6 and then flows back to the main heat exchanger 1 for rewarming.

[0094] In the first-stage distillation column 2, heavy component impurities with boiling points higher than silicon tetrafluoride are enriched in the reboiler and discharged through the heavy component residue discharge pipeline installed in the reboiler; light component impurities with boiling points lower than silicon tetrafluoride and silicon tetrafluoride itself are enriched at the top of the column and collected from the top and sent to the second-stage distillation column 3. At the same time, low-boiling-point non-condensable light component impurities (oxygen-argon mixture, nitrogen, hydrogen, etc.) are also enriched at the top of the column and discharged through the first light component tail gas discharge pipeline installed at the top of the column.

[0095] S4. The deweighted material is fed into a secondary distillation column for secondary distillation. A high-pressure refrigerant provided by a closed-loop refrigerant system is used to provide a heat source for vaporization of the material in the bottom of the column. A low-pressure, low-temperature refrigerant after throttling and expansion refrigeration is used to condense the gas phase at the top of the column. Light component impurities are discharged from the top of the column, and high-purity silicon tetrafluoride product is collected from the bottom of the column.

[0096] Specifically, the deweighted material from the top of the primary distillation column 2 enters the secondary distillation column 3 through the feed inlet. The operating pressure of the secondary distillation column 3 is 18 barA to 20 barA, the operating temperature at the top of the column is -40℃ to -35℃, and the operating temperature at the bottom of the column is -37℃ to -32℃.

[0097] Regarding reboiling heating: High-pressure gaseous refrigerant is introduced into the heat medium inlet of the second reboiler 5 through the first gas supply pipeline 10. In the second reboiler 5, it condenses and releases heat, providing a heat source for the vaporization of liquid tetrafluoride in the bottom of the secondary distillation column, so that the liquid tetrafluoride in the bottom of the column is heated and vaporized, and a reboiling cycle is established. After the refrigerant releases heat, it condenses into a liquid or gas-liquid mixture and is discharged from the reboiler.

[0098] Regarding the top condensation: The low-pressure, low-temperature liquid refrigerant is introduced into the cold medium inlet of the second condenser 7 through the second liquid supply line 12. It evaporates and absorbs heat in the second condenser 7, absorbing the latent heat of condensation of the gaseous silicon tetrafluoride at the top of the tower, causing the gaseous silicon tetrafluoride at the top of the tower to condense into liquid and reflux. The refrigerant itself is heated and completely vaporized into a low-pressure, low-temperature gaseous refrigerant of 1.15 barA and -44℃, which is discharged from the second condenser 7 and then refluxed back to the main heat exchanger 1 for rewarming.

[0099] In the secondary distillation column 3, low-boiling-point non-condensable light component impurities (oxygen-argon mixture, nitrogen, hydrogen, etc.) are enriched at the top of the column and discharged through the second light component tail gas discharge pipeline set at the top of the column; high-purity silicon tetrafluoride is enriched in the bottom of the column and is collected through the high-purity silicon tetrafluoride product outlet set in the bottom of the column. After two-stage distillation, the boron trifluoride impurity content in the silicon tetrafluoride product is reduced to below 5 ppm, and the product purity is 5N grade (99.999%).

[0100] In the above method, the heavy component residue discharged from the bottom of the first-stage distillation column 2, the first light component tail gas discharged from the top of the first-stage distillation column 2, and the second light component tail gas discharged from the top of the second-stage distillation column 3 are respectively connected to the tail gas inlet of the main heat exchanger 1 through their respective discharge pipelines. After being reheated by countercurrent heat exchange with the high-temperature feed in the main heat exchanger 1, they are collected and connected to the tail gas treatment tower for harmless treatment. The high-purity silicon tetrafluoride product collected from the bottom of the second-stage distillation column 3 enters the main heat exchanger 1 through the product inlet. After being reheated to room temperature by countercurrent heat exchange with the high-temperature feed, it sequentially enters the deep chemical adsorption unit 16 (filled with aluminum fluoride-based adsorbent, which selectively adsorbs trace amounts of boron trifluoride impurities by utilizing the strong coordination effect of the unsaturated coordination sites on the surface of boron trifluoride and aluminum fluoride, removing the boron trifluoride content in the product to the ppb level) and the product booster, and is then pressurized and transported to the product storage tank. Figure 3 As shown, silicon tetrafluoride raw material containing BF3 impurities enters the deep chemical adsorption unit 16 at approximately 2 bar A and 10°C. After adsorption treatment, the BF3 content in the product can be reduced to the ppb level, and then it is pressurized and transported to the product booster.

[0101] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0102] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A high-pressure continuous distillation purification system for silicon tetrafluoride, characterized in that, include: The raw material pressurization unit is used to pressurize the crude silicon tetrafluoride raw material under normal pressure to a high pressure condition; The raw material pretreatment unit is used to remove high-boiling-point polar impurities from high-pressure crude silicon tetrafluoride raw materials; The main heat exchanger, whose material inlet is connected to the outlet of the raw material pretreatment unit, is used to pre-cool the crude silicon tetrafluoride raw material after removing high-boiling-point polar impurities by countercurrent heat exchange with a low-temperature medium to partially liquefy it, forming a gas-liquid mixed phase. A primary distillation column, whose feed inlet is connected to the material outlet of the main heat exchanger, is used to separate heavy component impurities from the gas-liquid mixture. The bottom of the primary distillation column is equipped with a first reboiler, and the top of the column is equipped with a first condenser. The secondary distillation column has its feed inlet connected to the top outlet of the primary distillation column. It is used to separate light component impurities from the deweighted material. The reboiler of the secondary distillation column is equipped with a second reboiler, and the top of the column is equipped with a second condenser. The reboiler of the secondary distillation column is also equipped with a high-purity silicon tetrafluoride product outlet. A refrigerant closed-loop refrigeration system includes a refrigeration compressor, a first cooler, a first gas supply line connected to the first reboiler and the second reboiler respectively, a throttling expansion valve, and a second liquid supply line connected to the first condenser and the second condenser respectively.

2. The silicon tetrafluoride high-pressure continuous distillation purification system according to claim 1, characterized in that, The refrigeration compressor pressurizes the low-pressure gaseous refrigerant to a high-pressure gaseous state. After the compression heat is removed by the first cooler, the high-pressure refrigerant is divided into two paths: one path is introduced into the heat medium inlet of the first reboiler and the second reboiler through the first gas supply line, using the latent heat of phase change of the refrigerant to provide a vaporization heat source for the liquid silicon tetrafluoride in the bottom of the tower; the other path is pre-cooled by the main heat exchanger and then combined with the refrigerant after reboiling heat exchange, and sent to the throttling expansion valve for pressure reduction and refrigeration.

3. The silicon tetrafluoride high-pressure continuous distillation purification system according to claim 2, characterized in that, The throttling expansion valve throttles and depressurizes the high-pressure liquid refrigerant to a low-pressure, low-temperature liquid state, which is then fed into the cold medium inlets of the first condenser and the second condenser via the second liquid supply pipeline, absorbing the latent heat of condensation of the gaseous silicon tetrafluoride at the top of the tower. The low-pressure, low-temperature gaseous refrigerant, after heat exchange and vaporization, flows back to the main heat exchanger, where it undergoes countercurrent heat exchange with the high-temperature feed and returns to the inlet of the refrigeration compressor, completing a closed-loop cycle.

4. The silicon tetrafluoride high-pressure continuous distillation purification system according to claim 1, characterized in that, The raw material pressurization unit includes a raw material compressor, which is used to pressurize the crude silicon tetrafluoride raw material at atmospheric pressure from 1 barA to 18 barA to 22 barA. After pressurization, the raw material is cooled to 35°C to 45°C by a second cooler and then sent to the raw material pretreatment unit.

5. The silicon tetrafluoride high-pressure continuous distillation purification system according to claim 1, characterized in that, The raw material pretreatment unit is a temperature-switching adsorption device, which includes at least two adsorbers connected in parallel. Each adsorber is filled with a special adsorbent and is equipped with a regeneration electric heater to remove high-boiling-point polar impurities such as water, carbon dioxide, sulfur dioxide, and hydrogen fluoride from the high-pressure crude silicon tetrafluoride. The two sets of adsorbers alternately perform adsorption and thermal regeneration to achieve continuous production.

6. The silicon tetrafluoride high-pressure continuous distillation purification system according to claim 1, characterized in that, The primary distillation column is also used for the pre-separation of low-boiling-point non-condensable light component impurities; the pre-cooled gas-liquid mixed phase feed is fed from the bottom of the de-weighting column, and the low-boiling-point non-condensable light component impurities are enriched at the top of the column. The low-boiling-point non-condensable light component impurities include oxygen-argon mixture, nitrogen and hydrogen.

7. The silicon tetrafluoride high-pressure continuous distillation purification system according to claim 6, characterized in that, The first-stage distillation column is equipped with a heavy component residue discharge pipeline in the reboiler, and a first light component tail gas discharge pipeline is equipped at the top of the first-stage distillation column. The second-stage distillation column is equipped with a second light component tail gas discharge pipeline at the top of the column. The heavy component residue discharge pipeline, the first light component tail gas discharge pipeline, and the second light component tail gas discharge pipeline are respectively connected to the tail gas inlet of the main heat exchanger. After being reheated by the main heat exchanger, they are connected to the tail gas treatment tower. The product outlet of the reboiler of the secondary distillation column is connected to the product inlet of the main heat exchanger. The high-purity silicon tetrafluoride product is reheated to room temperature by the main heat exchanger and then pressurized and transported by the product booster.

8. The silicon tetrafluoride high-pressure continuous distillation purification system according to claim 7, characterized in that, The product booster is also connected to a deep chemical adsorption unit, which is filled with aluminum fluoride-based adsorbent. It selectively adsorbs trace amounts of boron trifluoride impurities by utilizing the strong coordination between boron trifluoride and the unsaturated coordination sites on the surface of aluminum fluoride, thereby removing the boron trifluoride content in the product to the ppb level.

9. The silicon tetrafluoride high-pressure continuous distillation purification system according to claim 1, characterized in that, The operating pressure of the first-stage distillation column is 14 barA to 20 barA, the operating temperature at the top of the column is -35℃ to -28℃, and the operating temperature at the bottom of the column is -30℃ to -25℃. The operating pressure of the second-stage distillation column is 18 barA to 20 barA, the operating temperature at the top of the column is -40℃ to -35℃, and the operating temperature at the bottom of the column is -37℃ to -32℃. After two-stage distillation, the boron trifluoride impurity content in the silicon tetrafluoride product is reduced to below 5 ppm, and the product purity is 5N grade.

10. A method for purifying silicon tetrafluoride by high-pressure continuous distillation, characterized in that, Based on the purification system according to any one of claims 1-9, it includes: S1. Pressurize the crude silicon tetrafluoride raw material under normal pressure to a high pressure condition, and remove high-boiling-point polar impurities through pretreatment to obtain pretreated raw material; S2. The pretreated raw material is introduced into the main heat exchanger and exchanged heat countercurrently with the low-temperature medium in the closed-loop refrigeration system of refrigerant, so that the pretreated raw material is pre-cooled to partial liquefaction and forms a gas-liquid mixed phase. S3. The gas-liquid mixture is fed into a primary distillation column for primary distillation. The high-pressure refrigerant provided by the closed-loop refrigerant system provides a heat source for vaporization of the bottom material. The low-pressure, low-temperature refrigerant after throttling expansion refrigeration is used to condense the top gas phase. The bottom liquid of the column is discharged from the heavy component residue enriched with high-boiling-point impurities, and the deweighted material is collected from the top of the column. S4. The deweighted material is fed into a secondary distillation column for secondary distillation. The high-pressure refrigerant provided by the closed-loop refrigerant system provides a heat source for vaporization of the material in the bottom of the column. The low-pressure, low-temperature refrigerant after throttling expansion refrigeration is used to condense the gas phase at the top of the column. Light component impurities are discharged from the top of the column, and high-purity silicon tetrafluoride product is collected from the bottom of the column.

Images