A method for purifying SiF4 from industrial off-gases

Abstract

This invention relates to the field of fluorine-containing resource separation and recovery technology, and discloses a method for purifying SiF4 from industrial tail gas. The method for purifying SiF4 from industrial tail gas provided by this invention employs ethanol dissolution of the tail gas followed by cryogenic distillation, wherein the top temperature of the cryogenic distillation column is -84℃ to -50℃. This method, through the synergistic effect of selective ethanol absorption and cryogenic distillation purification, forms a closed loop of "dissolution-desorption-distillation." Ethanol, as a solvent, can be recycled, improving the overall economic and environmental benefits of the process. Furthermore, the cryogenic distillation temperature is significantly higher than the boiling point of SiF4 (-86℃), avoiding excessive cryogenic cooling (e.g., below -100℃), reducing refrigeration energy consumption, and lowering energy consumption compared to traditional cryogenic methods.

Description

Technical Field

[0001] This invention relates to the field of fluorine-containing resource separation and recovery technology, specifically to a method for purifying SiF4 from industrial exhaust gas. Background Technology

[0002] Silicon tetrafluoride (SiF4) is a colorless gas with a pungent odor at room temperature and pressure. Its melting point is -90.2℃, and its boiling point is -86℃. It is soluble in ethanol, nitric acid, and hydrofluoric acid. As a fluorine-containing compound, SiF4 has important industrial applications in semiconductors, fluorochemicals, and optical materials. High-purity SiF4 is used in the semiconductor field for processing etching materials such as silicon nitride and tantalum silicide; as a silicon source to form the required silicon thin film on the surface of silicon wafers; as a silicon dopant to improve the electrical properties of silicon wafers; and extensively in the manufacture of high-purity silicon-based materials such as monocrystalline and polycrystalline silicon.

[0003] Currently, the main industrial synthesis processes for SiF4 include fluorite-sulfuric acid method, silicon-containing and fluorine-containing material synthesis method, hydrofluoric acid method, fluorosilicate pyrolysis method, and fluorosilicate method. However, these synthesis processes cause SiF4 to hydrolyze into fluorosilicone ether ((SiF3)2O) due to the water generated in the reaction, leading to pipeline blockage and safety hazards. In addition, the raw materials contain impurities (such as sulfates and heavy metals), which limits the purity of the product (usually ≤99.9%). Therefore, multiple purification processes (such as distillation and adsorption) are required to achieve electronic grade purity, resulting in high production costs. Industrial exhaust gas containing SiF4 mainly originates from byproducts generated during the production of chemical products such as hydrogen fluoride, aluminum fluoride, or phosphate fertilizers. The main components of this industrial exhaust gas also include PF5, CO2, N2, O2, SO2, and a small amount of HF. HF readily reacts with SiF4 to form fluorosilicic acid (H2SiF6), increasing the difficulty of separation. Traditional distillation methods can theoretically separate HF (boiling point 19.5℃) and SiF4 (boiling point -86℃) due to the significant difference in boiling points, but in practice, efficient purification is difficult to achieve due to equipment corrosion and side reactions. Furthermore, the exhaust gas contains gases such as SO2 and O2, which readily form complexes with SiF4, further reducing the recovery rate and making it difficult to achieve a product purity of 5N grade (99.999%).

[0004] The semiconductor industry requires SiF4 to reach a purity level of 99.999% (5N grade), which requires solving the problem of impurities such as fluorosilicone ether and HF. Chinese invention patent application publication number CN112755725A discloses a method for recovering and reusing the effective components of HF-containing industrial tail gas FTrPSA. This method has significant defects in terms of process complexity, high energy consumption, product purity, environmental protection and operational controllability. Summary of the Invention

[0005] The present invention aims to provide a method for purifying SiF4 from industrial exhaust gas, in order to solve the technical problems existing in the prior art of purifying SiF4 from industrial exhaust gas in terms of process complexity, high energy consumption, and raw material adaptability, product purity, environmental protection and operational controllability.

[0006] In a first aspect, the present invention provides a method for purifying SiF4 from industrial tail gas, which employs ethanol to dissolve the industrial tail gas and low-temperature distillation for purification, wherein the top temperature of the low-temperature distillation purification column is -84℃ to -50℃.

[0007] In one alternative implementation, the following steps are performed:

[0008] (1) First, pre-cool the industrial tail gas, then absorb it with ethanol to obtain SiF4-ethanol solution; (2) Heating the SiF4-ethanol solution causes SiF4 to desorb from the ethanol into a gas-liquid mixture. The SiF4 containing ethanol vapor is then separated to obtain the desorbed gas. (3) The desorbed gas is condensed and dried to obtain condensed gas, and the condensate is returned to the ethanol storage tank for recycling; (4) The condensed gas is passed into a first-stage distillation column with a bottom temperature of -15℃ and a top temperature of -60℃ to -50℃. Primary SiF4 gas is obtained at the top of the column. The primary SiF4 gas is passed into a secondary distillation column. The bottom temperature is -72℃ and the top temperature is -84℃ to -77.5℃. Secondary SiF4 gas is obtained at the top of the column.

[0009] In one optional embodiment, the pre-cooling temperature in step (1) is -10℃ to 20℃; the ethanol absorption temperature is 0℃ to 20℃, and the ethanol reacts with SiF4 in the industrial tail gas to generate ethyl fluorosilicate (EtOSiF3), which dissolves in the ethanol. And / or, the heating temperature in step (2) is 61°C to 75°C, and the heating medium is hot water; And / or, the condensation temperature in step (3) is -30℃ to -5℃.

[0010] In one optional embodiment, the heating temperature in step (2) is 70°C, and the drying in step (3) is performed using a 3A molecular sieve dryer, preferably with a pore size of 3 Å.

[0011] In one optional embodiment, the SiF4-containing industrial waste gas originates from hydrogen fluoride production waste gas, aluminum fluoride production waste gas, or phosphorus chemical production waste gas. The industrial exhaust gas contains 5-15 vol% SiF4 and impurities including PF5, CO2, N2, O2, SO2 and / or 0-1 vol% HF.

[0012] In one optional embodiment, the ethanol contains ≤30ppm of H2O.

[0013] In one optional embodiment, the condensation in step (3) uses an aqueous ethylene glycol solution as a refrigerant, wherein the mass percentage concentration of ethylene glycol in the aqueous ethylene glycol solution is 47-52%; preferably, the mass percentage concentration of ethylene glycol in the aqueous ethylene glycol solution is 50.2%.

[0014] In one optional implementation, the system pressure for distillation purification in step (4) is 0.015 to 0.30 MPa.

[0015] In one alternative implementation, the refrigerant used for distillation reflux condensation is ethanol or dichloromethane; The system pressure for distillation purification is 0.020–0.060 MPa.

[0016] In one optional embodiment, the distillation columns of the primary distillation and the secondary distillation have a theoretical plate number of ≥20, optionally 20 to 45, and the packing is Pall rings.

[0017] The equipment used for ethanol absorption of industrial tail gas is a stirred tank, with a dissolution and absorption speed of 140~700 rpm.

[0018] The technical solution of this invention has the following advantages: 1. The method for purifying SiF4 from industrial tail gas provided by this invention employs ethanol dissolution of the industrial tail gas and low-temperature distillation purification. The low-temperature distillation purification temperature is -84℃ to -50℃. Under the process conditions of -84℃ to -50℃, the boiling range distance between SiF4 and ethanol, H2O·HF, H2SiF6, and complexes is utilized to achieve efficient separation of SiF4 from impurities. Simultaneously, the low-temperature distillation temperature avoids excessive cryogenic treatment (e.g., below -100℃), reducing refrigeration energy consumption. Compared with traditional cryogenic methods, energy consumption is lower. The combined use of ethanol dissolution and low-temperature distillation forms a closed loop of "dissolution-desorption-distillation," and ethanol, as a solvent, can be recycled, improving the overall economic and environmental benefits of the process. Furthermore, this method is simple to operate, has a high yield, and avoids the risks of air and water pollution caused by direct emission or simple treatment of industrial tail gas, reduces corrosion damage to equipment caused by fluorides, and lowers environmental governance costs.

[0019] 2. The method for purifying SiF4 from industrial exhaust gas provided by this invention adopts a streamlined process of "pre-cooling-absorption-desorption-condensation-distillation" to avoid intermediate product retention and ensure the stability of continuous industrial production. The first-stage distillation removes light components (such as N2 and O2), and the second-stage distillation removes heavy components (such as HF). The purity of SiF4 is increased from industrial grade (≤99.5%) to electronic grade (≥99.999%), with a high impurity removal rate and an ethanol recovery rate of ≥95%.

[0020] 3. The method for purifying SiF4 from industrial exhaust gas provided by this invention achieves a desorption efficiency of ≥90% for SiF4 from ethanol at 61℃~75℃ (hot water medium), while avoiding ethanol volatilization loss due to high temperature (>80℃). The desorption efficiency and energy consumption are balanced. Controlling the condensation temperature can reduce ethanol residue: ethanol vapor is fully liquefied at a condensation temperature of -30℃~-5℃, reducing the load on subsequent distillation.

[0021] 4. In the method for purifying SiF4 from industrial exhaust gas provided by this invention, ethanol reacts with SiF4 at 0℃~20℃ to generate ethyl fluorosilicate (EtOSiF3), which preferentially dissolves SiF4 rather than impurities (such as SO2, CO2), thereby improving absorption selectivity; 70℃ is the optimal temperature for SiF4 to desorb from ethanol, which can avoid solvent degradation and further improve desorption efficiency; 3A molecular sieve (pore size 3Å) selectively adsorbs water molecules (kinetic diameter 2.8Å), while SiF4 molecules with a diameter greater than 3Å are not adsorbed, effectively removing trace impurities.

[0022] 5. The method for purifying SiF4 from industrial exhaust gas provided by this invention covers three typical exhaust gas sources: hydrogen fluoride, aluminum fluoride, and phosphorus chemical industry. It has wide adaptability. The SiF4 concentration of 5-15 vol% is a common range in industry. This avoids the problem of excessively high concentration causing blockage of the absorption tower, or excessively low concentration resulting in insufficient yield, thus ensuring economic feasibility.

[0023] 6. The trace amounts of water in the method for purifying SiF4 from industrial exhaust gas provided by this invention can trigger the hydrolysis of SiF4. The H2O content in anhydrous ethanol is ≤30ppm, which can completely eliminate the risk of hydrolysis, extend the life of the equipment, and finally obtain SiF4 with a purity of ≥99.999%.

[0024] 7. The method for purifying SiF4 from industrial exhaust gas provided by this invention has a mass percentage concentration of 47-52%, which can achieve the purpose of this invention. Preferably, the ethylene glycol aqueous solution with a mass percentage concentration of 50.2% is matched with the condensation temperature of -30℃ to -5℃ to avoid the refrigerant freezing and ensure the stable operation of the system. At the same time, the ethylene glycol aqueous solution is cheaper than refrigerants such as liquid nitrogen.

[0025] 8. The system pressure of distillation purification in step (4) of the method for purifying SiF4 from industrial tail gas provided by the present invention is 0.015 to 0.30 MPa. Within this pressure range, the theoretical plate number requirement can be reduced, thereby simplifying the process, further saving energy consumption, and also avoiding air intake, reducing the corrosion of stainless steel equipment by O2.

[0026] 9. In the method for purifying SiF4 from industrial tail gas provided by this invention, the refrigerant used for distillation reflux condensation is ethanol or dichloromethane; the pressure of the distillation purification system is 0.020~0.060MPa. The freezing point of ethanol or dichloromethane in the above scheme matches the distillation temperature (-84℃~-50℃), and 0.020~0.060MPa is the optimal pressure range for SiF4 condensation, resulting in a high yield of SiF4 gas.

[0027] 10. In the method for purifying SiF4 from industrial tail gas provided by this invention, the distillation columns of the primary and secondary distillations have a theoretical plate number of ≥20, and the packing material is Pall rings; the equipment used for ethanol absorption of tail gas is a stirred tank, with a dissolution absorption speed of 140~700 rpm. The above scheme uses 20~45 theoretical plates to ensure HF residue ≤0.08ppm, high impurity removal rate, and achieves SiF4 purity ≥99.999%, meeting semiconductor-grade purity requirements. The Pall rings have a large specific surface area and high mass transfer efficiency, and the speed of 140~700 rpm prevents emulsification of the ethanol-tail gas mixture and promotes phase separation. Attached Figure Description

[0028] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 The solubility diagram of SiF4 at different temperatures under normal pressure; Figure 2 This is a process flow diagram of the apparatus for purifying SiF4 from industrial exhaust gas according to the present invention. Figure 3 This is a gas chromatogram of an industrial exhaust gas sample dissolved in anhydrous ethanol. Explanation of reference numerals in the attached drawings: 1. Absorption tower; 2. Stirred vessel; 3. SiF4-C2H5OH storage tank; 4. Heater; 5. Gas-liquid separator; 6. Condenser; 7. Primary distillation column; 8. Secondary distillation column; 9. Polytetrafluoroethylene gas collection bag; 10. Ethanol tank; 11. Recovery tank 1; 12. Recovery tank 2; 13. Pump. Detailed Implementation

[0030] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0031] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0032] Ethanol: Anhydrous ethanol (colorless and transparent liquid): C2H5OH ≥ 99.7%, H2O ≤ 0.003%, acidity (as H+) + (Calculated) ≤0.04%, sulfate ≤0.0001%; Ethylene glycol industrial grade standard purity (≥99%).

[0033] Example 1 Reference Figure 2 Connect the following components: 1 is the absorption tower, 2 is the stirred tank, 3 is the SiF4-C2H5OH storage tank, 4 is the heater, 5 is the gas-liquid separator, 6 is the condenser, 7 is the primary distillation column, 8 is the secondary distillation column, 9 is the polytetrafluoroethylene gas collection bag, 10 is the ethanol tank, 11 is the recovery tank 1, 12 is the recovery tank 2, and 13 is the pump.

[0034] S1: Preparation of Absorbent Solution Raw material pretreatment Industrial tail gas containing SiF4 (mainly from hydrogen fluoride production tail gas) is continuously fed into the absorption tower at a flow rate of 1 Nm³ / h. The SiF4 concentration in the tail gas is 10 vol%, and it also contains impurities such as PF5, CO2, N2, O2, SO2 and trace amounts of HF 0.5 vol.

[0035] The exhaust gas is pre-cooled to -10℃ to remove some easily condensable, high-boiling impurities.

[0036] Ethanol absorption The equipment used for ethanol absorption is a stirred tank. The rotation speed is 140 rpm during absorption. The pretreated tail gas is fully contacted with anhydrous ethanol (H2O content ≤30ppm) for 30 minutes. The absorption temperature is controlled at 0℃ and the absorption pressure is atmospheric pressure.

[0037] It reacts with SiF4 to form ethyl fluorosilicate (EtOSiF3) and dissolves in ethanol to form a SiF4-ethanol solution. When this solution is introduced into a SiF4-ethanol storage tank, the solubility of SiF4 reaches 0.3193 g / mL.

[0038] S2: Desorption and gas-liquid separation Heating desorption Perform airtightness inspection with 0.3 MPa N2 (purity reaching 5N), confirm that there are no leakage points, and maintain the pressure for 24 h. After confirmation of compliance, conduct N2 replacement ventilation for 10 min for the entire process of the device process, which is regarded as qualified. Transfer the SiF4-ethanol solution in the SiF4-ethanol storage tank to the heater, and control the flow rate of the SiF4-ethanol solution entering the heater to be basically maintained at 5 ml / min through the flowmeter. Transfer for 30 min, heat to 61 °C with 65 °C hot water, and SiF4 is desorbed from ethanol into a gas-liquid mixed phase, and the SiF4 desorption efficiency is 93%.

[0039] The calculation method of the SiF4 desorption efficiency η1 is: η1 = the amount of desorbed SiF4 / the amount of initially dissolved SiF4 in the ethanol solution × 100%.

[0040] The amount of initially dissolved SiF4 in the ethanol solution is the amount of initially dissolved SiF4 in the ethanol solution before desorption: According to the SiF4-ethanol storage tank in step S1, the dissolution concentration of SiF4 in the SiF4-ethanol solution is 0.3193 g / mL, and the calculated amount of initially dissolved SiF4 in the ethanol solution is: 5 ml / min 30 min 0.3193 g / mL = 47.895 g; Determination of the amount of desorbed SiF4 (the amount of SiF4 in the gas phase after desorption): Pass the desorbed gas into a gas absorption bottle containing an excessive amount of 2M NaOH absorption solution. After the reaction is complete, use ion chromatography (IC) to determine the content of F - in the absorption solution is 32.523 g, and the amount of SiF4 is accurately calculated to be 44.542 g through material balance (Si:F = 1:4).

[0041] SiF4 desorption efficiency η1 = 44.542 g / 47.895 g = 93%.

[0042] Gas-liquid separation The gas-liquid mixture after desorption enters the gas-liquid separator to separate out SiF4 gas containing a small amount of ethanol vapor.

[0043] S3: Condensation and ethanol recovery Condensation and purification The desorbed gas passes through a condenser (ethylene glycol aqueous solution as the refrigerant, and the mass percentage concentration of ethylene glycol is 50.2%), the condensation temperature is -5 °C, to further remove residual ethanol vapor, and the condensate returns to the ethanol tank for recycling.

[0044] Gas drying The gas after condensation passes through a 3A molecular sieve dryer with a pore size of 3 Å to remove trace entrained substances.

[0045] S4: Low-temperature rectification and purification: The refrigerant used for distillation reflux condensation is anhydrous ethanol or dichloromethane, and the system operating pressure is controlled at 0.020 MPa.

[0046] First-stage distillation (removal of light components) The dry gas is fed into a distillation column (theoretical number of 20 plates), the packing is Pall rings, the bottom temperature is controlled at -15℃, the top temperature is -60℃, and the primary SiF4 gas is obtained at the top of the column.

[0047] After removing light components such as H2, N2, and O2, primary SiF4 gas is obtained at the top of the column.

[0048] Secondary distillation (complete removal of heavy components) The gas from the top of the column enters the secondary distillation column (bottom temperature -72℃, top temperature -84℃) to remove HF and SiF6. 2- Recombined components.

[0049] Finally, SiF4 gas with a purity of ≥99.999% (5N+ grade) was obtained at the top of the column, with HF residue of 0.05ppm, (SiF3)2O residue of 0.08ppm, SO2 residue of 0.04ppm, yield of 95.3%, and energy consumption of 10.2kWh / kg.

[0050] Purity detection method: Gas chromatography-mass spectrometry (GC-MS) was used to verify the purity to be ≥99.999% / 5N+ grade, with a detection limit of 0.01 ppm.

[0051] S5: Product Collection and Storage Collection and detection High-purity SiF4 gas was collected via PTFE pipe into a polytetrafluoroethylene gas collection bag (-80℃), and the impurity content was detected by gas chromatography-mass spectrometry (GC-MS) (HF limit 0.01ppm, (SiF3)2O limit 0.01ppm, SO2 limit 0.02ppm).

[0052] Filling and Transportation SiF4 gas meeting purity requirements is filled into high-pressure steel cylinders (316L stainless steel) at a filling pressure ≤15MPa for use in semiconductor etching or silicon wafer doping.

[0053] Calculation of ethanol recycling rate η2: η2=m 初始 / m 回收 ×100%, Example 1, Processing capacity 380kg / h SiF4: Initial ethanol addition: 500kg (calculated based on a liquid-to-gas ratio of 5:1); Ethanol recovery: 475kg / h (measured by a flow meter and weighing sensor); Ethanol recycling rate: η2=475 / 500×100%=95%.

[0054] Example 2 The implementation steps, detection methods, and calculation methods in this embodiment are basically the same as in Embodiment 1, but the specific process parameters are different, as follows: S1: The industrial tail gas (from phosphorus chemical tail gas) has a SiF4 concentration of 15 vol%, and contains impurities PF5, CO2, N2, O2, SO2 1.0 vol%, and trace amounts of HF; the tail gas is pre-cooled to 0℃, the ethanol absorption temperature is controlled at 20℃, and the absorption speed is 700 rpm.

[0055] S2 Desorption and Gas-Liquid Separation: The flow rate of the SiF4-ethanol solution into the heater is controlled by a flow meter to maintain approximately 5 ml / min. After 30 minutes of delivery, the solution is heated from 90℃ to 75℃ using hot water. SiF4 desorbs from the ethanol into a gas-liquid mixed phase. The initial amount of SiF4 dissolved in the ethanol solution is 5 ml / min. 30min 0.3193 g / mL = 47.895 g, determination of F in the absorption solution - The content was 33.222g. The amount of SiF4 desorbed was accurately calculated to be 44.542g through material balance (Si:F=1:4), and the SiF4 desorption efficiency was 95%.

[0056] S3 Condensation and Ethanol Recovery: The condensation temperature of the desorbed gas is -15℃, and the mass percentage concentration of the refrigerant ethylene glycol is 52%.

[0057] S4 Low-Temperature Distillation Purification: The system operating pressure is controlled at 0.30 MPa.

[0058] First-stage distillation (removal of light components): the bottom temperature is controlled at -15℃ and the top temperature is -50℃ (theoretical number of plates: 45).

[0059] Two-stage distillation (complete removal of heavy components): reboiler temperature -72℃, top temperature -77.5℃, removal of HF and SiF6. 2- Recombined components.

[0060] The final product obtained at the top of the column was SiF4 with a purity of 99.999% (5N+ grade), HF residue of 0.08ppm, (SiF3)2O residue of 0.06ppm, SO2 residue of ≤0.03ppm, yield of 92.2%, and energy consumption of 9.8kWh / kg.

[0061] S5: Product Collection and Storage The ethanol recycling rate is 95%.

[0062] Example 3 The implementation steps, detection methods, and calculation methods in this embodiment are basically the same as in Embodiment 1, but the specific process parameters are different, as follows: S1: The concentration of SiF4 in the industrial tail gas (from aluminum fluoride production tail gas) is 5 vol%, containing impurities PF5, CO2, N2, O2, SO2 0.8 vol%, and trace amounts of HF; the tail gas is pre-cooled to 10℃, the ethanol absorption temperature is controlled at 10℃, the absorption speed is 300 rpm, and the solubility of SiF4 in the SiF4-ethanol solution reaches 0.1780 g / mL.

[0063] S2 Desorption and Gas-Liquid Separation: The flow rate of the SiF4-ethanol solution into the heater was controlled by a flow meter to maintain approximately 6 ml / min. After 35 minutes of delivery, the solution was heated to 70°C using 75°C hot water. SiF4 desorbed from the ethanol into a gas-liquid mixture, with a desorption efficiency of 93%. The initial amount of SiF4 dissolved in the ethanol solution before desorption was 6 ml / min. 35min 0.1780 g / mL = 37.38 g, determine the F in the absorption solution. - The content was 25.38g. Through material balance (Si:F=1:4), the amount of SiF4 desorbed was accurately calculated to be 34.763g, and the SiF4 desorption efficiency was 93%.

[0064] S3 Condensation and Ethanol Recovery: The condensation temperature of the desorbed gas is -20℃.

[0065] S4 Low-Temperature Distillation Purification: The system operating pressure is controlled at 0.060 MPa.

[0066] First-stage distillation (removal of light components): the bottom temperature is controlled at -15℃ and the top temperature is -59℃.

[0067] Two-stage distillation (complete removal of heavy components): reboiler temperature -72℃, top temperature -80℃, removal of HF and SiF6. 2- Recombined components.

[0068] Finally, SiF4 gas with a purity of ≥99.999% (5N+ grade) was obtained at the top of the column, with HF residue of 0.04ppm, (SiF3)2O residue of 0.04ppm, SO2 residue of 0.05ppm, yield of 95.1%, and energy consumption of 9.8kWh / kg.

[0069] S5: Product Collection and Storage The ethanol recycling rate is 96%.

[0070] Example 4 The implementation steps, detection methods, and calculation methods in this embodiment are basically the same as in Embodiment 1, but the specific process parameters are different, as follows: S1: The concentration of SiF4 in the industrial tail gas (from phosphorus chemical tail gas) is 15 vol%, containing impurities PF5, CO2, N2, O2, SO2 0.3 vol%, and trace amounts of HF; the tail gas is pre-cooled to 20℃, the ethanol absorption temperature is controlled at 15℃, the absorption speed is 500 rpm, and the solubility of SiF4 in the SiF4-ethanol solution reaches 0.1732 g / mL.

[0071] S2 Desorption and Gas-Liquid Separation: The flow rate of the SiF4-ethanol solution into the heater was controlled by a flow meter to be maintained at approximately 8 ml / min. After 32 minutes of delivery, the solution was heated to 65°C using 70°C hot water. SiF4 desorbed from the ethanol into a gas-liquid mixed phase. The initial amount of SiF4 dissolved in the ethanol solution was 6 ml / min. 35min 0.1732 g / mL = 44.3392 g, determination of F in the absorption solution - The content was 29.14g. Through material balance (Si:F=1:4), the amount of SiF4 desorbed was accurately calculated to be 39.91g, and the SiF4 desorption efficiency was 90%.

[0072] S3 Condensation and Ethanol Recovery: The condensation temperature of the desorbed gas is -30℃, and the mass percentage concentration of the refrigerant ethylene glycol is 47%.

[0073] S4 Low-Temperature Distillation Purification: The system operating pressure is controlled at 0.015 MPa.

[0074] First-stage distillation (removal of light components): the bottom temperature is controlled at -15℃ and the top temperature is -58℃.

[0075] Secondary distillation (complete removal of heavy components): Bottom temperature -72℃, top temperature -79℃, removing trace amounts of heavy components such as HF.

[0076] The final product obtained at the top of the column was SiF4 with a purity of ≥99.999% (5N+ grade), HF residue of 0.08ppm, (SiF3)2O residue of 0.08ppm, SO2 residue of 0.05ppm, yield of 93.2%, and energy consumption of 9.8kWh / kg.

[0077] S5: Product Collection and Storage The ethanol recycling rate is 96%.

[0078] Example 5 SiF4 standard gas (purity 99.999%) was dissolved in anhydrous ethanol solution. The flow rate of the SiF4 standard gas was controlled at 25 ml / min using a rotor flow meter. The temperature of the anhydrous ethanol solution was adjusted to -30℃, -10℃, 0℃, 10℃, 20℃, and 70℃ using an ice-salt bath. The samples were dissolved and absorbed separately at each of these five temperatures for 1 hour, with the absorption rotor speed controlled at 300 rpm. The optimal dissolution and absorption temperature of SiF4 in anhydrous ethanol solution was determined. After dissolution and absorption, the samples were stored in a -18℃ freezer (e.g., ...). Figure 1 The solubility of SiF4 at different temperatures under normal pressure is shown in Table 1. The results show that the solubility of SiF4 in anhydrous ethanol solution gradually decreases with increasing temperature, and exhibits high solubility at -10℃, where the solubility of SiF4 in anhydrous ethanol can reach 36.4 g / 100 g.

[0079] Table 1. Solubility of SiF4 standard gas in anhydrous ethanol and gas chromatography response values ​​at different dissolution temperatures (SiF4 solubility g / mL)

[0080] Comparative Example 1 This comparative example uses the conventional process / fluorite-sulfuric acid method of existing technology to prepare SiF4. The raw material is fluorite (CaF2 + 98% concentrated sulfuric acid). The steps are: reaction of fluorite + concentrated sulfuric acid + quartz sand → multi-stage cryogenic separation → distillation.

[0081] The specific synthesis steps are as follows: Excess concentrated sulfuric acid with a molar ratio of H2SO4:CaF2 = 1.1~1.3:1 is thoroughly mixed with fluorite powder in a mixer to form a paste; this paste is then fed into a reactor preheated to 300-400℃, and the temperature is controlled within a stable range of 350-450℃ by a jacket; the generated gases are a mixture of HF, SiF4, H2O vapor, and impurities such as SO2 and CO2; the solid residue is mainly calcium sulfate (gypsum). The generated HF gas immediately reacts with excess quartz sand in the latter part of the reactor at 250-400℃ to generate SiF4.

[0082] Separation and purification steps: Dust removal is performed on the high-temperature crude gas, followed by cooling and impurity removal with frozen brine at -10 to 0°C. The gas is then passed through a concentrated sulfuric acid scrubbing tower to further remove moisture and residual HF. The purified gas is compressed to 0.8-1.5 MPa and subjected to multi-stage cryogenic separation at -40 to -100°C to obtain crude SiF4. Finally, SiF4 is purified by distillation at -90 to -70°C to obtain SiF4 with a purity of 99.9% (3N) to 99.99% (4N).

[0083] Comparative Example 2 SiF4 was obtained from industrial-grade crude SiF4 (purity ≤99.5%) using an adsorption method (activated carbon / molecular sieve).

[0084] The specific steps are as follows: First, the industrial-grade SiF4 crude gas is pre-cooled and dehumidified by passing it through a condenser at -10 to -20℃. Then, an activated carbon adsorption tower is used to remove heavy components. Two activated carbon adsorption towers, A / B, are connected in parallel, one in use and one on standby, allowing for switching and regeneration. The process conditions are set as follows: adsorption temperature: 20-40℃, pressure: 0.8-1.5MPa, empty tower gas velocity: 0.1-0.3m / s, adsorption cycle: 24-72 hours. Next, a molecular sieve adsorption tower is used to deeply remove light components and polar molecules. The process conditions are set as follows: adsorption temperature: 10-30℃, pressure: 1.0-2.0MPa, empty tower gas velocity: 0.05-0.15m / s, adsorption cycle: 48-120 hours. Finally, the gas exiting the adsorption tower is passed through a 0.01μm PTFE membrane filter to remove entrained dust.

[0085] The purity and residual impurities of SiF4 obtained by the methods of Comparative Examples 1, 2 and Example 1 were measured, and the process parameters and energy consumption were compared. The results are shown in Table 2.

[0086] Table 2 Comparison of SiF4 process parameters between Comparative Examples 1 and 2 and Example 1 of the present invention.

[0087] Table 3: Test results of SiF4 samples purified in Examples 1-4

[0088] From the data in Tables 1 to 3, we can see that: Solubility versus temperature (Table 1): The solubility of SiF4 in anhydrous ethanol decreased significantly with increasing temperature (0.3193 g / mL at -10℃ → 0.1317 g / mL at 20℃), indicating the feasibility of the low-temperature absorption temperature range of -30℃ to 20℃, with the optimal absorption temperature being -10℃.

[0089] The solubility change rate ΔS > 100 J / (mol·K) indicates that a heating temperature of 61℃~75℃ is the optimal choice for the desorption stage.

[0090] Advantages of the process comparison (Table 2): The purity of Example 1 of this invention is ≥99.999% / 5N+ grade, which is far superior to the traditional fluorite-sulfuric acid process (≤99.5%), and the HF residue is ≤0.05ppm (the traditional fluorite-sulfuric acid process is ≥1ppm), which meets the industry standard of the semiconductor industry (the semiconductor industry standard is 99.999% / 5N grade).

[0091] Raw material adaptability (Table 3): Under different exhaust gas concentrations (5-15 vol%), the purity of SiF4 is consistently ≥99.999% / 5N+ grade, and the HF residue is ≤0.08 ppm, proving that the process adaptability is strong.

[0092] Industrial feasibility: In Example 1, industrial tail gas containing SiF4 was continuously fed into the absorption tower at a flow rate of 1 Nm³ / h. After 72 hours of continuous operation, the residual impurities were measured to be stable (HF≤0.05ppm), and the yield was 95.3%.

[0093] from Figure 3 It can be seen that: Figure 3 Samples 1, 2, and 3 in the examples correspond to the SiF4 samples purified in Examples 1, 2, and 3, respectively.

[0094] Figure 3 The standard used is high-purity silicon tetrafluoride (SiF4), with a purity of 5N, which serves as a reference material.

[0095] Figure 3 Gas chromatography analysis was used to demonstrate the spectral characteristics of the standard and the SiF4 samples purified in Examples 1-3.

[0096] Standard sample spectrum: Retention time: 9.95 min, serving as the characteristic elution time of SiF4 and providing a qualitative benchmark. The characteristic ion peak at m / z 127 corresponds to ([SiF3)). + Fragment ions, and their m / z 80 counterparts ([SiF4)). + Molecular ion peaks. The appearance of these ion peaks verifies the specificity of GC-MS detection and avoids interference from analogues (such as SF6).

[0097] Spectra of purified SiF4 samples from Examples 1-3: Retention time: 9.95 min (consistent with the standard), confirming the presence of SiF4 in the SiF4 samples purified in Examples 1-3 without retention time drift, indicating high column stability. Peak area corresponds to impurity concentration ≤0.1 ppm (detection limit 0.01 ppm), indicating that the process of this invention can effectively control impurities.

[0098] Figure 3 The retention times of the standard sample overlapped and the ion peaks matched those of the SiF4 samples purified in Examples 1-3. The spectral baselines were stable and free of interference from extraneous peaks, further verifying the effectiveness of the pretreatment (such as ethanol dissolution) and instrument parameter optimization of the SiF4 samples purified in Examples 1-3 of this invention.

[0099] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for purifying SiF4 from industrial exhaust gas, characterized in that, The process involves dissolving industrial waste gas in ethanol and purifying it through low-temperature distillation. The top temperature of the low-temperature distillation purification column is -84℃ to -50℃.

2. The method for purifying SiF4 from industrial exhaust gas according to claim 1, characterized in that, Follow these steps: (1) First, pre-cool the industrial tail gas, then absorb it with ethanol to obtain SiF4-ethanol solution; (2) Heating the SiF4-ethanol solution causes SiF4 to desorb from the ethanol into a gas-liquid mixture. The SiF4 containing ethanol vapor is then separated to obtain the desorbed gas. (3) The desorbed gas is condensed, dried, and condensed gas is obtained. The condensate is returned to the ethanol storage tank for recycling. (4) The condensed gas is fed into a first-stage distillation column. The bottom temperature of the column is -15℃ and the top temperature is -60℃ to -50℃. Primary SiF4 gas is obtained at the top of the column. The primary SiF4 gas is passed into a secondary distillation column. The bottom temperature is -72℃ and the top temperature is -84℃ to -77.5℃. Secondary SiF4 gas is obtained at the top of the column.

3. The method for purifying SiF4 from industrial exhaust gas according to claim 2, characterized in that, The pre-cooling temperature in step (1) is -10℃ to 20℃; the ethanol absorption temperature is 0℃ to 20℃. And / or, the heating temperature in step (2) is 61°C to 75°C; And / or, the condensation temperature in step (3) is -30℃ to -5℃.

4. The method for purifying SiF4 from industrial exhaust gas according to claim 3, characterized in that, The drying process in step (3) uses a 3A molecular sieve dryer.

5. The method for purifying SiF4 from industrial exhaust gas according to claim 4, characterized in that, The industrial exhaust gas comes from hydrogen fluoride production, aluminum fluoride production, or phosphorus chemical production. The industrial exhaust gas contains 5-15 vol% SiF4 and impurities including PF5, CO2, N2, O2, SO2 and / or 0-1 vol% HF.

6. The method for purifying SiF4 from industrial exhaust gas according to claim 5, characterized in that, The ethanol contains ≤30ppm of H2O.

7. The method for purifying SiF4 from industrial exhaust gas according to claim 6, characterized in that, In step (3), the condensation is carried out using an aqueous solution of ethylene glycol as the refrigerant, and the mass percentage concentration of ethylene glycol in the aqueous solution is 47-52%.

8. The method for purifying SiF4 from industrial exhaust gas according to claim 7, characterized in that, The system pressure for distillation purification in step (4) is 0.015 to 0.30 MPa.

9. The method for purifying SiF4 from industrial exhaust gas according to claim 8, characterized in that, The refrigerant used for distillation reflux condensation is ethanol or dichloromethane; The system pressure for distillation purification is 0.020–0.060 MPa.

10. The method for purifying SiF4 from industrial exhaust gas according to claim 9, characterized in that, The distillation columns of the primary distillation and the secondary distillation have a theoretical plate number of ≥20, optionally 20 to 45, and the packing material is Pall rings; The equipment used for ethanol absorption of industrial tail gas is a stirred tank, with a dissolution and absorption speed of 140~700 rpm.

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