A method and device for synthesizing CF4 by activating SF6 using a two-stage dielectric barrier discharge

Abstract

The present invention discloses a method and apparatus for synthesizing CF4 by activating SF6 using a two-stage dielectric barrier discharge (DBD) plasma. The present invention proposes a two-stage DBD plasma activation method for degrading SF6 and introducing CO2 gas to synthesize CF4. The first-stage DBD plasma reactor degrades SF6 molecules, breaking them down into fluorine atoms and other low-fluorine and sulfur small molecules. This step not only effectively degrades SF6 but also provides the necessary fluorine source for subsequent CF4 synthesis. The second-stage DBD plasma reactor uses CO2 as a carbon source to react with the low-fluorine and sulfur small molecules produced in the first reaction to generate CF4 gas. The CF4-containing mixed gas undergoes a first-stage condensation process to condense some of the fluorine-containing acidic waste gas into a liquid state. The remaining mixed gas then undergoes a second-stage condensation process to condense the CF4 gas into a liquid state and collect it, achieving efficient product separation and purification. Some acidic gases that do not participate in the reaction are treated in an alkaline absorption tank to reduce environmental harm.

Description

Technical Field

[0001] The present invention belongs to the technical field of efficient degradation and resource utilization of sulfur hexafluoride, and in particular relates to a method and device for synthesizing CF4 by activating SF6 using a two-stage dielectric barrier discharge. Background Art

[0002] Sulfur hexafluoride (SF6) gas is colorless, odorless, non-toxic, and non-flammable. It is a synthetic fluoride with excellent electrical insulation and arc-extinguishing properties, and is commonly used in electrical insulation equipment. In recent years, with the rapid development of the power industry, the use of SF6 has increased year by year. However, annual power system equipment maintenance and replacement result in large amounts of SF6 gas being emitted. Due to its octahedral molecular structure and extreme stability, it is difficult to degrade naturally in the atmosphere. It is also a potent greenhouse gas with a greenhouse effect potential 23,500 times that of CO2. With the introduction of the dual carbon policy, the degradation of SF6 has become imperative.

[0003] Currently, SF6 degradation treatments primarily include thermal catalytic degradation, photocatalytic degradation, and plasma degradation. Plasma degradation utilizes high-energy electrons and active particles in the plasma to collide with SF6 gas molecules, causing them to dissociate in a short period of time. Depending on how the plasma is generated, it can be categorized as radio frequency discharge, electron beam discharge, microwave discharge, and dielectric barrier discharge plasma. Dielectric barrier discharge plasma utilizes continuous discharge breakdown and barrier formation between electrodes and an insulating medium to produce a large amount of active species. As a low-temperature plasma, it offers numerous advantages, including convenient and flexible equipment, mild reaction conditions, ease of control, high energy efficiency, and safe and reliable operation. It is widely used in waste gas treatment.

[0004] In recent years, carbon tetrafluoride (CF4) has been widely used in various electronics industries, such as semiconductor manufacturing and refrigeration. Traditional methods for synthesizing CF4 generally suffer from harsh reaction conditions, low efficiency, high energy consumption, and high cost. Currently, the main methods for preparing CF4 include direct fluorination of alkanes, direct fluorocarbon synthesis, and hydrofluoromethane fluorination. Direct fluorination of alkanes is the earliest method used in the industry to prepare fluoroalkanes. The process is relatively mature and simple to operate, but the reaction process is difficult to control, the products are complex, and the yield is low. Direct fluorocarbon synthesis utilizes carbon and fluorine gas to react. Although the yield is high, it carries significant safety risks and requires special methods to control the reaction conditions. Hydrofluoromethane fluorination is a simple process for synthesizing CF4, but the synthesis cost is high, making it difficult to apply on a large scale. These methods have harsh reaction conditions, low yield, high cost, and safety issues. Currently, there is an urgent need for a safe and reliable green synthesis technology with mild reaction conditions, high yield, high efficiency, and low cost to address these issues. Summary of the Invention

[0005] Based on the above-mentioned prior art, the present invention provides a method and device for synthesizing CF4 by activating SF6 through a two-stage dielectric barrier discharge. The present invention can not only achieve the simultaneous degradation of two greenhouse gases, CO2 and SF6, and reduce the harm of the greenhouse effect, but also synthesize CF4 electronic specialty gas, thereby realizing the resource utilization of SF6 fluorine and the preparation of high-value CF4 gas. The present invention can provide a new idea for the resource utilization of SF6, CO2 treatment and the synthesis of CF4 electronic specialty gas.

[0006] The technical solution adopted to achieve the above-mentioned purpose of the present invention is:

[0007] A method for synthesizing CF4 by activating SF6 by a two-stage dielectric barrier discharge, characterized by comprising the following steps:

[0008] S1. Passing background gas and sulfur hexafluoride gas into a first-stage DBD plasma reactor, the background gas is ionized to generate plasma, and the sulfur hexafluoride gas is ionized into fluorine atoms and low-fluorine sulfides after being activated by the plasma. The generated fluorine atoms and low-fluorine sulfides further react with oxygen and silicon dioxide to generate fluorine-containing small molecules;

[0009] S2. Subsequently, the fluorine-containing small molecules generated in step S1 enter the secondary DDB plasma reactor connected to the primary DBD plasma reactor, and carbon dioxide gas is introduced into the secondary DBD plasma reactor. Under the action of plasma, the low-fluorine sulfide reacts with carbon dioxide to generate carbon tetrafluoride gas.

[0010] Furthermore, the background gas is an inert gas.

[0011] Furthermore, in step S1, the discharge region in the first-stage DBD plasma reactor is filled with catalyst γ-Al2O3.

[0012] Furthermore, in step S2, the mixed gas containing carbon tetrafluoride flowing out from the outlet of the secondary DBD plasma reactor is first subjected to primary condensation to condense the fluorine-containing acidic waste gas into liquid, and then the remaining mixed gas is subjected to secondary condensation to condense the generated carbon tetrafluoride gas into liquid, and the liquid carbon tetrafluoride is collected.

[0013] Furthermore, the condensation temperature of the first-stage condensation is -60 to -50°C, and the condensation temperature of the second-stage condensation is -150 to -130°C.

[0014] A two-stage dielectric barrier discharge device for activating SF6 to synthesize CF4 comprises a sulfur hexafluoride gas supply unit, a background gas supply unit, a first-level DBD plasma reactor, a second-level DBD plasma reactor, a carbon dioxide gas supply unit, a first-level condensation unit, and a second-level condensation unit. The sulfur hexafluoride gas supply unit and the background gas supply unit are respectively connected to the inlet of the first-level DBD plasma reactor, the outlet of the first-level DBD plasma reactor and the carbon dioxide gas supply unit are respectively connected to the inlet of the second-level DBD plasma reactor, the outlet of the second-level DBD plasma reactor is connected to the inlet of the first-level condensation unit, and the gas outlet of the first-level condensation unit is connected to the inlet of the second-level condensation unit.

[0015] It also includes a gas mixer. The sulfur hexafluoride gas supply unit includes a sulfur hexafluoride gas cylinder, a first gas supply branch and a first pressure reducing valve. The upstream end of the first gas supply branch is connected to the sulfur hexafluoride gas cylinder, and the first pressure reducing valve is installed on the first gas supply branch. The background gas supply unit includes a background gas cylinder, a second gas supply branch and a second pressure reducing valve. The upstream end of the second gas supply branch is connected to the background gas cylinder, and the second pressure reducing valve is installed on the second gas supply branch. The downstream ends of the first gas supply branch and the second gas supply branch are respectively connected to the gas mixer, and the outlet of the gas mixer is connected to the inlet of the first-level DBD plasma reactor.

[0016] The carbon dioxide supply unit includes a carbon dioxide cylinder, a third gas supply branch pipe and a third pressure reducing valve. The upstream end of the third gas supply branch pipe is connected to the carbon dioxide cylinder, the third pressure reducing valve is installed on the third gas supply branch pipe, and the downstream end of the third gas supply branch pipe is connected to the inlet of the secondary DBD plasma reactor.

[0017] The primary condensing unit includes a primary condenser, which includes a first gas outlet and a first liquid outlet. The secondary condensing unit includes a secondary condenser, which includes a second gas outlet and a second liquid outlet. The secondary DBD plasma reactor outlet is connected to the primary condenser inlet, and the first gas outlet is connected to the secondary condenser inlet.

[0018] The secondary condensing unit further includes a CF4 collecting tank, and the second liquid outlet is connected to the CF4 collecting tank.

[0019] The condensing medium in the primary condenser is ethylene glycol aqueous solution, and the condensing medium in the secondary condenser is liquid nitrogen.

[0020] It also includes a tail gas treatment unit, which includes an alkali solution treatment pool and a tail gas pipe. Both ends of the tail gas pipe are connected to the alkali solution treatment pool and the second gas outlet respectively.

[0021] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0022] 1. This invention proposes a two-stage DBD plasma activation method for SF6 degradation and the introduction of CO2 gas to synthesize CF4. The first-stage DBD plasma reactor degrades SF6 molecules, breaking them down into fluorine atoms and other low-fluorine and sulfur small molecules. This step not only effectively degrades SF6 but also provides the necessary fluorine source for subsequent CF4 synthesis. The second-stage DBD plasma reactor uses CO2 as a carbon source to react with the fluorine-containing small molecules produced in the first reaction to produce CF4 gas. The CF4-containing mixed gas undergoes a primary condensation process to condense some of the fluorine-containing acidic waste gas small molecules into a liquid state. The remaining mixed gas then undergoes a secondary condensation process to condense the CF4 gas into a liquid state and collect it, achieving efficient product separation and purification. Some acidic gases that do not participate in the reaction are treated in an alkaline solution absorption tank to reduce environmental damage.

[0023] 2. By utilizing a two-stage DBD reaction structure, the present invention not only achieves efficient SF6 degradation but also significantly increases the synthesis rate of CF4. This invention not only addresses the limitations and shortcomings of traditional CF4 production methods but also provides a new approach for SF6 fluorine source utilization, CO2 greenhouse gas treatment, and the synthesis of high-value chemicals.

[0024] 3. The method of the present invention can not only achieve complete degradation of SF6, but also use SF6 as a fluorine source and CO2 as a carbon source to react under the action of plasma to synthesize CF4, a high-value electronic specialty gas in semiconductor manufacturing. It not only solves the problem that SF6 is difficult to handle, but also utilizes its fluorine resources to combine with CO2 to synthesize CF4, turning waste into treasure.

[0025] 4. The present invention adopts a two-stage DBD reaction structure. The two reaction devices have different discharge conditions and can discharge independently. The hierarchical treatment method helps to more effectively control the reaction process and improve the purity and yield of the product.

[0026] 5. The present invention can achieve complete degradation of SF6 by filling the first-stage plasma reactor with γ-Al2O3, so that more low-fluorine sulfides react with CO2 in the secondary reaction tube to generate CF4. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the structure of a device for activating SF6 to synthesize CF4 using a two-stage dielectric barrier discharge.

[0028] Figure 2 This is a gas chromatogram of the mixed gas at the outlet of the two-stage DBD plasma reactor in Example 2.

[0029] Figure 3 This is a gas chromatogram of the mixed gas at the outlet of the first-level DBD plasma reactor in Example 3.

[0030] Among them, 1-sulfur hexafluoride gas cylinder; 2-first gas supply branch; 3-first pressure reducing valve; 4-argon gas cylinder; 5-second gas supply branch; 6-second pressure reducing valve; 7-gas mixer; 8-carbon dioxide gas cylinder; 9-third gas supply branch; 10-third pressure reducing valve; 11-first-stage DBD plasma reactor; 12-second-stage DBD plasma reactor; 13-first-stage condenser: 1301-first gas outlet, 1302-first liquid outlet; 14-waste liquid pool; 15-second-stage condenser: 1501-second gas outlet, 1502-second liquid outlet; 16-CF4 collection tank; 17-alkali solution treatment pool; 18-exhaust pipe. DETAILED DESCRIPTION

[0031] The following is a detailed description of the double-stage dielectric barrier discharge device for activating SF6 to synthesize CF4 according to the present invention with reference to the accompanying drawings.

[0032] Example 1

[0033] The structure of the double-stage dielectric barrier discharge device for activating SF6 to synthesize CF4 provided in this embodiment is as follows: Figure 1 As shown, it includes a sulfur hexafluoride gas supply unit, an argon gas supply unit, a gas mixer 7, a first-level DBD plasma reactor 11, a second-level DBD plasma reactor 12, a carbon dioxide gas supply unit, a first-level condensation unit, a second-level condensation unit and an exhaust gas treatment unit.

[0034] The sulfur hexafluoride gas supply unit includes a sulfur hexafluoride gas cylinder 1, a first gas supply branch pipe 2 and a first pressure reducing valve 3. The upstream end of the first gas supply branch pipe 2 is connected to the sulfur hexafluoride gas cylinder 1, and the first pressure reducing valve 3 is installed on the first gas supply branch pipe 1.

[0035] The background gas supply unit includes an argon gas cylinder 4 , a second gas supply branch pipe 5 and a second pressure reducing valve 6 . The upstream end of the second gas supply branch pipe 5 is connected to the background gas cylinder 4 , and the second pressure reducing valve 6 is installed on the second gas supply branch pipe 5 .

[0036] The downstream ends of the first gas supply branch pipe 2 and the second gas supply branch pipe 5 are respectively connected to the gas mixer 7 . The sulfur hexafluoride gas or sulfur hexafluoride waste gas enters the gas mixer 7 and is evenly mixed in the gas mixer 7 .

[0037] The first-stage DBD plasma reactor 11 consists of a coaxial DBD reaction tube, a plasma power supply, and a voltage regulator. The voltage regulator and plasma power supply are used to control reaction conditions and parameters. The outlet of the gas mixer 7 is connected to the inlet of the coaxial DBD reaction tube of the first-stage DBD plasma reactor 11 via a pipeline. The pipeline connecting the outlet of the gas mixer 7 and the first-stage DBD plasma reactor 11 is equipped with an electromagnetic flowmeter and a solenoid valve.

[0038] The secondary DBD plasma reactor 12 comprises a coaxial DBD reaction tube, a plasma power supply, and a voltage regulator. The voltage regulator and plasma power supply control reaction conditions and parameters. The outlet of the coaxial DBD reaction tube of the primary DBD plasma reactor 11 is connected to the inlet of the coaxial DBD reaction tube of the secondary DBD plasma reactor 12 via a pipe.

[0039] The carbon dioxide supply unit includes a carbon dioxide cylinder 8, a third gas supply branch pipe 9, and a third pressure reducing valve 10. The upstream end of the third gas supply branch pipe 9 is connected to the carbon dioxide cylinder 8, and the third pressure reducing valve 10 is installed on the third gas supply branch pipe 9. The downstream end of the third gas supply branch pipe 9 is connected to the pipeline connecting the outlet of the coaxial DBD reaction tube of the first DBD plasma reactor 11 and the inlet of the coaxial DBD reaction tube of the second DBD plasma reactor 12. Carbon dioxide is introduced into the coaxial DBD reaction tube of the second DBD plasma reactor 12 through the carbon dioxide cylinder 8.

[0040] The primary condensation unit includes a primary condenser 13 and a waste liquid tank 14. The condensing medium in the primary condenser 13 is an ethylene glycol-water solution, and the condensation temperature of the primary condenser 13 is -60°C. The primary condenser 13 includes a first gas outlet 1301 and a first liquid outlet 1302. The coaxial DBD reaction tube outlet of the secondary DBD plasma reactor 12 is connected to the inlet of the primary condenser 13 via a pipe. The first liquid outlet 1302 is connected to the waste liquid tank 14 via a pipe, which is used to collect liquefied fluorine-containing acidic waste gas.

[0041] The secondary condensation unit includes a secondary condenser 15 and a CF4 collection tank 16. The condensing medium in the secondary condenser 15 is liquid nitrogen, and the condensing temperature of the secondary condenser 15 is -150°C. The secondary condenser 15 includes a second gas outlet 1501 and a second liquid outlet 1502. The first gas outlet 1301 is connected to the inlet of the secondary condenser 15. The second liquid outlet 1502 is connected to the CF4 collection tank 16 via a pipeline. The CF4 collection tank 16 is used to collect liquefied carbon tetrafluoride.

[0042] The tail gas treatment unit includes an alkaline solution treatment tank 17 and an exhaust pipe 18. The ends of the exhaust pipe 18 are connected to the alkaline solution treatment tank 17 and the second gas outlet 1501, respectively. Ca(OH)2 alkaline solution is placed in the alkaline solution treatment tank 17 to fully neutralize and absorb any unreacted acidic gases, preventing them from causing harm to the environment.

[0043] The method of activating SF6 to synthesize CF4 by two-stage dielectric barrier discharge of the present invention is described in detail below in conjunction with the above-mentioned device.

[0044] Example 2

[0045] 1. The discharge region of the coaxial DBD reaction tube of the first-stage DBD plasma reactor 11 is filled with a catalyst γ-Al2O3. A condensing medium, ethylene glycol aqueous solution, is added to the first-stage condenser 13 to set the condensation temperature of the first-stage condenser 13 to -60°C. Liquid nitrogen is added to the second-stage condenser 15 to set the condensation temperature of the second-stage condenser 15 to -150°C.

[0046] 2. According to the connection relationship of the above devices (such as Figure 1 As shown in the figure, assemble and connect the two-stage dielectric barrier discharge device for activating SF6 to synthesize CF4.

[0047] 3. Open the argon cylinder 4, the second pressure reducing valve 6 and the gas mixer 7, close the valve on the tail gas pipe 18, and pass argon to test the air tightness of the device to prevent the leakage of toxic gas during the reaction from causing harm to the staff and ensure that the reaction is carried out stably and orderly. After the test is completed, close the argon cylinder 4, the second pressure reducing valve 6 and the gas mixer 7.

[0048] 4. Set the input power of the first-stage DBD plasma reactor 11 to 100 W, and set the input power of the second-stage DBD plasma reactor 12 to 100 W. Turn on the first-stage DBD plasma reactor 11 and the second-stage DBD plasma reactor. The temperatures in the coaxial DBD reaction tubes of the first-stage DBD plasma reactor 11 and the second-stage DBD plasma reactor 12 begin to rise. After a period of time, the temperatures in the coaxial DBD reaction tubes of the first-stage DBD plasma reactor 11 and the second-stage DBD plasma reactor 12 stabilize at 105° C. and 115° C., respectively.

[0049] 5. Open the valves on the pipelines connecting the inlets of the first and second DBD plasma reactors 11 and 12, as well as the valve on the tail pipe 18, of the sulfur hexafluoride cylinder 1, the first pressure-reducing valve 3, the argon cylinder 4, the second pressure-reducing valve 6, and the gas mixer 7. The sulfur hexafluoride gas in the sulfur hexafluoride cylinder 1 and the argon gas in the argon cylinder 4 enter the gas mixer 7, where they are mixed evenly before entering the coaxial DBD reaction tube of the first DBD plasma reactor 11. An electromagnetic flowmeter and solenoid valve connected to the outlet of the gas mixer 7 precisely control the amount of sulfur hexafluoride and argon gases flowing in, thereby controlling the concentration of SF6 entering the first DBD plasma reactor 12.

[0050] In this embodiment, the flow rate of sulfur hexafluoride gas is controlled at 6 mL / min, the flow rate of argon gas is controlled at 294 mL / min, and the concentration of SF6 is 2%. SF6 and Ar are directly connected to two channels of the gas distribution instrument, forming a mixed gas within the gas mixer 7. The output flow rate of the mixed gas is 300 mL / min, which is precisely controlled by an electromagnetic flowmeter and then delivered to the first-stage DBD plasma reactor.

[0051] 6. In the coaxial DBD reaction tube of the first-stage DBD plasma reactor 11, argon gas is ionized to generate plasma. After plasma activation, sulfur hexafluoride gas is ionized into fluorine atoms and low-fluorine sulfides (such as SF5, SF4, etc.). The generated fluorine atoms and low-fluorine sulfides further react with oxygen and silicon dioxide to generate fluorine-containing small molecules, etc., which enter the coaxial DBD of the second-stage DBD plasma reactor 12.

[0052] 7. After the first-level DBD plasma reactor 11 discharges for 15 minutes, open the carbon dioxide cylinder 8 and the third pressure reducing valve 10, and the carbon dioxide enters the coaxial DBD of the second-level DBD plasma reactor 12, and reacts with the fluorine-containing small molecules in the coaxial DBD of the second-level DBD plasma reactor 12 to generate CF4 gas.

[0053] The mixed gas discharged from the outlet of the secondary DBD plasma reactor was detected by gas chromatography-mass spectrometry, and the obtained gas chromatogram was as follows: Figure 2 As shown by Figure 2 It can be seen that CF4 gas does exist in the mixed gas. In addition to CF4 gas, there are also SOF2, SOF4, C4F2, SO2, CH3F, SiF4, and SF4.

[0054] 8. The mixed gas composed of the generated CF4 gas and other gas products (SiF4, SOF2, SOF4 and SO2, etc.) enters the first condenser for condensation, and part of the fluorine-containing acidic waste gas (such as SOF2, SOF4) is condensed into liquid, and the liquid fluorine acidic waste enters the waste liquid pool 14 for collection.

[0055] 9. The remaining mixed gas enters the second condenser for condensation, and the CF4 gas is condensed into liquid. The liquid CF4 enters the CF4 collection tank 16 for collection.

[0056] 10. When the reaction needs to be stopped, close the sulfur hexafluoride gas cylinder 1 and the first pressure reducing valve 3. Ten minutes later, close the first DBD plasma reactor 11, the second DBD plasma reactor 12, the carbon dioxide gas cylinder 8, and the third pressure reducing valve 10, and continue to introduce argon gas to drive out the mixed gas in the coaxial DBD reaction tubes of the first DBD plasma reactor 11 and the second DBD plasma reactor 12. Ten minutes later, close the first condenser 13, the second condenser 15, the argon gas cylinder 4, and the second pressure reducing valve 6.

[0057] Example 3

[0058] Compared with Example 1, the input power of the first-stage DBD plasma reactor was changed, and the output flow rate of the mixed gas was changed to 150 mL / min. The SF6 concentration in the mixed gas discharged from the outlet of the first-stage DBD plasma reactor was detected by gas chromatograph. The degradation rate of SF6 was calculated based on the SF6 concentration detected at the outlet of the first-stage DBD plasma reactor. The data graph of the change of the SF6 degradation rate with the change of the input power of the first-stage DBD plasma reactor is shown in Table 1 below:

[0059] Table 1 Effect of input power of first-stage DBD plasma reactor on SF6 degradation rate

[0060]

[0061] It can be seen from Table 1 that with the increase of the input power of the first-stage DBD plasma reactor, the SF6 degradation rate also increases. When the input power of the first-stage DBD plasma reactor reaches 100W, the SF6 degradation rate reaches 99.8%, which is close to complete degradation.

[0062] In addition, the gas chromatograph was used to detect the mixed gas discharged from the outlet of the first-stage DBD plasma reactor, and the obtained chromatogram was as follows: Figure 3 As shown by Figure 3 It can be seen that the main components of the mixed gas discharged from the outlet of the first-stage DBD plasma reactor are SO2, SO2F2, SOF2, SOF4, SiF4, etc. These substances are speculated to be low-fluorine sulfides and fluorine atoms produced by the degradation of sulfur hexafluoride, which react with silicon dioxide or oxygen atoms to obtain fluorine-containing small molecules.

[0063] Example 4

[0064] Compared with Example 1, the input power of the secondary DBD plasma reactor was changed, and the CF4 concentration in the mixed gas discharged from the outlet of the secondary DBD plasma reactor was detected by gas chromatography-mass spectrometry. The CF4 yield was calculated based on the CF4 concentration detected at the outlet of the secondary DBD plasma reactor. The data graph of the CF4 yield changing with the input power of the secondary DBD plasma reactor is shown in Table 2 below:

[0065] Table 2 Effect of input power of two-stage DBD plasma reactor on CF4 yield

[0066] Power input power (W) <![CDATA[CF4 yield (%)]]> 60 7.6 70 14.7 80 19.3 90 25.1 100 29.4

[0067] It can be seen from Table 2 that as the input power of the secondary DBD plasma reactor increases, the CF4 yield also increases. When the input power of the secondary DBD plasma reactor reaches 100W, the CF4 yield reaches 29.4%, which is quite impressive.

Claims

1. A method for synthesizing CF4 by activating SF6 using a two-stage dielectric barrier discharge, characterized in that The steps include: S1. Passing background gas and sulfur hexafluoride gas or sulfur hexafluoride waste gas into a first-stage DBD plasma reactor, the background gas is ionized to generate plasma, and sulfur hexafluoride is ionized into fluorine atoms and low-fluorine sulfides after being activated by the plasma. The generated fluorine atoms and low-fluorine sulfides further react with oxygen and silicon dioxide to generate fluorine-containing small molecules; S2. Subsequently, the fluorine-containing small molecules generated in step S1 enter the secondary DDB plasma reactor connected to the primary DBD plasma reactor, and carbon dioxide gas is introduced into the secondary DBD plasma reactor. Under the action of plasma, the low-fluorine sulfide reacts with carbon dioxide to generate carbon tetrafluoride gas.

2. The method for synthesizing CF4 by activating SF6 by a two-stage dielectric barrier discharge according to claim 1, characterized in that: The background gas is an inert gas.

3. The method for synthesizing CF4 by activating SF6 by a two-stage dielectric barrier discharge according to claim 1, characterized in that: In the step S1, the discharge region in the first-stage DBD plasma reactor is filled with catalyst γ-Al2O3.

4. The method for synthesizing CF4 by activating SF6 by two-stage dielectric barrier discharge according to claim 1, characterized in that: In step S2, the mixed gas containing carbon tetrafluoride flowing out of the outlet of the secondary DBD plasma reactor is first subjected to primary condensation to condense the fluorine-containing acidic waste gas into liquid, and then the remaining mixed gas is subjected to secondary condensation to condense the generated carbon tetrafluoride gas into liquid, and the liquid carbon tetrafluoride is collected.

5. The method for synthesizing CF4 by activating SF6 by two-stage dielectric barrier discharge according to claim 4, characterized in that: The condensation temperature of the first-stage condensation is -60 to -50°C, and the condensation temperature of the second-stage condensation is -150 to -130°C.

6. A device based on the method of activating SF6 to synthesize CF4 by two-stage dielectric barrier discharge according to claim 1, characterized in that: The device comprises a sulfur hexafluoride gas supply unit, a background gas supply unit, a first-level DBD plasma reactor, a second-level DBD plasma reactor, a carbon dioxide gas supply unit, a first-level condensation unit and a second-level condensation unit. The sulfur hexafluoride gas supply unit and the background gas supply unit are respectively connected to the inlet of the first-level DBD plasma reactor, the outlet of the first-level DBD plasma reactor and the carbon dioxide gas supply unit are respectively connected to the inlet of the second-level DBD plasma reactor, the outlet of the second-level DBD plasma reactor is connected to the inlet of the first-level condensation unit, and the gas outlet of the first-level condensation unit is connected to the inlet of the second-level condensation unit.

7. The apparatus for the method of synthesizing CF4 by activating SF6 by a two-stage dielectric barrier discharge according to claim 6, characterized in that: It also includes a gas mixer. The sulfur hexafluoride gas supply unit includes a sulfur hexafluoride gas cylinder, a first gas supply branch and a first pressure reducing valve. The upstream end of the first gas supply branch is connected to the sulfur hexafluoride gas cylinder, and the first pressure reducing valve is installed on the first gas supply branch. The background gas supply unit includes a background gas cylinder, a second gas supply branch and a second pressure reducing valve. The upstream end of the second gas supply branch is connected to the background gas cylinder, and the second pressure reducing valve is installed on the second gas supply branch. The downstream ends of the first gas supply branch and the second gas supply branch are respectively connected to the gas mixer, and the outlet of the gas mixer is connected to the inlet of the first-level DBD plasma reactor.

8. The apparatus for the method of synthesizing CF4 by activating SF6 by a two-stage dielectric barrier discharge according to claim 6, characterized in that: The carbon dioxide supply unit includes a carbon dioxide cylinder, a third gas supply branch pipe and a third pressure reducing valve. The upstream end of the third gas supply branch pipe is connected to the carbon dioxide cylinder, the third pressure reducing valve is installed on the third gas supply branch pipe, and the downstream end of the third gas supply branch pipe is connected to the inlet of the secondary DBD plasma reactor.

9. The apparatus for the method of synthesizing CF4 by activating SF6 by a two-stage dielectric barrier discharge according to claim 6, characterized in that: The primary condensing unit includes a primary condenser, which includes a first gas outlet and a first liquid outlet. The secondary condensing unit includes a secondary condenser, which includes a second gas outlet and a second liquid outlet. The secondary DBD plasma reactor outlet is connected to the primary condenser inlet, and the first gas outlet is connected to the secondary condenser inlet.

10. The apparatus for the method of synthesizing CF4 by activating SF6 by a two-stage dielectric barrier discharge according to claim 9, characterized in that: The secondary condensing unit further includes a CF4 collecting tank, and the second liquid outlet is connected to the CF4 collecting tank.

11. The apparatus for the method of synthesizing CF4 by activating SF6 by a two-stage dielectric barrier discharge according to claim 9, characterized in that: The condensing medium in the primary condenser is ethylene glycol aqueous solution, and the condensing medium in the secondary condenser is liquid nitrogen.

12. The apparatus for the method of synthesizing CF4 by activating SF6 by a two-stage dielectric barrier discharge according to claim 9, characterized in that: It also includes a tail gas treatment unit, which includes an alkali solution treatment pool and a tail gas pipe. Both ends of the tail gas pipe are connected to the alkali solution treatment pool and the second gas outlet respectively.

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