Method and device for synthesizing CF4 by activating SF6 through two-stage dielectric barrier discharge

Abstract

The invention discloses a method and a device for synthesizing CF4 by activating SF6 through two-stage dielectric barrier discharge, and provides a method for synthesizing CF4 by activating and degrading SF6 through two-stage DBD plasma and introducing CO2 gas, SF6 molecules are degraded by a first-stage DBD plasma reactor and decomposed into fluorine atoms and other low-fluorine-sulfur small molecules, and the fluorine atoms and other low-fluorine-sulfur small molecules are introduced into a second-stage DBD plasma reactor; the step not only realizes effective degradation of SF6, but also provides a necessary fluorine source for subsequent CF4 synthesis. The second-stage DBD plasma reactor takes CO2 as a carbon source and reacts with low-fluorine sulfur small molecules generated by the first-stage reaction to generate CF4 gas, mixed gas containing the CF4 gas is subjected to first-stage condensation treatment, part of fluorine-containing acid waste gas is condensed into a liquid state, then the remaining mixed gas is subjected to second-stage condensation, the CF4 gas is condensed into the liquid state and collected, and the CF4 gas is discharged from the second-stage DBD plasma reactor. Efficient separation and purification of products are achieved, some acid gas which does not participate in the reaction is treated through the alkali liquor absorption cell, and harm to the environment can be reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of efficient degradation and resource utilization of sulfur hexafluoride, and specifically relates to a method and device for synthesizing CF4 by activating SF6 with 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 often 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, but every year the power system will cause a large amount of SF6 gas to be discharged due to equipment maintenance and replacement. Due to its octahedral molecular structure and extremely stable, it is difficult to degrade naturally in the atmosphere. As a strong greenhouse gas, its greenhouse effect potential is 23,500 times that of CO2. With the introduction of the dual carbon policy, the degradation of SF6 has become imperative.

[0003] At present, the degradation treatment of SF6 mainly includes: thermal catalytic degradation, photocatalytic degradation and plasma degradation. The plasma degradation method uses the high-energy electrons and active particles in the plasma to collide with the SF6 gas molecules, which can dissociate them in a short time. According to the different ways of plasma generation, it can be divided into radio frequency discharge, electron beam discharge, microwave discharge and dielectric barrier discharge plasma. Dielectric barrier discharge plasma uses the electrodes and insulating media to continuously discharge, break down and block to produce a large amount of active substances. As a low-temperature plasma, it has many advantages such as convenient and flexible equipment, mild reaction conditions, easy control, high energy efficiency and safe and reliable operation. It is widely used to treat waste gas.

[0004] In recent years, carbon tetrafluoride (CF4) has been widely used in various electronic industries, such as semiconductor manufacturing and refrigeration. The traditional method of synthesizing CF4 generally has problems such as harsh reaction conditions, low efficiency, high energy consumption and high cost. At present, the methods for preparing CF4 mainly include direct fluorination of alkanes, direct fluorocarbon synthesis and hydrofluoromethane fluorination. The direct fluorination of alkanes is the earliest method used to prepare fluoroalkanes in industry. At present, the process is relatively mature and the operation is simple, but the reaction process is difficult to control, the product is complex and the yield is low. The direct fluorocarbon synthesis method is to use carbon to react with fluorine gas. Although the yield is high, there is a great safety risk, and some special means are needed to control the reaction conditions. The hydrofluoromethane fluorination method is simple to synthesize CF4, but the synthesis cost is large and it is difficult to apply on a large scale. The above methods have harsh reaction conditions, low yield, high cost and safety issues. At present, there is an urgent need for a safe and reliable, mild reaction conditions, high yield, high efficiency and low cost green synthesis technology to solve such problems. 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 realize the simultaneous degradation of two greenhouse gases, CO2 and SF6, and reduce the harm of the greenhouse effect, but also synthesize CF4 electronic special gas, thereby realizing the resource utilization of SF6 fluorine and the preparation of CF4 high-value gas. The present invention can provide a new idea for the resource utilization of SF6, CO2 treatment and the synthesis of CF4 electronic special 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 two-stage dielectric barrier discharge, characterized by comprising the following steps:

[0008] S1. Passing background gas and sulfur hexafluoride gas into a primary DBD plasma reactor, the background gas is ionized to generate plasma, the sulfur hexafluoride gas is ionized into fluorine atoms and low-fluorine sulfides after plasma activation, and 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 produced in step S1 enter into a secondary DBD 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, low-fluorine sulfides react with carbon dioxide to generate carbon tetrafluoride gas.

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

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

[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 primary condensation is -60 to -50°C, and the condensation temperature of the secondary 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 primary DBD plasma reactor, a secondary DBD plasma reactor, a carbon dioxide gas supply unit, a primary condensation unit and a secondary condensation unit, wherein the sulfur hexafluoride gas supply unit and the background gas supply unit are respectively connected to the inlet of the primary DBD plasma reactor, the outlet of the primary DBD plasma reactor and the carbon dioxide gas supply unit are respectively connected to the inlet of the secondary DBD plasma reactor, the outlet of the secondary DBD plasma reactor is connected to the inlet of the primary condensation unit, and the gas outlet of the primary condensation unit is connected to the inlet of the secondary 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 condensation unit includes a primary condenser, which includes a first gas outlet and a first liquid outlet. The secondary condensation 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 comprises 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, and 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. The present invention proposes a method for degrading SF6 by double-stage DBD plasma activation and introducing CO2 gas to synthesize CF4. The first-stage DBD plasma reactor degrades SF6 molecules and decomposes SF6 molecules into fluorine atoms and other low-fluorine sulfur small molecules. This step not only achieves effective degradation of 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 by the primary reaction to generate CF4 gas. The mixed gas containing CF4 gas undergoes a primary condensation treatment to condense part of the fluorine-containing acidic waste gas small molecules into a liquid state. Subsequently, the remaining mixed gas undergoes a secondary condensation to condense the CF4 gas into a liquid state and collect it, thereby achieving efficient separation and purification of the product. Some acidic gases that do not participate in the reaction are treated in an alkaline solution absorption tank to reduce harm to the environment.

[0023] 2. The present invention not only achieves efficient degradation of SF6 by adopting a two-stage DBD reaction structure, but also significantly improves the synthesis rate of CF4. The present invention can not only solve the limitations and shortcomings of the traditional CF4 preparation method, but also provide a new way for the utilization of SF6 fluorine sources, the treatment of CO2 greenhouse gas 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 electronic special gas with high value in semiconductor manufacturing. It not only solves the problem that SF6 is difficult to handle, but also utilizes its fluorine resources in combination 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 graded 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 γ-Al2O3 in the first-stage plasma reactor, 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 synthesizing CF4 by activating SF6 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 DBD plasma reactor; 12-second DBD plasma reactor; 13-first condenser: 1301-first gas outlet, 1302-first liquid outlet; 14-waste liquid pool; 15-second condenser: 1501-second gas outlet, 1502-second liquid outlet; 16-CF4 collection tank; 17-alkali solution treatment pool; 18-tail gas pipe. DETAILED DESCRIPTION

[0031] The double-stage dielectric barrier discharge device for activating SF6 to synthesize CF4 of the present invention is described in detail below 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 primary DBD plasma reactor 11, a secondary DBD plasma reactor 12, a carbon dioxide gas supply unit, a primary condensation unit, a secondary condensation unit and a tail gas treatment unit.

[0034] The sulfur hexafluoride gas supply unit comprises 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 comprises 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 , and 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 includes a coaxial DBD reaction tube, a plasma power supply and a voltage regulator, and the reaction conditions and parameters are controlled by the voltage regulator and the plasma power supply. The outlet of the gas mixer 7 is connected to the coaxial DBD reaction tube inlet of the first-stage DBD plasma reactor 11 through a pipeline, and an electromagnetic flowmeter and an electromagnetic valve are provided on the pipeline connecting the outlet of the gas mixer 7 and the first-stage DBD plasma reactor 11.

[0038] The secondary DBD plasma reactor 12 comprises a coaxial DBD reaction tube, a plasma power supply and a voltage regulator, and the reaction conditions and parameters are controlled by the voltage regulator and the plasma power supply. 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 through a pipeline.

[0039] The carbon dioxide supply unit includes a carbon dioxide gas 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 gas 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 a pipeline connecting the coaxial DBD reaction tube outlet of the first DBD plasma reactor 11 and the coaxial DBD reaction tube inlet of the second DBD plasma reactor 11, and carbon dioxide is introduced into the coaxial DBD reaction tube of the second DBD plasma reactor 12 through the carbon dioxide gas cylinder 8.

[0040] The primary condensation unit includes a primary condenser 13 and a waste liquid pool 14. The condensing medium filled in the primary condenser 13 is an ethylene glycol aqueous 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 through a pipeline. The first liquid outlet 1302 is connected to the waste liquid pool 14 through a pipeline, and the waste liquid pool 14 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 filled in the secondary condenser 15 is liquid nitrogen, and the condensation 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 through a pipeline. The CF4 collection tank 16 is used to collect liquefied carbon tetrafluoride.

[0042] The tail gas treatment unit includes an alkali solution treatment tank 17 and a tail gas pipe 18, and both ends of the tail gas pipe 18 are respectively connected to the alkali solution treatment tank 17 and the second gas outlet 1501. Ca(OH)2 alkali solution is placed in the alkali solution treatment tank 17, and some unreacted acidic gases are fully neutralized and absorbed by the Ca(OH)2 alkali solution to avoid 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. Fill the discharge region of the coaxial DBD reaction tube of the first-stage DBD plasma reactor 11 with catalyst γ-Al2O3, add condensing medium ethylene glycol aqueous solution into the first-stage condenser 13, so that the condensing temperature of the first-stage condenser 13 is -60°C, and add liquid nitrogen into the second-stage condenser 15, so that the condensing temperature of the second-stage condenser 15 is -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 gas 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 gas 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 gas 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, and 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, respectively. 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 tend to stabilize at 105° C. and 115° C., respectively.

[0049] 5. Open the valves on the pipelines connecting the inlet of the sulfur hexafluoride gas cylinder 1, the first pressure reducing valve 3, the argon gas cylinder 4, the second pressure reducing valve 6, the gas mixer 7, the first DBD plasma reactor 11 and the second DBD plasma reactor 11, and the valve on the tail gas pipe 18. The sulfur hexafluoride gas in the sulfur hexafluoride gas cylinder 1 and the argon gas in the argon gas cylinder 4 enter the gas mixer 7, are mixed evenly in the gas mixer 7, and then enter the coaxial DBD reaction tube of the first DBD plasma reactor 11. The amount of the sulfur hexafluoride gas and the argon gas introduced is accurately controlled by the electromagnetic flowmeter and the electromagnetic valve connected to the outlet of the gas mixer 7, so as to control the concentration of SF6 introduced into the first DBD plasma reactor 12.

[0050] In this embodiment, the flow rate of sulfur hexafluoride gas is controlled to be 6 mL / min, the flow rate of argon gas is controlled to be 294 ml / min, and the concentration of SF6 is 2%. SF6 and Ar are directly connected to two channels of the gas distributor to form a mixed gas inside the gas mixer 7. The output flow rate of the mixed gas is 300 mL / min, and the output flow rate is accurately controlled by an electromagnetic flowmeter and then sent 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, and sulfur hexafluoride gas is ionized into fluorine atoms and low-fluorine sulfides (such as SF5, SF4, etc.) after plasma activation. The generated fluorine atoms and low-fluorine sulfides further react with oxygen and silicon dioxide to generate fluorine-containing small molecules, etc., and the fluorine-containing small molecules, etc. 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 a gas chromatograph-mass spectrometer, 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, and the liquid CF4 enters the CF4 collection tank 16 for collection.

[0056] 10. When it is necessary to stop the reaction, 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 tube 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 primary DBD plasma reactor is changed, and the output flow rate of the mixed gas is changed to 150 mL / min. The SF6 concentration in the mixed gas discharged from the outlet of the primary DBD plasma reactor is detected by a gas chromatograph. The degradation rate of SF6 is calculated according to the SF6 concentration detected at the outlet of the primary DBD plasma reactor. The data graph of the change of the SF6 degradation rate with the change of the input power of the primary 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 is used to detect the mixed gas discharged from the outlet of the first-stage DBD plasma reactor. The obtained chromatogram is 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 produced by the degradation of sulfur hexafluoride and fluorine atoms reacting 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 is changed, and the CF4 concentration in the mixed gas discharged from the outlet of the secondary DBD plasma reactor is detected by a gas chromatograph-mass spectrometer. The yield of CF4 is calculated based on the CF4 concentration detected at the outlet of the secondary DBD plasma reactor. The data graph of the change of the CF4 yield with the change of 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 with the increase of the input power of the secondary DBD plasma reactor, 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 considerable.

Claims

1. A method for synthesizing CF4 by activating SF6 by 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 primary DBD plasma reactor, the background gas is ionized to generate plasma, the sulfur hexafluoride gas is ionized into fluorine atoms and low-fluorine sulfides after plasma activation, and 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 produced in step S1 enter into a secondary DBD 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, low-fluorine sulfides react with carbon dioxide to generate carbon tetrafluoride gas.

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

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 from the outlet of the secondary DBD plasma reactor is firstly condensed 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 two-stage dielectric barrier discharge device for activating SF6 to synthesize CF4, characterized in that: The invention comprises a sulfur hexafluoride gas supply unit, a background gas supply unit, a primary DBD plasma reactor, a secondary DBD plasma reactor, a carbon dioxide gas supply unit, a primary condensation unit and a secondary condensation unit. The sulfur hexafluoride gas supply unit and the background gas supply unit are respectively connected to the inlet of the primary DBD plasma reactor, the outlet of the primary DBD plasma reactor and the carbon dioxide gas supply unit are respectively connected to the inlet of the secondary DBD plasma reactor, the outlet of the secondary DBD plasma reactor is connected to the inlet of the primary condensation unit, and the gas outlet of the primary condensation unit is connected to the inlet of the secondary condensation unit.

7. The device for synthesizing CF4 by activating SF6 by dielectric barrier discharge according to claim 1 is 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 device for synthesizing CF4 by activating SF6 by dielectric barrier discharge according to claim 1 is 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 device for synthesizing CF4 by activating SF6 by dielectric barrier discharge according to claim 1 is characterized in that: The primary condensation unit includes a primary condenser, which includes a first gas outlet and a first liquid outlet. The secondary condensation 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 double-stage dielectric barrier discharge activation SF6 to synthesize CF4 device according to claim 9, characterized in that: The secondary condensing unit further comprises a CF4 collecting tank, and the second liquid outlet is connected to the CF4 collecting tank.

11. The device for synthesizing CF4 by activating SF6 by 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 double-stage dielectric barrier discharge device for activating SF6 to synthesize CF4 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, and 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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