Method for efficiently and harmlessly degrading SF6 through plasma concerted catalysis based on oxide cathode

Abstract

The invention provides a method for catalyzing and degrading SF6 (sulfur hexafluoride) based on direct-current discharge of a metal oxide cathode. And a layer of metal oxide is coated on the surface of the metal substrate to serve as a discharge cathode. In the cathode, on one hand, the metal oxide has a higher secondary electron emission coefficient, plays a role in accumulating charges in the discharge process, forms a strong electric field on the surfaces of the coating and the metal substrate, and promotes efficient degradation of SF6; and on the other hand, the metal oxide has a certain adsorption catalysis effect on the SF6 degraded product, and cooperates with the plasma to fix S and F elements, so that the compounding of the SF6 is inhibited, and the harmless degradation of the SF6 is facilitated. The device has the advantages of being simple in structure, long in service life, high in degradation rate, beneficial to harmless degradation of SF6 and the like, and is suitable for the fields of industrial waste gas treatment and environmental protection.

Description

Technical Field

[0001] The present invention belongs to the field of waste gas treatment, and specifically relates to a method based on a metal oxide cathode to promote SF 6 Efficient and harmless degradation method. Background Art

[0002] Sulfur hexafluoride (SF 6 ) is a synthetic gas with very stable chemical properties, widely used in the electrical industry, and its greenhouse effect potential is CO 2 It is 23,900 times stronger than hydrogen and is very stable in the atmosphere, with a lifespan of 3,200 years. It has been banned and restricted internationally.

[0003] Degradation treatment SF 6 It is currently an effective way to reduce its damage to the environment and also a way to reduce SF 6 An effective method for environmental damage. Traditional SF 6 Degradation technologies such as thermal degradation, thermal catalytic degradation, and ultraviolet degradation have the disadvantages of high energy consumption, low degradation efficiency, and long degradation time, which limit their large-scale industrial application. Low-temperature plasma waste gas treatment technology has the advantages of achieving high degradation efficiency at room temperature, low equipment cost, simple operation, and low energy consumption. It is considered to be a promising SF 6 Waste gas degradation technology. Domestic and foreign researchers use various forms of low-temperature plasma to carry out SF 6 Degradation research, including radio frequency discharge, microwave discharge, electron beam, dielectric barrier discharge, etc.

[0004] Low temperature plasma degradation of sulfur hexafluoride (SF 6 ) will produce a variety of toxic gas byproducts, including sulfur oxides (SO 2 F 2 ), tetrafluorosulfite (SOF 4 ), sulfur dioxide (SO 2 ) etc. These gases are not only highly toxic, but also chemically stable, and can remain in the atmosphere for a long time and diffuse widely. Once these harmful gases leak into the environment, they will diffuse through atmospheric circulation, causing harm to the health of surrounding residents (such as causing respiratory diseases), and may accumulate in the food chain through bioaccumulation, causing persistent secondary pollution. Summary of the invention

[0005] Aiming at the gap in existing research, the present invention provides a metal oxide cathode to promote SF 6 Efficient degradation, achieving harmless regulation of degradation products, reducing SF 6 Secondary pollution problem of degradation products.

[0006] To achieve the above objectives, the present invention adopts the following technical solutions:

[0007] A method to enhance discharge intensity and promote SF 6 The harmless degradable metal oxide cathode is a cathode that is coated with a layer of metal oxide on the surface of a metal substrate; the metal substrate can be a conductive material such as nickel, copper, silver, etc., and the metal oxide coating can be magnesium oxide, aluminum oxide, zirconium oxide, and metal oxides with different doping ratios, with a thickness of 1 to 100um. By calcining the metal oxide at high temperature, it can be tightly coated on the surface of the metal substrate without falling off, and has the characteristics of strong stability and strong mechanical properties.

[0008] The metal oxide cathode has a larger cathode secondary electron emission coefficient than the common metal cathode, so that the gas can be broken down at a lower voltage.

[0009] The metal oxide cathode can accumulate charges to form a local strong electric field, which is beneficial to SF 6 Collision ionization occurs to achieve fragmentation, promoting SF 6 Efficient degradation.

[0010] The metal oxide cathode, in a plasma environment, SF 6 The low-sulfur fluoride produced after degradation undergoes a series of adsorption catalytic reactions on its surface to achieve the fixation of S and F elements, generating non-toxic metal fluoride oxides and metal sulfates, the general formula of which is M a F b O c With M a S b O c (M is a metal), such as MgF 2 、Al 2 F 3 , CaF 2 MgSO 4 、Al 2 (SO 4 ) 3 etc., inhibit SF 6 Compound, promoting SF 6 harmless degradation.

[0011] The preparation method of the metal oxide cathode is generally divided into two steps:

[0012] The first step is to prepare a metal oxide coating on the surface of the metal substrate by methods including electrophoresis, sol-gel, spin coating, plasma spraying, vapor deposition, electron beam evaporation or spray pyrolysis.

[0013] The second step is high-temperature calcination, which is carried out at a high temperature of 900-1200℃ for 1 to 5 hours, with a heating rate of 5℃ / min, from room temperature to the highest temperature, so that the metal oxide coating can be firmly attached to the metal substrate without falling off.

[0014] The advantages of the present invention include:

[0015] 1. The presence of metal oxide coating significantly improves the resistance to SF 6 The experimental results show that at the same discharge voltage, the discharge current and SF 6 The degradation efficiency has been significantly improved.

[0016] 2. Metal oxide coating on SF 6 The degradation products have a certain fixing effect. After discharge, non-toxic metal fluoride oxides and metal sulfates were detected on the surface coating, which is beneficial to SF 6 harmless degradation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the examples or the description of the prior art are briefly introduced below.

[0018] Figure 1 Schematic diagram of the reaction system of the present invention.

[0019] Figure 2 For different cathode discharge effects and SF 6 Schematic diagram of the degradation effect.

[0020] Figure 3 A schematic diagram of the characterization results.

[0021] Specific implementation cases

[0022] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0023] See attached Figure 1 The method for making the metal oxide cathode is as follows: the metal substrate is polished with sandpaper and then ultrasonically cleaned in anhydrous ethanol for 20 minutes. Nanoscale metal oxide particles with a certain doping ratio are dispersed in anhydrous ethanol, ultrasonically vibrated for 120 minutes to form a colloid, and hydrochloric acid is added dropwise under magnetic stirring to adjust the pH to 7.2. The oxide powder is deposited on the surface of the metal substrate by electrophoretic deposition, and the deposited metal oxide cathode is then heated from room temperature to 1000°C at a rate of 5°C / min, and calcined at high temperature for 2 hours to make it more compact and less likely to fall off.

[0024] Figure 1The schematic diagram of the system including the metal oxide cathode includes a gas source, a high voltage power supply, a multi-pin plate discharge device, and a DC galvanometer. The gas source generates a uniform SF 6 Gas is degraded through a discharge reaction device. Control SF 6 The initial concentration and gas flow rate are the same. According to the relationship between the discharge voltage and discharge power in the interval from the start of discharge to spark breakdown of different cathodes, and the different cathodes for SF 6 The difference in degradation effect is plotted as Figure 2 The discharge power and SF 6 Schematic diagram of degradation efficiency. It can be seen that the metal oxide cathode can significantly reduce the breakdown voltage, increase the discharge power of the reaction system, and promote SF 6 degradation.

[0025] Figure 3 The schematic diagram of XRD results before and after discharge shows that MgF is formed on the metal oxide cathode after discharge. 2 、Al 2 F 3 MgSO 4 and Al 2 (SO 4 ) 3 , which reflects the fixation of S and F elements by the metal oxide cathode and realizes SF 6 Regulation of degradation products promotes SF 6 harmless degradation.

[0026] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solution and the inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A metal oxide cathode that efficiently degrades SF6 and promotes harmless regulation of products, characterized in that: A layer of metal oxide with an adsorption catalytic effect on the decomposition of SF6 is coated on the surface of the metal substrate with a coating thickness of 1 to 100 um. On the one hand, the metal oxide has strong insulation and a large secondary electron emission coefficient, which promotes the efficient degradation of SF6. On the other hand, it can work together with the plasma to fix the S and F elements and achieve harmless regulation of the product.

2. The metal oxide cathode according to claim 1, characterized in that The selected metal oxide cathode can cooperate with the plasma to catalyze and fix the SF6 degradation products to generate metal fluoride oxides and metal sulfates, which are generally expressed as M a F b O c With M a S b O c (M is a metal), such as MgF2, Al2F3, CaF2 and MgSO4.

3. The metal oxide according to claim 2, characterized in that By fixing the degradation products of SF6, non-toxic metal fluorides are formed, which inhibits the generation of toxic gases such as SOF4, SO2, SO2F2 after SF6 degradation, thereby achieving harmless regulation of the products.

4. The metal oxide cathode according to claim 1, characterized in that The selected metal oxide has a large secondary electron emission coefficient and can accumulate charges to form a local strong electric field, which is beneficial to the collision ionization and decomposition of SF6 and promotes the efficient degradation of SF6.

5. The metal oxide cathode according to claim 1, characterized in that In a plasma environment, SF6 undergoes collision ionization, and the oxide cathode has an adsorption catalytic effect on the ionized S and F-containing ions or molecules, inhibiting the recombination of SF6, thereby promoting the efficient degradation of SF6.

6. The metal oxide cathode according to claim 1, characterized in that The metal oxide layer is nano-scale particles.

7. The metal oxide cathode according to claim 1, characterized in that The preparation method is usually divided into two steps: The first step is to prepare a metal oxide coating on the surface of the metal substrate by methods including electrophoresis, sol-gel, spin coating, plasma spraying, vapor deposition, electron beam evaporation or spray pyrolysis. The second step is high temperature calcination, which is carried out at a high temperature of 900-1200°C for 1 to 5 hours to form a compact and non-falling metal oxide coating on the metal substrate.

8. The method for preparing a metal oxide cathode according to claim 7, characterized in that: The raw material of the metal oxide is a powder material or an organic compound of a metal.

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