An efficient thermal degradation method for waste SF based on bimetallic synergistic catalysis 6 High-efficiency thermal degradation method

Abstract

The present invention discloses an efficient thermal degradation method for waste SF6 based on dual-metal synergistic catalysis, belonging to the technical field of treatment of air pollutants. This process includes the following steps: (1) Thermal catalytic degradation of SF6: SF6, a reducing gas and an inert gas are mixed, and the resulting mixed gas is subjected to thermal catalytic degradation under the action of a dual-metal synergistic catalyst, and the degraded exhaust gas is collected; the dual-metal synergistic catalyst is composed of a carbon skeleton film formed by nanoscale copper oxide, zinc oxide particles and ZIF-8 metal-organic framework, wherein the copper oxide and zinc oxide particles are wrapped by the carbon skeleton film; (2) Exhaust gas treatment: The degraded exhaust gas is subjected to alkali washing and drying to complete the recovery. The present invention has the advantages of high efficiency, environmental protection and economy, and can be widely applied to the degradation of SF6 exhaust gas and the recovery of its products, providing a reliable solution for the treatment of SF6 exhaust gas in industries such as the power industry, semiconductor industry and metal smelting industry.

Description

Technical Field

[0001] The present invention relates to the technical field of treatment of air pollutants, and particularly relates to an efficient thermal degradation method for waste SF 6 based on bimetallic synergistic catalysis. Background Art

[0002] SF 6 As a gas insulation medium with excellent insulation and arc extinguishing properties, it has been widely used in high-voltage and ultra- / extra-high-voltage power transmission and distribution equipment. According to incomplete data statistics, achieving efficient treatment of waste SF 6 is of great significance for mitigating the greenhouse effect and protecting the ecological environment.

[0003] Existing methods for treating waste SF 6 mainly include molecular sieve separation or alkali wash liquor recovery. For example, the Chinese utility model patent with the publication number CN207628186U discloses a sulfur hexafluoride separator and a sulfur hexafluoride separation device having the same, including: a separator, the separator includes a housing and a fiber separation structure disposed in the housing, the housing is provided with an air inlet, a permeate gas outlet and a finished gas outlet, the fiber separation structure is disposed between the air inlet and the permeate gas outlet, and the air inlet and the finished gas outlet are communicated with each other in the housing. The sulfur hexafluoride is separated from the air by using a fiber material, solving the problem of difficult separation and recovery of sulfur hexafluoride mixed gas in the prior art. The Chinese invention patent with the publication number CN110124512A discloses a method for treating sulfur hexafluoride waste gas, including the following steps: 1) introducing the sulfur hexafluoride waste gas into a reaction column containing a defluorinating agent to carry out a sulfur hexafluoride cracking reaction to obtain reaction tail gas; wherein the defluorinating agent is a mixture of a modified mesoporous molecular sieve and silicon powder, and the modified mesoporous molecular sieve is a mesoporous molecular sieve jointly modified by an alkali metal fluoride and an alkaline earth metal oxide; 2) sequentially introducing the reaction tail gas into a type A molecular sieve and activated carbon and then discharging it harmlessly. The above processes use a defluorinating agent or a mesoporous molecular sieve to purify the tail gas, but their recovery and purification processes are complex, the device volume is large and the cost is high, it is difficult to meet the needs of small and medium-sized insulating gas equipment, and it restricts the large-scale application of the process

[0004] In recent years, extensive research has been carried out on the degradation treatment of SF 6 . Currently, the methods for degrading SF 6 mainly include pyrolysis, photodegradation, and low-temperature plasma methods. Although the photodegradation method has low energy consumption and is effective in degrading SF 6 , the photodegradation reaction rate is too slow, and the amount that can be degraded and treated is very limited; the low-temperature plasma method can achieve satisfactory degradation efficiency, but at present, it can only treat waste gas with a low concentration, and the equipment is expensive and difficult to be widely promoted and applied at the industrial level. In addition, almost all SF 6Low-temperature plasma degradation solutions will all produce SO 2 F 2 、HF and other toxic, harmful and even corrosive products. Improving product selectivity is a key issue faced by this technology. To truly promote the catalytic degradation of waste SF 6 from the laboratory to large-scale industrial applications, breaking through the catalytic conversion rate and improving product selectivity are the keys. SUMMARY OF THE INVENTION

[0005] In view of the above-mentioned defects of the prior art, in the first aspect of the present invention, an efficient, environmentally friendly and economical thermal degradation method for waste SF 6 is provided, which is based on dual-metal synergistic catalysis and includes the following steps:

[0006] (1) Thermal catalytic degradation of SF 6 :

[0007] SF 6 , a reducing gas and an inert gas are mixed, and the resulting mixed gas is subjected to thermal catalytic degradation under the action of a dual-metal synergistic catalyst, and the degraded waste gas is collected;

[0008] The dual-metal synergistic catalyst is composed of carbon framework thin films formed by nano-scale copper oxide, zinc oxide particles and ZIF-8 metal organic frameworks, wherein the copper oxide and zinc oxide particles are wrapped by the carbon framework thin films;

[0009] (2) Waste gas treatment:

[0010] The degraded waste gas is subjected to alkali washing and drying to complete recovery.

[0011] Preferably, in the step (1), the reducing gas includes H 2 , NH 3 , CH 3 OH or at least one of them.

[0012] Preferably, in the step (1), the thermal catalytic degradation process is as follows: The mixed gas is introduced to the target air pressure, the air flow is allowed to flow through the dual-metal synergistic catalyst, and the environment is heated to the thermal catalytic degradation temperature within a certain time, and the SF 6 is fully reacted to complete the thermal catalytic degradation, and the degraded waste gas is collected.

[0013] More preferably, the target air pressure is 0.2-0.4 MPa; the heating duration is 20-60 min; the thermal catalytic degradation temperature is 400-700 °C.

[0014] This process has good applicability, and the mixing ratio of the mixed gas can be selected according to the conventional catalytic ratio in the art and determined in combination with the actual application requirements. For example, SF 6, The reducing gas and the inert gas can be mixed in a volume ratio of 2 to 10: 2 to 10: 80 to 96.

[0015] Preferably, in the step (1), the preparation of the bimetallic synergistic catalyst includes the following steps:

[0016] S1. Drop the zinc nitrate solution into the 2-methylimidazole solution, separate the precipitate, and obtain the ZIF-8 precursor through purification and refinement.

[0017] S2. Mix the ZIF-8 precursor with a solvent to form a suspension, add the nitrate of copper (II) to the suspension to form a dispersion; drop the aqueous solution of sodium borohydride into the dispersion, mix and separate the insoluble matter, and obtain Cu@ZIF-8 through purification and refinement.

[0018] S3. Subject Cu@ZIF-8 to calcination pyrolysis and refinement to obtain the bimetallic synergistic catalyst.

[0019] Using the above method, an organometallic nanoscale framework is used as a precursor, and a bimetallic synergistic catalyst is obtained through impregnation and calcination. Compared with traditional metal oxide catalysts, it has abundant active sites on the surface and can reduce the activation energy of the SF 6 reduction reaction and has better catalytic effect.

[0020] More preferably, in the S1, the zinc nitrate solution is prepared by dissolving at least one of zinc nitrate or its hydrate in a solvent; the concentration of the zinc nitrate solution is 0.06 to 0.07 mol / L.

[0021] More preferably, in the S1, the 2-methylimidazole solution is prepared by dissolving 2-methylimidazole in a solvent; the concentration of the 2-methylimidazole solution is 0.56 to 1.20 mol / L.

[0022] More preferably, in the S1, the molar ratio of zinc nitrate in the zinc nitrate solution to 2-methylimidazole in the 2-methylimidazole solution is 1: 8 to 16.

[0023] More preferably, in the S2, the nitrate of copper (II) includes at least one of zinc copperate and its hydrate.

[0024] More preferably, in the S2, the molar ratio of the nitrate of copper (II) to the precursor ZIF-8 is 1: 3 to 3: 1.

[0025] More preferably, in the S2, the molar ratio of the nitrate of copper (II) to sodium borohydride is 1: 5 to 8.

[0026] More preferably, in the S2, the concentration of the aqueous solution of sodium borohydride is 0.35 to 1.40 mol / L.

[0027] Further preferably, in S3, the heating rate of calcination pyrolysis is 1-5 °C / min, the target temperature is 350-600 °C, and the treatment duration is 6-8 h.

[0028] During the preparation of zinc nitrate solution, 2-methylimidazole solution and the suspension of ZIF-8 precursor, the choice of solvent is diverse, and those skilled in the art can select appropriate solvent types according to actual conditions. Among them, organic solvents are very suitable solvent types, including at least one solvent of methanol, ethanol, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, all of which can be applied to the preparation process of the bimetallic synergistic catalyst.

[0029] Preferably, in step (2), the solution for alkali washing includes at least one of sodium hydroxide standard solution and potassium hydroxide standard solution.

[0030] Preferably, in step (2), the desiccant for drying includes at least one of calcium hydroxide and calcium oxide.

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] The present invention provides a method for thermal degradation of waste SF 6 with the advantages of high efficiency, environmental protection and economy, and can be widely applied to the degradation of SF 6 waste gas and the recovery of its products, providing a reliable SF 6 waste gas treatment solution for industries such as the power industry, semiconductor industry, and metal smelting. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 XRD pattern of the bimetallic synergistic catalyst used in Example 1;

[0034] Figure 2 For the SF in Example 1 6 Thermal catalytic degradation conversion curve;

[0035] Figure 3 Curve of the concentration of degradation products changing with time in Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The present invention will be further described below by way of examples, but the present invention is not limited to the scope of the described examples. The experimental methods without specific conditions in the following examples are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0037] Example 1

[0038] Waste SF Based on Bimetallic Synergistic Catalysis 6 Thermal Degradation Method, the steps are as follows:

[0039] (1) Thermal Catalytic Degradation of SF 6 : Mix 1.0 g of bimetallic synergistic catalyst with 0.5 g of CaO powder (used for drying, chemically inert during thermal catalytic degradation and does not participate in the reaction), evenly sprinkle it on quartz wool and send it into the reaction section of the reactor; evacuate the gas chamber to vacuum, and introduce a mixed gas of 2% SF 6 +2% NH 3 +96% He at a flow rate of 5 mL / min until the air pressure reaches 0.2 MPa; set the thermal catalytic degradation temperature to 600 °C, the heating time to 30 min, record the reading of the K-type thermocouple thermometer after the heating ends, ensure that the temperature remains at 600 ± 5 °C, and carry out thermal catalytic degradation at this temperature. During the process, collect gas every 1 h using a special polyvinyl fluoride sampling bag, and qualitatively and quantitatively analyze the components of the reaction products using a GC-MS device until the SF 6 is completely degraded, collect the degraded waste gas, and recover the catalyst after the reaction;

[0040] (2) Waste Gas Treatment:

[0041] Evenly send the remaining gas inside the reactor into an alkali washing tank (containing a standard sodium hydroxide solution) and a drying tank device. After sufficient alkali washing and recovery, complete the treatment, disassemble and clean the device.

[0042] In this example, the bimetallic synergistic catalyst is self-made in the laboratory, and the steps are as follows:

[0043] S1. Dissolve 1.18 g of Zn(NO 3 ) 2 ·6H 2 O in 80 mL of methanol to obtain a zinc nitrate solution, and dissolve 3.70 g of 2-methylimidazole in 80 mL of methanol to obtain a 2-methylimidazole solution; add the zinc nitrate solution to the 2-methylimidazole solution, stir in a magnetic stirrer for 30 min, and let it stand for 24 h; after centrifugation, wash it thoroughly with methanol, and finally dry it in an oven at 70 °C for 12 h to obtain the ZIF-8 precursor white powder;

[0044] S2. Add 0.5 g of ZIF-8 precursor to 60 mL of methanol, stir at room temperature for 30 min to form a suspension, add 2.01 g of Cu(NO 3 ) 2 ·3H 2 O to the suspension, and ultrasonically treat it for 1 h to form a dispersion; dissolve 1.59 g of NaBH 4 in 60 mL of deionized water to obtain NaBH 4aqueous solution, which was added dropwise to the above dispersion within 4 min and reacted at room temperature for 1 h. Cu 2+ was reduced to Cu; after centrifugation, the product was washed 3 times with deionized water and ethanol, dried in vacuum for 12 h, and then ground to obtain Cu@ZIF-8;

[0045] S3. Cu@ZIF-8 was placed in a crucible and transferred to a muffle furnace, heated to 350 °C at a heating rate of 1 °C / min, and kept at this temperature for 6 h for sufficient pyrolysis to obtain a bimetallic synergistic catalyst.

[0046] The bimetallic synergistic catalyst was characterized by XRD, and the test results are as Figure 1 shown. It can be seen from Figure 1 that the main components of the catalyst are CuO and ZnO; among them, CuO mainly exists in (-1 1 1) and (2 0 0) crystal forms, and ZnO mainly exists in (11 1) and (2 2 0) crystal forms. The diffraction peaks of ZnO are weaker and wider than those of CuO, indicating that the grain size of ZnO is smaller and that of CuO is larger.

[0047] In the process of thermal catalytic degradation of SF 6 , based on the test results of the GC-MS equipment, a curve of the conversion rate of SF 6 changing with time was plotted, and the results are as Figure 2 shown. It can be seen from Figure 2 that under the catalytic performance test conditions of this example, for about 21 h, the conversion rate is greater than 99%; for about 40 h, the conversion rate is greater than 90%, indicating that the catalytic activity of this process is excellent.

[0048] Similarly, in the process of thermal catalytic degradation of SF 6 , based on the test results of the GC-MS equipment, a curve of the concentration of decomposition components changing with time was plotted, and the results are as Figure 3 shown. It can be seen from Figure 3 that under the catalytic performance test conditions of this example, the concentration of the recovered product SO 2 is significantly higher than that of other sulfur-containing products, indicating that the selectivity of this process is excellent and it has a good degradation effect.

[0049] Example 2

[0050] Based on the thermal degradation method of waste SF 6 by bimetallic synergistic catalysis, the steps are as follows:

[0051] (1) Thermal catalytic degradation of SF 6: Mix 1.0 g of the bimetallic synergistic catalyst with 1.0 g of CaO powder, evenly sprinkle it on the quartz wool, and send it into the reaction section of the reactor; evacuate the gas chamber to vacuum, and introduce a mixed gas of 2% SF 6 +6% H 2 +92% He at a flow rate of 10 mL / min until the gas pressure reaches 0.2 MPa; set the thermal catalytic degradation temperature to 400 °C, the heating time to 40 min, record the reading of the K-type thermocouple thermometer after the heating is completed, ensure that the temperature is maintained at 400 ± 5 °C, and carry out thermal catalytic degradation at this temperature. During the process, collect gas every 0.5 h using a special polytetrafluoroethylene sampling bag, and qualitatively and quantitatively analyze the components of the reaction products using a GC-MS device until SF 6 is completely degraded, collect the degraded waste gas, and recover the catalyst after the reaction;

[0052] (2) Waste gas treatment:

[0053] Evenly send the remaining gas inside the reactor into the alkali washing tank (containing a standard sodium hydroxide solution) and the drying tank device. After sufficient alkali washing and recovery, the treatment is completed, and the device is disassembled and cleaned.

[0054] In this example, the bimetallic synergistic catalyst is prepared in the laboratory, and the steps are as follows:

[0055] S1. Dissolve 2.70 g of Zn(NO 3 ) 2 ·6H 2 O in 160 mL of methanol to obtain a zinc nitrate solution, and dissolve 7.5 g of 2-methylimidazole in 160 mL of methanol to obtain a 2-methylimidazole solution; add the zinc nitrate solution to the 2-methylimidazole solution, and stir in a magnetic stirrer for 1 h, then let it stand for 24 h; after centrifugation, wash it thoroughly with methanol, and finally dry it in an oven at 80 °C for 12 h to obtain a white powder of ZIF-8 precursor;

[0056] S2. Add 0.5 g of the ZIF-8 precursor to 60 mL of methanol, stir at room temperature for 30 min to form a suspension, add 1.05 g of Cu(NO 3 ) 2 ·3H 2 O to the suspension, and ultrasonically treat it for 1 h to form a dispersion; dissolve 0.79 g of NaBH 4 in 40 mL of deionized water to obtain an aqueous solution of NaBH 4 , and add it dropwise to the above dispersion within 4 min, and react at room temperature for 1 h to reduce Cu 2+ to Cu; after centrifugation, wash the product 3 times with deionized water and ethanol, and vacuum dry it for 12 h, and then grind it to obtain Cu@ZIF-8;

[0057] S3. The Cu@ZIF-8 is placed in a crucible and transferred into a muffle furnace. It is heated to 500 °C at a heating rate of 5 °C / min and kept at this temperature for 6 h for sufficient pyrolysis to obtain a bimetallic synergistic catalyst.

[0058] Example 3

[0059] Waste SF based on bimetallic synergistic catalysis 6 Thermal degradation method, the steps are as follows:

[0060] (1) Thermal catalytic degradation of SF 6 : Mix 1.5 g of the bimetallic synergistic catalyst with 1.0 g of CaO powder, evenly sprinkle it on quartz wool and send it into the reaction section of the reactor; evacuate the gas chamber to vacuum, and introduce a mixed gas of 10% SF 6 +10% NH 3 +80% He at a flow rate of 5 mL / min until the air pressure reaches 0.3 MPa; set the thermal catalytic degradation temperature to 650 °C, the heating time to 30 min, record the reading of the K-type thermocouple thermometer after the heating ends, ensure that the temperature is maintained at 650 ± 5 °C, and carry out thermal catalytic degradation at this temperature. During the process, collect gas every 0.5 h using a special polytetrafluoroethylene sampling bag, and qualitatively and quantitatively analyze the components of the reaction products with a GC-MS device until the SF 6 is completely degraded, collect the degraded waste gas, and recover the catalyst after the reaction;

[0061] (2) Waste gas treatment:

[0062] Evenly send the remaining gas inside the reactor into an alkali washing tank (containing a standard sodium hydroxide solution) and a drying tank device. After sufficient alkali washing and recovery, the treatment is completed, and the device is disassembled and cleaned.

[0063] In this example, the bimetallic synergistic catalyst is self-made in the laboratory, and the steps are as follows:

[0064] S1. Dissolve 3.36 g of Zn(NO 3 ) 2 ·6H 2 O in 120 mL of methanol to obtain a zinc nitrate solution, and dissolve 14.80 g of 2-methylimidazole in 120 mL of methanol to obtain a 2-methylimidazole solution; add the zinc nitrate solution to the 2-methylimidazole solution, and stir in a magnetic stirrer for 1 h, then let it stand for 24 h; after centrifugation, wash it thoroughly with methanol, and finally dry it in an oven at 80 °C for 12 h to obtain a white powder of the ZIF-8 precursor;

[0065] S2. Add 0.5 g of the ZIF-8 precursor to 60 mL of methanol, stir at room temperature for 30 min to form a suspension, and add 1.05 g of Cu(NO 3 ) 2 ·3H2 O was added to the suspension, and ultrasonic treatment was carried out for 1 h to form a dispersion; 0.79 g of NaBH 4 was dissolved in 40 mL of deionized water to obtain an aqueous solution of NaBH 4 , and it was added dropwise to the above-mentioned dispersion within 4 min and reacted at room temperature for 1 h to reduce Cu 2+ to Cu; after centrifugation, the product was washed 3 times with deionized water and ethanol, vacuum dried for 12 h, and then ground to obtain Cu@ZIF-8;

[0066] S3. Cu@ZIF-8 was placed in a crucible and transferred to a muffle furnace, heated to 600 °C at a heating rate of 2 °C / min, and kept at this temperature for 7 h for sufficient pyrolysis to obtain a bimetallic synergistic catalyst.

[0067] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative labor. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field of the present invention through logical analysis, reasoning, or limited experiments based on the concept of the present invention on the basis of the prior art should be within the protection scope determined by the claims.

Claims

1. A method for thermal degradation of waste SF6, characterized in that: The steps include: (1) Thermal catalytic degradation of SF6: SF6, reducing gas and inert gas are mixed, and the resulting mixed gas is thermally catalytically degraded under the action of a bimetallic synergistic catalyst, and the degraded waste gas is collected; The bimetallic synergistic catalyst is composed of nano-scale copper oxide and zinc oxide particles and a carbon skeleton film formed by a ZIF-8 metal organic framework, wherein the copper oxide and zinc oxide particles are wrapped by the carbon skeleton film. The preparation method thereof is as follows: S1. Dissolve 1.18 g Zn(NO3)2·6H2O in 80 mL methanol to obtain zinc nitrate solution, and dissolve 3.70 g 2-methylimidazole in 80 mL methanol to obtain 2-methylimidazole solution; add the zinc nitrate solution to the 2-methylimidazole solution, stir in a magnetic stirrer for 30 min, and let stand for 24 h; after centrifugation, wash thoroughly with methanol, and finally dry in an oven at 70 °C for 12 h to obtain a white powder of ZIF-8 precursor; S2, 0.5 g ZIF-8 precursor was added to 60 mL methanol, stirred at room temperature for 30 min to form a suspension, 2.01 g Cu (NO3)2·3H2O was added to the suspension, and ultrasonic treatment was performed for 1 h to form a dispersion; 1.59 g NaBH4 was dissolved in 60 mL deionized water to obtain an aqueous solution of NaBH4, which was added dropwise to the above dispersion within 4 min and reacted at room temperature for 1 h to form Cu (NO3)2·3H2O. 2+ After centrifugation, the product was washed three times with deionized water and ethanol, dried under vacuum for 12 h, and then ground to obtain Cu@ZIF-8. S3 and Cu@ZIF-8 were placed in a crucible and transferred to a muffle furnace. The temperature was raised to 350 °C at a heating rate of 1 °C / min and kept at this temperature for 6 h for full pyrolysis to obtain a bimetallic synergistic catalyst. (2) Waste gas treatment: The degradation waste gas is recycled after alkali washing and drying.

2. The method according to claim 1, characterized in that: In the step (1), the reducing gas includes at least one of H2, NH3, and CH3OH.

3. The method according to claim 1, characterized in that In step (1), the thermal catalytic degradation process is as follows: introducing a mixed gas to a target gas pressure, allowing the gas flow to flow through a bimetallic synergistic catalyst, and raising the ambient temperature to a thermal catalytic degradation temperature within a certain period of time, allowing SF6 to fully react to complete thermal catalytic degradation, and collecting the degraded exhaust gas.

4. The method according to claim 3, characterized in that: The target gas pressure is 0.2-0.4 MPa; the heating time is 20-60 min; and the thermal catalytic degradation temperature is 400-700 °C.

5. The method according to claim 1, characterized in that: In the step (2), the alkali washing solution includes at least one of a sodium hydroxide standard solution and a potassium hydroxide standard solution; and the drying desiccant includes at least one of calcium hydroxide and calcium oxide.

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