Method for producing tetrafluoromethane by taking trifluoromethane as raw material, and cracking purification device

Abstract

The present invention relates to the technical field of resource utilization of trifluoromethane. Provided in the present invention are a method for producing tetrafluoromethane by taking trifluoromethane as a raw material, and a cracking purification device. In the present invention, trifluoromethane is introduced into a thermal plasma reactor, and same is subjected to a cracking reaction at 1500-5000 K to obtain tetrafluoromethane. Compared with conventional pyrolysis by means of a tubular furnace or high-temperature pyrolysis by means of a muffle furnace, the thermal plasma reactor used in the present invention can rely on the synergistic effect of high-temperature and high-activity electrons and heavy particles, such that the electron excitation effect is obvious. The efficient cleavage and directional recombination of chemical bonds in trifluoromethane molecules can be achieved under the condition of not using a catalyst and fluorine gas, the conversion rate of trifluoromethane is high, the selectivity of tetrafluoromethane is high, and the energy consumption is low. In addition, the method provided in the present invention has a short reaction time, a large treatment capacity, and is safe and controllable, the composition of the cracking reaction product is simple, and the method makes it easy to carry out separation and purification, has a low cost and low energy consumption, and is suitable for continuous large-scale industrial production.

Description

A method for producing tetrafluoromethane using trifluoromethane as raw material and a cracking and purification device

[0001] This application claims priority to a Chinese patent application filed with the Patent Office of China on August 7, 2023, with application number CN202310984672.X and invention name “A method for producing tetrafluoromethane using trifluoromethane as raw material”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present invention relates to the technical field of trifluoromethane resource utilization, and in particular to a method for producing tetrafluoromethane using trifluoromethane as a raw material and a cracking and purification device. Background Art

[0003] Trifluoromethane (R23) is an inevitable byproduct in the production of chlorodifluoromethane (HCFC-22) by reacting hydrogen fluoride with chloroform or cracking HCFC-22 to produce tetrafluoroethylene. Its application is relatively narrow, making it difficult to use as a chemical raw material in the production of other products. It has limited applications in fire extinguishing agents and semiconductor etchants. While R23 itself does not deplete the ozone layer, it can cause a significant greenhouse effect, with a global greenhouse effect potential (GWP) 14,800 times that of CO2, and can remain stable in the atmosphere for 264 years. Over the past few decades, the concentration of R23 in the atmosphere has steadily increased at a rate of 5% per year, posing a serious ecological risk. Currently, the main method for disposing of R23 is incineration, which completely decomposes it into substances such as HF and CO2, thereby preventing its environmental damage. However, due to its inherent stability, R23 is difficult to decompose even under combustion conditions. Incineration often requires extremely harsh reaction conditions, resulting in high processing costs and equipment investment, and no valuable product can be recovered. If the generated HF is not recovered, the fluoride salt must be post-processed, and the product's application value is relatively low. Therefore, there is an urgent need to develop new methods for resource-based R23 treatment that are clean, efficient, and can produce high-value-added products.

[0004] Tetrafluoromethane (R14) is the most widely used plasma etching gas in the microelectronics industry and has broad development potential. Currently, R14 is primarily synthesized industrially using hydrofluoromethane fluorination, chlorofluoromethane fluorination, and direct carbon-fluorine fluorination. However, with the gradual banning of CFCs and HCFCs, the availability of raw materials for the chlorofluoromethane fluorination method has become limited. Both the direct carbon-fluorine fluorination method and the hydrofluoromethane fluorination method present significant challenges, including highly exothermic reactions, potential explosion hazards, high equipment requirements, and complex product compositions. Therefore, the search for a safe, controllable, and efficient method for the preparation of R14 suitable for industrial scale-up is of great significance.

[0005] Summary of the Invention

[0006] In view of this, the object of the present invention is to provide a method for producing tetrafluoromethane using trifluoromethane as a raw material and a cracking and purification device. The method provided by the present invention has a high conversion rate of trifluoromethane, high selectivity of tetrafluoromethane, large processing capacity, safety and controllability, and is suitable for continuous industrial scale-up production.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for producing tetrafluoromethane using trifluoromethane as a raw material, comprising the following steps:

[0009] Trifluoromethane is introduced into a thermal plasma reactor for cracking reaction to obtain tetrafluoromethane; the temperature of the cracking reaction is 1500-5000K.

[0010] Preferably, the flow rate of trifluoromethane is 0.5 to 1000 Nm 3 / h.

[0011] Preferably, the thermal plasma reactor includes a radio frequency thermal plasma reactor, a microwave thermal plasma reactor or an arc thermal plasma reactor.

[0012] Preferably, the cleavage reaction time is on the order of milliseconds.

[0013] Preferably, after the cracking reaction, the cracking gas obtained by the cracking reaction is purified, and the purification includes:

[0014] The cracked gas is cooled and then subjected to gas-solid separation to obtain carbon black-removed cracked gas; the cooling comprises: cooling to 600-1000K by a first partition wall heat exchanger and then cooling to 298-400K by a second partition wall heat exchanger; the cooling medium of the second partition wall heat exchanger is trifluoromethane;

[0015] The carbon black-removed cracking gas is subjected to water-alkali washing to obtain hydrogen fluoride-removed cracking gas;

[0016] The dehydrogen fluoride-removed cracking gas is dried and then distilled to obtain high-purity tetrafluoromethane and a distillation residue, respectively; and the distillation residue is reused in the cracking reaction.

[0017] Preferably, the cooling medium of the first partition wall heat exchange cooling is water or refrigerant.

[0018] Preferably, the water-alkali washing includes water washing and / or alkaline aqueous solution washing; the mass concentration of the alkali in the alkaline aqueous solution is ≤40%; and the alkali includes sodium hydroxide and / or potassium hydroxide.

[0019] Preferably, the gas-solid separation is performed using a gas-solid separation device, which includes a single-stage solid separation device or a multi-stage gas-solid separation device.

[0020] Preferably, the gas-solid separation device includes a filter or a cyclone separator.

[0021] The present invention provides a method for producing tetrafluoromethane using trifluoromethane as a raw material, comprising the following steps: introducing trifluoromethane into a thermal plasma reactor for cracking reaction to obtain tetrafluoromethane; the temperature of the cracking reaction is 1500-5000K. Compared with conventional tubular furnace pyrolysis or muffle furnace high-temperature cracking, the thermal plasma reactor adopted in the present invention can rely on the synergistic effect of high temperature, highly active electrons and heavy particles to achieve a significant electron excitation effect, and can achieve efficient breaking and directional recombination of chemical bonds in trifluoromethane molecules without using a catalyst and fluorine gas. It has high trifluoromethane conversion rate, high tetrafluoromethane selectivity, short reaction time, large processing capacity, and is safe and controllable. The product composition of the cracking reaction is simple and easy to separate and purify. It has low cost and low energy consumption and is suitable for continuous industrial scale-up production. It realizes low-energy consumption and low-cost resource recovery and utilization of trifluoromethane. It is particularly suitable for resource conversion of by-product trifluoromethane in the production process of difluorochloromethane or the cracking of difluorochloromethane to prepare tetrafluoroethylene, etc., avoids the greenhouse effect caused by direct emission of trifluoromethane and the waste of resources caused by incineration, and produces high-value-added tetrafluoromethane products, with significant economic and social benefits. Moreover, the present invention does not use any catalyst, thus avoiding the problems of catalyst coking and deactivation, carbonization, and device clogging under high temperature conditions, and further improving the yield of tetrafluoromethane and reaction safety.

[0022] Furthermore, the present invention adopts a first partition wall heat exchange cooling to 600-1000K and then a second partition wall heat exchange cooling to 298-400K, and utilizes the waste heat of the second partition wall heat exchange cooling to preheat the trifluoromethane. On the one hand, it can avoid the high-temperature waste heat of the first partition wall heat exchange cooling causing the trifluoromethane to react and produce by-products, and can also fully utilize the waste heat of the second partition wall heat exchange cooling, greatly reducing the energy consumption and cost of production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a diagram of the cracking and purification device used to produce tetrafluoromethane using trifluoromethane as raw material, wherein 1-thermal plasma reactor, 2-cooling device, 3-gas-solid separation device, 4-water alkali washing device, 5-drying device, 6-distillation device, 7-tetrafluoromethane finished product storage device. DETAILED DESCRIPTION

[0024] The present invention provides a method for producing tetrafluoromethane using trifluoromethane as a raw material, comprising the following steps:

[0025] Trifluoromethane is introduced into a thermal plasma reactor for cracking reaction to obtain tetrafluoromethane; the temperature of the cracking reaction is 1500-5000K.

[0026] In the present invention, the flow rate of trifluoromethane is preferably 0.5 to 1000 Nm 3 / h, more preferably 1 to 800 Nm 3 / h, more preferably 3 to 600 Nm 3 / h. The present invention does not specifically limit the source of the trifluoromethane. Trifluoromethane produced in the production process of chlorodifluoromethane, trifluoromethane produced in the cracking process of chlorodifluoromethane to produce tetrafluoroethylene, trifluoromethane recovered from a factory-based cryogenic coolant containing trifluoromethane, or trifluoromethane recovered from other process routes, as is well known to those skilled in the art, can be used. The purity of the trifluoromethane is preferably ≥90%. The preparation method provided by the present invention can achieve resource utilization of trifluoromethane, a byproduct produced in the production process of chlorodifluoromethane or the cracking process of chlorodifluoromethane to produce tetrafluoroethylene, as well as trifluoromethane from other sources.

[0027] In the present invention, the thermal plasma reactor preferably includes a radio frequency thermal plasma reactor, a microwave thermal plasma reactor, or an arc thermal plasma reactor. The arc thermal plasma reactor is preferably a direct current arc plasma reactor, more preferably a magnetically rotating arc thermal plasma reactor. The direct current arc plasma reactor employed in the present invention has high mass and heat transfer efficiency, and a uniform and easily controllable residence time. The present invention utilizes a thermal plasma reactor to crack trifluoromethane, eliminating the need for any carrier gas for dilution or auxiliary cracking. The cracked gas obtained from the cracking reaction has a simple composition, further simplifying subsequent purification steps.

[0028] In the present invention, the temperature of the cracking reaction is preferably 2000-4500 K, more preferably 2500-4000 K, and even more preferably 3000-3500 K. In the present invention, during the cracking reaction, trifluoromethane is cracked in the presence of thermal plasma to produce tetrafluoromethane, a small amount of carbon black, and hydrogen fluoride. In addition, a small amount of trifluoromethane does not undergo cracking reaction.

[0029] After the cracking reaction, the present invention preferably further comprises purifying the cracked gas obtained from the cracking reaction, wherein the purification comprises:

[0030] The cracked gas is cooled and then subjected to gas-solid separation to obtain carbon black-removed cracked gas; the cooling comprises: cooling to 600-1000K by a first partition wall heat exchanger and then cooling to 298-400K by a second partition wall heat exchanger; the cooling medium of the second partition wall heat exchanger is trifluoromethane;

[0031] The carbon black-removed cracking gas is subjected to water-alkali washing to obtain hydrogen fluoride-removed cracking gas;

[0032] The dehydrogen fluoride-removed cracking gas is dried and then distilled to obtain high-purity tetrafluoromethane and a distillation residue, respectively; and the distillation residue is reused in the cracking reaction.

[0033] The present invention cools the cracked gas and then separates it into gas and solids to obtain carbon black-removed cracked gas. The cooling comprises: cooling to 600-1000K via a first partition wall heat exchanger followed by cooling to 298-400K via a second partition wall heat exchanger. In the present invention, the cooling medium for the first partition wall heat exchanger is preferably water or a refrigerant. The present invention has no particular requirements for the specific type of refrigerant; any refrigerant with a cooling function known to those skilled in the art, such as ethylene glycol, can be used. In the present invention, the temperature after cooling is preferably 298K, 350K, or 400K. In the present invention, the cooling medium for the second partition wall heat exchanger is trifluoromethane. Specifically, the waste heat from the second partition wall heat exchanger is used to preheat and cool the trifluoromethane, which is then passed into a thermal plasma reactor for cracking. This fully utilizes the heat of the cracked gas without causing side reactions in the trifluoromethane, further reducing energy consumption and production costs.

[0034] In the present invention, the gas-solid separation is preferably performed using a gas-solid separation device, which preferably includes a single-stage solid separation device or a multi-stage gas-solid separation device; the gas-solid separation device preferably includes a filter or a cyclone separator, and the purpose of the gas-solid separation is to remove carbon black. In the present invention, the multi-stage gas-solid separation device is preferably a two-stage gas-solid separation device, the first-stage gas-solid separation device of the two-stage gas-solid separation device is preferably a cyclone separator for capturing carbon black particles with a particle size of ≥5μm (larger carbon black particles or agglomerates of small carbon black particles), and the second-stage gas-solid separation device of the two-stage separation device is preferably a filter for capturing carbon black with a particle size of <5μm.

[0035] The gas-solid separation device preferably includes a filter or a cyclone separator; the purpose of the gas-solid separation is to remove carbon black.

[0036] After obtaining the carbon black-removed pyrolysis gas, the present invention performs aqueous alkali washing on the carbon black-removed pyrolysis gas to obtain hydrogen fluoride-removed pyrolysis gas. In the present invention, the aqueous alkali washing preferably includes water washing and / or aqueous alkali washing. The mass concentration of the alkali in the aqueous alkali washing is preferably ≤40%, more preferably 15-40%. The alkali preferably includes sodium hydroxide and / or potassium hydroxide, more preferably potassium hydroxide. The purpose of the washing is to remove hydrogen fluoride.

[0037] After obtaining the dehydrogen fluoride cracking gas, the present invention dries and then distills the dehydrogen fluoride cracking gas to obtain high-purity tetrafluoromethane and a distillation residue, respectively; the distillation residue is reused in the cracking reaction. The present invention has no special restrictions on the drying, as long as the water can be removed. The present invention has no special restrictions on the conditions of the distillation, and the distillation conditions familiar to those skilled in the art can be adopted. In the present invention, the distillation residue includes unreacted trifluoromethane and other by-products (including octafluoroisobutylene). The present invention cracks the distillation residue again, which can improve the utilization rate of trifluoromethane and the yield of tetrafluoromethane. The existing purification method requires the removal of octafluoroisobutylene and then recycling, while the purification method adopted by the present invention does not need to remove octafluoroisobutylene separately. Octafluoroisobutylene is cracked to generate tetrafluoromethane without being accumulated, thereby improving the yield of tetrafluoromethane.

[0038] After the drying, the present invention preferably further comprises sampling and testing the obtained dry pyrolysis gas after removal of hydrogen fluoride. The testing is preferably gas chromatography analysis to confirm the composition of the pyrolysis gas after removal of carbon black, HF and water (i.e., dry pyrolysis gas after removal of hydrogen fluoride).

[0039] In the present invention, the production of tetrafluoromethane (cracking reaction and purification) using trifluoromethane as raw material is preferably carried out in a cracking and purification device. According to the direction of material flow, the cracking and purification device preferably includes a thermal plasma reactor 1, a cooling device 2, a gas-solid separation device 3, a water-alkali washing device 4, a drying device 5 and a distillation device 6 connected by pipelines.

[0040] In the present invention, the thermal plasma reactor 1 is connected to a trifluoromethane feed pipe, and the thermal plasma reactor 1 is also provided with a cracking gas outlet and a distillation residue inlet; the type and input power of the thermal plasma reactor 1 are consistent with the cracking reaction step, and are not repeated here.

[0041] In the present invention, the cooling method adopted by the cooling device is a partition-type heat exchange cooling device; the partition-type heat exchange cooling device includes a first partition-type heat exchange cooling device and a second partition-type heat exchange cooling device, and the cooling medium of the first partition-type heat exchange cooling device is preferably water or refrigerant; the cooling medium of the second partition-type heat exchange cooling device is preferably trifluoromethane.

[0042] In the present invention, the gas-solid separation device 3 is described in the aforementioned purification part and will not be described again here; the gas-solid separation device 3 is provided with a carbon black outlet.

[0043] In the present invention, the water-alkali washing device 4 contains water or an alkaline aqueous solution, and the water-alkali washing device 4 is preferably further provided with a jacket, and the jacket is preferably provided with circulating water; the water-alkali washing device 4 is preferably a multi-stage water-alkali washing device, and the multi-stage water-alkali washing device is preferably composed of multiple absorption washing devices in series, each of which is preferably provided with a jacket, and the jacket is preferably provided with circulating water. The carbon black-removed cracking gas enters the first absorption washing device, and after washing, enters the subsequent absorption washing device to continue removing hydrofluoric acid. The alkaline water washing device used in the present invention can not only achieve the purpose of removing acid, but also cool the material to prevent secondary reactions.

[0044] The present invention has no special limitation on the drying device 5 , and any commonly used drying device in the chemical industry well known to those skilled in the art can be used.

[0045] In the present invention, the distillation device 6 is further provided with a distillation residue outlet and a tetrafluoromethane outlet, and the distillation residue outlet is connected to the distillation residue inlet of the thermal plasma reactor 1 through a pipeline.

[0046] In the present invention, a sampling port is preferably provided on the pipeline connecting the drying device 5 and the distillation device 6.

[0047] In the present invention, the cracking and purification device is preferably further provided with a tetrafluoromethane product storage device 7 whose inlet is connected to the tetrafluoromethane outlet of the distillation device 6 via a pipeline.

[0048] In the present invention, the materials of the connecting pipes used in the cooling device 2, gas-solid separation device 3, water-alkali washing device 4 and the cracking and purification device are preferably independently silicon carbide, Hastelloy C alloy, manganese nitride or stainless steel lined with polytetrafluoroethylene.

[0049] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0050] Example 1

[0051] Tetrafluoromethane is prepared using the cracking and purification device shown in Figure 1.

[0052] Trifluoromethane (flow rate of 3Nm 3 / h) is passed into a thermal plasma reactor, and after arcing (input power is 15kW), a rotating arc plasma is formed. At 3500K, a cracking reaction is carried out in milliseconds to obtain cracked gas. The cracked gas is sequentially subjected to interlayer heat exchange cooling (water or trifluoromethane as a cooling medium) to 350K, gas-solid separation, alkaline aqueous solution washing, and drying to obtain hydrogen fluoride-removed cracked gas. Sampling is performed for gas chromatography analysis and then distillation to obtain high-purity tetrafluoromethane and a distillation residue, respectively. The distillation residue (unreacted trifluoromethane and other by-products) is reintroduced into the thermal plasma reactor for cracking reaction to produce tetrafluoromethane. The cooling waste heat is reused to preheat the trifluoromethane.

[0053] According to gas chromatography detection and analysis calculation, the single-pass conversion rate of trifluoromethane is 99.2%, the purity of tetrafluoromethane in the hydrogen fluoride cracking gas is 92.3%, the selectivity of tetrafluoromethane is 94.2%, and the purity of high-purity tetrafluoromethane reaches electronic grade.

[0054] Example 2

[0055] Tetrafluoromethane is prepared using the cracking and purification device shown in Figure 1.

[0056] After heat exchange with the cracking gas, trifluoromethane (flow rate of 3Nm 3 / h) is passed into a thermal plasma reactor. After arc ignition (input power of 11 kW), a rotating arc plasma is formed. At 3300K, a cracking reaction occurs in milliseconds to produce cracked gas. The cracked gas is then subjected to inter-wall heat exchange cooling (water or trifluoromethane as the cooling medium) to 400K, followed by gas-solid separation, washing with an alkaline aqueous solution, and drying to produce cracked gas without hydrogen fluoride. Samples are taken for gas chromatography analysis and then distilled to obtain high-purity tetrafluoromethane and a distillation residue, respectively. The distillation residue (unreacted trifluoromethane and other by-products) is reintroduced into the thermal plasma reactor for a cracking reaction to produce tetrafluoromethane. The residual heat from cooling is reused to preheat the trifluoromethane.

[0057] Gas chromatography detection and analysis calculations show that the single-pass conversion rate of trifluoromethane is 99.0%, the purity of tetrafluoromethane in the cracked gas except hydrogen fluoride is 91.2%, the selectivity of tetrafluoromethane is 93.7%, and the purity of high-purity tetrafluoromethane reaches electronic grade.

[0058] Example 3

[0059] Tetrafluoromethane is prepared using the cracking and purification device shown in Figure 1.

[0060] After heat exchange with the cracking gas, trifluoromethane (flow rate of 12Nm 3 / h) is passed into a thermal plasma reactor, and after arcing (input power is 20kW), a rotating arc plasma is formed. At 3800K, a cracking reaction is performed in milliseconds to obtain cracked gas; the cracked gas is sequentially subjected to interlayer heat exchange cooling (ethylene glycol and trifluoromethane are used as cooling media) to 298K, gas-solid separation, alkaline aqueous solution washing and drying to obtain hydrogen fluoride-removed cracked gas, which is sampled for gas chromatography analysis and then distilled to obtain high-purity tetrafluoromethane and a distillation residue, respectively; the distillation residue (unreacted trifluoromethane and other by-products) is again passed into the thermal plasma reactor for cracking reaction to produce tetrafluoromethane. The cooling waste heat is reused to preheat the trifluoromethane.

[0061] According to gas chromatography detection and analysis calculation, the single-pass conversion rate of trifluoromethane is 99.3%, the purity of tetrafluoromethane in the cracked gas except hydrogen fluoride is 93.4%, the selectivity of tetrafluoromethane is 94.3%, and the purity of high-purity tetrafluoromethane reaches electronic grade.

[0062] Example 4

[0063] Tetrafluoromethane is prepared using the cracking and purification device shown in Figure 1.

[0064] After heat exchange with the cracking gas, trifluoromethane (flow rate of 600Nm 3 / h) is passed into a thermal plasma reactor, and after arcing (input power is 1MW), a rotating arc plasma is formed. At 4000K, a cracking reaction is carried out in milliseconds to obtain cracked gas; the cracked gas is sequentially subjected to interlayer heat exchange cooling (ethylene glycol and trifluoromethane are used as cooling media) to 298K, gas-solid separation, alkaline aqueous solution washing and drying to obtain hydrogen fluoride-removed cracked gas, which is sampled for gas chromatography analysis and then distilled to obtain high-purity tetrafluoromethane and a distillation residue, respectively; the distillation residue (unreacted trifluoromethane and other by-products) is again passed into the thermal plasma reactor for cracking reaction to produce tetrafluoromethane. The cooling waste heat is reused to preheat the trifluoromethane.

[0065] According to gas chromatography detection and analysis calculation, the single-pass conversion rate of trifluoromethane is 99.1%, the purity of tetrafluoromethane in the hydrogen fluoride cracking gas is 94.8%, the selectivity of tetrafluoromethane is 95.2%, and the purity of high-purity tetrafluoromethane reaches electronic grade.

[0066] Comparative Example 1

[0067] Trifluoromethane (at a flow rate of 100 mL / min) was introduced into a tubular furnace with a preheating outlet temperature of 895° C., a reaction middle temperature of 910° C., and a reaction residence time of 2 s. The cracked gas at the outlet of the tubular furnace was sequentially washed with an alkaline aqueous solution and then dried. The obtained deacidified cracked gas was sampled for gas chromatography analysis. Analysis and calculation showed that the single-pass conversion rate of trifluoromethane was 61.6%, the concentration of tetrafluoroethylene in the deacidified cracked gas was 5.1 wt %, the concentration of hexafluoropropylene was 46.8 wt %, and no tetrafluoromethane was detected.

[0068] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for producing tetrafluoromethane using trifluoromethane as a raw material, comprising the following steps: Trifluoromethane is introduced into a thermal plasma reactor for cracking reaction to obtain tetrafluoromethane; the temperature of the cracking reaction is 1500-5000K.

2. The method according to claim 1, characterized in that The flow rate of trifluoromethane is 0.5-1000 Nm 3 / h.

3. The method according to claim 1, characterized in that The thermal plasma reactor includes a radio frequency thermal plasma reactor, a microwave thermal plasma reactor or an arc thermal plasma reactor.

4. The method according to any one of claims 1 to 3, characterized in that: The time of the cleavage reaction is in milliseconds.

5. The method according to claim 1, characterized in that After the cracking reaction, the cracking gas obtained by the cracking reaction is purified, and the purification includes: The cracked gas is cooled and then separated into gas and solid to obtain the cracked gas without carbon black; the cooling comprises: cooling to 600-1000K by a first partition wall heat exchange and cooling to 298-400K by a second partition wall heat exchange; the cooling medium of the second partition wall heat exchange is trifluoromethane; The carbon black-removed pyrolysis gas is washed with water and / or an alkaline aqueous solution to obtain a pyrolysis gas that has been removed from hydrogen fluoride; The dehydrogen fluoride cracking gas is dried and then distilled to obtain high-purity tetrafluoromethane and distillation residue respectively; the distillation residue is reused in the cracking reaction.

6. The method according to claim 5, characterized in that The cooling medium of the first partition heat exchange cooling is water or refrigerant.

7. The method according to claim 5, characterized in that The mass concentration of the alkali in the alkali aqueous solution is ≤40%; the alkali comprises sodium hydroxide and / or potassium hydroxide.

8. The method according to claim 5, characterized in that The gas-solid separation is performed using a gas-solid separation device, which includes a single-stage solid separation device or a multi-stage gas-solid separation device.

9. The method according to claim 8, characterized in that The gas-solid separation device includes a filter or a cyclone separator.

10. A cracking and purification device for producing tetrafluoromethane from trifluoromethane, comprising, in order of material flow direction, a thermal plasma reactor (1), a cooling device (2), a gas-solid separation device (3), a water-alkali washing device (4), a drying device (5) and a distillation device (6) connected by pipelines; The thermal plasma reactor (1) is connected to a trifluoromethane feed pipe, and the thermal plasma reactor (1) is provided with a cracking gas outlet; The distillation device (6) is provided with a tetrafluoromethane outlet.

11. The pyrolysis and purification device according to claim 10, characterized in that: The cooling device (2) is a partition-type heat exchange cooling device.

12. The cleavage and purification device according to claim 11, characterized in that: The partition wall heat exchange cooling device comprises a first partition wall heat exchange cooling device and a second partition wall heat exchange cooling device; the cooling medium of the first partition wall heat exchange cooling device is water or refrigerant; the cooling medium of the second partition wall heat exchange cooling device is trifluoromethane.

13. The pyrolysis and purification device according to claim 11, characterized in that: The thermal plasma reactor (1) is also provided with an inlet for distillation residue; The distillation device (6) is also provided with a distillation residue outlet, and the distillation residue outlet is connected to the distillation residue inlet of the thermal plasma reactor (1) through a pipeline.

14. The pyrolysis and purification device according to any one of claims 10 to 13, characterized in that: The cracking and purification device is also provided with a tetrafluoromethane finished product storage device (7) whose inlet is connected to the tetrafluoromethane outlet of the distillation device (6) through a pipeline.

15. The cleavage and purification device according to claim 14, characterized in that: The materials of the cooling device (2), the gas-solid separation device (3), the water-alkali washing device (4) and the pipeline independently include silicon carbide, Hastelloy C alloy, manganese nitride or stainless steel lined with polytetrafluoroethylene.

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