Online decoking method for coke generated by cracking of fluorine-containing system

Abstract

The invention provides an online decoking method for coke generated by cracking of a fluorine-containing system, and relates to the technical field of chemical reaction engineering. The invention provides an on-line decoking method for coke generated by cracking of a fluorine-containing system. The on-line decoking method comprises the following step: introducing a perfluorinated decoking medium to carry out on-line decoking on the coke generated by cracking of the fluorine-containing system. The perfluorinated decoking medium adopted by the invention can be subjected to high-activity reaction with the coke body, a gaseous product generated by decoking is still fluorine-containing hydrocarbon, hydrofluoric acid and high-toxicity fluorine-containing substances (such as fluorophosgene) cannot be generated in the decoking process, a reaction device cannot be corroded in the online decoking process, the service life of the reaction device is long, and the cost is low. And the decoking process is good in safety and high in decoking efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical reaction engineering, and in particular to an online coke removal method for coke generated by cracking a fluorine-containing system. Background Art

[0002] With the rapid development of my country's semiconductor and aluminum industries, the emission of waste fluorinated compounds has increased year by year. If its terminal emissions are not effectively controlled, it will seriously restrict the development of related industries. At present, the main resource treatment method for waste fluorinated hydrocarbons is thermal cracking. Thermal cracking converts waste fluorinated hydrocarbons into fluorinated olefins with recycling value at high temperatures. Increasing the thermal cracking temperature and extending the reaction residence time can help improve the conversion rate of fluorinated wastes. However, excessively high reaction temperatures and excessively long residence times can complicate the cracking process, often causing the target product, fluorinated olefins, to undergo a disproportionation reaction to produce carbon, which is ultimately converted into coke. For example, in the process of preparing hexafluoropropylene by cracking fluorinated organic waste in a tubular furnace, the production of hexafluoropropylene releases a large amount of heat, making the reaction temperature difficult to control. When the temperature is too high or there is local overheating, tetrafluoroethylene will undergo a disproportionation reaction to produce carbon. The extreme heat release of this reaction will further lead to local overheating, promoting the disproportionation reaction. In severe cases, it can cause coking in the pipeline, blocking the reactor, and preventing the system from operating continuously. Therefore, in order to solve the coking problem caused by the cracking of fluorinated hydrocarbons, an efficient and thorough coke removal method is urgently needed.

[0003] For coking in conventional systems (hydrocarbon systems), common coke cleaning methods include steam-air coking, mechanical coking and online coking. Among them, steam-air coking is to introduce air and water (or water vapor) into the reactor, and directly react with the coke on the wall under heating conditions to achieve the purpose of rapid coking. The mechanical coking method is to use a scraper to remove the coke. This method can significantly reduce the pressure of the furnace tube and is safe and efficient. The steam-air coking and mechanical coking processes require regular shutdown for coking, and cannot be used to clean the coke when there is partial coking during operation. Online coking is to continuously and rapidly change the tube wall temperature and water vapor flow rate of the coke cleaning tube, and utilize the difference in thermal expansion coefficients between the furnace tube and the coke scale layer to peel off the coke blocks. This method has the characteristics of flexible operation, good coking effect on radiation tubes and low coking cost. However, fluorine-containing raw materials usually produce hydrogen fluoride during the cracking process. When the existing online coke cleaning technology is used in a fluorine-containing reaction system, the introduction of water vapor or air will produce hydrofluoric acid, which will corrode the reaction device and reduce the life of the device. Summary of the Invention

[0004] In view of this, the present invention aims to provide an online coke cleaning method for coke generated by cracking a fluorine-containing system. The online coke cleaning method provided by the present invention does not generate hydrofluoric acid during the coke cleaning process, has a long service life of the reaction device, and does not require stopping the process for coke cleaning.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The invention provides an online coke cleaning method for coke generated by cracking a fluorine-containing system, comprising the following steps: introducing a perfluorinated coke cleaning medium to perform online coke cleaning on the coke generated by cracking the fluorine-containing system.

[0007] Preferably, the perfluorodecoking medium includes one or more of nitrogen trifluoride, tetrafluoromethane, hexafluoroethane, perfluoropropane, perfluorobutane, perfluorocyclobutane, perfluorohexane and perfluorooctane.

[0008] Preferably, the molar ratio of the perfluorinated decoking medium to the fluorine-containing system is 1:2-5.

[0009] Preferably, the fluorine-containing system includes one or more of trifluoromethane, tetrafluoroethylene, fluorine-containing polymer, hexafluoroethane, hexafluoropropylene and octafluorobutene.

[0010] Preferably, the fluorine-containing polymer includes one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride, perfluoroethylene-propylene copolymer and ethylene-tetrafluoroethylene copolymer.

[0011] Preferably, the online decoking time is 1 to 25% of the cracking time.

[0012] Preferably, the online decoking is carried out in a reaction device, which includes a tubular furnace, a plasma reactor, an electromagnetic induction furnace or a fluidized bed reactor.

[0013] Preferably, when the reaction device is a tubular furnace, the online decoking conditions include: a temperature of 1200-2500K, a molar flow ratio of perfluorinated decoking medium to fluorine-containing system of 1:2-3, and an online decoking time of 20-25% of the cracking time;

[0014] When the reaction device is a plasma reactor, the online decoking conditions include: a temperature of 1200 to 4000 K, a molar flow ratio of a perfluorinated decoking medium to a fluorine-containing system of 1:4 to 5; an online decoking time of 1 to 10% of a cracking time, and an arc stabilizing gas of nitrogen or an inert gas;

[0015] When the reaction device is an electromagnetic induction furnace, the online decoking conditions include: a temperature of 1200-2200K, a molar flow ratio of perfluorinated decoking medium to fluorine-containing system of 1:2-3, and an online decoking time of 10-25% of the cracking time;

[0016] When the reaction device is a fluidized bed reactor, the online decoking conditions include: temperature of 1200-1500K, molar flow ratio of perfluorinated decoking medium to fluorine-containing system of 1:2-3, and online decoking time accounting for 10-25% of the cracking time.

[0017] Preferably, the online defocusing further includes monitoring the degree of online defocusing.

[0018] Preferably, when the reaction device is a tubular furnace, the monitored parameters include temperature, pressure, flow rate and composition of the gas at the outlet of the tubular furnace, and online coke cleaning is completed when the pressure of the reaction device drops to a difference of ±10 kPa from the cracking pressure;

[0019] When the reaction device is a plasma reactor, the monitored parameters include current, voltage, pressure, flow rate and gas composition at the outlet of the plasma reactor. When the voltage of the reaction device rises to ±10V of the initial voltage, online decoking is completed.

[0020] When the reaction device is an electromagnetic induction furnace, the monitored parameters include temperature, pressure, flow rate and gas composition at the outlet of the electromagnetic induction furnace. When the pressure of the reaction device drops to ±10 kPa of the cracking pressure, the online coke cleaning is completed.

[0021] When the reaction device is a fluidized bed reactor, the monitored parameters include temperature, pressure, flow rate and gas composition at the outlet of the fluidized bed reactor. When the pressure of the reaction device drops to ±10 kPa of the cracking pressure, online coke cleaning is completed.

[0022] The perfluorinated decoking medium used in the present invention can react with the coke body with high activity, and the gaseous products generated by decoking are still fluorine-containing hydrocarbons. The substances generated in the online decoking process are consistent with the fluorine-containing cracking products. Therefore, the online decoking process does not affect the composition of the cracking products, and no impurity elements such as H and O are introduced in the decoking process. Hydrofluoric acid and highly toxic fluorine-containing substances (such as fluorophosgene) will not be generated. The online decoking process will not corrode the reaction device, the service life of the reaction device is long, and the decoking process is safe. Due to the high reactivity of the perfluorinated decoking medium, the reaction efficiency of the online decoking process can be improved, the reaction time can be reduced, and other substances are not generated, thereby improving the purity of the product. Compared with the existing online decoking method, the online decoking method provided by the present invention has a higher decoking efficiency, does not require parking, and can also be used for decoking under the condition that there is partial coking during the cracking operation.

[0023] Existing online coke cleaning technologies, when used in fluorine-containing systems, suffer from drawbacks such as limited effectiveness when coking is severe, inability to remove coke from the convection section, and the need for mechanical decoking by furnace shutdown. The present invention, however, introduces a decoking medium directly into the fluorine-containing system, enabling online decoking within the fluorine-containing system cracking apparatus without requiring shutdown, and also effectively removes coke from the convection section. Compared to the prior art method of periodic decoking, the online decoking method provided by the present invention reduces revenue losses associated with short-term downtime, eliminates the need for additional labor and equipment, and offers a low cost per decoking session.

[0024] The perfluorinated decoking medium used in the present invention is suitable for different types of reactors and has a significant removal effect on coke of different hardness and thickness. The online decoking method provided by the present invention has good application prospects in the field of chemical reaction engineering and a wide range of applications.

[0025] The present invention uses a perfluorinated coke cleaning medium for coke cleaning, which does not produce CO, CO2, or other combustion exhaust gases, thereby reducing the production of greenhouse gases and benefiting environmental protection. The online coke cleaning method provided by the present invention has good environmental performance and helps reduce environmental pollution.

[0026] Furthermore, the perfluorinated decoking medium used in the present invention has high reactivity, and by controlling parameters such as temperature, flow rate, and time of online decoking, high-efficiency decoking can be achieved.

[0027] Furthermore, by directly switching the fluorine-containing system and the decoking medium, decoking can be achieved without stopping the machine; by controlling the flow rate of the fluorine-containing system and the decoking medium, the decoking time can be further controlled to achieve different decoking effects.

[0028] Furthermore, the present invention introduces nitrogen or an inert gas as an arc stabilizing gas, which can realize non-stop coke cleaning of the plasma reactor.

[0029] Furthermore, when existing online coke cleaning technologies are used in fluorine-containing reaction systems, the coke cleaning effect is not obvious when coking is severe, the coke in the convection section cannot be removed, and the furnace must be shut down for mechanical coke cleaning. In addition, during the online coke cleaning process, there are problems such as the inability to monitor the coke state in real time and the difficulty in regulating the coke cleaning process. The present invention monitors the degree of online coke cleaning and the fluctuations and increases in the arc voltage and pressure of the reaction device to accurately monitor and control the coke cleaning process and effect, achieving dynamic monitoring of the coke cleaning process and efficient and controllable coke cleaning, thus solving the problem of difficulty in dynamically monitoring and controlling the coke cleaning effect in the existing technology.

[0030] Furthermore, the present invention provides more precise control over reaction conditions, enabling real-time monitoring and control of parameters such as arc voltage (accuracy of ±1V), reaction temperature (accuracy of ±1K), device pressure (accuracy of ±1kPa), and reaction time (accuracy of ±1s). This effectively improves the depth of the decoking reaction. For example, the decoking effect is judged by real-time monitoring of the arc voltage and pressure of the reaction device. The decoking process ends when the arc voltage is ±10V of the initial value of the online decoking process or the pressure of the reaction device is ±10kPa of the initial value of the online decoking process. Compared to the prior art, the present invention provides more precise control over reaction conditions and a wider range of application scenarios. DETAILED DESCRIPTION

[0031] The invention provides an online coke cleaning method for coke generated by cracking a fluorine-containing system, comprising the following steps: introducing a perfluorinated coke cleaning medium to perform online coke cleaning on the coke generated by cracking the fluorine-containing system.

[0032] Unless otherwise specified, the materials and equipment used in the present invention are all commercially available products in the art.

[0033] In the present invention, the fluorine-containing system preferably includes one or more of trifluoromethane, tetrafluoroethylene, fluorine-containing polymer, hexafluoroethane, hexafluoropropylene and octafluorobutene; the fluorine-containing polymer preferably includes one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride, perfluoroethylene-propylene copolymer and ethylene-tetrafluoroethylene copolymer (ETFE); when the fluorine-containing polymer is polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride and perfluoroethylene-propylene copolymer, the fluorine-containing polymer is preferably a waste fluorine-containing polymer.

[0034] In the present invention, the perfluorodecoking medium preferably includes one or more of nitrogen trifluoride, tetrafluoromethane, hexafluoroethane, perfluoropropane, perfluorobutane, perfluorocyclobutane, perfluorohexane, and perfluorooctane; the perfluoropropane preferably includes linear perfluoropropane or cyclic perfluoropropane (c-C3F8). In the present invention, the perfluorooctane is preferably used in the form of perfluorooctane liquid or perfluorooctane gas; the perfluorooctane gas is preferably obtained by vaporizing perfluorooctane liquid. Compared with perfluorooctane liquid, perfluorooctane gas has a better decoking effect. Using water or air as a decoking medium can introduce other impurities during the online decoking process. However, the perfluorinated decoking medium used in the present invention can react with the coke body with high activity, and the gaseous products generated by decoking are still fluorinated hydrocarbons. No impurity elements such as H and O are introduced during the decoking process, and hydrofluoric acid and highly toxic fluorine-containing substances (such as fluorophosgene) are not generated. The online decoking process does not corrode the reaction device, the service life of the reaction device is long, and the decoking process is safe. Moreover, due to the high reactivity of the perfluorinated decoking medium, the reaction efficiency can be improved, the reaction time can be reduced, and other substances are not generated, thereby improving the purity of the product. Compared with existing online decoking methods, the online decoking method provided by the present invention has a higher decoking efficiency.

[0035] In the present invention, the molar ratio (dosage molar ratio) of the perfluorinated decoking medium and the fluorine-containing system is preferably 1:2-5, and in specific embodiments can be 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5 or 1:5.

[0036] In the present invention, the online decoking time is preferably 1 to 25% of the cracking time, and in specific embodiments may be 5%, 10%, 15%, 20% or 25%.

[0037] In the present invention, the cracking and online coke cleaning are carried out in a reaction device, which preferably includes a tubular furnace, a plasma reactor, an electromagnetic induction furnace or a fluidized bed reactor; the cracking and online coke cleaning are carried out in the same reaction device.

[0038] In the present invention, when the reaction device is a tubular furnace, the cracking conditions preferably include a temperature of 1200-2500K, and in specific embodiments, it can be 1200K, 1500K, 1800K, 2000K, 2200K or 2500K; the molar flow ratio of the perfluorinated decoking medium to the fluorine-containing system is 1:2-3, and in specific embodiments, it can be 1:2, 1:2.2, 1:2.5, 1:2.8 or 1:3; the online decoking time accounts for 20-25% of the cracking time, and in specific embodiments, it can be 20%, 21%, 22%, 23%, 24% or 25%.

[0039] In the present invention, when the reaction device is a plasma reactor, the cracking conditions preferably include a temperature of 1200-4000K, and in specific embodiments, it can be 1200K, 1500K, 1800K, 2000K, 2200K, 2500K, 2800K, 3000K, 3200K, 3500K, 3800K or 4000K; the molar flow ratio of the perfluorinated decoking medium to the fluorine-containing system is 1:4-5, and in specific embodiments, it can be 1:4, 1:4.2, 1:4.5, 1:4.8 or 1:5; the online decoking time accounts for 1-10% of the cracking time, and in specific embodiments, it can be 1%, 2%, 5%, 8% or 10%; the arc stabilizing gas is nitrogen or an inert gas, and the inert gas preferably includes argon or helium.

[0040] In the present invention, when the reaction device is an electromagnetic induction furnace, the cracking conditions preferably include a temperature of 1200-2200K, and in specific embodiments, it can be 1200K, 1500K, 1800K, 2000K or 2200K; the molar flow ratio of the perfluorinated decoking medium to the fluorine-containing system is 1:2-3, and in specific embodiments, it can be 1:2, 1:2.2, 1:2.5, 1:2.8 or 1:3; the online decoking time accounts for 10-25% of the cracking time, and in specific embodiments, it can be 10%, 12%, 15%, 18%, 20%, 22% or 25%;

[0041] In the present invention, when the reaction apparatus is a fluidized bed reactor, the cracking conditions preferably include a temperature of 1200-1500K, and in specific embodiments, it can be 1200K, 1300K, 1400K or 1500K; the molar flow ratio of the perfluorinated decoking medium to the fluorine-containing system is 1:2-3, and in specific embodiments, it can be 1:2, 1:2.2, 1:2.5, 1:2.8 or 1:3; the online decoking time accounts for 10-25% of the cracking time, and in specific embodiments, it can be 10%, 12%, 15%, 18%, 20%, 22% or 25%.

[0042] In the present invention, the online defocusing preferably also includes monitoring the degree of online defocusing.

[0043] In the present invention, when the reaction device is a tubular furnace, the monitored parameters preferably include temperature, pressure, flow rate and gas composition at the outlet of the tubular furnace. When the pressure of the reaction device drops to a difference of ±10 kPa from the cracking pressure, online coke cleaning is completed.

[0044] In the present invention, when the reaction device is a plasma reactor, the monitored parameters preferably include current, voltage, pressure, flow and plasma reactor outlet gas composition, and online decoking is completed when the voltage of the reaction device rises to ±10V of the initial voltage.

[0045] In the present invention, when the reaction device is an electromagnetic induction furnace, the monitored parameters preferably include temperature, pressure, flow rate and electromagnetic induction furnace outlet gas composition, and online coke cleaning is completed when the pressure of the reaction device drops to ±10kPa of the cracking pressure.

[0046] In the present invention, when the reaction device is a fluidized bed reactor, the monitored parameters preferably include temperature, pressure, flow rate and gas composition at the outlet of the fluidized bed reactor. When the pressure of the reaction device drops to ±10 kPa of the cracking pressure, the online decoking is completed.

[0047] The online decoking method provided by the present invention can accurately monitor and control the decoking process. By constructing a monitoring system during the cracking process and the decoking process to monitor the fluctuation and rise of the arc voltage or pressure, the decoking process and effect can be accurately monitored and controlled to achieve efficient and controllable decoking. The present invention constructs a sensor network: deploys multiple types of sensors to cover the key parameters of the entire cracking and decoking process, including temperature, pressure and flow, among which the plasma reaction requires additional voltage and current monitoring. The present invention monitors the online decoking process through a sensor network to ensure that the temperature remains within a preset range to prevent overheating from damaging the equipment or affecting the decoking effect. In the cracking process, due to the generation of coke, the reaction device is blocked, so the pressure of the device rises sharply. After switching to the online decoking process, due to the continuous reaction of the perfluorodecoking medium with the coke, the pressure gradually decreases after the device is unblocked. When it finally drops to ±10kPa of the initial (cracking) pressure, it is considered that the decoking is complete and the decoking is completed. For example, in a plasma reactor, the initial cracking pressure is generally 100±10kPa. During the cracking process, the pressure can rise to 300-400kPa. During the online decoking process, the pressure continues to drop until it reaches 100±10kPa. This is considered to be complete decoking, and online decoking is stopped, and cracking can continue. During the cracking process, due to the generation of coke, the reaction device is blocked, so the arc voltage continues to decrease. After switching to the decoking process, due to the continuous reaction of the perfluorinated decoking medium with the coke, the arc voltage gradually rises after the device is unblocked. When it finally rises to ±10V of the initial (cracking) voltage, it is considered to be complete decoking and the decoking process is terminated. For example, in a plasma reactor, the initial cracking pressure is generally 120±10V. During the cracking process, the voltage can drop to 50-80V. During the decoking process, the voltage continues to rise until it reaches 120±10V. This is considered to be complete decoking, and decoking is stopped, and cracking can continue. The continuous reduction of the arc current ensures the continuous occurrence of the decoking process and prevents excessive decoking. The coking condition of the reactor is judged according to the monitoring system, and the reaction temperature, reaction time, flow rate of perfluorinated decoking medium and other parameters are precisely controlled to achieve a good decoking effect.

[0048] The present invention switches between cracking and online coke cleaning by regulating the flow rate of the fluorine-containing system and the flow rate of the perfluorinated coke cleaning medium. Specifically, by adjusting parameters such as the flow rate of the fluorine-containing system, the flow rate of the perfluorinated coke cleaning medium, the temperature of online coke cleaning and the reaction time of online coke cleaning, a coke cleaning reaction occurs, completing the switching between the cracking / reaction process and the coke cleaning process, and realizing efficient, thorough and non-stop coke cleaning.

[0049] The online coke cleaning method provided by the present invention is applicable to various fluorine-containing system reaction devices. It does not require shutdown for coke cleaning, has low coke cleaning costs, and has low equipment requirements. Furthermore, the improved online coke cleaning method of the present invention can achieve precise monitoring and control of the coke cleaning process, with high controllability and safety, and can be widely adapted to various reactors. The online coke cleaning method provided by the present invention has great market demand and application prospects in the field of chemical reaction engineering.

[0050] The present invention performs online decoking in a plasma reactor. The plasma has high energy and high reactivity, which can realize a fast and controllable online decoking process, solving the key obstacle hindering the industrialization of the plasma cracking process. The online decoking method provided by the present invention also has good market demand and application prospects in the field of plasma chemistry.

[0051] To further illustrate the present invention, the online coke removal method for coke produced by cracking a fluorine-containing system provided by the present invention is described in detail below with reference to the following examples, but they should not be construed as limiting the scope of protection of the present invention.

[0052] Example 1

[0053] A plasma reactor was used to generate a plasma arc by discharging N2, and CHF3 (with a flow rate of 4 Nm 3 / h) into a plasma reactor, and under the condition of 3500K, a cracking reaction is carried out in milliseconds to obtain a cracking product; gas chromatography detection and analysis calculation show that the single-pass conversion rate of CHF3 is 99.2%, and the purity of CF4 in the cracking product is 82.3%.

[0054] After the cracking reaction was carried out for 2 hours, the CHF3 feed was stopped, the cracking reaction was terminated, and the coke was cleared. The coke clearing process was as follows: CF4 was used as the perfluorinated coke clearing medium (flow rate was 0.8 Nm 3 / h) is passed into a plasma reactor for decoking, the decoking temperature is 3810K, the decoking time is 12min, and a decoking gas product is obtained. During the cracking reaction and online decoking process, N2 is kept discharged, the arc is continuous and uninterrupted, and a continuous operation process is maintained. The decoking gas product is collected during the decoking process. After gas chromatography detection and analysis and calculation, the purity of CF4 is ≥90%. The composition of the decoking gas product is similar to that of the cracking product. No new impurities are introduced during the decoking process, and the concentration of CF4 in the decoking product is not lower than that of the cracking product. After the decoking is completed, the plasma reactor is opened. No coke residue remains in the plasma reactor, and thorough decoking is achieved.

[0055] Among them, during the cracking process, the initial pressure of the plasma reactor is 103kPa, and the arc voltage is 168V. As the cracking reaction proceeds, the pressure of the device continues to rise. After 2 hours, the pressure reaches 327kPa and the cracking stops. At this time, the arc voltage drops to 52V, and the perfluorinated decoking medium is switched and introduced into the plasma reactor. During the decoking process, the temperature of the plasma reactor is controlled at 3810K, and the flow rate of the perfluorinated decoking medium is controlled at 0.8Nm 3 As the decoking process progressed, the arc voltage gradually increased and the device pressure continued to decrease. Twelve minutes later, when the arc voltage rose to 176 V and the device pressure dropped to 97 kPa, decoking was completed and the cracking medium was reintroduced into the plasma reactor.

[0056] During the cracking and decoking reactions in the plasma reactor, the arc voltage, reaction temperature, perfluorinated decoking medium flow rate, device pressure, and reaction time are precisely controlled by a real-time monitoring system. The control accuracy of these parameters is ±1V, ±1K, ±1kPa, and ±1s, respectively. The decoking effect is assessed by the real-time monitoring of the arc voltage and device pressure. The decoking process ends when the arc voltage during the decoking process is equal to ±10V of the initial voltage and the device pressure is equal to ±10kPa of the initial pressure.

[0057] Comparative Example 1

[0058] The cracking reaction was carried out according to Example 1. After the cracking reaction was carried out for 2 hours, the CHF3 feed was stopped, the cracking reaction was terminated, and the coke was cleared. The coke clearing process was as follows: CF4 was used as the perfluorinated coke clearing medium (with a flow rate of 1 Nm 3 / h) and passed through a plasma reactor for decoking at a temperature of 1000K for 20 minutes. After decoking, the plasma reactor was opened. A large amount of coke remained in the reactor, indicating poor decoking performance. Chromatographic analysis of the gaseous product revealed a CF4 purity of ≥90%.

[0059] Comparative Example 2

[0060] The cracking reaction was carried out according to Example 1. After the cracking reaction was carried out for 2 hours, the CHF3 feed was stopped, the cracking reaction was terminated, and the coke was cleared. The coke clearing process was as follows: CF4 was used as the perfluorinated coke clearing medium (flow rate was 0.2 Nm 3 / h) and passed through a plasma reactor for decoking at a temperature of 2000K for 20 minutes. After decoking, the plasma reactor was opened. A large amount of coke remained in the reactor, indicating poor decoking performance. Chromatographic analysis of the gaseous product revealed a CF4 purity of ≥90%.

[0061] Comparative Example 3

[0062] The cracking reaction was carried out according to Example 1. After the cracking reaction was carried out for 2 h, the CHF3 feed was stopped, the cracking reaction was terminated, and the coke was cleared. The coke clearing process was as follows: air (flow rate of 2 Nm 3 / h) as a perfluorinated decoking medium, and decoking was performed at a temperature of 3000K for 18 minutes. After decoking, the plasma reactor was opened, revealing residual coke. Chromatographic analysis of the resulting decoking gas product revealed a CF4 purity of ≤10%. The decoking gas product contained CO2, CO, and air impurities, and its composition differed significantly from that of the cracking products.

[0063] Example 2

[0064] 10 mol / h CHClFCF3 and 50 mol / h C2F4 were introduced into an electromagnetic induction furnace, where a cracking reaction occurred at 1023-1233 K to obtain cracking products. Gas chromatography detection and analytical calculations showed that the single-pass conversion rate of C2F4 was 70.3%, and the purity of the main product C3F6 in the cracking products was 42.6%.

[0065] After the cracking reaction was carried out for 2 hours, the feeding of CHClFCF3 and C2F4 was stopped, the cracking reaction was terminated, and decoking was carried out. The decoking process was as follows: c-C3F8 was used as the perfluorinated decoking medium (flow rate was 18 mol / h) and passed into the electromagnetic induction furnace for decoking. The decoking temperature was 1280K and the decoking time was 30 minutes. The decoking gas products were collected during the decoking process. After gas chromatography detection and analysis and calculation, the purity of C3F6 in the decoking gas products was ≥45%. The composition of the decoking gas products was similar to that of the cracking products. No new impurities were introduced during the decoking process. After the decoking was completed, the electromagnetic induction furnace was opened and no coke residue remained in the electromagnetic induction furnace.

[0066] During the cracking process, the initial pressure of the electromagnetic induction furnace was 5kPa. As the cracking reaction proceeded, the pressure continued to rise. After 2 hours, the pressure reached 77kPa, and the cracking was stopped. The perfluorinated coke-clearing medium was switched and introduced into the electromagnetic induction furnace. During the coke-clearing process, the temperature of the electromagnetic induction furnace was controlled at 1280K, and the flow rate of the perfluorinated coke-clearing medium was controlled at 18mol / h. As the coke-clearing process progressed, the pressure of the device continued to decrease. After 30 minutes, when the pressure dropped to 2kPa, the coke-clearing was terminated, and the cracking medium was reintroduced into the electromagnetic induction furnace.

[0067] During the cracking and decoking reactions in the electromagnetic induction furnace, the reaction temperature, perfluorinated decoking medium flow rate, device pressure, and reaction time are precisely controlled by a real-time monitoring system. The control accuracy of these parameters is ±1K, ±1kPa, and ±1s, respectively. The decoking effect is assessed by the real-time monitoring of the device pressure. The decoking process ends when the inlet pressure during the decoking process equals ±10kPa of the initial pressure.

[0068] Comparative Example 4

[0069] A cracking reaction was carried out according to Example 2. After the cracking reaction had been carried out for 2 hours, the feeding of CHClFCF3 and C2F4 was stopped, the cracking reaction was terminated, and coke cleaning was carried out. The coke cleaning process was as follows: c-C3F8 was used as a perfluorinated coke cleaning medium (at a flow rate of 10 mol / h) and passed into an electromagnetic induction furnace for coke cleaning. The coke cleaning temperature was 800K and the coke cleaning time was 30 minutes. After the coke cleaning was completed, the electromagnetic induction furnace was opened. A large amount of coke still remained in the electromagnetic induction furnace, indicating poor coke cleaning effect. Chromatographic analysis of the gaseous product showed that the purity of C3F6 was ≥45%.

[0070] Example 3

[0071] Waste polytetrafluoroethylene powder (flow rate of 75 mol / h) was introduced into a fluidized bed reactor, where a cracking reaction occurred at 1000K to obtain cracking products. Gas chromatography detection and analytical calculations showed that the single-pass conversion rate of the fluoropolymer was 81.9%, and the purity of C2F4 in the cracking products was 51.7%.

[0072] After the cracking reaction was carried out for 2 hours, the feeding of polytetrafluoroethylene powder was stopped, the cracking reaction was terminated, and decoking was carried out. The decoking process was as follows: NF3 was used as the perfluorinated decoking medium (flow rate was 30 mol / h) and passed into the fluidized bed reactor for decoking. The decoking temperature was 1413K and the decoking time was 20 minutes. The decoking gas product was collected during the decoking process. After gas chromatography detection and analysis and calculation, the purity of C2F4 in the decoking gas product was ≥56%. The composition of the decoking gas product was similar to that of the cracking product, and no new impurities were introduced into the decoking gas product. After decoking was completed, the fluidized bed reactor was opened and no coke remained in the fluidized bed reactor.

[0073] During the cracking process, the initial pressure of the fluidized bed reactor was 21kPa. As the cracking reaction proceeded, the pressure continued to rise. After 2 hours, the pressure reached 189kPa, and the cracking was stopped. A perfluorinated decoking medium was switched and introduced into the fluidized bed reactor. During the decoking process, the temperature of the fluidized bed reactor was controlled at 1413K, and the perfluorinated decoking medium flow rate was controlled at 30mol / h. As the decoking process progressed, the pressure of the device continued to decrease. After 20 minutes, when the pressure dropped to 17kPa, decoking was terminated and the cracking medium was reintroduced into the fluidized bed reactor.

[0074] During the cracking and decoking reactions in the fluidized bed reactor, the reaction temperature, perfluorinated decoking medium flow rate, device pressure, and reaction time are precisely controlled by a real-time monitoring system. The control accuracy of these parameters is ±1K, ±1kPa, and ±1s, respectively. The decoking effect is assessed by the real-time monitoring of the device pressure. The decoking process ends when the inlet pressure during the decoking process equals ±10kPa of the initial pressure.

[0075] Comparative Example 5

[0076] A cracking reaction was carried out according to Example 3. After the cracking reaction had been carried out for 2 hours, the fluoropolymer feed was stopped, the cracking reaction was terminated, and coke cleaning was carried out. The coke cleaning process was as follows: NF3 was used as a perfluorinated coke cleaning medium (at a flow rate of 30 mol / h) and introduced into a fluidized bed reactor for coke cleaning. The coke cleaning temperature was 2500K and the coke cleaning time was 5 minutes. After the coke cleaning was completed, the fluidized bed reactor was opened. A large amount of coke still remained in the fluidized bed reactor, indicating poor coke cleaning effect. Chromatographic analysis of the coke cleaning gas product showed that the purity of C2F4 was ≥56%.

[0077] 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. An online coke removal method for coke generated by cracking a fluorine-containing system, comprising the following steps: The perfluorinated decoking medium is introduced to perform online decoking of the coke produced by the cracking of the fluorine-containing system.

2. The online decoking method according to claim 1, characterized in that: The perfluorodecoking medium includes one or more of nitrogen trifluoride, tetrafluoromethane, hexafluoroethane, perfluoropropane, perfluorobutane, perfluorocyclobutane, perfluorohexane and perfluorooctane.

3. The online decoking method according to claim 1 or 2, characterized in that: The molar ratio of the perfluorinated decoking medium to the fluorine-containing system is 1:2-5.

4. The online decoking method according to claim 3, characterized in that: The fluorine-containing system includes one or more of trifluoromethane, tetrafluoroethylene, fluorine-containing polymer, hexafluoroethane, hexafluoropropylene and octafluorobutene.

5. The online decoking method according to claim 4, characterized in that: The fluorine-containing polymer includes one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride, perfluoroethylene-propylene copolymer and ethylene-tetrafluoroethylene copolymer.

6. The online decoking method according to claim 1 or 2, characterized in that: The online decoking time is 1 to 25% of the cracking time.

7. The online decoking method according to claim 1, characterized in that: The online coke cleaning is carried out in a reaction device, which includes a tubular furnace, a plasma reactor, an electromagnetic induction furnace or a fluidized bed reactor.

8. The online decoking method according to claim 7, characterized in that: When the reaction device is a tubular furnace, the online decoking conditions include: a temperature of 1200-2500K, a molar flow ratio of the perfluorinated decoking medium to the fluorine-containing system of 1:2-3, and an online decoking time of 20-25% of the cracking time; When the reaction device is a plasma reactor, the online decoking conditions include: a temperature of 1200 to 4000 K, a molar flow ratio of a perfluorinated decoking medium to a fluorine-containing system of 1:4 to 5; an online decoking time of 1 to 10% of a cracking time, and an arc stabilizing gas of nitrogen or an inert gas; When the reaction device is an electromagnetic induction furnace, the online decoking conditions include: a temperature of 1200-2200K, a molar flow ratio of perfluorinated decoking medium to fluorine-containing system of 1:2-3, and an online decoking time of 10-25% of the cracking time; When the reaction device is a fluidized bed reactor, the online decoking conditions include: temperature of 1200-1500K, molar flow ratio of perfluorinated decoking medium to fluorine-containing system of 1:2-3, and online decoking time accounting for 10-25% of the cracking time.

9. The online decoking method according to claim 1, 7 or 8, characterized in that: The online defocusing also includes monitoring the degree of online defocusing.

10. The online decoking method according to claim 9, characterized in that: When the reaction device is a tubular furnace, the monitored parameters include temperature, pressure, flow rate and composition of the gas at the outlet of the tubular furnace. When the pressure of the reaction device drops to a difference of ±10 kPa from the cracking pressure, the online coke cleaning is completed. When the reaction device is a plasma reactor, the monitored parameters include current, voltage, pressure, flow rate and gas composition at the outlet of the plasma reactor. When the voltage of the reaction device rises to ±10V of the initial voltage, online decoking is completed. When the reaction device is an electromagnetic induction furnace, the monitored parameters include temperature, pressure, flow rate and gas composition at the outlet of the electromagnetic induction furnace. When the pressure of the reaction device drops to ±10 kPa of the cracking pressure, the online coke cleaning is completed. When the reaction device is a fluidized bed reactor, the monitored parameters include temperature, pressure, flow rate and gas composition at the outlet of the fluidized bed reactor. When the pressure of the reaction device drops to ±10 kPa of the cracking pressure, online coke cleaning is completed.