A method for removing perfluoroisobutene from a gas mixture

Abstract

The present application relates to the technical field of fluorinated chemical industry, and particularly relates to a method for removing perfluoroisobutene in mixed gas, comprising the following steps: passing the mixed gas containing perfluoroisobutene through a perfluoroisobutene absorption membrane to remove perfluoroisobutene therein; wherein the perfluoroisobutene absorption membrane comprises a perfluoroisobutene absorbent, the perfluoroisobutene absorbent comprises solid alcohol and solid acid, and the mass ratio of the solid alcohol to the solid acid is (70-95):(5-30). The method can completely absorb perfluoroisobutene in the mixed gas, the crude cracking gas generated in the process of producing hexafluoropropylene by thermal cracking is treated by the method, the perfluoroisobutene removal effect is good, the cracking gas is not polluted, no additional purification operation is needed, the utilization rate of the absorbent is more than 90%, and the method has good popularization and application value.

Description

Technical Field

[0001] This invention relates to the field of fluorochemical technology, and in particular to a method for removing perfluoroisobutylene from a mixed gas. Background Technology

[0002] Hexafluoropropylene (HFP) is an important raw material for fluorinated polymers, fluorinated intermediates, and fluorinated fine chemicals. It is mainly used in the production of fluororubber, fluoroplastics, and fluorinated fine chemicals, and has a wide range of applications. Currently, the main industrial method for producing hexafluoropropylene is the high-temperature cracking of tetrafluoroethylene and octafluorocyclobutane.

[0003] Perfluoroisobutylene (PFOS) is a highly toxic byproduct produced during the high-temperature pyrolysis of fluorinated olefins. The maximum permissible concentration of PFOS in the air is 0.1 mg / m³. 3 Perfluoroisobutylene has a narrow toxicity band and is highly dangerous; inhaling excessive amounts can cause pulmonary edema, leading to respiratory distress and death. Therefore, it must be properly handled during production.

[0004] Currently, the most common treatment method is to absorb perfluoroisobutylene from the cracked gas using lower alcohols to generate less toxic "fluoroethers"—α-perfluoroisobutylalkyl ethers. For example, European patent document EP0002098(A1) discloses a method for removing perfluoroisobutylene by absorbing it with lower alcohols. This method involves reacting a certain amount of cracked gas containing perfluoroisobutylene with a mixture of lower alcohols and hydrogen halides in a cylinder. Analysis revealed that the perfluoroisobutylene content in the cracked gas decreases with increasing reaction time. However, because this method is a batch reaction, it is not suitable for continuous production processes of fluorinated olefin products. Chinese patent CN200510044481.7 discloses a method for removing perfluoroisobutylene (PFOS) in the production of hexafluoropropylene. This method involves removing PFOS from the cracking furnace by absorbing it with alcohols, then absorbing any small amount of alcohol carried in the cracking gas with an aqueous sodium carbonate or calcium chloride solution, and finally drying the cracking gas with concentrated sulfuric acid or silica gel. However, in this method, the alcohols used in the PFOS removal process are not fully utilized, resulting in significant waste. The low-temperature calcium chloride brine spray requires a large amount of energy to operate normally, and the calcium chloride brine needs to undergo desorption treatment, which also consumes a large amount of steam. Furthermore, some of the calcium chloride brine needs to be periodically discharged and replenished, which also generates some liquid pollution.

[0005] Therefore, there is a need for a method that has good removal efficiency, simple process and low pollution to remove perfluoroisobutylene from mixed gas. Summary of the Invention

[0006] To address the aforementioned problems, the inventors provide a method for removing perfluoroisobutylene from a mixed gas. This method utilizes a perfluoroisobutylene absorption membrane to remove the toxic component—perfluoroisobutylene—from the cracking products in the hexafluoropropylene production process. The method achieves good removal of the toxic component without causing liquid pollution.

[0007] A method for removing perfluoroisobutylene from a gas mixture includes the following steps:

[0008] A mixed gas containing perfluoroisobutylene is passed through a perfluoroisobutylene absorption membrane to remove the perfluoroisobutylene.

[0009] The perfluoroisobutylene absorption membrane includes a perfluoroisobutylene absorbent, which comprises a solid alcohol and a solid acid, wherein the mass ratio of the solid alcohol to the solid acid is (70-95):(5-30).

[0010] In some embodiments, the mixed gas is crude pyrolysis gas produced in the process of producing hexafluoropropylene by thermal cracking, and the crude pyrolysis gas enters the distillation column after being absorbed by a perfluoroisobutylene absorption membrane.

[0011] In some preferred embodiments, the mass ratio of the solid alcohol to the solid acid is (90-95):(5-10).

[0012] In some embodiments, the solid alcohol is selected from C12-C15 monohydric alcohols or dihydric alcohols.

[0013] In some preferred embodiments, the solid alcohol is selected from one of dodecane alcohol, tridecane alcohol, tetradecane alcohol, and pentadecane alcohol.

[0014] In some embodiments, the solid acid is selected from one of the following: S- / Ti-Al-O type solid acid, SO4- / Fe3O4-Al2O3 type solid acid, and Ln-modified SO4- / TiO2-Ln3 type solid acid.

[0015] In some embodiments, the particle size of the mixture of solid alcohol and solid acid is 10 μm-500 μm. In some preferred embodiments, the particle size of the mixture of solid alcohol and solid acid is 20 μm-200 μm.

[0016] In some embodiments, the perfluoroisobutylene absorbent membrane further includes a support layer, with the perfluoroisobutylene absorbent coated between two support layers.

[0017] In some embodiments, the material of the support layer is selected from PTFE, PFA, and FEP, and the pore size of the support layer is 2μm-10μm, and the thickness is 40μm-120μm. In some preferred embodiments, the material of the support layer is a PFA film, and the pore size of the support layer is 5μm-8μm, and the thickness is 50μm-80μm.

[0018] In some embodiments, an effective separation layer is further disposed outside the support layer. The material of the effective separation layer is selected from PTFE, PFA, and FEP, with a pore size of 2nm-50nm and a thickness of 20μm-50μm. In some preferred embodiments, the material of the effective separation layer is a PFA film with a pore size of 5nm-10nm and a thickness of 30μm-40μm.

[0019] By setting an effective separation layer with different pore sizes and thicknesses than the support layer, the contact time between perfluoroisobutylene and the absorbent can be increased, allowing the perfluoroisobutylene to be fully absorbed without affecting the throughput of other components in the mixed gas.

[0020] Specifically, the perfluoroisobutylene absorption membrane is fixed in several parallel absorption pipes, and movable baffles are installed on the pipes. When the perfluoroisobutylene absorption membrane fails, it can be replaced without stopping the production, thereby maintaining the continuity of production.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] (1) This invention provides a method for removing perfluoroisobutylene from a mixed gas. The mixed gas containing perfluoroisobutylene is directly passed through a perfluoroisobutylene absorption membrane containing a perfluoroisobutylene absorbent, which can completely absorb the harmful component perfluoroisobutylene in the mixed gas. When the method of this invention is used to treat the crude cracked gas produced in the thermal cracking process of producing hexafluoropropylene, the perfluoroisobutylene in the crude cracked gas can be completely absorbed without causing pollution to the crude cracked gas. At the same time, no volatile substances are generated that affect the quality of hexafluoropropylene. The cracked gas after absorption by the absorption membrane can be directly entered into the distillation process without additional purification operations. The process and equipment are simple, there is no liquid waste pollution, and the energy consumption is low. When using the method of this invention to absorb perfluoroisobutylene, the utilization rate of the absorbent is over 90%, which has good promotion and application value.

[0023] (2) In the method of the present invention, the perfluoroisobutylene absorbent is composed of a mixture of solid alcohol and solid acid. The solid acid is used as a catalyst to make up for the defect of insufficient contact area between the solid alcohol as absorbent and perfluoroisobutylene. At the same time, the present invention uses the perfluoroisobutylene absorbent as an effective component to make a perfluoroisobutylene absorption membrane and controls the particle size of the absorbent to further increase the specific surface area between the absorbent and perfluoroisobutylene. This allows the perfluoroisobutylene to fully contact the absorbent during the absorption process, thereby matching the perfluoroisobutylene absorption rate with the hexafluoropropylene production process and ensuring that the perfluoroisobutylene in the crude cracked gas can be completely removed under normal production conditions. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a gas chromatogram of Example 1 of the present invention;

[0026] Figure 2 This is a gas chromatogram after continuous absorption treatment for 4.5 hours in Example 1 of the present invention;

[0027] Figure 3 This is the gas chromatogram of Comparative Example 1 of the present invention. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0029] The formula for calculating the utilization rate of solid alcohol in the perfluoroisobutylene absorbent in this invention is as follows:

[0030]

[0031] The formula for calculating the utilization rate of perfluoroisobutylene absorbent in this invention is as follows:

[0032] Absorbent utilization rate = Utilization rate of solid alcohol in absorbent × b

[0033] in:

[0034] t represents the maximum continuous absorption time of the perfluoroisobutylene absorption membrane;

[0035] m 吸 The content of perfluoroisobutylene absorbent in the perfluoroisobutylene absorption membrane;

[0036] b represents the mass percentage of solid alcohol in the perfluoroisobutylene absorbent;

[0037] q represents the amount of hexafluoropropylene cracked gas fed per unit time;

[0038] a represents the mass percentage of perfluoroisobutylene in the pyrolysis component;

[0039] M 醇 The relative molecular mass of the solid alcohol in the perfluoroisobutylene absorbent;

[0040] M is the relative molecular mass of perfluoroisobutylene.

[0041] Example 1

[0042] The crude cracked gas from the cracking of tetrafluoroethylene and octafluorocyclobutane to produce hexafluoropropylene is cooled to 16°C, and then fed through a perfluoroisobutylene absorption membrane at a rate of 300 kg / h at 16°C to remove the perfluoroisobutylene from the crude cracked gas before it enters the distillation column.

[0043] The content of perfluoroisobutylene in the crude pyrolysis gas is approximately 7%.

[0044] The perfluoroisobutylene absorbent membrane sequentially comprises a first support layer, a perfluoroisobutylene absorbent, a second support layer, and an effective separation layer. The first support layer, second support layer, and effective separation layer are PFA membranes. The pore size of the first and second support layers is 5 μm, and the thickness is 50 μm. The pore size of the effective separation layer is 5 nm, and the thickness is 30 μm. The perfluoroisobutylene absorbent contains 100 kg of perfluoroisobutylene and has a particle size of 20 μm. It is composed of dodecanoic acid and SO4- / Fe3O4-Al2O3 type solid acid in a mass ratio of 93:7.

[0045] After absorption by a perfluoroisobutylene absorption membrane, the pyrolyzed materials are analyzed by gas chromatography, such as... Figure 1 As shown, no peaks related to perfluoroisobutylene appeared in the gas chromatogram.

[0046] After continuous absorption treatment for 4.5 hours, as Figure 2 As shown, the gas chromatogram of the pyrolysis material after absorption by the perfluoroisobutylene absorption membrane shows peaks related to perfluoroisobutylene. Calculations show that the utilization rate of solid alcohol in the perfluoroisobutylene absorbent of this invention can reach 94.50%, and the utilization rate of the perfluoroisobutylene absorbent can reach 87.89%.

[0047] Example 2

[0048] The crude cracked gas from the cracking of tetrafluoroethylene and octafluorocyclobutane to produce hexafluoropropylene is cooled to 18°C, and then fed through a perfluoroisobutylene absorption membrane at a rate of 430 kg / h at 18°C ​​to remove the perfluoroisobutylene from the crude cracked gas before it enters the distillation column.

[0049] The content of perfluoroisobutylene in the crude pyrolysis gas is approximately 6%.

[0050] The perfluoroisobutylene absorption membrane comprises, in sequence, a first support layer, a perfluoroisobutylene absorbent, a second support layer, and an effective separation layer. The first support layer, the second support layer, and the effective separation layer are PFA membranes. The pore size of the first and second support layers is 7 μm, and the thickness is 50 μm. The pore size of the effective separation layer is 6 nm, and the thickness is 30 μm. The perfluoroisobutylene absorbent contains 100 kg of perfluoroisobutylene and has a particle size of 150 μm. It is composed of dodecanoic acid and S- / Ti-Al-O type solid acid mixed at a mass ratio of 95:5.

[0051] After absorption by the perfluoroisobutylene absorption membrane, the pyrolyzed material was analyzed by gas chromatography, and no peaks related to perfluoroisobutylene appeared in the spectrum.

[0052] After continuous absorption treatment for 3.6 hours, the gas chromatogram of the pyrolysis material after absorption by the perfluoroisobutylene absorption membrane showed peaks related to perfluoroisobutylene. Calculations show that the utilization rate of solid alcohol in the perfluoroisobutylene absorbent of this invention can reach 90.92%, and the utilization rate of the perfluoroisobutylene absorbent can reach 86.38%.

[0053] Example 3

[0054] The crude cracked gas from the cracking of tetrafluoroethylene and octafluorocyclobutane to produce hexafluoropropylene is cooled to 15°C, and then fed through a perfluoroisobutylene absorption membrane at a rate of 480 kg / h at 15°C to remove the perfluoroisobutylene from the crude cracked gas before it enters the distillation column.

[0055] The content of perfluoroisobutylene in the crude pyrolysis gas is approximately 8%.

[0056] The perfluoroisobutylene absorption membrane comprises, in sequence, a first support layer, a perfluoroisobutylene absorbent, a second support layer, and an effective separation layer. The first support layer, the second support layer, and the effective separation layer are FEP membranes. The pore size of the first and second support layers is 5 μm, and the thickness is 70 μm. The pore size of the effective separation layer is 5 nm, and the thickness is 35 μm. The perfluoroisobutylene absorbent contains 100 kg of perfluoroisobutylene and has a particle size of 15 μm. It is composed of pentadecanoic acid and S- / Ti-Al-O type solid acid mixed at a mass ratio of 90:10.

[0057] After absorption by the perfluoroisobutylene absorption membrane, the pyrolyzed material was analyzed by gas chromatography, and no peaks related to perfluoroisobutylene appeared in the spectrum.

[0058] After continuous absorption treatment for 1.9 hours, the gas chromatogram of the pyrolyzed material after absorption by the perfluoroisobutylene absorption membrane showed peaks related to perfluoroisobutylene. Calculations show that the utilization rate of solid alcohol in the perfluoroisobutylene absorbent of this invention can reach 92.42%, and the utilization rate of the perfluoroisobutylene absorbent can reach 83.17%.

[0059] Example 4

[0060] The crude cracked gas from the cracking of tetrafluoroethylene and octafluorocyclobutane to produce hexafluoropropylene is cooled to 18°C, and then fed through a perfluoroisobutylene absorption membrane at a rate of 450 kg / h at 18°C ​​to remove the perfluoroisobutylene from the crude cracked gas before it enters the distillation column.

[0061] The content of perfluoroisobutylene in the crude pyrolysis gas is approximately 8%.

[0062] The perfluoroisobutylene absorbent membrane sequentially comprises a first support layer, a perfluoroisobutylene absorbent, a second support layer, and an effective separation layer. The first support layer, second support layer, and effective separation layer are FEP membranes. The pore size of the first and second support layers is 5 μm, and the thickness is 70 μm. The pore size of the effective separation layer is 5 nm, and the thickness is 40 μm. The perfluoroisobutylene absorbent contains 100 kg of perfluoroisobutylene and has a particle size of 15 μm. It is composed of tetradecanoic acid and S- / Ti-Al-O type solid acid in a mass ratio of 94:6.

[0063] After absorption by the perfluoroisobutylene absorption membrane, the pyrolyzed material was analyzed by gas chromatography, and no peaks related to perfluoroisobutylene appeared in the spectrum.

[0064] After continuous absorption treatment for 2.2 hours, the gas chromatogram of the pyrolyzed material after absorption by the perfluoroisobutylene absorption membrane showed peaks related to perfluoroisobutylene. Calculations show that the utilization rate of solid alcohol in the perfluoroisobutylene absorbent of this invention can reach 90.15%, and the utilization rate of the perfluoroisobutylene absorbent can reach 84.74%.

[0065] Example 5

[0066] The crude cracked gas from the cracking of tetrafluoroethylene and octafluorocyclobutane to produce hexafluoropropylene is cooled to 20°C, and then fed through a perfluoroisobutylene absorption membrane at a rate of 350 kg / h at 20°C to remove the perfluoroisobutylene from the crude cracked gas before it enters the distillation column.

[0067] The content of perfluoroisobutylene in the crude pyrolysis gas is approximately 8%.

[0068] The perfluoroisobutylene absorption membrane comprises, in sequence, a first support layer, a perfluoroisobutylene absorbent, a second support layer, and an effective separation layer. The first support layer, the second support layer, and the effective separation layer are PTFE membranes. The pore size of the first and second support layers is 6 μm, and the thickness is 70 μm. The pore size of the effective separation layer is 5 nm, and the thickness is 35 μm. The perfluoroisobutylene absorbent contains 100 kg of perfluoroisobutylene and has a particle size of 12 μm. It is composed of pentadecanoic acid and SO4- / Fe3O4-Al2O3 type solid acid at a mass ratio of 90:10.

[0069] After absorption by the perfluoroisobutylene absorption membrane, the pyrolyzed material was analyzed by gas chromatography, and no peaks related to perfluoroisobutylene appeared in the spectrum.

[0070] After continuous absorption treatment for 2.6 hours, the gas chromatogram of the pyrolyzed material after absorption by the perfluoroisobutylene absorption membrane showed peaks related to perfluoroisobutylene. Calculations show that the utilization rate of solid alcohol in the perfluoroisobutylene absorbent of this invention can reach 92.21%, and the utilization rate of the perfluoroisobutylene absorbent can reach 82.99%.

[0071] Example 6

[0072] The crude cracked gas from the cracking of tetrafluoroethylene and octafluorocyclobutane to produce hexafluoropropylene is cooled to 15°C, and then fed through a perfluoroisobutylene absorption membrane at a rate of 280 kg / h at 15°C to remove the perfluoroisobutylene from the crude cracked gas before it enters the distillation column.

[0073] The content of perfluoroisobutylene in the crude pyrolysis gas is approximately 7.6%.

[0074] The perfluoroisobutylene absorption membrane comprises, in sequence, a first support layer, a perfluoroisobutylene absorbent, a second support layer, and an effective separation layer. The first support layer, the second support layer, and the effective separation layer are PTFE membranes. The pore size of the first and second support layers is 8 μm, and the thickness is 50 μm. The pore size of the effective separation layer is 8 nm, and the thickness is 30 μm. The perfluoroisobutylene absorbent contains 100 kg of perfluoroisobutylene and has a particle size of 25 μm. It is composed of tridecanoic acid and S- / Ti-Al-O type solid acid at a mass ratio of 92:8.

[0075] After absorption by the perfluoroisobutylene absorption membrane, the pyrolyzed material was analyzed by gas chromatography, and no peaks related to perfluoroisobutylene appeared in the spectrum.

[0076] After 4 hours of continuous absorption treatment, the gas chromatogram of the pyrolysis material after absorption by the perfluoroisobutylene absorption membrane showed peaks related to perfluoroisobutylene. Calculations show that the utilization rate of solid alcohol in the perfluoroisobutylene absorbent of this invention can reach 92.57%, and the utilization rate of the perfluoroisobutylene absorbent can reach 85.16%.

[0077] Example 7

[0078] The crude cracked gas from the cracking of tetrafluoroethylene and octafluorocyclobutane to produce hexafluoropropylene is cooled to 16°C, and then fed through a perfluoroisobutylene absorption membrane at a rate of 300 kg / h at 16°C to remove the perfluoroisobutylene from the crude cracked gas before it enters the distillation column.

[0079] The content of perfluoroisobutylene in the crude pyrolysis gas is approximately 7%.

[0080] The perfluoroisobutylene absorbent membrane sequentially comprises a first support layer, a perfluoroisobutylene absorbent, a second support layer, and an effective separation layer. The first support layer, second support layer, and effective separation layer are PFA membranes. The pore size of the first and second support layers is 5 μm, and the thickness is 50 μm. The pore size of the effective separation layer is 5 nm, and the thickness is 30 μm. The perfluoroisobutylene absorbent contains 100 kg of perfluoroisobutylene and has a particle size of 20 μm. It is composed of dodecanoic acid and SO4- / Fe3O4-Al2O3 type solid acid at a mass ratio of 80:20.

[0081] After absorption by a perfluoroisobutylene absorption membrane, the pyrolyzed materials are analyzed by gas chromatography, such as... Figure 1 As shown, no peaks related to perfluoroisobutylene appeared in the gas chromatogram.

[0082] After continuous absorption treatment for 3.7 hours, the gas chromatogram of the pyrolyzed material after absorption by the perfluoroisobutylene absorption membrane showed peaks related to perfluoroisobutylene. Calculations show that the utilization rate of solid alcohol in the perfluoroisobutylene absorbent of this invention can reach 90.32%, and the utilization rate of the perfluoroisobutylene absorbent can reach 72.26%.

[0083] Example 8

[0084] The crude cracked gas from the cracking of tetrafluoroethylene and octafluorocyclobutane to produce hexafluoropropylene is cooled to 16°C, and then fed through a perfluoroisobutylene absorption membrane at a rate of 300 kg / h at 16°C to remove the perfluoroisobutylene from the crude cracked gas before it enters the distillation column.

[0085] The content of perfluoroisobutylene in the crude pyrolysis gas is approximately 7%.

[0086] The perfluoroisobutylene absorption membrane comprises, in sequence, a first support layer, a perfluoroisobutylene absorbent, a second support layer, and an effective separation layer. The first support layer, the second support layer, and the effective separation layer are PFA membranes. The pore size of the first and second support layers is 5 μm, and the thickness is 50 μm. The pore size of the effective separation layer is 5 nm, and the thickness is 30 μm. The perfluoroisobutylene absorbent contains 100 kg of perfluoroisobutylene and has a particle size of 20 μm. It is composed of dodecanoic acid and SO4- / Fe3O4-Al2O3 type solid acid at a mass ratio of 70:30.

[0087] After absorption by a perfluoroisobutylene absorption membrane, the pyrolyzed materials are analyzed by gas chromatography, such as... Figure 1 As shown, no peaks related to perfluoroisobutylene appeared in the gas chromatogram.

[0088] After continuous absorption treatment for 3.3 hours, the gas chromatogram of the pyrolyzed material after absorption by the perfluoroisobutylene absorption membrane showed peaks related to perfluoroisobutylene. Calculations show that the utilization rate of solid alcohol in the perfluoroisobutylene absorbent of this invention can reach 92.07%, and the utilization rate of the perfluoroisobutylene absorbent can reach 64.45%.

[0089] Comparative Example 1

[0090] The difference between this comparative example and Example 1 is that the perfluoroisobutylene absorbent does not contain solid acid, specifically including the following steps:

[0091] The crude cracked gas from the cracking of tetrafluoroethylene and octafluorocyclobutane to produce hexafluoropropylene is cooled to 16°C, and then fed through a perfluoroisobutylene absorption membrane at a rate of 300 kg / h at 16°C to remove the perfluoroisobutylene from the crude cracked gas before it enters the distillation column.

[0092] The content of perfluoroisobutylene in the crude pyrolysis gas is approximately 7%.

[0093] The perfluoroisobutylene absorbent membrane sequentially comprises a first support layer, a perfluoroisobutylene absorbent, a second support layer, and an effective separation layer. The first support layer, second support layer, and effective separation layer are PFA membranes. The pore size of the first and second support layers is 5 μm, and the thickness is 50 μm. The pore size of the effective separation layer is 5 nm, and the thickness is 30 μm. The perfluoroisobutylene absorbent contains 100 kg of perfluoroisobutylene, has a particle size of 20 μm, and is composed of dodecyl alcohol.

[0094] After absorption by a perfluoroisobutylene absorption membrane, the pyrolyzed materials are analyzed by gas chromatography, such as... Figure 3 As shown, peaks related to perfluoroisobutylene appear in the gas chromatogram, indicating incomplete absorption of perfluoroisobutylene.

[0095] Comparative Example 2

[0096] The difference between this comparative example and Example 1 lies in the different ratios of solid alcohol and solid acid in the perfluoroisobutylene absorbent, specifically including the following steps:

[0097] The crude cracked gas from the cracking of tetrafluoroethylene and octafluorocyclobutane to produce hexafluoropropylene is cooled to 16°C, and then fed through a perfluoroisobutylene absorption membrane at a rate of 300 kg / h at 16°C to remove the perfluoroisobutylene from the crude cracked gas before it enters the distillation column.

[0098] The content of perfluoroisobutylene in the crude pyrolysis gas is approximately 7%.

[0099] The perfluoroisobutylene absorbent membrane sequentially comprises a first support layer, a perfluoroisobutylene absorbent, a second support layer, and an effective separation layer. The first support layer, second support layer, and effective separation layer are PFA membranes. The pore size of the first and second support layers is 5 μm, and the thickness is 50 μm. The pore size of the effective separation layer is 5 nm, and the thickness is 30 μm. The perfluoroisobutylene absorbent contains 100 kg of perfluoroisobutylene and has a particle size of 20 μm. It is composed of dodecanoic acid and SO4- / Fe3O4-Al2O3 type solid acid at a mass ratio of 98:2.

[0100] After absorption by the perfluoroisobutylene absorption membrane, the pyrolyzed material was analyzed by gas chromatography. Peaks related to perfluoroisobutylene appeared in the gas chromatogram, indicating that the absorption of perfluoroisobutylene was incomplete.

[0101] Comparative Example 3

[0102] This comparative example demonstrates an existing method for removing toxic components from pyrolysis products in hexafluoropropylene production processes. The specific steps are as follows:

[0103] The crude cracked gas from the cracking of tetrafluoroethylene and octafluorocyclobutane to produce hexafluoropropylene is fed into the alcohol absorption tower at a rate of 300 kg / h, and is subjected to ethanol spraying at a rate of 1 m³ / h. 3 / h, absorption pressure is normal or slightly positive, temperature is around -10℃ to 120℃.

[0104] The content of perfluoroisobutylene in the crude pyrolysis gas is approximately 6%.

[0105] After absorption by ethanol, the pyrolysis material is analyzed by gas chromatography, such as... Figure 2 As shown, no peaks related to perfluoroisobutylene appeared in the gas chromatogram. Further analysis revealed the presence of peaks related to ethanol, indicating that the crude pyrolysis gas after ethanol absorption contained ethanol.

[0106] After ethanol absorption, the material enters the compressor and is pressurized to 0.2MPa-0.6MPa, then enters the solvent absorption stage. The solvent absorption uses a 30% sodium carbonate aqueous solution, with the sodium carbonate aqueous solution flowing at a 1m... 3 The system uses a spray system with a flow rate of / h to remove small amounts of alcohols and acidic substances. After absorption, the material enters a silica gel drying and purification system to remove moisture introduced by the solvent absorption. The purified material is then further absorbed by sulfuric acid in a batch reactor, where the sulfuric acid is passed through in a bubbling manner. The material after sulfuric acid absorption then enters a distillation system.

[0107] The density of ethanol used for spraying is 789 kg / m³. 3 The ethanol spray volume is 1m 3Based on the mass flow rate, the ethanol spraying rate is 789 kg / h. Given that the mixed feed rate of tetrafluoroethylene and octafluorocyclobutane is 300 kg / h and the perfluoroisobutylene content in the cracking component is approximately 6%, the perfluoroisobutylene flow rate in the cracking component is 300 kg / h × 6% = 18 kg / h. Under ideal conditions, the ethanol usage is 18 kg / h × 46 / 200 = 4.14 kg / h. Therefore, the ethanol utilization rate is 4.14 kg / h ÷ 789 kg / h × 100% = 0.52%.

[0108] The above results show that the present invention uses solid alcohol and liquid alcohol as perfluoroisobutylene absorbents, which can completely absorb the toxic component perfluoroisobutylene in the cracking products of hexafluoropropylene production process without generating waste liquid pollution. The utilization rate of solid alcohol in the perfluoroisobutylene absorbent of the present invention is over 90%, and the utilization rate of absorbent can reach up to 88.35%. The overall utilization rate of solid alcohol and absorbent is greatly improved, the process is simple, and energy consumption is reduced, making it suitable for industrial application.

[0109] Comparing Example 1 and Comparative Example 2, it is evident that only when a solid acid is added to a solid alcohol in a certain proportion can the resulting perfluoroisobutylene absorbent completely absorb the perfluoroisobutylene in the cracked gas. This is because the absorbent of this invention is solid, and compared to liquid alcohol, its contact area with the perfluoroisobutylene in the cracked gas is relatively reduced. Therefore, a solid acid is needed as a catalyst to accelerate the etherification reaction between the solid alcohol and the perfluoroisobutylene, ensuring that the perfluoroisobutylene absorbent can completely absorb the perfluoroisobutylene within normal production time.

[0110] A comparison of Examples 1 and 7-8 shows that when the proportion of solid acid in the perfluoroisobutylene absorbent is increased, the content of solid alcohol decreases, meaning the content of the effective component in the perfluoroisobutylene absorbent decreases, and its absorption capacity for perfluoroisobutylene also decreases. Although increasing the proportion of solid acid still effectively absorbs perfluoroisobutylene from the cracked gas, in Example 1, 100 kg of absorbent can continuously absorb for 4.5 hours with a utilization rate of 88.35%, while in Examples 7 and 8, the same mass of absorbent can only continuously absorb for 4 hours and 3.7 hours, respectively, with utilization rates of only 72% and 64.4%. The utilization rate and service life of the absorbent are significantly lower than those of this application.

[0111] Comparing Example 1 and Comparative Example 3, it can be seen that when liquid alcohol is used as an absorbent in the prior art, the liquid alcohol will be mixed into the cracked gas, which requires the use of solvent for absorption. This will cause moisture to be mixed into the cracked gas, requiring further water removal, which increases the process flow. The liquid alcohol absorption and solvent absorption processes will generate a large amount of liquid waste. Furthermore, calculations in Comparative Example 1 show that the utilization rate of ethanol using ethanol spray treatment is only 0.52%, resulting in a large amount of ethanol waste.

[0112] In summary, this invention uses solid alcohol as an absorbent and solid acid as a catalyst to obtain a perfluoroisobutylene absorbent, which can effectively remove perfluoroisobutylene from mixed gases. In particular, when applied to remove perfluoroisobutylene from the cracking products in the hexafluoropropylene production process, the absorbent has a high utilization rate and does not generate waste liquid pollution or waste, making it suitable for industrial application.

[0113] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the nature and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all within the scope of protection of the present invention.

Claims

1. A method for removing perfluoroisobutylene from a mixed gas, characterized in that, Includes the following steps: A mixed gas containing perfluoroisobutylene is passed through a perfluoroisobutylene absorption membrane to remove the perfluoroisobutylene. The perfluoroisobutylene absorption membrane includes a perfluoroisobutylene absorbent, which includes a solid alcohol and a solid acid, wherein the mass ratio of the solid alcohol to the solid acid is (70-95):(5-30). The solid alcohol is selected from C12-C15 monohydric alcohols or dihydric alcohols; The solid acid is selected from one of the following: S- / Ti-Al-O type solid acid, SO4- / Fe3O4-Al2O3 type solid acid, and Ln-modified SO4- / TiO2-Ln3 type solid acid.

2. The method for removing perfluoroisobutylene from a mixed gas according to claim 1, characterized in that, The mixed gas is crude pyrolysis gas produced in the process of producing hexafluoropropylene by thermal cracking. The crude pyrolysis gas is absorbed by a perfluoroisobutylene absorption membrane and then enters a distillation column.

3. The method for removing perfluoroisobutylene from a mixed gas according to claim 1, characterized in that, The mass ratio of the solid alcohol to the solid acid is (90-95):(5-10).

4. The method for removing perfluoroisobutylene from a mixed gas according to claim 1, characterized in that, The solid alcohol is selected from one of dodecane alcohol, tridecane alcohol, tetradecane alcohol, and pentadecane alcohol.

5. The method for removing perfluoroisobutylene from a mixed gas according to claim 1, characterized in that, The particle size of the mixture of solid alcohol and solid acid is 10 μm-500 μm.

6. The method for removing perfluoroisobutylene from a mixed gas according to claim 1, characterized in that, The perfluoroisobutylene absorbent membrane further includes a support layer, and the perfluoroisobutylene absorbent is coated between the two support layers.

7. The method for removing perfluoroisobutylene from a mixed gas according to claim 6, characterized in that, The material of the support layer is selected from PTFE, PFA, and FEP, and the pore size of the support layer is 2μm-10μm and the thickness is 40μm-120μm.

8. The method for removing perfluoroisobutylene from a mixed gas according to claim 6, characterized in that, An effective separation layer is also provided outside the support layer. The material of the effective separation layer is selected from PTFE, PFA, and FEP, with a pore size of 2nm-50nm and a thickness of 20μm-50μm.

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