A system and method for preparing perfluoro n-propyl vinyl ether

Abstract

The invention belongs to the technical field of chemical synthesis, and discloses a system for preparing perfluoro n-propyl vinyl ether, comprising a sequentially connected reaction device, a condensing device and a gas absorption device; the reaction device is used to heat hexafluoropropylene oxide dimer, a salt-forming agent and a catalyst, and a salt-forming reaction and a decarboxylation reaction occur in sequence, and a salt-forming reaction product and a decarboxylation reaction product are obtained respectively; the condensing device is used to condense and reflux the hexafluoropropylene oxide dimer and the catalyst and separate the carbon dioxide gas in the two reaction products and the perfluoro n-propyl vinyl ether in the decarboxylation reaction product; the gas absorption device is used to absorb the carbon dioxide gas generated by the reaction. Based on the preparation system of the present invention and the method of reducing the addition of the salt-forming agent and recovering the excess hexafluoropropylene oxide dimer to produce perfluoro n-propyl vinyl ether, the purity and yield of the prepared PPVE and the by-product fluoride salt are both very high.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical synthesis, and in particular relates to a system and a method for preparing perfluoro n-propyl vinyl ether. Background Art

[0002] Perfluoro-n-propyl vinyl ether (PPVE) is a colorless transparent liquid at room temperature. It is a copolymer monomer of fluorinated vinyl ether and can be used as a copolymer or modified monomer to participate in polymerization to change certain properties of fluoropolymers. For example, when copolymerized with tetrafluoroethylene, it can synthesize fusible polytetrafluoroethylene with excellent thermoplastic processing properties. Therefore, it can be used as a modified monomer of polytetrafluoroethylene.

[0003] Existing perfluoro-n-propyl vinyl ether is usually prepared by two methods, namely solid phase decarboxylation and liquid phase decarboxylation. The solid phase decarboxylation method requires the use of a specific reactor to prepare perfluoro-n-propyl vinyl ether. Not only is the equipment expensive, the reaction temperature required in the preparation process is too high and consumes energy, and a large amount of by-products are produced during the reaction. The product purity is low and difficult to purify, and the yield does not exceed 60%. The liquid phase decarboxylation method requires the addition of a liquid catalyst to prepare perfluoro-n-propyl vinyl ether at a lower temperature. Compared with the solid phase decarboxylation method, its product has higher purity and yield, but it has problems such as low by-product utilization, large carbon emissions and low product purity. Summary of the invention

[0004] In view of the problems and shortcomings in the prior art, the object of the present invention is to provide a system and method for preparing perfluoro-n-propyl vinyl ether.

[0005] Based on the above purpose, the present invention adopts the following technical solution:

[0006] The first aspect of the present invention provides a preparation system for perfluoro n-propyl vinyl ether, the system comprising a reaction device, a condensation device, a finished product collection device and a gas absorption device connected in sequence; the upper discharge port of the reaction device is connected to the inlet of the condensation device; the condensation device comprises a first heat exchanger and a second heat exchanger connected in sequence, the outlet of the first heat exchanger is connected in parallel with a first branch pipe and a second branch pipe; wherein the outlet of the first branch pipe is connected to the inlet of the gas absorption device, the outlet of the second branch pipe is connected to the inlet of the second heat exchanger, and the outlet of the second heat exchanger is connected to the inlet of the finished product collection device; the top outlet pipe of the finished product collection device is connected to the gas absorption device; and the outlet of the gas collection device is connected to the atmosphere.

[0007] More preferably, the reaction device is used to heat the hexafluoropropylene oxide dimer, the salt-forming agent and the catalyst, so that the salt-forming reaction and the decarboxylation reaction occur in sequence, and the salt-forming reaction product and the decarboxylation reaction product are obtained respectively; the condensing device is used to condense the refluxed hexafluoropropylene oxide dimer and the catalyst and separate the carbon dioxide gas in the two reaction products and the perfluoro-n-propyl vinyl ether in the decarboxylation reaction product; and the gas absorption device is used to absorb the carbon dioxide gas generated by the reaction.

[0008] More preferably, the reaction device is provided with a raw material inlet, a gas inlet, an upper discharge port, a lower discharge port and a gas outlet.

[0009] More preferably, the gas outlet of the reaction device is connected to a vacuum pump for evacuating the reaction device.

[0010] Preferably, a first valve is provided at the starting end of the first branch pipeline along the material flow direction; and a second valve is provided at the starting end of the second branch pipeline along the material flow direction.

[0011] The second aspect of the present invention provides a method for preparing perfluoro-n-propyl vinyl ether using the system described in the first aspect, comprising the following steps:

[0012] (1) Salt-forming reaction: adding a salt-forming agent and a catalyst to the reaction device through the raw material inlet of the reaction device in the system, and closing the raw material inlet after the addition is completed; setting the cooling temperature (first condensation temperature) in the first heat exchanger to -20 to -30°C and opening the first valve; lowering the temperature in the reaction device to -20 to -30°C, and then adding hexafluoropropylene oxide dimer to the reaction device through the raw material inlet, and closing the raw material inlet after the addition is completed; then heating the reaction device to 50 to 60°C for salt-forming reaction, and obtaining a salt-forming reaction product after the reaction is completed, wherein the salt-forming reaction product includes the corresponding perfluoropolyether carboxylate and carbon dioxide gas; wherein the carbon dioxide gas enters the first branch pipeline through the first heat exchanger, and then enters the gas absorption device to be absorbed; the vaporized hexafluoropropylene oxide dimer is condensed by the first heat exchanger and then refluxed to the reaction device;

[0013] (2) Recovering the hexafluoropropylene oxide dimer: closing the first valve, connecting the vacuum pump to the gas outlet of the reaction device, and then opening the gas outlet of the reaction device to recover the hexafluoropropylene oxide dimer in the reaction device under reduced pressure; after the recovery is completed, closing the gas outlet of the reaction device and opening the gas inlet and the first valve of the reaction device, introducing protective gas into the reaction device until the pressure in the reaction device reaches one atmosphere, and then closing the gas inlet and the first valve of the reaction device;

[0014] (3) Decarboxylation reaction: the cooling temperature (first condensation temperature) in the first heat exchanger is set to 20 to 30°C (first condensation temperature), the cooling temperature (second condensation temperature) in the second heat exchanger is set to -20 to -30°C, and the second valve is opened; the reaction device is heated to 130 to 160°C for decarboxylation reaction, and a decarboxylation reaction product is obtained after the reaction is completed. The decarboxylation reaction product includes perfluoro-n-propyl vinyl ether and carbon dioxide gas; wherein the perfluoro-n-propyl vinyl ether is condensed in the second heat exchanger and then enters the finished product collecting device; the carbon dioxide gas enters the second branch pipeline through the first heat exchanger, and then enters the gas absorption device to be absorbed after passing through the second heat exchanger and the finished product collecting device.

[0015] More preferably, before the system is put into operation, the inlets and outlets of all devices and instruments and valves are closed by default.

[0016] More preferably, the catalyst is condensed by the first heat exchanger and then refluxed to the reaction device.

[0017] Preferably, the molar ratio of the hexafluoropropylene oxide dimer, the salt-forming agent and the catalyst is 1:(0.5-0.9):(1.5-2.0).

[0018] More preferably, the mass-to-volume ratio (kg / L) of the added mass of the hexafluoropropylene oxide dimer to the volume of the reaction device is no more than 1:5.

[0019] Preferably, the catalyst is any one of diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, N,N-dimethylformamide, N,N-dimethylacetamide, and N,N-dimethyldiacetamide.

[0020] Preferably, the salt-forming agent is at least one of sodium carbonate and potassium carbonate.

[0021] More preferably, the salt-forming agent and catalyst need to be dehydrated before being added to the preparation system; the dehydration treatment method of the salt-forming agent is drying at 250-300°C; the dehydration treatment method of the catalyst is adding a dehydrating agent to the catalyst, and after the dehydration treatment, the water content of the catalyst is 0-200ppm; the dehydrating agent is any one of calcium oxide, calcium hydride, 3A molecular sieve, and 4A molecular sieve.

[0022] Preferably, after the decarboxylation reaction in step (3) is completed, the mixed liquid in the reaction device is distilled to obtain the catalyst and the crude fluorine-containing inorganic salt in the two reaction products; the crude fluorine-containing inorganic salt is dried, acidified, distilled, ion exchanged and dried in sequence to obtain the fluorine-containing inorganic salt.

[0023] More preferably, the acidification method is 40% hydrofluoric acid acidification; the molar ratio of hydrofluoric acid to fluorine-containing inorganic salt is 1: (50-100).

[0024] More preferably, the ion exchange treatment method is to use a sodium or potassium salt-specific ion exchange resin for ion exchange.

[0025] More preferably, the preparation method of the hexafluoropropylene oxide dimer is: adding a nucleophilic catalyst and a polar solvent into a reactor and stirring them evenly, then introducing hexafluoropropylene oxide at a feed rate of 90 to 110 L / h, reacting at 30 to 50° C. to obtain a mixed solution; separating and distilling the mixed solution to obtain the hexafluoropropylene oxide dimer.

[0026] More preferably, the mass-to-volume ratio (kg / L) of the added mass of the hexafluoropropylene oxide to the reactor volume is 1:1.

[0027] More preferably, the nucleophilic catalyst is at least one of sodium fluoride, potassium fluoride, cesium fluoride and silver nitrate; and the molar ratio of the nucleophilic catalyst to hexafluoropropylene oxide is 1:(300-400).

[0028] More preferably, the polar solvent is at least one of acetonitrile, adiponitrile, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; and the molar ratio of the polar solvent to hexafluoropropylene oxide is 1:(2-4).

[0029] More preferably, the protective gas in step (2) is nitrogen or argon.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The preparation process of perfluoro n-propyl vinyl ether (PPVE) of the present invention adopts a method of reducing the addition of salt-forming agent and a process means of recovering excess hexafluoropropylene oxide dimer (HFPO dimer), thereby promoting 100% salt formation in the salt-forming reaction, while improving the purity of the product and making the by-product a single fluorine-containing inorganic salt. In one embodiment, the PPVE collected by the present invention has a purity of up to 99.94% after GC detection. The fluorine-containing inorganic salt has a high purity after post-treatment and recovery, and can be applied to the field of fine chemicals. In one embodiment, the purity of the by-product NaF recovered by the present invention reaches 99.96%, and in another embodiment, the purity of the by-product KF recovered reaches 99.3%. In addition, the present invention has extremely high conversion rates in both the salt-forming and decarboxylation stages, and the PPVE yield is close to 100%.

[0032] (2) The present invention adds a CO2 absorption device to the perfluoro n-propyl vinyl ether preparation system, and recovers CO2 twice in the salt-forming reaction and the decarboxylation reaction, thereby promoting the forward movement of the chemical reaction equilibrium, thereby increasing the conversion rate of the corresponding perfluoropolyether carboxylate and improving the PPVE yield, while achieving zero carbon emissions, which is in line with the "low carbon" concept. In addition, the present invention also adds a first heat exchanger and a second heat exchanger, which can recover the catalyst and the reaction product PPVE in steps, and can decarboxylate at a higher temperature, which can promote the rapid completion of the reaction and improve the purity of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The flowchart of the preparation system of perfluoro n-propyl vinyl ether in the embodiment of the present invention; wherein 1 is a HFPO dimer storage tank, 2 is a reaction tank, 3 is a first heat exchanger, 4 is a first valve, 5 is a second valve, 6 is a second heat exchanger, 7 is a PPVE storage tank, and 8 is a carbon dioxide absorption tower.

[0034] Figure 2 The figure is a schematic diagram of the process for preparing perfluoro-n-propyl vinyl ether in an embodiment of the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below through embodiments in combination with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0037] Example 1

[0038] This embodiment provides a system for preparing perfluoro-n-propyl vinyl ether, such as Figure 1 As shown, it includes a feeding device, a reaction device, a condensing device, a finished product collecting device and a gas absorption device, wherein the feeding device includes a HFPO dimer storage tank 1, the reaction device includes a reaction tank 2, the condensing device includes a first heat exchanger 3 and a second heat exchanger 6, the finished product collecting device includes a PPVE storage tank 7, and the gas absorption device includes a carbon dioxide absorption tower 8. The reaction device is used to heat the hexafluoropropylene oxide dimer, the salt-forming agent and the catalyst, and the salt-forming reaction and the decarboxylation reaction occur in sequence, and the salt-forming reaction product and the decarboxylation reaction product are obtained respectively; the condensing device is used to condense the refluxed hexafluoropropylene oxide dimer and the catalyst and separate the carbon dioxide gas in the two reaction products and the perfluoro-n-propyl vinyl ether in the decarboxylation reaction product; the gas absorption device is used to absorb the carbon dioxide gas generated by the reaction.

[0039] The HFPO dimer storage tank 1 is provided with a material inlet and a material outlet; the reaction tank 2 is provided with a salt-forming agent and a catalyst raw material inlet, a HFPO dimer raw material inlet, a gas inlet, an upper discharge port, a lower discharge port and a gas outlet; the first heat exchanger 3 and the second heat exchanger 6 are both provided with a material inlet and a material outlet; the PPVE storage tank 7 is provided with a material inlet, a gas outlet and a finished product discharge port; the carbon dioxide absorption tower 8 is provided with a gas inlet and a gas outlet.

[0040] The material outlet of the HFPO dimer storage tank 1 is connected to the HFPO dimer raw material inlet of the reaction tank 2; the material outlet of the reaction tank 2 is connected to the material inlet of the first heat exchanger 3; the material outlet of the first heat exchanger 2 is provided with two branch pipes in parallel, namely the first branch pipe and the second branch pipe, wherein the outlet of the first branch pipe is connected to the gas inlet of the carbon dioxide absorption tower 8, and the outlet of the second branch pipe is connected to the material inlet of the second heat exchanger 6; the material outlet of the second heat exchanger 6 is connected to the material inlet of the PPVE storage tank 7; the gas outlet of the PPVE storage tank 7 is connected to the gas inlet of the carbon dioxide absorption tower 8; the gas outlet of the carbon dioxide absorption tower 8 is connected to the atmosphere.

[0041] In addition, a first valve 4 is provided at the starting end of the first branch pipeline along the material flow direction; a second valve 5 is provided at the starting end of the second branch pipeline along the material flow direction; and a vacuum pump is provided at the gas outlet of the reaction tank 2.

[0042] Example 2

[0043] The present invention provides a method for preparing perfluoro-n-propyl vinyl ether using the system described in Example 1, wherein the process is as follows: Figure 2 As shown, the specific steps include:

[0044] (1) Preparation of HFPO dimer: 3 g of silver nitrate and 82 g of acetonitrile were added to a reactor and stirred at a speed of 500 r / min for 30 min, and then HFPO was continuously introduced at a feed rate of 100 L / h. At the same time, the temperature of the reactor was controlled between 30 and 50°C. When the HFPO in the reactor reached 1 kg, the feeding was stopped and the reaction was continued with stirring. When the pressure in the reactor no longer changed and the temperature dropped to room temperature, a mixed solution a was obtained. The mixed solution a was separated and the lower organic phase was collected for distillation to obtain 800 g of HFPO dimer (purity 99.8%).

[0045] (2) Dehydration treatment: Na2CO3 is dried by baking in a muffle furnace at 300°C for 24 hours to obtain dehydrated Na2CO3; quicklime is added to diethylene glycol dimethyl ether, and the mixture is heated under reflux at 160°C for 12 hours to obtain dehydrated diethylene glycol dimethyl ether.

[0046] (3) Salt-forming reaction: close the first valve 4, the second valve 5, the gas inlet, the gas outlet and the lower discharge port of the perfluoro n-propyl vinyl ether preparation system of the reaction tank 2; add 130 g of dehydrated Na2CO3 and 383 g of dehydrated diethylene glycol dimethyl ether into the reaction tank 2 through the salt-forming agent and catalyst raw material inlets of the reaction tank 2, and close the salt-forming agent and catalyst raw material inlets after the addition is completed; set the cooling temperature in the first heat exchanger to -30°C and open the first valve 4; then reduce the temperature in the reaction tank 2 to -25°C, slowly add 500 g of the HFPO dimer obtained in step (1) into the reaction tank 2 through the HFPO dimer raw material inlet of the reaction tank 2, and close the HFPO dimer raw material inlet after the addition is completed; then heat the reaction tank 2 to 60°C for salt-forming reaction to obtain a salt-forming reaction product, wherein the salt-forming reaction product includes sodium perfluoropolyether carboxylate, sodium fluoride and carbon dioxide gas; the by-product carbon dioxide gas enters the first branch pipeline through the first heat exchanger 3, and then enters the carbon dioxide absorption tower 8 to be absorbed. During the reaction, the vaporized HFPO dimer is condensed by the first heat exchanger 3 and then refluxed to the reaction tank 2 .

[0047] (4) Recovering HFPO dimer: close the first valve 4, connect the vacuum pump to the gas outlet of the reaction tank 2, then open the gas outlet of the reaction tank 2, and recover the HFPO dimer in the reaction device under reduced pressure; after the recovery is completed, close the gas outlet of the reaction tank 2 and open the gas inlet of the reaction tank 2 and the first valve 4, introduce nitrogen into the reaction device until the pressure in the reaction device reaches one atmosphere, and then close the gas inlet of the reaction tank 2 and the first valve 4.

[0048] (5) Decarboxylation reaction: the cooling temperature in the first heat exchanger 3 is set to 30°C, the cooling temperature in the second heat exchanger 6 is set to -30°C, and the second valve 5 is opened; the reaction tank 2 is heated to 150°C for decarboxylation reaction to obtain a decarboxylation reaction product, which includes perfluoro-n-propyl vinyl ether, sodium fluoride and carbon dioxide gas; the perfluoro-n-propyl vinyl ether is condensed by the second heat exchanger 6 and enters the PPVE storage tank 7, and 320g of PPVE is collected. The GC detection shows that the purity of PPVE is 99.94%; the carbon dioxide gas enters the second branch pipeline through the first heat exchanger, and then enters the second heat exchanger 6 and the PPVE storage tank 7, and then enters the carbon dioxide absorption tower 8 to be absorbed. During the reaction, the vaporized diethylene glycol dimethyl ether is condensed by the first heat exchanger 3 and then refluxed to the reaction tank 2.

[0049] (6) Post-treatment: After the decarboxylation reaction is completed, the reaction temperature in the reaction tank 2 is lowered to room temperature, the lower discharge port of the reaction tank 2 is opened to collect the mixed solution b in the reaction tank 2, and the mixed solution b is subjected to reduced pressure distillation at 130°C to recover diethylene glycol dimethyl ether and crude NaF salt from the two reaction products; the crude NaF salt is sequentially dried, acidified by stirring with 100 mL of 40% hydrofluoric acid for 6 h, and distilled to recover HF and NaF solutions; the NaF solution is adsorbed by a sodium-type ion exchange resin and dried again to collect 98 g of NaF solid, which is found to have a purity of 99.96% after testing.

[0050] Example 3

[0051] The present invention provides a method for preparing perfluoro-n-propyl vinyl ether using the system described in Example 1, wherein the process is as follows: Figure 2 As shown, the specific steps include:

[0052] (1) Preparation of HFPO dimer: 2.5 g of silver nitrate and 62 g of acetonitrile were added to a reactor and stirred at a speed of 500 r / min for 30 min, and then HFPO was continuously introduced at a feed rate of 110 L / h. At the same time, the temperature of the reactor was controlled between 30 and 50° C. When the HFPO in the reactor reached 1 kg, the feeding was stopped and the reaction was continued with stirring. When the pressure in the reactor no longer changed and the temperature dropped to room temperature, a mixed solution a was obtained. The mixed solution a was separated and the lower organic phase was collected for distillation to obtain 832 g of HFPO dimer (purity 99.8%).

[0053] (2) Dehydration treatment: K2CO3 is dried by baking in a muffle furnace at 300°C for 24 hours to obtain dehydrated K2CO3; quicklime is added to diethylene glycol dimethyl ether, and the mixture is heated under reflux at 160°C for 12 hours to obtain dehydrated diethylene glycol dimethyl ether.

[0054] (3) Salt-forming reaction: close the first valve 4, the second valve 5, the gas inlet, the gas outlet and the lower discharge port of the perfluoro n-propyl vinyl ether preparation system of the reaction tank 2; add 104 g of dehydrated K2CO3 and 202 g of dehydrated diethylene glycol dimethyl ether into the reaction tank 2 through the salt-forming agent and catalyst raw material inlets of the reaction tank 2, and close the salt-forming agent and catalyst raw material inlets after the addition is completed; set the cooling temperature in the first heat exchanger to -30°C and open the first valve 4; then reduce the temperature in the reaction tank 2 to -30°C, slowly add 500 g of the HFPO dimer obtained in step (1) into the reaction tank 2 through the HFPO dimer raw material inlet of the reaction tank 2, and close the HFPO dimer raw material inlet after the addition is completed; then heat the reaction tank 2 to 60°C for salt-forming reaction to obtain a salt-forming reaction product, wherein the salt-forming reaction product includes potassium perfluoropolyether carboxylate, potassium fluoride and carbon dioxide gas; the by-product carbon dioxide gas enters the first branch pipeline through the first heat exchanger 3, and then enters the carbon dioxide absorption tower 8 to be absorbed. During the reaction, the vaporized HFPO dimer is condensed by the first heat exchanger 3 and then refluxed to the reaction tank 2 .

[0055] (4) Recovering HFPO dimer: close the first valve 4, connect the vacuum pump to the gas outlet of the reaction tank 2, then open the gas outlet of the reaction tank 2, and recover the HFPO dimer in the reaction device under reduced pressure; after the recovery is completed, close the gas outlet of the reaction tank 2 and open the gas inlet of the reaction tank 2 and the first valve 4, introduce nitrogen into the reaction device until the pressure in the reaction device reaches one atmosphere, and then close the gas inlet of the reaction tank 2 and the first valve 4.

[0056] (5) Decarboxylation reaction: the cooling temperature in the first heat exchanger 3 is set to 25°C, the cooling temperature in the second heat exchanger 6 is set to -30°C, and the second valve 5 is opened; the reaction tank 2 is heated to 150°C for decarboxylation reaction to obtain a decarboxylation reaction product, which includes perfluoro n-propyl vinyl ether, potassium fluoride and carbon dioxide gas; the perfluoro n-propyl vinyl ether is condensed by the second heat exchanger 6 and enters the PPVE storage tank 7, and 196.5g of PPVE is collected, and the PPVE purity is 99.91% after GC detection; the carbon dioxide gas enters the second branch pipeline through the first heat exchanger, and then enters the second heat exchanger 6 and the PPVE storage tank 7, and then enters the carbon dioxide absorption tower 8 to be absorbed. During the reaction, the vaporized diethylene glycol dimethyl ether is condensed by the first heat exchanger 3 and refluxed to the reaction tank 2.

[0057] (6) Post-treatment: After the decarboxylation reaction is completed, the reaction temperature in the reaction tank 2 is lowered to room temperature, the lower discharge port of the reaction tank 2 is opened to collect the mixed solution b in the reaction tank 2, and the mixed solution b is subjected to reduced pressure distillation at 130°C to recover diethylene glycol dimethyl ether and KF crude salt from the two reaction products; the KF crude salt is dried, acidified by stirring with 100 mL of 40% hydrofluoric acid for 6 h, and distilled to recover HF and KF solutions; the KF solution is adsorbed by potassium-type ion exchange resin and dried again to collect 81 g of KF solid, and its purity is 99.3% after testing.

[0058] In summary, the present invention effectively overcomes the deficiencies in the prior art and has a high industrial utilization value. The above embodiments serve to illustrate the substantive content of the present invention, but do not limit the protection scope of the present invention. Those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and protection scope of the technical solution of the present invention.

Claims

1. A method for preparing perfluoro-n-propyl vinyl ether, characterized in that: The system is prepared by using a perfluoro n-propyl vinyl ether system, wherein the system comprises a reaction device, a condensation device, a finished product collection device and a gas absorption device connected in sequence; the upper discharge port of the reaction device is connected to the inlet of the condensation device; the condensation device comprises a first heat exchanger and a second heat exchanger connected in sequence, and the outlet of the first heat exchanger is connected in parallel with a first branch pipeline and a second branch pipeline; wherein the outlet of the first branch pipeline is connected to the inlet of the gas absorption device, the outlet of the second branch pipeline is connected to the inlet of the second heat exchanger, and the outlet of the second heat exchanger is connected to the inlet of the finished product collection device; the top outlet pipe of the finished product collection device is connected to the gas absorption device; the outlet of the gas absorption device is connected to the atmosphere; a first valve is provided at the starting end of the first branch pipeline along the material flow direction; a second valve is provided at the starting end of the second branch pipeline along the material flow direction; The method comprises the following steps: (1) Salt-forming reaction: adding a salt-forming agent and a catalyst to the reaction device, and closing the raw material inlet of the reaction device after the addition is completed; setting the cooling temperature in the first heat exchanger to -20 to -30°C and opening the first valve; lowering the temperature in the reaction device to -20 to -30°C, and then adding hexafluoropropylene oxide dimer, and closing the raw material inlet after the addition is completed; then heating the reaction device to 50 to 60°C for salt-forming reaction, and after the reaction is completed, the by-product carbon dioxide gas enters the first branch pipeline through the first heat exchanger, and then enters the gas absorption device to be absorbed; the vaporized hexafluoropropylene oxide dimer is condensed by the first heat exchanger and then refluxed to the reaction device; (2) Recovering the hexafluoropropylene oxide dimer: closing the first valve, opening the gas outlet of the reaction device to evacuate the reaction device, and recovering the hexafluoropropylene oxide dimer in the reaction device under reduced pressure; after the recovery is completed, closing the gas outlet of the reaction device and opening the gas inlet and the first valve of the reaction device, introducing protective gas into the reaction device until the pressure in the reaction device reaches one atmosphere, and then closing the gas inlet and the first valve of the reaction device; (3) Decarboxylation reaction: the cooling temperature in the first heat exchanger is set to 20 to 30°C, the cooling temperature in the second heat exchanger is set to -20 to -30°C, and the second valve is opened; the reaction device is heated to 130 to 160°C for decarboxylation reaction, and after the reaction, the product perfluoro n-propyl vinyl ether is condensed in the second heat exchanger and enters the finished product collection device; the by-product carbon dioxide gas enters the second branch pipeline through the first heat exchanger, and then passes through the second heat exchanger and the finished product collection device, and then enters the gas absorption device to be absorbed.

2. The method for preparing perfluoro-n-propyl vinyl ether according to claim 1, characterized in that: The molar ratio of the hexafluoropropylene oxide dimer, the salt-forming agent and the catalyst is 1: (0.5-0.9): (1.5-2.0).

3. The method for preparing perfluoro-n-propyl vinyl ether according to claim 1 or 2, characterized in that: The catalyst is any one of diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, N,N-dimethylformamide, N,N-dimethylacetamide and N,N-dimethyldiacetamide.

4. The method for preparing perfluoro-n-propyl vinyl ether according to claim 1 or 2, characterized in that: The salt-forming agent is at least one of sodium carbonate and potassium carbonate.

5. The method for preparing perfluoro-n-propyl vinyl ether according to claim 1, characterized in that: After the decarboxylation reaction in step (3) is completed, the mixed liquid in the reaction device is distilled to obtain a catalyst and a crude fluorine-containing inorganic salt; the crude fluorine-containing inorganic salt is then dried, acidified, distilled, ion exchanged and dried in sequence to obtain a fluorine-containing inorganic salt.

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