High-viscosity perfluoropolyether end group fluorination device and method

Abstract

The invention relates to the technical field of fluorine chemical industry, in particular to a high-viscosity perfluoropolyether end group fluorination device and method. Comprising a packed tower, a delivery pump and a storage tank, the packed tower comprises a tower body, a seal head, a cold trap and a tower kettle, and the cold trap is located at the center of the seal head and the tower body; the sealing head is connected with an outlet of the conveying pump through a feeding pipe; an inlet of the delivery pump is connected with the bottom of the storage tank; the cold trap is connected with the sealing head through a flange, an ultraviolet lamp is arranged in the cold trap, the cold trap is provided with a jacket layer, an inlet of the jacket layer is connected with a water inlet of the cold trap through a pipeline, and an outlet of the jacket layer is connected with a water outlet of the cold trap through a pipeline. Through the packed tower, the contact area of the high-viscosity perfluoropolyether and the fluorine gas mixture is increased, the mass transfer driving force is increased, the utilization rate of the fluorine gas is improved, and continuous production of the high-viscosity perfluoropolyether is realized.

Description

Technical Field

[0001] This invention relates to the field of fluorochemical technology, specifically to an apparatus and method for fluorinating high-viscosity perfluoropolyether end groups. Background Technology

[0002] Perfluoropolyethers (PFPEs) are important organofluorine compounds whose molecular structure is mainly composed of strong CF bonds. This unique structure endows them with excellent chemical inertness, thermal stability, low volatility, and superior lubricity. Viscosity is one of the key physical properties of PFPEs, directly determining their applicable scenarios. High-viscosity PFPEs, in particular, exhibit extremely high viscosity and very low evaporation loss, resulting in very high load-bearing capacity, making them suitable for high-load applications. Due to their superior performance, high-viscosity PFPEs play an irreplaceable role in aerospace equipment requiring long-term lubrication and in heavy-duty lubrication applications such as large industrial gears and bearings. They are widely used in high-end fields such as aerospace, nuclear, electronics and electrical, chemical, and automotive industries.

[0003] All perfluoropolyethers contain acyl fluoride groups (-COF) at the end groups upon polymerization. These acyl fluoride groups partially hydrolyze into carboxyl groups. Both acyl fluoride and carboxyl groups are highly reactive and can be used to prepare polyether derivatives with specific functions. However, perfluoropolyethers used for applications such as vacuum pump oils and lubricants must be inert, requiring the acyl fluoride groups to be treated with fluorination to form stable trifluoromethyl groups (-CF3). For perfluoropolyethers with a kinematic viscosity above 50 cSt at the reaction temperature, the fluorination end-capping treatment has limited effectiveness. High-viscosity perfluoropolyethers exhibit poor flowability, difficult mass transfer, low end-group fluorination reaction efficiency, and are prone to side reactions, resulting in low utilization of the fluorinating agent.

[0004] Chinese patent application CN103111253A, published on May 22, 2013, discloses a reactor that improves fluorine gas utilization by circulating fluorine gas through a hollow stirring shaft and a hollow multi-hole stirring paddle to contact the material. This allows the fluorinated gas above the liquid surface to be redistributed into the material through the hollow stirring shaft and paddle, thus improving fluorine gas utilization. However, this method cannot achieve continuous fluorination, and the fluorine gas utilization rate is low when fluorination is used for high-viscosity materials. Chinese patent application CN107383355A, published on November 24, 2017, discloses a method for continuous fluorination of perfluoropolyethers using a microchannel reactor. This method has high conversion rate, short reaction time, and is suitable for industrial scale-up. However, the narrow channels of the microchannel reactor result in high resistance and poor mixing effect when used for fluorination of high-viscosity perfluoropolyethers.

[0005] Therefore, there is an urgent need to develop a device suitable for the fluorination of high-viscosity perfluoropolyethers, to improve fluorination efficiency, reduce safety risks, and achieve continuous production. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a high-viscosity perfluoropolyether end-group fluorination device that can continuously and efficiently realize the fluorination end-capping of high-viscosity perfluoropolyether.

[0007] Another objective of this invention is to provide a method for fluorinating the end groups of high-viscosity perfluoropolyethers, which improves the activity of fluorine gas, lowers the reaction temperature, shortens the reaction time, reduces the amount of fluorine gas used, and saves raw material costs.

[0008] This invention is achieved using the following technical solution: The high-viscosity perfluoropolyether end-group fluorination device includes a packed tower, a delivery pump, and a storage tank. The packed tower includes a tower body, a head, a cold trap, and a bottom. The cold trap is located at the center of the head and the tower body. The head is connected to the outlet of the delivery pump via a feed pipeline. The inlet of the delivery pump is connected to the bottom of the storage tank. The cold trap is connected to the head via a flange. The cold trap is equipped with an ultraviolet lamp and has a jacket layer. The inlet of the jacket layer is connected to the inlet of the cold trap via a pipeline, and the outlet of the jacket layer is connected to the outlet of the cold trap via a pipeline.

[0009] The packed tower is equipped with a cold trap, with an ultraviolet lamp installed in the center of the cold trap. The tower body is filled with quartz packing material that transmits ultraviolet light. Perfluoropolyether containing acyl fluoride groups enters the packed tower from the top, while a fluorine gas mixture enters from the bottom. Ultraviolet light primarily irradiates the gas phase region, where activated fluorine atoms undergo a fluorination-end-capping reaction with the perfluoropolyether on the packing surface. Ultraviolet light enhances the fluorination-end-capping reactivity of the perfluoropolyether, lowers the reaction temperature, and increases the yield. This device can continuously end-cap the unsaturated end groups of high-viscosity perfluoropolyethers, offering advantages such as high reaction efficiency, safety, controllability, and suitability for large-scale production.

[0010] The tower body contains internal packing material, which is placed around the cold trap.

[0011] The end cap includes a feed pipe, a temperature sensor, an exhaust gas pipe, and a back pressure valve. The feed pipe, temperature sensor, and exhaust gas pipe are located on the side of the end cap. The back pressure valve is installed on the exhaust gas pipe. A distributor is located outside the cold trap and is connected to the feed pipe. Below the distributor is a ring with evenly distributed circular holes. The end of the perfluoropolyether feed pipe is connected to the ring distributor, which has evenly distributed circular holes at its lower end and is located around the cold trap.

[0012] The reboiler includes a temperature sensor, a coil, and an inlet pipe. The coil is located inside the reboiler, the temperature sensor is located below the coil, and the inlet pipe is located above the coil. Circulating water flows through the coil. The storage tank is equipped with a stirring system and a jacket. Heat transfer oil is circulated in the jacket for heating the perfluoropolyether inside the storage tank.

[0013] The cold trap is made of quartz with a purity ≥99.9%, and the distance between the outer wall of the cold trap and the inner wall of the tower ranges from 10-50 mm. The UV lamp power ranges from 300-1000W, and the effective wavelength range is 200-500 nm. The packed tower is made of steel lined with PTFE. A UV lamp is placed in the center of the cold trap, and coolant is circulated through the cold trap jacket for cooling the UV lamp. The packing material of the packed tower is also quartz, which has good light transmittance and is resistant to fluorine corrosion.

[0014] The cold trap is made of quartz with a purity of ≥99.9%; the filler is made of quartz with a purity of ≥99.9%, and the filler is in the shape of a ring or a saddle.

[0015] The fluorination method of the high-viscosity perfluoropolyether end-group fluorination device includes the following steps: (1) Pass coolant into the cold trap jacket, turn on the ultraviolet lamp, and pass circulating water into the coil of the tower bottom; (2) Introduce a fluorine gas mixture into the inlet pipeline, adjust the opening of the back pressure valve, and control the pressure inside the tower to 0.2-0.6 MPa; (3) Under ultraviolet light irradiation, the delivery pump is turned on, and the high viscosity perfluoropolyether in the storage tank enters the packed tower through the distributor and falls onto the surface of the packing to carry out the fluorination end-capping reaction.

[0016] First, coolant is introduced into the cold trap, and the ultraviolet lamp is turned on; the coolant removes the heat from the UV lamp. The tank agitator is then turned on, and heat transfer oil is introduced into the tank jacket to heat the perfluoropolyether inside the tank to a certain temperature. After the UV lamp stabilizes, a fluorine gas mixture is introduced into the packed tower. The transfer pump is turned on to deliver the perfluoropolyether into the packed tower, where the fluorine gas mixture and the perfluoropolyether undergo a countercurrent contact reaction on the packing surface for fluorination and end-capping. This invention uses a packed tower to solve the problem of poor mass transfer during the end-capping process of high-viscosity perfluoropolyether, and the introduction of ultraviolet light improves reaction efficiency and reduces reaction time, which is beneficial for industrial-scale production.

[0017] The molecular formula of the high-viscosity perfluoropolyether in step (3) is R. f1 (CF2CF2O) m -(C2F4O) n -CF2)R f2 R f1 (CF2CF(CF3) m (OCF2O) n R f2 or R f1 (CF(CF3)CF2O)mR f2 , where R f1 For -CF3, -C2F5, CF2COF or -CF(CF3)COF; R f2The values ​​are -CF2COF, -CF2CF2COF, -CF(CF3)COOH, -CF2COOH, and -CF2CF2COOH, with m and n ranging from 1 to 500, and m / n between 0.1 and 20.

[0018] In step (2), the fluorine gas mixture is a mixture of fluorine and at least one of nitrogen and helium, and the molar concentration of fluorine in the fluorine gas mixture is 1%-60%; in step (3), the density range of the perfluoropolyether is 1.6-1.9 kg / cm³. 3 The kinematic viscosity ranges from 50 cSt to 1500 cSt.

[0019] The molar ratio of fluorine gas in the acyl fluoride group and fluorine gas mixture of the perfluoropolyether is 1:(1-10); the reaction temperature of the fluorination end-capping reaction is 50℃-100℃, and the reaction pressure is 0.1-0.3MPa.

[0020] The preferred molar ratio of the perfluoropolyether with acyl fluoride groups to the fluorine gas mixture is 1:8-60. This preferred ratio of perfluoropolyether to fluorine gas mixture allows for control of the reaction rate and enables end-capping reactions to occur at lower temperatures.

[0021] The preferred reaction temperature for the fluorination end-capping reaction is 50℃-100℃, and the reaction pressure is 0.1-0.3MPa. The reaction pressure is controlled by a back pressure valve on the exhaust gas pipeline. Fluorine gas irradiated with ultraviolet light is activated into fluorine atoms. Utilizing these highly reactive fluorine atoms to fluorinate the perfluoropolyether allows the fluorination process to be carried out at a relatively low temperature of 20℃-60℃.

[0022] This invention uses perfluoropolyether R with acyl fluoride groups. f1 (CF2CF2O) m -(C2F4O) n -CF2)R f2 R f1 (CF2CF(CF3) m (OCF2O)R f2 or R f1 (CF(CF3)CF2O)mR f2 Using fluorine gas as raw material, under ultraviolet radiation conditions, a mixture of fluorine gas and fluorine gas is continuously passed into a light-filled tower to react and generate end-saturated perfluoropolyether.

[0023] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention increases the contact area between high-viscosity perfluoropolyether and fluorine gas mixture by using a packed tower, thereby increasing the mass transfer driving force and improving the utilization rate of fluorine gas, and realizing the continuous production of high-viscosity perfluoropolyether. Compared with the traditional batch reactor process, the material residence time in the reactor is consistent, there is no back-coagulation phenomenon, and the adverse effects of material back-coagulation on product yield and selectivity are avoided.

[0024] (2) The introduction of ultraviolet lamps enables perfluoropolyether and fluorine gas to react under ultraviolet radiation conditions, which improves the activity of fluorine gas, lowers the reaction temperature, shortens the reaction time, reduces the amount of fluorine gas used, and saves raw material costs.

[0025] (3) This invention solves the problems of poor mass and heat transfer, long reaction time and poor fluorine utilization during the end-capping process of high viscosity perfluoropolyether fluorination, improves fluorination efficiency, is safe and controllable, and is conducive to large-scale production. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the high-viscosity perfluoropolyether end-group fluorination device of the present invention; Figure 2 The infrared spectrum of the product obtained in Example 1 of this invention; Figure 3 The infrared spectrum of the product obtained in Example 2 of this invention; Figure 4 The infrared spectrum of the product obtained in Example 3 of this invention; Figure 5 The infrared spectrum of the product obtained in Comparative Example 1 of this invention; Figure 6 The infrared spectrum of the product obtained in Comparative Example 2 of this invention; In the diagram: 1. Packed tower; 2. Transfer pump; 3. Storage tank; 11. Tower body; 12. End cap; 13. Cold trap; 14. Tower bottom; 111. Packing; 121. Temperature sensor; 122. Tail gas pipeline; 123. Back pressure valve; 124. Feed pipeline; 125. Distributor; 131. Ultraviolet lamp; 132. Cold trap inlet; 133. Cold trap outlet; 141. Temperature sensor; 142. Coil; 143. Air inlet pipeline. Detailed Implementation

[0027] To make the objectives and technical solutions of this invention clearer, the invention will be further described in detail below.

[0028] like Figure 1As shown, the apparatus used in the embodiments and comparative examples is an apparatus for fluorinated end-capping of high-viscosity perfluoropolyether, including a packed tower 1, a transfer pump 2, and a storage tank 3. The packed tower 1 includes a tower body 11, an end cap 12, a cold trap 13, and a reboiler 14. The cold trap 13 is located at the center of the end cap 12 and the tower body 11. The end cap 12 is connected to the outlet of the transfer pump 2 via a feed pipe 124. The inlet of the transfer pump 2 is connected to the bottom of the storage tank 3. The cold trap 13 is connected to the end cap 12 via a flange. The cold trap 13 is equipped with an ultraviolet lamp 131. The cold trap 13 has a jacket layer. The inlet of the jacket layer is connected to the cold trap inlet 132 via a pipe, and the outlet of the jacket layer is connected to the cold trap outlet 133 via a pipe. The tower body 11 contains packing material 111, which is placed around the cold trap 13. The end cap 12 includes a feed pipe 124, a temperature sensor 121, an exhaust gas pipe 122, and a back pressure valve 123. The feed pipe 124, temperature sensor 121, and exhaust gas pipe 122 are located on the side of the end cap 12. The back pressure valve 123 is installed on the exhaust gas pipe 122. A distributor 125 is located outside the cold trap 13 and is connected to the feed pipe 124. Below the distributor 125 is a ring with evenly distributed circular holes. The reboiler 14 includes a temperature sensor 141, a coil 142, and an inlet pipe 143. The coil 142 is located inside the reboiler 14, the temperature sensor 141 is located below the coil 142, and the inlet pipe 143 is located above the coil 142. Circulating water flows through the coil 142. The cold trap 13 is made of quartz with a purity ≥99.9%, and the distance between the outer wall of the cold trap 13 and the inner wall of the tower body 11 is within 30mm. The effective wavelength range of the ultraviolet lamp 131 is 200-500nm. The cold trap 13 is made of quartz with a purity ≥99.9%, and the packing 111 is made of quartz with a purity ≥99.9%, and the packing 111 is annular or saddle-shaped.

[0029] Example 1 The method for fluorinating the end groups of high-viscosity perfluoropolyethers is as follows: First, coolant is introduced into the jacket of cold trap 13, and circulating water is introduced into coil 142. The ultraviolet mercury lamp (300W) is turned on. The stirring motor of storage tank 3 is turned on, and heat transfer oil is introduced into the jacket of storage tank 3 to control the temperature inside the tank at 50℃. A fluorine gas mixture is introduced into the bottom of tower 14 at a flow rate adjusted by back pressure valve 123 to control the pressure inside the tower at 0.2 MPa. The transfer pump 2 is turned on to deliver perfluoropolyether with acyl fluoride end groups to the top of packed tower 1 at a flow rate of 50 g / min. The fluorine gas mixture consists of fluorine and nitrogen, with fluorine accounting for 8% of the molar percentage. The viscosity of the perfluoropolyether is 840 cSt. The molar ratio of perfluoropolyether to the fluorine gas mixture is 1:35.

[0030] The yield of the terminally fluorinated perfluoropolyether was 46.2 g / min, reaching 92.4%. Infrared spectroscopy confirmed that the unsaturated terminal groups of the perfluoropolyether were completely fluorinated into stable -CF3 groups. The infrared spectrum of the product obtained in Example 1 is shown below. Figure 2 .

[0031] Example 2 The method for fluorinating the end groups of high-viscosity perfluoropolyethers is as follows: Coolant is introduced into the jacket of cold trap 13, and circulating water is introduced into coil 142. The ultraviolet mercury lamp (350W) is turned on. The stirring motor of storage tank 3 is turned on, and heat transfer oil is introduced into the jacket of storage tank 3 to control the temperature inside the tank at 55℃. A fluorine gas mixture is introduced into the bottom of tower 14 at a flow rate adjusted by back pressure valve 123 to control the pressure inside the tower at 0.25 MPa. Transfer pump 2 is turned on to deliver perfluoropolyether with acyl fluoride end groups to the top of packed tower 1 at a flow rate of 50 g / min. The fluorine gas mixture consists of fluorine and nitrogen, with fluorine accounting for 8% of the molar percentage. The viscosity of the perfluoropolyether is 1030 cSt. The molar ratio of perfluoropolyether to the fluorine gas mixture is 1:35.

[0032] The yield of the terminally fluorinated perfluoropolyether was 45.5 g / min, reaching 91%. Infrared spectroscopy confirmed that the unsaturated terminal groups of the perfluoropolyether were completely fluorinated into stable -CF3 groups. The infrared spectrum of the product obtained in Example 2 is shown below. Figure 3 .

[0033] Example 3 The method for fluorinating the end groups of high-viscosity perfluoropolyethers is as follows: Coolant is introduced into the jacket of cold trap 13, and circulating water is introduced into coil 142. The ultraviolet mercury lamp (500W) is turned on. The stirring motor of storage tank 3 is turned on, and heat transfer oil is introduced into the jacket of storage tank 3 to control the temperature inside the tank at 60℃. A fluorine gas mixture is introduced into the bottom of tower 14 at a flow rate adjusted by back pressure valve 123 to control the pressure inside the tower at 0.3 MPa. Transfer pump 2 is turned on to deliver perfluoropolyether with acyl fluoride end groups to the top of packed tower 1 at a flow rate of 50 g / min. The fluorine gas mixture consists of fluorine and nitrogen, with fluorine accounting for 8% of the molar percentage. The viscosity of the perfluoropolyether is 1250 cSt. The molar ratio of perfluoropolyether to the fluorine gas mixture is 1:35.

[0034] The yield of the terminally fluorinated perfluoropolyether was 46.9 g / min, reaching 93.8%. Infrared spectroscopy confirmed that the unsaturated terminal groups of the perfluoropolyether were completely fluorinated into stable -CF3 groups. The infrared spectrum of the product obtained in Example 3 is shown below. Figure 4 .

[0035] Comparative Example 1 The aforementioned fluorination device was constructed. Coolant was introduced into the jacket of cold trap 13, and circulating water was introduced into coil 142. The ultraviolet mercury lamp was kept off. The stirring motor of storage tank 3 was turned on, and heat transfer oil was introduced into the jacket of storage tank 3 to control the temperature inside the storage tank at 60°C. A fluorine gas mixture was introduced into the bottom of the tower 14 at a flow rate of 0.25 MPa by adjusting the back pressure valve 123. The transfer pump 2 was turned on to deliver perfluoropolyether with acyl fluoride end groups to the top of the packed tower 1 at a flow rate of 50 g / min. The fluorine gas mixture consisted of fluorine and nitrogen, with fluorine accounting for 20% of the molar percentage. The viscosity of the perfluoropolyether was 1050 cSt. The molar ratio of perfluoropolyether to the fluorine gas mixture was 1:30.

[0036] The yield of the fluorinated perfluoropolyether was 47.9 g / min. Infrared spectroscopy revealed a carbonyl absorption peak, indicating incomplete end-capping. The infrared spectrum of the product obtained in Comparative Example 1 is shown below. Figure 5 .

[0037] Comparative Example 2 The aforementioned fluorination device was constructed. Coolant was introduced into the jacket of cold trap 13, and circulating water was introduced into coil 142. The ultraviolet mercury lamp was kept off. The stirring motor of storage tank 3 was turned on, and heat transfer oil was introduced into the jacket of storage tank 3 to control the temperature inside the storage tank at 80°C. A fluorine gas mixture was introduced into the bottom of the tower 14 at a flow rate of 0.3 MPa, which was controlled by adjusting the back pressure valve 123. The transfer pump 2 was turned on to deliver perfluoropolyether with acyl fluoride end groups to the top of the packed tower 1 at a flow rate of 50 g / min. The fluorine gas mixture consisted of fluorine and nitrogen, with fluorine accounting for 10% of the molar percentage. The viscosity of the perfluoropolyether was 1250 cSt. The molar ratio of perfluoropolyether to the fluorine gas mixture was 1:35.

[0038] The yield of the fluorinated perfluoropolyether was 48.3 g / min. Infrared spectroscopy revealed a carbonyl absorption peak, indicating incomplete end-capping. The infrared spectrum of the product obtained in Comparative Example 2 is shown below. Figure 6 .

Claims

1. A high viscosity perfluoropolyether end group fluorination apparatus characterized by, The application relates to a high-viscosity fluorinated polyether synthesis device, which comprises a filler tower (1), a conveying pump (2) and a storage tank (3), the filler tower (1) comprises a tower body (11), a head (12), a cold trap (13) and a tower kettle (14), the cold trap (13) is located at the center of the head (12) and the tower body (11), the head (12) is connected with the outlet of the conveying pump (2) through a feeding pipeline (124), the inlet of the conveying pump (2) is connected with the bottom of the storage tank (3), the cold trap (13) is connected with the head (12) through flanges, the cold trap (13) is internally provided with an ultraviolet lamp (131), the cold trap (13) is provided with a jacket layer, the jacket layer inlet is connected with a cold trap water inlet (132) through a pipeline, and the jacket layer outlet is connected with a cold trap water outlet (133) through a pipeline.

2. The high viscosity perfluoropolyether end group fluorination apparatus of claim 1, wherein, The tower body (11) is internally provided with fillers (111), and the fillers (111) are arranged around the cold trap (13).

3. The high viscosity perfluoropolyether end group fluorination apparatus of claim 1, wherein, The head (12) comprises the feeding pipeline (124), a temperature sensor (121), a tail gas pipeline (122) and a back pressure valve (123), the outer side of the cold trap (13) is a distributor (125), the distributor (125) is connected with the feeding pipeline (124), and the distributor (125) is provided with a circular ring with uniformly distributed circular holes.

4. The high viscosity perfluoropolyether end group fluorination apparatus of claim 1, wherein, The tower kettle (14) comprises a temperature sensor (141), a coil pipe (142), and an air inlet pipeline (143), the coil pipe (142) is located inside the tower kettle (14), the temperature sensor (141) is located below the coil pipe (142), the air inlet pipeline (143) is located above the coil pipe (142), and the coil pipe (142) is connected with circulating water.

5. The high viscosity perfluoropolyether end group fluorination apparatus of claim 1, wherein, The cold trap (13) is made of quartz with a purity of greater than or equal to 99.9%, the distance between the outer wall of the cold trap (13) and the inner wall of the tower body (11) is 10-50 mm, the power of the ultraviolet lamp (131) is 300-1000 W, and the effective wavelength is 200-500 nm.

6. The high viscosity perfluoropolyether end group fluorination apparatus of claim 2, wherein, The cold trap (13) is made of quartz with a purity of greater than or equal to 99.9%, and the fillers (111) are made of quartz with a purity of greater than or equal to 99.9%, and the fillers (111) are annular or saddle-shaped.

7. A process for the fluorination of the end groups of a high viscosity perfluoropolyether according to any one of claims 1 to 6, characterized in that, The application further discloses a high-viscosity fluorinated polyether synthesis method comprising the following steps: (1) circulating water is introduced into the jacket of the cold trap (13), the ultraviolet lamp (131) is turned on, and circulating water is introduced into the coil pipe (142) of the tower kettle (14); (2) fluorine mixed gas is introduced into the air inlet pipeline (143), the opening degree of the back pressure valve (123) is adjusted, and the pressure in the tower is controlled to be 0.2-0.6 MPa; (3) under the irradiation of the ultraviolet lamp (131), the conveying pump (2) is started, the high-viscosity fluorinated polyether in the storage tank (3) is introduced into the filler tower (1) through the distributor (125), and the fluorinated end-capping reaction is carried out on the surface of the fillers (111).

8. The method of claim 7, wherein, The high viscosity perfluoropolyether in step (3) has a molecular formula of R f1 (CF2CF2O) m -(C2F4O) n -CF2)R f2 , R f1 (CF2CF(CF3) m (OCF2O) n R f2 or R f1 (CF(CF3)CF2O)mR f2 wherein R f1 is -CF3, -C2F5, CF2COF or -CF(CF3)COF; R f2 is -CF2COF, -CF2CF2COF, -CF(CF3)COOH, -CF2COOH, -CF2CF2COOH, m and n are independently 1 to 500, and m / n is between 0.1 and 20.

9. The method of claim 7, wherein, In the step (2), the fluorine mixed gas is a mixture of fluorine and at least one of nitrogen and helium, the molar concentration of fluorine in the fluorine mixed gas is 1%-60%, and the kinematic viscosity is 50 cSt-1500 cSt.

10. The method of claim 7, wherein, The molar ratio of the acyl fluoride group of the perfluoropolyether to fluorine in the mixed gas of the acyl fluoride group and fluorine is 1: (1-10); the reaction temperature of the fluorination capping reaction is 50-100 DEG C, and the reaction pressure is 0.1-0.3 MPa.

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