Method and device for decomposing peroxide group in perfluoropolyether

Abstract

The invention relates to the technical field of perfluoropolyether, in particular to a method and a device for decomposing peroxide groups in perfluoropolyether. The method comprises the following steps: 1) mixing perfluoropolyether containing peroxide groups, water and supercritical CO2 to obtain a mixed material; 2) performing ultraviolet radiation on the mixed material at the temperature of 20-100 DEG C to obtain a reaction material; 3) carrying out reduced pressure separation on the reaction material to obtain carbon dioxide and a liquid mixture; performing reduced pressure evaporation on the liquid mixture to obtain hydrofluoric acid and perfluoropolyether; in the step (1), the peroxide value of the perfluoropolyether containing the peroxide groups is larger than or equal to 0.5 mmol / g. According to the method, the peroxide groups in the perfluoropolyether can be safely and efficiently decomposed, the perfluoropolyether product which is low in peroxide value and suitable for follow-up modification is obtained, and cyclic utilization of materials and recovery of by-products can be achieved.

Description

Technical Field

[0001] This invention relates to the field of perfluoropolyether technology, and more particularly to a method and apparatus for the decomposition of peroxy groups in perfluoropolyethers. Background Technology

[0002] Perfluoropolyethers generally refer to a class of polymers whose main chain contains repeating ether bonds and whose hydrogen atoms are completely replaced by fluorine atoms. Due to their unique chemical structure, they exhibit good thermal stability, low intermolecular forces, and properties such as high hydrophobicity, low vapor pressure, chemical inertness, and non-flammability. Often referred to as liquid polytetrafluoroethylene, they have wide applications in various fields of defense and military industries. Perfluoropolyethers can be classified into K-type, D-type, Y-type, and Z-type according to their structure, and can be synthesized using two methods: anionic polymerization and photo-oxidative polymerization. Photo-oxidative polymerization is prepared by copolymerizing small-molecule perfluoroolefins with oxygen in an inert solvent. This reaction generates a perfluoropolyether peroxide primary product with randomly distributed peroxide groups. As is well known, peroxide groups are unstable; to ensure subsequent structural stability and safety in use, it is necessary to remove the peroxide groups contained in the primary product.

[0003] In the prior art, the peroxide decomposition method described in US3715378 involves heating at 100–250°C. However, directly heating the primary peroxide product of perfluoropolyether is highly dangerous and poses an explosion risk. US3665041 and US4664766 disclose a method for preparing perfluoropolyether oil by reacting a polyether containing reactive end groups (optionally containing peroxy groups) with fluorine gas at a pressure of about 0.2 to 10 atm and a temperature of about 100°C to 350°C. During the fluorination end-capping process, the peroxy groups also decompose. CN103724559B discloses a method for synthesizing perfluoropolyether from perfluoropolyether peroxide. The perfluoropolyether peroxide prepared by photo-oxidation is placed in an inert fluorine-containing solvent, and a perfluoroolefin is introduced under ultraviolet irradiation. After the perfluoroolefin and the peroxide react, a stable perfluoropolyether compound is formed. The reaction continues with the perfluoroolefin under ultraviolet irradiation. The decomposition product obtained by the above method is a perfluoropolyether oil with end-fluorinated end-capping, which is not reactive and has limited application scenarios. CN106317398B discloses a method for decomposing peroxides in perfluoropolyethers. One or more of a metal catalyst, a metal oxide catalyst, and a metal fluoride catalyst are added to a perfluoropolyether product prepared by photo-oxidation, and the peroxides in the perfluoropolyether product are decomposed at 80-150°C. The peroxide value of the perfluoropolyether material used before decomposition is 1-10 × 10⁻⁶. -2While peroxide values ​​within the range of mmol / g are generally considered safe, this method cannot address the decomposition of perfluoropolyether peroxides at higher peroxide values ​​(e.g., 0.5–5 mmol / g). Using raw materials with even higher peroxide values ​​increases the risk of the reaction and necessitates more stringent process control. Therefore, there is an urgent need for a novel method to decompose peroxide groups in perfluoropolyethers. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method and apparatus for decomposing peroxy groups in perfluoropolyethers. This invention can safely and efficiently decompose peroxy groups in perfluoropolyethers, yielding perfluoropolyether products with low peroxide values ​​suitable for subsequent modification. This invention also enables the recycling of materials and the recovery of byproducts. Using supercritical CO2 as a solvent, the perfluoropolyether containing peroxy groups is dissolved and then subjected to ultraviolet irradiation at a relatively low temperature, which can safely and effectively decompose the peroxy groups in the perfluoropolyether. Compared with methods using fluorinated solvents, supercritical CO2 is an environmentally friendly solvent that does not produce any chemical pollution. During the decomposition of peroxy groups, HF and COF2 are generated, the latter rapidly reacting with water to form HF and CO2. This invention utilizes the difference in vaporization temperatures between CO2, HF, and perfluoropolyether, and through process design, achieves the separation of the three substances, recovering the byproduct HF and realizing the recycling of CO2. Simultaneously, the activity of the end groups is maintained during the irradiation process, without affecting subsequent structural modification.

[0005] In a first aspect, the method for decomposing peroxy groups in perfluoropolyethers provided by the present invention includes: 1) Mix perfluoropolyether containing peroxy groups, water and supercritical CO2 to obtain a mixture.

[0006] 2) Irradiate the mixture with ultraviolet light at a temperature of 20~100℃ to obtain the reactant.

[0007] 3) The reactants are separated under reduced pressure to obtain a mixture of carbon dioxide and liquid; the liquid mixture is then evaporated under reduced pressure to obtain hydrofluoric acid and perfluoropolyether; in step 1), the peroxide value of the perfluoropolyether containing peroxide groups is ≥0.5 mmol / g. This invention uses supercritical CO2 as a solvent, which effectively reduces the concentration of peroxide groups in the reaction system by dissolving and dispersing the perfluoropolyether containing peroxide groups, ensuring a stable reaction. Simultaneously, operation at a relatively low temperature of 20~100℃ allows the cooling system to promptly remove the heat of reaction generated during the decomposition of peroxide groups, thus avoiding rapid decomposition of peroxide groups in a short time, resulting in higher safety. Utilizing the difference in vaporization temperatures among perfluoropolyether, CO2, and HF, the process design achieves the separation of the three substances, recovering the byproduct HF and enabling the recycling of CO2. This invention retains the activity of the end groups in the perfluoropolyether, facilitating subsequent end-group modification.

[0008] Preferably, in step 1), the amount of water added is 2% to 20% of the weight of the perfluoropolyether containing peroxy groups, and more preferably 3% to 8%. This is beneficial for absorbing and converting the COF2 generated during the decomposition process into HF and CO2, while avoiding excessive water content that could affect the quality of the perfluoropolyether and subsequent separation.

[0009] Preferably, in step 1), the weight ratio of the supercritical CO2 to the perfluoropolyether containing peroxide groups is 2~20:1, more preferably 4~8:1. This more effectively dissolves and dilutes the peroxide groups and facilitates subsequent processing.

[0010] Preferably, in step 1), the peroxide value of the perfluoropolyether containing peroxide groups is 0.5~5 mmol / g, preferably 2~5 mmol / g, such as 2 mmol / g, 3 mmol / g, 3.2 mmol / g, 3.5 mmol / g, 4 mmol / g, 4.5 mmol / g, 4.8 mmol / g, 5 mmol / g, etc. The method of this invention can more safely and effectively decompose perfluoropolyethers containing peroxide groups, especially showing better treatment effects on perfluoropolyethers with high peroxide values.

[0011] Further preferably, in step 1), the supercritical CO2 is obtained by treating liquid CO2 under conditions of 7.4~40 MPa and ≥31.1℃. This is more conducive to achieving efficient and uniform mixing and improving the reaction effect.

[0012] Preferably, in step 2), the temperature of the ultraviolet irradiation is 20~60℃, more preferably 35~50℃; for example, 35℃, 36℃, 37℃, 38℃, 39℃, 40℃, 41℃, 42℃, 43℃, 44℃, 45℃, 46℃, 47℃, 48℃, 49℃, 50℃, etc. Preferably, the duration of the ultraviolet irradiation is 4~24h; for example, 4h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 20h, 24h, etc. This ensures the peroxide groups remain reactive while avoiding localized overheating.

[0013] Further preferred, in step 2), the ultraviolet light source is selected from one or more of high-pressure mercury lamps, low-pressure mercury lamps, metal halide lamps, deuterium lamps, and ultraviolet LED lamps.

[0014] Preferably, in step 3), the pressure of the decompression separation is 0.5~7.3 MPa and the temperature is -50~80℃.

[0015] Further preferably, in step 3), the pressure of the reduced-pressure evaporation is 0.1~10 MPa, and the temperature is 20~100℃. Using these separation and evaporation conditions can better achieve phase separation.

[0016] Further preferably, step 3) further includes condensing the gaseous CO2 and recycling the condensed liquid CO2; preferably, the hydrofluoric acid is subjected to gas separation and recovery.

[0017] In this invention, the peroxy value (PO) of the perfluoropolyether is ≤0.2 mmol / g. For example, 0.18 mmol / g, 0.15 mmol / g, 0.13 mmol / g, 0.1 mmol / g, etc. Furthermore, the perfluoropolyether retains active end groups such as -COOH, -CF2Cl, etc.

[0018] Secondly, the present invention provides a reaction system for the above method, comprising a CO2 storage tank, a CO2 intermediate tank, a high-pressure pump, a heater, a peroxide decomposition vessel, a first pressure reducing valve, a crude product separator, a second pressure reducing valve, and an HF evaporator connected in sequence, wherein the peroxide decomposition vessel is equipped with an ultraviolet light source; preferably, the crude product separator is connected to the inlet of a cooler, and the outlet of the cooler is connected to the CO2 intermediate tank.

[0019] The beneficial effects of this invention are at least as follows: The supercritical CO2-assisted decomposition method for perfluoropolyethers proposed in this invention solves the problem of high risk during the decomposition of perfluoropolyethers. This method uses supercritical CO2 as a solvent to dissolve and disperse the perfluoropolyether containing peroxy groups, effectively reducing the concentration of peroxy groups in the reaction system. Furthermore, operating at lower temperatures allows the cooling system to promptly remove the heat of reaction generated during the peroxy group decomposition process, thus preventing rapid and short-term decomposition of the peroxy groups and enhancing safety. This method enables the recovery of the byproduct HF, the recycling of CO2, and the preparation of perfluoropolyether products with low peroxide values. In addition, this method preserves the activity of the end groups in the perfluoropolyether, facilitating subsequent end-group modification. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in this 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 some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the supercritical CO2-assisted peroxy group decomposition reaction process in perfluoropolyether provided in an embodiment of the present invention.

[0022] Figure 2 The infrared spectrum of the perfluoropolyether product obtained in Example 1 of this invention is shown. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0024] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0025] Unless otherwise specified, the techniques or conditions described in the literature of this invention shall apply, or the product instructions shall be followed. Devices, instruments, reagents, etc., without specified manufacturers are all conventional products that can be purchased from legitimate channels. In this invention, the peroxy group-containing perfluoropolyether has a peroxide value (PO) of 3.2-4.8 mmol / g, the active end groups include carboxyl groups or acyl fluorides, and the liquid CO2 is commercially available.

[0026] In some embodiments of the present invention, a method for supercritical CO2-assisted decomposition of peroxy groups in perfluoropolyethers, such as... Figure 1As shown, using supercritical CO2 as a solvent, perfluoropolyether peroxides (i.e., perfluoropolyethers containing peroxy groups) are dissolved and then subjected to ultraviolet irradiation at a relatively low temperature (20~100℃), which can safely and effectively decompose the peroxy groups in the perfluoropolyether. During the decomposition of the peroxy groups, HF and COF2, fluorine-containing small molecules, are mainly produced. COF2 reacts with water in the system to generate CO2 and HF. HF and CO2 are separated and recovered through depressurization and cooling operations. The reaction system in this embodiment includes a CO2 storage tank, a CO2 intermediate tank, a high-pressure pump, a heater, a decomposition vessel, a crude product separator, an HF evaporator, a cooler, and a pressure reducing valve. This reaction system uses liquid CO2 as the initial raw material. The CO2 is pressurized by the high-pressure pump to maintain the pressure within the range of 7.4~40 MPa, and then heated by the heater to a temperature ≥31.1℃. At this temperature and pressure, the CO2 is in a supercritical state. Perfluoropolyether containing peroxide groups is added to a peroxide decomposition reactor along with a small amount of water. Supercritical CO2 is then introduced, and the mixture is thoroughly mixed before UV irradiation. The irradiation time depends on the peroxide concentration in the perfluoropolyether. As the peroxide groups decompose, small molecules such as HF and COF2 are generated in the reaction system. COF2 reacts with water to produce CO2 and HF. In the peroxide decomposition reactor, the perfluoropolyether and HF are in a liquid state, while CO2 is in a supercritical state. The material output from the peroxide decomposition reactor is depressurized through pressure reducing valve 1, reducing the pressure to 0.5–7.3 MPa, and then directly enters the crude product separator. Because CO2 vaporizes and absorbs heat during depressurization, the crude product separator can be equipped with a heating device to maintain the temperature between -50 and 80°C as needed. After depressurization, CO2 is gaseous, while HF and perfluoropolyether are liquid, thus achieving the separation of CO2, HF, and perfluoropolyether. The HF and perfluoropolyether liquid mixture passes through pressure reducing valve 2, reducing the pressure to 0.1~10 MPa, and enters the HF evaporator. The evaporator temperature is maintained within the range of 20~100℃. Under this temperature and pressure, HF turns into gas and escapes, while the perfluoropolyether product remains liquid, further achieving the separation of perfluoropolyether and HF. The CO2 gas exiting the crude product separator is cooled to -40~25℃ by a cooler. During the cooling process, the CO2 condenses into liquid and returns to the CO2 intermediate tank to continue the next cycle. In a preferred embodiment, the above process can be intermittent or continuous operation; the CO2 stored in the CO2 storage tank and CO2 intermediate tank is in a liquid state, with a pressure of 0.5~50 MPa and a temperature of -40~30℃.The aforementioned peroxide decomposition vessel maintains a CO2 to perfluoropolyether peroxide weight ratio of 2-20, and the amount of water added is 2%-20% of the weight of the perfluoropolyether peroxide. The material of the parts of the equipment in contact with the material includes, but is not limited to, graphite, alloy steel, polytetrafluoroethylene (PTFE), and steel-lined PTFE. The ultraviolet light source includes, but is not limited to, high-pressure mercury lamps, low-pressure mercury lamps, metal halide lamps, deuterium lamps, and ultraviolet LED lamps. The material residence time in the peroxide decomposition vessel is 4-24 hours. The supercritical CO2-assisted decomposition method for peroxy groups in perfluoropolyether provided in this invention uses supercritical CO2 as a solvent to dissolve the perfluoropolyether containing peroxy groups, followed by ultraviolet irradiation at a relatively low temperature, which can safely and effectively decompose the peroxy groups in the perfluoropolyether. During the decomposition of peroxy groups, HF and COF2 are generated, and the latter rapidly generates HF and CO2 upon contact with water. By reducing pressure and cooling, CO2, HF and perfluoropolyether were separated, thus recovering the byproduct HF and recycling CO2.

[0027] Example 1 10.0 kg of perfluoropolyether containing peroxide groups (peroxide value PO = 3.2 mmol / g, active end group is carboxyl) and 500 g of water were added to the peroxide decomposition reactor. 50 kg of liquid CO2 was pressurized to 15.0 MPa using a high-pressure pump and then heated to 41°C using a heater to achieve a supercritical state. The supercritical CO2 was then fed into the peroxide decomposition reactor, mixed thoroughly with the materials, and subjected to ultraviolet irradiation using a low-pressure mercury lamp for 8 hours.

[0028] As the peroxide groups decompose, small molecule gaseous substances such as HF and COF2 are generated in the reaction system. Due to the presence of a small amount of water in the decomposition vessel, COF2 rapidly hydrolyzes to generate CO2 and HF. The material output from the peroxide decomposition vessel is a mixed liquid of HF, CO2, and perfluoropolyether. After being depressurized by pressure reducing valve 1 to 5.0 MPa, it flows into the crude product separator. At this point, the separation temperature is maintained at 30°C, thus obtaining a liquid mixture (HF and perfluoropolyether) and gaseous CO2. The gaseous CO2 is cooled to -15°C by a cooler and returned to the CO2 intermediate tank in liquid form. The liquid mixture passes through pressure reducing valve 2, and the pressure is reduced to atmospheric pressure of 0.1 MPa before entering the HF evaporator. At 0.1 MPa, the vaporization temperature of HF is 19°C. The evaporator temperature is maintained at 45°C, and the gaseous HF is collected, weighing 450g. The liquid phase is a perfluoropolyether product with low peroxide group content, and the PO content is determined by iodometric titration to be 0.15 mmol / g. The terminal group is a carboxyl group, and the infrared spectrum shows a value at 1780 cm⁻¹. -1 The carbonyl group shows a visible peak. (See...) Figure 2 .

[0029] Example 2 10 kg of perfluoropolyether containing peroxide groups (peroxide value PO = 4.8 mmol / g, active end group is carboxyl) and 580 g of water were added to the peroxide decomposition reactor. 50 kg of liquid CO2 was pressurized to 16 MPa using a high-pressure pump and then heated to 50°C using a heater to achieve a supercritical state. The supercritical CO2 was then fed into the peroxide decomposition reactor, mixed thoroughly with the materials, and subjected to ultraviolet irradiation using a low-pressure mercury lamp for 8 hours.

[0030] As the peroxide groups decompose, small molecule gaseous substances such as HF and COF2 are generated in the reaction system. Due to the presence of a small amount of water in the decomposition vessel, COF2 rapidly hydrolyzes to generate CO2 and HF. The material output from the peroxide decomposition vessel is a mixed liquid of HF, CO2, and perfluoropolyether. After being depressurized by pressure reducing valve 1 to 5 MPa, it flows into the crude product separator. At this point, the separation temperature is maintained at 25 °C, thus obtaining a liquid mixture (HF and perfluoropolyether) and gaseous CO2. The gaseous CO2 is cooled to -15 °C by a cooler and returned to the CO2 intermediate tank in liquid form. The liquid mixture passes through pressure reducing valve 2, and the pressure is reduced to atmospheric pressure of 0.1 MPa before entering the HF evaporator. At 0.1 MPa, the vaporization temperature of HF is 19 °C. The evaporator temperature is maintained at 45 °C, and the gaseous HF is collected, weighing 520 g. The liquid phase is a perfluoropolyether product with low peroxide group content, and the PO value is determined by iodometric titration to be 0.18 mmol / g. The terminal group is a carboxyl group. The carbonyl peak is visible in the infrared spectrum.

[0031] Example 3 10 kg of perfluoropolyether containing peroxide groups (peroxide value PO = 3.2 mmol / g, active end group is carboxyl) and 500 g of water were added to the peroxide decomposition reactor. 50 kg of liquid CO2 was pressurized to 15 MPa using a high-pressure pump and then heated to 41 °C using a heater to achieve a supercritical state. The supercritical CO2 was then fed into the peroxide decomposition reactor, mixed thoroughly with the materials, and subjected to ultraviolet irradiation using a low-pressure mercury lamp for 18 h.

[0032] As the peroxide groups decompose, small molecule gaseous substances such as HF and COF2 are generated in the reaction system. Due to the presence of a small amount of water in the decomposition vessel, COF2 rapidly hydrolyzes to generate CO2 and HF. The material output from the peroxide decomposition vessel is a mixed liquid of HF, CO2, and perfluoropolyether. After being depressurized by pressure reducing valve 1 to 6 MPa, it flows into the crude product separator. At this point, the separation temperature is maintained at 30 °C, thus obtaining a liquid mixture (HF and perfluoropolyether) and gaseous CO2. The gaseous CO2 is cooled to -15 °C by a cooler and returned to the CO2 intermediate tank in liquid form. The liquid mixture passes through pressure reducing valve 2, and the pressure is reduced to atmospheric pressure of 0.1 MPa before entering the HF evaporator. At 0.1 MPa, the vaporization temperature of HF is 19 °C. The evaporator temperature is maintained at 45 °C, and the gaseous HF is collected, weighing 470 g. The liquid phase is a perfluoropolyether product with low peroxide group content, and the PO content is determined by iodometric titration to be 0.05 mmol / g. The terminal group is a carboxyl group, and the carbonyl peak can be seen in the infrared spectrum.

[0033] Example 4 10 kg of perfluoropolyether containing peroxide groups (peroxide value PO = 3.2 mmol / g, active end group is carboxyl) and 500 g of water were added to the peroxide decomposition reactor. 150 kg of liquid CO2 was pressurized to 15 MPa using a high-pressure pump and then heated to 41°C using a heater to achieve a supercritical state. The supercritical CO2 was then fed into the peroxide decomposition reactor, mixed thoroughly with the materials, and subjected to ultraviolet irradiation using a low-pressure mercury lamp for 12 hours.

[0034] As the peroxide groups decompose, small gaseous substances such as HF and COF2 are generated in the reaction system. Due to the presence of a small amount of water in the decomposition vessel, COF2 rapidly hydrolyzes to generate CO2 and HF. The material output from the peroxide decomposition vessel is a mixed liquid of HF, CO2, and perfluoropolyether. After being depressurized by pressure reducing valve 1 to 6 MPa, it flows into the crude product separator. At this point, the separation temperature is maintained at 30°C, thus obtaining a liquid mixture (HF and perfluoropolyether) and gaseous CO2. The gaseous CO2 is cooled to -15°C by a cooler and returned to the CO2 intermediate tank in liquid form. The liquid mixture passes through pressure reducing valve 2, and the pressure is reduced to atmospheric pressure of 0.1 MPa before entering the HF evaporator. At 0.1 MPa, the vaporization temperature of HF is 19°C. The evaporator temperature is maintained at 45°C, and the gaseous HF is collected, weighing 465g. The liquid phase is a perfluoropolyether product with low peroxide group content, and the PO content is determined by iodometric titration to be 0.03 mmol / g. The terminal group is a carboxyl group, and the carbonyl peak can be seen in the infrared spectrum.

[0035] Example 5 10 kg of perfluorinated polyether containing peroxide groups (peroxide value PO = 3.2 mmol / g, active end group is acyl fluoride) and 600 g of water were added to the peroxide decomposition reactor. 50 kg of liquid CO2 was pressurized to 15 MPa using a high-pressure pump and then heated to 41°C using a heater to achieve a supercritical state. The supercritical CO2 was then fed into the peroxide decomposition reactor, mixed thoroughly with the materials, and subjected to ultraviolet irradiation using a metal halide lamp for 12 hours.

[0036] As the peroxide groups decompose, small molecule gaseous substances such as HF and COF2 are generated in the reaction system. Due to the presence of a small amount of water in the decomposition vessel, COF2 rapidly hydrolyzes to generate CO2 and HF. The material output from the peroxide decomposition vessel is a mixed liquid of HF, CO2, and perfluoropolyether. After being depressurized by pressure reducing valve 1 to 6 MPa, it flows into the crude product separator. At this point, the separation temperature is maintained at 40 °C, thus obtaining a liquid mixture (HF and perfluoropolyether) and gaseous CO2. The gaseous CO2 is cooled to -25 °C by a cooler and returned to the CO2 intermediate tank in liquid form. The liquid mixture passes through pressure reducing valve 2, and the pressure is reduced to atmospheric pressure of 0.1 MPa before entering the HF evaporator. At 0.1 MPa, the vaporization temperature of HF is 19 °C. The evaporator temperature is maintained at 45 °C, and the gaseous HF is collected, weighing 585 g. The liquid phase is a perfluoropolyether product with low peroxide group content, and the PO content is determined by iodometric titration to be 0.13 mmol / g. Because the system contains water, the acyl fluoride is converted into a carboxyl group, and the terminal group is a carboxyl group, which can be seen as a carbonyl peak in the infrared spectrum.

[0037] Comparative Example 1 In this comparative example, 10 kg of perfluoropolyether containing peroxy groups (peroxy value PO = 3.2 mmol / g, active end group is carboxylic acid) was placed in a photochemical reaction vessel. The photochemical reaction vessel was irradiated with a low-pressure mercury lamp. The temperature inside the vessel was maintained at 41 ℃. The reaction was carried out with stirring for 12 h. After the reaction was completed, the PO value was determined by iodometric titration to be 1.95 mmol / g.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for decomposing peroxy groups in perfluoropolyethers, characterized in that, include: 1) Mix perfluoropolyether containing peroxy groups, water, and supercritical CO2 to obtain a mixture; 2) The mixture is irradiated with ultraviolet light at a temperature of 20~100℃ to obtain the reactant; 3) The reactants are separated under reduced pressure to obtain a mixture of carbon dioxide and liquid; the liquid mixture is evaporated under reduced pressure to obtain hydrofluoric acid and perfluoropolyether; in step 1), the peroxide value of the perfluoropolyether containing peroxy groups is ≥0.5 mmol / g.

2. The method according to claim 1, characterized in that, In step 1), the amount of water added is 2% to 20% of the weight of the perfluoropolyether containing peroxy groups, preferably 3% to 8%.

3. The method according to claim 1 or 2, characterized in that, In step 1), the weight ratio of supercritical CO2 to perfluoropolyether containing peroxy groups is 2~20:1, preferably 4~8:

1.

4. The method according to claim 3, characterized in that, In step 1), the peroxy value of the perfluoropolyether containing peroxy groups is 0.5~5 mmol / g.

5. The method according to any one of claims 1-4, characterized in that, In step 2), the temperature of the ultraviolet irradiation is 20~60℃; and / or, the duration of the ultraviolet irradiation is 4~24h.

6. The method according to claim 5, characterized in that, In step 2), the ultraviolet light source is selected from one or more of high-pressure mercury lamps, low-pressure mercury lamps, metal halide lamps, deuterium lamps, and ultraviolet LED lamps.

7. The method according to any one of claims 1-6, characterized in that, In step 3), the pressure of the pressure reduction separation is 0.5~7.3 MPa and the temperature is -50~80℃.

8. The method according to any one of claims 1-7, characterized in that, In step 3), the pressure of the reduced pressure evaporation is 0.1~10 MPa and the temperature is 20~100℃.

9. The method according to any one of claims 1-8, characterized in that, Step 3) further includes condensing the gaseous CO2 and recycling the condensed liquid CO2; and / or performing gas separation and recovery of the hydrofluoric acid.

10. The reaction system of the method according to any one of claims 1-9, characterized in that, The system includes a CO2 storage tank, a CO2 intermediate tank, a high-pressure pump, a heater, a peroxide decomposition vessel, a first pressure reducing valve, a crude product separator, a second pressure reducing valve, and an HF evaporator connected in sequence. The peroxide decomposition vessel is equipped with an ultraviolet light source. Preferably, the crude product separator is connected to the inlet of a cooler, and the outlet of the cooler is connected to the CO2 intermediate tank.

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