Method for fluorinating end group of perfluoropolyether

Abstract

The invention belongs to the field of fluorine chemical synthesis, and particularly relates to a perfluoropolyether end group fluorination method, which comprises the following steps of: contacting non-inert perfluoropolyether with aluminum oxide, and introducing fluorine-containing inert mixed gas to carry out fluorination treatment at 50-150 DEG C; the volume fraction of fluorine gas in the fluorine-containing inert mixed gas is 5-50%, and the acid value of the obtained product is smaller than or equal to 10 mgKOH / g. According to the method disclosed by the invention, the non-inert perfluoropolyether end group can be selectively converted into the inert end group under a low-temperature condition by utilizing the synergy of the aluminum oxide and the diluted fluorine gas, so that the residual peroxide is low, and the stability is improved. Compared with a high-temperature or ultraviolet induction route, the method has the advantages that the temperature and the fluorine gas consumption are obviously reduced, the cracking side reaction is inhibited, the yield and the appearance quality are improved, equipment is more simplified and safer, and the continuity feasibility is better.

Description

Technical Field

[0001] This invention belongs to the field of fluorochemical synthesis, specifically relating to a method for fluorinating the end groups of perfluoropolyethers. Background Technology

[0002] Perfluoropolyethers possess excellent high and low temperature stability, chemical inertness, low surface tension, radiation resistance, and insulation and lubrication properties, making them widely used in high-end applications such as high vacuum pump oils, lubricants, insulating fluids, heat transfer fluids, and coolants. Industrially produced perfluoropolyethers are commonly classified into four main types based on their main chain backbone: the K-type obtained by ring-opening polymerization of hexafluoropropylene oxide, the Y-type obtained by photo-oxidation of hexafluoropropylene with oxygen, the Z-type obtained by oxidation of tetrafluoroethylene with oxygen, and the D-type obtained by anionic ring-opening polymerization of tetrafluorooxoheterocyclic butane followed by post-treatment.

[0003] The polyethers mentioned above typically contain active end groups such as acyl fluoride or carboxyl groups at the end of polymerization. While this facilitates subsequent derivatization, for applications such as vacuum pump oil and inert media, the end groups need to be thoroughly fluorinated to reduce acid value and residual reactivity. There are two main existing inertization routes: one is high-temperature gas-phase fluorination, which often requires temperatures ≥200℃ and a high volume fraction of fluorine gas, easily triggering cracking side reactions, resulting in low yields and darkening of color; the other is ultraviolet-induced fluorination, which can be carried out at lower temperatures, but the light source and casing are prone to corrosion and breakage in the fluorine gas and fluorine-containing byproduct environment, posing complex equipment requirements and safety hazards.

[0004] Therefore, there is an urgent need for a process that can still achieve high selectivity inertization of end groups and maintain high yield at lower temperatures and lower fluorine gas integrals. Summary of the Invention

[0005] To address the technical deficiencies of existing technologies, this invention provides a method for fluorinating the end groups of perfluoropolyethers, comprising: contacting uninertized perfluoropolyethers with alumina, introducing a fluorinated inert gas mixture and performing fluorination treatment at 50-150°C; subsequently purging with an inert gas and separating the solid to obtain an inert perfluoropolyether, wherein the volume fraction of fluorine in the fluorinated inert gas mixture is 5-50%, and the acid value of the obtained product is ≤10mgKOH / g.

[0006] Preferably, the volume fraction of fluorine in the fluorine-containing inert gas mixture is 20-30%, and the acid value of the resulting product is ≤6 mgKOH / g.

[0007] Preferably, the total gas flow rate for the fluorination process is 1-5 L / h, and the gas is continuously introduced for 24-96 h.

[0008] Preferably, the fluorine-containing inert gas mixture is a fluorine / nitrogen mixture.

[0009] Preferably, the alumina is γ-alumina with a specific surface area of ​​80-500 m².2 / g.

[0010] Preferably, the amount of γ-alumina added is 1-10 wt% of the mass of the uninertized perfluoropolyether. More preferably, it is 2-5 wt%.

[0011] Preferably, the fluorination treatment is carried out at 60-120℃, and more preferably, at 70-90℃.

[0012] Preferably, the non-inertized perfluoropolyether is selected from at least one of type K, type Y, type Z or type D or a mixture thereof, and has a number average molecular weight of 500-2000 g / mol.

[0013] Preferably, the uninertized perfluoropolyether has end groups containing acyl fluoride -COF and / or carboxyl group -COOH, and the main chain contains at least one repeating unit of -CF2-O-, -CF2-CF2-O- or -CF(CF3)-CF3-O-.

[0014] Preferably, the uninertized perfluoropolyether is an uninertized K-type perfluoropolyether with the structure F-[-CF(CF3)-CF2-O-]n-CF(CF3)-COF, where n represents the molecular chain length of the polymer, n=1-10, and the number average molecular weight is 500-2000 g / mol. The end groups are acyl fluoride (-COF) and / or carboxyl groups (-COOH).

[0015] Preferably, the uninertized perfluoropolyether is fractionated and collected at 100-300℃ before fluorination.

[0016] Preferably, the yield of the obtained product is ≥70%.

[0017] Preferably, the reaction vessel is made of Monel alloy and is equipped with a tail gas alkaline washing and activated carbon adsorption device.

[0018] Preferably, the inert gas purging flow rate is 2-6 L / h, and the purging time is 4-12 h.

[0019] Preferably, a method for fluorinating the end groups of a perfluoropolyether includes: contacting an uninertized perfluoropolyether with alumina and a metal fluoride, and subjecting the fluorination treatment to a fluorinated inert gas mixture at 50-150°C; subsequently purging with an inert gas and separating the solid to obtain an inert perfluoropolyether, wherein the volume fraction of fluorine in the fluorinated inert gas mixture is 5-50%, and the acid value of the obtained product is ≤10 mgKOH / g; wherein the metal fluoride is at least one of cesium fluoride and silver fluoride. The particle size D90 of cesium fluoride and silver fluoride is 10-100 μm.

[0020] Preferably, the total amount of γ-alumina and metal fluoride added is 1-10 wt% of the mass of the uninertized perfluoropolyether; the mass ratio of γ-alumina to metal fluoride is 1:9-9:1, preferably 3:7-7:3, and more preferably 1:1.

[0021] In this process, γ-alumina undergoes rapid in-situ fluorination at its surface under an F2 / HF / COF2 atmosphere, generating a high Lewis acidic active surface composed of an AlF3 phase and residual Al-O sites. This surface, on the one hand, heterogeneously polarizes and synergistically cleaves F2 at Al-F / Al-O sites, producing more electrophilic activated fluorine species. This allows the terminal R-COF (or R-COOH after in-situ conversion to acyl fluoride) to be directionally converted to R-CF3 at lower temperatures, releasing COF2. On the other hand, Al-F forms a strong interaction with HF, and the Al-O sites trap trace amounts of water and polar impurities, thereby reducing the effective acidity and the probability of side reactions, significantly inhibiting main chain β-cleavage and color increase, and stabilizing viscosity. Appropriate specific surface area and dosage ensure a balance between active site density and adsorption capacity. The above description is for illustrative purposes only and does not limit the mechanism of this invention.

[0022] This invention utilizes the synergistic effect of alumina and diluted fluorine gas to achieve selective fluorination of the end groups of non-inert perfluoropolyethers under low-temperature conditions, significantly reducing residual peroxide and improving thermal oxidation and chemical stability. Compared to high-temperature or UV-induced processes, this method reduces fluorine gas consumption and energy consumption while suppressing cracking side reactions, improving yield and appearance quality. It also simplifies equipment, enhances safety, and facilitates continuous scale-up, making it suitable for applications in vacuum pump oils, lubricants, and insulating fluids. Attached Figure Description

[0023] The accompanying drawings are provided to more clearly illustrate the technical solutions in the embodiments of this application. The drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The IR spectrum of perfluoropolyether before fluorination;

[0025] Figure 2 The image shows the IR spectrum of the perfluoropolyether after fluorination in Example 1. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0027] Raw material: Uninertized K-type perfluoropolyether (HFPO ring-opening polymerization), example structure F-[-CF(CF3)-CF2-O-]4-CF(CF3)-COF, with a number average molecular weight of 1250 g / mol. The end group is acyl fluoride (-COF).

[0028] Both cesium fluoride and silver fluoride have a particle size D90 of 50 μm.

[0029] Example 1:

[0030] Take 300g of uninertized K-type perfluoropolyether and place it in a 2L Monel alloy miniature autoclave; add 150m² of specific surface area... 2 10 g of γ-alumina was stirred at room temperature for 30 min to ensure uniform dispersion. The mixture was then heated to 70 °C and kept at a constant temperature. A 25% (v / v) F2 / nitrogen mixture was continuously introduced at a total flow rate of 3 L / h for 48 h. Subsequently, nitrogen was used for purging at a flow rate of 4 L / h for 8 h, followed by cooling to room temperature. After depressurization, the solid was removed by filtration, yielding 225 g of product, with a yield of 75.2%. The acid value was determined to be 5 mg KOH / g.

[0031] Figure 1 The characteristic absorption peaks of the acyl fluoride group -COF and carboxyl group -COOH in the uninertized perfluoropolyether were observed. Figure 2 This indicates that the fluorinated end group is transformed into an inert end group such as -CF3, the absorption peak of the acyl fluoride group is significantly weakened or disappears, and a new CF vibration feature appears, indicating that the fluorination reaction is successful.

[0032] Example 2:

[0033] The difference from Example 1 is 3g of γ-alumina.

[0034] Example 3:

[0035] The difference from Example 1 is that the specific surface area of ​​γ-alumina is 50 m². 2 / g.

[0036] Example 4:

[0037] The difference from Example 1 is that the specific surface area of ​​γ-alumina is 300 m². 2 / g.

[0038] Example 5:

[0039] The difference from Example 1 is that the specific surface area of ​​γ-alumina is 500 m². 2 / g.

[0040] Example 6:

[0041] The difference from Example 1 is that the temperature is raised to 140°C and kept constant.

[0042] Example 7:

[0043] Take 300g of uninertized K-type perfluoropolyether and place it in a 2L Monel alloy miniature autoclave; add 150m² of specific surface area... 2 5g of γ-alumina and 5g of cesium fluoride were mixed at room temperature and stirred for 30 minutes to ensure uniform dispersion. The mixture was then heated to 70°C and kept at a constant temperature. A 25% (v / v) F2 / nitrogen mixture was continuously introduced at a total flow rate of 3L / h for 48 hours. Subsequently, the mixture was purged with nitrogen at a flow rate of 4L / h for 8 hours, and then cooled to room temperature. After depressurization, the solids were removed by filtration to obtain the product.

[0044] Example 8:

[0045] Take 300g of uninertized K-type perfluoropolyether and place it in a 2L Monel alloy miniature autoclave; add 150m² of specific surface area... 2 5g of γ-alumina and 5g of silver fluoride were mixed at room temperature and stirred for 30 minutes to ensure uniform dispersion. The mixture was then heated to 70°C and kept at a constant temperature. A 25% (v / v) F2 / nitrogen mixture was continuously introduced at a total flow rate of 3L / h for 48 hours. Subsequently, nitrogen was used to purge at a flow rate of 4L / h for 8 hours, and the mixture was cooled to room temperature. After depressurization, the solids were removed by filtration to obtain the product.

[0046] Comparative Example 1:

[0047] The difference from Example 1 is that γ-alumina is not added. Specifically, 300g of uninertized K-type perfluoropolyether was placed in a 2L Monel alloy miniature autoclave. The temperature was raised to 70°C and kept constant. A 25% (v / v) F2 / nitrogen mixture was continuously introduced at a total flow rate of 3L / h for 48h. Then, nitrogen was used for purging at a rate of 4L / h for 8h, and the mixture was cooled to room temperature. After depressurization, the solids were removed by filtration. The end-group inert perfluoropolyether of this invention could not be obtained.

[0048] Comparative Example 2:

[0049] The difference from Example 1 is that γ-alumina is not added. Specifically, 300g of uninertized K-type perfluoropolyether is placed in a 2L Monel alloy miniature autoclave. The temperature is raised to 200℃ and kept constant. A 25% (v / v) F2 / nitrogen mixture is continuously introduced at a total flow rate of 3L / h for 48h. Then, nitrogen is switched to purge at a rate of 4L / h for 8h, and the temperature is lowered to room temperature. After depressurization, the solids are removed by filtration.

[0050] Comparative Example 3:

[0051] Take 300g of uninertized K-type perfluoropolyether and place it in a 2L Monel alloy miniature autoclave; add 10g of silver fluoride and stir at room temperature for 30min to disperse it evenly. Heat to 70℃ and maintain a constant temperature, then continuously purge with a 25% (v / v) F2 / nitrogen mixture at a total flow rate of 3L / h for 48h. Subsequently, switch to nitrogen at a flow rate of 4L / h for purging for 8h, and then cool to room temperature. After depressurization, filter to remove solids to obtain the product.

[0052] Comparative Example 4:

[0053] Take 300g of uninertized K-type perfluoropolyether and place it in a 2L Monel alloy miniature autoclave; add 10g of cesium fluoride and stir at room temperature for 30min to disperse it evenly. Heat to 70℃ and maintain a constant temperature, then continuously purge with a 25% (v / v) F2 / nitrogen mixture at a total flow rate of 3L / h for 48h. Subsequently, switch to nitrogen at a flow rate of 4L / h for purging for 8h, and then cool to room temperature. After depressurization, filter to remove solids to obtain the product.

[0054] Test Example 1:

[0055] Yield, % Acid value, mgKOH / g Example 1 75.2 5.0 Example 2 73.5 5.3 Example 3 72.0 5.5 Example 4 71.1 4.8 Example 5 70.4 4.0 Example 6 68.1 4.0 Example 7 77.8 4.9 Example 8 70.4 8.4 Comparative Example 1 78.2 ＞20 Comparative Example 2 0.5 9.5 Comparative Example 3 74.1 11.9 Comparative Example 4 73.8 10.5

[0056] Upon introduction of γ-alumina, in-situ fluorination occurs on its surface in an F2 / HF / COF2 atmosphere, forming a heterogeneous active layer dominated by the AlF3 phase and retaining some Al-O sites. This active layer can activate and polarize the F2 surface, lowering the energy barrier for end-group reactions, thereby promoting the selective conversion of -COF / -COOH end groups into inert end groups at lower temperatures. Simultaneously, Al-F sites form strong interactions with HF, and Al-O sites adsorb and buffer trace amounts of water and polar byproducts, reducing the effective acidity and polar interference of the system, inhibiting main chain cleavage, and improving appearance and viscosity stability. This effect is highly sensitive to the contrast surface area and dosage: insufficient dosage results in a low active site density and limited end-group conversion; excessive dosage leads to retention of acidic byproducts, increased filtration losses, and slight degradation due to excessive adsorption and limited mass transfer; under conditions where alumina is not used at all, low-temperature dilution fluorination cannot simultaneously achieve complete inertization of end groups and maintenance of main chain integrity.

[0057] Comparative Examples 3 and 4 show that both silver fluoride and cesium fluoride, as auxiliaries, can provide usable fluorinated reactive species and establish an ionic reaction environment. Cesium fluoride exhibits weak polarization and mild coordination, readily forming a stable fluoride-hydrogen salt phase with hydrogen fluoride, thereby reducing free acidity and facilitating the directional conversion of end groups. Silver fluoride is more reactive, accelerating end group consumption, but its main-chain selectivity and byproduct process control are relatively insufficient. Compared to systems using γ-alumina, the use of these salts alone generally results in weaker acid value control and overall quality.

[0058] In Example 6, the temperature was as high as 140°C, which made it easy for the material to escape and resulted in a lower yield.

[0059] In Example 7, γ-alumina forms an active surface dominated by aluminum fluoride in situ under a fluorine-containing atmosphere. This surface can mildly activate fluorine gas and adsorb hydrogen fluoride, trace water, and polar byproducts, thereby stabilizing the reaction microenvironment. Cesium fluoride provides mild ion regulation and acidity buffering, further reducing the peak values ​​of acidic and polar disturbances. The complementary functions of these two components simultaneously enhance end-group conversion and selectivity, while maintaining high main-chain integrity and good appearance and viscosity stability, exhibiting a reproducible synergistic effect. In contrast, the high activity and potential coordination or oxidation processes introduced by silver fluoride in Example 8 weaken the adsorption and buffering advantages of γ-alumina, leading to increased pressure from side reactions and residue management.

[0060] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for fluorinating the end groups of a perfluoropolyether, characterized in that, include: Uninertized perfluoropolyether is brought into contact with alumina, and a fluorinated inert gas mixture is introduced to perform fluorination treatment at 50-150℃. The solid was then purged with an inert gas and separated to obtain an inert perfluoropolyether.

2. The method for fluorination of end groups of perfluoropolyether as described in claim 1, characterized in that, The volume fraction of fluorine in the fluorine-containing inert gas mixture is 5-50%, and the acid value of the resulting product is ≤10mgKOH / g.

3. The method for fluorination of end groups of perfluoropolyether as described in claim 1, characterized in that, The volume fraction of fluorine in the fluorine-containing inert gas mixture is 20-30%, and the acid value of the resulting product is ≤6 mgKOH / g.

4. The method for fluorination of end groups of perfluoropolyether as described in claim 1, characterized in that, The total gas flow rate for the fluorination process is 1-5 L / h, and it is continuously introduced for 24-96 hours.

5. The method for fluorination of end groups of perfluoropolyether as described in claim 1, characterized in that, The fluorine-containing inert gas mixture is a fluorine / nitrogen mixture.

6. The method for fluorination of end groups of perfluoropolyether as described in claim 1, characterized in that, The alumina is γ-alumina with a specific surface area of ​​80-500 m². 2 / g, wherein the amount of γ-alumina added is 1-10wt% of the mass of the uninertized perfluoropolyether.

7. The method for fluorination of end groups of perfluoropolyether as described in claim 1, characterized in that, Fluorination is carried out at 60-120℃.

8. The method for fluorination of end groups of perfluoropolyether as described in claim 1, characterized in that, The uninertized perfluoropolyether has end groups containing acyl fluoride -COF and / or carboxyl group -COOH, and the main chain contains at least one repeating unit of -CF2-O-, -CF2-CF2-O- or -CF(CF3)-CF3-O-.

9. The method for fluorination of end groups of perfluoropolyether as described in claim 1, characterized in that, The inert gas purging flow rate is 2-6 L / h, and the purging time is 4-12 h.

10. The method for fluorinating the end groups of a perfluoropolyether as described in any one of claims 1-9, characterized in that, Uninertized perfluoropolyether is contacted with alumina and metal fluorides, and fluorinated with a fluorinated inert gas mixture at 50-150°C. Subsequently, the solid is purged with an inert gas and separated to obtain inert perfluoropolyether, wherein the volume fraction of fluorine in the fluorinated inert gas mixture is 5-50%, and the acid value of the obtained product is ≤10mgKOH / g.

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