A method for preparing high-purity perfluoropolyether carboxylic acid emulsifier

Abstract

The present invention discloses a method for preparing a high-purity perfluoropolyether carboxylic acid emulsifier, comprising the following steps: (a) Preparation of a catalyst: mixing a certain amount of potassium fluoride and aluminum oxide in deionized water, stirring, filtering, drying, grinding, activating the obtained powder to obtain an aluminum oxide-loaded potassium fluoride catalyst, and storing it in a vacuum dryer for standby use. (b) Synthesis of 7-carbon fluorocarboxylic acid fluoride: reacting carbonyl fluoride and hexafluoropropylene oxide in an organic solvent with the aluminum oxide-loaded potassium fluoride catalyst obtained in step (a) in a reactor to obtain a reaction solution containing 7-carbon fluorocarboxylic acid fluoride. (c) Refining of 7-carbon fluorocarboxylic acid fluoride. (d) Synthesis of 7-carbon fluorocarboxylic acid. (e) Refining of 7-carbon fluorocarboxylic acid.

Description

Technical Field

[0001] The invention relates to the field of synthesis of fluorine-containing fine chemicals, and in particular to a method for preparing a high-purity perfluoropolyether carboxylic acid emulsifier. Background Art

[0002] Fluorinated surfactants are surfactants with fluorinated carbon chains as non-polar groups, that is, fluorine atoms partially or completely replace hydrogen atoms on hydrocarbon chains. Perfluorooctanoic acid (PFOA) and its salts (such as ammonium salt, sodium salt) and perfluorooctane sulfonate (PFOS) are the most widely used varieties of fluorinated surfactants. However, this type of compound has been proven to be one of the most difficult to degrade organic pollutants known in the world, and this type of substance has been proven to be harmful to the human body. Therefore, research and development of low-toxic or even non-toxic, non-bioaccumulative fluorinated surfactants to replace PFOA has become a hot topic in the industry.

[0003] In order to improve the biodegradability of fluorinated surfactants, introducing ether bonds and methylene or similar groups into the fluorocarbon straight chain to modify the fluorocarbon chain structure is an important direction for the research and development of PFOA substitutes. 2,3,3,3-tetrafluoro-2-[1,1,2,3,3,3-hexafluoro-2-(trifluoromethoxy)propoxy]propionic acid, CAS No: 2479-73-4, chemical formula: CF30CF(CF3)CF20CF(CF3)C00H (hereinafter referred to as "7-carbon fluorocarboxylic acid"), because the fluorocarbon chain of this compound contains oxygen atoms, it is not a perfluorocarbon compound (PTC), and has the advantages of easy degradation in the body and environmental friendliness. At the same time, it has good dispersibility in aqueous solution and can be used as a dispersant in the polymerization reaction of fluorinated monomers. The 7-carbon fluorocarboxylic acid can be firstly prepared by reacting carbonyl fluoride and hexafluoropropylene oxide in a polar aprotic solvent to obtain 2,3,3,3-tetrafluoro-2-(1,1,2,3,3,3-hexafluoro-2-(trifluoromethoxy)propoxy)propionyl fluoride (chemical formula: CF30CF(CF3)CF20CF(CF3)COF, referred to herein as "7-carbon fluorocarboxylic acid fluoride"), and then obtained by hydrolysis of the 7-carbon fluorocarboxylic acid fluoride.

[0004] Patent WO2013 / 051565A1 reports a method for preparing 7-carbon fluorocarboxylic acid fluoride using carbonyl fluoride and hexafluoropropylene oxide as raw materials, using bis(dialkylamino)methane (general formula: R1R2N-CH2-NR3R4, wherein each of R1, R2, R3 and R4 is independently selected from methyl, ethyl, n-propyl and n-butyl) as a catalyst, but the selectivity of 7-carbon fluorocarboxylic acid fluoride is only 40.74%. PCT application document WO2010 / 038902A1 proposes using alkali metal fluoride (KF or CsF) as a main catalyst and tetramethyl urea as a co-catalyst, and carbonyl fluoride and hexafluoropropylene oxide react in a polar aprotic solvent to obtain 7-carbon fluorocarboxylic acid fluoride. Under the best reaction conditions, the selectivity of 7-carbon fluorocarboxylic acid fluoride is only 61.6%; then the 7-carbon fluorocarboxylic acid fluoride is hydrolyzed, washed (in order of water washing, 5% sulfuric acid washing, 10% sulfuric acid washing, concentrated sulfuric acid washing), and finally distilled under reduced pressure to obtain 7-carbon fluorocarboxylic acid. The method reported in the patent has the following problems: low selectivity of 7-carbon fluorocarboxylic acid fluoride; too long post-treatment process; low single-pot utilization; and harsh conditions for the synthesis of the co-catalyst tetramethylurea. At present, there is no patent in China that publicly reports a method for synthesizing 7-carbon fluorocarboxylic acid fluoride using carbonyl fluoride and hexafluoropropylene oxide as raw materials.

[0005] Therefore, for the preparation of 2,3,3,3-tetrafluoro-2-[1,1,2,3,3,3-hexafluoro-2-(trifluoromethoxy)propoxy]propionyl fluoride using carbonyl fluoride and hexafluoropropylene oxide as raw materials, it is still necessary to find a catalyst with high catalytic activity and low price to improve the selectivity of 7-carbon fluorocarboxylic acid fluoride. Developing a process route for the synthesis of 7-carbon fluorocarboxylic acid with simple process, low production cost and high product purity is a problem to be solved urgently. Summary of the invention

[0006] The content of the present invention is used to introduce the concepts in a brief form, which will be described in detail in the detailed implementation section below. The content of the present invention is not intended to identify the key features or essential features of the technical solution claimed for protection, nor is it intended to limit the scope of the technical solution claimed for protection.

[0007] In order to solve the technical problems mentioned in the above background technology section, some of the present invention provides a method for preparing a high-purity perfluoropolyether carboxylic acid emulsifier, comprising the following steps:

[0008] a. Preparation of catalyst: Potassium fluoride and aluminum oxide are mixed in deionized water, fully stirred, filtered, and dried; after drying, the powder is ground and activated at 150-200° C. for 8-12 hours; after activation, the aluminum oxide-loaded potassium fluoride catalyst is obtained and stored under vacuum drying conditions for later use;

[0009] b. Synthesis of 7-carbon fluorocarboxylic acid fluoride: reacting carbonyl fluoride and hexafluoropropylene oxide in an organic solvent with the alumina-supported potassium fluoride catalyst obtained in step a in a reactor to obtain a reaction solution containing 7-carbon fluorocarboxylic acid fluoride;

[0010] c. Purification of 7-C fluorocarboxylic acid fluoride: the reaction solution obtained in step b is allowed to stand in a kettle to obtain an organic phase containing the catalyst and a fluorine phase containing 7-C fluorocarboxylic acid fluoride, the fluorine phase is separated and transferred to a distillation tower kettle, and the 7-C fluorocarboxylic acid fluoride is obtained by distillation;

[0011] d. Synthesis of 7-carbon fluorocarboxylic acid: reacting the 7-carbon fluorocarboxylic acid fluoride obtained in step c with an aqueous sulfuric acid solution to separate and obtain a crude 7-carbon fluorocarboxylic acid product α1 and an aqueous sulfuric acid solution containing hydrogen fluoride β1;

[0012] e. Purification of 7-carbon fluorocarboxylic acid: Wash the crude 7-carbon fluorocarboxylic acid α1 obtained in step d with an aqueous sulfuric acid solution to separate the crude 7-carbon fluorocarboxylic acid α2 and the aqueous sulfuric acid solution β2 containing hydrogen fluoride; transfer the crude 7-carbon fluorocarboxylic acid α2 to the bottom of a distillation tower, and perform distillation to obtain a pure 7-carbon fluorocarboxylic acid.

[0013] Furthermore, the organic solvent used in step b is first dehydrated by distillation or drying with a desiccant, so that the water content of the solvent is ≤200 ppm.

[0014] Furthermore, in step a, the mass ratio of potassium fluoride to aluminum oxide is 1:1-9, the mass ratio of potassium fluoride to deionized water is 1:1-10, and the particle size of aluminum oxide is 100-300 meshes.

[0015] Further, in step b, the solvent is selected from any mixture of one or more of acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, tetrahydrofuran, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

[0016] Furthermore, in step b, the amount of the catalyst is 2-15 wt % of hexafluoropropylene oxide, and the molar ratio of carbonyl fluoride to hexafluoropropylene oxide is 0.5-0.6:1.0.

[0017] Furthermore, in step b, the reaction conditions are: reaction temperature [-30, -20]°C; reaction time 2-6h; reaction pressure not higher than 0.8Mpa.

[0018] Furthermore, in step c, the organic phase containing the catalyst and the organic solvent obtained after filtering, distilling, etc. the organic phase α1 containing the catalyst is directly recycled; and the number of times is 0-30 times.

[0019] Furthermore, in step c, the distillation is atmospheric distillation, the distillation temperature is 90-150°C, and the fraction temperature is 80-85°C.

[0020] Furthermore, in steps d and e, the concentration of the aqueous sulfuric acid solution is 5-30 wt %, the amount of the aqueous sulfuric acid solution is 1-3 times that of the 7-carbon fluorocarboxylic acid fluoride, and the reaction temperature is 25-60°C.

[0021] Furthermore, in step e, the distillation is vacuum distillation, the distillation temperature is 80-120° C., and the distillation pressure is 3-6 mbr.

[0022] The beneficial effects of the present invention are:

[0023] 1. The catalyst for synthesizing 7-carbon fluorocarboxylic acid fluoride of the present invention is an alumina-supported potassium fluoride catalyst, which is obtained by immobilizing KF on alumina using an impregnation method, effectively solving the problem of the potassium fluoride catalyst being difficult to dissolve and having low catalytic activity.

[0024] 2. The alumina-loaded potassium fluoride catalyst of the present invention overcomes the problems of strong corrosiveness of metal fluorides and low selectivity when using only metal fluorides.

[0025] 3. The catalyst carrier alumina used in the catalyst of the present invention has strong adsorption and surface acid-base adjustability and is inexpensive; the preparation method of the catalyst is simple and the production cost is low.

[0026] 4. The product obtained by the preparation method provided by the present invention has high purity and low impurity content, and the process route and equipment are simple, which is conducive to industrial scale-up; and the raw materials, catalysts, organic solvents, and aqueous sulfuric acid solution can be recycled, greatly reducing the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention, so that other features, purposes and advantages of the present invention become more obvious. The accompanying drawings and descriptions of the exemplary embodiments of the present invention are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0028] In addition, throughout the drawings, the same or similar reference numerals represent the same or similar elements. It should be understood that the drawings are schematic and that the components and elements are not necessarily drawn to scale.

[0029] In the attached picture:

[0030] Figure 1 is a schematic diagram of the chemical equation for synthesizing 7-carbon fluorocarboxylic acid fluoride in step b of Example 1 of the present invention;

[0031] Figure 2is a schematic diagram of the chemical equation for synthesizing a 7-carbon fluorocarboxylic acid in step d of Example 1 of the present invention;

[0032] Figure 3 It is a high-resolution mass spectrometer of 2,3,3,3-tetrafluoro-2-(1,1,2,3,3,3-hexafluoro-2-(trifluoromethoxy)propoxy)propionic acid synthesized in Example 1 of the present invention;

[0033] Figure 4 This is the nuclear magnetic resonance spectrum of 2,3,3,3-tetrafluoro-2-(1,1,2,3,3,3-hexafluoro-2-(trifluoromethoxy)propoxy)propionic acid synthesized in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] Embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as being limited to the embodiments set forth herein. On the contrary, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the drawings and embodiments of the present invention are only for exemplary purposes and are not intended to limit the scope of protection of the present invention.

[0035] It should also be noted that, for ease of description, only the parts related to the invention are shown in the drawings. In the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0036] It should be noted that the concepts such as "first" and "second" mentioned in the present invention are only used to distinguish different devices, modules or units, and are not used to limit the order or interdependence of the functions performed by these devices, modules or units.

[0037] It should be noted that the modifications of "one" and "plurality" mentioned in the present invention are illustrative rather than restrictive, and those skilled in the art should understand that, unless otherwise clearly indicated in the context, it should be understood as "one or more".

[0038] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0039] Overall embodiment

[0040] The preparation method of a high-purity perfluoropolyether carboxylic acid emulsifier comprises the following steps:

[0041] a Preparation of alumina-supported potassium fluoride catalyst

[0042] Potassium fluoride, aluminum oxide and deionized water are placed in a container with heating function, stirring function and temperature control function, the mass ratio of potassium fluoride to aluminum oxide is 1:1-9, the mass ratio of potassium fluoride to deionized water is 1:1-10, and the particle size of aluminum oxide is 100-300 mesh. The temperature is controlled at 50-60°C and stirred for 1-4 hours. After stirring, filter and dry; grind after drying, and activate the obtained powder at 150-200°C for 8-12 hours to obtain a catalyst of aluminum oxide loaded with potassium fluoride. Store under vacuum drying conditions for future use.

[0043] b7 Synthesis of carbon fluorocarboxylic acid fluoride:

[0044] Under nitrogen atmosphere, add 10-50g of dried alumina-supported potassium fluoride catalyst and dried organic solvent into a 1L stainless steel autoclave, seal the autoclave and start stirring; when the autoclave temperature is -15°C, introduce the first raw material gas carbonyl fluoride, lower the autoclave temperature to -10°C again, introduce the second raw material gas hexafluoropropylene oxide, react for 2-6h and then turn off stirring, the reaction pressure is not higher than 0.8Mpa, terminate the reaction, and obtain a reaction solution containing 7-carbon fluorocarboxylic acid fluoride. The organic solvent is selected from one or more of acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, tetrahydrofuran, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether. The amount of alumina-supported potassium fluoride catalyst is A, and the amount of hexafluoropropylene oxide is B. A is 2-15wt% of B, and the molar ratio of carbonyl fluoride to hexafluoropropylene oxide is 0.5-0.6:1.0.

[0045] The chemical formula for synthesizing 7-carbon fluorocarboxylic acid fluoride is:

[0046]

[0047] Purification of C7 fluorocarbon carboxylic acid fluoride:

[0048] The reaction solution obtained in step (b) is allowed to stand in a kettle, and the lower fluorine phase is separated and subjected to atmospheric distillation at a distillation temperature of 90-150° C. The fraction at 80-85° C. is collected to obtain a colorless transparent liquid, namely 2,3,3,3-tetrafluoro-2-(1,1,2,3,3,3-hexafluoro-2-(trifluoromethoxy)propoxy)propionyl fluoride.

[0049] Synthesis of d7 fluorocarbon carboxylic acid:

[0050] 500g of 2,3,3,3-tetrafluoro-2-(1,1,2,3,3,3-hexafluoro-2-(trifluoromethoxy)propoxy)propionyl fluoride is added to an equal amount of 5-30wt% sulfuric acid solution, and stirred at 25-60°C for 0.5-2h, and then the crude 7-carbon fluorocarboxylic acid α1 and the sulfuric acid aqueous solution β1 containing hydrogen fluoride are separated, and the sulfuric acid aqueous solution β1 containing hydrogen fluoride is recovered and stored.

[0051] The chemical formula for synthesizing 7-carbon fluorocarboxylic acid is:

[0052]

[0053] Refining of e7 fluorocarbon carboxylic acid:

[0054] A 5-30wt% sulfuric acid solution is mixed with a crude 7-carbon fluorocarboxylic acid α1, and stirred at room temperature for 0.5-2h to separate the crude 7-carbon fluorocarboxylic acid α2. The aqueous sulfuric acid solution β1 containing hydrogen fluoride recycled in step d is used to wash the crude 7-carbon fluorocarboxylic acid α2, and the crude 7-carbon fluorocarboxylic acid α2 is transferred to a vacuum distillation tower kettle at a distillation temperature of 80-120°C and a distillation pressure of 3-6mbr to obtain a colorless transparent liquid, which is a pure 7-carbon fluorocarboxylic acid. The washed aqueous sulfuric acid solution β1 containing hydrogen fluoride becomes an aqueous sulfuric acid solution β2 containing hydrogen fluoride. The amount of the aqueous sulfuric acid solution is 1-3 times that of the 7-carbon fluorocarboxylic acid fluoride.

[0055] Embodiment 1

[0056] The preparation method of a high-purity perfluoropolyether carboxylic acid emulsifier comprises the following steps:

[0057] a Preparation of alumina-supported potassium fluoride catalyst

[0058] Potassium fluoride, aluminum oxide and deionized water are placed in a container with heating function, stirring function and temperature control function, wherein potassium fluoride is 40g, aluminum oxide is 60g and deionized water is 100g. The temperature is controlled at 55°C and stirred for 2h. After stirring, filter and dry. After drying, grind the obtained powder, activate it at 180°C for 10h to obtain the catalyst of aluminum oxide loaded with potassium fluoride. Store it in a vacuum dryer for later use.

[0059] b7 Synthesis of carbon fluorocarboxylic acid fluoride:

[0060] Under a nitrogen atmosphere, add 25g of dried alumina-supported potassium fluoride catalyst and 460g of dried organic solvent into a 1L stainless steel autoclave, seal the autoclave and start stirring; when the autoclave temperature is -15°C, introduce 105g of the first raw material gas carbonyl fluoride, lower the autoclave temperature to -10°C again, introduce 484g of the second raw material gas hexafluoropropylene oxide, turn off stirring after reacting for 4h, terminate the reaction, and obtain a reaction solution containing 7-carbon fluorocarboxylic acid fluoride. The loading amount of potassium fluoride in the dried 25g alumina-supported potassium fluoride catalyst is specifically 20%. The organic solvent is selected from N,N-dimethylformamide.

[0061] Purification of C7 fluorocarbon carboxylic acid fluoride:

[0062] The reaction solution obtained in step (b) is allowed to stand in a kettle, and the lower fluorine phase is separated and subjected to atmospheric distillation at a distillation temperature of 90-150° C., and the 80-85° C. fraction is collected to obtain a colorless transparent liquid, namely 2,3,3,3-tetrafluoro-2-(1,1,2,3,3,3-hexafluoro-2-(trifluoromethoxy)propoxy)propionyl fluoride. Qualitative and quantitative analysis is performed by GC-MS, and the results show that the selectivity of 7-carbonyl fluoride is 82%, the yield is 80%, and the purity is 99.20%.

[0063] Synthesis of d7 fluorocarbon carboxylic acid:

[0064] 500 g of 2,3,3,3-tetrafluoro-2-(1,1,2,3,3,3-hexafluoro-2-(trifluoromethoxy)propoxy)propionyl fluoride was added to an equal amount of 30% sulfuric acid solution, and stirred at 50° C. for 2 h, and then the crude 7-carbon fluorocarboxylic acid α1 and the sulfuric acid aqueous solution β1 containing hydrogen fluoride were separated, and the sulfuric acid aqueous solution β1 containing hydrogen fluoride was recovered and stored.

[0065] Refining of e7 fluorocarbon carboxylic acid:

[0066] An equal amount of 30% sulfuric acid solution is mixed with the crude 7-carbon fluorocarboxylic acid α1, and stirred at room temperature for 1 hour to separate the crude 7-carbon fluorocarboxylic acid α2. The aqueous sulfuric acid solution containing hydrogen fluoride β1 recycled in step d is used to wash the crude 7-carbon fluorocarboxylic acid α2, and the crude 7-carbon fluorocarboxylic acid α2 is transferred to the vacuum distillation tower kettle at a distillation temperature of 80-120°C and a distillation pressure of 3-6mbr to obtain a colorless transparent liquid, which is a pure 7-carbon fluorocarboxylic acid. The washed aqueous sulfuric acid solution containing hydrogen fluoride β1 becomes an aqueous sulfuric acid solution containing hydrogen fluoride β2.

[0067] The purity of the product was determined by HPLC, and analysis showed that the purity of the 7-carbon fluorocarboxylic acid was 99.6%.

[0068] The fluoride ion content was determined by a fluoride ion meter, the water content of the sample was determined by a Karl Fischer titrator, and the purity of the sample was determined by high performance liquid chromatography HPLC. The test results are shown in Table 1.

[0069] Table 1 Fluorine phase composition after acidification, pickling and vacuum distillation

[0070]

[0071] Embodiment 2

[0072] The difference from Example 1 is that the loading amount of potassium fluoride in the 25 g of alumina-supported potassium fluoride catalyst after drying is specifically 30%.

[0073] Embodiment 3

[0074] The difference from Example 1 is that the loading amount of potassium fluoride in the 25 g of alumina-supported potassium fluoride catalyst after drying is specifically 35%.

[0075] Embodiment 4

[0076] The difference from Example 1 is that the loading amount of potassium fluoride in the 25 g of alumina-supported potassium fluoride catalyst after drying is specifically 40%.

[0077] Embodiment 5

[0078] The difference from Example 1 is that the loading amount of potassium fluoride in the 25 g of alumina-supported potassium fluoride catalyst after drying is specifically 50%.

[0079] Embodiment 6

[0080] The difference from Example 1 is that the amount of the dried alumina-supported potassium fluoride catalyst is 10 g and the loading amount of potassium fluoride in the catalyst is specifically 35%.

[0081] Embodiment 7

[0082] The difference from Example 1 is that the amount of the dried alumina-supported potassium fluoride catalyst is 20 g and the loading amount of potassium fluoride in the catalyst is specifically 35%.

[0083] Embodiment 8

[0084] The difference from Example 1 is that the amount of the dried alumina-supported potassium fluoride catalyst is 30 g and the loading amount of potassium fluoride in the catalyst is specifically 35%.

[0085] Embodiment 9

[0086] The difference from Example 1 is that the amount of the dried alumina-supported potassium fluoride catalyst is 40 g and the loading amount of potassium fluoride in the catalyst is specifically 35%.

[0087] Embodiment 10

[0088] The difference from Example 1 is that the amount of the dried alumina-supported potassium fluoride catalyst is 50 g and the loading amount of potassium fluoride in the catalyst is specifically 35%.

[0089] Comparative Example 1

[0090] The difference from Example 1 is that step a is omitted and under a nitrogen atmosphere, 25 g of alumina-supported potassium fluoride catalyst is replaced with 10 g of potassium fluoride.

[0091] Comparative Example 2

[0092] The difference from Comparative Example 1 is that cesium fluoride is used as a catalyst and the amount is 26 g.

[0093] The colorless transparent liquids obtained in the above-mentioned Examples 1 to 10 and Comparative Examples 1 and 2 were qualitatively and quantitatively analyzed by GC-MS. The results are shown in Table 2.

[0094] Table 2. Effect of different catalysts on reaction selectivity

[0095]

[0096] As can be seen from the above table, the alumina-supported potassium fluoride catalyst has good reaction selectivity for catalytic synthesis of 7-carbon fluorocarboxylic acid fluoride. When the loading amount of potassium fluoride in the catalyst is 35%, the selectivity is up to 90%, and the yield of the product can reach 88%. When the loading amount of potassium fluoride in the catalyst is 35%, the selectivity of 7-carbon fluorocarboxylic acid fluoride can reach 92% and the yield can reach 90% by using a catalyst mass of 30g. In the actual reaction formula, the selectivity and yield of 7-carbon fluorocarboxylic acid fluoride in Comparative Examples 1 and 2, which do not use alumina-supported potassium fluoride as a catalyst, are both below 60 and 60, which is far lower than the benefit of using alumina-supported potassium fluoride as a catalyst.

[0097] The reasons for the above structure are:

[0098] Potassium fluoride immobilized on alumina can release unsaturated fluoride ions, which are dispersed by being loaded on the surface of alumina, increasing the specific surface area of ​​the catalyst, thereby promoting the reaction. However, the degree of fluoride ion release of single alkali metal fluorides (cesium fluoride, potassium fluoride, etc.) is relatively poor.

[0099] In addition, when the KF loading is too much, it will exceed the monolayer dispersion threshold of the alumina surface, resulting in the overlap of potassium fluoride on the alumina surface and the overlapped potassium fluoride cannot form an effective surface active center with alumina, which will cause the number of surface basic centers to be mismatched with the loading of potassium fluoride, and further affect the selectivity of synthesizing 7-carbon fluorocarboxylic acid fluoride. Therefore, in actual production, it is preferred to use alumina loaded potassium fluoride as a catalyst, and the loading of potassium fluoride in the catalyst is 35%, and the mass is 30g.

[0100] Embodiment 11

[0101] The preparation method of a high-purity perfluoropolyether carboxylic acid emulsifier comprises the following steps:

[0102] a Preparation of alumina-supported potassium fluoride catalyst

[0103] The preparation method is the same as that of Example 8.

[0104] b7 Synthesis of carbon fluorocarboxylic acid fluoride:

[0105] The preparation method is the same as that of Example 8.

[0106] Purification of C7 fluorocarbon carboxylic acid fluoride:

[0107] The preparation method is the same as that of Example 8. The qualitative and quantitative analysis by GC-MS shows that the selectivity of 7-carbonyl fluoride is 92%, the yield is 90%, and the purity is 99.50%.

[0108] After the reaction of catalytic synthesis of 7-carbon fluorocarboxylic acid fluoride is completed, the reaction solution is clearly divided into layers, wherein the upper layer is an organic phase containing the catalyst; and the lower layer is a fluorine phase containing 7-carbon fluorocarboxylic acid fluoride.

[0109] The reaction liquid is completely discharged, and the separated organic phase is added to the kettle for continued use; or only a certain mass of the fluorine phase is taken out each time, and the reaction is continued, thereby realizing the recycling of the organic phase of the upper catalyst.

[0110] In this embodiment, the organic phase of the upper catalyst is recycled 0, 5, 10, 20, and 30 times in sequence, and the results are recorded.

[0111] The recycling results are shown in Table 3.

[0112] Table 3 Organic phase recycling experiment results

[0113]

[0114]

[0115] It can be seen from the above table that the recycling of the organic phase is feasible. As the number of recycling times increases, the selectivity of the reaction product gradually decreases. This is due to the accumulation of the fluorine phase in the organic phase, which causes an increase in by-products.

[0116] When the recycling times reaches 20 times, the selectivity of 7-carbon fluorocarboxylic acid fluoride is still ≥70%, which is much higher than that of the prior art.

[0117] The purpose of this embodiment is to realize large-scale industrial production by recycling the organic phase, on the one hand, with simple operation; on the other hand, raw materials are saved, so that the cost is greatly reduced.

[0118] Synthesis of d7 fluorocarbon carboxylic acid:

[0119] The same as Example 8, except that the concentration of sulfuric acid is 30 / wt%, and the amount used is 500g.

[0120] Refining of e7 fluorocarbon carboxylic acid:

[0121] The same as Example 8, except that the concentration of sulfuric acid is 30 / wt%, and the amount used is 500g.

[0122] Embodiment 12

[0123] The same as Example 11, except that the concentration of sulfuric acid is 20 / wt%, and the amount used is 500g.

[0124] Embodiment 13

[0125] The same as Example 11, except that the concentration of sulfuric acid is 10 / wt%, and the amount used is 500g.

[0126] Embodiment 14

[0127] The same as Example 11, except that the concentration of sulfuric acid is 5 / wt%, and the amount used is 500g.

[0128] Embodiment 15

[0129] The same as Example 11, except that the concentration of sulfuric acid is 30 / wt%, and the amount used is 1000g.

[0130] Embodiment 16

[0131] The same as Example 11, except that the concentration of sulfuric acid is 20 / wt%, and the amount used is 1000g.

[0132] Embodiment 17

[0133] The same as Example 11, except that the concentration of sulfuric acid is 10 / wt%, and the amount used is 1000g.

[0134] Embodiment 18

[0135] The same as Example 11, except that the concentration of sulfuric acid is 5 / wt%, and the amount used is 1000g.

[0136] The effects of the concentrations and amounts of different sulfuric acid used in Examples 11 to 18 are shown in Table 4.

[0137] Table 4 Effect of different sulfuric acid concentrations and dosages on fluorine phase composition

[0138]

[0139] As can be seen from the above table, when using sulfuric acid of different concentrations or different amounts, the purity of the obtained 7-carbon fluorocarboxylic acid after acidification, acid washing and vacuum distillation is ≥99.5%.

[0140] Further analysis found that when the same amount of sulfuric acid is used, the lower the concentration of sulfuric acid used, the lower the fluoride content of the finished product. This is because the hydrogen fluoride produced by the hydrolysis of acyl fluoride has excellent solubility in water. In addition, while keeping the sulfuric acid concentration unchanged, changing the amount of sulfuric acid can also achieve better results. For example, when the sulfuric acid concentration is 5%wt%, and the amount of sulfuric acid used is 500g and 100g, the purity of the 7-carbon fluorocarboxylic acid obtained when the sulfuric acid is 100g is better than when the amount of sulfuric acid is 500g.

[0141] The above descriptions are only some preferred embodiments of the present invention and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the embodiments of the present invention is not limited to the technical solutions formed by the specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the above inventive concept. For example, the above features are replaced with the technical features with similar functions disclosed in the embodiments of the present invention (but not limited to) to form a technical solution.

Claims

1. A method for preparing a high-purity perfluoropolyether carboxylic acid emulsifier, characterized in that: The following steps are involved: a. Preparation of catalyst: Mix potassium fluoride and aluminum oxide in deionized water, stir thoroughly, filter and dry; After drying, the powder is ground and activated at 150-200°C for 8-12h. After activation, the catalyst of potassium fluoride supported by aluminum oxide is obtained and stored under vacuum drying conditions for future use. b. Synthesis of 7-carbon fluorocarboxylic acid fluoride: reacting carbonyl fluoride and hexafluoropropylene oxide in an organic solvent with the alumina-supported potassium fluoride catalyst obtained in step a in a reactor to obtain a reaction solution containing 7-carbon fluorocarboxylic acid fluoride; c. Purification of 7-C fluorocarboxylic acid fluoride: the reaction solution obtained in step b is allowed to stand in a kettle to obtain an organic phase containing the catalyst and a fluorine phase containing 7-C fluorocarboxylic acid fluoride, the fluorine phase is separated and transferred to a distillation tower kettle, and the 7-C fluorocarboxylic acid fluoride is obtained by distillation; d. Synthesis of 7-carbon fluorocarboxylic acid: reacting the 7-carbon fluorocarboxylic acid fluoride obtained in step c with an aqueous sulfuric acid solution to separate and obtain a crude 7-carbon fluorocarboxylic acid product α1 and an aqueous sulfuric acid solution containing hydrogen fluoride β1; e. Purification of the 7-carbon fluorocarboxylic acid: washing the crude 7-carbon fluorocarboxylic acid α1 obtained in step d with an aqueous sulfuric acid solution to separate the crude 7-carbon fluorocarboxylic acid α2 and the aqueous sulfuric acid solution β2 containing hydrogen fluoride; transferring the crude 7-carbon fluorocarboxylic acid α2 to a distillation tower bottom, and performing distillation to obtain a pure 7-carbon fluorocarboxylic acid; In step a, the potassium fluoride loading in the activated alumina-loaded potassium fluoride catalyst is 35%; the mass ratio of potassium fluoride to deionized water is 1:1-10, and the particle size of the alumina is 100-300 meshes.

2. The method for preparing a high-purity perfluoropolyether carboxylic acid emulsifier according to claim 1, characterized in that: The organic solvent used in step b is first dehydrated by distillation or drying with a desiccant to make the water content of the solvent ≤ 200 ppm.

3. The method for preparing a high-purity perfluoropolyether carboxylic acid emulsifier according to claim 1, characterized in that: In step b, the solvent is selected from any mixture of one or more of acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, tetrahydrofuran, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

4. The method for preparing a high-purity perfluoropolyether carboxylic acid emulsifier according to claim 1, characterized in that: In step b, the amount of the catalyst is 2-15 wt % of hexafluoropropylene oxide, and the molar ratio of carbonyl fluoride to hexafluoropropylene oxide is 0.5-0.6:1.

0.

5. The method for preparing a high-purity perfluoropolyether carboxylic acid emulsifier according to claim 1, characterized in that: In step b, the reaction conditions are: reaction temperature -30-20°C; reaction time 2-6h; reaction pressure not higher than 0.8MPa.

6. The method for preparing a high-purity perfluoropolyether carboxylic acid emulsifier according to claim 1, characterized in that: In step c, the organic phase containing the catalyst and the organic solvent obtained after filtering and distilling the organic phase α1 containing the catalyst is directly recycled; and the number of times is 0-30 times.

7. The method for preparing a high-purity perfluoropolyether carboxylic acid emulsifier according to claim 1, characterized in that: In step c, the distillation is atmospheric distillation, the distillation temperature is 90-150°C, and the fraction temperature is 80-85°C.

8. The method for preparing a high-purity perfluoropolyether carboxylic acid emulsifier according to claim 1, characterized in that: In steps d and e, the concentration of the aqueous sulfuric acid solution is 5-30 wt %, the amount of the aqueous sulfuric acid solution is 1-3 times that of the 7-carbon fluorocarboxylic acid fluoride, and the reaction temperature is 25-60° C.

9. The method for preparing a high-purity perfluoropolyether carboxylic acid emulsifier according to claim 1, characterized in that: In step e, the distillation is vacuum distillation, the distillation temperature is 80-120° C., and the distillation pressure is 3-6 mbar.

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