CN118791375A - A continuous method, device and product for preparing fluorinated carboxylic acid - Google Patents

Abstract

The present application provides a continuous method for preparing fluorinated carboxylic acids, the method comprising: step A: continuously inputting reaction raw materials, fluorinating agents, solvents and catalysts into a synthesis reactor, so that the raw materials to be fluorinated react with the fluorinating agents in the synthesis reactor to generate fluorinated carboxylic acid esters, and at the same time, a crude product stream containing fluorinated carboxylic acid esters continuously flows out of the synthesis reactor; step B: separating and purifying the product stream to obtain a purified product stream; step C: hydrolyzing the purified product stream to obtain a hydrolyzate stream, wherein the hydrolyzate stream contains fluorinated carboxylic acids and/or salts thereof; step D: acidifying the hydrolyzate stream to obtain a crude fluorinated carboxylic acid; and step E: purifying the crude product. The present invention also provides a fluorinated carboxylic acid product prepared by the method and a reaction device for implementing the method. The method of the present invention is carried out in a continuous manner throughout the process, has a stable process, can achieve high automation, low energy consumption, high production capacity and high reliability, and the fluorinated carboxylic acid product can be well used as a substitute for biologically toxic perfluorooctanoic acid.

Description

A continuous method, device and product for preparing fluorinated carboxylic acid

Technical Field

The present application relates to the field of chemical industry, and more specifically to a method for preparing fluorine-containing carboxylic acid in a continuous manner, a fluorine-containing carboxylic acid product prepared by the method, and an apparatus for implementing the method.

Background Art

As an important polymerization aid, fluorinated carboxylic acid can effectively reduce the surface tension of aqueous solution and play an important role in stabilizing latex particles. At present, fluorinated carboxylic acid is widely used as a polymerization aid (such as surfactant or emulsifier) in various industrial synthesis and industrial modification processes, and the most excellent and widely used one is perfluorooctanoic acid, but perfluorooctanoic acid is a compound with great potential risks. Specifically, perfluorooctanoic acid is classified as a Class 2B carcinogen by the International Agency for Research on Cancer of the World Health Organization. It has potential persistence, bioaccumulation and toxicity. If perfluorooctanoic acid is used on a large scale as a polymerization aid in various industrial uses, it will inevitably remain in large quantities in the final polymerization products and process waste. Process waste will pollute the environment, and the residual perfluorooctanoic acid contained in waste and industrial products is likely to be ingested into the human body. Once perfluorooctanoic acid enters the human body, it will cause serious and irreversible damage to human health. Therefore, many countries and regions have introduced control measures for perfluorooctanoic acid and its derivatives. Therefore, there is an urgent need in the art to develop a fluorinated alkyl carboxylic acid product as a substitute for perfluorooctanoic acid. This substitute should also have the various properties of perfluorooctanoic acid, but its carcinogenic toxicity is significantly lower than that of perfluorooctanoic acid.

In addition, the existing synthesis and separation methods of fluorinated organic compounds (especially fluorinated carboxylic acids) are usually carried out in a step-by-step intermittent manner, with low automation, many manual operations, long time cycles, poor safety, and poor reliability. In addition, in the prior art, a dispersion process is required in the synthesis process of fluorinated organic compounds such as fluorinated carboxylic acids, which will produce wastewater containing a large amount of fluorinated organic compounds. In order to meet relevant environmental protection requirements and improve the recovery rate, the wastewater needs to be further purified twice or even more times, and the process steps are cumbersome and redundant, and the synthesis cost is significantly increased.

In order to solve the above problems, scientific research institutions and enterprises in related fields have invested a lot of scientific research funds and energy to make various improvements and optimizations on the synthesis processes of perfluorooctanoic acid substitutes and fluorinated organic compounds, but the technological progress achieved so far is still very limited.

In view of the above problems, the inventors of the present application have conducted a lot of in-depth research and unexpectedly developed a synthesis method that can be carried out in a continuous manner. The method can be carried out at a high level of automation, has low energy consumption, is suitable for industrial continuous production, and can also achieve process stability, low energy consumption, high production capacity and high reliability. In addition, the fluorinated carboxylic acid product synthesized by the present invention has a degradable structure, is non-bioaccumulative and non-toxic, and has excellent surface active properties, and can perfectly replace the carcinogenic substance perfluorooctanoic acid as a polymerization aid.

Summary of the invention

The first aspect of the present application provides a continuous method for preparing a fluorine-containing carboxylic acid, the method comprising:

Step A: continuously feeding a reaction raw material, a fluorinating agent, a solvent and a catalyst into a synthesis reactor 2, so that the reaction raw material to be fluorinated reacts with the fluorinating agent in the synthesis reactor 2 to generate a fluorine-containing carboxylic acid ester, and simultaneously a crude product stream f containing the fluorine-containing carboxylic acid ester continuously flows out of the synthesis reactor 2;

Step B: separating and purifying the product stream f to obtain a purified product stream m;

Step C: hydrolyzing the purified product stream m to obtain a hydrolyzed product stream s, wherein the hydrolyzed product stream s contains fluorinated carboxylic acid and/or a salt thereof;

Step D: acidifying the hydrolyzed product stream q to obtain a crude fluorinated carboxylic acid;

Step E: Purifying the crude fluorine-containing carboxylic acid to obtain a pure fluorine-containing carboxylic acid.

According to one embodiment of the first aspect of the present application, before the step A, the fluorination agent, the catalyst and the solvent are premixed in a dynamic mixer 1 to form a premix.

According to another embodiment of the first aspect of the present application, in step A, the premix is continuously fed into the synthesis reactor 2, and at the same time, the reaction raw materials are continuously fed into the synthesis reactor 2 independently of the premix.

According to another embodiment of the first aspect of the present application, the fluorinating agent is selected from one or more of the following: potassium fluoride, sodium fluoride, ammonium fluoride, calcium fluoride, lithium fluoride, and cesium fluoride.

According to another embodiment of the first aspect of the present application, the catalyst is selected from one or more quaternary ammonium salts of the following: benzyltriethylammonium chloride, tetrabutylammonium hydrogen sulfate, tetrabutylammonium bromide, hyperbranched quaternary ammonium salts, trifluoromethylthiotetramethylammonium salt, dibutyl phosphate tetrabutylammonium salt, malondialdehyde tetrabutylammonium salt.

According to another embodiment of the first aspect of the present application, the solvent is selected from one or more of the following: dimethylformamide, dimethylacetamide, acetonitrile, dimethyl sulfoxide, and methylpyrrolidone.

According to another embodiment of the first aspect of the present application, the reaction raw materials include halogenated olefins and halogenated esters; the halogenated olefins are selected from one or more of the following: halogenated C2-C12 olefins, halogenated C2-C12 olefin dimers, halogenated C2-C12 olefin trimers, halogenated C2-C12 olefin tetramers, halogenated C2-C12 olefin pentamers, halogenated C2-C12 olefin hexamers; the halogenated esters are selected from one or more of the following: halogenated C2-C12 carboxylic acid C1-C12 alkyl esters, halogenated C2-C12 carboxylic acid C3-C12 cycloalkyl esters, halogenated C2-C12 carboxylic acid C6-C12 aralkyl esters.

According to another embodiment of the first aspect of the present application, in the step A, the reaction is carried out at a temperature of 40-100° C., and the residence time of the reaction materials in the synthesis reactor 2 is 10 minutes to 2 hours.

According to another embodiment of the first aspect of the present application, the step B comprises the following operations: separation: the crude product stream f is subjected to solid-liquid separation in a centrifugal screw solid-liquid separator g to obtain solid waste salt and a liquid crude product stream g; purification: the liquid crude product stream g is extracted with an extractant h in an extraction agglomerator 4, and then distilled in a continuous distillation tower 5, the solvent and the extractant h are recovered to obtain a purified product stream m.

According to another embodiment of the first aspect of the present application, in step C, the purified product stream m is mixed with a hydrolysis solvent o and an alkaline solution p to undergo hydrolysis. According to another embodiment of the first aspect of the present application, the hydrolysis is performed at a temperature of 30-80°C.

According to another embodiment of the first aspect of the present application, the hydrolysis solvent o is a C1-C6 alcohol, and the weight ratio of the hydrolysis solvent o to the purified product stream m is 50:100 to 500:100.

According to another embodiment of the first aspect of the present application, the alkali solution p is a solution of an alkaline agent in water with a concentration of 5-40 wt %, the alkaline agent is an alkali metal hydroxide, and the weight ratio of the alkali solution p to the purified product stream m is 100:100 to 500:100.

According to another embodiment of the first aspect of the present application, in step D, the hydrolyzate stream is acidified and separated in the mixer-coalescer 8 to obtain a crude fluorinated carboxylic acid, and then the crude is purified in a purification device in step E to obtain a pure fluorinated carboxylic acid. According to another embodiment of the first aspect of the present application, the acidification is performed at a temperature of 0-80° C. According to another embodiment of the first aspect of the present application, the molar ratio of the acid r used in the acidification process to the fluorinated carboxylic acid salt contained in the hydrolyzate stream q is 1:1 to 4:1.

According to another embodiment of the first aspect of the present application, the fluorine-containing carboxylic acid is a C2-C15 fluorine-containing alkyl C2-C6 carboxylic acid.

According to another embodiment of the first aspect of the present application, the fluorinated carboxylic acid prepared by the method of the present invention does not include perfluorooctanoic acid. According to another embodiment of the first aspect of the present application, perfluorooctanoic acid that does not comply with relevant laws and regulations (such as domestic or global environmental protection laws and regulations and/or various industrial product fields) is not included in the fluorinated carboxylic acid prepared by the method of the present invention. According to another embodiment of the first aspect of the present application, the fluorinated carboxylic acid prepared by the method of the present invention does not include any fluorinated carboxylic acid that is toxic, harmful to the human body or accumulates in the human body.

The second aspect of the present application provides a fluorine-containing carboxylic acid product, which is prepared by the method of any embodiment of the first aspect of the present application.

The third aspect of the present application provides a continuous reaction device, which is used to implement the method described in any embodiment of the first aspect of the present application, and the device includes: a dynamic mixer 1, a synthesis reactor 2, a solid-liquid separation device 3, an extraction agglomerator 4, a continuous distillation tower 5, a hydrolysis device 6, a continuous distillation tower 7, a mixer-agglomerator 8, and a purification device 9.

In the following detailed description section, the method, device and apparatus of the present application are further described in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 shows a schematic diagram of the process flow of the method of the present application;

FIG2 shows a picture of the fluorine-containing carboxylic acid product crystals synthesized in the examples of the present application;

FIG3 shows a picture of the continuous reaction equipment used in the examples of the present application;

FIG4 shows a picture of a continuous distillation tower used in an embodiment of the present application;

FIG5 shows the nuclear magnetic resonance fluorine spectrum of the fluorine-containing carboxylic acid product, perfluorohexylacetic acid, synthesized in the examples of the present application;

FIG6 shows the hydrogen nuclear magnetic resonance spectrum of the fluorine-containing carboxylic acid product, perfluorohexylacetic acid, synthesized in the examples of the present application.

Reference numerals:

1 dynamic mixer; 2 synthesis reactor; 3 solid-liquid separation device; 4 extraction coalescer; 5 continuous distillation tower; 6 hydrolysis device; 7 continuous distillation tower; 8 mixing-coalescer; 9 purification device;

a halogenated olefins; halogenated esters; c fluorinating agent; d solvent; e catalyst; f crude product stream; g liquid crude product stream; h extractant; j extraction waste liquid stream; k extraction crude product stream; l tower top effluent; m purified product stream; n hydrolyzate stream; o solvent; p alkali solution; q purified hydrolyzate stream; r acidic reagent; s crude fluorinated carboxylic acid; t waste acid liquid; u pure fluorinated carboxylic acid; v tower bottom waste; w water.

DETAILED DESCRIPTION

"Range" disclosed herein is in the form of lower limit and upper limit. It can be one or more lower limits, and one or more upper limits respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a particular range. All ranges that can be defined in this way are inclusive and combinable, i.e. any lower limit can be combined with any upper limit to form a range. For example, a range of 60-120 and 80-110 is listed for a particular parameter, and it is understood that a range of 60-110 and 80-120 is also expected. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4 and 5 are listed, the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.

In this application, unless otherwise specified, the numerical range "a-b" represents an abbreviation of any real number combination between a and b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations.

In this application, unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined with each other to form a new technical solution.

In this application, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

In this application, if there is no special explanation, the "including" mentioned herein means open or closed. For example, the "including" may mean that other components not listed may also be included, or only the listed components may be included.

The method of the present application includes step A, step B, step C, step D and step E described above. According to one embodiment of the present application, the steps A-E are performed sequentially. According to one embodiment of the present application, the steps A-E and any other steps (such as a premixing step performed before step A, and other steps performed before or after any step) are performed in a continuous manner.

Next, the method of the present application will be described with reference to an exemplary embodiment of the method of the present application shown in FIG. 1 .

According to one embodiment of the present application, before performing step A, a premixing step is first performed, in which at least a portion of the reaction materials are mixed to form a premix, and then the premix and the remaining reaction materials (if any) are independently transported into the synthesis reactor 2 for reaction. In the embodiment shown in Figure 1, the premixing step is performed in a dynamic mixer 1. For example, the fluorinating agent c, the catalyst e and the solvent d can be continuously transported into the dynamic mixer 1, so that the fluorinating agent c, the catalyst e and the liquid solvent d are mixed to form a premix liquid material; then the premix liquid is transported into the synthesis reactor 2, and the reaction raw materials (which include halogenated olefins a and halogenated esters b) are independently input into the synthesis reactor 2 from the premix.

According to another embodiment different from Figure 1, the fluorinating agent c, catalyst e and solvent d can be continuously conveyed into the dynamic mixer 1, so that the halogenated olefin a, halogenated ester b, fluorinating agent c, catalyst e and liquid solvent d are mixed to form a premix liquid material, and then the premix liquid is conveyed into the synthesis reactor 2.

According to one embodiment of the present application, the solvent d is a liquid organic compound that can effectively dissolve or disperse the fluorinating agent c, catalyst e, halogenated olefin a and halogenated ester b, and will not interfere with the reaction and fluorination products. For example, the solvent d can be an aprotic organic solvent, for example, the solvent d can be selected from one or more of the following: dimethylformamide, dimethylacetamide, acetonitrile, dimethyl sulfoxide, methyl pyrrolidone; preferably dimethylformamide and/or methyl pyrrolidone. According to one embodiment of the present application, a portion of the solvent can be used to dissolve or disperse the above-mentioned fluorinating agent c, catalyst e, halogenated olefin a and halogenated ester b, and then added to the dynamic mixer 1 or the synthesis reactor 2.

According to one embodiment of the present application, the fluorinating agent c is an alkali metal fluoride, for example, it can be one or more of the following: potassium fluoride, sodium fluoride, ammonium fluoride, calcium fluoride, lithium fluoride, cesium fluoride, preferably the fluorinating agent c is potassium fluoride, cesium fluoride or a combination of the two. According to one embodiment of the present application, in all the materials finally input into the synthesis reactor 2, the weight ratio of the fluorinating agent c to the solvent d is 30:100 to 150:100, for example, it can be 40:100 to 120:100, or 42:100 to 50:100, or 100:100 to 120:100, or 40:100 to 80:100, or within the numerical range obtained by combining any two of the above end values.

According to one embodiment of the present application, the catalyst is a quaternary ammonium salt, for example, it can be selected from one or more of the following: benzyl triethylammonium chloride, tetrabutylammonium hydrogen sulfate, tetrabutylammonium bromide, hyperbranched quaternary ammonium salt, trifluoromethylthio tetramethylammonium salt, dibutyl phosphate tetrabutylammonium salt, malondialdehyde tetrabutylammonium salt; preferably, the catalyst can be selected from one or more of the following: tetrabutylammonium bromide, trifluoromethylthio tetramethylammonium salt. The "hyperbranched quaternary ammonium salt" described above means that at least one (e.g., one, two, three, four) of the four alkyl/aryl groups connected to the nitrogen atom has a highly branched structure, such as tert-butyl, isopropyl, tert-amyl, etc. An example of a hyperbranched quaternary ammonium salt is a Gemini quaternary ammonium salt. According to one embodiment of the present application, the weight ratio of catalyst e to solvent d in all the materials finally input into the synthesis reactor 2 is 2:100 to 30:100, for example, it can be 3:100 to 25:100, or 4:100 to 20:100, or 4.5:100 to 15:100, or 5:100 to 10:100, or 6:100 to 8:100, or within the numerical range obtained by combining any two of the above end values.

According to an embodiment of the application, the haloolefin is an olefin substituted with one or more halogen atoms, and the halogen atoms include, for example, fluorine, chlorine, bromine, iodine or any combination thereof, and the halogen atoms can replace 5-100% of the hydrogen atoms in the olefin, for example, 15-100%, or 30-100%, or 50-100%, or 60-100%, or 80-100%, or 90-100%, preferably a perhaloolefin. According to an exemplary embodiment, the haloolefin can be a fluoroolefin, preferably a perfluoroolefin.

Examples of the halogenated olefins are selected from one or more of the following: halogenated C2-C12 olefins, halogenated C2-C12 olefin dimers, halogenated C2-C12 olefin trimers, halogenated C2-C12 olefin tetramers, halogenated C2-C12 olefin pentamers, halogenated C2-C12 olefin hexamers; or selected from one or more of the following: fluorinated C2-C12 olefins, fluorinated C2-C12 olefin dimers, fluorinated C2-C12 olefin trimers, fluorinated C2-C12 olefin tetramers, fluorinated C2-C12 olefin pentamers, fluorinated C2-C12 olefin hexamers; or selected from one or more of the following: perfluorinated C2-C12 olefins, perfluorinated C2-C12 olefin dimer, perfluoro C2-C12 olefin trimer, perfluoro C2-C12 olefin tetramer, perfluoro C2-C12 olefin pentamer, perfluoro C2-C12 olefin hexamer; such as perfluoro C2-C8 olefin, perfluoro C2-C8 olefin dimer, perfluoro C2-C8 olefin trimer, perfluoro C2-C8 olefin tetramer, perfluoro C2-C8 olefin pentamer, perfluoro C2-C8 olefin hexamer; or perfluoro C3-C6 olefin, perfluoro C3-C6 olefin dimer, perfluoro C3-C6 olefin trimer, perfluoro C3-C6 olefin tetramer, perfluoro C3-C6 olefin pentamer, perfluoro C3-C6 olefin hexamer. For example, the halogenated olefin can include one or more of the following: hexafluoropropylene dimer, hexafluoropropylene trimer, hexafluoropropylene tetramer, preferably hexafluoropropylene dimer.

According to one embodiment of the present application, in all the materials finally input into the synthesis reactor 2, the weight ratio of the halogenated olefin a to the solvent d is 150:100 to 500:100, for example, it can be 200:100 to 400:100, or 210:100 to 310:100, or 200:100 to 220:100, or 230:100 to 250:100, or 280:100 to 310:100, or within the numerical range obtained by combining any two of the above end values.

According to one embodiment of the present application, the halogenated esters are selected from one or more of the following: halogenated C2-C12 carboxylic acid C1-C12 alkyl esters, halogenated C2-C12 carboxylic acid C3-C12 cycloalkyl esters, halogenated C2-C12 carboxylic acid C6-C12 aralkyl esters; for example, halogenated C2-C8 carboxylic acid C1-C8 alkyl esters, halogenated C2-C8 carboxylic acid C3-C10 cycloalkyl esters, halogenated C2-C8 carboxylic acid C6-C10 aralkyl esters; or halogenated C2-C6 carboxylic acid C1-C6 alkyl esters, halogenated C2-C6 carboxylic acid C3-C8 cycloalkyl esters, halogenated C2-C6 carboxylic acid C6-C8 aralkyl esters; or halogenated C2-C4 carboxylic acid C1-C4 alkyl esters, halogenated C2-C4 carboxylic acid C3-C6 cycloalkyl esters, halogenated C2-C4 carboxylic acid C6-C8 aralkyl esters. The "halogenated" in the "halogenated esters" means that the ester is substituted by one or more, such as one, two, three, four, five, six halogen atoms, such as perhalogenation; the halogen atoms may include fluorine, chlorine, bromine, iodine, or a combination of two or more of the above halogen atoms. According to an exemplary embodiment of the present application, examples of the halogenated esters include: (a) ethyl bromoacetate, (a) ethyl fluoroacetate, (a) ethyl chloroacetate.

According to one embodiment of the present application, in all the materials finally input into the synthesis reactor 2, the weight ratio of the halogenated ester b to the solvent d is 80:100 to 220:100, for example, it can be 100:100 to 200:100, or 120:100 to 175:100, or 110:100 to 130:100, or 130:100 to 150:100, or 160:100 to 180:100, or within the numerical range obtained by combining any two of the above end values.

According to one embodiment of the present application, the reaction of step A can be carried out in one or more synthesis reactors 2. Each synthesis reactor 2 may include a tank reactor, a tubular reactor, etc.; the tank reactor may include a vertical tank or a horizontal tank. Various stirring devices may be provided in the reactor. According to an exemplary embodiment, the stirring device may include a four-blade pitched propeller, a spiral ribbon stirring propeller, or a three-blade propeller.

In the case of using multiple synthesis reactors 2, the multiple synthesis reactors 2 can be connected in parallel or in series with each other, or the multiple synthesis reactors 2 can be arranged in a series-parallel manner, for example, four, six, eight, ten or twelve synthesis reactors are divided into two groups (a first group and a second group), the two groups are connected in series, and the reactors in each group are connected in parallel; or four, six, eight, ten or twelve synthesis reactors are divided into two groups (a first group and a second group), the two groups are connected in parallel, and the two reactors in each group are connected in series.

According to one embodiment of the present application, in the case of using multiple synthesis reactors, one or more separators, such as solid-liquid separators, may be provided between any synthesis reactor and the synthesis reactor located downstream thereof.

FIG. 3 shows a picture of an exemplary continuous reaction apparatus used to practice the present application.

As described above, at least a portion (part or all) of the reaction materials (for example, which may include part or all of one or more of the following materials: halogenated olefins, halogenated esters, fluorinating agents, solvents and catalysts) is premixed and fed into the synthesis reactor in the form of a premix, and the remaining portion (if any) of these reaction materials is transported into the synthesis reactor in the form of an independent stream. The reaction materials react in the synthesis reactor to form a fluorinated carboxylic acid ester in the reactor. According to one embodiment of the present application, the reaction materials enter the synthesis reactor in a continuous manner, and the proportions of the components in the reaction materials are as described above. After the materials react under the action of stirring to form a fluorinated carboxylic acid ester, the reacted materials in the reactor (including fluorinated carboxylic acid ester, unreacted reaction raw materials, solvents, catalysts, remaining fluorinating agents, a small amount of by-products, etc.) flow out of the synthesis reactor in a continuous flow, so that the total amount of materials in the synthesis reactor 2 remains constant. According to one embodiment of the present application, the material can be discharged passively by continuously increasing the amount of material in the synthesis reactor, or the material in the reactor 2 can be discharged by the action of a pump (such as a driving action, shearing power, pressure difference, etc.), for example, the material is actively discharged by the action of a screw pump. The continuous outflow from the synthesis reactor is designated herein as crude product stream f.

In an exemplary embodiment of the present application, the fluorine-containing carboxylic acid ester formed by fluorination reaction in the synthesis reactor can be a C2-C12 fluorine-containing carboxylic acid C2-C12 alkyl ester, such as a C3-C10 fluorine-containing carboxylic acid C2-C10 alkyl ester, or a C4-C8 fluorine-containing carboxylic acid C2-C8 alkyl ester, or a C6-C8 fluorine-containing carboxylic acid C2-C6 alkyl ester. According to an embodiment of the present application, the carboxylic acid portion in the "fluorine-containing carboxylic acid ester" (that is, the portion after the ester group excludes the alkoxy group) can have one or more substituted fluorine atoms, for example, the number of substituted fluorine atoms can be 1-24, or 2-20, or 3-16, or 4-16, or 6-16, or 8-16, or within the numerical range obtained by combining any two of the above end values. For example, the carboxylic acid portion in the "fluorine-containing carboxylic acid ester" can be perfluorinated.

According to another embodiment of the present application, the alcohol portion (alkoxy portion) in the "fluorine-containing carboxylic acid ester" may not contain substituted fluorine atoms, or may have one or more substituted fluorine atoms, for example, the number of substituted fluorine atoms may be 1-24, or 2-20, or 3-16, or 4-16, or 6-16, or 8-16, or within the numerical range obtained by combining any two of the above end values. For example, the alcohol portion in the "fluorine-containing carboxylic acid ester" may be completely unsubstituted by fluorine, or may be substituted by perfluorine.

According to a preferred embodiment of the present application, in the fluorinated carboxylic acid ester, the part derived from the halogenated olefin is perfluorinated, while the part derived from the halogenated ester is not perfluorinated. According to an exemplary embodiment of the present application, the fluorinated carboxylic acid ester is a C2-C12 fluorinated alkyl C2-C6 carboxylic acid C1-C8 alkyl ester, or can be a C2-C8 perfluoroalkyl C2-C4 carboxylic acid C2-C4 alkyl ester, for example, can be perfluorohexyl ethyl acetate. The corresponding fluorinated carboxylic acid can be perfluorohexyl acetic acid.

Without wishing to be limited to any particular theory, it is unexpectedly found that, compared with perfluorocarboxylic acids commonly used in the prior art such as perfluorohexanoic acid, the partially fluorinated carboxylic acids of the present application have good biodegradability, effectively overcome the defects of the perfluorocarboxylic acids of the prior art in terms of biological toxicity and accumulation in organisms, and have good various process properties, and can serve as a good substitute for the toxic and harmful perfluorocarboxylic acids of the prior art.

During the reaction in step A, the residence time of the material in the synthesis reactor 2 is 10 minutes to 2 hours, such as 20 minutes to 1 hour, or 10 to 20 minutes, or 40 minutes to 2 hours.

During the reaction in step A, the temperature in the synthesis reactor 2 may be 40-100°C, for example, 70-90°C.

Next, in step B, the crude product stream f is continuously transported to the solid-liquid separation device 3, in which the crude product stream f is continuously subjected to solid-liquid separation operation, and then the liquid crude product stream g from which solid impurities have been removed is continuously transported to the extractive coalescer 4. The extractant h is continuously transported into the extractive coalescer 4 through the extractant inlet on the extractive coalescer 4, and is fully mixed with the liquid crude product stream g, and then phase-separated, and the extraction waste liquid stream j (which mainly contains the solvent and the extractant) flows out from the independent outlet of the extractive coalescer 4, while the extraction crude product stream k (which contains relatively high purity fluorine-containing carboxylic acid ester) flows out continuously from the extractive coalescer 4 and enters the continuous distillation tower 5 located downstream thereof.

According to one embodiment of the present application, the extraction waste liquid stream j mainly contains the solvent and the extractant as described above, and the content of the product (fluorinated carboxylic acid ester) therein is less than 2% by weight, such as less than 1.5% by weight, or less than 1% by weight. According to another embodiment of the present application, the extraction waste liquid stream j can be further distilled, and the separated solvent can be transported to the premixing step or step A, the separated extractant can be recycled and reintroduced from the extractant inlet of the extraction coalescer 4, and the separated fluorinated carboxylic acid ester can be treated independently or transported to the downstream hydrolysis step C.

According to one embodiment of the present application, the content of fluorine-containing carboxylic acid ester in the crude extraction product stream k is further increased, for example, it may be greater than 85% by weight, or greater than 90% by weight.

According to one embodiment of the present application, the extractant h is selected from one or more of the following: water, aromatic hydrocarbons (e.g., C6-C16 aromatic hydrocarbons), ethers (e.g., C2-C12 ethers). According to one embodiment of the present application, the weight ratio of the extractant h continuously input into the extractor coalescer 4 to the liquid crude product stream g is 100:2 to 100:20, for example, 100:5 to 100:15, or 100:7 to 100:12, 100:8 to 100:10, or within the numerical range obtained by combining any two of the above end values.

According to one embodiment of the present application, the crude extraction product stream k is rectified in a continuous distillation tower 5 (also referred to as a "first continuous distillation tower"), and the residual solvent and a small amount of extractant contained in the mixture are discharged in the form of a tower top effluent l, while the content of the target product fluorinated carboxylic acid ester is further increased and flows out from the product outlet of the continuous distillation tower 5 as a purified product stream m. Some other impurities or by-products are discharged as a tower bottom effluent. FIG4 shows a picture of a continuous distillation tower used in the present application.

In the next step C, the purified product stream m is continuously fed into the hydrolysis device 6, and at the same time, an alkali solution p and a solvent (also referred to as a "hydrolysis solvent") o are continuously fed into the hydrolysis device 6, so that the fluorinated carboxylic acid ester in the purified product stream m is hydrolyzed to form the corresponding fluorinated carboxylic acid and/or its salt, and the obtained hydrolyzed product stream n continuously flows out of the hydrolysis device 6 and is transported to a continuous distillation tower 7 (also referred to as a "second continuous distillation tower").

According to one embodiment of the present application, one or more hydrolysis devices 6 may be used; in the case of using multiple hydrolysis devices 6, the multiple hydrolysis devices may be arranged in series or in parallel, preferably in series.

According to one embodiment of the present application, the residence time of the purified product stream m in the hydrolysis device 6 may be 1 minute to 2 hours, for example, 5-100 minutes, or 10-90 minutes, or 20-80 minutes, or 30-70 minutes.

According to one embodiment of the present application, the hydrolysis reaction temperature in the hydrolysis device 6 is 30-80°C, for example, 40-70°C, or 50-60°C.

According to one embodiment of the present application, the hydrolysis solvent o may include C1-C6 alcohol, such as methanol, ethanol, propanol, butanol, pentanol, hexanol, etc., preferably methanol.

According to one embodiment of the present application, the hydrolysis solvent o and the purified product stream m are continuously input into the hydrolysis device so that the weight ratio of the hydrolysis solvent o to the purified product stream m is 50:100 to 500:100; for example, the weight ratio can be 80:100 to 400:100; or 90:100 to 300:100; or 95:100 to 200:100; or 100:100 to 180:100.

According to one embodiment of the present application, the alkaline solution p continuously fed into the hydrolysis device is a solution of an alkaline agent in water with a concentration of 5-40 wt %. For example, the alkaline agent can be an alkali metal hydroxide, preferably sodium hydroxide, lithium hydroxide, potassium hydroxide, or a mixture thereof. According to one embodiment of the present application, the alkali solution p and the purified product stream m are continuously fed into the hydrolysis device so that the weight ratio of the hydrolysis solvent p to the purified product stream m is 100:100 to 500:100; for example, the weight ratio can be 110:100 to 400:100; or 120:100 to 200:100; or 130:100 to 180:100; or 140:100 to 160:100; or 150:100 to 300:100; or 180:100 to 250:100; or 200:100 to 240:100, or within the numerical range obtained by combining any two of the above end values.

According to one embodiment of the present application, the hydrolyzate stream n is continuously input into the continuous distillation tower 7 (second continuous distillation tower) and continuously subjected to distillation treatment (second distillation treatment), and the purified hydrolyzate stream q after distillation is transported to the downstream coalescer. According to one embodiment of the present application, a part or most of the other materials separated by the second continuous distillation tower can be recycled to the previous step. For example, as shown in FIG1 , one or both of the hydrolysis solvent flowing out of the top of the tower and the alkali solution flowing out of the bottom of the tower can be recycled back to the hydrolysis device 6 for hydrolysis operation without treatment or after necessary treatment and purification; in addition to the hydrolysis solvent and alkali solution recycled here, fresh hydrolysis solvent and alkali solution are also provided as needed, so that the weight ratio (flow ratio) of the hydrolysis solvent and alkali solution to the purified product stream m satisfies the description of the above paragraph.

The purified hydrolyzate stream q obtained by separation in the continuous distillation tower 7 is continuously fed into the mixer-coalescer 8. In addition, an acidic reagent r is fed into the mixer-coalescer 8 to acidify the purified hydrolyzate stream q, so that the fluorinated carboxylic acid salt is converted into the target fluorinated carboxylic acid. The product fluorinated carboxylic acid is continuously separated from the waste acid water t in the mixer-coalescer 8, and the obtained fluorinated carboxylic acid crude product s is continuously fed into the downstream purification device 9 for further purification, and finally a high-purity fluorinated carboxylic acid pure product v is obtained.

According to one embodiment of the present application, the temperature of the acidification step can be 0-80°C, preferably 20-50°C. According to one embodiment of the present application, the acidic reagent used in the acidification step can be an inorganic strong acid or an aqueous solution thereof. In the case of using an aqueous solution, the concentration of the aqueous solution can be 0.01-30% by weight, such as 0.1-20% by weight, or 0.2-10% by weight, or 0.5-5% by weight, or 0.8-2% by weight. The inorganic strong acid can be selected from hydrochloric acid, sulfuric acid, phosphoric acid, or a combination thereof. According to one embodiment of the present application, the acidic reagent r and the purified hydrolyzate stream q are continuously added to the mixer-coalescer 8, so that the molar ratio of the acid (hydrogen ion) to the fluorinated carboxylate contained in the purified hydrolyzate stream q is 1:1 to 4:1, for example, 1:1 to 3:1, or 1:1 to 2:1, or 1.1:1 to 1.5:1.

According to one embodiment of the present application, the mixer-coalescer 8 may include a mixer (for continuous acidification) and a coalescer (for continuous separation) connected in series; or may include a mixing section and a coalescing section in the same device.

According to one embodiment of the present application, the purification device 9 can be a continuous distillation device, a continuous rectification device, or a combination thereof. For example, the purification device 9 can be a continuous rectification tower (the third continuous rectification tower), which is used for further purification, wherein a trace amount of water w is discharged from the top of the tower and a high-purity fluorine-containing carboxylic acid pure product u is collected, and the bottom waste v is made to flow out at the bottom of the tower. The bottom waste v is a mixed impurity of fluorine-containing high-boiling substances. The trace water and fluorine-containing carboxylic acid pure product at the top of the tower can be collected by switching the valve as needed.

Compared with the prior art, the continuous production process of the present application can achieve the following advantages:

1. When synthesizing fluorinated carboxylic acid esters, the solid is made into a paste or slurry by premixing the solvent and solid materials in proportion, so that the solid materials can be continuously fed, and the overall raw materials are kept constant within a certain proportion, which can maintain the stability of production quality, and the solid phase materials are always in a dynamic state, and there will be no clogging of pipes or valves. After the synthesized fluorinated carboxylic acid ester passes through a continuous solid-liquid separation device, a continuous extraction and separation device, and a continuous distillation device, a high-purity fluorinated carboxylic acid ester can be obtained, which provides a raw material basis for the subsequent continuous production of fluorinated carboxylic acids;

2. High-purity fluorinated carboxylic acid esters enter the continuous hydrolysis device, and the hydrolysis rate can be adjusted in time according to the reaction conditions by adjusting the alkali ratio and solvent ratio, so as to be compatible with single or multiple series of kettles. The hydrolyzed fluorinated carboxylate enters the mixer, and the acid is continuously introduced for acidification, and continuously introduced into the coalescer for separation, so as to obtain a crude fluorinated carboxylic acid with high purity, and a high-purity fluorinated carboxylic acid can be obtained by continuous distillation and purification;

3. Compared with intermittent reaction, this continuous production process has high overall reaction efficiency, is less prone to blockage and overheating, has lower equipment failure rate, high degree of automation and continuity, and higher product stability;

4. The fluorinated carboxylic acid prepared by the method of the present invention is preferably the partially fluorinated fluorinated carboxylic acid described above, which can be used as a substitute for perfluorooctanoic acid, has lower toxicity, contains a degradable hydrocarbon structure, has good environmental protection, and has extremely low surface tension and critical micelle concentration.

In the following examples, the excellent effects that can be achieved by the method of the present application are specifically described. The purpose is to better understand the content of the present application. It should be understood that these examples are merely illustrative and not restrictive. The reagents used in the examples are conventionally purchased from the market unless otherwise specified. The methods and conditions used in the examples are conventional methods and conditions unless otherwise specified.

Example

All reagents used in the following examples were of analytical grade and used directly without further purification, and all water used was deionized water. The gas chromatograph used in this example was a 8890 gas chromatograph provided by Agilent.

Example 1

In this embodiment, the continuous reaction equipment shown in Figure 3 is used. Potassium fluoride, N,N-dimethylformamide and tetrabutylammonium bromide are first transported into a dynamic mixer at a mass ratio of 30:70:1, and are fully mixed therein to form a uniform slurry material. While the slurry material is continuously discharged at the outlet of the dynamic mixer, potassium fluoride, N,N-dimethylformamide and tetrabutylammonium bromide are continuously added to the dynamic mixer in the proportions described above to maintain continuous discharge of the mixed material.

The slurry material is continuously fed into the synthesis reactor, and ethyl bromoacetate and hexafluoropropylene dimer are continuously fed into the synthesis reactor at the same time, so that the mass flow ratio of the slurry material, ethyl bromoacetate and hexafluoropropylene dimer is 100:120:215. The temperature of the synthesis reactor is controlled at 70°C, and a stirring device is provided therein. The reaction mixture reacts in the synthesis reactor while being stirred and pushed by the newly added material to move toward the outlet of the reactor. The residence time of the reaction material in the reactor is about 20 minutes.

The material flowing out of the synthesis reactor is transported to a continuous solid-liquid separation device (LW220*880 centrifugal screw solid-liquid separator) for solid-liquid separation. The separated solid material is discharged as solid waste, and the separated liquid enters the No. 2 continuous synthesis reactor. Potassium fluoride and N,N-dimethylformamide are also added to the No. 2 continuous synthesis reactor, so that at any time, the mass flow ratio of the slurry material output from the dynamic mixer to ethyl bromoacetate and hexafluoropropylene dimer is 100:15:10. The temperature in the No. 2 continuous synthesis reactor is maintained at 90°C, and a stirring device is provided therein. The reaction mixture reacts in the synthesis reactor while stirring and pushing the newly added material as it moves toward the outlet of the reactor. The residence time of the reaction material in the reactor is about 20 minutes.

The product stream output from the No. 2 continuous synthesis reactor is continuously input into a continuous solid-liquid separation device (LW220*880 centrifugal screw solid-liquid separator), and the solid material obtained by separation is removed as waste. The obtained liquid phase is a crude product stream of fluorinated carboxylic acid ester with a purity of ≥73%. The reaction yield is 96% as measured by gas chromatography.

Next, the crude product stream of the fluorinated carboxylic acid ester is continuously conveyed into an extraction coalescer (M50 high-speed centrifugal extractor), and water is continuously introduced into the extraction coalescer so that the flow ratio (mass ratio) of the crude product of the fluorinated carboxylic acid ester to water is 10:1. After mixing, the crude products are phase-separated to obtain an extracted crude product stream (measured by gas chromatography, the purity of the fluorinated carboxylic acid ester is greater than 93%). The extracted crude product stream is continuously conveyed to a first continuous distillation tower. The phase separation also produces an aqueous solution of N,N-dimethylformamide. After dehydration, the N,N-dimethylformamide can be recovered and recycled.

In the first continuous distillation tower (as shown in FIG4 , a wire mesh packing is used in the continuous distillation tower, the pressure in the kettle is about 100 mbar, and the kettle temperature is about 47° C.), the extracted crude product stream is distilled, and the outlet near the top is collected to obtain a purified product stream, and the purity of the fluorinated carboxylic acid ester is measured by gas chromatography to be ≥99%, and the yield is greater than 90%).

The purified product stream was continuously fed into a hydrolysis device, and a 12 wt% aqueous sodium hydroxide solution and methanol were continuously added to the hydrolysis device, so that the flow ratio (weight) of the purified product stream: sodium hydroxide: methanol was 3:5:5. The temperature in the hydrolysis device was maintained at 50° C., and the residence time of the material in the hydrolysis device was about 35 minutes. The degree of hydrolysis was measured by nuclear magnetic resonance to be greater than 99%.

The hydrolyzate stream is fed into a second continuous distillation tower (the second continuous distillation tower is completely the same as the first continuous distillation tower, the kettle temperature is about 300 mbar, and the kettle temperature is about 75° C.) to distill the hydrolyzate stream, and the outlet near the bottom collects the purified hydrolyzate stream. Methanol with a purity of more than 99% is obtained at the top of the second continuous distillation tower, which can be directly transported to the hydrolysis device for recycling.

The purified hydrolyzate stream is conveyed into a mixer for continuous acidification, the acidification temperature is controlled at 50°C, and the pH of the acidified material is ensured to be less than 2. The acidified product is continuously passed into a coalescer for continuous separation, so as to obtain a fluorinated carboxylic acid with a phase purity of more than 90% and a waste acid solution. The above hydrolysis and acidification phase separation operation obtains a crude fluorinated carboxylic acid, wherein the loss rate of the fluorinated carboxylic acid is less than 1%.

Then, the crude fluorinated carboxylic acid is transported to a third continuous distillation tower (the third continuous distillation tower is exactly the same as the first continuous distillation tower, the temperature in the kettle is about 150 mbar, and the kettle temperature is about 120° C.) for distillation to obtain a pure fluorinated carboxylic acid, and its image after crystallization is shown in FIG2. The pure product is characterized by nuclear magnetic resonance technology, and the nuclear magnetic fluorine spectrum and nuclear magnetic hydrogen spectrum of the pure product are shown in FIG5 and FIG6 respectively. It is measured that the purity of the fluorinated carboxylic acid (perfluorohexyl-ethyl acetate) is greater than 99%, and the purification yield is ≥90%.

Example 2

In this embodiment, the same continuous reaction equipment as in Embodiment 1 is used. Potassium fluoride, N,N-dimethylformamide and tetrabutylammonium bromide are first transported into a dynamic mixer at a mass ratio of 45:90:2, and are fully mixed therein to form a uniform slurry material. While the slurry material is continuously discharged at the outlet of the dynamic mixer, potassium fluoride, N,N-dimethylformamide and tetrabutylammonium bromide are continuously added to the dynamic mixer in the proportions described above to maintain continuous discharge of the mixed material.

The slurry material is continuously fed into the synthesis reactor, and ethyl bromoacetate and hexafluoropropylene dimer are continuously fed into the synthesis reactor at the same time, so that the mass flow ratio of the slurry material, ethyl bromoacetate and hexafluoropropylene dimer is 137:120:215. The temperature of the synthesis reactor is controlled at 90°C, and a stirring device is provided therein. The reaction mixture reacts in the synthesis reactor while being stirred and pushed by the newly added material to move toward the outlet of the reactor. The residence time of the reaction material in the reactor is about 1 hour.

The material flowing out of the synthesis reactor is transported to a continuous solid-liquid separation device (LW220*880 centrifugal screw solid-liquid separator) for solid-liquid separation. The separated solid material is discharged as solid waste, and the separated liquid phase is a crude product stream of fluorinated carboxylic acid ester with a purity of ≥71%, and the reaction yield is 93% as measured by gas chromatography.

Next, the crude product stream of the fluorinated carboxylic acid ester is continuously conveyed into an extraction coalescer (M50 high-speed centrifugal extractor), and water is continuously introduced into the extraction coalescer so that the flow ratio (mass ratio) of the crude product of the fluorinated carboxylic acid ester to water is 10:1. After mixing, the crude product stream is phase-separated to obtain an extracted crude product stream (measured by gas chromatography, the purity of the fluorinated carboxylic acid ester is greater than 92%). The extracted crude product stream is continuously conveyed to a first continuous distillation tower. The phase separation also produces an aqueous solution of N,N-dimethylformamide. After dehydration, the N,N-dimethylformamide can be recovered and recycled.

In the first continuous distillation tower (the first continuous distillation tower is the same as the first continuous distillation tower used in Example 1, the pressure in the kettle is about 100 mbar, and the kettle temperature is about 47°C), the extracted crude product stream is distilled, and the outlet near the top is collected to obtain a purified product stream, and the purity of the fluorinated carboxylic acid ester is measured by gas chromatography to be ≥99%, and the yield is greater than 90%).

The purified product stream was continuously fed into a hydrolysis unit, and sodium hydroxide and methanol at a concentration of 12% by weight were continuously added to the hydrolysis unit, so that the flow ratio (weight) of the purified product stream: sodium hydroxide: methanol was 3:5:3. The temperature in the hydrolysis unit was maintained at 55° C., and the residence time of the material in the hydrolysis unit was about 70 minutes. The degree of hydrolysis was measured by nuclear magnetic resonance to be 99%.

The hydrolyzate stream is fed into a second continuous distillation tower (the second continuous distillation tower is completely the same as the first continuous distillation tower, the kettle temperature is about 300 mbar, and the kettle temperature is about 75° C.), the hydrolyzate stream is distilled, and the outlet near the bottom collects the purified hydrolyzate stream. Methanol with a purity of more than 99% is obtained at the top of the second continuous distillation tower, which can be directly transported to the hydrolysis device for recycling.

The purified hydrolyzate stream is conveyed into a mixer for continuous acidification, the acidification temperature is controlled to be lower than 50°C, and the pH of the acidified material is ensured to be less than 2. The acidified product is continuously passed into a coalescer for continuous separation, so as to obtain a fluorinated carboxylic acid with a phase purity of more than 90% and a waste acid solution. The above hydrolysis and acidification phase separation operation obtains a crude fluorinated carboxylic acid, wherein the loss rate of the fluorinated carboxylic acid is less than 1%.

Then, the crude fluorinated carboxylic acid is transported to a third continuous distillation tower (the third continuous distillation tower is exactly the same as the first continuous distillation tower, the temperature in the kettle is about 150 mbar, and the kettle temperature is about 120° C.), and distilled to obtain a pure fluorinated carboxylic acid. The purity of the fluorinated carboxylic acid is greater than 99% as measured by nuclear magnetic resonance, and the purification yield is ≥90%.

Example 3

In this embodiment, the same continuous reaction equipment as in Embodiment 1 is used. First, cesium fluoride, N,N-dimethylformamide and tetrabutylammonium bromide are transported into a dynamic mixer at a mass ratio of 117:100:1, and are fully mixed therein to form a uniform slurry material. While the slurry material is continuously discharged at the outlet of the dynamic mixer, potassium fluoride, N,N-dimethylformamide and tetrabutylammonium bromide are continuously added to the dynamic mixer in the proportions described above to maintain continuous discharge of the mixed material.

The slurry material is continuously fed into the synthesis reactor, and ethyl bromoacetate and hexafluoropropylene dimer are continuously fed into the synthesis reactor at the same time, so that the mass flow ratio of the slurry material, ethyl bromoacetate and hexafluoropropylene dimer is 218:120:215. The temperature of the synthesis reactor is controlled at 90°C, and a stirring device is provided therein. The reaction mixture reacts in the synthesis reactor while being stirred and pushed by the newly added material to move toward the outlet of the reactor. The residence time of the reaction material in the reactor is about 1 hour.

The material flowing out of the synthesis reactor is transported to a continuous solid-liquid separation device (LW220*880 centrifugal screw solid-liquid separator) for solid-liquid separation. The separated solid material is discharged as solid waste, and the separated liquid phase is a crude product stream of fluorinated carboxylic acid ester with a purity of ≥69%, and the reaction yield is 91% as measured by gas chromatography.

Next, the crude product stream of the fluorinated carboxylic acid ester is continuously conveyed into an extraction coalescer (M50 high-speed centrifugal extractor), and water is continuously introduced into the extraction coalescer so that the flow ratio (mass ratio) of the crude product of the fluorinated carboxylic acid ester to water is 10:1. After mixing, the crude product stream is phase-separated to obtain an extracted crude product stream (measured by gas chromatography, the purity of the fluorinated carboxylic acid ester is greater than 92%). The extracted crude product stream is continuously conveyed to a first continuous distillation tower. The phase separation also produces an aqueous solution of N,N-dimethylformamide. After dehydration, the N,N-dimethylformamide can be recovered and recycled.

In the first continuous distillation tower (the first continuous distillation tower is the same as the first continuous distillation tower used in Example 1, the pressure in the kettle is about 100 mbar, and the kettle temperature is about 47°C), the extracted crude product stream is distilled, and the outlet near the top is collected to obtain a purified product stream, and the purity of the fluorinated carboxylic acid ester is measured by gas chromatography to be ≥99%, and the yield is greater than 90%).

The purified product stream was continuously fed into a hydrolysis device, and a 15 wt% lithium hydroxide aqueous solution and methanol were continuously added to the hydrolysis device, so that the flow ratio (weight) of the purified product stream: lithium hydroxide: methanol was 4:3:5. The temperature in the hydrolysis device was maintained at 60° C., and the residence time of the material in the hydrolysis device was about 30 minutes. The degree of hydrolysis was measured by nuclear magnetic resonance to be 99%.

The hydrolyzate stream is fed into a second continuous distillation tower (the second continuous distillation tower is completely the same as the first continuous distillation tower, the kettle temperature is about 300 mbar, and the kettle temperature is about 75° C.), the hydrolyzate stream is distilled, and the outlet near the bottom collects the purified hydrolyzate stream. Methanol with a purity of more than 99% is obtained at the top of the second continuous distillation tower, which can be directly transported to the hydrolysis device for recycling.

The purified hydrolyzate stream is conveyed into a mixer for continuous acidification, the acidification temperature is controlled at 50°C, and the pH of the acidified material is ensured to be less than 2. The acidified product is continuously passed into a coalescer for continuous separation, so as to obtain a fluorinated carboxylic acid with a phase purity of more than 90% and a waste acid solution. The above hydrolysis and acidification phase separation operation obtains a crude fluorinated carboxylic acid, wherein the loss rate of the fluorinated carboxylic acid is less than 1%.

Then, the crude fluorinated carboxylic acid is transported to a third continuous distillation tower (the third continuous distillation tower is exactly the same as the first continuous distillation tower, the temperature in the kettle is about 150 mbar, and the kettle temperature is about 120° C.), and distilled to obtain a pure fluorinated carboxylic acid. The purity of the fluorinated carboxylic acid is greater than 99% as measured by nuclear magnetic resonance, and the purification yield is ≥90%.

Comparative Example 1

In this comparative example, a continuous reaction and purification process design was not adopted, and a premixing operation of the reaction materials was not adopted.

Specifically, potassium fluoride, N,N-dimethylformamide, bromobutylammonium bromide, hexafluoropropylene dimer and tetrabutylammonium bromide were added into the synthesis reactor at a weight ratio of 9:19:24:43:2 at one time. The temperature of the synthesis reactor was controlled at 90° C. and the reaction was continued for 1 hour.

After the reaction is completed, the materials in the synthesis reactor are transported to a solid-liquid separation device (LW220*880 centrifugal screw solid-liquid separator) for solid-liquid separation. The separated solid materials are discharged as solid waste, and the separated liquid phase is a crude product stream of fluorinated carboxylic acid ester with a purity of ≥70%, and the reaction yield is 80% as measured by gas chromatography.

Next, the crude product stream of the fluorinated carboxylic acid ester is transported into an extraction coalescer (M50 high-speed centrifugal extractor), and water is introduced into the extraction coalescer so that the mass ratio of the crude product of the fluorinated carboxylic acid ester to water is 10:1. The product is fully stirred and then allowed to stand for stratification. The upper layer is an aqueous solution of N,N-dimethylformamide, from which the N,N-dimethylformamide can be recycled and reused after dehydration. The lower layer is the extracted crude product (measured by gas chromatography, the purity of the fluorinated carboxylic acid ester is greater than 90%).

The extracted crude product is transported to a first distillation tower, in which the extracted crude product is distilled (the first distillation tower is the same as the first continuous distillation tower used in Example 1, with a kettle pressure of about 100 mbar and a kettle temperature of about 47°C), and a purified product is collected at an outlet near the top. The purity of the fluorinated carboxylic acid ester is determined by gas chromatography to be ≥99%, and the yield is greater than 90%).

The purified product was fed into a hydrolysis device, and sodium hydroxide and methanol with a concentration of 12% by weight were added to the hydrolysis device, so that the weight ratio of purified product flow: sodium hydroxide: methanol was 3:5:3. The temperature in the hydrolysis device was maintained at 55° C., and the retention time of the material in the hydrolysis device was 35 minutes. The degree of hydrolysis was measured to be 99%.

The hydrolyzate is fed into a second distillation tower (the second distillation tower is exactly the same as the first distillation tower, the temperature in the kettle is about 300 mbar, and the kettle temperature is about 75° C.), the hydrolyzate is distilled, and the purified hydrolyzate is collected at the outlet near the bottom. A mixed solution of methanol, ethanol and water is obtained at the top of the second distillation tower.

The purified hydrolyzate is conveyed into a mixer for continuous acidification, the acidification temperature is controlled below 50°C, and the pH of the acidified material is ensured to be less than 2. The acidified product is continuously passed into a coalescer for separation, to obtain fluorinated carboxylic acid and waste acid liquid with a phase separation purity of more than 90%.

Then, the crude fluorinated carboxylic acid is transported to a third distillation tower (the third distillation tower is exactly the same as the first distillation tower, the temperature in the kettle is about 150 mbar, and the kettle temperature is about 120° C.), and distilled to obtain a pure fluorinated carboxylic acid. The purity of the fluorinated carboxylic acid is greater than 99% as measured by nuclear magnetic resonance. In addition, the time required for single batch production of the same scale in the above Examples 1-3 and Comparative Example 1 is compared in the following table.

Table 1 shows the total time required for synthesizing batch products of the same scale in Examples 1-3 and Comparative Example 1.

It can be seen from Table 1 above that, excluding the influence of experimental errors, the intermittent reaction of Comparative Example 1 requires a lot of time to heat up, cool down and stand the materials, while the continuous production process of Examples 1-3 can save at least 30% of the time under the same scale of equipment.

In addition, the present invention also carried out the following Examples 4 and 5 to examine the effect of adjusting the process conditions on the results.

Example 4

In this Example 4, the steps of Example 1 were repeated, but in the hydrolysis step, the material stayed in the hydrolysis device, the process parameters of the hydrolysis device were adjusted, and samples were continuously taken from the hydrolysis device at intervals of 5 minutes to examine the degree of hydrolysis of the material therein. When the degree of hydrolysis reached 99%, the time at this time was recorded. The process parameters and the minimum time required for sufficient hydrolysis are summarized in the following table:

Table 1: Statistical table of hydrolysis reaction data (the alkali solution used is sodium hydroxide aqueous solution, and the solvent is methanol).

Example 5

In this Example 5, the steps of Example 1 were repeated, but in the acidification step, the process parameters of this step were adjusted, and the results after acidification were detected, which are summarized in the following Table 2:

Table 2 Effect of acidification reaction process parameters on acidification effect (acidic reagent is sulfuric acid solution)

Acidification formula Acid Ratio Acidification temperature ℃ Fluorinated carboxylic acid% Impurities% Residual acid % after separation 1 1.2 30 95 0 1 2 1.5 30 95 0 3 3 2 30 90 0 7 4 1.5 60 80 10 3

Claims (10)

1. A continuous method for preparing a fluorine-containing carboxylic acid, the method comprising: Step A: continuously feeding a reaction raw material, a fluorinating agent, a solvent and a catalyst into a synthesis reactor (2), so that the reaction raw material to be fluorinated reacts with the fluorinating agent in the synthesis reactor (2) to generate a fluorine-containing carboxylic acid ester, and simultaneously allowing a crude product stream (f) containing the fluorine-containing carboxylic acid ester to continuously flow out of the synthesis reactor (2); Step B: separating and purifying the crude product stream (f) to obtain a purified product stream (m); Step C: hydrolyzing the purified product stream (m) to obtain a hydrolyzed product stream (n), wherein the hydrolyzed product stream (n) contains fluorinated carboxylic acid and/or a salt thereof; Step D: acidifying the hydrolyzed product stream (n) to obtain a crude fluorinated carboxylic acid; Step E: Purifying the crude fluorine-containing carboxylic acid to obtain a pure fluorine-containing carboxylic acid. 2. The method according to claim 1, characterized in that, before step A, the fluorinating agent, the catalyst and the solvent are premixed in a dynamic mixer (1) to form a premix; Then, in step A, the premix is continuously fed into the synthesis reactor (2), while the reaction raw materials are continuously fed into the synthesis reactor (2) independently of the premix. 3. The method according to claim 1 or 2, characterized in that the fluorinating agent is selected from one or more of the following: potassium fluoride, sodium fluoride, ammonium fluoride, calcium fluoride, lithium fluoride, cesium fluoride; The catalyst is selected from one or more quaternary ammonium salts of the following: benzyltriethylammonium chloride, tetrabutylammonium hydrogen sulfate, tetrabutylammonium bromide, hyperbranched quaternary ammonium salts, trifluoromethylthiotetramethylammonium salts, dibutyl phosphate tetrabutylammonium salt, malondialdehyde tetrabutylammonium salt; The solvent is selected from one or more of the following: dimethylformamide, dimethylacetamide, acetonitrile, dimethyl sulfoxide, methyl pyrrolidone; The reaction raw materials include halogenated olefins and halogenated esters; the halogenated olefins are selected from one or more of the following: halogenated C2-C12 olefins, halogenated C2-C12 olefin dimers, halogenated C2-C12 olefin trimers, halogenated C2-C12 olefin tetramers, halogenated C2-C12 olefin pentamers, and halogenated C2-C12 olefin hexamers; the halogenated esters are selected from one or more of the following: halogenated C2-C12 carboxylic acid C1-C12 alkyl esters, halogenated C2-C12 carboxylic acid C3-C12 cycloalkyl esters, and halogenated C2-C12 carboxylic acid C6-C12 aralkyl esters. 4. The method according to claim 1 or 2, characterized in that, in the step A, the reaction is carried out at a temperature of 40-100°C, and the residence time of the reaction materials in the synthesis reactor (2) is 10 minutes to 2 hours. 5. The method according to claim 1 or 2, characterized in that step B comprises the following operations: Separation: The crude product stream (f) is subjected to solid-liquid separation in a centrifugal screw solid-liquid separator (g) to obtain solid waste salt and a liquid crude product stream (g); Purification: The liquid crude product stream (g) is extracted with an extractant (h) in an extractor coalescer (4) and then rectified in a continuous distillation column (5) to obtain a purified product stream (m). 6. The method according to claim 1 or 2, characterized in that in step C, the purified product stream (m) is mixed with a hydrolysis solvent (o) and an alkali solution (p) to cause hydrolysis; The hydrolysis is carried out at a temperature of 30-80°C; The hydrolysis solvent (o) is a C1-C6 alcohol, and the weight ratio of the hydrolysis solvent (o) to the purified product stream (m) is 50:100 to 500:100; The alkali solution (p) is a solution of an alkaline agent in water with a concentration of 5-40 weight %, the alkaline agent is an alkali metal hydroxide, and the weight ratio of the alkali solution (p) to the purified product stream (m) is 100:100 to 500:100. 7. The method according to claim 1 or 2, characterized in that in step D, the hydrolyzate stream (s) is acidified and separated in a mixer-coalescer (8), and then in step E, it is purified in a purification device (9) to obtain a pure fluorinated carboxylic acid; The acidification is carried out at a temperature of 0-80°C; The molar ratio of the acidic reagent (r) used in the acidification process to the fluorine-containing carboxylic acid salt contained in the hydrolyzate stream (n) is 1:1 to 4:1. 8. The method according to claim 1 or 2, characterized in that the fluorine-containing carboxylic acid is a C2-C12 fluorine-containing alkyl C2-C6 carboxylic acid. 9. A fluorinated carboxylic acid product, prepared by the method according to any one of claims 1 to 8, wherein the fluorinated carboxylic acid does not include perfluorooctanoic acid. 10. A continuous fluorination reaction equipment, which is used to implement the method according to any one of claims 1 to 8, and comprises: a dynamic mixer (1), a synthesis reactor (2), a solid-liquid separation device (3), an extraction coalescer (4), a continuous distillation tower (5), a hydrolysis device (6), a continuous distillation tower (7), a mixing-coalescing device (8), and a purification device (9).