Method for purifying alkali metal perfluorobutanesulfonate

Abstract

Disclosed is a method for purifying alkali metal perfluorobutane sulfonate, comprising the following steps: providing a reaction container with a filtering device and a temperature control device; placing a crude alkali metal perfluorobutane sulfonate product in the reaction container, adding a solvent and heating the solvent to dissolve the crude product; cooling the crude product to allow a portion of the alkali metal perfluorobutane sulfonate to crystallize and then filtering the portion of the crystals; further cooling the crude product to crystallize the crude product and filtering the crude product to obtain electronic grade alkali metal perfluorobutane sulfonate crystals.

Description

Technical Field

[0001] The present invention relates to a method for purifying electronic-grade alkali metal perfluorobutanesulfonate. The method can be used to obtain alkali metal perfluorobutanesulfonate with extremely low impurity fluoride ions and metal ions, such as electronic-grade potassium perfluorobutanesulfonate. Background Art

[0002] Potassium perfluorobutanesulfonate is a widely used new fluorine-containing material, mainly used as a special flame retardant. It can also be used in various applications in the fields of photoresist raw materials, secondary battery electrolytes, antistatic agents, perfluoroalkyl sulfonic acid catalysts, and perfluoroalkyl sulfonic acid ionic liquids.

[0003] At present, the application of potassium perfluorobutanesulfonate products in the electronics / electrical / battery industries is rapidly expanding. These new industry applications require that the product must be highly pure and have extremely low impurity fluoride ions and metal ions.

[0004] The prior art has proposed a variety of methods for purifying potassium perfluorobutanesulfonate. For example,

[0005] CN1935785A proposes adding 0.2% to 0.5% sulfuric acid to a potassium perfluorobutanesulfonate product with a known free fluoride ion concentration greater than 500 ppm, and heating the mixture at 120°C to 350°C for 2 to 6 hours to produce potassium perfluorobutanesulfonate with a free fluoride content of less than 65 ppm. This method forms a new byproduct by adding sulfuric acid, and the resulting fluoride ion content is greater than 10 ppm.

[0006] CN103097349B proposes to purify fluorinated alkane sulfonates by recrystallization to obtain fluorinated alkane sulfonates containing less than 500 μg of inorganic salt impurities per gram. However, the product obtained by this method has a high metal ion content and is not suitable for electronic grade applications.

[0007] CN102272096A uses adsorbents to reduce the fluoride ion content. However, since the adsorbent is composed of a large amount of metal ions, the use process not only fails to remove the metal ions, but also increases the residual metal ions.

[0008] Fractional recrystallization uses solubility differences to separate the various components in a mixture. That is, the mixture is repeatedly dissolved and crystallized under appropriate conditions (where the solubility difference of each component is the largest). After each dissolution and crystallization, the component with lower solubility is concentrated in the crystals, while the component with higher solubility is concentrated in the mother liquor. After repeated treatments, the purpose of separation can be achieved.

[0009] This field still needs to develop a new fluoride ion and metal ion removal process to improve the quality of potassium perfluorobutanesulfonate and meet the requirements of electronic / battery-grade ion residual indicators. Summary of the Invention

[0010] To solve the above technical problems, the present invention aims to provide a method for purifying alkali metal perfluorobutanesulfonate, which can effectively remove residual fluoride ions and metal ions in the preparation process of potassium perfluorobutanesulfonate, so that it meets the requirements for use as an electronic-grade chemical.

[0011] Therefore, one aspect of the present invention relates to a method for purifying alkali metal perfluorobutanesulfonate, comprising the steps of:

[0012] Providing a recrystallization reaction vessel with a filtering device and a temperature control device;

[0013] placing a crude alkali metal perfluorobutanesulfonate product in the reaction vessel, adding a solvent and heating the vessel to dissolve the crude product;

[0014] Lowering the temperature to allow a portion of the alkali metal perfluorobutanesulfonate to crystallize and then filtering off the crystals;

[0015] The temperature is further lowered to crystallize, and electronic grade alkali metal perfluorobutanesulfonate crystals are obtained by filtration. DETAILED DESCRIPTION

[0016] In the present invention, the term "electronic grade alkali metal perfluorobutanesulfonate" refers to an alkali metal perfluorobutanesulfonate having a free metal ion and silicon content of less than 5 ppm each and a free fluorine content of less than 9.5 ppm by weight.

[0017] The inventors of the present invention discovered that using fractional recrystallization to purify existing alkali metal perfluorobutanesulfonates, such as potassium perfluorobutanesulfonate obtained in CN103097349, which contains 500 ppm of inorganic salt impurities, is difficult to reduce the impurity content by another 1-2 orders of magnitude. However, the inventors discovered that during the recrystallization process, impurities accumulate in large quantities in the pre-formed crystals. This discovery led to the completion of the present invention.

[0018] Therefore, the purification method of the present invention comprises:

[0019] 1. Provide a recrystallization reaction vessel with a filtration device and a temperature control device;

[0020] There are no particular limitations on the filtration device used in the reaction vessel of the present invention, provided that it can filter out the formed crystals from the vessel. Similarly, there are no particular limitations on the temperature control device used in the reaction vessel of the present invention, provided that it can maintain the temperature of the reaction vessel at a predetermined temperature.

[0021] In one embodiment of the present invention, the reaction vessel comprises an upper and lower portion separated by a movable plate with a filter screen below the plate. The bottom of the reaction vessel is also equipped with a movable plate with a filter screen below the plate. The outer periphery of the reaction vessel is provided with a heat-insulating jacket.

[0022] In one embodiment of the present invention, the reaction container is further provided with a stirring device so as to stir the solution during dissolution to shorten the dissolution time or make the formed solution more uniform.

[0023] 2. Place the crude product of alkali metal perfluorobutanesulfonate in the reaction vessel, add solvent and heat to dissolve it

[0024] There is no particular limitation on the crude alkali metal perfluorobutanesulfonate product suitable for the method of the present invention. However, in order to improve the purification efficiency, conventional high-purity alkali metal perfluorobutanesulfonates known in the art are generally used, such as the alkali metal perfluorobutanesulfonate obtained in CN103097349 with an inorganic salt impurity content of no more than 500 ppm.

[0025] The solvent suitable for the method of the present invention is not particularly limited and can be a conventional solvent known in the art. For example, the solvent mentioned in CN103097349 (this document is inserted herein by reference as part of the present invention). In one embodiment of the present invention, the solvent is selected from acetone, methyl ethyl ketone, methanol, ethanol, isopropanol, acetonitrile, ethyl acetate, tetrahydrofuran, 1,2-dimethoxyethane and dimethyl carbonate or a mixture thereof. Preferred solvents include acetone, methanol and ethanol. If the solubility of the fluorinated alkane sulfonate in the preferred solvent is low (for example, less than about 20% by weight), a small amount of water (for example, less than about 2% by weight) can be added to the solvent or solvent mixture to increase the solubility of the fluorinated alkane sulfonate. Preferably, water is completely miscible with the solvent or solvent mixture.

[0026] In the method of the present invention, the amount of solvent used and the temperature for heating and dissolving are not particularly limited and may be the amount of solvent and the temperature for heating and dissolving commonly used in recrystallization. A person skilled in the art can readily determine the appropriate solvent, amount of solvent used, and heating temperature based on the solubility curve of the alkali metal perfluorobutanesulfonate.

[0027] In one embodiment of the present invention, the amount of solvent used is 4.5-5.5kg, preferably 4.8-5.2kg, most preferably 4.9-5.1kg, and preferably 5kg per kg of alkali metal perfluorobutanesulfonate; the heating temperature is 70-80°C, preferably 72-78°C, more preferably 74-76°C, and preferably 75°C.

[0028] In one embodiment of the present invention, stirring is performed while heating to shorten the dissolution time or form a uniform solution.

[0029] 3. Cool down to allow some alkali metal perfluorobutanesulfonate to crystallize and then filter out the crystals.

[0030] There are two main factors to consider when lowering the temperature during precipitation. The first is the solubility curve of the alkali metal perfluorobutanesulfonate. The second is whether the purity of the alkali metal perfluorobutanesulfonate finally formed meets the requirements. The third is the cost caused by discarding the early crystals.

[0031] In one embodiment of the present invention, the alkali metal perfluorobutanesulfonate is potassium perfluorobutanesulfonate, and the solvent is selected from ethanol and acetone, preferably ethanol. The temperature is initially raised to 70-80°C for dissolution, and then the temperature is lowered by 8-12°C, preferably 9-10°C to form the first crystals, which are then filtered off.

[0032] The method for filtering out the first crystals is not particularly limited and may be a conventional method known in the art.

[0033] In one embodiment of the present invention, the reaction vessel consists of an upper and lower portion separated by a movable plate with a filter screen below. The bottom of the reaction vessel is also equipped with a movable plate with a filter screen below. The outer periphery of the reaction vessel is provided with an insulating jacket. During use, an alkali metal perfluorobutylsulfonate is placed in the upper portion of the reaction vessel, a solvent is added, and the solution is heated to dissolve. The solution is then cooled to form a first crystal. The intermediate plate separating the upper and lower portions is opened, allowing the solution in the upper portion of the reaction vessel to fall through the filter screen into the lower portion at the same temperature, thereby filtering out the first crystals.

[0034] 4. Further cool down and crystallize, and filter to obtain electronic grade alkali metal perfluorobutanesulfonate crystals.

[0035] The method for further cooling and crystallization is not particularly limited and can be a conventional method known in the art. In one embodiment of the present invention, the temperature is further lowered to room temperature or to a temperature of 5-15° C. to form the final electronic grade alkali metal perfluorobutanesulfonate crystals.

[0036] In one embodiment of the present invention, the method of the present invention comprises the following steps:

[0037] The crude product of potassium perfluorobutanesulfonate was added to the reactor, and the solvent was added. Hot water was passed through the jacket to heat the solution in the reactor to 70-80°C and stirred to dissolve. The stirring time was 0.5-2 hours;

[0038] The reactor jacket is passed through warm water to cool the reactor, and the solution in the reactor is controlled to 60-70°C. After observing the crystallization of microcrystalline particles (microcrystalline particle diameter is 0.5-20 μm), the bottom valve is opened to pass through the filter, and the solution enters the recrystallization kettle, which is a stirred jacketed reactor. The temperature is lowered to 5-15°C to complete the recrystallization process of potassium perfluorobutanesulfonate. After filtration, it is dried to obtain electronic grade potassium perfluorobutanesulfonate.

[0039] In one embodiment of the present invention, the crude potassium perfluorobutanesulfonate product can be synthesized by a known method, such as the method described in CN111170898A, and has a metal ion (sodium, magnesium, iron, calcium, silicon) residual content of ≥30 ppm and a fluoride ion content of ≥50 ppm by weight.

[0040] In one embodiment of the present invention, a mixed solvent of ethanol and water is used, preferably the mass ratio of ethanol to water is 20-80:100.

[0041] In one embodiment of the present invention, the dissolution temperature is 70-80°C, preferably 72-78°C.

[0042] In one embodiment of the present invention, the precipitation temperature of the first crystallization is 60-70°C, preferably 64-68°C.

[0043] Example

[0044] The preferred embodiments of the present invention are described in detail below so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more precise definition of the protection scope of the present invention.

[0045] Example 1

[0046] To a 20 L jacketed reactor with a stirring volume, 3 kg of potassium perfluorobutanesulfonate was added, and the fluorine, sodium, magnesium, iron, calcium, and silicon ion contents thereof were as shown in Appendix 1; 5 L of ethanol and 10 L of water were added, stirring was started, and the mixture was heated to 75° C. and stirred for 1 hour until it was completely dissolved and no particulate matter was left; the warm water in the reactor jacket was replaced, and the reactor temperature was controlled to slowly and steadily drop to 65° C. When microcrystals with a maximum size of 2 μm appeared in the reactor, the bottom valve was opened, and the solution entered the recrystallization reactor, which was a 20 L stirred jacketed reactor, through a filter membrane with a pore size of 0.45 μm. The solution was cooled to about 10° C. to complete the recrystallization process of potassium perfluorobutanesulfonate. After filtration, the solution was dried to obtain electronic grade potassium perfluorobutanesulfonate, and the fluorine, sodium, magnesium, iron, calcium, and silicon ion contents thereof were as shown in Appendix 1.

[0047] Example 2

[0048] Referring to Example 1, other conditions remain unchanged and the crystallite size during filtration is set to a maximum of 5 μm crystallite.

[0049] Example 3

[0050] Referring to Example 1, other conditions remained unchanged, the added solvent was adjusted to pure water, the heating temperature was 95°C, and the temperature during filtration was 80°C.

[0051] Example 4

[0052] With reference to Example 1, other conditions remained unchanged, and the added solvent was adjusted to pure ethanol.

[0053] Comparative Example 1

[0054] To a 20L stirred reactor, add 3kg of potassium perfluorobutanesulfonate (fluorine, sodium, magnesium, iron, calcium, and silicon ion contents are shown in Appendix 1). Dissolve the mixture in 8kg of acetone, add 20g of molecular sieve 13X powder (compliant with national standard GB T36203-2018), and stir at room temperature for 2 hours. After filtering through a 0.2μm PTFE filter, the filtrate is concentrated to obtain potassium perfluorobutanesulfonate crystals. The fluorine, sodium, magnesium, iron, calcium, and silicon ion contents are shown in Appendix 1.

[0055] Comparative Example 2

[0056] To a 20 L stirred kettle, add 3 kg of potassium perfluorobutanesulfonate (the fluorine, sodium, magnesium, iron, calcium, and silicon ion contents are shown in Appendix 1). Then add 12 g of sulfuric acid, heat to 200°C, and stir for 3 hours. After evaporating the solvent, crystals of potassium perfluorobutanesulfonate are obtained. The fluorine, sodium, magnesium, iron, calcium, and silicon ion contents (unit: ppm) are shown in Appendix 1.

[0057] Comparative Example 3

[0058] To a 20-L jacketed reactor with stirring, 3 kg of potassium perfluorobutanesulfonate was added, the fluorine, sodium, magnesium, iron, calcium, and silicon ion contents of which were shown in Appendix 1; 5 L of ethanol and 10 L of water were added, stirring was started, and the mixture was heated to 85° C. and stirred for 1 hour until it was completely dissolved and no particulate matter was left; the temperature was lowered to approximately 10° C. to complete the recrystallization process of the potassium perfluorobutanesulfonate, and the mixture was filtered and dried to obtain potassium perfluorobutanesulfonate, the fluorine, sodium, magnesium, iron, calcium, and silicon ion contents of which were shown in Appendix 1.

[0059] Table 1

[0060] sample fluorine sodium magnesium iron calcium silicon Potassium perfluorobutanesulfonate before treatment 53.6 46 18 22 61 35 Example 1 6.5 <5 <5 <5 <5 <5 Example 2 5.7 <5 <5 <5 <5 <5 Example 3 9.2 <5 <5 <5 <5 <5 Example 4 8.5 <5 <5 <5 <5 <5 Comparative Example 1 22.3 55 16 20 55 45 Comparative Example 2 24.4 40 22 25 46 34 Comparative Example 3 31.8 37 17 19 42 31

[0061] From the above test results, it can be seen that the method of the present invention can advantageously obtain high-purity electronic grade alkali metal perfluorobutanesulfonate, while the recrystallization method cannot further reduce the impurity content by 1-2 orders of magnitude as desired.

Claims

1. A method for purifying alkali metal perfluorobutanesulfonate, comprising the following steps: Providing a reaction vessel with a filtering device and a temperature control device; Placing the crude product of alkali metal perfluorobutanesulfonate in the reaction container, adding a solvent and heating it to dissolve it; The temperature is lowered to 60-70°C to allow a portion of the alkali metal perfluorobutyl sulfonate to crystallize and then the crystals are filtered off; The temperature is further lowered for crystallization, and alkali metal perfluorobutyl sulfonate crystals having free metal ion and silicon contents less than 5 ppm and free fluorine content less than 9.5 ppm by weight are obtained by filtration. The solvent is selected from water, methanol, ethanol, dichloromethane, acetone, dimethyl carbonate, ethyl acetate or a combination of two or more thereof, In the crude potassium perfluorobutanesulfonate product, the residual amount of metal ions selected from sodium, magnesium, iron, calcium and silicon is ≥30 ppm by weight, the fluoride ion content is ≥50 ppm, and the inorganic salt impurities do not exceed 500 ppm.

2. The purification method according to claim 1, Features The alkali metal perfluorobutanesulfonate is potassium perfluorobutanesulfonate.

3. The purification method according to claim 1 or 2, Features The solvent is selected from a mixture of ethanol and water, and the mass ratio of ethanol to water is 20-80:

100.

4. The purification method according to claim 1 or 2, Features The crude alkali metal perfluorobutanesulfonate is placed in the reaction vessel, a solvent is added and the temperature is raised to 70-80° C. to dissolve the crude alkali metal perfluorobutanesulfonate.

5. The purification method according to claim 1 or 2, comprising the steps of: A jacketed reactor with stirring is provided, and a filter with a filter membrane is installed on the discharge pipe of the bottom valve of the reactor; Providing a recrystallization kettle, which is a stirred jacketed reactor; Add the crude product of alkali metal perfluorobutanesulfonate to a reaction kettle, add a solvent, pass hot water through the jacket to heat the solution in the kettle to 70-80°C, stir and dissolve, and stir for 0.5-2 hours until it is completely dissolved; Pass warm water into the jacket of the reactor to cool the reactor, control the temperature of the solution in the reactor to 60-70°C, and after crystallization of microcrystalline particles, open the bottom valve to pass the solution through the filter into the recrystallization reactor; The mixture is cooled to 5-15° C., filtered and dried to obtain an alkali metal perfluorobutyl sulfonate having a free metal ion and silicon content of less than 5 ppm and a free fluorine content of less than 9.5 ppm by weight.