Preparation method of phosphorus pentafluoride and lithium hexafluorophosphate

Abstract

The invention relates to a preparation method of phosphorus pentafluoride, which comprises the following steps: mixing a fluorocarbon compound with a phosphorus oxide compound and an oxidizing agent, reacting in a dry closed environment at high temperature and high pressure, collecting gas, and purifying to obtain the phosphorus pentafluoride. The invention also discloses a preparation method of lithium hexafluorophosphate, which comprises the following step: carrying out gas-solid reaction on the obtained phosphorus pentafluoride and lithium fluoride in a fluidized bed to prepare the lithium hexafluorophosphate. The method solves the problems of low purity of lithium hexafluorophosphate, difficulty in treatment of byproducts, low production efficiency and the like in the prior art.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium hexafluorophosphate preparation, and specifically relates to a method for preparing phosphorus pentafluoride and a method for preparing lithium hexafluorophosphate. Background Art

[0002] As a new type of lithium-ion battery electrolyte material, lithium hexafluorophosphate (LiPF6) has attracted widespread attention since the mid-20th century. It is difficult to synthesize, and it was not industrialized until 1996 by Morita Chemical Industries, Japan. With the development of industries such as portable electronic products, electric vehicles and electric bicycles, the demand for lithium batteries has increased dramatically, and the demand for lithium hexafluorophosphate has increased day by day. It is currently one of the most widely used lithium salts in commercial lithium-ion batteries.

[0003] There are many methods for preparing lithium hexafluorophosphate, mainly including gas-solid method, hydrogen fluoride solvent method, organic solvent method, complexation method, ion exchange method and conversion method, etc. Among them, the gas-solid method is simple and easy to operate, but the newly generated lithium hexafluorophosphate is easy to wrap on the surface of lithium fluoride particles, preventing the reaction from continuing, resulting in low purity of lithium hexafluorophosphate.

[0004] Phosphorus pentafluoride, one of the direct raw materials for synthesizing lithium hexafluorophosphate, is difficult to purchase directly due to its high toxicity and difficulty in storage. It is generally made in factories for immediate use. Patent CN117285021A discloses a method for preparing phosphorus pentafluoride gas, which includes the following steps: (1) reacting a phosphorus-containing compound with hydrogen fluoride and an organic acid anhydride dehydrating agent to generate a hexafluorophosphoric acid solution; (2) heating the hexafluorophosphoric acid solution to decompose it into gaseous hydrogen fluoride and phosphorus pentafluoride. This method produces a large amount of fluorine-containing organic acid as a byproduct, which is difficult to handle later.

[0005] Japanese patent JP2024542511A discloses a method for preparing high-purity lithium hexafluorophosphate, comprising the following steps: (a) reacting anhydrous hydrogen fluoride (AHF) gas with solid phosphorus pentachloride to generate high-purity phosphorus pentafluoride and hydrogen chloride gas; (b) reacting lithium fluoride dissolved in AHF with the phosphorus pentafluoride and hydrogen chloride gas mixture obtained in step (a) to obtain a lithium hexafluorophosphate mother liquor, which is LiPF6 dissolved in AHF; and (c) crystallizing LiPF6 from the mother liquor and separating the crystallized LiPF6 from the mother liquor. The phosphorus pentafluoride obtained in this method is mixed with a large amount of hydrogen chloride, and hydrogen chloride enters the reaction system together with phosphorus pentafluoride, so that the final lithium hexafluorophosphate product often contains chloride ion impurities. It is also difficult to separate hydrogen chloride and phosphorus pentafluoride because both are acidic gases and have very close boiling points.

[0006] CN102320584A discloses a method for preparing phosphorus pentafluoride, comprising (i) drying: removing moisture from a reactor and pipelines, (ii) feeding: adding two solid powders of phosphorus pentachloride and calcium fluoride into a reactor in a dry environment under the protection of an inert gas, (iii) evacuating: evacuating the reactor to -0.09 to -0.11 MPa, (iv) synthetic reaction: controlling the reaction temperature at 100 to 300°C, controlling the reactor pressure at -0.1 to 0.15 MPa, and reacting for more than 3 hours to generate crude phosphorus pentafluoride gas, and (v) purification. The raw material calcium fluoride of the method is non-toxic, and the toxicity of phosphorus pentachloride is very low. Although the use of hydrogen fluoride with poor safety is avoided, the synthetic reaction time is long, with the optimal time being 35 hours, and the production efficiency is low. Summary of the invention

[0007] In order to overcome the many shortcomings of the above-mentioned prior art, the present application provides a method for preparing phosphorus pentafluoride and lithium hexafluorophosphate, which is used to solve the problems of low purity of existing lithium hexafluorophosphate, difficult treatment of by-products, low production efficiency, etc.

[0008] To achieve the above object, the present invention adopts the following technical solution: In a first aspect, the present application provides a method for preparing phosphorus pentafluoride, which comprises mixing a fluorocarbon compound with an oxygen phosphorus compound and an oxidant, reacting them in a dry and closed environment at high temperature and high pressure, collecting the gas, and purifying it to obtain phosphorus pentafluoride.

[0009] Specifically, the fluorocarbon compound includes but is not limited to one or more selected from tetrafluorocarbon, perfluoroalkane, perfluoroolefin, polyperfluoroolefin, perfluoroalkyne, perfluoroaromatic, perfluorocycloalkane, etc. In order to facilitate production and charging, the fluorocarbon compound is generally selected from liquid or solid compounds at room temperature and pressure, for example, perfluoropentane, perfluorohexane, perfluoroheptane, perfluorooctane, perfluorodecane, perfluoro-2-methyl-2-pentene, polytetrafluoroethylene, polyperfluoropropylene, perfluoro-1-butyne, octafluorotoluene, perfluoronaphthalene, perfluoro(methylcyclohexane), etc. Further, in order to reduce the cost of raw materials, the fluorocarbon compound can be selected from recycled waste polytetrafluoroethylene materials, which can be crushed and cleaned before use.

[0010] Furthermore, the oxygen phosphorus compound can be selected from phosphorus pentoxide, etc., and the oxidant can be selected from oxygen or ozone, etc., all for the purpose of reducing the introduction of impurity elements. If polyphosphoric acid, hydrogen peroxide, etc. are selected, the reaction can also proceed, but more byproduct water will be generated, which will cause a burden for subsequent impurity removal.

[0011] Preferably, the amount of the fluorocarbon compound and the oxygen phosphorus compound satisfies the molar ratio of fluorine to phosphorus element of (5-5.2):1, and the amount of the fluorocarbon compound and the oxidant satisfies the molar ratio of carbon to oxygen element of 1:(2-2.2). The three are ground under the conditions of pressure 3-10MPa and temperature 200-500°C to produce a chemical reaction to generate phosphorus pentafluoride and carbon dioxide, and the reaction time is generally 60-180min.

[0012] Furthermore, in order to make the reaction easier, a promoter is mixed with the fluorocarbon compound, the oxyphosphorus compound and the oxidant, and the promoter is selected from one or more of alkali metal fluorides, such as lithium fluoride, sodium fluoride, potassium fluoride, cesium fluoride, etc., and the amount of the promoter is 3-10% of the mass of the fluorocarbon compound. After adding the promoter, the reaction temperature and pressure can be reduced, the reaction speed is faster, and the yield is higher.

[0013] After the reaction is completed, the gas is collected and filtered to remove dust, condensed, and distilled to obtain high-purity phosphorus pentafluoride.

[0014] In a second aspect, the present application provides a method for preparing lithium hexafluorophosphate, wherein high-purity phosphorus pentafluoride prepared by the above method is subjected to a gas-solid reaction with lithium fluoride in a fluidized bed to prepare lithium hexafluorophosphate.

[0015] Furthermore, the reaction temperature can be controlled to be 80-110°C and the reaction pressure to be 0.3-1MPa. The diameter of the lithium fluoride particles is distributed in the range of 5-200 μm, and the phosphorus pentafluoride intake speed is 10-100 L / min. During the fluidized reaction, the particles collide and rub against each other, and there is no phenomenon of lithium hexafluorophosphate wrapping lithium fluoride, and the purity of the obtained lithium hexafluorophosphate product meets the requirements.

[0016] Compared with the prior art, the advantages and beneficial effects of the method of the present invention are as follows: The present application uses fluorocarbon compounds, oxyphosphorus compounds and oxidants as raw materials to prepare phosphorus pentafluoride through grinding reaction under high temperature and high pressure. The raw materials are easy to obtain, especially when recycled polytetrafluoroethylene waste is used, the economic benefits are better; the whole process avoids the use of dangerous and toxic hydrogen fluoride to reduce safety risks; the feed amount design ensures that the oxyphosphorus compounds are completely reacted, and no difficult-to-separate impurities other than phosphorus pentafluoride are produced at the end of the reaction, and no difficult-to-treat by-products are produced. As a preferred method, an alkali metal fluoride promoter is additionally added during the reaction, which reduces the reaction temperature and pressure requirements, makes the reaction faster, and has a higher yield, greatly improves the production efficiency, and can be completed in 1 hour. DETAILED DESCRIPTION

[0017] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments. However, it should be clear to those skilled in the art that the embodiments described below are part of the embodiments of the present invention, rather than all of the embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0018] If no specific conditions are specified in the examples, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. The pressures shown are all absolute pressures. The yield of phosphorus pentafluoride is relative to phosphorus pentoxide, and the yield of lithium hexafluorophosphate is relative to lithium fluoride.

[0019] Example 1 This embodiment provides a method for preparing phosphorus pentafluoride, and the specific steps are as follows: 5000g of perfluoropentane was mixed with 2900g of phosphorus pentoxide and 2860g of oxygen (the molar ratio of fluorine to phosphorus was about 5.07:1, and the molar ratio of carbon to oxygen was about 1:2.01), and ground in a dry closed reactor at 10MPa and 300°C for 120min. The gas was collected and filtered with a sintered filter element to remove solid impurities, and then pressurized and condensed to -60°C to separate solid carbon dioxide. The temperature was continued to be lowered to obtain liquid phosphorus pentafluoride, which was then distilled to obtain 4044g of high-purity phosphorus pentafluoride with a yield of 78.58%.

[0020] Example 2 This embodiment provides a method for preparing phosphorus pentafluoride, and the specific steps are as follows: 5000g of perfluorooctane was mixed with 2810g of phosphorus pentoxide and 3200g of oxygen (the molar ratio of fluorine to phosphorus was about 5.19:1, and the molar ratio of carbon to oxygen was about 1:2.19), and ground in a dry closed reactor at 7MPa and 400℃ for 150min. The gas was collected and filtered with a sintered filter element to remove solid impurities, and then pressurized and condensed to -60℃ to separate solid carbon dioxide. The temperature was continued to be lowered to obtain liquid phosphorus pentafluoride, which was then distilled to obtain 3905g of high-purity phosphorus pentafluoride with a yield of 78.31%.

[0021] Example 3 This embodiment provides a method for preparing phosphorus pentafluoride, and the specific steps are as follows: 5000g of octafluorotoluene was mixed with 2400g of phosphorus pentoxide and 4980g of oxygen (the molar ratio of fluorine to phosphorus was about 5.01:1, and the molar ratio of carbon to oxygen was about 1:2.1), and ground in a dry closed reactor at 5MPa and 500°C for 100min. The gas was collected and filtered with a sintered filter element to remove solid impurities, and then pressurized and condensed to -60°C to separate solid carbon dioxide. The temperature was continued to be lowered to obtain liquid phosphorus pentafluoride, which was then distilled to obtain 3113g of high-purity phosphorus pentafluoride with a yield of 73.09%.

[0022] Example 4 This embodiment provides a method for preparing phosphorus pentafluoride, and the specific steps are as follows: 5000g of perfluoronaphthalene was mixed with 2050g of phosphorus pentoxide and 6150g of oxygen (the molar ratio of fluorine to phosphorus was about 5.09:1, and the molar ratio of carbon to oxygen was about 1:2.09), and ground in a dry closed reactor at 5MPa and 500℃ for 60min. The gas was collected and filtered with a sintered filter element to remove solid impurities, and then pressurized and condensed to -60℃ to separate solid carbon dioxide. The temperature was continued to be lowered to obtain liquid phosphorus pentafluoride, which was then distilled to obtain 2589g of high-purity phosphorus pentafluoride with a yield of 71.16%.

[0023] Example 5 This embodiment provides a method for preparing phosphorus pentafluoride, and the specific steps are as follows: 5000g of perfluoronaphthalene was mixed with 2050g of phosphorus pentoxide and 6100g of ozone (the molar ratio of fluorine to phosphorus was about 5.09:1, and the molar ratio of carbon to oxygen was about 1:2.07), and ground in a dry closed reactor at 5MPa and 500℃ for 90min. The gas was collected and filtered with a sintered filter element to remove solid impurities, and then pressurized and condensed to -60℃ to separate solid carbon dioxide. The temperature was continued to be lowered to obtain liquid phosphorus pentafluoride, which was then distilled to obtain 2534g of high-purity phosphorus pentafluoride with a yield of 69.65%.

[0024] Example 6 This embodiment provides a method for preparing phosphorus pentafluoride, and the specific steps are as follows: 5000g of perfluoronaphthalene was mixed with 2050g of phosphorus pentoxide, 6100g of ozone and 175g of sodium fluoride (the molar ratio of fluorine to phosphorus was about 5.09:1, the molar ratio of carbon to oxygen was about 1:2.07, and the mass of sodium fluoride was 3.5% of that of perfluoronaphthalene), and ground in a dry closed reactor at 5MPa and 300°C for 60min. The gas was collected and filtered with a sintered filter element to remove solid impurities, and then pressurized and condensed to -60°C to separate solid carbon dioxide. The temperature was continued to be lowered to obtain liquid phosphorus pentafluoride, which was then distilled to obtain 3412g of high-purity phosphorus pentafluoride with a yield of 93.79%.

[0025] Example 7 This embodiment provides a method for preparing phosphorus pentafluoride, and the specific steps are as follows: 5000g of perfluoronaphthalene was mixed with 2050g of phosphorus pentoxide, 6100g of ozone and 450g of potassium fluoride (the molar ratio of fluorine to phosphorus was about 5.09:1, the molar ratio of carbon to oxygen was about 1:2.07, and the mass of potassium fluoride was 9% of that of perfluoronaphthalene), and ground in a dry closed reactor at 3MPa and 400℃ for 60min. The gas was collected and filtered with a sintered filter element to remove solid impurities, and then pressurized and condensed to -60℃ to separate solid carbon dioxide. The temperature was continued to be lowered to obtain liquid phosphorus pentafluoride, which was then distilled to obtain 3630g of high-purity phosphorus pentafluoride with a yield of 99.78%.

[0026] Example 8 This embodiment provides a method for preparing phosphorus pentafluoride, and the specific steps are as follows: 5000g of recycled polytetrafluoroethylene waste was mixed with 2780g of phosphorus pentoxide, 3360g of ozone and 300g of potassium fluoride (the molar ratio of fluorine to phosphorus was about 5.11:1, the molar ratio of carbon to oxygen was about 1:2.1, and the mass of potassium fluoride was 6% of that of perfluoronaphthalene), and ground in a dry closed reactor at 4MPa and 300℃ for 60min. The gas was collected and filtered with a sintered filter element to remove solid impurities, and then pressurized and condensed to -60℃ to separate solid carbon dioxide. The temperature was continued to be lowered to obtain liquid phosphorus pentafluoride, which was then distilled to obtain 4818g of high-purity phosphorus pentafluoride with a yield of 97.66%.

[0027] Example 9 This embodiment provides a method for preparing lithium hexafluorophosphate, and the specific steps are as follows: The high-purity phosphorus pentafluoride obtained in Example 7 and 100 g of lithium fluoride with a purity of 99.99% were subjected to a gas-solid reaction in a fluidized bed. The reaction temperature was controlled at 90° C. and the pressure was 0.6 MPa. The lithium fluoride particles were selected to have a diameter distribution of 30-150 μm. The phosphorus pentafluoride gas inlet speed was 55 L / min. 560 g of lithium hexafluorophosphate was produced with a purity of 99.9%.

[0028] Example 10 This embodiment provides a method for preparing lithium hexafluorophosphate, and the specific steps are as follows: The high-purity phosphorus pentafluoride obtained in Example 8 and 100 g of lithium fluoride with a purity of 99.99% were subjected to a gas-solid reaction in a fluidized bed. The reaction temperature was controlled at 110° C. and the pressure was 0.3 MPa. The lithium fluoride particles were selected to have a diameter distribution of 30-150 μm. The phosphorus pentafluoride intake speed was 95 L / min. 568 g of lithium hexafluorophosphate was produced with a purity of 99.9%.

[0029] Comparative Example 1 This comparative example is similar to Example 1, except for the reaction pressure. The specific steps are as follows: 5000g of perfluoropentane was mixed with 2900g of phosphorus pentoxide and 2860g of oxygen (the molar ratio of fluorine to phosphorus was about 5.07:1, and the molar ratio of carbon to oxygen was about 1:2.01), and ground in a dry and closed reactor at 0.8MPa and 300°C for 120min. The gas was collected and no phosphorus pentoxide was detected in the gas.

[0030] Comparative Example 2 This comparative example is similar to Example 1, except for the reaction temperature. The specific steps are as follows: 5000g of perfluoropentane was mixed with 2900g of phosphorus pentoxide and 2860g of oxygen (the molar ratio of fluorine to phosphorus was about 5.07:1, and the molar ratio of carbon to oxygen was about 1:2.01), and ground in a dry and closed reactor at 10MPa and 190°C for 120min. The gas was collected and no phosphorus pentoxide was detected in the gas.

Claims

1. A method for preparing phosphorus pentafluoride, characterized in that: Fluorocarbon compounds are mixed with oxygen phosphorus compounds and oxidants, reacted in a dry and closed environment under high temperature and high pressure, and the gas is collected and purified to obtain phosphorus pentafluoride.

2. The method according to claim 1, characterized in that The fluorocarbon compound is selected from one or more of carbon tetrafluoride, perfluoroalkane, perfluoroolefin, polyperfluoroolefin, perfluoroalkyne, perfluoroaromatic hydrocarbon, and perfluorocycloalkane; the oxygen phosphorus compound is phosphorus pentoxide; and the oxidant is oxygen or ozone.

3. The preparation method according to claim 1, characterized in that: The amounts of the fluorocarbon compound and the oxygen-phosphorus compound used satisfy a molar ratio of fluorine to phosphorus of (5-5.2):1, and the amounts of the fluorocarbon compound and the oxidant used satisfy a molar ratio of carbon to oxygen of 1:(2-2.2).

4. The preparation method according to claim 1, characterized in that: The fluorocarbon compound, the oxyphosphorus compound and the oxidant are mixed with a promoter, and the promoter is selected from alkali metal fluorides.

5. The preparation method according to claim 4, characterized in that: The amount of the promoter is 3-10% of the mass of the fluorocarbon compound, and the alkali metal fluoride is selected from one or more of lithium fluoride, sodium fluoride, potassium fluoride and cesium fluoride.

6. The preparation method according to claim 1, characterized in that: The reaction under high temperature and high pressure is performed by grinding for 60-180 minutes at a pressure of 3-10 MPa and a temperature of 200-500°C.

7. The preparation method according to claim 1, characterized in that: The purification is to remove dust and rectify the gas.

8. A method for preparing lithium hexafluorophosphate, characterized in that: The phosphorus pentafluoride obtained by any preparation method according to claim 1-7 is subjected to gas-solid reaction with lithium fluoride in a fluidized bed to obtain lithium hexafluorophosphate.

9. The preparation method according to claim 8, characterized in that: The reaction temperature is controlled at 80-110°C and the reaction pressure is controlled at 0.3-1MPa.

10. The preparation method according to claim 8, characterized in that: The diameter of the lithium fluoride particles is distributed in the range of 5-200 μm, and the phosphorus pentafluoride intake speed is 10-100 L / min.