A method for preparing phosphorus pentafluoride from ammonium hexafluorophosphate

Abstract

The application belongs to the field of fluorinated chemicals, and specifically discloses a method for preparing phosphorus pentafluoride by using ammonium hexafluorophosphate as raw material. First, a phosphorus source and a fluorine source are mixed to prepare an aqueous solution of hexafluorophosphoric acid, ammonia gas is introduced or ammonia water is added to prepare an aqueous solution of ammonium hexafluorophosphate, and then the ammonium hexafluorophosphate is purified by anti-solvent sedimentation. After the mixed acid of ammonium hexafluorophosphate and sulfuric acid is heated and cracked, high-purity phosphorus pentafluoride gas can be prepared. Compared with the prior art, the aqueous solution of ammonium hexafluorophosphate is settled by using an anti-solvent to obtain a suspension of ammonium hexafluorophosphate, and a large amount of dehydrating agent such as fuming sulfuric acid is not needed, so that the generation of waste sulfuric acid is greatly reduced. The anti-solvent can be reused after distillation, and is environmentally friendly and economical.

Description

Technical Field

[0001] This invention relates to the field of fluorochemicals, and in particular to a method for preparing phosphorus pentafluoride using ammonium hexafluorophosphate as a raw material. Background Technology

[0002] Phosphorus pentafluoride is a phosphorus halide compound with the chemical formula PF5. It has a melting point of -93.8℃ and a boiling point of -84.6℃. At room temperature and pressure, it is a colorless gas with a pungent, irritating odor. Phosphorus pentafluoride is widely used in the electronics industry, polymer materials, and catalysts. In recent years, with the widespread adoption of lithium-ion batteries using lithium hexafluorophosphate as the electrolyte and related applications, phosphorus pentafluoride has found new applications as a major raw material for the synthesis of lithium hexafluorophosphate.

[0003] There are many methods for synthesizing phosphorus pentafluoride gas, but they can be broadly classified into three categories.

[0004] The first type uses phosphorus pentachloride as a raw material and anhydrous hydrogen fluoride or calcium fluoride to synthesize phosphorus pentafluoride. This process is currently the most widely used in China.

[0005] The second type uses phosphorus pentoxide, polyphosphoric acid, or phosphoric acid as raw materials. After reacting with anhydrous hydrogen fluoride, dehydrating agents such as fuming sulfuric acid are added to dehydrate the mixture, and finally the reaction mixture is heated to decompose the reaction mixture.

[0006] The third type involves reacting elemental phosphorus or phosphorus oxides with fluorine gas to prepare phosphorus pentafluoride.

[0007] Of the aforementioned preparation methods, the first type results in low phosphorus content in phosphorus pentachloride, low atom economy, and can only produce a mixture of phosphorus pentafluoride and hydrogen chloride, increasing the cost of subsequent product purification. The second type generates waste concentrated sulfuric acid at a molar ratio several times that of the product, making waste treatment difficult. The third type requires ultra-high temperature reaction conditions and fluorine gas, which is dangerous and costly, and has been abandoned by mainstream manufacturers. These three types of methods also suffer from complex processes and large quantities of hazardous chemicals. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a method for preparing phosphorus pentafluoride using ammonium hexafluorophosphate as a raw material.

[0009] To achieve the above objectives, the present invention is implemented according to the following technical solution:

[0010] A method for preparing phosphorus pentafluoride from ammonium hexafluorophosphate includes the following steps:

[0011] S1. Prepare an aqueous solution of hexafluorophosphate by mixing a phosphorus source and a fluorine source in a ratio of 1:(1-24) at a reaction temperature of -15 to 15℃.

[0012] S2. Prepare an ammonium hexafluorophosphate aqueous solution by adding an equimolar ratio of ammonia gas or ammonia water to an aqueous solution of hexafluorophosphate at a reaction temperature of 0-50℃.

[0013] S3. Precipitate the aqueous solution of ammonium hexafluorophosphate with an antisolvent to obtain an ammonium hexafluorophosphate suspension;

[0014] S4. Filter to obtain ammonium hexafluorophosphate solid, and then dry in a drying kettle to obtain anhydrous ammonium hexafluorophosphate solid;

[0015] S5. Mix solid ammonium hexafluorophosphate with an equimolar ratio of inorganic acid at 0-50℃, heat to 200-250℃ to decompose the mixture and produce crude phosphorus pentafluoride gas, which is then collected.

[0016] S6. The collected phosphorus pentafluoride crude gas is cooled, purified, and distilled to obtain high-purity phosphorus pentafluoride gas.

[0017] Furthermore, the phosphorus source is one or a combination of two of phosphoric acid and polyphosphoric acid.

[0018] Furthermore, the fluorine source is one or a combination of two of anhydrous hydrogen fluoride and aqueous hydrofluoric acid.

[0019] Furthermore, the antisolvent is an organic solvent miscible with water, and the organic solvent is one or a combination of methanol, tetrahydrofuran, 1,4-dioxane, and acetone.

[0020] Furthermore, the inorganic acid is one or more combinations of concentrated sulfuric acid, dilute sulfuric acid, and fuming sulfuric acid.

[0021] The specific chemical reaction formula for preparing phosphorus pentafluoride in this invention is as follows:

[0022] H3PO4 / H6P4O 13 +HF→HPF6+H2O

[0023] HPF6+NH3 / NH3·H2O→NH4PF6+H2O

[0024]

[0025] Further, step S6 specifically includes: condensing the collected phosphorus pentafluoride crude gas to below -10°C using a two-stage condenser to obtain phosphorus pentafluoride crude gas with a purity of over 99%; pressurizing the obtained crude gas to 0.9 MPa using a compressor, and then passing it into a high-pressure distillation column for distillation at -40 to -30°C to obtain high-purity phosphorus pentafluoride gas.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. This invention uses an anti-solvent to precipitate an aqueous solution of ammonium hexafluorophosphate to obtain an ammonium hexafluorophosphate suspension, eliminating the need for large amounts of dehydrating agents such as fuming sulfuric acid, thus greatly reducing the generation of waste concentrated sulfuric acid; the anti-solvent is removed by distillation and can be reused, making it environmentally friendly and economical.

[0028] 2. The present invention purifies ammonium hexafluorophosphate through anti-solvent precipitation, which can obtain high-purity phosphorus pentafluoride gas more efficiently.

[0029] 3. This invention can use aqueous hydrofluoric acid instead of anhydrous hydrogen fluoride as a reaction raw material, thereby increasing the safety of the process.

[0030] 4. The final byproduct of the process of heating and decomposing ammonium hexafluorophosphate and sulfuric acid to produce phosphorus pentafluoride gas is ammonium sulfate. The byproduct can be used as a raw material in the fertilizer industry. Compared with the traditional process where the byproduct is a strong inorganic acid such as hydrochloric acid or sulfuric acid, it produces less waste and is safer and easier to treat. Attached Figure Description

[0031] Figure 1 This is a process flow diagram for preparing phosphorus pentafluoride according to the present invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0033] Unless otherwise specified, all raw materials, reagents, equipment and tools used in the following examples are commercially available.

[0034] Example 1

[0035] See Figure 1 This embodiment exemplarily demonstrates a method for preparing phosphorus pentafluoride using ammonium hexafluorophosphate as a raw material. The specific preparation process is as follows:

[0036] 1) Preparation of hexafluorophosphate aqueous solution

[0037] Hydrofluoric acid was added to a fluoropolymer-lined steel reactor under ice-salt bath conditions (~-20℃), and phosphoric acid was added dropwise while controlling the temperature at -15 to 15℃. The molar ratio of phosphoric acid to hydrofluoric acid was 1:1. The reaction was carried out for 1.5 h to obtain crude hexafluorophosphate.

[0038] 2) Preparation of ammonium hexafluorophosphate

[0039] The reaction temperature was controlled to not exceed 20℃. Ammonia gas was slowly passed through the crude hexafluorophosphate obtained from the above reaction in an equimolar ratio until the reaction solution became neutral. Then, methanol (volume ratio of methanol to water) was added as an antisolvent. After stirring for 15 minutes, the reactants were transferred to a settling tank and allowed to stand for 30 minutes before filtration. The collected ammonium hexafluorophosphate solid was added to a distillation drying tank to remove the antisolvent and water. The solid was then dried to obtain solid ammonium hexafluorophosphate. The sedimentation yield of the solid reached approximately 85%. The remaining solution was repeatedly recovered and reused.

[0040] 3) Preparation of phosphorus pentafluoride gas by thermal decomposition

[0041] Solid hexafluorophosphate was added to the alloy cracking reactor. The reactor was then evacuated and purged with high-purity nitrogen to replace any impurities. The reactor was then evacuated again, and concentrated sulfuric acid, in an equimolar ratio with the solid ammonium hexafluorophosphate, was slowly added. The mixture was stirred for 30 minutes to ensure thorough mixing. The reactor was gradually heated to 200–250°C, with the heating rate controlled to ensure a uniform gas flow. The reaction ended when no more gas was generated. The generated crude gas was condensed in a two-stage condenser to below -10°C to remove impurities such as hydrogen fluoride, yielding crude phosphorus pentafluoride gas with a purity of over 99%. The obtained crude gas was pressurized to 0.9 MPa and then passed into a high-pressure distillation column for distillation at -40 to -30°C to obtain high-purity phosphorus pentafluoride gas. Testing showed that the purity of the phosphorus pentafluoride gas was greater than 99.96%, and no metal ions or moisture were detected.

[0042] Example 2

[0043] See Figure 1 This embodiment exemplarily demonstrates a method for preparing phosphorus pentafluoride using ammonium hexafluorophosphate as a raw material. The specific preparation process is as follows:

[0044] 1) Preparation of hexafluorophosphate aqueous solution

[0045] Anhydrous hydrogen fluoride was added to a fluorine-lined steel reactor under refrigerated brine cooling conditions. Polyphosphoric acid was added dropwise while the temperature was controlled at -15 to 15°C. The molar ratio of polyphosphoric acid to hydrogen fluoride was 1:24. The reaction was carried out for 1.5 hours to obtain crude hexafluorophosphate.

[0046] 2) Preparation of ammonium hexafluorophosphate

[0047] The reaction temperature was controlled to not exceed 20℃. Equimolar amounts of ammonia were added dropwise to the above reaction mixture until the reaction solution was neutral. Tetrahydrofuran, the antisolvent, was added at a volume ratio of 0.5–3 to water. After stirring for 15 minutes, the mixture was transferred to a settling tank and allowed to stand for 30 minutes before filtration. The filtered solid was collected and added to a distillation drying tank to remove residual antisolvent and water. The solid was then dried to obtain hexafluorophosphate solid. The sedimentation yield of the solid reached approximately 85%. The remaining solution was repeatedly recovered and reused.

[0048] 3) Preparation of phosphorus pentafluoride gas by thermal decomposition

[0049] Solid hexafluorophosphate was added to the alloy cracking reactor. The reactor was evacuated, then purged with high-purity nitrogen to replace any impurities before evacuation again. 65% fuming sulfuric acid, in an equimolar ratio to solid ammonium hexafluorophosphate, was added. The mixture was stirred for 30 minutes to ensure thorough mixing. The reactor was gradually heated to 200–250°C, with the heating rate controlled to ensure a uniform gas flow. The reaction ended when no more gas was generated. The generated crude gas was condensed in a two-stage condenser to below -10°C to remove impurities such as hydrogen fluoride, yielding crude phosphorus pentafluoride gas with a purity of over 99%. The crude gas was pressurized to 0.9 MPa and then passed through a high-pressure distillation column at -40 to -30°C to obtain high-purity phosphorus pentafluoride gas with a purity of over 99.95%. Testing showed that the purity of the phosphorus pentafluoride gas was greater than 99.99%, and no metal ions or moisture were detected.

[0050] Example 3

[0051] See Figure 1 This embodiment exemplarily demonstrates a method for preparing phosphorus pentafluoride using ammonium hexafluorophosphate as a raw material. The specific preparation process is as follows:

[0052] 1) Preparation of hexafluorophosphate aqueous solution

[0053] Anhydrous hydrogen fluoride was added to a fluorine-lined steel reactor under refrigerated brine cooling conditions. Polyphosphoric acid was added dropwise while the temperature was controlled at -15 to 15°C. The molar ratio of polyphosphoric acid to hydrogen fluoride was 1:24. The reaction was carried out for 1.5 hours to obtain crude hexafluorophosphate.

[0054] 2) Preparation of ammonium hexafluorophosphate

[0055] The reaction temperature was controlled to not exceed 20℃. Equimolar amounts of ammonia were added dropwise to the above reaction mixture until the reaction solution was neutral. Acetone, the antisolvent, was added at a volume ratio of 0.5–3 to water. After stirring for 15 minutes, the mixture was transferred to a settling tank and allowed to stand for 30 minutes before filtration. The filtered solid was collected and added to a distillation drying tank to remove residual water. The solid was then dried to obtain anhydrous hexafluorophosphate solid. The sedimentation yield of the solid reached approximately 90%, and the remaining aqueous solution was repeatedly recovered and reused.

[0056] 3. Preparation of phosphorus pentafluoride gas by thermal decomposition

[0057] Solid hexafluorophosphate was added to the alloy cracking reactor. The reactor was evacuated, then purged with high-purity nitrogen to replace any impurities before evacuation again. 65% fuming sulfuric acid, in an equimolar ratio to solid ammonium hexafluorophosphate, was added. The mixture was stirred for 30 minutes to ensure thorough mixing. The reactor was gradually heated to 200–250°C, with the heating rate controlled to ensure a uniform gas flow. The reaction ended when no more gas was generated. The generated crude gas was condensed in a two-stage condenser to below -10°C to remove impurities such as hydrogen fluoride, yielding crude phosphorus pentafluoride gas with a purity of over 99%. The crude gas was pressurized to 0.9 MPa and then passed through a high-pressure distillation column at -40 to -30°C to obtain high-purity phosphorus pentafluoride gas with a purity of over 99.95%. Testing showed that the purity of the phosphorus pentafluoride gas was greater than 99.99%, and no metal ions or moisture were detected.

[0058] Example 4

[0059] See Figure 1 This embodiment exemplarily demonstrates a method for preparing phosphorus pentafluoride using ammonium hexafluorophosphate as a raw material. The specific preparation process is as follows:

[0060] 1) Preparation of hexafluorophosphate aqueous solution

[0061] Hydrofluoric acid was added to a fluoropolymer-lined steel reactor under ice-salt bath conditions (~-20℃), and phosphoric acid was added dropwise while controlling the temperature at -15 to 15℃. The molar ratio of phosphoric acid to hydrofluoric acid was 1:1. The reaction was carried out for 1.5 h to obtain crude hexafluorophosphate.

[0062] 2) Preparation of ammonium hexafluorophosphate

[0063] The reaction temperature was controlled to not exceed 20℃. Ammonia gas was slowly passed through the crude hexafluorophosphate obtained from the above reaction in an equimolar ratio until the reaction solution became neutral. Then, 1,4-dioxane, an antisolvent with a volume ratio of 0.5–3 to water, was added. After stirring for 15 minutes, the mixture was transferred to a settling tank and allowed to stand for 30 minutes before filtration. The filtered solid was collected and added to a distillation drying tank to remove residual water. The solid was then dried to obtain anhydrous ammonium hexafluorophosphate. The sedimentation yield of the solid reached approximately 90%. The remaining aqueous solution was repeatedly recovered and reused.

[0064] 3) Preparation of phosphorus pentafluoride gas by thermal decomposition

[0065] Solid hexafluorophosphate was added to the alloy cracking reactor. The reactor was then evacuated and purged with high-purity nitrogen to replace any impurities. The reactor was then evacuated again, and concentrated sulfuric acid, in an equimolar ratio with the solid ammonium hexafluorophosphate, was slowly added. The mixture was stirred for 30 minutes to ensure thorough mixing. The reactor was gradually heated to 200–250°C, with the heating rate controlled to ensure a uniform gas flow. The reaction ended when no more gas was generated. The generated crude gas was condensed in a two-stage condenser to below -10°C to remove impurities such as hydrogen fluoride, yielding crude phosphorus pentafluoride gas with a purity of over 99%. The obtained crude gas was pressurized to 0.9 MPa and then passed into a high-pressure distillation column for distillation at -40 to -30°C to obtain high-purity phosphorus pentafluoride gas. Testing showed that the purity of the phosphorus pentafluoride gas was greater than 99.96%, and no metal ions or moisture were detected.

[0066] Example 5

[0067] See Figure 1 This embodiment exemplarily demonstrates a method for preparing phosphorus pentafluoride using ammonium hexafluorophosphate as a raw material. The specific preparation process is as follows:

[0068] 1) Preparation of hexafluorophosphate aqueous solution

[0069] Hydrofluoric acid was added to a fluoropolymer-lined steel reactor under ice-salt bath conditions (~-20℃), and phosphoric acid was added dropwise while controlling the temperature at -15 to 15℃. The molar ratio of phosphoric acid to hydrofluoric acid was 1:1. The reaction was carried out for 1.5 h to obtain crude hexafluorophosphate.

[0070] 2) Preparation of ammonium hexafluorophosphate

[0071] The reaction temperature was controlled to not exceed 20℃. Ammonia gas was slowly passed through the crude hexafluorophosphate obtained from the above reaction in an equimolar ratio until the reaction solution became neutral. Then, water and an antisolvent (tetrahydrofuran / acetone, V:V = 1:1, volume ratio) were added. After stirring for 15 min, the reactants were transferred to a settling tank and allowed to stand for 30 min before filtration. The collected ammonium hexafluorophosphate solid was added to a distillation drying tank to remove the antisolvent and water, and then dried to obtain solid ammonium hexafluorophosphate. The sedimentation yield of the solid reached approximately 80%, and the remaining aqueous solution was repeatedly recovered and reused.

[0072] 3) Preparation of phosphorus pentafluoride gas by thermal decomposition

[0073] Solid hexafluorophosphate was added to the alloy cracking reactor. The reactor was then evacuated and purged with high-purity nitrogen to replace any impurities. The reactor was then evacuated again, and concentrated sulfuric acid, in an equimolar ratio with the solid ammonium hexafluorophosphate, was slowly added. The mixture was stirred for 30 minutes to ensure thorough mixing. The reactor was gradually heated to 200–250°C, with the heating rate controlled to ensure a uniform gas flow. The reaction ended when no more gas was generated. The generated crude gas was condensed in a two-stage condenser to below -10°C to remove impurities such as hydrogen fluoride, yielding crude phosphorus pentafluoride gas with a purity of over 99%. The obtained crude gas was pressurized to 0.9 MPa and then passed into a high-pressure distillation column for distillation at -40 to -30°C to obtain high-purity phosphorus pentafluoride gas. Testing showed that the purity of the phosphorus pentafluoride gas was greater than 99.96%, and no metal ions or moisture were detected.

[0074] In summary, this invention purifies ammonium hexafluorophosphate by anti-solvent precipitation, and then heats and pyrolyzes the mixture of ammonium hexafluorophosphate and sulfuric acid to obtain high-purity phosphorus pentafluoride gas.

[0075] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing phosphorus pentafluoride from ammonium hexafluorophosphate, characterized in that, Includes the following steps: S1. Prepare an aqueous solution of hexafluorophosphate by mixing a phosphorus source and a fluorine source in a molar ratio of 1:(1~24) at a reaction temperature of -15~15℃. S2. Prepare an ammonium hexafluorophosphate aqueous solution by adding an equal molar ratio of ammonia gas or ammonia water to an aqueous solution of hexafluorophosphate at a reaction temperature of 0~50℃. S3. Precipitate the aqueous solution of ammonium hexafluorophosphate with an antisolvent to obtain an ammonium hexafluorophosphate suspension; the antisolvent is an organic solvent miscible with water, and the organic solvent is one of tetrahydrofuran, 1,4-dioxane and acetone; S4. Filter to obtain ammonium hexafluorophosphate solid, and then dry in a drying kettle to obtain anhydrous ammonium hexafluorophosphate solid; S5. Mix solid ammonium hexafluorophosphate with an equimolar ratio of inorganic acid at 0~50℃, heat to 200~250℃ to decompose the mixture and produce crude phosphorus pentafluoride gas, which is then collected. S6. The collected phosphorus pentafluoride crude gas is cooled, purified, and distilled to obtain high-purity phosphorus pentafluoride gas.

2. The method for preparing phosphorus pentafluoride from ammonium hexafluorophosphate according to claim 1, characterized in that: The phosphorus source is one or a combination of two of phosphoric acid and polyphosphoric acid.

3. The method for preparing phosphorus pentafluoride from ammonium hexafluorophosphate according to claim 1, characterized in that: The fluorine source is one or a combination of two of anhydrous hydrogen fluoride and aqueous hydrofluoric acid.

4. The method for preparing phosphorus pentafluoride from ammonium hexafluorophosphate according to claim 1, characterized in that: The inorganic acid is one or more combinations of concentrated sulfuric acid, dilute sulfuric acid, and fuming sulfuric acid.

5. The method for preparing phosphorus pentafluoride from ammonium hexafluorophosphate according to claim 1, characterized in that, Step S6 specifically includes: condensing the collected phosphorus pentafluoride crude gas to below -10°C using a two-stage condenser to obtain phosphorus pentafluoride crude gas with a purity of over 99%; pressurizing the obtained crude gas to 0.9 MPa using a compressor and then passing it into a high-pressure distillation column for distillation at -40 to -30°C to obtain high-purity phosphorus pentafluoride gas.

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