A method for preparing phosphorus pentafluoride by reacting polyphosphoric acid with anhydrous hydrogen fluoride

Abstract

The application relates to the technical field of phosphorus pentafluoride preparation, and specifically discloses a method for preparing phosphorus pentafluoride by reacting polyphosphoric acid with anhydrous hydrogen fluoride, which comprises the following steps: S1, raw material treatment: adding a viscosity reducer into polyphosphoric acid for mixing and stirring to obtain a polyphosphoric acid solution containing the viscosity reducer; the viscosity reducer is a fluorine-containing phosphonate compound with a boiling point greater than 180 DEG C; S2, fluorination reaction; S3, dehydration reaction; S4, pyrolysis reaction; and S5, condensation and purification. According to the method, the fluorine-containing phosphonate compound with a specific structure is selected as the viscosity reducer, the super-high stability of the C-F bond is utilized, the generation of by-products such as POF3 is inhibited from the root, the polyphosphoric acid can be pumped at a low temperature and continuous production is realized, and the high purity of the phosphorus pentafluoride product is ensured.

Description

Technical Field

[0001] This invention relates to the field of phosphorus pentafluoride preparation technology, specifically a method for preparing phosphorus pentafluoride by reacting polyphosphoric acid with anhydrous hydrogen fluoride. Background Technology

[0002] Phosphorus pentafluoride (PF5) is a highly toxic and corrosive gas. Its preparation processes are mainly divided into four categories: 1. Phosphorus pentachloride + anhydrous hydrogen fluoride method: The mainstream industrial method uses the reaction of phosphorus pentachloride with anhydrous hydrogen fluoride. The raw materials are readily available, the process is mature, and the product is purified by low-temperature condensation and distillation, making it suitable for large-scale production; 2. Hexafluorophosphate thermal decomposition method: Relying on the hexafluorophosphate industrial chain, the anhydrous hexafluorophosphate thermal decomposition method can be used. The product is free of chlorine impurities and has extremely high purity, suitable for high-purity scenarios and co-production needs; 3. Direct fluorination of yellow phosphorus: This method can produce ultra-high purity products, but the risks associated with fluorine and yellow phosphorus are high, and the equipment cost is expensive. It is mostly used in high-end fields such as semiconductors; 4. Fluoride salt + phosphorus oxide method: Simple routes such as co-heating of fluoride salts with phosphorus pentoxide and oxygen-fluorine-phosphorus conversion have low equipment requirements and can only produce crude products. For example, patent CN115974017B discloses a method for preparing phosphorus pentafluoride, which is the thermal decomposition method of hexafluorophosphoric acid. The method includes reacting polyphosphoric acid with hydrogen fluoride to obtain aqueous hexafluorophosphoric acid, and then dehydrating and decomposing the aqueous hexafluorophosphoric acid to obtain crude phosphorus pentafluoride.

[0003] However, polyphosphoric acid (PPA) is a viscous paste at room temperature. Its viscosity increases significantly with increasing P2O5 content. This high viscosity makes continuous feeding of PPA via pumping difficult, limiting its application in industrial production. To reduce the viscosity of PPA, existing technologies mainly employ two methods: one is heating to reduce viscosity, specifically heating PPA to 60-70°C to improve its fluidity. However, this heating presents the following problems: 1. The fluorination reaction between PPA and hydrogen fluoride is a strongly exothermic reaction. Heating the raw material at high temperature, coupled with the exothermic reaction itself, significantly increases the overall heat load. Since this fluorination reaction requires stable operation at low temperatures, after heating the raw material PPA at high temperature, to suppress the temperature rise and maintain the low-temperature reaction range, it is necessary to continuously increase the refrigerant circulation and refrigeration load, resulting in high refrigerant consumption, high overall process energy consumption, and increased production costs. 2. When high-temperature raw materials enter the reaction system, the instantaneous strong exothermic reaction easily leads to uneven material mixing and uneven heat and mass transfer. Local high-temperature hotspots easily form inside the reactor. The coexistence of local high temperatures and the water generated in the reaction can induce pyrolysis and hydrolysis side reactions of the generated hexafluorophosphoric acid, generating impurities such as phosphorus trifluorooxide. This not only significantly increases the impurity content of the process gas produced by cracking, greatly increasing the separation load and operational difficulty of subsequent purification processes such as condensation, but also makes it difficult to consistently obtain high-purity phosphorus pentafluoride products, thus affecting the quality and batch stability of downstream lithium hexafluorophosphate products. Secondly, viscosity reducers are added. For example, patent CN103221337B discloses the addition of alkyl phosphorus / phosphonate compounds such as tributyl phosphate (TBP) and dibutyl butylphosphonate to polyphosphoric acid to reduce its viscosity. However, when the above-mentioned alkyl phosphorus / phosphonate viscosity reducers are applied in the process of preparing phosphorus pentafluoride from polyphosphoric acid and anhydrous hydrogen fluoride, the following serious defects exist: 1. They are easily hydrolyzed under high-temperature and strong acid conditions. Alkyl phosphate / phosphonate compounds exhibit the general properties of esters, readily hydrolyzing under high temperature and strong acid conditions to generate corresponding alcohols and acidic phosphate esters. 2. Hydrolysis products react with hydrogen fluoride to produce water and fluorinated hydrocarbons. The alcohols generated from hydrolysis undergo fluorination in the presence of hydrogen fluoride, producing fluorinated hydrocarbons and water. Taking tributyl phosphate as an example, after hydrolysis to butanol, the butanol reacts with HF to produce fluorobutane and water, introducing additional water into the reaction system. 3. It triggers the hydrolysis of hexafluorophosphate, generating the difficult-to-remove POF3 impurity. The additional water generated reacts with the target product, phosphorus pentafluoride, to generate phosphorus trifluorooxyfluoride. POF3 and PF5 have similar properties, making complete separation difficult with conventional condensation purification, severely reducing the purity of the phosphorus pentafluoride product and increasing the energy consumption and difficulty of the purification process. 4. It creates a vicious cycle, exacerbating side reactions. The aforementioned chain reaction of "hydrolysis-fluorination-rehydrolysis" forms a vicious cycle, resulting in the continuous consumption of viscosity reducers, the continuous loss of the target product PF5, the continuous accumulation of POF3 impurities, and the ineffective consumption of reactant HF, which seriously affects the economics of the process and the quality of the product.5. Viscosity reducers cannot function continuously throughout the entire reaction process. Due to the continuous hydrolysis and inactivation of alkyl phosphates under reaction conditions, their viscosity-reducing function cannot be maintained throughout the entire preparation process, making it difficult to ensure the long-term stable operation of the process.

[0004] Therefore, there is an urgent need for a preparation method that does not hydrolyze under high temperature and strong acid conditions, does not produce alcohols and water, does not consume additional hydrogen fluoride, fundamentally inhibits the generation of byproducts such as POF3, and can achieve low temperature pumping and continuous production of polyphosphoric acid while ensuring the high purity of phosphorus pentafluoride products. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing phosphorus pentafluoride by reacting polyphosphoric acid with anhydrous hydrogen fluoride. This process can solve the technical problems in existing technologies, such as the easy hydrolysis of viscosity reducers at acidic high temperatures, which exacerbates side reactions, generates impurities, and consumes additional hydrogen fluoride.

[0006] To address the above technical problems, this invention provides a method for preparing phosphorus pentafluoride by reacting polyphosphoric acid with anhydrous hydrogen fluoride, comprising the following steps: S1. Raw material processing: The viscosity reducer is added to polyphosphoric acid and mixed and stirred to obtain a polyphosphoric acid solution containing the viscosity reducer; the viscosity reducer is a fluorophosphonic acid ester compound with a boiling point greater than 180℃; S2, Fluorination reaction: The polyphosphoric acid solution containing viscosity reducer obtained in S1 and anhydrous hydrogen fluoride are simultaneously added to the reaction vessel to carry out the fluorination reaction. The reaction temperature is controlled at 5~20℃ to obtain an aqueous solution of hexafluorophosphoric acid. S3, Dehydration reaction: The hexafluorophosphate aqueous solution obtained in S2 is sent to the dehydration reactor, and a dehydrating agent is added to carry out the dehydration reaction to obtain a dehydrated hexafluorophosphate solution. S4. Pyrolysis reaction: The dehydrated hexafluorophosphoric acid solution obtained in S3 is transported to a pyrolysis reactor to carry out a pyrolysis reaction, and a mixed gas is obtained. S5. Condensation and purification: The mixed gas obtained in S4 is introduced into the condensation system for gradient condensation. The uncondensed gas is collected to obtain phosphorus pentafluoride.

[0007] Furthermore, in S1, the fluorinated phosphonate compound includes one or more of the following: perfluoroalkyl phosphonate, perfluoroalkyl phosphonate polyfluoroalkyl phosphonate, and perfluoroalkyl phosphonate difluoroalkoxy ester.

[0008] Furthermore, the perfluoroalkyl phosphonate perfluoroalkyl ester includes one or more of trifluoromethylphosphonate di(perfluoropentyl) ester, trifluoromethylphosphonate di(perfluorohexyl) ester, pentafluoroethylphosphonate di(perfluorohexyl) ester, and trifluoromethylphosphonate (perfluoropentyl)(perfluorohexyl) ester; the perfluoroalkyl phosphonate polyfluoroalkyl ester includes one or more of trifluoromethylphosphonate bis(2,2,2-trifluoroethyl) ester, trifluoromethylphosphonate bis(2,2,3,3,3-pentafluoropropyl) ester, and pentafluoroethylphosphonate bis(2,2,2-trifluoroethyl) ester.

[0009] Furthermore, in S1, the stirring temperature is 30°C and the stirring time is 30 min; the amount of the viscosity reducer added is 0.5~2% of the mass of polyphosphoric acid.

[0010] Furthermore, in S2, the polyphosphoric acid solution containing the viscosity reducer and anhydrous hydrogen fluoride are added dropwise at a mass ratio of polyphosphoric acid to hydrogen fluoride of 1:1.4~1.5, with the dropping rate of anhydrous hydrogen fluoride being 1 kg / min; the dropping rate of the polyphosphoric acid solution containing the viscosity reducer being 0.67 kg / min; and the fluorination reaction time being 1 h.

[0011] Furthermore, in S3, the dehydrating agent is fuming sulfuric acid with a mass percentage concentration of 65%. The fuming sulfuric acid is added by dripping at a rate of 0.5 L / min for 3 hours. After the dripping is completed, the reaction is stirred for another 0.5 hours. The dehydration reaction temperature is below 30°C.

[0012] Furthermore, in S4, the temperature of the pyrolysis reaction is greater than 140°C.

[0013] Furthermore, the temperature of the pyrolysis reaction is 145°C.

[0014] Furthermore, in S5, the condensation system is a three-stage condensation system, including a first-stage condensation with a condensation temperature of 0°C to 5°C, a second-stage condensation with a condensation temperature of -10°C, and a third-stage condensation with a condensation temperature of -30°C to -50°C. The mixed gas passes through the first, second, and third condensation stages in sequence. The first-stage condensation stage is used to condense HSO3F, HF, and SO3, the second-stage condensation stage is used to condense HF, and the third-stage condensation stage is used to condense POF3.

[0015] Compared with existing technologies, this solution has the following advantages: 1. Inhibit the formation of byproducts such as POF3 at the source to ensure high product purity. This invention selects one or more of the following as viscosity reducers: perfluoroalkyl phosphonates, perfluoroalkyl polyfluoroalkyl phosphonates, and perfluoroalkyl difluoroalkoxy phosphonates. These compounds contain stable CF bonds with extremely high bond energies, making them resistant to breakage under high temperature (140-150°C) and strong acidic conditions (polyphosphoric acid, hydrogen fluoride, HSO3F), preventing hydrolysis and the production of alcohols and water. In contrast, existing alkylphosphide / phosphonate viscosity reducers such as tributyl phosphate (TBP) and dibutyl butyl phosphonate (DBBP) readily break and hydrolyze their POC ester bonds under high temperature and strong acid conditions, generating alcohols such as butanol. These alcohols further undergo fluorination in the presence of hydrogen fluoride to produce fluorinated hydrocarbons and water. The generated water then reacts with the target product, phosphorus pentafluoride, producing phosphorus trifluoride oxychloride impurities that are difficult to remove. This invention fundamentally breaks the chain of side reactions of "hydrolysis-fluorination-re-hydrolysis", avoiding the generation of impurities such as POF3, thereby ensuring the high purity of phosphorus pentafluoride products.

[0016] 2. The viscosity reducer remains chemically inert throughout the entire reaction process, thus continuously exerting its viscosity-reducing function. The fluorinated phosphonate viscosity reducer selected in this invention maintains its structural integrity throughout the entire preparation process due to the stability of its CF bond and the absence of free hydroxyl groups in its molecule. It does not decompose or become ineffective under high temperature or strong acid environments, and can continuously exert its viscosity-reducing effect throughout the reaction. In contrast, existing alkylphosphide / phosphonate viscosity reducers are continuously hydrolyzed and consumed under reaction conditions, and their viscosity-reducing function cannot be maintained throughout the entire preparation process, making it difficult to ensure the long-term stable operation of the process.

[0017] 3. Significantly reduces the viscosity of polyphosphoric acid, enabling low-temperature pumping and continuous production. The fluorinated phosphonate compounds selected in this invention possess both a strongly polar phosphoryl group (P=O) and a flexible fluoroalkyl side chain. The phosphoryl group competitively disrupts the numerous P-OH hydrogen bonds between polyphosphate molecules, effectively breaking down the associated entanglement structure of the polyphosphate chain segments. Simultaneously, the hydrophobic fluoroalkyl segments act as molecular separators and lubricants, inhibiting the re-aggregation and thickening of the long phosphate chains. The addition of these viscosity reducers significantly lowers the viscosity of the polyphosphate and dramatically improves its flowability, allowing for pumping and feeding at room temperature or low temperature without heating, thus enabling the subsequent fluorination reaction to proceed stably and continuously.

[0018] 4. Reduces refrigerant energy consumption and significantly saves production costs. Thanks to the use of viscosity reducers, polyphosphoric acid achieves good fluidity without heating and can be directly added to the reaction system at low temperatures. Compared to existing viscosity-reducing methods that require heating to 60-70°C, this invention avoids the energy consumption required for raw material preheating. Simultaneously, the low-temperature raw materials, combined with the exothermic reaction itself, result in a lower overall heat load, significantly reducing the required refrigerant circulation volume and refrigeration load. By reducing energy consumption through both raw material preheating and reaction temperature control, production costs are significantly saved.

[0019] 5. Improve reaction heat transfer efficiency, reduce side reactions, and increase product yield. When the low-temperature feedstock enters the reactor and reacts with anhydrous hydrogen fluoride, the heat transfer efficiency is higher, and the reaction temperature is more stable, effectively preventing premature decomposition of hexafluorophosphoric acid due to local overheating. This improves the yield of the target product, phosphorus pentafluoride, and reduces the burden on the subsequent purification stage.

[0020] 6. It does not introduce additional impurities and does not affect the acidity or degree of polymerization of the product. The fluorinated phosphonate compounds selected in this invention do not contain free hydroxyl groups, thus they do not promote further polycondensation of polyphosphoric acid and do not change the degree of polymerization or acidity of the product. Furthermore, these viscosity reducers all have boiling points above 180°C at normal pressure, and will not volatilize into the gaseous products under the pyrolysis reaction temperature conditions of this invention, ensuring that the final phosphorus pentafluoride gas is not contaminated by additional impurities.

[0021] 7. It does not consume additional hydrogen fluoride as a raw material, thus improving product purity and yield. Existing technologies using alkylphosphine / phosphonate viscosity reducers produce alcohols upon hydrolysis. These alcohols react with HF to generate water, which further reacts with PF5 to form POF3, creating a vicious cycle that continuously consumes the viscosity reducer, loses the target product, and accumulates impurities. This cycle not only leads to a significant decrease in product purity and yield but also consumes valuable hydrogen fluoride, increasing the burden and energy consumption of the purification process. This invention utilizes fluorinated phosphonate viscosity reducers containing CF bonds. Due to the extremely high stability of the CF bonds, these reducers do not hydrolyze, produce alcohols or water, or consume additional hydrogen fluoride under high-temperature and strongly acidic conditions. This fundamentally inhibits the formation of byproducts such as POF3. While achieving low-temperature pumping and continuous production of polyphosphoric acid, it also ensures high purity and high yield of phosphorus pentafluoride, achieving a significant advancement unmatched by existing technologies.

[0022] In summary, this invention utilizes fluorophosphonate compounds containing CF bonds as viscosity reducers, taking advantage of the exceptional stability of their CF bonds under high temperature and strong acid conditions. This enables low-temperature pumping and continuous production of polyphosphoric acid while fundamentally suppressing the formation of byproducts such as POF3, ensuring high purity and high yield of phosphorus pentafluoride. It overcomes the technical challenge of existing alkylphosphine / phosphonate viscosity reducers hydrolyzing and inducing chain reactions in the reaction system, demonstrating significant advancements and industrial application value. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1 This embodiment provides a method for preparing phosphorus pentafluoride by reacting polyphosphoric acid with anhydrous hydrogen fluoride, referring to... Figure 1 The specific steps are as follows: S1. Raw Material Processing: Weigh 40 kg of polyphosphoric acid (viscosity approximately 25000 mPa·s, 25℃) and add it to a pretreatment vessel equipped with a jacket and stirrer. Then add 0.4 kg of viscosity reducer, which is 1.0% of the mass of polyphosphoric acid. The viscosity reducer is bis(2,2,2-trifluoroethyl) trifluoromethylphosphonic acid. Start stirring and control the temperature inside the vessel at 30℃. Stir for 30 minutes to obtain a uniform, free-flowing polyphosphoric acid solution containing the viscosity reducer. The viscosity was measured to be reduced to approximately 2500 mPa·s (25℃).

[0026] S2, Fluorination Reaction: All the polyphosphoric acid solution containing the viscosity reducer obtained in S1 and 60 kg of anhydrous hydrogen fluoride were simultaneously added dropwise to the reactor via metering pumps to initiate the fluorination reaction. The feed mass ratio of polyphosphoric acid to hydrogen fluoride was controlled at 1:1.5, with the specific dropping rates controlled as follows: polyphosphoric acid solution dropping rate 0.67 kg / min, anhydrous hydrogen fluoride dropping rate 1.0 kg / min, ensuring synchronous mixing in the reactor. During the reaction, the reaction temperature was controlled between 10 and 15 °C using jacketed cooling water. After the addition was complete, an aqueous solution of hexafluorophosphoric acid was obtained.

[0027] S3. Dehydration reaction: Under stirring, fuming sulfuric acid (containing 65% SO3) was added dropwise at a rate of 0.5 L / min to the entire aqueous solution of hexafluorophosphoric acid obtained in S2 as a dehydrating agent, while controlling the reaction temperature at 20℃-25℃. After 3 hours of dropwise addition, the reaction was continued with stirring for 0.5 hours. After the reaction was completed, a dehydrated hexafluorophosphoric acid solution was obtained.

[0028] S4. Pyrolysis Reaction: All the dehydrated hexafluorophosphoric acid solution obtained in S3 is transferred to the pyrolysis reactor. All gas outlet valves are closed, leaving only the gas outlet connected to the condensation system. The pyrolysis reactor is heated to 145°C and the pyrolysis reaction is carried out at this constant temperature. The mixed gas produced by the reaction mainly contains phosphorus pentafluoride, as well as byproducts such as HSO3F, HF, SO3, and POF3, which are discharged from the gas outlet and proceed to the next stage.

[0029] S5. Condensation and Purification: The mixed gas exported from S4 is sequentially passed into a three-stage condensation system for gradient condensation. Wherein: First-stage condensation: The condensation temperature is set to 0℃~5℃, which is used to condense impurity gases such as HSO3F (boiling point about 165℃), HF and SO3 into liquid and remove them.

[0030] Second-stage condensation: The condensation temperature is set to -10℃, which is used to further condense and remove residual HF (boiling point 19.5℃).

[0031] Third-stage condensation: The condensation temperature is set to -40℃, which is used to condense and remove the byproduct POF3 (boiling point approximately -39.8℃).

[0032] After the mixed gas passes through the three-stage condenser described above, the uncondensed gas is collected, which is high-purity phosphorus pentafluoride gas.

[0033] In this embodiment, after the pyrolysis reaction, the residue in the pyrolysis vessel mainly consists of concentrated phosphoric acid and a small amount of undecomposed hexafluorophosphoric acid, as well as the fluorinated phosphonate viscosity reducer added in S1. This viscosity reducer did not decompose or volatilize during the pyrolysis reaction and remained stable in the waste acid system at the bottom of the pyrolysis vessel after the reaction. The waste acid system mainly includes sulfuric acid components introduced from the S3 dehydration step and the residual viscosity reducer. Due to the significant difference in polarity and poor miscibility between the two, they naturally separate into layers after standing. The viscosity reducer, due to its higher density, settles in the lower layer, while the upper layer consists of inorganic acid phases such as sulfuric acid and phosphoric acid. This stratification characteristic facilitates the classification, recovery, or centralized treatment of the viscosity reducer in the waste acid, reduces the difficulty of post-treatment of the waste liquid, and further demonstrates the environmental advantages of this invention.

[0034] Testing showed that the phosphorus pentafluoride prepared in this embodiment had a purity greater than 99.5% and a yield of 92% based on polyphosphoric acid.

[0035] Example 2 This embodiment provides a method for preparing phosphorus pentafluoride by reacting polyphosphoric acid with anhydrous hydrogen fluoride, referring to... Figure 1 The specific steps are as follows: S1. Raw Material Processing: Weigh 40 kg of polyphosphoric acid (viscosity approximately 25000 mPa·s, 25℃) and add it to a pretreatment vessel equipped with a jacket and stirrer. Then add 0.4 kg of viscosity reducer, which is 1.0% of the mass of polyphosphoric acid. The viscosity reducer is trifluoromethylphosphonic acid di(perfluorohexyl) ester, belonging to the perfluoroalkylphosphonic acid perfluoroalkyl ester category. Then start stirring, control the temperature inside the vessel at 30℃, and stir at a constant temperature for 30 minutes to obtain a uniform, free-flowing polyphosphoric acid solution containing the viscosity reducer. The viscosity was measured to be reduced to approximately 2600 mPa·s (25℃).

[0036] S2, Fluorination Reaction: All the polyphosphoric acid solution containing the viscosity reducer obtained in S1 and 60 kg of anhydrous hydrogen fluoride were simultaneously added dropwise to the reactor via metering pumps to initiate the fluorination reaction. The feed mass ratio of polyphosphoric acid to hydrogen fluoride was controlled at 1:1.5, with the specific dropping rates controlled as follows: polyphosphoric acid solution dropping rate 0.67 kg / min, anhydrous hydrogen fluoride dropping rate 1.0 kg / min, ensuring synchronous mixing in the reactor. During the reaction, the reaction temperature was controlled between 10 and 15 °C using jacketed cooling water. After the addition was complete, an aqueous solution of hexafluorophosphoric acid was obtained.

[0037] S3. Dehydration reaction: Under stirring, fuming sulfuric acid (containing 65% SO3) was added dropwise at a rate of 0.5 L / min to the entire aqueous solution of hexafluorophosphoric acid obtained in S2 as a dehydrating agent, while controlling the reaction temperature at 20℃-25℃. After 3 hours of dropwise addition, the reaction was continued with stirring for 0.5 hours. After the reaction was completed, a dehydrated hexafluorophosphoric acid solution was obtained.

[0038] S4. Pyrolysis Reaction: All the dehydrated hexafluorophosphoric acid solution obtained in S3 is transferred to the pyrolysis reactor. All gas outlet valves are closed, leaving only the gas outlet connected to the condensation system. The pyrolysis reactor is heated to 145°C and the pyrolysis reaction is carried out at this constant temperature. The mixed gas produced by the reaction mainly contains phosphorus pentafluoride, as well as byproducts such as HSO3F, HF, SO3, and POF3, which are discharged from the gas outlet and proceed to the next stage.

[0039] S5. Condensation and Purification: The mixed gas exported from S4 is sequentially passed into a three-stage condensation system for gradient condensation. Wherein: First-stage condensation: The condensation temperature is set to 0℃~5℃, which is used to condense impurity gases such as HSO3F (boiling point about 165℃), HF and SO3 into liquid and remove them.

[0040] Second-stage condensation: The condensation temperature is set to -10℃, which is used to further condense and remove residual HF (boiling point 19.5℃).

[0041] Third-stage condensation: The condensation temperature is set to -40℃, which is used to condense and remove the byproduct POF3 (boiling point approximately -39.8℃).

[0042] After the mixed gas passes through the three-stage condenser described above, the uncondensed gas is collected, which is high-purity phosphorus pentafluoride gas.

[0043] Testing showed that the phosphorus pentafluoride prepared in this embodiment had a purity greater than 99.5% and a yield of 91% based on polyphosphoric acid.

[0044] Example 3 This embodiment provides a method for preparing phosphorus pentafluoride by reacting polyphosphoric acid with anhydrous hydrogen fluoride, referring to... Figure 1 The specific steps are as follows: S1. Raw Material Processing: Weigh 40 kg of polyphosphoric acid (viscosity approximately 25000 mPa·s, 25℃) and add it to a pretreatment vessel equipped with a jacket and stirrer. Then add 0.4 kg of viscosity reducer, which is 1.0% of the mass of polyphosphoric acid. The viscosity reducer is a perfluoroalkylphosphonic acid difluoroalkoxy ester (specifically, a difluoroalkoxy-substituted trifluoromethylphosphonic acid ester). Then start stirring, control the temperature inside the vessel at 30℃, and stir at a constant temperature for 30 minutes to obtain a uniform, free-flowing polyphosphoric acid solution containing the viscosity reducer. The viscosity was measured to be reduced to approximately 2400 mPa·s (25℃).

[0045] S2, Fluorination Reaction: All the polyphosphoric acid solution containing the viscosity reducer obtained in S1 and 60 kg of anhydrous hydrogen fluoride were simultaneously added dropwise to the reactor via metering pumps to initiate the fluorination reaction. The feed mass ratio of polyphosphoric acid to hydrogen fluoride was controlled at 1:1.5, with the specific dropping rates controlled as follows: polyphosphoric acid solution dropping rate 0.67 kg / min, anhydrous hydrogen fluoride dropping rate 1.0 kg / min, ensuring synchronous mixing in the reactor. During the reaction, the reaction temperature was controlled between 10 and 15 °C using jacketed cooling water. After the addition was complete, an aqueous solution of hexafluorophosphoric acid was obtained.

[0046] S3. Dehydration reaction: Under stirring, fuming sulfuric acid (containing 65% SO3) was added dropwise at a rate of 0.5 L / min to the entire aqueous solution of hexafluorophosphoric acid obtained in S2 as a dehydrating agent, while controlling the reaction temperature at 20℃-25℃. After 3 hours of dropwise addition, the reaction was continued with stirring for 0.5 hours. After the reaction was completed, a dehydrated hexafluorophosphoric acid solution was obtained.

[0047] S4. Pyrolysis Reaction: All the dehydrated hexafluorophosphoric acid solution obtained in S3 is transferred to the pyrolysis reactor. All gas outlet valves are closed, leaving only the gas outlet connected to the condensation system. The pyrolysis reactor is heated to 145°C and the pyrolysis reaction is carried out at this constant temperature. The mixed gas produced by the reaction mainly contains phosphorus pentafluoride, as well as byproducts such as HSO3F, HF, SO3, and POF3, which are discharged from the gas outlet and proceed to the next stage.

[0048] S5. Condensation and Purification: The mixed gas exported from S4 is sequentially passed into a three-stage condensation system for gradient condensation. Wherein: First-stage condensation: The condensation temperature is set to 0℃~5℃, which is used to condense impurity gases such as HSO3F (boiling point about 165℃), HF and SO3 into liquid and remove them.

[0049] Second-stage condensation: The condensation temperature is set to -10℃, which is used to further condense and remove residual HF (boiling point 19.5℃).

[0050] Third-stage condensation: The condensation temperature is set to -40℃, which is used to condense and remove the byproduct HSO3F (boiling point approximately -39.8℃).

[0051] After the mixed gas passes through the three-stage condenser described above, the uncondensed gas is collected, which is high-purity phosphorus pentafluoride gas.

[0052] Testing showed that the phosphorus pentafluoride prepared in this embodiment had a purity greater than 99.5% and a yield of 93% based on polyphosphoric acid.

[0053] Comparative Example 1: No viscosity reducer added, no heating. This comparative example is basically the same as Example 1, except that no viscosity reducer is added in the S1 raw material processing step, and the polyphosphoric acid is not heated.

[0054] Results: 40 kg of polyphosphoric acid (viscosity approximately 25000 mPa·s, 25℃) was a viscous paste at room temperature, which could not be properly delivered to the reactor by a metering pump, nor could it be added simultaneously with anhydrous hydrogen fluoride. Due to the inability to deliver the material, the subsequent S2 fluorination reaction could not proceed in a continuous and controllable manner, resulting in the reaction failing to start normally and the preparation process failing.

[0055] Comparative Example 2: No viscosity reducer added, only heating This comparative example is basically the same as Example 1, except that no viscosity reducer is added in the raw material processing step S1. Instead, polyphosphoric acid is heated to 60~70°C to reduce its viscosity.

[0056] Results: When polyphosphoric acid is heated to 65°C, its viscosity decreases significantly to a transportable range (approximately 800 mPa·s), allowing it to be transported using a metering pump. However, the following problem exists: 1. High-temperature polyphosphoric acid places higher demands on the corrosion resistance and high-temperature resistance of the delivery pipelines and metering pumps, making equipment selection difficult and significantly increasing costs; 2. When high-temperature materials are mixed with low-temperature anhydrous hydrogen fluoride, the local temperature difference is large, the reaction is violent, the temperature control becomes more difficult, and runaway temperature is likely to occur, affecting the safety of the reaction and the product yield. 3. During long-term operation, the high-temperature environment accelerates equipment corrosion and increases maintenance costs.

[0057] Overall, while this method is barely feasible, its feasibility, economy, and safety for industrial implementation are significantly inferior to that of the present invention.

[0058] Comparative Example 3: Polyethylene glycol, a common viscosity reducer, was added. This comparative example is basically the same as Example 1, except that in the raw material processing step S1, the viscosity reducer is replaced with polyethylene glycol 400 (PEG-400, boiling point about 250°C).

[0059] Results: After adding PEG-400, the viscosity of polyphosphoric acid was effectively reduced, allowing for normal material transport, and both fluorination and dehydration reactions were completed. However, during the S4 pyrolysis reaction, PEG-400 decomposed and underwent fluorination under high temperature and strong acid conditions, resulting in the following serious problems: 1. A large amount of organic fluoride byproducts are generated and mixed into the final phosphorus pentafluoride gas, resulting in a significant decrease in product purity. After testing, the final phosphorus pentafluoride purity is only about 70%.

[0060] 2. The decomposition reaction releases trace amounts of water, which reacts with PF5 in the S5 condensation system to generate POF3 and HF, increasing the burden on the condensation and purification system.

[0061] 3. A large amount of black gelatinous substance remains inside the pyrolysis reactor, which is difficult to clean and seriously affects the stability of continuous production and the lifespan of the equipment.

[0062] Comparative Example 4: Addition of Tributyl Phosphate (TBP) This comparative example is basically the same as Example 1, except that in the raw material processing step S1, the viscosity reducer is replaced with tributyl phosphate (TBP, CAS No. 126-73-8, boiling point about 289°C).

[0063] Results: The viscosity of polyphosphoric acid was effectively reduced after the addition of tributyl phosphate, allowing for normal material transport, and both fluorination and dehydration reactions were completed. However, the following serious problems arose in subsequent processes: 1. Hydrolysis occurs under high temperature and strong acid conditions. Tributyl phosphate undergoes hydrolysis in a pyrolysis reaction (145℃) and a strong acidic environment (polyphosphoric acid, hydrogen fluoride, HSO3F) to produce butanol and phosphoric acid.

[0064] 2. The hydrolysis product, butanol, reacts with HF to produce water and fluorobutane. The butanol produced by hydrolysis undergoes a fluorination reaction in the presence of hydrogen fluoride to produce fluorobutane and water, thus introducing additional water into the reaction system.

[0065] 3. It triggers the hydrolysis of hexafluorophosphate, generating POF3 impurities. The additional water generated reacts with the target product, phosphorus pentafluoride, to form phosphorus trifluoride oxyfluoride, leading to a significant decrease in the purity of the final phosphorus pentafluoride. Testing revealed that the final phosphorus pentafluoride purity was only approximately 78%.

[0066] 4. Residues inside the pyrolysis reactor are difficult to clean. The hydrolysis products of tributyl phosphate and the complex mixtures formed by their reactions with other components in the system form viscous residues inside the pyrolysis reactor, affecting equipment lifespan and the stability of continuous production.

[0067] Comparative Example 5: Addition of dibutyl butylphosphonate (DBBP) This comparative example is basically the same as Example 1, except that in the raw material processing step S1, the viscosity reducer is replaced with dibutyl butylphosphonate (DBBP, CAS No. 78-46-6, boiling point about 289°C).

[0068] Results: The viscosity of polyphosphoric acid was effectively reduced after the addition of dibutyl butylphosphonate, allowing for normal material transport, and both fluorination and dehydration reactions were successfully completed. However, the following serious problems arose in subsequent processes: 1. Hydrolysis occurs under high temperature and strong acid conditions. Dibutyl butyl phosphonate undergoes hydrolysis in a pyrolysis reaction (145℃) and a strongly acidic environment, producing butanol and butylphosphonic acid.

[0069] 2. The hydrolysis product, butanol, reacts with HF to produce water and fluorobutane. The butanol produced by hydrolysis undergoes a fluorination reaction in the presence of hydrogen fluoride to produce fluorobutane and water, thus introducing additional water into the reaction system.

[0070] 3. It triggers the hydrolysis of hexafluorophosphate, generating POF3 impurities. The additional water generated reacts with the target product, phosphorus pentafluoride, to form phosphorus trifluoride oxyfluoride, leading to a significant decrease in the purity of the final phosphorus pentafluoride. Testing revealed that the final phosphorus pentafluoride purity was only approximately 75%.

[0071] 4. This creates a vicious cycle and exacerbates side reactions. The above-mentioned chain reaction of "hydrolysis-fluorination-re-hydrolysis" forms a vicious cycle, leading to the continuous consumption of viscosity reducers, the continuous loss of the target product PF5, the continuous accumulation of POF3 impurities, and the ineffective consumption of reactant HF.

[0072] 5. The viscosity reducer cannot function continuously throughout the entire reaction process. Because dibutyl butyl phosphonate continuously hydrolyzes and loses its effectiveness under reaction conditions, its viscosity-reducing function cannot be maintained throughout the entire preparation process, making it difficult to ensure the long-term stable operation of the process.

[0073] The comparative examples 1-5 above demonstrate that by selecting fluorinated phosphonate compounds with a boiling point greater than 180℃ as viscosity reducers, the present invention can effectively reduce the viscosity of polyphosphoric acid while being able to withstand the subsequent high-temperature pyrolysis reaction environment, without hydrolysis, decomposition, or the generation of by-products, thereby ensuring the high purity of the phosphorus pentafluoride product and the high efficiency and stability of the preparation process, achieving unexpected technical effects.

[0074] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing phosphorus pentafluoride by reacting polyphosphoric acid with anhydrous hydrogen fluoride, characterized in that: Includes the following steps: S1. Raw material processing: Add the viscosity reducer to polyphosphoric acid and mix and stir to obtain a polyphosphoric acid solution containing the viscosity reducer; The viscosity reducer is a fluorinated phosphonate compound with a boiling point greater than 180°C; S2, Fluorination reaction: The polyphosphoric acid solution containing viscosity reducer obtained in S1 and anhydrous hydrogen fluoride are simultaneously added to the reaction vessel to carry out the fluorination reaction. The reaction temperature is controlled at 5~20℃ to obtain an aqueous solution of hexafluorophosphoric acid. S3, Dehydration reaction: The hexafluorophosphate aqueous solution obtained in S2 is sent to the dehydration reactor, and a dehydrating agent is added to carry out the dehydration reaction to obtain a dehydrated hexafluorophosphate solution. S4. Pyrolysis reaction: The dehydrated hexafluorophosphoric acid solution obtained in S3 is transported to a pyrolysis reactor to carry out a pyrolysis reaction, and a mixed gas is obtained. S5. Condensation and purification: The mixed gas obtained in S4 is introduced into the condensation system for gradient condensation. The uncondensed gas is collected to obtain phosphorus pentafluoride.

2. The method for preparing phosphorus pentafluoride by reacting polyphosphoric acid with anhydrous hydrogen fluoride according to claim 1, characterized in that: In S1, the fluorinated phosphonate compound includes one or more of the following: perfluoroalkyl phosphonate, perfluoroalkyl phosphonate polyfluoroalkyl ester, and perfluoroalkyl phosphonate difluoroalkoxy ester.

3. The method for preparing phosphorus pentafluoride by reacting polyphosphoric acid with anhydrous hydrogen fluoride according to claim 2, characterized in that: The perfluoroalkyl phosphonate perfluoroalkyl esters include one or more of trifluoromethylphosphonate di(perfluoropentyl), trifluoromethylphosphonate di(perfluorohexyl), pentafluoroethylphosphonate di(perfluorohexyl), and trifluoromethylphosphonate (perfluoropentyl)(perfluorohexyl); the perfluoroalkyl phosphonate polyfluoroalkyl esters include one or more of trifluoromethylphosphonate bis(2,2,2-trifluoroethyl), trifluoromethylphosphonate bis(2,2,3,3,3-pentafluoropropyl), and pentafluoroethylphosphonate bis(2,2,2-trifluoroethyl).

4. The method for preparing phosphorus pentafluoride by reacting polyphosphoric acid with anhydrous hydrogen fluoride according to claim 1, characterized in that: In S1, the stirring temperature is 30°C and the stirring time is 30 min; the amount of viscosity reducer added is 0.5~2% of the mass of polyphosphoric acid.

5. The method for preparing phosphorus pentafluoride by reacting polyphosphoric acid with anhydrous hydrogen fluoride according to claim 1, characterized in that: In step S2, the polyphosphoric acid solution containing the viscosity reducer and anhydrous hydrogen fluoride are added dropwise at a mass ratio of polyphosphoric acid to hydrogen fluoride of 1:1.4~1.

5. The dropping rate of anhydrous hydrogen fluoride is 1 kg / min, and the dropping rate of the polyphosphoric acid solution containing the viscosity reducer is 0.67 kg / min. The fluorination reaction takes 1 hour.

6. The method for preparing phosphorus pentafluoride by reacting polyphosphoric acid with anhydrous hydrogen fluoride according to claim 1, characterized in that: In S3, the dehydrating agent is fuming sulfuric acid with a mass percentage concentration of 65%. The fuming sulfuric acid is added by dripping at a rate of 0.5 L / min for 3 hours. After the dripping is completed, the reaction is stirred for another 0.5 hours. The dehydration reaction temperature is below 30°C.

7. The method for preparing phosphorus pentafluoride by reacting polyphosphoric acid with anhydrous hydrogen fluoride according to claim 1, characterized in that: In S4, the temperature of the pyrolysis reaction is greater than 140°C.

8. The method for preparing phosphorus pentafluoride by reacting polyphosphoric acid with anhydrous hydrogen fluoride according to claim 7, characterized in that: The temperature of the pyrolysis reaction is 145℃.

9. The method for preparing phosphorus pentafluoride by reacting polyphosphoric acid with anhydrous hydrogen fluoride according to claim 1, characterized in that: In S5, the condensation system is a three-stage condensation system, including a first-stage condensation with a condensation temperature of 0℃ to 5℃, a second-stage condensation with a condensation temperature of -10℃, and a third-stage condensation with a condensation temperature of -30℃ to -50℃. The mixed gas passes through the first, second, and third condensation stages in sequence. The first-stage condensation stage is used to condense HSO3F, HF, and SO3, the second-stage condensation stage is used to condense HF, and the third-stage condensation stage is used to condense POF3.

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