A method for preparing phosphorus pentafluoride
By using a mixed acid of fluorosulfonic acid and anhydrous hydrogen fluoride as a dehydration raw material and controlling the pyrolysis temperature below 50℃, the problem of local overheating in the preparation of phosphorus pentafluoride was solved, the yield and production efficiency of phosphorus pentafluoride were improved, and the generation of phosphorus trifluoride was reduced.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- 新乡意盛科技有限公司
- Filing Date
- 2024-01-15
- Publication Date
- 2026-06-30
AI Technical Summary
In existing methods for preparing phosphorus pentafluoride, when fuming sulfuric acid or sulfur trioxide is used as a dehydration raw material, there is a problem of localized instantaneous overheating during the mixed dehydration process. This leads to instability of hexafluorophosphoric acid and a high content of phosphorus trifluoride byproducts, which affects production efficiency and equipment lifespan.
A mixed acid containing fluorosulfonic acid and anhydrous hydrogen fluoride was used as the dehydration raw material. It was mixed with hexafluorophosphoric acid solution and pyrolyzed at a controlled temperature below 50°C to reduce the production of phosphorus trifluoride and increase the yield of phosphorus pentafluoride.
It effectively avoids localized instantaneous overheating, lowers the pyrolysis temperature, significantly reduces the generation of phosphorus trifluoride, improves the yield and production efficiency of phosphorus pentafluoride, and reduces subsequent refining costs.
Abstract
Description
Technical Field
[0001] This invention belongs to the field of phosphorus halides, and specifically relates to a method for preparing phosphorus pentafluoride. Background Technology
[0002] Liquid lithium hexafluorophosphate is a carbonate single-agent solution with a lithium hexafluorophosphate content of about 30%. It makes electrolyte preparation more convenient and significantly improves preparation efficiency, so it is favored by electrolyte manufacturers. Liquid lithium hexafluorophosphate is also considered to be one of the important development directions of lithium salts in the future.
[0003] The existing process for liquid lithium hexafluorophosphate uses polyphosphoric acid or phosphorus pentoxide as raw materials. First, it reacts with anhydrous hydrogen fluoride to obtain a hexafluorophosphate solution with approximately 30% water content. Then, the hexafluorophosphate solution is added to high-concentration fuming sulfuric acid (or sulfur trioxide) for a mixed reaction and dehydration. Afterward, pyrolysis is performed to decompose the hexafluorophosphate into phosphorus pentafluoride gas. The phosphorus pentafluoride gas, after purification, is directly passed into a carbonate solution pre-containing lithium fluoride. The phosphorus pentafluoride gas reacts with the lithium fluoride to form a lithium hexafluorophosphate solution with a mass content of 25-30%. This lithium hexafluorophosphate solution is then deacidified and purified to obtain a liquid lithium hexafluorophosphate product that meets the quality requirements of the electrolyte.
[0004] Therefore, one of the key technologies for preparing liquid lithium hexafluorophosphate is to produce phosphorus pentafluoride gas quickly and easily.
[0005] Although existing phosphorus pentafluoride gas production technology has been mass-produced, it also has the following shortcomings based on publicly available information and theoretical analysis:
[0006] When dehydrating by directly mixing fuming sulfuric acid and hexafluorophosphate solution, using fuming sulfuric acid as the base solution and slowly adding hexafluorophosphate solution with approximately 30% water content, the temperature of the mixture will quickly rise from room temperature to around 140°C without forced cooling, indicating a very vigorous reaction. The reaction equation for the mixed dehydration is as follows:
[0007] SO3 + H2O = H2SO4
[0008] Before the water in the hexafluorophosphate solution was thoroughly mixed with the fuming sulfuric acid and removed, such a high temperature already caused most of the hexafluorophosphate in the mixture to decompose and generate phosphorus oxyfluoride gas. In fact, even with forced cooling measures during the addition of the hexafluorophosphate solution, localized instantaneous overheating was difficult to avoid. Hexafluorophosphate is also unstable in such a mixed acid. Therefore, pyrolysis will also produce a large amount of phosphorus oxyfluoride gas, sometimes exceeding 50%. The relevant reactions are as follows:
[0009] HPF6 = PF5 + HF
[0010] PF5 + H2O = POF3 + 2HF
[0011] When a mixed gas containing phosphorus trifluoride and phosphorus pentafluoride enters the downstream process, although measures can be taken to recover and reuse it, it increases the processing cost of gas purification and reduces production efficiency.
[0012] In addition, relevant literature reviews indicate that the temperature for producing phosphorus pentafluoride gas by pyrolysis of hexafluorophosphate is generally around 150℃. Such a high temperature not only results in high energy consumption, but also limits the selection of materials for the pyrolysis equipment and affects its lifespan.
[0013] If sulfur trioxide is used as the dehydration raw material for hexafluorophosphate solution, the reaction between sulfur trioxide and water generates more heat, the temperature rise is more pronounced, and the production of phosphorus trifluorooxygen as a byproduct is also more severe.
[0014] In summary, existing methods for preparing phosphorus pentafluoride gas mainly use fuming sulfuric acid or sulfur trioxide as dehydration raw materials. The problem of localized instantaneous overheating during the mixing and dehydration process is difficult to solve effectively. This also leads to a high content of phosphorus trifluoride oxyfluoride byproducts during the pyrolysis preparation of phosphorus pentafluoride gas, which is one of the technical difficulties in implementing this method. Summary of the Invention
[0015] The purpose of this invention is to provide a method for preparing phosphorus pentafluoride, thereby solving the problems of large local instantaneous heat release and high content of phosphorus trifluoride oxyfluoride byproduct in the phosphorus pentafluoride gas produced by existing technologies that use fuming sulfuric acid or sulfur trioxide as dehydration raw materials.
[0016] To achieve the above objectives, the technical solution adopted by this invention is as follows:
[0017] A method for preparing phosphorus pentafluoride includes the following steps:
[0018] (1) A first mixed acid containing fluorosulfonic acid and anhydrous hydrogen fluoride is mixed with a hexafluorophosphoric acid solution for dehydration to obtain a second mixed acid; the second mixed acid contains fluorosulfonic acid, sulfuric acid, hexafluorophosphoric acid and hydrogen fluoride;
[0019] (2) The second mixed acid is pyrolyzed to obtain a mixed gas containing phosphorus pentafluoride.
[0020] The method for preparing phosphorus pentafluoride provided by this invention uses a first mixed acid containing fluorosulfonic acid and anhydrous hydrogen fluoride as a dehydration raw material. The exothermic process of mixing and dehydration is much milder than that of using fuming sulfuric acid or sulfur trioxide as raw materials. Even without cooling measures, the temperature rise of the material does not exceed 50 degrees Celsius. This effectively avoids the problem of local instantaneous overheating when fuming sulfuric acid or sulfur trioxide is directly mixed with hexafluorophosphoric acid solution, which leads to instability of hexafluorophosphoric acid and a large amount of phosphorus trifluoride byproducts.
[0021] Meanwhile, adding anhydrous hydrogen fluoride to the first mixed acid is beneficial to the stability of hexafluorophosphoric acid when mixed with hexafluorophosphoric acid solution, thus reducing the production of phosphorus trifluoride during pyrolysis and thereby increasing the yield of phosphorus pentafluoride in the produced gas.
[0022] Preferably, the mass content of anhydrous hydrogen fluoride in the first mixed acid is 7-25%. The stability of hexafluorophosphate in the second mixed acid increases with the increase of hydrogen fluoride content, thus reducing the generation of phosphorus oxyfluoride during pyrolysis. However, excessive increase in hydrogen fluoride content will increase the hydrogen fluoride recovery load during pyrolysis.
[0023] More preferably, the mass content of anhydrous hydrogen fluoride in the first mixed acid is 10-18%. Anhydrous hydrogen fluoride can be added during the preparation of the fluorosulfonic acid solution or added later. Controlling the anhydrous hydrogen fluoride within the above range can further reduce the generation of phosphorus oxyfluoride during pyrolysis.
[0024] The second mixed acid contains fluorosulfonic acid, sulfuric acid, hexafluorophosphate, and hydrogen fluoride, which is both a combination of strong inorganic acids and a strong protic acid. The inventors discovered that under these conditions, the pyrolysis temperature of hexafluorophosphate is significantly lower than that of existing fuming sulfuric acid mixed pyrolysis processes. Preferably, the mass content of fluorosulfonic acid in the second mixed acid is 3-10%, and the mass content of hydrogen fluoride is 15-25%. Appropriately excessive addition of fluorosulfonic acid and hydrogen fluoride is beneficial for lowering the pyrolysis temperature, but it will increase the recovery load.
[0025] More preferably, the mass content of fluorosulfonic acid in the second mixed acid is 5-10%, and the mass content of hydrogen fluoride is 18-25%. Controlling the content of fluorosulfonic acid and hydrogen fluoride within the above range can effectively reduce the pyrolysis temperature to below 95°C.
[0026] Preferably, the first mixed acid further contains sulfuric acid, and the sulfuric acid and fluorosulfonic acid in the first mixed acid are obtained by reacting fuming sulfuric acid or sulfur trioxide with anhydrous hydrogen fluoride. Adding anhydrous hydrogen fluoride to the fuming sulfuric acid solution or sulfur trioxide liquid converts it into a mixed acid of sulfuric acid and fluorosulfonic acid or a perfluorosulfonic acid solution. Further addition of excess hydrogen fluoride, followed by mixing with an aqueous solution of hexafluorophosphate, reproduced the mildly exothermic experimental results. Although the fluorination process of adding anhydrous hydrogen fluoride to fuming sulfuric acid or sulfur trioxide also releases a large amount of heat, this heat can be removed by forced cooling. Crucially, hexafluorophosphate is not present in this exothermic fluorination process. This avoids the instability problem of hexafluorophosphate that easily occurs when fuming sulfuric acid or sulfur trioxide is directly mixed with hexafluorophosphate solution due to localized instantaneous overheating, which is clearly a significant discovery.
[0027] Preferably, in step (2), the pyrolysis temperature is below 95°C. For example, pyrolysis can occur at 60~95°C. The above pyrolysis temperature is significantly lower than the existing pyrolysis process of fuming sulfuric acid mixture, which is beneficial for further reducing the occurrence of side reactions and reducing corrosion of production equipment.
[0028] The temperature for mixing and dehydration is below 40°C. Preferably, the temperature for the mixing reaction and dehydration is below 10°C. Controlling the mixing reaction and dehydration temperature within the above range is beneficial for further improving the stability of hexafluorophosphoric acid and reducing the generation of phosphorus oxyfluoride gas during pyrolysis.
[0029] Preferably, in step (2), the mixed gas contains phosphorus pentafluoride and phosphorus trifluoride oxyfluoride, wherein the mass of phosphorus trifluoride oxyfluoride accounts for no more than 10% of the total mass of phosphorus pentafluoride and phosphorus trifluoride oxyfluoride. Controlling the content of phosphorus trifluoride oxyfluoride in the generated gas within the above range significantly reduces the phosphorus trifluoride oxyfluoride produced by directly mixing fuming sulfuric acid or sulfur trioxide with hexafluorophosphoric acid solution, dehydrating, and then pyrolyzing. This makes the subsequent purification of the generated phosphorus pentafluoride gas easier, greatly improves production efficiency, and promotes the technological progress of phosphorus pentafluoride production process. Detailed Implementation
[0030] In existing phosphorus pentafluoride gas production processes, the direct mixing of fuming sulfuric acid or sulfur trioxide with hexafluorophosphoric acid solution can cause localized instantaneous overheating, which can easily lead to instability of hexafluorophosphoric acid and high content of phosphorus trifluorooxygen byproducts in the produced gas.
[0031] This invention essentially provides a method for reducing the generation of phosphorus oxyfluoride byproducts during the preparation of phosphorus pentafluoride. Specifically, it involves mixing and dehydrating a first mixed acid containing fluorosulfonic acid and anhydrous hydrogen fluoride with a hexafluorophosphoric acid solution. This makes the exothermic reaction during mixing more mild and controllable, and further enhances the stability of hexafluorophosphoric acid by adding excess anhydrous hydrogen fluoride. Ultimately, this results in a significant reduction in phosphorus oxyfluoride gas generated during the pyrolysis of the second mixed acid. The phosphorus oxyfluoride content in the phosphorus-containing decomposition products (composed of phosphorus oxyfluoride and phosphorus pentafluoride) generated by the decomposition of hexafluorophosphoric acid is less than 10%, which is significantly lower than the phosphorus oxyfluoride generated by directly mixing fuming sulfuric acid or sulfur trioxide with a hexafluorophosphoric acid solution for dehydration and then pyrolysis.
[0032] Since the dehydration reaction is carried out using fluorosulfonic acid in the first mixed acid and water in the hexafluorophosphate solution to obtain hydrogen fluoride and sulfuric acid, the amount of fluorosulfonic acid in the first mixed acid should be in excess relative to the amount of water in the hexafluorophosphate solution to ensure sufficient water reaction. This yields a second mixed acid containing fluorosulfonic acid, sulfuric acid, hexafluorophosphate, and hydrogen fluoride. The second mixed acid is both a combination of inorganic strong acids and contains a strong protic acid. The inventors unexpectedly discovered that the pyrolysis temperature decreases significantly with the above changes, and the pyrolysis of hexafluorophosphate can be completed below 95 degrees Celsius (the pyrolysis temperature can be 60-95 degrees Celsius, more preferably 70-95 degrees Celsius), with a decomposition rate of approximately 97%. An excess of fluorosulfonic acid and hydrogen fluoride is beneficial for lowering the pyrolysis temperature (for example, it can be lowered to below 85 degrees Celsius), but too much excess will increase the recovery load. Preferably, the mass content of fluorosulfonic acid in the second mixed acid is 3-10%, and the mass content of hydrogen fluoride is 15-25%. More preferably, the mass content of fluorosulfonic acid in the second mixed acid is 5-10%, and the mass content of hydrogen fluoride is 18-25%.
[0033] The fluorosulfonic acid in the first mixed acid can be prepared using commercially available products or by reacting fuming sulfuric acid or sulfur trioxide liquid with anhydrous hydrogen fluoride. For the reaction of fuming sulfuric acid and anhydrous hydrogen fluoride, the amount of anhydrous hydrogen fluoride used is preferably the theoretical amount or in excess relative to the sulfur trioxide in the fuming sulfuric acid. This yields a mixed acid of sulfuric acid and fluorosulfonic acid (or containing a small amount of hydrogen fluoride). Further addition of the required amount of anhydrous hydrogen fluoride then yields the first mixed acid composed of sulfuric acid, fluorosulfonic acid, and anhydrous hydrogen fluoride. For the reaction of sulfur trioxide liquid and anhydrous hydrogen fluoride, the amount of anhydrous hydrogen fluoride used is preferably the theoretical amount or in excess relative to the sulfur trioxide. This yields a perfluorosulfonic acid solution (or containing a small amount of hydrogen fluoride). Further addition of the required amount of anhydrous hydrogen fluoride then yields the first mixed acid composed of fluorosulfonic acid and anhydrous hydrogen fluoride. The inventors discovered that increasing the anhydrous hydrogen fluoride content in the first mixed acid is beneficial to the stability of hexafluorophosphoric acid when mixed with hexafluorophosphoric acid solution, thus reducing the generation of phosphorus trifluoride oxyfluoride during pyrolysis. However, this increases the hydrogen fluoride recovery load during pyrolysis. Preferably, the mass content of anhydrous hydrogen fluoride in the first mixed acid is 7-25%, more preferably 7-18%, and even more preferably 10-18%. Correspondingly, the hydrogen fluoride content in the second mixed acid is preferably 15-25%, more preferably 18-25%.
[0034] The implementation process of this invention will be described in detail below with reference to examples. Unless otherwise specified, "%" refers to mass percentage.
[0035] Example 1
[0036] The preparation method of phosphorus pentafluoride in this embodiment includes the following steps:
[0037] (1) In a 3-liter jacketed reactor coated with fluorine 40, 2000 g of fluorosulfonic acid solution was added. While stirring, frozen brine was passed through the jacket to cool the fluorosulfonic acid solution to 10°C. Then, 352 g of anhydrous hydrogen fluoride solution at about 0°C was slowly added to obtain the first mixed acid composed of fluorosulfonic acid and anhydrous hydrogen fluoride. The hydrogen fluoride content in the first mixed acid was 15%, and the temperature was about 10°C.
[0038] (2) While stirring and cooling, 1090 g of hexafluorophosphate solution (HPF6: 60.3%, water: 29.8%, hydrogen fluoride: 9.9%; material temperature controlled at around 10℃) was sealed and added into the reactor. The water in the hexafluorophosphate solution reacted with the fluorosulfonic acid in the first mixed acid, with the temperature controlled below 10℃, to obtain a second mixed acid containing fluorosulfonic acid, hexafluorophosphate, sulfuric acid, and hydrogen fluoride. The second mixed acid contained 5.7% fluorosulfonic acid and 23.8% hydrogen fluoride.
[0039] (3) After the cooling brine in the reactor jacket is drained, heat transfer oil is introduced to heat the second mixed acid, and the temperature is gradually raised to 82°C and maintained until the pyrolysis reaction is completed (observe that no gas escapes). The final decomposition rate of hexafluorophosphate is 97.3%. During the heating process, a mixture of phosphorus pentafluoride, phosphorus trifluoride oxyfluoride and hydrogen fluoride gas continuously escapes. The mixed gas enters the phosphorus trifluoride oxyfluoride absorption device, the hydrogen fluoride removal device and the phosphorus pentafluoride absorption device in sequence for treatment.
[0040] The phosphorus oxyfluoride (PoxyF) absorber contains an anhydrous hydrogen fluoride solution (-10℃). In the mixed gas, PoxyF gas is trapped by the anhydrous hydrogen fluoride, forming hexafluorophosphate and water. The phosphorus pentafluoride (PPF) absorber contains a lithium fluoride and dimethyl carbonate solution. The PPF gas escaping from the PoxyF absorber further removes entrained hydrogen fluoride, forming lithium hexafluorophosphate within the PPF absorber. By detecting the hexafluorophosphate and lithium hexafluorophosphate content, the amount of PoxyF and PPF gases released is calculated. The total amount of PoxyF and PPF gases represents the phosphorus-containing decomposition products of hexafluorophosphate. A lower PoxyF content indicates less PoxyF byproduct and a higher amount of the target product, phosphorus pentafluoride.
[0041] In this embodiment, phosphorus trifluoride accounts for 7.6% of the mass content of phosphorus-containing decomposition products of hexafluorophosphate, and phosphorus pentafluoride accounts for 92.4% of the mass content of phosphorus-containing decomposition products of hexafluorophosphate.
[0042] Example 2
[0043] The preparation method of phosphorus pentafluoride in this embodiment includes the following steps:
[0044] (1) In a 3-liter jacketed reactor coated with fluorine 40, 2000 g of fluorosulfonic acid solution was added. While stirring, chilled brine was circulated through the jacket to cool the fluorosulfonic acid solution to 10°C. Then, 222 g of anhydrous hydrogen fluoride solution at approximately 0°C was slowly added. A first mixed acid consisting of fluorosulfonic acid and anhydrous hydrogen fluoride was obtained. The first mixed acid contained 10% hydrogen fluoride at approximately 10°C.
[0045] (2) While stirring and cooling, 1028 g of hexafluorophosphate solution (same as in Example 1) was sealed and added into the reaction vessel. The water in the hexafluorophosphate solution reacted with the fluorosulfonic acid in the first mixed acid, and the temperature was controlled below 10°C to obtain a second mixed acid containing fluorosulfonic acid, hexafluorophosphate, sulfuric acid, and hydrogen fluoride. The fluorosulfonic acid content in the second mixed acid was 9.2%, and the hydrogen fluoride content was 20.4%.
[0046] (3) After the cooling brine in the jacket of the reactor is drained, heat transfer oil is introduced to heat the second mixed acid, and the temperature is gradually increased to 73°C and maintained until the pyrolysis reaction is completed (observe that no gas is released). The final decomposition rate of hexafluorophosphate is 97.1%. During the heating process, mixed gases such as phosphorus pentafluoride are continuously released, of which phosphorus trifluoride accounts for 8.5% (phosphorus trifluoride accounts for the mass content of phosphorus-containing decomposition products of hexafluorophosphate, and the rest is phosphorus pentafluoride).
[0047] Example 3
[0048] The preparation method of phosphorus pentafluoride in this embodiment includes the following steps:
[0049] (1) In a 3-liter jacketed reactor coated with fluorine 40, 2406 g of 65% fuming sulfuric acid was added. While stirring, chilled brine was circulated through the jacket to lower the temperature to 10°C. Then, 391 g of anhydrous hydrogen fluoride solution at approximately 0°C was slowly added to prepare a fluorosulfonic acid solution. The material temperature was then maintained at 10°C, and 559 g of anhydrous hydrogen fluoride solution was added to obtain a first mixed acid composed of fluorosulfonic acid, sulfuric acid, and hydrogen fluoride. The first mixed acid contained 16.6% hydrogen fluoride at approximately 10°C.
[0050] (2) While stirring and cooling, 1028 g of hexafluorophosphate solution (same as in Example 1) was sealed and added to the first mixed acid in the reaction vessel. The water in the hexafluorophosphate solution reacted with the fluorosulfonic acid in the first mixed acid, and the temperature was controlled below 10°C to obtain a second mixed acid containing fluorosulfonic acid, hexafluorophosphate, sulfuric acid, and hydrogen fluoride. The second mixed acid contained 5.8% fluorosulfonic acid and 22.8% hydrogen fluoride.
[0051] (3) After the cooling brine in the jacket of the reactor is drained, heat transfer oil is introduced to heat the second mixed acid, and the temperature is gradually raised to 85°C and maintained until the pyrolysis reaction is completed (observe that no gas is released). The final decomposition rate of hexafluorophosphate is 97.1%. During the heating process, mixed gases such as phosphorus pentafluoride are continuously released, of which phosphorus trifluoride accounts for 9.5% (phosphorus trifluoride accounts for the mass content of phosphorus-containing decomposition products of hexafluorophosphate, and the rest is phosphorus pentafluoride).
[0052] Example 4
[0053] The preparation method of phosphorus pentafluoride in this embodiment includes the following steps:
[0054] (1) In a 3-liter jacketed reactor coated with fluorine 40, 1564 g of liquid sulfur trioxide was added, and the temperature was maintained at 35°C. Then, under stirring, chilled brine was introduced into the jacket, and 391 g of anhydrous hydrogen fluoride solution at approximately 0°C was slowly added. Throughout the addition process, the material in the reactor was kept in a liquid state. As fluorosulfonic acid was formed, the reaction temperature gradually decreased to approximately 10°C. After the addition of hydrogen fluoride, a perfluorosulfonic acid solution was obtained. Then, 345 g of anhydrous hydrogen fluoride was added to obtain the first mixed acid composed of fluorosulfonic acid and hydrogen fluoride. The first mixed acid contained 15% hydrogen fluoride, and the temperature was approximately 10°C.
[0055] (2) While stirring and cooling, 1028 g of hexafluorophosphate solution (same as in Example 1) was sealed and added into the reaction vessel. The water in the hexafluorophosphate solution reacted with the fluorosulfonic acid in the first mixed acid, and the temperature was controlled below 10°C to obtain a second mixed acid containing fluorosulfonic acid, hexafluorophosphate, sulfuric acid, and hydrogen fluoride. The fluorosulfonic acid content in the second mixed acid was 7.6%, and the hydrogen fluoride content was 23.6%.
[0056] (3) After the cooling brine in the jacket of the reactor is drained, heat transfer oil is introduced to heat the second mixed acid, and the temperature is gradually raised to 78°C and maintained until the pyrolysis reaction is completed (observe that no gas is released). The final decomposition rate of hexafluorophosphate is 97.5%. During the heating process, mixed gases such as phosphorus pentafluoride are continuously released, of which phosphorus trifluoride accounts for 7.2% (phosphorus trifluoride accounts for the mass content of phosphorus-containing decomposition products of hexafluorophosphate, and the rest is phosphorus pentafluoride).
[0057] Example 5
[0058] The preparation method of phosphorus pentafluoride in this embodiment includes the following steps:
[0059] (1) In a 3-liter jacketed reactor coated with fluorine 40, 2249 g of 65% fuming sulfuric acid was added. While stirring, chilled brine was circulated through the jacket to lower the temperature to 10°C. Then, 366 g of anhydrous hydrogen fluoride solution at approximately 0°C was slowly added to prepare a fluorosulfonic acid solution. The material temperature was then maintained at 10°C, and 461 g of anhydrous hydrogen fluoride solution was added to obtain a first mixed acid composed of fluorosulfonic acid, sulfuric acid, and hydrogen fluoride. The first mixed acid contained 15% hydrogen fluoride at approximately 10°C.
[0060] (2) While stirring and cooling, 1028 g of hexafluorophosphate solution (same as in Example 1) was sealed and added to the first mixed acid in the reaction vessel. The water in the hexafluorophosphate solution reacted with the fluorosulfonic acid in the first mixed acid, and the temperature was controlled below 10°C to obtain a second mixed acid containing fluorosulfonic acid, hexafluorophosphate, sulfuric acid, and hydrogen fluoride. The second mixed acid contained 3.1% fluorosulfonic acid and 22% hydrogen fluoride.
[0061] (3) After the cooling brine in the jacket of the reactor is drained, heat transfer oil is introduced to heat the second mixed acid, and the temperature is gradually increased to 90°C and maintained until the pyrolysis reaction is completed (observe that no gas is released). The final decomposition rate of hexafluorophosphate is 97.0%. During the heating process, mixed gases such as phosphorus pentafluoride are continuously released, of which phosphorus trifluoride accounts for 9.6% (phosphorus trifluoride accounts for the mass content of phosphorus-containing decomposition products of hexafluorophosphate, and the rest is phosphorus pentafluoride).
[0062] Example 6
[0063] The preparation method of phosphorus pentafluoride in this embodiment includes the following steps:
[0064] (1) In a 3-liter jacketed reactor coated with fluorine 40, 2406 g of 65% fuming sulfuric acid was added. While stirring, chilled brine was circulated through the jacket to lower the temperature to 10°C. Then, 391 g of anhydrous hydrogen fluoride solution at approximately 0°C was slowly added to prepare a fluorosulfonic acid solution. The material temperature was then maintained at 10°C, and 210 g of anhydrous hydrogen fluoride solution was added to obtain a first mixed acid composed of fluorosulfonic acid, sulfuric acid, and hydrogen fluoride. The first mixed acid contained 7% hydrogen fluoride at approximately 10°C.
[0065] (2) While stirring and cooling, 950 g of hexafluorophosphate solution (same as in Example 1) was sealed and added into the first mixed acid in the reaction vessel. The water in the hexafluorophosphate solution reacted with the fluorosulfonic acid in the first mixed acid, and the temperature was controlled below 10°C to obtain a second mixed acid containing fluorosulfonic acid, hexafluorophosphate, sulfuric acid, and hydrogen fluoride. The fluorosulfonic acid content in the second mixed acid was 9.6%, and the hydrogen fluoride content was 15.2%.
[0066] (3) After the cooling brine in the reactor jacket is drained, heat transfer oil is introduced to heat the second mixed acid, and the temperature is gradually increased to 93°C and maintained until the pyrolysis reaction is completed (observe that no gas is released). The final decomposition rate of hexafluorophosphate is 97.1%. During the heating process, mixed gases such as phosphorus pentafluoride are continuously released, of which phosphorus trifluoride accounts for 9.8% (phosphorus trifluoride accounts for the mass content of phosphorus-containing decomposition products of hexafluorophosphate, and the rest is phosphorus pentafluoride).
[0067] Comparative Example 1
[0068] The preparation method of phosphorus pentafluoride in this comparative example includes the following steps:
[0069] (1) In a 3-liter jacketed reactor coated with fluorine 40, 2092 g of 65% fuming sulfuric acid was added. While stirring, chilled brine was circulated through the jacket. While stirring and cooling, 1028 g of hexafluorophosphate solution (same as in Example 1) was slowly and tightly added to the reactor, controlling the material temperature at approximately 10°C. The water in the hexafluorophosphate solution reacted with the fuming sulfuric acid to produce a mixed acid containing sulfuric acid, hexafluorophosphate, and hydrogen fluoride, with a hydrogen fluoride content of 3.2%.
[0070] (2) After draining the cooling brine from the jacket of the reactor, heat transfer oil is introduced to heat the mixed acid, and the temperature is gradually increased to 151°C and maintained (the temperature is increased to 90°C and maintained, as the decomposition rate of hexafluorophosphate is relatively low; to achieve a decomposition rate of 97.2%, the temperature needs to be increased to this level), until the pyrolysis reaction is completed (no gas is observed to escape). The final decomposition rate of hexafluorophosphate is 97.2%. During the heating process, mixed gases such as phosphorus pentafluoride continuously escape, of which phosphorus trifluoride accounts for 48%.
[0071] Comparative Example 2
[0072] The preparation method of phosphorus pentafluoride in this comparative example includes the following steps:
[0073] (1) In a 3-liter fluorine-coated reaction vessel with a jacket, 2406 g of 65% fuming sulfuric acid was added. While stirring, frozen brine was introduced into the jacket to cool down to 10°C. Then, 391 g of anhydrous hydrogen fluoride solution at about 0°C was slowly added to prepare a fluorosulfonic acid solution, and the first mixed acid composed of fluorosulfonic acid and sulfuric acid was obtained.
[0074] (2) While stirring and cooling, 1028 g of hexafluorophosphate solution (same as in Example 1) was sealed and added to the first mixed acid in the reaction vessel. The water in the hexafluorophosphate solution reacted with the fluorosulfonic acid in the first mixed acid, and the temperature was controlled below 10°C to obtain a second mixed acid containing fluorosulfonic acid, hexafluorophosphate, sulfuric acid, and hydrogen fluoride. The fluorosulfonic acid content in the second mixed acid was 6.6%, and the hydrogen fluoride content was 8.9%.
[0075] (3) After draining the cooling brine from the jacket of the reactor, heat transfer oil is introduced to heat the second mixed acid, and the temperature is gradually increased to 125°C and maintained until the pyrolysis reaction is completed (observe that no gas is released). The final decomposition rate of hexafluorophosphate is 97%. During the heating process, mixed gases such as phosphorus pentafluoride are continuously released, of which phosphorus trifluoride accounts for 38% (phosphorus trifluoride accounts for the mass content of phosphorus-containing decomposition products of hexafluorophosphate, and the rest is phosphorus pentafluoride).
[0076] In summary, this invention solves key process problems such as the rapid exothermic reaction and instability of hexafluorophosphoric acid when using fuming sulfuric acid or sulfur trioxide as raw materials directly mixed with hexafluorophosphoric acid solution. This significantly reduces side reactions during phosphorus pentafluoride preparation and lowers the pyrolysis temperature. Consequently, the subsequent purification of the phosphorus pentafluoride gas produced by this invention is easier, greatly improving production efficiency and advancing the technological progress of phosphorus pentafluoride production processes.
Claims
1. A process for the preparation of phosphorus pentafluoride, characterized in that, Includes the following steps: (1) A solution of hexafluorophosphate is added to a first mixed acid containing fluorosulfonic acid and anhydrous hydrogen fluoride for a mixed reaction and dehydration to obtain a second mixed acid; the second mixed acid contains fluorosulfonic acid, sulfuric acid, hexafluorophosphate and hydrogen fluoride; the mass content of anhydrous hydrogen fluoride in the first mixed acid is 7~25%; the mass content of fluorosulfonic acid in the second mixed acid is 3~10%, and the mass content of hydrogen fluoride is 15~25%; (2) The second mixed acid is pyrolyzed at 60~95℃ to obtain a mixed gas containing phosphorus pentafluoride.
2. The method for preparing phosphorus pentafluoride as described in claim 1, characterized in that, The mass content of anhydrous hydrogen fluoride in the first mixed acid is 7-18%.
3. The method for preparing phosphorus pentafluoride as described in claim 2, characterized in that, The mass content of anhydrous hydrogen fluoride in the first mixed acid is 10-18%.
4. The method for preparing phosphorus pentafluoride as described in claim 1, characterized in that, In step (2), the pyrolysis temperature is 73~78℃.
5. The method for preparing phosphorus pentafluoride as described in claim 1, characterized in that, The second mixed acid contains 5-10% fluorosulfonic acid and 18-25% hydrogen fluoride by mass.
6. The method for preparing phosphorus pentafluoride according to claim 1, characterized in that, The first mixed acid also contains sulfuric acid, and the sulfuric acid and fluorosulfonic acid in the first mixed acid are obtained by reacting fuming sulfuric acid or sulfur trioxide with anhydrous hydrogen fluoride.
7. The method for preparing phosphorus pentafluoride according to claim 1, characterized in that, In step (2), the pyrolysis temperature is 70~95℃.
8. The method for preparing phosphorus pentafluoride according to any one of claims 1 to 7, characterized in that, In step (2), the mixed gas contains phosphorus pentafluoride and phosphorus trifluoride, wherein the mass of phosphorus trifluoride accounts for no more than 10% of the total mass of phosphorus pentafluoride and phosphorus trifluoride.