Method for preparing phosphorus pentafluoride

Abstract

The invention provides a method for preparing phosphorus pentafluoride, which comprises the following steps: (a) mixing sulfur and phosphorus, and reacting at the temperature of 320-340 DEG C to generate phosphorus pentasulfide; (b) reacting phosphorus pentasulfide with hydrogen fluoride gas at the temperature of 170-190 DEG C, cooling the reaction product to-85 to-60 DEG C, and performing low-temperature rectification separation to obtain pure phosphorus pentafluoride and byproduct hydrogen sulfide; the molar ratio of phosphorus pentasulfide to hydrogen fluoride gas is (1-9.5): 10.2. The phosphorus pentafluoride can be efficiently prepared in an environment-friendly manner by adjusting the reaction conditions and the raw material ratio and reacting the easily available raw materials; and moreover, an electrolysis technology is further introduced to treat the hydrogen sulfide byproduct, so that the purity and efficiency of sulfur recovery are optimized, the purposes of environment-friendly and efficient recovery and utilization of the byproduct are achieved, the overall economical efficiency and safety of the process are improved, and the whole process chain is further perfected.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic chemical synthesis and relates to a method for preparing phosphorus pentafluoride, in particular to a method for preparing phosphorus pentafluoride with high efficiency and environmental protection. Background Art

[0002] Lithium hexafluorophosphate is an inorganic compound with the chemical formula LiPF6. It is a white crystalline powder that is easily soluble in water, low-concentration methanol, ethanol, acetone, carbonates and other organic solvents. It is mainly used as an electrolyte material for lithium-ion batteries. Hexafluorophosphates including lithium hexafluorophosphate are usually produced using phosphorus pentafluoride as a raw material. The preparation process of phosphorus pentafluoride has been reported, but the existing methods have problems such as harsh reaction conditions, complex equipment or improper by-product treatment.

[0003] A Chinese invention patent with publication number CN117285021A discloses a method for preparing phosphorus pentafluoride gas, comprising the following steps: (1) reacting a phosphorus-containing compound with hydrogen fluoride and an organic anhydride dehydrating agent to generate a hexafluorophosphoric acid solution; (2) heating the hexafluorophosphoric acid solution to decompose it into gaseous hydrogen fluoride and phosphorus pentafluoride. The application requires the use of an organic anhydride dehydrating agent, and also produces hydrogen fluoride as a byproduct, so the environmental friendliness needs to be improved.

[0004] The Chinese invention patent with publication number CN116514081A discloses a method and application for preparing high-purity phosphorus pentafluoride gas, including: reacting polyphosphoric acid with anhydrous hydrogen fluoride to obtain a hexafluorophosphoric acid aqueous solution; dripping sulfur trioxide into the hexafluorophosphoric acid aqueous solution, heating, gas-liquid separation, obtaining a crude phosphorus pentafluoride gas product and sulfuric acid, wherein the molar ratio of sulfur trioxide to polyphosphoric acid is (12.2-14.0):1; refining the crude phosphorus pentafluoride gas product to obtain a high-purity phosphorus pentafluoride gas. The present invention can significantly reduce the content of hydrogen fluoride in the phosphorus pentafluoride gas by accurately controlling the molar ratio of sulfur trioxide to polyphosphoric acid, and at the same time make full use of the dehydration effect of sulfur trioxide on hexafluorophosphoric acid, thereby improving the utilization rate of raw materials and reducing the impurity content in the crude phosphorus pentafluoride product, thereby simplifying the refining step of the crude phosphorus pentafluoride product and realizing the preparation of high-purity phosphorus pentafluoride gas. However, polyphosphoric acid is used as a reaction raw material in the application, which will produce byproducts such as HCl and H2SO4, which will cause great corrosion to the production equipment. Summary of the invention

[0005] In order to solve the above technical problems, the object of the present invention is to provide a method for preparing phosphorus pentafluoride with mild conditions and low equipment requirements.

[0006] In order to achieve the above technical purpose, the present invention provides a method for preparing phosphorus pentafluoride, comprising the following steps:

[0007] (a) mixing sulfur and phosphorus and reacting them at a temperature of 320-340° C. to generate phosphorus pentasulfide;

[0008] (b) reacting the phosphorus pentasulfide with hydrogen fluoride gas at a temperature of 170 to 190° C., and then cooling the reaction product to -85 to -60° C. to separate the reaction product by cryogenic distillation to obtain pure phosphorus pentafluoride and byproduct hydrogen sulfide; the molar ratio of the phosphorus pentasulfide to the hydrogen fluoride gas is 1 to 9.5:10.2.

[0009] Optimally, the method further comprises the following steps:

[0010] (c) using the purified phosphorus pentafluoride and by-product hydrogen sulfide obtained by the cryogenic distillation separation to cool the reaction product in step (b) to reduce the consumption of refrigerant;

[0011] (d) electrolyzing the byproduct hydrogen sulfide with a platinum electrode as an anode, a graphite electrode as a cathode, and dilute sulfuric acid as an electrolyte solution to decompose the hydrogen sulfide into sulfur and hydrogen; the voltage of the electrolysis is 2.0 to 2.5 V and the current is 0.1 to 2 A / cm 2 , the concentration of sulfuric acid in the dilute sulfuric acid is 0.5-2 mol / L.

[0012] Optimally, in step (a), the molar ratio of sulfur to phosphorus is 2.5 to 3:1.

[0013] Furthermore, in step (d), the electrolysis temperature is 20-60° C. and the time is 1-3 h.

[0014] Furthermore, in step (d), the electrolysis is carried out in an electrolytic cell, and hydrogen sulfide is bubbled into the electrolytic cell from the bottom of the anode, absorbed by the dilute sulfuric acid electrolyte solution into the liquid phase, and participates in the electrolysis process reaction.

[0015] Furthermore, during the electrolysis process, most of the generated sulfur floats on the surface of the anode liquid of the electrolytic cell in the form of foam, and a small amount is deposited at the bottom, and the hydrogen is collected through a pipe at the top of the cathode of the electrolytic cell.

[0016] Furthermore, in step (d), the sulfur foam floating on the surface of the liquid at the anode of the electrolytic cell is drawn out by overflow, the sulfur is collected through solid-liquid separation, and the liquid is returned to the anode of the electrolytic cell; the sulfur deposited at the bottom of the electrolytic cell is regularly cleaned and collected by mechanical means; and the collected hydrogen is stored in a gas storage tank for subsequent use as fuel or as a raw material for chemical reactions.

[0017] Optimally, in step (d), the electrolyte solution is further added with Fe 3+ or / and Fe 2+ The total concentration of Fe ions is 0.25~2.5mol / L.

[0018] Furthermore, the Fe-containing 3+ or / and Fe 2+ The salt is chloride or sulfate of Fe.

[0019] The method for preparing phosphorus pentafluoride of the present invention can prepare phosphorus pentafluoride efficiently and in an environmentally friendly manner by adjusting reaction conditions and raw material ratios and performing reactions with easily available raw materials; and further introduces electrolysis technology to treat hydrogen sulfide byproducts, thereby optimizing the purity and efficiency of sulfur recovery, achieving the purpose of environmentally friendly and efficient recovery and utilization of byproducts, improving the overall economy and safety of the process, and further improving the entire process chain. DETAILED DESCRIPTION

[0020] The method for preparing phosphorus pentafluoride of the present invention comprises the following steps: (a) mixing sulfur and phosphorus, reacting at a temperature of 320-340°C to generate phosphorus pentasulfide; (b) reacting the phosphorus pentasulfide with hydrogen fluoride gas at a temperature of 170-190°C, and then cooling the reaction product to -85--60°C for low-temperature distillation separation to obtain pure phosphorus pentafluoride and byproduct hydrogen sulfide; the molar ratio of the phosphorus pentasulfide to the hydrogen fluoride gas is 1-9.5:10.2. By adjusting the reaction conditions and the ratio of raw materials, the reaction is carried out with easily available raw materials, so that phosphorus pentafluoride can be obtained efficiently and environmentally friendly; and further introducing electrolysis technology to treat the hydrogen sulfide byproduct, the purity and efficiency of sulfur recovery are optimized, the purpose of environmentally friendly and efficient recovery and utilization of byproducts is achieved, the overall economy and safety of the process are improved, and the entire process chain is further improved. The molar ratio of sulfur to phosphorus is 2.5-3:1.

[0021] The method for preparing phosphorus pentafluoride of the present invention further comprises the following steps: (c) using the pure phosphorus pentafluoride and the byproduct hydrogen sulfide obtained by the cryogenic distillation separation to cool the reaction product in step (b) to reduce the consumption of refrigerant; (d) electrolyzing the byproduct hydrogen sulfide with a platinum electrode as an anode, a graphite electrode as a cathode, and dilute sulfuric acid as an electrolyte solution to decompose the hydrogen sulfide into sulfur and hydrogen. The current of the electrolysis is preferably 0.1 to 2 A / cm 2 , to ensure the effective decomposition of sulfides, while avoiding excessive heating or side reactions caused by excessive current density); the electrolysis voltage is maintained between 2.0-2.5V. Too low voltage may lead to reduced electrolysis efficiency, while too high voltage may cause unnecessary side reactions, such as electrolysis of water. Electrolyte temperature: controlled between 20-60℃ to ensure the stability of the electrolysis process, while avoiding excessive temperature that causes sulfur dissolution or H2S volatilization. Electrolysis time: depending on the feed amount of hydrogen sulfide, the electrolysis time is usually controlled at 1 to 3 hours to ensure the complete decomposition of hydrogen sulfide.

[0022] The concentration of sulfuric acid in the dilute sulfuric acid is 0.5-2 mol / L. The electrolysis technology is further introduced to treat the hydrogen sulfide byproduct, which optimizes the purity and efficiency of sulfur recovery, achieves the purpose of environmentally friendly and efficient recovery and utilization of byproducts, improves the overall economy and safety of the process, and further improves the entire process chain. The temperature of the electrolysis is 20-60°C and the time is 1-3h.

[0023] In step (d), the electrolysis is carried out in an electrolyzer, and hydrogen sulfide is bubbled in from the bottom of the electrolyzer anode, absorbed by the dilute sulfuric acid electrolyte solution (which may also contain iron ions) into the liquid phase, and participates in the electrolysis process reaction. During the electrolysis process, most of the generated sulfur floats on the surface of the electrolyzer anode liquid in the form of foam, and a small amount is deposited at the bottom, and hydrogen is collected through a pipeline at the top of the electrolyzer cathode. The sulfur foam floating on the surface of the electrolyzer anode liquid is drawn out by overflow, and sulfur is collected through solid-liquid separation, and the liquid returns to the electrolyzer anode; the sulfur deposited at the bottom of the electrolyzer is regularly cleaned and collected by mechanical means; the collected hydrogen is also stored in a gas tank for subsequent fuel use or as a raw material for chemical reactions.

[0024] In step (d), the electrolyte solution is further added with Fe 3+ or / and Fe 2+ The total concentration of Fe ions is 0.25-2.5 mol / L (Fe 3+ with Fe 2+ The molar ratio is 1 to 3:1); the Fe-containing 3+ or / and Fe 2+ The salt is preferably a chloride or sulfate of Fe to ensure adequate conductivity while increasing the absorption-electrolysis efficiency of hydrogen sulfide from the gas phase to the liquid phase.

[0025] In addition, the following process controls can be performed: Gas handling: To avoid hydrogen sulfide leakage, the electrolysis system should be equipped with a gas monitoring device to detect the concentration of hydrogen and hydrogen sulfide in real time to ensure operation within a safe range. Temperature and voltage control: Use an automatic control system to adjust the temperature and voltage of the electrolyte to ensure that the entire process operates within the set parameter range to avoid sudden reactions or equipment damage.

[0026] The preferred embodiments of the present invention will be described in detail below.

[0027] Example 1

[0028] This embodiment provides a method for preparing phosphorus pentafluoride and recovering hydrogen sulfide to produce sulfur, comprising the following steps:

[0029] (a) sulfur (1553 kg) and phosphorus (500 kg) are mixed (the molar ratio of sulfur to phosphorus is about 3:1), and reacted at a temperature of 320-340°C to produce phosphorus pentasulfide (about 1704 kg, the quality of the product is not much different within this temperature range, the same below);

[0030] (b) reacting phosphorus pentasulfide (1704 kg) with hydrogen fluoride gas (1519 kg) at a temperature of 170-190° C., and then cooling the reaction product to −75° C. and separating the phosphorus pentafluoride (1904 kg) and the by-product hydrogen sulfide (1302 kg) by cryogenic distillation technology;

[0031] (c) using the -85°C phosphorus pentafluoride and -62°C hydrogen sulfide materials at the outlet of the cryogenic distillation to cool the reaction product of step (b). The reaction product can be cooled to -75°C before entering the cryogenic distillation. The refrigeration power required for the cryogenic distillation is 123 kW;

[0032] (d) Platinum electrode as anode, graphite electrode as cathode, and Fe 3+ and Fe 2+ Dilute sulfuric acid of sulfate (the concentration of sulfuric acid in dilute sulfuric acid is 2 mol / L, the concentration of Fe salt is 2 mol / L, among which Fe 3+ The concentration is 1.5 mol / L, Fe 2+ The concentration is 0.5 mol / L) as the electrolyte solution to absorb and electrolyze hydrogen sulfide so that hydrogen sulfide is decomposed into sulfur (1203 kg) and hydrogen (840 Nm 3 ); the electrolysis voltage is 2.0V and the current is 2A / cm 2 , the electrolysis temperature is 20℃, and the time is 1h (most of the generated sulfur floats on the surface of the anode liquid of the electrolytic cell in the form of foam and is led out by overflow. A small amount is deposited at the bottom of the electrolytic cell and is regularly cleaned and collected with a scraper. The hydrogen is collected through the pipe on the top of the electrolytic cell and stored in a gas tank).

[0033] Example 2

[0034] This embodiment provides a method for preparing phosphorus pentafluoride and recovering hydrogen sulfide to produce sulfur, which is basically the same as that in embodiment 1, except that in step (d), the dilute sulfuric acid does not contain Fe 3+ and Fe 2+ Sulfate; the final electrolysis decomposes hydrogen sulfide into sulfur (842kg) and hydrogen (583Nm 3 )

[0035] Example 3

[0036] This embodiment provides a method for preparing phosphorus pentafluoride and recovering hydrogen sulfide to produce sulfur, comprising the following steps:

[0037] (a) sulfur (1294 kg) and phosphorus (500 kg) are mixed (the molar ratio of sulfur to phosphorus is 2.5:1) and reacted at a temperature of 320-340°C to produce phosphorus pentasulfide (about 1668 kg, the quality of the product is not much different within this temperature range, the same below);

[0038] (b) reacting phosphorus pentasulfide (1668 kg) with hydrogen fluoride gas (1442 kg) at a temperature of 170-190° C., and then cooling the reaction product to −75° C. to separate phosphorus pentafluoride (1800 kg) and by-product hydrogen sulfide (1244 kg);

[0039] (c) using the -85°C phosphorus pentafluoride and -62°C hydrogen sulfide materials at the outlet of the cryogenic distillation to cool the reaction product of step (b). The reaction product can be cooled to -75°C before entering the cryogenic distillation. The refrigeration power required for the cryogenic distillation is 117 kW;

[0040] (d) Platinum electrode as anode, graphite electrode as cathode, and Fe 3+ and Fe 2+ Chloride dilute sulfuric acid (the concentration of sulfuric acid in dilute sulfuric acid is 0.5 mol / L, the total Fe ion concentration is 2.0 mol / L, among which Fe 3+ The concentration is 1.0 mol / L, Fe 2+ The concentration is 1.0 mol / L) as the electrolyte solution to absorb and electrolyze hydrogen sulfide so that hydrogen sulfide is decomposed into sulfur (1108 kg) and hydrogen (781 Nm 3 ); the electrolysis voltage is 2.5V and the current is 0.1A / cm 2 The electrolysis temperature is 60°C and the time is 3 hours (most of the generated sulfur floats on the surface of the anode liquid of the electrolytic cell in the form of foam and is discharged by overflow. A small amount is deposited at the bottom of the electrolytic cell and is regularly cleaned and collected by a scraper. The hydrogen is collected through the pipe on the top of the electrolytic cell and stored in a gas tank).

[0041] Example 4

[0042] This embodiment provides a method for preparing phosphorus pentafluoride and recovering hydrogen sulfide to produce sulfur, comprising the following steps:

[0043] (a) sulfur (1449 kg) and phosphorus (500 kg) are mixed (the molar ratio of sulfur to phosphorus is 2.8:1) and reacted at a temperature of 320-340°C to produce phosphorus pentasulfide (about 1695 kg, the product quality is not much different within this temperature range, the same below);

[0044] (b) reacting phosphorus pentasulfide (1695 kg) with hydrogen fluoride gas (1480 kg) at a temperature of 170-190° C., and then cooling the reaction product to −75° C. to separate phosphorus pentafluoride (1761 kg) and by-product hydrogen sulfide (1211 kg);

[0045] (c) using the -83°C phosphorus pentafluoride and -59°C hydrogen sulfide materials at the outlet of the cryogenic distillation to cool the reaction product of step (b). The reaction product can be cooled to -75°C before entering the cryogenic distillation. The refrigeration power required for the cryogenic distillation is 102 kW;

[0046] (d) Platinum electrode as anode, graphite electrode as cathode, and Fe 3+ and Fe 2+ The dilute sulfuric acid of sulfate is the electrolyte solution (the concentration of sulfuric acid in the dilute sulfuric acid is 1 mol / L, the total Fe ion concentration is 1.5 mol / L, and Fe 3+ The concentration is 1.0 mol / L, Fe 2+ The concentration is 0.5 mol / L) to absorb and electrolyze hydrogen sulfide to decompose it into sulfur (1154 kg) and hydrogen (813 Nm 3 ); the electrolysis voltage is 2.2V and the current is 1A / cm 2 The electrolysis temperature is 30°C and the time is 2h (most of the generated sulfur floats on the surface of the anode liquid of the electrolytic cell in the form of foam and is discharged by overflow. A small amount is deposited at the bottom of the electrolytic cell and is regularly cleaned and collected by a scraper. The hydrogen is collected through the pipe on the top of the electrolytic cell and stored in a gas tank).

[0047] Comparative Example 1

[0048] This example provides a method for preparing phosphorus pentafluoride and recovering hydrogen sulfide to produce sulfur, which is basically the same as that in Example 1, except that: in step (a), the reaction is carried out at a temperature of 250-260°C to generate phosphorus pentasulfide, thereby obtaining phosphorus pentafluoride (1145g).

[0049] Comparative Example 2

[0050] This example provides a method for preparing phosphorus pentafluoride and recovering hydrogen sulfide to produce sulfur, which is basically the same as that in Example 1, except that: in step (d), the electrolysis voltage is 3.0V and the current is 2.2A / cm 2 , decomposed into sulfur (1042kg) and hydrogen (708Nm 3 ).

[0051] Comparative Example 3

[0052] This example provides a method for preparing phosphorus pentafluoride and recovering hydrogen sulfide to produce sulfur, which is basically the same as that in Example 1, except that: in step (d), the electrolysis temperature is 80°C and the time is 1 hour, and the decomposition is sulfur (1073kg) and hydrogen (719Nm 3 ).

[0053] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing phosphorus pentafluoride, characterized in that: The following steps are involved: (a) mixing sulfur and phosphorus and reacting them at a temperature of 320-340° C. to generate phosphorus pentasulfide; (b) reacting the phosphorus pentasulfide with hydrogen fluoride gas at a temperature of 170 to 190° C., and then cooling the reaction product to -85 to -60° C. to separate the reaction product by cryogenic distillation to obtain pure phosphorus pentafluoride and byproduct hydrogen sulfide; the molar ratio of the phosphorus pentasulfide to the hydrogen fluoride gas is 1 to 9.5:10.

2.

2. The method for preparing phosphorus pentafluoride according to claim 1, characterized in that: The following steps are also included: (c) using the purified phosphorus pentafluoride and by-product hydrogen sulfide obtained by the cryogenic distillation separation to cool the reaction product in step (b) to reduce the consumption of refrigerant; (d) electrolyzing the byproduct hydrogen sulfide with a platinum electrode as an anode, a graphite electrode as a cathode, and dilute sulfuric acid as an electrolyte solution to decompose the hydrogen sulfide into sulfur and hydrogen; the voltage of the electrolysis is 2.0 to 2.5 V and the current is 0.1 to 2 A / cm 2 , the concentration of sulfuric acid in the dilute sulfuric acid is 0.5-2 mol / L.

3. The method for preparing phosphorus pentafluoride according to claim 1, characterized in that: In step (a), the molar ratio of sulfur to phosphorus is 2.5 to 3:

1.

4. The method for preparing phosphorus pentafluoride according to claim 2, characterized in that: In step (d), the electrolysis temperature is 20-60° C. and the time is 1-3 h.

5. The method for preparing phosphorus pentafluoride according to claim 2 or 4, characterized in that: In step (d), the electrolysis is carried out in an electrolytic cell, and hydrogen sulfide is bubbled into the bottom of the anode of the electrolytic cell, absorbed by the dilute sulfuric acid electrolyte solution into the liquid phase, and participates in the electrolysis process reaction.

6. The method for preparing phosphorus pentafluoride according to claim 5, characterized in that: During the electrolysis process, most of the generated sulfur floats on the surface of the anode liquid of the electrolytic cell in the form of foam, and a small amount is deposited at the bottom. The hydrogen is collected through a pipe at the top of the cathode of the electrolytic cell.

7. The method for preparing phosphorus pentafluoride according to claim 6, characterized in that: In step (d), the sulfur foam floating on the surface of the liquid at the anode of the electrolytic cell is drawn out by overflow, the sulfur is collected by solid-liquid separation, and the liquid is returned to the anode of the electrolytic cell; the sulfur deposited at the bottom of the electrolytic cell is regularly cleaned and collected by mechanical means; The collected hydrogen is also stored in a gas tank for subsequent use as fuel or as a raw material for chemical reactions.

8. The method for preparing phosphorus pentafluoride according to claim 2, characterized in that: In step (d), the electrolyte solution is further added with Fe 3+ or / and Fe 2+ The total concentration of Fe ions is 0.25~2.5mol / L.

9. The method for preparing phosphorus pentafluoride according to claim 8, characterized in that: The Fe-containing 3+ or / and Fe 2+ The salt is chloride or sulfate of Fe.