Preparation method of phosphorus pentafluoride

Abstract

The invention provides a preparation method of phosphorus pentafluoride. According to the invention, the charging mode of the existing phosphorus pentafluoride production is changed, the sulfur trioxide is dropwise added into the reaction kettle for dehydration while the polyphosphoric acid is dropwise added, and the reaction liquid at the bottom of the reaction kettle is pumped into the anhydrous sodium sulfate dehydration tower for cyclic dehydration; the water generated by the reaction of the dropwise added polyphosphoric acid and anhydrous hydrogen fluoride is synchronously removed by the sulfur trioxide and anhydrous sodium sulfate dehydrating tower, so that the reaction kettle is always in an anhydrous state, the polyphosphoric acid is prevented from being hydrolyzed into orthophosphoric acid, dehydration treatment is not needed after the reaction is completed, the production efficiency is improved, and the production cost is reduced. The consumption of raw materials such as polyphosphoric acid is reduced, and the energy consumption is reduced. The invention also improves the purification process of the phosphorus pentafluoride gas crude product.

Description

Technical Field

[0001] The present invention relates to a method for preparing phosphorus pentafluoride. Background Art

[0002] Phosphorus pentafluoride (PF5) is a colorless and odorless acidic gas under normal conditions. As a fluorinating agent, phosphorus pentafluoride is applied in the fields of electronics industry, battery manufacturing, polymer field, catalysts, etc. Phosphorus pentafluoride is also an important raw material for preparing lithium hexafluorophosphate, an electrolyte of lithium batteries.

[0003] The existing mainstream production technologies of phosphorus pentafluoride are mainly divided into two categories:

[0004] The first category is to react phosphorus pentachloride with hydrogen fluoride to produce phosphorus pentafluoride. In this process, hydrogen chloride with an equimolar amount to phosphorus pentafluoride is generated. Hydrogen chloride and phosphorus pentafluoride are both acidic gases and have close boiling points. It is difficult to remove hydrogen chloride to obtain high-purity phosphorus pentafluoride gas by this method, and dechlorination is required in the subsequent product, resulting in high costs.

[0005] The second category is to react an oxygen-containing phosphorus source such as phosphorus pentoxide or polyphosphoric acid with hydrogen fluoride to produce hexafluorophosphoric acid, and hexafluorophosphoric acid is further decomposed into phosphorus pentafluoride.

[0006] P2O5 + 12HF → 2HPF6 + 5H2O

[0007] HPF6 + SO3 + H2O → PF5 + H2SO4 + HF

[0008] The second method can obtain high-purity phosphorus pentafluoride after appropriate purification, but it is difficult to avoid generating a large amount of water during the formation of hexafluorophosphoric acid in the second method. A large amount of sulfur trioxide compounds need to be added subsequently to remove water to ensure the smooth progress of the subsequent reaction. The use of a large amount of dehydrating agents leads to the generation of a large amount of fluorine-containing waste concentrated sulfuric acid in the industrial production of the second method. The waste concentrated sulfuric acid needs to be defluorinated, and the amount is large, the corrosiveness is strong, and the harmless treatment is complex and costly.

[0009] The inventor of the present invention previously applied for a patent CN116101988A, which uses a fluorine gas stripping tower or an anhydrous sodium sulfate drying tower to remove a large amount of water generated during the reaction of hexafluorophosphoric acid, thereby significantly reducing the usage amount of fuming sulfuric acid, reducing the generation of waste concentrated sulfuric acid, and being more economical, environmentally friendly and efficient than the traditional process that solely relies on sulfides to remove water.

[0010] However, the inventor of the present invention found that the above-mentioned prior patent and other existing technologies first react anhydrous hydrogen fluoride with polyphosphoric acid to generate hexafluorophosphoric acid and water, and then add sulfur trioxide compounds subsequently to dehydrate, and pass through an anhydrous sodium sulfate dehydration tower to dehydrate. These methods have the following defects:

[0011] 1. The water generated by the reaction of anhydrous hydrogen fluoride and polyphosphoric acid will hydrolyze part of the polyphosphoric acid into orthophosphoric acid,

[0012] H n+2 P n O 3n+1 +(n - 1)H2O → nH3PO4, resulting in the consumption and waste of polyphosphoric acid;

[0013] 2. After the reaction of anhydrous hydrogen fluoride and polyphosphoric acid for 3 - 5 hours, sulfur trioxide is slowly added dropwise for dehydration, resulting in a reduction in production efficiency. Moreover, when sulfur trioxide is added dropwise for dehydration, it releases a large amount of heat. To prevent the boiling of the hexafluorophosphoric acid aqueous solution, the reaction kettle needs to be continuously cooled and temperature-controlled, greatly increasing the energy consumption. Summary of the Invention

[0014] The purpose of the present invention is to provide a method for preparing phosphorus pentafluoride, which can reduce the amount of waste acid, improve production efficiency, reduce the consumption of raw materials such as polyphosphoric acid, and lower energy consumption.

[0015] To achieve the above purpose, the technical solution adopted by the present invention is:

[0016] The present invention discloses a method for preparing phosphorus pentafluoride, comprising the following steps:

[0017] (1) First, add anhydrous hydrogen fluoride to the reaction kettle, and then add polyphosphoric acid dropwise to the reaction kettle to generate hexafluorophosphoric acid and water; while adding polyphosphoric acid dropwise, add sulfur trioxide dropwise to the reaction kettle for dehydration, and pump the reaction liquid at the bottom of the reaction kettle into the anhydrous sodium sulfate dehydration tower for cyclic dehydration;

[0018] (2) Pump the material after the completion of the reaction in step (1) into the gas - generating tower. Heat the gas - generating tower to decompose hexafluorophosphoric acid into gaseous phosphorus pentafluoride and hydrogen fluoride, and obtain the crude product of phosphorus pentafluoride gas from the gas phase of the gas - generating tower;

[0019] (3) Purify the crude product of phosphorus pentafluoride gas obtained in step (2) to obtain high - purity phosphorus pentafluoride.

[0020] As a preferred technical solution, in step (1), based on the P2O5 content in polyphosphoric acid, the molar ratio of polyphosphoric acid to anhydrous hydrogen fluoride is 1:48 - 72, and the molar ratio of polyphosphoric acid to sulfur trioxide is 1:1.5 - 2.5.

[0021] As a preferred technical solution, in step (1), sulfur trioxide is added in the form of fuming sulfuric acid.

[0022] As a preferred technical solution, in step (1), the dropping rate of polyphosphoric acid is 100 - 150 kg / h, the dropping rate of fuming sulfuric acid is 150 - 280 kg / h, and the temperature of the reaction system is controlled at - 15 - 18 °C.

[0023] As a preferred technical solution, in the step (2), the heating temperature is 100-150°C.

[0024] As a preferred technical solution, in the step (3), the purification process of the crude phosphorus pentafluoride gas includes: subjecting the crude phosphorus pentafluoride gas to a first condensation, then introducing it into a washing tower for washing with anhydrous hydrogen fluoride, compressing and subjecting the washed phosphorus pentafluoride gas to a second condensation, and finally introducing it into an adsorption tower filled with hydrogen fluoride adsorption packing to adsorb and remove hydrogen fluoride, obtaining high-purity phosphorus pentafluoride.

[0025] As a preferred technical solution, in the step (3), the first condensation is a two-stage condensation, with the temperature of the first-stage condensation being 10-30°C and the temperature of the second-stage condensation being -15 to -10°C; the second condensation is a two-stage condensation, with the condensation temperature being -45 to -40°C.

[0026] As a preferred technical solution, in the step (3), the bottom of the washing tower is provided with a bubbling washing area, and the top is provided with a spray washing area. After the phosphorus pentafluoride gas is bubbled and washed with anhydrous hydrogen fluoride at the bottom of the tower, it is then spray-washed with anhydrous hydrogen fluoride at the top of the tower.

[0027] As a preferred technical solution, in the step (3), the hydrogen fluoride adsorption packing is one or more of Al3F, Al2O3, CaO, and Ca3(PO4)2.

[0028] As a preferred technical solution, the purity of the high-purity phosphorus pentafluoride is ≥99.99%.

[0029] Advantages of the present invention:

[0030] 1. The present invention changes the feeding method of the existing phosphorus pentafluoride production. While dropping polyphosphoric acid, sulfur trioxide is dropped into the reaction kettle for dehydration, and the reaction liquid at the bottom of the reaction kettle is pumped into an anhydrous sodium sulfate dehydration tower for cyclic dehydration, so that the water generated by the reaction of the dropped polyphosphoric acid with anhydrous hydrogen fluoride is synchronously removed by sulfur trioxide and the anhydrous sodium sulfate dehydration tower, ensuring that the reaction kettle is always in an anhydrous state, avoiding the hydrolysis of polyphosphoric acid into orthophosphoric acid, and eliminating the need for dehydration treatment after the reaction is completed, improving the production efficiency, reducing the consumption of raw materials such as polyphosphoric acid, and reducing the energy consumption.

[0031] 2. The present invention also improves the purification process of the crude phosphorus pentafluoride gas. The phosphorus pentafluoride gas is washed by the method of bubbling washing area + spray washing, with better washing effect, and the trace hydrogen fluoride impurities in the phosphorus pentafluoride gas are removed by the adsorption method using an adsorption tower. Compared with the rectification method of the prior art, the energy consumption is lower. Description of the Drawings

[0032] Figure 1It is the process flow diagram for preparing the crude product of phosphorus pentafluoride gas in the present invention.

[0033] Figure 2 It is the process flow diagram for purifying the crude product of phosphorus pentafluoride gas in the present invention.

[0034] Figure 3 It is the schematic structural diagram of the scrubbing tower in the present invention. Specific embodiments

[0035] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described below with reference to the accompanying drawings.

[0036] Example 1

[0037] As Figure 1 and Figure 2 shown, a method for preparing phosphorus pentafluoride includes the following steps:

[0038] (1) Nitrogen displacement is carried out on the polytetrafluoroethylene reactor with a steel lining. The circulating pump and refrigeration equipment connected to the reactor are started, and the temperature in the reactor is controlled at -5°C. First, anhydrous hydrogen fluoride is added to the reactor, and then polyphosphoric acid is added dropwise to the reactor according to the molar ratio of polyphosphoric acid to anhydrous hydrogen fluoride of 1:50 (based on the P2O5 content in polyphosphoric acid, the P2O5 content in polyphosphoric acid is 85%). The dropping rate of polyphosphoric acid is 120 kg / h, generating hexafluorophosphoric acid and water;

[0039] While adding polyphosphoric acid dropwise, fuming sulfuric acid (the sulfur trioxide content in fuming sulfuric acid is 65%) is added dropwise to the reactor according to the molar ratio of polyphosphoric acid to sulfur trioxide of 1:1.5 for dehydration. The dropping rate of fuming sulfuric acid is 180 kg / h, and the reaction liquid at the bottom of the reactor is pumped into the anhydrous sodium sulfate dehydration tower for cyclic dehydration;

[0040] (2) The material after the reaction in step (1) is pumped into the gas generator. The gas generator is heated to 110°C to decompose hexafluorophosphoric acid into gaseous phosphorus pentafluoride and hydrogen fluoride. The crude product of phosphorus pentafluoride gas is obtained from the gas phase of the gas generator, and the liquid-phase sulfuric acid in the gas generator is pumped into the waste sulfuric acid treatment kettle from the bottom of the gas generator;

[0041] (3) The crude product of phosphorus pentafluoride gas obtained in step () is subjected to the first condensation. The first condensation includes two-stage condensation. The first-stage condensation is tap water condensation with a condensation temperature of 15°C, and the second-stage condensation is coolant condensation with a condensation temperature of -10°C. The condensed HF and SO3 are recycled to the reactor;

[0042] The phosphorus pentafluoride gas and the uncondensed HF and SO3 are introduced into the scrubbing tower, as Figure 3As shown in the figure, a bubbling washing area is provided at the bottom of the washing tower, and a spraying washing area is provided at the top of the tower. After the phosphorus pentafluoride gas is bubbling-washed with anhydrous hydrogen fluoride at the bottom of the tower, it is then spraying-washed with anhydrous hydrogen fluoride at the top of the tower; after washing and cooling, the liquid-phase HF and SO3 are recycled to the reaction kettle;

[0043] The washed phosphorus pentafluoride gas is then compressed and secondarily condensed. The secondary condensation includes two-stage condensation, with a condensation temperature of -40°C, and the condensed and collected HF is recycled to the reaction kettle;

[0044] Finally, the phosphorus pentafluoride gas is introduced into the adsorption tower. The adsorption tower is filled with Al2O3 packing. Al2O3 adsorbs and removes trace hydrogen fluoride, and high-purity phosphorus pentafluoride is obtained through the reaction Al2O3 + 6HF → 2AlF3 + 3H2O.

[0045] The purity, metal ion content, and hydrogen fluoride content of the phosphorus pentafluoride gas during the preparation process of Example 1 were detected. The detection results are shown in Table 1. It can be seen that the adsorption tower can greatly improve the purity of phosphorus pentafluoride and reduce the hydrogen fluoride content.

[0046]

[0047] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection required by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing phosphorus pentafluoride, characterized in that: It includes the following steps: (1) First, add anhydrous hydrogen fluoride into the reaction kettle, and then drop polyphosphoric acid into the reaction kettle to generate hexafluorophosphoric acid and water; While dropping polyphosphoric acid, drop sulfur trioxide into the reaction kettle for dehydration, and pump the reaction liquid at the bottom of the reaction kettle into the anhydrous sodium sulfate dehydration tower for cyclic dehydration; (2) Pump the material after the reaction in step (1) into the gas-generating tower. Heat the gas-generating tower to decompose hexafluorophosphoric acid into gaseous phosphorus pentafluoride and hydrogen fluoride, and obtain the crude product of phosphorus pentafluoride gas from the gas phase of the gas-generating tower; (3) Purify the crude product of phosphorus pentafluoride gas obtained in step (2) to obtain high-purity phosphorus pentafluoride.

2. The method for preparing phosphorus pentafluoride according to claim 1, characterized in that: In step (1), based on the content of P2O5 in polyphosphoric acid, the molar ratio of polyphosphoric acid to anhydrous hydrogen fluoride is 1:48 - 72, and the molar ratio of polyphosphoric acid to sulfur trioxide is 1:1.5 - 2.

5.

3. The method for preparing phosphorus pentafluoride according to claim 1 or 2, characterized in that: In step (1), sulfur trioxide is added in the form of fuming sulfuric acid.

4. The preparation method of phosphorus pentafluoride according to claim 3, characterized in that: In step (1), the dropping rate of polyphosphoric acid is 100 - 150 kg / h, and the dropping rate of fuming sulfuric acid is 150 - 280 kg / h, and the temperature of the reaction system is controlled at -15 - 18°C.

5. The preparation method of phosphorus pentafluoride according to claim 1, characterized in that: In step (2), the heating temperature is 100 - 150°C.

6. The method for preparing phosphorus pentafluoride according to claim 1, wherein: In step (3), the purification process of the crude product of phosphorus pentafluoride gas includes: condensing the crude product of phosphorus pentafluoride gas for the first time, then passing it into a washing tower to be washed with anhydrous hydrogen fluoride. After washing, the phosphorus pentafluoride gas is compressed and condensed for the second time, and finally passed into an adsorption tower filled with hydrogen fluoride adsorption filler to adsorb and remove hydrogen fluoride to obtain high-purity phosphorus pentafluoride.

7. The preparation method of phosphorus pentafluoride according to claim 6, characterized in that: In step (3), the first condensation is two-stage condensation, the temperature of the first-stage condensation is 10 - 30°C, and the temperature of the second-stage condensation is -15 - -10°C; the second condensation is two-stage condensation, and the condensation temperature is -45 - -40°C.

8. The preparation method of phosphorus pentafluoride according to claim 6, characterized in that: In step (3), the bottom of the washing tower is provided with a bubbling washing area, and the top of the tower is provided with a spraying washing area. After the phosphorus pentafluoride gas is bubbled and washed with anhydrous hydrogen fluoride at the bottom of the tower, it is then sprayed and washed with anhydrous hydrogen fluoride at the top of the tower.

9. The preparation method of phosphorus pentafluoride according to claim 6, characterized in that: In step (3), the hydrogen fluoride adsorption filler is one or more of Al3F, Al2O3, CaO, and Ca3(PO4)2.

10. The preparation method of phosphorus pentafluoride according to claim 1 or 6, characterized in that: The purity of high-purity phosphorus pentafluoride is ≥99.99%.

Images