CN117361458A - Continuous production method of phosphorus pentafluoride - Google Patents

Abstract

The invention discloses a continuous production method of phosphorus pentafluoride, which belongs to the technical field of phosphorus pentafluoride production. Phosphorus pentoxide and anhydrous hydrogen fluoride are used to synthesize an aqueous hexafluorophosphoric acid solution. An anhydrous hydrogen fluoride solution is used as the reaction substrate during the first start-up. material, during normal operation, hexafluorophosphoric acid aqueous solution is used as the reaction substrate. By continuously inputting phosphorus pentoxide and liquid hydrogen fluoride, and continuously extracting hexafluorophosphoric acid aqueous solution, the continuous synthesis of hexafluorophosphoric acid is achieved, and the continuous synthesis of pentafluoride is achieved. Phosphorus provides the prerequisite. It greatly reduces the reaction time for synthesizing hexafluorophosphoric acid. At the same time, the liquid reaction system has high heat transfer efficiency, making temperature control easier. The strength requirements for the stirrer are also much reduced, which has extremely high engineering value.

Description

A kind of continuous production method of phosphorus pentafluoride

Technical field

The invention relates to the technical field of phosphorus pentafluoride production, and in particular to a continuous production method of phosphorus pentafluoride.

Background technique

Phosphorus pentafluoride (PF ₅ ) is a gaseous substance at room temperature used in the electronics industry as a fluorinating agent in various chemical reactions. In particular, it is a starting material for the manufacture of hexafluorophosphate DPF ₆ (D = Li, Na, K, etc.) used in battery electrolytes. When D=Li, lithium hexafluorophosphate is an important substance as the electrolyte of lithium batteries. Lithium hexafluorophosphate is particularly safe and has excellent physical properties. It is regarded as an indispensable substance in lithium secondary batteries and is highly expected to be used in hybrid vehicles in the future.

The Chinese patent with the publication number CN101570328A and the publication date of 2013.06.12 uses phosphorus pentoxide and anhydrous hydrogen fluoride to react to prepare an aqueous solution of hexafluorophosphoric acid, and then adds fuming sulfuric acid to decompose phosphorus pentafluoride at 150°C, and The decomposed phosphorus pentafluoride is condensed at -40°C to obtain clean phosphorus pentafluoride, which is then combined with lithium fluoride in an environment where hydrogen fluoride is the solvent to synthesize lithium hexafluorophosphate. This method uses phosphorus pentoxide as a reaction substrate, drops liquid anhydrous hydrogen fluoride under stirring, and controls the reaction temperature to be around 0°C. Among them, because phosphorus pentoxide is a solid powder, dripping liquid hydrogen fluoride will inevitably produce localized severe heat, and the reaction temperature is extremely difficult to control. And when hydrogen fluoride is added to a certain amount, a large amount of solid agglomeration will appear in the reaction device, making stirring extremely difficult and further increasing the difficulty of cooling. Therefore, it is difficult to realize industrial production using this patented method.

The Chinese patent with the publication number CN104261369A and the publication date of 2023.07.21 uses polyphosphoric acid to react with hydrogen fluoride. Although it solves the problem of difficult heat transfer and difficulty in industrialization in the step of synthesizing hexafluorophosphoric acid aqueous solution, this method will cause hexafluorophosphoric acid aqueous solution. A substantial increase in the water content will inevitably lead to a substantial increase in the amount of fuming sulfuric acid and the amount of by-product sulfuric acid.

Contents of the invention

In view of the above-mentioned defects in the prior art, the present invention provides a continuous production method of phosphorus pentafluoride, which uses phosphorus pentoxide and anhydrous hydrogen fluoride to synthesize an aqueous hexafluorophosphoric acid solution, and uses an anhydrous hydrogen fluoride solution as the reaction substrate during the first start-up. , during normal operation, hexafluorophosphoric acid aqueous solution is used as the reaction substrate. By continuously inputting phosphorus pentoxide and liquid hydrogen fluoride, and continuously extracting hexafluorophosphoric acid aqueous solution, the continuous synthesis of hexafluorophosphoric acid is achieved. For the continuous synthesis of phosphorus pentafluoride Prerequisites are provided. It greatly reduces the reaction time for synthesizing hexafluorophosphoric acid. At the same time, the liquid reaction system has high heat transfer efficiency, making temperature control easier. The strength requirements for the stirrer are also much reduced, which has extremely high engineering value.

The purpose of the present invention is achieved through the following technical solutions:

A continuous production method of phosphorus pentafluoride, including the following steps:

Step 1: Add anhydrous hydrogen fluoride to the hexafluorophosphoric acid synthesis kettle. The molar ratio of hydrogen fluoride to phosphorus pentoxide is 12~24:1, start stirring and cooling, and control the temperature in the synthesis kettle at -5~5°C;

Step 2: Open the compressed air inlet valve and fully open the phosphorus pentoxide feed valve, and continuously feed phosphorus pentoxide powder into the synthesis kettle; at the same time, open the anhydrous hydrogen fluoride feed valve, and feed the phosphorus pentoxide powder into the hexafluorophosphoric acid synthesis kettle. Continuously feed anhydrous hydrogen fluoride;

Step 3: The reaction tail gas in the hexafluorophosphoric acid synthesis kettle is condensed through the condensation refluxer, and the condensed hydrogen fluoride is refluxed into the synthesis kettle; the uncondensed tail gas is discharged after passing through the tail gas washing system;

Step 4: After the liquid level of the hexafluorophosphoric acid synthesis kettle reaches 70%~80%, the hexafluorophosphate synthesis kettle begins to continuously produce the hexafluorophosphoric acid aqueous solution;

Step 5: When the liquid level of the decomposition kettle reaches 40%~50% of the total liquid level of the decomposition kettle, the hexafluorophosphoric acid aqueous solution is switched to other decomposition kettles, and then fuming sulfuric acid is added to the decomposition kettle containing the hexafluorophosphoric acid aqueous solution to prepare Decomposition at elevated temperatures;

Step 6: After adding fuming sulfuric acid, the hexafluorophosphoric acid solution is heated to 100~200℃ to decompose the crude phosphorus pentafluoride gas. The crude phosphorus pentafluoride gas is condensed and dried at -60~-70℃ to obtain phosphorus pentafluoride. product gas.

Preferably, in step one, the flow rate of the phosphorus pentoxide powder is controlled to 0.5kg/min through the rotation speed of the feeding screw, the stirring speed is 50~200r/min, and -15°C low-temperature heat transfer oil is used for cooling.

Preferably, in step two, the ratio of phosphorus pentoxide powder to compressed air is 0.1:1.

Preferably, in step three, the temperature of the condensation refluxer is set to -5~0°C.

Preferably, in the third step, the condensed uncondensed tail gas is washed with regular warm spray water, then rinsed with regular warm spray alkali and then emptied.

Preferably, in the fourth step, phosphorus pentoxide and liquid hydrogen fluoride are continuously added, and the hexafluorophosphoric acid aqueous solution is continuously extracted to maintain the liquid level in the kettle.

Preferably, in step five, the molar ratio of free sulfur trioxide in the fuming sulfuric acid to the phosphorus element in the hexafluorophosphoric acid aqueous solution is 3 to 5.

Preferably, in step six, the purity of the refined phosphorus pentafluoride is greater than 99%.

The beneficial effects of this technical solution are as follows:

1. A continuous production method of phosphorus pentafluoride provided by the invention uses phosphorus pentoxide and anhydrous hydrogen fluoride to synthesize a hexafluorophosphoric acid aqueous solution. An anhydrous hydrogen fluoride solution is used as the reaction substrate during initial start-up. During normal operation, hexafluorophosphate is used. Fluorophosphoric acid aqueous solution is used as the reaction substrate. By continuously inputting phosphorus pentoxide and liquid hydrogen fluoride, and continuously extracting hexafluorophosphoric acid aqueous solution, the continuous synthesis of hexafluorophosphoric acid is achieved, which provides prerequisites for the continuous synthesis of phosphorus pentafluoride or lithium hexafluorophosphate. . The reaction time for synthesizing hexafluorophosphoric acid is greatly reduced. At the same time, the liquid reaction system has high heat transfer efficiency, making temperature control easier. The strength requirements for the stirrer are also greatly reduced, which solves the problem of using phosphorus pentoxide as raw material to prepare phosphorus pentoxide. Phosphorus fluoride is difficult to engineer and has extremely high engineering value.

2. The invention provides a continuous production method of phosphorus pentafluoride. The invention uses phosphorus pentoxide as the raw material. Compared with using polyphosphoric acid as the raw material (the current industrial method), the amount of by-product sulfuric acid is greatly reduced (reduced). More than 1/3 of the by-product sulfuric acid amount). In addition, it reduces the temperature required for the decomposition of hexafluorophosphoric acid, saves energy consumption, and reduces the requirements for the material of the decomposition kettle (it is about 30°C lower than the decomposition temperature using polyphosphoric acid as raw material).

3. The present invention provides a continuous production method of phosphorus pentafluoride, which uses compressed air to blow phosphorus pentoxide into the synthesis kettle, which can prevent phosphorus pentoxide from reacting at the pipe mouth and causing pipeline blockage.

Description of the drawings

Figure 1 is a schematic structural diagram of the continuous production system of phosphorus pentafluoride in the present invention;

In the picture: 1. Synthesis kettle; 2. Decomposition kettle; 3. Anhydrous hydrogen fluoride inlet pipe; 4. Phosphorus pentoxide inlet pipe; 5. Condensation refluxer; 6. Hexafluorophosphoric acid aqueous solution feed pipe; 7. Smoke generation. Sulfuric acid inlet pipe; 8. Phosphorus pentafluoride refining system; 81. Condenser; 82. Gas-liquid separator; 9. Phosphorus pentoxide powder silo; 10. Compressed air inlet pipe; 11. Molecular sieve tower drying device; 12. Tail gas washing system; 121. Water washing tower; 122. Alkali washing tower; 13. Hydrogen fluoride feed valve; 14. Phosphorus pentoxide feed valve; 15. Compressed air inlet valve; 16. First thermometer.

Detailed ways

The present invention will be further described in detail below with reference to examples, but the implementation of the present invention is not limited thereto.

As shown in Figure 1, a continuous production system for phosphorus pentafluoride includes a hexafluorophosphoric acid synthesis kettle 1 and a hexafluorophosphate decomposition kettle 2. The hexafluorophosphate synthesis kettle 1 is connected with anhydrous hydrogen fluoride inlet pipe 3, pentoxide The diphosphorus inlet pipe 4 is connected to the condensation refluxer 5. The hexafluorophosphoric acid synthesis kettle 1 and the hexafluorophosphoric acid decomposition kettle 2 are connected through the hexafluorophosphoric acid aqueous solution feed pipe 6. The hexafluorophosphoric acid decomposition kettle 2 is also connected to the fume generator. The sulfuric acid inlet pipe 7 is connected to the phosphorus pentafluoride refining system 8 .

Wherein, the phosphorus pentafluoride refining system 8 includes a condenser 81 and a gas-liquid separator 82 .

Wherein, the phosphorus pentoxide inlet pipe 4 is connected to the phosphorus pentoxide powder silo 9 and the compressed air inlet pipe 10 .

Wherein, the compressed air inlet pipe 10 is provided with a molecular sieve tower drying device 11 .

Wherein, a screw feeder is provided at the lower end of the phosphorus pentoxide powder bin 9 .

Wherein, the condensation refluxer 5 is also connected to the exhaust gas scrubbing system 12 .

Wherein, the exhaust gas washing system 12 includes a water washing tower 121 and an alkali washing tower 122 connected in sequence.

Wherein, the anhydrous hydrogen fluoride inlet pipe 3 is provided with a hydrogen fluoride feed valve 13, the phosphorus pentoxide inlet pipe 4 is provided with a phosphorus pentoxide feed valve 14, and the compressed air inlet pipe 10 is provided with a compressed air inlet. Air valve 15.

Wherein, a first thermometer 16 is provided on the hexafluorophosphoric acid synthesis reactor 1 .

It also includes a DCS (Distributed Control System), which is connected to the hydrogen fluoride feed valve 13 , the phosphorus pentoxide feed valve 14 , the compressed air intake valve 15 , and the first thermometer 16 .

Examples 1 to 3 and Comparative Examples 1 to 4 all adopt the above-mentioned continuous production system of phosphorus pentafluoride.

Example 1

A continuous production method of phosphorus pentafluoride, including the following steps:

Step 1. Add anhydrous hydrogen fluoride to the hexafluorophosphoric acid synthesis kettle 1. The molar ratio of hydrogen fluoride to phosphorus pentoxide is 12:1. Start stirring and cooling, and control the temperature in the synthesis kettle 1 to be -5°C (first thermometer 16 Displayed as -5℃); the flow rate of phosphorus pentoxide powder is controlled by the feeding screw speed to 0.5kg/min, the stirring speed is 50r/min, and -15℃ low-temperature thermal oil cooling is used;

Step 2: Open the compressed air inlet valve 15 and fully open the phosphorus pentoxide feed valve 14, and continuously feed phosphorus pentoxide powder into the synthesis kettle 1. The ratio of phosphorus pentoxide powder to compressed air is 0.1 : 1; Open the anhydrous hydrogen fluoride feed valve 13 at the same time, and continuously feed anhydrous hydrogen fluoride into the hexafluorophosphoric acid synthesis reactor 1;

Step 3: The reaction tail gas in the hexafluorophosphoric acid synthesis kettle 1 is condensed through the condensation refluxer 5. The temperature of the condensation refluxer 5 is set to -5°C, and the condensed hydrogen fluoride is refluxed into the synthesis kettle 1; the uncondensed tail gas is passed through After exhaust gas washing system 12 is discharged, the condensed uncondensed exhaust gas is sprayed with water and then sprayed with alkali and then emptied;

Step 4: After the liquid level in the hexafluorophosphoric acid synthesis kettle 1 reaches 70%, continuously add phosphorus pentoxide and liquid hydrogen fluoride, and continuously extract the hexafluorophosphoric acid aqueous solution to maintain the liquid level in the synthesis kettle 1;

Step 5: When the liquid level of decomposition kettle 2 reaches 40% of the total liquid level of decomposition kettle 2, the hexafluorophosphoric acid aqueous solution is switched to other decomposition kettles 2, and then fuming sulfuric acid is added dropwise to the decomposition kettle 2 containing the hexafluorophosphoric acid aqueous solution. , ready for decomposition at elevated temperatures, where the molar ratio of free sulfur trioxide in oleum to phosphorus in the hexafluorophosphoric acid aqueous solution is 3;

Step 6: After adding fuming sulfuric acid, the hexafluorophosphoric acid solution is heated to 100°C to decompose the crude phosphorus pentafluoride gas. The crude phosphorus pentafluoride gas is condensed and dried at -60°C to obtain the phosphorus pentafluoride product gas.

The obtained phosphorus pentafluoride gas was reacted with excess lithium fluoride. By detecting the content of lithium hexafluorophosphate and the total mass increased when synthesizing lithium hexafluorophosphate, the purity of phosphorus pentafluoride was calculated to be 99.1% and the yield was 55%.

Example 2

A continuous production method of phosphorus pentafluoride, including the following steps:

Step 1. Add anhydrous hydrogen fluoride to the hexafluorophosphoric acid synthesis kettle 1. The molar ratio of hydrogen fluoride to phosphorus pentoxide is 18:1. Start stirring and cooling, and control the temperature in the synthesis kettle 1 to be 0°C (the first thermometer 16 displays is 0℃); the flow rate of phosphorus pentoxide powder is controlled by the feeding screw speed to 0.5kg/min, the stirring speed is 125r/min, and -15℃ low-temperature thermal oil cooling is used;

Step 2: Open the compressed air inlet valve 15 and fully open the phosphorus pentoxide feed valve 14, and continuously feed phosphorus pentoxide powder into the synthesis kettle 1. The ratio of phosphorus pentoxide powder to compressed air is 0.1 : 1; Open the anhydrous hydrogen fluoride feed valve 13 at the same time, and continuously feed anhydrous hydrogen fluoride into the hexafluorophosphoric acid synthesis reactor 1;

Step 3: The reaction tail gas in the hexafluorophosphoric acid synthesis kettle 1 is condensed through the condensation refluxer 5. The temperature of the condensation refluxer 5 is set to -2°C, and the condensed hydrogen fluoride is refluxed into the synthesis kettle 1; the uncondensed tail gas is passed through After exhaust gas washing system 12 is discharged, the condensed uncondensed exhaust gas is sprayed with water and then sprayed with alkali and then emptied;

Step 4: After the liquid level in the hexafluorophosphoric acid synthesis kettle 1 reaches 75%, continuously add phosphorus pentoxide and liquid hydrogen fluoride, and continuously extract the hexafluorophosphoric acid aqueous solution to maintain the liquid level in the synthesis kettle 1;

Step 5: When the liquid level of decomposition kettle 2 reaches 45% of the total liquid level of decomposition kettle 2, the hexafluorophosphoric acid aqueous solution is switched to other decomposition kettles 2, and then fuming sulfuric acid is added dropwise to the decomposition kettle 2 containing the hexafluorophosphoric acid aqueous solution. , ready for decomposition at elevated temperatures, where the molar ratio of free sulfur trioxide in fuming sulfuric acid to phosphorus in the aqueous hexafluorophosphoric acid solution is 4;

Step 6: After adding fuming sulfuric acid, the hexafluorophosphoric acid solution is heated to 150°C to decompose the crude phosphorus pentafluoride gas. The crude phosphorus pentafluoride gas is condensed and dried at -65°C to obtain the phosphorus pentafluoride product gas.

The obtained phosphorus pentafluoride gas was reacted with excess lithium fluoride, and by detecting the content of lithium hexafluorophosphate and the total mass increased during the synthesis of lithium hexafluorophosphate, the purity of phosphorus pentafluoride was calculated to be 99.3%, and the yield was 76%.

Example 3

A continuous production method of phosphorus pentafluoride, including the following steps:

Step 1. Add anhydrous hydrogen fluoride to the hexafluorophosphoric acid synthesis kettle 1. The molar ratio of hydrogen fluoride to phosphorus pentoxide is 24:1. Start stirring and cooling, and control the temperature in the synthesis kettle 1 to be 5°C (the first thermometer 16 displays is 5℃); the flow rate of phosphorus pentoxide powder is controlled by the feeding screw speed to 0.5kg/min, the stirring speed is 200r/min, and -15℃ low-temperature thermal oil cooling is used;

Step 2: Open the compressed air inlet valve 15 and fully open the phosphorus pentoxide feed valve 14, and continuously feed phosphorus pentoxide powder into the synthesis kettle 1. The ratio of phosphorus pentoxide powder to compressed air is 0.1 : 1; Open the anhydrous hydrogen fluoride feed valve 13 at the same time, and continuously feed anhydrous hydrogen fluoride into the hexafluorophosphoric acid synthesis reactor 1;

Step 3: The reaction tail gas in the hexafluorophosphoric acid synthesis kettle 1 is condensed through the condensation refluxer 5. The temperature of the condensation refluxer 5 is set to 0°C, and the condensed hydrogen fluoride is refluxed into the synthesis kettle 1; the uncondensed tail gas is passed through the tail gas After the washing system 12 is discharged, the condensed uncondensed tail gas is washed with water by spraying, and then washed by spraying alkali and then drained;

Step 4: After the liquid level in the hexafluorophosphoric acid synthesis kettle 1 reaches 80%, continuously add phosphorus pentoxide and liquid hydrogen fluoride, and continuously extract the hexafluorophosphoric acid aqueous solution to maintain the liquid level in the synthesis kettle 1;

Step 5: When the liquid level of decomposition kettle 2 reaches 50% of the total liquid level of decomposition kettle 2, the hexafluorophosphoric acid aqueous solution is switched to other decomposition kettles 2, and then fuming sulfuric acid is added dropwise to the decomposition kettle 2 containing the hexafluorophosphoric acid aqueous solution. , ready for decomposition at elevated temperatures, where the molar ratio of free sulfur trioxide in the fuming sulfuric acid to the phosphorus element in the aqueous hexafluorophosphoric acid solution is 5;

Step 6: After adding fuming sulfuric acid, the hexafluorophosphoric acid solution is heated to 200°C to decompose the crude phosphorus pentafluoride gas. The crude phosphorus pentafluoride gas is condensed and dried at -70°C to obtain the phosphorus pentafluoride product gas.

The obtained phosphorus pentafluoride gas was reacted with excess lithium fluoride, and by detecting the content of lithium hexafluorophosphate and the total mass increased during the synthesis of lithium hexafluorophosphate, the purity of phosphorus pentafluoride was calculated to be 99%, and the yield was 91%.

Comparative example 1

The difference between this comparative example and Example 1 is that the molar ratio of hydrogen fluoride to phosphorus pentoxide is 10:1.

The obtained phosphorus pentafluoride gas was reacted with excess lithium fluoride. By detecting the content of lithium hexafluorophosphate and the total mass increased during the synthesis of lithium hexafluorophosphate, the purity of phosphorus pentafluoride was calculated to be 96.5% and the yield was 23%.

Comparative example 2

The difference between this comparative example and Example 3 is that the molar ratio of hydrogen fluoride to phosphorus pentoxide is 26:1.

The obtained phosphorus pentafluoride gas was reacted with excess lithium fluoride, and by detecting the content of lithium hexafluorophosphate and the total mass increased when synthesizing lithium hexafluorophosphate, it was calculated that the purity of phosphorus pentafluoride was 99%, and the yield was 92%, which was compared with the Example 3 has no significant improvement.

Comparative example 3

The difference between this comparative example and Example 2 is that: the temperature in the synthesis kettle 1 is controlled at -10°C; the materials in the synthesis kettle are solidified.

Comparative example 4

The difference between this comparative example and Example 2 is that the molar ratio of free sulfur trioxide in the fuming sulfuric acid to the phosphorus element in the hexafluorophosphoric acid aqueous solution is 8, and the purity of phosphorus pentafluoride obtained is 99%, and the yield is 40%.

Finally, it should be noted that the above embodiments are only for illustration and do not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that the present invention can still be carried out. Modifications or equivalent substitutions, without departing from the spirit and scope of the present invention, shall be included in the scope of the claims of the present invention.

Claims (8)

1. A continuous production method of phosphorus pentafluoride, characterized in that it includes the following steps: Step 1: Add anhydrous hydrogen fluoride to the hexafluorophosphoric acid synthesis kettle. The molar ratio of hydrogen fluoride to phosphorus pentoxide is 12~24:1, start stirring and cooling, and control the temperature in the synthesis kettle at -5~5°C; Step 2: Open the compressed air inlet valve and fully open the phosphorus pentoxide feed valve, and continuously feed phosphorus pentoxide powder into the synthesis kettle; at the same time, open the anhydrous hydrogen fluoride feed valve, and feed the phosphorus pentoxide powder into the hexafluorophosphoric acid synthesis kettle. Continuously feed anhydrous hydrogen fluoride; Step 3: The reaction tail gas in the hexafluorophosphoric acid synthesis kettle is condensed through the condensation refluxer, and the condensed hydrogen fluoride is refluxed into the synthesis kettle; the uncondensed tail gas is discharged after passing through the tail gas washing system; Step 4: After the liquid level of the hexafluorophosphoric acid synthesis kettle reaches 70%~80%, the hexafluorophosphate synthesis kettle begins to continuously produce the hexafluorophosphoric acid aqueous solution; Step 5: When the liquid level of the decomposition kettle reaches 40%~50% of the total liquid level of the decomposition kettle, switch the hexafluorophosphoric acid aqueous solution into other decomposition kettles, and then add fuming sulfuric acid to the decomposition kettle containing the hexafluorophosphoric acid aqueous solution and prepare Decomposition at elevated temperatures; Step 6: After adding fuming sulfuric acid, the hexafluorophosphoric acid solution is heated to 100~200℃ to decompose the crude phosphorus pentafluoride gas. The crude phosphorus pentafluoride gas is condensed and dried at -60~-70℃ to obtain phosphorus pentafluoride. product gas. 2. A kind of continuous production method of phosphorus pentafluoride according to claim 1, characterized in that: in the step one, the flow rate of the phosphorus pentoxide powder is controlled to 0.5kg/min by the feeding screw speed, and the stirring The rotation speed is 50~200r/min, and it is cooled by -15℃ low-temperature heat transfer oil. 3. A continuous production method of phosphorus pentafluoride according to claim 1, characterized in that in step two, the ratio of phosphorus pentoxide powder to compressed air is 0.1:1. 4. A continuous production method of phosphorus pentafluoride according to claim 1, characterized in that in step three, the temperature of the condensation refluxer is set to -5~0°C. 5. A kind of continuous production method of phosphorus pentafluoride according to claim 1, characterized in that: in the step three, the condensed uncondensed tail gas is washed with water at normal temperature, and then sprayed with alkali at normal temperature. Empty after washing. 6. A kind of continuous production method of phosphorus pentafluoride according to claim 1, characterized in that: in the step four, phosphorus pentoxide and liquid hydrogen fluoride are continuously put in, the hexafluorophosphoric acid aqueous solution is continuously taken out, and the kettle is maintained. The internal liquid level remains unchanged. 7. A kind of continuous production method of phosphorus pentafluoride according to claim 1, characterized in that: in the step five, the molar ratio of free sulfur trioxide in the fuming sulfuric acid and the phosphorus element in the hexafluorophosphoric acid aqueous solution is 3~5. 8. A continuous production method of phosphorus pentafluoride according to claim 1, characterized in that in step six, the purity of the refined phosphorus pentafluoride is greater than 99%.