A method for preparing phosphorus pentafluoride with high purity and low waste acid

Abstract

The present invention provides a method for preparing phosphorus pentafluoride with high purity and low waste acid, comprising the following steps: (1) mixing hydrogen fluoride and polyphosphoric acid in an HPF6 synthesis kettle for reaction to obtain a mixed solution containing hexafluorophosphoric acid and water; (2) pumping the mixed solution into a fluorine gas stripping tower or an anhydrous sodium sulfate drying tower to remove water in the mixed solution by the fluorine gas stripping tower or the anhydrous sodium sulfate drying tower; (3) pumping the mixed solution into a mixed acid kettle, and simultaneously pumping in fuming sulfuric acid to further remove water in the mixed solution; (4) pumping the dehydrated material in the mixed acid kettle into a gas generating tower, heating the gas generating tower to decompose hexafluorophosphoric acid into gaseous PF5 and HF; the gas phase in the gas generating tower enters a rectifying tower after condensation, and phosphorus pentafluoride is obtained through rectification. The present invention improves the reaction yield and significantly shortens the reaction time required, and the new process significantly reduces the usage amount of fuming sulfuric acid, thereby significantly reducing the generation of waste concentrated sulfuric acid.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolytes, and particularly relates to a method for preparing phosphorus pentafluoride with high purity and low waste acid. 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 battery electrolyte lithium hexafluorophosphate.

[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 generate 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 similar 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 phosphoric acid with hydrogen fluoride to generate hexafluorophosphoric acid, and then 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. A large amount of sulfur trioxide compounds need to be added subsequently for water removal to ensure the smooth progress of the subsequent reaction. The use of a large amount of dehydrating agents in the second method leads to the generation of a large amount of fluorine-containing waste concentrated sulfuric acid during industrial production. The waste concentrated sulfuric acid needs to be defluorinated, and the amount is large, with strong corrosiveness. The harmless treatment is complex and costly. Summary of the Invention

[0009] The purpose of the present invention is to provide a method for preparing phosphorus pentafluoride with high purity and low waste acid, which can improve the quality and yield of phosphorus pentafluoride and significantly reduce the amount of waste acid treatment.

[0010] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0011] The present invention discloses a method for preparing phosphorus pentafluoride with high purity and low waste acid, comprising the following steps:

[0012] (1) Mix and react hydrogen fluoride and polyphosphoric acid in an HPF6 synthesis kettle to obtain a mixed solution containing hexafluorophosphoric acid and water;

[0013] (2) Pump the mixed solution obtained in step (1) into a fluorine gas stripping tower or an anhydrous sodium sulfate drying tower to remove water from the mixed solution in the fluorine gas stripping tower or the anhydrous sodium sulfate drying tower.

[0014] (3) Pump the mixed solution obtained in step (2) into a mixed acid kettle, and at the same time pump in fuming sulfuric acid to further remove water from the mixed solution.

[0015] (4) Pump the dehydrated material in the mixed acid kettle into a gas generation tower. Heat the gas generation tower to decompose hexafluorophosphoric acid into gaseous PF5 and HF. The gas phase in the gas generation tower enters the rectification tower after condensation, and phosphorus pentafluoride is obtained through rectification.

[0016] As a preferred technical solution, in step (1), before the reaction, first displace the air in the HPF6 synthesis kettle with high-purity nitrogen, and then fill in a mixture of fluorine gas and hydrogen fluoride.

[0017] As a preferred technical solution, in step (1), control the reaction temperature to be 0°C - 15°C.

[0018] As a preferred technical solution, in step (2), the flow rate of fluorine gas introduced into the fluorine gas stripping tower is 5% - 40% of the flow rate of the mixed solution.

[0019] As a preferred technical solution, in step (2), the hydrogen fluoride mixed gas obtained by the reaction in the fluorine gas stripping tower is recycled to step (1).

[0020] As a preferred technical solution, in step (3), the dosage of fuming sulfuric acid is 10% - 30% of the molar amount of hexafluorophosphoric acid.

[0021] As a preferred technical solution, in step (3), control the reaction temperature to be 30°C - 40°C.

[0022] As a preferred technical solution, in step (4), the heating temperature is 110°C - 170°C.

[0023] Advantages of the present invention:

[0024] The present invention 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 avoiding the problem of the reaction and decomposition of hexafluorophosphoric acid and phosphorus pentafluoride with water, improving the reaction yield and significantly shortening the reaction time required, and the new process significantly reduces the usage amount of fuming sulfuric acid, thereby significantly reducing the generation of waste concentrated sulfuric acid, and is more economical, environmentally friendly and efficient than the traditional process that solely relies on sulfides to remove water. Description of the drawings

[0025] Figure 1 It is the process flow chart of Comparative Examples 1 - 2.

[0026] Figure 2 It is the process flow diagram of Embodiments 1-2.

[0027] Figure 3 It is the process flow diagram of Embodiments 3-4. Specific Embodiments

[0028] In order 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.

[0029] Comparative Example 1

[0030] As Figure 1 shown, anhydrous hydrogen fluoride and polyphosphoric acid are pumped into the HPF6 synthesis kettle through a metering pump, stirring is started, anhydrous hydrogen fluoride is in excess, and the molar ratio is 12:1. After the feeding is completed, the temperature is maintained at 15°C by controlling the low-temperature heat-conducting oil in the jacket of the HPF6 synthesis kettle, and stirring is maintained under slightly positive pressure for reaction. The reaction time is about 4 h, and hexafluorophosphoric acid and water are generated after the reaction.

[0031] The generated hexafluorophosphoric acid, water and excess hydrogen fluoride are pumped into the mixed acid kettle, and then fuming sulfuric acid is pumped into the mixed acid kettle through a metering pump. The reaction temperature is controlled at 30-40°C by controlling the low-temperature heat-conducting oil in the jacket of the mixed acid kettle, and the reaction time is about 4 h. Fuming sulfuric acid reacts with water to generate sulfuric acid and remove water. During the reaction process, based on the amount of P2O5 in the added polyphosphoric acid, the dosage of fuming sulfuric acid is 110% of the molar amount of HPF6.

[0032] After the reaction is completed, the materials in the mixed acid kettle are slowly pumped into the gas-generating tower. The gas-generating tower is provided with heating coils to control the reaction temperature at 120°C. At this temperature, hexafluorophosphoric acid is completely decomposed into gaseous PF5 and HF. The gas phase in the gas-generating tower passes through a secondary condenser (low-temperature heat-conducting oil, condensation temperature -10°C, efficiency 70%) and then the recovered materials are returned to the HPF6 synthesis kettle for reuse. The remaining non-condensable gases (PF5, HF, SO3) enter the distillation column and are collected to obtain pure phosphorus pentafluoride product after rectification and condensation at -80°C.

[0033] Comparative Example 2

[0034] As Figure 1 shown, anhydrous hydrogen fluoride and polyphosphoric acid are pumped into the HPF6 synthesis kettle through a metering pump, stirring is started, anhydrous hydrogen fluoride is in excess, and the molar ratio is 12:1. After the feeding is completed, the temperature is maintained at 15°C by controlling the low-temperature heat-conducting oil in the jacket of the HPF6 synthesis kettle, and stirring is maintained under slightly positive pressure for reaction. The reaction time is about 4 h, and hexafluorophosphoric acid and water are generated after the reaction.

[0035] Pump the generated hexafluorophosphoric acid, water, and excessive hydrogen fluoride into the mixed acid kettle. Then, pump fuming sulfuric acid into the mixed acid kettle through a metering pump. Control the reaction temperature at 30 - 40 °C through the low-temperature heat-conducting oil in the jacket of the mixed acid kettle. The reaction time is about 4 hours. Fuming sulfuric acid reacts with water to form sulfuric acid, removing the water. During the reaction process, based on the amount of P2O5 in the added polyphosphoric acid, the dosage of fuming sulfuric acid is 10% of the molar amount of HPF6.

[0036] After the reaction is completed, slowly pump the materials in the mixed acid kettle into the gas-generating tower. The gas-generating tower is equipped with heating coils to control the reaction temperature at 120 °C through high-temperature heat-conducting oil. At this temperature, hexafluorophosphoric acid is completely decomposed into gaseous PF5 and HF. The gas phase in the gas-generating tower passes through a two-stage condenser (low-temperature heat-conducting oil, condensation temperature -10 °C, efficiency 70%) and then the recovered materials are returned to the HPF6 synthesis kettle for reuse. The remaining non-condensable gases (PF5, HF, SO3) enter the distillation tower and are collected as pure phosphorus pentafluoride product after rectification and condensation at -80 °C.

[0037] Example 1

[0038] As Figure 2 shown, displace the air in the HPF6 synthesis kettle with high-purity nitrogen, and then fill it with a mixture of fluorine and hydrogen fluoride containing 70% fluorine gas. Pump anhydrous hydrogen fluoride and polyphosphoric acid into the HPF6 synthesis kettle through a metering pump, start stirring. Anhydrous hydrogen fluoride is in excess, and the molar ratio is 12:1. After the feeding is completed, control the temperature at 15 °C through the low-temperature heat-conducting oil in the jacket of the HPF6 synthesis kettle, and keep stirring under slightly positive pressure for the reaction. The reaction time is about 4 hours, and hexafluorophosphoric acid and water are generated after the reaction.

[0039] Pass the generated hexafluorophosphoric acid, water, and excessive hydrogen fluoride through a fluorine gas stripping tower. The fluorine gas flow rate is 40% of the flow rate of the mixture introduced. The fluorine gas stripping tower removes the water in the mixed liquid. After the stripping is completed, pump the mixture into the mixed acid kettle. Then, pump fuming sulfuric acid into the mixed acid kettle through a metering pump. Control the reaction temperature at 30 - 40 °C through the low-temperature heat-conducting oil in the jacket of the mixed acid kettle. The reaction time is about 2 hours. Fuming sulfuric acid reacts with water to form sulfuric acid, removing the water. During the reaction process, based on the amount of P2O5 in the added polyphosphoric acid, the dosage of fuming sulfuric acid is 10% of the molar amount of HPF6.

[0040] After the reaction is completed, slowly pump the materials in the mixed acid kettle into the gas-generating tower. The gas-generating tower is equipped with heating coils to control the reaction temperature at 120 °C through high-temperature heat-conducting oil. At this temperature, hexafluorophosphoric acid is completely decomposed into gaseous PF5 and HF. The gas phase in the gas-generating tower passes through a two-stage condenser (low-temperature heat-conducting oil, condensation temperature -10 °C, efficiency 70%) and then the recovered materials are returned to the HPF6 synthesis kettle for reuse. The remaining non-condensable gases (PF5, HF, SO3) enter the distillation tower and are collected as pure phosphorus pentafluoride product after rectification and condensation at -80 °C.

[0041] Example 2

[0042] As Figure 2 shown, the air in the HPF6 synthesis kettle was replaced with high-purity nitrogen, and then a mixed gas of fluorine and hydrogen fluoride containing 70% fluorine gas was charged; anhydrous hydrogen fluoride and polyphosphoric acid were pumped into the HPF6 synthesis kettle through a metering pump, the stirring was started, and the anhydrous hydrogen fluoride was in excess with a molar ratio of 12:1. After the feeding was completed, the temperature was maintained at 15°C by controlling the low-temperature heat-conducting oil in the jacket of the HPF6 synthesis kettle, and the reaction was carried out under slightly positive pressure with stirring. The reaction time was about 4 h, and hexafluorophosphoric acid and water were generated after the reaction.

[0043] The generated hexafluorophosphoric acid, water, and excessive hydrogen fluoride, etc. were passed through a fluorine gas stripping tower, and the fluorine gas flow rate was 20% of the mixture flow rate. The water in the mixed liquid was removed by the fluorine gas stripping tower. After the stripping was completed, the mixture was pumped into a mixed acid kettle, and then fuming sulfuric acid was pumped into the mixed acid kettle through a metering pump. The reaction temperature was controlled at 30-40°C by controlling the low-temperature heat-conducting oil in the jacket of the mixed acid kettle, and the reaction time was about 2 h. The fuming sulfuric acid reacted with water to generate sulfuric acid and remove the water. During the reaction process, based on the amount of P2O5 in the added polyphosphoric acid, the dosage of fuming sulfuric acid was 10% of the molar amount of HPF6.

[0044] After the reaction was completed, the materials in the mixed acid kettle were slowly pumped into a gas generation tower. The gas generation tower was provided with heating coils to control the reaction temperature at 120°C. At this temperature, hexafluorophosphoric acid was completely decomposed into gaseous PF5 and HF. The gas phase in the gas generation tower was recycled to the HPF6 synthesis kettle for reuse after passing through a secondary condenser (low-temperature heat-conducting oil, condensation temperature -10°C, efficiency 70%). The remaining non-condensable gases (PF5, HF, SO3) entered a distillation column and were collected to obtain pure phosphorus pentafluoride product after rectification and condensation at -80°C.

[0045] Example 3

[0046] As Figure 3 shown, anhydrous hydrogen fluoride and polyphosphoric acid were pumped into the HPF6 synthesis kettle through a metering pump, the stirring was started, and the anhydrous hydrogen fluoride was in excess with a molar ratio of 12:1. After the feeding was completed, the temperature was maintained at 15°C by controlling the low-temperature heat-conducting oil in the jacket of the HPF6 synthesis kettle, and the reaction was carried out under slightly positive pressure with stirring. The reaction time was about 4 h, and hexafluorophosphoric acid and water were generated after the reaction.

[0047] The generated hexafluorophosphoric acid, water, excessive hydrogen fluoride, etc. are passed through an anhydrous sodium sulfate drying tower and circulated inside the tower at room temperature for 12 h. The anhydrous sodium sulfate drying tower removes the water in the mixed solution. The mixture is pumped into the mixed acid kettle, and then fuming sulfuric acid is pumped into the mixed acid kettle through a metering pump. The reaction temperature is controlled at 30 - 40 °C by low-temperature heat-conducting oil in the jacket of the mixed acid kettle, and the reaction time is about 0.5 h. The fuming sulfuric acid reacts with water to generate sulfuric acid and remove the water. During the reaction process, based on the amount of P2O5 in the added polyphosphoric acid, the dosage of fuming sulfuric acid is 10% of the molar amount of HPF6.

[0048] After the reaction is completed, the materials in the mixed acid kettle are slowly pumped into the gas-generating tower. The gas-generating tower is equipped with heating coils, and the reaction temperature is controlled at 120 °C by high-temperature heat-conducting oil. At this temperature, hexafluorophosphoric acid is completely decomposed into gaseous PF5 and HF. The gas phase in the gas-generating tower is recycled back to the HPF6 synthesis kettle for reuse after passing through a secondary condenser (low-temperature heat-conducting oil, condensation temperature -10 °C, efficiency 70%). The remaining non-condensable gases (PF5, HF, SO3) enter the distillation column and are collected as pure phosphorus pentafluoride product after rectification and condensation at -80 °C.

[0049] Example 4

[0050] As Figure 3 shown, anhydrous hydrogen fluoride and polyphosphoric acid are pumped into the HPF6 synthesis kettle through a metering pump. Stirring is started. The anhydrous hydrogen fluoride is in excess, and the molar ratio is 12:1. After the feeding is completed, the temperature is maintained at 15 °C by low-temperature heat-conducting oil in the jacket of the HPF6 synthesis kettle, and stirring is carried out under slightly positive pressure for the reaction. The reaction time is about 4 h, and hexafluorophosphoric acid and water are generated after the reaction.

[0051] The generated hexafluorophosphoric acid, water, excessive hydrogen fluoride, etc. are passed through an anhydrous sodium sulfate drying tower and circulated inside the tower at room temperature for 12 h. The anhydrous sodium sulfate drying tower removes the water in the mixed solution. The mixture is pumped into the mixed acid kettle, and then fuming sulfuric acid is pumped into the mixed acid kettle through a metering pump. The reaction temperature is controlled at 30 - 40 °C by low-temperature heat-conducting oil in the jacket of the mixed acid kettle, and the reaction time is about 4 h. The fuming sulfuric acid reacts with water to generate sulfuric acid and remove the water. During the reaction process, based on the amount of P2O5 in the added polyphosphoric acid, the dosage of fuming sulfuric acid is 10% of the molar amount of HPF6.

[0052] After the reaction is completed, the materials in the mixed acid kettle are slowly pumped into the gas-generating tower. The gas-generating tower is equipped with heating coils, and the reaction temperature is controlled at 120 °C by high-temperature heat-conducting oil. At this temperature, hexafluorophosphoric acid is completely decomposed into gaseous PF5 and HF. The gas phase in the gas-generating tower is recycled back to the HPF6 synthesis kettle for reuse after passing through a secondary condenser (low-temperature heat-conducting oil, condensation temperature -10 °C, efficiency 70%). The remaining non-condensable gases (PF5, HF, SO3) enter the distillation column and are collected as pure phosphorus pentafluoride product after rectification and condensation at -80 °C.

[0053] The products and waste sulfuric acid contents obtained in the above examples and comparative examples are shown in the following table:

[0054]

[0055] It can be seen that in Examples 1-4, a large amount of water generated during the hexafluorophosphoric acid reaction was removed by using a fluorine gas stripping tower or an anhydrous sodium sulfate drying tower, thus avoiding the problem of the decomposition of hexafluorophosphoric acid and phosphorus pentafluoride due to reaction with water. Moreover, the new process significantly reduced the usage amount of fuming sulfuric acid, thereby significantly reducing the generation of waste concentrated sulfuric acid. Compared with the processes of Comparative Examples 1-2 that solely relied on sulfides to remove water, it is more economical, environmentally friendly, and efficient.

[0056] 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 examples. What is described in the above examples 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 claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing phosphorus pentafluoride with high purity and low waste acid, characterized in that: It includes the following steps: (1) Mix hydrogen fluoride and polyphosphoric acid in an HPF6 synthesis kettle for reaction to obtain a mixed solution containing hexafluorophosphoric acid and water; (2) Pump the mixed solution obtained in step (1) into a fluorine gas stripping tower or an anhydrous sodium sulfate drying tower, and the fluorine gas stripping tower or the anhydrous sodium sulfate drying tower removes the water in the mixed solution; (3) Pump the mixed solution obtained in step (2) into a mixed acid kettle, and at the same time pump in fuming sulfuric acid to further remove the water in the mixed solution. The dosage of fuming sulfuric acid is 10% of the molar amount of HPF6; (4) Pump the dehydrated material in the mixed acid kettle into a gas generation tower, and heat the gas generation tower to decompose hexafluorophosphoric acid into gaseous PF5 and HF; The gas phase in the gas generation tower enters the rectification tower after condensation, and phosphorus pentafluoride is obtained through rectification; When the mixed solution obtained in step (1) is pumped into the fluorine gas stripping tower, the flow rate of the fluorine gas introduced into the fluorine gas stripping tower is 40% of the flow rate of the mixed solution. The reaction temperature is controlled at 30-40°C by low-temperature heat-conducting oil in the jacket of the mixed acid kettle, and the reaction time is 2 h; When the mixed solution obtained in step (1) is pumped into the anhydrous sodium sulfate drying tower, it circulates in the tower at room temperature for 12 h. The reaction temperature is controlled at 30-40°C by low-temperature heat-conducting oil in the jacket of the mixed acid kettle, and the reaction time is 0.5 h.

2. The method for preparing phosphorus pentafluoride with high purity and low waste acid according to claim 1, wherein: In step (1), before the reaction, the air in the HPF6 synthesis kettle is replaced with high-purity nitrogen, and then a mixed gas of fluorine gas and hydrogen fluoride is filled.

3. The preparation method of phosphorus pentafluoride with high purity and low waste acid according to claim 1, wherein: In step (1), the reaction temperature is controlled at 0°C - 15°C.

4. The preparation method of phosphorus pentafluoride with high purity and low waste acid according to claim 1, characterized in that: In step (2), the flow rate of the fluorine gas introduced into the fluorine gas stripping tower is 5% - 40% of the flow rate of the mixed solution.

5. The preparation method of phosphorus pentafluoride with high purity and low waste acid according to claim 1, characterized in that: In step (2), the hydrogen fluoride mixed gas obtained by the reaction in the fluorine gas stripping tower is recycled to step (1).

6. The method for preparing phosphorus pentafluoride with high purity and low waste acid according to claim 1, characterized in that: In step (3), the dosage of fuming sulfuric acid is 10% - 30% of the molar amount of hexafluorophosphoric acid.

7. The preparation method of phosphorus pentafluoride with high purity and low waste acid according to claim 1, characterized in that: In step (3), the reaction temperature is controlled at 30°C - 40°C.

8. The preparation method of phosphorus pentafluoride with high purity and low waste acid according to claim 1, characterized in that: In step (4), the heating temperature is 110°C - 170°C.

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