Method and product for preparing high-purity phosphorus pentafluoride by gas-liquid method

Abstract

The gas-liquid method for preparing high-purity phosphorus pentafluoride and the product disclosed in the present invention comprises the following steps: step 1, pre-drying sodium fluorosilicate solid and then pyrolyzing it to obtain crude silicon tetrafluoride gas; step 2, washing and removing impurities from the crude silicon tetrafluoride gas by two-stage concentrated sulfuric acid to obtain high-purity silicon tetrafluoride gas; step 3, adding phosphorus trichloride liquid raw material into a reactor, introducing high-purity silicon tetrafluoride gas and chlorine gas into the reactor, and reacting to generate silicon tetrachloride liquid and phosphorus pentafluoride gas; step 4, purifying the phosphorus pentafluoride gas by two-stage distillation to obtain a high-purity phosphorus pentafluoride product. Compared with the existing phosphorus pentafluoride preparation technology, the present invention has milder reaction conditions, easier reaction control, relatively lower activity of reaction raw materials, relatively lower risk, less impurity components and low content of reaction products, easier separation and impurity removal of reaction products, and high purity of the obtained phosphorus pentafluoride target product, which meets the use index requirements of related industries.

Description

Technical Field

[0001] The present invention belongs to the technical field of fluorine chemical industry, and specifically relates to a method for preparing high-purity phosphorus pentafluoride by a gas-liquid method. The present invention also relates to a high-purity phosphorus pentafluoride product prepared by the gas-liquid method. Background Art

[0002] Phosphorus pentafluoride is the core raw material of lithium hexafluorophosphate. Lithium hexafluorophosphate (LiPF6) is a lithium salt for lithium-ion battery electrolyte. It has the advantages of high energy density, strong electrochemical stability, high voltage, high conductivity, good low-temperature performance, and strong antioxidant ability. It is widely used in the production process of lithium-ion power batteries and lithium-ion energy storage batteries.

[0003] As a fluorine chemical product, phosphorus pentafluoride is widely used in many fields. With the accelerated development of the lithium-ion battery industry in the future, its market space will further expand. Phosphorus pentafluoride can also be used as a catalyst and fluorinating agent in the field of chemical synthesis. As a catalyst, phosphorus pentafluoride has the advantages of high catalytic activity, increased reaction yield, accelerated reaction rate, etc. It can participate in various chemical reactions such as arylation reaction and alkylation reaction; as a fluorinating agent, phosphorus pentafluoride can participate in organic synthesis reactions such as fluorinated aromatic hydrocarbons, aldehydes, alcohols, and ketones.

[0004] The existing preparation technologies of phosphorus pentafluoride mainly include the following: 1) Phosphorus pentafluoride is obtained by synthetic reaction of elemental phosphorus and elemental fluorine. This preparation method is a process in which elemental phosphorus is added to a specific reactor, and fluorine is introduced under certain conditions to react to generate phosphorus pentafluoride. Since a certain amount of fluorine is mixed in the generated phosphorus pentafluoride target product, it is necessary to separate the fluorine through a certain separation process to obtain a high-purity phosphorus pentafluoride target product. The main disadvantages of this process are that the chemical properties of fluorine are very active, the synthetic reaction with elemental phosphorus is extremely violent, the heat release is large, the reaction is difficult to control, and the engineering control is difficult; in addition, fluorine is a highly dangerous and highly toxic substance. After the synthetic reaction, fluorine and phosphorus pentafluoride are mixed, and separation is difficult. Related patent applications include CN107619028A, CN102674275A, etc.

[0005] 2) Phosphorus pentafluoride is obtained by fluorination reaction of phosphorus-containing compounds and fluorine-containing compounds. This preparation method mainly uses phosphorus trichloride, phosphorus pentachloride and other phosphorus-containing compounds with hydrogen fluoride, calcium fluoride and other fluorine-containing compounds for fluorination reaction to synthesize phosphorus pentafluoride. When phosphorus pentafluoride is synthesized using phosphorus-containing compounds and hydrogen fluoride as raw materials, the target product contains hydrogen chloride gas, which is difficult to separate. Generally, phosphorus pentafluoride containing hydrogen chloride is directly reacted with lithium fluoride to generate lithium hexafluorophosphate, and the hydrogen chloride gas is absorbed by the tail gas as a by-product of hydrochloric acid; when phosphorus-containing compounds are subjected to fluorination reaction with fluoride salts, the reaction conditions are harsh, and the generated phosphorus pentafluoride gas contains a certain amount of moisture and dust impurities. Therefore, the main disadvantages of this process are that the target product contains gas components that are difficult to separate, or the target product contains a certain amount of moisture, dust or other metal ions, and it is difficult to obtain high-purity phosphorus pentafluoride gas. Related patent applications include CN102951620A, CN103153847A, etc.

[0006] 3) Firstly, a hexafluorophosphoric acid aqueous solution is prepared by reacting a phosphorus-containing oxide with hydrogen fluoride, and then the hexafluorophosphoric acid aqueous solution is reacted with sulfur trioxide or fuming sulfuric acid at a certain temperature. The generated gas is condensed to obtain a crude phosphorus pentafluoride product, and then a high-purity phosphorus pentafluoride gas is obtained by multi-stage distillation purification. The main disadvantages of this process are that a large amount of impurity gas is generated during the acidification reaction, which needs to be purified by multi-stage distillation. In addition, a large amount of fluorine-containing sulfuric acid is generated after the acidification reaction, which is difficult to recycle and treat, has high energy consumption, and requires large investment. Related patent applications include CN101391760A, CN104310327A, etc. Summary of the invention

[0007] The object of the present invention is to provide a method for preparing high-purity phosphorus pentafluoride by gas-liquid method, which solves the problem that the product obtained by the existing preparation method has many impurity components and is difficult to separate.

[0008] Another object of the present invention is to provide a high-purity phosphorus pentafluoride product prepared by a gas-liquid process.

[0009] The first technical solution adopted by the present invention is: a method for preparing high-purity phosphorus pentafluoride by gas-liquid method, comprising the following steps: Step 1, pre-drying the sodium fluorosilicate solid and then pyrolyzing it to obtain crude silicon tetrafluoride gas; Step 2, washing the crude silicon tetrafluoride gas with two-stage concentrated sulfuric acid to remove impurities to obtain high-purity silicon tetrafluoride gas; Step 3, adding phosphorus trichloride liquid raw material into a reactor, and introducing high-purity silicon tetrafluoride gas and chlorine gas into the reactor to react and generate silicon tetrachloride liquid and phosphorus pentafluoride gas; Step 4: Purify the phosphorus pentafluoride gas by two-stage distillation to obtain a high-purity phosphorus pentafluoride product.

[0010] The first technical solution of the present invention is also characterized in that: In step 1, the purity of the sodium fluorosilicate solid is not less than 98.5wt%, and the moisture content is not more than 0.4wt%; the sodium fluorosilicate solid is pre-dried in a calcining furnace, the pre-drying temperature is 170-200° C., the pressure is -5-5kPa, and the time is 5-8h; after pre-drying, it is sent to a pyrolysis furnace for calcination and pyrolysis, the pyrolysis temperature is 560-640° C., and the pressure is -10--5kPa.

[0011] In step 2, the crude silicon tetrafluoride gas is sequentially sent to two-stage concentrated sulfuric acid washing towers for washing, the washing temperature of the first concentrated sulfuric acid washing tower is 30-50° C., and the pressure is -3-0 kPa; the washing temperature of the second concentrated sulfuric acid washing tower is 30-50° C., and the pressure is -5--2 kPa.

[0012] In step 3, the purity of phosphorus trichloride in the phosphorus trichloride liquid raw material is not less than 98.5wt%, and the molar ratio of the phosphorus trichloride liquid raw material, chlorine gas and high-purity silicon tetrafluoride gas is 1-1.1:1:1.25.

[0013] In step 3, the ventilation rate ratio of chlorine gas to high-purity silicon tetrafluoride gas is 1:1.25.

[0014] In step 3, the reaction temperature is 70-80° C., the pressure is 0.8-1.5 MPa, and the reaction time is 5.4-6.5 h.

[0015] In step 4, phosphorus pentafluoride gas is sequentially fed into two-stage distillation towers for distillation, wherein the distillation temperature of the first distillation tower is 30-40° C. and the pressure is 2.2-3.0 MPa; the distillation temperature of the second distillation tower is 42-55° C. and the pressure is 2.8-3.5 MPa.

[0016] The second technical solution adopted by the present invention is: a high-purity phosphorus pentafluoride product is prepared by the method for preparing high-purity phosphorus pentafluoride by the gas-liquid method as mentioned above.

[0017] The beneficial effects of the present invention are as follows: compared with the existing phosphorus pentafluoride preparation technology, the method and product of the present invention for preparing high-purity phosphorus pentafluoride by the gas-liquid method have milder reaction conditions, easier reaction control, relatively lower activity of reaction raw materials, relatively lower risk, less impurity components and lower content of reaction products, easier separation and impurity removal of reaction products, and high purity of the obtained phosphorus pentafluoride target product, which meets the use index requirements of relevant industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The present invention is a schematic flow chart of the method for preparing high-purity phosphorus pentafluoride by the gas-liquid method. DETAILED DESCRIPTION

[0019] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] The present invention provides a method for preparing high-purity phosphorus pentafluoride by gas-liquid method, such as Figure 1 As shown, the following steps are included: Step 1: Send sodium fluorosilicate solid with a purity of not less than 98.5wt% and a moisture content of not more than 0.4wt% into a calcining furnace for pre-drying. The pre-drying temperature is 170-200°C, the pre-drying pressure is -5-5kPa, and the pre-drying time is 5-8h. After pre-drying, the moisture content of sodium fluorosilicate is not more than 0.05wt%. The pre-dried sodium fluorosilicate is sent to a pyrolysis furnace for high-temperature calcination and pyrolysis. The pyrolysis temperature is 560-640°C and the pyrolysis pressure is -10--5kPa. Pyrolysis obtains crude silicon tetrafluoride gas and by-product sodium fluoride solid. After complete pyrolysis, the purity of the crude silicon tetrafluoride gas is not less than 90%, and the purity of the sodium fluoride solid is not less than 98.5wt%; Step 2, sending the crude silicon tetrafluoride gas obtained in step 1 to a two-stage concentrated sulfuric acid washing tower in sequence for washing and impurity removal, wherein the washing temperature of the first-stage concentrated sulfuric acid washing tower is 30-50° C., the washing pressure is -3-0 kPa, and the purity of the silicon tetrafluoride gas after the first-stage washing is not less than 95%; the washing temperature of the second-stage concentrated sulfuric acid washing tower is 30-50° C., the washing pressure is -5--2 kPa, and the purity of the silicon tetrafluoride gas after the second-stage washing is not less than 99%, thereby obtaining high-purity silicon tetrafluoride gas; Step 3, adding a phosphorus trichloride liquid raw material with a purity of not less than 98.5wt% into a reactor, controlling the reaction temperature to 70-80°C, the reaction pressure to 0.8-1.5MPa, introducing the high-purity silicon tetrafluoride gas and chlorine raw materials obtained in step 2 into the reactor, the ventilation rate ratio of chlorine gas to high-purity silicon tetrafluoride gas is 1:1.25, the molar ratio of the phosphorus trichloride liquid raw material, chlorine gas and high-purity silicon tetrafluoride gas is 1-1.1:1:1.25, and the redox reaction generates phosphorus pentafluoride gas and a byproduct silicon tetrachloride liquid, and the reaction time is 5.4-6.5h; Step 4, the phosphorus pentafluoride gas obtained in step 3 is sequentially sent to two-stage distillation towers for distillation and purification, wherein the distillation temperature of the first distillation tower is 30-40° C., the distillation pressure is 2.2-3.0 MPa, and the purity of the phosphorus pentafluoride purified by the first distillation tower is greater than 95%; the distillation temperature of the second distillation tower is 42-55° C., and the distillation pressure is 2.8-3.5 MPa, thereby obtaining a high-purity phosphorus pentafluoride product with a purity of not less than 99%.

[0021] Through the above-mentioned manner, the gas-liquid method of the present invention for preparing high-purity phosphorus pentafluoride adopts the gas-liquid method for preparing phosphorus pentafluoride, the process flow is simple, the reaction heat effect is easy to control, the phosphorus pentafluoride after distillation and purification has high purity, can be used to produce lithium hexafluorophosphate, and can be used as an electrolyte in the fields of new energy and energy storage. In addition, the byproduct silicon tetrachloride obtained after distillation has high purity, can be used to produce trichlorosilane, and can be used as a raw material to prepare silane coupling agents and other organosilicon products.

[0022] Compared with the existing technology for preparing phosphorus pentafluoride by synthesizing elemental fluorine and elemental phosphorus, the gas phase raw material of the present invention is only chlorine gas, the activity of the reaction raw material is relatively low, the degree of danger is relatively small, and the gas phase raw material can be completely reacted when synthesized with the gas phase intermediate product silicon tetrafluoride and the liquid phase raw material phosphorus trichloride, the final gas phase product has less impurity components, the reaction conditions are milder, and the reaction is easier to control.

[0023] Compared with the existing preparation technology of phosphorus pentafluoride synthesized from phosphorus-containing compounds and fluorine-containing compounds, the final gas phase product of the present invention is only phosphorus pentafluoride with less impurity components, the reaction product is easier to separate and remove impurities, and the obtained phosphorus pentafluoride target product has high purity and can meet the use index requirements of relevant industries.

[0024] Compared with the existing aqueous phase method for synthesizing phosphorus pentafluoride, the invention has the following characteristics: the introduced gaseous raw material is only chlorine gas, the gaseous intermediate product is only silicon tetrafluoride, and the gaseous raw material can react completely with the gaseous intermediate product, the final gaseous product is only phosphorus pentafluoride, the reaction product has less impurity components and low content, the reaction product is easier to separate and remove impurities, and the obtained phosphorus pentafluoride target product has high purity, and the whole process does not generate a large amount of fluorine-containing waste acid, thereby reducing the pressure on environmental protection treatment.

[0025] Example 1 The sodium fluorosilicate solid with a content of 98.8% is transported to the calcining furnace, heated to 180°C, and pre-dried under the condition of controlling the pressure to about -2kPa, and dried for 6 hours until the moisture content of the sodium fluorosilicate is less than 0.05%. The pre-dried sodium fluorosilicate solid that has passed the test is transported to the pyrolysis furnace, heated to 600°C, and the pressure of the pyrolysis furnace is controlled to -6kPa to generate crude silicon tetrafluoride gas.

[0026] The generated crude silicon tetrafluoride gas is sequentially passed into a two-stage concentrated sulfuric acid absorption tower at a temperature of 30°C and a pressure of about -3kPa for washing and impurity removal to obtain high-purity silicon tetrafluoride gas with a purity greater than 99% for standby use.

[0027] Phosphorus trichloride with a content of 98.7% is placed in a phosphorus pentafluoride reactor, stirring is started and the temperature is raised to 75°C, the reaction pressure is controlled to be 1.0MPa, chlorine and purified silicon tetrafluoride gas are introduced into the phosphorus pentafluoride reactor at a molar ratio of 1:1.25 to react with phosphorus trichloride for 6 hours, the molar ratio of phosphorus trichloride, chlorine and silicon tetrafluoride is 1.07:1:1.25, and phosphorus pentafluoride and silicon tetrachloride are generated.

[0028] The phosphorus pentafluoride generated by the reaction was transported to a primary distillation tower, and the distillation temperature was controlled at 35°C and the distillation pressure was controlled at 2.5MPa for preliminary purification. The purity of the phosphorus pentafluoride after purification in the primary distillation tower was greater than 95%. The phosphorus pentafluoride generated after purification in the primary distillation tower was transported to a secondary distillation tower, and the distillation temperature was controlled at 44°C and the distillation pressure was controlled at 3.2MPa for secondary purification to obtain a phosphorus pentafluoride product with a purity of 99.4%. The total yield of phosphorus pentafluoride was 90.2%.

[0029] Example 2 The sodium fluorosilicate solid with a content of 99% is transported to the calcining furnace, heated to 180°C, and pre-dried under the condition of controlling the pressure to about -2kPa, and dried for 6 hours until the moisture content of the sodium fluorosilicate is less than 0.05%. The pre-dried sodium fluorosilicate solid that has passed the test is transported to the pyrolysis furnace, heated to 600°C, and the pressure of the pyrolysis furnace is controlled to -6kPa to generate crude silicon tetrafluoride gas.

[0030] The generated crude silicon tetrafluoride gas is sequentially passed into a two-stage concentrated sulfuric acid absorption tower at a temperature of 40°C and a pressure of about -2kPa for washing and impurity removal to obtain high-purity silicon tetrafluoride gas with a purity greater than 99% for standby use.

[0031] Phosphorus trichloride with a content of 99% is placed in a phosphorus pentafluoride reactor, stirring is started and the temperature is raised to 75°C, the reaction pressure is controlled to be 1.0MPa, chlorine and purified silicon tetrafluoride gas are introduced into the phosphorus pentafluoride reactor at a molar ratio of 1:1.25 to react with phosphorus trichloride for 6 hours, the molar ratio of phosphorus trichloride, chlorine and silicon tetrafluoride is 1.07:1:1.25, and phosphorus pentafluoride and silicon tetrachloride are generated.

[0032] The phosphorus pentafluoride generated by the reaction was transported to a primary distillation tower, and the distillation temperature was controlled at 35°C and the distillation pressure was controlled at 2.5MPa for preliminary purification. The purity of the phosphorus pentafluoride after purification in the primary distillation tower was greater than 95%. The phosphorus pentafluoride generated after purification in the primary distillation tower was transported to a secondary distillation tower, and the distillation temperature was controlled at 44°C and the distillation pressure was controlled at 3.2MPa for secondary purification to obtain a phosphorus pentafluoride product with a purity of 99.5%. The total yield of phosphorus pentafluoride was 90.4%.

[0033] Example 3 The sodium fluorosilicate solid with a content of 99.1% is transported to the calcining furnace, heated to 180°C, and pre-dried under the condition of controlling the pressure to about -2kPa, and dried for 6 hours until the moisture content of the sodium fluorosilicate is less than 0.05%. The pre-dried sodium fluorosilicate solid that has passed the test is transported to the pyrolysis furnace, heated to 600°C, and the pressure of the pyrolysis furnace is controlled to -6kPa to generate crude silicon tetrafluoride gas.

[0034] The generated crude silicon tetrafluoride gas is sequentially passed into a two-stage concentrated sulfuric acid absorption tower at a temperature of 30°C and a pressure of about -3kPa for washing and impurity removal to obtain high-purity silicon tetrafluoride gas with a purity greater than 99% for standby use.

[0035] Phosphorus trichloride with a content of 98.8% is placed in a phosphorus pentafluoride reactor, stirring is started and the temperature is raised to 75°C, the reaction pressure is controlled to be 1.0MPa, chlorine and purified silicon tetrafluoride gas are introduced into the phosphorus pentafluoride reactor at a molar ratio of 1:1.25 to react with phosphorus trichloride for 6 hours, the molar ratio of phosphorus trichloride, chlorine and silicon tetrafluoride is 1.07:1:1.25, and phosphorus pentafluoride and silicon tetrachloride are generated.

[0036] The phosphorus pentafluoride generated by the reaction was transported to a primary distillation tower, and the distillation temperature was controlled at 35°C and the distillation pressure was controlled at 2.5MPa for preliminary purification. The purity of the phosphorus pentafluoride after purification in the primary distillation tower was greater than 95%. The phosphorus pentafluoride generated after purification in the primary distillation tower was transported to a secondary distillation tower, and the distillation temperature was controlled at 44°C and the distillation pressure was controlled at 3.2MPa for secondary purification to obtain a phosphorus pentafluoride product with a purity of 99.4%. The total yield of phosphorus pentafluoride was 90.5%.

[0037] Example 4 The sodium fluorosilicate solid with a content of 99% is transported to the calcining furnace, heated to 170°C, and pre-dried under the condition of controlling the pressure to about -5kPa, and dried for 5 hours until the moisture content of the sodium fluorosilicate is less than 0.05%. The pre-dried sodium fluorosilicate solid that has passed the test is transported to the pyrolysis furnace, heated to 560°C, and the pressure of the pyrolysis furnace is controlled to -10kPa to generate crude silicon tetrafluoride gas.

[0038] The generated crude silicon tetrafluoride gas is introduced into a primary concentrated sulfuric acid washing tower, the washing temperature is controlled at 30°C, the washing pressure is -3kPa, and preliminary washing is performed. The purity of silicon tetrafluoride gas after the primary washing is not less than 95%; the silicon tetrafluoride gas generated after washing in the primary concentrated sulfuric acid washing tower is introduced into a secondary concentrated sulfuric acid washing tower, the washing temperature is controlled at 30°C, the washing pressure is -3kPa, and secondary washing and impurity removal are performed to obtain high-purity silicon tetrafluoride gas with a purity greater than 99% for standby use.

[0039] Phosphorus trichloride with a content of 99% is placed in a phosphorus pentafluoride reactor, stirring is started and the temperature is raised to 70°C, the reaction pressure is controlled to be 0.8MPa, chlorine and purified silicon tetrafluoride gas are introduced into the phosphorus pentafluoride reactor at a molar ratio of 1:1.25 to react with phosphorus trichloride for 5.4 hours, the molar ratio of phosphorus trichloride, chlorine and silicon tetrafluoride is 1:1:1.25, and phosphorus pentafluoride and silicon tetrachloride are generated.

[0040] The phosphorus pentafluoride generated by the reaction was transported to a primary distillation tower, and the distillation temperature was controlled at 30°C and the distillation pressure was controlled at 2.2MPa for preliminary purification. The purity of the phosphorus pentafluoride after purification in the primary distillation tower was greater than 95%. The phosphorus pentafluoride generated after purification in the primary distillation tower was transported to a secondary distillation tower, and the distillation temperature was controlled at 42°C and the distillation pressure was controlled at 2.8MPa for secondary purification to obtain a phosphorus pentafluoride product with a purity of 99%. The total yield of phosphorus pentafluoride was 90.2%.

[0041] Example 5 The sodium fluorosilicate solid with a content of 99% is transported to the calcining furnace, heated to 200°C, and pre-dried under the condition of controlling the pressure to about 5kPa, and dried for 8 hours until the moisture content of the sodium fluorosilicate is less than 0.05%. The pre-dried sodium fluorosilicate solid that has passed the test is transported to the pyrolysis furnace, heated to 640°C, and the pressure of the pyrolysis furnace is controlled to -5kPa to generate crude silicon tetrafluoride gas.

[0042] The generated crude silicon tetrafluoride gas is introduced into a primary concentrated sulfuric acid washing tower, the washing temperature is controlled at 50°C, the washing pressure is controlled at 0kPa, and preliminary washing is performed. The purity of silicon tetrafluoride gas after primary washing is not less than 95%; the silicon tetrafluoride gas generated after washing in the primary concentrated sulfuric acid washing tower is introduced into a secondary concentrated sulfuric acid washing tower, the washing temperature is controlled at 50°C, the washing pressure is controlled at -5kPa, and secondary washing is performed to remove impurities, and high-purity silicon tetrafluoride gas with a purity greater than 99% is obtained for standby use.

[0043] Phosphorus trichloride with a content of 99% is placed in a phosphorus pentafluoride reactor, stirring is started and the temperature is raised to 80°C, the reaction pressure is controlled to be 1.5MPa, chlorine and purified silicon tetrafluoride gas are introduced into the phosphorus pentafluoride reactor at a molar ratio of 1:1.25 to react with phosphorus trichloride for 6.5 hours, and the molar ratio of phosphorus trichloride, chlorine and silicon tetrafluoride is 1.1:1:1.25 to generate phosphorus pentafluoride and silicon tetrachloride.

[0044] The phosphorus pentafluoride generated by the reaction is transported to a primary distillation tower, and the distillation temperature is controlled at 40°C and the distillation pressure is controlled at 3.0MPa for preliminary purification. The purity of the phosphorus pentafluoride after purification in the primary distillation tower is greater than 95%; the phosphorus pentafluoride generated after purification in the primary distillation tower is transported to a secondary distillation tower, and the distillation temperature is controlled at 55°C and the distillation pressure is controlled at 3.5MPa for secondary purification to obtain a phosphorus pentafluoride product with a purity of 99.7%. The total yield of phosphorus pentafluoride is 90.6%.

[0045] Example 6 (Comparative Example) The sodium fluorosilicate solid with a content of 99.2% is transported to the calcining furnace, heated to 180°C, and pre-dried under the condition of controlling the pressure to about -2kPa, and dried for 6 hours until the moisture content of the sodium fluorosilicate is less than 0.05%. The pre-dried sodium fluorosilicate solid that has passed the test is transported to the pyrolysis furnace, heated to 600°C, and the pressure of the pyrolysis furnace is controlled to -6kPa to generate crude silicon tetrafluoride gas.

[0046] The generated crude silicon tetrafluoride gas is sequentially passed into a two-stage concentrated sulfuric acid absorption tower at a temperature of 30°C and a pressure of about -3kPa for washing and impurity removal to obtain high-purity silicon tetrafluoride gas with a purity greater than 99% for standby use.

[0047] Phosphorus trichloride with a content of 98.8% is placed in a phosphorus pentafluoride reactor, stirring is started and the temperature is raised to 75°C, the reaction pressure is controlled to be 1.0MPa, chlorine and purified silicon tetrafluoride gas are introduced into the phosphorus pentafluoride reactor at a molar ratio of 1.1:1.25 to react with phosphorus trichloride for 6 hours, the molar ratio of phosphorus trichloride, chlorine and silicon tetrafluoride is 1.07:1.1:1.25, and phosphorus pentafluoride and silicon tetrachloride are generated.

[0048] The phosphorus pentafluoride generated by the reaction was transported to a primary distillation tower, and the distillation temperature was controlled at 35°C and the distillation pressure was controlled at 2.5MPa for preliminary purification; the phosphorus pentafluoride generated after purification in the primary distillation tower was transported to a secondary distillation tower, and the distillation temperature was controlled at 44°C and the distillation pressure was controlled at 3.2MPa for secondary purification to obtain a phosphorus pentafluoride product with a purity of 93.2%. The total yield of phosphorus pentafluoride was 90.1%.

Claims

1. A method for preparing high-purity phosphorus pentafluoride by a gas-liquid process, characterized in that: The following steps are involved: Step 1, pre-drying the sodium fluorosilicate solid and then pyrolyzing it to obtain crude silicon tetrafluoride gas; Step 2, washing the crude silicon tetrafluoride gas with two-stage concentrated sulfuric acid to remove impurities to obtain high-purity silicon tetrafluoride gas; Step 3, adding phosphorus trichloride liquid raw material into a reactor, and introducing high-purity silicon tetrafluoride gas and chlorine gas into the reactor to react and generate silicon tetrachloride liquid and phosphorus pentafluoride gas; Step 4: Purify the phosphorus pentafluoride gas by two-stage distillation to obtain a high-purity phosphorus pentafluoride product.

2. The method for preparing high-purity phosphorus pentafluoride by the gas-liquid method according to claim 1, characterized in that: In the step 1, the purity of the sodium fluorosilicate solid is not less than 98.5wt%, and the moisture content is not more than 0.4wt%; the sodium fluorosilicate solid is pre-dried in a calcining furnace, the pre-drying temperature is 170-200°C, the pressure is -5-5kPa, and the time is 5-8h; after pre-drying, it is sent to a pyrolysis furnace for calcination and pyrolysis, the pyrolysis temperature is 560-640°C, and the pressure is -10--5kPa.

3. The method for preparing high-purity phosphorus pentafluoride by the gas-liquid method according to claim 1, characterized in that: In the step 2, the crude silicon tetrafluoride gas is sequentially sent to two-stage concentrated sulfuric acid washing towers for washing, the washing temperature of the first concentrated sulfuric acid washing tower is 30-50° C., and the pressure is -3-0 kPa; the washing temperature of the second concentrated sulfuric acid washing tower is 30-50° C., and the pressure is -5--2 kPa.

4. The method for preparing high-purity phosphorus pentafluoride by the gas-liquid method according to claim 1, characterized in that: In the step 3, the purity of phosphorus trichloride in the phosphorus trichloride liquid raw material is not less than 98.5wt%, and the molar ratio of the phosphorus trichloride liquid raw material, chlorine gas and high-purity silicon tetrafluoride gas is 1-1.1:1:1.

25.

5. The method for preparing high-purity phosphorus pentafluoride by the gas-liquid method according to claim 1, characterized in that: In step 3, the ventilation rate ratio of chlorine gas to high-purity silicon tetrafluoride gas is 1:1.

25.

6. The method for preparing high-purity phosphorus pentafluoride by the gas-liquid method according to claim 1, characterized in that: In step 3, the reaction temperature is 70-80° C., the pressure is 0.8-1.5 MPa, and the reaction time is 5.4-6.5 h.

7. The method for preparing high-purity phosphorus pentafluoride by the gas-liquid method according to claim 1, characterized in that: In the step 4, phosphorus pentafluoride gas is sequentially fed into two-stage distillation towers for distillation, wherein the distillation temperature of the first distillation tower is 30-40° C. and the pressure is 2.2-3.0 MPa; the distillation temperature of the second distillation tower is 42-55° C. and the pressure is 2.8-3.5 MPa.

8. A high-purity phosphorus pentafluoride product obtained by the method for preparing high-purity phosphorus pentafluoride by the gas-liquid method as claimed in any one of claims 1 to 7.

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