Preparation method of phosphorus pentafluoride gas

Abstract

The invention discloses a preparation method of phosphorus pentafluoride gas, and belongs to the technical field of chemical engineering, the preparation method comprises the following steps: introducing HF gas into a polyphosphoric acid solution to generate a hexafluorophosphoric acid solution; adding a phosphorus pentoxide solid into the hexafluorophosphoric acid solution, and stirring to obtain a mixed acid solution; transferring the mixed acid solution to a gas production tower for gas-liquid separation, and carrying out sodium fluoride deacidification treatment on the gas to obtain phosphorus pentafluoride gas; the content of phosphorus pentafluoride in the phosphorus pentafluoride gas reaches 99.95% or above, and basically no by-product is generated.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical engineering, and in particular relates to a method for preparing phosphorus pentafluoride gas. Background Art

[0002] In recent years, among many new energy fields, lithium-ion batteries have been widely and deeply used in electric vehicles, portable electronic devices, energy storage systems and many other fields due to their significant advantages such as high energy density, long cycle life and green environmental protection, and their market size continues to expand. As a key component of lithium-ion batteries, electrolyte plays a vital role in the performance of batteries, so it has the reputation of "the blood of lithium-ion batteries", and its market demand has also shown a trend of significant increase year by year.

[0003] Among the numerous electrolyte raw materials, lithium hexafluorophosphate has become the most commonly used lithium salt in electrolytes due to its excellent electrochemical properties. At present, in the field of industrial production, a widely used process is to prepare lithium hexafluorophosphate by mixed acid gas production. Specifically, this process first uses the chemical reaction between hydrogen fluoride and polyphosphoric acid to prepare a hexafluorophosphate solution, then reacts the hexafluorophosphate solution with sulfuric acid to prepare phosphorus pentafluoride, and finally reacts phosphorus pentafluoride with a lithium salt to obtain the target product, lithium hexafluorophosphate.

[0004] However, during the implementation of this process, when the hexafluorophosphoric acid solution reacts with sulfuric acid, a series of by-products such as fluorosulfonic acid and phosphoric acid will be produced, and these by-products are usually mixed in the excess sulfuric acid. This not only makes the separation and purification of the by-products extremely difficult, but also the subsequent treatment process is very complicated. At the same time, if these by-products are not handled properly, they will cause serious pollution and damage to the surrounding ecological environment, greatly increase the environmental pressure and production costs of enterprises, and to a certain extent restrict the sustainable development of the entire industry.

[0005] In summary, the conventional method for preparing phosphorus pentafluoride gas produces a large amount of by-products which are difficult to handle during the preparation of phosphorus pentafluoride, and the obtained phosphorus pentafluoride gas has low purity. Summary of the invention

[0006] The invention provides a method for preparing phosphorus pentafluoride gas, so as to solve the technical problem of low purity of phosphorus pentafluoride prepared in the prior art.

[0007] In order to achieve the above-mentioned invention object, the technical solution provided by the present invention is as follows:

[0008] A method for preparing phosphorus pentafluoride gas comprises the following steps:

[0009] S1, adding the polyphosphoric acid solution into liquid HF to carry out reaction 1 to generate a hexafluorophosphoric acid solution;

[0010] S2, transferring the hexafluorophosphoric acid solution to a dehydration tank, adding phosphorus pentoxide solid and stirring for 4 to 5 hours to obtain a mixed acid solution;

[0011] S3, transferring the mixed acid solution to a gas production tower for gas-liquid separation, and then subjecting the separated gas to deacidification treatment with sodium fluoride to obtain phosphorus pentafluoride gas.

[0012] Preferably, the molar ratio of polyphosphoric acid to HF in S1 is 1:16.5-24.

[0013] Preferably, the reaction temperature of reaction 1 in S1 is ≤19.5°C, and the reaction time is 2 to 6 hours.

[0014] Preferably, the mass concentration of the hexafluorophosphoric acid solution in S1 is 60% to 71%.

[0015] Preferably, the molar ratio of phosphorus pentoxide to the polyphosphoric acid in the phosphorus pentoxide solid in S2 is 3 to 4.5:1.

[0016] Preferably, the temperature of the gas-liquid separation in S3 is 100-150° C., the pressure is 0.05-0.1 MPa, and the time is 4-5 hours.

[0017] Preferably, the water in the hexafluorophosphoric acid solution in S2 is absorbed by the phosphorus pentoxide solid.

[0018] Compared with the prior art, the beneficial effects of the present invention include:

[0019] (1) The phosphorus pentafluoride prepared by the present invention has only polyphosphoric acid, HF and phosphorus pentoxide as raw materials. The polyphosphoric acid solution is reacted with HF to generate a hexafluorophosphoric acid solution. The hexafluorophosphoric acid solution and phosphorus pentoxide solid are mixed to form a mixed acid solution, and then the gas-liquid separation is performed. After the gas is treated with sodium fluoride, high-purity phosphorus pentafluoride gas and polyphosphoric acid are obtained. The whole process does not generate by-product sulfuric acid, has little pressure on the environment, and saves the treatment cost of the by-product sulfuric acid.

[0020] (2) The phosphorus pentoxide in the present invention has a stronger water absorption than oleum. Therefore, phosphorus pentoxide is used to replace oleum in the traditional process to absorb the water in the hexafluorophosphoric acid solution. The generated polyphosphoric acid can continue to react with HF in the mixed acid and HF generated in the subsequent gas production process. Therefore, the phosphorus pentoxide added in the present invention has two functions of absorbing water and HF gas, which plays a role in improving the purity of phosphorus pentafluoride gas.

[0021] (3) The product of the mixed acid solution after the gas production process in the present invention is polyphosphoric acid, which can be reused as a raw material for synthesizing hexafluorophosphoric acid, thereby greatly improving the utilization rate of raw materials and saving raw material costs. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Example 1

[0024] This embodiment provides a method for preparing phosphorus pentafluoride gas, comprising the following steps:

[0025] S1. Take 24 mol of liquid HF, slowly add a polyphosphoric acid solution containing 1 mol of polyphosphoric acid thereto, and carry out reaction 1 at a reaction temperature of 10° C. for a reaction time of 6 h to generate a hexafluorophosphoric acid solution with a mass concentration of 71%;

[0026] S2, transferring the hexafluorophosphoric acid solution to a dehydration tank, adding 4.5 mol of phosphorus pentoxide solid and stirring for 5 hours to obtain a mixed acid solution; wherein the phosphorus pentoxide solid is used to remove water from the hexafluorophosphoric acid solution;

[0027] S3. The mixed acid solution is transferred to a gas production tower for gas-liquid separation. The gas-liquid separation temperature is 100° C., the pressure is 0.05 MPa, and the time is 6 hours. The gas is treated with sodium fluoride to obtain phosphorus pentafluoride gas.

[0028] Example 2

[0029] This embodiment provides a method for preparing phosphorus pentafluoride gas, comprising the following steps:

[0030] S1. Take 16.5 mol of liquid HF, slowly add a polyphosphoric acid solution containing 1 mol of polyphosphoric acid thereto, and carry out reaction 1 at a reaction temperature of 19.5° C. for a reaction time of 2 h to generate a hexafluorophosphoric acid solution with a mass concentration of 60%;

[0031] S2, transfer the hexafluorophosphoric acid solution to a dehydration tank, add 3 mol of phosphorus pentoxide solid and stir for 4 hours to obtain a mixed acid solution;

[0032] S3. The mixed acid solution is transferred to a gas production tower for gas-liquid separation. The gas-liquid separation temperature is 150° C., the pressure is 0.1 MPa, and the time is 2 hours. The gas is treated with sodium fluoride to obtain phosphorus pentafluoride gas.

[0033] Example 3

[0034] This embodiment provides a method for preparing phosphorus pentafluoride gas, comprising the following steps:

[0035] S1. Take 19.5 mol of liquid HF, slowly add a polyphosphoric acid solution containing 1 mol of polyphosphoric acid thereto, and carry out reaction 1 at a reaction temperature of 18.5° C. for 5 h to generate a hexafluorophosphoric acid solution with a mass concentration of 65%;

[0036] S2, transfer the hexafluorophosphoric acid solution to a dehydration tank, add 3.5 mol of phosphorus pentoxide solid and stir for 4.5 hours to obtain a mixed acid solution;

[0037] S3. The mixed acid solution is transferred to a gas production tower for gas-liquid separation. The gas-liquid separation temperature is 120° C., the pressure is 0.06 MPa, and the time is 5 hours. The gas is treated with sodium fluoride to obtain phosphorus pentafluoride gas.

[0038] Comparative Example

[0039] This comparative example provides a method for preparing phosphorus pentafluoride gas, comprising the following steps:

[0040] S1. Take a polyphosphoric acid solution containing 1 mol of polyphosphoric acid, introduce 24 mol of HF gas, and carry out reaction 1 at a reaction temperature of 10° C. for a reaction time of 6 h to generate a hexafluorophosphoric acid solution with a mass concentration of 71%;

[0041] S2, transferring the hexafluorophosphoric acid solution to a dehydration tank, adding 15 mol of fuming sulfuric acid to obtain a mixed acid solution;

[0042] S3. The mixed acid solution is transferred to a gas production tower for gas-liquid separation. The gas-liquid separation temperature is 100° C., the pressure is 0.05 MPa, and the time is 6 hours. The gas is treated with sodium fluoride to obtain phosphorus pentafluoride gas.

[0043] The comparative example adopts the traditional process. Compared with Example 1, the difference is that oleum is used as a dehydrating agent in the comparative example. Oleum itself has strong oxidizing and corrosive properties. During operation, the corrosion resistance of the equipment is extremely high, and there are safety risks. Once leaked, it will cause serious environmental pollution and safety accidents. Secondly, when oleum reacts with HF in the mixed acid solution, by-products such as fluorosulfonic acid and hydrofluoric acid may be generated. These substances are not only difficult to remove but also may corrode the equipment.

[0044] The phosphorus pentafluoride gas prepared in Examples 1-3 and the comparative example was taken and its purity was measured. The test results are shown in Table 1.

[0045] Table 1 Phosphorus pentafluoride gas detection results:

[0046] Group Phosphorus pentafluoride content HF content Moisture content Example 1 ≥99.95％ 15ppm 11ppm Example 2 ≥99.95％ 20ppm 8ppm Example 3 ≥99.95％ 18ppm 9ppm Comparative Example ≥99.95％ 40ppm 25ppm

[0047] It can be seen from the data in the table that the purity of the phosphorus pentafluoride gas obtained in the comparative example is significantly lower than that in Examples 1-3.

[0048] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. The protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for preparing phosphorus pentafluoride gas, characterized in that: The following steps are involved: S1, adding the polyphosphoric acid solution into liquid HF to carry out reaction 1 to generate a hexafluorophosphoric acid solution; S2, transferring the hexafluorophosphoric acid solution to a dehydration tank, adding phosphorus pentoxide solid and stirring for 4 to 5 hours to obtain a mixed acid solution; S3, transferring the mixed acid solution to a gas production tower for gas-liquid separation, and then subjecting the separated gas to deacidification treatment with sodium fluoride to obtain phosphorus pentafluoride gas.

2. The method for preparing phosphorus pentafluoride gas according to claim 1, characterized in that: The molar ratio of polyphosphoric acid to HF in S1 is 1:16.5-24.

3. The method for preparing phosphorus pentafluoride gas according to claim 1, characterized in that: The reaction temperature of reaction 1 in S1 is ≤19.5°C, and the reaction time is 2 to 6 hours.

4. The method for preparing phosphorus pentafluoride gas according to claim 1, characterized in that: The mass concentration of the hexafluorophosphoric acid solution in S1 is 60% to 71%.

5. The method for preparing phosphorus pentafluoride gas according to claim 1, characterized in that: The molar ratio of phosphorus pentoxide to polyphosphoric acid in the phosphorus pentoxide solid in S2 is 3 to 4.5:

1.

6. The method for preparing phosphorus pentafluoride gas according to claim 1, characterized in that: The temperature of the gas-liquid separation in S3 is 100-150° C., the pressure is 0.05-0.1 MPa, and the time is 4-5 hours.

7. The method for preparing phosphorus pentafluoride gas according to claim 1, characterized in that: The water in the hexafluorophosphoric acid solution in S2 is absorbed by the phosphorus pentoxide solid.