Method for recycling phosphorus pentafluoride in lithium hexafluorophosphate tail gas

Abstract

The invention discloses a method for recycling phosphorus pentafluoride in lithium hexafluorophosphate tail gas. The method specifically comprises the following steps: introducing the lithium hexafluorophosphate tail gas into an absorption and crystallizer to obtain a hexafluorophosphoric acid crystal; enabling the hexafluorophosphoric acid crystal to pass through a dehydrator and a generator to obtain a mixed gas of phosphorus pentafluoride and hydrogen fluoride, and introducing the mixed gas into a lithium hexafluorophosphate production system to obtain a lithium hexafluorophosphate product; the method provided by the invention effectively solves the problems of waste of phosphorus pentafluoride generated by wet synthesis of lithium hexafluorophosphate and treatment cost of fluorine-containing liquid; the quality and the yield of the lithium hexafluorophosphate product are improved; the quality of byproduct hydrofluoric acid is improved, and the added value of the product is increased; the consumption of hydrogen fluoride and PCl5 is reduced, and the use efficiency is improved.

Description

Technical Field

[0001] This invention relates to a method for reusing phosphorus pentafluoride in lithium hexafluorophosphate tail gas. Background Technology

[0002] Lithium hexafluorophosphate (LiPF6) is currently the optimal choice for lithium-ion battery electrolytes due to its excellent thermal stability and ionic conductivity. Currently, LiPF6 synthesized from PCl5, hydrogen fluoride, and LiF has significant advantages in terms of cost and industrial production. To improve the quality of LiPF6 (reduce the LiF insoluble content) and ensure complete LiF reaction, an additional 9% to 25% of PCl5 is required in production. However, the resulting excess phosphorus pentafluoride not only wastes raw materials but also harms the environment.

[0003] In the production process, phosphorus pentafluoride in lithium hexafluorophosphate tail gas is typically absorbed by large amounts of water, converting it into a mixed acid solution of phosphoric acid and hydrofluoric acid. Some companies, unaffected by acid quality, apply this mixed acid solution to industrial processes. While this directly utilizes the acid, it results in H3PO4 wastewater entering industrial wastewater. Treating phosphorus-containing wastewater has drawbacks such as high cost, complex processes, and long treatment times. Chemical precipitation is one of the fastest and most efficient methods for removing phosphorus, but the large amount of sludge generated further increases treatment costs and poses greater environmental risks.

[0004] Some companies have requirements regarding the presence of sulfur ions in their waste acids. Due to the special properties of sulfur ions, the reuse methods should be simplified to improve safety. However, in existing treatment methods, sulfur ion separation processes mostly use organic solvents (such as CCl4) for adsorption. But these toxic substances require highly skilled operators and also pose environmental hazards.

[0005] Therefore, this invention provides a method for reusing phosphorus pentafluoride in lithium hexafluorophosphate tail gas, which solves the environmental pollution and resource waste problems caused by excessive use of phosphorus pentafluoride from the source. Summary of the Invention

[0006] A method for reusing phosphorus pentafluoride in lithium hexafluorophosphate tail gas, wherein the lithium hexafluorophosphate tail gas contains hydrogen chloride, hydrogen fluoride, and phosphorus pentafluoride gas, with a hydrogen chloride content of 47%~52%, a hydrogen fluoride content of 12%~17%, and a phosphorus pentafluoride content of 33%~37%; characterized by the following steps: 1) The tail gas of lithium hexafluorophosphate is sequentially passed into an absorption tower to obtain hydrogen chloride gas and a mixed gas of hydrogen fluoride and phosphorus pentafluoride. The mixed gas of hydrogen fluoride and phosphorus pentafluoride is then passed into a crystallizer to obtain hexafluorophosphate crystals. 2) After passing the hexafluorophosphate crystals through a dehydrator and a generator, a mixture of hydrogen fluoride and phosphorus pentafluoride gas is obtained again; 3) The mixture of hydrogen fluoride and phosphorus pentafluoride obtained above is passed into the lithium hexafluorophosphate production system to obtain lithium hexafluorophosphate product.

[0007] According to claim 1, the method for reusing phosphorus pentafluoride in lithium hexafluorophosphate tail gas is further designed in step 1), wherein the lithium hexafluorophosphate tail gas is introduced into an absorption tower, the absorption tower operates at a temperature of less than 70°C, a pressure of -0.01 kPa to -1 kPa, and an absorption time of 10 h to 24 h.

[0008] According to claim 1, the method for reusing phosphorus pentafluoride in lithium hexafluorophosphate tail gas is further designed in step 1), wherein the lithium hexafluorophosphate tail gas is introduced into an absorption tower and the amount of absorption solution is 15% to 25% of the amount of absorption gas.

[0009] According to claim 1, a method for reusing phosphorus pentafluoride in lithium hexafluorophosphate tail gas is further designed in step 1), in which a mixed gas of hydrogen fluoride and phosphorus pentafluoride is introduced into a crystallizer, the crystallizer temperature is -5℃~5℃, the pressure inside the vessel is -0.01kPa~-1kPa, and the crystallization time is 10h~24h.

[0010] According to claim 1, the method for reusing phosphorus pentafluoride in lithium hexafluorophosphate tail gas is further designed in that the dehydrating agent in step 2) is fuming sulfuric acid, the dehydration temperature is controlled below 50°C, and the gas flow rate is 80 ml / min ~ 120 ml / min.

[0011] According to claim 1, the method for reusing phosphorus pentafluoride in lithium hexafluorophosphate tail gas is further designed such that the temperature in the generator in step 2) is 60℃~90℃ and the reaction pressure is 10kPa~50kPa.

[0012] According to claim 1, the method for reusing phosphorus pentafluoride in lithium hexafluorophosphate tail gas is further designed in that the total water content of the mixed gas introduced into the lithium hexafluorophosphate production system in step 3) is less than 1 ppm.

[0013] According to claim 1, the method for reusing phosphorus pentafluoride in lithium hexafluorophosphate tail gas is further designed in that the lithium hexafluorophosphate obtained in step 3) has a purity ≥99.95%, a free acid content ≤70ppm, an insoluble matter content ≤120ppm, a moisture content ≤5ppm, and a metal content ≤1ppm.

[0014] The beneficial effects of this invention are: 1. The wet synthesis of lithium hexafluorophosphate produces a mixed gas containing hydrogen fluoride, phosphorus pentafluoride, and HCl. This invention improves the quality of the by-product hydrochloric acid by means of crystallization.

[0015] 2. The present invention uses a phosphorus pentafluoride recycling process, which greatly improves the utilization rate of phosphorus pentafluoride and increases the product yield.

[0016] 3. The present invention uses a phosphorus pentafluoride recycling process, which reduces the phosphorus content in the by-product hydrofluoric acid and improves the quality of the by-product hydrofluoric acid. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the absorption tower and crystallizer used in step 2) of the present invention. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] The effects of the present invention are verified using the following embodiments: 1. Pass the lithium hexafluorophosphate tail gas (0.9t phosphorus pentafluoride, 1.25t HCl, 0.35t hydrogen fluoride) into the... Figure 1 The absorption tower and crystallizer shown are configured with a temperature of 60℃ and a pressure of -1 kPa, with an absorption solution of 0.5 t (water). The crystallizer is configured with a pressure of -5℃ and a pressure of -1 kPa. The absorption and crystallization process takes a total of 24 hours, yielding 1.3 t of hexafluorophosphate crystals, 0.45 t of hydrofluoric acid (with a phosphorus ion content of 4.2%), and 1.25 t of HCl gas.

[0020] 2. Hexafluorophosphate crystals are pumped at a rate of 80 ml / min to a fuming sulfuric acid solution for dehydration (the temperature inside the reactor is controlled at 40℃) to obtain a mixed gas of hydrogen fluoride and phosphorus pentafluoride of 0.95 t. The mixed gas of phosphorus pentafluoride and hydrogen fluoride is obtained by passing it through an 80℃, 50kPa generator. 3. Passing the above mixed gas into the lithium hexafluorophosphate production system yields 0.99t of lithium hexafluorophosphate product; The lithium hexafluorophosphate product obtained from the tail gas of lithium hexafluorophosphate production has a purity of 99.991%, a moisture content of 4 ppm, a free acid content of 60 ppm, a metal content of 1 ppm, an insoluble matter content of 40 ppm, and a phosphorus pentafluoride utilization rate of 91.66%.

[0021] The inventive point of this invention lies in using an absorption tower to separate hydrogen chloride, then using a crystallizer to obtain hexafluorophosphate crystals, and then using the hexafluorophosphate crystals to generate a mixed gas of hydrogen fluoride and phosphorus pentafluoride to participate in the lithium hexafluorophosphate production system, thereby reducing the phosphorus content in the by-product hydrofluoric acid and improving the quality of the by-product hydrofluoric acid.

Claims

1. A method for reusing phosphorus pentafluoride in lithium hexafluorophosphate tail gas, wherein the lithium hexafluorophosphate tail gas contains hydrogen chloride, hydrogen fluoride, and phosphorus pentafluoride gas, wherein the hydrogen chloride content is 47%~52%, the hydrogen fluoride content is 12%~17%, and the phosphorus pentafluoride content is 33%~37%; characterized in that... The following steps: 1) The tail gas of lithium hexafluorophosphate is sequentially passed into an absorption tower to obtain hydrogen chloride gas and a mixed gas of hydrogen fluoride and phosphorus pentafluoride. The mixed gas of hydrogen fluoride and phosphorus pentafluoride is then passed into a crystallizer to obtain hexafluorophosphate crystals. 2) After passing the hexafluorophosphate crystals through a dehydrator and a generator, a mixture of hydrogen fluoride and phosphorus pentafluoride gas is obtained again; 3) The mixture of hydrogen fluoride and phosphorus pentafluoride obtained above is passed into the lithium hexafluorophosphate production system to obtain lithium hexafluorophosphate product.

2. The method for reusing phosphorus pentafluoride in lithium hexafluorophosphate tail gas according to claim 1, characterized in that... In step 1), the lithium hexafluorophosphate tail gas is introduced into the absorption tower. The operating temperature of the absorption tower is less than 70°C, the pressure is -0.01kPa to -1kPa, and the absorption time is 10h to 24h.

3. The method for reusing phosphorus pentafluoride in lithium hexafluorophosphate tail gas according to claim 1, characterized in that... In step 1), the lithium hexafluorophosphate tail gas is introduced into the absorption tower, and the amount of absorption solution is 15% to 25% of the amount of absorption gas.

4. The method for reusing phosphorus pentafluoride in lithium hexafluorophosphate tail gas according to claim 1, characterized in that... In step 1), a mixture of hydrogen fluoride and phosphorus pentafluoride gas is introduced into the crystallizer. The crystallizer temperature is -5℃ to 5℃, the pressure inside the vessel is -0.01kPa to -1kPa, and the crystallization time is 10h to 24h.

5. The method for reusing phosphorus pentafluoride in lithium hexafluorophosphate tail gas according to claim 1, characterized in that... In step 2), the dehydrating agent is fuming sulfuric acid, the dehydration temperature is controlled below 50℃, and the gas flow rate is 80 ml / min ~ 120 ml / min.

6. The method for reusing phosphorus pentafluoride in lithium hexafluorophosphate tail gas according to claim 1, characterized in that... In step 2), the temperature in the generator is 60℃~90℃ and the reaction pressure is 10kPa~50kPa.

7. The method for reusing phosphorus pentafluoride in lithium hexafluorophosphate tail gas according to claim 1, characterized in that... In step 3), the total water content of the mixed gas introduced into the lithium hexafluorophosphate production system is less than 1 ppm.

8. The method for reusing phosphorus pentafluoride in lithium hexafluorophosphate tail gas according to claim 1, characterized in that... Step 3) The purity of the lithium hexafluorophosphate obtained is ≥99.95%, the free acid content is ≤70ppm, the insoluble matter content is ≤120ppm, the moisture content is ≤5ppm, and the metal content is ≤1ppm.

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