Continuous refining equipment and method for sodium hexafluorophosphate

Abstract

This invention discloses a continuous refining apparatus for sodium hexafluorophosphate, including a precooler. The precooler is sequentially connected to at least one refining unit, a buffer unit, and a solid-liquid separation unit. The liquid outlet of each refining unit is connected to the feed inlet via a heat exchanger, and the liquid outlet of the solid-liquid separation unit is connected to the feed inlet of the final refining unit. The invention also relates to a continuous refining apparatus and method for sodium hexafluorophosphate. The sodium hexafluorophosphate raw material liquid obtained from reaction synthesis is cooled by the precooler and then injected into the first-stage refining unit. The temperature inside the refining unit is controlled, and the slurry is continuously discharged from the outlet of the first-stage refining unit and sequentially injected into the buffer unit and the solid-liquid separation unit. Simultaneously, the mother liquor from each refining unit is cooled by the heat exchanger and then enters the feed inlet. The solid discharged from the solid-liquid separation unit is collected to obtain sodium hexafluorophosphate crystals, and the mother liquor discharged from the solid-liquid separation unit is returned to the final refining unit. This method can improve the quality of sodium hexafluorophosphate products.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical method technology, and relates to a continuous refining equipment for sodium hexafluorophosphate, as well as a refining method using the continuous refining equipment for sodium hexafluorophosphate. Background Technology

[0002] With the further development of human society, energy depletion and ecological pollution are gradually intensifying, making the development and exploration of sustainable new energy sources and the selection of suitable energy storage technologies imperative. New types of batteries, with advantages such as high energy density, low self-discharge rate, and long cycle life, have become the main development direction of the new energy storage industry. These new batteries are mainly lithium-ion batteries and sodium-ion batteries. Compared to lithium-ion batteries, sodium-ion batteries are widely available and inexpensive, making them a superior choice for energy storage and other fields where high energy density is not required. Sodium hexafluorophosphate (CAS: 21324-39-0, relative molecular mass: 167.954), with the molecular formula NaPF6 and a relative density of 2.369, is a colorless cubic crystal. It is sensitive to air and carbon dioxide, highly soluble in water, and also soluble in methanol, ethanol, acetone, and ethyl acetate. As an electrolyte for sodium-ion batteries, sodium hexafluorophosphate has advantages such as high conductivity and stable solid-state electrolyte interface, making it a hot topic in sodium-ion battery research. However, impurities can increase the internal resistance of sodium-ion batteries, threatening battery safety. Therefore, the refining of sodium hexafluorophosphate is crucial for the development of sodium-ion batteries.

[0003] CN113772694 A discloses a method for preparing high-purity sodium hexafluorophosphate, relating to the field of sodium-ion battery technology. The preparation steps include: (1) adding battery-grade LiPF6 to a pyrolysis reactor under nitrogen protection; (2) heating the pyrolysis reactor to a certain temperature and keeping it warm for a period of time to allow LiPF6 to decompose completely; (3) adding an appropriate amount of solvent to a synthesis reactor, and then adding a certain amount of high-purity sodium fluoride and stirring to dissolve it at a certain temperature; (4) introducing the gas generated in (2) into the synthesis reactor and fluidizing it under certain conditions to obtain a sodium hexafluorophosphate synthesis solution; (5) after the reaction is completed, filtering the synthesis solution to remove insoluble matter and obtaining a synthesis mother liquor; (6) cooling and crystallizing the synthesis mother liquor and filtering it; (7) vacuum drying the solid material to obtain the finished sodium hexafluorophosphate product, and recycling the crystallization mother liquor for dissolving sodium fluoride. CN114772614A discloses a low-temperature synthesis method for high-purity sodium hexafluorophosphate, comprising the following steps: dissolving sodium fluoride in an organic solvent solution containing Freon to obtain a solution; introducing phosphorus pentafluoride gas into the solution, reacting under low-temperature vacuum for a set time, then restoring to atmospheric pressure, evaporating Freon and the organic solvent to obtain sodium hexafluorophosphate; the reaction temperature under low-temperature vacuum is -50 to 10°C, and the reaction pressure is -0.2 to 0 MPa. CN115872385A relates to a purification method for sodium hexafluorophosphate, which involves removing acidic substances from a crude sodium hexafluorophosphate product solution, aging, filtering, and then spray-drying and intensively drying the filtered liquid to obtain purified sodium hexafluorophosphate.

[0004] The main evaluation indicators for product quality include crystal habit, particle size, moisture content, and quantitative content. Poor crystal habit and particle size can lead to a large amount of solvent residue, which in turn seriously affects the determination of mass fraction and reduces product quality. Currently, existing patents mainly focus on high-purity synthesis methods for sodium hexafluorophosphate, but refining technologies for obtaining sodium hexafluorophosphate products with uniform particle size and good flowability have not received sufficient attention. In addition, the preparation of sodium hexafluorophosphate crystals is mostly done through intermittent crystallization, which is prone to agglomeration, requiring crushing and re-drying, increasing production costs, and causing large batch-to-batch variations, thus limiting equipment utilization and capacity optimization. Summary of the Invention

[0005] The purpose of this invention is to provide a continuous refining equipment for sodium hexafluorophosphate, which solves the problem of poor particle size uniformity in the prior art.

[0006] The technical solution adopted in this invention is a continuous refining equipment for sodium hexafluorophosphate, including a precooler. The precooler is sequentially connected to at least one refining device, a buffer device, and a solid-liquid separation device. The liquid outlet of each refining device is connected to the feed inlet through a heat exchange device, and the liquid outlet of the solid-liquid separation device is connected to the feed inlet of the final refining device.

[0007] The invention is further characterized by:

[0008] The refining device is a crystallizer.

[0009] Another object of the present invention is to provide a continuous purification method for sodium hexafluorophosphate.

[0010] Another technical solution adopted in this invention is a continuous refining method for sodium hexafluorophosphate, which uses the aforementioned continuous refining equipment for sodium hexafluorophosphate and includes the following steps:

[0011] Step 1: After the sodium hexafluorophosphate raw material solution obtained by the reaction synthesis is cooled by a precooler, it is injected into the first-stage purification unit;

[0012] Step 2: Control the temperature inside the refining unit and maintain it for a period of time. Then, continuously discharge the slurry from the outlet of the primary refining unit and inject it into the buffer unit and solid-liquid separation unit in sequence. At the same time, the mother liquor of each refining unit is cooled by the heat exchanger and then enters the feed inlet.

[0013] Step 3: Collect the solid discharged from the solid-liquid separation device to obtain sodium hexafluorophosphate crystals. The mother liquor discharged from the solid-liquid separation device is returned to the final purification device.

[0014] The concentration of sodium hexafluorophosphate raw material solution is 10% to 30%, and the purity is not less than 98.5%.

[0015] The mass ratio of the feed rate to the mixing rate in the refining unit is 1:50-200, and the temperature difference between the refrigerant in the heat exchange unit and the crystallizing material is 0.5-8℃.

[0016] In step 1, the temperature of the sodium hexafluorophosphate feed solution after cooling in the precooler is 0-15℃.

[0017] The refining apparatus includes a primary refining apparatus and a secondary refining apparatus. The temperature of the primary refining apparatus is 0 to -15℃, the temperature of the secondary refining apparatus is -15 to -45℃, and the temperature of the buffer apparatus is -15 to -45℃.

[0018] The refining apparatus includes a primary refining apparatus, a secondary refining apparatus, and a tertiary refining apparatus. The temperature of the primary refining apparatus is 0 to -15℃, the temperature of the secondary refining apparatus is -15 to -35℃, and the temperature of the tertiary refining apparatus is -30 to -45℃. It is used for particle size classification. The temperature of the buffer apparatus is -30 to -45℃.

[0019] The residence time of the slurry in the primary refining unit is 0.5 to 5 hours, in the secondary refining unit it is 1 to 8 hours, and in the tertiary refining unit it is 1 to 8 hours.

[0020] The mass ratio of reflux flow rate to feed rate for each refining unit is 1:4 to 4:1.

[0021] The beneficial effects of this invention are as follows: The continuous refining method for sodium hexafluorophosphate replaces the traditional batch operation. While ensuring the purity of the sodium hexafluorophosphate product, it improves the product's bulk density and flowability, avoids batch-to-batch variations caused by operational errors, effectively guarantees the continuity and stability of product quality, and improves the overall quality of sodium hexafluorophosphate. Furthermore, the number of crystallizer stages in the production process can be adjusted according to the needs of sodium hexafluorophosphate production, reducing the number of equipment and significantly improving production efficiency. The continuous refining equipment for sodium hexafluorophosphate of this invention is rationally designed, has a simple structure, low manufacturing cost, is easy to install and disassemble, and occupies a small area. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the continuous refining equipment for sodium hexafluorophosphate of the present invention;

[0023] Figure 2 This is a schematic diagram of another embodiment of the sodium hexafluorophosphate continuous refining equipment of the present invention;

[0024] Figure 3 This is a schematic diagram of the third embodiment of the sodium hexafluorophosphate continuous refining equipment of the present invention.

[0025] In the diagram, 1. Precooler, 2. Buffer device, 3. Solid-liquid separation device, 4. Heat exchange device, 5. Refining device, 6. Vertical pump. Detailed Implementation

[0026] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0027] Continuous refining equipment for sodium hexafluorophosphate, such as Figure 1 As shown, the system includes a precooler 1, which is sequentially connected to at least one refining device 5, a buffer device 2, and a solid-liquid separation device 3. The liquid outlet of each refining device 5 is connected to the feed inlet via a heat exchanger 4. A vertical pump 6 is installed at the liquid outlet of each refining device 5 and is connected to the heat exchanger 4. The liquid outlet of the solid-liquid separation device 3 is connected to the feed inlet of the final refining device 5. The refining device 5 is a crystallizer.

[0028] The continuous purification method for sodium hexafluorophosphate specifically includes the following steps:

[0029] Step 1: The sodium hexafluorophosphate raw material solution obtained by reaction synthesis is transported to the precooler 1 by the feed pump and cooled to 0-15°C. The concentration of the sodium hexafluorophosphate raw material solution is 10%-30% and the purity is not less than 98.5%. Then it is injected into the purification device 5.

[0030] Step 2: Control the temperature inside the refining device 5 and maintain it for a period of time. Then, continuously discharge the slurry from the outlet of the primary crystallizer and inject it into the buffer device 2 and the solid-liquid separation device 3 in sequence. At the same time, the mother liquor of each refining device 5 is cooled by the heat exchange device 4 and then enters the feed inlet. The temperature difference between the refrigerant in the heat exchange device 4 and the crystallized material is 0.5 to 8°C. The mass ratio of the reflux flow rate to the feed rate of each refining device 5 is 1:4 to 4:1.

[0031] When there is more than one refining unit 5, the temperature inside the primary crystallizer is controlled to generate crystal nuclei. The slurry is continuously discharged from the outlet of the primary crystallizer to subsequent crystallizers. The temperature inside the subsequent crystallizers is controlled to allow crystal growth. The slurry is discharged from the outlet of the final crystallizer and sequentially injected into the buffer unit 2 and the solid-liquid separation unit 3. At the same time, the mother liquor from each refining unit 5 is cooled by the heat exchanger 4 before entering the feed inlet. The temperature difference between the refrigerant in the heat exchanger 4 and the crystallized material is 0.5 to 8°C. The mass ratio of the reflux flow rate to the feed rate of each refining unit 5 is 1:4 to 4:1.

[0032] like Figure 2 As shown, when the refining device 5 includes a primary crystallizer and a secondary crystallizer, the temperature of the primary crystallizer is 0 to -15℃, the temperature of the secondary crystallizer is -15 to -45℃, and the temperature of the buffer device is -15 to -45℃.

[0033] like Figure 3 As shown, the refining device 5 includes a primary crystallizer, a secondary crystallizer, and a tertiary crystallizer. The temperature of the primary crystallizer is 0 to -15°C and it is used for nucleation. The temperature of the secondary crystallizer is -15 to -35°C and it is used for crystal growth. The temperature of the tertiary crystallizer is -30 to -45°C and it is used for particle size classification. The temperature of the buffer device is -30 to -45°C.

[0034] Furthermore, the residence time of the slurry in the primary crystallizer is 0.5–5 hours, in the secondary crystallizer is 1–8 hours, and in the tertiary crystallizer is 1–8 hours.

[0035] Step 3: Collect the solid discharged from the solid-liquid separation device 3 to obtain sodium hexafluorophosphate crystals with a mesh size of 40-80 mesh and a proportion of >90%, and return the mother liquor discharged from the solid-liquid separation device 3 to the final crystallizer.

[0036] Through the above methods, the continuous refining method for sodium hexafluorophosphate of this invention replaces the traditional batch operation. While ensuring the purity of the sodium hexafluorophosphate product, it improves the product's bulk density and flowability, avoids batch-to-batch variations caused by operational errors, effectively guarantees the continuity and stability of product quality, and improves the overall quality of sodium hexafluorophosphate. The number of crystallizer stages in the production process can be changed according to the needs of sodium hexafluorophosphate production, reducing the number of equipment and significantly increasing production capacity. The continuous refining equipment for sodium hexafluorophosphate of this invention is rationally designed, simple in structure, low in manufacturing cost, easy to install and disassemble, and occupies a small area, making it suitable for industrial-scale production.

[0037] Example 1

[0038] Step 1: The 20% sodium hexafluorophosphate raw material solution is pumped to the precooler 1 and cooled to 7°C;

[0039] Step 2: Control the temperature difference between the crystallization liquid and the cooling medium to 1℃ through the corresponding heat exchange device 4. The mixing amount in the primary crystallizer is 60 times the feed amount. Maintain the temperature of the sodium hexafluorophosphate liquid in the primary crystallizer at -10℃. After crystallization for 3 hours, the crystal slurry is continuously discharged from the outlet of the primary crystallizer into the secondary crystallizer.

[0040] Step 3: Control the temperature difference between the crystallization liquid and the cooling medium to 2℃ through the corresponding heat exchange device 4. The mixing amount in the secondary crystallizer is 100 times the feed amount. Maintain the temperature of the sodium hexafluorophosphate liquid in the secondary crystallizer at -30℃. After crystallization for 3.5 hours, it enters the tertiary crystallizer.

[0041] Step 4: Control the temperature difference between the crystallization liquid and the cooling medium to 2.5℃ through the corresponding heat exchange device 4. The mixing amount in the third-stage crystallizer is 80 times the feed amount. Maintain the temperature of the sodium hexafluorophosphate liquid in the second-stage crystallizer at -40℃. After crystallization for 3 hours, it is transported to the buffer device 2 through the discharge pump.

[0042] Step 5: Maintain the temperature of the sodium hexafluorophosphate solution in the buffer device 2 at -40°C. After buffering for a certain period of time, continuously discharge the crystal slurry from the buffer device 2 and enter the solid-liquid separation device 3. In this embodiment, the solid-liquid separation device 3 is a filter.

[0043] Step 6: Collect the solid discharged from the solid-liquid separation device 3 to obtain sodium hexafluorophosphate crystals with a particle size of 40-80 mesh and a mesh ratio of 90%. The mother liquor discharged from the solid-liquid separation device 3 is returned to the secondary crystallizer. The ratio of return flow to feed flow is 4:1 to maintain continuous feeding and discharging and maintain the balance of feed and discharge in the system.

[0044] Example 2

[0045] Step 1: The 30% sodium hexafluorophosphate raw material solution is pumped to the precooler 1 and cooled to 7°C;

[0046] Step 2: Control the temperature difference between the crystallizing liquid and the cooling medium to 1.5℃ through the corresponding heat exchange device 4. The mixing amount in the primary crystallizer is 50 times the feed amount. Maintain the temperature of the sodium hexafluorophosphate liquid in the primary crystallizer at -6℃. After crystallization for 2 hours, the crystal slurry is continuously discharged from the outlet of the primary crystallizer into the secondary crystallizer.

[0047] Step 3: Control the temperature difference between the crystallization liquid and the cooling medium to 3°C through the corresponding heat exchange device 4. The mixing amount in the secondary crystallizer is 50 times the feed amount. Maintain the temperature of the sodium hexafluorophosphate liquid in the secondary crystallizer at -22°C. After crystallization for 2 hours, it enters the tertiary crystallizer.

[0048] Step 4: Control the temperature difference between the crystallization liquid and the cooling medium to 4.5℃ through the corresponding heat exchange device 4. The mixing amount in the third-stage crystallizer is 80 times the feed amount. Maintain the temperature of the sodium hexafluorophosphate liquid in the second-stage crystallizer at -32℃. After crystallization for 3 hours, it is transported to the buffer device 2 through the discharge pump.

[0049] Step 5: Maintain the temperature of the sodium hexafluorophosphate solution in the buffer device 2 at -32°C. After buffering for a certain period of time, continuously discharge the crystal slurry from the buffer device 2 and enter the solid-liquid separation device 3; in this embodiment, the solid-liquid separation device 3 is a filter.

[0050] Step 6: Collect the solid discharged from the solid-liquid separation device 3 to obtain sodium hexafluorophosphate crystals with a particle size of 40-80 mesh and a mesh ratio of 98%. The mother liquor discharged from the solid-liquid separation device 3 is returned to the three-stage crystallizer. The ratio of return flow to feed flow is 1:1 to maintain continuous feeding and discharging and maintain the balance of feed and discharge in the system.

[0051] Example 3

[0052] Step 1: The 18% sodium hexafluorophosphate raw material solution is pumped to the precooler 1 and cooled to 10°C;

[0053] Step 2: Control the temperature difference between the crystallization liquid and the cooling medium to 5°C through the corresponding heat exchange device 4. The mixing amount in the primary crystallizer is 200 times the feed amount. Maintain the temperature of the sodium hexafluorophosphate liquid in the primary crystallizer at -10°C. After crystallization for 2 hours, the crystal slurry is continuously discharged from the outlet of the primary crystallizer into the secondary crystallizer.

[0054] Step 3: Control the temperature difference between the crystallization liquid and the cooling medium to 8°C through the corresponding heat exchange device 4. The mixing amount in the secondary crystallizer is 150 times the feed amount. Maintain the temperature of the sodium hexafluorophosphate liquid in the secondary crystallizer at -40°C. After crystallization for 3 hours, it is transported to the buffer device 2 through the discharge pump.

[0055] Step 4: Maintain the temperature of the sodium hexafluorophosphate solution in the buffer device 2 at -40°C. After buffering for a certain period of time, continuously discharge the crystal slurry from the buffer device 2 and enter the solid-liquid separation device 3; in this embodiment, the solid-liquid separation device 3 is a filter.

[0056] Step 6: Collect the solid discharged from the solid-liquid separation device 3 to obtain sodium hexafluorophosphate crystals with a particle size of 40-80 mesh and a mesh ratio of 92%. The mother liquor discharged from the solid-liquid separation device 3 is returned to the secondary crystallizer. The ratio of return flow to feed flow is 1:1 to maintain continuous feeding and discharging and maintain the balance of feed and discharge in the system.

[0057] Example 4

[0058] Step 1: The 15% sodium hexafluorophosphate feed solution is pumped to the precooler 1 and cooled to 7°C.

[0059] Step 2: Control the temperature difference between the crystallization liquid and the cooling medium to 6°C through the corresponding heat exchange device 4. The mixing amount in the primary crystallizer is 100 times the feed amount. Maintain the temperature of the sodium hexafluorophosphate liquid in the primary crystallizer at -32°C. After crystallization for 4 hours, it is transported to the buffer device 2 through the discharge pump.

[0060] Step 3: Maintain the temperature of the sodium hexafluorophosphate solution in the buffer device 2 at -32°C. After buffering for a certain period of time, continuously discharge the crystal slurry from the buffer device 2 and enter the solid-liquid separation device 3. In this embodiment, the solid-liquid separation device 3 is a filter.

[0061] Step 6: Collect the solid discharged from the solid-liquid separation device 3 to obtain sodium hexafluorophosphate crystals with a particle size of 40-80 mesh and a mesh ratio of 90%. The mother liquor discharged from the solid-liquid separation device 3 is returned to the primary crystallizer. The ratio of return flow to feed flow is 1:4 to maintain continuous feeding and discharging and maintain the balance of feed and discharge in the system.

Claims

1. A continuous purification method for sodium hexafluorophosphate, characterized in that, A continuous refining apparatus for sodium hexafluorophosphate is used. The apparatus includes a precooler (1), which is sequentially connected to at least one refining device (5), a buffer device (2), and a solid-liquid separation device (3). The liquid outlet of each refining device (5) is connected to the feed inlet through a heat exchange device (4). The liquid outlet of the solid-liquid separation device (3) is connected to the feed inlet of the final refining device (5). The refining device (5) is a crystallizer. The method includes the following steps: Step 1: After the sodium hexafluorophosphate raw material liquid obtained by reaction synthesis is cooled by precooler (1), it is injected into the first-stage purification device (5). The temperature of the sodium hexafluorophosphate raw material solution after cooling by the precooler (1) is 0~15℃; The concentration of sodium hexafluorophosphate raw material solution is 10%~30%, and the purity is not less than 98.5%; Step 2: Control the temperature inside the refining device (5) and maintain it for a period of time. Then, continuously discharge the slurry from the outlet of the primary refining device (5) and inject it into the buffer device (2) and the solid-liquid separation device (3) in sequence. At the same time, the mother liquor of each refining device (5) is cooled by the heat exchange device (4) and then enters the feed inlet. The refining device (5) includes a primary refining device, a secondary refining device and a tertiary refining device. The temperature of the primary refining device is 0~-15℃, the temperature of the secondary refining device is -15~-35℃, the temperature of the tertiary refining device is -30~-45℃, and it is used for particle size classification. The temperature of the buffer device is -30~-45℃. Step 3: Collect the solid discharged from the solid-liquid separation device (3) to obtain sodium hexafluorophosphate crystals. The mother liquor discharged from the solid-liquid separation device (3) is returned to the final purification device (5).

2. The continuous purification method for sodium hexafluorophosphate according to claim 1, characterized in that, The mass ratio of the feed rate of the refining device (5) to the mixing rate inside the refining device (5) is 1:50-200, and the temperature difference between the refrigerant in the heat exchange device (4) and the crystallizing material is 0.5~8℃.

3. The continuous purification method for sodium hexafluorophosphate according to claim 1, characterized in that, The residence time of the slurry in the primary refining unit is 0.5~5h, in the secondary refining unit it is 1~8h, and in the tertiary refining unit it is 1~8h.

4. The continuous purification method for sodium hexafluorophosphate according to claim 1, characterized in that, The mass ratio of reflux flow rate to feed rate for each refining unit is 1:4 to 4:1.

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