A continuous dynamic crystallization device and a crystallization method of lithium hexafluorophosphate

Abstract

The present invention provides a continuous dynamic crystallization device and a crystallization method of lithium hexafluorophosphate, wherein the continuous dynamic crystallization device comprises a precooling device, a pressurized peristaltic device, a continuous oscillation crystallization device and a separation device connected in sequence; the continuous oscillation crystallization device comprises at least two sections of crystallization tubes connected in sequence along the material flow direction, the first section of the crystallization tube is connected to the pressurized peristaltic device, the last section of the crystallization tube is connected to the separation device, and the opening of the first section of the crystallization tube is connected to a piston; wherein, along the material flow direction, the temperature of two adjacent sections of the crystallization tube decreases in sequence. The continuous dynamic crystallization device can realize the dynamic continuous crystallization production of lithium hexafluorophosphate, and can obtain high-purity lithium hexafluorophosphate crystals with uniform particle size distribution and stable output, and continuous operation can also significantly reduce energy consumption and reduce production costs. Continuous dynamic crystallization is easy to realize automatic control, reduce manual intervention, and thus improve the safety and reliability of production.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic material preparation, and relates to a continuous dynamic crystallization device and a crystallization method of lithium hexafluorophosphate. Background Art

[0002] Lithium hexafluorophosphate is mainly used as an electrolyte for lithium-ion batteries. It has high ionic conductivity, good thermal stability and chemical stability. With the rapid development of electric vehicles, energy storage systems and portable electronic devices, the demand for high-performance lithium-ion batteries continues to increase, thus driving the demand for high-quality lithium hexafluorophosphate.

[0003] Traditional crystallization methods are usually intermittent, with low production efficiency and may lead to inconsistent quality between product batches, affecting battery performance. In addition, intermittent operation will increase energy consumption and production costs. In contrast, continuous dynamic crystallization technology can achieve continuous production, improve production efficiency and reduce downtime. By precisely controlling crystallization conditions, this technology can ensure product consistency and high quality. Continuous operation can also significantly reduce energy consumption and reduce production costs. In addition, continuous dynamic crystallization is easy to achieve automated control and reduce manual intervention, thereby improving production safety and reliability.

[0004] CN114788961A discloses a high-purity lithium hexafluorophosphate continuous dynamic crystallization process device and method, including a primary crystallization circulation system, a secondary crystallization circulation system and a fully enclosed filtering device. The raw material liquid is pumped into the primary crystallization circulation system, and cooled and crystallized under the action of the primary circulation pump. After the crystallization is completed, it is pumped into the secondary crystallization circulation system, and further cooled and crystallized under the action of the secondary circulation pump to obtain lithium hexafluorophosphate slurry; the obtained lithium hexafluorophosphate slurry is discharged by the secondary discharge pump and sent to the crystal slurry buffer tank for buffering, and then input into the filter for solid-liquid separation. Although this method realizes continuous feeding and discharging to a certain extent, it still requires a long residence time in the kettle, which makes it impossible to achieve complete continuous crystallization and the equipment occupies too much area.

[0005] CN114695952A discloses a system and method for producing lithium hexafluorophosphate by a dynamic constant temperature crystallization method, including a lithium fluoride modulation device, a reaction crystallization device and a mother liquid storage tank. The lithium fluoride modulation device is connected to a first high-purity nitrogen inlet pipe, a lithium fluoride inlet pipe, an anhydrous hydrofluoric acid or mother liquid inlet pipe, and the discharge port is connected to the reaction crystallization crystal feeding port, the reaction crystallization device is connected to a mother liquid inlet pipe, a second high-purity nitrogen inlet pipe and a PF5 / HCl mixed gas inlet pipe, and the discharge port is connected to a liquid-solid separation device, and the mother liquid separated in the liquid-solid separation device is transported to the mother liquid storage tank through a pipeline, and the separated lithium hexafluorophosphate is transported to a drying device. Although the obtained lithium hexafluorophosphate product has high purity and uniform particle size. However, the combination of synthesis reaction and crystallization leads to a wide range of operating conditions, which affects production efficiency.

[0006] CN116253337A discloses a dynamic crystallization device and process for lithium hexafluorophosphate, including a crystallizer, a filter and a dryer. The crystallizer is a dynamic crystallizer, including: a crystallizer body, an upward push-type stirring paddle, an isolation puddle, a crystal discharge port and a jacket. Although the product obtained by this method has high purity, the temperature required for crystallization is too low, resulting in a significant increase in energy consumption.

[0007] The dynamic crystallization device described in the above scheme has poor continuous production capacity, low production efficiency and high energy consumption, and is difficult to apply in practice. Summary of the invention

[0008] The purpose of the present invention is to provide a continuous dynamic crystallization device and a crystallization method of lithium hexafluorophosphate. The continuous dynamic crystallization device of the present invention can realize dynamic continuous crystallization production of lithium hexafluorophosphate, and can obtain high-purity lithium hexafluorophosphate crystals with uniform particle size distribution and stable output. Continuous operation can also significantly reduce energy consumption and production costs. In addition, continuous dynamic crystallization is easy to realize automatic control, reduce manual intervention, and thus improve the safety and reliability of production.

[0009] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a continuous dynamic crystallization device, which includes a pre-cooling device, a pressurized peristaltic device, a continuous oscillation crystallization device and a separation device connected in sequence.

[0011] The continuous oscillation crystallization device comprises at least two sections of crystallization tubes connected in sequence along the material flow direction, the first section of the crystallization tube is connected to a pressurized peristaltic device, the last section of the crystallization tube is connected to a separation device, and the opening of the first section of the crystallization tube is connected to a piston.

[0012] Among them, along the material flow direction, the temperature of two adjacent sections of the crystallization tube decreases successively.

[0013] The precooling device, the pressurized peristaltic device, the continuous oscillation crystallization device and the separation device of the present invention are connected in sequence through a conveying pipeline.

[0014] The continuous dynamic crystallization device of the present invention has high crystallization efficiency, high uniformity of crystals, uniform morphology, and can perform continuous feeding and discharging operations. Through continuous dynamic crystallization, high-purity crystals with uniform particle size distribution and stable output can be obtained. The present invention adopts a step-by-step cooling method to set the temperature of the crystallization tube, realizes segmented temperature control, can more accurately control the growth of crystals, and improves operational flexibility. It has significant advantages in improving production efficiency, ensuring product quality consistency, and saving energy and reducing consumption.

[0015] Taking a two-stage crystal tube as an example, the last stage of the crystal tube in the present invention is the second stage of the crystal tube. Taking a four-stage crystal tube as an example, the last stage of the crystal tube in the present invention is the fourth stage of the crystal tube, and so on.

[0016] In the two adjacent sections of the crystallization tubes described in the present invention, the temperature of the upper section of the crystallization tube is greater than the temperature of the lower section of the crystallization tube, that is, taking four sections of the crystallization tubes as an example, the temperature of the first section of the crystallization tube is greater than the temperature of the second section of the crystallization tube is greater than the temperature of the third section of the crystallization tube is greater than the temperature of the last section of the crystallization tube.

[0017] Preferably, the precooling device comprises a precooling kettle.

[0018] The precooling device of the present invention can reduce the temperature control range of the subsequent continuous oscillation crystallization device, thereby reducing energy consumption and equipment costs.

[0019] Preferably, a feed inlet is provided on the precooling device.

[0020] Preferably, the pressurized peristaltic device comprises a pressurized peristaltic pump.

[0021] Preferably, at least one baffle is arranged in the crystallization tube.

[0022] Preferably, two adjacent sections of crystallization tubes are connected via an arc-shaped pipeline.

[0023] Preferably, an observation window is provided on the arc-shaped pipe.

[0024] Preferably, a seed adding port is provided on the first section of the crystallization tube.

[0025] In the continuous dynamic crystallization device described in the present invention, a baffle is arranged in the crystallization tube. Under the interaction between the oscillation and the fluid and the baffle, a periodically moving vortex is generated in the crystallizer, so that each throttling area can be evenly mixed and have a good heat transfer effect. The present invention adds a window on the arc-shaped pipeline between two adjacent sections of the crystallization tube, so that the fluid situation in the crystallizer can be clearly observed. The present invention sets a seed injection port on the crystallization tube, and seeds can be added during the crystallization process, further improving the crystallization efficiency and operational flexibility of the crystallizer, which is conducive to improving the quality and yield of the crystals.

[0026] Preferably, the separation device comprises a horizontal screw centrifuge.

[0027] Preferably, a solid phase outlet and a liquid phase outlet are provided on the separation device.

[0028] The separation device of the present invention adopts a horizontal spiral centrifuge, and the horizontal spiral centrifuge separates the solid-liquid mixture through the action of centrifugal force and a spiral propeller, and can perform continuous feeding and discharging operations.

[0029] In a second aspect, the present invention provides a method for crystallizing lithium hexafluorophosphate, wherein the crystallization method is performed using the continuous dynamic crystallization device as described in the first aspect, and the crystallization method comprises the following steps:

[0030] (1) adding lithium hexafluorophosphate mother solution to a precooling device for precooling to obtain a precooled solution;

[0031] (2) transporting the precooled solution to the first crystallization tube through a pressurized peristaltic device, opening a piston connected to the first crystallization tube to reciprocate, and causing the precooled solution to flow through the crystallization tube to the next crystallization tube through reciprocating vibration, gradually cooling the solution to precipitate lithium hexafluorophosphate crystals, thereby obtaining a crystal solution;

[0032] (3) The crystal solution enters a separation device and is separated to obtain lithium hexafluorophosphate crystals.

[0033] In the crystallization method of the present invention, the lithium hexafluorophosphate mother liquid is first sent to a precooling kettle for precooling, and then sent to a tubular continuous oscillation crystallizer by a peristaltic pump. Under the interaction of the piston oscillation and the fluid and the baffle, the fluid generates a periodic vortex in the crystallizer. At the same time, the crystallization tube is provided with different temperature zones, so that the solution is gradually cooled to precipitate lithium hexafluorophosphate crystals during the flow process, and the precipitated crystals and the feed liquid are separated into solid and liquid by a spiral centrifuge, so that continuous feeding and discharging of materials can be achieved.

[0034] The lithium hexafluorophosphate mother liquor of the present invention is a reaction liquid obtained by preparing lithium hexafluorophosphate in a conventional method, and the reaction liquid comprises a lithium hexafluorophosphate-hydrogen fluoride solution.

[0035] Preferably, the mass concentration of lithium hexafluorophosphate in the lithium hexafluorophosphate mother liquor in step (1) is 10% to 30%, for example, 10%, 15%, 20%, 25% or 30%, etc., not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0036] Preferably, the temperature of the precooling treatment in step (1) is 0°C to 5°C, for example, 0°C, 1°C, 2°C, 3°C, 4°C or 5°C, etc., and is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] Preferably, stirring is performed during the precooling treatment in step (1).

[0038] Preferably, the stirring speed is 50 rpm to 100 rpm, for example, 50 rpm, 60 rpm, 70 rpm, 80 rpm, 90 rpm or 100 rpm, etc., and is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0039] Preferably, before opening the piston connected to the first-stage crystallization tube in step (2), lithium hexafluorophosphate seeds are added into the first-stage crystallization tube from the seed feeding port of the first-stage crystallization tube.

[0040] Preferably, the mass of the lithium hexafluorophosphate seed crystals is 0.1% to 0.5% of the mass of the lithium hexafluorophosphate in the pre-cooling solution, for example, 0.1%, 0.2%, 0.3%, 0.4% or 0.5%, etc., not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] Preferably, during the reciprocating oscillation process of step (2), the frequency of the piston is 1 Hz to 3 Hz, for example, 1 Hz, 1.5 Hz, 2 Hz, 2.5 Hz or 3 Hz, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0042] Preferably, during the reciprocating oscillation in step (2), the amplitude of the piston is 10 mm to 30 mm, for example, 10 mm, 15 mm, 20 mm, 25 mm or 30 mm, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0043] Preferably, during the flow in step (2), the temperature difference between two adjacent sections of the crystallization tubes is 1°C to 5°C, for example, 1°C, 2°C, 3°C, 4°C or 5°C, etc., not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] Preferably, the flow rate in step (2) is 200 g / min to 500 g / min, for example, 200 g / min, 250 g / min, 300 g / min, 400 g / min or 500 g / min, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0045] Preferably, the rotation speed of the separation treatment in step (3) is 1000rpm to 2000rpm, for example: 1000rpm, 1200rpm, 1500rpm, 1800rpm or 2000rpm, etc., not limited to the listed values, other values ​​not listed within the numerical range are also applicable.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] (1) The continuous dynamic crystallization device of the present invention can realize the dynamic continuous crystallization production of lithium hexafluorophosphate, and can obtain high-purity lithium hexafluorophosphate crystals with uniform particle size distribution and stable output. Continuous operation can also significantly reduce energy consumption and production costs. In addition, continuous dynamic crystallization is easy to realize automatic control, reduce manual intervention, and thus improve the safety and reliability of production.

[0048] (2) The yield of lithium hexafluorophosphate crystals obtained by using the continuous dynamic crystallization device of the present invention can reach more than 90.12%, the purity can reach more than 95.57%, and the acid content can reach less than 105.88 ppm. By controlling the conditions during the crystallization process, the yield of lithium hexafluorophosphate crystals can reach more than 96.68%, the purity can reach 99.99%, and the acid content can reach less than 20.47 ppm. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a schematic diagram of the structure of a continuous dynamic crystallization device provided in an embodiment of the present invention.

[0050] Among them: 1 is a precooling kettle, 1-1 is a feed port, 2 is a pressurized peristaltic pump, 3 is a conveying pipe, 4 is a piston, 5 is a first-stage crystallization tube, 6 is a second-stage crystallization tube, 7 is a third-stage crystallization tube, 8 is a fourth-stage crystallization tube, 9 is an observation window, 10 is a seed addition port, 11 is a baffle, 12 is a horizontal spiral centrifuge, 12-1 is a solid phase discharge port, and 12-2 is a liquid phase discharge port.

[0051] Figure 2 This is a SEM image of lithium hexafluorophosphate crystals obtained by the crystallization method described in Example 1 of the present invention. DETAILED DESCRIPTION

[0052] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0053] Example 1

[0054] This embodiment provides a method for crystallizing lithium hexafluorophosphate. The schematic diagram of the continuous dynamic crystallization device used in the crystallization method is as follows: Figure 1 As shown, the continuous dynamic crystallization device comprises:

[0055] A precooling kettle 1 is provided with a feed inlet 1 - 1 , and the precooling kettle 1 is connected to a pressurized peristaltic pump 2 , and the precooling kettle 1 and the pressurized peristaltic pump 2 are connected via a delivery pipeline 3 .

[0056] The pressurized peristaltic pump 2 is connected to the first section crystallization tube 5 of the continuous oscillation crystallization device through a conveying pipe 3. One side opening of the first section crystallization tube 5 is connected to the piston 4, and the other end is connected to the second section crystallization tube 6 through an arc pipe. The first section crystallization tube 5 is provided with a seed addition port 10. The second section crystallization tube 6 is connected to the third section crystallization tube 7 through an arc pipe, and the third section crystallization tube 7 is connected to the fourth section crystallization tube 8 through an arc pipe.

[0057] Baffles 11 are provided in the first section crystallization tube 5, the second section crystallization tube 6, the third section crystallization tube 7 and the fourth section crystallization tube 8, and observation windows 9 are provided on the arc-shaped pipes between the first section crystallization tube 5, the second section crystallization tube 6, the third section crystallization tube 7 and the fourth section crystallization tube 8.

[0058] The fourth stage crystallization tube 8 is connected to a horizontal spiral centrifuge 12 through a conveying pipeline 3 , and a solid phase discharge port 12 - 1 and a liquid phase discharge port 12 - 2 are arranged below the horizontal spiral centrifuge 12 .

[0059] The crystallization method of lithium hexafluorophosphate comprises the following steps:

[0060] (1) adding a lithium hexafluorophosphate-hydrogen fluoride solution having a lithium hexafluorophosphate mass concentration of 20% to a precooling kettle 1 through a feed port 1-1, and performing a precooling treatment at a stirring speed of 80 rpm and a temperature of 3° C. to obtain a precooled solution;

[0061] (2) The temperature difference between adjacent crystallization tubes is set to -3°C (i.e., the temperature of the previous crystallization tube is 3°C higher than that of the next crystallization tube), the precooled solution is transported to the first crystallization tube 5 through the pressurized peristaltic pump 2, 0.3% by mass of lithium hexafluorophosphate seeds are added into the first crystallization tube 5 from the seed injection port 10 of the first crystallization tube 5 (the mass of lithium hexafluorophosphate in the precooled solution is 100%), the piston 4 connected to the first crystallization tube 5 is opened, and the piston is controlled to oscillate at a speed of 2 Hz and an oscillation amplitude of 20 mm, and the precooled solution is controlled to flow to the second crystallization tube 6, the third crystallization tube 7 and the fourth crystallization tube 8 in the crystallization tube in turn at a flow rate of 300 g / min, and the temperature is gradually reduced to precipitate lithium hexafluorophosphate crystals to obtain a crystal solution;

[0062] (3) The crystal solution enters the horizontal spiral centrifuge 12 and is centrifuged at a speed of 1500 rpm. The lithium hexafluorophosphate crystals are output at the solid phase outlet 12-1 and dried to obtain the lithium hexafluorophosphate product. The waste liquid is output at the liquid phase outlet 12-2.

[0063] The SEM image of the lithium hexafluorophosphate crystal is as follows: Figure 2 shown.

[0064] Example 2

[0065] This embodiment provides a method for crystallizing lithium hexafluorophosphate. The schematic diagram of the continuous dynamic crystallization device used in the crystallization method is as follows: Figure 1 As shown, the continuous dynamic crystallization device comprises:

[0066] A precooling kettle 1 is provided with a feed inlet 1 - 1 , and the precooling kettle 1 is connected to a pressurized peristaltic pump 2 , and the precooling kettle 1 and the pressurized peristaltic pump 2 are connected via a delivery pipeline 3 .

[0067] The pressurized peristaltic pump 2 is connected to the first section crystallization tube 5 of the continuous oscillation crystallization device through a conveying pipe 3. One side opening of the first section crystallization tube 5 is connected to the piston 4, and the other end is connected to the second section crystallization tube 6 through an arc pipe. The first section crystallization tube 5 is provided with a seed addition port 10. The second section crystallization tube 6 is connected to the third section crystallization tube 7 through an arc pipe, and the third section crystallization tube 7 is connected to the fourth section crystallization tube 8 through an arc pipe.

[0068] Baffles 11 are provided in the first section crystallization tube 5, the second section crystallization tube 6, the third section crystallization tube 7 and the fourth section crystallization tube 8, and observation windows 9 are provided on the arc-shaped pipes between the first section crystallization tube 5, the second section crystallization tube 6, the third section crystallization tube 7 and the fourth section crystallization tube 8.

[0069] The fourth stage crystallization tube 8 is connected to a horizontal spiral centrifuge 12 through a conveying pipeline 3 , and a solid phase discharge port 12 - 1 and a liquid phase discharge port 12 - 2 are arranged below the horizontal spiral centrifuge 12 .

[0070] The crystallization method of lithium hexafluorophosphate comprises the following steps:

[0071] (1) adding a lithium hexafluorophosphate-hydrogen fluoride solution having a lithium hexafluorophosphate mass concentration of 20% to a precooling kettle 1 through a feed port 1-1, and precooling the kettle at 0° C. at a stirring speed of 100 rpm to obtain a precooled solution;

[0072] (2) The temperature difference between adjacent crystallization tubes is set to -1°C (i.e., the temperature of the previous crystallization tube is 1°C higher than that of the next crystallization tube), the precooled solution is transported to the first crystallization tube 5 through the pressurized peristaltic pump 2, 0.1% by mass of lithium hexafluorophosphate seeds are added to the first crystallization tube 5 from the seed injection port 10 of the first crystallization tube 5 (the mass of lithium hexafluorophosphate in the precooled solution is 100%), the piston 4 connected to the first crystallization tube 5 is opened, and the piston is controlled to oscillate at a speed of 3 Hz and an oscillation amplitude of 30 mm, and the precooled solution is controlled to flow to the second crystallization tube 6, the third crystallization tube 7 and the fourth crystallization tube 8 in the crystallization tube in turn at a flow rate of 500 g / min, and the lithium hexafluorophosphate crystals are precipitated by gradually cooling down to obtain a crystal solution;

[0073] (3) The crystal solution enters the horizontal spiral centrifuge 12 and is centrifuged at a speed of 1000 rpm. The lithium hexafluorophosphate crystals are output at the solid phase outlet 12-1 and dried to obtain the lithium hexafluorophosphate product. The waste liquid is output at the liquid phase outlet 12-2.

[0074] Example 3

[0075] This embodiment provides a method for crystallizing lithium hexafluorophosphate. The schematic diagram of the continuous dynamic crystallization device used in the crystallization method is as follows: Figure 1 As shown, the continuous dynamic crystallization device comprises:

[0076] A precooling kettle 1 is provided with a feed inlet 1 - 1 , and the precooling kettle 1 is connected to a pressurized peristaltic pump 2 , and the precooling kettle 1 and the pressurized peristaltic pump 2 are connected via a delivery pipeline 3 .

[0077] The pressurized peristaltic pump 2 is connected to the first section crystallization tube 5 of the continuous oscillation crystallization device through a conveying pipe 3. One side opening of the first section crystallization tube 5 is connected to the piston 4, and the other end is connected to the second section crystallization tube 6 through an arc pipe. The first section crystallization tube 5 is provided with a seed addition port 10. The second section crystallization tube 6 is connected to the third section crystallization tube 7 through an arc pipe, and the third section crystallization tube 7 is connected to the fourth section crystallization tube 8 through an arc pipe.

[0078] Baffles 11 are provided in the first section crystallization tube 5, the second section crystallization tube 6, the third section crystallization tube 7 and the fourth section crystallization tube 8, and observation windows 9 are provided on the arc-shaped pipes between the first section crystallization tube 5, the second section crystallization tube 6, the third section crystallization tube 7 and the fourth section crystallization tube 8.

[0079] The fourth stage crystallization tube 8 is connected to a horizontal spiral centrifuge 12 through a conveying pipeline 3 , and a solid phase discharge port 12 - 1 and a liquid phase discharge port 12 - 2 are arranged below the horizontal spiral centrifuge 12 .

[0080] The crystallization method of lithium hexafluorophosphate comprises the following steps:

[0081] (1) adding a lithium hexafluorophosphate-hydrogen fluoride solution having a lithium hexafluorophosphate mass concentration of 20% to a precooling kettle 1 through a feed port 1-1, and precooling the kettle at 5° C. at a stirring speed of 50 rpm to obtain a precooled solution;

[0082] (2) The temperature difference between adjacent crystallization tubes is set to -5°C (i.e., the temperature of the previous crystallization tube is 5°C higher than that of the next crystallization tube), the precooled solution is transported to the first crystallization tube 5 through the pressurized peristaltic pump 2, 0.5% by mass of lithium hexafluorophosphate seeds are added to the first crystallization tube 5 from the seed injection port 10 of the first crystallization tube 5 (the mass of lithium hexafluorophosphate in the precooled solution is 100%), the piston 4 connected to the first crystallization tube 5 is opened, and the piston is controlled to oscillate at a speed of 1 Hz and an oscillation amplitude of 10 mm, and the precooled solution is controlled to flow to the second crystallization tube 6, the third crystallization tube 7 and the fourth crystallization tube 8 in the crystallization tube in turn at a flow rate of 200 g / min, and the lithium hexafluorophosphate crystals are precipitated gradually to obtain a crystal solution;

[0083] (3) The crystal solution enters the horizontal spiral centrifuge 12 and is centrifuged at a speed of 2000 rpm. The lithium hexafluorophosphate crystals are output at the solid phase outlet 12-1 and dried to obtain the lithium hexafluorophosphate product. The waste liquid is output at the liquid phase outlet 12-2.

[0084] Example 4

[0085] The only difference between this embodiment and embodiment 1 is that the temperature of the precooling treatment is 8° C., and the other conditions and parameters are exactly the same as those in embodiment 1.

[0086] Example 5

[0087] The only difference between this embodiment and embodiment 1 is that the temperature difference between adjacent crystallization tubes is -10°C, and other conditions and parameters are exactly the same as those in embodiment 1.

[0088] Example 6

[0089] The only difference between this embodiment and embodiment 1 is that lithium hexafluorophosphate seed crystals are not added, and other conditions and parameters are exactly the same as those in embodiment 1.

[0090] Example 7

[0091] The only difference between this embodiment and embodiment 1 is that the frequency of the oscillation in step (2) is 0.5 Hz, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0092] Example 8

[0093] The only difference between this embodiment and embodiment 1 is that the frequency of the oscillation in step (2) is 5 Hz, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0094] Comparative Example 1

[0095] The only difference between this comparative example and Example 1 is that the temperatures between adjacent crystallization tubes are the same, and other conditions and parameters are exactly the same as those in Example 1.

[0096] Comparative Example 2

[0097] The difference between this comparative example and Example 1 is that a crystallization kettle is used to perform cooling crystallization in the form of static crystallization, and other conditions and parameters are exactly the same as those in Example 1.

[0098] Performance Test:

[0099] The finished lithium hexafluorophosphate product was analyzed according to HG / T 4066-2015, and the test results are shown in Table 1:

[0100] Table 1

[0101] Yield / % purity / % Acid content / ppm Example 1 98.07 99.99 14.13 Example 2 97.54 99.99 18.75 Example 3 96.68 99.99 20.47 Example 4 92.65 99.90 36.78 Example 5 93.87 95.57 105.88 Example 6 90.74 99.06 78.44 Example 7 91.32 99.12 68.09 Example 8 90.12 98.87 75.07 Comparative Example 1 78.14 90.67 180.98 Comparative Example 2 89.53 99.75 80.76

[0102] As can be seen from Table 1, from Examples 1-8, the yield of lithium hexafluorophosphate crystals obtained using the continuous dynamic crystallization device of the present invention can reach more than 90.12%, the purity can reach more than 95.57%, and the acid content can reach less than 105.88 ppm. By controlling the conditions during the crystallization process, the yield of lithium hexafluorophosphate crystals can reach more than 96.68%, the purity can reach 99.99%, and the acid content can reach less than 20.47 ppm.

[0103] By comparing Example 1 with Example 4, it can be seen that in the crystallization method of lithium hexafluorophosphate of the present invention, the lithium hexafluorophosphate mother liquor is first sent to a precooling kettle for precooling, which can reduce the temperature control range of the subsequent continuous oscillation crystallization device and reduce energy consumption and equipment costs.

[0104] By comparing Example 1 with Example 5, it can be seen that in the crystallization method of lithium hexafluorophosphate of the present invention, the temperature difference between adjacent crystallization tubes will affect the crystallization effect. When the temperature difference between adjacent crystallization tubes is controlled at 1°C to 5°C, the yield of lithium hexafluorophosphate is higher. If the temperature difference between adjacent crystallization tubes is too large, it may cause sudden nucleation due to the large temperature difference, and a large amount of crystals may suddenly precipitate, the acid content in lithium hexafluorophosphate will increase significantly, and the purity and yield will decrease significantly.

[0105] By comparing Example 1 and Example 6, it can be seen that in the crystallization method of lithium hexafluorophosphate of the present invention, by adding crystal seeds, crystal seeds can be added during the crystallization process, thereby further improving the crystallization efficiency and operation flexibility of the crystallizer, which is beneficial to improving the quality and yield of the crystals.

[0106] By comparing Example 1 with Examples 7-8, it can be seen that in the crystallization method of lithium hexafluorophosphate described in the present invention, the frequency of piston oscillation will affect the crystallization effect. When the frequency of piston oscillation is controlled at 1Hz to 3Hz, the crystallization effect of lithium hexafluorophosphate is better. If the frequency of piston oscillation is too large, the collision of the already formed crystals will be intensified, thereby causing the crystals to break and accelerating the wear of the internal components of the equipment. If the frequency of piston oscillation is too small, it will cause uneven solute distribution, forming a concentration gradient, affecting the consistency of crystal growth.

[0107] By comparing Example 1 with Comparative Example 1, it can be seen that the present invention adopts a step-by-step cooling method to set the temperature of the crystallization tube, realizes segmented temperature control, can more accurately control the growth of the crystal, and improves operational flexibility. It has significant advantages in improving production efficiency, ensuring product quality consistency, and saving energy and reducing consumption.

[0108] By comparing Example 1 and Comparative Example 2, it can be seen that the lithium hexafluorophosphate crystallization method using the continuous dynamic crystallization device of the present invention can realize the dynamic continuous crystallization production of lithium hexafluorophosphate, and can obtain high-purity lithium hexafluorophosphate crystals with uniform particle size distribution and stable yield. Continuous operation can also significantly reduce energy consumption and reduce production costs.

[0109] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A continuous dynamic crystallization device, characterized in that: The continuous dynamic crystallization device comprises a precooling device, a pressurizing peristaltic device, a continuous oscillating crystallization device and a separation device connected in sequence; The continuous oscillation crystallization device comprises at least two sections of crystallization tubes connected in sequence along the material flow direction, the first section of the crystallization tube is connected to the pressurized peristaltic device, the last section of the crystallization tube is connected to the separation device, and the opening of the first section of the crystallization tube is connected to the piston; Among them, along the material flow direction, the temperature of two adjacent sections of the crystallization tube decreases successively.

2. The continuous dynamic crystallization device according to claim 1, characterized in that: The precooling device comprises a precooling kettle; And / or, a feed inlet is provided on the precooling device; And / or, the pressurized peristaltic device includes a pressurized peristaltic pump.

3. The continuous dynamic crystallization device according to claim 1, characterized in that: At least one baffle is arranged in the crystallization tube; and / or, two adjacent sections of crystallization tubes are connected via an arc-shaped pipeline; And / or, an observation window is provided on the arc-shaped pipe; And / or, a seed adding port is arranged on the first section of the crystallization tube.

4. The continuous dynamic crystallization device according to claim 1, characterized in that: The separation device comprises a horizontal spiral centrifuge; And / or, a solid phase outlet and a liquid phase outlet are provided on the separation device.

5. A method for crystallizing lithium hexafluorophosphate, characterized in that: The crystallization method is carried out using the continuous dynamic crystallization device according to any one of claims 1 to 4, and the crystallization method comprises the following steps: (1) adding lithium hexafluorophosphate mother solution to a precooling device for precooling to obtain a precooled solution; (2) transporting the precooled solution to the first crystallization tube through a pressurized peristaltic device, opening a piston connected to the first crystallization tube to reciprocate, and causing the precooled solution to flow through the crystallization tube to the next crystallization tube through reciprocating vibration, gradually cooling the solution to precipitate lithium hexafluorophosphate crystals, thereby obtaining a crystal solution; (3) The crystal solution enters a separation device and is separated to obtain lithium hexafluorophosphate crystals.

6. The crystallization method according to claim 5, characterized in that The mass concentration of lithium hexafluorophosphate in the lithium hexafluorophosphate mother liquor of step (1) is 10% to 30%; And / or, the temperature of the precooling treatment in step (1) is 0°C to 5°C; and / or, stirring is performed during the precooling treatment in step (1); And / or, the stirring speed is 50 rpm to 100 rpm.

7. The crystallization method according to claim 5, characterized in that Before opening the piston connected to the first stage crystallization tube in step (2), lithium hexafluorophosphate seed crystals are added into the first stage crystallization tube from the seed adding port of the first stage crystallization tube; And / or, the mass of the lithium hexafluorophosphate seed crystals is 0.1% to 0.5% of the mass of the lithium hexafluorophosphate in the pre-cooled solution.

8. The crystallization method according to claim 5, characterized in that During the reciprocating oscillation of step (2), the frequency of the piston is 1 Hz to 3 Hz; And / or, during the reciprocating oscillation in step (2), the amplitude of the piston is 10 mm to 30 mm.

9. The crystallization method according to claim 5, characterized in that During the flow in step (2), the temperature difference between two adjacent sections of the crystallization tubes is 1°C to 5°C; And / or, the flow rate in step (2) is 200 g / min to 500 g / min.

10. The crystallization method according to claim 5, characterized in that The rotation speed of the separation treatment in step (3) is 1000rpm to 2000rpm.

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