A method and apparatus for crystallizing lithium hexafluorophosphate

Abstract

The present application relates to lithium hexafluorophosphate production technical field, disclose a kind of lithium hexafluorophosphate crystallization method and device, crystallization method includes: input lithium hexafluorophosphate mother liquor to crystallization kettle and crystallize, slurry of crystallization kettle is sent to separator and is separated, and the light phase obtained by separation is sent to adjustment kettle, and the heavy phase is separated to obtain crystalline particle, and the material in adjustment kettle is sent to crystallization kettle and continues to crystallize;Wherein, the particle size detection device is used to obtain the particle size distribution parameters of crystalline particle in crystallization kettle, and the temperature in crystallization kettle and adjustment kettle is controlled according to particle size distribution parameters.The present application can realize particle size full-process automatic control and real-time closed-loop control, and large particle crystal is extracted in time, reduces the risk of blockage, inhibits the excessive growth of crystal, and promotes fine crystal directional dissolution and recycling, so as to optimize product particle size distribution, reduce HF residue, improve purification efficiency and crystallization capacity.

Description

Technical Field

[0001] This invention relates to the field of lithium hexafluorophosphate production technology, specifically to a method and apparatus for crystallizing lithium hexafluorophosphate. Background Technology

[0002] Lithium hexafluorophosphate (LiPF6) is a key raw material for lithium-ion battery electrolytes, and its quality significantly impacts the battery's cycle life, safety performance, and operational stability. In industrial production, crystallization is typically used as an important method for the final purification of LiPF6.

[0003] Currently, the industry mostly uses multi-reactor parallel reactor crystallization processes, but this type of process still has significant drawbacks in practical applications. Firstly, lithium hexafluorophosphate crystals grow rapidly. During the cooling crystallization process, the initially formed crystals continue to grow within the reactor, with particle sizes sometimes exceeding 1 mm, making crystal suspension difficult and easily clogging the bottom outlet of the crystallization reactor. Once clogging occurs, hot hydrogen fluoride is usually introduced for unblocking, which not only affects production continuity but also easily causes production interruptions, thereby reducing overall capacity.

[0004] Secondly, during intermittent cooling crystallization, crystal nucleation and growth occur simultaneously. Crystals that nucleate earlier have a longer growth time, resulting in a significantly larger particle size than those formed later, ultimately leading to a wider particle size distribution in the product. Smaller crystals are prone to agglomeration, causing excessive hydrogen fluoride residue; larger crystals are also difficult to dry thoroughly, similarly leading to higher hydrogen fluoride residue, thus adversely affecting product quality and normal production.

[0005] Therefore, the existing multi-reactor parallel reactor crystallization technology has at least the following problems: First, it cannot remove large-diameter crystals in time, which can easily cause blockage of the bottom outlet of the crystallization reactor; second, the product has a wide particle size distribution and high hydrogen fluoride residue, which often requires additional screening processes, resulting in reduced production efficiency and limited capacity. Summary of the Invention

[0006] This invention provides a method and apparatus for crystallizing lithium hexafluorophosphate, which solves the problems in the prior art such as the inability to remove large crystal particles in a timely manner during the crystallization process, easy blockage of the bottom outlet of the crystallization vessel, wide particle size distribution of the product, high residual hydrogen fluoride, and limited production continuity and capacity.

[0007] In a first aspect, the present invention provides a method for crystallizing lithium hexafluorophosphate, comprising the following steps: Lithium hexafluorophosphate mother liquor is fed into the crystallization kettle for crystallization. The slurry in the crystallization kettle is sent to the separator for separation. The light phase obtained by separation is sent to the conditioning kettle, and the heavy phase is separated to extract crystal particles. The material in the conditioning kettle is sent back to the crystallization kettle for further crystallization. Among them, a particle size detection device is used to obtain the particle size distribution parameters of the crystallized particles in the crystallization kettle, and the crystallization kettle and the temperature inside the kettle are controlled according to the particle size distribution parameters.

[0008] In one optional implementation, controlling the temperature inside the reactor based on the obtained particle size includes: During the crystallization process, the temperature T inside the crystallization vessel is monitored. 结晶 Determine the temperature T 结晶 The saturation concentration C of lithium hexafluorophosphate mother liquor 饱和 The particle size detection device is used to detect the mass fraction a of crystalline particles with a diameter less than 100 μm in the crystallization vessel, and to obtain the solid content m of the slurry in the crystallization vessel. The liquid concentration C1 at the reactor outlet is calculated and adjusted according to the following formula: C1=C 饱和 +m×a×1.4; where C1 is in units of %; C 饱和 The units are %; m is %; a is %; 1.4 is the concentration correction factor; C 饱和 When m and a are substituted as percentages in the calculation, the result C1 is still expressed as a percentage.

[0009] Based on the solubility curve of lithium hexafluorophosphate in hydrogen fluoride, the saturation temperature corresponding to the liquid phase concentration C1 at the outlet of the adjustment vessel is determined, and this saturation temperature is taken as the target temperature T1 of the adjustment vessel. Preferably, the temperature of the regulating vessel is higher than that of the crystallizing vessel; Preferably, the temperature of the control vessel is 1-10°C higher than that of the crystallization vessel; Preferably, the temperature of the control vessel is 2-5°C higher than that of the crystallization vessel.

[0010] In one optional embodiment, a refrigerant cooling device is installed outside the adjusting vessel, and the temperature of the adjusting vessel is controlled by controlling the refrigerant flow rate F1, wherein the refrigerant flow rate F1 = 0.3 × F × (T1 - T) 结晶 ), where F is the flow rate of slurry supplied from the crystallizer to the separator; where F1 is in t / h; F is in t / h; T1 is in °C; T 结晶 The unit is ℃; T1-T 结晶 The unit is ℃; 0.3 is the refrigerant flow conversion factor.

[0011] In one optional implementation, the mass fraction a, solid content m, liquid phase concentration C1 at the outlet of the adjustment vessel, target temperature T1, and refrigerant flow rate F1 are updated at preset time intervals. Preferably, the preset time interval is 0.5-3 minutes, and more preferably 1 minute.

[0012] In one optional implementation, controlling the temperature inside the crystallization vessel based on the obtained particle size includes: During the crystallization process, the temperature T inside the crystallization vessel is monitored. 结晶 Determine the temperature T 结晶 The saturation concentration C of lithium hexafluorophosphate mother liquor 饱和 The particle size detection device is used to detect the mass fraction b of crystallized particles with a particle size greater than 150 μm in the crystallization vessel, and to obtain the solid content m of the slurry in the crystallization vessel, the liquid holding capacity M of the crystallization vessel, and the flow rate F of the slurry delivered from the crystallization vessel to the separator. The target concentration C2 in the crystallizer during the next control cycle is calculated using the following formula: C2=C 饱和 -1.3×F / 60×m×b / M; where C2 is in units of %; C 饱和 The units are %; F is t / h; F / 60 is the slurry delivery rate in minutes, in t / min; m is %; b is %; M is t; 1.3 is the concentration correction factor; C 饱 When , m, and b are all substituted as percentages in the calculation, the result C2 is still expressed as a percentage.

[0013] Based on the solubility curve of lithium hexafluorophosphate in hydrogen fluoride, the saturation temperature corresponding to the target concentration C2 is determined, and this saturation temperature is determined as the target temperature T2 of the crystallization vessel. Preferably, the cooling rate of the crystallization vessel is controlled at 0.05~0.5℃ / min; More preferably, the cooling rate of the crystallization vessel is controlled at 0.1~0.3℃ / min.

[0014] In one optional embodiment, a refrigerant cooling device is installed outside the crystallization vessel, and the temperature of the crystallization vessel is controlled by controlling the refrigerant flow rate F2, wherein the refrigerant flow rate F2 = 18 × M × (T) 结晶 -T2); F2 is in t / h; M is in t; T 结晶 The unit is ℃; T2 is in ℃; T 结晶 -T2 is in °C; 18 is the refrigerant flow conversion factor.

[0015] In one optional implementation, the mass fraction b, solid content m, liquid holdup M, flow rate F, target concentration C2, target temperature T2, and refrigerant flow rate F2 are updated at preset time intervals. Preferably, the preset time interval is 0.5 to 3 minutes, and more preferably 1 minute.

[0016] In one optional embodiment, the lithium hexafluorophosphate mother liquor has a lithium hexafluorophosphate mass concentration of 16% to 22% and a hydrogen fluoride mass concentration of 78% to 84%.

[0017] In one optional embodiment, the volume of the crystallization vessel is 3 m³ to 30 m³. During the crystallization process, the initial temperature of the crystallization vessel is 0℃ to 10℃, the final temperature is -40℃ to -25℃, the initial liquid level is 60% to 80%, and the final liquid level is 0% to 10%. In one optional embodiment, the volume of the adjusting vessel is 1 m³ to 10 m³. During the operation of the adjusting vessel, the initial temperature of the adjusting vessel is 0 °C to 10 °C, the final temperature is -35 °C to -20 °C, and the liquid level is maintained at 50% to 80%.

[0018] In a second aspect, the present invention provides a lithium hexafluorophosphate crystallization apparatus, comprising: The crystallization vessel includes a crystallization vessel, a separator, and an adjustment vessel. The crystallization vessel has a feed inlet, and the discharge outlet of the crystallization vessel is connected to the feed inlet of the separator. The light phase discharge outlet of the separator is connected to the feed inlet of the adjustment vessel, and the discharge outlet of the adjustment vessel is connected to the crystallization vessel. A particle size detection device is connected to the crystallization vessel and is used to detect the particle size distribution parameters of the crystallized particles in the crystallization vessel. The controller is connected to the particle size detection device, the crystallization vessel, and the adjustment vessel. The controller controls the temperature of the crystallization vessel and the adjustment vessel according to the particle size distribution parameters detected by the particle size detection device.

[0019] The technical solution of this invention has the following advantages: This invention acquires real-time particle size information of crystallized particles in the crystallization vessel using a particle size detection device, and adjusts the temperature of the crystallization vessel and the adjustment vessel according to the acquired particle size information. This enables dynamic control of crystal nucleation, growth, and fine crystal adjustment during the crystallization process, achieving full-process automatic control and real-time closed-loop control of crystallization particle size. Simultaneously, it allows for fine adjustment of the cooling process, reducing batch-to-batch fluctuations caused by manual intervention and improving the stability and consistency of the crystallization process. Furthermore, this invention separates the crystallized particles using a separator, continuously removing large-diameter crystallized particles. This prevents large crystals from remaining in the crystallization vessel and growing excessively, effectively reducing the risk of blockage at the bottom outlet of the crystallization vessel and improving purification efficiency. Simultaneously, the separated small-diameter crystallized particles are sent to the adjustment vessel for adjustment before returning to the crystallization vessel for continued crystallization, constructing a fine crystal circulation adjustment mechanism. This enables targeted dissolution of fine crystals, breaking the vicious cycle of fine crystal formation, inhibiting repeated nucleation of fine crystals, thereby optimizing the product particle size distribution, reducing the risk of HF residue, and increasing crystallization capacity.

[0020] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the assembly structure of the lithium hexafluorophosphate crystallization device of the present invention.

[0023] Explanation of reference numerals in the attached figures: 1. Adjustment vessel; 2. Crystallization vessel; 3. Circulation pump; 4. Separator; 5. Filter. Detailed Implementation

[0024] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0025] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0026] This invention provides a lithium hexafluorophosphate crystallization apparatus, such as... Figure 1 As shown, the lithium hexafluorophosphate crystallization device includes an adjustment vessel 1, a crystallization vessel 2, a circulating pump 3, a separator 4, a filter 5, a particle size detection device, and a controller.

[0027] The crystallization vessel 2 is used to receive the material to be crystallized and to crystallize lithium hexafluorophosphate. The crystallization vessel 2 has a feed inlet for introducing lithium hexafluorophosphate mother liquor into the crystallization vessel 2. The discharge port of the crystallization vessel 2 is connected to the feed port of the separator 4 through a circulation pump 3, which is used to transport the crystallized slurry formed in the crystallization vessel 2 to the separator 4.

[0028] The separator 4 is used to classify and separate the crystallization slurry output from the crystallization vessel 2 by particle size. Preferably, the separator 4 can be a hydrocyclone. The separator 4 has a light phase outlet and a heavy phase outlet. The light phase outlet is connected to the inlet of the adjusting vessel 1, and the heavy phase outlet is connected to the filter 5. The light phase separated by the separator 4 contains relatively small crystal particles, and the light phase enters the adjusting vessel 1 through the light phase outlet of the separator 4; the heavy phase separated by the separator 4 contains relatively large crystal particles, and the heavy phase enters the filter 5 through the heavy phase outlet of the separator 4.

[0029] The filter 5 is used to perform solid-liquid separation on the heavy phase output from the separator 4 to obtain lithium hexafluorophosphate crystals. The filter 5 can be a sedimentation centrifuge. After solid-liquid separation, lithium hexafluorophosphate crystals are obtained, and the mother liquor can be recovered or discharged according to process requirements.

[0030] The adjusting vessel 1 is used to receive the material containing small-diameter crystalline particles output from the light phase outlet of the separator 4, and to regulate the temperature of the material. The outlet of the adjusting vessel 1 is connected to the crystallizing vessel 2, so that the material in the adjusting vessel 1, after temperature regulation, returns to the crystallizing vessel 2 for further crystallization. By setting up the adjusting vessel 1, the small-diameter crystalline particles obtained from the separation can be regulated before entering the crystallizing vessel 2, which is beneficial for controlling the number of fine crystals and improving the crystal particle size distribution in the crystallizing vessel 2.

[0031] The particle size detection device is connected to the crystallization vessel 2 and is used for online detection of the particle size distribution parameters of the crystallized particles within the crystallization vessel 2. Specifically, the particle size detection device can be installed at the bottom of the crystallization vessel 2 to perform online detection of the crystal particles in the crystallizing slurry within the crystallization vessel 2. The particle size distribution parameters include, but are not limited to, the mass fraction of crystallized particles with a particle size smaller than a preset small particle size threshold, the mass fraction of crystallized particles with a particle size larger than a preset large particle size threshold, and one or more of D10, D50, and D90. In an optional embodiment, the particle size detection device is a PCM online crystallization monitoring system, which includes an in-situ microscopic imaging probe and an image analysis module for online acquisition of images of the crystallized particles within the crystallization vessel 2 and obtaining the particle size distribution parameters of the crystallized particles based on the images.

[0032] Both the adjusting vessel 1 and the crystallizing vessel 2 are equipped with refrigerant cooling devices. The adjusting vessel 1 is equipped with a first refrigerant cooling device for introducing refrigerant, and the crystallizing vessel 2 is equipped with a second refrigerant cooling device for introducing refrigerant. The first and second refrigerant cooling devices can be jacketed heat exchange structures, coiled heat exchange structures, or other structures capable of achieving refrigerant heat exchange and cooling.

[0033] The controller is connected to the particle size detection device, the adjusting vessel 1, and the crystallizing vessel 2. Furthermore, the controller is also connected to the refrigerant flow regulating valves of the adjusting vessel 1 and the crystallizing vessel 2. The controller receives the particle size distribution parameters detected by the particle size detection device and controls the temperature of the adjusting vessel 1 and the crystallizing vessel 2 according to the particle size distribution parameters.

[0034] Specifically, when the particle size analyzer detects a high proportion of small-diameter crystallized particles in the crystallization vessel 2, the controller determines the target temperature of the adjusting vessel 1 based on the mass fraction of small-diameter crystallized particles and the solid content of the slurry in the crystallization vessel 2, and adjusts the refrigerant flow rate of the adjusting vessel 1 to bring the material temperature in the adjusting vessel 1 to the target temperature, thereby promoting the conditioning of small-diameter crystallized particles. Simultaneously, when the particle size analyzer detects a change in the proportion of large-diameter crystallized particles in the crystallization vessel 2, the controller determines the target temperature of the crystallization vessel 2 based on the mass fraction of large-diameter crystallized particles, the solid content of the slurry in the crystallization vessel 2, the liquid holdup in the crystallization vessel 2, and the flow rate of the slurry delivered from the crystallization vessel 2 to the separator 4, and adjusts the refrigerant flow rate of the crystallization vessel 2 to lower the temperature in the crystallization vessel 2 according to the target requirements.

[0035] This invention also provides a method for crystallizing lithium hexafluorophosphate, the method being based on Figure 1 The lithium hexafluorophosphate crystallization apparatus shown is used for crystallization. The apparatus includes a conditioning vessel 1, a crystallization vessel 2, a circulating pump 3, a separator 4, and a filter 5. The crystallization vessel 2 is used to receive lithium hexafluorophosphate mother liquor and perform cooling crystallization. The circulating pump 3 is used to continuously or intermittently transport the crystallization slurry in the crystallization vessel 2 to the separator 4. The separator 4 is used to classify the crystallization slurry according to the particle size or sedimentation characteristics of the crystal particles. The filter 5 is used to perform solid-liquid separation on the heavy phase obtained by the separator 4. The conditioning vessel 1 is used to receive the light phase obtained by the separator 4 and to adjust the temperature of the small-diameter crystals therein.

[0036] Specifically, lithium hexafluorophosphate mother liquor is introduced into crystallization vessel 2 for crystallization. The mass concentration of lithium hexafluorophosphate in the lithium hexafluorophosphate mother liquor is 16% to 22%, for example, any value or a range between 16%, 17%, 18%, 19%, 20%, 21%, and 22%; the mass concentration of hydrogen fluoride is 78% to 84%, for example, any value or a range between 78%, 79%, 80%, 81%, 82%, 83%, and 84%.

[0037] Within the above concentration range, lithium hexafluorophosphate can form a suitable supersaturation during the cooling process, which is beneficial to the synergistic control of crystal nucleation and crystal growth. If the concentration of lithium hexafluorophosphate is too low, the amount of lithium hexafluorophosphate that can be precipitated per unit volume of mother liquor will be less, resulting in low crystallization efficiency. If the concentration of lithium hexafluorophosphate is too high, excessive supersaturation is easily formed during the cooling process, leading to an increase in the number of fine crystals, an increase in slurry viscosity, and an increase in the risk of blockage and crystal entrainment of mother liquor.

[0038] The volume of the crystallization vessel 2 is 3 m³ to 30 m³, for example, it can be any value or a range between 3 m³, 5 m³, 8 m³, 10 m³, 15 m³, 20 m³, 25 m³, and 30 m³.

[0039] During the crystallization process, the initial temperature of the crystallization vessel 2 is 0℃ to 10℃, for example, any value or a range between 0℃, 2℃, 5℃, 8℃, and 10℃; the final temperature is -40℃ to -25℃, for example, any value or a range between -40℃, -35℃, -30℃, -28℃, and -25℃; the initial liquid level is 60% to 80%, for example, any value or a range between 60%, 65%, 70%, 75%, and 80%; and the final liquid level is 0% to 10%, for example, any value or a range between 0%, 2%, 5%, 8%, and 10%.

[0040] The volume range of the crystallization vessel 2 described above is suitable for industrial-scale lithium hexafluorophosphate crystallization processes. It meets certain processing capacity requirements while facilitating online control of temperature, liquid level, circulation flow rate, and particle size distribution. Controlling the initial temperature between 0℃ and 10℃ ensures the lithium hexafluorophosphate mother liquor is in a suitable initial dissolution and crystallization induction state. Controlling the final temperature between -40℃ and -25℃ ensures sufficient crystallization of lithium hexafluorophosphate while avoiding excessively low temperatures that could lead to increased energy consumption or decreased slurry fluidity. Controlling the initial liquid level between 60% and 80% ensures sufficient processing capacity and space for stirring and circulation within the crystallization vessel 2. Controlling the final liquid level between 0% and 10% facilitates complete material discharge and reduces the impact of residual crystals on subsequent crystallization processes.

[0041] During the crystallization process, the slurry in crystallization vessel 2 is transported to separator 4 by circulating pump 3 for separation. The light phase separated by separator 4 is sent to adjustment vessel 1, and the heavy phase separated by separator 4 is further separated to obtain crystallized particles. The material in adjustment vessel 1 is sent to crystallization vessel 2 for continued crystallization.

[0042] The volume of the adjusting vessel 1 is 1 m³ to 10 m³, for example, it can be any value or a range between 1 m³, 2 m³, 3 m³, 5 m³, 8 m³, and 10 m³. During the operation of the adjusting vessel 1, the initial temperature of the adjusting vessel 1 is 0℃ to 10℃, for example, it can be any value or a range between 0℃, 2℃, 5℃, 8℃, and 10℃; the final temperature is -35℃ to -20℃, for example, it can be any value or a range between -35℃, -30℃, -27℃, -25℃, and -20℃; the liquid level is maintained at 50% to 80%, for example, it can be any value or a range between 50%, 55%, 60%, 65%, 70%, 75%, and 80%.

[0043] The adjusting vessel 1 is used to receive the light phase separated by separator 4 and to provide temperature regulation space for the fine crystals in the light phase. The volume of the adjusting vessel 1 is set within the aforementioned range to match the light phase flow rate of separator 4 and to provide appropriate residence time for partial dissolution or particle size rebalancing of the fine crystals. The temperature of the adjusting vessel 1 is usually higher than that of the crystallization vessel 2, which is beneficial to improve the solubility of lithium hexafluorophosphate in the light phase, thereby reducing the number of fine crystals and preventing them from returning to the crystallization vessel 2 to continue participating in repeated nucleation or agglomeration as crystal nuclei.

[0044] During the crystallization process, a particle size distribution device is used to obtain the particle size distribution parameters of the crystallized particles in crystallization vessel 2, and the temperature inside crystallization vessel 2 and vessel 1 is controlled and adjusted according to the particle size distribution parameters. The particle size distribution parameters include the mass fraction 'a' of crystallized particles with a particle size less than 100 μm and the mass fraction 'b' of crystallized particles with a particle size greater than 150 μm in crystallization vessel 2.

[0045] Crystalline particles with a diameter less than 100 μm can be understood as fine crystals. For example, crystal particles with diameters less than 50 μm, 60 μm, 80 μm, 90 μm, or 100 μm can be counted, with crystal particles with a diameter less than 100 μm being the preferred control target for fine crystals. Crystalline particles with a diameter greater than 150 μm can be understood as relatively large crystals. For example, crystal particles with diameters greater than 150 μm, 180 μm, 200 μm, 300 μm, or 500 μm can be counted, with crystal particles with a diameter greater than 150 μm being the preferred control target for large-diameter crystals.

[0046] Controlling and adjusting the temperature inside reactor 1 based on the obtained particle size distribution parameters includes the following steps: During the crystallization process, the temperature T inside the crystallization vessel 2 is monitored, and the temperature T is determined based on the solubility curve of lithium hexafluorophosphate in hydrogen fluoride. 结晶 The saturation concentration C of lithium hexafluorophosphate mother liquor 饱和The particle size detection device is used to detect the mass fraction a of crystalline particles with a diameter of less than 100 μm in the crystallization vessel 2, and to obtain the solid content m of the slurry in the crystallization vessel 2.

[0047] The liquid concentration C1 at the outlet of reactor 1 is calculated and adjusted according to the following formula: C1=C 饱和 +m×a×1.4; Based on the solubility curve of lithium hexafluorophosphate in hydrogen fluoride, the saturation temperature corresponding to the liquid phase concentration C1 at the outlet of the adjusting vessel 1 is determined, and this saturation temperature is taken as the target temperature T1 of the adjusting vessel 1. The temperature of the adjusting vessel 1 is controlled to be higher than the temperature of the crystallization vessel 2. Preferably, the temperature of the adjusting vessel 1 is controlled to be 1°C to 10°C higher than that of the crystallization vessel 2, for example, it can be 1°C, 2°C, 3°C, 4°C, 5°C, 6°C, 8°C, or 10°C higher; more preferably, the temperature of the adjusting vessel 1 is controlled to be 2°C to 5°C higher than that of the crystallization vessel 2, for example, it can be 2°C, 3°C, 4°C, or 5°C higher.

[0048] When the temperature difference between the adjusting vessel 1 and the crystallizing vessel 2 is within the aforementioned range, the adjusting vessel 1 can effectively regulate the fine crystals in the light phase. If the temperature difference is too small, the dissolution or rebalancing effect of the fine crystals will be insignificant; if the temperature difference is too large, it may lead to excessive dissolution of the already formed qualified crystals and increase the subsequent crystallization load. Therefore, the aforementioned temperature difference range can balance the fine crystal regulation effect and the crystallization efficiency.

[0049] A refrigerant cooling device is installed outside the adjusting vessel 1. The temperature of the adjusting vessel 1 is controlled by controlling the refrigerant flow rate F1, wherein the refrigerant flow rate F1 is determined according to the following formula: F1 = 0.3 × F × (T1 - T) 结晶 ); where F is the flow rate of slurry delivered from crystallizer 2 to separator 4.

[0050] During the temperature control process of adjusting vessel 1, the mass fraction a, solid content m, liquid phase concentration C1 at the outlet of adjusting vessel 1, target temperature T1, and refrigerant flow rate F1 are updated at preset time intervals. The preset time interval is 0.5–3 min, for example, 0.5 min, 1 min, 1.5 min, 2 min, 2.5 min, or 3 min, preferably 1 min. Updating the mass fraction a, mass fraction b, solid content m, target temperature T1, target temperature T2, and refrigerant flow rates F1 and F2 at these time intervals ensures that the temperature control process is synchronized with changes in crystal particle size. If the preset time interval is too short, the control system may adjust frequently, increasing control fluctuations; if the preset time interval is too long, the control response may lag, making it difficult to reflect changes in particle size distribution within crystallization vessel 2 in a timely manner.

[0051] Meanwhile, controlling the temperature inside the crystallization vessel 2 based on the obtained particle size distribution parameters includes the following steps: During the crystallization process, the temperature T in the crystallization vessel 2 is monitored, and the saturation concentration C of the lithium hexafluorophosphate mother liquor at the crystallization temperature T is determined based on the solubility curve of lithium hexafluorophosphate in hydrogen fluoride. The mass fraction b of crystallized particles with a particle size greater than 150 μm in the crystallization vessel 2 is detected using the particle size detection device, and the solid content m of the slurry in the crystallization vessel 2, the liquid holding capacity M of the crystallization vessel 2, and the flow rate F of the slurry delivered from the crystallization vessel 2 to the separator 4 are obtained.

[0052] The target concentration C2 in crystallizer 2 during the next control cycle is calculated using the following formula: C2=C 饱和 -1.3×F / 60×m×b / M.

[0053] Based on the solubility curve of lithium hexafluorophosphate in hydrogen fluoride, the saturation temperature corresponding to the target concentration C2 is determined, and this saturation temperature is set as the target temperature T2 of the crystallization vessel 2. The cooling rate of the crystallization vessel 2 is controlled at 0.05℃ / min to 0.5℃ / min, for example, 0.05℃ / min, 0.1℃ / min, 0.2℃ / min, 0.3℃ / min, 0.4℃ / min, or 0.5℃ / min; preferably, the cooling rate of the crystallization vessel 2 is controlled at 0.1℃ / min to 0.3℃ / min, for example, 0.1℃ / min, 0.2℃ / min, or 0.3℃ / min.

[0054] A refrigerant cooling device is installed outside the crystallizer 2. The temperature of the crystallizer 2 is controlled by controlling the refrigerant flow rate F2, wherein the refrigerant flow rate F2 is determined according to the following formula: F2 = 18 × M × (T) 结晶 -T2).

[0055] During the temperature control process in crystallization vessel 2, the mass fraction b, solid content m, liquid holdup M, flow rate F, target concentration C2, target temperature T2, and refrigerant flow rate F2 are updated at preset time intervals. The preset time interval is 0.5 to 3 minutes, preferably 1 minute.

[0056] The heavy phase separated by separator 4 enters filter 5 for solid-liquid separation to obtain lithium hexafluorophosphate crystal particles; the light phase separated by separator 4 enters adjustment vessel 1 and, after adjustment by adjustment vessel 1, returns to crystallization vessel 2 for further crystallization.

[0057] Using the above method, the particle size detection device obtains the particle size distribution parameters of the crystallized particles in the crystallization vessel 2 online, and links the particle size distribution parameters with the temperature control process of the adjustment vessel 1 and the crystallization vessel 2, so that the temperature of the adjustment vessel 1 and the crystallization vessel 2 can be dynamically adjusted according to the change of crystal particle size, which helps to reduce the residue of fine crystals and the formation of excessively large crystals, and makes the particle size distribution of lithium hexafluorophosphate crystals more concentrated.

[0058] It should be noted that in this invention, the formula C1=C 饱和 +m×a×1.4、C2=C 饱和 -1.3×F / 60×m×b / M, F1=0.3×F×(T1-T 结晶 ) and F2=18×M×(T 结晶 The numerical coefficients in -T2) are control correction coefficients determined based on the solubility characteristics of lithium hexafluorophosphate in the hydrogen fluoride system, the crystal grain size change law during crystallization, the heat exchange capacity of the crystallization vessel and the adjustment vessel, and the material circulation flow rate.

[0059] Among them, coefficient 1.4 is used to correct the influence of fine crystal content on the liquid phase concentration at the outlet of the adjusting vessel, so that the target temperature of the adjusting vessel can increase accordingly with the increase of the proportion of fine crystals, thereby promoting the dissolution of fine crystals or particle size adjustment; coefficient 1.3 is used to correct the influence of the extraction of large-diameter crystals on the target concentration in the crystallizing vessel, so that the target temperature of the crystallizing vessel can be dynamically adjusted with the change of the proportion and extraction amount of large-diameter crystals; coefficient 0.3 is used to convert the material flow rate and temperature difference of the adjusting vessel into the refrigerant flow rate adjustment amount; coefficient 18 is used to convert the liquid holdup and temperature difference of the crystallizing vessel into the refrigerant flow rate adjustment amount. Through the above control correction coefficients, the temperature control of the adjusting vessel and the crystallizing vessel can be matched with the change of crystal particle size distribution, thereby realizing dynamic control of fine crystals, excessively large crystals, and overall particle size distribution.

[0060] It should be noted that the solubility curve of lithium hexafluorophosphate in hydrogen fluoride in this invention can be a pre-calibrated solubility curve. Specifically, the saturation concentration of lithium hexafluorophosphate in the hydrogen fluoride system can be measured at different temperatures, and a corresponding relationship can be established with temperature as the abscissa and saturation concentration as the ordinate. During the control process, the corresponding saturation concentration or saturation temperature can be determined by looking up a table or interpolation based on the detected temperature or target concentration.

[0061] Example 1 This embodiment provides a method for crystallizing lithium hexafluorophosphate, as detailed below: Lithium hexafluorophosphate mother liquor, containing 20% ​​lithium hexafluorophosphate and 80% hydrogen fluoride, is added to crystallization vessel 2. Crystallization vessel 2 has a volume of 10 m³, an initial temperature of 10°C, and an initial liquid level of 75%. Discharge is stopped when the liquid level drops to 5%, and the next batch of material is fed. Adjustment vessel 1 has a volume of 5 m³, an initial temperature of 10°C, and a liquid level maintained at 70%.

[0062] The online particle size analyzer AT adopts the PCM online crystallization monitoring system. The monitoring position of the online particle size analyzer AT is set at the bottom of the crystallization vessel 2, and it is used to detect the particle size distribution parameters of the crystallized particles in the crystallization vessel 2 online.

[0063] During the crystallization process, the refrigerant flow rate of crystallization vessel 2 is controlled in cascade by an online particle size analyzer AT to control the cooling process of crystallization vessel 2, maintaining the cooling rate of crystallization vessel 2 at 0.2–0.3 °C / min, with the cooling endpoint at -30 °C. The online particle size analyzer AT monitors the particle size distribution of crystals within crystallization vessel 2 in real time. In this embodiment, the particle size distribution of crystals within crystallization vessel 2 is as follows: D10 is 60–100 μm, D50 is 150–250 μm, and D90 is 300–500 μm.

[0064] During the crystallization process, the temperature T inside the crystallization vessel 2 was detected. 结晶 The saturation concentration C of the lithium hexafluorophosphate mother liquor at -15℃ was determined based on the solubility curve of lithium hexafluorophosphate in hydrogen fluoride. 饱和 The content was 17.7%. The online particle size analyzer AT detected that the mass fraction b of the crystallized particles with a diameter greater than 150 μm in the crystallization vessel 2 was 60%, and the mass fraction a of the crystallized particles with a diameter less than 100 μm was 12%; the solid content m of the slurry in the crystallization vessel 2 was 1.2%, the liquid holding capacity M of the crystallization vessel 2 was 5 t, and the flow rate F of the slurry delivered from the crystallization vessel 2 to the separator 4 was 6 t / h.

[0065] The target concentration C2 in crystallizer 2 during the next control cycle is calculated using the following formula: C2=C 饱和 -1.3×F / 60×m×b / M; In this embodiment, the preset time interval is 1 min, C2=17.7%-1.3×6 / 60×1.2%×60% / 5=17.68%.

[0066] That is, in the next control cycle, the target concentration C2 of lithium hexafluorophosphate mother liquor in crystallization vessel 2 is 17.68%. Based on the solubility curve of lithium hexafluorophosphate in hydrogen fluoride, the saturation temperature corresponding to the target concentration C2 is determined, and this saturation temperature is taken as the target temperature T2 of crystallization vessel 2. In this embodiment, the target temperature T2 corresponding to the target concentration C2 is -15.2℃.

[0067] A refrigerant cooling device is installed outside the crystallizer 2. The temperature inside the crystallizer 2 is controlled by adjusting the refrigerant flow rate F2. The refrigerant flow rate F2 is determined according to the following formula: F2 = 18 × M × (T) 结晶 -T2); In this embodiment: F2 = 18 × 5 × [(-15) - (-15.2)] =18 t / h.

[0068] Therefore, within this control cycle, the refrigerant flow rate F2 of the crystallizer 2 is adjusted to 18 t / h. In this embodiment, the mass fraction b, solid content m, liquid holdup M, flow rate F, target concentration C2, target temperature T2, and refrigerant flow rate F2 are updated at preset time intervals of 1 min, thereby achieving dynamic adjustment of the cooling process of the crystallizer 2.

[0069] Meanwhile, the refrigerant flow rate F1 of the adjusting vessel 1 is controlled in cascade by an online particle size analyzer AT to ensure that the temperature of the adjusting vessel 1 is higher than that of the crystallizing vessel 2. In this embodiment, the temperature difference between the adjusting vessel 1 and the crystallizing vessel 2 is maintained at 2-3℃, and the final cooling temperature of the adjusting vessel 1 is -27℃.

[0070] The liquid concentration C1 at the outlet of reactor 1 is calculated and adjusted according to the following formula: C1=C 饱和 +m×a×1.4.

[0071] In this embodiment: C1=17.7%+1.2%×12%×1.4=17.90%.

[0072] That is, the liquid phase concentration C1 at the outlet of the adjustment vessel 1 is adjusted to 17.90%. Based on the solubility curve of lithium hexafluorophosphate in hydrogen fluoride, the saturation temperature corresponding to the liquid phase concentration C1 at the outlet of the adjustment vessel is determined, and this saturation temperature is taken as the target temperature T1 of the adjustment vessel 1. In this embodiment, the target temperature T1 corresponding to the liquid phase concentration C1 at the outlet of the adjustment vessel is -12.7℃.

[0073] A refrigerant cooling device is installed outside the regulating vessel 1. The temperature inside the regulating vessel 1 is controlled by controlling the refrigerant flow rate F1. The refrigerant flow rate F1 is determined according to the following formula: F1 = 0.3 × F × (T1 - T) 结晶 ).

[0074] In this embodiment: F1 = 0.3 × 6 × [(-12.7) - (-15)] = 4.14 t / h.

[0075] Therefore, within this control cycle, the refrigerant flow rate F1 of the adjusting vessel 1 is adjusted to 4.14 t / h. In this embodiment, the mass fraction a, solid content m, liquid phase concentration C1 at the outlet of the adjusting vessel, target temperature T1, and refrigerant flow rate F1 are updated at preset time intervals of 1 min, thereby achieving dynamic adjustment of the temperature of the adjusting vessel 1.

[0076] The slurry in crystallization vessel 2 is transported to separator 4 by circulation pump 3 for separation. In this embodiment, circulation pump 3 is a hydrocyclone pump with a flow rate of 6 t / h and a solid content of 1-2% in the crystallization system. Separator 4 is a hydrocyclone used for particle size classification of the slurry output from crystallization vessel 2.

[0077] After separation by separator 4, the bottom heavy phase has a flow rate of 2 t / h, a solid content of 26%, and a particle size distribution of D10: 120 μm, D50: 350 μm, and D90: 540 μm; the top light phase has a flow rate of 4 t / h, a solid content of 1%, and a particle size distribution of D10: 52 μm, D50: 130 μm, and D90: 270 μm.

[0078] The heavy phase discharged from the bottom of separator 4 is used as large-diameter crystalline particles and enters filter 5 for solid-liquid separation. Filter 5 is a sedimentation centrifuge. The light phase discharged from the top of separator 4 is used as small-diameter crystalline particles and sent to adjustment vessel 1. After adjustment by adjustment vessel 1, it is returned to crystallization vessel 2 for continued crystallization.

[0079] After centrifugation using a sedimentation centrifuge, lithium hexafluorophosphate crystals with acceptable particle size were finally obtained. The particle size distribution of the obtained lithium hexafluorophosphate crystals was D10: 120 μm, D50: 350 μm, and D90: 540 μm, and the residual hydrogen fluoride in the crystals was 50 ppm.

[0080] Comparative Example 1 This comparative example provides a method for crystallizing lithium hexafluorophosphate. The difference from Example 1 is that this comparative example does not use an online particle size analyzer AT, and does not dynamically adjust the refrigerant flow rate of crystallizing vessel 2 and adjusting vessel 1 based on the particle size distribution parameters of the crystallized particles in crystallizing vessel 2.

[0081] Specifically, lithium hexafluorophosphate mother liquor, the material to be crystallized, is added to crystallization vessel 2. The mass concentration of lithium hexafluorophosphate in the mother liquor is 20%, and the mass concentration of hydrogen fluoride is 80%. The volume of crystallization vessel 2 is 10 m³, the initial temperature is 10℃, and the initial liquid level is 75%. The volume of adjustment vessel 1 is 5 m³, the initial temperature is 10℃, and the liquid level is maintained at 70%.

[0082] During the crystallization process, the cooling process of crystallization vessel 2 is controlled by a refrigerant, maintaining a cooling rate of 0.2–0.3 °C / min, with the final cooling point of crystallization vessel 2 being -30 °C. Simultaneously, the temperature of adjusting vessel 1 is controlled by a refrigerant, ensuring that its temperature is always higher than that of crystallization vessel 2, with the temperature difference maintained at 2–3 °C, and the final cooling point of adjusting vessel 1 being -27 to -28 °C.

[0083] Since this comparative example does not have an online particle size analyzer (AT), it is impossible to obtain the particle size distribution parameters of the crystallized particles in the crystallization vessel 2 online. Therefore, it is impossible to calculate and adjust the target temperature of vessel 1 and the target temperature of crystallization vessel 2 in real time based on parameters such as the mass fraction of crystallized particles with a particle size less than 100 μm, the mass fraction of crystallized particles with a particle size greater than 150 μm, and the solid content of the slurry. It is also impossible to dynamically adjust the flow rate of the refrigerant based on the target temperature.

[0084] The slurry in crystallization vessel 2 is transported to separator 4 by circulating pump 3 for separation. Circulating pump 3 is a cyclone pump with a flow rate of 6 t / h, and the solid content of the crystallization system is 1-2%. The separated heavy phase enters filter 5 for solid-liquid separation, and filter 5 is a sedimentation centrifuge. After centrifugation, lithium hexafluorophosphate crystals are obtained.

[0085] Testing revealed that the obtained lithium hexafluorophosphate crystals had a particle size distribution of D10: 72 μm, D50: 370 μm, and D90: 750 μm. The residual hydrogen fluoride in the crystals was 160 ppm, exceeding the required 90 ppm. Because the obtained crystals contained both small-sized aggregated crystals and excessively large crystals, further particle size separation was necessary. After removing the unqualified crystals, the yield of qualified product was only 70%.

[0086] Test Example 1 This test example compares the particle size distribution and residual hydrogen fluoride content of lithium hexafluorophosphate crystals prepared in Example 1 and Comparative Example 1. The results are shown in Table 1 below.

[0087] The particle size distribution of lithium hexafluorophosphate crystals is characterized by D10, D50, and D90. D10 represents the particle size corresponding to a cumulative volume distribution of 10%, D50 represents the particle size corresponding to a cumulative volume distribution of 50%, and D90 represents the particle size corresponding to a cumulative volume distribution of 90%. The residual amount of hydrogen fluoride in the crystal is used to evaluate the degree of hydrogen fluoride entrainment or adsorption in the crystal.

[0088] The particle size distribution detection method and the hydrogen fluoride residue detection method in this test example are as follows: Particle size distribution detection method: A certain amount of lithium hexafluorophosphate crystal sample was weighed and graded using standard sieves of different aperture sizes. During the sieving process, the sieving time, vibration frequency, and sample volume of each group of samples were kept consistent. After sieving, the mass of crystals within each particle size range was weighed, and the cumulative particle size distribution was calculated based on the proportion of the crystal mass in each particle size range to the total sample mass, thus obtaining D10, D50, and D90. For the same sample, at least three parallel tests were performed, and the average value was taken as the final test result.

[0089] Method for detecting residual hydrogen fluoride: Accurately weigh 1g of lithium hexafluorophosphate crystal sample and add it to 20g of ice water at 0℃ to fully dissolve the sample; add 0.2 mL of bromothymol blue ethanol solution as an indicator to the resulting solution; titrate with a 0.02 mol / L sodium hydroxide standard solution. The titration endpoint is defined as when the solution color changes from yellow to blue and does not fade within 30 seconds. Calculate the residual hydrogen fluoride in the sample based on the volume of sodium hydroxide standard solution consumed. Each sample should be tested in parallel at least three times, and the average value should be taken as the final test result.

[0090] Table 1: Performance Test Results

[0091] As shown in Table 1, compared with Comparative Example 1, the lithium hexafluorophosphate crystals obtained in Example 1 have a more concentrated particle size distribution, and the proportions of fine crystals and oversized crystals are effectively controlled. This indicates that the present invention can coordinate and control the fine crystal adjustment, crystal growth, and large particle extraction processes by acquiring the crystal particle size distribution parameters in the crystallization vessel online and dynamically adjusting the temperature of the crystallization vessel according to the particle size distribution parameters, thereby improving the controllability of the crystal particle size distribution.

[0092] Meanwhile, the residual hydrogen fluoride in the lithium hexafluorophosphate crystals obtained in Example 1 was significantly lower than that in Comparative Example 1, indicating that the method of the present invention can reduce the inclusion or adsorption of hydrogen fluoride in the crystals, lower the risk of residual hydrogen fluoride, and improve the quality stability of lithium hexafluorophosphate crystal products. Comparative Example 1, due to the lack of dynamic temperature adjustment based on particle size distribution parameters, resulted in a wider crystal particle size distribution, easily leading to the simultaneous presence of both small and excessively large crystals, resulting in poor product particle size uniformity and increasing the difficulty of subsequent sieving and hydrogen fluoride residue control. Therefore, the method of the present invention can improve the controllability of particle size during the crystallization process and the product qualification rate, and is beneficial in reducing residual hydrogen fluoride in the crystals.

[0093] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for crystallizing lithium hexafluorophosphate, characterized in that, Includes the following steps: Lithium hexafluorophosphate mother liquor is fed into the crystallization kettle for crystallization. The slurry in the crystallization kettle is sent to the separator for separation. The light phase obtained by separation is sent to the conditioning kettle, and the heavy phase is separated to extract crystal particles. The material in the conditioning kettle is sent back to the crystallization kettle for further crystallization. Among them, a particle size detection device is used to obtain the particle size distribution parameters of the crystallized particles in the crystallization kettle, and the crystallization kettle and the temperature inside the kettle are controlled according to the particle size distribution parameters.

2. The method for crystallizing lithium hexafluorophosphate according to claim 1, characterized in that, Adjusting the temperature inside the reactor based on the obtained particle size includes: During the crystallization process, the temperature T inside the crystallization vessel is monitored. 结晶 Determine the temperature T 结晶 The saturation concentration C of lithium hexafluorophosphate mother liquor 饱和 The particle size detection device is used to detect the mass fraction a of crystalline particles with a diameter less than 100 μm in the crystallization vessel, and to obtain the solid content m of the slurry in the crystallization vessel. The liquid concentration C1 at the reactor outlet is calculated and adjusted according to the following formula: C1=C 饱和 +m×a×1.4; Based on the solubility curve of lithium hexafluorophosphate in hydrogen fluoride, the saturation temperature corresponding to the liquid phase concentration C1 at the outlet of the adjustment vessel is determined, and this saturation temperature is taken as the target temperature T1 of the adjustment vessel. Preferably, the temperature of the regulating vessel is higher than that of the crystallization vessel.

3. The method for crystallizing lithium hexafluorophosphate according to claim 2, characterized in that, A refrigerant cooling device is installed outside the adjusting vessel. The temperature of the adjusting vessel is controlled by controlling the refrigerant flow rate F1, where the refrigerant flow rate F1 = 0.3 × F × (T1 - T) 结晶 ), where F is the flow rate of slurry delivered from the crystallizer to the separator.

4. The method for crystallizing lithium hexafluorophosphate according to claim 3, characterized in that, The mass fraction a, solid content m, liquid phase concentration C1 at the outlet of the reactor, target temperature T1, and refrigerant flow rate F1 are updated according to a preset time interval. Preferably, the preset time interval is 0.5-3 minutes, and more preferably 1 minute.

5. A method for crystallizing lithium hexafluorophosphate according to any one of claims 1-4, characterized in that, The temperature inside the crystallization vessel is controlled based on the obtained particle size, including: During the crystallization process, the temperature T inside the crystallization vessel is monitored. 结晶 Determine the temperature T 结晶 The saturation concentration C of lithium hexafluorophosphate mother liquor 饱和 The particle size detection device is used to detect the mass fraction b of crystallized particles with a particle size greater than 150 μm in the crystallization vessel, and to obtain the solid content m of the slurry in the crystallization vessel, the liquid holding capacity M of the crystallization vessel, and the flow rate F of the slurry delivered from the crystallization vessel to the separator. The target concentration C2 in the crystallizer during the next control cycle is calculated using the following formula: C2=C 饱和 -1.3×F / 60×m×b / M; Based on the solubility curve of lithium hexafluorophosphate in hydrogen fluoride, the saturation temperature corresponding to the target concentration C2 is determined, and this saturation temperature is determined as the target temperature T2 of the crystallization vessel.

6. The method for crystallizing lithium hexafluorophosphate according to claim 5, characterized in that, A refrigerant cooling device is installed outside the crystallization vessel. The temperature of the crystallization vessel is controlled by controlling the refrigerant flow rate F2, where the refrigerant flow rate F2 = 18 × M × (T) 结晶 -T2).

7. The method for crystallizing lithium hexafluorophosphate according to claim 6, characterized in that, The mass fraction b, solid content m, liquid holdup M, flow rate F, target concentration C2, target temperature T2, and refrigerant flow rate F2 are updated according to a preset time interval. Preferably, the preset time interval is 0.5 to 3 minutes, and more preferably 1 minute.

8. A method for crystallizing lithium hexafluorophosphate according to any one of claims 1-7, characterized in that, The lithium hexafluorophosphate mother liquor has a mass concentration of 16%~22% and a mass concentration of 78%~84% for lithium hexafluorophosphate.

9. A method for crystallizing lithium hexafluorophosphate according to any one of claims 1-8, characterized in that, The volume of the crystallization vessel is 3 m³ to 30 m³. During the crystallization process, the initial temperature of the crystallization vessel is 0℃ to 10℃, and the final temperature is -40℃ to -25℃. And / or, the volume of the adjusting vessel is 1m³ to 10m³, and during the operation of the adjusting vessel, the initial temperature of the adjusting vessel is 0℃ to 10℃, the final temperature is -35℃ to -20℃, and the liquid level is maintained at 50% to 80%.

10. A crystallization apparatus for lithium hexafluorophosphate, characterized in that, include: The crystallization vessel includes a crystallization vessel, a separator, and an adjustment vessel. The crystallization vessel has a feed inlet, and the discharge outlet of the crystallization vessel is connected to the feed inlet of the separator. The light phase discharge outlet of the separator is connected to the feed inlet of the adjustment vessel, and the discharge outlet of the adjustment vessel is connected to the crystallization vessel. A particle size detection device is connected to the crystallization vessel and is used to detect the particle size distribution parameters of the crystallized particles in the crystallization vessel. The controller is connected to the particle size detection device, the crystallization vessel, and the adjustment vessel. The controller controls the temperature of the crystallization vessel and the adjustment vessel according to the particle size distribution parameters detected by the particle size detection device.

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