Process and apparatus for the production of lithium hexafluorophosphate

Abstract

The application discloses a method for preparing lithium hexafluorophosphate. According to an embodiment of the application, the method comprises: mixing a phosphorus pentafluoride gas with a lithium fluoride solution to obtain a first treatment product; and performing a reaction treatment on the first treatment product to obtain a reaction solution containing lithium hexafluorophosphate. The mixing treatment is performed in a first continuous flow reactor, and the reaction treatment is performed in a second continuous flow reactor. The method of the application overcomes the shortcomings of the existing batch production technology, effectively avoids the invalid operation time in the starting and ending stages of traditional production, and thus improves the production efficiency and the output per unit time.

Description

Technical Field

[0001] This application relates to the field of materials preparation, specifically to a method for preparing lithium hexafluorophosphate and an apparatus for preparing lithium hexafluorophosphate. Background Technology

[0002] In the current production of lithium hexafluorophosphate (LiPF6), the mainstream processes typically employ batch reaction or tower-type continuous reaction systems. Batch reaction processes involve batch mixing and reacting hydrogen fluoride (HF) with lithium-containing compounds (such as LiF, LiOH·H2O, etc.), followed by washing, evaporation, and crystallization steps to obtain the final product. However, this method has some technical drawbacks, such as low reaction efficiency, poor batch-to-batch product consistency, and low equipment utilization. Furthermore, due to the high acidity of the system during the reaction, controlling the insoluble matter content is difficult, potentially leading to unstable product quality and increased post-processing costs.

[0003] While tower-type continuous reactors improve the continuity and yield of the reaction to some extent, they still face the following problems: 1) Insufficient contact between hydrogen fluoride and phosphorus pentafluoride (PF5) gas leads to limited conversion rate; 2) The reaction is violent under high temperature and high pressure conditions, which places stringent requirements on equipment materials and results in high maintenance costs; 3) The internal mass transfer efficiency of traditional tower reactors is limited, especially for liquid-gas two-phase reaction systems, which may lead to local overheating or incomplete condensation, affecting the reaction effect and product separation.

[0004] Therefore, the preparation method of lithium hexafluorophosphate still needs further improvement. Summary of the Invention

[0005] This application aims to address at least one of the technical problems existing in the prior art, to at least some extent.

[0006] Therefore, in a first aspect of this application, a method for preparing lithium hexafluorophosphate is proposed. According to an embodiment of this application, the method includes: mixing phosphorus pentafluoride gas with a lithium fluoride solution to obtain a first processed product; reacting the first processed product to obtain a reaction solution containing lithium hexafluorophosphate; wherein the mixing process is carried out in a first continuous flow reactor; the reaction process is carried out in a second continuous flow reactor; the first and second continuous flow reactors are respectively selected from microchannel reactors, wherein the channel size of the first continuous flow reactor is larger than the channel size of the second continuous flow reactor; and the processing temperature of the mixing process is lower than the processing temperature of the reaction process.

[0007] The method of this application overcomes the shortcomings of existing batch production technologies. By achieving continuous input of raw materials, continuous reaction process, and continuous output of products, it effectively avoids the ineffective operation time in the start and stop stages of traditional production, thereby improving production efficiency and output per unit time. Furthermore, this method can monitor and precisely adjust key parameters such as temperature, pressure, and flow rate in real time during the production process, ensuring that reaction conditions remain optimal. This precise control not only improves the yield of lithium hexafluorophosphate but also effectively reduces the generation of by-products, ensuring the consistency and stability of product quality. Based on this, the method of this application optimizes reaction conditions by using different channel sizes in the first and second continuous flow reactors and different processing temperatures in the mixing and reaction processes. In the mixing process, gas-liquid mixing is homogeneous, and in the reaction process, the reaction is intensified, allowing phosphorus pentafluoride and lithium fluoride to react fully, thus increasing the yield of lithium hexafluorophosphate. In addition, this method can also achieve energy recycling, reducing energy consumption and production costs, making it suitable for industrial applications.

[0008] According to embodiments of this application, the method for preparing lithium hexafluorophosphate further includes at least one of the following additional technical features:

[0009] According to an embodiment of this application, the lithium fluoride solution contains lithium fluoride, hydrogen fluoride and water, wherein the solid content of the lithium fluoride in the lithium fluoride solution is less than 10%, and the concentration of the hydrogen fluoride in the lithium fluoride solution is 80-95% by mass.

[0010] According to an embodiment of this application, the lithium fluoride has a particle size of less than 200 μm.

[0011] According to an embodiment of this application, the channel size of the first continuous flow reactor is 100 μm to 500 μm; the channel size of the second continuous flow reactor is 10 μm to 99 μm.

[0012] According to an embodiment of this application, the reaction chamber temperature of the first continuous flow reactor is 0°C to 30°C, and the reaction chamber temperature of the second continuous flow reactor is 30°C to 150°C.

[0013] According to an embodiment of this application, the method satisfies at least one of the following conditions: the reaction chamber pressure of the first continuous flow reactor is 0-2 MPa; the mixing time is 0.1 min-2 min; the reaction chamber pressure of the second continuous flow reactor is 0-2 MPa; and the reaction time is 0.1 min-5 min.

[0014] According to an embodiment of this application, the method further includes: flash evaporating the reaction solution containing lithium hexafluorophosphate to obtain flash vapor and flash liquid; and crystallizing the flash liquid to obtain the lithium hexafluorophosphate.

[0015] According to an embodiment of this application, the first flash evaporation treatment satisfies at least one of the following conditions: the pressure reduction value of the reaction chamber of the flash evaporation treatment is 0.1 to 1 MPa; the temperature reduction value of the reaction chamber of the flash evaporation treatment is 20 to 60°C; and the feed flow rate of the flash evaporation treatment is 200 to 1000 kg / h.

[0016] According to an embodiment of this application, the crystallization process satisfies at least one of the following conditions: the temperature of the crystallization process is -50 to 0°C; and the time of the crystallization process is 100 to 500 min.

[0017] In a second aspect, this application discloses a lithium hexafluorophosphate. According to embodiments of this application, the lithium hexafluorophosphate is prepared by the method described in the first aspect. The lithium hexafluorophosphate prepared using the method of this application can significantly improve production efficiency and reduce costs while ensuring product quality.

[0018] In a third aspect, this application provides an apparatus for preparing lithium hexafluorophosphate. According to an embodiment of this application, the apparatus includes: a first continuous flow reactor adapted to mix phosphorus pentafluoride gas with a lithium fluoride solution to obtain a first processed product; and a second continuous flow reactor connected to the first continuous flow reactor, adapted to react the first processed product to obtain a reaction solution containing lithium hexafluorophosphate; wherein the first and second continuous flow reactors are respectively selected from microchannel reactors, and the channel size of the first continuous flow reactor is larger than the channel size of the second continuous flow reactor.

[0019] The equipment described in this application enables continuous production of lithium hexafluorophosphate, ensuring product quality while improving the overall production efficiency. Furthermore, it allows for energy recycling, reducing energy consumption and production costs, making it suitable for industrial applications.

[0020] According to an embodiment of this application, the device further includes: a flash evaporator connected to the second continuous flow reactor, the flash evaporator being adapted to flash-evaporate the reaction solution containing lithium hexafluorophosphate to obtain flash vapor and flash liquid; and a crystallizer connected to the flash evaporator, the crystallizer being adapted to crystallize the flash liquid to obtain the lithium hexafluorophosphate.

[0021] According to embodiments of this application, the first continuous flow reactor and the second continuous flow reactor are respectively selected from microchannel reactors.

[0022] According to an embodiment of this application, the flash evaporator is selected from a flash tank.

[0023] Additional aspects and advantages of this application 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 this application. Attached Figure Description

[0024] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0025] Figure 1 A schematic flowchart of a method for producing lithium hexafluorophosphate according to an embodiment of this application is shown;

[0026] Figure 2 A schematic diagram of an apparatus for producing lithium hexafluorophosphate according to an embodiment of this application is shown. Figure 1 ;

[0027] Figure 3 A schematic diagram of an apparatus for producing lithium hexafluorophosphate according to an embodiment of this application is shown. Figure 2 .

[0028] Figure label:

[0029] 10: Equipment for producing lithium hexafluorophosphate; 100: First continuous flow reactor; 200: Second continuous flow reactor;

[0030] 300: Flash evaporator; 400: Crystallizer; 500: Premixing equipment. Detailed Implementation

[0031] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0032] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0033] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is also expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers, and ranges defined in this way can include endpoints a and b. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0034] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this application but do not exclude other contents.

[0035] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more.

[0036] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0037] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0038] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0039] Lithium hexafluorophosphate (LiPF6) is a crucial component of lithium-ion battery electrolytes, primarily ensuring a sufficient supply of lithium ions for charge-discharge cycles. Due to its well-balanced performance across various parameters, including solubility, electrochemical stability, conductivity, high and low temperature performance, and cycle life, it has gained widespread commercial application. LiPF6 synthesis methods include gas-solid synthesis, hydrogen fluoride solvent synthesis, organic solvent synthesis, and ion exchange synthesis. The hydrogen fluoride solvent synthesis method is widely used in industry, accounting for over 50% of current production capacity, and has contributed significantly to the development of the lithium battery industry. However, it still suffers from drawbacks such as high energy consumption, high raw material consumption, complex production processes, particularly high safety risks and environmental hazards during synthesis, crystallization, separation, and drying processes, difficulty in achieving continuous and automated production, and inconsistent quality.

[0040] In view of this, this application employs a continuous reaction process to produce lithium hexafluorophosphate. Phosphorus pentafluoride and a lithium fluoride-containing solution are pre-mixed in a first continuous flow reactor. This pre-mixing process allows the phosphorus pentafluoride gas to form highly dispersed microbubbles or droplets at the microscopic level, and macroscopically facilitates better contact between the phosphorus pentafluoride gas and the lithium fluoride-containing solution, increasing the gas-liquid contact area and mass transfer efficiency. As the material flows into a second continuous flow reactor, the reaction between phosphorus pentafluoride and the lithium fluoride-containing solution is intensified, generating a reaction liquid containing lithium hexafluorophosphate. Compared to batch reactions, continuous production offers shorter reaction times, higher production efficiency, and allows for precise control of various conditions, ensuring the consistency and stability of the produced lithium hexafluorophosphate.

[0041] Methods for preparing lithium hexafluorophosphate and lithium hexafluorophosphate

[0042] This application discloses a method for preparing lithium hexafluorophosphate. According to embodiments of this application, see [link to embodiment]. Figure 1 The method includes:

[0043] S100: Mixed Processing

[0044] In some embodiments of this application, phosphorus pentafluoride gas and lithium fluoride solution are mixed in a first continuous flow reactor to obtain a first processed product. The lithium fluoride solution contains lithium fluoride, hydrogen fluoride, and water. To promote a full reaction between the phosphorus pentafluoride gas and the lithium fluoride solution, the phosphorus pentafluoride gas and lithium fluoride solution are pre-mixed to ensure better contact between them. As a specific example, the entry of phosphorus pentafluoride gas into the first continuous flow reactor can be precisely controlled using a mass flow meter and a pressure reducing valve. In the first continuous flow reactor, by utilizing fluid dynamics principles, such as designing specific fluid channels and flow patterns, these effects enable the phosphorus pentafluoride gas to form highly dispersed microbubbles or droplets with the lithium fluoride solution at the microscopic level. This facilitates direct contact between the phosphorus pentafluoride gas and the lithium fluoride solution at the macroscopic level, increasing the gas-liquid contact area and mass transfer efficiency.

[0045] In some embodiments of this application, the solid content of lithium fluoride in the lithium fluoride solution is less than 10%. For example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., or a range of any of the above values. Therefore, by keeping the solid content of lithium fluoride in the lithium fluoride solution within the above range, the fluidity of the lithium fluoride solution and the hydrodynamic characteristics within the first continuous flow reactor can be ensured, reducing the occurrence of fluid blockage or decreased mass transfer efficiency due to excessively high solid content.

[0046] In some embodiments of this application, the concentration of hydrogen fluoride in the lithium fluoride solution is 80–95% by mass. For example, it can be 80% by mass, 82% by mass, 85% by mass, 87% by mass, 90% by mass, 92% by mass, 95% by mass, etc., or a range of any of the above values. Therefore, by keeping the concentration of hydrogen fluoride in the lithium fluoride solution within the above range, the solid content of lithium fluoride can be controlled to be less than 10%.

[0047] In some embodiments of this application, the particle size of lithium fluoride is less than 200 μm. For example, it can be 10 μm, 30 μm, 50 μm, 80 μm, 100 μm, 120 μm, 140 μm, 150 μm, 180 μm, 200 μm, etc., or a range of any of the above values. Therefore, by controlling the particle size of lithium fluoride, on the one hand, it helps to achieve more uniform mixing and contact between lithium fluoride and hydrogen fluoride solution, improving the uniformity of the reaction; on the other hand, controlling the particle size can reduce the formation of large aggregates of lithium fluoride in the first continuous flow reactor, thereby reducing the occurrence of reaction inhomogeneity or microchannel blockage caused by these aggregates.

[0048] In some embodiments of this application, the lithium fluoride solution is prepared as follows: lithium fluoride with a Dv80 of less than 200 μm is mixed with a hydrogen fluoride solution with a concentration of 80–95% by mass to obtain a mixture. The mixture is then pulped to reduce the particle size and homogenize the lithium fluoride particles. Conventional wet grinding methods can be used, but specific innovative improvements may be employed, such as using high shear force or ultrasonic-assisted pulping to improve processing efficiency and consistency. The pulping product is then filtered using a screen filter (greater than 80 mesh) to remove large, insoluble lithium fluoride particles, thus obtaining the lithium fluoride solution.

[0049] In this application, the volume average particle size Dv80 refers to the particle size corresponding to the cumulative volume distribution percentage reaching 80%. For example, the volume average particle size Dv80 test method can refer to the standard GB / T 19077-2016 and be determined using a laser particle size analyzer (e.g., Malvern Master Size 3000).

[0050] In some embodiments of this application, the reaction chamber pressure of the first continuous flow reactor is 0–2 MPa. For example, it can be 0 MPa, 0.5 MPa, 1 MPa, 1.5 MPa, 2 MPa, or any range of the above values. The reaction chamber pressure can be measured using a pressure measuring instrument. Therefore, by ensuring the reaction chamber pressure of the first continuous flow reactor is within the above range, PF5 gas can be efficiently dissolved and rapidly dispersed, improving the mixing efficiency of PF5 gas and lithium fluoride solution.

[0051] In some embodiments of this application, the reaction chamber temperature of the first continuous flow reactor is 0°C to 30°C. For example, it can be 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, or any range of the above values. The reaction chamber temperature can be measured using a temperature measuring instrument. Since the first continuous flow reactor contains a large amount of phosphorus pentafluoride gas and lithium fluoride, and these two react violently upon contact (specifically, LiF + PF5 → LiPF6), setting the reaction chamber temperature of the first continuous flow reactor within the above range reduces the likelihood of such a violent reaction.

[0052] In some embodiments of this application, the channel size of the first continuous flow reactor is 100 μm to 500 μm. For example, it can be 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, 500 μm, etc., or any range of the above values. Since phosphorus pentafluoride gas and lithium fluoride solution are simultaneously introduced into the first continuous flow reactor, under high gas-liquid ratio conditions, by keeping the channel size of the first continuous flow reactor within the above range, on the one hand, the phosphorus pentafluoride gas can form highly dispersed microbubbles or droplets with the lithium fluoride solution at the microscopic level, which can help the phosphorus pentafluoride gas and lithium fluoride solution to contact better at the macroscopic level, thereby increasing the gas-liquid contact area and mass transfer efficiency; on the other hand, it can improve the heat transfer performance of the reactor, thereby enabling the exothermic reaction to be fully removed and controlling the temperature in the channel.

[0053] In some embodiments of this application, the mixing time is 0.1 min to 2 min. For example, it can be 0.1 min, 0.5 min, 0.8 min, 1 min, 1.5 min, 1.8 min, 2 min, etc., or a range of any of the above values. Therefore, by keeping the mixing time within the above range, more thorough contact between phosphorus pentafluoride gas and lithium fluoride solution can be promoted, increasing the gas-liquid contact area.

[0054] In some embodiments of this application, the first continuous flow reactor is selected from a microchannel reactor. The inner diameter of the reaction chamber in a microchannel reactor is on the micrometer level, allowing for rapid mixing of the introduced materials and facilitating sufficient contact between phosphorus pentafluoride gas and lithium fluoride solution.

[0055] Microchannel reactors are generally manufactured using microfabrication and precision machining techniques. Their characteristic feature is the presence of fluid flow channels with equivalent diameters ranging from micrometers to millimeters. The specific dimensions can be selected based on the physical state and chemical properties of the reactants, as well as the conditions of the chemical reaction. Both the height and width are perpendicular to the fluid flow direction. The length of the reaction chamber is typically long and can be selected according to production needs. The microchannel reactor described in this invention can employ a direct-flow channel structure or an enhanced mixing channel structure. The direct-flow channel structure is a tubular structure, while the cross-section of the enhanced mixing channel structure can have any shape, such as, but not limited to, the following: T-shaped, Z-shaped, V-shaped, S-shaped, spherical, hemispherical, spherical with baffles, teardrop-shaped, funnel-shaped, triangular, heart-shaped, or umbrella-shaped structures. The equivalent diameter of the channel is 10 μm to 3000 μm, preferably 15 μm to 200 μm, and the liquid holding volume is 10 ml to 4000 ml, preferably 25 to 50 ml. The specific type of microchannel reactor used in the mixing process of this application is not strictly limited, as long as it can form highly dispersed microbubbles or droplets between phosphorus pentafluoride gas and lithium fluoride solution. It can be a conventional type disclosed in the art, such as Corning G3 / G4 / G5 dynamic microchannel reactor or Guizhou Microchemical HL-300 dynamic microchannel reactor.

[0056] It should be noted that the reaction between phosphorus pentafluoride gas and lithium fluoride solution is not complete during the mixing stage. Therefore, a second continuous flow reactor is required to promote the full reaction by adjusting the reaction parameters.

[0057] S200: Reaction Processing

[0058] In some embodiments of this application, the first processed product is reacted in a second continuous flow reactor to obtain a reaction solution containing lithium hexafluorophosphate. Specifically, the reaction formula is LiF + PF5 → LiPF6. By conducting the reaction in a second continuous flow reactor, continuous production of lithium hexafluorophosphate can be achieved. Simultaneously, important parameters such as temperature, pressure, and flow rate can be monitored and precisely adjusted in real time to ensure that the reaction conditions are always optimal, promoting the full progress of the reaction, thereby increasing the yield of the target product, lithium hexafluorophosphate, and reducing the formation of by-products, ensuring the consistency and stability of product quality.

[0059] In some embodiments of this application, the reaction chamber pressure of the second continuous flow reactor is 0–2 MPa. For example, it can be 0 MPa, 0.5 MPa, 1 MPa, 1.5 MPa, 2 MPa, or any range of the above values. The reaction chamber pressure can be measured using a pressure measuring instrument. Therefore, by ensuring the reaction chamber pressure of the second continuous flow reactor is within the above range, PF5 can be rapidly reacted, thereby reducing the system pressure and equipment corrosion.

[0060] In some embodiments of this application, the reaction chamber temperature of the second continuous flow reactor is 30°C to 150°C. For example, it can be 30°C, 50°C, 70°C, 90°C, 100°C, 120°C, 140°C, 150°C, or any range of the above values. The reaction chamber temperature can be measured using a temperature measuring instrument. Since a portion of phosphorus pentafluoride gas and lithium fluoride is consumed during the mixing stage, the reaction temperature can be increased during the reaction stage, i.e., by keeping the reaction chamber temperature of the second continuous flow reactor within the above range, thereby promoting a more complete reaction between the phosphorus pentafluoride gas and the lithium fluoride solution. By increasing the temperature, the reaction rate between the phosphorus pentafluoride gas and the lithium fluoride solution can be increased, thereby increasing the yield of lithium hexafluorophosphate.

[0061] In some embodiments of this application, the channel size of the second continuous flow reactor is 10 μm to 99 μm. For example, it can be 10 μm, 20 μm, 40 μm, 60 μm, 80 μm, 90 μm, 99 μm, or any range of the above values. Because the mixing stage effectively promotes sufficient contact between phosphorus pentafluoride gas and lithium fluoride solution and consumes some lithium fluoride, the particle size of lithium fluoride is reduced. Therefore, by keeping the channel size of the second continuous flow reactor within the above range, the contact between phosphorus pentafluoride gas and lithium fluoride solution can be further promoted, thereby driving the reaction and increasing the yield of lithium hexafluorophosphate.

[0062] In some embodiments of this application, the reaction processing time is 0.1 min to 5 min. For example, it can be 0.1 min, 0.5 min, 1 min, 1.5 min, 2 min, 2.5 min, 3 min, 3.5 min, 4 min, 4.5 min, 5 min, or any range of the above values. The reaction processing time can be controlled by the feed flow rate. Therefore, by keeping the mixing processing time within the above range, the reaction can be made more complete, improving the yield and purity of lithium hexafluorophosphate.

[0063] In some embodiments of this application, the second continuous flow reactor is selected from a microchannel reactor. The reaction chamber diameter in a microchannel reactor is on the micrometer scale, which facilitates sufficient contact and reaction between phosphorus pentafluoride and lithium fluoride. Furthermore, this reactor exhibits excellent mass and heat transfer performance, which is beneficial for the formation of lithium hexafluorophosphate.

[0064] Microchannel reactors, with their thousands of microchannels, possess an extremely large specific surface area, hundreds or even thousands of times larger than that of conventional reactors. This results in excellent heat and mass transfer capabilities, with an optimal heat transfer coefficient reaching 1700 kW / (m²). 2 (·K). The reactants within the microchannel can exchange heat efficiently with the wall surface, resulting in good temperature uniformity and a near-constant temperature in the reaction bed. This allows the heat released by the reaction between PF5 and LiF in the HF solution to be conducted and absorbed instantly and efficiently, ensuring that lithium hexafluorophosphate does not decompose due to the heat of the reaction, forming insoluble substances. The reaction temperature fluctuates little and is stable, which is beneficial for the smooth progress of the chemical reaction. This application does not strictly limit the specific type of microchannel reactor used for the reaction process; it can be any conventional type disclosed in the art, such as Corning G3 / G4 / G5 silicon carbide microchannel reactors or the HL-300 dynamic microchannel reactor from Guizhou Microchemical Co., Ltd.

[0065] In some embodiments of this application, see Figure 1 The method further includes: S300 flash evaporation treatment and S400 crystallization treatment. Since the reaction solution containing lithium hexafluorophosphate discharged from the second continuous flow reactor contains not only lithium hexafluorophosphate, but also hydrogen fluoride and phosphorus pentafluoride gas dispersed in the reaction solution, in order to remove phosphorus pentafluoride gas and hydrogen fluoride from the reaction solution and obtain lithium hexafluorophosphate with higher purity, the reaction solution is subjected to flash evaporation treatment and crystallization treatment.

[0066] The following sections will describe each step in detail.

[0067] S300: Flash treatment

[0068] In this step, the reaction liquid containing lithium hexafluorophosphate is subjected to flash evaporation to obtain flash vapor and flash liquid. Since the reaction liquid containing lithium hexafluorophosphate discharged from the second continuous flow reactor contains not only lithium hexafluorophosphate but also hydrogen fluoride and unreacted phosphorus pentafluoride gas dispersed within the reaction liquid, and given that the second continuous flow reactor operates under high temperature and pressure, the discharged reaction liquid containing lithium hexafluorophosphate will have significant pressure and temperature. Flash evaporation utilizes this pressure and temperature to separate the gas and liquid components in the reaction liquid containing lithium hexafluorophosphate. Specifically, flash evaporation allows the phosphorus pentafluoride gas and hydrogen fluoride in the reaction liquid to evaporate and escape. The flash vapor containing phosphorus pentafluoride and hydrogen fluoride is collected and recycled as a raw material to continue the reaction and generate lithium hexafluorophosphate, effectively reducing waste emissions and achieving resource recycling and energy conservation.

[0069] In some embodiments, the reaction liquid containing lithium hexafluorophosphate discharged from the second continuous flow reactor can be directly flash-evaporated to achieve continuous production.

[0070] In some embodiments of this application, the pressure drop (also referred to as pressure decrease) in the reaction chamber of the flash evaporation treatment is 0.1 MPa to 1 MPa. For example, it can be 0.1 MPa, 0.3 MPa, 0.5 MPa, 0.8 MPa, 1 MPa, or any range of the above values. Therefore, by keeping the pressure drop of the flash evaporation treatment within the above range, phosphorus pentafluoride gas and hydrogen fluoride in the reaction solution can be evaporated and escaped, reducing the impurity content in the evaporation solution and improving the purity of lithium hexafluorophosphate.

[0071] In some embodiments of this application, the temperature reduction value of the reaction chamber in the flash evaporation treatment is 20°C to 60°C, for example, it can be 20°C, 30°C, 40°C, 50°C, 60°C, or any range of the above values. Therefore, by keeping the temperature reduction value of the flash evaporation treatment within the above range, the efficiency of flash evaporation can be improved, that is, the efficiency of evaporating and escaping phosphorus pentafluoride gas and hydrogen fluoride from the reaction solution can be improved, while ensuring the purity of lithium hexafluorophosphate.

[0072] In some embodiments of this application, the feed flow rate for the flash evaporation process is 200 kg / h to 1000 kg / h. For example, it can be 200 kg / h, 400 kg / h, 600 kg / h, 800 kg / h, 1000 kg / h, or any range of the above values. The feed flow rate can be measured using a flow meter. Therefore, by ensuring the feed flow rate meets the above range, phosphorus pentafluoride gas and hydrogen fluoride in the reaction solution can be better evaporated and escaped, further improving the purity and yield of lithium hexafluorophosphate in the evaporation solution.

[0073] S400: Crystallization treatment

[0074] In this step, the flash liquid is crystallized to obtain lithium hexafluorophosphate crystals.

[0075] In some embodiments of this application, the crystallization treatment temperature is -50°C to 0°C. For example, it can be -50°C, -40°C, -30°C, -20°C, -10°C, 0°C, or any range of the above values. The crystallization treatment temperature can be measured using a temperature measuring instrument. Therefore, by keeping the crystallization treatment temperature within the above range, lithium hexafluorophosphate crystals can be formed more easily, thus improving the crystallization yield of lithium hexafluorophosphate.

[0076] In some embodiments of this application, the crystallization treatment time is 100 min to 500 min. For example, it can be 100 min, 200 min, 300 min, 400 min, 500 min, etc., or it can be any range of the above values. Therefore, by keeping the crystallization treatment time within the above range, it is possible to facilitate crystal growth, reduce the inclusion of impurities, and improve the purity and crystallization yield of lithium hexafluorophosphate crystals.

[0077] This application discloses a lithium hexafluorophosphate. According to embodiments of this application, the lithium hexafluorophosphate is prepared using the method described above. The lithium hexafluorophosphate prepared by the method of this application has high yield and purity, while reducing the content of insoluble matter and the acidity of the reaction solution. Since the reaction between phosphorus pentafluoride and lithium fluoride is vigorous and exothermic, batch reactions often use large amounts of hydrogen fluoride solution to control the exothermic reaction, which not only increases the acidity of the reaction solution but also complicates subsequent processing. The continuous flow reactor used in this application has excellent heat transfer performance and can precisely control the reaction temperature, thus allowing for the use of less hydrogen fluoride solution. This not only reduces the acidity of the reaction solution but also reduces hydrogen fluoride consumption, lowers production costs, and mitigates potential environmental impact. Furthermore, during flash evaporation, residual hydrogen fluoride in the reaction solution is evaporated, further reducing the acidity of the reaction solution. Furthermore, the micron-level internal diameter design of the continuous flow reactor allows for a significant improvement in reaction efficiency. Even a small amount of lithium fluoride is sufficient to ensure the smooth progress of the reaction, which directly reduces the content of insoluble substances in the reaction solution and improves the purity of the final product.

[0078] Equipment for preparing lithium hexafluorophosphate

[0079] This application discloses an apparatus for preparing lithium hexafluorophosphate, said apparatus being used to implement the above-described method for preparing lithium hexafluorophosphate. According to embodiments of this application, refer to... Figure 2 The apparatus 10 includes: a first continuous flow reactor 100, a second continuous flow reactor 200, a flash evaporator 300, and a crystallizer 400. Each apparatus will be described in detail below.

[0080] In some embodiments of this application, the first continuous flow reactor 100 is adapted to mix phosphorus pentafluoride gas with lithium fluoride solution to obtain a first processed product. The first continuous flow reactor 100 allows for continuous mixing, meaning that phosphorus pentafluoride gas and lithium fluoride solution are separately introduced into the first continuous flow reactor 100 for mixing. Within the reactor, the phosphorus pentafluoride gas and lithium fluoride solution are in a continuous flow state. Under the influence of vortex flow or laminar shear effect in the first continuous flow reactor 100, the phosphorus pentafluoride gas and lithium fluoride solution can form highly dispersed microbubbles or droplets, increasing the gas-liquid contact area and mass transfer efficiency. Simultaneously, some of the contacted phosphorus pentafluoride gas and lithium fluoride solution react to form lithium hexafluorophosphate.

[0081] In some embodiments of this application, the second continuous flow reactor 200 is connected to the first continuous flow reactor 100. The second continuous flow reactor 200 is adapted to react the first processed product to obtain a reaction solution containing lithium hexafluorophosphate. Using the second continuous flow reactor 200 allows for continuous reaction processing; that is, the first processed product, after being mixed and processed in the first continuous flow reactor 100, can automatically enter the second continuous flow reactor 200 for reaction. In the reactor, the first processed product is in a continuous flow state, and unreacted phosphorus pentafluoride gas and lithium fluoride solution continuously generate a solution containing lithium hexafluorophosphate. After the reaction is complete, it automatically enters the next device. This facilitates rapid reaction between materials, better mass and heat transfer, and improves the yield and formation rate of lithium hexafluorophosphate.

[0082] In some embodiments of this application, the flash evaporator 300 is connected to the second continuous flow reactor. The flash evaporator 300 is adapted to flash-evaporate the reaction solution containing lithium hexafluorophosphate to obtain flash vapor and flash liquid. The flash vapor contains phosphorus pentafluoride gas and hydrogen fluoride gas, and the flash liquid contains lithium hexafluorophosphate. Using the flash evaporator 300 allows the phosphorus pentafluoride and hydrogen fluoride in the reaction solution containing lithium hexafluorophosphate to evaporate and escape, thereby improving the purity of lithium hexafluorophosphate.

[0083] In some embodiments of this application, the crystallizer 400 is connected to the flash evaporator 300, and the crystallizer 400 is adapted to crystallize the flash liquid to obtain the lithium hexafluorophosphate.

[0084] In some embodiments of this application, the first continuous flow reactor 100 and the second continuous flow reactor 200 are respectively selected from microchannel reactors, wherein the channel size of the first continuous flow reactor is larger than that of the second continuous flow reactor. The reaction chamber diameter in the microchannel reactor is at the micrometer level, allowing the introduced materials to mix rapidly and react fully. This facilitates sufficient contact and reaction between phosphorus pentafluoride gas and lithium fluoride solution. Furthermore, it possesses excellent mass and heat transfer properties, and while ensuring the normal progress of the reaction, it can reduce the use of hydrogen fluoride and lithium fluoride, thereby lowering the acidity and insoluble content of the generated lithium hexafluorophosphate.

[0085] In some embodiments of this application, the flash evaporator 300 is selected from a flash tank. Therefore, gas-liquid separation can be achieved, improving the purity of lithium hexafluorophosphate.

[0086] In some embodiments of this application, reference is made to Figure 3 The equipment further includes a premixing device 500, which is connected to a first continuous flow reactor and is suitable for pre-preparing a lithium fluoride solution, i.e., mixing lithium fluoride with a Dv80 of less than 200 μm with an 85-95% by mass hydrogen fluoride solution, and then subjecting the mixture to slurrying and filtration. Using the premixing device can reduce the particle size of lithium fluoride in the lithium fluoride solution and remove large particles of insoluble lithium fluoride.

[0087] In some embodiments of this application, the premixing device includes a wet mill and a screen filter. The wet mill is used to grind lithium fluoride into smaller sizes, and the screen filter is used to remove large particles of insoluble lithium fluoride.

[0088] The following will explain the solution of this application with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0089] Example 1

[0090] In this embodiment, lithium hexafluorophosphate crystals are prepared according to the following method:

[0091] 1. Add D to the wet grinding mill 80 Lithium fluoride raw material with a particle size of ≤200μm is mixed with a certain amount of hydrofluoric acid solution to ensure that the solid lithium fluoride content in the hydrofluoric acid solution does not exceed 10%. After grinding, the resulting mixture is filtered through an 80-mesh sieve to obtain the raw material solution.

[0092] 2. Inject the raw material solution into the first microchannel reactor at a flow rate of 500 kg / h. Simultaneously, precisely control the entry of phosphorus pentafluoride gas into the first microchannel reactor using a mass flow meter and a pressure reducing valve, with a gas flow rate of 82 m³ / h. 3 / h, wherein the pressure in the reaction chamber is 1.5MPa, the temperature is 25℃, the mixing time is 1.5min, the diameter of the reaction chamber is 200 micrometers, and a mixed liquid is obtained after mixing is completed;

[0093] 3. The mixture automatically enters the second microchannel reactor, where the pressure in the reaction chamber is 1.4 MPa, the temperature is 150 °C, the diameter of the reaction chamber is 50 micrometers, the reaction time is 4.5 min, and the reaction solution is obtained after the reaction is completed;

[0094] 4. The reaction liquid automatically enters the flash tank. The pressure drop in the reaction chamber of the flash tank is set to 0.7 MPa, accompanied by a temperature drop of 50°C. The feed flow rate of the reaction liquid is controlled at 745 kg / h, and the high-temperature flash vapor and flash liquid containing phosphorus pentafluoride are discharged separately.

[0095] 5. The flash liquid automatically enters the crystallizer for crystallization. The temperature in the crystallizer is -35℃, and the crystallization time is 240 minutes. After crystallization, lithium hexafluorophosphate crystals are obtained.

[0096] The preparation methods of Examples 2 to 36 are the same as those of Example 1, except that the specific parameters are different, as shown in Table 1.

[0097] Comparative Example 1 prepared lithium hexafluorophosphate crystals using a conventional batch reaction, the specific method of which is as follows:

[0098] To 1m 3 450 kg of hydrofluoric acid solution was introduced into the reactor, maintaining the temperature at 80°C and the pressure at atmospheric pressure. Then, 50 kg of solid lithium fluoride was added, and stirring was started for 2 hours to dissolve it. Subsequently, PF5 gas was introduced into the reactor at a flow rate of 10 m³ / h. 3 The feed rate was maintained at 0.5 MPa for 8 hours. After that, the feed was stopped and the reaction temperature was maintained at 100°C for aging reaction for 2 hours. The reaction pressure was then reduced to 0.2 MPa. Subsequently, the reaction was cooled and crystallized. The temperature inside the reactor was lowered to -45°C for static crystallization for 48 hours. After filtration and drying, lithium hexafluorophosphate crystals were obtained.

[0099] The preparation method of Comparative Example 2 is the same as that of Example 1, except that step 2 is omitted. The specific process of step 3 is as follows:

[0100] The raw material solution from step 1 is directly injected into the second microchannel reactor, with a flow rate set to 82 m / s. 3The reaction chamber has a pressure of 1.5 MPa and a temperature of 120 °C, and a reaction time of 5 min. After the reaction is completed, a reaction solution is obtained.

[0101]

[0102]

[0103]

[0104] Test case

[0105] The reaction solutions containing lithium hexafluorophosphate prepared in Examples 1-36, Comparative Examples 1 and 2, and the final lithium hexafluorophosphate crystals prepared were tested respectively. The specific testing methods are as follows:

[0106] The acidity of lithium hexafluorophosphate was tested using potentiometric titration, the solid content was detected using IC ion chromatography, and the insoluble matter was tested using gravimetric analysis. The particle size of lithium fluoride / lithium hexafluorophosphate was measured using a laser particle size analyzer.

[0107] The test results of Examples 1-36 and Comparative Examples 1 and 2 are shown in Table 2. It can be seen that the acidity and lithium fluoride insoluble content of the lithium hexafluorophosphate prepared using the method of this application are much lower than those of Comparative Examples 1 and 2. Comparative Example 1 uses a batch reaction in a reactor, which not only results in a long reaction time but also leads to higher acidity and lithium fluoride insoluble content in the product lithium hexafluorophosphate, affecting the purity of the lithium hexafluorophosphate. Comparative Example 2, without undergoing mixing treatment in the first microchannel reactor, directly enters the reaction stage, resulting in insufficient reaction between phosphorus pentafluoride gas and lithium fluoride solution. Compared to Examples 1-36, Comparative Example 2 has higher acidity and lithium fluoride insoluble content.

[0108] Furthermore, the particle size of lithium hexafluorophosphate is a key indicator of the product, with an ideal range of 200 μm to 400 μm. Excessively large particle sizes lead to slower dissolution rates and increased internal impurities, affecting cycle stability and safety. Conversely, excessively small particle sizes make the material prone to breakage, reducing its fluidity and impacting electrolyte mixing uniformity and overall battery performance. Compared to Comparative Examples 1 and 2, the lithium hexafluorophosphate prepared using the method described in this application achieves a particle size that meets the core market requirements for high-performance lithium-ion battery electrolytes, ensuring excellent electrolyte conductivity and high battery efficiency, while also improving battery cycle stability and safety.

[0109] Compared to Examples 4, 8, and 12, the experimental results of Examples 1-3, 5-7, and 9-11 demonstrate that the operating conditions of the first continuous flow reactor, including pressure, temperature, and chamber diameter, within a specific range, can reduce the acidity and lithium fluoride insoluble content in the product. When the reaction temperature exceeds a certain threshold, the solubility of the gas decreases, leading to an increase in reaction pressure and failure of back pressure regulation. Under these conditions, the lithium fluoride reaction is incomplete, resulting in a smaller product particle size and increased acidity. Furthermore, when the reactor chamber diameter is too large, the gas-liquid mixing efficiency decreases, and the gas may enter the second continuous flow reactor without sufficient mixing. Due to the higher temperature in the second continuous flow reactor, this further exacerbates the incomplete reaction, thereby affecting the quality of the final product.

[0110] Compared to Examples 17, 20, 24, and 27, the experimental results of Examples 15-16, 18-19, 21-23, and 25-26 demonstrate that the operating conditions of the second continuous flow reactor, including pressure, temperature, chamber diameter, and reaction time, within a specific range, can reduce the acidity and lithium fluoride insoluble content in the product. When the reaction temperature exceeds a certain threshold, the pressure inside the reactor increases, leading to gas loss and affecting the sufficiency of the reaction. This results in an increase in the content of lithium fluoride insolubles and acidity in the final product. Furthermore, when the chamber diameter of the second continuous flow reactor is too large, the gas-liquid mixing efficiency decreases, and gas may leave the reactor before fully reacting. Under these conditions, the reaction is incomplete, leading to a decrease in product quality. In addition, excessively long reaction times cause lithium hexafluorophosphate to remain at high temperatures for too long, and lithium hexafluorophosphate at high temperatures has poor stability and is easily decomposed, affecting product quality.

[0111] Table 2

[0112]

[0113]

[0114] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0115] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for preparing lithium hexafluorophosphate, characterized in that, include: Phosphorus pentafluoride gas was mixed with lithium fluoride solution to obtain the first treatment product; The first processed product was subjected to a reaction treatment to obtain a reaction solution containing lithium hexafluorophosphate. The mixing process is carried out in a first continuous flow reactor. The reaction process is carried out in a second continuous flow reactor; The first continuous flow reactor and the second continuous flow reactor are each selected from microchannel reactors, wherein the channel size of the first continuous flow reactor is larger than the channel size of the second continuous flow reactor; the processing temperature of the mixing process is lower than the processing temperature of the reaction process.

2. The method according to claim 1, characterized in that, The lithium fluoride solution contains lithium fluoride, hydrogen fluoride and water, wherein the solid content of the lithium fluoride in the lithium fluoride solution is less than 10%, and the concentration of the hydrogen fluoride in the lithium fluoride solution is 80-95% by mass.

3. The method according to claim 2, characterized in that, The lithium fluoride has a particle size of less than 200 μm.

4. The method according to claim 1, characterized in that, The channel size of the first continuous flow reactor is 100 μm to 500 μm; the channel size of the second continuous flow reactor is 10 μm to 99 μm; and / or, The reaction chamber temperature of the first continuous flow reactor is 0℃~30℃, and the reaction chamber temperature of the second continuous flow reactor is 30℃~150℃.

5. The method according to claim 1, characterized in that, At least one of the following conditions must be met: The reaction chamber pressure of the first continuous flow reactor is 0 MPa to 2 MPa; The mixing process takes 0.1 min to 2 min. The reaction chamber pressure of the second continuous flow reactor is 0 MPa to 2 MPa; The reaction treatment time is 0.1 min to 5 min.

6. The method according to claim 1, characterized in that, Further includes: The reaction solution containing lithium hexafluorophosphate was subjected to flash evaporation to obtain flash vapor and flash liquid. The flash liquid is crystallized to obtain lithium hexafluorophosphate.

7. The method according to claim 6, characterized in that, The flash evaporation treatment satisfies at least one of the following conditions: The pressure reduction value of the reaction chamber during the flash evaporation treatment is 0.1 MPa to 1 MPa; The temperature reduction of the reaction chamber during the flash evaporation treatment is 20℃~60℃; The feed flow rate for the flash evaporation process is 200 kg / h to 1000 kg / h.

8. The method according to claim 6, characterized in that, The crystallization process satisfies at least one of the following conditions: The temperature for the crystallization process is -50℃ to 0℃; The crystallization process takes 100 to 500 minutes.

9. A lithium hexafluorophosphate, characterized in that, It is prepared by the method described in any one of claims 1 to 7.

10. An apparatus for preparing lithium hexafluorophosphate, characterized in that, include: A first continuous flow reactor is adapted to mix phosphorus pentafluoride gas with lithium fluoride solution to obtain a first processed product. A second continuous flow reactor is connected to the first continuous flow reactor. The second continuous flow reactor is adapted to react the first processed product to obtain a reaction solution containing lithium hexafluorophosphate. The first continuous flow reactor and the second continuous flow reactor are respectively selected from microchannel reactors, and the channel size of the first continuous flow reactor is larger than the channel size of the second continuous flow reactor.

11. The device according to claim 10, characterized in that, Further includes: A flash evaporator connected to a second continuous flow reactor, the flash evaporator being adapted to flash-evaporate the reaction solution containing lithium hexafluorophosphate to obtain flash vapor and flash liquid; A crystallizer connected to the flash evaporator, the crystallizer being adapted to crystallize the flash liquid to obtain the lithium hexafluorophosphate.

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