Production method and production system of lithium hexafluorophosphate solution

Abstract

The invention discloses a production method and system of a lithium hexafluorophosphate solution, and in the production process, lithium fluoride solid continuously enters a first ball milling reactor, and PF5-containing feed gas is continuously introduced into a second ball milling reactor. The production method comprises the following steps: in a first ball-milling reactor, lithium fluoride solid and PF5-containing gas react to obtain lithium hexafluorophosphate, then the lithium hexafluorophosphate and unreacted lithium fluoride solid enter a second ball-milling reactor together, and the PF5-containing gas comes from a gas-phase product of the second ball-milling reactor; in a second ball-milling reactor, lithium fluoride from the first ball-milling reactor reacts with PF5-containing raw material gas, an obtained lithium hexafluorophosphate crude product continuously enters a third reactor, and a gas-phase product is continuously introduced into the first ball-milling reactor; in the third reactor, residual gas in the lithium hexafluorophosphate crude product is removed, and then the lithium hexafluorophosphate crude product enters a fourth reactor; and in a fourth reactor, dissolving the lithium hexafluorophosphate solid in the carbonic ester solvent, and filtering to obtain the lithium hexafluorophosphate solution. The lithium hexafluorophosphate gas-solid phase production process provided by the invention has the advantages of being high in raw material utilization rate, safe and efficient in reaction, capable of realizing continuous and stable production and the like.

Description

Technical Field

[0001] This invention relates to lithium-ion battery electrolytes, specifically to a method and system for producing lithium hexafluorophosphate solution. Background Technology

[0002] Lithium-ion batteries have larger capacity and higher output voltage than traditional batteries, and their cycle performance and conductivity are significantly improved. Therefore, they are widely used in electronics, information technology, computers, military, aerospace, electric vehicles, and other fields. Lithium hexafluorophosphate (LiPF6) is particularly valuable due to the small atomic radius of fluorine, low electronegativity, and high PF6 content. - With its appropriate radius, good ionic conductivity, and electrochemical stability, lithium hexafluorophosphate is currently the most widely used electrolyte salt in commercial lithium-ion batteries. Over the past decade, the lithium battery industry has developed rapidly, driving the rapid growth of upstream industries. The demand for lithium hexafluorophosphate has been continuously increasing, making its preparation methods a hot topic in the industry.

[0003] Currently, there are several main routes for preparing lithium hexafluorophosphate: gas-solid direct reaction method, HF solvent method, organic solvent method and ion exchange method. Among them, the HF solvent method is the most studied, the most mature technology and the most widely used in industrial applications.

[0004] The HF solvent method uses phosphorus pentachloride (PCl5) and HF as raw materials to generate phosphorus pentafluoride (PF5) and HCl gas. Then, the PF5 and HCl mixture reacts with lithium fluoride (LiF) in the HF solvent to produce lithium hexafluorophosphate (LiPF6). Finally, LiPF6 crystals are obtained through a cooling crystallization process. This process has advantages such as high raw material utilization, almost no by-products, high product purity, and the ability to achieve long-term HF recycling. However, anhydrous HF is highly corrosive and toxic, and the reaction process is extremely dangerous. Any leak can cause significant harm to the environment and personnel, placing high demands on equipment corrosion prevention, production environment, and personnel safety. Furthermore, the crystallization process is difficult to control and has a long crystallization time, resulting in low production efficiency.

[0005] The organic solvent method is a way to synthesize lithium hexafluorophosphate in carbonate solvents. Since carbonates are the solvent for preparing the electrolyte, the synthesized lithium hexafluorophosphate carbonate solution does not require additional separation of the solvent and lithium hexafluorophosphate, eliminating the complicated crystallization process and equipment, significantly improving production efficiency and reducing production costs. However, this method either still requires the use of highly corrosive anhydrous HF, and equipment and safety issues remain unresolved; or it requires the prior preparation of high-purity PF5 gas before reacting it with the lithium fluoride carbonate solution, but the preparation of high-purity PF5 gas is difficult and costly, and the preparation process still requires the use of anhydrous HF. Patents US20010041158A1, CN104261369A, CN116514081A, CN101570328A, and CN102491305A all disclose a method for preparing PF5 by using an oxygen-containing phosphorus source (orthophosphoric acid, polyphosphoric acid, phosphorus pentoxide, etc.) as raw material, reacting it with HF to first prepare an aqueous solution of hexafluorophosphoric acid (HPF6), and then reacting it with a dehydrating agent such as sulfur trioxide or fuming sulfuric acid. This method requires multi-stage pressurized distillation to purify the PF5 gas, and the aqueous, strong acid environment presents problems such as severe equipment corrosion and the disposal of byproducts containing fluorosulfates.

[0006] The gas-solid process for preparing lithium hexafluorophosphate is the earliest technology, simple to operate and solvent-free. However, during the gas-solid reaction, after LiPF6 forms on the LiF surface, the internal LiF cannot react with PF5, resulting in low LiF utilization and poor reaction efficiency. Therefore, it is necessary to improve the conversion rate of lithium fluoride by modifying its state or reaction mode.

[0007] In 1950, American fluorine scientist J. H. Simmons directly reacted porous LiF (pretreated with anhydrous HF) with PF5 gas in a nickel container under high temperature and high pressure to produce LiPF6. However, the LiPF6 produced by this method completely coated the solid LiF particles, preventing further reaction. Consequently, the obtained lithium hexafluorophosphate product had low purity and low yield, making large-scale production difficult. Patent JP1989072901A optimized this method by treating lithium fluoride with hydrofluoric acid gas and then further degassing it under vacuum at high temperature (170°C), resulting in highly active LiF with a utilization rate of 67.1%. However, the preparation process of this porous LiF still requires the use of highly corrosive anhydrous hydrogen fluoride.

[0008] Lanxess's German patent CN104093668A discloses the preparation of LiPF6 by reacting a PF5 / HCl mixture with LiF molded material or LiF powder and / or LiFxHF adduct in a fixed-bed reactor or fluidized-bed reactor, followed by dissolution with a carbonate solvent and filtration to obtain a low-chlorine-content lithium hexafluorophosphate liquid salt, but its LiF utilization rate is about 10.8%.

[0009] Therefore, improving the utilization rate of LiF and ensuring the safe, reliable, continuous, and stable production of high-purity products are key to the industrialization of the gas-solid method for preparing lithium hexafluorophosphate. Summary of the Invention

[0010] To address the aforementioned technical problems, this invention proposes a gas-solid phase method for preparing lithium hexafluorophosphate. This method is safe, efficient, and allows for continuous and stable production, making it suitable for industrial applications.

[0011] The objective of this invention is achieved through the following technical solution:

[0012] A method for producing lithium hexafluorophosphate solution, wherein in the production process, solid lithium fluoride enters a first ball mill reactor, and PF5-containing feed gas is introduced into a second ball mill reactor; the production method includes:

[0013] In the first ball mill reactor, lithium fluoride solid reacts with PF5-containing gas to obtain lithium hexafluorophosphate, which is then fed into the second ball mill reactor along with unreacted lithium fluoride solid. The PF5-containing gas is derived from the gaseous products of the second ball mill reactor.

[0014] In the second ball mill reactor, lithium fluoride from the first ball mill reactor reacts with PF5-containing feed gas to obtain crude lithium hexafluorophosphate, which enters the third reactor, while the obtained gaseous product is fed back into the first ball mill reactor.

[0015] In the third reactor, the residual gas in the crude lithium hexafluorophosphate is removed, and then it enters the fourth reactor.

[0016] In the fourth reactor, lithium hexafluorophosphate solid is dissolved in carbonate solvent, and after filtration, a lithium hexafluorophosphate solution is obtained.

[0017] The production method of this invention can be either batch or continuous. For continuous production, solid lithium fluoride is continuously fed into a first ball mill reactor, and PF5-containing feed gas is continuously fed into a second ball mill reactor. The solid materials of lithium hexafluorophosphate and lithium fluoride output from the first ball mill reactor are continuously fed into the second ball mill reactor, and the output tail gas is separated by a separation system. The crude lithium hexafluorophosphate obtained from the second ball mill reactor is continuously fed into a third reactor, and the output gaseous product stream is continuously fed back into the first ball mill reactor.

[0018] In industrial production, PF5-containing feed gas is prepared from phosphorus pentachloride and hydrogen fluoride, or from phosphorus trichloride, hydrogen fluoride, and liquid chlorine. The PF5 gas obtained through these two methods carries both HCl and HF gases. Using the production method of this invention, the prepared PF5 gas does not require purification and can be directly fed into the second ball mill reactor as feed gas.

[0019] Therefore, the PF5-containing raw material gas of the present invention includes PF5 gas, HCl gas and HF gas.

[0020] When preparing PF5-containing feed gas using phosphorus pentachloride and hydrogen fluoride, solid phosphorus pentachloride is added to liquid hydrogen fluoride, or liquid hydrogen fluoride or hydrogen fluoride gas is added to solid phosphorus pentachloride. The reaction temperature is controlled at -20 to 50°C, and the reaction pressure is controlled at 0.1 to 0.5 MPa.

[0021] When preparing PF5-containing feed gas using phosphorus trichloride, hydrogen fluoride, and liquid chlorine, the reaction temperature is controlled at -10 to 50°C, and the reaction pressure is controlled at 0.1 to 3.0 MPa.

[0022] In the production process of the lithium hexafluorophosphate solution of this invention, lithium fluoride solid powder is continuously added to the first ball mill reactor using a solid feeding device. The particle size of the lithium fluoride solid powder is 50-1000 mesh, preferably 300-800 mesh. In the first ball mill reactor, the lithium fluoride powder reacts with PF5 gas in the gaseous product stream output from the second ball mill reactor to obtain lithium hexafluorophosphate. The generated lithium hexafluorophosphate coats the surface of the lithium fluoride, and is removed from the surface of the lithium fluoride after ball milling and pulverization, thereby allowing the lithium fluoride to further react with PF5 gas and improving the utilization rate of the lithium fluoride.

[0023] To ensure complete reaction of PF5 gas from the gaseous product stream of the second ball mill reactor in the first ball mill reactor, the molar ratio of lithium fluoride to PF5 in the PF5-containing gas in the first ball mill reactor is (1-100):1, preferably (2-50):1. The residence time of lithium fluoride and PF5 gas in the first ball mill reactor is 10-600 seconds, preferably 30-300 seconds.

[0024] The first ball mill reactor is a pressure-bearing device with jacketed temperature control or inner plate temperature control. In the first ball mill reactor, the reaction temperature is -15 to 80°C and the reaction pressure is 0 to 1.5 MPa. Preferably, the reaction temperature in the first ball mill reactor is controlled to be 25 to 80°C and the reaction pressure is 0.2 to 1.0 MPa.

[0025] To improve the reaction efficiency of the gas-solid reaction, the first ball mill reactor rotates continuously during the reaction process, with a rotational speed of 100–5000 r / m, preferably 500–3000 r / m. The first ball mill reactor is equipped with grinding balls, and the ratio of the diameter of the grinding balls to the diameter of the first ball mill reactor is 1:(5–200), preferably 1:(10–50).

[0026] The tail gas output from the first ball mill reactor enters a separation system for separation. The PF5 content in the tail gas is ≤0.2%, meaning the utilization rate of PF5 in the PF5-containing feed gas is ≥99.8%. After compression and separation, the HCl in the tail gas can be used to prepare industrial hydrochloric acid, and the HF can be recycled.

[0027] According to the production method of the present invention, in the solid materials of lithium hexafluorophosphate and lithium fluoride output from the first ball mill reactor, the mass fraction of lithium hexafluorophosphate is 50-80%, and the remainder is unreacted lithium fluoride.

[0028] In the second ball mill reactor, unreacted lithium fluoride from the first ball mill reactor reacts continuously with PF5 from the continuously introduced PF5-containing feed gas, further converting the unreacted lithium fluoride into lithium hexafluorophosphate, thus improving the utilization rate of lithium fluoride. The molar ratio of the unreacted lithium fluoride to PF5 in the PF5-containing feed gas is 1:(1-100), preferably 1:(2-10). The residence time of lithium fluoride and PF5 in the second ball mill reactor is 10-600 seconds, preferably 30-300 seconds.

[0029] The second ball mill reactor is also a pressure vessel with jacketed or internal disc temperature control. In the second ball mill reactor, the reaction temperature is -15℃ to 80℃, and the pressure is 0 to 1.5 MPa. Preferably, the reaction temperature of the second ball mill reactor is controlled at 25 to 60℃, and the pressure at 0.2 to 1.0 MPa.

[0030] The second ball mill reactor also maintains continuous rotation during the reaction process, with a rotational speed of 100–5000 r / m, preferably 500–3000 r / m. Furthermore, the ratio of the diameter of the grinding balls in the second ball mill reactor to the diameter of the second ball mill reactor is 1:(5–200), preferably 1:(20–100).

[0031] According to the production method of the present invention, the mass fraction of lithium hexafluorophosphate in the crude lithium hexafluorophosphate output from the second ball mill reactor is ≥96%.

[0032] The crude lithium hexafluorophosphate enters the third reactor, which is a tubular reactor with a twin-screw extruder. After entering the third reactor from the hopper, the crude lithium hexafluorophosphate is agitated and continuously output under the drive of the twin-screw extruder. The third reactor is set with a vacuum degree ≥0.08 MPa and a temperature of 0–80°C. Residual HCl and HF gases in the crude lithium hexafluorophosphate are removed. The removed HCl and HF gases enter a dry separation system to obtain HCl and HF gases respectively. Preferably, the third reactor is set with a vacuum degree ≥0.09 MPa and a temperature of 50–80°C. The residence time of the crude lithium hexafluorophosphate in the third reactor is 10–300 min, preferably 30 min–120 min.

[0033] After the residual gas is removed, the lithium hexafluorophosphate solid and carbonate solvent enter the fourth reactor for dissolution. In order to control the dissolution rate and prevent material decomposition, the dissolution temperature is controlled at 0-50℃, preferably 10-30℃.

[0034] The carbonate solvent is pre-dried before entering the fourth reactor, and its moisture content is ≤20ppm. The carbonate solvent is selected from at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC). Preferably, the carbonate solvent is selected from dimethyl carbonate (DMC) and / or ethyl methyl carbonate (EMC).

[0035] In a preferred embodiment, lithium hexafluorophosphate solid and carbonate solvent are continuously introduced into the fourth reactor, and the mass ratio of lithium hexafluorophosphate solid to carbonate solvent is 1:(1-5). The residence time in the fourth reactor is 10-120 min, which is beneficial to the dissolution of lithium hexafluorophosphate. Preferably, the mass ratio of lithium hexafluorophosphate solid to carbonate solvent is 1:(2-3), and the residence time in the fourth reactor is 30-90 min.

[0036] The lithium hexafluorophosphate solution obtained from the fourth reactor is filtered to remove insoluble matter to obtain lithium hexafluorophosphate product, wherein the mass fraction of lithium hexafluorophosphate is 25-33 wt%, the chloride ion content is ≤2 ppm, the acidity is ≤50 ppm, and the color is ≤30 Hazen.

[0037] A second aspect of the present invention provides a production system for producing lithium hexafluorophosphate solution according to any of the above descriptions, the production system comprising:

[0038] In the first ball mill reactor, solid lithium fluoride enters through the first feed bin and reacts with the gaseous product stream output from the second ball mill reactor. The resulting solid product stream of lithium hexafluorophosphate and unreacted lithium fluoride enters the second ball mill reactor, while the gaseous product stream (i.e., tail gas) after the reaction is discharged from the first ball mill reactor. The gaseous product stream discharged from the first ball mill reactor can be further entered into the separation system for separation and collection.

[0039] The solid product from the first ball mill reactor enters the second ball mill reactor through the second feed hopper and reacts with the PF5-containing feed gas introduced into the second ball mill reactor. The crude lithium hexafluorophosphate obtained enters the third reactor, and the gaseous product obtained enters the first ball mill reactor.

[0040] The third reactor is a tubular reactor with a twin-screw extruder. After the crude lithium hexafluorophosphate enters the third reactor, the residual gas is removed under negative pressure, and then it enters the fourth reactor.

[0041] The fourth reactor, which is a reaction vessel, is used for stirring and dissolving crude lithium hexafluorophosphate. The resulting lithium hexafluorophosphate solution is filtered to remove insoluble matter, yielding a lithium hexafluorophosphate solution product, which is then stored in a storage device. The filter includes a general filter and a precision filter. The lithium hexafluorophosphate solution first enters the general filter and then enters the precision filter. The precision filter membrane has a pore size of 0.2–0.5 μm.

[0042] Furthermore, a third feeding hopper is provided between the second ball mill reactor and the third reactor for storing and feeding crude lithium hexafluorophosphate; a fourth feeding hopper is provided between the third reactor and the fourth reactor for storing and feeding degassed solid lithium hexafluorophosphate.

[0043] Furthermore, the production system also includes a PF5 generator for preparing PF5-containing feed gas.

[0044] The first and second ball mill reactors of the present invention have an aspect ratio of 1:(10-100), and both contain grinding balls. The grinding balls are made of a material selected from stainless steel, alumina, zirconia ceramic, agate, tungsten carbide or silicon carbide, preferably stainless steel, zirconia ceramic or tungsten carbide.

[0045] Specifically, the first and second ball mill reactors of the present invention are double-layer straight-cylinder dry ball mills. Specifically, the double-layer straight-cylinder dry ball mill consists of a cylinder, a motor, and a support. The cylinder is divided into inner and outer layers by straight cylindrical plates and filled with grinding balls for grinding the material. The outer cylinder has an outer feed inlet, an outer discharge inlet, an inner feed inlet, and a side discharge outlet. A heat exchange jacket is located on the outer side of the cylinder, and the heat exchange jacket has a heat exchange medium inlet and outlet.

[0046] The materials for the first and second ball mill reactors of this invention are selected from fluoropolymer-lined carbon steel, 304 stainless steel, 316L stainless steel, Inconel nickel alloy 600, or Hastelloy C alloy; the material for the third reactor is selected from 316L stainless steel, silicon carbide, or titanium; and the material for the fourth reactor is selected from 304 stainless steel, 316L stainless steel, or fluoropolymer-lined carbon steel. Preferably, the materials for the first and second ball mill reactors are selected from 316L stainless steel, Inconel nickel alloy 600, or Hastelloy C alloy; the material for the third reactor is selected from 316L stainless steel or silicon carbide; and the material for the fourth reactor is selected from 316L stainless steel or fluoropolymer-lined carbon steel.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] 1. This invention utilizes two reversible circulating ball mill reactors to achieve continuous gas-solid reaction preparation of lithium hexafluorophosphate. It uses only conventional lithium fluoride (without HF treatment to obtain highly active lithium fluoride) as raw material, significantly improving lithium fluoride utilization by ≥80%, and ensuring the product contains ≥96% lithium hexafluorophosphate. Simultaneously, through optimization of material ratios and reaction parameters, the utilization rate of phosphorus pentafluoride in the PF5-containing feed gas is improved, achieving almost complete conversion.

[0049] 2. The process of the present invention can directly use inexpensive and readily available PF5 mixed gas containing HCl and HF as raw material, without the need to use high-purity phosphorus pentafluoride, simplifying the process and reducing energy consumption and cost.

[0050] 3. In the reaction process of this invention, HCl and HF gases can be recovered and pure HCl and HF can be obtained by dry separation. HF can be recycled, and HCl can be used to prepare industrial hydrochloric acid. There are no other by-products in the reaction process, making it green and environmentally friendly. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the lithium hexafluorophosphate solution production system in an embodiment of the present invention. In the figure:

[0052] 1a. PF5 generator 1; 1b. PF5 generator 2; 2. Second feeding bin; 3. Second ball mill reactor; 4. First feeding bin; 5. First ball mill reactor; 6. Third feeding bin; 7. Third reactor; 8. Fourth feeding bin; 9. Fourth reactor; 10. General filter; 11. Precision filter; 12. Product collection tank;

[0053] Figure 2 and Figure 3 These are, respectively, a front view and a side view of the ball mill reactor used in the lithium hexafluorophosphate solution production system of this embodiment of the invention. Figure 2 and Figure 3 middle:

[0054] 13. Motor; 14. Cylinder; 15. Outer feed inlet; 16. Grinding ball; 17. Heat exchange jacket; 18. Jacket heat exchange medium outlet; 19. Outer discharge outlet; 20. Support; 21. Rotating shaft; 22. Jacket heat exchange medium inlet; 23. Cylinder support; 24. Straight cylinder plate; 25. Inner feed inlet; 26. Side discharge outlet. Detailed Implementation

[0055] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternatives, improvements, and equivalents that may be included within the scope of the claims.

[0056] Example 1

[0057] This embodiment provides a continuous production system for lithium hexafluorophosphate solution, as shown in the attached figure. Figure 1-3 As shown, the production system includes:

[0058] PF5 generating device 1 can be a single PF5 generating device, or PF5 generating device a and PF5 generating device b can be arranged in parallel for different processes to prepare PF5. The PF5 generating device is made of 316L stainless steel and is equipped with a condenser. It can produce PF5 by introducing phosphorus pentachloride and hydrogen fluoride, or by introducing phosphorus trichloride, liquid chlorine and hydrogen fluoride.

[0059] The first ball mill reactor 5 and the second ball mill reactor 3 are both double-layer straight-cylinder dry ball mills with a volume of 5L and an inner diameter of 80mm. The built-in stainless steel grinding balls have a diameter of 4mm. The specific structure includes a motor 13, a cylinder 14, and a cylinder support 23. The cylinder is divided into inner and outer layers by a straight cylindrical plate 24 and is filled with grinding balls to grind the material. The outer layer is provided with a feed inlet 15 and a discharge outlet 19, the inner layer has a feed inlet 25 and a side discharge outlet 26. The outer layer of the cylinder is provided with a heat exchange jacket, which has a heat exchange medium inlet 22 and an outlet 18.

[0060] A first feeding hopper 4 is provided above the first ball mill reactor 5 for storing and feeding LiF; a second feeding hopper 2 is provided above the second ball mill reactor 3, which is connected to the discharge port of the first ball mill reactor 5 for storing and feeding LiPF6 solid and unreacted lithium fluoride solid; the gas phase inlet of the second ball mill reactor 3 is connected to the outlet of the PF5 generator 1, the gas phase outlet is connected to the gas phase inlet of the first ball mill reactor 5, and the solid outlet is connected to the third reactor 7; a third feeding hopper 6 is provided between the second ball mill reactor 3 and the third reactor 7 for storing and feeding crude lithium hexafluorophosphate.

[0061] The system consists of a third reactor 7, a fourth feeding hopper 8, a fourth reactor 9, a filter 10, a precision filter 11, and a product collection tank 12, connected in sequence. The third reactor is a tubular reactor with a twin-screw extruder (5L volume) used for degassing crude lithium hexafluorophosphate. The fourth feeding hopper 8 is used for storing and feeding the degassed solid lithium hexafluorophosphate. The fourth reactor 9 is a stirred reactor (10L volume, steel-lined with PFA material) used for stirring and dissolving crude lithium hexafluorophosphate. The filter 10 is used to remove residual insoluble matter in the lithium hexafluorophosphate solution. The precision filter 11 has a filter membrane pore size of 0.25μm and is used to remove trace amounts of insoluble matter in the crude lithium hexafluorophosphate solution to obtain the lithium hexafluorophosphate solution product.

[0062] Example 2

[0063] This embodiment uses the continuous production system described in Example 1 to continuously produce lithium hexafluorophosphate solution, specifically including the following steps:

[0064] (1) Preparation of PF5-containing feed gas: Solid phosphorus pentachloride was added to the PF5 generator and sealed. Hydrogen fluoride was then sprayed into the reactor using a spray method. The molar ratio of phosphorus pentachloride to hydrogen fluoride was 1:7.5. The reaction occurred at approximately 60°C to produce phosphorus pentafluoride and hydrogen chloride. Due to the exothermic reaction, a small portion of unreacted hydrogen fluoride was released along with the phosphorus pentafluoride and hydrogen chloride to form a PF5-containing mixed gas. The mass fraction of phosphorus pentafluoride in the mixed gas was determined to be 38.5%.

[0065] (2) A PF5-containing mixed gas is continuously fed into the inner bottom inlet of the second ball mill reactor at a rate of 285 g / min. A solid mixture of lithium hexafluorophosphate and lithium fluoride, output from the first ball mill reactor, is continuously fed into the outer inlet of the second ball mill reactor at a rate of 30 g / min. Under rapid ball milling, the solid mixture of lithium hexafluorophosphate and lithium fluoride first enters the outer layer of the double-layer straight-cylinder dry ball mill, and gradually enters the inner layer as the feed rate increases. The mixed gas is introduced from the inner layer, first reacting with the solid mixture of lithium hexafluorophosphate and lithium fluoride in the inner layer. Unreacted gas sequentially enters the outer layer, and finally enters the first ball mill reactor from the outer gas phase outlet of the second ball mill reactor. The solid product from the second ball mill reactor is output to the lithium hexafluorophosphate crude product silo.

[0066] The lithium hexafluorophosphate content in the solid mixture of lithium hexafluorophosphate and lithium fluoride from the first ball mill reactor was 74.5%. The molar ratio of lithium fluoride to phosphorus pentafluoride in the second ball mill reactor was calculated to be 1:3. Simultaneously, the rotation speed of the second ball mill reactor was controlled at 1000 r / m, the reaction temperature at 50℃, the reaction pressure at 0.5 MPa, and the residence time of the reactants in the second reactor was 120 seconds.

[0067] The test results showed that the mass fraction of phosphorus pentafluoride in the mixed gas at the gas phase outlet of the second ball mill reactor was 31.5%, and the content of lithium hexafluorophosphate in the solid product of the second ball mill reactor was 97.5%. Therefore, the single-pass conversion rate of lithium fluoride in the second ball mill reactor was 90.2%.

[0068] (3) The mixed gas at the outer gas phase outlet of the second ball mill reactor is continuously fed from the inner gas inlet of the first ball mill reactor at a feed rate of 62.4 g / min. Lithium fluoride powder (500 mesh particle size) is continuously fed from the outer feed inlet of the first ball mill reactor at a feed rate of 12 g / min. Under rapid ball milling, the lithium fluoride powder first enters the outer layer of the ball mill, and gradually enters the inner layer as the feed rate increases. The mixed gas is introduced from the inner layer, first reacting with the lithium fluoride in the inner layer, and the unreacted gas then enters the outer layer, and finally enters the tail gas system from the outer gas phase outlet of the reactor. The reaction solid product enters the second ball mill reactor after passing through the lithium hexafluorophosphate and lithium fluoride silos.

[0069] During the reaction, the first ball mill reactor rotated at 1000 r / m, with a pressure of 0.5 MPa and a temperature of 50 °C; the molar ratio of lithium fluoride to phosphorus pentafluoride was approximately 3:1, and the material residence time was 120 seconds.

[0070] Tests showed that the solid product from the first ball mill reactor contained 74.5% lithium hexafluorophosphate, and the gaseous outlet of the first ball mill reactor contained 0.08% phosphorus pentafluoride.

[0071] (4) The crude lithium hexafluorophosphate powder output from the second ball mill reactor is continuously fed into the third reactor. A twin-screw agitator and vacuum device are activated, controlling the feed rate of the crude lithium hexafluorophosphate at 30 g / min, maintaining a vacuum of ≥0.095 MPa, a temperature of 60℃, and a residence time of 60 min to continuously obtain degassed solid lithium hexafluorophosphate. Testing revealed that the chloride ion content in the solid lithium hexafluorophosphate was 1.2 ppm, and the acidity was 55 ppm (calculated as HF).

[0072] (5) The degassed lithium hexafluorophosphate solid is continuously fed into the fourth reactor at a feed rate of 30 g / min; ethyl methyl carbonate (EMC, 8 ppm moisture, 99.996% purity) is continuously added to the fourth reactor at a feed rate of 70 g / min; lithium hexafluorophosphate is stirred and dissolved, and the dissolution temperature is controlled at about 10-15℃.

[0073] After continuous feeding for 60 minutes, the feeding was stopped. The LiPF6 solution was pumped to a filtration device for filtration, and then filtered through a precision filter to obtain a lithium hexafluorophosphate solution. The product analysis results are shown in Table 1.

[0074] Example 3

[0075] The operation of this embodiment is the same as that of embodiment 2, except that in step (2), the residence time of the reactants in the second reactor is increased from 120 seconds to 240 seconds, and all other operations remain unchanged.

[0076] The test results showed that the mass fraction of phosphorus pentafluoride in the mixed gas at the gas phase outlet of the second ball mill reactor was 28.8%; the content of lithium hexafluorophosphate in the solid product of the second ball mill reactor was 98.4%, and the single-pass conversion rate of lithium fluoride was 93.7%.

[0077] The quality analysis results of the prepared lithium hexafluorophosphate solution are shown in Table 1.

[0078] Example 4

[0079] The operation of this embodiment is the same as that of embodiment 2, except that in step (2), the feed rate of the solid mixture of lithium hexafluorophosphate and lithium fluoride is increased from 30 g / min to 45 g / min, so the molar ratio of lithium fluoride to phosphorus pentafluoride in the second ball mill reactor is 1:2, and other operations remain unchanged.

[0080] The analysis revealed that the lithium hexafluorophosphate content in the solid product from the second ball mill reactor was 96.1%, and the single-pass conversion rate of lithium fluoride was 84.7%. The quality analysis results of the prepared lithium hexafluorophosphate solution product are shown in Table 1.

[0081] Example 5

[0082] The operation of this embodiment is the same as that of embodiment 2, except that in step (2), the reaction temperature of the second ball mill reactor is reduced from 50°C to 30°C, and all other operations remain unchanged.

[0083] The analysis revealed that the lithium hexafluorophosphate content in the solid product from the second ball mill reactor was 96.5%, and the single-pass conversion rate of lithium fluoride was 86.3%. The quality analysis results of the prepared lithium hexafluorophosphate solution product are shown in Table 1.

[0084] Example 6

[0085] The operation of this embodiment is the same as that of embodiment 2, except that in step (2), the reaction pressure of the second ball mill reactor is reduced from 0.5MPa to 0.2MPa, and all other operations remain unchanged.

[0086] The analysis showed that the lithium hexafluorophosphate content in the solid product from the second ball mill reactor was 96.2%, and the single-pass conversion rate of lithium fluoride was 85.1%. The quality analysis results of the prepared lithium hexafluorophosphate solution product are shown in Table 1.

[0087] Example 7

[0088] The operation of this embodiment is the same as that of embodiment 2, except that in step (2), the rotational speed of the second ball mill reactor is increased from 1000 r / m to 2000 r / m, and all other operations remain unchanged.

[0089] The analysis results showed that the lithium hexafluorophosphate content in the solid product from the second ball mill reactor was 97.8%, and the single-pass conversion rate of lithium fluoride was 91.4%. The quality analysis results of the prepared lithium hexafluorophosphate solution product are shown in Table 1.

[0090] Example 8

[0091] The operation of this embodiment is the same as that of embodiment 2, except that in step (3), the residence time of the reactants in the first ball mill reactor is increased from 120 seconds to 240 seconds, and all other operations remain unchanged.

[0092] Tests showed that the lithium hexafluorophosphate content in the solid product of the first ball mill reactor was 80.2%, and the phosphorus pentafluoride content in the gas phase outlet of the first ball mill reactor was 0.05%.

[0093] The quality analysis results of the prepared lithium hexafluorophosphate solution are shown in Table 1.

[0094] Example 9

[0095] The operation of this embodiment is the same as that of embodiment 2, except that in step (3), the feed rate of the mixed gas output from the second ball mill reactor into the first ball mill reactor is increased from 62.4 g / min to 93.6 g / min, so the molar ratio of lithium fluoride to phosphorus pentafluoride is about 2:1, and other operating conditions remain unchanged.

[0096] Tests showed that the solid product from the first ball mill reactor contained 68.8% lithium hexafluorophosphate, and the gaseous outlet from the first ball mill reactor contained 0.20% phosphorus pentafluoride.

[0097] The quality analysis results of the prepared lithium hexafluorophosphate solution are shown in Table 1.

[0098] Example 10

[0099] The operation of this embodiment is the same as that of embodiment 2, except that in step (3), the reaction temperature of the first ball mill reactor is increased from 50°C to 80°C, and all other operations remain unchanged.

[0100] Tests showed that the solid product from the first ball mill reactor contained 77.5% lithium hexafluorophosphate, and the gaseous outlet from the first ball mill reactor contained 0.09% phosphorus pentafluoride.

[0101] The quality analysis results of the prepared lithium hexafluorophosphate solution are shown in Table 1.

[0102] Example 11

[0103] The operation of this embodiment is the same as that of embodiment 2, except that in step (3), the reaction pressure of the first ball mill reactor is increased from 0.5MPa to 1.0MPa, and all other operations remain unchanged.

[0104] Tests showed that the lithium hexafluorophosphate content in the solid product of the first ball mill reactor was 76.2%, and the phosphorus pentafluoride content in the gas phase outlet of the first ball mill reactor was 0.11%.

[0105] The quality analysis results of the prepared lithium hexafluorophosphate solution are shown in Table 1.

[0106] Example 12

[0107] The operation of this embodiment is the same as that of embodiment 2, except that in step (4), the residence time of crude lithium hexafluorophosphate in the third reactor is reduced from 60 min to 30 min, and all other operations remain unchanged.

[0108] The quality analysis results of the prepared lithium hexafluorophosphate solution are shown in Table 1.

[0109] Example 13

[0110] The operation of this embodiment is the same as that of embodiment 2, except that in step (4), the temperature of the third reactor is increased from 60°C to 80°C, and all other operations remain unchanged.

[0111] The quality analysis results of the prepared lithium hexafluorophosphate solution are shown in Table 1.

[0112] Example 14

[0113] The operation of this embodiment is the same as that of embodiment 2, except that in step (5), the solvent is replaced by dimethyl carbonate (DMC, water content 8ppm, purity 99.996%) instead of ethyl methyl carbonate (EMC, water content 12ppm, purity 99.995%). All other operations remain unchanged.

[0114] The quality analysis results of the prepared lithium hexafluorophosphate solution are shown in Table 1.

[0115] Example 15

[0116] This embodiment uses the continuous production system described in Example 1 to continuously produce lithium hexafluorophosphate solution, specifically including the following steps:

[0117] (1) Preparation of PF5-containing feed gas: Anhydrous hydrogen fluoride and liquid chlorine were added to the PF5 generator, stirring was started, and phosphorus trichloride liquid was continuously added. The pressure in the reactor was controlled at 0.6 MPa and the temperature at 10℃. The reaction yielded phosphorus pentafluoride gas. Due to the exothermic reaction, a small portion of hydrogen fluoride was mixed with phosphorus pentafluoride and hydrogen chloride to form a PF5-containing mixed gas. The mass fraction of phosphorus pentafluoride in the mixed gas was measured to be 40.0%.

[0118] (2) A PF5-containing mixed gas is continuously fed into the inner inlet of the second ball mill reactor at a feed rate of 278 g / min; a solid mixture of lithium hexafluorophosphate and lithium fluoride output from the first ball mill reactor is continuously fed into the outer inlet of the second ball mill reactor at a feed rate of 30 g / min; under rapid ball milling, the solid mixture of lithium hexafluorophosphate and lithium fluoride first enters the outer layer of the double-layer straight-cylinder dry ball mill, and gradually enters the inner layer as the feed rate increases; the mixed gas is introduced from the inner layer, first reacting with the solid mixture of lithium hexafluorophosphate and lithium fluoride in the inner layer, and the unreacted gas then enters the outer layer, finally entering the first ball mill reactor from the outer gas phase outlet of the second ball mill reactor. The solid product of the second ball mill reactor is output to the lithium hexafluorophosphate crude product silo. At the same time, the rotation speed of the second ball mill reactor is controlled at 1000 r / m, the reaction temperature at 50℃, the reaction pressure at 0.5 MPa, and the residence time of the reactants in the second reactor is 120 seconds.

[0119] Analysis revealed that the lithium hexafluorophosphate content in the solid mixture of lithium hexafluorophosphate and lithium fluoride from the first ball mill reactor was 74.3%, and the calculated molar ratio of lithium fluoride to phosphorus pentafluoride in the second ball mill reactor was 1:3. The mass fraction of phosphorus pentafluoride in the mixed gas at the gas phase outlet of the second ball mill reactor was 30.5%, the lithium hexafluorophosphate content in the solid product of the second ball mill reactor was 98.0%, and the single-pass conversion rate of lithium fluoride in the second ball mill reactor was 92.2%.

[0120] (3) The mixed gas at the top gas phase outlet of the second ball mill reactor is continuously fed from the bottom inlet of the first ball mill reactor at a feed rate of 63.6 g / min. Lithium fluoride powder (500 mesh particle size) is continuously fed from the outer inlet of the first ball mill reactor at a feed rate of 12 g / min. Under rapid ball milling, the lithium fluoride powder first enters the outer layer of the ball mill, and gradually enters the inner layer as the feed rate increases. The mixed gas is introduced from the inner inlet, first reacting with the lithium fluoride in the inner layer, and the unreacted gas then enters the outer layer, finally entering the tail gas system from the outer gas phase outlet of the reactor. The reaction solid product enters the second ball mill reactor after passing through the lithium hexafluorophosphate and lithium fluoride solid silos.

[0121] During the reaction, the first ball mill reactor rotated at 1000 r / m, with a pressure of 0.5 MPa and a temperature of 50 °C; the molar ratio of lithium fluoride to phosphorus pentafluoride was approximately 3:1, and the material residence time was 120 seconds.

[0122] Tests showed that the solid product from the first ball mill reactor contained 74.3% lithium hexafluorophosphate, and the gaseous outlet of the first ball mill reactor contained 0.09% phosphorus pentafluoride.

[0123] (4) The crude lithium hexafluorophosphate powder output from the second ball mill reactor is continuously fed into the third reactor. A twin-screw agitator and vacuum device are activated, controlling the feed rate of the crude lithium hexafluorophosphate at 30 g / min, maintaining a vacuum of ≥0.095 MPa, a temperature of 60℃, and a residence time of 60 min to continuously obtain degassed solid lithium hexafluorophosphate. Testing revealed that the chloride ion content in the solid lithium hexafluorophosphate was 1.8 ppm, and the acidity was 65 ppm (calculated as HF).

[0124] (5) The degassed lithium hexafluorophosphate solid is continuously fed into the fourth reactor at a feed rate of 30 g / min; ethyl methyl carbonate (EMC, 8 ppm water, 99.996% purity) is continuously added to the reactor at a feed rate of 70 g / min; lithium hexafluorophosphate is stirred and dissolved, and the dissolution temperature is controlled at about 10-15℃.

[0125] After continuous feeding for 60 minutes, the feeding was stopped. The synthesis liquid was pumped to a filter press for filtration and then filtered through a precision filter to obtain a lithium hexafluorophosphate solution. The product analysis results are shown in Table 1 below.

[0126] Table 1. Analysis Results of Lithium Hexafluorophosphate Solution Products

[0127]

[0128]

[0129] Note: Acidity is expressed in HF.

[0130] Comparative Example 1

[0131] This embodiment uses a single ball mill reactor to prepare lithium hexafluorophosphate solution. The reaction steps are as follows:

[0132] (1) Preparation of PF5-containing feed gas: The operation is the same as in Example 2, and a mixed gas containing HF, PF5 and HCl is obtained. The mass fraction of PF5 in the mixed gas is 38.5%.

[0133] (2) A mixed gas containing PF5, HCl and a small amount of HF is continuously fed from the inner air inlet of the ball mill reactor (a double-layer straight cylinder dry ball mill with a volume of 5L and an inner diameter of 80mm, and stainless steel grinding balls with a diameter of 4mm) at a feeding rate of 453g / min; lithium fluoride powder (500 mesh) is continuously fed from the outer air inlet of the ball mill reactor at a feeding rate of 12g / min; then PF5:LiF = 3:1.

[0134] In rapid ball milling, lithium fluoride powder first enters the outer layer of a double-layer straight-cylinder dry ball mill, and gradually enters the inner layer as the feed rate increases. Mixed gas is introduced from the inner layer, first reacting with the lithium fluoride powder inside. Unreacted gas sequentially enters the outer layer, and finally enters the tail gas system from the outer gas phase outlet of the ball mill reactor. The solid product from the ball mill reactor is directly output to the crude lithium hexafluorophosphate silo. The ball mill reactor speed is controlled at 1000 r / m, the reaction temperature at 50℃, the reaction pressure at 0.5 MPa, and the residence time of the reactants in the ball mill reactor is 120 seconds.

[0135] Testing revealed that the mass fraction of phosphorus pentafluoride in the mixed gas at the outlet of the ball mill reactor was 31.2%. Due to the difficulty in separating PF5 from HCl, a large amount of PF5 was wasted, and the fluorine and phosphorus levels in the byproduct hydrochloric acid exceeded the standards. The content of lithium hexafluorophosphate in the solid product of the ball mill reactor was 88.5%, and the single-pass conversion rate of lithium fluoride was 88.5%.

[0136] Comparative Example 2

[0137] The operation of this comparative example is the same as that of comparative example 1, except that in step (2), the feed rate of the mixed gas containing PF5, HCl and a small amount of HF is reduced to 50.3 g / min, and the feed rate of lithium fluoride powder is 12 g / min; therefore, PF5:LiF = 1:3. All other operations remain unchanged.

[0138] Tests showed that the mass fraction of phosphorus pentafluoride in the mixed gas at the outlet of the ball mill reactor was 0.15%, the content of lithium hexafluorophosphate in the solid product of the ball mill reactor was 72.2%, and the remaining components were mainly unreacted lithium fluoride.

[0139] Comparative Example 3

[0140] The operation of this comparative example is the same as that of comparative example 1, except that in step (2), the feed rate of the mixed gas containing -PF5, HCl and a small amount of HF is reduced to 151 g / min, and the feed rate of lithium fluoride powder is 12 g / min; then PF5:LiF = 1:1. All other operations remain unchanged.

[0141] Tests showed that the mass fraction of phosphorus pentafluoride in the mixed gas at the outlet of the ball mill reactor was 20.0%, the content of lithium hexafluorophosphate in the solid product of the ball mill reactor was 89.7%, and the remaining components were mainly unreacted lithium fluoride.

[0142] Comparative Example 4

[0143] The operation of this comparative example is the same as that of Example 2, except that the rotational speed of the first ball mill reactor and the second ball mill reactor is 0 r / m, that is, they do not rotate, and other conditions remain unchanged.

[0144] The test results showed that the mass fraction of phosphorus pentafluoride in the mixed gas at the gas phase outlet of the second ball mill reactor was 38.3%, the content of lithium hexafluorophosphate in the solid product of the second ball mill reactor was 6.5%, and the single-pass conversion rate of lithium fluoride was 1.27%.

[0145] Tests showed that the lithium hexafluorophosphate content in the solid product of the first ball mill reactor was 5.3%, and the phosphorus pentafluoride content in the gas phase outlet of the first ball mill reactor was 37.7%.

Claims

1. A method for producing lithium hexafluorophosphate solution, characterized in that: In the production process, solid lithium fluoride enters the first ball mill reactor, and PF5-containing feed gas is introduced into the second ball mill reactor; the production method includes: In the first ball mill reactor, lithium fluoride solid reacts with PF5-containing gas to obtain lithium hexafluorophosphate, which is then fed into the second ball mill reactor along with unreacted lithium fluoride solid. The PF5-containing gas is derived from the gaseous products of the second ball mill reactor. In the second ball mill reactor, lithium fluoride from the first ball mill reactor reacts with PF5-containing feed gas to obtain crude lithium hexafluorophosphate, which is continuously fed into the third reactor, while the obtained gaseous product is continuously fed into the first ball mill reactor. In the third reactor, the residual gas in the crude lithium hexafluorophosphate is removed, and then it enters the fourth reactor. In the fourth reactor, lithium hexafluorophosphate solid is dissolved in carbonate solvent, and after filtration, a lithium hexafluorophosphate solution is obtained.

2. The method for producing lithium hexafluorophosphate solution according to claim 1, characterized in that: The PF5-containing feed gas includes PF5 gas, HCl gas, and HF gas.

3. The method for producing lithium hexafluorophosphate solution according to claim 2, characterized in that: The PF5-containing feed gas is prepared from phosphorus pentachloride and hydrogen fluoride, or from phosphorus trichloride, hydrogen fluoride and liquid chlorine.

4. The method for producing lithium hexafluorophosphate solution according to claim 1, characterized in that: In the first ball mill reactor, the molar ratio of the added lithium fluoride solid to the PF5 in the PF5-containing gas is (1-100):

1.

5. The method for producing lithium hexafluorophosphate solution according to claim 4, characterized in that: In the first ball mill reactor, the residence time of the reactants is 10 to 600 seconds.

6. The method for producing lithium hexafluorophosphate solution according to claim 4, characterized in that: In the first ball mill reactor, the reaction temperature is -15 to 80°C and the reaction pressure is 0 to 1.5 MPa.

7. The method for producing lithium hexafluorophosphate solution according to claim 1, characterized in that: In the second ball mill reactor, the molar ratio of unreacted lithium fluoride from the first ball mill reactor to PF5 in the introduced PF5-containing feed gas is 1:(1-100).

8. The method for producing lithium hexafluorophosphate solution according to claim 7, characterized in that: In the second ball mill reactor, the residence time of the reactants is 10 to 600 seconds.

9. The method for producing lithium hexafluorophosphate solution according to claim 7, characterized in that: In the second ball mill reactor, the reaction temperature is -15 to 80°C and the reaction pressure is 0 to 1.5 MPa.

10. The method for producing lithium hexafluorophosphate solution according to claim 1, characterized in that: The third reactor is set with a vacuum degree ≥0.08MPa and a temperature of 0~80℃, so that the residual HCl and HF gases in the crude lithium hexafluorophosphate are removed.

11. The method for producing lithium hexafluorophosphate solution according to claim 1, characterized in that: In the fourth reactor, the water content of the carbonate solvent is ≤20 ppm and is selected from at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (VC), and propylene carbonate (PC).

12. The method for producing lithium hexafluorophosphate solution according to claim 11, characterized in that: In the fourth reactor, the dissolution temperature is controlled at 0–50°C to prevent material decomposition.

13. The method for producing lithium hexafluorophosphate solution according to claim 1, characterized in that: The lithium hexafluorophosphate solution obtained from the fourth reactor is filtered to remove insoluble matter, and then the lithium hexafluorophosphate solution product is obtained.

14. A lithium hexafluorophosphate solution production system for producing the lithium hexafluorophosphate solution according to any one of claims 1-13, characterized in that: The production system includes: In the first ball mill reactor, solid lithium fluoride enters through the first feed bin and reacts with the gaseous product stream output from the second ball mill reactor. The resulting solid product stream of lithium hexafluorophosphate and unreacted lithium fluoride enters the second ball mill reactor, while the gaseous product stream after the reaction is discharged from the first ball mill reactor. The solid product from the first ball mill reactor enters the second ball mill reactor through the second feed hopper and reacts with the PF5-containing feed gas introduced into the second ball mill reactor. The crude lithium hexafluorophosphate obtained enters the third reactor, and the gaseous product obtained enters the first ball mill reactor. The third reactor is a tubular reactor with a twin-screw extruder. After the crude lithium hexafluorophosphate enters the third reactor, the residual gas is removed under negative pressure, and then it enters the fourth reactor. The fourth reactor, which is a reaction vessel, is used for stirring and dissolving crude lithium hexafluorophosphate. The resulting lithium hexafluorophosphate solution is filtered to remove insoluble matter, and then the lithium hexafluorophosphate solution product is obtained and stored in a storage device.

15. The lithium hexafluorophosphate solution production system according to claim 14, characterized in that: The first and second ball mill reactors are double-layer straight-cylinder dry ball mills.

16. The lithium hexafluorophosphate solution production system according to claim 15, characterized in that: The double-layer straight-cylinder dry ball mill consists of a cylinder, a motor, and a support. The cylinder is divided into inner and outer layers by straight cylindrical plates. Both inner and outer layers are filled with grinding balls, which can grind the materials. The outer cylinder is provided with an outer layer feed inlet, an outer layer discharge inlet, an inner layer feed inlet, and a side discharge outlet. The outer side of the cylinder is provided with a heat exchange jacket, which is provided with a heat exchange medium inlet and outlet.

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