A method and apparatus for preparing a low-acidity lithium hexafluorophosphate solution

Abstract

This invention discloses a method for preparing a low-acidity lithium hexafluorophosphate solution and its production apparatus. The preparation method includes: (1) adding lithium fluoride solid to a first shear reactor and a second shear reactor, and starting the shear reactor; (2) introducing phosphorus pentafluoride-containing raw material gas sequentially into the first and second shear reactors, so that it reacts with the lithium fluoride solid therein in a fluidized state to generate lithium hexafluorophosphate; the mixed gas exiting the second shear reactor is compressed and pressurized and then returned to the first and second shear reactors for recycling reaction; (3) after the reaction is completed, the residual gas in the first and second shear reactors is removed, and the crude lithium hexafluorophosphate enters the third reactor, is dissolved in a carbonate solvent, and then filtered to obtain a lithium hexafluorophosphate solution. This invention has low raw material cost, simple preparation process, safe and controllable reaction, high phosphorus pentafluoride utilization rate, and the prepared lithium hexafluorophosphate solution has an acidity ≤20ppm, which can be directly used for electrolyte preparation.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and in particular to a method and apparatus for preparing a low-acidity lithium hexafluorophosphate solution. Background Technology

[0002] Lithium-ion batteries are the most promising energy storage batteries today. Compared to traditional batteries, they have larger capacity, higher average output voltage, and superior cycle performance and conductivity. They are widely used in electronics, information technology, computers, military, aerospace, and new energy vehicles. Lithium hexafluorophosphate is the most commonly used electrolyte in lithium-ion batteries, and lithium salts have many advantages as electrolytes in lithium-ion batteries.

[0003] Currently, the main methods for preparing lithium hexafluorophosphate include gas-solid reaction, HF solvent method, ion exchange method, and complexation method, but the HF solvent method is the most commonly used in industry. The HF solvent method typically uses phosphorus pentachloride (PCl5) and HF as raw materials to generate phosphorus pentafluoride (PF5) and HCl gas. Then, it reacts with lithium fluoride (LiF) in HF solvent to produce lithium hexafluorophosphate (LiPF6), and finally, LiPF6 crystals are obtained through a cooling crystallization process. While this process boasts high raw material utilization, almost no byproducts, high product purity, and the ability to achieve long-term HF recycling, anhydrous HF is highly corrosive and toxic, making the reaction process extremely dangerous. Any leak could cause significant harm to the environment and personnel, requiring high standards for equipment corrosion protection and the production environment, resulting in high equipment investment. Furthermore, it faces challenges such as difficulty in controlling the crystallization process, long cooling crystallization time, and low production efficiency. Therefore, preparing lithium hexafluorophosphate solutions has become an alternative.

[0004] Patent CN117599747A discloses a method for preparing liquid lithium hexafluorophosphate. This method uses high-purity phosphorus pentafluoride as a raw material, reacting it with lithium fluoride suspended in a carbonate solvent to obtain liquid lithium hexafluorophosphate. Due to the strong oxidizing properties of phosphorus pentafluoride, the product has excessively high acidity (500 ppm), necessitating the preparation of a special Li... + -NH2 / mesoporous carbon adsorbents are used to remove acidity from products, but the preparation process of this special adsorbent is relatively complex and the cost is relatively high.

[0005] Patent CN115849409A discloses a method for preparing liquid lithium hexafluorophosphate by continuously reacting a PF5 / HCl mixed gas with a lithium fluoride carbonate solution. The obtained liquid lithium hexafluorophosphate has a purity of over 99.95%, but it does not provide the composition of impurities in the product or indicators such as acidity and chloride ion content. However, it is conceivable that, due to the use of a PF5 / HCl mixed gas as a raw material, the removal of chloride ions from the product is a technical challenge; and the reaction is carried out directly in a carbonate solvent, making it difficult to control the acidity of the product.

[0006] Patent CN115818672A discloses a method for preparing phosphorus pentafluoride gas using oxygen-containing phosphorus source, anhydrous hydrogen fluoride and fuming sulfuric acid as raw materials, and then directly reacting it with lithium fluoride in carbonate solvent to prepare lithium hexafluorophosphate solution after distillation purification. Similarly, lithium hexafluorophosphate solution needs to be deacidified and purified by adsorption with deacidifying resin to obtain qualified product.

[0007] Therefore, the aforementioned methods for preparing liquid lithium hexafluorophosphate generally require the addition of other technologies to remove acidity from the product, which not only increases the complexity of the process, but may also introduce other impurities during the acid removal process.

[0008] Gas-solid reaction is the initial preparation process for lithium hexafluorophosphate, boasting advantages such as simplicity and solvent-free operation, making it a green synthesis method. Since the reaction process is solvent-free, there is no issue of phosphorus pentafluoride reacting with the solvent. Furthermore, after the gas-solid reaction, residual HF on the surface of lithium hexafluorophosphate can be removed under vacuum conditions, creating favorable conditions for preparing low-acidity lithium hexafluorophosphate solutions. However, the main problem with gas-solid reactions is their relatively low reaction efficiency and yield; improving reaction efficiency is key to the industrialization of this process.

[0009] Patent CN104093668A discloses a method for preparing LiPF6 in a fixed-bed reactor or a fluidized-bed reactor using a PF5 / HCl mixture and a LiF molded product, but the utilization rate of LiF in this method is about 10.8%.

[0010] Patent CN116002655A discloses a four-step process for preparing PF5 using fluorite, fuming sulfuric acid, polyphosphoric acid, or phosphorus pentoxide as raw materials. The PF5 gas is then reacted with a mixture of coarse and fine lithium fluoride particles in a fluidized bed at a temperature controlled below 15°C. The reaction product is extracted with ethylene glycol dimethyl ether, and after static separation and filtration, liquid lithium hexafluorophosphate is obtained. This liquid is then concentrated and crystallized to obtain solid lithium hexafluorophosphate. While the solid product meets the required acidity, the acidity of the liquid lithium hexafluorophosphate and the conversion rate of lithium fluoride are not disclosed. Summary of the Invention

[0011] To address the aforementioned technical problems, this invention proposes a method for preparing a low-acidity lithium hexafluorophosphate solution that features a simple preparation process, safe and controllable reaction, and high phosphorus pentafluoride utilization rate.

[0012] The objective of this invention is achieved through the following technical solution:

[0013] A method for preparing a low-acidity lithium hexafluorophosphate solution, the method comprising:

[0014] (1) Add solid lithium fluoride to the first shear reactor and the second shear reactor, and start the shear reactor;

[0015] (2) The phosphorus pentafluoride-containing raw material gas enters the first shear reactor and the second shear reactor in sequence, so that the lithium fluoride solid therein reacts with the phosphorus pentafluoride in a fluidized state to generate lithium hexafluorophosphate; the mixed gas flowing out of the second shear reactor is compressed and pressurized and then returned to the first and second shear reactors for recycling reaction;

[0016] (3) After the reaction is completed, the residual gas in the first and second shear reactors is removed, and the crude lithium hexafluorophosphate enters the third reactor. It is dissolved in carbonate solvent and then filtered to obtain a lithium hexafluorophosphate solution.

[0017] In the preparation process of the lithium hexafluorophosphate solution of the present invention, lithium fluoride solid is first added to two shear reactors arranged in series. The particle size of the lithium fluoride solid is selected from 100 to 2000 mesh, preferably 500 to 2000 mesh. Then, the two shear reactors are evacuated to negative pressure, and the temperature is controlled to rise to the reaction temperature before shearing is started. The phosphorus pentafluoride-containing feed gas enters the first and second shear reactors sequentially at a high inlet rate, serving as both feed gas and carrier gas, so that the lithium fluoride solid in the two shear reactors is in a fluidized state. The lithium hexafluorophosphate generated by the reaction on the lithium fluoride surface is continuously sheared and pulverized under high-speed shearing, allowing the inner lithium fluoride to continue to contact and react with phosphorus pentafluoride, thereby improving the utilization rate of lithium fluoride.

[0018] The phosphorus pentafluoride-containing feed gas includes phosphorus pentafluoride, hydrogen chloride, and hydrogen fluoride, and is prepared from phosphorus pentachloride and hydrogen fluoride, or from phosphorus trichloride, hydrogen fluoride, and liquid chlorine. This is prior art in the field and will not be described in detail here.

[0019] In the first and second shear reactors, the phosphorus pentafluoride-containing feed gas can be fed in one go or in batches. One-time feeding means that a set amount of phosphorus pentafluoride-containing feed gas is fed in at a set feed rate all at once. The pressurized mixture is then returned to the first and second shear reactors for further reaction. The reacted mixture is then pressurized again for further reaction, and this cycle continues until the reaction is complete. Batch feeding means that a set amount of phosphorus pentafluoride-containing feed gas is fed in batches at a set feed rate. Specifically, phosphorus pentafluoride-containing feed gas is introduced into the first and second shear reactors. During the feeding process, the system pressure (the pressure in the first and second shear reactors) is monitored. When the pressure reaches 0.3–1.0 MPa, the feed gas supply is stopped, the compressor is turned on, and the mixture in the pre-buffer tank is compressed to the post-buffer tank. Then, the mixture sequentially enters the first and second shear reactors for reaction. After the reaction, the mixture is compressed again and the cycle continues. During the mixed gas circulation reaction, gaseous materials are analyzed. When the phosphorus pentafluoride content in the mixed gas is ≤2%, the residual gas is discharged to the tail gas absorption device. The compressor is turned off, and fresh phosphorus pentafluoride-containing raw material gas is continuously introduced into the first shear reactor and the second shear reactor to repeat the above process until the set amount of phosphorus pentafluoride-containing raw material gas is fed.

[0020] Preferably, the phosphorus pentafluoride feed gas of the present invention is fed in batches. Compared with single-pass feeding, batch feeding can avoid the use of large-volume buffer tanks and ultra-high-pressure shear reactors.

[0021] The feed rate of the phosphorus pentafluoride-containing feed gas described in this invention is related to the volume of the shear reactor. Specifically, the feed rate of the phosphorus pentafluoride-containing feed gas is (100-3000) mL / min·L, that is, the feed rate is the volume of the shear reactor * (100-3000) mL / min. Preferably, the feed rate of the phosphorus pentafluoride-containing feed gas is (500-2000) mL / min·L. At this feed rate, not only is the lithium fluoride solid fluidized, but the generated lithium hexafluorophosphate solid and lithium fluoride are also separated into layers. Since the specific gravity of lithium hexafluorophosphate is higher than that of lithium fluoride, under high-speed shearing and fluidization, lithium hexafluorophosphate, as a heavy component, separates into layers with lithium fluoride, allowing the upper layer of lithium fluoride to better contact and react with the phosphorus pentafluoride gas.

[0022] This invention utilizes two shear reactors and a compressor connected in series to continuously circulate the feed gas containing phosphorus pentafluoride and react it with fluidized lithium fluoride, thereby significantly improving the feed utilization efficiency.

[0023] Throughout the reaction process, the molar ratio of phosphorus pentafluoride in the phosphorus pentafluoride feed gas to the total amount of lithium fluoride in the two shear reactors is 1:(0.8–1.2), preferably 1:(0.9–1.1). The amount of solid lithium fluoride in the first shear reactor and the amount of solid lithium fluoride in the second shear reactor can be evenly distributed or arbitrarily distributed. Preferably, the solid lithium fluoride is distributed evenly in batches.

[0024] In the first and second shear reactors, the reaction temperature is -15 to 100°C, and the reaction pressure is 0 to 3.0 MPa. Preferably, the reaction temperature is controlled at 15 to 80°C, and the reaction pressure is controlled at 0.3 to 1.0 MPa.

[0025] The shearing speed of the first shear reactor and the second shear reactor is 1000-20000 r / m; preferably, the shearing speed is 5000-20000 r / m.

[0026] The total residence time of the phosphorus pentafluoride feed gas in the first and second shear reactors is 5–300 min, preferably 30–120 min. The total residence time includes the reaction time during feed gas introduction and the reaction time during the mixed gas compression and circulation process.

[0027] After the reaction is complete, the residual gas in the first and second shear reactors is removed under conditions of vacuum ≥0.09 MPa and temperature 0℃~80℃. Preferably, the residual gas is removed under conditions of vacuum ≥0.95 MPa and temperature 50℃~80℃. The residual gas, which mainly consists of hydrogen chloride and hydrogen fluoride, may also contain phosphorus pentafluoride with a mass content ≤2%.

[0028] The crude lithium hexafluorophosphate after removing residual gas has a mass fraction of 95-99%.

[0029] The crude lithium hexafluorophosphate can be transported to a third reactor for dissolution via an inert gas (such as nitrogen).

[0030] First, add carbonate solvent to the third reactor, then add crude lithium hexafluorophosphate to dissolve it. The dissolution temperature is controlled at -10 to 50°C, preferably 5 to 20°C. The carbonate solvent is pre-dried, with a moisture content ≤10 ppm, and is selected from at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (PC).

[0031] After complete dissolution, the crude lithium hexafluorophosphate solution is fed to a primary filter to remove unreacted lithium fluoride, and then filtered through a precision filter to remove trace amounts of insoluble matter, finally yielding a lithium hexafluorophosphate solution.

[0032] The mass concentration range of the lithium hexafluorophosphate solution is 5-50%, preferably 25-35%, and more preferably 29-33%.

[0033] The crude lithium hexafluorophosphate powder of this invention is relatively fine (at least ≥500 mesh), which can avoid the encapsulation of HF inside the solid, thereby obtaining a low-acidity product. Specifically, the acidity value of the lithium hexafluorophosphate solution of this invention is ≤20ppm (calculated as HF).

[0034] A second aspect of the present invention provides a production apparatus for preparing any of the aforementioned low-acidity lithium hexafluorophosphate solutions, the production apparatus comprising:

[0035] The system comprises a PF5 generator, a first shear reactor, a second shear reactor, and a compression unit connected in sequence. The outlet of the compression unit is connected to the gas phase inlet of the first shear reactor. The PF5 generator is used for the preparation of phosphorus pentafluoride-containing feed gas and is existing technology in the field, so it will not be described in detail here. The first and second shear reactors have the same structure, including a high-speed motor, a fixed shaft, a stirring rod, a shearing disc, a solid feed component, a gas phase inlet, a gas phase outlet, and a solid discharge outlet. The high-speed motor drives the shearing disc to perform high-speed shearing. The compression unit includes a front buffer tank, a compressor, and a rear buffer tank connected in sequence.

[0036] The dissolving unit, filtration unit, and storage unit are connected in sequence. The outlets of the first and second shear reactors are both connected to the inlet of the dissolving unit. The dissolving unit includes a stirred reactor, the filtration unit includes a filter, and the storage unit is a storage tank.

[0037] Furthermore, the solid feeding component includes a hopper and a feeder, wherein the feeder is selected from a star feeder or a screw feeder.

[0038] The filtration unit includes a primary filter and a precision filter. The primary filter has a pore size of 1 to 5 μm and is used to filter out unreacted lithium fluoride. The precision filter has a pore size of 0.25 to 0.5 μm and is used to remove insoluble substances.

[0039] The first and second shear reactors of this invention are made of materials selected from 304 stainless steel, 316L stainless steel, Inconel nickel alloy 600, Hastelloy C alloy, fluoropolymer-lined carbon steel, or titanium. The stirred reactor is made of materials selected from Hastelloy C alloy, 316L stainless steel, or fluoropolymer-lined carbon steel.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] 1. This invention employs two high-speed shear reactors connected in series and pressurizes the gas using a compressor, allowing the raw gas to flow back and forth between the two shear reactors. This achieves high-speed shearing and fluidization of lithium fluoride, resulting in a phosphorus pentafluoride utilization rate of ≥95%. This significantly improves the utilization rate of lithium fluoride and phosphorus pentafluoride, creating industrial feasibility for the gas-solid reaction to prepare lithium hexafluorophosphate.

[0042] 2. This invention efficiently obtains lithium hexafluorophosphate solid through a gas-solid reaction, and then obtains a low-acidity lithium hexafluorophosphate solution after dissolution and filtration. This avoids the need for long-term crystallization processes and conventional adsorption deacidification processes. The process is simple, has high production efficiency, is safe and controllable, and is environmentally friendly. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the lithium hexafluorophosphate solution production apparatus of Embodiment 1 of the present invention.

[0044] In the diagram: 1. PF5 generator a; 2. PF5 generator b; 3. LiF silo a; 4. Star feeder a; 5. First shear reactor; 6. LiF silo b; 7. Star feeder b; 8. Second shear reactor; 9. Front buffer tank; 10. Compressor; 11. Rear buffer tank; 12. LiPF6 silo; 13. Dissolving vessel; 14. Primary filter; 15. Precision filter; 16. LiPF6 solution storage tank. Detailed Implementation

[0045] 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.

[0046] Example 1

[0047] This embodiment provides a production apparatus for lithium hexafluorophosphate solution, as shown in the attached diagram. Figure 1 As shown, the production apparatus includes:

[0048] The PF5 generating device can be a single PF5 generating device or PF5 generating device a and PF5 generating device b arranged in parallel for different processes to prepare phosphorus pentafluoride; the PF5 generating device is made of 316L stainless steel and is equipped with a condenser, and can be used to prepare phosphorus pentafluoride by introducing phosphorus pentachloride and hydrogen fluoride, or by introducing phosphorus trichloride, liquid chlorine and hydrogen fluoride.

[0049] The first and second shear reactors are connected in series. Both reactors have identical structures, including a vessel body and a jacket surrounding the vessel body, a high-speed motor, a stirring rod, a shearing disc, a LiF hopper, and a star-shaped feeder. The inner diameter of both shear reactors is 10 cm, and their height is 65 cm. The outlet of the PF5 generator is connected to the gas phase inlet of the first shear reactor, the gas phase outlet of the first shear reactor is connected to the gas phase inlet of the second shear reactor, and the gas phase outlet of the second shear reactor is connected to a compression unit. The solid outlets of both the first and second shear reactors are connected to a dissolving unit.

[0050] A compression unit, comprising a front buffer tank (20L), a compressor, and a rear buffer tank (10L) connected in sequence, wherein the outlet of the rear buffer tank is connected to the gas inlet of the first shear reactor;

[0051] The dissolution unit includes a LiPF6 silo and a stirred reactor (2L), the outlet of which is connected to a filter unit.

[0052] The filtration unit includes a primary filter (2μm pore size) and a precision filter (0.25μm pore size) connected in sequence, and the outlet of the precision filter is connected to a storage tank.

[0053] Storage tank for storing LiPF6 solution.

[0054] Example 2

[0055] This embodiment uses the production apparatus described in Example 1 to provide a method for preparing a low-acidity lithium hexafluorophosphate solution, specifically including the following steps:

[0056] (1) Preparation of phosphorus pentafluoride-containing feed gas: Solid phosphorus pentachloride was added to a PF5 reactor and sealed. Hydrogen fluoride was then sprayed into the reactor using a spray method. The molar ratio of phosphorus pentachloride to hydrogen fluoride was 1:1.5. The reaction was carried out at approximately 60°C to produce phosphorus pentafluoride and hydrogen chloride. Due to the exothermic reaction, a small portion of unreacted hydrogen fluoride formed a mixed gas with the phosphorus pentafluoride and hydrogen chloride. The average molecular weight of the mixed gas was determined to be 51, the mass fraction of phosphorus pentafluoride in the mixed gas was 39.5%, and the pressure was 0.8 MPa.

[0057] (2) Preparation of crude lithium hexafluorophosphate: ① Add 52g of spray-dried lithium fluoride powder (1000 mesh) to the first shear reactor and the second shear reactor respectively; evacuate the two shear reactors to a negative pressure of ≥0.095MPa, and introduce hot water into the jackets of the first and second shear reactors. After controlling the internal temperature at 50℃, start the high-speed shearing and adjust the shearing speed to 10000r / m; ② The raw material gas containing phosphorus pentafluoride enters the first and second shear reactors sequentially at an inlet rate of 6.0L / min, so that the lithium fluoride is fluidized. After the raw material gas reacts with the lithium fluoride, it enters the front buffer tank; as the inlet gas volume increases, the pressure in the system increases. After 30min (180L) of gas flow, when the system pressure is ≥0.5MPa (gauge pressure), close the raw material gas inlet valve and stop the gas flow. ③ Turn on the compressor to compress the material in the front buffer tank to the rear buffer tank. When the pressure in the rear buffer tank is ≥0.8MPa, open the regulating valve between the rear buffer tank and the first shear reactor to control the flow rate at 6.0L / min. The material in the rear buffer tank re-enters the first and second shear reactors to react with lithium fluoride, and finally enters the front buffer tank. After being compressed again by the compressor, it continues to enter the first and second shear reactors for reaction, and so on. After 60 minutes of reaction, the gas phase material is sampled and analyzed. The phosphorus pentafluoride content is 0.65%. The residual gas is discharged to the tail gas absorption device. ④ Open the raw material gas inlet valve and continue to introduce raw material gas containing phosphorus pentafluoride into the first and second shear reactors at an inlet rate of 6.0L / min. Repeat steps ② and ③ above until the total feed amount of raw material gas is 565L (the total molar ratio of phosphorus pentafluoride to lithium fluoride in the raw material gas is 1:1). ⑤ The first and second shear reactors were evacuated to a negative pressure of ≥0.095MPa and kept at 60℃ for 1h. Finally, the vacuum was broken with nitrogen, the high-speed shear was turned off, and the reaction was stopped to obtain crude lithium hexafluorophosphate.

[0058] Analysis revealed that the average phosphorus pentafluoride content in the exhaust gas was 1.06%, with an average phosphorus pentafluoride utilization rate of 97.3%. The first shear reactor yielded 285.6 g of crude lithium hexafluorophosphate with a purity of 98.7% and a yield of 92.7% (based on LiF). The second shear reactor yielded 275.9 g of lithium hexafluorophosphate with a purity of 97.9% and a yield of 88.9% (based on LiF).

[0059] (3) Preparation of lithium hexafluorophosphate solution: 1000g of methyl ethyl carbonate (5ppm water) was added to a stirred reactor. The stirring and cooling devices were turned on. 500g of crude lithium hexafluorophosphate (purity 98.3%) obtained in step (2) was added using a screw feeder. The internal temperature was controlled at 10-12℃. After adding the crude product, the solution was kept warm for 30 minutes and then filtered through a primary filter. The filtrate was then filtered through a precision filter and then entered into a lithium hexafluorophosphate solution storage tank for low-temperature and sealed storage.

[0060] The prepared lithium hexafluorophosphate solution was tested and found to have a concentration of 32.88%, a color of 12 Hazen, an acidity of 12 ppm, a chloride ion concentration of 0.6 ppm, and a moisture content of 4 ppm.

[0061] Example 3

[0062] The operation of this embodiment is the same as that of Embodiment 2, except that: in step (2), in step ②, the phosphorus pentafluoride-containing raw material gas enters the first shear reactor and the second shear reactor sequentially at an inlet rate of 12.0 L / min. After 15 min (180 L) of gas flow, when the system pressure is ≥0.5 MPa (gauge pressure), the raw material gas inlet valve is closed and the gas flow is stopped; in step ③, the material in the compression tank re-enters the first shear reactor and the second shear reactor at a flow rate of 12.0 L / min to react with lithium fluoride, and finally enters the pre-buffer tank, and so on. After 30 min of reaction, the gas phase material is sampled and analyzed. The phosphorus pentafluoride content is 1.25%, and the residual gas is discharged to the tail gas absorption device; in step ④, steps ② and ③ are repeated; all other operations remain unchanged.

[0063] After the reaction, the average phosphorus pentafluoride content in the tail gas was 1.62%, and the average phosphorus pentafluoride utilization rate was 95.9%. 282.7 g of lithium hexafluorophosphate was prepared in the first shear reactor with a purity of 98.4% and a yield of 91.5% (based on LiF). 272.0 g of lithium hexafluorophosphate was prepared in the second shear reactor with a purity of 97.6% and a yield of 87.3% (based on LiF).

[0064] (3) Preparation of lithium hexafluorophosphate solution: 1000g of methyl ethyl carbonate (5ppm water) was added to a stirred reactor. The stirring and cooling devices were turned on. 500g of crude lithium hexafluorophosphate (purity 98.0%) obtained in step (2) was added using a screw feeder. The internal temperature was controlled at 10-12℃. After adding the crude product, the solution was kept warm for 30 minutes and then filtered through a primary filter. The filtrate was then filtered through a precision filter and then entered into a lithium hexafluorophosphate solution storage tank for low-temperature and sealed storage.

[0065] The prepared lithium hexafluorophosphate solution was tested and found to have a concentration of 32.50%, a color of 8 Hazen, an acidity of 10 ppm, a chloride ion concentration of 0.5 ppm, and a moisture content of 5.5 ppm.

[0066] Example 4

[0067] The operation in this embodiment is the same as in embodiment 2, except that in step (2), after feeding the phosphorus pentafluoride-containing feed gas for 20 minutes (120L), the feed gas inlet valve is closed and the gas intake is stopped when the system pressure reaches ≥0.3MPa (gauge pressure). That is, when the phosphorus pentafluoride-containing feed gas reacts with lithium fluoride, the pressure in the first and second shear reactors is maintained at 0.3MPa to 0.4MPa. During the reaction of the mixed gas with lithium fluoride in the compression cycle, the reaction pressure is also maintained at 0.3MPa to 0.4MPa. Other operations remain unchanged.

[0068] After the reaction, the average phosphorus pentafluoride content in the tail gas was 1.25%, and the average phosphorus pentafluoride utilization rate was 96.8%. In the first reactor, 283.7 g of lithium hexafluorophosphate was prepared with a purity of 98.5% and a yield of 91.9% (based on LiF). In the second reactor, 274.9 g of lithium hexafluorophosphate was prepared with a purity of 97.8% and a yield of 88.5% (based on LiF).

[0069] (3) Preparation of lithium hexafluorophosphate solution: 1000g of methyl ethyl carbonate (5ppm water) was added to a stirred reactor. The stirring and cooling devices were turned on. 500g of crude lithium hexafluorophosphate (purity 98.2%) obtained in step (2) was added using a screw feeder. The internal temperature was controlled at 10-12℃. After adding the crude product, the solution was kept warm for 30 minutes and then filtered through a primary filter. The filtrate was then filtered through a precision filter and then entered into a lithium hexafluorophosphate solution storage tank for low-temperature and sealed storage.

[0070] The prepared lithium hexafluorophosphate solution was tested and found to have a concentration of 32.60%, a color of 10 Hazen, an acidity of 13 ppm, a chloride ion concentration of 0.6 ppm, and a moisture content of 6.0 ppm.

[0071] Example 5

[0072] The operation of this embodiment is the same as that of embodiment 2, except that the shearing speed of the first shear reactor and the second shear reactor is reduced to 5000 r / m, while all other operations remain unchanged.

[0073] After the reaction, the average phosphorus pentafluoride content in the tail gas was 1.95%, and the average phosphorus pentafluoride utilization rate was 95.06%. In the first reactor, 270.1 g of lithium hexafluorophosphate was prepared with a purity of 97.4% and a yield of 86.5% (based on LiF). In the second reactor, 265.2 g of lithium hexafluorophosphate was prepared with a purity of 97.0% and a yield of 84.6% (based on LiF).

[0074] (3) Preparation of lithium hexafluorophosphate solution: 1000g of methyl ethyl carbonate (5ppm water) was added to a stirred reactor. The stirring and cooling devices were turned on. 500g of crude lithium hexafluorophosphate (purity 97.2%) obtained in step (2) was added using a screw feeder. The internal temperature was controlled at 10-12℃. After adding the crude product, the solution was kept warm for 30 minutes and then filtered through a primary filter. The filtrate was then filtered through a precision filter and then entered into a lithium hexafluorophosphate solution storage tank for low-temperature and sealed storage.

[0075] The prepared lithium hexafluorophosphate solution was tested and found to have a concentration of 32.22%, a color of 8 Hazen, an acidity of 9 ppm, a chloride ion concentration of 0.8 ppm, and a moisture content of 8.0 ppm.

[0076] Example 6

[0077] The operation of this embodiment is the same as that of embodiment 2, except that in step (3), 500g of crude lithium hexafluorophosphate (purity 98.3%) obtained in step (2) is fed into the screw feeder, and the internal temperature is controlled at 18-20℃. All other operations remain unchanged.

[0078] The prepared lithium hexafluorophosphate solution was tested and found to have a concentration of 32.80%, a color of 15 Hazen, an acidity of 10 ppm, a chloride ion concentration of 0.8 ppm, and a moisture content of 6 ppm.

[0079] Example 7

[0080] This embodiment uses the production apparatus described in Example 1 to provide a method for preparing a low-acidity lithium hexafluorophosphate solution, including the following steps:

[0081] (1) Preparation of PF5-containing feed gas: Anhydrous hydrogen fluoride and liquid chlorine were added to a PF5 reactor made of 316L stainless steel with a condenser. Stirring was started and phosphorus trichloride liquid was continuously added. The pressure inside the reactor was controlled at 0.8 MPa and the temperature at 10°C. The reaction yielded phosphorus pentafluoride gas. Due to the exothermic reaction, a small portion of hydrogen fluoride formed a mixed gas with phosphorus pentafluoride and hydrogen chloride. The mass fraction of phosphorus pentafluoride in the mixed gas was measured to be 40.0%.

[0082] Steps (2) and (3) are the same as in Example 2. The results are as follows: After the reaction, the average content of phosphorus pentafluoride in the tail gas is 0.95%, and the average utilization rate of phosphorus pentafluoride is 97.6%. 289.5g of lithium hexafluorophosphate was prepared in the first reactor with a purity of 99.0% and a yield of 94.2% (based on LiF). 281.7g of lithium hexafluorophosphate was prepared in the second reactor with a purity of 98.4% and a yield of 91.2% (based on LiF).

[0083] (3) Preparation of lithium hexafluorophosphate solution: 1000g of methyl ethyl carbonate (5ppm water) was added to a stirred reactor. The stirring and cooling devices were turned on. 500g of crude lithium hexafluorophosphate (purity 98.7%) obtained in step (2) was added using a screw feeder. The internal temperature was controlled at 10-12℃. After adding the crude product, the solution was kept warm for 30 minutes and then filtered through a primary filter. The filtrate was then filtered through a precision filter and then entered into a lithium hexafluorophosphate solution storage tank for low-temperature and sealed storage.

[0084] The prepared lithium hexafluorophosphate solution was tested and found to have a concentration of 32.80%, a color of 12 Hazen, an acidity of 10 ppm, a chloride ion concentration of 0.4 ppm, and a moisture content of 8.0 ppm.

[0085] Comparative Example 1

[0086] The operation of this comparative example is the same as that of Example 2, except that in step (2), the rotation speed of the first shear reactor and the second shear reactor is reduced to 80 r / m, while other conditions remain unchanged. After the reaction, the average content of phosphorus pentafluoride in the tail gas is 37.3%, and the average utilization rate of phosphorus pentafluoride is 5.57%.

[0087] In the first reactor, 59.2 g of lithium hexafluorophosphate with a purity of 14.8% and a yield of 2.88% (based on LiF) was prepared.

[0088] In the second reactor, 58.9 g of lithium hexafluorophosphate was prepared with a purity of 14.3% and a yield of 2.77% (based on LiF).

[0089] (3) Preparation of lithium hexafluorophosphate solution: 200g of methyl ethyl carbonate (5ppm water) was added to a stirred reactor. The stirring and cooling devices were turned on. 100g of crude lithium hexafluorophosphate (purity 14.5%) obtained in step (2) was added using a screw feeder. The internal temperature was controlled at 10-12℃. After adding the crude product, the solution was kept warm for 30min and then filtered through a primary filter. The filtrate was then filtered through a precision filter and then entered into a lithium hexafluorophosphate solution storage tank for low-temperature and sealed storage.

[0090] The prepared lithium hexafluorophosphate solution was tested and found to have a concentration of 6.70%, a color of 12 Hazen, an acidity of 25 ppm, a chloride ion concentration of 0.8 ppm, and a moisture content of 12.0 ppm.

[0091] Comparative Example 2

[0092] The operation of this comparative example is the same as that of Example 2, except that in step (2), in step ②, the phosphorus pentafluoride-containing raw material gas is sequentially introduced into the first shear reactor and the second shear reactor at an inlet rate of 6.0 L / min, so that the lithium fluoride is fluidized, and the mixed gas after the reaction directly enters the tail gas treatment device. The pressure inside the two shear reactors is controlled at 0.5 MPa, the gas flow time is 280 min, and the amount of phosphorus pentafluoride used is 1510.8 g, which is much higher than the theoretical requirement of 504 g. After the gas flow is completed, the first and second shear reactors are evacuated to a negative pressure ≥0.095 MPa and kept at 60°C for 1 h. Finally, the vacuum is broken with nitrogen, the high-speed shear is closed, the reaction is stopped, and crude lithium hexafluorophosphate is obtained.

[0093] The experimental results were as follows: the average phosphorus pentafluoride content in the exhaust gas was 33.5%, and the average phosphorus pentafluoride utilization rate was 15.2%. In the first reactor, 228.9 g of lithium hexafluorophosphate was prepared with a purity of 93.2% and a yield of 70.2% (based on LiF). In the second reactor, 226.5 g of lithium hexafluorophosphate was prepared with a purity of 92.9% and a yield of 69.2% (based on LiF).

[0094] (3) Preparation of lithium hexafluorophosphate solution: 800g of methyl ethyl carbonate (5ppm water) was added to a stirred reactor. The stirring and cooling devices were turned on. 400g of crude lithium hexafluorophosphate (purity 93.1%) obtained in step (2) was added using a screw feeder. The internal temperature was controlled at 10-12℃. After adding the crude product, the solution was kept warm for 30 minutes and then filtered through a primary filter. The filtrate was then filtered through a precision filter and then entered a lithium hexafluorophosphate solution storage tank for low-temperature and sealed storage.

[0095] The prepared lithium hexafluorophosphate solution was tested and found to have a concentration of 31.60%, a color of 14 Hazen, an acidity of 14 ppm, a chloride ion concentration of 0.5 ppm, and a moisture content of 15.0 ppm.

Claims

1. A method for preparing a low-acidity lithium hexafluorophosphate solution, characterized in that: The preparation method includes: (1) Add solid lithium fluoride to the first shear reactor and the second shear reactor, and start the shear reactor; (2) The phosphorus pentafluoride-containing raw material gas enters the first shear reactor and the second shear reactor in sequence, so that it reacts with the lithium fluoride solid therein in a fluidized state to generate lithium hexafluorophosphate; the mixed gas flowing out of the second shear reactor is compressed and pressurized and then returned to the first and second shear reactors for a cycle reaction. (3) After the reaction is completed, the residual gas in the first and second shear reactors is removed, and the crude lithium hexafluorophosphate enters the third reactor, is dissolved in carbonate solvent, and then filtered to obtain a lithium hexafluorophosphate solution.

2. The method for preparing a low-acidity lithium hexafluorophosphate solution according to claim 1, characterized in that: The phosphorus pentafluoride-containing feed gas includes phosphorus pentafluoride, hydrogen chloride, and hydrogen fluoride, and is prepared from phosphorus pentachloride and hydrogen fluoride, or from phosphorus trichloride, hydrogen fluoride, and liquid chlorine.

3. The method for preparing a low-acidity lithium hexafluorophosphate solution according to claim 2, characterized in that: The feed rate of the phosphorus pentafluoride-containing feed gas is related to the volume of the shear reactor and is selected from (100 to 3000) mL / min·L.

4. The method for preparing a low-acidity lithium hexafluorophosphate solution according to claim 3, characterized in that: The ratio of the total molar amount of phosphorus pentafluoride introduced into the phosphorus pentafluoride feed gas to the total molar amount of lithium fluoride solid added to the first shear reactor and the second shear reactor is 1:(0.8~1.2).

5. The method for preparing a low-acidity lithium hexafluorophosphate solution according to claim 1, characterized in that: The particle size of the lithium fluoride solid is selected from 100 to 2000 mesh.

6. The method for preparing a low-acidity lithium hexafluorophosphate solution according to claim 1, characterized in that: The shearing speed of the first and second shear reactors is 1000 to 20000 r / m.

7. The method for preparing a low-acidity lithium hexafluorophosphate solution according to claim 1, characterized in that: In the first and second shear reactors, the reaction temperature is -15 to 100℃ and the reaction pressure is 0 to 3.0 MPa.

8. The method for preparing a low-acidity lithium hexafluorophosphate solution according to claim 1, characterized in that: The total residence time of the phosphorus pentafluoride-containing feed gas in the first and second shear reactors is 5 to 300 min.

9. The method for preparing a low-acidity lithium hexafluorophosphate solution according to claim 1, characterized in that: In step (3), the residual gas in the first and second shear reactors is removed under the conditions of vacuum degree ≥0.09MPa and temperature 0℃~80℃.

10. The method for preparing a low-acidity lithium hexafluorophosphate solution according to claim 1, characterized in that: In step (3), carbonate solvent is first added to the third reactor, followed by the addition of crude lithium hexafluorophosphate for dissolution, with the dissolution temperature controlled between -10 and 50°C; the carbonate solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, or propylene carbonate.

11. The method for preparing a low-acidity lithium hexafluorophosphate solution according to claim 10, characterized in that: The mass concentration range of lithium hexafluorophosphate solution is 5-50%, and the acidity value is ≤20ppm (calculated as HF).

12. A production apparatus for preparing the low-acidity lithium hexafluorophosphate solution according to any one of claims 1-11, characterized in that, The production apparatus includes: The system comprises a PF5 generator, a first shear reactor, a second shear reactor, and a compression unit connected in sequence. The outlet of the compression unit is connected to the gas phase inlet of the first shear reactor. The PF5 generator is used to prepare phosphorus pentafluoride-containing feed gas. The first and second shear reactors have the same structure, including a high-speed motor, a fixed shaft, a stirring rod, a shearing disc, a solid feed component, a gas phase inlet, a gas phase outlet, and a solid discharge outlet. The compression unit includes a front buffer tank, a compressor, and a rear buffer tank connected in sequence. The dissolving unit, filtration unit, and storage unit are connected in sequence. The outlets of the first and second shear reactors are both connected to the inlet of the dissolving unit. The dissolving unit includes a stirred reactor, the filtration unit includes a filter, and the storage unit is a storage tank.

13. The production apparatus according to claim 12, characterized in that: The solid feeding component includes a hopper and a feeder, wherein the feeder is selected from a star feeder or a screw feeder.

14. The production apparatus according to claim 12, characterized in that: The filtration unit includes a primary filter and a precision filter. The primary filter is used to filter out unreacted lithium fluoride, and the precision filter is used to remove insoluble substances.

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