Continuous cyclic preparation method of hexafluorophosphate

Abstract

The invention discloses a continuous cyclic preparation method of hexafluorophosphate. The method comprises the following steps: S1, preparation of a metal salt anhydrous hydrogen fluoride solution: adding anhydrous hydrogen fluoride and metal halide salt into a reaction kettle, and uniformly mixing, so that the metal halide salt is dissolved in the anhydrous hydrogen fluoride to obtain the metal salt anhydrous hydrogen fluoride solution; s2, preparing a hexafluorophosphate anhydrous hydrogen fluoride solution: adding phosphorus pentachloride into the reaction kettle under a temperature control condition for reaction; a hexafluorophosphate anhydrous hydrogen fluoride solution is obtained; and S3, separation of hexafluorophosphate: transferring the hexafluorophosphate anhydrous hydrogen fluoride solution into a drying tower for drying, condensing gasified anhydrous hydrogen fluoride at the top of the drying tower into liquid anhydrous hydrogen fluoride by a condenser, refluxing the liquid anhydrous hydrogen fluoride into the reaction kettle in the step S1, and collecting a hexafluorophosphate product at the bottom of the drying tower. The continuous cyclic preparation method of hexafluorophosphate has the characteristics of high raw material utilization rate, simple process and good production continuity.

Description

Technical Field

[0001] The invention relates to the technical field of secondary battery electrolytes, and in particular to a continuous cycle preparation method of hexafluorophosphate. Background Art

[0002] Hexafluorophosphate MPF6 (M is Li, Na, K, etc.) is the electrolyte solute of secondary batteries. Lithium hexafluorophosphate (LiPF6) is a lithium-ion battery electrolyte, mainly used in power batteries, energy storage batteries and batteries for other consumer electronic products. It has become an irreplaceable important raw material for lithium-ion batteries. Sodium hexafluorophosphate (NaPF6) is used in sodium-ion batteries. With the application of sodium-ion batteries in the fields of energy storage and low-speed power, sodium hexafluorophosphate has also attracted increasing attention. At present, the synthesis of lithium hexafluorophosphate and sodium hexafluorophosphate is mainly based on the hydrogen fluoride solvent method, which uses phosphorus pentafluoride to react with lithium fluoride (or sodium fluoride) dissolved in hydrogen fluoride to generate lithium hexafluorophosphate (or sodium hexafluorophosphate).

[0003] There are three main methods for preparing phosphorus pentafluoride: (1) direct reaction of red phosphorus with fluorine gas; (2) reaction of phosphorus pentoxide or polyphosphoric acid with anhydrous hydrogen fluoride to generate hexafluorophosphoric acid and water, which is then dehydrated with fuming sulfuric acid to obtain phosphorus pentafluoride gas; (3) phosphorus pentafluoride is obtained by reacting phosphorus pentachloride with anhydrous hydrogen fluoride. Among them, the direct reaction of red phosphorus with fluorine gas to prepare phosphorus pentafluoride is violent, difficult to control, and has poor safety. In addition, elemental phosphorus is easy to sublimate, cannot be fully utilized, and is easy to clog pipelines. Phosphorus pentafluoride prepared by the polyphosphoric acid method has a large number of reaction by-products, a high impurity content, and is difficult to remove. Method (3) uses phosphorus pentachloride and hydrofluoric acid to react to generate a large amount of HCl gas, which cannot be separated from phosphorus pentafluoride. Summary of the invention

[0004] The purpose of the present invention is to provide a continuous circulation preparation method of hexafluorophosphate, which saves the step of preparing phosphorus pentafluoride gas and has the characteristics of high raw material utilization rate, simple process and good production continuity.

[0005] The present invention can be implemented by the following technical solutions: The present invention discloses a continuous cycle preparation method of hexafluorophosphate, comprising the following steps: S1. Preparation of anhydrous hydrogen fluoride solution of metal salt: adding anhydrous hydrogen fluoride and metal halide salt into a reaction kettle and mixing them evenly, so that the metal halide salt is dissolved in anhydrous hydrogen fluoride to obtain anhydrous hydrogen fluoride solution of metal salt; S2. Preparation of anhydrous hydrogen fluoride solution of hexafluorophosphate: adding phosphorus pentachloride to a reaction kettle under temperature control conditions to react and obtain anhydrous hydrogen fluoride solution of hexafluorophosphate; S3, separation of hexafluorophosphate: the hexafluorophosphate anhydrous hydrogen fluoride solution is transferred to a drying tower for drying, the vaporized anhydrous hydrogen fluoride at the top of the drying tower is condensed into liquid anhydrous hydrogen fluoride by a condenser and refluxed into the reactor of step S1, and the hexafluorophosphate product is collected at the bottom of the drying tower.

[0006] Furthermore, the hexafluorophosphate product obtained in step S3 is further subjected to the following treatment: S4, neutralization and purification: dissolving the hexafluorophosphate product obtained in step S3 with the first organic solvent, adding alkali to neutralize the acid, filtering, heating and concentrating the filtrate, crystallizing it, and drying it to obtain hexafluorophosphate crystals.

[0007] Furthermore, the hexafluorophosphate crystals obtained in step S4 are further subjected to the following treatments: S5, liquefaction treatment: dissolving the hexafluorophosphate crystals with a second organic solvent, filtering out insoluble matter after impurities removal, and obtaining a liquid hexafluorophosphate solution, which is convenient for subsequent transfer and transportation. At the same time, further adding solvents and additives to the liquid product can produce an electrolyte for secondary batteries.

[0008] Furthermore, in step S1, the amount of hydrogen fluoride used is 6-30 times, preferably 8-18 times, the molar amount of the metal halide. If the amount of hydrogen fluoride used is small, the reaction is not thorough, and the hexafluorophosphate product generated in step S2 cannot be completely dissolved, which will hinder the effective reaction.

[0009] Furthermore, in step S2, the reaction temperature is controlled to be -20°C-15°C, preferably -10°C-10°C. The reaction temperature directly controls the progress and intensity of the reaction. If the temperature is lower than -20°C, the reaction proceeds too slowly, prolonging the feeding time of phosphorus pentachloride; if the temperature is higher than 15°C, the reaction is violent, easily causing boiling, and cannot proceed smoothly.

[0010] Furthermore, the chemical formula of the metal halide is MX, wherein M is one of Li, Na, and K, and X is one of F, Cl, and Br; the hexafluorophosphate is one of lithium hexafluorophosphate, sodium hexafluorophosphate, and potassium hexafluorophosphate. When the synthetic target product is lithium hexafluorophosphate, the alkali metal halide is selected from lithium fluoride, lithium chloride, and lithium bromide; when the synthetic target product is sodium hexafluorophosphate, the alkali metal halide is selected from sodium fluoride, sodium chloride, and sodium bromide; when the synthetic target product is potassium hexafluorophosphate, the alkali metal halide is selected from potassium fluoride, potassium chloride, and potassium bromide.

[0011] Furthermore, in step S3, the liquid anhydrous hydrogen fluoride is refluxed directly or buffered and stored in an anhydrous hydrogen fluoride storage tank.

[0012] Furthermore, in step S3, the drying method is spray drying, the drying gas is one or more of argon, nitrogen, and carbon dioxide, and the air flow temperature is 80-200°C. The gas enters the drying tower from the bottom, and the temperature in the tower decreases from bottom to top. As the atomized liquid flows downward, the anhydrous hydrogen fluoride is continuously gasified until it is separated from the hexafluorophosphate. By adjusting the gas entry temperature and flow rate, the temperature at the upper end of the drying tower is always above 20°C.

[0013] Further, in step S4, the drying method is air drying or vacuum drying, the air drying temperature is 80°C-150°C, the vacuum drying temperature is 40°C-120°C, and the vacuum degree is 0-50KPa. During the drying process, the residual HF further volatilizes, reducing the acidity of the hexafluorophosphate.

[0014] Further, in step S4, the first organic solvent is one or more of alcohols, cyclic carbonates, chain carbonates, cyclic esters, chain esters, cyclic ethers, chain ethers, nitriles, pyridine and its derivatives, and ketones; the second organic solvent is one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate; and the base is one or more of lithium, sodium or potassium alcohol salts, oxides, hydroxides, carbonates, bicarbonates, or amino compounds.

[0015] Specifically, the first organic solvent includes but is not limited to methanol, ethanol, n-butanol, isobutanol, ethylene glycol, n-hexanol, isopropanol, propylene glycol, ethylene carbonate, butylene carbonate, pentyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, γ-butyrolactone, methyl formate, ethyl formate, propyl formate, butyl formate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, propyl propionate, isopropyl propionate, dimethyl ether, diethyl ether, dipropyl ether, methyl tert-butyl ether, 1,1-dimethylethane, 1,2-dimethoxyethane, ethylene oxide, tetrahydrofuran, propylene oxide, acetonitrile, propionitrile, pyridine and its derivatives, etc. During crystallization, hexafluorophosphate is precipitated from these solvents, thereby being separated from other impurities such as water, free acid and metal ions, and then filtered and dried to obtain a hexafluorophosphate product with higher purity.

[0016] Further, steps S1-S3 are carried out in a sealed container, preferably in a fluorine-containing coating or polytetrafluoroethylene-lined container. The reaction is carried out under an inert gas protective atmosphere, and the inert gas is selected from one or more of nitrogen, helium, argon and neon.

[0017] Furthermore, the crystallization temperature in step S4 is -10°C to 10°C, preferably -5°C to 5°C. The crystallization temperature and the concentration of the crystallization solution are particularly important for the product morphology, purity and crystallization efficiency. When the temperature is high and the concentration is low, most products cannot be crystallized. When the temperature is too low and the concentration is too high, the product will be mixed with impurities and precipitate together, and cannot be used as a solute for battery electrolyte.

[0018] Another aspect of the present invention is to protect a hexafluorophosphate prepared by the above preparation method.

[0019] The continuous cycle preparation method of hexafluorophosphate of the present invention has the following beneficial effects: First, the raw material utilization rate is high. Hydrofluoric acid is both a reaction raw material and a solvent. After the reaction is completed, it evaporates in a drying tower and refluxes into the reactor after condensation, thus realizing the utilization of hydrofluoric acid to the greatest extent.

[0020] Second, the process is simple. The preparation method of the present invention does not need to prepare PF5 separately, and the hexafluorophosphate is generated in one reactor. During the reaction, PF5 is an intermediate product, which is combined with hydrofluoric acid and fluoride salt to form hexafluorophosphate. The present invention does not need to prepare PF5 separately, and there is no step of purifying PF5.

[0021] Third, the production continuity is good. The preparation method of the present invention realizes continuous circulation, which is beneficial to the efficient use of equipment and improves production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a flow chart of a continuous cyclic preparation method of hexafluorophosphate according to the present invention; Figure 2 The following is a nuclear magnetic resonance fluorine spectrum (19F-NMR) spectrum of a sodium hexafluorophosphate product according to an application example of the present invention. DETAILED DESCRIPTION

[0023] In order to enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention is further described in detail below in conjunction with embodiments.

[0024] like Figure 1 As shown, the present invention discloses a continuous cycle preparation method of hexafluorophosphate, comprising the following steps: S1. Preparation of anhydrous hydrogen fluoride solution of metal salt: adding anhydrous hydrogen fluoride and metal halide salt into a reaction kettle and mixing them evenly, so that the metal halide salt is dissolved in anhydrous hydrogen fluoride to obtain anhydrous hydrogen fluoride solution of metal salt; S2. Preparation of anhydrous hydrogen fluoride solution of hexafluorophosphate: adding phosphorus pentachloride to a reaction kettle under temperature control conditions to react and obtain anhydrous hydrogen fluoride solution of hexafluorophosphate; S3, separation of hexafluorophosphate: the hexafluorophosphate anhydrous hydrogen fluoride solution is transferred to a drying tower for drying, the vaporized anhydrous hydrogen fluoride at the top of the drying tower is condensed into liquid anhydrous hydrogen fluoride by a condenser and refluxed into the reactor of step S1, and the hexafluorophosphate product is collected at the bottom of the drying tower.

[0025] Furthermore, the hexafluorophosphate product obtained in step S3 is further subjected to the following treatment: S4, neutralization and purification: dissolving the hexafluorophosphate product obtained in step S3 with the first organic solvent, adding alkali to neutralize the acid, filtering, heating and concentrating the filtrate, crystallizing it, and drying it to obtain hexafluorophosphate crystals.

[0026] Furthermore, the hexafluorophosphate crystals obtained in step S4 are further subjected to the following treatments: S5, liquefaction treatment: dissolving the hexafluorophosphate crystals with a second organic solvent, filtering out insoluble matter after impurities removal, and obtaining a liquid hexafluorophosphate solution, which is convenient for subsequent transfer and transportation. At the same time, further adding solvents and additives to the liquid product can produce an electrolyte for secondary batteries.

[0027] Furthermore, in step S1, the amount of hydrogen fluoride used is 6-30 times, preferably 8-18 times, the molar amount of the metal halide. If the amount of hydrogen fluoride used is small, the reaction is not thorough, and the hexafluorophosphate product generated in step S2 cannot be completely dissolved, which will hinder the effective reaction.

[0028] Furthermore, in step S2, the reaction temperature is controlled to be -20°C-15°C, preferably -10°C-10°C. The reaction temperature directly controls the progress and intensity of the reaction. If the temperature is lower than -20°C, the reaction proceeds too slowly, prolonging the feeding time of phosphorus pentachloride; if the temperature is higher than 15°C, the reaction is violent, easily causing boiling, and cannot proceed smoothly.

[0029] Furthermore, the chemical formula of the metal halide is MX, wherein M is one of Li, Na, and K, and X is one of F, Cl, and Br; the hexafluorophosphate is one of lithium hexafluorophosphate, sodium hexafluorophosphate, and potassium hexafluorophosphate. When the synthetic target product is lithium hexafluorophosphate, the alkali metal halide is selected from lithium fluoride, lithium chloride, and lithium bromide; when the synthetic target product is sodium hexafluorophosphate, the alkali metal halide is selected from sodium fluoride, sodium chloride, and sodium bromide; when the synthetic target product is potassium hexafluorophosphate, the alkali metal halide is selected from potassium fluoride, potassium chloride, and potassium bromide.

[0030] Furthermore, in step S3, the liquid anhydrous hydrogen fluoride is refluxed directly or buffered and stored in an anhydrous hydrogen fluoride storage tank.

[0031] Further, in step S3, the drying method is spray drying, the drying gas is one or more of argon, nitrogen, and carbon dioxide, and the air flow temperature is 80-200°C. The gas enters the drying tower from the bottom, and the temperature decreases from bottom to top. In the process of the atomized liquid flowing downward, the anhydrous hydrogen fluoride is continuously gasified until it is separated from the hexafluorophosphate. By adjusting the gas entry temperature and flow rate, the temperature at the upper end of the drying tower is always above 20°C.

[0032] Further, in step S4, the drying method is air drying or vacuum drying, the air drying temperature is 80°C-150°C, the vacuum drying temperature is 40°C-120°C, and the vacuum degree is 0-50KPa. During the drying process, the residual HF further volatilizes, reducing the acidity of the hexafluorophosphate.

[0033] Further, in step S4, the first organic solvent is one or more of alcohols, cyclic carbonates, chain carbonates, cyclic esters, chain esters, cyclic ethers, chain ethers, nitriles, pyridine and its derivatives, and ketones; the second organic solvent is one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate; and the base is one or more of lithium, sodium or potassium alcohol salts, oxides, hydroxides, carbonates, bicarbonates, or amino compounds.

[0034] Specifically, the first organic solvent includes but is not limited to methanol, ethanol, n-butanol, isobutanol, ethylene glycol, n-hexanol, isopropanol, propylene glycol, ethylene carbonate, butylene carbonate, pentyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, γ-butyrolactone, methyl formate, ethyl formate, propyl formate, butyl formate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, propyl propionate, isopropyl propionate, dimethyl ether, diethyl ether, dipropyl ether, methyl tert-butyl ether, 1,1-dimethylethane, 1,2-dimethoxyethane, ethylene oxide, tetrahydrofuran, propylene oxide, acetonitrile, propionitrile, pyridine and its derivatives, etc. During crystallization, hexafluorophosphate is precipitated from these solvents, thereby being separated from other impurities such as water, free acid and metal ions, and then filtered and dried to obtain a hexafluorophosphate product with higher purity.

[0035] Further, steps S1-S3 are carried out in a sealed container, preferably in a fluorine-containing coating or polytetrafluoroethylene-lined container. The reaction is carried out under an inert gas protective atmosphere, and the inert gas is selected from one or more of nitrogen, helium, argon and neon.

[0036] Furthermore, the crystallization temperature in step S4 is -10°C to 10°C, preferably -5°C to 5°C. The crystallization temperature and the concentration of the crystallization solution are particularly important for the product morphology, purity and crystallization efficiency. When the temperature is high and the concentration is low, most products cannot be crystallized. When the temperature is too low and the concentration is too high, the product will be mixed with impurities and precipitate together, and cannot be used as a solute for battery electrolyte.

[0037] Example 1 This embodiment relates to a continuous cycle preparation method of hexafluorophosphate, comprising the following steps: S1. Preparation of anhydrous hydrogen fluoride solution of metal salt: anhydrous hydrogen fluoride and metal halide are added into a reaction kettle and mixed evenly to dissolve the metal halide in anhydrous hydrogen fluoride to obtain anhydrous hydrogen fluoride solution of metal salt. Specifically, the amount of hydrogen fluoride is 20 times the molar amount of the metal halide; the chemical formula of the metal halide is MX, wherein M is Li and X is F; and the hexafluorophosphate is lithium hexafluorophosphate.

[0038] S2. Preparation of anhydrous lithium hexafluorophosphate hydrogen fluoride solution: under temperature control, add phosphorus pentachloride into a reaction kettle to react to obtain anhydrous lithium hexafluorophosphate hydrogen fluoride solution. Specifically, the reaction temperature is controlled to be 5°C.

[0039] S3, separation of lithium hexafluorophosphate: the lithium hexafluorophosphate anhydrous hydrogen fluoride solution is put into a drying tower for drying, the anhydrous hydrogen fluoride vaporized at the top of the drying tower is condensed into liquid anhydrous hydrogen fluoride by a condenser and refluxed to the reactor in step S1, and the lithium hexafluorophosphate product is collected at the bottom of the drying tower. Specifically, the reflux method of the liquid anhydrous hydrogen fluoride is direct reflux; the drying method is spray drying, the drying gas is argon, and the gas flow temperature is 100°C.

[0040] S4, neutralization and purification: dissolving the lithium hexafluorophosphate product obtained in step S3 with the first organic solvent, adding alkali to neutralize the acid, filtering, heating and concentrating the filtrate, crystallizing, and drying to obtain lithium hexafluorophosphate crystals. Specifically, the drying method is air drying, the air drying temperature is 150°C; the crystallization temperature is 0°C.

[0041] S5, liquefaction treatment: dissolve the lithium hexafluorophosphate crystals with a second organic solvent, filter out insoluble matter after impurities removal, and obtain a liquid lithium hexafluorophosphate solution, which is convenient for subsequent transfer and transportation. At the same time, further adding solvents and additives to the liquid product can produce an electrolyte for lithium-ion batteries.

[0042] Example 2 This embodiment relates to a continuous cycle preparation method of sodium hexafluorophosphate, comprising the following steps: S1. Preparation of anhydrous hydrogen fluoride solution of metal salt: anhydrous hydrogen fluoride and metal halide are added into a reaction kettle and mixed evenly to dissolve the metal halide in anhydrous hydrogen fluoride to obtain anhydrous hydrogen fluoride solution of metal salt. Specifically, the amount of hydrogen fluoride is 15 times the molar amount of the metal halide; the chemical formula of the metal halide is MX, wherein M is Na and X is Cl; and the hexafluorophosphate is sodium hexafluorophosphate.

[0043] S2. Preparation of anhydrous sodium hexafluorophosphate hydrogen fluoride solution: under temperature control, add phosphorus pentachloride into a reaction kettle to react to obtain anhydrous sodium hexafluorophosphate hydrogen fluoride solution. Specifically, the reaction temperature is controlled to be -20°C.

[0044] S3, separation of sodium hexafluorophosphate: the anhydrous hydrogen fluoride solution of sodium hexafluorophosphate is put into a drying tower for drying, the anhydrous hydrogen fluoride vaporized at the top of the drying tower is condensed into liquid anhydrous hydrogen fluoride by a condenser and refluxed to the reactor in step S1, and the sodium hexafluorophosphate product is collected at the bottom of the drying tower. Specifically, the liquid anhydrous hydrogen fluoride is refluxed by buffer storage in an anhydrous hydrogen fluoride storage tank; the drying method is spray drying, the drying gas is nitrogen, and the air flow temperature is 200°C.

[0045] S4, neutralization and purification: dissolving the hexafluorophosphate product obtained in step S3 with the first organic solvent, adding alkali to neutralize the acid, filtering, heating and concentrating the filtrate, crystallizing, and drying to obtain sodium hexafluorophosphate crystals. Specifically, the drying method is vacuum drying, the vacuum drying temperature is 80°C, the vacuum degree is 5Kpa; the crystallization temperature is 10°C.

[0046] S5, liquefaction treatment: dissolving the sodium hexafluorophosphate crystals with a second organic solvent, filtering out insoluble matter after impurities removal, and obtaining a liquid sodium hexafluorophosphate solution. Meanwhile, further adding solvents and additives to the liquid product can produce an electrolyte for a secondary sodium battery.

[0047] Example 3 This embodiment relates to a continuous cycle preparation method of hexafluorophosphate, comprising the following steps: S1. Preparation of anhydrous hydrogen fluoride solution of metal salt: anhydrous hydrogen fluoride and metal halide are added into a reaction kettle and mixed evenly to dissolve the metal halide in anhydrous hydrogen fluoride to obtain anhydrous hydrogen fluoride solution of metal salt. Specifically, the amount of hydrogen fluoride is 12 times the molar amount of the metal halide; the chemical formula of the metal halide is MX, wherein M is K and X is Br; and the hexafluorophosphate is potassium hexafluorophosphate.

[0048] S2. Preparation of anhydrous potassium hexafluorophosphate hydrogen fluoride solution: under temperature control, add phosphorus pentachloride into a reaction kettle to react to obtain anhydrous potassium hexafluorophosphate hydrogen fluoride solution. Specifically, the reaction temperature is controlled to be 15°C.

[0049] S3, separation of potassium hexafluorophosphate: the potassium hexafluorophosphate anhydrous hydrogen fluoride solution is put into a drying tower for drying, the anhydrous hydrogen fluoride vaporized at the top of the drying tower is condensed into liquid anhydrous hydrogen fluoride by a condenser and refluxed to the reactor in step S1, and the potassium hexafluorophosphate product is collected at the bottom of the drying tower. Specifically, the reflux method of the liquid anhydrous hydrogen fluoride is direct reflux; the drying method is spray drying, the drying gas is carbon dioxide, and the air flow temperature is 80°C.

[0050] S4, neutralization and purification: dissolving the potassium hexafluorophosphate product obtained in step S3 with the first organic solvent, adding alkali to neutralize the acid, filtering, heating and concentrating the filtrate, crystallizing, and drying to obtain potassium hexafluorophosphate crystals. Specifically, the drying method is blast drying, the blast drying temperature is 150° C.; the crystallization temperature is 10° C.

[0051] S5, liquefaction treatment: dissolving potassium hexafluorophosphate crystals with a second organic solvent, filtering out insoluble matter after impurities removal, and obtaining a liquid potassium hexafluorophosphate solution. Meanwhile, further adding solvents and additives to the liquid product can produce an electrolyte for potassium secondary batteries.

[0052] Example 4 This embodiment relates to a continuous cycle preparation method of hexafluorophosphate, comprising the following steps: S1. Preparation of anhydrous hydrogen fluoride solution of metal salt: anhydrous hydrogen fluoride and metal halide are added into a reaction kettle and mixed evenly to dissolve the metal halide in anhydrous hydrogen fluoride to obtain anhydrous hydrogen fluoride solution of metal salt. Specifically, the amount of hydrogen fluoride is 30 times the molar amount of the metal halide; the chemical formula of the metal halide is MX, wherein M is Li and X is Cl; and the hexafluorophosphate is lithium hexafluorophosphate.

[0053] S2. Preparation of anhydrous hydrogen fluoride solution of lithium hexafluorophosphate: under temperature control, add phosphorus pentachloride into a reaction kettle to react to obtain anhydrous hydrogen fluoride solution of hexafluorophosphate. Specifically, the reaction temperature is controlled to be -10°C.

[0054] S3, separation of lithium hexafluorophosphate: the lithium hexafluorophosphate anhydrous hydrogen fluoride solution is put into a drying tower for drying, the anhydrous hydrogen fluoride vaporized at the top of the drying tower is condensed into liquid anhydrous hydrogen fluoride by a condenser and refluxed to the reactor in step S1, and the lithium hexafluorophosphate product is collected at the bottom of the drying tower. Specifically, the liquid anhydrous hydrogen fluoride is refluxed by buffer storage in an anhydrous hydrogen fluoride storage tank; the drying method is spray drying, the drying gas is argon and nitrogen, and the air flow temperature is 120°C.

[0055] S4, neutralization and purification: dissolving the lithium hexafluorophosphate product obtained in step S3 with the first organic solvent, adding alkali to neutralize the acid, filtering, heating and concentrating the filtrate, crystallizing, and drying to obtain lithium hexafluorophosphate crystals. Specifically, the drying method is vacuum drying, the vacuum drying temperature is 80°C, the vacuum degree is 50Kpa; the crystallization temperature is -10°C.

[0056] S5, liquefaction treatment: dissolve the lithium hexafluorophosphate crystals with a second organic solvent, filter out insoluble matter after impurities removal, and obtain a liquid lithium hexafluorophosphate solution, which is convenient for subsequent transfer and transportation. At the same time, further adding solvents and additives to the liquid product can produce an electrolyte for lithium secondary batteries.

[0057] Example 5 This embodiment relates to a continuous cycle preparation method of hexafluorophosphate, comprising the following steps: S1. Preparation of anhydrous hydrogen fluoride solution of metal salt: anhydrous hydrogen fluoride and metal halide are added into a reaction kettle and mixed evenly to dissolve the metal halide in anhydrous hydrogen fluoride to obtain anhydrous hydrogen fluoride solution of metal salt. Specifically, the amount of hydrogen fluoride is 20 times the molar amount of the metal halide; the chemical formula of the metal halide is MX, wherein M is Na and X is F; and the hexafluorophosphate is sodium hexafluorophosphate.

[0058] S2. Preparation of anhydrous hydrogen fluoride solution of hexafluorophosphate: under temperature control, add phosphorus pentachloride into a reaction kettle to react to obtain anhydrous hydrogen fluoride solution of hexafluorophosphate. Specifically, the reaction temperature is controlled to be -5°C.

[0059] S3, separation of hexafluorophosphate: the hexafluorophosphate anhydrous hydrogen fluoride solution is put into a drying tower for drying, the anhydrous hydrogen fluoride vaporized at the top of the drying tower is condensed into liquid anhydrous hydrogen fluoride by a condenser and refluxed to the reactor in step S1, and the hexafluorophosphate product is collected at the bottom of the drying tower. Specifically, the reflux method of the liquid anhydrous hydrogen fluoride is direct reflux; the drying method is spray drying, the drying gas is carbon dioxide, and the air flow temperature is 100°C.

[0060] S4, neutralization and purification: dissolving the hexafluorophosphate product obtained in step S3 with the first organic solvent, adding alkali to neutralize the acid, filtering, heating and concentrating the filtrate, crystallizing, and drying to obtain hexafluorophosphate crystals. Specifically, the drying method is blast drying, the blast drying temperature is 150°C; the crystallization temperature is 0°C.

[0061] S5, liquefaction treatment: dissolving the hexafluorophosphate crystals with a second organic solvent, filtering out insoluble matter after impurities removal, and obtaining a liquid hexafluorophosphate solution, which is convenient for subsequent transfer and transportation. At the same time, further adding solvents and additives to the liquid product can produce an electrolyte for secondary batteries.

[0062] In the present embodiments 1-5, the first organic solvent is one or more of alcohols, cyclic carbonates, chain carbonates, cyclic esters, chain esters, cyclic ethers, chain ethers, nitriles, pyridine and its derivatives, and ketones; the second organic solvent is one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate; the base is an alcohol salt, oxide, hydroxide, carbonate, bicarbonate, or amine compound of lithium, sodium, or potassium. Specifically, the first organic solvent includes but is not limited to methanol, ethanol, n-butanol, isobutanol, ethylene glycol, n-hexanol, isopropanol, propylene glycol, ethylene carbonate, butylene carbonate, pentyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, γ-butyrolactone, methyl formate, ethyl formate, propyl formate, butyl formate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, propyl propionate, isopropyl propionate, dimethyl ether, diethyl ether, dipropyl ether, methyl tert-butyl ether, 1,1-dimethylethane, 1,2-dimethoxyethane, ethylene oxide, tetrahydrofuran, propylene oxide, acetonitrile, propionitrile, pyridine and its derivatives.

[0063] Application Example 1 Put 72g of dry sodium chloride solid into a dry PTFE lined stainless steel reactor, control the temperature at 0-8°C, slowly add 420g of anhydrous hydrogen fluoride into the reactor, keep the reaction at a slightly positive pressure, and absorb the generated gas with alkali solution. Adjust the temperature to -30°C and keep stirring, add 209g of phosphorus pentachloride to the reactor in batches using a solid feeder, control the addition speed so that the reactor temperature does not exceed -10°C, and continue stirring the reaction for 30 minutes after the addition is completed to obtain a reaction solution containing sodium hexafluorophosphate and hydrofluoric acid.

[0064] Keep the temperature below 19°C, filter the obtained reaction solution to remove insoluble matter, transfer the filtrate to the spray drying tower, and flow from the top of the drying tower to the bottom of the tower along the spraying direction, while dry nitrogen at a temperature of 120°C is introduced from the bottom of the tower. As the wall temperature of the drying tower increases from top to bottom, the anhydrous hydrogen fluoride in the solution is continuously vaporized during the downward flow of the atomized liquid until the anhydrous hydrogen fluoride and the sodium hexafluorophosphate in the solution are separated, and the vaporized anhydrous hydrogen fluoride gas flows out through the outlet at the top of the drying tower, and is condensed into anhydrous hydrogen fluoride liquid by a hydrogen fluoride condenser, which is transferred into an anhydrous hydrogen fluoride storage tank and returned to the sodium hexafluorophosphate reactor as a solvent; the gas passing through the condenser contains phosphorus pentafluoride, hydrogen chloride, and a small amount of anhydrous hydrogen fluoride gas, which is buffered by a gas buffer tank and then introduced into the sodium hexafluorophosphate reactor together, wherein the phosphorus pentafluoride reacts with the sodium fluoride in the reactor to generate sodium hexafluorophosphate, and the hydrogen chloride gas that does not participate in the reaction is introduced into a tail gas absorption device to obtain hydrochloric acid; 173 g of crude sodium hexafluorophosphate is collected at the bottom of the drying tower.

[0065] The crude sodium hexafluorophosphate was dissolved in anhydrous ethanol, and a saturated ethanol solution of sodium ethoxide was added and stirred. A small amount of hydrofluoric acid was neutralized until the pH was about 7, and then filtered. The filtrate entered the crystallization kettle for concentration, and then cooled to -5°C-5°C for crystallization. After filtering and vacuum drying at 80°C, 139g of sodium hexafluorophosphate was obtained with a yield of 82.7%. The obtained sodium hexafluorophosphate was dissolved in dry ethyl methyl carbonate, and the insoluble matter was filtered out to obtain a liquid sodium hexafluorophosphate product. The free acid content of the product is less than 20ppm, the water content is less than 10ppm, and the 19F-NMR shows that the product purity is higher than 99.9%. It was found through testing that Figure 2 No other fluorine-containing impurities were found in the electrolyte, which meets the requirements for electrolyte salts for sodium ion batteries.

[0066] Application Example 2 Put 44g of dry solid lithium chloride into a dry PTFE-lined stainless steel reactor, control the temperature at 0-5°C, slowly add 480g of anhydrous hydrogen fluoride into the reactor, and absorb the gas generated by the reaction with water. Adjust the temperature to -35°C and keep stirring, add 209g of phosphorus pentachloride to the reactor in batches using a solid feeder, control the addition speed so that the temperature of the reactor does not exceed -10°C, and continue stirring the reaction for 30 minutes after the addition is completed to obtain a mixed solution containing lithium hexafluorophosphate and hydrofluoric acid.

[0067] The temperature was kept below 15°C, and the obtained reaction solution was filtered to remove insoluble matter. The filtrate was transferred to a spray drying tower and flowed from the top of the drying tower to the bottom of the tower along the spraying direction. The drying gas was nitrogen at a temperature of 120°C, which was introduced from the bottom of the tower. After separation, 161 g of crude lithium hexafluorophosphate was collected at the bottom of the drying tower.

[0068] The crude lithium hexafluorophosphate is dissolved in acetonitrile, melamine powder is added and stirred, a small amount of hydrofluoric acid is neutralized, and the acidity is tested by ice water method. When the acidity is less than 10ppm, the stirring is stopped, filtered, and the filtrate enters the crystallization kettle for concentration, and then cooled to -5℃-5℃ for crystallization. After filtering and vacuum drying the slurry, 115g of lithium hexafluorophosphate with high purity is obtained, with a yield of 76%. The lithium hexafluorophosphate is dissolved in ethyl methyl carbonate, and the insoluble matter is filtered to obtain a liquid lithium hexafluorophosphate product. The free acid content of the product is less than 30ppm, the water content is less than 10ppm, and the impurity content is low, which meets the requirements of electrolyte salts for lithium ion batteries.

[0069] The above embodiments are only specific embodiments of the present invention, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and these obvious replacement forms all belong to the protection scope of the present invention.

Claims

1. A continuous cycle preparation method of hexafluorophosphate, characterized in that The following steps are involved: S1. Preparation of anhydrous hydrogen fluoride solution of metal salt: adding anhydrous hydrogen fluoride and metal halide salt into a reaction kettle and mixing them evenly, so that the metal halide salt is dissolved in anhydrous hydrogen fluoride to obtain anhydrous hydrogen fluoride solution of metal salt; S2. Preparation of anhydrous hydrogen fluoride solution of hexafluorophosphate: adding phosphorus pentachloride to a reaction kettle under temperature control conditions to react and obtain anhydrous hydrogen fluoride solution of hexafluorophosphate; S3, separation of hexafluorophosphate: the hexafluorophosphate anhydrous hydrogen fluoride solution is transferred to a drying tower for drying, the anhydrous hydrogen fluoride vaporized at the top of the drying tower is condensed into liquid anhydrous hydrogen fluoride by a condenser and refluxed into the reactor of step S1, the hexafluorophosphate product is collected at the bottom of the drying tower, and the uncondensed gas is passed into a recovery system for recovery.

2. The continuous cycle preparation method of hexafluorophosphate according to claim 1, characterized in that: In step S1, the amount of hydrogen fluoride used is 6-30 times the molar amount of the metal halide salt.

3. The continuous cycle preparation method of hexafluorophosphate according to claim 1, characterized in that: In step S2, the reaction temperature is controlled to be -20°C-15°C.

4. The continuous cycle preparation method of hexafluorophosphate according to claim 1, characterized in that: The chemical formula of the metal halide is MX, wherein M is one or more of Li, Na, and K, and X is one or more of F, Cl, and Br; the hexafluorophosphate is one or more of lithium hexafluorophosphate, sodium hexafluorophosphate, and potassium hexafluorophosphate.

5. The continuous cycle preparation method of hexafluorophosphate according to claim 1, characterized in that: In step S3, the liquid anhydrous hydrogen fluoride is refluxed directly or buffered and stored in an anhydrous hydrogen fluoride storage tank.

6. The continuous cycle preparation method of hexafluorophosphate according to claim 1, characterized in that: In step S3, the drying method is spray drying, the drying gas is one or more of argon, nitrogen, and carbon dioxide, and the air flow temperature is 80-200°C.

7. The continuous cycle preparation method of hexafluorophosphate according to claim 1, characterized in that: The hexafluorophosphate product obtained in step S3 is further subjected to the following treatment: S4, neutralization and purification: dissolving the hexafluorophosphate product obtained in step S3 with the first organic solvent, adding alkali solution to neutralize the acid, filtering, heating and concentrating the filtrate, crystallizing it, and drying it to obtain hexafluorophosphate crystals.

8. The continuous cycle preparation method of hexafluorophosphate according to claim 7, characterized in that: The hexafluorophosphate crystals obtained in step S4 are further subjected to the following treatment: S5. Liquid treatment: dissolving the hexafluorophosphate crystals with a second organic solvent, removing impurities and filtering out insoluble matter to obtain a liquid hexafluorophosphate solution.

9. The continuous cycle preparation method of hexafluorophosphate according to claims 7 and 8, characterized in that: The first organic solvent is one or more of alcohols, cyclic carbonates, chain carbonates, cyclic esters, chain esters, cyclic ethers, chain ethers, nitriles, pyridine and its derivatives, and ketones; the second organic solvent is one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate; the solute of the alkali solution is one or more of metal alkoxides, metal oxides, metal hydroxides, metal carbonates, metal bicarbonates, and amino compounds.

10. A hexafluorophosphate, characterized in that: Prepared by any one of the preparation methods of claims 1-9.

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