One-pot process for the preparation of sodium hexafluorophosphate

Abstract

The application belongs to the technical field of sodium hexafluorophosphate and particularly relates to a one-pot preparation process of sodium hexafluorophosphate. The one-pot preparation process of sodium hexafluorophosphate comprises the following steps: (1) reaction: anhydrous hydrogen fluoride is put into a reactor, a sodium source and a phosphorus source are sequentially added at a temperature of -60 to -20 DEG C, then the temperature is increased to 0 to 10 DEG C for reaction, volatile substances are evaporated after the reaction is completed, and a sodium hexafluorophosphate primary product is obtained; (2) neutralization: an organic solvent is added to the sodium hexafluorophosphate primary product for dissolution, then an alkaline substance is added to adjust the pH value of the solution system to 7 to 9, filtration is performed, a sodium hexafluorophosphate solution is obtained, the organic solvent is evaporated by increasing the temperature, and a sodium hexafluorophosphate crude product is obtained after drying. The one-pot preparation process has the advantages of mild conditions, simple operation, fast reaction rate, easy separation of the product, high purity and high yield of the prepared sodium hexafluorophosphate crude product, and is suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the technical field of sodium hexafluorophosphate, specifically relating to a one-pot preparation process for sodium hexafluorophosphate. Background Technology

[0002] Sodium hexafluorophosphate (NaPF6) is a white crystalline or powdery inorganic salt. It exhibits high solubility in common organic solvents such as methanol, ethanol, acetone, and carbonates, enabling high conductivity. This is beneficial for sodium-ion batteries to achieve high energy density, long cycle life, and low self-discharge rate, making it a promising electrolyte salt for sodium-ion batteries. However, sodium hexafluorophosphate is highly soluble in water and prone to deliquescence. Meeting the purity, free acid, and moisture content requirements of battery-grade electrolytes necessitates strict process control, placing higher demands on large-scale industrial production.

[0003] Currently, the common method for preparing sodium hexafluorophosphate involves first preparing phosphorus pentafluoride, then passing phosphorus pentafluoride gas into a reactor containing sodium fluoride and anhydrous hydrogen fluoride for complete reaction to obtain sodium hexafluorophosphate. For example, the method disclosed in patent CN116534874A includes two stages: the preparation of phosphorus pentafluoride and sodium hexafluorophosphate. This process and equipment are relatively complex and require the separation and purification of the raw material gases.

[0004] Furthermore, the publicly available literature (Hexafluophosphates of Sodium, Ammonium, and Potassium, MMWoyski, WJShenk Jr., ERPellon, Inorganic Syntheses, Volume III) provides the following preparation method: first, a metal chloride is added to a reactor, then anhydrous hydrogen fluoride is added, and finally solid phosphorus pentachloride is added to generate crude hexafluorophosphate. When using this method to produce sodium hexafluorophosphate, the reaction involves rapid and large-scale exothermic reactions that are difficult to control; the reaction solution concentration is low, which is not conducive to low-cost and high-efficiency production; the obtained crude product contains water of crystallization and retains a large amount of free acid, water, and metal ions, resulting in low product purity, which is not conducive to subsequent purification processes; and the raw material is of a single type, which is not conducive to the comprehensive utilization of the process principle and further reduction of production costs. Summary of the Invention

[0005] The purpose of this invention is to provide a one-pot process for preparing sodium hexafluorophosphate, which is characterized by mild conditions, simple operation, fast reaction rate, easy product separation, high purity and high yield of the prepared crude sodium hexafluorophosphate, and is suitable for industrial production.

[0006] The one-pot preparation process of sodium hexafluorophosphate described in this invention includes the following steps:

[0007] (1) Reaction: Anhydrous hydrogen fluoride is added to the reactor, and sodium source and phosphorus source are added sequentially at a temperature of -60 to -20℃. Then the temperature is raised to 0 to 10℃ for reaction. After the reaction is completed, volatile substances are evaporated to obtain sodium hexafluorophosphate as the primary product.

[0008] (2) Neutralization: Add an organic solvent to the primary product of sodium hexafluorophosphate to dissolve it, then add an alkaline substance to adjust the pH of the solution system to 7-9, filter to obtain sodium hexafluorophosphate solution, then evaporate the organic solvent, and dry to obtain crude sodium hexafluorophosphate product.

[0009] In step (1), anhydrous hydrogen fluoride is used as both a reactant and a solvent, while sodium and phosphorus sources are used only as reactants. The molar ratio of phosphorus, sodium, and fluorine in all the reactants involved in the reaction is 1:(1-1.5):(6-7).

[0010] In step (1), the sodium source is at least one of NaOH, NaF, NaCl, Na2CO3, Na3PO4, and NaPO3.

[0011] In step (1), the phosphorus source is at least one of H3PO4, P2O5, PCl5, POCl3, Na3PO4, and NaPO3.

[0012] In step (1), the ratio of the volume of anhydrous hydrogen fluoride as a solvent to the number of moles of phosphorus in all reactants is (350-520) mL:1 mol.

[0013] In step (1), the sodium source addition rate is 20-50 g / (min·1LHF) and the phosphorus source addition rate is 10-25 g / (min·1LHF) based on the volume of anhydrous hydrogen fluoride added.

[0014] In step (1), when the temperature is raised to 0℃ for the reaction, the heating rate is 0.5~2℃ / min. Since the reaction is rapid, the reaction can be considered complete once the temperature rise is finished under good stirring conditions.

[0015] This invention prioritizes the addition of HF, which has a high specific heat capacity, and lowers it to a low temperature. Then, sodium and phosphorus sources are slowly added. By controlling the order and rate of addition, the dissolution and reaction exothermics are controlled, thereby achieving the purpose of regulating the stability of the system.

[0016] In step (1), after the reaction is completed, the temperature is increased to 20-60°C at a rate of 1-5°C / min and kept at this temperature for 1-4 hours to evaporate volatile substances, which are mainly hydrogen fluoride and hydrogen chloride.

[0017] In step (1), the reaction equations for different sodium and phosphorus sources are as follows:

[0018] 3NaOH+H3PO4+8HF→NaPF6+2NaF+7H2O;

[0019] 2NaF+P2O5+10HF→NaPF6+5H2O;

[0020] NaCl+PCl5+6HF→NaPF6+6HCl↑;

[0021] 2Na2CO3+2POCl3+8HF→2NaPF6+6HCl↑+2H2O+CO2↑;

[0022] Na3PO4+8HF→NaPF6+2NaF+4H2O;

[0023] NaPO3 + 6HF → NaPF6 + 3H2O.

[0024] The reaction tail gas of this invention mainly consists of HF and HCl, with small amounts of PF5 and PCl5. HF and HCl can be separated by condensation and recycled for use. The gas can also react with alkaline solutions such as sodium hydroxide (NaOH) to generate fluoride salts (NaF) and chloride salts (NaCl), and the by-products can be separated after treatment and further refined into high-value-added high-purity fluoride salts or chloride salts. The alkaline solution is not limited to NaOH.

[0025] In step (2), the organic solvent must simultaneously satisfy the requirement of being both a good solvent for sodium hexafluorophosphate and a poor solvent for other sodium salts besides sodium hexafluorophosphate (such as sodium fluoride, sodium chloride, etc.). It can be selected from alcohols, cyclic carbonates, chain carbonates, cyclic esters, chain esters, cyclic ethers, chain ethers, nitriles, pyridine, and acetone; preferably methanol, ethanol, n-butanol, isobutanol, ethylene glycol, n-hexanol, isopropanol, propylene glycol, ethylene carbonate, butyl carbonate, amyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, γ-butyrolactone, and methyl... The solvent is selected from the following: 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-dimethyl ethane, 1,2-dimethoxyethane, ethylene oxide, tetrahydrofuran, propylene oxide, acetonitrile, propionitrile, pyridine, and their derivatives; more preferably, a solvent capable of azeotropic reaction with water, and further selected from the following: ethanol, pyridine, dimethyl carbonate, diethyl carbonate, ethyl acetate, acetonitrile, diethyl ether, ethylene glycol dimethyl ether, methyl tert-butyl ether, and tetrahydrofuran.

[0026] This invention selects a solvent that has high solubility for sodium hexafluorophosphate, low solubility for impurities, is easy to evaporate and condense, and is azeotropic with water. On the one hand, it can quickly dissolve the primary product of sodium hexafluorophosphate, releasing the acidic substances that are encapsulated, attached, and coordinated in the product through dissolution. On the other hand, when removing organic solvents in the subsequent evaporation, azeotropic evaporation can be used to achieve efficient removal of residual water at a lower temperature.

[0027] In step (2), the ratio of the mass of sodium hexafluorophosphate primary product to the volume of organic solvent added is (0.1-1) kg: 1 L; the temperature at which the organic solvent is added is 0-40℃.

[0028] In step (2), the alkaline substance is one of sodium ethoxide, sodium methoxide, sodium hydroxide, sodium carbonate, sodium bicarbonate, ethylenediamine, diethylamine, and triethylamine; preferably sodium ethoxide.

[0029] When adding alkaline substances, either the alkaline substance itself or a saturated organic solvent solution containing the alkaline substance can be added directly. To facilitate the recycling of the organic solvent, the organic solvent used to dissolve the alkaline substance should be consistent with the organic solvent used to dissolve the primary sodium hexafluorophosphate product. Adding alkaline substances to adjust the pH of the solution system to 7–9 serves two purposes: firstly, adjusting the pH to a slightly alkaline level reduces the content of acidic substances that severely affect product stability; secondly, adjusting the pH can cause impurities present in the product to precipitate or form substances with low solubility, thus purifying the liquid phase.

[0030] In step (2), the pore size of the filter membrane during filtration is no higher than 0.22 μm. After filtration, a large amount of solid insoluble matter is removed, yielding an ethanol solution of sodium hexafluorophosphate. The solid insoluble matter mainly consists of sodium fluoride and fluorophosphate, which are dried and then recycled as reactants.

[0031] In step (2), the temperature is increased to 40–80°C at a rate of 1–5°C / min to evaporate the organic solvent. During the evaporation of the organic solvent, the azeotropic principle of the organic solvent and water is utilized to efficiently remove residual water at a lower temperature through azeotropic evaporation. After evaporation, the organic solvent is condensed and recovered, and wet crude sodium hexafluorophosphate is obtained after removing the organic solvent. During the evaporation of the organic solvent, vibration, shaking, and stirring can be used to prevent the product from agglomerating or clumping.

[0032] In step (2), the drying temperature is 80–150°C and the drying time is 12–48 h. Since sodium hexafluorophosphate is unstable under water and high temperature conditions, strict attention must be paid to the operating conditions during the further drying process. The residual solvent in the product can be gradually removed by gradient heating. The product must be protected by inert gas or vacuum during packaging.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] (1) The present invention uses a one-pot method to prepare sodium hexafluorophosphate. Compared with the two-step process, it reduces equipment costs and avoids the risk of corrosive gas leakage caused by material transfer. At the same time, by controlling the order and rate of raw material input, a small amount of phosphorus source reacts with a large amount of sodium source and HF in an instant. This is equivalent to controlling the entire reaction to proceed at a high reaction rate by increasing the concentration of sodium source and HF, avoiding the overflow and waste of intermediate products such as PF5 and POF3. It also avoids the cumbersome raw material separation and purification process, simplifies the operation steps, optimizes the step time, and greatly reduces the reaction cycle.

[0035] (2) The present invention neutralizes the sodium hexafluorophosphate primary product obtained after the reaction. On the one hand, a solvent with high sodium hexafluorophosphate solubility, low solubility for impurities, easy evaporation and condensation, and azeotropic properties with water is selected to dissolve the sodium hexafluorophosphate primary product. The acidic substances encapsulated, attached, and coordinated in the product are released through dissolution. On the other hand, the pH value is adjusted to weak alkalinity to reduce the content of acidic substances that seriously affect the stability of the product, so that the impurities present in the product precipitate or generate substances with low solubility, thereby achieving the purpose of purifying the liquid phase. In addition, by selecting a solvent that azeotropically reacts with water, the residual water can be removed efficiently at a lower temperature through azeotropic evaporation in the subsequent evaporation.

[0036] (3) The crude sodium hexafluorophosphate prepared by this invention has a purity of over 96%, a high yield, and the solvent is easy to recover and reuse. The tail gas can be treated by neutralization and absorption to generate by-products, which has the advantages of energy saving, emission reduction and high economic benefits. Attached Figure Description

[0037] Figure 1 The chromatogram is of the crude sodium hexafluorophosphate product prepared in Example 1. Detailed Implementation

[0038] The present invention will be further described below with reference to the embodiments. Unless otherwise specified, the raw materials used in the embodiments are all commercially available conventional raw materials; unless otherwise specified, the process methods used in the embodiments are all conventional methods in the art.

[0039] Sodium hexafluorophosphate is prepared using the one-pot method of this invention:

[0040] (1) Reaction: 440g of anhydrous hydrogen fluoride (22mol, 383mL) was added to the reactor. After cooling to -20℃ and maintaining stability, 72g of sodium chloride (1.23mol) was added at a rate of 8g / min. The temperature was maintained at -20℃ and stirred. Then, 209g of phosphorus pentachloride (1mol) was added at a rate of 4g / min.

[0041] Then, under stirring conditions, the temperature was increased to 0°C at a rate of 1°C / min to carry out the reaction. After the temperature increase was completed, the reaction was finished. The reaction solution was then further heated to 50°C at a rate of 3°C / min and kept at that temperature for 1 hour to evaporate and remove volatile substances, thus obtaining sodium hexafluorophosphate as the primary product.

[0042] (2) Neutralization: 357 mL of ethanol at 30°C was added to the primary sodium hexafluorophosphate product for dissolution. Then, a saturated ethanol solution of sodium ethoxide was added to adjust the pH of the solution to 8. The solution was filtered, with a filter membrane pore size not exceeding 0.22 μm, yielding a solid phase mainly composed of sodium fluoride and fluorophosphate, and an ethanol solution of sodium hexafluorophosphate. The solid phase was dried and recycled as a reactant. The ethanol solution of sodium hexafluorophosphate was heated to 78°C at a heating rate of 5°C / min, and the ethanol was evaporated (and recycled after condensation). The solution was then dried at 100°C for 12 h to obtain crude sodium hexafluorophosphate, weighing 165 g, with a yield of 98%. Analysis (chromatogram as shown) was performed. Figure 1 As shown in the figure, the purity is 98.96%.

[0043] Example 2

[0044] Sodium hexafluorophosphate is prepared using the one-pot method of this invention:

[0045] (1) Reaction: 480g of anhydrous hydrogen fluoride (24mol, 417mL) was added to the reactor, and after cooling to -20℃ and maintaining stability, 52g of sodium fluoride (1.23mol) was added at a rate of 15g / min. While maintaining the temperature at -20℃ and stirring, 135g of phosphorus oxychloride (0.88mol) was added at a rate of 5g / min.

[0046] Then, under stirring conditions, the temperature was increased to 0°C at a rate of 1°C / min to carry out the reaction. After the temperature increase was completed, the reaction was finished. The reaction solution was then further heated to 45°C at a rate of 3°C / min and kept at this temperature for 2 hours to evaporate and remove volatile substances, thus obtaining sodium hexafluorophosphate as the primary product.

[0047] (2) Neutralization: 394 mL of ethyl acetate at 25 °C was added to the primary sodium hexafluorophosphate product for dissolution. Then, sodium ethoxide solid powder was added to adjust the pH of the solution to 9. The solution was filtered, and the pore size of the filter membrane was not higher than 0.22 μm. A solid phase with sodium fluoride and fluorophosphate as the main components and an ethanol solution of sodium hexafluorophosphate were obtained. The solid phase was dried and recycled as a reactant. The ethyl acetate solution of sodium hexafluorophosphate was heated to 76 °C at a heating rate of 5 °C / min and the ethyl acetate was evaporated to remove the ethyl acetate (which was then condensed and recycled). The solution was then dried at 100 °C for 24 h to obtain crude sodium hexafluorophosphate product, weighing 141 g with a yield of 95%. The purity was tested to be 97.56%.

[0048] Example 3

[0049] Sodium hexafluorophosphate is prepared using the one-pot method of this invention:

[0050] (1) Reaction: 460g of anhydrous hydrogen fluoride (23mol, 400mL) was added to the reactor, and after cooling to -20℃ and maintaining stability, 66g of sodium carbonate (0.62mol) was added at a rate of 10g / min. While maintaining the temperature at -20℃ and stirring, 135g of phosphorus oxychloride (0.88mol) was added at a rate of 5g / min.

[0051] Then, under stirring conditions, the temperature was increased to 0°C at a rate of 1°C / min to carry out the reaction. After the temperature increase was completed, the reaction was finished. The reaction solution was then further heated to 40°C at a rate of 3°C / min and kept at that temperature for 3 hours to evaporate and remove volatile substances, thus obtaining sodium hexafluorophosphate as the primary product.

[0052] (2) Neutralization: 292 mL of acetone at 20 °C was added to the primary sodium hexafluorophosphate product for dissolution. Then, sodium hydroxide solution was added to adjust the pH of the solution system to 9. The solution was filtered, and the pore size of the filter membrane was not higher than 0.22 μm. A solid phase with sodium fluoride and fluorophosphate as the main components and an ethanol solution of sodium hexafluorophosphate were obtained. The solid phase was dried and recycled as a reactant. The acetone solution of sodium hexafluorophosphate was heated to 57 °C at a heating rate of 5 °C / min and the acetone was evaporated (and recycled after condensation). The solution was then dried at 100 °C for 24 h to obtain crude sodium hexafluorophosphate product, weighing 136 g, with a yield of 92%. The purity was tested to be 96.73%.

[0053] Example 4

[0054] Sodium hexafluorophosphate is prepared using the one-pot method of this invention:

[0055] (1) Reaction: 500g of anhydrous hydrogen fluoride (30mol, 435mL) was added to the reactor, and after cooling to -20℃ and maintaining stability, 125g of sodium metaphosphate (1.23mol) was added at a rate of 10g / min.

[0056] Then, under stirring conditions, the temperature was increased to 0°C at a rate of 1°C / min to carry out the reaction. After the temperature increase was completed, the reaction was finished. The reaction solution was then further heated to 45°C at a rate of 3°C / min and kept at this temperature for 2 hours to evaporate and remove volatile substances, thus obtaining sodium hexafluorophosphate as the primary product.

[0057] (2) Neutralization: 394 mL of acetonitrile at 40 °C was added to the primary sodium hexafluorophosphate product for dissolution. Then, ethylenediamine was added to adjust the pH of the solution to 8. The solution was filtered, and the pore size of the filter membrane was not higher than 0.22 μm. A solid phase with sodium fluoride and fluorophosphate as the main components and an ethanol solution of sodium hexafluorophosphate were obtained. The solid phase was dried and recycled as a reactant. The ethanol solution of sodium hexafluorophosphate was heated to 81 °C at a heating rate of 5 °C / min and the ethanol was evaporated (and recycled after condensation). The solution was then dried at 100 °C for 24 h to obtain crude sodium hexafluorophosphate product, weighing 200 g, with a yield of 97%. The purity was tested to be 96.31%.

[0058] Comparative Example 1

[0059] This comparative example uses a two-step method to prepare sodium hexafluorophosphate:

[0060] (1) Dissolving: Carefully add 420g of anhydrous hydrogen fluoride (21mol, 365ml) to reactor 1, slowly add 42g of sodium fluoride (1mol), stir to dissolve, and keep the temperature controlled at 10℃.

[0061] (2) Preparation of reaction gas: Add 417g of phosphorus pentachloride (2mol) to reaction vessel 2, and slowly add 300g of anhydrous hydrogen fluoride (15mol, 261mL). Condense and distill the generated gas to obtain the reaction gas:

[0062] (3) Reaction: The reaction gas is introduced into reactor 1 and stirred, and the temperature is controlled at 10℃ for 2 hours;

[0063] (4) After the reaction is complete, cool to 0°C, filter to obtain solid, and then dry at 100°C for 24 hours to obtain crude sodium hexafluorophosphate, weighing 141g, with a yield of 83% and a purity of 89%.

Claims

1. A one-pot process for the preparation of sodium hexafluorophosphate, characterized in that: The method comprises the following steps: (1) Reaction: anhydrous hydrogen fluoride is put into a reactor, and the reaction is carried out at 0-10°C after the sodium source and the phosphorus source are added in turn and the temperature is raised to 0-10°C; after the reaction is completed, volatile substances are evaporated to obtain the primary product of sodium hexafluorophosphate; and 60-80 20°C, and then the temperature is raised to 0-10°C to carry out the reaction; after the reaction is completed, volatile substances are evaporated to obtain the primary product of sodium hexafluorophosphate. (2) Neutralization: dissolving the sodium hexafluorophosphate primary product in an organic solvent, then adding a basic substance to adjust the pH value of the solution system to 7-9, filtering to obtain a sodium hexafluorophosphate solution, evaporating the organic solvent, and drying to obtain a sodium hexafluorophosphate crude product; In step (1), the volume ratio of anhydrous hydrogen fluoride as the solvent to the moles of phosphorus contained in all the reactants is (350-520) mL: 1 mol; In step (1), the addition rate of the sodium source is 20-50 g / (min·1 L HF) calculated by the volume of the added anhydrous hydrogen fluoride, and the addition rate of the phosphorus source is 10-25 g / (min·1 L HF); In step (2), the basic substance is one of sodium ethoxide, sodium methoxide, sodium hydroxide, sodium carbonate, sodium bicarbonate, ethylenediamine, diethylamine, and triethylamine.

2. The one-pot process for the preparation of sodium hexafluorophosphate according to claim 1, characterized in that: In step (1), anhydrous hydrogen fluoride is used as both a reactant and a solvent, and the sodium source and the phosphorus source are only used as reactants, and the molar ratio of phosphorus, sodium, and fluorine contained in all the reactants participating in the reaction is 1:(1-1.5):(6-7).

3. The one-pot process for the preparation of sodium hexafluorophosphate according to claim 1 or 2, characterized in that: The sodium source is at least one of NaOH, NaF, NaCl, Na2CO3, Na3PO4, and NaPO3; and the phosphorus source is at least one of H3PO4, P2O5, PCl5, POCl3, Na3PO4, and NaPO3.

4. The one-pot process for the preparation of sodium hexafluorophosphate according to claim 1, characterized in that: In step (1), when the reaction is carried out at a temperature of 0℃, the temperature increasing rate is 0.5-2℃ / min.

5. The one-pot process for the preparation of sodium hexafluorophosphate according to claim 1, characterized in that: In step (1), after the reaction is completed, the temperature is increased to 20-60℃ at a temperature increasing rate of 1-5℃ / min, and the temperature is kept constant for 1-4 h, and volatile substances are evaporated.

6. The one-pot process for the preparation of sodium hexafluorophosphate according to claim 1, characterized in that: In step (2), the organic solvent is a good solvent for sodium hexafluorophosphate and a poor solvent for other sodium salts except sodium hexafluorophosphate, and is azeotropic with water; and the organic solvent is one of ethanol, pyridine, dimethyl carbonate, diethyl carbonate, ethyl acetate, acetonitrile, diethyl ether, ethylene glycol dimethyl ether, methyl tert-butyl ether, and tetrahydrofuran; The ratio of the mass of the sodium hexafluorophosphate primary product to the volume of the added organic solvent is (0.1-1) kg: 1 L; The addition temperature of the organic solvent is 0-40℃.

7. The one-pot process for the preparation of sodium hexafluorophosphate according to claim 1, characterized in that: In step (2), the temperature is increased to 40-80℃ at a temperature increasing rate of 1-5℃ / min, and the organic solvent is evaporated.

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