Process for preparing high-purity alkali metal hexafluorophosphate and the alkali metal hexafluorophosphate prepared thereby
A controlled reaction process for alkali metal hexafluorophosphates minimizes impurities, achieving high purity and improved battery performance by using phosphorus pentachloride and hydrogen fluoride gases under a phosphorus pentafluoride atmosphere.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-03-20
- Publication Date
- 2026-04-10
AI Technical Summary
Conventional methods for preparing alkali metal hexafluorophosphates like NaPF6 and KPF6 result in high impurity levels, particularly fluorinated solids and metallic impurities, which degrade battery performance and are difficult to purify without complex processes.
A process involving controlled reaction of alkali metal fluoride with phosphorus pentachloride and hydrogen fluoride gases under a phosphorus pentafluoride atmosphere, followed by filtration and drying, to produce ultra-high purity alkali metal hexafluorophosphates with reduced impurities.
Achieves alkali metal hexafluorophosphates with purity greater than 99.5%, significantly reducing impurities such as fluorinated solids, metallic impurities, and water content, enhancing battery performance and safety.
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Abstract
Description
Technical Field
[0001] The present disclosure relates to a process for preparing alkali metal hexafluorophosphate salts. More specifically, the present invention relates to a process for preparing high purity alkali hexafluorophosphate salts based on Group 1 elements preferably selected from sodium hexafluorophosphate (NaPF6), potassium hexafluorophosphate (KPF6) and cesium hexafluorophosphate (CsPF6). Alkali hexafluorophosphate salts are useful as electrolytes in stationary batteries and batteries for low-speed electric vehicles.
Background Art
[0002] Since the commercialization of lithium-ion batteries (LIBs) in 1991, they have found applications in various fields over the years. Starting from their use in portable electronic devices, currently, the demand has shifted significantly towards applications in electric vehicles (EVs) and energy storage systems (ESSs). This has led to an unprecedented demand for the core raw material of LIBs, namely "lithium". Globally, the demand for lithium by 2030 is 2.5 million tons according to a report by Statista, while the demand for lithium in 2021 was 0.5 million tons. However, the problem is that lithium is not very abundant in the earth's crust, which poses a serious threat to the future availability of lithium. Therefore, in the short term, it is necessary to find a suitable alternative to lithium-ion batteries. Here, sodium-ion batteries come into play.
[0003] Sodium and potassium are classified in the same group as lithium in the periodic table and exhibit similar properties to lithium. Therefore, electrolytes based on sodium and potassium are of interest.
[0004] Sodium is the sixth most abundant element in the Earth's crust, and therefore, its availability is not threatened. While sodium-ion batteries (NIBs) currently have limitations in their suitability for high-speed electric vehicles (EVs), they are perfectly suited for energy storage systems (ESSs) and low-speed vehicle applications. Continued research and development activities for sodium-ion batteries (NIBs) over the next few years are expected to lead to their future applications in high-speed EVs as well. Thus, sodium-ion batteries could become a potential alternative to lithium-ion batteries in the future.
[0005] Similarly, potassium-ion batteries (KIBs) are emerging as a promising energy storage system due to the abundance of potassium. Potassium ions have several advantages over similar lithium-ion batteries (e.g., lithium-ion batteries). Cell design is simpler, and both materials and manufacturing procedures are cheaper. Key advantages are the abundance and low cost of potassium compared to lithium, which makes potassium batteries a promising candidate for home energy storage and large-scale batteries such as those for electric vehicles.
[0006] NaClO4 is the most studied electrolyte salt in sodium-ion batteries (NIBs), and KClO4 is the most studied electrolyte salt in potassium-ion batteries (KIBs), but the strong oxidizing properties of the perchlorate anion hinder commercial use. Similar to lithium hexafluorophosphate (LiPF6), sodium hexafluorophosphate (NaPF6), potassium hexafluorophosphate (KPF6), or cesium hexafluorophosphate (CsPF6) are electrolyte salts for sodium-ion batteries, potassium-ion batteries, or cesium-ion batteries, respectively. Therefore, they can succeed mature battery technologies that have been commercialized with Li battery salts that have good solubility and ionic conductivity in battery solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, etc., and mixtures thereof.
[0007] For long-term battery cycle life, the electrolyte salt must be extremely pure.
[0008] In conventional preparations of NaPF6, PF5 gas is passed through a solution of NaF in HF to form NaPF6. The HF is then removed, and the NaPF6 crystallizes. However, one drawback of this conventional approach is that a large amount of impurities, in the form of fluorinated solids, precipitate and mix with the NaPF6 crystals. Furthermore, reducing the amount of impurities, such as fluorinated solids, in NaPF6 without resorting to complex reactions, procedures, and additional purification steps is extremely difficult.
[0009] Similarly, for the preparation of KPF6, PF5 gas is passed through a solution of KF in HF to form KPF6. Then, the HF is removed and the KPF6 is crystallized. However, one drawback of the conventional approach is that a large amount of impurities in the form of fluorinated solids precipitate and mix with the KPF6 crystals. Furthermore, reducing the amount of impurities such as fluorinated solids in KPF6 without resorting to complex reactions, procedures, and additional purification steps is extremely difficult.
[0010] Impurities in the form of fluorinated solids cause electrode erosion, which directly affects the capacity and performance of the battery.
[0011] Furthermore, the presence of various metallic impurities, such as transition metal impurities, is detrimental to battery performance. For example, transition metal ions dissolved in the electrolyte can deposit on the anode surface. This can lead to the decomposition of NaPF6 and KPF6, causing sodium and potassium dendrites to grow from the negative electrode surface, potentially resulting in internal short circuits.
[0012] Water is yet another impurity of concern in sodium-ion and potassium-ion batteries. The presence of water negatively impacts battery performance. Excessive water can also cause the electrolyte to acidify more quickly, generating HF gas, which is one of the main reasons for battery flatulence, and such flatulence shortens the battery's lifespan.
[0013] Water can react with NaPF6 and KPF6, which can reduce the battery's capacity. The presence of water also contributes to reduced cycle performance and loss of active material. Water can break down the protective solid electrolyte interface layer and be reduced at the anode to produce H2 gas. The presence of H2 gas increases the internal pressure of the battery, creating an explosion hazard.
[0014] Furthermore, conventional preparation methods have drawbacks that prevent them from being implemented on a large scale, such as back pressure control, choking issues, and the need to maintain and control pressure for optimized purity. [Overview of the Initiative] [Problems that the invention aims to solve]
[0015] Therefore, it is necessary to develop a process for preparing high-purity alkali hexafluorophosphate salts, preferably selected from NaPF6, KPF6, or CsPF6, with reduced impurities, that addresses one or more of the aforementioned drawbacks. [Means for solving the problem]
[0016] In one embodiment, the present invention relates to a process (method) for preparing ultra-high purity alkali metal hexafluorophosphate (MPF6), comprising: (a) filling a first reactor "B" with alkali metal fluoride (MF) and flushing nitrogen gas through the first reactor "B"; (b) cooling the first reactor "B" to a predetermined temperature, then filling it with anhydrous hydrogen fluoride (AHF) gas and stirring a mixture containing alkali metal fluoride (MF) dissolved in AHF within the first reactor "B"; (c) cooling a mixture containing alkali metal fluoride (MF) dissolved in AHF within the first reactor "B" to a predetermined temperature; and (d) filling a second reactor "A" with phosphorus pentachloride (PCl5) and flushing the AHF through a lot The present invention provides a process (method) comprising: (e) adding the mixture in separate parts to produce high-purity phosphorus pentafluoride (PF5) and hydrogen chloride (HCl) gas; (d) reacting the alkali metal fluoride (MF) dissolved in AHF with the mixture of phosphorus pentafluoride (PF5) and hydrogen chloride (HCl) gas obtained in step (d) in a first reactor "B" to obtain a mother liquor of alkali metal hexafluorophosphate dissolved in AHF under a PF5 gas atmosphere (blanking); and (f) cooling the first reactor "B" to a predetermined temperature, maintaining the temperature of the mother liquor of alkali metal hexafluorophosphate dissolved in AHF for a predetermined time, followed by filtration and drying at a predetermined temperature to achieve alkali metal hexafluorophosphate (MPF6).
[0017] In another embodiment, the present invention provides an ultra-high purity alkali metal hexafluorophosphate with an improved yield of at least 99.50%, preferably at least 99.8%. [Brief explanation of the drawing]
[0018] Embodiments of the present invention may be referenced, and examples of such embodiments may be shown in the accompanying drawings. These drawings are illustrative and not intended to be limiting. While the present invention is generally described in the context of these embodiments, it should be understood that the scope of the invention is not intended to be limited to these specific embodiments. [Figure 1] Figure 1 shows a process flow diagram. **DETAILED DESCRIPTION OF THE INVENTION**
[0019] It should be noted that as used in this specification, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a composition containing "a compound" includes "a mixture of two or more compounds". It should also be noted that the term "or" is generally used in the sense of "and / or" unless the context clearly dictates otherwise.
[0020] Expressions of various amounts by "% " or "% w / w" mean weight percent of the whole solution or composition unless otherwise specified.
[0021] The present invention is directed to a process for preparing an ultra-high purity alkali metal hexafluorophosphate salt (MPF6), which is useful as an electrolyte in high-intensity batteries, preferably as an electrolyte in batteries for storage applications.
[0022] In one embodiment, the process for preparing an ultra-high purity alkali metal hexafluorophosphate salt MPF6 (preferably M = Na, K or Cs) is as follows a. Filling an alkali metal fluoride (MF) into a first reactor "B" and flowing nitrogen gas through this first reactor "B"; b. Cooling the first reactor "B" to a predetermined temperature, subsequently filling anhydrous hydrogen fluoride (AHF) gas, and stirring a mixture containing the alkali metal fluoride (MF) dissolved in AHF in the first reactor "B"; c. Cooling the mixture containing the alkali metal fluoride (MF) dissolved in AHF in the first reactor "B" to a predetermined temperature; d. Filling the second reactor "A" with phosphorus pentachloride (PCl5), adding AHF in batches, and generating high-purity phosphorus pentafluoride (PF5) and hydrogen chloride (HCl) gas; e. Reacting the alkali metal fluoride (MF) dissolved in AHF in the first reactor "B" with the PF5 and HCl gas mixture obtained in step (d) to obtain a mother liquor of alkali metal hexafluorophosphate dissolved in AHF under a PF5 gas atmosphere; f. Cooling the first reactor "B" to a predetermined temperature, maintaining the temperature of the mother liquor of alkali metal hexafluorophosphate dissolved in AHF for a predetermined time, then filtering and drying at a predetermined temperature to achieve an alkali metal hexafluorophosphate (MPF6); g. Crushing the dried crystals of MPF6 and optionally sieving to obtain MPF6 powder; including.
[0023] Whenever PF5 gas is purged into the MF / AHF solution, usually the dip pipe is blocked and back pressure is applied to the reactants, which causes losses. Therefore, the process reaction is carried out under a PF5 gas atmosphere, and the problems of back pressure control and choking can be completely solved by the process of the present invention.
[0024] Furthermore, according to the disclosed process, the pressure of the reactants can be controlled according to requirements. Overpressure is controlled by the slow batch addition of AHF to the PCl5-containing reactor. The generated HCl and PF5 gases are blanketed in the MF / HF reactor. Therefore, the pressure can be controlled by discharging excess gas into a scrubber having a basic pH, and the pressure can be more effectively maintained and controlled in the scrubber, so that the flow of acidic fumes is unidirectional.
[0025] In one embodiment, the alkali metal is selected from Na, K, and Cs, and the alkali metal hexafluorophosphate is selected from NaPF6, KPF6, or CsPF6.
[0026] In one embodiment, alkali metal fluorides are obtained from their respective metal carbonates and hydrogen fluoride (HF). For example, the sodium fluoride (NaF) and potassium fluoride (KF) used in the process are obtained from sodium carbonate (Na2CO3) or potassium carbonate (K2CO3) and hydrogen fluoride (HF), respectively.
[0027] In one embodiment of the present invention, the anhydrous hydrogen fluoride (AHF) gas is purified anhydrous hydrogen fluoride (AHF) gas containing 1 ppm or less of cationic (metallic) impurities, 1 ppm or less of anionic impurities, 1 ppm or less of water, or a combination thereof.
[0028] In yet another embodiment, purified anhydrous hydrogen fluoride (AHF) gas is reacted with a PCl5 solid bed reactor while stirring.
[0029] In yet another embodiment, anhydrous hydrogen fluoride (AHF) gas is purified by treatment with fluorine (F2) gas as an oxidizing agent.
[0030] In one embodiment of the process, PF5 and HCl gases from the second reactor "A" were introduced into the first reactor "B" through a venting system without a dip tube until a constant pressure was reached.
[0031] In one embodiment of the process, the predetermined temperatures in steps (b) and (c) are in the range of 0 to 15°C, preferably in the range of 5 to 10°C.
[0032] In one embodiment of the process, AHF is preferably added in multiple batches at a temperature of 25-40°C in the range of 200-300 g or 100-200 g.
[0033] In one embodiment of the process, the predetermined temperature and time for cooling in step (f) are in the range of -10 to -25°C for 5 to 7 hours.
[0034] In one embodiment of the process, the predetermined temperature and time for cooling in step (f) are 6 hours in the range of -15 to -20°C.
[0035] In one embodiment of the process, the predetermined temperature for drying in step (f) is in the range of 35 to 50°C, preferably 38 to 40°C.
[0036] In a preferred embodiment, the process involves the use of a static crystallizer that rotates once every 48 hours to allow the crystals to grow slowly to a large size and minimize the surface area for HF adsorption.
[0037] In another preferred embodiment, the mother liquor is reused by adding an alkali fluoride (preferably selected from NaF, KF, or CsF) at -15 to 15°C, preferably 10°C.
[0038] In a preferred embodiment, the crystallized alkali metal hexafluorophosphate is dried by hot water circulation in a drying oven jacket, after which dried N2 is passed through the dried crystals for about 6-7 hours.
[0039] In yet another embodiment, after drying the crystallized alkali metal hexafluorophosphate, solvent-assisted drying is performed, preferably using a solvent such as ether or dichloromethane.
[0040] Another aspect of the process involves using a mesh size such that larger crystals with lower HF adsorption are sieved as the final product. Smaller crystals with higher HF adsorption are recycled through the mother liquor. This reduces the total concentration of HF in the final product, resulting in the recovery of alkali metal hexafluorophosphate crystals for the next crystallization step, and also reduces manufacturing costs.
[0041] In a preferred embodiment, the sieving of the dry crystals of the alkali metal hexafluorophosphate is performed through a mesh size of 90 or less.
[0042] In another embodiment, the alkali metal fluoride (sodium fluoride, potassium fluoride, or cesium fluoride) used in the process is obtained by the steps of: dissolving an alkali metal carbonate (preferably selected from sodium carbonate, dipotassium carbonate, or cesium carbonate) in water to obtain an alkali metal carbonate solution; and reacting the alkali metal carbonate solution with ultra-high purity hydrogen fluoride to obtain an alkali metal fluoride such as sodium fluoride, potassium fluoride, or cesium fluoride. Na2CO3 + 2HF → 2NaF + CO2 + H2O, or K2CO3 + HF → KF + CO2 + H2O
[0043] In another embodiment, the alkali metal fluoride (sodium fluoride, potassium fluoride, or cesium fluoride) used in the process is obtained by the steps of: dissolving treated pure alkali metal hydroxide in ultrapure water to obtain an alkali metal hydroxide solution or an alkali solution (caustic alkali and caustic potash solution); and reacting the alkali metal hydroxide solution / caustic alkali / caustic potash with ultra-high purity hydrogen fluoride to obtain an alkali metal fluoride (sodium fluoride, potassium fluoride, or cesium fluoride). NaOH + HF → NaF + H2O, or KOH + HF → KF + H2O Subsequently, the alkali metal fluoride (NaF, KF, or CsF) obtained within the desired particle size range is dried and crushed.
[0044] In another embodiment, waste products from the reactor containing PF5, HCl, phosphorus oxides, and HF are re-introduced into the mother liquor for a second-stage reabsorption process, which improves the overall efficiency of the process.
[0045] In another embodiment, gaseous emissions from the mother liquor tank containing HCl and HF are reintroduced to a recovery system, which improves the overall efficiency of HF recovery.
[0046] Another aspect of the present invention relates to an ultra-high purity alkali metal hexafluorophosphate salt selected from NaPF6, KPF6, and CsPF6 having a purity of at least 98.50%, preferably at least 99.8%.
[0047] In a preferred embodiment of the present invention, an ultra-high-purity alkali metal salt of hexafluorophosphate (preferably selected from NaPF6, KPF6, or CsPF6) is used. • Insoluble material in amounts of 200 ppm or less, • Metal impurities present in amounts of 2 ppm or less, or • Hydrogen fluoride (HF) in amounts of 70 ppm or less, • A quantity of sulfate ions (SO4) of 10 ppm or less 2- ), or • Nitrate ions (NO3) in amounts of 5 ppm or less - ), or • Chloride ions (Cl) in amounts of 5 ppm or less - ), or • A quantity of water / moisture less than 10 ppm, or a combination thereof. Includes.
[0048] In preferred embodiments of the present invention, the ultra-high-purity alkali metal salt hexafluorophosphate (preferably selected from NaPF6, KPF6, or CsPF6) contains the following metal impurities. Na ≤ 2 ppm K ≤ 2 ppm Fe ≤ 2 ppm Zn ≤ 2 ppm Ni ≤ 2 ppm Mg ≤ 2 ppm Ca ≤ 2 ppm Pb ≤ 2 ppm Cr ≤ 2 ppm
[0049] According to the process of the present invention, high-purity phosphorus pentachloride (PCl5) is obtained from a commercial source. High-purity anhydrous hydrogen fluoride (AHF) in gaseous form reacts with solid phosphorus pentachloride (PCl5) to produce phosphorus pentafluoride (PF5) and hydrogen chloride (HCl).
[0050] Impurities in alkali hexafluorophosphate salts are a direct result of impurities present in the main raw materials, namely AHF and NaF or KF. Therefore, as described later, the AHF and NaF or KF or CsF used in this invention are purified to minimize water, insoluble impurities, and metallic impurities. In other words, only high-purity battery-grade AHF and NaF or KF or CsF are used in this invention.
[0051] Normally, PF5 is prepared by dissolving PCl5 in AHF. This results in the generation of impurities such as AsF5 and BF4. However, in this invention, gaseous AHF reacts with solid PCl5 in a packed-bed reactor. In addition to the arsenic and boron-producing gases mixed into the PF5, most of the impurities introduced into the PCl5 react with the PF5 to form high-boiling-point precipitated fluorides in the reactor, remaining in a solid state at the bottom. Subsequently, the obtained PF5 is passed through a filter to remove any PCl5 particles that may be suspended in the gas stream, yielding high-purity PF5 gas. Therefore, by carrying out this process in a packed-bed reactor using high-purity gaseous AHF, impurities and water in the PF5 gas are eliminated or minimized.
[0052] The PF5 produced in step (d) enters the first reactor "B," where it reacts with NaF or KF dissolved or suspended in AHF. This forms NaPF6, KPF6, or CsPF6 dissolved in AHF, also known as the mother liquor. Preferably, step (d) is carried out at a temperature in the range of -15 to 15°C, more preferably at 10°C.
[0053] The waste from the second reactor "A," containing PF5, HCl, phosphorus oxides, and HF, was re-introduced into the mother liquor for a second-stage reabsorption process, which improved the overall efficiency of the reaction, particularly by improving the recovery efficiency of PF5. Every hour, excess pressure with HCl gas was introduced into a scrubber with a basic pH. After HF and PCl5 were completely consumed (indicated by the absence of PF5 gas pressure), the reactor was cooled to -15 to -20°C.
[0054] In one embodiment of the process, crystallization is preferably carried out from the mother liquor in a static crystallization tank, where the mother liquor is cooled. The mother liquor is cooled over a long period of time.
[0055] The static crystallizer used in this invention rotates once every 48 hours. Alkali metal hexafluorophosphate crystals can grow slowly to large sizes. As the size of the NaPF6, KPF6, or CsPF6 crystals increases, the surface area on which HF is adsorbed decreases, resulting in NaPF6, KPF6, or CsPF6 with the lowest HF content. The crystals are separated by passing them through a mesh sieve. The separated, larger crystals of NaPF6, KPF6, or CsPF6 are crushed and dried under vacuum at a temperature of 60-70°C for about 6 hours to remove the largest amount of HF, thereby obtaining high-purity powdered NaPF6 or KPF6.
[0056] Smaller crystals of NaPF6, KPF6, or CsPF6 are reused by adding specific amounts of sodium fluoride (NaF), potassium fluoride (KF), or cesium fluoride (CsF), respectively, to the mother liquor at -15 to 5°C, preferably -10°C, and the process is repeated to obtain larger crystals.
[0057] When a constant-speed rotary crystallizer is used instead of a static crystallizer, smaller crystals with an HF content in the range of 150-300 ppm are obtained. If higher temperatures are used for drying, decomposition of NaPF6, KPF6, or CsPF6 crystals occurs, and HF is produced from these crystals.
[0058] Several representative embodiments of the present invention are discussed below.
[0059] In its broader embodiments, the present invention is not limited to specific details and representative processes. Exemplary examples are described in this section in relation to the embodiments and processes provided.
[0060] Figure 1 shows a process flow diagram for preparing NaPF6 according to one embodiment of the present disclosure. In this process, an HF solution (101) passes through a vaporizer (V1) and the HF is converted to a gaseous state (102). The HF gaseous state (102) obtained from the vaporizer (V1) reacts with PCl5 powder (103) in a first reactor (R1) to obtain the intermediate product PF5, HCl (g), and unreacted trace amounts of HF (105).
[0061] The intermediate product (105) is passed through a filter (F1) and sent to a second reactor (R2) to obtain a product solution (106) containing NaPF6 and HF solution, which is passed through a holding tank (V2). The product solution (106) from the holding tank (V2) is passed through a crystallizer (V3) where the product NaPF6 (107) is recovered and the mother liquor (108) is separated. The product (107) is passed through a sieve (S1) to obtain product NaPF6 of the desired size, and the remainder is recycled to the mother liquor tank (V4). The mother liquor (108) containing NaF and HF solution is sent to the mother liquor tank (V4), where HF solution and NaF (104) are further added, and the treated mother liquor (109) is recycled back to the second reactor (R2) to obtain a product solution (106) containing NaPF6 and HF solution. The vent gas (111) from the mother liquor tank (V4) is sent to the recovery system (S2) for reuse and recycling of HF gas (101), while the vent gas (110) that is not recovered is sent to the three-stage scrubber (S3) for disposal.
[0062] Impurities in NaPF6 are a direct result of impurities present in the main raw materials, namely AHF and NaF. Therefore, as discussed below, the AHF and NaF used in this invention are purified to minimize water, insoluble impurities, and metallic impurities. In other words, only high-purity AHF and NaF are used in this invention.
[0063] In commercially available HF, metals such as Fe, Ca, and Mg react with active PF5 in the synthesis reaction vessel to form FeF3, CaF2, and MgF2, which increase impurities in the NaPF6 / KPF6 crystal. Therefore, the AHF used in the present invention is purified before use in the process of the present invention.
[0064] Commercially available AHF is purified by treating it with fluorine (F2) as an oxidizing agent, fluorinating AHF impurities and removing most metals, including arsenic and boron compounds, as gaseous impurities. If AHF is not purified by reaction with F2, gaseous impurities such as metal fluorides, AsF5, and BF4 may contaminate the mother liquor. The use of purified AHF in this invention further minimizes impurities in the NaPF6 / KPF6 crystals of this invention.
[0065] Preparation of high-purity AHF: Pure fluorine gas is added to the reaction vessel at a concentration of 3 kg / cm³. 2 The mixture is purged into commercially available AHF at a pressure of 25°C for 3 minutes. After impurities precipitate as fluorides, the pure AHF is transferred from the reaction vessel to a distillation column. The impurity levels of commercially available AHF versus purified AHF are shown below. [Table 1]
[0066] Insoluble impurities such as silicates, fluorosilicates, and sulfates of metals like Fe, Ca, K, Na, Ni, Pb, Zn, Cr, Mg, Cu, and Al are present in NaF. Some metals do not dissolve in AHF and remain as solid particles. Some react with AHF to form fluoride materials, such as FeF3, NaF, CaF2, and MgF2. In these cases, the fluoride materials precipitate as solids at the bottom of the crystallizer and remain with the NaPF6 crystals. This is the main cause of impurities in NaPF6. These insoluble impurities eventually enter NaPF6, thereby increasing the total levels of Ca, Mg, Na, K, etc., to over 100 ppm. Therefore, in order to produce high-purity NaPF6, the NaF used in the process must be free of the above-mentioned metal impurities.
[0067] Preparation of high-purity NaF: A solution is prepared by mixing commercially available Na2CO3 with pure deionized water. Insoluble impurities are filtered out by passing this Na2CO3 solution through two series of cartridge filters. Then, soluble impurities are removed by passing this Na2CO3 solution through a cation and anion exchange resin column.
[0068] Next, the purified Na2CO3 solution is reacted with 50% HF to neutralize it and obtain NaF. The NaF thus formed is filtered and dried by evaporating the water at 130°C.
[0069] The purified NaF contains less than 2 ppm of metallic impurities and less than 5 ppm of anionic impurities such as chlorides and sulfates.
[0070] Alternatively, purified sodium hydroxide (NaOH) or a caustic alkali may be used instead of sodium carbonate (Na2CO3).
[0071] Preparation of NaPF6 - The high-purity AHF produced as described above is added to solid PCl5, and the mixture of PF5 + HCl + HF produced from this reaction is supplied to a solution of NaF + AHF to produce NaPF6 in the AHF solvent. NaPF6 is then crystallized from this solution, filtered, and dried to obtain the pure product.
[0072] The impurity levels of ultra-high-purity NaPF6 produced by this process are shown below. Impurity levels of ultra-high purity NaPF6: Fe ≤ 2 ppm Ca ≤ 2 ppm K ≤ 2 ppm Na ≤ 2 ppm Ni ≤ 2 ppm Pb ≤ 2 ppm Zn ≤ 2 ppm Cr ≤ 2 ppm Cu ≤ 2 ppm Mg ≤ 2 ppm
[0073] The NaPF6 obtained by the above process contains less than 200 ppm of insoluble material and / or metallic impurities, each present in an amount of less than 1 ppm, and / or contains less than 70 ppm of HF and / or less than 10 ppm of SO4. 2- Contains and / or NO3 in an amount of 5 ppm or less. - Contains and / or 5 ppm or less of Cl - It contains and / or water in an amount of 10 ppm or less, or a combination thereof.
[0074] The purity of NaPF6 obtained by the process of the present invention is at least 99.5%, preferably at least 99.8%.
[0075] If the AHF purification process, the preparation of high-purity NaF, and the crystallization and drying steps are omitted, metal impurities are carried over and become part of the final product, i.e., NaPF6. In that case, the NaPF6 impurity profile will have total metal impurities of 30-80 ppm, rather than less than 1 ppm.
[0076] Along a similar line, potassium hexafluorophosphate (KPF6) may be prepared by using potassium fluoride (KF) and phosphorus pentafluoride (PF5). Finally, potassium fluoride (KF) is prepared using potassium carbonate (K2CO3) or potassium hydroxide (KOH). PCl5 + 5HF → PF5 + 5HCl PF5 + KF → KPF6
[0077] Similarly, cesium hexafluorophosphate (CsPF6) may be prepared by using cesium fluoride (CsF) and phosphorus pentafluoride (PF5). Finally, cesium fluoride (CsF) is prepared using cesium carbonate (Cs2CO3) or cesium hydroxide (CsOH).
[0078] High-purity alkali metal hexafluorophosphates of other Group 1 elements (Rb and Fr) can also be prepared according to the scheme described above. [Examples]
[0079] The following examples are illustrative of the present invention and do not limit its scope.
[0080] Example 1: Synthesis of sodium hexafluorophosphate using a 1:1.2 molar ratio of sodium fluoride to phosphorus pentachloride. Two Hastelloy autoclaves (A and B) with non-metallic wetted sections were used to react NaF and PCl5 in a molar ratio of 1:1.2. High-purity sodium fluoride (100 g) was packed into reactor B. Nitrogen was flowed through this assembly. The assembly was cooled to 5-10°C. Battery-grade AHF (800 g) was packed from a cylinder under controlled conditions. This mixture was stirred. Reactor A was filled with PCl5 (594g). AHF was slowly added in batches of 100-200g at 25-40°C over a 24-30 hour timeframe (totaling 380g). During this time, the pressure generated in reactor A due to the formation of PF5 and HCl gases was introduced into reactor B through a venting system without any dip tubes, until a constant pressure was reached. PF5 gas was reacted with NaF in the AHF to obtain NaPF6 under a PF5 gas atmosphere. Every hour, the excess pressure due to HCl gas was released into a scrubber with a basic pH. After HF and PCl5 were completely consumed (identified by the absence of PF5 gas pressure), the reactor was cooled to -15 to -20°C, the reaction mixture was maintained at -15°C for 16 hours, and the solid was filtered under pressure. The solid was dried and removed. The weight of the isolated sodium hexafluorophosphate was 120 g. The isolated solid was checked for its sodium content assay by ion chromatography and found to be 99.85%.
[0081] Example 2: Synthesis of sodium hexafluorophosphate using a 1:1.4 molar ratio of sodium fluoride to phosphorus pentachloride Two Hastelloy autoclaves (A and B) with non-metallic wetted sections were used to react NaF and PCl5 in a molar ratio of 1:1.4. High-purity sodium fluoride (100 g) was packed into reactor B. Nitrogen was flowed through this assembly. This assembly was cooled to 5-10°C. Cell-grade AHF (400 g) was packed from a cylinder under controlled conditions. This mixture was stirred. Reactor A was filled with PCl5 (694g). AHF was slowly added in batches of 100-200g at 25-40°C over a 24-30 hour timeframe (totaling 443g). During this time, the pressure generated in reactor A due to the formation of PF5 and HCl gases was introduced into reactor B through a venting system without any dip tubes, until a constant pressure was reached. PF5 gas was reacted with NaF in the AHF to obtain NaPF6 under a PF5 gas atmosphere. Every hour, the excess pressure due to HCl gas was released into a scrubber with a basic pH. After HF and PCl5 were completely consumed (identified by the absence of PF5 gas pressure), the reactor was cooled to -15 to -20°C, the reaction mixture was maintained at -15°C for 16 hours, and the solid was filtered under pressure. The solid was dried and removed. The weight of the isolated sodium hexafluorophosphate was 321 g. The isolated solid was checked for sodium content by ion chromatography and found to be 99.8%.
[0082] Example 3: Synthesis of potassium hexafluorophosphate using a 1:1.4 molar ratio of potassium fluoride to phosphorus pentachloride Two Hastelloy autoclaves (A and B) were used to react KF and PCl5 in a molar ratio of 1:1.4. Reactor B was packed with high-purity potassium fluoride (58 g). Nitrogen was flowed through this assembly. The assembly was cooled to 5-10°C. Purified AHF (200 g) was packed from a cylinder under controlled conditions. This mixture was stirred. Reactor A was filled with PCl5 (312g), and 20 to 50 lots of AHF were slowly added at 25 to 40°C over a 24 to 30-hour timeframe (total 220g). During this time, the pressure generated in reactor A due to the formation of PF5 and HCl gases was introduced into reactor B through a venting system without any dip tubes, up to a constant pressure. PF5 gas was reacted with KF in the AHF to obtain KPF6 under a PF5 gas atmosphere. Every hour, the excess pressure due to HCl gas was released into a scrubber with a basic pH. After HF and PCl5 were completely consumed (confirmed by the absence of PF5 gas pressure), the reactor was cooled to -15 to -20°C, the reactants were maintained at -15°C for 16 hours, and the solid was filtered under pressure. The solid was dried and removed. The weight of the isolated potassium hexafluorophosphate was 158 g.
[0083] The above description of the present invention is provided merely to illustrate the invention and is not intended to limit it. Modifications of the disclosed embodiments that incorporate the spirit and essence of the invention may be conceivable to those skilled in the art, so the present invention should be construed as encompassing all of the scope of this disclosure.
Claims
1. Ultra-high purity alkali metal hexafluorophosphate (MPF) ６ A method for preparing the following: a. A step of filling the first reactor "B" with alkali metal fluoride (MF) and flowing nitrogen gas through the first reactor "B", b. The first reactor "B" is cooled to a predetermined temperature, then filled with anhydrous hydrogen fluoride (AHF) gas, and the mixture containing alkali metal fluoride (MF) dissolved in AHF is stirred in the first reactor "B". c. A step of cooling a mixture containing alkali metal fluoride (MF) dissolved in AHF in the first reactor "B" to a predetermined temperature, d. Phosphorus pentachloride (PCL) ５ The second reactor "A" is filled with ) and AHF is added in multiple batches to produce high-purity phosphorus pentafluoride (PF ５ ) and a step of generating hydrogen chloride (HCl) gas, e. The alkali metal fluoride (MF) dissolved in AHF in the first reactor "B" is converted to phosphorus pentafluoride (PF) obtained in step (d). ５ ) and a mixture of hydrogen chloride (HCl) gas are reacted to form a mother liquor of alkali metal hexafluorophosphate dissolved in AHF, which is then processed in PF. ５ Processes obtained under a gaseous atmosphere, f. The first reactor "B" is cooled to a predetermined temperature, the temperature of the mother liquor of alkali metal hexafluorophosphate dissolved in AHF is maintained for a predetermined time, then filtered, and dried at a predetermined temperature to obtain alkali metal hexafluorophosphate (MPF). ６ The process to achieve ) and g. Dry solid MPF ６ The process of obtaining comprising, wherein the alkali metal "M" is selected from Na, K, and Cs, and the alkali metal hexafluorophosphate salt is NaPF ６ , KPF ６ or CsPF ６ selected from, a method.
2. PF from the second reactor "A" ５ The method according to claim 1, wherein the HCl gas is introduced into the first reactor "B" through a ventilation system without a dip tube until it reaches a constant pressure.
3. The method according to claim 1, wherein the anhydrous hydrogen fluoride (AHF) gas is purified before use in the method, and the alkali metal fluoride used in the method is obtained from alkali metal bicarbonate and hydrogen fluoride.
4. The method according to claim 1, wherein the predetermined temperature in steps (b) and (c) is in the range of 5 to 15°C.
5. The method according to claim 1, wherein the addition of AHF is carried out in multiple batches at a temperature in the range of 25 to 40°C.
6. The method according to claim 1, wherein the predetermined temperature and predetermined time for cooling in step (f) are in the range of -10 to -25°C for 5 to 17 hours.
7. The method according to claim 1, wherein the predetermined temperature for drying in step (f) is in the range of 35 to 50°C.
8. NaPF obtained by the method described in claim 1 ６ KPF ６ and CsPF ６ An ultra-high purity alkali metal hexafluorophosphate selected from the above, having a purity of at least 99.8% w / w.
9. The ultra-high purity sodium hexafluorophosphate (NaPF) according to claim 8, comprising the following metal impurities. ６ ). Fe ≤ 2 ppm Ca ≤ 2 ppm K ≤ 2 ppm Na ≤ 2 ppm Ni ≤ 2 ppm Pb ≤ 2 ppm Zn ≤ 2 ppm Cr ≤ 2 ppm Cu ≤ 2 ppm Mg ≤ 2 ppm