A method and system for synthesizing liquid hexafluorophosphate

Abstract

This invention relates to the technical field of hexafluorophosphate synthesis, and in particular to a method and system for synthesizing liquid hexafluorophosphate. The method for synthesizing liquid hexafluorophosphate is a novel process route that uses phosphorus trichloride as the initial raw material and sequentially undergoes oxidation, fluorination, deep fluorination, and in-situ solvent-captured phosphorus pentafluoride reaction with alkali metal fluorides to obtain liquid hexafluorophosphate. The entire technical route has the advantages of being controllable, low-cost, green, highly safe, and low in impurities.

Description

Technical Field

[0001] This application relates to the technical field of hexafluorophosphate synthesis, and in particular to a method and system for synthesizing liquid hexafluorophosphate. Background Technology

[0002] In the field of new energy storage and power batteries, sodium-ion batteries have become a promising new type of rechargeable battery system due to their abundant resources, significant cost advantages, and excellent electrochemical performance. Their performance is closely related to the quality of core materials and the manufacturing process. Sodium hexafluorophosphate (NaPF6) is a key raw material in the electrolyte of sodium-ion batteries. With the continued growth in market demand for sodium-ion batteries, improving the production capacity and quality of NaPF6 and reducing production costs are becoming increasingly important for sodium-ion battery production.

[0003] Currently, traditional NaPF6 preparation processes mostly rely on the "sodium salt variant" route of the lithium hexafluorophosphate (LiPF6) process. This type of route typically uses phosphorus pentafluoride (PF5) or byproducts from the LiPF6 production process as starting materials. On the one hand, the acquisition cost of PF5 and LiPF6 byproducts is high, and the source of raw materials is limited by the lithium salt production process, making it difficult to effectively reduce the preparation cost of NaPF6, which is not conducive to large-scale industrial applications. On the other hand, some existing processes use commonly used polyphosphoric acid or phosphorus trichloride (PCl3) as raw materials to synthesize PF6, which generates a large number of gaseous products during the reaction and involves highly toxic substances. The process is highly complex, which not only increases the safety risks in the production process but also increases the difficulty of process control, which is not conducive to stable operation and safety management in industrial production.

[0004] In summary, it is necessary to provide a novel preparation process for NaPF6 to reduce production costs and improve production safety and controllability. Summary of the Invention

[0005] To address the aforementioned problems, the first aspect of this application aims to provide a method for synthesizing liquid hexafluorophosphate. This method not only prepares hexafluorophosphate but can also be used directly as a basic electrolyte. The entire technical route offers advantages such as process controllability, low cost, environmental friendliness, high safety, and low impurities.

[0006] The second aspect of this application aims to provide a system for synthesizing liquid hexafluorophosphate.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] On one hand, the present invention provides a method for synthesizing liquid hexafluorophosphate, comprising using phosphorus trichloride as the initial raw material, and reacting phosphorus pentafluoride (PF5) with alkali metal fluorides through oxidation, fluorination, deep fluorination, and in-situ solvent capture in sequence to obtain liquid hexafluorophosphate.

[0009] Preferably, a method for synthesizing liquid hexafluorophosphate includes:

[0010] S1. Oxidation: Phosphorus trichloride (PCl3) is oxidized to phosphorus oxychloride (POCl3);

[0011] S2. Fluorination: Phosphorus oxychloride (POCl3) reacts with hydrofluoric acid (HF), and is then condensed at low temperature to obtain phosphorus oxyfluoride (POF3);

[0012] S3. Deep fluorination: Phosphorus trifluoride (POF3) reacts with hydrofluoric acid (HF), and a dehydration operation is carried out during the reaction to obtain phosphorus pentafluoride (PF5);

[0013] S4. Absorption reaction: Phosphorus pentafluoride (PF5) is passed into a solvent and an alkali metal fluoride and reacted to obtain liquid hexafluorophosphate, wherein the liquid hexafluorophosphate is a solution containing hexafluorophosphate.

[0014] Preferably, the alkali metal fluoride is selected from sodium fluoride or lithium fluoride, and the solvent is selected from ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), or carboxylic acid esters.

[0015] Preferably, the alkali metal fluoride is selected from sodium fluoride; the solvent is selected from ethyl methyl carbonate (EMC).

[0016] In some embodiments, in step S2, phosphorus oxychloride (POCl3) reacts with hydrofluoric acid (HF), and the phosphorus oxyfluoride (POF3) and tail gas 1 are separated after low-temperature condensation. Tail gas 1 is removed by any one or more methods, such as dry adsorption, wet absorption tower adsorption, or membrane contact equipment. In particular, step S2 is preferably carried out at 70-110°C.

[0017] In some embodiments, the dehydration operation involves drying a mixture of phosphorus trifluoride (POF3) and hydrofluoric acid (HF) with phosphorus pentoxide (P2O5) to capture water; the captured phosphorus pentoxide containing water is then recycled after high-temperature pyrolysis.

[0018] In some embodiments, in S4, the phosphorus pentafluoride (PF5), the solvent, and the alkali metal fluoride form a solid-liquid mixture, wherein the solid content of the alkali metal fluoride in the solid-liquid mixture is 1%-40%.

[0019] It should be noted that in step S4, due to the presence of HF as a reactant in the preceding reaction, residual HF is usually present. HF helps to enhance the surface activity of NaF and the salt formation rate. Generally, the amount of residual HF is controlled between 10-5000 ppm, preferably 50-200 ppm.

[0020] In some embodiments, in S2, phosphorus oxychloride (POCl3) reacts with hydrofluoric acid (HF) at 70-110°C; the condensation temperature is less than or equal to -40°C.

[0021] In S3, phosphorus oxyfluoride (POF3) reacts with hydrofluoric acid (HF) at 70-110°C; the condensation temperature is 10°C or below.

[0022] In some embodiments, in S2, phosphorus oxychloride (POCl3) reacts with hydrofluoric acid (HF) at 70-110°C; the condensation temperature is less than or equal to -40°C.

[0023] By controlling the temperature here, the separation of different substances is easily achieved, which is beneficial to subsequent processes, reduces the generation of impurities, and also helps to achieve the recycling of heat.

[0024] In some embodiments, in S4, phosphorus pentafluoride (PF5) is passed into a solvent and an alkali metal fluoride to form a solid-liquid mixture. The solid-liquid mixture after the reaction is subjected to solid-liquid separation to obtain a filtrate and a filter residue. The filtrate is purified to obtain liquid hexafluorophosphate.

[0025] In some embodiments, filter residue is collected, the filter residue comprising alkali metal difluoride, the alkali metal difluoride is collected and regenerated by thermal decomposition to form hydrofluoric acid (HF) and alkali metal fluoride, wherein hydrofluoric acid (HF) is introduced into step S2 or S3 for reaction, and alkali metal fluoride is introduced into S4 to react with phosphorus pentafluoride.

[0026] Secondly, the present invention provides a system for synthesizing liquid hexafluorophosphate, used to implement any of the above-described methods for synthesizing liquid hexafluorophosphate, the system comprising:

[0027] An oxidation unit includes a phosphorus trichloride feeding device, an oxygen feeding device, and an oxidation reactor, wherein the feed end of the oxidation reactor is connected to the discharge end of the phosphorus trichloride feeding device and the discharge end of the oxygen feeding device.

[0028] A fluorination reaction unit includes a first hydrogen fluoride feeding device, a fluorination reaction device, and a condensation and retention device. The feed end of the fluorination reaction device is connected to the discharge end of the oxidation reactor and the discharge end of the first hydrogen fluoride feeding device. The discharge end of the fluorination reaction device is connected to the feed end of the condensation and retention device, and the discharge end of the condensation and retention device is connected to a first channel feed end.

[0029] The deep fluorination reaction unit includes a second hydrogen fluoride feeding device, a phosphorus pentoxide drying device, and a condensation buffer device. The feed end of the phosphorus pentoxide drying device is connected to the first channel and the discharge end of the second hydrogen fluoride feeding device. The discharge end of the phosphorus pentoxide drying device is connected to the feed end of the condensation buffer device. The discharge end of the condensation buffer device is connected to the second channel.

[0030] The absorption reaction unit includes a solvent feeding device, an alkali metal fluoride feeding device, and an in-situ salt formation device. The feed end of the in-situ salt formation device is connected to the second channel, the solvent feeding device, and the discharge end of the alkali metal fluoride feeding device.

[0031] In some embodiments, the system for synthesizing liquid hexafluorophosphate includes:

[0032] The purification unit includes a solid-liquid separator and a drying tower connected to each other. The discharge end of the in-situ salt-forming device is connected to the feed end of the solid-liquid separator. The solid-liquid separator is connected to a filtrate channel and a filter residue channel. The filtrate channel is connected to the feed end of the drying tower.

[0033] Based on the above technical solution, the present invention has the following technical effects:

[0034] 1. This invention provides a method for synthesizing liquid hexafluorophosphate. This method innovatively uses PCl3 as a starting material, reducing dependence on lithium salt processes and thus achieving low cost. Furthermore, the synthesis route primarily follows a cascade route of liquid-phase conversion of POCl3 to POF3 gas and then to PF5, avoiding the large-scale use of chlorine gas, thereby possessing high safety and high controllability.

[0035] In addition, most of the byproducts generated in this synthetic route can be recycled and reused, achieving a closed-loop fluorine source and improving material utilization. Simultaneously, fewer impurities are generated, making impurity removal easier. Furthermore, in this application, using phosphorus trichloride as the initial raw material, liquid hexafluorophosphate is obtained by sequentially undergoing oxidation, fluorination, deep fluorination, and in-situ solvent capture of PF5 reacting with alkali metal fluorides. The PF5 generated during the preparation process does not require independent storage; it reacts in situ to form hexafluorophosphate, which is then formed and dissolved in the solvent to form liquid hexafluorophosphate. This significantly avoids the storage risks and costs associated with PF5, shortens the process, and facilitates its direct use in electrolyte production.

[0036] 2. This invention provides a synthesis system for liquid hexafluorophosphate, used to prepare liquid hexafluorophosphate. This synthesis system is based on a novel synthetic route, with simplified equipment, enabling in-situ formation of liquid hexafluorophosphate. Simultaneously, the coordinated operation of various units within the synthesis system achieves closed-loop fluorine source and heat recovery. Furthermore, the synthesis system incorporates an acid removal device and a phosphorus pentoxide drying device, solving the problems of incomplete moisture removal from the HF system and the need for further deacidification of the product in traditional processes. The separation of different phases is achieved in multiple execution units, reducing impurity generation and improving material utilization efficiency through recycling, thus contributing to higher conversion rates. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the overall structure of a liquid hexafluorophosphate synthesis system according to the present invention.

[0038] Figure label:

[0039] 100. Oxidation unit; 11. Phosphorus trichloride feeding equipment; 12. Oxygen feeding equipment; 13. Oxidation reactor;

[0040] 200. Fluorination reaction unit; 21. First hydrogen fluoride feeding equipment; 22. Fluorination reaction equipment; 23. Condensation and retention equipment;

[0041] 300. Deep fluorination reaction unit; 31. Second hydrogen fluoride feeding equipment; 32. Phosphorus pentoxide drying equipment; 33. Condensation buffer equipment; 34. Pyrolysis furnace;

[0042] 400. Absorption reaction unit; 41. Solvent feeding equipment; 42. Alkali metal fluoride feeding equipment; 43. In-situ salt formation equipment. Detailed Implementation

[0043] To facilitate understanding of the present invention, a more comprehensive description will be provided below with reference to specific embodiments. Preferred embodiments are given herein. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0044] Before further describing in more detail the various embodiments of the compounds / compositions and methods of this disclosure through exemplary descriptions, examples, and results, it should be understood that the embodiments of this disclosure are not limited in application to the details of the methods and compositions described below. The descriptions provided herein are for illustrative purposes only and are not intended to be interpreted in a limiting sense. The inventive concept of this disclosure can have other embodiments or can be practiced or implemented in various ways. Therefore, the language used herein is intended to give the broadest scope and meaning; and the embodiments are intended to be exemplary, not exhaustive, and are not intended to limit this disclosure to these particular embodiments. Moreover, it should be understood that the wording and terminology used herein are for descriptive purposes and should not be considered limiting unless otherwise stated. Furthermore, numerous specific details are set forth in the following detailed description to provide a more thorough understanding of this disclosure.

[0045] However, it will be apparent to those skilled in the art that embodiments of this disclosure can be practiced without these specific details. In other instances, features well-known to those skilled in the art have not been described in detail to avoid unnecessary complexity. It is intended that all substitutions, replacements, modifications, and equivalents that are apparent to those skilled in the art are included within the scope of this disclosure. Based on this disclosure, all compounds / compositions disclosed herein, their preparation methods, applications, and uses can be prepared and implemented without excessive experimentation.

[0046] Therefore, although the compounds / compositions and methods of this disclosure have been described with reference to specific embodiments, it will be apparent to those skilled in the art that variations may be made to the formulations, compounds or compositions and / or methods, as well as the steps or sequence of steps of the methods described herein, without departing from the spirit and scope of the inventive concept of this disclosure.

[0047] As used herein, any reference to "an embodiment" or "an embodiment" means that a particular element, feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment. The phrase "in an embodiment" appearing in multiple places throughout the specification does not necessarily refer to the same embodiment.

[0048] Unless otherwise defined herein, scientific and technical terms used in connection with this disclosure shall have the meanings commonly understood by one of ordinary skill in the art. Furthermore, unless the context requires otherwise, singular terms shall include plural forms, and plural terms shall include singular forms.

[0049] This application provides a method for synthesizing liquid hexafluorophosphate and a related synthesis system.

[0050] Specifically, the general route for the synthesis of liquid hexafluorophosphate is as follows:

[0051] S1. Oxidation: PCl3 + ½O2 → POCl3;

[0052] S2. Fluorination: POCl3+3HF→POF3+3HCl↑;

[0053] S3. Deep fluorination: POF3 + 2HF PF5 + H2O;

[0054] S4. Absorption reaction: PF5 + XF → XPF6

[0055] It should be noted that the absorption reaction process involves the in-situ capture of PF5 by the solvent and its reaction with XF to obtain liquid hexafluorophosphate. Here, X in XF refers to an alkali metal element, preferably selected from NaF or LiF. The solvent can be ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), or a carboxylic acid ester, preferably ethyl methyl carbonate (EMC).

[0056] Therefore, this application uses PCl3 as the main starting material, combined with common bulk raw materials such as O2, HF, and NaF to prepare liquid hexafluorophosphate. Traditional NaPF6 mainly relies on "sodium salt variants" of the LiPF6 process, and these routes often start from expensive or rare PF5 / LiPF6 byproducts, resulting in high costs. Therefore, compared with current conventional technical solutions, the synthesis route of this invention reduces dependence on lithium salt processes, effectively lowering production costs. Furthermore, the overall synthesis route of this method employs a cascade route of POCl3 liquid-phase conversion to POF3 gas and then to PF5, avoiding the large-scale use of chlorine gas, thus possessing high safety and high controllability.

[0057] In this process, PF5 generated can react in situ to form hexafluorophosphate without separate storage. This hexafluorophosphate is then formulated in situ and combined with an electrolyte (EMC) to form a basic electrolyte, avoiding the storage risks and costs associated with PF5, shortening the process, and facilitating its direct use in electrolyte production. Unreacted substances or impurities present during this synthesis route can largely be processed and recycled, thus demonstrating high resource utilization efficiency.

[0058] Furthermore, this invention provides a synthesis system for liquid hexafluorophosphate, specifically comprising an oxidation unit, a fluorination reaction unit, a deep fluorination reaction unit, and an absorption reaction unit connected in sequence. This synthesis system is based on a novel synthetic route, features simplified equipment, and can achieve in-situ formation of liquid hexafluorophosphate. Simultaneously, the coordinated operation of the various units within the synthesis system enables closed-loop fluorine source management and heat recovery.

[0059] The fluorination reaction unit is used to realize the S2 production step. A condensation and retention device is introduced to separate the target product POF3, improving its purity and facilitating the recovery of impurity HCl. Traditionally, in the process of synthesizing PF5 from PCl3 or polyphosphoric acid as raw materials, and then synthesizing NaPF6, the product is usually a mixture of PF5 and HCl, both of which are strongly acidic gases. Separating them and recovering HCl is very difficult, and even after separation, there is often an excess of HCl residue, requiring a subsequent acid removal step. In the technical route of this invention, POF3, as a product of the S2 step, is easily separated from HCl, eliminating the need for a second acid removal step, reducing the impurity content in the target product, and facilitating further production.

[0060] The deep fluorination reaction unit is used to realize the S3 production step. It introduces a phosphorus pentoxide (POF3) drying device, solving the problem of incomplete moisture removal from the HF system in traditional processes. The phosphorus pentoxide drying device can be a P2O5 solid packed tower or a P2O5 moving bed. Simultaneously, in the deep fluorination reaction unit, the reaction mixture (POF3 / HF) contacts the P2O5 after passing through the phosphorus pentoxide drying device, capturing the H2O generated during the conversion of POF3 to PF5 in situ. This unidirectionalizes the reversible reaction of deep fluorination and also achieves water removal, reducing the water content in the target product. Furthermore, the used phosphorus pentoxide packing can be recycled by high-temperature pyrolysis to regenerate phosphorus pentoxide. Meanwhile, PF5 is complexed and absorbed by EMC in the next process, which helps reduce the partial pressure of gas-phase PF5 and also promotes the deep fluorination reaction to proceed to the right.

[0061] In some embodiments, a condensation buffer device is also introduced into the deep fluorination reaction unit. This condensation buffer device works in conjunction with a phosphorus pentoxide drying device to separate the products from the deep fluorination reaction and unreacted hydrogen fluoride gas. Water is captured by the phosphorus pentoxide drying device, and the condensation buffer device separates the products obtained in this step, yielding condensate and phosphorus pentafluoride. The condensate contains unreacted HF and can be recycled back to the fluorination reaction unit for reuse, contributing to a closed-loop fluorine source. After condensation, the phosphorus pentafluoride flows to the next process, further promoting the rightward movement of the deep fluorination reaction unit.

[0062] In the absorption reaction unit, including the in-situ salt formation equipment, phosphorus pentafluoride, alkali metal fluorides, and solvent slurry are fed into the in-situ salt formation equipment, react, and produce liquid hexafluorophosphate. This in-situ formation of liquid hexafluorophosphate helps eliminate the need for subsequent solvent replacement or concentration processes and associated losses.

[0063] The following is a specific example:

[0064] Example 1

[0065] This embodiment provides a system for synthesizing liquid hexafluorophosphate, such as... Figure 1 As shown, the synthesis system for liquid hexafluorophosphate specifically includes an oxidation unit 100, a fluorination reaction unit 200, a deep fluorination reaction unit 300, and an absorption reaction unit 400 connected in sequence.

[0066] The oxidation unit 100 includes a phosphorus trichloride feeding device 11, an oxygen feeding device 12, and an oxidation reactor 13. The feed end of the oxidation reactor 13 is connected to the discharge end of the phosphorus trichloride feeding device 11 and the discharge end of the oxygen feeding device 12. Oxygen and phosphorus trichloride undergo an oxidation reaction in the oxidation unit 100 to obtain phosphorus oxychloride.

[0067] In this embodiment, the oxidation reactor 13 can be a tubular oxidation reactor 13 or a microchannel oxidation reactor 13. It should be noted that, to reduce the influence of moisture on the reaction, the oxidation reactor 13 can be pre-purged with nitrogen to remove humid air and maintain an inert environment. Simultaneously, a phosphorus pentoxide / molecular sieve can be connected in series before the feed end of the oxidation reactor 13 to dry the phosphorus trichloride feed and oxygen, ensuring that the mixed gas of POF3 and HF is ≤10 ppm H2O throughout the process.

[0068] It should be noted that the oxidation unit 100 may also include a POCl3 storage tank, which is connected to the discharge end of the oxidation reactor 13 to provide buffer cooling for POCl3 and to supply material for subsequent processes.

[0069] The fluorination reaction unit 200 includes a first hydrogen fluoride feeding device 21, a fluorination reaction device 22, and a condensation and retention device 23. The feed end of the fluorination reaction device 22 is connected to the discharge end of the oxidation reactor 13 and the discharge end of the first hydrogen fluoride feeding device 21. The discharge end of the fluorination reaction device 22 is connected to the condensation and retention device 23, and the condensation and retention device 23 is connected to a first channel.

[0070] POCl3 and HF react to form a mixed gas in the fluorination reaction equipment 22. The mixed gas is then condensed and separated by the condensation and retention equipment 23 to obtain phosphorus oxyfluoride and tail gas 1. The phosphorus oxyfluoride passes through the first channel to the next process.

[0071] Specifically, the fluorination reaction apparatus 22 includes a spiral micro-mixer and a tubular reactor connected in sequence. POCl3 and anhydrous HF are metered and sequentially introduced into the spiral micro-mixer and the tubular reactor, where they react fully. A condensation and retention device 23 is connected in series with the tubular reactor to condense the reaction product, retaining POF3. It should be noted that the number of condensation and retention devices 23 is at least one. In some embodiments, multiple stages of condensation and retention devices 23 may be added.

[0072] The deep fluorination reaction unit 300 includes a second hydrogen fluoride feeding device 31, a phosphorus pentoxide drying device 32, and a condensation buffer device 33. The feed end of the phosphorus pentoxide drying device 32 is connected to the first channel and the discharge end of the second hydrogen fluoride feeding device 31. The condensation buffer device 33 is connected to the second channel and the third channel. The third channel is connected to the first hydrogen fluoride feeding device 21 and the second hydrogen fluoride feeding device 31.

[0073] The mixture of phosphorus oxyfluoride and hydrofluoric acid passes sequentially through a phosphorus pentoxide drying device 32 and a condensation buffer device 33. The water generated during the reaction is captured by the phosphorus pentoxide drying device 32 and forms a metaphosphoric acid stream. The phosphorus pentafluoride generated during the reaction and the unreacted HF are separated by the condensation buffer device 33. The phosphorus pentafluoride enters the next device through a second channel, while the HF, a major component of the tail gas, returns to the first hydrogen fluoride feeding device 21 and the second hydrogen fluoride feeding device 31 through a third channel.

[0074] In this embodiment, the phosphorus pentoxide drying device 32 refers to a drying tower or moving bed filled with solid P2O5. The water produced by the reaction of the mixed gas of POF3 and HF is captured by the phosphorus pentoxide drying device 32 and converted into metaphosphoric acid, while promoting the one-way reversible reaction.

[0075] Furthermore, in order to improve the environmental friendliness of this process, the phosphorus pentoxide drying equipment 32 is also connected to a pyrolysis furnace 34. Metaphosphoric acid flows through the pyrolysis furnace 34 and is pyrolyzed at high temperature to regenerate P2O5, which is then recycled back into the phosphorus pentoxide drying equipment 32.

[0076] The absorption reaction unit 400 includes a solvent feeding device 41, an alkali metal fluoride feeding device 42, and an in-situ salt formation device 43. The second channel, the outlet end of the solvent feeding device 41, and the outlet end of the alkali metal fluoride feeding device 42 are all connected to the inlet end of the in-situ salt formation device 43.

[0077] PF5, EMC and alkali metal fluorides are mixed in an in-situ salt-forming device 43 to obtain a solid-liquid mixture. After the reaction, the solid-liquid mixture is separated into solid and liquid components to obtain a mixed solution containing hexafluorophosphate and EMC, i.e., liquid hexafluorophosphate.

[0078] Specifically, to make the initially obtained liquid hexafluorophosphate more suitable for electrolyte production, the liquid hexafluorophosphate synthesis system also includes a purification unit. The purification unit comprises a solid-liquid separator and a drying tower connected in sequence. The solid-liquid mixture in the absorption reaction unit 400 passes sequentially through the solid-liquid separator and the drying tower to obtain purified liquid hexafluorophosphate. The solid-liquid separator is connected to a filtrate channel and a filter residue channel, and the filtrate channel is connected to the feed end of the drying tower.

[0079] The solid-liquid separator uses pressure filtration or membrane separation to remove unreacted alkali metal difluoride hydrides and other solid byproducts. The drying tower is a polishing drying tower, employing molecular sieves to reduce the moisture content in liquid hexafluorophosphate and polish trace amounts of HF. Specifically, the polishing drying tower can be constructed by connecting a 4Å molecular sieve in series with activated alumina.

[0080] Specifically, the solid-liquid mixture is separated into filtrate and filter residue by a solid-liquid separator. The filtrate is then dried in a drying tower to obtain liquid hexafluorophosphate. The filter residue consists of alkali metal difluorohydrides and unreacted alkali metal fluorides. The filter residue channel can also be connected to a reprocessing device, which collects the filter residue and regenerates it through thermal cracking to form HF and alkali metal fluorides. The HF is introduced into a fluorination unit or deep fluorination unit for reaction, while the alkali metal fluorides are reintroduced into the alkali metal fluoride feeder 42 and participate again in the absorption reaction unit 400 for reaction.

[0081] Furthermore, after passing through a drying tower, the filtrate can be further analyzed for concentration components to allow for further formulation and the acquisition of liquid hexafluorophosphate with the target concentration. Specifically, if the free acid content in the obtained liquid hexafluorophosphate exceeds 50 ppm, ion exchange resin or solid oxide adsorption can be used to remove the free acid, thereby allowing for further formulation and the acquisition of liquid hexafluorophosphate with the target concentration.

[0082] Example 2

[0083] This embodiment, based on Embodiment 1, also includes an acid production unit, comprising an acid production reactor, an acid production condenser, and an acid production drying unit. The feed end of the acid production reactor is connected to a feeder for fluorite (CaF2) and concentrated sulfuric acid. A mixed gas containing HF is prepared by reacting CaF2 with concentrated sulfuric acid. This mixed gas is condensed in the acid production condenser to obtain liquid HF, which is then dried in the acid production drying unit. The prepared HF can be stored in the first hydrogen fluoride feeder 21 and the second hydrogen fluoride feeder 31, with the remainder used to regenerate active NaF.

[0084] In some embodiments, a first heat exchange device is provided between the oxidation reactor 13 and the fluorination reaction device 22, and a second heat exchange device is provided between the oxidation reactor 13 and the phosphorus pentoxide drying device 32. The oxidation reactor 13 releases heat during the reaction, and the heat is recovered and utilized in the fluorination reaction device 22 and the phosphorus pentoxide drying device 32 through the first heat exchange device and the second heat exchange device, thereby reducing the steam load and improving the heat utilization rate.

[0085] The main component of the condensate is HCl. Therefore, in some embodiments, the fluorination reaction unit 200 also includes an acid removal device connected to the condensation trap 23. The condensation trap 23 is provided with a fourth channel for connecting to the acid removal device. The condensate moves to the acid removal device for removal under the guidance of the fourth channel, further reducing reaction impurities.

[0086] The acid removal equipment is connected in series with the condensation and retention equipment 23. The acid removal equipment can be a dry polishing acid removal device, specifically an adsorption tower containing a special acid removal agent / modified activated alumina / molecular sieve, etc., which are highly selective for HCl and must be strictly anhydrous. In some embodiments, the acid removal equipment can also be a membrane contactor or a wet absorption tower, or a combination of dry polishing acid removal equipment and a membrane contactor / wet absorption tower. The membrane contactor or wet absorption tower can safely and efficiently absorb HCl using water or NaOH. In this case, the acid removal equipment can also be equipped with a first recovery channel for selling the hydrochloric acid or salt obtained from the efficient absorption.

[0087] Example 3

[0088] This embodiment provides a method for synthesizing liquid hexafluorophosphate based on Example 1. The method involves using phosphorus trichloride as the initial raw material, and sequentially reacting PF5 with an alkali metal fluoride through oxidation, fluorination, deep fluorination, and in-situ solvent capture to obtain liquid hexafluorophosphate. In this embodiment, the alkali metal fluoride is NaF.

[0089] S1. 818 kg of PCl3 (purity: above 99%, national standard superior grade) and 95 kg of O2 (liquid oxygen) are introduced into the oxidation reactor and reacted fully at 80°C to produce 913 kg of POCl3. The POCl3 is stored in a POCl3 storage tank at a temperature of less than or equal to 100°C, wherein the moisture content in the POCl3 is less than 10 ppm.

[0090] S2. Under the condition of 85℃±15℃, 913kg of POCl3 and HF are fed into the fluorination reaction equipment at a molar ratio of 1:3 to react fully and obtain a first mixed gas containing POF3 and HCl. The first mixed gas is condensed and separated by a condensation interception equipment. The condenser temperature is maintained at no higher than -40℃ to obtain about 619kg of liquid POF3 and tail gas 1. Tail gas 1 is mainly composed of HCl. Tail gas 1 is removed by an acid removal equipment, and POF3 flows into a phosphorus pentoxide drying equipment.

[0091] S3. After the POF3 from the previous step is vaporized, POF3 and HF are introduced into a phosphorus pentoxide drying device at a molar ratio of 1:2. A deep fluorination reaction is carried out at 50℃ to obtain a second mixed gas. The second mixed gas is separated by a condensation buffer device to obtain condensate and gaseous PF5. The PF5 flows stably to the in-situ salt formation device. The condensation temperature is controlled at 5-10℃. The condensate is mainly composed of HF, and the recovered HF is returned to S2 and S3 for use as feedstock. The obtained PF5 gas maintains a moisture content below 10ppm and an HF content between 10-5000ppm.

[0092] In particular, the back end of the phosphorus pentoxide drying equipment uses a combination of dew point method and Karl Fischer vaporization to achieve online moisture monitoring. This is used to detect the moisture content of the second mixed gas and select to supplement HF or switch the operation of the phosphorus pentoxide drying equipment according to the moisture content, so as to ensure that the moisture content of the material always meets the requirements.

[0093] (4) The moisture content of the dried EMC in the in-situ salt-forming equipment must be controlled below 10 ppm. PF5, EMC, and the alkali metal fluoride are mixed and fed into the in-situ salt-forming equipment, stirred, and reacted at 5°C. The molar ratio of PF5 to the alkali metal fluoride is at least 1:1; the absorption rate of PF5 is 100%, and the mass concentration of PF5 in the dried EMC is 22.5%, ultimately yielding preliminary liquid hexafluorophosphate. In this embodiment, the alkali metal fluoride is NaF.

[0094] In particular, alkali metal fluorides are D 50 The ultrafine anhydrous NaF with a diameter of ≈1–3 μm undergoes surface activation treatment, or is coated with an extremely thin inorganic layer, to prevent NaF aggregation. In this embodiment, the alkali metal fluoride is NaF.

[0095] (5) After the reaction is completed, a solid-liquid mixture containing liquid hexafluorophosphate is obtained in the in-situ salt formation equipment. The solid-liquid mixture is separated into filtrate and filter residue by a solid-liquid separator. The filtrate is liquid hexafluorophosphate, which is further purified by a drying tower to obtain liquid hexafluorophosphate. In particular, the density, conductivity, and moisture content of the liquid hexafluorophosphate at the filtrate channel can be monitored online in real time, and the amount of ethyl methyl carbonate (EMC) added can be automatically adjusted to form a dynamic and stable closed-loop control to ensure that the composition ratio of liquid hexafluorophosphate is within the target range.

[0096] The filter residue is regenerated through thermal cracking in a reprocessing device to form HF and alkali metal fluorides. The HF is introduced into the fluorination unit or deep fluorination unit for reaction, while the alkali metal fluorides are reintroduced into the alkali metal fluoride feeding device and participate again in the absorption reaction unit for further reaction.

[0097] Example 4

[0098] Unlike Example 3, in this example, the alkali metal fluoride is LiF.

[0099] Example 5

[0100] Unlike Example 3, in this example, the solvent is DMC instead of EMC.

[0101] Example 6

[0102] Unlike Example 3, in this example, the solvent is ethyl acetate instead of EMC.

[0103] Comparative Example 1

[0104] Under the condition that the moisture content requirement of the reactants is the same as that in Example 1, NaPF6 liquid hexafluorophosphate is prepared by using the traditional NaPF6 preparation process. (1) 301.2 kg of PCl3 and Cl2 are introduced into the chlorination reactor at a molar ratio of 1:1 and reacted at a temperature of 60°C to generate PCl5. PCl5 is stored in liquid form.

[0105] (2) PCl5 and HF are introduced into a fluorination reactor at a molar ratio of 1:5 and reacted at 90°C to generate a mixed gas of PF5 and HCl. The mixed gas of PF5 and HCl is then passed through a low-temperature condenser at -30°C to -40°C and a pressurized distillation column to achieve the condensation and recovery of unreacted HF and the separation of PF5 and HCl, respectively. The PF5 gas obtained from the distillation is then sent to the next process.

[0106] (3) The PF5 gas obtained by the above distillation is directly passed into the solvent DMC containing NaF (75 kg, ordinary industrial grade, D50≈10–20 μm, unactivated) and reacted at a temperature of 25°C to generate preliminary liquid NaPF6.

[0107] (4) Crystallize NaPF6 from the liquid and separate the crystallized NaPF6 from the liquid.

[0108] (5) Dry the crystallized NaPF6 to allow HF to evaporate from the crystal surface;

[0109] (6) Pulverize the dried NaPF6 crystals and sieve the dried NaPF6 crystals with a sieve aperture size of less than or equal to 90 to obtain NaPF6 powder.

[0110] It should be noted that in step (2) of this embodiment, since PF5 and HCl have similar boiling points, it is difficult to completely separate them. Therefore, HCl is present as an impurity in the PF5 gas. As a result, the initially obtained liquid NaPF6 contains more than 50 ppm of chloride ions. Furthermore, since traditional dehydrating agents such as molecular sieves, silica gel, and alumina preferentially undergo irreversible chemical reactions or structural damage with HF / HCl, it is not convenient to remove water in this comparative example. Consequently, the water content in the resulting liquid NaPF6 is greater than 1 ppm. Therefore, the liquid NaPF6 needs to be recrystallized, dried, and then deacidified and dehydrated before it can be used.

[0111] The yield, HF acid content, moisture content, and chloride ion content of the liquid hexafluorophosphate obtained in Examples 3 to 5 and Comparative Example 1 were determined, and the results are shown in Table 1. The liquid hexafluorophosphate in Examples 3 to 6 was sampled from the filtrate, and Comparative Example 1 was sampled from a solution containing sodium hexafluorophosphate.

[0112] Table 1.

[0113]

[0114] The above description is merely an example and illustration of the structure of this invention, and while the description is specific and detailed, it should not be construed as limiting the scope of this invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this invention, and these obvious substitutions all fall within the protection scope of this invention.

Claims

1. A method for synthesizing liquid hexafluorophosphate, characterized in that, Using phosphorus trichloride as the initial raw material, liquid hexafluorophosphate is obtained through a liquid hexafluorophosphate synthesis system, wherein the liquid hexafluorophosphate synthesis system comprises an oxidation unit, a fluorination reaction unit, a deep fluorination reaction unit, and an absorption reaction unit connected in sequence. The oxidation unit includes an oxidation reactor; the fluorination reaction unit includes a fluorination reaction device and a condensation and retention device; the deep fluorination reaction unit includes a phosphorus pentoxide drying device and a condensation and buffer device; and the absorption reaction unit includes an in-situ salt formation device. The feed end of the fluorination reaction device is connected to the discharge end of the oxidation reactor; the discharge end of the fluorination reaction device is connected to the feed end of the condensation and retention device; the feed end of the phosphorus pentoxide drying device is connected to the discharge end of the condensation and retention device; the discharge end of the phosphorus pentoxide drying device is connected to the feed end of the condensation and buffer device; and the feed end of the in-situ salt formation device is connected to the discharge end of the condensation and buffer device. Phosphorus trichloride and oxygen are introduced into the oxidation reactor for oxidation to obtain phosphorus oxychloride. The phosphorus oxychloride flows out of the oxidation reactor and into the fluorination reaction equipment, where hydrogen fluoride is simultaneously introduced at 70-110°C to undergo fluorination to obtain a mixture of phosphorus oxychloride and hydrogen chloride. This mixture flows out of the fluorination reaction equipment and into the condensation and retention equipment, where the condensation temperature is less than or equal to -40°C, thus cooling and retaining the phosphorus oxychloride. The phosphorus oxychloride then flows out of the condensation and retention equipment and into the phosphorus pentoxide drying equipment, while... Hydrogen fluoride is introduced to carry out a deep fluorination reaction at 70-110°C to convert phosphorus trifluoride into phosphorus pentafluoride, resulting in a mixture of phosphorus pentafluoride and water. After the mixture of phosphorus pentafluoride and water is dehydrated by the phosphorus pentoxide drying equipment, the phosphorus pentafluoride flows out of the phosphorus pentoxide drying equipment and enters the condensation buffer equipment for condensation at 10°C or below, and then flows out of the condensation buffer equipment and enters the in-situ salt formation equipment. At the same time, a solvent and an alkali metal fluoride are introduced into the in-situ salt formation equipment to react the phosphorus pentafluoride captured by the solvent with the alkali metal fluoride to obtain the liquid hexafluorophosphate, which is a solution containing dissolved hexafluorophosphate.

2. The method for synthesizing liquid hexafluorophosphate according to claim 1, characterized in that, include: The alkali metal fluoride is selected from either sodium fluoride or lithium fluoride; The solvent is selected from methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, or carboxylic acid esters.

3. The method for synthesizing liquid hexafluorophosphate according to claim 1, characterized in that, Phosphorus oxychloride reacts with hydrogen fluoride, and after low-temperature condensation, phosphorus oxychloride and tail gas 1 are separated. Tail gas 1 is removed by any one or more methods such as dry adsorption, wet absorption tower adsorption, or membrane contact equipment.

4. The method for synthesizing liquid hexafluorophosphate according to claim 1, characterized in that, The phosphorus pentoxide containing water captured in the dehydration process is then repeatedly recycled after high-temperature pyrolysis.

5. The method for synthesizing liquid hexafluorophosphate according to claim 1, characterized in that, In the in-situ salt formation device, the phosphorus pentafluoride, the solvent, and the alkali metal fluoride form a solid-liquid mixture, wherein the solid content of the alkali metal fluoride in the solid-liquid mixture is 1%-40%.

6. The method for synthesizing liquid hexafluorophosphate according to claim 1, characterized in that, In the in-situ salt-forming device, phosphorus pentafluoride is passed into a solvent and an alkali metal fluoride to form a solid-liquid mixture. The solid-liquid mixture after the reaction is subjected to solid-liquid separation to obtain filtrate and filter residue. The filtrate is purified to obtain liquid hexafluorophosphate.

7. The method for synthesizing liquid hexafluorophosphate according to claim 6, characterized in that, It also includes collecting the filter residue, which includes alkali metal difluoride, collecting the alkali metal difluoride and regenerating it through thermal decomposition to form hydrofluoric acid and alkali metal fluoride, wherein the hydrofluoric acid is introduced into the fluorination reaction equipment or the phosphorus pentoxide drying equipment for reaction, and the alkali metal fluoride is introduced into the in-situ salt formation equipment to react with the phosphorus pentafluoride.

8. A system for synthesizing liquid hexafluorophosphate, characterized in that, A method for synthesizing liquid hexafluorophosphate according to any one of claims 1 to 7, wherein the system for synthesizing liquid hexafluorophosphate comprises: An oxidation unit includes a phosphorus trichloride feeding device, an oxygen feeding device, and an oxidation reactor, wherein the feed end of the oxidation reactor is connected to the discharge end of the phosphorus trichloride feeding device and the discharge end of the oxygen feeding device. A fluorination reaction unit includes a first hydrogen fluoride feeding device, a fluorination reaction device, and a condensation and retention device. The feed end of the fluorination reaction device is connected to the discharge end of the oxidation reactor and the discharge end of the first hydrogen fluoride feeding device. The discharge end of the fluorination reaction device is connected to the feed end of the condensation and retention device, and the discharge end of the condensation and retention device is connected to a first channel feed end. The deep fluorination reaction unit includes a second hydrogen fluoride feeding device, a phosphorus pentoxide drying device, and a condensation buffer device. The feed end of the phosphorus pentoxide drying device is connected to the first channel and the discharge end of the second hydrogen fluoride feeding device. The discharge end of the phosphorus pentoxide drying device is connected to the feed end of the condensation buffer device. The discharge end of the condensation buffer device is connected to the second channel. The absorption reaction unit includes a solvent feeding device, an alkali metal fluoride feeding device, and an in-situ salt formation device. The feed end of the in-situ salt formation device is connected to the second channel, the solvent feeding device, and the discharge end of the alkali metal fluoride feeding device.

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