Method for synthesizing hexafluorophosphate

Abstract

The present invention discloses a method for synthesizing hexafluorophosphate, which belongs to the technical field of chemical synthesis. A phosphorus pentahalide inert solvent solution in which phosphorus pentahalide is dissolved in an inert solvent and an alkali metal halide salt-hydrogen fluoride solution in which an alkali metal halide salt is dissolved in anhydrous hydrogen fluoride are charged into a reactor at a predetermined ratio to react with each other, and a mixture of hexafluorophosphate salt, hydrogen fluoride, an inert solvent and hydrogen halide salt is obtained. Then, hydrogen halide gas is removed by gas-liquid separation, hydrogen fluoride is recovered by heating evaporation, and finally, the inert solvent is recovered by solid-liquid separation, and the solid is dried to obtain hexafluorophosphate salt. The synthesis method of the present invention has the advantages of simple operation, excellent safety, high reaction yield, excellent product quality, and continuous production.

Description

[Technical field]

[0001] The present invention relates to the technical field of chemical synthesis, and in particular to a method for synthesizing hexafluorophosphate. [Background technology]

[0002] Global warming is a major challenge facing humans in the 21st century, affecting not only human development but also human survival. To solve the problem of global warming, it is most important to replace traditional high-pollution, high-emission petrochemical energy with new clean energy such as solar energy and wind energy, and reduce the generation of greenhouse gases such as carbon dioxide, so the development of green and environmentally friendly secondary batteries is the key to solving the problem. After more than half a century of research and industrialization, lithium-ion batteries have now been mass-produced and are expected to be used in energy storage and power, while the development of sodium-ion batteries is progressing rapidly and gradually entering the application stage, while the research of potassium-ion batteries is also attracting attention.

[0003] Hexafluorophosphates are electrolytes widely used in current secondary batteries. Among them, lithium hexafluorophosphate is widely used in the production of lithium ion batteries, sodium hexafluorophosphate is used in the production of sodium ion batteries, and potassium hexafluorophosphate is used in the research and production of potassium ion batteries as well as the production of lithium hexafluorophosphate and sodium hexafluorophosphate.

[0004] Methods for synthesizing hexafluorophosphate can be divided into the hexafluorophosphate ion exchange method, the fluorophosphoric acid method, and the phosphorus pentafluoride method, depending on the raw materials and main intermediates used. (1) Hexafluorophosphate ion exchange method [ka] (2) Fluorophosphate method: [ka] (3)Phosphorus pentafluoride method: [ka]

[0005] Among the above-mentioned methods for synthesizing hexafluorophosphate, the hexafluorophosphate ion exchange method does not use phosphorus pentafluoride gas or hydrogen fluoride as raw materials in the synthesis, so that the safety and convenience of production operation is high, but the raw materials themselves are expensive in the production of one hexafluorophosphate from the other hexafluorophosphate, so that it is not competitive in terms of synthesis cost. The fluorophosphoric acid method can avoid the use of phosphorus pentafluoride gas and reduce the difficulty of synthesis to a certain extent, but the water generated during the reaction adversely affects the quality of the hexafluorophosphate product, making it difficult to produce high-purity hexafluorophosphate. The phosphorus pentafluoride method uses phosphorus pentafluoride gas, but this method has the advantages of simple operation, low synthesis cost, high reaction yield, good product quality, etc., and is the most commonly used method for industrially synthesizing hexafluorophosphate. Depending on the phosphorus source, the phosphorus pentafluoride process includes the simple phosphorus process, the phosphoric acid process, the polyphosphoric acid process, the phosphorus trichloride process, and the phosphorus pentachloride process. (i) Elemental phosphorus method: [ka] (ii) Phosphoric acid method: [ka] (iii) Polyphosphate method: [ka] (iv) Phosphorus trichloride method: [ka] (v) Phosphorus pentachloride method: [ka]

[0006] The elemental phosphorus method is to put elemental phosphorus (red phosphorus, yellow phosphorus, white phosphorus, etc.) into a special reactor, introduce fluorine gas, and obtain phosphorus pentafluoride by gas-solid phase reaction. Its advantage is that the purity of the produced phosphorus pentafluoride is high, and high purity phosphorus pentafluoride can be obtained without complicated purification operations. Its disadvantage is that fluorine gas needs to be produced in advance by an additional electrolytic fluorine production process, and the reaction process is a gas-solid phase reaction, which has high requirements for the structure and material of the reactor and strict reaction conditions, making it difficult to apply industrially on a large scale. The phosphoric acid method is similar to the polyphosphoric acid method, and uses phosphoric acid or its polymer as raw material, reacts with hydrogen fluoride to obtain hydrous hexafluorophosphoric acid, and then dehydrates it with fuming sulfuric acid or sulfur trioxide to produce phosphorus pentafluoride. This method has low synthesis costs, but uses a large amount of fuming sulfuric acid or sulfur trioxide as a dehydrating agent, which is not environmentally friendly, and the fuming sulfuric acid and sulfur trioxide contain a large amount of impurities, making it difficult to produce high purity phosphorus pentafluoride. The phosphorus trichloride process and the phosphorus pentachloride process are similar. The phosphorus trichloride process first reacts phosphorus trichloride with chlorine gas to synthesize phosphorus pentachloride, and then reacts it with hydrogen fluoride to produce phosphorus pentafluoride. The phosphorus pentachloride process directly uses phosphorus pentachloride as a raw material and reacts it with hydrogen fluoride to produce phosphorus pentafluoride. The phosphorus pentachloride process reduces the chlorination reaction step compared to the phosphorus trichloride process, and is therefore competitive in terms of synthesis costs, product quality, environmental friendliness, etc., and is therefore the most commonly used method for industrially producing phosphorus pentafluoride.

[0007] Using phosphorus pentachloride as a raw material, first reacting it with hydrogen fluoride to produce phosphorus pentafluoride, and then reacting it with a fluoride salt to synthesize hexafluorophosphate, is currently the most industrially valuable method for synthesizing hexafluorophosphate, but this method also has many drawbacks.

[0008] (1): One of the reaction raw materials, phosphorus pentachloride solid, has a high melting point of 180℃, is easily sublimated, and cannot be converted into liquid by heating, so it is usually supplied as a solid. The other raw material, hydrogen fluoride, has a boiling point of only 19.5℃ and is very volatile. A small amount of local heat generation or gas emission during the reaction can lead to a large amount of hydrogen fluoride volatilization. On the other hand, the reaction between phosphorus pentachloride and hydrogen fluoride is very violent, and a solid-liquid phase reaction occurs at the moment the two raw materials come into contact, causing significant local heat generation, a large amount of hydrogen chloride gas is released, and a large amount of hydrogen fluoride volatilization occurs, which results in unnecessary hydrogen fluoride loss, which not only destroys the stability of the reaction system, but also poses safety hazards and is prone to production safety accidents. Therefore, how to solve the problem of phosphorus pentachloride input and how to mitigate the reaction process between phosphorus pentachloride and hydrogen fluoride are the main problems to be solved.

[0009] (2): Phosphorus pentafluoride, obtained by reacting phosphorus pentachloride with hydrogen fluoride, is a gas with a low boiling point of -84.6°C and is difficult to liquefy, making it difficult to purify, store, transport, and use, resulting in high synthesis costs and reduced production efficiency. Furthermore, phosphorus pentafluoride is highly active and easily decomposes during storage, transportation, and use, resulting in reduced reaction yields and product purity. Therefore, it is an important issue how to solve the problems of storing, transporting, and using phosphorus pentafluoride and make it possible to manufacture and use it whenever possible, or to synthesize it on-site so that it can be used on-site.

[0010] (3): The raw materials used in the synthesis of hexafluorophosphate are highly toxic and dangerous, and there are significant safety risks during the reaction. At present, batch reactions are commonly used in the synthesis of hexafluorophosphate, which brings about significant risks to production safety. Therefore, there is an urgent need to find a way to make the existing hexafluorophosphate synthesis process continuous and reduce the safety risks of production. Therefore, there are still many optimization efforts that need to be explored and studied to address the shortcomings of the synthesis technology of hexafluorophosphate. Summary of the Invention [Problem to be solved by the invention]

[0011] In view of the shortcomings of the conventional synthetic methods for hexafluorophosphate, the present invention provides a synthetic method for hexafluorophosphate, which has the advantages of being safe, reliable, suitable for industrialization, simple operation, excellent safety, high reaction yield, excellent product quality, and capable of continuous production. [Means for solving the problem]

[0012] The technical solutions adopted in the present invention are as follows:

[0013] (1) dissolving phosphorus pentahalide in an inert solvent to obtain a phosphorus pentahalide inert solvent solution (I); (2) dissolving an alkali metal halide salt in anhydrous hydrogen fluoride to obtain an alkali metal fluoride salt hydrogen fluoride solution (II); (3) charging the phosphorus pentahalide inert solvent solution (I) and the alkali metal fluoride salt hydrogen fluoride solution (II) in a reactor in a predetermined ratio to react with each other to obtain a mixture (III) consisting of a hexafluorophosphate salt, hydrogen fluoride, an inert solvent, and hydrogen halide; Step (4) of subjecting the mixture (III) obtained in step (3) to gas-liquid separation to separate the hydrogen halide gas and obtain a mixture (IV) consisting of a hexafluorophosphate, hydrogen fluoride and an inert solvent; Step (5) of removing hydrogen fluoride from the mixture (IV) obtained in step (4) to obtain a mixture (V) consisting of a hexafluorophosphate salt and an inert solvent; and step (6) of subjecting the mixture (V) obtained in step (5) to solid-liquid separation and drying to obtain a hexafluorophosphate.

[0014] The synthetic route used in the present invention may be represented by the following reaction scheme: [ka]

[0015] Further configurations of the present invention are as follows.

[0016] In step (1), The phosphorus pentahalide is one or two selected from phosphorus pentachloride and phosphorus pentabromide. The selection of the type of phosphorus pentahalide is not directly related to the synthesis of the hexafluorophosphate, that is, whether phosphorus pentachloride or phosphorus pentabromide is selected, or a mixture of the two, it can be used to synthesize any of the hexafluorophosphates, such as lithium hexafluorophosphate, sodium hexafluorophosphate, and potassium hexafluorophosphate. The phosphorus pentahalide is preferably either phosphorus pentachloride or phosphorus pentabromide, and the use of a mixture is not recommended. Therefore, the hydrogen halide gas generated in the subsequent reaction process is a single hydrogen halide such as hydrogen chloride or hydrogen bromide, which avoids the generation of a mixture of hydrogen chloride and hydrogen bromide, and can co-produce hydrogen chloride or hydrogen bromide solution when absorbed in water, which has a higher recycling value.

[0017] The inert solvent is required to have good solubility for phosphorus pentahalide, and is also required to not cause side reactions with raw materials, intermediates, products, etc. during the reaction. The inert solvent may be an alkane solvent, a halogenated alkane solvent, an aromatic hydrocarbon solvent, a halogenated aromatic hydrocarbon solvent, etc., and may be a single solvent or a mixed solvent consisting of a plurality of solvents. The alkane solvent is a linear, branched, or cyclic alkane having C4 to C10, and representative alkane solvents include n-pentane, n-hexane, cyclohexane, n-heptane, and methylcyclohexane. The halogenated alkane solvent is represented by the following general formula: C n H (2n+2-m) X m (wherein X=F, Cl, Br, n=1-10, m=1-4), the carbon chain of the halogenated alkane may be linear, branched, or cyclic, and representative halogenated alkane solvents include dichloromethane, trichloromethane, carbon tetrachloride, dichloroethane, bromoethane, and dibromoethane. Aromatic hydrocarbon solvents are represented by the following general formula: [ka] (wherein the substituent R is H, a linear, branched or cyclic alkyl substituent of C1 to C6, n=0 to 6, and when there are multiple alkyl substituents on the benzene ring, the alkyl substituents may be the same or different.) Representative aromatic hydrocarbon solvents include benzene, toluene, xylene, trimethylbenzene, ethylbenzene, methylethylbenzene, etc. Halogenated aromatic hydrocarbon solvents are represented by the following general formula: [ka] (wherein the substituent R is H, a linear, branched or cyclic alkyl substituent of C1-C6, n=0-6, the substituent X=F, Cl, Br, m=0-6, n+m≦6, and when a plurality of alkyl and halogen atoms are substituted on the benzene ring, the substituted alkyl and halogen atoms may be the same or different.) Representative halogenated aromatic hydrocarbon solvents include fluorobenzene, chlorobenzene, bromobenzene, difluorobenzene, dichlorobenzene, p-chlorofluorobenzene, p-fluorotoluene, etc. The amount of the inert solvent used is 1-20 times the mass of the phosphorus pentahalide.

[0018] Solvents containing atoms such as nitrogen and oxygen, such as nitrile solvents such as acetonitrile, ester solvents such as dimethyl carbonate, ether solvents such as ethylene glycol dimethyl ether, and ketone solvents such as acetone, have good solubility for phosphorus pentahalide, but are prone to side reactions such as decomposition and complexation with hydrogen fluoride, phosphorus pentafluoride, hexafluorophosphate, etc. during the reaction process, which can cause the color of the reaction solution to become dark, the appearance and purity of the product to be deteriorated, the reaction yield to be reduced, the solvent recovery rate to be reduced, and recycling of the solvent to be difficult, and therefore are not suitable for use as reaction solvents.

[0019] In order to shorten the dissolution process of phosphorus pentahalide in an inert solvent, the dissolution rate of phosphorus pentahalide in the inert solvent is increased by heating, and after dissolving phosphorus pentahalide, the temperature is lowered to a required temperature after ensuring that phosphorus pentahalide does not precipitate as a solid, and then the reaction is carried out in a reactor. Considering that the introduction of moisture will have a negative effect on the quality of the final product, the process of adding and dissolving phosphorus pentahalide, etc., is performed by blocking environmental water vapor by sealing, protection with dry inert gas, etc.

[0020] The operation scheme of dissolving phosphorus pentahalide in an inert solvent to obtain a phosphorus pentahalide inert solvent solution and then carrying out the next reaction is of great significance to whether the process can be carried out smoothly. As phosphorus pentahalide, both phosphorus pentachloride and phosphorus pentabromide are sublimable solids, among which phosphorus pentachloride solid has a high melting point of 180°C, and phosphorus pentabromide solid has no clear melting point and decomposes when the temperature exceeds 100°C. Therefore, the stable physical state of phosphorus pentachloride and phosphorus pentabromide is solid, and it is difficult to stably maintain phosphorus pentachloride and phosphorus pentabromide in liquid and gas forms. When phosphorus pentahalide is added as a solid, it can be applied to a batch kettle type reactor, but the addition rate cannot be precisely controlled. In addition, at the moment of contact between phosphorus pentahalide solid and hydrogen fluoride, a solid-liquid phase reaction occurs, which causes significant local heat generation and releases a large amount of hydrogen halide gas, which not only causes a large amount of material volatilization and gas entrainment loss, but also poses serious safety risks and is prone to production safety accidents. In other words, when phosphorus pentahalide is supplied as gas, due to the special physical and chemical properties of phosphorus pentahalide, the gas of phosphorus pentahalide is easily condensed into a solid, which will block the supply pipeline and affect the smoothness of the reaction. In addition, it is difficult to accurately measure the gas material and supply it accurately as needed, so in the batch reactor, inaccurate metering is still acceptable, but in the continuous flow reaction, the instantaneous supply control requires very high accuracy, so it cannot meet the requirements of the continuous flow reaction process. In addition, the continuous flow reactor is usually a pressurized reactor, and the gas material can only enter the reactor smoothly if it has a pressure higher than the internal pressure of the reactor. Therefore, the supply of phosphorus pentahalide as gas not only cannot meet the requirements of the process, but is also difficult to achieve industrially.

[0021] In step (2), The alkali metal halide salt is represented by the following general formula: [ka] When the product to be synthesized is lithium hexafluorophosphate, the alkali metal halide salt is one or more selected from lithium fluoride, lithium chloride, and lithium bromide, and when the product to be synthesized is sodium hexafluorophosphate, the alkali metal halide salt is one or more selected from sodium fluoride, sodium chloride, and sodium bromide.When the product to be synthesized is potassium hexafluorophosphate, the alkali metal halide salt is one or more selected from potassium fluoride, potassium chloride, and potassium bromide.

[0022] When the alkali metal halide salt is an alkali metal fluoride salt, the process of dissolving the alkali metal fluoride salt in anhydrous hydrogen fluoride is a pure dissolution process, with no significant dissolution heat, no gas generation, and a relatively mild dissolution process.When the alkali metal halide salt is an alkali metal chloride salt or an alkali metal bromide salt, the process of dissolving the alkali metal halide salt in anhydrous hydrogen fluoride is not only a dissolution process, but also a halogen exchange reaction process, and the reaction formula is as follows: [ka]

[0023] After dissolving an alkali metal chloride salt and an alkali metal bromide salt in anhydrous hydrogen fluoride, one molecule of hydrogen halide gas is generated at the same time as generating an alkali metal fluoride salt. When an alkali metal chloride salt is used, the hydrogen halide gas generated is hydrogen chloride, and when an alkali metal bromide salt is used, the hydrogen halide gas generated is hydrogen bromide. The alkali metal halide salt is preferably a single halogen element compound, and especially when the alkali metal halide salt is a chloride salt and a bromide salt, the hydrogen halide gas generated during the dissolution process is a single hydrogen halide, hydrogen chloride or hydrogen bromide, thereby avoiding the generation of a mixture of hydrogen chloride and hydrogen bromide, and when absorbed in water, hydrogen chloride or hydrogen bromide solution can be simultaneously produced, which has a higher recycling value. The process of dissolving an alkali metal chloride salt and an alkali metal bromide salt in anhydrous hydrogen fluoride involves a halogen exchange reaction, which generates one molecule of hydrogen halide, but the reaction process is mild, generates little heat, and can be controlled by adjusting the input speed, so that it is highly safe.

[0024] In order to further improve the synthesis efficiency and economy of hexafluorophosphate, when the alkali metal halide salt used in step (2) is an alkali metal chloride salt or an alkali metal bromide salt, the phosphorus pentahalide used in step (1) is phosphorus pentachloride or phosphorus pentabromide, i.e., when an alkali metal chloride salt is used in step (2), phosphorus pentachloride is used in step (1), and when an alkali metal bromide salt is used in step (2), phosphorus pentabromide is used in step (1). This allows the hydrogen halide treatment system to be shared between step (2) and step (4), which not only avoids the repeated construction of production equipment and reduces the running costs of the equipment, but also effectively avoids the generation of mixed hydrogen halide and improves the economic value of the co-produced hydrogen halide solution.

[0025] In particular, alkali metal halide salts are preferred alkali metal-derived salts because they produce only hydrogen halide gas without introducing moisture during the process of dissolution in anhydrous hydrogen fluoride and the subsequent reaction process. On the other hand, alkali metal-derived salts such as alkali metal carbonates, alkali metal hydrogencarbonates, and alkali metal hydroxides produce water when dissolved in anhydrous hydrogen fluoride, and such water introduced into the reaction system decomposes the product hexafluorophosphate to produce fluorooxyphosphate, which has an adverse effect on the quality of the final product, and therefore cannot be used as alkali metal-derived salts in the present invention.

[0026] The anhydrous hydrogen fluoride is liquid hydrogen fluoride, and since the boiling point of hydrogen fluoride is 19.5° C., in order to liquefy hydrogen fluoride, the temperature of the system must be less than 19.5° C. during the dissolution process and during the storage process of the alkali metal fluoride hydrogen fluoride solution, and the dissolution and storage temperatures are preferably −40 to 19° C. The amount of anhydrous hydrogen fluoride used is 1 to 20 times the mass of the alkali metal halide salt.

[0027] Considering the adverse effect that the introduction of moisture may have on the quality of the final product, environmental water vapor is blocked during the process of adding and dissolving the alkali metal halide salt by sealing or protecting with dry inert gas.

[0028] In step (3), The phosphorus pentahalide inert solvent solution (I) and the alkali metal fluoride hydrogen fluoride solution (II) are charged into a reactor in a predetermined ratio, and then the phosphorus pentahalide is reacted with hydrogen fluoride to generate phosphorus pentafluoride, and the generated phosphorus pentafluoride is reacted with an alkali metal fluoride salt on-site to generate hexafluorophosphate. By generating and reacting phosphorus pentafluoride on-site, the operations of separation, purification, storage, transportation, etc. of phosphorus pentafluoride can be avoided, the production process can be effectively simplified, the utilization rate of phosphorus pentafluoride can be improved, production efficiency can be improved, and synthesis costs can be reduced.

[0029] The reactor may be a batch reactor, a tubular reactor and a microreactor, preferably a tubular reactor and a microreactor, more preferably a microreactor. The use of a microreactor can effectively improve the reaction yield and the purity of the product, simplify the reaction operation and improve the safety of the reaction due to the following reasons: (1) The synthesis of phosphorus pentafluoride by the reaction of phosphorus pentahalide with hydrogen fluoride is very violent and releases a large amount of heat, so phosphorus pentahalide is dissolved in an inert solvent and fed in a solution state to avoid the more violent solid-liquid state reaction, and control the feed rate and the reaction intensity, so that the reaction can also be carried out in a batch reactor and a tubular reactor. However, compared with a batch reactor and a tubular reactor, a microreactor has a better mixing effect and a larger heat exchange area, which is advantageous for controlling the reaction under milder conditions. (2) In the process of synthesizing phosphorus pentafluoride by reacting phosphorus pentahalide with hydrogen fluoride, five molecules of hydrogen halide gas are generated, and hydrogen fluoride is not compatible with the inert solvent for dissolving phosphorus pentahalide. Therefore, in the reaction process, there is actually a three-phase heterogeneous reaction of gas, liquid, and liquid, and better mixing effect inevitably leads to better reaction effect. In terms of mixing effect, microreactors are more advantageous than batch reactors and tubular reactors. (3) In view of the particular characteristics of the reaction, the local heat generation at the moment phosphorus pentafluoride comes into contact with hydrogen fluoride is large, and five molecules of hydrogen halide gas are generated during the reaction process. In addition, the intermediate product phosphorus pentafluoride is in the form of gas, and hydrogen fluoride has a low boiling point and is highly volatile. Therefore, if a batch reactor is used, due to the local heat generation in the reaction system and the release of hydrogen halide gas during the reaction process, some of the intermediate product phosphorus pentafluoride will inevitably be carried out of the reaction system by the hydrogen halide gas and the volatilized hydrogen fluoride gas when it does not react with the alkali metal fluoride salt, and will be lost. The loss of hydrogen fluoride may destroy the stability of the reaction system, and more seriously, the remaining amount of hydrogen fluoride will be insufficient, which will affect the normal progress of the reaction.In the case of a tubular reactor, due to the insufficient mixing effect, phosphorus pentafluoride gas is mixed with hydrogen halide gas, and the gas-liquid phase is separated to a certain extent, so that phosphorus pentafluoride cannot fully react with the alkali metal fluoride salt in the hydrogen fluoride solution and is lost. The use of a microreactor can effectively avoid the above problem, and due to the excellent mixing effect, the reaction intermediate product phosphorus pentafluoride is completely contacted with the alkali metal fluoride salt in the hydrogen fluoride, and when it reaches the outlet of the microreactor, phosphorus pentafluoride has completely reacted and the reaction is terminated. At this time, even if a part of the hydrogen fluoride is lost with the hydrogen halide when the reaction liquid is separated into gas and liquid to remove the hydrogen halide, the reaction is terminated at that time, so the lost hydrogen fluoride does not have a negative effect on the reaction. (4) Hydrogen fluoride, the raw material for synthesizing hexafluorophosphate, the intermediate product phosphorus pentafluoride, and the mixed product (III) obtained by the reaction are highly toxic and pose a large safety risk during the reaction process, so the safety risk can be effectively reduced and avoided by reducing the liquid retention volume during the reaction process. The liquid retention volume of an industrial-grade microreactor is on the scale of several liters, and compared with the liquid retention volume of a batch reactor or a tubular reactor, the safety risk is almost negligible.

[0030] When a microreactor is used as a reactor, it may be a single microreactor or a group of microreactors in which multiple microreactors are closely combined, and the specific structure is determined by the process conditions. The reaction temperature distribution in the microreactor may be a uniform temperature, or a different temperature distribution may be formed in the microreactor as necessary. When a uniform reaction temperature is adopted, the reaction temperature is below the boiling point of anhydrous hydrogen fluoride to ensure that the hydrogen fluoride in the reaction mixture (III) flowing out from the outlet of the microreactor is liquid. When the inside of the microreactor has a different temperature distribution, a temperature higher than the boiling point of anhydrous hydrogen fluoride can be tolerated in the microreactor, and when the reaction mixture (III) flows toward the outlet of the microreactor, it can be cooled so that the temperature when the mixture (III) flows out of the microreactor is lower than the boiling point of anhydrous hydrogen fluoride. The reaction temperature of the microreactor is preferably -40 to 100°C. The intermediate product phosphorus pentafluoride produced during the reaction is a gas, and the hydrogen halide produced is also a gas, and the production of gas inevitably increases the pressure inside the microreactor, and when the reaction temperature of the microreactor is higher than the boiling point of anhydrous hydrogen fluoride, the gasification of hydrogen fluoride also generates pressure, so when selecting a microreactor, it is necessary to consider not only whether the material meets the corrosion resistance requirements, but also the pressure resistance of the microreactor to ensure the safety of the reaction process. The materials of the parts in contact with the material of the microreactor are silicon carbide as a nonmetallic material, and high-nickel alloy materials such as Monel alloy and Hastelloy as a metallic material, and the pressure resistance of the microreactor must be higher than the maximum pressure that may appear during the reaction process.

[0031] The supply ratio of the phosphorus pentahalide inert solvent solution (I) to the alkali metal fluoride salt hydrogen fluoride solution (II) is the ratio of the amount of phosphorus contained in the phosphorus pentahalide inert solvent solution supplied to the microreactor per unit time to the amount of alkali metal contained in the alkali metal fluoride salt hydrogen fluoride solution supplied to the microreactor per unit time. Preferably, the ratio of the amount of phosphorus to the amount of alkali metal supplied to the microreactor per unit time is (0.8-1.2):1, more preferably, the ratio of the amount of phosphorus to the amount of alkali metal supplied to the microreactor per unit time is (0.9-1.1):1.

[0032] The supply rates of the phosphorus pentahalide inert solvent solution (I) and the alkali metal fluoride hydrogen fluoride solution (II) are related to the concentration and temperature of the phosphorus pentahalide inert solvent solution, the concentration and temperature of the alkali metal fluoride hydrogen fluoride solution, the volume and structure of the microreactor, the temperature of the cooling system and the flow rate of the coolant, etc., and during the actual operation process, adjustments and checks should be made according to the relevant parameters to ensure that the temperature in the microreactor is controlled to the required temperature of the process. No matter how the supply rates of the phosphorus pentahalide inert solvent solution (I) and the alkali metal fluoride hydrogen fluoride solution (II) change, in terms of the supply ratio between the amount of phosphorus contained in the phosphorus pentahalide inert solvent solution (I) and the amount of alkali metal contained in the alkali metal fluoride hydrogen fluoride solution (II) can be accurately controlled to an optimal ratio for the process, and when the reaction solution reaches the outlet of the microreactor, both the phosphorus pentahalide and the alkali metal fluoride can be sufficiently reacted to produce hexafluorophosphate, which not only increases the utilization rate of materials, but also favors the improvement of product purity and reaction yield.

[0033] In step (4), The mixture (III) flowing out of the reactor is composed of hexafluorophosphate, hydrogen fluoride, an inert solvent, and hydrogen halide. Volatile hydrogen halide gas is separated from the mixture by gas-liquid separation to obtain a mixture (IV) composed of hexafluorophosphate, hydrogen fluoride, and an inert solvent. The gas-liquid separation step may be performed in a dedicated gas-liquid separator, or the mixture (IV) obtained by separation may be placed in a collector and gas-liquid separation operation may be performed in the collector. When gas-liquid separation is performed in the collector, the collector must have sufficient space to store the mixture (IV) and perform the gas-liquid separation operation, and must have functions such as temperature control, condensation, and defoaming. In order to keep the material in the collector uniform, it is preferable that the collector has a stirring function. The material of the part in contact with the gas-liquid separator and the material of the collector must be resistant to corrosion by hydrogen fluoride, hydrogen halide, etc., and may be lined with nonmetallic materials such as silicon carbide, high nickel alloy materials such as Monel alloy and Hastelloy, and corrosion-resistant polymer materials such as PTFE and PFA.

[0034] For the separated hydrogen halide gas, the hydrogen fluoride entrained in the hydrogen halide gas is condensed and recovered by a multi-stage advanced condensation method, and a small amount of residual hydrogen fluoride is removed by a multi-stage adsorption defluorination method to obtain high-purity hydrogen halide gas, which is absorbed with water to produce a hydrogen halide solution, which is used for commercial purposes and improves the economy. Of course, the hydrogen halide gas can also be refined and recycled by other appropriate methods and used, and the specific method is determined according to actual needs.

[0035] In the process of obtaining mixture (IV) by gas-liquid separation of mixture (III), liquid hydrogen fluoride volatilizes, increasing the load and difficulty of the defluorination purification operation of hydrogen halide gas. Therefore, an operation temperature equal to or lower than the boiling point of anhydrous hydrogen fluoride is required, and the preferred gas-liquid separation operation temperature is -40 to 19°C.

[0036] In step (5), The mixture (IV) is composed of hexafluorophosphate, hydrogen fluoride, and an inert solvent. After a predetermined amount of this mixture (IV) is collected, a hydrogen fluoride removal operation is performed to obtain a mixture (V) composed of hexafluorophosphate and an inert solvent. The hydrogen fluoride removal operation may be performed in a collector or in a dedicated desolvation vessel. When the hydrogen fluoride removal operation is performed in a desolvation vessel, the vessel must have functions such as stirring, temperature control, condensation, and defoaming, and the material of the part that comes into contact with the material of the desolvation vessel must be resistant to corrosion by hydrogen fluoride, and may be lined with a nonmetallic material such as silicon carbide, a high-nickel alloy material such as Monel alloy or Hastelloy, or a corrosion-resistant polymeric material such as PTFE or PFA.

[0037] The hydrogen fluoride removal operation mainly utilizes the low boiling point and high volatility characteristics of hydrogen fluoride to boil and evaporate hydrogen fluoride by heating and temperature increasing method, and removes hydrogen fluoride from the mixture. The hydrogen fluoride vapor is first condensed, and the entrained inert solvent is condensed and returned to the mixture, and the hydrogen fluoride vapor enters the hydrogen fluoride recovery system. In order to improve the hydrogen fluoride removal speed and removal effect of the mixture (IV), the mixture can be bubbled and purged with inert gas such as dry nitrogen, helium, argon, etc. during hydrogen fluoride removal, especially before the end of the hydrogen fluoride removal operation, so that the hydrogen fluoride is sufficiently removed and a mixture (V) without residual hydrogen fluoride can be obtained. The hydrogen fluoride gas entering the hydrogen fluoride recovery system is subjected to multi-stage advanced condensation to condense and recover hydrogen fluoride, and the exhaust gas from the advanced condensation is discharged as meeting the standard after passing through multi-stage water, alkali spray, or multi-stage adsorption and defluorination.

[0038] The hydrogen fluoride removal process requires an operating temperature higher than the boiling point of hydrogen fluoride and lower than the boiling point of the inert solvent, which ensures smooth removal of hydrogen fluoride while avoiding entrainment of the inert solvent in the hydrogen fluoride recovery system. The operating temperature for removing hydrogen fluoride is preferably 20 to 100°C. When hydrogen fluoride removal is completed, a mixture (V) consisting of hexafluorophosphate and an inert solvent is obtained. The solubility of hexafluorophosphate in the inert solvent is low, and the effect of the material temperature on the solubility of hexafluorophosphate is also small, but in order to facilitate the subsequent solid-liquid separation operation and increase the safety of the solid-liquid separation operation, it is desirable to keep the temperature of the mixture (V) below room temperature.

[0039] In step (6), The mixture (V) consisting of the hexafluorophosphate and the inert solvent is subjected to solid-liquid separation and dried to obtain a finished hexafluorophosphate product. For the solid-liquid separation of the mixture (V), general solid-liquid separation procedures such as centrifugation, pressure filtration, and suction filtration can be applied. The solid obtained by the solid-liquid separation is dried to obtain a finished hexafluorophosphate product with a purity of 99.8% or more and a yield of 99.0% or more.

[0040] In order to further improve the quality of the hexafluorophosphate and meet the demands of higher-end applications, the obtained hexafluorophosphate can be purified by recrystallization to produce ultra-high purity hexafluorophosphate with a purity of 99.99% or more and a yield of 98% or more. Effect of the Invention

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows: (1): By dissolving phosphorus pentahalide in an inert solvent to prepare a phosphorus pentahalide inert solvent solution and then supplying it, the conventional method of supplying phosphorus pentahalide as a solid or gas can be avoided, and the supply rate and accuracy of phosphorus pentahalide can be precisely controlled. This not only effectively solves the problem of the reaction between phosphorus pentahalide and hydrogen fluoride being too violent, but also fundamentally improves the safety and operability of the synthesis process. (2): By using a solvent that is inert to the reaction system, such as an alkane solvent, a halogenated alkane solvent, an aromatic hydrocarbon solvent, or a halogenated aromatic hydrocarbon solvent, instead of the nitrogen- or oxygen-containing solvents used in the prior art, it is possible to ensure that the solvent is completely inert in the reaction process, avoid side reactions such as decomposition and complexation involving the solvent, improve the reaction yield and product purity, simplify the solvent recovery operation, and improve the solvent recovery rate. (3) By adopting in-situ generation of phosphorus pentafluoride and in-situ reaction with alkali metal fluoride salt, operations such as separation, purification, storage, and transportation of phosphorus pentafluoride are avoided, the gas supply mode of phosphorus pentafluoride is abolished, the utilization rate of phosphorus pentafluoride is effectively increased, the operation process is simplified, the production efficiency is improved, and the synthesis cost is reduced. (4): By adopting a method of separating different components of materials step by step, the hydrogen halide produced in the reaction, the hydrogen fluoride of the reaction surplus raw material, the reaction inert solvent, and the hexafluorophosphate product are separated in sequence, the separation sequence is rationalized, the separation process is simplified, the separation effect is optimized, the generation of mixed materials is avoided to the greatest extent possible, the resource utilization of various materials is realized, and the waste gas, wastewater and solid waste are minimized. Among them, the recovered hydrogen halide can be used to produce high-purity hydrogen halide aqueous solution for commercial use, and the recovered hydrogen fluoride and inert solvent can be reused in the reaction, thereby maximizing the economic effect. (5): The hexafluorophosphate product is obtained by solid-liquid separation of a mixture of hexafluorophosphate and an inert solvent. This avoids the conventional technique of obtaining a hexafluorophosphate product by solid-liquid separation from a hydrogen fluoride solution, significantly improving the safety and operability of the solid-liquid separation process and the subsequent refining and drying processes, and further reducing the amount of residual hydrogen fluoride in the hexafluorophosphate obtained by separation, thereby improving the quality of the product. (6): In the method for synthesizing hexafluorophosphate of the present invention, except for the input of solids when the raw materials phosphorus pentahalide and alkali metal halide salt are used to produce a solution, and the discharge of solids when the final product is separated into solid-liquid and dried to obtain a finished product, all other processes can be realized as continuous flow and automated production, and the continuous reaction mode of "kettle type continuous-continuous flow-kettle type continuous" can be easily realized, which avoids the full kettle type intermittent reaction mode of the prior art, greatly improving the safety of the production process and improving production efficiency. The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Note that the following embodiments are only used to help understand the present invention and do not limit the present invention. The specific embodiments cannot cover all the technical features of the present invention, and the technical features related to the specification can be combined with each other to form a new embodiment as long as they are not contradictory to each other. [Brief description of the drawings]

[0042] [Figure 1] FIG. 1 is a schematic diagram of the “kettle continuous-continuous flow-kettle continuous” continuous synthesis process flow of the hexafluorophosphate of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] As shown in Figure 1, the present invention uses a continuous reaction process of "continuous kettle-continuous reactor flow-continuous gas-liquid separation-continuous kettle" to synthesize lithium hexafluorophosphate. The specific process flow is as follows:

[0044] (1): A phosphorus pentahalide inert solvent solution is prepared through two routes, A and B. The two routes, A and B, are operated alternately. When a phosphorus pentahalide solution is prepared through route A, the phosphorus pentahalide solution is supplied through route B. Conversely, when a phosphorus pentahalide solution is prepared through route B, the phosphorus pentahalide solution is supplied through route A. In this way, a phosphorus pentahalide inert solvent solution is continuously supplied. (2): The alkali metal fluoride hydrogen fluoride solution is prepared through two routes, A and B, which are operated alternately; when the alkali metal fluoride solution is prepared through route A, the alkali metal fluoride solution is supplied through route B, and vice versa, when the alkali metal fluoride solution is prepared through route B, the alkali metal fluoride solution is supplied through route A, thus realizing continuous supply of the alkali metal fluoride hydrogen fluoride solution. When an alkali metal chloride or alkali metal bromide is used as the alkali metal fluoride, the generated hydrogen halide gas is introduced into the hydrogen halide treatment system. (3): The phosphorus pentahalide inert solvent solution and the alkali metal fluoride hydrogen fluoride solution are fed into a continuous flow reactor at a predetermined ratio by a metering pump to react with each other. The feed ratio, feed rate, reaction temperature, residence time, etc. are set and adjusted according to the process requirements, and the reaction is carried out continuously, continuously fed, and continuously discharged. (4): The mixture (III) from the outlet of the continuous flow reactor is subjected to continuous gas-liquid separation to remove hydrogen halide to obtain a mixture (IV), and the removed hydrogen halide gas is introduced into a hydrogen halide treatment system. (5): Collect mixture (IV), remove hydrogen fluoride to obtain mixture (V), and separate mixture (V) into solid and liquid to obtain hexafluorophosphate. The above operations are carried out in two routes, A and B, which are operated alternately. When mixture (IV) is collected in route A, hydrogen fluoride is removed from mixture (IV) in route B to obtain mixture (V), and mixture (V) is subjected to solid-liquid separation to obtain hexafluorophosphate. When mixture (IV) is collected in route B, hydrogen fluoride is removed from mixture (IV) in route A to obtain mixture (V), and mixture (V) is subjected to solid-liquid separation to obtain hexafluorophosphate. In this way, while seamlessly connecting to a continuous gas-liquid separator, the operation of continuously removing hydrogen fluoride and separating it into solid and liquid is realized, ensuring continuous and stable operation of the synthesis process, and the removed hydrogen fluoride enters the hydrogen fluoride recovery system, and the inert gas obtained by solid-liquid separation returns to the preparation process of phosphorus pentahalide inert solvent solution. (6): The process of drying hexafluorophosphate to obtain the finished hexafluorophosphate product and packaging the finished hexafluorophosphate product is carried out in one route, and continuous drying and continuous packaging equipment is reasonably arranged based on actual production capacity to realize the continuous drying and continuous packaging operations of hexafluorophosphate.

[0045] Example 1 A microreactor was used as a continuous reactor to synthesize lithium hexafluorophosphate using phosphorus pentachloride, lithium chloride, and hydrogen fluoride as raw materials and toluene as an inert organic solvent. As shown in Flowchart 1, the synthesis process is as follows. (1): A specified amount of toluene is added to the phosphorus pentachloride toluene solution preparation kettle, and under nitrogen protection, a specified amount of phosphorus pentachloride solid is added, stirred and heated to 60-65°C. After the solid is completely dissolved, the temperature is lowered to 20-25°C to obtain a phosphorus pentachloride toluene solution with a concentration of 25% by mass, which is stored under nitrogen protection until use. There are two kettle A and B for preparing phosphorus pentachloride toluene solution, which are used alternately. (2): A specified amount of anhydrous hydrogen fluoride liquid was added to the lithium fluoride hydrogen fluoride solution preparation kettle, and the temperature was controlled to -10 to -5°C under nitrogen protection. A specified amount of lithium chloride solid was slowly added in batches and dissolved by stirring to obtain a lithium fluoride hydrogen fluoride solution with a concentration of 20% by mass, which was then stored under nitrogen protection at -10 to -5°C until use. The hydrogen chloride gas generated during the preparation process entered the hydrogen chloride treatment system. There are two lithium fluoride hydrogen fluoride solution preparation kettle, kettle A and kettle B, which are used alternately. (3): A phosphorus pentachloride toluene solution was continuously fed into the microreactor at a rate of 500g / min by a metering pump, and a lithium fluoride hydrogen fluoride solution was continuously fed into the microreactor at a rate of 77.85g / min by a metering pump. The two materials were thoroughly mixed at the inlet of the microreactor before entering the microreactor to carry out the reaction. The microreactor adopted stepwise temperature control, with the maximum temperature in the middle being controlled at 60-65°C and the temperature at the outlet being controlled at -15--10°C, and the residence time of the materials in the microreactor was about 80 seconds. (4): After the reaction liquid flows out of the microreactor, it enters a continuous gas-liquid separator controlled at a temperature of -15 to -10°C. The gas separated in the gas-liquid separator enters the hydrogen chloride treatment system, and the separated liquid phase enters a collection kettle controlled at a temperature of 0 to 5°C. There are two collection kettle types, A and B, which are used alternately. (5): After sufficient material was collected in the collecting vessel, the temperature of the collecting vessel was slowly raised to 40-45°C, hydrogen fluoride was evaporated and removed, and the hydrogen fluoride vapor was introduced into the hydrogen fluoride recovery system to remove most of the hydrogen fluoride. Dry nitrogen was then introduced and the material was purged at 40-45°C for 2 hours. After the purge was completed, the temperature of the collecting vessel was lowered to 5-10°C, the material was discharged and centrifuged to obtain lithium hexafluorophosphate wet solid, and the centrifuged mother liquor was recovered as toluene and returned to the toluene tank in the phosphorus pentachloride toluene solution preparation process. (6): The wet solid of lithium hexafluorophosphate was sent to a single-cone spiral belt dryer by a solids conveying system, dried under reduced pressure, and packaged by an automatic packaging system if it passed the inspection. Hydrogen chloride treatment system: The hydrogen chloride treatment system consists of a three-stage series condenser, a two-stage defluorination packed tower, a three-stage falling film absorption device, and a two-stage alkali spray tower. The three-stage series condenser contains a frozen liquid at -35 to -30°C and recovers the hydrogen fluoride condensate contained in hydrogen chloride. The two-stage defluorination packed tower is filled with hydrogen fluoride adsorption packing inside and removes the small amount of hydrogen fluoride remaining in the hydrogen chloride defluorinated by condensation. The high-purity hydrogen chloride obtained by the defluorination process is absorbed by water through the three-stage falling film absorption device, and a hydrogen chloride solution with a concentration of 35 to 36% is obtained. The exhaust gas is deoxidized by the two-stage alkali spray and discharged as it meets the standards. Hydrogen fluoride recovery system: The hydrogen fluoride recovery system consists of a three-stage series condenser, a three-stage falling film absorber, and a two-stage alkali spray tower. The three-stage series condenser contains a frozen liquid at -35 to -30°C, which condenses and recovers most of the hydrogen fluoride, and the hydrogen fluoride remaining in the exhaust gas passes through the three-stage falling film absorber and is absorbed by water, yielding a hydrofluoric acid solution with a concentration of 49±0.2%. The exhaust gas was deoxidized by the two-stage alkali spray and discharged as meeting the standards. In this example, it took 10 hours to synthesize lithium hexafluorophosphate from the start of supply to debugging to ensure stability. When timing was started after debugging was completed, stable operation for 300 hours resulted in a total of 2250 kg of phosphorus pentachloride and 458 kg of lithium chloride being consumed, and 1630 kg of lithium hexafluorophosphate was obtained, with a yield of 99.3% and a purity of 99.85%.

[0046] Example 2 The microreactor was used as a continuous reactor to synthesize sodium hexafluorophosphate using phosphorus pentachloride, sodium fluoride, and hydrogen fluoride as raw materials and chlorobenzene as an inert organic solvent. As shown in Flowchart 1, the synthesis process is as follows: (1): A specified amount of chlorobenzene is added to the phosphorus pentachloride chlorobenzene solution preparation kettle, and under nitrogen protection, a specified amount of phosphorus pentachloride solid is added, stirred and heated to 50-55°C. After the solid is completely dissolved, the temperature is lowered to 10-15°C to obtain a phosphorus pentachloride chlorobenzene solution with a concentration of 20% by mass, which is stored under nitrogen protection until use. There are two kettle A and B for preparing phosphorus pentachloride chlorobenzene solution, which are used alternately. (2): A specified amount of anhydrous hydrogen fluoride liquid was added to a sodium fluoride hydrogen fluoride solution preparation kettle, and under nitrogen protection, the temperature was controlled at 10-15°C. A specified amount of sodium fluoride solid was slowly added in batches and dissolved by stirring to obtain a sodium fluoride hydrogen fluoride solution with a concentration of 30% by mass, which was then stored under nitrogen protection at 10-15°C until use. The sodium fluoride hydrogen fluoride solution preparation kettle has kettle A and kettle B which are used alternately. (3): The phosphorus pentachloride chlorobenzene solution was continuously fed into the microreactor at a rate of 550g / min by a metering pump, and the sodium fluoride hydrogen fluoride solution was continuously fed into the microreactor at a rate of 73.94g / min by a metering pump. The two materials were thoroughly mixed at the inlet of the microreactor before entering the microreactor to carry out the reaction. The microreactor adopted stepwise temperature control, with the maximum temperature in the middle being controlled at 70-75°C and the temperature at the outlet being controlled at -10--5°C, and the residence time of the materials in the microreactor was about 70 seconds. (4): After the reaction liquid flows out of the microreactor, it enters a continuous gas-liquid separator controlled at a temperature of -5 to 0°C. The gas separated in the gas-liquid separator enters the hydrogen chloride treatment system, and the separated liquid phase enters a collection kettle controlled at a temperature of -5 to 5°C. There are two collection kettle, A kettle and B kettle, which are used alternately. (5): After sufficient material was collected in the collecting kettle, the temperature of the collecting kettle was slowly raised to 50-55°C, hydrogen fluoride was evaporated and removed, and the hydrogen fluoride vapor was introduced into the hydrogen fluoride recovery system to remove most of the hydrogen fluoride. Dry argon was then introduced and the material was purged at 50-55°C for 2 hours. After the purge was completed, the temperature of the collecting kettle was lowered to 20-25°C, the material was discharged and centrifuged to obtain sodium hexafluorophosphate wet solid, and the centrifuged mother liquor was recovered as chlorobenzene and returned to the chlorobenzene tank of the phosphorus pentachloride chlorobenzene solution preparation process. (6): The wet solid of sodium hexafluorophosphate was sent to a single-cone spiral belt dryer by a solids conveying system, dried under reduced pressure, and packaged by an automatic packaging system if it passed the inspection. Hydrogen chloride treatment system: The hydrogen chloride treatment system consists of a three-stage series condenser, a two-stage defluorination packed tower, a three-stage falling film absorption device, and a two-stage alkali spray tower. The three-stage series condenser contains a frozen liquid at -35 to -30°C and recovers the hydrogen fluoride condensate contained in hydrogen chloride. The two-stage defluorination packed tower is filled with hydrogen fluoride adsorption packing inside and removes the small amount of hydrogen fluoride remaining in the hydrogen chloride defluorinated by condensation. The high-purity hydrogen chloride obtained by the defluorination process is absorbed by water through the three-stage falling film absorption device, and a hydrogen chloride solution with a concentration of 35 to 36% is obtained. The exhaust gas is deoxidized by the two-stage alkali spray and discharged as it meets the standards. Hydrogen fluoride recovery system: The hydrogen fluoride recovery system consists of a three-stage series condenser, a three-stage falling film absorber, and a two-stage alkali spray tower. The three-stage series condenser contains a frozen liquid at -35 to -30°C, which condenses and recovers most of the hydrogen fluoride, and the hydrogen fluoride remaining in the exhaust gas passes through the three-stage falling film absorber and is absorbed by water, yielding a hydrofluoric acid solution with a concentration of 49±0.2%. The exhaust gas was deoxidized by the two-stage alkali spray and discharged as meeting the standards. In this embodiment, the synthesis of sodium hexafluorophosphate took 10 hours from the start of supply to debugging to ensure stability. When timing was started after debugging was completed, stable operation for 300 hours resulted in a total of 1980 kg of phosphorus pentachloride and 399 kg of sodium fluoride being consumed, and 1589 kg of finished sodium hexafluorophosphate was obtained, with a yield of 99.5% and a purity of 99.83%.

[0047] Example 3 A microreactor was used as a continuous reactor to synthesize potassium hexafluorophosphate using phosphorus pentachloride, potassium chloride, and hydrogen fluoride as raw materials and chloroform as an inert organic solvent. As shown in Flowchart 1, the synthesis process is as follows: (1): A specified amount of chloroform is added to the phosphorus pentachloride chloroform solution preparation kettle, and under nitrogen protection, a specified amount of phosphorus pentachloride solid is added, stirred and heated to 40-45°C. After the solid is completely dissolved, the temperature is lowered to 20-25°C to obtain a phosphorus pentachloride chloroform solution with a concentration of 30% by mass, which is stored under nitrogen protection until use. There are two kettle for preparing phosphorus pentachloride chloroform solution, kettle A and kettle B, which are used alternately. (2): A specified amount of anhydrous hydrogen fluoride liquid was added to the potassium fluoride hydrogen fluoride solution preparation kettle, and the temperature was controlled to -15 to -10°C under nitrogen protection. A specified amount of potassium chloride solid was slowly added in batches and dissolved by stirring to obtain a potassium fluoride hydrogen fluoride solution with a concentration of 35% by mass, which was then stored under nitrogen protection at -15 to -10°C until use. The hydrogen chloride gas generated during the preparation process entered the hydrogen chloride treatment system. There are two potassium fluoride hydrogen fluoride solution preparation kettle, Kettle A and Kettle B, which are used alternately. (3): The phosphorus pentachloride chloroform solution was continuously fed into the microreactor at a rate of 450g / min by a metering pump, and the potassium fluoride hydrogen fluoride solution was continuously fed into the microreactor at a rate of 107.62g / min by a metering pump. The two materials were thoroughly mixed at the inlet of the microreactor before entering the microreactor to carry out the reaction. The microreactor adopted stepwise temperature control, with the maximum temperature in the middle being controlled at 40-45°C and the temperature at the outlet being controlled at -15--10°C, and the residence time of the materials in the microreactor was about 90 seconds. (4): After the reaction liquid flows out of the microreactor, it enters a continuous gas-liquid separator controlled at a temperature of -10 to -5°C. The gas separated in the gas-liquid separator enters the hydrogen chloride treatment system, and the separated liquid phase enters a collection kettle controlled at a temperature of 0 to 5°C. There are two collection kettle, A and B, which are used alternately. (5): After sufficient material is collected in the collecting kettle, the temperature of the collecting kettle is slowly raised to 50-55°C, hydrogen fluoride is evaporated and removed, and the hydrogen fluoride vapor is fed into the hydrogen fluoride recovery system, and hydrogen fluoride removal is completed. After that, the temperature of the collecting kettle is lowered to 0-5°C, the material is discharged and pressure filtered to obtain potassium hexafluorophosphate wet solid, and the pressure filtration mother liquor is recovered as chloroform and returned to the chloroform tank of the phosphorus pentachloride chloroform solution preparation process. (6): The wet solid of potassium hexafluorophosphate was sent to a single-cone spiral belt dryer by a solids conveying system, dried under reduced pressure, and packaged by an automatic packaging system if it passed the inspection. Hydrogen chloride treatment system: The hydrogen chloride treatment system consists of a three-stage series condenser, a two-stage defluorination packed tower, a three-stage falling film absorption device, and a two-stage alkali spray tower. The three-stage series condenser contains a frozen liquid at -35 to -30°C and recovers the hydrogen fluoride condensate contained in hydrogen chloride. The two-stage defluorination packed tower is filled with hydrogen fluoride adsorption packing inside and removes the small amount of hydrogen fluoride remaining in the hydrogen chloride defluorinated by condensation. The high-purity hydrogen chloride obtained by the defluorination process is absorbed by water through the three-stage falling film absorption device, and a hydrogen chloride solution with a concentration of 35 to 36% is obtained. The exhaust gas is deoxidized by the two-stage alkali spray and discharged as it meets the standards. Hydrogen fluoride recovery system: The hydrogen fluoride recovery system consists of a three-stage series condenser, a three-stage falling film absorber, and a two-stage alkali spray tower. The three-stage series condenser contains a frozen liquid at -35 to -30°C, which condenses and recovers most of the hydrogen fluoride, and the hydrogen fluoride remaining in the exhaust gas passes through the three-stage falling film absorber and is absorbed by water, yielding a hydrofluoric acid solution with a concentration of 49±0.2%. The exhaust gas was deoxidized by the two-stage alkali spray and discharged as meeting the standards. In this embodiment, it took 10 hours from the start of supply to debugging to ensure stability in the synthesis of potassium hexafluorophosphate. When timing was started after debugging was completed, stable operation for 300 hours resulted in a total of 2430 kg of phosphorus pentachloride and 870 kg of potassium chloride being consumed, and 2131 kg of potassium hexafluorophosphate was obtained, with a yield of 99.2% and a purity of 99.88%.

[0048] Example 4 A microreactor was used as a continuous reactor to synthesize sodium hexafluorophosphate using phosphorus pentachloride, sodium chloride, and hydrogen fluoride as raw materials and m-dichlorobenzene as an inert organic solvent. As shown in Flowchart 1, the synthesis process is as follows: (1): A specified amount of m-dichlorobenzene is added to the phosphorus pentachloride m-dichlorobenzene solution preparation kettle, and under nitrogen protection, a specified amount of phosphorus pentachloride solid is added, stirred and heated to 70-75°C. After the solid is completely dissolved, the temperature is lowered to 25-30°C to obtain a phosphorus pentachloride m-dichlorobenzene solution with a concentration of 30% by mass, which is stored under nitrogen protection until use. There are two kettles for preparing phosphorus pentachloride m-dichlorobenzene solution, Kettles A and B, which are used alternately. (2): A specified amount of anhydrous hydrogen fluoride liquid was added to the sodium fluoride hydrogen fluoride solution preparation kettle, and the temperature was controlled at 0-5°C under nitrogen protection. A specified amount of sodium chloride solid was slowly added in batches and dissolved by stirring to obtain a sodium fluoride hydrogen fluoride solution with a concentration of 25% by mass, which was then stored under nitrogen protection at 0-5°C until use. The hydrogen chloride gas generated during the preparation process entered the hydrogen chloride treatment system. There are two sodium fluoride hydrogen fluoride solution preparation kettle, kettle A and kettle B, which are used alternately. (3): Phosphorus pentachloride m-dichlorobenzene solution was continuously fed into the microreactor at a rate of 450g / min by a metering pump, and sodium fluoride hydrogen fluoride solution was continuously fed into the microreactor at a rate of 108.89g / min by a metering pump. The two materials were thoroughly mixed at the inlet of the microreactor before entering the microreactor to carry out the reaction. The microreactor adopted stepwise temperature control, with the maximum temperature in the middle being controlled at 30-35°C and the temperature at the outlet being controlled at -5-0°C, and the residence time of the materials in the microreactor was about 90 seconds. (4): After the reaction liquid flows out of the microreactor, it enters a continuous gas-liquid separator controlled at a temperature of -5 to 0°C. The gas separated in the gas-liquid separator enters the hydrogen chloride treatment system, and the separated liquid phase enters a collection kettle controlled at a temperature of -5 to 0°C. There are two collection kettle, A and B, which are used alternately. (5): After sufficient material was collected in the collecting kettle, the temperature of the collecting kettle was slowly raised to 60-65°C, hydrogen fluoride was evaporated and removed, and the hydrogen fluoride vapor was fed into the hydrogen fluoride recovery system to remove most of the hydrogen fluoride. Dry nitrogen was then introduced and the material was purged at 60-65°C for 1 hour. After the purge was completed, the temperature of the collecting kettle was lowered to 15-20°C, the material was discharged and centrifuged to obtain sodium hexafluorophosphate wet solid, and the centrifuged mother liquor was recovered as m-dichlorobenzene and returned to the m-dichlorobenzene tank for the phosphorus pentachloride m-dichlorobenzene solution preparation process. (6): The wet solid of sodium hexafluorophosphate was sent to a single-cone spiral belt dryer by a solids conveying system, dried under reduced pressure, and packaged by an automatic packaging system if it passed the inspection. Hydrogen chloride treatment system: The hydrogen chloride treatment system consists of a three-stage series condenser, a two-stage defluorination packed tower, a three-stage falling film absorption device, and a two-stage alkali spray tower. The three-stage series condenser contains a frozen liquid at -35 to -30°C and recovers the hydrogen fluoride condensate contained in hydrogen chloride. The two-stage defluorination packed tower is filled with hydrogen fluoride adsorption packing inside and removes the small amount of hydrogen fluoride remaining in the hydrogen chloride defluorinated by condensation. The high-purity hydrogen chloride obtained by the defluorination process is absorbed by water through the three-stage falling film absorption device, and a hydrogen chloride solution with a concentration of 35 to 36% is obtained. The exhaust gas is deoxidized by the two-stage alkali spray and discharged as it meets the standards. Hydrogen fluoride recovery system: The hydrogen fluoride recovery system consists of a three-stage series condenser, a three-stage falling film absorber, and a two-stage alkali spray tower. The three-stage series condenser contains a frozen liquid at -35 to -30°C, which condenses and recovers most of the hydrogen fluoride, and the hydrogen fluoride remaining in the exhaust gas passes through the three-stage falling film absorber and is absorbed by water, yielding a hydrofluoric acid solution with a concentration of 49±0.2%. The exhaust gas was deoxidized by the two-stage alkali spray and discharged as meeting the standards. In this embodiment, the synthesis of sodium hexafluorophosphate took 10 hours from the start of supply to debugging to ensure stability. When timing was started after debugging was completed, stable operation for 300 hours resulted in a total of 2430 kg of phosphorus pentachloride and 682 kg of sodium chloride being consumed, and 1942 kg of lithium sodium hexafluorophosphate was obtained, with a yield of 99.1% and a purity of 99.90%.

[0049] Example 5 A microreactor was used as a continuous reactor, and lithium hexafluorophosphate was synthesized using phosphorus pentachloride, lithium fluoride, and hydrogen fluoride as raw materials and dichloroethane as an inert organic solvent. As shown in Flowchart 1, the synthesis process is as follows. (1): A specified amount of dichloroethane is added to the phosphorus pentachloride dichloroethane solution preparation kettle, and under nitrogen protection, a specified amount of phosphorus pentachloride solid is added, stirred and heated to 60-65°C. After the solid is completely dissolved, the temperature is lowered to 20-25°C to obtain a phosphorus pentachloride dichloroethane solution with a concentration of 25% by mass, which is stored under nitrogen protection until use. There are two kettle A and B for preparing phosphorus pentachloride dichloroethane solution, which are used alternately. (2): A specified amount of anhydrous hydrogen fluoride liquid was added to a lithium fluoride hydrogen fluoride solution preparation kettle, and the temperature was controlled to 5-10°C under nitrogen protection. A specified amount of lithium fluoride solid was slowly added in batches and dissolved by stirring to obtain a lithium fluoride hydrogen fluoride solution with a concentration of 25% by mass, which was then stored under nitrogen protection at 5-10°C until use. The lithium fluoride hydrogen fluoride solution preparation kettle has kettle A and kettle B which are used alternately. (3): The phosphorus pentachloride dichloroethane solution was continuously fed into the microreactor at a rate of 500g / min by a metering pump, and the lithium fluoride hydrogen fluoride solution was continuously fed into the microreactor at a rate of 62.28g / min by a metering pump. The two materials were thoroughly mixed at the inlet of the microreactor before entering the microreactor to carry out the reaction. The microreactor adopted stepwise temperature control, with the maximum temperature in the middle being controlled at 50-55°C and the temperature at the outlet being controlled at 0-5°C, and the residence time of the materials in the microreactor was about 80 seconds. (4): After the reaction liquid flows out of the microreactor, it enters a continuous gas-liquid separator controlled at a temperature of -20 to -15°C. The gas separated in the gas-liquid separator enters the hydrogen chloride treatment system, and the separated liquid phase enters a collection kettle controlled at a temperature of -5 to 5°C. There are two collection kettle, A and B, which are used alternately. (5): After sufficient material is collected in the collecting kettle, the temperature of the collecting kettle is slowly raised to 60-65°C, hydrogen fluoride is evaporated and removed, and the hydrogen fluoride vapor is fed into the hydrogen fluoride recovery system, and hydrogen fluoride removal is completed. After that, the temperature of the collecting kettle is lowered to 10-15°C, the material is discharged and centrifuged to obtain lithium hexafluorophosphate wet solid, and the centrifuged mother liquor is recovered as dichloroethane and returned to the dichloroethane tank of the phosphorus pentachloride dichloroethane solution preparation process. (6): The wet solid of lithium hexafluorophosphate was sent to a single-cone spiral belt dryer by a solids conveying system, dried under reduced pressure, and packaged by an automatic packaging system if it passed the inspection. Hydrogen chloride treatment system: The hydrogen chloride treatment system consists of a three-stage series condenser, a two-stage defluorination packed tower, a three-stage falling film absorption device, and a two-stage alkali spray tower. The three-stage series condenser contains a frozen liquid at -35 to -30°C and recovers the hydrogen fluoride condensate contained in hydrogen chloride. The two-stage defluorination packed tower is filled with hydrogen fluoride adsorption packing inside and removes the small amount of hydrogen fluoride remaining in the hydrogen chloride defluorinated by condensation. The high-purity hydrogen chloride obtained by the defluorination process is absorbed by water through the three-stage falling film absorption device, and a hydrogen chloride solution with a concentration of 35 to 36% is obtained. The exhaust gas is deoxidized by the two-stage alkali spray and discharged as it meets the standards. Hydrogen fluoride recovery system: The hydrogen fluoride recovery system consists of a three-stage series condenser, a three-stage falling film absorber, and a two-stage alkali spray tower. The three-stage series condenser contains a frozen liquid at -35 to -30°C, which condenses and recovers most of the hydrogen fluoride, and the hydrogen fluoride remaining in the exhaust gas passes through the three-stage falling film absorber and is absorbed by water, yielding a hydrofluoric acid solution with a concentration of 49±0.2%. The exhaust gas was deoxidized by the two-stage alkali spray and discharged as meeting the standards. In this example, it took 10 hours to synthesize lithium hexafluorophosphate from the start of supply to debugging to ensure stability. When timing was started after debugging was completed, stable operation for 300 hours resulted in a total of 2250 kg of phosphorus pentachloride and 280 kg of lithium fluoride being consumed, and 1631 kg of lithium hexafluorophosphate was obtained, with a yield of 99.4% and a purity of 99.86%.

[0050] Example 6 A microreactor was used as a continuous reactor to synthesize potassium hexafluorophosphate using phosphorus pentabromide, potassium bromide, and hydrogen fluoride as raw materials and methylcyclohexane as an inert organic solvent. As shown in Flowchart 1, the synthesis process is as follows: (1): A specified amount of methylcyclohexane is added to the phosphorus pentabromide methylcyclohexane solution preparation kettle, and under nitrogen protection, a specified amount of phosphorus pentabromide solid is added, and the mixture is stirred at 30-35°C to completely dissolve the solid, obtaining a phosphorus pentabromide methylcyclohexane solution with a concentration of 15% by mass, which is then stored under nitrogen protection until use. The phosphorus pentabromide methylcyclohexane solution preparation kettle has two kettle A and B, which are used alternately. (2): A specified amount of anhydrous hydrogen fluoride liquid was added to the potassium fluoride hydrogen fluoride solution preparation kettle, and the temperature was controlled to -5 to 0°C under nitrogen protection. A specified amount of potassium bromide solid was slowly added in batches and dissolved by stirring to obtain a potassium fluoride hydrogen fluoride solution with a concentration of 40% by mass, which was then stored under nitrogen protection at -5 to 0°C until use. The hydrogen bromide gas generated during the preparation process entered the hydrogen bromide treatment system. There are two potassium fluoride hydrogen fluoride solution preparation kettle, A kettle and B kettle, which are used alternately. (3): Phosphorus pentabromide methylcyclohexane solution was continuously fed into the microreactor at a rate of 600g / min by a metering pump, and potassium fluoride hydrogen fluoride solution was continuously fed into the microreactor at a rate of 30.37g / min by a metering pump. The two materials were thoroughly mixed at the inlet of the microreactor before entering the microreactor to carry out the reaction. The microreactor adopted stepwise temperature control, with the maximum temperature in the middle being controlled at 80-85°C and the temperature at the outlet being controlled at -10--5°C, and the residence time of the materials in the microreactor was about 60 seconds. (4): After the reaction liquid flows out of the microreactor, it enters a continuous gas-liquid separator controlled at a temperature of -10 to -5°C. The gas separated by the gas-liquid separator enters the hydrogen bromide treatment system, and the separated liquid phase enters a collection kettle controlled at a temperature of -5 to 5°C. There are two collection kettle types, A and B, which are used alternately. (5): After sufficient material is collected in the collecting vessel, the temperature of the collecting vessel is slowly raised to 70-75°C, hydrogen fluoride is evaporated and removed, and the hydrogen fluoride vapor is fed into the hydrogen fluoride recovery system, and hydrogen fluoride removal is completed. After that, the temperature of the collecting vessel is lowered to 20-25°C, and the material is discharged and pressure filtered to obtain potassium hexafluorophosphate wet solid, and the pressure filtered mother liquor is recovered as methylcyclohexane and returned to the methylcyclohexane tank of the phosphorus pentabromide methylcyclohexane solution preparation process. (6): The wet solid of potassium hexafluorophosphate was sent to a single-cone spiral belt dryer by a solids conveying system, dried under reduced pressure, and packaged by an automatic packaging system if it passed the inspection. Hydrogen bromide treatment system: The hydrogen bromide treatment system consists of a three-stage series condenser, a two-stage defluorination packed tower, a three-stage falling film absorber, and a two-stage alkali spray tower. The three-stage series condenser contains a frozen liquid at -35 to -30°C, which condenses and recovers the hydrogen fluoride contained in the hydrogen bromide. The two-stage defluorination packed tower is filled with hydrogen fluoride adsorption packing, which removes the small amount of hydrogen fluoride remaining in the defluorinated hydrogen bromide by condensation. The high-purity hydrogen bromide obtained by the defluorination process is absorbed by water through a three-stage falling film absorber, and a hydrogen bromide solution with a concentration of 46 to 48% is obtained. The exhaust gas is deoxidized by a two-stage alkali spray and discharged as it meets the standards. Hydrogen fluoride recovery system: The hydrogen fluoride recovery system consists of a three-stage series condenser, a three-stage falling film absorber, and a two-stage alkali spray tower. The three-stage series condenser contains a frozen liquid at -35 to -30°C, which condenses and recovers most of the hydrogen fluoride, and the hydrogen fluoride remaining in the exhaust gas passes through the three-stage falling film absorber and is absorbed by water, yielding a hydrofluoric acid solution with a concentration of 49±0.2%. The exhaust gas was deoxidized by the two-stage alkali spray and discharged as meeting the standards. In this embodiment, the synthesis of potassium hexafluorophosphate took 10 hours from the start of supply to debugging to ensure stability. When timing was started after debugging was completed, stable operation for 300 hours resulted in a total of 1620 kg of phosphorus pentabromide and 448 kg of potassium bromide being consumed, and 688 kg of potassium hexafluorophosphate was obtained, with a yield of 99.3% and a purity of 99.84%.

Claims

1. (1) dissolving phosphorus pentahalide in an inert solvent to obtain a phosphorus pentahalide inert solvent solution; (2) dissolving an alkali metal halide salt in anhydrous hydrogen fluoride to obtain an alkali metal fluoride salt-hydrogen fluoride solution; (3) charging the phosphorus pentahalide inert solvent solution and the alkali metal fluoride salt hydrogen fluoride solution into a reactor in a predetermined ratio to react with each other, thereby obtaining a mixture of hexafluorophosphate, hydrogen fluoride, an inert solvent, and hydrogen halide; (4) subjecting the mixture of hexafluorophosphate, hydrogen fluoride, inert solvent, and hydrogen halide obtained in step (3) to gas-liquid separation to separate hydrogen halide gas and obtain a mixture of hexafluorophosphate, hydrogen fluoride, and inert solvent; (5) removing hydrogen fluoride from the mixture of hexafluorophosphate, hydrogen fluoride, and the inert solvent obtained in step (4) to obtain a mixture of hexafluorophosphate and the inert solvent; and step (6) of subjecting the mixture of the hexafluorophosphate obtained in step (5) and the inert solvent to solid-liquid separation and drying to obtain the hexafluorophosphate.

2. 2. The method for synthesizing a hexafluorophosphate according to claim 1, wherein the hexafluorophosphate is any one of lithium hexafluorophosphate, sodium hexafluorophosphate, and potassium hexafluorophosphate.

3. 2. The method for synthesizing hexafluorophosphate according to claim 1, wherein in step (1), the phosphorus pentahalide is one or two selected from phosphorus pentachloride and phosphorus pentabromide.

4. In step (1), the inert solvent is one or more selected from the group consisting of alkane solvents, halogenated alkane solvents, aromatic hydrocarbon solvents, and halogenated aromatic hydrocarbon solvents; The alkane solvent is selected from C4 to C10 linear, branched or cyclic alkanes; The halogenated alkane solvent is represented by the following general formula: C ｎ H （２ｎ＋２－ｍ） X ｍ (wherein X=F, Cl, Br, n=1 to 10, m=1 to 4), the carbon chain of the halogenated alkane may be linear, branched or cyclic; The aromatic hydrocarbon solvent is represented by the following general formula: 【Chemistry 1】 (wherein the substituent R is H, a C1-C6 linear, branched or cyclic alkyl substituent, n=0-6, and when there are multiple alkyl substituents on the benzene ring, the alkyl substituents may be the same or different.) The halogenated aromatic hydrocarbon solvent is represented by the following general formula: 【Chemistry 2】 (wherein the substituent R is H, a C1-C6 linear, branched or cyclic alkyl substituent, n=0-6, the substituent X=F, Cl, Br, m=0-6, n+m≦6, and when a plurality of alkyl and halogen atoms are substituted on the benzene ring, the substituted alkyl and halogen atoms may be the same or different).

5. The method for synthesizing hexafluorophosphate according to claim 1, characterized in that in step (1), the amount of the inert solvent used is 1 to 20 times the mass of the phosphorus pentahalide.

6. 2. The method for synthesizing hexafluorophosphate according to claim 1, wherein in step (2), the alkali metal halide salt is represented by the following general formula MX (M=Li, Na, K, X=F, Cl, Br):

7. The method for synthesizing a hexafluorophosphate according to claim 1, characterized in that in step (2), the amount of hydrogen fluoride used is 1 to 20 times the mass of the alkali metal halide salt.

8. The method for synthesizing hexafluorophosphate according to claim 1, characterized in that in step (2), the operation temperature of dissolving alkali metal halide salt in anhydrous hydrogen fluoride to obtain alkali metal fluoride salt hydrogen fluoride solution and the storage temperature of alkali metal fluoride salt hydrogen fluoride solution are -40 to 19°C.

9. The method for synthesizing a hexafluorophosphate according to claim 1, characterized in that, when the synthesis product is lithium hexafluorophosphate, the alkali metal halide salt is one or more selected from lithium fluoride, lithium chloride, and lithium bromide; when the synthesis product is sodium hexafluorophosphate, the alkali metal halide salt is one or more selected from sodium fluoride, sodium chloride, and sodium bromide; and when the synthesis product is potassium hexafluorophosphate, the alkali metal halide salt is one or more selected from potassium fluoride, potassium chloride, and potassium bromide.

10. 2. The method for synthesizing hexafluorophosphate according to claim 1, wherein in step (3), the reactor is a microreactor.

11. The method for synthesizing a hexafluorophosphate according to claim 1, characterized in that in step (3), the ratio of the phosphorus pentahalide inert solvent solution and the alkali metal fluoride salt hydrogen fluoride solution fed to the reactor per unit time is 0.8 to 1.2:1, that is, the ratio of the amount of phosphorus contained in the phosphorus pentahalide inert solvent solution fed to the reactor per unit time to the amount of alkali metal contained in the alkali metal fluoride salt hydrogen fluoride solution.

12. The method for synthesizing hexafluorophosphate according to claim 1, wherein in step (3), the reaction temperature is −40 to 100° C. 。

13. The method for synthesizing hexafluorophosphate according to claim 1, characterized in that in step (4), the gas-liquid separation operation temperature is -40 to 19°C. 。

14. The method for synthesizing hexafluorophosphate according to claim 1, characterized in that in step (5), the temperature of the hydrogen fluoride removal operation is 20 to 100°C.

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