阅读说明：本技术 一种六氟磷酸锂的连续生产系统 (Continuous production system of lithium hexafluorophosphate ) 是由 任建纲 张海兵 马小红 刘海岛 杨青 章琪 陈慧闯 于 2019-12-10 设计创作，主要内容包括：本发明涉及一种六氟磷酸锂的连续生产系统。该连续生产系统包含五氟化磷发生器(2)、微通道反应器A(3)、气液分离器A(4)、微通道反应器B(6)、气液分离器B(7),五氟化磷发生器(2)生成的气体通入到微通道反应器A(3)中,微通道反应器A(3)的输出物料进入气液分离器A(4),气液分离器A(4)分离出来的气体进入微通道反应器B(6)作为反应原料继续反应。微通道反应器B(6)的输出物料进入气液分离器B(7),气液分离器B(7)分离出来液体组分,输送到微通道反应器A(3)中。循环利用原料和副产物,提高了原料的转化率和利用率,降低了成本。(The invention relates to a continuous production system of lithium hexafluorophosphate. The continuous production system comprises a phosphorus pentafluoride generator (2), a microchannel reactor A (3), a gas-liquid separator A (4), a microchannel reactor B (6) and a gas-liquid separator B (7), wherein gas generated by the phosphorus pentafluoride generator (2) is introduced into the microchannel reactor A (3), the output material of the microchannel reactor A (3) enters the gas-liquid separator A (4), and the gas separated by the gas-liquid separator A (4) enters the microchannel reactor B (6) to be used as reaction raw materials for continuous reaction. The output material of the microchannel reactor B (6) enters a gas-liquid separator B (7), and a liquid component is separated out by the gas-liquid separator B (7) and is conveyed to the microchannel reactor A (3). The raw materials and the byproducts are recycled, the conversion rate and the utilization rate of the raw materials are improved, and the cost is reduced.)

1. A continuous production system of lithium hexafluorophosphate is characterized in that: the continuous production system comprises a phosphorus pentafluoride generator (2), a microchannel reactor A (3), a gas-liquid separator A (4), a microchannel reactor B (6) and a gas-liquid separator B (7) so as to contain PF₅The gas and the HF solution dissolved with LiF are used as raw materials to carry out reverse circulation reaction, the gas generated by the phosphorus pentafluoride generator (2) is introduced into the microchannel reactor A (3), the output material of the microchannel reactor A (3) enters the gas-liquid separator A (4), the gas separated by the gas-liquid separator A (4) enters the microchannel reactor B (6) to be used as reaction raw materials to continue reaction, the output material of the microchannel reactor B (6) enters the gas-liquid separator B (7), and the liquid component separated by the gas-liquid separator B (7) is conveyed into the microchannel reactor A (3).

2. The system for the continuous production of lithium hexafluorophosphate of claim 1, wherein said reverse cycle reaction comprises the following features: phosphorus pentafluoride generationPF mixed gas generated in the device (2)₅HCl and entrained HF gas are introduced into a microchannel reactor A (3), and meanwhile, HF solution dissolved with LiF, PF is conveyed into the microchannel reactor A (3) by a pump₅And LiF in the HF solution in the microchannel reactor A (3).

3. The continuous lithium hexafluorophosphate production system of claim 1, wherein said microchannel reactor B (6) comprises at least two feed streams: the gas separated by the gas-liquid separator A (4) contains unreacted PF₅And entrained HF, HCl components, and another HF solution with dissolved LiF and LiPF 6.

4. The continuous production system of lithium hexafluorophosphate according to claim 3, wherein the reaction raw material PF in the microchannel reactor B (6) is controlled₅And LiF in a molar ratio of 1: 1-2.

5. The system for the continuous production of lithium hexafluorophosphate of claim 2, wherein said reverse cycle reaction further comprises the following features: the liquid component separated by the gas-liquid separator B (7) contains LiPF₆And unreacted LiF.

6. The system for the continuous production of lithium hexafluorophosphate of claim 2, wherein said reverse cycle reaction further comprises the following features: the output material of the microchannel reactor A (3) enters a gas-liquid separator A (4), the liquid mixture separated by the gas-liquid separator A (4) sequentially enters a synthesis liquid tank (5) and a crystallization tank (9) for crystallization of lithium hexafluorophosphate, and the product after crystallization and filtration contains LiPF₆Is fed to microchannel reactor B (6) as a third feed stream.

7. The continuous production system of lithium hexafluorophosphate according to claim 2, wherein said reverse circulation reaction further comprises the following features that the gas separated in the gas-liquid separator B (7) is sent to the HF-HCl separation system (8) through a pressurizing device, the HCl in the top of the separation system (8) is absorbed into industrial hydrochloric acid through water, and the HF in the bottom can be recycled as the reaction raw material.

8. The continuous production system of lithium hexafluorophosphate according to claim 6, wherein the crystallization tank (9) is used for crystallizing lithium hexafluorophosphate in a cooling state, and the drying system (10) is used for drying and removing acid after crystallization and filtration to obtain the lithium hexafluorophosphate product.

9. A lithium hexafluorophosphate product prepared by the continuous production system of lithium hexafluorophosphate of claim 1, wherein the purity of the product is 99.98% or more, and the impurity species and contents are as follows: water content less than or equal to 20ppm, free acid (calculated by HF) less than or equal to 90 ppm; insoluble matter is less than or equal to 200 ppm; sulfate (in SO)₄Calculated by Cl is less than or equal to 5ppm, chloride (calculated by Cl) is less than or equal to 2ppm, and other various metal ions are less than or equal to 1 ppm.

Technical Field

The invention relates to a continuous production system of lithium hexafluorophosphate, in particular to a continuous production system of lithium hexafluorophosphate based on a microchannel reactor and a lithium hexafluorophosphate product prepared by applying the continuous production system.

Background

Lithium hexafluorophosphate is currently the most widely used electrolyte salt in commercial lithium ion batteries. With the rapid development of the electronic industry and the continuous expansion of new energy fields in the future, the demand for high-performance batteries is increasing, and the market demand for lithium hexafluorophosphate will show a rapid increase trend. Lithium hexafluorophosphate, english name: lithonium hexafluoro phosphate, structural formula: LiPF₆The electrolyte is white crystal or powder, has the relative density of 1.5, is easy to absorb moisture and decompose when exposed in water or humid air, particularly quickly decomposes in the air due to the action of water vapor, and releases PF5 to generate white smoke, has an erosion effect on eyes, skin, particularly lung, is unstable in heating, does not react with strong oxidizing agents, strong acids and the like, is easy to dissolve in water, and is also soluble in organic solvents such as methanol, ethanol, acetone, carbonates and the like.

Based on the physicochemical property of lithium hexafluorophosphate, the lithium hexafluorophosphate is synthesized under the technological conditions of high temperature, low temperature and the like, the production process requires anhydrous and anaerobic operation, the raw materials require high-purity refining, and the lithium hexafluorophosphate has the characteristics of strong corrosivity and the like, the production difficulty is relatively high, and the requirements on equipment and operators are strict. Lithium hexafluorophosphate product should avoid being heated to damp as far as possible to avoid unstability, decomposition by heating, and easy moisture absorption decomposition when meeting water. Therefore, the preparation process of lithium hexafluorophosphate is relatively complex, the working conditions of vacuum/pressurization, strong corrosion, easy hydrolysis/pyrolysis of products are involved, a constant-temperature, constant-humidity and dust-free high-cleanness preparation environment is needed, the equipment investment is large, the production cost is high, and the development is limited by high cost.

At present, the preparation routes of lithium hexafluorophosphate mainly include the following: the gas-solid direct reaction method, the solvent method and the ion exchange method, wherein the HF solvent method is the process which is most researched, the technology is the most mature and the industrial application is the most extensive.

The gas-solid reaction method is the original preparation process of lithium hexafluorophosphate, and PF is used by U.S. fluorine scientist J.H. Simmons in 1950₅The gas and LiF directly react in a nickel container under the conditions of high temperature and high pressure to prepare lithium hexafluorophosphate, the specific process is that LiF is treated by anhydrous HF to form porous LiF, and then PF is introduced₅The gas reacts with porous LiF to obtain LiPF₆The reaction equation is as follows: PF (particle Filter)₅(gas) + LiF (solid) = LiPF₆

The generated lithium hexafluorophosphate completely coats LiF solid particles and prevents further reaction, so that the lithium hexafluorophosphate obtained by the method has low purity and low yield, and is difficult to realize large-scale production.

The ion exchange method is a method of obtaining lithium hexafluorophosphate by subjecting hexafluorophosphate and a lithium-containing compound to an ion exchange reaction in an organic solvent. Since sodium, potassium, ammonium and organic amine salts of hexafluorophosphate have better thermal stability and hydrothermal stability, and a high-purity substance is easily prepared, potassium hexafluorophosphate (KPF) is prepared first₆) Sodium hexafluorophosphate (NaPF)₆) And ammonium hexafluorophosphate (NH)₄PF₆) And then converted to lithium hexafluorophosphate. But the purity of the product prepared by the ion exchange method is relatively low,the other hexafluorophosphates used in the reaction are generally present in excess and must be further purified; by using Na⁺、K⁺、NH⁴⁺And the like, the method has the possibility of generating alcohols by side reaction with an organic solvent, increases the cost for removing impurities and the process flow, and has high cost, thereby causing difficulty in realizing industrialization.

The solvent method comprises the following steps: organic solvent processes and inorganic solvent processes. The commonly used organic solvent is low alkyl esters such as ethers, EC, DEC and DMC, and acetonitrile. The difficulty of the preparation process of the ether solvent is that the crystallization separation of lithium hexafluorophosphate in the ether solvent is difficult, and the lithium hexafluorophosphate and the ether solvent form a complex which is dissolved in the solvent. When only ether is used as a solvent, lithium hexafluorophosphate is difficult to cool, crystallize and separate, and when polyether is used as a solvent, the polyether ligand in the crystallized complex is difficult to remove.

EC. The low alkyl esters such as DEC, DMC and the like are common electrolyte solvents of lithium ion batteries, have good solubility for lithium hexafluorophosphate, and the method for preparing the lithium hexafluorophosphate has the advantages of easy reaction control and high yield. But PF is in the preparation process₅The color of the solvent is deepened and impurities are increased due to easy reaction with an organic solvent; meanwhile, the method is mainly used for preparing the electrolyte, and lithium hexafluorophosphate crystals are difficult to separate at present.

Acetonitrile has very little corrosion to equipment, and is also a promising method for preparing lithium hexafluorophosphate by using the acetonitrile as a solvent. Acetonitrile, however, also presents toxicity and may have adverse effects on both the operator and the environment.

In conclusion, the organic solvent method has the defects that the reaction raw materials and part of organic solvent can undergo polymerization, decomposition and other reactions, so that a high-purity product is difficult to obtain, and the method is suitable for preparing a lithium hexafluorophosphate liquid solvent product.

Common inorganic solvents are HF, SO₂By using SO₂As a solvent, the lithium hexafluorophosphate product has a very low HF content, but SO₂The content is higher, and the product can be used only by further purification.

The process for preparing lithium hexafluorophosphate by using the HF solvent method is a mature process at present and is a production method which is most easy to realize industrialization.

The HF solvent method is to dissolve raw material lithium halide in HF by using HF as a reaction medium, and then high-purity PF₅And after gasification, introducing the gas into a solvent for reaction to generate lithium hexafluorophosphate crystals, and after the reaction is finished, crystallizing, separating, drying and the like to obtain the lithium hexafluorophosphate product.

In 1960, R.D.W.Kmmitt et al used a stainless steel vessel, LiF was dissolved in anhydrous HF, and PF was introduced at 25 deg.C₅And volatilizing to remove HF after the reaction is maintained for 12 hours to obtain lithium hexafluorophosphate crystals.

Lithium hexafluorophosphate has a very high attention, but mass production cannot be achieved all the time, mainly because of the great difficulty of the production technology. The technical difficulties of the HF solvent method are analyzed as follows:

(1) production safety

The currently commonly used HF solvent method, PF₅The preparation of (A) is usually carried out in two ways, one being HF and PCl₅Reaction to form PF₅And HCl, and the other is the reaction of fluorine gas and yellow phosphorus to form PF₅。

In either way, the reaction process uses anhydrous HF as a carrier, and requires a very low temperature environment in order to dissolve LiF in anhydrous HF to form a homogeneous solution. The anhydrous HF has strong corrosivity, is toxic and harmful, has very dangerous reaction process, is usually explosive and difficult to control, and causes great harm to the environment and personnel when any point is leaked in the reaction process. When the reaction is complete, the large excess of HF must be removed. Many unsafe factors existing in the production are overcome, a large amount of reagents are consumed, the process can corrode equipment, high requirements on equipment corrosion resistance and production environment are provided, and equipment investment is high. Lithium hexafluorophosphate products are sensitive to moisture, and the guarantee of anhydrous operation is very important, so that strict sealing is required in the product transfer process in the reaction process, and the production cost of lithium hexafluorophosphate is greatly increased by the factors.

(2) Purity and control of free acid

The purity of lithium hexafluorophosphate and the content of free acid, insoluble substances and other metal ions are important indexes influencing the performance of the lithium battery, and the purity of the lithium hexafluorophosphate serving as a lithium hexafluorophosphate product for the lithium ion secondary battery is more than 99.95 percent, the residual acidity is less than or equal to 90ppm, and the moisture mass fraction is less than or equal to 0.0020 percent.

The free acid is mainly from the LiPF6. HF compound formed by the solvent HF and the LiPF6, and the LiPF6. HF compound is coated in the LiPF6 crystal and is difficult to remove, so that the HF content in the product is not easy to reduce to 10 multiplied by 10^－6. Free acid is generated, and has great influence on the performance of the lithium ion battery.

On the one hand, insoluble substances are from various impurities, and high-purity raw materials are adopted or subjected to high-purity treatment as far as possible, so that the contents of moisture, metals, free acid and the like in the raw materials are strictly limited; on the other hand, the lithium hexafluorophosphate is decomposed when meeting water and also when being heated, and insoluble substances are formed after decomposition, including some mixed element ions.

Therefore, the difficulty of realizing low free acid and low insoluble substances is very great only by controlling the production process. Moreover, the two indexes are restricted with each other, and if the purpose of reducing free acid is achieved, the production process needs to generate higher temperature, so that insoluble substances cannot be guaranteed.

In the production process of lithium hexafluorophosphate, in order to reduce the production cost and improve the product purity, there have been related studies and experiments to solve the above-mentioned difficulties by improving the process, particularly by adjusting the reaction apparatus, and the related patent applications have been made as follows:

CN1850593A proposes a method for purifying lithium hexafluorophosphate, which is to use an intermediate product PF in the production process of lithium hexafluorophosphate₅Purifying the HCl mixed gas, and introducing the HCl mixed gas into a drying device of lithium hexafluorophosphate to ensure that PF is carried out₅LiF and lithium phosphorus oxyfluoride LiPO entrained with lithium hexafluorophosphate in preparation process_xF_yThe impurities react and are converted to lithium hexafluorophosphate. The purification method has strong pertinence and single effect, achieves the effect of reducing the content of free acid, has the content of the free acid less than 100ppm, but cannot effectively control heavy metal ions of insoluble impuritiesAnd the content of insoluble matter in DMC.

US5935541A is modified by adjusting the feed mode and the process of the reactor, in particular by feeding (A) gaseous PF in countercurrent or cocurrent₅Or contains PF₅And HCl with (B) LiF in HF in a column (which may be an empty column, a packed column, or a sieve tray column) having sufficient units to effect PF at a selected temperature, pressure, and molar ratio of the two reactants₅Reaction with LiF, PF in the column₅Completely or substantially completely absorbed. The method has sufficient gas-liquid contact and high reaction efficiency, but the PF is adopted in the reaction₅Contact with LiF must be done with great care to avoid plugging while ensuring that the number of conversion units in the column is sufficient to achieve good conversion yields. Therefore, the required equipment has the problems of large volume and large investment.

CN101544361A, the raw material mixture enters a multistage tubular reactor (2) and then a multistage synthesis reaction is carried out; and a trace amount of unreacted LiF is again mixed with the PF of high concentration₅And the gas is in contact reaction in the post-mixing reactor, so that the complete conversion of LiF is realized. The utilization rate of LiF is improved by increasing the reactors, reaction circulation and raw material circulation are not realized in the true sense, and PF which is not completely reacted₅HF, impurities are not sufficiently removed, impurities in the lithium hexafluorophosphate product such as insoluble dimethyl carbonate (DMC), sulfates (in SO)₄Meter) is higher.

CN101423207A gaseous PF₅Introducing the solution into an ultramicro bubble generating device, generating microbubbles with the diameter of 0.1-2000 mu m, and reacting the microbubbles with LiF dissolved in anhydrous HF in advance in a reaction device to generate a lithium hexafluorophosphate crude product. The gas-liquid mixing efficiency is high and the reaction speed is high by using the ultramicro bubble generating device; the blockage phenomenon of a solid product cannot be generated, but the content of impurities in the obtained product is high, and the purity of the product can only reach 99.8%.

CN107244681A is provided with agitating unit in preparing lithium hexafluorophosphate continuous evaporation crystallizer, adopts agitating unit to realize that the crystal is more even. Compared with the traditional crystallizer, the crystallizer has smaller volume and high processing capacity. But larger and purer products can be obtained only under the evaporation condition of low vacuum degree; in addition, the entire crystallization process needs to be carried out under negative pressure operation to better evaporate the anhydrous HF. Therefore, the crystallization conditions are relatively strict, and vacuum and negative pressure are required, which puts high demands on auxiliary equipment for crystallization, thereby increasing the production cost.

CN 207756147U relates to a turbine reactor for preparing lithium hexafluorophosphate, which comprises a reactor body, an electric motor device and a gas introducing pipe. The motor device is fixed at the bottom of the reactor body and comprises an output shaft which is connected to a stirring blade, the stirring blade extends into the inner cavity, the PF₅Gas enters from the upper part and is dispersed into small bubbles under the action of the blades, so that the contact area with the solution is increased, the reaction speed is accelerated, and the PF (particle Filter) is improved₅The utilization ratio of (2).

CN106745096A mentions that phosphorus pentafluoride gas and alkali metal fluoride salt solution are metered and then are introduced into a microchannel reactor for mixing and reaction, and the obtained reaction liquid is crystallized and dried to obtain the hexafluorophosphate alkali metal salt. However, the yield of the lithium hexafluorophosphate product in the patent application is only 98.5% at most, and the pure phosphorus pentafluoride gas is adopted, so that the cost is high, and meanwhile, the specific purity of the lithium hexafluorophosphate product and a method for improving the quality of the lithium hexafluorophosphate product are not disclosed.

It is thus clear that traditional hydrofluoric acid solvent method is prepared lithium hexafluorophosphate, mostly is intermittent type nature technology, and production efficiency is not high, the purity is low, the production volume of accessory substance is big and difficult to handle, and present improvement technology or device only adjust to the reaction of single step, and the effect is limited, needs urgently to provide a production system of lithium hexafluorophosphate, improves lithium hexafluorophosphate purity, promotes easy operability, reduction in production cost.

Disclosure of Invention

Aiming at the problems, the invention provides a continuous production system of lithium hexafluorophosphate based on a microchannel reactor, which utilizes a reverse circulation mode to fully utilize and convert reaction raw materials, designs a separation and recovery device in the process and reduces the consumption of the raw materials.

The microchannel reactor comprises a straight-flow type channel structure or a reinforced hybrid type channel structure, wherein the straight-flow type channel structure is a tubular structure, the cross section of the reinforced hybrid type channel structure can have any shape, such as but not limited to a T-shaped structure, a Z-shaped structure, a V-shaped structure, an S-shaped structure, a spherical structure, a hemispherical structure, a spherical belt baffle structure, a water drop structure, a funnel structure, a triangular structure, a heart structure or an umbrella structure, and the channel equivalent diameter is 0.5mm ~ 10mm, preferably 1.5mm ~ 3mm, and the liquid holding volume is 10 ~ 4000ml, preferably 25 ~ 50 ml.

The microchannel reactor has thousands of microchannels, so that the microchannel reactor has extremely large specific surface area which can reach hundreds of even thousands of times of the specific surface area of a common reaction kettle, thereby having excellent heat transfer and mass transfer capacity, and the optimal heat transfer coefficient can reach 1700 kW/(m 2K). The reactants in the micro-channel can perform high-efficiency heat exchange with the wall surface, the temperature uniformity is good, and the reaction bed layer is close to constant temperature, so that the PF (positive pressure filter) can be used for removing the impurities₅The heat released by the reaction with LiF in the HF solution can be timely and efficiently conducted and instantly absorbed, so that the lithium hexafluorophosphate can not be heated and decomposed to form insoluble substances due to the reaction heat. The reaction temperature fluctuation is small and stable, and the stable operation of the chemical reaction is facilitated.

In the invention, a microchannel reactor is used for realizing high reaction speed and short reaction time, the reaction time of reactants in the reactor is 5 ~ 120 seconds, and is greatly shortened compared with the reaction time in the conventional reaction which is between 1 ~ 10 hours, moreover, the reactants containing HF enter the reactor in a continuous state, the reaction products containing LiPF6 are output from the reactor in a continuous state, the residence time of reaction materials HF and products LiPF6 in the reactor is short, the mutual interference is small, namely, the contact and reaction possibility of the products LiPF6 and the reactants HF are reduced, thereby effectively inhibiting the occurrence of side reaction of the lithium hexafluorophosphate and the HF, and achieving the purpose of reducing the free acid of the products.

The small channel size of microchannel reactors is an important safety factor, since the expansion of the flame is suppressed in the middle, so that such reactors can be operated in the explosive range without any additional special safety measures. When the method is applied to the preparation of lithium hexafluorophosphate by a hydrofluoric acid solvent method, although the problem of flame inhibition does not exist, the accident potential can be reduced, the accident hazard can be reduced, and the safety performance of operation is also improved.

The faces of the microchannel reactor reaction channel are defined by the reaction channel walls. These walls can be made of a hard material, so as to better ensure durability, corrosion resistance, high temperature resistance (200 ℃), high pressure resistance (100 bar) and good thermal conductivity. The hard material can be selected from: metals, metal alloys, silicon carbide, preferably the hard material is stainless steel, monel, nickel based alloy, hastelloy or silicon carbide.

And a continuous production system is adopted, so that the leakage caused by additionally arranging a device and transferring in the conventional batch reaction is avoided, and the safety is improved. Anhydrous HF is a high-risk chemical, and a series of reactions are carried out by dissolving LiF in HF, and the risk degree of crystallization, separation and drying treatment is relatively high. Meanwhile, the lithium hexafluorophosphate product is extremely sensitive to moisture and is easy to absorb moisture and hydrolyze, so that the operation in an anhydrous environment is extremely important. This requires good sealing of the equipment throughout the process. The continuous production system is easy to realize closed operation and is beneficial to improving the production efficiency.

The invention adopts two groups of micro-channel reactors, namely a micro-channel reactor A (3) and a micro-channel reactor B (6)And the full reaction of the raw materials is ensured by a reverse circulation mode. For a conventional two-stage series of microchannel reactors, the output stream A of microchannel reactor A (3) is typically fed to_{Output of}The product is directly used as an input material flow of the microchannel reactor B (6), so that the retention time of reactants in the reactor is prolonged, the content of reaction products is increased, the content of the reactants in the reactant flow is reduced, the LiF reaction or the PF5 reaction in the reactant flow cannot be completed, the LiF reactant in the reaction product is remained instead, the purity of the product cannot be ensured, and the incompletely reacted PF5 enters a gas post-treatment system along with HCL gas and is absorbed and treated by water, so that the consumption of raw materials is high. The output material flow of the microchannel reactor A (3) is conveyed to a gas-liquid separator A (4) for gas-liquid separation, and the liquid, namely the component containing lithium hexafluorophosphate, is conveyed to a synthesis liquid tank (5) for storage. The separated gas containing unreacted PF₅And entrained HF, HCl components, to microchannel reactor B (6), microchannel reactor B (6) comprising at least two feed streams: the gas separated by the gas-liquid separator A (4) contains unreacted PF₅And entrained HF, HCl components, and another HF solution with dissolved LiF and LiPF 6. PF (particle Filter)₅And LiF react to generate lithium hexafluorophosphate. Therefore, the invention adopts two groups of micro-channel reactors which are not simply connected in series, has the effect of not simply superposing the two groups of micro-channel reactors, combines the chemical reaction performance of the raw materials and the products, and adjusts the input material flow of the micro-channel reactor B (6), thereby realizing the purposes of controlling side reaction, improving the utilization rate of the raw materials and improving the purity of the products.

The continuous production system comprises a phosphorus pentafluoride generator (2), a microchannel reactor A (3), a gas-liquid separator A (4), a microchannel reactor B (6) and a gas-liquid separator B (7), wherein gas containing PCl5 and HF solution dissolved with LiF are used as raw materials to perform reverse circulation reaction, the gas generated by the phosphorus pentafluoride generator (2) is introduced into the microchannel reactor A (3), the output material of the microchannel reactor A (3) enters the gas-liquid separator A (4), the gas separated by the gas-liquid separator A (4) enters the microchannel reactor B (6) to be used as a reaction raw material to continue reaction, the output material of the microchannel reactor B (6) enters the gas-liquid separator B (7), and the liquid component separated by the gas-liquid separator B (7) is conveyed into the microchannel reactor A (3).

In order to reduce insoluble substances wrapped in a lithium hexafluorophosphate product and improve the product purity, LiF in the first microchannel reactor completely reacts, and PF5 in the second microchannel reactor completely reacts. Therefore, the method comprises the following steps:

microchannel reactor a (3) comprises at least two feed streams: one strand is HF solution dissolved with LiF; the other is mixed gas PF₅HCl and entrained HF gas. Further preferably, the PF in the microchannel reactor A (3) is controlled₅The raw materials are excessive so as to ensure the full conversion of reaction raw material LiF, and PF is preferably selected in the microchannel reactor A (3)₅And LiF in a molar ratio of 2 to 5:1, more preferably 2.5 to 4: 1.

Microchannel reactor B (6) comprises at least two feed streams: one is the gas separated by the gas-liquid separator A (4), namely the component containing unreacted PF5 and entrained HF and HCl, and the other is the HF solution dissolved with LiF and LiPF 6. The conversion rate can be further improved by adjusting the raw material ratio in the microchannel reactor B (6), and the excess of LiF raw material in the microchannel reactor B (6) is preferably controlled, so that the reaction raw material PF is ensured₅Preferably PF in the microchannel reactor B (6)₅And LiF in a molar ratio of 1:1 to 2, more preferably 1:1.1 to 1.3, still more preferably: 1:1.15-1.25.

It is further preferred that microchannel reactor a (3) comprises a third feed stream: a gas-liquid separator B (7) for separating a liquid component containing LiPF₆And unreacted LiF.

Further preferably, the output material of the microchannel reactor A (3) enters a gas-liquid separator A (4), the liquid mixture separated by the gas-liquid separator A (4) sequentially enters a synthesis liquid tank (5) and a crystallization tank (9) to crystallize lithium hexafluorophosphate, and the mother liquid after crystallization and filtration is stored in a mother liquid tank (11). The mother liquor in the mother liquor tank (11) is determined by quantitative analysisAfter the lithium hexafluorophosphate content is reached, the solution is sent to a LiF dissolving tank (12) to prepare a quantitative LiF dissolving solution. The HF solution containing lithium hexafluorophosphate dissolved a measured amount of LiF was fed to microchannel reactor B (6) for reaction, i.e. microchannel reactor B (6) contained a third feed stream: crystal filtered LiPF-containing₆An HF solution of (1).

In conclusion, the invention utilizes the good heat transfer performance of the microchannel reactor to shorten the reaction time from hours to dozens of seconds to several minutes, thereby obviously improving the efficiency and simultaneously ensuring the safety of anhydrous hydrofluoric acid reaction; the continuous production system is adopted, so that the closed operation is easy to realize, the leakage caused by the need of additionally arranging a device and transferring in the conventional intermittent reaction is avoided, and the production efficiency is improved; the reverse circulation mode is adopted, the raw materials and the byproducts are recycled, and the proportion of the reaction raw materials is further adjusted, so that the raw materials are reacted completely, the conversion rate of the raw materials is improved, and the cost of the raw materials is reduced; the HF and HCl separation system is arranged to fully separate HF and HCl, so that the treatment of mixed acid is reduced, industrial hydrochloric acid can be prepared, anhydrous HF can be recovered, and the consumption of raw materials and the treatment cost of three wastes are reduced.

The lithium hexafluorophosphate produced by the present invention may have a variety of application areas and, optionally, may be used as an electrolyte component for lithium ion batteries. When the lithium hexafluorophosphate is used as an electrolyte component of a lithium ion battery, the mass percentage of lithium hexafluorophosphate in the electrolyte is preferably 5-20 wt%. Preferably, the electrolyte also comprises LiPO₂F₂、LiBF₂C₂O₄. Preferably, the ratio of lithium hexafluorophosphate: LiPO₂F₂：LiBF₂C₂O₄The mass ratio of (50-90) to (5-40) to (5-30). Further preferred are (55-85), (10-30) and (10-25). The electrolyte also comprises 1, 2-bis (trifluoromethyl) benzene, and the mass percentage of the 1, 2-bis (trifluoromethyl) benzene in the electrolyte is 0.1-3 wt%. Preferably, the electrolyte also comprises ethylene carbonate, ethyl methyl carbonate and diethyl carbonate, the total mass percentage of the ethylene carbonate, the ethyl methyl carbonate and the diethyl carbonate in the electrolyte is 70-90wt%, and the ethylene carbonate, the ethyl methyl carbonate and the diethyl carbonate areThe mass ratio of the ethyl ester is 2.5-3.5: 4.5-5.5: 1.5-2.5.

Drawings

FIG. 1 shows a process flow diagram of a lithium hexafluorophosphate continuous production system of example 1;

FIG. 2 shows a process flow diagram of a lithium hexafluorophosphate continuous production system of example 2;

fig. 3 shows a process flow diagram of a lithium hexafluorophosphate continuous production system of example 3.

In the figure: 1-a solid conveyor; 2-a phosphorus pentafluoride generator; 3-microchannel reactor a; 4-gas-liquid separator a; 5-a synthesis liquid tank; 6-microchannel reactor B; 7-gas-liquid separator B; 8-a separation system; 9-a crystallization tank; 10-a drying system; 11-a mother liquor tank; 12-lithium fluoride dissolving tank.

Figure 4 shows an XRD pattern of a lithium hexafluorophosphate product of an embodiment of the present invention.

Detailed Description

The technical solution and effects of the present invention will be further described below by way of specific embodiments. The following embodiments are merely illustrative of the present invention, and the present invention is not limited to the following embodiments or examples. Simple modifications of the invention applying the inventive concept are within the scope of the invention as claimed.

The invention provides a continuous production system of lithium hexafluorophosphate based on a microchannel reactor, which comprises a PF₅A generator (2), a microchannel reactor A (3), a gas-liquid separator A (4), a microchannel reactor B (6), a gas-liquid separator B (7) to contain PF₅The gas and the HF solution dissolved with LiF are used as raw materials to carry out reverse circulation reaction.

The microchannel reactor A and the microchannel reactor B in the embodiment of the invention are reactors with the same structure, and are of reinforced mixed type channel structures, the cross section of each channel is of a heart-shaped structure, the equivalent diameter of each channel is 2mm, the liquid holding volume is 50ml, and the hard material of the channel wall is silicon carbide.

The continuous production system preferably uses PCl₅By having meteringThe solid conveyor (1) of the device conveys the HF-stored PF₅In the generator (2), PCl₅I.e. reaction with HF to form PF₅And HCl as a byproduct, as shown in formula (1). Further the solid conveyor (1), preferably a solid conveyor (1) with a metering device; the HF-stored phosphorus pentafluoride generator (2) is preferably an HF-stored phosphorus pentafluoride generator (2) having a cooling jacket, and is further preferably provided with a stirring device.

5HF+PCl₅→5HCl+PF₅（1）

Mixed gas PF generated in phosphorus pentafluoride generator (2)₅HCl and entrained HF gas are introduced into the microchannel reactor A (3), and the HF solution dissolved with LiF is simultaneously pumped into the microchannel reactor A (3). PF (particle Filter)₅And LiF in the HF solution rapidly react and emit reaction heat as shown in chemical formula (2).

LiF (liquid) + PF₅(gas) → LiPF₆（2）

Further preferably, the PF in the microchannel reactor A (3) is controlled₅The raw materials are in excess so as to ensure the sufficient conversion of the reaction raw material LiF, and the molar ratio of PF5 to LiF in the microchannel reactor A (3) is preferably 2-5:1, and more preferably 2.5-4: 1.

The reaction temperature of the microchannel reactor A (3) is controlled to be 0-17 ℃, and the preferred reaction temperature range is 3-10 ℃. The residence time of the reaction mass in the microchannel reactor A (3) is 5 to 120 seconds, with an optimum residence time of 5 to 30 seconds.

The gas-liquid mixed material coming out of the microchannel reactor A (3) mainly comprises a target product lithium hexafluorophosphate and unreacted PF₅And unreacted HCl and HF.

And the gas-liquid mixed material from the microchannel reactor A (3) enters a gas-liquid separator A (4) for gas-liquid separation, and the liquid, namely the component containing lithium hexafluorophosphate, is conveyed to a synthesis liquid tank (5) for storage. The separated gas containing unreacted PF₅And entrained HF, HCl components, are passed to microchannel reactor B (6), and LiF andand reacting LiPF6 in HF solution. PF (particle Filter)₅And LiF in the HF solution rapidly react and emit reaction heat as shown in chemical formula (3).

LiF + PF5 (gas) → LiPF₆（3）

It is further preferred to control the LiF feed in the microchannel reactor B (6) in excess to ensure sufficient conversion of the reaction feed PF5, and it is preferred that the molar ratio of PF5 to LiF in the microchannel reactor B (6) is 1:1 to 2, further preferred 1:1.1 to 1.3, further preferred: 1:1.15-1.25.

The reaction temperature of the microchannel reactor B (6) is controlled to be 0-17 ℃, and the preferred reaction temperature range is 3-10 ℃. The residence time of the reaction mass in the microchannel reactor B (6) is 5 to 120 seconds, with a residence time of 5 to 30 seconds being preferred.

The gas-liquid mixed material coming out of the micro-channel reactor B (6) mainly comprises target products of lithium hexafluorophosphate, HCl and HF.

And the gas-liquid mixed material from the micro-channel reactor B (6) enters a gas-liquid separator B (7), the gas separated in the gas-liquid separator B (7) contains HCl and HF, and the separated liquid contains lithium hexafluorophosphate and unreacted LiF.

The gas separated in the gas-liquid separator B (7) is preferably sent to an HF, HCl separation system (8) through a pressurizing means. The HCl at the top of the separation system (8) is absorbed by water to form industrial hydrochloric acid, and the HF at the bottom can be recycled as a reaction raw material. The HF and HCl separation system (8) is preferably a separation tower.

The liquid separated in the gas-liquid separator B (7), namely the mixed liquid containing lithium hexafluorophosphate and unreacted LiF is conveyed to the microchannel reactor A (3) to be continuously neutralized with PF in the microchannel reactor A₅And (4) reacting to ensure that the LiF in the mixed solution is completely reacted.

And (3) conveying the synthetic liquid in the synthetic liquid tank (5) to a crystallization tank (9) to crystallize lithium hexafluorophosphate, crystallizing the lithium hexafluorophosphate in a cooling state, filtering the crystals, and drying and removing acid in a drying system (10) to obtain a lithium hexafluorophosphate product.

Further preferably, the filtered mother liquor is stored in a mother liquor tank (11), the mother liquor in the mother liquor tank (11) is quantitatively analyzed to determine the content of lithium hexafluorophosphate in the mother liquor, then the mother liquor is sent to a LiF dissolving tank (12) to carry out quantitative preparation of LiF dissolving solution, and HF solution containing lithium hexafluorophosphate is dissolved with quantitative LiF and then is sent to a microchannel reactor B (6) to react, so that the reaction system can be continuously operated.

The lithium hexafluorophosphate product prepared by the continuous production system of lithium hexafluorophosphate can be obtained with high purity without further purification. The purity can reach more than 99.98 percent, and preferably more than 99.99 percent. The impurity species and contents are as follows: moisture content of less than or equal to 20ppm, preferably less than or equal to 15 ppm; free acid (calculated as HF) is less than or equal to 90ppm, preferably less than or equal to 80ppm, and more preferably less than or equal to 50 ppm; insoluble matter is less than or equal to 200ppm, preferably less than or equal to 160ppm, and more preferably less than or equal to 110 ppm; sulfate (in SO)₄Measured) is less than or equal to 5ppm, preferably less than or equal to 4 ppm; chloride (calculated by Cl) is less than or equal to 2 ppm; the content of other metal ions is less than or equal to 1 ppm.