Continuous preparation process and device of liquid lithium hexafluorophosphate

Abstract

Disclosed in the present invention are a continuous preparation process and device of liquid lithium hexafluorophosphate. The continuous preparation process comprises operation steps of: A10), continuously feeding a lithium fluoride suspension into the top of a hexafluorination reaction plate tower; and continuously feeding gas-phase high-purity phosphorus pentafluoride into the bottom of the hexafluorination reaction plate tower; A20), carrying out a reaction in the hexafluorination reaction plate tower, and enabling the reaction product to enter a tower bottom storage tank from the tower bottom of the hexafluorination reaction tower; A30), introducing part of the remaining reaction product output by means of a circulating heat exchanger into a liquid lithium hexafluorophosphate product extraction tank, and introducing the other part into a lithium fluoride suspension formulation kettle; and A40), connecting a filter to a product extraction end of the product extraction tank for removing redundant reacted solid-phase materials, so as to obtain liquid lithium hexafluorophosphate, wherein the hydrogen chloride content of the liquid lithium hexafluorophosphate is less than 25 ppm, and hydrogen fluoride is not detected. The present invention has a high continuous level and is stable, does not require an extra deacidification treatment, has a significantly higher output efficiency, and does not cause hidden dangers of halting production and maintenance due to problems of blocking, etc.

Description

Continuous preparation process and device of liquid lithium hexafluorophosphate

[0001] The present application claims priority to the Chinese patent application No. 2024109684838, filed on July 18, 2024, and entitled "Continuous preparation process and device of liquid lithium hexafluorophosphate", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application belongs to the technical field of battery electrolyte solutes, and specifically relates to a continuous preparation process and device of liquid lithium hexafluorophosphate. BACKGROUND

[0003] Lithium hexafluorophosphate (LiPF6) is currently the most preferred commercial electrolyte solute in lithium ion batteries because of its good ionic conductivity and electrochemical stability, and its waste battery processing technology is simple and has little impact on the ecological environment. The current synthesis method of lithium hexafluorophosphate mainly focuses on the synthesis of solid lithium hexafluorophosphate, and the main synthesis methods include gas-solid reaction method, HF solvent method, organic solvent method and ion exchange method, etc. However, these methods generally have the disadvantages of difficult continuous implementation and difficult removal.

[0004] Compared with solid lithium hexafluorophosphate, liquid lithium hexafluorophosphate not only has the advantages of storage stability and convenient transportation, but also can be directly used in lithium ion battery electrolyte without dissolution. Therefore, the development of liquid lithium hexafluorophosphate has great practical significance for reducing the industrialization cost of lithium ion batteries and improving market competitiveness.

[0005] Further, the existing continuous synthesis process of liquid lithium hexafluorophosphate contains a high content of hydrogen chloride after obtaining liquid lithium hexafluorophosphate, and hydrogen fluoride can also be detected, so a special deacidification process is still needed afterwards, the treatment process is relatively cumbersome, and the overall continuous degree of the synthesis process is also limited. In addition, in the preparation of lithium hexafluorophosphate, lithium fluoride needs to be mixed with an organic solvent (such as a carbonate solvent). Since lithium fluoride is difficult to dissolve in the organic solvent, although real-time stirring is used in the mixing preparation kettle, it is difficult to ensure that lithium fluoride and the organic solvent are always fully mixed, especially when the lithium fluoride suspension in the mixing preparation kettle is transported to the top of the synthesis tower, there may be a risk of blockage in the transportation pipeline, which affects the continuous synthesis of liquid lithium hexafluorophosphate.

[0006] Therefore, the present applicant hopes to conduct in-depth special research on the continuous synthesis process of liquid lithium hexafluorophosphate to further improve the industrialization batch continuous production efficiency. TECHNICAL PROBLEM

[0007] Therefore, the present application aims to provide a continuous preparation process and device for liquid lithium hexafluorophosphate, which has a high level of continuousness and stability, and does not have the problem of shutdown maintenance due to blockage and the like; and the high-purity liquid lithium hexafluorophosphate provided by the present application can be directly applied to industrialization without additional deacidification treatment, and has a significantly higher output efficiency. Technical solutions

[0008] The technical solutions adopted by the present application are as follows:

[0009] A continuous preparation process for liquid lithium hexafluorophosphate comprises the following operation steps:

[0010] A10) providing lithium fluoride suspension through a lithium fluoride suspension preparation kettle, and continuously feeding the lithium fluoride suspension to the top of a hexafluoride reaction plate column; providing gaseous high-purity phosphorus pentafluoride through a high-purity phosphorus pentafluoride storage tank, and continuously feeding the gaseous high-purity phosphorus pentafluoride to the bottom of the hexafluoride reaction plate column, wherein the purity of the gaseous high-purity phosphorus pentafluoride is greater than 96%;

[0011] A20) the lithium fluoride and the gaseous high-purity phosphorus pentafluoride react in the hexafluoride reaction plate column under normal temperature and pressure, and the reaction product enters a bottom storage tank from the bottom of the hexafluoride reaction column, wherein the mass ratio of the lithium fluoride to the gaseous high-purity phosphorus pentafluoride is 1:4-6;

[0012] A30) the bottom storage tank returns the reaction product to the hexafluoride reaction plate column through a circulating heat exchanger at a preset reflux ratio, and the remaining reaction product output by the circulating heat exchanger is divided into two parts, one part is punched into a liquid lithium hexafluorophosphate product extraction tank, and the other part is punched into the lithium fluoride suspension preparation kettle; and the preset reflux ratio is 4-8:1;

[0013] A40) a filter is connected to the product extraction end of the product extraction tank to remove the excess solid material after the reaction, and liquid lithium hexafluorophosphate is obtained, wherein the hydrogen chloride content of the liquid lithium hexafluorophosphate is less than 25 ppm, preferably less than 15 ppm, and no hydrogen fluoride is detected.

[0014] Preferably, the preparation step of the gaseous high-purity phosphorus pentafluoride comprises: feeding the phosphorus pentafluoride rectification column feed into a fluorosulfonate absorption column through a phosphorus pentafluoride buffer tank to adsorb and remove hydrogen fluoride and hydrogen chloride in the phosphorus pentafluoride rectification column feed under normal temperature and pressure, so as to obtain the gaseous high-purity phosphorus pentafluoride.

[0015] Preferably, the fluorosulfonate absorption column comprises a first fluorosulfonate absorption column and a second fluorosulfonate absorption column connected in series.

[0016] Preferably, in the lithium fluoride suspension preparation kettle, the lithium fluoride is fully mixed with the organic solvent by ultrasonic effect; wherein the solvent is any one or a mixture of any several of dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; and / or the mass ratio of lithium fluoride to organic solvent ranges from 1:8 to 20.

[0017] Preferably, the lithium fluoride is in powder form, and its maximum particle size is not more than 0.2 mm, preferably not more than 0.18 mm.

[0018] Preferably, the inner wall of the conveying pipeline between the lithium fluoride suspension preparation kettle and the top of the hexafluoro reaction plate tower is polished to be smooth, wherein the polishing accuracy of the inner wall of the conveying pipeline is less than or equal to 0.6 microns.

[0019] Preferably, the hexafluoro reaction plate tower is provided with at least 40 tower plates distributed in an up-down interval, wherein the tower plate sieve hole diameter of the tower plate close to the tower top is larger than the tower plate sieve hole diameter of the tower plate close to the tower kettle.

[0020] Preferably, the hexafluoro reaction plate tower comprises at least a first tower plate section, a second tower plate section, and a third tower plate section from bottom to top; wherein the first tower plate section is provided with at least 10 first tower plates distributed in an up-down interval, and the tower plate sieve hole diameter of the first tower plate ranges from 2 to 4 mm; the second tower plate section is provided with at least 10 second tower plates distributed in an up-down interval, and the tower plate sieve hole diameter of the second tower plate ranges from 6 to 9 mm; the third tower plate section is provided with at least 10 third tower plates distributed in an up-down interval, and the tower plate sieve hole diameter of the third tower plate ranges from 12 to 16 mm.

[0021] Preferably, a device for continuously preparing lithium hexafluorophosphate according to the above-mentioned process comprises a lithium fluoride suspension preparation kettle, a high-purity phosphorus pentafluoride storage tank, and a hexafluoro reaction plate tower; wherein the liquid outlet of the lithium fluoride suspension preparation kettle is connected to the top of the hexafluoro reaction plate tower through a suspension conveying pipeline, and the outlet of the high-purity phosphorus pentafluoride storage tank is connected to the tower kettle of the hexafluoro reaction plate tower through a conveying pipeline.

[0022] Preferably, the high-purity phosphorus pentafluoride storage tank is connected to the gas phase output end of a fluorosulfonate absorption tower, the gas phase input end of the fluorosulfonate absorption tower is connected to the incoming material outlet of a phosphorus pentafluoride rectification tower through a phosphorus pentafluoride buffer tank; a lithium fluoride suspension feed tank is provided on the suspension conveying pipeline, the lithium fluoride suspension preparation kettle is connected to the hexafluoro reaction plate tower through the lithium fluoride suspension feed tank; wherein the bottom of the hexafluoro reaction plate tower is connected to a bottom storage tank, the bottom storage tank is connected to the input end of a circulating heat exchanger, the output end of the circulating heat exchanger is connected to the hexafluoro reaction plate tower, the lithium hexafluorophosphate product extraction tank, and the lithium fluoride suspension preparation kettle. Beneficial effects

[0023] The present application first proposes to use gas phase high-purity phosphorus pentafluoride and lithium fluoride to carry out high-efficiency continuous reaction in a hexafluoride reaction plate tower. The present applicant surprisingly found that the conversion rate of phosphorus pentafluoride reached more than 99.99%, and the hydrogen chloride content of the obtained liquid lithium hexafluorophosphate was not more than 25 ppm, and no hydrogen fluoride was detected, which can be directly applied to industrialization without additional deacidification process treatment, and has obviously higher output efficiency. At the same time, the present application proposes to deliver a small amount of reaction product to the lithium fluoride suspension preparation kettle. Since the liquid lithium hexafluorophosphate can be well dissolved in the organic solvent, and the liquid lithium hexafluorophosphate and lithium fluoride have good compatibility, the lithium fluoride and the organic solvent can be fully mixed at all times, and the production maintenance risk caused by blockage and other problems can be avoided, so that the synthesis process provided by the present application has high-efficiency and stable continuous production level. BRIEF DESCRIPTION OF DRAWINGS

[0024] Fig. 1 is a synthesis process step block diagram of liquid lithium hexafluorophosphate in the specific embodiment of the present application;

[0025] Fig. 2 is a cross-sectional structure schematic diagram of a hexafluoride reaction plate tower in the specific embodiment of the present application;

[0026] Fig. 3 is a partial structure schematic diagram in Fig. 2;

[0027] Fig. 4 is a liquid lithium hexafluorophosphate product sample photograph prepared by Example 1 of the present application. Embodiment of the present application

[0028] The present embodiment discloses a device comprising a lithium fluoride suspension preparation kettle, a high-purity phosphorus pentafluoride storage tank and a hexafluoride reaction plate tower. The liquid outlet of the lithium fluoride suspension preparation kettle is connected to the top of the hexafluoride reaction plate tower through a suspension delivery pipeline, and the outlet of the high-purity phosphorus pentafluoride storage tank is connected to the tower kettle of the hexafluoride reaction plate tower through a delivery pipeline. Further preferably, in the present embodiment, the high-purity phosphorus pentafluoride storage tank is connected to the gas phase output end of the fluorosulfonate absorption tower, and the gas phase input end of the fluorosulfonate absorption tower is connected to the incoming material outlet of the phosphorus pentafluoride rectification tower through a phosphorus pentafluoride buffer tank. A lithium fluoride suspension feed tank is provided on the suspension delivery pipeline, and the lithium fluoride suspension preparation kettle is connected to the hexafluoride reaction plate tower through the lithium fluoride suspension feed tank. The bottom of the hexafluoride reaction plate tower is connected to a bottom tank, the bottom tank is connected to the input end of a circulating heat exchanger, the output end of the circulating heat exchanger is connected to the hexafluoride reaction plate tower, a liquid lithium hexafluorophosphate product extraction tank and the lithium fluoride suspension preparation kettle.

[0029] Please refer to Fig. 1, the present embodiment further proposes a continuous preparation process of liquid lithium hexafluorophosphate implemented by the above-mentioned device, comprising the following operation steps:

[0030] (A10) Lithium fluoride suspension is provided through a lithium fluoride suspension preparation vessel and continuously fed to the top of a hexafluoro reaction plate column; high-purity phosphorus pentafluoride in gaseous phase is provided through a high-purity phosphorus pentafluoride storage tank and continuously fed to the bottom of the hexafluoro reaction plate column, wherein the purity of the high-purity phosphorus pentafluoride in gaseous phase is greater than 96%.

[0031] Preferably, in this embodiment, the preparation step of high-purity gaseous phosphorus pentafluoride includes: conveying the feed from the phosphorus pentafluoride distillation column through a phosphorus pentafluoride buffer tank into a fluorosulfonate (specifically, in this embodiment, 1-(2-methoxyethyl)-3-ethylimidazolium trifluoromethylsulfonate ionic liquid) absorption column to adsorb and remove hydrogen fluoride and hydrogen chloride from the feed from the phosphorus pentafluoride distillation column under ambient temperature and pressure conditions, thereby obtaining high-purity gaseous phosphorus pentafluoride; more preferably, in order to ensure the purity of high-purity gaseous phosphorus pentafluoride, in this embodiment, the fluorosulfonate absorption column includes a first fluorosulfonate absorption column and a second fluorosulfonate absorption column connected together.

[0032] Preferably, in this embodiment, in the lithium fluoride suspension preparation vessel, the lithium fluoride and the organic solvent are fully fused by ultrasonic action; wherein the solvent is any one or a mixture of any of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; and / or the mass ratio of lithium fluoride to organic solvent is in the range of 1:8-20; preferably, in order to prevent the lithium fluoride suspension from depositing inside the pipeline during transportation, in this embodiment, the lithium fluoride is in powder form, and its maximum particle size does not exceed 0.2 mm, preferably not exceeding 0.18 mm; the inner wall of the conveying pipeline between the lithium fluoride suspension preparation vessel and the top of the hexafluoro reaction plate tower is polished to a smooth state, wherein the polishing precision of the inner wall of the conveying pipeline is less than or equal to 0.6 micrometers.

[0033] (A20) Lithium fluoride and gaseous high-purity phosphorus pentafluoride are reacted in a hexafluoro reaction plate column under normal temperature and pressure conditions. The reaction products enter the bottom storage tank from the bottom of the hexafluoro reaction column. The mass ratio of lithium fluoride to gaseous high-purity phosphorus pentafluoride is 1:4-6.

[0034] Preferably, further in combination with the embodiments shown in Figures 2 and 3, in the present embodiment, the hexafluoro reaction plate column 100 is provided with at least 40 tower plates 110 distributed in an up-down interval, wherein the tower plate screen hole aperture near the tower top a is larger than the tower plate screen hole aperture near the tower bottom b; further preferably, in the present embodiment, the hexafluoro reaction plate column 100 comprises at least a first tower plate section, a second tower plate section and a third tower plate section from bottom to top; wherein the first tower plate section is provided with at least 10 first tower plates 110a distributed in an up-down interval, the tower plate screen hole aperture of the first tower plate 110a ranges from 2-4 mm; the second tower plate section is provided with at least 10 second tower plates 110b distributed in an up-down interval, the tower plate screen hole aperture of the second tower plate 110b ranges from 6-9 mm; the third tower plate section is provided with at least 10 third tower plates 110c distributed in an up-down interval, the tower plate screen hole aperture of the third tower plate 110c ranges from 12-16 mm;

[0035] A30), the reaction product is refluxed to the hexafluoro reaction plate column through the circulating heat exchanger at a preset reflux ratio, the remaining reaction product output by the circulating heat exchanger is punched into a lithium hexafluorophosphate liquid product extraction tank in one way and a lithium fluoride suspension preparation kettle in another way; the preset reflux ratio is 4-8:1;

[0036] A40), after the filter connected to the product extraction end of the product extraction tank is used to remove the excess solid material after reaction, the liquid lithium hexafluorophosphate is obtained, the hydrogen chloride content of the liquid lithium hexafluorophosphate is less than 25 ppm, preferably less than 15 ppm, and no hydrogen fluoride is detected.

[0037] In order for those skilled in the art to better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should belong to the scope of protection of the present application.

[0038] On the basis of the above-described embodiments, the present application further proposes the following specific embodiments, Embodiment

[0039] In the present embodiment 1, the specifications of the phosphorus pentafluoride rectification tower feed and each device are as follows:

[0040] The mass percentage of hydrogen chloride in the phosphorus pentafluoride rectification tower feed is 52.72%, the mass percentage of phosphorus pentafluoride PF5 is 47.17%, and the content of hydrogen fluoride is 0.11%; the lithium fluoride is in powder form, and the maximum particle size is not more than 0.18 mm;

[0041] The specifications of the lithium fluoride suspension preparation kettle, lithium fluoride suspension feed tank, phosphorus pentafluoride buffer tank and high-purity phosphorus pentafluoride storage tank are all DN800*1200, and the materials are all S31603;

[0042] The matching ultrasonic working frequency of the lithium fluoride suspension preparation kettle is 25KHz, and the power is 550W;

[0043] The inner walls of the conveying pipelines between the lithium fluoride suspension preparation kettle and the tower top of the hexafluoro reaction plate tower are all polished, and the polishing precision is 0.5 microns;

[0044] The specifications of the first and second fluorosulfonate absorption towers are both DN1000*1600, and the tower conditions of the first and second fluorosulfonate absorption towers are both set as normal temperature and pressure, and the liquid of each absorption tower is 1-(2-methoxyethyl)-3-ethyl imidazole trifluoromethyl sulfonate ionic liquid;

[0045] The hexafluoro reaction plate tower is provided with a total of 65 tower plates which are distributed in an up-down interval, and the spacing between each adjacent tower plate is 380mm; the hexafluoro reaction plate tower comprises a first tower plate section, a fourth tower plate section, a second tower plate section, a fifth tower plate section and a third tower plate section from bottom to top; wherein the first tower plate section is provided with 15 first tower plates which are distributed in an up-down interval, and the tower plate screen hole diameter of the first tower plate is 3mm; the fourth tower plate section is provided with 10 fourth tower plates which are distributed in an up-down interval, and the tower plate screen hole diameter range of the fourth tower plate is 4.5mm; the second tower plate section is provided with 15 second tower plates which are distributed in an up-down interval, and the tower plate screen hole diameter of the second tower plate is 7mm; the fifth tower plate section is provided with 10 fifth tower plates which are distributed in an up-down interval, and the tower plate screen hole diameter of the fifth tower plate is 10mm; the third tower plate section is provided with 15 third tower plates which are distributed in an up-down interval, and the tower plate screen hole diameter range of the third tower plate is 14mm; the tower conditions of the hexafluoro reaction plate tower are set as normal temperature and pressure;

[0046] The specification of the bottom storage tank is DN1100*1600, the refrigerant of the circulating heat exchanger is selected as -15℃ cold water, and the specification of the product production tank is DN800*1200;

[0047] The purity detection is performed by a chromatography-mass spectrometry instrument.

[0048] The high-purity phosphorus pentafluoride feed: the phosphorus pentafluoride rectification tower is fed into the first fluorosulfonate absorption tower and the second fluorosulfonate absorption tower through the phosphorus pentafluoride buffer tank at a speed of 5.4kg / h, the gas phase output end of the second fluorosulfonate absorption tower is connected to the high-purity phosphorus pentafluoride storage tank (the purity of the high-purity phosphorus pentafluoride reaches 99.4% after purity detection), and the high-purity phosphorus pentafluoride storage tank is connected to the tower kettle of the hexafluoro reaction plate tower for continuous feeding;

[0049] Lithium fluoride suspension feed: raw lithium fluoride is fed into a lithium fluoride suspension preparation kettle at a flow rate of 0.52 kg / h, and methyl ethyl carbonate (EMC) is fed at a flow rate of 8.2 kg / h, under the action of ultrasonic waves, lithium fluoride and methyl ethyl carbonate are fully mixed to obtain lithium fluoride suspension, which is transferred to a lithium fluoride suspension feed tank, and the lithium fluoride suspension feed tank is connected to the top of the hexafluoride reaction plate tower for continuous feeding;

[0050] Reaction and reflux: lithium fluoride reacts with gaseous high-purity phosphorus pentafluoride in the hexafluoride reaction plate tower in the presence of methyl ethyl carbonate; liquid reaction products are collected from the bottom of the hexafluoride reaction plate tower, and after passing through the bottom tank, they are cooled by a circulating heat exchanger, then they are fed into the hexafluoride reaction tower 400 at a pre-set reflux ratio of 6:1, while the remaining reaction products from the circulating heat exchanger are fed into the product collection tank at a speed of 10.04 kg / h, and finally, after passing through a filter to remove excess solid materials (usually lithium fluoride) after the reaction, liquid lithium hexafluorophosphate product is obtained, and the other part is fed into the lithium fluoride suspension preparation kettle at a speed of 0.78 kg / h, forming another loop; the gaseous methyl ethyl carbonate with a flow rate of 1.29 kg / h is collected from the top of the hexafluoride reaction plate tower and is sent to the subsequent section for compression and condensation recovery.

[0051] After purity detection, the liquid lithium hexafluorophosphate product obtained in Example 1 (see Figure 4) contains 10 ppm of hydrogen chloride and no hydrogen fluoride, and does not need to be treated by deacidification, and the production efficiency of liquid lithium hexafluorophosphate is significantly higher, and the conversion rate of phosphorus pentafluoride is more than 99.99%.

[0052] Example 2: The remaining technical solutions of Example 2 are the same as those of Example 1, except that in Example 2, the second fluorosulfonate absorption tower is not provided, and only the first fluorosulfonate absorption tower is used, and the gaseous output end of the first fluorosulfonate absorption tower is directly connected to the high-purity phosphorus pentafluoride storage tank.

[0053] After detection, the purity of the high-purity phosphorus pentafluoride obtained in Example 2 is 96.5%, the liquid lithium hexafluorophosphate product contains 24 ppm of hydrogen chloride and no hydrogen fluoride, and the production efficiency of liquid lithium hexafluorophosphate is significantly higher, and the conversion rate of phosphorus pentafluoride is more than 99.99%.

[0054] Example 3: The remaining technical solutions of Example 3 are the same as those of Example 1, except that in Example 3, dimethyl carbonate is used instead of methyl ethyl carbonate in Example 1.

[0055] The purity detection shows that the hydrogen chloride content in the liquid lithium hexafluorophosphate product obtained in this embodiment 1 is 12 ppm, no hydrogen fluoride is detected, no subsequent deacidification treatment is needed, the output efficiency of the liquid lithium hexafluorophosphate is obviously higher, and the conversion rate of phosphorus pentafluoride reaches more than 99.99%.

[0056] Embodiment 4: The remaining technical solutions of this embodiment 4 are the same as those of embodiment 1, except that in this embodiment 4, 1:1 dimethyl carbonate and methyl ethyl carbonate are used to replace the methyl ethyl carbonate in embodiment 1.

[0057] The purity detection shows that the hydrogen chloride content in the liquid lithium hexafluorophosphate product obtained in this embodiment 4 is 11 ppm, no hydrogen fluoride is detected, no subsequent deacidification treatment is needed, the output efficiency of the liquid lithium hexafluorophosphate is obviously higher, and the conversion rate of phosphorus pentafluoride reaches more than 99.99%.

[0058] Embodiment 5: The remaining technical solutions of this embodiment 5 are the same as those of embodiment 1, except that in this embodiment 5, 1:1 dimethyl carbonate and diethyl carbonate are used to replace the methyl ethyl carbonate in embodiment 1.

[0059] The purity detection shows that the hydrogen chloride content in the liquid lithium hexafluorophosphate product obtained in this embodiment 5 is 13 ppm, no hydrogen fluoride is detected, no subsequent deacidification treatment is needed, the output efficiency of the liquid lithium hexafluorophosphate is obviously higher, and the conversion rate of phosphorus pentafluoride reaches more than 99.99%.

[0060] Embodiment 6: The remaining technical solutions of this embodiment 6 are the same as those of embodiment 1, except that this embodiment 6 includes the following operation steps:

[0061] High-purity phosphorus pentafluoride feed: The phosphorus pentafluoride rectification column feed is sequentially introduced into the first fluorosulfonate absorption tower and the second fluorosulfonate absorption tower through the phosphorus pentafluoride buffer tank at a speed of 6.5 kg / h, the gas phase output end of the second fluorosulfonate absorption tower is connected to the high-purity phosphorus pentafluoride storage tank (the purity of the high-purity phosphorus pentafluoride reaches 98.1% after purity detection), and the high-purity phosphorus pentafluoride storage tank is connected to the tower bottom of the hexafluoride reaction plate tower for continuous feeding;

[0062] Lithium fluoride suspension feed: the raw material lithium fluoride is introduced into the lithium fluoride suspension preparation kettle at a flow rate of 0.64 kg / h, and the methyl ethyl carbonate is introduced at a flow rate of 8.2 kg / h, under the action of ultrasonic waves, the lithium fluoride and the methyl ethyl carbonate are fully combined to obtain the lithium fluoride suspension, which is transferred to the lithium fluoride suspension feed tank, and the lithium fluoride suspension feed tank is connected to the top of the hexafluoride reaction plate tower for continuous feeding;

[0063] Reaction and reflux: the lithium fluoride reacts with the gaseous high-purity phosphorus pentafluoride in the atmosphere of methyl ethyl carbonate in the hexafluoro reaction plate column; the liquid reaction product is taken out from the bottom of the hexafluoro reaction plate column, and after the heat exchange and cooling by the circulating heat exchanger, it is punched into the hexafluoro reaction column 400 at a preset reflux ratio of 8:1, while the remaining reaction product output by the circulating heat exchanger is punched into the product taking tank at a speed of 11.75 kg / h, and finally, after the filter removes the excess solid material after the reaction, the liquid lithium hexafluorophosphate product is obtained, and the other way is punched into the lithium fluoride suspension preparation kettle at a speed of 0.82 kg / h, forming another loop; the gaseous methyl ethyl carbonate with a flow rate of 0.16 kg / h is taken out from the top of the hexafluoro reaction plate column and enters the subsequent section for compression and condensation recovery.

[0064] After purity detection, the hydrogen chloride content in the liquid lithium hexafluorophosphate product obtained in Example 6 is 15 ppm, and no hydrogen fluoride is detected, so that no subsequent deacidification treatment is needed, and the output efficiency of the liquid lithium hexafluorophosphate is obviously higher, and the conversion rate of phosphorus pentafluoride reaches more than 99.99%.

[0065] Example 7: The remaining technical solutions of Example 7 are the same as those of Example 1, except that in Example 7, each tray is set to a uniform size specification, which is the same as the first tray in Example 1; after actual application, the mass transfer efficiency of lithium fluoride is significantly slower, the output efficiency of liquid lithium hexafluorophosphate is significantly lower, and the conversion rate of phosphorus pentafluoride is less than 98%.

[0066] Example 8: The remaining technical solutions of Example 8 are the same as those of Example 1, except that in Example 8, each tray is set to a uniform size specification, which is the same as the third tray in Example 1; after actual application, the mass transfer efficiency of gaseous phosphorus pentafluoride is significantly slower, the output efficiency of liquid lithium hexafluorophosphate is significantly lower, and the conversion rate of phosphorus pentafluoride is less than 96%.

[0067] Comparative Example 1: The remaining technical solutions of Comparative Example 1 are the same as those of Example 1, except that in Comparative Example 1, the first and second fluorosulfonate absorption towers are cancelled, and the phosphorus pentafluoride rectification tower is directly connected to the phosphorus pentafluoride storage tank, that is, the phosphorus pentafluoride rectification tower feed is directly used as the hexafluoro reaction plate column feed;

[0068] After detection, the hydrogen chloride content in the liquid lithium hexafluorophosphate product obtained in Comparative Example 1 is greater than 600 ppm, and the hydrogen fluoride content is greater than 50 ppm, so that additional deacidification treatment is needed, and because the phosphorus pentafluoride rectification tower feed contains a large amount of hydrogen chloride gas, the conversion rate of phosphorus pentafluoride is relatively low, and the hexafluoro reaction plate column is in a strong acidic environment for a long time, so that the plate column needs to be frequently stopped for maintenance, affecting the continuity of production.

[0069] Comparative Example 2: The remaining technical solutions of Comparative Example 2 are the same as those of Example 1, except that in Comparative Example 2, the first sodium fluoride adsorber and the second sodium fluoride adsorber are used to replace the first fluorosulfonate absorber and the second fluorosulfonate absorber in Example 1;

[0070] It is detected that the gaseous phosphorus pentafluoride obtained after adsorption treatment still has a relatively high content of hydrogen chloride, which further causes the content of hydrogen chloride in the obtained liquid lithium hexafluorophosphate product to be greater than 600 ppm, hydrogen fluoride is not detected, and additional deacidification treatment is still required subsequently. Moreover, the sodium fluoride adsorber requires relatively harsh process conditions and the adsorption effect is unstable. In addition, as in Comparative Example 1, due to the presence of a large amount of hydrogen chloride gas in the feed of the phosphorus pentafluoride rectification tower, the conversion rate of phosphorus pentafluoride is relatively low, and the six-fluorine reaction plate tower is in a strong acidic environment for a long time, so the plate tower needs to be frequently stopped for maintenance, which affects the continuity of production.

[0071] Comparative Example 3: The remaining technical solutions of Comparative Example 3 are the same as those of Example 1, except that in Comparative Example 3, the connecting path between the output end of the circulating heat exchanger and the lithium fluoride suspension preparation kettle is cancelled, that is, the reaction product is no longer transported to the lithium fluoride suspension preparation kettle.

[0072] After actual circulation test, since the lithium fluoride particle size is small and the inner wall of the lithium fluoride suspension conveying pipeline is polished, no blockage problem is found in the pipeline part. However, the gas phase supplied in the six-fluorine reaction plate tower is the reaction raw material gas phase high-purity phosphorus pentafluoride, which no longer has a high content of hydrogen chloride gas, the mass transfer speed is slow, which will cause the screen holes of each tower plate to be blocked, and the output efficiency is significantly reduced, so it is not suitable for continuous production process application.

Claims

1. A continuous process for the preparation of liquid lithium hexafluorophosphate, characterized in that, The method comprises the following steps: A10), providing lithium fluoride suspension by a lithium fluoride suspension preparation kettle, and continuously feeding the lithium fluoride suspension to the top of a hexafluoride reaction plate tower; providing gaseous high-purity phosphorus pentafluoride by a high-purity phosphorus pentafluoride storage tank, and continuously feeding the gaseous high-purity phosphorus pentafluoride to the bottom of the hexafluoride reaction plate tower, wherein the purity of the gaseous high-purity phosphorus pentafluoride is greater than 96%; A20), the lithium fluoride and the gaseous high-purity phosphorus pentafluoride react in the hexafluoride reaction plate tower under normal temperature and pressure, and the reaction product enters a bottom storage tank from the bottom of the hexafluoride reaction tower, wherein the mass ratio of the lithium fluoride to the gaseous high-purity phosphorus pentafluoride is 1:4-6; A30), the bottom storage tank returns the reaction product to the hexafluoride reaction plate tower by a circulating heat exchanger at a preset reflux ratio, and the remaining reaction product output by the circulating heat exchanger is divided into two parts, one part is punched into a lithium hexafluorophosphate product extraction tank, and the other part is punched into the lithium fluoride suspension preparation kettle; the preset reflux ratio is 4-8:1; A40), a filter is connected to the product extraction end of the product extraction tank to remove the excess solid material after the reaction, and then liquid lithium hexafluorophosphate is obtained, wherein the hydrogen chloride content of the liquid lithium hexafluorophosphate is less than 25ppm, preferably less than 15ppm, and no hydrogen fluoride is detected.

2. The process for the continuous preparation of liquid lithium hexafluorophosphate according to claim 1, characterized in that, The preparation steps of the gaseous high-purity phosphorus pentafluoride include: under normal temperature and pressure, fluorine sulfonate absorption tower is used to adsorb and remove hydrogen fluoride and hydrogen chloride in the phosphorus pentafluoride rectification tower raw material to obtain the gaseous high-purity phosphorus pentafluoride.

3. The process for the continuous production of liquid lithium hexafluorophosphate according to claim 2, characterized in that, The fluorine sulfonate absorption tower comprises a first fluorine sulfonate absorption tower and a second fluorine sulfonate absorption tower connected in series.

4. The process for the continuous production of liquid lithium hexafluorophosphate according to claim 1, characterized in that, In the lithium fluoride suspension preparation kettle, the lithium fluoride and the organic solvent are fully combined by ultrasonic waves; wherein the solvent is any one or a mixture of any several of dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate; and / or the mass ratio of the lithium fluoride to the organic solvent ranges from 1:8 to 20.

5. The process for the continuous production of liquid lithium hexafluorophosphate according to claim 1 or 4, characterized in that, The lithium fluoride is in powder form, and the maximum particle size thereof is not more than 0.2mm, preferably not more than 0.18mm.

6. The process for the continuous production of liquid lithium hexafluorophosphate according to claim 5, characterized in that, The inner wall of the conveying pipeline between the lithium fluoride suspension preparation kettle and the top of the hexafluoride reaction plate tower is polished to be smooth, wherein the polishing precision of the inner wall of the conveying pipeline is less than or equal to 0.6μm.

7. The process for the continuous production of liquid lithium hexafluorophosphate according to claim 1, characterized in that, The hexafluoride reaction plate tower is provided with at least 40 tower plates distributed in an up-down interval, wherein the mesh size of the tower plate near the top is larger than the mesh size of the tower plate near the bottom.

8. The process for the continuous production of liquid lithium hexafluorophosphate according to claim 7, characterized in that, The hexafluoride reaction plate tower comprises at least a first tower plate section, a second tower plate section and a third tower plate section from bottom to top; wherein the first tower plate section is provided with at least 10 first tower plates distributed in an up-down interval, the mesh size of the first tower plate ranges from 2mm to 4mm; the second tower plate section is provided with at least 10 second tower plates distributed in an up-down interval, the mesh size of the second tower plate ranges from 6mm to 9mm; and the third tower plate section is provided with at least 10 third tower plates distributed in an up-down interval, the mesh size of the third tower plate ranges from 12mm to 16mm.

9. An apparatus for use in a continuous production process according to any one of claims 1-8, characterized in that, The fluorinated lithium suspension preparation kettle, the high-purity phosphorus pentafluoride storage tank and the hexafluorine reaction plate tower are connected.

10. The apparatus for use in the continuous production process according to claim 9, wherein, The high-purity phosphorus pentafluoride storage tank is connected with a gas phase output end of a fluorosulfonate absorption tower, the gas phase input end of the fluorosulfonate absorption tower is connected with a raw material outlet of a phosphorus pentafluoride rectifying tower through a phosphorus pentafluoride buffer tank; a fluorinated lithium suspension feeding tank is arranged on the suspension conveying pipeline, the fluorinated lithium suspension preparation kettle is connected with the fluorinated lithium suspension feeding tank and the hexafluorine reaction plate tower; a bottom tank is connected with the bottom of the hexafluorine reaction plate tower, the bottom tank is connected with an input end of a circulating heat exchanger, an output end of the circulating heat exchanger is connected with the hexafluorine reaction plate tower, a liquid lithium hexafluorophosphate product tank and the fluorinated lithium suspension preparation kettle.

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