CN117003262A - Process for purifying sodium hexafluorophosphate by complex recrystallization - Google Patents
Process for purifying sodium hexafluorophosphate by complex recrystallization Download PDFInfo
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- CN117003262A CN117003262A CN202311286223.4A CN202311286223A CN117003262A CN 117003262 A CN117003262 A CN 117003262A CN 202311286223 A CN202311286223 A CN 202311286223A CN 117003262 A CN117003262 A CN 117003262A
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- sodium hexafluorophosphate
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- hexafluorophosphate
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- -1 sodium hexafluorophosphate Chemical compound 0.000 title claims abstract description 148
- 238000001953 recrystallisation Methods 0.000 title claims abstract description 44
- 238000000034 method Methods 0.000 title claims abstract description 41
- 230000008569 process Effects 0.000 title claims abstract description 33
- 239000003960 organic solvent Substances 0.000 claims abstract description 72
- 238000001914 filtration Methods 0.000 claims abstract description 26
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 24
- 239000007788 liquid Substances 0.000 claims abstract description 24
- 239000012043 crude product Substances 0.000 claims abstract description 22
- 238000010438 heat treatment Methods 0.000 claims abstract description 18
- 230000032683 aging Effects 0.000 claims abstract description 14
- 239000000126 substance Substances 0.000 claims abstract description 13
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 12
- 239000007790 solid phase Substances 0.000 claims abstract description 12
- 239000007791 liquid phase Substances 0.000 claims abstract description 11
- 238000005406 washing Methods 0.000 claims abstract description 10
- 239000013078 crystal Substances 0.000 claims description 53
- WEVYAHXRMPXWCK-UHFFFAOYSA-N Acetonitrile Chemical compound CC#N WEVYAHXRMPXWCK-UHFFFAOYSA-N 0.000 claims description 27
- 239000000047 product Substances 0.000 claims description 23
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical group C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 claims description 19
- 239000011734 sodium Substances 0.000 claims description 19
- 229910052708 sodium Inorganic materials 0.000 claims description 19
- XTHFKEDIFFGKHM-UHFFFAOYSA-N Dimethoxyethane Chemical compound COCCOC XTHFKEDIFFGKHM-UHFFFAOYSA-N 0.000 claims description 16
- 238000001704 evaporation Methods 0.000 claims description 13
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 9
- ZMANZCXQSJIPKH-UHFFFAOYSA-N Triethylamine Chemical compound CCN(CC)CC ZMANZCXQSJIPKH-UHFFFAOYSA-N 0.000 claims description 9
- 238000006386 neutralization reaction Methods 0.000 claims description 9
- WQDUMFSSJAZKTM-UHFFFAOYSA-N Sodium methoxide Chemical compound [Na+].[O-]C WQDUMFSSJAZKTM-UHFFFAOYSA-N 0.000 claims description 8
- 238000002844 melting Methods 0.000 claims description 8
- 230000008018 melting Effects 0.000 claims description 8
- 239000007787 solid Substances 0.000 claims description 8
- 238000003756 stirring Methods 0.000 claims description 8
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 claims description 7
- RTZKZFJDLAIYFH-UHFFFAOYSA-N Diethyl ether Chemical compound CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 claims description 6
- 238000004090 dissolution Methods 0.000 claims description 6
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 claims description 4
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 claims description 4
- ZZXUZKXVROWEIF-UHFFFAOYSA-N 1,2-butylene carbonate Chemical compound CCC1COC(=O)O1 ZZXUZKXVROWEIF-UHFFFAOYSA-N 0.000 claims description 2
- PPMCFKAXXHZLMX-UHFFFAOYSA-N 1,3-dioxocan-2-one Chemical compound O=C1OCCCCCO1 PPMCFKAXXHZLMX-UHFFFAOYSA-N 0.000 claims description 2
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 2
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 claims description 2
- PIICEJLVQHRZGT-UHFFFAOYSA-N Ethylenediamine Chemical compound NCCN PIICEJLVQHRZGT-UHFFFAOYSA-N 0.000 claims description 2
- UIIMBOGNXHQVGW-DEQYMQKBSA-M Sodium bicarbonate-14C Chemical compound [Na+].O[14C]([O-])=O UIIMBOGNXHQVGW-DEQYMQKBSA-M 0.000 claims description 2
- HPNMFZURTQLUMO-UHFFFAOYSA-N diethylamine Chemical compound CCNCC HPNMFZURTQLUMO-UHFFFAOYSA-N 0.000 claims description 2
- VUPKGFBOKBGHFZ-UHFFFAOYSA-N dipropyl carbonate Chemical compound CCCOC(=O)OCCC VUPKGFBOKBGHFZ-UHFFFAOYSA-N 0.000 claims description 2
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 claims description 2
- FVSKHRXBFJPNKK-UHFFFAOYSA-N propionitrile Chemical compound CCC#N FVSKHRXBFJPNKK-UHFFFAOYSA-N 0.000 claims description 2
- RUOJZAUFBMNUDX-UHFFFAOYSA-N propylene carbonate Chemical compound CC1COC(=O)O1 RUOJZAUFBMNUDX-UHFFFAOYSA-N 0.000 claims description 2
- 229910000029 sodium carbonate Inorganic materials 0.000 claims description 2
- QDRKDTQENPPHOJ-UHFFFAOYSA-N sodium ethoxide Chemical compound [Na+].CC[O-] QDRKDTQENPPHOJ-UHFFFAOYSA-N 0.000 claims description 2
- 238000000746 purification Methods 0.000 abstract description 21
- 239000002253 acid Substances 0.000 abstract description 16
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 abstract description 16
- 238000005265 energy consumption Methods 0.000 abstract description 5
- 238000009776 industrial production Methods 0.000 abstract description 3
- 238000001035 drying Methods 0.000 abstract description 2
- 239000002904 solvent Substances 0.000 description 23
- 239000000243 solution Substances 0.000 description 22
- 239000012535 impurity Substances 0.000 description 12
- 230000000052 comparative effect Effects 0.000 description 10
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 9
- 239000012528 membrane Substances 0.000 description 9
- 238000002425 crystallisation Methods 0.000 description 8
- 230000008025 crystallization Effects 0.000 description 8
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 7
- 230000008020 evaporation Effects 0.000 description 7
- 239000011148 porous material Substances 0.000 description 7
- XEKOWRVHYACXOJ-UHFFFAOYSA-N Ethyl acetate Chemical compound CCOC(C)=O XEKOWRVHYACXOJ-UHFFFAOYSA-N 0.000 description 6
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 6
- 230000015572 biosynthetic process Effects 0.000 description 6
- 229910000040 hydrogen fluoride Inorganic materials 0.000 description 6
- 238000001228 spectrum Methods 0.000 description 6
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 5
- 150000002500 ions Chemical class 0.000 description 5
- 239000003446 ligand Substances 0.000 description 5
- FKNQFGJONOIPTF-UHFFFAOYSA-N Sodium cation Chemical compound [Na+] FKNQFGJONOIPTF-UHFFFAOYSA-N 0.000 description 4
- 230000002431 foraging effect Effects 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 239000012452 mother liquor Substances 0.000 description 4
- 230000006911 nucleation Effects 0.000 description 4
- 238000010899 nucleation Methods 0.000 description 4
- 238000001556 precipitation Methods 0.000 description 4
- PUZPDOWCWNUUKD-UHFFFAOYSA-M sodium fluoride Chemical compound [F-].[Na+] PUZPDOWCWNUUKD-UHFFFAOYSA-M 0.000 description 4
- 229910001415 sodium ion Inorganic materials 0.000 description 4
- 238000007614 solvation Methods 0.000 description 4
- 238000007738 vacuum evaporation Methods 0.000 description 4
- 238000005303 weighing Methods 0.000 description 4
- XGRSAFKZAGGXJV-UHFFFAOYSA-N 3-azaniumyl-3-cyclohexylpropanoate Chemical compound OC(=O)CC(N)C1CCCCC1 XGRSAFKZAGGXJV-UHFFFAOYSA-N 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- YMWUJEATGCHHMB-UHFFFAOYSA-N Dichloromethane Chemical compound ClCCl YMWUJEATGCHHMB-UHFFFAOYSA-N 0.000 description 3
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 3
- 229910019142 PO4 Inorganic materials 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 125000002091 cationic group Chemical group 0.000 description 3
- 238000001816 cooling Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000003792 electrolyte Substances 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 230000003993 interaction Effects 0.000 description 3
- 235000021317 phosphate Nutrition 0.000 description 3
- 230000009467 reduction Effects 0.000 description 3
- 229960004711 sodium monofluorophosphate Drugs 0.000 description 3
- KBVUALKOHTZCGR-UHFFFAOYSA-M sodium;difluorophosphinate Chemical compound [Na+].[O-]P(F)(F)=O KBVUALKOHTZCGR-UHFFFAOYSA-M 0.000 description 3
- 238000004781 supercooling Methods 0.000 description 3
- 230000009471 action Effects 0.000 description 2
- 150000001298 alcohols Chemical class 0.000 description 2
- 125000005907 alkyl ester group Chemical group 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 150000004649 carbonic acid derivatives Chemical class 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000004134 energy conservation Methods 0.000 description 2
- 150000002170 ethers Chemical class 0.000 description 2
- 239000012530 fluid Substances 0.000 description 2
- 150000002576 ketones Chemical class 0.000 description 2
- 150000002825 nitriles Chemical class 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 2
- 239000010452 phosphate Substances 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
- 239000011775 sodium fluoride Substances 0.000 description 2
- 235000013024 sodium fluoride Nutrition 0.000 description 2
- 238000001291 vacuum drying Methods 0.000 description 2
- 230000002378 acidificating effect Effects 0.000 description 1
- 150000001335 aliphatic alkanes Chemical class 0.000 description 1
- 150000001350 alkyl halides Chemical class 0.000 description 1
- 150000001450 anions Chemical class 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000000536 complexating effect Effects 0.000 description 1
- 238000005538 encapsulation Methods 0.000 description 1
- 150000002148 esters Chemical class 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 239000000706 filtrate Substances 0.000 description 1
- 125000000524 functional group Chemical group 0.000 description 1
- 229910017053 inorganic salt Inorganic materials 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 239000012046 mixed solvent Substances 0.000 description 1
- 230000005311 nuclear magnetism Effects 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 150000003013 phosphoric acid derivatives Chemical class 0.000 description 1
- 238000004321 preservation Methods 0.000 description 1
- 238000004886 process control Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 239000012047 saturated solution Substances 0.000 description 1
- 239000011343 solid material Substances 0.000 description 1
- 239000002912 waste gas Substances 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D13/00—Compounds of sodium or potassium not provided for elsewhere
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/80—Compositional purity
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/80—Compositional purity
- C01P2006/82—Compositional purity water content
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Inorganic Chemistry (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
The invention relates to the technical field of sodium hexafluorophosphate purification, in particular to a process for purifying sodium hexafluorophosphate by complex recrystallization. The method comprises the following steps: dissolving a sodium hexafluorophosphate crude product into an organic solvent at the temperature of 30-50 ℃, adding an alkaline substance to adjust the pH value to 8-9, standing and aging; aging, performing primary filtration, recrystallizing the liquid phase obtained after filtration at the temperature of-10-20 ℃, then filtering again, washing the obtained solid phase with an organic solvent, heating to completely melt the solid phase into liquid, continuously heating to evaporate the organic solvent, introducing nitrogen, and drying to obtain purified sodium hexafluorophosphate. The method has the advantages of low energy consumption, low purification cost, high overall purification yield, high purity of the purified sodium hexafluorophosphate of more than 99.95 percent, low free acid content of less than 5ppm and low water content of less than 10ppm, and is suitable for industrial production.
Description
Technical Field
The invention relates to the technical field of sodium hexafluorophosphate purification, in particular to a process for purifying sodium hexafluorophosphate by complex recrystallization.
Background
Sodium hexafluorophosphate (NaPF) 6 ) Is a white crystal or powdery inorganic salt which is easy to dissolve in common organic solvents such as methanol, ethanol, acetone, carbonic ester and the like, can realize high conductivity, is favorable for sodium ion batteries to simultaneously obtain high energy density, long cycle life and low self discharge rate, and is a promising electrolyte salt for sodium ion batteries. But NaPF is 6 Is very soluble in water and deliquescent, and strict process control is required to meet the indexes of battery-grade electrolyte such as purity, free acid, moisture and the like, and the purification of sodium hexafluorophosphate is also required to be higher.
At present, the purification method of sodium hexafluorophosphate is mainly to directly recrystallize the target product, namely, the solubility of the solvent to sodium hexafluorophosphate and impurities is different, so that the sodium hexafluorophosphate is separated out of supersaturated solution, and all or most of impurities remain in the solution. The crystallization process is a process of forming crystals by arranging substances in a lattice form, so that impurities do not participate in crystal formation, and the purification effect is achieved.
Common sodium hexafluorophosphate recrystallization processes include: naPF is cooled 6 Directly crystallizing from anhydrous hydrogen fluoride; dissolving sodium hexafluorophosphate in a solvent, and recrystallizing the sodium hexafluorophosphate from the solvent through a cooling or evaporating process; sodium hexafluorophosphate is dissolved in a benign solvent and recrystallized therefrom by the addition of a poor solvent. Wherein, the direct crystallization from anhydrous hydrogen fluoride requires a long time>48h) Low temperature environment of<-30 ℃ and a large amount of free acid and water can be reserved in the product, so that the quality of the product is affected; solvents such as methanol, ethanol, ethyl acetate, acetone and the like can well dissolve sodium hexafluorophosphate, but the solubility of the sodium hexafluorophosphate is not obvious along with the temperature change, recrystallization is difficult in a cooling mode, the recrystallization temperature is generally lower than-40 ℃, and evaporation quantity is difficult to control for evaporation crystallization; the recrystallization condition is easy to meet by adopting the process of 'good solvent + poor solvent', but the generated mixed solvent needs to be separated again for reuse, which leads to complex operation flow.
Disclosure of Invention
The purpose of the invention is that: the process for purifying the sodium hexafluorophosphate by complex recrystallization is safe and controllable in condition, low in energy consumption, low in purification cost, high in overall purification yield, high in purity of the purified sodium hexafluorophosphate, low in free acid content of 5ppm and low in water content of 10ppm, and is suitable for industrial production.
The process for purifying sodium hexafluorophosphate by complex recrystallization comprises the following steps:
(1) Dissolution and neutralization: dissolving a sodium hexafluorophosphate crude product in an organic solvent at the temperature of 30-50 ℃ to obtain a sodium hexafluorophosphate crude product solution, adding an alkaline substance to neutralize, adjusting the pH value to 8-9, standing and aging;
(2) And (5) recrystallizing: aging, performing primary filtration, recrystallizing the liquid phase obtained after filtration at the temperature of-10-20 ℃, then filtering again, and washing the obtained solid phase with an organic solvent, wherein the obtained solid phase is sodium hexafluorophosphate-organic solvent complex crystals;
(3) Melting and evaporating: heating the washed sodium hexafluorophosphate-organic solvent complex crystal to completely melt into liquid, continuing heating to evaporate the organic solvent, introducing nitrogen after the liquid is gelatinous, stirring until the gelatinous state is converted into powdery solid, stopping introducing nitrogen and heating, and obtaining the purified sodium hexafluorophosphate.
In the sodium hexafluorophosphate crude product, the content of sodium hexafluorophosphate is more than or equal to 85 wt%, the content of sodium fluoride is less than or equal to 5 wt%, the content of hydrogen fluoride is less than or equal to 6 wt%, the content of water is less than or equal to 2 wt%, the total content of sodium difluorophosphate, sodium monofluorophosphate and phosphate is less than or equal to 1 wt%, and the total content of various cationic impurities is less than or equal to 1 wt%.
In the step (1), the organic solvent is one or more of nitriles, carbonates and ethers; preferably acetonitrile, propionitrile, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, ethylene carbonate, butylene carbonate, pentylene carbonate, ethylene glycol dimethyl ether, diethyl ether; further preferred is one of acetonitrile, dimethyl carbonate and ethylene glycol dimethyl ether.
In the step (1), the mass volume ratio of the crude sodium hexafluorophosphate product to the organic solvent is (0.2-0.5) g/1 ml.
Action of organic solvent: firstly, fully dissolving a sodium hexafluorophosphate crude product; and secondly, forming a complex with sodium hexafluorophosphate as a ligand, and crystallizing and separating out in a complex form during recrystallization.
In selecting the organic solvent, the following factors need to be considered: on one hand, the organic solvent has good solubility for sodium hexafluorophosphate; on the other hand, the organic solvent is capable of forming a complex with sodium hexafluorophosphate and crystallizing under relatively mild conditions in preference to sodium hexafluorophosphate alone. The organic solvent selected by the invention has a functional group containing lone pair electrons, and the solvent ligand can form strong field action with the central atom, preferably the ligand can contribute more than 1 to the separation energy of the functional group compound, such as ethers, carbonates and nitriles; common organic solvents such as alcohols, ketones, alkyl esters, alkanes, haloalkanes are not suitable.
In selecting the amount of organic solvent, the following factors need to be considered: on one hand, the dosage of the organic solvent can fully dissolve the crude sodium hexafluorophosphate, so that crystals are not separated out from the solution during aging; on the other hand, coordination number of the complex formed by sodium hexafluorophosphate is generally about 5-7, and the organic solvent needs to be fully saturated by complexing with sodium hexafluorophosphate. Under the condition of ensuring complete formation of the complex, too little organic solvent can lead to crystal precipitation and impurity encapsulation in the aging process, and the purity and yield of the product are reduced; excessive amounts of organic solvents can lead to reduced precipitation of complex crystals during recrystallization, reducing product yields. Therefore, the amount of the organic solvent should be not less than 5 to 7 times the amount of the sodium hexafluorophosphate substance.
In the step (1), the alkaline substance is one of sodium methoxide, sodium ethoxide, sodium hydroxide, sodium carbonate, sodium bicarbonate, ammonia gas, ethylenediamine, diethylamine and triethylamine.
In some embodiments, the alkaline substance may be dissolved in an appropriate amount of organic solvent, and then added to the crude sodium hexafluorophosphate solution for neutralization, where the organic solvent is the same as the organic solvent in which the crude sodium hexafluorophosphate is dissolved.
According to the invention, the alkaline substance is added to adjust the pH value of the sodium hexafluorophosphate crude product solution to be slightly alkaline, so that on one hand, the content of acidic substances which seriously affect the stability of the product can be reduced; on the other hand, impurities in the product can be precipitated or substances with low solubility can be generated, so that the purpose of purifying the solution is achieved. The pH value is adjusted to be slightly alkaline, and then the pH value is aged for a period of time, so that small insoluble particles in the solution can be flocculated and aggregated, and separation is facilitated.
In the step (1), standing and ageing are carried out for 1-6 hours.
In the step (2), the pore diameter of the filter membrane for primary filtration is less than or equal to 0.22 mu m. The solid phase obtained after filtration is a small amount of solid insoluble matters; the obtained liquid phase is sodium hexafluorophosphate solution, the filtrate is kept at the temperature of-10-20 ℃ for 2-4 hours, and crystals are separated out from the solution in the process to form solid and liquid phases.
During the recrystallization, the crystals precipitated by the supersaturated solution are sodium hexafluorophosphate-organic solvent complex crystals, not sodium hexafluorophosphate crystals.
For the recrystallization process temperature selection, a temperature at which the gradient of the solubility of the object to be crystallized to the temperature is large is generally selected for the heat-retaining operation. The recrystallization generally comprises two stages of nucleation and crystal growth, wherein the nucleation rate decreases with the increase of supercooling degree, and the crystal growth rate increases with the increase of supercooling degree, and the recrystallization is generally carried out at a temperature at which both nucleation and crystal growth reach a higher rate, or at a temperature at which the nucleation rate is faster for a period of time, and then cooled to a temperature at which the crystal growth rate is faster for standing. The recrystallization target of the present invention is a sodium hexafluorophosphate-organic solvent complex instead of sodium hexafluorophosphate, so the recrystallization temperature is closer to room temperature, and the recrystallization temperature is adjusted according to the type of organic solvent (ligand).
In the step (2), the pore diameter of the filtering membrane filtered again is less than or equal to 1 mu m. The liquid phase obtained after filtration is mother liquor after recrystallization, and the main components of the mother liquor are sodium hexafluorophosphate, soluble impurities and organic solvents, and the mother liquor is recovered for dissolving sodium hexafluorophosphate crude products; the solid phase obtained is sodium hexafluorophosphate-organic solvent complex crystal.
In the step (2), the organic solvent at the temperature of-20-0 ℃ is used for washing, the organic solvent used for washing is the same as the organic solvent for dissolving the sodium hexafluorophosphate crude product, and the washed organic solvent is recycled for dissolving the sodium hexafluorophosphate crude product.
In the step (3), the temperature is 45-60 ℃ when the washed sodium hexafluorophosphate-organic solvent complex crystal is heated and melted. This temperature is higher than the melting point temperature of the corresponding sodium hexafluorophosphate-organic solvent complex crystal, for example, the heating melting temperature of the sodium hexafluorophosphate-acetonitrile complex crystal may be 45 ℃.
In the step (3), when the organic solvent is evaporated by continuing heating, the organic solvent is preferably evaporated by heating to 50 to 80 ℃ under vacuum. And regulating the system pressure according to the selected solvent type to ensure that the boiling point is 50-80 ℃.
The sodium hexafluorophosphate-organic solvent complex crystal obtained by recrystallization is composed of sodium hexafluorophosphate and a certain proportion of organic solvent molecules, the complex crystal can be heated and melted into liquid, a large amount of organic solvent molecules can be dissociated after the complex crystal is melted, the organic solvent is removed and recovered by evaporation, and the partially recovered organic solvent can be used for dissolving sodium hexafluorophosphate crude products or washing sodium hexafluorophosphate-organic solvent complex crystals. Most of the organic solvent is evaporated and then the liquid is converted into viscous colloidal fluid, and the viscous colloidal fluid can be stirred and dried by a drying airflow to further remove the residual organic solvent, so that a powdery and dried sodium hexafluorophosphate product is finally obtained.
The invention mainly achieves the aim of purifying the crude sodium hexafluorophosphate product through a recrystallization process, but unlike the traditional recrystallization process, the invention does not directly recrystallize sodium hexafluorophosphate, but recrystallizes sodium hexafluorophosphate-organic solvent complex, and then separates out the organic solvent through a melting evaporation mode. It is necessary to distinguish the difference between sodium hexafluorophosphate-organic solvent complex and sodium hexafluorophosphate, solvent (ligand), sodium hexafluorophosphate is dissolved in solvent to form solution, sodium hexafluorophosphate coordinates with solvent in solution to form complex, and complex can be crystallized out under proper condition.
The principle of the invention is to purify sodium hexafluorophosphate by adopting a complex recrystallization method. By selecting appropriate solvents and process conditions, solvation is utilized to form complexes of ions with solvent molecules. Solvation is a process in which solvent molecules accumulate around ions through interactions with the ions, giving off a large amount of heat, and it is desirable to maintain temperature stability within a certain range while continuing to cool. According to the invention, a proper solvent is selected to dissolve the sodium hexafluorophosphate crude product to form a sodium hexafluorophosphate solution, and a complex formed by solvation of sodium hexafluorophosphate and solvent molecules in the solution is crystallized and separated out under proper conditions. Complex recrystallization has the following advantages over direct recrystallization of sodium hexafluorophosphate: firstly, the sodium hexafluorophosphate forms a complex, so that the interaction between the sodium hexafluorophosphate and impurities can be weakened, and the purity of the sodium hexafluorophosphate can be improved; secondly, compared with sodium hexafluorophosphate, the complex is easier to crystallize, the recrystallization temperature is relatively high, and the energy conservation and consumption reduction are facilitated; thirdly, the formation of a complex can also avoid the contact of sodium hexafluorophosphate with acid and moisture, improve the stability of sodium hexafluorophosphate in the operation process, and further reduce the acid content and the water content in the pure sodium hexafluorophosphate.
Compared with the prior art, the invention has the following beneficial effects:
(1) According to the invention, by selecting proper solvent types and recrystallization process conditions, a complex of ions and solvent molecules is formed by solvation, and crystallization is performed under proper conditions, so that compared with the direct recrystallization of sodium hexafluorophosphate, the sodium hexafluorophosphate-organic solvent complex crystal selected by the invention has milder crystallization conditions and is easier to crystallize, thereby being beneficial to energy conservation and consumption reduction, and the complex formed by sodium hexafluorophosphate can weaken the interaction of sodium hexafluorophosphate and impurities, and simultaneously avoid the contact of sodium hexafluorophosphate with acid and water, thereby improving the purity of sodium hexafluorophosphate and reducing the acid content and water content in sodium hexafluorophosphate pure products;
(2) The purification process disclosed by the invention is safe and controllable in condition, low in energy consumption, safe and environment-friendly, and suitable for industrial production, and the solvent can be recycled, the recrystallization filtration mother liquor can be recycled for purification, the purification cost is low, the overall purification yield is high, and no waste gas and waste liquid are generated in theory;
(3) The purification process provided by the invention realizes the reduction of impurities such as moisture, free acid, solid insoluble substances, metal cations, anions and the like in the crude sodium hexafluorophosphate, the purity of the purified sodium hexafluorophosphate is higher than 99.95%, the content of free acid is lower than 5ppm, the content of water is lower than 10ppm, the requirements of electrolyte salt for sodium ion batteries are met, and the performance of the sodium ion batteries is improved.
Drawings
FIG. 1 is a chromatogram of sodium hexafluorophosphate after purification in example 1 of the present invention.
Detailed Description
The present invention will be further illustrated by the following examples, wherein the raw materials used in the examples are commercially available conventional raw materials unless otherwise specified; the process used in the examples, unless otherwise specified, is conventional in the art.
In the examples, the content of sodium hexafluorophosphate product related substances was analyzed with reference to standard GB/T19282-2014.
Example 1
The purification process of the invention is used for purifying the sodium hexafluorophosphate crude product, wherein the sodium hexafluorophosphate crude product contains 87wt.% of sodium hexafluorophosphate, 4wt.% of sodium fluoride, 5wt.% of hydrogen fluoride, 2wt.% of water, 1wt.% of the sum of sodium difluorophosphate, sodium monofluorophosphate and phosphate, and 1wt.% of the sum of various cationic impurities.
The purification steps are as follows:
(1) Dissolution and neutralization: dissolving 150g of sodium hexafluorophosphate crude product in 363mL of acetonitrile at 40 ℃ to obtain sodium hexafluorophosphate crude product solution, adding sodium methoxide for neutralization, adjusting the pH value to 8, and standing for 1h for aging;
(2) And (5) recrystallizing: aging, performing primary filtration, wherein the pore diameter of a filter membrane is less than or equal to 0.22 mu m, stirring the liquid phase obtained after filtration at the temperature of 7 ℃ for 1h at the rotating speed of 40rpm, standing at the temperature of-10 ℃ for 2h, filtering again, wherein the pore diameter of the filter membrane is less than or equal to 1 mu m, and the obtained solid phase is sodium hexafluorophosphate-acetonitrile complex crystal, and washing 3 times with acetonitrile at the temperature of-10 ℃ and 10mL of acetonitrile each time;
(3) Melting and evaporating: the washed sodium hexafluorophosphate-acetonitrile complex crystal (289 g) is heated to 45 ℃ to be completely melted into liquid, then the liquid is heated to 55 ℃ for vacuum evaporation, dry nitrogen is introduced after the liquid is gelatinous and stirred, the gelatinous liquid is converted into powdery solid, the nitrogen is stopped to be introduced and heated, the purified sodium hexafluorophosphate is obtained, the weight of the sodium hexafluorophosphate is 117g, 162g of liquid is collected in the evaporation process, acetonitrile is identified by nuclear magnetism hydrogen spectrum and carbon spectrum, and the crystal product is sodium hexafluorophosphate-acetonitrile complex crystal instead of sodium hexafluorophosphate crystal.
The purity of the purified sodium hexafluorophosphate is detected, the ion chromatogram is shown in figure 1, the purity of the sodium hexafluorophosphate is 99.99%, the free acid is not detected, and the water content is 6ppm.
Example 2
The purification process of the invention is adopted to purify the crude sodium hexafluorophosphate, and the composition of the crude sodium hexafluorophosphate is the same as that of the example 1.
The purification steps are as follows:
(1) Dissolution and neutralization: at 30 ℃, 150g of sodium hexafluorophosphate crude product is dissolved in 499mL of ethylene glycol dimethyl ether to obtain sodium hexafluorophosphate crude product solution, sodium hydroxide is added to neutralize, the pH value is adjusted to 9, and standing is carried out for 2 hours for aging;
(2) And (5) recrystallizing: aging, performing primary filtration, wherein the aperture of a filter membrane is less than or equal to 0.22 mu m, stirring the liquid phase obtained after filtration at the temperature of 12 ℃ for 2 hours at the rotating speed of 40rpm, standing at the temperature of-10 ℃ for 4 hours, filtering again, wherein the aperture of the filter membrane is less than or equal to 1 mu m, and the obtained solid phase is sodium hexafluorophosphate-ethylene glycol dimethyl ether complex crystal, and washing 3 times by using ethylene glycol dimethyl ether at the temperature of-20 ℃ and 20mL of ethylene glycol dimethyl ether each time;
(3) Melting and evaporating: heating the washed sodium hexafluorophosphate-ethylene glycol dimethyl ether complex crystal (343 g) to 50 ℃ to completely melt the sodium hexafluorophosphate-ethylene glycol dimethyl ether complex crystal into liquid, then heating the liquid to 65 ℃ for vacuum evaporation, introducing dry nitrogen after the liquid is gelatinous, stirring the liquid until the liquid is gelatinous, turning the gelatinous into powdery solid, stopping introducing nitrogen and heating to obtain purified sodium hexafluorophosphate, weighing the purified sodium hexafluorophosphate to 119g, collecting 214g of liquid in the evaporation process, and identifying the ethylene glycol dimethyl ether as the ethylene glycol dimethyl ether by nuclear magnetic hydrogen spectrum and carbon spectrum characteristics, wherein the crystal product is sodium hexafluorophosphate-ethylene glycol dimethyl ether complex crystal but not sodium hexafluorophosphate crystal.
And detecting the purity of the purified sodium hexafluorophosphate, wherein the purity of the sodium hexafluorophosphate is 99.96%, the free acid content is 4ppm, and the water content is 8ppm.
Example 3
The purification process of the invention is adopted to purify the crude sodium hexafluorophosphate, and the composition of the crude sodium hexafluorophosphate is the same as that of the example 1.
The purification steps are as follows:
(1) Dissolution and neutralization: dissolving 150g of sodium hexafluorophosphate crude product in 524mL of dimethyl carbonate at 50 ℃ to obtain sodium hexafluorophosphate crude product solution, adding triethylamine to neutralize, adjusting the pH value to 8.5, and standing for 6h for aging;
(2) And (5) recrystallizing: aging, performing primary filtration, wherein the pore diameter of a filter membrane is less than or equal to 0.22 mu m, stirring the liquid phase obtained after filtration at 20 ℃ for 2 hours at the rotating speed of 40rpm, standing at 5 ℃ for 4 hours, filtering again, wherein the pore diameter of the filter membrane is less than or equal to 1 mu m, and the obtained solid phase is sodium hexafluorophosphate-dimethyl carbonate complex crystal, and is washed 3 times by using 0 ℃ dimethyl carbonate, and 20mL of dimethyl carbonate is used each time;
(3) Melting and evaporating: heating the washed sodium hexafluorophosphate-dimethyl carbonate complex crystal (328 g) to 60 ℃ to completely melt the sodium hexafluorophosphate-dimethyl carbonate complex crystal into liquid, then heating the liquid to 80 ℃ for vacuum evaporation, introducing dry nitrogen after the liquid is gelatinous, stirring the liquid until the gelatinous state is changed into powdery solid, stopping introducing nitrogen and heating to obtain purified sodium hexafluorophosphate, weighing the purified sodium hexafluorophosphate to 114g, collecting 194g of liquid in the evaporation process, and confirming the dimethyl carbonate through nuclear magnetic hydrogen spectrum and carbon spectrum characteristics to indicate that the crystal product is sodium hexafluorophosphate-dimethyl carbonate complex crystal but not sodium hexafluorophosphate crystal.
And detecting the purity of the purified sodium hexafluorophosphate, wherein the purity of the sodium hexafluorophosphate is 99.98%, the free acid content is 3ppm, and the water content is 7ppm.
Comparative example 1
In this comparative example, a crude sodium hexafluorophosphate product was purified by recrystallization from hydrogen fluoride, and the composition of the crude sodium hexafluorophosphate product was the same as in example 1.
The method comprises the following specific steps:
(1) Dissolving: at the temperature of minus 10 ℃, 150g of crude sodium hexafluorophosphate is dissolved in 433mL of anhydrous hydrogen fluoride, and the system is stable;
(2) And (5) recrystallizing: adding a filter grid into the solution, cooling to-40 ℃, preserving heat for 48 hours, taking out the filter grid, collecting crystals on the filter grid, introducing dry nitrogen, stirring, then vacuum drying the solid material at 78 ℃ and-0.065 MPa, and weighing 106g of purified sodium hexafluorophosphate.
And detecting the purity of the purified sodium hexafluorophosphate, wherein the purity of the sodium hexafluorophosphate is 98.85 percent, the free acid content is 83ppm, and the water content is 17ppm.
Comparative example 2
In this comparative example, a crude sodium hexafluorophosphate product was purified by a good solvent-poor solvent method, and the composition of the crude sodium hexafluorophosphate product was the same as in example 1.
The method comprises the following specific steps:
(1) Dissolution and neutralization: dissolving 150g of sodium hexafluorophosphate crude product in 363mL of acetonitrile at 40 ℃ to obtain sodium hexafluorophosphate crude product solution, adding saturated solution of sodium methoxide for neutralization, adjusting pH value to 8, and standing for 1.5h for aging;
(2) And (5) recrystallizing: aging, performing primary filtration, wherein the pore diameter of a filter membrane is less than or equal to 0.22 mu m, concentrating a liquid phase obtained after filtration by a vacuum evaporation mode, adding 1089ml of poor solvent dichloromethane for crystallization to obtain a sodium hexafluorophosphate wet product, and then performing vacuum drying at 90 ℃ to obtain purified sodium hexafluorophosphate, and weighing 78g.
And detecting the purity of the purified sodium hexafluorophosphate, wherein the purity of the sodium hexafluorophosphate is 99.95%, the free acid content is 15ppm, and the water content is 16ppm. The product quality is relatively good, the purity is high, but the process yield is low, and the mass production is not facilitated.
Comparative examples 3 to 5
In order to examine the influence of the type of organic solvent on the formation of sodium hexafluorophosphate-organic solvent complex crystals, comparative examples 3 to 5 were different from example 1 in that methanol (alcohols), ethyl acetate (alkyl esters), acetone (ketones) were used as the organic solvents, respectively, and when recrystallization was performed, the temperature was lowered to-40 ℃ without any crystal precipitation.
Comparative example 6
To examine the effect of the amount of organic solvent on the formation of sodium hexafluorophosphate-organic solvent complex crystals, this comparative example was different from example 1 in that in step (1), 150g of crude sodium hexafluorophosphate was dissolved in 2230mL of acetonitrile, and as a result, the temperature was lowered to-40 ℃ during recrystallization, no crystals were precipitated, indicating that too low a solution concentration could not achieve precipitation of sodium hexafluorophosphate-organic solvent complex crystals.
Comparative example 7
To examine the effect of recrystallization temperature on the formation of sodium hexafluorophosphate-organic solvent complex crystals, this comparative example was different from example 1 in that in step (2), the liquid phase obtained after filtration was cooled to-5 ℃ for heat preservation, at which point needle-like solids rapidly appeared in the solution; the remaining steps are the same as in the examples.
And detecting the purity of the purified sodium hexafluorophosphate, wherein the purity is 98.8%, the free acid content is 8ppm, and the water content is 10ppm. This is because excessive supercooling in operation leads to an excessively high crystallization rate, sodium difluorophosphate, sodium monofluorophosphate and phosphates and various cationic impurities are encapsulated in the crystal during crystallization, and cannot be effectively removed in operation after recrystallization, resulting in a decrease in product purity.
Claims (9)
1. A process for purifying sodium hexafluorophosphate by complex recrystallization is characterized in that: the method comprises the following steps:
(1) Dissolution and neutralization: dissolving a sodium hexafluorophosphate crude product in an organic solvent at the temperature of 30-50 ℃, adding an alkaline substance to neutralize, adjusting the pH value to 8-9, standing and aging;
(2) And (5) recrystallizing: aging, performing primary filtration, recrystallizing the liquid phase obtained after filtration at the temperature of-10-20 ℃, then filtering again, and washing the obtained solid phase with an organic solvent, wherein the obtained solid phase is sodium hexafluorophosphate-organic solvent complex crystals;
(3) Melting and evaporating: heating the washed sodium hexafluorophosphate-organic solvent complex crystal to completely melt into liquid, continuing heating to evaporate the organic solvent, introducing nitrogen after the liquid is gelatinous, stirring until the gelatinous state is converted into powdery solid, stopping introducing nitrogen and heating, and obtaining the purified sodium hexafluorophosphate.
2. The process for purifying sodium hexafluorophosphate by complex recrystallization according to claim 1, wherein: the organic solvent is one of acetonitrile, propionitrile, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, ethylene carbonate, butylene carbonate, pentylene carbonate, ethylene glycol dimethyl ether and diethyl ether.
3. The process for purifying sodium hexafluorophosphate by complex recrystallization according to claim 1, wherein: in the step (1), the mass volume ratio of the crude sodium hexafluorophosphate product to the organic solvent is (0.2-0.5) g/1 ml.
4. The process for purifying sodium hexafluorophosphate by complex recrystallization according to claim 1, wherein: in the step (1), the alkaline substance is one of sodium methoxide, sodium ethoxide, sodium hydroxide, sodium carbonate, sodium bicarbonate, ammonia gas, ethylenediamine, diethylamine and triethylamine.
5. The process for purifying sodium hexafluorophosphate by complex recrystallization according to claim 1, wherein: in the step (1), standing and ageing are carried out for 1-6 hours.
6. The process for purifying sodium hexafluorophosphate by complex recrystallization according to claim 1, wherein: in the step (2), the organic solvent used in the washing is the same as the organic solvent used for dissolving the crude sodium hexafluorophosphate.
7. The process for purifying sodium hexafluorophosphate by complex recrystallization according to claim 1, wherein: in the step (2), washing is carried out by using an organic solvent at the temperature of-20-0 ℃.
8. The process for purifying sodium hexafluorophosphate by complex recrystallization according to claim 1, wherein: in the step (3), the temperature is 45-60 ℃ when the washed sodium hexafluorophosphate-organic solvent complex crystal is heated and melted.
9. The process for purifying sodium hexafluorophosphate by complex recrystallization according to claim 1, wherein: in the step (3), when the organic solvent is evaporated by continuing heating, the organic solvent is heated to 50-80 ℃ under vacuum condition, and the organic solvent is evaporated.
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