Separation and purification method and separation and purification system of sodium difluoro (oxalato) borate

Abstract

The invention discloses a separation and purification method and a separation and purification system for sodium difluoro (oxalato) borate. The separation and purification method comprises the following steps: performing ultrafiltration on a mixed solution containing NaDFOB and NaBF to obtain an ultrafiltration production solution; then carrying out nanofiltration separation on the ultrafiltration production liquid to obtain a NaDFOB nanofiltration concentrated liquid and a NaBF nanofiltration production liquid; carrying out enrichment, crystallization and solid-liquid separation on the nanofiltration concentrated solution to obtain a NaDFOB solid; and carrying out crystallization and solid-liquid separation on the nanofiltration production liquid to obtain a NaBF solid. The separation and purification method and the separation and purification system of the sodium difluoro (oxalato) borate have the characteristics of high selectivity, high separation efficiency and high product purity.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion battery electrolytes, and specifically refers to a method and system for separating and purifying sodium difluorooxalate borate. Background Art

[0002] Due to its safety and cost advantages, sodium-ion battery technology is becoming the most promising secondary battery system with large-scale commercialization potential after lithium-ion batteries. As a core component of the battery system, the sodium-ion battery electrolyte constructs an ion transport channel through the scientific ratio of solvents, sodium salt electrolytes, and functional additives, and its performance directly determines the voltage platform and energy density of the battery.

[0003] In the sodium-ion battery electrolyte system, the selection of sodium salts has a decisive impact on electrochemical performance. As a charge carrier, sodium salts not only affect the ionic conductivity of the electrolyte, but also are related to the cycle stability of the battery. The dissolution characteristics of sodium salts may cause electrode interface failure, while the solvation structure of sodium ions (including geometric configuration and electron cloud distribution) will significantly affect its diffusion kinetics at the electrode / electrolyte interface. In addition, the chemical stability and thermal stability of sodium salts directly restrict the battery safety, and its toxicity and corrosiveness have become important considerations in practical applications.

[0004] Sodium difluorooxalate borate (NaDFOB, chemical formula: C2BF2NaO4), as a new type of electrolyte salt, exhibits breakthrough performance advantages:

[0005] Composite structure advantage: It cleverly combines the molecular characteristics of sodium tetrafluoroborate (NaBF4) and sodium bis(oxalato)borate (NaBOB), and has both high ionic conductivity and interfacial stability;

[0006] Universal solvent compatibility: It shows excellent performance in multi-solvent systems such as EC:DEC (1:1), EC:PC (1:1), EC:DMC (1:1), etc., breaking through the dependence of traditional sodium salts (NaClO4, NaPF6) on specific solvents;

[0007] Excellent electrochemical performance: Based on the Na / Na 0.44 MnO2 half-cell test shows that it maintains a capacity retention rate of >85% (1C rate, 500 cycles) in a wide range of solvent systems, which is more than 30% higher than the traditional system;

[0008] Environmentally friendly characteristics: No dangerous by-products such as HF and ClO - are detected in the air / water exposure experiment, and the safety performance meets the industrial application standard.

[0009] This electrolyte salt with both high performance and safety has been successfully applied to the sodium-ion secondary battery system. Its 20% cost reduction (compared with the lithium-ion battery system) and the thermal stability threshold of 150 °C provide key technical support for large-scale energy storage applications.

[0010] The current mainstream preparation process of sodium difluoro(oxalato)borate (NaDFOB) uses sodium oxalate and boron trifluoride as starting materials, and the target product is obtained through chemical reactions followed by filtration and purification. However, this synthesis system has significant defects: during the reaction process, due to side reactions, a large amount of sodium tetrafluoroborate (NaBF4) impurities are generated in the product.

[0011] Since the solubility of NaDFOB and NaBF4 in common organic solvents (such as carbonates and ethers) is highly similar, it is difficult to effectively separate them by traditional recrystallization methods. Usually, the impurity content needs to be gradually reduced through multiple repeated operations. However, this process has industrial bottlenecks such as high solvent consumption, low product yield, and high operation complexity. Summary of the Invention

[0012] The purpose of the present invention is to provide a method and system for the separation and purification of sodium difluoro(oxalato)borate, which have the characteristics of high selectivity, high separation efficiency, and high product purity.

[0013] The present invention can be realized through the following technical solutions:

[0014] The present invention relates to a method for the separation and purification of sodium difluoro(oxalato)borate, including the following steps: ultrafiltrating a mixed solution containing NaDFOB and NaBF4 to obtain an ultrafiltration product solution; then subjecting the ultrafiltration product solution to nanofiltration separation to obtain a NaDFOB nanofiltration concentrate and a NaBF4 nanofiltration product solution; enriching, crystallizing, and performing solid-liquid separation on the nanofiltration concentrate to obtain NaDFOB solid; and crystallizing and performing solid-liquid separation on the nanofiltration product solution to obtain NaBF4 solid.

[0015] Further, the nanofiltration membrane used in the nanofiltration process is an organic nanofiltration membrane and / or an inorganic nanofiltration membrane. The organic nanofiltration membrane is one or more of cellulose acetate membranes, polyamide membranes, sulfonated polysulfone membranes, sulfonated polyethersulfone membranes, polycarbonate membranes, and polyester membranes, and the inorganic nanofiltration membrane is one or more of alumina membranes, silica membranes, zirconia membranes, and titanium dioxide membranes.

[0016] Further, the solvent of the mixed solution is one or more of water, alcohol solvents, nitrile solvents, ether solvents, heterocyclic organic solvents, sulfone solvents, and ester solvents, specifically such as isopropanol, acetonitrile, adiponitrile, diethyl ether, dipropyl ether, diisopropyl ether, ethylene glycol dimethyl ether, dioxolane, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, sulfolane, etc.

[0017] Furthermore, the solid-liquid separation method is one or more of gravitational sedimentation, filtration, centrifugal separation, and pressing separation.

[0018] Furthermore, the crystallization method is one or more of evaporation crystallization, cooling crystallization, salting-out crystallization, and reaction crystallization.

[0019] Furthermore, the pore size of the ultrafiltration membrane used in the ultrafiltration process is 1 - 100 nm to ensure the retention of suspended particles and microorganisms.

[0020] Furthermore, the inlet and outlet pressures of the ultrafiltration process are controlled at 2 - 10 bar, and the working temperature is 20 - 60 °C. High temperature can increase the ion diffusion rate, but exceeding 60 °C will accelerate membrane aging or fouling.

[0021] Furthermore, the pore size of the nanofiltration membrane used in the nanofiltration process is 0.5 - 1.5 nm to ensure the effective retention of NaDFOB while allowing NaBF4 to pass through.

[0022] Furthermore, the inlet and outlet pressures of the nanofiltration process are controlled at 2 - 10 bar, and the working temperature is 20 - 60 °C.

[0023] Furthermore, the control end point of the enrichment of the nanofiltration concentrate is the concentration ratio of NaDFOB to NaBF4, and this ratio must be much greater than the concentration ratio of the co-saturated solution of NaDFOB and NaBF4 to facilitate subsequent crystallization separation treatment.

[0024] Another aspect of the present invention is to protect a separation and purification system for sodium difluorooxalate borate. The system includes a mixed liquid tank, an ultrafiltration device, a nanofiltration device, a nanofiltration product liquid tank, a nanofiltration concentrate tank, a crystallization device, a solid-liquid separation device, a NaDFOB storage tank, a NaBF4 storage tank, and an end point detection and control device; the liquid outlet of the mixed liquid tank is connected to the liquid inlet of the ultrafiltration device, the ultrafiltration product liquid outlet of the ultrafiltration device is connected to the nanofiltration liquid inlet of the nanofiltration device, and the nanofiltration product liquid outlet of the nanofiltration device is connected to the inlet of the nanofiltration product liquid tank; the outlet of the nanofiltration product liquid tank is connected to the inlet of the first crystallization device, the outlet of the first crystallization device is connected to the inlet of the first solid-liquid separation device, and the solid separated by the first solid-liquid separation device is transported to the NaBF4 storage tank; the outlet of the nanofiltration concentrate tank is connected to the inlet of the second crystallization device, the outlet of the second crystallization device is connected to the inlet of the second solid-liquid separation device, and the solid separated by the second solid-liquid separation device is transported to the NaDFOB storage tank.

[0025] Furthermore, the liquid I obtained by the first solid-liquid separation device is connected to the nanofiltration liquid inlet pipeline through a pipeline to realize the recycling treatment of the liquid; the liquid II coming out of the second solid-liquid separation device is connected to the nanofiltration liquid inlet pipeline through a pipeline to realize the recycling treatment of the liquid; the ultrafiltration concentrate outlet of the ultrafiltration device is connected to the liquid inlet pipeline of the ultrafiltration device to realize the recycling ultrafiltration treatment of the ultrafiltration concentrate.

[0026] Further, the membrane modules of the ultrafiltration device and the nanofiltration device are spiral wound membrane modules and / or cassette type membrane modules, and cross-flow filtration is achieved through the membrane modules.

[0027] Further, the nanofiltration concentrated solution outlet of the nanofiltration device is connected to an end-point detection and control device, and the end-point detection and control device includes a detection sensor and a three-way valve controller; through the judgment of the detection sensor, when the concentration ratio of NaDFOB and NaBF4 in the nanofiltration concentrated solution is less than a certain specific value, the nanofiltration concentrated solution is all introduced into the nanofiltration feed pipeline through the three-way valve; when the concentration ratio of NaDFOB and NaBF4 in the nanofiltration concentrated solution is greater than or equal to a certain specific value, the nanofiltration concentrated solution is all introduced into the nanofiltration concentrated solution tank through the three-way valve.

[0028] The separation and purification method and system of sodium difluorooxalate borate of the present invention have the following beneficial effects:

[0029] Compared with the traditional separation method that only relies on the solubility difference between NaDFOB and NaBF4 in the solvent for extraction and crystallization, the present invention separates NaDFOB and NaBF4 by nanofiltration. There are differences in the anion composition and structure between NaDFOB and NaBF4, resulting in different anion sizes, charges carried, and charge densities. The nanofiltration membrane can precisely regulate the charge properties and pore sizes on the membrane surface, and use electrostatic repulsion and steric hindrance effects to selectively separate and enrich these two substances, realizing an efficient and precise separation process, effectively improving the purity of the two products of NaDFOB and NaBF4, with low energy consumption, large processing throughput, and enabling large-scale production expansion.

[0030] The present invention also proposes a separation and purification system for NaDFOB and NaBF4. It has a compact structure, can recycle waste liquid, has a very small burden on waste liquid treatment in the later stage, and greatly reduces the three-waste treatment cost. In the later stage, the separation, enrichment, and purification efficiency of NaDFOB and NaBF4 can be effectively improved by further optimizing and regulating performance parameters such as membrane composition, structure, pore size, porosity, and surface charge, and the product purity and the service life of the membrane can be improved.

[0031] In the present invention, the nanofiltration membrane separation technology and the crystallization method are integrated and coupled to form a more efficient separation system. The nanofiltration separation process is usually carried out under mild conditions, without extreme conditions such as high temperature and high pressure, with relatively low requirements for equipment, reducing equipment investment and operating costs, while also improving operation safety, reducing energy consumption and equipment wear, and having good economic efficiency and practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the system composition of a separation and purification system for sodium difluorooxalate borate of the present invention. Detailed implementation manners

[0033] To enable those skilled in the art to better understand the technical solutions of the present invention, the products of the present invention will be further described in detail below in conjunction with embodiments.

[0034] The present invention relates to a method for separating and purifying sodium difluorooxaloborate, comprising the following steps: subjecting a mixed solution containing NaDFOB and NaBF4 to ultrafiltration to obtain an ultrafiltration product solution; then subjecting the ultrafiltration product solution to nanofiltration separation to obtain a NaDFOB nanofiltration concentrate and a NaBF4 nanofiltration product solution; subjecting the nanofiltration concentrate to enrichment, crystallization, and solid-liquid separation to obtain NaDFOB solid; and subjecting the nanofiltration product solution to crystallization and solid-liquid separation to obtain NaBF4 solid.

[0035] Further, the nanofiltration membrane used in the nanofiltration process is an organic nanofiltration membrane and / or an inorganic nanofiltration membrane. The organic nanofiltration membrane is one or more of an acetate fiber membrane, a polyamide membrane, a sulfonated polysulfone membrane, a sulfonated polyethersulfone membrane, a polycarbonate membrane, and a polyester membrane, and the inorganic nanofiltration membrane is one or more of an alumina membrane, a silica membrane, a zirconia membrane, and a titanium dioxide membrane.

[0036] Further, the solvent of the mixed solution is one or more of water, alcohol solvents, nitrile solvents, ether solvents, heterocyclic organic solvents, sulfone solvents, and ester solvents, specifically such as isopropanol, acetonitrile, adiponitrile, ether, dipropyl ether, diisopropyl ether, ethylene glycol dimethyl ether, dioxolane, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, sulfolane, etc.

[0037] Further, the method of solid-liquid separation is one or more of gravity sedimentation, filtration, centrifugal separation, and pressing separation.

[0038] Further, the crystallization method is one or more of evaporation crystallization, cooling crystallization, salting-out crystallization, and reaction crystallization.

[0039] Further, the pore size of the ultrafiltration membrane used in the ultrafiltration process is 1-100 nm.

[0040] Further, the inlet and outlet pressures of the ultrafiltration process are controlled to be 2-10 bar, and the working temperature is 20-60 °C.

[0041] Further, the pore size of the nanofiltration membrane used in the nanofiltration process is 0.5-1.5 nm.

[0042] Further, the inlet and outlet pressures of the nanofiltration process are controlled to be 2-10 bar, and the working temperature is 20-60 °C.

[0043] Further, the control end point of the enrichment of the nanofiltration concentrate is the concentration ratio of NaDFOB to NaBF4.

[0044] As Figure 1 shown, another aspect of the present invention is to protect a separation and purification system for sodium difluoro(oxalato)borate. The system includes a mixed liquid tank, an ultrafiltration device, a nanofiltration device, a nanofiltration product liquid tank, a nanofiltration concentrated liquid tank, a crystallization device, a solid-liquid separation device, a NaDFOB storage tank, a NaBF4 storage tank, and an end-point detection and control device; the liquid outlet of the mixed liquid tank is connected to the liquid inlet of the ultrafiltration device, the ultrafiltration product liquid outlet of the ultrafiltration device is connected to the nanofiltration liquid inlet of the nanofiltration device, and the nanofiltration product liquid outlet of the nanofiltration device is connected to the inlet of the nanofiltration product liquid tank; the outlet of the nanofiltration product liquid tank is connected to the inlet of the first crystallization device, the outlet of the first crystallization device is connected to the inlet of the first solid-liquid separation device, and the solid separated by the first solid-liquid separation device is transported to the NaBF4 storage tank; the outlet of the nanofiltration concentrated liquid tank is connected to the inlet of the second crystallization device, the outlet of the second crystallization device is connected to the inlet of the second solid-liquid separation device, and the solid separated by the second solid-liquid separation device is transported to the NaDFOB storage tank.

[0045] Furthermore, the liquid I obtained by the first solid-liquid separation device is connected to the nanofiltration liquid inlet pipeline through a pipeline to realize the recycling treatment of the liquid; the liquid II coming out of the second solid-liquid separation device is connected to the nanofiltration liquid inlet pipeline through a pipeline to realize the recycling treatment of the liquid; the ultrafiltration concentrated liquid outlet of the ultrafiltration device is connected to the liquid inlet pipeline of the ultrafiltration device to realize the recycling ultrafiltration treatment of the ultrafiltration concentrated liquid.

[0046] Furthermore, the membrane modules of the ultrafiltration device and the nanofiltration device are spiral wound membrane modules and / or cassette type membrane modules, and cross-flow filtration is realized through the membrane modules.

[0047] Furthermore, the nanofiltration concentrated liquid outlet of the nanofiltration device is connected to the end-point detection and control device. The end-point detection and control device includes a detection sensor and a three-way valve controller; through the judgment of the detection sensor, when the concentration ratio of NaDFOB and NaBF4 in the nanofiltration concentrated liquid is less than a certain specific value, the nanofiltration concentrated liquid is all introduced into the nanofiltration liquid inlet pipeline through the three-way valve; when the concentration ratio of NaDFOB and NaBF4 in the nanofiltration concentrated liquid is greater than or equal to a certain specific value, the nanofiltration concentrated liquid is all introduced into the nanofiltration concentrated liquid tank through the three-way valve.

[0048] In the present invention, the mixed liquid tank is used to store the mixed liquid to be processed and is the starting point of the entire process flow. From this tank, the mixed liquid enters the ultrafiltration stage. The ultrafiltration unit performs ultrafiltration on the mixed liquid to trap impurities and microorganisms in the mixed liquid and separate the mixed liquid into an ultrafiltration product liquid and an ultrafiltration concentrate. The nanofiltration unit receives the ultrafiltration product liquid, liquid I, liquid II, and the nanofiltration concentrate that requires further recycling. This serves as the nanofiltration feed liquid. After nanofiltration, the nanofiltration product liquid and the nanofiltration concentrate are separated. The nanofiltration product tank is used to store the nanofiltration product liquid enriched in NaBF4, which then enters the crystallization stage and undergoes solid-liquid separation to obtain the solid product NaBF4. The nanofiltration concentrate tank is used to store the nanofiltration concentrate enriched in NaDFOB, as determined by the endpoint detection control device. Crystallization and solid-liquid separation operations are then carried out to obtain the solid product NaDFOB. The liquid II obtained by solid-liquid separation is returned to the nanofiltration unit for recycling and recycling. The endpoint detection control device detects the nanofiltration concentrate and controls its flow direction to ensure the precise operation of the entire process. The crystallization equipment crystallizes the liquids output from the nanofiltration liquid production tank and the nanofiltration concentrate tank, respectively, to precipitate the target substance in solid form. The solid-liquid separation equipment separates the crystallized material into two solid products, NaBF4 and NaDFOB, respectively.

[0049] Example 1

[0050] This embodiment relates to the separation and purification of NaDFOB and NaBF4, and the separation and purification method using the corresponding separation and purification system includes the following steps:

[0051] Step 1: Place the salt mixture (81.2% by mass of NaDFOB and 18.7% by mass of NaBF4) into a mixing tank, add water as a solvent, and prepare an initial mixed solution with a salt content of 30 g / L;

[0052] Step 2: The obtained primary mixed liquid enters the ultrafiltration device for ultrafiltration. The ultrafiltration membrane is a polyamide membrane with a pore size of 30nm. The ultrafiltration pressure is controlled at 5 bar and the temperature is controlled at 40°C. The generated ultrafiltration concentrate is refluxed and combined with the ultrafiltration feed liquid to enter the ultrafiltration cycle. The ultrafiltration product liquid is obtained.

[0053] Step 3: The obtained ultrafiltration product liquid is used as the nanofiltration feed liquid for the next step and enters the nanofiltration device. The nanofiltration membrane is a polyamide membrane with a pore size of 1 nm. The nanofiltration pressure is controlled at 5 bar and the temperature is controlled at 40 ° C during nanofiltration to separate the different anion components in the mixed liquid to form a nanofiltration concentrate and a nanofiltration product liquid. Among them, the main component of the nanofiltration concentrate is NaDFOB, and the main component of the nanofiltration product liquid is NaBF4;

[0054] Step 4: The nanofiltration concentrate obtained in Step 3 is combined with the ultrafiltration permeate as the nanofiltration feed and enters the nanofiltration circulation treatment. After circulating several times, enrichment is carried out to make the concentration ratio of NaDFOB to NaBF4 salts reach 14.5;

[0055] Step 5: The nanofiltration concentrate meeting the concentration requirements is introduced into the nanofiltration concentrate tank and then enters the cooling crystallization device to obtain a solid-liquid mixture;

[0056] Step 6: The solid-liquid mixture obtained in Step 5 is centrifuged, and the mother liquor is returned to the nanofiltration device for cyclic concentration, and the solid product NaDFOB is collected;

[0057] Step 7: The nanofiltration permeate obtained in Step 3 is introduced into the nanofiltration permeate tank and then enters the cooling crystallization device to obtain a solid-liquid mixture;

[0058] Step 8: The solid-liquid mixture obtained in Step 7 is centrifuged, and the mother liquor is returned to the nanofiltration device for cyclic concentration, and the solid product NaBF4 is collected.

[0059] Example 2

[0060] This example relates to the separation and purification of NaDFOB and NaBF4. The separation and purification method using the corresponding separation and purification system includes the following steps:

[0061] Step 1: The mixed salt (where the mass of NaDFOB accounts for 41.3% and the mass of NaBF4 accounts for 58.5%) is put into the mixed liquid tank, and dimethyl carbonate is added as the solvent to prepare a primary mixed liquid with a salt content of 30 g / L;

[0062] Step 2: The obtained primary mixed liquid enters the ultrafiltration device for ultrafiltration. The ultrafiltration membrane is a polyamide membrane with a pore size of 30 nm. The ultrafiltration pressure is controlled at 5 bar, and the temperature during ultrafiltration is controlled at 40 °C. The ultrafiltration concentrate reflux is combined with the ultrafiltration feed and enters the ultrafiltration circulation treatment, and the ultrafiltration permeate is obtained;

[0063] Step 3: The obtained ultrafiltration permeate enters the nanofiltration device as the next-stage nanofiltration feed. The nanofiltration membrane is a silicon oxide membrane with a pore size of 1 nm. The nanofiltration pressure is controlled at 5 bar, and the temperature during nanofiltration is controlled at 40 °C. Different anion components in the mixed liquid are separated to form a nanofiltration concentrate and a nanofiltration permeate. Among them, the main component of the nanofiltration concentrate is NaDFOB, and the main component of the nanofiltration permeate is NaBF4;

[0064] Step 4: The nanofiltration concentrate obtained in Step 3 is combined with the ultrafiltration permeate as the nanofiltration feed and enters the nanofiltration circulation treatment. After circulating several times, enrichment is carried out to make the concentration ratio of NaDFOB to NaBF4 salts reach 14.5;

[0065] Step 5: The nanofiltration concentrate meeting the concentration requirements is introduced into the nanofiltration concentrate tank and then enters the cooling crystallization device to obtain a solid-liquid mixture;

[0066] Step 6: Centrifuge the solid-liquid mixture obtained in Step 5, return the mother liquor to the nanofiltration device for cyclic concentration, and collect the solid product NaDFOB;

[0067] Step 7: Introduce the nanofiltration product solution obtained in Step 3 into a nanofiltration product solution tank, and then enter a cooling crystallization device to obtain a solid-liquid mixture;

[0068] Step 8: Centrifuge the solid-liquid mixture obtained in Step 7, return the mother liquor to the nanofiltration device for cyclic concentration, and collect the solid product NaBF4.

[0069] Example 3

[0070] This example relates to the separation and purification of NaDFOB and NaBF4. The separation and purification method using the corresponding separation and purification system includes the following steps:

[0071] Step 1: Put the mixed salt (where the mass of NaDFOB accounts for 81.2% and the mass of NaBF4 accounts for 18.7%) into a mixed liquid tank, add isopropanol as a solvent, and prepare a preliminary mixed liquid with a salt content of 30 g / L;

[0072] Step 2: The obtained preliminary mixed liquid enters an ultrafiltration device for ultrafiltration. The ultrafiltration membrane is a polyamide membrane with a pore size of 30 nm. The ultrafiltration pressure is controlled at 5 bar, and the temperature during ultrafiltration is controlled at 40 °C. The ultrafiltration concentrated liquid is refluxed and combined with the ultrafiltration feed liquid for ultrafiltration cyclic treatment. And obtain the ultrafiltration product solution;

[0073] Step 3: The obtained ultrafiltration product solution enters a nanofiltration device as the next nanofiltration feed liquid. The nanofiltration membrane is a cellulose acetate membrane with a pore size of 1 nm. The nanofiltration pressure is controlled at 10 bar, and the temperature during nanofiltration is controlled at 20 °C. Separate different anion components in the mixed liquid to form a nanofiltration concentrated liquid and a nanofiltration product solution. Among them, the main component of the nanofiltration concentrated liquid is NaDFOB, and the main component of the nanofiltration product solution is NaBF4;

[0074] Step 4: The nanofiltration concentrated liquid obtained in Step 3 is combined with the ultrafiltration product solution as the nanofiltration feed liquid for nanofiltration cyclic treatment. Cycle several times to enrich the concentration ratio of NaDFOB to NaBF4 salt to reach 14.5;

[0075] Step 5: Introduce the nanofiltration concentrated liquid that meets the concentration requirements into a nanofiltration concentrated liquid tank, and then enter a cooling crystallization device to obtain a solid-liquid mixture;

[0076] Step 6: Centrifuge the solid-liquid mixture obtained in Step 5, return the mother liquor to the nanofiltration device for cyclic concentration, and collect the solid product NaDFOB;

[0077] Step 7: Introduce the nanofiltration product solution obtained in Step 3 into a nanofiltration product solution tank, and then enter a cooling crystallization device to obtain a solid-liquid mixture;

[0078] Step 8: Centrifuge the solid-liquid mixture obtained in Step 7, return the mother liquor to the nanofiltration device for cyclic concentration, and collect the solid product NaBF4.

[0079] Example 4

[0080] This example relates to the separation and purification of NaDFOB and NaBF4. The separation and purification method using the corresponding separation and purification system includes the following steps:

[0081] Step 1: Put the mixed salt (where the mass of NaDFOB accounts for 81.2% and the mass of NaBF4 accounts for 18.7%) into the mixed liquid tank, add acetonitrile as the solvent, and prepare a preliminary mixed liquid with a salt content of 30 g / L.

[0082] Step 2: The obtained preliminary mixed liquid enters the ultrafiltration device for ultrafiltration. The ultrafiltration membrane is a polyamide membrane with a pore size of 30 nm. The ultrafiltration pressure is controlled at 5 bar, and the temperature during ultrafiltration is controlled at 40 °C. The ultrafiltration concentrated liquid generated is refluxed and combined with the ultrafiltration feed liquid, and enters the ultrafiltration cyclic treatment. And obtain the ultrafiltration product liquid.

[0083] Step 3: The obtained ultrafiltration product liquid enters the nanofiltration device as the next nanofiltration feed liquid. The nanofiltration membrane is a sulfonated polysulfone membrane with a pore size of 1 nm. The nanofiltration pressure is controlled at 8 bar, and the temperature during nanofiltration is controlled at 20 °C. Separate different anion components in the mixed liquid to form a nanofiltration concentrated liquid and a nanofiltration product liquid. Among them, the main component of the nanofiltration concentrated liquid is NaDFOB, and the main component of the nanofiltration product liquid is NaBF4.

[0084] Step 4: The nanofiltration concentrated liquid obtained in Step 3 is combined with the ultrafiltration product liquid and enters the nanofiltration cyclic treatment as the nanofiltration feed liquid. Cycle several times to enrich the concentration ratio of NaDFOB to NaBF4 salt to reach 14.5.

[0085] Step 5: The nanofiltration concentrated liquid meeting the concentration requirements is introduced into the nanofiltration concentrated liquid tank and then enters the cooling crystallization device to obtain a solid-liquid mixture.

[0086] Step 6: Centrifuge the solid-liquid mixture obtained in Step 5, return the mother liquor to the nanofiltration device for cyclic concentration, and collect the solid product NaDFOB.

[0087] Step 7: The nanofiltration product liquid obtained in Step 3 is introduced into the nanofiltration product liquid tank and then enters the cooling crystallization device to obtain a solid-liquid mixture.

[0088] Step 8: Centrifuge the solid-liquid mixture obtained in Step 7, return the mother liquor to the nanofiltration device for cyclic concentration, and collect the solid product NaBF4.

[0089] Example 5

[0090] This embodiment relates to the separation and purification of NaDFOB and NaBF4. The separation and purification method using the corresponding separation and purification system includes the following steps:

[0091] Step 1: Put the mixed salt (where the mass of NaDFOB accounts for 81.2% and the mass of NaBF4 accounts for 18.7%) into the mixed liquid tank, add ether as the solvent, and configure it into a primary mixed liquid with a salt content of 30 g / L.

[0092] Step 2: The obtained primary mixed liquid enters the ultrafiltration device for ultrafiltration. The ultrafiltration membrane is a polyamide membrane with a pore size of 30 nm. The ultrafiltration pressure is controlled at 5 bar, and the temperature during ultrafiltration is controlled at 40°C. The ultrafiltration concentrate is refluxed and combined with the ultrafiltration feed liquid, and enters the ultrafiltration circulation treatment. And the ultrafiltration product liquid is obtained.

[0093] Step 3: The obtained ultrafiltration product liquid enters the nanofiltration device as the next nanofiltration feed liquid. The nanofiltration membrane is a polycarbonate membrane with a pore size of 0.5 nm. The nanofiltration pressure is controlled at 6 bar, and the temperature during nanofiltration is controlled at 40°C. Different anion components in the mixed liquid are separated to form a nanofiltration concentrate and a nanofiltration product liquid. Among them, the main component of the nanofiltration concentrate is NaDFOB, and the main component of the nanofiltration product liquid is NaBF4.

[0094] Step 4: The nanofiltration concentrate obtained in Step 3 is combined with the ultrafiltration product liquid as the nanofiltration feed liquid and enters the nanofiltration circulation treatment. After circulating several times, the concentration ratio of NaDFOB to NaBF4 salt is enriched to reach 14.5.

[0095] Step 5: The nanofiltration concentrate meeting the concentration requirement is introduced into the nanofiltration concentrate tank, and then enters the cooling crystallization device to obtain a solid-liquid mixture.

[0096] Step 6: The solid-liquid mixture obtained in Step 5 is centrifuged, and the mother liquor is returned to the nanofiltration device for cyclic concentration, and the solid product NaDFOB is collected.

[0097] Step 7: The nanofiltration product liquid obtained in Step 3 is introduced into the nanofiltration product liquid tank, and then enters the cooling crystallization device to obtain a solid-liquid mixture.

[0098] Step 8: The solid-liquid mixture obtained in Step 7 is centrifuged, and the mother liquor is returned to the nanofiltration device for cyclic concentration, and the solid product NaBF4 is collected.

[0099] Example 6

[0100] This embodiment relates to the separation and purification of NaDFOB and NaBF4. The separation and purification method using the corresponding separation and purification system includes the following steps:

[0101] Step 1: Put the mixed salt (where the mass of NaDFOB accounts for 81.2% and the mass of NaBF4 accounts for 18.7%) into the mixed liquid tank, add 1,3-dioxolane as the solvent, and prepare a preliminary mixed liquid with a salt content of 30 g / L;

[0102] Step 2: The obtained preliminary mixed liquid enters the ultrafiltration device for ultrafiltration. The ultrafiltration membrane is a polyamide membrane with a pore size of 30 nm. The ultrafiltration pressure is controlled at 5 bar, and the temperature during ultrafiltration is controlled at 40 °C. The ultrafiltration concentrate is refluxed and combined with the ultrafiltration feed liquid to enter the ultrafiltration circulation treatment, and the ultrafiltration product liquid is obtained;

[0103] Step 3: The obtained ultrafiltration product liquid enters the nanofiltration device as the next-stage nanofiltration feed liquid. The nanofiltration membrane is an alumina membrane with a pore size of 0.5 nm. The nanofiltration pressure is controlled at 5 bar, and the temperature during nanofiltration is controlled at 40 °C. Different anion components in the mixed liquid are separated to form a nanofiltration concentrate and a nanofiltration product liquid. Among them, the main component of the nanofiltration concentrate is NaDFOB, and the main component of the nanofiltration product liquid is NaBF4;

[0104] Step 4: The nanofiltration concentrate obtained in Step 3 is combined with the ultrafiltration product liquid as the nanofiltration feed liquid to enter the nanofiltration circulation treatment. After circulating several times, the concentration ratio of NaDFOB to NaBF4 salts is enriched to reach 14.5;

[0105] Step 5: The nanofiltration concentrate meeting the concentration requirements is introduced into the nanofiltration concentrate tank and then enters the cooling crystallization device to obtain a solid-liquid mixture;

[0106] Step 6: The solid-liquid mixture obtained in Step 5 is centrifuged. The mother liquor is returned to the nanofiltration device for cyclic concentration, and the solid product NaDFOB is collected;

[0107] Step 7: The nanofiltration product liquid obtained in Step 3 is introduced into the nanofiltration product liquid tank and then enters the cooling crystallization device to obtain a solid-liquid mixture;

[0108] Step 8: The solid-liquid mixture obtained in Step 7 is centrifuged. The mother liquor is returned to the nanofiltration device for cyclic concentration, and the solid product NaBF4 is collected.

[0109] Example 7

[0110] This example relates to the separation and purification of NaDFOB and NaBF4. The separation and purification method using the corresponding separation and purification system includes the following steps:

[0111] Step 1: Put the mixed salt (where the mass of NaDFOB accounts for 81.2% and the mass of NaBF4 accounts for 18.7%) into the mixed liquid tank, add sulfolane as the solvent, and prepare a preliminary mixed liquid with a salt content of 30 g / L;

[0112] Step 2: The obtained initial mixture enters an ultrafiltration device for ultrafiltration. The ultrafiltration membrane is a polyamide membrane with a pore size of 30 nm. The ultrafiltration pressure is controlled at 5 bar, and the temperature during ultrafiltration is controlled at 40 °C. The ultrafiltration concentrate is refluxed and combined with the ultrafiltration feed liquid, and enters the ultrafiltration circulation treatment. And the ultrafiltration permeate is obtained;

[0113] Step 3: The obtained ultrafiltration permeate enters the nanofiltration device as the next nanofiltration feed liquid. The nanofiltration membrane is a titanium dioxide membrane with a pore size of 1.5 nm. The nanofiltration pressure is controlled at 2 bar, and the temperature during nanofiltration is controlled at 60 °C. Different anion components in the mixed liquid are separated to form a nanofiltration concentrate and a nanofiltration permeate. Among them, the main component of the nanofiltration concentrate is NaDFOB, and the main component of the nanofiltration permeate is NaBF4;

[0114] Step 4: The nanofiltration concentrate obtained in Step 3 is combined with the ultrafiltration permeate and enters the nanofiltration circulation treatment as the nanofiltration feed liquid. After circulating several times, the concentration ratio of NaDFOB to NaBF4 salts is enriched to reach 18.5;

[0115] Step 5: The nanofiltration concentrate meeting the concentration requirements is introduced into the nanofiltration concentrate tank and then enters the cooling crystallization device to obtain a solid-liquid mixture;

[0116] Step 6: The solid-liquid mixture obtained in Step 5 is centrifuged, and the mother liquor is returned to the nanofiltration device for cyclic concentration, and the solid product NaDFOB is collected;

[0117] Step 7: The nanofiltration permeate obtained in Step 3 is introduced into the nanofiltration permeate tank and then enters the cooling crystallization device to obtain a solid-liquid mixture;

[0118] Step 8: The solid-liquid mixture obtained in Step 7 is centrifuged, and the mother liquor is returned to the nanofiltration device for cyclic concentration, and the solid product NaBF4 is collected.

[0119] Comparative Example 1

[0120] This example uses solvent recrystallization for separation and purification, and its specific steps include:

[0121] Step 1: Transfer 100 g of the mixed salt (where the mass of NaDFOB accounts for 81.2% and the mass of NaBF4 accounts for 18.7%) to 2 L of diethyl ether, heat to 30 °C, and stir for 5 h;

[0122] Step 2: Filter the stirred solid-liquid mixture with an organic filter paper;

[0123] Step 3: For the obtained filtrate, the solvent is evaporated under reduced pressure at 30 °C to obtain NaDFOB.

[0124] To compare the purification effects of the device for separating and purifying sodium difluoro(oxalato)borate (NaDFOB) and sodium tetrafluoroborate (NaBF4) of the present invention, Table 1 shows the relevant parameters of Examples 1-7 and Comparative Example 1 and the product purities of NaDFOB and NaBF4 obtained after purification:

[0125] Table 1 Relevant Parameters and Performance Test Results of Examples

[0126] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Comparative Example 1 <![CDATA[Mass ratio of mixed salts: NaDFOB: NaBF4]]> 81.2：18.7 41.3：58.5 81.2：18.7 81.2：18.7 81.2：18.7 81.2：18.7 81.2：18.7 81.2：18.7 Nanofiltration membrane type Polyamide Silica Cellulose acetate Sulfonated polysulfone Polycarbonate Aluminum oxide Titanium dioxide - Solvent type Water Dimethyl carbonate Isopropyl alcohol Acetonitrile Diethyl ether 1,3 - Dioxolane Sulfolane Diethyl ether Nanofiltration membrane working environment 40°C, 5 bar 40°C, 5 bar 20°C, 10 bar 20°C, 8 bar 40°C, 6 bar 40°C, 5 bar 60°C, 2 bar - Nanofiltration membrane pore size (nm) 1 1 1 1 0.5 0.5 1.5 - Enrichment concentration ratio 14.5 14.5 14.5 14.5 14.5 14.5 18.5 - Purity of NaDFOB (%) 99.2 98.3 99.4 99.2 98.9 98.2 98.5 97.4 <![CDATA[Purity (%) of NaBF4]]> 99.3 99.3 98.7 99.0 98.4 98.3 98.2 -

[0127] According to the test results of Examples 1 and 2 in the table, it can be seen that when the purity of sodium difluoro(oxalato)borate in the mixed salt is at a medium level (41.3%) or high (81.2%), battery-grade products can be obtained by using the purification method of the present invention. The present invention has a wide range of applications and can be used for the purification of most reactions that generate sodium tetrafluoroborate impurities.

[0128] Comparing the test results of Examples 1-7 in Table 1, it can be seen that by using the nanofiltration enrichment-crystallization separation process of the present invention, key parameters such as the filter membrane material, pore size gradient, solvent system, operating temperature, and nanofiltration pressure are systematically combined and verified. Under all 7 groups of process conditions, the purities of NaDFOB and NaBF4 are stably maintained above 98%, and the system exhibits excellent separation selectivity, confirming that the process design has good operating flexibility.

[0129] Comparing the test results of Examples 1-7 and Comparative Example 1 in Table 1, it can be seen that the method of the present invention can obtain higher-purity NaDFOB compared with the solvent method for purification and can simultaneously purify NaBF4.

[0130] The above-mentioned examples are only specific examples of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these obvious replacement forms all belong to the protection scope of the present invention.

Claims

1. A method for separating and purifying sodium difluoro(oxalato)borate, characterized in that It includes the following steps: Ultrafilter the mixed solution containing NaDFOB and NaBF4 to obtain an ultrafiltration product solution; then separate the ultrafiltration product solution by nanofiltration to obtain a NaDFOB nanofiltration concentrate and a NaBF4 nanofiltration product solution; enrich, crystallize, and perform solid-liquid separation on the nanofiltration concentrate to obtain solid NaDFOB; crystallize and perform solid-liquid separation on the nanofiltration product solution to obtain solid NaBF4.

2. The method for separating and purifying sodium difluoro(oxalato)borate according to claim 1, characterized in that: The nanofiltration membrane used in the nanofiltration process is an organic nanofiltration membrane and / or an inorganic nanofiltration membrane. The organic nanofiltration membrane is one or more of cellulose acetate membranes, polyamide membranes, sulfonated polysulfone membranes, sulfonated polyethersulfone membranes, polycarbonate membranes, and polyester membranes. The inorganic nanofiltration membrane is one or more of alumina membranes, silica membranes, zirconia membranes, and titanium dioxide membranes.

3. The method for separating and purifying sodium difluoro(oxalato)borate according to claim 1, characterized in that: The solvent of the mixed solution is one or more of water, alcohol solvents, nitrile solvents, ether solvents, heterocyclic organic solvents, sulfone solvents, and ester solvents.

4. The method for separating and purifying sodium difluoro(oxalato)borate according to claim 1, wherein: The method of solid-liquid separation is one or more of gravity sedimentation, filtration, centrifugal separation, and pressing separation.

5. The method for separating and purifying sodium difluoro(oxalato)borate according to claim 1, wherein: The crystallization method is one or more of evaporation crystallization, cooling crystallization, salting-out crystallization, and reaction crystallization.

6. The method for separating and purifying sodium difluoro(oxalato)borate according to claim 1, wherein: The pore size of the ultrafiltration membrane used in the ultrafiltration process is 1 - 100 nm. The inlet and outlet pressure of the ultrafiltration process is controlled at 2 - 10 bar, and the working temperature is 20 - 60 °C. The pore size of the nanofiltration membrane used in the nanofiltration process is 0.5 - 1.5 nm. The inlet and outlet pressure of the nanofiltration process is controlled at 2 - 10 bar, and the working temperature is 20 - 60 °C. The control end point of the enrichment of the nanofiltration concentrate is the concentration ratio of NaDFOB to NaBF4.

7. A separation and purification system for sodium difluorooxalate, characterized in that: The system includes a mixed solution tank, an ultrafiltration device, a nanofiltration device, a nanofiltration product solution tank, a nanofiltration concentrate tank, a crystallization device, a solid-liquid separation device, a NaDFOB storage tank, a NaBF4 storage tank, and an end point detection and control device. The liquid outlet of the mixed solution tank is connected to the liquid inlet of the ultrafiltration device. The ultrafiltration product solution outlet of the ultrafiltration device is connected to the nanofiltration inlet of the nanofiltration device. The nanofiltration product solution outlet of the nanofiltration device is connected to the inlet of the nanofiltration product solution tank. The outlet of the nanofiltration product solution tank is connected to the inlet of the first crystallization device. The outlet of the first crystallization device is connected to the inlet of the first solid-liquid separation device. The solid separated by the first solid-liquid separation device is transported to the NaBF4 storage tank. The outlet of the nanofiltration concentrate tank is connected to the inlet of the second crystallization device. The outlet of the second crystallization device is connected to the inlet of the second solid-liquid separation device. The solid separated by the second solid-liquid separation device is transported to the NaDFOB storage tank.

8. The separation and purification system of sodium difluoro(oxalato)borate according to claim 7, characterized in that: The liquid I obtained by the first solid-liquid separation device is connected to the nanofiltration inlet pipeline through a pipeline to realize the recycling treatment of the liquid. The liquid II coming out of the second solid-liquid separation device is connected to the nanofiltration inlet pipeline through a pipeline to realize the recycling treatment of the liquid. The ultrafiltration concentrate outlet of the ultrafiltration device is connected to the inlet pipeline of the ultrafiltration device to realize the recycling ultrafiltration treatment of the ultrafiltration concentrate.

9. The separation and purification system of sodium difluoro(oxalato)borate according to claim 7, characterized in that: The membrane modules of the ultrafiltration device and the nanofiltration device are spiral wound membrane modules and / or cassette type membrane modules, and cross-flow filtration is realized through the membrane modules.

10. The method for separating and purifying sodium difluoro(oxalato)borate according to claim 7, wherein: The nanofiltration concentrate outlet of the nanofiltration device is connected to the end point detection and control device. The end point detection and control device includes a detection sensor and a three-way valve controller.

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