A method for purifying cyclic sulfate for lithium batteries

Abstract

The present invention discloses a method for purifying cyclic sulfate for lithium batteries, belonging to the technical field of new lithium battery materials. A crude solution is subjected to processes such as dehydration, pH value control, continuous distillation control crystallization, separation, and drying to obtain a cyclic sulfate product with a purity of ≥99.99%. The method is advantageous in controlling secondary decomposition during the purification process, removing residual acid by using an organic amine acid-binding agent, and combining it with continuous distillation control crystallization technology to achieve stable and orderly crystallization of the product, resulting in a product with high crystallinity and few impurities.

Description

Technical Field

[0001] The present invention belongs to the technical field of new lithium battery materials, and in particular relates to a method for purifying cyclic sulfate for lithium batteries. Background Art

[0002] Cyclic sulfate compounds represented by vinyl sulfate are very important additives in lithium-ion batteries. They can be oxidized to form a film on the surface of the positive electrode of the lithium-ion battery and reduced to a low-impedance film on the surface of the negative electrode, effectively improving the high and low temperature cycle performance and high-temperature storage performance of the lithium-ion battery. Cyclic sulfate compounds containing different substituent groups have different performance and advantages in application and have broad application prospects. As the quality specifications of lithium battery electrolytes gradually improve, higher requirements are also placed on the purity of various additives. The current purity requirement for high-quality vinyl sulfate products is ≥99.99%, which poses a severe challenge to current production and purification processes. Most processes find it difficult to achieve this standard, or the process cost is very high. There is an urgent need to propose a more efficient and low-cost product purification method.

[0003] The mainstream production process of cyclic sulfates is to prepare sulfates by oxidation of sulfite, generally using oxides, chlorides, and complexes of the transition metal ruthenium as catalysts, with potassium permanganate, sodium hypochlorite, and sodium periodate as oxidants. Due to the problems of high production costs and the generation of large amounts of saline organic wastewater, manufacturers have developed hydrogen peroxide catalytic oxidation routes. Patent CN109422719A reports that hydrogen peroxide is added dropwise to a mixture of cyclic sulfate, an organic solvent, and a TS-1 molecular sieve catalyst to carry out a catalytic oxidation reaction to prepare sulfates. Patent CN114195757A reacts thionyl chloride with ethylene glycol at low temperatures through a microchannel reactor to obtain vinyl sulfate, washes the liquid after the reaction, then reacts vinyl sulfate with hydrogen peroxide at low temperatures through a microchannel reactor, washes the liquid after the reaction, and finally recrystallizes at low temperatures to obtain vinyl sulfate. Regardless of the method described above, the purity of the obtained product is generally lower than 99.9%, which cannot meet the requirements of high-quality products, or multiple recrystallization operations are required to meet the purity requirements, but the crystallization yield will be reduced to <90%, resulting in an increase in production costs.

[0004] In summary, the current synthesis process for cyclic sulfate esters lacks an efficient purification method to effectively improve product purity, resulting in the inability of current mainstream market products to meet the development needs of lithium battery electrolytes. Therefore, new solutions to the problems existing in the purification process are urgently needed. Summary of the Invention

[0005] In order to solve the problems of low crystallization yield of cyclic sulfate and product purity failing to meet high quality requirements, the present invention provides a method for purifying cyclic sulfate for lithium batteries.

[0006] To achieve the above-mentioned purpose, the present invention is implemented through the following technical solutions:

[0007] A method for purifying cyclic sulfate for lithium batteries comprises the following steps:

[0008] (1) Adding the crude cyclic sulfate and a good solvent to a dissolving kettle to prepare a crude solution, pumping the crude solution to a molecular sieve continuous dehydration system, and conveying the dehydrated material to a crystallization kettle;

[0009] (2) After the material enters the crystallization kettle, organic amine is added, the pH value of the system is adjusted to 8.5-9.0, the system temperature is controlled to 10-20°C, and the vacuum distillation system is turned on. When the solvent begins to distill out, the poor solvent replenishment valve is opened to keep the liquid level in the crystallization kettle constant;

[0010] (3) When the solution in the crystallization kettle changes from clear to turbid, add solid seed crystals, close the vacuum distillation system, and keep warm and stir to crystallize;

[0011] (4) After crystallization by stirring and heat preservation for 0.5-3 hours, the vacuum distillation system is opened, and distillation is continued while adding poor solvent to maintain a constant liquid level. The distillation and addition of poor solvent are stopped when the mass content of the good solvent in the system drops below 20%.

[0012] (5) Start the nitrogen filter press system to obtain the product wet cake, and transport the wet cake to the drying equipment with nitrogen flow for drying to obtain high-purity cyclic sulfate.

[0013] The structural formula of the cyclic sulfate is:

[0014] , wherein R1 and R2 independently represent -H, -F, -Cl or -Br substituents.

[0015] The good solvent is selected from one or more of dichloromethane, dichloroethane, trichloroethane, dimethyl carbonate, ethyl methyl carbonate and methyl acetate.

[0016] The poor solvent is selected from one or more of petroleum ether, n-pentane, n-hexane and 2-methylpentane.

[0017] The organic amine is selected from one or both of pyridine and triethylamine.

[0018] The mass concentration of the crude cyclic sulfate in the crude solution in step (1) is 5-50%.

[0019] The water content of the crude product solution in step (1) after passing through the molecular sieve continuous dehydration system is <100 ppm.

[0020] Preferably, the water content of the crude product solution in step (1) after passing through the molecular sieve continuous dehydration system is less than 10 ppm.

[0021] The seed crystals in step (3) are corresponding cyclic sulfates with a purity of ≥99.99%, and the amount of the seed crystals added is 0.5-10.0% of the mass of the cyclic sulfate in the crude cyclic sulfate.

[0022] Preferably, when the mass content of the good solvent in step (4) is reduced to below 5%, distillation and addition of the poor solvent are stopped.

[0023] Experimental studies have shown that the purity of cyclic sulfate ester crystals is affected by three major factors: ① Water in the reaction system will cause the product or raw material to decompose, and the decomposed impurities are difficult to completely remove by recrystallization; ② In the presence of water, the decomposition rate of cyclic sulfate esters is directly related to temperature: the higher the temperature, the faster the decomposition rate; ③ Impurities are trapped during the crystallization process of cyclic sulfate esters, and this problem becomes more significant after the production scale is expanded. Therefore, controlling the moisture content of the crystallization process plays an important role.

[0024] The traditional crystallization process requires heating to dissolve and then cooling to crystallize. The dissolution temperature is often >35°C. Experiments have shown that the product will decompose more rapidly when the temperature is >30°C, and this phenomenon will be more serious when the water content of the system is >0.1%. The present invention uses vacuum distillation to gradually remove the good solvent under low temperature conditions, further improving the purity of the product.

[0025] The crude cyclic sulfate will undergo a hydrolysis side reaction, the reaction formula is:

[0026] (where R1 and R2 independently represent -H, -F, -Cl or -Br substituents), the hydrolysis process produces sulfuric acid and diol impurities. Experiments show that acidic H + It is difficult to completely remove it by recrystallization. + The residue will cause the acid value of the product to exceed the standard. The existing processes all choose to reduce the crystallization yield to improve the product purity. The present invention uses organic amine as an acid binding agent to bind H + It is converted into organic amine salt macromolecules, making it difficult to be adsorbed or entrained by the product, effectively controlling the acid value of the product.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1) By removing moisture from the crystallization liquid through a molecular sieve continuous drying system, the moisture introduced in the reaction stage can be completely removed, and the moisture content of the system can be controlled to <100ppm. This completely avoids the hydrolysis of the product and the impurities generated by hydrolysis during the crystallization process. Only the impurities introduced in the previous stage are retained in the mother liquor during the crystallization process. This not only improves the crystallization purity of the product, but also effectively controls the total amount of impurities in the crystallization mother liquor, significantly increases the number of batches of the crystallization mother liquor, and thus reduces the total amount of production waste and production costs.

[0029] 2) The present invention uses vacuum distillation to gradually remove the good solvent under low temperature conditions, thereby gradually increasing the supersaturation of the product and completing the crystallization process. The system temperature is always <20°C, effectively avoiding the problem of reduced purity caused by thermal decomposition of the product and decomposition of impurities.

[0030] 3) The present invention adopts a mixed solvent system of a good solvent and a poor solvent, but it is not a simple mixture of two solvents. The system is initially a good solvent system. As the reduced pressure distillation proceeds, the proportion of the good solvent gradually decreases and the proportion of the poor solvent increases. The solution volume of the entire system remains basically unchanged, and the solid gradually precipitates, so that the crystallization rate can reach >95% and the solid content of the system remains <50%. This not only prevents impurity inclusion, but also helps to improve product purity and facilitates material transfer and solid-liquid separation.

[0031] 4) The solvent combination and continuous distillation method selected in the present invention can play an effective regulatory role in the product crystal growth process. A dynamic equilibrium process of dissolution and crystallization continuously occurs on the crystal surface, avoiding impurity entrapment and achieving stable production of high-purity products.

[0032] 5) The present invention adopts organic amine as acid binding agent to bind H + It is converted into organic amine salt macromolecules, making it less likely to be adsorbed or entrained by the product, effectively controlling the acid value of the product and thus improving the purity of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a gas chromatogram of vinyl sulfate prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] In order to better understand the technical solutions of the present invention, the following is a further detailed description of the above content of the present invention through specific implementation methods in the form of examples. However, this should not be construed as limiting the scope of the above subject matter of the present invention to the following examples. All technologies implemented based on the above content of the present invention fall within the scope of the present invention.

[0035] In the following examples, the structural formula of cyclic sulfate is:

[0036] , wherein R1 and R2 independently represent -H, -F, -Cl, or -Br substituents.

[0037] Example 1 When R1=R2=H, the cyclic sulfate is vinyl sulfate.

[0038] (1) 200 kg of crude vinyl sulfate (purity 99.81%) and 800 kg of dichloromethane were added to a dissolving kettle to prepare a crude solution with a mass concentration of 20%. The crude solution was continuously pumped to a molecular sieve continuous dehydration system. The dehydrated solution was transported to a crystallization kettle. The water content of the sample was tested to be 5.1 ppm.

[0039] (2) Add 235g of triethylamine to the crystallization kettle, adjust the pH value of the system to 8.65, turn on the temperature control system to control the temperature in the kettle to 15℃, turn on the vacuum distillation system, and when dichloromethane begins to distill out, open the n-hexane replenishment valve to add n-hexane dropwise to the kettle to keep the liquid level in the kettle constant; (3) After continuous distillation for about 60 minutes, the solution in the kettle becomes turbid colloidal, add 10kg of vinyl sulfate product (purity 99.99%), turn off the vacuum distillation system, and keep warm and stir to crystallize; (4) After 30 minutes of warm crystallization, the solution in the kettle is no longer turbid and colloid and crystal particles appear. The vacuum distillation system is turned on, and distillation is continued while adding n-hexane to maintain the liquid level until the content of dichloromethane in the kettle is reduced to 2.4% by sampling and testing. Then the distillation and solvent addition are stopped. (5) The nitrogen filter press system is turned on to obtain the product wet cake. The filter cake is transported to the drying equipment with nitrogen flow for drying. Finally, 195.6 kg of vinyl sulfate product is obtained with a product purity of 99.99% and a crystallization yield of about 98.0%. Its gas phase detection spectrum is as follows: Figure 1 As shown in FIG, the chromatographic conditions for gas detection are: chromatographic column HP-5 (30m*0.32mm*0.25um), vaporization chamber temperature 230°C, column temperature 60°C maintained for 3 min, heating to 210°C at 10°C / min, maintained for 2 min, detector temperature 250°C, flow rate 1.0 mL / min.

[0040] Example 2 When R1=R2=H, the cyclic sulfate is vinyl sulfate.

[0041] (1) 50 kg of crude vinyl sulfate (purity 99.81%) and 950 kg of ethylene dichloride were added to a dissolving kettle to prepare a crude solution with a mass concentration of 5%. The crude solution was continuously pumped to a molecular sieve continuous dehydration system. The dehydrated solution was transported to a crystallization kettle. The water content of the sample was tested to be 3.0 ppm.

[0042] (2) Add 58.0 g of triethylamine to the crystallization kettle, adjust the pH value of the system to 8.75, turn on the temperature control system to control the temperature in the kettle to 10 ° C, turn on the vacuum distillation system, and when dichloroethane begins to distill out, open the petroleum ether replenishing valve to add petroleum ether dropwise to the kettle to keep the liquid level in the kettle constant; (3) After continuous distillation for about 60 minutes, the solution in the kettle is in a turbid colloidal state, add 0.25 kg of vinyl sulfate product (purity 99.99%), turn off the vacuum distillation system, and keep warm and stir to crystallize; ( 4) After 3 hours of crystallization, the solution in the kettle is no longer turbid and colloid and crystal particles appear. The vacuum distillation system is turned on, and distillation is continued while adding petroleum ether to maintain the liquid level until the content of dichloroethane in the kettle is reduced to 1.0% by sampling and testing. The distillation and solvent addition are stopped. (5) The nitrogen filter press system is turned on to obtain a wet filter cake of the product. The filter cake is transported to a drying equipment with nitrogen flow for drying. Finally, 49.4 kg of vinyl sulfate product is obtained with a product purity of 99.99% and a crystallization yield of about 99.0%.

[0043] Example 3 When R1 = H, R2 = F, the cyclic sulfate is 4-fluoro-vinyl sulfate.

[0044] (1) 100 kg of crude 4-fluoro-vinyl sulfate (purity 99.12%) and 900 kg of dimethyl carbonate were added to a dissolving kettle to prepare a crude solution with a mass concentration of 10%. The crude solution was continuously pumped to a molecular sieve continuous dehydration system. The dehydrated solution was transported to a crystallization kettle. The water content of the sample was tested to be 4.9 ppm.

[0045] (2) Add 29.0 g of triethylamine to the crystallization kettle, adjust the pH value of the system to 8.58, turn on the temperature control system to control the temperature in the kettle to 20°C, turn on the vacuum distillation system, and when dimethyl carbonate begins to distill out, open the n-pentane replenishment valve to add n-pentane dropwise to the kettle to keep the liquid level in the kettle constant; (3) After continuous distillation for about 60 minutes, the solution in the kettle becomes turbid colloidal, add 10 kg of 4-fluoro-vinyl sulfate (purity 99.99%), turn off the vacuum distillation system, and keep warm and stir to crystallize; (4) After 2.5 h of crystallization, the solution in the kettle was no longer turbid and colloid and crystal particles appeared. The vacuum distillation system was turned on, and distillation was continued while adding n-pentane to maintain the liquid level until the content of dimethyl carbonate in the kettle was reduced to 2.1% by sampling and testing. The distillation and solvent addition were stopped. (5) The nitrogen filter press system was turned on to obtain a wet cake of the product. The cake was transported to a drying device with nitrogen flow for drying. Finally, 97.6 kg of 4-fluoro-vinyl sulfate product was obtained with a product purity of 99.99% and a crystallization yield of about 98.5%.

[0046] Example 4 When R1= R2=F, the cyclic sulfate is 4,5-difluoro-ethylene sulfate.

[0047] (1) 300 kg of crude 4,5-difluoro-vinyl sulfate (purity 99.23%) and 700 kg of ethyl methyl carbonate were added to a dissolving kettle to prepare a crude solution with a mass concentration of 30%. The crude solution was continuously pumped to a molecular sieve continuous dehydration system. The dehydrated solution was transported to a crystallization kettle. The water content of the sample was tested to be 3.9 ppm.

[0048] (2) Add 85.0 g of triethylamine to the crystallization kettle, adjust the pH value of the system to 8.91, turn on the temperature control system to control the temperature in the kettle to 15 ° C, turn on the vacuum distillation system, and when ethyl methyl carbonate begins to distill out, open the 2-methylpentane replenishing valve to add 2-methylpentane dropwise to the kettle to keep the liquid level in the kettle constant; (3) After continuous distillation for about 120 minutes, the solution in the kettle is in a turbid colloidal state, add 15 kg of 4,5-difluoro-vinyl sulfate (purity 99.99%), turn off the vacuum distillation system, and keep warm and stir to crystallize; ( 4) After 3 hours of crystallization, the solution in the kettle is no longer turbid and colloid and crystal particles appear. The vacuum distillation system is turned on, and distillation is continued while adding 2-methylpentane to maintain the liquid level until the content of ethyl methyl carbonate in the kettle is reduced to 1.8% by sampling and testing. The distillation and solvent addition are stopped. (5) The nitrogen filter press system is turned on to obtain a wet filter cake of the product. The filter cake is transported to a drying equipment with nitrogen flow for drying. Finally, 296.2 kg of 4,5-difluoro-vinyl sulfate product is obtained with a product purity of 99.99% and a crystallization yield of about 99.5%.

[0049] Example 5 When R1 = H, R2 = Cl, the cyclic sulfate is 4-chloro-vinyl sulfate.

[0050] (1) 200 kg of crude 4-chloro-vinyl sulfate (purity 99.35%) and 800 kg of methyl acetate were added to a dissolving kettle to prepare a crude solution with a mass concentration of 20%. The crude solution was continuously pumped to a molecular sieve continuous dehydration system. The dehydrated solution was transported to a crystallization kettle. The water content of the sample was tested to be 3.5 ppm.

[0051] (2) Add 59.5 g of triethylamine to the crystallization kettle, adjust the pH value of the system to 8.48, turn on the temperature control system to control the temperature in the kettle to 15 ° C, turn on the vacuum distillation system, and when methyl acetate begins to distill out, open the n-pentane replenishment valve to add n-pentane dropwise to the kettle to keep the liquid level in the kettle constant; (3) After continuous distillation for about 60 minutes, the solution in the kettle becomes turbid colloidal. Add 10 kg of 4-chloro-vinyl sulfate (purity 99.99%), turn off the vacuum distillation system, and keep warm and stir to crystallize; (4) After 2 hours of crystallization, the solution in the kettle is no longer turbid and colloid and crystal particles appear. The vacuum distillation system is turned on, and distillation is continued while adding n-pentane to maintain the liquid level until the content of methyl acetate in the kettle is reduced to 1.1% by sampling and testing. The distillation and solvent addition are stopped. (5) The nitrogen filter press system is turned on to obtain a wet cake of the product. The cake is transported to the drying equipment with nitrogen flow for drying. Finally, 197.2 kg of 4-chloro-vinyl sulfate product is obtained with a product purity of 99.99% and a crystallization yield of about 99.23%.

[0052] Example 6 When R1 = H, R2 = Br, the cyclic sulfate is 4-bromo-vinyl sulfate.

[0053] (1) 400 kg of crude 4-bromo-vinyl sulfate (purity 99.0%) and 600 kg of dimethyl carbonate were added to a dissolving kettle to prepare a crude solution with a mass concentration of 40%. The crude solution was continuously pumped to a molecular sieve continuous dehydration system. The dehydrated solution was transported to a crystallization kettle. The water content of the sample was tested to be 7.9 ppm.

[0054] (2) Add 80.5 g of triethylamine to the crystallization kettle, adjust the pH value of the system to 8.95, turn on the temperature control system to control the temperature in the kettle to 10 ° C, turn on the vacuum distillation system, and when dimethyl carbonate begins to distill out, open the n-pentane replenishment valve to add n-pentane dropwise to the kettle to keep the liquid level in the kettle constant; (3) After continuous distillation for about 120 minutes, the solution in the kettle becomes turbid colloidal, add 20 kg of 4-bromo-vinyl sulfate (purity 99.99%), turn off the vacuum distillation system, and keep warm and stir to crystallize; (4) After 1.5 h of crystallization at room temperature, the solution in the kettle was no longer turbid and colloid and crystal particles appeared. The vacuum distillation system was turned on, and distillation was continued while adding n-pentane to maintain the liquid level until the content of dimethyl carbonate in the kettle was reduced to 1.1% by sampling and testing. The distillation and solvent addition were stopped. (5) The nitrogen filter press system was turned on to obtain a wet cake of the product. The cake was transported to a drying device with nitrogen flow for drying. Finally, 391.6 kg of 4-bromo-vinyl sulfate product was obtained with a product purity of 99.99% and a crystallization yield of about 98.9%.

[0055] The cyclic sulfates prepared in Examples 1 to 6 of the present invention were tested, and the test results are shown in Table 1.

[0056]

[0057] It can be seen from the results in Table 1 that the purity of the cyclic sulfate products prepared by the purification method of cyclic sulfate for lithium batteries of the present invention can reach 99.99%, and the impurity content of the products is less than 0.01%.

Claims

1. A method for purifying cyclic sulfate for lithium batteries, characterized in that: The following steps are involved: (1) Adding the crude cyclic sulfate and a good solvent to a dissolving kettle to prepare a crude solution, pumping the crude solution to a molecular sieve continuous dehydration system, and conveying the dehydrated material to a crystallization kettle; (2) After the material enters the crystallization kettle, organic amine is added, the pH value of the system is adjusted to 8.5-9.0, the system temperature is controlled to 10-20°C, and the vacuum distillation system is turned on. When the solvent begins to distill out, the poor solvent replenishment valve is opened to keep the liquid level in the crystallization kettle constant; (3) When the solution in the crystallization kettle changes from clear to turbid, add solid seed crystals, close the vacuum distillation system, and keep warm and stir to crystallize; (4) After crystallization by stirring and heat preservation for 0.5-3 hours, the vacuum distillation system is opened, and distillation is continued while adding poor solvent to maintain a constant liquid level. The distillation and addition of poor solvent are stopped when the mass content of the good solvent in the system drops below 20%. (5) Start the nitrogen filter press system to obtain the product wet cake, and transport the wet cake to the drying equipment with nitrogen flow for drying to obtain cyclic sulfate.

2. The method for purifying cyclic sulfate for lithium batteries according to claim 1, wherein: The structural formula of the cyclic sulfate is: , wherein R1 and R2 independently represent -H, -F, -Cl, or -Br substituents.

3. The method for purifying cyclic sulfate for lithium batteries according to claim 1, wherein: The good solvent is selected from one or more of dichloromethane, dichloroethane, trichloroethane, dimethyl carbonate, ethyl methyl carbonate and methyl acetate.

4. The method for purifying cyclic sulfate for lithium batteries according to claim 1, wherein: The poor solvent is selected from one or more of petroleum ether, n-pentane, n-hexane and 2-methylpentane.

5. The method for purifying cyclic sulfate for lithium batteries according to claim 1, wherein: The organic amine is selected from one or both of pyridine and triethylamine.

6. The method for purifying cyclic sulfate for lithium batteries according to claim 1, wherein: The mass concentration of the crude cyclic sulfate in the crude solution in step (1) is 5-50%.

7. The method for purifying cyclic sulfate for lithium batteries according to claim 1, wherein: The water content of the crude product solution in step (1) after passing through the molecular sieve continuous dehydration system is <100 ppm.

8. The method for purifying cyclic sulfate for lithium batteries according to claim 1, wherein: The water content of the crude product solution in step (1) after passing through the molecular sieve continuous dehydration system is <10 ppm.

9. The method for purifying cyclic sulfate for lithium batteries according to claim 1, wherein: The seed crystals in step (3) are corresponding cyclic sulfates with a purity of ≥99.99%, and the amount of the seed crystals added is 0.5-10.0% of the mass of the cyclic sulfate in the crude cyclic sulfate.

10. The method for purifying cyclic sulfate for lithium batteries according to claim 1, wherein: When the mass content of the good solvent in step (4) is reduced to below 5%, the distillation is stopped and the poor solvent is added.

Images