Method for separating, purifying and recovering electrolyte

Abstract

The present disclosure relates to a method for separating, purifying and recovering an electrolyte, which method comprises the following steps: (1) mixing an electrolyte of a power battery with a stabilizer, and then subjecting same to a first reduced-pressure distillation treatment, so as to obtain an electrolyte solvent; (2) subjecting the electrolyte solvent obtained in step (1) to a second reduced-pressure distillation treatment, and separating same to obtain a first light component and a heavy component; and dehydrating the obtained first light component, so as to obtain a second light component; and (3) rectifying the second light component obtained in step (2), so as to obtain dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate; and crystallizing and melting the heavy component obtained in step (2), so as to obtain ethylene carbonate. In the present disclosure, all the solvents in the electrolyte of a power battery are separated and purified to obtain a re-commercializable carbonate product having a high yield and a high purity, thereby achieving green cyclic utilization of the electrolyte.

Description

A method for separating, purifying and recovering electrolyte Technical Field

[0001] The present disclosure relates to the technical field of lithium-ion battery recycling, and in particular to a method for separating, purifying and recycling an electrolyte. Background Art

[0002] The new energy vehicle industry and green energy storage are booming, and lithium-ion power batteries are widely used. Meanwhile, the disposal of retired batteries has become a research hotspot. While numerous solutions for recycling valuable metals are emerging in lithium battery recycling, research on the recycling and resource utilization of electrolytes, a key component of lithium batteries, remains scarce.

[0003] The electrolyte accounts for about 15% of the mass of lithium batteries and is consumed in huge quantities. It is generally composed of high-purity organic solvents (such as dimethyl carbonate, ethylene carbonate, etc.), electrolyte lithium salts (such as lithium hexafluorophosphate, etc.) and necessary additives and other raw materials. The composition is complex and there are many types. Among them, organic solvents have a stable structure, are difficult to oxidize and degrade, and have a low boiling point. They are easy to volatilize and escape into the ambient air, affecting the quality of the ecological environment and human health. At present, the treatment of electrolytes mostly adopts high-temperature incineration tail gas treatment and oxidation method to treat electrolyte wastewater. This not only causes a huge waste of resources, but also increases the processing cost of retired batteries. With the explosive growth in the number of retired power batteries, the pressure on electrolyte processing is also increasing day by day, and the resource recycling and utilization of electrolytes is imperative.

[0004] In the composition of electrolyte, organic solvent accounts for more than 80%, which is the key target of electrolyte recovery. Existing electrolyte solvent recovery methods mainly include supercritical CO2 extraction and vacuum distillation-rectification. CN113471515A discloses a method for recovering lithium battery electrolyte by combining supercritical extraction rectification and molecular distillation. The lithium battery electrolyte is passed into an extraction distillation tower, and supercritical carbon dioxide or supercritical carbon dioxide mixed with an entrainer is passed into the bottom of the extraction distillation tower to perform continuous countercurrent extraction. The gas phase after extraction rectification is discharged from the top of the extraction distillation tower, and the liquid phase is discharged from the bottom of the extraction distillation tower; the gas phase discharged from the extraction distillation tower is collected, and the carbon dioxide is released by decompression to obtain an organic solvent; the low-boiling point organic solvent in the organic solvent is separated by vacuum distillation, and the chain carbonate and cyclic carbonate are separated by molecular distillation. However, this method needs to be carried out in a special separation and recovery system, which has extremely high requirements for equipment and is difficult to achieve industrial application.

[0005] CN 113363610A discloses a harmless treatment method for the electrolyte of retired lithium-ion batteries. The method comprises the following steps: the battery is fully discharged and then disassembled, and a vacuum distillation is first performed to obtain a gas phase I and a material I. The gas phase I is cooled and collected to obtain light components in the electrolyte. High-temperature water vapor is then introduced into the material I to decompose the solutes in the electrolyte to produce a gas phase II and a material II. The gas phase II is introduced into a solution containing a lithium salt, a calcium salt, an aluminum salt, or a magnesium salt to generate fluoride products such as lithium fluoride, calcium fluoride, aluminum fluoride, and magnesium fluoride. The material II is subjected to a secondary vacuum distillation to collect heavy components in the electrolyte. The light components and the heavy components are respectively distilled to obtain pure solvent I and pure solvent II, thereby ultimately achieving harmless treatment and high-value utilization of the electrolyte.

[0006] Vacuum distillation-rectification can separate, purify, and recover components by leveraging differences in the boiling points of electrolyte solvents. While simple to operate, electrolytes recovered from retired lithium-ion batteries can still contain impurities, and additives are prone to polymerization at high temperatures, resulting in low yields of carbonate products recovered through distillation separation. Furthermore, purifying high-boiling-point solvents requires high energy consumption and operating costs.

[0007] In view of the shortcomings of the existing technology, it is necessary to provide an electrolyte separation, purification and recovery method with high purity and yield of carbonate products and low recovery cost.

[0008] Summary of the Invention

[0009] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0010] The purpose of the present disclosure is to provide a method for separating, purifying and recovering an electrolyte, by separating and purifying the various solvents in the power battery electrolyte to obtain a high-yield, high-purity, and commercially viable carbonate product, while reducing the recovery cost, thereby achieving green recycling of the electrolyte, reducing the cost and pressure of electrolyte treatment, and solving the problems of environmental pollution and resource waste caused by waste electrolyte.

[0011] To achieve this purpose, the present disclosure adopts the following technical solutions:

[0012] The present disclosure provides a method for separation, purification and recovery of an electrolyte, the method comprising the following steps:

[0013] (1) mixing a power battery electrolyte and a stabilizer and performing a first reduced pressure distillation process to obtain an electrolyte solvent;

[0014] (2) subjecting the electrolyte solvent obtained in step (1) to a second reduced pressure distillation treatment to obtain a first light component and a heavy component after separation; and dehydrating the obtained first light component to obtain a second light component;

[0015] (3) subjecting the second light component obtained in step (2) to distillation to obtain dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate; and subjecting the heavy component obtained in step (2) to crystallization and melting to obtain ethylene carbonate.

[0016] The electrolyte separation, purification and recovery method provided by the present invention removes salt from the power battery electrolyte through a vacuum distillation step and removes water impurities in the organic solvent through a dehydration treatment, thereby greatly improving the purity and yield of the low-boiling point solvent product, and separating and purifying the various components between the solvents through multi-stage distillation to obtain industrial-grade standard carbonate products, thereby realizing the recycling of waste electrolytes; for high-boiling point electrolyte solvents, the product quality is further improved by adding stabilizers, and the melt crystallization technology is coupled with the vacuum distillation and distillation technologies, thereby significantly reducing the energy consumption and processing costs of the waste electrolyte separation, purification and refined products.

[0017] In one embodiment, the temperature of the first reduced pressure distillation treatment in step (1) is 140-180°C, for example, 140°C, 160°C, 165°C, 175°C or 180°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] In one embodiment, the pressure of the first reduced pressure distillation treatment in step (1) is -90 to -100 kPa, for example, it can be -90 kPa, -92 kPa, -95 kPa, -98 kPa or -100 kPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] In one embodiment, the mass ratio of the stabilizer to the power battery electrolyte in step (1) is (0.02-0.5):100, for example, it can be 0.02:100, 0.05:100, 0.2:100, 0.3:100 or 0.5:100, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0020] In one embodiment, the stabilizer in step (1) includes any one of hydroquinone, p-tert-butylcatechol or 2,6-di-tert-butyl-p-cresol.

[0021] Due to the complex raw material composition of power battery electrolyte, some organic components are prone to polymerization reactions at high temperatures. For example, VC (vinylene carbonate) is prone to initiate organic polymerization when the temperature is higher than 80°C, resulting in a decrease in the yield or purity of the distillation recovery product. Therefore, a stabilizer needs to be added in the first reduced pressure distillation treatment to improve the quality of the recovered carbonate product.

[0022] In one embodiment, the power battery electrolyte in step (1) includes at least one of electrolyte recovered from battery discharge wastewater, electrolyte recovered from water breaking wastewater, electrolyte drying condensate, battery drying condensate, electrolyte production waste electrolyte or battery production waste electrolyte.

[0023] The electrolyte recovered from battery discharge wastewater refers to the electrolyte recovered by physical or chemical methods from the electrolyte wastewater generated when retired batteries are immersed in salt water for discharge; the electrolyte recovered from water-breaking wastewater refers to the electrolyte separated and recovered from the high-concentration electrolyte wastewater generated in the underwater crushing process of power batteries; the electrolyte and battery drying condensate refers to the electrolyte obtained by converting the electrolyte into gas volatilization through a low-temperature or high-temperature drying process after the dry crushing of retired batteries, and then condensing and recovering it; the electrolyte production waste electrolyte refers to the unqualified waste electrolyte generated in the production or preparation process of the electrolyte; the battery production waste electrolyte refers to the waste electrolyte recovered from the liquid-filled batteries discarded in the battery production process.

[0024] In one embodiment, the temperature of the second reduced pressure distillation treatment in step (2) is 65-130°C, for example, it can be 65°C, 78°C, 85°C, 88°C, 100°C or 130°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] In one embodiment, the pressure of the second reduced pressure distillation treatment in step (2) is -45 to -55 kPa, for example, -45 kPa, -46 kPa, -50 kPa, -52 kPa or -55 kPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] In one embodiment, the dehydration treatment in step (2) is performed using a pervaporation membrane.

[0027] Under the action of the vapor partial pressure difference on both sides of the pervaporation membrane, the difference in solubility and diffusion rates of the organic liquid and water in the membrane can be utilized to efficiently separate the water in the organic light components, so that the moisture content of the organic light components in the subsequent distillation process can be effectively controlled, the separation difficulty caused by water azeotropy is reduced, and the purity and yield of the purified and recovered products are improved.

[0028] In one embodiment, the pervaporation membrane comprises a NaA zeolite molecular sieve membrane.

[0029] In one embodiment, the moisture content of the second light component in step (2) is less than 200 ppm, for example, it can be 190 ppm, 180 ppm, 160 ppm, 150 ppm or 120 ppm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] In one embodiment, the specific steps of the distillation treatment in step (3) include: performing a first distillation treatment on the second light component to obtain dimethyl carbonate and a third light component; performing a second distillation treatment on the third light component to obtain ethyl methyl carbonate and a fourth light component; and performing a third distillation treatment on the fourth light component to obtain ethyl methyl carbonate and diethyl carbonate.

[0031] By performing step-by-step distillation on the second light component, dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate in the second light component can be separated and purified, thereby improving the purity and yield of carbonate products, reducing recycling costs, and obtaining high-quality carbonate products that can be commercialized again, thereby realizing the green recycling of electrolytes and reducing the emissions of electrolytes and their pollutants.

[0032] The dimethyl carbonate is collected from the top of the distillation tower, and the third light component is collected from the bottom of the distillation tower; ethyl methyl carbonate and the fourth light component are collected from the top of the distillation tower; ethyl methyl carbonate obtained by the third distillation treatment is collected from the side line of the distillation tower, and diethyl carbonate is collected from the bottom of the distillation tower.

[0033] In one embodiment, the temperature of the first distillation treatment is 90-100°C, for example, 90°C, 92°C, 95°C, 98°C or 100°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] In one embodiment, the pressure of the first distillation treatment is 90-102 kPa, for example, 90 kPa, 92 kPa, 95 kPa, 100 kPa or 102 kPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] In one embodiment, the purity of the dimethyl carbonate is greater than 99.50%, for example, it can be 99.55%, 99.60%, 99.70%, 99.80% or 99.90%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0036] In one embodiment, the temperature of the second distillation treatment is 100-110°C, for example, 100°C, 102°C, 105°C, 108°C or 110°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] In one embodiment, the pressure of the second distillation treatment is 95-105 kPa, for example, 95 kPa, 98 kPa, 100 kPa, 102 kPa or 105 kPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] In one embodiment, the purity of the ethyl methyl carbonate is greater than 99.95%, for example, it can be 99.955%, 99.96%, 99.97%, 99.98% or 99.99%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0039] In one embodiment, the temperature of the third distillation treatment is 100-120°C, for example, 100°C, 110°C, 118°C or 120°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] In one embodiment, the pressure of the third distillation treatment is 80-100 kPa, for example, 80 kPa, 85 kPa, 90 kPa, 95 kPa or 100 kPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] In one embodiment, the purity of the diethyl carbonate is greater than 99.90%, for example, it can be 99.95%, 99.96%, 99.97%, 99.98% or 99.99%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0042] In one embodiment, the crystallization and melting treatment in step (3) includes cooling crystallization, sweating treatment and melting treatment performed in sequence.

[0043] After separating the light components, the present invention utilizes the melting point of ethylene carbonate, which is 35-38°C, close to room temperature, to purify the ethylene carbonate using melt crystallization technology, thereby significantly reducing the energy consumption of recycling the electrolyte into products.

[0044] In one embodiment, the cooling crystallization step comprises: cooling to 25-33° C. at a rate of 0.1-2° C. / min and keeping warm for 2-3 hours.

[0045] The cooling rate of the cooling crystallization is 0.1-2°C / min, for example, it can be 0.1°C / min, 0.5°C / min, 1°C / min, 1.5°C / min or 2°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0046] The cooling end point of the cooling crystallization is 25-33°C, for example, it can be 25°C, 28°C, 30°C or 33°C, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0047] The holding time of the cooling crystallization is 2-3 hours, for example, it can be 2 hours, 2.2 hours, 2.5 hours, 2.8 hours or 3 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0048] In one embodiment, the sweating treatment step comprises: heating to 38-43°C at a rate of 0.1-2°C / min and keeping warm for 3-5 hours.

[0049] The heating rate of the sweating treatment is 0.1-2°C / min, for example, it can be 0.1°C / min, 0.5°C / min, 1°C / min, 1.5°C / min or 2°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0050] The temperature end point of the sweating treatment is 38-43°C, for example, 38°C, 39°C, 40°C, 42°C or 43°C, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0051] The heat preservation time of the sweating treatment is 3-5 hours, for example, it can be 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0052] In one embodiment, the melt treatment step comprises: heating to 43-48° C. at a rate of 0.1-2° C. / min, and maintaining the temperature until the ethylene carbonate is in liquid state.

[0053] The heating rate of the melt treatment is 0.1-2°C / min, for example, 0.1°C / min, 0.5°C / min, 1°C / min, 1.5°C / min or 2°C / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0054] The temperature end point of the melt treatment is 43-48°C, for example, 43°C, 45°C, 46°C, 47°C or 48°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0055] In one embodiment, the purity of the ethylene carbonate in step (3) is greater than 99.50%, for example, it can be 99.55%, 99.60%, 99.70%, 99.80% or 99.90%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0056] Compared with the prior art, the present disclosure has the following beneficial effects:

[0057] The present invention provides a method for separating, purifying and recovering an electrolyte. The method removes salt from the power battery electrolyte by a vacuum distillation step and removes water impurities from the organic solvent by dehydration. This overcomes the effects of various impurities on the separation and purification of the electrolyte solvent components during the distillation process, significantly improves the purity and yield of low-boiling-point solvent products, and separates and purifies the various components between the solvents to obtain industrial-grade standard carbonate products, thereby realizing the recycling of waste electrolytes. For high-boiling-point electrolyte solvents, the product quality is further improved by adding stabilizers, and melt crystallization technology is coupled with vacuum distillation and distillation technologies, significantly reducing the energy consumption and processing costs of waste electrolyte separation, purification and refined products. The present invention provides a reliable path for high-value recovery of waste electrolytes, which can not only reduce the discharge of electrolytes and their pollutants, but also obtain high-purity, stable-quality products. The purities of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate and ethylene carbonate can reach 99.99%, 99.99%, 99.97% and 99.92%, respectively, and the total product yield can reach 86%, with good environmental and economic benefits.

[0058] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0059] The technical solution of the present disclosure is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present disclosure and should not be regarded as specific limitations of the present disclosure.

[0060] Example 1

[0061] This embodiment provides a method for separation, purification and recovery of an electrolyte, the method comprising the following steps:

[0062] (1) mixing 2,6-di-tert-butyl-p-cresol with an electrolyte drying condensate at a mass ratio of 0.05:100, and performing a first reduced pressure distillation treatment at 160° C. and −95 kPa to obtain an electrolyte solvent;

[0063] (2) subjecting the electrolyte solvent obtained in step (1) to a second reduced pressure distillation treatment at 85° C. and −50 kPa to obtain a first light component and a heavy component after separation; the obtained first light component is dehydrated through a NaA type zeolite molecular sieve membrane to obtain a second light component having a moisture content of 120 ppm;

[0064] (3) subjecting the second light component obtained in step (2) to a first distillation treatment at 95° C. and 100 kPa to obtain dimethyl carbonate and a third light component; subjecting the third light component to a second distillation treatment at 110° C. and 100 kPa to obtain ethyl methyl carbonate and a fourth light component; and subjecting the fourth light component to a third distillation treatment at 120° C. and 100 kPa to obtain ethyl methyl carbonate and diethyl carbonate;

[0065] The heavy component obtained in step (2) was cooled to 30°C at a rate of 1°C / min and kept warm for 2.5 hours; then heated to 40°C at a rate of 0.5°C / min and kept warm for 4 hours; then heated to 45°C at a rate of 0.5°C / min and kept warm until liquid ethylene carbonate was obtained.

[0066] Example 2

[0067] This embodiment provides a method for separation, purification and recovery of an electrolyte, the method comprising the following steps:

[0068] (1) mixing p-tert-butylcatechol with an electrolyte recovered from water-breaking wastewater in a mass ratio of 0.02:100, and performing a first reduced pressure distillation treatment at 140° C. and −90 kPa to obtain an electrolyte solvent;

[0069] (2) subjecting the electrolyte solvent obtained in step (1) to a second reduced pressure distillation treatment at 65° C. and −45 kPa to obtain a first light component and a heavy component after separation; the obtained first light component is dehydrated through a NaA type zeolite molecular sieve membrane to obtain a second light component with a moisture content of 150 ppm;

[0070] (3) subjecting the second light component obtained in step (2) to a first distillation treatment at 90° C. and 90 kPa to obtain dimethyl carbonate and a third light component; subjecting the third light component to a second distillation treatment at 100° C. and 95 kPa to obtain ethyl methyl carbonate and a fourth light component; and subjecting the fourth light component to a third distillation treatment at 100° C. and 80 kPa to obtain ethyl methyl carbonate and diethyl carbonate;

[0071] The heavy component obtained in step (2) was cooled to 33°C at a rate of 0.1°C / min and kept warm for 3 hours; then heated to 43°C at a rate of 0.1°C / min and kept warm for 3 hours; then heated to 48°C at a rate of 0.1°C / min and kept warm until liquid ethylene carbonate was obtained.

[0072] Example 3

[0073] This embodiment provides a method for separation, purification and recovery of an electrolyte, the method comprising the following steps:

[0074] (1) mixing hydroquinone with a mass ratio of 0.5:100 with battery drying condensate, and performing a first reduced pressure distillation treatment at 180° C. and −100 kPa to obtain an electrolyte solvent;

[0075] (2) subjecting the electrolyte solvent obtained in step (1) to a second reduced pressure distillation treatment at 130° C. and −55 kPa to obtain a first light component and a heavy component after separation; the obtained first light component is dehydrated through a NaA type zeolite molecular sieve membrane to obtain a second light component having a moisture content of 190 ppm;

[0076] (3) subjecting the second light component obtained in step (2) to a first distillation treatment at 100° C. and 102 kPa to obtain dimethyl carbonate and a third light component; subjecting the third light component to a second distillation treatment at 110° C. and 105 kPa to obtain ethyl methyl carbonate and a fourth light component; and subjecting the fourth light component to a third distillation treatment at 110° C. and 100 kPa to obtain ethyl methyl carbonate and diethyl carbonate;

[0077] The heavy component obtained in step (2) was cooled to 25°C at a rate of 2°C / min and kept warm for 2 hours; then heated to 38°C at a rate of 2°C / min and kept warm for 5 hours; then heated to 43°C at a rate of 2°C / min and kept warm until liquid ethylene carbonate was obtained.

[0078] Example 4

[0079] This embodiment provides a method for separating, purifying and recovering an electrolyte. The difference from Example 1 is that the temperature of the first reduced pressure distillation treatment in step (1) is adjusted to 120°C and the pressure is adjusted to -80 kPa, and the temperature of the second reduced pressure distillation treatment in step (2) is adjusted to 50°C and the pressure is adjusted to -40 kPa. The rest is the same as Example 1.

[0080] Example 5

[0081] This embodiment provides a method for separating, purifying and recovering an electrolyte. The difference from Example 1 is that the temperature of the first reduced pressure distillation treatment in step (1) is adjusted to 190°C and the pressure is adjusted to -110 kPa, and the temperature of the second reduced pressure distillation treatment in step (2) is adjusted to 140°C and the pressure is adjusted to -60 kPa. The rest is the same as Example 1.

[0082] Example 6

[0083] This embodiment provides a method for separation, purification and recovery of an electrolyte. The difference from Example 1 is that in step (3), the temperature of the first distillation treatment is adjusted to 80°C and the pressure is adjusted to 80 kPa, the temperature of the second distillation treatment is adjusted to 90°C and the pressure is adjusted to 90 kPa, and the temperature of the third distillation treatment is adjusted to 90°C and the pressure is adjusted to 70 kPa. The rest is the same as in Example 1.

[0084] Example 7

[0085] This embodiment provides a method for separation, purification and recovery of an electrolyte. The difference from Example 1 is that in step (3), the temperature of the first distillation treatment is adjusted to 110°C and the pressure is adjusted to 105 kPa, the temperature of the second distillation treatment is adjusted to 120°C and the pressure is adjusted to 110 kPa, and the temperature of the third distillation treatment is adjusted to 130°C and the pressure is adjusted to 110 kPa. The rest is the same as in Example 1.

[0086] Example 8

[0087] This embodiment provides a method for separation, purification and recovery of an electrolyte. The difference from Example 1 is that in step (3), the heavy component obtained in step (2) is cooled to 40°C at a rate of 0.05°C / min and kept warm for 3.5 hours; then heated to 45°C at a rate of 0.05°C / min and kept warm for 5.5 hours; then heated to 55°C at a rate of 0.05°C / min. The rest is the same as in Example 1.

[0088] Example 9

[0089] This embodiment provides a method for separation, purification and recovery of an electrolyte. The difference from Example 1 is that in step (3), the heavy component obtained in step (2) is cooled to 20°C at a rate of 2.5°C / min and kept warm for 1.5 hours; then heated to 35°C at a rate of 2.5°C / min and kept warm for 2.5 hours; then heated to 40°C at a rate of 2.5°C / min. The rest is the same as in Example 1.

[0090] Example 10

[0091] This embodiment provides a method for separation, purification and recovery of an electrolyte. The difference from Example 1 is that the dehydration treatment in step (2) is carried out using a separatory tank, and the rest is the same as Example 1.

[0092] Comparative Example 1

[0093] This comparative example provides a method for separation, purification and recovery of an electrolyte. The difference from Example 1 is that 2,6-di-tert-butyl-p-cresol is not added in step (1), and the rest is the same as Example 1.

[0094] Comparative Example 2

[0095] This comparative example provides a method for separation, purification and recovery of an electrolyte. The difference from Example 1 is that the crystallization and melting treatment in step (3) is replaced by distillation treatment, and the rest is the same as Example 1.

[0096] The electrolyte was treated using the separation, purification and recovery methods provided in Examples 1-10 and Comparative Examples 1 and 2. The purities of the obtained dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate and ethylene carbonate were tested according to GB / T 33107-2016, HG / T 5158-2017, HG / T 5157-2017 and HG / T 5391-2018, respectively. The total product yield was calculated as (DMC+EMC+DEC+EC in the obtained product) / (DMC+EMC+DEC+EC in the raw material)*100%. The results are shown in Table 1.

[0097] Table 1

[0098] As can be seen from Table 1, the electrolyte separation, purification and recovery method provided by the present disclosure separates and purifies the various solvents in the power battery electrolyte, and the obtained carbonate product has a high yield and purity, a low recovery cost, and can achieve green recycling of the electrolyte;

[0099] From the comparison between Example 1 and Examples 4-9, it can be seen that if the temperature and pressure of the vacuum distillation treatment, the rectification treatment, and the crystallization and melting treatment are too low or too high, the separation and purification effect of the electrolyte will be adversely affected, resulting in a decrease in the purity and yield of the carbonate product; from the comparison between Example 1 and Example 10, it can be seen that the use of a separatory tank instead of a pervaporation membrane significantly reduces the dehydration effect, which will reduce the purity and yield of the purified and recovered carbonate product;

[0100] By comparing Example 1 with Comparative Example 1, it can be seen that no stabilizer is added in the first reduced pressure distillation treatment, which easily induces high-temperature polymerization of organic matter, resulting in a decrease in the yield and purity of the carbonate product; by comparing Example 1 with Comparative Example 2, it can be seen that the use of distillation instead of crystallization and melting treatment for the heavy components consumes more energy and will increase the processing cost of the electrolyte.

[0101] In summary, the electrolyte separation, purification and recovery method provided by the present disclosure removes salt from the power battery electrolyte through the reduced pressure distillation step and removes water impurities in the organic solvent through dehydration treatment, thereby overcoming the influence of various impurities on the separation and purification of the electrolyte solvent components during the distillation process, greatly improving the purity and yield of the low-boiling point solvent product, and separating and purifying the various components between the solvents to obtain industrial-grade standard carbonate products, thereby realizing the recycling of waste electrolytes; for high-boiling point electrolyte solvents, the product quality is further improved by adding stabilizers, and The coupling of melt crystallization technology with high-pressure distillation and rectification technology significantly reduces the energy consumption and processing costs of separating, purifying and refining products from waste electrolytes; the present disclosure provides a reliable path for high-value recovery of waste electrolytes, which can not only reduce the discharge of electrolytes and their pollutants, but also obtain high-purity and stable-quality products. The purities of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate and ethylene carbonate can reach 99.99%, 99.99%, 99.97% and 99.92% respectively, and the total product yield can reach 86%, with good environmental and economic benefits.

Claims

1. A method for separation, purification and recovery of an electrolyte, the separation, purification and recovery method comprising the following steps: (1) mixing a power battery electrolyte and a stabilizer and performing a first reduced pressure distillation treatment to obtain an electrolyte solvent; (2) subjecting the electrolyte solvent obtained in step (1) to a second reduced pressure distillation treatment to obtain a first light component and a heavy component after separation; and subjecting the obtained first light component to a dehydration treatment to obtain a second light component; (3) subjecting the second light component obtained in step (2) to distillation to obtain dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate; and subjecting the heavy component obtained in step (2) to crystallization and melting to obtain ethylene carbonate.

2. The separation, purification and recovery method according to claim 1, wherein: The temperature of the first reduced pressure distillation treatment in step (1) is 140-180°C.

3. The separation, purification and recovery method according to claim 1 or 2, wherein: The pressure of the first reduced pressure distillation treatment in step (1) is -90 to -100 kPa.

4. The separation, purification and recovery method according to any one of claims 1 to 3, wherein: The mass ratio of the stabilizer to the power battery electrolyte in step (1) is (0.02-0.5):

100.

5. The separation, purification and recovery method according to any one of claims 1 to 4, wherein: The stabilizer in step (1) includes any one of hydroquinone, p-tert-butylcatechol or 2,6-di-tert-butyl-p-cresol.

6. The separation, purification and recovery method according to any one of claims 1 to 5, wherein: The power battery electrolyte in step (1) includes at least one of electrolyte recovered from battery discharge wastewater, electrolyte recovered from water breaking wastewater, electrolyte drying condensate, battery drying condensate, electrolyte production waste electrolyte or battery production waste electrolyte.

7. The separation, purification and recovery method according to any one of claims 1 to 6, wherein: The temperature of the second reduced pressure distillation treatment in step (2) is 65-130°C.

8. The separation, purification and recovery method according to any one of claims 1 to 7, wherein: The pressure of the second reduced pressure distillation treatment in step (2) is -45 to -55 kPa.

9. The separation, purification and recovery method according to any one of claims 1 to 8, wherein: The dehydration treatment in step (2) is carried out using a pervaporation membrane.

10. The separation, purification and recovery method according to claim 9, wherein: The pervaporation membrane comprises a NaA type zeolite molecular sieve membrane.

11. The separation, purification and recovery method according to any one of claims 1 to 10, wherein: Step (2) The moisture content of the second light component is less than 200 ppm.

12. The separation, purification and recovery method according to any one of claims 1 to 11, wherein: The specific steps of the distillation treatment in step (3) include: performing a first distillation treatment on the second light component to obtain dimethyl carbonate and a third light component; performing a second distillation treatment on the third light component to obtain ethyl methyl carbonate and a fourth light component; and performing a third distillation treatment on the fourth light component to obtain ethyl methyl carbonate and diethyl carbonate.

13. The separation, purification and recovery method according to claim 12, wherein: The temperature of the first distillation treatment is 90-100°C.

14. The separation, purification and recovery method according to claim 12 or 13, wherein: The pressure of the first distillation treatment is 90-102 kPa.

15. The separation, purification and recovery method according to any one of claims 12 to 14, wherein: The purity of the dimethyl carbonate is >99.50%.

16. The separation, purification and recovery method according to any one of claims 12 to 15, wherein: The temperature of the second distillation treatment is 100-110°C; Optionally, the pressure of the second distillation treatment is 95-105 kPa; Optionally, the purity of the ethyl methyl carbonate is >99.95%.

17. The separation, purification and recovery method according to any one of claims 12 to 16, wherein: The temperature of the third distillation treatment is 100-120°C; Optionally, the pressure of the third distillation treatment is 80-100 kPa; Optionally, the purity of the diethyl carbonate is >99.90%.

18. The separation, purification and recovery method according to any one of claims 1 to 17, wherein: The crystallization and melting treatment in step (3) includes cooling crystallization, sweating treatment and melting treatment performed in sequence.

19. The separation, purification and recovery method according to claim 18, wherein: The cooling crystallization step comprises: cooling to 25-33°C at a rate of 0.1-2°C / min, and keeping warm for 2-3h; Optionally, the sweating treatment step includes: heating to 38-43°C at a rate of 0.1-2°C / min, and keeping warm for 3-5h; Optionally, the melt treatment step comprises: heating to 43-48° C. at a rate of 0.1-2° C. / min, and maintaining the temperature until the ethylene carbonate is in liquid state; Optionally, the purity of the ethylene carbonate in step (3) is >99.50%.

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