Preparation process of high-purity ethylene carbonate for lithium battery

Abstract

The invention relates to the technical field of organic synthesis, and discloses a preparation process of high-purity ethylene carbonate for a lithium battery, which comprises the following steps: (1) preparing raw materials; (2) synthesis reaction; (3) crude separation; (4) refining and purifying; (5) adsorption treatment; (6) filtering and rectifying; according to the preparation process of the high-purity ethylene carbonate for the lithium battery provided by the invention, the product purity is remarkably improved through cooperation of all the steps, and according to the technical scheme, porous silicon dioxide is mainly used as a carrier, and a zinc compound and an aluminum compound are loaded as active components. The porous silicon dioxide has a relatively large specific surface area and a rich pore channel structure, and can provide a good dispersion platform for active components and increase the number of active sites; the zinc-aluminum active components form an active center which is highly dispersed and has a synergistic catalysis effect under specific loading and calcining conditions, so that the catalytic efficiency of the reaction of ethylene oxide and carbon dioxide is remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, in particular to a preparation process of high-purity ethylene carbonate for lithium batteries. Background Art

[0002] With the rapid development of the new energy industry, lithium batteries, as the core power source for electric vehicles and portable electronic devices, have placed higher demands on ethylene carbonate (EC) in order to improve their performance. As a key solvent for the electrolyte, the purity of ethylene carbonate directly affects the solubility of lithium salts and the efficiency of ion transfer. Studies have shown that high-purity ethylene carbonate can effectively inhibit the growth of lithium dendrites, reduce the internal resistance of the battery and extend the cycle life by forming a stable SEI film (solid electrolyte interface film). For example, in the NCM811 / graphite battery system, the synergistic effect of high-purity ethylene carbonate and dimethyl carbonate (DMC) can increase the lithium ion transfer number to 0.48, significantly improving the high-rate (8-10C) charge and discharge performance.

[0003] The lithium battery industry currently has high requirements for EC purity. This is because impurities (such as moisture and acidic substances) can cause the electrolyte to decompose and produce gas, causing battery expansion and even thermal runaway. To this end, the industry is promoting production process innovation.

[0004] In the future, with the popularization of solid-state electrolytes and high-nickel ternary positive electrode materials, the application of ethylene carbonate in new electrolyte systems (such as fluoroethylene carbonate derivatives) will become more extensive.

[0005] Currently, the mainstream industrial processes for producing ethylene carbonate mostly use methods such as the direct reaction of ethylene oxide with carbon dioxide or the alcoholysis of urea with ethylene glycol. However, these existing processes generally suffer from low product purity. Taking the reaction of ethylene oxide with carbon dioxide as an example, the relatively low conversion rate of ethylene oxide leads to the occurrence of side reactions during the reaction, which easily produces various organic impurities and results in low product purity. In the alcoholysis process using urea with ethylene glycol, insufficient catalyst activity and selectivity result in a large amount of unreacted raw materials and byproducts remaining in the reaction product, further reducing the purity of the ethylene carbonate.

[0006] These problems not only limit the application scope of ethylene carbonate, but also increase the production costs and quality control difficulty of downstream lithium battery manufacturers.

[0007] Therefore, developing a process that can efficiently prepare high-purity ethylene carbonate has become a key issue that needs to be urgently addressed in the industry. Summary of the Invention

[0008] In view of the problems in the prior art, the present invention provides a process for preparing high-purity ethylene carbonate for lithium batteries.

[0009] The technical solution adopted by the present invention to solve the technical problem is: a preparation process of high-purity ethylene carbonate for lithium batteries, comprising the following steps:

[0010] (1) Raw material preparation: prepare ethylene oxide, carbon dioxide gas, and a supported catalyst, wherein the catalyst uses porous silica as a carrier, the active components are zinc compounds and aluminum compounds, and the active component loading amount is 10%-16% of the carrier mass;

[0011] (2) Synthesis reaction: Ethylene oxide and the catalyst are added to a reactor, carbon dioxide gas is introduced, the reaction temperature is controlled at 80-100°C and the pressure is 2-2.5 MPa, and the reaction is carried out for 3-4 hours. During the reaction, carbon dioxide is continuously added to maintain the pressure;

[0012] (3) Crude separation: The reaction product is subjected to vacuum distillation at a controlled pressure of 18-20 kPa and a temperature of 60-65° C. to remove unreacted ethylene oxide and low-boiling impurities to obtain crude ethylene carbonate;

[0013] (4) Refining and purification: The crude ethylene carbonate is molecularly distilled at an operating pressure of 0.1-0.3 Pa, a temperature of 110-120° C., and a feed rate of 1-1.5 mL / min to remove high-boiling point impurities and organic impurities;

[0014] (5) Adsorption treatment: Mix the molecular distillation product with activated carbon, stir and adsorb for 1.5-2 hours at 30-40°C, with the amount of activated carbon being 0.8%-1% of the mass of ethylene carbonate, to remove trace impurities and pigments;

[0015] (6) Filtration and distillation: After filtering to remove the activated carbon, the filtrate is distilled, and the top temperature of the distillation tower is controlled at 160-175°C, the bottom temperature at 180-190°C, and the reflux ratio is 5-8 to obtain ethylene carbonate with a purity of ≥99.99%.

[0016] As a further technical solution, the catalyst in step (1) is prepared by the following method: immersing porous silica in a mixed solution of zinc nitrate and aluminum nitrate in a mass ratio of 1:10-14, stirring at room temperature for 12-24 hours, filtering, washing, and drying, and then calcining at 540-580°C for 3-4 hours;

[0017] As a further technical solution, the molar ratio of zinc ions to aluminum ions in the mixed solution is 1:(0.8-1.2).

[0018] As a further technical solution, the amount of catalyst used in step (2) is 3%-5% of the mass of ethylene oxide, and the amount of carbon dioxide introduced is monitored and adjusted in real time by a pressure sensor during the reaction so that the reaction pressure fluctuation range is ≤±0.2MPa.

[0019] As a further technical solution, the reduced pressure distillation in step (3) adopts a falling film evaporator, the evaporation rate is controlled to be 50-80 L / h·㎡, and the unreacted ethylene oxide is recovered during the distillation process.

[0020] As a further technical solution, the molecular distillation in step (4) adopts a horizontal thin film evaporator, and the distance between the evaporation surface and the condensation surface is 5-10 mm.

[0021] As a further technical solution, the activated carbon in step (5) is coconut shell activated carbon with a pore size of 10-20 nm, and the stirring rate during the adsorption process is controlled to be 100-300 rpm so that the activated carbon is uniformly suspended in the ethylene carbonate.

[0022] As a further technical solution, the distillation tower in step (6) is a packed tower, the packing is stainless steel θ ring packing, and the packing height is 3-4m.

[0023] Beneficial effects of the present invention:

[0024] The process for preparing high-purity ethylene carbonate for lithium batteries provided by the present invention significantly improves the purity of the product through the coordinated cooperation of various steps:

[0025] The technical solution of the present invention mainly uses porous silica as a carrier, loading zinc compounds and aluminum compounds as active components. Porous silica has a large specific surface area and rich pore structure, which can provide a good dispersion platform for the active components and increase the number of active sites. Under specific loading and calcination conditions, the zinc and aluminum active components form highly dispersed active centers with synergistic catalytic effects, significantly improving the catalytic efficiency of the reaction between ethylene oxide and carbon dioxide, promoting the main reaction, inhibiting side reactions, and reducing impurities at the source, thereby significantly improving product purity.

[0026] By regulating the reaction temperature, pressure, time, and catalyst dosage, and by monitoring and adjusting the amount of carbon dioxide introduced, suitable reaction conditions can enable the reaction to achieve optimal thermodynamic and kinetic balance, ensure sufficient reaction between ethylene oxide and carbon dioxide, increase the conversion rate of ethylene oxide, and thus increase the production rate of ethylene carbonate, and reduce the residual unreacted raw materials; stable pressure control effectively avoids the occurrence of side reactions caused by pressure fluctuations, further reducing the impurity content.

[0027] A falling film evaporator is used for reduced pressure distillation to efficiently remove unreacted ethylene oxide and low-boiling point impurities under specific pressure and temperature conditions, while recovering unreacted ethylene oxide. This not only improves the utilization rate of raw materials, but also reduces the impact of impurities on subsequent refining processes, and initially improves product purity.

[0028] A horizontal thin-film evaporator performs molecular distillation, with a specific spacing between the evaporation and condensation surfaces, effectively separating high-boiling-point and organic impurities. Coconut shell activated carbon with a pore size of 10-20 nm is used to efficiently adsorb trace impurities and pigments under specific temperature, stirring rate, and adsorption time. The activated carbon's porous structure and large specific surface area enable it to fully absorb impurities. Uniform stirring ensures full contact between the activated carbon and the ethylene carbonate, ensuring more thorough impurity removal.

[0029] The packed tower uses stainless steel θ-ring packing. By precisely controlling the top temperature, bottom temperature and reflux ratio of the distillation tower and utilizing the difference in boiling points of each component, the fine separation of ethylene carbonate is achieved, and residual trace impurities are removed, ultimately obtaining an ethylene carbonate product with a purity of ≥99.99%.

[0030] Each step works synergistically to control the generation of impurities at the source of the reaction, and gradually remove various impurities during the separation and refining process, significantly improving the purity of ethylene carbonate, meeting the demand for high-quality solvents in lithium battery electrolytes, and improving raw material utilization. DETAILED DESCRIPTION

[0031] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0032] The process for preparing high-purity ethylene carbonate for lithium batteries of the present invention comprises reacting ethylene oxide with carbon dioxide gas in the presence of a specific supported catalyst, followed by steps of crude separation, refining and purification, adsorption treatment, filtration and distillation, thereby efficiently and highly purified ethylene carbonate suitable for lithium batteries.

[0033] Raw material preparation

[0034] The raw materials used in this method, such as ethylene oxide, carbon dioxide gas, porous silica, zinc nitrate, aluminum nitrate, and activated carbon, are all commercially available chemically pure or analytically pure reagents.

[0035] Catalyst preparation:

[0036] Porous silica is immersed in a mixed solution of zinc nitrate and aluminum nitrate at a mass ratio of 1:10-14, wherein the molar ratio of zinc ion to aluminum ion in the mixed solution is 1:(0.8-1.2). The mixture is stirred at room temperature for 12-24 hours, filtered, washed, and dried, and then calcined at 540-580°C for 3-4 hours to obtain a supported catalyst with the porous silica as the carrier and the active components being the zinc compound and the aluminum compound, with the active component loading being 10%-16% of the carrier mass.

[0037] Ethylene carbonate preparation steps

[0038] Synthesis reaction:

[0039] In a reactor equipped with a stirrer, pressure sensor, and gas inlet, add ethylene oxide and the prepared catalyst at a rate of 3%-5% by mass of the ethylene oxide. Seal the reactor and introduce carbon dioxide gas. Control the reaction temperature at 80-100°C and the pressure at 2-2.5 MPa for 3-4 hours. During the reaction, monitor and adjust the amount of carbon dioxide introduced in real time using a pressure sensor to maintain a pressure fluctuation range of ≤±0.2 MPa. Continue replenishing carbon dioxide to maintain pressure.

[0040] Coarse separation:

[0041] The reaction product is subjected to reduced pressure distillation using a falling film evaporator with the pressure controlled at 18-20 kPa, the temperature at 60-65°C, and the evaporation rate at 50-80 L / h·m2 to remove unreacted ethylene oxide and low-boiling impurities, while recovering the unreacted ethylene oxide to obtain crude ethylene carbonate.

[0042] Refining and purification:

[0043] The crude ethylene carbonate is molecularly distilled using a horizontal thin film evaporator with a distance of 5-10 mm between the evaporation surface and the condensation surface. The operating pressure is controlled at 0.1-0.3 Pa, the temperature is 110-120° C., and the feed rate is 1-1.5 mL / min to remove high-boiling point impurities and organic impurities.

[0044] Adsorption treatment:

[0045] The molecular distillation product is mixed with coconut shell activated carbon with a pore size of 10-20nm, stirred and adsorbed at 30-40℃ at a stirring rate of 100-300rpm for 1.5-2 hours. The amount of activated carbon used is 0.8%-1% of the mass of ethylene carbonate to remove trace impurities and pigments.

[0046] Filtration and distillation:

[0047] After filtering to remove the activated carbon, the filtrate is distilled. The distillation tower is packed with stainless steel θ-ring packing, with a packing height of 3-4 meters. The top temperature of the distillation tower is controlled at 160-175°C, the bottom temperature at 180-190°C, and the reflux ratio is controlled at 5-8 to obtain ethylene carbonate with a purity of ≥99.99%.

[0048] The following are specific embodiments

[0049] Example 1

[0050] Catalyst preparation: Porous silica was immersed in a mixed solution of zinc nitrate and aluminum nitrate with a molar ratio of zinc ion to aluminum ion of 1:10 by mass, stirred at room temperature for 12 hours, filtered, washed, and dried, and calcined at 540°C for 3 hours to obtain a catalyst with an active component loading of 10%.

[0051] Preparation of ethylene carbonate:

[0052] Synthesis reaction:

[0053] In a reactor equipped with a stirrer, pressure sensor, and gas inlet, ethylene oxide was added, along with the prepared catalyst at a rate of 3% by mass of ethylene oxide. The reactor was sealed, and carbon dioxide gas was introduced. The reaction temperature was maintained at 80°C and the pressure at 2 MPa for 3 hours. During the reaction, the pressure sensor monitored and adjusted the amount of carbon dioxide introduced, maintaining a pressure fluctuation range of ≤±0.2 MPa. Carbon dioxide was continuously added to maintain pressure.

[0054] Coarse separation:

[0055] The reaction product was subjected to reduced pressure distillation using a falling film evaporator with a controlled pressure of 18 kPa, a temperature of 60°C, and an evaporation rate of 50 L / h·m2 to remove unreacted ethylene oxide and low-boiling point impurities, while recovering unreacted ethylene oxide to obtain crude ethylene carbonate.

[0056] Refining and purification:

[0057] Crude ethylene carbonate was molecularly distilled using a horizontal thin film evaporator with a distance of 5 mm between the evaporation surface and the condensation surface. The operating pressure was controlled at 0.1 Pa, the temperature was 110°C, and the feed rate was 1 mL / min to remove high-boiling point impurities and organic impurities.

[0058] Adsorption treatment:

[0059] The molecular distillation product was mixed with coconut shell activated carbon with a pore size of 10 nm, and stirred at 30°C at a stirring rate of 100 rpm for 1.5 hours. The amount of activated carbon used was 0.8% of the mass of ethylene carbonate to remove trace impurities and pigments.

[0060] Filtration and distillation:

[0061] After filtering to remove the activated carbon, the filtrate was distilled. The distillation tower was packed with stainless steel theta rings, with a height of 3 meters. The top temperature was controlled at 160°C, the bottom temperature at 180°C, and the reflux ratio at 5. The resulting ethylene carbonate was tested to have a purity of 99.996%.

[0062] Example 2

[0063] Catalyst preparation: Porous silica was immersed in a mixed solution of zinc nitrate and aluminum nitrate with a molar ratio of zinc ion to aluminum ion of 1:12 by mass. The mixture was stirred at room temperature for 18 hours. After filtering, washing, and drying, it was calcined at 560°C for 3.5 hours to obtain a catalyst with an active component loading of 13%.

[0064] Preparation of ethylene carbonate:

[0065] Synthesis reaction:

[0066] In a reactor equipped with a stirrer, pressure sensor, and gas inlet, ethylene oxide was added, along with the prepared catalyst at a rate of 4% by mass of ethylene oxide. The reactor was sealed, and carbon dioxide gas was introduced. The reaction temperature was maintained at 90°C and the pressure at 2.1 MPa for 3.5 hours. During the reaction, the pressure sensor monitored and adjusted the amount of carbon dioxide introduced, maintaining a pressure fluctuation range of ≤±0.2 MPa. Carbon dioxide was continuously added to maintain pressure.

[0067] Coarse separation:

[0068] The reaction product was subjected to reduced pressure distillation using a falling film evaporator with a controlled pressure of 19 kPa, a temperature of 62°C, and an evaporation rate of 60 L / h·m2 to remove unreacted ethylene oxide and low-boiling point impurities, while recovering unreacted ethylene oxide to obtain crude ethylene carbonate.

[0069] Refining and purification:

[0070] Crude ethylene carbonate was molecularly distilled using a horizontal thin film evaporator with a distance of 8 mm between the evaporation surface and the condensation surface. The operating pressure was controlled at 0.2 Pa, the temperature was 116°C, and the feed rate was 1.2 mL / min to remove high-boiling point impurities and organic impurities.

[0071] Adsorption treatment:

[0072] The molecular distillation product was mixed with coconut shell activated carbon with a pore size of 15 nm, and adsorbed at 34°C with a stirring rate of 200 rpm for 1.8 hours. The amount of activated carbon used was 0.9% of the mass of ethylene carbonate to remove trace impurities and pigments.

[0073] Filtration and distillation:

[0074] After filtering to remove the activated carbon, the filtrate was distilled. The distillation tower was packed with stainless steel theta rings, with a height of 3.5 meters. The tower top temperature was controlled at 170°C, the tower bottom temperature at 185°C, and the reflux ratio at 6. The resulting ethylene carbonate was tested to have a purity of 99.998%.

[0075] Example 3

[0076] Catalyst preparation: Porous silica was immersed in a mixed solution of zinc nitrate and aluminum nitrate with a molar ratio of zinc ion to aluminum ion of 1:1.2 at a mass ratio of 1:14. The mixture was stirred at room temperature for 24 hours. After filtering, washing, and drying, it was calcined at 580°C for 4 hours to obtain a catalyst with an active component loading of 16%.

[0077] Preparation of ethylene carbonate:

[0078] Synthesis reaction:

[0079] In a reactor equipped with a stirrer, pressure sensor, and gas inlet, ethylene oxide was added, along with the prepared catalyst at a rate of 5% by mass of the ethylene oxide. The reactor was sealed, and carbon dioxide gas was introduced. The reaction temperature was maintained at 100°C and the pressure at 2.5 MPa for 4 hours. During the reaction, the pressure sensor monitored and adjusted the amount of carbon dioxide introduced, maintaining a pressure fluctuation range of ≤±0.2 MPa. Carbon dioxide was continuously added to maintain pressure.

[0080] Coarse separation:

[0081] The reaction product was subjected to reduced pressure distillation using a falling film evaporator with a controlled pressure of 20 kPa, a temperature of 65°C, and an evaporation rate of 80 L / h·m2 to remove unreacted ethylene oxide and low-boiling impurities, while recovering unreacted ethylene oxide to obtain crude ethylene carbonate.

[0082] Refining and purification:

[0083] Crude ethylene carbonate was molecularly distilled using a horizontal thin film evaporator with a distance of 10 mm between the evaporation surface and the condensation surface. The operating pressure was controlled at 0.3 Pa, the temperature was 120°C, and the feed rate was 1.5 mL / min to remove high-boiling point impurities and organic impurities.

[0084] Adsorption treatment:

[0085] The molecular distillation product was mixed with coconut shell activated carbon with a pore size of 20 nm, and stirred at 40°C at a stirring rate of 300 rpm for 2 hours. The amount of activated carbon used was 1% of the mass of ethylene carbonate to remove trace impurities and pigments.

[0086] Filtration and distillation:

[0087] After filtering to remove the activated carbon, the filtrate was distilled. The distillation tower was packed with stainless steel theta rings, with a height of 4 meters. The top temperature was controlled at 175°C, the bottom temperature at 190°C, and the reflux ratio at 8. The resulting ethylene carbonate was tested to have a purity of 99.993%.

[0088] The following is a comparative example

[0089] Comparative Example 1

[0090] The difference from Example 2 is that a common commercial catalyst (zinc oxide) is used, and the other operations are the same. The final ethylene carbonate product obtained has a purity of 96.53%, indicating that the catalyst prepared by the present invention has better catalytic performance and helps to improve product purity.

[0091] Comparative Example 2

[0092] The difference from Example 2 is that no aluminum ions were added during the catalyst preparation process, and the other operations were the same. The purity of the ethylene carbonate product obtained by the reaction was 97.97%, indicating that the combination of zinc and aluminum ions helps to improve the activity of the catalyst and the purity of the product.

[0093] Comparative Example 3

[0094] The catalyst preparation differs from Example 2 in that porous silica, at a mass ratio of 1:10, was immersed in a mixed solution of zinc nitrate and aluminum nitrate with a zinc ion to aluminum ion molar ratio of 1:0.8. The mixture was stirred at room temperature for 12 hours. After filtration, washing, and drying, the mixture was calcined at 440°C for 3 hours to obtain a catalyst with a 10% active component loading. The remaining procedures were identical. The resulting ethylene carbonate product had a purity of 99.02%, demonstrating that a suitable molecular distillation operating pressure is crucial for removing impurities and improving product purity.

[0095] test

[0096] Purity detection experiment

[0097] Test Method: Purity testing of the products of Examples 1-3 and Comparative Examples 1-3 was performed with reference to relevant high performance liquid chromatography (HPLC) testing standards and instrument operating specifications. A C18 reverse phase chromatography column (4.6×250 mm, 5 μm) was used, with a mobile phase of acetonitrile-water (volume ratio of 15:85), a flow rate of 1.0 mL / min, a column temperature of 30°C, a detection wavelength of 243 nm, and an injection volume of 10 μL. A standard curve was drawn using an ethylene carbonate standard, and sample purity was calculated by the peak area external standard method.

[0098] Table 1

[0099]

[0100]

[0101] As can be seen from the data in Table 1, the product obtained by the present invention has a high purity.

[0102] Comparison of ethylene oxide conversion:

[0103] According to the amount of ethylene oxide before and after the reaction, the conversion rate of ethylene oxide is calculated according to the following formula:

[0104] Conversion rate (%) = (n 初始 -n 剩余 / n 初始 )×100%;

[0105] Among them, n 初始 is the amount of ethylene oxide added at the beginning of the reaction (1 mol), n 剩余 The amount of ethylene oxide remaining after the reaction is completed as determined by gas chromatography;

[0106] Table 2

[0107]

[0108]

[0109] As can be seen from Table 2, the process of the present invention can greatly improve the conversion rate of ethylene oxide.

[0110] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A process for preparing high-purity ethylene carbonate for lithium batteries, characterized in that: The following steps are involved: (1) Raw material preparation: prepare ethylene oxide, carbon dioxide gas, and a supported catalyst, wherein the catalyst uses porous silica as a carrier, the active components are zinc compounds and aluminum compounds, and the active component loading amount is 10%-16% of the carrier mass; (2) Synthesis reaction: Ethylene oxide and the catalyst are added to a reactor, carbon dioxide gas is introduced, the reaction temperature is controlled at 80-100°C and the pressure is 2-2.5 MPa, and the reaction is carried out for 3-4 hours. During the reaction, carbon dioxide is continuously added to maintain the pressure; (3) Crude separation: The reaction product is subjected to vacuum distillation at a controlled pressure of 18-20 kPa and a temperature of 60-65° C. to remove unreacted ethylene oxide and low-boiling impurities to obtain crude ethylene carbonate; (4) Refining and purification: The crude ethylene carbonate is molecularly distilled at an operating pressure of 0.1-0.3 Pa, a temperature of 110-120° C., and a feed rate of 1-1.5 mL / min to remove high-boiling point impurities and organic impurities; (5) Adsorption treatment: Mix the molecular distillation product with activated carbon, stir and adsorb for 1.5-2 hours at 30-40°C, with the amount of activated carbon being 0.8%-1% of the mass of ethylene carbonate, to remove trace impurities and pigments; (6) Filtration and distillation: After filtering to remove the activated carbon, the filtrate is distilled, and the top temperature of the distillation tower is controlled at 160-175°C, the bottom temperature at 180-190°C, and the reflux ratio is 5-8 to obtain ethylene carbonate with a purity of ≥99.99%.

2. The preparation process according to claim 1, characterized in that The catalyst in step (1) is prepared by the following method: immersing porous silica in a mixed solution of zinc nitrate and aluminum nitrate in a mass ratio of 1:10-14, stirring at room temperature for 12-24 hours, filtering, washing, drying, and calcining at 540-580°C for 3-4 hours.

3. The preparation process according to claim 2, characterized in that The molar ratio of zinc ions to aluminum ions in the mixed solution is 1:(0.8-1.2).

4. The preparation process according to claim 1, characterized in that The amount of catalyst used in step (2) is 3%-5% of the mass of ethylene oxide. During the reaction, the amount of carbon dioxide introduced is monitored and adjusted in real time by a pressure sensor to ensure that the reaction pressure fluctuation range is ≤±0.2 MPa.

5. The preparation process according to claim 1, characterized in that: In the step (3), the reduced pressure distillation adopts a falling film evaporator, and the evaporation rate is controlled to be 50-80 L / h·㎡, and the unreacted ethylene oxide is recovered during the distillation process.

6. The preparation process according to claim 1, characterized in that In the step (4), the molecular distillation adopts a horizontal thin film evaporator, and the distance between the evaporation surface and the condensation surface is 5-10 mm.

7. The preparation process according to claim 1, characterized in that The activated carbon in step (5) is coconut shell activated carbon with a pore size of 10-20 nm. The stirring rate during the adsorption process is controlled to be 100-300 rpm so that the activated carbon is uniformly suspended in the ethylene carbonate.

8. The preparation process according to claim 1, characterized in that In the step (6), the distillation tower adopts a packed tower, the packing is stainless steel θ ring packing, and the packing height is 3-4m.

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