A method for preparing methyl ethyl carbonate and diethyl carbonate by ester transesterification at normal temperature and pressure

Abstract

This invention discloses a method for preparing methyl ethyl carbonate and diethyl carbonate via transesterification under ambient temperature and pressure. Using dimethyl carbonate and ethyl acetate as raw materials, and sodium methoxide or sodium ethoxide as a catalyst, the raw materials are continuously added to a reaction vessel at 5-25℃ and 0.1MPa±0.02MPa. The stirring rate is 50-100 r / min, the temperature fluctuation is ≤±1℃, and the material residence time is 5-30 minutes, reaching reaction equilibrium when the dimethyl carbonate conversion rate fluctuation is ≤±0.5%. After the reaction, the generated Na₂CO₃, NaHCO₃, and CH₃COONa mixed solids are removed by vacuum filtration, pressure filtration, or centrifugation. The equilibrium liquid is sent to a continuous distillation column for separation and purification through multi-column distillation to obtain methyl ethyl carbonate and diethyl carbonate. Unreacted raw materials are recycled, and the byproduct methyl acetate is sold as a chemical product. This invention features mild reaction conditions, low equipment requirements, high reaction efficiency, low energy consumption, simple separation, no azeotropic interference, high resource utilization, and is suitable for continuous production.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a method for preparing methyl ethyl carbonate and diethyl carbonate by transesterification under normal temperature and pressure. Background Technology

[0002] Ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), as important organic carbonate compounds, possess excellent dielectric properties and low-temperature fluidity, playing a core solvent role in lithium-ion battery electrolytes. They are also widely used in fine chemicals, pharmaceutical synthesis, and high-performance extractants. With the rapid development of new energy vehicles and energy storage industries, the demand for high-purity EMC and DEC is increasing, driving continuous optimization of related preparation processes.

[0003] In traditional industrial production, the main synthetic route for EMC and DEC involves the transesterification reaction of dimethyl carbonate (DMC) with ethanol. This process relies on alkali metal alkoxides such as sodium methoxide or sodium ethoxide as catalysts, and is carried out under high temperature and high pressure conditions, typically at 90–110 °C and 1.0–1.5 MPa. These conditions not only require reaction equipment to withstand high temperatures and pressures, leading to a significant increase in equipment investment and maintenance costs, but also introduce potential safety hazards, such as the risk of leakage under high pressure. Furthermore, the kinetic characteristics of this reaction result in a low conversion rate, typically requiring several hours to reach equilibrium, further reducing production efficiency. Simultaneously, the high-temperature environment promotes side reactions, affecting product selectivity.

[0004] More challenging is the formation of various azeotropic mixtures in the ester-alcohol exchange system, including methanol-dimethyl carbonate, ethanol-dimethyl carbonate, and ethanol-ethyl methyl carbonate. The presence of these azeotropes significantly complicates subsequent separation and purification processes. To overcome this challenge, existing processes often employ reactive distillation, where distillation is performed simultaneously with the reaction to remove the azeotropes and shift the equilibrium towards the positive side. However, this process further exacerbates energy consumption due to the need to maintain high column temperatures and precise reflux ratio control. Simultaneously, the catalyst dissolves in the byproduct methanol after the reaction, making early separation difficult. Upon entering the distillation system with the material, it easily crystallizes, leading to scaling on the column walls and pipe blockage, severely impacting equipment stability and lifespan.

[0005] To alleviate these problems, existing technologies attempt to introduce novel catalyst systems. For example, ionic liquid catalysts have been proposed as alternatives to traditional alkoxides, offering advantages such as lower reaction temperatures and improved selectivity. However, the synthesis of ionic liquids is complex and costly, and the recovery process involves multiple separation steps, making large-scale industrial applications difficult. Similarly, solid resin catalysts, such as strongly basic ion exchange resins, have been explored for fixed-bed catalysis to facilitate separation. However, these catalysts exhibit low activity, are prone to deactivation, and have stringent requirements for raw material purity, failing to meet the stability requirements of continuous production. Furthermore, some research focuses on process optimization, such as using reactive extractive distillation combined with extractants to treat azeotropes. However, this increases the number and complexity of operating units, and the overall economic efficiency remains unsatisfactory.

[0006] In general, existing EMC and DEC preparation processes suffer from common drawbacks such as harsh reaction conditions, high energy consumption, difficult separation, and limitations in continuous production. These shortcomings not only restrict capacity expansion and cost control but also affect the purity requirements for lithium battery electrolyte applications. For example, achieving electronic-grade standards with methanol content below 20 ppm and moisture content below 30 ppm often necessitates additional purification steps. Therefore, developing a novel synthetic route under mild conditions is a crucial issue urgently needing to be addressed in the field of new energy chemicals. This route should start with raw material selection and reaction mechanisms to achieve efficient conversion, simple separation, and low energy consumption, thus meeting the practical needs of large-scale industrial production. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing methyl ethyl carbonate and diethyl carbonate by transesterification under normal temperature and pressure.

[0008] The technical solution of the present invention is as follows:

[0009] A method for preparing methyl ethyl carbonate and diethyl carbonate by transesterification at room temperature and pressure includes the following steps:

[0010] (1) Raw material preparation: Dimethyl carbonate and ethyl acetate are selected as raw materials. The molar ratio of dimethyl carbonate to ethyl acetate is controlled at 1:1.0-2.5. The purity of the raw materials is not less than 99.5%, and the water content is controlled within 0.05%.

[0011] (2) Catalyst addition: Sodium methoxide or sodium ethoxide in methanol or ethanol solution is selected as catalyst and added at 0.1%-2.0% of the total mass of raw materials;

[0012] (3) Ester-ester exchange reaction: Dimethyl carbonate and ethyl acetate were continuously added to a reactor equipped with a stirrer at 5-25℃ and 0.1MPa±0.02MPa. The stirring rate was maintained at 50-100r / min, the temperature fluctuation of the reaction system was ≤±1℃, and the material residence time was 5-30 min. When the conversion rate of dimethyl carbonate fluctuated ≤±0.5%, the reaction was determined to have reached equilibrium.

[0013] (4) Removal of catalyst conversion products: Vacuum filtration, pressure filtration or centrifugation are used to remove the mixed fine solid particles of Na2CO3, NaHCO3 and CH3COONa generated in the reaction, so that the reaction equilibrium liquid does not contain catalyst conversion products;

[0014] (5) Product separation and purification: The reaction equilibrium liquid after removing the catalyst conversion product is sent to a continuous distillation column. A multi-tower distillation process is adopted to obtain methyl ethyl carbonate, diethyl carbonate, methyl acetate, and unreacted dimethyl carbonate and ethyl acetate by taking advantage of the difference in boiling points of each component. The unreacted raw materials are recycled.

[0015] In a preferred embodiment of the present invention, in step (1), the molar ratio of dimethyl carbonate to ethyl acetate is 1:1.2-2.0.

[0016] In a preferred embodiment of the present invention, in step (1), the moisture content of the raw material is controlled to be less than 0.03%.

[0017] In a preferred embodiment of the present invention, in step (2), the amount of catalyst used is 0.2-1.0% of the total mass of the raw materials.

[0018] In a preferred embodiment of the present invention, in step (3), the reaction temperature is 5-25°C and the material residence time is 5-10 min.

[0019] In a preferred embodiment of the present invention, in step (4), the catalyst conversion product is removed by centrifugation.

[0020] In a preferred embodiment of the present invention, in step (5), four continuous distillation columns are used for separation. The top temperature of the first column is controlled at 57°C to collect methyl acetate, the top temperature of the second column is controlled at 90°C to collect unreacted dimethyl carbonate and ethyl acetate, the top temperature of the third column is controlled at 108°C to collect methyl ethyl carbonate, and the top temperature of the fourth column is controlled at 127°C to collect diethyl carbonate.

[0021] In a preferred embodiment of the present invention, the catalyst is sodium methoxide, and it is added in the form of a sodium methoxide methanol solution, wherein the sodium methoxide content is 30%.

[0022] In a preferred embodiment of the present invention, the methyl acetate extracted in step (5) has a purity of ≥99.0%.

[0023] In a preferred embodiment of the present invention, the obtained methyl ethyl carbonate and diethyl carbonate products have a purity of ≥99.99%, a methanol content of ≤20ppm, and a water content of ≤30ppm.

[0024] The beneficial effects of this invention are:

[0025] 1. The reaction conditions of this invention are mild and the equipment requirements are reduced: the ester-ester exchange reaction is carried out under normal temperature and pressure, avoiding the need for traditional high temperature and high pressure processes, reducing the dependence on special pressure-resistant equipment, thereby reducing equipment procurement and maintenance costs, and significantly improving operational safety and process scalability.

[0026] 2. This invention has high reaction efficiency and significantly optimized energy consumption: By optimizing the raw material ratio and catalyst selection, the reaction equilibrium can be reached quickly, shortening the overall production cycle. At the same time, the energy input of heating and pressurization is eliminated, improving the economic benefits per unit product.

[0027] 3. The catalyst of this invention is easy to process and has improved selectivity: It adopts a mature alkali metal alkoxide catalyst, which avoids material decomposition and side reactions under mild conditions, and the product selectivity is higher; after the reaction, the catalyst is converted into easily separable solid particles, which are easy to remove by filtration and avoid the pollution problem of entering the separation system.

[0028] 4. The separation and purification process of the present invention is simplified and there is no azeotropic interference: the by-product is easily separable methyl acetate, rather than alcohols in traditional processes, which avoids the formation of complex azeotropes, making the distillation process more efficient, reducing separation energy consumption and operational complexity, and making it easier to obtain high-purity products.

[0029] 5. The present invention has high resource utilization and is environmentally friendly: unreacted raw materials can be recycled, and by-products can be recovered as bulk chemical commodities, achieving near-zero waste; the overall process conforms to the principles of green chemistry, reducing waste emissions and energy consumption, and promoting sustainable industrial production.

[0030] 6. The present invention has strong potential for continuous production and good industrial adaptability: the ease of catalyst removal and the absence of equipment scaling risk provide a guarantee for continuous operation, facilitate large-scale scaling, and are suitable for applications in high-demand fields such as lithium battery electrolytes. Attached Figure Description

[0031] Figure 1 The above are process flow diagrams for Embodiments 1 and 2 of the present invention. Detailed Implementation

[0032] The technical solution of the present invention will be further explained and described below with reference to specific embodiments and accompanying drawings.

[0033] The process flow of Examples 1 and 2 is as follows: Figure 1 As shown, each raw material is transported to the reactor via a raw material storage tank and undergoes an ester-ester exchange reaction under the action of a catalyst. After the reaction is completed, the reaction liquid is sent to a centrifuge to remove the catalyst conversion products. The filtered equilibrium liquid enters the clear liquid tank and then enters the distillation columns T-01, T-02, T-03, and T-04, where methyl acetate, recycled material, methyl ethyl carbonate, diethyl carbonate, and a very small amount of reactor residue are collected, respectively.

[0034] Example 1

[0035] (1) Ester-ester exchange reaction

[0036] 100 kg of dimethyl carbonate (99.6% purity) and 110 kg of ethyl acetate (99.7% purity) were selected, with a molar ratio of 1:1.2. The moisture content of both raw materials was controlled to be less than 0.03%. 0.3% (0.63 kg) of industrial sodium methoxide methanol solution (containing 30% sodium methoxide) was added to the system as a catalyst via continuous feeding. Dimethyl carbonate and ethyl acetate were continuously added to a reactor equipped with a stirrer. The reaction was carried out at 20℃ and 0.1 MPa ± 0.02 MPa, maintaining a stirring rate of 80 r / min, a temperature fluctuation of ≤ ±1℃, and a material residence time of 10 min. Samples were taken through the sampling port, and the product composition was analyzed using gas chromatography. The reaction was considered to have reached equilibrium when the dimethyl carbonate conversion rate fluctuated by ≤ ±0.5%. The reaction mixture was centrifuged for solid-liquid separation to remove the generated fine particulate solid mixture of Na₂CO₃, NaHCO₃, and CH₃COONa, yielding 208 kg of a clear ester-transfer equilibrium solution free of catalyst conversion products and 0.25 kg of catalyst conversion products. The clarified equilibrium solution was analyzed by gas chromatography, and the peak area ratio of each component was methyl acetate:methanol:dimethyl carbonate:ethyl acetate:methyl ethyl carbonate:diethyl carbonate = 26:0.2:14:11:35:13.

[0037] (2) Product separation and purification

[0038] The above-mentioned equilibrium clarified liquid is fed into the first distillation column, with a reflux ratio controlled at 2.0, a top pressure of 0.1 MPa, and a top temperature of 57°C. Methyl acetate is collected with a purity ≥99.0%. The bottoms of the first column are fed into the second distillation column, with a reflux ratio controlled at 2.0, a top pressure of 0.1 MPa, and a top temperature of 90°C. Unreacted dimethyl carbonate and ethyl acetate are collected, and these products are recycled for the transesterification process. The bottoms of the second column are fed into the third distillation column, with a reflux ratio controlled at 3.0, a top pressure of 0.1 MPa, and a top temperature of 108°C. Ethyl methyl carbonate is collected with a purity of approximately 99%, which can be further purified to a purity ≥99.99%, methanol content ≤20 ppm, and water content ≤30%. The product is an electronic grade product with a purity of ppm. The bottom product of the third column is fed into the fourth distillation column, where the reflux ratio is controlled at 3.0, the top pressure is 0.1 MPa, and the top temperature is 127°C. Diethyl carbonate is collected with a purity of about 99%, which can be further refined into an electronic grade product with a purity ≥99.99%, a methanol content ≤20 ppm, and a water content ≤30 ppm. The bottom product is a small amount of distillation residue.

[0039] Example 2

[0040] (1) Ester-ester exchange reaction

[0041] 100 kg of dimethyl carbonate (99.6% purity) and 180 kg of ethyl acetate (99.7% purity) were selected, with a molar ratio of 1:2.0. The moisture content of both raw materials was controlled to be less than 0.03%. 0.4% (1.12 kg) of industrial sodium methoxide methanol solution (containing 30% sodium methoxide) was added to the system as a catalyst via continuous feeding. Dimethyl carbonate and ethyl acetate were continuously added to a reactor equipped with a stirrer. The reaction was carried out at 20℃ and 0.1 MPa ± 0.02 MPa, maintaining a stirring rate of 80 r / min, a temperature fluctuation of ≤ ±1℃, and a material residence time of 10 min. Samples were taken through the sampling port, and the product composition was analyzed using gas chromatography. The reaction was considered to have reached equilibrium when the dimethyl carbonate conversion rate fluctuated by ≤ ±0.5%. The reaction mixture was centrifuged for solid-liquid separation to remove the generated fine particulate solid mixture of Na₂CO₃, NaHCO₃, and CH₃COONa, yielding 276 kg of a clear ester-ester exchange equilibrium solution free of catalyst conversion products and 0.42 kg of catalyst conversion products. The clarified equilibrium solution was analyzed by gas chromatography, and the peak area ratio of each component was methyl acetate:methanol:dimethyl carbonate:ethyl acetate:methyl ethyl carbonate:diethyl carbonate = 30:0.2:11:14:36:9.

[0042] (2) Product separation and purification

[0043] The above-mentioned equilibrium clarified liquid is fed into the first distillation column, with a reflux ratio controlled at 2.5, a top pressure of 0.1 MPa, and a top temperature of 57°C. Methyl acetate is collected with a purity ≥99.0%. The bottoms of the first column are fed into the second distillation column, with a reflux ratio controlled at 2.5, a top pressure of 0.1 MPa, and a top temperature of 90°C. Unreacted dimethyl carbonate and ethyl acetate are collected, and these products are recycled for the transesterification process. The bottoms of the second column are fed into the third distillation column, with a reflux ratio controlled at 3.5, a top pressure of 0.1 MPa, and a top temperature of 108°C. Ethyl methyl carbonate is collected with a purity of approximately 99%, which can be further purified to a purity ≥99.99%, methanol content ≤20 ppm, and water content ≤30%. The product is an electronic grade product with a purity of ppm. The bottom product of the third column is fed into the fourth distillation column, where the reflux ratio is controlled at 3.5, the top pressure is 0.1 MPa, and the top temperature is 127°C. Diethyl carbonate is collected with a purity of about 99%, which can be further refined into an electronic grade product with a purity ≥99.99%, methanol content ≤20 ppm, and water content ≤30 ppm. The bottom product is a small amount of distillation residue.

[0044] Comparative Example 1 (Traditional Ester-Alcohol Exchange Process)

[0045] To further highlight the advantages of this invention, Comparative Example 1 employs a traditional transesterification process: 100 kg of dimethyl carbonate (99.6% purity) and 79 kg of ethanol (99.8% purity) are selected, with a molar ratio of 1:1.2. A sodium methoxide methanol solution (1.5% of the total raw material mass, i.e., 2.7 kg) is added to the system as a catalyst. The reaction is carried out at a temperature of 100°C and a pressure of 1.2 MPa for 4 hours, yielding 180 kg of transesterification equilibrium solution. Due to the presence of alcohols in the system, only a small portion of the catalyst-converted product appears as a precipitate, with the majority remaining dissolved in the equilibrium solution, which cannot be completely removed even by centrifugation. Gas chromatography analysis of the clarified equilibrium solution revealed a peak area ratio of methanol:ethanol:dimethyl carbonate:methyl ethyl carbonate:diethyl carbonate = 18:21:25:28:8, showing a significant difference in product composition compared to the process of this invention.

[0046] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for preparing methyl ethyl carbonate and diethyl carbonate by transesterification at room temperature and pressure, characterized in that: Includes the following steps: (1) Raw material preparation: Dimethyl carbonate and ethyl acetate are selected as raw materials. The molar ratio of dimethyl carbonate to ethyl acetate is controlled at 1:1.0-2.

5. The purity of the raw materials is not less than 99.5%, and the water content is controlled within 0.05%. (2) Catalyst addition: Sodium methoxide or sodium ethoxide is selected as the catalyst and added at 0.1%-2.0% of the total mass of raw materials; (3) Ester-ester exchange reaction: Dimethyl carbonate and ethyl acetate were continuously added to a reactor equipped with a stirrer at 5-25℃ and 0.1MPa±0.02MPa. The stirring rate was maintained at 50-100r / min, the temperature fluctuation of the reaction system was ≤±1℃, and the material residence time was 5-30 min. When the conversion rate of dimethyl carbonate fluctuated ≤±0.5%, the reaction was determined to have reached equilibrium. (4) Removal of catalyst conversion products: Vacuum filtration, pressure filtration or centrifugation are used to remove the mixed fine solid particles of Na2CO3, NaHCO3 and CH3COONa generated in the reaction, so that the reaction equilibrium liquid does not contain catalyst conversion products; (5) Product separation and purification: The reaction equilibrium liquid after removing the catalyst conversion product is sent to a continuous distillation column. A multi-tower distillation process is adopted to obtain methyl ethyl carbonate, diethyl carbonate, methyl acetate, and unreacted dimethyl carbonate and ethyl acetate by taking advantage of the difference in boiling points of each component. The unreacted raw materials are recycled.

2. The method as described in claim 1, characterized in that: In step (1), the molar ratio of dimethyl carbonate to ethyl acetate is 1:1.2-2.

0.

3. The method as described in claim 1, characterized in that: In step (1), the moisture content of the raw materials is controlled to be within 0.03%.

4. The method as described in claim 1, characterized in that: In step (2), the amount of catalyst used is 0.2-1.0% of the total mass of the raw materials.

5. The method as described in claim 1, characterized in that: In step (3), the reaction temperature is 5-25℃ and the material residence time is 5-10min.

6. The method as described in claim 1, characterized in that: In step (4), the catalyst conversion product is removed by centrifugation.

7. The method as described in claim 1, characterized in that: In step (5), four continuous distillation columns are used for separation. The top temperature of the first column is controlled at 57°C to collect methyl acetate. The top temperature of the second column is controlled at 90°C to collect unreacted dimethyl carbonate and ethyl acetate. The top temperature of the third column is controlled at 108°C to collect methyl ethyl carbonate. The top temperature of the fourth column is controlled at 127°C to collect diethyl carbonate.

8. The method according to any one of claims 1 to 7, characterized in that: The catalyst is sodium methoxide, and it is added in the form of a sodium methoxide methanol solution, wherein the sodium methoxide content is 30%.

9. The method as described in claim 1, characterized in that: The purity of the methyl acetate extracted in step (5) is ≥99.0%.

10. The method as described in claim 1, characterized in that: The resulting methyl ethyl carbonate and diethyl carbonate products have a purity of ≥99.99%, a methanol content of ≤20ppm, and a water content of ≤30ppm.

Images