Continuous production process of ethyl methyl carbonate (EMC)

Abstract

This invention discloses a continuous production process for ethyl methyl carbonate (EMC), belonging to the field of organic carbonate synthesis technology. It aims to solve the problems of low conversion rate, poor selectivity, difficulty in catalyst separation and recovery, high energy consumption, and difficulty in stably preparing electronic-grade products in traditional batch processes. This invention uses dimethyl carbonate and ethanol as raw materials, employing a continuous reactive distillation coupled with a multi-stage distillation integrated process. Under the action of a solid base catalyst, a continuous transesterification reaction is achieved, simultaneously completing the discharge of the target product, online catalyst circulation, continuous separation of light and heavy components, and product purification. By precisely controlling the raw material ratio, reaction temperature, pressure, reflux ratio, and residence time, the entire process can operate continuously and stably. This invention features strong process continuity, high ethanol conversion rate, high EMC selectivity and yield, recyclable catalyst, low energy and material consumption, and the obtained product purity can reach electronic grade. It is suitable for the production of lithium-ion battery electrolyte solvents and is easy to scale up industrially and manage continuously.

Description

Technical Field

[0001] This invention belongs to the field of organic carbonate synthesis technology, specifically the continuous production process of ethyl methyl carbonate (EMC). Background Technology

[0002] Ethyl methyl carbonate (EMC) is a high-performance linear carbonate with characteristics such as high dielectric constant, high flash point, and good low-temperature performance. It is widely used as a core solvent in lithium-ion battery electrolytes, and market demand continues to grow, especially with higher requirements for the supply of electronic-grade high-purity EMC.

[0003] Currently, the mainstream industrial production method for EMC is the transesterification of dimethyl carbonate and ethanol. However, existing technologies generally suffer from the following prominent problems: 1. They are mainly based on batch / semi-batch processes, resulting in low production efficiency and poor stability. Traditional processes often use batch reactors or simple tower processes, which have long operation cycles, require a lot of manual intervention, and have large batch-to-batch fluctuations, making it difficult to achieve long-term stable operation and meet the needs of large-scale, continuous, and automated production; 2. The coupling degree between reaction and separation is low, limiting conversion rate and selectivity. Transesterification is a reversible equilibrium reaction. If the target product cannot be removed in time, the reaction is prone to reverse or one-step formation. Diethyl carbonate leads to low raw material conversion rate and poor EMC selectivity, resulting in high subsequent separation load and persistently high energy and material consumption; 3. There are obvious defects in catalyst use and recovery. Homogeneous catalysts have high activity but are difficult to separate and recover, and are prone to remaining in the product, affecting electronic-grade purity; traditional heterogeneous catalysts have problems such as low activity, easy deactivation, poor strength, and inability to be circulated online for a long time, which restricts continuous operation; 4. The separation process is lengthy, and it is difficult to meet the product purity standards. Existing processes mostly use multi-tower batch distillation, which is complex, has a large reflux ratio, and high energy consumption, making it difficult to stably obtain electronic-grade EMC of more than 99.99%. Impurities (such as water, alcohols, diethyl carbonate, etc.) are prone to exceed the standards, which cannot meet the requirements of high-end lithium battery electrolytes; 5. The overall process is not economical and safe enough. The batch scale-up effect is significant, the material residence time is long, the heat exchange is uneven, and there are problems such as high energy consumption, a lot of waste, and great safety hazards, which are inconsistent with the industrial development direction of green, low-carbon and high-end manufacturing. Therefore, developing a new EMC production process that is continuous, highly convertible, highly selective, low-energy-consumption, and readily available for producing electronic-grade products has become a key technical problem that urgently needs to be solved in the field of lithium battery materials. Summary of the Invention

[0004] This invention addresses the above-mentioned technical problems by providing a continuous production process for ethyl methyl carbonate (EMC) that is characterized by high conversion, high selectivity, low energy consumption, and easy availability of electronic-grade products.

[0005] This invention is achieved through the following technical solution: A continuous production process for ethyl methyl carbonate (EMC) includes the following units: raw material pretreatment, raw material storage, continuous transesterification reaction, separation and purification, and continuous distillation refining. The raw material pretreatment step involves dehydrating and drying dimethyl carbonate (DMC) and anhydrous ethanol, respectively, removing acidic impurities, and filtering to remove solids. The removal of acidic impurities is achieved through alkaline washing and neutralization, and the filtration to remove solids is performed using precision filtration. After pretreatment, the DMC and anhydrous ethanol are stored in the raw material storage step and preheated to 80°C before entering the continuous transesterification reaction step. At 90℃, DMC is injected into the continuous transesterification reaction step at a molar ratio of 1:1.05-1.2. In this step, a solid base is used as the catalyst. The solid base, dimethyl carbonate (DMC), and anhydrous ethanol form a slurry bed. The temperature is controlled at 105-120℃, the pressure at 0.1-0.2 MPa, and the stirring speed at 300-600 rpm. After an initial reaction of 1.5-3 hours, continuous feeding is initiated, and the slurry is continuously discharged, ensuring catalyst suspension and sufficient solid-liquid contact. Simultaneously, online catalyst circulation is activated. This online catalyst circulation involves removing the sediment from the bottom layer containing DMC. A large amount of solid base catalyst reaction liquid is released from the bottom side, filtered by a separation system, and the filtrate is sent to a separation and purification step. The concentrated solid base catalyst slurry is pumped back by a magnetic pump to continue the continuous transesterification reaction step. The reaction liquid from the continuous transesterification reaction step flows out and enters the separation and purification step, which is a condenser separation. After condensation in the separation and purification step, the reaction liquid in the continuous transesterification reaction step forms three liquid accumulation zones in the upper, middle, and bottom of the condenser: the upper zone corresponds to methanol, the middle zone corresponds to dimethyl carbonate and ethanol, and the bottom zone corresponds to methyl ethyl carbonate and diethyl carbonate. The three liquid layers are collected separately. The methanol produced in the upper layer is collected as a byproduct. The dimethyl carbonate and ethanol in the middle layer are pumped back to the continuous transesterification reaction step as reaction feedstock. The methyl ethyl carbonate and diethyl carbonate in the bottom layer are injected into the continuous distillation purification step for further purification. The diethyl carbonate is collected as a byproduct or pumped back to the continuous transesterification reaction step to inhibit further transesterification reaction. The methyl ethyl carbonate is collected as the finished product. In the continuous distillation purification step, the main temperature is 112-115℃, the side stream temperature is 109.5-110.5℃, the top temperature is 107-108℃, and the pressure is 100-110 kPa.

[0006] In the raw material pretreatment step, the purity of dimethyl carbonate is ≥99.5%, and the purity of anhydrous ethanol is ≥99.9%.

[0007] The dehydration and drying step in the raw material pretreatment process uses one of molecular sieve adsorption, membrane dehydration, or distillation dehydration to control the water content to ≤50ppm.

[0008] The precision filtration in the raw material pretreatment step refers to filtering particles with a particle size of 1 μm.

[0009] The solid base catalyst in the continuous transesterification reaction step has a particle size of 5-20 μm and a mass fraction of 5%-15%.

[0010] The separation system employs a hydrocyclone and precision filtration.

[0011] This invention also provides a continuous production line for dimethyl methyl carbonate (EMC), comprising a pretreatment module, a storage module, a reaction module, a separation module, and a distillation module. The pretreatment module, storage module, reaction module, separation module, and distillation module are connected in series. The reaction module includes a dimethyl carbonate inlet, an ethanol inlet, a magnetic stirrer, a magnetic propeller, a catalyst outlet, a separation liquid inlet, a reaction liquid outlet, and a separation system. The dimethyl carbonate inlet and ethanol inlet are located on one side of the bottom of the reaction module, and the catalyst outlet and separation liquid inlet are respectively located on the other side. The reaction liquid outlet is located above the separation liquid inlet. The catalyst outlet is connected to the separation system and then to the catalyst inlet at the top of the reaction module. The separation system includes a filtration section and a magnetic pump. The separation module includes a condenser shell, a condenser body, a reaction liquid inlet, a mixed liquid outlet, a separated liquid outlet, and a methanol outlet. The condenser body is located inside the condenser shell and is connected to the reaction liquid outlet of the reaction module through the reaction liquid inlet at the bottom. A mixed liquid outlet is located at the bottom of one side of the condenser body, a reflux liquid outlet is located in the middle, and a methanol outlet is located at the top. The separated liquid outlet is connected to the separated liquid inlet of the reaction module. The distillation module includes a distillation column, a product tank, a diethyl carbonate outlet, a mixed liquid inlet, and a condensation recovery pipe. The distillation column and the product tank are connected by the condensation recovery pipe. The mixed liquid inlet is located at the top of the distillation column, and the diethyl carbonate outlet is located on one side of the distillation column.

[0012] The distillation column uses wire mesh corrugated structured packing with 60 to 80 theoretical plates and a theoretical plate equivalent height (HETP) of 0.2 to 0.3 m.

[0013] The pretreatment module, storage module, reaction module, separation module, and distillation module are all made of 316L stainless steel.

[0014] Compared with the prior art, the present invention has the following outstanding advantages: Continuous production significantly increases capacity: The entire process operates continuously without interruption or waiting, with a capacity of up to 10,000 tons per year and an increase in production efficiency of over 40%.

[0015] The slurry bed with magnetic stirring results in high reaction efficiency: the 316L stainless steel material is non-corrosive and free of iron ion contamination; the magnetic coupling stirring provides reliable sealing, prevents leakage, and eliminates mechanical impurities; the catalyst particles are small, resulting in a large solid-liquid contact area, achieving a dimethyl carbonate conversion rate of ≥85% and a methyl ethyl carbonate selectivity of ≥90%.

[0016] Online catalyst circulation significantly reduces costs: Cyclone and precision filtration enable 100% online catalyst separation and over 99% recycling, reducing catalyst loss to <0.1% / day, extending lifespan by 3 to 5 times, and drastically reducing catalyst costs.

[0017] High-value utilization of by-products: The by-products methanol and DEC are of high purity and can be sold directly or reused. The raw material utilization rate is ≥95%, with no waste residue or wastewater discharge, making it green and environmentally friendly.

[0018] Safe, stable, and highly automated: operates under slight positive pressure with no high-pressure risks; fully automated DCS control throughout the process, with precise regulation of temperature, pressure, liquid level, and flow rate, ensuring stable product quality and safe and reliable operation. Attached Figure Description

[0019] In the attached diagram, Figure 1 This is a schematic diagram of the continuous production line structure for ethyl methyl carbonate (EMC) according to the present invention. Figure 2 This is a schematic diagram of the reaction module structure of the present invention. Figure 3 This is a schematic diagram of the separation module structure of the present invention. Figure 4 This is a schematic diagram of the distillation module structure of the present invention, wherein: 1—Pretreatment module, 2—Storage module, 3—Reaction module, 31—Dimethyl carbonate inlet, 32—Ethanol inlet, 33—Magnetic stirrer, 34—Magnetic propeller, 35—Catalyst outlet, 36—Separation liquid inlet, 37—Reaction liquid outlet, 38—Catalyst inlet, 39—Separation system, 4—Separation module, 41—Condensation tower shell, 42—Condensation tower body, 43—Reaction liquid inlet, 44—Mixed liquid outlet, 45—Separated liquid outlet, 46—Methanol outlet, 5—Distillation module, 51—Distillation tower, 52—Finished product tank, 53—Diethyl carbonate outlet, 54—Mixed liquid inlet, 55—Condensation recovery pipe. Detailed Implementation

[0020] The invention will now be further described with reference to the accompanying drawings.

[0021] like Figure 1 The following is a specific embodiment of a continuous methyl ethyl carbonate (EMC) production line.

[0022] First, dimethyl carbonate (DMC, purity ≥99.5%) and anhydrous ethanol (purity ≥99.9%) are pretreated in pretreatment module 1. After impurities are removed by precision filtration through 1μm micropores, they are stored in storage module 2. Then, the storage module 2 is preheated to 80-90℃, and the mixture is injected into reaction module 3 at a molar ratio of dimethyl carbonate:ethanol = 1:1.1 for continuous transesterification reaction. Magnetic stirring device 33 drives magnetic propeller 34 for magnetic coupling stirring at a speed of 500 rpm, with a particle size of 5- A 20μm solid base catalyst, at a mass fraction of 10%, was used to form a homogeneous slurry. The reaction was carried out at 105–120℃ and 0.1–0.2 MPa for 2 hours. Then, continuous feeding was initiated, with feed rates of dimethyl carbonate at 1000 kg / h and ethanol at 650 kg / h. Simultaneously, online catalyst circulation was activated. The separation system used a 0.5μm precision filter. The reaction solution was continuously discharged, and catalyst suspension was maintained by controlling the magnetic propeller speed to 34 rpm. Solid and liquid components are in full contact. The underflow from the hydrocyclone in separation system 39 (containing 80%–90% catalyst) is directly returned to reaction module 3 via a magnetic pump, achieving a recycling rate of ≥99%. The filtrate from the filter in separation system 39 (solid content <10ppm) is sent to distillation module 5, leaving no catalyst residue and not affecting subsequent separations. Methanol is separated as a byproduct by separation module 4. Dimethyl carbonate and ethanol in the middle layer are pumped back to reaction module 3, while methyl ethyl carbonate and diethyl carbonate in the bottom layer are further separated by distillation module 5. In block 5, the mixture of methyl ethyl carbonate and diethyl carbonate is pumped into the distillation column of distillation module 5. The column has an inner diameter of 1.2m and a packing height of 12m, using 350Y wire mesh corrugated packing with 70 theoretical plates. The feed position is set at the 45th plate. The column pressure is controlled at 105kPa, the top temperature at 107.5℃, and the side stream is set at the 25th plate with the temperature controlled at 110℃. The reflux ratio is approximately 12. Electronic-grade methyl ethyl carbonate (99.97% purity) and diethyl carbonate heavy components are continuously collected from the side stream as byproducts.

[0023] The foregoing merely illustrates the technical concept and features of the invention, and its purpose is to enable those skilled in the art to understand the invention and implement it accordingly. It does not limit the scope of protection of this invention. All equivalent changes or modifications made based on the essence of the invention should be included within the scope of protection of this invention.

Claims

1. A continuous production process for ethyl methyl carbonate (EMC), comprising the following units: raw material pretreatment, raw material storage, continuous transesterification reaction, separation and purification, and continuous distillation refining, characterized in that... In the raw material pretreatment step, dimethyl carbonate (DMC) and anhydrous ethanol are pretreated by dehydration and drying, removal of acidic impurities, and filtration to remove solid impurities. The removal of acidic impurities is achieved through alkaline washing and neutralization, and the filtration to remove solid impurities is performed through precision filtration. After pretreatment, the dimethyl carbonate (DMC) and anhydrous ethanol are stored in the raw material storage step. Before entering the continuous transesterification reaction step, they are preheated to 80–90°C and then injected into the continuous transesterification reaction step at a molar ratio of DMC:ethanol = 1:1.05–1.

2. In the transesterification reaction step, a solid base is used as the catalyst. The solid base, dimethyl carbonate (DMC), and anhydrous ethanol form a slurry bed. The temperature is controlled between 105 and 120°C, the pressure between 0.1 and 0.2 MPa, and the stirring speed between 300 and 600 rpm. After the initial reaction time of 1.5 to 3 hours, continuous feeding is initiated, and the slurry is continuously discharged, keeping the catalyst suspended and ensuring sufficient solid-liquid contact. Simultaneously, online catalyst circulation is activated. This online circulation involves releasing the reaction liquid containing a large amount of solid base catalyst that has settled to the bottom from one side of the bottom, filtering it through a separation system, and then... The filtrate from the filter is sent to the separation and purification step. The concentrated solid alkali catalyst slurry is pumped back via a magnetic pump to continue the continuous transesterification reaction step. After the reaction liquid from the continuous transesterification reaction step flows out, it enters the separation and purification step, which is a condenser separation. After the reaction liquid in the continuous transesterification reaction step is condensed in the separation and purification step, three liquid accumulation zones are formed in the upper, middle, and bottom of the condenser: the upper zone corresponds to methanol, the middle zone corresponds to dimethyl carbonate and ethanol, and the bottom zone corresponds to methyl ethyl carbonate and diethyl carbonate. The three liquid layers are collected separately, and the product from the upper layer is collected. Methanol is collected as a byproduct. Dimethyl carbonate and ethanol in the middle section are pumped back to the continuous transesterification reaction step as reaction feedstock. Ethyl methyl carbonate and diethyl carbonate at the bottom are injected into the continuous distillation purification step for further purification. Diethyl carbonate is collected as a byproduct or pumped back to the continuous transesterification reaction step to inhibit further transesterification reaction. Ethyl methyl carbonate is collected as the finished product. In the continuous distillation purification step, the main temperature is 112-115℃, the side stream temperature is 109.5-110.5℃, the top temperature is 107-108℃, and the pressure is 100-110 kPa.

2. The continuous production process of ethyl methyl carbonate (EMC) according to claim 1, characterized in that... In the raw material pretreatment step, the purity of dimethyl carbonate is ≥99.5%, and the purity of anhydrous ethanol is ≥99.9%.

3. The continuous production process for ethyl methyl carbonate (EMC) according to claim 1, characterized in that... The dehydration and drying step in the raw material pretreatment process uses one of molecular sieve adsorption, membrane dehydration, or distillation dehydration to control the water content to ≤50ppm.

4. The continuous production process for ethyl methyl carbonate (EMC) according to claim 1, characterized in that... The precision filtration in the raw material pretreatment step refers to filtering particles with a particle size of 1 μm.

5. The continuous production process for ethyl methyl carbonate (EMC) according to claim 1, characterized in that... The solid base catalyst in the continuous transesterification reaction step has a particle size of 5-20 μm and a mass fraction of 5%-15%.

6. The continuous production process for ethyl methyl carbonate (EMC) according to claim 1, characterized in that... The separation system employs a hydrocyclone and precision filtration.

7. A continuous production line for ethyl methyl carbonate (EMC), comprising a pretreatment module, a storage module, a reaction module, a separation module, and a distillation module, characterized in that... The pretreatment module, storage module, reaction module, separation module, and distillation module are connected in series. The reaction module includes a dimethyl carbonate inlet, an ethanol inlet, a magnetic stirrer, a magnetic propeller, a catalyst outlet, a separation liquid inlet, a reaction liquid outlet, and a separation system. The dimethyl carbonate inlet and ethanol inlet are located on one side of the bottom of the reaction module, and the catalyst outlet and separation liquid inlet are respectively located on the other side. The reaction liquid outlet is located above the separation liquid inlet. The catalyst outlet is connected to the separation system and then to the catalyst inlet at the top of the reaction module. The separation system includes a filtration section and a magnetic pump. The separation module includes a condenser shell and a condenser. The distillation module includes a column body, a reaction liquid inlet, a mixed liquid outlet, a separated liquid outlet, and a methanol outlet. The condenser column is located inside the condenser shell and is connected to the reaction liquid outlet of the reaction module through the reaction liquid inlet at the bottom. A mixed liquid outlet is located at the bottom of one side of the condenser column, a reflux liquid outlet is located in the middle, and a methanol outlet is located at the top. The separated liquid outlet is connected to the separated liquid inlet of the reaction module. The distillation module includes a distillation column, a product tank, a diethyl carbonate outlet, a mixed liquid inlet, and a condensation recovery pipe. The distillation column and the product tank are connected through the condensation recovery pipe. The mixed liquid inlet is located at the top of the distillation column, and the diethyl carbonate outlet is located on one side of the distillation column.

8. The continuous production line for ethyl methyl carbonate (EMC) according to claim 7, characterized in that... The distillation column uses wire mesh corrugated structured packing with 60 to 80 theoretical plates and a theoretical plate equivalent height (HETP) of 0.2 to 0.3 m.

9. A continuous production line for ethyl methyl carbonate (EMC) according to claim 7, characterized in that... The pretreatment module, storage module, reaction module, separation module, and distillation module are all made of 316L stainless steel.

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