A method for synthesizing methyl ethyl carbonate by means of a backpack type reaction rectification method with DBU as catalyst

Abstract

The application discloses a method for synthesizing EMC by using a small-molecule organic base DBU as a catalyst through a back-pack type reaction rectification process, and belongs to the technical field of EMC preparation. Firstly, dimethyl carbonate (DMC) and ethanol are pre-reacted by using DBU as a catalyst, and then the obtained reaction product is input into a reaction rectification tower from the lower part of a reaction section, and a proper amount of DBU is supplemented from the upper part of the reaction section, so that the ester exchange reaction is continuously carried out in the reaction rectification tower and a back-pack reactor, the methanol and DMC azeotrope is collected from the top of the tower, and EMC, DMC, diethyl carbonate (DEC) and the catalyst DBU are collected from the tower bottom. The back-pack type reaction rectification technology can increase the reaction residence time by adding the back-pack, and can timely remove the product EMC from the reaction zone in situ to break the chemical reaction balance, so that the reaction conversion rate is significantly improved, and finally the ethanol conversion rate reaches 99.5%, and the EMC selectivity is more than 95.0%.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of preparation of ethyl methyl carbonate (EMC), and particularly relates to a method for preparing EMC by using a homogeneous organic base catalyst and a backpack type reaction rectification device. BACKGROUND

[0002] Energy is the basic guarantee for the continuation and development of human social civilization, and is the driving force for the development of modern industrial economy. Under the major strategic decision of carbon peak and carbon neutral, building a new type of power system mainly composed of wind energy, solar energy, ocean energy and other new energy has become an important part of energy strategy adjustment, and the energy storage technology taking lithium ion battery as the core is the key technology to solve the intermittency and volatility of new energy in use, which has important economic and social significance for promoting the large-scale application of new energy power generation.

[0003] In order to develop lithium ion batteries with excellent performance, researchers strive to seek breakthroughs and innovations in electrode materials mainly composed of lithium salt and graphite carbon, and also turn their sights to lithium ion battery electrolyte. The main function of lithium ion battery electrolyte is ion conduction, which guarantees high voltage and high specific energy of lithium ion battery. It is generally composed of carbonic acid ester organic electrolyte dissolving lithium salt, mainly including vinyl carbonate, propylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (EMC), etc. Due to the small steric hindrance and asymmetry of EMC in structure, it can increase the solubility of lithium salt, thereby improving the capacity density and electric quantity of the battery. It is the largest solvent in lithium ion battery electrolyte, accounting for about 30-35% of the electrolyte. According to statistics, the global lithium battery capacity reached 957.7GWh in 2022, and the global lithium ion battery shipment will reach 2211.8GWh and 6080.4GWh in 2025 and 2030 respectively, with a compound growth rate of 22.8%. According to the calculation of 1100-1200t / GWh of electrolyte usage in lithium battery, the annual demand of EMC will reach 2.5 million tons. Therefore, it is of great significance to find an efficient and inexpensive EMC preparation technology. EMC is mainly prepared by ester exchange reaction rectification process of DMC and ethanol, and the catalyst used is mainly sodium alcoholate. However, sodium alcoholate has poor solubility in the reaction system and is easy to precipitate, which makes it difficult to fully exert the advantages of reaction rectification technology. The high activity of sodium alcoholate will promote the further ester exchange of EMC and ethanol, reducing the selectivity of EMC. At the same time, sodium alcoholate catalyst is easy to deactivate and cannot be recycled and reused, and a large amount of solid hazardous waste is generated, which has high treatment cost and has become a "neck" problem in the green synthesis of EMC. Therefore, it is urgent to develop an alkaline catalyst with high activity and high selectivity to replace sodium alcoholate catalyst to ensure high conversion rate and high selectivity of DMC and ethanol ester exchange reaction.

[0004] Developing a suitable reactive distillation process is another key to guarantee the efficient production of EMC. In the DMC and ethanol ester exchange reactive distillation process, if the reaction of DMC and ethanol to prepare EMC does not proceed completely, then there are multiple azeotropic systems of the products EMC, DEC, methanol and the incompletely reacted DMC and ethanol, which makes the product separation and purification difficult and the subsequent separation energy consumption high. In order to realize complete reaction, if the ethanol is excessive, the DMC is completely reacted, then the EMC is easy to further react with the excessive ethanol in the reaction process to reduce the selectivity of EMC; on the contrary, if the DMC is excessive, it is beneficial to improve the selectivity of EMC, but the subsequent product separation and purification energy consumption is high, so it is necessary to match with the catalyst activity to realize high conversion rate and high selectivity, and reduce the DMC / ethanol feed ratio. Therefore, on the basis of the research and development of high-performance catalyst, the development of the matching reactive distillation coupling technology can guarantee the high selectivity of EMC and realize the high conversion rate of DMC, which is the key to improve the efficiency of the synthesis process of EMC, guarantee the product quality of EMC and ensure the sustainable development of EMC industry. SUMMARY

[0005] The purpose of the present application is to provide a 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) catalyzed EMC synthesis back-pack type reactive distillation method to solve the problems of the traditional catalysts in the ester exchange preparation of EMC, such as the inability to be recovered, high catalyst treatment cost and poor EMC selectivity.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] The present application uses DMC and ethanol as raw materials, DBU as catalyst, and utilizes a back-pack type reactive distillation column to prepare EMC, wherein the back-pack type reactive distillation column comprises a pre-reactor, a back-pack reactor and a reactive distillation column, the reactive distillation column comprises a reaction section, a distillation section and a stripping section, and the back-pack reactor is connected with the reaction section.

[0008] A DBU catalyzed EMC synthesis back-pack type reactive distillation method, specifically comprising the following steps: the feed of DMC is kept excessive, the raw materials DMC and ethanol are fully contacted with the catalyst DBU in the pre-reactor and react for a period of time, the generated reaction product is used as raw material and input into the reactive distillation column from the lower part of the reaction section, an appropriate amount of DBU is supplemented from the upper part of the reaction section, the ester exchange reaction is continuously carried out in the reactive distillation column and the back-pack reactor, the methanol and DMC azeotrope is collected from the top of the column, and the EMC, DMC, DEC and catalyst DBU are collected from the column bottom.

[0009] In the above step, the molar ratio of the mixed feed of DMC and ethanol is 1:1-3:1.

[0010] In the above step, the flow rate of the feed of DMC is 1000 kg / h-8500 kg / h.

[0011] The amount of DBU added in the pre-reactor in the above step is 1-10% of the mass of DMC, and the amount of DBU supplemented at the upper part of the reaction section is 0.5-5% of the amount of EMC feed.

[0012] The residence time of the mixture of DMC, ethanol and DBU in the pre-reactor in the above step is 0.5-1.5h.

[0013] The number of back-pack reactors in the present application is 1-5, and the total volume is 10-80% of the volume of the reaction section.

[0014] The operating temperature of the pre-reactor in the present application is 60-80℃, and the operating pressure is 0.1-0.15bar.

[0015] The number of theoretical plates in the rectifying section of the reaction rectifying column in the present application is 25-50, and the number of theoretical plates in the stripping section is 15-30.

[0016] EMC is a main raw material for lithium ion battery electrolyte, which is mainly prepared by ester exchange reaction rectification of DMC and ethanol, but the commonly used homogeneous basic catalyst such as sodium alcoholate has problems such as easy deactivation and difficult separation and recovery. Therefore, the inventors use DBU with high basic strength to catalyze the synthesis of EMC, which can balance the catalytic activity and selectivity, replace the traditional homogeneous sodium alcoholate catalyst, and be applied to the process of ester exchange reaction for synthesizing EMC, thereby completely solving the problems of the traditional catalysts such as unable to be recovered and high cost of catalyst treatment. By optimizing the reaction and separation process, the back-pack reaction rectification technology is developed, which realizes high conversion rate and high selectivity, reduces the feed ratio of DMC and ethanol, and reduces the unit consumption and energy consumption of EMC production.

[0017] The beneficial effects of the present application are:

[0018] (1) The present application uses organic base DBU as catalyst, which can replace the traditional sodium alcoholate catalyst, effectively solve the problems of traditional sodium alcoholate such as easy deactivation, unable to be recycled, and large amount of solid waste, etc., can greatly reduce the environmental pressure of EMC production enterprises, and reduce the production cost.

[0019] (2) The DBU catalyst is used to develop a new EMC synthesis back-pack reaction rectification process, which can effectively improve the conversion rate and selectivity of ester exchange reaction, significantly reduce the unit consumption and energy consumption of EMC, and realize the greenization and low carbonization of EMC synthesis. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The present application is an EMC synthesis back-pack reaction rectification process flow chart using DBU as catalyst.

[0021] Figure 2The catalytic performance of DBU on the transesterification reaction of DMC and ethanol at different temperatures. DETAILED DESCRIPTION

[0022] In order to make the content of the present application more convenient to understand, the technical solutions of the present application will be further described below in combination with specific embodiments, but the present application is not limited to this.

[0023] Example 1

[0024] The DBU was used as catalyst to carry out the batch reaction experiment, and the catalytic activity of DBU was investigated. The test conditions were as follows: temperature 75, 80, 90 ℃, catalyst dosage 10% wt (DMC), EtOH: DMC = 0.8:1, and sampling analysis was carried out at 30 min, 60 min, 120 min and 180 min, respectively. As shown in Figure 2 DBU showed certain catalytic activity in the preparation of EMC by the transesterification reaction of DMC and ethanol, but the reaction rate was slow. If complete conversion of ethanol is to be achieved, the height of the reaction section needs to be increased, so the pre-reactor is increased, and the reaction rectifying column is combined with the back pack, which greatly increases the residence time of the reaction material and DBU catalyst, improves the conversion rate of ethanol, and reduces the height of the reaction section.

[0025] Example 2

[0026] The DBU was used as catalyst to carry out the pre-reaction, and the reaction conditions were as follows: temperature 75 ℃, DBU catalyst dosage: 5% wt (DMC), EtOH: DMC = 1:2.5, residence time in the pre-reactor 1 h, and the reacted material was input into the reaction rectifying column from the lower part of the reaction section (the inner diameter of the reaction rectifying column: 22 mm; reaction section: 900 mm; rectifying section: 500 mm; stripping section: 200 mm; back pack volume: 100 mL; back pack number: 2). The DBU catalyst with 2% wt (DMC) was supplemented from the upper part of the reaction section, the reflux ratio was 5.0, and the transesterification reaction was continued in the reaction rectifying column and the back pack. The methanol and DMC azeotrope was collected from the top of the column, and the EMC, DMC, DEC and catalyst DBU were collected from the bottom of the column. As shown in Table 1, the ethanol was basically completely converted, and the conversion rate could reach 99.97%. In addition, the EMC also had high selectivity, and the selectivity could reach 96.73%.

[0027] Table 1. DBU catalytic reaction rectification results

[0028]

[0029] Example 3

[0030] Pre-reaction with DBU as catalyst, reaction conditions: temperature 75°C, DBU catalyst dosage: 5%wt(DMC), EtOH:DMC=1:2.0, residence time in pre-reactor 1h, the reacted material was input into the reactive distillation column from the lower part of the reaction section (reactive distillation column inner diameter: 22mm; reaction section: 900mm; rectification section: 500mm; stripping section: 200mm; back pack volume: 100mL; back pack number: 2), 2%wt(DMC) DBU catalyst was supplemented from the upper part of the reaction section, reflux ratio 6.0, the transesterification reaction was continued in the reactive distillation column and the back pack, the methanol, DMC azeotrope was collected from the top of the column, and EMC, DMC, DEC and catalyst DBU were collected from the column bottom. The results are shown in Table 2, and the ethanol conversion rate can reach 99.98%, in addition, EMC also has high selectivity, the selectivity is as high as 95.78%.

[0031] Table 2. DBU catalytic reaction distillation results

[0032]

[0033] Example 4

[0034] Pre-reaction with DBU as catalyst, reaction conditions: temperature 75°C, DBU catalyst dosage: 5%wt(DMC), EtOH:DMC=1:2.0, residence time in pre-reactor 1h, the reacted material was input into the reactive distillation column from the lower part of the reaction section (reactive distillation column inner diameter: 22mm; reaction section: 900mm; rectification section: 500mm; stripping section: 200mm; back pack volume: 100mL; back pack number: 1), 2%wt(DMC) DBU catalyst was supplemented from the upper part of the reaction section, reflux ratio 5.0, the transesterification reaction was continued in the reactive distillation column and the back pack, the methanol, DMC azeotrope was collected from the top of the column, and EMC, DMC, DEC and catalyst DBU were collected from the column bottom. The results are shown in Table 3, and the ethanol conversion rate can reach 93.41%, in addition, EMC also has high selectivity, the selectivity is as high as 97.01%.

[0035] Table 3. DBU catalytic reaction distillation results

[0036]

[0037] Example 5

[0038] The pre-reaction was carried out with DBU as catalyst, the reaction conditions were: temperature 75°C, DBU catalyst dosage: 5%wt(DMC), EtOH: DMC=1:2.0, residence time in pre-reactor 1h, the reacted material was inputted into the reaction distillation column from the lower part of the reaction section(reaction distillation column inner diameter: 22mm; reaction section: 900mm; distillation section: 500mm; stripping section: 200mm; back pack volume: 100mL; back pack number: 2), 2%wt(DMC) DBU catalyst was supplemented from the upper part of the reaction section, reflux ratio 5.0, the transesterification reaction was continued in the reaction distillation column and the back pack, the methanol, DMC azeotrope was collected from the top of the column, EMC, DMC, DEC and catalyst DBU were collected from the bottom of the column. The results are shown in Table 4, the ethanol was basically completely converted, the conversion rate could reach 99.93%, in addition, EMC also had high selectivity, the selectivity was as high as 95.87%. From the results of ethanol conversion rate and EMC selectivity in the continuous operation process of the reaction distillation column, basically no ethanol existed, which also showed that the reaction distillation column process with pre-reactor and back pack reactor with DBU as catalyst could realize the complete conversion of ethanol in the transesterification reaction of DMC and ethanol.

[0039] Table 4. DBU catalytic reaction distillation results

[0040]

[0041] Table 5. DBU catalytic reaction distillation continuous operation results

[0042]

[0043] The above only describes the preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the patent application of the present application shall belong to the scope of the present application.

Claims

1. A backpack-style reactive distillation method for EMC synthesis using DBU as a catalyst, characterized in that: EMC was prepared using DMC and ethanol as raw materials and DBU as catalyst via a backpack-type reactive distillation column. The backpack-type reactive distillation column includes a pre-reactor, a backpack reactor, and a reactive distillation column; The reactive distillation column includes a reaction section, a rectification section, and a stripping section; The backpack reactor is connected to the reaction section; The process includes the following steps: The feedstock DMC is kept in excess, and it reacts fully with ethanol and catalyst DBU in a pre-reactor. The resulting reaction product is fed into a reactive distillation column from the lower part of the reaction section. DBU is added to the upper part of the reaction section. The transesterification reaction continues in the reactive distillation column and backpack reactor. The methanol-DMC azeotrope is collected from the top of the column, and EMC, DMC, DEC, and catalyst DBU are collected from the bottom of the column. The EMC is ethyl methyl carbonate; the DMC is dimethyl carbonate; the DEC is diethyl carbonate; and the DBU is 1,8-diazabicyclo[5.4.0]undec-7-ene.

2. The method according to claim 1, characterized in that: The molar ratio of DMC to ethanol in the mixed feed is 1:1 to 3:

1.

3. The method according to claim 1, characterized in that: The feed flow rate of DMC is 1000 kg / h - 8500 kg / h.

4. The method according to claim 1, characterized in that: The amount of DBU added in the pre-reactor is 1%-10% of the mass of DMC, and the amount of DBU added in the upper part of the reaction section is 0.5%-5% of the EMC in the reaction products generated by the pre-reactor.

5. The method according to claim 1, characterized in that: The residence time of the mixture of DMC, ethanol and DBU in the pre-reactor is 0.5-1.5 h.

6. The method according to claim 1, characterized in that: The number of backpack reactors is 1-5, and the total volume is 10%-80% of the reaction section volume.

7. The method according to claim 1, characterized in that: The pre-reactor operates at a temperature of 60-80℃ and a pressure of 0.1-0.15 bar.

8. The method according to claim 1, characterized in that: The theoretical plate number of the rectifying section of a reactive distillation column is 25-50, and the theoretical plate number of the stripping section is 15-30.

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