Process method for preparing carbonic ester through high-flux micro-channel cascade conversion

Abstract

The invention relates to a process method for preparing carbonic ester by high-flux micro-channel cascade conversion, which comprises the following steps: feeding CO2 and epoxide from the bottom of a first-section bubble tower reactor, reacting under the action of an ionic liquid catalyst, separating the reaction discharge, and obtaining the carbonic ester. And a liquid phase which is not completely reacted and contains the reactant epoxide and CO2 enters the second-stage deepening micro-channel reactor for further reaction, so that gradient conversion and efficient synthesis of cyclic carbonate are realized. The continuous production process of cyclic carbonate provided by the invention is reasonable in process flow, greatly reduces the volume of the reactor, shortens the reaction retention time, realizes process reinforcement, simplifies the process flow, is an efficient and feasible cyclic carbonate continuous synthesis process, and has a good industrial application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of cyclic carbonates, and in particular to a method for coupling a microchannel reactor with a bubbling bed reactor to realize CO 2 A process for synthesizing cyclic carbonates by continuous and efficient stepwise conversion. Background Art

[0002] CO 2 It is currently the main source of the greenhouse effect, but CO 2 At the same time, it is a rich C1 resource, realizing CO 2 Capture and utilization are important ways to solve carbon emissions. 2 The preparation of cyclic carbonates has been applied in industrial production. The reaction has the advantages of atom economy and few by-products, which conforms to the concept of green chemistry. Cyclic carbonates are important chemical intermediates that can be used as polar solvents, electrolyte solutions, and intermediates in medicine and chemicals. They can also be used in the synthesis of a variety of polymers. 2 The process of preparing cyclic carbonates by coupling with epoxides usually uses homogeneous catalysts and is carried out in a bubbling bed. 2 The efficient conversion of CO has important research significance. 2 The research on the synthesis of cyclic carbonates mainly focuses on catalysts and processes.

[0003] Patent CN 105777543 A discloses an epoxide and CO 2 The method and process system for preparing linear carbonate and co-producing diols use a fixed bed or bubbling bed tubular reactor filled with a heterogeneous solid catalyst. The process system has strong continuity and stable and reliable production. However, when the alkylene oxide is converted to a certain extent, the reaction rate drops sharply, and a longer residence time and a smaller reaction space velocity are required to completely convert the material, and the production efficiency is low. Patent CN 106478586 A discloses a synthesis process for ethylene carbonate. After the reactants ethylene oxide and carbon dioxide are reacted in a synthesis reactor (fixed bed, bubbling bed or fluidized bed), part of the liquid phase circulation flow (50%-99%) is further reacted in the synthesis reactor. This process solves the problems of incomplete reaction of ethylene oxide and difficulty in recovery, but a large amount of liquid phase logistics circulation is produced, and the energy consumption is high.

[0004] In order to enhance gas-liquid mass transfer, patents CN 110003163 A and CN 110028483 A disclose a method for preparing cyclic carbonate by a circulating jet gas-liquid contact process. 2The cyclic carbonate is efficiently prepared by coupling reaction with alkylene oxide. In this preparation process, the gas-liquid contact only occurs at the throat, so the time for the reactants to pass through the throat is very short. The requirements for reaction temperature and reaction pressure are relatively stringent, which has a significant effect on strengthening the feed. However, CO 2 The cycloaddition reaction process is kinetically controlled at low concentrations, and the problem of low conversion rate at low concentrations in the prior art has not been solved.

[0005] Microchannel reactors have the characteristic of a significantly larger specific surface area, which can simultaneously enhance the mass transfer and heat transfer rate, thereby shortening the diffusion time, achieving rapid mixing of fluids and stable temperature control. CN 114478462A, CN115960071B and CN 117777087 A respectively provide a device and method for preparing cyclic carbonates by microchannel reaction, using low eutectic ionic liquids and microchannel reactors with different tube diameters to successfully break through the rate limits of cycloaddition reaction and gas-liquid mass transfer, and achieve CO 2 The mild conversion with epoxides, however, uses one or more microchannel reactors in series. Due to the structural characteristics of the microchannel reactor, it cannot be applied in large-scale industry and is not suitable for the preparation of bulk chemical carbonates.

[0006] In summary, the existing CO 2 The technology of preparing cyclic carbonates by cycloaddition using traditional industrial reactors cannot solve the problem of complete conversion of trace amounts of alkylene oxides, and also faces the difficulties of large equipment structure size and complex system. The new technology utilizes the advantages of small channel size, large specific surface area, and high mass and heat transfer efficiency of microchannel reactors to shorten the reaction time, but due to its small flux and complex system, it is not suitable for large-scale preparation of bulk chemical carbonates. Summary of the invention

[0007] In order to overcome the existing CO 2 In view of the shortcomings existing in the process of synthesizing cyclic carbonate from epoxide, the present invention develops a process method for preparing carbonate by high-throughput microchannel cascade conversion, which solves the problem that the microchannel reactor has low flux and is not suitable for the preparation of large-scale bulk chemicals; by utilizing the excellent characteristics of small volume and compact size of the microchannel, the floor space and cost of the reaction system can be further reduced, the mass transfer process of the reaction process is strengthened, and the problems of insufficient epoxide reaction, long residence time, and large reactor volume are solved; at the same time, a bubbling bed reactor is coupled to achieve high-throughput preparation of carbonate, providing a new process method for industrial production.

[0008] To achieve the above object, the present invention provides a process for preparing carbonate by high-throughput microchannel cascade conversion, the process comprising a first-stage bubbling bed reactor and a second-stage microchannel reactor system connected to each other, the liquid outlet of the first-stage bubbling bed reactor being connected to the liquid inlet of the second-stage microchannel reactor through a pipeline, the liquid outlet of the second-stage microchannel reactor being connected to the liquid inlet of the first-stage bubbling bed reactor, and specifically comprising the following steps:

[0009] a. Raw material CO 2 and epoxide, fed from the bottom of a bubbling bed reactor, react under the action of an ionic liquid catalyst; to ensure that the reaction proceeds fully, the CO 2 The feed ratio of epoxide is controlled at (1.5-3) / 1, where the excess CO 2 The gas-liquid separation tank after the bubbling bed reactor is separated and then recycled;

[0010] b. The reaction product is separated into gas and liquid, and the unreacted epoxide and CO 2 The liquid phase further undergoes CO 2 / epoxide cycloaddition reaction; wherein the equivalent inner diameter of the microchannel reactor is 0.1-5.0 mm, and the heat exchange medium of the microchannel reactor is any one of hot water and heat transfer oil;

[0011] c. After the liquid phase passes through the second-stage microchannel reactor, 70% to 90% is pressurized and cooled in a cooler and then circulated to the bottom of the first-stage bubbling bed reactor, and the remaining 10% to 30% is pressurized by a pump and discharged into the separation and recovery system;

[0012] At the same time, the present invention provides a method for realizing CO 2 A microchannel coupled bubbling bed reaction device for a cascade conversion process for synthesizing cyclic carbonates, the set of reaction devices comprising a first-stage bubbling bed reactor and a second-stage microchannel reactor, the second-stage microchannel reactor being selected from commercially available plate-type, tubular-type and different structure-enhanced microchannel reactors and parallel and integrated microchannel reaction modules, wherein the material of the microchannel reactor can be selected from one or a combination of any two of stainless steel, alloy, ceramic, PMMA or silicon carbide glass.

[0013] Preferably, to achieve excess CO 2 In order to achieve efficient conversion and improve the purity of the product, a gas-liquid separation tank is arranged on the pipeline connecting the liquid outlet of the first-stage bubbling bed reactor and the liquid inlet of the second-stage microchannel reactor, and the liquid outlet of the gas-liquid separation tank is connected to the liquid inlet of the second-stage microchannel reactor.

[0014] Preferably, in order to strengthen the reaction process and improve the gas-liquid mass transfer efficiency, a filler is provided in the first stage bubbling bed reactor, and the filler is preferably any one of a wire mesh, a porcelain ball or a resin loaded with a catalyst; a gas distributor is provided in the lower space, and the gas distributor is connected to the gas inlet of the bubbling bed reactor through a pipeline. Preferably, the gas distributor is 0.2 to 1.5 meters away from the liquid inlet of the bubbling bed reactor.

[0015] To ensure the reaction efficiency of the device, the liquid inlet of the first-stage bubbling bed reactor is arranged at the bottom, and is connected to the feed pipeline of epoxide and the liquid outlet of the hot material channel of the second-stage microchannel reactor through pipelines; the liquid outlet of the first-stage bubbling bed reactor is arranged at the top, and is connected to the liquid inlet of the hot material channel of the second-stage microchannel reactor through pipelines.

[0016] Preferably, in order to facilitate excess CO 2 A gas-liquid separation tank is provided on the connecting pipe between the top liquid outlet of the first-stage bubbling bed reactor and the hot material channel liquid inlet of the second-stage microchannel reactor. The material from the top liquid outlet of the bubbling bed reactor is firstly separated into excess CO in the gas-liquid separation tank. 2 The separated solution is then sent to the second-stage microchannel reactor for in-depth reaction.

[0017] To achieve microchannel enhanced CO 2 The conversion efficiency is improved, and the two-stage microchannel reactor is respectively provided with a hot material channel and a cold material channel, and the hot material channel and the cold material channel are respectively provided with a liquid inlet and a liquid outlet; wherein the liquid inlet of the two-stage microchannel reactor is the liquid inlet of the hot material channel, the liquid outlet of the microchannel reactor is the liquid outlet of the hot material channel, and the liquid inlet and outlet of the cold material channel are respectively connected to the inlet and outlet pipes of the heat exchange medium.

[0018] In order to facilitate the transfer of materials and the stable control of the bed temperature of the first-stage bubbling bed reactor, a booster pump and a cooler are provided on the connecting pipe between the liquid outlet of the second-stage microchannel reactor and the liquid inlet of the first-stage bubbling bed reactor, and the cooler controls the discharge temperature by hot water.

[0019] The high-throughput microchannel cascade conversion process for preparing carbonates of the present invention is to overcome the problems of low throughput, limited scale preparation, and CO 2 / Epoxide synthesis of cyclic carbonate process has shortcomings. 2The process for synthesizing cyclic carbonates is mostly completed in a single bubbling bed. As the reaction proceeds, when the epoxide is converted to a certain extent, the reaction rate drops sharply. Therefore, this process proposes a microchannel step-by-step conversion process for synthesizing cyclic carbonates, in which the unreacted liquid phase flow in the first bubbling bed is further reacted in the second microchannel reactor. Benefiting from the advantages of small characteristic size, large specific surface area, short diffusion distance, high mixing efficiency, and high heat and mass transfer efficiency of the microchannel reactor, for typical gas-liquid two-phase reactions, the mass transfer efficiency can be significantly improved and the reaction time can be shortened. The unreacted liquid containing epoxides and CO 2 The liquid phase flow reacts quickly in the second-stage microchannel reactor, solving the problems of insufficient epoxide reaction, long residence time and large reactor volume. To ensure the effect of the reaction, the equivalent inner diameter of the second-stage microchannel reactor is 0.1-5.0mm, which can ensure a high reaction efficiency; to maintain the temperature stability of the microchannel reactor and ensure the reaction efficiency, the heat exchange medium in the cold material channel of the microchannel reactor is any one of hot water and heat transfer oil. In order to control the temperature stability of the second-stage microchannel reactor and realize heat exchange, the temperature of the heat exchange medium is preferably 80-120℃.

[0020] At the same time, in order to avoid the accumulation of reaction heat in the first stage bubbling bed reactor causing the bed to run hot, the discharge of the second stage microchannel reactor in step c is pressurized and cooled by the cooler in proportion to 70% to 90% and then circulated to the bottom of the first stage bubbling bed reactor, and the remaining 10% to 30% of the discharge enters the subsequent separation and recovery system. To ensure the stability of the bed temperature of the first stage bubbling bed reactor, the proportion of the discharge circulating to the bottom of the first stage bubbling bed reactor is preferably 90%, and the proportion of the discharge entering the separation and recovery system is preferably 10%; at the same time, the cooler in step c controls the discharge temperature by a cooling medium, and the cooling medium is 40°C hot water.

[0021] As a limitation of the above method, in step a, the reaction temperature in the bubbling bed reactor is 120° C.-150° C., the pressure is 2.0-4.0 MPa, and the residence time is 10-30 min.

[0022] In order to ensure the effect of the two-stage microchannel reactor, a micro mixer can be set before the feeding of the two-stage microchannel reactor. The micro mixer can be selected from standard and non-standard channel chips that can achieve efficient mixing of gas and liquid phases, such as T-type mixers for industrial amplification, microchannel chips, etc. Among them, the material of the two-stage microchannel reactor can be selected from stainless steel, alloy, ceramic, PMMA or silicon carbide glass.

[0023] As a limitation of the above method, in step b, the reaction temperature in the second-stage microchannel reactor is 80°C-120°C, the pressure is 0.5-2.0 MPa, and the residence time is 10s-10min.

[0024] By adopting the technical solution of the present invention and utilizing the process solution of microchannel coupled bubbling bed, efficient stepwise conversion synthesis of cyclic carbonate can be achieved, which has the significant advantages of short residence time, high flux and high conversion rate, specifically including:

[0025] (1) The microchannel reactor also functions as a bubbling bed external circulation cooler, and has the excellent characteristics of small size and compact size, which can further reduce the footprint and cost of the cycloaddition system; at the same time, the heat exchange efficiency is high, and the reaction temperature can be stably and uniformly controlled, which is conducive to the deep conversion of trace alkylene oxides;

[0026] (2) The microchannel is used to replace the traditional two-stage bubbling bed reactor, which further strengthens the low-temperature mass transfer process of trace alkylene oxide, and can achieve low-temperature and efficient conversion of trace alkylene oxide, solving the problem of slow conversion rate of low-concentration alkylene oxide and reverse reaction at high temperature;

[0027] (3) A bubbling bed coupled microchannel reaction system scheme was proposed. The bubbling bed is used as the main reaction facility to meet the industrial needs of large-scale, high-throughput, and efficient preparation of cyclic carbonates. At the same time, the compactness of the reaction system and the advantages of small footprint make it suitable for the transformation and upgrading of existing traditional cycloaddition reaction systems, which is convenient for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a system connection diagram for preparing carbonate by high-throughput microchannel stepwise conversion as described in Examples 1 to 4 of the present invention;

[0029] Among them, 1-a first-stage bubbling bed reactor, 2-a second-stage microchannel reactor, 3-a gas-liquid separation tank, 4-a cooler, S1-S8 are material pipelines, and S9-S10 are heat exchange medium inlet and outlet pipelines.

[0030] Figure 2 This is a connection diagram of the process system for preparing cyclic carbonate on a conventional industrial scale in Comparative Example 1;

[0031] Among them, 1-a first-stage bubbling bed reactor, 2-a second-stage bubbling bed reactor, 3A / B-a gas-liquid separation tank, and 4-a cooler. DETAILED DESCRIPTION

[0032] The present invention is further illustrated by examples below, but the present invention is not limited thereto. Without departing from the above technical ideas of the present invention, various substitutions and changes can be made according to common technical knowledge and customary means in the field, which should all be included in the scope of the present invention.

[0033] Embodiment 1:

[0034] The raw material S2 from the propylene oxide raw material tank is pressurized and enters the bottom of a bubbling bed reactor 1 (reactor diameter 0.24m, reactor height 2.2m, reactor volume 0.1m 3 ), the liquid phase feed rate S2 is controlled to be 0.71kg / h, the gas phase feed rate S1 is controlled to be 0.07kg / h, the gas-liquid ratio is 2.5 / 1, and the outlet pressure of the first stage bubbling bed reactor is controlled to be 3.0MPa by the gas extraction rate, the reaction residence time is 40min, the reaction temperature is 150°C, and the propylene oxide conversion rate is 90%. The reaction output S3 is separated in the gas-liquid separation tank 3 and the gas S4 is extracted. The liquid phase contains unreacted propylene oxide and CO 2 The discharge S5 is pressurized into the second-stage microchannel reactor 2 (stainless steel plate structure, reactor channel diameter 2mm, volume 0.16L), and the temperature of the second-stage microchannel reactor 2 is controlled to 100°C by the heat exchange medium 95°C hot water S9, the residence time is 5min, and the propylene oxide conversion rate is 99%. In order to avoid the accumulation of reaction heat, the discharge S6 of the second-stage microchannel reactor controls 90% of the material S7 to circulate to the feed port of the first-stage bubbling bed reactor 1 after passing through the cooler 4, and the circulating material is cooled by 80°C hot water to control the reaction temperature of the first-stage bubbling bed reactor 1 to 125°C; the remaining 10% of the material S8 enters the subsequent separation system to prepare propylene carbonate with a purity of 99.0%.

[0035] In this embodiment, the conversion rate of propylene oxide reaches 99.9%, which is better than the conversion effect of the traditional reactor system structure and achieves the goal of strengthening the reaction process.

[0036] Embodiment 2:

[0037] The raw material S2 from the propylene oxide raw material tank is pressurized and enters the bottom of a bubbling bed reactor 1 (reactor diameter 0.24m, reactor height 2.2m, reactor volume 0.1m 3 ), the liquid phase feed rate S2 is controlled to be 0.71kg / h, the gas phase feed rate S1 is controlled to be 0.07kg / h, the gas-liquid ratio is 2 / 1, and the outlet pressure of the first stage bubbling bed reactor is controlled to be 3.0MPa by the gas extraction rate, the reaction residence time is 25min, the reaction temperature is 100℃, and the propylene oxide conversion rate is 75%. The reaction discharge is separated in the gas-liquid separation tank 3 and the gas S4 is extracted. The liquid phase contains unreacted propylene oxide and CO 2The discharge S5 is pressurized into the second-stage microchannel reactor 2 (ceramic tubular structure, reactor material channel diameter 0.6mm, volume 0.38L), and the temperature of the second-stage microchannel reactor 2 is controlled to 120°C by the heat exchange medium 100°C hot water S9, the residence time is 8min, and the propylene oxide conversion rate is 99.7%. In order to avoid the accumulation of reaction heat, the discharge S6 of the second-stage microchannel reactor 1 controls 85% of the material S7 to circulate to the first-stage bubbling bed reactor 1 after the cooler 4, and the circulating material is cooled and cooled by 40°C hot water, and the reaction temperature of the first-stage bubbling bed reactor 1 is controlled to be 130°C; the remaining 15% of the material S8 enters the subsequent separation system to prepare propylene carbonate with a purity of 99.1%. In this embodiment, the conversion rate of propylene oxide reaches 99.92%, which is far higher than the conversion efficiency of the traditional bubbling bed reaction system, and reduces the second-stage reaction temperature, achieving the goal of strengthening the reaction process.

[0038] Embodiment 3:

[0039] The raw material S2 from the propylene oxide raw material tank is pressurized and enters the bottom of a bubbling bed reactor 1 (reactor diameter 0.24m, reactor height 2.2m, reactor volume 0.1m 3 ), the liquid phase feed rate S2 is controlled to be 0.71kg / h, the gas phase feed rate S1 is controlled to be 0.07kg / h, the gas-liquid ratio is 1.5 / 1, and the outlet pressure of the first stage bubbling bed reactor 1 is controlled to be 2.5MPa by the gas extraction rate, the reaction residence time is 15min, the reaction temperature is 100°C, and the propylene oxide conversion rate is 75%. The reaction discharge S3 is separated in the gas-liquid separation tank 3 and the gas S4 is extracted. The liquid phase contains unreacted propylene oxide and CO 2 The discharge S5 is pressurized into the second-stage microchannel reactor 2 (silicon carbide spiral tube structure, reactor material channel diameter 5mm, volume 0.38L), and the temperature of the second-stage microchannel reactor 2 is controlled to 90°C by the heat exchange medium 80°C hot water S9, the residence time is 2min, the propylene oxide conversion rate is 99%, and a small amount of impurities are halogenated alcohols. In order to avoid the accumulation of reaction heat, the discharge S6 of the second-stage microchannel reactor 2 controls 80% of the material S7 to circulate to the feed port of the first-stage bubbling bed reactor 1 after the cooler 4, and the circulating material is cooled by 40°C hot water to control the reaction temperature of the first-stage bubbling bed reactor 1 to 80°C; the remaining 20% ​​of the material S8 enters the subsequent separation system to prepare propylene carbonate with a purity of 99.0%.

[0040] In this embodiment, the conversion rate of propylene oxide reaches 99.75%, which exceeds the conversion efficiency of the traditional bubbling bed reactor, indicating that the conversion efficiency of propylene oxide is deepened by using the microchannel reactor.

[0041] Embodiment 4:

[0042] The raw material S2 from the propylene oxide raw material tank is pressurized and enters the bottom of the bubbling bed reactor 1 (reactor diameter 0.24m, reactor height 2.2m, reactor volume 0.1m 3 ), control the liquid phase feed rate S2 to 0.71kg / h, the gas phase feed rate S1 to 0.07kg / h, the gas-liquid ratio to 3 / 1 and control the outlet pressure of the first stage reactor 1 to 3.5MPa through the gas extraction rate, the reaction residence time to 40min, the reaction temperature to 140°C, and the propylene oxide conversion rate to 95%. The reaction discharge S3 is separated by the gas-liquid separation tank 3 and the gas S4 is extracted, and the liquid phase discharge S5 is pressurized into the second stage microchannel reactor 2 (alloy plate structure, reactor material channel diameter 0.1mm, volume 0.10L), and the temperature of the second stage microchannel reactor 2 is controlled to 100°C by the heat exchange medium 90°C heat transfer oil S9, the residence time is 30s, the propylene oxide conversion rate is 99%, and a small amount of impurities are halogenated alcohols. To avoid the accumulation of reaction heat, 70% of the material S7 from the discharge S6 of the second-stage microchannel reactor 2 is circulated to the feed inlet of the first-stage bubbling bed reactor 1 after passing through the cooler 4, and 40°C hot water is used to withdraw the reaction heat to control the reaction temperature of the first-stage bubbling bed reactor 1 to 140°C; the remaining 30% of the material S8 enters the subsequent separation system to prepare propylene carbonate with a purity of 99.4%.

[0043] In this embodiment, the conversion rate of propylene oxide reaches 99.95%, which exceeds the conversion efficiency of the traditional bubbling bed reactor, indicating that the use of the microchannel reactor can achieve a deeper conversion efficiency of propylene oxide.

[0044] Comparative Example 1:

[0045] A conventional process for large-scale preparation of cyclic carbonate, the only difference between the device system connection diagram and Example 1 is that the second-stage microchannel reactor 2 is replaced by a conventional second-stage bubbling bed reactor, and a gas-liquid separation tank 3A is added, wherein the characteristic dimensions of the second-stage bubbling bed reactor are a reactor diameter of 0.15m and an effective volume of 10L; in order to achieve stable control of the process, the discharge of the first-stage bubbling bed reactor passes through the gas-liquid separation tank 3A and then enters the second-stage bubbling bed reactor in gas phase, and the liquid phase enters the first-stage reactor and the second-stage reactor respectively in proportion. The high-throughput advantage of the tubular bubbling bed is utilized to achieve large-scale preparation of cyclic carbonate.

[0046] When other components, feed and operating conditions of the process system remain unchanged, the reaction residence time is extended to 26 minutes due to the increase in the volume of the bubbling bed reactor. After the system is running stably, the conversion rate of the first bubbling bed reactor remains almost unchanged, the conversion rate of propylene oxide is 90%, the conversion rate of the second bubbling bed reactor can only reach 92%, and the total conversion rate of propylene oxide is 99.2%.

[0047] It can be seen that when the residence time of the traditional two-stage bubbling bed reactor is extended by more than 5 times, due to the low gas-liquid mass transfer efficiency of the bubbling bed reactor, the propylene oxide conversion rate is significantly lower than that of the microchannel reactor enhanced process, indicating that the process for preparing cyclic carbonates by using microchannel enhanced alkylene oxide conversion proposed in the present invention has significant advantages.

[0048] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A process for preparing carbonate esters by high-throughput microchannel stepwise conversion, characterized in that: The process comprises a first-stage bubbling bed reactor and a second-stage microchannel reactor which are connected to each other, wherein the liquid outlet of the first-stage bubbling bed reactor is connected to the liquid inlet of the second-stage microchannel reactor through a pipeline, and the liquid outlet of the second-stage microchannel reactor is connected to the liquid inlet of the first-stage bubbling bed reactor; the process comprises the following steps: a. Raw materials CO2 and epoxide are fed from the bottom of a bubbling bed reactor and reacted under the action of an ionic liquid catalyst, wherein the feed ratio of CO2 to epoxide is controlled at (1.5-3) / 1; b. The reaction material is separated into gas and liquid, and the unreacted liquid phase containing epoxide and dissolved CO2 further undergoes a cycloaddition reaction of CO2 and epoxide in the second-stage microchannel reactor; c. After the liquid phase passes through the second-stage microchannel reactor, 70% to 90% of the liquid phase is pressurized and cooled in the cooler in proportion and then enters the first-stage bubbling bed reactor from the bottom liquid inlet, and the remaining 10% to 30% of the liquid phase is sent to the separation and recovery system. In order to enhance the reaction and mass transfer efficiency, a filler is arranged in the first-stage bubbling bed reactor, and the filler is any one of a wire mesh, a porcelain ball or a catalyst-loaded resin; a gas distributor is arranged in the lower space of the first-stage bubbling bed reactor, and the gas distributor is connected to the gas inlet of the bubbling bed reactor through a pipeline, and the gas distributor is 0.2 to 1.5 meters away from the liquid inlet of the bubbling bed reactor; a gas-liquid separation tank is arranged on the pipeline connecting the liquid outlet of the first-stage bubbling bed reactor and the liquid inlet of the second-stage microchannel reactor, and the liquid outlet of the gas-liquid separation tank is connected to the liquid inlet of the second-stage microchannel reactor.

2. The process for preparing carbonate ester by high-throughput microchannel cascade conversion according to claim 1, characterized in that: The equivalent inner diameter of the microchannel reactor is 0.1-5.0 mm; the residence time of the material in the microchannel reactor is 10 s-10 min.

3. The process for preparing carbonate ester by high-throughput microchannel cascade conversion according to claim 1, characterized in that: The two-stage microchannel reactor is selected from commercially available plate-type, tubular-type and different structure-enhanced microchannel reactors and parallel and integrated microchannel reaction modules; the material of the two-stage microchannel reactor can be selected from stainless steel, alloy, ceramic, PMMA or silicon carbide glass.

4. The process for preparing carbonate ester by high-throughput microchannel cascade conversion according to claim 1, characterized in that: The two-stage microchannel reactor is respectively provided with a hot material channel and a cold material channel, and the hot material channel and the cold material channel are respectively provided with a liquid inlet and a liquid outlet; wherein the liquid inlet of the two-stage microchannel reactor is the liquid inlet of the hot material channel, and the liquid outlet of the microchannel reactor is the liquid outlet of the hot material channel; the liquid inlet and outlet of the cold material channel are respectively connected to the inlet and outlet pipes of the heat exchange medium, and the heat exchange medium is any one of hot water at 80-120°C and heat transfer oil.

5. The process for preparing carbonate ester by high-throughput microchannel cascade conversion according to claim 1, characterized in that: The liquid inlet of the first-stage bubbling bed reactor is arranged at the bottom of the reactor, and the liquid outlet of the first-stage bubbling bed reactor is arranged at the top of the reactor; wherein the bottom liquid inlet is connected to the feed pipeline of epoxide and the liquid outlet of the hot material channel of the second-stage microchannel reactor through pipelines respectively; and the top liquid outlet is connected to the liquid inlet of the hot material channel of the second-stage microchannel reactor through a pipeline.

6. The process for preparing carbonate ester by high-throughput microchannel cascade conversion according to claim 1, characterized in that: A cooler is provided on the pipeline connecting the liquid outlet of the hot material channel of the second-stage microchannel reactor and the bottom liquid outlet of the first-stage bubbling bed reactor.

7. The process for preparing carbonate ester by high-throughput microchannel cascade conversion according to claim 1, characterized in that: In the step c, the liquid phase discharge ratio entering the bottom liquid inlet of the first-stage bubbling bed reactor is preferably 90%, and the liquid phase discharge ratio entering the separation and recovery system is preferably 10%.

8. The process for preparing carbonate ester by high-throughput microchannel cascade conversion according to claim 1, characterized in that: The cooler in step c controls the discharge temperature through a cooling medium, and the cooling medium is hot water at 40°C.

9. The process for preparing carbonate ester by high-throughput microchannel cascade conversion according to claim 1, characterized in that: In the step a, the reaction temperature in the first bubbling bed reactor is 120° C.-150° C., the pressure is 2.0-4.0 MPa, and the residence time is 10-30 min.

10. The process for preparing carbonate ester by high-throughput microchannel cascade conversion according to claim 1, characterized in that: In the step c, the reaction temperature in the second-stage microchannel reactor is 80° C.-120° C., and the pressure is 0.5-2.0 MPa.

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