A high-throughput microchannel stepwise conversion process for preparing carbonates

Abstract

This invention relates to a high-throughput microchannel stepwise conversion process for preparing carbonates. The process includes: feeding CO2 and epoxides into a first-stage bubble column reactor at the bottom, where they react under the action of an ionic liquid catalyst. The reaction product is separated, and the unreacted epoxide-containing liquid phase with CO2 enters a second-stage deep-channel reactor for further reaction, thereby achieving the stepwise conversion and efficient synthesis of cyclic carbonates. The continuous production process of cyclic carbonates provided by this invention is reasonable, significantly reducing reactor volume, shortening reaction residence time, achieving process intensification, and simplifying the process. It is a highly efficient and feasible continuous synthesis process for cyclic carbonates with good industrial application prospects.

Description

Technical Field

[0001] This invention relates to the field of cyclic carbonate preparation technology, specifically a process for the continuous and efficient stepwise conversion of CO2 into cyclic carbonates using a microchannel reactor coupled with a bubble bed reactor. Background Technology

[0002] CO2 is currently the main source of the greenhouse effect, but it is also an abundant C1 resource. Therefore, CO2 capture and utilization is a crucial way to address carbon emissions. The preparation of cyclic carbonates from CO2 has been applied in industrial production. This reaction has advantages such as atom economy and few byproducts, aligning with the concept of green chemistry. Cyclic carbonates are important chemical intermediates, serving as polar solvents, electrolyte solutions, and intermediates in pharmaceuticals and chemicals, and can also be used in the synthesis of various polymers. Currently, the process of coupling CO2 with epoxides to prepare cyclic carbonates mostly uses homogeneous catalysts and is carried out in a bubble bed. Improving the gas-liquid mass transfer rate and achieving efficient CO2 conversion is of significant research importance. In recent years, research on the synthesis of cyclic carbonates from CO2 has mainly focused on catalysts and processes.

[0003] Patent CN 105777543 A discloses a method and process system for preparing chain carbonates and producing diols from epoxides and CO2. It uses a fixed-bed or bubble-bed tubular reactor packed with a heterogeneous solid catalyst. This process system offers strong continuity and stable, reliable production. However, once the epoxides are converted to a certain extent, the reaction rate drops sharply, requiring a longer residence time and a lower space velocity to ensure complete conversion, resulting in low production efficiency. Patent CN 106478586 A discloses a synthesis process for ethylene carbonate. The reactants ethylene oxide and carbon dioxide are reacted in a synthesis reactor (fixed-bed, bubble-bed, or fluidized-bed), and a portion of the liquid phase (50%-99%) is recycled back to the synthesis reactor for further reaction. This process solves the problems of incomplete ethylene oxide reaction and difficulty in recovery, but the large-scale recycling of the liquid phase results in high energy consumption.

[0004] To enhance gas-liquid mass transfer, patents CN 110003163 A and CN 110028483 A disclose a method for preparing cyclic carbonates using a circulating jet gas-liquid contact process. This method efficiently prepares cyclic carbonates through a coupled reaction of CO2 and epoxides in a circulating jet reactor. In this process, gas-liquid contact occurs only at the throat, resulting in a very short time for the reactants to pass through the throat. This process places stringent requirements on reaction temperature and pressure, significantly enhancing feed efficiency. However, the CO2 cycloaddition reaction at low concentrations is kinetically controlled, and the problem of low conversion rates at low concentrations remains unresolved in existing technologies.

[0005] Microchannel reactors possess a significantly larger specific surface area, which can simultaneously enhance mass and heat transfer rates, thereby shortening diffusion time and enabling rapid fluid mixing and stable temperature control. CN 114478462A, CN115960071B, and CN 117777087A have successively provided apparatus and methods for preparing cyclic carbonates using microchannel reactions. Utilizing eutectic ionic liquids and microchannel reactors with combinations of different tube diameters, they successfully overcame the rate limitations of cycloaddition reactions and gas-liquid mass transfer, achieving a mild conversion of CO2 with epoxides. However, the use of single-stage or multi-stage microchannel reactors in series, limited by the structural characteristics of microchannel reactors, prevents large-scale industrial applications and is unsuitable for the preparation of bulk chemical carbonates.

[0006] In summary, existing technologies for the cycloaddition of CO2 to prepare cyclic carbonates cannot solve the problem of complete conversion of trace amounts of epoxides using traditional industrial reactors, and also face the challenges of large equipment size and complex systems. New technologies can shorten reaction time by utilizing the advantages of microchannel reactors, such as small channel size, large specific surface area, and high mass and heat transfer efficiency, but due to their low throughput and complex systems, they are not suitable for large-scale preparation of bulk chemical carbonates. Summary of the Invention

[0007] To overcome the shortcomings of existing CO2 / epoxide synthesis processes for cyclic carbonates, this invention develops a high-throughput microchannel stepwise conversion process for carbonate preparation. This method solves the problems of low throughput and unsuitability for large-scale chemical production using microchannel reactors. Utilizing the small volume and compact size of microchannels, the footprint and cost of the reaction system are further reduced, while mass transfer is enhanced, addressing issues such as incomplete epoxide reaction, long residence time, and large reactor volume. Simultaneously, a bubble bed reactor is coupled to achieve high-throughput carbonate preparation, providing a novel process for industrial production.

[0008] To achieve the above objectives, this invention provides a high-throughput microchannel stepwise conversion process for preparing carbonates. The process includes a first-stage bubbling bed reactor and a second-stage microchannel reactor system connected to each other. The outlet of the first-stage bubbling bed reactor is connected to the inlet of the second-stage microchannel reactor via a pipe, and the outlet of the second-stage microchannel reactor is connected to the inlet of the first-stage bubbling bed reactor. The process specifically includes the following steps:

[0009] a. The raw materials CO2 and epoxide are fed from the bottom of a first-stage bubbling bed reactor and react under the action of an ionic liquid catalyst. To ensure the full progress of the reaction, the feed ratio of CO2 and epoxide is controlled at (1.5~3) / 1, wherein the excess CO2 is separated by a gas-liquid separator after the bubbling bed reactor and then recycled.

[0010] b. After gas-liquid separation, the unreacted liquid phase containing epoxides and CO2 undergoes a further CO2 / epoxide cycloaddition reaction in a two-stage microchannel reactor; 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 either hot water or heat transfer oil.

[0011] c. After passing through the two-stage microchannel reactor, 70% to 90% of the liquid phase is successively pressurized and cooled by a cooler before being circulated to the bottom of the first-stage bubbling bed reactor. The remaining 10% to 30% is pressurized by a pump and discharged into the separation and recovery system.

[0012] Meanwhile, the present invention provides a microchannel coupled bubble bed reactor for realizing a step-by-step conversion process of CO2 to cyclic carbonates. The reactor includes a bubble bed reactor and a microchannel reactor. The microchannel reactor is selected from commercially available plate, tubular, and other microchannel reactors with different reinforced structures, as well as their parallel or integrated microchannel reaction modules. The material of the microchannel reactor can be selected from stainless steel, alloy, ceramic, PMMA, or silicon carbide glass, or any combination of two of them.

[0013] Preferably, in order to achieve efficient conversion of excess CO2 and improve product purity, a gas-liquid separator is provided on the pipeline connecting the outlet of the first-stage bubbling bed reactor and the inlet of the second-stage microchannel reactor, and the outlet of the gas-liquid separator is connected to the inlet of the second-stage microchannel reactor.

[0014] Preferably, to enhance the reaction process and improve gas-liquid mass transfer efficiency, the bubbling bed reactor is equipped with packing material, preferably any one of wire mesh, ceramic balls, or catalyst-loaded resin; a gas distributor is installed in the lower space, and the gas distributor is connected to the gas inlet of the bubbling bed reactor via a pipe. 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 inlet of the first-stage bubbling bed reactor is located at the bottom and is connected to the feed line of the epoxide and the outlet of the hot material channel of the second-stage microchannel reactor through pipes; the outlet of the first-stage bubbling bed reactor is located at the top and is connected to the inlet of the hot material channel of the second-stage microchannel reactor through pipes.

[0016] Preferably, to facilitate the separation and recycling of excess CO2, a gas-liquid separator is installed on the pipe connecting the top outlet of the first-stage bubbling bed reactor and the inlet of the hot material channel of the second-stage microchannel reactor. The material coming from the top outlet of the bubbling bed reactor first achieves the separation of excess CO2 in the gas-liquid separator, and the separated solution is then sent to the second-stage microchannel reactor for further reaction.

[0017] To enhance the efficiency of CO2 conversion through microchannels, the two-stage microchannel reactor is equipped with a hot material channel and a cold material channel, each with an inlet and an outlet. The inlet of the two-stage microchannel reactor is the inlet of the hot material channel, and the outlet of the microchannel reactor is the outlet of the hot material channel. The inlet and outlet of the cold material channel are connected to the inlet and outlet pipes of the heat exchange medium, respectively.

[0018] To facilitate material transfer and ensure stable temperature control of the first-stage bubbling bed reactor, a booster pump and a cooler are installed on the connecting pipe between the outlet of the second-stage microchannel reactor and the inlet of the first-stage bubbling bed reactor. The cooler controls the discharge temperature using hot water.

[0019] The high-throughput microchannel stepwise conversion process for preparing carbonates of this invention aims to overcome the shortcomings of existing microchannel processes, such as low throughput, limited large-scale production, and the synthesis of cyclic carbonates from CO2 / epoxide compounds. Currently, most traditional CO2-to-cyclic carbonate synthesis processes are completed in a single-stage bubbling bed. As the reaction proceeds, the reaction rate drops sharply after the epoxides have been converted to a certain extent. Therefore, this process proposes a microchannel stepwise conversion process for synthesizing cyclic carbonates, further reacting the incompletely reacted liquid phase stream from the single-stage bubbling bed in a two-stage microchannel reactor. Benefiting from the advantages of microchannel reactors, such as small characteristic dimensions, large specific surface area, short diffusion distance, high mixing efficiency, and high heat and mass transfer efficiency, the mass transfer efficiency can be significantly improved and the reaction time shortened for typical gas-liquid two-phase reactions. The incompletely reacted liquid phase stream containing epoxides and CO2 reacts rapidly in the two-stage microchannel reactor, solving the problems of incomplete epoxide reaction, long residence time, and large reactor volume. To ensure the effectiveness of the reaction, the equivalent inner diameter of the two-stage microchannel reactor is 0.1-5.0 mm, which ensures high reaction efficiency. To maintain the temperature stability of the microchannel reactor and ensure reaction efficiency, the heat exchange medium in the cold material channel of the microchannel reactor is either hot water or thermal oil. To control the temperature stability of the two-stage microchannel reactor and achieve heat exchange, the temperature of the heat exchange medium is preferably 80-120℃.

[0020] Meanwhile, to avoid heat buildup in the bubbling bed reactor causing bed temperature spikes, in step c, 70%–90% of the material from the second-stage microchannel reactor is successively pressurized and cooled by a cooler before being circulated back to the bottom of the first-stage bubbling bed reactor, with the remaining 10%–30% entering the subsequent separation and recovery system. To ensure stable bed temperature in the first-stage bubbling bed reactor, the proportion circulating to the bottom of the reactor is preferably 90%, and the proportion entering the separation and recovery system is preferably 10%. Simultaneously, the cooler in step c controls the outlet temperature using a cooling medium, which 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℃-150℃, the pressure is 2.0-4.0MPa, and the residence time is 10-30min.

[0022] To ensure the effectiveness of the two-stage microchannel reactor, a micromixer can be installed before the feed into the reactor. The micromixer can be selected from standard or non-standard channel chips capable of efficient gas-liquid two-phase mixing, such as industrial scale-up T-mixers or microchannel chips. The material of the two-stage microchannel reactor can be 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 two-stage microchannel reactor is 80℃-120℃, the pressure is 0.5-2.0MPa, and the residence time is 10s-10min.

[0024] The technical solution of this invention, utilizing a microchannel-coupled bubbling bed process, enables highly efficient stepwise conversion synthesis of cyclic carbonates, exhibiting significant advantages such as short residence time, high throughput, and high conversion rate. Specifically, it includes:

[0025] (1) The microchannel reactor also functions as an external circulation cooler for a bubble bed. It has the excellent characteristics of small size and compact dimensions, which can further reduce the footprint and cost of the cycloaddition system. At the same time, it has high heat exchange efficiency and the reaction temperature can be controlled stably and uniformly, which is beneficial to the deep conversion of trace amounts of epoxides.

[0026] (2) The use of microchannels to replace the traditional two-stage bubbling bed reactor further enhances the low-temperature mass transfer process of trace epoxides, enabling the low-temperature and efficient conversion of trace epoxides, and solving the problems of slow conversion rate and high-temperature reverse reaction of low-concentration epoxides.

[0027] (3) A reaction system scheme with a bubbling bed coupled to a microchannel was proposed. The bubbling bed serves as the main reaction facility, meeting the industrial demand for large-scale, high-throughput, and efficient preparation of cyclic carbonates. Simultaneously, the compactness and small footprint of the reaction system make it suitable for upgrading existing traditional cycloaddition reaction systems, facilitating its widespread application. Attached Figure Description

[0028] Figure 1 This is a system connection diagram of the high-throughput microchannel step-by-step conversion for preparing carbonates as described in Examples 1-4 of this invention;

[0029] Among them, 1-first stage bubble bed reactor, 2-second stage microchannel reactor, 3-gas-liquid separator, 4-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 traditional industrial-scale preparation process system for cyclic carbonates in Comparative Example 1;

[0031] Among them, 1-first stage bubble bed reactor, 2-second stage bubble bed reactor, 3A / B-gas-liquid separator, 4-cooler. Detailed Implementation

[0032] The present invention is further illustrated by the following examples, but the present invention is not limited thereto. Various substitutions and modifications made based on common technical knowledge and conventional means in the art without departing from the above-described technical concept of the present invention should be included within the scope of the present invention.

[0033] Example 1:

[0034] Feed S2 from the propylene oxide feed tank is pressurized and then enters the bottom of a first-stage bubbling bed reactor 1 along with feed carbon dioxide S1 (reactor diameter 0.24m, reactor height 2.2m, reactor volume 0.1m³). 3The liquid phase feed rate S2 was controlled at 0.71 kg / h, the gas phase feed rate S1 at 0.07 kg / h, the gas-liquid ratio at 2.5 / 1, and the outlet pressure of the first-stage bubbling bed reactor was controlled at 3.0 MPa by the gas output rate. The reaction residence time was 40 min, the reaction temperature was 150℃, and the propylene oxide conversion rate was 90%. The reaction output S3 was separated by gas-liquid separator 3, and the gas S4 was collected. The liquid phase containing incompletely reacted propylene oxide and CO2 was discharged as output S5 and pressurized into the second-stage microchannel reactor 2 (stainless steel plate structure, reactor channel diameter 2 mm, volume 0.16 L). The temperature of the second-stage microchannel reactor 2 was controlled at 100℃ by the heat exchange medium of 95℃ hot water S9, the residence time was 5 min, and the propylene oxide conversion rate was 99%. To avoid heat buildup during reaction, 90% of the material S7 from the two-stage microchannel reactor is circulated to the inlet of the first-stage bubbling bed reactor 1 after passing through cooler 4. The circulating material is cooled with 80°C hot water, and the reaction temperature of the first-stage bubbling bed reactor 1 is controlled at 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 reached 99.9%, which is superior to the conversion effect of traditional reactor system structures, thus achieving the goal of enhancing the reaction process.

[0036] Example 2:

[0037] Feed S2 from the propylene oxide feed tank is pressurized and then enters the bottom of a first-stage bubbling bed reactor 1 along with feed carbon dioxide S1 (reactor diameter 0.24m, reactor height 2.2m, reactor volume 0.1m³). 3The liquid phase feed rate S2 was controlled at 0.71 kg / h, the gas phase feed rate S1 at 0.07 kg / h, the gas-liquid ratio at 2 / 1, and the outlet pressure of the first-stage bubbling bed reactor was controlled at 3.0 MPa by the gas output rate. The reaction residence time was 25 min, the reaction temperature was 100℃, and the propylene oxide conversion rate was 75%. After separation by gas-liquid separator 3, the gas S4 was collected, and the liquid phase containing unreacted propylene oxide and CO2 S5 was pressurized and entered the second-stage microchannel reactor 2 (ceramic tube structure, reactor material channel diameter 0.6 mm, volume 0.38 L). The temperature of the second-stage microchannel reactor 2 was controlled at 120℃ by the heat exchange medium of 100℃ hot water S9, the residence time was 8 min, and the propylene oxide conversion rate was 99.7%. To avoid heat buildup, 85% of the material S7 from the second-stage microchannel reactor 1 is circulated through cooler 4 to the first-stage bubbling bed reactor 1. The circulating material is cooled with 40°C hot water, maintaining the reaction temperature of the first-stage bubbling bed reactor 1 at 130°C. The remaining 15% of the material S8 enters a subsequent separation system to obtain propylene carbonate with 99.1% purity. In this embodiment, the conversion rate of propylene oxide reaches 99.92%, far exceeding the conversion efficiency of traditional bubbling bed reaction systems, and the second-stage reaction temperature is reduced, achieving the goal of intensified reaction process.

[0038] Example 3:

[0039] Feed S2 from the propylene oxide feed tank is pressurized and then enters the bottom of a first-stage bubbling bed reactor 1 along with feed carbon dioxide S1 (reactor diameter 0.24m, reactor height 2.2m, reactor volume 0.1m³). 3 The liquid phase feed rate S2 was controlled at 0.71 kg / h, the gas phase feed rate S1 at 0.07 kg / h, the gas-liquid ratio at 1.5 / 1, and the outlet pressure of the first-stage bubbling bed reactor 1 was controlled at 2.5 MPa by controlling the gas output rate. The reaction residence time was 15 min, the reaction temperature was 100℃, and the propylene oxide conversion rate was 75%. The reaction output S3 was separated by gas-liquid separator 3, and the gas S4 was collected. The liquid phase, containing unreacted propylene oxide and CO2, was discharged as output S5 and pressurized into the second-stage microchannel reactor 2 (silicon carbide spiral tube structure, reactor material channel diameter 5 mm, volume 0.38 L). The temperature of the second-stage microchannel reactor 2 was controlled at 90℃ by using 80℃ hot water S9 as the heat exchange medium. The residence time was 2 min, and the propylene oxide conversion rate was 99%. It contained a small amount of impurities, namely haloalcohols. To avoid heat buildup during reaction, 80% of the material S7 from the two-stage microchannel reactor 2 is circulated to the inlet of the first-stage bubbling bed reactor 1 after passing through the cooler 4. The circulating material is cooled with 40°C hot water, and the reaction temperature of the first-stage bubbling bed reactor 1 is controlled at 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 reached 99.75%, which exceeded the conversion efficiency of the traditional bubble bed reactor, indicating that the microchannel reactor was used to improve the conversion efficiency of propylene oxide.

[0041] Example 4:

[0042] Feed S2 from the propylene oxide feed tank is pressurized and then enters the bottom of the bubble bed reactor 1 along with feed carbon dioxide S1 (reactor diameter 0.24m, reactor height 2.2m, reactor volume 0.1m³). 3 The liquid phase feed rate S2 was controlled at 0.71 kg / h, the gas phase feed rate S1 at 0.07 kg / h, the gas-liquid ratio at 3 / 1, and the outlet pressure of the first-stage reactor 1 was controlled at 3.5 MPa by controlling the gas output rate. The reaction residence time was 40 min, the reaction temperature was 140℃, and the propylene oxide conversion rate was 95%. The reaction output S3 was separated into gas and liquid phases by gas-liquid separator 3, and the gas was collected as S4. The liquid phase output S5 was pressurized and entered the second-stage microchannel reactor 2 (alloy plate structure, reactor material channel diameter 0.1 mm, volume 0.10 L). The temperature of the second-stage microchannel reactor 2 was controlled at 100℃ by heat exchange medium 90℃ heat transfer oil S9, the residence time was 30 s, the propylene oxide conversion rate was 99%, and it contained a small amount of impurities, namely halogenated alcohols. To avoid the accumulation of reaction heat, 70% of the material S7 from the discharge S6 of the two-stage microchannel reactor 2 is circulated to the inlet of the first-stage bubbling bed reactor 1 after passing through the cooler 4. The reaction heat is removed by using 40℃ hot water, and the reaction temperature of the first-stage bubbling bed reactor 1 is controlled at 140℃. 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 reached 99.95%, which exceeded the conversion efficiency of the traditional bubble bed reactor, indicating that the microchannel reactor was used to improve the conversion efficiency of propylene oxide.

[0044] Comparative Example 1:

[0045] A conventional process for the large-scale preparation of cyclic carbonates differs from Example 1 only in that the two-stage microchannel reactor 2 is replaced with a conventional two-stage bubbling bed reactor, and a gas-liquid separator 3A is added. The two-stage bubbling bed reactor has a characteristic dimensions of 0.15 m in diameter and an effective volume of 10 L. To achieve stable process control, the effluent from the first-stage bubbling bed reactor is separated into gas phase and then enters the second-stage bubbling bed reactor via the gas-liquid separator 3A, while the liquid phase enters the first-stage and second-stage reactors in proportion. The high-throughput advantage of the tubular bubbling bed allows for the large-scale preparation of cyclic carbonates.

[0046] With other components of the process system, feed, and operating conditions remaining unchanged, the increased volume of the bubbling bed reactor extends the reaction residence time to 26 minutes. After the system stabilizes, the conversion rate of the first-stage bubbling bed reactor remains almost unchanged, with a propylene oxide conversion rate of approximately 90%. The conversion rate of the second-stage bubbling bed reactor only reaches 92%, resulting in an overall propylene oxide conversion rate of 99.2%.

[0047] Therefore, it can be seen that when the residence time of a traditional two-stage bubbling bed reactor is extended by more than 5 times, the gas-liquid mass transfer efficiency of the bubbling bed reactor is low, and the propylene oxide conversion rate is significantly lower than that of the microchannel reactor enhanced process. This indicates that the microchannel enhanced process for preparing cyclic carbonates by converting alkyl epoxides proposed in this invention has significant advantages.

[0048] The applicant declares that the above description is only a specific embodiment 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 conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A high-throughput microchannel stepwise conversion process for preparing carbonates, characterized in that, The process includes a first-stage bubbling bed reactor and a second-stage microchannel reactor connected to each other. The outlet of the first-stage bubbling bed reactor is connected to the inlet of the second-stage microchannel reactor via a pipe, and the outlet of the second-stage microchannel reactor is connected to the inlet of the first-stage bubbling bed reactor. The process includes the following steps: a. The raw materials CO2 and epoxide are fed from the bottom of a first-stage bubbling bed reactor and react under the action of an ionic liquid catalyst, wherein the feed ratio of CO2 and epoxide is controlled at (1.5~3) / 1; b. After gas-liquid separation, the unreacted liquid phase containing epoxides and dissolved CO2 undergoes a further cycloaddition reaction between CO2 and epoxides in a two-stage microchannel reactor. c. After passing through the two-stage microchannel reactor, 70% to 90% of the liquid phase is successively pressurized and cooled by a cooler before entering the first-stage bubbling bed reactor through the bottom inlet, while the remaining 10% to 30% of the liquid phase is sent to the separation and recovery system. To enhance reaction and mass transfer efficiency, the first-stage bubbling bed reactor is equipped with packing material, which may be any one of wire mesh, ceramic balls, or catalyst-loaded resin. A gas distributor is installed 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 via a pipe, with the gas distributor located 0.2 to 1.5 meters away from the liquid inlet of the bubbling bed reactor. A gas-liquid separator is installed on the pipe 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 separator is connected to the liquid inlet of the second-stage microchannel reactor.

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

3. The process for preparing carbonates using high-throughput microchannel stepwise conversion according to claim 1, characterized in that, The two-stage microchannel reactor is selected from commercially available plate, tubular, and structurally enhanced microchannel reactors and their parallel or 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 carbonates using high-throughput microchannel stepwise conversion according to claim 1, characterized in that, The two-stage microchannel reactor is provided with a hot material channel and a cold material channel, each with an inlet and an outlet. The inlet of the two-stage microchannel reactor is the inlet of the hot material channel, and the outlet of the microchannel reactor is the outlet of the hot material channel. The inlet and outlet of the cold material channel are connected to the inlet and outlet pipes of the heat exchange medium, which is either hot water at 80-120℃ or thermal oil.

5. The process for preparing carbonates using high-throughput microchannel stepwise conversion according to claim 1, characterized in that, The inlet of the first-stage bubbling bed reactor is located at the bottom of the reactor, and the outlet of the first-stage bubbling bed reactor is located at the top of the reactor; wherein, the bottom inlet is connected to the feed pipeline of the epoxide and the hot material channel outlet of the second-stage microchannel reactor through pipes respectively; the top outlet is connected to the hot material channel inlet of the second-stage microchannel reactor through a pipe.

6. The process for preparing carbonates using high-throughput microchannel stepwise conversion according to claim 1, characterized in that, A cooler is installed on the pipe connecting the hot material channel outlet of the two-stage microchannel reactor to the bottom outlet of the first-stage bubbling bed reactor.

7. The process for preparing carbonates using high-throughput microchannel stepwise conversion according to claim 1, characterized in that, In step c, the liquid phase discharge ratio entering the bottom inlet of the 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 carbonates using high-throughput microchannel stepwise conversion according to claim 1, characterized in that, The cooler in step c controls the discharge temperature through a cooling medium, which is hot water at 40°C.

9. The process for preparing carbonates using high-throughput microchannel stepwise conversion according to claim 1, characterized in that, In step a, the reaction temperature in the bubbling bed reactor is 120℃-150℃, the pressure is 2.0-4.0MPa, and the residence time is 10-30min.

10. The process for preparing carbonates using high-throughput microchannel stepwise conversion according to claim 1, characterized in that, In step c, the reaction temperature in the two-stage microchannel reactor is 80℃-120℃, and the pressure is 0.5-2.0MPa.

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