Molecular sieve catalyst for synthesizing methyl ethyl carbonate by transesterification method and regeneration method of molecular sieve catalyst

Abstract

The invention discloses a molecular sieve catalyst for synthesizing methyl ethyl carbonate by a transesterification method and a regeneration method, and relates to the technical field of molecular sieve catalysts, the molecular sieve catalyst comprises a microporous double-active-center inner core and an amphoteric mesoporous shell; the microporous double-active-center core takes the X-type zeolite as a carrier to load potassium, cesium, lanthanum and barium; the amphoteric mesoporous shell is an MCM-41 and SBA-15 composite mesoporous silica layer coating the outer part of the inner core and has a double-mesoporous structure, amino propyl triethoxy silane and carboxyethyl triethoxy silane are grafted on the surface of the amphoteric mesoporous shell, and zirconium and titanium are co-doped. According to the invention, collaborative optimization of active centers and mass transfer channels is realized through a core-shell structure of a microporous double-active-center core and an amphoteric mesoporous shell. The activity and selectivity of catalytic transesterification are remarkably improved by the microporous core; due to the double-mesoporous structure and surface functional modification of the amphoteric mesoporous shell, the mass transfer efficiency of reactants and products is improved, and the adaptability of the catalyst to a reaction system is enhanced.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve catalyst technology, and in particular to molecular sieve catalysts for the transesterification synthesis of ethyl methyl carbonate and their regeneration methods. Background Technology

[0002] Ethyl methyl carbonate (MEC), an important organic carbonate, combines the excellent properties of both dimethyl carbonate and diethyl carbonate, and has broad application prospects in fields such as lithium-ion battery electrolyte solvents and organic synthesis intermediates. Due to its mild reaction conditions and readily available raw materials, transesterification has become one of the mainstream processes for synthesizing MEC.

[0003] Currently, the catalysts used in the transesterification synthesis of methyl ethyl carbonate mainly include homogeneous catalysts and heterogeneous catalysts. Homogeneous catalysts, such as alkali metal alkoxides and organic amines, have high catalytic activity, but suffer from problems such as difficult separation and recovery, high product purification costs, and severe equipment corrosion. Heterogeneous catalysts, such as single zeolites, mesoporous silica materials, and metal oxides, have solved the separation problem of homogeneous catalysts, but still have shortcomings such as uneven distribution of active sites, low catalytic selectivity, and poor mass transfer efficiency. Furthermore, they are prone to activity decline due to carbon buildup after long-term use, and their regeneration performance is poor, making it difficult to meet the requirements of high efficiency, stability, and economy for industrial production.

[0004] Therefore, developing a heterogeneous catalyst with high activity, high selectivity, excellent stability and high regeneration performance is of great significance for promoting the development of the transesterification process for synthesizing methyl ethyl carbonate. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a molecular sieve catalyst for the transesterification synthesis of methyl ethyl carbonate and a method for its regeneration. The technical solution is as follows: Molecular sieve catalysts for the transesterification synthesis of ethyl methyl carbonate include a microporous dual-active-center core and an amphoteric mesoporous shell. The microporous dual active center core is and X-type zeolite with a molar ratio of 2.2-2.8 is used as a support, and 9wt%-11wt% of potassium, 2.5wt%-3.5wt% of cesium, 1.5wt%-2.5wt% of lanthanum and 0.8wt%-1.2wt% of barium are loaded. The amphoteric mesoporous shell is a composite mesoporous silica layer of MCM-41 and SBA-15 covering the core, with a dual mesoporous structure. The surface is grafted with 3wt%-4wt% aminopropyltriethoxysilane and 1wt%-2wt% carboxyethyltriethoxysilane, and co-doped with 1.2wt%-1.8wt% zirconium and 0.5wt%-1wt% titanium.

[0006] Optionally, the amphoteric mesoporous shell has a dual mesoporous structure of 4nm-6nm and 10nm-15nm, with a shell thickness of 150-250nm.

[0007] Optionally, the total specific surface area of ​​the molecular sieve catalyst is 700m² / g-800m² / g, and the micropore to mesopore volume ratio is 1:4.

[0008] A method for preparing a molecular sieve catalyst for the transesterification synthesis of ethyl methyl carbonate includes the following steps: Step 1, Preparation of the microporous dual-active-center core: Pretreated X-type zeolite is impregnated with... , , and The mixed solution was impregnated with rotary evaporation and then vacuum dried, followed by programmed temperature calcination to obtain a dual-active-center core. Step 2, Construction of the amphoteric mesoporous shell: using CTAB and P123 as composite template agents and TEOS as the silicon source, and As a doping source, a sol-gel reaction is carried out in an alkaline core suspension, followed by calcination to remove the template agent after aging; Step 3, Functionalization modification: The product from step 2 is reacted with an ethanol solution of APTES and CETES, and refluxed at 50℃-60℃ for 4-6 hours to obtain a core-shell catalyst with an amphoteric mesoporous shell.

[0009] Optionally, the pretreated X-type zeolite is X-type zeolite pretreated with 0.5 mol / L nitric acid for 2 h; The rotary evaporation-assisted impregnation conditions were 55-60 rpm and 55-58℃, and the vacuum drying conditions were -0.08 MPa and 75-80℃ for 3.5-4 hours. The programmed temperature rise calcination was carried out at 4.5℃ / min-5℃ / min to 300℃ and held for 0.8-1 hours, and then at 2.8℃ / min-3℃ / min to 580℃ and held for 4.5-5 hours.

[0010] Optionally, in the mixed solution , , , The molar concentration ratio is (8-10):(1-1.5):(0.8-1):(0.3-0.5).

[0011] Optionally, in step 2, the mass ratio of CTAB to P123 in the composite template agent is 1:(1.2-1.5); TEOS is added dropwise, with the dropping rate controlled at 0.5 mL / min-1.0 mL / min; after the gelation reaction, static aging is performed at 95℃-100℃ for 36-48 hours; the calcination procedure is as follows: in flowing air, the temperature is increased to 300℃ at 1℃ / min and held for 2 hours, then increased to 500℃ at 0.5℃ / min and held for 5 hours.

[0012] A method for regenerating a molecular sieve catalyst used in the transesterification synthesis of methyl ethyl carbonate, characterized by employing a three-in-one regeneration technology combining ultrasound, ozone, and microwave, comprising the following steps: Step a, Ultrasonic-assisted oxidation: Place the deactivated catalyst in the reaction chamber, introduce an ozone-oxygen mixture of 80mg / -100mg / L, turn on dual-frequency ultrasound and 400W microwave, and treat at 70℃-80℃ for 40-50 minutes. Step b, microwave deep degradation: Increase the concentration of the ozone-oxygen mixture to 120mg / L-150mg / L, adjust the microwave power to 800W, and treat at 90℃-100℃ for 50-60 minutes until the exhaust gas is completely degraded. Concentration less than 0.5 vol% Step c, activity restoration: Dry under 300W microwave with nitrogen purging, then treat with a mixture of ammonia and nitrogen to repair alkaline sites.

[0013] Optionally, in step a, the dual-frequency ultrasound is 28kHz and 40kHz ultrasound working alternately, with a power density of 15W / L-20W / L for each. The ozone-oxygen mixture flow rate is 150 mL / min-200 mL / min; In step b, the microwave power is increased from 400W to 800W in a stepwise manner, increasing by 100W every 10 minutes, while controlling the temperature rise rate of the catalyst bed to not exceed 2℃ / min.

[0014] Optionally, in step c, the ammonia gas fraction in the ammonia-nitrogen mixture is 5%-8%, the processing temperature is 180℃-220℃, and the processing time is 30-40 minutes. The entire regeneration process is dynamically controlled by a digital twin model. The digital twin model collects data on ultrasonic cavitation intensity, microwave reflection power, multi-point temperature of the bed, and exhaust gas composition in real time, and adaptively adjusts ozone concentration, microwave power, and treatment time to ensure that the carbon removal rate is greater than 97% and the aluminum removal rate is less than 2%.

[0015] In summary, the present invention has at least one of the following beneficial technical effects: This invention provides a molecular sieve catalyst for the transesterification synthesis of methyl ethyl carbonate and its regeneration method. Through the core-shell structure design of a microporous dual-active-center core and an amphoteric mesoporous shell, the active center and mass transfer channel are synergistically optimized.

[0016] The microporous core loaded with multiple metal components forms a dual active center, which significantly improves the activity and selectivity of the catalytic transesterification reaction; the dual mesoporous structure of the amphoteric mesoporous shell and the surface functionalization modification improve the mass transfer efficiency between reactants and products, while enhancing the catalyst's adaptability to the reaction system.

[0017] Furthermore, the integrated regeneration technology combining ultrasound, ozone, and microwave can efficiently remove carbon deposits and effectively protect the catalyst framework structure, ensuring excellent regeneration performance and long-term cycle stability of the catalyst, thereby reducing the cost of industrial applications. Attached Figure Description

[0018] Figure 1 This is a schematic flowchart of the preparation method of the molecular sieve catalyst for the transesterification synthesis of methyl ethyl carbonate according to the present invention. Figure 2 This is a schematic flowchart of the regeneration method of the molecular sieve catalyst used in the transesterification synthesis of methyl ethyl carbonate according to the present invention. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the accompanying drawings.

[0020] This invention discloses a molecular sieve catalyst for the transesterification synthesis of ethyl methyl carbonate and its regeneration method.

[0021] Reference Figure 1 and Figure 2 Example 1, a molecular sieve catalyst for the transesterification synthesis of methyl ethyl carbonate, comprising a microporous dual-active-center core and an amphoteric mesoporous shell; The microporous dual active center core is and X-type zeolite with a molar ratio of 2.2-2.8 is used as a support, and 9wt%-11wt% of potassium, 2.5wt%-3.5wt% of cesium, 1.5wt%-2.5wt% of lanthanum and 0.8wt%-1.2wt% of barium are loaded. The amphoteric mesoporous shell is a composite mesoporous silica layer of MCM-41 and SBA-15 covering the core, with a dual mesoporous structure. The surface is grafted with 3wt%-4wt% aminopropyltriethoxysilane and 1wt%-2wt% carboxyethyltriethoxysilane, and co-doped with 1.2wt%-1.8wt% zirconium and 0.5wt%-1wt% titanium.

[0022] Example 2: The amphoteric mesoporous shell has a dual mesoporous structure with a thickness of 4nm-6nm and 10nm-15nm, and a shell thickness of 150-250nm.

[0023] Example 3: The molecular sieve catalyst has a total specific surface area of ​​700m² / g-800m² / g and a micropore to mesopore volume ratio of 1:4.

[0024] By adopting the above technical solution, the microporous dual-active-center core... and X-type zeolite supports with a molar ratio of 2.2-2.8 possess a specific framework structure and acidic sites. Loaded potassium and cesium provide basic active centers, while lanthanum and barium regulate the electronic environment and dispersion of these active centers. The synergistic effect of acidic and basic sites promotes the breaking of ester bonds and the formation of new bonds during transesterification. The mesoporous structure constructed from the MCM-41 and SBA-15 composite mesoporous silica layer of the amphoteric mesoporous shell provides mass transfer channels for reactants and products. Surface-grafted aminopropyltriethoxysilane and carboxyethyltriethoxysilane impart amphoteric surface properties to the shell, regulating the reaction microenvironment and enhancing the adsorption and activation capacity of reactants. Co-doped zirconium and titanium improve the structural stability and surface catalytic activity of the shell, further optimizing catalytic performance.

[0025] The amphoteric mesoporous shell has a dual mesoporous structure with a diameter of 4nm-6nm and 10nm-15nm. The smaller mesopores increase the specific surface area, providing more adsorption and reaction sites for the reaction, while the larger mesopores accelerate the diffusion of reactants to the active core and the desorption of products, reducing mass transfer resistance. The shell thickness of 150-250nm ensures effective coating and protection of the core, preventing the loss of active centers, while avoiding excessively long mass transfer paths due to excessive shell thickness. This achieves a balance between structural stability and mass transfer efficiency, ensuring the continuous and efficient catalytic reaction.

[0026] The total specific surface area of ​​700-800 m² / g provides abundant surface sites for the catalyst, which is beneficial for the adsorption and activation of reactants and increases the probability of catalytic reaction. A 1:4 micropore to mesopore pore volume ratio ensures that the microporous region can fully accommodate dual active centers, guaranteeing a high-density distribution of active centers, while the mesopore region occupies the dominant pore volume, enhancing mass transfer efficiency. This well-matched ratio achieves synergistic optimization of active center utilization efficiency and mass transfer rate, avoiding the problems of limited mass transfer due to excessive micropores or insufficient active centers due to excessive mesopores, thus ensuring the overall high efficiency of the catalyst's catalytic performance.

[0027] Example 4: A method for preparing a molecular sieve catalyst for the transesterification synthesis of methyl ethyl carbonate, comprising the following steps: Step 1, Preparation of the microporous dual-active-center core: Pretreated X-type zeolite is impregnated with... , , and The mixed solution was impregnated with rotary evaporation and then vacuum dried, followed by programmed temperature calcination to obtain a dual-active-center core. Step 2, Construction of the amphoteric mesoporous shell: using CTAB and P123 as composite template agents and TEOS as the silicon source, and As a doping source, a sol-gel reaction is carried out in an alkaline core suspension, followed by calcination to remove the template agent after aging; Step 3, Functionalization modification: The product from step 2 is reacted with an ethanol solution of APTES and CETES, and refluxed at 50℃-60℃ for 4-6 hours to obtain a core-shell catalyst with an amphoteric mesoporous shell.

[0028] Example 5: The pretreated X-type zeolite was X-type zeolite pretreated with 0.5 mol / L nitric acid for 2 h; The rotary evaporation-assisted impregnation conditions were 55-60 rpm and 55-58℃, and the vacuum drying conditions were -0.08 MPa and 75-80℃ for 3.5-4 hours. The programmed temperature rise calcination was carried out at 4.5℃ / min-5℃ / min to 300℃ and held for 0.8-1 hours, and then at 2.8℃ / min-3℃ / min to 580℃ and held for 4.5-5 hours.

[0029] Example 6, in the mixed solution , , , The molar concentration ratio is (8-10):(1-1.5):(0.8-1):(0.3-0.5).

[0030] In Example 7, in step 2, the mass ratio of CTAB to P123 in the composite template agent is 1:(1.2-1.5); TEOS is added dropwise, with the dropping rate controlled at 0.5 mL / min-1.0 mL / min; after the gelation reaction, static aging is performed at 95℃-100℃ for 36-48 hours; the calcination procedure is as follows: in flowing air, the temperature is increased to 300℃ at 1℃ / min and held for 2 hours, then increased to 500℃ at 0.5℃ / min and held for 5 hours.

[0031] By adopting the above technical solution, in step 1, the impregnation method makes... , , and Metal ions in the mixed solution are uniformly adsorbed on the surface and pores of the pretreated X-type zeolite. Rotary evaporation can accelerate solvent evaporation and promote deep penetration and dispersion of metal ions. Vacuum drying can quickly remove residual solvent at a lower temperature and avoid the migration and aggregation of metal salts. Programmed temperature calcination decomposes metal nitrates into corresponding oxides, forming uniformly distributed dual active centers.

[0032] In step 2, the CTAB and P123 composite template agents work synergistically to guide the hydrolytic condensation of TEOS through self-assembly, forming a composite mesoporous structure of MCM-41 and SBA-15. and The mesoporous silica framework is uniformly doped into the sol-gel process, aging further stabilizes the gel structure, and calcination can completely remove the template agent and solidify the mesoporous structure.

[0033] In step 3, the reflux condition of 50℃-60℃ provides a suitable temperature for the grafting reaction of APTES and CETES with the hydroxyl groups on the surface of mesoporous silica, promotes the stable grafting of silane coupling agent, endows the shell with amphoteric surface properties, and finally forms a core-shell structure catalyst.

[0034] Pretreatment of type X zeolite with 0.5 mol / L nitric acid for 2 hours selectively removes impurity ions and some non-framework aluminum from the zeolite surface and pores, adjusts the distribution and number of acidic sites on the support surface, and enhances the adsorption capacity of the support for metal ions. Rotary evaporation at 55-60 rpm and 55-58℃ ensures uniform heating of the mixed solution while preventing agglomeration of metal salts due to excessively high local concentrations caused by excessively fast rotation speed or temperature. Vacuum drying at -0.08 MPa and 75-80℃ for 3.5-4 hours lowers the solvent boiling point, efficiently removing the solvent while reducing metal ion migration. Programmed temperature calcination first raises the temperature to 300℃ at 4.5-5℃ / min and holds for 0.8-1 hour to achieve gradual decomposition of metal nitrates, then raises the temperature to 580℃ at 2.8-3℃ / min and holds for 4.5-5 hours to promote crystallization and stabilization of active species, preventing damage to the catalyst framework structure due to excessively rapid heating.

[0035] In the mixed solution , , , The molar concentration ratio is (8-10):(1-1.5):(0.8-1):(0.3-0.5), which makes the basic active center ( , ) and electronically modulating components ( , To achieve optimal synergy, a higher proportion of... and Ensure sufficient basic active sites to promote nucleophilic attack in transesterification reactions; appropriate amount and The strength and dispersion of basic sites can be adjusted through electronic effects to avoid side reactions caused by excessive alkalinity, while enhancing the stability of active centers, thereby achieving a balance between catalyst activity and selectivity.

[0036] In the composite template agent, the mass ratio of CTAB to P123 is 1:(1.2-1.5). CTAB primarily forms smaller mesoporous structures, while P123 facilitates the construction of larger mesoporous structures. A suitable ratio allows for precise control of the pore size and distribution of the dual mesoporous structure. TEOS is added dropwise with a controlled dropping rate of 0.5 mL / min-1.0 mL / min, allowing for slow hydrolysis and condensation of the silicon source, preventing mesoporous structure disorder caused by excessively high local silicon source concentration. Static aging at 95℃-100℃ for 36-48 hours provides sufficient time for the full growth and orderly arrangement of the mesoporous structure, enhancing its regularity and stability. The calcination process first increases the temperature to 300℃ at 1℃ / min and holds for 2 hours to allow the template agent to slowly decompose and volatilize, then increases the temperature to 500℃ at 0.5℃ / min and holds for 5 hours to thoroughly remove residual template agent and solidify the mesoporous silicon framework, preventing rapid heating from causing mesoporous collapse or structural damage.

[0037] Example 8: A method for regenerating a molecular sieve catalyst used in the transesterification synthesis of methyl ethyl carbonate, characterized by employing a three-in-one regeneration technology of ultrasound, ozone, and microwave, comprising the following steps: Step a, Ultrasonic-assisted oxidation: Place the deactivated catalyst in the reaction chamber, introduce an ozone-oxygen mixture of 80mg / -100mg / L, turn on dual-frequency ultrasound and 400W microwave, and treat at 70℃-80℃ for 40-50 minutes. Step b, microwave deep degradation: Increase the concentration of the ozone-oxygen mixture to 120mg / L-150mg / L, adjust the microwave power to 800W, and treat at 90℃-100℃ for 50-60 minutes until the exhaust gas is completely degraded. Concentration less than 0.5 vol% Step c, activity restoration: Dry under 300W microwave with nitrogen purging, then treat with a mixture of ammonia and nitrogen to repair alkaline sites.

[0038] By adopting the above technical solution, in step a, the ozone in the ozone-oxygen mixture has strong oxidizing properties, which can initially oxidize and decompose the carbon deposits on the surface of the deactivated catalyst; the vibration and cavitation effect generated by dual-frequency ultrasound can destroy the carbon deposit layer on the catalyst surface, increase the contact area between ozone and carbon deposits, and at the same time enhance the mass transfer process and improve the ozone utilization rate; 400W microwave provides gentle heating, keeping the reaction system at 70℃-80℃. This temperature can promote the oxidation reaction while avoiding damage to the catalyst skeleton caused by high temperature. The processing time of 40-50 minutes ensures that the initial oxidation effect is sufficient.

[0039] In step b, the ozone concentration is increased to 120mg / L-150mg / L and the microwave power is adjusted to 800W to enhance oxidation capacity and heating intensity. A temperature environment of 90℃-100℃ accelerates the deep degradation of residual carbon deposits; exhaust gas Using a concentration of less than 0.5 vol% as the endpoint criterion allows for precise control of the degree of carbon removal and avoids overtreatment.

[0040] In step c, the 300W microwave drying under nitrogen purging can quickly remove residual oxidation products and moisture from the catalyst surface; the ammonia in the ammonia-nitrogen mixture can combine with the alkaline sites that may be lost due to oxidation on the catalyst surface, repair the alkaline active centers, restore the catalytic activity of the catalyst, and ensure the stability of the catalyst performance after regeneration.

[0041] Example 9, in step a, the dual-frequency ultrasound is 28kHz and 40kHz ultrasound working alternately, with a power density of 15W / L-20W / L for each. The ozone-oxygen mixture flow rate is 150 mL / min-200 mL / min; In step b, the microwave power is increased from 400W to 800W in a stepwise manner, increasing by 100W every 10 minutes, while controlling the temperature rise rate of the catalyst bed to not exceed 2℃ / min.

[0042] By adopting the above technical solution, in step a, the dual-frequency ultrasound, operating alternately at 28kHz and 40kHz, has a stronger cavitation effect at 28kHz, which can effectively break down the thick carbon deposit layer on the catalyst surface. The high-frequency ultrasound at 40kHz can penetrate deep into the micropores of the catalyst and act on fine carbon deposits. The alternating synergy of these two technologies enables efficient stripping of carbon deposits of different sizes and locations. A power density of 15W / L-20W / L ensures the intensity of the ultrasound action to achieve the ideal carbon loosening effect while avoiding excessive power that could cause mechanical damage to the catalyst framework. An ozone-oxygen mixed gas flow rate of 150mL / min-200mL / min ensures a continuous and sufficient supply of ozone to meet the oxidation reaction requirements and promptly removes the oxidation products generated in the reaction, maintaining a stable ozone concentration within the reaction system and improving oxidation efficiency.

[0043] In step b, the microwave power is increased stepwise from 400W to 800W every 10 minutes by 100W. This allows the catalyst bed temperature to rise slowly and evenly, avoiding excessive local temperature due to a sudden increase in power. Controlling the bed temperature rise rate to no more than 2℃ / min further prevents the catalyst from collapsing due to thermal shock or the active components from sintering. At the same time, it allows residual carbon deposits to be steadily and thoroughly degraded during the gradual temperature increase, ensuring regeneration efficiency and catalyst structural stability.

[0044] In Example 10, in step c, the ammonia gas fraction in the ammonia-nitrogen mixture is 5%-8%, the processing temperature is 180℃-220℃, and the processing time is 30-40 minutes. The entire regeneration process is dynamically controlled by a digital twin model. The digital twin model collects data on ultrasonic cavitation intensity, microwave reflection power, multi-point temperature of the bed, and exhaust gas composition in real time, and adaptively adjusts ozone concentration, microwave power, and treatment time to ensure that the carbon removal rate is greater than 97% and the aluminum removal rate is less than 2%.

[0045] By adopting the above technical solution, in step c, the ammonia-nitrogen mixture contains 5%-8% ammonia gas. This ensures sufficient ammonia to combine with the missing basic sites on the catalyst surface, effectively repairing the basic active centers. It also avoids excessive ammonia adsorption on the catalyst surface, which could negatively impact subsequent catalytic reactions. A treatment temperature of 180℃-220℃ provides a suitable reaction environment for the interaction between ammonia and the basic sites, promoting efficient repair reactions while preventing excessive temperature from altering the catalyst framework structure or causing loss of active components. A treatment time of 30-40 minutes ensures the repair reaction is fully completed, restoring the catalyst's basic activity to the ideal level.

[0046] Throughout the regeneration process, the digital twin model collects real-time data on ultrasonic cavitation intensity, microwave reflection power, multi-point bed temperature, and exhaust gas composition. This data comprehensively reflects the catalyst state and reaction progress during regeneration. By analyzing and processing the data, the ozone concentration, microwave power, and treatment time are adaptively adjusted to achieve precise matching of regeneration conditions. This ensures that the carbon removal rate is greater than 97%, guaranteeing full recovery of catalyst activity, while controlling the aluminum removal rate of the skeletal framework to be less than 2%, avoiding damage to the catalyst skeleton structure and ensuring the stability and service life of the regenerated catalyst.

[0047] The following specific examples illustrate the implementation principle of the molecular sieve catalyst and its regeneration method for the transesterification synthesis of methyl ethyl carbonate of the present invention: Molecular sieve catalysts for the transesterification synthesis of methyl ethyl carbonate comprise a microporous dual-active-center core and an amphoteric mesoporous shell. The microporous dual-active-center core... and The catalyst uses X-type zeolite with a molar ratio of 2.5 as a support, loaded with 10 wt% potassium, 3 wt% cesium, 2 wt% lanthanum, and 1 wt% barium. The amphoteric mesoporous shell is a composite mesoporous silica layer of MCM-41 and SBA-15 covering the core, with a dual mesoporous structure of 5 nm and 12 nm, a shell thickness of 200 nm, and a surface grafted with 3.5 wt% aminopropyltriethoxysilane and 1.5 wt% carboxyethyltriethoxysilane, and co-doped with 1.5 wt% zirconium and 0.8 wt% titanium. The total specific surface area of ​​the catalyst is 750 m² / g, and the micropore to mesopore volume ratio is 1:4.

[0048] The preparation method includes: Step 1, impregnating X-type zeolite pretreated with 0.5 mol / L nitric acid for 2 h in... , , , A mixed solution with a molar concentration ratio of 9:1.2:0.9:0.4 was impregnated by rotary evaporation at 58 rpm and 56 °C, then vacuum dried at -0.08 MPa and 78 °C for 3.8 h, followed by heating to 300 °C at 4.8 °C / min and holding for 0.9 h, and then heating to 580 °C at 2.9 °C / min and holding for 4.8 h to obtain a dual-active-center core; in step 2, CTAB and P123 in a mass ratio of 1:1.3 were used as a composite template agent, and TEOS was used as the silicon source. and As a dopant source, TEOS was added dropwise at 0.8 mL / min to an alkaline core suspension to carry out a sol-gel reaction. After static aging at 98 °C for 42 hours, the temperature was increased to 300 °C at 1 °C / min and held for 2 hours in flowing air, and then calcined at 0.5 °C / min to 500 °C and held for 5 hours to remove the template agent. In step 3, the product of step 2 was refluxed with an ethanol solution of APTES and CETES at 55 °C for 5 hours to obtain the core-shell catalyst.

[0049] The regeneration method is as follows: Step a, place the deactivated catalyst in the reaction chamber, introduce a 90 mg / L ozone-oxygen mixture (flow rate 180 mL / min), turn on dual-frequency ultrasound (power density 18 W / L) alternating between 28 kHz and 40 kHz and microwave 400 W, and treat at 75°C for 45 minutes; Step b, increase the concentration of the ozone-oxygen mixture to 135 mg / L, increase the microwave power from 400 W to 800 W in a stepwise manner every 10 minutes by 100 W, control the bed temperature rise rate to not exceed 2°C / min, and treat at 95°C for 55 minutes until the exhaust gas is released. Concentration less than 0.5 vol%; Step c: Microwave drying at 300W under nitrogen purging, followed by ammonia-nitrogen mixture with 6% ammonia gas volume, and treatment at 200℃ for 35 minutes. The entire process is dynamically controlled by a digital twin model.

[0050] The performance test results of the prepared molecular sieve catalyst for the transesterification synthesis of methyl ethyl carbonate are shown in Table 1: Table 1

[0051] The product performance test table covers the performance of directly prepared molecular sieve catalysts and regenerated molecular sieve catalysts: the total specific surface area, micropore to mesopore volume ratio, amphoteric mesoporous shell double mesopore diameter, shell thickness, dimethyl carbonate conversion rate, ethyl methyl carbonate selectivity, and conversion rate retention rate after 50 hours of continuous reaction are the performance of directly prepared molecular sieve catalysts; the conversion rate recovery rate after regeneration is the performance of regenerated molecular sieve catalysts.

[0052] Table 2 shows a comparison of the performance of the prepared molecular sieve catalysts for the transesterification synthesis of methyl ethyl carbonate with that of traditional molecular sieve catalysts. Table 2

[0053] Comparative results show that the catalyst of this technology is significantly superior to the traditional X-type zeolite-supported potassium cesium catalyst in all key performance indicators. In terms of catalytic activity, the conversion rate of dimethyl carbonate is increased by nearly 17 percentage points; in terms of selectivity, the selectivity of ethyl methyl carbonate is increased by more than 11 percentage points; the stability is more outstanding, with a conversion rate retention rate 26 percentage points higher after 50 hours of continuous reaction; the regeneration performance is significantly superior, with a conversion rate recovery rate of about 19 percentage points after regeneration; and the mass transfer efficiency is significantly enhanced due to the substantial increase in the proportion of mesoporous pore volume, exhibiting the outstanding characteristics of high efficiency, stability, and easy regeneration.

[0054] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A molecular sieve catalyst for the transesterification synthesis of methyl ethyl carbonate, characterized in that: It includes a microporous dual-active-center core and an amphipathic mesoporous shell; The microporous dual active center core is and X-type zeolite with a molar ratio of 2.2-2.8 is used as a support, and 9wt%-11wt% of potassium, 2.5wt%-3.5wt% of cesium, 1.5wt%-2.5wt% of lanthanum and 0.8wt%-1.2wt% of barium are loaded. The amphoteric mesoporous shell is a composite mesoporous silica layer of MCM-41 and SBA-15 covering the core, with a dual mesoporous structure. The surface is grafted with 3wt%-4wt% aminopropyltriethoxysilane and 1wt%-2wt% carboxyethyltriethoxysilane, and co-doped with 1.2wt%-1.8wt% zirconium and 0.5wt%-1wt% titanium.

2. The molecular sieve catalyst for the transesterification synthesis of methyl ethyl carbonate according to claim 1, characterized in that: The amphoteric mesoporous shell has a dual mesoporous structure of 4nm-6nm and 10nm-15nm, with a shell thickness of 150-250nm.

3. The molecular sieve catalyst for the transesterification synthesis of methyl ethyl carbonate according to claim 2, characterized in that: The molecular sieve catalyst has a total specific surface area of ​​700m² / g-800m² / g and a micropore to mesopore volume ratio of 1:

4.

4. A method for preparing the molecular sieve catalyst for the transesterification synthesis of methyl ethyl carbonate as described in claim 3, characterized in that, Includes the following steps: Step 1, Preparation of the microporous dual-active-center core: Pretreated X-type zeolite is impregnated with... , , and The mixed solution was impregnated with rotary evaporation and then vacuum dried, followed by programmed temperature calcination to obtain a dual-active-center core. Step 2, Construction of the amphoteric mesoporous shell: using CTAB and P123 as composite template agents and TEOS as the silicon source, and As a doping source, a sol-gel reaction is carried out in an alkaline core suspension, followed by calcination to remove the template agent after aging; Step 3, Functionalization modification: The product from step 2 is reacted with an ethanol solution of APTES and CETES, and refluxed at 50℃-60℃ for 4-6 hours to obtain a core-shell catalyst with an amphoteric mesoporous shell.

5. The preparation method according to claim 4, characterized in that: The pretreated X-type zeolite was X-type zeolite pretreated with 0.5 mol / L nitric acid for 2 h; The rotary evaporation-assisted impregnation conditions were 55-60 rpm and 55-58℃, and the vacuum drying conditions were -0.08 MPa and 75-80℃ for 3.5-4 hours. The programmed temperature rise calcination was carried out at 4.5℃ / min-5℃ / min to 300℃ and held for 0.8-1 hours, and then at 2.8℃ / min-3℃ / min to 580℃ and held for 4.5-5 hours.

6. The preparation method according to claim 5, characterized in that: The mixed solution , , , The molar concentration ratio is (8-10):(1-1.5):(0.8-1):(0.3-0.5).

7. The preparation method according to claim 6, characterized in that: In step 2, the mass ratio of CTAB to P123 in the composite template agent is 1:(1.2-1.5); TEOS is added dropwise, with the dropping rate controlled at 0.5 mL / min-1.0 mL / min; after the gelation reaction, static aging is carried out at 95℃-100℃ for 36-48 hours; the calcination program is as follows: in flowing air, the temperature is increased to 300℃ at 1℃ / min and held for 2 hours, then increased to 500℃ at 0.5℃ / min and held for 5 hours.

8. A method for regenerating the molecular sieve catalyst for the transesterification synthesis of methyl ethyl carbonate as described in claim 3, characterized in that: The regeneration technology employs a three-in-one approach combining ultrasound, ozone, and microwave, and includes the following steps: Step a, Ultrasonic-assisted oxidation: Place the deactivated catalyst in the reaction chamber, introduce an ozone-oxygen mixture of 80mg / -100mg / L, turn on dual-frequency ultrasound and 400W microwave, and treat at 70℃-80℃ for 40-50 minutes. Step b, microwave deep degradation: Increase the concentration of the ozone-oxygen mixture to 120mg / L-150mg / L, adjust the microwave power to 800W, and treat at 90℃-100℃ for 50-60 minutes until the exhaust gas is completely degraded. Concentration less than 0.5 vol% Step c, activity restoration: Dry under 300W microwave with nitrogen purging, then treat with a mixture of ammonia and nitrogen to repair alkaline sites.

9. The regeneration method according to claim 8, characterized in that, In step a, the dual-frequency ultrasound consists of alternating 28kHz and 40kHz ultrasound waves with a power density of 15W / L-20W / L. The ozone-oxygen mixture flow rate is 150 mL / min-200 mL / min; In step b, the microwave power is increased from 400W to 800W in a stepwise manner, increasing by 100W every 10 minutes, while controlling the temperature rise rate of the catalyst bed to not exceed 2℃ / min.

10. The regeneration method according to claim 9, characterized in that, In step c, the ammonia gas fraction in the ammonia-nitrogen mixture is 5%-8%, the processing temperature is 180℃-220℃, and the processing time is 30-40 minutes. The entire regeneration process is dynamically controlled by a digital twin model. The digital twin model collects data on ultrasonic cavitation intensity, microwave reflection power, multi-point temperature of the bed, and exhaust gas composition in real time, and adaptively adjusts ozone concentration, microwave power, and treatment time to ensure that the carbon removal rate is greater than 97% and the aluminum removal rate is less than 2%.

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