Preparation method of basic molecular sieve catalyst for one-step synthesis of dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate from dimethyl oxalate and ethanol

Abstract

This invention belongs to the field of catalyst preparation technology, specifically relating to a method for preparing an alkaline molecular sieve catalyst for the one-step synthesis of dimethyl oxalate, diethyl oxalate, and diethyl methyl carbonate from dimethyl oxalate and ethanol. The catalyst uses an alkali metal as the active component and a molecular sieve as the support. An alkali metal-supported molecular sieve catalyst is prepared by impregnation, and SiO2 is further deposited on the catalyst surface by chemical liquid phase deposition. The mass fraction of the alkali metal is 0.5%~25%. This catalyst exhibits a dimethyl oxalate (DMO) conversion rate of over 90% and a total selectivity of over 95% for dimethyl carbonate + diethyl methyl carbonate + diethyl carbonate (DMC+EMC+DEC), making it a high-performance catalyst with promising industrial applications.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to a method for preparing an alkaline molecular sieve catalyst for the one-step synthesis of dimethyl oxalate, diethyl oxalate, and methyl ethyl ester from dimethyl oxalate and ethanol. Background Technology

[0002] With the increasing global emphasis on sustainable and low-carbon energy, lithium-ion batteries have become a promising advanced energy storage strategy, providing innovative solutions for energy infrastructure transformation. The four main materials of new energy batteries are the cathode material, anode material, separator, and electrolyte. The electrolyte solvent is a crucial carrier for ion exchange. Common electrolyte solvents include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), among other carbonates (see: Discussion on the Environmental Impact and Benefits of New Energy Storage Industry. Huang Hewen et al., *Comprehensive Utilization of Resources in China*, 2024, Vol. 42, pp. 165-167). Among these, DMC, as a green chemical with excellent environmental performance and wide applications, has received considerable attention in the chemical industry in recent years (See: Green separation of azeotropes in dimethyl carbonate synthesis by transesterification. Yan M., et al. *Renewable and Sustainable Energy Reviews*, 2024, Vol. 202, pp. 114687). Besides its use as an electrolyte solvent, dimethyl carbonate (DMC) is also irreplaceable in the synthesis of polycarbonate, gasoline additives, and fine chemicals in pharmaceuticals and pesticides. Notably, dimethyl carbonate can also be used as an important raw material for the transesterification synthesis of ethyl methyl carbonate and diethyl carbonate with ethanol. In recent years, with the booming production and sales of new energy vehicles, the demand for new energy batteries has continued to rise. DMC, EMC, and DEC, as important electrolyte solvents for new energy batteries, have a very broad application market (Research on the process of preparing diethyl carbonate by transesterification of dimethyl carbonate and ethanol. Wang Zhenbei et al. Guangzhou Chemical Industry, 2022, Vol. 50, pp. 86-89).

[0003] The main synthesis methods for DMC include the phosgene method, methanol oxidative carbonylation method, transesterification method, direct synthesis of CO2 and methanol method, urea alcoholysis method, and dimethyl oxalate decarbonylation method (CO direct esterification to dimethyloxalate and dimethyl carbonate: the key functional motifs for catalytic selectivity. Wang Z., et al. Nanoscale. 2020, Vol. 39, p. 20131). The phosgene process is being phased out due to the high toxicity of its raw materials and severe environmental pollution. While the methanol oxidative carbonylation method has the advantage of readily available raw materials, the simultaneous presence of carbon monoxide and oxygen generates competing carbon dioxide, reducing methanol conversion and producing water as a byproduct, significantly impacting catalyst lifespan. The transesterification method, although simple to operate and with mild reaction conditions, faces difficulties in separating and purifying the target product, leading to high costs. The one-step synthesis of methanol and carbon dioxide uses readily available raw materials, but the activation and application of carbon dioxide remain challenging, resulting in low catalytic activity. The uric acid alcoholysis method also faces difficulties in subsequent separation due to the use of homogeneous catalysts. Therefore, how to synthesize DMC in a green and efficient manner is a problem that researchers need to solve. With the continuous rise in domestic coal raw material prices, the economic benefits of coal-to-ethylene glycol processes are low, while dimethyl oxalate, a downstream product of coal chemical industry, is in severe surplus and readily available. Using dimethyl oxalate as a raw material to produce dimethyl carbonate through decarbonylation under catalysis would have high economic benefits. The main synthetic methods for EMC and DEC include the phosgene method, oxidative carbonylation method, and transesterification method (The reactions of dimethyl carbonate and its derivatives. Tundo P., et al. Green Chemistry, 2018, Vol. 20, pp. 28-85). Compared with other synthetic routes, the transesterification method of dimethyl carbonate and ethanol is more environmentally friendly and can simultaneously synthesize methyl ethyl carbonate and diethyl carbonate.

[0004] Currently, in industry, dimethyl carbonate (DMC) is mainly produced via propylene oxide transesterification. However, this reaction is limited by its relatively small thermodynamic equilibrium constant, requiring the addition of methanol in much higher-than-stoichiometric amounts to drive the reaction forward. Methanol significantly increases the difficulty and energy consumption of subsequent separations due to its azeotropic reaction with DMC. The synthesis of methyl ethyl carbonate (MEC) and diethyl carbonate (DEC) typically involves transesterification of DMC with ethanol. To simultaneously obtain DMC, EMC, and DEC, the traditional process requires first synthesizing DMC via propylene oxide transesterification, separating its azeotropic mixture with methanol, further transesterifying DMC with ethanol to generate EMC and DEC, and finally performing complex separation of the multiple azeotropic systems formed in the reaction products.

[0005] Regarding the reaction system for the catalytic synthesis of dimethyl carbonate from dimethyl oxalate via decarbonylation, Zhang Shixiang et al. loaded alkali / alkaline earth metals and Group III and IV inorganic acid salts onto supports such as activated carbon, nanostructured silica, and metal-organic frameworks (MOFs) using an equal-volume impregnation method. The DMO conversion reached 95%, and the DMC conversion reached 71% (A catalytic system for the direct decarbonylation of dimethyl oxalate to dimethyl carbonate. Zhang Shixiang et al., CN113181894B, 2023-08-18). Zhang Haoyang prepared K2CO3 / AC, Rb2CO3 / AC, and Cs2CO3 / AC catalysts via equal-volume impregnation. Studies showed that the carbonate catalysts could achieve high conversion rates within two hours, with selectivity approaching 100%. However, the catalyst exhibits low stability, with the DMO conversion dropping to 15% in the second reaction (Study on solid base catalysts for the decarbonylation of dimethyl oxalate to dimethyl carbonate. Zhang Haoyang, Shanghai Normal University, 2017, Vol. 2). Huang Xiejun studied the gas-phase catalytic decarbonylation of dimethyl oxalate to dimethyl carbonate using a SiO2-supported Cs2CO3 catalyst. The optimal conversion and selectivity were 73.1% and 70.5%, respectively. However, after five cycles, both the selectivity and yield decreased to 65.3% and 35.8%, respectively (Cs2CO3 catalyzes the decarbonylation of dimethyl oxalate to dimethyl carbonate. Huang Xiejun et al., Industrial Catalysis, 2021, Vol. 29, pp. 71-74). In recent years, there have been numerous studies and reports on catalysts for the transesterification reaction of DMC and ethanol. Among them, catalysts with high catalytic activity are characterized by strong basicity. Li Guangxing's research group studied the catalytic performance of K2CO3 in the transesterification reaction of ethanol and DMC. The optimal reaction result was an EMC yield of 86.5% and a selectivity close to 99.7% (Transesterification of Ethyl Methyl Carbonate, Li Lin et al., Synthetic Chemistry, 2004, pp. 197-200). However, homogeneous catalysts generally suffer from problems such as difficulty in recovery and poor cycle stability.

[0006] Molecular sieves are considered excellent catalyst supports due to their large specific surface area, regular pore structure, tunable acidity and basicity, excellent thermal stability, and abundant hydroxyl groups. Researchers at Hebei University of Technology prepared a Cs₂CO₃ / HZSM-5 catalyst with a 20% cesium carbonate loading using a wet impregnation method. When used in the decarbonylation of dimethyl oxalate to dimethyl carbonate, it showed a 99% dimethyl oxalate conversion rate. However, after four reactions, the DMO conversion rate decreased to 87%, indicating that the catalyst still had poor stability. (Decarbonylation of dimethyl oxalate todimethyl carbonate over Cs₂CO₃ / HZSM-5. Jv N, et al. New Journal of Chemistry. 2024, Vol. 48, pp. 9062-9075).

[0007] The aforementioned solid base catalysts generally suffer from deactivation due to the loss of active components. Silica (SiO2) coating, as a catalyst modification strategy, has shown significant application potential in molecular sieve catalytic systems. The core of this method lies in constructing a dense silica protective layer on the surface of the molecular sieve, utilizing its synergistic effect of physical isolation and chemical protection to significantly enhance the stability and durability of the catalyst. Qi et al. used tetraethyl orthosilicate (TEOS) as a modifier to modify the HZSM-5 catalyst through Si deposition and investigated its effect on the methanol-to-olefins (MTO) reaction performance. Characterization results showed that TEOS modification did not destroy the framework structure of HZSM-5, but SiO2 coating effectively modulated the pore size and passivated the acidity, thereby significantly improving the MTO catalytic activity (Influence of Si Modification on MTO Performance of HZSM-5 Catalyst. Qi et al., Applied Chemical Industry, 2019, Vol. 48, pp. 559-562).

[0008] In summary, the propylene oxide transesterification method for synthesizing DMC has been industrialized, but this process requires a super-stoichiometric ratio of methanol, and the subsequent products present the challenge of methanol-DMC azeotropic separation. Further synthesis of EMC and DEC from DMC and ethanol via transesterification involves multiple reaction steps and extraction separation of multiple azeotropic systems, resulting in high energy consumption. Therefore, this study proposes a novel one-step process for synthesizing dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate from DMO and ethanol. Addressing the issue of poor stability caused by the easy loss of active components from solid base catalysts, an alkali metal catalyst supported on a molecular sieve was designed. Furthermore, SiO2 was deposited on the catalyst surface using chemical liquid phase deposition to prepare a highly stable and active alkaline molecular sieve catalyst, enabling the one-step synthesis of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate from dimethyl oxalate and ethanol. Summary of the Invention

[0009] To address the problems existing in the prior art, the purpose of this invention is to provide a method for preparing and applying a highly selective, high-conversion, high-stability, and environmentally friendly alkaline molecular sieve catalyst, especially a high-performance catalyst for the one-step synthesis of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate from dimethyl oxalate and ethanol in syngas or coal-to-ethylene glycol processes.

[0010] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A method for preparing an alkaline molecular sieve catalyst for the one-step synthesis of dimethyl oxalate, diethyl oxalate, and methyl ethyl ester from dimethyl oxalate and ethanol is characterized by using a molecular sieve as a support, and through the anchoring effect of its silanol groups on the alkali metal, loading an alkali metal active component with a mass fraction of 0.5% to 25% onto the molecular sieve to form a supported catalyst with synergistic catalytic effect between the alkali metal and the molecular sieve; further, coating the catalyst surface with a SiO2 layer to inhibit the loss of the alkali metal active component, obtaining an alkali metal / molecular sieve@SiO2 catalyst, which significantly improves the stability of the alkali metal molecular sieve catalyst; the molecular sieve has a specific surface area of ​​100 to 800 m² / g, an average crystal size of 0.1 to 5 µm, and a SiO2 layer coating thickness of 0.5 to 200 nm; the catalyst is used in the one-step synthesis of dimethyl oxalate, diethyl oxalate, and methyl ethyl ester from dimethyl oxalate and ethanol at a reaction temperature of 100 to 400 °C and a reaction pressure of 0.01 to 5 ℃. The catalytic reaction is carried out under conditions of MPa and a reaction time of 30~1500 min; the preparation method of the alkali metal / molecular sieve@SiO2 catalyst includes the following steps: 1) Preparation of alkali metal / molecular sieve: An alkali metal salt is dissolved in solvent A to obtain a solution containing the alkali metal salt. Then, the solution containing the alkali metal salt is impregnated onto a molecular sieve support by impregnation. After standing at 20~80 °C for 1~24 hours, it is ultrasonicated at 20~60 °C for 10~90 minutes and dried at 20~120 °C for 0.5~12 hours. Then, the catalyst is transferred to a muffle furnace and calcined at 150~650 °C for 0.5~6 hours to obtain the alkali metal / molecular sieve catalyst. 2) Coating with SiO2 layer: The alkali metal / molecular sieve catalyst prepared in step 1) is suspended in solvent B, and then a silicon source is added. The mixture is stirred for 0.5~12 h, dried at 50~150 ℃, and then calcined at 200~650 ℃ for 2~8 h to obtain the alkaline molecular sieve catalyst of alkali metal / molecular sieve@SiO2.

[0011] As a preferred embodiment, the method for preparing an alkaline molecular sieve catalyst for one-step synthesis of dimethyl oxalate, diethyl oxalate, and methyl ethyl ester from dimethyl oxalate and ethanol is characterized in that the molecular sieve support selected in step 1) is one or a combination of several of FAU, BEA, MCM-41, MFI, and LTA.

[0012] As a preferred embodiment, the method for preparing an alkaline molecular sieve catalyst for one-step synthesis of dimethyl oxalate, diethyl oxalate, and methyl ethyl ester from dimethyl oxalate and ethanol is characterized in that the alkali metal salt in step 1) is one or a combination of several of sodium chloride, potassium chloride, rubidium chloride, cesium chloride, sodium carbonate, potassium carbonate, rubidium carbonate, cesium carbonate, and potassium acetate.

[0013] As a preferred embodiment, the method for preparing an alkaline molecular sieve catalyst for one-step synthesis of dimethyl oxalate, diethyl oxalate, and methyl ethyl ester from dimethyl oxalate and ethanol is characterized in that the silicon source in step 2) is one or a combination of several of tetramethyl silicate, tetraethyl silicate, silica sol, polydimethylsiloxane, nano-silica, and sodium silicate.

[0014] As a preferred embodiment, the method for preparing an alkaline molecular sieve catalyst for one-step synthesis of dimethyl oxalate, diethyl oxalate, and methyl ethyl ester from dimethyl oxalate and ethanol is characterized in that, in step 1), solvent A is one or a combination of glycerol, ethanol, methanol, isopropanol, hexane, acetonitrile, water, and ammonia; and in step 2), solvent B is one or a combination of methanol, ethanol, isopropanol, n-hexane, cyclohexane, toluene, petroleum ether, acetonitrile, and water.

[0015] As a preferred embodiment, the method for preparing an alkaline molecular sieve catalyst for one-step synthesis of dimethyl oxalate, diethyl oxalate, and methyl ethyl ester from dimethyl oxalate and ethanol is characterized in that, in step 2), the heating rate during calcination is 0.1~10℃ / min.

[0016] As a preferred embodiment, the method for preparing an alkaline molecular sieve catalyst for one-step synthesis of dimethyl oxalate, diethyl oxalate, and methyl ethyl ester from dimethyl oxalate and ethanol is characterized in that the alkaline molecular sieve catalyst is applied to the reaction process of one-step synthesis of dimethyl oxalate, diethyl oxalate, and methyl ethyl ester from dimethyl oxalate and ethanol.

[0017] Compared with the prior art, the method for preparing a basic molecular sieve catalyst for one-step synthesis of dimethyl oxalate, diethyl oxalate, and methyl ethyl ester from dimethyl oxalate and ethanol according to the present invention has the following significant features: (1) By coupling decarbonylation and transesterification reactions, three carbonates—dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate—are synthesized in one step, solving the problems of complex processes, environmental pollution, high risk, and high energy consumption in the traditional industrial synthesis of dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate. Compared with current industrial production routes for dimethyl carbonate, such as the phosgene route, transesterification route, and methanol liquid-phase oxidative carbonylation route, this process uses dimethyl oxalate and ethanol as reactants, and simultaneously carries out decarbonylation and transesterification reactions under the catalysis of a catalyst. This process has mild reaction conditions, is green and environmentally friendly, and the catalyst used has the characteristics of high activity, high selectivity, and high stability, and is easy to recover.

[0018] (2) Molecular sieves have a large specific surface area and regular pore structure, which is conducive to the adsorption of reactants and the confinement of active components; they have abundant hydroxyl groups, which can be used to anchor alkali metals. At the same time, the synergistic catalytic effect of molecular sieves and alkali metals can achieve high conversion rate, high selectivity and excellent stability.

[0019] (3) The SiO2 layer can effectively encapsulate the active components through specific chemical reactions, thereby effectively inhibiting the loss of active components and significantly improving the cycle stability of the catalyst. The alkaline molecular sieve catalyst prepared in this invention is an environmentally friendly catalyst with high selectivity, high conversion rate, and high stability, and is especially suitable for the reaction of dimethyl oxalate and ethanol to synthesize dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Attached Figure Description

[0021] Figure 1 A route diagram for the synthesis of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate from novel dimethyl oxalate and ethanol; Figure 2 This is a SEM image of the alkali metal / molecular sieve catalyst prepared in Example 3; Figure 3 This is a SEM image of the alkali metal / molecular sieve catalyst prepared in Example 5; Figure 4 The image shows a SEM image of the alkali metal / molecular sieve catalyst prepared in Example 6. Figure 5 The XRD pattern of the alkali metal / molecular sieve catalyst prepared in Example 6 is shown below. Figure 6 TEM image of the alkali metal / molecular sieve catalyst prepared in Example 6; Figure 7 This is a TEM image of the alkali metal / molecular sieve@SiO2 alkaline molecular sieve catalyst prepared in Example 6; Figure 8 The stability test results are shown for the alkali metal / molecular sieve@SiO2 alkaline molecular sieve catalyst prepared in Example 6. Detailed Implementation

[0023] To facilitate understanding of the present invention, the following embodiments are provided. These embodiments are merely illustrative and should not be considered as specific limitations of the invention. Because the present invention can also be described and explained through other solutions that do not depart from its technical features, all modifications within the scope of the present invention or its equivalents should fall within the protection scope of the present invention.

[0024] The present invention will be further illustrated below with reference to embodiments, comparative examples, and application examples.

[0025] Example 1 1) Preparation of alkali metal / molecular sieve: 0.05 g of sodium carbonate was dissolved in 1.2 g of glycerol to obtain a sodium carbonate glycerol solution. Then, the sodium carbonate glycerol solution was impregnated onto the MCM-41 molecular sieve support by impregnation. After standing at 20 °C for 1 hour, the solution was sonicated at 20 °C for 10 minutes and dried at 20 °C for 12 hours. The catalyst was then transferred to a muffle furnace and calcined from room temperature to 150 °C at a heating rate of 0.1 °C / min for 6 hours to obtain the sodium carbonate / MCM-41 catalyst. 2) Coating with SiO2 layer: 1 g of the alkali metal / molecular sieve catalyst prepared in step 1) was suspended in 10 mL of ethanol, and then 5 g of silica sol was added. The mixture was stirred for 1 h, dried at 50 °C for 12 h, and then calcined at 200 °C for 8 h to obtain the sodium carbonate / MCM-41@SiO2 alkaline molecular sieve catalyst.

[0026] Example 2 1) Preparation of alkali metal / molecular sieve: 0.05 g of rubidium chloride was dissolved in 1.2 g of ammonia water to obtain an ammonia solution of rubidium chloride. Then, the ammonia solution containing rubidium chloride was impregnated onto an ITQ-29 (LTA type) molecular sieve support by impregnation. After standing at 30 °C for 2 hours, it was sonicated at 30 °C for 20 minutes and dried at 50 °C for 6 hours. Then, the catalyst was transferred to a muffle furnace and heated from room temperature to 500 °C at a heating rate of 1 °C / min and calcined for 0.5 hours to obtain the rubidium chloride / ITQ-29 catalyst. 2) Coating with SiO2 layer: 1 g of the alkali metal / molecular sieve catalyst prepared in step 1) was suspended in 10 mL of toluene, and then 4 g of tetramethyl silicate was added. The mixture was stirred for 4 h, dried at 150 °C for 0.5 h, and then calcined at 650 °C for 2 h to obtain the rubidium chloride / ITQ-29@SiO2 alkaline molecular sieve catalyst.

[0027] Example 3 1) Preparation of alkali metal / molecular sieve: 0.05 g of potassium carbonate was dissolved in 1.2 g of methanol to obtain a methanol solution of potassium carbonate. Then, the methanol solution containing potassium carbonate was impregnated onto a NaZSM-5 (SiO2 / Al2O3=200, MFI type) molecular sieve support by impregnation. After standing at 40 °C for 5 hours, it was sonicated at 40 °C for 40 minutes and dried at 80 °C for 2 hours. Then, the catalyst was transferred to a muffle furnace and heated from room temperature to 600 °C at a heating rate of 10 °C / min. The calcination was carried out for 3 hours to obtain the potassium carbonate / NaZSM-5 catalyst. 2) Coating with SiO2 layer: 1 g of the alkali metal / molecular sieve catalyst prepared in step 1) was suspended in 10 mL of isopropanol, and then 1 g of sodium silicate was added. The mixture was stirred for 6 h, dried at 120 °C for 2 h, and then calcined at 500 °C for 4 h to obtain the potassium carbonate / NaZSM-5@SiO2 alkaline molecular sieve catalyst.

[0028] Figure 2 The image shows the SEM image of the catalyst prepared in Example 3. It can be seen that the NaZSM-5 molecular sieve has a regular morphology, and the introduction of alkaline potassium carbonate did not disrupt the morphology of the NaZSM-5 molecular sieve.

[0029] Example 4 1) Preparation of alkali metal / molecular sieve: 0.05 g of rubidium carbonate was dissolved in 1.2 g of deionized water to obtain an aqueous solution of rubidium carbonate. Then, the aqueous solution containing rubidium carbonate was impregnated onto a Silicalite-1 (MFI type) molecular sieve support by impregnation. After standing at 60 °C for 12 hours, it was sonicated at 30 °C for 50 minutes and dried at 100 °C for 0.5 hours. Then, the catalyst was transferred to a muffle furnace and heated from room temperature to 500 °C at a heating rate of 5 °C / min and calcined for 3 hours to obtain the rubidium carbonate / Silicalite-1 catalyst. 2) Coating with SiO2 layer: 1 g of the alkali metal / molecular sieve catalyst prepared in step 1) was suspended in 10 mL of cyclohexane, and then 3 g of polydimethylsiloxane was added. The mixture was stirred for 12 h, dried at 110 °C for 3 h, and then calcined at 400 °C for 4 h to obtain the rubidium carbonate / Silicalite-1@SiO2 alkaline molecular sieve catalyst.

[0030] Example 5 1) Preparation of alkali metal / molecular sieve: 0.05 g of cesium carbonate was dissolved in 1.2 g of ethanol to obtain an ethanol solution of cesium carbonate. Then, the ethanol solution containing cesium carbonate was impregnated onto a Beta (SiO2 / Al2O3=∞, BEA type) molecular sieve support by impregnation. After standing at 80 °C for 18 hours, it was sonicated at 60 °C for 90 minutes and dried at 120 °C for 12 hours. Then, the catalyst was transferred to a muffle furnace and heated from room temperature to 650 °C at a heating rate of 8 °C / min and calcined for 5 hours to obtain the cesium carbonate / Beta catalyst. 2) Coating with SiO2 layer: 1 g of the alkali metal / molecular sieve catalyst prepared in step 1) was suspended in 10 mL of n-hexane, and then 1.5 g of tetraethyl silicate (TEOS) was added. The mixture was stirred for 12 h, dried at 80 °C for 6 h, and then calcined at 650 °C for 6 h to obtain the cesium carbonate / Beta@SiO2 alkaline molecular sieve catalyst.

[0031] Figure 3 The image shows the SEM image of the catalyst prepared in Example 5. It can be seen that the Beta molecular sieve has a regular morphology, and the introduction of alkaline cesium carbonate did not disrupt the morphology of the Beta molecular sieve.

[0032] Example 6 1) Preparation of alkali metal / molecular sieve: 0.05 g of cesium carbonate was dissolved in 1.2 g of deionized water to obtain an aqueous solution of cesium carbonate. Then, the aqueous solution containing cesium carbonate was impregnated onto a Silicalite-1 (MFI type) molecular sieve support by impregnation. After standing at 30 °C for 24 hours, the catalyst was sonicated at 30 °C for 60 minutes and dried at 30 °C for 11 hours. The catalyst was then transferred to a muffle furnace and calcined from room temperature to 300 °C at a heating rate of 2 °C / min for 2 hours to obtain the cesium carbonate / Silicalite-1 catalyst. 2) Coating with SiO2 layer: 1 g of the alkali metal / molecular sieve catalyst prepared in step 1) was suspended in 10 mL of n-hexane, and then 2 g of nano-silica was added. The mixture was stirred for 1 h, dried at 120 °C for 2 h, and then calcined at 450 °C for 4 h to obtain the cesium carbonate / Silicalite-1@SiO2 alkaline molecular sieve catalyst.

[0033] Figure 4 The image shows the SEM image of the cesium carbonate / Silicalite-1 catalyst prepared in Example 6. It can be seen that the Silicalite-1 molecular sieve has a regular morphology, and the active component cesium carbonate is evenly distributed on the surface without agglomeration. Figure 5 The image shows the XRD pattern of the cesium carbonate / Silicalite-1 catalyst prepared in Example 6. It can be seen that the catalyst has high crystallinity and no characteristic diffraction peaks of cesium carbonate, indicating that cesium carbonate has high dispersion. Figure 6 This is a TEM image of the cesium carbonate / Silicalite-1 catalyst prepared in Example 6, showing that cesium carbonate is uniformly loaded on the surface. Figure 7 This is a TEM image of the cesium carbonate / Silicalite-1@SiO2 alkaline molecular sieve catalyst prepared in Example 6, showing that SiO2 was successfully coated on the surface of the cesium carbonate / Silicalite-1 catalyst. Figure 8 The results show the stability test of the cesium carbonate / Silicalite-1@SiO2 alkaline molecular sieve catalyst prepared in Example 6. It can be seen that the cesium carbonate / Silicalite-1@SiO2 catalyst can be recycled at least five times, and has good stability.

[0034] Comparative Example 1 1) Preparation of alkali metal / molecular sieve: 0.05 g of cesium carbonate was dissolved in 10 g of deionized water to obtain an aqueous solution of cesium carbonate. Then, the cesium carbonate solution was loaded onto a NaY (FAU type) molecular sieve support by ion exchange. The solution was stirred at 80 °C for 6 h. The resulting solution was washed with deionized water until neutral and then dried in an oven at 80 °C for 12 h. The catalyst was then transferred to a muffle furnace and calcined from room temperature to 500 °C at a heating rate of 1 °C / min for 3 h to obtain the cesium / NaY catalyst. 2) Coating with SiO2 layer: 1 g of the alkali metal / molecular sieve catalyst prepared in step 1) was suspended in 10 mL of n-hexane, and then 2 g of tetraethyl silicate (TEOS) was added. The mixture was stirred for 4 h, dried at 80 °C for 6 h, and then calcined at 550 °C for 2 h to obtain the cesium / NaY@SiO2 alkaline molecular sieve catalyst.

[0035] Comparative Example 2 1) Preparation of alkali metal / molecular sieve: 0.05 g of cesium chloride was dissolved in 10 g of deionized water to obtain an aqueous solution of cesium chloride. Then, the cesium carbonate-containing solution was loaded onto a NaY (FAU type) molecular sieve support by ion exchange. The solution was stirred at 80 °C for 6 h. The resulting solution was washed with deionized water until neutral and then dried in an oven at 80 °C for 12 h. The catalyst was then transferred to a muffle furnace and calcined from room temperature to 500 °C at a heating rate of 1 °C / min for 3 h to obtain the cesium / NaY catalyst. 2) Coating with SiO2 layer: 1 g of the alkali metal / molecular sieve catalyst prepared in step 1) was suspended in 10 mL of n-hexane, and then 2 g of tetraethyl silicate (TEOS) was added. The mixture was stirred for 4 h, dried at 110 °C for 2 h, and then calcined at 650 °C for 4 h to obtain the cesium / NaY@SiO2 alkaline molecular sieve catalyst.

[0036] Application Example 1 The catalysts prepared in Examples 1-6 and Comparative Examples 1-2 were evaluated for catalytic activity in a reactor. The catalyst loading was 0.7 g. The reaction used dimethyl oxalate and ethanol as raw materials (molar ratio of DMO:EtOH = 1:1), the reaction temperature was 260 °C, and the reaction pressure was 0.01-5 MPa. A certain mass of isopropanol was added as an internal standard to the obtained products, and offline liquid chromatography was used for analysis. A 10 µL syringe was used for injection. The liquid phase products included the main products dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and the raw material dimethyl oxalate (DMO). The by-products mainly included ethyl methyl oxalate (EMO) and diethyl oxalate (DEO). The gas phase products included carbon monoxide (CO) and a very small amount of carbon dioxide (CO2). The liquid phase conversion rate X of dimethyl oxalate was calculated from this. DMO Liquid-phase selectivity of dimethyl carbonate (S) DMC Liquid-phase selectivity of methyl ethyl carbonate (S) EMC Liquid-phase selectivity of diethyl carbonate (S) DEC and the total selectivity S of dimethyl carbonate + ethyl methyl carbonate + diethyl carbonate DMC+EMC+DEC .

[0037] As shown in Table 1, the catalysts of Examples 1-6 exhibited high DMO conversion and total selectivity for DMC+EMC+DEC. Example 6 showed the highest DMO conversion and total selectivity for DMC+EMC+DEC. Subsequently, Comparative Examples 1-2 were prepared using cesium carbonate and cesium chloride as active components and NaY molecular sieve as the catalyst support via ion exchange. Compared to Comparative Examples 1-2, the catalysts of Examples 1-6 demonstrated better catalytic performance, indicating that the basic molecular sieve catalysts prepared in this application possess high total selectivity for DMC+EMC+DEC and high DMO conversion.

[0038] Table 1 Catalytic performance of catalysts in Examples 1-6 and Comparative Examples 1-2 catalyst <![CDATA[X DMO / %]]> <![CDATA[S DMC / %]]> <![CDATA[S EMC / %]]> <![CDATA[S DEC / %]]> <![CDATA[S DMC+EMC+DEC / %]]> Example 1 98.1 38.5 36.8 15.8 91.1 Example 2 93.7 44.6 38.2 9.7 92.5 Example 3 93.3 39.9 39.4 10.9 90.2 Example 4 93.7 40.2 43.2 9.5 92.9 Example 5 91.5 40.1 42.5 10.4 93.0 Example 6 99.2 43.6 45.2 9.9 98.7 Comparative Example 1 62.0 1.1 1.4 1.1 3.6 Comparative Example 2 50.2 0.2 0.9 0.6 1.7 Reaction evaluation revealed that Examples 1-6 exhibited high DMO conversion rates and overall selectivity for DMC+EMC+DEC. However, due to differences in alkali metal and support type, the overall selectivity for DMC+EMC+DEC also varied significantly, with the catalyst in Example 6 showing the highest DMO conversion rate and overall selectivity. In Comparative Examples 1-2, cesium carbonate and cesium chloride were used as active components, and NaY molecular sieves were used as catalyst supports. Catalysts prepared via ion exchange showed significantly lower DMO conversion rates and overall selectivity for DMC+EMC+DEC compared to the catalysts in Examples 1-6. This is attributed to the higher number of acidic sites in the molecular sieves of Comparative Examples 1-2, which hinders the catalytic activity of the basic active components. Figure 6The stability test chart of the catalyst in Example 6 under the reaction conditions of Application Example 1 shows that the catalyst exhibits excellent stability. After five consecutive reaction evaluations, the conversion rate of dimethyl oxalate and the total selectivity of dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate remained essentially unchanged. Therefore, the basic molecular sieve catalyst of the present invention for the synthesis of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate from dimethyl oxalate and ethanol possesses high catalytic activity and excellent cycle stability.

[0039] Based on the reaction results of the above examples and comparative examples, the following conclusions can be drawn: The alkaline molecular sieve catalyst prepared by the present invention exhibits high activity and is chloride-free. This catalyst is particularly suitable for the reaction of dimethyl oxalate and ethanol to synthesize dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate.

Claims

1. A method for preparing a basic molecular sieve catalyst for the one-step synthesis of dimethyl oxalate, diethyl oxalate, and methyl ethyl ester from dimethyl oxalate and ethanol, characterized in that, Using molecular sieves as a support, alkali metal active components with a mass fraction of 0.5%–25% are loaded onto the molecular sieves through the anchoring effect of their silanol groups, forming a supported catalyst with synergistic catalytic effect between alkali metals and molecular sieves. Furthermore, a SiO2 layer is coated on the catalyst surface to inhibit the loss of alkali metal active components, resulting in an alkali metal / molecular sieve@SiO2 catalyst. This catalyst significantly improves the stability of the alkali metal molecular sieve catalyst. The molecular sieve has a specific surface area of ​​100–800 m² / g, an average crystal size of 0.1–5 µm, and a SiO2 layer coating thickness of 0.5–200 nm. The catalyst is used in the one-step synthesis of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate from dimethyl oxalate and ethanol, under the conditions of a reaction temperature of 100–400 °C, a reaction pressure of 0.01–5 MPa, and a reaction time of 30–1500 min. The preparation method of the alkali metal / molecular sieve@SiO2 catalyst includes the following steps: 1) Preparation of alkali metal / molecular sieve: An alkali metal salt is dissolved in solvent A to obtain a solution containing the alkali metal salt. Then, the solution containing the alkali metal salt is impregnated onto a molecular sieve support by impregnation. After standing at 20~80 °C for 1~24 hours, it is ultrasonicated at 20~60 °C for 10~90 minutes and dried at 20~120 °C for 0.5~12 hours. Then, the catalyst is transferred to a muffle furnace and calcined at 150~650 °C for 0.5~6 hours to obtain the alkali metal / molecular sieve catalyst. 2) Coating with SiO2 layer: The alkali metal / molecular sieve catalyst prepared in step 1) is suspended in solvent B, and then a silicon source is added. The mixture is stirred for 1 to 12 h, dried at 50 to 150 °C for 0.5 to 12 h, and then calcined at 200 to 650 °C for 2 to 8 h to obtain the alkaline molecular sieve catalyst of alkali metal / molecular sieve@SiO2.

2. The method for preparing a basic molecular sieve catalyst for one-step synthesis of dimethyl oxalate, diethyl oxalate, and methyl ethyl ester from dimethyl oxalate and ethanol as described in claim 1, characterized in that, The molecular sieve support selected in step 1) is one or a combination of several of FAU, BEA, MCM-41, MFI, and LTA.

3. The method for preparing a basic molecular sieve catalyst for one-step synthesis of dimethyl oxalate, diethyl oxalate, and methyl ethyl ester from dimethyl oxalate and ethanol as described in claim 1, characterized in that, In step 1), the alkali metal salt is one or a combination of several of the following: sodium chloride, potassium chloride, rubidium chloride, cesium chloride, sodium carbonate, potassium carbonate, rubidium carbonate, cesium carbonate, and potassium acetate.

4. The method for preparing a basic molecular sieve catalyst for one-step synthesis of dimethyl oxalate, diethyl oxalate, and methyl ethyl ester from dimethyl oxalate and ethanol as described in claim 1, characterized in that, In step 2), the silicon source is one or a combination of several of the following: tetramethyl silicate, tetraethyl silicate, silica sol, polydimethylsiloxane, nano-silica, and sodium silicate.

5. The method for preparing a basic molecular sieve catalyst for one-step synthesis of dimethyl oxalate, diethyl oxalate, and methyl ethyl ester from dimethyl oxalate and ethanol as described in claim 1, characterized in that, In step 1), solvent A is one or a combination of glycerol, ethanol, methanol, isopropanol, hexane, acetonitrile, water, and ammonia; in step 2), solvent B is one or a combination of methanol, ethanol, isopropanol, n-hexane, cyclohexane, toluene, petroleum ether, acetonitrile, and water.

6. The method for preparing a basic molecular sieve catalyst for one-step synthesis of dimethyl oxalate, diethyl oxalate, and methyl ethyl ester from dimethyl oxalate and ethanol as described in claim 1, characterized in that, In step 2), the heating rate during calcination is 0.1~10 ℃ / min.

7. The method for preparing a basic molecular sieve catalyst for one-step synthesis of dimethyl oxalate, diethyl oxalate, and methyl ethyl ester from dimethyl oxalate and ethanol as described in claim 1, characterized in that, The alkaline molecular sieve catalyst described above is used in the one-step synthesis of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate from dimethyl oxalate and ethanol.

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