A process for the preparation of ethylene carbonate

Abstract

The present application relates to the field of biochemical pharmaceutical intermediate preparation, in particular to a preparation process of ethylene carbonate. The present application provides a preparation process of ethylene carbonate, the main feature of which is to use a modified eutectic solvent as a catalyst, and to combine solidification and a micro-channel reactor to improve the product yield and selectivity of the preparation reaction, and to improve the recycling number and stability of the catalyst itself.

Description

Technical Field

[0001] This invention relates to the field of preparation of biochemical pharmaceutical intermediates, specifically to a preparation process for ethylene carbonate. Background Technology

[0002] Ethylene carbonate (EC), as a high-value-added organic compound, has seen a significant increase in demand in recent years for its application as a biochemical pharmaceutical intermediate, becoming a core raw material for drug synthesis, preparation of bioactive substances, and development of novel drug delivery systems. Its molecular structure contains both ester and cyclic carbonate groups, allowing for the derivation of various functional intermediates through ring-opening reactions and transesterification. For example, the synthesis of antibiotics, antiviral drugs, anticancer drugs, and hormone compounds all rely on the efficient conversion of EC. EC is a key precursor in the synthesis of β-lactam antibiotics such as amoxicillin and cephalosporins, and its cyclic structure can enhance reaction selectivity in drug molecule framework construction. Simultaneously, EC-derived polycarbonate materials are widely used in the preparation of drug sustained-release carriers and medical polymer materials due to their biocompatibility and biodegradability.

[0003] However, traditional EC synthesis processes face the following technical bottlenecks when used for the production of pharmaceutical intermediates:

[0004] Early phosgene processes required the use of highly toxic phosgene, and the byproduct chlorine-containing waste was difficult to treat, which seriously conflicted with the green production standards of the pharmaceutical industry. Transesterification relied on raw materials such as dimethyl carbonate, with a lengthy reaction path and low atom economy, resulting in insufficient purity of pharmaceutical-grade EC (usually below 99%), making it difficult to meet the strict requirements for impurity control in drug synthesis.

[0005] While the direct synthesis of ethylene oxide (EO) from CO2 aligns with green chemistry principles, existing homogeneous catalysts (such as quaternary phosphonium salts and potassium iodide) require operation at high temperatures (>100°C) and high pressures (>5 MPa), which can easily trigger EO self-polymerization into polyether byproducts, leading to EC selectivity dropping below 85% in pharmaceutical intermediate synthesis. Furthermore, homogeneous catalysts are difficult to recover, and residual metal ions may contaminate the final product, increasing pharmaceutical purification costs.

[0006] Traditional batch reactors have low gas-liquid-solid three-phase mass transfer efficiency, limited CO2 solubility in the liquid phase, and kinetic control of the reaction rate, requiring extended residence time to several hours, which exacerbates the decomposition risk of heat-sensitive pharmaceutical intermediates.

[0007] In recent years, eutectic solvents (DES) have been attempted for EC synthesis due to their designable hydrogen bond networks, high catalytic activity, and biodegradability. For example, patent WO2020177631A1 uses the ChCl-urea system, and patent US2018036245A1 uses supercritical CO2 as an additional condition. However, problems such as product separation difficulties and easy catalyst deactivation still exist.

[0008] To address the aforementioned issues, this invention proposes modifying a eutectic solvent and immobilizing it on a microchannel support to construct a heterogeneous catalytic system that combines high catalytic activity with stability, meeting the stringent requirements for catalyst residue control in pharmaceutical manufacturing. This technical approach not only overcomes the environmental and efficiency shortcomings of traditional processes but also provides a reliable guarantee for the large-scale application of EC in the field of high-end pharmaceutical intermediates. Summary of the Invention

[0009] Based on the problems summarized above, this invention provides a process for preparing ethylene carbonate, characterized by using a modified eutectic solvent as a catalyst, combined with immobilization and a microchannel reactor to improve the product yield and selectivity of the preparation reaction, while simultaneously increasing the number of times the catalyst can be recycled and its stability. The specific technical solution is as follows:

[0010] A process for preparing ethylene carbonate includes the following steps:

[0011] S1: The purified and pretreated hydrogen bond acceptor and hydrogen bond donor are placed in a container at a certain molar ratio and heated and stirred until a colorless and transparent solution is formed. A certain amount of modifier is added to the colorless and transparent solution, and after stirring and reacting, the mixture is cooled to room temperature and filtered to obtain solution catalyst A.

[0012] S2: The pretreated solid medium carrier is laid flat in a vacuum impregnation tank. After depressurization and exhaust, the pretreated solution catalyst A is slowly injected. The injection is stopped when the liquid level is a certain height above the solid medium carrier. Vacuum impregnation is then carried out, followed by staged drying to obtain the supported catalyst B.

[0013] S3: Disperse the supported catalyst B in an ethanol-water mixture, then inject the dispersed supported catalyst B into a microchannel reactor after plasma cleaning, spread it evenly, dry it, and heat treat it to fix the supported catalyst B.

[0014] S4: Ethylene oxide and carbon dioxide are mixed in a certain molar ratio, preheated, and then introduced into the microchannel reactor for reaction. The product after reaction is separated by vacuum distillation to obtain ethylene carbonate.

[0015] Furthermore, the hydrogen bond acceptor described in S1 is choline chloride, and the hydrogen bond donor described in S1 is malonic acid.

[0016] The molar ratio described in S1 is 1:1;

[0017] The heating and stirring described in S1 is carried out in an 80°C oil bath.

[0018] Furthermore, the modifier mentioned in S1 is 3% of the total mass of KH550, and the stirring reaction conditions mentioned in S1 are stirring at 80°C for 4 hours.

[0019] Furthermore, the solid medium carrier described in S2 is a porous silica medium carrier.

[0020] Furthermore, the liquid level being higher than the solid medium carrier by a certain height as described in S2 is at least 2 cm higher than the solid medium carrier.

[0021] The vacuum impregnation described in S2 is performed under the condition of maintaining a vacuum of -0.095 MPa for 60 minutes.

[0022] The staged drying described in S2 is performed under the following conditions: 50°C vacuum drying for 4 hours, followed by treatment at 80°C under a nitrogen atmosphere for 2 hours.

[0023] Furthermore, the supported catalyst B described in S3 is dispersed in an ethanol-water mixture, wherein the volume ratio of the ethanol-water mixture is 7:3, and the solid content of the supported catalyst B is 20 wt%.

[0024] The drying and heat treatment described in S3 are performed under the following conditions: drying at 80°C for 2 hours and heat treatment at 150°C in a nitrogen atmosphere for 1 hour.

[0025] Furthermore, the final coating thickness of the supported catalyst B ranges from 20 to 80 μm.

[0026] Furthermore, the mixing according to a certain molar ratio mentioned in S4 is a mixing in a molar ratio of 1:1 to 1:1.8.

[0027] Furthermore, the preheating described in S4 ultimately reaches a temperature of 60°C;

[0028] The reaction described in S4 is carried out in the microchannel reactor under the following conditions: reaction temperature 80-100℃, pressure 1.5-2.0MPa, and residence time 15-30min.

[0029] Furthermore, the microchannel reactor has a multi-layered serpentine flow channel structure.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The present invention improves the catalytic efficiency of the preparation reaction by introducing a eutectic solvent catalyst system. Eutectic solvent catalysts are easy to synthesize and their raw materials are widely available, safe and non-toxic.

[0032] (2) By modifying the eutectic solvent, the present invention improves the selectivity of the preparation reaction, facilitates the subsequent catalyst immobilization, and makes the catalyst more stable and less prone to loss during the preparation reaction.

[0033] (3) This invention utilizes porous silica media to immobilize the catalyst, thereby achieving a phase transformation of the catalyst. It also utilizes the properties of porous silica itself to form a microchannel catalytic environment. Combined with the subsequent use of a microchannel reactor with a multi-layer serpentine flow channel structure, this invention significantly improves the product yield and selectivity of the preparation reaction, while also increasing the number of cycles and stability of the catalyst itself. Attached Figure Description

[0034] Figure 1 This is a process flow diagram for preparing ethylene carbonate according to the present invention;

[0035] Figure 2 This is a comparison chart of the thermogravimetric analysis results of the KH550 modified supported catalyst and the unmodified supported catalyst of this invention.

[0036] Figure 3 This is a schematic diagram of the multilayer serpentine flow channel microchannel reactor of the present invention;

[0037] Figure 4 This is a diagram illustrating the catalytic reaction mechanism of carbon dioxide and ethylene oxide according to the present invention. Detailed Implementation

[0038] The following embodiments further explain and illustrate the technical solutions of the present invention. It should be specifically noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0039] This invention proposes a process for preparing ethylene carbonate, as shown in the attached figure. Figure 1 As shown, the specific steps include:

[0040] 1. Synthesis and modification of eutectic solvents:

[0041] 1.1 Pretreatment of hydrogen bond acceptors and synthesis of eutectic solvents

[0042] Before preparing the eutectic solvent, the hydrogen bond acceptor choline chloride was pretreated: half the volume of anhydrous ethanol was added to the reaction vessel, and the mixture was heated and stirred at 60°C under reflux. Then, the choline chloride to be used was added to the vessel in four portions. After the choline chloride was completely dissolved, stirring was stopped, and the mixture was allowed to cool to room temperature. The vessel was then water-cooled at 15°C until choline chloride crystals precipitated. After crystallization, the choline chloride was separated from the ethanol by vacuum filtration. Finally, the choline chloride powder was vacuum-dried at 80°C for 24 hours before use.

[0043] Dry choline chloride and malonic acid are placed in a container at a molar ratio of 1:1 and heated and stirred in an oil bath at 80°C until a colorless and transparent solution is formed.

[0044] 1.2 Modification of Eutectic Solvents

[0045] KH550 (γ-aminopropyltriethoxysilane) was added dropwise to the synthesized eutectic solvent at a rate of 1 mL / min, with the addition amount being 3% of the total mass of the eutectic solvent. The entire addition process was carried out under constant temperature of 60°C and nitrogen protection. After the addition was completed, the temperature was raised to 80°C and the reaction was stirred for another 4 hours. After the reaction solution was cooled to room temperature, it was filtered through a 0.22 μm polytetrafluoroethylene filter membrane to remove unreacted KH550 aggregates, thus obtaining the modified eutectic solution catalyst.

[0046] In the selection and combination of eutectic solvents in the above steps, the hydroxyl group on the choline cation and the Cl- anion... － The synergistic catalytic effect, plus the hydrogen bond donor and Cl － The formation of a hydrogen bond network weakens the electrostatic interaction between choline chloride cations and anions, and enhances the Cl- － Nucleophilicity, and can reduce Cl － The interaction force with the epoxide facilitates the ring-opening of the epoxide and the formation of Cl. － The timely removal of the solvent accelerates the reaction rate and improves product selectivity; in addition, the eutectic solvent is easy to synthesize, the raw materials are widely available, and it is safe and non-toxic.

[0047] The modification process of KH550 described above includes: the ethoxy group (-OCH2CH3) of KH550 is gradually hydrolyzed to silanol (-Si(OH)3), and the silanol undergoes dehydration condensation with the hydroxyl group (-OH) in the eutectic solvent to form a stable Si-OC bond. By introducing the silane coupling agent KH550, amino (-NH2) functional groups are modified on the surface of the eutectic solvent, enhancing the chemical bonding ability between the eutectic solvent and the subsequent immobilized porous silica (SiO2). The amino group reacts with the Cl- in the eutectic solvent... －Strong hydrogen bonds are formed, allowing the eutectic solvent to be more uniformly dispersed on the support surface. Furthermore, the propyl chain (-CH2CH2CH2-) of KH550 can alleviate volume expansion stress during immobilization, preventing catalyst layer cracking. Modification of KH550 can solve the problem of catalyst loss during traditional immobilization processes, while simultaneously improving the stability of catalytic active sites.

[0048] 2. Immobilization of modified eutectic solution catalysts

[0049] Carrier preparation: Select a carrier with a pore size range of 50–100 nm and a specific surface area ≥300 m². 2 / g porous silica medium carrier; the carrier was immersed in a 5% nitric acid solution and ultrasonically treated at 60°C for 2 hours to remove surface impurities and increase hydroxyl density; after acid washing and activation, it was vacuum dried at 120°C for 6 hours to ensure that the surface groups (-Si-OH) were fully exposed, providing active sites for subsequent KH550 bonding.

[0050] Pretreatment of modified eutectic solution: Dissolve the modified eutectic solution (containing 3% KH550 modification) in anhydrous ethanol, and control the concentration of the modified eutectic solution at 30wt%; then sonicate for 30 minutes, with the ultrasonic frequency set at 40kHz and the ultrasonic power set at 300W to ensure uniform dispersion and avoid agglomeration.

[0051] Vacuum impregnation: The pretreated porous silica medium carrier is placed in a vacuum impregnation tank and spread into a single layer (thickness ≤ 5 mm). The vacuum pump is started, and the pressure inside the tank is reduced to -0.095 MPa and maintained for 20 minutes to expel air from the carrier pores. The pretreated modified eutectic solution is slowly injected until the liquid level is more than 2 cm above the carrier layer. Injection is stopped, and the vacuum degree is maintained at -0.095 MPa for 60 minutes. Under negative pressure, the air inside the pores is replaced, and the solution penetrates deep into the carrier pores through capillary action, achieving uniform loading of the modified eutectic solution catalyst.

[0052] Gradient drying and curing: The vacuum-impregnated supported catalyst was dried under reduced pressure at 50°C for 4 hours to remove ethanol (recovery rate >95%); then treated at 80°C under a nitrogen atmosphere for 2 hours to promote the complete formation of Si-O-Si bonds between the catalyst and the support.

[0053] The above steps employ vacuum impregnation, utilizing capillary effect to immobilize the modified eutectic solution catalyst onto a porous silica medium support. The principle can be referenced from the Young-Laplace equation: Where γ is the surface tension of the solution, θ is the contact angle, and r is the pore radius; negative pressure (ΔP) can drive the solution to fill the nanopores rapidly, ensuring that the modified eutectic solution catalyst penetrates deep into the support.

[0054] In the above steps, the -Si-OH groups on the surface of the porous silica medium support condense with the -Si-OH groups of KH550, forming covalent bonds; the Cl in the modified eutectic solution catalyst... － The binding force between the amino groups (-NH2) on the surface of the porous silica medium support is enhanced by hydrogen bonding. Based on the synergistic effect of such Si-O-Si covalent bonds and hydrogen bonds, the cycle life of the catalyst can be improved.

[0055] As attached Figure 2 As shown in the figure, the thermogravimetric analysis (TGA) results of the KH550-modified supported catalyst and the unmodified supported catalyst are compared. The specific test steps of TGA are as follows: the sample is ground into a uniform powder (particle size <100μm), vacuum dried, weighed and recorded, and the test instrument is calibrated for baseline and temperature before the test begins. The test conditions are under a nitrogen protective atmosphere, calcined at 600℃ to remove the supported material, and finally the weight loss ratio is calculated for data comparison. The comparison results in the figure show that in the range of around 200℃, the weight loss of the unmodified supported catalyst is significantly greater than that of the modified supported catalyst, and the decomposition temperature of the modified supported catalyst is delayed. This illustrates the effect of KH550 modification on the supported catalyst and verifies the above discussion on enhanced binding force.

[0056] Table 1 shows the results of BET specific surface area testing (nitrogen adsorption method) and mercury intrusion porosimetry porosimetry. The specific testing steps for BET specific surface area testing (nitrogen adsorption method) are as follows: the sample is heated to 150℃ in a vacuum degassing station and continuously degassed for 6 hours, then connected to the analysis station and immersed in a liquid nitrogen bath (-196℃). Automatic testing and data recording are performed using analytical instruments. The specific testing steps for mercury intrusion porosimetry porosimetry are as follows: the sample is dried in a 105℃ oven for 4 hours, accurately weighed, and then placed in a dilatometer. A vacuum is drawn to <50 μmHg. Within a pressure range of 0.5-50 psi, the mercury intrusion volume is measured, and the macropore distribution is calculated. The pressure is then gradually increased from 50 psi to 60000 psi, and the mercury intrusion volume at each pressure point is recorded. Finally, the pore size is calculated using the Washburn equation, and the porosity is obtained. From the results in the table, it can be seen that after solidification, the specific surface area increases from 320 m² / s² to 60000 psi. 2 / g decreased to 260m 2 / g indicates that the eutectic solution catalyst successfully filled the channels, and the porosity decreased from 85% to 72%. The reduction in pore volume matches the loading, further proving that the catalyst immobilization was completed.

[0057] Table 1. Results of BET specific surface area and mercury intrusion porosimetry test.

[0058]

[0059] 3. Immobilized catalyst coated onto microchannel reactor

[0060] The sol-gel method was used for coating the supported catalyst.

[0061] Catalyst dispersion: The supported catalyst was dispersed in an ethanol-water mixture (volume ratio 7:3) with a solid content of 20 wt%.

[0062] Microchannel inner wall pretreatment: plasma cleaning (power 300W, Ar gas flow rate 50sccm, 10min) to improve surface energy;

[0063] Coating and gradient sintering: The dispersed supported catalyst is injected into the microchannel reactor, spread evenly, dried at 80°C for 2 hours, and then heat-treated at 150°C in a nitrogen atmosphere for 1 hour. The final coating thickness ranges from 20 to 80 μm.

[0064] The microchannel reactor in the above steps preferably adopts a multi-layer serpentine flow channel structure, with the length of a single layer controlled between 1.5 and 2.5 m. The upper and lower layers can be staggered through vertical connecting holes. The flow channel material is preferably 316L stainless steel, which can withstand reaction corrosion. (See attached...) Figure 3 The diagram shown is a schematic of a microchannel reactor. The specific structure can be adjusted according to the production scale and environment of the reaction.

[0065] 4. Continuous synthesis of carbon dioxide and ethylene oxide

[0066] Ethylene oxide and carbon dioxide were mixed at a molar ratio of 1:1 to 1:1.8, preheated to 60°C, and then introduced into a microchannel reactor. The reaction temperature was 80–100°C, the pressure was 1.5–2.0 MPa, and the residence time was 15–30 min. The product was separated by vacuum distillation, and the catalyst could be recycled. The detailed conditions were set as follows:

[0067] —Raw Material Specifications and Purification

[0068] Ethylene oxide (EO): purity ≥ 99.9%, moisture content ≤ 50 ppm (processed through a 3A molecular sieve drying tower);

[0069] Carbon dioxide (CO2): food grade purity (≥99.99%), with sulfides and hydrocarbon impurities removed by activated carbon adsorption.

[0070] —Metrology and Control

[0071] Ethylene oxide liquid feed: using a mass flow meter (accuracy ±0.5%), flow range 0.1-5 L / min;

[0072] Carbon dioxide gaseous feed: The flow rate is adjusted to 1 to 1.8 times the molar ratio of ethylene oxide using a Coriolis mass flow meter (accuracy ±0.3%).

[0073] Mixing device: Static mixer to ensure uniform mixing of gas and liquid phases.

[0074] —Reaction condition control method

[0075] Reaction temperature: External circulating oil bath (±0.5℃);

[0076] Reaction pressure: piezoelectric ceramic back pressure valve;

[0077] Residence time: Flow rate adjustment (0.2-0.5 m / s).

[0078] Based on the reaction results and accumulated experience, the catalytic reaction mechanism of carbon dioxide and ethylene oxide in the above steps is as follows: Figure 4 As shown, firstly, the hydroxyl group on the choline cation forms a hydrogen bond with the oxygen atom of ethylene oxide to activate the ethylene oxide. Simultaneously, the Cl- anion... － (By combining with a malonic acid molecule) a nucleophilic attack on the sterically less hindered β-carbon atom of ethylene oxide causes ring-opening, yielding the ring-opening intermediate—the alkoxide anion. The alkoxide anion then nucleophilically attacks carbon dioxide, forming an alkyl carbonate anion. Finally, intramolecular ring closure generates ethylene carbonate, regenerating the catalyst. In this catalytic cycle, the catalyst's activity primarily depends on the reaction between the choline chloride cation and Cl... － The synergistic catalytic effect. The role of malonic acid, the hydrogen bond donor, mainly lies in its ability to react with Cl-. － The formation of a hydrogen bond network weakens the electrostatic interaction between choline chloride cations and anions, thereby enhancing the Cl- － The nucleophilicity of Cl is also reduced. － The interaction force with ethylene oxide facilitates the ring-opening of the substrate and the formation of Cl. － Timely departure allows the catalytic cycle to continue and improves the selectivity of the reaction.

[0079] Example 1

[0080] A process for preparing ethylene carbonate is as follows:

[0081] S1: Purified and pretreated choline chloride and malonic acid were placed in a container at a molar ratio of 1:1 and heated and stirred in an oil bath at 80°C until a colorless and transparent solution was formed. 3% of the total mass of KH550 was added to the aforementioned colorless and transparent solution. After stirring and reacting at 80°C for 4 hours, the mixture was cooled to room temperature and filtered to obtain the modified eutectic solution catalyst.

[0082] S2: The porous silica medium carrier, which has been pretreated by acid washing and activation, is spread in a vacuum impregnation tank. After depressurization and exhaust, the modified eutectic solution, which has been pretreated by dispersion, is slowly injected. The injection is stopped when the liquid level is more than 2 cm above the carrier layer. The vacuum degree is maintained at -0.095 MPa for 60 minutes. The catalyst is dried under reduced pressure at 50°C for 4 hours and then treated at 80°C under a nitrogen atmosphere for 2 hours to obtain the supported catalyst.

[0083] S3: Disperse the supported catalyst in an ethanol-water mixture (volume ratio 7:3) with a solid content of 20wt%; then inject the dispersed supported catalyst into a microchannel reactor after plasma cleaning, spread it evenly, dry it at 80℃ for 2h, and then heat treat it at 150℃ in a nitrogen atmosphere for 1h. The final coating thickness ranges from 20 to 80μm.

[0084] S4: Ethylene oxide and carbon dioxide are mixed at a molar ratio of 1:1 to 1:1.4, preheated to 60°C, and introduced into a microchannel reactor; the reaction temperature is 90°C, the pressure is 1.8 MPa, and the residence time is 25 min; then separated by vacuum distillation to obtain ethylene carbonate.

[0085] Example 2

[0086] A process for preparing ethylene carbonate is as follows:

[0087] S1: Purified and pretreated choline chloride and malonic acid were placed in a container at a molar ratio of 1:1 and heated and stirred in an oil bath at 80°C until a colorless and transparent solution was formed. 3% of the total mass of KH550 was added to the aforementioned colorless and transparent solution. After stirring and reacting at 80°C for 4 hours, the mixture was cooled to room temperature and filtered to obtain the modified eutectic solution catalyst.

[0088] S2: The porous silica medium carrier, which has been pretreated by acid washing and activation, is spread in a vacuum impregnation tank. After depressurization and exhaust, the modified eutectic solution, which has been pretreated by dispersion, is slowly injected. The injection is stopped when the liquid level is more than 2 cm above the carrier layer. The vacuum degree is maintained at -0.095 MPa for 60 minutes. The catalyst is dried under reduced pressure at 50°C for 4 hours and then treated at 80°C under a nitrogen atmosphere for 2 hours to obtain the supported catalyst.

[0089] S3: The supported catalyst was dispersed in an ethanol-water mixture (volume ratio 7:3) with a solid content of 20 wt%; the dispersed supported catalyst was then injected into a microchannel reactor after plasma cleaning.

[0090] After being evenly spread, the coating is dried at 80°C for 2 hours, and then heat-treated at 150°C in a nitrogen atmosphere for 1 hour. The final coating thickness ranges from 20 to 80 μm.

[0091] S4: Ethylene oxide and carbon dioxide are mixed in a 1:1 molar ratio, preheated to 60°C, and introduced into a microchannel reactor; the reaction temperature is 80°C, the pressure is 1.5 MPa, and the residence time is 15 min; then separated by vacuum distillation to obtain ethylene carbonate.

[0092] Example 3

[0093] A process for preparing ethylene carbonate is as follows:

[0094] S1: Purified and pretreated choline chloride and malonic acid were placed in a container at a molar ratio of 1:1 and heated and stirred in an oil bath at 80°C until a colorless and transparent solution was formed. 3% of the total mass of KH550 was added to the aforementioned colorless and transparent solution. After stirring and reacting at 80°C for 4 hours, the mixture was cooled to room temperature and filtered to obtain the modified eutectic solution catalyst.

[0095] S2: The porous silica medium carrier, which has been pretreated by acid washing and activation, is spread in a vacuum impregnation tank. After depressurization and exhaust, the modified eutectic solution, which has been pretreated by dispersion, is slowly injected. The injection is stopped when the liquid level is more than 2 cm above the carrier layer. The vacuum degree is maintained at -0.095 MPa for 60 minutes. The catalyst is dried under reduced pressure at 50°C for 4 hours and then treated at 80°C under a nitrogen atmosphere for 2 hours to obtain the supported catalyst.

[0096] S3: The supported catalyst was dispersed in an ethanol-water mixture (volume ratio 7:3) with a solid content of 20 wt%; the dispersed supported catalyst was then injected into a microchannel reactor after plasma cleaning.

[0097] After being evenly spread, the coating is dried at 80°C for 2 hours, and then heat-treated at 150°C in a nitrogen atmosphere for 1 hour. The final coating thickness ranges from 20 to 80 μm.

[0098] S4: Ethylene oxide and carbon dioxide are mixed at a molar ratio of 1:1.8, preheated to 60°C, and introduced into a microchannel reactor; the reaction temperature is 100°C, the pressure is 2.0 MPa, and the residence time is 30 min; then separated by vacuum distillation to obtain ethylene carbonate.

[0099] Example 4

[0100] A process for preparing ethylene carbonate is as follows:

[0101] S1: Purified and pretreated choline chloride and malonic acid were placed in a container at a molar ratio of 1:1 and heated and stirred in an oil bath at 80°C until a colorless and transparent solution was formed. 3% of the total mass of KH550 was added to the aforementioned colorless and transparent solution. After stirring and reacting at 80°C for 4 hours, the mixture was cooled to room temperature and filtered to obtain the modified eutectic solution catalyst.

[0102] S2: The porous silica medium carrier, which has been pretreated by acid washing and activation, is spread in a vacuum impregnation tank. After depressurization and exhaust, the modified eutectic solution, which has been pretreated by dispersion, is slowly injected. The injection is stopped when the liquid level is more than 2 cm above the carrier layer. The vacuum degree is maintained at -0.095 MPa for 60 minutes. The catalyst is dried under reduced pressure at 50°C for 4 hours and then treated at 80°C under a nitrogen atmosphere for 2 hours to obtain the supported catalyst.

[0103] S3: The supported catalyst was dispersed in an ethanol-water mixture (volume ratio 7:3) with a solid content of 20 wt%; the dispersed supported catalyst was then injected into a microchannel reactor after plasma cleaning.

[0104] After being evenly spread, the coating is dried at 80°C for 2 hours, and then heat-treated at 150°C in a nitrogen atmosphere for 1 hour. The final coating thickness ranges from 20 to 80 μm.

[0105] S4: Ethylene oxide and carbon dioxide are mixed at a molar ratio of 1:1.2, preheated to 60°C, and introduced into a microchannel reactor; the reaction temperature is 90°C, the pressure is 1.8 MPa, and the residence time is 20 min; then separated by vacuum distillation to obtain ethylene carbonate.

[0106] Example 5

[0107] A process for preparing ethylene carbonate is as follows:

[0108] S1: Purified and pretreated choline chloride and malonic acid were placed in a container at a molar ratio of 1:1 and heated and stirred in an oil bath at 80°C until a colorless and transparent solution was formed. 3% of the total mass of KH550 was added to the aforementioned colorless and transparent solution. After stirring and reacting at 80°C for 4 hours, the mixture was cooled to room temperature and filtered to obtain the modified eutectic solution catalyst.

[0109] S2: The porous silica medium carrier, which has been pretreated by acid washing and activation, is spread in a vacuum impregnation tank. After depressurization and exhaust, the modified eutectic solution, which has been pretreated by dispersion, is slowly injected. The injection is stopped when the liquid level is more than 2 cm above the carrier layer. The vacuum degree is maintained at -0.095 MPa for 60 minutes. The catalyst is dried under reduced pressure at 50°C for 4 hours and then treated at 80°C under a nitrogen atmosphere for 2 hours to obtain the supported catalyst.

[0110] S3: The supported catalyst was dispersed in an ethanol-water mixture (volume ratio 7:3) with a solid content of 20 wt%; the dispersed supported catalyst was then injected into a microchannel reactor after plasma cleaning.

[0111] After being evenly spread, the coating is dried at 80°C for 2 hours, and then heat-treated at 150°C in a nitrogen atmosphere for 1 hour. The final coating thickness ranges from 20 to 80 μm.

[0112] S4: Ethylene oxide and carbon dioxide are mixed at a molar ratio of 1:1.6, preheated to 60°C, and introduced into a microchannel reactor; the reaction temperature is 100°C, the pressure is 2.0 MPa, and the residence time is 25 min; then separated by vacuum distillation to obtain ethylene carbonate.

[0113] Comparative Example 1

[0114] A process for preparing ethylene carbonate is as follows:

[0115] The preparation steps are the same as in Example 1, except that the eutectic solvent in step S1 is not modified using KH550.

[0116] Comparative Example 2

[0117] A process for preparing ethylene carbonate is as follows:

[0118] The preparation steps are the same as in Example 1, except that the immobilization in step S2 is omitted. In step S3, the modified eutectic solution catalyst obtained in step S1 is directly injected into the microchannel reactor after plasma cleaning. After the reactor is filled, the process proceeds directly to step S4.

[0119] Comparative Example 3

[0120] A process for preparing ethylene carbonate is as follows:

[0121] The preparation steps are the same as in Example 1, except that a microchannel reactor is not used in step S3. Instead, the supported catalyst obtained in S2 is spread in a conventional reactor and then directly enters step S4.

[0122] Experimental Example 1

[0123] The reaction products obtained in Examples 1-5 and Comparative Examples 1-3 were sampled and quantitatively analyzed using gas chromatography. The chromatographic column was an Agilent DB-624 (30m × 0.32mm × 1.80μm), the detector was a flame ionization detector (FID), and the carrier gas was N2. The injection port temperature was 250℃, the detector temperature was 320℃, and the temperature program was: 80℃ held for 1 min, then increased to 260℃ at a rate of 60℃-min-1 and held for 14 min. Conversion and selectivity were calculated.

[0124] Ethylene oxide conversion rate:

[0125] Product yield:

[0126] Product selectivity:

[0127] In the above formula Represents the total amount of ethylene oxide before the reaction; N P This represents the total amount of ethylene oxide after the reaction; N i This represents the amount of ethylene carbonate produced.

[0128] Experiment Example 2

[0129] The conditions of Examples 1-5 and Comparative Examples 1-3 were subjected to 10 sequential cycles of reaction. The product yield and selectivity after each reaction were recorded according to Experimental Example 1. If the conversion or selectivity decreased to below 90% of the initial value, the catalyst was considered deactivated. The overall activity retention rate of the catalyst after 10 cycles was calculated using the following formula:

[0130]

[0131] The results of the comparative experiments of Experiment 1 and Experiment 2 are as follows:

[0132] Table 2 Comparison of experimental results between Examples 1-5 and Comparative Examples 1-3

[0133]

[0134]

[0135] The comparison results show that Comparative Example 1, without KH550 modification, failed to form a strong covalent interaction between the eutectic solvent and the porous silica medium during immobilization. This resulted in the easy loss of the effective contents of the catalyst supported on the support during subsequent reactions, impacting the catalyst's recyclability. Comparative Example 2, without immobilization, prevented the formation of microchannels using the porous silica medium, affecting both product yield and selectivity. However, its reaction without immobilization was a homogeneous catalytic reaction, compensating for some product yield. The severe catalyst loss and difficulty in recovery under homogeneous reaction conditions significantly reduced the catalyst's recyclability. Comparative Example 3, using a conventional reactor instead of a microchannel reactor, reduced the reaction efficiency per unit time, affecting both yield and selectivity for the same reaction time. Extending the reaction time would be necessary to improve product yield.

Claims

1. A process for the preparation of ethylene carbonate, characterized in that, It comprises the following steps: S1: The purified pretreated hydrogen bond acceptor and hydrogen bond donor are placed in an oil bath pot at a molar ratio of 1:1 and heated and stirred at 80°C until a colorless transparent solution is formed. A certain amount of modifier is added to the colorless transparent solution, and after stirring and reaction, it is cooled to room temperature and filtered to obtain solution catalyst A; the hydrogen bond acceptor is choline chloride, and the hydrogen bond donor is malonic acid; the modifier is 3% of the total mass of KH550; S2: The pretreated solid medium carrier is laid in a vacuum impregnation tank, and after being degassed, the pretreated dispersion solution catalyst A is slowly injected. After the liquid level is higher than the solid medium carrier by a certain height, the injection is stopped. After vacuum impregnation and then stage drying, solid catalyst B is obtained; the solid medium carrier is a porous silica medium carrier; the stage drying conditions are 50°C, 4 hours of reduced pressure drying, and then 80°C, 2 hours of nitrogen atmosphere treatment; S3: The solid catalyst B is dispersed in an ethanol-water mixture with a volume ratio of 7:3, and then the dispersed solid catalyst B is injected into the plasma cleaned microchannel reactor, evenly coated, dried, and heat treated to fix the solid catalyst B; S4: Ethylene oxide and carbon dioxide are mixed at a certain molar ratio, preheated, and then introduced into the microchannel reactor for reaction. The reaction product is separated by reduced pressure distillation to obtain ethylene carbonate.

2. The process for preparing ethylene carbonate according to claim 1, wherein The stirring reaction conditions in S1 are 80°C stirring reaction for 4 hours.

3. The preparation process of ethylene carbonate according to claim 1, characterized in that, The liquid level in S2 is higher than the solid medium carrier by more than 2 cm; The vacuum impregnation in S2 is carried out at a vacuum degree of -0.095 MPa for 60 minutes.

4. The preparation process of ethylene carbonate according to claim 1, characterized in that, The solid catalyst B in S3 is dispersed in an ethanol-water mixture, and the solid content of the solid catalyst B is 20 wt%; The drying and heat treatment in S3 are carried out at 80°C for 2 hours of drying and 150°C for 1 hour of nitrogen atmosphere heat treatment.

5. The process for preparing ethylene carbonate according to claim 4, wherein The final coating thickness of the solid catalyst B is in the range of 20-80 μm.

6. The process for preparing ethylene carbonate according to claim 1, wherein The mixing in S4 is at a molar ratio of 1:1-1:1.

8.

7. The preparation process of ethylene carbonate according to claim 1, characterized in that, The preheating in S4 reaches a final temperature of 60°C; The reaction in S4 is carried out at a reaction temperature of 80-100°C, a pressure of 1.5-2.0 MPa, and a residence time of 15-30 minutes.

8. A process for the preparation of ethylene carbonate according to any one of claims 4, 5, 6 or 7, characterized in that, The microchannel reactor is a multi-layer serpentine flow channel structure.

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