A method for preparing ethylene carbonate by directly reacting carbon dioxide and ethylene glycol

Abstract

The application provides a method for preparing ethylene carbonate (EC) by directly reacting carbon dioxide (CO2) and ethylene glycol (EG). CO2, EG, 2-cyanopyridine (2-CP) and a catalyst are mixed, and under the action of the catalyst, CO2 and ethylene glycol undergo a cyclization dehydration reaction to obtain an ethylene carbonate (EC) product with high selectivity and high yield; meanwhile, the hydration reaction of the dehydration agent 2-CP is coupled, and 2-CP is hydrated to generate 2-pyridinecarboxamide (2-PA); 2-PA is separated and further prepared through a dehydration reaction to generate 2-CP for recycling. The method can avoid the problems in the traditional production method of EC, such as harsh reaction conditions, difficult product separation, expensive raw materials and environmental pollution, and is an economical and environment-friendly EC production method, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, specifically to a method for preparing ethylene carbonate by direct reaction of carbon dioxide and ethylene glycol, wherein the method uses a cobalt-cerium bimetallic catalyst as the catalyst. Background Technology

[0002] Ethylene carbonate (EC) is an important organic carbonate with excellent physical and chemical properties, making it applicable in multiple fields. For example, EC can be used as a decarbonizing agent in natural gas and syngas; as a good absorbent and solvent for organic matter; as an electrolyte in lithium-ion batteries; and also as a plasticizer, spinning solvent, oily solvent, and extractant for olefins and aromatic hydrocarbons. EC is an environmentally friendly chemical raw material with numerous production processes that continuously evolve to meet market demands.

[0003] Methods for synthesizing ethylene carbonate mainly include: phosgene synthesis, transesterification, haloalcohol synthesis, direct oxidation of ethylene and carbon dioxide, cycloaddition of ethylene oxide and carbon dioxide, and urea alcoholysis. Patent CN113842858A discloses a reaction tower with a shallow reaction pool, using urea alcoholysis to prepare ethylene carbonate. The staged reaction significantly improves the yield of ethylene carbonate, reaching over 95%. However, this method is costly, and the byproduct ammonia gas leads to catalyst deactivation or dissolution, and the separation process is complex. Patent CN107915707A discloses a method for preparing ethylene carbonate using a bimetallic catalyst of M1O and M2O (where M1 is selected from at least one of Ca, Mg, Sr, or Ba; and M2 is selected from at least one of Zr or Ti) via the cycloaddition of ethylene oxide and carbon dioxide. This method improves catalytic activity, achieving a 96.8% ethylene oxide conversion rate and a 98.7% ethylene carbonate selectivity. However, this method requires harsh operating conditions, the raw material ethylene oxide has a high risk factor, and produces many byproducts. Other preparation methods also have their own serious drawbacks. For example, the phosgene method uses highly toxic raw materials, and the byproducts corrode equipment; the transesterification method uses expensive raw materials, and the production process causes significant environmental pollution; the haloalcohol method requires harsh reaction conditions and produces many byproducts; and the direct oxidation of ethylene and carbon dioxide is a complex process with an explosion risk.

[0004] The direct synthesis of ethylene carbonate from carbon dioxide and ethylene glycol is a promising approach that balances economic efficiency and environmental friendliness. This method has already been successfully implemented in the reaction of monoalcohols (such as methanol and ethanol) with carbon dioxide. Therefore, exploring suitable reaction conditions and modifying catalyst preparation methods to obtain high-yield, highly selective ethylene carbonate under milder conditions is a crucial step in promoting the development of the carbonate industry. Summary of the Invention

[0005] This invention proposes a novel method for preparing ethylene carbonate, utilizing cobalt-doped cerium dioxide as a catalyst to achieve the esterification reaction of CO2 with ethylene glycol and coupled with a 2-CP dehydration reaction. This method overcomes many drawbacks of traditional production methods, such as expensive raw materials, harsh reaction conditions, difficult product separation, and environmental pollution, achieving both economic efficiency and environmental friendliness, and has broad application prospects.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for synthesizing ethylene carbonate using a cobalt-cerium bimetallic catalyst includes:

[0008] 1) CO2, EG, 2-cyanopyridine (2-CP) and catalyst are mixed, and CO2 reacts with ethylene glycol in the presence of the catalyst to produce ethylene carbonate (EC) product.

[0009] 2) Simultaneously, the hydration reaction of the dehydrating agent 2-CP is coupled, and 2-CP hydrates to generate 2-pyridinecarboxamide (2-PA).

[0010] Preferably, the Co-CeO2 catalyst is prepared by the following method:

[0011] Cobalt(II) nitrate hexahydrate and cerium(III) nitrate hexahydrate with a cobalt-cerium atomic molar ratio of 0.03–0.1:1 were dissolved in deionized water to obtain a mixed solution. This mixed solution was added dropwise to an aqueous NaOH solution and stirred at 20–40 °C for 20–40 min. The mixture was then transferred to a hydrothermal reactor and aged for 10–15 h. The turbid liquid was separated by centrifugation, and then washed, dried, and calcined to obtain a Co-CeO2 catalyst with a target concentration of 3–10%.

[0012] The washing, drying, and calcination processes are as follows:

[0013] The product was washed with anhydrous ethanol and deionized water until neutral, freeze-dried for 20–30 h, and finally calcined in air at 550–650 °C for 3–10 h.

[0014] Preferably, the divalent cobalt salt or its hydrate is cobalt(II) nitrate hexahydrate;

[0015] The trivalent cerium salt or its hydrate is cerium(III) nitrate hexahydrate.

[0016] Ethylene carbonate was prepared by catalyzing the reaction of CO2 and ethylene glycol with a 5% Co-CeO2 catalyst in the presence of a certain amount of solvent and the dehydrating agent 2-cyanopyridine (2-CP). The catalyst dosage was 0.1 g-0.5 g, the reaction pressure was 1 MPa-4 MPa, the reaction temperature was 100℃-160℃, the reaction time was 0.5 h-5 h, and the stirring speed was 400-800 rpm.

[0017] The solvent in the scheme is one of tetrahydrofuran (THF), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO), preferably DMF.

[0018] Preferably, the molar ratio of ethylene glycol to 2-CP is 1:1.5 to 3;

[0019] The ratio of ethylene glycol to solvent is 1-3 mmol: 1-4 mL;

[0020] The ratio of the Co-CeO2 catalyst to the ethylene glycol is 1–3 g: 50–150 mmol.

[0021] Preferably, the reaction pressure is 1 MPa-4 MPa, the reaction temperature is 100℃-160℃, and the reaction time is 0.5h-5h. More preferably, the reaction pressure is 3-4 MPa, the reaction temperature is 120-140℃, and the reaction time is 1-2h.

[0022] Preferably, the reaction is carried out at a rotational speed of 400-800 rpm.

[0023] Preferably, the method further includes the following steps:

[0024] 2-PA was separated from the product and further dehydrated to obtain 2-CP for recycling.

[0025] The reaction equation for this process is:

[0026]

[0027] Figure 3 This is the reaction mechanism of the present invention.

[0028] The advantages of using the method described in this invention are:

[0029] (1) The catalyst prepared by this invention is small in size and has a uniform nanorod structure with numerous oxygen vacancies and acid-base sites on its surface. It can effectively adsorb and activate ethylene glycol and CO2, and can effectively catalyze the reaction of ethylene glycol and CO2. When combined with a dehydrating agent, it can obtain ethylene carbonate with high yield and selectivity.

[0030] (2) The present invention uses a method for preparing ethylene carbonate by direct reaction of ethylene glycol and CO2. Compared with traditional methods, it overcomes the disadvantages of expensive raw materials, harsh reaction conditions, difficult product separation, and environmental pollution, and is suitable for industrial production. Attached Figure Description

[0031] The present invention will now be described in further detail with reference to the accompanying drawings.

[0032] Figure 1 This is a process flow diagram for preparing ethylene carbonate according to the present invention.

[0033] Figure 2 These are TEM images and particle size distributions of the 5% Co-CeO2 catalyst prepared in this invention.

[0034] Figure 3 This is the HAADF diagram of the 5% Co-CeO2 catalyst prepared in this invention.

[0035] Figure 4 This is a schematic diagram of the mechanism by which the 5% Co-CeO2 catalyst prepared in this invention catalyzes the reaction of CO2 and ethylene glycol to prepare ethylene carbonate. Detailed Implementation

[0036] Figure 1 The process flow diagram for preparing ethylene carbonate according to the present invention is as follows:

[0037] CO2, EG, catalyst, dehydrating agent, and solvent are mixed. Under the action of the catalyst, CO2 undergoes a cyclization dehydration reaction with ethylene glycol. After the reaction, gas-liquid separation is performed, and the resulting carbon dioxide is returned to the cyclization dehydration reaction for reuse. The resulting liquid substance is further separated in a separation unit to obtain crude ethylene carbonate (EC) and a solution of 2-PA. The crude ethylene carbonate (EC) from the separation unit is purified to obtain the EC product. The 2-PA solution from the separation unit undergoes solvent recovery, and the obtained solvent is returned to the cyclization dehydration reaction for reuse. Simultaneously, the 2-PA after solvent recovery is regenerated by a dehydrating agent, and the resulting dehydrating agent is reused in the cyclization dehydration reaction. The entire process achieves the reuse of dehydrating agent and solvent.

[0038] The catalyst and catalytic reaction in this invention are further illustrated below with reference to specific embodiments. These embodiments are implemented based on the technical solution of this invention, providing detailed implementation methods and processes. However, the scope of protection of this invention includes, but is not limited to, the following embodiments.

[0039] Example 1

[0040] Cobalt(II) nitrate hexahydrate and cerium(III) nitrate hexahydrate (with a cobalt-cerium atomic molar ratio of 0.05:1, wherein the mass of cerium(III) nitrate hexahydrate was 4.3 g) were dissolved in 25 ml of deionized water, while 48 g of NaOH was dissolved in 175 ml of deionized water. The mixed solution of cerium nitrate and cobalt nitrate was added dropwise to the NaOH solution, stirred at room temperature for 30 min, and then transferred to a hydrothermal reactor for aging for 12 h. The turbid liquid was separated by centrifugation, and the product was washed with anhydrous ethanol and deionized water until neutral, and then freeze-dried for 24 h. Finally, it was calcined in air at 600 °C for 5 h to obtain the target 5% Co-CeO2 catalyst. The TEM image and particle size distribution of the catalyst are shown in [Figure number missing]. Figure 1 See HAADF chart Figure 2 ,Depend on Figure 1 and Figure 2 It can be seen that the obtained Co-CeO2 catalyst has a small size and a uniform nanorod structure.

[0041] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of ethylene glycol was 10 mmol, the amount of DMSO solvent was 10 ml, the amount of 2-CP was 20 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0042] Example 2

[0043] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0044] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of ethylene glycol was 10 mmol, the amount of dioxane solvent was 10 ml, the amount of 2-CP was 20 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0045] Example 3

[0046] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0047] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of ethylene glycol was 10 mmol, the amount of THF solvent was 10 ml, the amount of 2-CP was 20 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0048] Example 4

[0049] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0050] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of ethylene glycol was 10 mmol, the amount of NMP solvent was 10 ml, the amount of 2-CP was 20 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0051] Example 5

[0052] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0053] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of ethylene glycol was 10 mmol, the amount of DMF solvent was 10 ml, the amount of 2-CP was 20 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0054] Example 6

[0055] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0056] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of ethylene glycol was 10 mmol, the amount of DMF solvent was 10 ml, the amount of 2-CP was 30 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0057] Example 7

[0058] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0059] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of ethylene glycol was 5 mmol, the amount of DMF solvent was 10 ml, the amount of 2-CP was 30 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Back-sampling was performed for GC analysis, and the results, based on the ratio of reactants to products, are shown in Table 1.

[0060] Example 8

[0061] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0062] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of ethylene glycol was 15 mmol, the amount of DMF solvent was 10 ml, the amount of 2-CP was 30 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0063] Example 9

[0064] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0065] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of ethylene glycol was 10 mmol, the amount of DMF solvent was 5 ml, the amount of 2-CP was 30 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Back-sampling was performed for GC analysis, and the results, based on the ratio of reactants to products, are shown in Table 1.

[0066] Example 10

[0067] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0068] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of ethylene glycol was 10 mmol, the amount of DMF solvent was 15 ml, the amount of 2-CP was 30 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0069] Example 11

[0070] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0071] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of ethylene glycol was 10 mmol, the amount of DMF solvent was 10 ml, the amount of 2-CP was 15 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0072] Example 12

[0073] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0074] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of ethylene glycol was 10 mmol, the amount of DMF solvent was 10 ml, the amount of 2-CP was 20 mmol, the amount of catalyst was 0.15 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0075] Example 13

[0076] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0077] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of ethylene glycol was 10 mmol, the amount of DMF solvent was 10 ml, the amount of 2-CP was 20 mmol, the amount of catalyst was 0.25 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0078] Example 14

[0079] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0080] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of ethylene glycol was 10 mmol, the amount of DMF solvent was 10 ml, the amount of 2-CP was 20 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 3 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0081] Example 15

[0082] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0083] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of ethylene glycol was 10 mmol, the amount of DMF solvent was 10 ml, the amount of 2-CP was 20 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 2 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0084] Example 16

[0085] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0086] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of ethylene glycol was 10 mmol, the amount of DMF solvent was 10 ml, the amount of 2-CP was 20 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 4 MPa, the reaction temperature was 130 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0087] Example 17

[0088] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0089] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of ethylene glycol was 10 mmol, the amount of DMF solvent was 10 ml, the amount of 2-CP was 20 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 4 MPa, the reaction temperature was 110 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0090] Example 18

[0091] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0092] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of ethylene glycol was 10 mmol, the amount of DMF solvent was 10 ml, the amount of 2-CP was 20 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 2 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0093] Example 19

[0094] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0095] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of ethylene glycol was 10 mmol, the amount of DMF solvent was 10 ml, the amount of 2-CP was 20 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 0.5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0096] Comparative Example 1

[0097] 4.3 g of cobalt(II) nitrate hexahydrate and cerium(III) nitrate hexahydrate (cobalt:cerium atomic molar ratio of 0.03:1) were dissolved in 25 mL of deionized water, while 48 g of NaOH was dissolved in 175 mL of deionized water. The cerium nitrate and cobalt nitrate mixed solution was added dropwise to the NaOH solution, stirred at room temperature for 30 min, and then transferred to a hydrothermal reactor for aging for 12 h. The turbid liquid was separated by centrifugation, and the product was washed with anhydrous ethanol and deionized water until neutral, and then freeze-dried for 24 h. Finally, it was calcined in air at 600 °C for 5 h to obtain the target 3% Co-CeO2 catalyst.

[0098] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 3% Co-CeO2 catalyst. The amount of ethylene glycol was 10 mmol, the amount of DMF solvent was 10 ml, the amount of 2-CP was 20 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0099] Comparative Example 2

[0100] 4.3 g of cobalt(II) nitrate hexahydrate and cerium(III) nitrate hexahydrate (cobalt:cerium atomic molar ratio 0.1:1) were dissolved in 25 mL of deionized water, while 48 g of NaOH was dissolved in 175 mL of deionized water. The mixed solution of cerium nitrate and cobalt nitrate was added dropwise to the NaOH solution, stirred at room temperature for 30 min, and then transferred to a hydrothermal reactor for aging for 12 h. The turbid liquid was separated by centrifugation, and the product was washed with anhydrous ethanol and deionized water until neutral, and then freeze-dried for 24 h. Finally, it was calcined in air at 600 °C for 5 h to obtain the target 10% Co-CeO2 catalyst.

[0101] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 10% Co-CeO2 catalyst. The amount of ethylene glycol was 10 mmol, the amount of DMF solvent was 10 ml, the amount of 2-CP was 20 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0102] Comparative Example 3

[0103] Aluminum(III) nonahydrate and cerium(III) hexahydrate (4.3 g) with an aluminum-cerium atomic molar ratio of 0.05:1 were dissolved in 25 mL of deionized water, while 48 g of NaOH was dissolved in 175 mL of deionized water. The cerium nitrate and aluminum nitrate mixed solution was added dropwise to the NaOH solution, stirred at room temperature for 30 min, and then transferred to a hydrothermal reactor for aging for 12 h. The turbid liquid was separated by centrifugation, and the product was washed with anhydrous ethanol and deionized water until neutral, and then freeze-dried for 24 h. Finally, it was calcined in air at 600 °C for 5 h to obtain the target 5% Al-CeO2 catalyst.

[0104] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using 5% Al-CeO2 catalysis. The amount of ethylene glycol was 10 mmol, the amount of DMF solvent was 10 ml, the amount of 2-CP was 20 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0105] Comparative Example 4

[0106] Copper(II) nitrate trihydrate and cerium(III) nitrate hexahydrate (4.3 g) with an atomic molar ratio of 0.05:1 were dissolved in 25 mL of deionized water, while 48 g of NaOH was dissolved in 175 mL of deionized water. The cerium nitrate and copper nitrate mixed solution was added dropwise to the NaOH solution, stirred at room temperature for 30 min, and then transferred to a hydrothermal reactor for aging for 12 h. The turbid liquid was separated by centrifugation, and the product was washed with anhydrous ethanol and deionized water until neutral, and then freeze-dried for 24 h. Finally, it was calcined in air at 600 °C for 5 h to obtain the target 5% Cu-CeO2 catalyst.

[0107] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Cu-CeO2 catalyst. The amount of ethylene glycol was 10 mmol, the amount of DMF solvent was 10 ml, the amount of 2-CP was 20 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0108] Comparative Example 5

[0109] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0110] Propylene carbonate was prepared by reacting CO2 and 1,3-propanediol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of 1,3-propanediol was 10 mmol, the amount of DMF solvent was 10 ml, the amount of 2-CP was 20 mmol, the amount of catalyst was 0.2 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis, and the reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0111] Comparative Example 6

[0112] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0113] Glyceryl carbonate was prepared by reacting CO2 and glycerol in a 50 ml stirred tank lined with polytetrafluoroethylene (PTFE) using a 5% Co-CeO2 catalyst. The amount of glycerol was 10 mmol, the amount of DMF solvent was 10 ml, the amount of 2-CP was 30 mmol, the amount of catalyst was 0.34 g, the reaction pressure was 4 MPa, the reaction temperature was 140 °C, the reaction time was 5 h, and the stirring speed was 500 rpm. Reaction samples were taken for GC analysis, and the results, based on the ratio of reactants to products, are shown in Table 1.

[0114] Comparative Example 7

[0115] The preparation method of the 5% Co-CeO2 catalyst is the same as in Example 1.

[0116] Ethylene carbonate was prepared by reacting CO2 and ethylene glycol in a 50 ml stirred tank with 5% Co-CeO2 catalyst. The amount of ethylene glycol was 12 g, 2-CP was 15 g, and catalyst was 0.2 g. The reaction pressure was 2 MPa, the reaction temperature was 130 °C, the reaction time was 6 h, and the stirring speed was 500 rpm. Samples were taken for GC analysis. The reaction results, based on the ratio of reactants to products, are shown in Table 1.

[0117] Table 1. Reaction results of Examples 1-19 and Comparative Examples 1-7

[0118]

[0119]

[0120] As shown in Table 1, using 5% Co-CeO2 as a catalyst and 2-CP as a dehydrating agent, the direct synthesis of EC from ethylene glycol and carbon dioxide under the solvation effect of DMF can achieve a high yield of EC while producing very few byproducts. Furthermore, this method is also applicable to the reaction of other polyols with carbon dioxide. This demonstrates that the present invention is a highly efficient method for synthesizing cyclic carbonates and holds promise for industrial applications.

Claims

1. A method for preparing ethylene carbonate by direct reaction of carbon dioxide and ethylene glycol, characterized in that: include: 1) CO2, EG, 2-cyanopyridine (2-CP) and catalyst are mixed, and CO2 reacts with ethylene glycol in the presence of the catalyst to produce ethylene carbonate (EC) product. 2) Simultaneously, the hydration reaction of the dehydrating agent 2-CP is coupled, and 2-CP hydrates to generate 2-pyridinecarboxamide (2-PA). The catalyst is a Co-CeO2 catalyst, which has a nanorod structure and is prepared using the following method: A mixed solution was obtained by dissolving divalent cobalt salt or its hydrate and trivalent cerium salt or its hydrate in deionized water with a cobalt-cerium atomic molar ratio of 0.03~0.05:

1. The mixed solution was added dropwise to NaOH aqueous solution and stirred at 20~40℃ for 20~40 min. The solution was then transferred to a hydrothermal reactor and aged for 10~15 h. The turbid liquid was separated by centrifugation, and then washed, dried and calcined to obtain the target 3~5% Co-CeO2 catalyst. The reaction is carried out in a solvent, namely N,N-dimethylformamide; The product was washed with anhydrous ethanol and deionized water until neutral, freeze-dried for 20-30 h, and finally calcined in air at 550-650 ℃ for 3-10 h.

2. The method according to claim 1, characterized in that, The divalent cobalt salt or its hydrate is cobalt(II) nitrate hexahydrate; The trivalent cerium salt or its hydrate is cerium(III) nitrate hexahydrate.

3. The method according to claim 1, characterized in that, The molar ratio of ethylene glycol to 2-cyanopyridine is 1:1.5~3; The ratio of ethylene glycol to solvent is 1-3 mmol: 1-4 mL; The ratio of the Co-CeO2 catalyst to the ethylene glycol is 1~3g:50~150 mmol.

4. The method according to claim 1, characterized in that, The reaction pressure is 1 MPa to 4 MPa, the reaction temperature is 100℃ to 160℃, and the reaction time is 0.5 h to 5 h.

5. The method according to claim 4, characterized in that, The reaction pressure is 3~4 MPa, the reaction temperature is 120~140℃, and the reaction time is 1~2 h.

6. The method according to claim 1, characterized in that, The reaction was carried out at a rotation speed of 400-800 rpm.

7. The method according to claim 1, characterized in that, It also includes the following steps: 2-PA was separated from the product and further dehydrated to obtain 2-CP for recycling.

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