A catalyst for preparing cyclic carbonates and a method for preparing cyclic carbonates.

Abstract

This invention discloses a catalyst for preparing cyclic carbonates and a method for preparing cyclic carbonates. The catalyst includes a main catalyst and a co-catalyst; the co-catalyst is a metal halide salt; the preparation method of the main catalyst is as follows: epichlorohydrin and ethylene oxide are added dropwise to an amino polyether at 30-80°C, and the reaction is maintained at this temperature for 1.0-5.0 h after the addition is complete. Then, a quaternizing agent is added, and the reaction is carried out at 80-120°C and 0.1-0.4 MPa for 1.0-8.0 h. This catalyst has high catalytic efficiency and good selectivity, and can promote the contact and reaction probability of epoxides and carbon dioxide in the liquid phase during the preparation of cyclic carbonates, thereby improving the reaction efficiency of cyclic carbonates.

Description

Technical Field

[0001] This invention relates to a catalyst for preparing cyclic carbonates and a method for preparing cyclic carbonates. Background Technology

[0002] The global climate and ecosystem changes caused by greenhouse gas emissions, primarily carbon dioxide (CO2), are receiving widespread attention, with annual global CO2 emissions reaching tens of billions of tons. Controlling CO2 emissions and its recovery, fixation, utilization, and recycling have become serious concerns for countries worldwide. Meanwhile, from a resource utilization perspective, CO2 is the world's most abundant and inexpensive C1 (carbon-1) resource. Therefore, vigorously developing green CO2 utilization technologies, developing a green, high-tech, and fine chemical industry chain, and increasing product added value are of great significance.

[0003] Cyclic carbonates, especially ethylene / propylene carbonate, are basic chemical raw materials that can be used in high-value-added fine chemicals such as lithium battery electrolytes, polycarbonates, non-isocyanate polyurethanes, biodegradable plastics, heterocyclic compounds, dimethyl carbonate, vinylene carbonate, chloroethylene carbonate, and fluoroethylene carbonate (Chen Songcong et al., Indirect Utilization of Carbon Dioxide: Research Progress on the Application of Ethylene Carbonate [J], Molecular Catalysis, 2010, 24(6), 556-568). Currently, the synthetic methods for cyclic carbonates include phosgene method, transesterification method, chlorohydrin method, urea alcoholysis method, and synthesis method using epoxides and CO2 (Yang Chao, Research on the Synthesis and Application of Ethylene Carbonate [D], Xi'an: Northwestern Polytechnical University, 2010). The direct cycloaddition synthesis method of CO2 and epoxides is one of the main methods for industrial mass production and is also the process route that best conforms to the scientific concepts of "atom economy" and "green chemistry".

[0004] Catalysts for the direct cycloaddition of CO2 and epoxides to synthesize cyclic carbonates can be broadly classified into homogeneous and heterogeneous catalysts. Homogeneous catalysts are characterized by low dosage, high catalytic efficiency, and mild reaction conditions, and include quaternary phosphate salts, quaternary ammonium salts, ionic liquids, alkali metal salts, and organometallic salts (Tan Yanan et al., Research progress on catalysts for the synthesis of ethylene carbonate from ethylene oxide and carbon dioxide [J], Chemical Industry and Engineering Progress, 2017, 36(S1):241-246.). Heterogeneous catalysts facilitate the separation of catalysts and reactants, reducing separation energy consumption and costs. In this context, heterogeneous catalysts mainly involve loading catalytically active catalysts onto materials such as silica, molecular sieves, zeolites, silicon-based materials, and polystyrene resins, or using metal oxides with Lewis acid and Lewis base active sites. Furthermore, MOF catalysts with abundant acid and base active sites and rich pores have been derived (Zhang Guangyu et al., Research progress on CO2 catalytic conversion to propylene carbonate: catalyst design, performance and reaction mechanism [J]. Chemical Industry and Engineering Progress, 2022, 41(S1):177-189.).

[0005] The aforementioned catalysts exhibit excellent catalytic activity and selectivity in the addition reaction of CO2 and epoxides, but some problems and shortcomings also exist. Currently, homogeneous catalysts are mainly used in the industrial application of cyclic carbonates. The main problems are the large amount of homogeneous catalysts required and the high energy consumption for separation from the reaction liquid. Heterogeneous catalysts are still in the theoretical research stage, and the main problems they face include the following: First, the preparation process of heterogeneous catalysts is relatively complex; catalysts supported by physical adsorption or complexation are easily incorporated into the reaction liquid, leading to a decrease in catalytic efficiency. Second, ethylene carbonate itself is a high-performance organic solvent; using resin as a support, it is also prone to continuous dissolution in the high-temperature reaction liquid, leading to structural damage and performance degradation of the catalyst itself. Third, when using zeolites, molecular sieves, etc., as support carriers, the processing and shaping of the catalyst is a significant problem. Furthermore, the reaction process of CO2 and epoxides is a supercritical vapor-liquid interface reaction, which places higher demands on the contact and mixing of materials. Current research on homogeneous or heterogeneous catalysts rarely addresses how to improve material contact and mixing through catalyst modification. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a catalyst for the preparation of cyclic carbonates, which has high catalytic efficiency and good selectivity, and can promote the contact and reaction probability of epoxides and carbon dioxide in the liquid phase during the preparation of cyclic carbonates, thereby improving the reaction efficiency of cyclic carbonates.

[0007] The present invention also provides a method for preparing cyclic carbonates, using the catalyst described in the present invention as the catalyst. This method achieves high selectivity and high yield of cyclic carbonates in the simplest and most economical way.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A catalyst for preparing cyclic carbonates includes a main catalyst and a co-catalyst; the co-catalyst is a metal halide salt; the main catalyst is prepared as follows: epichlorohydrin and ethylene oxide are added dropwise to an amino polyether at 30-80℃, and the reaction is maintained at this temperature for 1.0-5.0 h after the addition is complete, then a quaternizing agent is added, and the reaction is carried out at 80-120℃ and 0.1-0.4 MPa for 1.0-8.0 h.

[0010] The mass ratio of the main catalyst to the co-catalyst is 5 to 10:1; the molar ratio of the amino polyether, epichlorohydrin, ethylene oxide and quaternizing agent is 1:x:(c+2-x):x, where x≤(c+2) and c is a positive integer between 0 and 9.

[0011] The structural formula of the amino polyether is as follows: Among them, R 1 It is one of H, CH3, and CH3CH2; a is a positive integer between 0 and 10; b is a positive integer between 3 and 40; c is a positive integer between 0 and 9.

[0012] The quaternizing agent is an alkyl tertiary amine, preferably one of trimethylamine or triethylamine.

[0013] The cocatalyst is at least one of sodium bromide, potassium bromide, zinc bromide, ferrous bromide, ferric bromide, cuprous bromide, copper bromide, chromium bromide, tin bromide, cobalt bromide, sodium iodide, potassium iodide, zinc iodide, ferrous iodide, ferric iodide, cuprous iodide, copper iodide, chromium iodide, tin iodide, and cobalt iodide.

[0014] The structural formula of the main catalyst is: Among them, R 1 It is one of H and CH3; R 2 It is one of CH3 and CH3CH2-; a is a positive integer between 0 and 10; b is a positive integer between 3 and 40; c is a positive integer between 0 and 9; d ≤ c and is a positive integer.

[0015] The present invention also provides a method for preparing cyclic carbonates, the method comprising the following steps: mixing the catalyst of the present invention with a complexing stabilizer and a base cyclic carbonate, and under the protection of an inert gas, introducing epoxides and carbon dioxide, and reacting at 110-150°C and 0.1-2.0 MPa for 1.0-1.5 h.

[0016] The cyclic carbonate prepared by the method is ethylene carbonate (EC) or propylene carbonate (PC).

[0017] The carbon dioxide purity is ≥99.9%.

[0018] The epoxides have a water content ≤1000ppm, a gas phase purity ≥99%, and an aldehyde content ≤100ppm, including one of ethylene oxide (EO) and propylene oxide (PO).

[0019] The complexing stabilizer is a cyclic crown ether, including one of 12-crown-4, 15-crown-5, and 18-crown-6 crown ethers. Crown ethers are cyclic heterocyclic macromolecules with extremely high thermal stability, and have good complexing ability and stabilizing effect on both quaternary ammonium salts and metal halide salts, which can improve the catalytic effect of the catalyst to a certain extent.

[0020] The cyclic carbonate used as a base is the same as the prepared cyclic carbonate; that is, if the prepared cyclic carbonate is ethylene carbonate, then ethylene carbonate is used as the base, and if the prepared cyclic carbonate is propylene carbonate, then propylene carbonate is used as the base. The base cyclic carbonate is an excellent solvent for carbon dioxide and epoxides, enhancing their solubility in the liquid phase and promoting their contact and reaction.

[0021] The mass ratio of the alkyl epoxide to carbon dioxide is 1:1.1 to 2.0; the amount of catalyst used is 1% to 5% of the mass of the alkyl epoxide; the amount of crown ether used is 0.1% to 0.5% of the mass of ethylene oxide; and the amount of the base cyclic carbonate used is 10% to 20% of the mass of the alkyl epoxide.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The catalyst for preparing cyclic carbonates provided by the present invention is obtained by chemically synthesizing quaternary ammonium salt groups onto polyether macromonomers. The molecular structure of the main catalyst contains quaternary ammonium salt groups, tertiary amine groups, hydroxyl groups, and ether bonds. It can not only exert the catalytic effect of quaternary ammonium salt, but also the oxygen atoms in the tertiary amine groups, hydroxyl groups, and ether bonds have a certain complexing effect, which can stabilize the ion pairs of the quaternary ammonium salt catalyst and ensure the catalytic effect of the catalyst.

[0024] 2. The catalyst provided by this invention for preparing cyclic carbonates contains a basic tertiary amine group in its main catalyst structure, which has a good adsorption effect on acidic carbon dioxide gas, and can promote the contact and reaction probability of cyclic alkane and carbon dioxide in the liquid phase during the preparation of cyclic carbonates, thereby improving the reaction efficiency of cyclic carbonates.

[0025] 3. The co-catalyst in the catalyst for preparing cyclic carbonates provided by the present invention mainly serves to provide the main catalyst with halide ions such as bromine and iodine with large ionic radii, which exchange with chloride ions in the quaternary ammonium salt to form brominated quaternary ammonium salt and iodinated quaternary ammonium salt with higher catalytic activity.

[0026] 4. In the method for preparing cyclic carbonates provided by the present invention, cyclic crown ethers are used as complexing stabilizers, which have excellent complexing and coordination effects on cations such as metal ions, and can significantly enhance the stability of quaternary ammonium salt ion pairs, thus ensuring the catalytic effect of the catalyst.

[0027] 5. The catalytic system provided by the present invention, which combines the main catalyst and the co-catalyst, achieves the preparation of cyclic carbonates with high selectivity and high yield in the simplest and most economical way. Attached Figure Description

[0028] Figure 1 A schematic diagram of the main catalyst;

[0029] Figure 2 This is a GC test result of the ethylene carbonate reaction solution in Example 2;

[0030] Figure 3 This is a GC test image of the ethylene carbonate reaction solution in Example 6. Detailed Implementation

[0031] The preparation methods of the amino polyethers in each embodiment include the following steps:

[0032] (1) Preparation of polyether: Weigh the initiator R in sequence 1 1 mol of -OH and 0.01 mol of potassium hydroxide catalyst were added to the polyether reaction apparatus. The apparatus was purged with nitrogen three times and then evacuated to -0.1 MPa. The reaction apparatus was heated to 110°C, and 1 mol of propylene oxide and 1 mol of ethylene oxide were introduced sequentially. During the feeding process, the temperature of the reaction apparatus was controlled at 140±10°C and the pressure at 0.3±0.1 MPa. After the feeding was completed, the reaction was continued at this temperature for 1.0 h. The temperature was then lowered to 70±10°C and the product was discharged, yielding a light brownish-yellow liquid with a certain viscosity, which is the polyether. The structural formula of the polyether is: R 1 It is either H or CH3; a is a positive integer between 0 and 10; b is a positive integer between 3 and 40;

[0033] (2) Preparation of chlorinated polyether: Weigh 1.0 mol of polyether and add it to a three- or four-necked glass reaction flask. Connect the stirring and reflux condenser and seal the flask. Turn on the stirring and heat to 100℃. Volatilize at 100℃ and -0.1 MPa for 1.0 h to remove water and other volatile components from the polyether. Then pressurize with nitrogen to atmospheric pressure and cool the reaction flask to 80℃. Under N2 protection, add 1.3 mol of chlorinated reagent SOCl2 dropwise to the reaction over 1.0 h at a temperature of 80±10℃. After the addition is complete, continue the reaction at this temperature for 2.0 h, then volatilize at 80±10℃ and -0.1 MPa for 1.0 h to remove acidic gases, unreacted chlorinated reagents, and other volatile components from the reaction system, resulting in a brownish-red liquid with a certain viscosity, which is the chlorinated polyether.

[0034] The structural formula of the chlorinated polyether is as follows:

[0035] (3) Preparation of amino polyether: In a pressurized reactor equipped with a thermometer, stirrer, nitrogen and vacuum lines, 0.5 mol of chlorinated polyether, 0.5 mol of amination reagent, and 1 × 10⁻⁶ tetraethylammonium chloride (quaternary ammonium salt) catalyst were added sequentially. -4 The solution was added in mol, then diluted with deionized water to a solid content of 80±20%. Nitrogen was purged three times and then evacuated to -0.1 MPa. The reaction apparatus was heated to 140±20℃, and nitrogen was added to pressurize to 0.3±0.1 MPa. The reaction was maintained at this temperature for 10.0 h. After the reaction was complete, the reaction system was cooled to 100±10℃ and volatilized at -0.1 MPa for 1.0 h to remove water and other volatile components, yielding a wine-red liquid with a certain viscosity, which is the amino polyether. The amination reagent includes any one of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethylenepolyamine, and polyethyleneimine. All the above amination reagents are chemically pure and purchased from Aladdin Reagents.

[0036] The main catalyst described in this invention is a supported quaternary ammonium salt, and the quaternization conversion rate is tested using chemical titration. Since the C-Cl bond is very stable and will not react with silver nitrate to form a precipitate, only the quaternized chloride ions can react with silver nitrate to form silver chloride precipitate. Based on this characteristic, chemical titration is used to test the quaternary ammonium salt conversion rate. The silver nitrate titration method in the national standard GB / T13025.5-2012 "General Test Methods for Salt Industry: Determination of Chloride Ions" is used for testing. The chloride ion content in the quaternary ammonium salt is the chloride ion content in the quaternary ammonium salt obtained by subtracting the chloride ion content in the amino polyether from the chloride ion content participating in the reaction in the main catalyst. The percentage of this subtraction to the theoretical chloride ion content is the quaternization conversion rate.

[0037] The reaction solution of the cyclic carbonate described in this invention was tested using a Shimadzu 2030 gas chromatograph with an Agilent DB-1701 column (column length * inner diameter * coating thickness: 30 μm * 0.53 mm * 0.50 μm). The sample was prepared using acetonitrile at a mass ratio of 1:1. The test conditions were: injection volume of 0.4 μL, split ratio of 20:1, injection port temperature set to 270 °C, detector temperature set to 290 °C, and column oven set to programmed temperature ramp (initial 100 °C, hold for 2 min, ramp to 120 °C at 10 °C / min, ramp to 220 °C at 20 °C / min, hold for 5 min, ramp to 240 °C at 20 °C / min, hold for 20 min). GC testing only recorded the percentage peak area of ​​key components such as alkylene oxides, ethylene / propylene glycol, diethylene / propylene glycol, and cyclic carbonates.

[0038] The present invention will now be described in detail with reference to the embodiments.

[0039] The amino polyethers and their codes are shown in Table 1 below.

[0040] Table 1. Raw materials and codes for amino polyethers

[0041]

[0042] Example 1 Synthesis of the main catalyst

[0043] 100 parts of amino polyether A-2 were weighed and added to a reactor. The reactor was heated to 80°C. 31.3 parts of epichlorohydrin and 5.6 parts of ethylene oxide were weighed and added dropwise to the reactor continuously under constant pressure, controlling the reaction temperature at 80±5°C. After the addition was complete, the reaction was maintained at this temperature for 1.0 h. 20.0 parts of trimethylamine were weighed and added to the reactor all at once. The reactor was sealed and purged with nitrogen three times. The reactor was heated to 80°C, the reaction pressure was set to 0.4 MPa, and the reaction was maintained at this temperature for 8.0 h. After the reaction was complete, a brownish-yellow liquid was obtained, which was the main catalyst, named ZC-2. The quaternization conversion rate was tested to be 97.6%.

[0044] Similarly, the main catalysts shown in Table 2 were prepared following the same reaction steps.

[0045] The raw material ratios and synthesis process parameters for the main catalyst are shown in Table 2.

[0046] Table 2. Raw material ratios and synthesis process parameters for the main catalyst (unit: parts by weight)

[0047]

[0048]

[0049] Example 2 Synthesis of Cyclic Carbonates

[0050] Weigh 10 parts of ethylene carbonate, 0.83 parts of main catalyst ZC-1, 0.17 parts of co-catalyst NaBr, and 0.5 parts of complexing stabilizer 12-crown-4, and add them sequentially to the reactor. Seal the reactor and perform nitrogen purging three times. Heat the reactor to 110℃. Weigh 100 parts of ethylene oxide (EO) and 110 parts of carbon dioxide, setting the CO2 feed rate to 1.1 times that of EO. Control the reaction temperature at 110±5℃ and the reaction pressure at 2.0MPa (the pressure difference is supplemented by nitrogen). After the feeding is complete, continue the reaction at this temperature for 1.0h to obtain a light brownish-yellow ethylene carbonate reaction solution. Take a sample for GC testing.

[0051] Similarly, the following cyclic carbonates were prepared by following the same reaction steps.

[0052] Table 3. Material ratios for the synthesis of cyclic carbonates (unit: parts by weight)

[0053]

[0054] The synthetic route for cyclic carbonates is shown below:

[0055]

[0056] The synthesis process parameters and GC test results for each embodiment are shown in Table 4.

[0057] Table 4. Synthesis process parameters and GC tests of cyclic carbonates

[0058]

[0059] Comparative Example 1

[0060] Weigh 20 parts of ethylene carbonate, 5 parts of polyethylene glycol, and 2.5 parts of KI catalyst into a reactor. Seal the reactor and purge with nitrogen three times. Heat the reactor to 150℃. Weigh 100 parts of ethylene oxide (EO) and 120 parts of carbon dioxide (CO2) as feed. Set the CO2 feed rate to 1.2 times that of EO. Control the reaction temperature at 150±5℃ and the reaction pressure at 1.5MPa (additional pressure is made up with nitrogen). After feeding, continue the reaction at this temperature for 1.0 h to obtain a light brownish-yellow ethylene carbonate reaction solution. Take a sample for GC testing (peak area percentage / %): ethylene glycol 5.5%, diethylene glycol 1.54%, ethylene oxide 0.45%, ethylene carbonate 92.51%.

[0061] In this comparative example, the main catalyst described in this invention was not used, nor was a cyclic crown ether used as a complexing stabilizer. Instead, a mixture of polyethylene glycol and potassium iodide was used as the catalyst, resulting in a low yield of ethylene carbonate.

[0062] Comparative Example 2

[0063] Weigh 15 parts of ethylene carbonate, 3.5 parts of the main catalyst tetrabutylammonium bromide, and 0.4 parts of the co-catalyst ZnBr into a reactor. Seal the reactor and purge with nitrogen three times. Heat the reactor to 140℃. The feed rate of ethylene oxide is 100 parts, and the feed rate of carbon dioxide is 130 parts. Set the CO2 feed rate to 1.3 times that of EO. Control the reaction temperature at 130±5℃ and the reaction pressure at 1.8MPa (the pressure is supplemented by nitrogen if necessary). After the feed is complete, continue the reaction at this temperature for 1.0 h to obtain a light brownish-yellow ethylene carbonate reaction solution. Perform GC analysis on a sample (peak area percentage / %): ethylene glycol 4.2%, diethylene glycol 1.72%, ethylene oxide 0.68%, ethylene carbonate 93.4%.

[0064] In this comparative example, unsupported tetrabutylammonium bromide was used as the main catalyst, and cyclic crown ethers were not used as complexing stabilizers, resulting in a low yield of ethylene carbonate.

[0065] Comparative Example 3

[0066] Weigh out 16 parts of propylene carbonate (PC), 2.4 parts of A-3, 0.8 parts of epichlorohydrin, 0.2 parts of ethylene oxide, 0.8 parts of triethylamine, 0.3 parts of KBr co-catalyst, and 0.3 parts of 18-crown-6, and add them sequentially to the reactor. Seal the reactor and purge with nitrogen three times. Heat the reactor to 150℃. Feed 100 parts of propylene oxide (PO) and 110 parts of carbon dioxide (CO2), setting the CO2 feed rate to 1.1 times that of PO. Control the reaction temperature at 150±5℃ and the reaction pressure at 1.3MPa (the pressure will be supplemented by nitrogen if necessary). After the feed is completed, the reaction is continued at a constant temperature for 1.0 h to obtain a light brownish-yellow propylene carbonate reaction solution. A sample is taken for GC testing (peak area percentage / %): propylene glycol 9.0%, dipropylene glycol 2.82%, propylene oxide 0.41%, propylene carbonate 87.77%.

[0067] In this comparative example, the main catalyst was directly replaced with a mixture of raw materials used in the preparation of the main catalyst, i.e., the main catalyst was not synthesized by chemical reaction beforehand, resulting in a lower yield of ethylene carbonate.

[0068] The above detailed description of a catalyst for preparing cyclic carbonates and a method for preparing cyclic carbonates, with reference to the embodiments, is illustrative rather than limiting. Several embodiments may be listed within the defined scope. Therefore, variations and modifications without departing from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A catalyst for preparing cyclic carbonates, characterized in that, It includes a main catalyst and a co-catalyst; the co-catalyst is a metal halide salt; the preparation method of the main catalyst is as follows: epichlorohydrin and ethylene oxide are added dropwise to amino polyether at 30-80℃, and the reaction is maintained at this temperature for 1.0-5.0h after the addition is completed, then a quaternizing agent is added, and the reaction is carried out at 80-120℃ and 0.1-0.4MPa for 1.0-8.0h; The structural formula of the main catalyst is: Among them, R 1 It is one of H, CH3, or CH3CH2; R 2 It is one of CH3 and CH3CH2-; a is a positive integer between 0 and 10; b is a positive integer between 3 and 40; c is a positive integer between 0 and 9; d ≤ c and is a positive integer.

2. The catalyst for preparing cyclic carbonates according to claim 1, characterized in that, The mass ratio of the main catalyst to the co-catalyst is 5 to 10:1; the molar ratio of the amino polyether, epichlorohydrin, ethylene oxide and quaternizing agent is 1:x:(c+2-x):x, where x≤(c+2) and c is a positive integer between 0 and 9.

3. The catalyst for preparing cyclic carbonates according to claim 1 or 2, characterized in that, The structural formula of the amino polyether is as follows: Among them, R 1 It is one of H, CH3, and CH3CH2; a is a positive integer between 0 and 10; b is a positive integer between 3 and 40; c is a positive integer between 0 and 9.

4. The catalyst for preparing cyclic carbonates according to claim 1 or 2, characterized in that, The quaternizing agent is an alkyl tertiary amine.

5. The catalyst for preparing cyclic carbonates according to claim 4, characterized in that, The quaternizing agent is one of trimethylamine and triethylamine.

6. The catalyst for preparing cyclic carbonates according to claim 1 or 2, characterized in that, The cocatalyst is at least one of sodium bromide, potassium bromide, zinc bromide, ferrous bromide, ferric bromide, cuprous bromide, copper bromide, chromium bromide, tin bromide, cobalt bromide, sodium iodide, potassium iodide, zinc iodide, ferrous iodide, ferric iodide, cuprous iodide, copper iodide, chromium iodide, tin iodide, and cobalt iodide.

7. A method for preparing a cyclic carbonate, characterized in that, The preparation method includes the following steps: mixing the catalyst described in any one of claims 1-6 with a complexing stabilizer and a base cyclic carbonate, and introducing epoxide and carbon dioxide under the protection of an inert gas, and reacting at 110-150°C and 0.1-2.0 MPa for 1.0-1.5 h.

8. The method for preparing cyclic carbonates according to claim 7, characterized in that, The complexing stabilizer is a cyclic crown ether; the cyclic carbonate used as a base is the same as the prepared cyclic carbonate.

9. The method for preparing cyclic carbonates according to claim 8, characterized in that, The mass ratio of the alkyl oxidant to carbon dioxide is 1:1.1 to 2.0; the amount of catalyst used is 1% to 5% of the mass of the alkyl oxidant; the amount of the cyclic crown ether used is 0.1% to 0.5% of the mass of the alkyl oxidant; and the amount of the base cyclic carbonate used is 10% to 20% of the mass of the alkyl oxidant.

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