A method for synthesizing cyclic carbonates by alcoholysis of urea

Abstract

The application provides a method for synthesizing cyclic carbonate by alcoholysis of urea, which comprises the following steps: urea and dihydric alcohol are used to synthesize cyclic carbonate under the action of an ionic liquid modified ceria catalyst, the molar ratio of the urea to the dihydric alcohol is 1:(1-5), the amount of the ionic liquid modified ceria catalyst is 1%-10% of the mass of the urea, the reaction temperature for synthesizing the cyclic carbonate is 130-170 DEG C, and the reaction pressure is 5-30 kPa. The method is simple to operate, does not need to add any solvent, the product is easy to separate from the catalyst, and continuous production can be easily realized; and the ionic liquid modified ceria catalyst used has simple preparation process, low cost, high catalytic performance, good selectivity and is easy to recycle.

Description

Technical Field

[0001] This invention relates to the field of chemical synthesis technology, and in particular to a method for synthesizing cyclic carbonates by urea alcoholysis. Background Technology

[0002] Cyclic carbonates are important environmentally friendly chemical products, serving as high-performance organic solvents in petrochemicals, cosmetics, gas separation, and electrochemistry. They are also a primary raw material for the production of dimethyl carbonate and polycarbonate. The main methods for synthesizing cyclic carbonates include the phosgene process, transesterification, CO2 cycloaddition, and urea alcoholysis. The traditional phosgene process has been phased out due to the highly toxic phosgene, complex processes, severe equipment corrosion, and significant environmental pollution. The transesterification process is also limited in industrial application due to the high cost of catalysts. The CO2 cycloaddition process is currently the mainstream process for synthesizing cyclic carbonates, but its widespread application is limited by the flammability and explosiveness of the raw material ethylene oxide, its small transport radius, and high explosion-proof requirements. In recent years, the urea alcoholysis process has become the greenest and most economical process for synthesizing cyclic carbonates due to its inexpensive and readily available raw materials, mild reaction conditions, low cost, and environmental friendliness.

[0003] The design and development of catalysts is a key research focus in the synthesis of cyclic carbonates from urea alcoholysis. Currently reported catalysts for urea alcoholysis mainly include metal salts, metal oxides, supported catalysts, and ionic liquids. Juanjuan Chen et al. investigated the catalytic activity of different ionic liquids in the reaction of urea and glycerol. Due to the synergistic effect of anions and cations, neutral ionic liquids exhibited better catalytic performance. Among them, under the reaction conditions of 50 mmol glycerol, 75 mmol urea, 3 mmol ionic liquid, 150℃, and 4 h, the highest yield of glycerol carbonate was only 52% (see Juanjuan Chen, et al. Ionic liquids as eco-friendly catalysts for converting glyceroland urea into high value-added glycerol carbonate. Chinese Journal of Catalysis, 2015, 36(3), 336-343). Liu Chunyan et al. used the ionic liquid [Bmim]BF4 for the synthesis of propylene carbonate, but the final content of propylene carbonate obtained was only 20.27% (see "The Role of Ionic Liquids in the Synthesis of Propylene Carbonate", Liu Chunyan et al., Vol. 18, No. 6, pp. 13-17). Qibiao Li et al. studied the catalytic performance of different metal oxides in the synthesis of ethylene carbonate from urea and ethylene glycol. Under the conditions of reaction temperature of 150℃ and reaction pressure of 11kPa for 3h, the yield of ethylene carbonate can reach 28.7-93.1%, but the preparation process of metal oxides is relatively complicated (see Qibiao Li, et al. Synthesis of cyclic carbonates from urea and diols over metal oxides. Catalysis Today, 2006, 115(1-4), 111-116).Xinqiang Zhao et al. reported the synthesis of ethylene carbonate from urea and ethylene glycol catalyzed by zinc-iron oxide catalyst ZnO / ZnFe2O4. Under optimal reaction conditions of 2.5 h reaction time, 150 °C reaction temperature, 1.5% catalyst mass fraction, and urea / ethylene glycol molar ratio of 1:8, the highest yield of ethylene carbonate was 66.1% (see Xinqiang Zhao, et al. Synthesis of ethylene carbonate from urea and ethylene glycol over zinc / iron oxide catalyst. Journal of Chemical Technology and Biotechnology, 2008, 83, 750-755). CN105664953A discloses a zinc chloride-iron oxide composite catalyst for the synthesis of ethylene carbonate from urea alcoholysis. Under conditions of 1%-5% catalyst dosage (by mass of total reactants), reaction pressure of 0.005-0.02 MPa, and reaction temperature of 120-150℃ for 3-9 hours, the yield of ethylene carbonate can reach 79.1-92.0%, but the preparation conditions of the composite catalyst are quite demanding. CN101544627A discloses a method for synthesizing organic carbonates. Under relatively demanding reaction conditions—a urea to ethylene glycol molar ratio of 1:1-100, a urea to calcium phosphorus catalyst mass ratio of 1:0.001-0.1, reaction temperature of 50-250℃, reaction pressure of 0.0001-0.5 MPa, and reaction time of 0.5-20 hours—the yield of propylene carbonate is 30.2%-98.5%. CN110156742A discloses a method for synthesizing cyclic carbonates from urea and diols using ionic liquid catalysis. This method employs a composite catalyst of imidazole ionic liquid and metal salt to catalyze the reaction of urea and diols to synthesize cyclic carbonates, achieving a yield of up to 94.1% and significantly improving catalytic performance. However, this homogeneous catalytic system suffers from separation difficulties, making it challenging to recover and recycle the catalytic components from the reaction system.

[0004] In summary, numerous catalysts for the synthesis of cyclic carbonates from urea alcoholysis have been reported, but they generally suffer from low catalytic efficiency, relatively complex preparation processes, and harsh reaction conditions. Therefore, there is a need to develop a heterogeneous catalytic system that is simple to prepare, low in cost, operates under mild reaction conditions, is highly efficient and stable, and is easily separable, to realize the industrial application of urea alcoholysis in the production of cyclic carbonates. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method uses an ionic liquid modified cerium dioxide catalyst to catalyze the synthesis of cyclic carbonates from urea and diols under specific reaction temperature and pressure conditions. The catalyst is simple to prepare, has stable performance, and is easy to separate and recycle. The obtained cyclic carbonate product has a high yield and high selectivity, and has broad application prospects.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] This invention provides a method for synthesizing cyclic carbonates by urea alcoholysis, the method comprising:

[0008] Cyclic carbonates are synthesized from urea and diols in the presence of an ionic liquid-modified cerium dioxide catalyst, according to the following general reaction formula:

[0009]

[0010] R1 and R2 are each selected from any one of C1 to C4 alkyl groups;

[0011] The molar ratio of urea to diol is 1:(1-5);

[0012] The amount of the ionic liquid-modified cerium dioxide catalyst used is 1% to 10% of the urea mass;

[0013] The reaction temperature for synthesizing the cyclic carbonate is 130–170 °C, and the reaction pressure is 5–30 kPa.

[0014] The method for synthesizing cyclic carbonates by urea alcoholysis according to this invention is simple to operate, requires no solvent, and utilizes an ionic liquid-modified cerium dioxide catalyst to catalyze the synthesis of cyclic carbonates from urea alcoholysis under reaction conditions of 130–170°C and 5–30 kPa. The ionic liquid-modified cerium dioxide catalyst used is low in cost, easy to separate, and environmentally friendly. Furthermore, compared to single cerium oxide or single ionic liquid, this ionic liquid-modified cerium dioxide catalyst exhibits significantly improved catalytic performance, with a selectivity exceeding 95%. The ionic liquid-modified cerium dioxide catalyst in the method described in this invention is easy to separate, facilitates continuous production, and has broad application prospects.

[0015] When the amount of ionic liquid-modified cerium dioxide catalyst is small, it cannot effectively catalyze the alcoholysis of urea to synthesize cyclic carbonates, resulting in a decrease in the yield of cyclic carbonates. This is related to the acid-base sites on the catalyst surface. When the amount of ionic liquid-modified cerium dioxide catalyst is large, it will increase the cost of synthesizing cyclic carbonates, resulting in poor economic efficiency.

[0016] When the reaction temperature for the synthesis of cyclic carbonates from urea alcoholysis is low, the yield of cyclic carbonates decreases because the reaction is endothermic, and low temperatures are not conducive to the synthesis of cyclic carbonates. Conversely, when the reaction temperature is too high, it will promote the decomposition of urea and the occurrence of side reactions, which will also reduce the yield of cyclic carbonates.

[0017] The molar ratio of urea to diol described in this invention is 1:(1 to 5), for example, it can be 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4 or 1:5, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] The amount of the ionic liquid modified cerium dioxide catalyst used is 1% to 10% of the urea mass, for example, it can be 1%, 2%, 3%, 5%, 7%, 8%, 9% or 10%, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] The reaction temperature for synthesizing the cyclic carbonate is 130–170°C, for example, it can be 130°C, 135°C, 140°C, 150°C, 155°C, 160°C or 170°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] The reaction pressure is 5 to 30 kPa, for example, it can be 5 kPa, 8 kPa, 10 kPa, 15 kPa, 20 kPa, 25 kPa or 30 kPa, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] Preferably, the diol includes any one of ethylene glycol, 1,2-propanediol, 1,2-butanediol, cyclohexanediol, catechol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 3-chloro-1,2-propanediol, or phenylethylene glycol.

[0022] Preferably, the reaction time for synthesizing the cyclic carbonate is 1 to 6 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 4.5 hours, 5 hours, or 6 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] Preferably, the feed molar ratio of urea to diol is 1:3.

[0024] Preferably, the amount of the ionic liquid-modified cerium dioxide catalyst used is 5% of the urea mass.

[0025] Preferably, the reaction temperature for synthesizing the cyclic carbonate is 160°C, the reaction pressure is 10 kPa, and the reaction time is 5 h.

[0026] Preferably, the preparation method of the ionic liquid modified cerium dioxide catalyst includes the following steps:

[0027] (1) Mix the ionic liquid, cerium salt and solvent, stir until the ionic liquid and cerium salt are completely dissolved, and then evaporate at a temperature of 30-80℃ to obtain a colloidal solution.

[0028] (2) Vacuum dry the gel-like solution described in step (1) to crystallize the solution;

[0029] (3) The crystallized product in step (2) is washed, centrifuged and dried in sequence to obtain the ionic liquid modified cerium dioxide catalyst.

[0030] The preparation method of the ionic liquid modified cerium dioxide catalyst of the present invention is simple to operate and low in cost. The reaction conditions are mild, and the ionic liquid modified cerium dioxide catalyst prepared by rotary evaporation at a temperature of 30-80°C has good catalytic performance, is environmentally friendly, has stable performance and is easy to recycle, and is suitable for mass production.

[0031] Preferably, the ionic liquid in step (1) comprises an imidazole salt and / or a quaternary phosphine salt, the structures of which are shown in formulas I and II below:

[0032]

[0033] In the structure of the ionic liquid, R3, R4, R5, and R6 are each selected from any one of C1 to C8 alkyl groups;

[0034] The rotary evaporation described in this invention is carried out at a temperature of 30 to 80°C, for example, 30°C, 40°C, 50°C, 55°C, 60°C, 65°C, 70°C, or 80°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] Preferably, anion X - It is selected from any one of the following anions: fluoride ion, chloride ion, bromide ion, iodide ion, hydroxide ion, tetrafluoroborate ion, hexafluorophosphate ion, carbonate ion, sulfate ion, hydrogen sulfate ion, hydrogen phosphate ion, bis(trifluoromethanesulfonyl)imide ion, formate ion, acetate ion, benzoate ion, p-toluenesulfonate ion, or alanine ion.

[0036] Preferably, the solvent in step (1) includes any one of water, ethanol, methanol, ethyl acetate, acetone, dimethyl sulfoxide, N,N-dimethylformamide, dichloromethane, chloroform, carbon tetrachloride, isopropanol, n-hexane, isooctane, or toluene.

[0037] Preferably, the cerium salt in step (1) includes any one of cerium nitrate hexahydrate, cerium chloride heptahydrate, cerium chloride hexahydrate, cerium sulfate tetrahydrate, cerium sulfate octahydrate, cerium carbonate pentahydrate, cerium acetate tetrahydrate, cerium acetate pentahydrate, or cerium phosphate pentahydrate.

[0038] Preferably, the molar ratio of the ionic liquid to the cerium salt in step (1) is 1:(1 to 20), for example, it can be 1:1, 1:3, 1:5, 1:10, 1:12, 1:14, 1:17 or 1:20, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] Preferably, the vacuum drying temperature in step (2) is 80 to 200°C, for example, it can be 80°C, 90°C, 100°C, 120°C, 150°C, 180°C or 200°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] Preferably, the vacuum drying time in step (2) is 12 to 48 hours, for example, it can be 12 hours, 15 hours, 18 hours, 20 hours, 25 hours, 30 hours, 35 hours, 40 hours or 48 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] Preferably, the number of centrifugations in step (3) is 3 to 5 times, for example, 3, 4 or 5 times.

[0042] Preferably, the drying temperature in step (3) is 50 to 100°C, for example, it can be 50°C, 60°C, 70°C, 80°C, 85°C, 90°C or 100°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] Preferably, the drying time in step (3) is 6 to 24 hours, for example, it can be 6 hours, 8 hours, 10 hours, 15 hours, 20 hours, 22 hours, 23 hours or 24 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0044] As a preferred technical solution of the present invention, the method includes:

[0045] Cyclic carbonates are synthesized from urea and diols in the presence of an ionic liquid-modified cerium dioxide catalyst, according to the following general reaction formula:

[0046]

[0047] R1 and R2 are each selected from any one of C1 to C4 alkyl groups;

[0048] The molar ratio of urea to diol is 1:(1-5);

[0049] The amount of the ionic liquid-modified cerium dioxide catalyst used is 1% to 10% of the urea mass;

[0050] The reaction temperature for synthesizing the cyclic carbonate is 130–170°C, the reaction pressure is 5–30 kPa, and the reaction time is 1–6 h.

[0051] The preparation method of the ionic liquid modified cerium dioxide catalyst includes the following steps:

[0052] (1) Mix the ionic liquid, cerium salt and solvent, stir until the ionic liquid and cerium salt are completely dissolved, and then evaporate at a temperature of 30 to 80°C to obtain a gel-like solution; the molar ratio of the ionic liquid to the cerium salt is 1:(1 to 20);

[0053] (2) The gel-like solution described in step (1) is vacuum dried at a temperature of 80 to 200°C for 12 to 48 hours to crystallize the solution;

[0054] (3) The crystallized product described in step (2) is washed and centrifuged 3 to 5 times, and dried at a temperature of 50 to 100°C for 6 to 24 hours to obtain the ionic liquid modified cerium dioxide catalyst.

[0055] The ionic liquid comprises imidazole salts and / or quaternary phosphine salts, with structures shown in Formulas I and II below:

[0056]

[0057] In the structure of the ionic liquid, R3, R4, R5, and R6 are each selected from any one of C1 to C8 alkyl groups.

[0058] Compared with the prior art, the present invention has at least the following beneficial effects:

[0059] (1) The method for synthesizing cyclic carbonates by urea alcoholysis provided by the present invention is simple to operate, requires no addition of any solvent, and the product and catalyst are easy to separate, making it easy to achieve continuous production;

[0060] (2) The ion liquid modified cerium dioxide catalyst in the method for synthesizing cyclic carbonates by urea alcoholysis provided by the present invention has a simple preparation process, low cost, high catalytic performance, selectivity of over 95%, and is environmentally friendly, stable and easy to recycle, making it suitable for mass production. Attached Figure Description

[0061] Figure 1 The images show the XRD patterns of commercially available cerium dioxide and the ionic liquid-modified cerium dioxide catalysts in Examples 1-5 of this invention. Detailed Implementation

[0062] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0063] The present invention will now be described in further detail. However, the examples described below are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0064] Example 1

[0065] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis, the method comprising the following steps:

[0066] Add 15 mmol of urea and 60 mmol of ethylene glycol to a 25 mL round-bottom flask, with a urea to ethylene glycol molar ratio of 1:4. Connect the flask to a reflux condenser, an ammonia absorption device, and a vacuum pump in sequence. Gradually heat and continuously stir in a constant-temperature oil bath until the urea is completely dissolved in the ethylene glycol. Then weigh 0.045 g of ionic liquid-modified cerium dioxide catalyst (5% of the urea feed amount) and add it to the flask. Continue heating to 160 °C while maintaining the pressure at 10 kPa for 3 hours using the vacuum pump. After the reaction is complete, allow the product to cool and the pressure in the system to return to atmospheric pressure. Separate and recycle the ionic liquid-modified cerium dioxide catalyst by centrifugation.

[0067] The preparation method of the ionic liquid modified cerium dioxide catalyst described in this embodiment includes the following steps:

[0068] (1) Weigh 50 mL of anhydrous ethanol and add it to a 100 mL round-bottom flask. Then weigh 1 mmol of tetrabutylphosphine bromide and 10 mmol of cerium nitrate hexahydrate. At this point, the molar ratio of the ionic liquid to the cerium salt is 1:10. Add these to the flask containing anhydrous ethanol and stir at room temperature until the tetrabutylphosphine bromide and cerium nitrate hexahydrate are completely dissolved. Rotate the well-mixed solution at 55 °C until the ethanol evaporates and the solution becomes gel-like.

[0069] (2) Dry the round-bottom flask containing the gelatinous solution under vacuum at 100°C and let it stand for 48 hours to allow the solution to crystallize.

[0070] (3) The well-crystallized product was washed with ethanol, centrifuged 3-5 times, and then transferred to an oven and dried at 80°C for 24 hours to obtain the ionic liquid modified cerium dioxide catalyst.

[0071] Example 2

[0072] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. Except for the ionic liquid used in step (1) of the preparation method of the ionic liquid modified cerium dioxide catalyst, which is 2 mmol tetrabutylphosphine bromide, the rest of the method is the same as in Example 1.

[0073] Example 3

[0074] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. Except for the ionic liquid used in step (1) of the preparation method of the ionic liquid modified cerium dioxide catalyst, which is 3 mmol tetrabutylphosphine bromide, the method is the same as in Example 1.

[0075] Example 4

[0076] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. Except for the ionic liquid used in step (1) of the preparation method of the ionic liquid modified cerium dioxide catalyst, which is 4 mmol tetrabutylphosphine bromide, the method is the same as in Example 1.

[0077] Example 5

[0078] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. Except for the ionic liquid used in step (1) of the preparation method of the ionic liquid modified cerium dioxide catalyst, which is 5 mmol tetrabutylphosphine bromide, the method is the same as in Example 1.

[0079] Example 6

[0080] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. Except for the ionic liquid used in step (1) of the preparation method of the ionic liquid modified cerium dioxide catalyst, which is tetrabutylphosphine hexafluorophosphate, the method is the same as in Example 1.

[0081] Example 7

[0082] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. Except for the ionic liquid used in step (1) of the preparation method of the ionic liquid modified cerium dioxide catalyst, which is tetrabutylphosphine hydroxide, the method is the same as that in Example 1.

[0083] Example 8

[0084] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. Except for the ionic liquid used in step (1) of the preparation method of the ionic liquid modified cerium dioxide catalyst, which is tetrabutylphosphine bis(trifluoromethanesulfonyl)imide salt, the method is the same as in Example 1.

[0085] Example 9

[0086] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. Except for the ionic liquid used in step (1) of the preparation method of the ionic liquid modified cerium dioxide catalyst, which is tetraphenylphosphine bromide, the method is the same as that in Example 1.

[0087] Example 10

[0088] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. Except for the ionic liquid used in step (1) of the preparation method of the ionic liquid modified cerium dioxide catalyst, which is ethyltriphenylphosphine bromide, the method is the same as in Example 1.

[0089] Example 11

[0090] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. Except for the ionic liquid used in step (1) of the preparation method of the ionic liquid modified cerium dioxide catalyst, which is 1-butyl-3-methylimidazolium tetrafluoroborate, the rest of the method is the same as in Example 1.

[0091] Example 12

[0092] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. Except for the ionic liquid used in step (1) of the preparation method of the ionic liquid modified cerium dioxide catalyst, which is 1-butyl-3-methylimidazolium iodide, the rest of the method is the same as in Example 1.

[0093] Example 13

[0094] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. Except for the ionic liquid used in step (1) of the preparation method of the ionic liquid modified cerium dioxide catalyst, which is 1-butyl-3-methylimidazolium bromide, the rest of the method is the same as in Example 1.

[0095] Example 14

[0096] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. Except for the solvent used in step (1) of the preparation method of the ionic liquid modified cerium dioxide catalyst, which is anhydrous methanol, the method is the same as that in Example 1.

[0097] Example 15

[0098] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. Except for the solvent used in step (1) of the preparation method of the ionic liquid modified cerium dioxide catalyst, which is ethyl acetate, the method is the same as that in Example 1.

[0099] Example 16

[0100] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. Except for the solvent used in step (1) of the preparation method of the ionic liquid modified cerium dioxide catalyst, which is deionized water, the method is the same as that in Example 1.

[0101] Example 17

[0102] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. Except for the solvent used in step (1) of the preparation method of the ionic liquid modified cerium dioxide catalyst, which is acetone, the method is the same as that in Example 1.

[0103] Example 18

[0104] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1 except that 22.5 mmol of ethylene glycol is added.

[0105] Example 19

[0106] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1 except that 30 mmol of ethylene glycol is added.

[0107] Example 20

[0108] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1 except that 45 mmol of ethylene glycol is added.

[0109] Example 21

[0110] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1 except that 75 mmol of ethylene glycol is added.

[0111] Example 22

[0112] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1 except that 0.027g of ionic liquid modified cerium dioxide catalyst is added, and the amount of catalyst used is 3% of the urea feed amount.

[0113] Example 23

[0114] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1 except that 0.036g of ionic liquid modified cerium dioxide catalyst is added, and the amount of catalyst used is 4% of the urea feed amount.

[0115] Example 24

[0116] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1 except that 0.054g of ionic liquid modified cerium dioxide catalyst is added, and the amount of catalyst used is 6% of the urea feed amount.

[0117] Example 25

[0118] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that 0.063g of ionic liquid modified cerium dioxide catalyst is added, and the amount of catalyst used is 7% of the urea feed amount.

[0119] Example 26

[0120] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that the reaction temperature for synthesizing cyclic carbonates is 130°C.

[0121] Example 27

[0122] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that the reaction temperature for synthesizing cyclic carbonates is 140°C.

[0123] Example 28

[0124] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that the reaction temperature for synthesizing cyclic carbonates is 150°C.

[0125] Example 29

[0126] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that the reaction temperature for synthesizing cyclic carbonates is 170°C.

[0127] Example 30

[0128] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that the reaction pressure for synthesizing cyclic carbonates is 5 kPa.

[0129] Example 31

[0130] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that the reaction pressure for synthesizing cyclic carbonates is 15 kPa.

[0131] Example 32

[0132] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that the reaction pressure for synthesizing cyclic carbonates is 20 kPa.

[0133] Example 33

[0134] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that the reaction pressure for synthesizing cyclic carbonates is 25 kPa.

[0135] Example 34

[0136] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that the reaction time for synthesizing cyclic carbonates is 1 hour.

[0137] Example 35

[0138] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that the reaction time for synthesizing cyclic carbonates is 2 hours.

[0139] Example 36

[0140] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that the reaction time for synthesizing cyclic carbonates is 4 hours.

[0141] Example 37

[0142] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that the reaction time for synthesizing cyclic carbonates is 5 hours.

[0143] Example 38

[0144] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that the reaction time for synthesizing cyclic carbonates is 6 hours.

[0145] Example 39

[0146] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that 45 mmol of ethylene glycol is added and the reaction time for synthesizing cyclic carbonates is 5 hours.

[0147] Example 40

[0148] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. Except for step (2) of the preparation method of the ionic liquid modified cerium dioxide catalyst, in which the vacuum drying temperature is 150°C to allow the solution to crystallize, the method is the same as in Example 39.

[0149] Example 41

[0150] This embodiment provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that 45 mmol of 1,2-propanediol is added, at which point the molar ratio of urea to 1,2-propanediol is 1:3, and the reaction time for synthesizing cyclic carbonates is 5 hours.

[0151] Comparative Example 1

[0152] This comparative example provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that 0.045g of ionic liquid modified cerium dioxide catalyst is replaced with 0.045g of commercially available cerium dioxide, and the amount of catalyst used is 5% of the urea feed amount.

[0153] Comparative Example 2

[0154] This comparative example provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that 0.045g of ionic liquid modified cerium dioxide catalyst is replaced with 0.045g of 1-butyl-3-methylimidazolium bromide. In this case, the amount of catalyst used is 5% of the urea feed amount.

[0155] Comparative Example 3

[0156] This comparative example provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that 0.045 g of ionic liquid modified cerium dioxide catalyst is replaced with 0.0225 g of 1-butyl-3-methylimidazolium bromide and 0.0225 g of commercially available cerium dioxide.

[0157] Comparative Example 4

[0158] This comparative example provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that 0.0045g of ionic liquid modified cerium dioxide catalyst is added, where the amount of ionic liquid modified cerium dioxide catalyst is 0.5% of the urea feed amount.

[0159] Comparative Example 5

[0160] This comparative example provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that 0.1170g of ionic liquid modified cerium dioxide catalyst is added, at which time the amount of ionic liquid modified cerium dioxide catalyst is 13% of the urea feed amount.

[0161] Comparative Example 6

[0162] This comparative example provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that the reaction temperature for synthesizing cyclic carbonates is 100°C.

[0163] Comparative Example 7

[0164] This comparative example provides a method for synthesizing cyclic carbonates by urea alcoholysis. The method is the same as in Example 1, except that the reaction temperature for synthesizing cyclic carbonates is 200°C.

[0165] The yield and selectivity of ethylene carbonate in the above examples and comparative examples are shown in Table 1.

[0166] Table 1

[0167]

[0168]

[0169]

[0170] The following points can be observed from Table 1:

[0171] (1) As can be seen from Examples 1 to 41, the present invention uses ionic liquid modified cerium dioxide catalyst to achieve good catalytic effect in the reaction of urea and diol to prepare cyclic carbonates. The yield of cyclic carbonates can reach 83.42% and the selectivity can reach 97.86%.

[0172] (2) As can be seen from Examples 1 to 5, when preparing ionic liquid modified cerium oxide catalyst, the activity of the synthesized catalyst decreases with the increase of the amount of ionic liquid, which is related to the acid and base sites on the catalyst surface.

[0173] (3) As can be seen from Examples 18-21, with the continuous increase of ethylene glycol addition, the yield and selectivity of ethylene carbonate both show a pattern of first increasing and then decreasing; as can be seen from Examples 22-25, with the continuous increase of ionic liquid-modified cerium dioxide catalyst addition, the yield and selectivity of ethylene carbonate both show a pattern of first increasing and then decreasing; as can be seen from Examples 26-29, with the continuous increase of reaction temperature for synthesizing cyclic carbonates, the yield and selectivity of ethylene carbonate both increase, followed by a decreasing trend; as can be seen from Examples 30-33, with the continuous increase of reaction temperature for synthesizing cyclic carbonates, the yield and selectivity of ethylene carbonate both increase, followed by a decreasing trend; as can be seen from Examples 30-33, with the continuous increase of reaction temperature for synthesizing cyclic carbonates, the yield and selectivity of ethylene carbonate both increase, followed by a decreasing trend. As the reaction pressure for synthesizing cyclic carbonates increases, the yield and selectivity of ethylene carbonate both show a pattern of first increasing and then decreasing. A comprehensive review of Examples 34-38 shows that as the reaction time for synthesizing cyclic carbonates increases, both the yield and selectivity of ethylene carbonate both show a pattern of first increasing and then decreasing. Under the conditions of Example 41, i.e., a urea to diol molar ratio of 1:3, a catalyst dosage of 5% of the urea feed, a reaction temperature of 160°C, a pressure of 10 kPa, and a time of 5 h, the yield of cyclic carbonates is highest at 83.42%, and the selectivity is 97.16%.

[0174] (4) It can be seen from the combined results of Example 1 and Comparative Examples 1 to 3 that when the reaction catalyst is a single ionic liquid or cerium dioxide, the yield of ethylene carbonate is only 15.10% at most; when the ionic liquid and cerium dioxide are simply combined to catalyze the urea alcoholysis reaction, the catalytic performance is not improved.

[0175] (5) It can be seen from the combined examples 1 and 4-5 that when the amount of ionic liquid modified cerium dioxide catalyst is small, the yield and selectivity of ethylene carbonate will decrease; when the amount of ionic liquid modified cerium dioxide catalyst is large, although the yield and selectivity of ethylene carbonate are high, the cost of synthesizing cyclic carbonates will increase, resulting in poor economic efficiency.

[0176] (6) It can be seen from the combined examples 1 and 6-7 that when the reaction temperature for synthesizing cyclic carbonates is low, it is not conducive to the synthesis of ethylene carbonate, and its yield and selectivity will decrease; when the reaction temperature for synthesizing cyclic carbonates is high, it will accelerate the decomposition of urea and the occurrence of side reactions, resulting in a decrease in the yield and selectivity of ethylene carbonate.

[0177] In this invention Figure 1 These are XRD patterns of commercially available cerium dioxide and the ionic liquid-modified cerium dioxide catalysts synthesized in Examples 1-5 of this invention. Figure 1 It can be seen that the diffraction peaks of the synthesized catalyst are consistent with the standard peaks of cerium dioxide, and there are no other obvious impurity peaks, indicating that the method can successfully prepare ionic liquid modified cerium dioxide catalytic materials.

[0178] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for synthesizing cyclic carbonates by urea alcoholysis, characterized in that, The method includes: Cyclic carbonates are synthesized from urea and diols in the presence of an ionic liquid-modified cerium dioxide catalyst, according to the following general reaction formula: R1 and R2 are each selected from any one of C1 to C4 alkyl groups, or the diol includes any one of ethylene glycol, 1,2-propanediol, 1,2-butanediol or cyclohexanediol; The molar ratio of urea to diol is 1:(1~5); The amount of the ionic liquid-modified cerium dioxide catalyst used is 1% to 10% of the urea mass. The reaction temperature for synthesizing the cyclic carbonate is 130~170℃, and the reaction pressure is 5~30kPa; The preparation method of the ionic liquid modified cerium dioxide catalyst includes the following steps: (1) Mix the ionic liquid, cerium salt and solvent, stir until the ionic liquid and cerium salt are completely dissolved, and then evaporate at a temperature of 30~80℃ to obtain a gel-like solution; (2) The colloidal solution described in step (1) is vacuum dried to crystallize the solution and obtain the crystallized product; the vacuum drying temperature is 80~200℃; (3) The crystallized product in step (2) is washed, centrifuged and dried in sequence to obtain the ionic liquid modified cerium dioxide catalyst; The ionic liquid is selected from imidazole salts and / or quaternary phosphine salts, and its structure is shown in Formulas I and II below: Formula I Formula II In the structure of the ionic liquid, R3, R4, R5, and R6 are each selected from any one of C1 to C8 alkyl groups; Anion X - It is selected from any one of the following anions: fluoride ion, chloride ion, bromide ion, iodide ion, hydroxide ion, tetrafluoroborate ion, hexafluorophosphate ion, hydrogen sulfate ion, bis(trifluoromethanesulfonyl)imide ion, formate ion, acetate ion, p-toluenesulfonate ion, or alanine ion.

2. The method according to claim 1, characterized in that, The reaction time for synthesizing the cyclic carbonate is 1 to 6 hours.

3. The method according to claim 1, characterized in that, The feed molar ratio of urea to diol is 1:

3.

4. The method according to claim 1, characterized in that, The amount of the ionic liquid-modified cerium dioxide catalyst used is 5% of the urea mass.

5. The method according to claim 1, characterized in that, The reaction temperature for synthesizing the cyclic carbonate was 160℃, the reaction pressure was 10kPa, and the reaction time was 5h.

6. The method according to claim 1, characterized in that, The solvent in step (1) includes any one of water, ethanol, methanol, ethyl acetate, acetone, dimethyl sulfoxide, N,N-dimethylformamide, dichloromethane, chloroform, carbon tetrachloride, isopropanol, n-hexane, isooctane, or toluene.

7. The method according to claim 1, characterized in that, The cerium salt in step (1) includes any one of cerium nitrate hexahydrate, cerium chloride heptahydrate, cerium chloride hexahydrate, cerium sulfate tetrahydrate, cerium sulfate octahydrate, cerium carbonate pentahydrate, cerium acetate tetrahydrate, cerium acetate pentahydrate, or cerium phosphate pentahydrate.

8. The method according to claim 1, characterized in that, The molar ratio of the ionic liquid to the cerium salt in step (1) is 1:(1~20).

9. The method according to claim 1, characterized in that, The vacuum drying time in step (2) is 12~48h.

10. The method according to claim 1, characterized in that, The number of centrifugations in step (3) is 3 to 5.

11. The method according to claim 1, characterized in that, The drying temperature in step (3) is 50~100℃.

12. The method according to claim 1, characterized in that, The drying time in step (3) is 6 to 24 hours.

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