Method for synthesizing cyclic carbonate by urea alcoholysis

Abstract

The present application provides a method for synthesizing cyclic carbonate by urea alcoholysis. The method comprises: synthesizing urea and diol into cyclic carbonate under the action of an ionic liquid modified cerium dioxide catalyst, wherein the molar ratio of the urea to the diol is 1:(1-5), the dosage of the ionic liquid modified cerium dioxide catalyst is 1%-10% of the mass of the urea, and the synthesized cyclic carbonate has a reaction temperature of 130-170°C, and a reaction pressure of 5-30 kPa. The method of the present application is simple and convenient to operate, no solvent needs to be added, the product and the catalyst are easy to separate, and continuous production is easy to realize. Moreover, the used ionic liquid modified cerium dioxide catalyst has a simple preparation process, low costs, high catalytic performance and good selectivity, and is easy to recycle.

Description

A method for synthesizing cyclic carbonate by alcoholysis of urea Technical Field

[0001] The present application relates to the technical field of chemical synthesis, for example, a method for synthesizing cyclic carbonates by alcoholysis of urea. Background Art

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

[0003] The design and development of catalysts is the research focus of urea alcoholysis to synthesize cyclic carbonates. The catalysts currently reported for urea alcoholysis reactions mainly include metal salts, metal oxides, supported catalysts, ionic liquids, etc. 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 showed better catalytic performance. Among them, under the reaction conditions of 50 mmol of glycerol, 75 mmol of urea, 3 mmol of ionic liquid, 150°C, and 4h, the maximum yield of glycerol carbonate was only 52% (see Juanjuan Chen, et al. Ionic liquids as eco-friendly catalysts for converting glycerol and 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 content of the propylene carbonate finally 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 reaction conditions of reaction temperature of 150° C. and reaction pressure of 11 kPa for 3 hours, the yield of ethylene carbonate can reach 28.7-93.1%, but the preparation process of the 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 using a zinc / iron oxide catalyst ZnO / ZnFe2O4. Under the optimal reaction conditions of a reaction time of 2.5 h, a reaction temperature of 150° C., a catalyst mass fraction of 1.5%, and a urea / ethylene glycol molar ratio of 1:8, the maximum 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 an iron-zinc oxide-compounded zinc chloride catalyst for the alcoholysis of urea to synthesize ethylene carbonate. Under conditions where the catalyst dosage is 1%-5% of the total mass of the reactants, the reaction pressure is 0.005-0.02 MPa, and the reaction temperature is 120-150°C for 3-9 hours, the yield of ethylene carbonate can reach 79.1-92.0%. However, the preparation conditions of the composite catalyst are relatively harsh. CN101544627A discloses a method for synthesizing organic carbonates. Under the relatively harsh reaction conditions of 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, a reaction temperature of 50-250°C, a reaction pressure of 0.0001-0.5 MPa, and a 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 liquids. The method uses an imidazolium ionic liquid and a metal salt composite catalyst to catalyze the reaction of urea and diols to synthesize cyclic carbonates. The yield of cyclic carbonates can reach 94.1%, significantly improving catalytic performance. However, this homogeneous catalytic system suffers from separation difficulties, making it difficult to recover and recycle the urea from the reaction system.

[0004] In summary, numerous catalysts for the alcoholysis of urea to synthesize cyclic carbonates have been reported, but they still suffer from common problems such as 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, requires mild reaction conditions, is highly efficient and stable, and can be easily separated, to achieve the industrial application of urea alcoholysis to prepare cyclic carbonates.

[0005] Summary of the Invention

[0006] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0007] The present application provides a method for synthesizing cyclic carbonates by alcoholysis of urea, which uses an ionic liquid-modified ceria catalyst to catalyze the synthesis of cyclic carbonates from urea and a diol under specific reaction temperature and pressure conditions. The catalyst used has a simple preparation method, stable performance, and is easy to separate and recycle. The resulting cyclic carbonate product has a high yield and high selectivity, and has broad application prospects.

[0008] The present application provides a method for synthesizing cyclic carbonates by alcoholysis of urea, the method comprising:

[0009] Urea and diols are used to synthesize cyclic carbonates in the presence of an ionic liquid-modified ceria catalyst. The general reaction formula is as follows:

[0010] Wherein 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 ceria catalyst is 1% to 10% of the urea quality;

[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 alcoholysis of urea described herein is simple to operate and does not require the addition of any solvent. Under reaction conditions of 130-170°C and 5-30kPa, an ionic liquid-modified ceria catalyst is used to catalyze the alcoholysis of urea to synthesize cyclic carbonates. The ionic liquid-modified ceria catalyst used is low-cost and easy to separate, and is environmentally friendly. Furthermore, the ionic liquid-modified ceria catalyst exhibits significantly improved catalytic performance compared to single ceria or single ionic liquids, with selectivity exceeding 95%. The ionic liquid-modified ceria catalyst in the method described herein is easy to separate, facilitates continuous production, and has broad application prospects.

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

[0016] When the reaction temperature of urea alcoholysis to synthesize cyclic carbonates is low, the yield of cyclic carbonates decreases. This is because the reaction is an endothermic reaction and low temperature is not conducive to the synthesis of cyclic carbonates. When the reaction temperature is too high, it will promote the decomposition of urea and the occurrence of side reactions, and the yield of cyclic carbonates will also be reduced.

[0017] The molar ratio of urea to diol described in this application is 1:(1-5), 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, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] The amount of the ionic liquid modified ceria catalyst is 1% to 10% of the mass of the urea, for example, 1%, 2%, 3%, 5%, 7%, 8%, 9% or 10%, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0019] The reaction temperature for synthesizing the cyclic carbonate is 130-170°C, for example, 130°C, 135°C, 140°C, 150°C, 155°C, 160°C or 170°C, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

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

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

[0022] In one embodiment, 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, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

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

[0024] In one embodiment, the amount of the ionic liquid modified ceria catalyst is 5% of the mass of the urea.

[0025] In one embodiment, 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] In one embodiment, the method for preparing the ionic liquid modified ceria catalyst comprises the following steps:

[0027] (1) mixing an ionic liquid, a cerium salt, and a solvent, stirring until the ionic liquid and the cerium salt are completely dissolved, and then rotary evaporating at a temperature of 30 to 80° C. to obtain a colloidal solution;

[0028] (2) vacuum drying the colloidal solution of step (1) to crystallize the solution;

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

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

[0031] In one embodiment, the ionic liquid in step (1) comprises an imidazolium salt and / or a quaternary phosphonium salt, the structures of which are shown in the following formulas I and II:

[0032] Wherein, in the structure of the ionic liquid, R3, R4, R5, and R6 are each selected from any one of C1 to C8 alkyl groups;

[0033] The rotary evaporation at a temperature of 30 to 80°C described in this application can be, 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 values ​​not listed within this numerical range are also applicable.

[0034] In one embodiment, the anion X - Any one selected from the group consisting of fluoride, chloride, bromide, iodide, hydroxide, tetrafluoroborate, hexafluorophosphate, carbonate, sulfate, hydrogensulfate, hydrogenphosphate, bis(trifluoromethanesulfonyl)imide, formate, acetate, benzoate, p-toluenesulfonate, and alanine anions.

[0035] In one embodiment, the solvent in step (1) comprises any one of water, ethanol, methanol, ethyl acetate, acetone, dimethyl sulfoxide, N,N-dimethylformamide, dichloromethane, chloroform, carbon tetrachloride, isopropanol, n-hexane, isooctane or toluene.

[0036] In one embodiment, 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.

[0037] In one embodiment, the molar ratio of the ionic liquid to the cerium salt in step (1) is 1:(1-20), for example, it can be 1:1, 1:3, 1:5, 1:10, 1:12, 1:14, 1:17 or 1:20, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0038] In one embodiment, the vacuum drying temperature in step (2) is 80-200°C, for example, 80°C, 90°C, 100°C, 120°C, 150°C, 180°C or 200°C, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0039] In one embodiment, 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 is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0040] In one embodiment, the number of centrifugation in step (3) is 3 to 5 times, for example, 3 times, 4 times or 5 times.

[0041] In one embodiment, the drying temperature in step (3) is 50-100°C, for example, 50°C, 60°C, 70°C, 80°C, 85°C, 90°C or 100°C, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0042] In one embodiment, the drying time in step (3) is 6 to 24 hours, for example, 6 hours, 8 hours, 10 hours, 15 hours, 20 hours, 22 hours, 23 hours or 24 hours, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0043] As an optional technical solution of this application, the method includes:

[0044] Urea and diols are used to synthesize cyclic carbonates in the presence of an ionic liquid-modified ceria catalyst. The general reaction formula is as follows:

[0045] Wherein R1 and R2 are each selected from any one of C1 to C4 alkyl groups;

[0046] The molar ratio of urea to diol is 1:(1-5);

[0047] The amount of the ionic liquid modified ceria catalyst is 1% to 10% of the urea quality;

[0048] 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 hours.

[0049] The preparation method of the ionic liquid modified ceria catalyst comprises the following steps:

[0050] (1) mixing an ionic liquid, a cerium salt, and a solvent, stirring until the ionic liquid and the cerium salt are completely dissolved, and then rotary evaporating at a temperature of 30 to 80° C. to obtain a colloidal solution; the molar ratio of the ionic liquid to the cerium salt is 1:(1 to 20);

[0051] (2) vacuum drying the colloidal solution of step (1) at a temperature of 80 to 200° C. for 12 to 48 hours to crystallize the solution;

[0052] (3) The crystallized product of step (2) is washed and centrifuged 3 to 5 times in sequence, and dried at a temperature of 50 to 100° C. for 6 to 24 hours to obtain the ionic liquid-modified ceria catalyst;

[0053] The ionic liquid includes an imidazolium salt and / or a quaternary phosphonium salt, and its structure is shown in the following formula I and II:

[0054] Wherein, in the structure of the ionic liquid, R3, R4, R5, and R6 are each selected from any one of C1 to C8 alkyl groups.

[0055] Compared with the related art, this application has at least the following beneficial effects:

[0056] (1) The method for synthesizing cyclic carbonates by alcoholysis of urea provided in this application is simple to operate, does not require the addition of any solvent, is easy to separate the product from the catalyst, and is easy to achieve continuous production;

[0057] (2) The ionic liquid-modified cerium dioxide catalyst in the method for synthesizing cyclic carbonates by alcoholysis of urea provided in this application has a simple preparation process, low cost, high catalytic performance, and a selectivity of more than 95%. It is also environmentally friendly, has stable performance, and is easy to recycle, making it suitable for mass production.

[0058] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0060] FIG1 is an XRD graph of commercially available ceria and the ionic liquid-modified ceria catalysts in Examples 1 to 5 of the present application. DETAILED DESCRIPTION

[0061] The technical solution of the present application is further illustrated below with reference to the accompanying drawings and through specific embodiments.

[0062] The following is a further detailed description of the present application. However, the following examples are merely simplified examples of the present application and do not represent or limit the scope of protection of the present application. The scope of protection of the present application shall be subject to the claims.

[0063] Example 1

[0064] This embodiment provides a method for synthesizing cyclic carbonate by alcoholysis of urea, the method comprising the following steps:

[0065] To a 25 mL round-bottom flask, 15 mmol of urea and 60 mmol of ethylene glycol were added, with a molar ratio of urea to ethylene glycol of 1:4. The flask was then connected to a reflux condenser, an ammonia absorber, and a vacuum pump. The flask was gradually heated in a constant-temperature oil bath with constant stirring until the urea was completely dissolved in the ethylene glycol. Subsequently, 0.045 g of an ionic liquid-modified ceria catalyst (5% of the urea feed) was added to the flask. The reaction was continued to heat to 160°C while maintaining a vacuum pump at 10 kPa for 3 hours. After the reaction was complete, the product was cooled and the pressure in the system returned to normal. The ionic liquid-modified ceria catalyst was separated and recovered by centrifugation for recycling.

[0066] The preparation method of the ionic liquid modified ceria catalyst described in this embodiment includes the following steps:

[0067] (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. The molar ratio of the ionic liquid to the cerium salt is 1:10. Add the mixture to the flask containing anhydrous ethanol and stir at room temperature until the tetrabutylphosphine bromide and cerium nitrate hexahydrate are completely dissolved. The mixed solution is rotary evaporated at 55°C to evaporate the ethanol until the solution becomes gelatinous.

[0068] (2) The round-bottom flask containing the colloidal solution was vacuum dried at 100°C for 48 hours to allow the solution to crystallize.

[0069] (3) The well-crystallized product was washed with ethanol and centrifuged 3-5 times, and then transferred to an oven again and dried at 80°C for 24 hours to obtain an ionic liquid-modified ceria catalyst.

[0070] Example 2

[0071] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1, except that the ionic liquid used in step (1) of the preparation method of the ionic liquid-modified ceria catalyst is 2 mmol of tetrabutylphosphine bromide.

[0072] Example 3

[0073] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1, except that the ionic liquid used in step (1) of the preparation method of the ionic liquid-modified ceria catalyst is 3 mmol of tetrabutylphosphine bromide.

[0074] Example 4

[0075] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1, except that the ionic liquid used in step (1) of the preparation method of the ionic liquid-modified ceria catalyst is 4 mmol of tetrabutylphosphine bromide.

[0076] Example 5

[0077] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1, except that the ionic liquid used in step (1) of the preparation method of the ionic liquid-modified ceria catalyst is 5 mmol of tetrabutylphosphine bromide.

[0078] Example 6

[0079] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1, except that the ionic liquid used in step (1) of the preparation method of the ionic liquid-modified ceria catalyst is tetrabutylphosphine hexafluorophosphate.

[0080] Example 7

[0081] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1, except that the ionic liquid used in step (1) of the preparation method of the ionic liquid-modified ceria catalyst is tetrabutylphosphine hydroxide.

[0082] Example 8

[0083] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1, except that the ionic liquid used in step (1) of the preparation method of the ionic liquid-modified ceria catalyst is tetrabutylphosphine bistrifluoromethanesulfonyl imide.

[0084] Example 9

[0085] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1, except that the ionic liquid used in step (1) of the preparation method of the ionic liquid-modified ceria catalyst is tetraphenylphosphine bromide.

[0086] Example 10

[0087] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1, except that the ionic liquid used in step (1) of the preparation method of the ionic liquid-modified ceria catalyst is ethyltriphenylphosphine bromide.

[0088] Example 11

[0089] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1, except that the ionic liquid used in step (1) of the preparation method of the ionic liquid-modified ceria catalyst is 1-butyl-3-methylimidazolium tetrafluoroborate.

[0090] Example 12

[0091] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1, except that the ionic liquid used in step (1) of the preparation method of the ionic liquid-modified ceria catalyst is 1-butyl-3-methylimidazolium iodide.

[0092] Example 13

[0093] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1, except that the ionic liquid used in step (1) of the preparation method of the ionic liquid-modified ceria catalyst is 1-butyl-3-methylimidazolium bromide.

[0094] Example 14

[0095] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1, except that the solvent used in step (1) of the preparation method of the ionic liquid-modified ceria catalyst is anhydrous methanol.

[0096] Example 15

[0097] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1, except that the solvent used in step (1) of the preparation method of the ionic liquid-modified ceria catalyst is ethyl acetate.

[0098] Example 16

[0099] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1, except that the solvent used in step (1) of the preparation method of the ionic liquid-modified ceria catalyst is deionized water.

[0100] Example 17

[0101] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1, except that the solvent used in step (1) of the preparation method of the ionic liquid-modified ceria catalyst is acetone.

[0102] Example 18

[0103] This example provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1 except that 22.5 mmol of ethylene glycol is added.

[0104] Example 19

[0105] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1 except that 30 mmol of ethylene glycol is added.

[0106] Example 20

[0107] This example provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1 except that 45 mmol of ethylene glycol is added.

[0108] Example 21

[0109] This example provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1 except that 75 mmol of ethylene glycol is added.

[0110] Example 22

[0111] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1 except that 0.027 g of ionic liquid-modified ceria catalyst is added, and the catalyst dosage is 3% of the urea feed amount.

[0112] Example 23

[0113] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1 except that 0.036 g of ionic liquid-modified ceria catalyst is added, and the catalyst dosage is 4% of the urea feed amount.

[0114] Example 24

[0115] This example provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as Example 1 except that 0.054 g of ionic liquid-modified ceria catalyst is added, and the catalyst dosage is 6% of the urea feed amount.

[0116] Example 25

[0117] This example provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as Example 1 except that 0.063 g of ionic liquid-modified ceria catalyst is added, and the catalyst dosage is 7% of the urea feed amount.

[0118] Example 26

[0119] This embodiment provides a method for synthesizing cyclic carbonate by alcoholysis of urea. The method is the same as that of Example 1 except that the reaction temperature for synthesizing cyclic carbonate is 130°C.

[0120] Example 27

[0121] This embodiment provides a method for synthesizing cyclic carbonate by alcoholysis of urea. The method is the same as that of Example 1 except that the reaction temperature for synthesizing cyclic carbonate is 140°C.

[0122] Example 28

[0123] This embodiment provides a method for synthesizing cyclic carbonate by alcoholysis of urea. The method is the same as that of Example 1 except that the reaction temperature for synthesizing cyclic carbonate is 150°C.

[0124] Example 29

[0125] This embodiment provides a method for synthesizing cyclic carbonate by alcoholysis of urea. The method is the same as that of Example 1 except that the reaction temperature for synthesizing cyclic carbonate is 170°C.

[0126] Example 30

[0127] This embodiment provides a method for synthesizing cyclic carbonate by alcoholysis of urea. The method is the same as that of Example 1 except that the reaction pressure for synthesizing cyclic carbonate is 5 kPa.

[0128] Example 31

[0129] This embodiment provides a method for synthesizing cyclic carbonate by alcoholysis of urea. The method is the same as that of Example 1 except that the reaction pressure for synthesizing cyclic carbonate is 15 kPa.

[0130] Example 32

[0131] This embodiment provides a method for synthesizing cyclic carbonate by alcoholysis of urea. The method is the same as that of Example 1 except that the reaction pressure for synthesizing cyclic carbonate is 20 kPa.

[0132] Example 33

[0133] This embodiment provides a method for synthesizing cyclic carbonate by alcoholysis of urea. The method is the same as that of Example 1 except that the reaction pressure for synthesizing cyclic carbonate is 25 kPa.

[0134] Example 34

[0135] This embodiment provides a method for synthesizing cyclic carbonate by alcoholysis of urea. The method is the same as that of Example 1 except that the reaction time for synthesizing the cyclic carbonate is 1 h.

[0136] Example 35

[0137] This embodiment provides a method for synthesizing cyclic carbonate by alcoholysis of urea. The method is the same as that of Example 1 except that the reaction time for synthesizing the cyclic carbonate is 2 h.

[0138] Example 36

[0139] This embodiment provides a method for synthesizing cyclic carbonate by alcoholysis of urea. The method is the same as that of Example 1 except that the reaction time for synthesizing the cyclic carbonate is 4 hours.

[0140] Example 37

[0141] This embodiment provides a method for synthesizing cyclic carbonate by alcoholysis of urea. The method is the same as that of Example 1 except that the reaction time for synthesizing the cyclic carbonate is 5 h.

[0142] Example 38

[0143] This embodiment provides a method for synthesizing cyclic carbonate by alcoholysis of urea. The method is the same as that of Example 1 except that the reaction time for synthesizing the cyclic carbonate is 6 hours.

[0144] Example 39

[0145] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 1 except that 45 mmol of ethylene glycol is added and the reaction time for synthesizing the cyclic carbonate is 5 h.

[0146] Example 40

[0147] This embodiment provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as that of Example 39, except that the vacuum drying temperature in step (2) of the preparation method of the ionic liquid-modified cerium dioxide catalyst is 150°C to allow the solution to crystallize.

[0148] Example 41

[0149] This example provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as Example 1 except that 45 mmol of 1,2-propylene glycol is added, the molar ratio of urea to 1,2-propylene glycol is 1:3, and the reaction time for synthesizing the cyclic carbonate is 5 hours.

[0150] Comparative Example 1

[0151] This comparative example provides a method for synthesizing cyclic carbonates by alcoholysis of urea, which is the same as Example 1 except that 0.045 g of the ionic liquid-modified cerium dioxide catalyst is replaced by 0.045 g of commercially available cerium dioxide, and the catalyst dosage is 5% of the urea feed amount.

[0152] Comparative Example 2

[0153] This comparative example provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as Example 1 except that 0.045 g of the ionic liquid-modified cerium dioxide catalyst is replaced by 0.045 g of 1-butyl-3-methylimidazolium bromide, and the catalyst dosage is 5% of the urea feed amount.

[0154] Comparative Example 3

[0155] This comparative example provides a method for synthesizing cyclic carbonates by alcoholysis of urea. The method is the same as Example 1 except that 0.045 g of the ionic liquid-modified ceria catalyst is replaced with 0.0225 g of 1-butyl-3-methylimidazolium bromide and 0.0225 g of commercially available ceria.

[0156] Comparative Example 4

[0157] This comparative example provides a method for synthesizing cyclic carbonates by alcoholysis of urea, which is the same as Example 1 except that 0.0045 g of ionic liquid-modified ceria catalyst is added, and the amount of ionic liquid-modified ceria catalyst used is 0.5% of the urea feed amount.

[0158] Comparative Example 5

[0159] This comparative example provides a method for synthesizing cyclic carbonates by alcoholysis of urea, which is the same as Example 1 except that 0.1170 g of ionic liquid-modified ceria catalyst is added, and the amount of ionic liquid-modified ceria catalyst used is 13% of the urea feed amount.

[0160] Comparative Example 6

[0161] This comparative example provides a method for synthesizing cyclic carbonate by alcoholysis of urea. The method is the same as Example 1 except that the reaction temperature for synthesizing cyclic carbonate is 100°C.

[0162] Comparative Example 7

[0163] This comparative example provides a method for synthesizing cyclic carbonate by alcoholysis of urea. The method is the same as Example 1 except that the reaction temperature for synthesizing cyclic carbonate is 200°C.

[0164] The yield and selectivity results of ethylene carbonate in the above examples and comparative examples are shown in Table 1.

[0165] Table 1

[0166] From Table 1, we can see the following points:

[0167] (1) Based on Examples 1 to 41, it can be seen that the ionic liquid-modified ceria catalyst used in this application achieves a good catalytic effect in the reaction of urea and diols to prepare cyclic carbonates, with a yield of cyclic carbonates of up to 83.42% and a selectivity of up to 97.86%.

[0168] (2) Based on Examples 1 to 5, it can be seen that when preparing ionic liquid-modified cerium oxide catalysts, as the amount of ionic liquid increases, the catalytic activity of the synthesized catalyst decreases, which is related to the acid-base sites on the catalyst surface;

[0169] (3) From Examples 18 to 21, it can be seen that as the amount of ethylene glycol added continues to increase, the yield and selectivity of ethylene carbonate both show a pattern of first increasing and then decreasing; from Examples 22 to 25, it can be seen that as the amount of ionic liquid modified cerium dioxide catalyst added continues to increase, the yield and selectivity of ethylene carbonate both show a pattern of first increasing and then decreasing; from Examples 26 to 29, it can be seen that as the reaction temperature for synthesizing cyclic carbonates continues to increase, the yield and selectivity of ethylene carbonate both increase, and then show a downward trend; from Examples 30 to 33, it can be seen that as the reaction temperature for synthesizing cyclic carbonates continues to increase, the yield and selectivity of ethylene carbonate both increase, and then show a downward trend; As the reaction pressure for synthesizing cyclic carbonates increases, the yield and selectivity of ethylene carbonate both increase first and then decrease. A comprehensive review of Examples 34 to 38 shows that as the reaction time for synthesizing cyclic carbonates increases, the yield and selectivity of ethylene carbonate both increase first and then decrease. 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 amount, a reaction temperature of 160°C, a pressure of 10 kPa, and a reaction time of 5 h, the yield of cyclic carbonate was the highest, at 83.42%, and the selectivity was 97.16%.

[0170] (4) Based on Example 1 and Comparative Examples 1 to 3, it can be seen that when the reaction catalyst is a single ionic liquid or ceria, the maximum yield of ethylene carbonate is only 15.10%. When the ionic liquid and ceria are simply combined to catalyze the urea alcoholysis reaction, the catalytic performance is not improved.

[0171] (5) It can be seen from Example 1 and Comparative Examples 4 to 5 that when the amount of the ionic liquid-modified ceria catalyst is small, the yield and selectivity of ethylene carbonate are reduced; when the amount of the ionic liquid-modified ceria catalyst is large, although the yield and selectivity of ethylene carbonate are high, the cost of synthesizing cyclic carbonates is increased, and the economic efficiency is poor;

[0172] (6) It can be seen from Example 1 and Comparative Examples 6 to 7 that when the reaction temperature for synthesizing cyclic carbonate is low, it is not conducive to the synthesis of ethylene carbonate, and its yield and selectivity will both decrease; when the reaction temperature for synthesizing cyclic carbonate 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.

[0173] Figure 1 in the present application is an XRD diagram of commercially available cerium dioxide and the ionic liquid-modified cerium dioxide catalyst synthesized in Examples 1 to 5 of the present application. It can be seen from Figure 1 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 this method can successfully prepare ionic liquid-modified cerium dioxide catalytic materials.

[0174] The applicant declares that the above is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Technical personnel in the relevant technical field should understand that any changes or substitutions that can be easily thought of by technical personnel in the relevant technical field within the technical scope disclosed in this application fall within the protection scope and disclosure scope of this application.

Claims

1. A method for synthesizing cyclic carbonates by alcoholysis of urea, which comprises: Urea and diol react under the action of an ionic liquid-modified cerium dioxide catalyst to synthesize cyclic carbonates, and the general reaction formula is as follows: wherein R 1 and R 2 are each independently selected from any one of C 1 to C 4 alkyl groups; The molar ratio of the urea to the diol is 1∶(1 - 5); The dosage of the ionic liquid modified cerium dioxide catalyst is 1% - 10% of the mass of the urea; The reaction temperature for synthesizing the cyclic carbonate is 130 - 170 °C, and the reaction pressure is 5 - 30 kPa.

2. The method according to claim 1, wherein, 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.

3. The method according to claim 1 or 2, wherein, The reaction time for synthesizing the cyclic carbonate is 1 - 6 h.

4. The method according to any one of claims 1 - 3, wherein, The feed molar ratio of the urea to the diol is 1∶3.

5. The method according to any one of claims 1 - 4, wherein, The dosage of the ionic liquid modified cerium dioxide catalyst is 5% of the mass of the urea.

6. The method according to any one of claims 1 - 5, wherein, The reaction temperature for synthesizing the cyclic carbonate is 160 °C, the reaction pressure is 10 kPa, and the reaction time is 5 h.

7. The method according to any one of claims 1 - 6, wherein, The preparation method of the ionic liquid modified cerium dioxide catalyst comprises 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 perform rotary evaporation at a temperature of 30 - 80 °C to obtain a colloidal solution; (2) Vacuum - dry the colloidal solution obtained in step (1) to crystallize the solution; (3) Wash, centrifuge and dry the product obtained after crystallization in step (2) to obtain the ionic liquid modified cerium dioxide catalyst.

8. The method according to claim 7, wherein, The ionic liquid described in step (1) includes imidazolium salts and / or phosphonium salts, and their structures are shown in the following formulas I and II: Among them, in the structure of the ionic liquid, R 3 , R 4 , R 5 , R 6 are each independently selected from any one of C 1 -C 8 alkyl groups; Optionally, the anion X - is selected from any one of fluoride ion, chloride ion, bromide ion, iodide ion, hydroxide, tetrafluoroborate, hexafluorophosphate, carbonate, sulfate, hydrogen sulfate, hydrogen phosphate, bis(trifluoromethanesulfonyl)imide, formate, acetate, benzoate, p-toluenesulfonate or alaninate anions.

9. The method according to claim 7 or 8, wherein, 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.

10. The method according to any one of claims 7 - 9, wherein, 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.

11. The method according to any one of claims 7 - 10, wherein, The molar ratio of the ionic liquid to the cerium salt in step (1) is 1∶(1 - 20).

12. The method according to any one of claims 7 - 11, wherein, The temperature of the vacuum drying in step (2) is 80 - 200 °C; Optionally, the time of the vacuum drying in step (2) is 12 - 48 h.

13. The method according to any one of claims 7 - 12, wherein, The number of centrifugation times in step (3) is 3 - 5 times.

14. The method according to any one of claims 7 to 13, wherein, the temperature of the drying in step (3) is 50 to 100 °C; optionally, the time of the drying in step (3) is 6 to 24 h.

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