Ionic liquid modified Zn-based composite oxide catalyst as well as preparation method and application thereof

Abstract

According to the preparation method of the ionic liquid modified Zn-based composite oxide catalyst, through compounding of the second metal oxide, the problems of active component loss and cycle performance reduction in the cycle process of a single ZnO catalyst are solved, meanwhile, the ionic liquid is added to regulate and control the acid-base sites of the metal oxide, and the cycle performance of the catalyst is improved. Therefore, the preparation of the composite catalyst which is high in activity, high in stability and easy to separate and recycle is realized. The catalyst prepared by the method is applied to synthesis of cyclic carbonate from urea and dihydric alcohol, realizes high-efficiency implementation of urea alcoholysis reaction under mild conditions, and has very important significance in industrial application of high-efficiency preparation of cyclic carbonate from urea alcoholysis.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of ionic liquid modified composite oxide catalysts, and particularly to a preparation method of an ionic liquid modified Zn-based composite oxide catalyst and its application in catalytic alcoholysis of urea to synthesize cyclic carbonates. Background Art

[0002] Cyclic carbonates are important organic reaction intermediates and have wide applications in fields such as petrochemical industry, cosmetics, gas separation, and electrochemistry, and are the main raw materials for producing dimethyl carbonate (DMC) and polycarbonate.

[0003] Among the methods for preparing cyclic carbonates, the preparation of cyclic carbonates by alcoholysis of urea has the characteristics of inexpensive and easily available raw materials, mild reaction conditions, low cost, and environmental friendliness. Moreover, the cyclic carbonates prepared by the alcoholysis reaction route of urea can react with methanol as reactants in the transesterification reaction to produce dimethyl carbonate (DMC), and the by-product diol generated in the transesterification reaction process is one of the raw materials for the alcoholysis reaction of urea, thus enabling the high-value utilization of excess ethylene glycol and gradually developing into a green economic process route for synthesizing cyclic carbonates.

[0004] Developing an efficient and stable catalytic system to improve the selectivity and yield of synthetic products is the research focus for realizing the industrial application of this process route. Currently, the catalysts used in the urea alcoholysis reaction system are mainly divided into two categories: homogeneous and heterogeneous. The homogeneous catalytic system has high catalytic efficiency but suffers from the problem of difficult separation; while the heterogeneous catalyst with high activity and high stability not only ensures the efficient progress of the reaction between urea and diol, but also is easily separated from the reaction system and thus favored in industrial application research.

[0005] In the existing literature, Qibiao Li et al. (Catalysis Today, 2006, 115(1-4), 111-116) prepared and investigated the performance of metal oxides as catalysts for the alcoholysis of urea to synthesize ethylene carbonate (EC). Among them, zinc oxide (ZnO) showed relatively high catalytic activity in this reaction system. Under relatively mild experimental conditions (150 °C, 11 kPa, 3 h), the yield of EC could reach 93.1%. However, the preparation conditions of the oxides were relatively harsh. At the same time, the characterization results showed that catalysts with appropriate acid-base sites were more conducive to the synthesis of cyclic carbonates. The patent (CN 103357394 B) provided a binary metal oxide catalyst and applied it to the reaction of urea and glycerol to synthesize glycerol carbonate (GC). Under the reaction conditions of a raw material molar ratio of 1:2 to 2:1, a catalyst dosage of 3% to 7% of the glycerol feed amount, a temperature of 120 to 160 °C, a pressure of 2 to 6 kPa, and a time of 3 to 7 h, the conversion rate of glycerol was 80% to 85%, and the yield of GC was 73% to 83%. Xinqiang Zhao et al. (Journal of Chemical Technology and Biotechnology, 2008, 83, 750-755) prepared zinc-iron oxides as catalysts for the alcoholysis of urea to prepare EC. Under the optimal reaction conditions (n(urea):n(ethylene glycol)=1:8, 150 °C, 2.5 h), the yield of EC was 66.1%.

[0006] As described above, the catalytic performance of binary metal oxides is relatively stable, which to a certain extent improves the problem of the loss of regenerated active components of single oxides, enhances the cyclic stability of the catalyst, and reduces the production cost. However, traditional binary catalysts have problems such as relatively complex preparation processes, harsh conditions, and a significant reduction in the yield of synthetic products compared to homogeneous catalysts. Therefore, exploring binary metal oxide catalysts with better catalytic performance to achieve the industrial application of the alcoholysis of urea to synthesize cyclic carbonates under mild conditions has practical application value. Summary of the Invention

[0007] Aiming at the problems of harsh preparation conditions and low yield of heterogeneous catalysts existing at present, the present invention provides a preparation method of an ionic liquid-modified Zn-based composite oxide catalyst. The catalyst prepared by this method has high catalytic activity, good stability, and is easy to separate and recycle, and can improve the conversion rate of urea and the selectivity of cyclic carbonates in the synthesis of cyclic carbonates from urea and diols, thereby increasing the yield of cyclic carbonates.

[0008] The object of the present invention is achieved by the following technical solutions:

[0009] A preparation method of an ionic liquid-modified Zn-based composite oxide catalyst, comprising the following steps:

[0010] Step S1: Add any one of metal salts such as calcium salt, magnesium salt, iron salt, aluminum salt, copper salt, lanthanum salt, zirconium salt and cerium salt and zinc salt into a solvent, and while fully mixing, slowly inject an ionic liquid;

[0011] Step S2: Thermostatically heat the material after adding the ionic liquid in Step S1 for uniform precipitation;

[0012] Step S3: After precipitation ends, centrifuge, wash and dry the product, and then calcine it to obtain an ionic liquid-modified Zn-based composite oxide catalyst;

[0013] In the above Step S1, the molar ratio of the zinc salt to the metal salt is 1:5 to 5:1, the added ionic liquid and the total molar ratio of the zinc salt to the metal salt ≤ 20%, and the structural general formula of the ionic liquid is any one of the following formulas I, II and III,

[0014]

[0015] Among them, in the structure of the ionic liquid, R 1 , R 2 , R 3 , R 4 are all any one of C1-C8 alkyl groups; the anion X - is any one of halide ions, hydroxide, tetrafluoroborate, hexafluorophosphate, carboxylate, imide.

[0016] The preparation method of the catalyst of the present invention is to mix zinc salt with any one of metal salts such as calcium, magnesium, iron, aluminum, copper, lanthanum, zirconium and cerium salts, and highly disperse any one of the above ionic liquids in the mixed solution of zinc salt and metal salt, and then carry out heating for uniform precipitation and finally calcine to obtain a Zn-based composite oxide catalyst. The composite of the second metal in the catalyst forms a bimetallic site catalytic mechanism with the Zn-based. The addition of the ionic liquid can regulate the Lewis acid-base sites of the catalyst, inhibit the formation of inactive substances, promote the release of catalytic active sites, and has a synergistic effect with the bimetallic site catalysis, improving the activity of the catalyst active sites and the selectivity of the product. At the same time, the composite of the second metal salt and the modification of the ionic liquid can change the surface morphology of the composite metal oxide, reduce unnecessary reactions on the ZnO surface that may cause the loss of active components, thereby making up for the problems of the loss of active components and the reduction of cycle performance during the cycle of a single ZnO catalyst.

[0017] Preferably, the anions of the zinc salt and the metal salt are any one of halide ions, nitrate, sulfate, carbonate, acetate and phosphate. In a preferred embodiment, the ionic liquid is a methanol solution of tetraethylammonium hydroxide. In another preferred embodiment, the ionic liquid is an aqueous solution of tetrabutylphosphonium hydroxide.

[0018] Preferably, the solvent is any one of water, methanol, ethanol, N,N-dimethylformamide, n-hexane, isopropanol, ethyl acetate, acetone, dimethyl sulfoxide, dichloromethane, and chloroform. In practice, water, methanol, or ethanol is generally preferred.

[0019] Preferably, in step S2, the uniform precipitation temperature is 50-200° C., and the uniform precipitation time is 0.5-24 h.

[0020] Preferably, in step S3, the firing temperature is 200-800° C., and the firing time is 1-10 hours.

[0021] The present invention also provides an ion-modified Zn-based composite oxide catalyst prepared according to the above implementation method.

[0022] The present invention also provides a method for synthesizing cyclic carbonate from urea and diol using the above catalyst, and the method steps are as follows:

[0023] Step A1: adding urea and diol into a synthesis device, gradually heating and fully stirring;

[0024] Step A2: adding an ionic liquid modified Zn-based composite oxide catalyst into a synthesis device to catalyze the materials in step A1 for a synthesis reaction;

[0025] The molar ratio of urea to diol is 1:5 to 2:1, the amount of the catalyst added is 1wt% to 10wt% of the amount of urea added, and the general structural formula of the diol is as follows:

[0026]

[0027] In the structural formula, R 5 and R 6 Each of them is H or any one of C1~C4 alkyl.

[0028] In the above reaction, catalytic synthesis can be carried out without adding additional solvent, and the general reaction process is as follows:

[0029]

[0030] Preferably, in the step A2, the synthesis reaction temperature is 120-180° C., the synthesis reaction pressure is 1-50 kPa, and the synthesis reaction time is 1-6 h.

[0031] In the above reaction, urea first decomposes to generate isocyanic acid, which then undergoes an esterification reaction with a diol to generate a key intermediate, which then undergoes cyclization to generate a cyclic carbonate.

[0032] Using the ionic liquid-modified Zn-based composite oxide catalyst prepared above, since the acid-base sites of the Zn-based composite oxide are regulated, the activity of the active sites of the catalyst is enhanced. In the synthesis of cyclic carbonates by the alcoholysis of urea, the reactants are activated, the esterification reaction is promoted, and the stability and dissociation rate of the key reaction intermediates are affected, thereby accelerating the effective and stable conversion of urea into the key intermediates and making it easier to convert into specific cyclic carbonates, thus improving the conversion rate of urea and the selectivity of cyclic carbonates.

[0033] The present invention has the following beneficial effects:

[0034] 1. The ionic liquid-modified Zn-based composite oxide catalyst provided by the present invention makes up for the problems of loss of active components and reduction of cyclic performance during the cycle of a single ZnO catalyst through the composite of the second metal oxide. At the same time, an ionic liquid is added to regulate the acid-base sites of the metal oxide, thereby realizing the preparation of a catalyst with high activity and high stability.

[0035] 2. The ionic liquid-modified Zn-based composite oxide catalyst provided by the present invention does not require the additional addition of a solvent in the synthesis of cyclic carbonates from urea and diols, and exhibits excellent catalytic performance under relatively mild synthesis conditions.

[0036] 3. The ionic liquid-modified Zn-based composite oxide catalyst of the present invention is prepared by co-precipitation of a zinc salt and a second metal salt with an ionic liquid in a certain molar ratio, and has the advantages of simple preparation, stable performance and easy separation and recovery. Detailed implementation manners

[0037] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below. Unless otherwise specified, various reagents, reaction equipment, etc. used in the following examples can be known in the art and can be obtained through market purchase or preparation by existing technologies.

[0038] The preparation method and application of the ionic liquid-modified Zn-based composite oxide catalyst provided by the present invention will be specifically described below in combination with several specific examples. Obviously, the described examples are only some preferred examples of the present invention, rather than all examples, and should not be construed as any limitation to the present invention.

[0039] Example 1

[0040] In this example, an ionic liquid-modified Zn-based composite oxide catalyst was prepared through the following steps:

[0041] Step S1: Weigh 5.94 g of zinc nitrate hexahydrate and 25.60 g of magnesium nitrate hexahydrate (the molar ratio of zinc to magnesium is 1:5) and add them to a 100 mL round-bottom flask containing 50 mL of methanol. Stir vigorously, and at the same time, add 4.14 g of an aqueous solution of 40 wt.% tetrabutylphosphonium hydroxide (the ionic liquid accounts for 5% of the total molar ratio of zinc and magnesium);

[0042] Step S2: Place the flask in a constant-temperature oil bath at 50 °C, heat it while stirring continuously for 0.5 h to carry out homogeneous precipitation;

[0043] Step S3: After the precipitation is completed, centrifuge the product and wash it with methanol 3 - 5 times. Transfer it to a vacuum drying oven at 60 °C and dry it for 12 h; finally, calcine it at 200 °C for 1 h to obtain a zinc-magnesium composite oxide catalyst.

[0044] The zinc-magnesium composite oxide catalyst prepared by the above steps is applied to catalyze the synthesis of cyclic carbonate from urea and 1,2-propanediol. The application includes the following steps:

[0045] Weigh 1.8 g of urea and 11.4 g of 1,2-propanediol (the molar ratio of urea to 1,2-propanediol is 1:5) and add them to a 50 mL round-bottom flask. The round-bottom flask is successively connected to a reflux condenser, an ammonia absorption device, a vacuum pump, etc. Gradually heat it in a constant-temperature oil bath while stirring continuously. Subsequently, weigh 0.02 g of the catalyst (the catalyst addition is 1% of the urea feed amount) and add it to the round-bottom flask. Continue heating and react at 120 °C and 1 kPa for 1 h. After the reaction is completed, cool it at room temperature, centrifuge it, and wash it 3 - 5 times to separate and recover the catalyst.

[0046] Example 2

[0047] This example prepares an ionic liquid-modified Zn-based composite oxide catalyst through the following steps:

[0048] Step S1: Weigh 5.94 g of zinc nitrate hexahydrate and 1.50 g of aluminum nitrate nonahydrate (the molar ratio of zinc to aluminum is 5:1) and add them to a 100 mL round-bottom flask containing 50 mL of methanol. Stir vigorously, and at the same time, add 2.82 g of a methanol solution of 25 wt.% tetraethylammonium hydroxide (the ionic liquid accounts for 20% of the total molar ratio of zinc and magnesium);

[0049] Step S2: Place the flask in a constant-temperature oil bath at 200 °C, heat it while stirring continuously for 24 h to carry out homogeneous precipitation;

[0050] Step S3: After the precipitation is completed, centrifuge the product and wash it with methanol 3 - 5 times. Transfer it to a vacuum drying oven at 60 °C and dry it for 12 h; finally, calcine it at 800 °C for 10 h to obtain a zinc-aluminum composite oxide catalyst.

[0051] The catalyst prepared through the above steps is applied to catalyze the synthesis of ethylene carbonate from urea and ethylene glycol. The application includes the following steps:

[0052] Weigh 1.8 g of urea and 0.93 g of ethylene glycol (the molar ratio of urea to ethylene glycol is 2:1), add them to a 50 mL round-bottom flask. The round-bottom flask is successively connected to a reflux condenser, an ammonia absorption device, a vacuum pump, etc. Gradually heat it in a constant-temperature oil bath and stir continuously. Subsequently, weigh 0.18 g of the catalyst (the catalyst addition is 10% of the urea feed amount) and add it to the round-bottom flask. Continue heating and react for 6 h under the conditions of 180 °C and 50 kPa. After the reaction is completed, cool it at room temperature, centrifuge and wash it 3 - 5 times to separate and recover the catalyst.

[0053] Example 3

[0054] In this example, an ionic liquid-modified Zn-based composite oxide catalyst is prepared through the following steps:

[0055] Step S1: Weigh 5.94 g of zinc nitrate hexahydrate and 12.80 g of magnesium nitrate hexahydrate (the molar ratio of zinc to magnesium is 1:2.5), add them to a 100 mL round-bottom flask containing 50 mL of methanol, stir vigorously, and at the same time add 4.12 g of a methanol solution of 25 wt.% tetraethylammonium hydroxide (the ionic liquid accounts for 10% of the total molar ratio of zinc and magnesium);

[0056] Step S2: Place the flask in a 100 °C constant-temperature oil bath, heat it and stir continuously for 12 h for homogeneous precipitation;

[0057] Step S3: After the precipitation is completed, centrifuge the product and wash it with methanol 3 - 5 times, transfer it to a 60 °C vacuum drying oven and dry it for 12 h; finally, calcine it at 500 °C for 5 h to obtain a zinc-magnesium composite oxide catalyst.

[0058] The catalyst prepared through the above steps is applied to catalyze the synthesis of ethylene carbonate from urea and ethylene glycol. The application includes the following steps:

[0059] Weigh 1.8 g of urea and 5.58 g of ethylene glycol (the molar ratio of urea to ethylene glycol is 1:3), add them to a 50 mL round-bottom flask. The round-bottom flask is successively connected to a reflux condenser, an ammonia absorption device, a vacuum pump, etc. Gradually heat it in a constant-temperature oil bath and stir continuously. Subsequently, weigh 0.09 g of the catalyst (the catalyst addition is 5% of the urea feed amount) and add it to the round-bottom flask. Continue heating and react for 3 h under the conditions of 150 °C and 25 kPa. After the reaction is completed, cool it at room temperature, centrifuge and wash it 3 - 5 times to separate and recover the catalyst.

[0060] Example 4

[0061] In this example, an ionic liquid-modified Zn-based composite oxide catalyst is prepared through the following steps:

[0062] Step S1: Weigh 5.94 g of zinc nitrate hexahydrate and 1.28 g of magnesium nitrate hexahydrate (the molar ratio of zinc to magnesium is 4:1) and add them to a 100 mL round-bottom flask containing 50 mL of methanol. Stir vigorously, and at the same time, add 0.74 g of a methanol solution of 25 wt.% tetraethylammonium hydroxide (the ionic liquid accounts for 5% of the total molar ratio of zinc and magnesium);

[0063] Step S2: Place the flask in a constant-temperature oil bath at 100 °C, heat it with continuous stirring for 3 h to carry out homogeneous precipitation;

[0064] Step S3: After the precipitation is completed, centrifuge the product and wash it with methanol 3 - 5 times. Transfer it to a vacuum drying oven at 60 °C and dry it for 12 h; finally, calcine it at 500 °C for 3 h to obtain a Zn-based composite oxide catalyst. In this example, a zinc-magnesium composite oxide catalyst is obtained.

[0065] The catalyst prepared through the above steps is applied to the synthesis of cyclic carbonate from urea and ethylene glycol. The application includes the following steps:

[0066] Weigh 1.8 g of urea and 5.58 g of ethylene glycol (the molar ratio of urea to ethylene glycol is 1:3) and add them to a 50 mL round-bottom flask. The round-bottom flask is successively connected to a reflux condenser, an ammonia absorption device, a vacuum pump, etc. Gradually heat it in a constant-temperature oil bath with continuous stirring. Subsequently, weigh 0.09 g of the catalyst (the catalyst addition is 5% of the urea feed amount) and add it to the round-bottom flask, and continue heating. React at 160 °C and 10 kPa for 3 h. After the reaction is completed, cool it at room temperature, centrifuge and wash it 3 - 5 times to separate and recover the catalyst.

[0067] Example 5

[0068] In this example, an ionic liquid-modified Zn-based composite oxide catalyst is prepared through the following steps:

[0069] Step S1: Weigh 5.94 g of zinc nitrate hexahydrate and 2.56 g of magnesium nitrate hexahydrate (the molar ratio of zinc to magnesium is 2:1) and add them to a 100 mL round-bottom flask containing 50 mL of methanol. Stir vigorously, and at the same time, add 1.04 g of an aqueous solution of 40 wt.% tetrabutylphosphonium hydroxide (the ionic liquid accounts for 5% of the total molar ratio of zinc and magnesium);

[0070] Step S2: Place the flask in a constant-temperature oil bath at 100 °C, heat it with continuous stirring for 3 h to carry out homogeneous precipitation;

[0071] Step S3: After the precipitation is completed, centrifuge the product and wash it with methanol 3 - 5 times. Transfer it to a vacuum drying oven at 60 °C and dry it for 12 h; finally, calcine it at 500 °C for 3 h to obtain a Zn-based composite oxide catalyst. In this example, a zinc-magnesium composite oxide catalyst is obtained.

[0072] The catalyst prepared by the above steps is applied to catalyze the synthesis of cyclic carbonate from urea and ethylene glycol. The application includes the following steps:

[0073] Weigh 1.8 g of urea and 5.58 g of ethylene glycol (the molar ratio of urea to ethylene glycol is 1:3), and add them to a 50 mL round-bottom flask. The round-bottom flask is successively connected to a reflux condenser, an ammonia absorption device, a vacuum pump, etc. It is gradually heated in a constant-temperature oil bath and continuously stirred. Subsequently, weigh 0.09 g of the catalyst (the catalyst addition is 5% of the urea feed amount) and add it to the round-bottom flask, and continue heating. The reaction is carried out at 160 °C and 10 kPa for 3 h. After the reaction is completed, it is cooled at room temperature, centrifuged, and washed 3 - 5 times to separate and recover the catalyst.

[0074] Example 6:

[0075] The catalyst preparation method provided in this example is the same as that in Example 4 except that the ionic liquid accounts for 10% of the total molar ratio of zinc and magnesium. The synthesis steps of the prepared catalyst applied to catalyze the synthesis of cyclic carbonate from urea and ethylene glycol are also the same as those in Example 4.

[0076] Example 7:

[0077] The catalyst preparation method provided in this example is the same as that in Example 4 except that the ionic liquid accounts for 20% of the total molar ratio of zinc and magnesium. The synthesis steps of the prepared catalyst applied to catalyze the synthesis of cyclic carbonate from urea and ethylene glycol are also the same as those in Example 4.

[0078] Example 8:

[0079] The catalyst preparation method provided in this example is the same as that in Example 4 except that the molar ratio of zinc salt to magnesium salt added is 1:5. The synthesis steps of the prepared catalyst applied to catalyze the synthesis of cyclic carbonate from urea and ethylene glycol are also the same as those in Example 4.

[0080] Example 9:

[0081] The catalyst preparation method provided in this example is the same as that in Example 4 except that the molar ratio of zinc salt to magnesium salt added is 5:1. The synthesis steps of the prepared catalyst applied to catalyze the synthesis of cyclic carbonate from urea and ethylene glycol are also the same as those in Example 4.

[0082] Example 10:

[0083] The catalyst preparation method provided in this example is the same as that in Example 4 except that the homogeneous precipitation temperature during the preparation process is 40 °C. The synthesis steps of the prepared catalyst applied to catalyze the synthesis of cyclic carbonate from urea and ethylene glycol are also the same as those in Example 4.

[0084] Example 11:

[0085] The catalyst preparation method provided in this example is the same as that in Example 4 except that the homogeneous precipitation temperature during the preparation process is 220°C, and the synthesis steps of the prepared catalyst for catalyzing the synthesis of cyclic carbonate from urea and ethylene glycol are also the same as those in Example 4.

[0086] Example 12:

[0087] The catalyst preparation method provided in this example is the same as that in Example 4 except that the homogeneous precipitation time during the preparation process is 0.3 h, and the synthesis steps of the prepared catalyst for catalyzing the synthesis of cyclic carbonate from urea and ethylene glycol are also the same as those in Example 4.

[0088] Example 13:

[0089] The catalyst preparation method provided in this example is the same as that in Example 4 except that the calcination temperature during the preparation process is 1000°C, and the synthesis steps of the prepared catalyst for catalyzing the synthesis of cyclic carbonate from urea and ethylene glycol are also the same as those in Example 4.

[0090] Example 14:

[0091] The catalyst preparation method provided in this example is the same as that in Example 4 except that the calcination time during the preparation process is 0.5 h, and the synthesis steps of the prepared catalyst for catalyzing the synthesis of cyclic carbonate from urea and ethylene glycol are also the same as those in Example 4.

[0092] Example 15:

[0093] The catalyst preparation method provided in this example is the same as that in Example 4 except that the calcination time during the preparation process is 12 h, and the synthesis steps of the prepared catalyst for catalyzing the synthesis of cyclic carbonate from urea and ethylene glycol are also the same as those in Example 4.

[0094] Example 16:

[0095] In the synthesis step of using the catalyst provided in this example to catalyze the synthesis of cyclic carbonate from urea and ethylene glycol, the synthesis reaction temperature is 100°C, and the others are the same as those in Example 4.

[0096] Example 17:

[0097] In the synthesis step of using the catalyst provided in this example to catalyze the synthesis of cyclic carbonate from urea and ethylene glycol, the synthesis reaction temperature is 200°C, and the others are the same as those in Example 4.

[0098] Example 18:

[0099] The catalyst provided in this example is applied to the synthesis step of catalytically synthesizing cyclic carbonates from urea and ethylene glycol. The synthesis reaction pressure is 0.5 kPa, and other conditions are the same as those in Example 4.

[0100] Example 19:

[0101] The catalyst provided in this example is applied to the synthesis step of catalytically synthesizing cyclic carbonates from urea and ethylene glycol. The synthesis reaction pressure is 55 kPa, and other conditions are the same as those in Example 4.

[0102] Example 20:

[0103] The catalyst provided in this example is applied to the synthesis step of catalytically synthesizing cyclic carbonates from urea and ethylene glycol. The synthesis reaction time is 7 h, and other conditions are the same as those in Example 4.

[0104] Example 21:

[0105] The catalyst provided in this example is applied to the synthesis step of catalytically synthesizing cyclic carbonates from urea and ethylene glycol. The synthesis reaction time is 0.5 h, and other conditions are the same as those in Example 4.

[0106] Comparative Example 1:

[0107] The catalyst provided in this example is commercially available zinc oxide, which is used to catalyze the synthesis of cyclic carbonates from urea and ethylene glycol. The synthesis steps are the same as those in Example 4.

[0108] Comparative Example 2:

[0109] The catalyst provided in this example is commercially available magnesium oxide, which is used to catalyze the synthesis of cyclic carbonates from urea and ethylene glycol. The synthesis steps are the same as those in Example 4.

[0110] Comparative Example 3:

[0111] The preparation method of the catalyst provided in this example is the same as that in Example 4 except that no ionic liquid is added. The prepared catalyst is also applied to the synthesis step of catalytically synthesizing cyclic carbonates from urea and ethylene glycol, which is the same as that in Example 4.

[0112] In the above examples and comparative examples, after synthesizing cyclic carbonates from urea and diols, gas chromatography was used to quantitatively analyze the product ethylene carbonate.

[0113] Table 1 Results of the alcoholysis reaction of urea in examples and comparative examples

[0114]

[0115]

[0116] As can be seen from the above Examples 4 and Comparative Examples 1 and 2, under the same other conditions, when using the ionic liquid-modified Zn-based composite oxide catalyst to catalyze the synthesis of cyclic carbonates from urea and diols, the urea conversion rate is greatly improved compared with that using single metal oxide catalysts, while the selectivity of cyclic carbonates is similar to that of single metal oxide catalysts, so the yield of cyclic carbonates can be greatly increased.

[0117] In Example 5, the zinc-magnesium composite oxide catalyst modified by tetrabutylphosphonium hydroxide ionic liquid was used to catalyze the preparation of cyclic carbonates from urea and diols under the reaction conditions of 160 °C, 10 kPa, and 3 h. The urea conversion rate can be as high as 93.68%, and the selectivity of ethylene carbonate is as high as 99.14%.

[0118] As can be seen from the comparison between Example 4 and Comparative Example 3 above, when using the ionic liquid-modified Zn-based composite oxide catalyst to catalyze the synthesis of cyclic carbonates from urea and diols, compared with using a binary metal oxide catalyst alone, both the urea conversion rate and the selectivity of cyclic carbonates are greatly improved; compared with Examples 6 and 7, when preparing catalysts to catalyze the synthesis of ethylene carbonate from urea and ethylene glycol only under different molar ratios of ionic liquid to the total zinc and magnesium (5%, 10%, and 20% respectively), the preferred value of the molar ratio of ionic liquid to the total zinc and magnesium is 5%.

[0119] As can be seen from the above Examples 4 and Examples 8 and 9, when other preparation conditions and the conditions applied to the urea alcoholysis synthesis reaction are the same, when zinc nitrate hexahydrate is used as the zinc salt and magnesium nitrate hexahydrate is used as the metal salt, when preparing catalysts and applying them to the synthesis of ethylene carbonate from urea and ethylene glycol only under different molar ratios of the two (4:1, 1:5, 5:1 respectively) and evaluating their catalytic performance, the preferred zinc-magnesium molar ratio is 4:1.

[0120] As can be seen from the above Examples 4 and Examples 10 - 15, during the preparation process, the homogeneous precipitation temperature and time, and the calcination temperature and time have a certain impact on the product selectivity and the reaction substrate urea conversion rate for the subsequent catalysis of the synthesis of ethylene carbonate from urea and ethylene glycol, and need to be controlled during the preparation process.

[0121] As can be seen from the above Examples 4 and Examples 16 - 21, during the process of using the prepared catalyst to catalyze the synthesis of ethylene carbonate from urea and ethylene glycol, the reaction conditions have a great impact on the catalytic performance of the catalyst, and it is necessary to control the synthesis temperature, pressure, and time range during the synthesis process.

[0122] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Claims

1. A method for preparing an ionic liquid modified Zn-based composite oxide catalyst, characterized in that: The preparation method comprises the following steps: Step S1: adding any metal salt of calcium salt, magnesium salt, iron salt, aluminum salt, copper salt, lanthanum salt, zirconium salt, cerium salt and zinc salt to a solvent, and slowly injecting an ionic liquid while fully mixing; Step S2: heating the material after adding the ionic liquid in step S1 at a constant temperature to uniformly precipitate; Step S3: After the precipitation is completed, the product is centrifuged, washed, dried, and then calcined to obtain an ionic liquid-modified Zn-based composite oxide catalyst; In the step S1, the molar ratio of the zinc salt to the metal salt is 1:5 to 5:1, the total molar ratio of the added ionic liquid to the zinc salt to the metal salt is ≤20%, and the general structural formula of the ionic liquid is any one of the following formulas I, II and III: Wherein, in the ionic liquid structure, R1, R2, R3, and R4 are any one of C1 to C8 alkyl groups; the anion X - It is any one of a halogen ion, a hydroxide, a tetrafluoroborate, a hexafluorophosphate, a carboxylate, and an imide.

2. The preparation method according to claim 1, characterized in that: The anion of the zinc salt is any one of halogen ion, nitrate, sulfate, carbonate, acetate and phosphate, and the anion of the metal salt is any one of halogen ion, nitrate, sulfate, carbonate, acetate and phosphate.

3. The preparation method according to claim 1, characterized in that: The solvent is any one of water, methanol, ethanol, N,N-dimethylformamide, n-hexane, isopropanol, ethyl acetate, acetone, dimethyl sulfoxide, dichloromethane and chloroform.

4. The preparation method according to claim 1, characterized in that: In the step S2, the uniform precipitation temperature is 50-200° C., and the uniform precipitation time is 0.5-24 hours.

5. The preparation method according to claim 1, characterized in that: In the step S3, the firing temperature is 200-800° C., and the firing time is 1-10 hours.

6. An ionic liquid modified Zn-based composite oxide catalyst, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 5.

7. A method for synthesizing cyclic carbonates from urea and diols, characterized in that: The ionic liquid-modified Zn-based composite oxide catalyst according to claim 6 is used for catalytic synthesis.

8. The method according to claim 7, characterized in that The method steps are as follows: Step A1: adding urea and diol into a synthesis device, gradually heating and fully stirring; Step A2: adding an ionic liquid modified Zn-based composite oxide catalyst into a synthesis device to catalyze the materials in step A1 for a synthesis reaction; The molar ratio of urea to diol is 1:5 to 2:1, the amount of the catalyst added is 1wt% to 10wt% of the amount of urea added, and the general structural formula of the diol is as follows: In the general structural formula of the diol, R5 and R6 are respectively H or any one of C1-C4 alkyl.

9. The method according to claim 8, characterized in that In the step A2, the synthesis reaction temperature is 120-180° C., the synthesis reaction pressure is 1-50 kPa, and the synthesis reaction time is 1-6 hours.

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