A highly efficient and stable strongly alkaline heterogeneous catalyst and its in situ synthesis method and application

Abstract

The present application discloses a highly efficient and stable strongly basic heterogeneous catalyst and its in situ synthesis method and application, belonging to the field of chemistry and chemical engineering. The strongly basic heterogeneous catalyst is a product of a precursor activated by reactants in a fixed bed reactor; the strongly basic heterogeneous catalyst has a strong nucleophilicity, a zwitterionic structure and an N-carbene-CO2 adduct structure. The catalyst preparation adopts a novel online synthesis method; the reactants include esters and alcohols; the esters are selected from at least one of oxalates, acetates, cyclic carbonates, linear carbonates, and acrylates; the alcohols are selected from at least one of methanol, ethanol, and ethylene glycol. The prepared strongly basic heterogeneous catalyst is applied to catalyze various transesterification reactions, preferably solving the problem of difficult separation of homogeneous catalysts and insufficient activity of heterogeneous catalysts.

Description

Technical Field

[0001] The present application relates to an efficient and stable strongly alkaline heterogeneous catalyst and an in-situ synthesis method and application thereof, belonging to the field of chemistry and chemical engineering, specifically to the technical field of ester exchange reaction catalysts. Background Art

[0002] With the advancement of the "dual carbon" goal, reducing fossil energy consumption and utilizing CO2 emitted from industry and people's livelihoods as a resource have become hot topics in current research. The conversion of CO2 into carbonates can achieve 100% utilization of CO2 atoms and has extremely high atomic utilization value. Carbonates, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), are now widely used as organic solvents, lithium battery electrolytes, drug synthesis intermediates, and new material raw materials due to their good organic solubility, conductivity, multiple functional groups, and low toxicity.

[0003] Dimethyl carbonate (DMC), a versatile, low-toxic, or even nontoxic chemical, has found widespread application in lithium-ion battery electrolytes, gasoline additives, polycarbonate raw materials, and pharmaceutical intermediates. Currently, to meet the surging market demand for these products, the industry is using transesterification to produce carbonates. Transesterification catalysts are primarily categorized as homogeneous or heterogeneous, depending on the phases of the catalyst and reactants in the reaction system. Homogeneous catalysts, such as NaOH and sodium methoxide, are widely used due to their low cost, availability, good solubility, and high catalytic activity. Ionic liquids, with their wide liquidus temperature range, environmental friendliness, low volatility, low saturated vapor pressure, and structural designability, have emerged as novel homogeneous catalysts. However, these homogeneous catalysts are readily soluble in the reaction system, making their separation difficult. Consequently, in actual industrial production, product purification and catalyst separation processes are complex and energy-intensive. Another factor hindering the development of this type of catalyst is that homogeneous catalysts are sensitive to water, have poor stability, and generate large amounts of strongly alkaline solid waste during the production process, limiting the development of high-purity carbonate products using homogeneous catalysts. Heterogeneous catalysts effectively overcome the problem of catalyst separation difficulties, but they also have some unavoidable problems, such as low catalytic activity, easy loss of active components, and the need for the reaction to be carried out under high temperature and high pressure conditions. Therefore, the difficulty of separating homogeneous catalysts and their sensitivity to water, and the low activity of heterogeneous catalysts, easy loss of active components, and harsh reaction conditions are the main barriers to the development of transesterification catalysts. Summary of the Invention

[0004] To address the problems of difficult separation of homogeneous catalysts, water sensitivity, generation of strongly alkaline solid waste during use, low activity of heterogeneous catalysts, easy loss of active components, and complex catalyst preparation processes, this application uses a precursor activated by ester exchange reaction raw materials to provide a highly efficient and stable strongly alkaline heterogeneous catalyst and its in situ synthesis method and application. Utilizing the strong nucleophilicity, zwitterionic structure, and N-carbene-CO2 adduct structure of the catalyst structure, it exhibits superior stability and excellent activity in ester exchange reactions.

[0005] This application adopts the following technical solutions:

[0006] A highly efficient and stable strongly basic heterogeneous catalyst, wherein the highly efficient and stable strongly basic heterogeneous catalyst has a structure shown in Formula I:

[0007]

[0008] Wherein, R is selected from C1-C6 alkylene, X is one of the structures represented by Formula A1-Formula A3, and n=1000-3000;

[0009]

[0010] Optionally, it is characterized in that the base strength of the strongly basic heterogeneous catalyst is 9.3 to 12.2.

[0011] Optionally, it is characterized in that the strong alkaline heterogeneous catalyst has an N-carbene-CO2 adduct structure.

[0012] According to another aspect of the present application, a method for preparing the above-mentioned efficient and stable strongly basic heterogeneous catalyst is provided, comprising the following steps:

[0013] S1, swell the chloromethyl polystyrene resin in a solvent, then add a nitrogen-containing heterocycle and react to obtain a precursor;

[0014] S2, placing the precursor obtained in step S1 in a fixed bed reactor, and continuously introducing the reaction raw materials into the fixed bed reactor to contact the precursor, so that the precursor is activated to obtain the strong alkaline heterogeneous catalyst;

[0015] The reaction raw materials include alcohol raw materials and ester raw materials.

[0016] Optionally, in step S2, the activation conditions include: an activation temperature of 70 to 110°C, an activation time of 1 to 8 hours, and a mass space velocity of 1 to 5 hours during the activation process. -1 .

[0017] Optionally, in step S2, in the activation conditions, the activation temperature is selected from any value among 70°C, 80°C, 90°C, 100°C, 110°C, or any range between the two.

[0018] Optionally, in step S2, in the activation conditions, the activation time is selected from any value among 1h, 2h, 4h, 6h, 8h, or any range between them.

[0019] Optionally, in step S2, in the activation conditions, the mass space velocity of the reaction raw materials during the activation process is selected from 1h -1 , 2h -1 , 3h -1 , 4h -1 , 5h -1 Any value in , or any range of values ​​in between.

[0020] Among the activation conditions, the activation time is preferably 2 h, the activation temperature is preferably 110 ° C, and the mass space velocity of the reaction raw materials during the activation process is selected to be 5 h -1 .

[0021] Optionally, the fixed bed reactor is made of stainless steel, has a length of 410 mm, an outer diameter of 160 mm, and a wall thickness of 30 mm.

[0022] Optionally, in step S2, the alcohol raw material is selected from at least one of methanol (MeOH), ethanol (EtOH), and ethylene glycol (EG);

[0023] Optionally, in step S2, the ester raw material is selected from at least one of cyclic carbonates, chain carbonates, acrylates, acetates, and oxalates.

[0024] Preferably, the ester raw material is selected from ethylene carbonate.

[0025] Optionally, in step S2, the molar ratio of the ester raw material to the alcohol raw material is 1:1 to 15, preferably 1:6.

[0026] Optionally, in step S1, the molar ratio of chlorine element to nitrogen-containing heterocycle in the chloromethyl polystyrene resin is 1:1 to 10;

[0027] Optionally, in step S1, the chloromethyl polystyrene resin has a structure as described in Formula II:

[0028] Wherein, R is selected from C1-C6 alkylene, n=1000-3000; preferably, R is C1. The formula I in which R is C1 is abbreviated as PS-Cl.

[0029] Optionally, in step S1, the cross-linking degree of the chloromethyl polystyrene resin is 4-10%, and the chlorine content is 15-25%.

[0030] Optionally, in step S1, the cross-linking degree of the chloromethyl polystyrene resin is preferably 7%, and the chlorine content is preferably 20%.

[0031] Optionally, in step S1, the solvent is selected from at least one of acetonitrile, methanol, ethanol, diethyl ether, and acetone;

[0032] Optionally, in step S1, the reaction conditions include: stirring for 18 to 36 hours.

[0033] Optionally, in step S1, the swelling conditions include: stirring at 60-80°C for 0.5-2h.

[0034] Optionally, in step S1, the swelling time of the chloromethyl polystyrene resin is 0.5 to 2 hours.

[0035] Optionally, in step S1, the nitrogen-containing heterocycle has a structure described in any one of formulas A3 to A6:

[0036]

[0037] Optionally, in step S2, the obtained strong alkaline catalyst is preferably a compound having a structure shown in Formula II:

[0038]

[0039] The strong basic catalyst of formula III is referred to as PS-IMILs.

[0040] Optionally, in step S1, the precursor is preferably a structure described in formula IV:

[0041] The precursor of formula IV is referred to as PS-IM.

[0042] According to another aspect of the present application, there is also provided an application of at least one of the above-mentioned highly efficient and stable strongly alkaline heterogeneous catalyst or the highly efficient and stable strongly alkaline heterogeneous catalyst obtained according to the above-mentioned preparation method in an ester exchange reaction.

[0043] Optionally, the transesterification reaction is selected from the group consisting of a transesterification reaction between a cyclic carbonate and an alcohol, a transesterification reaction between a chain carbonate and an alcohol, a transesterification reaction between an oxalate and an alcohol, a transesterification reaction between an acetate and an alcohol, a transesterification reaction between different oxalates, a transesterification reaction between different carbonates, and a transesterification reaction between an acetate and a formate.

[0044] Optionally, the temperature of the transesterification reaction is the azeotropic temperature of the reaction raw materials.

[0045] The abbreviations in this application have the following meanings:

[0046] In this application, “PS-Cl” is chloromethyl polystyrene resin;

[0047] In this application, “PS-IM” refers to the synthesized precursor;

[0048] In this application, “PS-IMILs” refers to the prepared heterogeneous catalyst PS-IMILs;

[0049] In this application, “EC” refers to ethylene carbonate;

[0050] In this application, “PC” is propylene carbonate;

[0051] In this application, "DEC" is diethyl carbonate;

[0052] In this application, "DMC" is dimethyl carbonate;

[0053] In this application, "EMC" is ethyl methyl carbonate;

[0054] In this application, “EtOH” means ethanol;

[0055] In this application, "MeOH" is methanol;

[0056] In this application, “EG” means ethylene glycol;

[0057] The beneficial effects of this application include:

[0058] The highly efficient and stable strongly basic heterogeneous catalyst provided by the present application has a strong nucleophilicity, a zwitterionic structure and an N-carbene-CO2 adduct structure, and exhibits super stability and excellent activity in transesterification reactions. The prepared strongly basic heterogeneous catalyst has good substrate adaptability in a variety of transesterification reactions. It solves the problems of harsh reaction conditions, low catalyst activity, and poor stability of heterogeneous catalysts in the prior art. The preparation method of the highly efficient and stable strongly basic heterogeneous catalyst provided by the present application synthesizes the precursor by a simple method, and deactivates the precursor with common transesterification reaction raw materials. The preparation process is simple and the operation is friendly, which not only shortens the catalyst preparation process, but also overcomes the problem that the strongly basic catalyst in the prior art is easily exposed to water and the catalytic activity of carbon dioxide is reduced during production and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 Schematic diagram of the synthesis process of precursors and heterogeneous catalysts in this application.

[0060] Figure 2 Image of the fixed-bed reactor used for this application.

[0061] Figure 3 The temperature operation procedure of the fixed bed reactor for this application.

[0062] Figure 4 This is the solid 13C NMR spectrum of the heterogeneous catalyst PS-IMILs prepared in this application.

[0063] Figure 5 This application relates to infrared spectroscopy of catalyst samples.

[0064] Figure 6 This is the XPS spectrum of the heterogeneous catalyst PS-IMILs prepared in this application.

[0065] Figure 7 This is the high-resolution N1s spectrum of the heterogeneous catalyst PS-IMILs prepared in this application.

[0066] Figure 8 This is the O1s high-resolution spectrum of the heterogeneous catalyst PS-IMILs prepared in this application.

[0067] Figure 9 This is the thermogravimetric-differential thermal diagram of the heterogeneous catalyst PS-IMILs prepared in this application under N2 atmosphere.

[0068] Figure 10 The SEM images of the samples involved in this application are (ab) PS-Cl, (c) PS-IM, (df) PS-IMILs; the EDS images of the samples involved in this application are (g) C, (h) N, (i) O, (j) Cl, and (k) element content distribution.

[0069] Figure 11 This is the synthesis mechanism of the heterogeneous catalyst PS-IMILs prepared in this application.

[0070] Figure 12 Evaluation of heterogeneous catalyst PS-IMILs prepared under different synthesis conditions in this application: (a) synthesis temperature, (b) synthesis time.

[0071] Figure 13 Effect of reaction temperature on transesterification.

[0072] Figure 14 Effect of reaction space velocity on transesterification reaction.

[0073] Figure 15 This is the stability evaluation of the heterogeneous catalyst PS-IMILs prepared in this application.

[0074] Figure 16 The catalytic performance of the heterogeneous catalyst PS-IMILs prepared in this application was evaluated in different ester exchange reactions. DETAILED DESCRIPTION

[0075] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0076] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0077] Chloromethylated polystyrene (PS-Cl, Cl content 20 wt.%) was supplied by Jiangsu Saisi Resin Co., Ltd. Ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) were provided by Shenghua New Materials Group Co., Ltd. Acetonitrile and imidazole were purchased from Damao Chemical Reagent Factory. Methanol (MeOH) and ethanol (EtOH) were provided by Tianjin Fuyu Fine Chemical Co., Ltd. Hammett indicators, including neutral red (H_=6.8), bromothymol blue (H_=7.2), phenolphthalein (H_=9.8), and 2,4-dinitroaniline (H_=15.0), were purchased from Damao Chemical Reagent Factory. All materials are analytical reagents.

[0078] Unless otherwise specified, all test methods were conventional, and all instrument settings were manufacturer-recommended. The characterization and analysis methods, including FT-IR, XRD, XPS, SEM, TG-DTA, and alkali strength and alkali content determination in the examples were all conventional procedures, and those skilled in the art can operate according to the instrument specifications.

[0079] The products in this application were analyzed by GC-2010plus gas chromatography. The formulas for calculating the EC conversion, the selectivity of each intermediate product, and the yield of DMC are as follows.

[0080]

[0081] Yield DMC =Con. EC ×Sel. DMC ×100(2.5)

[0082] Where: Con. EC is the conversion rate of ethylene carbonate, %; n DMC , n HEMC and n DHEMC The amounts of dimethyl carbonate, 2-hydroxyethyl methyl carbonate and di-2-hydroxyethyl carbonate, mol; Rem.n EC is the amount of unreacted ethylene carbonate substance, mol; Sel. DMC , Sel. HEMC and Sel. DHEMC Selectivity of dimethyl carbonate, 2-hydroxyethyl methyl carbonate and di-2-hydroxyethyl carbonate, %; Yield DMCis the yield of dimethyl carbonate, %.

[0083] Example 1 Preparation of PS-IM Precursor

[0084] 10g PS-Cl was added to acetonitrile and stirred for 1h, then 4g imidazole was dissolved in the above solution and stirred for 24h. The obtained precursor was washed with acetonitrile and dried at -0.1MPa and 70℃ for 12h. It was named PS-IM precursor. The synthesis mechanism is as follows: Figure 1 shown.

[0085] Examples 2 to 10 One-step in-situ synthesis of heterogeneous catalysts PS-IMILs

[0086] The one-step in situ synthesis method is as follows: 4 g of PS-IM was added to a fixed bed reactor, and then the strong basic catalyst PS-IMILs samples were prepared by adding materials (EC and MeOH, molar ratio of 1:6) under different synthesis conditions. The synthesis mechanism is as follows Figure 1 The parameters of activation time, activation temperature and feed mass space velocity are shown in Table 1. The specific parameters of the fixed bed reactor are: reactor length 410 mm, outer diameter 160 mm, inner diameter 100 mm, fixed bed reactor as shown in Table 1. Figure 2 shown.

[0087] Table 1 Preparation parameters of strong basic heterogeneous catalysts

[0088] Molar ratio of transesterification raw materials Synthesis temperature Synthesis time Resultant airspeed Example 2 EC:MeOH=1:6 70℃ 2h <![CDATA[5h -1 ]]> Example 3 EC:MeOH=1:6 80 ℃ 2h <![CDATA[5h -1 ]]> Example 4 EC:MeOH=1:6 90 ℃ 2h <![CDATA[5h -1 ]]> Example 5 EC:MeOH=1:6 100 ℃ 2h <![CDATA[5h -1 ]]> Example 6 EC:MeOH=1:6 110 ℃ 2h <![CDATA[5h -1 ]]> Example 7 EC:MeOH=1:6 110 ℃ 1h <![CDATA[5h -1 ]]> Example 8 EC:MeOH=1:6 110 ℃ 4h <![CDATA[5h -1 ]]> Example 9 EC:MeOH=1:6 110 ℃ 6h <![CDATA[5h -1 ]]> Example 10 EC:MeOH=1:6 110 ℃ 8h <![CDATA[5h -1 ]]>

[0089] Test Example 1 Nuclear Magnetic Resonance (NMR) Characterization

[0090] Taking the strong alkaline catalyst PS-IMILs sample prepared in Example 5 as an example, 13 C solid-state nuclear magnetic resonance to analyze the chemical structure of PS-IMILs. Figure 4 As shown. Since solid-state NMR technology is affected by factors such as sample morphology, crystal structure, and intermolecular interactions, the shape and peak position of the spectrum will be affected, resulting in peak overlap and hysteresis. When the chemical shift is 12, 13, and 14 ppm, the signal peaks that appear are the signal peaks of different structures C in the imidazole ring. When the chemical shift is at 229 ppm, N-COO - The signal peaks of , indicating that PS-IMILs have active functional groups with NHC-CO2 structure.

[0091] Test Example 2 Fourier Transform Infrared Spectroscopy (FT-IR) Characterization

[0092] Taking the strong alkaline catalyst PS-IMILs sample prepared in Example 5 as an example, the chemical structure of the prepared sample was analyzed by FT-IR spectroscopy. The results are as follows: Figure 5As shown. PS-Cl has a wavelength of 1260-1280 cm -1 A distinct characteristic peak appears at 1260-1280 cm-1, which is attributed to the stretching vibration of the C-Cl bond. -1 The characteristic peak at 701 cm-1 almost disappeared. This indicates that during the reaction of PS-Cl and imidazole to prepare PS-IM, most Cl elements were not replaced by imidazole, but there were still a few Cl elements that were not completely replaced by imidazole. Since PS-Cl is a highly polymerized structure, it is speculated that the Cl elements that failed to undergo substitution reaction with imidazole are mainly distributed in the pore structure of the resin, making it difficult for imidazole molecules to enter, resulting in incomplete reaction. Compared with PS-Cl, PS-IM and PS-IMILs both have a peak at 701 cm-1. -1 and 1558cm -1 New absorption peaks were observed at 1674 cm-1, which were attributed to the stretching vibration peaks of CN and C=N in the imidazole ring, proving that the imidazole ring was successfully combined with the resin matrix in a covalent bond. -1 A distinct characteristic peak was observed in PS-IMILs, which was attributed to the stretching vibration peak of C=O. This indicates that after the PS-IM was activated by EC, an active functional group with an NHC-CO2 structure was generated.

[0093] Test Example 3X-ray Photoelectron Spectroscopy (XPS)

[0094] Taking the strongly basic catalyst PS-IMILs sample prepared in Example 5 as an example, the elemental composition and chemical environment in the PS-IMILs structure were studied using XPS characterization. Figure 6 The XPS spectrum of PS-IMILs is given. From the full XPS spectrum, it can be seen that PS-IMILs contain four elements: O, N, C and Cl. Among them, the Cl element is distributed in the pore structure of the resin via C-Cl bonds, which is consistent with the results of FT-IR analysis. Figure 7 The high-resolution spectrum of N1s is given. When the binding energy is 398.7 and 396.5 eV, the characteristic peaks of NR3 and =N- groups appear, respectively, which is consistent with the environment of N in the imidazole ring. When the binding energy is 399.5 eV, R4N appears. + This indicates that after PS-IM is activated by EC, a group with quaternary ammonium characteristics appears in the imidazole ring. Figure 8 The high-resolution spectrum of O1s is given. When the binding energy is 527.2 and 529.6 eV, the characteristic peaks of CO and C=O groups appear, respectively, proving the existence of active functional groups with NHC-CO2 structure in PS-IMILs.

[0095] Test Example 4 Thermogravimetric-differential thermal analysis (TG-DTA) characterization

[0096] Taking the strong alkaline catalyst PS-IMILs sample prepared in Example 5 as an example, Figure 9 TG, DTA, and DTG data of PS-IMILs are presented. It can be seen that with increasing temperature, the PS-IMILs exhibit four weight loss stages. The first weight loss stage is from room temperature to 135.5°C, with a weight loss of 3.5%, attributed to water adsorbed on the catalyst surface and thermal decomposition of a small amount of sample. The second weight loss stage is from 135.5°C to 258.8°C, with a weight loss of 5.3%, attributed to the thermal decomposition of carboxylic acid groups and alkyl side chains in the sample. As the temperature continues to rise to 388.9°C, a third weight loss stage occurs, with a weight loss of 17.4%, attributed to the thermal decomposition of imidazole rings covalently linked to the polystyrene resin. When the temperature continues to rise to 600°C, a fourth weight loss stage occurs, with a weight loss of 47.9%, attributed to the thermal decomposition of the polystyrene resin. Finally, approximately 23.5 g of residual mass remains, which represents carbon deposits.

[0097] Test Example 5 Scanning Electron Microscope Energy Dispersive Spectrometer (SEM-EDS) Characterization

[0098] The PS-IMILs sample prepared in Example 5 was used as a typical example. The microstructure of the prepared catalyst was characterized and analyzed by SEM. The results are as follows: Figure 10 The microscopic morphology of PS-Cl at different magnifications is shown in Figure 10 As shown in (ab). It can be seen that although the surface of PS-Cl has been subjected to some mechanical wear, the overall morphology is smooth and flat. The SEM characterization of the precursor PS-IM is shown in Figure 10 As shown in (c), the surface of PS-IM is significantly rougher than that of PS-Cl, which is due to the presence of covalently bonded imidazole rings on the surface of the resin spheres. Figure 10 (de) shows the micromorphology of PS-IMILs at different magnifications. It can be seen that the surface becomes very rough, which is attributed to the large amount of generation and accumulation of active sites. In order to investigate the distribution of different elements in PS-IMILs, Figure 10 (fj) shows the EDS graph of PS-IMILs. The results show that the presence of four elements, C, N, O, and Cl, were also observed in PS-IMILs, which is consistent with the XPS analysis results. At the same time, it was observed that the distribution of N and O elements was relatively uniform, which indicates that the active sites of the obtained catalyst were evenly distributed. EDS quantitative results show that the N content in PS-IMILs is 7.6%, and the O content is 14.3%. The molar ratio of the two is about 2:3, which is consistent with the structure of PS-IMILs. In order to further verify this result, organic element analysis was carried out. Figure 10The results in (k) show that the carbon content of the PS-IMILs is 63.4%, the nitrogen content is 7.8%, the oxygen content is 14.8%, and the hydrogen content is 6.7%. The molar ratio of nitrogen to oxygen is also close to 2:3. This indicates the presence of NHC-CO2 structures in the PS-IMILs. However, due to factors such as sensitivity and accuracy of different analytical methods, there are some differences in the values ​​of the organic element analysis results and the EDS quantitative results.

[0099] Examples 11 to 21

[0100] The strongly basic catalyst PS-IMILs sample prepared in Example 5 was used as a typical example and was used as a heterogeneous catalyst in the transesterification reaction of EC and MeOH. The parameters affecting the reaction conditions are shown in Table 2.

[0101] Table 2 Parameters affecting reaction conditions in transesterification of EC and MeOH

[0102] Molar ratio of transesterification raw materials Reaction temperature Reaction space velocity Example 11 EC:MeOH=1:6 30℃ <![CDATA[5h -1 ]]> Example 12 EC:MeOH=1:6 45℃ <![CDATA[5h -1 ]]> Example 13 EC:MeOH=1:6 55℃ <![CDATA[5h -1 ]]> Example 14 EC:MeOH=1:6 68℃ <![CDATA[5h -1 ]]> Example 15 EC:MeOH=1:6 75℃ <![CDATA[5h -1 ]]> Example 16 EC:MeOH=1:6 90℃ <![CDATA[5h -1 ]]> Example 17 EC:MeOH=1:6 68 ℃ <![CDATA[2.5h -1 ]]> Example 18 EC:MeOH=1:6 68 ℃ <![CDATA[7.5h -1 ]]> Example 19 EC:MeOH=1:6 68℃ <![CDATA[10.0h -1 ]]> Example 20 EC:MeOH=1:6 68℃ <![CDATA[12.5h -1 ]]> Example 21 EC:MeOH=1:6 68℃ <![CDATA[15.0h -1 ]]>

[0103] Example 22 Synthesis Mechanism of PS-IMILs

[0104] The synthesis mechanism of PS-IMILs is as follows Figure 11 As shown. The nitrogen atom at position 3 of the imidazole ring in the precursor PS-IMILs has a lone pair of electrons, giving it strong nucleophilic ability. Since the electronegativity of the O atom is greater than that of the carbon atom, the carbonyl carbon atom in ethylene carbonate (EC) has a lower electronegativity and good electrophilic properties. Under high temperature conditions, the nitrogen atom at position 3 of the imidazole ring in PS-IMILs easily undergoes an SN2 reaction with the carbonyl carbon atom in EC to form intermediate I. According to DFT calculation results, intermediate I is found to have a high energy content and an unstable structure. Therefore, the CO bond connected to the carbonyl group will break and undergo a nucleophilic rearrangement reaction and proton transfer reaction with the carbon atom at position 2 of the 1-methylimidazolium cation to form the thermodynamically stable product PS-IMILs.

[0105] Example 23 Equipment Operation Procedure for In-Situ Synthesis of PS-IMILs

[0106] In combination with Examples 2-10, Figure 3The equipment control procedures for the in situ synthesis of PS-IMILs are described, using the catalyst preparation conditions of Example 5 and the transesterification reaction conditions of Example 14. First, the PS-IM is placed in a fixed-bed reactor and maintained at different temperatures for varying periods of time while continuously feeding the reaction feedstock. After the fixed-bed reactor is cooled to 68°C over 1 hour, the resulting heterogeneous catalyst can achieve efficient, stable, and continuous catalysis of the transesterification reaction. During the in situ synthesis of PS-IMILs and the transesterification reaction, the feedstocks (EC and MeOH) are continuously fed into the fixed-bed reactor at a space velocity of 5 h⁻¹.

[0107] Test Example 6 Evaluation of the Effect of Synthesis Conditions on the Catalytic Performance of Heterogeneous Catalyst PS-IMILs

[0108] The catalytic performance of the prepared strong alkaline heterogeneous catalyst in the transesterification reaction of EC and MeOH under the conditions of Example 2-10 was evaluated using the method of Example 23:

[0109] Effect of synthesis temperature: Figure 12 The effects of preparation conditions on catalyst activity are given. Figure 12 (a) shows the effect of reaction temperature on the performance of the synthesized catalyst. It can be seen that as the synthesis temperature increases, the EC conversion, DMC selectivity, and yield all show an upward trend. Notably, at a synthesis temperature of 100°C, the EC conversion is 76.2%, and the DMC selectivity and yield are 88.7% and 67.6%, respectively. At a synthesis temperature of 110°C, the EC conversion is 77.6%, and the DMC selectivity and yield are 88.1% and 68.4%, respectively. This is similar to the catalytic activity exhibited at a synthesis temperature of 100°C.

[0110] The impact of synthesis time: Figure 12 (b) shows the effect of reaction time on the performance of the synthesized catalyst. It can be seen that with increasing reaction time, EC conversion, DMC selectivity, and yield all show an initial increase followed by a decrease. When the synthesis time is 2 h, EC conversion reaches 76.2%, and DMC selectivity and yield reach 88.7% and 67.6%, respectively, reaching their maximum values.

[0111] Test Example 7 Evaluation of the Effect of Reaction Conditions on the Catalytic Performance of Heterogeneous Catalyst PS-IMILs

[0112] The catalytic performance of the prepared strong alkaline heterogeneous catalyst in the transesterification reaction of EC and MeOH under the conditions of Example 2-10 was evaluated using the method of Example 23:

[0113] Effect of reaction temperature: Temperature is an important parameter in transesterification reactions, having a significant impact on reaction rate and product selectivity. Generally, increasing the temperature can accelerate the reaction rate. Figure 13 The effect of reaction temperature on the transesterification reaction is presented, with 68°C being the azeotropic temperature for a molar ratio of EC to MeOH of 1:6. The results show that with increasing reaction temperature, EC conversion, DMC selectivity, and yield all show an upward trend. When the reaction temperature rises from 30°C to 68°C, DMC selectivity increases rapidly. This is because high temperatures favor the conversion of MeOH to methoxy groups, while high methoxy concentrations facilitate the ring opening of EC and promote the cleavage of the CO bond between carbonyl groups. When the temperature is further increased to 90°C, DMC selectivity continues to increase, but at a slower rate, indicating that the reaction is approaching equilibrium.

[0114] Influence of mass space velocity: Mass space velocity is another important parameter affecting the transesterification reaction. When the mass space velocity is higher, the residence time of the raw materials on the catalyst surface is shorter, the reaction depth is reduced, but the raw material processing capacity is higher. When the mass space velocity is lower, the residence time of the raw materials on the catalyst surface is longer, the reaction depth is increased, but the processing capacity is reduced. Figure 14 The effect of mass space velocity on transesterification reaction is given. With the increase of mass space velocity, EC conversion, DMC selectivity and yield all show a downward trend. However, it is worth noting that when the mass space velocity is increased to 15.0h -1 The yield of DMC was still 37.7%. This shows that PS-IMILS has excellent catalytic activity and can be used for large-scale and efficient production of DMC.

[0115] Test Example 8 Evaluation of Catalytic Stability of Heterogeneous Catalyst PS-IMILs

[0116] The stability of the catalyst is very important for the durability and economy of the catalytic reaction. The high-stability catalyst prepared using the technical solution of this application can reduce the replacement frequency and cost, reduce waste generation, and is crucial for the sustainable development of industrial catalytic processes. The catalyst of Example 5 was evaluated for its performance in the long-term catalytic reaction of EC and MeOH esters according to Example 14. The results are as follows: Figure 15 The results showed that after 300 hours of continuous use, the EC conversion rate was 75.9%, and the DMC selectivity and conversion rate were 83.5% and 63.4%, respectively, which were basically consistent with the initial stage of the reaction. In addition, Figure 5 The FT-IR characterization of PS-IMILs after continuous use for 300 hours was given. The results showed that the catalytic performance of PS-IMILs did not change significantly compared with before use, indicating that PS-IMILs have good stability.

[0117] Test Example 9 Evaluation of Various Transesterification Reactions Catalyzed by Heterogeneous Catalyst PS-IMILs

[0118] The catalyst of Example 5 was used to catalyze the transesterification reaction of EC and MeOH, the transesterification reaction of EC and EtOH, the transesterification reaction of PC and MeOH, the transesterification reaction of DMC and EtOH, the transesterification reaction of DEC and MeOH, and the transesterification reaction of DMC and DEC in a fixed bed reactor. The ratio of reaction raw materials, reaction temperature, and reaction space velocity are shown in Table 3. The amount of catalyst was 1% of the mass of esters in the system. Sampling was performed after 24 hours of stable operation in the fixed bed reactor, and the composition of all liquid samples was analyzed using gas chromatograph.

[0119] Table 3

[0120] catalyst Molar ratio of transesterification raw materials Reaction temperature Reaction space velocity PS-IMILs EC:MeOH=1:6 68℃ <![CDATA[5h -1 ]]> PS-IMILs EC:EtOH=1:6 82℃ <![CDATA[1h -1 ]]> PS-IMILs PC:MeOH=1:6 70℃ <![CDATA[1h -1 ]]> PS-IMILs DMC:EtOH=1:6 95℃ <![CDATA[1h -1 ]]> PS-IMILs DEC:MeOH=1:6 95℃ <![CDATA[1h -1 ]]> PS-IMILs DMC:DEC=1:1 110℃ <![CDATA[1h -1 ]]>

[0121] Figure 16The catalytic performance of PS-IMILs in various transesterification reactions is presented, and the corresponding transesterification reaction equations are provided in the SI. It can be seen that PS-IMILs exhibit good catalytic activity in a variety of transesterification reactions, however, their catalytic performance varies depending on the reaction system. When PS-IMILs catalyzed the transesterification of EC and MeOH, the EC conversion was 76.2%, and the selectivity and yield of the target product DMC were 88.7% and 67.6%, respectively. When PS-IMILs catalyzed the transesterification of EC and EtOH, the EC conversion was 68.7%, and the selectivity and yield of the target product DEC were 31.7% and 21.8%, respectively. This indicates that the transesterification reaction between EC and MeOH is more efficient than that between EC and EtOH. This is because the OH bond energy of MeOH molecules is lower, making them more easily activated by PS-IMILs to methoxy groups, thereby promoting the transesterification reaction. When PS-IMILs catalyzed the transesterification reaction between PC and MeOH, the PC conversion was 45.5%, and the selectivity and yield of the target product, DMC, were 81.4% and 37.1%, respectively. This indicates that the transesterification reaction between EC and MeOH was more efficient than that between PC and MeOH. This is due to the presence of -CH3 in the PC structure, which not only reduces electron delocalization in the CO bond but also increases steric hindrance, thus reducing the efficiency of the PC transesterification reaction. When PS-IMILs catalyzed the transesterification reaction between DMC and EtOH, the DMC conversion was 83.5%, and the selectivity and yield of the target product, DEC, were 58.0% and 48.4%, respectively. When PS-IMILs catalyzed the transesterification reaction between DMC and EtOH, the DEC conversion was 86.7%, and the selectivity and yield of the target product, DMC, were 75.1% and 65.1%, respectively. This indicates that the transesterification reaction between DEC and MeOH was more efficient than that between DMC and EtOH. This is also related to the lower OH bond energy of the MeOH molecule, which is more easily activated to methoxy groups. When PS-IMILs catalyzed the transesterification of DMC and DEC, the DMC conversion was 41.1%. Since no byproducts were produced in this reaction, the selectivity for the target product, EMC, was as high as 99.9%, resulting in a calculated EMC yield of 41.0%. This demonstrates that the prepared PS-IMILs catalyst exhibits excellent catalytic activity not only in alcohol-ester transesterification reactions but also in ester-ester reactions.

[0122] The above descriptions are merely a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, they are not intended to limit the present application. Any technical personnel familiar with the present profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A highly efficient and stable in-situ synthesis method of a strongly basic heterogeneous catalyst, characterized in that: The steps include: S1, swell the chloromethyl polystyrene resin in a solvent, then add a nitrogen-containing heterocycle and react to obtain a precursor; S2, placing the precursor obtained in step S1 in a fixed bed reactor, and continuously introducing the reaction raw materials into the fixed bed reactor to contact the precursor, so that the precursor is activated to obtain the strong alkaline heterogeneous catalyst; The reaction raw materials are ester exchange reaction raw materials; The reaction raw materials include alcohol raw materials and ester raw materials; The highly efficient and stable strongly alkaline heterogeneous catalyst has a structure shown in Formula I: Wherein, R is selected from C1 to C6 alkylene, X is one of the structures represented by Formula A1 to Formula A3, and n=1000 to 3000; The strongly basic heterogeneous catalyst has an N-carbene-CO2 adduct structure.

2. The synthesis method according to claim 1, wherein The base strength of the strongly basic heterogeneous catalyst is 9.3 to 12.

2.

3. The in-situ synthesis method according to claim 1, wherein In step S2, the activation conditions include: activation temperature of 70-110°C, activation time of 1-8 hours, and mass space velocity of the reaction raw materials during the activation process of 1-5 hours. -1 .

4. The in-situ synthesis method according to claim 1, wherein In step S2, the alcohol raw material is selected from at least one of methanol, ethanol, and ethylene glycol.

5. The in-situ synthesis method according to claim 1, characterized in that In step S2, the ester raw material is selected from at least one of cyclic carbonate, chain carbonate, acrylate, acetate, and oxalate.

6. The in-situ synthesis method according to claim 1, characterized in that In step S2, the molar ratio of the ester raw material to the alcohol raw material is 1:1-15.

7. The in-situ synthesis method according to claim 1, characterized in that In step S1, the molar ratio of chlorine element to nitrogen-containing heterocycle in the chloromethyl polystyrene resin is 1:1-10.

8. The in-situ synthesis method according to claim 1, characterized in that In step S1, the chloromethyl polystyrene resin has a structure as described in Formula II: Wherein, R is selected from C1-C6 alkylene, and n=1000-3000.

9. The in-situ synthesis method according to claim 1, characterized in that In step S1, the solvent is selected from at least one of acetonitrile, methanol, ethanol, diethyl ether, and acetone.

10. The in-situ synthesis method according to claim 1, characterized in that In step S1, the reaction conditions include: stirring for 18 to 36 hours.

11. The in-situ synthesis method according to claim 1, characterized in that In step S1, the swelling conditions include: stirring at 60-80°C for 0.5-2h.

12. The in-situ synthesis method according to claim 1, characterized in that In step S1, the nitrogen-containing heterocycle has a structure described in any one of formulas A3 to A6:

13. Use of at least one of the highly efficient and stable strongly basic heterogeneous catalysts obtained according to the in situ synthesis method according to any one of claims 1 to 12 in a transesterification reaction.

14. The use according to claim 13, characterized in that The transesterification reaction is selected from the group consisting of a transesterification reaction between a cyclic carbonate and an alcohol, a transesterification reaction between a chain carbonate and an alcohol, a transesterification reaction between an oxalate and an alcohol, a transesterification reaction between an acetate and an alcohol, a transesterification reaction between different oxalates, a transesterification reaction between different carbonates, and a transesterification reaction between an acetate and a formate.

15. The use according to claim 13, characterized in that The temperature of the transesterification reaction is the azeotropic temperature of the reaction raw materials.

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