Method for preparing diphenyl carbonate through transesterification
Through a synergistic catalyst system of 4-dimethylaminopyridine, nano cerium oxide and tetramethylurea, combined with a high-boiling solvent diphenyl ether and nitrogen-protected transesterification reaction, the problem of low catalyst stability and conversion in diphenyl carbonate synthesis is solved, and efficient and green diphenyl carbonate production is achieved.
Patent Information
- Application Number
- CN202510805711.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-17
- Publication Date
- 2025-08-01
AI Technical Summary
The existing diphenyl carbonate synthesis methods have problems such as poor catalyst stability, difficulty in recycling, high separation cost from products, low reaction reversibility and low conversion rate, resulting in the yield of diphenyl carbonate generally less than 50%.
The synergistic catalyst system of 4-dimethylaminopyridine, nano cerium oxide and tetramethylurea is adopted, combined with high boiling point solvent diphenyl ether and inert gas nitrogen protection, dimethyl carbonate was added dropwise by temperature control and methanol was absorbed using 3A molecular sieve, and thermal filtration and low-temperature crystallization process were combined to optimize the transesterification reaction conditions.
The phenol conversion rate is greater than 99.5%, and the diphenyl carbonate yield is greater than 99%, which significantly improves the reaction efficiency and product purity, and meets the requirements of green chemical industry.
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Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of organic synthesis, and particularly relates to a method for preparing diphenyl carbonate by transesterification reaction. Background Art
[0002] Diphenyl carbonate is a non-toxic, non-corrosive, and pollution-free organic carbonate with good chemical stability and thermal stability. It is mainly used for synthesizing polycarbonate, which has excellent comprehensive properties and is widely used in fields such as electronic appliances, automotive industry, and construction. With the development of related industries, the demand for diphenyl carbonate is increasing continuously. In addition, other applications of diphenyl carbonate may be continuously developed, such as its applications in preparing other high-performance polymer materials and pharmaceutical intermediates. And as an environmentally friendly chemical material, under the background of the increasing global attention to environmental protection, diphenyl carbonate meets the requirements of sustainable development and will receive policy support and promotion, with great potential.
[0003] Traditional synthesis methods of diphenyl carbonate include phosgene method, oxidative carbonylation method, and transesterification method.
[0004] The phosgene method has been gradually phased out due to the high toxicity and strong corrosiveness of phosgene.
[0005] The oxidative carbonylation method uses phenol, CO, and O2 as raw materials, requires a noble metal (such as palladium) catalyst, and has harsh reaction conditions (high temperature and high pressure). The by-product water is difficult to remove in time, resulting in the easy oxidation of CO to CO2, reducing the yield (usually less than 50%), and the catalyst cost is high, with poor industrial economy.
[0006] Currently, the industrial preparation of diphenyl carbonate (DPC) mainly relies on the transesterification method. The technical characteristics and problems are as follows:
[0007] 1. Mainly uses homogeneous catalysts such as titanate and tin, with the conversion rate generally at 70%-75% and the selectivity at 60%-65%. However, there are problems such as poor catalyst stability, difficult recovery, and high cost of separation from the product.
[0008] 2. Although it is a green alternative route, the reaction is reversible and the equilibrium constant is low, and it is necessary to continuously remove the by-products to promote the reaction. Existing technologies are difficult to efficiently break the equilibrium, resulting in a low conversion rate.
[0009] 3. The by-products reduce the selectivity of DPC, and the DPC yield of existing processes is generally less than 50%. Summary of the Invention
[0010] The present invention precisely aims at the above problems and provides a method for preparing diphenyl carbonate by transesterification reaction, which is a method for preparing diphenyl carbonate by transesterification reaction, and particularly designs the synergistic optimization of the catalyst system and process parameters.
[0011] To achieve the above object, the present invention is realized by the following technical solution:
[0012] The present invention discloses a method for preparing diphenyl carbonate by transesterification, comprising the following steps:
[0013] 1) Add 4-dimethylaminopyridine, nano-ceria and tetramethylurea into a multifunctional crushing and mixing device, and after uniformly dispersing at room temperature, obtain a composite catalyst;
[0014] 2) Under nitrogen protection, add phenol, the catalyst obtained in step 1), and diphenyl ether into a reaction kettle, start stirring, and heat up to 70-90 °C, and fully stir until the solution is uniformly dispersed;
[0015] 3) Subsequently, dropwise add dimethyl carbonate, control the dropping time within 2-3 hours, and control the temperature at 100-120 °C. During the process, use nitrogen to carry the methanol vapor generated by the reaction, connect the nitrogen outlet to a 3A molecular sieve absorption column to absorb methanol. After the dropping is completed, continue to keep the temperature for reaction for 1-2 h;
[0016] 4) After the reaction is completed, slowly cool down to 80-90 °C, carry out hot filtration, separate and recover the solid catalyst, continue to cool down the obtained filtrate to 50-60 °C to precipitate diphenyl carbonate crystals, keep the temperature for crystal cultivation for 1-2 h, and then carry out suction filtration to obtain mother liquor and crude diphenyl carbonate;
[0017] 5) Wash the crude diphenyl carbonate with toluene, and vacuum dry to obtain white diphenyl carbonate solid, and the mother liquor is directly recycled back to the reaction system.
[0018] As a further improvement, the nano-ceria in step 1) of the present invention is prepared by a melting-gel method and modified with acetylacetone, and the particle diameter is 5-10 nm.
[0019] As a further improvement, the mass ratio of 4-dimethylaminopyridine:nano-ceria:tetramethylurea in step 1) of the present invention is 122:40.7-73.2:227-366.
[0020] As a further improvement, the mass ratio of phenol:catalyst:solvent in step 2) of the present invention is 94:1.88-4.7:850-1700.
[0021] As a further improvement, the ratio of phenol:dimethyl carbonate in step 3) of the present invention is 94:49.5-58.5.
[0022] As a further improvement, the phenol conversion rate in the method of the present invention is greater than 99.5%, and the diphenyl carbonate yield is greater than 99%.
[0023] The beneficial effects of the present invention are as follows:
[0024] 1. An efficient solvent, diphenyl ether, is adopted. By virtue of its high boiling point (259 °C), the reaction is ensured to proceed. The low solubility at 50 - 60 °C is utilized to achieve efficient crystallization of DPC, while meeting the requirements of high-temperature safety and green chemistry.
[0025] 2. Through the synergistic catalytic effect of 4-dimethylaminopyridine, nano-ceria, and tetramethylurea in the present invention, DMAP, as a strong nucleophilic catalyst, activates phenol. After nano-CeO2 (5 - 10 nm) is modified with acetylacetone, the surface Lewis acid sites are highly dispersed, significantly activating the carbonyl group of dimethyl carbonate (DMC). Tetramethylurea activates the carbonyl group of DMC and accelerates the reaction of DMC. And when the mass ratio of 4-dimethylaminopyridine : nano-ceria : tetramethylurea is 122 : 40.7 - 73.2 : 227 - 366, the catalytic effect is the best, enabling the yield of DMC to break through and be greater than 99%, far higher than the level of 70 - 75% of the traditional transesterification method.
[0026] 2. Aiming at the core problems of the reversibility of the transesterification reaction and the low equilibrium constant, the present invention creatively adopts the strategy of temperature-controlled dropping combined with purging with an inert gas (N2). The reaction temperature is controlled at 100 - 120 °C, dimethyl carbonate is dropped, and at the same time, methanol is continuously removed by nitrogen and a 3A molecular sieve adsorption column is connected to adsorb the removed methanol. The dropping time is controlled within 2 - to 3 hours to make the dropping rate match the efficiency of methanol removal from the system. Such a design cuts off the reverse reaction path completely while ensuring an efficient reaction, strongly promoting the forward progress of the reaction.
[0027] 3. By means of hot filtration at 80 - 90 °C, not only the efficient recovery of nano-ceria is ensured, but also the precipitation of other substances is avoided, improving the product purity. Then, by utilizing the property of DPC to crystallize at a low temperature of 50 - 60 °C and performing crystal cultivation for 🌡️1 - 2 h, the product quality is ensured. Finally, primary separation of the product is achieved through simple suction filtration, combined with toluene washing, avoiding traditional distillation and completely avoiding high-temperature degradation of the product. The process has significant advantages in terms of safety, mildness of operating conditions, raw material cost, environmental friendliness, and ultimate economic benefits, meeting the development direction of green chemical engineering. Detailed implementation modes
[0028] The technical solutions of the present invention will be further described in detail below in conjunction with specific embodiments, but the scope of the present invention is not limited to the embodiments.
[0029] Example 1
[0030] Preparation of the catalyst
[0031] 1) 10 g of cerium nitrate hexahydrate was added to 50 mL of absolute ethanol and stirred until dissolved. 5 mL of acetylacetone was added dropwise, followed by 2 mL of deionized water, and the mixture was stirred at 80 °C until a transparent sol was formed.
[0032] 2) It was left standing at 60 °C for 24 h, dried at 120 °C for 6 h, and calcined in air at 500 °C for 4 h to obtain nano-CeO2 (particle size 5 - 10 nm).
[0033] Preparation of the product
[0034] 1) 122 g of 4-dimethylaminopyridine, 40.7 g of the nano-ceria prepared above, and 227 g of tetramethylurea were added to a multi-functional crushing and mixing device. After being dispersed evenly at room temperature, a composite catalyst was obtained. The multi-functional crushing and mixing device is the device in Patent CN114453118B.
[0035] 1) Under nitrogen protection, 94 phenol, 1.88 g of the catalyst obtained in step 1), and 850 g of diphenyl ether were added to a reaction kettle. Stirring was started and the temperature was raised to 70 °C. After sufficient stirring until the solution was evenly dispersed.
[0036] 2) Subsequently, 49.5 g of dimethyl carbonate was added dropwise over 2 hours, and the temperature was controlled at 100 °C. During the process, the methanol vapor generated by the reaction was carried by nitrogen, and the nitrogen outlet was connected to a 3A molecular sieve absorption column to absorb methanol. After the dropwise addition was completed, the reaction was continued under insulation for 1 h.
[0037] 3) After the reaction was completed, the temperature was slowly lowered to 80 °C, and hot filtration was carried out to separate and recover the solid catalyst. The obtained filtrate was further cooled to 50 °C to precipitate diphenyl carbonate crystals. After holding for 1 h for crystal growth, suction filtration was carried out to obtain the mother liquor and crude diphenyl carbonate.
[0038] 4) The crude diphenyl carbonate was washed with toluene and dried under vacuum to obtain white diphenyl carbonate solid, and the mother liquor could be directly recycled back to the reaction system.
[0039] The experimental results are shown in the following table
[0040] Table 1 is the result table of Example 1
[0041] Phenol conversion rate DPC yield 99.6％ 99.4％
[0042] Example 2
[0043] 1) 122 g of 4-dimethylaminopyridine, 57 g of the nano-ceria prepared in Example 1, and 297 g of tetramethylurea were added to a multi-functional crushing and mixing device. After being dispersed evenly at room temperature, a composite catalyst was obtained.
[0044] 2) Under nitrogen protection, 94 g of phenol, 3.29 g of the catalyst obtained in step 1), and 1275 g of diphenyl ether were added to the reaction kettle. Stirring was started and the temperature was raised to 80 °C. After sufficient stirring until the solution was evenly dispersed.
[0045] 3) Subsequently, 54 g of dimethyl carbonate was added dropwise over 2.5 hours, and the temperature was controlled at 110 °C. During the process, nitrogen was used to carry the methanol vapor generated by the reaction, and the nitrogen outlet was connected to a 3A molecular sieve absorption column to absorb methanol. After the addition was completed, the reaction was continued under insulation for 1.5 h.
[0046] 4) After the reaction was completed, the temperature was slowly lowered to 85 °C, and hot filtration was carried out to separate and recover the solid catalyst. The obtained filtrate was further cooled to 55 °C to precipitate diphenyl carbonate crystals. After holding the temperature for crystal growth for 1.5 h, suction filtration was carried out to obtain the mother liquor and crude diphenyl carbonate.
[0047] 5) The crude diphenyl carbonate was washed with toluene and dried under vacuum to obtain white diphenyl carbonate solid, and the mother liquor could be directly recycled back to the reaction system.
[0048] The experimental results are shown in the following table
[0049] Table 2 Results of Example 2
[0050] Phenol conversion rate DPC yield 99.8％ 99.9％
[0051] Example 3
[0052] 1) 122 g of 4-dimethylaminopyridine, 73.2 g of the nano-ceria prepared in Example 1, and 366 g of tetramethylurea were added to a multi-functional crushing and mixing device. After being evenly dispersed at room temperature, a composite catalyst was obtained.
[0053] 2) Under nitrogen protection, 94 g of phenol, 4.7 g of the catalyst obtained in step 1), and 1700 g of diphenyl ether were added to the reaction kettle. Stirring was started and the temperature was raised to 90 °C. After sufficient stirring until the solution was evenly dispersed.
[0054] 3) Subsequently, 58.5 g of dimethyl carbonate was added dropwise over 3 hours, and the temperature was controlled at 120 °C. During the process, nitrogen was used to carry the methanol vapor generated by the reaction, and the nitrogen outlet was connected to a 3A molecular sieve absorption column to absorb methanol. After the addition was completed, the reaction was continued under insulation for 2 h.
[0055] 4) After the reaction was completed, the temperature was slowly lowered to 90 °C, and hot filtration was carried out to separate and recover the solid catalyst. The obtained filtrate was further cooled to 60 °C to precipitate diphenyl carbonate crystals. After holding the temperature for crystal growth for 2 h, suction filtration was carried out to obtain the mother liquor and crude diphenyl carbonate.
[0056] 5) The crude diphenyl carbonate was washed with toluene and dried under vacuum to obtain white diphenyl carbonate solid, and the mother liquor could be directly recycled back to the reaction system.
[0057] The experimental results are shown in the following table
[0058] Table 3 is the result table of Example 3
[0059] Phenol conversion rate DPC yield 99.7％ 99.6％
[0060] Example 4
[0061] The mother liquor of Example 2 was directly applied to the next round of reaction, and phenol and DMC were supplemented and applied continuously for 5 times. The experimental results are shown in the following table
[0062] Table 4 is the performance test table of mother liquor application
[0063]
[0064]
[0065] Comparative Example 1
[0066] The solvent was changed to toluene, and the experiment was carried out according to Example 2. The results are shown in the following table
[0067] Table 5 is the result table of Comparative Example 1
[0068] Phenol conversion rate DPC yield 65.4％ 72.5％
[0069] Comparative Example 2
[0070] The solvent was changed to o-dichlorobenzene, and the experiment was carried out according to Example 2. The results are shown in the following table
[0071] Table 6 is the result table of Comparative Example 2
[0072] DPC yield DPC purity 85..6％ 76.4％
[0073] It can be seen that by comparing Comparative Examples 1-2 with Example 2, compared with the low-boiling solvent toluene, the high boiling point of diphenyl ether effectively avoids the significant volatilization loss during the high-temperature stage of the reaction, ensures the stability of the reaction system concentration and good mass transfer efficiency, and thus significantly improves the DPC yield. Compared with other high-boiling solvents (such as o-dichlorobenzene), diphenyl ether provides a more suitable solubility and reaction medium environment, with higher yield and product purity
[0074] Comparative Example 3
[0075] Only DMAP was added, and the experiment was carried out according to Example 2. The results are shown in the following table
[0076] Table 7 is the result table of Comparative Example 3
[0077] Phenol conversion rate DPC yield 74.2％ 75.3％
[0078] Comparative Example 4
[0079] Without adding nano-cerium oxide, experiments were carried out according to Example 2, and the results are shown in the following table.
[0080] Table 8 is the result table of Comparative Example 4.
[0081] Phenol conversion rate DPC yield 76.8％ 80.4％
[0082] Comparative Example 5
[0083] Without adding tetramethylurea, experiments were carried out according to Example 2, and the results are shown in the following table.
[0084] Table 9 is the result table of Comparative Example 5.
[0085] Phenol conversion rate DPC yield 78.7％ 82.5％
[0086] It can be seen that by comparing Comparative Examples 3-5 with Example 2, for the single catalyst or the pairwise paired system, compared with the synergistic catalysis of DMAP, nano-cerium oxide and urea derivatives (such as tetramethylurea), the conversion rate of phenol and the selectivity of DPC decreased significantly.
[0087] Comparative Example 6
[0088] Using ordinary CeO2, experiments were carried out under the same conditions as in Example 2, and the results are shown in the following table.
[0089] Table 10 is the result table of Comparative Example 6.
[0090] Phenol conversion rate DPC yield 85％ 88％
[0091] It can be seen that after nano-CeO2 (5-10 nm) is modified by acetylacetone, the surface Lewis acid sites are highly dispersed, significantly activating the carbonyl group of dimethyl carbonate (DMC).
[0092] Comparative Example 7
[0093] Without using the dropping method, phenol and dimethyl carbonate were added together, and the other conditions were the same as in Example 2, and the results are shown in the following table.
[0094] Table 11 is the result table of Comparative Example 7.
[0095] Phenol conversion rate DPC yield 84.3％ 75.2％
[0096] It can be seen that the dropping method has obvious advantages over the one-time addition. By using the dropping method, the local concentration of dimethyl carbonate can be controlled, avoiding its excessive accumulation in the initial stage of the reaction and maintaining the positive shift of the chemical equilibrium.
[0097] Comparative Example 8
[0098] Experiments were carried out according to Example 2, but without the methanol removal step, and the results are shown in the following table.
[0099] Table 12 is the result table of comparative example 8
[0100]
[0101]
[0102] It can be seen that the present invention completely cuts off the reverse reaction pathway by continuously and efficiently removing the by-product methanol vapor and immediately adsorbing the removed methanol with molecular sieves, strongly promoting the forward reaction, and greatly improving the DMC conversion rate and DPC selectivity.
[0103] Finally, it should be noted that the examples listed above are merely specific implementation examples of the present invention. Obviously, the present invention is not limited to the examples listed above and is subject to numerous variations. Any variations that can be directly derived or conceived by a person skilled in the art from the disclosure of this invention should be considered within the scope of protection of the present invention.
Claims
1. A method for preparing diphenyl carbonate by transesterification, characterized in that, The following steps are involved: 1) adding 4-dimethylaminopyridine, nano-cerium oxide, and tetramethylurea into a multifunctional crushing and mixing device, and uniformly dispersing them at room temperature to obtain a composite catalyst; 2) Under nitrogen protection, phenol, the catalyst obtained in step 1), and diphenyl ether were added to a reaction kettle, stirring was started, and the temperature was raised to 70-90° C., and stirred thoroughly until the solution was evenly dispersed; 3) Dimethyl carbonate was then added dropwise over a period of 2-3 hours, and the temperature was controlled at 100-120°C. During the process, nitrogen was used to carry the methanol vapor generated by the reaction. The nitrogen outlet was connected to a 3A molecular sieve absorption column to absorb the methanol. After the addition was completed, the reaction was continued at this temperature for 1-2 hours. 4) After the reaction is completed, the temperature is slowly lowered to 80-90° C., hot filtration is performed to separate and recover the solid catalyst, and the resulting filtrate is further cooled to 50-60° C. to precipitate diphenyl carbonate crystals, which are then kept warm for 1-2 hours and then filtered to obtain a mother liquor and crude diphenyl carbonate; 5) The crude diphenyl carbonate was washed with toluene and dried in vacuo to obtain a white diphenyl carbonate solid. The mother liquor was directly returned to the reaction system.
2. The method for preparing diphenyl carbonate by transesterification according to claim 1, characterized in that, The nano-cerium oxide in step 1) is prepared by a melt-gel method and modified with acetylacetone, with a particle diameter of 5-10 nm.
3. The method for preparing diphenyl carbonate by transesterification according to claim 1 or 2, characterized in that, The mass ratio of 4-dimethylaminopyridine: nano-cerium oxide: tetramethylurea in the step 1) is 122:40.7-73.2:227-366.
4. The method for preparing diphenyl carbonate by transesterification according to claim 3, characterized in that, The mass ratio of phenol:catalyst:solvent in the step 2) is 94:1.88-4.7:850-1700.
5. The method for preparing diphenyl carbonate by transesterification according to claim 4, characterized in that, In the step 3), the ratio of phenol to dimethyl carbonate is 94:49.5-58.
5.
6. The method for preparing diphenyl carbonate by transesterification according to claim 1 or 2 or 4 or 5, characterized in that, In the method, the phenol conversion rate is greater than 99.5%, and the diphenyl carbonate yield is greater than 99%.