Use of a supported metal catalyst in the transesterification of dimethyl carbonate with phenol

Abstract

The application discloses application of a supported metal catalyst in a dimethyl carbonate and phenol ester exchange reaction, the supported metal catalyst comprising an active component and a carrier, the active component being supported on the carrier; the active component being selected from one or more of Co, Ni, Cu, Ag, Pd; and the carrier being selected from at least one of alumina, silica, ZSM-5, MCM-41, SBA-15 or activated carbon. The catalyst has high activity, and when used in preparation of diphenyl carbonate, the catalyst can achieve high one-way conversion of phenol and effectively break through the limitation of thermodynamic equilibrium, thus providing a possibility for subsequent new processes.

Description

Technical Field

[0001] This invention belongs to the field of diphenyl carbonate preparation technology, specifically relating to the application of a supported metal catalyst in the transesterification reaction of dimethyl carbonate and phenol. Background Technology

[0002] Polycarbonate (PC) is one of the five major engineering plastics with huge market demand. Its traditional production process is the phosgene process, but it faces severe environmental and safety pressures due to the use of highly toxic phosgene. Using dimethyl carbonate (DMC) and phenol as raw materials, the non-phosgene synthesis of diphenyl carbonate (DPC) (a key monomer of polycarbonate) through transesterification is a green synthesis route that has attracted much attention. This route is essentially a two-step reversible reaction in series: (1) First step transesterification: DMC + phenol (1) Toluene carbonate (MPC) + methanol; (2) Second step transesterification: MPC + phenol DPC + methanol. However, the equilibrium constants for both steps are extremely low (typically, K_eq1 and K_eq2 are much less than 1). Due to the strict limitations of this thermodynamic equilibrium, the single-pass conversion of phenol and the yield of DPC are extremely low in conventional fixed-bed transesterification reactors, making them uneconomical.

[0003] To drive the reaction, current industrial technologies generally employ intensified reactive distillation processes. This involves simultaneously conducting the two reactions in a reactive distillation column packed with a solid catalyst, continuously removing the byproduct methanol from the column, thus shifting the reaction equilibrium to the right. While this process achieves the synthesis of DPC, the superimposed equilibrium constraints of the two steps result in a complex reaction system (containing DMC, phenol, MPC, methanol, and DPC). The close boiling points of these components make separation extremely difficult, requiring very high reflux ratios and energy inputs, leading to substantial equipment investment, complex operation, and extremely high energy consumption. Furthermore, in this complex intensified process system, the intrinsic activity of the catalyst is masked, resulting in insufficient catalyst activity.

[0004] To fundamentally reduce energy consumption, researchers proposed the following steps: First, a highly active catalyst is used to obtain MPC in a high-yield transesterification reaction. Then, taking advantage of the relatively large boiling point difference between MPC and components such as phenol, DMC, and methanol, they are efficiently separated via conventional distillation. Finally, the purified MPC is subjected to a disproportionation reaction (2MPC) in another reactor. The disproportionation reaction (DPC + DMC) generates the target product DPC. This disproportionation reaction is unaffected by phenol and methanol, making it thermodynamically more favorable and expected to achieve a high MPC conversion rate. However, this pathway faces a core bottleneck: the activity of existing catalysts is generally low, making them unsuitable for this method. For example, various solid catalysts reported in the literature (such as metal oxides and hydrotalcite) generally achieve single-pass phenol conversion rates below 2%, resulting in insufficient MPC production, making subsequent separation and disproportionation economically infeasible.

[0005] Therefore, there is an urgent need to develop a catalyst with ultra-high intrinsic activity to achieve a high phenol conversion rate. Summary of the Invention

[0006] To overcome the aforementioned technical bottlenecks, the primary objective of this invention is to provide an application of a supported metal catalyst in the transesterification reaction of dimethyl carbonate and phenol. The catalyst possesses extremely high intrinsic activity, which can significantly overcome the thermodynamic equilibrium limitations of the first step of the transesterification reaction, laying the foundation for a new low-energy-consumption process route of "transesterification-separation-disproportionation".

[0007] Another objective of this invention is to provide a method for preparing diphenyl carbonate based on the above-mentioned supported metal catalyst. This method can be used in a highly efficient fixed-bed process or in a simplified reactive distillation process, thereby significantly reducing energy consumption and cost.

[0008] Based on this, the technical solution of the present invention is as follows: The application of a supported metal catalyst in the transesterification reaction of dimethyl carbonate and phenol to prepare diphenyl carbonate, wherein the supported metal catalyst comprises an active component and a support, and the active component is supported on the support; The active component is selected from one or more of Co, Ni, Cu, Ag, and Pd, preferably Ag; the support is selected from at least one of alumina (Al2O3), silicon dioxide (SiO2), ZSM-5, MCM-41, SBA-15, or activated carbon (AC).

[0009] According to an embodiment of the present invention, the carrier is preferably activated carbon (AC).

[0010] According to an embodiment of the present invention, in the supported metal catalyst, the loading of the active component is 0.1-10 wt%, preferably 1-5 wt%, for example 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%.

[0011] According to an embodiment of the present invention, the particle size of the carrier is 1-5 mm, preferably 1-3 mm, and the shape of the carrier is spherical or columnar.

[0012] According to an embodiment of the present invention, when the carrier is activated carbon (AC), its specific surface area is preferably 800-1200 m². 2 / g, with a preferred pore size of 2-50 nm.

[0013] According to an embodiment of the present invention, when the support is activated carbon, the preparation method of the supported metal catalyst is as follows: (S1) Dissolve the salt containing the active component in a solvent to obtain a mixed solution, impregnate the carrier with the obtained mixed solution, and let it stand; (S2) The impregnated support obtained in step (S1) is calcined in an inert atmosphere to obtain the supported metal catalyst.

[0014] In this invention, when the carrier is activated carbon, the salt containing the active component is preferably a nitrate or carbonate of the corresponding metal. During the preparation process, it first thermally decomposes into a metal oxide, and then the activated carbon carrier acts as a reducing agent, reducing the metal oxide in situ to zero-valent metal nanoparticles through a carbothermic reduction reaction (MO + C → M + CO). This process does not require the introduction of additional reducing gas, is completed in one step, and is simple and efficient.

[0015] According to an embodiment of the present invention, when the support is selected from at least one of alumina (Al2O3), silicon oxide (SiO2), ZSM-5, MCM-41, and SBA-15, the method for preparing the supported metal catalyst is as follows: (K1) Dissolve the salt containing the active component in a solvent to obtain a mixed solution, impregnate the carrier with the obtained mixed solution, and let it stand; (K2) The sample obtained in step (K1) is calcined in air or an inert atmosphere; (K3) The sample obtained in step (K2) is reduced with a reducing gas to obtain the supported metal catalyst.

[0016] According to an embodiment of the present invention, in step (S1) or step (K1), the carrier may be subjected to a calcination treatment before impregnation to adjust its surface properties. For example, the calcination temperature is 500-1000℃, the calcination time is 1-6h, and the calcination atmosphere is an inert atmosphere or an air atmosphere.

[0017] According to an embodiment of the present invention, in step (S1) or step (K1), the salt containing the active component includes a nitrate, carbonate, or acetylacetone salt containing the active component. For example, it is selected from at least one of cobalt nitrate, nickel nitrate, copper nitrate, silver nitrate, palladium nitrate, etc.

[0018] According to an embodiment of the present invention, in step (S1) or step (K1), the solvent is selected from at least one of water, ethanol, ammonia, etc.

[0019] According to an embodiment of the present invention, in step (S1) or step (K1), the concentration of the salt containing the active component in the mixed solution is 0.02-0.5 mol / L. -1 .

[0020] According to an embodiment of the present invention, in step (S1) or step (K1), the mass of the salt containing the active component is 0.1 to 15% of the mass of the carrier, preferably 3 to 6%.

[0021] According to an embodiment of the present invention, in step (S1) or step (K1), the volume of the mixed solution is not particularly limited, as long as it can fully or partially impregnate the carrier.

[0022] According to an embodiment of the present invention, in step (S1) or step (K1), the settling time is 12-24 h and the settling temperature is 15-35°C, for example, room temperature.

[0023] According to an embodiment of the present invention, in step (S2) or step (K2), before calcination, the impregnated carrier obtained in step (1) can also be dried, for example, at a drying temperature of 90-120°C and a drying time of 6-12h, for example 12h.

[0024] According to an embodiment of the present invention, in step (S2), the calcination temperature is 500-900℃, preferably 500-800℃, the calcination time is 2-6h, the heating rate during calcination is 2-5℃ / min, and the atmosphere during calcination is an inert atmosphere.

[0025] According to an embodiment of the present invention, in step (K2), the calcination temperature is 300-600℃, preferably 350-500℃, the calcination time is 2-5h, the heating rate during calcination is 2-5℃ / min, and the atmosphere during calcination is air.

[0026] According to an embodiment of the present invention, in step (K3), the reduction temperature is 200-400℃ and the reduction time is 2-6h.

[0027] According to an embodiment of the present invention, in step (K3), the reducing gas can be pure hydrogen or a mixture of hydrogen and an inert gas; the inert gas is, for example, nitrogen or argon. Preferably, it is a mixture of nitrogen and hydrogen in a ratio of 4:1.

[0028] This invention further provides a method for preparing diphenyl carbonate, the method comprising: (1) Mix dimethyl carbonate (DMC), phenol and the above supported metal catalyst and react them.

[0029] According to an embodiment of the present invention, in step (1), the molar ratio of dimethyl carbonate and phenol is 1-6:1, for example 1:1, 2:1, 3:1, 4:1, 5:1 or 6:1.

[0030] According to an embodiment of the present invention, in step (1), the reaction temperature is 150-220°C, preferably 180-200°C, and the reaction pressure is atmospheric pressure.

[0031] According to an embodiment of the present invention, in step (1), the liquid hourly space velocity (LHSV) of the catalyst is 0.5~3.0 h. -1 .

[0032] According to an embodiment of the present invention, the method further includes a step (2) separation process: the mixture obtained in step (1) is subjected to distillation separation, and unreacted DMC, phenol, and byproduct methanol are separated by utilizing the difference in boiling points to obtain intermediate MPC. Preferably, phenol can be recycled. The distillation separation process of the present invention can be any process known in the art.

[0033] According to an embodiment of the present invention, the method further includes step (3) disproportionation reaction: the MPC obtained in step (2) is passed into another fixed-bed transesterification reactor containing the same or different catalysts (preferably the above-mentioned supported metal catalysts), and heated to carry out disproportionation reaction (2MPC → DPC + DMC) to generate the target products DPC and DMC (which can be recycled to step 1); or the MPC obtained in step (2) and the above-mentioned supported metal catalysts are mixed and added to a reaction vessel to carry out disproportionation reaction to obtain the target products DPC and DMC.

[0034] According to an embodiment of the present invention, in step (3), the mass of the supported metal catalyst is 0.5-3 wt% of MPC.

[0035] According to an embodiment of the present invention, in step (3), the temperature of the disproportionation reaction is 180-220℃ and the time of the disproportionation reaction is 2-6h.

[0036] According to an embodiment of the present invention, in step (3), the DMC obtained by the disproportionation reaction can be reused in step (1).

[0037] According to an embodiment of the present invention, the method is carried out in a diphenyl carbonate preparation apparatus, the apparatus comprising a fixed-bed transesterification reactor (3), an intermediate product separation unit (4), and a disproportionation reactor (7) connected in sequence. The fixed-bed transesterification reactor (3) is also connected to the phenol feed tank (1) and the DMC feed tank (2), respectively.

[0038] Preferably, the top of the intermediate product separation unit (4) is also connected to the feed end of the fixed-bed transesterification reactor (3) for recycling the phenol and DMC separated by the intermediate product separation unit (4) to the fixed-bed transesterification reactor (3).

[0039] The beneficial effects of this invention are: 1. The catalyst of this invention has high activity. When used in the preparation of diphenyl carbonate, it results in a high single-pass conversion rate of phenol, effectively breaking through the limitations of thermodynamic equilibrium and providing possibilities for subsequent new processes.

[0040] 2. In the preparation of diphenyl carbonate of the present invention, the separated intermediate MPC is used for the subsequent disproportionation reaction, thus unlocking a new path of "ester exchange-separation-disproportionation reaction". This path avoids the high energy consumption of separating multi-component azeotropes in traditional reactive distillation, and only requires conventional distillation to separate MPC, thereby significantly reducing equipment investment and operating energy consumption.

[0041] 3. The catalyst of this invention adopts a "one-step" process, which cleverly utilizes the reducing properties of activated carbon to combine decomposition and reduction into one process. It requires no washing or external reducing agent, has a short process, is environmentally friendly, and is suitable for industrial scale-up. Attached Figure Description

[0042] Figure 1 This is a diagram of the apparatus for preparing diphenyl carbonate in Example 1 of the present invention; Figure 1 The components are: 1. Phenol feed tank; 2. DMC feed tank; 3. Fixed-bed transesterification reactor; 4. Intermediate product separation unit; 5. Phenol and DMC recycling; 6. Toluene carbonate; 7. Disproportionation reactor; 8. Disproportionation reaction products. Figure 2 This is a TEM image of the Ag / AC catalyst sample from Example 1, showing clearly visible Ag nanoparticles. Detailed Implementation

[0043] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0044] Unless otherwise stated, the raw materials and reagents used in the following examples are all commercially available products.

[0045] The methods in Examples 1-6 were carried out in a diphenyl carbonate preparation apparatus, which includes a fixed-bed transesterification reactor (3), an intermediate product separation unit (4), and a disproportionation reactor (7) connected in sequence. The fixed-bed transesterification reactor (3) is also connected to the phenol feed tank (1) and the DMC feed tank (2), respectively.

[0046] The top of the intermediate product separation unit (4) is also connected to the feed end of the fixed-bed transesterification reactor (3) for recycling the phenol and DMC separated by the intermediate product separation unit (4) to the fixed-bed transesterification reactor (3).

[0047] Example 1: One-step preparation of Ag / AC catalyst and evaluation of transesterification reaction 1. Preparation: a) Carrier pretreatment: 5.0 g of coconut shell activated carbon (AC) was washed three times with deionized water and dried at 110 °C for 12 hours. Then, it was placed in a tube furnace and heated to 800 °C at 5 °C / min under a N2 atmosphere, held for 2 hours, and cooled for later use. b) Impregnation: 0.1598 g of AgNO3 was weighed and dissolved in 10 ml of deionized water. The 5.0 g of pretreated activated carbon was completely impregnated using an equal-volume impregnation method and allowed to stand at room temperature for 24 hours. c) Drying: The impregnated material was dried at 110 °C for 12 hours. d) Calcination and reduction: The dried material was calcined at 700 °C at 2 °C / min under a N2 atmosphere for 4 hours, and then naturally cooled to obtain the Ag / AC catalyst. The calculated Ag loading was 3 wt%.

[0048] The preparation of diphenyl carbonate includes the following steps: (1) In a fixed-bed transesterification reactor, 2.0 g of the above catalyst (particle size 1-2 mm) was loaded. The feed ratio of n(DMC):n(phenol) was 3:1, the reaction temperature was 200℃, the pressure was atmospheric, and the liquid hourly space velocity (LHSV) was 1.0 h⁻¹. -1 After the reaction stabilized for 2 hours, samples were taken online for gas chromatography analysis.

[0049] Results: Phenol conversion rate was 8.5%, MPC selectivity was 78.3%, and DPC selectivity was 5.2% (total selectivity of MPC+DPC was 83.5%).

[0050] (2) Separation process: The mixture obtained in step (1) is separated by distillation in the intermediate product separation unit (4). By utilizing the difference in boiling points, unreacted DMC, phenol and by-product methanol are separated to obtain intermediate MPC.

[0051] (3) Disproportionation reaction: The MPC obtained in step (2) was mixed with the above-mentioned supported metal catalyst and reacted in a sealed high-pressure reactor (i.e., disproportionation reactor (7)). The amount of catalyst used was 2% of the MPC, the reactant was pure MPC, the reaction temperature was 190℃, and the reaction time was 3~5h. The reaction results showed that the MPC conversion rate was 76.8% and the DPC selectivity was 88.5%. This proved the feasibility of the MPC disproportionation pathway.

[0052] Example 2: Preparation and Evaluation of Ag / γ-Al2O3 Catalyst 1. Preparation: a) Support pretreatment: 5.0 g of γ-Al2O3 support was calcined in air at 500 °C for 4 hours. b) Impregnation and drying: γ-Al2O3 was impregnated with an equal volume of AgNO3 solution (the content of AgNO3 was such that the Ag loading was 3 wt%), allowed to stand at room temperature for 24 hours, and then dried at 110 °C for 12 hours. c) Calcination and decomposition: Calcination was carried out in static air at 400 °C for 4 hours. d) Reduction: Reduction was carried out in a 10% H2 / N2 mixed gas at 200 °C for 4 hours to obtain the Ag / γ-Al2O3 catalyst.

[0053] 2. Evaluation: The transesterification reaction was evaluated under exactly the same conditions as in Example 1. Results: Phenol conversion rate 3.2%, MPC selectivity 70.1%.

[0054] Examples 3-6 The difference between Examples 3-6 and Example 1 is that AgNO3 in Example 1 is replaced with Co(NO3)2, Ni(NO3)2, Cu(NO3)2, and Pd(NO3)2 to prepare the corresponding M / AC catalysts, wherein the loading of the active component is 3% in the same way.

[0055] The activity data for Examples 3-6 are shown in Table 1 below.

[0056] Table 1

[0057] The embodiments of the present invention have been described above by way of example. However, the scope of protection of the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The application of a supported metal catalyst in the transesterification reaction of dimethyl carbonate and phenol, characterized in that, The supported metal catalyst includes an active component and a support, wherein the active component is supported on the support. The active component is selected from one or more of Co, Ni, Cu, Ag, and Pd; the support is selected from at least one of alumina, silicon dioxide, ZSM-5, MCM-41, SBA-15, or activated carbon.

2. The application according to claim 1, characterized in that, In the supported metal catalyst, the loading of the active component is 0.1-10 wt%.

3. The application according to claim 1, characterized in that, When the support is activated carbon, the preparation method of the supported metal catalyst is as follows: (S1) Dissolve the salt containing the active component in a solvent to obtain a mixed solution, impregnate the carrier with the obtained mixed solution, and let it stand; (S2) The impregnated support obtained in step (S1) is calcined in an inert atmosphere to obtain the supported metal catalyst; Preferably, when the support is selected from at least one of alumina, silica, ZSM-5, MCM-41, and SBA-15, the preparation method of the supported metal catalyst is as follows: (K1) Dissolve the salt containing the active component in a solvent to obtain a mixed solution, impregnate the carrier with the obtained mixed solution, and let it stand; (K2) The sample obtained in step (K1) is calcined in air or an inert atmosphere; (K3) The sample obtained in step (K2) is reduced with a reducing gas to obtain the supported metal catalyst.

4. The application according to claim 3, characterized in that, In step (S1) or step (K1), the concentration of the salt containing the active component in the mixed solution is 0.02-0.5 mol / L. -1 ; Preferably, in step (S1) or step (K1), the mass of the salt containing the active component is 0.1 to 15% of the mass of the carrier.

5. The application according to claim 3, characterized in that, In step (S2), the calcination temperature is 500-900℃, the calcination time is 2-6h, the heating rate during calcination is 2-5℃ / min, and the atmosphere during calcination is an inert atmosphere. Preferably, in step (K2), the calcination temperature is 300-600℃, the calcination time is 2-5h, the heating rate during calcination is 2-5℃ / min, and the atmosphere during calcination is air. Preferably, in step (K3), the reduction temperature is 200-400℃ and the reduction time is 2-6 hours; Preferably, in step (K3), the reducing gas can be pure hydrogen or a mixture of hydrogen and an inert gas.

6. A method for preparing diphenyl carbonate, characterized in that, The method includes: (1) The dimethyl carbonate (DMC), phenol and the supported metal catalyst used in any of the claims 1-5 are mixed and reacted.

7. The method according to claim 6, characterized in that, In step (1), the molar ratio of dimethyl carbonate to phenol is 1-6:1; Preferably, in step (1), the reaction temperature is 150-220℃ and the reaction pressure is atmospheric pressure; Preferably, in step (1), the liquid hourly space velocity (LHSV) of the catalyst is 0.5~3.0 h⁻¹. -1 .

8. The method according to claim 6, characterized in that, The method further includes step (2) separation process: the mixture obtained in step (1) is separated by distillation, and unreacted dimethyl carbonate, phenol and by-product methanol are separated by the difference in boiling points to obtain the intermediate toluene carbonate.

9. The method according to claim 8, characterized in that, The method further includes step (3) disproportionation reaction: the toluene carbonate obtained in step (2) is passed into another fixed-bed transesterification reactor containing the same or different catalysts, and heated to carry out disproportionation reaction to generate the target products diphenyl carbonate and dimethyl carbonate; or the toluene carbonate obtained in step (2) is mixed with the above-mentioned supported metal catalyst and added to the reactor to carry out disproportionation reaction to obtain the target products diphenyl carbonate and dimethyl carbonate. Preferably, in step (3), the mass of the supported metal catalyst is 0.5-3 wt% of toluene carbonate; Preferably, in step (3), the temperature of the disproportionation reaction is 180-220℃, and the time of the disproportionation reaction is 2-6h; Preferably, in step (3), the dimethyl carbonate obtained by the disproportionation reaction can be reused in step (1).

10. The method according to claim 9, characterized in that, The method is carried out in a diphenyl carbonate preparation apparatus, which includes a fixed-bed transesterification reactor (3), an intermediate product separation unit (4), and a disproportionation reactor (7) connected in sequence. The fixed-bed transesterification reactor (3) is also connected to the phenol feed tank (1) and the dimethyl carbonate feed tank (2), respectively; Preferably, the top of the intermediate product separation unit (4) is also connected to the feed end of the fixed-bed transesterification reactor (3) for recycling the phenol and dimethyl carbonate separated by the intermediate product separation unit (4) to the fixed-bed transesterification reactor (3).

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