Catalyst for catalytic synthesis of dimethyl carbonate, preparation method and application

Abstract

The invention provides a catalyst for catalytic synthesis of dimethyl carbonate as well as a preparation method and application of the catalyst. The catalyst comprises a carrier formed by a covalent organic framework, the active metal and the assistant metal are loaded on the carrier by using an ultrasonic-assisted in-situ complexation method, so that the active metal and the assistant metal are stably complexed to form a monatomic active metal structure with an out-of-plane coordination configuration; the active metal is a metal palladium compound, and the loading capacity of the active metal is 0.01-0.2 w.t.% on the basis of the catalyst; the loading capacity of the auxiliary agent metal is 0.01-5w. T.%; and the carrier is a COF material. The catalyst has a binary metal system with a synergistic effect, the catalyst is prepared through an ultrasonic-assisted in-situ complexation method, and in the process of synthesizing dimethyl carbonate through reaction of carbon monoxide and methyl nitrite, the catalyst achieves high conversion rate and selectivity with low palladium loading capacity.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts for gas-phase synthesis of dimethyl carbonate, and particularly relates to a catalyst for catalytic synthesis of dimethyl carbonate, a preparation method and application thereof. Background Art

[0002] Dimethyl carbonate (DMC) is a widely used organic compound and an important chemical product. It can be used as an organic solvent, electrolyte, methylation reagent, etc., and has a wide range of applications in the fields of medicine, pesticides, materials, fuels, batteries, etc. DMC has low toxicity and is a clean, green, environmentally friendly organic chemical raw material, which conforms to the current sustainable development concept of the chemical industry. DMC has excellent solubility and can be used as a low-toxic solvent to replace some highly toxic or harmful solvents; DMC contains carbonyl groups in its structure and can be used as a carbonylation reagent to synthesize carbonates, polycarbonates, etc.; DMC contains methyl groups in its structure and can be used as a low-toxic methylation reagent in organic synthesis reactions; it has a high octane number and can be used as a gasoline or diesel additive; in recent years, driven by industries such as new energy vehicles, the demand for fuel cells has increased day by day, and DMC can be used as an electrolyte for fuel cells, and its demand has also greatly increased. Therefore, DMC has a wide range of uses and a large demand, and its synthesis process is one of the current research hotspots.

[0003] In the synthesis process of DMC, the low-pressure gas phase carbonylation synthesis process has great advantages. This process uses CO and methyl nitrite (MN) as raw materials, belongs to the coal chemical process, and the raw materials used come from the downstream products of coal chemical industry, which is in line with the national conditions of abundant coal. This process has the characteristics of mild conditions, environmental friendliness, and easy separation of products, and is considered to be the most promising DMC production process. This process was first proposed by UBE Company of Japan and has been industrialized. The active center of this type of catalyst is palladium, and the carrier is mainly activated carbon, alumina, spinel and molecular sieve. Some catalysts for the catalytic synthesis of dimethyl carbonate use activated carbon as a carrier, the main active component is palladium chloride, the auxiliary active component is cupric chloride, and the DMC space-time yield can reach an optimal 725 g / (L·h) when the palladium loading is 1wt%, but it can only be stable for about 8 hours; in some other schemes, the catalyst uses NaY molecular sieve as a carrier. When the active metal palladium loading is 1wt%, the catalyst stability can reach 1000 hours, but the reaction space-time yield is low, only 306 g / (L·h).

[0004] In summary, in the currently developed low-pressure gas-phase DMC synthesis catalysts, the catalysts all use the precious metal palladium as the active metal, but the palladium loading is relatively high, most of which are 1wt% or more, resulting in a high cost of the catalyst. The reason why a higher loading is used is that the catalytic activity is low, and a large amount of active metal needs to be added to achieve the target conversion rate. Therefore, it is urgent to develop a catalyst with high activity and low precious metal loading, which is a technical problem that those skilled in the art need to solve. Summary of the invention

[0005] The present application aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the purpose of the present application is to propose a catalyst, preparation method and application for catalytic synthesis of dimethyl carbonate, wherein the catalyst in the present application has a synergistic binary metal system, wherein palladium (Pd) is used as an active metal, nickel (Ni) is used as an auxiliary agent, and a covalent organic framework (COF) is used as a carrier, and the catalyst is prepared by an ultrasound-assisted in-situ complexation method, and in the process of synthesizing dimethyl carbonate by reacting carbon monoxide with methyl nitrite, the catalyst achieves a higher conversion rate and selectivity with a lower palladium loading.

[0006] To achieve the above-mentioned purpose, according to the first aspect of the present application, a catalyst for catalytic synthesis of dimethyl carbonate is proposed, characterized in that it includes a carrier formed by a covalent organic framework; and an active metal and an auxiliary metal are loaded on the carrier by an ultrasound-assisted in-situ complexation method, so that the active metal and the auxiliary metal are stably complexed to form a structure of a single-atom active metal with an "out-of-plane" coordination configuration; wherein the active metal is a metal palladium compound, and based on the catalyst, the loading amount of the active metal is 0.01-0.2wt%; the loading amount of the auxiliary metal is 0.01-5w.t.%; and the carrier is a COF material.

[0007] In some embodiments, the promoter metal is a metal nickel compound.

[0008] In some embodiments, the active metal is selected from one of palladium chloride, palladium acetate or palladium nitrate.

[0009] In some embodiments, the auxiliary metal is selected from nickel chloride, nickel acetate or nickel nitrate.

[0010] According to a second aspect of the present application, a method for preparing the above catalyst is proposed, comprising:

[0011] Preparation of COF materials;

[0012] Adding the COF material into a solvent and dispersing the solvent through ultrasonication to prepare a first suspension;

[0013] Adding active metal and auxiliary metal into the solvent to dissolve and prepare a second suspension;

[0014] The first suspension and the second suspension are mixed so that the amount of active metal added is 0.1-2 g / L; the mixture is stirred for a set time for complexation; and then the mixture is evaporated and dried to obtain a catalyst.

[0015] In some embodiments, the solvent is selected from at least one of water, ethanol, methanol, acetone, benzene, toluene, dichloromethane, chloroform, tetrahydrofuran, dimethyl sulfoxide, and dimethylformamide.

[0016] In some embodiments, the stirring setting time is 8 hours.

[0017] In some embodiments, the evaporation and drying conditions are 60-250° C., and the drying time is 1-20 hours.

[0018] According to a third aspect of the present application, it is proposed that any of the above-mentioned catalysts is used in the reaction of carbon monoxide and methyl nitrite to synthesize dimethyl carbonate.

[0019] In some embodiments, CO and methyl nitrite are used as reaction raw materials, and dimethyl carbonate product is synthesized using the catalyst described in any one of claims 1 to 4; wherein the reaction temperature is 100-130° C., the raw gas composition (volume fraction) is CO 5-50%, MN 5-50%, and the rest is nitrogen, and the space velocity is 2000-5000h -1 .

[0020] Compared with the prior art, this application has the following advantages:

[0021] The present application catalyst has a synergistic binary metal system, wherein palladium (Pd) is used as an active metal, and nickel (Ni) is used as an auxiliary agent, and the two metals produce a synergistic effect, and by adding cheap metal nickel, the addition amount of precious metal palladium is greatly reduced. The key to achieving this advantage is to use COF (covalent organic framework) material as a carrier, and the COF material has an aperture and a higher specific surface area that match the reaction intermediate and transition state size. In addition, there are a large number of bidentate and multidentate coordination sites in COF materials, and the stable complexation of active metal palladium and auxiliary agent nickel is achieved, so as to form the structure of the single-atom palladium of the "out-of-plane" coordination configuration, and the single-atom palladium and the adjacent nickel atoms can be under the complexation of COF, and the efficient transfer of charge occurs, so as to play a synergistic effect, and the catalytic activity of palladium in the reaction is improved, so as to achieve a higher conversion rate and selectivity of the reaction, and greatly reduce the amount of precious metal palladium. The present invention solves the problem of the high loading of precious metals in the catalyst for synthesizing dimethyl carbonate at present, and meets the needs of the green and sustainable development of the current chemical industry.

[0022] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0024] Figure 1 It is a flow chart of a method for preparing a catalyst proposed in one embodiment of the present application. DETAILED DESCRIPTION

[0025] Embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be construed as limiting the present application. On the contrary, the embodiments of the present application include all changes, modifications and equivalents that fall within the spirit and connotation of the appended claims.

[0026] Example 1

[0027] like Figure 1 , weigh iso-tritylaldehyde (0.65 g, 4 mmol), 2,4,6-trimethyl-1,3,5-triazine (0.49 g, 4 mmol) and benzoic anhydride (2.72 g, 12 mmol) into a heat-resistant glass tube. The system was degassed by freezing and pumping with liquid nitrogen and circulating 3 times, and then sealed under vacuum. The test tube was transferred to an oven and heated at 180°C for 100 hours. After the reaction was completed, the solid was collected to obtain the COF material. 5.0 g of COF material was weighed, 10 mL of acetone was added, and ultrasonic dispersion was performed to form a suspension. 8.3 mg of palladium chloride and 61.3 mg of nickel chloride were weighed, 10 mL of acetone was added, and ultrasonic dissolution was performed. After mixing the two liquids, they were stirred at room temperature for 8 hours, and then heated in a water bath at 60°C to remove the solvent. Drying at 180°C in vacuum for 12 hours gave catalyst 1.

[0028] Example 2

[0029] Weigh 10.65 g, 4 mmol, 2,4,6-trimethyl-1,3,5-triazine (0.49 g, 4 mmol) and benzoic anhydride (2.72 g, 12 mmol) into a heat-resistant glass tube. Degas the system by freezing and pumping with liquid nitrogen for 3 cycles, and then seal it under vacuum. Transfer the test tube to an oven and heat it at 180°C for 100 hours. After the reaction is completed, collect the solid to obtain the COF material. Weigh 5.0 g of COF material, add 10 mL of acetone, and disperse it by ultrasonication to form a suspension. Weigh 10.7 mg of palladium acetate and 83.5 mg of nickel acetate, add 10 mL of acetone, and dissolve it by ultrasonication. After mixing the two liquids, stir at room temperature for 8 hours, and then heat in a water bath at 60°C to remove the solvent. Dry it in a vacuum at 180°C for 12 hours to obtain catalyst 2.

[0030] Example 3

[0031] Weigh tribenzaldehyde (0.65 g, 4 mmol), 2,4,6-trimethyl-1,3,5-triazine (0.49 g, 4 mmol) and benzoic anhydride (2.72 g, 12 mmol) into a heat-resistant glass tube. Degas the system by freezing and pumping with liquid nitrogen for 3 cycles, and then seal it under vacuum. Transfer the test tube to an oven and heat it at 180°C for 100 hours. After the reaction is completed, collect the solid to obtain the COF material. Weigh 5.0 g of COF material, add 10 mL of acetone, and disperse it by ultrasonication to form a suspension. Weigh 8.0 mg of palladium nitrate and 86.3 mg of nickel nitrate, add 10 mL of acetone, and dissolve it by ultrasonication. After mixing the two liquids, stir at room temperature for 8 hours, and then heat in a water bath at 60°C to remove the solvent. Dry it in a vacuum at 180°C for 12 hours to obtain catalyst 3.

[0032] Example 4

[0033] Weigh 1,2-diphenylaldehyde (0.65 g, 4 mmol), 2,4,6-trimethyl-1,3,5-triazine (0.49 g, 4 mmol) and benzoic anhydride (2.72 g, 12 mmol) into a heat-resistant glass tube. Degas the system by freezing and pumping with liquid nitrogen for 3 cycles, and then seal it under vacuum. Transfer the test tube to an oven and heat it at 180°C for 100 hours. After the reaction is completed, collect the solid to obtain the COF material. Weigh 5.0 g of COF material, add 10 mL of acetone, and disperse it by ultrasonication to form a suspension. Weigh 5.4 mg of palladium acetate and 41.8 mg of nickel acetate, add 10 mL of acetone, and dissolve it by ultrasonication. After mixing the two liquids, stir at room temperature for 8 hours, and then heat in a water bath at 60°C to remove the solvent. Dry it in a vacuum at 180°C for 12 hours to obtain catalyst 4.

[0034] Comparative Example

[0035] Weigh 1.5 g of triphenylmethane (0.65 g, 4 mmol), 2,4,6-trimethyl-1,3,5-triazine (0.49 g, 4 mmol) and benzoic anhydride (2.72 g, 12 mmol) into a heat-resistant glass tube. Degas the system by freezing and pumping with liquid nitrogen for 3 cycles, and then seal it under vacuum. Transfer the test tube to an oven and heat it at 180°C for 100 hours. After the reaction is completed, collect the solid to obtain the COF material. Weigh 5.0 g of COF material, add 10 mL of acetone, and disperse it by ultrasonication to form a suspension. Weigh 5.4 mg of palladium acetate, add 10 mL of acetone, and dissolve it by ultrasonication. After mixing the two liquids, stir at room temperature for 8 hours, and then heat in a water bath at 60°C to remove the solvent. Dry it in a vacuum at 180°C for 12 hours to obtain catalyst 5.

[0036] Application Examples

[0037] The above catalysts 1-5 were applied to the reaction of synthesizing DMC by low-pressure gas phase carbonylation to examine their catalytic performance. The reaction temperature was 100-130°C, the raw gas composition (volume fraction) was CO 5-50%, MN 5-50%, and the rest was nitrogen, and the space velocity was 2000-5000h -1 .

[0038]

[0039] The above results indicate that the catalyst achieves higher conversion rate and selectivity while greatly reducing the loading amount of active metal palladium.

[0040] It should be noted that, in the description of this application, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. In addition, in the description of this application, unless otherwise specified, the meaning of "plurality" is two or more.

[0041] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, segment or portion of code that includes one or more executable instructions for implementing the steps of a specific logical function or process, and the scope of the preferred embodiments of the present application includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in the reverse order depending on the functions involved, which should be understood by technicians in the technical field to which the embodiments of the present application belong.

[0042] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0043] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in the field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A catalyst for catalytic synthesis of dimethyl carbonate, characterized in that: The invention comprises a carrier formed by a covalent organic framework; and an active metal and an auxiliary metal are loaded on the carrier by an ultrasound-assisted in-situ complexation method, so that the active metal and the auxiliary metal are stably complexed to form a structure of a single-atom active metal with an "out-of-plane" coordination configuration; wherein the active metal is a metal palladium compound, and based on the catalyst, the loading amount of the active metal is 0.01-0.2wt%; the loading amount of the auxiliary metal is 0.01-5w.t.%; and the carrier is a COF material.

2. The catalyst according to claim 1, characterized in that The auxiliary metal is a metal nickel compound.

3. The catalyst according to claim 2, characterized in that The active metal is selected from palladium chloride, palladium acetate or palladium nitrate.

4. The catalyst according to claim 2, characterized in that The auxiliary metal is selected from nickel chloride, nickel acetate or nickel nitrate.

5. A method for preparing a catalyst according to any one of claims 1 to 4, characterized in that: include Preparation of COF materials; Adding the COF material into a solvent and dispersing the solvent through ultrasonication to prepare a first suspension; Adding active metal and auxiliary metal into the solvent to dissolve and prepare a second suspension; The first suspension and the second suspension are mixed so that the amount of active metal added is 0.1-2 g / L; the mixture is stirred for a set time for complexation; and then the mixture is evaporated and dried to obtain a catalyst.

6. The method according to claim 5, characterized in that The solvent is selected from at least one of water, ethanol, methanol, acetone, benzene, toluene, dichloromethane, chloroform, tetrahydrofuran, dimethyl sulfoxide and dimethylformamide.

7. The method according to claim 5, characterized in that The stirring time is set to 8h.

8. The method according to claim 5, characterized in that The evaporation and drying conditions are 60-250°C, and the drying time is 1-20 hours.

9. Use of any one of the catalysts described in claims 1-4 in the synthesis of dimethyl carbonate by the reaction of carbon monoxide and methyl nitrite.

10. The use according to claim 9, characterized in that: Using CO and methyl nitrite as reaction raw materials, using the catalyst described in any one of claims 1-4 to synthesize dimethyl carbonate product; wherein the reaction temperature is 100-130°C, the raw gas composition (volume fraction) is CO 5-50%, MN 5-50%, and the rest is nitrogen, and the space velocity is 2000-5000h -1 .

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