Supported metallocene catalysts, processes for their preparation and use

Abstract

The application relates to the technical field of material preparation, in particular to a supported metallocene catalyst and a preparation method and application thereof. The supported metallocene catalyst comprises a modified biomass carbon carrier and an active component; the active component comprises a metallocene compound and a cocatalyst component; the preparation method of the modified biomass carbon carrier comprises the following steps: preliminary drying of biomass carbon in a nitrogen atmosphere at 105 DEG C to 160 DEG C for 2 h to 4 h; adding a weak acid, stirring for 24 h to 48 h, then standing for 5 h to 12 h, removing the supernatant to leave the precipitate; then, second drying is carried out in a nitrogen atmosphere. The biomass carbon material can be flexibly adjusted in a large range in specific surface area and pore volume and pore size by changing the preparation conditions such as activation temperature and time, so that the demand of different polymerization reactions for the carrier can be better met, and the activity and selectivity of the polymerization reaction are remarkably improved.

Description

Technical Field

[0001] This application relates to the field of materials preparation technology, specifically to a supported metallocene catalyst, its preparation method, and its application. Background Technology

[0002] Metallocene catalyst loading technology is a key technology for solving problems such as easy deactivation of active centers and excessive co-catalyst dosage in homogeneous metallocene catalysts. Common loading techniques include: impregnation, which involves immersing the support in a solution containing metallocene compounds and co-catalysts, allowing them to adsorb onto the support surface and within the pores; for example, patent document CN102153681A uses titanium dioxide nanotubes as a support to obtain a supported metallocene catalyst through specific steps. Chemical grafting involves chemically bonding metallocene compounds to the active groups on the support surface through a chemical reaction, improving catalyst stability and activity. In-situ synthesis involves introducing metallocene compounds into the structure of the support during the synthesis process, ensuring uniform dispersion within it; for example, adding metallocene compounds to the synthesis system when preparing metal-organic frameworks (MOFs). Vapor deposition utilizes metallocene compounds and co-catalysts in the gas phase to deposit on the support surface under conditions such as high temperature or plasma, allowing for precise control of loading and uniformity.

[0003] Currently, the main supports for metallocene catalysts are divided into inorganic and organic supports. Among inorganic supports, silica possesses high specific surface area, suitable pore volume and size, good fluidity and mechanical strength, and is inexpensive. However, its surface hydroxyl groups are not well-defined, it lacks catalytic activity, it has weak interactions with metallocene compounds, its particle morphology is inhomogeneous, and its structural tunability is poor. Alumina has high mechanical strength and thermal stability, and its surface active sites can interact with metallocenes and co-catalysts. However, its specific surface area and pore volume and size have a narrow tunable range, and its activity and selectivity for certain polymerization reactions need to be improved. Titanium dioxide has good photocatalytic performance and chemical stability, and its crystal form, particle size, and pore structure can be tunable. However, its surface properties are complex, and its interaction mechanism with metallocene compounds requires further investigation to achieve better loading effects and catalytic performance. Organic polymer supports have the following problems: low mechanical strength, which may lead to swelling or breakage under intense polymerization conditions; small specific surface area, resulting in lower loading and activity; relatively high cost; and complex preparation.

[0004] It is necessary to provide a new supported catalyst to solve the problems of low loading efficiency and poor overall activity of existing metallocene catalysts. Summary of the Invention

[0005] Therefore, it is necessary to address the problems of low loading efficiency and poor overall activity of existing metallocene catalysts and propose a supported metallocene catalyst that can improve the loading of metallocene compounds and enhance catalytic activity.

[0006] First, this application provides a supported metallocene catalyst, comprising a modified biomass carbon support and an active component; the active component comprises a metallocene compound and a cocatalyst component;

[0007] The preparation method of modified biomass carbon carrier includes the following steps:

[0008] The biomass carbon is initially dried in a nitrogen atmosphere at 105℃~160℃ for 2h~4h; a weak acid is added, and the reaction is stirred for 24h~48h, then allowed to stand for 5h~12h. The supernatant is removed, leaving a precipitate, which is washed with anhydrous ethanol at least three times, stirring for at least 30min each time, and finally rinsed with toluene; then a second drying is carried out in a nitrogen atmosphere at a temperature of 400℃~600℃ for 20h~24h.

[0009] Preferably, the particle size of the biomass carbon is 100 mesh to 200 mesh.

[0010] Preferably, the weak acid is selected from one or more of formic acid, oxalic acid, acetic acid, citric acid, benzoic acid, hydrofluoric acid, hypochlorous acid, and carbonic acid.

[0011] Preferably, the ratio of biomass carbon to weak acid is 1 g : (0.1~20) mL. More preferably, the ratio of biomass carbon to weak acid is 1 g : (1~3) mL.

[0012] Preferably, the metallocene compound is dimethylsilylbis(indenyl)zirconium dichloride.

[0013] Preferably, the co-catalyst is methylaluminoxane.

[0014] Preferably, the mass ratio of the modified biomass carbon support, the metallocene compound, and the cocatalyst is (5~100):1:(10~500), more preferably, the mass ratio of the modified biomass carbon support, the metallocene compound, and the cocatalyst is (5~50):1:(50~400).

[0015] Based on a general inventive concept, this application also provides a method for preparing a supported metallocene catalyst, comprising the following steps:

[0016] S1. Initially dry the biomass carbon in a nitrogen atmosphere at 105℃~160℃ for 2h~4h; add a weak acid, stir and react for 24h~48h, then let it stand for 5h~12h, remove the supernatant to leave the precipitate, wash the precipitate with anhydrous ethanol at least three times, stirring for at least 30min each time, and finally rinse with toluene; then perform a second drying under a nitrogen atmosphere at a temperature of 400℃~600℃ for 20h~24h.

[0017] S2. In a nitrogen atmosphere, the modified biomass carbon support, co-catalyst and organic solvent are stirred and mixed at 40℃~60℃ for 5h~12h, filtered, and the catalyst precursor is obtained.

[0018] S3. The catalyst precursor and the metallocene compound are mixed in an organic solvent and reacted at 40℃~60℃ for 5h~6h. After filtration, the supported metallocene catalyst is obtained.

[0019] Preferably, in steps S1 and S2, the organic solvent is toluene.

[0020] Preferably, in step S1, before stirring and mixing the modified biomass carbon support, co-catalyst and organic solvent, the modified biomass carbon support is dried for 10h to 12h under a nitrogen atmosphere and at 100℃ to 105℃.

[0021] Preferably, in step S2, after the reaction is complete, the solid precipitate is obtained by filtration, and the solid precipitate is washed with toluene, and the washing is repeated at least 3 times.

[0022] Based on a general inventive concept, this application provides an application of a supported metallocene catalyst in the polymerization of propylene to prepare polypropylene.

[0023] Preferably, the reaction conditions for propylene polymerization include: a reaction temperature of 40℃~60℃ and a reaction time of 1h~2h.

[0024] Preferably, the mass ratio of the supported metallocene catalyst to the propylene is 1:(3~6).

[0025] Compared with the prior art, this application has the following beneficial effects:

[0026] First, biomass carbon has a wide range of sources, relatively low cost, and is environmentally friendly. It has a cost advantage in large-scale application and is in line with the development strategy of sustainable development and turning waste into treasure. It can apply agricultural by-products to high value-added and high-precision fields and improve the utilization rate of waste.

[0027] Secondly, its surface chemical properties are rich and easily tunable, which contrasts sharply with traditional inorganic supports such as silica. Through simple acid-base treatments and other chemical methods, surface functional groups can be precisely introduced or adjusted to enhance interactions with metallocenes, thereby effectively improving catalytic activity and overcoming the weakness of the interaction between silica and metallocenes. Simultaneously, using specific preparation processes, porous materials with relatively uniform morphology can be produced, reducing the fine powder rate by 30% during polymerization evaluation. This demonstrates excellent structural tunability, compensating for the inhomogeneity and poor structural tunability of silica particles.

[0028] Furthermore, biomass-based porous carbon materials possess abundant pore structures and pore volumes and sizes. Compared to alumina, although alumina has higher mechanical strength and thermal stability, its specific surface area and pore volume and size range are relatively narrow. In contrast, biomass carbon materials can flexibly adjust their specific surface area and pore volume and size within a wider range by changing preparation conditions such as activation temperature and time. This better meets the needs of different polymerization reactions for the support and significantly improves the activity and selectivity of polymerization reactions. Detailed Implementation

[0029] The embodiments described in this specification are merely for explaining this application and are not intended to limit this application.

[0030] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit, combined with any other point or individual value, or combined with other lower or upper limits to form an unspecified range.

[0031] The present application is further illustrated below with reference to embodiments. It should be understood that these embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0032] Example 1

[0033] (1) Preparation of catalyst support:

[0034] Biomass carbon was sieved, and 1 g of biomass carbon with a particle size of 100-200 mesh was selected. The carbon material was initially dried at 150℃ under a nitrogen atmosphere for 4 h. The initially dried biomass carbon was placed in 2 mL of benzoic acid solution and stirred under a nitrogen atmosphere for 48 h. After stirring, it was allowed to stand for 5 h, and the supernatant was removed, leaving a precipitate. Anhydrous ethanol was added, and the mixture was stirred and washed three times, with each stirring lasting at least 30 min. Finally, the mixture was rinsed with toluene, and the precipitate was retained. The precipitate was dried again under a nitrogen purging atmosphere at a temperature controlled at 400℃ for 24 h to obtain the biomass carbon carrier.

[0035] (2) Catalyst support pretreatment:

[0036] The biomass carbon support prepared in step (1) was dried at 105°C for 10 h under a nitrogen atmosphere. Then, 1 g of the dried biomass carbon support was transferred to a nitrogen-protected dry reaction flask, and 10 mL of 30% methylaluminoxane (MAO) solution and 30 mL of toluene were added sequentially. The mixture was stirred at 50°C for 2 h. After the reaction was completed, the mixture was filtered, and the solid was washed with 15 mL of toluene. The washing operation was repeated at least 3 times to obtain the MAO-supported silica gel support.

[0037] (3) Preparation of metallocene catalysts:

[0038] Add the MAO-supported silica support obtained in step (2) and 0.05 g of metallocene compound (dimethylsilylbis(indenyl)zirconia) to 30 mL of toluene, and stir the reaction at 50 °C for 4 hours. After the reaction is completed, filter the product and wash the solid product with 15 mL of toluene. Repeat the washing operation at least 3 times. Finally, dry the obtained solid under vacuum to obtain a metallocene catalyst that can be used for olefin polymerization.

[0039] (4) Synthesis of olefin polymerization:

[0040] Using a 5L high-pressure reactor, the reactor was first thoroughly purged with nitrogen, and then purified with triethylaluminum to ensure that the reaction system was clean and free of impurities. The temperature of the pretreated reactor was adjusted to 40°C, and 0.3g of the metallocene catalyst prepared in step (3) was added. Then 1.5kg of propylene was introduced. The reaction temperature was maintained at 60°C, and the polymerization reaction was carried out for 1 hour to complete the olefin polymerization process.

[0041] Examples 2-4

[0042] The preparation methods of Examples 2-4 are basically the same as those of Example 1, except that the initial drying and secondary drying conditions and the standing time are different during the preparation of biomass carbon carriers. For details, please refer to Table 1.

[0043] Examples 5-6

[0044] The preparation methods of Examples 5 and 6 are basically the same as those of Example 1, except that the acid components used in the preparation of biomass carbon carriers are different, as detailed in Table 1.

[0045] Examples 7-8

[0046] The preparation methods of Examples 5 and 6 are basically the same as those of Example 1, except that the mass ratio of biomass carbon carrier, MAO and metallocene compound is different when preparing biomass carbon carrier, as detailed in Table 1.

[0047] Examples 9-10

[0048] The preparation methods of Examples 9 and 10 are basically the same as those of Example 1. The only difference is that the amount of biomass carbon and weak acid added in steps (3) and (4) is different. For details, please refer to Table 1.

[0049] Comparative Examples 1-4

[0050] The preparation methods of Comparative Examples 1 to 4 are basically the same as those of Example 1, except that the initial drying and secondary drying conditions and the standing time are different during the preparation of biomass carbon carriers. For details, please refer to Table 1.

[0051] Table 1. Process conditions for preparing biomass carbon supports in each example and comparative example.

[0052]

[0053] Note: In the table, the ratios between modified biomass carbon carrier, metallocene compound, and MAO are by mass.

[0054] Performance testing

[0055] (1) The specific surface area, pore volume, and pore size of the catalyst supports prepared in each embodiment and comparative example were determined using a Quantachrome NOVA 4200e fully automated specific surface area and pore size distribution analyzer. The specific operation procedure was as follows: the sample was first pretreated, the degassing temperature was set to 300℃, and the degassing time was 3 hours. After the sample cooled to room temperature, the mass of the degassed sample was accurately weighed. Subsequently, isothermal adsorption and desorption analysis of the sample was performed at 77K.

[0056] (2) Based on the formula: polymerization activity = mass of polypropylene / mass of catalyst, calculate the polymerization activity of the metallocene catalysts prepared in each example and comparative example in the olefin polymerization process.

[0057] The results of each performance test are shown in Table 2.

[0058] Table 2 Performance test table for each embodiment and comparative example

[0059]

[0060] Note: gPP in the table refers to the mass of polypropylene; gCAT refers to the amount of metallocene catalyst used.

[0061] As shown in Table 2, the catalyst supports provided in Examples 1-10 of the present invention have a larger specific surface area, pore size and pore volume compared with Comparative Examples 1-4. Furthermore, the metallocene catalysts prepared using the catalyst supports provided in Examples 1-10 of the present invention can achieve polymerization activity of more than 4900 gPP / gCat in olefin polymerization, which is significantly better than the polymerization activity of the metallocene catalysts prepared in the comparative examples of the present invention.

[0062] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A supported metallocene catalyst, characterized in that, It includes a modified biomass carbon support and an active component; the active component includes a metallocene compound and a cocatalyst component; the mass ratio of the modified biomass carbon support, the metallocene compound and the cocatalyst is (5~100):1:(10~500); The preparation method of the modified biomass carbon carrier includes the following steps: The biomass char was initially dried in a nitrogen atmosphere at 105℃~160℃ for 2h~4h; a weak acid was added, and the mixture was stirred for 24h~48h, then allowed to stand for 5h~12h. The supernatant was removed, leaving a precipitate, which was washed with anhydrous ethanol at least three times, stirring for at least 30min each time, and finally rinsed with toluene. Then, a second drying was carried out under a nitrogen atmosphere at a temperature of 400℃~600℃ for 20h~24h. The ratio of biomass char to the weak acid was 1g:(0.1~20)mL.

2. The supported metallocene catalyst according to claim 1, characterized in that, The biomass carbon has a particle size of 100-200 mesh.

3. The supported metallocene catalyst according to claim 1, characterized in that, The weak acid is selected from one or more of formic acid, oxalic acid, acetic acid, citric acid, benzoic acid, hydrofluoric acid, hypochlorous acid, and carbonic acid.

4. The supported metallocene catalyst according to claim 1, characterized in that, The metallocene compound is dimethylsilylbis(indenyl)zirconium dichloride; the cocatalyst is methylaluminoxane.

5. The method for preparing the supported metallocene catalyst according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. The biomass carbon is initially dried in a nitrogen atmosphere at 105℃~160℃ for 2h~4h; a weak acid is added, and the mixture is stirred for 24h~48h, then allowed to stand for 5h~12h. The supernatant is removed, leaving a precipitate. The precipitate is washed with anhydrous ethanol at least three times, stirring for at least 30min each time, and finally rinsed with toluene. Then, a second drying is carried out under a nitrogen atmosphere at a temperature of 400℃~600℃ for 20h~24h. S2. In a nitrogen atmosphere, the modified biomass carbon support, the co-catalyst, and the organic solvent are stirred and mixed at 40℃~60℃ for 2~12h, filtered, and the catalyst precursor is obtained. S3. The catalyst precursor and the metallocene compound are mixed in a nonpolar organic solvent and reacted at 40℃~60℃ for 5h~6h. After filtration, the supported metallocene catalyst is obtained.

6. The application of the supported metallocene catalyst according to any one of claims 1 to 4 in the polymerization of propylene to prepare polypropylene.

7. The application according to claim 6, characterized in that, The reaction conditions for the propylene polymerization include: a reaction temperature of 40℃~60℃ and a reaction time of 1h~2h.

8. The application according to claim 7, characterized in that, The mass ratio of the supported metallocene catalyst to the propylene is 1:(3~6).

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