Novel propylene polymerization composite catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of chemical catalysis, and discloses a novel propylene polymerization composite catalyst and a preparation method and application thereof.The preparation method of the novel propylene polymerization composite catalyst comprises the following steps that a silicon source is added into ethyl alcohol, then a magnesium chloride aqueous solution is added, a reaction is conducted, then ammonia water and gel are dropwise added, aging and drying are conducted, and an MgCl2-SiO2 carrier is obtained; the preparation method comprises the following steps: mixing an MgCl2-SiO2 carrier with toluene, cooling, adding a titanium tetrachloride / toluene mixed solution, heating, adding an internal electron donor, heating, carrying out a thermal insulation reaction, carrying out suction filtration, washing, mixing a washed filter cake with the titanium tetrachloride / toluene mixed solution, heating, carrying out a thermal insulation reaction, carrying out suction filtration, repeating the above operations, and purifying to obtain the novel propylene polymerization composite catalyst. The novel propylene polymerization composite catalyst provided by the invention has a good catalytic effect on a propylene polymerization process, and the obtained polypropylene has the advantages of high isotacticity and narrow particle size distribution.

Description

Technical Field

[0001] This invention relates to the field of chemical catalysis technology, and in particular to a novel propylene polymerization composite catalyst, its preparation method, and its application. Background Technology

[0002] Polypropylene is typically a translucent, colorless solid. It is non-toxic, odorless, has low density, and good processing performance, making it the lightest general-purpose plastic currently available. It features high impact resistance, strong mechanical properties, and resistance to various organic solvents and acid / alkali corrosion. It is widely used in home appliances, automobile manufacturing, pharmaceuticals, food packaging, and other fields, and is a common polymer material. The main production method of polypropylene is propylene polymerization. With the diversification of polypropylene products, the catalysts used with it are also constantly being improved. Introducing suitable polypropylene catalysts can not only reduce process costs but also improve product quality. Currently, there are four main types of polypropylene catalysts: Ziegler-Natta (ZN), metallocene, post-transition metals, and composite catalysts.

[0003] The main research system for ZN catalysts is the Ti-Mg system, including the active center Ti. 3+ The catalyst, consisting of MgCl2 support, alkylaluminum co-catalyst, and internal and external electron donors, has achieved a stable catalytic effect through continuous improvement. The components of this catalyst interact to form active metal-carbon bonds, which are crucial for the repeated insertion of propylene monomer molecules into the polypropylene macromolecular chain. In recent years, research on Zn catalysts has mainly focused on: the generation methods, activation, morphology control, and impact on catalyst activity of MgCl2; the selection of co-catalysts, their molar ratio to the main catalyst, their interaction, and mechanisms; and the role, mechanism, and impact on catalyst performance of internal and external electron donors.

[0004] Supports with good morphology, uniform size distribution, high specific surface area, and good mechanical strength and wear resistance have a significant impact on the activity, orientation ability, polymer morphology, structure and performance of Zn catalysts. The synthesized catalyst needs to have a high specific surface area, porosity and narrow particle size distribution, with uniform distribution of active species Ti in the particles. In addition, the presence of δ-MgCl2 in the system fully activates the catalyst. The high activity of propylene polymerization is mainly attributed to the complete activation and porous structure of the catalyst. At the same time, the perfect spherical structure, uniform Ti distribution and narrow particle size distribution of the catalyst also confirm that it can produce less fine polymer particles.

[0005] In polymerization reactions, the co-catalyst mainly plays the role of activating the main catalyst, that is, transforming the inactive Ti into a catalyst. 4+ Reduced to catalytically active Ti 3+Alkyl aluminum is a commonly used co-catalyst for Zn catalysts. It interacts with internal electron donors in the catalyst and transfers them from the catalyst surface, thereby affecting the isotacticity of the product. However, as the amount of alkyl aluminum introduced increases, the number of fine particles on the catalyst surface increases and the degree of small particle aggregation increases, which can easily lead to the production of fine powder and affect the stable operation of the unit. Therefore, it is necessary to control the appropriate amount of co-catalyst introduced.

[0006] Internal and external electron donors are important components of polypropylene catalyst systems. Internal electron donors are introduced during catalyst preparation and can change the molecular weight distribution (MWD) of polypropylene, improve the stereoisotacticity of the polymer, and improve hydrogen sensitivity during polymerization. External electron donors are introduced during polymerization and are also known as selectivity control agents. They are commonly used in polypropylene production for stereoselectivity control and product performance adjustment. By adding external electron donors, the distribution of active sites during propylene polymerization is changed, and the proportion of highly isotactic active sites and chain growth rate are increased by affecting kinetics, thereby improving the isotacticity of polypropylene.

[0007] To improve catalytic activity, many patents employ different physical or chemical methods to prepare active magnesium chloride supports, which are then loaded with transition metal titanides and electron-donating compounds to form active catalyst centers. Supports prepared by the loading method typically have an average particle size of ~50 μm, which limits the loading amount of active components on the support and results in low catalyst activity. Another type involves making spherical supports from magnesium chloride alkoxides, but these spherical catalysts have a large particle size and are prone to breakage during propylene polymerization, which is not conducive to industrial production. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a method for preparing a novel propylene polymerization composite catalyst, comprising the following steps: Step 1: At 40-80℃, add silicon source to ethanol, then add magnesium chloride aqueous solution, stir and react for 24-72h, then add ammonia hydrogel dropwise, age at 40-60℃ for 20-30h, dry, and obtain MgCl2-SiO2 support. Step 2: Mix the MgCl2-SiO2 support with toluene, cool, add 0.8-1.2wt% titanium tetrachloride / toluene mixed solution dropwise, heat to 60-80℃, add an internal electron donor, continue heating to 100-120℃, maintain the temperature and continue the reaction for 2 hours, filter, wash, mix the washed filter cake with a titanium tetrachloride / toluene mixed solution with a volume ratio of 10:1, heat to 100-120℃, maintain the temperature and react for 1 hour, filter, repeat the above operation of treating the filter cake with a titanium tetrachloride / toluene mixed solution with a volume ratio of 10:1, filter, wash, and vacuum dry to obtain a novel propylene polymerization composite catalyst.

[0009] Preferably, in step one, the silicon source includes at least one of silicate, silica sol, and tetraethyl orthosilicate.

[0010] Preferably, in step one, the mass ratio of the silicon source to the magnesium chloride aqueous solution, based on SiO2, is (0.5-5):2; and the mass ratio of the ammonia solution to the magnesium chloride aqueous solution is 14.7:20.

[0011] Preferably, in step two, the internal electron donor includes an aliphatic polycarboxylic acid ester or an aromatic polycarboxylic acid ester; the aliphatic polycarboxylic acid ester includes diethyl malonate and dibutyl adipate, and the aromatic polycarboxylic acid ester includes diethyl phthalate, diisobutyl phthalate, and diisooctyl phthalate.

[0012] Preferably, in step two, the ratio of the MgCl2-SiO2 support, the 0.8-1.2wt% titanium tetrachloride / toluene mixed solution, and the internal electron donor is 15g:60mL:2mL.

[0013] In the above process, the addition of silicon source in step one can reduce the agglomeration of active components, increase the specific surface area of ​​the support, and improve the dispersibility of active components, thus significantly improving the catalyst activity. In step two, a novel propylene polymerization composite catalyst is prepared by impregnation. During the impregnation process, titanium tetrachloride needs to be dispersed in liquid hydrocarbon (such as toluene) at an appropriate concentration to form a uniform titanium-supported system. Generally, the concentration of titanium tetrachloride in liquid hydrocarbon needs to be controlled within a reasonable range (0.8-1.2 wt%) to ensure that the support (such as MgCl2-SiO2) fully absorbs the titanium source, while avoiding excessive concentration that could lead to particle agglomeration.

[0014] The novel propylene polymerization composite catalyst was prepared using the aforementioned method.

[0015] The application of the novel propylene polymerization composite catalyst in the propylene polymerization process.

[0016] Preferably, the propylene polymerization process is as follows: In a nitrogen atmosphere, an external electron donor, triethylaluminum, and a novel propylene polymerization composite catalyst are added sequentially to the reaction vessel, followed by hydrogen and liquid propylene. After stirring is started, the temperature is raised to 60-80℃, and the reaction is stopped after 1-2 hours of polymerization to obtain polypropylene.

[0017] Preferably, the external electron donor comprises an organosilicon compound, which includes any one of dimethoxysilane, n-propyltriethylsilane, diethylphosphorylethyltriethoxysilane, and vinyltrimethoxysilane.

[0018] Preferably, the ratio of the external electron donor, triethylaluminum, and the novel propylene polymerization composite catalyst is 1 mL:1.5 mL:8 mg; the volume ratio of hydrogen to liquid propylene is 1:2; and the amount of the novel propylene polymerization composite catalyst is 0.0005-0.001% of the total mass of the raw materials.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The novel propylene polymerization composite catalyst of the present invention has high catalytic activity, the catalyst particles are solid and not easily broken during polymerization, and the polypropylene obtained by polymerization has a uniform particle size distribution and few fine particles. 2. The novel propylene polymerization composite catalyst of the present invention has good hydrogen sensitivity, and the synthesized polypropylene still has high isotacticity even at a high melt flow index. 3. The present invention provides a novel MgCl2-SiO2 support for a propylene polymerization composite catalyst. The addition of a silicon source can reduce the agglomeration of active components, increase the specific surface area of ​​the support, thereby improving the dispersibility of active components and having a significant effect on improving catalyst activity. Furthermore, the catalyst activity can be adjusted by adjusting the type of silicon source or by regulating the Mg / Si ratio. 4. The MgCl2-SiO2 support of the novel propylene polymerization composite catalyst of the present invention has good particle shape and pore characteristics. Therefore, the polypropylene obtained also has high porosity and large pore size, which is beneficial to the synthesis of impact copolymer polypropylene with high ethylene content. Attached Figure Description

[0020] Figure 1 This is a comparison chart of the catalyst polymerization activity tests in the propylene polymerization process of Examples 4-6 of the present invention and Comparative Example 2; Figure 2 This is a comparison chart of isotacticity tests of polypropylene prepared in Examples 4-6 of the present invention and Comparative Example 2; Figure 3 This is a comparison chart of the particle size distribution tests of polypropylene prepared in Examples 4-6 and Comparative Example 2 of the present invention. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] Example 1 This embodiment discloses a method for preparing a novel propylene polymerization composite catalyst, including the following steps: Step 1: At 50℃, 28.2g of tetraethyl orthosilicate was added dropwise to 32g of ethanol, followed by 20g of 50wt% magnesium chloride aqueous solution. The mixture was stirred for 24h, and then 14.7g of 25wt% ammonia was added dropwise. The resulting gel was aged at 50℃ for 24h and dried to obtain the MgCl2-SiO2 support. Step 2: Mix 15g of MgCl2-SiO2 support with 5mL of toluene in a reactor, purge with liquid nitrogen to cool to -10℃, add 60mL of 1wt% titanium tetrachloride / toluene mixed solution dropwise, and slowly raise the temperature to 70℃ after the addition is complete. Add 2mL of diethyl phthalate, rapidly raise the temperature to 110℃, and continue the reaction for 2h. After vacuum filtration, wash the filter cake three times with toluene. Mix the washed filter cake with 20mL of titanium tetrachloride and 2mL of toluene, raise the temperature to 110℃, and keep the reaction for 1h. After vacuum filtration again, mix the resulting filter cake with 20mL of titanium tetrachloride and 2mL of toluene, raise the temperature to 110℃, and keep the reaction for 1h. Filter and wash the filter cake five times with hexane, and vacuum dry to obtain a pale yellow novel propylene polymerization composite catalyst.

[0023] Example 2 This embodiment discloses a method for preparing a novel propylene polymerization composite catalyst, including the following steps: Step 1: At 50℃, 14.1g of tetraethyl orthosilicate was added dropwise to 32g of ethanol, and then 20g of 50wt% magnesium chloride aqueous solution was added. The mixture was stirred for 24h, and then 14.7g of 25wt% ammonia was added dropwise. The resulting gel was aged at 50℃ for 24h and dried to obtain MgCl2-SiO2 support. Step 2: Mix 15g of MgCl2-SiO2 support with 5mL of toluene in a reactor, purge with liquid nitrogen to cool to -10℃, add 60mL of 1wt% titanium tetrachloride / toluene mixed solution dropwise, and slowly raise the temperature to 70℃ after the addition is complete. Add 2mL of diethyl phthalate, rapidly raise the temperature to 110℃, and continue the reaction for 2h. After vacuum filtration, wash the filter cake three times with toluene. Mix the washed filter cake with 20mL of titanium tetrachloride and 2mL of toluene, raise the temperature to 110℃, and keep the reaction for 1h. After vacuum filtration again, mix the resulting filter cake with 20mL of titanium tetrachloride and 2mL of toluene, raise the temperature to 110℃, and keep the reaction for 1h. Filter and wash the filter cake five times with hexane, and vacuum dry to obtain a pale yellow novel propylene polymerization composite catalyst.

[0024] Example 3 This embodiment discloses a method for preparing a novel propylene polymerization composite catalyst, including the following steps: Step 1: At 50℃, 28.2g of silica sol was added dropwise to 32g of ethanol, and then 20g of 50wt% magnesium chloride aqueous solution was added. The mixture was stirred for 24h, and then 14.7g of 25wt% ammonia was added dropwise. The resulting gel was aged at 50℃ for 24h and dried to obtain MgCl2-SiO2 support. Step 2: Mix 15g of MgCl2-SiO2 support with 5mL of toluene in a reactor, purge with liquid nitrogen to cool to -10℃, add 60mL of 1wt% titanium tetrachloride / toluene mixed solution dropwise, and slowly raise the temperature to 70℃ after the addition is complete. Add 2mL of diethyl phthalate, rapidly raise the temperature to 110℃, and continue the reaction for 2h. After vacuum filtration, wash the filter cake three times with toluene. Mix the washed filter cake with 20mL of titanium tetrachloride and 2mL of toluene, raise the temperature to 110℃, and keep the reaction for 1h. After vacuum filtration again, mix the resulting filter cake with 20mL of titanium tetrachloride and 2mL of toluene, raise the temperature to 110℃, and keep the reaction for 1h. Filter and wash the filter cake five times with hexane, and vacuum dry to obtain a pale yellow novel propylene polymerization composite catalyst.

[0025] Example 4 This embodiment discloses a propylene polymerization process: Nitrogen was used to purge a 5L stainless steel reactor. 1mL of dimethoxysilane, 1.5mL of triethylaluminum, and 8mg of the novel propylene polymerization composite catalyst prepared in Example 1 were added to the reactor in sequence. Then, 1L (standard volume) of hydrogen and 2L of liquid propylene were added. After stirring, the temperature was raised to 70°C. The reaction was stopped after 1 hour of polymerization to obtain polypropylene.

[0026] Example 5 This embodiment discloses a propylene polymerization process: Nitrogen was used to purge a 5L stainless steel reactor. 1mL of dimethoxysilane, 1.5mL of triethylaluminum, and 8mg of the novel propylene polymerization composite catalyst prepared in Example 2 were added to the reactor in sequence. Then, 1L (standard volume) of hydrogen and 2L of liquid propylene were added. After stirring, the temperature was raised to 70°C. The reaction was stopped after 1 hour of polymerization to obtain polypropylene.

[0027] Example 6 This embodiment discloses a propylene polymerization process: Nitrogen was used to purge a 5L stainless steel reactor. 1mL of dimethoxysilane, 1.5mL of triethylaluminum, and 8mg of the novel propylene polymerization composite catalyst prepared in Example 3 were added to the reactor in sequence. Then, 1L (standard volume) of hydrogen and 2L of liquid propylene were added. After stirring, the temperature was raised to 70°C. The reaction was stopped after 1 hour of polymerization to obtain polypropylene.

[0028] Comparative Example 1 This comparative example discloses a method for preparing a conventional propylene polymerization catalyst, comprising the following steps: Step 1: Slowly add the solution formed by 10g of distilled water and 10g of anhydrous magnesium chloride to 10g of commercially available SiO2 support, stir evenly, and dry to obtain MgCl2-SiO2 support; Step 2: Mix 15g of MgCl2-SiO2 support with 5mL of toluene in a reactor, purge with liquid nitrogen to cool to -10℃, add 60mL of 1wt% titanium tetrachloride / toluene mixed solution dropwise, and slowly raise the temperature to 70℃ after the addition is complete. Add 2mL of diethyl phthalate, rapidly raise the temperature to 110℃, and continue the reaction for 2h. After vacuum filtration, wash the filter cake three times with toluene. Mix the washed filter cake with 20mL of titanium tetrachloride and 2mL of toluene, raise the temperature to 110℃, and keep the reaction for 1h. After vacuum filtration again, mix the resulting filter cake with 20mL of titanium tetrachloride and 2mL of toluene, raise the temperature to 110℃, and keep the reaction for 1h. Filter and wash the filter cake five times with hexane, and vacuum dry to obtain a pale yellow traditional propylene polymerization catalyst.

[0029] Comparative Example 2 This embodiment discloses a propylene polymerization process: Nitrogen was used to purge a 5L stainless steel reactor. 1mL of dimethoxysilane, 1.5mL of triethylaluminum, and 8mg of the conventional propylene polymerization composite catalyst prepared in Comparative Example 1 were added to the reactor in sequence. Then, 1L (standard volume) of hydrogen and 2L of liquid propylene were added. After stirring, the temperature was raised to 70℃. The reaction was stopped after 1 hour of polymerization to obtain polypropylene.

[0030] Experimental Example The polypropylene prepared by the propylene polymerization process in Examples 4-6 and Comparative Example 2 was subjected to performance testing. I. Polymerization Activity Test: Catalyst activity is calculated based on the mass ratio of the polymer produced in the reaction to the catalyst added; II. Isotactic Index (Isotacticity) Test: According to GB / T 2412—2008, the test was conducted using the boiling n-heptane extraction method with a FY-SXT-02 Soxhlet extractor from Hangzhou Feiyue Instrument Co., Ltd., with an extraction time of 6 hours. III. Particle size sieving: The polypropylene polymer powders prepared in Examples 4-6 and Comparative Example 2 were sieved and statistically analyzed. The test results are shown in Table 1: Table 1 As can be seen from the test results in Table 1, and as demonstrated in Examples 4-6, the activity of the novel propylene polymerization composite catalyst of the present invention can be effectively adjusted by changing the Mg / Si ratio for the same silicon source. In addition, catalysts with different catalytic activities can be obtained by adjusting the type of silicon source. As can be seen from the comparison between Comparative Example 2 and the Examples, the novel propylene polymerization composite catalyst of the present invention has better catalytic effect, higher product isotacticity, and the obtained polypropylene polymer has a narrower particle size distribution, which is beneficial to the polymerization of propylene.

[0031] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a novel propylene polymerization composite catalyst, characterized by, The method comprises the following steps: Step one, at 40-80℃, add silicon source into ethanol, then add magnesium chloride aqueous solution, stir for 24-72h, then add ammonia water, gel, at 40-60℃, age for 20-30h, dry, to obtain MgCl2-SiO2 carrier; Step two, mix MgCl2-SiO2 carrier with toluene, cool, add 0.8-1.2wt% titanium tetrachloride / toluene mixed solution dropwise, heat to 60-80℃, add internal electron donor, continue to heat to 100-120℃, keep warm and continue to react for 2h, filter, wash, mix the filter cake after washing with volume ratio of 10:1 titanium tetrachloride / toluene mixed solution, heat to 100-120℃, keep warm and react for 1h, filter, repeat the above operation of treating filter cake with volume ratio of 10:1 titanium tetrachloride / toluene mixed solution, filter, wash, vacuum dry, to obtain new propylene polymerization composite catalyst.

2. The process for the preparation of novel propylene polymerization composite catalyst according to claim 1, characterized in that, In step one, the silicon source comprises at least one of silicate, silica sol and tetraethyl orthosilicate.

3. The process for the preparation of novel propylene polymerization composite catalyst according to claim 1, characterized in that, In step one, the mass ratio of silicon source to magnesium chloride aqueous solution is (0.5-5):2, and the mass ratio of ammonia water to magnesium chloride aqueous solution is 14.7:20, calculated based on SiO2.

4. The process for preparing the novel propylene polymerization composite catalyst according to claim 1, characterized in that, In step two, the internal electron donor comprises aliphatic polycarboxylic acid ester or aromatic polycarboxylic acid ester; the aliphatic polycarboxylic acid ester comprises diethyl malonate and dibutyl adipate, and the aromatic polycarboxylic acid ester comprises diethyl phthalate, diisobutyl phthalate and diisooctyl phthalate.

5. The process for preparing the novel propylene polymerization composite catalyst according to claim 1, characterized in that, In step two, the mass ratio of MgCl2-SiO2 carrier, 0.8-1.2wt% titanium tetrachloride / toluene mixed solution and internal electron donor is 15g:60mL:2mL.

6. A new propylene polymerization composite catalyst prepared by the method according to any one of claims 1-5.

7. Application of the new propylene polymerization composite catalyst according to claim 6 in propylene polymerization process.

8. Use according to claim 7, characterized in that, The propylene polymerization process comprises the following steps: In a nitrogen atmosphere, add external electron donor, triethylaluminum and new propylene polymerization composite catalyst into a reaction container in sequence, then add hydrogen and liquid propylene, start stirring, heat to 60-80℃, stop the reaction after polymerization for 1-2h, to obtain polypropylene.

9. Use according to claim 8, characterized in that, The external electron donor comprises organosilicon compound, and the organosilicon compound comprises at least one of dimethoxysilane, n-propyltriethylsilane, diethylphosphoryl ethyl triethoxysilane and vinyltrimethoxysilane.

10. Use according to claim 8, characterized in that, The mass ratio of external electron donor, triethylaluminum and new propylene polymerization composite catalyst is 1mL:1.5mL:8mg; the volume ratio of hydrogen and liquid propylene is 1:2; and the amount of new propylene polymerization composite catalyst is 0.0005-0.001% of the total mass of raw materials.

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