CN116948069A - A kind of preparation method of high melt index polypropylene - Google Patents

Abstract

The invention discloses a preparation method of high-melt-index polypropylene, which uses a supported heterocyclic metallocene polyolefin catalyst in propylene polymerization. The supported heterocyclic metallocene polyolefin catalyst is prepared by reacting the following components: component a sulfur or oxygen containing heterocyclic zirconocene compound; the carrier component B is silica gel or modified montmorillonite and titanium phosphate clay; component C alkylaluminum or methylaluminoxane. The catalyst adopted by the preparation method has high hydrogen regulation sensitivity, the molecular weight of the polymer is controlled by adding hydrogen during propylene polymerization, and the polymer with high melt index can be obtained, and the molecular weight distribution of the polymer is narrow.

Description

A kind of preparation method of high melt index polypropylene

Technical field

The invention belongs to the field of preparing high melting index polypropylene, and in particular relates to a preparation method of high melting index polypropylene, which is catalyzed by a supported metallocene catalyst.

Background technique

High melt index polypropylene generally refers to polypropylene resin with a melt index ≥20, including homopolymer polypropylene, impact copolymer polypropylene and other types. Generally, the melt flow rate of polypropylene increases, the crystallinity becomes larger, the melting point and heat distortion temperature increase, the tensile yield strength, flexural modulus, and hardness of polypropylene also increase, and the elongation at break decreases. High melting index polypropylene can be used as high melting index fiber material, special material for rapid injection molding, etc. High-melt polypropylene can greatly increase the processing speed during processing and application, thereby significantly improving production efficiency. In addition, due to the excellent melt fluidity, more sophisticated injection molded parts can be produced.

The production of high melt index polypropylene special resin mainly uses controlled degradation method and hydrogen adjustment method:

The controlled degradation method is to add organic peroxide to the low melt index polypropylene base resin produced during the granulation process to control chemical degradation, such as patent CN104589523B, to improve the melt index of the product. However, the quality of the product obtained by this method will be unstable due to uneven distribution of the degradation agent. The decomposition of peroxide will produce volatile substances such as tert-butyl alcohol, as well as oxide residues, which will cause discoloration and odor of the product, thus limiting its application in food packaging and other fields. For injection molded products, the surface of products using this technology is prone to flow streaks, and oxide residues and short-chain oligomers will also affect the physical properties of the product. The irregular flow behavior of the resin melt caused by peroxide degradation can cause surface defects in the product.

The hydrogen modulation method has high requirements on the polymerization process and catalyst. For traditional polypropylene catalyst systems, polymers with higher melt flow rates can be obtained by increasing the amount of hydrogen added during the polymerization process. However, in production, the upper limit of the polymerization reactor pressure limits the hydrogen partial pressure, which affects the degree of improvement of the resin melt flow rate.

Metallocene catalysts have different characteristics from traditional Z-N catalysts. Metallocene catalysts often have only one active center structure, and the resulting polymer has a high degree of uniformity, and the molecular weight distribution is much lower than that of titanium-based Z-N catalysts or chromium-based catalysts. By changing the central transition metal atom, ligand, bridging group and other substituents of the metallocene compound, metallocene catalysts with different structures can be obtained. Their structural symmetry, electronic effects and spatial environment are different, and they can be suitable for different polymerizations. system and achieve molecular tailoring of polymers. By changing the structure of metallocene compounds, the molecular weight and distribution of the polymer, copolymer composition and distribution, chain structure, polymer density and crystallinity, etc. can be changed, greatly broadening the range of products.

Although homogeneous metallocene catalysts have many outstanding properties, their wide application in industry still faces two major problems: First, the morphology of the polymer is difficult to control and there is a serious sticking phenomenon, which makes it unsuitable for Gas-phase polymerization and slurry polymerization require the use of a large amount of cocatalyst (mainly methylaluminoxane (MAO)) to achieve high catalytic activity, which results in higher production costs. The literature (JACS 2001, 123, 4763-4773) reports a sulfur-containing heterocyclic metallocene compound, rac-dimethylsilylbis(2,5-dimethyl-3-phenyl-6-cyclopentadien) Enzo[2,3-b]thiophene)zirconium dichloride has a catalytic propylene polymerization activity of 1953kgPP/mmol Zr·h, but requires the use of a large amount of cocatalyst MAO, and the aluminum-zirconium ratio reaches 215000.

The loading of metallocene catalysts can improve the morphology of the polymer, increase the apparent density of the polymer, and make it easier to control the particle size distribution of the polymer. Supporting can make the active center of the catalyst less likely to be deactivated by bimolecular association, significantly reduce the amount of cocatalyst (such as aluminum to zirconium ratio), reduce the production cost of the catalyst, and increase the added value of metallocene polyolefin products.

Contents of the invention

The object of the present invention is to provide a method for preparing high melting index polypropylene. The preparation method uses a supported heterocyclic metallocene polyolefin catalyst, which can be used directly in existing polymerization devices instead of traditional polypropylene catalysts. During polymerization, it is added Hydrogen, hydrogen/propylene = 50-300ppm does not need to add external electron donors, and high melting index polypropylene can be obtained, with a melt index of 30-4000, a narrow polymer molecular weight distribution, Mw/Mn ≤ 3, and good polymer morphology.

To this end, the present invention provides a method for preparing high-melting polypropylene. Under the catalysis of a supported heterocyclic metallocene polyolefin catalyst, hydrogen is added during the polymerization of propylene. Hydrogen/propylene = 50-300ppm to obtain high-melting polypropylene. Refers to polypropylene. The melt index of polypropylene is 30-4000g/10min. The polymer molecular weight distribution is narrow, Mw/Mn≤3;

The heterocyclic metallocene polyolefin catalyst is obtained by reacting component A, component B and component C: the component A is a sulfur- or oxygen-containing heterocyclic zirconium compound; the component B is silica gel, Modified montmorillonite or titanium phosphate clay, and component B serves as the carrier of the catalyst; the component C is an alkyl aluminum or methylaluminoxane, and in the catalyst, the mass content of zirconium is 0.1- 0.4%, the mass content of aluminum is 10%-20%.

In the preparation method of high-melting polypropylene according to the present invention, it is preferred that the structure of the sulfur- or oxygen-containing heterocyclic zirconocene compound is as shown in formula (I):

In formula (I), X and Y are sulfur or oxygen respectively.

The method for preparing high-melt polypropylene according to the present invention is preferably that X and Y in formula (I) are the same or different.

In the preparation method of high-melting polypropylene according to the present invention, it is preferred that the sulfur- or oxygen-containing heterocyclic zirconocene compound is rac-dimethylsilylbis(2,5-dimethyl-3 -Phenyl-6-cyclopenta[2,3-b]thiophene)zirconium dichloride, rac-dimethylsilylbis(2,5-dimethyl-3-phenyl-6-cyclo) Penta[2,3-b]furan) zirconium dichloride, rac-dimethylsilyl(2,5-dimethyl-3-phenyl-6-cyclopenta[2,3 - At least one of -b]thiophene) (2,5-dimethyl-3-phenyl-6-cyclopenta[2,3-b]furan) zirconium dichloride.

In the method for preparing high-melting polypropylene of the present invention, it is preferred that the alkyl aluminum is at least one of triethylaluminum, triisobutylaluminum, and trioctyl aluminum.

In the method for preparing high-melting polypropylene of the present invention, it is preferred that the aluminum alkyl is triisobutylaluminum.

In the preparation method of high-melting polypropylene of the present invention, it is preferred that the heterocyclic metallocene polyolefin catalyst is prepared by the following method, under anhydrous and oxygen-free conditions, including the following steps:

1) Disperse component B in toluene as a carrier to form a suspension, add component C for reaction, the mass ratio of component C to carrier is 0.3-0.6, and the reaction temperature is 20°C-80°C;

2) Dissolve component A in toluene to form a solution, add component C to react, the mass ratio of component C to component A is 1-5, and the reaction temperature is 20°C-80°C;

3) Add the solution obtained after the reaction in step (2) into step (1), the mass ratio of component A to the carrier is 0.015-0.03, and the reaction temperature is 20°C-80°C;

4) Wash the reaction product obtained in step (3) with toluene to remove unreacted raw materials, and then dry to obtain the catalyst.

In the method for preparing high-melting polypropylene of the present invention, it is preferred that the modified montmorillonite is acid-modified montmorillonite.

In the method for preparing high-melt polypropylene of the present invention, it is preferred that the acid modification uses an inorganic acid.

In the preparation method of high-melting polypropylene according to the present invention, it is preferred that the acid modification of the montmorillonite includes the following steps: after treating the sodium-based montmorillonite with sulfuric acid, it is washed with deionized water until the pH of the filtrate is reached. =6-7, vacuum dry the filter cake at 200°C, and then naturally cool it to room temperature under nitrogen protection for later use.

The present invention also provides a preparation method for the above-mentioned supported heterocyclic metallocene polyolefin catalyst. Preferably, the specific technical solutions are as follows:

The supported heterocyclic metallocene polyolefin catalyst of the present invention is obtained by reacting component A, component B and component C:

Component A is a sulfur- or oxygen-containing heterocyclic zirconocene compound;

Component B is a solid carrier;

Component C is an aluminum alkyl or methylaluminoxane.

The structure of component A is shown in formula (I):

In formula (I), X and Y are sulfur or oxygen, and may be the same or different.

Further preferably, the sulfur- or oxygen-containing heterocyclic zirconocene compound is rac-dimethylsilylbis(2,5-dimethyl-3-phenyl-6-cyclopenta[2, 3-b]thiophene) zirconium dichloride (rac-Me2Si(2,5-Me2-3-Ph-6-Cp[b]Tp)2ZrCl2), rac-dimethylsilylbis(2,5-di Methyl-3-phenyl-6-cyclopenta[2,3-b]furan)zirconium dichloride (rac-Me2Si(2,5-Me2-3-Ph-6-Cp[b]Fr )2ZrCl2), rac-dimethylsilyl(2,5-dimethyl-3-phenyl-6-cyclopenta[2,3-b]thiophene)(2,5-dimethyl- 3-Phenyl-6-cyclopenta[2,3-b]furan)zirconium dichloride (rac-Me2Si(2,5-Me2-3-Ph-6-Cp[b]Tp)(2 ,5-Me2-3-Ph-6-Cp[b]Fr)ZrCl2),

Further preferably, the solid carrier in component B is silica gel, modified montmorillonite, or titanium phosphate clay.

Further preferably, the alkyl aluminum in component C is at least one of triethylaluminum, triisobutylaluminum and trioctyl aluminum, and even more preferably triisobutylaluminum.

Further preferably, the preparation process of the catalyst includes the following steps under anhydrous and oxygen-free conditions:

1) Silica gel or modified montmorillonite or titanium phosphate clay is used as a carrier and dispersed in toluene to form a suspension. Add alkyl aluminum or methylaluminoxane for reaction. The mass ratio of alkyl aluminum or methylaluminoxane to the carrier is 0.3-0.6, and the reaction temperature is 20℃-80℃;

2) The heterocyclic zirconocene compound containing sulfur or oxygen is dissolved in toluene to form a solution, and an aluminum alkyl or methylaluminoxane is added for reaction. The mass ratio of the aluminum alkyl or methylaluminoxane to the zirconocene compound is 1- 5. Reaction temperature is 20℃-80℃;

3) Add the solution obtained in step (2) to the suspension obtained in step (1), the mass ratio of the zirconocene compound to the carrier is 0.015-0.03, and the reaction temperature is 20°C-80°C;

4) Wash the reaction product obtained in step (3) with toluene to remove unreacted raw materials, and dry the solid material to obtain the catalyst; in the catalyst, the mass content of zirconium is 0.1-0.4%, and the mass content of aluminum is 10% -20%.

The beneficial effects of the present invention are: the catalyst has high sensitivity to hydrogen adjustment, can directly produce high melting index polypropylene through the hydrogen adjustment method, does not require a degradation process, uses a low amount of hydrogen during polymerization, and is suitable for the operation process of existing production equipment. conditions, the polymer molecular weight distribution is narrow.

Description of the drawings

Figure 1 is the molecular weight distribution curve of the polymer obtained in Example 8.

Figure 2 is a molecular weight distribution curve of the polymer obtained in Example 10.

Detailed ways

The following is a detailed description of the embodiments of the present invention: This embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation modes and processes are given. However, the protection scope of the present invention is not limited to the following examples.

The following examples are all operated under anhydrous and oxygen-free conditions unless otherwise specified, and all raw materials used are dehydrated and purified in advance. After the silica gel carrier was vacuum dried at 400°C, it was naturally cooled to room temperature under nitrogen protection for use. After the modified montmorillonite carrier is treated with sodium montmorillonite (NaMMT) with sulfuric acid, it is washed with deionized water until the filtrate pH=6-7. After vacuum drying the filter cake at 200°C, it is naturally cooled to Set aside at room temperature. The preparation of the titanium phosphate clay carrier is not particularly limited. Please refer to patent CN106167254B. After the prepared titanium phosphate clay is vacuum dried at 200°C, it is naturally cooled to room temperature under nitrogen protection for use.

The mass content of zirconium and aluminum in the catalyst was obtained by testing the soluble content of the catalyst in a sulfuric acid aqueous solution and analyzing it using an atomic emission spectrometer (ICP). The polymer melt index is measured according to GB/T 3682 "Determination of melt mass flow rate and melt volume flow rate of thermoplastic plastics". The polymer molecular weight was measured by gel permeation chromatography (GPC) using 1,2,4-trichlorobenzene as the solvent.

Example 1

Weigh 10g of silica gel, add 50mL of toluene at room temperature, raise the temperature to 40°C, stir for 0.5 hours, add 50ml of MAO toluene solution (6wt%), and continue stirring and reaction at 40°C for 2 hours to obtain an activated carrier suspension.

Weigh 0.15g metallocene compound rac-Me ₂ Si(2,5-Me ₂ -3-Ph-6-Cp[b]Tp) ₂ ZrCl ₂ , dissolve it in 25mL toluene at 20°C, and add 25ml triisobutyl Aluminum toluene solution (0.1M) and 3ml MAO toluene solution (6wt%) were stirred and reacted at 40°C for 1 hour to obtain an activated metallocene compound solution.

Add the activated metallocene compound solution dropwise into the activated carrier suspension system, and stir for 2 hours at 40°C. After the reaction, stop the reaction, filter the solvent, add 50 mL of toluene and wash twice, then add 50 mL of hexane and wash once, and vacuum dry the solid product at 50°C, which is recorded as cat1.

The zirconium content in the catalyst is 0.2% and the aluminum content is 10%.

Example 2

Weigh 10 g of silica gel, add 50 mL of toluene at room temperature, raise the temperature to 80°C, stir for 0.5 hours, add 100 ml of MAO toluene solution (6wt%), and continue stirring and reaction at 80°C for 1 hour to obtain an activated carrier suspension.

Weigh 0.15g metallocene compound rac-Me ₂ Si(2,5-Me ₂ -3-Ph-6-Cp[b]Tp) ₂ ZrCl ₂ , dissolve it in 25mL toluene at 40°C, and add 30ml triisobutyl Aluminum toluene solution (0.1M) and 3ml MAO toluene solution (6wt%) were stirred and reacted at 40°C for 1 hour to obtain an activated metallocene compound solution.

Add the activated metallocene compound solution dropwise into the activated carrier suspension system, and stir for 1 hour at 80°C. After the reaction is completed, stop the reaction, filter the solvent, add 50 mL of toluene and wash twice, then add 50 mL of hexane and wash once, and vacuum dry the solid product at 50°C, which is recorded as cat2.

The zirconium content in the catalyst is 0.1% and the aluminum content is 20%.

Example 3

Weigh 10g of the modified montmorillonite carrier, add 50 mL of toluene at 20°C, stir for 0.5 hours, add 60ml of MAO toluene solution (6wt%), and continue stirring and reacting at 20°C for 2 hours to obtain an activated carrier suspension.

Weigh 0.3g metallocene compound rac-Me ₂ Si(2,5-Me ₂ -3-Ph-6-Cp[b]Fr) ₂ ZrCl ₂ , dissolve it in 25mL toluene at 20°C, and add 5ml MAO toluene solution ( 6wt%), the activated metallocene compound solution was obtained after stirring and reacting at 20°C for 1 hour.

Add the activated metallocene compound solution dropwise into the activated carrier suspension system, and stir for 1 hour at 20°C. After the reaction is completed, stop the reaction, filter the solvent, add 50 mL of toluene and wash twice, then add 50 mL of hexane and wash once, and vacuum the solid product to dryness at 50°C, which is recorded as cat3.

The zirconium content in the catalyst is 0.3% and the aluminum content is 20%.

Example 4

Weigh 10 g of titanium phosphate clay carrier, add 50 mL of toluene at room temperature, raise the temperature to 80°C, stir for 0.5 hours, add 100 ml of MAO toluene solution (6wt%), and continue stirring and reaction at 80°C for 1 hour to obtain an activated carrier suspension.

Weigh 0.18g metallocene compound rac-Me ₂ Si(2,5-Me ₂ -3-Ph-6-Cp[b]Tp)(2,5-Me2-3-Ph-6-Cp[b]Fr )ZrCl ₂ , dissolve in 25 mL toluene at 80°C, add 20 ml trioctyl aluminum toluene solution (0.1M) and 3 ml MAO toluene solution (6wt%), stir and react at 80°C for 1 hour to obtain an activated metallocene compound solution.

Add the activated metallocene compound solution dropwise into the activated carrier suspension system, and stir for 1 hour at 80°C. After the reaction, stop the reaction, filter the solvent, add 50 mL of toluene and wash twice, then add 50 mL of hexane and wash once, and vacuum the solid product to dryness at 50°C, which is recorded as cat4.

The zirconium content in the catalyst is 0.4% and the aluminum content is 10%.

Example 5

Weigh 10 g of titanium phosphate clay carrier, add 50 mL of toluene at room temperature, raise the temperature to 50°C, stir for 0.5 hours, add 100 ml of MAO toluene solution (6wt%), and continue stirring and reaction at 50°C for 1 hour to obtain an activated carrier suspension.

Weigh 0.2g of the metallocene compound rac-Me ₂ Si(2,5-Me ₂ -3-Ph-6-Cp[b]Tp) ₂ ZrCl ₂ , dissolve it in 25 mL of toluene at 50°C, and add 20 ml of triethylaluminum Toluene solution (0.1M) and 3ml MAO toluene solution (10wt%) were stirred and reacted at 50°C for 1 hour to obtain an activated metallocene compound solution.

Add the activated metallocene compound solution dropwise into the activated carrier suspension system, stir and react at 50°C for 1 hour. After the reaction, stop the reaction, filter the solvent, add 50 mL of toluene and wash twice, then add 50 mL of hexane and wash once, and vacuum the solid product to dryness at 50°C, which is recorded as cat5.

The zirconium content in the catalyst is 0.2% and the aluminum content is 20%.

Example 6

In the 5L stainless steel high-pressure polymerization kettle, after fully replacing it with nitrogen, add 1.5kg liquid propylene, add 1ml triethylaluminum (2.4mol/L hexane solution), then add 200mg catalyst cat2, raise the temperature to 70°C for reaction 1 hour; the measured activity of the catalyst is 1400gPP/gcat.

Examples 7-11

The polymerization conditions of Examples 7-11 are basically the same as those of Example 6, except that hydrogen is first added to the kettle before adding liquid propylene. The amount of hydrogen used and the polymerization evaluation results are shown in Table 1.

Table 1 Aggregation evaluation results

It can be seen that the supported heterocyclic metallocene polyolefin catalyst involved in the present invention has high hydrogen modulation sensitivity and can prepare high melting index polymers.

The weight average molecular weight Mw of the polypropylene obtained in Example 8 is 188,000, the number average molecular weight Mn is 92,000, the molecular weight distribution Mw/Mn=2.0, and the molecular weight distribution curve is shown in Figure 1; the weight average molecular weight of the polypropylene obtained in Example 10 Mw is 136,000, the number average molecular weight Mn is 67,000, the molecular weight distribution Mw/Mn=2.0, and the molecular weight distribution curve is shown in Figure 2. It can be seen that the supported heterocyclic metallocene polyolefin catalyst involved in the present invention has the characteristics of a single active center and can prepare narrow molecular weight distribution polymers.

Of course, the present invention can also have various other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention. However, these corresponding changes and deformations shall all fall within the protection scope of the present invention.

Claims (10)

1. A method for preparing high melting index polypropylene, which is characterized in that, under the catalysis of a supported heterocyclic metallocene polyolefin catalyst, hydrogen is added during the polymerization of propylene, hydrogen/propylene = 50-300ppm, to obtain a high melting index. Polypropylene, the melt index of polypropylene is 30-4000g/10min, the polymer molecular weight distribution is narrow, Mw/Mn≤3; The heterocyclic metallocene polyolefin catalyst is obtained by reacting component A, component B and component C: the component A is a sulfur- or oxygen-containing heterocyclic zirconium compound; the component B is silica gel, Modified montmorillonite or titanium phosphate clay, and component B serves as the carrier of the catalyst; the component C is an alkyl aluminum or methylaluminoxane, and in the catalyst, the mass content of zirconium is 0.1- 0.4%, the mass content of aluminum is 10%-20%. 2. The preparation method of high melting index polypropylene according to claim 1, characterized in that the structure of the sulfur- or oxygen-containing heterocyclic zirconocene compound is as shown in formula (I): In formula (I), X and Y are sulfur or oxygen respectively. 3. The method for preparing high melting index polypropylene according to claim 2, characterized in that X and Y in formula (I) are the same or different. 4. The preparation method of high melting index polypropylene according to claim 2, characterized in that the sulfur- or oxygen-containing heterocyclic zirconocene compound is rac-dimethylsilyl bis(2,5-dimethyl -3-phenyl-6-cyclopenta[2,3-b]thiophene)zirconium dichloride, rac-dimethylsilylbis(2,5-dimethyl-3-phenyl- 6-cyclopenta[2,3-b]furan)zirconium dichloride, rac-dimethylsilyl(2,5-dimethyl-3-phenyl-6-cyclopenta[ At least one of 2,3-b]thiophene) (2,5-dimethyl-3-phenyl-6-cyclopenta[2,3-b]furan) zirconium dichloride. 5. The method for preparing high melting index polypropylene according to claim 1, characterized in that the alkyl aluminum is at least one of triethylaluminum, triisobutylaluminum and trioctyl aluminum. 6. The method for preparing high melting index polypropylene according to claim 5, wherein the aluminum alkyl is triisobutylaluminum. 7. The preparation method of high melting index polypropylene according to claim 1, characterized in that the heterocyclic metallocene polyolefin catalyst is prepared by the following method, under anhydrous and oxygen-free conditions, including the following steps: 1) Disperse component B in toluene as a carrier to form a suspension, add component C for reaction, the mass ratio of component C to carrier is 0.3-0.6, and the reaction temperature is 20°C-80°C; 2) Dissolve component A in toluene to form a solution, add component C to react, the mass ratio of component C to component A is 1-5, and the reaction temperature is 20°C-80°C; 3) Add the solution obtained after the reaction in step (2) into step (1), the mass ratio of component A to the carrier is 0.015-0.03, and the reaction temperature is 20°C-80°C; 4) Wash the reaction product obtained in step (3) with toluene to remove unreacted raw materials, and then dry to obtain the catalyst. 8. The preparation method of high melting index polypropylene according to claim 1, characterized in that the modified montmorillonite is acid-modified montmorillonite. 9. The method for preparing high melting index polypropylene according to claim 8, characterized in that the acid modification uses an inorganic acid. 10. The preparation method of high melting index polypropylene according to claim 9, characterized in that the acid modification of the montmorillonite includes the following steps: after treating the sodium montmorillonite with sulfuric acid, washing with deionized water When the pH of the filtrate is equal to 6-7, the filter cake is vacuum dried at 200°C and then naturally cooled to room temperature under nitrogen protection for use.