Low-isotacticity polypropylene catalyst, and preparation method therefor and use thereof

Abstract

Disclosed in the present invention are a low-isotacticity polypropylene catalyst, and a preparation method therefor and a use thereof, aiming at providing a low-isotacticity polypropylene catalyst preparation method which has a simple preparation process, achieves reduced use of hazardous reagents and low hazardous waste emissions, and is economical and environmentally-friendly. When the prepared catalyst is used to prepare a polymer, the molecular weight of the polymer has a wide adjustable range, the molecular weight distribution is relatively broad, and the product has good processing and application performance. The technical solution comprises the following steps: 1) mixing magnesium ethylate, a chlorination reagent, and alkoxy silane in a solvent, heating the mixture to 50-150°C, stirring the mixture for 0.2-5 h, then performing cooling and standing, and filtering off a supernatant to obtain a solid; and 2) adding a solvent to the solid obtained in step 1) and then adding titanium tetrachloride and a nitrogen-containing heterocyclic compound to form a mixture in the solvent, heating the mixture to 50-150°C, stirring the mixture for 0.2-5 h, then performing cooling and standing, filtering off a supernatant, and washing the obtained solid with the solvent to obtain the catalyst. The present invention relates to the technical field of catalysts.

Description

Low isotactic polypropylene catalyst and its preparation method and application Technical Field

[0001] The present invention relates to a polypropylene catalyst, in particular to a low-isotactic polypropylene catalyst. The present invention also relates to a preparation method and application of the catalyst, belonging to the technical field of catalysts. Technical Background

[0002] Low-isotactic polypropylene (LP) is typically a byproduct of the industrial production of isotactic polypropylene. Due to its adverse effects on PP performance, early PP production required the separation of low-isotactic or atactic PP byproducts. Due to its unique properties, this low-isotactic PP finds widespread application in adhesives, sealing, polymer modification, and asphalt modification. With advancements in PP catalyst technology, the amount of low-isotactic PP byproduct in production has been significantly reduced, eliminating the need for the removal process. Consequently, a supply gap has emerged in the market for low-isotactic PP products.

[0003] The key to producing low-isotactic polypropylene with excellent performance lies in the catalyst. The catalysts that can be used to produce low-isotactic polypropylene include supported Ziegler-Natta catalysts and metallocene catalysts. Metallocene catalysts are single-site catalysts, and the polymers prepared have a relatively regular polymer chain structure and a narrow molecular weight distribution of the resulting polymer. However, metallocene catalysts as olefin polymerization catalysts can result in high production costs. At the same time, the low-isotactic polymers prepared by metallocene catalysts generally have a lower melting point and are not as good as polymers prepared by Ziegler-Natta catalysts in terms of product heat resistance. Therefore, considering the comprehensive production cost and product performance requirements, supported Ziegler-Natta catalysts are still the more preferred low-isotactic polypropylene catalysts in industry.

[0004] However, industrial Ziegler-Natta catalysts are typically supported on MgCl2. To meet the requirements for producing low-isotactic polypropylene, MgCl2 needs to have a sufficiently large specific surface area and certain crystal defects to combine with TiCl4 to produce low-isotactic catalytic active centers. Therefore, MgCl2 requires a series of treatments to meet the requirements of an active support.

[0005] There are two methods for preparing active MgCl2 supports: physical and chemical. The physical method is generally a milling method, which involves milling anhydrous MgCl2 or co-milling it with other inorganic substances (such as aluminum chloride) to obtain fine particles with a large specific surface area. In addition, during the milling process, the MgCl2 crystal form will partially convert into a crystal form with crystal defects, which is more conducive to combining with TiCl4 to form low isotactic active sites. However, when the solid MgCl2 support contacts the liquid TiCl4, it is difficult to form a completely uniform contact surface, resulting in an uneven catalyst. At the same time, some TiCl4 does not combine with MgCl2 to form the target catalytic center, and often requires solvent washing to remove it.

[0006] In contrast, chemically prepared active MgCl2 supports and corresponding catalysts offer advantages. One approach involves complexing MgCl2 with an alcohol and then decomplexing it with an aluminum alkyl or TiCl4 to form a MgCl2 support with a large surface area. However, this method requires hazardous aluminum alkyls or TiCl4, increasing the process risk and generating more hazardous waste. Consequently, research on catalysts for low-isotactic polypropylene has become a hot topic.

[0007] For example, US Patent 4777216 describes a catalyst for producing low-isotactic polypropylene by co-grinding MgCl2 and TiCl4. Patent CN1315885C mentions co-grinding anhydrous MgCl2 and anhydrous AlCl3 with TiCl4 to produce a catalyst with a low titanium loading, producing polypropylene with an isotacticity of 25-40%. Patent CN101942053A describes a catalyst for the polymerization of α-olefins by grinding anhydrous MgCl2 and LiCl with TiCl4 to produce a high-atacticity catalyst.

[0008] There are also reports on the preparation of supported catalysts through chemical reactions. Patent CN1016423A discloses a method for chlorinating dialkylmagnesium to form a MgCl2 support, which is then loaded with TiCl4. This method uses Cl2, HCl, CCl4, etc. as chlorination reagents. Patent CN1067693A describes a method for preparing a support by combining Mg(OEt)2 with a chlorination reagent in the presence of an electron donor, which is then reacted with a toluene solution of TiCl4 to obtain a supported catalyst. Patent CN1122048A reports a method for preparing a random polypropylene catalyst. This method involves complexing magnesium chloride with an alcohol, adding clay, and then reacting the complex of alkylaluminum and magnesium chloride to form a support MgCl2. TiCl4 is then added for catalyst loading to obtain the catalyst. Patent CN101942053 also discloses a method for preparing a highly random α-olefin polymerization catalyst. This method involves dispersing Mg(OEt)2 and LiCl in a solvent and adding TiCl4 for loading to obtain the catalyst. The above methods more or less have disadvantages such as complicated catalyst preparation process, low catalyst activity, and high polypropylene isotacticity, which are not conducive to industrial production.

[0009] Summary of the Invention

[0010] In view of the shortcomings of the existing technology, the first object of the present invention is to develop a method for preparing a low-isotactic polypropylene catalyst through reasonable selection and matching of reaction materials, which has a simple preparation process, uses less hazardous reagents, has low hazardous waste emissions, and is economical and environmentally friendly.

[0011] The second object of the present invention is to provide a catalyst which, when used to prepare polymers, has a wide adjustable range of polymer molecular weight, a wide molecular weight distribution, and good processing and application properties.

[0012] The third object of the present invention is to provide applications of the catalyst.

[0013] To this end, the first technical solution provided by the present invention is as follows:

[0014] A method for preparing a low-isotactic polypropylene catalyst comprises the following steps in sequence:

[0015] 1) Mixing magnesium ethoxide, a chlorination agent, and an alkoxysilane in a solvent, heating to 50-150° C. and stirring for 0.2-5 hours, then cooling and allowing to stand, filtering off the supernatant to obtain a solid;

[0016] 2) adding a solvent to the solid obtained in step 1), and then adding titanium tetrachloride and a nitrogen-containing heterocyclic compound, heating the mixture formed in the solvent to 50-150° C. and stirring for 0.2-5 hours, then cooling and allowing to stand, filtering off the supernatant, and washing the resulting solid with a solvent to obtain a catalyst;

[0017] The molar ratio of Mg, Al, Si, Ti and N in the magnesium ethoxide, chlorination reagent, alkoxysilane, titanium tetrachloride and nitrogen-containing heterocyclic compound is 10:0.5:0.2:1:0.1-10:15:20:15:20.

[0018] Furthermore, in the preparation method of the above-mentioned low-isotactic polypropylene catalyst, the chlorination agent is one of carbon tetrachloride, aluminum trichloride, silicon tetrachloride, and phosphorus pentachloride; preferably carbon tetrachloride, aluminum trichloride, and silicon tetrachloride; more preferably aluminum trichloride; which can undergo a chlorination reaction with Mg(OEt)2 to generate various chlorides of MgCl2;

[0019] Furthermore, in the above-mentioned method for preparing a low-isotactic polypropylene catalyst, the alkoxysilane is a structure represented by R1Si(OR2)(OR3)(OR4) or R1R1'Si(OR2)(OR3), wherein R1 and R1' are each one of methyl, ethyl, cyclopentyl, cyclohexyl, and phenyl; and R2 and R3 are methyl or ethyl. More preferably, the alkoxysilane is one of phenyltrimethoxysilane, phenyltriethoxysilane, methylcyclopentyldimethoxysilane, methylcyclohexyldimethoxysilane, and diphenyldimethoxysilane. In this case, the addition of an alkoxysilane not only promotes the chlorination reaction, but also has no significant disadvantage in terms of isotactic selectivity of the prepared catalyst and can also improve the polymerization activity of the catalyst.

[0020] Furthermore, in the above-mentioned method for preparing the low-isotactic polypropylene catalyst, the nitrogen-containing heterocyclic compound is one of the structures shown in the following formula:

[0021] Wherein R5, R6, and R7 are independently selected from one of hydrogen, methyl, ethyl, chlorine, and bromine.

[0022] More preferably, the nitrogen-containing heterocyclic compound 2,5-dimethylpyrrolidine, 2,5-dichloropyrrolidine, 2,5-dimethylpyrrole, 2,5-dichloropyrrole, 2,6-dimethylpyridine, 2-chloro-6-methylpyridine, 2,6-dichloropyridine. In this case, a nitrogen heterocyclic compound is used as an auxiliary agent added during the catalyst loading process. Before TiCl4 is loaded on the active MgCl2 carrier, the nitrogen-containing heterocyclic compound is first contacted and mixed with TiCl4, which has no adverse effect on the preparation of low isotactic polypropylene by the obtained catalyst. At the same time, the catalytic activity of the obtained catalyst and the performance of the polymer product can be improved, the polymer molecular weight can reach a high level (Mw>200000), and the hydrogen sensitivity is good, the polymer product molecular weight distribution is wide, and it is suitable for processing and application.

[0023] In the above-mentioned method for preparing the low-isotactic polypropylene catalyst, the solvent is selected from inert hydrocarbon compounds with different boiling points. The preferred solvent is one of hexane, heptane, decane, toluene, xylene, and chlorobenzene, so as to meet the specific reaction temperature.

[0024] In this case, the choice of temperature is also related to the boiling point of the solvent. As a preferred embodiment, the temperature range for catalyst preparation is 60-120°C, and the solvent is heptane, toluene, or chlorobenzene.

[0025] The second technical solution provided by the present invention is a low-isotactic polypropylene catalyst prepared by the method described in the first technical solution.

[0026] The third technical solution provided by the present invention is to use the above-mentioned low-isotactic polypropylene catalyst to catalyze propylene polymerization.

[0027] The catalyst provided in this case can be used for propylene polymerization using common methods in the industry, such as bulk method, solution method, slurry method, gas phase method, and a combination of these methods. The solvent used can be a common solvent suitable for preparing the target polypropylene, including but not limited to hexane, heptane, mixed alkanes, paraffin oil, toluene, xylene, etc. When the catalyst provided by the present invention catalyzes propylene polymerization, it is necessary to add alkyl aluminum or alkyl aluminum chloride, or a mixture of the first two organoaluminums. Alkyl aluminum includes but is not limited to trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, tri-n-octylaluminum, etc. Alkyl aluminum chloride includes but is not limited to diethyl aluminum monochloride and ethyl aluminum dichloride.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1) The catalyst preparation method provided by the present invention has the characteristics of simple process, reduces the use of hazardous reagents, reduces the emission of hazardous waste during the catalyst preparation process, and is environmentally friendly;

[0030] 2) The catalyst prepared by the present invention produces polypropylene with low isotacticity. Due to the addition of an internal electron donor, the polypropylene has good polymerization activity. Therefore, the polymerization product does not require a process flow for removing ash, which greatly simplifies the process and improves production efficiency.

[0031] 3) When the catalyst provided by the present invention is used to prepare a polymer, the polymer molecular weight has a wide adjustable range and a wide molecular weight distribution, and the product has good processing and application properties.

[0032] 4) The catalyst provided by the present invention uses alkoxymagnesium Mg(OR)2 as a raw material to react with a chlorination agent to obtain an active MgCl2 carrier when preparing a polymer, which has greater operational flexibility and process safety. DETAILED DESCRIPTION

[0033] The present invention is described below by way of examples, but the technical scope of the present invention is not limited to the following examples.

[0034] The reagents used in the present invention were purchased from Anaiji Chemical Reagent Company (Anhui Zesheng Technology Co., Ltd.).

[0035] Example 1 Catalyst Preparation

[0036] 1) To a 1 L glass bottle that had been previously vacuum-dried and replaced with nitrogen, 600 mL of toluene, 28.5 g (0.25 mol) of Mg(OEt)2, 20.6 mL (0.18 mol) of SiCl4, and 35.7 mL (0.18 mol) of phenyltrimethoxysilane were added in sequence at room temperature. Stirring was initiated and the temperature was raised to 80°C. After 1 hour, heating was turned off, the mixture was cooled to room temperature, and the supernatant was filtered to obtain a solid.

[0037] 2) 500 mL of toluene was added to the solid obtained in step 1) to disperse it. 22.0 mL (0.20 mol) of TiCl4 and 6.1 mL (0.05 mol) of 2,5-dimethylpyrrolidine were then added sequentially at room temperature. Stirring was initiated and the temperature was raised to 80° C. After 1 hour, heating was stopped and the temperature was cooled to room temperature. The supernatant liquid was filtered and the resulting solid was dried to obtain a catalyst. Elemental analysis of the Mg, Al, Si, and Ti content of the resulting catalyst is shown in Table 1 below.

[0038] Example 2 Catalyst Preparation

[0039] The method of this embodiment is basically the same as that of Example 1, except that 26.7 g (0.20 mol) of AlCl3 is added as the chlorination reagent.

[0040] The Mg, Al, Si and Ti content of the catalyst obtained by elemental analysis is listed in Table 1 below.

[0041] Example 3 Catalyst Preparation

[0042] The method of this embodiment is substantially the same as that of embodiment 1, except that the alkoxysilane added is 30.0 mL (0.15 mol) of methylcyclohexyldimethoxysilane.

[0043] The Mg, Al, Si and Ti content of the catalyst obtained by elemental analysis is listed in Table 1 below.

[0044] Example 4 Catalyst Preparation

[0045] The method of this embodiment is basically the same as that of Example 1, except that the amount of TiCl4 is 16.5 mL (0.20 mol).

[0046] The Mg, Al, Si and Ti content of the catalyst obtained by elemental analysis is listed in Table 1 below.

[0047] Example 5 Catalyst Preparation

[0048] The method of this embodiment is basically the same as that of Example 1, except that the nitrogen heterocyclic compound added is 3.10 mL (0.03 mol) of 2,5-dimethylpyrrole.

[0049] The Mg, Al, Si and Ti content of the catalyst obtained by elemental analysis is listed in Table 1 below.

[0050] Comparative Example 1

[0051] The method of this embodiment is basically the same as that of Example 1, except that alkoxysilane and nitrogen heterocyclic compound are not added.

[0052] The Mg, Al, Si and Ti content of the catalyst obtained by elemental analysis is listed in Table 1 below.

[0053] Table 1 Content of each element in the catalyst

[0054] Example 6 Preparation of polypropylene

[0055] Propylene bulk polymerization: A 10L stainless steel reactor was first heated to 100°C in a vacuum and dried, then replaced with propylene gas three times and cooled to room temperature. 4L of liquid propylene, 1.89mL of a 1.0M solution of triisobutylaluminum in n-hexane (so that Al / Ti is 125), 25mg of a dispersion of the catalyst prepared in Example 1 (the solvent is hexane, 100mL), 1L of hydrogen, and then 1L of liquid propylene were added to the reactor. Stirring was started, and the temperature was raised to 60°C for polymerization reaction. The reaction was stopped after 1 hour, and the obtained polymer was collected and dried. The test data related to the polymerization reaction are listed in Table 2 below.

[0056] Preparation of polypropylene in Examples 7-10

[0057] The method of the embodiment is basically the same as that of embodiment 6, except that the catalysts added are prepared in the order of embodiment 2 to embodiment 5. The test data related to the polymerization reaction are listed in the following Table 2.

[0058] Example 11 Preparation of polypropylene

[0059] The method of this embodiment is substantially the same as that of embodiment 6, except that the alkyl aluminum added is triethyl aluminum. The test data related to the polymerization reaction are listed in Table 2 below.

[0060] Example 12 Preparation of polypropylene

[0061] The method of this embodiment is substantially the same as that of embodiment 6, except that 3 L of hydrogen is added. The test data related to the polymerization reaction are listed in Table 2 below.

[0062] Example 13 Preparation of polypropylene

[0063] The method of this embodiment is substantially the same as that of Example 6, except that the polymerization temperature is 80° C. The test data related to the polymerization reaction are listed in Table 2 below.

[0064] Comparative Example 2

[0065] The method of this example is basically the same as that of Example 6, except that the catalyst added is the catalyst prepared in Comparative Example 1. The test data related to the polymerization reaction are listed in Table 2 below.

[0066] In order to demonstrate the effectiveness of the technical solution provided by this application, the following are the conventional analytical test methods and test results used in the present invention:

[0067] 1) Isotacticity: n-heptane extraction method. A certain weight of polymer sample is extracted in boiling heptane. The mass percentage of the insoluble portion is the isotacticity, also known as the isotactic index.

[0068] 2) Molecular weight and molecular weight distribution: Determined by high-temperature gel permeation chromatography (GPC). A calibration curve was prepared on a PL-GPC220 gel permeation chromatography instrument using styrene as the standard, trichlorobenzene as the solvent, and the test temperature was 150°C. The number average molecular weight (Mn), weight average molecular weight (Mw), and molecular weight distribution (PDI, i.e., Mw / Mn) were obtained. The molecular weight referred to herein is the weight average molecular weight (Mw).

[0069] 3) Catalyst element content: Determined by inductively coupled plasma emission spectrometry (ICP). The catalyst sample is digested (dissolved) with acid and then fixed to volume before testing.

[0070] 4) Melting point (Tm) and glass transition temperature (Tg): measured by differential scanning calorimetry (DSC).

[0071] 5) Polymerization activity: the ratio of the weight of the polymerization product to the weight of the catalyst, the unit is kgPP / gTi.

[0072] Table 2 Propylene polymerization test results

[0073] As can be seen from the above table, the polymer molecular weight obtained by the technical solution provided by the present application has a wide adjustable range, low isotacticity, high melting point, and the product has good processing and application performance. When the catalyst (Comparative Example 1) is added with alkoxysilane and nitrogen heterocyclic compound, when catalyzing propylene polymerization, its polymerization activity is significantly lower and the isotacticity is higher, indicating that the addition of alkoxysilane and nitrogen heterocyclic compound in the technical solution provided by the present application can not only promote the chlorination reaction, but also improve the polymerization activity of the catalyst, and the polymer molecular weight can reach a high level (Mw>200000), and the hydrogen adjustment sensitivity is good, the molecular weight distribution of the polymer product is wide, and it is suitable for processing and application.

Claims

1. A method for preparing a low isotactic polypropylene catalyst, characterized in that: The steps are as follows: 1) Mixing ethoxymagnesium, a chlorination agent and alkoxysilane in a solvent, heating to 50-150° C. and stirring for 0.2-5 h, then cooling and standing, filtering off the clear liquid to obtain a solid; 2) adding a solvent to the solid obtained in step 1), and then adding titanium tetrachloride and a nitrogen-containing heterocyclic compound, heating the mixture formed in the solvent to 50-150° C. and stirring for 0.2-5 h, then cooling and standing, filtering off the clear liquid, and washing the obtained solid with a solvent to obtain a catalyst; The molar ratio of Mg, Al, Si, Ti and N in the ethoxymagnesium, chlorination reagent, alkoxysilane, titanium tetrachloride and nitrogen-containing heterocyclic compound is 10:0.5:0.2:1:0.1-10:15:20:15:

20.

2. The method for preparing a low isotactic polypropylene catalyst according to claim 1, characterized in that: The chlorination agent is one of carbon tetrachloride, aluminum trichloride, silicon tetrachloride and phosphorus pentachloride.

3. The method for preparing a low isotactic polypropylene catalyst according to claim 2, characterized in that: The chlorination reagent is carbon tetrachloride, aluminum trichloride, silicon tetrachloride; preferably aluminum trichloride.

4. The method for preparing a low isotactic polypropylene catalyst according to claim 1, characterized in that: The alkoxysilane is a structure represented by R1Si(OR2)(OR3)(OR4) or R1R1'Si(OR2)(OR3), wherein R1 and R1' are each one of methyl, ethyl, cyclopentyl, cyclohexyl and phenyl; and R2 and R3 are methyl or ethyl.

5. The method for preparing a low isotactic polypropylene catalyst according to claim 4, characterized in that: The alkoxysilane is one of phenyltrimethoxysilane, phenyltriethoxysilane, methylcyclopentyldimethoxysilane, methylcyclohexyldimethoxysilane and diphenyldimethoxysilane.

6. The method for preparing a low isotactic polypropylene catalyst according to claim 1, characterized in that: The nitrogen-containing heterocyclic compound is one of the structures shown in the following formula: Wherein R5, R6, and R7 are independently selected from one of hydrogen, methyl, ethyl, chlorine, and bromine.

7. The method for preparing a low isotactic polypropylene catalyst according to claim 6, characterized in that: The nitrogen-containing heterocyclic compounds include 2,5-dimethylpyrrolidine, 2,5-dichloropyrrolidine, 2,5-dimethylpyrrole, 2,5-dichloropyrrole, 2,6-dimethylpyridine, 2-chloro-6-methylpyridine and 2,6-dichloropyridine.

8. The method for preparing a low isotactic polypropylene catalyst according to claim 1, characterized in that: The solvent is one of hexane, heptane, decane, toluene, xylene and chlorobenzene.

9. A low isotactic polypropylene catalyst, characterized in that: Prepared by the method described in claim 1.

10. The low isotactic polypropylene catalyst according to claim 9 is used for catalyzing propylene polymerization.

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