Low isotactic polypropylene catalyst, process for its preparation and use

Abstract

The application discloses a low isotactic polypropylene catalyst and a preparation method and application thereof, and aims to provide a preparation method of the low isotactic polypropylene catalyst, which is simple in preparation process, low in use of dangerous reagents, low in waste discharge, economic and environmental protection; when the prepared catalyst is used for preparing a polymer, the polymer has a wide adjustable range of molecular weight and a wide molecular weight distribution, and the product has good processing and application performance; the technical scheme comprises the following steps: 1) mixing ethoxymagnesium, a chlorination reagent and an alkoxysilane in a solvent, stirring at 50-150 DEG C for 0.2-5h, then cooling and standing, filtering the clear liquid to obtain a solid; 2) adding a solvent to the solid obtained in the step 1), then adding titanium tetrachloride and a nitrogen-containing heterocyclic compound, stirring the mixture formed in the solvent at 50-150 DEG C for 0.2-5h, then cooling and standing, filtering the clear liquid, washing the obtained solid with the solvent to obtain the catalyst; and belongs to the technical field of catalysts.

Description

TECHNICAL FIELD

[0001] The present application relates to a polypropylene catalyst, in particular to a low isotacticity polypropylene catalyst, and a preparation method and application thereof, and belongs to the technical field of catalysts. TECHNICAL BACKGROUND

[0002] Low isotactic polypropylene is generally a by-product generated in the industrial production of isotactic polypropylene. Due to its adverse effect on the performance of polypropylene, early polypropylene production needs to separate the low isotactic or atactic polypropylene by-product. This part of low isotactic polypropylene is widely used in the fields of bonding, sealing, polymer modification, asphalt modification, etc. due to its unique performance. With the upgrading of polypropylene catalyst technology, the content of low isotactic polypropylene by-product in production has been greatly reduced, and the process of removing low isotactic polypropylene is no longer needed. Therefore, there is a supply gap of low isotactic polypropylene products in the market.

[0003] To produce low isotactic polypropylene with excellent performance, the key 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 belong to single-site catalysts, and the polymers prepared have relatively regular polymer chain structures, and the molecular weight distribution of the obtained polymers is narrow. 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 heat-resistant as the polymers prepared by Ziegler-Natta catalysts. Therefore, considering the production cost and product performance requirements, supported Ziegler-Natta catalysts are still the preferred low isotactic polypropylene catalysts in industry.

[0004] However, Ziegler-Natta catalysts in industry are generally supported on MgCl2 carriers. In order to meet the requirements of preparing low isotactic polypropylene, the MgCl2 needs to have a large enough specific surface area and certain crystal defects to combine with TiCl4 to produce low isotactic catalytic active center sites. Therefore, the MgCl2 needs to be treated in a series of processes to meet the requirements of becoming an active carrier.

[0005] There are two methods to prepare active MgCl2 support, physical method and chemical method. Physical method is generally milling method, that is, milling anhydrous MgCl2 or co-milling with other inorganic substances (such as AlCl3) to get fine particles with large specific surface area. During the milling process, the crystal form of MgCl2 is partially converted into crystal form with crystal defects, which is more conducive to the combination with TiCl4 to form low stereoregularity active sites. However, when the solid MgCl2 support is in contact with liquid TiCl4, it is difficult to form a completely uniform contact surface, resulting in uneven catalyst. At the same time, part of TiCl4 is not combined with MgCl2 to form the target catalyst center, often requiring solvent washing to remove.

[0006] In contrast, the active MgCl2 support and the corresponding catalyst prepared by chemical method have more advantages. One method is to complex MgCl2 with alcohol first, and then to decomplex it with alkyl aluminum or TiCl4 to form MgCl2 support with large specific surface area. However, this method requires dangerous alkyl aluminum or TiCl4, which not only increases the risk of the process, but also generates more hazardous waste. Therefore, the research on catalysts for low stereoregularity polypropylene has also become a research hotspot.

[0007] In patent US4777216, MgCl2 and TiCl4 are co-milled to prepare a catalyst for low stereoregularity polypropylene. Patent CN1315885C mentions co-milling anhydrous MgCl2 and anhydrous AlCl3 with TiCl4 to obtain a catalyst with low titanium load, and the prepared polypropylene has a stereoregularity of 25-40%. Patent CN101942053A introduces a method of milling anhydrous MgCl2 and LiCl with TiCl4 to prepare a high-randomness α-olefin polymerization catalyst.

[0008] There are also reports on the preparation of carrier catalysts by chemical reactions. Patent CN1016423A discloses a method for forming MgCl2 carrier by chlorinating dialkyl magnesium to form MgCl2, and then loading TiCl4. Cl2, HCl, CCl4, etc. are used as chlorinating reagents. Patent CN1067693A introduces a method for preparing a carrier by reacting Mg(OEt)2 with a chlorinating reagent in the presence of an electron donor, and then reacting with a toluene solution of TiCl4 to obtain a carrier catalyst. Patent CN1122048A reports a method for preparing a random polypropylene catalyst. In this method, magnesium chloride is complexed with alcohol, clay is added, and then the complex of aluminum alkyl and magnesium chloride is reacted to form a carrier MgCl2, and then TiCl4 is added to load the catalyst. In patent CN101942053, a method for preparing a high random α-olefin polymerization catalyst is also disclosed. In this method, Mg(OEt)2 and LiCl are dispersed in a solvent, and then TiCl4 is loaded to obtain a catalyst. In the above methods, there are more or less disadvantages such as complicated catalyst preparation process, low catalyst activity, high isotacticity of polypropylene, etc., which are not conducive to industrial production. SUMMARY

[0009] In view of the deficiencies of the prior art, the first object of the present application is to develop a preparation method for a low isotacticity polypropylene catalyst, which has simple preparation process, less use of hazardous reagents, low waste discharge, and is economical and environmentally friendly, by selecting and matching reasonable reaction materials.

[0010] The second object of the present application is to provide a catalyst, which has a wide adjustable range of polymer molecular weight and a wide molecular weight distribution when preparing a polymer, and the product has good processing and application performance.

[0011] The third object of the present application is to provide the application of the catalyst.

[0012] To this end, the first technical solution provided by the present application is as follows:

[0013] A preparation method of a low isotacticity polypropylene catalyst, comprising the following steps in sequence:

[0014] 1) mixing ethoxy magnesium, a chlorinating reagent and an alkoxy silane in a solvent, stirring at a temperature of 50-150℃ for 0.2-5h, then cooling and standing, filtering the clear liquid to obtain a solid;

[0015] 2) adding a solvent to the solid obtained in step 1), then adding titanium tetrachloride and a nitrogen-containing heterocyclic compound to form a mixture in the solvent, stirring at a temperature of 50-150℃ for 0.2-5h, then cooling and standing, filtering the clear liquid, and washing the obtained solid with a solvent to obtain a catalyst;

[0016] The molar ratio of Mg, Al, Si, Ti, N in the ethoxy magnesium, chlorinating agent, alkoxysilane, titanium tetrachloride, and nitrogen-containing heterocyclic compound is 10:0.5:0.2:1:0.1-10:15:20:15:20.

[0017] Further, in the above-mentioned method for preparing a low isotactic polypropylene catalyst, the chlorinating 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 react with Mg(OEt)2 to form various chlorides of MgCl2.

[0018] Further, in the above-mentioned method for preparing a low isotactic polypropylene catalyst, the alkoxysilane is one of R1Si(OR2)(OR3)(OR4) or R1R1'Si(OR2)(OR3), wherein R1 and R1' are 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, methylcyclopentyl dimethoxysilane, methylcyclohexyl dimethoxysilane, and diphenyl dimethoxysilane. In this case, the addition of the alkoxysilane not only promotes the chlorination reaction, but also does not adversely affect the isotactic selectivity of the prepared catalyst, and can improve the polymerization activity of the catalyst.

[0019] Further, in the above-mentioned method for preparing a low isotactic polypropylene catalyst, the nitrogen-containing heterocyclic compound is one of the following structures:

[0020]

[0021] wherein R5, R6, and R7 are each independently one of hydrogen, methyl, ethyl, chlorine, and bromine.

[0022] More preferably, the nitrogen-containing heterocyclic compound is 2,5-dimethylpyrrolidine, 2,5-dichloropyrrolidine, 2,5-dimethylpyrrole, 2,5-dichloropyrrole, 2,6-dimethylpyridine, 2-chloro-6-methylpyridine, and 2,6-dichloropyridine. In this case, the nitrogen-containing heterocyclic compound is used as an additive in the catalyst loading process, and is mixed with TiCl4 before being loaded on the active MgCl2 carrier. The obtained catalyst does not have an adverse effect on the preparation of low isotactic polypropylene, and the catalytic activity of the obtained catalyst and the properties of the polymerization product can be improved, the molecular weight of the polymer can reach a high level (Mw>200000), the hydrogen sensitivity is good, the molecular weight distribution of the polymerization product is wide, and the polymerization product is suitable for processing and application.

[0023] The solvent is selected from inert hydrocarbon compounds with different boiling points. Preferably, the solvent is one of hexane, heptane, decane, toluene, xylene, and chlorobenzene, so as to meet the specific reaction temperature.

[0024] In the present application, the temperature selection is also related to the boiling point of the solvent. As a preferred embodiment, the temperature range for catalyst preparation is 60-120℃, and the solvent is heptane, toluene, or chlorobenzene.

[0025] The second technical solution provided by the present application 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 application is the low isotactic polypropylene catalyst described above for catalyzing propylene polymerization.

[0027] The catalyst provided by the present application can be used in the industry for propylene polymerization, such as bulk method, solution method, slurry method, gas phase method, and the combination of these methods. The solvent used can be a common solvent suitable for preparing target polypropylene, including but not limited to hexane, heptane, mixed alkanes, paraffin oil, toluene, xylene, etc. The catalyst provided by the present application needs to add alkyl aluminum or chlorinated alkyl aluminum, or a mixture of the above two organoaluminum when catalyzing propylene polymerization. The alkyl aluminum includes but is not limited to trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, tri-n-octyl aluminum, etc. The chlorinated alkyl aluminum includes but is not limited to dichlorodiethyl aluminum and dichloroethyl aluminum.

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

[0029] 1) The catalyst preparation method provided by the present application has the characteristics of simple process, reduces the use of hazardous reagents, and reduces the hazardous waste emissions in the catalyst preparation process, which is environmentally friendly.

[0030] 2) The catalyst prepared by the present application has low isotactic polypropylene. Due to the addition of internal electron donors, the polymerization activity is good, so the polymerization product does not need to remove ash, greatly simplifying the process and improving the production efficiency.

[0031] 3) The catalyst provided by the present application has a wide adjustable range of polymer molecular weight and a wide molecular weight distribution when preparing polymers, and the product has good processing and application performance.

[0032] 4) The catalyst provided by the present application has the advantages of operation flexibility and process safety when preparing polymers using alkoxy magnesium Mg(OR)2 as raw material and obtaining active MgCl2 carrier by reacting with chlorinating reagent. DETAILED DESCRIPTION

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

[0034] The reagents used in the present application were purchased from Angene Chemical Reagent Co., Ltd. (Anhui Zesheng Science and Technology Co., Ltd.).

[0035] Example 1 Catalyst Preparation

[0036] 1) Into a 1 L glass bottle which was 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 sequentially added at room temperature. The stirring was started and the temperature was raised to 80°C. After 1 hour, the heating was stopped and the temperature was lowered to room temperature. The supernatant liquid was filtered to obtain a solid.

[0037] 2) The solid obtained in step 1) was dispersed in 500 mL of toluene, and 22.0 mL (0.20 mol) of TiCl4 and 6.1 mL (0.05 mol) of 2,5-dimethylpyrrolidine were sequentially added at room temperature. The stirring was started and the temperature was raised to 80°C. After 1 hour, the heating was stopped and the temperature was lowered to room temperature. The supernatant liquid was filtered and the obtained solid was dried to obtain the catalyst. The elemental analysis of the obtained catalyst showed the contents of Mg, Al, Si, and Ti elements as shown in Table 1 below.

[0038] Example 2 Catalyst Preparation

[0039] The method of this example was basically the same as that of Example 1, except that the chlorinating agent added was 26.7 g (0.20 mol) of AlCl3.

[0040] The elemental analysis of the obtained catalyst showed the contents of Mg, Al, Si, and Ti elements as shown in Table 1 below.

[0041] Example 3 Catalyst Preparation

[0042] The method of this example was basically the same as that of Example 1, except that the alkoxy silane added was 30.0 mL (0.15 mol) of methylcyclohexyldimethoxysilane.

[0043] The elemental analysis of the obtained catalyst showed the contents of Mg, Al, Si, and Ti elements as shown in Table 1 below.

[0044] Example 4 Catalyst Preparation

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

[0046] The elemental analysis test results of the contents of Mg, Al, Si, and Ti in the catalysts are shown in Table 1 below.

[0047] Example 5 Catalyst Preparation

[0048] The method of this example 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 elemental analysis test results of the contents of Mg, Al, Si, and Ti in the catalysts are shown in Table 1 below.

[0050] Comparative Example 1

[0051] The method of this example is basically the same as that of Example 1, except that no alkoxysilane and nitrogen heterocyclic compound are added.

[0052] The elemental analysis test results of the contents of Mg, Al, Si, and Ti in the catalysts are shown in Table 1 below.

[0053] Table 1 Contents of Elements in Catalysts

[0054] No. Mg wt% Si wt% Ti wt% Example 1 20.5 0.8 2.9 Example 2 22.3 0.3 3.1 Example 3 21.2 0.6 3.0 Example 4 20.8 0.7 2.1 Example 5 19.7 0.6 2.7 Comparative Example 1 23.3 - 3.5

[0055] Example 6 Preparation of Polypropylene

[0056] Bulk polymerization of propylene: A 10 L stainless steel reactor was first dried by heating under vacuum to 100°C, then replaced three times with propylene gas, and cooled to room temperature. 4 L of liquid propylene was added to the reactor, 1.89 mL of triisobutylaluminum in n-hexane (1.0 M) (to make Al / Ti = 125), 25 mg of the dispersion of the catalyst prepared in Example 1 (solvent: hexane, 100 mL), 1 L of hydrogen gas, and 1 L of liquid propylene were added. The polymerization reaction was carried out by stirring and heating to 60°C. The reaction was stopped after 1 hour, and the obtained polymer was collected and dried. The test data related to the polymerization reaction are shown in Table 2 below.

[0057] Examples 7-10 Preparation of Polypropylene

[0058] The method of this example is basically the same as that of Example 6, except that the catalysts added are those prepared in Examples 2-5 in order. The test data related to the polymerization reaction are shown in Table 2 below.

[0059] Example 11 Preparation of Polypropylene

[0060] The method of this example is basically the same as that of Example 6, except that the alkylaluminum added is triethylaluminum. The test data related to the polymerization reaction are shown in Table 2 below.

[0061] Example 12 Preparation of Polypropylene

[0062] The method of this example is basically the same as that of Example 6, except that the hydrogen gas added is 3 L. The test data related to the polymerization are listed in Table 2 below.

[0063] Example 13 Preparation of polypropylene

[0064] The method of this example is basically the same as that of Example 6, except that the polymerization temperature is 80°C. The test data related to the polymerization are listed in Table 2 below.

[0065] Comparative Example 2

[0066] The method of this example is basically the same as that of Example 6, except that the catalyst added is prepared in Comparative Example 1. The test data related to the polymerization are listed in Table 2 below.

[0067] In order to prove the effect of the technical solutions provided in the present application, the following gives the conventional analysis test methods adopted by the present application and the test results thereof:

[0068] 1) Isotacticity: n-heptane extraction method. A certain weight of the polymer sample is extracted in boiling heptane, and the mass percentage of the insoluble part is the isotacticity, also known as the isotactic index.

[0069] 2) Molecular weight and molecular weight distribution: determined by high-temperature gel chromatography. In a PL-GPC220 gel chromatograph, a standard curve is prepared with styrene as a standard sample, trichlorobenzene as a solvent, and the test temperature is 150°C. The number average molecular weight Mn, the weight average molecular weight Mw, and the molecular weight distribution (PDI, i.e. Mw / Mn) are obtained by testing. The molecular weight referred to herein is the weight average molecular weight Mw.

[0070] 3) Catalyst element content: determined by inductively coupled plasma emission spectrometry (ICP). The catalyst sample is digested (dissolved) with acid, and then tested after being diluted to volume.

[0071] 4) Melting point (Tm), glass transition temperature (Tg): determined by differential scanning calorimetry (DSC).

[0072] 5) Polymerization activity: the ratio of the weight of the polymerization product to the weight of the catalyst, with the unit being kgPP / gTi.

[0073] Table 2 Test results of propylene polymerization

[0074] No. Polymerization activity kg / g Ti Tm °C Tg °C Mw10 3 KDa PDI Isotacticity % Example 6 36.7 153.4 -17.8 168 4.2 12.5 Example 7 29.5 155.2 -18.3 203 5.5 12.3 Example 8 38.2 154.8 -18.7 153 5.1 16.7 Example 9 40.5 153.9 -19.4 144 6.3 11.9 Example 10 37.5 154.2 -18.1 126 5.9 9.8 Example 11 33.5 154.6 -17.7 189 5.2 10.9 Example 12 39.3 153.7 -19.2 136 4.5 11.7 Example 13 41.1 155.8 -18.9 145 5.3 13.3 Comparative Example 2 16.2 155.3 -17.4 89 4.0 25.2

[0075] As can be seen from the above table, the polymer molecular weight obtained by the technical scheme provided in the application has a wide adjustable range, the isotacticity is low, the melting point is high, and the product has good processing and application performance. When the catalyst (comparative example 1) is added with alkoxysilane and nitrogen heterocyclic compound, the polymerization activity is obviously lower, the isotacticity is higher, which shows that the addition of alkoxysilane and nitrogen heterocyclic compound in the technical scheme provided in the application not only promotes the chlorination reaction, but also improves the polymerization activity of the catalyst, and the polymer molecular weight can reach a high level (Mw>200000), the hydrogen regulation sensitivity is good, the molecular weight distribution of the polymerization product is wide, and it is suitable for processing and application.

Claims

1. A process for the preparation of a low isotacticity polypropylene catalyst characterized in that, The method comprises the following steps in sequence: 1) mixing ethoxy magnesium, chlorination reagent and alkoxysilane in solvent, stirring at 50-150℃ for 0.2-5h, then cooling and standing, filtering the clear liquid to obtain solid; 2) adding solvent to the solid obtained in step 1), then adding titanium tetrachloride and nitrogen-containing heterocyclic compound, stirring the mixture formed in solvent at 50-150℃ for 0.2-5h, then cooling and standing, filtering the clear liquid, and washing the obtained solid with solvent to obtain catalyst; The molar ratio of Mg, Al, Si, Ti and N in the ethoxy magnesium, chlorination reagent, alkoxysilane, titanium tetrachloride and nitrogen-containing heterocyclic compound is 10:0.5:0.2:1:0.1-10:15:20:15:20; The nitrogen-containing heterocyclic compound is one of the following structures: ； wherein R5, R6 and R7 are individually selected from one of hydrogen, methyl, ethyl, chlorine and bromine; The chlorination reagent is aluminum trichloride; The alkoxysilane is one of phenyltrimethoxysilane, phenyltriethoxysilane, methylcyclopentyl dimethoxysilane, methylcyclohexyl dimethoxysilane and diphenyl dimethoxysilane.

2. The process for the preparation of a low isotacticity polypropylene catalyst according to claim 1, characterized in that, The nitrogen-containing heterocyclic compound is 2,5-dimethylpyrrolidine, 2,5-dichloropyrrolidine, 2,5-dimethylpyrrole, 2,5-dichloropyrrole, 2,6-dimethylpyridine, 2-chloro-6-methylpyridine and 2,6-dichloropyridine.

3. The process for the preparation of a low isotacticity polypropylene catalyst according to claim 1, characterized in that, The solvent is one of hexane, heptane, decane, toluene, xylene and chlorobenzene.

4. A low isotacticity polypropylene catalyst characterized by, The catalyst is prepared by the method of claim 1.

5. The low isotactic polypropylene catalyst of claim 4 is used for catalyzing propylene polymerization.

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