Bimodal polyethylene catalyst, and preparation method therefor and use thereof

Abstract

The present invention belongs to the field of olefin polymerization catalysts, and particularly relates to a bimodal polyethylene catalyst, and a preparation method therefor and the use thereof. The bimodal polyethylene catalyst comprises a solid catalyst in which a large-particle carrier and a self-formed small-particle carrier are used together as a carrier, wherein titanium active centers in the solid catalyst are uniformly dispersed on the large-particle carrier and the self-formed small-particle carrier; and the self-formed small-particle carrier comprises a magnesium alkoxide compound. Compared with the prior art, the present invention solves the defect in the prior art that the properties (activity, hydrogen sensitivity and copolymerization performance) of a Ziegler-Natta bimodal polyethylene catalyst still need to be improved; and the solution provides a new bimodal polyethylene catalyst, and both the bulk density and the copolymerization unit content of a polymerized powder prepared by using the catalyst system are greatly improved.

Description

Bimodal polyethylene catalyst, its preparation method and application TECHNICAL FIELD

[0001] The present application belongs to the field of olefin polymerization catalysts, and particularly relates to a bimodal polyethylene catalyst, its preparation method and application. BACKGROUND

[0002] Polyolefins are the largest yield and most widely used polymer materials, widely used in petroleum chemical industry, aerospace, advanced manufacturing and many other fields of basic materials, and are a pillar industry related to the national economy and people's livelihood. China is the world's largest polyolefin importer and consumer, but China's polyolefin production capacity still cannot meet the demand for consumption, especially high-end polyolefin products, which are heavily dependent on imports, making the polyolefin industry more prominent in structure and contradictions, and low-end products are seriously homogenized. This is mainly due to the late start of domestic catalyst preparation technology, which is severely restricted by foreign technology blockade, seriously limiting the development of high value-added products of the device.

[0003] Generally, the development of high-end polyolefin products is through improving the polymerization process and developing new catalyst systems, which can control the distribution of comonomers in the polymer molecular chain and more accurately control the crystallization of the polymer. For example, bimodal polyethylene products with bimodal molecular weight distribution are widely used as a kind of general resin. Compared with ordinary polyethylene, bimodal polyethylene not only has good mechanical properties, but also has excellent processing performance, and is widely used in the fields of film, building materials, pipes and blow molding materials, etc., and belongs to polyethylene products with high added value. Bimodal polyethylene products have a large market prospect at home and abroad, and the demand is increasing year by year. At present, the technical research and development capability of most domestic polyethylene production enterprises is weak, and basically all the production processes of bimodal polyethylene come from foreign patent companies. Therefore, accelerating the development of domestic bimodal polyethylene catalyst technology and the research and development pace of the device is conducive to adjusting the product structure, improving the market competitiveness of enterprises and increasing economic benefits.

[0004] Generally, the production process of bimodal polyethylene mainly includes slurry method, gas phase method and solution method, and the type of reactor mainly includes loop reactor, stirred tank reactor and gas phase fluidized bed reactor. The combination of two or more of the above reactors can obtain bimodal products.

[0005] As for the bimodal polyethylene catalyst, patent CN1279069C uses dibutyl magnesium as magnesium source, and finally obtains a bimodal polyethylene catalyst with high activity and good hydrogen regulation by alcohol combination, silica gel loading, titanium loading washing and alkylation. However, this catalyst is only suitable for the process of North European Chemical Industry to develop high value-added products, and dibutyl magnesium is expensive and dependent on imports, which makes the raw material cost of the catalyst product high and the economic benefit relatively low.

[0006] If a Ziegler-Natta bimodal polyethylene catalyst with high activity, good hydrogen sensitivity and good copolymerization performance is developed, it will have great value. SUMMARY

[0007] The present application aims to solve at least one of the above problems by providing a bimodal polyethylene catalyst, its preparation method and application. The performance of the Ziegler-Natta bimodal polyethylene catalyst in the prior art (activity, hydrogen sensitivity and copolymerization performance) still needs to be improved. The present application provides a new type of bimodal polyethylene catalyst. The bulk density and copolymer unit content of the polymer powder prepared using the catalyst system are greatly improved.

[0008] The inventors have found that: (1) two types of carriers are used to prepare catalysts. The self-formed small particle carrier loaded with titanium can be used to produce high molecular weight polyethylene products, improving the impact resistance of polyethylene. The large particle carrier loaded with titanium can be used to produce linear low density or high density products, ensuring that the catalyst has good hydrogen regulation performance and can produce polymers with lower molecular weight. (2) The self-formed small particles are mixed with the large particle carrier and then titanium is loaded, so that the two types of carriers can be titaniumized at the same time, ensuring uniform dispersion of the titanium active centers of the catalyst, and the conventional active components and modified active components can function independently without mutual exclusion.

[0009] Based on the above findings, the present application is proposed.

[0010] The object of the present application is achieved by the following technical solutions.

[0011] The present application discloses a bimodal polyethylene catalyst, which comprises a large particle carrier and a self-formed small particle carrier as a solid catalyst.

[0012] The titanium active centers in the solid catalyst are uniformly dispersed on the large particle carrier and the self-formed small particle carrier.

[0013] The self-formed small particle carrier comprises a magnesium alcoholate.

[0014] Preferably, the self-formed small particle carrier is ethoxymagnesium.

[0015] The large particle carrier comprises activated carbon, diatomite, kaolin, montmorillonite, alumina and silicon dioxide. The large particle carrier refers to a carrier substance with a large specific surface area and pore volume.

[0016] More preferably, the large particle carrier is silicon dioxide.

[0017] The second aspect of the present application discloses a preparation method of the bimodal polyethylene catalyst as described above, comprising the following steps:

[0018] (1) Preparation of self-forming small particle carriers:

[0019] The magnesium compound and the alcohol compound are dispersed in the electron donor and reacted, and then a poly-electron donor is added for further reaction, and the precipitated particles are self-forming small particle carriers;

[0020] (2) Activation of large particle carriers:

[0021] The large particle carriers are purged under a nitrogen atmosphere;

[0022] The large particle carriers after nitrogen purging are added with pentane and triethylaluminum for reaction, and the alkylated large particle carriers are obtained after drying;

[0023] (3) Preparation of magnesium-titanium composite:

[0024] The magnesium chloride, the electron donor and the titanium compound are mixed and reacted to obtain the magnesium-titanium composite;

[0025] (4) Preparation of titanium-containing solid catalyst:

[0026] The alkylated large particle carriers obtained in (2) are added to the solution in (1) to form a mixed carrier solution;

[0027] The magnesium-titanium composite obtained in (3) is added dropwise to the mixed carrier solution, and then the titanium-containing solid catalyst is obtained after drying;

[0028] (5) Preparation of bimodal polyethylene catalyst:

[0029] The triethylaluminum is mixed with the obtained titanium-containing solid catalyst to obtain the bimodal polyethylene catalyst.

[0030] Preferably, in (1):

[0031] The magnesium compound is magnesium chloride;

[0032] The alcohol compound includes methanol, ethanol, ethylene glycol, glycerol, 1,4-butanediol, propanol, isopropanol, butanol, isobutanol, tert-butyl alcohol, hexanol, cyclohexanol, octanol, isooctanol, decanol, benzyl alcohol and phenethyl alcohol;

[0033] The electron donor includes an organic compound containing an element with a lone pair of electrons;

[0034] The poly-electron donor includes propylene glycol, 1,3-butanediol, 1,4-butanediol, pentanediol and isomers of pentanediol;

[0035] The molar ratio of the magnesium compound, the alcohol compound and the polydentate electron donor is 1:(0.1-1.5):(0.5-2.5);

[0036] The temperature of the reaction is 45-80℃, preferably 65℃, and the reaction time is 2-8h, preferably 3.5h;

[0037] The temperature of the continued reaction is 50-80℃, preferably 65℃, and the time is 2h.

[0038] More preferably, the alcohol compound is at least one of ethanol and isooctanol.

[0039] More preferably, the polydentate electron donor is at least one of propylene glycol and 1,4 butanediol.

[0040] In (3), preferably:

[0041] The electron donor includes an organic compound containing an element with a lone pair of electrons;

[0042] The titanium compound includes TiCl4, TiBr4, TiI4, Ti(OC2H5)Cl3, Ti(OCH3)Cl3, Ti(OC4H9)Cl3, Ti(OC2H5)Br3, Ti(OC2H5)2Cl2, Ti(OCH3)2Cl2, Ti(OCH3)2I2, Ti(OC2H5)3Cl, Ti(OCH3)3Cl and Ti(OC2H5)3I;

[0043] The molar ratio of the magnesium chloride and the titanium compound is 1:(0.01-0.25);

[0044] The temperature of the reaction is 70℃, and the time is 6h.

[0045] More preferably, the titanium compound is at least one of TiCl4, Ti(OC2H5)Cl3, Ti(OCH3)Cl3 and Ti(OC4H9)Cl3.

[0046] Further preferably, the titanium compound is TiCl4.

[0047] In the compound containing an element with a lone pair of electrons, preferably, the element includes oxygen, nitrogen and sulfur.

[0048] More preferably, the electron donor is tetrahydrofuran, which also serves as a solvent.

[0049] In (2), preferably:

[0050] The temperature of the purging is 600℃, and the time is 4-18h;

[0051] The temperature of the reaction is 60℃, and the time is 1h.

[0052] Preferably, in (4):

[0053] The temperature of the reaction is 60℃, and the time is 1h.

[0054] The temperature of the reaction is 60℃, and the time is 1h.

[0055] Preferably, in (5):

[0056] The molar ratio of the triethyl aluminum to the titanium-aluminum of the titanium-activated solid catalyst is 500.

[0057] The third aspect of the present application discloses an application of the bimodal polyethylene catalyst in preparing bimodal polyethylene.

[0058] Compared with the prior art, the present application has the following beneficial effects:

[0059] The catalyst for olefin polymerization of the present application uses self-formed small particle magnesium alcohol compound (self-formed small particle carrier, specifically ethoxymagnesium) and large particle carrier as the common carrier of the catalyst, carries out titanium activation after blending, so that the two types of carriers can be titanium activated at the same time, ensuring the uniform dispersion of the titanium active center in the catalyst on different carriers, realizing the respective functions of the conventional active component and the modified active component center, and not excluding each other, thereby improving the activity, hydrogen regulation sensitivity and copolymerization performance of the catalyst.

[0060] In addition, the bulk density and copolymer unit content of the polymerized powder prepared by using the catalyst system of the present application are greatly improved. DETAILED DESCRIPTION

[0061] The present application will be described in detail below in conjunction with specific examples, but is by no means a limitation on the present application.

[0062] In the following description, if not specifically stated, the reagents used are conventional commercially available products, and the methods used are well-known means in the art.

[0063] The bimodal polyethylene catalyst for olefin polymerization is prepared by the following method:

[0064] (1) Preparation of self-formed small particle carrier

[0065] The magnesium compound and the alcohol compound are dispersed in the electron donor, reacted at a certain temperature to form a transparent solution, then a multi-electron donor is added to continue the reaction for a period of time to precipitate white particles.

[0066] (2) Activation of large particle carrier

[0067] The large-particle support was continuously heated to 600°C under nitrogen fluidization for 4-18 hours, gradually cooled to room temperature and stored for use. A certain amount of the heat-treated large-particle support was added to pentane and triethylaluminum, dried after reaction at 60°C for 1 hour to obtain an alkylated large-particle support.

[0068] (3) Preparation of titanium compound

[0069] A certain amount of magnesium chloride, electron donor and titanium compound were reacted at 70°C for 3.5 hours to form a magnesium-titanium complex.

[0070] (4) Titaniumization and drying

[0071] The dried large-particle support of (2) was added to the solution of (1), and the two supports were uniformly dispersed by stirring the mixture at room temperature for 30 minutes. Then, the magnesium-titanium complex of (3) was slowly added (dropwise addition rate: 0.2-0.5 mL / min) to the uniformly mixed support solution to achieve uniform dispersion. After the addition was completed, the temperature was increased to 70°C and reacted for 2 hours, and then dried at 80°C to obtain the main component of the catalyst (titaniumized solid catalyst).

[0072] wherein:

[0073] The magnesium compound is magnesium chloride.

[0074] The electron donor is selected from organic compounds of elements having unpaired electrons, including O, N and S. Preferably, the electron donor is tetrahydrofuran, which also serves as a solvent.

[0075] The alcohol compound can be an alcohol compound commonly used in the art, and is preferably at least one of methanol, ethanol, ethylene glycol, glycerol, 1,4-butanediol, propanol, isopropanol, butanol, isobutanol, tert-butanol, hexanol, cyclohexanol, octanol, isooctanol, decanol, benzyl alcohol and phenethyl alcohol. Further preferably, it is at least one of ethanol and isooctanol.

[0076] The polyatomic electron donor is not limited to propylene glycol, 1,3-butanediol, 1,4-butanediol, pentanediol and various isomers thereof, and is preferably at least one of propylene glycol and 1,4-butanediol.

[0077] The titanium compound can be selected from at least one of TiCl4, TiBr4, TiI4, Ti(OC2H5)Cl3, Ti(OCH3)Cl3, Ti(OC4H9)Cl3, Ti(OC2H5)Br3, Ti(OC2H5)2Cl2, Ti(OCH3)2Cl2, Ti(OCH3)2I2, Ti(OC2H5)3Cl, Ti(OCH3)3Cl and Ti(OC2H5)3I. Preferably, it is at least one of TiCl4, Ti(OC2H5)Cl3, Ti(OCH3)Cl3and Ti(OC4H9)Cl3. More preferably, the titanium compound is TiCl4.

[0078] The large-particle carrier is a carrier substance having a large specific surface area and pore volume, such as activated carbon, diatomite, kaolin, montmorillonite, alumina, silica, etc. Preferably, it is silica, commercially available as PQ Corporation's ES70W brand.

[0079] Example 1

[0080] (1) In a 250 mL three-necked glass reaction flask, 60 mL of tetrahydrofuran, 3 g of magnesium chloride, and 1.25 mL of ethanol were added, and the reaction was carried out at 65°C for 3.5 hours. Then, 4 mL of 1,4-butanediol was added dropwise to the flask, and after the dropwise addition was completed, the reaction was continued for 2 hours. White solid particles (ethoxymagnesium) were precipitated.

[0081] (2) Silica was selected, and after being purged with nitrogen at 600°C for 4.5 hours, it was naturally cooled to room temperature under a nitrogen atmosphere, and then pentane and triethylaluminum were added. After being sufficiently stirred at 60°C for 1 hour, the solvent was evaporated to obtain thermally activated silica.

[0082] (3) In another 250 mL three-necked flask, 60 mL of tetrahydrofuran was added, and then 2 g of anhydrous magnesium chloride and 0.5 g of titanium trichloride were added thereto. While being stirred, 2 mL of ethanol was added, and the reaction was carried out at 70°C for 3.5 hours to obtain a magnesium-titanium complex.

[0083] (4) The dried silica of (2) was added to the reaction flask of (1), and the two carriers were uniformly dispersed by stirring at room temperature for 30 minutes. Subsequently, the magnesium-titanium complex of (3) was reacted with the mixed carriers, and the reaction was continued at 70°C for 2 hours, and then the temperature was increased to 80°C to dry the product, thereby obtaining a solid catalyst (titanium-treated solid catalyst) component having good fluidity.

[0084] Titanium-treated catalyst component: Mg m Ti n Cl 2m+3n Al 0.3n (OR) 2.5m (m = 0 ~ 2, n = 0 ~ 4, and both m and n are not 0);

[0085] Titanized catalyst component: Mg: 4.65 wt%; Ti: 0.89 wt%; Al: 1.3 wt%; Cl: 15.23 wt%.

[0086] Application Example

[0087] Homopolymerization: In a 2L stainless steel reactor, after purging with high purity nitrogen, 1.2L hexane, 1.0 mL triethylaluminum and 0.030g solid catalyst (titanized solid catalyst) component prepared in Example 1 were added, the temperature was raised to 70°C, hydrogen was introduced to make the pressure in the reactor 0.2MPa, and then ethylene was introduced to make the total pressure in the reactor 0.8MPa, and the polymerization was carried out at 80°C for 2 hours. The catalyst activity was 4952kgPE / kgCat, the bulk density was 0.35g / mL, and the molecular weight distribution MWD was 8.9.

[0088] Example 2

[0089] The other steps were the same as in Example 1, except that:

[0090] (3) Another 250mL three-necked flask was selected, 60mL tetrahydrofuran was added, then 2g anhydrous magnesium chloride and 0.5g titanium trichloride were added, under stirring, 1mL ethanol was added, heated to 70°C, and reacted for 3.5 hours to obtain a magnesium-titanium complex.

[0091] The laboratory evaluation conditions of the catalyst were the same: the catalyst activity was 4708kgPE / kgCat, the bulk density was 0.30g / mL, and the molecular weight distribution MWD was 8.3.

[0092] Comparative Example 1

[0093] The carrier activation step was the same as in Example 1, except that:

[0094] (1) Under nitrogen protection, 60mL tetrahydrofuran was added to a 250mL three-necked flask, then 2g anhydrous magnesium chloride and 0.5g titanium trichloride were added, under stirring, 2mL ethanol was added, heated to 70°C, and reacted for 3.5 hours to obtain a magnesium-titanium complex.

[0095] (2) To (1), the activated silica was added and stirred for 2h, then heated to 80°C to dry, to obtain a solid catalyst (titanized solid catalyst) component with good fluidity.

[0096] The laboratory evaluation conditions of the catalyst were the same: the catalyst activity was 3154kgPE / kgCat, the bulk density was 0.34g / mL, and the molecular weight distribution MWD was 6.5.

[0097] The foregoing description of the embodiments has been presented for the purpose of illustration and description. It is not intended to be exhaustive or to limit the application to the precise form disclosed. Modifications and variations are possible in light of the above teachings or can be acquired from practice of the application. As well, the description is presented in the context of the preferred embodiments as a number of alternatives. It is not intended to limit the application to the precise form described.

Claims

1. A bimodal polyethylene catalyst characterized in that, The solid catalyst comprises a large-particle carrier and self-forming small-particle carriers as carriers; The titanium active centers in the solid catalyst are uniformly dispersed on the large-particle carrier and the self-forming small-particle carriers; The self-forming small-particle carriers comprise a magnesium alcoholate.

2. The bimodal polyethylene catalyst of claim 1, wherein, The self-forming small-particle carriers are ethoxymagnesium; The large-particle carrier comprises activated carbon, diatomite, kaolin, montmorillonite, alumina and silica.

3. A process for the preparation of a bimodal polyethylene catalyst as claimed in claim 1 or 2, characterized in that, The method comprises the following steps: (1) Preparation of self-forming small-particle carriers: The magnesium compound and the alcohol compound are dispersed in an electron donor to react, and then a multi-electron donor is added to continue the reaction, and the precipitated particles are the self-forming small-particle carriers; (2) Activation of large-particle carriers: The large-particle carriers are purged under a nitrogen atmosphere; The large-particle carriers purged by nitrogen are taken and reacted with pentane and triethylaluminum, and then dried to obtain alkylated large-particle carriers; (3) Preparation of magnesium-titanium compound: The magnesium chloride, the electron donor and the titanium compound are mixed and reacted to obtain a magnesium-titanium compound; (4) Preparation of titanium-containing solid catalyst: The alkylated large-particle carriers obtained in (2) are added to the solution in (1) to uniformly disperse and form a mixed carrier solution; The magnesium-titanium compound obtained in (3) is added dropwise to the mixed carrier solution, reacted by heating, and then dried to obtain the titanium-containing solid catalyst; (5) Preparation of bimodal polyethylene catalyst: The triethylaluminum is mixed with the obtained titanium-containing solid catalyst to obtain the bimodal polyethylene catalyst.

4. The process for preparing a bimodal polyethylene catalyst according to claim 3, characterized in that, In (1): The magnesium compound is magnesium chloride; The alcohol compound comprises methanol, ethanol, ethylene glycol, glycerol, 1,4-butanediol, propanol, isopropanol, butanol, isobutanol, tert-butanol, hexanol, cyclohexanol, octanol, isooctanol, decanol, benzyl alcohol and phenethyl alcohol; The electron donor comprises an organic compound containing an element with a lone pair of electrons; The multi-electron donor comprises propylene glycol, 1,3-butanediol, 1,4-butanediol, pentanediol and isomers of pentanediol; The molar ratio of the magnesium compound, the alcohol compound and the multi-electron donor is 1:(0.1-1.5):(0.5-2.5); The reaction temperature is 45-80℃, and the reaction time is 2-8h; The temperature of the continued reaction is 50-80℃, and the reaction time is 2h.

5. The process for preparing a bimodal polyethylene catalyst according to claim 3, characterized in that, In (3): The electron donor comprises an organic compound containing an element with a lone pair of electrons; The titanium compound comprises TiCl4, TiBr4, TiI4, Ti(OC2H5)Cl3, Ti(OCH3)Cl3, Ti(OC4H9)Cl3, Ti(OC2H5)Br3, Ti(OC2H5)2Cl2, Ti(OCH3)2Cl2, Ti(OCH3)2I2, Ti(OC2H5)3Cl, Ti(OCH3)3Cl and Ti(OC2H5)3I; The molar ratio of the magnesium chloride and the titanium compound is 1:(0.01-0.25); The reaction temperature is 70℃, and the reaction time is 6h.

6. A process for the preparation of a bimodal polyethylene catalyst according to claim 4 or 5, characterized in that, The element containing a lone pair of electrons comprises oxygen, nitrogen and sulfur.

7. The method for preparing a bimodal polyethylene catalyst according to claim 3, characterized in that, In (2): The purging temperature is 600 DEG C, and the time is 4-18h; The reaction temperature is 60 DEG C, and the time is 1h.

8. The process for preparing a bimodal polyethylene catalyst according to claim 3, characterized in that, In (4), the temperature of the temperature-increasing reaction is 70 DEG C, and the time is 2h; The drying temperature is 80 DEG C. In (5), the aluminum-titanium molar ratio of the triethyl aluminum to the titanium-converted solid catalyst is 500.

9. The process for preparing a bimodal polyethylene catalyst according to claim 3, characterized in that, 10. Use of the bimodal polyethylene catalyst according to claim 1 or 2 for the preparation of a bimodal polyethylene. ​ ​