Polyolefin catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalysts, and particularly relates to a polyolefin catalyst and a preparation method and application thereof. Specifically, the polyolefin catalyst comprises a main catalyst, a co-catalyst, an activity promoting component and a solvent, wherein the main catalyst is a transition metal acetylacetone complex, the cocatalyst is aluminum alkyl, and the activity promoting component is C4-C6 chain alkane. Through the activity promoting component, the vinyl polymerization activity of a catalytic system taking the transition metal acetylacetone complex as a main catalyst is greatly improved by 1-2 orders of magnitude compared with the prior art. And moreover, the molecular weight of the polymer and the comonomer content of the copolymer can be regulated and controlled by regulating and controlling the addition amount of the activity promoting component.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of catalysts, and particularly relates to a polyolefin catalyst and a preparation method and application thereof. BACKGROUND

[0002] Since the advent of Ziegler-Natta catalysts in the 1950s, people have been exploring the application of efficient transition metal compounds in olefin polymerization. Transition metal acetylacetone complexes, as an important class of complexes, have shown significant potential in the polymerization of dienes, styrene and acrylic monomers. However, there are few reports on the application of such complexes in ethylene polymerization, the main reason being that their activity is much lower than that of the commonly used TiCl x Catalytic system. The prior art uses Ti(acac)3 or TiO(acac)2 with diethyl aluminum chloride for ethylene polymerization research, and finds that the two have similar catalytic behavior, with a maximum activity of 50 kg PE / mol Ti / h. When DEAC is used as a cocatalyst for Cr(acac)3-catalyzed ethylene polymerization, it is found that only one polymer chain is generated per Cr site, which exhibits the characteristics of "living polymerization", but the activity is less than 10 kg PE / mol Cr / h. There is also research on the ethylene polymerization performance of Cr(acac)3 with MAO as a cocatalyst, which obtains a maximum activity of 28 kg PE / mol Cr / h under the condition of Al / Cr=200 (molar ratio). And using MAO cocatalyst, the catalytic activity of Cr(acac)3 is improved to 122 kg PE / mol Cr / h under 3 MPa ethylene pressure. Recently, research has shown that the activity of V(acac)3, VO(acac)2 and Ti(acac)2Cl2 is doubled when DEAC and Mg(C4H9)2 are used as a binary activator, and the activity of Ti(acac)2Cl2 is as high as 800 kg PE / mol Ti / h.

[0003] For Cr(acac)3 system, many studies have attempted to load it on Al-MCM-41, MgCl2 and other carriers for ethylene polymerization, but the activity is still low. Research has found that air calcination of Cr(acac)3 / carrier (carrier is Al-MCM-41 and AlSBA-15) is needed to remove the acetylacetone ligand to obtain high activity. Recently, the prior art has systematically studied the effect of carrier acidity on the performance of Cr(acac)3, and found that a strong acidic carrier is the key to achieving satisfactory activity, and a superacidic carrier can obtain a maximum activity of about 104 kg PE / mol Cr / h under 3.79 MPa ethylene pressure. Research shows that an acidic carrier can enhance the electron deficiency of the transition metal center, thereby improving its reactivity with the electron-rich olefin monomer.

[0004] The above prior art operation or preparation method is relatively cumbersome, and there is an urgent need to develop a catalyst system which can realize high activity of ethylene homopolymerization and copolymerization without being subjected to loading or high temperature calcination to remove ligands. SUMMARY

[0005] The present application aims to provide a new homogeneous catalyst system with transition metal acetylacetone complex as the main catalyst and its preparation method and application, which can realize high activity of ethylene homopolymerization and copolymerization without being subjected to loading or high temperature calcination to remove ligands, so as to solve the above problems. The catalyst system can be used for ethylene homopolymerization and copolymerization, and the polymerization activity is much higher than that of the prior art homogeneous catalyst system with transition metal acetylacetone complex as the main catalyst.

[0006] According to a first aspect of the present application, a polyolefin catalyst is provided, which comprises a main catalyst, a cocatalyst, an activity promoting component and a solvent; wherein the main catalyst is a transition metal acetylacetone complex, the cocatalyst is an alkyl aluminum, and the activity promoting component is a chain low-carbon alkane with extremely low solubility to the main catalyst transition metal acetylacetone complex, which can be a C4-C6 chain alkane.

[0007] In some embodiments, the mass of transition metal of the main catalyst transition metal acetylacetone complex accounts for 0.01-3wt% of the total mass of the catalyst system; the ratio of the added moles of the cocatalyst alkyl aluminum to the moles of the transition metal acetylacetone complex is 10-1000; the solvent accounts for 0-100% of the total volume of the catalyst system; and the activity promoting component accounts for 1-100% of the total volume of the catalyst system.

[0008] Preferably, the mass of transition metal of the main catalyst transition metal acetylacetone complex accounts for 0.1-1wt% of the total mass of the catalyst system; the ratio of the added moles of the cocatalyst alkyl aluminum to the moles of the transition metal acetylacetone complex is 30-300; the solvent accounts for 30-70% of the total volume of the catalyst system; and the activity promoting component accounts for 20-80% of the total volume of the catalyst system.

[0009] In some embodiments, the transition metal acetylacetone complex comprises at least one of titanium (IV) acetylacetone oxide, zirconium (IV) acetylacetone, hafnium (IV) acetylacetone, vanadium (V) acetylacetone oxide, vanadium (III) acetylacetone, chromium (III) acetylacetone, molybdenum (VI) bisacetylacetone dioxide, iron (III) acetylacetone, manganese (III) acetylacetone, cobalt (III) acetylacetone, cobalt (II) acetylacetone, nickel (II) acetylacetone, tris (hexafluoroacetylacetone) iron, tris (hexafluoroacetylacetone) chromium (III), trifluoroacetylacetone copper (II), hexafluoroacetylacetone tin (II), hexafluoroacetylacetone cobalt (II), and trifluoroacetylacetone nickel (II).

[0010] In some embodiments, the alkyl aluminum includes at least one of trimethyl aluminum, triethyl aluminum, diethyl aluminum chloride, monoethyl aluminum dichloride, diisobutyl aluminum chloride, triisobutyl aluminum, tributyl aluminum, trioctyl aluminum.

[0011] In some embodiments, the activity promoting component is at least one of n-butane, isobutane, n-pentane, isopentane, n-hexane, isohexane.

[0012] In some embodiments, the solvent is a good solvent for the transition metal acetylacetone complex, including at least one of benzene, toluene, xylene, ethylbenzene, cumene, n-propylbenzene, p-ethyltoluene, naphthalene, dichloromethane, trichloromethane, tetrachloromethane, dichloroethane.

[0013] According to a second aspect of the present application, a method for preparing the above-mentioned polyolefin catalyst is provided, including the following steps: obtaining by mixing the main catalyst, the co-catalyst, the activity promoting component and the solvent. The mixing order is generally arbitrary.

[0014] In some embodiments, the main catalyst, the co-catalyst and the activity promoting component can be premixed first, and then mixed with the solvent; the premixing time is 1-120 minutes, and the premixing temperature is 20-80°C.

[0015] In some embodiments, the main catalyst, the main catalyst and the solvent can be premixed first, and then mixed with the activity promoting component; the premixing time is 1-120 minutes, and the premixing temperature is 20-80°C.

[0016] According to a third aspect of the present application, the above-mentioned polyolefin catalyst is provided for use in ethylene polymerization.

[0017] In some embodiments, the polyolefin catalyst is used in ethylene homopolymerization or ethylene copolymerization, wherein the comonomer of the ethylene copolymerization includes at least one of propylene, 1-butene, 1-hexene, 1-octene, styrene, isoprene, butadiene.

[0018] According to a fourth aspect of the present application, a method for preparing an ethylene polymer by using the above-mentioned polyolefin catalyst is provided, including the following steps: (1) The high-pressure polymerization reactor is vacuumed at 95-105°C for 0.8-1.2 hours to remove water and oxygen impurities in the reactor, and then nitrogen is introduced to normal pressure; (2) The alkyl aluminum and the solvent are first added to the high-pressure polymerization reactor, and then the transition metal acetylacetone complex, the activity promoting component and the alkyl aluminum are premixed at 20-80°C for 1-120 minutes, and then added to the reactor, and finally 1 MPa of ethylene is added to start the polymerization reaction, the reaction temperature is 65-75°C, and the reaction time is 0.8-1.2 hours.

[0019] Thus, the alkyl aluminum is added to the reaction system twice, which can remove trace amounts of water and oxygen contained in the solvent as a solvent and impurity remover, and also can act as an alkylating agent and reducing agent for the metal center of the main catalyst.

[0020] In some embodiments, a molecular weight regulator can be added during the polymerization, and the hydrogen gas is added at a partial pressure of 3-30% of the ethylene partial pressure, and the ethylene partial pressure is 0.5-4 MPa.

[0021] In some embodiments, in step (2), the alkyl aluminum and the solvent can also be added to the high-pressure polymerization reactor together with a comonomer, such as at least one of propylene, 1-butene, 1-hexene, 1-octene, styrene, isoprene, and butadiene. The comonomer is added in liquid form, and the volume of the comonomer is 1-10% of the total volume of the solvent and the activity promoting component.

[0022] According to a fifth aspect of the present application, an ethylene polymer obtained by the above preparation method is provided. The ethylene polymer can be an ethylene homopolymer or an ethylene copolymer, and the comonomer includes at least one of propylene, 1-butene, 1-hexene, 1-octene, styrene, isoprene, and butadiene.

[0023] Compared with the prior art, the present application has the following beneficial effects: 1. The present application greatly improves the ethylene polymerization activity of the catalytic system with a transition metal acetylacetone complex as the main catalyst through the activity promoting component, which is 1-2 orders of magnitude higher than the prior art. This is because the activity promoting component forms a coordination competition relationship with the solvent molecules, mainly by regulating the coordination environment of the active center to change its activity and the properties of the polymer. Specifically, the transition metal acetylacetone complex is easily soluble in aromatic polar solvents, and the interaction between these aromatic solvent molecules and the active center is too strong, resulting in a large steric hindrance, which is not conducive to the insertion of ethylene and comonomers such as olefins. The transition metal acetylacetone complex is insoluble in short-chain alkanes, but the addition of short-chain alkanes can regulate the polar environment around the active center and weaken the coordination strength of the solvent to the active center, thus greatly improving the catalytic activity.

[0024] 2. The addition amount of the activity promoting component can be regulated to control the molecular weight of the polymer and the comonomer content of the copolymer. Specifically, the short-chain alkane activity promoting component can reduce the steric hindrance of the active center by weakening the coordination strength of the solvent to the active center, making chain transfer easier, and thus the molecular weight of the polymer is lower. By changing the addition ratio of the activity promoting component, the coordination environment of the metal center can be regulated, and the controllable adjustment of the molecular weight of the polymer can be realized. DETAILED DESCRIPTION

[0025] The application will be further described in detail below with specific examples. It is worth mentioning that the following examples are only for better explaining the content of the application and do not limit the scope of the application. The process steps not disclosed in the examples are prior art. Unless otherwise specified, the following raw materials are commercially available. The "atmospheric pressure" in the application refers to "atmospheric pressure".

[0026] The olefin polymerization catalyst system involved in the application is sensitive to water, oxygen and other substances, so measures such as nitrogen filling glove box, Schlenk technique or nitrogen protection are taken to prevent water and oxygen pollution during catalyst preparation and polymerization process. The high-pressure polymerization reactor (300 mL) used is subjected to vacuuming at 100 ℃ for 1 hour to remove water and oxygen impurities in the reactor before the polymerization experiment, and then nitrogen is introduced to normal pressure, and finally the polymerization experiment is carried out. The stirring paddle in the reactor is continuously stirred at 600 rpm during the polymerization process. The ethylene pressure of all polymerization experiments is 1 MPa, the reaction temperature is 70 ℃, the reaction time is 1 hour, and the ethylene pressure is kept constant during the whole polymerization process by the front pressure reducing valve. After the polymerization is completed, the product is filtered and vacuum dried and weighed for activity calculation. The various polymer properties in the examples are measured according to the following methods: The weight average molecular weight and molecular weight distribution are determined by high temperature gel chromatography (HT-GPC): a PL-220 type high temperature gel permeation chromatograph (Polymer Laboratories Company) is used to determine the molecular weight and molecular weight distribution of polyethylene. In the experiment, 1,2,4-trichlorobenzene is used as the solvent, and the determination is carried out at 160 ℃. The data are processed by universal calibration method using narrow distribution polystyrene as standard sample.

[0027] The short chain branch content of the polymer is determined by 13 C high temperature nuclear magnetic carbon spectrum (HT- 13 CNMR): a Bruker Avance III 500 type nuclear magnetic resonance instrument is used to determine the short chain branch content of polyethylene. In the experiment, deuterated p-dichlorobenzene is used as the solvent, and the determination is carried out at 110 ℃. The carbon signal (shift at 30.00 ppm) on the polyethylene backbone is used as the internal standard to calculate the short chain branch content.

[0028] Examples 1-1 to 1-8: different transition metal acetylacetone complexes First, 200 μmol of triisobutylaluminum and 100 mL of toluene solvent are added to the polymerization reactor, then about 2 μmol of transition metal acetylacetone complex (the acetylacetone complexes of titanium, zirconium, vanadium, chromium, nickel and iron used in examples 1-1 to 1-8 are acetylacetone titanium, acetylacetone zirconium, acetylacetone vanadyl, acetylacetone chromium, acetylacetone nickel, acetylacetone iron, tris (hexafluoroacetylacetone) chromium, and trifluoroacetylacetone nickel, respectively) are taken, 50 mL of n-hexane and 5 μmol of triisobutylaluminum are pre-mixed at 40 ℃ for 5 minutes, and then added to the reactor, and finally 1 MPa of ethylene is added to start the polymerization reaction.

[0029] Examples 2-1 to 2-4: Use of different active promoting components First, 200 μmol of triisobutyl aluminum and 100 mL of toluene were added to a polymerization reactor, then about 2 μmol of chromium acetylacetonate, 50 mL of an active promoting component (n-butane, isobutane, n-pentane and n-heptane were used in Examples 2-1 to 2-4, respectively), and 5 μmol of triisobutyl aluminum were mixed at 40°C for 5 minutes, and then added to the reactor, and finally 1 MPa of ethylene was added to start the polymerization reaction.

[0030] Examples 3-1 to 3-3: Use of different alkyl aluminum First, 200 μmol of alkyl aluminum cocatalyst (trimethyl aluminum, triethyl aluminum, trioctyl aluminum were used in Examples 3-1 to 3-3, respectively) and 100 mL of toluene were added to a polymerization reactor, then about 2 μmol of chromium acetylacetonate, 50 mL of n-hexane and 5 μmol of alkyl aluminum cocatalyst were mixed at 40°C for 5 minutes, and then added to the reactor, and finally 1 MPa of ethylene was added to start the polymerization reaction.

[0031] Examples 4-1 to 4-3: Use of different solvents First, 200 μmol of triisobutyl aluminum and 100 mL of solvent (benzene, xylene, ethylbenzene were used in Examples 4-1 to 4-3, respectively) were added to a polymerization reactor, then about 2 μmol of chromium acetylacetonate, 50 mL of n-hexane and 5 μmol of triisobutyl aluminum were mixed at 40°C for 5 minutes, and then added to the reactor, and finally 1 MPa of ethylene was added to start the polymerization reaction.

[0032] Examples 5-1 to 5-4: Use of different amounts of main catalyst chromium acetylacetonate First, 200 μmol of triisobutyl aluminum and 100 mL of toluene were added to a polymerization reactor, then a certain amount of chromium acetylacetonate (0.5 μmol, 1 μmol, 5 μmol, 10 μmol were used in Examples 5-1 to 5-4, respectively), 50 mL of n-hexane and 5 μmol of triisobutyl aluminum were mixed at 40°C for 5 minutes, and then added to the reactor, and finally 1 MPa of ethylene was added to start the polymerization reaction.

[0033] Examples 6-1 to 6-3: Use of different amounts of cocatalyst triisobutyl aluminum First, 200 μmol of triisobutyl aluminum and 100 mL of toluene were added to a polymerization reactor, then 2 μmol of chromium acetylacetonate, 50 mL of n-hexane and a certain amount of triisobutyl aluminum (1 μmol, 2 μmol, 10 μmol were used in Examples 6-1 to 6-3, respectively) were mixed at 40°C for 5 minutes, and then added to the reactor, and finally 1 MPa of ethylene was added to start the polymerization reaction.

[0034] Example 7-1 to 7-7: Different amounts of solvent toluene, activity promoting component n-hexane First, 200 μmol of triisobutylaluminum and a certain amount of toluene (149 mL, 140 mL, 120 mL, 80 mL, 50 mL, 5 mL, 0 mL for Examples 7-1 to 7-7, respectively) were added to a polymerization reactor, then 2 μmol of acetylacetone chromium, a certain volume of n-hexane (1 mL, 10 mL, 30 mL, 70 mL, 100 mL, 145 mL, 150 mL for Examples 7-1 to 7-7, respectively) and 5 μmol of triisobutylaluminum were mixed at 40°C for 5 minutes, and then added to the reactor, and finally 1 MPa of ethylene was added to start the polymerization reaction.

[0035] Example 8-1 to 8-3: Different mixing times First, 200 μmol of triisobutylaluminum and 100 mL of toluene were added to a polymerization reactor, then about 2 μmol of acetylacetone chromium, 50 mL of n-hexane and 5 μmol of triisobutylaluminum were mixed at 40°C for a certain time (1 minute, 10 minutes, 60 minutes for Examples 8-1 to 8-3, respectively) and then added to the reactor, and finally 1 MPa of ethylene was added to start the polymerization reaction.

[0036] Example 9-1 to 9-3: Different mixing temperatures First, 200 μmol of triisobutylaluminum and 100 mL of toluene were added to a polymerization reactor, then about 2 μmol of acetylacetone chromium, 50 mL of n-hexane and 5 μmol of triisobutylaluminum were mixed at a certain temperature (20°C, 60°C, 80°C for Examples 9-1 to 9-3, respectively) for 5 minutes and then added to the reactor, and finally 1 MPa of ethylene was added to start the polymerization reaction.

[0037] Example 10-1 First, 200 μmol of triisobutylaluminum and 50 mL of n-hexane were added to a polymerization reactor, then about 2 μmol of acetylacetone chromium, 100 mL of toluene and 5 μmol of triisobutylaluminum were mixed at 40°C for 5 minutes and then added to the reactor, and finally 1 MPa of ethylene was added to start the polymerization reaction.

[0038] Example 10-2 About 2 μmol of acetylacetone chromium, 50 mL of n-hexane, 100 mL of toluene and 5 μmol of triisobutylaluminum were mixed for 5 minutes and then added to the reactor, and finally 1 MPa of ethylene was added to start the polymerization reaction.

[0039] Example 11-1 to 11-4: Different comonomers First, 200 μmol of triisobutylaluminum, 100 mL of toluene solvent, and 8 mL of a comonomer (1-butene, 1-hexene, 1-octene, styrene, used in Examples 11-1 to 11-4, respectively) were added to a polymerization reactor, and then about 2 μmol of chromium acetylacetonate, 50 mL of n-hexane, and 5 μmol of triisobutylaluminum were mixed for 5 minutes and added to the reactor, and finally, 1 MPa of ethylene was added to start the polymerization.

[0040] Examples 12-1 to 12-3: Use of hydrogen gas at different pressures First, 200 μmol of triisobutylaluminum, 100 mL of toluene solvent, and a certain pressure of hydrogen gas (0.03 MPa, 0.05 MPa, 0.1 MPa, used in Examples 12-1 to 12-3, respectively) were added to a polymerization reactor, and then about 2 μmol of chromium acetylacetonate, 50 mL of n-hexane, and 5 μmol of triisobutylaluminum were mixed for 5 minutes and added to the reactor, and finally, 1 MPa of ethylene was added to start the polymerization.

[0041] Comparative Examples 1-1 to 1-8 Comparative Examples 1-1 to 1-8 differ from Examples 1-1 to 1-8 in that, in Comparative Examples 1-1 to 1-8, the active promoting component was not added when the transition metal acetylacetonate complex was mixed with triisobutylaluminum. In addition, the total volume of the solvent and the active promoting component was 150 mL in Examples 1-1 to 1-8, and since the active promoting component was not added in Comparative Examples 1-1 to 1-8, the amount of the solvent was increased to 150 mL (the same applies hereinafter).

[0042] First, 200 μmol of triisobutylaluminum and 150 mL of toluene solvent were added to a polymerization reactor, and then about 2 μmol of a transition metal acetylacetonate complex (titanium acetylacetonate, zirconium acetylacetonate, vanadyl acetylacetonate, chromium acetylacetonate, nickel acetylacetonate, iron acetylacetonate, chromium tris(hexafluoroacetylacetonate), nickel trifluoroacetylacetonate, used in Comparative Examples 1-1 to 1-8, respectively) and 5 μmol of triisobutylaluminum were mixed at 40°C for 5 minutes and added to the reactor, and finally, 1 MPa of ethylene was added to start the polymerization.

[0043] Comparative Examples 2-1 to 2-3 Comparative Examples 2-1 to 2-3 differ from Examples 3-1 to 3-3 in that, in Comparative Examples 2-1 to 2-3, the active promoting component was not added when chromium acetylacetonate was mixed with an alkylaluminum.

[0044] First, 200 μmol of an alkylaluminum cocatalyst (trimethylaluminum, triethylaluminum, trioctylaluminum, used in Comparative Examples 2-1 to 2-3, respectively) and 150 mL of toluene solvent were added to a polymerization reactor, and then about 2 μmol of chromium acetylacetonate and 5 μmol of the alkylaluminum cocatalyst were mixed at 40°C for 5 minutes and added to the reactor, and finally, 1 MPa of ethylene was added to start the polymerization.

[0045] Comparative Examples 3-1 to 3-3 Comparative Examples 3-1 to 3-3 differ from Examples 4-1 to 4-3 in that no active promoting component was added when the chromium acetylacetonate was premixed with triisobutylaluminum in Comparative Examples 3-1 to 3-3.

[0046] First, 200 μmol of triisobutylaluminum and 150 mL of solvent (benzene, xylene, ethylbenzene, in this order, for Comparative Examples 3-1 to 3-3) were added to a polymerization reactor, then about 2 μmol of chromium acetylacetonate and 5 μmol of triisobutylaluminum were premixed at 40°C for 5 minutes and added to the reactor, and finally 1 MPa of ethylene was added to start the polymerization.

[0047] Comparative Examples 4-1 to 4-4 Comparative Examples 4-1 to 4-4 differ from Examples 5-1 to 5-4 in that no active promoting component was added when the chromium acetylacetonate was premixed with triisobutylaluminum in Comparative Examples 4-1 to 4-4.

[0048] First, 200 μmol of triisobutylaluminum and 150 mL of toluene were added to a polymerization reactor, then a certain molar amount of chromium acetylacetonate (0.5 μmol, 1 μmol, 5 μmol, 10 μmol, in this order, for Comparative Examples 4-1 to 4-4) and 5 μmol of triisobutylaluminum were premixed at 40°C for 5 minutes and added to the reactor, and finally 1 MPa of ethylene was added to start the polymerization.

[0049] Comparative Examples 5-1 to 5-3 Comparative Examples 5-1 to 5-3 differ from Examples 6-1 to 6-3 in that no active promoting component was added when the chromium acetylacetonate was premixed with triisobutylaluminum in Comparative Examples 5-1 to 5-3.

[0050] First, 200 μmol of triisobutylaluminum and 150 mL of toluene were added to a polymerization reactor, then 2 μmol of chromium acetylacetonate and a certain molar amount of triisobutylaluminum (1 μmol, 2 μmol, 10 μmol, in this order, for Comparative Examples 5-1 to 5-3) were premixed at 40°C for 5 minutes and added to the reactor, and finally 1 MPa of ethylene was added to start the polymerization.

[0051] Comparative Examples 6-1 to 6-3 Comparative Examples 6-1 to 6-3 differ from Examples 8-1 to 8-3 in that no active promoting component was added when the chromium acetylacetonate was premixed with triisobutylaluminum in Comparative Examples 6-1 to 6-3.

[0052] First, 200 μmol of triisobutylaluminum and 150 mL of toluene solvent were added to a polymerization reactor, and then about 2 μmol of acetylacetone chromium and 5 μmol of triisobutylaluminum were added to the reactor after being pre-mixed at 40°C for a certain time (1 minute, 10 minutes, and 60 minutes, respectively, for Comparative Examples 6-1 to 6-3), and finally, 1 MPa of ethylene was added to start the polymerization reaction.

[0053] Comparative Examples 7-1 to 7-3 Comparative Examples 7-1 to 7-3 and Example 9-1 to 9-3 differ in that, in Comparative Examples 7-1 to 7-3, no active promoting component was added when acetylacetone chromium was pre-mixed with triisobutylaluminum.

[0054] First, 200 μmol of triisobutylaluminum and 150 mL of toluene solvent were added to a polymerization reactor, and then about 2 μmol of acetylacetone chromium and 5 μmol of triisobutylaluminum were added to the reactor after being pre-mixed at a certain temperature (20°C, 60°C, and 80°C, respectively, for Comparative Examples 7-1 to 7-3) for 5 minutes, and finally, 1 MPa of ethylene was added to start the polymerization reaction.

[0055] Comparative Example 8-1 Comparative Example 8-1 and Example 10-1 differ in that, in Comparative Example 8-1, no active promoting component was added when triisobutylaluminum was added to the polymerization reactor.

[0056] First, 200 μmol of triisobutylaluminum was added to a polymerization reactor, and then about 2 μmol of acetylacetone chromium, 150 mL of toluene, and 5 μmol of triisobutylaluminum were added to the reactor after being pre-mixed at 40°C for 5 minutes, and finally, 1 MPa of ethylene was added to start the polymerization reaction.

[0057] Comparative Example 8-2 Comparative Example 8-2 and Example 10-2 differ in that, in Comparative Example 8-2, no active promoting component was added.

[0058] About 2 μmol of acetylacetone chromium, 150 mL of toluene, and 5 μmol of triisobutylaluminum were pre-mixed for 5 minutes, and then added to a reactor, and finally, 1 MPa of ethylene was added to start the polymerization reaction.

[0059] Comparative Examples 9-1 to 9-4 Comparative Examples 9-1 to 9-4 and Examples 11-1 to 11-4 differ in that, in Comparative Examples 9-1 to 9-4, no active promoting component was added.

[0060] First, 200 μmol of triisobutylaluminum, 150 mL of toluene solvent, and 8 mL of comonomer (1-butene, 1-hexene, 1-octene, and styrene were used in Comparative Examples 9-1 to 9-4, respectively) were added to a polymerization reactor, and then about 2 μmol of chromium acetylacetonate and 5 μmol of triisobutylaluminum were mixed for 5 minutes and added to the reactor, and finally, 1 MPa of ethylene was added to start the polymerization.

[0061] Comparative Examples 10-1 to 10-3 Comparative Examples 10-1 to 10-3 and Examples 12-1 to 12-3 differ in that Comparative Examples 10-1 to 10-3 do not include an activity promoting component.

[0062] First, 200 μmol of triisobutylaluminum, 150 mL of toluene solvent, and 8 mL of comonomer (1-butene, 1-hexene, 1-octene, and styrene were used in Comparative Examples 9-1 to 9-4, respectively) were added to a polymerization reactor, and then about 2 μmol of chromium acetylacetonate and 5 μmol of triisobutylaluminum were mixed for 5 minutes and added to the reactor, and finally, 1 MPa of ethylene was added to start the polymerization.

[0063] Table 1: Summary of Ethylene Polymerization Results of Examples and Comparative Examples

[0064] Explanation: In the table, a indicates kg of polyethylene / mol of metal / hour; b indicates 10 5 g / mol; c indicates mol%.

[0065] As can be seen from the examples and comparative examples, when the type of main catalyst is different (Examples 1-1 to 1-8 and Comparative Examples 1-1 to 1-8), the type of cocatalyst is different (Examples 3-1 to 3-3 and Comparative Examples 2-1 to 2-3), the type of solvent is different (Examples 4-1 to 4-3 and Comparative Examples 3-1 to 3-3), the content of main catalyst is different (Examples 5-1 to 5-4 and Comparative Examples 4-1 to 4-4), the content of cocatalyst is different (Examples 6-1 to 6-3 and Comparative Examples 5-1 to 5-3), the mixing time is different (Examples 8-1 to 8-3 and Comparative Examples 6-1 to 6-3), the mixing temperature is different (Examples 9-1 to 9-3 and Comparative Examples 7-1 to 7-3), and the mixing order is different (Examples 10-1 to 10-2 and Comparative Examples 8-1 to 8-2), the examples in which the activity promoting component is added always show several times higher polymerization activity than the comparative examples in which the activity promoting component is not added, and the weight average molecular weight of the polymer is reduced by 30 to 50%.

[0066] From the examples and comparative examples, it can be seen that when the types of comonomers are different (Examples 1-1 to 1-8 and Comparative Examples 1-1 to 1-8), the examples with the addition of the activity promoting component always exhibit higher comonomer insertion rates than the comparative examples without the addition of the activity promoting component; From Examples 12-1 to 12-3 and Comparative Examples 10-1 to 10-3, it can be seen that both exhibit good hydrogen response capability, i.e., the molecular weight of the polymer is greatly reduced after the addition of a small amount of hydrogen. At the same hydrogen partial pressure, the polymers synthesized in Examples 12-1 to 12-3 have lower molecular weights. From Examples 7-1 to 7-7, it can be seen that by increasing the amount of n-hexane added as the activity promoting component, the polymerization activity can be significantly improved, and the molecular weight of the polymer is greatly reduced.

[0067] The above only describes some specific embodiments of the present application. For those of ordinary skill in the art, without departing from the inventive concept of the present application, several modifications and improvements can be made, which are all within the protection scope of the present application.

Claims

1. A polyolefin catalyst characterized in that, The catalyst comprises a main catalyst, a cocatalyst, an activity promoting component and a solvent; wherein the main catalyst is a transition metal acetylacetone complex, the mass of the transition metal in the catalyst is 0.01-3wt%; the cocatalyst is an alkyl aluminum, the ratio of the moles of the alkyl aluminum to the moles of the transition metal acetylacetone complex is 10-1000; the activity promoting component is a C4-C6 chain alkane, the amount of the component accounts for 1-100% of the total volume of the catalyst; the solvent accounts for 0-100% of the total volume of the catalyst.

2. The polyolefin catalyst of claim 1, wherein, The mass of the transition metal in the main catalyst is 0.01-1wt%, the ratio of the moles of the cocatalyst to the moles of the main catalyst is 30-300, the solvent accounts for 30-70% of the total volume of the catalyst, and the activity promoting component accounts for 20-80% of the total volume of the catalyst.

3. The polyolefin catalyst of claim 1, wherein, The transition metal acetylacetone complex comprises at least one of titanium acetylacetone oxide, zirconium acetylacetone, hafnium acetylacetone, vanadium acetylacetone oxide, vanadium acetylacetone, chromium acetylacetone, molybdenum dioxide bis-acetylacetone, iron acetylacetone, manganese acetylacetone, cobalt acetylacetone, cobalt acetylacetone, nickel acetylacetone, tris (hexafluoroacetylacetone) iron, tris (hexafluoroacetylacetone) chromium, copper trifluoroacetylacetone, tin hexafluoroacetylacetone, cobalt hexafluoroacetylacetone, and nickel trifluoroacetylacetone.

4. The polyolefin catalyst according to any one of claims 1 to 3, characterized in that, The alkyl aluminum comprises at least one of trimethyl aluminum, triethyl aluminum, monochlorodiethyl aluminum, dichloroethyl aluminum, monochlorodiisobutyl aluminum, triisobutyl aluminum, tributyl aluminum, and trioctyl aluminum.

5. The polyolefin catalyst of claim 4, wherein, The activity promoting component is at least one of n-butane, isobutane, n-pentane, isopentane, n-hexane, and isohexane.

6. The polyolefin catalyst of claim 5, wherein, The solvent comprises at least one of benzene, toluene, xylene, ethylbenzene, isopropylbenzene, n-propylbenzene, methyl ethyl benzene, naphthalene, dichloromethane, trichloromethane, tetrachloromethane, and dichloroethane.

7. Application of the polyolefin catalyst according to any one of claims 1-6 in ethylene polymerization.

8. Process for the preparation of ethylene polymers using the polyolefin catalyst according to any one of claims 1 to 6, characterized in that, The steps are as follows: (1) The high-pressure polymerization reactor is vacuumized at 95-105℃ for 0.8-1.2 hours, and then nitrogen is introduced to normal pressure; (2) The alkyl aluminum and the solvent are first added to the high-pressure polymerization reactor, and then the transition metal acetylacetone complex, the activity promoting component, and the alkyl aluminum are pre-mixed at 20-80℃ for 1-120 minutes before being added to the reactor, and finally 1MPa ethylene is added to start the polymerization reaction, the reaction temperature is 65-75℃, and the reaction time is 0.8-1.2 hours.

9. The method of claim 8, wherein, A molecular weight regulator can also be added during the polymerization process.

10. The method according to claim 8 or 9, characterized in that, In step (2), the alkyl aluminum and the solvent can also be added to the high-pressure polymerization reactor, and a copolymerization monomer can also be added, the copolymerization monomer is added in liquid phase, and the volume of the copolymerization monomer accounts for 1-10% of the total volume of the solvent and the activity promoting component.

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