Process for preparing morphology-improved polyethylene powder

Abstract

A process for preparing a morphology improved polyethylene powder, the process comprising: contacting ethylene with a reactive olefin prepolymer in a gas phase reactor to prepare a morphology improved polyethylene powder via gas phase polymerization; wherein the reactive olefin prepolymer comprises a component that is a polyolefin and a component that is an active metallocene derivative of a spray-dried silica supported metallocene catalyst; wherein the reactive olefin prepolymer has a prepolymer / catalyst weight / weight ratio of from 10: 1.0 to 50: 1.0 wherein the weight of the prepolymer is the total weight of the reactive olefin prepolymer and the weight of the catalyst is the weight of the spray-dried silica supported metallocene catalyst.

Description

Technical Field

[0001] Polymerizing ethylene using a catalyst in a gas-phase reactor. Background Art

[0002] Patent applications published, patents, and unpublished patent applications in or related to this field include EP1939226A1, US2008 / 0182950A1, US5654248, US7592410B2, WO1992 / 012182A1, WO1997 / 002297A1, WO2002 / 074818A1, WO2005 / 005495A2, WO2007 / 033941A1, WO 2016 / 172567 A1, WO2021 / 242800A1, WO2021 / 242801A1, PCT / US2022 / 031696, and PCT / US2022 / 043943.

[0003] Gas-phase reactors lack the large amount of heat-absorbing substances present in solution-phase reactors, which contain a large amount of solvent. Since ethylene polymerization is a highly exothermic reaction, gas-phase polymerization of ethylene is particularly prone to overheating. When overheating occurs, the rate of reactor fouling increases significantly. Mitigating factors alleviate these problems for higher olefin monomers. These factors include the steric hindrance of the olefin monomer molecules and the melting temperature of the polyolefin. All other things being equal, as the size of the olefin monomer being polymerized increases, the heat release decreases. In addition, as the melting temperature of the polyolefin increases, the reactor fouling problem decreases because higher melting particles are less likely to fuse together at a given temperature than lower melting particles. In fact, the propylene molecule is larger than the ethylene molecule, and the melting temperature of polypropylene is significantly higher than that of polyethylene. The combined effect of these differences means that the problems of gas-phase polymerization of ethylene are unique in type and degree.

[0004] In the field of fluidized beds, the gas-phase polymerization of olefin monomers to prepare polyolefin polymer powders, the particle size and particle size distribution of the polyolefin powder in the gas-phase reactor during polymerization can affect the process and its products. This effect is particularly felt in processes for preparing polyolefin polymers having a multimodal (e.g., bimodal or trimodal) molecular weight distribution. If there are too many small polyolefin particles (referred to herein as polyolefin fines) in the reactor, these fines can foul reactor equipment, such as compressors and other equipment. When the gas-phase reactor is a fluidized bed reactor, the fines can also have a negative impact on the fluidization of the polyolefin particle bed (fluidized bed) in the gas-phase reactor and can cause sintering effects, resulting in the formation of polymer lumps and sheets. Moreover, the discharge of the polyolefin powder from the reactor and its conveyance to downstream unit operations (e.g., purification bins) are negatively affected. A wide variation in particle size affects bed fluidization because particles with sizes significantly deviating from the average size behave significantly differently in the fluidized bed. The threats posed by particles of such relatively large or small sizes to the process include different reactivity, different cooling capabilities, and particle sintering. The result of this problem is that the resulting particles have different polymer properties. This problem is referred to as chemical inhomogeneity. In addition, a broader particle size distribution may lead to segregation of the polyolefin powder, resulting in processing challenges. Moreover, due to different melt behaviors and gel formation in the final polyolefin powder, this problem may result in physical inhomogeneity. All other things being equal, a narrower particle size distribution of the polyolefin powder prepared in a gas-phase polymerization reactor is preferred. Summary of the Invention

[0005] Embodiments of our technical solution to this problem include transforming the particle size distribution of the polyolefin powder prepared in the gas-phase reactor to larger-sized particles such that the amount of polyolefin fines is minimized. However, a simple transformation of the particle size distribution to larger particle size values, i.e., by shifting the particle size range by a certain amount, does not inherently change the breadth of the distribution. For example, shifting the particle size distribution from a first range of 60 μm to 200 μm to a second range of, e.g., 20 μm to 80 μm to 220 μm does not change the breadth of the particle size distribution: in both the first and second ranges, the breadth of the distribution is the same: 140 μm. The present invention includes preparing a reactive polyolefin prepolymer. This reactive polyolefin prepolymer enables narrowing the particle size distribution of the polyolefin powder prepared in a fluidized bed gas-phase reactor. This can be accomplished by adjusting the temperature used to prepare the prepolymer or by varying the catalyst loading in the prepolymer or both. In some embodiments, the present invention includes a method for preparing a polyolefin powder, wherein the polyolefin particles have a narrower particle size distribution than the particle size distribution of a comparative polyethylene powder.

[0006] The present invention generally relates to a process for preparing a morphology-improved polyethylene powder during the gas-phase polymerization of ethylene catalyzed by the active metallocene derivative of a spray-dried silica-supported metallocene catalyst (“SD / SiS-metallocene catalyst”). Without such a process, the SD / SiS-metallocene catalyst would result in polyethylene powder having too much fines and too small an average particle size (APS).

[0007] When preparing polyethylene powder by catalyzing the polymerization of ethylene by feeding a dry or slurry form of the SD / SiS-metallocene catalyst into the reaction zone of a gas-phase reactor, we observed overheating in the reaction zone. Surprisingly, this problem gave rise to the opposite particle size defect. On the one hand, the overheating produced polyethylene fines, which are defined as polyethylene particles having a diameter of 74 microns or less. Without being bound by theory, this may be due to the overheating causing some of the SD / SiS-metallocene catalyst particles in the SD / SiS-metallocene catalyst particles to fracture into smaller sizes, and these SD / SiS-metallocene catalyst particles contain or produce polyethylene fines. Some of the polyethylene fines may be due to catalyst particle fines that may be present in the starting SD / SiS-metallocene catalyst. On the other hand, the overheating caused fouling in the reaction zone, as illustrated by reactor wall flaking or distribution plate blockage. Without being bound by theory, this fouling may be due to the overheating causing the polyethylene powder to fuse into agglomerated particles and sheets.

[0008] One attempt to address these problems was to switch from a simple single-tube injector body to a tube-in-tube injector body to feed the SD / SiS-metallocene catalyst into the reaction zone. The tube-in-tube injector body feeds the SD / SiS-metallocene catalyst through one of the tubes and feeds the carrier gas through the other tube. Compared with dispersion from a single-tube injector, this tube-in-tube configuration disperses the supported metallocene catalyst in the reaction zone faster and more extensively. The tube-in-tube injector did not eliminate the overheating problem.

[0009] The path of this technical solution starts from the following observation: all other things being equal, when sprayed into a gas-phase reactor, the SD / SiS-metallocene catalyst has a significantly faster ignition than a conventionally dried system. Catalyst ignition means how quickly the fresh catalyst starts an exothermic reaction with the monomer after being sprayed into the reactor and / or how quickly the temperature in the reactor rises once the reaction starts. Generally, there is a lag period between the zero time point when the fresh catalyst is sprayed into the reactor and the starting time point when the catalyst begins to prepare the polymer. If the lag period is too short, the fresh catalyst may not have time to disperse widely in the reaction zone before starting to prepare the polymer. This is worse for a single-tube injector. This may lead to local overheating. Once the fresh catalyst starts polymerizing ethylene, the reaction generates significant heat release. If the heat release is too strong, even a widely dispersed catalyst may overheat and cause fouling. All other things being equal, the earlier the heat release starts (i.e., the shorter the lag period) and / or the faster the temperature rise rate, the faster the catalyst ignition. Conversely, the later the heat release starts (i.e., the longer the lag period) and / or the slower the reactor temperature rise rate, the slower the catalyst ignition. The lag period and heat release of the catalyst can be quantified by spraying the fresh catalyst into a vial containing 1-octene at room temperature as the monomer and recording the time and temperature, such as described later in the ignition vial test method.

[0010] When studying using a scanning electron microscope (SEM), we found morphological differences between the particles of the SD / SiS-metallocene catalyst and the particles of the conventionally dried supported metallocene catalyst. Since the same reactants and amounts were used to prepare these catalysts, these morphological differences seem to be an inherent result of different drying methods.

[0011] The conventionally dried supported metallocene catalyst is prepared by evaporating and concentrating a mixture of a metallocene precatalyst, a silica support, an activator, and a hydrocarbon solvent to obtain conventional catalyst particles. The conventional drying method produces a particle morphology that is a tight blend of different particles of the metallocene catalyst and different particles of the activator / silica support. The SD / SiS-metallocene catalyst is prepared by spray-drying a mixture of a metallocene precatalyst, a silica support, an activator, and a hydrocarbon solvent to obtain conventional catalyst particles. Spray drying flash-evaporates the hydrocarbon solvent and produces particles with a core-shell morphology, where the metallocene catalyst and the excess activator are mainly in the form of a thin shell disposed on the surface of the silica support, and the silica support contains the core of the core-shell particles. The different particle morphologies produced by the conventional drying method and the spray-drying method can be visualized by a scanning electron microscope (SEM). It is believed that the differences in particle morphology result in different catalyst ignition curves and different catalyst activities.

[0012] Without being bound by theory, we believe that the morphological differences between conventional dried metallocene catalysts and SD / SiS-metallocene catalysts explain the significantly faster ignition of SD / SiS-metallocene catalysts in a gas-phase reactor. The difference in ignition "efficiency" can be quantified using an ignition vial test method.

[0013] Therefore, the problem we solve is how to inhibit the ignition of SD / SiS-metallocene catalysts in ethylene polymerization in a gas-phase reactor, but not too much.

[0014] This problem is solved by the method of the present invention. The method includes preparing a polyethylene powder with improved morphology, and the method includes: contacting ethylene with a reactive olefin prepolymer in a gas-phase reactor to prepare a polyethylene powder with improved morphology via gas-phase polymerization; wherein the reactive olefin prepolymer contains a component that is a polyolefin and a component that is an active metallocene derivative of a spray-dried silica-supported metallocene catalyst; wherein the reactive olefin prepolymer has a prepolymer / catalyst weight / weight ratio of 10:1.0 to 50:1.0, wherein the weight of the prepolymer is the total weight of the reactive olefin prepolymer, and the weight of the catalyst is the weight of the spray-dried silica-supported metallocene catalyst.

[0015] Unexpectedly, solving the catalyst ignition problem also improves the morphology of the polyolefin powder prepared in gas-phase polymerization. The improved morphology includes: (i) inhibiting the formation of polyethylene particles that are too small (fine powder), which are defined as polyethylene particles having a diameter of 74 microns or less; (ii) changing the average particle size (APS) of the polyethylene particles; (iii) narrowing the particle size distribution of the polyolefin particles (e.g., polyethylene particles); (iv) both feature (i) and feature (ii); (v) both feature (i) and feature (iii); (vi) both feature (ii) and feature (iii); or (vii) each of features (i), (ii), and (iii). Description of the Drawings

[0016] Figure 1 is a graph of the volume percentage (volume %) (y-axis) of the SD / SiS-metallocene catalyst versus the particle size in microns (μm) (x-axis) for Sample A and Sample B of Preparation 1.

[0017] Figure 2 is a graph of the volume fraction in percentage (fraction, %) (y-axis) versus the particle size in microns (particle size (microns)) on a scale from 0 μm to 2,000 μm.

[0018] Figure 3It is a graph showing the weight percentage (wt%) of particles and the mesh size (MSH) of particles for comparing two polyethylene powders and two morphology-improved polyethylene powders of the present invention.

[0019] Figure 4 It is a cartoon drawing showing the particle morphology of a plurality of conventionally dried catalyst particles.

[0020] Figure 5 It is a cartoon drawing showing the core-shell particle morphology of a single spray-dried catalyst particle. Detailed Description

[0021] Disclosed is a method for preparing a morphology-improved polyethylene powder, the method comprising: contacting ethylene with a reactive olefin prepolymer in a gas-phase reactor to prepare a morphology-improved polyethylene powder via gas-phase polymerization; wherein the reactive olefin prepolymer comprises a component that is a polyolefin and a component that is an active metallocene derivative of a spray-dried silica-supported metallocene catalyst (“SD / SiS-metallocene catalyst”); wherein the reactive olefin prepolymer has a prepolymer / catalyst weight / weight ratio of 10:1.0 to 50:1.0, wherein the weight of the prepolymer is the total weight of the reactive olefin prepolymer and the weight of the catalyst is the weight of the spray-dried silica-supported metallocene catalyst. The total weight of the reactive olefin prepolymer includes the weight of the olefin prepolymer plus the weight of the SD / SiS-metallocene catalyst. The weight of the reactive olefin prepolymer is the measured amount thereof added to the gas-phase reactor before and during the contacting step. In some embodiments, the method comprises the step of adding a measured amount of the reactive olefin prepolymer to the gas-phase reactor before, during, or before and during the contacting step. The weight of the SD / SiS-metallocene catalyst is the measured amount of the SD / SiS-metallocene catalyst used to obtain the reactive olefin prepolymer according to the method for preparing the reactive olefin prepolymer described herein.

[0022] The method as described above, which includes preparing a reactive olefin prepolymer by: mixing a measured preliminary amount of an olefin monomer with a measured amount of a spray-dried silica-supported metallocene catalyst in a liquid alkane phase in a slurry-phase reactor at a temperature of 30 °C to 70 °C, an ethylene partial pressure not exceeding 861 kPa (not exceeding about 125 psi), and a total reactor pressure not exceeding 2445 kPa (not exceeding about 355 psi) to prepare a reactive olefin prepolymer via slurry-phase polymerization; wherein the measured preliminary amount of the olefin monomer and the measured amount of the spray-dried silica-supported metallocene catalyst result in a prepolymer / catalyst weight / weight ratio of the reactive olefin prepolymer of 10:1.0 to not exceeding 50:1.0, where the weight of the prepolymer is the total weight of the reactive olefin prepolymer and the weight of the catalyst is the weight of the spray-dried silica-supported metallocene catalyst. The prepolymer / catalyst weight / weight ratio can be adjusted within this range by using a higher or lower amount of the spray-dried silica-supported metallocene catalyst relative to the amount of the olefin monomer.

[0023] The method as described above has any one of the limitations (i) to (iii): (i) the prepolymer / catalyst weight / weight ratio is 10:1.0 to 45:1.0, 15:1.0 to 35:1.0, or 15:1.0 to 25:1.0; (ii) the temperature of the slurry-phase reactor in claim 2 is 35 °C to 70 °C, 40 °C to 60 °C, or 45 °C to 55 °C; or (iii) the prepolymer / catalyst weight / weight ratio is 15:1.0 to 25:1.0 and the temperature of the slurry-phase reactor in claim 2 is 45 °C to 55 °C.

[0024] The method as described above has limitation (i) and limitation (ii) or (iii): (i) the reactive olefin prepolymer is a reactive ethylene prepolymer and the polyolefin of the reactive ethylene prepolymer is ethylene homopolymer or ethylene / (C4-C 10 ) α-olefin copolymer; and (ii) the gas-phase reactor does not contain an olefin comonomer and the morphology-improved polyethylene powder is ethylene homopolymer; or (iii) the gas-phase reactor contains a (C4-C 10 ) α-olefin comonomer and the morphology-improved polyethylene powder is ethylene / (C4-C 10 ) α-olefin copolymer.

[0025] The method as described above includes: (i) directly feeding a reactive olefin prepolymer from a slurry-phase reactor into a gas-phase reactor (i.e., without feeding the reactive olefin prepolymer into an intermediate vessel such as a dryer, a purification tank, or a storage tank); or (ii) feeding the reactive olefin prepolymer from the slurry-phase reactor into an intermediate vessel (such as a dryer, a purification tank, or a storage tank), waiting for a period of time, and then feeding the reactive olefin prepolymer from the intermediate vessel into the gas-phase reactor.

[0026] The method as described above, wherein the reactive olefin prepolymer is fed into the gas-phase reactor via a single inlet pipe, and the single inlet pipe has an inner diameter of 0.3 centimeters (cm) to 1.0 cm.

[0027] The method as described above includes: preparing a spray-dried silica-supported metallocene catalyst by any one of (i) to (iii): (i) spray-drying a mixture of a metallocene precatalyst, a silica support, an activator, and a hydrocarbon diluent to prepare a spray-dried silica-supported metallocene catalyst; (ii) spray-drying a mixture of a silica support, an activator, and a hydrocarbon diluent to obtain a spray-dried supported activator, and contacting the spray-dried supported activator with a metallocene precatalyst to prepare a spray-dried silica-supported metallocene catalyst; or (iii) spray-drying a mixture of a metallocene precatalyst, a silica support, and a hydrocarbon diluent to obtain a spray-dried supported metallocene precatalyst, and contacting the spray-dried supported metallocene precatalyst with an activator to prepare a spray-dried silica-supported metallocene catalyst; wherein the hydrocarbon diluent is selected from the group consisting of alkanes, aromatics, alkyl-substituted aromatics, aryl-substituted alkanes, or a blend of any two or more thereof.

[0028] The method as described above, wherein the metallocene precatalyst has the formula (I): wherein M is Ti, Hf, or Zr; each R 1 to R 5 is independently an unsubstituted (C1-C6) alkyl group, or R 1 and R 2 bonded together to include a divalent subhydrocarbyl group selected from the group consisting of -C(R a )=C(R b )-C(R c )=C(R d )- and -C(R a )2-C(R b )2-C(R c )2-C(R d )2-, wherein R ato R d each of which is independently H or methyl; and each X is a leaving group.

[0029] The method as described above, wherein the metallocene pre-catalyst is selected from the group consisting of: bis(η 5 -tetramethylcyclopentadienyl)zirconium dichloride; bis(η 5 -tetramethylcyclopentadienyl)zirconium dimethyl; bis(η 5 -pentamethylcyclopentadienyl)zirconium dichloride; bis(η 5 -pentamethylcyclopentadienyl)zirconium dimethyl; (1,3-dimethyl-4,5,6,7-tetrahydroindenyl)(1-methylcyclopentadienyl)zirconium dimethyl; bis(1-methyl-3-n-butylcyclopentadienyl)zirconium dichloride; bis(1-methyl-3-n-butylcyclopentadienyl)zirconium dimethyl; bis(n-propylcyclopentadienyl)hafnium dichloride; bis(n-propylcyclopentadienyl)hafnium dimethyl; bis(n-butylcyclopentadienyl)zirconium dichloride; (cyclopentadienyl)(1,5-dimethylindenyl)zirconium dimethyl; (methylcyclopentadienyl)(1,5-dimethylindenyl)zirconium dimethyl; (cyclopentadienyl)(1,4-dimethylindenyl)zirconium dimethyl; (methylcyclopentadienyl)(1,4-dimethylindenyl)zirconium dimethyl; and bis(n-butylcyclopentadienyl)zirconium dimethyl.

[0030] The method as described above, wherein the morphology of the morphology-improved polyethylene powder is further improved by removing at least some of the catalyst fines from the spray-dried silica-supported metallocene catalyst before preparing the reactive olefin prepolymer therefrom, wherein the catalyst fines are defined as catalyst particles having a diameter of 10 micrometers (μm) or less.

[0031] The improved morphology includes: (i) inhibiting the formation of polyolefin particles (e.g., polyethylene particles) that are too small (fines), which are defined as polyolefin particles (e.g., polyethylene particles) having a diameter of 74 micrometers or less; (ii) changing the average particle size (APS) of the polyolefin particles (e.g., polyethylene particles); (iii) narrowing the particle size distribution of the polyolefin particles (e.g., polyethylene particles); (iv) both feature (i) and feature (ii); (v) both feature (i) and feature (iii); (vi) both feature (ii) and feature (iii); or (vii) each of features (i), (ii), and (iii).

[0032] In some embodiments, the improved morphology includes feature (i), and the suppression of the formation of polyolefin fines (polyethylene fines) having a diameter of 74 microns or less includes a reduction in the percentage of fines to 5% to 60%, or 9% to 55%, or 20% to 55%, or 30% to 55%, or 45% to 59%.

[0033] In some embodiments, the improved morphology includes feature (ii) and an increase in the APS of the polyolefin particles (e.g., polyethylene particles), which indicates an overall shift of the particle size distribution curve towards higher diameters. In some embodiments, the APS of the polyolefin particles increases by 9% to 50%, or 9% to 42%, or 30% to 55%. All other things being equal, polyolefin particles (e.g., polyethylene particles) having an increased APS may advantageously have fewer polyolefin fines (e.g., polyethylene fines) and / or may have improved flow characteristics and be more easily transferred from the gas-phase reactor to another unit operation, such as a dryer or a purification tank or a storage tank. In other embodiments, the improved morphology includes feature (ii) and a decrease in the APS of the polyolefin particles (e.g., polyethylene particles), which indicates an overall shift of the particle size distribution curve towards lower diameters. In other embodiments, the APS of the polyolefin particles decreases by 5% to 30%, or 12% to 22%, or 14% to 20%. All other things being equal, polyolefin particles (e.g., polyethylene particles) having a decreased APS may advantageously have easier processability in a melt extruder / granulator operation.

[0034] In some embodiments, the improved morphology includes feature (iii) narrowing the particle size distribution of polyolefin particles (e.g., polyethylene particles). To provide a way to quantify the narrowing of the particle size distribution, we use herein the particle size ratio d90 / d10, where d90 is the particle size at 90% volume fraction of the polyolefin powder, and d10 is the particle size at 10% volume fraction of the polyolefin powder (e.g., polyethylene powder). The 90% volume fraction refers to the particle size greater than 90 volume % of all particles in the polyolefin powder, and the 10% volume fraction refers to the particle size greater than 10 volume % of all particles in the polyolefin powder. The smaller the particle size ratio d90 / d10, the narrower the particle size distribution. In some embodiments, the particle size ratio d90 / d10 is from 3.0 to 4.0, or from 3.10 to 3.75. In some embodiments, feature (iii) is described as a percentage reduction of the d90 / d10 of the present invention relative to the comparative d90 / d10. In some embodiments, feature (iii) includes a percentage reduction of 4% to 30%, or 10% to 30%, or 11% to 28%, or 23% to 28% of the d90 / d10 of the present invention relative to the comparative d90 / d10. The comparative d90 / d10 is measured on a comparative polyolefin powder (e.g., comparative polyethylene powder) prepared under the same gas phase polymerization conditions as the polyolefin powder (polyethylene powder) of the present invention, except that an SD / SiS-metallocene catalyst is used in the comparative polymerization instead of the reactive polyolefin prepolymer (e.g., reactive polyethylene prepolymer) of the present invention.

[0035] The method as described above, wherein the morphology of the morphology-improved polyethylene powder comprises: (i) the amount of polyethylene fines is 5% to 60%, or 9% to 55%, or 20% to 55%, or 30% to 55% lower than the amount of polyethylene fines in a comparative polyethylene powder prepared by the same gas-phase polymerization, the difference being that a spray-dried silica-supported metallocene catalyst is used instead of a reactive olefin prepolymer; and (ii) the average particle size (APS) is 9% to 50%, or 9% to 42%, or 30% to 50% higher than the APS of the comparative polyethylene powder; and (iii) the percentage of d90 / d10 of the present invention relative to the comparative d90 / d10 is reduced by 10% to 30%, or 11% to 28%, or 23% to 28%. Alternatively, the method as described above, wherein the morphology of the morphology-improved polyethylene powder comprises: (i) the amount of polyethylene fines is 5% to 60%, or 9% to 55%, or 20% to 55%, or 30% to 55% lower than the amount of polyethylene fines in a comparative polyethylene powder prepared by the same gas-phase polymerization, the difference being that a spray-dried silica-supported metallocene catalyst is used instead of a reactive olefin prepolymer; (ii) the average particle size (APS) is 11% to 20%, or 14% to 19% lower than the APS of the comparative polyethylene powder; and (iii) the percentage of d90 / d10 of the present invention relative to the comparative d90 / d10 is reduced by 4% to 30%, or 10% to 30%, or 11% to 28%, or 23% to 28%.

[0036] The method as described above, wherein the greater the amount of polyethylene fines in the comparative polyethylene powder, the greater the percentage reduction of polyethylene fines in the morphology-improved polyethylene powder.

[0037] The method as described above, wherein, compared with a comparative polyethylene powder made from an SD / SiS-metallocene catalyst, when determined by screening a polyethylene powder through a stack of sieve apertures with gradually decreasing sizes, the particle size distribution (PSD) of the morphology-improved polyethylene powder is narrower. A narrower PSD means a smaller particle size range, which means a smaller difference between the maximum particle size and the minimum particle size. This is illustrated in Figure 3 which. Figure 3 is a graph of the weight percentage (wt%) of particles versus the mesh size (MSH) of particles for two comparative polyethylene powders (both designated "G1 t-in-t, side stream 16-PL"), two morphology-improved polyethylene powders of the present invention (designated "20g / g@50C, side stream 16-PL" and "40g / g@50C, side stream 16-PL", where 20g / g and 40g / g refer to 20 grams or 40 grams of reactive olefin prepolymer / 1.0 gram of SD / SiS-metallocene catalyst used to obtain the prepolymer, and 50C refers to 50 °C). In Figure 3In this context, "sidestream" means that nitrogen is fed into the reactor via a side inlet, and 16-PL is the batch number. For this measurement and as shown in Figure 3 The U.S. sieve mesh sizes shown in range from the largest opening to the smallest opening as: 10 mesh (10 MSH, 2000 μm), 18 mesh (18 MSH, 1000 μm), 35 mesh (35 MSH, 500 μm), 60 mesh (60 MSH, 250 μm), 120 mesh (120 MSH, 125 μm), 200 mesh (200 MSH, 74 μm), and PAN (less than 74 μm). Optionally, a 325 mesh (44 μm) sieve can be inserted between 200 mesh and PAN. Figure 3 The wt% values in are the masses of polyethylene powder captured by different sieve mesh sizes.

[0038] The method as described above, having any one of the limitations (i) to (iii): (i) wherein the morphology-improved polyethylene powder has 2.5 weight percent (wt%) to not more than 5.5 wt% of polyethylene fines, where polyethylene fines are defined as polyethylene particles having a diameter of 74 micrometers (μm) or less; (ii) wherein the morphology-improved polyethylene powder has an average particle size of 0.360 mm to 0.480 mm; or (iii) both limitations (i) and (ii).

[0039] The method as described above, having any one of the limitations (i) to (iii): (i) the temperature of the gas-phase reactor is 70 °C to 120 °C, 80 °C to 115 °C, or 81 °C to 89 °C; (ii) the gas-phase reactor also contains 1 weight percent (wt%) to 20 wt% of an induced condensation agent ("ICA") selected from (C5-C7) alkanes, based on the total weight of the contents in the gas-phase reactor, where preferably the ICA is isopentane; or (iii) both limitations (i) and (ii).

[0040] This method inhibits catalyst ignition as well as reactor overheating and fouling. This method inhibits the ignition of the SD / SiS-metallocene catalyst and reduces overheating and fouling in the gas-phase reactor. This method improves the operability of the gas-phase reactor by extending the time between reactor shutdowns for cleaning and improves the quality and consistency of the composition, resin properties, and the performance of the polyethylene powder thus prepared.

[0041] Conventionally dried silica-supported metallocene catalysts are typically fed into the gas-phase reactor without causing significant overheating or fouling.

[0042] This method improves the morphology of polyethylene powder. This method also improves the morphology of polyethylene powder. The morphological improvement includes: (i) inhibiting the formation of polyethylene particles that are too small (fine powder), which are defined as polyethylene particles having a diameter of 74 microns or less; and (ii) increasing the average particle size (APS), which indicates a shift of the particle size distribution curve towards higher diameters.

[0043] This method uses a reactive olefin prepolymer. The reactive olefin prepolymer contains a component that is a polyolefin and a component that is an active metallocene derivative of a spray-dried silica-supported metallocene catalyst ("SD / SiS-metallocene catalyst"). The reactive olefin prepolymer has a prepolymer / catalyst weight / weight ratio of 10:1.0 to 50:1.0, where the weight of the prepolymer is the total weight of the reactive olefin prepolymer and the weight of the catalyst is the weight of the spray-dried silica-supported metallocene catalyst. If the prepolymer / catalyst weight / weight ratio is too low, i.e., less than 10:1.0, there may be too little olefin prepolymer component, and thus the ignition of the SD / SiS-metallocene catalyst may be too fast and may not be sufficiently inhibited, which may lead to greater overheating and fouling in the gas-phase reactor. If the prepolymer / catalyst weight / weight ratio is too high, i.e., greater than 50:1.0, there may be too much olefin prepolymer component, and thus the ignition of the SD / SiS-metallocene catalyst may be too slow and may be overly inhibited, which may reduce the catalytic activity of this method.

[0044] The reactive olefin prepolymer is prepared by polymerizing an olefin monomer in a hydrocarbon diluent using a spray-dried silica-supported metallocene catalyst under mild conditions. The reactive olefin prepolymer is prepared by mixing a measured preliminary amount of an olefin monomer with a measured amount of a spray-dried silica-supported metallocene catalyst in an alkane liquid phase in a slurry-phase reactor at a temperature of 30 °C to 70 °C, an ethylene partial pressure of no more than 861 kPa, and a total reactor pressure of no more than 2450 kPa to prepare the reactive olefin prepolymer via slurry-phase polymerization. The measured preliminary amount of the olefin monomer and the measured amount of the spray-dried silica-supported metallocene catalyst result in a prepolymer / catalyst weight / weight ratio of the reactive olefin prepolymer of 10:1.0 to no more than 50:1.0, where the weight of the prepolymer is the total weight of the reactive olefin prepolymer and the weight of the catalyst is the weight of the spray-dried silica-supported metallocene catalyst. The prepolymer / catalyst weight / weight ratio can be adjusted within this range by using a higher or lower amount of the spray-dried silica-supported metallocene catalyst relative to the amount of the olefin monomer. If the polymerization temperature is too low, i.e., below 30 °C, the slurry-phase polymerization may take too long to prepare the reactive olefin prepolymer and / or the weight / weight ratio of the prepolymer / catalyst may be too low, which may cause the problems discussed above. If the polymerization temperature is too high, i.e., above 70 °C, the slurry-phase polymerization may overheat and / or the weight / weight ratio of the prepolymer / catalyst may be too high, which may cause the problems discussed above. In some embodiments, the olefin monomer used to prepare the reactive olefin prepolymer comprises at least 90 wt% ethylene or consists of 100 wt% ethylene, and the reactive olefin prepolymer is the reactive ethylene prepolymer described previously.

[0045] Spray-dried silica-supported metallocene catalyst. Any spray-dried silica-supported metallocene catalyst can be used in the method. The SD / SiS-metallocene catalyst is prepared by spray-drying a mixture of two or more of its reactants in a hydrocarbon diluent. Any spray-drying method can be used. The reactants used to prepare the SD / SiS-metallocene catalyst comprise a metallocene pre-catalyst, a silica support, and an activator. The SD / SiS-metallocene catalyst has a core-shell particle morphology. The particle morphology of the SD / SiS-metallocene catalyst is different from that of a conventionally dried silica-supported metallocene catalyst prepared from the same components. These differences in particle morphology are illustrated by comparing Figure 4 and Figure 5 in the cartoon drawings. Figure 4The catalyst particle morphology of a plurality of conventionally dried silica-supported metallocene catalyst particles is shown, where "SiO2" represents silica support particles and "active metal" represents metallocene catalyst particles. The conventionally dried catalyst comprises a matrix of different particles predominantly of silica and different particles predominantly of active metallocene catalyst. Figure 5 The core-shell catalyst particle morphology of a single particle of a spray-dried silica-supported metallocene catalyst is shown. The spray-dried silica-supported metallocene catalyst comprises a plurality of such core-shell particles. In each core-shell particle, the core is predominantly silica and the shell is predominantly active metallocene catalyst. In both cases, the active metallocene catalyst refers to the product obtained by contacting a metallocene precatalyst (e.g., bis(n-propylcyclopentadienyl)dimethylhafnium) with an activator (e.g., MAO). The morphology is based on information obtained from SEM images of the conventionally dried or spray-dried catalyst particles. The cartoon drawings are not necessarily to scale (particle size is ignored) and are only used to roughly depict these morphological differences. Compare Figure 4 with Figure 5 shows how the conventionally dried silica-supported metallocene catalyst particles are a heterogeneous blend of different types of different particles: some particles are metallocene catalyst particles and other particles are activator / silica particles. In contrast, the SD / SiS-metallocene catalyst particles are a homogeneous blend of core-shell particles, where the activator and metallocene catalyst components are in the shell and the silica support is in the core of the core-shell particles.

[0046] Metallocene precatalyst. In some embodiments, the metallocene precatalyst is as described in US7873112B2, column 11, line 17 to column 22, line 21. In some aspects, the metallocene precatalyst is the substance named in US7873112B2, column 18, line 51 to column 22, line 5.

[0047] In some embodiments, the metallocene precatalyst is a compound of formula (I): where M is Ti, Hf or Zr; each R 1 to R 5 is independently an unsubstituted (C1-C6) alkyl group, or R 1 and R 2 bonded together to comprise a divalent alkylene group selected from the group consisting of: -C(R a )=C(R b )-C(R c )=C(R d )- and -C(R a )2-C(R b )2-C(Rc ) 2-C(R d ) 2-, where R a to R d each of which is independently H or methyl; and each X is a leaving group selected from the group consisting of: halogen, an unsubstituted (C1-C6) alkyl group, benzyl, and trimethylsilylmethyl.

[0048] In some aspects, the metallocene precatalyst is selected from: bis(η 5 -tetramethylcyclopentadienyl)zirconium dichloride; bis(η 5 -tetramethylcyclopentadienyl)zirconium dimethyl; bis(η 5 -pentamethylcyclopentadienyl)zirconium dichloride; bis(η 5 -pentamethylcyclopentadienyl)zirconium dimethyl; (1,3-dimethyl-4,5,6,7-tetrahydroindenyl)(1-methylcyclopentadienyl)zirconium dimethyl; bis(1-methyl-3-n-butylcyclopentadienyl)zirconium dichloride; bis(1-methyl-3-n-butylcyclopentadienyl)zirconium dimethyl; bis(n-propylcyclopentadienyl)hafnium dichloride; bis(n-propylcyclopentadienyl)hafnium dimethyl; bis(n-butylcyclopentadienyl)zirconium dichloride; (cyclopentadienyl)(1,5-dimethylindenyl)zirconium dimethyl; (methylcyclopentadienyl)(1,5-dimethylindenyl)zirconium dimethyl; (cyclopentadienyl)(1,4-dimethylindenyl)zirconium dimethyl; (methylcyclopentadienyl)(1,4-dimethylindenyl)zirconium dimethyl; and bis(n-butylcyclopentadienyl)zirconium dimethyl. In some aspects, the metallocene catalyst is the product of the activation reaction of an activator with any one of the foregoing metallocene precatalysts.

[0049] In some embodiments, the compound of formula (I) is a compound of formula (Ia):

[0050] where M is Hf or Zr, each R 1 is independently a (C1-C6) alkyl group, and each X is a leaving group. In some embodiments, the metallocene precatalyst has the formula (Ia), where M is Hf, each R 1 is CH2CH2CH3, and each X is Cl or methyl. The latter metallocene precatalysts are bis(n-propylcyclopentadienyl)hafnium dichloride and bis(n-propylcyclopentadienyl)hafnium dimethyl.

[0051] Silica support. The silica support is a particulate solid of amorphous silica. The silica support can be semi-porous or porous. The silica support can independently be untreated pyrogenic silica, alternatively calcined untreated pyrogenic silica, alternatively pyrogenic silica treated with a hydrophobizing agent, alternatively pyrogenic silica treated with calcination and a hydrophobizing agent.

[0052] Before contacting with a catalyst or a pre-catalyst, the silica support can be pretreated by heating the silica support in air to obtain a calcined silica support. The pretreatment includes heating the silica support at a peak temperature of 350 °C to 850 °C, alternatively 400 °C to 800 °C, alternatively 400 °C to 700 °C, alternatively 500 °C to 650 °C, and for a period of 2 hours to 24 hours, alternatively 4 hours to 16 hours, alternatively 8 hours to 12 hours, alternatively 1 hour to 4 hours, thereby preparing a calcined silica support. The silica support can be a calcined silica support.

[0053] The silica support has a variable surface area, pore volume, and average particle size. In some embodiments, the silica support has a surface area of 10 square meters per gram (m 2 / g) to 1000 m 2 / g, an average particle size of 20 micrometers (μm) to 300 μm, or both. The surface area is 200 m 2 / g to 600 m 2 / g. The silica support can have a surface area in the range of about 10 m 2 / g to about 700 m 2 / g, a pore volume in the range of about 0.1 cm 3 / g to about 4.0 cm 3 / g, and an average particle size in the range of about 20 micrometers to about 500 μm.

[0054] The silica support can have a pore volume of 0.5 cubic centimeters per gram (cc / g) to 6.0 cc / g or 1.1 cc / g to 1.8 cc / g, and a surface area of 245 m 2 / g to 375 m 2 / g. Alternatively, the pore volume is 2.4 cc / g to 3.7 cc / g, and the surface area is 410 m 2 / g to 620 m 2 / g. Alternatively, the pore volume is 0.9 cc / g to 1.4 cc / g, and the surface area is 390 m 2 / g to 590 m 2 / g. Each of these properties is measured using conventional techniques known in the art.

[0055] The silica support can be amorphous silica, alternatively high surface area amorphous silica (e.g., 500 m 2 / g to 1000 m 2 / g). Such silica can be commercially available from several sources, including the Davison Chemical Division of W.R. Grace and Company (e.g., Davison 952 and Davison 955 products) and PQ Corporation (e.g., ES70 product). The silica support can be in the form of spherical particles obtained by a spray drying method. Alternatively, the MS3050 product is silica from PQ Corporation that has not been spray dried. As obtained, these silicas are not calcined (i.e., not dehydrated). Silica that has been calcined before purchase can also be used as the support material.

[0056] The pyrogenic silica can be hydrophilic (untreated), alternatively hydrophobic (treated). In some aspects, the silica support is hydrophobic pyrogenic silica. Hydrophobic pyrogenic silica is the product of pretreating hydrophilic pyrogenic silica (untreated) with a silicon-based hydrophobizing agent selected from: trimethylsilyl chloride, dimethyldichlorosilane, polydimethylsiloxane fluid, hexamethyldisilazane, octyltrialkoxysilane (e.g., octyltrimethoxysilane) and any combination of two or more thereof; alternatively, dimethyldichlorosilane. An example of hydrophobic pyrogenic silica is CAB-O-SIL hydrophobic pyrogenic silica available from Cabot Corporation, Alpharetta, Georgia, USA. When the hydrophobizing agent is dimethyldichlorosilane, an example of the hydrophobic pyrogenic silica is CAB-O-SIL TS610 from Cabot Corporation. In some aspects, the silica support is hydrophobic pyrogenic silica that has been surface treated with dimethyldichlorosilane ((CH3)2SiCl2); this silica support can be Cabosil TM TS-610 and is commercially available from Cabot Corporation.

[0057] Activators. Any activators can be the same as or different from each other and can independently be a Lewis acid, a non-coordinating ionic activator or an ionizing activator or a Lewis base, an alkylaluminum or an alkylaluminoxane. The alkylaluminum can be a trialkylaluminum, an alkylaluminum halide or an alkylaluminum alkoxide (diethyl ethoxyaluminum). The trialkylaluminum can be trimethylaluminum, triethylaluminum (“TEAl”), tripropylaluminum or tri(2-methylpropyl)aluminum. The alkylaluminum halide can be diethylaluminum chloride. The alkylaluminum alkoxide can be diethyl ethoxyaluminum. The alkylaluminoxane can be methylaluminoxane (MAO), ethylaluminoxane, 2-methylpropyl-aluminoxane or modified methylaluminoxane (MMAO). Each alkyl of the alkylaluminum or alkylaluminoxane can independently be a (C1-C7)alkyl, alternatively a (C1-C6)alkyl, alternatively a (C1-C4)alkyl. The molar ratio of the metal (Al) of the activator to the metal (catalytic metal, e.g., Zr) of the specific catalyst compound can be from 1000:1 to 0.5:1, alternatively from 300:1 to 1:1, alternatively from 150:1 to 1:1. Suitable activators are commercially available.

[0058] The spray-dried silica-supported metallocene catalyst (“SD / SiS-metallocene catalyst”) is prepared by spray-drying a mixture of a metallocene pre-catalyst, a silica support, an activator and a hydrocarbon diluent. Spray-drying methods and equipment are well known in the art of catalysts and include those described in US5648310.

[0059] Hydrocarbon diluents. The hydrocarbon diluents can be alkanes, aromatics, alkyl aromatics (e.g., toluene), or aryl alkanes (e.g., phenylpropane). Examples of hydrocarbon diluents are alkanes such as mineral oil, pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, etc., and toluene and xylene. In one embodiment, the hydrocarbon diluent is an alkane or a mixture of alkanes, where each alkane independently has 4 to 20 carbon atoms, alternatively 5 to 12 carbon atoms, alternatively 5 to 10 carbon atoms. Each alkane can independently be acyclic or cyclic. Each acyclic alkane can independently be straight-chain or branched. The acyclic alkanes can be 2-methylpropane (isobutane), pentane, 1-methylbutane (isopentane), hexane, 1-methylpentane (isohexane), heptane, 1-methylhexane (isoheptane), octane, nonane, decane, or a mixture of any two or more of them. The cyclic alkanes can be cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, methylcyclopentane, methylcyclohexane, dimethylcyclopentane, or a mixture of any two or more of them. Additional examples of suitable alkanes include Isopar-C, Isopar-E, and mineral oils such as paraffin oil. In some aspects, the hydrocarbon diluent does not contain mineral oil. The hydrocarbon diluent can consist of one or more (C5-C 12 ) alkanes. In some embodiments, the hydrocarbon diluent is isopentane.

[0060] The SD / SiS-metallocene catalysts differ from the conventional dry-supported metallocene catalysts in terms of composition and catalytic activity in their different drying preparations.

[0061] Olefin monomers. The olefin monomers for preparing the reactive olefin prepolymer and the olefin monomers for preparing the polyethylene powder can be the same or different. The olefins for preparing the polyethylene powder include ethylene. The olefin monomers for preparing the reactive olefin prepolymer can be any olefin selected from the group consisting of ethylene, propylene, (C4-C 20 ) α-olefins, or any combination of two or more of them. In some embodiments, the olefin monomers for preparing the prepolymer and the powder are the same. (C4-C 20 ) α-olefins can be (C4-C 10 ) α-olefins or (C4-C8) α-olefins. In an embodiment, the (C4-C8) α-olefins can independently be 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, or 1-octene; alternatively 1-butene, 1-hexene, or 1-octene; alternatively 1-butene or 1-hexene; alternatively 1-hexene or 1-octene; alternatively 1-butene; alternatively 1-hexene; alternatively 1-octene; alternatively a combination of 1-butene and 1-hexene; alternatively a combination of 1-hexene and 1-octene. Generally, the 1-olefin can be 1-hexene.

[0062] Slurry phase reactor. Slurry phase reactors are well known in the art. Any slurry phase reactor capable of polymerizing ethylene can be used.

[0063] Gas phase reactor. Gas phase reactors and processes are well known in the art. Any gas phase reactor for polymerizing ethylene can be used. For example, FB-GPP reactors / processes can be as described in US 3,709,853; US 4,003,712; US 4,011,382; US 4,302,566; US 4,543,399; US 4,882,400; US 5,352,749; US 5,541,270; EP-A-0802 202; and Belgian Patent No. 839,380. These SB-GPP and FB-GPP polymerization reactors and processes mechanically agitate or fluidize the polymerization medium inside the reactor by the continuous flow of gaseous monomers and diluents. Other useful reactors / processes contemplated include tandem or multi-stage polymerization processes such as those described in US 5,627,242; US 5,665,818; US 5,677,375; EP-A-0 794 200; EP-B1-0 649 992; EP-A-0 802 202; and EP-B-634421.

[0064] The gas phase reactor can be a fluidized bed gas phase polymerization (FB-GPP) reactor, and the effective polymerization conditions can include the following reaction conditions: the FB-GPP reactor has a fluidized bed with a bed temperature of 70 degrees Celsius (°C) to 120 °C; the FB-GPP reactor receives a feed of a reactive olefin prepolymer and an olefin comonomer with an independently controlled amount of ethylene and an optional ethylene / comonomer molar ratio. The gas phase reactor can optionally receive a feed of hydrogen gas (H2) for controlling the molecular weight of the polyethylene powder in terms of the hydrogen to ethylene (H2 / C2) molar ratio or in terms of the ratio of parts per million by weight of H2 to mole percent of C2 (H2 ppm / C2 mol%). The gas phase reactor can also receive a feed of an induced condensing agent (ICA) for controlling the heat in the reactor.

[0065] In some embodiments, the FB-GPP reactor is a commercial scale reactor described by Savatsky et al. for Univation Technologies, LLC, Houston, Texas in WO 2016 / 172567 A1.

[0066] In some embodiments, the FB-GPP reactor is a commercial-scale reactor, such as UNIPOL available from Univation Technologies, LLC, a subsidiary of The Dow Chemical Company, Midland, Michigan, USA. TM reactor.

[0067] Induced Condensing Agent (ICA). In a gas-phase reactor, the ICA can be used in a condensing mode to absorb the heat of the exothermic polymerization reaction. The ICA is typically one or more (C5-C 10 ) alkanes. The ICA can be fed separately into the FB-GPP reactor or as part of a mixture that also contains a reactive olefin prepolymer. The ICA can be (C5-C 20 ) alkanes, alternatively (C5-C 10 ) alkanes, alternatively (C5) alkanes, such as pentane or 2-methylbutane; hexane; heptane; octane; nonane; decane; or a combination of any two or more thereof. Typically, the ICA is isopentane (2-methylbutane). Aspects of the polymerization process using the ICA can be referred to as Induced Condensation Mode Operation (ICMO). ICMO is described in US 4,453,399; US 4,588,790; US 4,994,534; US 5,352,749; US 5,462,999; and US 6,489,408. The ICA concentration in the reactor is indirectly measured as the total concentration of the discharged ICA by calibrating the peak area percentage to mole percentage (mol%) using a gas mixture standard of suitable gas components with known concentrations by gas chromatography.

[0068] The polymerization conditions can also include one or more additives, such as a chain transfer agent or a promoter.

[0069] The reactive olefin prepolymer is prepared by slurry-phase polymerization in a slurry-phase reactor that is different from the gas-phase polymerization and reactor for preparing the morphology-improved polyethylene powder. The components of the reactive olefin prepolymer are in the same particles. That is, the particles of the olefin prepolymer component are not blended with the particles of the catalyst component.

[0070] The step of removing catalyst fines from the spray-dried silica-supported metallocene catalyst may include screening or electrostatic filtering the spray-dried silica-supported metallocene catalyst. In some embodiments, the spray-dried silica-supported metallocene catalyst has from 10 weight percent (wt%) to no more than 40 wt% of catalyst fines, which are defined as catalyst particles having a diameter of 10 micrometers (μm) or less. In some embodiments, the SD / SiS-metallocene catalyst has from 20 wt% to 35 wt% of catalyst fines, alternatively from 24 wt% to 31 wt% of catalyst fines, alternatively from 23 wt% to 27 wt% of catalyst fines, alternatively from 28 wt% to 32 wt% of catalyst fines, alternatively 25 wt% ± 1 wt% of catalyst fines, alternatively 30 wt% ± 1 wt% of catalyst fines.

[0071] The spray-dried silica-supported metallocene catalyst is prepared and separated from the reactive olefin prepolymer prior to its preparation, and the reactive olefin polymer is prepared and separated from the polyolefin powder prior to its preparation.

[0072] The morphology-improved polyethylene powder has a reduced amount of polyethylene aggregates relative to the amount of polyethylene aggregates in the comparative polyethylene powder.

[0073] When measured by gas-phase polymerization in a reactor with ethylene at an ethylene partial pressure of 85 °C, 1034 kPa and a total reactor pressure of 2447 kPa, the catalytic activity of the reactive olefin prepolymer is from 90% to less than or equal to 100% of the catalytic activity of the spray-dried silica-supported metallocene catalyst.

[0074] The weight / weight ratio of the alkane liquid phase to the total olefin monomer is from 5:1.0 to 800:1.0.

[0075] The alkane in the liquid phase has from 4 to 10 carbon atoms per molecule.

[0076] The olefin prepolymer has a number average molecular weight (M n ) of from 5,000 grams per mole to 50,000 g / mol.

[0077] In some embodiments, the metallocene precatalyst is bis(n-propylcyclopentadienyl)hafnium dichloride or bis(n-propylcyclopentadienyl)hafnium dimethyl, which is a metallocene precatalyst of formula (Ia):

[0078] where M is Hf, each R 1 is CH2CH2CH3, and each X is Cl or methyl.

[0079] The catalytic activity is the mass of polyethylene powder produced per unit weight of catalyst per hour.

[0080] Alternatively, before different embodiments. ASTM means the standardization organization, ASTM International, West Conshohocken, Pennsylvania, USA. Any comparative example is for illustrative purposes only and should not be prior art. Free of or lacking means completely absent; alternatively undetectable. ISO is the International Organization for Standardization, Chemin de Blandonnet 8, CP 401 - 1214, Vernier, Geneva, Switzerland. IUPAC is the International Union of Pure and Applied Chemistry (IUPAC Secretariat, Research Triangle Park, North Carolina, USA). An option may be granted, but is not essential. Operable means functionally capable or effective. Optional(ly) means absent (or excluded) alternatively present (or included). PAS is the Publicly Available Specification, Deutsches Institut für Normunng e.V. (DIN, German Institute for Standardization), and properties can be measured using standard test methods and conditions. A range includes endpoints, sub - ranges, and integral and / or fractional values contained therein, except for an integral range excluding fractional values. Room temperature: 23 °C ± 1 °C.

[0081] Unless otherwise defined, the terms used herein have their IUPAC meanings. See, for example, Compendium of Chemical Terminology. Gold Book, 2.3.3 edition, February 24, 2014.

[0082] Ignition vial test method: Add a mineral oil slurry of a catalyst with fast ignition loaded on treated fumed silica or a mineral oil / toluene slurry of a weakened post-metallocene catalyst loaded on treated fumed silica to a dry 40 mL glass vial. Add 5.5 mL or 11 mL of 1-octene to the vial and seal the vial with a septum cap. Record the addition time as T0 (0.00 minutes). Manually shake (without stirring) the vial to prevent caking. Then place the shaken vial in different holes of a foam block located on a hot plate / stirrer. Immediately insert a thermocouple through the septum cap below the liquid level in the vial and record the temperature (°C) of the vial contents every 5 seconds from T0 to 300 minutes after T0. Download the temperature and time data to a spreadsheet and plot a thermokinetic curve for analysis. The results of these runs can be graphically depicted as a plot of the reaction temperature of the batch reactor contents on the y-axis versus the time starting from Time0 at addition on the x-axis.

[0083] Example

[0084] The experimental method involves slurry-phase polymerization of olefin monomers using an SD / SiS metallocene catalyst in a suitable solvent under milder conditions (35 °C to 50 °C, ethylene partial pressure up to 861 kPa, and total reactor pressure up to 2450 kPa (355 pounds per square inch (psi))) to prepare a reactive olefin prepolymer with controlled morphology in the first step. To maintain the catalytic activity of this reactive olefin prepolymer without reduction, the prepolymer is then directly fed into a gas-phase reactor to polymerize ethylene in the second step to produce polyethylene powder. This two-step sequence results in controlled catalytic activity in the gas-phase reactor and allows control of the level of fines generated in the gas-phase reactor and thus control of the morphology of the product polyethylene powder. Advantageously, the controlled morphology of the reactive olefin prepolymer in the first step enables us to feed the prepolymer into the gas-phase reactor using a simple 0.635 cm (1 / 4 inch) inner diameter feed injection tube instead of a complex tube-in-tube feed injector system typically used to feed an SD / SiS metallocene catalyst into the gas-phase reactor.

[0085] Fines test method: Measure fines using a 200 mesh sieve (74 μm).

[0086] Average particle size (APS) and particle size distribution (PSD) test method: Measure the average particle size (APS) and particle size distribution (PSD) using a series of sieve mesh sizes from 10 mesh size to 325 mesh size, alternatively from 10 mesh size to 200 mesh size. The various mesh sizes and their respective micron sizes are described elsewhere herein. This is the test method for measuring the APS data of the examples shown in Table 1 later and generating Figure 3 the particle size distribution of the examples shown.

[0087] Volume fraction particle size test method: The volume fraction particle size is measured using a Mastersizer 3000 particle size analyzer instrument from Malvern Panalytical Ltd (a Spectris company), including the d90 particle size at 90% volume fraction and the d10 particle size at 10% volume fraction. This is the test method used to generate the d90 and d10 data, which are used to calculate the d90 / d10 ratio shown later in Table 1.

[0088] Preparation 1: For the examples, the SD / SiS-metallocene catalyst was prepared as follows. A mixture of a metallocene precatalyst, bis(n-propylcyclopentadienyl)dimethylhafnium, a hydrophobic pyrogenic silica support, pyrogenic silica treated with dichlorodimethylsilane, and an activator (methylaluminoxane (MAO)) in mineral oil / ISOPAR C was prepared. The mixture contained 16.4 wt% of solid powder. Based on the total weight of the solid powder, the solid powder contained 0.8 wt% of Hf atoms and 16.4 wt% of aluminum atoms. The mixture was spray-dried under the following conditions to prepare the SD / SiS-metallocene catalyst, i.e., a spray-dried silica-supported bis(n-propylcyclopentadienyl)dimethylhafnium catalyst. Spray-drying conditions: The spray dryer apparatus had an outlet temperature of 80 °C and an atomizer speed of 22,500 revolutions per minute (rpm). The resulting spray-dried silica-supported bis(n-propylcyclopentadienyl)dimethylhafnium catalyst contained 0.045 millimoles (mmol) of Hf atoms and 6 mmol of Al atoms (from the activator) per 1.0 gram of total weight of the SD / SiS-metallocene. If used to polymerize ethylene in a gas-phase reactor in the comparative example, this catalyst could produce a comparative polyethylene powder containing up to 10 wt% of polyethylene fines. The catalyst of Preparation 1 was prepared in one batch. Two samples (Sample A and Sample B) were taken from this batch at different times, and it was found that they had different amounts of catalyst fines. Sample A contained 30.2 wt% of catalyst fines (particles with a diameter of 10 μm or less), and Sample B contained 25 wt% of catalyst fines.

[0089] Figure 1 is a graph of the volume percentage (volume %) (y-axis) versus the particle size in micrometers (μm) (x-axis) for the SD / SiS-metallocene catalysts of Sample A and Sample B of Preparation 1. In Figure 1 it, the graph of Sample A had the shortest peak with the maximum volume % at a particle size of approximately 15 μm, and Sample B had the tallest peak with the maximum volume % at a particle size of approximately 16 μm.

[0090] Comparative Example 1 (CE1): In a gas-phase reactor at a temperature of 85 °C, an ethylene partial pressure of 1034 kPa, a total reaction pressure of 2413 kPa and containing 15% isopentane, the gas-phase polymerization of ethylene was catalyzed by the spray-dried silica-supported bis(n-propylcyclopentadienyl)hafnium catalyst of Sample A of Preparation 1 to prepare a comparative polyethylene powder, which had: (i) 6.0 wt% of polyethylene fines having a diameter greater than 0 μm to 74 μm; and (ii) an average particle size (APS) of 0.333 millimeters (mm).

[0091] Comparative Example 2 (CE2): In a gas-phase reactor at a temperature of 85 °C, an ethylene partial pressure of 1034 kPa, a total reaction pressure of 2413 kPa and containing 15% isopentane, the gas-phase polymerization of ethylene was catalyzed by the spray-dried silica-supported bis(n-propylcyclopentadienyl)hafnium catalyst of Sample B of Preparation 1 to prepare a comparative polyethylene powder, which had: (i) 3.0 wt% of polyethylene fines having a diameter greater than 0 μm to 74 μm; and (ii) an APS of 0.457 mm.

[0092] Examples of the method of the present invention are as follows to improve the morphology of the polyethylene powder. Examples of reactive olefin prepolymers containing spray-dried silica-supported bis(n-propylcyclopentadienyl)dimethylhafnium catalysts with different loadings were prepared by slurry-phase polymerization of ethylene monomer at different reactor temperatures.

[0093] Inventive Example 1A (IE1A, 35 °C, 20 g / 1.0 g): A reactive olefin prepolymer, which is a reactive ethylene prepolymer, was prepared by slurry-phase polymerization of a measured amount of ethylene with a measured amount of the spray-dried silica-supported bis(n-propylcyclopentadienyl)hafnium catalyst of Sample A of Preparation 1 in isopentane at a reactor temperature of 35 °C, an ethylene partial pressure of 158.7 kPa and a total reaction pressure of 2447 kPa to prepare a reactive ethylene prepolymer containing a component that is a polyethylene prepolymer and a component that is an active metallocene derivative of the spray-dried silica-supported bis(n-propylcyclopentadienyl)hafnium catalyst, wherein the reactive ethylene prepolymer has a prepolymer / catalyst weight / weight ratio of 20 grams:1.0 gram, where the prepolymer weight is the total weight of the reactive ethylene prepolymer and the catalyst weight is the weight of the spray-dried silica-supported metallocene catalyst.

[0094] Inventive Example 1B (IE1B): At a temperature of 85 °C, an ethylene partial pressure of 1034 kPa, and a total reactor pressure of 2413 kPa, gas-phase polymerization of ethylene with the reactive ethylene prepolymer of IE1A in a gas-phase reactor produces polyethylene powder with improved morphology, having: (i) 5.3 wt% of polyethylene fines having a diameter greater than 0 μm to 74 μm, a 11% reduction in polyethylene fines relative to the comparative polyethylene powder of Comparative Example 1; and (ii) an APS of 0.363 mm, a 9.0% increase relative to the APS of the comparative polyethylene powder.

[0095] Inventive Example 2A (IE2A, 50 °C, 20 g / 1.0 g): A reactive olefin prepolymer, which is a reactive ethylene prepolymer, is prepared by slurry-phase polymerization of a measured amount of ethylene with a measured amount of the spray-dried silica-supported bis(n-propylcyclopentadienyl)hafnium catalyst of Sample A of Preparation 1 in isopentane at a reactor temperature of 50 °C, an ethylene partial pressure of 158.7 kPa, and a total reaction pressure of 2447 kPa to prepare a reactive ethylene prepolymer comprising a component that is a polyethylene prepolymer and a component that is an active metallocene derivative of the spray-dried silica-supported bis(n-propylcyclopentadienyl)hafnium catalyst, wherein the reactive ethylene prepolymer has a prepolymer / catalyst weight / weight ratio of 20 g:1.0 g, where the prepolymer weight is the total weight of the reactive ethylene prepolymer and the catalyst weight is the weight of the spray-dried silica-supported metallocene catalyst.

[0096] Inventive Example 2B (IE2B): At a temperature of 85 °C, an ethylene partial pressure of 1034 kPa, and a total reactor pressure of 2413 kPa, gas-phase polymerization of ethylene with the reactive ethylene prepolymer of IE2A in a gas-phase reactor produces polyethylene powder with improved morphology, having: (i) 2.6 wt% of polyethylene fines having a diameter greater than 0 μm to 74 μm, a 56% reduction in polyethylene fines relative to the comparative polyethylene powder of Comparative Example 1; and (ii) an APS of 0.467 mm, a 40.2% increase relative to the APS of the comparative polyethylene powder.

[0097] Inventive Example 3A (IE3A, 50 °C, 40 g / 1.0 g): A reactive olefin prepolymer, which is a reactive ethylene prepolymer, was prepared by slurry-phase polymerizing a measured amount of ethylene with a spray-dried silica-supported bis(n-propylcyclopentadienyl)hafnium catalyst of Sample A of Preparation 1 in isopentane at a reactor temperature of 50 °C, an ethylene partial pressure of 279.2 kPa, and a total reaction pressure of 2447 kPa to prepare a reactive ethylene prepolymer comprising a component that is a polyethylene prepolymer and a component that is an active metallocene derivative of a spray-dried silica-supported bis(n-propylcyclopentadienyl)hafnium catalyst, wherein the reactive ethylene prepolymer has a prepolymer / catalyst weight / weight ratio of 40 g:1.0 g, wherein the prepolymer weight is the total weight of the reactive ethylene prepolymer, and the catalyst weight is the weight of the spray-dried silica-supported metallocene catalyst.

[0098] Inventive Example 3B (IE3B): Gas-phase polymerization of ethylene with the reactive ethylene prepolymer of IE3A in a gas-phase reactor at a temperature of 85 °C, an ethylene partial pressure of 1034 kPa, and a total reactor pressure of 2413 kPa produced a polyethylene powder with improved morphology, having: (i) 3.10 wt% of polyethylene fines having a diameter greater than 0 μm to 74 μm, a 48% reduction relative to the polyethylene fines of the polyethylene powder of Comparative Example 1; and (ii) an APS of 0.470 mm, a 41.1% increase relative to the APS of the comparative polyethylene powder.

[0099] Figure 2 It is a graph of volume fraction (fraction, %) (y-axis) versus particle size in micrometers (particle size (micrometers)) on a scale of 0 μm to 2,000 μm for Comparative Example 1 and Inventive Examples 1B, 2B, and 3B. "Micrometer" is also denoted as μm. Figure 2 The results shown illustrate the reduction in fines and increase in APS of the polyethylene powder with improved morphology relative to the comparative polyethylene powder.

[0100] Inventive Example 4A (IE4A, 50 °C, 20 g / 1.0 g): A reactive olefin prepolymer, which is a reactive ethylene prepolymer, was prepared by slurry-phase polymerization of a measured amount of ethylene with a spray-dried silica-supported bis(n-propylcyclopentadienyl)hafnium catalyst of the sample B of Preparation 1 in isopentane at a reactor temperature of 50 °C, an ethylene partial pressure of 83.2 kPa, and a total reaction pressure of 2447 kPa to prepare a reactive ethylene prepolymer comprising a component that is a polyethylene prepolymer and a component that is an active metallocene derivative of the spray-dried silica-supported bis(n-propylcyclopentadienyl)hafnium catalyst, wherein the reactive ethylene prepolymer has a prepolymer / catalyst weight / weight ratio of 20 g:1.0 g, where the prepolymer weight is the total weight of the reactive ethylene prepolymer and the catalyst weight is the weight of the spray-dried silica-supported metallocene catalyst.

[0101] Inventive Example 4B (IE4B): Gas-phase polymerization of ethylene with the reactive ethylene prepolymer of IE4A in a gas-phase reactor at a temperature of 85 °C, an ethylene partial pressure of 1034 kPa, and a total reactor pressure of 2413 kPa produced a polyethylene powder with improved morphology, which had: (i) 2.0 wt% of polyethylene fines with a diameter greater than 0 μm to 74 μm, a 33% reduction in polyethylene fines compared to the comparative polyethylene powder of Comparative Example 2; and (ii) an APS of 0.381 mm, a 16.6% reduction in APS compared to the comparative polyethylene powder.

[0102] The results of Comparative Example 1 and Comparative Example 2 and Inventive Examples 1B, 2B, 3B, and 4B are shown in Table 1.

[0103] Table 1: Weight percentage and APS of fine powder 。

[0104]

[0105] In Table 1, the method of the present invention improves the morphology of the polyethylene powder prepared in the gas-phase reactor by reducing the wt% of polyethylene (PE) fines. The polyethylene powders with improved morphology of IE1B to IE3B have an increased average particle size (APS) of the polyethylene powder of the present invention compared to their comparative polyethylene powders. The polyethylene powder with improved morphology of IE4B has a reduced average particle size (APS) of the polyethylene powder of the present invention compared to its comparative polyethylene powder.

Claims

1. A method for preparing polyethylene powder with improved morphology, the method comprising: Contacting ethylene with a reactive olefin prepolymer in a gas phase reactor to prepare polyethylene powder with improved morphology via gas phase polymerization; Wherein the reactive olefin prepolymer comprises a component that is a polyolefin and a component that is an active metallocene derivative of a spray-dried silica-supported metallocene catalyst; wherein the reactive olefin prepolymer has a prepolymer / catalyst weight / weight ratio of 10:1.0 to 50:1.0, wherein the weight of the prepolymer is the total weight of the reactive olefin prepolymer, and the weight of the catalyst is the weight of the spray-dried silica-supported metallocene catalyst.

2. The method according to claim 1, the method comprising: The reactive olefin prepolymer is prepared by: mixing a measured preparatory amount of olefin monomer with a measured amount of the spray-dried silica-supported metallocene catalyst in an alkane liquid phase in a slurry phase reactor at a temperature of 30 °C to 70 °C, an ethylene partial pressure not exceeding 861 kPa, and a total reactor pressure not exceeding 2450 kPa to prepare the reactive olefin prepolymer via slurry phase polymerization; wherein the measured preparatory amount of olefin monomer and the measured amount of the spray-dried silica-supported metallocene catalyst produce a prepolymer / catalyst weight / weight ratio of 10:1.0 to not exceeding 50:1.0, wherein the weight of the prepolymer is the total weight of the reactive olefin prepolymer, and the weight of the catalyst is the weight of the spray-dried silica-supported metallocene catalyst.

3. The method according to claim 1 or claim 2, the method having any one of the limitations (i) to (iii): (i) The prepolymer / catalyst weight / weight ratio is 10:1.0 to 45:1.0, 15:1.0 to 35:1.0 or 15:1.0 to 25:1.0; (ii) The temperature of the slurry phase reactor in claim 2 is 35 °C to 70 °C, 40 °C to 60 °C or 45 °C to 55 °C; or (iii) The prepolymer / catalyst weight / weight ratio is 15:1.0 to 25:1.0, and the temperature of the slurry phase reactor in claim 2 is 45 °C to 55 °C.

4. The method according to any one of claims 1 to 3, the method having any one of the limitations (ii) or (iii) and the limitation (i): (i) The reactive olefin prepolymer is a reactive ethylene prepolymer, and the polyolefin of the reactive ethylene prepolymer is a polyethylene homopolymer or ethylene / (C4-C 10 ) α-olefin copolymer; and (ii) The gas phase reactor does not contain an olefin comonomer, and the polyethylene powder with improved morphology is a homopolymer of ethylene; or (iii) The gas-phase reactor contains a (C4-C 10 ) α-olefin comonomer, and the morphology-improved polyethylene powder is an ethylene / (C4-C 10 ) α-olefin copolymer.

5. The method according to any one of claims 1 to 4, the method comprising: (i) Feeding the reactive olefin prepolymer directly from the slurry phase reactor into the gas phase reactor; Or (ii) Feeding the reactive olefin prepolymer from the slurry phase reactor into an intermediate container, waiting for a period of time, and then feeding the reactive olefin prepolymer from the intermediate container into the gas phase reactor.

6. The method according to any one of claims 1 to 5, wherein the reactive olefin prepolymer is fed into the gas-phase reactor via a single inlet tube, and the single inlet tube has an inner diameter of 0.3 centimeters (cm) to 1.0 cm.

7. The method according to any one of claims 1 to 6, the method comprising: The spray-dried silica-supported metallocene catalyst is prepared by preparing any one of (i) to (iii): (i) spray-drying a mixture of a metallocene precatalyst, a silica support, an activator, and a hydrocarbon diluent to prepare the spray-dried silica-supported metallocene catalyst; (ii) spray-drying a mixture of a silica support, an activator, and a hydrocarbon diluent to obtain a spray-dried supported activator, and contacting the spray-dried supported activator with a metallocene precatalyst to prepare the spray-dried silica-supported metallocene catalyst; or (iii) spray-drying a mixture of a metallocene precatalyst, a silica support, and a hydrocarbon diluent to obtain a spray-dried supported metallocene precatalyst, and contacting the spray-dried supported metallocene precatalyst with an activator to prepare the spray-dried silica-supported metallocene catalyst; wherein the hydrocarbon diluent is selected from the group consisting of alkanes, aromatics, alkyl-substituted aromatics, aryl-substituted alkanes, or blends of any two or more thereof.

8. The method according to claim 7, wherein the metallocene pre-catalyst has the formula (I): wherein M is Ti, Hf or Zr; each R 1 to R 5 is independently an unsubstituted (C1-C6) alkyl group, or R 1 and R 2 on one of the cyclopentadienyl rings in the cyclopentadienyl ring are bonded together to comprise a divalent alkylene group selected from the group consisting of: -C(R a )=C(R b )-C(R c )=C(R d )- and -C(R a )2-C(R b )2-C(R c )2-C(R d )2-, wherein each of R a to R d is independently H or methyl; and each X is a leaving group.

9. The method according to claim 7 or claim 8, wherein the metallocene precatalyst is selected from the group consisting of: (I) Bis(η 5 -tetramethylcyclopentadienyl)zirconium dichloride; Bis(η 5 -tetramethylcyclopentadienyl)dimethylzirconium; Bis(η 5 -Pentamethylcyclopentadienyl)zirconium dichloride; Bis(η 5 -pentamethylcyclopentadienyl)dimethylzirconium; (1,3-dimethyl-4,5,6,7-tetrahydroindenyl)(1-methylcyclopentadienyl)dimethylzirconium; bis(1-methyl-3-n-butylcyclopentadienyl)zirconium dichloride; bis(1-methyl-3-n-butylcyclopentadienyl)dimethylzirconium; bis(n-propylcyclopentadienyl)hafnium dichloride; bis(n-propylcyclopentadienyl)dimethylhafnium; bis(n-butylcyclopentadienyl)zirconium dichloride; (cyclopentadienyl)(1,5-dimethylindenyl)dimethylzirconium; (methylcyclopentadienyl)(1,5-dimethylindenyl)dimethylzirconium; (cyclopentadienyl)(1,4-dimethylindenyl)dimethylzirconium; (methylcyclopentadienyl)(1,4-dimethylindenyl)dimethylzirconium; and bis(n-butylcyclopentadienyl)dimethylzirconium.

10. The method according to any one of claims 1 to 9, wherein the morphology of the morphology-improved polyethylene powder is further improved by removing at least some catalyst fines from the spray-dried silica-supported metallocene catalyst before using it to prepare the reactive olefin prepolymer, wherein the catalyst fines are defined as catalyst particles having a diameter of 10 micrometers (μm) or less.

11. The method according to any one of claims 1 to 10, wherein the morphology of the morphology-improved polyethylene powder comprises: (i) The amount of fine polyethylene powder is 5% to 60%, or 9% to 55%, or 20% to 55%, or 30% to 55% lower than the amount of fine polyethylene powder in a comparative polyethylene powder prepared by the same gas-phase polymerization, with the difference that the spray-dried silica-supported metallocene catalyst is used instead of the reactive olefin prepolymer; and (ii) The average particle size (APS) is 9% to 50%, or 9% to 42%, or 30% to 50% higher than the APS of the comparative polyethylene powder; or (ii) the APS of the polyolefin particles is reduced by 5% to 30%, or 12% to 22%, or 14% to 20%; (iii) The particle size distribution is described as a percentage reduction of 4% to 30%, or 10% to 30%, or 11% to 28%, or 23% to 28% of the present invention's d90 / d10 relative to the comparative d90 / d10; (iv) Both feature (i) and feature (ii); (v) Both feature (i) and feature (iii); (vi) Both feature (ii) and feature (iii); or (vii) Each of features (i), (ii), and (iii).

12. The method according to claim 11, wherein the greater the amount of fine polyethylene powder in the comparative polyethylene powder, the greater the percentage reduction of fine polyethylene powder in the morphology-improved polyethylene powder.

13. The method according to any one of claims 1 to 10, wherein the morphology of the morphology-improved polyethylene powder includes: (i) The amount of fine polyethylene powder is 10% to 60%, or 20% to 55%, or 30% to 55% lower than the amount of fine polyethylene powder in a comparative polyethylene powder prepared by the same gas-phase polymerization, with the difference that the spray-dried silica-supported metallocene catalyst is used instead of the reactive olefin prepolymer; (ii) The average particle size (APS) is 11% to 20%, or 14% to 19% lower than the APS of the comparative polyethylene powder; or (iii) Both (i) and (ii).

14. The method according to any one of claims 1 to 13, the method having any one of the limitations (i) to (iii): (i) The morphology-improved polyethylene powder has 2.5 weight percent (wt%) to no more than 5.5 wt% of fine polyethylene powder, the fine polyethylene powder being defined as polyethylene particles having a diameter of 74 micrometers (μm) or less; (ii) The morphology-improved polyethylene powder has an average particle size of 0.360 mm to 0.480 mm; or (iii) Both limitations (i) and (ii).

15. The method according to any one of claims 1 to 14, the method having any one of the limitations (i) to (iii): (i) The temperature of the gas-phase reactor is 70 °C to 120 °C, 80 °C to 115 °C, or 81 °C to 89 °C; (ii) The gas-phase reactor further contains an induction condensation agent ("ICA") selected from (C5-C7) alkanes in an amount of 1 weight percent (wt%) to 20 wt% based on the total weight of the contents in the gas-phase reactor, wherein preferably the ICA is isopentane; or (iii) Both (i) and (ii) are restricted.

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