Use of 1-hexene in multi-stage polyolefin production

Abstract

This disclosure relates to a method for polymerizing olefins in a multi-stage polymerization process configuration, the method comprising: a) in a first polymerization step, optionally in the presence of at least one other α-olefin comonomer, polymerizing ethylene in the presence of a polymerization catalyst to form a first polymer component (A); and b) in a second polymerization step, optionally in the presence of at least one other α-olefin comonomer, polymerizing in the gas phase in the presence of the first polymer component (A) from step a) a predetermined monomer mixture comprising ethylene and 1-hexene to form a second polymer component (B), wherein the multimodal polyethylene polymer produced by this method comprises a 1-hexene comonomer and at least one additional C4-10 comonomer, and wherein the predetermined monomer mixture comprising ethylene and 1-hexene is fed into the second polymerization step at startup of the second polymerization step. This disclosure further relates to the use of 1-hexene in the gas-phase olefin polymerization step for improving the performance of a single-point polymerization catalyst in a multi-stage olefin copolymerization method. This disclosure further relates to a method for improving the performance of a single-point polymerization catalyst in multi-stage olefin polymerization, comprising feeding a predetermined monomer mixture comprising ethylene and 1-hexene into the gas-phase polymerization step at the start of the gas-phase polymerization step.

Description

Technical Field

[0001] This disclosure relates to the copolymerization of olefins, and more specifically to a multi-stage polyolefin production method for producing ethylene / 1-butene / 1-hexene terpolymers. This disclosure further relates to the use of 1-hexene in the gas-phase polymerization step for improving the performance of a single-point catalyst in a multi-stage olefin copolymerization method. Background Technology

[0002] Multi-stage polyolefin production methods (e.g., Borstar PE, PP, and Spheripol PP) consist of multi-stage reactor configurations to impart multi-peak capabilities for achieving resins with desired, easily processable mechanical properties. In such methods, a combination of tandem slurry loop reactors followed by gas-phase reactors is used to produce a full range of polyolefin grades.

[0003] One of the key features of multi-stage olefin polymerization methods is ensuring appropriate catalyst performance throughout all stages of the process, and more specifically, ensuring the proper selection of gas-phase reactor operating conditions that will result in smooth operability in the GPR. This can be challenging for single-point catalysts with superior comonomer incorporation capabilities compared to first-generation catalysts. The presence of small particles (also known as Stocke particles: particles with buoyancy exceeding gravity in a gas-solid fluidization environment) that tend to be entrained by the fluidizing gas can cause problems related to reactor fouling (polymer coatings on reactor walls), flakes and agglomeration, and fouling of the circulating gas compressor and heat exchanger units. In this context, optimizing catalyst performance in eliminating small particle populations in the GPR is crucial and represents a key aspect of successful catalyst implementation in multi-stage ethylene copolymerization methods. Summary of the Invention

[0004] The purpose of this disclosure is to provide a method for polymerizing olefins in a multi-stage polymerization process configuration to overcome the aforementioned disadvantages.

[0005] The objective of this disclosure is achieved by a method characterized by the contents described in the independent claim. Preferred embodiments of this disclosure are disclosed in the dependent claims.

[0006] This disclosure is based on the idea of ​​injecting 1-hexene into a gas-phase reactor from the gas-phase start-up stage. This ensures appropriate catalyst performance in all stages of the multi-stage polymerization process, and more specifically, ensures proper selection of gas-phase reactor operating conditions that will produce smooth operability in the GPR.

[0007] More specifically, this disclosure establishes a start-up strategy for gas-phase reactors with appropriate injection of comonomers, intended to improve catalyst performance, which in turn enhances reactor operability and process performance, while enabling the production of demanding products (e.g., low-density, low-MFR). Detailed Implementation

[0008] This disclosure relates to a method for polymerizing olefins in a multi-stage polymerization process configuration, the method comprising:

[0009] a) In the first polymerization step, optionally in the presence of at least one other α-olefin comonomer and in the presence of a polymerization catalyst, ethylene is polymerized to form the first polymer component (A); and

[0010] b) In the second polymerization step, optionally in the presence of at least one other α-olefin comonomer and in the presence of the first polymer component (A) from step a), a predetermined monomer mixture comprising ethylene and 1-hexene is polymerized in the gas phase to form the second polymer component (B).

[0011] The multimodal polyethylene polymer produced by the method of the present invention contains a 1-hexene comonomer and at least one additional C4-10 comonomer, and

[0012] A predetermined monomer mixture containing ethylene and 1-hexene is fed into the second polymerization step at the start of the second polymerization step.

[0013] Starting from the gas-phase process operation, introducing a predetermined monomer mixture containing ethylene and 1-hexene into the gas-phase reactor in the second polymerization step reduces the population of small-sized particles (less than 80 μm), thereby improving catalyst performance during gas-phase reactor operation.

[0014] Choosing a start-up strategy that favors the initial particle growth rate of individual polymer particles to reduce the population of small polymer particles during the initial stages of the gas-phase reaction, and ensuring appropriate operating conditions in the gas-phase reactor, is a key aspect of achieving good catalyst performance and thus obtaining smooth GPR operability and reactor performance. This, in turn, will establish appropriate polymerization conditions to produce the desired product target.

[0015] Therefore, the method of the present invention allows the use of a single-point catalyst (a highly comonomer-sensitive catalyst) capable of incorporating a large number of comonomers, while achieving stable catalyst performance without experiencing the process limitations caused by agglomeration, clumping, and reactor fouling, which are mainly caused by the presence of small-sized polymer particles (fine particles).

[0016] method

[0017] This disclosure relates to a multi-stage polymerization method using a polymerization catalyst, the method comprising an optional but preferred prepolymerization step, followed by a first polymerization step and a second polymerization step.

[0018] Preferably, the same polymerization catalyst is used in each step, and ideally, it is sequentially transferred from prepolymerization to subsequent polymerization steps in a well-known manner. A preferred process configuration is based on... Type cascade, especially 2G type cascade, preferred 3G type cascade.

[0019] Therefore, the method of the present invention for polymerizing olefins in a multi-stage polymerization process configuration includes

[0020] a) In the first polymerization step, optionally in the presence of at least one other α-olefin comonomer and in the presence of a polymerization catalyst, ethylene is polymerized to form the first polymer component (A); and

[0021] b) In the second polymerization step, optionally in the presence of at least one other α-olefin comonomer, in the presence of the first polymer component (A) from step a), a predetermined monomer mixture comprising ethylene and 1-hexene is polymerized in the gas phase to form the second polymer component (B).

[0022] The multimodal polyethylene polymer produced by the method of the present invention comprises a 1-hexene comonomer and at least one additional C4-10 comonomer.

[0023] Prepolymerization step

[0024] A prepolymerization step may precede the polymerization step. The purpose of prepolymerization is to polymerize a small amount of polymer onto the catalyst at low temperature and / or low monomer concentration. Prepolymerization can improve the performance of the catalyst in the slurry and / or alter the properties of the final polymer. The prepolymerization step is preferably carried out in the slurry, and the amount of polymer produced in the optional prepolymerization step is expressed as the amount (wt%) of the ethylene polymer component (A).

[0025] When a prepolymerization step is present, it is preferable to introduce all the catalyst components into the prepolymerization step. Preferably, the reaction products of the prepolymerization step are then introduced into the first polymerization step.

[0026] However, when the solid catalyst component and the co-catalyst can be fed separately, only a portion of the co-catalyst can be introduced into the prepolymerization stage, with the remainder introduced into the subsequent polymerization stage. Similarly, in such cases, it is necessary to introduce such a large amount of co-catalyst into the prepolymerization stage to ensure sufficient polymerization reaction.

[0027] Within the scope of this invention, it should be understood that the amount of polymer produced in the prepolymerization is between 1 and 7 wt% relative to the final multimodal (co)polymer. This can be considered as part of the first polymer component (A) produced in the first polymerization step a).

[0028] First polymerization step a)

[0029] In the method of the present invention, the first polymerization step a) involves polymerizing an ethylene monomer and optionally at least one olefin comonomer.

[0030] In one embodiment, the first polymerization step involves polymerizing ethylene to produce an ethylene homopolymer.

[0031] In another embodiment, the first polymerization step involves polymerizing ethylene and at least one olefin comonomer to produce an ethylene copolymer.

[0032] The first polymerization step can be carried out in any suitable reactor or a series of reactors. The first polymerization step can be carried out in one or more slurry polymerization reactors. Preferably, the first polymerization step is carried out in one or more slurry polymerization reactors, more preferably in at least three slurry phase reactors (including a slurry phase reactor for prepolymerization).

[0033] Polymerization in the first polymerization zone is preferably carried out in a slurry. The polymer particles formed during polymerization are then suspended in a fluid hydrocarbon along with a catalyst that has been crushed and dispersed within the particles. The slurry is agitated to allow the reactants to transfer from the fluid into the particles.

[0034] Slurry polymerization is typically carried out in an inert diluent, which is usually a hydrocarbon diluent such as methane, ethane, propane, n-butane, isobutane, pentane, hexane, heptane, octane, etc., or mixtures thereof. Preferably, the diluent is a low-boiling-point hydrocarbon or a mixture of such hydrocarbons having 1 to 4 carbon atoms. A particularly preferred diluent is propane, which may contain small amounts of methane, ethane, and / or butane.

[0035] The ethylene content in the slurry fluid phase can be from 2 to about 50 mol%, preferably from about 3 to about 20 mol%, and particularly from about 5 to about 15 mol%. The benefit of having a high ethylene concentration is increased catalyst productivity, but the disadvantage is that more ethylene needs to be recycled compared to lower concentrations.

[0036] The temperature during slurry polymerization is typically 50 to 115°C, preferably 60 to 110°C, and particularly 70 to 100°C. The pressure is 1 to 150 bar, preferably 10 to 100 bar.

[0037] The pressure in the first polymerization step is typically 35 to 80 bar, preferably 40 to 75 bar, and especially 45 to 70 bar.

[0038] The residence time in the first polymerization step is typically 0.15 h to 3.0 h, preferably 0.20 h to 2.0 h, and particularly 0.30 h to 1.5 h.

[0039] Slurry polymerization is sometimes advantageous at temperatures and pressures above the critical temperature and pressure of the fluid mixture. Such operations are described in US-A-5391654. In such operations, the temperature is typically 85 to 110°C, preferably 90 to 105°C, and the pressure is 40 to 150 bar, preferably 50 to 100 bar.

[0040] Slurry polymerization can be carried out in any known reactor used for slurry polymerization. Such reactors include continuous stirred tank reactors and loop reactors. Polymerization is particularly preferred in loop reactors. In a loop reactor, the slurry is circulated at high speed along a closed pipe using a circulation pump. Loop reactors are generally known in the art, and examples are given, for example, in US-A-4582816, US-A-3405109, US-A-3324093, EP-A-479186, and US-A-5391654.

[0041] The slurry can be drawn from the reactor continuously or intermittently. A preferred method for intermittent drawing is to use a settling leg, in which the slurry is concentrated before a batch of concentrated slurry is drawn from the reactor. Uses of settling legs are disclosed in particular in US-A-3374211, US-A-3242150, and EP-A-1310295. Continuous drawing is disclosed in particular in EP-A-891990, EP-A-1415999, EP-A-1591460, and WO-A-2007 / 025640. As disclosed in EP-A-1310295, EP-A-1591460, and EP3178853B1, continuous drawing is advantageously combined with suitable concentration methods.

[0042] Cyclone separators can be placed at the outlet of the decommissioning zone (recirculated gas line) to collect entrained particles (estimated particle size) and prevent small particles from passing through the gas compressor and heat exchanger.

[0043] As is known in the art, hydrogen can be fed into the reactor to control the molecular weight of the polymer. Additionally, one or more α-olefin comonomers can be added to the reactor to control the density of the polymer product. The actual amounts of such hydrogen and comonomer feed depend on the catalyst used and the desired melt index (or molecular weight) and density (or comonomer content) of the resulting polymer.

[0044] Second polymerization step b)

[0045] The first polymer component (A) is transferred from the first polymerization step to the second polymerization step.

[0046] In the method of the present invention, the second polymerization step b) involves polymerizing an ethylene monomer and a 1-hexene comonomer, as well as optionally at least one other α-olefin comonomer.

[0047] In one embodiment, the second polymerization step involves polymerizing ethylene and 1-hexene, along with at least one olefin comonomer, to produce an ethylene terpolymer.

[0048] In another embodiment, the second polymerization step involves polymerizing ethylene and 1-hexene and 1-butene to produce an ethylene / 1-butene / 1-hexene terpolymer.

[0049] The second polymerization step is carried out in one or more gas-phase polymerization reactors.

[0050] Gas-phase polymerization can be carried out in any known reactor used for gas-phase polymerization. Such reactors include fluidized bed reactors, fast fluidized bed reactors, or settling bed reactors, or any combination thereof. When a combination of reactors is used, the polymer is transferred from one polymerization reactor to another. Furthermore, some or all of the polymer from the polymerization stage can be returned to the previous polymerization stage.

[0051] Gas-phase polymerization is typically carried out in gas-solid fluidized beds (also known as gas-phase reactors (GPRs)). Gas-solid olefin polymerization reactors are commonly used for the polymerization of alpha-olefins such as ethylene and propylene because they allow for relatively high flexibility in polymer design and the use of various catalyst systems. A common variant of gas-solid olefin polymerization reactors is the fluidized bed reactor.

[0052] A gas-solid olefin polymerization reactor is a polymerization reactor used for the heterogeneous polymerization of gaseous olefin monomers into polyolefin powder particles. It comprises three zones: in the bottom zone, fluidizing gas is introduced into the reactor; in the middle zone, which is typically generally cylindrical, the olefin monomers present in the fluidizing gas are polymerized to form polymer particles; and in the top zone, the fluidizing gas is extracted from the reactor. In some types of gas-solid olefin polymerization reactors, a fluidizing grid (also called a distribution plate) separates the bottom zone from the middle zone. In some types of gas-solid olefin polymerization reactors, the top zone forms a desorption or entrainment zone, where the fluidizing gas expands and desorbs from the polyolefin powder due to its increased diameter compared to the middle zone.

[0053] The dense phase refers to the region in the middle zone of a gas-solid olefin polymerization reactor that has an increased packing density due to the formation of polymer particles. In some types of gas-solid olefin polymerization reactors (i.e., fluidized bed reactors), the dense phase is formed by the fluidized bed.

[0054] The temperature in gas-phase polymerization is typically 40 to 120°C, preferably 50 to 100°C, and more preferably 65 to 90°C.

[0055] The pressure in gas-phase polymerization is typically 5 to 40 bar, preferably 10 to 35 bar, and more preferably 15 to 30 bar.

[0056] The residence time in gas-phase polymerization is typically 1.0 h to 4.5 h, preferably 1.5 h to 4.0 h, and particularly 2.0 h to 3.5 h.

[0057] The molar ratio of the reactants can be adjusted as follows: the C6 / C2 ratio is 0.0001-0.1 mol / mol, and the H2 / C2 ratio is 0-0.1 mol / mol.

[0058] The polymer production rate in the gas phase reactor can be from 10 tn / h to 65 tn / h, preferably from 12 tn / h to 58 tn / h, and particularly from 13 tn / h to 52.0 tn / h. Therefore, the total polymer extraction rate from the gas phase reactor can be from 15 tn / h to 100 tn / h, preferably from 18 tn / h to 90 tn / h, and particularly from 20 tn / h to 80.0 tn / h.

[0059] The yield split (second polymer component (B)% / first polymer component (A)%) can be from 0.65 to 2.5, preferably from 0.8 to 2.3, and most preferably from 1.0 to 1.65.

[0060] The method of the present invention requires that 1-hexene be introduced into the second polymerization step b) from the start of the gas phase reaction, that is, introduced into the first gas phase reactor.

[0061] This can be achieved by introducing a predetermined monomer mixture of ethylene and 1-hexene into the second polymerization step.

[0062] In the second polymerization step, the molar ratio of 1-hexene to ethylene is typically in the range of 7 mol / kmol to 80 mol / kmol, preferably 8.0 mol / kmol to 60.0 mol / kmol, and particularly 9.0 mol / kmol to 50.0 mol / kmol.

[0063] The feed ratio of the 1-hexene / ethylene mixture is 70 kg / t to 400 kg / t, preferably 75 kg / t to 350 kg / t, and more preferably 80 kg / t to 280 kg / t.

[0064] 1-Hexene can be introduced into the reaction vessel, for example, via a comonomer fresh injection line located downstream of the cooler, and mixed with a recirculated gas stream, which is then introduced into the gas-phase reactor. Therefore, 1-Hexene is preferably introduced simultaneously with ethylene, and particularly not as a separate mixture of 1-hexene and ethylene.

[0065] The growth rate of a single polymer particle is proportional to the polymerization rate (i.e., catalyst activity) and inversely proportional to the particle size and the density of the polymer phase in the particles. Therefore, the presence of 1-hexene from the start of GPR operation (GPR initiation) leads to the following positive effects on particle growth: i) it increases the solubility of the smaller permeabilizer (i.e., ethylene) in the gas-phase reactor due to the co-solubility effect (i.e., high molecular weight olefins are used as solvents for low molecular weight olefins), thus increasing the local polymerization rate; ii) it decreases the polymer phase density of the particles due to the swelling effect; iii) it decreases the overall polymer density due to reduced crystallinity, thus resulting in a higher amorphous fraction of the polymer phase in the polymer particles compared to the case without comonomers in the reactor, leading to a further increase in reactant adsorption, which in turn increases the local polymerization rate and therefore the particle growth rate; and iv) it provides the time required for the 1-hexene adsorption process in the polymer particles, resulting in a more uniform distribution of the 1-hexene adsorption concentration in the polymer particles (increased reactant homogeneity at the particle level).

[0066] Polymerization catalyst

[0067] The polymerization catalyst used in the method of this invention is a metallocene catalyst. Polymerization catalysts typically comprise (i) a transition metal complex, (ii) a co-catalyst, and optionally (iii) a support.

[0068] Preferably, the first polymerization step and the second polymerization step use the same metallocene catalyst, that is, they are carried out in the presence of the same metallocene catalyst.

[0069] The method of this invention preferably utilizes single-point catalysis. In contrast to Ziegler-Natta catalysis, polyethylene copolymers prepared using single-point catalysis possess properties that allow them to be distinguished from Ziegler-Natta materials. Specifically, the comonomer distribution is more uniform. This can be shown using TREF or Crystaf techniques. Catalyst residues can also indicate the catalyst used. Ziegler-Natta catalysts will not contain, for example, Group (IV) metals such as Zr or Hf.

[0070] Transition metal complexes (i)

[0071] Transition metal complexes include transition metals (M) of elements in groups 3 to 10 of the periodic table (IUPAC 2007), or of the actinides or lanthanides.

[0072] The term "transition metal complex" according to the present invention includes any metallocene or nonmetallocene compound of a transition metal that carries at least one organic (coordinating) ligand and exhibits catalytic activity alone or in conjunction with a co-catalyst. Transition metal compounds are well known in the art, and the present invention covers compounds of metals from Groups 3 to 10 of the Periodic Table (IUPAC 2007) (e.g., Groups 3 to 7 or Groups 3 to 6, such as Groups 4 to 6) and lanthanides or actinides.

[0073] In the implementation scheme, the transition metal complex has the following formula (iI):

[0074] (L) m R n MX q (iI)

[0075] in

[0076] “M” represents transition metals (M) in groups 3 to 10 of the periodic table (IUPAC 2007).

[0077] Each "X" is independently a monoanion ligand, such as a σ-ligand.

[0078] Each "L" is an independent organic ligand that coordinates with a transition metal "M".

[0079] “R” is a bridging group that connects the organic ligand (L).

[0080] “m” can be 1, 2, or 3, with 2 being preferred.

[0081] “n” can be 0, 1, or 2, preferably 0 or 1.

[0082] "q" can be 1, 2, or 3, with 2 being preferred.

[0083] m+q equals the valence of the transition metal (M).

[0084] "M" is preferably selected from the group consisting of free zirconium (Zr), hafnium (Hf), or titanium (Ti), and more preferably from the group consisting of free zirconium (Zr) and hafnium (Hf). "X" is preferably a halogen, and most preferably Cl.

[0085] Most preferably, the transition metal complex (i) is a metallocene complex comprising a transition metal compound as defined above, wherein the transition metal compound contains a cyclopentadienyl, indenyl, or fluorenyl ligand as a substituent "L". Furthermore, the ligand "L" may have one or more substituents, such as alkyl, aryl, arylalkyl, alkylaryl, silyl, siloxy, alkoxy, or other heteroatomic groups. Suitable metallocene catalysts are known in the art, and are disclosed in particular in WO-A-95 / 12622, WO-A-96 / 32423, WO-A-97 / 28170, WO-A-98 / 32776, WO-A-99 / 61489, WO-A-03 / 010208, WO-A-03 / 051934, WO-A-03 / 051514, WO-A-2004 / 085499, EP-A-1752462 and EP-A-1739103.

[0086] In one embodiment of the invention, the metallocene complex is bis(1-methyl-3-n-butylcyclopentadienyl)zirconium chloride (IV).

[0087] In another embodiment, the transition metal complex (i) has the following formula (i-II):

[0088]

[0089] Each X is independently a halogen atom, a C1-6-alkyl group, a C1-6-alkoxy group, a phenyl group, or a benzyl group;

[0090] Each Het is independently a monocyclic heteroaromatic group containing at least one heteroatom selected from O or S;

[0091] L is -R'2Si-, where each R' is independently a C1-20 hydrocarbon or C1-10 alkyl group, which is substituted with an alkoxy group having 1 to 10 carbon atoms;

[0092] M is Ti, Zr, or Hf;

[0093] Each R1 may be the same or different and is a C1-6 alkyl or C1-6 alkoxy;

[0094] Each n is between 1 and 2;

[0095] Each R2 may be the same or different and is a C1-6 alkyl, C1-6 alkoxy, or -Si(R)3 group;

[0096] Each R is a C1-10 alkyl or phenyl group, optionally substituted with 1 to 3 C1-6 alkyl groups; and

[0097] Each p is between 0 and 1.

[0098] Preferably, the compound of formula (i-II) has structure (i-III).

[0099]

[0100] Each X is independently a halogen atom, a C1-6-alkyl group, a C1-6-alkoxy group, a phenyl group, or a benzyl group;

[0101] L is Me2Si-;

[0102] Each R1 may be the same or different and is a C1-6 alkyl group, such as methyl or tert-butyl;

[0103] Each n is between 1 and 2;

[0104] R2 is a -Si(R)3 alkyl group; each p is 1;

[0105] Each R is a C1-6 alkyl or phenyl group.

[0106] The highly preferred transition metal complex of formula (i-III) is

[0107]

[0108]

[0109] Co-catalyst (ii)

[0110] To form the polymerization catalyst, a co-catalyst, also known as an activator, is used, as is well known in the art. Co-catalysts containing Al or B are well known and can be used herein. Aluminoxanes (e.g., MAO) or boron-based co-catalysts (such as borates) are preferred.

[0111] Suitable cocatalysts are metal alkyl compounds known in the art, and especially alkylaluminum compounds. Particularly suitable activators for use with metallocene catalysts are alkylaluminoxane compounds, such as methylaluminoxane (MAO), tetraisobutylaluminoxane (TIBAO), or hexaisobutylaluminoxane (HIBAO).

[0112] Preferably, the co-catalyst is methylaluminoxane (MAO).

[0113] Carrier (iii)

[0114] The polymerization catalyst of the present invention can be used in solid but unsupported form according to the scheme in WO03 / 051934. The polymerization catalyst of the present invention is preferably used in solid supported form. The particulate support material used can be an inorganic porous support, such as silica, alumina, or mixed oxides, such as silica-alumina, especially silica.

[0115] Silica carrier is preferred.

[0116] Particularly preferred is that the carrier is a porous material, which allows the complex to be loaded into the pores of the particulate carrier, for example using methods similar to those described in WO94 / 14856, WO95 / 12622, WO2006 / 097497 and EP1828266.

[0117] The average particle size of supports such as silica carriers can typically be between 10 and 100 μm. Average particle size (i.e., median particle size, D) 50 The particle size distribution can be determined using a Malvern Mastersizer 3000 laser diffraction particle size analyzer. The sample dispersion is dry powder.

[0118] The average pore size of supports such as silica supports can be in the range of 10 to 100 nm, and the pore volume can be 1 to 3 mL / g.

[0119] Examples of suitable support materials are, for example, ES757 manufactured and sold by PQ, Sylopol 948 manufactured and sold by Grace, or SUNSPERA DM-L-303 silica manufactured by AGC Si-Tech. The support may optionally be calcined prior to its use in catalyst preparation to achieve optimal silanol group content.

[0120] The catalyst may contain 5 to 500 μmol (e.g. 10 to 100 μmol) of transition metal per gram of support (e.g., silica) and 3 to 15 mmol of Al per gram of support (e.g., silica).

[0121] Multi-peak polyethylene polymer

[0122] This invention relates to the preparation of multimodal polyethylene copolymers. The density of the multimodal ethylene copolymer can be from 900 to 980 kg / m³. 3 Preferred weight is 905 to 940 kg / m³. 3 Especially 910 to 935 kg / m 3 .

[0123] If the multimodal polyethylene polymer is a copolymer, it is preferred. More preferably, the multimodal polyethylene copolymer is LLDPE. It can have a strength of 905 to 940 kg / m³. 3 The preferred weight is 910 to 935 kg / m³. 3 More preferably 915 to 930 kg / m 3 Especially 916 to 928 kg / m 3 The density. In one embodiment, a density of 910 to 928 kg / m³ is preferred. 3The term LLDPE, as used herein, refers to linear low-density polyethylene. LLDPE is preferably multimodal.

[0124] The term "multimodal" includes polymers that are multimodal with respect to MFR, and therefore also includes bimodal polymers. The term "multimodal" can also refer to the multimodality of the "comonomer distribution".

[0125] Polymers containing at least two polyethylene fractions are typically referred to as "multimodal" polymers, which are produced under different polymerization conditions, resulting in different (weight-average) molecular weights and molecular weight distributions. The prefix "multimodal" refers to the number of different polymer fractions present in the polymer. Thus, for example, the term multimodal polymer includes so-called "bimodal" polymers composed of two fractions. The molecular weight distribution curve of a multimodal polymer (e.g., LLDPE), that is, the appearance of a graph showing the polymer weight fraction as a function of its molecular weight, may show two or more maximum values, or be significantly wider than the curve of a single fraction. Typically, the final MWD curve will be broad, sloping, or show shoulders.

[0126] Ideally, the molecular weight distribution curve of the multimodal polymer of the present invention will show two distinct maximum values. Alternatively, the polymer fractions have similar MFRs and are bimodal in terms of comonomer content. Polymers containing at least two polyethylene fractions are also referred to as “multimodal”, said at least two polyethylene fractions being produced under different polymerization conditions, resulting in different comonomer contents in said fractions.

[0127] For example, in a continuous multi-stage process, if a polymer is produced using reactors coupled in series and different conditions in each reactor, the polymer fractions produced in each reactor will each have their own molecular weight distribution and weight-average molecular weight. When recording the molecular weight distribution curves of such polymers, superimposing the individual curves from these fractions onto the molecular weight distribution curve of the resulting total polymer product typically produces curves with two or more distinct maximum values.

[0128] In any multimodal polymer, there may be a lower molecular weight component (LMW) and a higher molecular weight component (HMW). The LMW component has a lower molecular weight than the higher molecular weight component. This difference is preferably at least 5000 g / mol.

[0129] The multimodal polyethylene polymer produced by the method of the present invention comprises a 1-hexene comonomer and at least one additional C4-10 comonomer. The 1-hexene comonomer is present in the second polymer component (B). Other comonomers may be present in the HMW component (or the second component (B) produced in the second polymerization step) or the LMW component (or the first component (A) produced in the first polymerization step) or both. From this point forward, the term LMW / HMW component will be used, but the described embodiments apply to the first and second components respectively.

[0130] The HMW component preferably contains at least one C4-10 comonomer. Then, the LMW component can be an ethylene homopolymer, or may also contain at least one C4-10 comonomer. In a preferred embodiment, the multimodal polyethylene polymer contains at least two (e.g., exactly two) C4-10 comonomers.

[0131] In one embodiment, the multimodal polyethylene polymer is a terpolymer and comprises a hexene comonomer and at least one C4-10 comonomer. In this case, the HMW component may be a terpolymer component, and the lower molecular weight (LMW) component may be an ethylene homopolymer component or a copolymer component. Alternatively, both the LMW and HMW components may be copolymers, such that at least two C4-10 comonomers are present.

[0132] Therefore, the multimodal polyethylene polymer can be a polymer in which the HMW component comprises repeating units derived from ethylene and at least two other C4-10α olefin monomers (such as 1-butene and a C6-10α olefin monomer). Ethylene preferably forms the majority of the LMW or HMW component. In the most preferred embodiment, the LMW component may comprise an ethylene-1-butene copolymer, and the HMW component may comprise an ethylene-1-hexene copolymer.

[0133] The total monomer content in the multimodal polyethylene polymer can be, for example, 0.2 to 14.0 mol%, preferably 0.3 to 12 mol%, more preferably 0.5 to 10.0 mol%, and most preferably 0.6 to 8.5 mol%.

[0134] 1-Butene may be present in amounts from 0.05 to 6.0 mol% (such as 0.1 to 5 mol%, more preferably 0.15 to 4.5 mol%, and most preferably 0.2 to 4 mol%).

[0135] C6 to C10 α-olefins may be present in amounts of 0.2 to 6 mol%, preferably 0.3 to 5.5 mol%, more preferably 0.4 to 4.5 mol%.

[0136] Preferably, the LMW component has a lower amount (mol%) of comonomer than the HMW component. For example, the amount of 1-butene comonomer in the LMW component is preferably 0.05 to 0.9 mol%, more preferably 0.1 to 0.8 mol%, while the amount of 1-hexene comonomer in the HMW component (B) is preferably 1.0 to 8.0 mol%, more preferably 1.2 to 7.5 mol%.

[0137] Therefore, multimodal polyethylene copolymers can be formed from ethylene with at least one of 1-butene, 1-hexene, or 1-octene. The multimodal polyethylene polymer can be an ethylene-butene-hexene terpolymer, for example, in which the HMW component is an ethylene-butene-hexene terpolymer and the LMW is an ethylene homopolymer component. Terpolymers using ethylene comonomers of 1-octene and 1-hexene are also envisioned.

[0138] In another embodiment, the multimodal polyethylene copolymer may comprise two ethylene copolymers, such as two ethylene-butene copolymers, or an ethylene-butene copolymer (e.g., as an LMW component) and an ethylene-hexene copolymer (e.g., as an HMW component). It is also possible to combine ethylene copolymer components and ethylene terpolymer components, such as an ethylene-butene copolymer (e.g., as an LMW component) and an ethylene-butene-hexene terpolymer (e.g., as an HMW component).

[0139] The LMW component of the multimodal polyethylene polymer may have an MFR2 of 0.5 to 3000 g / 10 min, more preferably 1.0 to 1000 g / 10 min. In some embodiments, the MFR2 of the LMW component may be 50 to 3000 g / 10 min, more preferably 100 to 1000 g / 10 min, for example, when the target is a cast film.

[0140] The molecular weight (Mw) of the LMW component should preferably be in the range of 20,000 to 180,000 (e.g., 40,000 to 160,000). It may have a molecular weight of at least 925 kg / m³. 3 (for example, at least 940 kg / m) 3 The density is between 930 and 950 kg / m³. 3 Optimal weight is 935 to 945 kg / m³. 3 Densities within a certain range are possible.

[0141] The HMW component of a multimodal polyethylene polymer can, for example, have an MFR2 of less than 1 g / 10 min (such as 0.2 to 0.9 g / 10 min, preferably 0.3 to 0.8 g / 10 min, and more preferably 0.4 to 0.7 g / 10 min). It can have an MFR2 of less than 915 kg / m³. 3 (e.g., less than 910 kg / m) 3 Preferably less than 905 kg / m3 The density of the higher molecular weight component (Mw) can be in the range of 70,000 to 1,000,000, preferably 100,000 to 500,000.

[0142] The LMW component can form 30 to 70 wt% of the multimodal polyethylene polymer, such as 35 to 65 wt%, especially 38 to 62 wt%.

[0143] The HMW component can form 30 to 70 wt% of the multimodal polyethylene polymer, such as 35 to 65 wt%, especially 38 to 62 wt%.

[0144] In one embodiment, there are 40 to 45 wt% LMW component and 60 to 55 wt% HMW component.

[0145] In one embodiment, the polyethylene polymer consists of HMW and LMW components as the sole polymer components.

[0146] The multimodal polyethylene polymer of the present invention may have an MFR2 of 0.01 to 50 g / 10 min, preferably 0.05 to 25 g / 10 min, and especially 0.1 to 10 g / 10 min.

[0147] The molecular weight distribution (MWD, Mw / Mn) of the polyethylene terpolymer of the present invention is in the range of 2.0 to 15.0, preferably in the range of 2.2 to 10.0, and more preferably in the range of 2.4 to 4.6.

[0148] Example

[0149] Polymer analysis and characterization

[0150] Volume density

[0151] The bulk density of polymer powders can be determined according to standard methods such as ISO 60:1977 or ASTM D1895-17.

[0152] MFR

[0153] Melt flow rate (MFR) is determined according to ISO 1133 and indicated in g / 10 min. MFR is an indicator of the polymer's flowability and therefore its processability. A higher melt flow rate generally indicates a lower polymer viscosity. The MFR2 for polypropylene was measured at 230°C and a load of 2.16 kg, the MFR5 for polyethylene was measured at 190°C and a load of 5 kg, and the MFR2 for polyethylene was measured at 190°C and a load of 2.16 kg.

[0154] density

[0155] The density of the polymer is measured according to ISO 1183-2 / 1872-2B.

[0156] GPC

[0157] The average molecular weight (Mw and Mn), molecular weight distribution (MWD), and their widths described by the polydispersity index PDI = Mw / Mn (where Mn is the number-average molecular weight and Mw is the weight-average molecular weight) were determined by gel permeation chromatography (GPC) according to ISO 16014-1:2003, ISO 16014-2:2003, ISO 16014-4:2003, and ASTM D 6474-12, using the following formula:

[0158]

[0159]

[0160]

[0161] For a constant elution volume interval ΔV i A i and M i These are respectively related to the elution volume V i The relevant chromatographic peak slice area and polyolefin molecular weight (MW) are used, where N equals the number of data points obtained from the chromatogram between the integration limits.

[0162] A high-temperature GPC instrument equipped with an infrared (IR) detector (IR4 or IR5 from PolymerChar (Valencia, Spain)) and guard columns of 3x Agilent-PLgel Olexis and 1x Agilent-PLgel Olexis. 1,2,4-trichlorobenzene (TCB) stabilized with 250 mg / L 2,6-di-tert-butyl-4-methylphenol was used as both solvent and mobile phase. The chromatographic system was operated at 160 °C and a constant flow rate of 1 mL / min. 200 μL of sample solution was injected for each analysis. Data collection was performed using Agilent Cirrus software version 3.3 or PolymerChar GPC-IR control software.

[0163] The column assembly was calibrated using a universal calibration (according to ISO 16014-2:2003) with 19 narrow MWD polystyrene (PS) standards ranging from 0.5 kg / mol to 11500 kg / mol. The PS standards were dissolved at room temperature for several hours. The conversion of the peak molecular weight of polystyrene to the molecular weight of polyolefins was achieved using the Mark Houwink equation and the following Mark Houwink constant:

[0164] K PS =19 x 10 -3 mL / g,∝ PS =0.655

[0165] K PE =39x10 -3 mL / g,∝ PE =0.725

[0166] K PP =19x10 -3 mL / g,∝ PP =0.725.

[0167] Third-order polynomial fitting was used to fit the calibration data.

[0168] All samples were prepared in the concentration range of 0.5-1 mg / mL and dissolved at 160 °C for 2.5 hours (for PP) or 3 hours (for PE) with continuous gentle shaking.

[0169] catalyst

[0170] Loading of SiO2:

[0171] Add 10 kg of silica (PQ ES757, calcined at 600°C) from the feeding drum and inertize it in the reactor until the O2 level reaches below 2 ppm.

[0172] Preparation of MAO / tol / MC:

[0173] 30 wt% MAO (14.1 kg) in toluene was added from a balance to another reactor, followed by the addition of toluene (4.0 kg) at 25°C (oil circulation temperature) with stirring at 95 rpm. After the addition of toluene, the stirring speed was increased from 95 rpm to 200 rpm for 30 min. 477 g of metallocene racemic dimethylsilanediylbis{2-(5-(trimethylsilyl)furan-2-yl)-4,5-dimethylcyclopentadien-1-yl}zirconium dichloride was added from a metal cylinder, followed by rinsing with 4 kg of toluene (total toluene 8.0 kg). The reactor stirring speed was changed to 95 rpm for MC feed and then returned to 200 rpm for a 3 h reaction time. After the reaction time, the MAO / tol / MC solution was transferred to a feed vessel.

[0174] Catalyst preparation:

[0175] The reactor temperature was set to 10℃ (oil circulation temperature) and MAO / tol / MC was added with stirring at 40 rpm. The MAO / tol / MC solution (target 22.5 kg, actual 22.2 kg) was added over 205 min, followed by 60 min of stirring (oil circulation temperature set to 25℃). After stirring, the "dry mixture" was stabilized at 25℃ (oil circulation temperature) for 12 h with stirring at 0 rpm. The reactor was rotated 20° (back and forth) and stirring was started at 5 rpm once per hour for several cycles.

[0176] After stabilization, the catalyst was dried at 60°C (oil circulation temperature) under a nitrogen flow of 2 kg / h for 2 h, and then dried under vacuum (with the same nitrogen flow and stirring at 5 rpm) for 13 h. Samples of the dried catalyst were taken, and the HC content was measured using thermogravimetric analysis in a glove box equipped with a Sartorius moisture analyzer (model MA45). The target HC level was <2% (actual 1.3%).

[0177] Example 1 (Comparison)

[0178] LLDPE membranes were produced using a single-point catalyst with an initial size of 25 micrometers and a span (i.e., (d90-d10) / d50) of 1.6 (target MFR2 = 1.3, target density = 912-920 kg / m3). The catalyst was first prepolymerized in a prepolymerization reactor at T = 50 °C and P = 56 bar (gauge pressure). More specifically, 40.7 g / h of catalyst, 4 kg / h of ethylene, 85 g / h of 1-butene, 0.03 g / h of hydrogen, and 46 kg / h of propane (diluent) were fed into the prepolymerization reactor, with an average residence time of 23 min. The yield fraction was 3.0 wt%.

[0179] The product was transferred to a split loop reactor configuration, in which ethylene (C2), propane (C3), 1-butene (C4), and hydrogen (H2) were fed into the first loop reactor under polymerization conditions of T = 85°C and P = 54 bar (gauge pressure), with an average residence time of 0.31 h. The C2 concentration in the liquid phase was 3.9 mol%, and the molar ratios of H2 / C2 and C4 / C2 were 0.38 mol / kmol and 35 mol / kmol, respectively. The yield split in the first loop reactor of the split loop configuration was 18.5 wt%, and the resulting material had an MFR2 of 4.7 (g / 10 min) and a yield of 940.7 kg / m³. 3 The density.

[0180] The product was then transferred to a second loop reactor configured with a split loop reactor, where polymerization conditions were T = 85°C, P = 52 bar (gauge pressure), and an average residence time of 0.60 h. The C2 concentration in the liquid phase was 4.3 mol%, and the molar ratios of H2 / C2 and C4 / C2 were 0.76 mol / kmol and 29 mol / kmol, respectively. The yield split in the second loop reactor was 21.6 wt%, and the material collected after the second loop reactor had an MFR2 of 5.8 (g / 10 min) and a yield of 940.2 kg / m³. 3 The density is such that the total catalyst productivity in the loop reactor configuration process is 1.0 kg PE / g catalyst.

[0181] The material was then flash-distilled in a high-pressure separator, and the polymer particles were subsequently transferred to a gas-phase reactor (GPR) operating at a total pressure of 19 bar (gauge) and a temperature of 75°C. Under steady-state conditions, the feed rates of the components were 0.007 kg / h H2, 103.9 kg / h C2, and 3.37 kg / h C6, resulting in H2 / C2 = 0.78 mol / kmol and C6 / C2 = 4.18 mol / kmol, respectively. The total residence time in the GPR was 2.8 h, and the apparent gas velocity was chosen to be 0.32 m / s. The yield fraction in the GPR was 56.9 wt%, and the final pellet material collected after the GPR had an MFR2 (g / 10 min) of 1.1 and a yield of 932.1 kg / m³. 3 The density, and the total catalyst productivity including loop and GPR reactor configuration processes is 2.3 kg PE / g catalyst.

[0182] In the example above, C6 is fed into the GPR several hours after the GPR is started.

[0183] Two and a half days after feeding 1-hexene, severe operability issues related to flake-forming and agglomeration occurred, leading to GPR shutdown. Just prior to GPR shutdown, the GPR point sample had an MFR2 of 0.55 g / 10 min and a concentration of 926.8 kg / m³ at a GPR split of 58.7 wt%. 3 The density is only 47.5 kg / t, compared to the highest C6 / C2 feed rate of GPR.

[0184] Examples 2 and 3 (of the present invention)

[0185] Repeat the procedure for CE1, except that C6 has been fed into the GPR during startup.

[0186] In this scenario, GPR was observed to operate smoothly and perform well for approximately 10 days without any operability issues, thus producing the target material properties described in IE1 and IE2. The highest C6 / C2 feed rate ratio with GPR was 162.8 kg / t.

[0187] Table 1.

[0188]

[0189]

[0190]

Claims

1. A process for polymerizing olefins in a multi-stage polymerization process configuration, the process comprising: a) polymerizing ethylene, optionally in the presence of at least one other alpha olefin comonomer, in the presence of a polymerization catalyst, in a first polymerization step to form a first polymer component (A); and b) polymerizing a predetermined monomer mixture comprising ethylene and 1-hexene in the gas phase, optionally in the presence of at least one other alpha olefin comonomer, in the presence of the first polymer component (A) of step a), in a second polymerization step to form a second polymer component (B), wherein the multimodal polyethylene polymer produced by the process comprises 1-hexene comonomer and at least one further C4-10 comonomer, and wherein the predetermined monomer mixture comprising ethylene and 1-hexene is fed into the second polymerization step from the start of the second polymerization step, wherein the polymerization catalyst is a single site catalyst comprising (i) a transition metal complex, (ii) a co-catalyst, and optionally (iii) a support, wherein the transition metal complex (i) has the following formula (i-II): (i-ii); wherein each X is independently a halogen atom, a Ci-6-alkyl group, a Ci-6-alkoxy group, a phenyl group, or a benzyl group; each Het is independently a monocyclic heteroaromatic group containing at least one heteroatom selected from O or S; L is -R'2Si-, wherein each R' is independently a Ci-20 hydrocarbon group or a Ci-10 alkyl group, which is substituted with an alkoxy group having 1 to 10 carbon atoms; M is Ti, Zr, or Hf; each R1 is the same or different and is a Ci-6 alkyl group or a Ci-6 alkoxy group; each n is 1 to 2; each R2 is the same or different and is a Ci-6 alkyl group, a Ci-6 alkoxy group, or a -Si(R)3 group; each R is a Ci-10 alkyl group or a phenyl group, which is optionally substituted with 1 to 3 Ci-6 alkyl groups; and each p is 0 to 1.

2. The process according to claim 1, wherein in the second polymerization step, the molar ratio of 1-hexene to ethylene is in the range of 7 mol / kmol to 80 mol / kmol.

3. The process according to claim 1, wherein in the second polymerization step, the molar ratio of 1-hexene to ethylene is in the range of 8.0 mol / kmol to 60.0 mol / kmol.

4. The process according to claim 1, wherein in the second polymerization step, the molar ratio of 1-hexene to ethylene is in the range of 9.0 mol / kmol to 50.0 mol / kmol.

5. The process according to claim 1, wherein the temperature in the gas phase polymerization is typically 40 to 120 °C.

6. The process according to claim 1, wherein the temperature in the gas phase polymerization is typically 50 to 100 °C.

7. The process according to claim 1, wherein the pressure in the gas phase polymerization is 5 to 40 bar.

8. The process according to claim 1, wherein the residence time in the gas phase polymerization is 1.0 h to 4.0 h.

9. The process of claim 1, wherein the residence time in the gas phase polymerization is from 1.5 h to 4.0 h.

10. The process of claim 1, wherein the residence time in the gas phase polymerization is from 2.0 h to 3.5 h.

11. Use of 1-hexene in a gas phase olefin polymerization step for improving the performance of a single site polymerization catalyst comprising (i) a transition metal complex of formula (i-II) as defined in claim 1, (ii) a cocatalyst and optionally (iii) a support, in a multi-stage olefin copolymerization process, wherein a predetermined monomer mixture comprising ethylene and 1-hexene is fed into the gas phase polymerization step from the start of the gas phase polymerization step.

12. The use of claim 11, wherein in the gas phase olefin polymerization step the molar ratio of 1-hexene to ethylene is in the range of 7 mol / kmol to 40 mol / kmol.

13. The use of claim 11, wherein in the gas phase olefin polymerization step the molar ratio of 1-hexene to ethylene is in the range of 8.0 mol / kmol to 30.0 mol / kmol.

14. The use of claim 11, wherein in the gas phase olefin polymerization step the molar ratio of 1-hexene to ethylene is in the range of 9.0 mol / kmol to 25.0 mol / kmol.

15. The use of claim 11, wherein the predetermined 1-hexene / ethylene mixture is fed at a rate of 70 kg / t to 400 kg / t.

16. The use of claim 11, wherein the predetermined 1-hexene / ethylene mixture is fed at a rate of 75 kg / t to 350 kg / t.

17. The use of claim 11, wherein the predetermined 1-hexene / ethylene mixture is fed at a rate of 80 kg / t to 280 kg / t.

18. A process for improving the performance of a single site polymerization catalyst in a multi-stage olefin polymerization, said single site polymerization catalyst comprising (i) a transition metal complex of formula (i-II) as defined in claim 1, (ii) a cocatalyst and optionally (iii) a support, said process comprising feeding a predetermined monomer mixture comprising ethylene and 1-hexene into a gas phase polymerization step from the start of the gas phase polymerization step in the presence of the single site polymerization catalyst.

19. The process of claim 18, wherein in the second polymerization step the molar ratio of 1-hexene to ethylene is generally in the range of 7 mol / kmol to 40 mol / kmol.

20. The process of claim 18, wherein in the second polymerization step the molar ratio of 1-hexene to ethylene is generally in the range of 8.0 mol / kmol to 30.0 mol / kmol.

21. The process of claim 18, wherein in the second polymerization step the molar ratio of 1-hexene to ethylene is generally in the range of 9.0 mol / kmol to 25.0 mol / kmol.

22. The process of claim 18, wherein the predetermined 1-hexene / ethylene mixture feed ratio is from 70 kg / t to 400 kg / t.

23. The process of claim 18, wherein the predetermined 1-hexene / ethylene mixture feed ratio is from 75 kg / t to 350 kg / t.

24. The process of claim 18, wherein the predetermined 1-hexene / ethylene mixture feed ratio is from 80 kg / t to 280 kg / t.

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