Use of swelling agents in multi-stage polyolefin production

Abstract

The present disclosure relates to a process for polymerizing olefins in a multi-stage polymerization process configuration, comprising a) polymerizing a first olefin monomer in a first polymerization step, optionally in the presence of at least one other alpha olefin monomer, in the presence of a polymerization catalyst, to form a first polymer component (A), and b) polymerizing a second olefin monomer in a second polymerization step 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) and a swelling-inducing agent, to provide a second polymer component (B), wherein the first polymer component (A) and the second polymer component (B) are such that the second polymer component (B) satisfies ) to the first polymer component (A), the method comprising the steps of: i) determining a first weight ratio of the second polymer component (B) to the first polymer component (A) in the second polymerization step, and ii) if the determined first weight ratio is less than the predetermined target weight ratio, increasing the concentration of the swelling-inducing agent in the second polymerization step, or iii) if the determined first weight ratio is greater than the predetermined target weight ratio, decreasing the concentration of the swelling-inducing agent in the second polymerization step, or iv) if the determined first weight ratio is equal to the predetermined target weight ratio, maintaining the concentration of the swelling-inducing agent in the second polymerization step. The present disclosure also relates to the use of the swelling-inducing agent in the gas phase polymerization step of a multi-stage olefin polymerization process for improving gas phase production splitting.

Description

Technical Field

[0001] The present disclosure relates to the polymerization of olefins, and more particularly to a multi-stage polyolefin production process. The present disclosure also relates to the use of a swelling-inducing agent in a gas-phase polymerization step in a multi-stage olefin polymerization process to improve gas-phase reactor production segmentation. Background Art

[0002] Multi-stage polyolefin production processes (e.g. Borstar PE, PP and Spheripol PP) consist of a multi-stage reactor configuration to provide multi-modal capabilities for achieving easy processing of resins with desired mechanical properties. In this type of process, a series of slurry loop reactors are used in combination, followed by a gas phase reactor, to produce various polyolefins.

[0003] A key feature of the above materials produced in a multi-stage olefin polymerization process is to achieve the desired production split so that the product portfolio requirements are met without compromising production throughput. Generally, if the GPR production split can be increased for a given production throughput, the product portfolio can be greatly broadened / enhanced.

[0004] Among other process parameters and operating procedures, GPR production split is primarily determined by catalyst kinetic characteristics. For example, catalytic systems that exhibit rapidly decaying activity (i.e., high initial activity in a loop reactor and decaying activity in a gas-phase reactor) present numerous challenges in achieving the desired production split. Furthermore, even with catalysts that exhibit slowly decaying activity (i.e., a relatively flat catalyst activity profile), additional means or methods for GPR production splitting are needed in multi-stage reactor configurations.

[0005] In recent years, numerous challenges have been observed in achieving the desired loop / GPR split when employing single-site catalysts. Decreased catalyst activity in gas-phase fluidized bed reactors combined with relatively slow particle growth rates makes it difficult to achieve the desired split, resulting in difficulties in producing the desired product alignment. Summary of the Invention

[0006] It is an object of the present disclosure to provide a process for polymerizing olefins in a multi-stage polymerization process configuration that overcomes the above-mentioned problems.

[0007] The objects of the present disclosure are achieved by a method and a use which are characterized by what is stated in the independent claims. Preferred embodiments of the present disclosure are disclosed in the dependent claims.

[0008] The present disclosure is based on the concept of adjusting the concentration of the swelling-inducing agent in the second polymerization step to a desired level that allows control of the production rate and meets a predetermined target weight ratio of the second polymer to the first polymer. This increases the catalyst productivity in the second polymerization step, further improves the production split in the second polymerization step, and broadens the product window of a multi-stage polymerization process operated at a long total residence time. DETAILED DESCRIPTION

[0009] The present disclosure relates to a method for polymerizing olefins in a multi-stage polymerization process configuration, the method comprising:

[0010] a) polymerizing a first olefin monomer in a first polymerization step, optionally in the presence of at least one other alpha olefin monomer, in the presence of a polymerization catalyst to form a first polymer component (A), and

[0011] b) polymerizing in a second polymerization step in the gas phase a second olefin monomer in the presence of the first polymer component (A) of step a) and a swelling-inducing agent, optionally in the presence of at least one other alpha-olefin comonomer, to form a second polymer component (B),

[0012] wherein the first polymer component (A) and the second polymer component (B) are produced at a production rate that satisfies a predetermined target weight ratio of the second polymer component (B) to the first polymer component (A), the method comprising the steps of:

[0013] i) determining a first weight ratio of the second polymer component (B) to the first polymer component (A) in the second polymerization step, and

[0014] ii) if the measured first weight ratio is less than the predetermined target weight ratio, increasing the concentration of the swelling-inducing agent in the second polymerization step, or

[0015] iii) if the measured first weight ratio is greater than the predetermined target weight ratio, reducing the concentration of the swelling-inducing agent in the second polymerization step, or

[0016] iv) if the determined first weight ratio is equal to the predetermined target weight ratio, maintaining the concentration of the swelling-inducing agent in the second polymerization step.

[0017] The present disclosure also relates to the use of an induced swelling agent in a gas phase polymerization step of a multi-stage olefin polymerization process for improving gas phase production splitting. According to one embodiment of the present disclosure, the induced swelling agent is an inert C4-10 alkane and / or a C5-10 comonomer, preferably selected from the group consisting of butane, pentane, heptane, 1-pentene, 1-hexene, and mixtures thereof, in particular n-butane, n-pentane, n-heptane, 1-pentene, 1-hexene, and mixtures thereof. Preferably, the induced swelling agent is an inert C4-10 alkane, more preferably selected from the group consisting of butane, pentane, heptane, and mixtures thereof.

[0018] Adjusting the concentration of the swelling-inducing agent in the second polymerization reactor to a desired level increases catalyst productivity and further improves GPR production split and broadens the product window of a multi-stage polymerization process operating at long total residence times.

[0019] method

[0020] The present disclosure relates to a multi-stage polymerization process using a polymerization catalyst, the process comprising an optional but preferred prepolymerization step followed by a first polymerization step and a second polymerization step.

[0021] Preferably, the same catalyst is used in each step and ideally the catalyst is transferred sequentially from the prepolymerisation step to the subsequent polymerisation steps in a known manner.

[0022] Thus, the process of the present invention for polymerizing olefins in a multi-stage polymerization process configuration comprises:

[0023] a) polymerizing a first olefin monomer in a first polymerization step, optionally in the presence of at least one other alpha olefin monomer, in the presence of a polymerization catalyst to form a first polymer component (A), and

[0024] b) polymerizing in a second polymerization step in gas phase, optionally in the presence of at least one other alpha olefin comonomer, a second olefin monomer in the presence of the first polymer component (A) of step a) and a swelling inducing agent to provide a second polymer component (B).

[0025] Prepolymerization step

[0026] The polymerization step may be preceded by a prepolymerization step. The purpose of the prepolymerization is to polymerize a small amount of polymer onto the catalyst at low temperatures and / or low monomer concentrations. Prepolymerization may improve the performance of the catalyst in the slurry and / or change the characteristics of the final polymer. The prepolymerization step is preferably carried out in a slurry and the amount of the polymer produced in the optional prepolymerization step is calculated as the amount (weight %) of the ethylene polymer component (A).

[0027] When a prepolymerisation step is present, preferably the catalyst components are all introduced into the prepolymerisation step. Preferably, the reaction product of the prepolymerisation step is then introduced into the first polymerisation step.

[0028] However, in the case where the solid catalyst component and the cocatalyst can be fed separately, it is possible to introduce only a portion of the cocatalyst into the prepolymerization stage and the remainder into the subsequent polymerization stage. In such a case as well, it is necessary to introduce into the prepolymerization stage so much cocatalyst that a sufficient polymerization reaction is achieved.

[0029] It is to be understood that within the scope of the present invention the amount of polymer produced in the prepolymerisation is in the range of 1 to 7 wt% relative to the final multimodal (co)polymer. This can be regarded as part of the first ethylene polymer component (A) produced in the first polymerisation step a).

[0030] First polymerization step a)

[0031] In the present process, the first polymerization step a) involves polymerizing an olefin monomer and optionally at least one olefin comonomer.

[0032] In one embodiment, the first polymerization step involves polymerizing ethylene to produce an ethylene homopolymer.

[0033] In another embodiment, the first polymerization step involves polymerizing ethylene and at least one olefin comonomer to produce an ethylene copolymer.

[0034] The first polymerization step may take place in any suitable reactor or series of reactors. The first polymerization step may be carried out in one or more slurry polymerization reactors or in a gas phase polymerization reactor or a combination thereof. Preferably, the first polymerization step is carried out in one or more slurry polymerization reactors, more preferably in at least three (e.g., exactly three) slurry phase reactors, including a slurry phase reactor for carrying out prepolymerization.

[0035] The polymerization in the first polymerization zone is preferably carried out in a slurry. The polymer particles formed in the polymerization are then suspended in a fluid hydrocarbon together with the catalyst broken up and dispersed within the particles. The slurry is stirred to transfer the reactants from the fluid to the particles.

[0036] Slurry polymerization often occurs in an inert diluent (typically a hydrocarbon diluent such as methane, ethane, propane, n-butane, isobutane, pentane, hexane, heptane, octane, or a mixture thereof). Preferably, the diluent is a low-boiling hydrocarbon having 1 to 4 carbon atoms or a mixture of such hydrocarbons. A particularly preferred diluent is propane, which may contain small amounts of methane, ethane, and / or butane.

[0037] The ethylene content of the fluid phase of the slurry may be from 2 mol% to about 50 mol%, preferably from about 3 mol% to about 20 mol%, and particularly from about 5 mol% 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 recovered than at lower concentrations.

[0038] The temperature of the slurry polymerization is generally 50 to 115° C., preferably 60 to 110° C., in particular 70 to 100° C. The pressure is from 1 to 150 bar, preferably 10 to 100 bar.

[0039] The pressure in the first polymerization step is generally from 35 to 80 bar, preferably from 40 to 75 bar, in particular from 45 to 70 bar.

[0040] The residence time of the first polymerization stage is generally from 0.15 to 3.0 hours, preferably from 0.20 to 2.0 hours, in particular from 0.30 to 1.5 hours.

[0041] Sometimes it is advantageous to carry out a slurry polymerization at a pressure above the critical temperature and fluid mixture. Such an operation is described in US-A-5391654. In such an operation, the temperature is generally 85°C to 110°C, preferably 90°C to 105°C, and the pressure is 40 bar to 150 bar, preferably 50 bar to 100 bar.

[0042] Slurry polymerization can be carried out in any known reactor for slurry polymerization. Such reactors include continuous stirred tank reactors and loop reactors. Particularly preferred is carrying out the polymerization in a loop reactor. In such a reactor, the slurry is circulated at high speed along a closed tube using a circulation pump. Loop reactors are generally known in the art, and examples thereof are given, for example, in US-A-4582816, US-A-3405109, US-A-3324093, EP-A-479186 and US-A-5391654.

[0043] The slurry can be drawn from the reactor continuously or intermittently. A preferred mode for intermittent drawing is to use settling legs that allow the slurry to concentrate and then draw a batch of concentrated slurry from the reactor. The use of settling legs is disclosed in US-A-3374211, US-A-3242150, and EP-A-1310295, etc. Continuous drawing is disclosed in EP-A-891990, EP-A-1415999, EP-A-1591460, and WO-A-2007 / 025640, etc. Continuous drawing is advantageously combined with a suitable concentration method, as disclosed in EP-A-1310295, EP-A-1591460, and EP3178853B1.

[0044] Hydrogen can be fed into the reactor to control the molecular weight of the polymer, as is known in the art. Additionally, one or more alpha-olefin comonomers can be added to the reactor to control the density of the polymer product. The actual amount of such hydrogen and comonomer feed depends on the catalyst used and the desired melt index (or molecular weight) and density (or comonomer content) of the resulting polymer.

[0045] Second polymerization step b)

[0046] The first polymer component is transferred from the first polymerization step to the second polymerization step.

[0047] In the present process, the second polymerisation step b) involves polymerising an olefin monomer and optionally at least one olefin comonomer.

[0048] In one embodiment, the second polymerization step involves polymerizing ethylene and optionally at least one olefin comonomer to produce an ethylene homopolymer or an ethylene copolymer, respectively.

[0049] The second polymerization step takes place in one or more gas phase polymerization reactors.

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

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

[0052] A gas-solid olefin polymerization reactor is a polymerization reactor for heterogeneously polymerizing gaseous olefin monomers into polyolefin powder particles, and comprises three zones: a bottom zone, in which a fluidizing gas is introduced into the reactor; a middle zone, which typically has a generally cylindrical shape, in which olefin monomers present in the fluidizing gas are polymerized to form polymer particles; and a top zone, in which the fluidizing gas is withdrawn from the reactor. In certain types of gas-solid olefin polymerization reactors, a fluidizing grid (also known as a distributor plate) separates the bottom zone from the middle zone. In certain types of gas-solid olefin polymerization reactors, the top zone forms a separation zone or entrainment zone, in which, due to its enlarged diameter compared to the middle zone, the fluidizing gas expands and the gas is separated from the polyolefin powder.

[0053] The dense phase refers to the region within the middle zone of a gas-solid olefin polymerization reactor which has an increased bulk density due to the formation of polymer particles. In certain types of gas-solid olefin polymerization reactors, namely fluidized bed reactors, the dense phase is formed by the fluidized bed.

[0054] The temperature of the gas phase polymerization is usually 50 to 100°C, preferably 65 to 90°C.

[0055] The pressure of the gas phase polymerization is generally from 5 bar to 40 bar, preferably from 10 bar to 35 bar, preferably from 15 bar to 30 bar.

[0056] The residence time for the gas phase polymerization is from 1.0 to 4.5 hours, preferably from 1.5 to 4.0 hours, in particular from 2.0 to 3.5 hours.

[0057] The molar ratios of the reactants were adjusted as follows: the molar ratio of C6 / C2 was 0.0001 mol / mol to 0.1 mol / mol, and the molar ratio of H2 / C2 was 0 mol / mol to 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, especially from 13 tn / h to 52.0 tn / h, and thus the total polymer uptake 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, especially from 20 tn / h to 80.0 tn / h.

[0059] The production split (A / B) can be 30% to 60% of the first polymer component and 70% to 40% of the second polymer component, preferably 35% to 55% of the first polymer component and 65% to 45% of the second polymer component, especially 38% to 50% of the first polymer component and 62% to 50% of the second polymer component.

[0060] Gas phase polymerization can be carried out in any known reactor for gas phase polymerization. Such reactors include fluidized bed reactors, fast fluidized bed reactors, or settled bed reactors, or any combination of these reactors. When a combination of reactors is used, polymer is transferred from one polymerization reactor to another. In addition, some or all of the polymer from a polymerization stage can be returned to the previous polymerization stage.

[0061] Control the predetermined target weight ratio

[0062] In the present method, the predetermined target weight ratio is controlled by adjusting the amount of the swelling-inducing agent in the second polymerization step.

[0063] The term "predetermined target weight ratio" refers to the ratio of the second polymer component (B) produced in the second polymerization step to the first polymer component (A) produced in the first polymerization step.

[0064] The predetermined target weight ratio (B) / (A) is generally from 0.65 to 2.5, preferably from 0.8 to 2.3, more preferably from 0.92 to 1.9, most preferably from 1.0 to 1.65.

[0065] The predetermined weight ratio is controlled by:

[0066] (i) determining the weight ratio of the second polymer component (B) to the first polymer component (A) in the second polymerization reactor;

[0067] (ii) if the measured weight ratio of the second polymer to the first polymer in the second polymerization reactor is less than the target weight ratio, increasing the concentration of the swelling-inducing agent in the second polymerization reactor; or

[0068] (iii) if the measured weight ratio of the second polymer to the first polymer in the second polymerization reactor is greater than the target weight ratio, reducing the concentration of the swelling-inducing agent in the second polymerization reactor; or

[0069] (iv) If the measured weight ratio of the second polymer to the first polymer in the second polymerization reactor is equal to the target weight ratio, substantially maintaining the concentration of the swelling-inducing agent in the second polymerization reactor.

[0070] Swelling-inducing agent

[0071] As used herein, the term "swelling-inducing agent" refers to a compound capable of penetrating the polymer particle shell and causing the polymer particle core to swell, particularly due to mass absorption. Thus, in the presence of the polymer particles and monomers, and particularly under the conditions of the specific process in which the swelling agent is used, the swelling-inducing agent is capable of being adsorbed into the polymer particles produced in the polymerization process. As used herein, the term "inducing" specifically refers to intentionally producing a swelling effect that is not solely due to the ambient presence of components otherwise required by the process. Preferably, the swelling-inducing agent is used to produce the highest possible degree of swelling.

[0072] The swelling-inducing agent may be the same comonomer as that used in the second polymerization step and / or an inert compound as part of the reaction medium. The swelling-inducing agent is a high molecular weight hydrocarbon, preferably selected from C4-10 alkanes (such as n-heptane, n-butane, n-pentane and any isomers thereof) and C5-10 comonomers (such as 1-hexene). Preferably, the swelling-inducing agent is butane, pentane, heptane, 1-pentene or 1-hexene or a mixture thereof, more preferably n-butane, n-pentane, n-heptane, 1-pentene or 1-hexene or a mixture thereof.

[0073] The concentration of the swelling-inducing agent in the second polymerization step b) is controlled by the total concentration of oligomers (ie expressed as C6-C14 components) in the gas phase reactor as measured by an online gas chromatograph.

[0074] The total concentration of oligomers (ie, C6-14 components) in the second polymerization step is typically in the range of 50 ppm to 1200 ppm of the total reaction mixture, preferably below 600 ppm, more preferably below 500 ppm, most preferably below 400 ppm.

[0075] The swelling-inducing agent can be introduced into the reactor through an injection line located at the bottom of the gas phase reactor and mixed with the circulating gas stream, which is then introduced into the gas phase reactor.

[0076] The presence of inducing swelling agents, such as high molecular weight hydrocarbons, in the gas phase polymerization step is surprisingly a key factor in improving catalyst productivity in gas phase polymerization when single-site catalysts are involved, especially when it is not necessary to operate the reactor in condensing mode. The adsorption of heavy alkanes or olefins into the polymer particles significantly affects the concentrations of reactants and chain transfer agents (e.g., ethylene, hydrogen, higher alpha olefins, etc.) during PE gas phase polymerization and therefore plays a key role in improving catalyst productivity in the gas phase reactor in a multi-stage, heterogeneous PE polymerization process.

[0077] polymerization catalysts

[0078] The polymerization catalyst used in the present process is a metallocene catalyst. The polymerization catalyst generally comprises (i) a transition metal complex, (ii) a cocatalyst and optionally (iii) a support.

[0079] Preferably, the first polymerization step and the second polymerization step are performed using the same metallocene catalyst, ie in the presence of the same metallocene catalyst.

[0080] The present method preferably utilizes single-site catalysis. Unlike Ziegler-Natta catalysis, polyethylene copolymers prepared using single-site catalysis have properties that allow them to be distinguished from Ziegler-Natta materials. In particular, 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 do not contain, for example, Zr or Hf Group (IV) metals.

[0081] Transition metal complexes (i)

[0082] The transition metal complex comprises a transition metal (M) from Groups 3 to 10 of the Periodic Table (IUPAC 2007) or an actinide or lanthanide transition metal.

[0083] The term "transition metal complex" according to the present invention includes any metallocene or non-metallocene compound of a transition metal which carries at least one organic (coordinating) ligand and which exhibits catalytic activity alone or together with a cocatalyst. Transition metal compounds are well known in the art and the present invention encompasses compounds of metals from Groups 3 to 10, for example Groups 3 to 7 or Groups 3 to 6, such as Groups 4 to 6, and the lanthanides or actinides of the Periodic Table (IUPAC 2007).

[0084] In one embodiment, the transition metal complex (i) has the following formula (ii):

[0085] (L) m R n MX q (iI)

[0086] in

[0087] "M" is a transition metal (M) of Groups 3 to 10 of the Periodic Table (IUPAC 2007),

[0088] Each "X" is independently a monoanionic ligand, such as a sigma-ligand,

[0089] Each "L" is independently an organic ligand coordinated to the transition metal "M",

[0090] "R" is a bridging group connecting the organic ligand (L),

[0091] "m" is 1, 2 or 3, preferably 2,

[0092] "n" is 0, 1 or 2, preferably 0 or 1,

[0093] "q" is 1, 2 or 3, preferably 2, and

[0094] m+q equals the valence of the transition metal (M).

[0095] “M” is preferably selected from zirconium (Zr), hafnium (Hf) or titanium (Ti), more preferably selected from zirconium (Zr) and hafnium (Hf).

[0096] "X" is preferably a halogen, most preferably Cl.

[0097] More preferably, the transition metal complex (i) is a metallocene complex comprising a transition metal compound as defined above comprising a cyclopentadienyl, indenyl or fluorenyl ligand as a substituent "L". In addition, the ligand "L" may have one or more substituents such as an alkyl group, an aryl group, an arylalkyl group, an alkylaryl group, a silyl group, a siloxy group, an alkoxy group or other heteroatom groups. Suitable metallocene catalysts are known in the art and are disclosed 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, among others.

[0098] In one embodiment of the present invention, the metallocene complex is bis(1-methyl-3-n-butylcyclopentadienyl)zirconium(IV) dichloride.

[0099] In another embodiment, the transition metal complex (i) has the following formula (i-II):

[0100]

[0101] wherein each X is independently a halogen atom, a C1-6 alkyl group, a C1-6 alkoxy group, a phenyl group or a benzyl group;

[0102] Each Het is independently a monocyclic heteroaromatic group containing at least one heteroatom selected from O or S;

[0103] L is -R'2Si-, wherein each R' is independently a C1-20 hydrocarbon group or a C1-10 alkyl group substituted with an alkoxy group having 1 to 10 carbon atoms;

[0104] M is Ti, Zr or Hf;

[0105] Each R1 is the same or different and is a C1-6 alkyl group or a C1-6 alkoxy group;

[0106] Each n is 1 to 2;

[0107] Each R2 is the same or different and is a C1-6 alkyl group, a C1-6 alkoxy group or a -Si(R)3 group;

[0108] each R is a C1-10 alkyl or phenyl group optionally substituted with 1 to 3 C1-6 alkyl groups; and

[0109] Each p is 0 to 1.

[0110] Preferably, the compound of formula (i-II) has structure (i-III):

[0111]

[0112] wherein each X is independently a halogen atom, a C1-6 alkyl group, a C1-6 alkoxy group, a phenyl group or a benzyl group;

[0113] L is Me2Si-;

[0114] Each R1 is the same or different and is a C1-6 alkyl group, such as methyl or t-Bu;

[0115] Each n is 1 to 2;

[0116] R2 is a -Si(R)3 alkyl group; each p is 1;

[0117] Each R is a C1-6 alkyl group or a phenyl group.

[0118] Highly preferred transition metal complexes of formula (i-II) are

[0119]

[0120]

[0121] Co-catalyst (ii)

[0122] To form the polymerization catalyst, a cocatalyst, also known as an activator, is used, as is well known in the art. Cocatalysts comprising Al or B are well known and can be used herein. Preferably, aluminoxanes (e.g., MAO) or boron-based cocatalysts (such as borates) are used.

[0123] Suitable cocatalysts are metal alkyl compounds, especially alkylaluminum compounds known in the art. Particularly suitable activators for use with metallocene catalysts are alkylaluminumoxy compounds, such as methylaluminoxane (MAO), tetraisobutylaluminoxane (TIBAO) or hexaisobutylaluminoxane (HIBAO).

[0124] Preferably, the cocatalyst is methylaluminoxane (MAO).

[0125] Carrier (iii)

[0126] According to the scheme in WO03 / 051934, it is possible to use the present polymerization catalyst in solid but unsupported form. Preferably, the present polymerization catalyst is used in solid supported form. The particulate support material used may be an inorganic porous support such as silica, alumina or a mixed oxide such as silica-alumina, in particular silica.

[0127] Preference is given to using a silica support.

[0128] Particularly preferably, the support is a porous material so that the complex can be loaded into the pores of the particulate support, for example using methods similar to those described in WO94 / 14856, WO95 / 12622, WO2006 / 097497 and EP1828266.

[0129] The average particle size of a support such as a silica support may typically be from 10 μm to 100 μm. The average particle size (ie, median particle size, D 50 ) can be measured using a laser diffraction particle size analyzer Malvern Mastersizer 3000, sample dispersion: dry powder.

[0130] The average pore size of the support, such as a silica support, may be in the range of 10 nm to 100 nm, and the pore volume in the range of 1 mL / g to 3 mL / g.

[0131] Examples of suitable support materials are for example ES757 produced and sold by PQ Corporation, Sylopol 948 produced and sold by Grace or SUNSPERA DM-L-303 produced by AGC Si-Tech Co. The support may optionally be calcined before use in catalyst preparation in order to achieve an optimum silanol group content.

[0132] The catalyst may contain 5 to 500 μmol, such as 10 to 100 μmol, of transition metal per gram of support, such as silica, and 3 to 15 mmol of Al per gram of support, such as silica.

[0133] Multimodal polyethylene polymers

[0134] The present invention relates to the preparation of multimodal polyethylene homopolymer or copolymer. The density of the multimodal ethylene homopolymer or copolymer can be between 900 kg / m 3 Up to 980kg / m 3 between, preferably between 905kg / m 3 Up to 940kg / m 3 between, especially 910kg / m 3 Up to 935kg / m 3 between.

[0135] Preferably, the multimodal polyethylene polymer is a copolymer. More preferably, the multimodal polyethylene copolymer is LLDPE. Its density may be 905 kg / m 3 Up to 940kg / m 3 , preferably 910 kg / m3 Up to 935kg / m 3 , more preferably 915kg / m 3 Up to 930kg / m 3 , especially 916kg / m 3 Up to 928kg / m 3 In one embodiment, 910 kg / m 3 Up to 928kg / m 3 The term "LLDPE" as used herein means linear low density polyethylene. The LLDPE is preferably multimodal.

[0136] The term "multimodal" includes polymers that are multimodal with respect to the MFR and thus also includes bimodal polymers.The term "multimodal" may also mean multimodality with respect to the "comonomer distribution".

[0137] In general, polymers are said to be "multimodal" if they comprise at least two polyethylene fractions, which have been produced under different polymerisation conditions, resulting in the fractions having different (weight average) molecular weights and molecular weight distributions. The prefix "multi" relates to the number of different polymer fractions present in the polymer. Thus, for example, the term "multimodal polymer" includes so-called "bimodal" polymers consisting of two fractions. The form of the molecular weight distribution curve, i.e. the appearance of a plot of the polymer weight fraction as a function of its molecular weight, of a multimodal polymer such as LLDPE may show two or more maxima, or at least be significantly broadened compared to the curves for the individual fractions. Typically the final MWD curve will be broad, needle-shaped or show a shoulder.

[0138] Ideally, the molecular weight distribution curve of the multimodal polymer used in the present invention will show two distinct maxima. Alternatively, the polymer fractions have similar MFR and are bimodal with respect to comonomer content. A polymer comprising at least two polyethylene fractions produced under different polymerization conditions resulting in the fractions having different comonomer contents is also referred to as "multimodal."

[0139] For example, if a polymer is produced in a sequential multi-stage process using reactors connected in series and using different conditions in each reactor, the polymer fractions produced in the different reactors will each have their own molecular weight distribution and weight average molecular weight. When a molecular weight distribution curve for such a polymer is recorded, the individual curves from these fractions are superimposed on the molecular weight distribution curve for the total resulting polymer product, typically producing a curve with two or more distinct maxima.

[0140] 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. The difference is preferably at least 5000 g / mol.

[0141] The multimodal polyethylene polymer produced by the present process preferably comprises at least one C4-10 comonomer. The comonomer 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 in both. Hereinafter, the term "LMW / HMW component" will be used, but the embodiments described apply to both the first and second components, respectively.

[0142] It is preferred that the HMW component comprises at least one C4-10 comonomer. The LMW component may then be an ethylene homopolymer or may also comprise at least one C4-10 comonomer. In one embodiment, the multimodal polyethylene polymer comprises a single comonomer. In a preferred embodiment, the multimodal polyethylene polymer comprises at least two, for example exactly two, C4-10 comonomers.

[0143] The total comonomer content in the multimodal polyethylene polymer may be, for example, from 0.2 mol% to 14.0 mol%, preferably from 0.3 mol% to 12 mol%, more preferably from 0.5 mol% to 10.0 mol%, and most preferably from 0.6 mol% to 8.5 mol%.

[0144] 1-Butene may be present in an amount of 0.05 mol% to 6.0 mol%, such as 0.1 mol% to 5 mol%, more preferably 0.15 mol% to 4.5 mol%, and most preferably 0.2 mol% to 4 mol%.

[0145] The C6 to C10 alpha olefins may be present in an amount of 0.2 mol% to 6 mol%, preferably 0.3 mol% to 5.5 mol%, more preferably 0.4 mol% to 4.5 mol%.

[0146] Preferably, the LMW component has a smaller amount (mol %) of comonomer than the HMW component, for example the amount of comonomer (preferably 1-butene) in the LMW component is from 0.05 mol % to 0.9 mol %, more preferably from 0.1 mol % to 0.8 mol %, while the amount of comonomer (preferably 1-hexene) in the HMW component (B) is from 1.0 mol % to 8.0 mol %, more preferably from 1.2 mol % to 7.5 mol %.

[0147] The LMW component of the multimodal polyethylene polymer may have an MFR2 of from 0.5 g / 10 min to 3000 g / 10 min, more preferably from 1.0 g / 10 min to 1000 g / 10 min. In some embodiments, the MFR2 of the LMW component may be from 50 g / 10 min to 3000 g / 10 min, more preferably from 100 g / 10 min to 1000 g / 10 min, for example where cast film is the target.

[0148] The molecular weight (Mw) of the LMW component should preferably be in the range of 20,000 to 180,000, for example 40,000 to 160,000. Its density may be at least 925 kg / m 3 , for example at least 940 kg / m 3 930kg / m 3 Up to 950kg / m 3 , preferably 935kg / m 3 Up to 945kg / m 3 A range of densities is possible.

[0149] The HMW component of the multimodal polyethylene polymer may for example have an MFR2 of less than 1 g / 10 min, such as from 0.2 g / 10 min to 0.9 g / 10 min, preferably from 0.3 g / 10 min to 0.8 g / 10 min, and more preferably from 0.4 g / 10 min to 0.7 g / 10 min. It may have a density of less than 915 kg / m 3 , for example less than 910kg / m 3 , preferably less than 905kg / m 3 The Mw of the higher molecular weight component may be in the range of 70,000 to 1,000,000, preferably 100,000 to 500,000.

[0150] The LMW component may form 30 to 70 wt%, such as 35 to 65 wt%, especially 38 to 62 wt% of the multimodal polyethylene polymer.

[0151] The HMW component may form 30 to 70 wt%, such as 35 to 65 wt%, especially 38 to 62 wt% of the multimodal polyethylene polymer.

[0152] In one embodiment, there is 40 to 45 wt% of the LMW component and 60 to 55 wt% of the HMW component.

[0153] In one embodiment, the polyethylene polymer consists of HMW and LMW as the only polymer components.

[0154] The multimodal polyethylene polymer of the present invention may have an MFR2 of 0.01 g / 10 min to 50 g / 10 min, preferably 0.05 g / 10 min to 25 g / 10 min, especially 0.1 g / 10 min to 10 g / 10 min.

[0155] Example

[0156] catalyst

[0157] SiO2 loading:

[0158] 10 kg of silica (PQ Corporation ES757, calcined at 600° C.) was added from a drum feeder and inerted in the reactor until an O 2 level below 2 ppm was achieved.

[0159] Preparation of MAO / tol / MC:

[0160] At 25 ℃ (oil circulation temperature), a toluene solution (14.1 kg) of 30 wt % MAO was added to another reactor under equilibrium and stirred at 95 rpm, followed by addition of toluene (4.0 kg). After adding toluene, stirring speed was increased from 95 rpm to 200 rpm for 30 minutes. From a metal cylinder, 477 g of metallocene Rac-dimethylsilanediylbis{2-(5-(trimethylsilyl)furan-2-yl)-4,5-dimethylcyclopentadiene-1-yl}zirconium dichloride was added, followed by rinsing with 4 kg of toluene (total toluene amount was 8.0 kg). For MC feed, the reactor stirring speed was changed to 95 rpm and returned to 200 rpm within 3 hours of reaction time. After the reaction time, the MAO / tol / MC solution was transferred to a feed container.

[0161] Preparation of catalyst:

[0162] Reactor temperature is set to 10 ℃ (oil circulation temperature) and stirs with 40rpm after MAO / tol / MC adds.In 205 minutes, add MAO / tol / MC solution (target value 22.5kg, actual value 22.2kg), 60 minutes stirring time (oil circulation temperature is set to 25 ℃) subsequently.After stirring, make " dry mix " stable 12 hours under 25 ℃ (oil circulation temperature), stir with 0rpm.Make reactor return 20 ℃ (repeatedly) and start to stir several rounds with 5rpm, one hour once.

[0163] After stabilization, the catalyst was dried at 60°C (oil circulation temperature) under a 2 kg / h nitrogen flow for 2 hours, followed by drying under vacuum for 13 hours (same nitrogen flow with stirring at 5 rpm). The dried catalyst was sampled and the HC content was measured using thermogravimetric methods with a Sartorius moisture analyzer (model MA45) in a glove box. The target HC level was <2% (actual value was 1.3%).

[0164] Example 1 (Comparative Example)

[0165] LLDPE film was produced using a single-site catalyst with an initial size of 25 μm and a span (i.e., (d90–d10) / d50) of 1.6. The catalyst was first prepolymerized in a prepolymerization reactor at T = 50°C and P = 65 barg. More specifically, 900 kg / h of ethylene, 95 kg of 1-butene / tn ethylene, 0.27 kg of hydrogen / tn propane, and 6.50 tn propane / h (diluent) were fed into the prepolymerization reactor with an average residence time of 30 minutes. The product was transferred to a volume equal to 80 m 3 A split loop reactor was prepared. Ethylene (C2), propane (diluent), 1-butene (C4) and hydrogen (H2) were fed to the reactor under polymerization conditions of T = 85°C, P = 64 barg and an average residence time of 1.0 h. The molar ratios of H2 / C2 and C4 / C2 were 2 mol / kmol and 100 mol / kmol, respectively, and the total production rate in the loop reactor was 25 tn / h (total yield 2.5 kg / gcat). The material was then flushed out in a high-pressure separator and n-heptane was added in varying concentrations during the transition from the slurry to the gas phase process (Examples 2-3). In all cases, the polymerization process in the gas phase reactor was continued with a residence time of 2.5 hours (in all examples), a total pressure of 20 barg, a temperature of 75°C and a gas phase composition of 52.5 mol% propane, 10 mol% nitrogen, 32.5 mol% ethylene, 5 mol% C6 and H2 / C2 = 0.5 mol / kmol. The dimensions of the gas phase reactor were 3.5 m in diameter, 17 m in fluidized bed height, and a superficial gas velocity (SGV) equal to 0.5 m / s. The total mass flow rate of the recirculating gas was 520 tn / h, and the final material properties were: density equal to 914 kg / m 3 , MFI equals 1.2.

[0166] In this example, no n-heptane (i.e., ISA) was added to the gas phase reaction. The total catalyst productivity in the GPR was 3.5 kg / gcat. The production split was 55%, equivalent to 30.6 tn / h of production and 55.6 tn / h of total throughput in the GPR.

[0167] Example 2 (Example of the Present Invention—IE1)

[0168] The procedure of Example 1 was repeated, except that n-heptane was added to the GPR to a heptane concentration of 0.5 mol% in the gas phase (nitrogen concentration in the gas phase was 9.5 mol%). The catalyst productivity in the GPR was 4.0 kg / gcat. The production split was 58%, corresponding to a production of 34.5 tn / h and a total throughput of 59.5 tn / h in the GPR.

[0169] Example 3 (Embodiment IE2 of the present invention)

[0170] The procedure of Example 1 was repeated, except that n-heptane was added to the GPR to a heptane concentration of 1.0 mol% in the gas phase (nitrogen concentration in the gas phase was 9.0 mol%). The catalyst productivity in the GPR was 4.3 kg / gcat. The production split was 60%, corresponding to a production of 37.5 tn / h and a total throughput of 62.5 tn / h in the GPR.

[0171] Table 1 summarizes the results of the examples.

[0172] Table 1: Summary of results.

[0173]

[0174] The presence of the swelling-inducing agent in the gas phase reactor results in a significant increase in catalyst productivity, which in turn leads to an increase in the production rate and overall throughput in the gas phase reactor without affecting the final product characteristics and reactor operability.

Claims

1. A method for polymerizing olefins in a multi-stage polymerization process configuration, the method comprising: a) polymerizing a first olefin monomer in a first polymerization step, optionally in the presence of at least one other alpha olefin monomer, in the presence of a polymerization catalyst to form a first polymer component (A), and b) polymerizing in a second polymerization step in the gas phase a second olefin monomer in the presence of said first polymer component (A) of step a) and a swelling-inducing agent, optionally in the presence of at least one other alpha-olefin comonomer, to form a second polymer component (B), wherein the first polymer component (A) and the second polymer component (B) are produced at a production rate that satisfies a predetermined target weight ratio of the second polymer component (B) to the first polymer component (A), the method comprising the steps of: i) determining a first weight ratio of the second polymer component (B) to the first polymer component (A) in the second polymerization step, and ii) if the determined first weight ratio is less than the predetermined target weight ratio, increasing the concentration of the swelling inducing agent in the second polymerization step, or iii) if the determined first weight ratio is greater than the predetermined target weight ratio, reducing the concentration of the swelling-inducing agent in the second polymerization step, or iv) if the determined first weight ratio is equal to the predetermined target weight ratio, maintaining the concentration of the swelling-inducing agent in the second polymerization step.

2. The method according to claim 1, wherein the swelling-inducing agent is an inert C4-10 alkane and / or a C5-10 comonomer.

3. The method according to claim 2, wherein the swelling-inducing agent is selected from the group consisting of butane, pentane, heptane, 1-pentene, 1-hexene, and mixtures thereof.

4. The process according to claim 1, wherein in the second polymerization step, the pressure is from 3 bar to 30 bar and the residence time is at least 1.5 hours.

5. The method of claim 1, wherein the polymerization catalyst is a single-site catalyst. The method according to claim 5 , wherein the polymerization catalyst is a metallocene catalyst.

7. The method of claim 1, wherein the polymerization catalyst comprises (i) a transition metal complex, (ii) a cocatalyst, and optionally (iii) a support.

8. The process according to claim 1, wherein the total concentration of oligomers, i.e., C6-14 components, in the second polymerization step is in the range of 50 ppm to 1200 ppm of the total reaction mixture.

9. The process according to claim 8, wherein the total concentration of oligomers, i.e., C6-14 components, in the second polymerization step is less than 600 ppm of the total reaction mixture.

10. The process according to claim 8, wherein the total concentration of oligomers, i.e., C6-14 components, in the second polymerization step is less than 500 ppm of the total reaction mixture.

11. The process according to claim 8, wherein the total concentration of oligomers, i.e., C6-14 components, in the second polymerization step is less than 400 ppm of the total reaction mixture.

12. The method of claim 1, wherein the predetermined target weight ratio (B) / (A) is between 0.65 and 2.

5.

13. The method according to claim 12, wherein the predetermined target weight ratio (B) / (A) is between 0.8 and 2.

3.

14. The method of claim 12, wherein the predetermined target weight ratio (B) / (A) is between 0.92 and 1.

9.

15. The method of claim 12, wherein the predetermined target weight ratio (B) / (A) is between 1.0 and 1.

65.

16. Use of a swelling-inducing agent in a gas phase polymerization step in a multi-stage olefin polymerization process for improving gas phase production splitting, wherein the multi-stage olefin polymerization process is the process according to any one of claims 1 to 15.

17. The use according to claim 16, wherein the swelling-inducing agent is an inert C4-10 alkane.

18. The use according to claim 17, wherein the swelling-inducing agent is selected from the group consisting of butane, pentane, heptane and mixtures thereof.

19. The use according to claim 16, wherein the total concentration of oligomers, i.e. C6-10 components, in the gas phase polymerization step is in the range of 50 ppm to 1200 ppm of the total reaction mixture.

20. The use according to claim 19, wherein the total concentration of oligomers, i.e. C6-14 components, in the gas phase polymerization step is less than 600 ppm of the total reaction mixture.

21. The use according to claim 19, wherein the total concentration of oligomers, i.e. C6-14 components, in the gas phase polymerization step is less than 500 ppm of the total reaction mixture.

22. The use according to claim 19, wherein the total concentration of oligomers, i.e. C6-14 components, in the gas phase polymerization step is less than 400 ppm of the total reaction mixture.

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