Multistage polymerisation of propylene

Abstract

There is provided a process for polymerising propylene, optionally in the presence of ethylene and / or at least one alpha-olefin comonomer having 4 to 12 carbon atoms, in multistage polymerisation process configuration. The process comprises polymerising propylene in the presence of particles of a supported single site metallocene catalyst (polymerisation catalyst) in a first reactor to produce a first polymer component; and polymerising propylene in the presence of the first polymer component in at least one downstream reactor. The particles of the supported single site metallocene catalyst have a median particle size, D50, of up to 40 µm, preferably 15 to 40 µm, and / or a particle size distribution that has a relative span of less than 0.9, preferably 0.8 or less. The relative span is defined by the equation: relative span = (D90 - D10) / D50, whereby 90 volume % of the particles of the supported single site metallocene catalyst have a diameter of D90 or less; 50 volume % of the particles of the supported single site metallocene catalyst have a diameter of D50 or less; and 10 volume % of the particles of the supported single site metallocene catalyst have a diameter of D10 or less, relative to the total volume of the particles of the supported single site catalyst.

Description

MULTISTAGE POLYMERISATION OF PROPYLENEBACKGROUND

[0001] The invention relates to a process for polymerising propylene in multistage polymerisation process configuration.

[0002] Multimodal polyolefins are usually polymerised in multi-stage processes in which the different fractions of the multimodal polyolefin resins are polymerised in polymerisation reactors connected in series.

[0003] For example, a multi-stage polymerisation process may be performed by polymerising olefin in e.g., one or more bulk reactor(s), followed by a subsequent polymerization stage in a gas phase reactor. By using such a process, the reaction conditions in each stage can be tailored to provide a broad polymer product portfolio, while maintaining product homogeneity in terms of molecular weight distribution and comonomer concentration distribution. The particle size distribution of the eventual polymer product can also be optimised.

[0004] Gas phase reactors used in polyolefin industry typically employ fluidised beds in which gas and solids come into contact in a defined hydrodynamic regime. In fluidized bed reactors the gases can enter the reactor via a distribution plate. The catalytic particles may be maintained as a fluidised bed by e.g., controlling the circulation of e.g. fluidization gas through the reactor. Polymer produced in the polymerisation reaction may initially form on the surface of catalyst particles, and become detached from the catalyst particles as polymerisation proceeds.

[0005] W02014 / 016318 relates to a process for preparing a polyethylene resin having a multimodal molecular weight distribution in at least two loop slurry reactors connected in series, comprising the step of: polymerizing ethylene in the presence of at least one supported metallocene catalyst, a diluent, optionally one or more co-monomers, and optionally hydrogen, thereby obtaining the polyethylene resin, wherein the supported metallocene catalyst has a particle size distribution of a span value lower than 2.5 and a D50 value within the range of from 5 pm to 20 pm.

[0006] WO 2020 / 064484 relates to a multi-stage process for producing a C2 to C8 olefin polymer composition in a process comprising at least two reactors, wherein a pre-polymerized solid Ziegler-Natta catalyst is prepared by carrying out an off-line pre-polymerization of a solid Ziegler-Natta catalyst component with a C2 to C4 olefin monomer before feeding to the1Sensitivity: Internalpolymerization process, wherein the pre-polymerized solid Ziegler-Natta catalyst has a particle size distribution span (D90 - Dw) / Dso) of below 1 .5.

[0007] WO 2020 / 025757 relates to a process for polymerizing ethylene or copolymerizing ethylene and at least one alpha-olefin comonomer in the presence of a supported polymerization catalyst in a multi-stage process in which the last polymerization stage is a gas phase reactor, the use of said process for reducing particle carry-over in the last polymerization stage and the use of a supported polymerization catalyst with a certain median particle size to polymerize an ethylene homo- or copolymer in said multi-stage process with a span of its particle size distribution which can be predicted from the median particle size of the catalyst.

[0008] WO 2024 / 133045 relates to a process for producing a high-flow polypropylene homopolymer. US 2018 / 142045 relates to a catalyst system for forming propylene polymers having multimodal molecular weight distribution. US 2018 / 142046 relates to supported olefin polymerization catalyst systems.Definitions

[0009] The particle size and particle size distribution (PSD) can be used to measure the size of the supported single site catalyst particles, and / or the size of polymer particles produced in the process described herein.

[0010] The d-values (Dw, Dso and D90) represent the intercepts for 10 volume %, 50 volume % and 90 volume %, respectively, of the total volume of the sample, d-values are well-known in the art and are typically used to provide an indication of the size distribution of particles in a sample.

[0011] For example, the D10 value is indicative of the particle size at which 10 volume % of the sample is comprised of particles with a size less than the Dw value. D50 is indicative of the threshold where 50% of a sample's volume has a smaller particle size that the D50 value, and 50% of a sample's volume has a larger particle size than the D50 value. D90 is indicative of the size at which 90% of the sample's volume is comprised of particles with a size less than the dgo value. The D50 value is also called median particle size. From laser diffraction measurements according to ASTM 13320-1 the volumetric D-values are obtained, based on the volume distribution. The D-values based on mass (weight) can be determined from the2Sensitivity: Internaldensity of the particles. Provided that particle density does not change with particle size then the volume-based PSD and the mass-based PSD are the same, which means that the characteristic values of Dw, Dsoand D90 are the same for the volume and mass-based particle size distributions (PSDs). Thus, weight-based D10, D50 and D90 values are generally interchangeably with volume-based Dw, D50 and D90 which can be determined by laser diffraction measurements according to ASTM 13320-1.

[0012] The distribution span of the particle size distribution is calculated from the d-values according to the formula: (D90 - Dw) / Dso, whereby 90 volume % of the particles of the supported single site catalyst have a diameter of D90 or less; 50 volume % of the particles of the supported single site catalyst have a diameter of Dso or less; and 10 volume % of the particles of the supported single site catalyst have a diameter of Dw or less.Detailed Description

[0013] According to a first aspect of the present invention, there is provided a process for polymerising propylene, optionally in the presence of ethylene and / or at least one alpha-olefin comonomer having 4 to 12 carbon atoms, in multistage polymerisation process configuration. The process comprises polymerising propylene in the presence of particles of a supported single site metallocene catalyst (polymerisation catalyst) in a first reactor to produce a first polymer component; and polymerising propylene in the presence of the first polymer component in at least one downstream reactor. The particles of the supported single site metallocene catalyst have a median particle size, D50, of up to 40 pm, preferably 15 to 40 pm, and / or a particle size distribution that has a relative span of less than 0.9, preferably 0.8 or less. The relative span is defined by the equation: relative span = (D90 - Dw) / Dso, whereby 90 volume % of the particles of the supported single site metallocene catalyst have a diameter of D90 or less; 50 volume % of the particles of the supported single site metallocene catalyst have a diameter of Dso or less; and 10 volume % of the particles of the supported single site metallocene catalyst have a diameter of Dwor less, relative to the total volume of the particles of the supported single site catalyst.

[0014] Preferably, the particles of the supported single site metallocene catalyst have a median particle size, D50, of up to 40 pm, preferably within the range of from 15 to 40 pm.

[0015] The particles of the supported single site metallocene catalyst have a particle size distribution that has a relative span of less than 0.9, preferably 0.80 or less.3Sensitivity: Internal

[0016] The particles of the supported single site metallocene catalyst may have a median particle size, D50, of up to 40 pm and a span of less than 0.9. Preferably, the particles of the supported single site metallocene catalyst may have a median particle size, D50, within the range of from 15 to 40 pm and a span selected from a span less than 0.9 or 0.8 or less.

[0017] More preferably, the supported single site metallocene catalyst has a particle size distribution that has a relative span of at least 0.2, preferably at least 0.3, more preferably at least 0.4. The relative span may be within the range of from 0.2 to 0.8, more preferably from 0.3 to 0.8, even more preferably from 0.4 to 0.8, such as from 0.5 to 0.7.

[0018] It has been found that the mean particle size and / or relative particle size of the supported single site metallocene catalyst can improve the characteristics of the polypropylene produced in multistage polymerisation configuration.

[0019] When the supported single site metallocene catalyst has a relatively small median particle size, and / or a relatively small relative span, heat transfer characteristics around the growing polymer as well as the initial fragmentation pattern of the catalyst particles during polymerisation can be better controlled. For example, the external heat transfer limitations around the growing polymer particles can be decreased when the median particle size and / or relative particle span of the supported single site catalysts fall below certain thresholds. This, in turn, can result in reduced overheating of the polymer particles. As a result, the tendency for particle agglomeration may be reduced.

[0020] Conversely, when the median particle size and / or relative span of the supported single site metallocene catalysts exceed certain thresholds, overheating during polymerisation can occur, increasing the probability of growing polymer particles colliding to form agglomerates or chunks. Such agglomerates can be undesirable for certain applications. In addition, uncontrollable fragmentation pattern result in generation of very small size catalyst particles (also known as catalyst fines) as well as in forming growing polymer particles with poor morphological features (i.e., irregular external surface, low sphericity particles, particle to particle inhomogeneities) On the other hand, if the median particle size of the supported polymer particles falls below certain threshold values, the operability and performance of the polymerisation process can be compromised. By using supported single site metallocene catalyst particles having an optimised median particle size and / or relative span, the morphology of the resulting polymer can be improved, while maintaining desirable polymerisation performance.4Sensitivity: Internal

[0021] There is no need to prepolymerise the supported single site metallocene catalyst prior to introduction into the first reactor. Thus, the process for polymerising propylene in multistage polymerisation process configuration as disclosed herein can be devoid of any off-line prepolymerisation of the supported single site metallocene catalyst. Preferably, the process for polymerising propylene in multistage polymerisation process configuration as disclosed herein is devoid of any off-line prepolymerisation of the supported single site metallocene catalyst

[0022] Advantageously, by using supported single site metallocene catalyst particles having an optimised median particle size and / or relative span, the polypropylene particles produced according to the process of the present disclosure can also have desirable particle size characteristics. For example, the polypropylene produced in the at least one downstream reactor, particularly the most downstream of the downstream reactor(s), may be in the form of particles having a volume-based D90 within the range of from 300 to 2800 pm, more preferably from 400 to 2600 pm and most preferably from 500 to 2300 pm, relative to the total volume of the polypropylene particles. Polypropylene particles having such a particle size distribution may be advantageous. For example, where a gas phase reactor is employed, fluidisation conditions can be maintained, while minimising the risk of segregation, poor mixing and / or small polymer particles being lost by being entrained in the fluidisation gas.

[0023] Advantageously, the polymerisation performance of the process of the present disclosure is also desirable. For example, the activity profiles of the sequence of reactors used in the process of the present disclosure may be optimised. For example, the supported single site metallocene catalyst may be selected to provide the desired activity profiles. For example, the catalyst activity in the first reactor is at least 30 kg / gcat / h; and the catalyst activity in each downstream reactor is not more than 85% of the catalyst activity in the first reactor. More preferably, the catalyst activity in the first reactor is at least 35 kg / gcat / h; and the catalyst activity in each downstream reactor is not more than 80% of the catalyst activity in the first reactor. Most preferably, the catalyst activity in the first reactor is at least 40 kg / gcat / h; and the catalyst activity in each downstream reactor is not more than 75% of the catalyst activity in the first reactor. Catalyst activity is a variable that is significantly influenced by catalyst selection. In particular, morphological properties such as span and mean particle size, as well as physical characteristics like skeletal catalyst density, play a crucial role. These parameters directly impact catalyst fragmentation behavior, reduce heat transfer limitations and particle agglomeration, and ensure optimal activity and kinetics throughout the multi-scale polyolefin process.5Sensitivity: Internal

[0024] Preferably, the at least one downstream reactor is a gas phase reactor. Alternatively or additionally, the at least one downstream reactor comprises a plurality of downstream reactors, wherein the most downstream of the plurality of downstream reactors is a gas phase reactor.

[0025] The gas phase reactor may be operated at a temperature within the range of from 65 to 90 °C, preferably from 70 to 85 °C.

[0026] The process for polymerising propylene in the multistage polymerisation process configuration described herein may be a homopolymerisation or copolymerisation process. For example, in the multistage polymerisation first reactor and / or at least one downstream reactor is a copolymerisation process in which propylene is copolymerised with at least one olefin comonomer having 2 or 4 to 12, preferably 4 to 10, carbon atoms. The olefin comonomer is advantageously an alpha-olefin comonomer. Suitable comonomers include ethylene, butene, pentene, hexene, heptene, octene, nonene, decene, undecane and dodecane. Preferably, where comonomers are used, the comonomer is selected from at least one of ethylene, butene, pentene, hexene, heptene and / or octene.

[0027] Preferably, the first reactor is a bulk phase reactor. The first reactor may be operated at a temperature within the range of from 55 to 75 °C, preferably from 60 to 70 °C.

[0028] The downstream reactor may consist of one downstream reactor. Alternatively, the at least one downstream reactor may comprise at least two downstream reactors, wherein the first of the downstream reactor is a bulk phase reactor and wherein the last of said downstream reactors is a gas phase reactor.

[0029] The process for polymerising propylene in the multistage polymerisation process configuration described herein may further comprise polymerising propylene in the presence of particles of supported single site n catalyst in a prepolymerisation reactor upstream of the first reactor. The prepolymerisation reactor may be an in-line prepolymerisation process. For instance, the prepolymerised polymer produced in the prepolymerisation reaction may be passed into the first reactor in an in-line process. As discussed above, the process may be devoid of any offline prepolymerisation step.

[0030] The process may be a process whereby any polymer produced in the first reactor is passed down into at least one of the downstream reactors. The process may be a process6Sensitivity: Internalwhereby polymerisation in any given downstream reactor takes place in the presence of polymer produced in one or more (e.g., each) of the upstream reactor(s).

[0031] The process for polymerising propylene in the multistage polymerisation process configuration may be a homopolymerisation or copolymerisation process. For example, polymerisation in each reactor may be independently selected from a homopolymerisation or copolymerisation stage. Accordingly, the process may produce a polypropylene that is a homopolymer, copolymer or terpolymer of propylene.

[0032] The supported single site catalyst may comprise a particulate support, such as silica. The particulate support of the supported single site catalyst may have a skeletal density of at least 1.3 g / ml, more preferably at least 1.4 g / ml and most preferably at least 1.5 g / ml. Suitably the skeletal density of the particulate support of the supported single site catalyst is 3.0 g / ml or less, preferably 2.8 g / ml or less, more preferably 2.5 g / ml or less. The skeletal density may be 1.3 g / ml to 3.0 g / ml, preferably 1.4 g / ml to 2.8 g / ml, more preferably 1.5 to 2.7 g / ml, such as 1.7 to 2.5 g / ml.

[0033] The skeletal density (also termed absolute, true, or real density) of the particulate support refers to the density of the material used to form the particulate support. Accordingly, the skeletal density is obtained when the volume of a particle measured excludes the pores, cavities as well as the void spaces between the particles within the bulk sample. The skeletal powder density or absolute powder density is defined according to British Standards Institution as the mass of powder per unit of absolute powder volume whereby the absolute powder volume is defined as the volume occupied by a powder excluding all pores and voids. The skeletal density can be measured by using water or another liquid which is expected to fill the pores in the sample, thus removing their volume from the measurement. The skeletal density can also be measured by employing an apparatus, called Pycnometer, distributed by Micromeritics, Norcross (USA) that utilizes helium or any other inert gas. See also US12 / 043687B2 and example section below. Where the particulate support is formed of silica, for example, the skeletal density of the particulate support is the skeletal density of silica.

[0034] It has been found that more stable operating conditions in the last polymerization stage can be obtained when the particulate support of the supported single site catalyst has a skeletal density above a certain lower limit.Advantageously, by employing supported a single site metallocene catalyst comprising a particulate support having a skeletal density above a threshold value, the likelihood of the supported single site catalyst particles fragmenting during any upstream polymerisation stage7Sensitivity: Internalcan be better controlled so that undesirable (e.g., violent) fragmentation that in turn can result in significant operability challenges as well as poor catalyst activity can be reduced. Fragmentation can change the kinetic profile of the catalyst, and this can alter the activity and polymerisation rates in the various polymerization stages, making operational conditions more difficult to control. By using a supported single site metallocene catalyst comprising a particulate support having a skeletal density above a certain threshold, undesirable (e.g., violent) fragmentation patterns can be reduced. This can help to maintain the median particle size and / or relative span of the supported single site catalyst particles over the course of the process. This, in turn, can result in the formation of polymer particles having a stable and desirable particle size distribution. This can be advantageous, for example, in gas phase polymerisation reactions downstream where fluidisation conditions can be maintained while reducing the risk of small polymer and catalyst particles being lost from the reactor by being entrained in the fluidisation gas.Polymerisation

[0035] As mentioned above, the process of the present disclosure is a process for polymerising olefins preferably in multistage polymerisation process configuration. The process comprises polymerising, in a first reactor, propylene, in the presence of a supported single site catalyst to produce a first polymer component; and polymerising, in a downstream reactor, propylene in the presence of the first polymer component to produce a second polymer component.

[0036] The first polymer component may be transferred to the downstream reactor from the first reactor, such that the second olefin polymer component is produced in the presence of first polymer component. Additionally, the single site catalyst may be transferred from the first reactor to the downstream reactor so that the second olefin monomer is produced in the presence of both the first polymer component and the single site catalyst.

[0037] Preferably, the same catalyst is used in each step and may be transferred from prepolymerisation (if employed) to subsequent polymerisation steps in sequence. Where more than one downstream reactor is employed, the catalyst may be transferred in sequence from the prepolymerisation reactor (if used), the first reactor and to each downstream reactor in sequence. Where more than one downstream reactor is employed, the catalyst may be transferred in sequence from the prepolymerisation reactor (if used) to the first reactor and then to each downstream reactor in sequence. Any polymer produced in each reactor may also be transferred in sequence to any reactor located downstream.8Sensitivity: Internal

[0038] Where one downstream reactor is used, the downstream reactor may be a gas phase reactor. Where more than one downstream reactor is used, at least the most downstream of the downstream reactors may be a gas phase reactor. Preferably, a product stream comprising polymer and unreacted olefin monomer may be withdrawn from the gas phase reactor. This product stream may be recovered from any gas phase reactor where more than one gas phase reactor is employed. Preferably, where more than one downstream gas phase reactor is used, the product stream is recovered from the most downstream of the downstream gas phase reactors.

[0039] The product stream may be withdrawn from a reactor outlet and introduced to a separation unit. In the separation unit, the polymer may be separated from gases, including unreacted olefin monomers that may be adsorbed or contained within the polymer. Unreacted olefin monomer may be recovered from the separated gases, e.g., by distillation. The recovered unreacted olefin monomer may be recycled to the process, preferably to a gas phase reactor as recycled monomer feed.Prepolymerisation

[0040] The process may include a prepolymerisation step, preferably an in-line prepolymerisation step. The purpose of the prepolymerisation is to polymerise a small amount of polymer onto the catalyst at a low temperature and / or a low monomer concentration. By prepolymerisation, it may be possible to improve the performance of the catalyst in the subsequent polymerization process stages.

[0041] The catalyst components are preferably all introduced to the prepolymerisation step when a prepolymerisation step is present. Preferably, the reaction product of the prepolymerisation step is introduced to the polymerisation in which the first polymer component is produced.

[0042] Preferably, prepolymerisation may be performed by polymerising propylene in the presence of particles of a supported single site metallocene catalyst. This supported single site metallocene catalyst may be transferred to the first reactor and downstream reactor(s) in sequence. Thus, this supported single site metallocene catalyst may be used to catalyse more than one, for example, two or three, and more preferably all the polymerisation stages in the process.9Sensitivity: Internal

[0043] The particles of the supported single site metallocene catalyst have a median particle size, D50, of up to 40 pm, preferably within the range of from 15 to 40 pm, and / or a particle size distribution that has a relative span of less than 0.9, preferably 0.8 or less. The relative span is defined by the equation: relative span = (D90 - Dio) / Dso, whereby 90 volume % of the particles of the supported single site metallocene catalyst have a diameter of Dgo or less; 50 volume % of the particles of the supported single site metallocene catalyst have a diameter of D50 or less; and 10 volume % of the particles of the supported single site metallocene catalyst have a diameter of D10 or less.

[0044] Preferably, the particles of the supported single site metallocene catalyst have a median particle size, D50, of up to 40 pm, preferably within the range of from 15 to 40 pm.

[0045] Preferably, the particles of the supported single site metallocene catalyst have a particle size distribution that has a relative span of less than 0.9, preferably 0.8 or less.

[0046] More preferably, the supported single site metallocene catalyst has a particle size distribution that has a relative span of at least 0.2, preferably within the range of from 0.2 to 0.8, more preferably from 0.3 to 0.8, even more preferably from 0.4 to 0.8, such as from 0.5 to 0.7.

[0047] The particles of the supported single site metallocene catalyst may have a median particle size, Dso. of up to 40 pm, and a particle size distribution that has a relative span of less than 0.9, preferably 0.8 or less. Preferably, the particles of the supported single site metallocene catalyst may have a median particle size, D50, within the range of from 15 to 40 pm and a span selected from a span of less than 0.9 or less or 0.8 or less.

[0048] In some instances, catalyst and a cocatalyst can be fed separately into the prepolymerisation stage. Here, it is possible that only a part of the cocatalyst is introduced into the prepolymerisation stage and the remaining part into subsequent polymerisation stages. Also, in such cases it may not be necessary to introduce as much cocatalyst into the prepolymerisation stage to achieve sufficient polymerisation therein.

[0049] It is understood within the scope of the invention that the amount or polymer produced in the prepolymerisation lies within 1 to 7 wt% in respect to the final multimodal (co)polymer. Polymer produced in the prepolymerisation stage may not be detectable in the final polymer product.10Sensitivity: Internal

[0050] Prepolymerisation was carried out at a temperature within the range of from 15 to 40 °C, preferably from 20 to 35 °C, for example, 30 °C. Prepolymerisation pressures may range from 40 to 70 barg, preferably from 50 to 65 barg.Producing the first polymer component

[0051] As discussed above, the process of the present disclosure preferably comprises polymerising, in first reactor, propylene, optionally in the presence of at least one alpha olefin comonomer, to produce a first polymer component.

[0052] The propylene may be polymerised to form a homopolymer as the first polymer component. Alternatively, the propylene may be polymerised to form a copolymer of the propylene and the at least one alpha olefin comonomer as the first polymer component.

[0053] Where an alpha olefin comonomer is used, the alpha olefin comonomer may be selected from a C2 to C12 alkene, preferably a C2 to C10 alkene. For the avoidance of doubt, the alpha olefin comonomer is not propylene. Suitable alpha olefin comonomers include ethylene, 1 -butene, 1 -pentene, 1 -hexene, 1 -heptene, 1 -hexene, 1 -octene, 1 -nonene and 1- decene, 1 -undecene and 1 -dodecene. Preferably, the alpha olefin comonomer is selected from at least one of ethylene, 1 -butene, 1 -hexene, and 1 -octene. One or more alpha comonomers may be employed. Preferably, one or two alpha comonomers are employed.

[0054] The alpha olefin comonomer content of the first polymer component may be within the range from 0 to 10 mol%, preferably from 0 to 8 mol%, more preferably from 0 to 6 mol%.

[0055] The first polymer component may be formed in a bulk reactor(s). The first polymer component may be formed in one or more slurry polymerisation reactor(s) or in a gas phase polymerisation reactor, or a combination thereof. Preferably, the first polymer component may be formed by slurry polymerisation, preferably in a slurry loop reactor(s). Thus, the first reactor may comprise or consist of a slurry loop reactor(s).

[0056] The first polymer component may be formed in one or more slurry polymerisation reactor(s), more preferably in at least two (e.g., two) or at least three (e.g. three) slurry phase reactors. Where, for example, at least three (e.g., three) slurry reactors are used, this does not include a slurry reactor for prepolymerisation.11Sensitivity: Internal

[0057] Slurry polymerisation can take place in an inert diluent, typically a hydrocarbon diluent such as methane, ethane, propane, n-butane, isobutane, pentanes, hexanes, heptanes, octanes etc., or their mixtures. Preferably the diluent is a low-boiling hydrocarbon having from 1 to 4 carbon atoms or a mixture of such hydrocarbons. An especially preferred diluent is propane, possibly containing minor amount of methane, ethane and / or butane. In bulk propylene polymerization, propylene can act as monomer and diluent at the same time.

[0058] Polymer particles of the first polymer component formed by polymerisation, together with the catalyst fragmented and dispersed within the particles, may be suspended in inert diluent. The slurry can be agitated to enable the transfer of reactants from the fluid into the particles.

[0059] The olefin content in the fluid phase of the slurry may be from 2 to about 99 % by mole, preferably from about 3 to about 96% by mole and in particular from about 5 to about 90 % by mole. The propylene content in the fluid phase of the slurry may be from 2 to about 99 % by mole, preferably from about 3 to about 96 % by mole and in particular from about 5 to about 90 % by mole. The benefit of using higher olefin concentration is that the productivity of the catalyst can be increased.

[0060] The temperature in the first reactor may be within the range from 50 to 80 °C, preferably from 55 to 75 °C, more preferably from 60 to 70 °C. The pressure may be within the range from 20 to 150 barg, preferably from 40 to 100 barg, more preferably 50 to 70 barg.

[0061] The residence time in the first reactor and any prepolymerisation reactor employed may be typically within the range from 0.15 h to 3.0 h, preferably from 0.20 h to 2.0 h and in particular from 0.30 to 1 .5 h.

[0062] Where the first polymer component is formed by slurry polymerisation, the slurry polymerisation may be conducted in any known reactor used for slurry polymerisation. Such reactors include a continuous stirred tank reactor and a loop reactor.

[0063] It is especially preferred to conduct the polymerisation in loop reactor. In such reactors the slurry is circulated with a high velocity along a closed pipe by using a circulation pump. Loop reactors are generally known in the art and examples are given, for instance, in US A- 4582816, US-A-3405109, US-A-3324093, EP-A-479186, and US-A-5391654. The slurry may be withdrawn from the reactor either continuously or intermittently. A preferred way of intermittent withdrawal is the use of settling legs where slurry is allowed to concentrate before12Sensitivity: Internalwithdrawing a batch of the concentrated slurry from the reactor. The use of settling legs is disclosed, among others, in US-A-3374211 , US-A-3242150 and EP- A-1310295. Continuous withdrawal is disclosed, among others, in EP-A-891990, EP-A- 1415999, EP-A-1591460 and WO-A-2007 / 025640. The continuous withdrawal is advantageously combined with a suitable concentration method, as disclosed in EP-A- 1310295, EP-A-1591460, and EP3178853B1.

[0064] Hydrogen may be fed into the reactor to control the molecular weight of the polymer as known in the art. Furthermore, one or more alpha-olefin comonomers may be added into the reactor to control the density of the polymer product. The actual amount of such hydrogen and comonomer feeds depends on the catalyst that is used and the desired melt index (or molecular weight) and density (or comonomer content) of the resulting polymer.Polymerisation downstream of the first reactor

[0065] As mentioned above, the process of the present disclosure comprises polymerising propylene in the presence of the first polymer component in at least one downstream reactor. Where one downstream reactor is used, the downstream reactor is a gas phase reactor. Where more than one downstream reactor is used, at least the most downstream of the downstream reactors is a gas phase reactor. Preferably, the process comprises an optional prepolymerisation step, followed by polymerisation in at least one bulk reactor and at least one gas phase reactor. The at least one bulk phase reactor comprise at least one slurry reactor, for instance, two or three slurry reactors coupled as a loop.

[0066] Polymerisation in the at least one downstream reactor (e.g., gas phase reactor) may be a homopolymerisation or copolymerisation reaction.

[0067] Where the reaction is a copolymerisation reaction, propylene is polymerised with at least one alpha olefin comonomer. The alpha olefin comonomer may be selected from a C2 to C12 alkene, preferably C2 to C10 alkene. For the avoidance of doubt, the alpha olefin comonomer is not propylene. Suitable alpha olefin comonomers include ethylene, 1 -butene, 1 -pentene, 1 -hexene, 1 -heptene, 1 -hexene, 1 -octene, 1 -nonene, 1 -decene, 1 -undecene and 1 -dodecene. Preferably, the alpha olefin comonomer is selected from at least one of ethylene, 1 -butene, 1 -hexene, and 1 -octene. One or more alpha comonomers may be employed. For example, one or two alpha comonomers are employed.13Sensitivity: Internal

[0068] The alpha olefin comonomer content of the polymer component formed in the gas phase reactor may be within the range from 0 to 10 mol%, preferably from 0 to 8 mol%, more preferably from 0 to 6 mol%.

[0069] Where an alpha olefin monomer is used to form the first polymer component and any polymer component in the at least one downstream reactor, the same of different alpha olefin comonomer may be used. Alternatively, one or all the first polymer component and any polymer component in the at least one downstream reactor is a homopolymer.

[0070] Where the downstream reactor comprises a gas phase polymerisation, the gas phase polymerisation may be conducted in any known reactor used for gas phase polymerisation. An example of such a reactor is a fluidized bed reactor. Furthermore, a part or whole of the polymer from a polymerisation stage may be returned into a prior polymerisation stage.

[0071] The temperature of gas phase polymerisation may be within the range from 60 to 100°C, preferably from 65 to 90 °C, more preferably from 70 to 85 °C.

[0072] Generally, the operating pressure in the gas phase polymerisation may be within the range from 5 to 30 barg. For example, from 5 to 29 barg. Preferably, the operating pressure may be from 10 to 27 barg, yet more preferably from 15 to 22 barg. Where the second olefin monomer is propylene, the operating pressure may be from 5 to 30 barg, more preferably from 10 to 27 barg, yet more preferably from 15 to 22 barg.

[0073] The residence time of any gas phase polymerisation may be within the range from 1.0 h to 4.5 h, preferably from 1.5 h to 4.0 h and in particular from 2.0 to 3.5 h. The residence time in the gas phase polymerisation may be longer than the residence time in the first reactor (e.g., bulk reactor) by at least 30%, preferably at least 40% or at least 50%.

[0074] The polymer production rate in the gas phase reactor may be within the range from 10 tn / h to 65 tn / h, preferably from 12 tn / h to 58 tn / h and in particular from 13 tn / h to 52.0 tn / h, and thus the total polymer withdrawal rate from the gas phase reactor may be from 15 tn / h to 100 tn / h, preferably from 18 tn / h to 90 tn / h and in particular from 20 tn / h to 80.0 tn / h.

[0075] Where gas phase polymerisation takes place, the gas phase polymerisation is preferably conducted in a gas-solids fluidized bed(s).14Sensitivity: Internal

[0076] An example of a suitable downstream gas phase polymerisation reactor may comprise three zones: a) a bottom zone where fluidization gas is introduced into the reactor; b) a middle zone, which may have a generally cylindrical shape, where olefin monomer(s) present in the fluidization gas are polymerised to form the polymer particles; and c) a top zone, where fluidization gas is withdrawn from the reactor. A fluidization grid (also named distribution plate) may be employed to separate the bottom zone from the middle zone. The top zone may also act as a disengaging or entrainment zone in which, due to its expanding diameter compared to the middle zone, the fluidization gas can expand and disengage from the polyolefin powder.Polymerization catalyst

[0077] The polymerization in the multi-stage olefin polymerization reactors is conducted in the presence of an olefin single site catalyst. The catalyst may be any single site catalyst which can produce the desired olefin polymer. Suitable single site catalysts comprise a transition metal complex, a co-catalyst or activator and a carrier.

[0078] The transition metal complex may be a metallocene comprising a Group 3-12 transition metal. Preferably, the transition metal complex is a Group 4 metal metallocene. More preferably, the transition metal complex is a hafnium or zirconium complex.

[0079] The co-catalyst or activator may be a boron containing compound, an aluminium containing compound or a combination of both. Preferably, the boron containing compound is a borate compound. Preferably, the aluminium containing compound is an aluminoxane such as methylaluminoxane.

[0080] The catalyst employed in the process of the present disclosure is a supported catalyst. The catalyst support is a particulate support. The particulate support can be an inorganic oxide support, such as silica, alumina, titania, silica-alumina and silica-titania. Preferably, the support is silica.

[0081] The particles of the support can have a median particle size, Dso, of up to 40 pm, preferably 15 to 40 pm, and / or a particle size distribution that has a relative span of less than 0.9 or less, preferably 0.8 or less. The relative span is defined by the equation: relative span = (D90 - Dio) / Dso, whereby 90 volume % of the particles of the support have a diameter of D90 or less; 50 volume % of the particles of the support have a diameter of D50 or less; and 10 volume % of the particles of the support have a diameter of D10 or less.15Sensitivity: Internal

[0082] Preferably, the particles of the support have a median particle size, Dso, of up to 40 pm, preferably within the range from 15 to 40 pm.

[0083] Preferably, the particles of the support have a particle size distribution that has a relative span of less than 0.9 or less, preferably 0.8 or less.

[0084] The particles of the support may have a median particle size, Dso, of up to 40 pm and a span of less than 0.9, preferably 0.8 or less. Preferably, the particles of the support may have a median particle size, Dso, of within the range from 15 to 40 pm and a span selected from a span of less than 0.9 or 0.8 or less.

[0085] More preferably, the support particles have a particle size distribution that has a relative span of at least 0.2, preferably within the range from 0.2 to 0.8, more preferably 0.3 to 0.8, even more preferably 0.4 to 0.8, such as from 0.5 to 0.7.

[0086] The support particles may have a skeletal density of at least 1.3 g / ml, more preferably at least 1.4 g / ml and most preferably at least 1.5 g / ml. Suitably the skeletal density of the supported polymerization catalyst is 3.0 g / ml or less, preferably 2.8 g / ml or less, more preferably 2.7 g / ml or less. The skeletal density may be within the range of from 1.3 g / ml to 3.0 g / ml, preferably from 1.4 g / ml to 2.8 g / ml, more preferably from 1.5 to 2.7 g / ml, such as 1.7 to 2.5 g / ml. Methods of measuring skeletal density are described, for example, in US12 / 043687B2 and described in the example section below.

[0087] Metallocene catalysts are preferably used. Metallocene catalysts comprise a transition metal compound which contains a cyclopentadienyl, indenyl or fluorenyl ligand. Preferably the catalyst contains two cyclopentadienyl, indenyl or fluorenyl ligands, which may be bridged by a group preferably containing silicon and / or carbon atom(s). Further, the ligands may have substituents, such as alkyl groups, aryl groups, arylalkyl groups, alkylaryl groups, silyl groups, siloxy groups, alkoxy groups or other heteroatom groups or the like. Suitable metallocene catalysts are known in the art and are disclosed, among others, 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 .ExamplesSkeletal Density MeasurementPrinciple:16Sensitivity: Internal

[0088] In the present measurement skeletal density was measured as the difference of the masses of a dry sample under current conditions and after filling the pores with n- heptane.Analysis:

[0089] Firstly, the density of n-heptane under current conditions was measured by taking a 10 ml bottle and filling the bottle with a pre-determined volume of dry n-heptane. The weight of the n-heptane was measured and the density of the n-heptane was calculated using the formula density = mass / volume.

[0090] In a second step, the weight of a new dry clean bottle was measured. Approximately 2 g catalyst was added into the bottle, and the weight of the catalyst was measured accurately using a high precision balance placed in a glove box.

[0091] A bottle containing the sample was placed in a vacuum impregnator in the glove box. A tube was inserted into the cap of the bottle and a vacuum was applied.

[0092] Vacuum was applied on the bottle such that a pressure of 150 mbar was obtained within 30 seconds. The pressure of 150 mbar was maintained for 5 min. While maintaining the vacuum on the bottle, n-heptane was carefully introduced into the bottle by opening the valve to cover the catalyst sample fully with n-heptane.

[0093] Afterwards, the valve was closed to prevent further n-heptane influx and the vacuum was turned off.

[0094] The bottle was filled to a pre-determined mark with n-heptane. The weight of the filled bottle was measured and then the skeletal density was calculated.Bulk Density

[0095] Bulk density can be determined according to standard methods such as ISO 60:1977 or ASTM D1895-17.Melt flow rate

[0096] The melt flow rate (MFR) was determined according to ISO 1133 and is indicated in g / 10 min. The MFR is an indication of the flowability, and hence the processability, of the17Sensitivity: Internalpolymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR is determined at 190 °C for polyethylene. MFR may be determined at different loadings such as 2.16 kg (MFR2), 5 kg (MFR5) or 21.6 kg (MFR21).Particle Size, Particle Size Distribution

[0097] Particle size distribution [volume percent] and particle sizes were determined by laser diffraction measurements by use of, for example, Mastersizer or Coulter instruments.

[0098] The particle size and particle size distribution is a measure for the size of the particles. The D-values (Dw (or dw), Dso (or dso) and D90 (or dgo)) represent the intercepts for 10%, 50% and 90% of the cumulative volume of sample. The D-values can be thought of as the diameter of the sphere which divides the sample’s volume into a specified percentage when the particles are arranged on an ascending volume basis. For example the D10 is the diameter at which 10% of the sample's volume is comprised of particles with a diameter less than this value. The D50 is the diameter of the particle where 50% of a sample's volume is smaller than and 50% of a sample's volume is larger than this value. The D90 is the diameter at which 90% of the sample's volume is comprised of particles with a diameter less than this value. The D50 value is also called median particle size. From laser diffraction measurements according to ASTM 13320-1 the volumetric D-values are obtained, based on the volume distribution

[0099] The distribution width or span of the particle size distribution (PSD) is calculated from the D-values Dw, D50 and D90 according to the below formula:D90 - D10 Sp“n =DSO

[0100] The mean particle size corresponds to the average particle size. From laser diffraction measurements according to ASTM 13320-1 the volume based mean particle size is obtained and calculated as follows:wherein D = the average or mean particle size(p-q) = the algebraic power of 13pq, whereby p>q Dj = the diameter of the ith particleZ = the summation of DjPor Djqrepresenting all particles in the sample18Sensitivity: Internal

[0101] Only in symmetric particle size distributions the mean particle size and the median particle size D50 have the same value.

[0102] Unless specifically otherwise defined, the percentage numbers (Dw, D50 and D90) used herein refer to percentage by volume.

[0103] The volume-based fraction of each size class (d), of the particle size distribution is providing by the following formula,

[0104] The corresponding mass-based fraction of each size class (d), of the distribution can be calculated by the following formula considering the density of the size class, (pt) and the overall density of the material (tot), i.e. ,

[0105] Provided that the ptis equal to ptot, (assuming particle density does not change with particle size) then the volume-based PSD and the mass-based PSD are the same, that in turn means that the characteristic values of D10, D50 and D90 are the same for the volume and mass-based PSDs.Catalyst preparation

[0106] The single site zirconium-based metallocene catalysts used in the following examples were prepared in a similar manner as disclosed in Examples ICS1 to ICS13 of WO 2020 / 239598.

[0107] In the following catalyst preparations, the silica used as catalyst support was ES757 supplied by Ecovyst. This silica is spray-dried silica calcined at a temperature of 600 °C. The batch of ES757 used for the preparation of the catalysts had a volume-based median particle size (D50) of 31.0 pm (determined by laser diffraction measurement according to ASTM 13320- 1) and a skeletal density of 2.2 g / ml (determined by the above disclosed method). The span (i.e. (D90 - Dw) / D50) of the silica batch was calculated to be 0.64 (see Table 1). It may be noted that there may be variations in measured D-values between different batches of the same silica product.19Sensitivity: InternalSilica sieving

[0108] The silica support used in the preparation of the catalysts of the invention has been sieved into different fractions under inert conditions according to the following method. Selected sieves are kept in an oven at a temperature of 50 °C for at least 12 hours before being moved into a glovebox. The weight of each sieve is recorded inside the glovebox then the sieving tower is built from smallest to largest mesh size and the silica sample is distributed evenly on the top sieve (largest mesh) before recording the total weight of the sieving tower and sample. After vigorously shaking the sieving tower during the time needed to achieve proper distribution of the different silica particle size fractions in the respective sieves, the bottom pan and the different sieves are weighed inside the glovebox and the sieved fractions are determined by the weight difference with the initial weight of the respective sieve.Catalyst A

[0109] The silica ES757 was fractionated using sieve of size >32 pm and sieve of size <90 pm. The span (i.e. (D90 - D10) / D50) of the fractionated silica (A) was calculated to be 0.90 based upon the measured D values as presented in Table 1.

[0110] The sieved silica fraction (A) was used to prepare a supported single site metallocene catalyst system comprising a zirconium-based metallocene complex, methylaluminoxane (MAO), and trityl borate (= trityl tetrakis(pentafluoro-phenyl) borate).

[0111] The span of the catalyst is assumed to be approximately equivalent to the span of the silica, i.e. about 0.90. The volume-based median particle size (D50) of the catalyst is assumed to be equivalent to the volume-based median particle size (D50) of the silica, i.e. 48.20 pm.Catalyst B

[0112] The silica ES757 was sieved using sieves with mesh sizes of smaller than 32 pm. The resulting sieved silica (B) was determined by calculation to have a span of 0.73 as based upon the measured D values as presented in Table 1.

[0113] The sieved silica fraction (B) was used to prepare a supported single site metallocene catalyst system comprising the same metallocene complex as Catalyst A, methylaluminoxane (MAO), and trityl borate following the same preparation procedure as used for preparation of Catalyst A.20Sensitivity: Internal

[0114] The span of the catalyst is assumed to be equivalent to the span of the sieved silica, i.e. about 0.73. The volume-based median particle size (Dso) of the catalyst is assumed to be equivalent to the volume-based median particle size (Dso) of the sieved silica, i.e. 23.50.Catalyst C

[0115] The silica ES757 was sieved using sieves with mesh sizes of 15 pm and 50 pm. The resulting sieved silica (C) was determined by calculation to have a span of 0.55 as shown based upon the measured D values as presented in Table 1.

[0116] The sieved silica fraction (C) was used to prepare a supported single site metallocene catalyst system comprising the same metallocene complex as Catalyst A, methylaluminoxane (MAO), and trityl borate, following the same preparation procedure as used for preparation of Catalyst A.

[0117] The span of the catalyst is assumed to be equivalent to the span of the sieved silica support, i.e. about 0.55. The volume-based median particle size (Dso) of the catalyst is assumed to be equivalent to the volume-based median particle size (Dso) of the sieved silica, i.e. 30.55 pm .Table 1volume based D values determined by laser diffraction according to ASTM 13320-1 .21Sensitivity: InternalExample 1 (Comparative - CE1)

[0118] Catalyst A having a span of 0.90 was used to produce propylene-ethylene copolymers.

[0119] Hydrogen, propylene, and the catalyst were fed to the pre-polymerisation reactor. The prepolymerisation reactor was operated at 56.5 barg and 25°C temperature and a mean residence time of 30 mins.

[0120] The pre-polymer along with additional propylene and hydrogen for molecular weight control were fed to the bulk loop reactor. The reaction took place in bulk propylene at 63°C, 54.5 barg, with a mean residence time of 45 mins. The slurry concentration was approximately 30 wt% and the average catalyst activity in the loop was 25 kg / gcat / h.

[0121] The slurry from the loop reactor was fed directly to the gas phase reactor (GPR) operated at 75°C and 20 barg. The overall residence time in the GPR was 2.5 hr and the average catalyst activity in GPR was 10 kg / gcat / h.

[0122] The process was continuously operated for three days. After that it was shut down due to operational problems caused by agglomerates formed in the loop and GPR reactors. Severe issues with powder flowability inside the flashing pipe between the loop and the GPR were also encountered, as well as disturbances in fluidization. The process was stopped, the reactors opened, inspected and many large agglomerates were found with average size being above 10 cm.Example 2 (Inventive - IE1)

[0123] In Example 2, the polymerization series described in Example 1 was repeated except for that Catalyst B with a span of 0.73 was used.

[0124] The average catalyst activity in loop was 32 kg / gcat / h and the average catalyst activity in GPR was 15 kg / gcat / h.

[0125] The operation of the process was smooth, and process was continuously operated for three weeks without any operational challenges.Example 3 (Inventive - IE2)22Sensitivity: Internal

[0126] In Example 3, the polymerization series described in Example 1 was repeated except for that Catalyst C with a span of 0.55 was used.

[0127] The average catalyst activity in loop was 40 kg / gcat / h and the average catalyst activity in GPR was 18 kg / gcat / h.

[0128] The operation of the process was smooth, and process was continuously operated for three weeks without any operational challenges.Table 2: Summary of polymerization conditions Example 1 (Comparative) and Examples 2 and 3 (Inventive).23Sensitivity: Internal* after removing / sieving particles of size above 2.5 mm as well as agglomerates of size above 10 cm.24Sensitivity: Internal

Claims

CLAIMS1 . A process for polymerising propylene, optionally in the presence of ethylene and / or at least one alpha-olefin comonomer having 2 or 4 to 8 carbon atoms, in multistage polymerisation process configuration, said process comprising: polymerising propylene in the presence of particles of a supported single site metallocene catalyst in a first reactor to produce a first polymer component; and polymerising propylene in the presence of the first polymer component in at least one downstream reactor; wherein the particles of the supported single site metallocene catalyst have a particle size distribution that has a relative span of less than 0.9, preferably 0.8 or less; wherein the relative span is defined by the equation: relative span = D90 - D10) / D50 whereby 90 volume % of the particles of the supported single site metallocene catalyst have a diameter of D90 or less; 50 volume % of the particles of the supported single site metallocene catalyst have a diameter of Dso or less; and 10 volume % of the particles of the supported single site metallocene catalyst have a diameter of D or less, relative to the total volume of the particles of the supported single site metallocene catalyst, wherein the particle sizes are measured according to ASTM 13320-1 , and wherein the supported single site metallocene catalyst is selected such that the catalyst activity in the first reactor is at least 30 kg / gcat / h; and wherein the catalyst activity in each downstream reactor is not more than 85% of the catalyst activity in the first reactor.

2. The process as claimed in claim 1 , wherein the supported single site metallocene catalyst comprises a particulate support having a skeletal density of at least 1.3 g / ml, more preferably at least 1 .4 g / ml and most preferably at least 1 .5 g / ml.

3. The process as claimed in any one of the preceding claims, wherein the supported single site metallocene catalyst has a particle size distribution that has a relative span of at least 0.2, preferably within the range of from 0.2 to 0.8, more preferably from 0.3 to 0.8, even more preferably from 0.4 to 0.8.

4. The process as claimed in any one of the preceding claims, wherein the at least one downstream reactor is a gas phase reactor.Sensitivity: Internal5. The process as claimed in any one of claims 1 to 3, wherein the at least one downstream reactor comprises a plurality of downstream reactors and wherein the most downstream of the plurality of downstream reactors is a gas phase reactor.

6. The process as claimed in claim 4 or 5, wherein the gas phase reactor is operated at a temperature within the range of from 65 to 90 °C, preferably from 70 to 85 °C.

7. The process as claimed in any one of the preceding claims, wherein polymerisation of propylene in the first reactor and / or at least one downstream reactor is a copolymerisation process in which propylene is copolymerised with ethylene and / or at least one olefin monomer having 4 to 8 carbon atoms.

8. The process as claimed in any one of the preceding claims, wherein the particles of the supported single site metallocene catalyst have a median particle size, Dso, of up to 40 pm, preferably within the range of from 15 to 40 pm.

9. The process as claimed in any one of the preceding claims, wherein the supported single site metallocene catalyst comprises particles comprising a transition metal; preferably wherein the supported single site metallocene catalyst comprises supported metallocene catalyst particles.

10. The process as claimed in any one of the preceding claims, wherein the first reactor is a bulk phase reactor.

11. The process as claimed any one of the preceding claims, wherein the first reactor is operated at a temperature within the range of from 55 to 75 °C, preferably from 60 to 70 °C.

12. The process as claimed in claim 10 or 11 , wherein the at least one downstream reactor comprises at least two downstream reactors, wherein the first of the downstream reactor is a bulk phase reactor and wherein the last of said downstream reactors is a gas phase reactor.

13. The process as claimed in any one of the preceding claims, which further comprises polymerising propylene in the presence of particles of supported single site metallocene catalyst in a prepolymerisation reactor upstream of the first reactor.26Sensitivity: Internal4. The process as claimed in any one of the preceding claims, wherein the polypropylene produced in the at least one downstream reactor is in form of particles with a volumebased D90 within the range of from 300 to 2300 pm, relative to the total volume of polypropylene particles.27Sensitivity: Internal

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