Process for producing a multimodal polyolefin composition with an extruder device

Abstract

A continuous process for producing a multimodal polyolefin composition comprising one or more antioxidants, the process comprising: producing a multimodal polyolefin in the form of a polyolefin powder having a mass median diameter D50 of the polyolefin particles in the range of 300 μm to 2500 μm in a series of polymerization reactors; mixing the polyolefin powder with an organic peroxide without melting the polyolefin powder; melting and homogenizing the mixture in an extruder device; adding one or more antioxidants to the molten polyolefin composition; homogenizing the combination of the molten polyolefin composition and the antioxidant to form a molten polyolefin composition with the antioxidant added; and pelletizing the molten polyolefin composition with the antioxidant added.

Description

[Technical field]

[0001] The present disclosure provides a process for preparing a polyethylene composition, including a bimodal or multimodal polyethylene. In particular, the present disclosure provides a continuous process for producing a multimodal polyolefin composition, including one or more antioxidants, from a multimodal polyolefin in the form of a polyolefin powder, utilizing an organic peroxide. [Background technology]

[0002] Polyolefins are widely used commercial polymers. To achieve and maintain desired properties, additional substances are added to the polymers. These so-called plastic additives are auxiliary compounds that, despite being added in small amounts, have a significant effect on the polymer's properties, making the polymer commercially useful. The additives are usually mixed directly with the polyolefins after they have been polymerized during the pelletizing step. Antioxidants are one type of additive that is widely used. These polymer additives inhibit the degradation of the polymer caused by reactions with atmospheric oxygen. Antioxidants are effective at all stages of the polymer's life cycle. Their use allows plastic products to be produced faster and with fewer defects, extending the product's useful life and making it easier to recycle.

[0003] A particular type of additive that can be added after polymerization to be present in the pelletization step of the polyolefin is a free radical generator, such as a peroxide, which can be used, for example, to modify the molecular structure of the polyolefin.

[0004] An important use of polyolefins is in the manufacture of pipes, particularly pressure pipes, i.e., pipes designed to transport fluids under conditions where the pressure inside the pipe is higher than that outside the pipe. Suitable materials for manufacturing polyolefin pipes with excellent mechanical properties, including good pressure resistance and good chemical resistance over a long period, are bimodal or multimodal polyethylene with a density of 0.940 g / cm 3 ~0.968 g / cm 3 of.

[0005] For application in pipe manufacturing, the polyolefin must have good pipe extrusion processability. One of the characteristics in this processability, especially in the manufacture of large-diameter pipes, is high resistance to the "sagging" of the resulting pipe. "Sagging" refers to a phenomenon in which during the melt extrusion of the pipe, a part of the melt flows from the upper part to the lower part of the pipe, resulting in unacceptable variations in the pipe wall thickness around the pipe.

[0006] To improve the sagging behavior of pipes made from bimodal or multimodal polyethylene, peroxides can be added during the pelletization of bimodal or multimodal polyethylene. For example, WO2013 / 101767A2 discloses manufacturing a bimodal high-density polyethylene polymer composition by supplying a bimodal high-density polyethylene base resin and a peroxide to an extruder and mixing the polymer composition and the peroxide in the extruder until they are substantially homogeneous.

[0007] WO2016 / 005044A1 relates to a multimodal polyethylene composition that can be used to manufacture pipes. The multimodal polyethylene composition includes a high-density multimodal ethylene polymer component and an ultra-high molecular weight ethylene polymer component. The high-density multimodal polyethylene composition is preferably manufactured in a compounding step before the pipe extrusion step. It is also disclosed that a peroxide masterbatch is added during compounding to induce an LCB / crosslinking reaction.

[0008] WO2016 / 064984A1 relates to a crosslinked metallocene catalyst polyethylene copolymer and articles (e.g., pipes) made therefrom. The crosslinked metallocene catalyst polyethylene copolymer can be obtained by contacting a polyethylene copolymer base resin with a peroxide modifier. The peroxide modifier can be used as a powder, as a masterbatch, as a carrier (e.g., polypropylene, calcium carbonate, etc.), or as a combination thereof.

[0009] WO2017 / 112642A1 discloses a polyethylene blend comprising a partially crosslinked multimodal polyethylene composition that can be extruded into articles of various shapes, such as pipes. The polyethylene blend is obtained by combining a multimodal polyethylene resin and a peroxide masterbatch.

[0010] WO2018 / 022885A1 discloses a pipe comprising a bimodal high molecular weight high density polyethylene extruded in the presence of one or more organic peroxides. In the method for manufacturing the pipe, a porous polypropylene random copolymer is used as a carrier for the organic peroxide.

[0011] EP29661223A1 discloses a multimodal polyethylene composition that can be used to produce pipes exhibiting improved pressure resistance and creep resistance. Optionally, a free radical generator such as a peroxide can be added to produce a modified polymer composition and increase the η 0.05 value.

[0012] EP3450127A1 discloses a process for producing a polyolefin composition, comprising supplying a bimodal or multimodal polyolefin in the form of a polyolefin powder having a mass median diameter D50 in the range of 400 m to 2500 m and one or more additives to a mixing device, mixing the polyolefin powder and the additives, and transferring the mixture to an extruder device to melt and homogenize the mixture.

[0013] However, it is necessary to provide a polyethylene composition containing bimodal or multimodal polyethylene that has high sag resistance and a reduced gel level. SUMMARY OF THE INVENTION

[0014] The present disclosure is a continuous process for producing a multimodal polyolefin composition containing one or more antioxidants, the process comprising the following steps. Step a) of producing a multimodal polyolefin in the form of a polyolefin powder having a mass median diameter D50 of the polyolefin particles in the range of 300 μm to 2500 μm by polymerizing one or more 1-olefins in the presence of an olefin polymerization catalyst at a pressure of 0.5 MPa to 10 MPa and a temperature of 30 °C to 160 °C in a series of two or more polymerization reactors, wherein in step a) the multimodal polyolefin is multimodal polyethylene, said step a), Step b) of supplying an organic peroxide to the polyolefin powder in an amount of 20 ppm or more and less than 100 ppm, preferably 25 ppm or more and 95 ppm or less, more preferably 28 ppm or more and 80 ppm or less, Step c) of mixing the polyolefin powder produced in step a) and the organic peroxide supplied in step b) at a temperature in the range of 10 °C to 100 °C without melting the polyolefin powder to form a polyolefin peroxide mixture, Step d) of melting and homogenizing the polyolefin peroxide mixture obtained in step c) in an extruder device, where at least 90% by weight of the organic peroxide decomposes to form a molten polyolefin composition, Step e) of adding one or more antioxidants to the molten polyolefin composition obtained in step d) to form a combination of the molten polyolefin composition and the antioxidant, Step f) of homogenizing the combination of the molten polyolefin composition and the antioxidant to form a molten polyolefin composition with the antioxidant added, g) Provide a continuous process for pelletizing a melt polyolefin composition to which an antioxidant is added.

[0015] In some embodiments, the multimodal polyolefin in the form of polyolefin powder is produced in one or more gas-phase polymerization reactors, and at least one of the gas-phase polymerization reactors is a multi-zone circulation reactor in which one polymerization zone is a riser in which growing polymer particles flow upward under high-velocity fluidization or transport conditions, and the other polymerization zone is a sub-zone of a downcomer in which growing polymer particles flow downward in a high-density form. The riser and the downcomer are interconnected, and the polymer particles exiting the riser enter the downcomer, and the polymer particles exiting the downcomer enter the riser, thereby establishing a circulation of polymer particles through the riser and the downcomer.

[0016] In some embodiments, the series of polymerization reactors includes a fluidized bed reactor upstream of the multi-zone circulation reactor.

[0017] In some embodiments, the olefin polymerization catalyst is a Ziegler catalyst or a Ziegler-Natta catalyst comprising a reaction product of an aluminum alkyl and a titanium compound supported on a magnesium halide.

[0018] In some embodiments, the extruder device is a combination of two co-rotating twin-screw extruders. The polyolefin powder and the organic peroxide are transferred to the first twin-screw extruder, where step d) is performed. A stream of the melt polyolefin composition formed in step d) is supplied to the second twin-screw extruder, where step f) is performed, or the extruder device is a counter-rotating continuous mixer equipped with a gear pump or a co-rotating twin-screw extruder equipped with a gear pump.

[0019] In some embodiments, pass the melt polyolefin composition to which the antioxidant is added through a melt filter before pelletizing.

[0020] In some embodiments, the multimodal polyolefin in the form of the polyolefin powder produced in step a) and the organic peroxide provided in step b) are fed into a mixing device, and the mixing in step c) is carried out in the mixing device.

[0021] In some embodiments, the multimodal polyolefin in the form of the polyolefin powder produced in step a) is directly fed into the extruder device, or a multimodal polyolefin composition in the form of the polyolefin powder produced in step a) is fed into a mixing device, where it is mixed with one or more additives different from the antioxidant and the organic peroxide, and a mixture containing the polyolefin powder and the additives different from the antioxidant and the organic peroxide is transferred from the mixing device to the extruder device, and the organic peroxide supplied in step b) is fed into the extruder device at a position where the polyolefin powder or the mixture containing the polyolefin powder and the additives different from the antioxidant and the organic peroxide is not yet melted.

[0022] In some embodiments, the mixing in step c) is carried out in an atmosphere with a reduced oxygen content, and the oxygen content in the gas phase in the mixing device is less than 5% by volume.

[0023] In some embodiments, in step b), the organic peroxide is supplied as a liquid or as a liquid component, or the organic peroxide is supplied in the form of a mixture of the organic peroxide and the polyolefin powder.

[0024] In some embodiments, in step b), the organic peroxide is supplied as a liquid or as a liquid component, and the liquid containing the organic peroxide is added to the polyethylene powder by passing the liquid through a spring injector including a preload spring at an injection pressure of 0.5 to 4 MPa.

[0025] In some embodiments, the organic peroxide is supplied as a peroxide solution having an active oxygen content in the range of 0.1 wt% to 10 wt%.

[0026] In some embodiments, the multimodal polyolefin produced in step a) has an M w / M n of 15 to 40.

[0027] In some embodiments, the multimodal polyolefin produced in step a) is multimodal polyethylene, preferably having a density measured according to DIN EN ISO 1183-1:2004 at 23 °C of 0.940 g / cm 3 to 0.968 g / cm 3 of multimodal polyethylene.

[0028] In some embodiments, the present disclosure provides step a) of producing a multimodal polyolefin composition by the process according to any one of claims 1 to 14, and step b) of shaping the multimodal polyolefin composition into a pipe, and provides a process for manufacturing a pipe.

Brief Description of the Drawings

[0029]

Figure 1

Figure 2

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[0030] The present disclosure provides a continuous process for manufacturing a multimodal polyolefin composition containing one or more antioxidants. This process includes, as step a), a step of manufacturing a multimodal polyolefin in the form of polyolefin powder.

[0031] Step a) of the process of the present disclosure refers to manufacturing a multimodal poly(ethylene) by homopolymerizing or copolymerizing ethylene. Preferred comonomers in ethylene polymerization are C 3 -C 8 -1-alkenes, preferably 1-butene, 1-pentene, 1-hexene, 1-octene, or mixtures thereof up to 40% by weight. Particularly preferred is a process of copolymerizing ethylene with one or more C 3 -C 8 -1 alkenes in an amount of 0.01% to 20% by weight, more preferably 0.05% to 12% by weight. Particularly preferred comonomers for copolymerizing ethylene are 1-hexene and / or 1-butene.

[0032] The polyolefin in the form of polyolefin powder according to the present disclosure is a multimodal polyolefin. The term "multimodal" can refer to the aspect of the molecular weight distribution. Such multimodal polyolefins can be obtained by polymerizing or copolymerizing one or more olefins in a series of two or more polymerization reactors under different reaction conditions, or by using a mixed catalyst system containing two or more types of polymerization catalysts that produce polyolefins of different molecular weights under the same polymerization conditions. Thus, "modality" refers to the number of different polymerization conditions used in the production of the polyolefin, or the number of different types of polymerization catalysts included in the mixed polymerization catalyst system, regardless of whether this modality of the molecular weight distribution can be recognized as a separated maximum of the gel permeation chromatography (GPC) curve. The term "multimodal", which is frequently used in the art and is also used herein, can include bimodal. In addition to the molecular weight distribution, the polyolefin polymer can also have a comonomer distribution, and preferably, the average comonomer content of the polymer chains having a higher molecular weight is higher than the average comonomer content of the polymer chains having a lower molecular weight. However, it is also possible to employ the same or very similar reaction conditions in all of the polymerization reactors of a series of polymerization reactors to produce a polyolefin with a narrow molecular weight. However, the complexity in producing a multimodal polyolefin in a series of polymerization reactors operating under different reaction conditions is caused by the different residence times of the individual polyolefin particles in the different reactors, and the composition of the individual polyolefin particles in the polyolefin powder can vary greatly.

[0033] All polymerization methods known in the industry can be used in the production of multimodal polyolefins. These polymerization processes include solution processes, suspension processes, and gas phase processes. This type of process is generally known to those skilled in the art. Among the above polymerization processes, gas phase polymerization in a gas phase fluidized bed reactor or a multi-zone circulation reactor, and suspension polymerization in a loop reactor or a stirred tank reactor in particular are preferred.

[0034] The polymerization for producing the multimodal polyolefin in step a) of the process of the present disclosure is carried out at a pressure of 0.5 MPa to 10 MPa, preferably 1.0 MPa to 8 MPa, particularly 1.5 MPa to 4 MPa, and these pressures, like all pressures shown in the present disclosure, must be understood as absolute pressures, i.e., pressures having the dimension of MPa (abs). The polymerization is carried out at a temperature of 30 °C to 160 °C, preferably 65 °C to 125 °C. The upper limit temperature of this range is preferred for producing relatively high-density ethylene polymers, and the lower limit temperature of this range is preferred for producing relatively low-density ethylene copolymers.

[0035] The multimodal polyolefin in the form of polyolefin powder produced in step a) of the process of the present disclosure is produced by polymerizing one or more 1-olefins in a series of two or more polymerization reactors. Preferably, at least one of the polymerization reactors is a gas-phase polymerization reactor. In a preferred embodiment, the multimodal polyolefin is produced in a series of reactors comprising two or more series of gas-phase polymerization reactors, preferably two or more series of fluidized-bed reactors, or a multizone circulation reactor and one or more different gas-phase polymerization reactors (e.g., fluidized-bed reactors), or the multimodal polyolefin is first produced in one or more series of suspension polymerization reactors (e.g., loop reactors) and then in one or more gas-phase polymerization reactors (e.g., fluidized-bed reactors).

[0036] In a preferred embodiment of the present disclosure, at least one of the polymerization reactors in a series of polymerization reactors is a gas-phase polymerization reactor, and the gas-phase polymerization reactor includes a riser unit in which growing polymer particles flow upward under fluidization, high-velocity fluidization, or transport conditions, and a downcomer in which growing polymer particles flow downward in a high-density form.

[0037] The riser unit in which growing polymer particles flow upward may include a fluidized bed of growing polymer particles. The riser unit operates as a completely mixed gas-phase reactor such as a fluidized bed reactor. The fluidized bed reactor is a reactor in which polymerization is carried out in a bed of polymer particles maintained in a fluidized state by supplying a reaction gas mixture from the lower end of the reactor (usually below a gas distribution grid having a function of distributing the gas flow) and withdrawing the gas again from the upper end. The reaction gas mixture is then returned to the lower end of the reactor via a recycle line equipped with a compressor and a heat exchanger for removing the heat of polymerization. The velocity of the reaction gas mixture must be high enough to fluidize the mixed bed of fine polymers present in the tube functioning as the polymerization zone first and high enough to effectively remove the heat of polymerization second.

[0038] When a polymerization unit including a fluidized bed of growing polymer particles is used as the riser unit, the downcomer can be arranged inside, around, or adjacent to the gas-phase reactor. As the downcomer in which growing polymer particles flow downward in a high-density form, two or more separated polymerization units can also be used.

[0039] In a particularly preferred embodiment of the present disclosure, the riser unit is a riser in which an upward movement of growing polymer particles occurs under fast fluidization or transport conditions. Fast fluidization conditions in the riser are established by supplying the reaction gas mixture at a velocity higher than the transport velocity of the polymer particles. The velocity of the reaction gas mixture is generally 0.5 to 15 m / s, preferably 0.8 to 5 m / s. The terms "transport velocity" and "fast fluidization conditions" are well known in this field. For the definitions of these terms, see, for example, "D. Geldart, Gas Fluidization Technology, page 155 et seq., J. Wiley & Sons Ltd., 1986".

[0040] The part of the polymerization reactor where the growing polymer particles flow downward in a high-density form is sometimes called a "downcomer", but may also be called a "moving bed" or "sedimentation bed" unit or reactor. The term "high-density form" needs to be understood in the sense that the ratio of the mass of the polymer to the volume of the reactor exceeds 80% of the "injected bulk density" of the resulting polymer. Thus, for example, if the bulk density of the polymer is 420 kg / m 3 , "high-density form" means that the ratio of the mass of the polymer to the volume of the reactor is at least 3 . The "injected bulk density" of the polymer is a parameter well known to those skilled in the art and can be measured according to DIN EN ISO60:1999. The density of the solid in the reactor is defined as the mass of the polymer per volume of the reactor occupied by the polymer.

[0041] Typically, a downcomer is part of a polymerization reactor that contains a layer of growing polymer particles that move downward in a substantially plug flow mode. "Plug flow mode" means that there is little or preferably no backmixing of the polymer particles.

[0042] To replace the reacted olefin and control the gas flow in the downcomer, a gaseous or liquid feed stream can be introduced at one or more positions in the downcomer. The feed stream preferably contains ethylene and may further contain one or more comonomers, an inert component such as propane, or hydrogen. Depending on the amount of the gas or liquid feed stream added to the downcomer and the pressure conditions in the downcomer, the gas medium surrounding the polymer particles is designed to move downward simultaneously with the polymer particles or to move upward in countercurrent to the polymer particles. When a liquid stream is fed to the downcomer, these liquid streams preferably vaporize in the downcomer and contribute to the composition of the reaction gas mixture in the downcomer. When operating the downcomer with multiple feed streams, the feed points for introducing the feed streams into the downcomer are preferably evenly distributed over the height of the downcomer.

[0043] In the most preferred embodiment of the present disclosure, one of the polymerization reactors is a multi-zone circulation reactor. Such reactors are described, for example, in WO97 / 04015A1 and WO00 / 02929A1 and include two interconnected polymerization zones, namely a riser in which growing polymer particles flow upward under fast fluidization or transport conditions and a downcomer in which growing polymer particles flow in a high-density form under the action of gravity. The polymer particles exiting the riser enter the downcomer, and the polymer particles exiting the downcomer are reintroduced into the riser, thereby establishing polymer circulation between the two polymerization zones and the polymer passes through these two zones alternately a plurality of times. In such a polymerization reactor, a solid / gas separator is disposed above the downcomer to separate the polyolefin and reaction gas mixture coming from the riser. The growing polyolefin particles enter the downcomer, and the separated reaction gas mixture of the riser is continuously recycled through a gas recycle line to one or more reintroduction points to the polymerization reactor. Preferably, most of the recycled gas is recycled to the bottom of the riser. The recycle line is preferably equipped with a compressor and a heat exchanger for removing the polymerization heat. Preferably, a line for catalyst supply is disposed above the riser and a polymer discharge system is disposed at the bottom of the downcomer. The introduction of make-up monomer, comonomer, hydrogen, and / or inert components can occur at various points along the riser and downcomer.

[0044] According to a preferred embodiment of the present disclosure, the reaction gas mixture exiting the riser unit is partially or completely prevented from entering the downcomer in order to establish different polymerization conditions between the riser unit and at least a part of the downcomer. This can be achieved, for example, by supplying a barrier fluid in the form of a gas and / or liquid mixture to the downcomer, preferably to the upper part of the downcomer. The barrier fluid needs to have a suitable composition different from the gas mixture present in the riser unit. The amount of the barrier fluid added can be adjusted such that the upward flow of the gas countercurrent to the flow of the polymer particles is generated, especially at its upper part, and functions as a barrier to the gas mixture entrained by the particles coming from the riser unit.

[0045] The barrier fluid is preferably obtained from a recycle gas stream, more preferably by partially condensing the stream. As a result, the barrier fluid can also contain, in addition to the monomers to be polymerized, inert compounds used as polymerization diluents such as nitrogen, alkanes having 1 to 10 carbon atoms, hydrogen, or other components of the reaction gas mixture.

[0046] The polymerization in the gas-phase polymerization reactor of a series of polymerization reactors can also be carried out in a condensation mode or a super-condensation mode, in which case a part of the circulating reaction gas mixture is cooled below the dew point and returned to the reactor separately as a liquid and a gas phase or together as a two-phase mixture to further utilize the evaporation enthalpy for cooling the reaction gas.

[0047] In a preferred embodiment of the present disclosure, a series of polymerization reactors includes a gas-phase polymerization reactor including a riser unit and a downcomer, and further polymerization reactors of the series of polymerization reactors can be any type of low-pressure polymerization reactor such as a gas-phase reactor or a suspension reactor. When suspension polymerization is included in the polymerization process of the series of polymerization reactors, it is preferred that the suspension polymerization is carried out upstream of the gas-phase polymerization. Reactors suitable for carrying out such suspension polymerization include, for example, loop reactors or stirred tank reactors. Suitable suspension media include, inter alia, inert hydrocarbons such as isobutane, mixtures of hydrocarbons, or the monomer itself. Such an additional polymerization stage carried out in suspension may also include a prepolymerization stage. When the multi-stage polymerization of olefins includes an additional polymerization stage carried out in the gas phase, the additional gas-phase polymerization reactor can be any type of gas-phase reactor such as a horizontally or vertically stirred gas-phase reactor, a fluidized bed reactor, or a multi-zone circulation reactor. Such an additional gas-phase polymerization reactor can be arranged downstream or upstream of the gas-phase polymerization reactor. In a particularly preferred embodiment of the present disclosure, the gas-phase polymerization reactor including the riser unit and the downcomer is part of a series of polymerization reactors in which a fluidized bed polymerization reactor is arranged upstream of the gas-phase polymerization reactor.

[0048] Figure 1 schematically shows a setup of a series of polymerization reactors including a fluidized bed reactor and a multi-zone circulation reactor for producing a multimodal polyolefin according to step a) of the process of the present disclosure.

[0049] The fluidized bed reactor (1), which is the first gas-phase reactor, includes a fluidized bed (2) of polyolefin particles, a gas distribution grid (3), and a velocity reduction zone (4). The velocity reduction zone (4) generally has a larger diameter compared to the diameter of the fluidized bed portion of the reactor. The polyolefin bed is kept in a fluidized state by the upward flow of gas supplied through the gas distribution grid (3) disposed at the bottom of the reactor (1). The gas stream of the reaction gas mixture discharged from the upper part of the velocity reduction zone (4) via the recycle line (5) is compressed by the compressor (6), sent to the heat exchanger (7), cooled there, and then recycled to a point below the gas distribution grid (3) at position (8) at the bottom of the fluidized bed reactor (1). If appropriate, the recycle gas can be cooled below the dew point of one or more of the recycle gas components in the heat exchanger to operate the reactor in a condensate material, i.e., in a condensation mode. The recycle gas can include, in addition to unreacted monomers, inert condensable gases such as alkanes, and inert non-condensable gases such as nitrogen. The make-up monomer, hydrogen, and any inert gas or process additive can be supplied to the reactor (1) at various positions, such as via line (9) upstream of the compressor (6). Generally, the catalyst is preferably supplied to the reactor (1) via line (10) disposed at the lower part of the fluidized bed (2).

[0050] The polyolefin particles obtained in the fluidized bed reactor (1) are discharged discontinuously via line (11) and supplied to the solid / gas separator (12) to avoid the gas mixture coming from the fluidized bed reactor (1) entering the second gas-phase reactor. The gas exiting the solid / gas separator (12) is discharged from the reactor via line (13) as offgas, and the separated polyolefin particles are supplied to the second gas-phase reactor via line (14).

[0051] The second gas-phase reactor is a multi-zone circulation reactor (21) including a riser (22) and a downcomer (23) through which the polyolefin particles repeatedly pass. In the riser (22), the polyolefin particles flow upward along the direction of the arrow (24) under high-speed fluidization conditions. In the downcomer (23), the polyolefin particles flow downward along the direction of the arrow (25) due to the action of gravity. The riser (22) and the downcomer (23) are appropriately interconnected by interconnecting bends (26) and (27).

[0052] After passing through the riser (22), the polyolefin particles and the reaction gas mixture exit the riser (22) and are transported to the solid / gas separation zone (28). This solid / gas separation can be carried out using conventional separation means such as a centrifuge like a cyclone. From the separation zone (28), the polyolefin particles enter the downcomer (23).

[0053] The reaction gas mixture exiting the separation zone (28) is recycled to the riser (22) by a recycle line (29) equipped with a compressor (30) and a heat exchanger (31). Between the compressor (30) and the heat exchanger (31), the recycle line (29) branches and the gas mixture is split into two separate streams. Line (32) sends a part of the recycle gas to the interconnecting bend (27), and line (33) sends another part of the recycle gas to the bottom of the riser (22) to establish high-speed fluidization conditions within the riser (22).

[0054] The polyolefin particles coming from the first gas-phase reactor via line (14) enter the multi-zone circulation reactor (21) from the interconnecting bend (27) at position (34). The polyolefin particles obtained in the multi-zone circulation reactor (21) are continuously discharged from the bottom of the downcomer (23) via the discharge line (35).

[0055] A portion of the gas mixture exiting the separation zone (28), after passing through the compressor (30), exits the recycle line (29) and is sent through line (36) to the heat exchanger (37), where it is cooled to a temperature at which the monomer and any inert gas are partially condensed. A separation vessel (38) is disposed downstream of the heat exchanger (37). The separated liquid is removed from the separation vessel (38) via line (39) and supplied by pump (44) via lines (40), (41), (42) and (43) to the downcomer (23). The feed stream introduced via line (40) is supplied to create a barrier to prevent the reaction gas mixture in the riser (22) from entering the downcomer (23). Make-up monomer, make-up comonomer, and optionally inert gas and / or process additives are introduced via lines (45), (46) and (47) into lines (41), (42) and (43) and then supplied to the downcomer (23) at monomer feed points (48), (49) and (50). Make-up monomer, make-up comonomer, and optionally inert gas and / or process additives can be further introduced via line (51) into the recycle line (29). The gas mixture obtained as the gas phase in the separation vessel (38) is recycled via line (52) to the recycle line (29).

[0056] At the bottom of the downcomer (23), a control valve (53) is provided having an adjustable opening for regulating the flow rate of polyolefin particles flowing from the downcomer (23) through the interconnecting bend (27) to the riser (22). Above the control valve (53), the amount of recycle gas mixture coming from the recycle line (29) via line (54) is introduced into the downcomer (23) to facilitate the flow of polyolefin particles through the control valve (53).

[0057] The polymerization for producing the multimodal polyolefin can be carried out using all conventional olefin polymerization catalysts. That is, the polymerization can be carried out using, for example, a Phillips catalyst based on chromium oxide, a Ziegler catalyst or Ziegler-Natta catalyst based on titanium, a single-site catalyst, or a mixture of such catalysts. The production and use of these catalysts for olefin polymerization are generally known. In a preferred embodiment of the present disclosure, the polymerization catalyst is a Ziegler catalyst or Ziegler-Natta catalyst comprising a reaction product of an aluminum alkyl and a titanium compound supported on a magnesium halide.

[0058] The multimodal polyolefin produced in step a) of the process of the present disclosure is obtained in the form of polyolefin powder, i.e., in the form of relatively small particles. The mass median diameter D50 of these polyolefin particles is in the range of 300 μm to 2500 μm, preferably 400 μm to 2300 μm, particularly 800 μm to 2100 μm, as measured by dry sieving analysis in accordance with DIN 53477 (November 1992).

[0059] The multimodal polyolefin produced in step a) of the process of the present disclosure is preferably a multimodal polyethylene having a density of 0.940 to 0.968 g / cm 3 Preferably, the density ranges from 0.945 to 0.965 g / cm 3 and particularly from 0.945 to 0.955 g / cm 3 It should be understood that the density is the density measured by pressing a compression-molded plate with a thickness of 2 mm at 180 °C and 20 MPa for 8 minutes and then crystallizing it in boiling water for 30 minutes in accordance with DIN EN ISO 1183-1:2004, Method A (immersion).

[0060] The preferred polyolefin produced in step a) of the process of the present disclosure has a melt flow rate MFR at 190 °C under a load of 21.6 kg, measured in accordance with DIN EN ISO 1133:2005, Condition G 21.6It is a multimodal polyethylene with a value of 0.5 to 300 g / 10 min, more preferably 1 to 100 g / 10 min, even more preferably 1.2 to 100 g / 10 min, and particularly 1.5 to 50 g / 10 min. A preferred multimodal polyethylene has an M w / M n value of 15 to 40, particularly 20 to 35, where M w is the weight average molecular weight and M n is the number average molecular weight measured by GPC (gel permeation chromatography). GPC is preferably high-temperature gel permeation chromatography performed as described in ISO 16014-1, -2, -4 issued in 2003, where 1,2,4-trichlorobenzene (TCB) is used as the solvent, the temperature of the apparatus and the solution is 135 °C, and an infrared detector capable of being used with TCB is employed as the concentration detector.

[0061] In step b) of the process of the present disclosure, an organic peroxide is supplied to the polyolefin powder in an amount of 20 ppm to less than 100 ppm. Examples of suitable organic peroxides include dicumyl peroxide, di-tert-butyl peroxide, tert-butyl peroxybenzoate, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 3,6,9-triethyl-3,6,9-trimethyl-1,2,4,5,7,8-hexoxonan, representative examples of 3,6,9-trimethyl-3,6,9-tris(alkyl)-1,2,4,5,7,8-hexoxonan where the alkyl group is propyl or ethyl, tert-butyl peroxyneodecanoate, tert-amyl peroxypivalate, 1,3-bis(tert-butylperoxyisopropyl)benzene, and the like. Preferably, the organic peroxide is 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 3,6,9-triethyl-3,6,9-trimethyl-1,2,4,5,7,8-hexoxonan, or a representative of 3,6,9-trimethyl-3,6,9-tris(alkyl)-1,2,4,5,7,8-hexoxonan where the alkyl group is propyl or ethyl.

[0062] In a preferred embodiment of the present disclosure, the organic peroxide is used in the form of a polyolefin mixture, which is preferably produced by adding to the polyolefin powder as a pure form of the organic peroxide or a solution in a diluent such as a hydrocarbon. A preferred polyolefin mixture has an organic peroxide content in the polyolefin mixture in the range of 0.5 to 25% by weight, preferably 1 to 20% by weight, more preferably 2 to 10% by weight.

[0063] In a particularly preferred embodiment of the present disclosure, in step b) of the process of the present disclosure, a liquid containing an organic peroxide is supplied. The liquid containing the organic peroxide may be a liquid peroxide, or the liquid containing the organic peroxide can be a solution of the peroxide. Preferably, the liquid containing the organic peroxide is a solution of the peroxide. The liquid containing the organic peroxide is supplied in an amount of 20 ppm to less than 100 ppm, preferably 25 ppm to 95 ppm, more preferably 28 ppm to 80 ppm or 40 ppm to 95 ppm, particularly 45 ppm to 95 ppm of the organic peroxide with respect to the polyolefin powder. In other words, the liquid containing the organic peroxide is added in an amount corresponding to the addition of 20 ppm to less than 100 ppm, preferably 25 ppm to 95 ppm, more preferably 28 ppm to 80 ppm or 40 ppm to 95 ppm, particularly 45 ppm to 95 ppm of the organic peroxide. Preferably, the organic peroxide is used in the form of a solution in a diluent such as a hydrocarbon. A preferred peroxide solution has an active oxygen content in the range of 0.1% by weight to 10% by weight, preferably 0.2% by weight to 5% by weight, more preferably 0.3% by weight to 2% by weight, particularly 0.5% by weight to 1% by weight.

[0064] Several steps for manufacturing a polyolefin composition comprising one or more antioxidants of the present disclosure are carried out within an extruder device. An extruder device suitable for the process of the present disclosure is an extruder or a continuous mixer. These extruders or mixers are single-stage or two-stage machines that melt and homogenize the polyethylene composition. Examples of extruders include pin-type extruders, planetary extruders, co-rotating disk processors, etc. Other possibilities include a combination of a mixer and a discharge screw and / or a gear pump. A preferred extruder is a screw extruder, particularly an extruder configured as a twin-screw machine. Particularly preferred are twin-screw extruders with discharge elements and continuous mixers, in particular continuous mixers with counter-rotating twin rotors, or those in which the extruder device includes at least one co-rotating twin-screw extruder. This type of machine is common in the plastics industry and is manufactured, for example, by Coperion GmbH in Stuttgart, Germany, KraussMaffei Berstorff GmbH in Hanover, Germany, Nippon Steel Corporation in Tokyo, Japan, Farrel in Ansonia, USA, or Kobe Steel, Ltd. in Japan. A suitable extruder device is usually further equipped with a unit for pelletizing the melt, such as a water bath pelletizer.

[0065] In a particularly preferred embodiment of the present disclosure, the extruder device is a combination of two co-rotating twin-screw extruders, a mixture comprising polyolefin powder and an organic peroxide is transferred to the first twin-screw extruder, the second twin-screw extruder is supplied with a molten polymer stream from the first twin-screw extruder, and the second twin-screw extruder completes the homogenization process. In another particularly preferred embodiment of the present disclosure, the polyethylene composition is manufactured using a counter-rotating continuous mixer equipped with a gear pump, or a co-rotating twin-screw extruder equipped with a gear pump.

[0066] Step c) of the process of the present disclosure provides for mixing the polyolefin powder produced in step a) and the organic peroxide of step b) at a temperature in the range of 10°C to 100°C without melting the polyethylene powder. Preferably, the mixing in step c) is carried out at a temperature in the range of 20°C to 90°C, more preferably 60°C to 80°C.

[0067] Preferably, the mixing in step c) is carried out in an atmosphere with a reduced oxygen content, preferably achieved by injecting nitrogen into the mixing device. Preferably, the oxygen content in the gas phase in the mixing device is less than 5% by volume, more preferably less than 1% by volume, and particularly less than 0.2% by volume.

[0068] In a preferred embodiment of the present disclosure, the mixing in step c) is carried out in a mixing device. In these embodiments, the multimodal polyolefin in the form of the polyolefin powder produced in step a) and the organic peroxide supplied in step b) are supplied to the mixing device and mixed. The mixing device can be any device that enables dry mixing of the particles. The mixing device can operate continuously or discontinuously. Preferably, the mixing device operates continuously.

[0069] A preferred dry mixing device is a paddle mixer comprising one or two horizontal rotating shafts, more preferably two horizontal counter-rotating shafts. The shafts are equipped with paddles of suitable shape. The rotating shafts move the composition of polyethylene powder and additive horizontally along the axis of the shafts and at the same time mix the composition powerfully. Such paddle mixers are commercially available, for example, from Kollemann GmbH in Adenau, Germany or J. Engelsmann AG in Ludwigshafen, Germany. A preferred mixing device is a vertical batch mixer such as Henschel-Mixers (registered trademark) available from Zeppelin Systems GmbH in Kassel, Germany. A preferred dry mixing device is also a single-screw conveyor with mixing elements. Preferably, such mixing elements are adjustable devices such as paddles or flights with slots that can be adjusted to control the mixing level.

[0070] In other preferred embodiments of the present disclosure, the mixing in step c) is carried out in an extruder device. In these embodiments, the multimodal polyolefin in the form of polyolefin powder produced in step a) and the organic peroxide supplied in step b) are supplied to the extruder device for mixing. Preferably, the polyolefin powder is transferred to the hopper of the extruder device and then introduced into the extruder device from the hopper. Preferably, the transfer of the polyolefin powder to the extruder device is carried out by gravity. Preferably, the introduction of the polyolefin powder into the extruder device is carried out in an atmosphere with a reduced oxygen content, preferably achieved by injecting nitrogen into the hopper. Preferably, the oxygen content in the gas phase in the hopper is less than 5% by volume, more preferably less than 1% by volume, particularly less than 0.2% by volume.

[0071] In a preferred embodiment of the present disclosure, the organic peroxide is supplied in a liquid form, and the liquid containing the organic peroxide is passed through a spring injector including a preload spring with an injection pressure of 0.5 to 4 MPa, more preferably 1 to 2 MPa, and supplied to a mixing device or an extruder device to be added to the polyethylene powder.

[0072] Figure 2 schematically shows a spring injector for adding a liquid containing an organic peroxide to polyethylene powder. The spring injector (61) is composed of a main body (62) including an injection port (63), an internal needle (64), a sealing device (65), a compression spring (66), and a compression adjustment knob (67) including an injection chamber (68) used to set the spring preload. The liquid containing the organic peroxide is continuously supplied to the injection chamber (68) through a supply pipe (69). The compression spring (66) presses the needle (64) against the injection port (63) according to the pre-pressure of the compression spring (66). When the pressure in the injection chamber (68) exceeds the preload of the compression spring (66), the hydrogen peroxide solution is finely sprayed onto the polyethylene powder. Further, due to the preload of the compression spring (66), powder materials such as polyethylene fine particles and additives are prevented from entering the injection chamber (68) and causing clogging.

[0073] In the extruder device, in step d), the mixture containing the polyolefin powder and the organic peroxide is melted and homogenized to form a molten polyethylene composition. This preferably occurs by applying heat and mechanical energy to the polyolefin peroxide mixture. The conditions in the extruder device and the chemical structure of the organic peroxide are selected such that at least 90% by weight, more preferably at least 95% by weight, particularly 98% to 100% by weight of the organic peroxide decomposes.

[0074] Subsequently, in step e) of the process of the present disclosure, one or more antioxidants are added to the molten polyolefin composition obtained in step d) to form a combination of the molten polyolefin composition and the antioxidant.

[0075] The subsequent step f) of the process of the present disclosure is a step of homogenizing a combination of a molten polyolefin composition and an antioxidant to form a molten polyolefin composition added with the antioxidant. By step f), the polyolefin melt is further homogenized, and one or more antioxidants are uniformly dispersed in the polyethylene melt.

[0076] In a preferred embodiment of the present disclosure, the extruder device is a combination of two co-rotating twin-screw extruders. The polyolefin powder and the organic peroxide are transferred to the first twin-screw extruder, where step d) is performed. The second twin-screw extruder is supplied with a stream of the molten polyolefin composition formed in step d) of the first twin-screw extruder, and step f) is performed. In other preferred embodiments of the present disclosure, the extruder device is a counter-rotating continuous mixer equipped with a gear pump, or a co-rotating twin-screw extruder equipped with a gear pump.

[0077] Preferably, the specific energy, that is, the combined amount of heat and mechanical energy added per unit throughput of the material, is 120 kW / t to 350 kW / t, more preferably 160 kW / t to 300 kW / t, particularly 200 kW / t to 260 kW / t.

[0078] In a preferred embodiment of the present disclosure, the molten polyolefin composition added with the antioxidant passes through a melt filter before being pelletized. A suitable melt filter is composed of one or more active screens having a mesh opening of 50 μm to 400 μm. Particularly preferred melt filters are melt filters including one or more active screens having a mesh opening of 75 μm to 200 μm, or melt filters including at least two screens having a mesh opening of 205 μm to 350 μm. Such a combination of screens is described, for example, in WO2012 / 152775A1.

[0079] In subsequent step g) of the process of the present disclosure, the molten polyethylene composition containing the multimodal polyolefin and an antioxidant containing one or more antioxidants is pelletized. In step g), the molten polyethylene composition is converted into pellets.

[0080] In addition to adding antioxidants and organic peroxides, it is also a standard method to further add additives in the production of polyolefin compositions. Examples of suitable additional additives for producing polyolefin compositions include, for example, melt stabilizers, light stabilizers, acid scavengers, lubricants, processing aids, antiblocking agents, slip agents, antistatic agents, antifogging agents, pigments or dyes, nucleating agents, flame retardants or fillers, etc. It is common for multiple additives to be added to the polyethylene composition. The multiple additives may be different types of additives. However, it is also possible to add several representative examples of one type of additive to one polyethylene composition. All these types of additives are generally commercially available and are described, for example, in "Plastic Additives Handbook, 5th Edition, Munich, 2001" by Hans Zweifel.

[0081] In a preferred embodiment of the process of the present disclosure, additional additives different from the antioxidants and organic peroxides are added to the molten polyolefin composition obtained in step d) together with one or more antioxidants in step e).

[0082] In other preferred embodiments of the process of the present disclosure, in addition to the multimodal polyolefin in the form of polyolefin powder produced in step a), antioxidants and additional additives different from organic peroxides are fed into the mixing device, where they are mixed to form a polyolefin powder mixture without melting the polyolefin powder. In these embodiments, the organic peroxide fed in step b) can also be fed into the mixing device. That is, the mixing in the mixing device represents step c) of the process of the present disclosure, and additional additives different from antioxidants and organic peroxides are added to the polyolefin powder together with the organic peroxide. However, it is also possible that the organic peroxide is fed into the extruder device, the organic peroxide is not fed into the mixing device, and the antioxidants and additional additives different from the organic peroxide are mixed with the polyolefin powder in the mixing device, and as a result, the polyolefin powder additive mixture is transferred from the mixing device to the extruder device. That is, according to this possibility of the process of the present disclosure, step c) of the process of the present disclosure is to mix the organic peroxide fed in step b) with the polyolefin powder additive mixture obtained in the mixing device at a position where the polyolefin powder additive mixture has not yet melted in the extruder device.

[0083] Figure 3 schematically shows a setup for producing a polyolefin composition according to the present disclosure, in which a liquid containing an organic peroxide is added to polyolefin powder in a mixing device, and a masterbatch of one or more antioxidants is added to the molten homogeneous mixture of the polyolefin powder and the peroxide solution.

[0084] The polyolefin powder is supplied to the hopper (101) of the dosing device (102) actuated by the motor (103). The dosing device (102) supplies the polyolefin powder to the hopper (106) of the screw conveyor (107) actuated by the motor (108). The hydrogen peroxide solution is transferred from the storage container (111) to the screw conveyor (107) by the pump (110) and injected into the screw conveyor (107) at the position (113) downstream of the hopper (109) via the injector (112).

[0085] The screw conveyor (107) supplies the mixture of the polyolefin powder and the peroxide solution to the hopper (114) of the first extruder (115) actuated by the motor (116). Inside the extruder (115), the mixture of the polyolefin powder and the peroxide solution is melted and homogenized, and the peroxide is decomposed.

[0086] The extruder (115) supplies the molten mixture of the polyolefin powder after the decomposition of the organic peroxide to the second extruder (118) actuated by the motor (119) via the line (117). A masterbatch produced from one or more antioxidants and the polyolefin powder is supplied to the hopper (131) of the dosing device (132) actuated by the motor (133), and the dosing device (132) supplies the masterbatch to the hopper (134) of the second extruder (118). Inside the extruder (118), the masterbatch supplied to the hopper (134) is melted, and the mixture of the molten masterbatch and the melt supplied by the extruder (115) is homogenized. The homogenized melt passes through the start valve (120) and the melt filter (121) and is transferred to the underwater pelletizer (122) actuated by the motor (123), where pellets are formed.

[0087] Figure 4 schematically shows a setup for manufacturing a polyolefin composition according to the present disclosure, in which a liquid containing an organic peroxide is added to polyolefin powder in an extruder device, and a masterbatch of one or more antioxidants is added to the molten and homogenized mixture of the polyolefin powder and the peroxide solution.

[0088] The setup for manufacturing the polyolefin composition shown in Figure 4 is the same as the setup for manufacturing the polyolefin composition shown in Figure 3, except that the peroxide solution is transferred from the storage container (111) to the first extruder (115) by a pump (110) and injected into the extruder (115) at a position (126) downstream of the hopper (114) via an injector (125), and the polyolefin powder is not yet melted. Further, a mixture of additives that are neither organic peroxides nor antioxidants is supplied to the hopper (141) of a further dosing device (142) operated by a motor (143). The dosing device (142) supplies the mixture of additives that are neither organic peroxides nor antioxidants to the hopper (109) of the screw conveyor (107) located downstream of the hopper (106).

[0089] Figure 5 schematically shows a comparative setup for manufacturing a polyolefin composition in which a liquid containing an organic peroxide and a mixture of additives containing one or more antioxidants are added to polyolefin powder in a mixing device.

[0090] By the process of the present disclosure, a polyolefin composition containing a multimodal polyolefin can be produced from polyolefin powder having a mass median diameter D50 of the polyolefin particles in the range of 400 μm to 2500 μm. The pipes produced from these polyolefin compositions have good sagging behavior and have a combination of excellent properties such as a low gel content. Further, this process can be continuously carried out by economical means.

[0091] In another aspect, the present disclosure provides a method for manufacturing a pipe, comprising step a) of manufacturing a polyolefin composition by the method according to the present disclosure, and step b) of shaping the polyolefin composition into a pipe. The pipe is preferably a pipe having a SAG value of 10 to 17. Examples

[0092] Melt flow rate MFR 5 was measured at a temperature of 190 °C and a load of 5 kg in accordance with DIN EN ISO1133-1:2012-03.

[0093] The SAG value was measured with a rotational parallel plate rheometer under the conditions of a plate opening of 1 mm, a shear stress of 300 Pa, a temperature of 230 °C, and 5200 seconds. The SAG value is 1 / 10 of the percentage of the creep strain measured at the end of the test. th and is defined as. The lower the SAG value, the more uniform the pipe thickness.

[0094] The gel number and gel area were determined by preparing a cast film, analyzing film defects with an optical scanning device, and classifying and counting the film defects according to their size (diameter of the circle). The film was produced with an extruder (type Collin25) equipped with a chill roll and a winder (model Collin Chill Roll 144 / 230), and analyzed with an optical film surface analyzer, model FSA100 (manufactured by OCS Optical Control Systems GmbH, Witten, Germany) equipped with a flash camera system. This device has the following features. - Screw diameter: 25 mm, - Screw length: 25D, - Compression ratio: 3.5:1, - Screw layout 27D: 9D feeding, 7D compression, 9D metering, - Die width (slit die): 150 mm, - Resolution: 25 μm × 25 μm. Operates under the following conditions. - T1: 200 °C, - T2: 210 °C, - T3: 220 °C, - T4, 5 (Adapter): 230 °C, - T6, 7, 8 (Die): 240 °C, - Take-up speed: 3.0 m / min, - Screw speed: Adjusted to a film thickness of 50 μm. - Throughput: 1.0 - 1.5 kg / h (target 1.15 kg / h) - Air shower: On, - Chiller roll temperature: 60 °C, - Camera threshold Threshold 1: 50% - Threshold 2: 45%. To start the measurement, the extruder and the take-off unit were set to the specified conditions and started using a material with a known gel level. When the temperature and melt pressure of the extruder showed a stable state, the film inspection software was launched. After operating the extruder with the starting material for at least 30 minutes or after the gel number reached the known gel level, the first sample to be measured was fed into the extruder. After reaching a stable gel level for 45 minutes, the counting process was started until the camera inspected at least 3 m 2 of the film area. Then, the next sample was fed into the extruder, and after reaching the stable gel number again for 45 minutes, the counting process for the next sample was started. The counting process for all samples was set to normalize the number of defects in each measured size glass to 1 m 2 of the film. 2 The particle size distribution of the manufactured polyethylene powder was measured by dry sieving analysis using an AS200 reference sieve shaker (Retsch GmbH, Haan, Germany) and seven calibration sieve sets (125 μm, 250 μm, 500 μm, 710 m, 1000 μm, 1400 μm, 2000 μm) based on DIN 53477 (November 1992). The mass median diameter D50 of the polyolefin particles was obtained by weighing the fractions on each sieve and then calculating the particle size distribution using the device's software Easy Sieve 4.0.

[0095] Example 1 Example 1

[0096] As shown in Figure 1, polyethylene was produced in a series of fluidized bed reactors and a multi-zone circulation reactor (MZCR) having two interconnected reaction zones.

[0097] A 12 g / h Ziegler-Natta catalyst produced according to Example 6 of WO2018 / 114453A1 was fed to a first stirred pre-contact vessel using 0.7 kg / h of liquid propane, and further dosed with triisobutylaluminum (TIBA) and diethylaluminum chloride (DEAC) therein. The weight ratio of TIBA to DEAC was 7:1. The weight ratio of aluminum alkyl to catalyst solid was 5:1. The first pre-contact vessel was maintained at 50 °C and the residence time was 30 minutes. The catalyst suspension in the first pre-contact vessel was continuously transferred to a second stirred pre-contact vessel operated with a residence time of 30 minutes and maintained at 50 °C. Then, the catalyst suspension was continuously transferred to the fluidized bed reactor (1) via line (10).

[0098] In the fluidized bed reactor (1), hydrogen was used as a molecular weight regulator and ethylene was polymerized in the presence of propane as an inert diluent. 50 kg / h of ethylene and 230 g / h of hydrogen were fed to the fluidized bed reactor (1) via line (9). No comonomer was added. The polymerization was carried out at a temperature of 80 °C and a pressure of 2.9 MPa.

[0099] The polyethylene obtained in the fluidized bed reactor (1) had an MFR 2.16 of 80 g / 10 min and a density of 0.967 g / cm 3 3.

[0100] The polyethylene obtained in the fluidized bed reactor (1) was continuously transferred to a multi-zone circulation reactor (21) operated at a pressure of 2.5 MPa and a temperature of 80 °C measured at the starting point of line (29) immediately after the reaction gas mixture exited the separation zone (28). The inner diameter of the riser (22) was 200 mm and the length was 19 m. The downcomer (23) had a total length of 18 m and was divided into an upper 5 m with an inner diameter of 300 mm, a lower 13 m with an inner diameter of 150 mm, and a conical section with a length of 0.43 m between the upper and lower parts. The final polymer was discharged discontinuously via line (35).

[0101] A liquid stream of 50 kg / h was supplied as a barrier fluid to the upper part of the downcomer (23) via line (40). The liquid for generating the barrier was produced by partially condensing the recycle gas mixture in a heat exchanger (37) under operating conditions of 60 °C and 2.5 MPa and separating the liquid component and the gas component in a separation vessel (38). The composition of the liquid barrier fluid was such that the gas generated by vaporizing the barrier fluid was 4.2 vol.% ethylene, 0.02 vol.% hydrogen, 0.6 vol.% 1-hexene, and 95.18 vol.% propane.

[0102] Additional monomers were supplied to the downcomer from three monomer supply points below the barrier. The total amount of fresh monomers supplied to the downcomer (23) was 20 kg / h of ethylene and 1.7 kg / h of 1-hexene. Further, 5 kg / h of propane, 25.5 kg / h of ethylene, and 1.3 g / h of hydrogen were supplied to the recycle line (29) via line (51).

[0103] Of the polyethylene finally obtained in the series of the fluidized bed reactor (1) and the multi-zone circulation reactor (21), 51 wt% was produced in the fluidized bed reactor (1) and 49 wt% was produced in the multi-zone circulation reactor (21).

[0104] The MFR of the finally obtained polyethylene 5 was 0.21 g / 10 min and the density was 0.948 g / cm 3It was. The mass median diameter D50 of the polyethylene powder was 1624 μm. Example 2

[0105] The obtained additive powder premix and the polyethylene powder prepared in Example 1 were weighed at two different supply points as shown in Fig. 3, and supplied to a screw conveyor provided by Somef Officina Meccanica E Fonderia (Ossero, Italy), where they were intimately mixed. A homogeneous solution of 6 wt% 2,5-dimethyl-2,5-di-(tert-butylperoxy)-hexane (Peroxy HX provided by PERGAN (Bocholt, Germany)) and 94 wt% paraffin oil OB 22 AT (provided by Conqord Oil S.R.L. (Castelguidone, Italy)) was weighed by a screw conveyor at an injection pressure of 1 MPa using the liquid injector shown in Fig. 2 (provided by Coperion (Stuttgart, Germany)) as shown in Fig. 3. The above homogeneous solution resulted in a solution containing 0.606 wt% active oxygen. The addition amount of the peroxide solution was 500 weight ppm with respect to the final polyethylene composition (equivalent to 40 weight ppm of 2,5-dimethyl-2,5-di-(tert-butylperoxy)-hexane). To prevent the presence of oxygen, nitrogen was injected into the screw conveyor at a supply rate of 0.5 m 3 / h.

[0106] The homogeneous mixture of polyethylene powder and peroxide produced by the screw conveyor mixer was supplied to the feed hopper of the twin-screw extruder ZSK 50 of the ZSK NT 50 / 58 extrusion line (Coperion GmbH, Stuttgart, Germany) including the first twin-screw extruder ZSK 50 and the second twin-screw extruder ZSK 58. In the ZSK 50 extruder, the mixture of polyethylene powder and peroxide was melted and homogenized.

[0107] To the polyethylene powder obtained in Example 1, additives, Songnox 1010 (provided by SONGWON Industrial Co., Ltd., Ulsan, Korea), Irgafos 168 (provided by BASF SE, Port Ludwig, Germany), and calcium stearate "M" (provided by So.G.I.S., Industria Chimica S.p.A., Sospiro, Italy) were supplied and mixed in a Mixaco LAB high-speed mixer (MIXACO Maschinenbau, Neuenrade, Germany) to form a homogeneous powder premix. The resulting masterbatch of additives was directly supplied to a ZSK 58 twin-screw extruder, which is the second stage of the ZSK NT 50 / 58 extrusion line, at a feed rate of 4.07 kg / h, as shown in Figure 3. The amount of additives added corresponded to the additive content in the final polyethylene composition, with Songnox 1010 at 1600 ppm by weight, Irgafos 168 at 1600 ppm by weight, and calcium stearate M at 1200 ppm by weight.

[0108] In the ZSK 58 extruder, the mixture of the masterbatch and the polyethylene melt supplied from the ZSK 50 extruder was further subjected to homogenization and melt filtration steps and finally pelletized using a Filtec UW50 underwater pelletizing system (manufactured by Filtec srl, Badia Polesine, Italy). In the filtration of the melt, the melt was passed through a screen pack composed of three 60-mesh metal nets and a 20-mesh metal net that functioned as a mechanical support.

[0109] Table 1 shows the applied operating conditions and the results of the characteristic evaluation of the obtained pellet samples. Comparative Example A

[0110] The process of Example 2 was repeated under the same conditions. However, as shown in Figure 3, instead of first manufacturing the masterbatch of the additive and supplying the masterbatch to a ZSK 58 twin-screw extruder, according to the setup shown in Figure 5, Irganox 1010, Irgafos 168, and calcium stearate "M" were mixed in a Mixaco LAB high-speed mixer (manufactured by MIXACO Maschinenbau, Neuenrade, Germany) to form a homogeneous powder premix. The resulting additive powder premix, polyethylene powder, and peroxide solution were all metered and supplied to a screw conveyor at two different supply points and thoroughly mixed therein. The homogeneous mixture of polyethylene powder, additive, and peroxide produced by the screw conveyor mixer was fed into the feed hopper of a ZSK 50 extruder of a ZSK NT 50 / 58 extrusion line. The content of the additive in the final polyethylene composition was the same as in Example 2, and the addition amount of 2,5-dimethyl-2,5-di-(tert-butylperoxy)-hexane was also 40 ppm by weight in this case. Table 1 shows the applied operating conditions and the results of the characteristic evaluation of the obtained pellet samples. Comparative Example B

[0111] The process of Comparative Example B was repeated under the same conditions except that a peroxide mixture (equivalent to 80 ppm by weight of 2,5-dimethyl-2,5-di-(tert-butylperoxy)-hexane) at 400 ppm by weight was added to the final polyethylene composition. Table 1 shows the applied operating conditions and the results of the characteristic evaluation of the obtained pellet samples.

Table 1

[0112] The comparison between Example 2 and Comparative Example A shows that when antioxidant Sonnox 1010 and Irgafos 168 are added to a molten polyethylene composition obtained by melting and homogenizing a mixture of a multimodal polyethylene in the form of polyethylene powder and an organic peroxide, a multimodal polyethylene composition can be obtained that can produce pipes with a very low level of large gels and high resistance to sagging. In contrast, when the same amount of peroxide and antioxidant are used with the same multimodal polyethylene powder and the antioxidant is added to the polyethylene powder together with the peroxide, the sagging behavior significantly deteriorates and the amount of large gels increases. The comparison between Comparative Example A and Comparative Example B further shows that increasing the amount of peroxide under the same process conditions improves the resistance to sagging, but at the expense of an increase in the level of even larger gels.

Claims

1. A continuous process for producing a multimodal polyolefin composition comprising one or more antioxidants, comprising: In a series of two or more polymerization reactors, one or more 1-olefins are polymerized in the presence of an olefin polymerization catalyst at a pressure of 0.5 MPa to 10 MPa and a temperature of 30 °C to 160 °C to produce a multimodal polyolefin in the form of polyolefin powder having a mass median diameter D50 in the range of 300 μm to 2500 μm. Step a), wherein the multimodal polyolefin produced in step a) is multimodal polyethylene, said step a) and, Step b) of supplying an organic peroxide to the polyolefin powder in an amount of 20 ppm or more and less than 100 ppm; Mixing the polyolefin powder produced in step a) and the organic peroxide supplied in step b) at a temperature in the range of 10 °C to 100 °C without melting the polyolefin powder to form a polyolefin peroxide mixture. Step c); Melting and homogenizing the polyolefin peroxide mixture obtained in step c) in an extruder, wherein at least 90% by weight of the organic peroxide is decomposed to form a molten polyolefin composition. Step d); Adding one or more antioxidants to the molten polyolefin composition obtained in step d) to form a combination of the molten polyolefin composition and the antioxidant. Step e); Homogenizing the combination of the molten polyolefin composition and the antioxidant to form a molten polyolefin composition with added antioxidant. Step f); Pelletizing the molten polyolefin composition with added antioxidant. Step g), a continuous process.

2. The process according to claim 1, wherein the multimodal polyolefin in the form of the polyolefin powder is produced in one or more gas-phase polymerization reactors, at least one of the gas-phase polymerization reactors being a multi-zone circulation reactor in which one polymerization zone is a riser in which growing polymer particles flow upward under high-velocity fluidization or transport conditions, and the other polymerization zone is a sub-zone of a downcomer in which growing polymer particles flow downward in a high-density form, the riser and the downcomer being interconnected such that the polymer particles exiting the riser enter the downcomer and the polymer particles exiting the downcomer enter the riser, thereby establishing a circulation of polymer particles through the riser and the downcomer, said process.

3. The process according to claim 2, wherein the series of polymerization reactors includes a fluidized bed reactor upstream of the multi-zone circulation reactor, said process.

4. The process according to any one of claims 1 to 3, wherein the olefin polymerization catalyst is a Ziegler catalyst or a Ziegler-Natta catalyst comprising a reaction product of an alkyl aluminum and a titanium compound supported on a magnesium halide, said process.

5. The process according to any one of claims 1 to 4, wherein the extruder device is a combination of two co-rotating twin-screw extruders, the polyolefin powder and the organic peroxide being transferred to the first twin-screw extruder where step d) is carried out, and a stream of the molten polyolefin composition formed in step d) being supplied to the second twin-screw extruder where step f) is carried out, or the extruder device being a counter-rotating continuous mixer equipped with a gear pump or a co-rotating twin-screw extruder equipped with a gear pump, said process.

6. The process according to any one of claims 1 to 5, wherein the molten polyolefin composition to which the antioxidant has been added is passed through a melt filter before being pelletized, said process.

7. The process according to any one of claims 1 to 6, wherein the multimodal polyolefin in the form of the polyolefin powder produced in step a) and the organic peroxide supplied in step b) are supplied to a mixing device, and the mixing in step c) is carried out within the mixing device, said process.

8. The process according to any one of claims 1 to 6, wherein the multimodal polyolefin in the form of polyolefin powder produced in step a) is directly supplied to the extruder device, or a multimodal polyolefin composition in the form of polyolefin powder produced in step a) is supplied to a mixing device, where it is mixed with one or more additives different from the antioxidant and the organic peroxide, and a mixture containing the polyolefin powder and the additives different from the antioxidant and the organic peroxide is transferred from the mixing device to the extruder device, and the organic peroxide supplied in step b) is supplied to the extruder device at a position where the polyolefin powder or the mixture containing the polyolefin powder and the additives different from the antioxidant and the organic peroxide has not yet melted, the process.

9. The process according to any one of claims 1 to 8, wherein the mixing in step c) is carried out in an atmosphere with a reduced oxygen content, and the oxygen content in the gas phase in the mixing device is less than 5% by volume, the process.

10. The process according to any one of claims 1 to 9, wherein in step b), the organic peroxide is supplied as a liquid or as a liquid component, or the organic peroxide is supplied in the form of a mixture of the organic peroxide and the polyolefin powder, the process.

11. The process according to any one of claims 1 to 10, wherein in step b), the organic peroxide is supplied as a liquid or as a liquid component, and the liquid containing the organic peroxide is added to the polyethylene powder by passing the liquid through a spring injector including a preload spring at an injection pressure of 0.5 to 4 MPa, the process.

12. The process according to claim 11, wherein the organic peroxide is supplied as a peroxide solution having an active oxygen content in the range of 0.1% to 10% by weight, the process.

13. The process according to any one of the preceding claims, wherein M of the multimodal polyolefin produced in step a) ｗ / M ｎ is from 15 to 40, said process.

14. The process according to any one of the preceding claims, wherein the multimodal polyolefin produced in step a) is The process is a multimodal polyethylene having a density measured at 23 °C in accordance with DIN EN SO 1183-1:2004 of 0.940 g / cm ３ to 0.968 g / cm ３ ​

15. A process for manufacturing a pipe, step a) of manufacturing a multimodal polyolefin composition by the process according to any one of claims 1 to 14, Step b) of shaping the multimodal polyolefin composition into a pipe, and a process comprising the same.

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