Process for producing multimodal polyolefin compositions using an extruder.

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] This disclosure provides a process for preparing polyethylene compositions comprising bimodal or multimodal polyethylene. In particular, this disclosure provides a continuous process for producing a multimodal polyolefin composition comprising one or more antioxidants from multimodal polyolefins in the form of polyolefin powders, utilizing organic peroxides. [Background technology]

[0002] Polyolefins are widely used commercial polymers. Additional substances are added to the polymers to achieve and maintain desired properties. These so-called plastic additives, though added in small amounts, significantly influence the polymer's properties and are auxiliary compounds that make the polymer commercially useful. Additives are typically mixed directly with the polyolefin after polymerization during the pelletizing step. Antioxidants are another type of widely used additive. These polymer additives suppress the degradation of the polymer caused by reaction with oxygen in the atmosphere. Antioxidants are effective at all stages of the polymer's lifecycle. Using antioxidants allows for faster production of plastic products with fewer defects, extends product lifespan, and facilitates recycling.

[0003] Certain types of additives that can be added after polymerization in order to be present in the pelletization step of polyolefins are free radical generators such as peroxides. Free radical generators can be used, for example, to alter the molecular structure of polyolefins.

[0004] A key application 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 the pressure outside. Suitable materials for manufacturing polyolefin pipes with excellent mechanical properties, including good pressure resistance over long periods and good chemical resistance, have a density of 0.940 g / cm³. 3 ~0.968 g / cm³ 3 It is bimodal or multimodal polyethylene.

[0005] For pipe manufacturing to be applicable, polyolefins must have good extrusion properties. One of the characteristics of this processability, especially in the manufacture of large-diameter pipes, is the high resistance to "sag" in the resulting pipes. "Sag" is a phenomenon in which, during the molten extrusion of the pipe, some of the molten material flows from the top to the bottom of the pipe, resulting in unacceptable variations in the pipe wall thickness around the pipe.

[0006] To improve the sag behavior of pipes made from bimodal or multimodal polyethylene, peroxides can be added during the pelletizing of bimodal or multimodal polyethylene. For example, WO2013 / 101767A2 discloses a method for producing 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 substantially homogeneous.

[0007] WO2016 / 005044A1 relates to a multimodal polyethylene composition that can be manufactured into pipes. The multimodal polyethylene composition comprises 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 prior to the pipe extrusion step. Furthermore, it is disclosed that a peroxide masterbatch was added during compounding to induce an LCB / crosslinking reaction.

[0008] WO2016 / 064984A1 relates to crosslinked metallocene-catalyzed polyethylene copolymers and articles (e.g., pipes) produced therefrom. Crosslinked metallocene-catalyzed polyethylene copolymers can be obtained by contacting a polyethylene copolymer-based 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 in combination thereof.

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

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

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

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

[0013] However, it is necessary to provide polyethylene compositions containing bimodal or multimodal polyethylene that have high resistance to sagging and reduced gel levels. [Overview of the Initiative]

[0014] This disclosure relates to a continuous process for producing a multimodal polyolefin composition comprising one or more antioxidants, the process comprising the following steps: Step a) is a method for producing a multimodal polyolefin in the form of a polyolefin powder having a median mass diameter D50 of polyolefin particles in the range of 300 μm to 2500 μm, by polymerizing one or more types of 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 the multimodal polyolefin in step a) is multimodal polyethylene, and the method is as described above. Step b) supplying an organic peroxide 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 relative to the polyolefin powder, Step c) involves 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) involves melting and homogenizing the polyolefin peroxide mixture obtained in step c) in an extruder apparatus, where at least 90% by weight of the organic peroxide decomposes to form a molten polyolefin composition, Step e) involves 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 antioxidants, Step f) 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 where growing polymer particles flow upward under high-velocity fluidization or transport conditions, and the other polymerization zone is a sub-zone of a downcomer where 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 carried out. A stream of the melt polyolefin composition formed in step d) is supplied to the second twin-screw extruder, where step f) is carried out, 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 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 polyolefin powder produced in step a) is directly fed into the extruder device, or a composition of the multimodal polyolefin in the form of 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 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 additives different from the antioxidant and the organic peroxide has 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% to 10% by weight.

[0026] In some embodiments, the multimodal polyolefin produced in step a) is M w / M n The range is 15-40.

[0027] In some embodiments, the multimodal polyolefin produced in step a) is multimodal polyethylene, preferably with a density of 0.940 g / cm³ measured at 23°C according to DINEN ISO 1183-1:2004. 3 ~0.968 g / cm³ 3 It is multimodal polyethylene.

[0028] In some embodiments, this disclosure is, Step a) for producing a multimodal polyolefin composition by the process described in any one of claims 1 to 14, The present invention provides a process for manufacturing a pipe, comprising step b) forming a multimodal polyolefin composition into a pipe. [Brief explanation of the drawing]

[0029] [Figure 1] Figure 1 schematically shows the reactor setup for producing bimodal or multimodal polyethylene used in the processes of this disclosure. [Figure 2] Figure 2 schematically shows a spring injector for adding a liquid containing an organic peroxide to polyethylene powder. [Figure 3] 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 apparatus, and a masterbatch of one or more antioxidants is added to a molten and homogenized mixture of polyolefin powder and peroxide solution. [Figure 4] Figure 4 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 an extruder, and a masterbatch of one or more antioxidants is added to a molten and homogenized mixture of the polyolefin powder and the peroxide solution. [Figure 5] Figure 5 schematically shows a comparative setup for producing a polyolefin composition, in which a mixture of a liquid containing an organic peroxide and an additive containing one or more antioxidants is added to polyolefin powder in a mixing apparatus. [Modes for carrying out the invention]

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

[0031] Step a) of the process of this disclosure refers to producing multimodal polypolyethylene by homopolymerizing or copolymerizing ethylene. Preferred comonomers in ethylene polymerization are C3-C8-1-alkenes, preferably 1-butene, 1-pentene, 1-hexene, 1-octene, or mixtures thereof, up to 40% by weight. Particularly preferred is the process of copolymerizing ethylene with one or more C3-C8-1-alkenes in 0.01% to 20% by weight, more preferably 0.05% to 12% by weight. Particularly preferred comonomers for copolymerization of ethylene are 1-hexene and / or 1-butene.

[0032] The polyolefins in the form of polyolefin powders according to this disclosure are multimodal polyolefins. The term “multimodal” may 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 comprising two or more types of polymerization catalysts that produce polyolefins of different molecular weights under the same polymerization conditions. Thus, “modality” indicates 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 molecular weight distribution can be recognized as a separated maximum value of a gel permeation chromatography (GPC) curve. The term “multimodal,” which is frequently used in the art and is also used herein, may include bimodal. In addition to molecular weight distribution, polyolefin polymers can also have a comonomer distribution, preferably the average comonomer content of polymer chains with higher molecular weights is higher than the average comonomer content of polymer chains with lower molecular weights. However, it is also possible to produce polyolefins of narrow molecular weights by employing identical or very similar reaction conditions in all polymerization reactors of a series of polymerization reactors. However, the complexity of producing multimodal polyolefins in a series of polymerization reactors operating under different reaction conditions stems from the different residence times of individual polyolefin particles in the different reactors, which can lead to significant variations in the composition of individual polyolefin particles in the polyolefin powder.

[0033] All industrially known polymerization methods can be used for the production of multimodal polyolefins. These polymerization processes include solution processes, suspension processes, and gas-phase processes. These types of processes are generally known to those skilled in the art. Of the above polymerization processes, gas-phase polymerization in a fluidized bed reactor or multizone circulating reactor, and suspension polymerization in a loop reactor or stirred tank reactor are particularly preferred.

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

[0035] The multimodal polyolefin in the form of a 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 two or more gas-phase polymerization reactors, preferably two or more series of fluidized bed reactors, or a series of reactors including a multizone circulating reactor and one or more different gas-phase polymerization reactors (e.g., fluidized bed reactors), or the multimodal polyolefin is produced first in a 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 preferred embodiments of the present disclosure, at least one of a series of polymerization reactors is a gas-phase polymerization reactor, which includes a riser unit through which growing polymer particles flow upward under fluidization, high-speed fluidization, or transport conditions, and a downcomer through which growing polymer particles flow downward in a high-density form.

[0037] A riser unit, through which growing polymer particles flow upward, may contain a fluidized bed of growing polymer particles. The riser unit operates as a fully mixed gas-phase reactor, such as a fluidized bed reactor. A fluidized bed reactor is a reactor in which polymerization takes place in a bed of polymer particles that is kept in a fluid state by supplying a reaction gas mixture from the lower end of the reactor (usually below a gas distribution grid that functions to distribute the gas flow) and drawing the gas back out from the upper end. The reaction gas mixture is then returned to the lower end of the reactor via a recycling line equipped with a compressor and heat exchanger to remove the heat of polymerization. The velocity of the reaction gas mixture must be high enough, firstly, to fluidize the mixed bed of fine polymer present in the tubes that function as the polymerization zone, and secondly, to effectively remove the heat of polymerization.

[0038] When a polymerization unit containing a fluidized bed of growing polymer particles is used as a riser unit, the downcomer may be located inside, around, or adjacent to the gas phase reactor. Two or more separate polymerization units can also be used as downcomers, with the growing polymer particles flowing downwards in a high-density form.

[0039] In a particularly preferred embodiment of this disclosure, the riser unit is a riser that causes upward movement of growing polymer particles under high-speed fluidization or transport conditions. High-speed fluidization conditions are established in the riser by supplying a reaction gas mixture at a rate faster than the transport rate of the polymer particles. The rate of the reaction gas mixture is generally 0.5 to 15 m / s, preferably 0.8 to 5 m / s. The terms “transport rate” and “high-speed fluidization conditions” are well known in the art. For 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 may be called a "downcomer", but may also be called a "moving bed" or "settling 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 "bulk density of injection" of the resulting polymer. Thus, for example, when 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 "bulk density of injection" 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 a part of a polymerization reactor that includes a layer of growing polymer particles that move downward in a substantially plug flow mode. The "plug flow mode" means that there is little or preferably no backmixing of the polymer particles.

[0042] To replace the reacted olefins 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 countercurrently 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 circulating 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 high-speed fluidization or transport conditions, and a downcomer in which growing polymer particles flow in a high-density form due to the action of gravity. Polymer particles exiting the riser enter the downcomer, and polymer particles exiting the downcomer are reintroduced into the riser, thereby establishing a circulation of polymer between the two polymerization zones, and the polymer passes through these two zones alternately multiple times. In such a polymerization reactor, a solid / gas separator is located above the downcomer to separate the polyolefin and reaction gas mixture coming from the riser. Growing polyolefin particles enter the downcomer, and the separated reaction gas mixture from the riser is continuously recycled through a gas recycling line to one or more reintroduction points into the polymerization reactor. Preferably, the majority of the recycled gas is recycled to the bottom of the riser. The recycling line is preferably equipped with a compressor and heat exchanger to remove polymerization heat. Preferably, a line for catalyst supply is located on the riser and a polymer discharge system is located at the bottom of the downcomer. The introduction of supplemental monomers, comonomers, hydrogen, and / or inert components may occur at various points along the riser and downcomer.

[0044] According to preferred embodiments 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 portion 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 top 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 barrier fluid added can be adjusted so that an upward flow of gas, which is counterflowing with the flow of polymer particles, is generated particularly at its top, and acts as a barrier against the gas mixture entrained by the particles coming from the riser unit.

[0045] The barrier fluid is preferably obtained from a recycled gas stream, and more preferably by partially condensing the flow. As a result, the barrier fluid may 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] Polymerization in a series of polymerization reactors, specifically in a gas-phase polymerization reactor, can also be carried out in condensation mode or supercondensation mode, in which case a portion of the circulating reaction gas mixture is cooled below the dew point and returned to the reactor separately as liquid and gas phases, or together as a two-phase mixture, to further utilize the enthalpy of evaporation for cooling the reaction gas.

[0047] In preferred embodiments of the present disclosure, a series of polymerization reactors includes a gas-phase polymerization reactor comprising a riser unit and a downcomer, and further polymerization reactors in 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 the polymerization process of the series of polymerization reactors includes suspension polymerization, it is preferable that the suspension polymerization is carried out upstream of the gas-phase polymerization. Suitable reactors for carrying out such suspension polymerization include, for example, loop reactors or stirred-tank reactors. Suitable suspension media include, among others, inert hydrocarbons such as isobutane, mixtures of hydrocarbons, or the monomers themselves. Such additional polymerization steps carried out in suspension may also include pre-polymerization steps. When the multi-stage polymerization of olefins includes an additional polymerization step carried out in the gas phase, the additional gas-phase polymerization reactor can be any type of gas-phase reactor, such as a gas-phase reactor stirred horizontally or vertically, a fluidized-bed reactor, or a multi-zone circulating reactor. Such additional gas-phase polymerization reactors may be located downstream or upstream of the gas-phase polymerization reactor. In a particularly preferred embodiment of the present disclosure, a gas-phase polymerization reactor including a riser unit and a downcomer is part of a series of polymerization reactors in which a fluidized bed polymerization reactor is located upstream of the gas-phase polymerization reactor.

[0048] Figure 1 schematically shows a set of polymerization reactors, including a fluidized bed reactor and a multizone circulating reactor, for producing multimodal polyolefins according to step a) of the process of this disclosure.

[0049] The first gas-phase reactor, a fluidized bed reactor (1), includes a fluidized bed (2) of polyolefin particles, a gas distribution grid (3), and a rate reduction zone (4). The rate reduction zone (4) is typically larger in diameter than the fluidized bed portion of the reactor. The polyolefin bed is kept fluid by an upward flow of gas supplied through the gas distribution grid (3) located at the bottom of the reactor (1). The gas stream of the reaction gas mixture discharged from the top of the rate reduction zone (4) via a recycle line (5) is compressed by a compressor (6) and sent to a heat exchanger (7), where it is cooled and then recycled at the bottom of the fluidized bed reactor (1) to a point below the gas distribution grid (3) at position (8). Where appropriate, the recycled gas can be cooled below the dew point of one or more of the recycled gas components in the heat exchanger to operate the reactor in condensable mode. The recycled gas may contain unreacted monomers as well as inert condensable gases such as alkanes and inert non-condensable gases such as nitrogen. Replenishment monomers, hydrogen, and any inert gases or process additives can be supplied to the reactor (1) at various locations, such as via a line (9) upstream of the compressor (6). Generally, the catalyst is supplied to the reactor (1) via a line (10) preferably located below the fluidized bed (2).

[0050] The polyolefin particles obtained in the fluidized bed reactor (1) are discontinuously discharged via line (11) to prevent the gas mixture coming from the fluidized bed reactor (1) from entering the second gas phase reactor, and are supplied to the solid / gas separator (12). The gas that exits the solid / gas separator (12) is discharged from the reactor as off-gas via line (13), 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 circulating reactor (21) including a riser (22) and a downcomer (23) through which polyolefin particles repeatedly pass. In the riser (22), the polyolefin particles flow upward along the direction of arrow (24) under high-speed fluidization conditions. In the downcomer (23), the polyolefin particles flow downward along the direction of arrow (25) due to the action of gravity. The riser (22) and the downcomer (23) are appropriately interconnected by interconnection bends (26) and (27).

[0052] After passing through the riser (22), the polyolefin particles and 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 that exits the separation zone (28) is recycled to the riser (22) by a recycling line (29) equipped with a compressor (30) and a heat exchanger (31). Between the compressor (30) and the heat exchanger (31), the recycling line (29) branches, splitting the gas mixture into two separate streams. Line (32) sends part of the recycled gas to an interconnection bend (27), and line (33) sends another part of the recycled gas to the bottom of the riser (22), establishing high-speed fluidization conditions within the riser (22).

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

[0055] A portion of the gas mixture that leaves the separation zone (28) passes through the compressor (30), then exits the recycling 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 gases partially condense. A separation vessel (38) is located downstream of the heat exchanger (37). The separated liquid is taken out of the separation vessel (38) via line (39) and supplied by a pump (44) to the downcomer (23) via lines (40), (41), (42), and (43). A supply stream introduced via line (40) is supplied to create a barrier to prevent the reaction gas mixture from the riser (22) from entering the downcomer (23). Replenishment monomers, replenishment comonomers, and optionally inert gases and / or process additives are introduced into lines (41), (42), and (43) via lines (45), (46), and (47), and then supplied to the downcomer (23) at monomer supply points (48), (49), and (50). Replenishment monomers, replenishment comonomers, and optionally inert gases and / or process additives can be further introduced into the recycling line (29) via line (51). The gas mixture obtained as a gas phase in the separation vessel (38) is recycled to the recycling line (29) via line (52).

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

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

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

[0059] The multimodal polyolefin produced in step a) of the process of this disclosure preferably has a density of 0.940 to 0.968 g / cm³. 3 It is a multimodal polyethylene. Preferably, the density is 0.945 to 0.965 g / cm³. 3 This range is particularly 0.945~0.955 g / cm³. 3 It is within this range. The density should be understood to be the density measured by pressing a 2 mm thick compression-molded plate at 180°C and 20 MPa for 8 minutes, and then crystallizing it in boiling water for 30 minutes, according to DIN EN ISO1183-1:2004, Method A (immersion).

[0060] The preferred polyolefin produced in step a) of the process of this disclosure has a melt flow rate (MFR) measured at 190°C under a load of 21.6 kg, according to DIN EN ISO1133:2005 condition G. 21.6The multimodal polyethylene has a concentration 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 is M w / M n The range is 15-40, especially 20-35, and here M w This is the weight-average molecular weight, M n This 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 published in 2003, where 1,2,4-trichlorobenzene (TCB) is used as the solvent, the apparatus and solution temperature is 135°C, and an infrared detector usable with TCB is employed as the concentration detector.

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

[0062] In preferred embodiments of the present disclosure, the organic peroxide is used in the form of a polyolefin mixture, which is preferably produced by adding the organic peroxide in its pure form or a solution of a diluent such as a hydrocarbon to a polyolefin powder. The preferred polyolefin mixture has an organic peroxide content in the polyolefin mixture ranging from 0.5 to 25% by weight, preferably 1 to 20% by weight, and 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 it may be a solution of peroxide. Preferably, the liquid containing the organic peroxide is a solution of peroxide. The liquid containing the organic peroxide is supplied in an amount of organic peroxide 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, and particularly 45 ppm to 95 ppm, relative to the polyolefin powder. In other words, the liquid containing the organic peroxide is added in an amount equivalent to an 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, and particularly 45 ppm to 95 ppm of 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 of 0.1% to 10% by weight, preferably 0.2% to 5% by weight, more preferably 0.3% to 2% by weight, and particularly 0.5% to 1% by weight.

[0064] Several steps for producing a polyolefin composition containing one or more antioxidants of the present disclosure are carried out in an extruder apparatus. Suitable extruder apparatus for the processes of the present disclosure are extruders or continuous mixers. These extruders or mixers are single-stage or two-stage machines that melt and homogenize the polyethylene composition. Examples of extruders include pin extruders, planetary extruders, and co-rotating disk processors. Other possibilities include combinations of mixers with discharge screws and / or gear pumps. Preferred extruders are screw extruders, and in particular extruders configured as twin-screw machines. Particularly preferred are twin-screw extruders with discharge elements and continuous mixers, in particular continuous mixers with twin rotors rotating in opposite directions, or extruder apparatuses that include 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; Japan Steel Works, Ltd. in Tokyo, Japan; Farrel Ltd. in Ansonia, USA; or Kobe Steel, Ltd. A suitable extruder system is usually further equipped with a unit for pelletizing the molten material, such as an underwater pelletizer.

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

[0066] Step c) of the process of this disclosure provides 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 reduced oxygen content, which is preferably achieved by injecting nitrogen into the mixing apparatus. Preferably, the oxygen content in the gas phase within the mixing apparatus is less than 5% by volume, more preferably less than 1% by volume, and particularly less than 0.2% by volume.

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

[0069] A preferred dry mixing apparatus 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 appropriate shape. The rotating shafts move the composition of polyethylene powder and additives horizontally along the axis of the shaft, simultaneously mixing the composition vigorously. Such paddle mixers are commercially available, for example, from Kollemann GmbH in Adenau, Germany, or J. Engelsmann AG in Ludwigshafen, Germany. A preferred mixing apparatus is a vertical batch mixer, such as the Henschel-Mixers® available from Zeppelin Systems GmbH in Kassel, Germany. A preferred dry mixing apparatus is also a single-screw conveyor with a mixing element. Preferably, such a mixing element is a modifiable device, such as an adjustable paddle or slotted flight, that allows control of the mixing level.

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

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

[0072] Figure 2 schematically shows a spring injector for adding a liquid containing an organic peroxide to polyethylene powder. The spring injector (61) consists of a body (62) including a nozzle (63), an internal needle (64), a sealing device (65), a compression spring (66), and a compression adjustment knob (67) used to set the spring preload and including an injection chamber (68). The liquid containing the organic peroxide is continuously supplied to the injection chamber (68) via a supply pipe (69). The compression spring (66) presses the needle (64) against the nozzle (63) according to the preload 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. Furthermore, the preload of the compression spring (66) prevents powder materials such as polyethylene fine particles and additives from entering the injection chamber (68) and potentially causing clogging.

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

[0074] Next, in step e) of the process of this 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] A subsequent step f) of the process of the present disclosure is to homogenize the combination of the molten polyolefin composition and the antioxidant to form a molten polyolefin composition with the antioxidant added. Step f) further homogenizes the polyolefin molten material and uniformly disperses one or more antioxidants within the polyethylene molten material.

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

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

[0078] In preferred embodiments of the present disclosure, the molten polyolefin composition with added antioxidants passes through a molten filter before being pelletized. A suitable molten filter consists of one or more active screens having mesh openings of 50 μm to 400 μm. Particularly preferred molten filters are those comprising one or more active screens having mesh openings of 75 μm to 200 μm, or those comprising at least two screens having mesh openings of 205 μm to 350 μm. Such screen combinations are described, for example, in WO2012 / 152775A1.

[0079] In a subsequent step g) of the process of this disclosure, the molten polyethylene composition, to which multimodal polyolefins and antioxidants, including one or more antioxidants, are added, 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 standard practice to add further additives in the manufacture of polyolefin compositions. Suitable additional additives for manufacturing 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. It is common for polyethylene compositions to contain multiple additives. These multiple additives may be of different types. However, it is also possible to add several representative examples of one type of additive to a single polyethylene composition. All of these types of additives are generally commercially available and are described, for example, in Hans Zweifel's "Handbook of Plastic Additives, 5th Edition, Munich, 2001".

[0081] In a preferred embodiment of the process of this disclosure, further additives different from 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), further additives different from antioxidants and organic peroxides are supplied to a mixer and mixed therein to form a polyolefin powder mixture without melting the polyolefin powder. In these embodiments, the organic peroxide supplied in step b) can also be supplied to the mixer. That is, mixing in the mixer represents step c) of the process of the present disclosure, in which further additives different from antioxidants and organic peroxides are added to the polyolefin powder together with the organic peroxides. However, it is also possible that the organic peroxide is supplied to an extruder and not supplied to the mixer, and the further additives different from antioxidants and organic peroxides and the polyolefin powder are mixed in the mixer, and as a result the polyolefin powder additive mixture is transferred from the mixer to the extruder. 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 supplied in step b) and the polyolefin powder additive mixture obtained in the mixer in the extruder while the polyolefin powder additive mixture is still melted.

[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 apparatus, and a masterbatch of one or more antioxidants is added to a molten homogenized mixture of polyolefin powder and peroxide solution.

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

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

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

[0087] Figure 4 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 an extruder, 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 producing the polyolefin composition shown in Figure 4 is identical to the setup for producing the polyolefin composition shown in Figure 3, except that the peroxide solution is transferred by a pump (110) from a storage container (111) to a first extruder (115), and injected into the extruder (115) at a position (126) downstream of the hopper (114) via an injector (125), while the polyolefin powder is still not melted. Furthermore, a mixture of additives that are neither organic peroxides nor antioxidants is supplied to a 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 a hopper (109) of a screw conveyor (107) located downstream of the hopper (106).

[0089] Figure 5 schematically shows a comparative setup for producing a polyolefin composition, in which a mixture of a liquid containing an organic peroxide and an additive containing one or more antioxidants is added to polyolefin powder in a mixing apparatus.

[0090] The process described herein allows for the production of polyolefin compositions containing multimodal polyolefins from polyolefin powder in which the median mass diameter D50 of the polyolefin particles is in the range of 400 μm to 2500 μm. These polyolefin compositions produce pipes with excellent properties, such as good sag behavior and low gel content. Furthermore, this process can be carried out continuously by economical means.

[0091] In another embodiment, the Disclosure provides a method for manufacturing a pipe, comprising the steps of a) manufacturing a polyolefin composition by the method according to the Disclosure, and b) forming the polyolefin composition into a pipe. The pipe is preferably a pipe having a SAG value of 10 to 17. Examples

[0092] The melt flow rate (MFR5) was measured according to DIN EN ISO1133-1:2012-03 at a temperature of 190°C and a load of 5 kg.

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

[0094] The number of gels and gel area were determined by preparing cast films, analyzing film defects using an optical scanning device, and classifying and counting the film defects according to their size (diameter of the circle). The films were manufactured in an extruder (Type Collin 25) equipped with chill rolls 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: 25mm, -Screw length: 25D, - Compression ratio: 3.5:1, - Screw layout 27D: 9D feed, 7D compression, 9D metering, - Die width (slit die): 150 mm, - Resolution: 25μm × 25μm. It operates under the following conditions: -T1: 200℃, -T2:210℃, -T3: 220℃, -T4, 5 (adapter): 230℃, -T6, 7, 8 (die): 240℃, - Pickup speed: 3.0 m / min, -Screw speed: Adjust to a film thickness of 50 μm. -Throughput: 1.0~1.5 kg / h (Target: 1.15 kg / h) -Air shower: On, - Chill roll temperature: 60℃, -Camera thresholds: Threshold 1: 50% - Threshold 2: 45%. To begin the measurement, the extruder and takeoff unit were set to the specified conditions, and the measurement was started using a material with a known gel level. The film inspection software was launched when the extruder temperature and melt pressure showed stable conditions. After the extruder was run with the starting material for at least 30 minutes, or after the number of gels reached a known gel level, the first sample to be measured was fed into the extruder. After reaching a stable gel level for 45 minutes, the camera was set to at least 3m 2 The counting process was started until the film area was inspected. Then, the next sample was fed into the extruder, and after 45 minutes, once a stable gel count was reached, the counting process for the next sample was started. The counting process for all samples was completed with the camera at least 3m 2 The film area was inspected, and the number of defects in each size glass was measured per 1m². 2 The settings are configured to normalize the film.

[0095] Based on DIN 53477 (November 1992), the particle size distribution of the manufactured polyethylene powder was measured by dry sieve analysis using an AS200 control vibrating sieve (Retsch GmbH, Haan, Germany) and seven calibration sieve sets (125 μm, 250 μm, 500 μm, 710 μm, 1000 μm, 1400 μm, and 2000 μm). The median mass diameter D50 of polyolefin particles was obtained by gravimetrically measuring the fractions on each sieve and then calculating the particle size distribution using the instrument's software, Easy Sieve 4.0. Example 1

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

[0097] 12 g / h of Ziegler-Natta catalyst, prepared according to Example 6 of WO2018 / 114453A1, was supplied to a first stirred pre-contact vessel using 0.7 kg / h of liquid propane, to which triisobutylaluminum (TIBA) and diethylaluminum chloride (DEAC) were further added. 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, which had been operated for a residence time of 30 minutes and maintained at 50°C. The catalyst suspension was then continuously transferred to a fluidized bed reactor (1) via line (10).

[0098] In the fluidized bed reactor (1), ethylene was polymerized using hydrogen as a molecular weight modifier and propane as an inert diluent. 50 kg / h of ethylene and 230 g / h of hydrogen were supplied to the fluidized bed reactor (1) via line (9). No comonomers were added. 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) is MFR 2.16 It has a density of 0.967 g / cm³, with a volume of 80 g / 10 mins. 3 That was the case.

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

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

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

[0103] Of the polyethylene ultimately obtained in the series of fluidized bed reactor (1) and multizone circulating reactor (21), 51% by weight was produced in the fluidized bed reactor (1) and 49% by weight was produced in the multizone circulating reactor (21).

[0104] The final polyethylene obtained had an MFR5 of 0.21 g / 10 min and a density of 0.948 g / cm³. 3 The median mass 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 Figure 3, and fed onto a screw conveyor provided by Somef Officina Meccanica E Fonderia (Occhiobello, Italy), where they were densely mixed. A homogeneous solution of 6 wt% 2,5-dimethyl-2,5-di-(tert-butylperoxy)-hexane (peroxy HX provided by PERGAN GmbH (Boholt, Germany)) and 94 wt% paraffin oil OB 22 AT (provided by Conqord Oil SRL GmbH (Castella Guidobono, Italy)) was weighed on the screw conveyor at an injection pressure of 1 MPa using the liquid injector shown in Figure 2 (provided by Coperion GmbH (Stuttgart, Germany)), as shown in Figure 3, yielding a solution containing 0.606 wt% active oxygen. The amount of peroxide solution added was 500 ppm by weight relative to the final polyethylene composition (equivalent to 40 ppm by weight of 2,5-dimethyl-2,5-di-(tert-butylperoxy)-hexane). To prevent the presence of oxygen, 0.5 m of nitrogen was added. 3 It was injected into the screw conveyor at a supply rate of / h.

[0106] The homogeneous mixture of polyethylene powder and peroxide produced by the screw conveyor mixer was fed into the supply hopper of twin-screw extruder ZSK 50 in the ZSK NT 50 / 58 extrusion line (Coperion GmbH, Stuttgart, Germany), which includes twin-screw extruder ZSK 50 and 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, Sonnocks 1010 (supplied by SONGWON Industrial Co., Ltd. (Ulsan, South Korea)), Irgafoss 168 (supplied by BASFSE (Port Ludwig, Germany)), and calcium stearate "M" (supplied by So.GIS (Industria Chimica Spa, Sospiro, Italy)) were added and mixed in a Mixaco LAB high-speed mixer (MIXACO Maschinenbau (Neuenrade, Germany)) to form a homogeneous powder premix. The resulting additive masterbatch was fed directly to the ZSK 58 twin-screw extruder, 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 amounts of the added additives correspond to the total additive content in the final polyethylene composition, with Sonnox 1010 at 1600 ppm by weight, Irgaphos 168 at 1600 ppm by weight, and calcium stearate M at 1200 ppm by weight.

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

[0109] Table 1 shows the applied operating conditions and the results of the characterization of the obtained pellet samples. Comparative example A

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

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

[0112] A comparison between Example 2 and Comparative Example A shows that when a multimodal polyethylene composition is produced according to the process of the present disclosure by adding antioxidants Sonnox 1010 and Irgaphos 168 to a molten polyethylene composition obtained by melting and homogenizing a mixture of multimodal polyethylene in the form of polyethylene powder and an organic peroxide, a multimodal polyethylene composition is 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 were used with the same multimodal polyethylene powder, and the antioxidant was added to the polyethylene powder along with the peroxide, the sagging behavior deteriorated significantly and the amount of large gels increased. A comparison between Comparative Example A and Comparative Example B further shows that increasing the amount of peroxide under the same process conditions improves resistance to sagging, but at the cost of an even greater increase in the level of large gels.

Claims

1. A continuous process for producing a multimodal polyolefin composition containing one or more antioxidants, Step a) comprising polymerizing one or more types of 1-olefins in a series of two or more polymerization reactors at a pressure of 0.5 MPa to 10 MPa and a temperature of 30°C to 160°C in the presence of an olefin polymerization catalyst to produce a multimodal polyolefin in the form of a polyolefin powder having a median mass diameter D50 in the range of 300 μm to 2500 μm, wherein the multimodal polyolefin produced in step a) is multimodal polyethylene, and Step b) supplying organic peroxide to the polyolefin powder in an amount of 20 ppm to 80 ppm, Step c) involves 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) involves melting and homogenizing the polyolefin peroxide mixture obtained in step c) in an extruder, thereby decomposing at least 90% by weight of the organic peroxide to form a molten polyolefin composition, Step e) involves 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 antioxidants, Step f) homogenizing the combination of the molten polyolefin composition and the antioxidant to form a molten polyolefin composition with the antioxidant added, A continuous process comprising step g) pelletizing a molten polyolefin composition to which the antioxidant has been added.

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

3. The process according to claim 2, wherein the series of polymerization reactors includes a fluidized bed reactor upstream of the multizone circulating reactor.

4. The process according to claim 1 or 2, wherein the extruder apparatus is a combination of two co-rotating twin-screw extruders, the polyolefin powder and the organic peroxide are transferred to a first twin-screw extruder where step d) is performed, and a stream of the molten polyolefin composition formed in step d) is supplied to a second twin-screw extruder where step f) is performed, or the extruder apparatus is a counter-rotating continuous mixer with a gear pump or a co-rotating twin-screw extruder with a gear pump.

5. The process according to claim 1 or 2, wherein the multimodal polyolefin in the form of polyolefin powder produced in step a) is directly supplied to the extruder apparatus, or the multimodal polyolefin composition in the form of polyolefin powder produced in step a) is supplied to a mixing apparatus, where it is mixed with one or more additives different from antioxidants and organic peroxides, the mixture containing the polyolefin powder and the additives different from antioxidants and organic peroxides is transferred from the mixing apparatus to the extruder apparatus, and the organic peroxide supplied in step b) is supplied to the extruder apparatus at a position where the polyolefin powder or the mixture containing the polyolefin powder and the additives different from antioxidants and organic peroxides has not yet melted.

6. The process according to claim 1 or 2, wherein the mixing in step c) is carried out in an atmosphere with reduced oxygen content, and the oxygen content in the gas phase within the mixing apparatus is less than 5% by volume.

7. The process according to claim 1 or 2, wherein in step b), the organic peroxide is supplied as a liquid or as a component of a liquid, or the organic peroxide is supplied in the form of a mixture of the organic peroxide and the polyolefin powder, and / or, in step b), the organic peroxide is supplied as a liquid or as a component of a liquid, 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.

8. The process according to claim 7, 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.

9. The multimodal polyolefin produced in step a) above ｗ / M ｎ The ratio is 15 to 40, and / or the multimodal polyolefin produced in step a) has a density of 0.940 g / cm³ measured at 23°C according to DIN EN ISO 1183-1:2004. ３ ~0.968g / cm ３ The process according to claim 1 or 2, wherein the polyethylene is multimodal polyethylene.

10. A process for manufacturing pipes, Step a) of producing a multimodal polyolefin composition by the process described in any one of claims 1 to 3, A process comprising step b) forming the multimodal polyolefin composition into a pipe.

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