WO2025177030A1

WO2025177030A1 - Polymerization reactor system and process for producing a multimodal polyethylene composition, a multimodal polyethylene composition obtained therefrom and a pipe comprising the said composition

Info

Publication number: WO2025177030A1
Application number: PCT/IB2024/051793
Authority: WO
Inventors: Patcharaporn CHUAYPLOD; Sanchai THONGKHAM; Danai KITKANNIKA
Original assignee: IRPC PCL
Current assignee: IRPC PCL
Priority date: 2024-02-25
Filing date: 2024-02-25
Publication date: 2025-08-28
Anticipated expiration: 2026-08-25

Abstract

The present invention relates to a polymerization reactor system and a process for producing a multimodal polyethylene composition. The polymerization reactor system comprises a first parallel reactor and an associated first degassing unit, a second parallel reactor and an associated second degassing unit, and a serial reactor. The first and second parallel reactors operate concurrently, while the serial reactor operates sequentially after the first and second parallel reactors. The process of this invention utilizes the mentioned reactor system and involves the steps of polymerizing ethylene in the first parallel reactor and undergoing hydrogen removal; polymerizing ethylene in the second parallel reactor and undergoing hydrogen removal; and subsequently polymerizing ethylene, the hydrogen-depleted first reaction stream, and the hydrogen-depleted second reaction stream in the serial reactor. Additionally, the invention relates to a multimodal polyethylene composition obtained from this process, and a pipe comprising this composition.

Description

POLYMERIZATION REACTOR SYSTEM AND PROCESS FOR PRODUCING A MULTIMODAL POLYETHYLENE COMPOSITION, A MULTIMODAL POLYETHYLENE COMPOSITION OBTAINED THEREFROM

AND A PIPE COMPRISING THE SAID COMPOSITION

TECHNICAL FIELD

The present invention relates to a polymerization reactor system and a process for producing a multimodal polyethylene composition, a multimodal polyethylene composition obtained therefrom and a pipe comprising the said composition.

BACKGROUND OF THE INVENTION

Multimodal polyolefin resins, particularly those made of polyethylene (PE), are widely used in industrial applications due to their combined advantages: enhanced processability from a lower molecular weight fraction and superior physical properties attributed to a higher molecular weight component. One of the traditional ways to create these multimodal resins often involves blending different resins with varying molecular weight distributions, however, this method is troubled by extra processing steps and the challenge of achieving a uniform product. Such blends not only add to production costs but also tend to yield resins with inferior properties compared to those produced via in situ methods.

A more efficient approach involves preparing a multimodal polyethylene via a multistage reaction sequence comprising successive polymerization steps carried out under predetermined different reaction conditions in respective reactors arranged in series so as to obtain polyethylene fractions with different molecular weights. For example, a process of this type can be performed in conditions where monomers and a molar mass regulator, preferably hydrogen, are firstly polymerized in a first reactor under initial reaction conditions in the presence of a suspension medium and a suitable catalyst. The resulting product is then transferred to a second reactor for further polymerization under different reaction conditions. If, for instance, trimodal polyethylene is the desired outcome, it can be further transferred to a third reactor and polymerized under third reaction conditions, distinct from the first and second conditions, to obtain three polyethylene fractions with different molecular weights.

Examples of patent documents disclosing the use of a multistage reaction system for producing multimodal polyethylene compositions are as follows: US 6,716,936 B 1 discloses the utilization of two or more light solvent boiling pool reactors in series, enabling the polymerization of ethylene and comonomers to yield bimodal polyethylene copolymers. The process involves introducing catalyst solely into the first reactor, operating it at high hydrogen compositions, and utilizing a series of connected flash drums to eliminate hydrogen from the polymer slurry product stream of the first reactor. This method facilitates the production of homogeneous, high molecular weight bimodal polyethylene resins.

US 2003/0191251 Al discloses a polyethylene production process utilizing a series of slurry reactors, incorporating an intermediate slurry transfer reactor and a hydrogen removal apparatus. The production of a multimodal polymer occurs within interconnected reactors. The first reactor employs a light solvent as the slurry medium and hydrogen to regulate polymer molecular weight. The polymer output from the first reactor undergoes thorough hydrogen removal before entering a subsequent polymerization reactor. This subsequent reactor operates at low hydrogen pressure to produce a high molecular weight olefin.

WO 2007/022908 A2 discloses a polyethylene molding composition having a multimodal molecular mass distribution which is suitable for producing pipes having excellent mechanical properties. The PE molding composition is prepared in a cascaded suspension polymerization process which is carried out with the highest hydrogen concentration being set in the first reactor. In the subsequent, further reactors, the hydrogen concentration is gradually reduced, so that the hydrogen concentration used in the third reactor is lower with respect to hydrogen concentration used in the second reactor.

The patent documents mentioned above outline the utilization of multiple reactors for producing multimodal polyethylene compositions. These prior arts involve a hydrogen removal step and implement specific conditions in each reactor to regulate the properties of polyethylene compositions. However, none of these prior arts offer specific details regarding the content of the removed hydrogen in each stage, which could potentially result in polyethylene resin compositions precisely tailored for intended end applications. Additionally, the serially connected multi-reactor configuration used in these prior arts is typically conventional.

Hence there is still a need to improve a reactor system and process for producing a multimodal polyethylene composition, emphasizing the optimization of the multi-reactor configuration and fine-tuning of conditions within each reactor. Specifically, improving the control of hydrogen removal within the reactor system and process is crucial for achieving the desired properties in the resulting multimodal polyethylene composition.

SUMMARY OF THE INVENTION

The present invention is developed to address the aforementioned need, and in the first aspect, it aims to provide a polymerization reactor system. This reactor system is adapted for producing a multimodal polyethylene composition by improving reactor configuration, optimizing polymerization conditions within each reactor, and controlling hydrogen removal content at each stage. These improvements aim to produce a multimodal polyethylene composition that meets specified criteria.

Another objective of the present invention is to introduce a process for producing a multimodal polyethylene composition, utilizing the aforementioned reactor system. This process is developed to yield the multimodal polyethylene composition with desired properties.

Yet another objective of the present invention is to provide a multimodal polyethylene composition obtained from the system and process of the present invention, featuring improved properties. Specifically, this polyethylene composition exhibits characteristics suitable for pipe, blow molded, and extrusion molding applications. More specifically, it possesses attributes necessary to meet the specifications of PE100 pipes.

In the first aspect, the present invention relates to a polymerization reactor system for producing a multimodal polyethylene composition. The reactor system comprises: a first parallel reactor configured to polymerize ethylene and produce a first reaction stream comprising a low molecular weight polyethylene homopolymer with a weight average molecular weight (Mw) ranging from 25,000-55,000 g/mol, as determined by gel permeation chromatography (GPC); a first degassing unit, in communication with the first parallel reactor, configured to remove hydrogen from the first reaction stream, resulting in a hydrogen-depleted first reaction stream; a second parallel reactor configured to polymerize ethylene and produce a second reaction stream comprising a first high molecular weight polyethylene homopolymer or copolymer with a weight average molecular weight ranging from 100,000-650,000 g/mol, as determined by GPC; a second degassing unit, in communication with the second parallel reactor, configured to remove hydrogen from the second reaction stream, resulting in a hydrogen-depleted second reaction stream; and a serial reactor configured to polymerize ethylene, the hydrogen-depleted first reaction stream, and the hydrogen-depleted second reaction stream and produce a third reaction stream comprising a second high molecular weight polyethylene copolymer with a weight average molecular weight ranging from 150,000-380,000 g/mol, as determined by GPC.

According to a specific embodiment, the first and second parallel reactors are configured to operate concurrently in parallel, while the serial reactor is configured to operate sequentially after the first and second parallel reactors. More preferably, the first degassing unit is configured to remove at least 97% by weight of hydrogen from the total hydrogen content within the first reaction stream, and the second degassing unit is configured to remove at least 99% by weight of hydrogen from the total hydrogen content within the second reaction stream.

In the second aspect, the present invention relates to a process for producing a multimodal polyethylene composition which utilizes the polymerization reactor system of the first aspect. The process comprises the steps of:

(i) polymerizing ethylene in a first parallel reactor, in a hydrocarbon medium, in the presence of a catalyst, co-catalyst, and hydrogen, to produce a first reaction stream comprising a low molecular weight polyethylene homopolymer with a weight average molecular weight (Mw) ranging from 25,000-55,000 g/mol, as determined by GPC, then transferring the first reaction stream to a first degassing unit;

(ii) removing hydrogen from the first reaction stream in the first degassing unit, resulting in a hydrogen-depleted first reaction stream;

(iii) polymerizing ethylene in a second parallel reactor, in a hydrocarbon medium, in the presence of a catalyst, co-catalyst, and optionally hydrogen and comonomer, to produce a second reaction stream comprising a first high molecular weight polyethylene homopolymer or copolymer with a weight average molecular weight ranging from 100,000-650,000 g/mol, as determined by GPC, then transferring the second reaction stream to a second degassing unit;

(iv) removing hydrogen from the second reaction stream in the second degassing unit, resulting in a hydrogen-depleted second reaction stream; and

(v) polymerizing ethylene, the hydrogen-depleted first reaction stream, and the hydrogen-depleted second reaction stream in a serial reactor, in the presence of a comonomer, to produce a third reaction stream comprising a second high molecular weight polyethylene copolymer with a weight average molecular weight ranging from 150,000-380,000 g/mol, as determined by GPC.

Preferably, the steps (i) and (iii) operate concurrently in parallel, while the step (v) operates sequentially after the steps (ii) and (iv). More preferably, the step (ii) operates to remove at least 97% by weight of hydrogen from the total hydrogen content within the first reaction stream, and the step (iv) operates to remove at least 99% by weight of hydrogen from the total hydrogen content within the second reaction stream.

The third aspect of this invention relates to a multimodal polyethylene composition obtained from the process according to the present invention. The multimodal polyethylene composition of the present invention comprises:

(a) 45-55% by weight of the low molecular weight polyethylene homopolymer based on the total weight of the multimodal polyethylene composition;

(b) 15-35% by weight of the first high molecular weight polyethylene homopolymer or copolymer based on the total weight of the multimodal polyethylene composition; and

(c) 20-35% by weight of the second high molecular weight polyethylene copolymer based on the total weight of the multimodal polyethylene composition.

The last aspect of the present invention pertains to a pipe comprising the multimodal polyethylene composition as described in the third aspect of the invention. Specifically, this pipe is a PElOO-qualified pipe designed for applications under a pressure of at least 10.0 MPa.

The reactor configuration and operational conditions within the present invention's reactor system and process result in polyethylene powder products exhibiting desirable properties. These properties are particularly crucial for meeting the specifications of pipe materials with a designation code PE100, encompassing attributes like Notch Charpy impact resistance tested in accordance with ISO 790, strain hardening capabilities, and suitability for hydrostatic pressure applications.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 illustrates a simplified diagram of the polymerization reactor system for producing a multimodal polyethylene composition according to the present invention.

DETAILED DESCRIPTION

Unless otherwise indicated, any aspects shown herein shall encompass the application to other aspects of the present invention as well.

Unless otherwise specified, technical and scientific terms used herein have the definitions which are understood by a person skilled in the art.

The terms “ consist( s) of’ and its variation such as “ consisting of’ and “ consisted of’ , “ comprise( s) ” and its variation such as “comprising” and “comprised” , “ has/ have/ having” , “contain(s)”, “ include( s) ” and its variation such as “ including” and “ included” are open- ended verbs. For example, any methods that “consist of’, “comprise”, “have” or “include” one or more components or steps are not limited only to the one or more components or steps, but also cover the components or steps that are not mentioned.

The terms “a”, “an”, “the”, when used to refer to a singular noun, are intended to include a plural of that noun as well unless otherwise specified.

Any tools, equipment, methods, materials, or chemicals mentioned herein, unless otherwise indicated, mean the tool, equipment, methods, materials, or chemicals generally used or practiced by a person skilled in the art.

All disclosed materials, polymers, components, and/ or methods and the claims of the present invention are intended to cover the aspects of the invention obtained from any actions, practices, modifications, or changes made to the factors without conducting significantly different experiments from the present invention, and to obtain an object with properties, utilities and effects that are similar to the aspects of the present invention according to the opinions of a person having ordinary skill in the art, although not particularly indicated in the claims. Therefore, the object that is equivalent or similar to the aspects of the present invention, including any slight modification or change apparent to a person of ordinary skill in the art, should also be considered to be within the spirit, scope, and concept of the present invention.

The terms “multimodal polyethylene composition” or “multimodal polyethylene” used in the present invention refer to a polyethylene composition or polyethylene characterized by a molecular mass distribution curve displaying multimodal features. This indicates the presence of numerous ethylene polymer fractions, each possessing individual and discernible molecular weights.

The term "polyethylene homopolymer," as used herein, refers to a polymer primarily composed of repeating units derived from ethylene. These homopolymers typically contain a high percentage of such units, with compositions ranging from at least 99% to 100% by weight originating from ethylene.

The term "polyethylene copolymer," as used herein, refers to a polymer incorporating repeating units sourced from both ethylene and a minimum of one other monomer. Typically, polyethylene copolymers will not comprise more than 15 % by weight of repeat units deriving from monomers other than ethylene.

The term “hydrogen-depleted reaction stream” used in the present invention refers to a stream resulting from a reaction that contains less hydrogen than the initial amount supplied to the reactors during the polymerization process. Specifically, the "hydrogen-depleted first reaction stream" refers to the stream processed by the first degassing unit, containing no more than 3% by weight of hydrogen from the initial hydrogen content within that particular reaction stream. Meanwhile, the "hydrogen-depleted second reaction stream" refers to the stream processed by the second degassing unit, holding no more than 1 % by weight of hydrogen from the total hydrogen content within that second reaction stream. Ideally, the second reaction stream devoid of hydrogen is preferred.

In this invention, the terms "low/lower" and "high/higher" are used comparatively. Therefore, a low molecular weight polyethylene refers to a polymer with a molecular weight lower than that of a high molecular weight polyethylene.

The term "molecular weight," when used, refers to the weight average molecular weight unless explicitly stated otherwise.

The first aspect of the present invention involves a polymerization reactor system designed for producing a multimodal polyethylene composition. This system comprises three distinct reactors connected in a mixed mode: the first and second parallel reactors run concurrently, operating in parallel, while the third reactor operates sequentially after the first and second parallel reactors. Each reactor is set with different reaction conditions.

Fig. 1 provides a simplified diagram illustrating an embodiment of the polymerization reactor system according to the present invention. This reactor system includes a first parallel reactor (RIA) and a second parallel reactor (RIB) configured to operate simultaneously in parallel. The first parallel reactor (RIA) is designed to polymerize ethylene, generating a first reaction stream that consists of a low molecular weight polyethylene homopolymer. This homopolymer possesses a weight average molecular weight (Mw) ranging from 25,000-55,000 g/mol, as determined via gel permeation chromatography (GPC). Concurrently, the second parallel reactor (RIB) polymerizes ethylene to produce a second reaction stream containing a high molecular weight polyethylene homopolymer or copolymer. This product showcases an average molecular weight ranging from 100,000-650,000 g/mol, as determined by GPC. Each parallel reactor (RIA and RIB) is in communication with a first degassing unit (DI) and a second degassing unit (D2), respectively. The function of these degassing units (D 1 and D2) is to eliminate hydrogen from the respective reaction streams obtained from the parallel reactors (RIA and RIB). This process results in hydrogen-depleted first and second reaction streams, respectively.

Moreover, the reactor system comprises a serial reactor (R2) operating after the first and second parallel reactors (RIA and RIB). This serial reactor (R2) polymerizes ethylene, along with the hydrogen-depleted first and second reaction streams, to produce a third reaction stream. This third reaction stream contains a high molecular weight polyethylene copolymer characterized by a weight average molecular weight ranging from 150,000-380,000 g/mol, determined via GPC.

In this invention, it is preferable for the first degassing unit (DI) to remove at least 97% by weight of hydrogen from the total hydrogen content within the first reaction stream. And, the second degassing unit (D2) should remove at least 99% by weight of hydrogen from the total hydrogen content within the second reaction stream. This level of hydrogen removal has been demonstrated to yield the desired properties in the multimodal polyethylene composition.

In an embodiment, the present reactor system may further incorporate a flash vessel (F), in communication with the first and second degassing units (DI and D2). In this configuration, the first and second degassing units (DI and D2) in conjunction with the flash vessel (F) will employ a pressure balance mechanism to facilitate hydrogen removal process. The polymerization conditions in each reactor are optimized to achieve the desired polyethylene product. Preferably, the first parallel reactor (RIA) operates at a temperature ranging from 80-85°C and a pressure ranging from 8-9 bar. The second parallel reactor (RIB) operates at a temperature ranging from 70-80°C and a pressure ranging from 1.5-3 bar. And, the serial reactor (R2) operates at a temperature ranging from 70-75°C and a pressure ranging from 1.5-3 bar.

In an exemplary embodiment, the first degassing unit (DI) operates at a temperature ranging from 60-70°C and a pressure ranging from 1.2- 1.6 bar. The second degassing unit (D2) operates at a temperature ranging from 65-80°C and a pressure ranging from 1.2- 1.6 bar. The flash vessel operates at a pressure equal to or less than 1.3 bar.

The second aspect of the present invention relates to a process for producing a multimodal polyethylene composition. The process involves employing the previously described polymerization reactor system and comprises the following steps:

(i) polymerizing ethylene in the first parallel reactor (RIA), in a hydrocarbon medium, in the presence of a catalyst, co-catalyst, and hydrogen, to produce a first reaction stream comprising a low molecular weight polyethylene homopolymer with a weight average molecular weight (Mw) ranging from 25,000-55,000 g/mol, as determined by GPC, then transferring the first reaction stream to the first degassing unit (DI);

(ii) removing hydrogen from the first reaction stream in the first degassing unit (DI), resulting in a hydrogen-depleted first reaction stream;

(iii) polymerizing ethylene in the second parallel reactor (RIB), in a hydrocarbon medium, in the presence of a catalyst, co-catalyst, and optionally hydrogen and comonomer, to produce a second reaction stream comprising a first high molecular weight polyethylene homopolymer or copolymer with a weight average molecular weight ranging from 100,000-650,000 g/mol, as determined by GPC, then transferring the second reaction stream to the second degassing unit (D2);

(iv) removing hydrogen from the second reaction stream in the second degassing unit (D2), resulting in a hydrogen-depleted second reaction stream; and

(v) polymerizing ethylene, the hydrogen-depleted first reaction stream, and the hydrogen-depleted second reaction stream in the serial reactor (R2), in the presence of a comonomer, to produce a third reaction stream comprising a second high molecular weight polyethylene copolymer with a weight average molecular weight ranging from 150,000-380,000 g/mol, as determined by GPC,

Preferably, the steps (i) and (iii) operate concurrently in parallel, while the step (v) operates sequentially after the steps (ii) and (iv).

More preferably, the step (ii) operates to remove at least 97% by weight of hydrogen from the total hydrogen content within the first reaction stream, and the step (iv) operates to remove at least 99% by weight of hydrogen from the total hydrogen content within the second reaction stream.

In an embodiment, the steps (ii) and (iv) operate in conjunction with a flash vessel to employ a pressure balance mechanism to remove hydrogen.

Similar to the operating conditions specified for the reactor system as described above, the step (i) operates at a temperature ranging from 80-85°C and a pressure ranging from 8-9 bar. The step (iii) operates at a temperature ranging from 70-80°C and a pressure ranging from 1.5-3 bar. Additionally, the step (v) operates at a temperature ranging from 70-75°C and a pressure ranging from 1.5-3 bar.

In an exemplary embodiment, the step (ii) operates at a temperature ranging from 60-70°C and a pressure ranging from 1.2- 1.6 bar. The step (iv) operates at a temperature ranging from 65-80°C and a pressure ranging from 1.2- 1.6 bar.

In a preferred embodiment, the process of this invention is a slurry polymerization process.

During the polymerization in the steps (i) and (iii) within the first and second parallel reactors (RIA and RIB), respectively, a suitable catalyst is preferably introduced alongside the hydrocarbon medium, co-catalyst, and optionally hydrogen and comonomer. Examples of catalysts well-suited for this invention include Ziegler-Natta catalysts and metallocene. An example of the co-catalyst used is trialkylaluminium, such as trimethylaluminium, triethylaluminium, or a combination thereof. Nontheless, the use of other catalysts and co-catalysts deemed appropriate is also feasible.

When present in the step (v) and optionally step (iii), the comonomer is preferably a C4 to Cl 2 a-olefin comonomer. Preferably, the comonomer is n-butene or n-pentene and most preferably it is n-butene, such as 1 -butene.

The hydrocarbon medium is preferably a hydrocarbon of 3-10 carbon atoms. One example used in this invention is hexane. In accordance with this invention, hydrogen is introduced into the process at step (i) and optionally at step (iii) to act as a regulator for molecular weight. Subsequently, this hydrogen undergoes removal in two stages, with specific quantities removed at each stage. The initial removal of hydrogen occurs within the first degassing unit (DI), achieving a removal rate of at least 97% by weight. The subsequent removal takes place in the second degassing unit (D2), targeting a removal rate of at least 99% by weight, in comparison to the total hydrogen content within the reaction stream from the first and second parallel reactors (RIA and RIB), respectively. It's crucial to emphasize that this reactor configuration and the specified hydrogen removal rates differ significantly from conventional methods and haven't been disclosed in prior literature.

In an exemplary embodiment, the hydrogen is removed via pressure balancing from both the first and second degassing units (DI and D2), functioning at high pressures (around 1.2- 1.6 bar), and channeled to the flash vessel (F) operating at a comparatively lower pressure (not exceeding 1.3 bar, for example).

In a further embodiment, the multimodal polyethylene composition obtained from step (v) may undergo a drying process and preferably subsequent pelletization.

The third aspect of this invention concerns a multimodal polyethylene composition obtained from the aforementioned process. Specifically, the multimodal polyethylene composition comprises the following components:

In a preferred embodiment, the low molecular weight polyethylene homopolymer has a density ranging from 0.967-0.972 g/cm³. The first high molecular weight polyethylene homopolymer or copolymer has a density ranging from 0.930-0.950 g/cm³. The second high molecular weight polyethylene copolymer has a density ranging from 0.945-0.962 g/cm³. More preferably, the second high molecular weight polyethylene copolymer has the density ranging from 0.945-0.954 g/cm³. All specified densities were measured in accordance with ISO 1183. In an exemplary embodiment, the low molecular weight polyethylene homopolymer preferably has a melt flow index (MFI5) ranging from 800-1,200 g/10 min. The first high molecular weight polyethylene homopolymer or copolymer preferably has a melt flow index (MFI5) ranging from 0.05-1.20 g/10 min, preferably 0.10-0.55, more preferably 0.10-0.22 g/10 min. The second high molecular weight polyethylene copolymer preferably has a melt flow index ranging from 0.10-0.55 g/10 min. All specified MFI5 were measured in accordance with ISO 1133.

In a further preferred embodiment, the multimodal polyethylene composition in this invention exhibits a melt flow index (MFI5) within a range of 0.10-0.80 g/10 min, preferably in the range of 0.15-0.50 g/10 min, as measured according to ISO 1133.

In a yet preferred embodiment, the multimodal polyethylene composition of the present invention has a total comonomer content ranging from 0.5-5.0 mol%, preferably ranging from 1.0-3.5 mol%.

The multimodal polyethylene composition of the present invention exhibits enhanced mechanical and physical properties. Preferably, this composition has a crystallinity ranging from 63-78%, more preferably, ranging from 63-73%. Additionally, the composition has a molecular weight distribution (Mw/Mn) ranging from 27-39, as determined by GPC, and a strain hardening modulus (Gp) of at least 21.5 MPa.

The multimodal polyethylene composition of this invention may be compounded with additional additives to yield a polyethylene resin with improved mechanical and physical properties. These additional additives can be any substance recognized within the polymer field, such as heat stabilizers, antioxidants, UV absorbers, light stabilizers, fillers, reinforcing materials, plasticizers, lubricants, emulsifiers, pigments, optical brighteners, flame retardants, antistatics, blowing agents, or their combinations. The quantity of these additional additives can be adjusted to align with the desired properties of the resin product. Typically, the amount of additional additives can range from 0-50% by weight, preferably 0-10% by weight range based on the total weight of the resin mixture. The obtained polyethylene resin may then be molded or extruded to a desired product.

The polyethylene composition according to this invention, as well as the polyethylene resin comprising this composition proves particularly well-suited for the production of pipes, blow molding, and extrusion molding applications. This multimodal polyethylene composition and the resulting polymer resin exhibit enhanced mechanical properties, including Notch Charpy impact resistance tested in accordance with ISO 790, robust strain hardening capabilities, and suitability for hydrostatic pressure applications. These properties are especially crucial for manufacturing end products that demand high-pressure resistance, such as a PElOO-qualified pipe utilized in applications operating under pressures of at least 10.0 MPa.

EXAMPLES

After providing a description of this invention, a more detailed comprehension can be acquired by referring to specific examples outlined herein for illustrative purposes. These examples do not intend to impose restrictions unless otherwise stated.

Production of examples of the multimodal polyethylene composition of the present invention

Preparations of examples of the multimodal polyethylene composition, as described in the present invention, were conducted using a three-reactor system configured as explained earlier. This configuration entails the first parallel reactor (RIA), linked to the first degassing unit (DI), operating in parallel with the second parallel reactor (RIB), connected to the second degassing unit (D2). Following these parallel reactors (RIA and RIB), the serial reactor (R2) operates subsequently. Additionally, the system incorporates the flash vessel (F), in communication with both the first and second degassing units (DI and D2) to facilitate hydrogen removal process.

The slurry polymerization process involves feeding raw materials, including ethylene, hexane, Ziegler-Natta catalyst, trialkylaluminium, and hydrogen, into the first parallel reactor (RIA). Simultaneously, raw materials, including ethylene, hexane, Ziegler-Natta catalyst, trialkylaluminium, and optionally hydrogen and 1 -butene as the comonomer, were fed into the second parallel reactor (RIB). Further, raw materials, including ethylene and 1-butene, were fed to the serial reactor (R2).

The polymerization in the first parallel reactor (RIA) was carried out to produce a first reaction stream, subsequently transferred to the first degassing unit (DI). Concurrently, the polymerization in the second parallel reactor (RIB) was carried out to produce a second reaction stream, which was then directed to the second degassing unit (D2). In the first degassing unit (DI), hydrogen was partially removed from the first reaction stream, resulting in a hydrogen-depleted first reaction stream subsequently transferred to the serial reactor (R2). Similarly, in the second degassing unit (D2), all or almost all hydrogen was removed from the second reaction stream, resulting in a hydrogen-depleted second reaction stream also transferred to the serial reactor (R2). Subsequently, the raw materials supplied to the serial reactor (R2), along with the hydrogen-depleted first and second reaction streams, underwent polymerization within the serial reactor (R2), generating a third reaction stream. The controlled parameters of the polymerization and the properties of the raw materials and resulting stream for each of the reactors (RIA, RIB, and R2) are outlined in Table 1.

Table 1

Table 2 provides a more detailed breakdown of the varied polymerization parameters in each reactors for each example. Table 2

Remark ⁽¹⁾ : In the context of polymerization type, the abbreviation “Homo” stands for homopolymerization and “Copo” stands for copolymerization.

The weight fraction content of polyethylene homopolymers/copolymers obtained from the reactors RIA, RIB, and R2, present in the resulting multimodal polyethylene composition for each example, is provided in Table 3. Table 3

Remark ⁽¹⁾ : “EE ratio RIA” refers to the content in wt% of the low molecular weight polyethylene homopolymer obtained from the first parallel reactor (RIA), based on the total weight of the multimodal polyethylene composition. Remark ⁽²⁾ : “EE ratio RIB” refers to the content in wt% of the first high molecular weight polyethylene homopolymer/copolymer obtained from the second parallel reactor (RIB), based on the total weight of the multimodal polyethylene composition.

Remark ⁽³⁾ : “EE ratio R2” refers to the content in wt% of the second high molecular weight polyethylene copolymer obtained from the serial reactor (R2), based on the total weight of the multimodal polyethylene composition.

The properties of the polyethylene homopolymers/copolymers obtained from the reactors RIA, RIB, and R2 for each example, is provided in Table 4.

Table 4 In each example, the polyethylene composition was compounded into resin pellets, combined with the following additives:

2.0-2.5 wt% of carbon black;

500-2,000 ppm of Ca/Zn stearate; - 2,000-3,000 ppm of hindered phenol/phosphate stabilizer; and

500-2,000 ppm of processing aid.

Subsequently, the obtained resin pellets underwent property testing, and the results are shown in Table 5.

Table 5 Remarks: MFI5 was measured according to ISO 1133. MFI21 was measured according to

ISO 1133. Melt flow rate was measured according to ISO 1133. Density was measured according to ISO 1183. Complex viscosity was measured on controlled stress rotational from Anton Paar Rheometers. Sample plaques were tested using parallet plate geometry of 25 mm and measurement Gap 1.75 mm at temperature 190°C. Tensile strength at yield was measured according to ASTM D638. Tensile strength at break was measured according to ASTM D638. Elongation at break was measured according to ASTM D638. Notch Charpy impact was measured according to ISO 790.

Strain hardening modulus was measured according to ISO 18488.

Beyond the aforementioned properties exhibited by the resin pellets, those containing the polyethylene composition of Examples 2 and 3 underwent an additional hydrostatic test at 20°C according to ISO 1167. The results showed that those resin pellets passed the requirement of PE100 pipe according to ISO 4427.

Based on the experimental findings, it is evident that the polymerization reactor system and process of the present invention yield a multimodal polyethylene composition showcasing enhanced properties, particularly those crucial for manufacturing pipes, blow-molded, and extrusion-molded products. The resin pellets containing this invention's composition demonstrate commendable traits, notably a high strain hardening capacity - each example presenting a strain hardening value surpassing 30 MPa. Furthermore, these resin pellets, incorporating the composition of this invention, successfully meet the criteria for the hydrostatic test at 20°C.

Claims

1. A polymerization reactor system for producing a multimodal polyethylene composition, comprising: a first parallel reactor configured to polymerize ethylene and produce a first reaction stream comprising a low molecular weight polyethylene homopolymer with a weight average molecular weight (Mw) ranging from 25,000-55,000 g/mol, as determined by gel permeation chromatography (GPC); a first degassing unit, in communication with the first parallel reactor, configured to remove hydrogen from the first reaction stream, resulting in a hydrogen-depleted first reaction stream; a second parallel reactor configured to polymerize ethylene and produce a second reaction stream comprising a first high molecular weight polyethylene homopolymer or copolymer with a weight average molecular weight ranging from 100,000-650,000 g/mol, as determined by GPC; a second degassing unit, in communication with the second parallel reactor, configured to remove hydrogen from the second reaction stream, resulting in a hydrogen-depleted second reaction stream; and a serial reactor configured to polymerize ethylene, the hydrogen-depleted first reaction stream, and the hydrogen-depleted second reaction stream and produce a third reaction stream comprising a second high molecular weight polyethylene copolymer with a weight average molecular weight ranging from 150,000-380,000 g/mol, as determined by GPC, wherein the first and second parallel reactors are configured to operate concurrently in parallel, while the serial reactor is configured to operate sequentially after the first and second parallel reactors.

2. The polymerization reactor system according to claim 1 , wherein the first degassing unit is configured to remove at least 97% by weight of hydrogen from the total hydrogen content within the first reaction stream.

3. The polymerization reactor system according to claim 1 , wherein the second degassing unit is configured to remove at least 99% by weight of hydrogen from the total hydrogen content within the second reaction stream.

4. The polymerization reactor system according to claim 1, further comprises a flash vessel, in communication with the first and second degassing units, wherein the first and second degassing units, in conjunction with the flash vessel, employ a pressure balance mechanism to remove hydrogen,

5. The polymerization reactor system according to claim 1, wherein the first parallel reactor operates at a temperature ranging from 80-85°C and a pressure ranging from 8-9 bar.

6. The polymerization reactor system according to claim 1, wherein the second parallel reactor operates at a temperature ranging from 70-80°C and a pressure ranging from 1.5-3 bar.

7. The polymerization reactor system according to claim 1 , wherein the serial reactor operates at a temperature ranging from 70-75°C and a pressure ranging from 1.5-3 bar.

8. A process for producing a multimodal polyethylene composition, the process employing the polymerization reactor system according to claim 1 and comprising the steps of:

(i) polymerizing ethylene in the first parallel reactor, in a hydrocarbon medium, in the presence of a catalyst, co-catalyst, and hydrogen, to produce a first reaction stream comprising a low molecular weight polyethylene homopolymer with a weight average molecular weight (Mw) ranging from 25,000-55,000 g/mol, as determined by GPC, then transferring the first reaction stream to the first degassing unit;

(iii) polymerizing ethylene in the second parallel reactor, in a hydrocarbon medium, in the presence of a catalyst, co-catalyst, and optionally hydrogen and comonomer, to produce a second reaction stream comprising a first high molecular weight polyethylene homopolymer or copolymer with a weight average molecular weight ranging from 100,000-650,000 g/mol, as determined by GPC, then transferring the second reaction stream to the second degassing unit;

(iv) removing hydrogen from the second reaction stream in the second degassing unit, resulting in a hydrogen-depleted second reaction stream; and (v) polymerizing ethylene, the hydrogen-depleted first reaction stream, and the hydrogen-depleted second reaction stream in the serial reactor, in the presence of a comonomer, to produce a third reaction stream comprising a second high molecular weight polyethylene copolymer with a weight average molecular weight ranging from 150,000-380,000 g/mol, as determined by GPC, wherein the steps (i) and (iii) operate concurrently in parallel, while the step (v) operates sequentially after the steps (ii) and (iv).

9. The process according to claim 8, wherein the step (ii) operates to remove at least 97% by weight of hydrogen from the total hydrogen content within the first reaction stream.

10. The process according to claim 8, wherein the step (iv) operates to remove at least 99% by weight of hydrogen from the total hydrogen content within the second reaction stream.

11. The process according to claim 8, wherein the steps (ii) and (iv) operate in conjunction with a flash vessel to employ a pressure balance mechanism to remove hydrogen.

12. The process according to claim 8, wherein the step (i) operates at a temperature ranging from 80-85°C and a pressure ranging from 8-9 bar.

13. The process according to claim 8, wherein the step (iii) operates at a temperature ranging from 70-80°C and a pressure ranging from 1.5-3 bar.

14. The process according to claim 8, wherein the step (v) operates at a temperature ranging from 70-75°C and a pressure ranging from 1.5-3 bar.

15. The process according to claim 8, wherein the catalyst used in the step (i) and (iii) is Ziegler-Natta catalyst or metallocene.

16. The process of claim 8, wherein the co-catalyst used in the step (i) and (iii) is tri alkylaluminium.

17. The process of claim 16, wherein the co-catalyst used in the step (i) and (iii) is trimethylaluminium, triethylaluminium, or a combination thereof.

18. The process of claim 8, wherein the comonomer used in the step (iii) and (v) is a C4 to C12 a-olefin comonomer.

19. A multimodal polyethylene composition obtained from the process according to claim 8, comprising: (a) 45-55% by weight of the low molecular weight polyethylene homopolymer based on the total weight of the multimodal polyethylene composition;

20. The multimodal polyethylene composition according to claim 19, wherein the low molecular weight polyethylene homopolymer has a density ranging from 0.967-0.972 g/cm³ according to ISO 1183.

21. The multimodal polyethylene composition according to claim 19, wherein the first high molecular weight polyethylene homopolymer or copolymer has a density ranging from 0.930-0.950 g/cm³ according to ISO 1183.

22. The multimodal polyethylene composition according to claim 19, wherein the second high molecular weight polyethylene copolymer has a density ranging from 0.945-0.962 g/cm³ according to ISO 1183.

23. The multimodal polyethylene composition according to claim 22, wherein the second high molecular weight polyethylene copolymer has the density ranging from 0.945-0.954 g/cm³ according to ISO 1183.

24. The multimodal polyethylene composition according to claim 19, which has a melt flow index (MFI5) ranging from 0.10-0.80 g/10 min according to ISO 1133.

25. The multimodal polyethylene composition according to claim 24, which has the melt flow index (MFI5) ranging from 0.15-0.50 g/10 min according to ISO 1133.

26. The multimodal polyethylene composition according to claim 19, which has a total comonomer content ranging from 0.5-5.0 mol%.

27. The multimodal polyethylene composition according to claim 26, which has the total comonomer content ranging from 1.0-3.5 mol%.

28. The multimodal polyethylene composition according to claim 19, which has a crystallinity ranging from 63-78%.

29. The multimodal polyethylene composition according to claim 28, which has the crystallinity ranging from 63-73%

30. The multimodal polyethylene composition according to claim 19, which has a molecular weight distribution (Mw/Mn) ranging from 27-39, as determined by GPC.

31. The multimodal polyethylene composition according to claim 19, which has a strain hardening modulus (Gp) of at least 21.5 MPa.

32. A pipe comprising the multimodal polyethylene composition according to claim 19.

33. The pipe according to claim 32, which is PElOO-qualified pipe utilized in applications operating under pressures of at least 10.0 MPa.