Process for production of polyethylene by high pressure centrifugation

Abstract

Embodiments of a process for producing polyethylene include: introducing a monomer feed stream comprising ethylene monomer and optionally comonomer into a compressor system to produce a high pressure ethylene stream having a pressure of at least 1,000 bar; introducing the high pressure ethylene stream to a high pressure centrifugation unit wherein the high pressure centrifugation unit separates solid particles and droplets from the high pressure ethylene stream to produce an enriched effluent comprising the solid particles and the droplets and an upgraded high pressure ethylene stream comprising a remainder of the high pressure ethylene stream; withdrawing the enriched effluent from the high pressure centrifugal separation unit; and introducing the upgraded high pressure ethylene stream into a polymerization reactor to produce the polyethylene from the upgraded high pressure ethylene stream.

Description

[0001] Cross - reference to related applications

[0002] This application claims the benefit of U.S. Provisional Application Serial No. 63 / 385,500, filed on November 30, 2022, the entire disclosure of which is incorporated herein by reference. Technical field

[0003] The embodiments described herein generally relate to the production of polyethylene and, in particular, to the production of low - density polyethylene (LDPE), which includes high - pressure centrifugal separation of solid particles and droplets from a high - pressure ethylene monomer feed. Background art

[0004] Polyethylene resins are used in a variety of products and can be blended with additives or formed into polymer blends or compositions. The end - use of the formed polyethylene or polymer blend may impose purity or quality limitations on the final - formed product. Although polyethylene resins preferably used for the production of polyvinyl products are completely pure and free of trace contaminants, this is not realistic in a real - world environment. Thus, current polyethylene polymerization systems attempt to remove contaminants from the ethylene monomer or monomer blend provided to the reactor where polymerization occurs. Such purification is typically carried out before increasing the pressure of the ethylene monomer stream using conventional separation techniques such as gravity separation or vortex tubes. However, purification after pressurization of the ethylene monomer stream has not been traditionally achieved, resulting in any contaminants introduced during the pressurization process being passed on to the reactor where polymerization occurs.

[0005] Accordingly, there has been a continuing need for an improved method of producing polyethylene in which contaminants are removed from the ethylene monomer stream after pressurization of the ethylene monomer stream. Summary of the invention

[0006] Embodiments of the present disclosure meet this need for a method of producing polyethylene in which contaminants are removed from the ethylene monomer stream after pressurization of the ethylene monomer stream. Specifically, embodiments of the present disclosure achieve this by utilizing a high - pressure centrifugal separation unit located after a compressor system that raises the pressure of a monomer feed stream containing ethylene monomer. Such an arrangement allows for the removal of particles or contaminants introduced into the monomer feed stream from the compressor system.

[0007] According to one embodiment, a method for producing polyethylene is provided. The method includes: introducing a monomer feed stream comprising ethylene monomer and optionally a comonomer into a compressor system to generate a high-pressure ethylene stream having a pressure of at least 1,000 bar; introducing the high-pressure ethylene stream into a high-pressure centrifugal separation unit, wherein the high-pressure centrifugal separation unit separates solid particles and droplets from the high-pressure ethylene stream to generate an enriched effluent comprising the solid particles and the droplets and a refined high-pressure ethylene stream comprising the remainder of the high-pressure ethylene stream; withdrawing the enriched effluent from the high-pressure centrifugal separation unit; and introducing the refined high-pressure ethylene stream into a polymerization reactor to generate the polyethylene from the refined high-pressure ethylene stream.

[0008] These and additional embodiments are described in more detail in the following detailed description in conjunction with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The following detailed description of specific embodiments of the present disclosure may be best understood when read in conjunction with the following drawings, in which like reference numerals indicate like structures and in which:

[0010] Figure 1 is a schematic diagram of a method for producing polyethylene according to one or more embodiments of the present disclosure;

[0011] Figure 2 is a schematic diagram of a method for producing polyethylene according to one or more embodiments of the present disclosure, in which a bypass is provided;

[0012] Figure 3 is as Figure 2 illustrated is a schematic diagram of a method for producing polyethylene according to one or more embodiments of the present disclosure, in which a recycle line is also provided; and

[0013] Figure 4 is a schematic diagram of a method for producing polyethylene according to one or more embodiments of the present disclosure, in which a qualified product stream from a high-pressure centrifugal separation unit is recycled to the compressor system. DETAILED DESCRIPTION

[0014] Specific embodiments of the present application will now be described. These embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the scope of the claimed subject matter to those skilled in the art.

[0015] The term "polymer" refers to a polymeric compound prepared by polymerizing the same type or different types of monomers. Thus, the general term polymer encompasses the term "homopolymer", which generally refers to a polymer prepared from only one type of monomer, and "copolymer", which refers to a polymer prepared from two or more different monomers. The term "interpolymer" refers to a polymer prepared by polymerizing at least two different types of monomers. Thus, the general term interpolymer includes copolymers or polymers prepared from more than two different types of monomers, such as terpolymers.

[0016] "Polyethylene" or "ethylene-based polymer" shall mean a polymer comprising greater than 50 mole % of units derived from ethylene monomers. This includes ethylene-based homopolymers or copolymers (meaning units derived from two or more comonomers). Common forms of ethylene-based polymers known in the art include, but are not limited to: low density polyethylene (LDPE); linear low density polyethylene (LLDPE); ultra low density polyethylene (ULDPE); very low density polyethylene (VLDPE); single-site catalyzed linear low density polyethylene, including both linear low density resins and substantially linear low density resins (m-LLDPE); medium density polyethylene (MDPE); and high density polyethylene (HDPE).

[0017] As used herein, the term "composition" refers to the materials of the composition, as well as a mixture of reaction products and decomposition products formed from the materials of the composition.

[0018] "Blend", "polymer blend" and similar terms mean a composition of two or more polymers. Such blends may or may not be miscible. Such blends may or may not be phase-separated. Such blends may or may not contain one or more domain configurations, as determined by transmission electron spectroscopy, light scattering, x-ray scattering, and any other method known in the art. A blend is not a laminate, but one or more layers of a laminate may contain a blend. Such blends may be prepared as dry blends, formed in situ (e.g., in a reactor), melt blends, or using other techniques known to those skilled in the art.

[0019] As used herein, the term "supercritical fluid" refers to a substance at a temperature and pressure above its critical point but below the pressure required to compress it into a solid, at which critical point there is no distinct liquid and gas phase.

[0020] The terms "comprising", "including", "having", and derivatives thereof are not intended to exclude the presence of any additional components, steps, or procedures, whether or not specifically disclosed. For the avoidance of any doubt, unless stated to the contrary, all compositions claimed by use of the term "comprising" may include any additional additives, adjuvants, or compounds, whether polymeric or otherwise. In contrast, the term "consisting essentially of" excludes any other components, steps, or procedures from any subsequent recited scope, except those that are not essential to the operability. The term "consisting of" excludes any component, step, or procedure not specifically recited or listed.

[0021] A particularly useful application of the disclosed embodiments of the polyethylene production method is the production of crosslinkable polyethylene (XLPE) used in the manufacture of extra-high voltage cables, such as 500 kilovolt (kV) power transmission cables. The production of such cables typically involves introducing additives into an LDPE base resin by compounding or liquid immersion, and then adding a vulcanizing agent such as peroxide to enable crosslinking of the polyethylene during cable manufacture. It should be understood that under the extreme operating conditions of such cables, the smallest impurities can cause cable failure. Therefore, both the base resin and the additive package must be free of impurities to avoid inclusion of such impurities in the final cable. However, unexpectedly it was determined that when new cylinders or packings are introduced as part of the routine maintenance of a compressor system to pressurize the ethylene monomer feed in LDPE production, there is a break-in period during which the peaks on the cylinders or packings are worn off, generating small metal particles that are carried with the ethylene monomer feed into the polyethylene reactor. These small metal particles must be removed to obtain an LDPE base resin meeting the specifications for the production of extra-high voltage cables. While this example application and the need for post-pressurization purification of the ethylene monomer relate to XLPE for extra-high voltage cables, it should be understood that such methods may be useful and advantageous for other end products, as polymer resins free of or with reduced impurities are generally desired.

[0022] Embodiments of the method for producing polyethylene according to the present invention will now be described. Referring Figure 1 to the system 10, a monomer feed stream 5 containing ethylene monomer is fed to a compressor system 20 to produce a high-pressure ethylene stream 22 having a pressure of at least 1000 bar. Although not shown, in some embodiments it is contemplated that the monomer feed stream 5 may be pressurized before being delivered to the compressor system 20. For example, the monomer feed stream 5 may be delivered to the compressor system 20 at a pressure of less than 100 bar, or less than 50 bar, or less than 20 bar. All pressure measurements in this disclosure are absolute pressure values.

[0023] In one or more embodiments, the monomer feed stream 5 may further comprise one or more comonomers combined with the ethylene monomer. Suitable comonomers may include, but are not limited to, ethylenically unsaturated monomers, especially C 3-20 α-olefins, dienes, polyenes, and polar comonomers. These polar comonomers may include, but are not limited to, those having carboxylic acid, acrylate, or acetate functional groups, such as methacrylic acid, acrylic acid, vinyl acetate, methyl acrylate, isobutyl acrylate, n-butyl acrylate, glycidyl methacrylate, and monoethyl maleate.

[0024] Referring again to Figure 1 , the compressor system 20 may include one or more compressors in parallel or in series. As Figure 1 shown, the compressor system 20 may include a main compressor 24 and an auxiliary compressor 26 downstream of the main compressor 24. The main compressor 24 may pressurize the monomer feed stream 5 such that the partially pressurized feed stream 28 to the auxiliary compressor 26 has a pressure of at least 200 bar. In one or more embodiments, the main compressor 24 may compress the monomer feed stream 5 to a pressure of 200 bar to 1000 bar, or 300 bar to 900 bar. To achieve this compression, the main compressor 24 may include one or more compression stages.

[0025] The auxiliary compressor 26 (which may also be referred to as a hypercompressor) pressurizes the partially pressurized feed stream 28 to a pressure of at least 1000 bar, or at least 2000 bar, or at least 2500 bar, or at least 3000 bar. Like the main compressor 24, the auxiliary compressor 26 may include one or more compression stages. In one or more embodiments, the auxiliary compressor 26 may include a piston reciprocating compressor and may be composed of a single or multiple compressor stages.

[0026] In various embodiments, the high-pressure ethylene stream 22 exiting the compressor system 20 includes a pressure of at least 1000 bar, or at least 2000 bar, or at least 2500 bar, or at least 3000 bar. Additionally, in various embodiments, the high-pressure ethylene stream 22 exiting the compressor system 20 may alternatively be defined as having a pressure such that the high-pressure ethylene stream 22 is a supercritical fluid.

[0027] Referring again to Figure 1, a high-pressure ethylene stream 22 leaving the compressor system 20 is transferred to a high-pressure centrifugal separation unit 30. The high-pressure centrifugal separation unit 30 separates solid particles and droplets from the high-pressure ethylene stream 22 to generate an enriched effluent 34 containing solid particles and droplets and a refined high-pressure ethylene stream 32 containing the remainder of the high-pressure ethylene stream. Consistent with terms understood in the art, the enriched effluent 34 can be considered as waste or a waste stream, and the refined high-pressure ethylene stream 32 can be considered as a qualified product or a qualified product stream. Thus, the enriched effluent 34 can be withdrawn from the high-pressure centrifugal separation unit 30 and further processed or disposed of.

[0028] It should be understood that due to incomplete separation within the high-pressure centrifugal separation unit 30, in addition to solid particles and droplets, the enriched effluent 34 may also contain ethylene or other liquid components or gas components. For example, in continuous operation, the enriched effluent may contain more than 99 wt% ethylene, while in batch or semi-batch operation, the enriched effluent may contain up to 50 wt% ethylene.

[0029] In one or more embodiments, the solid particles and droplets are collected in a separate part of the high-pressure centrifugal separation unit 30 for periodic removal. Specifically, the enriched effluent 34 is directed to a storage container provided as part of the high-pressure centrifugal separation unit 30, where the enriched effluent is isolated for periodic discharge or removal.

[0030] In one or more embodiments, the solid particles and droplets are withdrawn from the high-pressure centrifugal separation unit 30 via a first stream to drive the enriched effluent 34 away from the high-pressure centrifugal separation unit 30. Specifically, the enriched effluent 34 and the solid particles and droplets contained therein can be transported away from the high-pressure centrifugal separation unit 30 for disposal or further processing. For example, the first stream can be an underflow that removes solid particles and droplets in a semi-continuous or continuous manner.

[0031] According to one or more embodiments, a plurality of high-pressure centrifugal separation units 30 are provided. According to different embodiments, the plurality of high-pressure centrifugal separation units 30 can be provided in series or in parallel. In various embodiments, the system 10 can include 1, 2, 3, 4, 5, or more than 5 individual high-pressure centrifugal separation units 30. It should be understood that a plurality of high-pressure centrifugal separation units 30 in series allow for the stepwise purification of the refined high-pressure ethylene stream 32 by continuously removing solid particles and droplets. Similarly, it should be understood that a plurality of high-pressure centrifugal separation units 30 in parallel allow for an increase in the production rate of the refined high-pressure ethylene stream 32 by simultaneously removing solid particles and droplets using the plurality of high-pressure centrifugal separation units 30.

[0032] In one or more embodiments, the high-pressure ethylene stream 22 is introduced into the high-pressure centrifugal separation unit 30 in a pulsating manner. Specifically, as would be understood by those skilled in the art, the high-pressure ethylene stream 22 leaving the compressor system 20 can be discontinuous. For example, a reciprocating compressor can produce a stream with a pulsed or unsteady flow rate. Thus, the high-pressure centrifugal separation unit 30 can be configured to handle the pulsating introduction of the high-pressure ethylene stream 22. It should be understood that the volume of the high-pressure centrifugal separation unit 30 relative to the inlet stream pulsations can be used to modulate the effect of the pulsed stream by considering the frequency of the compressor and based on the residence time of the high-pressure ethylene stream 22 within the high-pressure centrifugal separation unit 30.

[0033] Referring again to Figure 1 , the upgraded high-pressure ethylene stream 32 leaving the high-pressure centrifugal separation unit 30 is transferred to a polymerization reactor 40 to produce polyethylene from the upgraded high-pressure ethylene stream 32. Although any high-pressure polymerization reactor can be used in accordance with the present disclosure, examples of specific reactors and reactor types are provided to fully describe the method for producing polyethylene, but should not be considered limiting. In one or more embodiments, the polymerization reactor 40 can be a free-radical polymerization reactor. Additionally, in one or more embodiments, a polymerization initiator 44 can be added to the polymerization reactor 40.

[0034] The polymerization reactor 40 can include one or more autoclave reactors or tubular reactors. The pressure in each autoclave reactor zone or tubular reactor zone can be from 1000 bar to 4000 bar, or from 1500 bar to 3600 bar, or from 2000 bar to 3200 bar. The polymerization temperature in each tubular reactor zone can be from 100 °C to 400 °C, or from 150 °C to 360 °C, or from 180 °C to 340 °C. The polymerization temperature in each autoclave reactor zone can be from 150 °C to 300 °C, more typically from 165 °C to 290 °C, and even more typically from 180 °C to 280 °C.

[0035] Referring to Figure 1 , the reactor effluent 42 from the polymerization reactor 40 contains the polyethylene produced in the polymerization reactor 40 and the unreacted components of the upgraded high-pressure ethylene stream 32. It should be understood that if the polymerization initiator 44 is provided to the polymerization reactor 40, the polymerization initiator may also be present in the reactor effluent 42.

[0036] Referring to Figure 2, in one or more embodiments, a high-pressure ethylene stream 22 is provided to a bypass control valve 50 to controllably direct the high-pressure ethylene stream 22 to a high-pressure centrifugal separation unit 30, or to a bypass line 52 to introduce the high-pressure ethylene stream 22 directly into a polymerization reactor 40. When the bypass control valve 50 is in a separation mode configuration, the high-pressure ethylene stream 22 is directed to the high-pressure centrifugal separation unit 30 via a separator feed line 54, and a refined high-pressure ethylene stream 32 from the high-pressure centrifugal separation unit 30 is directed to the polymerization reactor 40 via a separator effluent line 56 connected to a reactor inlet line 36. Conversely, when the bypass control valve 50 is in a bypass mode configuration, the high-pressure ethylene stream 22 is directed to the polymerization reactor 40 via the bypass line 52 and the reactor inlet line 36 to introduce the high-pressure ethylene stream 22 directly into the polymerization reactor 40. In one or more embodiments, the system 10 may additionally include a reflux control valve 60 provided at the junction of the bypass line 52 and the separator effluent line 56 to prevent reflux through the bypass line 52 in the separation mode configuration and prevent reflux through the separator effluent line 56 in the bypass mode configuration.

[0037] Continuing to refer Figure 2 , it should be understood that the bypass control valve 50 and the reflux control valve 60 (if present) can be configured to allow splitting of the high-pressure ethylene stream 22 such that a portion of the high-pressure ethylene stream 22 passes through the high-pressure centrifugal separation unit 30, and the remainder of the high-pressure ethylene stream 22 is passed directly to the polymerization reactor 40.

[0038] According to at least Figure 2 one embodiment, the system 10 can be operated in a separation mode where the high-pressure ethylene stream 22 passes through the high-pressure centrifugal separation unit 30 for a period of time after changing a cylinder or packing, at which time metal particles are expected to be generated during a break-in period. After the break-in period, the system 10 can be changed to a bypass mode configuration where the high-pressure centrifugal separation unit 30 is omitted from the process flow because metal particles are no longer expected to be generated from the break-in of the cylinder or packing. However, it should be understood that if other solid particles or waxes from one or more different sources are expected to be present in the high-pressure ethylene stream 22, the system 10 can still be operated in the separation mode configuration.

[0039] Referring Figure 3 , at least a portion of the refined high-pressure ethylene stream 32 is recycled to the compressor system 20. Specifically, in one or more embodiments, at least a portion of the refined high-pressure ethylene stream 32 is recycled back to the compressor system 20 via a recycle line 38, where the remainder of the refined high-pressure ethylene stream 32 is passed to the polymerization reactor 40 via the separator effluent line 56.

[0040] In one or more embodiments, all of the refined high-pressure ethylene stream 32 is recycled back to the compressor system 20 for at least a period of time. It should be understood that recycling at least a portion of the refined high-pressure ethylene stream 32 back to the compressor system 20 guides this portion of the refined high-pressure ethylene stream 32 to pass through the high-pressure centrifugal separation unit 30 at least one more time.

[0041] Recycling at least a portion of the refined high-pressure ethylene stream 32 back to the compressor system 20 allows for the repeated separation of solid particles and droplets from the high-pressure ethylene stream 22 to achieve a desired purity or a reduced concentration of solid particles and droplets in the refined high-pressure ethylene stream 32 when supplied to the polymerization reactor 40.

[0042] Reference Figure 4 , all of the refined high-pressure ethylene stream 32 can be recycled to the compressor system 20 via the recycle line 38. Additionally, the bypass control valve 50 controls the portion of the high-pressure ethylene stream 22 supplied to the high-pressure centrifugal separation unit 30 and the portion of the high-pressure ethylene stream 22 directly supplied to the polymerization reactor 40. It should be understood that Figure 4 The embodiments of Figure 3 are variations of the embodiments of

[0043] It should be understood that positioning the high-pressure centrifugal separation unit 30 after the compressor system 20 but before the polymerization reactor 40 allows for the removal of any solid particles and droplets introduced in the initial stages of the process. However, such removal is also achieved prior to polymerization in the polymerization reactor 40, thus avoiding the challenges associated with separating from the polymer product.

[0044] Solid particles

[0045] According to one or more embodiments, the solid particles removed in the enriched effluent 34 are metallic. For example, the solid particles can be copper, bronze, steel, iron, zinc, aluminum, or any other metallic substance. In one or more specific embodiments, the solid particles can be filings or other wear products from one or more unit operations that process components of the monomer feed stream prior to introduction into the high-pressure centrifugal separation unit 30. For example, the solid particles can include copper particles or bronze particles worn off from components of the compressor system 20.

[0046] In one or more embodiments, the solid particles have a longest dimension of less than 1,000 microns. In various additional embodiments, the solid particles have a longest dimension of less than 500 microns, less than 200 microns, less than 150 microns, or less than 100 microns. It should be appreciated that smaller particle sizes present unique challenges in their removal or separation from the stream, and these challenges are exacerbated by the high pressures of current systems. However, it should also be appreciated that the methods discussed in the present disclosure address such challenges in a unique and novel manner by implementing a high-pressure centrifugal separation unit 30 between the compressor system 20 and the polymerization reactor 40.

[0047] Droplets

[0048] In accordance with one or more embodiments, the droplets removed in the enriched effluent 34 contain wax. Generally, the wax is low molecular weight polyethylene that forms as droplets or small particles in the ethylene stream.

[0049] Polymer

[0050] In one or more embodiments, the polymerization reactor 40 specifically produces low density polyethylene (LDPE).

[0051] In one embodiment, the density of the LDPE is from 0.914 grams per cubic centimeter (g / cc or g / cm 3 ) to 0.930 g / cc or g / cm 3 , more typically from 0.916 g / cc or g / cm 3 to 0.930 g / cc or g / cm 3 , and even more typically from 0.918 g / cc or g / cm 3 to 0.926 g / cc or g / cm 3 , which is prepared in accordance with ASTM D4703 and measured within one hour of sample pressing in accordance with ASTM D792 method B. In one embodiment, the LDPE has a melt index (I2) of from 0.1 g / 10 min to 40 g / 10 min or from 0.2 g / 10 min to 25 g / 10 min, which is measured at 190 °C and a load of 2.16 kg in accordance with ASTM D-1238 (method B). In some embodiments, the LDPE may have a lower I2 of from 0.1 g / 10 min to 10 g / 10 min or from 0.1 g / 10 min to 1 g / 10 min. Alternatively, the LDPE may have a higher I2 of from 5 g / 10 min to 40 g / 10 min, or from 10 g / 10 min to 25 g / 10 min, or from 15 g / 10 min to 25 g / 10 min.

[0052] Application

[0053] The polyethylene formed by the method disclosed according to the present invention can be used in various conventional thermoplastic manufacturing processes to produce useful articles, including, for example, films; molded articles such as blow molded articles, injection molded articles or rotomolded articles; foams; wires and cables, fibers, extrusion coatings, and woven or non-woven fabrics.

[0054] Example

[0055] To demonstrate the process improvements resulting from the integration of the high-pressure centrifugal separation unit 30 between the compressor system 20 and the polymerization reactor 40, the reduction of solid particles in the upgraded high-pressure ethylene stream 32 entering the polymerization reactor 40 was modeled. The model utilized the smallest particles with a length of 50 μm, a width of 20 μm, and a height of 2 μm, which is equivalent to a spherical diameter of 15.6 μm at a concentration of less than 0.1 volume% of the feed stream. Comparative Example 1 represents that no separator is provided between the compressor system 20 and the polymerization reactor 40, Comparative Example 2 represents that a gravity separator is provided between the compressor system 20 and the polymerization reactor 40, and Example 3 of the present invention represents that a high-pressure centrifugal separation unit 30 is provided between the compressor system 20 and the polymerization reactor 40.

[0056] The simulated separation results for each of Comparative Examples 1 and 2 and Example 3 of the present invention are provided in Table 1. It should be noted that the cut size exists as a d50 value, which represents the size of the particles at which 50% particle separation efficiency is achieved. In addition, the fouling resistance was quantified based on the expected impact on the performance characteristics within the typical operating cycle of fouling buildup in this unit. The performance characteristics considered include pressure drop, cut size, and the safe operation of the unit, where "high" fouling resistance indicates no impact or a negligible impact on performance, as represented by an increase in pressure drop and / or cut size of less than 5%.

[0057] Table 1 - Performance of the modeled separator

[0058]

[0059] It can be noted that compared to the base case of Comparative Example 1, Example 3 of the present invention according to the present disclosure exhibits a 98% increase in particle separation efficiency, a minimum pressure drop, and high fouling resistance.

[0060] It is obvious that modifications and variations are possible without departing from the scope of the present disclosure as defined in the appended claims. More specifically, although some aspects of the present disclosure may be identified herein as preferred or particularly advantageous, upon consideration, the present disclosure need not be limited to these aspects.

Claims

1. A method for producing polyethylene, the method comprising: introducing a monomer feed stream comprising ethylene monomer and optionally a comonomer into a compressor system to generate a high-pressure ethylene stream having a pressure of at least 1,000 bar; introducing the high-pressure ethylene stream into a high-pressure centrifugal separation unit, wherein the high-pressure centrifugal separation unit separates solid particles and droplets from the high-pressure ethylene stream to generate an enriched effluent comprising the solid particles and the droplets and a purified high-pressure ethylene stream comprising the remainder of the high-pressure ethylene stream; removing the enriched effluent from the high-pressure centrifugal separation unit; and introducing the purified high-pressure ethylene stream into a polymerization reactor to generate the polyethylene from the purified high-pressure ethylene stream.

2. The method according to claim 1, wherein the pressure of the high-pressure ethylene stream is at least 2,000 bar.

3. The method according to any one of the preceding claims, wherein the high-pressure ethylene stream is a supercritical fluid.

4. The method according to any one of the preceding claims, wherein the high-pressure ethylene stream is provided to a bypass control valve to controllably direct the high-pressure ethylene stream to the high-pressure centrifugal separation unit, or provided to a bypass line to directly introduce the high-pressure ethylene stream into the polymerization reactor.

5. The method according to any one of the preceding claims, wherein the purified high-pressure ethylene stream is at least partially recycled to the compressor system.

6. The method according to any one of the preceding claims, wherein the solid particles and the droplets are collected in a separate part of the high-pressure centrifugal separation unit for periodic removal.

7. The method according to any one of the preceding claims, wherein the solid particles and the droplets are removed from the high-pressure centrifugal separation unit via a first stream to drive the enriched effluent away from the high-pressure centrifugal separation unit.

8. The method according to any one of the preceding claims, wherein a plurality of high-pressure centrifugal separation units are provided in series or in parallel.

9. The method according to any one of the preceding claims, wherein the solid particles are metallic.

10. The method according to claim 9, wherein the solid particles comprise a longest dimension of less than 1,000 microns.

11. The method according to claim 9, wherein the solid particles comprise a longest dimension of less than 200 microns.

12. The method according to any one of the preceding claims, wherein the droplets comprise wax.

13. The method according to any one of the preceding claims, wherein the high-pressure ethylene stream is introduced into the high-pressure centrifugal separation unit in a pulsating manner.

14. The method according to any one of the preceding claims, wherein the polyethylene is low-density polyethylene (LDPE).

15. The method according to any one of the preceding claims, wherein introducing the compressed monomer feed stream comprises the ethylene monomer and the comonomer.

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