Processes for polymerizing ethylene

Abstract

According to some embodiments of the present disclosure, a process for producing low-density polyethylene (LDPE) may comprise compressing a first fresh ethylene stream, a first inhibitor stream, and a low-pressure recycle stream in a first primary compressor, thereby producing a first medium-pressure stream; compressing a second fresh ethylene stream and a second inhibitor stream in a second primary compressor, thereby producing a second medium-pressure stream; compressing the first medium-pressure stream and the second medium-pressure stream in one or more hyper-compressors, thereby producing a first high-pressure stream and a second highpressure stream; and introducing the first high-pressure stream and the second high-pressure stream into a high-pressure reactor, thereby producing the LDPE via free radical polymerization at a pressure of at least 1000 bar.

Description

PROCESSES FOR POLYMERIZING ETHYLENECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application Serial No. 63 / 586,458 filed September 29, 2023, the contents of which are incorporated in their entirety herein.TECHNICAL FIELD

[0002] Embodiments of the present disclosure relate to processes for the production of ethylenebased polymers, and more specifically, to the production of low-density polyethylene.BACKGROUND

[0003] The production of low-density polyethylene is an important chemical process. In the production of low-density polyethylene, fresh ethylene and chain transfer agent (CTA) are introduced to the high-pressure reactor at different points along the reactor length. Varying the concentration of fresh ethylene and CTA along the reactor can provide product differentiation.

[0004] Inhibitors may be used to avoid / minimize polymerization of the ethylene in the hypercompressor and the preheater. Such polymerization can necessitate plant shutdowns and cleanups, and can decrease overall production rate / plant capacity. Oxygen is generally considered the cheapest and simplest inhibitor. Inhibitor is usually fed into the suction of the primary compressors. While oxygen could be fed to the suction of the hyper-compressors, this would usually require additional oxygen flow control mechanisms as the pressure after the primary compressors is generally similar to the pressure in an oxygen cylinder.

[0005] Referring now to FIG. 1, a conventional system for producing low-density polyethylene (LDPE) comprises a first fresh ethylene stream 102, a first inhibitor stream 104, and a low- pressure recycle stream 106 upstream from, and in fluid communication with, a first primary compressor 108. The conventional system comprises a first medium-pressure stream 110 in fluid communication with the first primary compressor 108 and the first hyper-compressor 112. The conventional system comprises a first chain transfer agent stream 114 in fluid communication with the first medium-pressure stream 110, upstream of the first hyper-compressor 112. The conventional system comprises a first high-pressure stream 150 in fluid communication with thefirst hyper-compressor 112 and a preheater 116. The preheater 116 is in fluid communication with a high-pressure reactor 118 and the first hyper-compressor 112.

[0006] The conventional system further comprises a second primary compressor feed stream 160. The second primary compressor feed stream 160 is an offshoot of the first fresh ethylene stream 102 and the low-pressure recycle stream 106. The second primary compressor feed stream 160 is in fluid communication with the second primary compressor 124. The second primary compressor 124 compresses the second primary compressor feed stream 160 to produce a second medium-pressure stream 126. Generally, in the conventional system, at least a portion of the low- pressure recycle stream 106 is compressed in the second primary compressor 124. The second primary compressor 124 may be in fluid communication with the second hyper-compressor 128 through the second medium-pressure stream 126. The second hyper-compressor 128 may produce a second high-pressure stream 130 which may be introduced to the high-pressure reactor 118, such as through a side input of the high-pressure reactor 118.

[0007] In the conventional TDPE production process described in FIG. 1, the feeds to the first primary compressor 108 and the second primary compressor 124 are substantially the same composition and pressure as one another.BRIEF SUMMARY

[0008] Processes for the production of ethylene, which can increase production rates and reduce fouling while maintaining product properties are desired. Embodiments of the present disclosure meet this need by providing separate feeds to the first and second primary compressors. Without being bound by theory, separating these feeds allows the feed to the second primary compressor to be at a different (such as higher) pressure than the feed to the first primary compressor, thereby increasing overall production rates. Additionally, these separate feeds allow for distinct concentrations of inhibitor to be fed to the front and side of the high-pressure reactor, improving product properties and reducing fouling. In some embodiments, these separate feeds may further prevent the introduction of unreacted initiator to the second primary compressor and second hyper-compressor, as no recycle is fed to the second primary compressor.

[0009] According to some embodiments, a process for producing low-density polyethylene (LDPE) may comprise compressing a first fresh ethylene stream, a first inhibitor stream, and a low-pressure recycle stream in a first primary compressor, thereby producing a first medium-pressure stream having a pressure of at least 180 bar; compressing a second freshethylene stream and a second inhibitor stream in a second primary compressor, thereby producing a second medium-pressure stream having a pressure of at least 180 bar; compressing the first medium-pressure stream and the second medium-pressure stream in one or more hyper-compressors, thereby producing a first high-pressure stream having a pressure of at least 2000 bar and a second high-pressure stream having a pressure of at least 2000 bar; and introducing the first high-pressure stream and the second high-pressure stream into a high-pressure reactor, thereby producing the LDPE via free radical polymerization at a pressure of at least 2000 bar.

[0010] These and other embodiments are described in more detail in the Detailed Description. It is to be understood that both the foregoing general description and the following detailed description present embodiments of the presently disclosed technology, and are intended to provide an overview or framework for understanding the nature and character of the technology as it is claimed. The accompanying drawings are included to provide a further understanding of the presently disclosed technology and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments and, together with the description, serve to explain the principles and operations of the presently disclosed technology. Additionally, the drawings and descriptions are meant to be merely illustrative, and are not intended to limit the scope of the claims in any manner.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0011] The following detailed description of specific embodiments of the present disclosure can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

[0012] FIG. 1 is a schematic diagram of a comparative system used for forming LDPE.

[0013] FIG. 2 is a schematic diagram of a system for forming low-density polyethylene, in accordance with one embodiment described and disclosed herein.

[0014] FIG. 3 is a schematic diagram of a comparative system used for forming LDPE.

[0015] For the purpose of describing the simplified schematic illustrations and descriptions of the relevant figures, the numerous valves, temperature sensors, electronic controllers and the like that may be employed and well known to those of ordinary skill in the art of certain chemical processing operations are not included. Further, accompanying components that are often included in typical chemical processing operations, such as air supplies, catalyst hoppers, and flue gashandling systems, are not depicted. However, operational components, such as those described in the present disclosure, may be added to the embodiments described in this disclosure.

[0016] It should further be noted that arrows in the drawings refer to process streams. However, the arrows may equivalently refer to transfer lines which may serve to transfer process streams between two or more system components. Additionally, arrows that connect to system components define inlets or outlets in each given system component. The arrow direction corresponds generally with the major direction of movement of the materials of the stream contained within the physical transfer line signified by the arrow. Furthermore, arrows which do not connect two or more system components signify a product stream which exits the depicted system or a system inlet stream which enters the depicted system. Product streams may be further processed in accompanying chemical processing systems or may be commercialized as endproducts. System inlet streams may be streams transferred from accompanying chemical processing systems or may be non-processed feedstock streams. Some arrows may represent recycle streams, which are effluent streams of system components that are recycled back into the system. However, it should be understood that any represented recycle stream, in some embodiments, may be replaced by a system inlet stream of the same material, and that a portion of a recycle stream may exit the system as a system product.

[0017] Additionally, arrows in the drawings may schematically depict process steps of transporting a stream from one system component to another system component. For example, an arrow from one system component pointing to another system component may represent “passing” a system component effluent to another system component, which may include the contents of a process stream “exiting” or being “removed” from one system component and “introducing” the contents of that product stream to another system component. It should be understood that arrows in the relevant figures are not indicative of necessary or essential steps.

[0018] It should be understood that according to the embodiments presented in the relevant figures, an arrow between two system components may signify that the stream is not processed between the two system components. In other embodiments, the stream signified by the arrow may have substantially the same composition throughout its transport between the two system components. Additionally, it should be understood that in one or more embodiments, an arrow may represent that at least 75 wt.%, at least 90 wt.%, at least 95 wt.%, at least 99 wt.%, at least 99.9 wt.%, or even 100 wt.% of the stream is transported between the system components. Assuch, in some embodiments, less than all of the streams signified by an arrow may be transported between the system components, such as if a slip stream is present.

[0019] It should be understood that two or more process streams are “mixed” or “combined” when two or more lines intersect in the schematic flow diagrams of the relevant figures. Mixing or combining may also include mixing by directly introducing both streams into a like reactor, separation device, or other system component. For example, it should be understood that when two streams are depicted as being combined directly prior to entering a separation unit or reactor, that in some embodiments the streams could equivalently be introduced into the separation unit or reactor and be mixed in the reactor.

[0020] Reference will now be made in greater detail to various embodiments, some embodiments of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or similar parts.DETAILED DESCRIPTION

[0021] The term “polymer” refers to a polymeric compound prepared by polymerizing monomers, whether of the same or a different type. The generic term polymer thus embraces the term “homopolymer,” usually employed to refer to polymers prepared from only one type of monomer as well as “copolymer” which refers to polymers prepared from two or more different monomer types.

[0022] “Polyethylene” or “ethylene-based polymer” shall mean polymers comprising greater than 50% by weight derived from ethylene monomer. This includes polyethylene homopolymers or copolymers (meaning units derived from two or more monomer types). Common forms of polyethylene known in the art include 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 and substantially linear low density resins (m-LLDPE); Medium Density Polyethylene (MDPE); and High Density Polyethylene (HDPE).

[0023] The term “LDPE” may also be referred to as “high-pressure ethylene polymer” or “highly branched polyethylene” and is defined to mean that the polymer is partly or entirely homopolymerized or copolymerized in autoclave or tubular reactors at pressures above 14,500 psi (100 MPa) with the use of free-radical initiators, such as peroxides (see, for example, U.S. PatentNo. 4,599,392, which is hereby incorporated by reference in its entirety). LDPE resins typically have a density in the range of 0.916 g / cm3to 0.930 g / cm3.

[0024] The term “LLDPE,” includes resin made using Ziegler-Natta catalyst systems as well as resin made using single-site catalysts, including, but not limited to, bis-metallocene catalysts (sometimes referred to as “m-LLDPE”), phosphinimine, and constrained geometry catalysts, and resins made using post-metallocene, molecular catalysts, including, but not limited to, bis(biphenylphenoxy) catalysts (also referred to as polyvalent aryloxy ether catalysts). LLDPE includes linear, substantially linear, or heterogeneous ethylene-based copolymers. LLDPEs contain less long chain branching than LDPEs and include the substantially linear ethylene polymers, which are further defined in U.S. Patent No. 5,272,236, U.S. Patent No. 5,278,272, U.S. Patent No. 5,582,923 and U.S. Patent No. 5,733,155 each of which are incorporated herein by reference in their entirety; the homogeneously branched linear ethylene polymer compositions such as those in U.S. Patent No. 3,645,992 which is incorporated herein by reference in its entirety; the heterogeneously branched ethylene polymers such as those prepared according to the process disclosed in U.S. Patent No. 4,076,698 which is incorporated herein by reference in its entirety; and blends thereof such as those disclosed in U.S. Patent No. 3,914,342 and U.S. Patent No. 5,854,045 which are incorporated herein by reference in their entirety. The LLDPE resins can be made via gas-phase, solution-phase, or slurry polymerization or any combination thereof, using any type of reactor or reactor configuration known in the art.

[0025] As used herein, a “booster compressor” refers to a compressor operable to increase the pressure of a low-pressure recycle stream up to a pressure of from 10 bar to 50 bar, such as from 10 to 30 bar.

[0026] As used herein, a “primary compressor” refers to a compressor operable to increase the pressure of a low-pressure stream up to a pressure of at least 180 bar, such as from 180 to 500 bar, from 180 to 300 bar, from 200 to 300 bar, or from 200 to 250 bar.

[0027] As used herein, a “hyper-compressor” refers to a compressor operable to compress a medium-pressure stream up to a pressure of at least 1000 bar, such as at least 1200 bar, at least 1500 bar, at least 1700 bar, or at least 2000 bar.

[0028] Each primary compressor and / or hyper-compressor may comprise one or more plunger cylinders. As used herein, the term “compressor” refers to one or a group of cylinderswhich produces a single output stream, regardless of how the cylinders are arranged otherwise.

[0029] Referring now to FIG. 2, a process for producing low-density polyethylene (LDPE), may utilize a system 100 for producing LDPE. The system 100 may comprise a first fresh ethylene stream 102, a first inhibitor stream 104, and a low-pressure recycle stream 106 upstream from, and in fluid communication with, a first primary compressor 108. The system 100 may comprise a first medium-pressure stream 110 which provides fluid communication between the first primary compressor 108 and one or more hyper compressors (such as the first hyper-compressor 112 or the second hyper-compressor 128). The system 100 may comprise a first chain transfer agent stream 114 in fluid communication with and upstream of the one or more hyper compressors (such as the first hyper-compressor 112). The system 100 may comprise a first high-pressure stream in fluid communication with the one or more hyper compressors (such as the first hyper-compressor 112) and a preheater 116. The preheater 116 may be in fluid communication with a high-pressure reactor 118.

[0030] The system 100 may further comprise a second fresh ethylene stream 120 and a second inhibitor stream 122 upstream from, and in fluid communication with, a second primary compressor 124. The second primary compressor 124 may compress the second fresh ethylene stream 120 and the second inhibitor stream 122 to produce a second medium-pressure stream 126. In embodiments, the low-pressure recycle stream 106 may not be compressed in the second primary compressor 124. The second primary compressor 124 may be in fluid communication with the one or more hyper compressors (such as the first hyper-compressor 112 or the second hyper-compressor 128) through the second medium-pressure stream 126. The one or more hyper compressors (such as the first hyper-compressor 112 or second hyper-compressor 128) may produce a second high-pressure stream 130 which may be introduced to the high-pressure reactor 118, such as through a side inlet of the high-pressure reactor 118. The first medium-pressure stream 110 and the second medium-pressure stream 126 may be compressed in a single hyper compressor or in separate hyper-compressors.

[0031] In embodiments, the preheater 116 may be a bank of tubes connected to and upstream from a reaction zone within the high-pressure reactor 118. There may be one or more initiator streams 132 injected into the high-pressure reactor 118. The injection sites for each of the initiator streams 132 may form the beginning of a reaction zone. The high-pressure reactor 118 may comprise 2, 3, 4, 5, or more initiator streams 132, each with separate injection points and eachinjection point demarcating the start of a new reaction zone. Accordingly, the high-pressure reactor 118 may comprise 2, 3, 4, 5, or more reaction zones. The high-pressure reactor 118 may produce a reactor output stream 134, which may contain a relatively great amount of solvent. The reactor output stream 134 may pass to one or more separators 136. The one or more separators 136 may produce the low-pressure recycle stream 106, a high-pressure recycle stream 138, and a process outlet stream 140. The high-pressure recycle stream 138 may be combined with one or both of the medium-pressure streams and fed to the one or more hyper-compressors. The low- pressure recycle stream 106 may pass through a booster compressor 142 and be combined with the first fresh ethylene stream 102 before entering the first primary compressor 108.

[0032] The process may comprise compressing the first fresh ethylene stream 102, the first inhibitor stream 104, and the low-pressure recycle stream 106 in the first primary compressor 108, thereby producing the first medium-pressure stream 110. The process may further comprise compressing a second fresh ethylene stream 120 and a second inhibitor stream 122 in a second primary compressor 124, thereby producing a second medium-pressure stream 126.

[0033] The process may comprise introducing a chain transfer agent to the first medium-pressure stream 110 at the suction of the one or more hyper-compressors (such as the first hypercompressor 112 or the second hyper-compressor 128) and introducing a chain transfer agent to the second medium-pressure stream 126 at the suction of the one or more hyper-compressors (such as the first hyper-compressor 112 or the second hyper-compressor 128). The chain transfer agent may mix with the respective medium-pressure streams downstream of the introduction of the high pressure recycle streams 138 and upstream of the one or more hyper-compressors.

[0034] The first medium-pressure stream 110 may be compressed in a first hyper-compressor 112, thereby producing a first high-pressure stream 150 and the second medium-pressure stream 126 may be compressed in a second hyper-compressor 128, thereby producing a second high- pressure stream 130. In another embodiment, the first medium-pressure stream 110 may be compressed in the second hyper-compressor 128, thereby producing the second high-pressure stream 130 and the second medium-pressure stream 126 may be compressed in the first hypercompressor 112, thereby producing the first high-pressure stream 150. In yet another embodiment, the first medium-pressure stream 110 and the second medium-pressure stream 126 may be compressed together in one or more hyper-compressors, thereby producing a mixed high- pressure stream. The mixed high-pressure stream may then be divided to form a first high-pressure stream 150 and a second high-pressure stream 130.

[0035] The first high-pressure stream 150 may be introduced to a front inlet of a high-pressure reactor 118 and the second high-pressure stream 130 may be introduced in one or more side inlets of the high-pressure reactor 118. The first high-pressure stream 150 may be heated in a preheater 116, upstream of the high-pressure reactor 118.

[0036] In embodiments, at least 90 wt. %, such as at least 95 wt. %, at least 98 wt. %, at least 99 wt. %, or even at least 99.9 wt. % of the first high-pressure stream 150 may be introduced to the front inlet of the high-pressure reactor 118, on the basis of the total weight of the first high- pressure stream 150. In embodiments, at least 90 wt. %, such as at least 95 wt. %, at least 98 wt. %, at least 99 wt. %, or even at least 99.9 wt. % of the second high-pressure stream 130 may be introduced to the one or more side inlets of the high-pressure reactor 118, on the basis of the total weight of the second high-pressure stream 130.

[0037] The process may further comprise producing low-density polyethylene (TDPE) from the first high-pressure stream 150 and the second high-pressure stream 130 in the high-pressure reactor 118 at a pressure of at least 2000 bar.

[0038] The first fresh ethylene stream 102 may comprise ethylene, such as at least 80 wt. %, at least 90 wt. %, at least 95 wt. %, at least 99 wt. %, or even at least 99.99 wt. % of ethylene.

[0039] The first fresh ethylene stream 102 may have a pressure of at least 10 bar, such as at least 15 bar, from 10 bar to 30 bar, from 10 bar to 20 bar, from 15 bar to 30 bar, from 15 bar to 20 bar, from 13 bar to 18 bar, or any subset thereof.

[0040] The second fresh ethylene stream 120 may comprise ethylene, such as at least 80 wt. %, at least 90 wt. %, at least 95 wt. %, at least 99 wt. %, or even at least 99.99 wt. % of ethylene.

[0041] The second fresh ethylene stream 120 may have a pressure of at least 18 bar, such as at least 20 bar, from 18 bar to 50 bar, from 18 bar to 30 bar, from 18 bar to 25 bar, at least 20 bar, from 20 bar to 30 bar, or any subset thereof.

[0042] The first fresh ethylene stream, the first inhibitor stream, and the low-pressure recycle stream may be combined to form a first low-pressure stream. The second fresh ethylene stream and the second inhibitor stream may be combined to form a second low- pressure stream. The second low-pressure stream may be at a higher pressure than the first low-pressure stream. In embodiments the pressure of the second low-pressure stream may be at least 1 bar, at least 2 bar, at least 3 bar, at least 4 bar, at least 5 bar, or at least 6 bar greater than the pressure of the first low-pressure stream. Without being limited by theory, it is believed thatwhen the second low-pressure stream has a higher pressure than the first fresh low-pressure stream, the second primary compressor 124 can operate at a higher flowrate than the first primary compressor 108, thereby increasing the overall production rate of LDPE.

[0043] The second fresh ethylene stream 120 may have a greater flowrate than the first fresh ethylene stream 102. In embodiments, the flowrate of the second fresh ethylene stream 120 may be at least 5 %, at least 10 %, at least 15 %, at least 20 %, at least 25 %, at least 30 %, at least 40 %, at least 50 %, or even at least 60 % greater than the flowrate of the first fresh ethylene stream 102.

[0044] The first inhibitor stream 104, the second inhibitor stream 122, or both may comprise an inhibitor. Without being limited by theory, inhibitors may be used to minimize polymerization in the compressors (such as the one or more hyper-compressors 112, 128), and the preheater 116. Such polymerization outside of the high-pressure reactor 118 can necessitate plant shutdowns for cleaning. Suitable inhibitors may include oxygen, butylated hydroxytoluene, Sumilizer GS (2(1- (2-Hydroxy-3,5-di-t-pentylphenyl)ethyl)-4,6-di-t-pentylphenyl acryl, CAS-no. 123968-93- 7), or a combination thereof. The first inhibitor stream 104, the second inhibitor stream 122, or both may comprise an oxygen containing gas, such as air; air enriched in oxygen; a mixture of oxygen and other gasses, such as inert gasses; or pure oxygen. The oxygen containing gas may comprise at least 10 mol. %, at least 15 mol. %, at least 20 mol. %, at least 25 mol. %, at least 40 mol. %, at least 60 mol. %, at least 80 mol. %, from 15 mol. % to 80 mol. %, from 15 mol. % to 50 mol. %, from 15 mol. % to 25 mol. %, or any subset thereof, of oxygen.

[0045] The first inhibitor stream 104, the second inhibitor stream 122, or both may comprise at least 80 wt. %, at least 90 wt. %, at least 95 wt. %, or at least 99 wt. % of the inhibitor, on the basis of the total weight of the respective inhibitor stream. In embodiments, the first inhibitor stream 104, second inhibitor stream 122, or both may independently comprise at least 90 mol. % of oxygen.

[0046] A flowrate of the first inhibitor stream 104 may be different from a flowrate of the second inhibitor stream 122. In embodiments, a flowrate of the first inhibitor stream 104 may be greater than a flowrate of the second inhibitor stream 122, such as at least 1 %, at least 2.5 %, or at least 5 % greater than a flowrate of the second inhibitor stream 122.

[0047] The first primary compressor 108 may compress the first fresh ethylene stream 102 from a pressure of from 10 to 30 bar to a pressure of from 230 bar to 250 bar. The second primarycompressor 124 may compress the second fresh ethylene stream 120 from a pressure of from 10 to 30 bar to a pressure of from 230 bar to 250 bar.

[0048] The first primary compressor 108 and the second primary compressor 124 may be operated in parallel. In embodiments, the first primary compressor 108 and the second primary compressor 124 may not be in direct fluid communication. For example, when the first primary compressor 108 increases a pressure of its output (the first medium-pressure stream 110), it may not alter the pressure of the output of the second primary compressor 124 (the second mediumpressure stream 126).

[0049] Before injection of the chain transfer agent and a high-pressure recycle stream 138, the first medium-pressure stream 110 may comprise ethylene, inhibitor, optionally unreacted initiator, and optionally unreacted chain transfer agent. In embodiments, the first medium-pressure stream 110 may comprise at least 80 wt. %, at least 90 wt. %, at least 95 wt. %, at least 99 wt. %, at least 99.9 wt. %, or even at least 99.99 wt. % of the combined weight of ethylene, inhibitor, chain transfer agent, and initiator, on the basis of the total weight of the first medium-pressure stream 110.

[0050] The first medium-pressure stream 110 may comprise at least 1 ppmw of the inhibitor. In embodiments, the first medium-pressure stream 110 may comprise at least 2 ppmw, at least 3 ppmw, from 1 ppmw to 5 ppmw, from 1 ppmw to 4 ppmw, from 1 ppmw to 3 ppmw, from 1 ppmw to 2 ppmw, from 2 ppmw to 5 ppmw, from 3 ppmw to 5 ppmw, from 4 ppmw to 5 ppmw, from 2 ppmw to 4 ppmw, or any subset thereof, of the inhibitor, on the basis of the total weight of the first medium-pressure stream 110.

[0051] The first medium-pressure stream 110 may have a pressure from 180 to 500 bar, such as 180 to 300 bar, 200 to 500 bar, 200 to 300 bar, 200 to 250 bar, 230 to 250 bar, or any subset thereof. The first medium-pressure stream 110 may have a temperature of less than a polymerization temperature, such as less than 140 °C, less than 120 °C, or less than 100 °C.

[0052] Before injection of the chain transfer agent and optionally, a high-pressure recycle stream 138, the second medium-pressure stream 126 may comprise ethylene and inhibitor. In embodiments, the second medium-pressure stream 126 may comprise at least 80 wt. %, at least 90 wt. %, at least 95 wt. %, at least 99 wt. %, at least 99.9 wt. %, or even at least 99.99 wt. % of the combined weight of ethylene and inhibitor, on the basis of the total weight of the second medium-pressure stream 126.

[0053] The second medium-pressure stream 126 may comprise from 1 parts per million by weight (“ppmw”) to 3 ppmw, 1.5 ppmw to 3 ppmw, 2 ppmw to 3 ppmw, 1 ppmw to 2.5 ppm, 1 ppmw to 2 ppmw, 1.5 ppmw to 2.5 ppmw, or any subset thereof, of the inhibitor, on the basis of the total weight of the second medium-pressure stream 126.

[0054] The second medium-pressure stream 126 may have a pressure from 180 to 500 bar, such as 180 to 300 bar, 200 to 500 bar, 200 to 300 bar, 200 to 250 bar, 230 to 250 bar, or any subset thereof. The first medium-pressure stream 110 and the second medium-pressure stream 126 may have the same pressure. The second medium-pressure stream 126 may have a temperature of less than a polymerization temperature, such as less than 140 °C, less than 120 °C, or less than 100 °C.

[0055] Chain transfer agent (CTA) may be supplied to the process by the first chain transfer agent stream 114, the second chain transfer agent stream 152, or both. The term CTA may include both a single CTA, or a mixture of CTAs, added to the polymerization process. Chain transfer agents (CTAs), or “telogens”, are often used to control the melt index in a free- radical polymerization process. “Chain transfer” involves the termination of growing polymer chains, thus limiting the ultimate molecular weight of the polymer material. Chain transfer agents are typically hydrogen atom donors that react with a growing polymer chain and stop the polymerization reaction of the chain. Known CTAs include many types of hydrogen atom donor compounds, such as saturated or unsaturated hydrocarbons, aldehydes, ketones, and alcohols. By manipulating the concentration and type of chain transfer agent used in a process, one can affect the average length and molecular weight distribution of the polymer chains. This in turn affects the melt index (12 or MI), which is related to molecular weight.

[0056] Many chain transfer agents are known in the art for use in high-pressure, low density polyethylene production. References that disclose the use of chain transfer agents in free-radical polymerization of ethylene and ethylene-based polymers include Ehrlich, P., and Mortimer, G. A., “Fundamentals of the Free-Radical Polymerization of Ethylene”, Advanced Polymers, Vol. 7, 386-448 (1970); Mortimer, George A., “Chain Transfer in Ethylene Polymerization — IV. Additional Study at 1360 Atm and 130° C.”, Journal of Polymer Science, Part A-l, Vol. 8, 1513- 23 (1970); Mortimer, George A., “Chain Transfer in Ethylene Polymerization — VI. The Effect of Pressure”, Journal of Polymer Science, Part A-l, Vol. 8, 1543-48 (1970); Mortimer, George A., “Chain Transfer in Ethylene Polymerization — VIE Very Reactive andDepletable Transfer Agents”, Journal of Polymer Science, Part A-l, Vol. 10, 163-168 (1972); Great Britain Patent No. 997,408 (Cave); U.S. Pat. No. 3,377,330 (Mortimer); U.S. Patent Publication No. 2004 / 0054097 (Maehling, et al.); and U.S. Pat. Nos. 6,596,241; 6,673,878; and 6,899,852 (Donck).

[0057] After hydrogen atom donation, it is known that a chain transfer agent may form a radical which can start a new polymer chain. The result is that the original CTA is incorporated into a new or existing polymer chain, thereby introducing a new functionality into the polymer chain associated with the original CTA. The CTA may introduce new functionality into the polymer chain that is not normally the result of the monomer / comonomer polymerization.

[0058] The CTA supplied by the first chain transfer agent stream 114 and the second chain transfer agent stream 152 may be the same compounds or different compounds. A flowrate of the first chain transfer agent stream 114 to the second chain transfer agent stream 152 may be from 0.2 to 1.0, such as from 0.2 to 0.8, from 0.2 to 0.6, from 0.2 to 0.4, from 0.4 to 1.0, from 0.6 to 1.0, from 0.8 to 1.0, or any subset thereof.

[0059] The one or more hyper-compressors (such as the first hyper-compressor 112 and the second hyper-compressor 128) may be operable to increase the pressure of the first mediumpressure stream 110 and the second medium-pressure stream 126 to a pressure of at least 2000 bar, such as from 2000 bar to 4000 bar or from 2000 bar to 3200 bar.

[0060] Where two hyper-compressors are used, the first hyper-compressor 112 may operate in parallel with the second hyper-compressor 128. In embodiments, the first hyper-compressor 112 and the second hyper-compressor 128 may not be in direct fluid communication. For example, when the first hyper-compressor 112 increases a pressure of its output (the first high-pressure stream 150), it may not alter the pressure of the output of the second hyper-compressor 128 (the second high-pressure stream 130).

[0061] The first high-pressure stream 150 may comprise ethylene, inhibitor, chain transfer agent, and optionally unreacted initiator. In embodiments, the first high-pressure stream 150 may comprise at least 80 wt. %, at least 90 wt. %, at least 95 wt. %, at least 99 wt. %, at least 99.9 wt. %, or even at least 99.99 wt. % of the combined weight of ethylene, inhibitor, chain transfer agent, and unreacted initiator, on the basis of the total weight of the first high-pressure stream 150. Unreacted initiator may have been provided to the first high-pressure stream 150 through both the high-pressure recycle stream 138 and the low-pressure recycle stream 106.

[0062] The first high-pressure stream 150 may have a pressure of at least 2000 bar, such as from 2000 bar to 4000 bar or from 2000 bar to 3200 bar. The first high-pressure stream 150 may have a temperature of less than a polymerization temperature, such as less than 140 °C, less than 120 °C, or less than 100 °C.

[0063] The second high-pressure stream 130 may comprise ethylene, inhibitor, chain transfer agent, and optionally unreacted initiator. In embodiments, the second high-pressure stream 130 may comprise at least 80 wt. %, at least 90 wt. %, at least 95 wt. %, at least 99 wt. %, at least 99.9 wt. %, or even at least 99.99 wt. % of the combined weight of ethylene, inhibitor, and chain transfer agent, on the basis of the total weight of the second high-pressure stream 130. Unreacted initiator may have been provided to the first high-pressure stream 150 through the high-pressure recycle stream 138.

[0064] The second high-pressure stream 130 may have a pressure of at least 2000 bar, such as from 2000 bar to 4000 bar or from 2000 bar to 3200 bar. The second high-pressure stream 130 may have a temperature of less than a polymerization temperature, such as less than 140 °C, less than 120 °C, or less than 100 °C.

[0065] The first high-pressure stream 150, the second high-pressure stream 130, or both may comprise less than 1 ppmw of inhibitor, such as less than or equal to 0.5 ppm of inhibitor, at their respective inlets to the high-pressure reactor. Without being limited by theory, it is believed that inhibitor (oxygen) concentrations above 1 ppm may impact the temperature profiles in the high- pressure reactor, and therefore negatively alter the product properties (such as density and optics) and the product production rate.

[0066] A ratio of the weight of inhibitor fed to the front of the high-pressure reactor 118 to the weight of inhibitor fed to the side of the high-pressure reactor 118 may be from 0.75 to 1.25, such as from 0.8 to 1.2, from 0.9 to 1.1, or any subset thereof.

[0067] The high-pressure reactor 118 may be an autoclave reactor or a tubular reactor. In embodiments, the high-pressure reactor 118 may be a tubular reactor. The polymerization pressure may be in the range of at least 1000 bar, from 1000 to 5000 bar, from 1200 to 4000 bar, or from 1500 to 3500 bar. The polymerization temperature may be in the range of about 140 °C to about 330 °C. All individual values and subranges in the range of about 140 °C to about 330 °C are included herein and disclosed herein; for example, polymerization temperature is in the range of 150 °C to 320 °C.

[0068] Where the high-pressure reactor 118 is a tubular reactor, the preheater 116 may comprise a series of tubes upstream of the first reaction zone. The first reaction zone may begin at the first injection of initiator. The preheater 116 may operate to increase the temperature of the first high- pressure stream 150 to the polymerization temperature.

[0069] The initiator may be introduced into the front inlet of the high-pressure reactor 118 and the side inlet of the high-pressure reactor 118. The initiator may comprise a radical forming compound, such as a peroxide. Non-limiting examples of initiators include organic peroxides such as cyclic peroxides, diacyl peroxides, dialkyl peroxides, hydroperoxides, peroxycarbonates, peroxydicarbonates, peroxyesters, peroxyketals, t-butyl peroxy pivalate, di-t-butyl peroxide, t-butyl peroxy acetate and t-butyl peroxy-2-hexanoate, and combinations thereof. In an embodiment, these organic peroxy initiators are used in an amount from 0.001 wt. % to 0.2 wt. %, based upon the weight of polymerizable monomers.

[0070] In embodiments, the ethylene may contact the initiator in the high-pressure reactor 118 at an initiator concentration of less than 100 ppm, such as less than 10 ppm, less than 1 ppm, less than 0.1 ppm, or even less than 0.001 ppm.

[0071] The separator 136 may function to separate the reactor output stream 134 into a high- pressure recycle stream 138, a low-pressure recycle stream 106, and a process outlet stream 140. The separator 136 may include one or more separation devices, such as a high-pressure separator and a low-pressure separator. The high-pressure separator may be upstream of the low-pressure separator.

[0072] The process outlet stream 140 may comprise an TDPE, such as at least 80 wt. %, at least 90 wt. %, at least 95 wt. %, or at least 99 wt. % of TDPE, on the basis of the total weight of the process outlet stream 140.

[0073] The TDPE may have a density of from 0.916 g / cm3to 0.930 g / cm3, such as from 0.916 g / cm3to 0.928 g / cm3, from 0.916 g / cm3to 0.925 g / cm3, from 0.918 g / cm3to 0.930 g / cm3, from 0.920 g / cm3to 0.930 g / cm3, from 0.924 g / cm3to 0.930 g / cm3, or any subset thereof.

[0074] The TDPE may have an Mw / Mn (also referred to herein as “molecular weight distribution” and “polydispersity index”) of less than 30 such as less than 20, from 2 to 30, from 5 to 30, from 10 to 30, from 20 to 30, from 2 to 25, from 2 to 20, , from 2 to 15, or any subset thereof.. Mw and Mn may be determined according to conventional gel permeation chromato gr aphy .

[0075] The LDPE may have a melt index (I2) of from 0.1 dg / min to 100 dg / min, such as 0.1 to 75 d / min, 0.1 to 50 dg / min, 0.1 to 25 dg / min, 0.1 to 12 dg / min, 0.1 to 5 dg / min, 0.1 to 2.5 dg / min, 0.1 to 2.0 dg / min, 0.5 to 100 dg / min, 1.0 to 100 dg / min, or any subset thereof.TEST METHODS

[0076] Melt index

[0077] Melt index I2 of polymer samples were measured in accordance to ASTM D-1238 (method B) at 190 °C and at 2.16 kg load, respectively.

[0078] Density

[0079] Samples for density measurement were prepared according to ASTM D4703. Measurements were made, according to ASTM D792, Method B, within one hour of sample pressing.

[0080] Gel Permeation Chromatography Size Exclusion Chromatography (SEC) (Conventional GPC)

[0081] The GPC-SEC (Conventional GPC) measurements were performed according to the test procedure defined in PCT Publication WO2021195502A1.EXAMPLES

[0082] A series of examples and comparative examples were then prepared using the reactor layout of either FIG. 2 or FIG. 3. The valves VI to V5 were open or closed as is shown in Table 1, thereby providing the correct reactor configuration. Results are shown in Table 2.

[0083] In comparative process 1 (CP-A), no inhibitor was supplied to the process. Where inhibitor was used (e.g. CP-B to CP-E, P-1, and P-2), the inhibitor was oxygen. The LDPE produced in each example had a melt index (I2) of 2.0 dg / min and a density from 0.916 g / cc to 0.930 g / cc.Table 1Table 2

[0084] As can be seen in Table 2, the embodiments of the present disclosure where the first ethylene feed and the second ethylene feed were compressed separately (P-1 and P-2) enabled increased overall production of LDPE (as shown by the “improved primary capacity”). More directly, “improved primary capacity” refers to the total quantity of ethylene which passes throughthe two primary compressors, relative to the amount which could be used if the pressure in the first and second primary compressor inlets was the same.

[0085] When pressure drop across the preheaters and interstage coolers increases by more than 50 % (P3 months / P initial > 1.5) during operation for at least 3 months, the “Fouling in Preheater” is listed as high. Interstage coolers refers to coolers between the compression stages of a hypercompressor.

[0086] For the purposes of describing and defining the present disclosure it is noted that the terms “about” or “approximately” are utilized in this disclosure to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The terms “about” and / or “approximately” are also utilized in this disclosure to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.

[0087] It is noted that one or more of the following claims utilize the term “wherein” as a transitional phrase. For the purposes of defining the present technology, it is noted that this term is introduced in the claims as an open-ended transitional phrase that is used to introduce a recitation of a series of characteristics of the structure and should be interpreted in like manner as the more commonly used open-ended preamble term “comprising.”

[0088] Any quantitative value expressed in the present application may be considered to include open-ended embodiments consistent with the transitional phrases “comprising” or “including” as well as closed or partially closed embodiments consistent with the transitional phrases “consisting of’ and “consisting essentially of.”

[0089] It is also noted that recitations herein of “at least one” component, element, etc., should not be used to create an inference that the alternative use of the articles “a” or “an” should be limited to a single component, element, etc.

Claims

AMENDED CLAIMS received by the International Bureau on 3 March 2025 (03.03.2025)1. A process for producing low-density polyethylene (LDPE), the process comprising: compressing a first fresh ethylene stream, a first inhibitor stream, and a low-pressure recycle stream in a first primary compressor, thereby producing a first mediumpressure stream having a pressure of at least 180 bar; compressing a second fresh ethylene stream and a second inhibitor stream in a second primary compressor, thereby producing a second medium-pressure stream having a pressure of at least 180 bar, wherein the low-pressure recycle stream is not compressed in the second primary compressor; compressing the first medium-pressure stream and the second medium-pressure stream in one or more hyper-compressors, thereby producing a first high-pressure stream having a pressure of at least 1000 bar and a second high-pressure stream having a pressure of at least 1000 bar; and introducing the first high-pressure stream and the second high-pressure stream into a high-pressure reactor, thereby producing the LDPE via free radical polymerization at a pressure of at least 1000 bar.

2. The process of claim 1, wherein the second primary compressor is in parallel with the first primary compressor.

3. The process of claim 1 or 2, wherein the first inhibitor stream and the second inhibitor stream independently comprise oxygen.

4. The process of any one of claims 1 to 3, wherein:an inhibitor concentration in the first medium-pressure stream is from 1 ppmw to 5 ppmw, on the basis of the total weight of the first medium-pressure stream; and an inhibitor concentration in the second medium-pressure stream is from 1 ppmw to 3 ppmw, on the basis of the total weight of the second medium-pressure stream.

5. The process of any one of claims 1 to 4, wherein: the first fresh ethylene stream, the first inhibitor stream, and the low-pressure recycle stream together comprise a first low-pressure stream; the second fresh ethylene stream and the second inhibitor stream together comprise a second low-pressure stream; and the second low-pressure stream is at a higher pressure than the first low-pressure stream.

6. The process of any one of claims 1 to 5, wherein a flowrate of the second fresh ethylene stream is greater than a flowrate of the first fresh ethylene stream.

7. The process of any one of claims 1 to 6, further comprising introducing a chain transfer agent to the first medium-pressure stream upstream of the first hyper-compressor.

8. The process of any one of claims 1 to 7, further comprising introducing a chain transfer agent to the second medium-pressure stream upstream of the second hyper-compressor.

9. The process of any one of claims 1 to 8, heating the first high-pressure stream in a preheater, upstream of the high-pressure reactor.

10. The process of any one of claims 1 to 9, wherein:the high-pressure reactor is a tubular reactor; the first high-pressure stream has a pressure of at last 2000 bar; the second high-pressure stream has a pressure of at least 2000 bar; and producing the LDPE via free radical polymerization occurs at a pressure of at least 2000 bar.

11. The process of any one of claims 1 to 10, further comprising introducing initiator into a front inlet of the high-pressure reactor and the side inlet of the high-pressure reactor, wherein the first high-pressure stream is introduced to the front inlet of the high-pressure reactor and the second high-pressure stream is introduced to the side inlet of the high-pressure reactor.

12. The process of any one of claims 1 to 11, wherein the first medium-pressure stream is compressed in a first hyper-compressor and the second medium-pressure stream is compressed in a second hyper-compressor.

13. The process of any one of claims 1 to 12, wherein the LDPE has an Mw / Mn of less than 30.

14. The process of any one of claims 1 to 13, wherein the LDPE has a melt index (I2) of from0.1 dg / min to 100 dg / min and a density of from 0.915 to 0.930 g / cm3.

15. An LDPE resin produced from the process of any preceding claim.

Images