Antifouling Agents and Processes

Abstract

The present disclosure provides a process. In one embodiment, the process includes introducing an antifouling agent into an ethylene feed of a reactor system. The reactor system includes an ethylene feed, a hypercompressor, a preheater, and a polymerization reactor. The ethylene feed is located upstream of the hypercompressor. The antifouling agent comprises an inhibitor, molecular oxygen, and optionally a solvent. Because the ethylene feed is located upstream of the hypercompressor, the process includes introducing the antifouling agent into the ethylene feed upstream of the hypercompressor. The process further includes adding a free radical initiator to the polymerization reactor. The process further includes polymerizing the ethylene in the polymerization reactor under high-pressure free radical polymerization conditions and forming an ethylene-based polymer.

Description

[Background technology]

[0001] A major obstacle facing industrial-scale low-density polyethylene (LDPE) production is fouling that occurs within the reactor system. Prepolymerization of ethylene occurring upstream of the polymerization reactor leads to prepolymer buildup on compressor components and prepolymer caking on the interior walls of pipes and piping located upstream of the polymerization reactor. This buildup of prepolymer on system components is detrimental to LDPE production because it results in reduced production rates and reactor downtime for buildup removal.

[0002] Conventional LDPE production systems typically add fouling inhibitors to the oil used to lubricate the hypercompressor plunger. This approach is problematic. When the inhibitor is incorporated into the lubricating oil, it is difficult to control and manage the amount of inhibitor that actually reaches the region where prepolymerization occurs. Therefore, the art has recognized a need for an improved process for reducing and preventing prepolymerization fouling in LDPE production. Summary of the Invention

[0003] The present disclosure provides a process. In one embodiment, the process includes introducing an antifouling agent into an ethylene feed of a reactor system. The reactor system includes an ethylene feed, a hypercompressor, a preheater, and a polymerization reactor. The ethylene feed is located upstream of the hypercompressor. The antifouling agent comprises an inhibitor, molecular oxygen, and optionally a solvent. Because the ethylene feed is located upstream of the hypercompressor, the process includes introducing the antifouling agent into the ethylene feed upstream of the hypercompressor. The process further includes adding a free radical initiator to the polymerization reactor. The process further includes polymerizing the ethylene in the polymerization reactor under high-pressure free radical polymerization conditions and forming an ethylene-based polymer. [Brief explanation of the drawings]

[0004] [Figure 1] FIG. 1 is a schematic diagram of a flow scheme for a reactor system according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic diagram of the equipment used to replicate the operating conditions of the hyper compressor and preheater in a large-scale industrial LDPE reactor system. The equipment in FIG. 2 is used to generate comparative examples and inventive examples. [Figure 3] Two photographs of the staining level of Comparative Sample 1 are shown. [Figure 4] Two photographs of the staining level of Comparative Sample 2 are shown. [Figure 5] Two photographs of the staining level of Comparative Sample 3 are shown. [Figure 6] Two photographs of the staining level of Comparative Sample 4 are shown. [Figure 7] 2 shows two photographs of the soiling level of Example 1 of the present invention.

[0005] definition Any reference to the Periodic Table of the Elements is to that published by CRC Press, Inc., 1990-1991. References to element groups in this table are by the new notation for numbering groups.

[0006] For purposes of United States patent practice, the contents of any referenced patent, patent application, or publication are incorporated by reference in their entirety (or the equivalent United States version thereof is so incorporated by reference), particularly with respect to disclosure of definitions (to the extent not inconsistent with any definitions specifically provided in this disclosure).

[0007] Numerical ranges disclosed herein include all values, inclusive, between and including the lower and upper limits. Ranges containing explicit values ​​(e.g., 1 or 2, or 3-5, or 6, or 7) include all subranges between any two explicit values ​​(e.g., the 1-7 range above includes subranges of 1-2, 2-6, 5-7, 3-7, 5-6, etc.).

[0008] Unless stated to the contrary, implicit from the context, or customary in the art, all parts and percentages are by weight and all test methods are current as of the filing date of this disclosure.

[0009] The terms "blend" or "polymer blend," as used, refer to a mixture of two or more polymers. A blend may or may not be miscible (not phase separated at the molecular level). A blend may or may not be phase separated. A blend may or may not contain one or more domain configurations as determined from transmission electron spectroscopy, light scattering, x-ray scattering, and other methods known in the art. Blending can be achieved by physically mixing two or more polymers at the macro level (e.g., melt blending or compounding) or at the micro level (e.g., co-forming in the same reactor).

[0010] The term "composition" refers to a mixture of materials that comprise the composition, as well as reaction products and decomposition products formed from the materials of the composition.

[0011] The terms "comprising," "including," "having," and their derivatives are not intended to exclude the presence of any additional component, step, or procedure, whether specifically disclosed or not. For the avoidance of doubt, all compositions claimed through the use of the term "comprising" may include any additional additive, adjuvant, or compound, whether polymeric or not, unless stated to the contrary. In contrast, the term "consisting essentially of" excludes any other component, step, or procedure from the scope of any succeeding description, except those that are not essential to operability. The term "consisting of" excludes any component, step, or procedure not expressly delineated or listed. The term "or," unless otherwise stated, refers to the listed members individually as well as in any combination. The use of the singular includes the use of the plural, and vice versa.

[0012] As used herein, the term "ethylene-based polymer" refers to a polymer that, in polymerized form, contains greater than 50 weight percent, or a majority amount, of ethylene, based on the weight of the polymer, and may optionally include at least one comonomer or other molecule.

[0013] As used herein, the term "ethylene monomer" refers to a chemical unit having two carbon atoms with a double bond between them, and each carbon bonded to two hydrogen atoms, that polymerizes with other such chemical units to form an ethylene-based polymer composition.

[0014] The term "fouling" refers to the buildup (temporary or permanent) of prepolymer (or polymer) layers on the surfaces of components in a polymerization reactor system or other equipment used in a polymerization reactor system (e.g., an LDPE reactor system). A prepolymer (or polymer) layer of this nature in a hypercompressor (or on a hypercompressor check valve) can adversely affect the total ethylene throughput in the reactor. A prepolymer (or polymer) layer of this nature in a preheater or polymerization reactor can affect the overall heat transfer rate in one or more components of a reactor system used to produce LDPE, thus reducing the polymer production rate.

[0015] As used herein, the term "hydrocarbon-based molecule" refers to a chemical entity that contains only carbon and hydrogen atoms.

[0016] The term "low density polyethylene" (or LDPE) as used herein refers to an ethylene-based polymer having a density of 0.909 g / cc to less than 0.940 g / cc, or 0.917 g / cc to 0.930 g / cc, and long chain branching with a broad molecular weight distribution (MWD greater than 3.0). LDPE is distinct from linear low density polyethylene. The term "linear low density polyethylene" (or "LLDPE") as used herein refers to an ethylene-based polymer having units derived from ethylene and at least one C3-C10 LLDPE refers to linear ethylene / α-olefin copolymers containing a heterogeneous distribution of short chain branches, including units derived from α-olefins or C4-C8 α-olefin comonomers. LLDPE is characterized by little, if any, long chain branching, in contrast to conventional LDPE, which has long chain branching. LLDPE has a density of 0.910 g / cc to less than 0.940 g / cc. Non-limiting examples of LLDPE include TUFLIN™ linear low density polyethylene resin (available from The Dow Chemical Company), DOWLEX™ polyethylene resin (available from The Dow Chemical Company), and MARLEX™ polyethylene (available from Chevron Phillips).

[0017] As used herein, the term "molecular oxygen" refers to a diatomic molecule consisting of two oxygen atoms covalently bonded to each other. Molecular oxygen is referred to interchangeably as elemental oxygen, or O. Non-limiting examples of sources of molecular oxygen include, for example, air (about 21% molecular oxygen by volume), O gas, liquid O, and blends of O in other inert gases such as nitrogen, N, etc. The oxygen can be added as a gas stream or pre-dissolved in a solvent.

[0018] As used herein, the term "polymer" or "polymeric material" refers to a compound prepared by polymerizing monomers, whether of the same or different types, to provide, in polymerized form, the multiple and / or repeating "units" or "mer units" that make up the polymer. Thus, the general term polymer encompasses the term homopolymer, which is commonly used to refer to a polymer prepared from only one type of monomer, and the term copolymer, which is commonly used to refer to a polymer prepared from at least two types of monomer. It also encompasses all forms of copolymers, e.g., random, block, etc. The terms "ethylene / α-olefin polymer" and "propylene / α-olefin polymer" refer to the aforementioned copolymers prepared from polymerizing ethylene or propylene with one or more additional polymerizable α-olefin monomers, respectively. While polymers are often referred to as "made of" one or more particular monomers, "based on" particular monomers or monomer types, "containing" particular monomer content, etc., it should be noted that in this context, the term "monomer" is understood to refer to the polymerized residue of a particular monomer, and not to the unpolymerized species. Generally, polymers herein are referred to in terms of "units" that are the polymerized form of the corresponding monomers.

[0019] Test Method Density is measured according to ASTM D792, Method B. Results are reported in grams per cubic centimeter (g / cc).

[0020] Melt Index As used herein, the term "melt index" or "MI" refers to a measure of how easily a thermoplastic polymer flows when in a molten state. Melt index, or I2, is measured in accordance with ASTM D 1238, Condition 190°C / 2.16 kg, and is reported in grams dissolving per 10 minutes (g / 10 min). I10 is measured in accordance with ASTM D 1238, Condition 190°C / 10 kg, and is reported in grams dissolving per 10 minutes (g / 10 min). DETAILED DESCRIPTION OF THE INVENTION

[0021] The present disclosure provides a process. In one embodiment, the process includes introducing an antifouling agent into an ethylene feed of a reactor system. The reactor system includes an ethylene feed, a hypercompressor, a preheater, and a polymerization reactor. The ethylene feed is located upstream of the hypercompressor. The antifouling agent comprises an inhibitor (or a mixture of one or more inhibitors), molecular oxygen, and optionally a solvent, and the antifouling agent is introduced into the ethylene feed upstream of the hypercompressor. The process includes adding a free radical initiator to the polymerization reactor and polymerizing ethylene in the polymerization reactor under high-pressure free radical polymerization conditions. The process includes forming an ethylene-based polymer composition.

[0022] The process includes introducing an antifouling agent into the ethylene feed of a polymerization reactor system. As used herein, "reactor system" refers to components and devices used to polymerize one or more olefin monomers. The reactor system includes a hypercompressor, a preheater, and a polymerization reactor in fluid communication with each other. The polymerization reactor is one or more high-pressure polymerization reactors. Non-limiting examples of suitable high-pressure polymerization reactors include an autoclave reactor, a tubular reactor, or a combination of an autoclave reactor in operative communication with a tubular reactor.

[0023] The reactor system includes an ethylene feed, a hypercompressor, a preheater, and a polymerization reactor, each of which is in fluid or otherwise operative communication with one another. As used herein, a "hypercompressor" is a compressor that compresses one or more ethylene feeds to a pressure of at least 100 MPa. The ethylene feed is located upstream of the hypercompressor. Downstream movement through the reactor system includes (i) the ethylene feed in fluid communication with the hypercompressor, (iii) the hypercompressor in fluid communication with the preheater, and (iv) the preheater in fluid communication with the polymerization reactor. The preheater heats the contents of the polymerization reactor prior to injection of the free radical initiator. The reactor system may include other components in addition to these components.

[0024] FIG. 1 illustrates an embodiment of a flow scheme for the present reactor system. Ethylene monomer is introduced into the reactor system as one or more ethylene feeds. The ethylene monomer can be (i) a fresh ethylene feed (1), (ii) a recycled ethylene feed (18), or (iii) a combination of (i) and (ii), i.e., a combined ethylene feed (3) comprised of both the fresh ethylene feed (1) and the recycled ethylene feed (18). The recycled ethylene feed (18) is ethylene monomer separated from the polymerization reaction mixture by a high-pressure separator ("HPS" in FIG. 1). Any of the aforementioned ethylene feeds may (or may not) contain trace amounts of potential oxygen. It is understood that molecular oxygen is separate and distinct from any trace amounts of oxygen present in the ethylene feed.

[0025] Ethylene feed (1), (18), and / or (3) supplies ethylene monomer to a hypercompressor ("Hypercompressor" in Figure 1). The hypercompressor supplies the ethylene feed to a polymerization reactor ("Reactor" in Figure 1) and compresses it to a level sufficient to create high-pressure free-radical polymerization conditions. A preheater ("Preheater" in Figure 1) receives the output from the hypercompressor and heats it to a temperature for high-pressure free-radical polymerization, or a temperature between 130°C and 170°C. The polymerization reactor receives the output from the preheater and increases the temperature to 250°C to 360°C. Polymerization occurs in the polymerization reactor at a temperature between 250°C and 360°C. As used herein, the term "high pressure free radical polymerization conditions" refers to the environment in a polymerization reactor (autoclave reactor and / or tubular reactor) having (i) a pressure of at least 100 MPa (1000 bar), (ii) a temperature of 150°C to 360°C, and (iii) the presence of a free radical initiator.

[0026] In one embodiment, a fresh ethylene feed (1) is compressed by a primary compressor ("Primary" in FIG. 1) together with the outlet of a booster compressor ("Booster" in FIG. 1) to produce an ethylene feed (2). In a further embodiment, the ethylene feed (2) is combined with a recycled ethylene stream (18) to form a combined ethylene feed (3) that is distributed across the suction inlet of a hyper compressor ("Hyper Compressor" in FIG. 1).

[0027] The process includes introducing an antifouling agent into the ethylene feed of a reactor system. The antifouling agent consists of (i) an inhibitor (or one or more inhibitors), (ii) molecular oxygen, and (iii) optionally a solvent (or one or more solvents). In other words, the antifouling agent consists of only two components (inhibitor and molecular oxygen) or only three components (inhibitor, molecular oxygen, and solvent). In the absence of the optional solvent, the antifouling agent consists of two components: inhibitor (or one or more inhibitors) and molecular oxygen.

[0028] In one embodiment, the inhibitor and molecular oxygen are the only components of the antifouling agent and are added to the ethylene feed. The inhibitor and molecular oxygen can each be added separately to the ethylene, each can be added at the same location, or each can be added at different locations upstream of the hyper compressor.

[0029] In one embodiment, the process includes introducing the antifouling agent into the ethylene feed by simultaneously or substantially simultaneously introducing molecular oxygen and an inhibitor into the ethylene stream at the same location. The process includes dispersing or otherwise dissolving the inhibitor and molecular oxygen in a solvent. Non-limiting examples of suitable inhibitors include phenothiazine, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), derivatives of TEMPO, monomethyl ether hydroquinone (MEHQ), butylated hydroxytoluene (BHT), Irganox 1010, Irganox 1076, vitamin E, and combinations thereof.

[0030] The solvent system can be a single solvent or a mixture of two or more solvents. Non-limiting examples of solvents suitable for the solvent system include aliphatic C3-C6 hydrocarbons (propane, butane, pentane, hexane), olefinic C3-C6 hydrocarbons (propylene, butene, pentene, hexene), C1-C6 ketones (acetone, methyl ethyl ketone), C1-C6 aldehydes, C1-C6 alcohols (methanol, ethanol, propanol, butanol, pentanol, hexanol), and combinations thereof.

[0031] In one embodiment, the process comprises dispersing or otherwise dissolving the inhibitor and molecular oxygen in a solvent before or after introducing the antifouling agent into the ethylene feed. In a further embodiment, the process comprises dispersing (prior to introducing the antifouling agent into the ethylene feed) molecular oxygen and an inhibitor selected from phenothiazine (PTZ), (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), derivatives of TEMPO, monomethyl ether hydroquinone (MEHQ), butylated hydroxytoluene (BHT), Irganox 1010, Irganox 1076, vitamin E, and combinations thereof, in a solvent selected from aliphatic C3-C6 hydrocarbons, olefinic C3-C6 hydrocarbons, C1-C6 ketones, C1-C6 aldehydes, C1-C6 alcohols, and combinations thereof to form the antifouling agent.

[0032] The antifouling agent is introduced into one, some, or all of the following ethylene feeds: ethylene feed (1), and / or ethylene feed (2), and / or combined ethylene feed (3), and / or recycled ethylene feed (18).

[0033] Because the antifoulant is introduced into the ethylene feed (and the ethylene feed is upstream of the hyper-compressor), the point at which antifoulant addition occurs is upstream of the hyper-compressor. Because the antifoulant is introduced upstream of the hyper-compressor (and the hyper-compressor is upstream of the preheater), the point at which antifoulant addition occurs is upstream of the preheater. Because the antifoulant is introduced upstream of the preheater (and the preheater is upstream of the polymerization reactor), the point at which antifoulant addition occurs is upstream of the polymerization reactor.

[0034] In one embodiment, the process comprises introducing an antifouling agent into the fresh ethylene feed (1).

[0035] In one embodiment, the process includes introducing an antifouling agent into the ethylene feed (2).

[0036] In one embodiment, the process includes introducing an antifouling agent into the combined ethylene feed (3).

[0037] In one embodiment, the process includes introducing an antifouling agent into the recycled ethylene feed (18).

[0038] In one embodiment, the reactor system includes one or more antifoulant inlets in fluid communication with each of the one or more ethylene feeds. The antifoulant inlets are in direct fluid communication with the ethylene feed. The term "direct fluid communication" refers to a configuration in which a first structure (i.e., the antifoulant inlet) is in immediate fluid communication with a second structure (i.e., the ethylene feed), such that there is no intervening third structure between the first and second structures. The process includes introducing an antifoulant into the antifoulant inlet and into the ethylene feed.

[0039] In one embodiment, the reactor system includes antifoulant inlet 1 a in direct fluid communication with ethylene feed (1), and / or antifoulant inlet 2 a in direct fluid communication with ethylene feed (2), and / or antifoulant inlet 3 a in direct fluid communication with combined ethylene feed (3), and / or antifoulant inlet 18 a in direct fluid communication with recycled ethylene feed (18).

[0040] In one embodiment, the antifouling agent consists solely of a liquid inhibitor, molecular oxygen, and solvent, and the antifouling agent is introduced into antifouling agent inlets (1a), and / or (2a), and / or (3a), and / or (18a).

[0041] The antifoulant inlet is located upstream of the hypercompressor, so that the point at which the antifoulant inlet introduces the antifoulant into the ethylene feed is upstream of the hypercompressor, the antifoulant inlet is also upstream of the preheater, and the antifoulant inlet is also upstream of the polymerization reactor.

[0042] In one embodiment, the process involves introducing the antifoulant into the antifoulant inlet (1a) and directly into the fresh ethylene feed (1).

[0043] In one embodiment, the process includes introducing the antifoulant into the antifoulant inlet (2a) and directly into the ethylene feed (2).

[0044] In one embodiment, the process includes introducing an antifoulant into the antifoulant inlet (3a) and directly into the combined ethylene feed (3).

[0045] In one embodiment, the process includes introducing the antifoulant into the antifoulant inlet (18a) and directly into the recycled ethylene feed (18).

[0046] In one embodiment, a process includes introducing an antifoulant into an ethylene feed by introducing molecular oxygen as a gas into an ethylene stream at a first location within a reactor system and separately introducing an inhibitor into the ethylene stream at a second location within the reactor system, the first and second locations being different. The first and second locations are each upstream of a hypercompressor. The process includes (i) introducing molecular oxygen gas at a first location selected from upstream of a booster (location 13 in FIG. 1 ) or primary (location 1 in FIG. 1 ); and (ii) separately introducing an inhibitor at a second location selected from fresh ethylene feed (1), antifoulant inlet (1 a), ethylene feed (2), antifoulant inlet (2 a), combined ethylene feed (3), antifoulant (3 a), recycled ethylene feed (18), antifoulant inlet (18 a), and any combination thereof.

[0047] In one embodiment, the process includes introducing an antifoulant into the ethylene feed by introducing molecular oxygen as a gas into the ethylene stream at a first location within the reactor system and separate from the addition of an inhibitor to the ethylene stream at a second location within the reactor system. The process includes (i) introducing molecular oxygen gas at a first location upstream of the booster (location (13) in Figure 1 ), and (ii) separately introducing the inhibitor at a second location selected from fresh ethylene feed (1), antifoulant inlet (1 a), ethylene feed (2), antifoulant inlet (2 a), combined ethylene feed (3), antifoulant (3 a), recycled ethylene feed (18), antifoulant inlet (18 a), and any combination thereof.

[0048] In one embodiment, one or more chain transfer agents (CTAs) are fed to the hypercompressor for introduction into the polymerization reactor to control the molecular weight of the resulting ethylene-based polymer. Non-limiting examples of suitable CTAs include propylene, isobutane, n-butane, 1-butene, methyl ethyl ketone, acetone, ethyl acetate, propionaldehyde, ISOPAR (ExxonMobil Chemical Co.), isopropanol, and combinations thereof. The amount of CTA used in the process is from 0.01 weight percent to 10 weight percent, or from 0.01 weight percent to 5 weight percent, or from 0.1 weight percent to 1.0 weight percent, or from 0.1 weight percent to 0.5 weight percent, or from 0.01 weight percent to 0.1 weight percent of the total reaction mixture.

[0049] In one embodiment, the solvent for the antifouling agent is a high-pressure free-radical polymerization CTA. As a result, the addition of the CTA occurs simultaneously or substantially simultaneously with the introduction of the antifouling agent into the ethylene feed. In a further embodiment, the process includes introducing the CTA (the CTA component of the antifouling agent as a solvent for the inhibitor) into the ethylene feed along with the antifouling agent, with the introduction of the CTA occurring upstream of the hypercompressor.

[0050] In one embodiment, the reaction system includes a CTA stream (4) and / or a recycle CTA stream (5). The CTA stream (4) and / or the CTA recycle stream (5) can essentially be distributed freely across the main compressed stream, which is fed and / or distributed across the side stream (8) and the head stream (9). The CTA stream (4) and / or the CTA recycle stream (5) can be fed to the inlet, interstage, or outlet of the hypercompressor, and / or to the inlet of the reaction zone in the polymerization reactor.

[0051] If the solvent for the antifoulant is CTA, CTA stream (4) and / or recycled CTA stream (5) operate in conjunction with the antifoulant feed to provide the appropriate amount of CTA to the reactor system. If the solvent for the antifoulant is not CTA, CTA stream (4) and / or recycled CTA stream (5) are the only sources of CTA for the reactor system.

[0052] In one embodiment, the reactor system includes a branching agent stream (6) and / or a polymerizable comonomer stream (7). The branching agent feed (6) and / or the polymerizable comonomer stream (7) can essentially be distributed freely across the main compressor stream, fed and / or distributed across the side stream (8) and / or head stream (9). The branching agent feed (6) and / or the polymerizable comonomer stream (7) can be fed to the inlet, interstage, or outlet of the hypercompressor, a separate ethylene feed stream to the reactor, or fed directly into the reaction zone.

[0053] The hyper compressor has a discharge temperature of 60°C to 110°C. The preheater heats the ethylene feed (and other feeds) received from the hyper compressor to a temperature of 130°C to 170°C. After passing through the hyper compressor and preheater, the ethylene monomer with antifouling agent flows into or otherwise enters a polymerization reactor ("Reactor" in FIG. 1). The process includes adding a free radical initiator to the polymerization reactor and polymerizing the ethylene in the polymerization reactor under high-pressure free radical polymerization conditions to form an ethylene-based polymer.

[0054] The free radical initiator is added directly to one or more reaction zones of the polymerization reactor. Alternatively, the free radical initiator is introduced into the polymerization reactor via a side stream (8). Non-limiting examples of suitable free radical initiators include organic peroxides, cyclic peroxides, diacyl peroxides, dialkyl peroxides, hydroperoxides, peroxycarbonates, peroxydicarbonates, peroxyesters, peroxyketals, t-butyl peroxypivalate, di-t-butyl peroxide, t-butyl peroxyacetate, and t-butyl peroxy-2-hexanoate, and combinations thereof. In one embodiment, the free radical initiator contains at least one peroxide group incorporated into a ring structure. Non-limiting examples of free radical initiators having a peroxide group incorporated into the ring structure include TRIGONOX 301 (3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonaan) and TRIGONOX 311 (3,3,5,7,7-pentamethyl-1,2,4-trioxepane), both available from Akzo Nobel, and HMCH-4-AL (3,3,6,6,9,9-hexamethyl-1,2,4,5-tetroxonane), available from United Initiators. The organic peroxy initiator is used in an amount of 0.001% to 0.2% by weight, based on the weight of the polymerizable monomer.

[0055] In one embodiment, the high-pressure free radical polymerization occurs in a tubular reactor having multiple reactor zones (3 to 6 reactor zones). The maximum temperature in each reactor zone is from 150° C. to 360° C., or from 170° C. to 350° C., or from 200° C. to 340° C. The pressure in each reactor zone is from 100 MPa to 380 MPa, from 110 MPa to 340 MPa, or from 110 MPa to 300 MPa.

[0056] As used herein, "prepolymerization" (or "prepolymer") refers to the early polymerization of ethylene (and optional branching agent and / or optional polymerizable comonomer) in the hypercompressor and / or preheater. The prepolymer formed in the hypercompressor (and in the interstage cooler) and preheater is a high-density (0.930-0.965 g / cc) high-molecular-weight (150,000-500,000 g / mol) polymer that phase separates to form solid deposits, thus interfering with the operation of the hypercompressor and reducing heat transfer in the interstage cooler and preheater. In one embodiment, the process involves using an antifouling agent to reduce or otherwise prevent prepolymerization (or prepolymer composed of ethylene and / or optional branching agent and / or optional polymerizable comonomer) in the hypercompressor and / or preheater.

[0057] Applicant developed a soiling rating scale with a rating of "1" being very soiled (Comparative Example 1 having a rating of "1" being very soiled as shown in FIG. 3), a rating of "4" being very clean (Inventive Example 1 having a rating of "4" being very clean as shown in FIG. 7), and a rating of "5" being completely clean. In one embodiment, the process includes introducing an antifouling agent into an ethylene feed to form an ethylene feed containing 0.01 mol ppm to 5 mol ppm of inhibitor and 0.05 ppm to 3 ppm of molecular oxygen, or 0.05 mol ppm to 3 mol ppm of inhibitor and 0.1 ppm to 1.0 ppm of molecular oxygen, or 0.07 mol ppm to 2 mol ppm of inhibitor and 0.2 ppm to 0.5 ppm of molecular oxygen, or 0.1 mol ppm to 1.0 mol ppm of inhibitor and 0.2 ppm to 0.5 ppm of molecular oxygen, and the process further includes reducing or otherwise preventing prepolymerization (or prepolymer formation) in the hypercompressor and / or preheater (a fouling rating of 4 to 5, or "prevention" of 5). While the inhibitor or molecular oxygen may each individually act as an antifouling agent, applicants have discovered that combining the inhibitor and molecular oxygen together results in an antifouling agent with a greater ability to reduce / prevent prepolymer formation compared to the inhibitor alone or molecular oxygen alone. This inhibitor / molecular oxygen combination allows for the use of lower levels of inhibitor and oxygen, each of which can cause reactor instability at higher concentrations.

[0058] In one embodiment, the process includes adding a polymerizable comonomer to a polymerization reactor via polymerizable comonomer stream (7) and forming an ethylene copolymer. Non-limiting examples of suitable polymerizable comonomers include one or more C3-C 20 Suitable C3 to C6 copolymers include α-olefin comonomers, acrylates, (meth)acrylic acid, (meth)acrylic acid esters, carbon monoxide, maleic anhydride, vinyl acetate, vinyl propionate, monoesters of maleic acid, diesters of maleic acid, vinyltrialkoxysilanes, vinyltrialkylsilanes, and any combination thereof. 20Non-limiting examples of α-olefin comonomers include one or more linear or branched C-C 12 It comprises an α-olefin comonomer, or one or more linear or branched C4 to C8 α-olefin comonomers, such as propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, and 1-octene.

[0059] In one embodiment, the antifouling agent does not include or otherwise excludes polymerizable comonomers.

[0060] After the reaction is completed (see FIG. 1 ) and multiple cooling steps are applied, the reaction mixture is depressurized and / or cooled in (10) and separated in a high-pressure separator (HPS). The high-pressure separator separates the reaction mixture into an ethylene-rich stream (15) containing small amounts of wax and / or entrained polymer, and a polymer-rich stream (11) sent to a low-pressure separator (LPS) for further separation. The ethylene stream (15) is cooled and washed in stream (17). Stream (16) is a purge stream to remove impurities and / or inerts. The ethylene-based polymer separated in the LPS is further processed in (12). The ethylene removed in the LPS is fed to a booster compressor ("Booster" in FIG. 1 ), where, during compression, condensates such as solvents, lubricating oils, and other liquids are recovered and removed through stream (14). The outlet of the booster compressor ("Booster" in Figure 1) is combined with the fresh ethylene feed (1) and further compressed by the primary compressor ("Primary" in Figure 1).

[0061] The reactor system includes a lubricant feed for the hyper compressor. The lubricant may (or may not) contain an antioxidant. Some lubricant may leak into the compression chamber of the hyper compressor and thus into the ethylene. The process advantageously adds the antifoulant directly to the ethylene feed upstream of the hyper compressor, avoiding the need to dissolve the antifoulant in the lubricant. In one embodiment, the antifoulant does not include or otherwise exclude the lubricant when added to the ethylene feed.

[0062] By way of example, and not limitation, some embodiments of the present disclosure will now be described in detail in the following examples. [Example]

[0063] Processes used in the inventive examples and comparative samples FIG. 2 shows a schematic diagram of the equipment used to prepare comparative examples and inventive examples. A 300 ml continuous polymerization reactor (CPR) is used to replicate the hypercompressor and preheater sections of an industrial-scale LDPE production system. Ethylene monomer is added to the CPR at 7 lb / hr. Upstream of this ethylene stream and the hypercompressor, propionaldehyde (which functions as both a chain transfer agent and antifouling solvent) is added to the ethylene at 1000 mol ppm. The ethylene and propionaldehyde are then pressurized to 30,000 psi (206,800 kiloPascals (kPa)) in the hypercompressor through the use of a valve. The CPR is heated to 140° C. to replicate the temperature in the hypercompressor and preheater sections of an industrial-scale LDPE production system. The ethylene and propionaldehyde are flowed through the CPR reactor at 140° C. for 18 hours to further replicate the hypercompressor and preheater sections of an industrial-scale LDPE production system. All prepolymer formed during the course of 18 hours is collected and weighed. At the end of 18 hours, the CPR is opened and inspected for levels of fouling (hereafter referred to as Process 1).

[0064] Comparison sample In Comparative Examples 1-4 (CE1-4), Process 1 is carried out using various amounts of molecular oxygen (CE1 0 ppm, CE2 1 ppm, CE3 5 ppm, CE4 0 ppm) added to the solvent (propionaldehyde). In CE4, 0.5 ppm of MEHQ is dissolved in propionaldehyde without adding molecular oxygen to CE4.

[0065] Examples of the present invention In one example of the present invention (IE1), Process 1 is carried out using a three-component antifoulant consisting of 0.5 ppm molecular oxygen dissolved in Isopar-E solvent and 0.5 ppm MEHQ dissolved in propionaldehyde. The antifoulant is added to the reactor system simultaneously with the ethylene monomer. Process 1 is carried out for each of CS1-4 and IE1, and is carried out five separate times.

[0066] The amount of prepolymer recovered over the course of 18 hours is measured for each run. The reactor is then opened and the level of fouling in the comparative and inventive examples is rated on a scale of 1 to 5, with 1 being very dirty and 5 being completely clean. The results are shown in Table 1 below.

[0067] [Table 1] CE=Comparative example IE = Example of the present invention

[0068] As can be seen in Table 1 and illustrated in Figures 3-7, the direct addition of antifouling agents (inhibitor, molecular oxygen, and solvent) to the reaction system with ethylene monomer acts to reduce or eliminate / prevent the amount of prepolymer produced at the operating conditions of the hypercompressor and preheater. The combination of inhibitor and molecular oxygen acts synergistically to reduce the amount of prepolymer formed at temperatures and pressures below the reaction conditions, i.e., the operating conditions of the hypercompressor and / or preheater. IE1 produces little fouling and prepolymer buildup on component surfaces and results in less polymer formation over the course of the experiment than either of the comparative examples. Applicants have discovered that molecular oxygen in combination with an inhibitor acts synergistically as an effective antifouling agent, allowing for reduced molecular oxygen (0.1 ppm to less than 1.0 ppm, or 0.1 ppm to 0.5 ppm molecular oxygen) and reduced inhibitor (0.1 ppm to less than 1.0 ppm, or 0.1 ppm to 0.5 ppm inhibitor), while still achieving little or no prepolymer buildup. Reduced molecular oxygen is advantageous because oxygen is known to cause reactor instability at higher concentrations.

[0069] IE1 (0.5 ppm O2 / 0.5 ppm MEHQ) compared to CE2 (1.0 ppm O2 / 0 ppm MEHQ) demonstrates the synergistic effect of the O2 / inhibitor combination, with IE1 exhibiting 0.33 lb of prepolymer accumulation compared to approximately 4 times more prepolymer accumulation for CE2 (O2 only) at 1.2 lb.

[0070] IE1 (0.5 ppm O2 / 0.5 ppm MEHQ) compared to CE4 (0 ppm O2 / 1.0 ppm MEHQ) demonstrates the synergistic effect of the O2 / inhibitor combination, with IE1 exhibiting 0.33 lb of prepolymer accumulation compared to approximately twice as much prepolymer accumulation as CE4 (inhibitor only) at 0.62 lb.

[0071] The present disclosure is not limited to the embodiments and examples contained herein, but is expressly intended to include portions of the embodiments and modified forms of those embodiments, including combinations of elements of different embodiments, to the extent that they fall within the scope of the following claims. The present application also relates to the following aspects: (1) A process comprising: introducing an antifouling agent into an ethylene feed of a reactor system, the reactor system including the ethylene feed, a hypercompressor, a preheater, and a polymerization reactor, the ethylene feed being located upstream of the hypercompressor, the antifouling agent consisting of an inhibitor, molecular oxygen, and an optional solvent; adding a free radical initiator to the polymerization reactor; polymerizing the ethylene in the polymerization reactor under high pressure free radical polymerization conditions; forming an ethylene-based polymer. (2) The process described in (1), comprising using the antifouling agent to prevent prepolymerization of the ethylene in a component selected from the group consisting of the hypercompressor, the preheater, and combinations thereof. (3) dispersing the inhibitor and the molecular oxygen in the solvent prior to the introducing, wherein the inhibitor is selected from the group consisting of phenothiazine, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) or a derivative thereof, monomethyl ether hydroquinone (MEHQ), butylated hydroxytoluene (BHT), and combinations thereof; The solvent is an aliphatic C 3 ~C 6 Hydrocarbons, olefinic C 3 ~C 6 Hydrocarbons, C 1 ~C 6 Ketone, C 1 ~C 6 Aldehyde, C 1 ~C 6 The process according to (1) or (2), further comprising dispersing the mixture in a solvent selected from the group consisting of alcohols, and combinations thereof. (4) adding a polymerizable comonomer to the polymerization reactor; forming an ethylene copolymer. (5) introducing an antifouling agent into said ethylene feed comprising from 0.01 mol ppm to less than 1.0 ppm of an inhibitor, from 0.01 mol ppm to less than 1.0 ppm of molecular oxygen, and optionally a solvent; Preventing the formation of prepolymers in components selected from the group consisting of the hyper compressor, the preheater, and combinations thereof. (6) introducing an antifouling agent into the ethylene feed comprising from 0.01 mol ppm to less than 1.0 ppm of monomethyl ether hydroquinone (MEHQ), from 0.01 mol ppm to less than 1.0 ppm of molecular oxygen, and an optional solvent; Preventing prepolymer formation in components selected from the group consisting of the hyper compressor, the preheater, and combinations thereof.

Claims

1. A process comprising: introducing an antifouling agent into the ethylene feed of a reactor system, introducing the reactor system including the ethylene feed, a hyper compressor, a preheater, and a polymerization reactor, the ethylene feed being located upstream of the hyper compressor, and the antifouling agent consisting of an inhibitor at greater than or equal to 0.01 mol ppm and less than 1.0 mol ppm, molecular oxygen at greater than or equal to 0.01 mol ppm and less than 1.0 mol ppm, and an optional solvent; adding a free radical initiator to the polymerization reactor; polymerizing the ethylene in the polymerization reactor under high pressure free radical polymerization conditions; forming an ethylene-based polymer; The inhibitors include phenothiazine, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), monomethyl ether hydroquinone (MEHQ), butylated hydroxytoluene (BHT), pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate. 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), vitamin E, and combinations thereof; process.

2. 10. The process of claim 1, comprising using the antifouling agent to prevent prepolymerization of the ethylene in a component selected from the group consisting of the hypercompressor, the preheater, and combinations thereof.

3. dispersing the inhibitor and the molecular oxygen in the solvent prior to said introducing, wherein the inhibitor is selected from the group consisting of phenothiazine, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), monomethyl ether hydroquinone (MEHQ), butylated hydroxytoluene (BHT), and combinations thereof; The solvent is an aliphatic C ３ ~C ６ Hydrocarbon, olefinic C ３ ~C ６ Hydrocarbons, C １ ~C6 ketone, C １ ~C ６ Aldehyde, C １ ~C ６ 3. The process of claim 1 or 2, comprising dispersing the cellulose acetate solution in a solvent selected from the group consisting of: alcohol, and combinations thereof.

4. adding a polymerizable comonomer to the polymerization reactor; and forming an ethylene copolymer.

5. The process of any one of claims 1 to 3, wherein the ethylene-based polymer is low density polyethylene (LDPE).

6. introducing into said ethylene feed an antifouling agent consisting of an inhibitor at greater than or equal to 0.01 mol ppm and less than 1.0 mol ppm, molecular oxygen at greater than or equal to 0.01 mol ppm and less than 1.0 mol ppm, and optional solvent; and preventing prepolymer formation in a component selected from the group consisting of the hyper compressor, the preheater, and combinations thereof.

7. introducing into said ethylene feed an antifouling agent consisting of equal to or greater than 0.01 mol ppm and less than 1.0 mol ppm monomethyl ether hydroquinone (MEHQ), equal to or greater than 0.01 mol ppm and less than 1.0 mol ppm molecular oxygen, and optional solvent; and preventing prepolymer formation in a component selected from the group consisting of the hyper compressor, the preheater, and combinations thereof.

8. 8. The process of any one of claims 1 to 7, wherein the molecular oxygen is separate and different from any trace amounts of oxygen present in the ethylene feed.

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