Antifouling agents and methods

Abstract

The present disclosure provides a method. In one embodiment, the method includes introducing an anti-fouling agent into an ethylene feed of a reactor system. The reactor system includes the ethylene feed, a supercompressor, a preheater, and a polymerization reactor. The ethylene feed is positioned upstream of the supercompressor. The anti-fouling agent consists of an inhibitor, molecular oxygen, and optionally a solvent. When the ethylene feed is positioned upstream of the supercompressor, the method includes introducing the anti-fouling agent into the ethylene feed located upstream of the supercompressor. The method further includes adding a free radical initiator to the polymerization reactor. The method further includes: polymerizing ethylene in the polymerization reactor under high pressure free radical polymerization conditions; and forming an ethylene-based polymer.

Description

Background Art

[0001] A significant obstacle to industrial-scale low-density polyethylene (LDPE) production is fouling that occurs within the reactor system. The pre-polymerization of ethylene that occurs upstream of the polymerization reactor results in the build-up of pre-polymers on the compressor components and the caking of pre-polymers on the inner walls of the conduits and pipes located upstream of the polymerization reactor. This build-up of pre-polymers on the system components is detrimental to LDPE production as the build-up results in a reduced production rate and causes reactor shutdowns to remove the build-up.

[0002] Conventional LDPE production systems typically add a fouling inhibitor to the oil used to lubricate the supercompressor plunger. This method 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 area where pre-polymerization occurs. Accordingly, there is a recognized need in the art for improved methods for reducing and preventing pre-polymerization fouling in LDPE production. Summary of the Invention

[0003] The present disclosure provides a method. In one embodiment, the method includes introducing an anti-fouling agent into the ethylene feed of a reactor system. The reactor system includes the ethylene feed, a supercompressor, a preheater, and a polymerization reactor. The ethylene feed is located upstream of the supercompressor. The anti-fouling agent consists of an inhibitor, molecular oxygen, and optionally a solvent. When the ethylene feed is located upstream of the supercompressor, the method includes introducing the anti-fouling agent into the ethylene feed located upstream of the supercompressor. The method further includes adding a radical initiator to the polymerization reactor. The method further includes: polymerizing ethylene in the polymerization reactor under high-pressure radical polymerization conditions; and forming an ethylene-based polymer. Brief Description of the Drawings

[0004] Figure 1 is a schematic representation of a flowchart of a reactor system according to an embodiment of the present disclosure.

[0005] Figure 2 is a schematic representation of equipment for replicating the operating conditions of a supercompressor and a preheater in a large-scale industrial LDPE reactor system, and Figure 2 the equipment in is used to generate comparative examples and examples of the present invention.

[0006] Figure 3 Two photographs showing the fouling level of Comparative Sample 1.

[0007] Figure 4 Two photographs showing the fouling level of Comparative Sample 2.

[0008] Figure 5 Two photographs showing the fouling level of Comparative Sample 3.

[0009] Figure 6 Two photographs showing the fouling levels of Comparative Sample 4 are presented.

[0010] Figure 7 Two photographs showing the fouling levels of Example 1 of the present invention are presented.

[0011] Definition

[0012] Any reference to the Periodic Table of the Elements is to the Periodic Table published by CRC Press, Inc. in 1990 - 1991. A group of elements in the table is referred to by the new notation used for numbering the groups.

[0013] For the purposes of U.S. patent practice, the contents of any reference patent, patent application, or published document are incorporated by reference in their entirety (or the equivalent U.S. version is incorporated by reference), particularly with respect to the disclosure of definitions (to the extent not inconsistent with any definitions specifically provided in this disclosure).

[0014] The numerical ranges disclosed herein include all values from the lower limit value to the upper limit value, and include the lower limit value and the upper limit value. For ranges containing definite values (e.g., 1 or 2 or 3 to 5 or 6 or 7), any sub - range between any two definite values is included (e.g., the above range 1 - 7 includes sub - ranges 1 to 2; 2 to 6; 5 to 7; 3 to 7; 5 to 6; etc.).

[0015] Unless stated to the contrary, implied by the context, or conventional in the art, all parts and percentages are by weight, and all test methods are the current methods as of the filing date of this disclosure.

[0016] As used, the term "blend" or "polymer blend" refers to a mixture of two or more polymers. The blend may be miscible or may be immiscible (not phase - separated at the molecular level). The blend may or may not be phase - separated. The blend may or may not contain one or more domain configurations, as determined by transmission electron spectroscopy, light scattering, x - ray scattering, and other methods known in the art. A blend can be effected by physically mixing two or more polymers at the macroscopic level (e.g., melt - blending resins or compounding) or at the microscopic level (e.g., forming simultaneously within the same reactor).

[0017] 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.

[0018] The terms "comprising", "including", "having", and derivatives thereof are not intended to exclude the presence of any additional components, steps, or procedures, whether or not specifically disclosed. For the avoidance of any doubt, unless stated to the contrary, all compositions claimed by use of the term "comprising" may include any additional additives, adjuvants, or compounds, whether in polymeric form or otherwise. In contrast, the term "consisting essentially of" excludes from the scope of any subsequent recitation any other components, steps, or procedures (except those that are not essential to the operability) and the term "consisting of" excludes any component, step, or procedure not specifically recited or listed. Unless otherwise stated, the term "or" 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.

[0019] As used herein, the term "ethylene-based polymer composition" refers to a polymer that comprises more than 50 wt% or a majority amount of ethylene in polymeric form, based on the weight of the polymer, and optionally may comprise at least one comonomer or other molecule.

[0020] As used herein, the term "ethylene monomer" refers to a chemical unit having two carbon atoms with a double bond therebetween and each carbon bonded to two hydrogen atoms, wherein the chemical unit polymerizes with other such chemical units to form an ethylene-based polymer composition.

[0021] The term "fouling" refers to the deposition (temporary or permanent) of a prepolymer layer (or polymer layer) on the surface of components in a polymerization reactor system or other devices used in a polymerization reactor system (such as an LDPE reactor system). A prepolymer (or polymer) layer of this nature in a supercompressor (or on the check valve of a supercompressor) can have a negative impact on the total ethylene flux in the reactor. A prepolymer (or polymer) layer of this nature in a preheater or in a polymerization reactor can affect the overall heat transfer coefficient in one or more components of the reactor system used to produce LDPE, thereby reducing the polymer production rate.

[0022] As used herein, the term "hydrocarbon molecule" refers to a chemical component having only carbon and hydrogen atoms.

[0023] As used herein, the term "low density polyethylene" (or LDPE) refers to an ethylene-based polymer having a density of from 0.909 g / cc to less than 0.940 g / cc, or from 0.917 g / cc to 0.930 g / cc and having a broad molecular weight distribution of long chain branches (MWD greater than 3.0). LDPE is different from linear low density polyethylene. As used herein, the term "linear low density polyethylene" (or "LLDPE") refers to a linear ethylene / α-olefin copolymer containing a heterogeneous short chain branching distribution, which contains units derived from ethylene and units derived from at least one C 3 -C 10 α-olefin or C 4 -C 8 α-olefin comonomer. LLDPE is characterized by very little long chain branching (if any) compared to conventional LDPE having long chain branching. LLDPE has a density of from 0.910 g / cc to less than 0.940 g / cc. Non-limiting examples of LLDPE include TUFLIN TM Linear low density polyethylene resin (available from The Dow Chemical Company), DOWLEX TM Polyethylene resin (available from The Dow Chemical Company) and MARLEX TM Polyethylene (available from Chevron Phillips).

[0024] As used herein, the term "molecular oxygen" refers to a diatomic molecule composed of two oxygen atoms covalently bonded to each other. Molecular oxygen can be interchangeably referred to as elemental oxygen or O 2 . For example, non-limiting examples of sources of molecular oxygen include air (about 21 vol% molecular oxygen), O 2 gas, liquid O 2 and O 2 in blends with other inert gases such as nitrogen N 2 . Oxygen can be added as a gas stream or pre-dissolved in a solvent.

[0025] As used herein, the term "polymer" or "polymeric material" refers to a compound prepared by polymerizing monomers, whether of the same type or different types, which provides multiple and / or repeating "units" or "monomer units" that make up the polymer in polymeric form. 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 monomers. It also encompasses all forms of copolymers, such as random copolymers, block copolymers, etc. The terms "ethylene / α-olefin polymer" and "propylene / α-olefin polymer" denote copolymers prepared as described above by polymerizing ethylene or propylene and one or more additional polymerizable α-olefin monomers, respectively. It should be noted that although polymers are commonly referred to as "made from" one or more specified monomers, "based on" specified monomers or monomer types, "containing" a specified monomer content, etc., in this context, the term "monomer" should be understood to refer to the polymerized residue of the specified monomer rather than the unpolymerized material. Generally, the polymers herein are referred to as being based on "units" that are the polymerized form of the corresponding monomers.

[0026] Test method

[0027] The density is measured according to ASTM D792 Method B. The results are reported in grams per cubic centimeter (g / cc).

[0028] Melt index

[0029] 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. The melt index or I is measured according to ASTM D 1238, Condition 190 °C / 2.16 kg 2 , and is reported in grams eluted per 10 minutes (g / 10 min). I10 is measured according to ASTM D 1238, Condition 190 °C / 10 kg, and is reported in grams eluted per 10 minutes (g / 10 min). Detailed Description

[0030] The present disclosure provides a method. In one embodiment, the method includes introducing an anti-fouling agent into the ethylene feed of a reactor system. The reactor system includes the ethylene feed, a supercompressor, a preheater, and a polymerization reactor. The ethylene feed is located upstream of the supercompressor. The anti-fouling agent consists of an inhibitor (or a mixture of one or more inhibitors), molecular oxygen, and optionally a solvent; the anti-fouling agent introduced into the ethylene feed located upstream of the supercompressor. The method includes: adding a radical initiator to the polymerization reactor and polymerizing ethylene in the polymerization reactor under high-pressure radical polymerization conditions. The method includes forming an ethylene-based polymer.

[0031] The method includes introducing an anti-fouling agent into the ethylene feed of a polymerization reactor system. As used herein, "reactor system" refers to the components and equipment for polymerizing one or more olefin monomers. The reactor system includes a super compressor, a preheater, and a polymerization reactor that are 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 autoclave reactors, tubular reactors, or a combination of an autoclave reactor and a tubular reactor operatively connected.

[0032] The reactor system includes an ethylene feed, a super compressor, a preheater, and a polymerization reactor, with each component in fluid communication with or otherwise operatively connected to each other. As used herein, "super compressor" is a compressor that pressurizes one or more ethylene feeds to a pressure of at least 100 MPa. The ethylene feed is located upstream of the super compressor. Moving through the reactor system in the upstream-to-downstream direction, the reactor system includes (i) an ethylene feed in fluid communication with (ii) the super compressor, the super compressor in fluid communication with (iii) the preheater, and the preheater in fluid communication with (iv) the polymerization reactor. The preheater heats the polymerization reactor contents before injecting a free radical initiator. In addition to these components, the reactor system may include other components.

[0033] Figure 1 An embodiment of a flowchart for the reactor system of the present invention is shown. 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) consisting of a fresh ethylene feed (1) and a recycled ethylene feed (18). The recycled ethylene feed (18) is ethylene monomer separated from the polymerization reaction mixture by the "HPS" in the high-pressure separator. Figure 1 Any of the above ethylene feeds may (or may not) include trace amounts of potential oxygen. It should be understood that molecular oxygen is separated from and different from any trace amounts of oxygen present in the ethylene feed.

[0034] The ethylene feeds (1), (18), and / or (3) feed ethylene monomer into the super compressor Figure 1 in the "super compressor". The super compressor pressurizes the ethylene feed to a level sufficient to feed the polymerization reactor Figure 1 in the "reactor" and create high-pressure free radical polymerization conditions. The preheater Figure 1The "preheater" receives the output from the supercompressor and heats this output to a temperature for high-pressure free radical polymerization or a temperature of 130°C to 170°C. The polymerization reactor receives the output from the preheater and increases the temperature from 250°C to 360°C; polymerization occurs in the polymerization reactor at a temperature of 250°C to 360°C. As used herein, the term "high-pressure free radical polymerization conditions" refers to the environment in the polymerization reactor (autoclave reactor and / or tubular reactor) where (i) the pressure is at least 100 MPa (1000 bar), (ii) the temperature is 150°C to 360°C and (iii) a free radical initiator is present.

[0035] In one embodiment, the fresh ethylene feed (1) is compressed by a primary compressor ( Figure 1 "boost" in) together with the outlet of the boost compressor ( Figure 1 "primary" in) to produce an ethylene feed (2). In a further embodiment, the ethylene feed (2) is combined with a recycle ethylene stream (18) to form a combined ethylene feed (3) and is distributed above the suction inlet of the supercompressor ( Figure 1 "supercompressor" in).

[0036] The method includes introducing an anti-fouling agent into the ethylene feed of the reactor system. The anti-fouling 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 anti-fouling agent consists of only two components (inhibitor and molecular oxygen), or only three components (inhibitor, molecular oxygen and solvent). When the optional solvent is absent, the anti-fouling agent consists of two components, namely an inhibitor (or one or more than one inhibitor) and molecular oxygen.

[0037] In one embodiment, the inhibitor and molecular oxygen are the only components of the anti-fouling agent and are added to the ethylene feed. The inhibitor and molecular oxygen can each be added separately to the ethylene, can each be added at the same location, or can each be added at different locations upstream of the supercompressor.

[0038] In one embodiment, the method includes introducing the anti-fouling agent into the ethylene feed by simultaneously or substantially simultaneously introducing molecular oxygen and an inhibitor at the same location into the ethylene stream. The method 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)oxy (TEMPO), derivatives of TEMPO, monomethyl ether hydroquinone (MEHQ), butylated hydroxytoluene (BHT), Irganox 1010, Irganox 1076, vitamin E and combinations thereof.

[0039] The solvent system can be a single solvent or a mixture of two or more solvents. Non-limiting examples of suitable solvents for the solvent system include aliphatic C 3 -C 6 hydrocarbons (propane, butane, pentane, hexane), olefinic C 3 -C 6 hydrocarbons (propylene, butene, pentene, hexene), C 1 -C 6 ketones (acetone, methyl ethyl ketone), C 1 -C 6 aldehydes, C 1 -C 6 alcohols (methanol, ethanol, propanol, butanol, pentanol, hexanol) and combinations thereof.

[0040] In one embodiment, the method includes dispersing or otherwise dissolving the inhibitor and molecular oxygen into the solvent before or prior to introducing the anti-fouling agent into the ethylene feed. In a further embodiment, the method includes: dispersing molecular oxygen and an inhibitor selected from phenothiazine (PTZ), (2,2,6,6-tetramethylpiperidin-1-yl)oxy (TEMPO), derivatives of TEMPO, monomethyl ether hydroquinone (MEHQ), butylated hydroxytoluene (BHT), Irganox 1010, Irganox 1076, vitamin E, and combinations thereof into a solvent selected from: aliphatic C 3 -Chydrocarbons, olefinic C 3 -C 6 hydrocarbons, C 1 -C 6 ketones, C 1 -C 6 aldehydes, C 1 -C 6 alcohols and combinations thereof; and forming an anti-fouling agent.

[0041] Introducing the anti-fouling agent 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 recycle ethylene feed (18).

[0042] Since the anti-fouling agent is introduced into the ethylene feed (and the ethylene feed is located upstream of the supercompressor), the point at which the anti-fouling agent is added is located upstream of the supercompressor. Since the anti-fouling agent is introduced upstream of the supercompressor (and the supercompressor is located upstream of the preheater), the point at which the anti-fouling agent is added is located upstream of the preheater. Since the anti-fouling agent is introduced upstream of the preheater (and the preheater is upstream of the polymerization reactor), the point at which the anti-fouling agent is added is located upstream of the polymerization reactor.

[0043] In one embodiment, the method includes introducing an anti-fouling agent into the fresh ethylene feed (1).

[0044] In one embodiment, the method includes introducing an anti-fouling agent into the ethylene feed (2).

[0045] In one embodiment, the method includes introducing an anti-fouling agent into the combined ethylene feed (3).

[0046] In one embodiment, the method includes introducing an anti-fouling agent into the recycled ethylene feed (18).

[0047] In one embodiment, the reactor system includes one or more anti-fouling agent inlets in fluid communication with the respective one or more ethylene feeds. The anti-fouling agent inlets are in direct fluid communication with the ethylene feeds. The term "direct fluid communication" refers to an arrangement whereby a first structure (i.e., the anti-fouling agent inlet) is in direct fluid communication with a second structure (i.e., the ethylene feed) such that no intervening third structure is located between the first and second structures. The method includes introducing an anti-fouling agent into the anti-fouling agent inlets and into the ethylene feeds.

[0048] In one embodiment, the reactor system includes an anti-fouling agent inlet 1a in direct fluid communication with the ethylene feed (1) and / or an anti-fouling agent inlet 2a in direct fluid communication with the ethylene feed (2) and / or an anti-fouling agent inlet 3a in direct fluid communication with the combined ethylene feed (3) and / or an anti-fouling agent inlet 18a in direct fluid communication with the recycled ethylene feed (18).

[0049] In one embodiment, the anti-fouling agent consists only of a liquid inhibitor, molecular oxygen, and a solvent, and the anti-fouling agent is introduced into the anti-fouling agent inlet (1a) and / or (2a) and / or (3a) and / or (18a).

[0050] Since the anti-fouling agent inlet is located upstream of the super compressor, the point at which the anti-fouling agent inlet introduces the anti-fouling agent into the ethylene feed is upstream of the super compressor, and the anti-fouling agent inlet is also upstream of the preheater, and the anti-fouling agent inlet is also upstream of the polymerization reactor.

[0051] In one embodiment, the method includes introducing an anti-fouling agent into the anti-fouling agent inlet (1a) and directly into the fresh ethylene feed (1).

[0052] In one embodiment, the method includes introducing an anti-fouling agent into the anti-fouling agent inlet (2a) and directly into the ethylene feed (2).

[0053] In one embodiment, the method includes introducing an anti-fouling agent into the anti-fouling agent inlet (3a) and directly into the combined ethylene feed (3).

[0054] In one embodiment, the method includes introducing an anti-fouling agent into the anti-fouling agent inlet (18a) and directly into the recycle ethylene feed (18).

[0055] In one embodiment, the method includes introducing an anti-fouling agent into the ethylene feed by introducing molecular oxygen as a gas into the ethylene stream at a first location in the reactor system and introducing an inhibitor separately into the ethylene stream at a second location in the reactor system, the second location being different from the first location. The first location and the second location are each upstream of the supercompressor. The method includes: (i) introducing molecular oxygen at a first location selected from upstream of the boost ( Figure 1 at location 13 therein) or upstream of the primary ( Figure 1 at location 1 therein); and (ii) separately introducing an inhibitor at a second location selected from: fresh ethylene feed (1), anti-fouling agent inlet (1a), ethylene feed (2), anti-fouling agent inlet (2a), combined ethylene feed (3), anti-fouling agent (3a), recycle ethylene feed (18), anti-fouling agent inlet (18a), and any combination thereof.

[0056] In one embodiment, the method includes introducing an anti-fouling agent into the ethylene feed by introducing molecular oxygen as a gas into the ethylene stream at a first location in the reactor system and separately from adding an inhibitor to the ethylene stream at a second location in the reactor system. The method includes: (i) introducing molecular oxygen at a first location upstream of the boost ( Figure 1 at location (13) therein); and (ii) separately introducing an inhibitor at a second location selected from: fresh ethylene feed (1), anti-fouling agent inlet (1a), ethylene feed (2), anti-fouling agent inlet (2a), combined ethylene feed (3), anti-fouling agent (3a), recycle ethylene feed (18), anti-fouling agent inlet (18a), and any combination thereof.

[0057] In one embodiment, one or more chain transfer agents (CTAs) are fed to the supercompressor 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.), isopropyl alcohol, and combinations thereof. The amount of CTA used in the method 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.

[0058] In one embodiment, the solvent for the anti-fouling agent is a CTA for high-pressure free radical polymerization. Thus, the addition of the CTA occurs simultaneously with or substantially simultaneously with the introduction of the anti-fouling agent into the ethylene feed. In a further embodiment, the process of the invention comprises introducing the CTA (as a component of the solvent for the inhibitor, CTA, and the anti-fouling agent) together with the anti-fouling agent into the ethylene feed, and the introduction of the CTA occurs upstream of the supercompressor.

[0059] In one embodiment, the reaction system comprises a CTA stream (4) and / or a recycled CTA stream (5). The CTA stream 4 and / or the CTA recycle stream (5) can in principle be freely distributed over the main compression stream of the feed and / or over the branch stream (8) and the pre-stream (9). The CTA stream (4) and / or the CTA recycle stream (5) can be fed at the inlet, interstage, outlet of the supercompressor and / or at the inlet of the reaction zone in the polymerization reactor.

[0060] When the solvent for the anti-fouling agent is CTA, the CTA stream (4) and / or the recycled CTA stream (5) operate together with the anti-fouling agent feed to provide an appropriate amount of CTA to the reaction system. When the solvent for the anti-fouling agent is not CTA, the CTA stream (4) and / or the recycled CTA stream (5) is the sole source of CTA for the reactor system.

[0061] In one embodiment, the reactor system comprises a branching agent stream (6) and / or a copolymerizable comonomer stream (7). The branching agent feed (6) and / or the copolymerizable comonomer stream (7) can in principle be freely distributed over the main compression stream of the feed and / or over the branch stream (8) and / or the pre-stream (9). The branching agent stream (6) and / or the copolymerizable comonomer stream (7) can be fed at the inlet, interstage, outlet of the supercompressor, with a separate ethylene feed stream being fed into the reactor or directly into the reaction zone.

[0062] The discharge temperature of the supercompressor is from 60 °C to 110 °C. The preheater heats the ethylene feed (and other feeds) received from the supercompressor to a temperature of from 130 °C to 170 °C. After passing through the supercompressor and the preheater, the ethylene monomer with the anti-fouling agent flows or otherwise enters the polymerization reactor ( Figure 1 "reactor" in). The process comprises adding a free radical initiator to the polymerization reactor and polymerizing ethylene in the polymerization reactor under high-pressure free radical polymerization conditions to form an ethylene-based polymer.

[0063] A free radical initiator is added directly to one or more reaction zones of a polymerization reactor. Alternatively, the free radical initiator is introduced into the polymerization reactor via a tributary (8). Non-limiting examples of suitable free radical initiators include organic peroxides, cyclic peroxides, diacyl peroxides, dialkyl peroxides, hydroperoxides, peroxycarbonates, diperoxycarbonates, peroxy esters, peroxy ketals, tert-butyl peroxy pivalate, di-tert-butyl peroxide, tert-butyl peroxyacetate, and tert-butyl peroxy-2- hexanoate, and combinations thereof. In one embodiment, the free radical initiator includes at least one peroxide group incorporated in a ring structure. Non-limiting examples of free radical initiators having a peroxide group incorporated in a ring structure include TRIGONOX 301 (3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxynonane) and TRIGONOX 311 (3,3,5,7,7-pentamethyl-1,2,4-trioxepane), available from Akzo Nobel, and HMCH-4-AL (3,3,6,6,9,9-hexamethyl-1,2,4,5-tetraoxanonane), available from United Initiators. These organic peroxide initiators are used in an amount of 0.001 wt% to 0.2 wt% based on the weight of the polymerizable monomer.

[0064] In one embodiment, high-pressure free radical polymerization occurs in a tubular reactor having a plurality of reactor zones (three to six reactor zones). The maximum temperature of each reactor zone is 150 °C to 360 °C, or 170 °C to 350 °C, or 200 °C to 340 °C. The pressure in each tubular reactor zone is typically 100 MPa to 380 MPa, 110 MPa to 340 MPa, or 110 MPa to 300 MPa.

[0065] As used herein, "prepolymerization" (or "prepolymer") is the premature polymerization of ethylene (and optionally a branching agent and / or an optional copolymerizable comonomer) in a supercompressor and / or a preheater. The prepolymer formed in the supercompressor (and also in the interstage cooler) and the preheater is a high-density (0.930 g / cc - 0.965 g / cc) high-molecular-weight (150,000 g / mol - 500,000 g / mol) polymer that phase separates and forms a solid deposit, thereby interfering with the operation of the supercompressor and reducing heat transfer in the interstage cooler and the preheater. In one embodiment, the method includes reducing or otherwise preventing prepolymerization (or prepolymers consisting of ethylene and / or an optional branching agent and / or an optional copolymerizable comonomer) in the supercompressor and / or the preheater with an anti-fouling agent.

[0066] The applicant has developed a fouling rating scale, where rating "1" is highly fouled (Comparative Example 1 with a highly fouled rating of "1", as Figure 3 shown), rating "4" is very clean (Example 1 of the present invention with a rating of "4" being very clean, as Figure 7 shown), and rating "5" is completely clean. In one embodiment, the method includes introducing an anti-fouling agent into the ethylene feed to form an ethylene feed comprising 0.01 mol ppm to 5 mol ppm inhibitor and 0.05 ppm to 3 ppm molecular oxygen, or 0.05 mol ppm to 3 mol ppm inhibitor and 0.1 ppm to 1.0 ppm molecular oxygen, or 0.07 mol ppm to 2 mol ppm inhibitor and 0.2 ppm to 0.5 ppm molecular oxygen, or 0.1 mol ppm to 1.0 mol ppm inhibitor and 0.2 ppm to 0.5 ppm molecular oxygen; the method further includes reducing or otherwise preventing ("preventing" being fouling rating 4 - 5 or 5) pre-polymerization (or formation of pre-polymers) in the supercompressor and / or preheater. Although the inhibitor or molecular oxygen can each be used alone as an anti-fouling agent, the applicant has found that combining the inhibitor and molecular oxygen produces an anti-fouling agent with a greater ability to reduce / prevent pre-polymer formation compared to the inhibitor alone or molecular oxygen alone. This inhibitor / molecular oxygen combination can use lower levels of inhibitor and oxygen, each of which can cause reactor instability at higher concentrations.

[0067] In one embodiment, the method includes: adding a polymerizable comonomer to a polymerization reactor through a polymerizable comonomer stream (7) and forming an ethylene copolymer. Non-limiting examples of suitable polymerizable comonomers include one or more C 3 -C 20 α-olefin comonomers, acrylates, (meth)acrylic acid, (meth)acrylates, carbon monoxide, maleic anhydride, vinyl acetate, vinyl propionate, maleic monoester, maleic diester, vinyltrialkoxysilane, vinyltrialkylsilane, and any combination thereof. Non-limiting examples of suitable C 3 -C 20 α-olefin comonomers include one or more linear or branched C 3 -C 12 α-olefin comonomers, or one or more linear or branched C 4 -C 8 α-olefin comonomers, such as propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, and 1-octene.

[0068] In one embodiment, the anti-fouling agent does not contain or otherwise exclude polymerizable comonomers.

[0069] After completion of the reaction (and referring to Figure 1 ), and after applying a plurality of cooling steps, 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) comprising trace wax and / or entrained polymer and a polymer-rich stream (11) that is transferred to a low-pressure separator (LPS) for further separation. The ethylene stream (15) is cooled and cleaned in stream (17). Stream (16) is a purification stream that removes impurities and / or inert substances. The ethylene-based polymer separated in the LPS is further processed in (12). The ethylene removed in the LPS is fed to a boost compressor ( Figure 1 “boost” in Figure 1 ), where condensable substances such as solvents, lubricating oils, and other liquids are collected and removed through stream (14) during compression. The outlet of the boost compressor ( Figure 1 “primary” in

[0070] The reactor system includes a lubricant feed for the supercompressor. The lubricating oil may (or may not) include an antioxidant. Some lubricant may leak into the compression chamber of the supercompressor and thus into the ethylene. The method of the present invention advantageously adds an anti-fouling agent directly to the ethylene feed located upstream of the supercompressor, obviating the need to dissolve the anti-fouling agent in the lubricating oil. In one embodiment, the anti-fouling agent is free of or otherwise excludes lubricating oil when added to the ethylene feed.

[0071] By way of example and not limitation, some embodiments of the present disclosure will now be described in detail in the following examples.

[0072] Example

[0073] Method for the examples of the present invention and comparative samples

[0074] Figure 2A schematic representation of the equipment used to prepare the comparative examples and the examples of the present invention is shown. A 300 ml continuous polymerization reactor (CPR) was used to replicate the supercompressor and preheater sections of an industrial scale LDPE production system. Ethylene monomer was added to the CPR at 7 pounds per hour. Propionaldehyde (used as both a chain transfer agent and an anti-fouling agent solvent) was added to this ethylene stream at 1000 mol ppm upstream of the supercompressor. The ethylene and propionaldehyde were then pressurized to 30,000 psi (206,800 kPa) in the supercompressor by using a valve. The CPR was heated to 140 °C to replicate the temperature in the supercompressor and preheater sections of an industrial scale LDPE production system. The ethylene and propionaldehyde were passed through the CPR reactor at 140 °C for 18 hours to further replicate the supercompressor and preheater sections of an industrial scale LDPE production system. During the 18-hour process, all the prepolymers formed were collected and weighed. At the end of 18 hours, the CPR was opened and the fouling level (hereinafter referred to as Method 1) was checked.

[0075] Comparative sample

[0076] In Comparative Examples 1-4 (CE1-4), Method 1 was carried out using different 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 MEHQ was dissolved in propionaldehyde in the absence of added molecular oxygen in CS4.

[0077] Examples of the present invention

[0078] In an example of the present invention (IE1), Method 1 was carried out using 0.5 ppm molecular oxygen dissolved in Isopar-E solvent and 0.5 ppm MEHQ dissolved in propionaldehyde as a three-component anti-fouling agent. The anti-fouling agent was added to the reactor system simultaneously with the ethylene monomer. Method 1 was carried out five times, once for each of CS1-4 and IE1.

[0079] For each run, the amount of prepolymer collected during the 18-hour process was measured. Then, after opening the reactor, the fouling levels in the comparative examples and the examples of the present invention were rated on a scale of 1 to 5, where 1 was highly fouled and 5 was completely clean. The results are shown in Table 1 below.

[0080] Table 1

[0081]

[0082] CE = Comparative Example

[0083] IE = Example of the Present Invention

[0084] As can be seen in Table 1 and shown in Figures 3 - 7 , the direct addition of an anti-fouling agent (inhibitor, molecular oxygen, and solvent) together with the ethylene monomer into the reaction system completely reduces or completely prevents / prevents the amount of prepolymer formed under the operating conditions of the super-compressor and the preheater. The combination of the inhibitor and molecular oxygen synergistically acts to reduce the amount of prepolymer formed at temperatures and pressures below the reaction conditions, i.e., under the operating conditions of the super-compressor and / or the preheater. IE1 hardly produces fouling and prepolymer accumulation on the component surfaces and results in less polymer formation during the experiment than any of the comparative examples of the comparative examples. The applicant has found that molecular oxygen and the inhibitor work synergistically as an effective anti-fouling agent, capable of reducing molecular oxygen (from 0.1 ppm to less than 1.0 ppm, or from 0.1 ppm to 0.5 ppm molecular oxygen) and reducing the inhibitor (from 0.1 ppm to less than 1.0 ppm, or from 0.1 ppm to 0.5 ppm inhibitor), while still achieving little or no prepolymer accumulation. The reduction of molecular oxygen is advantageous because oxygen is known to cause reactor instability at higher concentrations.

[0085] Compared with CE2 (1.0 ppm O 2 / 0 ppm MEHQ), IE1 (0.5 ppm O 2 / 0.5 ppm MEHQ) shows the synergistic effect of the O 2 / inhibitor combination, where compared with about four times more prepolymer accumulation in CE2 (only O 2 ) at 1.2 lb, IE1 exhibits 0.33 lb of prepolymer accumulation.

[0086] Compared with CE4 (0 ppm O 2 / 1.0 ppm MEHQ), IE1 (0.5 ppm O 2 / 0.5 ppm MEHQ) shows the synergistic effect of the O 2 / inhibitor combination, where compared with about twice more prepolymer accumulation in CE4 (only inhibitor) at 0.62 lb, IE1 exhibits 0.33 lb of prepolymer accumulation.

[0087] Particularly desirable is that the present disclosure is not limited to the embodiments and descriptions contained herein, but includes modifications of those embodiments, such modifications including combinations of parts of the embodiments and elements of different embodiments that fall within the scope of the following claims.

Claims

1. A method, the method comprises: introducing an anti-fouling agent into the ethylene feed of a reactor system, the reactor system comprising the ethylene feed, a supercompressor, a preheater and a polymerization reactor, the ethylene feed being located upstream of the supercompressor, the anti-fouling agent consisting of an inhibitor from 0.01 mol ppm to less than 1.0 mol ppm, molecular oxygen from 0.01 mol ppm to less than 1.0 mol ppm and an optional solvent, the inhibitor being monomethyl ether hydroquinone (MEHQ); forming an ethylene feed comprising an inhibitor from 0.01 mol ppm to less than 1.0 mol ppm and a total molecular oxygen from 0.05 mol ppm to less than 3 mol ppm; preventing the formation of prepolymers in components selected from the group consisting of: the supercompressor, the preheater and combinations thereof, wherein the discharge temperature of the supercompressor is from 60 °C to 110 °C, and the preheater heats the ethylene feed received from the supercompressor to a temperature of from 130 °C to 170 °C; adding a free radical initiator to the polymerization reactor; polymerizing ethylene in the polymerization reactor under high pressure free radical polymerization conditions; and forming an ethylene-based polymer.

2. The method according to claim 1, the method comprising using the anti-fouling agent to prevent the pre-polymerization of ethylene in components selected from the group consisting of: the supercompressor, the preheater and combinations thereof.

3. The method according to claim 1, the method comprising dispersing the inhibitor and the molecular oxygen into the solvent before the introduction, The solvent is selected from the group consisting of: aliphatic C 3 -C 6 -hydrocarbons, olefinic C 3 -C 6 -hydrocarbons, C 1 -C 6 -ketones, C 1 -C 6 -aldehydes, C 1 -C 6 -alcohols and combinations thereof.

4. The method according to claim 2, the method comprising dispersing the inhibitor and the molecular oxygen into the solvent before the introduction, The solvent is selected from the group consisting of: aliphatic C 3 -C 6 -hydrocarbons, olefinic C 3 -C 6 -hydrocarbons, C 1 -C 6 -ketones, C 1 -C 6 -aldehydes, C 1 -C 6 -alcohols and combinations thereof.

5. The method according to any one of claims 1 to 4, the method comprises: adding a copolymerizable comonomer capable of polymerization to the polymerization reactor; and forming an ethylene copolymer.

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