PROCESSES TO PREVENT REACTOR FOULING

FIELD OF THE INVENTION

[0001] This invention generally relates to the use of dual modifiers in high pressure polyethylene polymerization processes to prevent fouling on the inner walls of the reactor and associated equipment.

BACKGROUND

[0002] Modifiers, referred to interchangeably herein as "chain transfer agents," may be used in high pressure polyethylene ("HPPE") polymerization processes in tubular reactors to control the viscosity and density of the final products. Chain transfer agents may have a high or low activity for hydrogen transfer. Chain transfer agents with a high activity for hydrogen have been used in conventional processes. These high activity chain transfer agents are readily consumed during the polymerization reaction, and their concentration thus depletes along the length of the tubular reactor. This depletion leads to the formation of high molecular weight byproduct fractions in the polymer product formed. These high molecular weight byproducts tend to precipitate from the bulk product and deposit on the walls of the tubular reactor and associated equipment, an effect referred to as "fouling."

[0003] Fouling restricts the heat transfer capability of the reactor. As the polymerization reaction is exothermic, fouling causes temperatures within the reactor to progressively increase until they reach a point where they restrain production or create the potential for other problems, such as a runaway reaction. At this point, some action generally must be taken. For example, one option is to reduce reaction rates to stay within established constraints. Another option is to have a defouling procedure in place, where the reactor is periodically shut down and washed or piped out, using a suitable solvent or wash liquid to remove the built-up byproducts. Both options are obviously undesirable for productivity and cost reasons.

[0004] It would be advantageous to provide an improvement that could reduce or prevent fouling in HPPE polymerization processes in tubular reactors, and thus prevent the need for restrained production or periodic reactor defouling procedures. This invention is directed to such an improvement.

SUMMARY

[0005] This invention is directed to the use of dual modifiers in HPPE polymerization processes to prevent fouling on the inner walls of the reactor and associated equipment. [0006] In an embodiment, this invention relates to a process for producing HPPE in a tubular reactor, the reactor having at least two reaction zones, and the process comprising:

a. providing to at least one reaction zone a chain transfer composition comprising a first chain transfer agent and a second chain transfer agent, wherein the first chain transfer agent has a reactivity greater than the second chain transfer agent;

b. maintaining the pressure in the reactor at between about 2,200 and about 3000 bar (220 and 300 MPa); and

c. recovering HPPE from the reactor.

[0007] In an embodiment of the invention, the first chain transfer agent comprises a C2 to C12 linear or branched and substituted or unsubstituted aldehyde or ketone, or mixtures thereof. In an embodiment of the invention, the second chain transfer agent comprises a C2 to C12 linear or branched and substituted or unsubstituted olefin, or mixtures thereof, and is preferably an alpha-olefin.

[0008] The processes of this invention significantly reduce or eliminate fouling on the inner walls of the reactor and associated equipment in an HPPE polymerization process. As such, the processes of this invention can reduce or eliminate the temperature rise within a reactor caused by the reactor's reduced heat transfer capability due to fouling. In an embodiment of the invention, the reactor is able to operate continuously at a steady state temperature without the need for a periodic defouling procedure. In an embodiment of the invention, the reactor is able to operate continuously at a steady state temperature without the need for a defouling procedure for at least three days (72 hours), at least five days (120 hours), at least seven days (168 hours), at least 10 days (240 hours), or longer, depending on desired production rates, product parameters, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a graphical representation of a dual modifier test in an HPPE polymerization process in a tubular reactor.

[0010] Figure 2 shows a high pressure polymerization system suitable for the HPPE polymerization processes disclosed herein.

DETAILED DESCRIPTION

[0011] This invention is directed to the use of dual modifiers in HPPE polymerization processes to prevent fouling on the inner walls of the reactor and associated equipment. It has been discovered that, by using an optimal combination of a high activity chain transfer agent and a low activity chain transfer agent, fouling in these processes can be significantly reduced or eliminated. In processes in a tubular reactor using only a chain transfer agent with a high activity for hydrogen, the chain transfer agent is consumed during the polymerization reaction, and its concentration is thus reduced along the length of the tubular reactor. By replacing part of the high activity chain transfer agent with a low activity chain transfer agent, the concentration of high activity chain transfer agent remains more evenly spread across the length of the tubular reactor. This mitigates or prevents the formation of high molecular weight byproduct, thus reducing or eliminating fouling and its undesirable effects. High Pressure Polymerization Process

[0012] The improvements disclosed herein may be useful in many polymerization processes using many different reactor systems and configurations, but they are especially useful in HPPE polymerization processes in tubular reactors.

[0013] Figure 2 depicts an exemplary HPPE tubular reactor polymerization system 1 suitable for the processes disclosed herein. System 1 can include a monomer feed source 3 that supplies ethylene monomer to a primary compressor 5 that pressurizes the monomer to a pressure of about 150 to about 200 bar (15 MPa to 20 MPa), or about 200 bar to about 300 bar (20 MPa to 30 MPa), or about 300 bar to about 350 bar (30 MPa to 35 MPa). Under normal operating conditions, all or substantially all of the monomer discharged from the primary compressor 5 is directed to a jet pump 7 via line 8. A secondary compressor 10 located downstream of, and in fluid communication with the primary compressor 5, increases the pressure of the feed stream 1 1, which includes the monomer feed discharged from the first compressor 5. The secondary compressor 10 boosts the feed stream 1 1 to a pressure of greater than or equal to about 1,500 bar (150 MPa), greater than or equal to about 2,000 bar (200 MPa), greater than or equal to about 2,500 bar (250 MPa), or greater than or equal to about 3,000 bar (300 MPa). In another embodiment of the invention, the secondary compressor 10 boosts the feed 1 1 to a pressure of less than or equal to about 3,000 bar (300 MPa), or less than or equal to about 2,770 bar (277 MPa). In another embodiment of the invention, the secondary compressor 10 boosts the feed 11 to a pressure of between about 2,000 and about 3,000 bar (200 and 300 MPa), between about 2,200 and about 3,000 bar (220 and 300 MPa), between about 2,300 and about 2,770 bar (220 and 277 MPa), or between about 2,300 and about 2,600 bar (230 and 260 MPa).

[0014] The compressed reactor feed stream exiting the secondary compressor 10 can be split into two or more streams. At least one split stream can be heated in one or more heaters 20, and at least two other split streams can be cooled in one or more coolers 22a/22b before entering the reactor 18. As indicated in Figure 2, other reaction components can be injected into the suction inlet of the secondary compressor 10 along with the monomer, including one or more comonomers from comonomer feed 14.

[0015] The reaction feed may also comprise one or more initiators. These can be injected into the reactor 18 from an injection system that can include one or more initiator sources 26, one or more initiator storage vessels 28, and one or more initiator mix and charge systems 30. Suitable initiators can include, but are not limited to, oxygen, peroxide compounds such as hydrogen peroxide, decanoyl peroxide, t-butyl peroxy neodecanoate, t-butyl peroxypivalate, 3,5,5-trimethyl hexanoyl peroxide, diethyl peroxide, t-butyl peroxy-2 -ethyl hexanoate, t-butyl peroxy isobutyrate, benzoyl peroxide, t-butyl peroxy acetate, t-butyl peroxy benzoate, di-t- butyl peroxide, di (2-ethyl, hexyl) peroxydicarbonate, and 1,1,3,3-tetramethyl butyl hydroperoxide; alkali metal persulfates, perborates and percarbonates; and azo compounds such as azo bis isobutyronitrile. Organic peroxide initiators are preferred. Suitable organic peroxide initiators can include t-butyl peroxy neodecanoate, t-butyl peroxypivalate, t-butyl peroxy-2-ethyl hexanoate, t-butyl peroxy isobutyrate, and di (2-ethyl, hexyl) peroxydicarbonate. Preferably, the reaction feed contains less than 0.25 wt% of initiator, based on the total weight of the reaction feed. The amount of the initiator(s) can also range from a low of about 0.01 wt%, 0.025 wt%, 0.035 wt%, or 0.05 wt% to a high of about 0.06 wt%, 0.08 wt%, 0.10 wt%, 0.15 wt%, 0.2 wt% or 0.25 wt%, based on the total weight of the reaction feed.

[0016] In an embodiment of the invention, one or more diluents/solvents can be added to the initiator(s). Suitable diluents/solvents include one or more non-coordinating, inert liquids such as straight and branched-chain hydrocarbons like propane, isobutane, butane, pentane, isopentane, hexane, isohexane, heptane, octane, n-octane, dodecane, isododecane, and mixtures thereof; cyclic and alicyclic hydrocarbons such as cyclohexane, cycloheptane, methylcyclohexane, methylcycloheptane, and mixtures thereof including commercial products such as Isopars™ (available from ExxonMobil Chemical Company, a company with a business office in Houston, Texas); perhalogenated hydrocarbons such as perfluorinated C ₄ to Cio alkanes, chlorobenzene, and aromatic and alkylsubstituted aromatic compounds such as benzene, toluene, mesitylene, and xylene. Suitable diluents/solvents also include liquid olefins which may act as monomers or comonomers including ethylene, propylene, 1-butene, isobutylene, 1-hexene, 1-pentene, 3 -methyl- 1-pentene, 4-methyl- 1 -pentene, 1-octene, and 1- decene. In certain embodiments of the invention, the diluent/solvent can include butane, n- octane, or a mixture of one or more C9 to C12 paraffinic hydrocarbons. [0017] The reaction feed also comprises a chain transfer composition. This composition comprises a first chain transfer agent and a second chain transfer agent. The first chain transfer agent has a higher activity rate for hydrogen transfer than the second chain transfer agent. This activity rate may be represented by a chain transfer constant. Chain transfer in polymerization processes generally involves a free radical removing an atom from another molecule, resulting in an inactive polymer and a new radical. The chain transfer constant is defined herein as the ratio of the rate constants of this transfer reaction and the normal addition of the monomer, and thus measures the relative activity of the growing radical toward the transfer substance. In an embodiment of the invention, the first chain transfer agent has a chain transfer constant > 0.05, preferably > 0.10, and more preferably > 0.15. In an embodiment of the invention, the second chain transfer agent has a chain transfer constant < 0.050, preferably < 0.025, and more preferably < 0.020.

[0018] In an embodiment of the invention, the first chain transfer agent comprises a carbonyl group. In an embodiment of the invention, the first chain transfer agent comprises a C2 to C12 linear or branched, substituted or unsubstituted aldehyde or ketone, or mixtures thereof. Suitable examples of aldehydes that may be useful for the first chain transfer agent include formaldehyde, acetaldehyde, n-valeraldehyde, etc. Suitable examples of ketones that may be useful for the first chain transfer agent include acetone, diethyl ketone, diamyl ketone, diisobutyl ketone, methyl-ethyl-ketone, methyl isopropyl ketone, methyl isobutyl ketone, ethylpropyl ketone, ethylbutyl ketone, 2-pentanone, etc. In an embodiment of the invention, the first chain transfer agent consists essentially of propionaldehyde.

[0019] In an embodiment of the invention, the second chain transfer agent comprises a C2 to C12 linear or branched, substituted or unsubstituted alkane or olefin, preferably an alpha- olefin, or mixtures thereof. Suitable examples of olefins that may be useful for the second chain transfer agent include 1-butene, isobutylene, 3 -methyl- 1-butene, 4-methyl- 1 -butene, 1- hexene, 1-pentene, 3 -methyl- 1-pentene, 1-octene, 1-nonene, 1-decene, 1-dodecene, etc. In an embodiment of the invention, the second chain transfer agent consists essentially of propylene.

[0020] In an embodiment of the invention, the diluents/solvents may comprise the same components as the chain transfer agent(s). In this embodiment of the invention, the amount of diluent/solvent fed to the reactor reduces the amount of chain transfer agent(s) required. Typically, the amount of diluent/solvent is low relative to the amount of chain transfer agent(s) and thus, in this embodiment of the invention, the modifying effect of the diluent is low relative to the modifying effect of the chain transfer agent(s). Where concentrations or weight percents of chain transfer agents(s) are provided herein, those concentrations include both the chain transfer agent(s) and the diluent/solvent for embodiments of the invention where those two items comprise the same components.

[0021] The reactor 18 comprises two or more reaction zones along its length. In an embodiment of the invention, the reactor 18 comprises a minimum of at least two reaction zones, at least three reaction zones, or at least four reaction zones, and/or a maximum of at least five reaction zones, at least six reaction zones, at least seven reaction zones, or at least eight reaction zones. The multiple zones of the reactor 18 allow for manipulation of the temperature profile throughout the polymerization process, which allows for tailoring of certain product properties. The one or more initiators may be split into portions and injected into the reactor at one or more of the reaction zones, or at each of the reaction zones.

[0022] In an embodiment of the invention, as shown in Figure 1, the chain transfer composition can be injected into the suction inlet of the secondary compressor 10 along with the monomer feed. In another embodiment of the invention, the chain transfer composition can be injected into the process, in whole or in part, at at least one point upstream of the reactor. In another embodiment of the invention (not shown in Figure 1), the chain transfer composition can be fed to the reactor 18 directly to at least one reaction zone, and may be split and fed in portions to any number or all of the reaction zones. In an embodiment of the invention, it is useful to maintain a relatively steady concentration of the first chain transfer agent across the length of the tubular reactor. The first chain transfer agent is consumed in the reaction along the length of the reactor, so in this embodiment of the invention, it is useful to feed the chain transfer composition into the reactor in portions to each of the reaction zones. In an embodiment of the invention, the reactor 18 comprises from two to six reaction zones and the chain transfer composition is injected into the reactor 18 at each of the two to six reaction zones.

[0023] The polymerization reaction is conducted in the presence of a catalyst system. Suitable catalysts and catalyst systems are well known in the art. The reaction temperature is from about 300°C or less, about 250°C or less, or about 200°C or less. In an embodiment of the invention, the reaction temperature ranges from about 140.0°C to about 250.0°C. The reaction pressure is at least about 1,800 bar (180 MPa), at least about 1,900 bar (190 MPa), at least about 2,000 bar (200 MPa), at least about 2,500 bar (250 MPa), at least about 2,700 bar (270 MPa), at least about 2,900 bar (290 MPa), or at least about 3,000 bar (300 MPa). In an embodiment of the invention, the reaction pressure is less than about 3,000 bar (300 MPa), less than about 2,900 bar (290 MPa), less than about 2,800 bar (280 MPa), or less than about 2,770 bar (277 MPa).

[0024] From the reactor 18, the exiting mixture of polymer alone or in combination with unreacted monomer ("the product stream") via stream 31 can pass through a high pressure let down valve 32. The high pressure let down valve 32 can be controlled to maintain the desired pressure in the reactor 18. From the high pressure let down valve 32, the product stream can flow through the jet pump 7 into a separation system that can include one or more high pressure separation ("HPS") vessels 36 and one or more low pressure separation ("LPS") vessels 39.

[0025] The HPS vessel(s) 36 can separate the product stream 31 into a stream of unreacted monomer gas 37 and a polymer rich liquid or liquid phase 38. The separated monomer gas can be directed to a recycle gas system 12. The recycle gas system 12 can comprise one or more waste heat boilers, one or more coolers for cooling the recycle gas, and one or more knock-out pots for dewaxing. The cooled and dewaxed gas exiting the recycle system 12 can flow back to the feed stream 11 to the secondary compressor 10.

[0026] The polymer rich liquid 38 can be further separated in the one or more LPS vessels 39. The LPS vessel(s) 39 can operate at a pressure of from 0.5 to 2.0 bar (50 to 200 kPa). Molten polymer leaves the LPS vessel(s) 39 via an outlet 40 in the bottom of the vessel(s) and passes through a conduit into the intake of one or more hot melt extruders (HMEX) 41. One or more additives to modify the properties of the extruded polymer can be added to the HMEX 41 via one or more sources 42 of masterbatch additives. The one or more HMEX 41 convert the molten polymer into strings that are chopped, cooled, and dried via one or more dryers 44, and then transferred to one or more blenders 46. The polymer resin can then be packaged and shipped to end users.

[0027] In the LPS vessel(s) 39, at least a portion, if not all, of the remaining monomer is recovered as an off gas that is compressed in one or more purge gas compressors 48. Any portion of the compressed purge gas can be sent to appropriate storage systems or processing equipment 49a and 49b. Likewise, any portion of the compressed purge gas can be recycled to the inlet of the primary compressor 5 via the purge gas recycle (PGR) stream 49c. For example, up to about 10.0 vol%, 20.0 vol%, 30.0 vol%, 40.0 vol%, 50.0 vol%, 60.0 vol%, 70.0 vol%, 80.0 vol%, 90.0 vol%, or 95.0 vol% of the compressed purge gas can be sent to the storage systems or processing equipment 49a and 49b, and the balance can be recycled to the inlet of the primary compressor 5 via the PGR stream 49c. [0028] Inerts from the purge gas, however, can have a detrimental effect on the crosslinkability of the resin and thus are best removed or significantly reduced by purging from the reaction mixture via the purge gas storage system of processing equipment 49a. In some embodiments of the invention, the amount of recycle to the inlet of the primary compressor 5 via the PGR stream 49c can be reduced to assist in removing inerts from the system. Reducing or even eliminating the PGR stream 49c increases the modifier content in the reaction mixture, which can result in better crosslinkability of the HPPE resin product for a given melt index. The modifier content can be determined based on the modifier consumption rate, which is the ratio of the modifier added to the reaction feed via line 16 to the polymer production rate via line 40 (modifier to production ratio). In an embodiment of the invention, the modifier to production ratio is preferably about 0.4 wt% to about 4.0 wt%.

[0029] In some embodiments of the invention, unreacted comonomer can be separated out in system 49b. The separated comonomer can then be recycled to the inlet of the secondary compressor 10 via recycle stream 52. The amount of the recycle stream 52 can vary depending on the desired melt index and crosslinkability of the composition.

[0030] In an embodiment of the invention, the reactor is able to operate continuously at a steady state temperature without the need for a periodic defouling procedure. In an embodiment of the invention, the reactor is able to operate continuously at a steady state temperature without the need for a defouling procedure for at least three days (72 hours), at least five days (120 hours), at least seven days (168 hours), at least 10 days (240 hours), or longer, depending on desired production rates, product parameters, etc. Steady state is defined herein as maintaining a temperature fluctuation within the reactor, or within each of the various zones of the reactor, of less than about ±5°C, preferably less than about ±3°C, and more preferably less than about ±2°C in an HPPE polymerization process.

HPPE Resin

[0031] The HPPE resins may be characterized by a density, measured at 23°C according to ASTM D1505. In an embodiment of the invention, the HPPE resin can have a density of 0.9 g/cm ³ to 1.2 g/cm ³ , 0.92 g/cm ³ to 1.0 g/cm ³ , 0.94 g/cm ³ to 0.98 g/cm ³ , or 0.92 g/cm ³ to 0.96 g/cm ³ . In an embodiment of the invention, the density can also be from a low of about 0.90 g/cm ³ , 0.92 g/cm ³ , or 0.94 g/cm ³ to a high of about 0.96 g/ cm ³ , 0.98 g/cm ³ , 1.0 g/cm ³ , or 1.2 g/cm ³ .

[0032] The HPPE resins may also be characterized by a melt index ("MI"). MI, measured according to ASTM D 1238, is a measure of the viscosity of a polymer expressed as the weight of material which flows from a capillary under a 2.16 kg load at 190°C for a period of time. In an embodiment of the invention, the HPPE resin can have a melt index of less than 500.0 g/10 min, less than 400.0 g/10 min, less than 300.0 g/10 min, less than 200.0 g/10 min, less than 100.0 g/10 min, less than 50.0 g/10 min, or less than 40.0 g/10 min. In an embodiment of the invention, the MI can also be from a low of about 0.10 g/10 min, 1.0 g/10 min, 5.0 g/10 min, or 10.0 g/10 min to a high of about 20.0 g/10 min, 30.0 g/10 min, 40.0 g/10 min, 50.0 g/10 min, 100.0 g/10 min, 200.0 g/10 min, 350.0 g/10 min, or 500.0 g/10 min. The MI can also be from a low of about 15.0 g/10 min, 25.0 g/10 min, or 40.0 g/10 min to a high of about 45.0 g/10 min, 50.0 g/10 min, or 55.0 g/10 min.

[0033] The HPPE resins may also be characterized according to a crosslink index (MH - ML). MH - ML is the difference in torque level of the molten resin before curing (ML) and after full curing (MH). The cure torque profile is measured over 15 minutes on an MDR 2000 Rheometer (available from Alpha Technologies, a company with a business office in Akron, Ohio) at 150°C. A sample of the resin is combined with 1.5 phr of the peroxide OO- tert-butyl 0-(2-ethylhexyl)monoperoxycarbonate in a preliminary low temperature (well above the melt temperature of the polymer, but also well below the initiation temperature of the peroxide, preferably below 100°C, or below 90°C) blending step using a blend mixer or other mixing equipment until a homogeneous blend is formed. In an embodiment of the invention, the (MH - ML) can be a value from about 1.0 dN*m to about 6.0 dN*m. In an embodiment of the invention, the (MH - ML) can be from a low of about 1.0 dN*m, 1.5 dN*m, or 1.8 dN*m to a high of about 2.0 dN*m, 2.2 dN*m, or 4.5 dN*m. In another embodiment of the invention, the (MH - ML) can be from a low of about 1.2 dN*m, 1.8 dN*m, or 2.2 dN*m to a high of about 2.4 dN*m, 2.9 dN*m, or 3.3 dN*m. In other embodiments of the invention, the (MH - ML) can be at least 2.0 dN*m, at least 2.2 dN*m, or at least 2.4 dN*m.

[0034] The HPPE resins may also be characterized by a melting point, measured by Differential Scanning Calorimetry (DSC). In an embodiment of the invention, the melting point of the HPPE resin can be about 40°C or less. In an embodiment of the invention, the melting point of the HPPE resin can be from about 40.0°C to about 90.0°C. In an embodiment of the invention, the melting point of the HPPE resin can also be from a low of about 40.0°C, 45.0°C, or 50.0°C to a high of about 55.0°C, 65.0°C, or 75.0°C. In an embodiment of the invention, the melting point of the HPPE resin can also be 40.0°C to 80.0°C, 50.0°C to 70.0°C, 55.0°C to 65.0°C, or about 60.0°C.

[0035] The HPPE resin products may also be characterized by a Vicat softening point, measured according to ASTM D 1525. In an embodiment of the invention, the Vicat softening point of the HPPE resin can be about 20.0°C to about 80.0°C. In an embodiment of the invention, the Vicat softening point can also be from a low of about 20°C, 25.0°C, or 30.0°C to a high of about 35.0°C, 40.0°C, or 50.0°C. In an embodiment of the invention, the Vicat softening point of the HPPE resin can also be 20.0°C to 70.0°C, 30.0°C to 60.0°C, 35.0°C to 45.0°C, about 35.0°C, or about 40.0°C.

[0036] The HPPE resins have about 5.0 wt% to about 100.0 wt% of units derived from ethylene, based on the total weight of the resin. In an embodiment of the invention, the amount of ethylene is about 50.0 wt% to about 99.0 wt%, about 55.0 wt% to about 95.0 wt%, about 60.0 wt% to about 90.0 wt%, or about 65.0 wt% to about 95.0 wt%, based on the total weight of the resin. In an embodiment of the invention, the amount of ethylene is from a low of about 50.0 wt%, 51.0 wt%, or 55.0 wt% to a high of about 80.0 wt%, 90.0 wt%, or 98.0 wt%, based on the total weight of the resin.

[0037] The HPPE resins can optionally include polymer units derived from one or more comonomers. The amount of polymer units derived from one or more comonomers can be from about 0 wt% to about 95.0 wt%. In an embodiment of the invention, the amount can also be from about 1.0 wt% to about 5.0 wt%, about 1.0 wt% to about 49.0 wt%, about 5.0 wt% to about 45.0 wt%, about 10.0 wt% to about 50.0 wt%, about 10.0 wt% to about 40.0 wt%, about 20.0 wt% to about 40.0 wt%, about 30.0 wt% to about 45.0 wt%, or about 30.0 wt% to about 35.0 wt%, based on the total weight of the resin. In an embodiment of the invention, the amount of polymer units derived from one or more comonomers can also be from a low of about 1.0 wt%, 4.0 wt%, or 7.0 wt% to a high of about 30.0 wt%, 40.0 wt%, or 45.0 wt%, based on the total weight of the resin.

[0038] Suitable comonomers include, but are not limited to: vinyl ethers such as vinyl methyl ether, vinyl n-butyl ether, vinyl phenyl ether, vinyl beta-hydroxy-ethyl ether, and vinyl dimethylamino-ethyl ether; olefins such as propylene, butene-1, cis-butene-2, trans- butene-2, isobutylene, 3,3,-dimethylbutene-l, 4-methylpentene-l, octene-1, and styrene; vinyl type esters such as vinyl acetate, vinyl butyrate, vinyl pivalate, and vinylene carbonate; haloolefins such as vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, vinyl chloride, vinylidene chloride, tetrachloroethylene, and chlorotrifluoroethylene; acrylic -type esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, alpha-cyanoisopropyl acrylate, beta-cyanoethyl acrylate, o-(3-phenylpropan-l,3,- dionyl)phenyl acrylate, methyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, methyl methacrylate, glycidyl methacrylate, beta-hydroxethyl methacrylate, beta-hydroxpropyl methacrylate, 3-hydroxy-4- carbo-methoxy-phenyl methacrylate, N,N-dimethylaminoethyl methacrylate, t- butylaminoethyl methacrylate, 2-(l-aziridinyl)ethyl methacrylate, diethyl fumarate, diethyl maleate, and methyl crotonate; other acrylic -type derivatives such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, methyl hydroxy, maleate, itaconic acid, acrylonitrile, fumaronitrile, Ν,Ν-dimethylacrylamide, N-isopropylacrylamide, N-t-butylacrylamide, N- phenylacrylamide, diacetone acrylamide, methacrylamide, N-phenylmethacrylamide, N- ethylmaleimide, and maleic anhydride; and other compounds such as allyl alcohol, vinyltrimethylsilane, vinyltriethoxysilane, N-vinylcarbazole, N-vinyl-N-methylacetamide, vinyldibutylphosphine oxide, vinyldiphenylphosphine oxide, bis-(2-chloroethyl) vinylphosphonate, and vinyl methyl sulfide.

[0039] The HPPE resins can also comprise one or more antioxidants. Phenolic antioxidants are preferred, such as butylated hydroxytoluene (BHT) or other derivatives containing butylated hydroxytoluene units such as Irganox® 1076 or Irganox® 1010 (available from BASF, a company with a business office in Florham Park, NJ) and the like. In an embodiment of the invention, the one or more antioxidants can be present at less than 0.05 wt%, based on the total weight of the resin. In an embodiment of the invention, the amount of the antioxidant(s) can be from a low of about 0.001 wt%, 0.005 wt%, 0.01 wt%, or 0.015 wt% to a high of about 0.02 wt%, 0.03 wt%, 0.04 wt%, or 0.05 wt%, based on the total weight of the resin.

[0040] The HPPE resins can further comprise one or more additives. Suitable additives can include, but are not limited to: stabilization agents such as antioxidants or other heat or light stabilizers, anti-static agents, crosslink agents or co-agents, crosslink promotors, release agents, adhesion promotors, plasticizers, or any other additives and derivatives known in the art. Suitable additives can further include one or more anti-agglomeration agents, such as oleamide, stearamide, erucamide, or other derivatives with the same activity as known to the person skilled in the art. Preferably, the additives, if present, are present at less than 0.15 wt%, based on the total weight of the resin. In an embodiment of the invention, the amount of the additives can be from a low of about 0.01 wt%, 0.02 wt%, 0.03 wt%, or 0.05 wt% to a high of about 0.06 wt%, 0.08 wt%, 0.11 wt%, or 0.15 wt%, based on the total weight of the resin.

[0041] The HPPE resins may be further incorporated into polymer blends, and such blends may be made into articles. In an embodiment of the invention, the article is a film. EXAMPLES

[0042] The following example is provided to demonstrate the invention. One of ordinary skill in the art will readily appreciate that additional embodiments are possible without departing from the scope and spirit of the invention. Any process details not included in the example below are considered readily determinable by one of ordinary skill in the art, and/or not relevant to the material aspects of the invention (and are thus excluded for the sake of brevity).

Example 1

[0043] A test was conducted using a commercial scale tubular reactor in a high pressure polyethylene process to produce a low density polyethylene resin. The reactor had six reaction zones, and was maintained at an inlet pressure of between about 2400 bar and 2500 bar (240 mPa and 250 mPa). All feeds to the reactor were compressed at a point upstream of the reactor such that they were fed to the inlet of the reactor at about the inlet pressure of the reactor. Ethylene monomer was thus compressed and fed at a rate of about 85,000 kg/hour. An initiator was also compressed and fed at a rate of about 20 kg/hour.

[0044] At the start of the test, the reactor was operating using a single modifier, propionaldehyde, compressed and fed to the inlet of the reactor at a rate of about 40 kg/hour. When operated at these conditions, the reactor also utilized a defoul frequency of 24 to 36 hours to maintain desired production rates.

[0045] The test involved the use of dual modifiers, with the first modifier being propionaldehyde, and the second modifier being propylene. During the use of the dual modifiers, propylene was compressed and fed to the inlet of the reactor at a rate of about 100 kg/hour. Once the propylene feed began, the propionaldehyde feed rate was reduced by 10 kg/hour to a feed rate of about 30 kg/hour. After the propylene feed was stopped, the propionaldehyde feed rate was increased by 10 kg/hour, back to the initial feed rate of about 40 kg/hour.

[0046] Figure 1 shows the course of the test. The x-axis in Figure 1 represents time in hounminute format, with the test data beginning at about 2: 10 and concluding at about 19:40. The temperature in degrees Celsius of the reactor is shown on the first y-axis, with the relative rates of change in temperature of the reactor over given time periods intended to be a way to represent the relative fouling rates within the reactor. The rate of injection of propylene is shown on the second y-axis in kg/hour.

[0047] Figure 1 shows that the temperature in the reactor prior to the defouling procedure (i.e., from about 2: 10 to about 8:40) was increasing at about 0.81°C/hour. Operations were stopped and the defouling procedure was completed between about 8:40 and 10:00. After the defouling procedure, operations were restarted and from about 10:30 to 12:30, the temperature in the reactor was increasing by about 3.6°C/hour. Use of dual modifiers started at about 12:35 with the feed of propylene at about 100 kg/hour and the feed rate of propionaldehyde being reduced to about 30 kg/hour, as described above. From about 12:35 to about 15:35, while the dual modifiers were in use, the reactor maintained a steady state temperature, indicating that fouling was not occurring to a degree significant enough to affect the reactor's heat transfer ability. After stopping the propylene feed at about 16:00 and returning to the use of a single modifier, the temperature in the reactor increased again at a rate of about 1.28°C/hour from about 16:00 to the end of the test at 20:00, indicating that fouling was occuring again.

[0048] The use of propionaldehyde generally increases the density of the final product in a high pressure reactor, while reducing the reaction pressure generally decreases the density. This example demonstrates that use of the dual modifier at reduced reaction pressure achieves a substantial improvement in fouling and produces a final product with a suitable balance of properties (e.g. haze increase had no unacceptable magnitude).

Particular Embodiments

[0049] Exemplary, but non-limiting embodiments of the invention are described below.

[0050] Embodiment A: A process for producing HPPE in a tubular reactor, said reactor having at least two reaction zones, and said process comprising:

a. providing to at least one reaction zone a chain transfer composition comprising a first chain transfer agent and a second chain transfer agent, wherein said first chain transfer agent has a reactivity greater than said second chain transfer agent; b. maintaining the pressure in said reactor at less than about 3000 bar (300 MPa); and

c. recovering HPPE from the reactor.

[0051] Embodiment B: The process of Embodiment A wherein said first chain transfer agent has a chain transfer constant > 0.05, preferably > 0.10, and more preferably > 0.15.

[0052] Embodiment C: The process of Embodiment A wherein said second chain transfer agent has a chain transfer constant < 0.050, preferably < 0.025, preferably < 0.020.

[0053] Embodiment D: The process of Embodiment A wherein said first chain transfer agent comprises a C2 to C12 linear or branched and substituted or unsubstituted aldehyde or ketone, or mixtures thereof. [0054] Embodiment E: The process of Embodiment D wherein said first chain transfer agent consists essentially of propionaldehyde.

[0055] Embodiment F: The process of Embodiment A wherein said second chain transfer agent comprises a C ₂ to Ci ₂ linear or branched and substituted or unsubstituted alkane or olefin, or mixtures thereof, and is preferably an alpha-olefin.

[0056] Embodiment G: The process of Embodiment F wherein said second chain transfer agent consists essentially of propylene.

[0057] Embodiment H: The process of Embodiment A wherein the reactor comprises from two to six reaction zones and said chain transfer composition is injected into said reactor at each of the two to six reaction zones.

[0058] Embodiment I: The process of Embodiment H wherein said chain transfer composition is injected into said reactor at at least one of the two to six reaction zones.

[0059] Embodiment J: The process of Embodiment A wherein said chain transfer composition is injected into the process at at least one point upstream from the inlet of the reactor.

[0060] Embodiment K: The process of Embodiment A wherein the reactor operates continuously at a steady state temperature for at least three days without requiring a periodic defouling procedure.

[0061] Embodiment L: The process of Embodiment A wherein the reactor pressure is not more than 2,770 bar (277 MPa).

[0062] Embodiment M: The process of Embodiment A wherein the reaction temperature is from about 140.0°C to about 250.0°C.

[0063] Embodiment N: The process of Embodiment A wherein one or more initiator is used.

[0064] Embodiment O: The process of Embodiment N wherein one or more diluents/solvents is added to the one or more initiators.

[0065] Embodiment P: An HPPE produced by the process of Embodiment A.

[0066] Embodiment Q: The HPPE of Embodiment P wherein the density is from 0.9 to

1.2 g/cm ³ .

[0067] Embodiment R: The HPPE of Embodiment P comprising about 5.0 wt% to about 100.0 wt% of polymer units derived from ethylene and about 0 wt% to about 95.0 wt% of polymer units derived from a comonomer, based on the total weight of the HPPE. [0068] Embodiment S: The HPPE of Embodiment R wherein the HPPE comprises about 50.0 wt% to about 99.0 wt% of polymer units derived from ethylene, based on the total weight of the HPPE.

[0069] Embodiment T: The HPPE of Embodiment R comprising about 10.0 wt% to about 50.0 wt% of polymer units derived from a comonomer, based on the total weight of the HPPE.

[0070] Embodiment U: The HPPE of Embodiment R wherein the comonomer is vinyl acetate.

[0071] Embodiment V: The HPPE of Embodiment P having a melt index of about 0.10 g/10 min to about 350 g/10 min, preferably about 0.10 g/10 min to about 50.0 g/10 min.

[0072] Embodiment W: The HPPE of Embodiment P having a crosslink index of from about 1.0 dN*m to about 6.0 dN*m.

[0073] Embodiment X: The HPPE of Embodiment P having a melting point of from about 40.0°C to about 90.0°C.

[0074] Embodiment Y: The HPPE of Embodiment P having a Vicat softening point of from about 20.0°C to about 80.0°C.

[0075] Embodiment Z: The HPPE of Embodiment P comprising one or more antioxidants, preferably one or more phenolic antioxidants.

[0076] Embodiment AA: The HPPE of Embodiment Z wherein the amount of said one or more antioxidants is from about 0.001 wt% to about 0.05 wt%, based on the total weight of the resin.

[0077] Embodiment AB: The HPPE of Embodiment P comprising one or more additives.

[0078] Embodiment AC: The HPPE of Embodiment AB wherein the amount of said one or more additives is from about 0.01 wt% to about 0.15 wt%, based on the total weight of the resin.

[0079] Embodiment AD: A polymer blend comprising the HPPE of Embodiment P.

[0080] Embodiment AE: An article comprising at least one component that comprises the polymer blend of Embodiment AD.

[0081] Embodiment AF: A film comprising the polymer blend of Embodiment AD.