Gas phase polymerization process

Abstract

A method and system for removing contaminants from liquid feeds in polyethylene production processes is disclosed. The method involves using reactor cycle gas as a stripping gas to remove dissolved gases from contaminated liquid feeds to produce treated hydrocarbons and discharging the stripped gases through a flare system. The method is particularly useful for removing unknown poisons and light gases that can adversely affect catalyst performance and reactor productivity in gas-phase polyethylene reactors. In some embodiments, the system can be integrated into existing polyethylene production facilities and allow for reversible implementation, enabling plants to maintain operational continuity and product quality in the face of feed contamination challenges.

Description

GAS PHASE POLYMERIZATION PROCESSFIELD OF THE INVENTION

[0001] The present disclosure relates to methods and systems for removing contaminants from liquid feeds used in gas phase polyethylene production processes.BACKGROUND OF THE INVENTION

[0002] Polyethylene production processes often utilize comonomers such as hexene and butene, as well as inert condensing agents (ICAs), to control the properties of the final polymer product. These raw materials are typically supplied via pipeline or rail car and stored in internal floating roof tanks or pressurized storage at production facilities. However, the reactive nature of alpha olefins like hexene and butene, combined with the potential for contaminants to enter the system during handling and transportation, can lead to the presence of dissolved or reacted contaminants that adversely affect the polyethylene production process. Inert condensing agents (ICAs), while lacking a reactive double bond, are also susceptible to contaminants dissolving into them during the handling process and can cause similar problems.

[0003] Historically, conventional methods for addressing these contaminants involved the installation of dedicated degassing columns and / or sparging facilities in day tanks downstream of the supply tanks. However, in recent years, driven by the push for capital efficiency and improvements in raw material supplier quality and handling practices, newer plants have often eliminated these specialized degassing and sparging facilities. While this approach has reduced capital costs, it has left these facilities more vulnerable to contamination events.

[0004] Typical contaminants of concern include oxygen from the atmosphere, other light gases such as carbon dioxide (CO2) through cross-contamination from transportation or unloading lines, and various unknown poisons that may not be easily identified or removed after delivery to an onsite feed tank. These contaminants can have severe impacts on the polyethylene production process, ranging from reduced catalyst productivity to complete reactor shutdowns, particularly in the case of highly sensitive metallocene catalysts.

[0005] Existing mitigation strategies, such as the use of dryer vessels with desiccants, are primarily designed for the removal of polar impurities and have limited capability to adsorb light gases like oxygen. Alternative methods like tank sparging, while effective, required additional capital costs and often result in significant raw material losses to flare systems.

[0006] U.S. Pat. No. 11,117,980 B2 discloses a gas phase fluidized bed polymerization processwherein loss of ethylene or propylene accompanying inert gas removal is reduced by passing an ethylene- or propylene-containing purge stream through a vent column to contact a hydrocarbon liquid flowing through the vent column countercurrent to the purge stream. Unreacted ethylene or propylene in the purge stream portion is dissolved in the hydrocarbon liquid to produce an ethylene- or propylene-enriched liquid stream and an ethylene- or propylene-depleted gaseous stream. The ethylene- or propylene-enriched liquid stream is then recycled to the fluidized bed reactor, while at least part of the ethylene- or propylene-depleted gaseous stream is purged.

[0007] U.S. Pat. No. 11,155,652 B2 discloses a gas phase fluidized bed polymerization process, wherein an olefin monomer is polymerized to produce a particulate polymer product containing unreacted monomer. The polymer product is contacted with an inert gas to strip hydrocarbon impurities therefrom and produce a stripped polymer product and a gaseous first effluent stream containing inert gas and hydrocarbons. The first effluent stream is compressed and cooled to condense hydrocarbons contained therein and produce a gaseous second effluent stream and a heavies vent stream. A vent stream is removed from the cycle gas line and passed upwardly through a packed vent column to contact the remainder of the second effluent stream flowing downwardly through the packed vent column. Unreacted ethylene is stripped from the vent stream and returned to the cycle gas line leaving an ethylene-depleted vent stream which flows out of the top of the packed vent column to mix with the heavies vent stream, which is then supplied to a vent gas combustion system.

[0008] PCT publication WO 2023 / 091854 discloses a gas phase fluidized bed polymerization process wherein a portion of the reactor overhead can be withdrawn from the reactor to a vent column and contacted with a liquid stripping medium (L) within the vent column to remove at least a portion of the olefin monomer to produce a vent column overhead (G) and a vent column bottoms. The vent column bottoms (rich in the olefin monomer and lean in the carrier gas) are recycled to the reactor. The ratio of L*N to C*G ratio is controlled to avoid carryover of hydrocarbon with the vent column overhead.

[0009] The need for an efficient and cost-effective method to remove these contaminants becomes particularly critical during reactor startups or when dealing with unexpected contamination events. Ideally, such a method must be capable of handling various types of contaminants, including those that may not be easily identified, while minimizing raw material losses and avoiding the need for extensive new capital investments. Ideally, such treatment couldbe implemented with commonly used equipment and familiar techniques to provide treated hydrocarbons free of meaningful levels of contaminants.SUMMARY OF THE INVENTION

[0010] This disclosure provides a method and system for removing contaminants from liquid feeds in a gas phase polyethylene production process. In some embodiments, the method is implemented by repurposing a cycle gas vent column as a degassing column. This method provides an efficient contaminant removal system in polyethylene production facilities without requiring significant capital investment.

[0011] A method disclosed herein comprises contacting hydrogen, nitrogen, ethylene, one or more alpha-olefin comonomers, one or more induced condensing agents (ICAs), and a polymerization catalyst composition in a fluidized bed reaction zone of the gas phase polymerization reactor under polymerization conditions effective to produce polyethylene particles and a reactor gas. A portion of the polyethylene particles are withdrawn from the fluidized bed reaction zone as a product, and a portion of the reactor gas is withdrawn from the fluidized bed reaction zone as a first recycle stream. The first recycle stream is compressed and cooled to produce a second recycle gas stream. A portion of the second recycle gas stream is withdrawn as a first vent stream, and the remainder of the second recycle gas stream is added to the fluidized bed reaction zone.

[0012] Liquid hydrocarbon feed streams are provided, including one or more alpha-olefin comonomers and the one or more induced condensing agents (ICAs), wherein at least one of the liquid hydrocarbon feed streams is a contaminated hydrocarbon. The contaminated hydrocarbon comprises a first amount of a gas dissolved in the contaminated hydrocarbon, and the gas comprises a catalyst poison. The contaminated hydrocarbon is contacted with the first vent stream to produce a treated hydrocarbon stream and a second vent stream. The treated hydrocarbon stream comprises a second amount of the gas. The second vent gas stream comprises a third amount of the gas. The second and third amounts equal the first amount of gas.

[0013] The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter, which form the subject matter of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilizedas a basis for modifying or designing other catalyst compositions and / or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its compositions and methods, together with further objects and advantages will be better understood from the following description.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The claimed subject matter may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:

[0015] FIG. 1 is a schematic diagram of a gas phase polymerization system, according to one embodiment;

[0016] FIG. 2 is a diagram of a control system for controlling a gas phase polymerization process, according to one embodiment;

[0017] FIG. 3 shows a graphical representation of a computer simulation of a vent column configured to strip oxygen from hexene comonomer;

[0018] FIG. 4 shows trends of a first poisoned butene event for normalized catalyst productivity versus time for contaminated butene comonomer feed routed directly to reactor or through vent column before sending to reactor, according to embodiments of the disclosure; and.

[0019] FIG. 5 shows trends of a second poisoned butene event for polymer production versus time for contaminated butene comonomer feed routed directly to reactor or through vent column before sending to reactor, according to embodiments of the disclosure.

[0020] While the disclosed process and system are susceptible to various modifications and alternative forms, the drawings illustrate specific embodiments and / or aspects herein described in detail by way of example. It should be understood, however, that the description herein of a specific embodiment is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.DETAILED DESCRIPTION OF THE INVENTION

[0021] Illustrative embodiments of the subject matter claimed below will now be disclosed. In the interest of clarity, some features of some actual implementations may not be described inthis specification. It will be appreciated that in the development of any such actual embodiments, numerous implementation-specific decisions must be made to achieve the developer’s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort, even if complex and time-consuming, would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

[0022] The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than the broadest meaning understood by skilled artisans, such a special or clarifying definition will be expressly set forth in the specification in a definitional manner that provides the special or clarifying definition for the term or phrase.

[0023] For example, the following discussion contains a non-exhaustive list of definitions of several specific terms used in this disclosure (other terms may be defined or clarified in a definitional manner elsewhere herein). These definitions are intended to clarify the meanings of the terms used herein. It is believed that the terms are used in a manner consistent with their ordinary meaning, but the definitions are nonetheless specified here for clarity.Definitions

[0024] As used herein, “iCT’ and “isobutane” refer to 2-methylpropane.

[0025] As used herein, “nCf’ and “n-butane” refer to normal -butane.

[0026] As used herein, “iCs” and “isopentane” refer to 2-methylbutane.

[0027] As used herein, “nCs” and “n-pentane” refer to normal-pentane.

[0028] As used herein, “neoCs” and “neo-pentane” refer to 2,2-dimethylpropane.

[0029] As used herein, “nCe” and “n-hexane” refer to normal-hexane.

[0030] As used herein, “Ce inerts” refers to various hexane and hexene isomers that are inert to reaction conditions and may include nCe, 2-methylpentane, 3 -methylpentane, 2,2-dimethyl butane, 2, 3 -dimethylbutane, 2-hexene, and / or 3-hexene.

[0031] As used herein, “carrier gas” refers to the gas for transporting the polymerization catalyst to the reactor and for fluidizing the growing polymer particles in the reactor. In someembodiments, the carrier gas is nitrogen, though it can be any gas that would not react with the catalyst nor alter the polymerization reaction (i.e. inert). Carrier gases for gas phase fluidized bed polymerization reactors are well known in the art, and their identity is not the focus of the present disclosure.

[0032] As used herein, “comprising” is to be interpreted as specifying the presence of the stated features, integers, steps, or components as referred to, but does not preclude the presence or addition of one or more features, integers, steps, or components, or groups thereof. Moreover, each of the terms “by”, “comprising,” “comprises”, “comprised of’ “including,” “includes,” “included,” “involving,” “involves,” “involved,” and “such as” are used in their open, non-limiting sense and may be used interchangeably. Further, the term “comprising” is intended to include examples and aspects encompassed by the terms “consisting essentially of’ and “consisting of.” Similarly, the term “consisting essentially of’ is intended to include examples encompassed by the term “consisting of.”

[0033] As used herein, “ICA” refers to a condensing agent. “ICAs” refers to condensing agents. “ICA composition” refers to the total condensing agent in the reactor and encompasses compositions with two or more condensing agents. ICAs suitable for use in methods of the present disclosure may include C3-C6 hydrocarbons or combinations thereof. For example, ICAs suitable for use may include n-butane, isobutane, n-pentane, isopentane, neo-pentane, hexane, isohexane, and other hydrocarbon compounds that are similarly non-reactive in the polymerization process. A “binary ICA composition” is an ICA composition that includes two ICAs, and a “ternary ICA composition” is an ICA composition that includes three ICAs.

[0034] As used herein, “linear low density polyethylene” (LLDPE) refers to polyethylene having a density in the range of from 0.900 g / cm3to 0.945 g / cm3, from 0.901 g / cm3to 0.940 g / cm3, from 0.902 g / cm3to 0.935 g / cm3, from 0.903 g / cm3to 0.930 g / cm3, from 0.904 g / cm3to 0.925, or from 0.905 g / cm3to 0.920 g / cm3. In some embodiments, LLDPE herein can be produced with one or more Ziegler-Natta catalysts, one or more single-site transition metal catalysts, such as, but not limited to, metallocene catalysts, or a combination thereof. In some embodiments, LLDPE herein can be produced in one or more gas phase reactors.

[0035] As used herein, “melt index” refers to a measure of the use of flow of the melt of the thermoplastic polymer. Melt index may be measured according to ASTM DI 238- 13 at suitable weight and temperature. Generally, the melt index of polyolefins is measured at 2.16 kg at 190°C(h), 5 kg at 190°C (Is), 10 kg at 190°C (Iio), or 21.6 kg at 190°C (I21). In some embodiments, LLDPEs herein have an I2 in the range of from 0.1 dg / min. to 30 dg / min., from 0.2 dg / min. to 20 dg / min., from 0.3 dg / min. to 10 dg / min., from 0.4 dg / min. to 5 dg / min., or from 0.5 dg / min. to 2 dg / min.

[0036] As used herein, “polyethylene” denotes a polymer of ethylene and optionally one or more C3-C18 alpha-olefins, while the term “polyolefin” denotes a polymer of one or more C2-C18 alpha-olefins and optionally one or more comonomers. An “olefin” is an unsaturated hydrocarbon that contains at least one carbon-carbon double bond. An alpha-olefin is a hydrocarbon that contains at least one carbon-carbon double bond at one end of a carbon chain (e.g., 1 -butene, vinyl-cyclohexane). For the purposes of this disclosure, ethylene shall be considered an a-olefin.

[0037] As used herein, “reactor gas” refers to the gas that leaves the reactor and is a gas mixture that can include ethylene and other optional monomer(s) (e.g., unreacted monomer gas leaving the reactor) and at least a portion of the carrier gas used to fluidize the catalyst and transport the catalyst into the reactor in the first place. The reactor gas may further include hydrogen (used, e.g., as a chain transfer agent in polymerization) as well as reaction and other process byproducts such as water, ammonia, methane, higher alkanes, carbon dioxide, and / or other compounds of oxygen, carbon, and / or hydrogen.Gas phase polymerization

[0038] The present disclosure relates to processes for production of polyolefins in a gas phase reactor. In some embodiments, hexene and butene are used as comonomers in the gas phase polymerization process. These comonomers are typically supplied via pipeline or rail car to the production facility and stored in a tank having an internal floating roof or pressurized storage to manage vapor pressure. While the simplicity of this handling scheme is attractive, the reactive nature of these alpha olefins, coupled with potential for contaminants to enter the system through the handling process, makes them vulnerable to either dissolved or reacted contaminants that adversely affect the PE process by temporarily poisoning the polymerization catalyst. Typical contaminants of concern include oxygen from atmosphere or other lights (such as CO2) through cross-contamination from transportation / unloading lines. ICAs, while lacking a reactive double bond, are also susceptible to contaminants dissolving into them during the handling process and can cause similar problems in the polymerization process. Comonomer and / or ICA feeds may alsocontain poisons due to a problem in a supplier’s manufacturing process or other contamination prior to delivery.

[0039] Historically, these contaminants were handled by installing degassing columns and / or sparging facilities in a day tank downstream of a supply tank. Overtime, improved quality control and handling practices by suppliers resulted in a lower frequency of contamination exposure. This reduced risk coupled with the drive toward capital efficiency has resulted in newer plants eliminating these degassing and sparging facilities. Although the frequency of contamination events was greatly reduced, gas phase polymerization operations remain vulnerable to operational limitations and upsets due to dissolved gases in liquid hydrocarbon feed streams. Further, most facilities sites have dryer vessels but the desiccant is designed primarily for removal of polar impurities and have relatively little capability to adsorb light gases like oxygen. Sparging of tanks, while effective, involves a relatively large amount of raw material losses to the flare to remove the dissolved gas from a contaminated liquid hydrocarbon feed.

[0040] In some embodiments, a method for removing dissolved gases, such as but not limited to oxygen, carbon dioxide, carbon monoxide, water, ammonia, or a combination thereof, from a comonomer stream (e.g., hexene) is required to continue operation of the gas phase polymerization process when the polymerization catalyst is a metallocene catalyst due to metallocene’s extreme sensitivity to such poisons. History has also shown that the negative effects of such contaminants in a comonomer stream (e.g., butene) can range from a catalyst productivity problem to a complete shutdown of the process even when the polymerization catalyst is a Ziegler-Natta catalyst. Similar contamination of ICAs can normally be handled by reducing flow and production rate at steady state but can be intolerable during a reactor startup when a large amount must be charged to the reactor to operate in condensed mode. In summary, there is a need for process steps and / or equipment to address contamination of comonomer and / or ICAs to mitigate or prevent production rate limitations or even shutdown. It has been discovered that an existing cycle gas vent column that uses liquid hydrocarbons to strip ethylene from carrier gas can be repurposed with minor piping modifications to using cycle gas to strip dissolved gases from liquid comonomers and / or ICAs.

[0041] The vent column on a gas phase polymerization reactor system was installed as a means to improve control of the concentration of inerts in the reactor gas. The existing vent column, in particular, is used to strip ethylene and heavier hydrocarbons such as ICAs and comonomer fromthe vent gas and return it to the cycle gas line for reuse in the process. Described herein is an alternative solution for stripping light poisons from liquid feeds using the vent column, in effect using it as needed as an efficient degassing column that does not require a reboiler or condenser. In the event of contamination of one-or-more liquid feeds the vent column could be configured to no longer receive recycled liquids from vent recovery and instead be fed fresh hexene, butene, or ICA. Contaminated liquid is routed to the vent column inlet instead of through the normal feed manifold. The reactor cycle gas is then used as the stripping gas to remove the light gas poisons from contaminated hydrocarbon liquids rather than using recycled liquids to recover ethylene from the cycle gas. The vent column overhead stream, containing the poisons stripped from the contaminated hydrocarbon liquids, would then be routed to the flare.Polymerization Reactor

[0042] The methods described may be used in pilot plant or commercial size reactors including a variety of designs. For example, the model can be used in commercial-scale reactions, such as gas-phase fluidized-bed polymerization reactions, that can be monitored and optionally also controlled. Some such reactions can occur in a reactor having the geometry of the fluidized bed reactor 101 discussed with respect to FIG. 1. In other embodiments, a reactor is monitored and optionally also controlled while operating to perform polymerization using any of a variety of different processes (e.g., slurry or gas phase processes).

[0043] Generally, in a gas-phase fluidized-bed process used for producing polymers, a gaseous stream containing one or more monomers is continuously cycled through a fluidized bed in the presence of a catalyst under reactive conditions. The gaseous stream is withdrawn from the fluidized bed and recycled back into the reactor. Simultaneously, polymer product is withdrawn from the reactor and fresh monomer is added to replace the polymerized monomer. (See, for example, U.S. Pat. Nos. 4,543,399; 4,588,790; 5,028,670; 5,317,036; 5,352,749; 5,405,922; 5,436,304; 5,453,471; 5,462,999; 5,616,661; and 5,668,228; all of which are incorporated by reference.)

[0044] FIG. 1 is a schematic diagram of a polymerization system 100 that can be monitored and controlled in accordance with embodiments described. The polymerization system 100 includes a fluidized bed reactor 101. The fluidized bed reactor 101 has a bottom end 103, a straight section 105, a top expanded section 107, and a distributor plate 109 within the straight section 105.A fluidized bed 111 of granular polymer (once formed) and catalyst particles is contained withinthe straight section 105 and may optionally extend slightly into the top expanded section 107. The bed is fluidized by the steady flow of recycle gas through the distributor plate 109. The recycle gas enters fluidized bed reactor through line 113, additional reaction and inert gases (including ICAs) may be added in adjustable ratios through line 115. Aluminum alkyl (optional) may be added through line 117. The flow rate of the recycle gas is regulated to maintain circulation of fluidized bed 111. In some embodiments, a recycle gas velocity of from about 1 ft / sec to about 3 ft / sec, such as from about 2 ft / sec to about 3 ft / sec, or from about 2.4 ft / sec to about 2.8 ft / sec is used to maintain a fluidized bed 111 in the reactor 101 while operating the reactor 101 at a total pressure of about 4200 kPa or less, about 700 kPa to about 4200 kPa, about 1300 kPa to about 2800 kPa, or about 1700 kPa to about 2500 kPa.

[0045] The polymerization system 100 has one or more catalyst lines 119 for controlling the addition of polymerization catalyst to a reaction zone (not shown) within fluidized bed 111, and generally within straight section 105. Within the reaction zone, the catalyst particles react with reaction gases including an olefin monomer (e.g., ethylene) and optionally a comonomer and other reaction gases (e.g., hydrogen) to produce the granular polymer particles. As new polymer particles are produced, other polymer particles are continually withdrawn from the fluidized bed 111 through a product discharge line 121 to product recovery system 123. The fluidized bed 111 may be maintained at a constant height by withdrawing a portion of the fluidized bed 111 at a rate equal to the rate of formation of particulate product. The product may be removed continuously or nearly continuously via a series of valves (not shown) into a fixed volume chamber (not shown), which is simultaneously vented back to the reactor. The fixed volume chamber and venting back to the reactor allows for highly efficient removal of the product, while recycling a large portion of the unreacted gases back to the reactor.

[0046] Unreacted olefins and ICA composition within the product recovery system may be removed via line 125, compressed in compressor 127, and travel via line 129 to heat exchanger 131 to be cooled before being recycled (e.g., via line 133) to line 113. The particles within product recovery system 123 may be degassed (or “purged”) with a flow of inert gas such as nitrogen through line 135 to remove substantially all of the dissolved hydrocarbon materials. In some instances, the polymer granules may be treated with a small stream of humidified nitrogen to deactivate trace quantities of residual catalyst. The purge gas may be removed via line 137 to be vented to flare or recycled with further processing.

[0047] The polymerization system 100 also has a cooling loop which includes a first recycle gas line 139, compressor 141, a second recycle gas line 143, and cooling system 145 (such as a circulating gas cooler), coupled with the fluidized bed reactor 101. Cooling system 145 may accept cooling water via line 147 and expel heated water via line 149. Cooling of the recycle gas is a method used to cool polymerization system 100 to reduce or eliminate issues that may arise from exothermic polyolefin production. During operation, the cooled circulating gas from cooling system 145 flows via line 113 through inlet 151 into the fluidized bed reactor 101, then propagates upward through fluidized bed 111 and out from the fluidized bed reactor 101 via outlet 153.

[0048] The top expanded section 107 may also be known as a “velocity reduction zone,” and is designed to reduce the quantities of particle entrainment in the recycle gas line from the fluidized bed. The diameter of the top expanded section 107 generally increases with the distance from straight section 105. The increased diameter causes a reduction in the speed of the gas stream, which allows most of the entrained particles to settle back into the fluidized bed 111, thereby minimizing the quantities of solid particles that are “carried over” from the fluidized bed 111 through the recycle gas line 139. In some instances, a screen (not shown) may be included upstream of the compressor 141 to remove larger material.

[0049] Catalyst is supplied from line 119 to the reaction zone 111 of a fluidized bed reactor 101 by way of an inert (such as nitrogen, ethane, propane, etc.) feed gas. In the reaction zone 111, the catalyst contacts a bed of growing polymer particles and formed polymer particles fluidized by a gaseous stream containing ethylene or propylene and any optional comonomers. Product is removed from the reaction zone 111 and conveyed via line 101 to a product recovery system 123.Unreacted monomers and nitrogen exit the reactor 101 by way of recycle gas line 139 to a cycle gas compressor 141 and then a cycle gas cooler 145.

[0050] During standard operation, after leaving the cooler 145, most of the cycle gas is transported by line 146, initially for mixing with fresh ICA(s), supplied by line 115, and fresh monomer(s), supplied by line 116, and then returned to the reaction zone 111. In addition, a minor portion of the cycle gas leaving the cooler 145 is fed via line 163 to a vertically disposed packed vent column 165. Liquid C4+ hydrocarbons from the recovery section of the plant are supplied via line 133a to the vent column 165 above packed bed 167 of the vent column 165. Liquid C4+ hydrocarbons from the recovery section contact the cycle gas from line 146 in packed bed 167.Ethylene in the cycle gas is absorbed by the hydrocarbons from the recovery section, and theethylene-rich hydrocarbon liquid is returned to the cycle gas line 146 via line 163 at the bottom of vent column 165.

[0051] In some embodiments, during implementation of the method disclosed herein, the dispositions of the liquid hydrocarbon feeds and the liquid hydrocarbons from the recovery section 123 are swapped. The liquid hydrocarbons from the recovery section 123 are added directly to the reaction zone 111 via lines 133 and 113, and flow though line 133a is terminated. Contaminated liquid ICA stream is fed to the vent column 165 above the packed bed 167 via line 115a, and flow through line 115 is terminated, and / or contaminated liquid monomer stream is fed to the vent column 165 above the packed bed 167 via line 116a, and flow through line 116 is terminated. The liquid hydrocarbons from the recovery section 123 are added directly to the reaction zone 111 via lines 133 and 113, and flow though line 133a is terminated. The first vent stream comprising a portion of the gas in line 146 is fed to vent column 165 below packed bed 167 via line 163. The second vent stream (vent column overhead) comprising the gas removed from the contaminated monomer(s) and / or contaminated ICA(s) is fed by line 137 to a flare system (not shown). The treated liquid hydrocarbon stream (having some or all of the poison removed) is added feed to the reaction zone 111 via line 163 at the bottom of vent column 165 and line 113.

[0052] To maintain a reactor temperature, the temperature of the recycle gas may be continuously adjusted up or down to accommodate changes in the rate of heat generation due to the polymerization reaction. One or more temperature sensors 155 may be located in the fluidized bed and used with a control system and the cooling loop to control the temperature of the fluidized bed 111 near the process set-point. Heated reactor gas, which carries heat energy from the fluidized bed reactor 101, is withdrawn from the outlet 153 and is pumped by the compressor 141 via line 143 to cooling system 145 where the temperature of the heated reactor gas is reduced and at least a portion of the ICA composition present is condensed to a liquid. The recycle gas from the cooling system 145, including condensed liquids, flows via line 113 to the reactor inlet 151 to cool the fluidized bed 111. Temperature sensors (not shown) near the inlet and outlet of the cooling system 145 may provide feedback to a control system (not shown) to regulate the amount by which cooling system 145 reduces the temperature of the recycle gas entering the fluidized bed reactor 101.

[0053] The fluidized bed reactor 101 may also include skin temperature sensors 157, mounted in positions along a wall of the straight section 105 of the fluidized bed reactor 101 so as to protrudeinto the bed from the reactor wall by a small amount (e.g., about one eighth to one quarter of an inch (3-6 mm)). The skin temperature sensors 157 may be configured and positioned to sense the temperature of the resin near the wall of the fluidized bed reactor 101 during operation.

[0054] The temperature sensors 155 in the fluidized bed 111 can include a resistance temperature sensor positioned and configured to sense bed temperature during reactor operation at a location within the fluidized bed reactor 101 away from the reactor wall. The resistance temperature sensor can be mounted so as to protrude into the bed more deeply than the skin temperature sensors 157 (e.g., about 8 to 18 inches (20-46 cm) away from the reactor wall).

[0055] Other sensors and other apparatuses may be employed to measure other reaction parameters during a polymerization reaction. The reaction parameters may include instantaneous and bed-averaged resin product properties (e.g., melt index and density of the polymer resin product being produced by the polymerization system 100 during a polymerization reaction). Resin product properties may be measured by periodically sampling the resin when exiting the reactor (e g., about once per hour), and performing the appropriate tests in a quality control laboratory.

[0056] Other measured reaction parameters may include reactor gas composition (e.g., concentrations and partial pressures of reactant gases, ICA, and other inert gases, such as nitrogen, inert hydrocarbon, and the like). The reactor gas composition may be measured by removal of gas from upper portion 107 via line 159 to a gas chromatograph (“GC”) system 161. GC system 161 may also be connected by lines (not shown) other than line 159 to other parts of polymerization system 100, such as recycle gas line 139, compressor 141, line 143 or any combination thereof.

[0057] The process control variables may be controlled to obtain the desired productivity for the polymerization system 100 and properties for the resin. For example, the parameters used to control gas phase composition within the fluidized bed reactor 101 can include the concentration (partial pressure) and composition of the ICA composition and comonomer, the partial pressure of monomer, the type and properties of catalysts, and the temperature of the reaction process. For example, a polymerization reaction during a transition from production of a certain grade of polyolefin to a different grade may be controlled by controlling process control variables to ensure that the product (e.g., the granular resin) has properties compliant with an initial specification set at the start of the transition, the product produced during the transition ceases to comply with the initial specification set at a first time, and the product has properties compliant with a finalspecification set at the end of the transition. In the processes described herein, stickiness of the resin during the reaction may be controlled by a control system adjusting (or regulating) the temperature in the reaction zone and / or the concentration (partial pressure) of the ICA composition used in the reaction.

[0058] FIG. 2 is a block diagram of a control system 200 that can be used to control the polymerization system 100. The control system 200 may be a distributed control system (DCS), a direct digital controller (DDC), a programmable logic controller (PLC), or other suitable systems or combination of systems. The control system 200 has a processor 201 that implements machine readable instructions from a storage system 203. Illustrative processors may include a single core processor, a multiple core processor, a virtual processor, a virtual processor in a cloud implementation, an application specific integrated circuit (ASIC), or a combination of these systems. Illustrative storage systems 203 can include random access memory (RAM), read only memory (ROM), hard drives, virtual hard drives, RAM drives, cloud storage systems, optical storage systems, physically encoded instructions (for example, in an ASIC), or a combination of these systems.

[0059] Adjustments to control settings may be determined based on the input of data from temperature sensors 155 and 157, the GC 161, and lab data 205, among others. After determining new control settings, the control system 200 may make in real time, or recommend, adjustments, for example, to the process cooling systems 207, the ICA addition and recycling systems 209, flow control systems 211, and termination systems 213, among others.

[0060] The reactor and associated methods may be an element of a staged reactor employing two or more reactors in series, where one reactor may produce, for example, a high molecular weight polyolefin and another reactor may produce a low molecular weight polyolefin.Polyolefin Production

[0061] Polyolefin polymerization may be performed by contacting in a reactor (such as the fluidized bed reactor 101 of FIG. 1) an olefin monomer (optionally with a comonomer) with one or more catalysts (supported or not) in the presence of ICA composition and optionally hydrogen. The individual flow rates of olefin monomer, optional comonomer, optional hydrogen, and ICA composition (or individual components thereof) may be controlled to maintain fixed gas composition targets. The concentration of all gases may be measured with a chromatograph. A solid catalyst, a catalyst slurry, or liquid solution of the catalyst(s) may be injected directly intothe reactor using a carrier gas (e.g., purified nitrogen), where the feed rate of catalyst(s) may be adjusted to change or maintain the catalyst inventory in the reactor.

[0062] In some embodiments, the polymerization reaction may be performed at a reactor pressure of about 4,200 kPa or less, about 700 kPa to about 4,200 kPa, about 1,300 kPa to about 2,800 kPa, or about 1,700 kPa to about 2,500 kPa.

[0063] Generally, the olefin monomer concentration is controlled and monitored by the olefin monomer partial pressure. In some embodiments, the olefin partial pressure may be at about 4200 kPa or less, such as about 500 kPa to about 2,000 kPa, about 1,000 kPa to about 1,800 kPa, about 1,200 kPa to about 1,700 kPa, or about 1,400 kPa to about 1,600 kPa.

[0064] The comonomer concentration may be controlled and monitored by a comonomer to olefin monomer mole ratio (or alternatively, the flow rates of comonomer and olefin monomer are held at a fixed ratio). When present, the comonomer may be at a relative concentration to the olefin monomer that will achieve the desired weight percent incorporation of the comonomer into the finished polyolefin. In some embodiments, the comonomer may be present with the olefin monomer in a mole ratio in the gas phase of from about 0.0001 to about 50 (comonomer to olefin monomer), from about 0.0001 to about 5, from about 0.0005 to about 1.0, or from about 0.001 to about 0.5.

[0065] The olefin monomer or comonomers, for example, may be a C2-C18 alpha-olefin. In some embodiments, the olefin monomer is ethylene, and a comonomer is a C3-C12 alpha olefin. In some embodiments, the olefin monomer may be ethylene or propylene, and a comonomer may include C4-C10 alpha-olefins. For example, C2-C18 alpha-olefins that may be utilized as a comonomer in embodiments described may include: ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1 -heptene, 1 -octene, 4-methylpent-l-ene, 1 -decene, 1 -dodecene, 1 -hexadecene, and the like, and a combination thereof. Additionally, a polyene may be used as a comonomer according to some embodiments described. For example, polyenes may include: 1,3 -hexadiene, 1,4-hexadiene, cyclopentadiene, dicyclopentadiene, 4-vinylcyclohex-l-ene, methyloctadiene, 1-m ethyl- 1,6-octadiene, 7-methyl-l,6-octadiene, 1,5 -cyclooctadiene, norbomadiene, ethylidene norbomene, 5-vinylidene-2-norbomene, 5-vinyl-2-norbomene, and olefins formed in situ in the polymerization medium. When olefins are formed in situ in the polymerization medium, the formation of polyolefins containing long chain branching may occur. Additional examples ofcomonomers may include isoprene, styrene, butadiene, isobutylene, chloroprene, acrylonitrile, and cyclic olefins. Combinations of the foregoing may be utilized in the methods described.

[0066] Examples of polymers that can be produced in accordance with the method described may include the following: homopolymers and copolymers of C2-C18 alpha olefins; polyvinyl chlorides, ethylene propylene rubbers (EPRs); ethylene-propylene diene rubbers (EPDMs); polyisoprene; polystyrene; polybutadiene; polymers of butadiene copolymerized with styrene; polymers of butadiene copolymerized with isoprene; polymers of butadiene with acrylonitrile; polymers of isobutylene copolymerized with isoprene; ethylene butene rubbers and ethylene butene diene rubbers; polychloroprene; norbornene homopolymers and copolymers with one or more C2-C18 alpha olefin; and terpolymers of one or more C2-C18 alpha olefins with a diene. In some embodiments, the polyolefin produced by the method described may include olefin homopolymers (e.g., homopolymers of ethylene or propylene). In some instances, the polyolefin produced may be copolymers, terpolymers, and the like of the olefin monomer and the comonomer.

[0067] In some embodiments, the polyolefin produced may be a polyethylene or a polypropylene. Exemplary polyethylenes produced by the methods described may be homopolymers of ethylene or copolymers of ethylene (or terpolymers of ethylene) having at least one alpha-olefin (comonomer) where the ethylene content may be at least about 50% by weight of the total monomers involved. Exemplary polypropylenes produced by the methods described may be homopolymers of propylene or interpolymers of propylene and at least one alpha-olefin (comonomer) where the propylene content may be at least about 50% by weight of the total monomers involved.

[0068] Hydrogen gas is often used in olefin polymerization to control the final properties of the polyolefin. For some types of catalyst systems, increasing concentrations (or partial pressures) of hydrogen may alter the molecular weight or melt index of the polyolefin generated. The melt index can thus be influenced by the hydrogen concentration. Generally, the amount of hydrogen in the polymerization is expressed as a mole ratio relative to the total polymerizable monomer (e.g., relative to ethylene or relative to a blend of ethylene and hexene or propylene). The amount of hydrogen used in some polymerization processes is an amount necessary to achieve the desired melt index (or molecular weight) of the final polyolefin resin. In some embodiments, the mole ratio in the gas phase of hydrogen to total polymerizable monomer (H2 to monomer) may be about0.00001 or greater, about 0.0005 or greater, about 0.001 or greater, about 10 or less, about 5 or less, about 3 or less, or about 0.10 or less, where a range may include a combination of an upper mole ratio with a lower mole ratio described.Catalyst

[0069] Exemplary catalysts suitable for use in the embodiments described may include: Ziegler Natta catalysts, chromium based catalysts, vanadium based catalysts (e.g., vanadium oxychloride and vanadium acetylacetonate), metallocene catalysts and other single-site or singlesite-like catalysts, cationic forms of metal halides (e.g., aluminum trihalides), anionic initiators (e.g., butyl lithiums), cobalt catalysts and mixtures thereof, nickel catalysts and mixtures thereof, rare earth metal catalysts (i.e., those containing a metal having an atomic number in the Periodic Table of 57 to 103), such as compounds of cerium, lanthanum, praseodymium, gadolinium and neodymium. A single catalyst may be used, or a mixture of catalysts may be employed, if desired. The catalyst may be soluble or insoluble, supported or unsupported. Further, the catalyst may be a prepolymer, spray dried with or without a fdler, a liquid, or a solution, slurry / suspension, or dispersion.

[0070] Traditional Ziegler-Natta catalysts are transitional metal catalysts that are well known in the art. Examples of transition metal catalysts are discussed in U.S. Pat. Nos. 4,115,639, 4,077,904, 4,482,687, 4,564,605, 4,721,763, 4,879,359 and 4,960,741, the disclosures of which are hereby fully incorporated herein by reference. The transition metal catalyst compounds that may be used in the present invention include transition metal compounds from Groups 3 to 17, preferably 4 to 12, more preferably 4 to 6 of the Periodic Table of Elements.

[0071] Transition metal catalyst compounds based on magnesium / titanium electron-donor complexes that are useful in the invention are described in, for example, U.S. Pat. Nos. 4,302,565 and 4,302,566, the disclosures of which are hereby fully incorporated herein by reference.

[0072] British Patent Application No. 2,105,355 and U.S. Pat. No. 5,317,036, the disclosures of which are hereby incorporated herein by reference, describe various vanadium catalyst compounds.

[0073] Still other transition metal catalyst compounds and catalyst systems suitable for use in the present invention are disclosed in U.S. Pat. Nos. 4,124,532, 4,302,565, 4,302,566, 4,376,062, 4,379,758, 5,066,737, 5,763,723, 5,849,655, 5,852,144, 5,854,164 and 5,869,585 and publishedEP-A20416815 A2 and EP-A1 0420436, the disclosures of which are hereby fully incorporated herein by reference.

[0074] Other catalysts may include cationic catalysts such as A1C13, and other cobalt, iron, nickel and palladium catalysts well known in the art. See for example U.S. Pat. Nos. 3,487,112, 4,472,559, 4,182,814 and 4,689,437, the disclosures of which are hereby fully incorporated herein by reference.

[0075] For more details on Ziegler-Natta catalysts, see for example, U.S. Pat. Nos. 3,687,920, 4,086,408, 4,376,191, 5,019,633, 4,482,687, 4,101,445, 4,560,671, 4,719,193, 4,755,495, 5,070,055, the disclosures of which are hereby incorporated herein by reference.

[0076] Also or instead, a catalyst compound of the present disclosure can be a chromium or chromium-based catalyst. Such catalysts and polymerization processes have been described, for example, in U.S. Patent Application Publication No. 2011 / 0010938 and U.S. Pat. Nos. 7,915,357, 8,129,484, 7,202,313, 6,833,417, 6,841,630, 6,989,344, 7,504,463, 7,563,851, 8,420,754, and 8,101,691.

[0077] In some embodiments processes disclosed herein utilize single-site transition metal catalysts. Exemplary single-site transition metal catalysts suitable for use in the embodiments described may include metallocene catalysts and other single-site or single-site-like catalysts. A single catalyst may be used, or a mixture of catalysts may be employed, if desired. The catalyst may be soluble or insoluble, supported or unsupported. Further, the catalyst may be a prepolymer, spray dried with or without a filler, a liquid, or a solution, slurry / suspension, or dispersion.

[0078] Metallocenes may include “half sandwich” and “full sandwich” compounds having one or more pi-bonded ligands (e.g., cyclopentadienyl and ligands isolobal to cyclopentadienyl) bound to at least one Group 3 to Group 12 metal atom (including the Lanthanide series and Actinide series elements), and one or more leaving groups bound to the at least one metal atom. The metallocene may be supported on a support material and may be supported with or without another catalyst component.

[0079] The structure of the metallocene catalyst compound may take on many forms, such as those disclosed in, for example, U.S. Pat. Nos. 5,026,798, 5,703,187, and 5,747,406, including a dimer or oligomeric structure, such as disclosed in, for example, U.S. Pat. Nos. 5,026,798 and 6,069,213. Others include those catalysts described in U.S. Patent Application Publication Nos. US2005 / 0124487A1, US2005 / 0164875A1, and US2005 / 0148744. In some embodiments, themetallocene may be formed with a hafnium metal atom (e.g., bis(n-propylcyclopentadienyl) hafnium Xn, bis(n-butylcyclopentadienyl) hafnium Xn, or bis(n-pentylcyclopentadienyl) hafnium Xn, where X is one of chloride or fluoride and n is 2), such as is described in U.S. Pat. Nos.6,242,545 and 7,157,531.

[0080] A catalyst compound of the present disclosure can be a chromium or chromium-based catalyst. Chromium-based catalysts include chromium oxide (CrO3) and silylchromate catalysts. Chromium catalysts have been the subject of much development in the area of continuous fluidized-bed gas-phase polymerization for the production of polyethylene polymers. Such catalysts and polymerization processes have been described, for example, in U.S. Patent Application Publication No. 2011 / 0010938 and U.S. Pat. Nos. 7,915,357, 8,129,484, 7,202,313, 6,833,417, 6,841,630, 6,989,344, 7,504,463, 7,563,851, 8,420,754, and 8,101,691.

[0081] Other catalysts for use in processes of the present disclosure include “non-metallocene complexes” that are defined to be transition metal complexes that do not feature a cyclopentadienyl anion or substituted cyclopentadienyl anion donors (e.g., cyclopentadienyl, fluorenyl, indenyl, methylcyclopentadienyl). Examples of families of non-metallocene complexes that may be suitable can include late transition metal pyridylbisimines (e.g., U.S. Pat. No. 7,087,686), group 4 pyridyldiamidos (e.g., U.S. Pat. No. 7,973,116), quinolinyldiamidos (e.g., U.S. Pub. No.2018 / 0002352 Al), pyridylamidos (e.g., U.S. Pat. No. 7,087,690), phenoxyimines (e.g., Accounts of Chemical Research 2009, 42, 1532-1544), and bridged bi-aromatic complexes (e g., U.S. Pat. No. 7,091,292), the substance of which are fully incorporated herein by reference.Treatment of contaminated liquid hydrocarbons

[0082] In some instances, during operation of a gas phase polymerization reactor, there are unexpected excursions in quality of hydrocarbon feeds. Disclosed herein is a process to polymerize olefins in a gas phase polymerization reactor to produce a polyethylene. In a first group of embodiments, the process comprises contacting hydrogen, nitrogen, ethylene, one or more alpha-olefin comonomers, one or more induced condensing agents (ICAs), and a polymerization catalyst composition in a fluidized bed reaction zone of the gas phase polymerization reactor under polymerization conditions effective to produce polyethylene particles and a reactor gas. A portion of the polyethylene particles are withdrawn as product and a portion of the reactor gas is withdrawn as a first recycle stream. The first recycle stream is compressed and cooled to produce a second recycle gas stream. A portion of the second recyclegas stream is withdrawn as a first vent stream, and the remainder of the second recycle gas stream is added to the fluidized bed reaction zone.

[0083] In some embodiments, liquid hydrocarbon feed streams are provided. The liquid hydrocarbon feed streams comprise one or more alpha-olefin comonomers and the one or more ICAs, wherein at least one of the liquid hydrocarbon feed streams is a contaminated hydrocarbon. The contaminated hydrocarbon comprises a first amount of a gas dissolved in the contaminated hydrocarbon, and the gas comprises a catalyst poison. The contaminated hydrocarbon is contacted with the first vent stream to produce a treated hydrocarbon stream and a second vent stream. The treated hydrocarbon stream comprises a second amount of the gas. The second vent gas stream comprises a third amount of the gas. The second and third amounts of gas equal the first amount of gas. The liquid hydrocarbon streams other than the at least one contaminated hydrocarbon and the treated hydrocarbon stream are added to the fluidized bed reaction zone.

[0084] In some embodiments, the one or more alpha-olefin comonomers have the formula CH2=CHR, where Ris H ora 1-18 carbon linear or branched alkyl group. In some embodiments, the one or more alpha-olefin comonomers are linear or branched alkyls containing 4 to 12 carbon atoms. In some embodiments, the one or more alpha-olefin comonomers are linear alkyls containing 4 to 8 carbon atoms. In some embodiments, any of the forgoing have the olefinic unsaturation at one end of the alkyl group. In some embodiments, the one or more alpha-olefin comonomers are butene-1, hexene- 1, octene- 1, or a combination thereof.

[0085] In some embodiments, the one or more alpha-olefin comonomers are present in an amount up to 20 wt%, based on the total weight of the ethylene and the one or more alpha-olefin comonomers. In some embodiments, the one or more alpha-olefin comonomers are present in an amount in the range of from 0.5 wt% to 14 wt%, based on the total weight of the ethylene and the one or more alpha-olefin comonomers.

[0086] In some embodiments, the polymerization catalyst comprises one or more Ziegler-Natta catalysts, one or more metallocene catalysts, or a combination thereof.

[0087] In some embodiments, the ratio of the second amount of gas to the first amount of gas is less than or equal to 0.10, less than or equal to 0.09, less than or equal to 0.08, less than or equal to 0.07, or less than or equal to 0.06. In some embodiments, the ratio of the second amount of gas to the first amount of gas is greater than or equal to 0.006, greater than or equal to 0.007, greater than or equal to 0.008, greater than or equal to 0.009, or greater than or equal to 0.010. In someembodiments, the ratio of the second amount of gas to the first amount of gas is in the range of from 0.006 to 0.10, from 0.007 to 0.09, from 0.008 to 0.08, from 0.009 to 0.07, from 0.010 to 0.06.

[0088] In some embodiments, the first amount of gas is greater than or equal to 1 ppmw, greater than or equal to 2 ppmw, greater than or equal to 5 ppmw, or greater than or equal to 10 ppmw, based on the weight of the contaminated hydrocarbon. In some embodiments, the first amount of gas is less than or equal to 15 ppmw, less than or equal to 14 ppmw, less than or equal to 13 ppmw, or less than or equal to 12 ppmw, based on the weight of the contaminated hydrocarbon. In some embodiments, the first amount of gas is in the range of from 1 ppmw to 15 ppmw, from 2 ppmw to 14 ppmw, from 5 ppmw to 13 ppmw, or from 10 ppmw to 12 ppmw, based on the weight of the contaminated hydrocarbon.

[0089] In some embodiments, the second amount of gas is less than or equal to 1.0 ppmw, less than or equal to 0.5 ppmw, less than or equal to 0.2 ppmw, or less than or equal to 0.1 ppmw, based on the weight of the contaminated hydrocarbon. In some embodiments, the second amount of gas is greater than or equal to 0.001 ppmw, greater than or equal to 0.002 ppmw, greater than or equal to 0.003 ppmw, or greater than or equal to 0.004 ppmw, based on the weight of the contaminated hydrocarbon. In some embodiments, the second amount of gas is in the range of from to 0.001 ppmw to 1.0 ppmw, greater than or equal to 0.002 ppmw to 0.5 ppmw, greater than or equal to 0.003 ppmw to 0.2 ppmw, or greater than or equal to 0.004 ppmw to 0.1 ppmw, based on the weight of the contaminated hydrocarbon.

[0090] In some embodiments, step f) of the process is performed in a vent column.

[0091] In some embodiments, the vent column is operated at a temperature greater than or equal to 5°C, greater than or equal to 10°C, greater than or equal to 15°C, or greater than or equal to 20°C. In some embodiments, the vent column is operated at a temperature less than or equal to 45°C, less than or equal to 40°C, less than or equal to 35°C, or less than or equal to 30°C. In some embodiments, the vent column is operated at a temperature in the range of from 5°C to 45°C, from 10°C to 40°C, from 15°C to 35°C, or from 20°C to 30°C.

[0092] In some embodiments, the vent column is operated at a pressure gradient (pressure at bottom of column minus pressure at top or column) less than or equal to 1.5 psi (10.3 kPa), less than or equal to 1.0 psi (6.9 kPa), less than or equal to 0.75 psi (5.2 kPa), or less than or equal to 0.5 psi (3.4 kPa). In some embodiments, the vent column is operated at a pressure gradient greater than or equal to 0.1 psi (0.69 kPa), greater than or equal to 0.2 psi (1.38 kPa), greater than or equalto 0.25 psi ( 1.72 kPa), or greater than or equal to 0.3 psi (2.1 kPa). In some embodiments, the vent column is operated at a pressure gradient in the range of from 0.1 psi (0.69 kPa) to 1.5 psi 10.3 kPa), from 0.2 psi (1.38 kPa) to 1.0 psi (6.9 kPa), from 0.25 psi (1.72 kPa) to 0.75 psi (5.2 kPa), or from 0.3 psi (2.1 kPa) to 0.5 psi (3.4 kPa).

[0093] Typically, nitrogen is removed through the vent column rather than a direct cycle gas vent to flare or product purge bin. Vent columns significantly reduce hydrocarbon losses associated with nitrogen venting to the flare. Under certain conditions, hydrocarbon breakthrough can occur in the vent column, meaning hydrocarbon can carry over with the nitrogen. Hydrocarbon breakthrough can be managed by the method disclosed in PCT publication WO 2023 / 091854, the substance of which is fully incorporated herein by reference.

[0094] In normal operation when the vent column is operated to use liquid hydrocarbon to strip ethylene and other hydrocarbons from a portion of the recycle gas to be routed to the flare, the L*N to CXG ratio is maintained above a pre-determined value, wherein the total liquid stripping medium flow (L) to the vent column can be controlled to ensure the LXN to CXG ratio is kept above the pre-determined value for a given reactor gas composition. The vent column overhead gas flow (“G”) can also be controlled to ensure the LXN to CXG ratio is kept above the pre-determined value for a given reactor gas composition. The ethylene concentration (C) within the vent column overhead line can also be controlled to ensure the LxN to CxG ratio is kept above the pre-determined value for a given reactor gas composition. The nitrogen or inert concentration (N) (mol%) in the recycle gas stream to the reactor can also be controlled to ensure the LxN to CXG ratio is kept above the pre-determined value for a given reactor. In certain embodiments, any two or more of the L, N, C, G can be controlled to ensure the LXN to CXG ratio is kept above the pre-determined value for a given reactor. In certain embodiments, any three or more of the L, N, C, G can be controlled to ensure the LXN to CXG ratio is kept above the pre-determined value for a given reactor. In certain embodiments, all four of the L, N, C, G can be controlled to ensure the LXN to CXG ratio is kept above the pre-determined value for a given reactor.

[0095] In contrast to the normal operation of the vent column, in the process disclosed herein when the vent column is operated to use the portion of the recycle gas to be routed to the flare to strip dissolved has from a liquid hydrocarbon, the L'XN' to C'XG' ratio is maintained below a predetermined value, wherein the total liquid to be stripped (L') to the vent column can be controlled to ensure the L'xN' to C'XG' ratio is kept below the pre-determined value for a given reactor gascomposition. The vent column overhead gas flow (G') can also be controlled to ensure the L'xN' to C'XG' ratio is kept below the pre-determined value for a given reactor gas composition. The ethylene concentration (C') within the vent column overhead line can also be controlled to ensure the L'xN' to C'xG' ratio is kept below the pre-determined value for a given reactor gas composition. The nitrogen or inert concentration (N) (mol%) in the recycle gas stream to the reactor can also be controlled to ensure the L'xN' to C'x'G' ratio is kept below the pre-determined value for a given reactor. In certain embodiments, any two or more of the L', N', C, and G' can be controlled to ensure the L'xN' to C'XG' ratio is kept below the pre-determined value for a given reactor. In certain embodiments, any three or more of the L', N', C', and G' can be controlled to ensure the L'xN' to C'XG' ratio is kept below the pre-determined value for a given reactor. In certain embodiments, all four of the L', N', C', and G' can be controlled to ensure the L'xN' to C'xG' ratio is kept above the pre-determined value for a given reactor.

[0096] In some embodiments, the vent column is operated at a ratio of (L'xN') / (C'xG') less than or equal to 8.0, 7.5, 7.0, 6.5, 6.0, 5.5, 5.0, 4.5, 4.0, 3.5, or 3.0, wherein:L' is a liquid monomer and / or ICA flow to the vent column, wherein the liquid flow comprises the contaminated hydrocarbon (kg / hr) and optionally liquid hydrocarbon from a recovery section receiving polymer product from the gas phase polymerization reactor (kg / hr);N' is the carrier gas concentration in the reactor overhead to the vent column (mol%);C' is the ethylene concentration in the reactor overhead to the vent column (mol%); and G' is the vent column overhead (kg / hr).

[0097] In some embodiments, the vent column is operated at a ratio of (L'xN') / (C'xG') greater than or equal to 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or 1.1. In some embodiments, the vent column is operated at a ratio of (L'xN') / (C'xG') in the range of from 0.1 to 8.0, from 0.2 to 7.5, from 0.3 to 7.0, from 0.4 to 6.5, from 0.5 to 6.0, from 0.6 to 5.5, from 0.7 to 5.0, from 0.8 to 4.5, from 0.9 to 4.0, from 1.0 to 3.5, or from 1.1 to 3.0.

[0098] In some embodiments, the vent column comprises a packed bed. In some embodiments, the packed bed comprises structured packing or unstructured packing. In some embodiments, the contaminated hydrocarbon is added to the vent column above the packed bed. In some embodiments, the first vent stream is added to the vent column below the packed bed. In some embodiments, the second vent stream is withdrawn from the vent column above the packedbed. In some embodiments, the treated hydrocarbon stream is withdrawn from the vent column below the packed bed.

[0099] An advantage of flow configuration disclosed herein is that it avoids capital cost investment in a separate degassing facility when comonomer and / or ICA quality is typically very good thereby not requiring treatment prior to feeding to the reaction zone of the gas phase polymerization reactor. However, this method provides the option to remove dissolved gases (constituting a catalyst poison) when present in a highly abnormal situation, which without this method would result in the inability to run a gas phase reactor, severely limit its production rates, and / or require disposal and replacement of the contaminated hydrocarbon feed.

[0100] In some embodiments, the method provides the option to use the vent column only during startup when poisons are especially problematic because of the amount of feed (e.g., ICA) charged to the reactor. Depending on the poison severity, the feeds can be returned to their normal configuration once the startup is complete.

[0101] Without this system, if a hydrocarbon feed tank became contaminated there would be no onsite method to remove the dissolved gas, such as but not limited to oxygen, carbon dioxide, carbon monoxide, water, ammonia, or a combination thereof, unless the tank had internal sparging capabilities, temporary facilities were installed, or contaminated material was disposed of or downgraded to a lower value disposition. Even with these steps, sparging could result in loss of raw materials, temporary facilities could result production delays for installation, and disposal of or downgrade of materials all result in higher costs.Polyolefin Products

[0102] Polymer products herein include copolymers of C2 to C40 olefins, preferably C2 to C20 olefins, preferably a copolymer of an alpha-olefin and another olefin or alpha-olefin (ethylene is defined to be an alpha-olefin for purposes of this invention). Preferably, the polymers are or include ethylene copolymerized with one or more of propylene, butene or hexene, and optional dienes. Preferred examples include thermoplastic polymers such as ultra low density polyethylene (“ULDPE”), very low density polyethylene (“VLDPE”), linear low density polyethylene (“LLDPE”), low density polyethylene (“LDPE”), medium density polyethylene (“MDPE”), and high density polyethylene (“HDPE”).

[0103] Polyethylene polymers produced in a gas phase polymerization process are characterized by a number of parameters, including, but not limited to, density, melt index (I2),high load melt index (I21 or HLMI), melt index ratio (MIR), number average molecular weight (Mn), weight average molecular weight (Mw), Z-average molecular weight (Mz), molecular weight distribution (Mw / Mnor MWD), the ratio of the Z-average molecular weight to the weight average molecular weight (Mz / Mw), composition distribution melt index, and branching index (g'). These parameters are related to physical characteristics of polymer chains, including, but not limited to, lengths of polymer chains, distribution of lengths of polymer chains, comonomer distribution among and along polymer chains, and length and number of branches on polymer chains. These physical characteristics of polymer chains lead to different mechanical properties that make different polyethylene polymers suitable for a broad range of end-use applications.Certain Embodiments

[0104] Disclosed herein is a process to polymerize olefins in a gas phase polymerization reactor to produce a polyethylene. In first group of embodiments, the process comprises:a) contacting hydrogen, nitrogen, ethylene, one or more alpha-olefin comonomers, one or more induced condensing agents (ICAs), and a polymerization catalyst composition in a fluidized bed reaction zone of the gas phase polymerization reactor under polymerization conditions effective to produce polyethylene particles and a reactor gas; b) withdrawing from the fluidized bed reaction zone a portion of the polyethylene particles as product and a portion the reactor gas as a first recycle stream; c) compressing and cooling the first recycle gas stream to produce a second recycle gas stream;d) withdrawing a portion of the second recycle gas stream as a first vent stream and adding the remainder of the second recycle gas stream to the fluidized bed reaction zone; e) providing liquid hydrocarbon feed streams, comprising the one or more alpha-olefin comonomers and the one or more ICAs, wherein at least one of the liquid hydrocarbon feed streams is a contaminated hydrocarbon, the contaminated hydrocarbon comprises a first amount of a gas dissolved in the contaminated hydrocarbon, and the gas comprises a catalyst poison;f) contacting the contaminated hydrocarbon with the first vent stream to produce a treated hydrocarbon stream and a second vent stream, wherein the treated hydrocarbon stream comprises a second amount of the gas, the second vent gas stream comprises a third amount of the gas, and the second and third amounts equal the first amount of gas; andg) adding the liquid hydrocarbon streams, other than the at least one contaminated hydrocarbon, and the treated hydrocarbon stream to the fluidized bed reaction zone.

[0105] In a second group of embodiments, in addition to the foregoing limitations, the process is characterized by one of more of the following:a) the one or more alpha-olefin comonomers contain 4 to 12 carbon atoms, and in further embodiments, the one or more alpha-olefin comonomers contain 4 to 8 carbon atoms; b) the one or more alpha-olefin comonomers are present in an amount up to 20 wt%, based on the total weight of the ethylene and the one or more alpha-olefin comonomers, and in further embodiments, the one or more alpha-olefin comonomers are present in an amount in the range of from 0.5 wt% to 14 wt%, based on the total weight of the ethylene and the one or more alpha-olefin comonomers;c) the polymerization catalyst comprises: i) one or more Ziegler-Natta catalysts; ii) one or more metallocene catalysts; or iii) a combination thereof;d) the ratio of the second amount of gas to the first amount of gas is less than or equal to 0.10, less than or equal to 0.09, less than or equal to 0.08, less than or equal to 0.07, or less than or equal to 0.06; greater than or equal to 0.006, greater than or equal to 0.007, greater than or equal to 0.008, greater than or equal to 0.009, or greater than or equal to 0.010; or in the range of from 0.006 to 0.10, from 0.007 to 0.09, from 0.008 to 0.08, from 0.009 to 0.07, from 0.010 to 0.06e) the first amount of gas is greater than or equal to 1 ppmw, greater than or equal to 2 ppmw, greater than or equal to 5 ppmw, or greater than or equal to 10 ppmw, based on the weight of the contaminated hydrocarbon;f) the second amount of gas is less than 1.0 ppmw, less than or equal to 0.5 ppmw, less than or equal to 0.2 ppmw, or less than or equal to 0.1 ppmw, based on the weight of the contaminated hydrocarbon.

[0106] In a third group of embodiments, in addition to the foregoing limitations of the first and second groups of embodiments, step f) is performed in a vent column. In further embodiments of the third group of embodiments, the vent column is operated:a) at a temperature greater than or equal to 5°C, greater than or equal to 10°C, greater than or equal to 15°C, or greater than or equal to 20°C; less than or equal to 45°C, less than or equal to 40°C, less than or equal to 35°C, or less than or equal to 30°C; or in therange of from 5°C to 45°C, from 10°C to 40°C, from 15°C to 35°C, or from 20°C to 30°C;b) at a pressure gradient (pressure at bottom of column minus pressure at top or column) less than or equal to 1.5 psi (10.3 kPa), less than or equal to 1.0 psi (6.9 kPa), less than or equal to 0.75 psi (5.2 kPa), or less than or equal to 0.5 psi (3.4 kPa); or at a pressure gradient greater than or equal to 0.1 psi (0.69 kPa), greater than or equal to 0.2 psi (1.38 kPa), greater than or equal to 0.25 psi (1.72 kPa), or greater than or equal to 0.3 psi (2.1 kPa); or at a pressure gradient in the range of from 0.1 psi (0.69 kPa) to 1.5 psi 10.3 kPa), from 0.2 psi (1.38 kPa) to 1.0 psi (6.9 kPa), from 0.25 psi (1.72 kPa) to 0.75 psi (5.2 kPa), or from 0.3 psi (2.1 kPa) to 0.5 psi (3.4 kPa);c) at a ratio of (L'xN') / (C'xG') less than or equal to 8.0, 7.5, 7.0, 6.5, 6.0, 5.5, 5.0, 4.5, 4.0, 3.5, or 3.0; greater than or equal to 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or 1.1; or in the range of from 0.1 to 8.0, from 0.2 to 7.5, from 0.3 to 7.0, from 0.4 to 6.5, from 0.5 to 6.0, from 0.6 to 5.5, from 0.7 to 5.0, from 0.8 to 4.5, from 0.9 to 4.0, from 1.0 to 3.5, or from 1.1 to 3.0, wherein:L' is a liquid monomer and / or ICA flow to the vent column, wherein the liquid flow comprises the contaminated hydrocarbon (kg / hr) and optionally liquid hydrocarbon from a recovery section receiving polymer product from the gas phase polymerization reactor (kg / hr);N' is the carrier gas concentration in the reactor overhead to the vent column (mol%); C' is the ethylene concentration in the reactor overhead to the vent column (mol%);andG' is the vent column overhead (kg / hr).

[0107] In a fourth group of embodiments, in addition to the foregoing limitations of the third group of embodiments, the vent column comprises a packed bed. In further embodiments of the fourth group of embodiments, the process is further characterized by one or more of the following:a) the packed bed comprises structured packing or unstructured packing;b) the contaminated hydrocarbon is added to the vent column above the packed bed; c) the first vent stream is added to the vent column below the packed bed;d) the second vent stream is withdrawn from the vent column above the packed bed; ande) the treated hydrocarbon stream is withdrawn from the vent column below the packed bed.EXAMPLES

[0108] The following examples are included to demonstrate some embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventor to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.

[0109] Computer simulations were run using PRO / II™ ver. 9.3 to estimate the effectiveness of an existing vent column to effectively strip dissolved oxygen from hexene is demonstrated. Starting material to be fed to the vent column was assumed to be 1 -hexene containing 2.2 ppmw of O2. The simulations show that oxygen concentration in the treated hydrocarbon liquid effluent from the vent column as a function of the number of theoretical stages in the column. The number of theoretical stages is a function of both the liquid flowrate and the height of the column. The higher the liquid flowrate correlates to more theoretical stages, provided flow is limited to prevent flooding. FIG.3 shows the reduction in O2 in hexene is for 1, 2, and 3 theoretical stages.

[0110] One skilled in the art would understand how to determine the height of a theoretical plate (HETP) for a given set of conditions. For example, if a calculated theoretical stage equates to 1.5 m of a selected packing and the packed bed is 6 m tall, the packed bed would be four theoretical stages. At other conditions a theoretical stage might require a height of packing more or less than the above 1.5 m. In the simulations, liquid hexene-1 temperature is 80°F (27°C) and at a flow rate is 9,366 Ibs / hr (4,248 kg / hr). Outlet gas flow rate varies because of the change in theoretical stages: 370 Ibs / hr (109 kg / hr) for 1 stage and 241 Ibs / hr (168 kg / hr) for 3 stages.

[0111] Table 1 below shows the results of a series of computer simulations using PRO / II™ ver. 9.3 for a C2= / Ce=polyethylene grade produced using a metallocene catalyst and having a density of 0.912 g / cm3and an MI of 1.0 dg / min. (ASTM D1238, 2.16 kg @ 190°C) wereperformed to examine the effect of temperature of contaminated hexene comonomer supplied to the vent column.

[0112] Example 2 shows operation of the vent column in its normal service using cold mixed hydrocarbons from the product recovery section of the plant to recover hydrocarbons from vented cycle gas.

[0113] Example 3 shows operation of the vent column using the vented cycle gas to remove dissolved O2 from liquid hexene- 1 feed containing 1 ppmw O2.

[0114] Example 4 shows operation of the vent column under the same conditions as Example 3 except that the hexene- 1 feed was at an ambient temperature of about 80°F (27°C).

[0115] Example 5 shows operation of the vent column under the same conditions as Example 3 except that the hexene- 1 feed contained 10 ppmw dissolved O2.

[0116] Example 6 shows operation of the vent column under the same conditions as Example 5 except that the hexene-1 feed was at an ambient temperature of about 80°F (27°C).

[0117] Example 7 shows operation of the vent column under the same conditions as Example 6 except that the hexene-1 feed contained 2.2 ppmw dissolved O2.

[0118] The analysis shows that temperature has a large impact on the quality of the O2 removal from the stream. Therefore, care must be exercised if deciding to mix recovered liquids which are cold with fresh feed requiring stripping to ensure maximum dissolved gas removal.TABLE 1

[0119] On two occasions, referred to herein as the first contamination event (Example 8) and the second contamination event (Example 9), the method disclosed herein was implemented to address contamination of comonomer feed. For both Examples 8 and 9, a gas phase reactor was operating with a Ziegler-Natta catalyst and butene- 1 as a comonomer. In both instances, a severe drop in catalyst activity and polyethylene production were tracked to contaminated butene sources. Routing the contaminated butene to the vent column as disclosed herein produced immediate improvement in observed catalyst productivity and production rates. Once the amount of contaminated butene was calculated to be minimal, routing of the butene through the vent column was terminated. Butene was again routed directly in the cycle gas line while retaining expected catalyst activity and polyethylene production rates.- Example 8

[0120] In one instance, a butene comonomer supply tank was contaminated with an unknown poison. The contamination affected roughly 600 klbs (272 metric tons) of butene in the pipeline and on-site tank. The gas phase reactor operating with Ziegler Natta catalyst was forced to run in dry mode for several days because it could not feed enough catalyst to maintain rates in condensed mode. The unknown poison was not adsorbed in butene purification beds and did not react with TEAL A temporary connection was made between the contaminated butene tank and the vent column. The normal vent column feed of cold liquids from the recovery section was rerouted directly to the cycle gas line. By venting 500-750 Ibs / hr (227-340 kg / hr) of gas through the top of the vent column, the poison was effectively stripped out. The reactor was able to resume operations at near-normal rates and economically consume the contaminated butene by routing it through the vent column instead of directly through to the reactor instead of having to dispose of the contaminated butene as waste. This methodology was also proposed for stripping dissolved oxygen from contaminated hexene, but in this instance, the method was able to successfully strip an unknown poison (not dissolved oxygen, CO2, water, NH3, or CO based on laboratory testing) from butene.

[0121] FIG. 4 shows a timeline for Example 8. Time period T1 shows catalyst productivity dropping significantly to a steady state greater than or equal to about 2,500 lb. PE / lb. catalyst. This corresponds to an increase in the concentration of contaminated butene in the feed to the reactor from 0 to about 58 wt% and a decrease in the concentration of “clean” butene in the feed to thereactor from 100 wt% to about 42 wt%. Reactor conditions were limited to dry mode operation during time period T2 due to inability to add enough catalyst to the reactor to support condensed mode. Catalyst activity remained at less than or equal to about 1,000 lb. PE / lb. catalyst. Time period T3 shows the sharp increase in catalyst activity to greater than or equal to about 3,500 lb. PE / lb. catalyst when the butene was routed through the vent column. Time period T4 shows another sharp drop in catalyst activity to about 1,000 lb. PE / lb. catalyst when the reactor was returned to dry mode operation with contaminated butene routed directly to the reactor. The reactor was shut down during time period T5. After shutting down vent column operation to upgrade a temporary connection routing the contaminated butene to permanent piping, reactor operation was resumed during time period T6. Catalyst activity again reached greater than or equal to about 3,500 lb. PE / lb. catalyst.- Example 9

[0122] FIG. 5 shows a timeline for Example 9. Time period T1 shows adequate catalyst productivity while contaminated butene is routed to the vent column. Although the contamination was not CO, the unknown contaminant caused a reading on the CO monitor. Time period T2 shows catalyst activity / production rate deteriorating after contaminated butene is removed from the vent column and routed back to the reactor, and liquids from the recovery section are routed to the vent column. After the dispositions of the contaminated butene and liquids from the recovery section are swapped again with contaminated butene routed to the vent column, time period T3 shows that catalyst productivity begins to recover again.

[0123] During time period Tl, contaminated butene- 1 was being fed to the vent column while recovered hydrocarbons were routed directly to the reactor as shown by line 510 (i.e., recovered hydrocarbon liquids routed to reactor since flow of recovered hydrocarbons to vent column is zero). The CO analyzer did not indicate any CO to the reactor (line 502), and the polyethylene production rate (line 504) was about 170 klb / hr (77 tonne / hr). Catalyst productivity (line 506) was about 3,200 lb PE / lb cat (3,200 kg / kg cat). The vent column overhead flow rate (line 508) was about 600 Ib / hr (272 kg / hr).

[0124] Early in time period T2, butene-1 was routed back to the reactor, and recovered hydrocarbons were routed to the vent column to the reactor as shown by line 510. This line-up was only maintained for a few minutes as indicated by the spike upwards in line 510 at about 5 hours. The CO analyzer showed a spike in CO to the reactor (line 502) and corresponding dropsin polyethylene production rate (line 504) to about 140 klb / hr (64 tonne / hr) and catalyst productivity (line 506) to about 2,000 lb PE / lb cat (907 kg / kg cat) wer observed. The vent column overhead flow rate (line 508) was about 100 Ib / hr (45 kg / hr) before routing butene to the reactor and just after routing butene back to the vent column. After returning butene feed to the vent column and increasing vent column overhead flow rate (line 508) was increased back to about 500 Ib / hr (227 kg / hr), the CO to the reactor (line 502), the polyethylene production rate (line 504), and the catalyst productivity (line 506) returned to about the same values as during time period Tl.

[0125] At the beginning of time period T3, the vent column overhead flow rate (line 508) was reduced to zero while butene remained lined up to the vent column. This again resulted in corresponding drops in polyethylene production rate (line 504) to about 140 klb / hr (64 tonne / hr) and catalyst productivity (line 506) to about 2,000 lb PE / lb cat (907 kg / kg cat). When overhead flow rate (line 508) was increased back to about 500 Ib / hr (227 kg / hr), the CO to the reactor (line 502), the polyethylene production rate (line 504), and the catalyst productivity (line 506) returned to about the same values as during time period TE

[0126] At the beginning of time period T4, butene-1 was routed back to the reactor, and recovered hydrocarbons were routed to the vent column to the reactor as shown by line 510.However, in contrast to operations during time period T2, the overhead flow rate (line 508) was maintained at about 500 Ib / hr (227 kg / hr). Once again, the CO analyzer showed an upward trend (line 502) and polyethylene production rate (line 504) and catalyst productivity (line 506) showed corresponding downward trends. When butene-1 was routed back to the vent column, and recovered hydrocarbons were routed to the reactor as indicated by line 510, the CO to the reactor (line 502), the polyethylene production rate (line 504), and the catalyst productivity (line 506) returned to about the same values as during time period Tl .

[0127] At the beginning of time period T5, the vent column overhead flow rate (line 508) was reduced to zero while butene remained lined up to the vent column. However, other potential sources CO, such as the CO catalyst kill system, were isolated to confirm that there were no leaks that created an additional source of poisons to the reactor system other than the contaminated comonomer. This again resulted in corresponding drops in polyethylene production rate (line 504) to about 140 klb / hr (64 tonne / hr) and catalyst productivity (line 506) to about 2,000 lb PE / lb cat (907 kg / kg cat). When overhead flow rate (line 508) was increased back to about 500 Ib / hr (227kg / hr), the CO to the reactor (line 502), the polyethylene production rate (line 504), and the catalyst productivity (line 506) returned to about the same values as during time period Tl.

[0128] Additional lab testing of the contaminated butene determined that the contamination was not CO. The contamination was such that it caused a reading on the CO analyzer even though the contamination was not CO. The contaminated tank of butene was processed prior to obtaining additional samples for further testing. Therefore, although the exact composition of the catalyst poison was never determined, the above results show that any gas dissolved in a liquid hydrocarbon might be removed using the process disclosed herein

[0129] For the sake of brevity, only certain ranges are explicitly disclosed herein. However, in addition to recited ranges, any lower limit may be combined with any upper limit to recite a range not explicitly recited, as well as ranges from any lower limit may be combined with any other lower limit to recite a range not explicitly recited, in the same way, ranges from any upper limit may be combined with any other upper limit to recite a range not explicitly recited. Additionally, within a range includes every point or individual value between its end points even though not explicitly recited. Thus, every point or individual value may serve as its own lower or upper limit combined with any other point or individual value or any other lower or upper limit, to recite a range not explicitly recited.

[0130] Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the processes, machines, means, processes, and / or steps described in the specification. As one of the ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, means, processes, and / or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein, may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, means, processes, and / or steps.

Claims

CLAIMSWhat is claimed is:

1. A process to polymerize olefins in a gas phase polymerization reactor to produce a polyethylene, the process comprising:a) contacting hydrogen, nitrogen, ethylene, one or more alpha-olefin comonomers, one or more induced condensing agents (ICAs), and a polymerization catalyst composition in a fluidized bed reaction zone of the gas phase polymerization reactor under polymerization conditions effective to produce polyethylene particles and a reactor gas;b) withdrawing from the fluidized bed reaction zone a portion of the polyethylene particles as product and a portion the reactor gas as a first recycle stream; c) compressing and cooling the first recycle gas stream to produce a second recycle gas stream;d) withdrawing a portion of the second recycle gas stream as a first vent stream and adding the remainder of the second recycle gas stream to the fluidized bed reaction zone;e) providing liquid hydrocarbon feed streams, comprising the one or more alpha-olefin comonomers and the one or more ICAs, wherein at least one of the liquid hydrocarbon feed streams is a contaminated hydrocarbon, the contaminated hydrocarbon comprises a first amount of a gas dissolved in the contaminated hydrocarbon, and the gas comprises a catalyst poison;f) contacting the contaminated hydrocarbon with the first vent stream to produce a treated hydrocarbon stream and a second vent stream, wherein the treated hydrocarbon stream comprises a second amount of the gas, the second vent gas stream comprises a third amount of the gas, and the second and third amounts equal the first amount of gas; andg) adding the liquid hydrocarbon streams other than the at least one contaminated hydrocarbon and the treated hydrocarbon stream and to the fluidized bed reaction zone.

2. The process of claim 1, wherein the one or more alpha-olefin comonomers contain 4 to 12 carbon atoms.

3. The process of claim 1, wherein the one or more alpha-olefin comonomers contain 4 to 8 carbon atoms.

4. The process of claim 1, wherein the one or more alpha-olefin comonomers are present in an amount up to 20 wt%, based on the total weight of the ethylene and the one or more alpha-olefin comonomers.

5. The process of claim 1, wherein the one or more alpha-olefin comonomers are present in an amount in the range of from 0.5 wt% to 14 wt%, based on the total weight of the ethylene and the one or more alpha-olefin comonomers.

6. The process of claim 1, wherein the polymerization catalyst comprises:a) one or more Ziegler-Natta catalysts;b) one or more metallocene catalysts; orc) a combination thereof.

7. The process of claim 1, wherein the ratio of the second amount of gas to the first amount of gas is less than or equal to 0.10.

8. The process of claim 1, wherein the first amount of gas is greater than or equal to1.0 ppmw, based on the weight of the contaminated hydrocarbon.

9. The process of claim 1, wherein the second amount of gas is less than 1.0 ppmw, based on the weight of the contaminated hydrocarbon.

10. The process of claim 1, wherein step f) is performed in a vent column.

11. The process of claim 10, wherein the vent column is operated at a temperature greater than or equal to 5 °C.

12. The process of claim 10, wherein the vent column is operated at a pressure gradient less than or equal to 1.5 psi (10.3 kPa).

13. The process of claim 10, wherein the vent column is operated at a ratio of (L'xN') / (C'xG') is less than 8.0, wherein:L' is a liquid monomer and / or ICA flow to the vent column, wherein the liquid flow comprises the contaminated hydrocarbon (kg / hr) and optionally liquid hydrocarbon from a recovery section receiving polymer product from the gas phase polymerization reactor (kg / hr);N' is the carrier gas concentration in the reactor overhead to the vent column (mol%); C' is the ethylene concentration in the reactor overhead to the vent column (mol%); and G' is the vent column overhead (kg / hr).

14. The process of claim 13, wherein L' further comprises liquid hydrocarbon from a recovery section receiving polymer product from the gas phase polymerization reactor.

15. The process of claim 10, wherein the vent column comprises a packed bed.

16. The process of claim 15, wherein the packed bed comprises structured packing or unstructured packing.

17. The process of claim 15, wherein the contaminated hydrocarbon is added to the vent column above the packed bed.

18. The process of claim 15, wherein the first vent stream is added to the vent column below the packed bed.

19. The process of claim 15, wherein the second vent stream is withdrawn from the vent column above the packed bed.

20. The process of claim 15, wherein the treated hydrocarbon stream is withdrawn from the vent column below the packed bed.

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