Gas phase fluidized bed reactor product discharge system

Abstract

An apparatus may include: a reactor including: a distributor plate, a reactor neck: a reactor straight section having a height H defined from the distributor plate to the reactor neck; a liquid disposed above the distributor plate and having a liquid height; and a fluidized bed comprising electrically insulating granules; and a. product offload line fluidically connected to the reactor and a product discharge tank, wherein the product offload line is configured to discharge the electrically insulating granules to the product discharge tank and wherein the product offload line is positioned on the reactor straight section at a height within a range from greater than 5% to about 95% of height H.

Description

GAS PHASE FLUIDIZED BED REACTOR PRODUCT DISCHARGE SYSTEM CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application 63 / 601,431 filed November 21, 2023, entitled “Gas Phase Fluidized Bed Reactor Product Discharge System”, the entirety of which is incorporated by reference herein. FIELD OF THE INVENTION

[0002] The present disclosure relates to gas phase production of polyolefins. In particular, the present disclosure relates to methods for discharging polymer resin product from fluidized bed reactors. BACKGROUND

[0003] Polyolefins may be produced using gas phase polymerization processes. If the process is a gas phase fluidized bed polymerization process, the process may include a gas stream including one or more monomers continuously passed through a fluidized bed of catalyst and growing polymer particles. As polymerization occurs, a portion of the monomers are consumed and the gas stream is heated in the reactor by the heat of polymerization. A portion of the gas stream exits the reactor and may be recycled back to the reactor with additional monomers and additives. At certain intervals in the process, as granules of polyolefin are formed in the reactor, they must be removed or discharged in order to maintain a workable bed level as well as to obtain the desired commercial product. This is preferably accomplished in a cyclic fashion wherein batches of granules are discharged at once. Since a typical gas phase reactor operates under pressurized conditions, such as 250, 290, 320, 350 psig or more, the process to discharge the granules must be performed by transferring the granules to a lower-pressure environment for processing into a commercial product. This is a cyclic process that involves several steps, some of which can create bottlenecks in the discharge process.

[0004] For example, shutdown or transition procedures in gas phase polymerization reactors can be caused by a buildup of catalyst and polymer on the walls of the reactor, which is known as “sheeting” and “chunking.” Another common problem is the buildup of catalyst and polymer on the internal distribution plate, injection nozzle(s), and / or product discharge nozzle(s), which is known as “plugging” or “plate fouling.” Sheeting, chunking, fouling, and plugging can force a complete reactor shutdown for cleaning and removal of the polymer chunks, which could take several days. Various mechanisms have been proposed to explain these phenomena, includingelectrostatic charges of particles within a reactor, zones of elevated temperature in a reactor leading to excessive polymer stickiness, solids carryover in recycle streams, and the like.

[0005] Some references of potential interest in this regard include: US Patent Nos.9,360,453; 8,441,250; 7,985,811; 7,799,876; 7,774,178; 7,634,937; 6,831,140; and 5,462,999; as well as WO2009 / 014682 and WO2022 / 109518. SUMMARY

[0006] The present systems and methods for gas phase polymerization are believed to offer many advantages, including reduced sheeting and / or other fouling. Disclosed herein is an example reactor system including an apparatus that includes: a reactor including a distributor plate; a reactor neck; a reactor straight section having a height H defined from the distributor plate to the reactor neck; a liquid disposed above the distributor plate and having a liquid height; and a fluidized bed comprising electrically insulating granules; and a product offload line fluidically connected to the reactor and a product discharge tank, wherein the product offload line is configured to discharge the electrically insulating granules to the product discharge tank and wherein the product offload line is positioned on the reactor straight section at a height corresponding to about 5% to about 95% of height H.

[0007] Further disclosed herein is a method including: introducing a feed stream comprising a monomer into a reactor, the reactor comprising: a distributor plate; a reactor neck; a reactor straight section having a height H defined from the distributor plate to the reactor neck; a liquid disposed above the distributor plate and having a liquid height; and a fluidized bed comprising electrically insulating granules; polymerizing at least a portion of the monomer to produce additional electrically insulating granules; and withdrawing a product stream comprising at least a portion of the electrically insulating granules from the reactor to a product discharge tank, wherein the product stream is withdrawn through a product offload line fluidically connected to the reactor and the product discharge tank, and wherein the product offload line is positioned on the reactor straight section at a height corresponding to about 5% to about 95% of height H.

[0008] These and other features and attributes of the disclosed apparatus and methods of the present disclosure and their advantageous applications and / or uses will be apparent from the detailed description which follows.BRIEF DESCRIPTION OF THE DRAWING

[0009] To assist those of ordinary skill in the relevant art in making and using the subject matter hereof, reference is made to the appended drawings, wherein:

[0010] FIG. 1 depicts a schematic of an illustrative gas phase polymerization system in accordance with certain embodiments of the present disclosure.

[0011] FIG. 2 depicts a schematic of an illustrative gas phase polymerization system in accordance with certain embodiments of the present disclosure.

[0012] FIG.3A depicts an illustrative gas phase polymerization system for making polymers with a modified product discharge system, according to one or more embodiments.

[0013] FIG. 3B depicts an illustrative gas phase polymerization system for making polymers with a modified product discharge system, according to one or more embodiments.

[0014] FIG. 3C depicts an illustrative gas phase polymerization system for making polymers with a modified product discharge system, according to one or more embodiments.

[0015] FIG.4 is a graph of the time versus discharge location for a simulation of a gas phase polyethylene reactor, according to one or more embodiments.

[0016] FIG.5 is a graph of the time versus discharge location for a simulation of a gas phase polyethylene reactor, according to one or more embodiments. DETAILED DESCRIPTION

[0017] Disclosed herein are methods of gas phase production of polyolefins. In particular, the present disclosure relates to methods for discharging polymer resin product from fluidized bed reactors during the production of polyethylene.

[0018] 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.

[0019] 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.

[0020] “Cn” as used herein, and unless otherwise specified, the term means hydrocarbon(s) having n carbon atom(s) per molecule, wherein n is a positive integer.

[0021] As used herein, the indefinite article “a” or “an” shall mean “at least one” unless specified to the contrary or the context clearly indicates otherwise. Thus, embodiments using “an alpha-olefin” include embodiments where one, two or more alpha-olefins are used, unless specified to the contrary or the context clearly indicates that only one alpha-olefin is used.

[0022] As used herein, “wt.%” means percentage by weight, “vol%” means percentage by volume, “mol%” means percentage by mole, “ppm” means parts per million, and “ppm wt” and “wppm” are used interchangeably and mean parts per million on a weight basis. All concentrations herein, unless otherwise stated, are expressed on the basis of the total amount of the composition in question.

[0023] “Olefin,” alternatively referred to as “alkene,” is a linear, branched, or cyclic compound of carbon and hydrogen having at least one double bond. For purposes of this specification and the claims appended thereto, when a polymer or copolymer is referred to as “comprising” an olefin, the olefin present in such polymer or copolymer is the polymerized form of the olefin. For example, when a copolymer is described as having an “ethylene” content of 35 wt.% to 55 wt.%, it is understood that the mer unit in the copolymer is derived from ethylene in the polymerization reaction and the derived units are present at 35 wt.% to 55 wt.%, based upon the weight of the copolymer.

[0024] “Polyethylene,” as used herein, means an ethylene homopolymer or a copolymer comprising at least 86 wt.% ethylene. The terms “polyethylene polymer,” “polyethylene,” “ethylene polymer,” “ethylene copolymer,” and “ethylene-based polymer” have the same meaning as polyethylene copolymer, except where otherwise indicated (e.g. where a polyethylene homopolymer is referred to, this means a polymer formed from ethylene monomer without comonomer units, e.g., 100 wt.% ethylene-derived units).

[0025] A “polyethylene grade” is a discrete polyethylene product having a consistent set of properties and is produced using a particular corresponding catalyst and a unique set ofpolymerization conditions. “Polyethylene grade slate,” as used herein, means a discrete number of polyethylene products produced in a selected polymerization reaction zone, wherein each polyethylene product has a consistent set of properties and is produced using a particular corresponding catalyst and a unique set of polymerization conditions.

[0026] A “polymer” has two or more of the same or different repeating units / mer units or simply units. A “homopolymer” is a polymer having units that are the same. A “copolymer” is a polymer having two or more units that are different from each other. A “terpolymer” is a polymer having three units that are different from each other. The term “different” as used to refer to units indicates that the units differ from each other by at least one atom or are different isomerically. The definition of copolymer, as used herein, includes terpolymers and the like. Likewise, the definition of polymer, as used herein, includes homopolymers, copolymers, and the like. Furthermore, the terms “polyethylene copolymer”, “ethylene copolymer”, and “ethylene-based polymer” are used interchangeably to refer to a copolymer that includes at least 50 mol% of units derived from ethylene.

[0027] “Polymerization conditions,” as used herein, means conditions conducive to the reaction of one or more olefin monomers when contacted with an activated olefin polymerization catalyst to produce a polyolefin polymer, including a skilled artisan’s selection of temperature, pressure, reactant concentrations, optional solvent / diluents, reactant mixing / addition parameters, and other conditions within at least one polymerization reactor.

[0028] Nomenclature of elements and groups thereof used herein are pursuant to the NEW NOTATION published in HAWLEYS CONDENSED CHEMICAL DICTIONARY, Thirteenth Edition, John Wiley & Sons, Inc., (1997) (reproduced there with permission from IUPAC), unless reference is made to the Previous IUPAC form noted with Roman numerals (also appearing in the same), or unless otherwise noted.

[0029] “Operating temperature (Top),” as used herein, means the target operating temperature for the polymerization zone in a gas phase reactor to produce a desired grade of polyethylene. The operating temperature (Top) is the target reactor temperature within the set of polymerization conditions associated with the desired grade of polyethylene. The operating temperature (Top) is below the kill temperature (Tk) by a threshold amount. Operating Temperature (Top) is the temperature at which the polymerization reaction is operated in order to prevent reaching the kill temperature (Tk). The threshold amount can vary based on one or more of polyethylene grade, particular reactor configurations, and / or preference of the operatorof a particular reactor. In some embodiments, the threshold amount is 14°F (7.8°C), 15°F (8.3°C), 16°F(8.9°C), or 17°F (9.4°C).

[0030] “Polymerization conditions,” as used herein, means conditions conducive to the reaction of one or more olefin monomers when contacted with an activated olefin polymerization catalyst to produce a polyolefin polymer, including a skilled artisan’s selection of temperature, pressure, reactant concentrations, optional solvent / diluents, reactant mixing / addition parameters, and other conditions within at least one polymerization reactor.

[0031] “Reactor system,” as used herein, means the reactor and piping and equipment containing the circulating loop of cycle fluid, including, but not limited to, the cycle fluid heat exchanger.

[0032] “Chunking,” as used herein, means agglomeration of adjacent polymer particles where such agglomeration forms polymer chunks withing the polymerization zone of the reactor. Chunking occurs when one or more sections of the reactor lose effective fluidization or mixing. Without adequate mixing, the rate of heat removal from these sections is diminished. With the diminished heat removal and continued reaction in these sections, overheating of the polymer can result. The overheating can cause agglomeration or melting or agglomeration of the polymer material, which results in the formation of solid masses, or chunks of polymer. In some cases (such as that described by DeChellis in U.S. Pat. No.5,352,749) fluidization and mixing can be lost throughout the entire fluid bed, resulting in a large chunk comprising essentially all of the reactor contents.

[0033] “Fouling,” as used herein, means agglomeration of adjacent polymer particles where such agglomeration forms resin deposits in holes, piping, and / or tubing that restrict flow in the reactor system. Distributor plate fouling is one of the leading causes of downtime with commercial fluidized bed polymerization reactor systems. Fouling is generally caused by deposition of polymer resin in the numerous small holes in the distributor plate, resulting in reduced fluid flow therethrough or complete blockage thereof. Good mixing of the fluidized bed is needed for uniform temperature control. As the holes in the distributor plate become partially or fully blocked, the ability of the cycle gas entering the fluidized bed to carry heat away from the reacting materials is reduced. Moreover, “hot spots” can develop in areas of low fluid velocity in the fluidized bed (particularly those areas immediately above the partially or fully blocked holes), leading to chunking. Fouling may also occur in the cycle line and / or cycle fluid exchanger.

[0034] “Sheeting,” as used herein, means agglomeration of adjacent polymer particles where such agglomeration forms polymer sheets. In sheeting, tacky particles gather on a surface of the reactor system, such as the walls and / or dome of the reactor vessel, forming a sheet of polymer particles. Progressive cycles in this process may eventually result in the growth of the sheet and its falling into the fluid bed. These sheets can interrupt fluidization, circulation of gas and withdrawal of the product from the reactor and may require a reactor shutdown for removal. Polymerization Process

[0035] FIG.1 depicts an illustrative gas phase polymerization system 100 for making polymers, according to one or more embodiments. The polymerization system 100 can include a reactor 101 in fluid communication with one or more discharge tanks 155, compressors 170, and heat exchangers 175. The polymerization system 100 can also include more than one reactor 101 arranged in series, parallel, or configured independent from the other reactors, each reactor having its own associated discharge tanks 155, compressors 170, and heat exchangers 175, or alternatively, sharing any one or more of the associated discharge tanks 155, compressors 170, and heat exchangers 175. For simplicity and ease of description, the polymerization system 100 will be further described in the context of a single reactor train.

[0036] Reactor 101 can include a cylindrical section 103, a transition section 105, and a velocity reduction zone or dome 107. The cylindrical section 103 is disposed vertically adjacent to the transition section 105. The transition section 105 can expand from a first diameter that corresponds to the diameter of the cylindrical section 103 to a larger diameter adjacent the dome 107. The location or junction at which the cylindrical section 103 connects to the transition section 105 is referred to as the “neck” or the “reactor neck” 104. Dome 107 has a bulbous shape. One or more cycle fluid lines 115 and vent lines 118 can be in fluid communication with the dome 107. Reactor 101 can include the fluidized bed 112 in fluid communication with the dome 107.

[0037] In general, the height to diameter ratio of the cylindrical section 103 can vary in the range of from about 2:1 to about 5:1. The range, of course, can vary to larger or smaller ratios and depends, at least in part, upon the desired production capacity and / or reactor dimensions. The cross-sectional area of dome 107 is typically within the range of from about 2 to about 3 multiplied by the cross-sectional area of the cylindrical section 103.

[0038] The velocity reduction zone or dome 107 has a larger inner diameter than the fluidized bed 112. As the name suggests, the velocity reduction zone slows the velocity of the gas due tothe increased cross-sectional area. This reduction in gas velocity allows particles entrained in the upward moving gas to fall back into the bed 112, allowing primarily only gas to exit overhead of reactor 101 through the cycle fluid line 115. The cycle fluid recovered via cycle fluid line 115 can contain less than about 10 wt.%, less than about 8 wt.%, less than about 5 wt.%, less than about 4 wt.%, less than about 3 wt.%, less than about 2 wt.%, less than about 1 wt.%, less than about 0.5 wt.%, or less than about 0.2 wt.% of entrained particles from the fluidized bed 112.

[0039] The reactor feed via line 110 can be introduced to the polymerization system 100 at any point. For example, the reactor feed via line 110 can be introduced to the cylindrical section 103, the transition section 105, the velocity reduction zone, to any point within the cycle fluid line 115, or any combination thereof. Preferably, reactor feed 110 is introduced to the cycle fluid in cycle fluid line 115 before or after the heat exchanger 175. In the Figure, the reactor feed via line 110 is depicted entering the cycle fluid in cycle fluid line 115 after the heat exchanger 175. The catalyst feed via line 113 can be introduced to the polymerization system 100 at any point. Preferably the catalyst feed via line 113 is introduced to the fluidized bed 112 within the cylindrical section 103.

[0040] The cycle fluid via cycle fluid line 115 can be compressed in compressor 170 and then passed through heat exchanger 175 where heat can be exchanged between the cycle fluid and a heat transfer medium. For example, during normal operating conditions a cool or cold heat transfer medium via line 171 can be introduced to the heat exchanger 175 where heat can be transferred from the cycle fluid in cycle fluid line 115 to produce a heated heat transfer medium via line 177 and a cooled cycle fluid via cycle fluid line 115. In another example, during idling of the reactor 101 a warm or hot heat transfer medium via line 171 can be introduced to the heat exchanger 175 where heat can be transferred from the heat transfer medium to the cycle fluid in cycle fluid line 115 to produce a cooled heat transfer medium via line 177 and a heated cycle fluid via cycle fluid line 115. The terms “cool heat transfer medium” and “cold heat transfer medium” refer to a heat transfer medium having a temperature less than the fluidized bed 112 within reactor 101. The terms “warm heat transfer medium” and “hot heat transfer medium” refer to a heat transfer medium having a temperature greater than the fluidized bed 112 within reactor 101. The heat exchanger 175 can be used to cool the fluidized bed 112 or heat the fluidized bed 112 depending on the operating conditions of the polymerization system 100, e.g., reactor start-up, normal operation, idling, and shut down. Illustrative heat transfer mediums caninclude, but are not limited to, water, air, glycols, or the like. It is also possible to locate the compressor 170 downstream from the heat exchanger 175 or at an intermediate point between several heat exchangers 175.

[0041] After cooling, all, or a portion of the cycle fluid via cycle fluid line 115 can be returned to reactor 101. The cooled cycle fluid in cycle fluid line 115 can absorb the heat of reaction generated by the polymerization reaction. The heat transfer medium in line 171 can be used to transfer heat to the cycle fluid in cycle fluid line 115 thereby introducing heat to the polymerization system 100 rather than removing heat therefrom. The heat exchanger 175 can be of any type of heat exchanger. Illustrative heat exchangers can include, but are not limited to, shell and tube, plate and frame, U-tube, and the like. For example, the heat exchanger 175 can be a shell and tube heat exchanger where the cycle fluid via cycle fluid line 115 can be introduced to the tube side and the heat transfer medium can be introduced to the shell side of the heat exchanger 175. If desired, several heat exchangers can be employed, in series, parallel, or a combination of series and parallel, to lower or increase the temperature of the cycle fluid in stages.

[0042] Preferably, the cycle gas via cycle fluid line 115 is returned to reactor 101 and to the fluidized bed 112 through fluid distributor plate (“plate”) 119. The plate 119 is preferably installed at the inlet to the reactor 101 to prevent polymer particles from settling out and agglomerating into a solid mass and to prevent liquid accumulation at the bottom of the reactor 101 as well to facilitate easy transitions between processes which contain liquid in the cycle fluid line 115 and those which do not and vice versa. Although not shown, the cycle gas via cycle fluid line 115 can be introduced into reactor 101 through a deflector disposed or located intermediate an end of the reactor 101 and the distributor plate 119.

[0043] The catalyst feed via line 113 can be introduced to the fluidized bed 112 within reactor 101 through one or more injection nozzles in fluid communication with line 113. The catalyst feed is preferably introduced as pre-formed particles in one or more liquid carriers (i.e., a catalyst slurry). Suitable liquid carriers can include mineral oil and / or liquid or gaseous hydrocarbons including, but not limited to, propane, butane, isopentane, hexane, heptane octane, or mixtures thereof. A gas that is inert to the catalyst slurry such as, for example, nitrogen or argon can also be used to carry the catalyst slurry into reactor 101. In one example, the catalyst can be a dry powder. In another example, the catalyst can be dissolved in a liquid carrier and introduced into reactor 101 as a solution. The catalyst via line 113 can be introducedinto reactor 101 at a rate sufficient to maintain polymerization of the monomer(s) therein. Hydrogen is added via line 114.

[0044] Fluid via line 161 can be separated from a polymer product recovered via line 117 from reactor 101. The fluid can include unreacted monomer(s), hydrogen, induced condensing agents (ICAs), and / or inert materials. The separated fluid can be introduced to reactor 101. The separated fluid can be introduced to cycle fluid line 115. The separation of the fluid can be accomplished when fluid and product leave reactor 101 via line 117 and enter the product discharge tanks 155 through valve 157, which can be, for example, a ball valve designed to have minimum restriction to flow when opened. Positioned above and below the product discharge tank 155 can be conventional valves 159, 167. Valve 167 allows passage of product therethrough. For example, to discharge the polymer product from reactor 101, valve 157 and valve 159 can be opened while valve 167 is in a closed position. Product and fluid enter the product discharge tank 155. Valve 157 is closed, and the product is allowed to settle in the product discharge tank 155. Valve 159 is then opened permitting fluid to flow via line 161 from product discharge tank 155 to reactor 101. Valve 159 can then be closed and valve 167 can be opened and any product in the product discharge tank 155 can flow into and be recovered via line 168. Valve 167 can then be closed. Although not shown, the product via line 168 can be introduced to a plurality of purge bins or separation units, in series, parallel, or a combination of series and parallel, to further separate gases and / or liquids from the product. The particular timing sequence of the valves 157, 159, 167, can be accomplished by use of conventional programmable controllers which are well known in the art.

[0045] Reactor 101 can be equipped with one or more vent lines 118 to allow venting the bed during start up, idling, and / or shut down. Reactor 101 can be free from the use of stirring and / or wall scraping. The cycle fluid line 115 and the elements therein (compressor 170, heat exchanger 175) can be smooth surfaced and devoid of unnecessary obstructions so as not to impede the flow of cycle fluid or entrained particles.

[0046] The conditions for polymerizations vary depending upon the monomers, catalysts, catalyst systems, and equipment availability. The specific conditions are known or readily derivable by those skilled in the art. For example, the temperatures can be within the range of 70°C to about 110°C. Pressures can be within the range of from about 10 kPag to about 10,000kPag, such as about 500 kPag to about 5,000 kPag, or about 1,000 kPag to about 2,200 kPag, for example. Catalyst Systems

[0047] The term “catalyst system” includes at least one “catalyst component” and at least one “activator,” alternately at least one co-catalyst. The catalyst system can also include other components, such as supports, and is not limited to the catalyst component and / or activator alone or in combination. The catalyst system can include any number of catalyst components in any combination as described, as well as any activator in any combination as described.

[0048] The term “catalyst component” includes any compound that, once appropriately activated, is capable of catalyzing the polymerization or oligomerization of olefins. Preferably, the catalyst component includes at least one Group 3 to Group 12 atom and optionally at least one leaving group bound thereto. The term “leaving group” refers to one or more chemical moieties bound to the metal center of the catalyst component that can be abstracted from the catalyst component by an activator, thereby producing the species active towards olefin polymerization or oligomerization. Suitable activators are described in detail below.

[0049] In some embodiments, the catalyst component used in the polymerization includes a polymerization catalyst selected from the group consisting of metallocene catalysts, Ziegler- Natta catalysts, chromium catalysts, atypical single-site catalysts (e.g., such as pyridyldiamide- transition metal catalysts, bis(2-pentamethylphenylamido)ethyl)amine-transition metal catalysts, Schiff base-transition metal catalysts, etc.), and combinations thereof. In embodiments, the catalyst is a metallocene catalyst, which are particularly susceptible to sheeting and / or chunking triggered by changing polymerization conditions. Metallocene catalysts produce in the gas phase polymerization process produce linear low density polyethylene (LLDPE). LLDPEs made using one or more metallocene catalysts are labeled herein as mLLDPE. The mLLDPE can include copolymers of 80 to 99.9 wt.% ethylene-derived units, with the balance of units derived from one or more C3 to C12 -olefin comonomers (and in particular one or more of butene, hexene, octene; and more preferably hexene). Metallocene catalysts include, but are not limited to: Type 1: an unbridged bis-cyclopentadienyl Group 4 and substituted versions thereof; Type 2: a bridged bis-cyclopentadienyl Group 4 and substituted versions thereof; Type 3: a substituted bulky ligand hafnium transition metal metallocene-type catalyst compound and substituted versions thereof; and Type 4: a dualcatalyst system comprising a bridged bis-cyclopentadienyl Group 4 metal catalyst and an unbridged bis-cyclopentadienyl Group 4 metal catalyst

[0050] As used herein, in reference to Periodic Table “Groups” of Elements, the “new” numbering scheme for the Periodic Table Groups are used as in the CRC Handbook of Chemistry and Physics (David R. Lide, ed., CRC Press 81st ed.2000).

[0051] As used herein, the terms “activator” refers to any compound or combination of compounds, supported or unsupported, which can activate a catalyst compound or component, such as by creating a cationic species of the catalyst component. For example, this can include the abstraction of at least one leaving group (the “X” group in the single site catalyst compounds described herein) from the metal center of the catalyst compound / component. Activators can include Lewis acids such as cyclic or oligomeric poly(hydrocarbylaluminum oxides) and so called non-coordinating activators (“NCA”) (alternately, “ionizing activators” or “stoichiometric activators”), or any other compound that can convert a neutral metallocene catalyst component to a metallocene cation that is active with respect to olefin polymerization. Illustrative Lewis acids include, but are not limited to, aluminoxane (e.g., methylaluminoxane “MAO”), modified aluminoxane (e.g., modified methylaluminoxane “MMAO” and / or tetraisobutyldialuminoxane “TIBAO”), and alkylaluminum compounds. Ionizing activators (neutral or ionic) such as tri (n-butyl)ammonium tetrakis(pentafluorophenyl)boron may be also be used. Further, a trisperfluorophenyl boron metalloid precursor may be used. Any of those activators / precursors can be used alone or in combination with the others. There are a variety of methods for preparing aluminoxane and modified aluminoxanes known in the art.

[0052] The catalyst compositions can include a support material or carrier. As used herein, the terms “support” and “carrier” are used interchangeably and are any support material, including a porous support material, for example, talc, inorganic oxides, and inorganic chlorides. The catalyst component(s) and / or activator(s) can be deposited on, contacted with, vaporized with, bonded to, or incorporated within, adsorbed or absorbed in, or on, one or more supports or carriers. Other support materials can include resinous support materials such as polystyrene, functionalized or crosslinked organic supports, such as polystyrene divinyl benzene polyolefins or polymeric compounds, zeolites, clays, or any other organic or inorganic support material and the like, or mixtures thereof

[0053] Inorganic oxides supports can include Group 2, 3, 4, 5, 13 or 14 metal oxides. The preferred supports include silica, which may or may not be dehydrated, fumed silica, alumina,silica-alumina and mixtures thereof. Other useful supports include magnesia, titania, zirconia, magnesium chloride, montmorillonite, phyllosilicate, zeolites, talc, clays, and the like. Also, combinations of these support materials may be used, for example, silica-chromium, silica- alumina, silica-titania and the like. Additional support materials may include those porous acrylic polymers described in EP 0767184, which is incorporated herein by reference.

[0054] The polymer product(s) produced in the reactor can be or include any type of polymer or polymeric material. For example, the polymer product can include homopolymers of olefins (e.g., homopolymers of ethylene), and / or copolymers, terpolymers, and the like of olefins, particularly ethylene, and at least one other olefin. Illustrative polymers can include, but are not limited to, polyolefins, polyamides, polyesters, polycarbonates, polysulfones, polyacetals, polylactones, acrylonitrile-butadiene-styrene polymers, polyphenylene oxide, polyphenylene sulfide, styrene-acrylonitrile polymers, styrene maleic anhydride, polyimides, aromatic polyketones, or mixtures of two or more of the above. Suitable polyolefins can include, but are not limited to, polymers comprising one or more linear, branched or cyclic C2to C40olefins, preferably polymers comprising propylene copolymerized with one or more C3 to C40 olefins, preferably a C3 to C20 alpha olefin, more preferably C3 to C10 alpha-olefins. More preferred polyolefins include, but are not limited to, polymers comprising ethylene including but not limited to ethylene copolymerized with a C3 to C40 olefin, preferably a C3 to C20 alpha olefin, more preferably propylene and or butene. Polymer Products

[0055] Preferred polymers include homopolymers or copolymers of C2to C40olefins, 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 homo polyethylene, homo polypropylene, propylene copolymerized with ethylene and or butene, 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”), high density polyethylene (“HDPE”), polypropylene, isotactic polypropylene, highly isotactic polypropylene, syndiotactic polypropylene, random copolymer of propylene and ethylene and / or butene and / or hexene, elastomers such as ethylene propylene rubber, ethylene propylene diene monomer rubber, neoprene, and blends ofthermoplastic polymers and elastomers, such as for example, thermoplastic elastomers and rubber toughened plastics.

[0056] 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 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.

[0057] Polymerization conditions in a fluidized bed in a polymerization reaction zone can be controlled both to produce polyethylene polymers having a desired combination of parameters and to maintain the stability of polymerization reaction in a gas phase reactor. Such polymerization conditions include, but are not limited to, reactor temperature, reactor pressure, ethylene monomer feed rate, comonomer type and feed rate, catalyst type and feed rate, comonomer-to-ethylene ratio, rate of addition of hydrogen, an amount of one or more induced condensing agents, an amount of one or more continuity additives, and delta melt initiation temperature (dMIT; see U.S. Pat. No.7,683,140, the contents of which are fully incorporated by reference herein).

[0058] Polyethylene producers typically identify each polyethylene polymer having a particular set of properties by a grade name and / or number. Density and melt index (I2) are generally key parameters associated with each polyethylene polymer grade. For the producer, each such polyethylene polymer grade is associated with a particular set of polymerization conditions. Continuity Additive / Static Control Agent

[0059] In gas-phase polyethylene production processes, it may be desirable to use one or more static control agents to aid in regulating static levels in the reactor. As used herein, a static control agent is a chemical composition which, when introduced into a fluidized bed reactor, may influence or drive the static charge (negatively, positively, or to zero) in the fluidized bed. The specific static control agent used may depend upon the nature of the static charge, and thechoice of static control agent may vary dependent upon the polymer being produced and the single site catalyst compounds being used.

[0060] Control agents such as aluminum stearate may be employed. The static control agent used may be selected for its ability to receive the static charge in the fluidized bed without adversely affecting productivity. Other suitable static control agents may also include aluminum distearate, ethoxylated amines, and anti-static compositions such as those provided by Innospec Inc. under the trade name OCTASTAT. For example, OCTASTAT 2000 is a mixture of a polysulfone copolymer, a polymeric polyamine, and oil soluble sulfonic acid.

[0061] Any of the mentioned control agents may be employed either alone or in combination as a control agent. For example, the carboxylate metal salt may be combined with an amine containing control agent (e.g., a carboxylate metal salt with any family member belonging to the KEMAMINE® (available from Crompton Corporation) or ATMER® (available from ICI Americas Inc.) family of products).

[0062] Other useful continuity additives include ethyleneimine additives useful in embodiments disclosed herein may include polyethyleneimines having the following general formula: —(CH2—CH2—NH)n-, where n may be from about 10 to about 10,000. The polyethyleneimines may be linear, branched, or hyper branched (e.g., forming dendritic or arborescent polymer structures). They can be a homopolymer or copolymer of ethyleneimine or mixtures thereof (referred to as polyethyleneimine(s) hereafter). Although linear polymers represented by the chemical formula —(CH2—CH2—NH)n- may be used as the polyethyleneimine, materials having primary, secondary, and tertiary branches can also be used. Commercial polyethyleneimine can be a compound having branches of the ethyleneimine polymer.

[0063] Under normal polymerization conditions, gas phase fluidized bed reactors have several distinct zones where different phases of matter exist. For example, near the top of the fluidized bed, primarily solid granules (e.g., comprising polymer resin and / or one or more solid catalyst components) and cycle gas are present. Near the bottom of the fluidized bed a combination of solid granules (e.g., comprising polymer resin and / or one or more solid catalyst components), cycle gas, and liquid are present. Near the distributor plate, a combination of liquid and cycle gas are typically present. Liquids in the reactor can come from several sources. One source is from the reactor feed such as when induced condensing agents such as inert hydrocarbons (for example, isomers of butane, pentane, hexane, etc.) are utilized. Additional liquid can come frompolymer melt where the polymer produced becomes molten from the heat generated by the exothermic polymerization reaction. Liquid can also be produced when the reaction conditions such as pressure and temperature cause some the monomer such as ethylene and a co-monomer such as 1-butene or 1-hexene condense to form a liquid phase. The composition of the liquid in the reactor may vary depending on the particular reactor but in general comprises polyethylene (or other polymer melt), monomer and comonomer, as well as catalyst.

[0064] The location of the liquid in the reactor can vary depending on the specific design of the gas-phase fluidized bed reactor. In most reactors, the liquid hold-up is dispersed throughout as droplets suspended in the gas phase. Polymer particles grow by the continuous adsorption of monomer onto the surface. The reaction is exothermic producing heat which is sufficient to produce a liquid layer of polymer melt on the particle. The liquid layer can then be stripped away by the rising gas, forming droplets which are swept upwards with the gas flow but may also drip down due to gravity, thus creating a circulating liquid phase within the reactor.

[0065] The current industry gas phase processes for producing polymers discharge product from only a bottom portion of the reactor. In discharging the polymer product from the bottom portion of the reactor, a relatively large volume of liquid is also discharged with the product. As discussed above in FIG. 1, fluid containing polymer, unreacted monomer(s), hydrogen, induced condensing agents (ICAs), and / or inert materials, is withdrawn from the reactor, and the liquid is separated from polymer and reintroduced into the reactor.

[0066] As discussed above, sheeting and other fouling mechanisms can be quite problematic in such polymerization reactors. For instance, the granules are thought to agglomerate due to any number of effects, such as stickiness resulting from excessive reactor temperature spots, electrostatic charges, and other agglomeration factors. These effects can be even greater in larger polymerization reactors, where additional mass of particles may present operational challenges including increased chunking and sheeting as more particles are available to form sheets or chunks in the reactor. For instance, polymer product particulates near the top of the reactor, such as in the dome of the reactor, tend to be smaller and hotter particles. Smaller and hotter particles have an increased tendency to stick together to form agglomerates which may lead to increased fouling through sheeting and chunking. As the reactor size is scaled up, the number of smaller hotter particles is also increased which further increases the tendency to form sheets and chunks. Conventional gas phase fluidized bed reactors have a product discharge system which offloads product from a location of about 0.5% H to about 5% H, where H is theheight of the straight section of the reactor defined as the section of the rector above the distributor plate to the neck of the reactor. Figs. 3A-3C illustrate H in detail. The product discharge system is positioned slightly above the distributor plate to allow for chunks and sheets to be removed from the reactor.

[0067] Without being limited by theory, the present inventors have surprisingly found that the offloading of polymer product from additional locations in the straight section of the reactor at locations above 5% H to about 95% H has several advantages over offloading the product from the conventional location of about 0.5% H to about 5% H, including that the smaller hotter particles can be removed, thereby reducing sheeting, chunking, and / or other fouling mechanisms within the reactor. Additionally, when the product discharge is located at about 0.5% H to about 5% H, a relatively large volume of liquid is removed when product is discharged from the reactor The liquid portion removed from the reactor is typically routed to the liquid recovery system associated with the reactor to separate the polymer melt from the other component of the liquid such as monomers and catalyst, which are then recycled to the reactor. The liquid recovery system presents a process inefficiency in the production of polymer product as the liquid recovery unit does not contribute to producing more product while still requiring energy to operate. Offloading polymer product from one or more locations in the straight section of the reactor at locations above 5% H to about 95% H has the effect of reducing the amount of liquid withdrawn from the reactor as the liquid concentration at locations relatively higher in the straight section tends to be less than near the distributor plate. Liquid concentration includes the liquid which is absorbed into the polymer product as well as free liquid which has condensed. Thus, withdrawing product from locations above 5% H to about 95% H reduces the load on the liquid recovery system thereby reducing the energy required to operate the liquid recovery system as compared to only discharging product from a location of about 0.5% H to about 5% H.

[0068] Another advantage of discharging polymer from the straight section of the reactor at locations above 5% H to about 95% H is that the particle size distribution of the polymer product can be more readily selected. In reactors where the product is only discharged from a location of about 0.5% H to about 5% H, the particle size distribution of the discharged product is dependent in part on the run time of the reactor between product drops, where a shorter drop time interval generally produces a product with a relatively smaller size and a relatively longer drop time interval generally produces a product with a relatively larger size product. However,the distribution of relatively larger sized particles is reduced with shorter drop times and conversely the distribution of relatively smaller sized particles is reduced with longer drop times. Thus, with conventional product discharge systems discharging from about 0.5% H to about 5% H, the mean particle size d50 tends to start at a relatively lower value which increases when the time between product drops is increased. However, the distribution of particle sizes, such as width of distribution or whether the distribution is multi-modal, or other characteristics of the particle size distribution are not necessarily controllable variables as the time between product offload cycles primarily determines what characteristics of the particle size distribution are. When the polymerized product is withdrawn at one or more locations above 5% H to about 95% H and at the conventional location of 0.5% H to about 5% H, the relatively smaller particles can be removed at a relatively higher location in the straight section and the relatively larger particles can be removed at a relatively lower location in the straight section. A control scheme to discharge a portion of the smaller particles and a portion of the larger particles allows for fine tuning of the final particle size distribution which is withdrawn from the reactor. The bed fluidization can also be controlled by selectively removing larger and smaller particles by observing pressure drop within the reactor and / or fouling rate observed in the rector.

[0069] A further advantage of discharging polymer from the straight section of the reactor at locations above 5% H to about 95% H is that the rate of chunking can be more readily controlled for. As discussed above with reference to FIG.1, the product via line 168 can be introduced to a plurality of purge bins or separation units, in series, parallel, or a combination of series and parallel, to further separate gases and / or liquids from the product. Under normal operating conditions, a portion of the product produced will be unsuitable for use or sale as it does not meet the required product specification. For example, relatively larger chunks of the product may not meet the required product specification and are typically screened out into a purge bin in a downstream product handling system. A screener chunk rate monitor configured to monitor the product from line 168 in a downstream product handling system can be utilized to inform process operators or control systems to the rate of chunking in the reactor. In response to the chunking rate, the product discharge rate from the different locations in the straight section can be adjusted to reduce the chunking rate, such as by removing relatively more of the smaller particles from locations ranging from above 5% H to about 95% H. The screener chunk rate monitor can use any suitable method to measure chunk rate including manual observation or automated monitoring such as using an acoustic monitor or a computer vision program todetermine the chunking rate which can then be used as an input signal in a control system, such as a distributed control system (DCS). The control system can then initiate a control loop and send a signal to discharge polymer product at a location in the straight section above 5% H to offload polymer product with relatively smaller particle size than particles discharged below 5% H.

[0070] Another advantage of discharging polymer from the straight section of the reactor at locations ranging from above 5% H to about 95% H includes that the distributor plate fouling can be reduced. One source of distributor plate fouling is the carry-over of fine particles into the cycle fluid line 115 and / or vent lines 118 as shown in FIG. 1. As discussed above, the polymer product particles in the upper section of the reactor tend to be smaller and therefore have a higher propensity for becoming entrained in the gases flowing upwards in the reactor. Discharging polymer product at relatively higher locations in the straight section allows for removal of a greater fraction of the finer particles which have a higher tendency to carry-over into cycle fluid and vent lines. One method to monitor carry-over rate of fine particles includes utilizing a probe such as a cycle gas static probe and / or an acoustic probe attached to a component of the cycle gas loop such as the piping, heat exchanger, and / or compressor. The probe can output a signal which corresponds to a carry-over rate of fine particles within the cycle fluid and / or vent lines which can be used as an input to a control system, such as a DCS, which can adjust one or more operating parameters to bring the rate of carry-over closer to a setpoint. For example, the control system can issue a command to a control valve to discharge polymer product at a location in the straight section above 5% H to offload polymer product with relatively smaller particle size than particles discharged below 5% H.

[0071] FIG.2 depicts a simplified, illustrative gas phase polymerization system 200 for making polymers with a modified product discharge system, according to one or more embodiments. Gas phase polymerization system 200 includes fluidized bed reactor 202 such as those previously described having a distributor plate 220 disposed therein. As shown in FIG. 2, straight section 216 has a height H defined between distributor plate 220 and neck 218 where 0% H corresponds to the straight section 216 at distributor plate 220, 100% H corresponds to the end of the straight section 216 meeting neck 218, and 50% H corresponds to half the distance between the distributor plate 220 and neck 218. Product offload line 204 is positioned so as to withdraw a product stream from a position in the straight section 216 which corresponds to at least 5% H, preferably greater than 5% H. As discussed above, positioning product offload line204 at a location of at least 5% H, preferably above 5% H, allows for finer control of polymerization system 200 by controlling the amount of liquid which is withdrawn from fluidized bed reactor 202 as well as for selecting the particle sizes of the withdrawn polymer product. For example, a product stream (e.g., as measured in line 204 in the illustration of FIG. 2) may contain 10 wt.% liquid by volume or less, such as within a range from a low of any one of about 0, 0.1, 0.2, 0.5, 0.7, 0.8, 0.9, or 1.0 wt.% liquid by volume to a high of any one of about 1.5, 2, 3, 4, 5, 6, 7, 8, 9, or 10 wt.% liquid by volume, with ranges from any foregoing low end to any foregoing high end contemplated. Liquid includes dissolved liquid in the polymer product plus liquid droplets that leave the reactor.

[0072] To facilitate offloading less liquid and smaller particle sizes from the reactor during an offloading cycle (drop cycle) the product offload line 204 may be positioned above the distributor plate 220 in the fluidized bed reactor 202, above a liquid level within the fluidized bed reactor, or at a position higher than about halfway up the fluidized bed (as measured from the bottom of the fluidized bed). This could be phrased in terms of % of height H of the straight section 216. In general, a product offload line 204 may be positioned along a vertical length of the reactor corresponding to about 0.1% to about 95% of the height H of the straight section 216. For example, a product offload line 204 can be positioned along the vertical length of the reactor at a height above the distributor plate 220 and corresponding to X% of the height H of the straight section 216, where X can be within the range from a low of any one of about 0.1, 0.5, 1, 5, 8, 10, 15, 20, 30, 40, 50, 60, 70, 80, or 90; to a high of any one of about 0.5, 510, 20, 30, 40, 50, 60, 70, 80, 90, or 95, with ranges from any foregoing low end to any foregoing high end contemplated (provided the high end is greater than the low end), such as from about 10% to about 95% of H; or about 50% to about 75% of H; or about 50% to about 95% of H; or about 70% to about 95% of H; or about 90% to 95% of H. While not shown in FIG.2, it should be understood that a conventional product offload line location corresponding to 5% or less of H can also be employed to withdraw polymer product from fluidized bed reactor 202.

[0073] It should be noted that the height of the product offload line along the reactor will affect the motive pressure within the product offload line to move the polymer within the product offload line. Thus, in general, the higher the discharge line the lower the motive pressure within the discharge line. A lower motive pressure may reduce product tank fill efficiency for each product drop. Therefore, it can be beneficial to utilize a product offload line height that balancesthe lower motive pressure encountered at greater heights against the reduced amount of liquid offload enjoyed at greater heights.

[0074] In some embodiments, the product offload line 204 may include a dielectric coating on the interior such as titanium dioxide, silicon dioxide, and / or aluminum oxide, for example; other examples include polymeric coatings (e.g., epoxy, natural or synthetic rubbers, urethane-based polymers, polyvinyl chloride, acrylic-based polymers, or the like). Moreover, it is envisioned that any equipment in communication with the product offload line 204 can be provided with such dielectric coatings, such as portions or all of a discharge tank (e.g., discharge tank 206), and / or portions of the wall of the reactor 202 proximate to the offload line 204, as well as any and all valves along the offload line 204. As an alternative to dielectric coating on an offload line 204, an interior tube or other conduit made of any one or more of the dielectric materials just discussed could be disposed within the offload line 204 for conveying granules within the product offload line 204.

[0075] Flow through product offload line 204 into discharge tank 206 can be controlled by at least one valve (e.g., as shown in FIG.2 along line 204). Once a desired amount of product is offloaded from the reactor, the valve may close and isolate discharge tank 206. Gas may be withdrawn from discharge tank 206 using line 210, and a portion of the gas may optionally be purged as stream 212 (e.g., sent to flare or other processing outside the reaction system), and the remaining gas may be reintroduced into reactor 202 through return line 214. Return line 214 can be located on the straight section 216 at a location corresponding to about 80% H to about 100% H with the proviso that the return line 214 is positioned in the straight section 216 above product offload line 204. Product stream 208 may be withdrawn from discharge tank 206 and sent to a product handing unit for further processing such as separation of further gasses and / or liquids from the polymer product and other finishing operations well known in the art.

[0076] Moreover, in various embodiments, multiple product offload lines may be utilized, each fluidly connected to the reactor at a location along the reactor at a respective percentage of height H of straight section 216. Each product offload line can, respectively, be located at any of the heights discussed above in connection with product offload line 204. For instance, a first product offload line can be fluidly connected to the reactor at a first height corresponding to 10-50% of the fluidized bed height H; and a second product offload line can be fluidly connected to the reactor at a second height corresponding to 50-95% of H. It will be appreciated that each of the first height and the second height can independently be within any of thepercentages of H recited above for line 204; and furthermore that a third, fourth, or more product offload line can be utilized (each likewise at a respective height within the range of %H previously disclosed).

[0077] For example, FIG.3A depicts an illustrative gas phase polymerization system 300 for making polymers with a modified product discharge system, according to one or more embodiments. Gas phase polymerization system 300 includes fluidized bed reactor 302 such as those previously described. Fluidized bed reactor 302 includes straight section 324 which has a height H defined between distributor plate 316 and reactor neck 322. As shown in FIG.3A, first product offload line 304 is positioned at a height of the straight section 324 corresponding to a conventional product discharge system location of about 0.5% H to 5% H, A second product offload line 306 is positioned above first product offload line 304 and separated from first product offload line 304 by a height “X.” The position of the second product offload line 306 on straight section 324 can be from about 5% H up to about 95% H; preferably, the second product offload line 306 is also located below the height of return line 328, as illustrated in FIG. 3A.

[0078] Each of first product offload line 304 and second product offload line 306 are fluidically connected to an interior of the reactor, such that each product offload line can withdraw a product stream from the corresponding position on the straight section 324 of the reactor. Once a desired amount of product is offloaded from the reactor through first product offload line 304, second product offload line 306, or a combination thereof, the valve corresponding to each product offload line may close and isolate discharge tank 312. Gas may be withdrawn from discharge tank 312 using line 308, and a portion of the gas may optionally be purged as stream 326 (e.g., sent to flare or other processing outside the reaction system), and the remaining gas may be reintroduced into fluidized bed reactor 302 through return line 328. Return line 328 can be located on the straight section 324 at a location corresponding to about 80% H to about 100% H with the proviso that the return line 328 is preferably positioned in the straight section 324 above second product offload line 306. A cycle gas purge line 320 (such as cycle fluid line 115 described in FIG.1) can be provided to sweep remaining gases, liquids, and / or products from first product offload line 304, second product offload line 306, or a combination thereof.

[0079] FIG. 3B depicts an alternative illustrative gas phase polymerization system 300 for making polymers with a modified product discharge system, according to one or more embodiments. Gas phase polymerization system 300 includes fluidized bed reactor 302 such asthose previously described. As shown in FIG.3B, first product offload line 304 and a second product offload line 306 are separated by height “Y,” where “Y” is greater than “X” from FIG. 3A.

[0080] FIG. 3C depicts an alternative illustrative gas phase polymerization system 300 for making polymers with a modified product discharge system, according to one or more embodiments. Gas phase polymerization system 300 includes fluidized bed reactor 302 such as those previously described. As shown in FIG. 3C, the system 300 includes a first product offload line 304, a second product offload line 306 located at a height “X” above the first product offload line 304, and a third product offload line 330 located at a height “Y” above the first product offload line 304.

[0081] With further reference to FIGs. 3A-3C, to facilitate offloading less liquid from the reactor during an offloading cycle (drop cycle), product offload valves associated with each of first product offload line 304, second product offload line 306, and / or third product offload line 330, are opened and product is withdrawn into product chamber 312. The product offload valves associated with each of the product offload lines can be individually controlled such that the product offloaded has the desired properties as discussed above including for example selecting for particle size of the withdrawn product. Once the drop cycle is completed, the product offload valves are closed, and the polymer product is transferred to product blow tank 314 and withdrawn as product stream 318, which may optionally be sent to a finishing section for further processing as is known in the art (e.g., blending with one or more additives, extrusion and pelletization, and / or the like). A cycle purge gas 320 can be introduced to purge any remaining product from each of the product offload lines.

[0082] A product discharge system can include the product offload valves disposed on each of the product offload lines and a controller for controlling the position of the product offload valves. Optionally, the product discharge system further includes instrumentation to measure a property of the product that is offloaded from each of the locations in the reactor. For example, the instrumentation can measure temperature, density, particle size distribution, liquid volume %, solid volume %, or any other desired physical properties. Instrumentation can include temperature probes, density measurement devices, particle size measurement devices such as optical devices, and combinations thereof. In embodiments, the product discharge system is integrated into a control system, such as a local control system or a distributed control system.

[0083] A distributed control system (DCS) is a computer-based control system that is used to monitor and control processes in a chemical plant. A DCS can be used to control a wide variety of processes, including distillation columns, reactors, and pumps, for example and may be integrated across several units such that simultaneous control of multiple units in response to a single signal may be accomplished. A DCS typically consists of a number of components, including: sensors: these devices measure the physical properties of the process, such as temperature, pressure, and flow rate, controllers: these devices use the data from the sensors to calculate the necessary adjustments to the process, actuators: these devices implement the control commands from the controllers, such as opening or closing valves, and a human- machine interface (HMI): this is the graphical user interface that allows operators to monitor and control the process. The DCS uses various types of logic control such as PID controllers, ladder logic, and sequential function charts to control the processes. The logic control is programmed into the DCS software and is used to ensure that the equipment operates within predefined limits.

[0084] For example, the controller associated with the product discharge system or the DCS can issue a control signal to open one or more of the product offload valves to initiate a product drop cycle. During the product drop cycle, instrumentation reports back to the controller or DCS physical properties of the product within the offload line such as particle size distribution, temperature, liquid percent, or any other useful physical property. The controller or DCS can monitor the physical properties of the product and compare the measured property to a setpoint property and in response, adjust a position of one or more the product offload valves.

[0085] In various embodiments, the controller can operate the product offload valves (which can also be referred to as product discharge valves) in several ways. For example, the controller could control the product offload valves to alternate between a “top” and “bottom” product drop whereby a product offload valve disposed on an offload line at a relatively higher portion of the reactor and a product offload valve disposed on an offload line at a relatively lower portion of the reactor are opened in an alternating manner. Additionally, the controller can control the product offload valves to discharge a desired volume or mass from a top position on the reactor and a desired volume or mass from a bottom position on the reactor. In such a scheme, a controller such as a PID controller, opens the product offload valves by an amount such that the desired mass / volume distribution of product is withdrawn from the reactor. Additionally, the controller can control the product offload valves to perform a desired number of bottom or topproduct drops or control the number of alternating product drops between the bottom and top. In such a scheme, the controller can alternate between the number of drops from the top and bottom such as 1 bottom drop followed by 1 top product drop, or, 2 bottom product drops followed by 2 top product drops, or, 1 bottom product drop followed by 3 top product drops, for example.

[0086] The offload valve from the reactor can be sized such that a discharge rate of product to flow through the offload valve at a rate of at least 0.01 ton granules / second, for example in a range of 0.05 to 0.1 ton granules / second. Alternatively, 0.01 to 0.05 ton granules / second, 0.05 to 0.1 ton granules / second, 0.1 ton granules / second to 0.2 ton granules / second, or any ranges therebetween. In embodiments, the offload valve has a diameter in a range of from 6 inches (152 mm) to 20 inches (508 mm). Alternatively, from 6 inches (152 mm) to 8 inches (203.2 mm), from 8 inches (203.2 mm) to 14 inches (355.6 mm), from 14 inches (355.6 mm) to 20 inches (508 mm), or any ranges therebetween.

[0087] The granules discharged through the system comprise solid polymer product (such as any polymer product described herein). In some instances, the granules can comprise primarily solid polymer product, and may also include one or more solid catalyst components in minor amounts.

[0088] Furthermore, although the discussion herein is related primarily to fluidized bed polymerization reactors, it is believed that the principles described herein could be equally applied to other industrial fluidized bed contexts. ADDITIONAL EMBODIMENTS

[0089] Accordingly, the present disclosure relates to methods for discharging polymer resin product from fluidized bed reactors. The methods and systems may include any of the various features disclosed herein, including one or more of the following embodiments.

[0090] Embodiment 1. An apparatus comprising: a reactor comprising: a distributor plate; a reactor neck; a reactor straight section having a height H defined from the distributor plate to the reactor neck; a liquid disposed above the distributor plate and having a liquid height; and a fluidized bed comprising a plurality of granules (optionally wherein said granules comprise a polymer product); and a product offload line fluidically connected to the reactor and a product discharge tank, wherein the product offload line is configured to discharge the granules to the product discharge tank and wherein the product offload line is positioned on the reactor straight section at a height within a range from greater than 5% to about 95% of height H (such as withina range from a low of any one of about 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90% of height H to a high of any one of about 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95% of height H, with ranges from any foregoing low end to any foregoing high end contemplated, such as from 20% to 50% H, or 25% to 35% H, or 30% to 70% H, or 35% to 55% H, or 20% to 80% H, etc.).

[0091] Embodiment 2. The apparatus of embodiment 1, further comprising a return line fluidically coupled to the product discharge tank and the reactor straight section, wherein the return line is positioned on the reactor straight section at a position corresponding to about 80% to about 100% of height H, and wherein the return line is positioned on the reactor straight section above the product offload line.

[0092] Embodiment 3. The apparatus of any of embodiments 1-2, further comprising a second product offload line fluidically coupled to the reactor and the product discharge tank and / or a second product discharge tank, wherein the second product offload line is positioned on the reactor straight section at a height between the first product offload line and the return line.

[0093] Embodiment 4. The apparatus of embodiment 2, further comprising a second product offload line fluidically coupled to the reactor and the product discharge tank and / or a second product discharge tank, wherein the second product offload line is positioned on the reactor straight section at a height corresponding to less than about 5% H.

[0094] Embodiment 5. The apparatus of embodiment 4, further comprising a third product offload line fluidically coupled to the reactor and any one of the product discharge tank, a second product discharge tank, and / or a third product discharge tank, wherein the third product offload tank is positioned on the reactor straight section at a height between the second product offload line and the return line.

[0095] Embodiment 6. The apparatus of embodiment 3, wherein the product offload line and / or the second product offload line comprise a dielectric material disposed on an interior surface of the product offload line.

[0096] Embodiment 7. The apparatus of embodiment 6, wherein the dielectric material comprises at least one material selected from the group consisting of titanium dioxide, silicon dioxide, aluminum oxide, and combinations thereof.

[0097] Embodiment 8. The apparatus of any of embodiments 1-6, wherein the product discharge tank has a top portion and a bottom portion, wherein the product discharge tankcomprises an inlet at the top portion fluidly connected to the product offload line and wherein the product discharge tank comprises an outlet fluidically coupled to a product blow tank.

[0098] Embodiment 9. A method comprising: introducing a feed stream comprising a monomer into a reactor, the reactor comprising: a distributor plate; a reactor neck; a reactor straight section having a height H defined from the distributor plate to the reactor neck; a liquid disposed above the distributor plate and having a liquid height; and a fluidized bed comprising a plurality of granules (optionally wherein said granules comprise a polymer product); polymerizing at least a portion of the monomer to produce additional granules; and withdrawing a product stream comprising at least a portion of the granules from the reactor to a product discharge tank, wherein the product stream is withdrawn through a product offload line fluidically connected to the reactor and the product discharge tank, and wherein the product offload line is positioned on the reactor straight section at a height within a range from greater than 5% to about 95% of height H (such as within a range from a low of any one of about 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90% of height H to a high of any one of about 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95% of height H, with ranges from any foregoing low end to any foregoing high end contemplated, such as from 20% to 50% H, or 25% to 35% H, or 30% to 70% H, or 35% to 55% H, or 20% to 80% H, etc.).

[0099] Embodiment 10. The method of embodiment 9, further comprising withdrawing a second product stream through a second product offload line fluidically coupled to the reactor and the product discharge tank and / or a second product discharge tank, wherein the second product offload line is positioned on the reactor straight section at a height corresponding to less than about 5% H.

[0100] Embodiment 11. The method of embodiment 10, wherein the product stream and the second product stream are withdrawn from the reactor simultaneously.

[0101] Embodiment 12. The method of embodiment 10, wherein the product stream and the second product steam are withdrawn from the reactor separately.

[0102] Embodiment 13. The method of embodiment 10, wherein the product offload line and / or the second product offload line comprises a dielectric material disposed on an interior of the product offload line.

[0103] Embodiment 14. The method of embodiment 13, wherein the dielectric material comprises at least one material selected from the group consisting of titanium dioxide, silicon dioxide, aluminum oxide, and combinations thereof.

[0104] Embodiment 15. The method of embodiment 10, wherein the reactor further comprises: dome disposed above the reactor neck; a cycle fluid line fluidically coupled to the dome and a bottom portion of the distributor plate; and a means to monitor a carry-over rate of the granules from the dome into the cycle fluid line.

[0105] Embodiment 16. The method of embodiment 15, wherein the means to monitor the carry-over rate comprises a cycle gas static probe and / or an acoustic probe.

[0106] Embodiment 17. The method of embodiment 15, further comprising withdrawing the product stream from the product offload line in response to the carry over rate of the granules.

[0107] Embodiment 18. The method of embodiment 10, further comprising measuring a chunking rate of the granules and withdrawing the product stream from the product offload line in response to the chunking rate of the granules.

[0108] Embodiment 19. The method of embodiment 18, wherein measuring the chunking rate of the granules comprises utilizing an acoustic probe and / or a computer vision system.

[0109] Embodiment 20. The method of embodiment 9, wherein the reactor further comprises a return line fluidically coupled to the product discharge tank and the reactor straight section, wherein the return line is positioned on the reactor straight section at a position corresponding to about 80% to about 100% of height H, and wherein the return line is positioned on the reactor straight section above the product offload line.

[0110] Embodiment 21. The method of any one of embodiments 9-20, wherein the granules comprise a polymer product.

[0111] Embodiment 22. The method of Embodiment 21, wherein the polymer product comprises an ethylene homopolymer or a copolymer of ethylene and one or more olefin comonomers.

[0112] Embodiment 23. The method of Embodiment 22, wherein the one or more olefin comonomers are selected from the group consisting of 1-butene, 1-hexene, and 1-octene.To facilitate a better understanding of the present invention, the following examples of certain aspects of some embodiments are given. In no way should the following examples be read to limit, or define, the entire scope of the disclosure.EXAMPLE

[0113] In this example, sample data from a gas phase fluidized bed reactor was used as an input to a computational fluid dynamics computer simulation. The simulation was performed with varying heights for the product nozzle discharge location along the vertical height of the reactor. The simulation was used to calculate an estimated resin discharge time at each nozzle discharge location, the estimated resin temperature difference at the discharge location as compared to median bed temperature across the entire bed and estimated liquid loading of the product. Gas phase fluidized bed reactors are typically operated in “humid” environment where for a particular resin product grade and / or type of catalyst used, the reactor conditions and feed composition are set such that a portion of the gas phase is condensed back to liquid (this is sometimes referred to as condensed mode operation of such reactors). In this example, the resin vs. bed temperature simulation was performed with 3 condensing assumptions of 25, 20, and 15 wt.% condensing.

[0114] The results of the simulation are shown in Table 1. In Table 1, the nozzle discharge location is the vertical height (in feet) above the distributor plate (the height of which is defined as 0 ft). The % of straight section is the percentage height of the discharge nozzle relative to the height H of the straight section of the gas phase fluidized bed reactor, and may alternatively be referred to as %H as is done throughout this disclosure. Estimated resin discharge time is time period (in sec) for discharge of the resin (e.g., time during which a batch or a single “dump” of resin is discharged via the offtake line(s) before the valves on the offtake line(s) are closed). The effective capacity is an estimated amount of product which can be discharged from the nozzle location relative to the control case (defined as having 100% effective capacity) for ease of comparison. As the nozzle location height is increased, the motive force to discharge product is decreased, resulting in a decreased capacity to discharge product from the reactor. The estimated liquid loading is the amount of liquid absorbed into the solid product granules, reported as wt.% of the total weight of solid and liquid measured at the discharge nozzle.Table 1 Control Case 1 Case 2 Case 3 Case 4 Comments N l Di h

[0115] In addition, expected discharge time vs. discharge height (as %H) was plotted for various different values of %H and is plotted in FIG. 4; likewise, a similar plot of expected discharge time vs. height (in ft) is presented in FIG.5. From reviewing the modeled estimates in FIGS.4 and 5, as well as the modeled discharge times in the Control Case and Cases 1-4 as reported in Table 1, it was observed that discharging the product from higher in the reactor corresponded to hotter and drier product particles. For example, in case 4 it was observed thatthe discharge temperature is close to the median bed temperature whereas in case 1 the discharge temperature is relatively cooler than the median bed temperature. Additionally, liquid loading in case 4 is lower compared to the control. It was further observed that the change in temperature was relatively stable for each of the cases of 15 wt.%, 20 wt.%, and 25 wt.% condensing. For the tested cases, case 3 provided relatively highest performance as compared to case 1, case 2, and case 4 with the liquid loading being close to that of case 4 while having nearly the same effective capacity as case 2. This reflects a good balance of the trade-off between slower discharge (at greater height) vs. greater sheeting prevention (discharge of particles having relatively warmer temperatures at greater height, and further having relatively less liquid loading), and suggests that a particularly advantageous location of a product offload line may be at height within a range from about 25% H to about 35% H.

[0116] 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. Ranges for various characteristics and attributes disclosed herein are listed as sequentially narrowing ranges. However, it should be understood that any lower endpoint of any ranges can be paired with any upper endpoint for the same characteristic or attribute, and such pairings are also intended to be disclosed herein. All patents, test procedures, and other documents cited in this application are fully incorporated herein by reference for all jurisdictions in which such incorporation is permitted. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the processes, machines, means, methods, 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, methods, 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, methods, and / or steps.

Claims

CLAIMS 1. An apparatus comprising: a reactor comprising: a distributor plate; a reactor neck; a reactor straight section having a height H defined from the distributor plate to the reactor neck; a liquid disposed above the distributor plate and having a liquid height; and a fluidized bed comprising a plurality of granules; and a product offload line fluidically connected to the reactor and a product discharge tank, wherein the product offload line is configured to discharge the granules to the product discharge tank and wherein the product offload line is positioned on the reactor straight section at a height within a range from greater than 5% to about 95% of height H.

2. The apparatus of claim 1, further comprising a return line fluidically coupled to the product discharge tank and the reactor straight section, wherein the return line is positioned on the reactor straight section at a position corresponding to about 80% to about 100% of height H, and wherein the return line is positioned on the reactor straight section above the product offload line.

3. The apparatus of claim 2, further comprising a second product offload line fluidically coupled to the reactor and the product discharge tank and / or a second product discharge tank, wherein the second product offload line is positioned on the reactor straight section at a height between the first product offload line and the return line.

4. The apparatus of claim 2, further comprising a second product offload line fluidically coupled to the reactor and the product discharge tank and / or a second product discharge tank, wherein the second product offload line is positioned on the reactor straight section at a height corresponding to less than 5% H.

5. The apparatus of claim 4, further comprising a third product offload line fluidically coupled to the reactor and any one of the product discharge tank, a second product discharge tank, and / ora third product discharge tank, wherein the third product offload tank is positioned on the reactor straight section at a height between the second product offload line and the return line.

6. The apparatus of claim 1 or any one of claims 2-5, wherein one or more of the product offload lines comprises a dielectric material disposed on an interior surface of the product offload line.

7. The apparatus of claim 6, wherein the dielectric material comprises at least one material selected from the group consisting of titanium dioxide, silicon dioxide, aluminum oxide, and combinations thereof.

8. The apparatus of claim 1 or any one of claims 2-7, wherein the product discharge tank has a top portion and a bottom portion, wherein the product discharge tank comprises an inlet at the top portion fluidly connected to the product offload line and wherein the product discharge tank comprises an outlet fluidically coupled to a product blow tank.

9. A method comprising: introducing a feed stream comprising a monomer into a reactor, the reactor comprising: a distributor plate; a reactor neck; a reactor straight section having a height H defined from the distributor plate to the reactor neck; a liquid disposed above the distributor plate and having a liquid height; and a fluidized bed comprising a plurality of granules; polymerizing at least a portion of the monomer to produce additional electrically insulating granules; and withdrawing a product stream comprising at least a portion of the electrically insulating granules from the reactor to a product discharge tank, wherein the product stream is withdrawn through a product offload line fluidically connected to the reactor and the product discharge tank, and wherein the product offload line is positioned on the reactor straight section at a height within a range from greater than 5% to about 95% of height H.

10. The method of claim 9, further comprising withdrawing a second product stream through a second product offload line fluidically coupled to the reactor and the product discharge tank and / or a second product discharge tank, wherein the second product offload line is positioned on the reactor straight section at a height corresponding to less than 5% H.

11. The method of claim 10, wherein the product stream and the second product stream are withdrawn from the reactor simultaneously.

12. The method of claim 10, wherein the product stream and the second product steam are withdrawn from the reactor separately.

13. The method of claim 9 or any one of claims 10-12, wherein the one or more of the product offload lines comprises a dielectric material disposed on an interior of the product offload line.

14. The method of claim 13, wherein the dielectric material comprises at least one material selected from the group consisting of titanium dioxide, silicon dioxide, aluminum oxide, polymeric coatings, and combinations thereof.

15. The method of claim 10, wherein the reactor further comprises: a dome disposed above the reactor neck; a cycle fluid line fluidically coupled to the dome and a bottom portion of the distributor plate; and a means to monitor a carry-over rate of the electrically insulating granules from the dome into the cycle fluid line.

16. The method of claim 15, wherein the means to monitor the carry-over rate comprises a cycle gas static probe and / or an acoustic probe.

17. The method of claim 15, further comprising withdrawing the product stream from the product offload line in response to the carry over rate of the electrically insulating granules.

18. The method of claim 10, further comprising measuring a chunking rate of the electrically insulating granules and withdrawing the product stream from the product offload line in response to the chunking rate of the electrically insulating granules.

19. The method of claim 18, wherein measuring the chunking rate of the electrically insulating comprises granules comprise utilizing an acoustic probe and / or a computer vision system.

20. The method of claim 9, wherein the reactor further comprises a return line fluidically coupled to the product discharge tank and the reactor straight section, wherein the return line is positioned on the reactor straight section at a position corresponding to about 80% to about 100% of height H, and wherein the return line is positioned on the reactor straight section above the product offload line.

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