WO2019173030A1 - Methods of preparing and monitoring a seed bed for polymerization reactor startup - Google Patents

Abstract

Methods of preparing a polymerization reactor for startup including the step of providing an alkyl solution to the polymerization reactor to remove moisture from the seed bed followed by additional step(s) are provided herein.

Description

METHODS OF PREPARING AND MONITORING A SEED BED

FOR POLYMERIZATION REACTOR STARTUP

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit to Serial No. 62/640,328, filed March 8, 2018, the disclosure of which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

[0002] The present disclosure is generally directed toward polymerization reactor startups, and more specifically directed to a polymerization reactor startup process that includes drying polymer granules in the seed bed with an alkyl solution injected into the reactor and onto the seed bed.

BACKGROUND OF THE INVENTION

[0003] Reactor start-up is an important aspect of reactor operability and process continuity in polymerization processes. For example, during a gas phase polymerization process, a fluidized bed reactor can contain a fluidized dense-phase bed including a mixture of reaction gas, polymer (resin) particles, a catalyst system, and optionally catalyst modifiers or other additives. Before such a polymerization reaction begins, a seed bed is loaded into the polymerization reactor, or is already present in the reactor from a previous polymerization. The seed bed is typically granular material of polymer particles.

[0004] Moisture trapped in polyethylene granules can generate electrostatic charges in the seed bed and has been a leading cause for poor/failed startups. To mitigate electrostatic charges, the seed bed requires low levels of residual moisture. Hot nitrogen can be passed through the seed bed to assist in moisture removal. However, it is uneconomical to use only nitrogen because of its decreased removal efficiency when the concentration of trapped moisture in the polyethylene granules become low.

[0005] A need exists, therefore, to economically reduce moisture from the seed bed after nitrogen drying efficiency decreases thus increasing the likelihood of success of the polymerization reactor startup.

SUMMARY OF THE INVENTION

[0006] Methods of preparing a polymerization reactor having a seed bed for reactor startup are provided herein. The present methods comprise the steps of injecting an alkyl solution onto the seed bed; soaking the seed bed for at least one hour; determining the ethane concentration in the reactor where soaking the seed bed is continued if ethane concentration is increasing; and commencing reactor startup when ethane concentration has reached an equilibrium. As provided herein, a rising ethane concentration is indicative of moisture in the seed bed of the polymerization reactor. Equilibrium of the ethane concentration indicates that moisture has been removed from the seed bed through a reaction between water and an alkyl. In an aspect, the alkyl solution comprises triethylaluminum (TEAL).

[0007] During preparation of the reactor additional optional steps can be performed including, but not limited to, loading the seed bed into the polymerization reactor, purging oxygen from the polymerization reactor, drying out the polymerization reactor, increasing the pressure of the polymerization reactor, testing the polymerization reactor for high and low pressure leaks, supplying the polymerization reactor with ethylene, purging the polymerization reactor with nitrogen, purging the polymerization reactor with an inert, and removing ethylene and/or poisons from the reactor. In an aspect, the inert gas is nitrogen. In an aspect, the flow rate of the alkyl solution to the reactor is at least about 20 kilograms/hour and the polymerization reactor has a pressure of up to 2200 kPag. In an aspect, the polymerization reactor maintains a temperature greater than or equal to 75°C. In an aspect, ethylene is added to the polymerization reactor at a rate of up to 6 tons per hour.

[0008] Also, provided herein are methods for monitoring dryness of a polymerization reactor having a seed bed for reactor startup comprising the steps of: (1) injecting TEAL onto the seed bed; (2) soaking the seed bed for at least one hour; monitoring an ethane concentration in the reactor, where TEAL and water react in the polymerization reactor and the ethane concentration attains equilibrium upon complete exhaustion of absorbed water reacting with TEAL; and (3) commencing with reactor startup upon completion of the TEAL and water reaction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a graph depicting the temperature readings of a six-inch elevation plate temperature indicators over time during Startup A as described in Example III.

[0010] FIG. 2 is a graph depicting the temperature readings of a six-inch elevation plate temperature indicators over time during Startup B as described in Example III.

[0011] FIG. 3 is a graph depicting the temperature readings from the 3 feet elevation skin temperature indicator during Startup A as described in Example III.

[0012] FIG. 4 is a graph depicting the temperature readings from the 3 feet elevation skin temperature indicator during Startup B as described in Example III.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Before the present compounds, components, compositions, and/or methods are disclosed and described, it is to be understood that unless otherwise indicated this invention is not limited to specific compounds, components, compositions, reactants, reaction conditions, ligands, catalyst structures, metallocene structures, or the like, as such may vary, unless otherwise specified. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0014] As used herein, the terms“a” and“the” as used herein are understood to encompass the plural as well as the singular.

[0015] The term,“activator” is used interchangeably with the term co-catalyst and refers to a compound that can activate a catalyst compound by converting the neutral polymerization catalyst to a catalytically active catalyst cation compound. Non-limiting activators, for example, include alumoxanes, aluminum alkyls, ionizing activators, which can be neutral or ionic, and conventional-type cocatalysts. A description of different activators and activation methods. See e.g., PatentNo. 7,858,719, Col. 14, line 21 to Col. 17, line 30, incorporated herein by reference.

[0016] The term, “catalyst compound” can be used interchangeably with the terms “catalyst,”“catalyst precursor,”“transition metal compound,”“transition metal complex,” and “precatalyst.”

[0017] The term,“catalyst system” refers to a catalyst compound and an activator capable of polymerizing monomers.

[0018] The term,“a continuous process” is a process that operates (or is intended to operate) without interruption or cessation but can be interrupted for customary maintenance or an occasional disrupting event. For example, a continuous process to produce a polymer would be one in which the reactants are continuously introduced into one or more reactors (referred to herein in the singular as a“polymerization reactor”) and polymer product is continually or semi-continually withdrawn.

[0019] The term,“metallocene catalyst” refers to an organometallic compound with at least one p-bound cyclopentadienyl (Cp) moiety (or substituted cyclopentadienyl moiety such as indenyl or fluorenyl), and more frequently two p-bound cyclopentadienyl moieties or substituted cyclopentadienyl moieties. This includes other p-bound moieties such as indenyls or fluorenyls or derivatives thereof. When used in relation to metallocene catalysts, the term “substituted” means that a hydrogen group has been replaced with a hydrocarbyl group, a heteroatom, or a heteroatom containing group. For example, methylcyclopentadiene is a Cp group substituted with a methyl group.

[0020] The term, “polymerizable conditions” refers to the process conditions and equipment that are suitable to polymerize olefins into polyolefins. [0021] The term, “polyolefin” and “olefin polymer,” or plural forms thereof, are interchangeable terms referring to a reaction product of a polymerization process where the reaction product contains at least 75 mole%, at least 80 mole%, at least 85 mole%, at least 90 mole%, at least 95 mole%, and/or at least 99 mole% of polymer derived from a hydrocarbon monomer. A hydrocarbon monomer is a monomer made up of carbon and hydrogen. For example, the monomer can be aliphatic or alicyclic hydrocarbons (as defined under “Hydrocarbon” in Hawley's Condensed Chemical Dictionary, 13th edition, R. J. Lewis ed., John Wiley and Sons, New York, 1997).

[0022] The terms,“provide(d),”“pre-load(ed)” and“load(ed)” can be used interchangeably herein to cover all aspects of preloading and loading a seed bed.

[0023] The term,“scavenger” refers to a compound that is typically added to facilitate oligomerization or polymerization by scavenging impurities. Some scavengers can also act as activators and can be referred to as co-activators. A co-activator, that is not a scavenger, can also be used in conjunction with an activator in order to form an active catalyst. A co-activator can be pre-mixed with the transition metal compound to form an alkylated transition metal compound.

[0024] The terms,“support” or“carrier” are used interchangeably and are any porous or non-porous support material. A porous support material, for example, talc, inorganic oxides and inorganic chlorides, for example silica or alumina. Other carriers include resinous support materials such as polystyrene, a functionalized or crosslinked organic support, such as polystyrene divinyl benzene polyolefins or polymeric compounds, or any other organic or inorganic support material and the like, or mixtures thereof.

[0025] The term,“transition metal” refers to a catalyst precursor, a transition metal catalyst, a polymerization catalyst, or a catalyst compound, and these terms are used interchangeably. Examples of transition metal catalysts are in U.S. Patent Nos. 4,115,639, 4,077,904 4,482,687, 4,564,605, 4,721,763, 4,879,359 and 4,960,741. The catalysts to be deactivated include transition metal compounds from Groups 3 to 10, or 4 to 6 of the Periodic Table of Elements.

[0026] The term,“Ziegier-Natta catalyst” means and includes heterogeneous supported catalysts based on titanium compounds as used in polymerization reactions, often m combination with cocatalysts, and homogeneous catalysts based on the complexes of Ti, Zr or Hf that can be used in combination with different organoaluminium cocatalyst, methylaluminoxane or methylalumoxane. Generally, the Ziegier-Natta catalysts are small, solid particles, but certain soluble forms and supported catalysts can be used. [0027] As described herein, a“seed bed” refers to one or more materials, including but not limited to, granular polyolefin resin made of polyolefin product produced in a catalyst system comprising a catalyst such as a Ziegler-Natta catalyst, a chromium containing catalyst, a metallocene catalyst, a Group 15 atom and metal containing catalyst, or mixtures thereof, including bimetallic and mixed catalyst systems described herein. The seed bed can have a narrow or wide range of particle size distribution. In an aspect, the seed bed can or cannot have the same polymer properties as of the polymer product to be produced. The one or more materials (also referred to sometimes as“seed bed material”) can be stored in silos or hopper cars and loaded into a reactor (sometimes referred to herein as a“polymerization reactor”), or remain in the reactor from a previous polymerization process. Often the stored seed bed is exposed to air and moisture.

[0028] A polymerization reactor (a“reactor”) can be "pre-load(ed)" with the one or more materials present in the reactor before the start of the polymerization process. The term, pre- loaded) refers to a reactor startup where the seed bed comprising one or more materials was made in-situ (already present in a reactor) before the startup process begins and prior to charging the seed bed. An example of pre-loading can be found in U.S. Patent Publication No. 2007/0073012. Alternatively, the seed bed can be transferred to the reactor or“loaded” prior to charging the reactor.

[0029] Due to its function, the seed bed in the polymerization reactor is always "pre- loaded" in the reactor in the sense that it is loaded prior to the startup of the polymerization process and reaction. Both terms“pre-load(ed)” and“load(ed)” are used interchangeably with regard to preparing the reactor for startup. In the present methods, the seed bed comprising one or more materials (i.e., granular material and/or polymer particles, and the like) must be pre-loaded or loaded into a reactor and then charged before reactor startup and before the start of a polymerization reaction. Before reactor startup, to remove oxygen from the seed bed, the seed bed and the reactor can be purged using an inert such as nitrogen. As described herein, nitrogen can supplement the removal of a portion of the moisture of the seed bed.

[0030] The one or more materials that comprise the seed bed can be loaded into the polymerization reactor in any of a number of different ways, introducing the one or more materials with (and during) loading of a seed bed into the reactor; introducing of the one or more materials directly into the seed bed via a tube inserted into the seed bed (e.g., through a support tube); and/or introducing the one or more materials via a carrier, for example, such as a liquid or a pressurized gas into the reactor. [0031] Further, the loading/pre-loading step can be accomplished by drying the seed bed previously in the reactor (e.g., the seed bed from a previous polymerization operation) before the start of a new polymerization reaction. The seed bed from the previous polymerization reaction can use the same or a different catalyst system as that of the polymerization reaction to be employed and with the same or different monomer types. In an aspect, the amount of the one or more materials comprising the seed bed is based on the weight of the seed bed in, or to be loaded into, the reactor.

[0032] In performing the present methodologies, an alkyl solution such as TEAL is inj ected (referred to herein as part of the TEAL soak step) into the reactor and onto the seed bed. Triethylaluminium (“TEAL”) is an organoaluminium compound having the formula Al(C₂H₅)3, or AlEt3 where Et = ethyl. It is a volatile, colorless liquid, highly pyrophoric (ignites immediately upon exposure to air or water) and typically stored in stainless steel containers either as a pure liquid or as a solution in hydrocarbon solvents such as hexane, heptane, or toluene. TEAL can be used as a co-catalyst in the industrial production of polyethylene, polypropylene and to produce medium chain alcohols.

[0033] In general, the methodology presented herein includes the steps of providing the seed bed, removing oxygen from the polymerization reactor by purging, and charging the seed bed. The reactor is first prepared for pressure up and then pressurized. The step of removing oxygen generates an 02-free reactor which means and includes a reactor having less than 10000 ppm oxygen present. Prior to and after charging the seed bed, testing of the reactor and reactor system for low and high pressure leaks can be performed. To charge the seed bed, certain auxiliary systems are prepared and made ready for operation. In an aspect, upon starting a cycle gas compressor, nitrogen is provided (supplied) to the polymerization reactor. Then, as described below in Example II, a step of Dry out Reactor can be optionally performed, as required. Once nitrogen is provided to the reactor, ethylene is then provided (also referred to herein as“supplied”) to the reactor. TEAL is then injected into the reactor and onto the seed bed. The seed bed is soaked for at least one hour prior to the next step of small TEAL charge to ensure ethane stabilization followed by purging the polymerization reactor gases and poisons. The TEAL soak step is followed by reactor startup.

[0034] Upon startup and once steady state is obtained, olefins are polymerized under anhydrous conditions in the presence of catalyst and an inert hydrocarbon diluent such as Pentanes, Butanes, toluene, xylene, hexane, heptane, or purified kerosene to produce polyolefins. In gas phase processes, polymerizing one or more monomer(s) can be carried out in the presence of at least one catalyst and, as described below, a condensable agent where the process is operated in a condensed mode. The monomers polymerized can be linear or branched alpha-olefins, C2 to C40 linear or branched alpha-olefins, or C2 to C20 linear or branched alpha-olefins, e.g., ethylene, propylene, butene, pentene, hexene, heptene, octene, nonene, decene, undecene, dodecene, or mixtures thereof. Monomers can also be two or more olefin monomers of ethylene, propylene, butene- 1, pentene- l,4-methyl-pentene-l, hexene- 1, octene- 1, decene- 1, and mixtures thereof. Other monomers include ethylenically unsaturated monomers, diolefms having 4 to 18 carbon atoms, conjugated or nonconjugated dienes, polyenes, vinyl monomers and cyclic olefins. Additional non-limiting examples of specific monomers include butadiene, norbomene, norbomadiene, isobutylene, vinylbenzocyclobutane, ethylidene norbomene, isoprene, dicyclopentadiene and cyclopentane.

[0035] For example, as described herein, gas phase polyethylene processing includes the steps of contacting one or more monomers, at least one catalyst and optionally a condensing agent under polymerizable conditions to produce polyolefins. Condensable agents can include hydrocarbons with little to no solvent power regarding the polymer product(s). Condensing agents include C4-C8 hydrocarbons and mixtures thereof, C4-C6 hydrocarbons and mixtures thereof, including, but not limited to, linear, branched, cyclic, substituted hydrocarbons, as well as the respective isomers. More specifically, the condensing agent can be 2,2- dimethylpropane. 2,2-dimethylpropane, also called neopentane, is a double-branched-chain alkane with five carbon atoms. 2,2-dimethylpropane is the simplest alkane with a quaternary carbon. It is one of the three structural isomers with the molecular formula C5H12 (pentanes), the other two being n-pentane and isopentane.

[0036] Furthermore, polyethylene polymer produced can have a density in the range of 0.860 g/cc to 0.970 g/cc, including but not limited to, in the ranges from 0.880 g/cc to 0.965 g/cc, from 0.900 g/cc to 0.960 g/cc, from 0.905 g/cc to 0.950 g/cc, from 0.910 g/cc to 0.940 g/cc, and/or greater than 0.912 g/cc.

[0037] In an aspect, polyethylene polymers produced by the polymerization reactors described herein can have a weight average molecular weight to number average molecular weight (Mw/Mn) of about 1.5 to about 30, particularly about 2 to about 15, about 2 to about 10, about 2.2 to less than about 8, or about 2.5 to about 8. The ratio of Mw/Mn (or the molecular weight distribution) can be measured by gel permeation chromatography techniques.

[0038] Further, polyethylene polymers produced can have a narrow or broad composition distribution as measured by Composition Distribution Breadth Index (“CDBI”). Further details of determining the CDBI of a copolymer are known to those skilled in the art. See e.g., WO 93/03093. CDBI's can be generally in the range of greater than 50% to 99%, in the range of 55% to 85%, 60% to 80%, greater than 60%, and greater than 65%. Alternatively, CDBI's can be generally less than 50%, less than 40%, and less than 30%.

[0039] Moreover, polyethylene polymers produced in the polymerization reactors described herein can have a melt index (“MI”) as measured by ASTM-D-1238-E in ranges that include, but are not limited to, from about 0.01 dg/min to about 1000 dg/min, from about 0.01 dg/min to about 100 dg/min, from about 0.1 dg/min to about 50 dg/min, or from about 0.1 dg/min to about 10 dg/min. Polyethylene polymers have a melt index ratio (I21.6/I2.16 or for a shorthand“I21/I2”) (measured by ASTM-D-1238-F) from 10 to less than 25, or from about 15 to less than 25. Polymers can have a melt index ratio (I21/I2) of greater than 25, greater than 30, greater than 40, greater than 50, and greater than 65. Further, polyethylene polymers can have a melt index ratio (I21/I2) in the range from 15 to 40, in the range from about 20 to about 35, in the range from about 22 to about 30, or in the range from 24 to 27.

[0040] Described below are polymerization reactions which can be performed in the polymerization reactor comprising the seed bed that has been loaded, charged and treated prior to startup in accordance with the present methods described herein.

Subsequent Operation of the Polymerization Reactor

[0041] As provided herein, after startup and upon reaching a steady state, the polymerization reactor can operate to perform polymerization using any of a variety of different processes including solution, slurry, or gas phase processes. For example, the polymerization reactor can be a fluidized bed reactor that is operated to produce polyolefin polymers by a gas phase polymerization process. Further, the polymerization reactor can be a staged reactor where two or more reactors are employed in series, where a first reactor can produce, for example, a high molecular weight component and a second reactor can produce a low molecular weight component. In operation, polymerization medium can be mechanically agitated or fluidized by the continuous flow of the gaseous monomer and diluent.

[0042] More specifically, in a continuous gas phase fluidized bed reactor, the polymerization reactor comprises a fluidized bed of dense phase material. At startup, the seed bed comprising polymer granules is loaded into the polymerization reactor. Liquid or gaseous feed streams of a primary monomer and hydrogen together with a liquid or gaseous comonomer are combined and then introduced into the fluidized bed, often via an upstream recycle gas line. The fluidized bed reactor for performing a continuous gas phase process typically comprises a reaction zone and a so-called velocity reduction zone. The reaction zone comprises a bed of growing polymer particles, formed polymer particles, and a minor amount of catalyst particles (collectively sometimes referred to herein as “dense phase material”) fluidized by the continuous flow of the gaseous monomer and/or comonomers and diluent to remove heat of polymerization through the reaction zone. Optionally, re-circulated gases (recycled gas) can be cooled and compressed to form liquids that increase the heat removal capacity of the circulating gas stream when readmitted to the reaction zone. This method of operation is referred to as "condensed mode."

[0043] A suitable rate of gas flow into the fluidized bed reactor can be readily determined by simple experiment. The flow rates of monomer and circulating gas into the polymerization reactor is approximately equal to the rate that polymer product and unreacted monomer are withdrawn. The composition of the gas passing through the reactor can be adjusted to maintain a steady state gaseous composition within the reaction zone. Gas leaving the reaction zone is passed to the velocity reduction zone where entrained particles settle down back into the dense phase zone. Gas is compressed in a compressor and passed through a heat exchanger wherein the heat of polymerization is removed, and the gas is returned to the reaction zone.

[0044] To maintain a constant reactor temperature, the temperature of circulating gas can be continuously adjusted up or down to accommodate any changes in the rate of heat generation due to the polymerization. The fluidized bed can be maintained at a constant height by withdrawing a portion of the bed at a rate equal to the rate of formation of particulate product. Polymer product can be removed semi-continuously via a series of valves into a fixed volume chamber, which is simultaneously vented back to the reactor for efficient removal of the product. At the same time, a significant portion of the unreacted gases are recycled into the reactor. Polymer product is purged to remove entrained hydrocarbons and can be treated with a small steam of humidified nitrogen to deactivate any trace quantities of residual catalyst.

[0045] Furthermore, the reactor temperature of the fluidized bed reactor can range from 30°C to l50°C. In general, the reactor temperature is operated at the highest temperature that is feasible, taking into account the sintering temperature of the polymer product within the reactor. The polymerization temperature or reaction temperature typically must be below the melting or "sintering" temperature of the polymer to be formed. Thus, in an aspect, the upper temperature limit is the melting temperature of the polyolefin produced in the reactor.

[0046] Alternatively, the present methods can be used for startup processes of polymerization reactors which can be operated to effect polymerization by a slurry polymerization process. The slurry polymerization process is typically carried out at pressures in the range of from 1 to 50 atmospheres or greater and temperatures in the range of 0°C to l20°C, more particularly from 30°C to l00°C. In slurry polymerization, a suspension of solid, particulate polymer is formed in a liquid polymerization diluent medium to which monomer and comonomers and often hydrogen along with catalyst are added. The suspension including diluent is intermittently or continuously removed from the reactor where the volatile components are separated from the polymer and recycled, optionally after a distillation, to the reactor. The liquid diluent employed in the polymerization medium is typically an alkane having from 3 to 7 carbon atoms, a branched alkane in one embodiment. The polymerization medium employed should be liquid under the conditions of polymerization and relatively inert. When a propane medium is used, the process must be operated above the reaction diluent critical temperature and pressure. In an aspect, a hexane, isopentane or isobutane medium is employed.

[0047] In an aspect, the methods for polymerization reactor startup described herein are useful for the reactor that can perform particle form polymerization, or a slurry process where the temperature is kept below the temperature at which the polymer goes into solution. Furthermore, the polymerization reactor can be a loop reactor or one of a plurality of stirred reactors in series, parallel, or combinations thereof. Non-limiting examples of slurry processes include continuous loop or stirred tank processes.

[0048] As described herein, the polymerization reactor used in connection with the present methodologies can be operated to produce homopolymers of olefins, e.g., ethylene, and/or copolymers, terpolymers, and the like, of olefins, particularly ethylene, and at least one other olefin. For example, the polymerization reactor can produce polyethylenes. Such polyethylenes can be homopolymers of ethylene and interpolymers of ethylene and at least one a-olefm wherein the ethylene content is at least about 50% by weight of the total monomers involved. Exemplary olefins that can be utilized in the reactor are ethylene, propylene, 1- butene, l-pentene, 1 -hexene, l-heptene, l-octene, 4-methylpent-l-ene, l-decene, l-dodecene, l-hexadecene and the like. Also utilizable herein are polyenes such as l,3-hexadiene, 1,4- hexadiene, cyclopentadiene, dicyclopentadiene, 4-vinylcyclohex-l-ene, l,5-cyclooctadiene, 5- vinylidene-2-norbomene and 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 can occur.

[0049] In the production of polyethylene or polypropylene, comonomers can be present in the polymerization reactor. When present, the comonomer can be present at any level with the ethylene or propylene monomer that will achieve the desired weight percent incorporation of the comonomer into the finished resin.

[0050] In addition, hydrogen gas is often used in olefin polymerization to control the final properties of the polyolefin. For some types of catalyst systems, it is known that increasing concentrations (partial pressures) of hydrogen increase the melt flow (MF) and/or melt index (MI) of the polyolefin generated. The MF or MI can thus be influenced by the hydrogen concentration. The amount of hydrogen in the polymerization can be expressed as a mole ratio relative to the total polymerizable monomer, for example, ethylene, or a blend of ethylene and hexane or propene. The amount of hydrogen used in some polymerization processes is an amount necessary to achieve the desired MF or MI of the final polyolefin resin.

[0051] As described herein, the polymerization reactor can be operated to implement a slurry or gas phase processing in the presence of a metallocene catalyst system. As an option, the process can be essentially free of scavengers such as triethylaluminium, trimethylaluminum, tri-isobutylaluminium and tri-n-hexylaluminium and diethyl aluminium chloride, dibutyl zinc and the like. By "essentially free," it is meant that these compounds are not deliberately added to the reactor or any reactor components.

[0052] In the polymerization reactor, supported catalyst(s) can be combined with activators and can be combined by tumbling and/or other suitable means, with up to 2.5 wt.% (by weight of the catalyst composition) of an antistatic agent, such as an ethoxylated or methoxylated amine, an example of which is Atmer AS-990 (Ciba Specialty Chemicals, Basel, Switzerland). Other antistatic compositions include the Octastat family of compounds, more specifically Octastat 2000, 3000, and 5000.

[0053] Examples of polymers that can be produced include but are not limited to 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; norbomene homopolymers and copolymers with one or more C2- C18 alpha olefin; and terpolymers of one or more C2-C18 alpha olefins with a diene.

[0054] Monomers that can be present in the polymerization reactor include one or more of: C2-C18 alpha olefins such as ethylene, propylene, and optionally at least one diene, for example, hexadiene, dicyclopentadiene, octadiene including methyloctadiene (e.g., l-methyl- l,6-octadiene and 7-methyl- l,6-octadiene), norbomadiene, and ethylidene norbomene; and readily condensable monomers, for example, isoprene, styrene, butadiene, isobutylene, chloroprene, acrylonitrile, cyclic olefins such as norbomenes.

[0055] As described herein, any one of many different types of polymerization catalysts can be used in the polymerization process performed in the polymerization reactor. A single catalyst can be used, or a mixture of catalysts can be employed, if desired. The catalyst can be soluble or insoluble, supported or unsupported. It can be a prepolymer, spray dried with or without a filler, a liquid, or a solution, slurry/suspension or dispersion. The catalysts can be used with cocatalysts and promoters well known in the art. Typically these are alkylaluminiums, alkylaluminium halides, alkylaluminium hydrides, as well as aluminoxanes.

[0056] For illustrative purposes only, examples of suitable catalysts include Ziegler-Natta catalysts, chromium based catalysts, vanadium based catalysts (e.g., vanadium oxychloride and vanadium acetylacetonate), metallocene catalysts and single-site or single-site-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.

Catalyst Components and Catalyst Systems

[0057] The following is a non-limiting disclosure of the various catalysts that can be used to produce the polyethylene polymers. All numbers and references to the Periodic Table of Elements are based on the new notation as set out in Chemical and Engineering News, 63(5), 27 (1985), unless otherwise specified.

Conventional Catalysts

[0058] Conventional-type transition metal catalysts are generally referred to as Ziegler Natta catalysts or Phillips-type chromium catalysts. Examples of conventional-type transition metal catalysts are disclosed in U.S. Patent Nos. 4,115,639, 4,077,904 4,482,687, 4,564,605, 4,721,763, 4,879,359 and 4,960,741. The conventional catalyst compounds can be activated using the transition metal compounds from Groups 3 to 10, preferably Groups 4 to 6 of the Periodic Table of Elements.

[0059] These conventional-type transition metal catalysts can be represented by the formula:

MR_X (I),

where M is a metal from Groups 3 to 10, preferably Group 4, more preferably titanium; R is a halogen or a hydrocarbyloxy group; and x is the valence of the metal M, preferably x is 1, 2, 3 or 4, more preferably x is 4. Non-limiting examples of R include alkoxy, phenoxy, bromide, chloride and fluoride. Non-limiting examples of conventional-type transition metal catalysts where M is titanium include TiCb, TiCk, TiBn, Ti(OC2H5)3Cl, Ti(OC2H5)Cb, Ti(OC4H9)3Cl, Ti(OC3H₇)2Cl₂, Ti(OC₂H₅)2Br2, TiCl3. l/3AlCb and Ti(OCi2H₂₅)Cl3. [0060] Conventional chrome catalysts, often referred to as Phillips-type catalysts, can include CrCb, chromocene, silyl chromate, chromyl chloride (CrChCh). chromium-2-ethyl- hexanoate, chromium acetylacetonate (Cr(AcAc)3). Non-limiting conventional chrome catalysts are disclosed in U.S. Patent Nos. 2,285,721, 3,242,099 and 3,231,550.

[0061] For optimization, conventional catalysts can require at least one cocatalyst. Cocatalysts are described U.S. Patent No. 7,858,719, Col. 6, 1. 46 through Col. 7, 1. 45, incorporated herein by reference.

Metallocene Catalysts

[0062] Catalysts that can be used to produce the polyethylene polymer include one or more metallocene compounds (also referred to herein as metallocenes or metallocene catalysts). Metallocene catalysts are generally described as containing one or more ligand(s) and one or more leaving group(s) bonded to at least one metal atom, optionally with at least one bridging group. The ligands are generally represented by one or more open, acyclic, or fused ring(s) or ring system(s) or a combination thereof. These ligands, the ring(s) or ring system(s), can comprise one or more atoms selected from Groups 13 to 16 of the Periodic Table of Elements; in an aspect, the atoms are selected from the group consisting of carbon, nitrogen, oxygen, silicon, sulfur, phosphorous, germanium, boron, and aluminum or a combination thereof. Further, the ring(s) or ring system(s) comprise carbon atoms such as, but not limited to, those cyclopentadienyl ligands or cyclopentadienyl-type ligand structures or other similar functioning ligand structures such as a pentadiene, a cyclooctatetraendiyl, or an imide ligand. The metal atom can be selected from Groups 3 through 15 and the lanthanide or actinide series of the Periodic Table of Elements. The metal can be a transition metal from Groups 4 through 12, and often transition metals can be from Groups 4, 5, and 6, particularly from Group 4.

[0063] Exemplary metallocene catalysts and catalyst systems are described in U.S. Patent Nos. 4,530,914, 4,871,705, 4,937,299, 5,017,714, 5,055,438, 5,096,867, 5,120,867, 5,124,418, 5,198,401, 5,210,352, 5,229,478, 5,264,405, 5,278,264, 5,278,119, 5,304,614, 5,324,800,

5,347,025, 5,350,723, 5,384,299, 5,391,790, 5,391,789, 5,399,636, 5,408,017, 5,491,207,

5,455,366, 5,534,473, 5,539,124, 5,554,775, 5,621,126, 5,684,098, 5,693,730, 5,698,634,

5,710,297, 5,712,354, 5,714,427, 5,714,555, 5,728,641, 5,728,839, 5,753,577, 5,767,209,

5,770,753, 5,770,664; EP-A-0 591 756, EP-A-0 520-732, EP-A-0 420 436, EP-B1 0 485 822, EP-B1 0 485 823, EP-A2-0 743 324, EP-B1 0 518 092; WO 91/04257, WO 92/00333, WO 93/08221, WO 93/08199, WO 94/01471, WO 96/20233, WO 97/15582, WO 97/19959, WO 97/46567, WO 98/01455, WO 98/06759, and WO 98/011144. Mixed Catalysts

[0064] The present methods can also activate a mixed catalyst, i.e., two or more of the same or different types of catalysts, such as the ones described herein. For example, a metallocene catalyst can be combined with one or more of a conventional catalysts, other metallocene catalyst, or advanced catalysts known in the art. An example of such catalyst is PRODIGY™ Bimodal Catalyst available from Univation Technologies, LLC, Houston, TX.

Activator and Activation Methods

[0065] The above described catalysts, particularly, metallocene catalysts, can be activated in various ways to yield catalysts having a vacant coordination site that will coordinate, insert, and polymerize olefm(s).

[0066] As used herein, the term“activator” refers to any compound that can activate any one of the catalyst compounds described herein by converting the neutral polymerization catalyst compound to a catalytically active catalyst cation compound. Non-limiting activators, for example, include alumoxanes, aluminum alkyls, ionizing activators, which can be neutral or ionic, and conventional-type cocatalysts. Activators and activation methods can be found in Patent No. 7,858,719, col. 14, line 21, bridging col. 17, line 30.

Method for Supporting

[0067] The above described catalysts and catalyst systems can be combined with one or more support materials or carriers. As used herein, the terms“support” or“carrier” are used interchangeably and are any porous or non-porous support material, preferably, a porous support material, for example, talc, inorganic oxides and inorganic chlorides, silica, or alumina. Other carriers include resinous support materials that are a functionalized or crosslinked organic support such as polystyrene, polystyrene divinyl benzene polyolefins, polymeric compounds, or any other organic or inorganic support material of the like, or mixtures thereof.

[0068] Carriers further include inorganic oxides that include those Group 2, 3, 4, 5, 13 or 14 metal oxides. The supports also include silica, alumina, silica-alumina, magnesium chloride, and mixtures thereof. Other useful supports include magnesia, titania, zirconia, montmorillonite and the like. Also, combinations of these support materials can be used, for example, silica-chromium and titania-silica.

[0069] Examples of supported metallocene catalyst systems are described in U.S. Patent Nos. 4,701,432, 4,808,561, 4,912,075, 4,925,821, 4,937,217, 5,008,228, 5,238,892, 5,240,894, 5,332,706, 5,346,925, 5,422,325, 5,466,649, 5,466,766, 5,468,702, 5,529,965, 5,554,704, 5,629,253, 5,639,835, 5,625,015, 5,643,847, 5,648,310, 5,665,665, 5,698,487, 5,714,424, 5,723,400, 5,723,402, 5,731,261, 5,743,202, 5,759,940, 5,767,032, 5,688,880, 5,770,755 and 5,770,664; WO 95/32995, WO 95/14044, WO 96/06187, WO96/11960, and W096/00243.

[0070] Examples of supported conventional catalyst systems are described in U.S. Patent Nos. 4,894,424, 4,376,062, 4,395,359, 4,379,759, 4,405,495, 4,540,758 and 5,096,869.

Gas Phase Polymerization Process

[0071] A gas phase polymerization process can include fluidized bed or stirred bed processes. A continuous cycle can be employed where one part of the cycle of a reactor system, a cycling gas stream, otherwise known as a recycle stream or fluidizing medium, is heated in the reactor by the heat of polymerization. Heat is removed from the recycle composition in another part of the cycle by a cooling system external to the reactor. In a gas phase fluidized bed polymerization process, a gaseous stream containing one or more monomers is continuously cycled through a fluidized bed in the presence of at least one catalyst under polymerizable conditions. A condensable agent is introduced to the process for purposes of increasing the cooling capacity of the recycle stream. Introduction of a condensable agent into a gas phase process is sometimes referred to as a“condensed mode process.” A gaseous stream is withdrawn from the fluidized bed and recycled back into the reactor. Simultaneously, polymer product is withdrawn from the reactor and fresh reactants including monomers are added to the reactor. Examples of gas phase polymerization processes can be found in 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.

[0072] It is to be understood that while the invention has been described in conjunction with the specific embodiments thereof, the foregoing description is intended to illustrate and not limit the scope of the invention. Other aspects, advantages and modifications will be apparent to those skilled in the art to which the invention pertains.

[0073] Therefore, the following examples are put forth so as to provide those skilled in the art with a complete disclosure and description and are not intended to limit the scope of that which the inventors regard as their invention.

EXAMPLE I

[0074] It is to be understood that while the invention has been described in conjunction with the specific embodiments thereof, the foregoing description is intended to illustrate and not limit the scope of the invention. Other aspects, advantages and modifications will be apparent to those skilled in the art to which the invention pertains. [0075] Therefore, the following examples are put forth so as to provide those skilled in the art with a complete disclosure and description and are not intended to limit the scope of that which the inventors regard as their invention.

[0076] Following a startup of a polymerization reactor after a plate cleaning shutdown, the reactor incurred a massive sheeting event most likely caused by impurities built up with the impurities present from the open reactor (plate cleaning). During the shutdown to clean the plate, excessive mineral oil was injected into the reactor to flush the TEAL nozzles. The excessive oil was cleaned using ISOPAR™ from the lower two to three meters of reactor wall and distributor plate. ISOPAR™ are commercially available isoparaffmic fluids that eliminate unwanted impurities, such as aromatics, unsaturated olefins and reactive polar compounds. However, resulting residual oil film is believed to contribute to the sudden and massive nature of the sheeting.

[0077] However, further improvements in efficiency and operability of the polymerization reaction were needed. Particularly, there is a continued need to address the vulnerability of the polymerization reactor to sheeting and/or fouling during the critical initial stage(s) of the polymerization reaction.

[0078] Sheeting is a phenomenon during which catalyst and resin particles adhere to the reactor walls or a site proximate the reactor wall possibly due to electrostatic forces. If the catalyst and resin particles remain stationary long enough under a reactive environment, excess temperatures can result in particle fusion which in turn can lead to the formation of undesirable thin fused agglomerates (sheets) that appear in the granular products. The sheets of fused resin vary widely in size, but are similar in most respects. They are usually about 1/4 to l/2-inch- thick and about 1 to 5 feet long, with some sheets being even longer. Sheets can have a width of about 3 to 18 inches or more. The sheets are often composed of a core of fused polymer that can be oriented in the length dimension of the sheets and their surfaces are covered with granular resin fused to the core. The edges of the sheets can have a hairy appearance from strands of fused polymer.

[0079] In gas phase reactors, sheeting is generally characterized by the formation of solid masses of polymer on the walls of the reactor. These solid masses of polymer (e.g., the sheets) eventually become dislodged from the walls and fall into the reaction section, where they interfere with fluidization, block the product discharge port, plug the distributor plate, and usually force a reactor shut-down for cleaning, any one of which can be termed a "discontinuity event", which in general is a disruption in the continuous operation of a polymerization reactor. The terms "sheeting, chunking and/or fouling" while used synonymously herein, can describe different manifestations of similar problems, in each case they can lead to a reactor discontinuity event.

[0080] There are at least two distinct forms of sheeting that occur in gas phase reactors. The two forms (or types) of sheeting are described as wall sheets or dome sheets, depending on where they are formed in the reactor. Wall sheets are formed on the walls (generally vertical sections) of the reaction section. Dome sheets are formed much higher in the reactor, on the conical section of the dome, or on the hemi-spherical head on the top of the reactor

[0081] More specifically in the present example, the polymerization reactor was undergoing a startup following a plate cleaning. The reactor was shut down with the catalyst pulled 20 minutes after the catalyst was started because of cycle gas density calculation problems that resulted in incorrect high superficial gas velocity. Closure of the ethylene feed supply stopped ethylene flow to the purge header and initiated a reactor kill from loss of cycle gas compressor seal flow.

[0082] Upon restart, calculation errors were corrected, the polymerization reactor was purged to < 0.2ppm CO and was restarted with catalyst. Bed static was negative but trending upwards to approximately -30 to ~0 v when catalyst was started. In order to maintain concentration ratios reactor pressure was trending high (2500 kpag) and a 500 kg/hr reactor vent was established to reduce the pressure. The static became more active and trended downward. The static activity became less active and settled out in -60 volts to -70 volts range when the vent was increased to 700 kg/h. The vent was increased to 2500 kg/h for over 3 hours.

[0083] During a transition to condensed mode, a reactor inlet was within 3°C of dew point at 13:35 0°C was reached at 13:45 and 5% condensation by 14:02. From 13:35 onward the static became significantly more active (spiking), trending more negative with an increasing band width. This change coincided with the CG inlet reaching the dew point and the reactor vent being dropped from 2000 kg/hr to <500 kg/hr.

[0084] A massive sheeting event began at 1.5 meters skin, spreading quickly to other skin TI's, with all skin TI's at the 2.1 meter, 1.5 meter level and the 0.9 meter level. The sheeting continued until the polymerization reactor was killed.

[0085] Initial observations included static increasing upon startup; yet static settled down when reactor vent exceed 700 kilograms per hour. Static became active coincidental with start of going condensed (delta Dew Point = 0) and reducing Rx vent (2000 kg/h to 500 kg/h). Static continued to increase in activity and trend negative. [0086] It was later observed that the sheeting was limited to a reactor wall that was wetted with mineral oil and wiped down with Isopar. No sheeting was observed higher up in the bed or in the dome. A study of the analyzer data showed no evidence of abnormal impurities in nitrogen (LPPN), butene, pentane, and ethylene feed streams. The source of plant nitrogen supply had not changed. The polymerization reactor was wetted with approximately 1 barrel of mineral oil (TEAL nozzle flushing) on shutdown for plate cleaning. "ISOPAR L" used to clean (wipe down reactor wall, and deck plates.). Mineral oil leaking from compressor seals has not caused static or sheeting at other facilities. ISOPAR™ has been used for some time as a cleaning solvent for clean service areas with no apparent problem.

[0087] A review of catalyst transfers, feeder fills, and pick up block operation showed no correlation of catalyst feeder operation (catalyst batches, PUB's etc.) with the static activity or sheeting. Normal startup procedures used successfully on previous startups were being followed. Static activity indicated "impurities" in polymerization reactor. These impurities are being controlled with a high (>700 kg/h) reactor vent. Reducing the vent caused a buildup that initiated the sheeting. The impurities are from the reactor exposure to air/moisture (an open reactor startup), aggravated by the mineral oil and Isopar on the reactor walls. This film can have contained oxygen and moisture, and was thought to explain the sudden and massive nature of the sheeting. While it is possible that an unknown feed impurity was present, no evidence was found to point to this possibility. Further, high activity and negative trend of the static caused by entrance to condensed mode could have been the result of residual mineral oil washed into polymerization reactor by condensing liquid.

EXAMPLE II

[0088] A procedure was developed to prepare the polymerization reactor for startup in order to avoid sheeting and electrostatic charges in the seed bed. This methodology was used to prepare the reactors for startup in Example III below.

[0089] When performing the present method steps described in this example, the order of the steps can vary and certain steps or details can be omitted. For example, as described herein, pressurizing up and removing oxygen from the polymerization reactor (referred to as“Ch-Free reactor” step) is not required if the reactor is not opened after a previous polymerization process has been completed. Additionally, low pressure leak checks can be omitted if the reactor has no high-risk openings such as openings of manways and flanges from a straight section from a deck plate to the reactor neck. Table 1 is a chart that indicates an order of steps which can be taken depending upon three particular scenarios. [0090] In Table 1, the method steps taken are represented by letters as follows:

A. Prepared the Polymerization Reactor for Pressure Up

B. Pressured Up Reactor

C. C -Free Reactor to Atmosphere

D. Low and High Pressure Leak Testing of the Reactor System

E. Charged Seed Bed to the Reactor

F. Started Cycle Gas Compressor

G. Low Pressure and High Pressure Leak Checked After Seedbed Charging

H. Dry Out Reactor for Metallocene (MCN)

I. Dry Out Reactor for C4LL

J. TEAL/Ethylene or TEAL/Nitrogen Soak Reaction System (TEAL Soak) for

C4LL

TABLE 1

[0091] Typically, a reactor startup is performed after maintenance job completion and handover. Reactor startups are non-routine, and as such, the level of safety awareness should be raised. For example, the operating crew often holds a safety meeting before proceeding with the startup. Approximately, two days before the use of nitrogen, equipment such as moisture and C analyzers is checked. Also, sufficiency of the seed bed inventory to transfer is confirmed. A. Preparing for Reactor Pressure Up

[0092] To startup the reactor, the reactor is prepared for pressurizing and the step of “pressure up reactor” is performed. Before pressurizing the reactor, a cycle gas compressor’s primary and any secondary seal system are placed into service. Furthermore, to prepare the reactor, certain other steps can be taken such as commissioning seals, lining up turbine outlet block valves and verifying line-up, opening vents to atmosphere, hooking up nitrogen hoses for low pressure leak checks and removing oxygen from the reactor. If the reactor has not been opened (in other words, there has not been a reactor opening), then the seed bed can be charged without implementing the steps of preparing for reactor pressure up, pressure up of the reactor and/or the C -free reactor step desired below.

B. Pressure Up of the Reactor

[0093] In the present methods, the reactor is pressurized with nitrogen which can include additional steps of opening valves on the nitrogen supply lines, opening the turbine blowdown line valves, isolating the turbine outlet line from the flare, removing oxygen from the system of oxygen, supplying nitrogen to the reactor, pressuring the reactor with nitrogen, and opening the blowdown turbine valve. In addition, testing for leakage can be performed at this time.

C. C -Free Reactor

[0094] Provided there is a reactor opening, the next step is to remove the oxygen from the reactor or implement an Ch-Free Reactor. Low pressure nitrogen (120 kpag to atmosphere) is used to remove oxygen and the reactor is pressure purged six times with nitrogen before lining it up to a flare. With this step, it is important not to over pressurize the turbine and outlet piping as this can damage equipment and cause injury to personnel. The turbine outlet can be opened to prevent over pressure.

D. Low Pressure and High Pressure Leak Testing of Reactor

[0095] After oxygen is purged, the reactor is tested at both low and high pressures for leaks. Here, the reactor is pressurized with nitrogen. Testing is performed by low pressure and high pressure leak checks on all openings, blind locations, disconnects, and manways. The low pressure leak test can be conducted when the reactor pressure is about 100 kPag. The high pressure leak check can be conducted when the reactor reaches 1900 kPag. Once the leak checks are completed, the reactor is depressurized to about 20 kPag and preparations for seed bed charging can commence. E. Charging the Seed Bed

[0096] To charge the seed bed, auxiliary systems can be first prepared by systems, including but not limited to, an IPDS system, a recovery system, catalyst feeders, and starting a tempered water system. Other steps taken before pressurizing the reactor include blinding a reactor seed bed charge nozzle.

F. Start Up Cycle Gas Compressor

[0097] Once the seed bed has been charged, the gas compressor is started. Before this is done, however, other steps can include closing the reactor valves and providing nitrogen to the reactor at a maximum flow. When reactor pressure is about 1000 kPag, the cycle gas compressor is started. Addition steps can include purging remaining water in a reactor hydrolysis injection nozzle via nitrogen. At this time, gases are purged from the cycle gas compressor discharge to the IPDS now fully commissioned. Further steps can include opening manual valves, and commissioning the reaction auto blowback. To remove any trapped CO or moisture, the IPDS auto valves are stroked. Other steps involved in the startup cycle gas compressor include lining up the LPS to the startup heater, opening steam lines, heating the reactor to about 85°C, isolating the tempered water supply to two or more heat exchangers, closing valves to minimize the nitrogen in the reactor when it is being heated up, and shutting down and confirming that the reactor vents and blowdowns are shut to allow the reactor to pressure up. The reactor should only be blowdown if the pressure hits about 2000 kPag. With this step, it is important that the temperature of the water inlet does not exceed about 89°C to prevent fouling of the cycle gas cooler. The reactor bed temperature should be set and maintained at 85°C.

G. Low Pressure and High Pressure Leak Checks After Seed Bed Charging

[0098] After the seed bed is charged, the reactor is checked for leaks as necessary. Certain steps can be taken as necessary such as closing and opening necessary valves, reducing the SGV to about 0.51 m/s, setting the purge header selector to high pressure plant nitrogen, lining up instrument tap purges, commissioning the cycle gas compressor to discharge purged gas to IPDS, and commissioning the reactor auto blowback. At this point, a low pressure leak check is performed, provided the low pressure leak check was not done before the seed bed charge. To prepare for high pressure leak checks, the high pressure plant nitrogen supply is lined up to the reactor and the correct valves are open. While the reactor is pressuring up, personnel performs leak checks. Other activities performed during the reactor pressurization in preparation of the high pressure leak checks include blowing taps using the auto blowback and manual sequence, verifying the cycle gas flow and fluidization when the instrument tap purges are opened, optimizing the high pressure plant nitrogen flow to the reactor, and setting the pressure control at about 2200 kPag. Once the reactor pressure reaches about 1900 kPag, high pressure leak checks can begin if they were not performed before the seed bed charge. The leak check should be performed on all manways and flanges opened during any maintenance work. After the leak check is completed and once the bed temperature is in control, the reactor pressure is lowered by ensuring valves are closed. If a dry-out is not required or has already been performed, the reactor is slowly depressurized to flare until the pressure reaches about 830 kPag. If a dry-out is required, the pressure in the reactor is maintained.

H Dry Out Reactor

I. Dry Out Reactor for Metallocene (MCN) Startup

[0099] In aspect, once the reactor bed is about 80°C, the nitrogen totalizer is reset. If the reactor was opened, the total nitrogen target is set at to accumulate about 90 T (“tons”) of nitrogen. If the reactor was not open, the total nitrogen target is set at about 80 T nitrogen accumulated. If the cooler was changed out, the total nitrogen target is set at 120 T nitrogen accumulated and the moisture is set at about < 6 ppm or about < 4 ppm, depending on the product being made. The valve at the cooler outlet can be set to flare for about 1 hour at the start of dry-out. The reactor is then depressurized to about 830 kPag. Nitrogen flowing to the reactor is maximized. Catalyst support tubes and purge valves are lined up as necessary. Approximately 4 hours after the cycle gas compressor is started up, and during the nitrogen purge, the portable moisture measurement analyzer is connected and purged with nitrogen for at least about 24 hours before commissioning. The SGV is maintained at about 0.51 m/sec. Once the portable moisture measurement analyzer is commissioned, moisture measurements can begin to be taken. At about 40 ppm moisture, the cycle gas moisture analyzer can be commissioned. About 10 MCN pressure purges on each IPDS system should be performed using the auto purge logic about six hours after the reactor dry out starts. Purging continues until the target moisture levels is about < 6 ppm. At this point, the reactor cycle gas moisture analyzer is checked. If the moisture is about < 6ppm or about < 4 ppm and nitrogen accumulator has reached target, additional startup procedures can begin. If not, the moisture readings can be cross-checked with the portable moisture measurement analyzer to analyze that moisture levels have been reached and additional startup procedures can begin. At this point the reactor can be prepared for startup by minimizing nitrogen flow to the reactor.

2 Dry Out Reactor for C4LL Startup

[00100] For a C4LL reactor startup, the reactor is maintained at about 700 kPag by adjusting the reactor blowdown accordingly. A nitrogen flow purge is started to the reactor at maximum flow while venting to the flare. The nitrogen flow can be optimized by using high pressure plant nitrogen flow to the reactor, maximizing compressor capacity, or using a jump over line to minimize dry out time. The reactor is maintained at about >80°C. Then, the portable moisture measurement analyzer is connected and purged with nitrogen for at least about 24 hours before commissioning. Once the portable moisture measurement analyzer is commissioned, moisture measurements can begin to be taken. The portable moisture measurement analyzer should only be switched on to cycle gas momentarily for taking the moisture reading to prevent saturation and flare measurements. At about 40 ppm moisture, the cycle gas moisture analyzer can be commissioned.

[00101] If the reactor is going from MCN to C4LL service, the following steps can be taken. Once the reactor temperature reaches about 80°C, the nitrogen totalizer can be started, which can happen prior to this step. For this situation, the nitrogen totalizer is reset when the reactor bed temperature is about >80°C. The reactor bed temperature is likely to continue to rise to about 80°C. If the reactor was opened, the total nitrogen target is set at about 70 T nitrogen accumulated. If the reactor was not opened, the total nitrogen target is set at about 60 T nitrogen accumulated. If the cycle gas cooler was changed out, the total nitrogen target is set at 100 T nitrogen accumulated. When the moisture is about < 40 ppm, and the nitrogen accumulator has reached target, then the reactor is ready to undergo the TEAL/ethylene soak in section J. If, however, the moisture is about < 40 ppm and the nitrogen accumulator did not reach target, or if the moisture is about > 40 ppm and the nitrogen accumulator did reach target, then the nitrogen purge is continued.

[00102] If the reactor is going from C4LL service to C4LL service, then the following steps can be taken. If the moisture is about > 40 ppm, then the nitrogen purge is continued. If the moisture is about < 40 ppm, then the next step of TEAL/ethylene soak can be performed. Analyzer readings can be confirmed prior to proceeding with a TEAL/ethylene soak reaction (TEAL soak) step described below.

J TEAL/Ethylene Soak Reaction System (TEAL Soak)

[00103] After the reactor has been dried with nitrogen, steps including, but not limited to, decommissioning the O2 and moisture analyzers can be performed. While maintaining high pressure nitrogen on a purge header, block valves are closed for certain instruments and nozzles including, but not limited to, vent valves and flow meter. Valves at the venturi are not isolated. Other purging of reactor instruments continues at about 5 kg/hr.

[00104] To prevent contamination or possible damages to other gas chromatographs, a cycle gas analyzer system is lined up for the step of TEAL soak. Blocking certain purge taps provides margin from the high pressure plant nitrogen compressors to control the C2PP from getting too high during this step (TEAL soak) and minimizes reactor venting. C2PP is adjusted by controlling catalyst support tube flows and increasing nitrogen concentration. Purging of other instruments continues including a kill nozzle support tube at about 50 kg/h and TEAL support tubes at about 180 kg/h. Each catalyst support tube flow controller is set on minimum purge flow of about 50 kg/h. At this point, high pressure plant nitrogen to the reactor is shut off. When the reactor pressure is at about 700 kPag, the reactor vent is closed.

[00105] During the step of TEAL soak, reactor vent and blowdown are closed until the reactor pressure reaches about 2200 kPag. Throughout the step of TEAL soak, the reactor temperature is maintained at about greater than or equal to 75°C by ensuring the steam heater is in auto mode. The C2/N2 selector and the purge header are both switched to ethylene (C2) supply. At least 100 tons of seed bed has been transferred to the reactor at this point. For TEAL soak, ethylene can be added to the reactor at about 6 T/h. Ethylene enters through catalyst support tubes and a purge header.

[00106] TEAL injection then commences. TEAL is injected onto the seed bed at a rate of about 20 kg/hr and until the TEAL concentration of the seed bed reaches a desired level of more than 400 wt. ppm based on seed bed. While maintaining reactor pressure between about 1000 kPag to 1500 kPag, a TEAL soak is initiated and commences for at least one hour. For example, for approximately 430 ppm TEAL by bed weight, TEAL soak is about 2 hours. If the bed weight is 100 metric tons, reaching 430 ppm TEAL by bed weight requires approximately 43 kilograms (kg) of TEAL. At this point, the reactor is vented as little as possible. The superficial gas velocity (“SGV”) is set at about 0.6 m/sec or between about 0.57m/sec to 0.63 m/sec. During TEAL soak, the SGV is maintained at a rate of 0.6 m/sec, the reactor temperature is at least about 80°C or greater, maximum reactor pressure is about 2200 kPag, and the C2PP is between about 700 kPag to about 800 kPag. When the TEAL totalizer reaches target, TEAL injection is discontinued and the TEAL Emergency Block Valve (“EBV”) is tripped.

[00107] Once the C2PP reaches about 600 kPag, ethylene supply is discontinued and ethylene supply to the catalyst support tubes is minimized at about 20 kg/hr. C2PP is maintained between about 700 kPag and about 800 kPag. Each time the C2PP reaches about 800 kPag, high pressure plant nitrogen flow is increased. Once the C2PP drops below about 800 kPag, the ethylene flow is increased by opening the catalyst support tube flows.

[00108] To determine whether the step of TEAL soak is complete, ethane concentration is determined. If ethane concentration is trending upwards (increasing concentration in the polymerization reactor), then unreacted moisture in the reactor system exists and TEAL soak should be continued. If the concentration of ethane has stabilized, i.e., is not erratic or increasing, TEAL spiking can begin. To carry out the TEAL spike step, TEAL is injected at 20 kg/hr for 15 minutes. For the next 20 minutes, at least three analyzer updates are taken and ethane concentration trends are observed. If ethane concentration is stable or reduced, the procedure can continue. If ethane concentration is not stable or increases, another TEAL spike must be performed.

[00109] Upon completion of the TEAL soak step, the following steps can be performed: line up reach feed streams for startup, open certain block valves, and determine that the correct block valves are open and closed. By opening the blown down valves and depressurizing the reactor to flare, the reactor is blown down to a pressure of 700 kPag.

[00110] At this time, the purge header is switched from ethylene to high pressure high purity nitrogen. To minimize disruption to the reactor operation, the high pressure high purity nitrogen compressor and purge header are monitored. The C2/N2 selector is then switched to nitrogen supply. The reactor pressure control is set at about 2300 kPag.

[00111] To remove poisons from the TEAL/ethylene reaction, high pressure plant nitrogen and pipeline nitrogen are used to purge the reactor until the C2 (ethylene) concentration is less than about 10%. If the high pressure plant nitrogen compressors are not at their maximum capacity, maximizing the high press plant nitrogen flow via a jump over line is important to speed up the drying process.

[00112] After purging is completed, reactor temperature is maintained at about 85°C. The purge header flow is re-established by reopening certain instrument, nozzles, and valves. To complete the procedure, the auto blowback is switched on and the high pressure purified nitrogen feed to the reactor is shut off. Reactor startup can begin.

EXAMPLE III

COMPARATIVE STARTUPS AFTER TEAL SOAK

[00113] After treating the seed bed with the methods described herein, two reactor startups, Startup A and Startup B, were performed. Startup A was successful. Startup B was unsuccessful. Table 2

Preparation Steps - Startup A and Startup B

[00114] From a comparison, Startup A and Startup B shows no obvious differences in operation. However, the reactor in Startup B was not in condition for catalyst injection because the skin temperatures rose and did not drop, and sheeting began on startup.

[00115] More particularly, for Startup B, the TEAL soak step was continued for two hours and the reactor purged to remove hydrocarbons. The seedbed was dried with nitrogen to a moisture level less than about 17 ppm as verified with a portable moisture meter and on-line reactor analyzer. However, abnormal cold bands were indicated at the plate thermocouple and for the three feet and five feet skin temperature readings. After TEAL soak, to mitigate cold bands, concentration build began shortly after the nitrogen purge. As flows were increased, the reactor vent was started. Reactor skin temperature rose from 20°C below bed temperature to within 5 to 10 degrees below seed bed temperature. Catalyst injection flow was increased from 1 kg/hr. to 2.5 kg/hr. The catalyst charged was 0.5 kg. After about 5 minutes, skin temperatures started to spike, which proliferated to other skins at different levels. When temperatures did not drop after 10 minutes, a mini -kill was injected into the reactor. After the temperature remained too high after mini-kill, the polymerization reaction was killed to prevent a large sheeting event.

[00116] FIG. 1 shows the 6” plate temperature readings during the successful startup A FIG. 2 shows the same 6” plate temperature readings during the failed startup B. During Startup A, there were only small differences in the plate thermocouple reading during and after the TEAL/ethylene soak as shown in the circled section of the figure. In Startup B, after the TEAL/ethylene soak started, the plate thermocouples went cold as shown in the circled section of the FIG. 2, indicating possible granule buildup at the reactor wall. It remained cold for some time.

[00117] Similarly, FIG. 3 shows the 3 feet skin temperature indication trend during Startup A. FIG. 4 shows the 3 feet skin temperature indication trend during the Startup B. During Startup A, the 3 feet skin temperature indication remains cold for a period of time, and then begins to heat up as shown in the circled section of the figure. Conversely, as shown in FIG. 4 in the circled section, for Startup B; however, at the start of the TEAL/ethylene soak, the 3 feet skin temperature indication is progressively colder and does not rise during the TEAL soak step or subsequent purge. Instead, the skin temperature rises during concentration build.

[00118] After the failed Startup B, a number of observations were recorded. The dumping of the bed resulted in smooth, thin sheets at the hopper. One sheet, however, had minor granules and fines on plate. The dome and expanded section looked good. The reactor was killed in time, and no other abnormality appeared. Multiple levels of cold band initiated with the TEAL/Ethylene soak. Abnormal conditions were present before start. Although concentration build does mitigate cold band, it cannot be good enough for a transition. Startup B failed as soon as the catalyst was injected, which is different from other failed startups. While other failed startups have been smooth with no skin temperature activity for about the first five to about 8 hours, this particular reactor has seen similar issues in the past with occurrences of high skin temperature activity at startup. These events, though, have been ahributed to mineral oil ingress into the reactor.

[00119] A number of possible root causes for the failed startup B were developed. One possible root cause was an ingress of a static generating poison during the TEAL/ethylene soak causing granules and fines to stick to the wall and generate cold bands. This ingress of poison could have come from the TEAL or ethylene during the soak, and might include mineral oil from the SPP (inadequate displacement of oil during maintenance or preservation, or a stagnant section from SPP isolation valve to SPE, est. 20 kg). However, poison from the ethylene was determined as very unlikely because there were no productivity or continuity issues elsewhere.

[00120] Another possible root cause is the seed bed having moisture or not adequately drying. However, bed dryness was confirmed with a portable moisture analyzer reading under about 40 ppm, and the reactor moisture analyzer reading about 17 ppm. Additionally, startup B used the same procedure and criteria as other startups which saw no such immediate startup issues.

[00121] Another possible cause for the failed Startup B were fines from previous run left in the reactor. Fines can be neutralized by CO, CO2, moisture, or air. Yet, Startup A was successful and the same procedure and steps were followed in the same sequence except for a variation in reactor temperature control and the depressurization cycle required to clear a lower explosive limit alarm. [00122] Subsequently, we determined that the failed Startup B was likely due to ingress of poison during TEAL soak and differs from previous failed transition startups. Furthermore, a similar startup failure and high skin temperature activity has been noted when a catalyst interacts with mineral oil. Possible mitigations of this problem include flushing the initial mineral oil content in TEAL line into the reactor and dump the content with the seed bed. Additional purging steps can also be explored. Noteworthy is that the presence of excess fines (if any) are reduced with seed bed dumps. Furthermore, the reactor that is opened and exposed to atmosphere increases the probability of a successful startup.

[00123] The phrases, unless otherwise specified, "consists essentially of and "consisting essentially of do not exclude the presence of other steps, elements, or materials, whether or not, specifically mentioned in this specification, so long as such steps, elements, or materials, do not affect the basic and novel characteristics of the invention, additionally, they do not exclude impurities and variances normally associated with the elements and materials used.

[00124] For the sake of brevity, only certain ranges are explicitly disclosed herein. However, ranges from 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.

[00125] All priority documents are herein fully incorporated by reference for all jurisdictions in which such incorporation is permitted and to the extent such disclosure is consistent with the description of the present invention. Further, all documents and references cited herein, including testing procedures, publications, patents, journal articles, etc. are herein fully incorporated by reference for all jurisdictions in which such incorporation is permitted and to the extent such disclosure is consistent with the description of the present invention.

[00126] While the invention has been described with respect to a number of embodiments and examples, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope and spirit of the invention as disclosed herein.

Claims

Claims We Claim :

1. A method of preparing a polymerization reactor having a seed bed for reactor startup comprising the steps of:

injecting an alkyl solution onto the seed bed;

soaking the seed bed for at least one hour;

determining an ethane concentration in the reactor wherein soaking the seed bed is continued if ethane concentration is increasing; and

commencing reactor startup when ethane concentration has reached an equilibrium.

2. The method of claim 1, wherein the ethane concentration indicates a moisture level of the seed bed in the polymerization reactor.

3. A method for monitoring dryness of a polymerization reactor having a seed bed for reactor startup comprising the steps of:

injecting triethylaluminum (TEAL) onto the seed bed;

soaking the seed bed for at least one hour;

monitoring an ethane concentration in the reactor wherein TEAL and water react in the polymerization reactor and the ethane concentration attains equilibrium upon completion of the TEAL and water reaction; and

commencing with reactor startup upon completion of the TEAL and water reaction.

4. The method of any one of the preceding claims, wherein the alkyl solution comprises TEAL.

5. The method of any one of the preceding claims, further comprising the step of purging the polymerization reactor with an inert gas.

6. The method of any one of the preceding claims, wherein the inert gas is nitrogen.

7. The method of any one of the preceding claims, further comprising the step of supplying ethylene to the polymerization reactor.

8. The method of any one of the preceding claims, wherein the flow rate of the alkyl solution to the reactor is at least about 20 kilograms/hour.

9. The method of any one of the preceding claims, wherein the polymerization reactor has a pressure of up to 2200 kPag.

10. The method of any one of the preceding claims, wherein the polymerization reactor maintains a temperature greater than or equal to 75°C.

11. The method of any one of the preceding claims, wherein ethylene is added to the polymerization reactor at a rate of up to 6 tons per hour.

12. The method of any one of the preceding claims, wherein the reactor startup includes the step of removing poisons from the reactor.

13. The method of any one of the preceding claims, further comprising the step of loading the seed bed into the polymerization reactor.

14. The method of any one of the preceding claims, further comprising the step of purging oxygen from the polymerization reactor.

15. The method of any one of the preceding claims, further comprising the step of drying out the polymerization reactor.

16. The method of any one of the preceding claims, further comprising the step of charging the seed bed in the polymerization reactor.

17. The method of any one of the preceding claims, further comprising the step of increasing the pressure in the polymerization reactor.

18. The method of any one of the preceding claims, further comprising the step of testing the polymerization reactor for high pressure leaks.

19. The method of any one of the preceding claims, further comprising the step of testing the polymerization reactor for low pressure leaks.