MXPA00009207A - Polymerization process - Google Patents

Abstract

The present invention relates to a continuous process for the polymerization of olefin(s) utilizing a metallocene catalyst or catalyst system in a continuous slurry or gas phase polymerization process. The invention is more particularly drawn to a gas phase polymerization process for polymerizing one or more olefin(s) in the presence of a metallocene catalyst system in a fluidized bed reactor in the absence of or with a low amount of a scavenger.

Description

POLYMERIZATION PROCESS Field of the Invention The present invention relates to a continuous process for the polymerization of olefins using as a catalyst a bulky ligand transition metal compound, particularly in a continuous gas phase or slurry polymerization process. The invention is directed more particularly to a gas phase polymerization process for polymerizing one or more olefins in the presence of a metallocene catalyst system in a fluidized bed reactor in the absence of or in the presence of a low amount of a stripping component. BACKGROUND OF THE INVENTION It is widely known that gas phase and slurry polymerization processes using bulky ligand transition metal catalysts, otherwise known as metallocene catalysts, have been used to produce a diverse group of novel polymers for Use in a wide variety of applications and products. It is well known in the art that these catalysts and metallocene catalyst systems are quite soluble in many liquids, particularly those diluents or reactive components used in a typical polymerization process. In addition, metallocene catalysts can also be chemically and physically affected by various components typically used in a commercial polymerization process. The metallocene catalyst components and the catalyst system components have a tendency to fail and / or to be laminated in a gas phase polymerization process. In a continuous process in slurry, in particular, rolling on the walls of the reactor, which act as a heat transfer surface, can result in many problems, including poor heat transfer in the polymerization process. The polymer particles adhering to the walls of the reactor continue to polymerize and often melt together and form pieces, which can be harmful in a continuous process, particularly a fluidized bed process. In continuous process in gas phase, a continuous recirculation current is used. The recirculation current is heated by the polymerization heat, and in another part of the cycle, the heat is removed by a cooling system external to the reactor. Lamination in a continuous process in the gas phase can lead to ineffective operation of various reactor systems, for example the cooling system, temperature probes, and the distribution plate, which are often used in a bed polymerization process. fluidized gas phase. As a result of the operability aspects of the reactor associated with the use of catalysts and metallocene catalyst systems, various techniques have been developed to support or produce a metallocene catalyst system with reduced tendency to lamination. For example, U.S. Patent No. 5,283,218 is directed to the pre-polymerization of a metallocene catalyst. U.S. Patent No. 5,332,706 has resorted to a particular technique to form a catalyst by "incipient impregnation". Although all these possible solutions can reduce the failure or lamination to some extent, some are expensive to employ and / or can not reduce both the failure and the lamination at a level sufficient for the successful operation of a continuous process, particularly a commercial process or on a large scale. In this way, it would be highly advantageous to have a polymerization process capable of operating continuously, commercially, with improved operability of the reactor, while at the same time producing polymers having improved physical properties. SUMMARY OF THE INVENTION This invention relates to a continuous slurry or gaseous phase polymerization process for polymerizing one or more olefins using a bulky ligand transition metal catalyst., for example a catalyst or metallocene catalyst system. In one embodiment, the invention provides a continuous process for polymerizing one or more olefins, alone or in combination, in the presence of a metallocene catalyst system, wherein the process involves the removal or reduction of a stripping component. In a preferred embodiment, the above process of the invention is a slurry polymerization process, preferably a gas phase polymerization process. In another preferred embodiment, the process of the invention consists of gas phase polymerization processes operating in a condensed mode. In yet another embodiment, the invention relates to a continuous process in gas or slurry phase to polymerize monomer (s) in a fluidized bed reactor to produce a polymer product, said process comprising the steps "of: (a) ) introduce a recycle stream in the reactor, the recycle stream comprising the monomer (s); (b) introducing a metallocene catalyst system into the reactor; (c) introducing less than 300 ppm, preferably less than 250 ppm of a stripper, based on the total weight of the bed and then discontinuing the introduction of the stripping agent and / or introducing a quantity of a stripping agent based on the total weight of the stripping agent. bed such that the polymer product comprises less than 50 ppm by weight of olefinic C14 to C18 oligomers; (d) removing the recycle stream from the reactor; (e) cooling the recycle stream; (f) introducing into said recycle stream additional monomer (s) to replace the polymerized monomer (s); (g) re-entering the recycle stream in the reactor; and (h) removing a polymer product from the reactor. In a further embodiment, the invention relates to a continuous process in the gas or slurry phase, preferably a gas phase continuous process, for polymerizing one or more olefins in a reactor in the presence of a metallocene catalyst component. , said process operating in the absence of a stripping agent. In a specific embodiment, the invention is directed to a gas phase continuous process for polymerizing one or more olefins, alone or in combination, in the presence of a supported metallocene catalyst system, said process being essentially free of a selected scavenger of the group consisting of triethyl aluminum, triisobutyl aluminum, trimethyl aluminum, ethyl magnesium and diethyl zinc, and mixtures thereof. Detailed Description of the Invention The invention is directed toward a continuous polymerization process having improved operability and capable of producing improved polymer products using a bulky ligand transition metal metallocene catalyst component. It has been discovered that the use of a stripping component typically used as an additive, in particular in a slurry polymerization process and especially in the gas phase, to remove impurities from the reactor, increases faults and lamination, which can lead to unemployment of the reactor. The stripping component can also increase the production of fine particles. Typically, these stripping components serve a double function. Not only do they remove impurities but they also serve as an activator or co-catalyst for particularly those traditional Ziegler-Natta catalysts, for example titanium and vanadium halides. Also, the use of a stripping component can result in a poorer polymer product containing gels. In addition, too much stripping can result in a reduction in catalytic activity and result in low molecular weight olefinic oligomers. In this way, the removal or reduction of an otherwise well-known and widely used component, a stripping agent, provides the process of the invention, which has improved reactor operability, improved catalyst activity and a polymer product substantially free of gels. . Catalyst Components and Catalyst Systems of the Invention Metallocene catalysts, for example, are typically those bulky ligand transition metal compounds derivable from the formula: [L] raM [A] n where L is a bulky ligand; A is a leaving group, M is a transition metal, and m and n are such that the total value of the ligand corresponds to the valence of the transition metal. Preferably, the catalyst is four coordinated such that the compound is ionizable at a state of charge 1+. Ligands L and a may be bridged together, and if two ligands L and / or A are present, they may be bridged. The metallocene compound may be a complete sandwich compound having two or more ligands L, which may be cyclopentadienyl ligands or cyclopentadiene-derived ligands, or sandwich-mediated compounds having a ligand L, which is a cyclopentadienyl ligand or a ligand derivative. In an embodiment, at least one ligand L has a multiplicity of linked atoms, preferably carbon atoms, which is typically a cyclic structure such as, for example, a cyclopentadienyl ligand, substituted or unsubstituted, or ligand derived from cyclopentadienyl or any other ligand capable of bond -5 to the transition metal atom. One or more bulky ligands can be linked to the transition metal atom. The transition metal atom may be a transition metal of group 4, 5 or 6 and / or a metal of the lanthanide and actinide series. Other ligands may be linked to the transition metal, such as a leaving group, such as but not limited to a hydrocarbyl ligand, hydrogen or any other univalent anionic ligand. Non-limiting examples of metallocene catalysts and catalyst systems are discussed, for example, in U.S. Patents 4,530,914; 4,952,716; 5,124,418; 4,808,561; 4,897,455; 5,278,264; 5,278,119; 5,304,614, all of which are incorporated herein by reference. Also, the disclosures of documents EP-A-0 129 368; EP A 0 591 756; EP-A-0 520 732; EP-A-0 420 436; WO 91/04257; WO 92/00333; WO 93/08221; and WO 93/08199, all fully incorporated herein by reference. Various forms of the metallocene catalyst system may be used in the polymerization process of this invention. Exemplary of the development of metallocene catalysts in the field of ethylene polymerization is the disclosure of United States Patents 4,871,705; 4,937,299; and 5,324,800; 5,017,714; and 5,120,867, all of which are incorporated herein by reference. These publications teach the structure of metallocene catalysts and include alumoxane as co-catalyst. There are a variety of methods for preparing alumoxane, non-limiting examples of which are described in U.S. Patents 4,665,208; 4,952,540; 5,091,352; 5,206,199; 5,204,419; 4,874,734; 4,924,018; 4,908,463; 4,968,827; 5,308,815; 5,329,032; 5,248,801; 5,235,081; 5,157,137; 5,103,031; and EP-A-0 561 476, EP-B1-0 279 586; EP-A-0 594 218 and WO 94/10180, all of which are incorporated herein by reference. In addition, the metallocene catalyst component of the invention can be a compound containing a monocyclopentadienyl heteroatom. This heteroatom is activated either by an alumoxane, an ionizing activator, a Lewis acid or a combination of these, to form an active polymerization catalyst system. These types of catalyst systems are described, for example, in PCT international publications WO 92/00333, WO 94/07928 and WO 91/04257, WO 94/03506, United States patents 5,057,475; 5,096,867; 5,055,438; 5,198,401; 5,227,440; and 5,264,405, and EP-A-0 420 436, all of which are incorporated herein by reference. In addition, the metallocene catalysts useful in this invention may include cyclopentadienyl catalyst components or auxiliary ligands such as edges or carbolides in combination with a transition metal. Additionally, it is not beyond the scope of this invention that catalysts and catalyst systems may be those described in U.S. Patents 5,064,802; 5,149,819; 5,243,001; 5,239,022; 5,276,208; 5,296,434; 5,321,106; 5,329,031; and 5,304,614; PCT publications WO 93/08221 and WO 93/08199 and EP-A-0 578 838, all of which are incorporated herein by reference.

The preferred transition metal component of the catalyst of the invention is group 4, particularly zirconium, titanium and hafnium. The transition metal may be in any oxidation state, preferably +3 or +4 or a mixture thereof. For the purposes of this patent description, the term "metallocene" is defined to contain one or more cyclopentadienyls or substituted or unsubstituted cyclopentadienyl moieties in combination with a transition metal. In one embodiment, the metallocene catalyst component is represented by the general formula (C) mMRnR 'p, wherein at least one Cp is an unsubstituted cyclopentadienyl ring or, preferably, substituted, symmetrically or asymmetrically substituted; M is a transition metal of group 4, 5 or 6; R and R 'are independently selected from halogen, a hydrocarbyl group, or hydrocarboxyl groups having 1-20 carbon atoms or combinations thereof; m = l-3, n = 0-3, p = 0-3, and the sum of m + n + p is equal to the oxidation state of, preferably m = 2, n = l and p = l. In another embodiment, the metallocene catalyst component is represented by the formulas: (C5R'ra) pR "s (C5R 'MQ3.px or R" S (CSR' 2MQ 'where Me is a transition metal of group 4 , 5 or 6, at least one C5R'm is a substituted cyclopentadienyl, each R ', which may be the same or different, is hydrogen, alkyl, alkenyl, aryl, alkylaryl or arylalkyl radical having from 1 to 20 carbon atoms or two carbon atoms joined together to form a part of substituted or unsubstituted ring or rings having 4 to 20 carbon atoms, R "is one or more of a combination of a carbon, germanium, silicon, phosphorus or nitrogen atom containing a radical which bypasses two rings (C5R'm), or bypassing a ring (C5R'm) to M, when p = 0 and x = l, otherwise "x" is always equal to 0, each Q, which may be equal or different, is an aryl, alkyl, alkenyl, alkylaryl or arylalkyl radical having from 1 to 20 carbon atoms, halogen, or alkoxy two, Q 'is an alkylidene radical having 1 to 20 carbon atoms, s is 0 or 1, and when s is 0, m is d and p is O, so 2, and when s is 1, m is 4 and p is 1 For the purposes of this patent description, the terms "co-catalysts" and "activators" are used interchangeably and are defined as any compound or component that can activate a bulky ligand transition metal compound or a metallocene, as defined above. It is also within the scope of this invention to use alumoxane as an activator and / or also to use ionizing, neutral or ionic activators, or compounds such as tri (n-butyl) ammonium tetra bis (pentafluorophenyl) boron or precursor of the metalloid trisperfluoro phenyl boron , which ionize the neutral metallocene compound. Such ionizing compounds may contain an active proton, or some other cation associated with but not coordinated or only comfortably coordinated with the remaining ion of the ionizing compound. Such compounds and the like are described in EP-A-0 570 982; EP-A-0 520 732; EP-A-0 495 375; EP-A-0 426 637; EP-A-500 944; EP-A-0 277 003; and EP-A-0 277 004, and U.S. Patents 5,153,157; 5,198,401; 5,066,741; 5,206,197; and 5,241,025, and U.S. Patent Application Serial No. 08 / 285,380, filed August 3, 1994, which are all incorporated herein by reference. Combinations of activators, for example alumoxane and ionizing activators in combinations are also contemplated by the invention; see, for example, WO 94/07928. In another embodiment of the invention, two or more metallocene catalyst components can be combined in the catalyst system of the invention. For example, those mixed catalysts described in U.S. Patent 5,281,679, incorporated herein by reference. Also, in another embodiment of the invention, at least one metallocene catalyst can be combined with a traditional non-metallocene or Ziegler-Natta catalyst or catalyst system, non-limiting examples being described in United States Patents 4,701,432; 5,124,418; 5,077,255; and 5,183,867, all of which are incorporated herein by reference. For the purposes of this patent description, the terms "cer" or "cer" are interchangeable and may be any cer material, preferably a porous cer material, such as, for example, talc, inorganic oxides, inorganic chlorides, for example magnesium chloride and resinous support materials such as polystyrene or polystyrene polyolefins, divinyl benzene or polymeric compounds or any other organic support material and the like, or mixtures thereof. Preferred support materials are inorganic oxide materials, including those of the metal oxides of groups 2, 3, 4, 5, 13 or 14. In a preferred embodiment, the catalyst support materials include silica, alumina, silica-alumina, and their mixtures. Other inorganic oxides can be used either alone or in combination with silica, alumina or silica-alumina, and are magnesia, titania, zirconia, and the like. It is preferred that the catalyst cer of this invention have a surface area in the range of about 10 to about 700 m / g, pore volume in the range of about 0.1 to about 4.0 cc / g, and average size of particle in the range of about 10 to about 500 μm. More preferably, the surface area is in the range of about 50 to about 500 m2 / g, pore volume of about 0.5 to about 3.5 cc / g, and average particle size of about 20 to about 200 μm. More preferably, the range of surface area is from about 100 to about 400 m / g, the pore volume from about 0.8 to about 3.0 cc / g, and the average particle size is about 10 a around 100 μm. The pore size of the cer of the invention is typically in the range of 10 to 1,000 Angstroms, preferably 50 to about 500 Angstroms, and most preferably 75 to about 350 Angstroms. The catalyst system of the invention can be made in a variety of different ways, as previously described. In one embodiment, the catalyst is not supported, see U.S. Patent No. 5,317,036 and EP-A-0 593 083, incorporated herein by reference. In the preferred embodiment, the catalyst system of the invention is supported. Examples of support of the catalyst system used in the invention are described in U.S. Patent Nos. 4,937,217; 4,912,075; 4,935,397; 4,937,301; 4,914,253; 5,008,228; 5,086,025; 5,147,949; 4,808,561; 4,897,455; 4,701,432; 5,238,892; 5,240,894; 5,332,706; and WO 95/10542, published April 20, 1995; WO 95/07939, published March 3, 1995; WO 94/26793, published on November 24, 1994; and WO 95/12622, published May 11, 1995. In one embodiment of the process of the invention, olefin (s), preferably C2 to C20 alpha-olefins, preferably ethylene or propylene or combinations thereof, are prepolymerized. of these, in the presence of the catalyst or catalyst system of the invention before the main polymerization. The prepolymerization can be carried out in charges or continuously in gaseous phase, solution or slurry, including at high pressures. The pre-polymerization can take place with any alpha-olefin monomer or combination and / or in the presence of any molecular weight control agent, such as hydrogen. For details of the pre-polymerization, see U.S. Patent Nos. 4,923,833; 5,283,278; and 4,921,825; and EP-B-0 279 863, all of which are incorporated herein by reference. In another embodiment of the invention, the supported catalyst system of the invention includes an anti-static agent, for example those described in U.S. Patent No. 5,283,278, which is fully incorporated herein by reference. Non-limiting examples of anti-static agents include alcohol, thiol, silanol, diol, ester, ketone, aldehyde, acid, amine, and ether compounds. Tertiary amines, ethoxylated amines, and polyether compounds are preferred. The anti-static agent can be added at any stage in the formation of the supported catalyst system of the invention; however, it is preferred that it be added after the supported catalyst system of the invention is formed, either in a slurry or in the dry state. In another embodiment of the invention, the supported catalyst system of the invention includes a polyolefin wax or tackifier, or the like. The preferred method for producing the catalyst of the invention is described below and can be found in U.S. Patent Applications Serial Nos. 265,533, filed on June 24, 1994, and 265,532, filed on June 24, 1994. , both being incorporated herein by reference in their entirety. In a preferred embodiment, the metallocene catalyst component is typically slurried in a liquid to form a metallocene solution and a separate solution is formed, containing an activator and a liquid. The liquid can be any compatible solvent or other liquid capable of forming a solution or the like with at least one metallocene catalyst component and / or at least one activator. In the preferred embodiment, the liquid is a cyclic aliphatic or aromatic hydrocarbon, most preferably toluene. The metallocene and activator solutions are preferably mixed together and added to a porous support such that the total volume of the metallocene solution and the activator solution or metallocene solution and activator is less than four times the pore volume of the metallocene and activator solution. porous support, more preferably less than three times, even more preferably less than twice, and more preferably in the range of 1-1.5 times to 2.5-4 times, and most preferably in the range of 1.5 to 3 times times. Also, in the preferred embodiment, an anti-static agent is added to the catalyst preparation. In a preferred embodiment, a substantially homogeneous catalyst system is preferred. For the purposes of this patent disclosure and the appended claims, a "substantially homogeneous catalyst" is one in which the molar ratio of the transition metal of the catalyst component, preferably to an activator, is uniformly distributed through a porous support . The method for measuring the total pore volume of a porous support is well known in the art. Details of these procedures are not discussed in volume 1, Experimental Methods in Catalytic Research (Academic Press, 1968) (specifically, see pages 67-96). This preferred method involves the use of a classic BET apparatus for nitrogen absorption. Another well-known method in the art is described in Innes, Total Porosity and Particle Density and Fluid Catalysts by Liquid Ti tration, vol. 28, No. 3, Analytical Chemistry 332-334 (March 1956). The molar ratio of the metal of the activating component to the transition metal of the metallocene component is in the range of ratios between 0.3: 1 to 1,000: 1, preferably 20: 1 to 800: 1, and most preferably 50: 1 to 500: 1. Where the activator is an ionizing activator as previously described, the molar ratio of the metal of the activating component to the transition metal component is preferably in the range of ratios between 0.3: 1 to 3: 1. Polymerization Process of the Invention The catalysts and catalyst systems of this invention are suitable for the polymerization of monomers and optionally co-monomers in any polymerization / gas or slurry process, most preferably using a gas phase process. In the preferred embodiment, this invention is directed to gas phase or slurry polymerization or copolymerization reactions involving the polymerization of one or more alpha-olefin monomers having from 2 to 20 carbon atoms, preferably 2-12 atoms of carbon. The invention is particularly suitable for copolymerization reactions involving the polymerization of one or more of the monomers, for example alpha-olefin monomers of ethylene, propylene, butene-1, pentene-1, 4-methylpentene-1-, hexene- 1, octene-1, decene-1, and cyclic olefins such as cyclopentene, and styrene, or a combination thereof. Other monomers may include polar vinyl, diolefins such as dienes, polyenes, norbornene, norbornadiene, acetylene and aldehyde monomers. Preferably, an ethylene or propylene copolymer is produced. Preferably, the co-monomer is an alpha-olefin having from 3 to 15 carbon atoms, preferably 4 to 12 carbon atoms, and most preferably 4 to 10 carbon atoms. In another embodiment, ethylene or propylene is polymerized with at least two different co-monomers to form a terpolymer and the like, the preferred co-monomers being a combination of alpha-olefin monomers having 3 to 10 carbon atoms, with higher 4 to 8 carbon atoms preference. In another embodiment, ethylene or propylene is polymerized with at least two different co-monomers to form a terpolymer and the like, the preferred co-monomers being a combination of alpha-olefin monomers having 3 to 10 carbon atoms, with higher 3 to 8 carbon atoms, optionally with at least one diene monomer. Preferred terpolymers include combinations such as ethylene / butene-1 / exo-1, ethylene / propylene / butene-1, propylene / ethylene / butene-1, propylene / ethylene / hexene-1, ethylene-propylene / norbornadiene , and similar. Typically in a gas phase polymerization process a continuous cycle is employed where in a part of a reactor cycle, a cycle gas stream, otherwise known as recycle stream or fluidization medium, is heated in the reactor by the heat of polymerization. This heat is removed in another part of the cycle by a cooling system external to the reactor. (See, for example, U.S. Patent Nos. 4,543,399; 4,588,790; 5,028,670; 5,352,749; 5,405,922; and 5,436,304, all of which are hereby incorporated by reference in their entirety.) Generally, in a gas fluidized bed process for producing polymer from monomers, a gaseous stream containing one or more monomers is continuously cycled through a fluidized bed in the presence of a catalyst under reactive conditions. The gas stream is removed from the fluidized bed and recycled back to the reactor. Simultaneously, the polymer product is removed from the reactor and fresh or new monomer is added to replace the polymerized monomer. A slurry polymerization process generally uses pressures in the range of about 1 to about 50 atmospheres and even higher, and temperatures in the range of 0 to about 200 ° C. In a slurry polymerization, a suspension of solid, particulate polymer is formed in a liquid polymerization medium to which ethylene and co-monomers are added and often hydrogen together with the catalyst. The liquid used in the polymerization medium can be alkane or cycloalkane, or an aromatic hydrocarbon such as toluene, ethylbenzene or xylene. The medium used must be liquid under the conditions of polymerization and relatively inert. Preferably, hexane or isobutane are used. Non-limiting examples of slurry processes include stirred or spin tank processes. In one embodiment, the reactor used in the present invention is capable of producing more than 500 lbs / hr (227 kg / hr) at about 200,000 lbs / hr (90,900 kg / hr) or more polymer, preferably more of 1,000 lbs / hr (455 kg / hr), more preferably more than 10,000 lbs / hr (4,540 kg / hr), even more preferably more than 25,000 lbs / hr (11,300 kg / hr), still with the greatest preference more than 35,000 Ibs / hr (15,900 kg / hr), even more preferably more than 50,000 lbs / hr (22,700 kg / hr), and most preferably more than 65,000 lbs / hr (29,000 kg / hr), more than 100,000 lbs / hr (45,500 kg / hr). In another embodiment of the process of the invention, the process produces more than 1,000 lbs (455 kg) of the polymer product per hour, preferably more than 10,000 lbs (4,540 kg) of the polymer product per hour, more preferably more than 50,000 Ibs (22,700 kg) of the polymer product per hour. For the purposes of this patent description and the appended claims, a "stripping agent" is any organometallic compound that is reactive towards oxygen and / or water and / or polar compounds, and that does not include the catalyst components, for example the catalyst component. of metallocene, activator, optional carrier or components remaining in or on the catalyst used in its preparation, for example toluene, including any organometallic compounds used in the preparation of the catalyst. Non-limiting examples of the stripping compounds are those represented by the general formula RnA, where A is an element of group 12 or 13, each R, which may be the same or different, is a straight or branched chain alkyl radical, substituted or not substituted, cyclic hydrocarbyl, alkyl-cyclohydrocarbyl radical, aromatic radical, or alkoxide radical, where n is 2 or 3. In another embodiment, the stripping agent is an aluminum hydrocarbon compound of the formula AlR (3_a) Xa, where R is alkyl, cycloalkyl, aryl or a hydride radical. Each alkyl radical can be straight or branched chain, having from 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms. X is a halogen or hydride, for example chlorine, bromine or iodine; chlorine is preferred; a is 0, 1 or 2. Illustrative but not limiting examples of such compounds of the above formula may include, when M is aluminum (Al), the trialkyl alumins such as trimethyl aluminum, triethyl aluminum, tri-n-propyl aluminum, tri -isopropyl aluminum, tri-n-butyl aluminum, tri-sec-butyl aluminum, tri-t-butyl aluminum, tri-isobutyl aluminum, tri-n-pentyl aluminum, tricyclopentyl aluminum, tri-n-hexyl aluminum, tri- ( 4-methylpentyl) aluminum, tri- (3-methylpentyl) aluminum, tricyclohexyl aluminum, and the like; aluminum alkyl, such as dimethylethyl aluminum, methyldiethyl aluminum, ethyldimethyl aluminum, dimethyl-n-propyl aluminum, methyl di-n-propyl aluminum, dimethylisopropyl aluminum, dimethylcyclohexyl aluminum, methylethylpropyl aluminum, and the like; substituted aryl and alkyl aluminum, such as triphenyl aluminum, tri-p-tolyl aluminum, tri-m-tolyl aluminum, tri-p-ethyl aluminum, and the like. Other non-limiting examples of typical scavengers include dialkyl aluminum halides, for example diethyl aluminum chlorides, ethyl aluminum dichlorides, bromides and iodides and dialkyl aluminum sesquichlorides, bromides and iodides; aluminum alkoxides and aryloxides, such as dimethyl aluminum methoxide, dimethyl aluminum ethoxide, diethyl aluminum ethoxide, diethyl aluminum isopropoxide, methyl ethyl aluminum methoxide, dimethyl aluminum 4-methyl phenoxide, dimethyl aluminum 3-methylphoxide, dimethyl aluminum 2,6-diisopropylphenoxide, dimethyl aluminum 2,6-di-t-butyl-4-methylphenoxide, and the like. A similar list of illustrative compounds of the group 13 element, where M is boron, can be made for the trialkyl boranes, alkyl boranes and borane alkyl alkoxides. A similar list can also be given for the gallium and indium analogues. Such a list would be almost identical to that already presented with respect to the aluminum species and therefore such a list of the borane analogs and other analogues of group 13 elements is not necessary for a full disclosure. Typically preferred spoilers are those of the above formula, where M is aluminum or boron. Of the aluminum species of the group 13 compound compounds, those most often used as strippers are trilakyl aluminum, and of the trialkyl aluminum, the most preferred are triethyl aluminum, triisobutyl aluminum, and trimethyl aluminum. Other specific scavengers include such organometallic compounds as, for example, BX3, where X is a halogen, RxR2Mg, ethyl magnesium, R4C0RMg, RCNR, ZnR2, CdR2, LiR, SnR4, where R are hydrocarbon groups which may be the same or different . Other organometallic compounds useful as depowers include those compounds of groups 1, 2, 3 and 4 such as alkyls, alkoxides and organometallic halides. Preferred organometallic compounds are lithium alkyls, magnesium or zinc alkyls, magnesium alkyl halides, aluminum alkyls, silicon alkyl, silicon alkoxides and silicon alkyl halides. More preferred organometallic compounds useful as depowers are aluminum alkyls and magnesium alkyls. The most preferred organometallic compounds useful as depowers are aluminum alkyls, for example triethyl aluminum (TEAL), trimethyl aluminum (TMAL), tri-isobutyl aluminum (TIBAL), and tri-n-hexyl aluminum (TNHAL) and diethyl aluminum chloride ( DEAC) and the like. TEAL is the most widely used spoiler. In one embodiment of the process of the invention, the process is essentially free of a stripper. For the purposes of this patent description and the appended claims, the term "essentially free" means that during the process of the invention no more than 10 ppm of a stripper is present, based on the total weight of the recycle stream, at any given point in time during the process of the invention. In another embodiment of the process of the invention, the process is substantially free of a stripper. For the purposes of this patent description and the appended claims, the term "substantially free" is defined so that during the process of the invention no more than 50 ppm of a stripper, based on the total weight of a fluidized bed, are present at any given point in time during the process of the invention. In one embodiment of the process of the invention, the amount of the stripping agent within the reactor is less than 30 ppm, preferably less than 20 ppm, even more preferably less than 10 ppm., and most preferably in the range of 0 to 15 ppm. In one embodiment during reactor startup to remove impurities and ensure that polymerization is initiated, a stripping agent is present in an amount of less than 300 ppm, preferably less than 250 ppm, more preferably less than 200 ppm, even with higher preferably less than 150 ppm, still more preferably less than 100 ppm, and most preferably less than 50 ppm, based on the total bed weight of a fluidized bed during the first 12 hours from the time the catalyst in the reactor, preferably up to 6 hours, more preferably less than 3 hours, even more preferably less than 2 hours, and most preferably less than 1 hour, and then the introduction of the stripping agent is stopped. In another embodiment of the process of the invention, the stripper is present in a sufficient amount until the catalyst of the invention has reached a catalyst productivity on a basis of weight ratio of more than 1,000 g of polymer per gram of catalyst , preferably more than about 1,500, more preferably more than 2,000, even more preferably more than 2,500, and most preferably more than 3,000. In another embodiment of the process of the invention, during the start-up the stripper is present in a sufficient amount until the catalyst of the invention has achieved a catalyst productivity 40% of the stable state, preferably less than 30%, even more preferably less than 20%, and most preferably less than 10%. For the purposes of this patent description and the appended claims, "steady state" in the rate of production, the weight of the polymer that is being produced per hour. The productivity of the catalyst or catalyst system is influenced by the partial pressure of the main monomer (ie, ethylene or propylene). The preferred molar percentage of the monomer, ethylene or propylene, is about 25 to 90 mol%, and the monomer partial pressure is in the range of about 75 to about 300 psia (517 to 2,069 kPa), which are typical in a gas phase polymerization process. When a stripper is used in the process of the invention, the stripper may typically be introduced into the reactor directly or indirectly into the recycle stream or into any external means capable of introducing the stripper into the reactor. Preferably, the stripper enters directly into the reactor, and most preferably directly to the reactor bed or below the distributor plate in a typical gas phase process, preferably after the bed is in a fluidized state. In one embodiment, the stripping agent can be introduced once, intermittently or continuously, into the reactor system. The stripper used in the process of the invention is introduced to the reactor at a rate equivalent to 10 to 100 ppm based on the steady state production rate, and then the introduction of stripping is stopped. In yet another embodiment particularly during the start-up, the stripper, when used, is introduced at a rate sufficient to provide an increase in catalyst productivity on a basis of weight ratio of a rate of 200 grams of polymer per gram. of catalyst per minute, preferably at a rate of 300, even more preferably at a rate of 400, and most preferably at a rate of 500. In another embodiment, the molar ratio of the metal of the stripping agent to the metal of transition of the metallocene catalyst component is equal to about 0.2 multiplied by the ppm of a stripper based on the rate of production, multiplied by the catalyst productivity in kilograms of polymer per gram of catalyst. The range of the molar ratio is around 300 to 10. In a preferred embodiment, where an aluminum alkyl is used as the stripping agent, the molar ratio is represented as aluminum (Al) to transition metal, for example zirconium, where the moles of Al are based on the total amount of stripping used. It is also preferred that no hydrogen is added to the system simultaneously with the stripping agent. It is also within the scope of this invention that the stripper can be introduced into a carrier separate from the one used when using a metallocene catalyst system supported in the process of the invention. It has been found that the lamination is influenced by the presence of low molecular weight, mainly volatile olefinic oligomers. These oligomers are generally even-numbered carbon molecules having a molecular weight of less than 1,000 which form about less than or equal to 1% by weight of the polymer. Hydrocarbon oligomers of up to about 30 carbon atoms can be measured by ordinary techniques in the art using a TD-2 short path thermal desorption unit, from Scientific Instru- 23 -ment Services, of Ringoes, New Jersey, United States, in interface with a Hewlett-Packard 5890 GC equipment equipped with capillary boiling column (DB-5) and a selective mass detector Hewlett-Packard 5970. For the detection method, a method of measuring olefins of single fraction / weight percentage, as is well known in the art. In one embodiment, the ratio of the weight percentage of olefin oligomers to the weight percentage of the aliphatic oligomers, as measured in the polymer product, should be in the range of from about 0 to about 25, preferably from from about 0 to about 20, more preferably from about 0 to about 10, and most preferably from about 0 to about 5. It has also been found that by reducing the amount of depressant introduced into the reactor environment, which includes the reactor and its external systems and tubing, the total number of olefinic or unsaturated oligomers is greatly reduced with some reduction in the aliphatic or saturated oligomers. In one embodiment of the invention, the process, preferably a gas phase process, is operated such that the weight fraction of olefinic hydrocarbon oligomers having less than or equal to 30 carbon atoms is less than 0.06 in the polymer product. It is within the scope of the invention that a system external to the reactor to remove deporators introduced in the process of the invention of the recycle stream can be used or that the fluidization medium be treated to remove the despojador; see, for example, U.S. Patent No. 4,460,755, incorporated herein by reference. In another embodiment, the stripping agent is introduced in a sufficient amount such that the oligomers C30 or less, preferably C14 to C18, total unsaturates are less than 50 ppm in the polymer product, preferably less than 40 or 30 ppm, even more preferably less than 20 ppm, and most preferably less than 10 ppm. The fine particles for the purposes of this patent description and the appended claims are polymer particles smaller than 125 μ (0.0125 cm) in size. Fine particles of this size can be measured using a standard screen sieve of 120 mesh units. In a preferred embodiment, the amount of stripper present in the reactor at any given point in time during the process of the invention is such that the level of fine particles less than 125 μ (0.0125 cm) is less than 10%, preferably less than 1%, more preferably less than 0.85 to less than 0.05%. It is within the scope of the invention that a system external to the reactor can be used to remove debris introduced in the process of the invention from the recycle stream. This would then prevent the recycle of the stripper back to the reactor and prevent the accumulation of stripper in the reactor system. It is preferred that such a system be placed before the heat exchanger or compressor in the line of the recycle stream. It is contemplated that such a system would condense the stripper out of the fluidizing medium in the recycle stream line. It would be preferred that the fluidizing medium be treated to remove the stripping agent; see, for example, U.S. Patent No. 4,460,755, incorporated herein by reference. It is also contemplated by the process of the invention that the stripper may be introduced intermittently during the process where more than 90%, preferably more than 95% of all the removed stripper is removed from the recycle stream. It is also contemplated by this invention that the catalyst or catalyst system or components thereof of the invention can be used at startup as a stripping agent; however, this would be an expensive procedure. In the most preferred embodiment of the invention, the process is a gas phase polymerization process that operates in a condensed mode. For the purposes of this patent description and the appended claims, the process of intentionally introducing a recycle stream having a liquid phase and a gas phase in a reactor such that the weight percentage of the liquid based on the total weight of the recycle stream is greater than about 2.0% by weight is defined as operating a gas phase polymerization process in a "condensed mode". In one embodiment of the process of the invention, the weight percentage of the liquid in the recycle stream, based on the total weight of the recycle stream, is in the range of from about 2 to about 50% by weight , preferably more than 10% by weight, and more preferably more than 15% by weight, and even more preferably more than 20% by weight, and most preferably in the range of between about 20 and about 40 %. However, any level of condensate can be used, depending on the desired production rate. In another embodiment of the process of the invention, the amount of scavenger used, if any, must be in a molar ratio less than 100, preferably less than 50, more preferably less than about 25, based on the molar ratio of the transition metal stripper to the metallocene transition metal, where the stripper is an organometallic compound containing aluminum and the transition metal of the metallocene is a group 4 metal, then the above molar ratio is based on moles of aluminum with moles of group 4 metal of the catalyst. "Lamination" is a term used to describe the accumulation of polymer deposits on the surfaces of a reactor. Lamination is harmful to all parts of a polymerization process, including the reactor and its systems, equipment, etc. associates Lamination is especially severe in areas that restrict the flow of gas or liquid. The two main areas of concern are the heat exchanger and the distributor plate. The heat exchanger consists of a series of small diameter tubes arranged in a bundle of tubes. The distributor plate is a solid plate containing numerous small diameter holes through which the gas contained in a recycle stream is passed before entering the reaction zone or distributed to a bed of solid polymer in a bed reactor fluidized such as that described in U.S. Patent No. 4,933,149, incorporated herein by reference. The lamination manifests itself as an increase in pressure drop through either the plate, the cooler, or both. Once the pressure drop becomes too high, gas or liquid can no longer be efficiently circulated by the compressor, and it is often necessary to stop the reactor. Cleaning the reactor can take several days and is very time consuming and expensive. Lamination can also occur in recycle gas pipes and the compressor for it, but usually accompanies lamination of the plate and the cooler. To quantify the rolling rate, it is useful to define a rolling factor, F. F is a fraction of the area of a hole that is laminated. If F = 0 (0%), then there is no rolling. Conversely, if F = l (100%), the hole is completely plugged. It is possible to relate the lamination to the pressure drop, deltaP, at a given time in terms of the pressure drop of a clean system, deltaP0. As lamination increases, deltaP increases and is greater than the initial pressure drop, deltaP0. F is given by the following expressions: (I) Plate lamination F = l- [deltaP0 / deltaP] 12 (II) Coolant lamination F = l- [deltaP0 / deltaP] 2? In general, where F is greater than about 0.3 to about 0.4 (30-40%), reactor shutdown is inevitable. Preferably, F is less than 40%, preferably less than 30%, more preferably less than 20%, still more preferably less than 15%, and most preferably less than 10% to 0%. The rolling rate, the change of F as a function of time, is used to quantify the lamination. If lamination does not occur, the rolling rate is zero. A minimum, acceptable lamination rate for a commercial operation is around 12% / month or 0.4% / day, preferably less than 0.3% / day, more preferably less than 0.2% / day, and most preferably less of 0.1% / day. Examples In order to provide a better understanding of the present invention, including advantages and limitations representative thereof, the following examples are offered. The properties of the polymer were determined by the following test methods: The melt index is measured according to the method ASTM-D-128, condition E. The density is measured according to the method ASTM-D-1238. Bulk density is measured as follows: the resin is poured via a 7/8"(2.2 cm) diameter pipette into a fixed volume cylinder of 400 ce; Bulk density is measured as the weight of resin in the cylinder divided by 400 cc to give a value in g / cc. The particle size is determined as follows: the particle size is measured by determining the weight of the material collected on a series of standard U.S. and determining the average heavy particle size. Fine particles are defined as the percentage of the total distribution that passes through a standard 120 mesh screen. Comparative Example 1 The operation using a metallocene catalyst based on bis (1,3-methyl-n-butyl cyclopentadienyl) zirconium dichloride is described in this example. It shows the rolling effect of operating a commercial reactor using TEAL. This example includes information on starting a commercial reactor with a metallocene catalyst. Catalyst Preparation The metallocene catalyst was prepared from silica dehydrated at 600 ° C. The catalyst was a commercial scale catalyst prepared in a mixing vessel with a stirrer. An initial charge of 1.156 lbs (462 kg) of toluene was added to the mixer. This was followed by mixing 925 lbs (421 kg) of 30% by weight aluminoxane methyl in toluene. This was followed with 100 lbs (46 kg) of bis (1,3-methyl-n-butyl cyclopentadienyl) zirconium dichloride at 20% by weight in toluene (20.4 lbs (9.3 kg) of metallocene content). 144 lbs were added. { 66 kg) of toluene to the mixer, to wipe the metallocene feed cylinder and let it mix for 30 minutes at ambient conditions. This was followed by 54.3 lbs (25 kg) of an AS-990 in toluene, a surface modifier solution containing 5.3 lbs (2.4 kg) of AS-990 content. An additional 100 lbs (46 kg) of toluene wiped the surface modifier container and added to the mixer. The resulting slurry was dried under vacuum at 3.2 psia (70.6 kPa) at 175 ° F (79 ° C) until a free-flowing powder was obtained. The final catalyst weight was 1.093 lbs (497 kg). The catalyst had a final zirconium filler of 0.40% and an aluminum filler of 12.0%. Polymerization The polymerization was conducted in a commercial scale continuous gas phase fluidized bed reactor. The fluidized bed is formed of polymer granules. The gaseous feed streams of ethylene and hydrogen are introduced below the reactor bed into the recycle gas line. The hexene co-monomer is introduced below the reactor bed in a line separated from the recycle gas line. An inert hydrocarbon such as isopentane is also introduced to the reactor in the recycle gas line. Isopentane is added to provide additional thermal capacity to the reactor recycle gases. The individual flow rates of ethylene, hydrogen and co-monomer were controlled to maintain fixed composition objectives. The ethylene concentration was controlled to maintain a constant ratio of hydrogen to ethylene. The concentration of the gases was measured by an in-line gas chromatograph to ensure a relatively constant composition in the recycle gas stream. Triethyl aluminum (TEAL) was introduced as a 20% by weight solution in an isopentane carrier solvent onto the fluidized bed distributor plate, directly into the fluidized bed. The solid catalyst was injected directly into the fluidized bed using purified nitrogen. The catalyst rate was adjusted to maintain a constant production rate. The reactive bed of polymer particles that are developed is maintained in a fluidized state by means of a continuous-flow of the feed gas and of recycle through the reaction zone. The reactor was operated at a total pressure of 310 psig (2,138 kPa). To maintain a constant reactor temperature, the temperature of the recycle gas is continuously adjusted up or down to accommodate any changes in the rate of heat generation due to polymerization. The fluidized bed was maintained at a constant height by removing a portion of the bed at a rate equal to the formation of the particulate product. The product is removed in a semi-continuous way via a series of valves to containers of fixed volume. These fixed volume containers are ventilated back to the reactor through a recycle gas compressor that recovers the gases from the reactor. The product is transferred to a purge vessel to remove trapped hydrocarbons and treated with humidified nitrogen to deactivate the residual catalyst. Experimental Results Experimental run conditions demonstrating lamination in a commercial gas phase reactor are described below. This experiment was run when starting the reactor from the absence of reaction. TEAL was continuously fed to the reactor for this experiment. The run lasted 18 hours before the run was finished due to the lamination of the distributor plate and the reactor cooler. Table 1 Run Conditions Comparative Example 2 The operation of a pilot plant reactor using a metallocene catalyst based on bis (1,3-methyl-n-butyl cyclopentadienyl) zirconium dichloride is described in this example. It shows the effect of rolling on operation at two different temperatures using the same catalyst described above. Catalyst Preparation The metallocene catalyst was identical to that of Example 1. Polymerization The polymerization was conducted in a fluidized bed reactor, gas phase, continuous. The fluidized bed is formed of polymeric granules. The gaseous feed streams of ethylene and hydrogen, together with liquid co-monomer, were mixed together in a T-arrangement and introduced below the reactor bed to the recycle gas line. Hexene was used as co-monomer. Aluminum triethyl (TEAL) was mixed with this stream as a 1% by weight solution in isopentane carrier solvent. The individual flow rates of ethylene, hydrogen and co-monomer were controlled to maintain a constant ethylene partial pressure. The individual flow rates of ethylene, hydrogen and co-monomer were controlled to maintain fixed composition targets. The ethylene concentration was controlled to maintain a constant partial pressure of ethylene. The hydrogen was controlled to maintain a constant molar ratio of hydrogen to ethylene. The concentration of all gases was measured by means of an in-line gas chromatograph to ensure a relatively constant composition in the recycle gas stream. The solid catalyst was injected directly into the fluidized bed using purified nitrogen as carrier. Its rate was adjusted to maintain a constant rate of production.

The reaction bed of polymer particles in development is maintained in a fluidized state by the continuous flow of the feed gases and recycle through the reaction zone. A surface gas velocity of 1-3 ft / sec was used to achieve the above. The reactor was operated at a total pressure of 300 psi. To maintain a constant temperature in the reactor, the temperature of the recycle gas is continuously adjusted up or down to adapt to any changes in the rate of heat generation due to polymerization. The fluidized bed was maintained at a constant height by removing a jousting of the bed at a rate equal to the rate of formation of the particulate product. The product is removed semi-continuously via a series of valves in a fixed volume chamber, which is simultaneously vented back to the reactor. This allows the highly efficient removal of the product, while at the same time recirculating a large portion of the unreacted gases back to the reactor. This product is purged to remove trapped hydrocarbons and treated with a small stream of humidified nitrogen to deactivate any trace amounts of residual catalyst. Results The reactor was stable, producing an ethylene / hexene copolymer with a melt index of 1 and a density of 0.917. The running conditions were the following: Table 2 Corrida conditions These results show high lamination rates in both the cooler and the plate, well beyond the minimum acceptable rate of 0.4% / day. The rolling rate is higher at higher temperature. Comparative Example 3 The operation of a pilot plant reactor using a metallocene catalyst based on bis (1,3-methyl-n-butyl cyclopentadienyl) zirconium dichloride is described in this example.

It shows the effect of rolling on operation at two different temperatures using the same catalyst described above. A higher partial pressure of ethylene is operated, as compared to Example 2. Preparation of the Catalyst The metallocene catalyst was identical to that of Example 1. Polymerization The polymerization was conducted in a continuous gas-phase fluidized-bed reactor, as shown in FIG. described in Example 2. Results The reactor was stable, producing an ethylene / hexene copolymer with a melt index of 1 and a density of 0.917. The run conditions were as follows: Table 3 Run Conditions These results show high lamination rates both in the cooler and in the plate, well beyond the minimum acceptable rate of 0.4% / day. The rolling rate is higher at higher temperature. The rolling rate of the cooler is not affected by the partial pressure of ethylene; however, the plate rolling rate is higher at higher ethylene concentration, as compared to Example 2. Example 4 The operation of a pilot plant reactor using a metallocene catalyst based on bis (1, 3) dichloride. -methyl-n-butyl cyclopentadienyl) zirconium is described in this example. It shows the effect of the lamination on the operation at a lower concentration of TEAL. Preparation of the Catalyst The metallocene catalyst was identical to that of Example 1. Polymerization The polymerization was conducted in a continuous, gas-phase fluidized-bed reactor, as described in Example 2. Results The reactor was in a stable state, producing an ethylene / hexene copolymer with a melt index of 1 and a density of 0.917. The running conditions were the following: Table 4 Running conditions These results show reduced lamination rates on both the cooler and the plate, as compared to Example 3. However, they are still far beyond the minimum acceptable rate of 0.4% / day. Example 5 Operation of a pilot plant reactor using a metallocene catalyst based on bis (1) dichloride, 3-methyl-n-butyl cyclopentadienyl) zirconium is described in this example. It shows the effect of rolling on the operation at a zero concentration of TEAL. Preparation of the Catalyst The metallocene catalyst was identical to that of Example 1. Polymerization The polymerization was conducted in a continuous gas-phase fluidized-bed reactor as described in Example 2. Results The reactor was stable, producing a Hexene copolymer with a melt index of 1 and a density of 0.917. The running conditions were the following: Table 5 Run conditions These results show reduced lamination rates on both the cooler and the plate, compared to the previous examples. However, they were still slightly above the minimum acceptable rate of 0.4% / day. This is due to the fact that Examples 2-5 were all conducted during the same polymerization run. The results without alkyl aluminum were obtained at the same end of the run in a highly laminated reactor. Given this rather severe restriction, this result shows that the rolling rate was still considerably reduced.

Example 6 The operation of a pilot plant reactor using a metallocene catalyst based on bis (1,3-methyl-n-butyl cyclopentadienyl) zirconium dichloride is described in this example. It shows the effect of rolling on the operation at a zero concentration of TEAL. The reactor was started with TEAL, which was removed quickly after a few hours of operation. The reactor conditions were selected to match those that had the highest rolling rate (see Example 3). Preparation of the Catalyst The metallocene catalyst was identical to that of Example 1. Polymerization The polymerization was conducted in a continuous gas-phase fluidized-bed reactor as described in Example 2. Results The reactor was stable, producing a Hexene copolymer with a melt index of 1 and a density of 0.917. The running conditions were the following: Table 6 Run Conditions These results show reduced lamination rates on both the cooler and the plate, in all the examples. The rolling rate was well beyond the minimum acceptable rate of 0.4% / day. The reactor was opened after this run and inspected. Naked metal surfaces were observed both on the plate and the cooler. In contrast, it was found that the reactor contained a heavy polymer build-up both on the cooler and the plate of the previous examples. Example 7 The operation of a pilot plant reactor using a metallocene catalyst based on bis (1,3-methyl-n-butyl cyclopentadienyl) zirconium dichloride is described in this example. It shows the importance of using an alkyl aluminum during the start of the reactor. Trimethyl aluminum (TMA), a more volatile and reactive alkyl aluminum, was used. Preparation of the Catalyst The metallocene catalyst was identical to that of Example 1. Polymerization The polymerization was conducted in a continuous gas-phase fluidized-bed reactor as described in Example 2. Results The reactor pressure was purged to remove all of the traces of oxygen and moisture for several hours. The reaction conditions were established as specified in the table below. The reactor was pre-treated with 150 ppm by weight of TMA.

Table 7 Run Conditions TMA was not fed to the reactor. The catalyst was ripped off. It was continuously fed at an increasing rate for five hours. At this point, a solution of TMA in isopentane was introduced at a rate of 150 cc / hr. The reaction started rather vigorously and uncontrolled after 60 minutes. The TMA feeding was stopped and the reaction began to fall. TMA was re-introduced and the reaction started again in an uncontrolled manner. This "peak" of TMA continued for several hours until the reaction was able to self-sustain without TMA. Example 8 The operation of a pilot plant reactor using a metallocene catalyst based on bis (1,3-methyl-n-butyl cyclopentadienyl) zirconium dichloride is described in this example. It shows the importance of using an alkyl aluminum during the start of the reactor. It also demonstrates the successful completion of the alkyl aluminum feed rate while maintaining catalyst activity.

Catalyst Preparation The metallocene catalyst was identical to that of Example 1. Polymerization The polymerization was conducted in a continuous gas-phase fluidized-bed reactor, as described in Example 2. Results The reactor was purged of pressure to remove all traces of oxygen and moisture for several hours. The reactor conditions were established as stipulated in the table below. The reactor was not post-treated with stripper. Table 8 Run Conditions TEAL was added as a solution in isopentane upon introducing the feed gases to achieve the above concentrations, together with the catalyst. The reaction was observed immediately upon introduction of the catalyst. The TEAL feed was continued until 25% of the expected production rate was achieved. The TEAL feed was finished and the reaction continued to continue until the entire production rate was achieved. TEAL was fed for only 95 minutes with the catalyst. The total reaction rate was achieved after four hours in the absence of TEAL. This result shows the importance of a stripper, in the present alkyl aluminum, to start the reaction. It also shows the ability to remove TEAL and sustain the reaction once it started. Example 9 Examples 9A to 9E illustrate the effect of TEAL concentration, in a slurry polymerization reactor, by fillers, on the activity of the metallocene catalyst. All polymerizations were carried out as described below with the appropriate amount of TEAL shown in Table 1 for each example. Catalyst Preparation In a two-gallon reactor, 1.1 liters of toluene were charged first, then 0.93 liters of 30% by weight MAO solution in toluene, available from Albermarle, followed by 20.1 g of bis (1,3-methyl) dichloride. -n-butyl cyclopentadienyl) zirconium as a 10% solution in toluene. The mixture was stirred for 30 minutes at room temperature, after which 350 g of silica (Davison MS948, dehydrated at 600 ° C) was added to the liquid with slow stirring. The stirring speed was increased by approximately 10 minutes to ensure dispersion of the silica in the liquid and then two portions of 17 ~~ g of additional silica were added with slow stirring, followed by increased stirring. After all of the silica (700 g) was introduced to the reactor, 0.6 liter of toluene was added to form a slurry from liquid to solid having a consistency of 4 cc / g of silica. Mixing was continued for 15 minutes at 120 rpm after 5 g of surface modifier AS-990 (available from Witco Chemical Corporation, Houston, Texas, United States) was dissolved in 100 ml of toluene and added and stirred for 15 minutes. minutes Vacuum drying and some purging with N2 at 175 ° F (79.4 ° C) was then initiated. When it seemed that the catalyst flowed freely, it was cooled and discharged in a vessel purged with nitrogen. An approximate yield of 1.0 kg of dry catalyst was obtained. Polymerization In a two-liter autoclave reactor, under nitrogen purge, the appropriate amount of aluminum triethyl (TEAL) was charged, followed by 60 ml of hexene-1 co-monomer and 800 ml of isobutane diluent. The contents of the reactor were heated to 80 ° C, after which 100 mg of catalyst was introduced concurrently with ethylene to create a total manometric pressure in the 325 psi (2,241 kPa) reactor. The temperature of the reactor was maintained at 85 ° C and the polymerization was allowed to proceed for 40 minutes. After 40 minutes, the reactor was cooled, ethylene was vented and the polymer was dried and weighed to obtain the yield. Table 9 provides the performance and activity data. Table 9 Since the stripping agent is TEAL and the transition metal of the metallocene is zirconium (Zr), the molar ratio for this table is expressed as Al: Zr. Example 9 above illustrates that a certain level of stripper, in this TEAL example, was required in the polymerization reactor to remove impurities. On a certain level, the despojador acts like a poison to the catalyst, as it can be seen by the reduction in the activity. Example 10 The operation of a pilot plant reactor using a metallocene catalyst based on bis (1,3-methyl-n-butyl cyclopentadienyl) zirconium dichloride is described in this example. It shows the effect of operating the process of the invention without TEAL on the quality of the film, as reflected by the gel content in the films made in the process of the invention.

The gels refer to the inclusion of small regions highly visible in the film, typically containing a higher molecular weight and / or a higher density compared to the base polymer. Preparation of the Catalyst The metallocene catalyst was identical to that of Example 1. Polymerization The polymerizations, runs 1A and IB, were conducted in a continuous gas-phase fluidized-bed reactor, as described in Example 2. Results The reactor was a steady state, producing an ethylene / hexene copolymer with a melt index of 1 and a density of 0.917. The run conditions were the following: Table 10 The IB run film was substantially free of occlusions, while the run film 1A had a large number of small occlusions, similar to "sanding" in appearance. Commercially useful films typically contain only a small amount of gels. In this example, the film was made of polymer produced with the stripping agent, TEAL, in the reactor, once the flow of TEAL to the reactor was stopped, the appearance of the film improved considerably from a commercially unacceptable film to a film. having excellent clarity, particularly for use in stretched films. Examples 11-16 Preparation of the Catalyst The metallocene catalyst was prepared from 800 lbs (364 kg) of silica (Davison 948) dehydrated at 600 ° C. The catalyst was a commercial scale catalyst prepared in a mixing vessel with a stirrer. An initial charge of 1.156 lbs (525 kg) of toluene was added to the mixer. This was followed by mixing 925 lbs (420 kg) of methyl 30% alumoxane in toluene. This was followed by 100 lbs (46 kg) of bis (1,3-methyl-n-butyl cyclopentadienyl) zirconium dichloride in toluene (20.4 lbs (9.3 kg) of contained metallocene). An additional 144 lbs (66 kg) of toluene was added to the mixer to wipe the metallocene feed cylinder and allowed to mix for 30 minutes at ambient conditions. The above mixture was added to the silica after which 54.3 lbs (25 kg) of Kemamine AS-990 was added in toluene, a surface modifier solution containing 5.3 lbs (2.4 kg) of Kemamine AS-990 content. An additional 100 lbs (46 kg) of toluene wiped the surface modifier container and added to the mixer. The resulting slurry was dried under vacuum at 3.2 psia (70.6 kPa) at 175 ° F (79 ° C) until a free flowing powder was obtained. The final catalyst weight was 1.093 lbs (497 kg). The catalyst had a final zirconium filler of 0.40% by weight and an aluminum filler of 12.0% by weight. Polymerization The polymerization was conducted in a continuous gas-phase fluidized-bed reactor. The fluidized bed is formed of polymer granules. The gaseous feed streams of ethylene and hydrogen, together with liquid co-monomer, were mixed together in a T-arrangement and introduced below the reactor bed to the recycle gas line. Hexene was used as co-monomer. Aluminum triethyl (TEAL) was mixed with this stream as a 1% by weight solution in isopentane carrier solvent. The individual flow rates of ethylene, hydrogen and co-monomer were controlled to maintain fixed composition objectives. The ethylene concentration was controlled to maintain a constant partial pressure of ethylene. The hydrogen was controlled to maintain a constant molar ratio of hydrogen to ethylene. The concentration of all gases was measured by an in-line gas chromatograph to ensure a relatively constant composition in the recycle gas stream. The solid catalyst was injected directly into the fluidized bed using purified nitrogen as carrier. Its rate was adjusted to maintain a constant rate of production. The reagent bed of polymer particles in development is maintained in a fluidized state by the continuous flow of feed gas and recycle through the reaction zone. A superficial gas velocity of 1-3 ft / sec (30.5-91.4 cm / sec) was used to achieve this. The reactor was operated at a total pressure of 300 psi (2, 069 kPa). To maintain a constant temperature of the reactor, the temperature of the recycle gas is continuously adjusted upward or downward to accommodate any changes in the rate of heat generation due to polymerization. The fluidized bed was maintained at a constant height by removing a portion of the bed at a rate equal to the rate of formation of the particulate product. The product is removed in a semi-continuous way via a series of valves to a fixed volume chamber, which is ventilated simultaneously back to the reactor. This allows the highly efficient removal of the product, while at the same time recycling a large portion of the unreacted gases back to the reactor. This product is purged to remove entrapped hydrocarbons and treated with a small stream of humidified nitrogen to deactivate any traces of residual catalyst.

Table 11 15 20 * Total in ppm by weight of olefinic and aliphatic oligomers having a molecular weight less than 430 in the polymer The polymers produced by this invention can be used in a wide variety of end-use products and applications. The polymers typically have a density in the range of 0.900 to 0.970 g / cc, preferably in the range of 0.905 to 0.965 g / cc, more preferably in the range of 0.910 to 0.915 g / cc to about 0.935 to 0.940 g / cc, most preferably more than 0.915 g / cc. The polymers produced by the process of the invention are useful in forming operations such as extrusion and co-extrusion of films, sheets and fibers, as well as in blow molding, injection molding and rotomolding. Films include blown or cast films formed by co-extrusion or lamination useful as shrink film, bond film, stretched films, sealed films, oriented films, snack packaging films, heavy duty bags, food bags , packaging for baked and frozen foods, medical packaging, industrial liners, membranes, etc., in applications of contact with food and non-food. The fibers include fiber operations by spinning in the melted state, spinning in solution and blowing in the melted state for use in woven or non-woven form for making filters, diaper cloths, medical garments, geo-textiles, etc. Extruded items include medical tubes, wire and cable liners, geo-membranes and pool liners. Molded articles include single-layer and multi-layer constructions in the form of bottles, tanks, large hollow articles, rigid food containers and toys, etc. Although the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those skilled in the art that the invention lends itself to variations not necessarily illustrated herein. For example, it is within the scope of this invention to include an apparatus for removing oligomers in the recycle stream, such as is described in U.S. Patent No. 5,126,414, incorporated herein by reference. Also, the process of the invention can be used in a single reactor in a series reactor or even in series in which one reactor is a slurry reactor and the other is a gas phase reactor. It is also contemplated that when using a series reactor system that a traditional Ziegler-Natta catalyst can be used in a reactor in any of the patented processes previously described and the process of the invention used in a second reactor. For this reason, then, reference should be made only to the appended claims for purposes of determining the true scope of the present invention.

Claims (38)

1. CLAIMS 1. A continuous gas phase process for polymerizing one or more olefins, alone or in combination, in the presence of a metallocene catalyst system and in a reactor capable of producing more than 1,000 lb / hr of a polymeric product, wherein said The process is operated essentially free of stripper, with less than about 1% of any fine particles present in the reactor of size less than 125μ, and the metallocene catalyst system exhibiting a productivity greater than 2,500 grams of polymer per gram of catalyst.
2. 2. The process of claim 1, wherein the polymer product has a density of between 0.88 g / cc and about 0.970 g / cc.
3. 3. The process of claim 1, wherein one of the olefin (s) is ethylene.
4. 4. The process of claim 1, wherein the process is a gas phase fluidized bed process operating in a condensed mode.
5. 5. A continuous gas phase process for polymerizing one or more olefins in a reactor capable of producing more than 1,000 lb / hr of polymer product and in the presence of a metallocene transition metal catalyst component, where said process operates in the absence of stripping agent and the catalyst exhibits a productivity greater than 2,500 grams of polymer per gram of catalyst.
6. 6. A continuous gas phase process for polymerizing monomer (s) in a fluidized bed reactor, said process comprising the steps of: a) introducing a recycle stream into the reactor, the recycle stream comprising the monomer (s); b) introducing a metallocene catalyst system into the reactor; c) introducing less than 300 ppm of stripper based on the total weight of the bed; d) discontinuing the introduction of the stripping agent when a catalyst productivity of 2,500 grams of polymer per gram of metallocene catalyst is reached; e) removing the recycle stream from the reactor; f) cool the recycle stream; g) introducing into said recycle stream additional monomer (s) to replace the polymerized monomer (s) and continue the polymerization in the presence of the metallocene catalyst system in the absence of stripping agent; h) re-entering the recycle stream in the reactor; and i) removing a polymer product from the reactor at a rate greater than 500 lbs / hr.
7. The process of claim 6, wherein the recycle stream is cooled to form a liquid and a gas phase that is introduced into the reactor.
8. 8. The process of claim 6, wherein the liquid and the gas phase are introduced into the reactor separately.
9. The process of claim 6, wherein only the gas phase of the cooled recycle stream is introduced into the reactor.
10. The process of claim 6, wherein the monomer (s) is ethylene and alpha-olefins having from 3 to 20 carbon atoms.
11. The process of claim 6, wherein the liquid phase in the recycle stream is greater than about 2 and about 40% by weight based on the total weight of the recycle stream.
12. The process of claim 10, wherein the stripping agent is introduced into the reactor in an amount less than 250 ppm.
13. The process of claim 10, wherein the stripping agent is introduced with the metallocene catalyst system.
14. The process of claim 10, wherein the introduction of the stripping agent is discontinued within 3 hours from the time that the metallocene catalyst system is introduced into the reactor.
15. 15. The process of claim 10, wherein the introduction of the stripping agent is discontinued once a catalyst productivity greater than 3,000 grams of polymer per gram of metallocene catalyst system is reached.
16. 16. The process of claim 6, wherein the process produces more than 1,000 lbs of polymer product per hour.
17. 17. The process of claim 6, wherein the process produces more than 10,000 lbs of polymer product per hour.
18. 18. The process of claim 6, where the process produces more than 50,000 lbs of polymer product per hour.
19. 19. The process of claim 6, wherein the polymer product has a density between 0.88 g / cc and about 0.970 g / cc.
20. The process of claim 10, wherein the stripping agent is condensed out of the recycle stream after the recycle stream is removed from the reactor.
21. 21. The process of claim 10, wherein the stripping agent is introduced into the reactor in an amount less than 50 ppm.
22. 22. The process of claim 10, wherein the introduction of the stripping agent is discontinued within 6 hours from the time that the metallocene catalyst system is introduced into the reactor.
23. 23. The process of claim 10, wherein less than about 1% of any fine particles present in the reactor are smaller than 125μ.
24. 24. In a gas phase process to polymerize one or more olefins in the presence of a metallocene catalyst system in a reactor where a stripping agent is introduced into the reactor, the improvement comprising discontinuing the introduction of any stripping agent into the reactor during the first twelve hours after the time in which the metallocene catalyst is introduced into the reactor, and subsequently continuing the polymerization reaction in the presence of a metallocene catalyst in the absence of stripping, where the catalyst system exhibits a productivity greater than 2,500 grams of polymer per gram of catalyst.
25. 25. The process of claim 2, wherein the reactor is capable of producing more than 10,000 lbs / hr of polymer product.
26. 26. The process of claim 25, wherein less than about 0.85% of any fine particles present in the reactor are smaller than 125μ.
27. 27. The process of claim 26, wherein the reactor is capable of producing more than 50,000 lbs / hr 'of polymer product.
28. The process of claim 27, wherein less than about 0.15% of any fine particles present in the reactor are smaller than 125μ.
29. 29. The process of claim 27, wherein less than about 1% of any fine particles present in the reactor are smaller than 125μ.
30. 30. The process of claim 29, wherein the reactor is capable of producing more than 10,000 lbs / hr of polymer product.
31. 31. The process of claim 30, wherein less than about 0.85% of any fine particles present in the reactor are smaller than 125μ.
32. 32. The process of claim 31, wherein the reactor is capable of producing more than 50,000 Ibs / hr of polymer product.
33. 33. The process of claim 32, wherein less than about 0.15% of any fine particles present in the reactor are smaller than 120μ.
34. 34. The process of claim 5, wherein the stripping agent is aluminum alkyl.
35. 35. The process of claim 5, wherein the catalyst exhibits a productivity greater than 3,000 grams of polymer per gram of catalyst.
36. 36. The process of claim 5, wherein the process produces more than 10,000 Ibs of polymer product per hour.
37. 37. The process of claim 5, wherein the process produces more than 50,000 lbs of polymer product per hour.
38. 38. The process of claim 5, wherein the polymer product has a density between 0.88 g / cc and about 0.970 g / cc. The present invention relates to a continuous process for the polymerization of olefins using a catalyst or metallocene catalyst system in a continuous slurry or gas phase polymerization process. The invention is directed more particularly to a gas phase polymerization process for polymerizing one or more olefins in the presence of a metallocene catalyst system in a fluidized bed reactor in the absence of or with a low amount of a stripping agent.