MXPA97009501A - Process to transition between incompatib polymerization catalysts - Google Patents

Abstract

This invention relates to a process for transitioning between polymerization catalyst systems that are incompatible with each other. Particularly, the invention relates to a process for transitioning from an olefin polymerization reaction using a traditional Ziegler-Natta catalyst system to an olefin polymerization reaction using a metallocene catalyst system.

Description

PROCESS TO TRANSITION BETWEEN INCOMPATIBLE POLYMERIZATION CATALYSTS Field of the Invention This invention relates to a process for transitioning between polymerization catalyst systems that are incompatible with each other. Particularly, the invention relates to a process for transitioning between an olefin polymerization reaction using a traditional Ziegler-Natta catalyst system and an olefin polymerization reaction using a metallocene catalyst system, and vice versa. BACKGROUND OF THE INVENTION During the production of olefin polymers in a commercial reactor it is often necessary to transition from a type of catalyst system that produces polymers having certain properties and characteristics to another catalyst system capable of producing polymers of different chemical attributes and / or physical The transition between traditional Ziegler-Natta, similar catalysts, or compatible catalysts generally takes place in an easy manner. However, where catalysts or different types are incompatible, the process is typically complicated. For example, in the case of the transition between a traditional Ziegler-Natta catalyst and a chromium-based catalyst, two incompatible catalysts have been found that some of the components of the traditional Ziegler catalyst and the co-catalyst / activator act as poisons for the chromium-based catalyst. Consequently, these poisons prevent the chromium catalyst from promoting polymerization. In the past, to achieve an effective transition between incompatible catalysts, the first catalysed olefin polymerization process is stopped by various techniques known in the art. The reactor is then emptied, recharged and a second catalyst is introduced into a reactor. Such catalyst conversions are time consuming and expensive due to the need to stop the reactor for a prolonged period of time during the transition. The term "catalyst killers" or "deactivating agents" refers to deactivation of the catalyst, which may be a partial or complete suppression of a polymerization reaction. It is known to use polar gases or low molecular weight polar liquids in order to "kill" traditional Ziegler-Natta catalyst systems. For example, EP-A-116917 discloses using carbon dioxide and alcohol as killers of Ziegler-Natta catalyst. U.S. Patent No. 4,701,489 discloses the use of water to suppress a polymerization process with traditional Ziegler-Natta catalyst. It is also known to use high molecular weight products such as polyglycols, epoxides, ethylene copolymers, organic titanium compounds, alkoxysilanes, peroxides, zeolites as a carrier of water, or surfactants to kill traditional Ziegler-Natta catalysts. U.S. Patent No. 4,460,755 describes a process for converting a polymerization reaction catalyzed by a Ziegler-natta-type catalyst into one catalyzed by a chromium-based catalyst. This particular transition process uses a hydroxyl-containing compound that interacts with the Ziegler-Natta type catalyst by physical or chemical means. Recently, metallocene-type catalyst systems are being used in polymerization processes to produce polyolefins having generally superior physical and chemical attributes than those products of the traditional Ziegler-Natta catalyst processes. There are a variety of murderers of known metallocene catalysts. For example, catalyst killers for metallocene / alumoxane based catalyst systems include methanol and n-butanol. PCT International Publication No. WO 92/14766, published on September 3, 1992, describes the use of volatile and non-volatile assassins of metallocene-based catalysts in a high-pressure polymerization process. It would be highly advantageous to have a process to transition between incompatible catalysts, without the need to stop the polymerization reaction, by emptying the reactor to discard the original catalyst system and re-start the reaction of polymerization with another catalyst system. In addition, this process to transition must not adversely affect polymer products. SUMMARY OF THE INVENTION The invention is directed to a process for transitioning between at least two catalyst and / or incompatible catalyst systems in a polymerization process. In one embodiment, the process of the invention comprises the steps of: a) discontinuing the introduction of one of the catalysts or incompatible catalyst systems in a reactor; b) introducing and dispersing a deactivating agent through the reactor; c) purging the reactor of any remaining deactivating agent; and d) introducing into the reactor, in the absence of any stripping material, a second catalyst or catalyst system incompatible with the first catalyst system. As used herein, the phrase "in the absence of any stripping material" means that the reactor is essentially kept free of any stripping material. The period of time during which this occurs is equivalent to the time for essentially a "turn" of the second catalyst system, or the period of time required for the production of an amount of polymer equivalent to the weight of the reactor bed. After completing a "turn", despoiling materials may be used, if desired. Optionally, the deactivating agent can be introduced and dispersed in an active polymerization zone of the reactor.

The phrase "active polymerization zone", as used herein, means that the polymerization conditions are maintained throughout the transition. In one embodiment of the invention, a process for transitioning between a polymerization reaction catalyzed by a traditional Ziegler-Natta type catalyst system to a polymerization reaction catalyzed by a metallocene-type catalyst system is provided, and vice versa. Typically, where the first catalyst employed is a Ziegler-Natta type catalyst, and the second catalyst employed is a metallocene type catalyst, the first polymer produced has a molecular weight distribution greater than 3.5, and the second polymer has a molecular weight distribution of less than 3.3. In a preferred embodiment, the transition process of the invention is continuous. Detailed Description of the Invention Introduction The invention relates to a process for transiting between catalysts and / or incompatible catalyst systems to convert from a reactor that produces polymer with one type of system to produce polymer with another type of system, with minimum downtime of the reactor. In particular, in a preferred embodiment, the process is aimed at transitioning between a catalyst / traditional Ziegler-Natta catalyst system and a catalyst / metallocene catalyst system. For the purposes of this patent description and the appended claims, the terms "catalysts" and "catalyst systems" are used interchangeably. The process of this invention can be used in a gas phase polymerization process, in solution phase, in slurry or in bulk phase. A gas phase polymerization process in a fluidized bed reactor is preferred. In a typical continuous gaseous fluidized bed polymerization process, for the production of polymer from monomer, a gaseous stream comprising monomer is passed through a fluidized bed reactor in the presence of a catalyst under reactive conditions. A polymeric product is removed. A stream of cycle gas, which is continuously circulated and usually cooled, is also removed, and together with additional monomer sufficient to replace the polymerized monomer, is returned to the reactor. In one embodiment, the cycle gas stream is cooled to form a mixture of a gas and a liquid phase which is then introduced into the reactor. For a detailed description of a gas phase process, see U.S. Patent Nos. 4,543,399; 4,588,790; 5,028,670; 5,352,769; and 5,405,922, all of which are incorporated herein by reference in their entirety. When transitioning between compatible catalysts, typically there are only small differences in their performance towards hydrogen and co-monomer; However, transitioning to an incompatible catalyst is not so direct. For example, the extreme differences in response to molecular weight regulators, such as hydrogen and the co-monomer, from traditional Ziegler-Natta catalysts and metallocene catalysts, make these catalysts incompatible. Any traces of active Ziegler-Natta catalyst will produce a product of extremely high molecular weight under metallocene catalyst reactor conditions. Furthermore, particularly in a continuous transition process, the interaction between the two incompatible catalysts can lead to the production of high levels of small particles smaller than about 125 microns, called "fine particles". These fine particles can induce operational problems in the reactor such as rolling and flaking. In addition, these operational problems often result in a lower polymer product, since for example a film made of this product will often have a considerable amount of gels. The inventors have discovered a process for transitioning between two or more incompatible catalysts, particularly useful in a continuous gas phase polymerization process, thereby mitigating or eliminating the aforementioned problems. During the transition from a first catalyst to a second catalyst, particularly in a continuous process, it is reasonable to expect interaction or contact of the two to occur. catalysts. For compatible catalysts, the transition normally occurs by interrupting the feeding of the first catalyst while feeding the second catalyst. Typically, it can take many hours, such as up to about 72 hours, or typically five or more times the residence time in the reactor, until the first catalyst is completely consumed. In this way, for a long period of time the resin produced is a mixture of both the first and the second catalyst. Catalyst Compatibility As previously discussed, compatible catalysts are those catalysts that have similar kinetics of termination and insertion of monomer and co-monomer (s) and / or do not interact negatively with each other. For the purposes of this patent description and the appended claims, "incompatible catalysts" are those that satisfy one or more of the following criteria: 1) those catalysts which in the presence of others reduce the activity of at least one of the catalysts in more 50%; 2) those catalysts that under the same reactive conditions, one of the catalysts produces polymers having a molecular weight greater than two times that of any other catalyst in the system; and 3) those catalysts that differ in co-monomer incorporation or reactivity ratio under the same conditions in more than about 30%.

Although in the preferred embodiment the process of the invention focuses directly on the transition between a traditional Ziegler-Natta catalyst and a metallocene catalyst, it is within the scope of this invention that the process of the invention can be applied to any transition between incompatible catalysts. For example, the transition between a traditional Ziegler-Natta catalyst and a chromium catalyst or the transition between a chromium catalyst and a metallocene catalyst or even the transition between a traditional Ziegler-Natta titanium catalyst to a Ziegler vanadium catalyst. Natta This invention contemplates that the direction of the transition between incompatible catalysts is not limited; however, it is preferred that the process of the invention be the transition from any other catalyst incompatible with a metallocene catalyst. Traditional Ziegler-Natta catalysts typically comprise a transition metal halide in the material, such as titanium or vanadium halide, and an organometallic compound of a metal of group 1, 2 or 3, typically trialkylaluminum compounds, which serve as an activator for the transition metal halide. Some Ziegler-Natta catalyst systems incorporate an internal electron donor that is complexed with aluminum alkyl or transition metal. The transition metal halide may be supported on magnesium compounds or complexed therewith. East Active Ziegler-Natta catalyst can also be impregnated on an inorganic support such as silica or alumina. For the purposes of this patent disclosure, chromium catalysts, for example described in U.S. Patent No. 4,460,755, which is incorporated herein by reference, are also considered as traditional Ziegler-Natta catalysts. For more details on traditional Ziegler-Natta catalysts, see for example U.S. Patent Nos. 3,687,920; 4,086,408; 4,376,191; 5,019,633; 4,482,687; 4,101,445; 4,560,671; 4,719,193; 4,755,495; and 5,070,055, all of which are incorporated herein by reference. Metallocene catalysts, for example, are typically those voluminous transition metal ligand complexes derivable from the formula:. { [(It ') - M (A «) n] tk} 11 [B'-i] i where L is a bulky ligand bound to M, p is the anionic charge of L and m is the number of ligands L and m is 1, 2 or 3; A is a ligand linked to M and capable of inserting an olefin between the bond MA, q is the anionic charge of A and n is the number of ligands A and n is 1, 2, 3 or 4, M is a metal, preferably a transition metal, and (pxm) + (qxn) + k corresponds to the formal oxidation state of the metal center; where k is the charge on the cation and k is 1, 2, 3 or 4, and B 'is a non-nucleophilic, chemically stable anionic complex, preferably having a molecular diameter of 4 Angstroms or more, and j is the anionic charge on B ', h is the number of charge cations k, and i is the number of charge anions j such that hxk = jxi. Any two ligands L and / or A may be bridged together. The catalyst compound may be complete sandwich compounds having two or more ligands L, which may be cyclopentadienyl ligands or substituted cyclopentadienyl ligands, or sandwich medium compounds having a ligand L, which is a cyclopentadienyl ligand or cyclopentadienyl ligand substituted with heteroatom or ligand substituted hydrocarbyl cyclopentandienyl such as an indenyl ligand, a benzin-denyl ligand or a fluorenyl ligand and the like or any other ligand capable of n5 bonding to a transition metal atom (M). One or more of these bulky ligands is pi-linked to the transition metal atom. Each L can be substituted with a combination of substituents, which can be the same or different, including hydrogen or linear, branched or cyclic alkyl, alkenyl or aryl radicals, for example. The metal atom (M) can be a transition metal of group 4, 5 or 6 or a metal of the series of lanthanides and actinides, preferably the transition metal is of group 4, particularly titanium, zirconium and hafnium in any formal oxidation state, preferably +4. Other ligands can be linked to the transition metal, such as a leaving group, such as but not limited to weak bases such as amines, phosphines, ether and the like. In addition to the transition metal, these ligands may be optionally linked to A or L. In one embodiment, the metallocene catalyst system used in this invention is formed from a catalyst compound represented by the general formula: (LP) mM (Aq) n (Er) 0 and a aluminum alkyl, alumoxane, modified alumoxane or any other organometallic compound containing oxy or non-coordinating ionic activators, or a combination thereof. Where L, M, A and p, m, q and n are as defined above and E is an anionic leaving group such as but not limited to hydrocarbyl, hydrogen, halide or any other anionic ligand; r is the anionic charge of E and o is the number of ligands E and o is 1, 2, 3 or 4 such that (pxm) + (qxn) + (rxo) is equal to the formal oxidation state of the metal center. Non-limiting examples of metallocene catalyst components and metallocene catalyst systems are discussed, for example, in U.S. Patent Nos. 4,530,914; 4,805,561; 4,937,299; 5,124,418; 5,017,714; 5,057,475; 5,064,802; 5,278,264; 5,278,119; 5,304,614; 5,324,800; 5,347,025; 5,350,723; 5,391,790; and 5,391,789, all of which are incorporated herein by reference in their entirety. Also the descriptions of EP-A-0 591 756; EP-A-0 520 732; EP-1-0 578 838; EP-A-0 638 595; EP-A-0 420 436; WO 91/04257; WO 92/00333; WO 93/08221; WO 93/08199; WO 94/01471; WO 94/07928; WO 94/03506; and WO 95/07140, all of which are incorporated herein by reference in their whole. In a preferred embodiment, the metallocene catalyst used in this invention is deposited on support materials known in the art, for example any porous support material such as inorganic chlorides and inorganic oxides, such as silica, alumina, magnesia, chloride of magnesium or any polymeric material, such as polyethylene and polystyrene divinyl benzene. In another embodiment, the metallocene catalyst used in this invention is unsupported and is as described in U.S. Patent No. 5,317,036, incorporated herein by reference. Polymerization and Catalyst Inhibitors In order to inhibit the polymerization of a first incompatible catalyst, it is necessary to interrupt the injection of the catalyst into a reactor. Stopping the feed of the first catalyst to the reactor does not immediately stop the polymerization reactions occurring inside the reactor, because the fluidized bed contains catalyst particles that can still polymerize for a prolonged period of time. Even if the polymerization reactions within the reactor were allowed to continue for a period of time, the catalyst within the reactor would not be fully deactivated for a considerable period of time. In this way, to substantially end these polymerization reactions inside the reactor, "deactivating agents" are employed. For the purposes of this patent disclosure, the deactivating agents do not include that minor portion of material that functions as a catalyst killer and may be contained in the monomer or co-monomer feed streams during normal polymerization conditions (e.g. , internal olefins). The deactivating agents used in this invention are those killers or inhibitors that inactivate the ability of a catalyst to polymerize olefins. The deactivating agents of the invention include, but are not limited to, for example, carbon dioxide, sulfur oxides, sulfur trioxides, glycols, phenols, ethers, carbonyl compounds such as ketones, aldehydes, carboxylic acids, esters, fatty acids. , alkynes such as acetylene, amines, nitriles, nitroso compounds, pyridine, pyroids, carbonylsulfide, organic halides such as carbon tetrachloride and mercaptans. It is also important that the deactivating agent does not include oxygen, alcohol or free water. It has been found that the use of these compounds, such as alcohols, results in the adhesion of the fine polymer particles to the walls of the reactor and the subsequent lamination of the reactor, as shown in the following examples. In one embodiment, the deactivating agent is a porous, inorganic or organic material, such as silica, by example containing water that is either absorbed or adsorbed. Preferably, the porous material containing water has an ignition weight loss of 3% by weight. Ignition loss is measured by determining the weight loss of the porous material maintained at a temperature of about 1,000 ° C for 16 hours. In another embodiment, the porous material is silica that is dehydrated at a temperature of less than 200 ° C. It is within the scope of this invention that these deactivating agents can be used in any combination; however, a technician in the field will recognize that some of these killers can react to each other and thus are better introduced separately. In the preferred embodiment in the process of the invention, once the feeding of the incompatible first catalyst has been interrupted, a deactivating agent is introduced to the reactor for a sufficient period of time to substantially deactivate the catalyst in the reactor and from this way to substantially prevent further polymerization from occurring. The use of the deactivating agent decreases the possibility of lamination and / or flaking occurring in the reactor where the process of the invention takes place within the reactor in which the polymerization with the first catalyst was occurring. The preferred deactivating agent is carbon dioxide. The amount of deactivating agent used depends on the size of the reactor and the amount and type of catalysts and co-catalysts. in the reactor. The minimum amount of deactivating agent used is important. It is necessary before introducing a second incompatible catalyst that the first catalyst is substantially deactivated and can not be reactivated. Preferably, the deactivating agent of the invention in one embodiment is used in an amount based on the total atom grams of the transition metal components of the catalyst in the reactor. However, where any activator or co-catalyst is used with the first catalyst, and such an activator or co-catalyst is capable of reacting with the second catalyst, the deactivating agent is used in an amount based on the total atom grams of the components transition metal of the first catalyst and any activator. In one embodiment, the deactivating agent is used in an amount greater than 1 molar equivalent, preferably greater than 2 molar equivalents based on the total atom grams of the transition metal of the first catalyst in the reactor. Thus, in another embodiment, the amount of deactivating agent introduced into the reactor is in the range of a molar ratio of 1 to 10,000 of deactivating agent to the total metal of the first catalyst and any activator in the reactor, preferably 1 to 1,000, more preferably about 1 to about 100. Often, when a Ziegler-Natta catalyst is used, a stripping component is used. In In some circumstances, the activator or co-catalyst also functions as a stripper. In this way, the deactivating agent must be used under these circumstances in an amount such that the molar ratio of the deactivating agent to the total metal of the catalyst and activator and / or stripping agent exceeds about 1, preferably greater than about 1.5. In another embodiment, the deactivating agent is used in an amount in the range of 100 to 125% of that necessary to completely inactivate all of the first active catalyst. In yet another embodiment, once the deactivating agent has been introduced into the reactor, a period of time of about 5 minutes to about 24 hours, preferably from about 1 hour to about 12 hours, occurs with greater preferably from about 1 hour to 6 hours, and most preferably from about 1 to 2 hours, before continuing with the transition process. The duration depends on the nature and amount of catalyst and the volume of the reactor, and the reactivity of the deactivating agent. In a gas phase reactor there is a bed which is typically of extremely large size and very large amount of polymer. In this way, a sufficient period of time is necessary to allow the deactivating agent to disperse throughout the reactor, particularly through any polymeric product within the reactor. For this and other reasons, it is a preferred embodiment that the deactivating agent is a gas or vapor at the reaction conditions. Typically, in the process of the invention it is important to substantially free the reactor of impurities, particularly the deactivating agent, which can render the second catalyst inactive upon entering the reactor. Thus, in the preferred embodiment of the invention, pressure purge or flow purge methods, known in the art, are used to remove the deactivating agent and any other impurities or byproducts. In a typical process, the first incompatible catalyst is a traditional Ziegler-Natta catalyst and an organometallic compound is introduced to the reactor acting either as an activator or a stripper, or both. These organometallic compounds can include, for example, BX3, where X is a halogen, R ^ Mg, ethyl magnesium, R4C0RMg, RCNR, ZnR2, CdR2, LiR, SnR4, where each of the R groups is a hydrocarbon group that can be the same or different. Other organometallic compounds typically used are those compounds of organometallic alkyl of group 1, 2, 3 and 4, alkoxides and halides. Preferred organometallic compounds used with lithium alkyls, magnesium or zinc alkyls, magnesium alkyl halides, aluminum alkyls, silicon alkyl, silicon alkoxides and silicon alkyl halides, the most preferred organometallic compounds being aluminum alkyls and magnesium alkyls. In one embodiment, these compounds organometallics are a hydrocarbyl aluminum 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 halogen, for example chlorine, bromine or iodine, with chlorine being preferred; a is 0, 1 or 2. The most preferred organometallic compounds used are aluminum alkyls, for example triethylaluminum (TEAL), trimethylaluminum (TMAL), tri-isobutylaluminum (TIBAL), and tri-n-hexylaluminum (TNHAL) and the like , and the more widely used alkyl aluminum that is used as a stripping agent or an activator, or both, is TEAL. In the preferred embodiment of transitioning from a traditional Ziegler-Natta catalyst to a metallocene catalyst, it is preferred that substantially all of the activating and / or despoiling compounds, for example TEAL, be removed from the process of the invention prior to the introduction of the metallocene catalyst. metallocene catalyst. In one embodiment of the process when transitioning to a metallocene-type catalyst, the process is operated essentially free of a stripping agent prior to the introduction of the metallocene-type catalyst. 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, based on the total weight of the recycle stream, are present. just before the introduction of the metallocene catalyst. As well It is important that a common catalyst feed system is used, which is also substantially free of any residual residual incompatible catalyst. In another embodiment, the deactivating agent is any component capable of reacting with any of the above organometallic compounds to produce at least one compound having a carboxylic acid functionality. Non-limiting examples of carboxylic acid compounds include acetic acid, propionic acid, isopentanoic acid and heptanoic acid. Start-up Procedures During polymerization with the first incompatible catalyst, gases accumulate inside the reactor, which originate from the electron donor when the first catalyst is especially a Ziegler-Natta catalyst. These gases are typically poisonous to the first catalyst, and particularly to the second incompatible catalyst. These gases of a traditional Ziegler-Natta catalyst include, for example, tetrahydrofuran (THF), ethanol, ethyl benzoate and the like. Also, the introduction of the deactivating agent produces side products that can be negative to any polymerization process. In this way, as previously mentioned, before introducing the second incompatible catalyst, the content of the reactor is subjected to what is known in the art as a purge of pressure. Typically, the method is used in the handling of any air or moisture sensitive materials to remove, purge or reduce in the process of the invention, for example, catalytic killers and byproducts thereof and reagents at a lower level . Once this procedure is complete, the gas composition in the reactor system, as a direct consequence of the first catalyst, is adjusted for the second catalyst. For a given catalyst to produce a given product of a certain density and a certain melt index, which generally depends on how well a catalyst incorporates the co-monomer, a certain gas composition must be present in the reactor. Generally, the gas composition contains one or more of the monomer (s), including ethylene alone or in combination with one or more linear or branched monomers having from 3 to 20 carbon atoms, preferably 3 to 12 carbon atoms. The process is particularly well suited to ethylene gas compositions in combination with one or more monomers, for example, propylene alpha-olefin monomers, butene-1, pentene-1,4-methylpentene-1, hexene-1, octene-1. , cyclic and polycyclic decene-1, styrene and olefins such as cyclopentene, norbornene and cyclohexene or a combination thereof. Other monomers for use with ethylene may include polar vinyl monomers, diolefins such as 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, norborne neno, norbornadiene and other unsaturated monomers including acetylene, 1-alkynes and aldehyde monomers. Higher alpha-olefins and polyenes or macróraeros can also be used. 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, the gas composition contains ethylene 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 3 to 8 carbon atoms more preferably, optionally with at least one diene monomer. Preferred terpolymers include combinations such as ethylene-butene-1-hexene-1, ethylene / propylene / butene-1, ethylene / propylene / hexene-1, ethylene / propylene / norbornadiene, ethylene / propylene-not , 4-hexadiene, and the like. Typically, the gas composition also contains an amount of hydrogen to control the melt index of the polymer to be produced. Under typical circumstances, the gas also contains an amount of a component that increases the dew point, the remainder of the gaseous composition constituted by non-condensable inerts, for example nitrogen. Depending on the second catalyst to be introduced into the reactor, the gaseous composition, such as the co-monomer and the hydrogen gas concentrations, may be increased or decrease. In the preferred embodiment, the gaseous composition is decreased, particularly when a metallocene catalyst is used as the second catalyst in the process of the invention. Typically, the reactive gas composition is diluted as before, for example either by pressure purge or flow purge methods, which are well known in the art. During this step, as discussed above, impurities such as electron donors are also removed from the catalyst. Once the reagent concentrations are sufficiently diluted to accommodate the second catalyst and all poisons are substantially removed, the next step in the invention is to introduce the second catalyst. Most preferred when transitioning to a metallocene catalyst is that no stripping component, for example any of the organometallic compounds described above, is introduced into the reactor, especially just prior to the introduction of the metallocene catalyst. In a preferred embodiment, the fluidized bed is maintained in a fluidized condition during the process of this invention. Once the bed is fluidized and the new gaseous composition introduced into the reactor, the second catalyst is introduced into the reactor under reactive conditions. In a preferred embodiment, the agent Carbon dioxide deactivator is injected into a gas phase reactor. One method would be to pump liquid carbon dioxide to the gas phase reactor. Another method would be to vaporize carbon dioxide contained in a pressure vessel with an external heat source and inject the vapor into the gas phase reactor. In the preferred embodiment, liquid carbon dioxide, under its own vapor pressure, flows into the circulating cycle gas stream of the gas phase reactor. This circulating gas stream provides sufficient heat and turbulent mixture to vaporize most of the carbon dioxide before it reaches the reactor. As the carbon dioxide leaves the vessel, the pressure inside the cylinder is reduced, causing it to vaporize additional carbon dioxide present in the vessel, thereby cooling the vessel, and reducing the vapor pressure of the carbon dioxide present. If the carbon dioxide is removed only as a vapor, a considerable portion of the carbon dioxide can remain in the vessel without pumping or without additional heat to aid its removal. To avoid the need to use a pump, the carbon dioxide container must be at a temperature above 60 ° F (16 ° C), when a reactor operating at a gauge pressure of 300 psi (2,069 kPag) is fed. The use of a "drip tube" in the carbon dioxide container, a piece of tubing that extends below the liquid level in the container.

When carbon dioxide is being drained, it will allow the removal of a substantial portion (such as about 80%) of the carbon dioxide present in the vessel under its own steam pressure, without heating or pumping complements. The preferred embodiment also includes the use of a stainless steel injection fitting, which is a piece of stainless steel tubing that extends through a packing gland into the flowing gaseous stream. This prevents contact between cold carbon dioxide and carbon steel, the predominant type of metal in the reaction system. Carbon steel is susceptible to catastrophic brittle fracture at temperatures below -20 ° F (-29 ° C), such as those that may occur when vaporizing carbon dioxide. Examples The properties of the polymers of the following examples were determined by the following test methods: melt index: ASTM D-1238-condition E Density: ASTM D-1505 Bulk density: the resin is poured via a pipette of 7 / 8"(2.22 cm) in diameter to a cylinder with a fixed volume of 400 cc Bulk density is measured as the weight of the resin divided by 400 cc to give a value in g / cc.

Particle size: the particle size is measured by determining the weight of the material collected on a series of U.S. Standard and determining the average heavy particle size based on the series of sieves used. The fine particles are defined as the percentage of the total distribution that passes through a standard screen of 120 mesh. It has an equivalent particle size of 120 microns. Fine particles are important because high levels of them can lead to lamination and flaking of the reaction cycle gas system. This results in scaling of the distributor plate of the heat exchanger, requiring shutdown of the reactor for cleaning. The experimental indicators of operability problems use the measurement of temperatures that exist in the reactor wall. The temperature can be measured using any appropriate device, but in general the most common are thermocouple devices. As the temperature being measured is close to the reactor wall or "epidermis", they are referred to as epidermal thermocouples. Typically, epidermal thermocouples are 5-10 ° F (1-4 ° C) below the internal bed temperature. Deviations from the baseline are indicative of reactor operability problems. These deviations can be positive or negative. The positive deviations of epidermis thermocouple are the result of rolling of the reactor due to a reaction that moves away on the wall of the reactor. As the temperature continues to increase, it reaches the melting point of the polymer, at which point a solid strip of polymer forms and dislocates from the main body of the reactor, resulting in severe operational problems. In many cases, reactor shutdown is required from several hours to even days to remove the sheets before re-initiating the polymerization process. Negative deviations of epidermis thermocouple are less serious because they are representative of "cold" polymer being located in the wall of the reactor. However, this can present a problem if they persist since a solid insulating layer is formed in the walls of the reactor. If this layer continues to grow, it can quickly transform into a reactor sheet. This phenomenon is referred to as a "cold band". It has been found that cold bands are often associated with the adhesion of small polymer particles or "fine particles" to the reactor wall. Example 1 The transition from a Ziegler-Natta catalyst to a metallocene catalyst based on bis (1,3-methyl-n-butyl-cyclopentadienyl) zirconium dichloride is described in this example. It uses a deactivating agent that reacts with both the aluminum alkyl and the Ziegler-Natta catalyst. The process did not result in fine particles adhering to the walls of the reactor, measured by means of "cold bands" or lamination of the reactor. Also, the products produced did not result in the formation of gels in the film products. Finally, the transition time between catalysts was relatively fast. Catalyst Preparations The metallocene catalyst was prepared from silica at 600 ° C having a water content of 1.3% by weight (Davison 948 silica, available from W.R. Grace, Davison Chemical Division, Baltimore, Maryland, United States). This catalyst was prepared by mixing 850 pounds (386 kg) of silica with 340 pounds (154 kg) of a catalyst precursor. The catalyst precursor was prepared separately by mixing together 82 pounds (37 kg) of a 28% by weight solution of bis (l-methyl-3-n-butyl-cyclopentadienyl) zirconium dichloride in toluene with 1.060 pounds (481 kg) ) of a 30% by weight solution of methylalumoxane, available from Albermarle Corporation, Baton Rouge, Louisiana, United States. Additional 1,300 lbs (590 kg) of toluene were added and the mixture was maintained at 80 ° F (27 ° C) for 1 hour, after which 6 lbs (3 kg) of a surface modifier was added (Kemamine AS- 990, available from Witco Chemical Corporation, Houston, Texas, United States) and allowed to mix for one hour. Vacuum was applied and the catalyst was allowed to dry for 15 hours. Then it was dried at 175 ° F (79 ° C) until it became free flowing powder. The final weight of the catalyst was 1.216 lbs (552 kg). The final catalyst had a load of zirconium of 0.40% and a load of aluminum of 12.5%. The Ziegler-Natta catalyst was prepared by impregnating a complex of titanium chloride, magnesium chloride and tetrahydrofuran (THF) on a silica support from a THF solution. The silica is first dehydrated at 600 ° C to remove water and chemically treated with aluminum triethyl to further remove the remaining water. The catalyst was treated by adding tri-n-hexylaluminum (TNHAL) and diethylaluminum chloride (DEAC) in isopentane solution and drying to become the final Ziegler-Natta catalyst. The final catalyst had a titanium content of 1% and the molar ratio DEAC / THF was 0.26 and the TNHAL / THF ratio was 0.29. The preparation of this catalyst is similar to that described in EP-A-0 369 436. Fluidized Bed 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 the liquid co-monomer, were mixed together in a mixer T arrangement and introduced downstream of the reactor bed to the recycle gas line. Both butene and hexene were used as co-monomers. Triethylaluminium (TEAL) was mixed with this stream as a 2% by weight solution in isopentane carrier solvent. The individual flow rates of ethylene, hydrogen and monomers were controlled to maintain fixed composition goals. The ethylene concentration was controlled to maintain a constant partial pressure of ethylene. The ethylene concentration was controlled to maintain a constant partial pressure of ethylene. 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 Ziegler-Natta catalyst was injected directly into a fluidized bed using purified nitrogen as a carrier. Its rate was adjusted to maintain a constant rate of production. The reactive bed of polymeric particles in growth is maintained in a fluidized state by the continuous flow of the feed and the recycle gas through the reaction zone. A surface gas velocity of 1-3 ft / sec (30 cm / sec - 91 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 incoming recycle gas is continuously adjusted up or down using a gas cooler 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 particulate product. The product was removed in a semi-continuous manner via a series of valves to a fixed volume chamber, which is simultaneously ventilated via a series of valves to a fixed volume chamber. This allows 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 trapped hydrocarbons and treated with a small current of humidified nitrogen to deactivate any trace amounts of residual catalyst. The reactor was equipped with 26 thermocouples mounted on the external surface of the reactor and the expanded section. These were monitored continuously using a Honeywell TDC 3000 process computer. These thermocouples are referred to as "epidermis thermocouples". Experimental Results The reactor was stable using a conventional Ziegler-Natta catalyst producing an ethylene / butene copolymer with a melt index of 23 and a density of 0.923. The run conditions are given in Table 1: Table 1 The transition was stopped by reducing the concentration of TEAL to 150 ppm. After 4 hours, the catalyst and TEAL feed was stopped. The reaction was allowed to continue for 8 hours. After the waiting period of 8 hours, carbon dioxide was injected and allowed to circulate for 4 hours. The target amount of carbon dioxide was around 17,000 ppm, based on the volume of reactor gas. The gas analysis of the reactor content resulted in a carbon dioxide level of 12,500 ppm. The reactor was then depressurized to remove the high concentration of carbon dioxide and other impurities and byproducts by multiple pressure purges with nitrogen from 10.7 to 5.2. bars (10.6 to 5.1 atm). The composition of the reactor was then adjusted by bringing fresh gaseous components to the following levels: Ethylene (% molar) 50 Hydrogen (% molar) 0.0185 (185 ppm) Hexeno (% molar) 1.2 No increase in reactor temperature was observed when the concentrations, indicated the absence of any reaction by the Ziegler-Natta catalyst. The metallocene catalyst was then stripped off at 9 g / h. The catalyst feed was increased in increments of 1 g / h to increase the reaction rate. The reaction started immediately upon the addition of the metallocene catalyst. After 12 hours, the reaction rate achieved steady-state conditions. The conditions of the ethylene / hexene copolymer product at steady state were of a melt index of 3.0 and a density of 0.9153 g / cc. The corresponding run conditions are shown in Table 2: Table 2 Polymer samples were collected at yield rates of 1, 2, 3, 4 and 5 beds (bed yield = bed weight / total production). These samples were then analyzed for gels using a ribbon extruder manufactured by Haake. There was no evidence of gels. The melt index during the transition was measured and there was no evidence of an abnormally low melt index production. The epidermis thermocouples were carefully monitored throughout the run and no significant deviation from the reactor temperature was observed. This indicates the absence of fine particles adhering to the reactor wall, as measured by "cold bands", and the absence of lamination measured by positive excursions of the thermocouples of epidermis. These results were verified by the total absence of sheets or chips in the polymer product. These results show that the use of carbon dioxide results in the successful transition from a Ziegler-Natta catalyst to a scale-free metallocene catalyst or reactor lamination, without the formation of high molecular weight gels in the resulting polymer product. The transition time was relatively short, requiring less than 22 hours. Example 2 The transition from a Ziegler-Natta catalyst to a metallocene catalyst based on bis (l-methyl-3-n-butylcyclopentadienyl) zirconium dichloride is described in this example. It uses an absorbent which can be any porous material such as inorganic oxides, inorganic chlorides and the like. In this example, silica containing water was used to deactivate the Ziegler-Natta catalyst. The transition process of this example did not result in the formation of gels in the resulting film product. However, the reaction products formed resulted in fine particles adhering to the walls of the reactor, as measured by "cold bands", and the transition time was relatively fast. Preparation of the Catalyst The metallocene and Ziegler-Natta catalysts used in this example were identical to those of Example 1.

Fluidized Bed Polymerization Polymerization was conducted in the continuous reactor, as described in Example 1. Experimental Results The reactor was operating at steady state using the conventional Ziegler-Natta catalyst producing an ethylene / butene copolymer with melt index of 24. (° / min) and a density of 0.924 g / cc. Run conditions were as shown in Table 3 below: Table 3 The transition was initiated by reducing the concentration of TEAL to 150 ppm. After 4 hours, the catalyst and TEAL feed was stopped. The reaction was allowed to continue for 12 hours. After the waiting period of 12 hours, the reactor was depressurized by means of multiple pressure purges with nitrogen of 10.7 to 5.2 bar (10.6 to 5.1 atm). The reactor was re-pressurized to 21.7 bar (21.4 atm) with nitrogen. Wet silica (Davison 948), with a moisture content of 9.95%, determined by ignition loss (LOI), was added to the reactor over a period of 7 hours. (The LOI can be measured by determining the weight loss of the absorbent, the silica, which was maintained at a temperature of about 1,000 ° C for 16 hours.) Silica with a 1.750 ppm weight basis was added to the bed of the absorber. reactor. The content of the reactor was circulated with silica for an additional 4 hours. The by-products of the reaction were then removed by purging the reactor pressure as described above. The composition of the reactor was then adjusted by bringing fresh gas composition to the following levels: Ethylene (% molar) 50 Hydrogen (% molar) 0.0815 (185 ppm) Hexeno (% molar) 1.2 No increase in reactor temperature was observed when the concentrations, indicating the total absence of any reaction by the Ziegler-Natta catalyst. The metallocene catalyst was then stripped off at 5 g / h. The catalyst feed was increased in increments of 0.5 g / h to increase the reaction rate. The reaction was slow to start, requiring approximately 4 hours from the catalyst injection time. After 18 hours, the reaction rate achieved steady state conditions. The conditions of the ethylene / hexene copolymer product at steady state were a melt index of 3.5 (° / min) and a density of 0.919 g / cc. Corresponding run conditions are shown in Table 4: Table 4 Polymer samples were collected at yields of 1, 2, 3, 4 and 5 beds. These samples were then analyzed for gels, using the Haake extruder. No gels were formed. The melt index during the transition was measured and a low production of the melt index was indicated. The epidermis thermocouples were monitored during the whole transition. No significant deviation of the reactor temperature was observed until the silica feed was started. At this point, the epidermis thermocouples were reduced considerably, resulting in the formation of "cold bands" indicating fine particles that adhere to the walls of the reactor. The epidermis temperature readings were reduced by as much as 15 ° C. Once the silica feed was stopped, the epidermis thermocouples began to recover back to their baseline. However, they did not fully recover until well after the catalyst was started. No positive deviations of the epidermis thermocouples occurred. These results show that the use of wet silica results in the successful transition of a Zie-gler-Natta catalyst to a metallocene catalyst free of rolling or flaking of the reactor, without the formation of high molecular weight gels. It is believed that the formation of "cold bands" is due to the adhesion of silica to the walls of the reactor. Although it is undesirable, it did not have a negative effect on the performance of the reactor. The transition time was longer than that of Example 1, requiring more than 48 hours. Comparative Example 1 The transition from a Ziegler-Natta catalyst to a metallocene catalyst based on bis (l-methyl-3-n-butylcyclopentadienyl) zirconium dichloride is described in this example.

No deactivating agent is used to deactivate the Ziegler-Natta catalyst and shows the negative effect on the properties of the product and the operability of the reactor. Preparation of the Catalyst The metallocene and Ziegler-Natta catalysts used in this example were identical to those of Example 1. Fluidized Bed Polymerization The polymerization was conducted in the same continuous reactor as in Example 1. Experimental Results The reactor was in a stable state using the Ziegler-Natta catalyst, producing an ethylene / butene copolymer with a melt index of 18 and a density of 0.925 g / cc. The running conditions are given in Table 5: Table 5 The transition was initiated by stopping the catalyst feed and TEAL. The reaction was left to die for 24 hours. The reactor was depressurized by multiple pressure purges with nitrogen of 10.7 to 5.2 bar (10.6 to 5.1 atm). The composition of the reactor was then adjusted to bring the fresh gas composition to the following levels: Ethylene (% molar) 50 Hydrogen (% molar) 0.0185 (185 ppm) Hexene (mole%) 1.2 Upon introduction of the etiyen, a sudden increase in the reactor temperature. It increased rapidly from 85 to 91 ° C, after which it decreased back to 85 ° C. The metallocene catalyst was then stripped off at 9 g / h. The catalyst feed was increased in increments of 1 g / h to increase the reaction rate. The metallocene reaction started immediately and continued to progress at a steady state production rate for the next 12 hours. The melt index dropped very rapidly during the initial period to a value as low as 0.48 ° / min. This was the result of the re-initiation of the Ziegler-Natta catalyst. After 12 hours, the reaction rate reached steady state conditions. The conditions of the ethylene / hexene product at steady state were a melt index of 3.1 (° / min) and a density of 0.916 g / cc. The corresponding run conditions are listed in Table 6 below: Table 6 Polymer samples were collected at yields of 1, 2, 3, 4 and 5 beds. These samples were then analyzed for gels using the same ribbon extruder of Example 1. There was a massive amount of gels in the product. These gels persisted for various bed yields, and resulted in an unacceptable film quality. The epidermis thermocouples were monitored. During the initial period of the transition, a significant positive deviation of the reactor temperature was observed for several of the epidermis thermocouples, indicating the occurrence of rolling in the reactor. This persisted for a period of 4 hours, after which normal readings were obtained. Negative deviations of the epidermis thermocouples were not observed, indicating the absence of fine particles that adhere to the reactor wall. Several sheets and chips were observed in the product shortly after the deviation of epidermis thermocouples. These results demonstrate the negative effects without using a deactivating agent. The formation of the low melt index polymer resulted in severe gel formation and unacceptable product quality. The continuity of the reactor was also disturbed as a result of the rolling of the reactor for a short period of time. The transition time was quite long, requiring a total time of 36 hours. Comparative Example 2 The transition from a Ziegler-Natta catalyst to a metallocene catalyst based on bis (l-methyl-3-n-butylcyclopentadienyl) zirconium dichloride is described in this example. It uses methanol to deactivate the Ziegler-Natta catalyst and shows the harmful effect on the properties of the product and the operability of the reactor. Preparation of the Catalyst The metallocene and Ziegler-Natta catalysts used in this example were similar to those of Example 1. Fluidized Bed Polymerization The polymerization was conducted in a continuous reactor similar to that of Example 1.

Experimental Results The reactor was stable using the conventional Ziegler-Natta catalyst, producing an ethylene / butene copolymer with a melt index of 1 (° / min) and a density of 0.918 g / cc. The run conditions were as shown in Table 7: Table 7 The transition was initiated by reducing the concentration of TEAL to 150 ppm. After 4 hours, the catalyst and TEAL feed was stopped. Methanol was then injected into the reactor. The methanol was added at a stoichiometric ratio of 1.33: 1 catalyst and activator. The reactor was left to circulate for 4 hours, after which it was depressurized by means of Multiple pressure purges with nitrogen from 10.7 to 5.2 bar (10.6 to 5.1 atm). The composition of the reactor was then adjusted to the following objectives of fresh gas composition: Ethylene (% molar) 55 Hydrogen (% molar) 0.0105 (105 ppm) Hexeno (% molar) 1.2 Positive significant deviations were observed thermocouple epidermis temperature of the reactor after only one bed yield at various points. Slides began to appear in the product, and shortly thereafter, reactor shutdown was required due to plugging of the reactor product discharge system. The melt index fell during the initial period to a value as low as 0.47 ° / min, indicating the formation of a high molecular weight polymer. Polymer samples were collected at 1 bed yield. These samples were then analyzed for gels using the same ribbon extruder of Example 1. The film produced from the polymer in this example contained an excessive amount of gels. The presence of gels confirmed the fall of the melt index. These results show the negative effects of a deactivating agent forming an alkoxy-type by-product. The continuity of the reactor was unacceptable due to the rolling of the reactor. Finally, the polymer formation of Low melt index resulted in severe gel formation and unacceptable product quality. Example 3 This example illustrates the use of carbon dioxide injection equipment in a commercial scale transition of a Ziegler-Natta catalyst to a metallocene catalyst. The commercial reactor had a bed weight of 130,000 lbs (59,000 kg). Equipment Description Carbon dioxide, used as a deactivating agent, was received in 6 standard cylinders, each containing 50 lbs (22.7 kg) of carbon dioxide. These cylinders contained drip tubes, to allow the liquid to be fed from the bottom of the cylinder first. The initial temperature of the cylinder was 60 ° F. The stainless steel pipe ran from these cylinders through a packing gland, to the cycle gas pipe. Experimental Results With the reactor at a pressure of 300 psi (2,069 kPag), the valves were opened to simultaneously drain the 6 cylinders. The flow proceeded at high rates and then dropped substantially after 17 minutes, when the temperature of the liquid carbon dioxide in the cylinder dropped to 10 ° F, causing the cylinder pressure to drop to a gauge pressure of 325 psi (2,241 kPag). ). The cylinders were heavy, showing that 245 lbs (111 kg) of carbon dioxide had entered the reactor. This weight of carbon dioxide is equal to 82% of the initial content of the cylinder. Although the present invention has been described and illustrated by reference to particular embodiments, those skilled in the art will appreciate that the invention lends itself to variations not necessarily illustrated herein. For example, it is not beyond the scope of this invention to transition between one or more mixed catalysts to one or more incompatible mixed catalysts and vice versa, or between a Ziegler-Natta catalyst and a chromium catalyst. It is also contemplated by the invention that one or more reactors can be used, wherein the process of the invention takes place within a first reactor or within a second reactor or at an intermediate location before entering the first reactor (when a reactor is used) or to the second reactor (when two or more are being used reactors in series or otherwise). For this reason, then, it should refer only to the appended claims to determine the true scope of the present invention.

Claims (11)

1. CLAIMS 1. A process for transitioning from a polymerization reaction catalyzed by a first catalyst to one catalyzed by a second catalyst comprising a metallocene catalyst, wherein said first and second catalysts are incompatible, said process comprising the steps of: a) discontinuing the introduction of the first catalyst to a reactor; b) introducing into and dispersing throughout the reactor a deactivating agent in an amount greater than about 1 molar equivalent, based on the total metal atom grams of the first catalyst in the reactor; c) purging the reactor; and d) introducing the second catalyst into the reactor in the absence of any stripping agent.
2. 2. A process for converting a continuous olefin polymerization reaction catalyzed by a first catalyst which is a Ziegler-Natta type catalyst comprising a transition metal halide and an organometallic compound of groups 1, 2 or 3, to a reaction of continuous polymerization of olefins catalyzed by a second catalyst which is a metallocene-type catalyst comprising a metallocene component and an activator, said process for converting comprising the steps of: a) discontinuing the introduction of the first catalyst to a reactor; b) introducing into and dispersing throughout the reactor a deactivating agent in an amount greater than about 1 molar equivalent based on the total metal atom grams of the first catalyst in the reactor; c) purging the reactor of any remaining deactivating agent; and d) introducing the second catalyst into the reactor in the absence of any stripping agent.
3. 3. The process of claim 1, wherein the first catalyst comprises a traditional Ziegler-Natta catalyst.
4. The process of any of the preceding claims, wherein the amount of deactivating agent is greater than about 2 molar equivalents, based on the grams of total metal atom of the first catalyst in the reactor.
5. 5. The process of any of the preceding claims, wherein said polymerization reaction is a gas phase process.
6. The process of any of the preceding claims, wherein the stripping agent is an organometallic compound represented by the formula AlR (3_a) Xa, wherein R is a straight or branched chain alkyl or cycloalkyl or a hydride radical having from 1 to 30 carbon atoms, x is a halogen, is already 0, 1 or 2.
7. 7. The process of any of the claims precedents, where the deactivating agent is carbon dioxide.
8. The process of any of the preceding claims, wherein the molar ratio of the deactivating agent to the total metal of the first catalyst and any activator and any stripping agent in the reactor is in the range of more than 1 to about 1,000.
9. 9. The process of any of the preceding claims, wherein the polymerization is conducted in a fluidized bed reactor. The process of any of claims 6-9, wherein the deactivating agent is reactive toward the organometallic compound to form at least one compound to form at least one compound having a carboxylic acid functionality. The process of any of the preceding claims, wherein the first catalyst in the presence of the second catalyst under the same reactive conditions reduces the activity of the second catalyst by more than 50%.