RU2307838C2 - Latent matallocene catalytic systems for polymerization - Google Patents

Abstract

FIELD: polymerization catalysts.

SUBSTANCE: invention provides a method for temporary and reversible passivation of active matallocene catalytic system, which method is accomplished by contacting this catalytic system with unsaturated hydrocarbon selected from group consisting of C₄-C₁₄-alkines, C₄-C₁₄-alkenes, and polycyclic alkenes containing non- reactive β-hydrogen. Also proposed is method of polymerization of C₂-C₁₄-olefins comprising (i) a step wherein above-mentioned passivated catalytic system is supplied in amount of about 1 to about 5 equivalents per 1 equivalent zirconium in common with at least one C₂-C₁₄-olefin to polymerization reactor, (ii) a step wherein above-mentioned catalytic system is dispersed in polymerization medium, and (iii) catalytic system reactivation step.

EFFECT: enabled reduction of catalytic system activity to a level, which allows supplying the system to reactor in contact with olefin monomer and properly dispersing catalyst in polymer bed within reactor until catalyst is reactivated.

10 cl, 2 tbl, 22 ex

Description

BACKGROUND OF THE INVENTION

This invention relates to metallocene catalyst systems for the polymerization of olefins. More specifically, this invention relates to a method for the temporary and reversible passivation of metallocene catalysts to obtain metallocene compositions suitable as latent olefin polymerization catalysts.

Latent olefin polymerization catalysts according to this invention, after activation, are particularly suitable for the polymerization of alkenes, including 1-olefins, such as propylene, in a gas phase reactor.

The production technology of polypropylene (PP) has evolved towards the improvement of catalysts from complex processes in suspension using an inert hydrocarbon diluent to simpler processes in bulk using a liquid propylene diluent and to even simpler processes in the gas phase.

Processes in a gas phase reactor are widely known and well described in the art, including methods carried out in a continuously stirred reactor and in a fluidized bed. Examples of such reactors are described in US patents 3957448, 3965083, 3971786, 3970611, 4129701, 4101289, 3652527 and 4003712. Typical olefin gas phase polymerization reactor systems include at least one reaction vessel into which olefin monomer and catalyst components can be added and in which contains a mixed layer of polymer particles. Typically, the catalyst components are added together or separately through one or more channels with control valves in one or in the first, if several, reactor. The olefin monomer can be introduced into the reactor through a gas recycle system in which unreacted monomer removed as off-gas and a new portion of the starting monomer are mixed and injected into the reaction vessel. The polymerization is carried out under conditions that exclude the presence of oxygen, water and other substances that act as poisons for the catalysts. The molecular weights of the polymers are regulated by additives, such as hydrogen, by methods well known in the art.

The Amoco gas phase process can generally be described as a process carried out using two horizontal sequentially coupled gas phase bed reactors. Plug reactors use a blocking system that separates the first stage homopolymer reactor from the second stage copolymer reactor. This method provides its inherent short residence time in combination with optimized mixing, minimal temperature deviations and leads to a more uniform product consistency. The Amoco process is described generally in the Polypropylene Handbook, p.p. 297-298 of Hanser Publications, NY (1996) and is described in more detail in US Pat. No. 3,957,448 and Simplified Gas-Phase Polypropylene Process Technology, presented in Petrochemical Review March, 1993.

Rubber-modified polypropylene polymers are produced on an industrial scale for the most part by mixing separately obtained homopolymer and copolymer at the mixing stage. Processes in reactors when the homopolymer formed from the first monomer in the first reactor then reacts with the second monomer in the second reactor are also disclosed and described in the prior art. Processes in gas phase reactors, such as those described in Hydrocarbon Processing, 74, p.p. 140-142, are suitable for the production of impact-resistant PP polymers. The two-stage horizontal gas phase reactor described in Polyolefins VI SPE RETEC, Houston, TX (1991), p. 68, was also used to produce high impact polypropylene. Methods for producing copolyolefins are also described in Petrochemical Review March, 1993, in US Pat. No. 3,957,448 and in Chemical Engineering Science, vol. 47, 9-11 (1992), p.p.2591-2596.

The polymerization catalysts commonly used in carrying out these methods were typically Ziegler-Natta type catalysts. For example, the Amco gas phase process, as described in the prior art, uses the fourth generation of supported catalysts consisting of three components: a proprietary solid CD catalyst, an aluminum trialkyl activator or cocatalyst, and a modifier or donor. Separately, the components of the catalyst are inactive. Therefore, the CD catalyst and activator can be suspended in propylene and fed to the reactor as separate streams without initiating polymer formation in the feed lines of the starting materials.

Recently, a technology has been developed for the preparation of catalysts based on metallocene compounds, called the sixth generation of catalysts in E. Albizzati et al. in the Polypropylene Handbook. Metallocene catalysts, more commonly described as Group 4 or 5 metallocenes, are soluble organic complexes that are formed by the reaction of biscyclopentadienyl transition metal complexes (metallocenes) with a catalyst, usually an aluminum compound. Most metallocene catalysts used for the polymerization of propylene are obtained on the basis of zirconium, and the most widely used cocatalyst is methylaluminoxane (MAO), obtained on the basis of trimethylaluminum (TMA). Other metallocene catalyst systems described in the prior art include combinations of dialkylmetallocenes with boron compounds and optionally aluminum trialkyl compounds.

Supported metallocene based catalyst systems are also known, described as highly active supported metallocene based catalyst systems immobilized on a carrier with particles having a narrow size distribution such as finely divided silica, alumina, MgCl ₂ , zeolite, and the like. Polymerization methods in solution and in the bulk of ethylene and propylene using supported metallocene catalysts are widely known in the art.

Metallocene catalysts are difficult to use directly in conventional polymerization processes, and especially in gas phase processes, when the catalyst system is dispersed in a hydrocarbon or in a monomer and dosed to the reactor through feed lines. Supported metallocene catalysts have optimal activity if they are preactivated, namely, they are connected to the cocatalyst before being fed to the reactor. Dispersion of such catalysts in an olefin monomer stream for direct feed into the system of reactors leads to the formation of polymer and causes intense blockage of the feed lines. Moreover, polymerization occurs before the catalyst system is completely and uniformly dispersed in the polymer layer in the reactor, which leads to the appearance of very active sites that promote lump formation and cladding. The reactor quickly becomes clogged, the yield per catalyst decreases, and frequent shutdowns are required to clean the reactor.

Inert gases, hydrocarbons, and the like were used as diluents and carriers for use with Ziegler-Natta catalysts. These methods have been quite successful with the use of soluble metallocene catalysts in solution and bulk polymerization systems. When carrying out gas-phase processes using a continuous mixing reactor and a fluidized bed, the use of such diluents and carriers for supplying supported metallocene catalyst systems to the reactor in an olefin stream was not generally successful. Although it is possible to solve the clogging problem by dispersing the supported catalyst in an inert hydrocarbon such as propane and separately dispensing the mixture into the reactor, it is difficult to adequately quickly disperse the catalyst in the polymer layer in the reactor in order to avoid the formation of lumps and bundles.

A temporary decrease in the activity of metallocene catalysts is also described. For example, it has been described as a method of controlling the addition of dialkylborane or dialkaluminium to the reactor during the polymerization to temporarily reduce the activity of metallocene catalysts. However, with this treatment, the activity of the catalyst is only partially reduced. Catalysts directly treated with dialkyl borane or dialkyl aluminum retain sufficient activity and initiate polymerization when dispersed in the feed of the starting monomer. Moreover, the regeneration period is very short, too short for the catalyst system to be adequately dispersed in the stirred bed of the gas phase reactor before the catalyst is regenerated and polymerization begins.

It is known that metallocene catalysts are deactivated by Lewis acids. Reactivation of a Lewis acid-treated catalyst after it has been dispersed in a reactor requires the addition of an excess of MAO, which is poorly dispersed due to its low volatility. It is also described that in order to avoid clumping and formation of polymer on the walls during suspension polymerisation of ethylene polymers and copolymers, it is possible to separately add alkali metal alkyl or alkaline earth metal alkyl and a fully active supported metallocene catalyst in the reactor before contacting with the monomer. The prior art also describes the use of Lewis bases to slow or break metallocene-catalyzed polymerization as a means of controlling the process. The resumption of polymerization, accompanied by the addition of excess MAO, may require the addition of the same amount of MAO as was used in the initial preparation of the catalyst. Due to the low volatility, uniform dispersion of MAO in the reactor bed is difficult and the polymerization activity after renewal can be significantly reduced. Moreover, many Lewis bases are irreversible poisons for catalysts. During the continuous process, such poisons will accumulate over time in the reactor, which will require termination of the process and cleaning of the reactor.

Thus, there is still no way to temporarily and reversibly passivate metallocene catalysts, in which the activity of the catalyst decreases to a level that will allow the catalyst to be fed into the reactor in contact with the olefin monomer and adequately disperse the catalyst in the polymer layer in the reactor until the catalyst is reactivated.

SUMMARY OF THE INVENTION

This invention relates to a method for temporarily and reversibly passivating metallocene catalysts, wherein fully active metallocene catalysts can be temporarily and reversibly passivated by contacting with an effective amount of a passivating compound.

The temporarily and reversibly passivated metallocene catalysts of the invention, further characterized as latent olefin polymerization catalysts, have significantly lower activity in the polymerization of olefins, therefore, the latent catalyst can be dispersed in an olefin monomer such as propylene, then sent to the reactor and dispersed in the polymer layer in reactor without significant polymerization of the monomer. Preferably, the latent catalyst remains inactive as a catalyst for the polymerization of olefins under reactor operating conditions until it is reactivated again, for example, by contacting with an effective amount of activator in a subsequent reaction step.

The invention will now be described and described as related to a gas phase olefin polymerization process, including reversible passivation of a conventional metallocene catalyst to produce a latent catalyst, supply of a latent catalyst to the reactor, possibly in contact with the monomer, subsequent reactivation of the catalyst and polymerization.

Description of Preferred Options

Metallocene catalyst systems suitable for carrying out the invention, also referred to in the prior art as metallocene catalysts and metallocene catalyst complexes, include metallocenes selected from Group 4 and Group 5 metallocenes (IUPAC nomenclature), and a suitable cocatalyst, preferably an alumoxane cocatalyst, such as methylaluminoxane (MAO )

The prior art describes a large number of metallocenes suitable for producing metallocene catalyst systems, including compounds of titanium, zirconium, hafnium, vanadium, niobium and tantalum. Examples of such complexes are:

dimethylsilyl bis- (2-methyl-4,5-benzo [e] indenyl) zirconium dichloride;

dimethylsilanediyl bis- (3-tert-butyl-5-methylcyclopentadienyl) zirconium dichloride;

diethylsilanediyl bis- (3-tert-butyl-5-methylcyclopentadienyl) zirconium dichloride;

methylethylsilanediyl-bis- (3-tert-butyl-5-methylcyclopentadienyl) zirconium dichloride;

dimethylsilanediyl-bis- (3-tert-butyl-5-ethylcyclopentadienyl) zirconium dichloride;

dimethylsilanediyl-bis- (3-tert-butyl-5-methylcyclopentadienyl) dimethyl zirconium;

dimethylsilanediyl bis- (2-methylindenyl) zirconium dichloride;

diethylsilanediyl bis- (2-methylindenyl) zirconium dichloride;

dimethylsilanediyl bis- (2-ethylindenyl) zirconium dichloride;

dimethylsilanediyl bis- (2-isopropylindenyl) zirconium dichloride;

dimethylsilanediyl bis- (2-tert. butylindenyl) zirconium dichloride;

diethylsilanediyl bis- (2-methylindenyl) zirconium dibromide;

dimethyl sulfide bis- (2-methylindenyl) zirconium dichloride;

dimethylsilanediyl bis- (2-methyl-5-methylcyclopentadienyl) zirconium dichloride;

dimethylsilanediyl bis- (2-methyl-5-ethylcyclopentadienyl) zirconium dichloride;

dimethylsilanediyl bis- (2-ethyl-5-isopropylcyclopentadienyl) zirconium dichloride;

dimethylsilanediyl bis- (2-methylindenyl) zirconium dichloride;

dimethylsilanediyl bis- (2-methylbenzindenyl) zirconium dichloride;

dimethylsilanediyl bis- (2-methylindenyl) hafnium dichloride;

dimethylsilyl bis- (2-methyl-4-phenylindenyl) zirconium dichloride;

dimethylsilyl bis- (2-ethyl-4-phenylindenyl) zirconium dichloride;

dimethylsilyl bis- (2-methyl-4-naphthylindenyl) zirconium dichloride;

dimethylsilyl bis- (2-ethyl-4-phenylindenyl) zirconium dichloride;

dimethylsilyl bis- (2-methyl-4-isopropylindenyl) zirconium dichloride;

dimethylsilyl bis- (2-ethyl-4-isopropylindenyl) zirconium dichloride and

isopropylidene- (3-tert-butyl-cyclopentadienyl) (fluorenyl) zirconium dichloride.

It was found that zirconium-based metallocenes are especially suitable for creating catalytic systems for the polymerization of propylene.

Metallocene catalyst systems also contain cocatalyst. Particularly suitable are aluminoxane compounds, more commonly referred to as poly (hydrocarbylaluminium oxide). Alumoxanes are well known in the art and can be prepared by reacting water with an aluminum alkyl. Typically, upon receipt of aluminoxanes from, for example, trimethylaluminum and water, a mixture of linear and cyclic compounds is obtained.

Alumoxanes can be obtained in various ways. For example, aluminum alkyl may be treated with water as a wet solvent. In addition, alkylaluminum, for example trimethylaluminum, can be brought into contact with a salt hydrate, for example iron sulfate hydrate, for example, by treating a dilute solution of trimethylaluminum in toluene with a suspension of iron sulfate heptahydrate. Methylaluminoxanes can also be prepared by reacting tetraalkyldiallyumoxane containing C ₂ -alkyl groups or alkyl groups with a large number of carbon atoms with trimethylaluminum using trimethylaluminum in an amount less than a stoichiometric excess.

The preparation of methylaluminoxanes can also be carried out by reacting a trialkylaluminum or tetraalkyldiallyumoxane containing C ₂ -alkyl groups or alkyl groups with a large number of carbon atoms with water to form polyalkylaluminoxane, which then reacts with trimethylaluminum. The synthesis of methylaluminoxanes, also known as modified aluminoxanes, by reacting a polyalkylaluminoxane containing C ₂ -alkyl groups or alkyl groups containing a greater number of carbon atoms with trimethylaluminum and then with water is described, for example, in US Pat. No. 5,041,584. Suitable aluminoxanes can be obtained from commercial sources, including Albemarle Corporation and Akzo-Nobel.

Suitable methods for combining the metallocene and cocatalyst to produce the metallocene catalyst systems used in the practice of this invention are well known and described in the art. The amounts of alumoxane and metallocene commonly used in the preparation of a catalytically active product can vary widely. The molar ratio of aluminum atoms contained in aluminoxane to metal atoms contained in the metallocene is usually in the range of from about 2: 1 to about 100,000: 1, preferably in the range of from about 10: 1 to about 10,000: 1 and, more more preferably in the range of from about 50: 1 to about 2,000: 1.

The reaction products of metallocene and aluminoxane are usually solids that can be isolated by well-known methods. For example, upon receipt of aliphatic solvents in the medium, the solid product is separated and can be isolated from the liquid by filtration under vacuum or decantation; upon receipt of aromatic solvents in the medium, the reaction products can be precipitated with a miscible solvent and then collected or isolated by evaporation of the solvent. The isolated catalytically active solid product can then be dried in a stream of pure dry nitrogen or other inert gas, under vacuum, or by any other known method.

The metallocene catalyst system can be used on its own in the polymerization of olefins as a soluble catalyst, or it can be applied to a suitable carrier, such as, for example, finely divided silica, alumina, MgCl ₂ , zeolite, layered clays, mesoporous molecular sieves, or the like. P. For this purpose, particulate polymer substrates can also be used, for example a finely divided polyolefin. The carrier particles preferably have a diameter in the range from 1 to 300 μm and, more preferably, from 20 to 70 μm. Carriers can be used directly or they can be used with pre-treated MAO before applying the metallocene component; in the prior art MAO / silica supports are described for use in metallocene catalytic systems for the polymerization of propylene. Preparative methods for the preparation of fully active supported metallocene catalyst systems suitable for use in accordance with this invention are described in the prior art, including EP 567952 and EP 578838 and in EP 810233. Various substrates suitable for use in the practice of the invention, including MAO / dioxide silicon are available from commercial sources, such as, for example, Witco Corporation. Particularly suitable silica substrates are available from Grace-Davison, PQ Corporation, Crosfield Chemicals and Degussa Corporation.

Typically, a supported catalyst can be prepared by precipitating the metallocene component from a suspension on an MAO / silica substrate, followed by drying. According to an alternative preferred method for preparing a supported catalyst system, the metallocene complex is supported on a suitable carrier, for example, dried silica suspended in a suitable solvent, such as, for example, toluene, then treated with MAO or another aluminoxane compound and metallocene complex. The mixture together with the suspended substrate can then be precipitated using a miscible non-solvent such as dodecane, followed by precipitation of the catalyst components on a support. Then the catalyst is filtered off and dried. Alternatively, the mixture may be evaporated to dryness.

The molar ratios of Al in aluminoxane to Zr or another metal in the metallocene complex are from 50: 1 to 2000: 1, preferably from 100: 1 to 100: 1, even more preferably from 200: 1 to 600: 1. The amount of the impregnating solution is chosen so that the carrier impregnated with a solution of the metallocene complex and the aluminoxane compound contains from 5 to 50 μmol of metallocene per 1 g of carrier after drying.

The active metallocene catalyst can be temporarily and reversibly passivated for use in the practice of the invention when contacted with an effective amount of a passivating compound to produce a latent metallocene catalyst. Compounds suitable for use as passivating compounds in the practice of this invention are unsaturated hydrocarbons selected from the group consisting of C ₄ -C ₁₄ alkynes, for example, 1-hexine, 3-hexine and the like, C ₄ - With ₁₄ allenes, for example 3-methyl-1,2-butadiene, etc., and polycyclic alkenes containing non-reactive beta hydrogen, usually containing up to 20 carbon atoms, such as, for example, norbornylene, tetracyclo [4.4.0.1 ^{2 5} , 1 ^7,10 ] -3-dodecene and the like.

The metallocene catalyst may be contacted with the passivator by any conventional method, for example, by suspending the catalyst in a suitable liquid medium containing the passivator. The amount of passivator is usually sufficient to provide from about 1 to about 5 equivalents of passivator per equivalent of metal in the catalyst complex. The temperature during passivation is not particularly critical and therefore the method can be carried out at any convenient temperature for a period of time sufficient to complete the reaction. Temperatures below room temperature or room temperature are usually suitable, although passivation is completed more quickly at elevated temperatures of the order of 50-100 ° C. or higher, and preferably at temperatures below the volatility temperatures of the passivator and the selected medium. A passivated or latent metallocene catalyst can then be collected by filtration and dried or used directly without isolation.

The latent metallocene catalyst after dispersion in the reactor will be reactivated and combined with the olefin monomer to carry out the polymerization. The ideal case is when the catalyst, being in contact with the olefin monomer, is thermally reactivated upon reaching the polymerization temperature or shortly thereafter and does not require the addition of an activator. However, depending on the particular combination of passivator and catalyst, thermal reactivation can occur very slowly under such conditions. Achieving acceptable levels of catalytic activity over an acceptable period of time may require the addition of an activator capable of reacting with the latent catalyst to replace and thereby remove the substitution group. The activating agent is selected depending on the particular passivating agent used. Among the substances that may be suitable for this purpose are hydrogen, metal alkyls such as trialkylaluminium and the like.

Not limited to any particular theory, it can be considered that deactivation occurs when an unsaturated hydrocarbon passivator is embedded in a metallocene complex with the formation of a passivator-metallocene complex containing a bulky group that blocks or significantly slows down the corresponding incorporation of the olefin monomer, which is necessary for the polymerization of olefins. For example, it turns out that treatment of the metallocene complex with norbornylene leads to the formation of a norbornyl – metallocene complex, which, in turn, leads to the incorporation of an olefin monomer, such as propylene, at a very low rate under reaction conditions. Thus, a slight polymerization of propylene is observed or it does not occur at all.

However, as soon as propylene is integrated into the complex, the blocking group is displaced from the active site, forming active catalyst fragments. The rate at which reactivation of the catalyst occurs is influenced by several factors, including monomer concentration and reaction temperature. If the rate of such auto-reactivation is very low, an activator, for example, a compound capable of reducing or alkylating the blocking group, such as, for example, hydrogen, alkylaluminum, etc., can be used to remove the blocking group and regenerate the active metallocene catalyst complex.

For this purpose, hydrogen has been found to be particularly effective in promoting the removal of the blocking group during hydrogenolysis and the formation of inert hydrocarbons as a by-product.

The amount of activator used depends in part on the particular hydrocarbon component used to passivate the metallocene catalyst and on the rate at which thermal activation occurs in the reactor, as well as on the type of particular activator. Therefore, the amount of activator is selected so that it is effective to provide an active catalyst for the polymerization of monomers under reaction conditions. Typically, if an activator is used, an amount of this activator that is effective for this purpose is in the range of from about 0.1 to about 100 equivalents, preferably from about 0.1 to about 10 equivalents per equivalent of unsaturated hydrocarbon contained in the latent catalyst.

The latent catalyst compositions of this invention are suitable for the polymerization of olefins, preferably alpha olefins, to produce polymers in any process known in the art for producing polyolefins, including those carried out in suspension, in solution in an inert liquid hydrocarbon, in bulk, i.e. in a liquid monomer medium and in a stirred or fluidized bed in a gas phase reactor and the like. Used in this application, the term "polyolefin" means homopolymers, copolymers and ternary copolymers of such olefins, which may contain units of dienes, aromatic compounds with vinyl unsaturation and / or carbon monoxide.

Typically, olefin monomers suitable for these purposes contain from 2 to 14 carbon atoms and usually include, without limitation, ethylene, propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, styrene, substituted styrene and the like The dienes that can be copolymerized with olefins are non-conjugated dienes and can be linear, branched or cyclic dienes containing from about 5 to about 15 carbon atoms. Examples of suitable linear non-conjugated acyclic dienes are 1,4-hexadiene, 1,5-hexadiene, 1,7-octadiene, 1,9-decadiene and 1,6-octadiene; branched acyclic dienes - 5-methyl-1,4-hexadiene, 3,7-dimethyl-1,6-octadiene, 3,7-dimethyl-1,7-octadiene and mixed isomers of dihydromyricin and dihydrocinene. Also suitable are unicyclic acyclic dienes such as 1,3-cyclopentadiene, 1,4-cyclohexadiene, 1,5-cycloctadiene and 1,5-cyclododecadiene and multicyclic acyclic fused and bridged dienes such as tetrahydroindene, methyltetrahydroindene, dicyclopentadiene, bicyclo- (2,2,1) hepta-2,5-diene, alkenyl-, alkylidene-, cycloalkenyl- and cycloalkylidenenorbornenes such as 5-methylene-2-norbornene, 5-propenyl-2-norbornene, 5-isopropylidene-2- norbornene, 5- (4-cyclopentenyl) -2-norbornene, 5-cyclohexylidene-2-norbornene, 5-vinyl-2-norbornene and nor Tornadoes.

Regardless of the method of polymerization used, the polymerization or copolymerization should be carried out at sufficiently high temperatures to ensure acceptable polymerization rates and to avoid the need for too long residence time in the reactor. Typically, temperatures from about 0 ° C to about 120 ° C, preferably from about 20 ° C to about 95 ° C, are used to achieve good catalyst performance and high reaction rates. It is more preferable to carry out the polymerization at temperatures from about 50 ° C to about 80 ° C.

The polymerization or copolymerization of olefins according to the invention can be carried out at a pressure of monomers from about atmospheric and higher. Generally, monomer pressures range from about 20 to about 600 lb / ⁱⁿ² (from 137.89 kPa to 4136.8 kPa), although in vapor phase monomer pressure should not be below the vapor pressure at the polymerization temperature of the olefin undergoing polymerization or copolymerization.

The duration of the polymerization usually ranges from 1/2 hour to several hours in a batch process with the corresponding average residence time of the reactants during continuous process. A polymerization time of from about 1 to about 4 hours is typical for reactions in an autoclave. In the case of suspension methods, the polymerization time is properly controlled. With continuous suspension processes, the polymerization time is from about 1/2 hour to several hours.

Inert hydrocarbon diluents suitable for use in the suspension process include alkanes and cycloalkanes such as pentane, hexane, heptane, n-octane, isooctane, cyclohexane and methylcyclohexane; aromatic and alkyl aromatic compounds such as benzene, toluene, xylene, ethylbenzene, ethyl toluene and the like. It is often desirable to purify the polymerization medium prior to use, for example, by distillation, percolation through molecular sieves, contacting with an absorber, such as aluminum alkyl, capable of removing traces of impurities, or other suitable methods.

Typical gas phase olefin polymerization reactor systems include at least one reaction vessel into which olefin monomer and catalyst components can be added and which contains a mixed bed of particles of the resulting polymer. Typically, the catalyst components are added together or separately through one or more openings with a control valve in a single or first reaction vessel. The olefin monomer is typically fed to the reactor through a gas recycle system in which unreacted monomer removed as off-gas and a fresh portion of the monomer are mixed and injected into the reaction vessel.

Regardless of the particular polymerization process used, in the presence of reactivated metallocene catalyst systems according to this invention, it is carried out under conditions that exclude the presence of oxygen, water and other substances that may be poisons for the catalysts. Using methods well known in the art, additives can be used to control the molecular weight of the polymer or copolymer, such as, for example, hydrogen. Although this is not usually required, it will be apparent to those skilled in the art of polymerization that, after completion of the reaction, a suitable catalyst deactivator can be added to terminate the polymerization.

The products obtained in accordance with this invention are usually solid polyolefins. The yield of homopolymers or copolymers is high enough based on the amount of catalyst used, and therefore useful products can be obtained without isolating catalyst residues. Polymer products obtained in the presence of a catalyst according to the invention can be processed into many useful products, including molded products, fiber and films, by extrusion, injection molding and other methods well known in the art and commonly used for compounding and manufacturing such plastics.

The invention will become more apparent after reading the following illustrative examples and comparative examples, which are given to illustrate and not limit the invention. In these examples, all parts and percentages are by weight unless otherwise specified.

Examples.

Preparation of the catalyst.

The supported metallocene catalyst used in the following examples was prepared by suspending dimethylsilyl bis (2-methyl-4,5-benzo [e] indenyl) zirconium dichloride obtained from Boulder Scientific Corporation as BSC 366 and methylaluminoxane in toluene with MAO-treated silica gel according to the method described in Example 2 of published application EP 810 233.

Typically, the preparation of the catalyst, storage and transportation are carried out using carefully dried reagents and vessels in a dry container in an atmosphere of inert gas, such as dry nitrogen or argon.

A norbornylene-passivated catalyst was prepared by adding 0.55 g of a metallocene catalyst on a support to a solution treated with alumina-activated alumina containing 7 g of norbornylene in 14 ml of heptane under dry conditions. The resulting suspension was stirred at 50 ° C. for 1 hour, and then the catalyst was isolated by filtration.

Passivated catalysts were also prepared using 3-hexine, 1-hexine, 3-methyl-1,2-butadiene and styrene as passivators. These catalysts were prepared practically by the method described for the preparation of catalysts passivated by norbornylene.

The catalysts used in the control experiments were suspended in heptane at 50 ° C and isolated by filtration to obtain catalysts for comparison.

Screening.

Suspension polymerization at low pressure on a laboratory scale was carried out for screening to demonstrate the effectiveness of the olefin as a passivating agent for metallocene catalysts. Screening was carried out in 250 ml pressure flasks equipped with a magnetic stirrer and a gas inlet. The flasks were dried and washed with nitrogen, placed in a drying box and treated with 1 ml of a solution of triisobutylaluminum in hexane (60 mg / ml) as a scavenger. Then, hexane dried with molecular sieves and a catalyst were charged into the reactors. The flasks were sealed, removed from the drying casing, placed in a heat bath pre-heated to the selected reaction temperature, a magnetic stirrer was installed and connected to a dried, nitrogen-washed comb through a gas inlet. The system was purged and filled with propylene. Then hydrogen was added to the flasks to a predetermined pressure value. After the start of mixing to maintain a working pressure of 80 lbs / ⁱⁿ² (551.5 kPa) was continuously fed propylene. After 30 minutes, the propylene flow was stopped and the excess propylene was blown off. The flasks were removed from the comb and the polymer was collected by filtration and dried.

In the following Examples 1-14, each example represents the sum of six experiments, three with a passivated catalyst and three with the corresponding control catalyst. The reaction temperatures were chosen in order to simulate the conditions in a gas-phase propylene polymerization reactor - 50 ° C for the feed lines and 70 ° C for the layer in the reactor. The reaction parameters, passivators and the amount of H2 activator used in each experiment together with the results averaged for successfully completed experiments are summarized in the following Table I.

Table I Note No. Passivator Temp. ° C Time min H ₂ O / ⁱⁿ² Control ¹ g / g / hour Passive activity. catalysis. g / g / hour % ³ one * norbornylene fifty 10 0 104.9 54,2 52 2 Norbornylene fifty 10 0 71.9 9.6 13 3 Norbornylene fifty 10 0 174.7 2,5 one four Norbornylene fifty 10 23 131.4 66.3 fifty 5 Norbornylene fifty 10 60 632.6 181.5 29th 6 Norbornylene fifty 10 10 429.5 107.9 25 7 Norbornylene fifty 10 10 286.6 142.3 53 8 Norbornylene 70 10 0 84.6 14.5 17 9 Norbornylene 70 thirty 0 115.3 43.6 38 10 Norbornylene 70 thirty twenty 118.2 81.6 69 eleven Norbornylene 70 thirty twenty 139.0 94.6 68 12 3-hexine fifty 10 0 156.5 5.2 3 13 3-hexine 70 thirty 0 144.7 37.6 26 fourteen 3-hexine 70 thirty twenty 177.3 132.9 75 fifteen 3-me-BDE ⁴ fifty 10 0 98.5 12,4 13 16 3-me-BDE ** 70 thirty twenty 871 513 59 17 1-hexine fifty 10 0 92.2 3.4 four eighteen 1-hexine 70 thirty twenty 664.5 33.9 5 19 styrene fifty 10 0 129.1 77.5 60 Notes: 1) control, g / g / hour = amount of polypropylene (PP) obtained with the control catalyst (average value); 2) passive activity. catalysis, g / g / h = amount of polypropylene (PP) obtained in the presence of a passivated catalyst (average value); 3)% - the ratio of activity to the passive. catalysis / activity counter, cat. (× 100); 4) 3-me-BDE = 3-methyl-1,2-butadiene. *) passivation of the catalyst was carried out at room temperature; **) conducted only one control experiment and one experiment with a passive. catalysis.

From these examples presented in Table I, it is seen that the catalysts passivated by a cyclic olefin, such as norbornylene, have significantly lower activity, which leads to the formation of a small amount of polymer at a temperature in the feed line of 50 ° C; see Examples 1-3.

As can be seen from Table I, the catalyst passivated by norbornylene under the reaction conditions in the reactor at 70 ° C is activated slowly, see Examples 8 and 9. Further addition of hydrogen acts as an activator and leads to a significant increase in the polymerization activity as at a temperature in the feed line ( Examples 3-6), and at the polymerization temperature in the reactor (Examples 10 and 11).

Similar results were observed for alkyn passivated catalysts such as 3-hexine. Passivation proceeds efficiently at a lower temperature (feed line), while at a higher temperature (polymerization) the catalyst is activated slowly, compare Example 12 with Example 13. The added hydrogen reactivates the catalyst again and significantly increases the polymerization activity, see Example 14.

Similar results were also obtained for catalysts passivated with a non-conjugated branched diene, 3-methyl-1,2-butadiene, see Examples 15 and 16. The catalysts were also passivated successfully with 1-hexine, but the catalyst did not react at 70 ° C using hydrogen. see Examples 17 and 18. Catalysts are ineffectively passivated by styrene treatment for the purposes of this invention. A significant degree of polymerization occurred when using a styrene-treated catalyst at 50 ° C, see Example 19.

It was also found that triisobutylaluminum is effective for reactivation of an inactive metallocene catalyst. An inactive metallocene catalyst on a support was prepared by adding MAO-treated silica to a solution of metallocene in toluene, filtering, washing with pentane and drying. When triisobutylaluminum is added to the flask reactor and then contacted with liquid propylene and kept at 50 ° C for 1 hour, polypropylene powder is obtained in good yield.

Gas phase polymerization.

The activity of passivated catalysts and especially the ability of such catalysts to remain passivated in the bed in the reactor for a period of time sufficient to disperse them adequately in the catalyst bed was evaluated by polymerization of propylene in a laboratory gas-phase reactor.

These experiments were carried out in a 1 gallon (3.8 L) horizontal cylindrical gas phase reactor with a diameter of 10 cm and a length of 30 cm of the type described in US Pat. No. 3,956,083. The reactor was provided with an opening for gas recycle through the condenser and back through the recycle line to nozzles for recycling in the reactor. Liquid propylene was used to terminate the reaction to facilitate the removal of heat generated in the reactor during polymerization. During operation, the polypropylene powder obtained in the reactor layer passes over the shutter to be discharged through the polymer discharge system into a second closed vessel filled with nitrogen. The polymer layer was mixed with a paddle mixer attached to a longitudinal shaft in a reactor that rotates at a speed of about 50 rpm. The temperature and pressure in the reactor was equal to 70 ° C and 300 lb / ⁱⁿ² (2068 kPa), respectively. The catalyst was introduced into the reactor either as a dry powder or dispersed in mineral oil through a nozzle washed with liquid propylene. Hydrogen was fed into the reactor in order to maintain a melt flow rate of the powder of 2.5-3 g / 10 min. Hydrogen was introduced into the reactor through an opening from a pressure vessel with 300 cm ³ hydrogen.

The specific pressure drop from the vessel can be correlated to the specific hydrogen concentration in the reactor, which in turn corresponds to the specific flow rate of the polymer melt; the yield was approximately 0.5 psi (225 g / hour).

The experiment was carried out using catalysts passivated with 3-hexine and 1-hexine. The catalysts were obtained in quantities sufficient for these experiments, according to the method used for screening. The passivation of the catalyst was also carried out using the same procedure, however, passivation with 1-hexine was carried out by stirring in dry hexane for 30 minutes at room temperature, while passivation with 3-hexine was carried out in dry hexane heated at 50 ° C for approximately 30 minutes.

Triethyl aluminum (TEA) diluted with heptane was added to the catalyst reactor. TEA acts as an absorber and may promote reactivation; hydrogen supplied to control molecular weight also facilitates reactivation. In experiments conducted with a passivated catalyst, the catalyst was fed into a reactor with liquid propylene, while no plugs formed in the supply lines. In a control experiment using a fully active catalyst, clogging of the feed lines was avoided by dispersing the catalyst in mineral oil and feeding the mixture of catalyst and TEA solution into the reactor through a liquid propylene feed line.

The starting components and experimental results are shown in the following Table II.

Table II Experience No. Passivator TEA, g / g H ₂ / C ₃ Yield, g / g Lumps, wt.% Experience time, hour one 3-hexine 0.1 2.3 × 10 ^-4 1120 2 eleven 2 3-hexine 0.1 2 × 10 ^-3 1420 2,4 12 3 1-hexine 0.1 2 × 10 ^-3 1675 2.6 8

When considering the examples presented in Table II, it can be seen that the passivated catalysts remain passivated after entering the reactor long enough so that the catalyst is dispersed in the polymer layer, while overheating is avoided. In experiments 1-3, only small amounts of lumps formed, they were small - 0.3-1.2 cm in diameter - and did not interfere with polymerization.

In a separate experiment using a fully active metallocene catalyst dispersed in mineral oil, large pieces were formed with a diameter of about 50 cm, clogging the layer in the reactor and preventing stirring, which necessitated stopping the reactor for cleaning after about 12 hours.

The yields per catalyst in Tests 1-3 were approximately half of the yield obtained using a fully active supported catalyst. In screening experiments (in bottles), the catalyst passivated with 1-hexine was not reactivated with hydrogen at temperatures in the reactor. However, in a gas-phase reactor, a catalyst passivated by 1-hexene (experiment 3) provided a higher yield than the yield obtained in the presence of a catalyst passivated by 3-hexene, see experiments 1 and 2.

Thus, as can be seen, this invention is directed to a method for passivating fully active metallocene catalysts, including a metallocene selected from Group 4 and Group 5 metallocenes, and a cocatalyst, such as alumoxane, the method of the invention comprising contacting the metallocene catalyst with about 1-5 eq of unsaturated hydrocarbon passivator per eq of metal in the catalytic complex and said unsaturated hydrocarbon is selected from the group consisting of C ₄ -C ₁₄ alkynes, C ₄ -C ₁₄ allens and cycloalkenes.

The activity of passivated metallocene catalysts obtained according to the method according to the invention, defined as the yield per catalyst in the polymerization of olefins in the absence of an activator, can be reduced to less than about 20%, preferably less than about 15%, even more preferably less than 0-10 % of the activity of the metallocene catalyst under comparable conditions prior to passivation. The activity of the catalysts for comparison can be determined using any of many polymerization methods. Data for comparison can be easily obtained using the low pressure suspension polymerization catalytic method carried out for propylene at 50 ° C. in the absence of an activator, mainly as described above. It will be apparent to those skilled in the art that process conditions may be changed if other olefin monomers are used.

The passivated metallocene catalysts obtained according to this invention can be further characterized and described as latent olefin polymerization catalysts containing 4 or 5 Group metallocenes, alumoxane, and an unsaturated hydrocarbon passivator selected from the group consisting of C ₄ -C ₁₄ alkynes, C ₄ -C ₁₄ non-conjugated branched alkadienes and cycloalkenes, preferably polycyclic alkenes containing a non-reactive beta-hydrogen atom.

Passivation is temporary or reversible. Latent olefin polymerization catalysts can become reactivated at some point in the polymerization conditions, or they can be reactivated using an activator, for example hydrogen, or a compound capable of alkylating an unsaturated hydrocarbon moiety of a latent catalyst, for example metal alkyl, for example, aluminum alkyl.

Reactivated catalysts are effective as catalysts for the polymerization of olefins and are thus suitable for the preparation of polyolefins, such as polypropylene, by polymerization. Thus, this invention relates to a method for the polymerization of C ₄ -C ₁₄ olefins in the presence of a metallocene catalyst system, said catalyst being temporarily and reversibly passivated by contact with an unsaturated hydrocarbon passivator dispersed in a polymerization medium and then becomes reactivated under reaction conditions.

Although the invention has been described and illustrated using specific metallocene catalysts containing zirconium-based metallocenes and alumoxane cocatalysts, the process of the invention can be used for a variety of metallocene catalyst systems, including those derived from other metals of Groups 4 and 5 Groups and others cocatalysts such as boron compounds and the like. Unsaturated hydrocarbons other than those used in the examples are also suitable for these purposes. Specialists in this field it is obvious that the examples given in this application only illustrate the invention, but do not limit its scope defined by the claims.

Claims (10)

1. A method for temporary and reversible passivation of an active metallocene catalyst system, characterized in that the said catalyst system is contacted with an unsaturated hydrocarbon selected from the group consisting of C ₄ -C ₁₄ alkynes, C ₄ -C ₁₄ allens and polycyclic alkenes containing non-reactive beta hydrogen. 2. The method according to claim 1, characterized in that said metallocene catalyst system contains a metallocene of Group 4 or 5 and a cocatalyst. 3. The method according to claim 1, characterized in that said metallocene catalyst system contains metallocene of zirconium and aluminum. 4. The method according to claim 1, characterized in that said hydrocarbon is selected from the group consisting of 1-hexine, 3-hexine, 3-methyl-1,2-butadiene, norbornylene and tetracyclo [4.4.0.1 ^2,5 , 1 ^7,10 ] -3-dodecene. 5. The method according to claim 1, characterized in that said metallocene catalyst system is a supported metallocene catalyst system containing a metallocene of an IVB Group or VB Group, a cocatalyst and a suitable carrier. 6. The method according to claim 1, characterized in that the supported active metallocene catalyst system containing zirconium metallocene, alumoxane and a suitable carrier is temporarily and reversibly passivated by contacting said catalyst system with an unsaturated hydrocarbon selected from the group consisting of C ₄ - C ₁₄ alkynes, C ₄ -C ₁₄ allens and polycyclic alkenes containing non-reactive beta-hydrogen, in an amount providing from about 1 to about 5 equivalents of unsaturated hydrocarbon per 1 equivalent of zirconium, wherein said catalyst system after contacting with said unsaturated hydrocarbon has an activity defined as the yield calculated on the catalyst during olefin polymerization that is not more than 20% of the activity of the catalyst system before contacting with said unsaturated hydrocarbon. 7. A method for the polymerization of C ₂ -C ₁₄ olefins, comprising the steps of feeding a latent catalyst for the polymerization of olefins and at least one C ₂ -C ₁₄ olefin to a polymerization reactor, dispersing said latent catalyst in a polymerization medium contained in the reactor and reactivating said a latent catalyst, said latent catalyst comprising a zirconium-based metallocene, a cocatalyst and an unsaturated hydrocarbon selected from the group consisting of C ₄ -C ₁₄ alkynes, C ₄ -C ₁₄ allens and polycyclic alkenes containing non-reactive beta hydrogen in an amount of from about 1 to about 5 equivalents per 1 equivalent of zirconium. 8. The method according to claim 7, characterized in that it comprises the steps of feeding a latent catalyst for the polymerization of olefins of at least one C ₂ -C ₁₄ olefin and hydrogen into a polymerization reactor, dispersing said latent catalyst in a polymerization medium contained in the reactor, and holding said polymerization medium at an elevated temperature sufficient to reactivate said catalyst and polymerize said monomer. 9. The method according to claim 7, characterized in that said latent catalyst comprises a zirconium-based metallocene and from about 1 to about 5 equivalents per 1 equivalent of zirconium of an unsaturated hydrocarbon selected from the group consisting of C ₄ -C ₁₄ alkynes, C ₄ -C ₁₄ allens and polycyclic alkenes containing non-reactive beta-hydrogen. 10. The method according to claim 7, characterized in that said olefin is propylene, ethylene or a mixture of propylene and ethylene.