RU2330862C2 - Latent metallocene catalytic systems for olephine polymerisation - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention concerns metallocene catalytic systems for olephine polymerisation. It claims a method of temporal reversible passivation with further reactivation of active metallocene catalytic system. The catalytic system includes substrate coated with metallocene of 4 or 5 group metal and alumoxane co-catalyst with mol ratio of co-catalyst aluminum for metallocene metal of 50:1 to 2000:1. The method involves contacting of the catalytic system with an effective amount of passivator selected out of oxygen, metal alkoxides, simple ethers, cyclic ethers, alkylamines, cycloalkylamines, metal amides and morpholine; introduction of passivated metallocene catalytic system to a polymerisation reactor and further reactivation of the metallocene catalytic system in the reactor by contacting with metal alkylating reagent taken in the effective amount for monomer polymerisation catalyst activation in polymerisation environment. After passivation and further reactivation the catalytic system activity in polymerisation environment is reduced not more than by 50% of the catalytic system activity before contact with the passivator. Also the invention claims a method of C₂-C₁₄olephine polymerisation including stages (a) of temporary reversible passivation of active metallocene catalytic system.

EFFECT: reduction of the catalyst activity to the level sufficient for catalyst feeding to the reactor together with olephine monomer and for adequate dispersion of the catalyst in polymer layer in the reactor before the catalyst is reactivated.

6 cl, 7 ex, 2 tbl

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 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 recycling system in which the 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 Amoco gas phase process, as described in the prior art, uses the fourth generation of supported catalysts consisting of three components: a patented 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, referred to as 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. The prior art methods of polymerization in solution and in the mass of ethylene and propylene using supported catalysts based on metallocenes are widely known.

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 was described as a control method 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 dialkaluminium 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 a polymer on the walls during suspension polymerization of ethylene polymers and copolymers, it is possible to separately add an 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 for 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, feeding the 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 trimethylaluminium 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 trimethylaluminium and then with water is described, for example, in US Pat. No. 5,041,584. Suitable aluminoxanes can be prepared 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 even more preferably ranging 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 of 1 to 300 μm, and more preferably 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, EP 578838 and EP 810233. Various substrates suitable for use in the practice of this 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 of 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 present invention by contacting with an effective amount of a passivating compound to obtain a latent metallocene catalyst. Compounds suitable for use as passivating compounds in the practice of this invention can be generally described as being selected from molecular oxygen (O ₂ ), oxygen-containing compounds typically containing 2-20, preferably 3-12, carbon atoms, including metal alkoxides ( typically 2-13 Group metals, preferably aluminum) such as aluminum trimethoxide, aluminum triethoxide and the like, ethers and cyclic ethers, including dimethyl ether, diethyl ether, tetrahydrofuran and the like; ketones and aldehydes are not preferred.

Suitable nitrogen-containing compounds include alkyl amines and cycloalkyl amines, usually containing 2-20, preferably 3-12, carbon atoms such as trimethylamine, tetramethylethylenediamine, N-methylpyrrolidone, N-methylpiperidine and the like, and metal amides such as alkali metal dialkylamides for example lithium dimethylamide and the like, as well as derivatives of dialkylamines and trialkylaluminium. Di- and trialkylamines are preferred, trialkylamines are particularly preferred. Similar compounds containing both oxygen and nitrogen, for example morpholine, can also be used.

The metallocene catalyst may be contacted with the passivator in any known manner, for example, by suspending the catalyst in a suitable liquid medium containing the passivator in an amount effective to reduce the activity of the metallocene catalyst to a value less than about 50% of the activity of the metallocene catalyst system prior to passivation. Amounts of about 1-5 equivalents of passivator per 1 equivalent of metal in the catalyst complex are usually effective. However, the required amount of passivator partially depends on the type of passivator and components of the metallocene catalyst. For example, if oxygen is used to passivate a zirconium-based metallocene catalyst system on a support, oxygen in an amount of more than about 1 equivalent. by 1 equiv. metal can prevent the catalyst from reactivation. Therefore, the use of a passivator in an excessive amount relative to the amount required to provide the desired level of activity should be avoided. The activity of passivated metallocene catalysts obtained according to the method according to the invention can be determined by measuring the yield per catalyst during olefin polymerization. A method that is convenient to make such a determination is a method using a low pressure suspension polymerization process and is described below.

The temperature used in the passivation is not particularly critical, and the process can be carried out at any suitable temperature for a period of time providing a complete reaction. Temperatures equal to room temperature or lower are usually suitable, although passivation is completely faster if it is carried out at an elevated temperature, at 50-100 ° C. or higher, preferably at a temperature lower than the volatility temperature of the passivator and the selected medium. A passivated or latent metallocene catalyst can then be isolated by filtration and dried or used immediately without isolation.

Latent metallocene catalyst can be fed into the reactor in contact with the monomer without initiating polymerization, which leads to clogging of the supply lines and fouling of the reactor.

After dispersion in the reactor, the catalyst is reactivated and combined with the olefin monomer to effect polymerization. Ideally, the latent catalyst brought into contact with the olefin monomer becomes 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 may not occur or may occur very slowly under such conditions.

Acceptable levels of catalyst activity can be achieved within a reasonable amount of time by adding an activator, commonly described as an alkylating agent. Metallalkyls including trialkylaluminum are suitable for this purpose.

The rate at which the catalyst is reactivated in the presence of an alkylating agent depends on several factors, including monomer concentration and reaction temperature. Typically, the incorporation of the starting monomer proceeds slowly, providing an induction period during which the catalyst can be dispersed adequately in the reactor, reducing or eliminating the formation of hot polymer sites and eliminating clumping and clogging of the reactor.

The amount of activator used depends in part on the type of particular compound used in the passivation of the metallocene catalyst, and on the particular activator selected. The amount of activator should be selected so that it is effective to provide an active polymerization catalyst for monomers in the polymerization conditions used in the process. Typically, the amount of activator that will be 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 metal in the metallocene complex contained in the latent catalyst.

The latent catalyst compositions of the invention are suitable for the polymerization of olefins, preferably alpha olefins, to produce polymers by any known method of producing polyolefins, including methods carried out in suspension, in solution in an inert liquid hydrocarbon, in bulk, i.e. in a liquid monomer, and in a stirred or a fluidized bed during gas phase polymerization and the like. As used herein, the term “polyolefin” encompasses homopolymers, copolymers and ternary copolymers of such olefins, which may also contain diene units, vinyl unsaturated aromatics and / or carbon monoxide units.

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 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-di-methyl-1,6-octadiene, 3,7-dimethyl-1,7-octadiene and mixed isomers of dihydro-myricin and dihydrocinene. Also suitable are cyclic acyclic dienes such as 1,3-cyclopentadiene, 1,4-cyclohexadiene, 1,5-cycloctadiene and 1,5-cyclododecadiene, and multicyclic fused and bridged dienes such as tetrahydroindene, methyl tetrahydroindene, 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 norb ornamental.

Regardless of the polymerization method used, the polymerization or copolymerization should be carried out at temperatures high enough to ensure acceptable polymerization rates and to avoid an unreasonably long residence time in the reactor. Typically, from the point of view of achieving good catalyst performance and high polymer formation rates, temperature ranges from about 0 ° C to about 120 ° C are used, a range from about 20 ° C to about 95 ° C is preferred. It is more preferable to carry out the polymerization process according to this invention at temperatures from about 50 ° C to about 80 ° C.

The polymerization and copolymerization of olefins according to the invention is carried out at a monomer pressure of about atmospheric or higher. Generally, monomer pressures range from about 20 to about 600 lb / ⁱⁿ² (137,89-4136,8 kPa), although in vapor phase polymerization of monomers pressure value should not be below the vapor pressure at the polymerization temperature of the olefin undergoing polymerization or copolymerization.

The polymerization time usually ranges from about 1/2 hour to several hours in the case of batch processes with the corresponding average residence time in the reactor in the case of continuous processes. In autoclave type reactions, the polymerization time is usually from about 1 to about 4 hours. In the case of suspension methods, the polymerization time can be adjusted as desired. With a continuous suspension process, the polymerization time is usually from about 1/2 hour to several hours.

Inert hydrocarbon diluents suitable for use in suspension polymerization processes include alkanes and cycloalkanes such as pentane, hexane, heptane, n-octane, isooctane, cyclohexane and methyl cyclohexane; 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.

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

Regardless of the particular method used, polymerization with metallocene catalyst systems that have been passivated and then reactivated is carried out under conditions that exclude oxygen, water and other substances that can act as poisons for the catalysts. To regulate the molecular weight of the polymers or copolymers, additives such as, for example, hydrogen may be added; these additives are well known in the art. Although this is not usually required, it will be apparent to those skilled in the art that after completion of the process, a suitable catalyst deactivator can be added to terminate the polymerization.

The products obtained according to the method according to the invention are usually solid polyolefins. The yields of the homopolymer or copolymer are quite high with respect to the amount of catalyst used, therefore suitable products can be obtained without separation from the catalyst residues. The polymer products obtained in the presence of a catalyst according to the invention can be processed into various products, including molded products, fiber and film, by extrusion, injection molding and other methods well known in the art and commonly used for compounding and manufacturing such products.

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

Examples

Catalyst Preparation

The supported metallocene catalyst used in the following examples was prepared by suspending dimethylsilyl bis (2-methyl-4,5-benzo [e] indenyl) zirconium dichloride, supplied by Boulder Scientific Corporation under the name BSC 366, and methylaluminoxane in toluene with silica gel treated with MAO, according to the method of Example 2 of published application EP 810233.

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

An oxygen passivated catalyst having an eq. oxygen: equiv. Zirconium equal to 1 was obtained by adding 3.43 ml of oxygen (10% in nitrogen) to 0.5 g of a fully activated metallocene catalyst on a support contained in a tube without air, using a syringe in dry conditions. The tube containing the catalyst and gas was stirred at room temperature for 30 minutes, then stored in an absorber for later use.

A second experiment using 17.34 ml of oxygen provided an oxygen-passivated catalyst with an equiv. oxygen: equiv. zirconium equal to 5.

A dimethylamine / triethyl aluminum passivated catalyst was prepared by introducing 9.8 ml of hexane, 0.1 ml of triethyl aluminum and 0.1 ml of diethylamine into a dried ampoule and stirring the mixture for 60 minutes at room temperature. A fully activated supported metallocene catalyst (0.35 g) was placed in a dry tube along with 10 ml of dry hexane to give a suspension. 0.166 ml aliquots of a dimethylamine / triethyl aluminum solution were added to the tube, and then the suspension was stirred for 45 minutes at room temperature. Then, the supernatant was decanted and the remaining volatile components were removed in vacuo to obtain a passivated catalyst on a support in the form of a free flowing powder. The catalyst was stored in a sealed tube in a dry absorber.

A passivated aluminum triethoxide catalyst was prepared by placing 0.35 g of a fully activated metallocene catalyst and 3.3 mg of aluminum triethoxide in a tube, 5 ml of dry hexane was added, and the resulting suspension was stirred for 3 hours. Then the supernatant was decanted and the remaining volatile components were removed in vacuo to obtain a passivated catalyst on a support in the form of a free flowing powder. The catalyst was stored in a sealed tube in a dry absorber.

Passivated catalysts were also prepared using triphenylboron and triphenylphosphine oxide as passivators. They were obtained mainly by the method described for the preparation of a passivated aluminum triethoxide catalyst.

Screening Examples

Laboratory-scale low pressure suspension polymerization was performed for screening to demonstrate olefin as a passivating agent for metallocene catalysts. Screening experiments were carried out in 250 ml pressure flasks equipped with a magnetic stirrer and a gas inlet. The flasks were dried, washed with nitrogen, placed in an absorber, and treated with 1.0 ml of a solution of triisobutylaluminum in hexane (60 mg / ml) as an absorber. Then, the reactors were charged with molecular sieve dried hexane and a catalyst. The flasks were sealed, removed from the absorber, placed in a bath preheated to the selected reaction temperature, a magnetic stirrer was installed and connected to a comb washed with nitrogen through a gas inlet. The system was washed and filled with propylene. If hydrogen was used, it was then added to the bottles to a predetermined pressure. With the start of mixing the propylene was added continuously to maintain a working pressure of about 80 lb / ⁱⁿ² (551.58 kPa). After 30 minutes, the supply of propylene was stopped and the excess propylene was blown off. The flasks were separated from the comb, the polymer was collected by filtration and dried.

In the following Examples 1-4, each example reflects the result of experiments in six reactors, in three with a passivated catalyst, in three with a suitable control catalyst. The reaction temperature was chosen so as to simulate the polymerization conditions in a gas-phase polymerization reactor of propylene of -50 ° C in the supply lines and 70 ° C for the layer in the reactor. Trimethylaluminum (TMA) as an activator was then charged to reactors with a temperature of 70 ° C. Comparative experiments C1-C2 were carried out in the same way as to provide a comparison with compounds that are ineffective as passivators and with compounds that passivate irreversibly under these conditions.

The reaction parameters, types of passivators and the amount of passivator used in each experiment, as well as the results averaged for successful experiments, are shown in Table I.

Table I Example
No. Passivator Rel eq. passive / Zr Catalysis activity, 50 ° C Catalysis activity, 70 ° C ¹ g / g / hour ² % ¹ g / g / hour ² % one Oxygen one 150 eighteen 980 90 2 Oxygen 5 150 eighteen 225 twenty 3 Oxygen one 137 fifteen 1131 112 four DiMeAmin-TEA 1,2 125 16 585 54 5 DiMeAmin-TEA one hundred eleven 616 61 6 Triethoxide A1 2 <30 <5 730 66 7 Triethoxide A1 26 2 887 88 C1 BPh ₃ 2 400 48 320 29th C2 OPPh ₃ 2 245 thirty 215 19 Notes:
Rel eq. passive. / Zr = ratio of passivator equivalents to zirconium equivalents;
Catalysis activity: 1) g / g / hour = the amount of PP obtained in the presence of a passivated catalyst (averaged); 2)% - the ratio of passivated activity / control activity (× 100).

When considering the examples presented in Table I, it is seen that the oxygen-passivated catalysts have significantly lower activity, which leads to a small amount of polymer at a feed line temperature of 50 ° C; see Examples 1-3. When treating TMA as an activator at 70 ° C, the catalyst passivated by excess oxygen did not reactivate, see Example 3. Metallocenes passivated by one equivalent of oxygen, Examples 1 and 2, had activity reaching 90% of the initial catalyst activity when Reactivated TMA.

The catalysts were effectively passivated for use using aluminum triethoxide, Examples 4 and 5, and diethylamine-TEA, Examples 6 and 7. Passivation using these agents is reversible when contacted with TMA at 70 ° C.

It can be concluded that the catalysts are not adequately passivated for use in contact with propylene at 50 ° C, when they were treated with boranes such as triphenylborane or triphenylphosphine oxide, and the activity level remained unacceptably low when treated with TMA at 70 ° C, see Examples C 1 and C2.

The use of alkyl and aryl boranes for reversible retardation of metallocene-catalyzed polymerization of ethylene in bulk and in solution is described in the prior art. As indicated above, in the polymerization of propylene in suspension in the presence of supported metallocene catalyst systems, triphenylboron acts as a weak poison for the catalyst, while the catalyst does not reactivate when TMA is processed and heated to 70 ° C in contact with the monomer.

In the following comparative examples C3-C8, the supported metallocene catalyst systems were treated with various borane compounds and alkyl aluminum hydride with a passivator: zirconium ratio of 5: 1, followed by polymerization in suspension according to the method described for the preparation of supported catalysts passivated with aluminum ethoxide. These treated catalysts were evaluated in a laboratory scale scale suspension polymerization process of low pressure propylene, carried out practically as described above.

The boron compounds that were studied in these experiments include:

9-BBN = 9-borabicyclo [3.3.1] nonane

A-pinylBH2 = alpha-pinylborane

Pinacol BH = Pinacolborane

tert.hexylBH2 = terthexylborane or 1,1,2-trimethylpropylborane

A catalyst treated with an aluminum compound, diisomethylaluminum hydride (Di-isobutyl AlH) was also investigated.

Reaction parameters, reactions, types of passivators and average results of successful experiments are summarized in Table II.

Table II Example
No. Passivator Temper. ° C Time,
min ¹ Control.
g / g / hour Assets. liabilities. catalysis. g / g / hour ³ % C3 9-BBN fifty 10 74,4 67.3 90 C4 PinacolVN fifty 10 216.7 182.4 84 C5 tert.hexylBH2 fifty 10 116.3 62.5 54 C6 A-vinylBH2 fifty 10 240.8 40.5 17 C7 A-vinylBH2 70 60 98.9 57.2 58 C8 Di-Isobutyl AlH fifty 10 91.6 105.0 115 Notes: Types of passivators see text above.
1) Control g / g / hour = the amount of PP formed in the presence of a control catalyst (averaged);
Activity passive. Catalysis: 2) g / g / hr = the amount of PP formed in the presence of a passivated catalyst (averaged); 3)% - (passive / counter.) (X100).

As a result of reviewing the data presented in Table II, it becomes apparent that alkyl and arylboranes are usually ineffective as passivating compounds for supported metallocene catalyst systems. In many cases, the degree of passivation is insufficient to prevent the occurrence of significant polymerization when brought into contact with propylene at the temperatures observed in the supply lines, which causes clogging of the supply lines, see Examples C3-C5. The degree of passivation of the metallocene catalyst on a support treated with alpha-pinylborane at 50 ° C is hardly acceptable. However, at a temperature of 70 ° C, in the presence of TMA as an activator, the activity of the catalyst did not increase to an acceptable level for an hour, see Examples C6 and C7. The treatment of the catalysts with dialkylaluminum hydride does not lead to significant passivation, if any, see Example C8.

Gas phase polymerization.

The activity of passivated catalysts, and especially the ability of the catalyst to remain passivated in the bed in the reactor for a period of time sufficient for adequate distribution in the catalyst bed, can be achieved by propylene polymerization in a laboratory gas phase reactor.

For this, the polymerization of propylene can be carried out continuously in a horizontal, cylindrical gas phase reactor with a diameter of 10 cm and a length of 30 cm with a volume of 1 gallon (3.8 L), similar to that described in US patent No. 3965083. The reactor is provided with an opening for gas recycle through the condenser and a recycle line to the reactor nozzle. Liquid propylene is used as a liquid to terminate the reaction to facilitate the removal of heat generated in the reactor during polymerization. During operation, the polypropylene powder formed in the bed in the reactor passes over the drain wall and is discharged through the powder discharge system into a second closed vessel filled with nitrogen. The polymer layer is mixed with blades attached to a longitudinal shaft in a reactor rotating at a speed of about 50 rpm.

Usually, it has been found that passivated catalysts remain passivated after being introduced into the reactor long enough so that the catalyst becomes dispersed in the polymer layer, without the formation of sections of the “hot” polymer. Experiments with the use of a fully activated metallocene catalyst show that large lumps are formed that clog the layer in the reactor and impede movement, making it necessary to stop the reactor for cleaning after short-term operation.

The yield per catalyst during gas phase polymerization after reactivation can be increased, while it varies from about half the yield obtained in the presence of a fully active catalyst on the support to a value equal to the yield of the polymer obtained in the presence of an untreated catalyst, and above.

Thus, as can be seen, this invention relates to a method for passivation of fully active supported metallocene catalysts comprising a metallocene selected from Group 4 and Group 5 metallocenes and an alumoxane cocatalyst, the method according to the invention comprising contacting the metallocene catalyst with oxygen or an oxygen-containing or nitrogen-containing a compound selected from the group consisting of elemental oxygen, metal alkoxides, ethers and cyclic ethers, alkyls s, cycloalkyl and metal amides, in an amount effective to reduce the activity of a metallocene catalyst to about 50% of the activity of the metallocene catalyst system prior to the passivation, preferably in an amount of from about 1 to about 5 eq. by 1 equiv. metal in the catalytic complex.

The activity of passivated metallocene catalysts obtained according to the method according to the invention, expressed as the yield per catalyst in the polymerization of the olefin, is less than about 50%, preferably less than about 30%, more preferably less than 15%, even more preferably 0 to about 10% of activity values of the metallocene catalyst prior to passivation.

The activity of the catalysts, taken for comparison, can be determined using any of the known methods of polymerization and any known conditions. Data for comparison can be obtained using the method of low pressure catalytic suspension polymerization using propylene at 50 ° C in the absence of an activator, as described above. It will be apparent to those skilled in the art that process conditions can be adapted for other olefin monomers.

Passivated metallocene catalysts obtained according to the invention can also be described and characterized as latent olefin polymerization catalysts containing a Group 4 or Group 5 metallocene, aluminoxane and oxygen, or an oxygen-containing compound, or a nitrogen-containing compound selected from the group consisting of metal alkoxides, ethers and cyclic ethers, alkyl amines and cycloalkyl amines and metal amides.

Passivation is temporary or reversible. Latent olefin polymerization catalysts of the invention can be reactivated using an activator, for example, a compound capable of alkylating a passivated catalyst, such as aluminum alkyl. Reactivated catalysts are effective catalysts for the polymerization of olefins, and thus, they can be used in polymerization processes to produce polyolefins, such as polypropylene. The present invention is further directed to a process for the polymerization of C ₂ -C ₁₄ olefins in the presence of a metallocene catalyst system, said catalyst being temporarily and reversibly passivated by contact with oxygen or an oxygen-containing or nitrogen-containing compound dispersible in a polymerization medium and then reactivated under polymerization conditions.

Although the invention has been described and illustrated using specific metallocene catalysts containing zirconium metallocenes and alumoxane cocatalysts, the method of the invention can be used with various metallocene catalyst systems, including systems based on other metals of Group 4 and Group 5 and other cocatalysts, such as boron and etc. Further, other oxygen-containing compounds and nitrogen-containing compounds may be suitable for these purposes, in addition to those described in the examples. Specialists in this field it is obvious that the examples above only illustrate the invention and are not intended to limit its scope defined by the claims.

Claims (6)

1. The method of temporary and reversible passivation followed by reactivation of the active metallocene catalyst system containing a metallocene of a metal of 4 groups or 5 groups and an alumoxane cocatalyst in a molar ratio of aluminum in the cocatalyst to metal in the metallocene from 50: 1 to 2000: 1, deposited on a substrate, comprising in contacting the catalyst system with an effective amount of a passivator, which is selected from oxygen, metal alkoxides, ethers, cyclic ethers, alkylamines, cycloalkylamines, metal amides and morpholine; introducing a passivated metallocene catalyst system into the polymerization reactor and then reactivating the metallocene catalyst system in the reactor by contact with a metal alkyl alkylating reagent, taken in an amount effective to provide an active catalyst for the polymerization of monomers under polymerization conditions; after passivation and subsequent reactivation, the activity of the catalytic system under polymerization conditions decreases by no more than 50% of the activity of the catalytic system before contact with the passivator. 2. The method according to claim 1, in which the passivator is selected from oxygen, metal alkoxides, ethers and cyclic ethers. 3. The method according to claim 2, in which the passivator is oxygen. 4. A method for the polymerization of C ₂ -C ₁₄ olefins, comprising stages (a) of temporary and reversible passivation of an active metallocene catalyst system containing a metallocene of a metal of group 4 or 5 groups and an alumoxane cocatalyst in a molar ratio of aluminum in the cocatalyst to metal in the metallocene from 50: 1 up to 2000: 1, deposited on a substrate, which consists in contacting the catalytic system with an effective amount of a passivator, which is selected from oxygen, metal alkoxides, ethers, cyclic ethers, alkyl amines, cycloalkyl amines, metal amides and morpholine; (b) introducing a passivated metallocene catalyst system and at least one C ₂ -C ₁₄ olefin monomer into the polymerization reactor; (c) dispersing a passivated catalyst system; (d) reactivating the metallocene catalyst system in the reactor by contact with a metal alkyl alkylating reagent, taken in an amount effective to provide an active catalyst for the polymerization of monomers under polymerization conditions; and (e) polymerizing an olefin monomer; after passivation and subsequent reactivation of the activity of the catalytic system under polymerization conditions it decreases by no more than 50% of the activity of the catalytic system before contact with the passivator. 5. The method according to claim 4, in which the passivator is selected from oxygen, metal alkoxides, ethers and cyclic ethers. 6. The method according to claim 5, in which the passivator is oxygen.