| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | May 1, 2001 |
| PATENT TITLE |
Process for preparing catalyst supports and supported polyolefin catalysts and also their use for the preparation of polyolefins |
| PATENT ABSTRACT |
A process for preparing a catalyst support in which a hydrophilic inorganic oxide of an element of main groups 2, 13 or 14 or transition group 4 of the Periodic Table or a mixture or mixed oxide thereof is dried at from 110 to 800.degree. C., subsequently reacted, if desired, with alumioxanes or aluminum alkyls and subsequently reacted simultaneously with aluminoxanes and bisphenol A as a polyfunctional organic crosslinker. In a further stage, the catalyst support can be brought into contact with a polyolefin catalyst, giving a supported polyolefin catalyst which is used, in particular, for the polymerization of olefins. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | February 8, 1999 |
| PATENT FOREIGN APPLICATION PRIORITY DATA | This data is not available for free |
| PATENT REFERENCES CITED | T. Tsutsui et al., Polymer, vol. 32, No. 14, pp. 2671-2673, 1991. |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What we claim is: 1. A supported polyolefin catalyst comprising the reaction product of a catalyst support produced by a process which comprises: a) drying a hydrophilic inorganic oxide of an element of Groups 2, 13 or 14 or transition Group 4 of the Periodic Table or a mixture of said oxides or their mixed oxides at from 110 to 800.degree. C., subsequently b) optionally reacting free hydroxyl groups of the oxide completely or partially with alumoxanes or aluminum alkyls, and subsequently c) reacting the oxide simultaneously with alumoxanes and bisphenol A and subsequently with one or more polyolefin catalysts. 2. A supported polyolefin catalyst, comprising the reaction product of a catalyst support produced by a process which comprises: a) drying a hydrophilic inorganic oxide of an element of Groups 2, 13 or 14 or transition Group 4 of the Periodic Table or a mixture of said oxides or their mixed oxides at from 110 to 800.degree. C., subsequently b) optionally reacting free hydroxyl groups of the oxide completely or partially with alumoxanes or aluminum alkyls, and subsequently c) reacting the oxide simultaneously with alumoxanes and bisphenol A and subsequently with one or more metallocenes. 3. A process for preparing polyolefins comprising polymerizing olefins in the presence of a catalyst as claimed in claim 1. 4. The process for preparing polyolefins as claimed in claim 3, wherein the polymerization is conducted in the further presence of at least one aluminum alkyl. 5. A process for preparing polyolefins comprising polymerizing olefins in the presence of a catalyst as claimed in claim 2. 6. The process for preparing polyolefins as claimed in claim 5, wherein the polymerization is conducted in the further presence of at least one aluminum alkyl. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
The invention relates to catalyst supports based on inorganic oxides, supported polyolefin catalysts prepared for using these catalyst supports and also their use in olefin polymerization. Polypropylene can be prepared, for example as described in EP-A-530 647, by the use of polyolefin catalysts comprising a metallocene and an activator or cocatalyst such as methylaluminoxane (MAO) or a perfluorotetraphenylborate. However, use of such homogenous catalysts in the polymerization gives powders having only a low bulk density. The particle morphology of such products can in principle be somewhat improved by a specific pretreatment of the metallocene with the cocatalyst (EP-302 424). However, such a process has the disadvantage of, in particular, heavy deposit formation in industrial reactors (EPA 563 917). Although the use of methylaluminoxane, which is insoluble in aliphatic solvents, as support material does give a certain improvement in the activity, it likewise leads to pulverulent products (Polymer 1991, Vol. 32, 2671-2673); in addition, the process is uneconomical. Supporting the metallocene on oxidic materials such as silicon oxide or aluminum oxide with pretreatment of the starting material, which may be partially dehydrated, with the cocatalyst is a method known from WO 91/09882 which is used in homopolymerization and copolymerization of ethylene. However, in this method, the particle size of the polymer particle is determined essentially by the particle size of the support material so that limits are placed on an increase in particle size compared with conventional catalysts supported on magnesium chloride. Further processes describe the modification of the oxidic support using MAO and the subsequent application of the metallocene (EPA 0206794). However, this method restricts the ability to control the particle size by means of the properties of the support material. EP-A-685494 describes a further supported catalyst which is prepared by the Application of methylaluminoxane to a hydrophilic oxide, subsequent crosslinking of the MAO using a polyfunctional organic crosslinker and subsequent application of an activated MAO/metallocene complex. A disadvantage of this supported catalyst is that at the relatively high polymerization conversions achieved in industrial plants the strength of the supported catalyst is not sufficient to ensure a compact, granular morphology of the polymer product. The result is a lowering of the bulk density and an increase in the proportion of fines, which causes considerable problems from a technical point of view. It is therefore an object of the invention to develop a process which allows the preparation of a supported polyolefin catalyst which can be used for the polymerization of olefins and avoids the disadvantages described even at high polymerization conversions. Surprisingly, it has now been found that when a specific support material is used and the catalyst is subsequently fixed to the support, the use of these supported polyolefin catalysts in the polymerization of olefins gives high polymerization conversions and bulk densities of the products and the particle size and particle size distribution of the polymers can be set in a targeted way. The present invention accordingly provides a process for preparing a catalyst support, which comprises a) drying a hydrophilic inorganic oxide of an element of main groups 2, 13 or 14 or transition group 4 of the Periodic Table or a mixture or mixed oxide thereof at from 110 to 800.degree. C., subsequently. b) if desired reacting the free hydroxyl groups of the oxide completely or partially with aluminoxanes or aluminum alkyls and subsequently c) reacting the oxide simultaneously with aluminoxanes and polyfunctional organic crosslinkers. The hydrophilic, hydroxyl-containing oxides used usually contain water. They are preferably macroporous and finely divided and usually have a mean particle size of from 10 to 300 microns, preferably from 30 to 100 microns. The support oxides are commercially available; preference is given to using aluminum oxide, silicon oxide, magnesium oxide, titanium oxide and zirconium oxide. Particular preference is given to using silicon dioxides of the Grace Davison type. However, other suitable starting materials are finely divided oxides, for example those described in DE-C 870 242 or EP-A-585 544, which are prepared by the high-temperature hydrolysis method from gaseous metal chlorides or silicon compounds. The invention also provides the catalyst support prepared by the process of the invention. The catalyst support of the invention is prepared from a hydrophilic inorganic oxide in a multistage reaction. In the first stage (a), the oxide is dehydrated in a stream of nitrogen or under reduced pressure at temperatures of from 110 to 800.degree. C. over a period of from 1 to 24 hours. The concentration of free hydroxyl groups established as a function of the drying temperature selected is then measured. The free hydroxyl groups can be reacted completely or partially with aluminoxanes or aluminum alkyls in stage (b). In stage (c), the dried oxide is reacted simultaneously with aluminoxanes and at least one polyfunctional organic crosslinker, with it being suspended, for example, in a suitable hydrocarbon solvent such as toluene in such a way that it is covered with the solvent. The solvents for the aluminoxane and for the crosslinker have to be miscible and the same solvents are preferably used. Particular preference is given to using toluene. According to the present invention, the aluminoxane used is one of the formula I: ##STR1## for the linear type and/or the formula II: ##STR2## for the cyclic type, where, in the formulae I and II, the radicals R can be identical or different and are each a C.sub.1 -C.sub.6 -alkyl group and n is an integer in the range 1-50. Preferably, the radicals R are identical and are methyl, isobutyl, phenyl or benzyl. The aluminoxane can be prepared in various ways by known methods. One possibility is, for example, the reaction of aluminum alkyls with aluminum sulfate containing a water of crystallization (Hoechst EP-A-302424). In the present invention, preference is given to using commercial methylaluminoxane (MAO, from Witco) which is dissolved in toluene. In the preparation of the catalyst support, the molar ratio of aluminum (as aluminoxane) to surface hydroxyl groups is between 1 and 50, preferably between 1 and 30, particularly preferably between 5 and 20. To prepare the solution needed in stage c), the solvent used for the crosslinker can be the same as for the MAO solution. Owing to the temperature dependence of the solubility of these crosslinkers in the solvent used, the desired concentration can be set in a targeted manner by the choice of the temperature of the solution. Particularly advantageous is the selection of a solvent whose boiling point is below the decomposition temperature of the solid prepared in stage c). Preference is given to using aromatic solvents such as xylene, benzene or toluene. Toluene is particularly suitable. Suitable polyfunctional organic crosslinkers to be used according to the invention are all organic compounds having more than one functional group which can react with a metal-carbon bond. Preference is given to using a bifunctional crosslinker. Such bifunctional organic compounds can be, for example, aliphatic or aromatic diols, aldehydes, dicarboxylic acids, primary or secondary diamines, diepoxy compounds. To avoid interfering secondary reactions or reaction products which would require additional purification, preference is given to using aliphatic and aromatic diols, secondary amines or diepoxy compounds or mixtures thereof. Particular preference is given to using ethylene glycol, butanediol, bisphenol A and 1,4-butanediol diglycidyl ether. Tri- or higher-functional crosslinkers which can be used are, for example, triethanolamine, glycerol, phloroglucinol or tetraethylenepentamine. When using the polyfunctional crosslinkers, it is also possible, in a further reaction stage, to deactivate unreacted reactive groups using, for example, alkylaluminum compounds, preferably using trimethylaluminum. The molar ratio between the aluminum used in stage c) as aluminoxane and the crosslinker can vary within a wide range and is between 1 and 100, preferably between 1 and 40, particularly preferably between 10 and 25. It is dependent, in particular, on the type and pretreatment of the metal oxides, the type of aluminoxanes used, on the respective molar ratio of Al (as aluminoxane) to the surface hydroxyl groups on the metal oxide and on the type of crosslinker. Higher molar ratios of Al to crosslinker are used particularly when use is made of tri- or higher-functional crosslinkers which can form a correspondingly higher number of crosslinks. The suspended dried oxide from the stage a) is preferably treated with a solution of aluminoxane and a solution of one or more polyfunctional organic crosslinkers in the same solvent. If desired, it is also possible in stage b) to react the free hydroxyl groups of the oxide with an up to equimolar amount of an aluminoxane or an aluminum alkyl solution, for example trimethylaluminium, prior to the crosslinking reaction. Preference is given to using MAO for this purpose. It has been found to be particularly advantageous if all hydroxyl groups have been reacted. However, even a partial reaction of these groups gives a positive effect. The metering in of the solutions is carried out simultaneously and continuously and the crosslinker solution is heated/cooled if desired. The temperature to which the solution is heated/cooled depends on the solubility of the crosslinker in the solvent selected and on the desired crosslinking density on the support surface. The rate at which the two streams are metered in can be set by means of metering pumps and is in a range between 0.1 and 1000 ml per minute, preferably between 0.5 and 250 ml per minute, particularly preferably between 1 and 50 ml per minute. The reaction is preferably carried out in such a way that all the MAO has been reacted after the simultaneous metering in of the two solutions. Under some circumstances, fluctuations in the reaction conditions on the industrial scale can lead to unreacted MAO remaining in the solution. The usable catalyst supports as described in EP-A-685494 display a soluble Al proportion in the solvent used of preferably less than 1.4 mol % based on MAO used. In this case, it is possible to carry out one or more washing steps in order to reduce the concentration to below the desired limit. After metering in is complete, the reaction mixture is stirred further for about 60 minutes and the solvent is then removed. The residue can be dried under reduced pressure, but it is preferably used further in the moist state. The catalyst support prepared by the process of the invention can advantageously be used for the preparation of a supported polyolefin catalyst. The invention accordingly also provides a supported polyolefin catalyst comprising the reaction product of (A) an above-described catalyst support according to the invention with (B) a polyolefin catalyst or a mixture of a plurality of polyolefin catalysts. Possible polyolefin catalysts are, for example, metallocenes, with it being possible in principle to react any metallocene or mixture of metallocenes. Possible metallocenes are, for example, unbridged, unsubstituted or substituted cyclopentadienyl, indenyl and fluorenyl compounds of metals of group IVb, Vb or VIb of the Periodic Table, for example bis(1,2-dimethylcyclopentadienyl)zirconium dichloride (EP-A-283739); bridged, unsubstituted or substituted, asymmetric or symmetric cyclopentadienyl, indenyl and fluorenyl compounds of metals of group IVb, Vb or VIb of the Periodic Table, for example dimethylsilanediylbis(indenyl)zirconium dichloride (EP-A-574597), dimethylsilanediylbis(2-methylindenyl)zirconium dichloride (EP-A-485822), bis(trimethylsilyl)silanediylbis(2-methylindenyl)zirconium dichloride (German Application 19527047) or isopropylidene(cyclopentadienyl)(fluorenyl)zirconium dichloride (EP-A-351391). The supported metallocene catalyst is prepared by suspending the catalyst support of the invention in an inert hydrocarbon, preferably toluene, and bringing it into contact with the metallocene. In this procedure, the metallocene is, dissolved, for example, in an inert hydrocarbon. Inert solvents which can be used are, for example, aliphatic or aromatic hydrocarbons, preferably toluene. The metallocenes are preferably used in an amount of from 0.3% by mass to 5% by mass based on the total mass of the supported catalyst. The mixing time is from 5 minutes to 24 hours, preferably from 1 to 6 hours. The mixing is carried out at a temperature of from -10 to +80.degree. C., in particular from 20 to 70.degree. C. The application of the metallocene is preferably carried out subsequent to the synthesis of the support in order to save a drying step. After the reaction is complete, the solvent is decanted and taken off under reduced pressure until a free-flowing solid remains. The metallocene content of the supported catalyst is in the range from 0.01 to 5% by weight, preferably from 0.1 to 3% by weight, based on the mass of the supported catalyst. Also possible are polyolefin catalysts based on transition metal salts of transition groups IV to VIII of the Periodic Table of the Elements, as are known, for example, as Ziegler/Natta catalysts and described, for example, in the European Patent Application 95110693. The invention further provides a process for preparing polyolefins by polymerization or copolymerization of olefins, wherein the polymerization catalyst used is the supported polyolefin catalyst of the invention, and also provides for the use of supported polyolefin catalysts according to the invention in the polymerization or copolymerization of olefins for preparing polyolefins. The supported catalyst of the invention can be introduced into the polymerization mixture either as a powder or as a suspension in an inert hydrocarbon, for example pentane, hexane, cyclohexane or a mineral oil. The polymerization is carried out in a known manner by a solution, suspension or gas-phase process, continuously or batchwise at a temperature of from -10 to +200.degree. C., preferably from +20 to +80.degree. C. The supported catalyst of the invention is polymerization-active without further activating additives. However, it has been found to be particularly advantageous to use aluminum alkyls, preferably trimethylaluminum, triethylaluminum or triisobutylaluminum, as scavenger and as additional activator. The amount used is, based on the aluminum, 50-5000 mol, preferably 100-500 mol, per mol of transition metal of the polyolefin catalyst. Polymerization or copolymerization is carried out on olefins of the formula R.sup.a --CH.dbd.CH--R.sup.b. In this formula, R.sup.a and R.sup.b are identical or different and are each a hydrogen atom or an alkyl radical having from 1 to 20 carbon atoms. However, R.sup.a and R.sup.b together with the carbon atoms connecting them can also form a ring. For example, olefins such as ethylene, propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, cyclopentene, norbornene or norbornadiene are polymerized or copolymerized. Preference is given to polymerizing or copolymerizing ethylene, propylene and butene, particularly preferably ethylene and propylene. If required, hydrogen is added as molecular weight regulator. The total pressure in the polymerization is usually 0.5-150 bar. Polymerization is preferably carried out in the pressure range of 1-40 bar. If the polymerization is carried out as a suspension or solution polymerization, an inert solvent is used. For example, aliphatic or cycloaliphatic hydrocarbons such as pentane, hexane or cyclohexane can be used. It is also possible to use toluene. Preference is given to carrying out the polymerization in the liquid monomer. In the copolymerization of ethylene with propylene, the polymerization is preferably carried out in liquid propylene or in hexane as suspension medium. In the polymerization in liquid propylene, the ethylene is preferably fed in an amount such that a partial pressure ratio P.sub.C3 /P.sub.C2 >0.5, in particular >1.0, is established over the liquid phase (P.sub.C2 =partial pressure of the ethylene in the gas phase over the suspension; P.sub.C3 =partial pressure of the propylene in the gas phase over the suspension). In the copolymerization in hexane as suspension medium, an ethylene/propylene gas mixture having a propylene content of from 1 to 50 mol %, preferably from 5 to 30 mol %, is fed in. The total pressure is kept constant during the polymerization by metering in a further amount. The total pressure is from 0.5 to 40 bar, preferably from 1 to 20 bar. The polymerization time is from 10 minutes to 6 hours, preferably from 30 minutes to 2 hours. The supported catalysts used according to the invention make possible the preparation of homopolymers, copolymers and block copolymers. Their use makes it possible to control the particle size of the polymers in a targeted manner as a function of the preparation conditions used for the support. The particular advantage of the catalyst of the invention is therefore the factor that the particle size of the polymers can be matched to the respective requirements of the technology used. Apart from the opportunity of controlling the particle size and the particle size of distribution in a targeted manner, the process of the invention has the further advantage that the polyolefins are obtained in granular form and that, in particular as high polymerization conversions too, they have a high bulk density and a low fines content. Further advantages are given by the preparation technology. The catalyst can, in principle, be prepared by a "single-vessel process"; with an appropriate reaction procedure, no interfering by-products are formed and the solvents used are recyclable. The following examples illustrate the invention. Abbreviations used are: MC Metallocene MAO Methylaluminoxane TIBAL Triisobutylaluminum M.sub.w Weight average molar mass in g/mol determined by GPC M.sub.n Number average molar mass in g/mol determined by GPC M.sub.w /M.sub.n Polydispersity d.sub.50 Mean particle diameter determined by sieve analysis T.sub.m Melting point determined by DSC. |
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| PATENT PHOTOCOPY | available on request |
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