Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Plural component system comprising a - group i to iv metal...
Reexamination Certificate
1999-02-08
2001-05-01
Bell, Mark L. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Plural component system comprising a - group i to iv metal...
C502S111000, C526S142000, C526S160000, C526S943000
Reexamination Certificate
active
06225252
ABSTRACT:
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° 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° 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:
for the linear type and/or the formula II:
for the cyclic type, where, in the formulae I and II, the radicals R can be identical or different and are each a C
1
-C
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, alky
Ernst Eberhard
Reussner Jens
Bell Mark L.
Borealis AG
Pasterczyk J.
Wenderoth , Lind & Ponack, L.L.P.
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