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
1997-09-10
2002-06-04
Wood, Elizabeth D. (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...
C502S126000, C502S127000, C502S132000, C502S134000
Reexamination Certificate
active
06399533
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to components of catalysts for the polymerization of olefins, the catalysts obtained therefrom and the use of said catalysts in the polymerization of olefins CH
2
═CHR, in which R is hydrogen or an alkyl, cycloalkyl or aryl radical with 1-10 carbon atoms. Another aspect of the present invention relates to the polymers obtained using said catalysts.
Catalysts are known from the literature that are obtained from compounds ML
x
in which M is a transition metal, especially Ti, Zr and Hf, L is a ligand coordinating to the metal, x is the valence of the metal and at least one of the ligands L has cyclo-alkadienyl structure. Catalysts of this type using compounds Cp
2
TiCl
2
or Cp
2
ZrCl
2
(Cp=cyclopentadienyl) are described in U.S. Pat. Nos. 2,827,446 and 2,924,593. The compounds are used together with alkyl-Al compounds in the polymerization of ethylene. The catalytic activity is very low. Catalysts with very high activity are obtained from compounds Cp
2
ZrCl
2
or Cp
2
TiCl
2
and from their derivatives substituted in the cyclopentadienyl ring, in which the Cp ring can also be condensed with other rings, and from polyalumoxane compounds containing the repeating unit —(R)AlO—, in which R is a lower alkyl, preferably methyl (U.S. Pat. No. 4,542,199 and EP-A-129368).
Catalysts of the type mentioned above, in which the metallocene compound contains two indenyl or tetrahydro-indenyl rings bridge-bonded through lower alkylenes or through other divalent radicals, are suitable for the preparation of stereoregular polymers of propylene and other &agr;-olefins (EP-A-185918).
Stereospecific catalysts are also obtained from dicyclopentadienyl compounds in which the two rings are substituted differently with groups having steric hindrance such as to prevent rotation of the rings about the axis of coordination with the metal.
Substitution of indenyl or tetrahydroindenyl in suitable positions gives catalysts that have very high stereospecificity (EP-A-485823, EP-A-485820, EP-A-519237, U.S. Pat. No. 5,132,262 and U.S. Pat. No. 5,162,278).
The metallocene catalysts described above produce polymers with a very narrow molecular weight distribution (Mw/Mn of about 2).
Some of these catalysts also have the property of forming copolymers of ethylene with &agr;-olefins of the LLDPE type or ethylene/propylene elastomeric copolymers with very uniform distribution of the comonomer units. The LLDPE polyethylene obtained is further characterized by low solubility in solvents such as xylene or n-decane.
The polypropylene obtained with the highly stereospecific catalysts mentioned above has greater crystallinity and a higher deformation temperature compared with the polymer that can be obtained with the conventional Ziegler-Natta catalysts.
However, these metallocene catalysts have a considerable drawback with respect to the possibility of being employed in industrial processes for production of polyolefins that are not carried out in solution, owing to the fact that they are soluble in the reaction medium in which they are prepared and in the liquid medium of polymerization.
In order to be usable in gas-phase polymerization processes, the catalysts must be supported on suitable supports which endow the polymer with appropriate morphological properties.
Supports of various kinds have been used, including, among others, porous metal oxides such as silica or porous polymeric supports such as polyethylene, polypropylene and polystyrene. The halides of magnesium are also used as supports. In some cases magnesium halides are also used as counterion of an ion pair in which the metallocene compound supplies the cation and a compound, such as a Mg halide, supplies the anion.
When Mg halide is used for supplying the anion, the catalytic system is formed by the halide present in solid form and the metallocene compound dissolved in a solvent. A system of this type cannot be used in gas-phase polymerization processes. Mg halide is preferably used in finely divided form that can be obtained by grinding.
As support, Mg halide is used in pulverized form, obtainable by grinding. Catalysts obtained in this way are not of high performance. Sufficiently high yields can only be obtained when the Mg halide is used in a form in which it is partially complexed with an electron-donor compound, obtained by a special method of preparation.
Japanese Application No. 168408/88 (published on 12.7.1988) describes the use of magnesium chloride as support for metallocene compounds, such as Cp
2
TiCl
2
, Cp
2
ZrCl
2
, Cp
2
Ti(CH
3
)
2
for forming, with trialkyl aluminium and/or polymethylalumoxane (MAO), catalysts for the polymerization of ethylene. The component containing the magnesium chloride is prepared by grinding MgCl
2
with the metallocene compound, also working in the presence of electron-donor compounds. Alternatively, the component is prepared by treating the metallocene with a liquid MgCl
2
-alcohol adduct and subsequent reaction with AlEt
2
Cl. The catalyst activity, referred to MgCl
2
is very low.
Catalysts comprising a metallocene compound of the type Cp
2
ZrCl
2
supported on MgCl
2
in spherical form and partially complexed with an electron-donor compound are described in U.S. Pat. No. 5,106,804. The performance of these catalysts is better than that described in Japanese Application No. 168408/88 but is still not satisfactory, since it is not possible to obtain polymers containing sufficiently low residues of the catalyst. The electron donor used must be free from atoms of active hydrogen and in addition must be uniformly distributed in the bulk of the Mg halide. Suitable supports cannot be obtained by mere mixing of the components. Homogeneous dispersion of the electron donor is obtained by forming the Mg halide (by halogenation of Mg-dialkyls) in the presence of a solvent containing the electron donor in dissolved form. The surface area of the Mg halide is not greater than 100 m
2
/g, and is preferably between 30 and 60 m
2
/g. No information is given with respect to the porosity of the support. The electron-donor compound is used in a quantity of from 0.5 to 15 mol % based on the Mg halide; its presence is necessary. The catalysts obtained have performance that is much lower than that of the corresponding unsupported catalysts in which the metallocene compound is used in solution.
Application EP-A-318048 describes catalysts in which a solid component comprising a compound of Ti supported on a magnesium chloride that has particular characteristics of surface area and of porosity and possibly an electron-donor compound, is used with benzyl compounds of Ti or Zr or with metallocene compounds of the type Cp
2
Ti(CH
3
)
2
and bis-(indenyl)-Zr(CH
3
)
2
for forming catalysts for polymerization of ethylene and of propylene. The weight ratio of metallocene to magnesium chloride is very high (greater than 1), so it is necessary to remove the metallocene from the obtained polymer. The catalysts are used in processes that are carried out in the presence of a liquid polymerization medium.
Application EP-A-439964 describes bimetallic catalysts suitable for the preparation of ethylene polymers with broad molecular weight distribution (Mw/Mn between 4 and 14) obtained by supporting a metallocene on a solid component containing a Ti compound supported on MgCl
2
. MAO or its mixtures with alkyl-Al are used as cocatalyst. Trialkyl-Al compounds are also used as cocatalysts but the catalytic activity is low. The yields of these mixed catalysts with active centres derived either from the Ti compound supported on MgCl
2
or from the metallocene compound are very high when the catalysts are used in a hydrocarbon medium; on the other hand they are low when polymerization is effected in the gas phase. This is probably due to the fact that, when using a hydrocarbon medium, as the metallocene compound is not fixed to the support in a stable form, it dissolves in the hydrocarbon polymerization solvent. In practice, the obtained catalyst corresponds to a homogeneous catalys
Govoni Gabriele
Pasquali Stefano
Sacchetti Mario
Basell Technology Company bv
Cave LLP Bryan
Pasterczyk J.
Wood Elizabeth D.
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