Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2003-01-16
2004-11-16
Choi, Ling Siu (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S127000, C526S943000, C526S129000, C526S131000
Reexamination Certificate
active
06818712
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to supported catalysts suitable for the polymerisation of olefins and in particular to supported metallocene catalysts providing advantages for operation in gas phase processes.
In recent years there have been many advances in the production of polyolefin homopolymers and copolymers due to the introduction of metallocene catalysts. Metallocene catalysts offer the advantage of generally a higher activity than traditional Ziegler catalysts and are usually described as catalysts which are single site in nature. There have been developed several different families of metallocene complexes. In earlier years catalysts based on bis(cyclopentadienyl) metal complexes were developed, examples of which may be found in EP 129368 or EP 206794. More recently complexes having a single or mono cyclopentadienyl ring have been developed. Such complexes have been referred to as ‘constrained geometry’ complexes and examples of these complexes may be found in EP 416815 or EP 420436. In both of these complexes the metal atom eg. zirconium is in the highest oxidation state.
Other complexes however have been developed in which the metal atom may be in a reduced oxidation state. Examples of both the bis(cyclopentadienyl) and mono(cyclopentadienyl) complexes have been described in WO 96/04290 and WO 95/00526 respectively.
The above metallocene complexes are utilised for polymerisation in the presence of a cocatalyst or activator. Typically activators are aluminoxanes, in particular methyl aluminoxane or compounds based on boron compounds. Examples of the latter are borates such as trialkyl-substituted ammonium tetraphenyl- or tetrafluorophenyl-borates. Catalyst systems incorporating such borate activators are described in EP 561479, EP 418044 and EP 551277.
The above metallocene complexes may be used for the polymerisation of olefins in solution, slurry or gas phase. When used in the gas phase the metallocene complex and/or the activator are suitably supported. Typical supports include inorganic oxides eg. silica or polymeric supports may alternatively be used.
Examples of the preparation of supported metallocene catalysts for the polymerisation of olefins may be found in WO 94/26793, WO 95/07939, WO 96/00245, WO 96/04318, WO 97/02297 and EP 642536.
A preferred gas phase process for polymerising olefins in the presence of a metallocene catalyst is one operating in a fluidised bed. In such processes the molecular weight of the polyolefin produced by the metallocene complex is determined by the competing rates of chain propagation, chain termination and chain transfer. These rates are in turn determined by the intrinsic kinetics of the catalyst and the reaction environment. In order to produce commercially interesting polyolefins the catalysts must make a high molecular weight polymer. Furthermore at commercial reactor conditions the catalyst must make a molecular weight that exceeds that of commercially interesting polymers such that the molecular weight can be controlled at the desired value with a chain transfer agent such as hydrogen.
WO 98/27119 describes supported catalyst components comprising ionic compounds comprising a cation and an anion in which the anion contains at least one substituent comprising a moiety having an active hydrogen. In this disclosure supported metallocene catalysts are exemplified in which the catalyst is prepared by treating the aforementioned ionic compound with a trialkylaluminium compound followed by subsequent treatment with the support and the metallocene. When used in the gas phase such supported catalysts are extremely active but the molecular weight of the produced polymer is lower than that required for commercial operation.
WO 98/27119 also describes a method for activating a substantially inactive catalyst precursor comprising (a) an ionic compound comprising a cation and an anion containing at least one substituent comprising a moiety having an active hydrogen, (b) a transition metal compound and optionally, (c) a support by treatment with an organometallic compound thereby forming an active catalyst.
Various methods have been utilised to prepare supported catalysts of this type. For example WO 98/27119 describes several methods of preparing the supported catalysts disclosed therein in which the support is impregnated with the ionic compound. The volume of the ionic compound may correspond from 20 volume percent to greater than 200 volume percent of the total pore volume of the support. In a preferred preparative route the volume of the solution of the ionic compound does not exceed substantially, and is preferably equal to, the total pore volume of the support. Such methods of preparation may be referred to as incipient precipitation or incipient wetness techniques.
We have now developed an improved method which may be used to prepare supported metallocene catalyst systems resulting in increased productivities particularly when used in the gas phase.
SUMMARY OF THE INVENTION
Thus according to the present invention there is provided a method for the preparation of a supported metallocene catalyst system said method comprising the steps of:
(i) mixing together in a suitable solvent
(a) an organometallic compound, and
(b) an ionic activator comprising a cation and an anion,
(ii) addition of the mixture from step (i) to a support material,
(iii) addition of a metallocene complex in a suitable solvent,
(iv) further addition of an organometallic compound in a suitable solvent, and
(v) removal of the solvent.
REFERENCES:
patent: 5783512 (1998-07-01), Jacobsen et al.
patent: 5807938 (1998-09-01), Kaneko et al.
patent: 6458982 (2002-10-01), Schottek et al.
patent: WO 98/27119 (1998-06-01), None
Mealares Christel Marie-Claude
Taylor Michael John
BP Chemicals Limited
Choi Ling Siu
Finnegan, Henderson Farabow, Garrett and Dunner L.L.P.
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