Catalyst system for high yield synthesis of polyolefins

Details Catalyst system for high yield synthesis of polyolefins Catalyst system for high yield synthesis of polyolefins

1999-09-17

2002-11-12

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S075000, C526S114000, C526S160000, C526S133000, C526S905000, C526S943000, C526S348500, C526S348600, C502S104000, C502S117000, C502S152000

Reexamination Certificate

active

06479599

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a supported metallocene catalyst system for the high yield synthesis of polyolefins, to methods of preparation of the catalyst system, to polymerization processes which use the catalyst system and to polyolefin polymers produced by the polymerization processes.
BACKGROUND OF THE INVENTION
Recently there have been a number of advances in the production of polyolefin copolymers due to the introduction of metallocene catalysts. Metallocene catalysts offer a number of advantages including improved activity compared to traditional Ziegler catalysts under a given set of conditions. Also, metallocene catalysts are often described as being single-site in nature. Because of this single-site nature, the polyolefins produced with these catalysts are often very uniform in their molecular structure.
In order for metallocene catalysts to be commercially useful as supported catalysts in a gas phase, solution or slurry process, the catalysts employed preferably are highly active. High productivity of the catalyst in a polymerization processes is desired to reduce catalyst costs and to avoid the expense of catalyst residue removal procedures. Thus, the catalyst residue in the polymer must be low enough that it can be left in the polymer without causing any undue problems to either the resin manufacturer, or to a party fabricating articles from the resin, or to an ultimate user of such fabricated articles. When a highly active catalyst is used in a gas phase, solution or slurry process, the transition metal content of the polymer should be on the order of less than 1 part per million (ppm) of transition metal at a productivity level of greater than 1,000,000 pounds of polymer per pound of transition metal, One of the features of a gas phase polymerization reactor is that the gas velocity in the reactor is limited to prevent excess carry-over of the solid particles from the fluid bed, which would happen if the velocity is set too high. If the gas velocity is set too low, reactor fouling may occur due to fallout of polymer from the bed. Since the gas velocity is limited, the amount of heat which can be removed when operating at a given set of conditions is also limited. The limitations on heat removal place limitations on the rate of productivity for a given reactor. Attempts at improving the productivity of a gas phase reactor by increasing the catalyst feed rate will often not be met with success because of the heat removal limitations of the reactor.
A major improvement in reactor output and a partial solution to the heat removal limitations is described in U.S. Pat. Nos. 4,543,399, 5,352,749, EP 89691, WO 94/25495 and WO 94/28032, which are hereby incorporated by reference, where a volatile liquid is fed to the reactor. The volatile liquid evaporates in the hot fluidized bed to form a gas which mixes with the fluidizing gas. The evaporated liquid exits the top of the reactor as part of the recycle gas and passes through the heat exchange part of the recycle loop. The evaporated liquid condenses in the heat exchanger and is then feed to the reactor as a volatile liquid.
In practice, in the gas phase commercial copolymers are made using monomers having 2 to 8 carbon atoms because of the lower concentrations possible in the reactor for alpha-olefins with greater carbon numbers. Traditional Ziegler catalysts are not particularly efficient or effective at incorporating the alpha-olefin comonomers having greater numbers of carbon atoms into the polymer. To date, highly active and highly efficient supported metallocene catalysts, which do have high rates of alpha-olefin comonomer incorporation into the polymer, have not been demonstrated.
Up to now, supported metallocene catalysts useful for producing polyolefin homopolymers and copolymers in gas phase and slurry processes have had reported catalyst efficiencies of less than 50,000,000 grams polymer/mole catalyst/hour for Zr based catalysts and 24,000,000 grams polymer/mole catalyst/hour for Ti based catalysts except when used with exceptionally high ratios of cocatalyst to catalyst. A variety of metallocene loadings and catalyst concentrations have been reported with no obvious trends. Indeed, due to the nonuniformity in the conventions used to report the data, and imprecision in the definitions of various terms in the disclosures, there appears to be little relationship between the use of various classes of metallocene complexes or any optimal ranges for the various process variables employed.
SUMMARY OF THE INVENTION
There is a need for a supported olefin polymerization catalyst system that can be used more efficiently, effectively and economically to polymerize olefins or to copolymerize ethylene or propylene with higher alpha-olefins having from about 3 to about 20 carbon atoms in gas phase and slurry processes.
We have made the surprising discovery that, for supported metallocene catalysts with a formulation having less than 25 &mgr;mol metallocene/gram support and a relatively low cocatalyst/catalyst ratio, the measured catalyst efficiencies are invariably greater than 50,000,000 grams polymer/mole catalyst/hour for Zr based catalysts and 24,000,000 grams polymer/mole catalyst/hour for Ti based catalysts and, in a preferred embodiment can be greater than about 50,000,000 grams polymer/mole catalyst/hour for Ti based catalysts. This phenomenon is independent of the choice of metallocene, the choice of cocatalyst, the choice of support and the method of preparation of the support or the method of preparation of the formulated catalyst or the method of activation of the catalyst or the method of injection of the formulated catalyst into the reactor.
In one embodiment, this invention provides a process for the polymerization of an olefin monomer, or of an olefin monomer and one or more comonomers, to produce a polymer, the process carried out in a polymerization reactor in the presence of a supported olefin polymerization catalyst system produced from catalyst components comprising:
1) a support material component comprising one or more dehydrated support materials;
2) a metallocene complex component comprising one or more metallocene complexes used in a total loading range of from about 0.1 to about 25 &mgr;mol of metallocene complex/gram of support material component;
3) an activator component comprising one or more activators used in a range of molar ratios of total moles of activator to total moles of metallocene complex of from about 0.5 to about 2.5;
where the catalyst system is used at a catalyst concentration in the range of from about 0.01×10
−6
to about 6×10
−6
moles of active catalyst/mole of monomer, and a catalyst efficiency results that is at least 2.4×10
7
g polymer/mol catalyst hour.
In another embodiment, this invention provides a process for the polymerization of an olefin monomer, or of an olefin monomer and one or more comonomers, to produce a polymer, the process carried out in a polymerization reactor in the presence of a supported olefin polymerization catalyst system produced from catalyst components comprising:
1) a support material component comprising one or more dehydrated support materials;
2) a metallocene complex component comprising one or more metallocene complexes all of which have as a central metal Ti used in a total loading range of from about 0.1 to about 25 &mgr;mol of metallocene complex/gram of support material component;
3) an activator component comprising one or more activators used in a range of molar ratios of total moles of activator to total moles of metallocene complex of from about 0.5 to about 2.5;
where a catalyst efficiency results that is at least 2.4×10
7
g polymer/mol catalyst/hour.
In another embodiment, this invention provides a process for the polymerization of an olefin monomer, or of an olefin monomer and one or more comonomers, to produce a polymer, the process carried out in a polymerization reactor in the presence of a supported olefin polymerization catalyst system produced from catalyst compon

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