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
1998-12-31
2001-05-29
Wu, David W. (Department: 1713)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Plural component system comprising a - group i to iv metal...
C502S108000, C502S109000, C526S160000, C526S127000, C526S129000, C526S943000, C526S130000
Reexamination Certificate
active
06239060
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a new type of supported metallocene catalyst system having a modified support useful for the polymerization of olefins. More particularly, but not by way of limitation, the present invention relates to a supported metallocene system having a support modified with a source of a Group XIII element. In another aspect the present invention relates to an method for polymerization of olefins using the inventive supported metallocene catalyst system.
BACKGROUND OF THE INVENTION
Metallocene catalyst systems are extensively used in a variety of polymerization systems, including the polymerization of olefins. The term “metallocene” as used herein refers to a derivative of cyclopentadienyl which is a metal derivative containing at least one cyclopentadienyl-type group which is bonded to a transition metal. The transition metal is selected from Groups IVB, VB, and VIB, preferably IVB and VIB. Examples include titanium, zirconium, hafnium, chromium and vanadium. Generally, the more preferred catalysts in the polymerization of olefins are metallocenes of Zr, Hf, or Ti.
Generally, in order to obtain the highest activity from metallocene catalysts, it has been necessary to use them with an organoaluminoxane cocatalyst, such as methylaluminoxane. This resulting catalyst system is generally referred to as a homogenous catalyst system since at least part of the metallocene or the organoaluminoxane is in solution in the polymerization media. These homogenous catalysts systems have the disadvantage that when they are used under slurry polymerization conditions, they produce polymer which sticks to reactor walls during the polymerization process (generally referred to as “fouling”) and/or polymer having small particle size and low bulk density which limits the commercial utility.
Various methods have been proposed in an effort to overcome the disadvantages of the homogenous metallocene catalyst systems. Typically, these procedures have involved the prepolymerization of the metallocene aluminoxane catalyst system and/or supporting the catalyst system components on a porous carrier (also known as a “particulate solid” or “support”).
Another important consideration in development of metallocene catalysts is the yield of solid polymer that is employed by employing a given quantity of catalyst in a given amount of time. This is know as the “activity” of the catalyst. There is an ongoing search for metallocene catalysts and techniques for preparing such catalysts which give improved activity for the polymerization of olefins. An evaluation of these catalysts and techniques has revealed that there is still room for improvement.
An object of the present invention is to provide a new method for preparing a supported metallocene catalyst system. In accordance with another aspect of the present invention, a method is provided for polymerizing olefins using the new type of supported metallocene catalyst system.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides a process for preparing a supported metallocene catalyst system which includes the steps of impregnating a support selected from the group consisting of inorganic oxides with a source of an element selected from the group consisting of Group XIII elements; and contacting the support with a liquid catalyst system prepared by combining in a liquid an organo aluminoxane and a metallocene having two cyclopetadienyl-type ligands selected from substituted or unsubstituted cyclopentadienyl, indenyl, benzoindenyl, tetrahdroindenyl, benzofluorenyl, octahydrofluorenyl, and fluorenyl ligands to form a supported metallocene catalyst system. In preferred embodiments the process further includes conducting prepolymerization of at least one olefin in the presence of the supported metallocene catalyst system to produce a prepolymerized metallocene catalyst system. The prepolymerized metallocene catalyst system prepared in this manner yields substantially increased activity for the polymerization of olefins.
In another aspect, the present invention provides a process for polymerizing an olefin using the inventive supported metallocene catalyst system. The process includes the steps of: (a) impregnating a support selected from the group consisting of inorganic oxides with a source of an element selected from the group consisting of Group XIII elements; (b) contacting the support with a liquid catalyst system prepared by combining in a liquid an organo aluminoxane and a metallocene having two cyclopetadienyl-type ligands selected from substituted or unsubstituted cyclopentadienyl, indenyl, benzoindenyl, tetrahdroindenyl, benzofluorenyl, octahydrofluorenyl, and fluorenyl ligands to form a supported metallocene catalyst system; and (c) contacting the olefin with the supported metallocene catalyst system. In a preferred embodiment, the process further includes the step of conducting prepolymerization of at least one olefin in the presence of the supported metallocene catalyst system to produce a prepolymerized supported metallocene catalyst system prior to step (c).
In particularly preferred embodiments, the metallocene is a bridged metallocene having bis-indenyl, fluorenyl and fluorenyl-containing components.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a particulate solid or “support,” modified with a source of a Group XIII element, useful in forming a liquid catalyst system for the polymerization of olefins. Any number of supports can be employed as the particulate solid to be modified. Typically the support can be any inorganic oxide, including Groups II, III, IV or V metal oxides such as silica, alumina, silica-alumina, and mixtures thereof. Other examples of inorganic oxides are magnesia, titania, zirconia, and the like. It is within the scope of the present invention to use a mixture of one or more of the particulate solids.
In accordance with the present invention, the support is modified by impregnation to incipient wetness by drop-wise addition of a solution containing a source of an element selected from Group XIII of the Periodic Table of Elements, such as B, Al and Ga. In the preferred embodiment, impregnation is accomplished by drop-wise addition of the solution to incipient wetness; thus, the volume of solution added will be equal to or less than the pore volume of the support. In preferred embodiments, the solution used to modify the support will include a borate and/or a borate ester, such as boric acid, sodium tetraborate decahydrate (“borax”) or trimethylborate. Various solvents may be used for the solution, including water and alcohols such as methanol, preferably methanol. If necessary, a small amount of acid can be used to ensure that the source of the Group XIII element is fully dissolved. The concentration of the solution serving as the boron source is sufficient to yield a boron loading of less than about 20 weight percent in the dried, modified support, preferably from about 0.1 to about 1.0 weight percent.
It is generally desirable for the solid to be thoroughly dehydrated prior to use. Preferably the solid is dehydrated so as to contain less that 1% loss on ignition. Thermal dehydration treatment may be carried out in vacuum or while purging with a dry inert gas such as nitrogen or dry air at a temperature of about 20° C. to about 1000° C., and preferably, from about 300° C. to about 800° C. Pressure considerations are not critical. The duration of thermal treatment can be from about 1 to about 24 hours. However, shorter or longer times can be employed provided equilibrium is established with the surface hydroxyl groups.
In a preferred embodiment, the above described thermal dehydration of the support is carried out by first drying the support in a vacuum oven and then calcining at a temperature of from about 400° C. to about 800° C. for about four
Dockter David W.
Hauger Bryan E.
Muninger Randall S.
Welch M. Bruce
Bowman Edward L.
Choi Ling-Siu
Phillips Petroleum Company
Wu David W.
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