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
1998-03-09
2001-01-23
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...
C502S103000, C502S116000, C502S117000, C502S158000, C502S124000, C502S128000
Reexamination Certificate
active
06177375
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to olefin polymerization catalysts, particularly &agr;-olefin polymerization catalysts, and methods for preparing such catalysts.
BACKGROUND OF THE INVENTION
Silica-supported catalysts for use in the polymerization of ethylene, propylene, and the copolymerization of ethylene with 1-butene, 1-hexene, 1-octene, and other alkenes are well-known. One type of these silica-supported catalysts is Ziegler-Natta catalysts, which are comprised of reaction mixtures of transition metal compounds and organometallic compounds, primarily organometallic compounds of magnesium and aluminum. Ziegler-Natta catalysts are commonly supported on MgCl
2
but silica-supported Ziegler-Natta catalysts are also known. U.S. Pat. No. 3,787,384 discloses catalyst synthesis by reaction of silica with an organomagnesium compound and subsequent treatment of the product with titanium tetrachloride. U.S. Pat. No. 4,374,753 discloses a method in which the silica support is reacted with certain organic silicon compounds to give higher activity, higher melt index capability, and narrower molecular weight distribution. U.S. Pat. No. 4,388,220 discloses a method in which the organomagnesium compound is reacted with alcohols, amines, or carboxylic acids prior to reaction with the silica support, followed by subsequent treatment with the titanium component.
A primary goal of catalyst development is to improve the catalyst activity, typically measured as the rate of polymer production per unit weight of catalyst.
The polyolefins that are made with silica-supported catalysts are suitable for many applications, including injection molding and injection blow molding of thick walled bottles and other containers, coatings for wires and cables, containers such as bags, among many other known uses.
SUMMARY OF THE INVENTION
The present invention is directed to methods for making silica-supported catalysts for the polymerization of &agr;-olefins and the catalysts produced by such methods. A method of the present invention includes the steps of treating a silica support with an organosilane compound to form a silylated silica support, then contacting the silylated silica support with a transition metal compound selected from a metal chloride or a metal chloroalkoxide to form an intermediate. The transition metal can be either titanium, vanadium, or zirconium, but preferably is titanium. Thereafter, the intermediate is contacted with an alkylmagnesium alkoxide to form the catalyst.
According to a preferred embodiment of the present invention, the process steps are carried out in the presence of an aliphatic organic solvent. According to this embodiment, the silica support is treated with an organosilane compound to form a silylated silica support, and the silylated silica support is slurried in a solvent to form a first slurry. The first slurry is then contacted with a first solution of the solvent and a transition metal compound selected from a transition metal chloride or chloroalkoxide to form an intermediate. This intermediate is then contacted with a second solution of the solvent and an alkylmagnesium alkoxide to form a second slurry containing the catalyst. The catalyst in a powder form is isolated by drying the second slurry.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention. Catalysts of the present invention are designed to be used with aluminum co-catalysts also.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to silica supported catalysts suitable for the polymerization of &agr;-olefins. Catalysts of the present invention can be used to produce a wide range of polyolefins including, but not limited to, polyethylene, polyethylene copolymers with propylene, and other &agr;-olefins which form as solids under the conditions of known gas phase and slurry polymerization processes.
In general, three steps are involved in preparing the silica supported catalyst of the present invention and are carried out in the following order:
1. Treating a silica support with an organosilane compound to form a silylated silica support;
2. Contacting the silylated silica support with a transition metal chloride or chloroalkoxide; and
3. Contacting the intermediate from step 2 with an alkylmagnesium alkoxide to form the catalyst.
Before step 1 above, a silica support must be provided. Silica supports, and their methods of preparation, are well-known in the art. The silica supports used in connection with the present invention may be those available from commercial sources or can be made by art-accepted processes using methods of preparation and purification known in the prior art. For example, the silica supports used in connection with the present invention can be prepared by the methods described in U.S. Pat. No. 5,232,883.
The porous silica supports suitable for this invention may have surface areas from about 200 to about 800 m
2
/g and pore volumes from about 1.0 to about 4.0 ml/g. The particles may be spherical in shape or angular with diameters of about 20 to about 200 microns. Silica supports have surface reactive groups which typically consist of or include hydroxyl groups. The total surface hydroxyl content may vary from 1.0 to 4.0 mmol/g after drying at 200° C. for five hours, depending on the surface area of the support. After silane treatment, surface hydroxyl content may vary from 0.30 to 1.3 mmol/g, depending on the surface area of the support.
The shape of the particles which make up the silica component may be spherical and/or granular, although they are preferably spherical for better flowability. The range of surface areas, pore volumes, and pore diameters specified above preferably includes substantially all of the particles of the porous silica component. If there are spherical-shaped and granular-shaped particles in a mixture, both types individually should preferably have the specified characteristics. The silica component of the present invention may contain up to a total of 5% weight/weight (w/w) of a compound including titanium, aluminum, boron, magnesium or other elements. The silica component of the catalyst of the present invention preferably contains from about 60 to about 98% and preferably at least 80% w/w silica, the remaining amount being the catalytic compound. Preferably, at least 70% of the initial pore volume of the silica support remains in the catalysts after synthesis.
Prior to treating the silica support with an organosilane compound, the silica may be dried to completely remove surface water at a temperature less than about 800° C. Alternatively, the drying may be partial in some cases in order to leave a small amount of water or the drying can be eliminated entirely depending on the structure of the organosilane compound. Usually, it is preferable to at least partially remove the surface water from the silica support. For example, in the case of hexamethyldisilazane, a controlled amount of water on silica catalyzes the reaction of hexamethyldisilazane with silica.
The silica support is first treated with an organosilane compound to form a silylated silica support. As used herein, the term “organosilane compound” shall have the same meaning as described in U.S. Pat. No. 4,374,753, incorporated herein by reference. In particular, the organosilane compounds useful in this invention have the following chemical formulae:
(R
3
Si)
2
NH;
or
R
n
SiX
m
wherein m is 1, 2, or 3, n is 3, 2, or 1, respectively, the total of m+n=4, and X is a group chemically reactive with the hydroxyl groups of the silica support such as chloride, amide, alkoxide, phenoxide, and the like. The invention requires at least one such reactive group. If more than one are used, they may be the same or different. Examples of reactive groups are —F, —Cl, —Br, —OCH
3
, —OCH
2
CH
3
, —NH
2
, —N(CH
3
)
2
, —N(H-)Si(CH
3
)
3
, —CH
2
CH
2
CH
2
Cl, —CH
2
CH
2
CH
2
NH
2
, —OCH
2
CH
2
OCH
3
, —O
2
CCH
3
, and —CH
2
CH
2
CH
2
SH. The R group is a hydroca
Pullukat Thomas J.
Shinomoto Ronald S.
Bell Mark L.
Pasterczyk J.
PQ Corporation
Ratner & Prestia
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