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
1998-02-27
2001-05-08
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...
C502S104000, C502S115000, C502S132000, C502S134000, C526S129000, C526S156000, C526S124300
Reexamination Certificate
active
06228792
ABSTRACT:
This invention concerns catalysts and components thereof supported on a porous medium, their method of preparation, and their use for the polymerization of ethylene.
Olefin monomers, such as ethylene, propylene, and the higher alpha-olefins, can be polymerized using the so-called Ziegler-Natta catalysts. The term “Ziegler-Natta catalyst” is generally used to mean a catalyst system obtained from a compound of a transition metal of Groups 4 to 6 of the Periodic Table, together with an organo-metallic compound of a non-transition metal of Groups 1, 2 and 13 of the Periodic Table.
The particular composition of Ziegler-Natta catalyst is for the most part dictated and controlled by properties sought to be imparted to polymer made from the catalyst and the particular configuration in which the polymer will be utilized.
In this regard, it is well known that polyethylene is associated with different property goals than polymers made from higher alpha-olefins such as propylene, in that, unlike propylene, polyethylene does not have multiple stereo specific configurations which need to be controlled.
For example, polypropylene can be characterized as crystalline or amorphous. It is normally accepted that crystalline polypropylene generally has the isotactic or syndiotactic structure and that amorphous polypropylene generally has considerable atactic structure. Giulio Natta's U.S. Pat. Nos. 3,112,300 and 3,112,301 describe isotactic polypropylene and give structural formulae for isotactic and syndiotactic polypropylene. The isotactic configuration is a straight chain of propylene units wherein the pendant methyl groups are all aligned on one side of the polymer chain. In the syndiotactic configuration, the pendant methyl groups are uniformly alternated from one side of the chain to the other. In atactic polypropylene, the methyl groups are arranged randomly on the two sides of the chain.
Almost all of the polypropylene which is used commercially is crystalline isotactic polypropylene. These products are well known and have been the subject of many patents and articles. Amorphous polypropylenes, which have very little strength, are used commercially, primarily in adhesives and asphalt additives.
Thus, Ziegler-Natta catalysts which are designed to impart a desired stereoregularity to propylene polymers and copolymers may not be particularly suited for the preparation of ethylene polymers and copolymers where stereoregularity is not a factor to be controlled. Similarly, a Ziegler-Natta catalyst designed for polymerizing ethylene may exhibit poor activity and stereoregularity when used for polymerizing propylene.
More specifically, one property frequently sought to be controlled in the polymerization and copolymerization of ethylene is the molecular weight distribution (MWD) of the polymer.
It is desired to produce an ethylene polymer having a narrow distribution of molecular weight to render it suitable for use in injection molding and to provide film having excellent optical and strength characteristics. When ethylenic polymer prepared by polymerizing ethylene alone or copolymerizing with &agr;-olefin is subjected to solvent extraction analysis using a solvent such as cyclohexane, the amount of extremely low molecular weight polymer found in the extract is related to the MWD of the polymer. The presence of such extremely low-molecular weight polymers causes problems during processing of the polymer, such as smoking, nozzle dirt (dirt formed by the oozing of extremely low molecular weight polymers from molds) and unpleasant odor. Furthermore, in the course of the polymerization of the ethylenic polymer, fouling (i.e., attachment of polymers to the walls of a reactor and other apparatuses) or bridging in a hopper in the after-treating step (e.g., pelletizing step) can occur.
These phenomena are more prominent in the case of copolymers prepared by copolymerizing ethylene with &agr;-olefin. Particularly, in the case of medium density polyethylene comprising ethylene and a relatively large amount of &agr;-olefin and low density polyethylene, the extract content using a solvent such as n-hexane increases. This extract is composed of extremely low molecular weight polymers and extremely low density polymers. The amount of the extremely low density portion is determined by the breadth of the distribution of densities (the distribution of degrees of branching) which occurs during the copolymerization.
One test method which is indicative of MWD is the melt flow ratio (MFR) of the polymer, namely, the lower the MFR the narrower the MWD. Thus, for the polymerization of ethylene, one seeks to minimize MFR and maximize activity (expressed in polymer grams per gram of catalyst) for certain end use applications such as injection molding, film forming, and the like.
Accordingly, for ethylene polymerization, typical known catalysts contain a magnesium dihalide and a Ti compound supported on a porous medium containing inorganic oxides, such as silica, alumina, and others.
Such catalyst components can be obtained by impregnating the porous support medium with a solution of a magnesium compound capable of being transformed into magnesium halide or dihalide by reaction with a halogenating agent, evaporating the solvent, and treating the solid thus obtained with a titanium compound such as TiCl
4
.
For propylene and higher olefin polymerizations, typical Ziegler-Natta catalysts do not employ porous supports of silica or alumina, and typically rely instead on magnesium halide to support a titanium compound. While there have been proposals to support the Ziegler-Natta catalyst components on a support, such supported catalysts typically have been of lower activity.
The process variations for preparation of these basic types of catalysts are quite numerous, and activity enhancements are continually being sought.
It is also known to modify such catalysts with an electron donor, sometimes also referred to as a Lewis Base. The use of electron donors is quite common for both ethylene and propylene polymerization. However, the electron donor is typically employed for polypropylene catalysts to improve or control stereospecificity. However, should the catalysts be modified with electron donor compounds in order to render them stereospecific and thus suited for stereoregular polymerization of propylene or other alpha-olefins, one often observes a considerable reduction in activity relative to use for ethylene polymerization.
The present invention is based in part on the discovery that certain hindered aromatic nitrogen heterocyclic compounds, when used as electron donors for certain Ziegler-Natta catalysts adapted for ethylene polymerization, improve (i.e. decrease) the MFR of the polymers. Improvements (increases) in polymer bulk density also are observed.
The broad use of nitrogen or amine containing compounds as electron donors for various Ziegler-Natta catalysts is disclosed in the following patents: U.S. Pat. Nos. 4,381,252; 4,496,660; 4,826,794; 5,064,799; 5,139,985; 5,633,419; and EP 506,704.
The use of pyridine as an electron donor for various types of Ziegler-Natta catalysts is disclosed in the following patents: U.S. Pat. Nos. 4,252,670; 4,263,168; 4,301,029; 4,324,691; 4,410,672; 4,468,477; and EP 136,163.
The use of substituted pyridines, but not lutidine (2,6-dimethyl pyridine), as electron donor for various types of Ziegler-Natta catalysts is disclosed in the following patents: U.S. Pat. Nos. 4,107,413 (2-dimethylamino pyridine), and 4,471,066 (methyl pyridine); EP No. 193,280 (2-methyl pyridine; 2,6-diisopropyl pyridine), and EP No. 208,524 (methyl substituted pyridine, i.e. 2-, 3-, or 4-methyl pyridine).
The use of lutidine as a selectivity control agent in the polymerization of ethylene/propylene to form rubbery copolymers having enhanced randomness to improve the elastomeric and hence processibility properties of the polymer is disclosed in U.S. Pat. No. 5,134,209. However, the internal electron donors employed for the catalyst do not include amines. (See also U.S. Pat. No. 5,229,477.) It will be furt
Chol Ling-Slu
Maggio Robert A.
W. R. Grace & Co.,-Conn.
Wu David W.
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