Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-06-09
2002-09-10
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...
C526S124200, C526S124300, C526S125700, C526S151000, C526S153000, C526S201000, C526S904000, C502S109000
Reexamination Certificate
active
06448348
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for polymerizing olefins of the formula CH
2
CHR in which R=H or a C
1
-C
10
alkyl group, and copolymerizing said olefins with alpha olefins of C
3
-C
8
carbons in a slurry or gas phase process using new Ziegler-Natta catalyst systems. More particularly, this invention relates to catalytic homopolymerization of ethylene and copolymerization of ethylene with alpha olefins using a catalyst which contains at least magnesium, aluminum and titanium chemically anchored on a polymeric material. The product polyethylene polymer and copolymers have a density of about 0.91 to 0.97, molecular weight of about 500 to 900,000 grams/mole, a very low level of fines, uniform spherical particles, very good thermal stability and excellent optical properties.
2. Description of the Prior Art
Several publications are referenced in this application. These references describe the state of the art to which this invention pertains, and are incorporated herein by reference.
The field of olefin polymerization catalysis has witnessed many remarkable discoveries during the last 50 years. In particular two broad areas of invention stand out. Firstly, the discovery of Ziegler-Natta catalysts in the 1950's, which are still being used extensively in the polyolefins industry. Secondly, and more recently, the discovery of the highly active metallocene-based catalysts. Since the discoveries of these systems, extensive research work was conducted in order to improve their performance.
However, despite the progress in these areas, there are still certain limitations as recognized by those of ordinary skill in the art. For example, conventional silica supported Ziegler-Natta catalysts often display limited activity, which reflects on the high catalyst residues. On the other hand, heterogeneous metallocene-based catalysts intrinsically possess high activity, though the catalyst precursors and, in particular the cocatalysts required for polymerization, such as aluminoxanes or borane compounds, are very expensive and troublesome in use. Further, another limitation that both catalyst systems share is the lengthy method of preparation and relatively high levels of fines generated in the polymers.
Traditionally, the active components of both Ziegler-Natta and metallocene catalysts are supported on inert carriers to enhance the catalyst productivity and to improve and control the product morphology. Magnesium chloride and silica have predominantly been used for the preparation of supported olefin polymerization catalysts.
U.S. Pat. No. 4,173,547 to Graff describes a supported catalyst prepared by treating a support, for example silica, with both an organoaluminum and an organomagnesium compound. The treated support was then contacted with a tetravalent titanium compound. In a simpler method, U.S. Pat. No. 3,787,384 to Stevens et al. discloses a catalyst prepared by first reacting a silica support with a Grignard reagent and then combining the mixture with a tetravalent titanium compound.
However, procedures typically used for the preparation of suitable magnesium chloride and silica supports such as spray drying or re-crystallization processes are complicated and expensive. Hence, all methods described in the aforementioned patents of catalyst preparation present the inconvenience of being complicated, expensive and do not allow consistency of particle size and particle size distribution. Also, despite the extensive and increasing use of the described supports for Ziegler-Natta catalysts, the support materials themselves have several deficiencies. For example, in the case of silica, high calcination temperatures are required to remove water, which is a common catalyst poison. This represents a significant proportion of the preparation of the catalyst. The use of silica as a support results in the support remaining largely in the product, which can affect product properties, such as optical properties or processability.
Certain polymeric materials have also been used for supporting titanium and magnesium compounds. However, most of the polymeric supports used so far have been based on polystyrene or styrene-divinylbenzene copolymers. U.S. Pat. No. 5,118,648 to Furtek and Gunesin describe a catalyst prepared using styrene-divinylbenzene as a polymeric support. The preparation of the catalyst was carried out by suspending the polymeric support in a solution of a magnesium dihalide or a magnesium compound capable of being transformed into a magnesium dihalide, for example, by titanium tetrachloride treatment, and subsequently evaporating the solvent. Hence, the active catalyst components were deposited on the polymeric support by physical impregnation. Other physical impregnation methods include those described in U.S. Pat. No. 4,568,730 to Graves whereby polymer resins of styrene-divinylbenzene are partially softened and the active catalyst components are homogeneously mixed in the resin to form a mass, which was subsequently pelletized or extruded into catalyst particles. However, the activity of the above-described polymer supported catalysts is not higher than that of metal oxide supported Ziegler-Natta catalysts.
Polypropylene and polyethylene have also found use as polymeric supports, where the polymeric material is typically ground with the catalyst components, which represents a difficult and complicated catalyst preparation procedure. In addition, there remains a significant concern as to the ability of the support material to retain the active species, deposited by physical impregnation, during polymerization conditions and thus generate, for example, fines. Hsu et al, Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 32,2135 (1994), have used poly(ethylene-co-acrylic acid) as a support for Ziegler-Natta catalysts and the catalyst activity was found to be similar to that of the magnesium chloride supported catalyst.
OBJECTS OF THE INVENTION
It is an object of the invention to overcome the above-identified deficiencies.
It is another object of the invention to provide a process for the production of olefin homopolymers and copolymers, especially ethylene homopolymers and copolymers.
It is a further object of the invention to provide polymers having a very low level of fines. The foregoing and other objects and advantages of the invention will be set forth in or become apparent from the following description.
SUMMARY OF THE INVENTION
This present invention provides a process of making ethylene polymers and ethylene/alpha olefins (C
3
-C
8
) copolymers in slurry or gas phase, having a wide density range of about 0.91 to 0.97 grams/cm
3
and weight average molecular weight (Mw) of about 500 to 900,000 grams/mole and molecular weight distribution range of 2 to 10. The product ethylene homopolymers and copolymers have a uniform spherical particle morphology, very low level of fines and catalyst residues, improved thermal stability, excellent optical and better environmental stress cracking resistance (ESCR) than products made with other catalysts heretofore known in the art. The ethylene homopolymers and copolymers can be produced with the very highly active new Ziegler-Natta catalyst systems including at least a transition metal compound, a magnesium compound and an aluminum compound, chemically anchored on polymeric particles having labile active sites.
As a result of the present invention olefin and especially polyethylene polymers and copolymers are provided which have a density of from about 0.91 to about 0.97 grams/cm
3
molecular weight of from about 500 to about 900,000 grams/mole, a very low level of fines, uniform spherical particles, very good thermal stability and excellent optical properties. Additionally, by using the process of the present invention copolymers of ethylene with alpha olefins are obtained at a productivity ≧1,000,000 gm PE/gm Ti.
DETAILED DESCRIPTION OF THE INVENTION
The ethylene homopolymers and copolymers which may be prepared by the process of the present invention ca
Abu-Raqabah Atieh
Hamed Orass
Moman Akhlaq
Raghavan Raju
Kramer Levin Naftalis & Frankel
Rabago R.
Saudi Basic Industries Corporation
Wu David W.
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