Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2003-03-28
2004-05-04
Lu, Caixia (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C502S108000, C502S118000, C502S152000, C526S160000, C526S348000, C526S943000
Reexamination Certificate
active
06730758
ABSTRACT:
TECHNICAL FIELD
This invention relates to novel, highly effective solid aluminoxane/metallocene olefin polymerization catalysts, their preparation, and their use.
BACKGROUND
Hydrocarbylaluminoxanes (also known as alumoxanes) complexed with transition metal compounds, such as metallocenes, have been found to be effective olefin polymerization catalysts. Methylaluminoxanes are especially effective catalyst components in forming homogeneous catalyst systems with various metallocenes. However, these catalyst systems have proven to be considerably less effective in productivity per unit weight of catalyst when used as supported heterogeneous catalysts, either in the form of dispersions in a liquid medium or as supported solid catalysts in gas-phase polymerizations. For example, in U.S. Pat. No. 5,126,301 issued Jun. 30, 1992 to Tsutsui et al. it is pointed out that when an olefin is polymerized or copolymerized in a dispersion or gas-phase polymerization system by utilizing carrier-supported metallocene-aluminoxane catalysts, polymerization activity is markedly reduced, that the properties inherent to the catalyst comprising the transition metal compound and the aluminoxane catalyst component are not fully exerted, and that powder properties such as bulk density of the thus prepared polymer were insufficient. The approach taken by Tsutsui et al. was to form a solid catalyst by contacting an &agr;-olefin with a mixture obtained by mixing an organoaluminum compound having a branched alkyl radical, an aluminoxane of specified aluminum content, a fine-particle carrier, and a transition metal metallocene compound.
Despite various improvements made during the course of extensive research activities by various laboratories, a need has existed for olefin polymerization catalysts having even better performance characteristics. For example, U.S. Pat. No. 5,498,581 issued Mar. 12, 1996 to Welch et al., points out that evaluation of attempts disclosed in U.S. Pat. Nos. 5,240,894; 4,871,705; and 5,106,804 to overcome the disadvantages of metallocene catalysts has revealed that there is still room for improvement, particularly when the catalyst is one which is to be used in a slurry-type polymerizations. The techniques disclosed in U.S. Pat. Nos. 5,240,894; 4,871,705; and 5,106,804 involve prepolymerization of the metallocene-aluminoxane catalyst system either in the presence or absence of a support.
The improved method of Welch et al. U.S. Pat. No. 5,498,581 for preparing a solid metallocene-containing catalyst system comprises (a) combining in a liquid an organoaluminoxane and at least one metallocene having at least one cyclopentadienyl, indenyl, tetrahydroindenyl, octahydrofluorenyl, or fluorenyl ligand having at least one olefinically unsaturated substituent to form a liquid catalyst system, (b) conducting prepolymerization of at least one olefin in the presence of said catalyst system to produce a prepolymerized solid catalyst containing no more than about 95 weight percent prepolymer, and (c) separating the resulting solid from the liquid and components dissolved in the liquid. The patent reports in Table I that by use of the Welch et al. method, catalysts having productivities as high as 9840 grams of polyethylene per gram of catalyst per hour were formed.
SUMMARY OF THE INVENTION
This invention provides solid olefin polymerization catalysts that are believed to have substantially higher productivities than any previously-known heterogeneous olefin catalyst or catalyst system devoid of an inorganic support and any other kind of preformed support. In addition, the polymerization catalysts of this invention possess a variety of beneficial morphological characteristics, such as for example an average (mean) particle size in the range of about 20 to about 60 microns, and a desirably narrow particle size distribution, e.g., a mean:median particle size ratio in the range of about 0.7:1 to about 1.5:1, and preferably in the range of about 0.8:1 to about 1.3:1. In fact it has been found possible to provide self-supported catalysts of this invention (i.e., particulate catalysts which are not formed using a preexisting support such as silica or preformed polyolefin particles) in which the mean:median particle size ratio is in the exceptionally narrow range of about 0.9:1 to about 1.1:1.
In addition to productivities of at least 12,000 grams of polyethylene per gram of catalyst in one hour under test conditions described hereinafter, this invention thus makes possible the provision of catalysts that have excellent morphology and handling characteristics, and that are capable of producing olefin homopolymers and copolymers having a combination of very desirable physical attributes and properties. In fact, the morphology of the particulate catalysts formed in the preferred manner of this invention is comparable to (on a par with) the best particulate catalysts previously made in these laboratories or received heretofore from outside sources. It is worth observing that such prior catalysts were formed using a silica support.
In accordance with another embodiment of this invention there is provided a particulate vinylolefin prepolymer-Group 4 metallocene-aluminoxane catalyst composition having (i) a productivity of at least 15,000 grams, and preferably at least 18,000 grams, of polyethylene per gram of catalyst in one hour, (ii) an average particle size in the range of about 20 to about 60 microns, and preferably in the range of about 22 to about 55 microns, and a mean:median particle size ratio in the range of about 0.7:1 to about 1.5:1, and preferably in the range of about 0.8:1 to about 1.3:1. More preferably the self-supported catalysts of this embodiment of the invention have a mean:median particle size ratio in the range of about 0.9:1 to about 1.1:1.
Preferred catalysts are those in which this productivity characteristic is at least 25,000, and particularly preferred catalysts are those in which this productivity characteristic is at least 30,000.
It has been discovered that particulate olefin polymerization catalysts having such exceptionally high productivities and desirable morphology can be prepared by prepolymerizing at least one vinylolefin, preferably a gaseous 1-alkene, with a Group 4 metallocene-aluminoxane solution, provided the proportion of vinylolefin (most preferably, ethylene) relative to the Group 4 metallocene(s) used in forming the solution is suitably controlled. Typically these reactants are proportioned so that the prepolymerized catalyst composition contains (i. e., is formed by prepolymerization of) from about 150 to about 1500, and preferably in the range of about 175 to about 1000, moles of vinylolefin per mole of metallocene. It is also important in carrying out this process to use a solution in which the atom ratio of aluminum to Group 4 metal in the solution is within a suitable range, e.g., in a range of at least about 50:1 or more usually at least about 100:1, and in either case up to about 1500:1, or more usually up to about 1000:1. Typically the atom ratio of aluminum to Group 4 metal is the range of about 150:1 to about 1500:1, and preferably in the range of about 175:1 to about 1000:1. In addition, the Group 4 metallocene ingredient used in forming these new, highly productive catalysts has in its molecular structure at least one polymerizable olefinic substituent. Of these Group 4 metallocenes, the zirconium metallocenes are most preferred, especially those containing two cyclopentadienyl moiety-containing groups in the molecule. These two groups can be unbridged, but preferably are connected to each other by a bridging group.
Another feature of these catalysts is that they are self-supporting catalysts. By this is meant that the catalyst particles do not contain, and thus are not produced in the presence of, a preformed support such as an inorganic compound (silica or etc.) or a preformed particulate polymeric support. Instead, the prepolymer is formed in the presence of the combination of at least one Group 4 metallocene and at least one aluminoxane in an in
Albemarle Corporation
Lu Caixia
Spielman, Jr. Edgar E.
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