Process of producing self-supported catalysts

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

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C502S103000, C502S152000, C526S075000, C526S165000

Reexamination Certificate

active

06677265

ABSTRACT:

TECHNICAL FIELD
This invention relates to process technology for producing particulate aluminoxane/metallocene olefin polymerization catalysts which are devoid of preformed supports.
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.
In commonly-owned WO 99/29738 published Jun. 17, 1999 and in commonly-owned copending U.S. application Ser. No. 09/571,480, filed May 16, 2000, and Ser. No. 09/571,542, filed May 16, 2000, one of us has described 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. Such catalysts are prepared by a process which comprises (a) mixing together in an inert hydrocarbon solvent medium at least one Group 4 metallocene having at least one polymerizable olefinic substituent in the molecule, and at least one aluminoxane, to form a catalytic solution; and (b) contacting catalytic solution from (a) with a controlled amount of vinylolefin monomer, such as ethylene, under polymerization conditions such that particulate solids are formed having a specific surface area of no more than about 20 square meters per gram (m
2
/g). Another process described in these prior documents comprises (a) mixing together in an inert hydrocarbon solvent medium at least one Group 4 metallocene having at least one polymerizable olefinic substituent in the molecule, and at least one aluminoxane, to form a catalytic solution wherein the atom ratio of aluminum to Group 4 metal in said solution is in the range of about 150:1 to about 1500:1; and (b) contacting catalytic solution from (a) with an amount of ethylene such that the mole ratio of ethylene to Group 4 metallocene used in forming said solution is in the range of about 150:1 to about 1500:1, and under polymerization conditions such that particulate solids are formed having a productivity, when fresh and if tested for productivity, of at least 18,000 grams of polyethylene per gram of catalyst in one hour.
SUMMARY OF THE INVENTION
This invention provides improved process technology for producing particulate self-supported olefin polymerization catalysts devoid of inorganic and any other kind of preformed catalyst support, catalysts such as are described in the commonly-owned prior documents referred to above. More particularly, the process technology of this invention makes it possible to prepare particulate self-supported olefin polymerization catalysts devoid of preformed catalyst support in a batch process, or in a semi-continuous process, or in a continuous process. Moreover, while it is deemed possible to operate the processes of this invention at elevated temperatures, e.g. at 50° C. or above, the processes can be very effectively carried out at temperatures of 30° C. and below. In addition, this process technology can be adapted for efficient, economical, environmentally-friendly operation on an industrial plant scale.
For ease of reference the particulate self-supported olefin polymerization catalysts devoid of inorganic and any other kind of preformed catalyst support produced pursuant to this invention are sometimes referred to hereinafter in the singular as “prepolymerized catalyst” and in the plural as “prepolymerized catalysts”.
This invention makes possible the production of prepolymerized catalysts that exhibit excellent productivity, that have desirable morphology and handling characteristics, and that are capable of producing olefin homopolymers and copolymers having desirable physical attributes and properties.
In addition, this invention makes it possible to increase reactor throughput and thereby substantially improve the economics of the operation. These advantages are realized by conducting a semi-continuous or continuous feed of metallocene-aluminoxane catalyst and aluminoxane cocatalyst into a reaction mixture containing a liquid phase to maintain a steady production of nuclei/seed particles which are grown in the process to the preferred size and prepolymer content.
This invention thus features, inter alia, concurrent continuous or substantially continuous feeds of the components used in forming the prepolymerized catalyst. These feeds are into a liquid phase in which the prepolymerization occurs, preferably under suitable relatively mild reaction conditions. Steady state operating conditions can be achieved soon after these concurrent feeds have been initiated. By maintaining the continued presence of the reaction components in appropriate proportions in the liquid phase by means of such concurrent feeds, particulate prepolymerized self-supported catalyst composition is formed in the reaction mixture substantially continuously during the concurrence of these feeds.
Accordingly, pursuant to this invention there is provided as one of its embodiments, a process which comprises concurrently feeding:
a) separate continuous or substantially continuous feeds of (i) at least one polymeriza

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