Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-02-21
2004-11-02
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...
C526S127000, C526S129000, C526S134000, C526S170000, C526S141000
Reexamination Certificate
active
06812304
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for preparing improved premixed catalysts useful for producing broad MWD polyolefins. The process comprises premixing a supported boraaryl catalyst with a organoaluminum compound utilizing an incipient wetness procedure wherein a controlled amount of organoaluminum compound, sufficient to fill 90-150 percent of the pore volume of the supported boraaryl catalyst while achieving the desired Al to catalyst metal ratio, is used. Premixed catalysts obtained by the process are useful for the preparation of broad and/or bimodal molecular weight distribution polyolefins and, surprisingly, exhibit improved storage stability.
BACKGROUND OF THE INVENTION
Interest in metallocene and non-metallocene single-site catalysts has continued to grow rapidly in the polyolefin industry. These catalysts are more active than conventional Ziegler-Natta catalysts, and they produce polymers with improved physical properties. The improved properties include narrow molecular weight distribution, reduced low molecular weight extractables, enhanced incorporation of &agr;-olefin comonomers, and lower polymer density. Examples of non-metallocene single-site catalysts include catalysts containing a boraaryl moiety such as borabenzene, boranaphthalene or boraphenanthrene. See U.S. Pat. No. 5,554,775 and PCT Int. Appl. WO 97/23512.
Unfortunately, the uniformity of molecular weight distribution (MWD) reduces the thermal processing ability of polyolefins made with single-site catalysts. These polyolefins also have a higher tendency to melt fracture, especially at higher molecular weights. These disadvantages combine to make it difficult to process polyolefins produced by single-site catalysts under conditions normally used for Ziegler-Natta polymers. Controllable broadening of MWD is therefore a desired advance in single-site catalyst technology.
One method of increasing processability and broadening MWD of polyolefins produced by single-site catalysts is to physically mix two or more different polyolefins to produce a blended polyolefin mixture with a multimodal, broad molecular weight distribution. For example, see U.S. Pat. No. 4,461,873. In addition, olefin polymerization has been performed in a dual reactor system in order to broaden MWD. The olefin is polymerized by a catalyst in one reactor under one set of conditions, and then the polymer is transferred to a second reactor under a different set of conditions. The first reactor typically produces a high-molecular-weight component, and the second reactor produces a low-molecular-weight component. See U.S. Pat. Nos. 4,338,424, 4,414,369, 4,420,592, and 4,703,094. Lastly, a one-reactor, two-catalyst process has also been used to make multimodal, broad-MWD polymers. The olefin is polymerized in one reactor by two catalysts with different reactivity to form a reactor blend having broad and/or multimodal molecular weight distribution. The catalysts may be either two (or more) separate metallocenes or a metallocene and a Ziegler-Natta component. See, for example, U.S. Pat. Nos. 4,937,299 and 4,530,914, in which at least two separate metallocenes are used in one reactor to form multimodal polymers. See U.S. Pat. Nos. 5,032,562 and 5,539,076 for examples of the metallocene/Zeigler-Natta catalyst mixture in one reactor.
A significant disadvantage of each of these methods is the added cost of using two reactors or two catalysts in the polymerization process. A simpler method would use a single catalyst system that produces broad MWD polymers in a one-reactor process. For example, EP 719,797 A2 discloses an olefin polymerization process in which conventional metallocenes and at least two different co-catalysts are used to produce broad/bimodal MWD polyolefins. In addition, copending application Ser. No. 09/439,462 discloses a method for producing broad and/or bimodal polyolefins using a catalyst comprising an activator and an organometallic compound that incorporates a modified boraaryl ligand.
Premixed catalyst systems obtained by reacting an organoaluminum with a supported boraaryl catalyst have now unexpectedly been found to be useful for the production of broad MWD polyolefins. These results are particularly surprising since co-pending U.S. application Ser. No. 09/318,009 teaches that olefin polymerization with a boraaryl catalyst produces polyolefins with narrow MWD when organoaluminums are added to the reactor, without a premixing step.
While the catalysts produced in this manner, i.e., by premixing, are extremely useful and exhibit high activity when freshly prepared, the instability of alkylated transition metal catalyst complexes of this type has been a recognized and long-standing problem, particularly in the presence of trace impurities. It would be highly advantageous if premixed catalysts having improved storage stability suitable for the production of broad and/or bimodal MWD polyolefin resins and having other desirable properties were available. These and other advantages are achieved with the catalyst preparation process described hereafter.
SUMMARY OF THE INVENTION
The invention is a process for preparing premixed catalysts for the production of broad MWD polyolefins. More particularly, the process is directed to a process for the production of premixed supported boraaryl catalysts which have increased shelf life, i.e., the period of time which the catalyst can be stored and still be suitable for use is extended. Specifically the process comprises (1) preparing a supported catalyst comprising an inorganic oxide support which has been chemically and thermally dehydroxylated to remove substantially all hydroxyl from the support surface and an organometallic compound comprising a group 3-10 transition metal or lanthanide metal and at least one boraaryl ligand; (2) contacting the supported catalyst from (1) with a organoaluminum compound to fill from about 90 to 150 percent of the pore volume of the supported catalyst and provide a mole ratio of aluminum to transition/lanthanide metal from 0.5:1 to 50:1; and (3) recovering the premixed catalyst powder.
Contacting of the catalyst with the organoaluminum compound is carried out utilizing an incipient wetness procedure wherein a controlled amount of hydrocarbon solution containing the organoaluminum compound sufficient to achieve the desired molar ratio of aluminum to transition/lanthanide metal without being in significant excess of what is required to fill the pore volume is used. In this way highly active free-flowing catalyst powders are produced with little or no drying. Furthermore, it has unexpectedly been found that premixed catalysts produced in this manner retain their activity even after extended periods of storage.
In a particularly useful embodiment of the invention the inorganic support is silica which is chemically treated with a hexaalkyl disilazane, preferably hexamethyldisilazane, and calcined at 200-700° C. The organoaluminum compounds employed for the premixing are preferably trimethylaluminum, triethylaluminum or triisobutylaluminum. An ionic borate or aluminate activator, most notably tri(n-butyl)ammonium tetrakis(pentafluorophenyl)borate, trityl tetrakis(pentafluorophenyll)borate and trityl tetrakis(pentofluorophenyl)aluminate, is preferably included with the organometallic compound and dehydroxylated silica when preparing the supported catalyst.
DETAILED DESCRIPTION OF THE INVENTION
The process of the invention comprises preparing a catalyst system by premixing an organoaluminum compound with a supported catalyst comprising a support and an organometallic compound comprising a Group 3-10 transition or lanthanide metal and at least one boraaryl ligand. The premixed supported catalyst component is effective for polymerizing olefins when combined with an activator and additional organoaluminum compound, which may be the same as or different from the organoaluminum used for preparation of the premixed catalyst component. Also, the activator may advantageously be incorporated with the premixed supported catalyst component.
The supp
Lynch Michael W.
Meverden Craig C.
Baracka Gerald A.
Heidrich William A.
Lee Rip
Wu David W.
LandOfFree
Process for producing improved premixed supported boraaryl... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for producing improved premixed supported boraaryl..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for producing improved premixed supported boraaryl... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3324613