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
1999-12-28
2002-09-03
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, C502S117000, C502S133000, C502S152000, C526S114000, C526S116000, C526S123100, C526S129000, C526S160000, C526S943000
Reexamination Certificate
active
06444605
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a self supported cycloalkadienyl catalyst and to a hybrid catalyst system, each containing a mixed metal alkoxide portion and a cycloalkadienyl portion, which is useful for producing polyolefins including broad molecular weight and bimodal polyolefins. The invention also relates to methods of making the self supported cycloalkadienyl catalyst and the hybrid catalyst, and their use in making polyolefins having a broad molecular weight distribution, and their use in making bimodal polyolefins.
2. Description of Related Art
For certain applications of polyethylene, toughness, strength and environmental stress cracking resistance are important considerations. These properties are enhanced when the polyethylene is of high molecular weight. However, as the molecular weight of the polymer increases, the processability of the resin usually decreases. By providing a polymer with a broad or bimodal molecular weight distribution, the properties characteristic of high molecular weight resins are retained and processability, particularly extrudability, is improved.
Bimodal molecular weight distribution of a polyolefin indicates that the polyolefin resin comprises two components of different average molecular weight, and implicitly requires a relatively higher molecular weight component and low molecular weight component. A number of approaches have been proposed to produce polyolefin resins with broad or bimodal molecular weight distributions. One is post-reactor or melt blending, in which polyolefins of at least two different molecular weights are blended together before or during processing. U.S. Pat. No. 4,461,873 discloses a method of physically blending two different polymers to produce a bimodal polymeric blend. These physically produced blends, however, usually contain high gel levels, and consequently, they are not used in film applications and other resin applications because of deleterious product appearance due to those gels. In addition, this procedure of physically blending resins suffers from the requirement for complete homogenization and attendant high cost.
A second approach to making bimodal polymers is the use of multistage reactors. Such a process relies on a two (or more) reactor set up, whereby in one reactor, one of the two components of the bimodal blend is produced under a certain set of conditions, and then transferred to a second reactor, where a second component is produced with a different molecular weight, under a different set of conditions from those in the first reactor. These bimodal polyolefins are capable of solving the above-mentioned problem associated with gels, but there are obvious process efficiency and capital cost concerns when multiple reactors are utilized. In addition, it is difficult to avoid producing polyolefin particles that have not incorporated a low molecular weight species, particularly, when the high molecular weight component is produced in the first reactor.
A third and more desirable strategy is direct production of a polyolefin having a broad or bimodal molecular weight distribution by use of a catalyst mixture in a single reactor. In fact, Scott, Alex, “Ziegler-Natta Fends off Metallocene Challenge,”
Chemical Week
, pg. 32 (May 5, 1999) states that one “of the holy grails [of polyolefin research] is getting bimodal performance in one reactor for PE and PP” (quoting Chem Systems consultant Roger Green). The art recently has attempted to solve the aforementioned problems by using two different catalysts in a single reactor to produce a polyolefin product having a broad molecular weight distribution, or bimodal molecular weight distribution. Such a process is reported to provide component resin portions of the molecular weight distribution system simultaneously in situ, the resin particles being mixed on the subparticle level. For example, U.S. Pat. Nos. 4,530,914 and 4,935,474 to Ewen relate to broad molecular weight distribution polyolefins prepared by polymerizing ethylene or higher alpha-olefins in the presence of a catalyst system comprising two or more metallocenes each having different propagation and termination rate constants and aluminoxane. Similarly, U.S. Pat. No. 4,937,299 to Ewen relates to the production of polyolefin reactor blends in a single polymerization process using a catalyst system comprising two or more metallocenes having different reactivity ratios for the monomers being polymerized.
It is known that metallocenes may be affixed to a support to simulate an insoluble catalyst. U.S. Pat. No. 4,808,561 discloses reacting a metallocene with an aluminoxane and forming a reaction product in the presence of a support. The support is a porous material like talc, inorganic oxides such as Group IIA, IIIA IVA OR IVB metal oxides like silica, alumina, silica-alumina, magnesia, titania, zirconia and mixtures thereof, and resinous material such as polyolefins like finely divided polyethylene. The metallocenes and aluminoxanes are deposited on the dehydrated support material.
An advantage of a homogeneous (metallocene) catalyst system is the very high activity of the catalyst and the narrow molecular weight distribution of the polymer produced with a metallocene catalyst system. The metallocene catalysts suffer from a disadvantage in that the ratio of alumoxane cocatalyst to metallocene is high. In addition, the polymers produced using metallocene catalysts often are difficult to process and lack a number of desirable physical properties due to the single homogeneous polymerization reaction site. Moreover, these catalyst are limited in that they are single site catalysts, and consequently, produce polymer having very narrow molecular weight distribution.
Heterogeneous catalyst systems also are well known, and typically are used to prepare polymers having broad molecular weight distribution. The multiple (e.g., heterogeneous) active sites generate a number of different polymer particles of varying length and molecular weight. These heterogeneous catalyst systems typically are referred to as Ziegler-Natta catalysts. The disadvantage of many Ziegler-Natta catalysts is that it is difficult to control the physical properties of the resulting polymer, and the activity typically is much lower than the activity of the metallocene catalysts. Ziegler-Natta catalyst alone are not capable of making satisfactory polyolefins having a bimodal molecular weight distribution, and metallocene catalysts containing cycloalkadienyl groups supported on silica or aluminum alone are not capable of making satisfactory polyolefins having a broad molecular weight distribution.
The art recently has recognized a method of making bimodal resin by using a mixed catalyst system containing Ziegler-Natta and metallocene catalyst components. These mixed catalyst systems typically comprise a combination of a heterogeneous Ziegler-Natta catalyst and a homogenous metallocene catalyst. These mixed systems can be used to prepare polyolefins having broad molecular weight distribution or bimodal polyolefins, and they provide a means to control the molecular weight distribution and polydispersity of the polyolefin.
W.O Pat. 9513871, and U.S. Pat. No. 5,539,076 disclose a mixed metallocene
on-metallocene catalyst system to produce a specific bimodal, high density copolymer. The catalyst system disclosed therein is supported on an inorganic support. Other documents disclosing mixed Ziegler-Natta/metallocene catalyst on a support such as silica, alumina, magnesium-chloride and the like include, W.O. Pat. 9802245, U.S. Pat. No. 5,183,867, E.P Pat. 0676418A1, EP 717755B1, U.S. Pat. No. 5,747,405, E.P. Pat. 0705848A2, U.S. Pat. No. 4,659,685, U.S. Pat. No. 5,395,810, E.P. Pat. 0747402A1, U.S. Pat. No. 5,266,544, and W.O. 9613532, the disclosures of which are incorporated herein by reference in their entirety.
Supported Ziegler-Natta and metallocene systems suffer from many drawbacks, one of which is an attendant loss of activity due to the bulky support material. Delivery
Job Robert Charles
Reichle Walter Thomas
Harlan R.
Union Carbide Chemicals & Plastics Technology Corporation
Wu David W.
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