Process for production of polyolefins

Details Process for production of polyolefins Process for production of polyolefins

2001-01-30

2003-07-01

Wilson, D. R. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S114000, C526S115000, C526S117000, C526S160000, C526S064000, C526S065000, C526S352000, C525S240000, C585S012000, C585S329000, C585S517000

Reexamination Certificate

active

06586541

ABSTRACT:

FIELD OF THE INVENTION
Branched polyethylene can be made in a multi-step process by contacting ethylene, a catalyst that can oligomerize ethylene to one or more alpha-olefins, and a polymerization catalyst which can copolymerize ethylene and &agr;-olefins, in a first step (such as in a continuous stirred tank reactor), then continuing the reaction in a subsequent step (such as in a plug flow reactor) in the substantial absence of added ethylene.
TECHNICAL BACKGROUND
Polyolefins are useful items of commerce, being made in immense annual quantities and used for a variety of purpose, such as molding resins, films, elastomers, and other items. Polyolefins are most often prepared by polymerization processes in which a transition metal containing catalyst system is used. Depending on the process conditions used and the catalyst system chosen, polymers, even those made from the same monomer(s) may have varying properties. Some of the properties which may change are molecular weight and molecular weight distribution, crystallinity, melting point, branching, and glass transition temperature. Except for molecular weight and molecular weight distribution, branching can affect all the other properties mentioned.
Various reports of “simultaneous” oligomerization and polymerization of ethylene to form (in most cases) branched polyethylenes have appeared in the literature, see for instance WO90/15085, WO99/50318 (corresponding to U.S. application. Ser. No. 09/619,509, filed Jul. 19, 2000, now abandoned, which is a continuation of U.S. application. Ser. No. 09/273,409, filed Mar. 22, 1999), now U.S. Pat. Nos. 6,214,761, 5,753,785, 5,856,610, 5,686,542, 5,137,994 and 5,071,927; C. Denger, et al,
Makromol. Chem. Rapid Commun.,
vol. 12, p. 697-701 (1991); and E. A. Benham, et al.,
Polymer Engineering and Science,
vol. 28, p. 1469-1472 (1988). All of the above are incorporated by reference herein for all purposes as if fully set forth.
In most of these systems one or more &agr;-olefins is produced by catalysis with an ethylene oligomerization catalyst, and then a copolymer of the &agr;-olefin(s) and ethylene is produced by (another) polymerization catalyst. The result is normally a branched polyethylene made from ethylene alone (although other olefins such as &agr;-olefins may also be added if desired).
In most instances, the rate of formation of polymer is faster than the rate of oligomerization, so that the incorporation of &agr;-olefin(s) is often quite low, and of course the resulting branching is quite low. When the rate of &agr;-olefin production is comparable to the rate of polymer production it is possible to make relatively more &agr;-olefin, and consequently to obtain a higher branching level in the polymer, see for instance previously incorporated World Patent Application 99/50318 (corresponding to U.S. application Ser. No. 09/619,509, filed Jul. 19, 2000, now abandoned, which is a continuation of U.S. application. Ser. No. 09/273,409, filed Mar. 22, 1999now U.S. Pat. No. 6,214,761). However this can lead to another problem, namely, the presence of residual &agr;-olefin(s) in the resulting polymer product.
While this may not be too serious if the &agr;-olefin(s) are relatively volatile (say containing 8 or fewer carbon atoms), when less volatile &agr;-olefin(s) are present, their removal may be come difficult, and their presence in the polymer deleterious from a flammability, toxicity or end use (e.g., in contact with food, as food wrapping) viewpoint. Thus a production method that minimizes or even substantially eliminates the presence of these &agr;-olefin(s) in the final product is desirable.
SUMMARY OF THE INVENTION
This invention concerns a process for the production of a branched polyethylene comprising the steps of contacting, under polymerization conditions:
(a) ethylene;
(b) an oligomerization catalyst that oligomerizes ethylene to one or more &agr;-olefins of the formula R
20
CH═CH
2
, wherein R
20
is n-alkyl containing an even number of carbon atoms, and
(c) a transition metal polymerization catalyst that co-polymerizes ethylene and one or more of the &agr;-olefins produced by the oligomerization catalyst, to produce a first (intermediate) product comprising a predominant amount of a branched polyethylene, a first residual &agr;-olefin content and, optionally, an amount of unreacted ethylene; then
(2) allowing the first product to further react under conditions to (co)polymerize at least a portion of the first residual &agr;-olefin content, in the substantial absence of added ethylene, to result in a second (end) product comprising a branched polyolefin having a second residual &agr;-olefin content, provided that said second residual &agr;-olefin content is at least 20% less than said first residual &agr;-olefin content.
This invention also concerns a process for the production of a branched polyethylene, comprising the step of contacting, under polymerizing conditions:
(a) ethylene,
(b) an ethylene oligomerization catalyst which is capable under the process conditions of producing one or more olefins of the formula R
20
CH═CH
2
wherein R
20
is n-alkyl containing an even number of carbon atoms, and
(c) a polymerization catalyst which contains one or more transition metals and which is capable under process conditions of copolymerizing ethylene and one or more olefins of the formula R
21
CH═CH
2
, wherein R
21
is n-alkyl, provided that a major portion of the branched polyethylene is produced first in a continuous stirred tank reactor (CSTR) or its equivalent, and that a minor portion of said branched polyethylene is produced subsequently in a plug flow reactor (PFR) or its equivalent.


REFERENCES:
patent: 5071927 (1991-12-01), Benham et al.
patent: 5137994 (1992-08-01), Goode et al.
patent: 5686542 (1997-11-01), Ostoja-Starzewski et al.
patent: 5753785 (1998-05-01), Reddy et al.
patent: 5856610 (1999-01-01), Tamura et al.
patent: WO 99/50318 (1999-10-01), None
Benham, E. A. et al., A Process for the Simultaneous Oligomerization and Copolymerization of Ethylene, Polymer Engineering and Science, Nov. 1988, p. 1469-1472, vol. 28, No. 22.
Denger, C. et al., Simultaneous oligomerization and polymerization of ethylene, Makromol. Chem., Rapid Commun., 1991, p. 697-701, vol. 12.

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