Olefin polymerization process

Details Olefin polymerization process Olefin polymerization process

2001-02-14

2003-09-30

Wu, David W. (Department: 1713)

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

Synthetic resins

Polymerizing in tubular or loop reactor

C526S113000, C526S129000, C526S090000, C526S351000, C526S352000, C526S348000, C526S170000, C526S065000, C526S901000, C526S943000, C526S905000

Reexamination Certificate

active

06627706

ABSTRACT:

This invention relates to a process for the preparation of olefin polymers, preferably a multi-stage process, in which hydrogen is used to control the molecular weight of the olefin polymer produced in a continuous reactor, in particular a process wherein a metallocene or other single site catalyst is present in the polymerization reaction mixture, as well as to olefin polymers produced thereby.
Such preparation of polymers is effected by the use of a variety of catalyst systems, e.g. Ziegler-Natta catalysts, metallocene catalysts, and chromocene-silica catalysts. Typically such polymerisation may be performed in gas phase, slurry or solution phase continuous reactors. It is furthermore known to use hydrogen in polymerisation reactors in order to produce polymers of the desired molecular weight. Such molecular weight control is effected through control of the concentration of hydrogen. We have now surprisingly found that such molecular weight control may be performed more efficiently through control of the consumption of hydrogen.
Viewed from one aspect the invention provides a process for olefin polymerization, preferably for the production of an ethylene or propylene homo or copolymer, in particular for the preparation of ethylene copolymers, comprising polymerising at least one &agr;-olefin in a continuous reactor in the presence of hydrogen and an olefin polymerization catalyst, preferably a catalyst comprising a metallocene or other single site catalyst, the hydrogen consumption rate being controlled during the polymerization whereby to control the molecular weight of the polymer product at the desired value.
Viewed from an alternative aspect the invention provides a process for olefin polymerization, preferably for the production of an ethylene or propylene homo or copolymer, in particular for the preparation of ethylene copolymers, comprising polymerising at least one &agr;-olefin in a continuous, mixed reactor in the presence of hydrogen and an olefin polymerization catalyst, preferably a metallocene or other single site catalyst, control of the molecular weight of polyolefin produced being effected by controlling the ratio between
A. The rate of hydrogen consumption in the reactor system from a mass balance
B. The rate of production of polymer in the reactor system.
The term molecular weight is to be understood as relating to any molecular weight parameter of the polymer such as weight average MW, MFR, melt index (MFR
2
), high load melt index (MFR
21
), melt viscosity, intrinsic viscosity, viscosity average MW etc.
Viewed from another aspect the invention provides a process for olefin polymerization, preferably for the production of an ethylene or propylene homo or copolymer, in particular for the preparation of ethylene copolymers, which process comprises at least two continuous polymerization stages, a relatively earlier of said stages comprising polymerizing at least one &agr;-olefin in the presence of hydrogen and an olefin polymerization catalyst whereby to produce a first polymerization product, and a relatively later of said stages comprising polymerizing said at least one &agr;-olefin in the presence of an olefin polymerization catalyst whereby to yield a polymerization product having a lower MFR
2
than said first polymerization product, wherein the hydrogen consumption rate is controlled in said relatively early stage whereby to control the molecular weight of said first product.
It is preferred to use catalysts that are responsive to hydrogen: thus such a catalyst system might comprise a combination of metallocene and chromium catalysts especially where the chromium catalyst is in form of chromium oxide, preferably on particulate supports, especially with both loaded together on the same support particles.
The polymer product of the single stage process of the invention if used with a single site catalyst will have a relatively narrow molecular weight distribution (e.g. a low MFR
21
/MFR
2
ratio) and thus may be suitable for rotomoulding, injection moulding or production of LLDPE film.
Alternatively where the invention is used in a multistage process, or where a catalyst system having catalyst sites very responsive to hydrogen concentration and sites less responsive or non-responsive to hydrogen concentration is used, the polymerization product will have a bimodal or multimodal, ie. broad, molecular weight distribution and may be suitable for blow moulding, film, pipe, wire, fibre or cable. By responsive to hydrogen concentration is meant a catalyst for which the molecular weight of the polymer product is altered if the hydrogen concentration used in the reaction mixture is varied, ie. a hydrogen consuming catalyst. Typically metallocene catalysts are more hydrogen responsive than Ziegler or chromium catalysts: thus such a catalyst system might comprise a metallocene catalyst alone or a combination of metallocene and chromium catalysts, preferably on particulate supports, especially with both loaded together on the same support particles.
The process of the invention may optionally comprise: further polymerisation stages before or after the hydrogen controlled stage, e.g. to produce a heterophasic polymer; drying steps; blending of the polymer product with one or more further materials, e.g. further polymers, antioxidants, radiation (e.g. UV-light) stabilizers, antistatic agents, fillers, plasticizers, carbon black, colors, etc.; granulation, extrusion and pelletization; etc.
Viewed from further aspects the invention provides an olefin polymer produced by a process according to the invention as well as the use of such polymers for the production of moulded articles, fibres, pipes, films, blow moulded, injection moulded and rotomoulded articles and products for wire and cable applications.
The process of the invention is one for the polymerization of &agr;-olefins, in particular C
2-10
&agr;-olefins, more particularly ethylene and propylene, especially ethylene. The polymer product of each polymerization stage may be a homopolymer or a copolymer (which term is used to include polymers deriving from two or more monomer species). Where the product is a copolymer, preferably at least 50% by weight of the polymer derives from a C
2-10
&agr;-olefin monomer, more particularly from a C
2-4
&agr;-olefin monomer, preferably ethylene or propylene. The other monomer(s) may be any monomers capable of copolymerization with the olefin monomer, preferably mono or polyunsaturated C
2-20
compounds, in particular monoenes or dienes, especially C
2-10
&agr;-olefins such as ethene, propene, but-l-ene, pent-l-ene, hex-l-ene, oct-l-ene or mixtures thereof. Bulky comonomers, e.g. styrene or norbornene may also be used. Generally, the polymer produced in the polymerization stages will comprise the same &agr;-olefin monomer, e.g. as the sole monomer or as the comonomer from which at least 50%, preferably 60 to 99.8% of the copolymer derives. Thus the polymer product will preferably be an ethylene homopolymer, an ethylene copolymer, a propylene homopolymer or a propylene copolymer.
If several reactors are used, the catalysts used in the different polymerization stages may be the same or different; however the use of the same catalyst is preferred. The catalysts employed may be any catalyst capable of catalysing olefin polymerization and consuming hydrogen, e.g. Ziegler catalysts (e.g. Ziegler Natta catalysts), chromocene/silica catalysts, metallocene (ie. &eegr;-ligand complexed metals), etc. What is required is that the catalyst which is used in the hydrogen controlled stage be one which depletes the reaction mixture of hydrogen. It should preferably be a catalyst which uses up hydrogen more rapidly than the conventional Ziegler Natta or non-metallocene chromium catalysts. In this regard it is particularly preferred to use single site catalysts such as the catalytically effective metal:&eegr;-ligand complexes, ie. complexes in which the metal is complexed by the extended Π-orbital system of an organic ligand. Metallocenes are an example of complexes in which a metal is co

Affiliated with

Also associated with

Rating

Olefin polymerization process does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Olefin polymerization process, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Olefin polymerization process will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3110702