Gas phase polymerization process

Details Gas phase polymerization process Gas phase polymerization process

2003-02-18

2004-06-22

Teskin, Fred (Department: 1713)

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S092000, C526S114000, C526S118000, C526S119000, C526S901000, C526S905000

Reexamination Certificate

active

06753390

ABSTRACT:

FIELD OF INVENTION
The present invention relates to polymerization processes, and more particularly, to gas phase polymerization processes that utilize bimetallic catalyst systems.
BACKGROUND
Bimodal polymers produced using two or more different catalyst types—bimetallic catalysts—are of increasing interest, especially in producing polyethylene and other polyolefins. See, for example, U.S. Pat. No. 5,525,678. However, problems exist in using these bimetallic catalysts, especially in the gas phase. One problem is catalyst activity, which should be as high as possible in order to economize the process, as catalysts costs are significant.
One method of improving catalyst efficiency in gas phase processes is to increase the residence time of the catalyst in the fluidized bed of the gas phase reactor. Residence time can be increased by increasing the fluidized bulk density of the system, or lowering the voidage of the system. There are many factors that can influence the residence time of the catalyst. However, determining the right combination of factors for a given catalyst is complex and costly, and is compounded by the presence of a bimetallic system. What is needed is a method of improving the economy of producing bimodal polymers. The present invention is directed towards solving this and other problems.
SUMMARY
The present invention provides a polymerization process, gas phase polymerization processes in one embodiment. At least one specific embodiment of the invention relates to a gas phase polymerization process for producing a polyolefin composition, including passing a gaseous stream containing hydrogen gas and one or more monomers, including ethylene monomers, through a reactor that includes a fluidized bed, under reactive conditions, in the presence of a catalyst that includes metallocene, to provide a polyolefin composition, wherein: (a) the fluidized bulk density is 60% or more of the settled bulk density; (b) the reactor temperature is 100° C. or below; and (c) the molar ratio of hydrogen gas to ethylene in the gaseous stream is 0.015 or below.
In particular embodiments, the fluidized bulk density is 65% or more of the settled bulk density. In other embodiments, the fluidized bulk density is 70% or more of the settled bulk density.
In yet a more particular embodiment, (a) the reactor temperature is from 80° C. to 97° C.; and (b) the molar ratio of hydrogen gas to ethylene in the gaseous stream is from 0.003 to 0.009.
In yet another embodiment, the molar ratio of hydrogen gas to ethylene in the gaseous stream is less than 0.008. In a more particular embodiment, the molar ratio of hydrogen gas to ethylene in the gaseous stream can be from 0.003 to 0.008. In yet a more particular embodiment, the molar ratio of hydrogen gas to ethylene in the gaseous stream can be from 0.003 to 0.007. And in yet a more particular embodiment, the molar ratio of hydrogen gas to ethylene in the gaseous stream is from 0.003 to 0.006.
In one embodiment of the processes disclosed herein, the reactor temperature is maintained at 96° C. or below. Alternatively, the reactor temperature may be maintained at 95° C. or below in another embodiment. Also, the reactor temperature may maintained at 94° C. or below in yet another embodiment.
In a particular embodiment, the catalyst is a supported bimetallic catalyst. Even more particularly, the catalyst is a supported bimetallic catalyst that includes a metallocene catalyst compound. Even more particularly, the catalyst is a supported bimetallic catalyst that includes a metallocene catalyst compound having at least one fluoride or fluorine containing leaving group.
In one embodiment of the processes disclosed herein, the polyolefin composition resulting from the polymerization process is a bimodal polyolefin composition that includes a high molecular weight polyolefin component and a low molecular weight polyolefin component.
In one embodiment of the processes disclosed herein, the catalyst includes a support material comprising silica dehydrated at a temperature of 800° C. or more.
DETAILED DESCRIPTION
General Definitions
As used herein, in reference to Periodic Table “Groups” of Elements, the “new” numbering scheme for the Periodic Table Groups are used as in the CRC Handbook of Chemistry and Physics (David R. Lide ed., CRC Press 81
st
ed. 2000).
As used herein, the phrase “catalyst system” includes at least one “catalyst component” and at least one “activator”, both of which are described further herein. The catalyst system may also include other components, such as supports, etc., and is not limited to the catalyst component and/or activator alone or in combination. The catalyst system may include any number of catalyst components in any combination as described herein, as well as any activator in any combination as described herein.
As used herein, the phrase “catalyst compound” includes any compound that, once appropriately activated, is capable of catalyzing the polymerization or oligomerization of olefins, the catalyst compound comprising at least one Group 3 to Group 12 atom, and optionally at least one leaving group bound thereto.
As used herein, the phrase “leaving group” refers to one or more chemical moieties bound to the metal center of the catalyst component that can be abstracted from the catalyst component by an activator, thus producing the species active towards olefin polymerization or oligomerization. The activator is described further below.
As used herein, the term “fluorinated catalyst component” means a catalyst compound having at least one fluoride or fluorine containing leaving group, preferably a metallocene or metallocene-type catalyst compound having at least one fluoride or fluorine containing leaving group.
As used herein, a “hydrocarbyl” includes aliphatic, cyclic, olefinic, acetylenic and aromatic radicals (i.e., hydrocarbon radicals) comprising hydrogen and carbon that are deficient by one hydrogen. A “hydrocarbylene” is deficient by two hydrogens.
As used herein, an “alkyl” includes linear, branched and cyclic paraffin radicals that are deficient by one hydrogen. Thus, for example, a —CH
3
group (“methyl”) and a CH
3
CH
2
— group (“ethyl”) are examples of alkyls.
As used herein, an “alkenyl” includes linear, branched and cyclic olefin radicals that are deficient by one hydrogen; alkynyl radicals include linear, branched and cyclic acetylene radicals deficient by one hydrogen radical.
As used herein, “aryl” groups includes phenyl, naphthyl, pyridyl and other radicals whose molecules have the ring structure characteristic of benzene, naphthylene, phenanthrene, anthracene, etc. For example, a C
6
H
5
−
aromatic structure is an “phenyl”, a C
6
H
4
2−
aromatic structure is an “phenylene”. An “arylalkyl” group is an alkyl group having an aryl group pendant therefrom; an “alkylaryl” is an aryl group having one or more alkyl groups pendant therefrom.
As used herein, an “alkylene” includes linear, branched and cyclic hydrocarbon radicals deficient by two hydrogens. Thus, —CH
2
— (“methylene”) and —CH
2
CH
2
— (“ethylene”) are examples of alkylene groups. Other groups deficient by two hydrogen radicals include “arylene” and “alkenylene”.
As used herein, the phrase “heteroatom” includes any atom other than carbon and hydrogen that can be bound to carbon, and in one embodiment is selected from the group consisting of B, Al, Si, Ge, N, P, O, and S. A “heteroatom-containing group” is a hydrocarbon radical that contains a heteroatom and may contain one or more of the same or different heteroatoms, and from 1 to 3 heteroatoms in a particular embodiment. Non-limiting examples of heteroatom-containing groups include radicals of imines, amines, oxides, phosphines, ethers, ketones, oxoazolines heterocyclics, oxazolines, thioethers, and the like.
As used herein, an “alkylcarboxylate”, “arylcarboxylate”, and “alkylarylcarboxylate” is an alkyl, aryl, and alkylaryl, respectively, that possesses a carboxyl group in any position. Examples include C
6
H
5
CH
2
C(O)O
−
, CH
3
C(O)O
−
, etc.
As used herein, the term “

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